STEAM ITS GENERATION AND USE [Illustration] THE BABCOCK & WILCOX CO. NEW YORK Thirty-fifth Edition 4th Issue Copyright, 1919, by The Babcock & Wilcox Co. * * * * * Bartlett Orr Press New York THE BABCOCK & WILCOX CO. 85 LIBERTY STREET, NEW YORK, U. S. A. _Works_ BAYONNE NEW JERSEYBARBERTON OHIO _Officers_ W. D. HOXIE, _President_E. H. WELLS, _Chairman of the Board_A. G. PRATT, _Vice-President_ _Branch Offices_ ATLANTA Candler BuildingBOSTON 35 Federal StreetCHICAGO Marquette BuildingCINCINNATI Traction BuildingCLEVELAND New Guardian BuildingDENVER 435 Seventeenth StreetHAVANA, CUBA 104 Calle de AguiarHOUSTON Southern Pacific BuildingLOS ANGELES I. N. Van Nuy's BuildingNEW ORLEANS Shubert ArcadePHILADELPHIA North American BuildingPITTSBURGH Farmers' Deposit Bank BuildingSALT LAKE CITY Kearns BuildingSAN FRANCISCO Sheldon BuildingSEATTLE L. C. Smith BuildingTUCSON, ARIZ. Santa Rita Hotel BuildingSAN JUAN, PORTO RICO Royal Bank Building _Export Department, New York: Alberto de Verastegni, Director_ TELEGRAPHIC ADDRESS: FOR NEW YORK, "GLOVEBOXES"FOR HAVANA, "BABCOCK" [Illustration: Works of The Babcock & Wilcox Co. , at Bayonne, New Jersey] [Illustration: Works of The Babcock & Wilcox Co. , at Barberton, Ohio] [Illustration: Works of Babcock & Wilcox, Limited, Renfrew, SCOTLAND] BABCOCK & WILCOX Limited ORIEL HOUSE, FARRINGDON STREET, LONDON, E. C. WORKS: RENFREW, SCOTLAND _Directors_ JOHN DEWRANCE, _Chairman_ CHARLES A. KNIGHTARTHUR T. SIMPSON J. H. R. KEMNALWILLIAM D. HOXIE _Managing Director_E. H. WELLS WALTER COLLS, _Secretary_ _Branch Offices in Great Britain_ GLASGOW: 29 St. Vincent PlaceBIRMINGHAM: Winchester HouseCARDIFF: 129 Bute StreetBELFAST: Ocean Buildings, Donegal Square, E. MANCHESTER: 30 Cross StreetMIDDLESBROUGH: The ExchangeNEWCASTLE: 42 Westgate RoadSHEFFIELD: 14 Bank Chambers, Fargate _Offices Abroad_ BOMBAY: Wheeler's Building, Hornby Road, FortBRUSSELS: 187 Rue RoyalBILBAO: 1 Plaza de AlbiaCALCUTTA: Clive BuildingJOHANNESBURG: Consolidated BuildingsLIMA: PeruLISBON: 84-86 Rua do CommercioMADRID: Ventura de la VegaMELBOURNE: 9 William StreetMEXICO: 22-23 TiburcioMILAN: 22 Via Principe UmbertoMONTREAL: College Street, St. HenryNAPLES: 107 Via Santa LuciaSHANGHAI: 1a Jinkee RoadSYDNEY: 427-429 Sussex StreetTOKYO: JapanTORONTO: Traders' Bank Building _Representatives and Licensees in_ ADELAIDE, South AustraliaATHENS, GreeceAUCKLAND, New ZealandBAHIA, BrazilBANGKOK, SiamBARCELONA, SpainBRUNN, AustriaBUCHAREST, RoumaniaBUDAPEST, HungaryBUENOS AYRES, Argentine Rep. CAIRO, EgyptCHILE, Valparaiso, So. AmericaCHRISTIANIA, NorwayCOLOMBO, CeylonCOPENHAGEN, DenmarkESKILSTUNA, SwedenGIJON, SpainHELSINGFORS, FinlandHENGELO, HollandKIMBERLEY, South AfricaMOSCOW, RussiaPERTH, Western AustraliaPOLAND, BerlinRANGOON, BurmaRIO DE JANEIRO, BrazilSMYRNA, Asia MinorSOURABAYA, JavaST. PETERSBURG, RussiaTAMMERFORS, FinlandTHE HAGUE, Holland TELEGRAPHIC ADDRESS FOR ALL OFFICES EXCEPT BOMBAY AND CALCUTTA: "BABCOCK"FOR BOMBAY AND CALCUTTA: "BOILER" [Illustration: Fonderies et Ateliers de la Courneuve, Chaudières Babcock& Wilcox, Paris, France] FONDERIES ET ATELIERS DE LA COURNEUVECHAUDIÈRES BABCOCK & WILCOX 6 RUE LAFERRIÈRE, PARIS WORKS: SEINE--LA COURNEUVE _Directors_ EDMOND DUPUIS J. H. R. KEMNALETIENNE BESSON IRÉNÉE CHAVANNECHARLES A. KNIGHT JULES LEMAIRE _Branch Offices_ BORDEAUX: 30 Boulevard Antoine GautierLILLE: 23 Rue FaidherbeLYON: 28 Quai de la GuillotierMARSEILLE: 21 Cours DevilliersMONTPELLIER: 1 Rue BoussairollesNANCY: 2 Rue de LorraineST. ETIENNE: 13 Rue de la Bourse REPRESENTATIVE FOR SWITZERLAND: SPOERRI & CIE, ZURICH TELEGRAPHIC ADDRESS: "BABCOCK-PARIS" [Illustration: Wrought-steel Vertical Header Longitudinal DrumBabcock & Wilcox Boiler, Equipped with Babcock & Wilcox Superheater andBabcock & Wilcox Chain Grate Stoker] THE EARLY HISTORY OF THE GENERATION AND USE OF STEAM While the time of man's first knowledge and use of the expansive forceof the vapor of water is unknown, records show that such knowledgeexisted earlier than 150 B. C. In a treatise of about that time entitled"Pneumatica", Hero, of Alexander, described not only existing devices ofhis predecessors and contemporaries but also an invention of his ownwhich utilized the expansive force of steam for raising water above itsnatural level. He clearly describes three methods in which steam mightbe used directly as a motive of power; raising water by its elasticity, elevating a weight by its expansive power and producing a rotary motionby its reaction on the atmosphere. The third method, which is known as"Hero's engine", is described as a hollow sphere supported over acaldron or boiler by two trunnions, one of which was hollow, andconnected the interior of the sphere with the steam space of thecaldron. Two pipes, open at the ends and bent at right angles, wereinserted at opposite poles of the sphere, forming a connection betweenthe caldron and the atmosphere. Heat being applied to the caldron, thesteam generated passed through the hollow trunnion to the sphere andthence into the atmosphere through the two pipes. By the reactionincidental to its escape through these pipes, the sphere was caused torotate and here is the primitive steam reaction turbine. Hero makes no suggestions as to application of any of the devices hedescribes to a useful purpose. From the time of Hero until the latesixteenth and early seventeenth centuries, there is no record ofprogress, though evidence is found that such devices as were describedby Hero were sometimes used for trivial purposes, the blowing of anorgan or the turning of a skillet. Mathesius, the German author, in 1571; Besson, a philosopher andmathematician at Orleans; Ramelli, in 1588; Battista Delia Porta, aNeapolitan mathematician and philosopher, in 1601; Decause, the Frenchengineer and architect, in 1615; and Branca, an Italian architect, in1629, all published treatises bearing on the subject of the generationof steam. To the next contributor, Edward Somerset, second Marquis of Worcester, is apparently due the credit of proposing, if not of making, the firstuseful steam engine. In the "Century of Scantlings and Inventions", published in London in 1663, he describes devices showing that he had inmind the raising of water not only by forcing it from two receivers bydirect steam pressure but also for some sort of reciprocating pistonactuating one end of a lever, the other operating a pump. Hisdescriptions are rather obscure and no drawings are extant so that it isdifficult to say whether there were any distinctly novel features to hisdevices aside from the double action. While there is no direct authenticrecord that any of the devices he described were actually constructed, it is claimed by many that he really built and operated a steam enginecontaining pistons. In 1675, Sir Samuel Moreland was decorated by King Charles II, for ademonstration of "a certain powerful machine to raise water. " Thoughthere appears to be no record of the design of this machine, themathematical dictionary, published in 1822, credits Moreland with thefirst account of a steam engine, on which subject he wrote a treatisethat is still preserved in the British Museum. [Illustration: 397 Horse-power Babcock & Wilcox Boiler in Course ofErection at the Plant of the Crocker Wheeler Co. , Ampere, N. J. ] Dr. Denys Papin, an ingenious Frenchman, invented in 1680 "a steamdigester for extracting marrowy, nourishing juices from bones byenclosing them in a boiler under heavy pressure, " and finding dangerfrom explosion, added a contrivance which is the first safety valve onrecord. The steam engine first became commercially successful with ThomasSavery. In 1699, Savery exhibited before the Royal Society of England(Sir Isaac Newton was President at the time), a model engine whichconsisted of two copper receivers alternately connected by a three-wayhand-operated valve, with a boiler and a source of water supply. Whenthe water in one receiver had been driven out by the steam, cold waterwas poured over its outside surface, creating a vacuum throughcondensation and causing it to fill again while the water in the otherreservoir was being forced out. A number of machines were built on thisprinciple and placed in actual use as mine pumps. The serious difficulty encountered in the use of Savery's engine was thefact that the height to which it could lift water was limited by thepressure the boiler and vessels could bear. Before Savery's engine wasentirely displaced by its successor, Newcomen's, it was considerablyimproved by Desaguliers, who applied the Papin safety valve to theboiler and substituted condensation by a jet within the vessel forSavery's surface condensation. In 1690, Papin suggested that the condensation of steam should beemployed to make a vacuum beneath a cylinder which had previously beenraised by the expansion of steam. This was the earliest cylinder andpiston steam engine and his plan took practical shape in Newcomen'satmospheric engine. Papin's first engine was unworkable owing to thefact that he used the same vessel for both boiler and cylinder. A smallquantity of water was placed in the bottom of the vessel and heat wasapplied. When steam formed and raised the piston, the heat was withdrawnand the piston did work on its down stroke under pressure of theatmosphere. After hearing of Savery's engine, Papin developed animproved form. Papin's engine of 1705 consisted of a displacementchamber in which a floating diaphragm or piston on top of the water keptthe steam and water from direct contact. The water delivered by thedownward movement of the piston under pressure, to a closed tank, flowedin a continuous stream against the vanes of a water wheel. When thesteam in the displacement chamber had expanded, it was exhausted to theatmosphere through a valve instead of being condensed. The engine was, in fact, a non-condensing, single action steam pump with the steam andpump cylinders in one. A curious feature of this engine was a heaterplaced in the diaphragm. This was a mass of heated metal for the purposeof keeping the steam dry or preventing condensation during expansion. This device might be called the first superheater. Among the various inventions attributed to Papin was a boiler with aninternal fire box, the earliest record of such construction. While Papin had neglected his earlier suggestion of a steam and pistonengine to work on Savery's ideas, Thomas Newcomen, with his assistant, John Cawley, put into practical form Papin's suggestion of 1690. Steamadmitted from the boiler to a cylinder raised a piston by its expansion, assisted by a counter-weight on the other end of a beam actuated by thepiston. The steam valve was then shut and the steam condensed by a jetof cold water. The piston was then forced downward by atmosphericpressure and did work on the pump. The condensed water in the cylinderwas expelled through an escapement valve by the next entry of steam. This engine used steam having pressure but little, if any, above that ofthe atmosphere. [Illustration: Two Units of 8128 Horse Power of Babcock & Wilcox Boilersand Superheaters at the Fisk Street Station of the Commonwealth EdisonCo. , Chicago, Ill. , 50, 400 Horse Power being Installed in this Station. The Commonwealth Edison Co. Operates in its Various Stations a Total of86, 000 Horse Power of Babcock & Wilcox Boilers, all Fitted with Babcock& Wilcox Superheaters and Equipped with Babcock & Wilcox Chain GrateStokers] In 1711, this engine was introduced into mines for pumping purposes. Whether its action was originally automatic or whether dependent uponthe hand operation of the valves is a question of doubt. The storycommonly believed is that a boy, Humphrey Potter, in 1713, whose duty itwas to open and shut such valves of an engine he attended, by suitablecords and catches attached to the beam, caused the engine toautomatically manipulate these valves. This device was simplified in1718 by Henry Beighton, who suspended from the bottom, a rod called theplug-tree, which actuated the valve by tappets. By 1725, this engine wasin common use in the collieries and was changed but little for a matterof sixty or seventy years. Compared with Savery's engine, from theaspect of a pumping engine, Newcomen's was a distinct advance, in thatthe pressure in the pumps was in no manner dependent upon the steampressure. In common with Savery's engine, the losses from the alternateheating and cooling of the steam cylinder were enormous. Thoughobviously this engine might have been modified to serve many purposes, its use seems to have been limited almost entirely to the pumping ofwater. The rivalry between Savery and Papin appears to have stimulatedattention to the question of fuel saving. Dr. John Allen, in 1730, called attention to the fact that owing to the short length of time ofthe contact between the gases and the heating surfaces of the boiler, nearly half of the heat of the fire was lost. With a view to overcomingthis loss at least partially, he used an internal furnace with a smokeflue winding through the water in the form of a worm in a still. Inorder that the length of passage of the gases might not act as a damperon the fire, Dr. Allen recommended the use of a pair of bellows forforcing the sluggish vapor through the flue. This is probably the firstsuggested use of forced draft. In forming an estimate of the quantity offuel lost up the stack, Dr. Allen probably made the first boiler test. Toward the end of the period of use of Newcomen's atmospheric engine, John Smeaton, who, about 1770, built and installed a number of largeengines of this type, greatly improved the design in its mechanicaldetails. [Illustration: Erie County Electric Co. , Erie, Pa. , Operating 3082 HorsePower of Babcock & Wilcox Boilers and Superheaters, Equipped withBabcock & Wilcox Chain Grate Stokers] The improvement in boiler and engine design of Smeaton, Newcomen andtheir contemporaries, were followed by those of the great engineer, James Watt, an instrument maker of Glasgow. In 1763, while repairing amodel of Newcomen's engine, he was impressed by the great waste of steamto which the alternating cooling and heating of the engine gave rise. His remedy was the maintaining of the cylinder as hot as the enteringsteam and with this in view he added a vessel separate from thecylinder, into which the steam should pass from the cylinder and bethere condensed either by the application of cold water outside or by ajet from within. To preserve a vacuum in his condenser, he added an airpump which should serve to remove the water of condensation and airbrought in with the injection water or due to leakage. As the cylinderno longer acted as a condenser, he could maintain it at a hightemperature by covering it with non-conducting material and, inparticular, by the use of a steam jacket. Further and with the sameobject in view, he covered the top of the cylinder and introduced steamabove the piston to do the work previously accomplished by atmosphericpressure. After several trials with an experimental apparatus based onthese ideas, Watt patented his improvements in 1769. Aside from theirhistorical importance, Watt's improvements, as described in hisspecification, are to this day a statement of the principles which guidethe scientific development of the steam engine. His words are: "My method of lessening the consumption of steam, and consequently fuel, in fire engines, consists of the following principles: "First, That vessel in which the powers of steam are to be employed to work the engine, which is called the cylinder in common fire engines, and which I call the steam vessel, must, during the whole time the engine is at work, be kept as hot as the steam that enters it; first, by enclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and, thirdly, by suffering neither water nor any other substance colder than the steam to enter or touch it during that time. "Secondly, In engines that are to be worked wholly or partially by condensation of steam, the steam is to be condensed in vessels distinct from the steam vessels or cylinders, although occasionally communicating with them; these vessels I call condensers; and, whilst the engines are working, these condensers ought at least to be kept as cold as the air in the neighborhood of the engines, by application of water or other cold bodies. "Thirdly, Whatever air or other elastic vapor is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam vessels or condensers by means of pumps, wrought by the engines themselves, or otherwise. "Fourthly, I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner in which the pressure of the atmosphere is now employed in common fire engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the air after it has done its office. .. . "Sixthly, I intend in some cases to apply a degree of cold not capable of reducing the steam to water, but of contracting it considerably, so that the engines shall be worked by the alternate expansion and contraction of the steam. "Lastly, Instead of using water to render the pistons and other parts of the engine air and steam tight, I employ oils, wax, resinous bodies, fat of animals, quick-silver and other metals in their fluid state. " The fifth claim was for a rotary engine, and need not be quoted here. The early efforts of Watt are typical of those of the poor inventorstruggling with insufficient resources to gain recognition and it wasnot until he became associated with the wealthy manufacturer, MattheuBoulton of Birmingham, that he met with the success upon which hispresent fame is based. In partnership with Boulton, the business of themanufacture and the sale of his engines were highly successful in spiteof vigorous attacks on the validity of his patents. Though the fourth claim of Watt's patent describes a non-condensingengine which would require high pressures, his aversion to such practicewas strong. Notwithstanding his entire knowledge of the advantagesthrough added expansion under high pressure, he continued to usepressures not above 7 pounds per square inch above the atmosphere. Toovercome such pressures, his boilers were fed through a stand-pipe ofsufficient height to have the column of water offset the pressure withinthe boiler. Watt's attitude toward high pressure made his influence feltlong after his patents had expired. [Illustration: Portion of 9600 Horse-power Installation of Babcock &Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox ChainGrate Stokers at the Blue Island, Ill. , Plant of the Public Service Co. Of Northern Illinois. This Company Operates 14, 580 Horse Power ofBabcock & Wilcox Boilers and Superheaters in its Various Stations] In 1782, Watt patented two other features which he had invented as earlyas 1769. These were the double acting engine, that is, the use of steamon both sides of the piston and the use of steam expansively, that is, the shutting off of steam from the cylinder when the piston had made buta portion of its stroke, the power for the completion of the strokebeing supplied by the expansive force of the steam already admitted. He further added a throttle valve for the regulation of steam admission, invented the automatic governor and the steam indicator, a mercury steamgauge and a glass water column. It has been the object of this brief history of the early developmentsin the use of steam to cover such developments only through the time ofJames Watt. The progress of the steam engine from this time through thestages of higher pressures, combining of cylinders, the application ofsteam vehicles and steamboats, the adding of third and fourth cylinders, to the invention of the turbine with its development and theaccompanying development of the reciprocating engine to hold its place, is one long attribute to the inventive genius of man. While little is said in the biographies of Watt as to the improvement ofsteam boilers, all the evidence indicates that Boulton and Wattintroduced the first "wagon boiler", so called because of its shape. In1785, Watt took out a number of patents for variations in furnaceconstruction, many of which contain the basic principles of some of themodern smoke preventing furnaces. Until the early part of the nineteenthcentury, the low steam pressures used caused but little attention to begiven to the form of the boiler operated in connection with the enginesabove described. About 1800, Richard Trevithick, in England, and OliverEvans, in America, introduced non-condensing, and for that time, highpressure steam engines. To the initiative of Evans may be attributed thegeneral use of high pressure steam in the United States, a feature whichfor many years distinguished American from European practice. The demandfor light weight and economy of space following the beginning of steamnavigation and the invention of the locomotive required boilers designedand constructed to withstand heavier pressures and forced the adoptionof the cylindrical form of boiler. There are in use to-day many examplesof every step in the development of steam boilers from the first plaincylindrical boiler to the most modern type of multi-tubular locomotiveboiler, which stands as the highest type of fire-tube boilerconstruction. The early attempts to utilize water-tube boilers were few. A briefhistory of the development of the boilers, in which this principle wasemployed, is given in the following chapter. From this history it willbe clearly indicated that the first commercially successful utilizationof water tubes in a steam generator is properly attributed to George H. Babcock and Stephen Wilcox. [Illustration: Copyright by Underwood & Underwood Woolworth Building, New York City, Operating 2454 Horse Power ofBabcock & Wilcox Boilers] BRIEF HISTORY OF WATER-TUBE BOILERS[1] As stated in the previous chapter, the first water-tube boiler was builtby John Blakey and was patented by him in 1766. Several tubesalternately inclined at opposite angles were arranged in the furnaces, the adjacent tube ends being connected by small pipes. The firstsuccessful user of water-tube boilers, however, was James Rumsey, anAmerican inventor, celebrated for his early experiments in steamnavigation, and it is he who may be truly classed as the originator ofthe water-tube boiler. In 1788 he patented, in England, several forms ofboilers, some of which were of the water-tube type. One had a fire boxwith flat top and sides, with horizontal tubes across the fire boxconnecting the water spaces. Another had a cylindrical fire boxsurrounded by an annular water space and a coiled tube was placed withinthe box connecting at its two ends with the water space. This was thefirst of the "coil boilers". Another form in the same patent was thevertical tubular boiler, practically as made at the present time. [Illustration: Blakey, 1766] The first boiler made of a combination of small tubes, connected at oneend to a reservoir, was the invention of another American, John Stevens, in 1804. This boiler was actually employed to generate steam for runninga steamboat on the Hudson River, but like all the "porcupine" boilers, of which type it was the first, it did not have the elements of acontinued success. [Illustration: John Stevens, 1804] Another form of water tube was patented in 1805 by John Cox Stevens, ason of John Stevens. This boiler consisted of twenty vertical tubes, 1¼inches internal diameter and 40½ inches long, arranged in a circle, theoutside diameter of which was approximately 12 inches, connecting awater chamber at the bottom with a steam chamber at the top. The steamand water chambers were annular spaces of small cross section andcontained approximately 33 cubic inches. The illustration shows the capof the steam chamber secured by bolts. The steam outlet pipe "A" is apipe of one inch diameter, the water entering through a similar apertureat the bottom. One of these boilers was for a long time at the StevensInstitute of Technology at Hoboken, and is now in the SmithsonianInstitute at Washington. [Illustration: John Cox Stevens, 1805] About the same time, Jacob Woolf built a boiler of large horizontaltubes, extending across the furnace and connected at the ends to alongitudinal drum above. The first purely sectional water-tube boilerwas built by Julius Griffith, in 1821. In this boiler, a number ofhorizontal water tubes were connected to vertical side pipes, the sidepipes were connected to horizontal gathering pipes, and these latter inturn to a steam drum. In 1822, Jacob Perkins constructed a flash boiler for carrying what wasthen considered a high pressure. A number of cast-iron bars having 1½inches annular holes through them and connected at their outer ends by aseries of bent pipes, outside of the furnace walls, were arranged inthree tiers over the fire. The water was fed slowly to the upper tier bya force pump and steam in the superheated state was discharged to thelower tiers into a chamber from which it was taken to the engine. [Illustration: Joseph Eve, 1825] The first sectional water-tube boiler, with a well-defined circulation, was built by Joseph Eve, in 1825. The sections were composed of smalltubes with a slight double curve, but being practically vertical, fixedin horizontal headers, which headers were in turn connected to a steamspace above and a water space below formed of larger pipes. The steamand water spaces were connected by outside pipes to secure a circulationof the water up through the sections and down through the externalpipes. In the same year, John M'Curdy of New York, built a "Duplex SteamGenerator" of "tubes of wrought or cast iron or other material" arrangedin several horizontal rows, connected together alternately at the frontand rear by return bends. In the tubes below the water line were placedinterior circular vessels closed at the ends in order to expose a thinsheet of water to the action of the fire. [Illustration: Gurney, 1826] In 1826, Goldsworthy Gurney built a number of boilers, which he used onhis steam carriages. A number of small tubes were bent into the shape ofa "U" laid sidewise and the ends were connected with larger horizontalpipes. These were connected by vertical pipes to permit of circulationand also to a vertical cylinder which served as a steam and waterreservoir. In 1828, Paul Steenstrup made the first shell boiler withvertical water tubes in the large flues, similar to the boiler known asthe "Martin" and suggesting the "Galloway". The first water-tube boiler having fire tubes within water tubes wasbuilt in 1830, by Summers & Ogle. Horizontal connections at the top andbottom were connected by a series of vertical water tubes, through whichwere fire tubes extending through the horizontal connections, the firetubes being held in place by nuts, which also served to make the joint. [Illustration: Stephen Wilcox, 1856] Stephen Wilcox, in 1856, was the first to use inclined water tubesconnecting water spaces at the front and rear with a steam space above. The first to make such inclined tubes into a sectional form was Twibill, in 1865. He used wrought-iron tubes connected at the front and rear withstandpipes through intermediate connections. These standpipes carriedthe system to a horizontal cross drum at the top, the entrained waterbeing carried to the rear. Clarke, Moore, McDowell, Alban and others worked on the problem ofconstructing water-tube boilers, but because of difficulties ofconstruction involved, met with no practical success. [Illustration: Twibill, 1865] It may be asked why water-tube boilers did not come into more generaluse at an early date, that is, why the number of water-tube boilersbuilt was so small in comparison to the number of shell boilers. Thereason for this is found in the difficulties involved in the design andconstruction of water-tube boilers, which design and constructionrequired a high class of engineering and workmanship, while the plaincylindrical boiler is comparatively easy to build. The greater skillrequired to make a water-tube boiler successful is readily shown in thegreat number of failures in the attempts to make them. [Illustration: Partial View of 7000 Horse-power Installation of Babcock& Wilcox Boilers at the Philadelphia, Pa. , Plant of the BaldwinLocomotive Works. This Company Operates in its Various Plants a Total of9280 Horse Power of Babcock & Wilcox Boilers] REQUIREMENTS OF STEAM BOILERS Since the first appearance in "Steam" of the following "Requirements ofa Perfect Steam Boiler", the list has been copied many times either wordfor word or clothed in different language and applied to some specifictype of boiler design or construction. In most cases, although fullcompliance with one or more of the requirements was structurallyimpossible, the reader was left to infer that the boiler underconsideration possessed all the desirable features. It is noteworthythat this list of requirements, as prepared by George H. Babcock andStephen Wilcox, in 1875, represents the best practice of to-day. Moreover, coupled with the boiler itself, which is used in the largestand most important steam generating plants throughout the world, thelist forms a fitting monument to the foresight and genius of theinventors. REQUIREMENTS OF A PERFECT STEAM BOILER 1st. Proper workmanship and simple construction, using materials whichexperience has shown to be the best, thus avoiding the necessity ofearly repairs. 2nd. A mud drum to receive all impurities deposited from the water, andso placed as to be removed from the action of the fire. 3rd. A steam and water capacity sufficient to prevent any fluctuation insteam pressure or water level. 4th. A water surface for the disengagement of the steam from the water, of sufficient extent to prevent foaming. 5th. A constant and thorough circulation of water throughout the boiler, so as to maintain all parts at the same temperature. 6th. The water space divided into sections so arranged that, should anysection fail, no general explosion can occur and the destructive effectswill be confined to the escape of the contents. Large and free passagesbetween the different sections to equalize the water line and pressurein all. 7th. A great excess of strength over any legitimate strain, the boilerbeing so constructed as to be free from strains due to unequalexpansion, and, if possible, to avoid joints exposed to the directaction of the fire. 8th. A combustion chamber so arranged that the combustion of the gasesstarted in the furnace may be completed before the gases escape to thechimney. 9th. The heating surface as nearly as possible at right angles to thecurrents of heated gases, so as to break up the currents and extract theentire available heat from the gases. 10th. All parts readily accessible for cleaning and repairs. This is apoint of the greatest importance as regards safety and economy. 11th. Proportioned for the work to be done, and capable of working toits full rated capacity with the highest economy. 12th. Equipped with the very best gauges, safety valves and otherfixtures. The exhaustive study made of each one of these requirements is shown bythe following extract from a lecture delivered by Mr. Geo. H. Babcock atCornell University in 1890 upon the subject: THE CIRCULATION OF WATER IN STEAM BOILERS You have all noticed a kettle of water boiling over the fire, the fluidrising somewhat tumultuously around the edges of the vessel, andtumbling toward the center, where it descends. Similar currents are inaction while the water is simply being heated, but they are notperceptible unless there are floating particles in the liquid. Thesecurrents are caused by the joint action of the added temperature and twoor more qualities which the water possesses. 1st. Water, in common with most other substances, expands when heated; astatement, however, strictly true only when referred to a temperatureabove 39 degrees F. Or 4 degrees C. , but as in the making of steam werarely have to do with temperatures so low as that, we may, for ourpresent purposes, ignore that exception. 2nd. Water is practically a non-conductor of heat, though not entirelyso. If ice-cold water was kept boiling at the surface the heat would notpenetrate sufficiently to begin melting ice at a depth of 3 inches inless than about two hours. As, therefore, the heated water cannot impartits heat to its neighboring particles, it remains expanded and rises byits levity, while colder portions come to be heated in turn, thussetting up currents in the fluid. Now, when all the water has been heated to the boiling pointcorresponding to the pressure to which it is subjected, each added unitof heat converts a portion, about 7 grains in weight, into vapor, greatly increasing its volume; and the mingled steam and water risesmore rapidly still, producing ebullition such as we have noticed in thekettle. So long as the quantity of heat added to the contents of thekettle continues practically constant, the conditions remain similar tothose we noticed at first, a tumultuous lifting of the water around theedges, flowing toward the center and thence downward; if, however, thefire be quickened, the upward currents interfere with the downward andthe kettle boils over (Fig. 1). [Illustration: Fig. 1] If now we put in the kettle a vessel somewhat smaller (Fig. 2) with ahole in the bottom and supported at a proper distance from the side soas to separate the upward from the downward currents, we can force thefires to a very much greater extent without causing the kettle to boilover, and when we place a deflecting plate so as to guide the risingcolumn toward the center it will be almost impossible to produce thateffect. This is the invention of Perkins in 1831 and forms the basis ofvery many of the arrangements for producing free circulation of thewater in boilers which have been made since that time. It consists individing the currents so that they will not interfere each with theother. [Illustration: Fig. 2] But what is the object of facilitating the circulation of water inboilers? Why may we not safely leave this to the unassisted action ofnature as we do in culinary operations? We may, if we do not care forthe three most important aims in steam-boiler construction, namely, efficiency, durability, and safety, each of which is more or lessdependent upon a proper circulation of the water. As for efficiency, wehave seen one proof in our kettle. When we provided means to preservethe circulation, we found that we could carry a hotter fire and boilaway the water much more rapidly than before. It is the same in a steamboiler. And we also noticed that when there was nothing but theunassisted circulation, the rising steam carried away so much water inthe form of foam that the kettle boiled over, but when the currents wereseparated and an unimpeded circuit was established, this ceased, and amuch larger supply of steam was delivered in a comparatively dry state. Thus, circulation increases the efficiency in two ways: it adds to theability to take up the heat, and decreases the liability to waste thatheat by what is technically known as priming. There is yet another wayin which, incidentally, circulation increases efficiency of surface, andthat is by preventing in a greater or less degree the formation ofdeposits thereon. Most waters contain some impurity which, when thewater is evaporated, remains to incrust the surface of the vessel. Thisincrustation becomes very serious sometimes, so much so as to almostentirely prevent the transmission of heat from the metal to the water. It is said that an incrustation of only one-eighth inch will cause aloss of 25 per cent in efficiency, and this is probably within the truthin many cases. Circulation of water will not prevent incrustationaltogether, but it lessens the amount in all waters, and almost entirelyso in some, thus adding greatly to the efficiency of the surface. [Illustration: Fig. 3] A second advantage to be obtained through circulation is durability ofthe boiler. This it secures mainly by keeping all parts at a nearlyuniform temperature. The way to secure the greatest freedom from unequalstrains in a boiler is to provide for such a circulation of the water aswill insure the same temperature in all parts. 3rd. Safety follows in the wake of durability, because a boiler which isnot subject to unequal strains of expansion and contraction is not onlyless liable to ordinary repairs, but also to rupture and disastrousexplosion. By far the most prolific cause of explosions is this samestrain from unequal expansions. [Illustration: Fig. 4] [Illustration: 386 Horse-power Installation of Babcock & Wilcox Boilersat B. F. Keith's Theatre, Boston, Mass. ] Having thus briefly looked at the advantages of circulation of water insteam boilers, let us see what are the best means of securing it underthe most efficient conditions We have seen in our kettle that oneessential point was that the currents should be kept from interferingwith each other. If we could look into an ordinary return tubular boilerwhen steaming, we should see a curious commotion of currents rushinghither and thither, and shifting continually as one or the othercontending force gained a momentary mastery. The principal upwardcurrents would be found at the two ends, one over the fire and the otherover the first foot or so of the tubes. Between these, the downwardcurrents struggle against the rising currents of steam and water. At asudden demand for steam, or on the lifting of the safety valve, thepressure being slightly reduced, the water jumps up in jets at everyportion of the surface, being lifted by the sudden generation of steamthroughout the body of water. You have seen the effect of this suddengeneration of steam in the well-known experiment with a Florence flask, to which a cold application is made while boiling water under pressureis within. You have also witnessed the geyser-like action when water isboiled in a test tube held vertically over a lamp (Fig. 3). [Illustration: Fig. 5] If now we take a U-tube depending from a vessel of water (Fig. 4) andapply the lamp to one leg a circulation is at once set up within it, andno such spasmodic action can be produced. Thus U-tube is therepresentative of the true method of circulation within a water-tubeboiler properly constructed. We can, for the purpose of securing moreheating surface, extend the heated leg into a long incline (Fig. 5), when we have the well-known inclined-tube generator. Now, by addingother tubes, we may further increase the heating surface (Fig. 6), whileit will still be the U-tube in effect and action. In such a constructionthe circulation is a function of the difference in density of the twocolumns. Its velocity is measured by the well-known Torricellianformula, V = (2gh)^{½}, or, approximately V = 8(h)^{½}, h being measuredin terms of the lighter fluid. This velocity will increase until therising column becomes all steam, but the quantity or weight circulatedwill attain a maximum when the density of the mingled steam and water inthe rising column becomes one-half that of the solid water in thedescending column which is nearly coincident with the condition of halfsteam and half water, the weight of the steam being very slight comparedto that of the water. [Illustration: Fig. 6] It becomes easy by this rule to determine the circulation in any givenboiler built on this principle, provided the construction is such as topermit a free flow of the water. Of course, every bend detracts a littleand something is lost in getting up the velocity, but when the boiler iswell arranged and proportioned these retardations are slight. Let us take for example one of the 240 horse-power Babcock & Wilcoxboilers here in the University. The height of the columns may be takenas 4½ feet, measuring from the surface of the water to about the centerof the bundle of tubes over the fire, and the head would be equal tothis height at the maximum of circulation. We should, therefore, have avelocity of 8(4½)^{½} = 16. 97, say 17 feet per second. There are in thisboiler fourteen sections, each having a 4-inch tube opening into thedrum, the area of which (inside) is 11 square inches, the fourteenaggregating 154 square inches, or 1. 07 square feet. This multiplied bythe velocity, 16. 97 feet, gives 18. 16 cubic feet mingled steam and waterdischarged per second, one-half of which, or 9. 08 cubic feet, is steam. Assuming this steam to be at 100 pounds gauge pressure, it will weigh0. 258 pound per cubic foot. Hence, 2. 34 pounds of steam will bedischarged per second, and 8, 433 pounds per hour. Dividing this by 30, the number of pounds representing a boiler horse power, we get 281. 1horse power, about 17 per cent, in excess of the rated power of theboiler. The water at the temperature of steam at 100 pounds pressureweighs 56 pounds per cubic foot, and the steam 0. 258 pound, so that thesteam forms but 1/218 part of the mixture by weight, and consequentlyeach particle of water will make 218 circuits before being evaporatedwhen working at this capacity, and circulating the maximum weight ofwater through the tubes. [Illustration: A Portion of 9600 Horse-power Installation of Babcock &Wilcox Boilers and Superheaters Being Erected at the South Boston, Mass. , Station of the Boston Elevated Railway Co. This Company Operatesin its Various Stations a Total of 46, 400 Horse Power of Babcock &Wilcox Boilers] [Illustration: Fig. 7] It is evident that at the highest possible velocity of exit from thegenerating tubes, nothing but steam will be delivered and there will beno circulation of water except to supply the place of that evaporated. Let us see at what rate of steaming this would occur with the boilerunder consideration. We shall have a column of steam, say 4 feet high onone side and an equal column of water on the other. Assuming, as before, the steam at 100 pounds and the water at same temperature, we will havea head of 866 feet of steam and an issuing velocity of 235. 5 feet persecond. This multiplied by 1. 07 square feet of opening by 3, 600 secondsin an hour, and by 0. 258 gives 234, 043 pounds of steam, which, thoughonly one-eighth the weight of mingled steam and water delivered at themaximum, gives us 7, 801 horse power, or 32 times the rated power of theboiler. Of course, this is far beyond any possibility of attainment, sothat it may be set down as certain that this boiler cannot be forced toa point where there will not be an efficient circulation of the water. By the same method of calculation it may be shown that when forced todouble its rated power, a point rarely expected to be reached inpractice, about two-thirds the volume of mixture of steam and waterdelivered into the drum will be steam, and that the water will make 110circuits while being evaporated. Also that when worked at only aboutone-quarter its rated capacity, one-fifth of the volume will be steamand the water will make the rounds 870 times before it becomes steam. You will thus see that in the proportions adopted in this boiler thereis provision for perfect circulation under all the possible conditionsof practice. [Illustration: Fig. 8 [Developed to show Circulation]] In designing boilers of this style it is necessary to guard againsthaving the uptake at the upper end of the tubes too large, for ifsufficiently large to allow downward currents therein, the whole effectof the rising column in increasing the circulation in the tubes isnullified (Fig. 7). This will readily be seen if we consider the uptakevery large when the only head producing circulation in the tubes will bethat due to the inclination of each tube taken by itself. This objectionis only overcome when the uptake is so small as to be entirely filledwith the ascending current of mingled steam and water. It is alsonecessary that this uptake should be practically direct, and it shouldnot be composed of frequent enlargements and contractions. Take, forinstance, a boiler well known in Europe, copied and sold here underanother name. It is made up of inclined tubes secured by pairs intoboxes at the ends, which boxes are made to communicate with each otherby return bends opposite the ends of the tubes. These boxes and returnbends form an irregular uptake, whereby the steam is expected to rise toa reservoir above. You will notice (Fig. 8) that the upward current ofsteam and water in the return bend meets and directly antagonizes theupward current in the adjoining tube. Only one result can follow. Iftheir velocities are equal, the momentum of both will be neutralized andall circulation stopped, or, if one be stronger, it will cause a backflow in the other by the amount of difference in force, with practicallythe same result. [Illustration: 4880 Horse-power Installation of Babcock & Wilcox Boilersat the Open Hearth Plant of the Cambria Steel Co. , Johnstown, Pa. ThisCompany Operates a Total of 52, 000 Horse Power of Babcock & WilcoxBoilers] [Illustration: Fig. 9] In a well-known boiler, many of which were sold, but of which none arenow made and a very few are still in use, the inventor claimed that thereturn bends and small openings against the tubes were for the purposeof "restricting the circulation" and no doubt they performed well thatoffice; but excepting for the smallness of the openings they were not asefficient for that purpose as the arrangement shown in Fig. 8. [Illustration: Fig. 10] Another form of boiler, first invented by Clarke or Crawford, and latelyrevived, has the uptake made of boxes into which a number, generallyfrom two to four tubes, are expanded, the boxes being connected togetherby nipples (Fig. 9). It is a well-known fact that where a fluid flowsthrough a conduit which enlarges and then contracts, the velocity islost to a greater or less extent at the enlargements, and has to begotten up again at the contractions each time, with a corresponding lossof head. The same thing occurs in the construction shown in Fig. 9. Theenlargements and contractions quite destroy the head and practicallyovercome the tendency of the water to circulate. A horizontal tube stopped at one end, as shown in Fig. 10, can have noproper circulation within it. If moderately driven, the water maystruggle in against the issuing steam sufficiently to keep the surfacecovered, but a slight degree of forcing will cause it to act like thetest tube in Fig. 3, and the more there are of them in a given boilerthe more spasmodic will be its working. The experiment with our kettle (Fig. 2) gives the clue to the best meansof promoting circulation in ordinary shell boilers. Steenstrup or"Martin" and "Galloway" water tubes placed in such boilers also assistin directing the circulation therein, but it is almost impossible toproduce in shell boilers, by any means the circulation of all the waterin one continuous round, such as marks the well-constructed water-tubeboiler. As I have before remarked, provision for a proper circulation of waterhas been almost universally ignored in designing steam boilers, sometimes to the great damage of the owner, but oftener to the jeopardyof the lives of those who are employed to run them. The noted case ofthe Montana and her sister ship, where some $300, 000 was thrown away intrying an experiment which a proper consideration of this subject wouldhave avoided, is a case in point; but who shall count the cost of lifeand treasure not, perhaps, directly traceable to, but, nevertheless, dueentirely to such neglect in design and construction of the thousands ofboilers in which this necessary element has been ignored? In the light of the performance of the exacting conditions of presentday power-plant practice, a review of this lecture and of the foregoinglist of requirements reveals the insight of the inventors of the Babcock& Wilcox boiler into the fundamental principles of steam generatordesign and construction. Since the Babcock & Wilcox boiler became thoroughly established as adurable and efficient steam generator, many types of water-tube boilershave appeared on the market. Most of them, failing to meet enough of therequirements of a perfect boiler, have fallen by the wayside, while afew failing to meet all of the requirements, have only a limited fieldof usefulness. None have been superior, and in the most cases the mostardent admirers of other boilers have been satisfied in looking up tothe Babcock & Wilcox boiler as a standard and in claiming that the newerboilers were "just as good. " Records of recent performances under the most severe conditions ofservices on land and sea, show that the Babcock & Wilcox boiler can berun continually and regularly at higher overloads, with higherefficiency, and lower upkeep cost than any other boiler on the market. It is especially adapted for power-plant work where it is necessary touse a boiler in which steam can be raised quickly and the boiler placedon the line either from a cold state or from a banked fire in theshortest possible time, and with which the capacity, with clean feedwater, will be largely limited by the amount of coal that can be burnedin the furnace. The distribution of the circulation through the separate headers andsections and the action of the headers in forcing a maximum andcontinuous circulation in the lower tubes, permit the operation of theBabcock & Wilcox boiler without objectionable priming, with a higherdegree of concentration of salts in the water than is possible in anyother type of boiler. Repeated daily performances at overloads have demonstrated beyond adoubt the correctness of Mr. Babcock's computation regarding thecirculating tube and header area required for most efficientcirculation. They also have proved that enlargement of the area ofheaders and circulating tubes beyond a certain point diminishes the headavailable for causing circulation and consequently limits the ability ofthe boiler to respond to demands for overloads. In this lecture Mr. Babcock made the prediction that with thecirculating tube area proportioned in accordance with the principleslaid down, the Babcock & Wilcox boiler could be continuously run atdouble its nominal rating, which at that time was based on 12 squarefeet of heating surface per horse power. This prediction is beingfulfilled daily in all the large and prominent power plants in thiscountry and abroad, and it has been repeatedly demonstrated that withclean water and clean tube surfaces it is possible to safely operate atover 300 per cent of the nominal rating. In the development of electrical power stations it becomes more and moreapparent that it is economical to run a boiler at high ratings duringthe times of peak loads, as by so doing the lay-over losses arediminished and the economy of the plant as a whole is increased. The number and importance of the large electric lighting and powerstations constructed during the last ten years that are equipped withBabcock & Wilcox boilers, is a most gratifying demonstration of themerit of the apparatus, especially in view of their satisfactoryoperation under conditions which are perhaps more exacting than those ofany other service. Time, the test of all, results with boilers as with other things, in thesurvival of the fittest. When judged on this basis the Babcock & Wilcoxboiler stands pre-eminent in its ability to cover the whole field ofsteam generation with the highest commercial efficiency obtainable. Yearafter year the Babcock & Wilcox boiler has become more firmlyestablished as the standard of excellence in the boiler making art. [Illustration: South Boston Station of the Boston Elevated Ry. Co. , Boston, Mass. 9600 Horse Power of Babcock & Wilcox Boilers andSuperheaters Installed in this Station] [Illustration: 3600 Horse-power Installation of Babcock & Wilcox Boilersat the Phipps Power House of the Duquesne Light Company, Pittsburgh, Pa. ] EVOLUTION OF THE BABCOCK & WILCOX WATER-TUBE BOILER Quite as much may be learned from the records of failures as from thoseof success. Where a device has been once fairly tried and found to beimperfect or impracticable, the knowledge of that trial is of advantagein further investigation. Regardless of the lesson taught by failure, however, it is an almost every-day occurrence that some device orconstruction which has been tried and found wanting, if not worthless, is again introduced as a great improvement upon a device which has shownby its survival to be the fittest. The success of the Babcock & Wilcox boiler is due to many years ofconstant adherence to one line of research, in which an endeavor hasbeen made to introduce improvements with the view to producing a boilerwhich would most effectively meet the demands of the times. During theperiods that this boiler has been built, other companies have placed onthe market more than thirty water-tube or sectional water-tube boilers, most of which, though they may have attained some distinction and sale, have now entirely disappeared. The following incomplete list will serveto recall the names of some of the boilers that have had a vogue atvarious times, but which are now practically unknown: Dimpfel, Howard, Griffith & Wundrum, Dinsmore, Miller "Fire Box", Miller "American", Miller "Internal Tube", Miller "Inclined Tube", Phleger, Weigant, theLady Verner, the Allen, the Kelly, the Anderson, the Rogers & Black, theEclipse or Kilgore, the Moore, the Baker & Smith, the Renshaw, theShackleton, the "Duplex", the Pond & Bradford, the Whittingham, theBee, the Hazleton or "Common Sense", the Reynolds, the Suplee or Luder, the Babbit, the Reed, the Smith, the Standard, etc. , etc. It is with the object of protecting our customers and friends from lossthrough purchasing discarded ideas that there is given on the followingpages a brief history of the development of the Babcock & Wilcox boileras it is built to-day. The illustrations and brief descriptions indicateclearly the various designs and constructions that have been used andthat have been replaced, as experience has shown in what way improvementmight be made. They serve as a history of the experimental steps in thedevelopment of the present Babcock & Wilcox boiler, the value andsuccess of which, as a steam generator, is evidenced by the fact thatthe largest and most discriminating users continue to purchase themafter years of experience in their operation. [Illustration: No. 1] No. 1. The original Babcock & Wilcox boiler was patented in 1867. Themain idea in its design was safety, to which all other features weresacrificed wherever they conflicted. The boiler consisted of a nest ofhorizontal tubes, serving as a steam and water reservoir, placed aboveand connected at each end by bolted joints to a second nest of inclinedheating tubes filled with water. The tubes were placed one above theother in vertical rows, each row and its connecting end forming a singlecasting. Hand-holes were placed at each end for cleaning. Internal tubeswere placed within the inclined tubes with a view to aiding circulation. No. 2. This boiler was the same as No. 1, except that the internalcirculating tubes were omitted as they were found to hinder rather thanhelp the circulation. Nos. 1 and 2 were found to be faulty in both material and design, castmetal proving unfit for heating surfaces placed directly over the fire, as it cracked as soon as any scale formed. No. 3. Wrought-iron tubes were substituted for the cast-iron heatingtubes, the ends being brightened, laid in moulds, and the headers caston. The steam and water capacity in this design were insufficient to secureregularity of action, there being no reserve upon which to draw duringfiring or when the water was fed intermittently. The attempt to dry thesteam by superheating it in the nest of tubes forming the steam spacewas found to be impracticable. The steam delivered was either wet, dryor superheated, according to the rate at which it was being drawn fromthe boiler. Sediment was found to lodge in the lowermost point of theboiler at the rear end and the exposed portions cracked off at thispoint when subjected to the furnace heat. [Illustration: No. 4] No. 4. A plain cylinder, carrying the water line at its center andleaving the upper half for steam space, was substituted for the nest oftubes forming the steam and water space in Nos. 1, 2 and 3. The sectionswere made as in No. 3 and a mud drum added to the rear end of thesections at the point that was lowest and farthest removed from thefire. The gases were made to pass off at one side and did not come intocontact with the mud drum. Dry steam was obtained through the increaseof separating surface and steam space and the added water capacityfurnished a storage for heat to tide over irregularities of firing andfeeding. By the addition of the drum, the boiler became a serviceableand practical design, retaining all of the features of safety. As thedrum was removed from the direct action of the fire, it was notsubjected to excessive strain due to unequal expansion, and itsdiameter, if large in comparison with that of the tubes formerly used, was small when compared with that of cylindrical boilers. Difficultieswere encountered in this boiler in securing reliable joints between thewrought-iron tubes and the cast-iron headers. [Illustration: No. 5] No. 5. In this design, wrought-iron water legs were substituted for thecast-iron headers, the tubes being expanded into the inside sheets and alarge cover placed opposite the front end of the tubes for cleaning. Thetubes were staggered one above the other, an arrangement found to bemore efficient in the absorption of heat than where they were placed invertical rows. In other respects, the boiler was similar to No. 4, except that it had lost the important element of safety through theintroduction of the very objectionable feature of flat stayed surfaces. The large doors for access to the tubes were also a cause of weakness. An installation of these boilers was made at the plant of the CalvertSugar Refinery in Baltimore, and while they were satisfactory in theiroperation, were never duplicated. [Illustration: No. 6] No. 6. This was a modification of No. 5 in which longer tubes were usedand over which the gases were caused to make three passes with a view ofbetter economy. In addition, some of the stayed surfaces were omittedand handholes substituted for the large access doors. A number ofboilers of this design were built but their excessive first cost, thelack of adjustability of the structure under varying temperatures, andthe inconvenience of transportation, led to No. 7. [Illustration: No. 7] No. 7. In this boiler, the headers and water legs were replaced byT-heads screwed to the ends of the inclined tubes. The faces of these Tswere milled and the tubes placed one above the other with the milledfaces metal to metal. Long bolts passed through each vertical section ofthe T-heads and through connecting boxes on the heads of the drumsholding the whole together. A large number of boilers of this designwere built and many were in successful operation for over twenty years. In most instances, however, they were altered to later types. [Illustration: No. 8] [Illustration: No. 9] Nos. 8 and 9. These boilers were known as the Griffith & Wundrum type, the concern which built them being later merged in The Babcock & WilcoxCo. Experiments were made with this design with four passages of thegases across the tubes and the downward circulation of the water at therear of the boiler was carried to the bottom row of tubes. In No. 9 anattempt was made to increase the safety and reduce the cost by reducingthe amount of steam and water capacity. A drum at right angles to theline of tubes was used but as there was no provision made to secure drysteam, the results were not satisfactory. The next move in the directionof safety was the employment of several drums of small diameter insteadof a single drum. [Illustration: No. 10] This is shown in No. 10. A nest of small horizontal drums, 15 inches indiameter, was used in place of the single drum of larger diameter. A setof circulation tubes was placed at an intermediate angle between themain bank of heating tubes and the horizontal drums forming the steamreservoir. These circulators were to return to the rear end of thecirculating tubes the water carried up by the circulation, and in thisway were to allow only steam to be delivered to the small drums above. There was no improvement in the action of this boiler over that of No. 9. The four passages of the gas over the tubes tried in Nos. 8, 9 and 10were not found to add to the economy of the boiler. [Illustration: No. 11] No. 11. A trial was next made of a box coil system, in which the waterwas made to transverse the furnace several times before being deliveredto the drum above. The tendency here, as in all similar boilers, was toform steam in the middle of the coil and blow the water from each end, leaving the tubes practically dry until the steam found an outlet andthe water returned. This boiler had, in addition to a defectivecirculation, a decidedly geyser-like action and produced wet steam. [Illustration: No. 12] All of the types mentioned, with the exception of Nos. 5 and 6, hadbetween their several parts a large number of bolted joints which weresubjected to the action of the fire. When these boilers were placed inoperation it was demonstrated that as soon as any scale formed on theheating surfaces, leaks were caused due to unequal expansion. No. 12. With this boiler, an attempt was made to remove the joints fromthe fire and to increase the heating surface in a given space. Watertubes were expanded into both sides of wrought-iron boxes, openingsbeing made for the admission of water and the exit of steam. Fire tubeswere placed inside the water tubes to increase the heating surface. Thisdesign was abandoned because of the rapid stopping up of the tubes byscale and the impossibility of cleaning them. [Illustration: No. 13] No. 13. Vertical straight line headers of cast iron, each containing tworows of tubes, were bolted to a connection leading to the steam andwater drum above. [Illustration: No. 14] No. 14. A wrought-iron box was substituted for the double cast-ironheaders. In this design, stays were necessary and were found, as always, to be an element to be avoided wherever possible. The boiler was animprovement on No. 6, however. A slanting bridge wall was introducedunderneath the drum to throw a larger portion of its heating surfaceinto the combustion chamber under the bank of tubes. This bridge wall was found to be difficult to keep in repair and was ofno particular benefit. [Illustration: No. 15] No. 15. Each row of tubes was expanded at each end into a continuousheader, cast of car wheel metal. The headers had a sinuous form so thatthey would lie close together and admit of a staggered position of thetubes when assembled. While other designs of header form were triedlater, experience with Nos. 14 and 15 showed that the style here adoptedwas the best for all purposes and it has not been changed materiallysince. The drum in this design was supported by girders resting on thebrickwork. Bolted joints were discarded, with the exception of thoseconnecting the headers to the front and rear ends of the drums and thebottom of the rear headers to the mud drum. Even such joints, however, were found objectionable and were superseded in subsequent constructionby short lengths of tubes expanded into bored holes. [Illustration: No. 16] No. 16. In this design, headers were tried which were made in the formof triangular boxes, in each of which there were three tubes expanded. These boxes were alternately reversed and connected by short lengths ofexpanded tubes, being connected to the drum by tubes bent in a manner toallow them to enter the shell normally. The joints between headersintroduced an element of weakness and the connections to the drum wereinsufficient to give adequate circulation. [Illustration: No. 17] No. 17. Straight horizontal headers were next tried, alternately shiftedright and left to allow a staggering of tubes. These headers wereconnected to each other and to the drums by expanded nipples. Theobjections to this boiler were almost the same as those to No. 16. [Illustration: No. 18] [Illustration: No. 19] Nos. 18 and 19. These boilers were designed primarily for fireprotection purposes, the requirements demanding a small, compact boilerwith ability to raise steam quickly. These both served the purposeadmirably but, as in No. 9, the only provision made for the securing ofdry steam was the use of the steam dome, shown in the illustration. Thisdome was found inadequate and has since been abandoned in nearly allforms of boiler construction. No other remedy being suggested at thetime, these boilers were not considered as desirable for general use asNos. 21 and 22. In Europe, however, where small size units were more indemand, No. 18 was modified somewhat and used largely with excellentresults. These experiments, as they may now be called, although manyboilers of some of the designs were built, clearly demonstrated that thebest construction and efficiency required adherence to the followingelements of design: 1st. Sinuous headers for each vertical row of tubes. 2nd. A separate and independent connection with the drum, both front andrear, for each vertical row of tubes. [Illustration: No. 20A] [Illustration: No. 20B] 3rd. All joints between parts of the boiler proper to be made withoutbolts or screw plates. 4th. No surfaces to be used which necessitate the use of stays. 5th. The boiler supported independently of the brickwork so as to allowfreedom for expansion and contraction as it is heated or cooled. 6th. Ample diameter of steam and water drums, these not to be less than30 inches except for small size units. 7th. Every part accessible for cleaning and repairs. With these points having been determined, No. 20 was designed. Thisboiler had all the desirable features just enumerated, together with anumber of improvements as to detail of construction. The general form ofNo. 15 was adhered to but the bolted connections between sections anddrum and sections and mud drum were discarded in favor of connectionsmade by short lengths of boiler tubes expanded into the adjacent parts. This boiler was suspended from girders, like No. 15, but these in turnwere carried on vertical supports, leaving the pressure parts entirelyfree from the brickwork, the mutually deteriorating strains presentwhere one was supported by the other being in this way overcome. Hundreds of thousands of horse power of this design were built, givinggreat satisfaction. The boiler was known as the "C. I. F. " (cast-ironfront) style, an ornamental cast-iron front having been usuallyfurnished. [Illustration: No. 21] The next step, and the one which connects the boilers as described aboveto the boiler as it is built to-day, was the design illustrated in No. 21. These boilers were known as the "W. I. F. " style, the frontsfurnished as part of the equipment being constructed largely of wroughtiron. The cast-iron drumheads used in No. 20 were replaced bywrought-steel flanged and "bumped" heads. The drums were made longer andthe sections connected to wrought-steel cross boxes riveted to thebottom of the drums. The boilers were supported by girders and columnsas in No. 20. [Illustration: No. 22] No. 22. This boiler, which is designated as the "Vertical Header" type, has the same general features of construction as No. 21, except that thetube sheet side of the headers is "stepped" to allow the headers to beplaced vertically and at right angles to the drum and still maintain thetubes at the angle used in Nos. 20 and 21. [Illustration: No. 23] No. 23, or the cross drum design of boiler, is a development of theBabcock & Wilcox marine boiler, in which the cross drum is usedexclusively. The experience of the Glasgow Works of The Babcock &Wilcox, Ltd. , with No. 18 proved that proper attention to details ofconstruction would make it a most desirable form of boiler whereheadroom was limited. A large number of this design have beensuccessfully installed and are giving satisfactory results under widelyvarying conditions. The cross drum boiler is also built in a verticalheader design. Boilers Nos. 21, 22 and 23, with a few modifications, are now thestandard forms. These designs are illustrated, as they are constructedto-day, on pages 48, 52, 54, 58 and 60. The last step in the development of the water-tube boiler, beyond whichit seems almost impossible for science and skill to advance, consists inthe making of all pressure parts of the boiler of wrought steel, including sinuous headers, cross boxes, nozzles, and the like. Thisconstruction was the result of the demands of certain Continental lawsthat are coming into general vogue in this country. The Babcock & WilcoxCo. Have at the present time a plant producing steel forgings that havebeen pronounced by the _London Engineer_ to be "a perfect triumphof the forgers' art". The various designs of this all wrought-steel boiler are fullyillustrated in the following pages. [Illustration: Wrought-steel Vertical Header Longitudinal Drum Babcock &Wilcox Boiler, Equipped with Babcock & Wilcox Superheater and Babcock &Wilcox Chain Grate Stoker] THE BABCOCK & WILCOX BOILER The following brief description of the Babcock & Wilcox boiler willclearly indicate the manner in which it fulfills the requirements of theperfect steam boiler already enumerated. The Babcock & Wilcox boiler is built in two general classes, thelongitudinal drum type and the cross drum type. Either of these designsmay be constructed with vertical or inclined headers, and the headers inturn may be of wrought steel or cast iron dependent upon the workingpressure for which the boiler is constructed. The headers may be ofdifferent lengths, that is, may connect different numbers of tubes, andit is by a change in the number of tubes in height per section and thenumber of sections in width that the size of the boiler is varied. The longitudinal drum boiler is the generally accepted standard ofBabcock & Wilcox construction. The cross drum boiler, though originallydesigned to meet certain conditions of headroom, has become popular fornumerous classes of work where low headroom is not a requirement whichmust be met. LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type ofboiler is made up of a drum or drums, depending upon the width of theboiler extending longitudinally over the other pressure parts. To thedrum or drums there are connected through cross boxes at either end thesections, which are made up of headers and tubes. At the lower end ofthe sections there is a mud drum extending entirely across the settingand connected to all sections. The connections between all parts are byshort lengths of tubes expanded into bored seats. [Illustration: Forged-steel Drumhead with Manhole Plate in Position] The drums are of three sheets, of such thickness as to give the requiredfactor of safety under the maximum pressure for which the boiler isconstructed. The circular seams are ordinarily single lap riveted thoughthese may be double lap riveted to meet certain requirements of pressureor of specifications. The longitudinal seams are properly proportionedbutt and strap or lap riveted joints dependent upon the pressure forwhich the boilers are built. Where butt strap joints are used the strapsare bent to the proper radius in an hydraulic press. The courses arebuilt independently to template and are assembled by an hydraulicforcing press. All riveted holes are punched one-quarter inch smallerthan the size of rivets as driven and are reamed to full size after theplates are assembled. All rivets are driven by hydraulic pressure andheld until black. [Illustration: Forged-steel Drumhead Interior] The drumheads are hydraulic forged at a single heat, the manhole openingand stiffening ring being forged in position. Flat raised seats forwater column and feed connections are formed in the forging. All heads are provided with manholes, the edges of which are turnedtrue. The manhole plates are of forged steel and turned to fit manholeopening. These plates are held in position by forged-steel guards andbolts. The drum nozzles are of forged steel, faced, and fitted with taperthread stud bolts. [Illustration: Forged-steel Drum Nozzle] Cross boxes by means of which the sections are attached to the drums, are of forged steel, made from a single sheet. Where two or more drums are used in one boiler they are connected by across pipe having a flanged outlet for the steam connection. [Illustration: Forged-steel Cross Box] The sections are built of 4-inch hot finished seamless open-hearth steeltubes of No. 10 B. W. G. Where the boilers are built for workingpressures up to 210 pounds. Where the working pressure is to be abovethis and below 260 pounds, No. 9 B. W. G. Tubes are supplied. [Illustration: Inside Handhole Fittings Wrought-steel Vertical Header] The tubes are expanded into headers of serpentine or sinuous form, whichdispose the tubes in a staggered position when assembled as a completeboiler. These headers are of wrought steel or of cast iron, the latterbeing ordinarily supplied where the working pressure is not to exceed160 pounds. The headers may be either vertical or inclined as shown inthe various illustrations of assembled boilers. [Illustration: Wrought-steel Vertical Header] Opposite each tube end in the headers there is placed a handhole ofsufficient size to permit the cleaning, removal or renewal of a tube. These openings in the wrought steel vertical headers are elliptical inshape, machine faced, and milled to a true plane back from the edge asufficient distance to make a seat. The openings are closed by insidefitting forged plates, shouldered to center in the opening, theirflanged seats milled to a true plane. These plates are held in positionby studs and forged-steel binders and nuts. The joints between platesand headers are made with a thin gasket. [Illustration: Inside Handhole Fitting Wrought-steel Inclined Header] In the wrought-steel inclined headers the handhole openings are eithercircular or elliptical, the former being ordinarily supplied. Thecircular openings have a raised seat milled to a true plane. Theopenings are closed on the outside by forged-steel caps, milled andground true, held in position by forged-steel safety clamps and securedby ball-headed bolts to assure correct alignment. With this style offitting, joints are made tight, metal to metal, without packing of anykind. [Illustration: Wrought-steel Inclined Header] Where elliptical handholes are furnished they are faced inside, closedby inside fitting forged-steel plates, held to their seats by studs andsecured by forged-steel binders and nuts. The joints between plates and header are made with a thin gasket. [Illustration: Cast-iron Vertical Header] The vertical cast-iron headers have elliptical handholes with raisedseats milled to a true plane. These are closed on the outside bycast-iron caps milled true, held in position by forged-steel safetyclamps, which close the openings from the inside and which are securedby ball-headed bolts to assure proper alignment. All joints are madetight, metal to metal, without packing of any kind. The mud drum to which the sections are attached at the lower end of therear headers, is a forged-steel box 7¼ inches square, and of such lengthas to be connected to all headers by means of wrought nipples expandedinto counterbored seats. The mud drum is furnished with handholes forcleaning, these being closed from the inside by forged-steel plates withstuds, and secured on a faced seat in the mud drum by forged-steelbinders and nuts. The joints between the plates and the drum are madewith thin gaskets. The mud drum is tapped for blow-off connection. All connections between drums and sections and between sections and muddrum are of hot finished seamless open-hearth steel tubes of No. 9B. W. G. Boilers of the longitudinal drum type are suspended front and rear fromwrought-steel supporting frames entirely independent of the brickwork. This allows for expansion and contraction of the pressure parts withoutstraining either the boiler or the brickwork, and also allows ofbrickwork repair or renewal without in any way disturbing the boiler orits connections. [Illustration: Babcock & Wilcox Wrought-steel Vertical Header Cross DrumBoiler] CROSS DRUM CONSTRUCTION--The cross drum type of boilers differs from thelongitudinal only in drum construction and method of support. The drumin this type is placed transversely across the rear of the boiler and isconnected to the sections by means of circulating tubes expanded intobored seats. The drums for all pressures are of two sheets of sufficient thickness togive the required factor of safety. The longitudinal seams are doubleriveted butt strapped, the straps being bent to the proper radius in anhydraulic press. The circulating tubes are expanded into the drums atthe seams, the butt straps serving as tube seats. The drumheads, drum fittings and features of riveting are the same inthe cross drum as in the longitudinal types. The sections and mud drumare also the same for the two types. Cross drum boilers are supported at the rear on the mud drum which restson cast-iron foundation plates. They are suspended at the front from awrought-iron supporting frame, each section being suspendedindependently from the cross members by hook suspension bolts. Thismethod of support is such as to allow for expansion and contractionwithout straining either the boiler or the brickwork and permits ofrepair or renewal of the latter without in any way disturbing the boileror its connections. The following features of design and of attachments supplied are thesame for all types. FRONTS--Ornamental fronts are fitted to the front supporting frame. These have large doors for access to the front headers and panels abovethe fire fronts. The fire fronts where furnished have independent framesfor fire doors which are bolted on, and ashpit doors fitted with blastcatches. The lugs on door frames and on doors are cast solid. The facesof doors and of frames are planed and the lugs milled. The doors andframes are placed in their final relative position, clamped, and theholes for hinge pins drilled while thus held. A perfect alignment ofdoor and frame is thus assured and the method is representative of thecare taken in small details of manufacture. The front as a whole is so arranged that any stoker may be applied withbut slight modification wherever boilers are set with sufficient furnaceheight. [Illustration: Cross Drum Boiler Front] In the vertical header boilers large wrought-iron doors, which giveaccess to the rear headers, are attached to the rear supporting frame. [Illustration: Wrought-steel Inclined Header Longitudinal Drum Babcock &Wilcox Boiler, Equipped with Babcock & Wilcox Superheater] [Illustration: Automatic Drumhead Stop and Check Valve] FITTINGS--Each boiler is provided with the following fittings as part ofthe standard equipment: Blow-off connections and valves attached to the mud drum. Safety valves placed on nozzles on the steam drums. A water column connected to the front of the drum. A steam gauge attached to the boiler front. Feed water connection and valves. A flanged stop and check valve ofheavy pattern is attached directly to each drumhead, closingautomatically in case of a rupture in the feed line. All valves and fittings are substantially built and are of designs whichby their successful service for many years have become standard with TheBabcock & Wilcox Co. The fixtures that are supplied with the boilers consist of: Dead plates and supports, the plates arranged for a fire brick lining. A full set of grate bars and bearers, the latter fitted with expansionsockets for side walls. Flame bridge plates with necessary fastenings, and special fire brickfor lining same. Bridge wall girder for hanging bridge wall with expansion sockets forside walls. A full set of access and cleaning doors through which all portions ofthe pressure parts may be reached. A swing damper and frame with damper operating rig. There are also supplied with each boiler a wrench for handhole nuts, awater-driven turbine tube cleaner, a set of fire tools and a metal steamhose and cleaning pipe equipped with a special nozzle for blowing dustand soot from the tubes. Aside from the details of design and construction as covered in theforegoing description, a study of the illustrations will make clear thefeatures of the boiler as a whole which have led to its success. The method of supporting the boiler has been described. This allows itto be hung at any height that may be necessary to properly handle thefuel to be burned or to accommodate the stoker to be installed. Theheight of the nest of tubes which forms the roof of the furnace is thusthe controlling feature in determining the furnace height, or thedistance from the front headers to the floor line. The sides and frontof the furnace are formed by the side and front boiler walls. The rearwall of the furnace consists of a bridge wall built from the bottom ofthe ashpit to the lower row of tubes. The location of this wall may beadjusted within limits to give the depth of furnace demanded by the fuelused. Ordinarily the bridge wall is the determining feature in thelocating of the front baffle. Where a great depth of furnace isnecessary, in which case, if the front baffle were placed at the bridgewall the front pass of the boiler would be relatively too long, apatented construction is used which maintains the baffle in what may beconsidered its normal position, and a connection made between the baffleand the bridge wall by means of a tile roof. Such furnace constructionis known as a "Webster" furnace. [Illustration: Longitudinal Drum Boiler--Front View] A consideration of this furnace will clearly indicate its adaptability, by reason of its flexibility, for any fuel and any design of stoker. Theboiler lends itself readily to installation with an extension or Dutchoven furnace if this be demanded by the fuel to be used, and in generalit may be stated that a satisfactory furnace arrangement may be made inconnection with a Babcock & Wilcox boiler for burning any fuel, solid, liquid or gaseous. The gases of combustion evolved in the furnace above described are ledover the heating surfaces by two baffles. These are formed of cast-ironbaffle plates lined with special fire brick and held in position by tubeclamps. The front baffle leads the gases through the forward portion ofthe tubes to a chamber beneath the drum or drums. It is in this chamberthat a superheater is installed where such an apparatus is desired. Thegases make a turn over the front baffle, are led downward through thecentral portion of the tubes, called the second pass, by means of ahanging bridge wall of brick and the second baffle, around which theymake a second turn upward, pass through the rear portion of the tubesand are led to the stack or flue through a damper box in the rear wall, or around the drums to a damper box placed overhead. The space beneath the tubes between the bridge wall and the rear boilerwall forms a pocket into which much of the soot from the gases in theirdownward passage through the second pass will be deposited and fromwhich it may be readily cleaned through doors furnished for the purpose. The gas passages are ample and are so proportioned that the resistanceoffered to the gases is only such as will assure the proper abstractionof heat from the gases without causing undue friction, requiringexcessive draft. [Illustration: Partial Vertical Section Showing Method of IntroducingFeed Water] The method in which the feed water is introduced through the frontdrumhead of the boiler is clearly seen by reference to the illustration. From this point of introduction the water passes to the rear of thedrum, downward through the rear circulating tubes to the sections, upward through the tubes of the sections to the front headers andthrough these headers and front circulating tubes again to the drumwhere such water as has not been formed into steam retraces its course. The steam formed in the passage through the tubes is liberated as thewater reaches the front of the drum. The steam so formed is stored inthe steam space above the water line, from which it is drawn through aso-called "dry pipe. " The dry pipe in the Babcock & Wilcox boiler ismisnamed, as in reality it fulfills none of the functions ordinarilyattributed to such a device. This function is usually to restrict theflow of steam from a boiler with a view to avoid priming. In the Babcock& Wilcox boiler its function is simply that of a collecting pipe, and asthe aggregate area of the holes in it is greatly in excess of the areaof the steam outlet from the drum, it is plain that there can be norestriction through this collecting pipe. It extends nearly the lengthof the drum, and draws steam evenly from the whole length of the steamspace. [Illustration: Cast-iron Vertical Header Longitudinal Drum Babcock &Wilcox Boiler] [Illustration: Closed Open Patented Side Dusting Doors] The large tube doors through which access is had to the front headersand the doors giving such access to the rear headers in boilers of thevertical header type have already been described and are shown clearlyby the illustrations on pages 56 and 74. In boilers of the inclinedheader type, access to the rear headers is secured through the chamberformed by the headers and the rear boiler wall. Large doors in the sidesof the setting give full access to all parts for inspection and forremoval of accumulations of soot. Small dusting doors are supplied forthe side walls through which all of the heating surfaces may be cleanedby means of a steam dusting lance. These side dusting doors are apatented feature and the shutters are self closing. In wide boilersadditional cleaning doors are supplied at the top of the setting toinsure ease in reaching all portions of the heating surface. The drums are accessible for inspection through the manhole openings. The removal of the handhole plates makes possible the inspection of eachtube for its full length and gives the assurance that no defect canexist that cannot be actually seen. This is particularly advantageouswhen inspecting for the presence of scale. The materials entering into the construction of the Babcock & Wilcoxboiler are the best obtainable for the special purpose for which theyare used and are subjected to rigid inspection and tests. The boilers are manufactured by means of the most modern shop equipmentand appliances in the hands of an old and well-tried organization ofskilled mechanics under the supervision of experienced engineers. [Illustration: Cast-iron Vertical Header Cross Drum Babcock & WilcoxBoiler] ADVANTAGES OF THE BABCOCK & WILCOX BOILER The advantages of the Babcock & Wilcox boiler may perhaps be mostclearly set forth by a consideration, 1st, of water-tube boilers as aclass as compared with shell and fire-tube boilers; and 2nd, of theBabcock & Wilcox boiler specifically as compared with other designs ofwater-tube boilers. WATER-TUBE _VERSUS_ FIRE-TUBE BOILERS Safety--The most important requirement of a steam boiler is that itshall be safe in so far as danger from explosion is concerned. If theenergy in a large shell boiler under pressure is considered, the thoughtof the destruction possible in the case of an explosion is appalling. The late Dr. Robert H. Thurston, Dean of Sibley College, CornellUniversity, and past president of the American Society of MechanicalEngineers, estimated that there is sufficient energy stored in a plaincylinder boiler under 100 pounds steam pressure to project it in case ofan explosion to a height of over 3½ miles; a locomotive boiler at 125pounds pressure from one-half to one-third of a mile; and a 60horse-power return tubular boiler under 75 pounds pressure somewhat overa mile. To quote: "A cubic foot of heated water under a pressure of from60 to 70 pounds per square inch has about the same energy as one poundof gunpowder. " From such a consideration, it may be readily appreciatedhow the advent of high pressure steam was one of the strongest factorsin forcing the adoption of water-tube boilers. A consideration of thethickness of material necessary for cylinders of various diameters undera steam pressure of 200 pounds and assuming an allowable stress of12, 000 pounds per square inch, will perhaps best illustrate this point. Table 1 gives such thicknesses for various diameters of cylinders nottaking into consideration the weakening effect of any joints which maybe necessary. The rapidity with which the plate thickness increases withthe diameter is apparent and in practice, due to the fact that rivetedjoints must be used, the thicknesses as given in the table, with theexception of the first, must be increased from 30 to 40 per cent. In a water-tube boiler the drums seldom exceed 48 inches in diameter andthe thickness of plate required, therefore, is never excessive. Thethinner metal can be rolled to a more uniform quality, the seams admitof better proportioning, and the joints can be more easily and perfectlyfitted than is the case where thicker plates are necessary. All of thesepoints contribute toward making the drums of water-tube boilers betterable to withstand the stress which they will be called upon to endure. The essential constructive difference between water-tube and fire-tubeboilers lies in the fact that the former is composed of parts ofrelatively small diameter as against the large diameters necessary inthe latter. The factor of safety of the boiler parts which come in contact with themost intense heat in water-tube boilers can be made much higher thanwould be practicable in a shell boiler. Under the assumptions consideredabove in connection with the thickness of plates required, a number 10gauge tube (0. 134 inch), which is standard in Babcock & Wilcox boilersfor pressures up to 210 pounds under the same allowable stress as wasused in computing Table 1, the safe working pressure for the tubes is870 pounds per square inch, indicating the very large margin of safetyof such tubes as compared with that possible with the shell of a boiler. TABLE 1 PLATE THICKNESS REQUIRED FOR VARIOUS CYLINDER DIAMETERS ALLOWABLE STRESS, 12000 POUNDS PER SQUARE INCH, 200 POUNDS GAUGE PRESSURE, NO JOINTS +---------+-----------+|Diameter | Thickness ||Inches | Inches |+---------+-----------+| 4 | 0. 033 || 36 | 0. 300 || 48 | 0. 400 || 60 | 0. 500 || 72 | 0. 600 || 108 | 0. 900 || 120 | 1. 000 || 144 | 1. 200 |+---------+-----------+ A further advantage in the water-tube boiler as a class is theelimination of all compressive stresses. Cylinders subjected to externalpressures, such as fire tubes or the internally fired furnaces ofcertain types of boilers, will collapse under a pressure much lower thanthat which they could withstand if it were applied internally. This isdue to the fact that if there exists any initial distortion from itstrue shape, the external pressure will tend to increase such distortionand collapse the cylinder, while an internal pressure tends to restorethe cylinder to its original shape. Stresses due to unequal expansion have been a fruitful source of troublein fire-tube boilers. In boilers of the shell type, the riveted joints of the shell, withtheir consequent double thickness of metal exposed to the fire, givesrise to serious difficulties. Upon these points are concentrated allstrains of unequal expansion, giving rise to frequent leaks andoftentimes to actual ruptures. Moreover, in the case of such rupture, the whole body of contained water is liberated instantaneously and adisastrous and usually fatal explosion results. Further, unequal strains result in shell or fire-tube boilers due to thedifference in temperature of the various parts. This difference intemperature results from the lack of positive well defined circulation. While such a circulation does not necessarily accompany all water-tubedesigns, in general, the circulation in water-tube boilers is much moredefined than in fire-tube or shell boilers. A positive and efficient circulation assures that all portions of thepressure parts will be at approximately the same temperature and in thisway strains resulting from unequal temperatures are obviated. If a shell or fire-tubular boiler explodes, the apparatus as a whole isdestroyed. In the case of water-tube boilers, the drums are ordinarilyso located that they are protected from intense heat and any rupture isusually in the case of a tube. Tube failures, resulting from blisters orburning, are not serious in their nature. Where a tube ruptures becauseof a flaw in the metal, the result may be more severe, but there cannotbe the disastrous explosion such as would occur in the case of theexplosion of a shell boiler. To quote Dr. Thurston, relative to the greater safety of the water-tubeboiler: "The stored available energy is usually less than that of any ofthe other stationary boilers and not very far from the amount stored, pound for pound, in the plain tubular boiler. It is evident that theiradmitted safety from destructive explosion does not come from thisrelation, however, but from the division of the contents into smallportions and especially from those details of construction which make ittolerably certain that any rupture shall be local. A violent explosioncan only come from the general disruption of a boiler and the liberationat once of large masses of steam and water. " Economy--The requirement probably next in importance to safety in asteam boiler is economy in the use of fuel. To fulfill such arequirement, the three items, of proper grate for the class of fuel tobe burned, a combustion chamber permitting complete combustion of gasesbefore their escape to the stack, and the heating surface of such acharacter and arrangement that the maximum amount of available heat maybe extracted, must be co-ordinated. Fire-tube boilers from the nature of their design do not permit thevariety of combinations of grate surface, heating surface, andcombustion space possible in practically any water-tube boiler. In securing the best results in fuel economy, the draft area in a boileris an important consideration. In fire-tube boilers this area is limitedto the cross sectional area of the fire tubes, a condition furtheraggravated in a horizontal boiler by the tendency of the hot gases topass through the upper rows of tubes instead of through all of the tubesalike. In water-tube boilers the draft area is that of the space outsideof the tubes and is hence much greater than the cross sectional area ofthe tubes. Capacity--Due to the generally more efficient circulation found inwater-tube than in fire-tube boilers, rates of evaporation are possiblewith water-tube boilers that cannot be approached where fire-tubeboilers are employed. Quick Steaming--Another important result of the better circulationordinarily found in water-tube boilers is in their ability to raisesteam rapidly in starting and to meet the sudden demands that may bethrown on them. In a properly designed water-tube boiler steam may be raised from a coldboiler to 200 pounds pressure in less than one-half hour. For the sake of comparison with the figure above, it may be stated thatin the U. S. Government Service the shortest time allowed for getting upsteam in Scotch marine boilers is 6 hours and the time ordinarilyallowed is 12 hours. In large double-ended Scotch boilers, such as aregenerally used in Trans-Atlantic service, the fires are usually started24 hours before the time set for getting under way. This length of timeis necessary for such boilers in order to eliminate as far as possibleexcessive strains resulting from the sudden application of heat to thesurfaces. Accessibility--In the "Requirements of a Perfect Steam Boiler", asstated by Mr. Babcock, he demonstrates the necessity for completeaccessibility to all portions of the boiler for cleaning, inspection andrepair. Cleaning--When the great difference is realized in performance, both asto economy and capacity of a clean boiler and one in which the heatingsurfaces have been allowed to become fouled, it may be appreciated thatthe ability to keep heating surfaces clean internally and externally isa factor of the highest importance. Such results can be accomplished only by the use of a design in boilerconstruction which gives complete accessibility to all portions. Infire-tube boilers the tubes are frequently nested together with a spacebetween them often less than 1¼ inches and, as a consequence, nearly theentire tube surface is inaccessible. When scale forms upon such tubes itis impossible to remove it completely from the inside of the boiler andif it is removed by a turbine hammer, there is no way of knowing howthorough a job has been done. With the formation of such scale there isdanger through overheating and frequent tube renewals are necessary. [Illustration: Portion of 29, 000 Horse-power Installation of Babcock &Wilcox Boilers in the L Street Station of the Edison ElectricIlluminating Co. Of Boston, Mass. This Company Operates in its VariousStations a Total of 39, 000 Horse Power of Babcock & Wilcox Boilers] In Scotch marine boilers, even with the engines operating condensing, complete tube renewals at intervals of six or seven years are required, while large replacements are often necessary in less than one year. Inreturn tubular boilers operated with bad feed water, complete tuberenewals annually are not uncommon. In this type of boiler much sedimentfalls on the bottom sheets where the intense heat to which they aresubjected bakes it to such an excessive hardness that the only method ofremoving it is to chisel it out. This can be done only by omitting tubesenough to leave a space into which a man can crawl and the discomfortsunder which he must work are apparent. Unless such a deposit is removed, a burned and buckled plate will invariably result, and if neglected toolong an explosion will follow. In vertical fire-tube boilers using a water leg construction, a depositof mud in such legs is an active agent in causing corrosion and thedifficulty of removing such deposit through handholes is well known. Acomplete removal is practically impossible and as a last resort toobviate corrosion in certain designs, the bottom of the water legs insome cases have been made of copper. A thick layer of mud and scale isalso liable to accumulate on the crown sheet of such boilers and maycause the sheet to crack and lead to an explosion. The soot and fine coal swept along with the gases by the draft willsettle in fire tubes and unless removed promptly, must be cut out with aspecial form of scraper. It is not unusual where soft coal is used tofind tubes half filled with soot, which renders useless a large portionof the heating surface and so restricts the draft as to make itdifficult to burn sufficient coal to develop the required power fromsuch heating surface as is not covered by soot. Water-tube boilers in general are from the nature of their design morereadily accessible for cleaning than are fire-tube boilers. Inspection--The objections given above in the consideration of theinability to properly clean fire-tube boilers hold as well for theinspection of such boilers. Repairs--The lack of accessibility in fire-tube boilers further leads todifficulties where repairs are required. In fire-tube boilers tube renewals are a serious undertaking. Theaccumulation of hard deposit on the exterior of the surfaces so enlargesthe tubes that it is oftentimes difficult, if not impossible, to drawthem through the tube sheets and it is usually necessary to cut out suchtubes as will allow access to the one which has failed and remove themthrough the manhole. When a tube sheet blisters, the defective part must be cut out byhand-tapped holes drilled by ratchets and as it is frequently impossibleto get space in which to drive rivets, a "soft patch" is necessary. Thisis but a makeshift at best and usually results in either a reduction ofthe safe working pressure or in the necessity for a new plate. If thelatter course is followed, the old plate must be cut out, a new onescribed to place to locate rivet holes and in order to obtain room fordriving rivets, the boiler will have to be re-tubed. The setting must, of course, be at least partially torn out andreplaced. In case of repairs, of such nature in fire-tube boilers, the workingpressure of such repaired boilers will frequently be lowered by theinsurance companies when the boiler is again placed in service. In the case of a rupture in a water-tube boiler, the loss willordinarily be limited to one or two tubes which can be readily replaced. The fire-tube boiler will be so completely demolished that the questionof repairs will be shifted from the boiler to the surrounding property, the damage to which will usually exceed many times the cost of a boilerof a type which would have eliminated the possibility of a disastrousexplosion. In considering the proper repair cost of the two types ofboilers, the fact should not be overlooked that it is poor economy toinvest large sums in equipment that, through a possible accident to theboiler may be wholly destroyed or so damaged that the cost of repairs, together with the loss of time while such repairs are being made, wouldpurchase boilers of absolute safety and leave a large margin beside. Thepossibility of loss of human life should also be considered, though thismay seem a far cry from the question of repair costs. Space Occupied--The space required for the boilers in a plant oftenexceeds the requirements for the remainder of the plant equipment. Anysaving of space in a boiler room will be a large factor in reducing thecost of real estate and of the building. Even when the boiler plant iscomparatively small, the saving in space frequently will amount to aconsiderable percentage of the cost of the boilers. Table 2 shows thedifference in floor space occupied by fire-tube boilers and Babcock &Wilcox boilers of the same capacity, the latter being taken asrepresenting the water-tube class. This saving in space will increasewith the size of the plant for the reason that large size boiler unitswhile common in water-tube practice are impracticable in fire-tubepractice. TABLE 2 COMPARATIVE APPROXIMATE FLOOR SPACE OCCUPIED BY BABCOCK & WILCOX AND H. R. T. BOILERS +------------+----------------+---------------+|Size of unit|Babcock & Wilcox| H. R. T. ||Horse Power |Feet and Inches |Feet and Inches|+------------+----------------+---------------+| 100 | 7 3 × 19 9 | 10 0 × 20 0 || 150 | 7 10 × 19 9 | 10 0 × 22 6 || 200 | 9 0 × 19 9 | 11 6 × 23 10 || 250 | 9 0 × 19 9 | 11 6 × 23 10 || 300 | 10 2 × 19 9 | 12 0 × 25 0 |+------------+----------------+---------------+ BABCOCK & WILCOX BOILERS AS COMPARED WITH OTHER WATER-TUBE DESIGNS It must be borne in mind that the simple fact that a boiler is of thewater-tube design does not as a necessity indicate that it is a good orsafe boiler. Safety--Many of the water-tube boilers on themarket are as lacking as are fire-tube boilers in the positivecirculation which, as has been demonstrated by Mr. Babcock's lecture, isso necessary in the requirements of the perfect steam boiler. In boilersusing water-leg construction, there is danger of defective circulation, leaks are common, and unsuspected corrosion may be going on in portionsof the boiler that cannot be inspected. Stresses due to unequalexpansion of the metal cannot be well avoided but they may be minimizedby maintaining at the same temperature all pressure parts of the boiler. The result is to be secured only by means of a well defined circulation. The main feature to which the Babcock & Wilcox boiler owes its safety isthe construction made possible by the use of headers, by which the waterin each vertical row of tubes is separated from that in the adjacentrows. This construction results in the very efficient circulationproduced through the breaking up of the steam and water in the frontheaders, the effect of these headers in producing such a positivecirculation having been clearly demonstrated in Mr. Babcock's lecture. The use of a number of sections, thus composed of headers and tubes, hasa distinct advantage over the use of a common chamber at the outlet endsof the tubes. In the former case the circulation of water in onevertical row of tubes cannot interfere with that in the other rows, while in the latter construction there will be downward as well asupward currents and such downward currents tend to neutralize any goodeffect there might be through the diminution of the density of the watercolumn by the steam. Further, the circulation results directly from the design of the boilerand requires no assistance from "retarders", check valves and the like, within the boiler. All such mechanical devices in the interior of aboiler serve only to complicate the design and should not be used. This positive and efficient circulation assures that all portions of thepressure parts of the Babcock & Wilcox boiler will be at approximatelythe same temperature and in this way strains resulting from unequaltemperatures are obviated. Where the water throughout the boiler is at the temperature of the steamcontained, a condition to be secured only by proper circulation, dangerfrom internal pitting is minimized, or at least limited only to effectsof the water fed the boiler. Where the water in any portion of theboiler is lower than the temperature of the steam corresponding to thepressure carried, whether the fact that such lower temperatures exist asa result of lack of circulation, or because of intentional design, internal pitting or corrosion will almost invariably result. Dr. Thurston has already been quoted to the effect that the admittedsafety of a water-tube boiler is the result of the division of itscontents into small portions. In boilers using a water-leg construction, while the danger from explosion will be largely limited to the tubes, there is the danger, however, that such legs may explode due to thedeterioration of their stays, and such an explosion might be almost asdisastrous as that of a shell boiler. The headers in a Babcock & Wilcoxboiler are practically free from any danger of explosion. Were such anexplosion to occur, it would still be localized to a much larger extentthan in the case of a water-leg boiler and the header construction thusalmost absolutely localizes any danger from such a cause. Staybolts are admittedly an undesirable element of construction in anyboiler. They are wholly objectionable and the only reason for thepresence of staybolts in a boiler is to enable a cheaper form ofconstruction to be used than if they were eliminated. In boilers utilizing in their design flat-stayed surfaces, or stayboltconstruction under pressure, corrosion and wear and tear in servicetends to weaken some single part subject to continual strain, the resultbeing an increased strain on other parts greatly in excess of that forwhich an allowance can be made by any reasonable factor of safety. Wherethe construction is such that the weakening of a single part willproduce a marked decrease in the safety and reliability of the whole, itfollows of necessity, that there will be a corresponding decrease in theworking pressure which may be safely carried. In water-leg boilers, the use of such flat-stayed surfaces underpressure presents difficulties that are practically unsurmountable. Suchsurfaces exposed to the heat of the fire are subject to unequalexpansion, distortion, leakage and corrosion, or in general, to many ofthe objections that have already been advanced against the fire-tubeboilers in the consideration of water-tube boilers as a class incomparison with fire-tube boilers. [Illustration: McAlpin Hotel, New York City, Operating 2360 Horse Powerof Babcock & Wilcox Boilers] Aside from the difficulties that may arise in actual service due to thefailure of staybolts, or in general, due to the use of flat-stayedsurfaces, constructional features are encountered in the actualmanufacture of such boilers that make it difficult if not impossible toproduce a first-class mechanical job. It is practically impossible inthe building of such a boiler to so design and place the staybolts thatall will be under equal strain. Such unequal strains, resulting fromconstructional difficulties, will be greatly multiplied when such aboiler is placed in service. Much of the riveting in boilers of thisdesign must of necessity be hand work, which is never the equal ofmachine riveting. The use of water-leg construction ordinarily requiresthe flanging of large plates, which is difficult, and because of thenumber of heats necessary and the continual working of the material, maylead to the weakening of such plates. In vertical or semi-vertical water-tube boilers utilizing flat-stayedsurfaces under pressure, these surfaces are ordinarily so located as tooffer a convenient lodging place for flue dust, which fuses into a hardmass, is difficult of removal and under which corrosion may be going onwith no possibility of detection. Where stayed surfaces or water legs are features in the design of awater-tube boiler, the factor of safety of such parts must be mostcarefully considered. In such parts too, is the determination of thefactor most difficult, and because of the "rule-of-thumb" determinationfrequently necessary, the factor of safety becomes in reality a factorof ignorance. As opposed to such indeterminate factors of safety, in theBabcock & Wilcox boiler, when the factor of safety for the drum or drumshas been determined, and such a factor may be determined accurately, thefactors for all other portions of the pressure parts are greatly inexcess of that of the drum. All Babcock & Wilcox boilers are built witha factor of safety of at least five, and inasmuch as the factor of thesafety of the tubes and headers is greatly in excess of this figure, itapplies specifically to the drum or drums. This factor represents agreater degree of safety than a considerably higher factor applied to aboiler in which the shell or any riveted portion is acted upon directlyby the fire, or the same factor applied to a boiler utilizingflat-stayed surface construction, where the accurate determination ofthe limiting factor of safety is difficult, if not impossible. That the factor of safety of stayed surfaces is questionable may perhapsbe best realized from a consideration of the severe requirements as tosuch factor called for by the rules and regulations of the Board ofSupervising Inspectors, U. S. Government. In view of the above, the absence of any stayed surfaces in the Babcock& Wilcox boiler is obviously a distinguishing advantage where safety isa factor. It is of interest to note, in the article on the evolution ofthe Babcock & Wilcox boiler, that staybolt construction was used inseveral designs, found unsatisfactory and unsafe, and discarded. Another feature in the design of the Babcock & Wilcox boiler tendingtoward added safety is its manner of suspension. This has been indicatedin the previous chapter and is of such nature that all of the pressureparts are free to expand or contract under variations of temperaturewithout in any way interfering with any part of the boiler setting. Thesectional nature of the boiler allows a flexibility under varyingtemperature changes that practically obviates internal strain. In boilers utilizing water-leg construction, on the other hand, theconstruction is rigid, giving rise to serious internal strains and themethod of support ordinarily made necessary by the boiler design is notonly unmechanical but frequently dangerous, due to the fact that properprovision is not made for expansion and contraction under temperaturevariations. Boilers utilizing water-leg construction are not ordinarily providedwith mud drums. This is a serious defect in that it allows impuritiesand sediment to collect in a portion of the boiler not easily inspected, and corrosion may result. Economy--That the water-tube boiler as a class lends itself more readilythan does the fire-tube boiler to a variation in the relation of gratesurface, heating surface and combustion space has been already pointedout. In economy again, the construction made possible by the use ofheaders in Babcock & Wilcox boilers appears as a distinct advantage. Because of this construction, there is a flexibility possible, in anunlimited variety of heights and widths that will satisfactorily meetthe special requirements of the fuel to be burned in individual cases. An extended experience in the design of furnaces best suited for a widevariety of fuels has made The Babcock & Wilcox Co. Leaders in the fieldof economy. Furnaces have been built and are in successful operation forburning anthracite and bituminous coals, lignite, crude oil, gas-housetar, wood, sawdust and shavings, bagasse, tan bark, natural gas, blastfurnace gas, by-product coke oven gas and for the utilization of wasteheat from commercial processes. The great number of Babcock & Wilcoxboilers now in satisfactory operation under such a wide range of fuelconditions constitutes an unimpeachable testimonial to the ability tomeet all of the many conditions of service. The limitations in the draft area of fire-tube boilers as affectingeconomy have been pointed out. That a greater draft area is possible inwater-tube boilers does not of necessity indicate that proper advantageof this fact is taken in all boilers of the water-tube class. In theBabcock & Wilcox boiler, the large draft area taken in connection withthe effective baffling allows the gases to be brought into intimatecontact with all portions of the heating surfaces and renders suchsurfaces highly efficient. In certain designs of water-tube boilers the baffling is such as torender ineffective certain portions of the heating surface, due to thetendency of soot and dirt to collect on or behind baffles, in this waycausing the interposition of a layer of non-conducting material betweenthe hot gases and the heating surfaces. In Babcock & Wilcox boilers the standard baffle arrangement is such asto allow the installation of a superheater without in any way alteringthe path of the gases from furnace to stack, or requiring a change inthe boiler design. In certain water-tube boilers the baffle arrangementis such that if a superheater is to be installed a complete change inthe ordinary baffle design is necessary. Frequently to insuresufficiently hot gas striking the heating surfaces, a portion isby-passed directly from the furnace to the superheater chamber withoutpassing over any of the boiler heating surfaces. Any such arrangementwill lead to a decrease in economy and the use of boilers requiring itshould be avoided. Capacity--Babcock & Wilcox boilers are run successfully in every-daypractice at higher ratings than any other boilers in practical service. The capacities thus obtainable are due directly to the efficientcirculation already pointed out. Inasmuch as the construction utilizingheaders has a direct bearing in producing such circulation, it is alsoconnected with the high capacities obtainable with this apparatus. Where intelligently handled and kept properly cleaned, Babcock & Wilcoxboilers are operated in many plants at from 200 to 225 per cent of theirrated evaporative capacity and it is not unusual for them to be operatedat 300 per cent of such rated capacity during periods of peak load. Dry Steam--In the list of the requirements of the perfect steam boiler, the necessity that dry steam be generated has been pointed out. TheBabcock & Wilcox boiler will deliver dry steam under higher capacitiesand poorer conditions of feed water than any other boiler nowmanufactured. Certain boilers will, when operated at ordinary ratings, handle poor feed water and deliver steam in which the moisture contentis not objectionable. When these same boilers are driven at highoverloads, there will be a direct tendency to prime and the percentageof moisture in the steam delivered will be high. This tendency is theresult of the lack of proper circulation and once more there is seen theadvantage of the headers of the Babcock & Wilcox boiler, resulting as itdoes in the securing of a positive circulation. In the design of the Babcock & Wilcox boiler sufficient space isprovided between the steam outlet and the disengaging point to insurethe steam passing from the boiler in a dry state without entraining oragain picking up any particles of water in its passage even at highrates of evaporation. Ample time is given for a complete separation ofsteam from the water at the disengaging surface before the steam iscarried from the boiler. These two features, which are additional causesfor the ability of the Babcock & Wilcox boiler to deliver dry steam, result from the proper proportioning of the steam and water space of theboiler. From the history of the development of the boiler, it is evidentthat the cubical capacity per horse power of the steam and water spacehas been adopted after numerous experiments. That the "dry pipe" serves in no way the generally understood functionof such device has been pointed out. As stated, the function of the "drypipe" in a Babcock & Wilcox boiler is simply that of a collecting pipeand this statement holds true regardless of the rate of operation of theboiler. In certain boilers, "superheating surface" is provided to "dry thesteam, " or to remove the moisture due to priming or foaming. Suchsurface is invariably a source of trouble unless the steam is initiallydry and a boiler which will deliver dry steam is obviously to bepreferred to one in which surface must be supplied especially for suchpurpose. Where superheaters are installed with Babcock & Wilcox boilers, they are in every sense of the word superheaters and not driers, thesteam being delivered to them in a dry state. The question has been raised in connection with the cross drum design ofthe Babcock & Wilcox boiler as to its ability to deliver dry steam. Experience has shown the absolute lack of basis for any such objection. The Babcock & Wilcox Company at its Bayonne Works some time ago made aseries of experiments to see in what manner the steam generated wasseparated from the water either in the drum or in its passage to thedrum. Glass peepholes were installed in each end of a drum in a boilerof the marine design, at the point midway between that at which thehorizontal circulating tubes entered the drum and the drum baffle plate. By holding a light at one of these peepholes the action in the drum wasclearly seen through the other. It was found that with the boileroperated under three-quarter inch ashpit pressure, which, with the fuelused would be equivalent to approximately 185 per cent of rating forstationary boiler practice, that each tube was delivering with greatvelocity a stream of solid water, which filled the tube for half itscross sectional area. There was no spray or mist accompanying suchdelivery, clearly indicating that the steam had entirely separated fromthe water in its passage through the horizontal circulating tubes, whichin the boiler in question were but 50 inches long. [Illustration: Northwest Station of the Commonwealth Edison Co. , Chicago, Ill. This Installation Consists of 11, 360 Horse Power ofBabcock & Wilcox Boilers and Superheaters, Equipped with Babcock &Wilcox Chain Grate Stokers] These experiments proved conclusively that the size of the steam drumsin the cross drum design has no appreciable effect in determining theamount of liberating surface, and that sufficient liberating surface isprovided in the circulating tubes alone. If further proof of the abilityof this design of boiler to deliver dry steam is required, such proof isperhaps best seen in the continued use of the Babcock & Wilcox marineboiler, in which the cross drum is used exclusively, and with whichrates of evaporation are obtained far in excess of those secured inordinary practice. Quick Steaming--The advantages of water-tube boilers as a class overfire-tube boilers in ability to raise steam quickly have been indicated. Due to the constant and thorough circulation resulting from thesectional nature of the Babcock & Wilcox boiler, steam may be raisedmore rapidly than in practically any other water-tube design. In starting up a cold Babcock & Wilcox boiler with either coal or oilfuel, where a proper furnace arrangement is supplied, steam may beraised to a pressure of 200 pounds in less than half an hour. With aBabcock & Wilcox boiler in a test where forced draft was available, steam was raised from an initial temperature of the boiler and itscontained water of 72 degrees to a pressure of 200 pounds, in 12½minutes after lighting the fire. The boiler also responds quickly instarting from banked fires, especially where forced draft is available. In Babcock & Wilcox boilers the water is divided into many small streamswhich circulate without undue frictional resistance in thin envelopespassing through the hottest part of the furnace, the steam being carriedrapidly to the disengaging surface. There is no part of the boilerexposed to the heat of the fire that is not in contact with waterinternally, and as a result there is no danger of overheating onstarting up quickly nor can leaks occur from unequal expansion such asmight be the case where an attempt is made to raise steam rapidly inboilers using water leg construction. Storage Capacity for Steam and Water--Where sufficient steam and watercapacity are not provided in a boiler, its action will be irregular, thesteam pressure varying over wide limits and the water level beingsubject to frequent and rapid fluctuation. Owing to the small relative weight of steam, water capacity is ofgreater importance in this respect than steam space. With a gaugepressure of 180 pounds per square inch, 8 cubic feet of steam, which isequivalent to one-half cubic foot of water space, are required to supplyone boiler horse power for one minute and if no heat be supplied to theboiler during such an interval, the pressure will drop to 150 pounds persquare inch. The volume of steam space, therefore, may be over rated, but if this be too small, the steam passing off will carry water with itin the form of spray. Too great a water space results in slow steamingand waste of fuel in starting up; while too much steam space adds to theradiating surface and increases the losses from that cause. That the steam and water space of the Babcock & Wilcox boiler are theresult of numerous experiments has previously been pointed out. Accessibility--Cleaning. That water-tube boilers are more accessible asa class than are fire-tube boilers has been indicated. All water-tubeboilers, however, are not equally accessible. In certain designs, due tothe arrangement of baffling used it is practically impossible to removeall deposits of soot and dirt. Frequently, in order to cheapen theproduct, sufficient cleaning and access doors are not supplied as partof the boiler equipment. The tendency of soot to collect on the crownsheets of certain vertical water-tube boilers has been noted. Suchdeposits are difficult to remove and if corrosion goes on beneath such acovering the sheet may crack and an explosion result. [Illustration: Rear View--Longitudinal Drum Vertical Header Boiler, Showing Access Doors to Rear Headers] It is almost impossible to thoroughly clean water legs internally, andin such places also is there a tendency to unsuspected corrosion underdeposits that cannot be removed. In Babcock & Wilcox boilers every portion of the interior of the heatingsurfaces can be reached and kept clean, while any soot deposited on theexterior surfaces can be blown off while the boiler is under pressure. Inspection--The accessibility which makes possible the thorough cleaningof all portions of the Babcock & Wilcox boiler also provides a means fora thorough inspection. Drums are accessible for internal inspection by the removal of themanhole plates. Front headers may be inspected through large doorsfurnished for the purpose. Rear headers in the inclined header designsmay be inspected from the chamber formed by such headers and the rearwall of the boiler. In the vertical header designs rear tube doors arefurnished, as has been stated. In certain designs of water-tube boilersin order to assure accessibility for inspection of the rear ends of thetubes, the rear portion of the boiler is exposed to the atmosphere withresulting excessive radiation losses. In other designs the means ofaccess to the rear ends of the tubes are of a makeshift andunworkmanlike character. By the removal of handhole plates, all tubes in a Babcock & Wilcoxboiler may be inspected for their full length either for the presence ofscale or for suspected corrosion. Repairs--In Babcock & Wilcox boilers the possession of great strength, the elimination of stresses due to uneven temperatures and of theresulting danger of leaks and corrosion, the protection of the drumsfrom the intense heat of the fire, and the decreased liability of thescale forming matter to lodge on the hottest tube surfaces, all tend tominimize the necessity for repairs. The tubes of the Babcock & Wilcoxboiler are practically the only part which may need renewal and theseonly at infrequent intervals When necessary, such renewals may be madecheaply and quickly. A small stock of tubes, 4 inches in diameter, ofsufficient length for the boiler used, is all that need be carried tomake renewals. Repairs in water-leg boilers are difficult at best and frequentlyunsatisfactory when completed. When staybolt replacements are necessary, in order to get at the inner sheet of the water leg, several tubes mustin some cases be cut out. Not infrequently a replacement of an entirewater leg is necessary and this is difficult and requires a lengthyshutdown. With the Babcock & Wilcox boiler, on the other hand, even ifit is necessary to replace a section, this may be done in a few hoursafter the boiler is cool. In the case of certain staybolt failures the working pressure of arepaired boiler utilizing such construction will frequently be loweredby the insurance companies when the boiler is again placed in service. The sectional nature of the Babcock & Wilcox boiler enables it tomaintain its original working pressure over long periods of time, almostregardless of the nature of any repair that may be required. [Illustration: 1456 Horse-power Installation of Babcock & Wilcox Boilersat the Raritan Woolen Mills, Raritan, N. J. The First of These Boilerswere Installed in 1878 and 1881 and are still Operated at 80 PoundsPressure] Durability--Babcock & Wilcox boilers are being operated in every-dayservice with entirely satisfactory results and under the same steampressure as that for which they were originally sold that have beenoperated from thirty to thirty-five years. It is interesting to note inconsidering the life of a boiler that the length of life of a Babcock &Wilcox boiler must be taken as the criterion of what length of life ispossible. This is due to the fact that there are Babcock & Wilcoxboilers in operation to-day that have been in service from a time thatantedates by a considerable margin that at which the manufacturer of anyother water-tube boiler now on the market was started. Probably the very best evidence of the value of the Babcock & Wilcoxboiler as a steam generator and of the reliability of the apparatus, isseen in the sales of the company. Since the company was formed, therehave been sold throughout the world over 9, 900, 000 horse power. A feature that cannot be overlooked in the consideration of theadvantages of the Babcock & Wilcox boiler is the fact that as a part ofthe organization back of the boiler, there is a body of engineers ofrecognized ability, ready at all times to assist its customers in everypossible way. [Illustration: 2400 Horse-power Installation of Babcock & Wilcox Boilersin the Union Station Power House of the Pennsylvania Railroad Co. , Pittsburgh, Pa. This Company has a Total of 28, 500 Horse Power ofBabcock & Wilcox Boilers Installed] HEAT AND ITS MEASUREMENT The usual conception of heat is that it is a form of energy produced bythe vibratory motion of the minute particles or molecules of a body. Allbodies are assumed to be composed of these molecules, which are heldtogether by mutual cohesion and yet are in a state of continualvibration. The hotter a body or the more heat added to it, the morevigorous will be the vibrations of the molecules. As is well known, the effect of heat on a body may be to change itstemperature, its volume, or its state, that is, from solid to liquid orfrom liquid to gaseous. Where water is melted from ice and evaporatedinto steam, the various changes are admirably described in the lectureby Mr. Babcock on "The Theory of Steam Making", given in the nextchapter. The change in temperature of a body is ordinarily measured bythermometers, though for very high temperatures so-called pyrometers areused. The latter are dealt with under the heading "High TemperatureMeasurements" at the end of this chapter. [Illustration: Fig. 11] By reason of the uniform expansion of mercury and its greatsensitiveness to heat, it is the fluid most commonly used in theconstruction of thermometers. In all thermometers the freezing point andthe boiling point of water, under mean or average atmospheric pressureat sea level, are assumed as two fixed points, but the division of thescale between these two points varies in different countries. Thefreezing point is determined by the use of melting ice and for thisreason is often called the melting point. There are in use threethermometer scales known as the Fahrenheit, the Centigrade or Celsius, and the Réaumur. As shown in Fig. 11, in the Fahrenheit scale, the spacebetween the two fixed points is divided into 180 parts; the boilingpoint is marked 212, and the freezing point is marked 32, and zero is atemperature which, at the time this thermometer was invented, wasincorrectly imagined to be the lowest temperature attainable. In thecentigrade and the Réaumur scales, the distance between the two fixedpoints is divided into 100 and 80 parts, respectively. In each of thesetwo scales the freezing point is marked zero, and the boiling point ismarked 100 in the centigrade and 80 in the Réaumur. Each of the 180, 100or 80 divisions in the respective thermometers is called a degree. Table 3 and appended formulae are useful for converting from one scaleto another. In the United States the bulbs of high-grade thermometers are usuallymade of either Jena 58^{III} borosilicate thermometer glass or Jena16^{III} glass, the stems being made of ordinary glass. The Jena16^{III} glass is not suitable for use at temperatures much above 850degrees Fahrenheit and the harder Jena 59^{III} should be used inthermometers for temperatures higher than this. Below the boiling point, the hydrogen-gas thermometer is the almostuniversal standard with which mercurial thermometers may be compared, while above this point the nitrogen-gas thermometer is used. In both ofthese standards the change in temperature is measured by the change inpressure of a constant volume of the gas. In graduating a mercurial thermometer for the Fahrenheit scale, ordinarily a degree is represented as 1/180 part of the volume of thestem between the readings at the melting point of ice and the boilingpoint of water. For temperatures above the latter, the scale is extendedin degrees of the same volume. For very accurate work, however, thethermometer may be graduated to read true-gas-scale temperatures bycomparing it with the gas thermometer and marking the temperatures at 25or 50 degree intervals. Each degree is then 1/25 or 1/50 of the volumeof the stem in each interval. Every thermometer, especially if intended for use above the boilingpoint, should be suitably annealed before it is used. If this is notdone, the true melting point and also the "fundamental interval", thatis, the interval between the melting and the boiling points, may changeconsiderably. After continued use at the higher temperatures also, themelting point will change, so that the thermometer must be calibratedoccasionally to insure accurate readings. TABLE 3 COMPARISON OF THERMOMETER SCALES +---------------+----------+----------+----------+| |Fahrenheit|Centigrade| Réaumur |+---------------+----------+----------+----------+|Absolute Zero | -459. 64 | -273. 13 | -218. 50 || | 0 | -17. 78 | -14. 22 || | 10 | -12. 22 | -9. 78 || | 20 | -6. 67 | -5. 33 || | 30 | -1. 11 | -0. 89 ||Freezing Point | 32 | 0 | 0 ||Maximum Density| | | || of Water | 39. 1 | 3. 94 | 3. 15 || | 50 | 10 | 8 || | 75 | 23. 89 | 19. 11 || | 100 | 37. 78 | 30. 22 || | 200 | 93. 33 | 74. 67 ||Boiling Point | 212 | 100 | 80 || | 250 | 121. 11 | 96. 89 || | 300 | 148. 89 | 119. 11 || | 350 | 176. 67 | 141. 33 |+---------------+----------+----------+----------+ F = 9/5C+32° = 9/4R+32° C = 5/9(F-32°) = 5/4R R = 4/9(F-32°) = 4/5C As a general rule thermometers are graduated to read correctly for totalimmersion, that is, with bulb and stem of the thermometer at the sametemperature, and they should be used in this way when compared with astandard thermometer. If the stem emerges into space either hotter orcolder than that in which the bulb is placed, a "stem correction" mustbe applied to the observed temperature in addition to any correctionthat may be found in the comparison with the standard. For instance, fora particular thermometer, comparison with the standard with both fullyimmersed made necessary the following corrections: _Temperature_ _Correction_ 40°F 0. 0 100 0. 0 200 0. 0 300 +2. 5 400 -0. 5 500 -2. 5 When the sign of the correction is positive (+) it must be added to theobserved reading, and when the sign is a negative (-) the correctionmust be subtracted. The formula for the stem correction is as follows: Stem correction = 0. 000085 × n (T-t) in which T is the observed temperature, t is the mean temperature of theemergent column, n is the number of degrees of mercury column emergent, and 0. 000085 is the difference between the coefficient of expansion ofthe mercury and that in the glass in the stem. Suppose the observed temperature is 400 degrees and the thermometer isimmersed to the 200 degrees mark, so that 200 degrees of the mercurycolumn project into the air. The mean temperature of the emergent columnmay be found by tying another thermometer on the stem with the bulb atthe middle of the emergent mercury column as in Fig. 12. Suppose thismean temperature is 85 degrees, then Stem correction = 0. 000085 × 200 × (400 - 85) = 5. 3 degrees. As the stem is at a lower temperature than the bulb, the thermometerwill evidently read too low, so that this correction must be added tothe observed reading to find the reading corresponding to totalimmersion. The corrected reading will therefore be 405. 3 degrees. Ifthis thermometer is to be corrected in accordance with the calibratedcorrections given above, we note that a further correction of 0. 5 mustbe applied to the observed reading at this temperature, so that thecorrect temperature is 405. 3 - 0. 5 = 404. 8 degrees or 405 degrees. [Illustration: Fig. 12] [Illustration: Fig. 13] Fig. 12 shows how a stem correction can be obtained for the case justdescribed. Fig. 13 affords an opportunity for comparing the scale of a thermometercorrect for total immersion with one which will read correctly whensubmerged to the 300 degrees mark, the stem being exposed at a meantemperature of 110 degrees Fahrenheit, a temperature often prevailingwhen thermometers are used for measuring temperatures in steam mains. Absolute Zero--Experiments show that at 32 degrees Fahrenheit a perfectgas expands 1/491. 64 part of its volume if its pressure remains constantand its temperature is increased one degree. Thus if gas at 32 degreesFahrenheit occupies 100 cubic feet and its temperature is increased onedegree, its volume will be increased to 100 + 100/491. 64 = 100. 203 cubicfeet. For a rise of two degrees the volume would be 100 + (100 × 2) /491. 64 = 100. 406 cubic feet. If this rate of expansion per one degreeheld good at all temperatures, and experiment shows that it does abovethe freezing point, the gas, if its pressure remained the same, woulddouble its volume, if raised to a temperature of 32 + 491. 64 = 523. 64degrees Fahrenheit, while under a diminution of temperature it wouldshrink and finally disappear at a temperature of 491. 64 - 32 = 459. 64degrees below zero Fahrenheit. While undoubtedly some change in the lawwould take place before the lower temperature could be reached, there isno reason why the law may not be used within the range of temperaturewhere it is known to hold good. From this explanation it is evident thatunder a constant pressure the volume of a gas will vary as the number ofdegrees between its temperature and the temperature of -459. 64 degreesFahrenheit. To simplify the application of the law, a new thermometricscale is constructed as follows: the point corresponding to -460 degreesFahrenheit, is taken as the zero point on the new scale, and the degreesare identical in magnitude with those on the Fahrenheit scale. Temperatures referred to this new scale are called absolute temperaturesand the point -460 degrees Fahrenheit (= -273 degrees centigrade) iscalled the absolute zero. To convert any temperature Fahrenheit toabsolute temperature, add 460 degrees to the temperature on theFahrenheit scale: thus 54 degrees Fahrenheit will be 54 + 460 = 514degrees absolute temperature; 113 degrees Fahrenheit will likewise beequal to 113 + 460 = 573 degrees absolute temperature. If one pound ofgas is at a temperature of 54 degrees Fahrenheit and another pound is ata temperature of 114 degrees Fahrenheit the respective volumes at agiven pressure would be in the ratio of 514 to 573. [Illustration: Ninety-sixth Street Station of the New York Railways Co. , New York City, Operating 20, 000 Horse Power of Babcock & Wilcox Boilers. This Company and its Allied Companies Operate a Total of 100, 000 HorsePower of Babcock & Wilcox Boilers] British Thermal Unit--The quantitative measure of heat is the Britishthermal unit, ordinarily written B. T. U. This is the quantity of heatrequired to raise the temperature of one pound of pure water one degreeat 62 degrees Fahrenheit; that is, from 62 degrees to 63 degrees. In themetric system this unit is the _calorie_ and is the heat necessaryto raise the temperature of one kilogram of pure water from 15 degreesto 16 degrees centigrade. These two definitions lead to a discrepancy of0. 03 of 1 per cent, which is insignificant for engineering purposes, andin the following the B. T. U. Is taken with this discrepancy ignored. The discrepancy is due to the fact that there is a slight difference inthe specific heat of water at 15 degrees centigrade and 62 degreesFahrenheit. The two units may be compared thus: 1 Calorie = 3. 968 B. T. U. 1 B. T. U. = 0. 252 Calories. _Unit_ _Water_ _Temperature Rise_1 B. T. U. 1 Pound 1 Degree Fahrenheit1 Calorie 1 Kilogram 1 Degree centigrade But 1 kilogram = 2. 2046 pounds and 1 degree centigrade = 9/5 degreeFahrenheit. Hence 1 calorie = (2. 2046 × 9/5) = 3. 968 B. T. U. The heat values in B. T. U. Are ordinarily given per pound, and the heatvalues in calories per kilogram, in which case the B. T. U. Per poundare approximately equivalent to 9/5 the calories per kilogram. As determined by Joule, heat energy has a certain definite relation towork, one British thermal unit being equivalent from his determinationsto 772 foot pounds. Rowland, a later investigator, found that 778 footpounds were a more exact equivalent. Still later investigations indicatethat the correct value for a B. T. U. Is 777. 52 foot pounds orapproximately 778. The relation of heat energy to work as determined isa demonstration of the first law of thermo-dynamics, namely, that heatand mechanical energy are mutually convertible in the ratio of 778 footpounds for one British thermal unit. This law, algebraically expressed, is W = JH; W being the work done in foot pounds, H being the heat inB. T. U. , and J being Joules equivalent. Thus 1000 B. T. U. 's would becapable of doing 1000 × 778 = 778000 foot pounds of work. Specific Heat--The specific heat of a substance is the quantity of heatexpressed in thermal units required to raise or lower the temperature ofa unit weight of any substance at a given temperature one degree. Thisquantity will vary for different substances For example, it requiresabout 16 B. T. U. To raise the temperature of one pound of ice 32degrees or 0. 5 B. T. U. To raise it one degree, while it requiresapproximately 180 B. T. U. To raise the temperature of one pound ofwater 180 degrees or one B. T. U. For one degree. If then, a pound of water be considered as a standard, the ratio of theamount of heat required to raise a similar unit of any other substanceone degree, to the amount required to raise a pound of water one degreeis known as the specific heat of that substance. Thus since one pound ofwater required one B. T. U. To raise its temperature one degree, and onepound of ice requires about 0. 5 degrees to raise its temperature onedegree, the ratio is 0. 5 which is the specific heat of ice. To be exact, the specific heat of ice is 0. 504, hence 32 degrees × 0. 504 = 16. 128B. T. U. Would be required to raise the temperature of one pound of icefrom 0 to 32 degrees. For solids, at ordinary temperatures, the specificheat may be considered a constant for each individual substance, although it is variable for high temperatures. In the case of gases adistinction must be made between specific heat at constant volume, andat constant pressure. Where specific heat is stated alone, specific heat at ordinarytemperature is implied, and _mean_ specific heat refers to the averagevalue of this quantity between the temperatures named. The specific heat of a mixture of gases is obtained by multiplying thespecific heat of each constituent gas by the percentage by weight ofthat gas in the mixture, and dividing the sum of the products by 100. The specific heat of a gas whose composition by weight is CO_{2}, 13 percent; CO, 0. 4 per cent; O, 8 per cent; N, 78. 6 per cent, is found asfollows: CO_{2} : 13 × 0. 217 = 2. 821CO : 0. 4 × 0. 2479 = 0. 09916O : 8 × 0. 2175 = 1. 74000N : 78. 6 × 0. 2438 = 19. 16268 -------- 100. 0 23. 82284 and 23. 8228 ÷ 100 = 0. 238 = specific heat of the gas. The specific heats of various solids, liquids and gases are given inTable 4. Sensible Heat--The heat utilized in raising the temperature of a body, as that in raising the temperature of water from 32 degrees up to theboiling point, is termed sensible heat. In the case of water, thesensible heat required to raise its temperature from the freezing pointto the boiling point corresponding to the pressure under whichebullition occurs, is termed the heat of the liquid. Latent Heat--Latent heat is the heat which apparently disappears inproducing some change in the condition of a body without increasing itstemperature If heat be added to ice at freezing temperature, the icewill melt but its temperature will not be raised. The heat so utilizedin changing the condition of the ice is the latent heat and in thisparticular case is known as the latent heat of fusion. If heat be addedto water at 212 degrees under atmospheric pressure, the water will notbecome hotter but will be evaporated into steam, the temperature ofwhich will also be 212 degrees. The heat so utilized is called thelatent heat of evaporation and is the heat which apparently disappearsin causing the substance to pass from a liquid to a gaseous state. TABLE 4 SPECIFIC HEATS OF VARIOUS SUBSTANCES+--------------------------------------------------------------------+| SOLIDS |+-------------------------------+----------------+-------------------+| | Temperature[2]| || | Degrees | Specific || | Fahrenheit | Heat |+-------------------------------+----------------+-------------------+| Copper | 59-460 | . 0951 || Gold | 32-212 | . 0316 || Wrought Iron | 59-212 | . 1152 || Cast Iron | 68-212 | . 1189 || Steel (soft) | 68-208 | . 1175 || Steel (hard) | 68-208 | . 1165 || Zinc | 32-212 | . 0935 || Brass (yellow) | 32 | . 0883 || Glass (normal ther. 16^{III}) | 66-212 | . 1988 || Lead | 59 | . 0299 || Platinum | 32-212 | . 0323 || Silver | 32-212 | . 0559 || Tin | -105-64 | . 0518 || Ice | | . 5040 || Sulphur (newly fused) | | . 2025 |+-------------------------------+----------------+-------------------+| LIQUIDS |+-------------------------------+----------------+-------------------+| | Temperature[2]| || | Degrees | Specific || | Fahrenheit | Heat |+-------------------------------+----------------+-------------------+| Water[3] | 59 | 1. 0000 || Alcohol | 32 | . 5475 || | 176 | . 7694 || Mercury | 32 | . 03346 || Benzol | 50 | . 4066 || | 122 | . 4502 || Glycerine | 59-102 | . 576 || Lead (Melted) | to 360 | . 0410 || Sulphur (melted) | 246-297 | . 2350 || Tin (melted) | | . 0637 || Sea Water (sp. Gr. 1. 0043) | 64 | . 980 || Sea Water (sp. Gr. 1. 0463) | 64 | . 903 || Oil of Turpentine | 32 | . 411 || Petroleum | 64-210 | . 498 || Sulphuric Acid | 68-133 | . 3363 |+-------------------------------+----------------+-------------------+| GASES |+--------------------------+---------------+--------------+----------+| | | Specific | Specific || | Temperature[2]| Heat at | Heat at || | Degrees | Constant | Constant || | Fahrenheit | Pressure | Volume |+--------------------------+---------------+--------------+----------+| Air | 32-392 | . 2375 | . 1693 || Oxygen | 44-405 | . 2175 | . 1553 || Nitrogen | 32-392 | . 2438 | . 1729 || Hydrogen | 54-388 | 3. 4090 | 2. 4141 || Superheated Steam | | See table 25 | || Carbon Monoxide | 41-208 | . 2425 | . 1728 || Carbon Dioxide | 52-417 | . 2169 | . 1535 || Methane | 64-406 | . 5929 | . 4505 || Blast Fur. Gas (approx. ) | . .. | . 2277 | . .. || Flue gas (approx. ) | . .. | . 2400 | . .. |+--------------------------+---------------+--------------+----------+ Latent heat is not lost, but reappears whenever the substances passthrough a reverse cycle, from a gaseous to a liquid, or from a liquid toa solid state. It may, therefore, be defined as stated, as the heatwhich apparently disappears, or is lost to thermometric measurement, when the molecular constitution of a body is being changed. Latent heatis expended in performing the work of overcoming the molecular cohesionof the particles of the substance and in overcoming the resistance ofexternal pressure to change of volume of the heated body. Latent heat ofevaporation, therefore, may be said to consist of internal and externalheat, the former being utilized in overcoming the molecular resistanceof the water in changing to steam, while the latter is expended inovercoming any resistance to the increase of its volume duringformation. In evaporating a pound of water at 212 degrees to steam at212 degrees, 897. 6 B. T. U. Are expended as internal latent heat and72. 8 B. T. U. As external latent heat. For a more detailed descriptionof the changes brought about in water by sensible and latent heat, thereader is again referred to the chapter on "The Theory of Steam Making". Ebullition--The temperature of ebullition of any liquid, or its boilingpoint, may be defined as the temperature which exists where the additionof heat to the liquid no longer increases its temperature, the heatadded being absorbed or utilized in converting the liquid into vapor. This temperature is dependent upon the pressure under which the liquidis evaporated, being higher as the pressure is greater. TABLE 5 BOILING POINTS AT ATMOSPHERIC PRESSURE +---------------------+--------------+| | Degrees || | Fahrenheit |+---------------------+--------------+| Ammonia | 140 || Bromine | 145 || Alcohol | 173 || Benzine | 212 || Water | 212 || Average Sea Water | 213. 2 || Saturated Brine | 226 || Mercury | 680 |+---------------------+--------------+ Total Heat of Evaporation--The quantity of heat required to raise a unitof any liquid from the freezing point to any given temperature, and toentirely evaporate it at that temperature, is the total heat ofevaporation of the liquid for that temperature. It is the sum of theheat of the liquid and the latent heat of evaporation. To recapitulate, the heat added to a body is divided as follows: Total heat = Heat to change the temperature + heat to overcome the molecular cohesion + heat to overcome the external pressure resisting an increase of volume of the body. Where water is converted into steam, this total heat is divided asfollows: Total heat = Heat to change the temperature of the water + heat to separate the molecules of the water + heat to overcome resistance to increase in volume of the steam, = Heat of the liquid + internal latent heat + external latent heat, = Heat of the liquid + total latent heat of steam, = Total heat of evaporation. The steam tables given on pages 122 to 127 give the heat of the liquidand the total latent heat through a wide range of temperatures. Gases--When heat is added to gases there is no internal work done; hencethe total heat is that required to change the temperature plus thatrequired to do the external work. If the gas is not allowed to expandbut is preserved at constant volume, the entire heat added is thatrequired to change the temperature only. Linear Expansion of Substances by Heat--To find the increase in thelength of a bar of any material due to an increase of temperature, multiply the number of degrees of increase in temperature by thecoefficient of expansion for one degree and by the length of the bar. Where the coefficient of expansion is given for 100 degrees, as in Table6, the result should be divided by 100. The expansion of metals per onedegree rise of temperature increases slightly as high temperatures arereached, but for all practical purposes it may be assumed to be constantfor a given metal. TABLE 6 LINEAL EXPANSION OF SOLIDS AT ORDINARY TEMPERATURES (Tabular values represent increase per foot per 100 degrees increase in temperature, Fahrenheit or centigrade) +-------------------+--------------+----------------+----------------+| | Temperature | | || | Conditions[4]|Coefficient per |Coefficient per || Substance | Degrees | 100 Degrees | 100 Degrees || | Fahrenheit | Fahrenheit | Centigrade |+-------------------+--------------+----------------+----------------+|Brass (cast) | 32 to 212 | . 001042 | . 001875 ||Brass (wire) | 32 to 212 | . 001072 | . 001930 ||Copper | 32 to 212 | . 000926 | . 001666 ||Glass (English | | | ||flint) | 32 to 212 | . 000451 | . 000812 ||Glass (French | | | ||flint) | 32 to 212 | . 000484 | . 000872 ||Gold | 32 to 212 | . 000816 | . 001470 ||Granite (average) | 32 to 212 | . 000482 | . 000868 ||Iron (cast) | 104 | . 000589 | . 001061 ||Iron (soft forged) | 0 to 212 | . 000634 | . 001141 ||Iron (wire) | 32 to 212 | . 000800 | . 001440 ||Lead | 32 to 212 | . 001505 | . 002709 ||Mercury | 32 to 212 | . 009984[5] | . 017971 ||Platinum | 104 | . 000499 | . 000899 ||Limestone | 32 to 212 | . 000139 | . 000251 ||Silver | 104 | . 001067 | . 001921 ||Steel (Bessemer | | | ||rolled, hard) | 0 to 212 | . 00056 | . 00101 ||Steel (Bessemer | | | ||rolled, soft) | 0 to 212 | . 00063 | . 00117 ||Steel (cast, | | | ||French) | 104 | . 000734 | . 001322 ||Steel (cast | | | ||annealed, English) | 104 | . 000608 | . 001095 |+-------------------+--------------+----------------+----------------+ High Temperature Measurements--The temperatures to be dealt with insteam-boiler practice range from those of ordinary air and steam to thetemperatures of burning fuel. The gases of combustion, originally at thetemperature of the furnace, cool as they pass through each successivebank of tubes in the boiler, to nearly the temperature of the steam, resulting in a wide range of temperatures through which definitemeasurements are sometimes required. Of the different methods devised for ascertaining these temperatures, some of the most important are as follows: 1st. Mercurial pyrometers for temperatures up to 1000 degrees Fahrenheit. 2nd. Expansion pyrometers for temperatures up to 1500 degrees Fahrenheit. 3rd. Calorimetry for temperatures up to 2000 degrees Fahrenheit. 4th. Thermo-electric pyrometers for temperatures up to 2900 degrees Fahrenheit. 5th. Melting points of metal which flow at various temperatures up to the melting point of platinum 3227 degrees Fahrenheit. 6th. Radiation pyrometers for temperatures up to 3600 degrees Fahrenheit. 7th. Optical pyrometers capable of measuring temperatures up to 12, 600 degrees Fahrenheit. [6] For ordinary boiler practice however, their range is 1600 to 3600 degrees Fahrenheit. [Illustration: 228 Horse-power Babcock & Wilcox Boiler, Installed at theWentworth Institute, Boston, Mass. ] Table 7 gives the degree of accuracy of high temperature measurements. TABLE 7 ACCURACY OF HIGH TEMPERATURE MEASUREMENTS[7] +------------------------+------------------------+| Centigrade | Fahrenheit |+-------------+----------+-------------+----------+| | Accuracy | | Accuracy || Temperature | Plus or | Temperature | Plus or || Range | Minus | Range | Minus || | Degrees | | Degrees |+-------------+----------+-------------+----------+| 200- 500 | 0. 5 | 392- 932 | 0. 9 || 500- 800 | 2 | 932-1472 | 3. 6 || 800-1100 | 3 | 1472-2012 | 5. 4 || 1100-1600 | 15 | 2012-2912 | 27 || 1600-2000 | 25 | 2912-3632 | 45 |+-------------+----------+-------------+----------+ Mercurial Pyrometers--At atmospheric pressure mercury boils at 676degrees Fahrenheit and even at lower temperatures the mercury inthermometers will be distilled and will collect in the upper part of thestem. Therefore, for temperatures much above 400 degrees Fahrenheit, some inert gas, such as nitrogen or carbon dioxide, must be forced underpressure into the upper part of the thermometer stem. The pressure at600 degrees Fahrenheit is about 15 pounds, or slightly above that of theatmosphere, at 850 degrees about 70 pounds, and at 1000 degrees about300 pounds. Flue-gas temperatures are nearly always taken with mercurialthermometers as they are the most accurate and are easy to read andmanipulate. Care must be taken that the bulb of the instrument projectsinto the path of the moving gases in order that the temperature maytruly represent the flue gas temperature. No readings should beconsidered until the thermometer has been in place long enough to heatit up to the full temperature of the gases. Expansion Pyrometers--Brass expands about 50 per cent more than iron andin both brass and iron the expansion is nearly proportional to theincrease in temperature. This phenomenon is utilized in expansionpyrometers by enclosing a brass rod in an iron pipe, one end of the rodbeing rigidly attached to a cap at the end of the pipe, while the otheris connected by a multiplying gear to a pointer moving around agraduated dial. The whole length of the expansion piece must be at auniform temperature before a correct reading can be obtained. This fact, together with the lost motion which is likely to exist in the mechanismconnected to the pointer, makes the expansion pyrometer unreliable; itshould be used only when its limitations are thoroughly understood andit should be carefully calibrated. Unless the brass and iron are knownto be of the same temperature, its action will be anomalous: forinstance, if it be allowed to cool after being exposed to a hightemperature, the needle will rise before it begins to fall. Similarly, arise in temperature is first shown by the instrument as a fall. Theexplanation is that the iron, being on the outside, heats or cools morequickly than the brass. Calorimetry--This method derives its name from the fact that the processis the same as the determination of the specific heat of a substance bythe water calorimeter, except that in one case the temperature is knownand the specific heat is required, while in the other the specific heatis known and the temperature is required. The temperature is found asfollows: A given weight of some substance such as iron, nickel or fire brick, isheated to the unknown temperature and then plunged into water and therise in temperature noted. If X = temperature to be measured, w = weight of heated body in pounds, W = weight of water in pounds, T = final temperature of water, t =difference between initial and final temperatures of water, s = knownspecific heat of body. Then X = T + Wt ÷ ws Any temperatures secured by this method are affected by so many sourcesof error that the results are very approximate. Thermo-electric Pyrometers--When wires of two different metals arejoined at one end and heated, an electromotive force will be set upbetween the free ends of the wires. Its amount will depend upon thecomposition of the wires and the difference in temperature between thetwo. If a delicate galvanometer of high resistance be connected to the"thermal couple", as it is called, the deflection of the needle, after acareful calibration, will indicate the temperature very accurately. In the thermo-electric pyrometer of Le Chatelier, the wires used areplatinum and a 10 per cent alloy of platinum and rhodium, enclosed inporcelain tubes to protect them from the oxidizing influence of thefurnace gases. The couple with its protecting tubes is called an"element". The elements are made in different lengths to suitconditions. It is not necessary for accuracy to expose the whole length of theelement to the temperature to be measured, as the electromotive forcedepends only upon the temperature of the juncture at the closed end ofthe protecting tube and that of the cold end of the element. Thegalvanometer can be located at any convenient point, since the length ofthe wires leading to it simply alter the resistance of the circuit, forwhich allowance may be made. The advantages of the thermo-electric pyrometer are accuracy over a widerange of temperatures, continuity of readings, and the ease with whichobservations can be taken. Its disadvantages are high first cost and, insome cases, extreme delicacy. Melting Points of Metals--The approximate temperature of a furnace orflue may be determined, if so desired, by introducing certain metals ofwhich the melting points are known. The more common metals form a seriesin which the respective melting points differ by 100 to 200 degreesFahrenheit, and by using these in order, the temperature can be fixedbetween the melting points of some two of them. This method lacksaccuracy, but it suffices for determinations where approximate readingsare satisfactory. The approximate melting points of certain metals that may be used fordeterminations of this nature are given in Table 8. Radiation Pyrometers--These are similar to thermo-electric pyrometers inthat a thermo-couple is employed. The heat rays given out by the hotbody fall on a concave mirror and are brought to a focus at a point atwhich is placed the junction of a thermo-couple. The temperaturereadings are obtained from an indicator similar to that used withthermo-electric pyrometers. Optical Pyrometers--Of the optical pyrometers the Wanner is perhaps themost reliable. The principle on which this instrument is constructed isthat of comparing the quantity of light emanating from the heated bodywith a constant source of light, in this case a two-volt osmium lamp. The lamp is placed at one end of an optical tube, while at the other aneyepiece is provided and a scale. A battery of cells furnishes thecurrent for the lamp. On looking through the pyrometer, a circle of redlight appears, divided into distinct halves of different intensities. Adjustment may be made so that the two halves appear alike and a readingis then taken from the scale. The temperatures are obtained from a tableof temperatures corresponding to scale readings. For standardizing theosmium lamp, an amylacetate lamp, is provided with a stand for holdingthe optical tube. TABLE 8 APPROXIMATE MELTING POINTS OF METALS[8] +-----------------+------------------+| Metal | Temperature || |Degrees Fahrenheit|+-----------------+------------------+|Wrought Iron | 2737 ||Pig Iron (gray) | 2190-2327 ||Cast Iron (white)| 2075 ||Steel | 2460-2550 ||Steel (cast) | 2500 ||Copper | 1981 ||Zinc | 786 ||Antimony | 1166 ||Lead | 621 ||Bismuth | 498 ||Tin | 449 ||Platinum | 3191 ||Gold | 1946 ||Silver | 1762 ||Aluminum | 1216 |+-----------------+------------------+ Determination of Temperature from Character of Emitted Light--As afurther means of determining approximately the temperature of a furnace, Table 9, compiled by Messrs. White & Taylor, may be of service. Thecolor at a given temperature is approximately the same for all kinds ofcombustibles under similar conditions. TABLE 9 CHARACTER OF EMITTED LIGHT AND CORRESPONDING APPROXIMATE TEMPERATURE[9] +--------------------------------------+-----------+| Character of Emitted Light |Temperature|| | Degrees || | Fahrenheit|+--------------------------------------+-----------+|Dark red, blood red, low red | 1050 ||Dark cherry red | 1175 ||Cherry, full red | 1375 ||Light cherry, bright cherry, light red| 1550 ||Orange | 1650 ||Light orange | 1725 ||Yellow | 1825 ||Light yellow | 1975 ||White | 2200 |+--------------------------------------+-----------+ THE THEORY OF STEAM MAKING [Extracts from a Lecture delivered by George H. Babcock, at CornellUniversity, 1887[10]] The chemical compound known as H_{2}O exists in three states orconditions--ice, water and steam; the only difference between thesestates or conditions is in the presence or absence of a quantity ofenergy exhibited partly in the form of heat and partly in molecularactivity, which, for want of a better name, we are accustomed to call"latent heat"; and to transform it from one state to another we haveonly to supply or extract heat. For instance, if we take a quantity ofice, say one pound, at absolute zero[11] and supply heat, the firsteffect is to raise its temperature until it arrives at a point 492Fahrenheit degrees above the starting point. Here it stops growingwarmer, though we keep on adding heat. It, however, changes from ice towater, and when we have added sufficient heat to have made it, had itremained ice, 283 degrees hotter or a temperature of 315 degreesFahrenheit's thermometer, it has all become water, at the sametemperature at which it commenced to change, namely, 492 degrees aboveabsolute zero, or 32 degrees by Fahrenheit's scale. Let us stillcontinue to add heat, and it will now grow warmer again, though at aslower rate--that is, it now takes about double the quantity of heat toraise the pound one degree that it did before--until it reaches atemperature of 212 degrees Fahrenheit, or 672 degrees absolute (assumingthat we are at the level of the sea). Here we find another criticalpoint. However much more heat we may apply, the water, as water, at thatpressure, cannot be heated any hotter, but changes on the addition ofheat to steam; and it is not until we have added heat enough to haveraised the temperature of the water 966 degrees, or to 1, 178 degrees byFahrenheit's thermometer (presuming for the moment that its specificheat has not changed since it became water), that it has all becomesteam, which steam, nevertheless, is at the temperature of 212 degrees, at which the water began to change. Thus over four-fifths of the heatwhich has been added to the water has disappeared, or become insensiblein the steam to any of our instruments. It follows that if we could reduce steam at atmospheric pressure towater, without loss of heat, the heat stored within it would cause thewater to be red hot; and if we could further change it to a solid, likeice, without loss of heat, the solid would be white hot, or hotter thanmelted steel--it being assumed, of course, that the specific heat of thewater and ice remain normal, or the same as they respectively are at thefreezing point. After steam has been formed, a further addition of heat increases thetemperature again at a much faster ratio to the quantity of heat added, which ratio also varies according as we maintain a constant pressure ora constant volume; and I am not aware that any other critical pointexists where this will cease to be the fact until we arrive at that veryhigh temperature, known as the point of dissociation, at which itbecomes resolved into its original gases. The heat which has been absorbed by one pound of water to convert itinto a pound of steam at atmospheric pressure is sufficient to havemelted 3 pounds of steel or 13 pounds of gold. This has been transformedinto something besides heat; stored up to reappear as heat when theprocess is reversed. That condition is what we are pleased to calllatent heat, and in it resides mainly the ability of the steam to dowork. [Graph: Temperature in Fahrenheit Degrees (from Absolute Zero)against Quantity of Heat in British Thermal Units] The diagram shows graphically the relation of heat to temperature, thehorizontal scale being quantity of heat in British thermal units, andthe vertical temperature in Fahrenheit degrees, both reckoned fromabsolute zero and by the usual scale. The dotted lines for ice and watershow the temperature which would have been obtained if the conditionshad not changed. The lines marked "gold" and "steel" show the relationto heat and temperature and the melting points of these metals. All theinclined lines would be slightly curved if attention had been paid tothe changing specific heat, but the curvature would be small. It isworth noting that, with one or two exceptions, the curves of allsubstances lie between the vertical and that for water. That is to say, that water has a greater capacity for heat than all other substancesexcept two, hydrogen and bromine. In order to generate steam, then, only two steps are required: 1st, procure the heat, and 2nd, transfer it to the water. Now, you have itlaid down as an axiom that when a body has been transferred ortransformed from one place or state into another, the same work has beendone and the same energy expended, whatever may have been theintermediate steps or conditions, or whatever the apparatus. Therefore, when a given quantity of water at a given temperature has been made intosteam at a given temperature, a certain definite work has been done, anda certain amount of energy expended, from whatever the heat may havebeen obtained, or whatever boiler may have been employed for thepurpose. A pound of coal or any other fuel has a definite heat producingcapacity, and is capable of evaporating a definite quantity of waterunder given conditions. That is the limit beyond which even perfectioncannot go, and yet I have known, and doubtless you have heard of, caseswhere inventors have claimed, and so-called engineers have certified to, much higher results. The first step in generating steam is in burning the fuel to the bestadvantage. A pound of carbon will generate 14, 500 British thermal units, during combustion into carbonic dioxide, and this will be the same, whatever the temperature or the rapidity at which the combustion maytake place. If possible, we might oxidize it at as slow a rate as thatwith which iron rusts or wood rots in the open air, or we might burn itwith the rapidity of gunpowder, a ton in a second, yet the total heatgenerated would be precisely the same. Again, we may keep thetemperature down to the lowest point at which combustion can take place, by bringing large bodies of air in contact with it, or otherwise, or wemay supply it with just the right quantity of pure oxygen, and burn itat a temperature approaching that of dissociation, and still the heatunits given off will be neither more nor less. It follows, therefore, that great latitude in the manner or rapidity of combustion may be takenwithout affecting the quantity of heat generated. But in practice it is found that other considerations limit thislatitude, and that there are certain conditions necessary in order toget the most available heat from a pound of coal. There are three ways, and only three, in which the heat developed by the combustion of coal ina steam boiler furnace may be expended. 1st, and principally. It should be conveyed to the water in the boiler, and be utilized in the production of steam. To be perfect, a boilershould so utilize all the heat of combustion, but there are no perfectboilers. 2nd. A portion of the heat of combustion is conveyed up the chimney inthe waste gases. This is in proportion to the weight of the gases, andthe difference between their temperature and that of the air and coalbefore they entered the fire. 3rd. Another portion is dissipated by radiation from the sides of thefurnace. In a stove the heat is all used in these latter two ways, either it goes off through the chimney or is radiated into thesurrounding space. It is one of the principal problems of boilerengineering to render the amount of heat thus lost as small as possible. The loss from radiation is in proportion to the amount of surface, itsnature, its temperature, and the time it is exposed. This loss can bealmost entirely eliminated by thick walls and a smooth white or polishedsurface, but its amount is ordinarily so small that these extraordinaryprecautions do not pay in practice. It is evident that the temperature of the escaping gases cannot bebrought below that of the absorbing surfaces, while it may be muchgreater even to that of the fire. This is supposing that all of theescaping gases have passed through the fire. In case air is allowed toleak into the flues, and mingle with the gases after they have left theheating surfaces, the temperature may be brought down to almost anypoint above that of the atmosphere, but without any reduction in theamount of heat wasted. It is in this way that those low chimneytemperatures are sometimes attained which pass for proof of economy withthe unobserving. All surplus air admitted to the fire, or to the gasesbefore they leave the heating surfaces, increases the losses. We are now prepared to see why and how the temperature and the rapidityof combustion in the boiler furnace affect the economy, and that thoughthe amount of heat developed may be the same, the heat available for thegeneration of steam may be much less with one rate or temperature ofcombustion than another. Assuming that there is no air passing up the chimney other than thatwhich has passed through the fire, the higher the temperature of thefire and the lower that of the escaping gases the better the economy, for the losses by the chimney gases will bear the same proportion to theheat generated by the combustion as the temperature of those gases bearsto the temperature of the fire. That is to say, if the temperature ofthe fire is 2500 degrees and that of the chimney gases 500 degrees abovethat of the atmosphere, the loss by the chimney will be 500/2500 = 20per cent. Therefore, as the escaping gases cannot be brought below thetemperature of the absorbing surface, which is practically a fixedquantity, the temperature of the fire must be high in order to securegood economy. The losses by radiation being practically proportioned to the timeoccupied, the more coal burned in a given furnace in a given time, theless will be the proportionate loss from that cause. It therefore follows that we should burn our coal rapidly and at a hightemperature to secure the best available economy. [Illustration: Portion of 9880 Horse-power Installation of Babcock &Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox ChainGrate Stokers at the South Side Elevated Ry. Co. , Chicago, Ill. ] PROPERTIES OF WATER Pure water is a chemical compound of one volume of oxygen and twovolumes of hydrogen, its chemical symbol being H_{2}O. The weight of water depends upon its temperature. Its weight at fourtemperatures, much used in physical calculations, is given in Table 10. TABLE 10 WEIGHT OF WATER AT TEMPERATURES USED IN PHYSICAL CALCULATIONS +---------------------------+----------+----------+| Temperature Degrees |Weight per|Weight per|| Fahrenheit |Cubic Foot|Cubic Inch|| | Pounds | Pounds |+---------------------------+----------+----------+|At 32 degrees or freezing | | || point at sea level | 62. 418 | 0. 03612 ||At 39. 2 degrees or point of| | || maximum density | 62. 427 | 0. 03613 ||At 62 degrees or standard | | || temperature | 62. 355 | 0. 03608 ||At 212 degrees or boiling | | || point at sea level | 59. 846 | 0. 03469 |+---------------------------+----------+----------+ While authorities differ as to the weight of water, the range of valuesgiven for 62 degrees Fahrenheit (the standard temperature ordinarilytaken) being from 62. 291 pounds to 62. 360 pounds per cubic foot, thevalue 62. 355 is generally accepted as the most accurate. A United States standard gallon holds 231 cubic inches and weighs, at 62degrees Fahrenheit, approximately 8-1/3 pounds. A British Imperial gallon holds 277. 42 cubic inches and weighs, at 62degrees Fahrenheit, 10 pounds. The above are the true weights corrected for the effect of the buoyancyof the air, or the weight in vacuo. If water is weighed in air in theordinary way, there is a correction of about one-eighth of one per centwhich is usually negligible. TABLE 11 VOLUME AND WEIGHT OF DISTILLED WATER AT VARIOUS TEMPERATURES[12] +-----------+---------------+----------+|Temperature|Relative Volume|Weight per|| Degrees | Water at 39. 2 |Cubic Foot|| Fahrenheit| Degrees = 1 | Pounds |+-----------+---------------+----------+| 32 | 1. 000176 | 62. 42 || 39. 2 | 1. 000000 | 62. 43 || 40 | 1. 000004 | 62. 43 || 50 | 1. 00027 | 62. 42 || 60 | 1. 00096 | 62. 37 || 70 | 1. 00201 | 62. 30 || 80 | 1. 00338 | 62. 22 || 90 | 1. 00504 | 62. 11 || 100 | 1. 00698 | 62. 00 || 110 | 1. 00915 | 61. 86 || 120 | 1. 01157 | 61. 71 || 130 | 1. 01420 | 61. 55 || 140 | 1. 01705 | 61. 38 || 150 | 1. 02011 | 61. 20 || 160 | 1. 02337 | 61. 00 || 170 | 1. 02682 | 60. 80 || 180 | 1. 03047 | 60. 58 || 190 | 1. 03431 | 60. 36 || 200 | 1. 03835 | 60. 12 || 210 | 1. 04256 | 59. 88 || 212 | 1. 04343 | 59. 83 || 220 | 1. 0469 | 59. 63 || 230 | 1. 0515 | 59. 37 || 240 | 1. 0562 | 59. 11 || 250 | 1. 0611 | 58. 83 || 260 | 1. 0662 | 58. 55 || 270 | 1. 0715 | 58. 26 || 280 | 1. 0771 | 57. 96 || 290 | 1. 0830 | 57. 65 || 300 | 1. 0890 | 57. 33 || 310 | 1. 0953 | 57. 00 || 320 | 1. 1019 | 56. 66 || 330 | 1. 1088 | 56. 30 || 340 | 1. 1160 | 55. 94 || 350 | 1. 1235 | 55. 57 || 360 | 1. 1313 | 55. 18 || 370 | 1. 1396 | 54. 78 || 380 | 1. 1483 | 54. 36 || 390 | 1. 1573 | 53. 94 || 400 | 1. 167 | 53. 5 || 410 | 1. 177 | 53. 0 || 420 | 1. 187 | 52. 6 || 430 | 1. 197 | 52. 2 || 440 | 1. 208 | 51. 7 || 450 | 1. 220 | 51. 2 || 460 | 1. 232 | 50. 7 || 470 | 1. 244 | 50. 2 || 480 | 1. 256 | 49. 7 || 490 | 1. 269 | 49. 2 || 500 | 1. 283 | 48. 7 || 510 | 1. 297 | 48. 1 || 520 | 1. 312 | 47. 6 || 530 | 1. 329 | 47. 0 || 540 | 1. 35 | 46. 3 || 550 | 1. 37 | 45. 6 || 560 | 1. 39 | 44. 9 |+-----------+---------------+----------+ Water is but slightly compressible and for all practical purposes may beconsidered non-compressible. The coefficient of compressibility rangesfrom 0. 000040 to 0. 000051 per atmosphere at ordinary temperatures, thiscoefficient decreasing as the temperature increases. Table 11 gives the weight in vacuo and the relative volume of a cubicfoot of distilled water at various temperatures. The weight of water at the standard temperature being taken as 62. 355pounds per cubic foot, the pressure exerted by the column of water ofany stated height, and conversely the height of any column required toproduce a stated pressure, may be computed as follows: The pressure in pounds per square foot = 62. 355 × height of column infeet. The pressure in pounds per square inch = 0. 433 × height of column infeet. Height of column in feet = pressure in pounds per square foot ÷ 62. 355. Height of column in feet = pressure in pounds per square inch ÷ 0. 433. Height of column in inches = pressure in pounds per square inch × 27. 71. Height of column in inches = pressure in ounces per square inch × 1. 73. By a change in the weights given above, the pressure exerted and heightof column may be computed for temperatures other than 62 degrees. A pressure of one pound per square inch is exerted by a column of water2. 3093 feet or 27. 71 inches high at 62 degrees Fahrenheit. Water in its natural state is never found absolutely pure. In solventpower water has a greater range than any other liquid. For common salt, this is approximately a constant at all temperatures, while with suchimpurities as magnesium and sodium sulphates, this solvent powerincreases with an increase in temperature. TABLE 12 BOILING POINT OF WATER AT VARIOUS ALTITUDES +--------------+----------------+-------------+---------------+|Boiling Point | Altitude Above | Atmospheric | Barometer || Degrees | Sea Level | Pressure | Reduced || Fahrenheit | Feet | Pounds per | to 32 Degrees || | | Square Inch | Inches |+--------------+----------------+-------------+---------------+| 184 | 15221 | 8. 20 | 16. 70 || 185 | 14649 | 8. 38 | 17. 06 || 186 | 14075 | 8. 57 | 17. 45 || 187 | 13498 | 8. 76 | 17. 83 || 188 | 12934 | 8. 95 | 18. 22 || 189 | 12367 | 9. 14 | 18. 61 || 190 | 11799 | 9. 34 | 19. 02 || 191 | 11243 | 9. 54 | 19. 43 || 192 | 10685 | 9. 74 | 19. 85 || 193 | 10127 | 9. 95 | 20. 27 || 194 | 9579 | 10. 17 | 20. 71 || 195 | 9031 | 10. 39 | 21. 15 || 196 | 8481 | 10. 61 | 21. 60 || 197 | 7932 | 10. 83 | 22. 05 || 198 | 7381 | 11. 06 | 22. 52 || 199 | 6843 | 11. 29 | 22. 99 || 200 | 6304 | 11. 52 | 23. 47 || 201 | 5764 | 11. 76 | 23. 95 || 202 | 5225 | 12. 01 | 24. 45 || 203 | 4697 | 12. 26 | 24. 96 || 204 | 4169 | 12. 51 | 25. 48 || 205 | 3642 | 12. 77 | 26. 00 || 206 | 3115 | 13. 03 | 26. 53 || 207 | 2589 | 13. 30 | 27. 08 || 208 | 2063 | 13. 57 | 27. 63 || 209 | 1539 | 13. 85 | 28. 19 || 210 | 1025 | 14. 13 | 28. 76 || 211 | 512 | 14. 41 | 29. 33 || 212 | Sea Level | 14. 70 | 29. 92 |+--------------+----------------+-------------+---------------+ Sea water contains on an average approximately 3. 125 per cent of itsweight of solid matter or a thirty-second part of the weight of thewater and salt held in solution. The approximate composition of thissolid matter will be: sodium chloride 76 per cent, magnesium chloride 10per cent, magnesium sulphate 6 per cent, calcium sulphate 5 per cent, calcium carbonate 0. 5 per cent, other substances 2. 5 per cent. [Illustration: 7200 Horse-power Installation of Babcock & Wilcox Boilersand Superheaters at the Capital Traction Co. , Washington, D. C. ] The boiling point of water decreases as the altitude above sea levelincreases. Table 12 gives the variation in the boiling point with thealtitude. Water has a greater specific heat or heat-absorbing capacity than anyother known substance (bromine and hydrogen excepted) and its specificheat is the basis for measurement of the capacity of heat absorption ofall other substances. From the definition, the specific heat of water isthe number of British thermal units required to raise one pound of waterone degree. This specific heat varies with the temperature of the water. The generally accepted values are given in Table 13, which indicates thevalues as determined by Messrs. Marks and Davis and Mr. Peabody. TABLE 13 SPECIFIC HEAT OF WATER AT VARIOUS TEMPERATURES +----------------------+--------------------------------+| MARKS AND DAVIS | PEABODY || From Values of | From Values of || Barnes and Dieterici | Barnes and Regnault |+-----------+----------+---------------------+----------+|Temperature| Specific | Temperature | Specific |+-----------+ Heat +----------+----------+ Heat || Degrees | | Degrees | Degrees | ||Fahrenheit | |Centigrade|Fahrenheit| |+-----------+----------+----------+----------+----------+| 30 | 1. 0098 | 0 | 32 | 1. 0094 || 40 | 1. 0045 | 5 | 41 | 1. 0053 || 50 | 1. 0012 | 10 | 50 | 1. 0023 || 55 | 1. 0000 | 15 | 59 | 1. 0003 || 60 | 0. 9990 | 16. 11 | 61 | 1. 0000 || 70 | 0. 9977 | 20 | 68 | 0. 9990 || 80 | 0. 9970 | 25 | 77 | 0. 9981 || 90 | 0. 9967 | 30 | 86 | 0. 9976 || 100 | 0. 9967 | 35 | 95 | 0. 9974 || 110 | 0. 9970 | 40 | 104 | 0. 9974 || 120 | 0. 9974 | 45 | 113 | 0. 9976 || 130 | 0. 9979 | 50 | 122 | 0. 9980 || 140 | 0. 9986 | 55 | 131 | 0. 9985 || 150 | 0. 9994 | 60 | 140 | 0. 9994 || 160 | 1. 0002 | 65 | 149 | 1. 0004 || 170 | 1. 0010 | 70 | 158 | 1. 0015 || 180 | 1. 0019 | 75 | 167 | 1. 0028 || 190 | 1. 0029 | 80 | 176 | 1. 0042 || 200 | 1. 0039 | 85 | 185 | 1. 0056 || 210 | 1. 0052 | 90 | 194 | 1. 0071 || 220 | 1. 007 | 95 | 203 | 1. 0086 || 230 | 1. 009 | 100 | 212 | 1. 0101 |+-----------+----------+----------+----------+----------+ In consequence of this variation in specific heat, the variation in theheat of the liquid of the water at different temperatures is not aconstant. Table 22[13] gives the heat of the liquid in a pound of waterat temperatures ranging from 32 to 340 degrees Fahrenheit. The specific heat of ice at 32 degrees is 0. 463. The specific heat ofsaturated steam (ice and saturated steam representing the other forms inwhich water may exist), is something that is difficult to define in anyway which will not be misleading. When no liquid is present the specificheat of saturated steam is negative. [14] The use of the value of thespecific heat of steam is practically limited to instances wheresuperheat is present, and the specific heat of superheated steam iscovered later in the book. BOILER FEED WATER All natural waters contain some impurities which, when introduced into aboiler, may appear as solids. In view of the apparent present-daytendency toward large size boiler units and high overloads, theimportance of the use of pure water for boiler feed purposes cannot beover-estimated. Ordinarily, when water of sufficient purity for such use is not at hand, the supply available may be rendered suitable by some process oftreatment. Against the cost of such treatment, there are many factors tobe considered. With water in which there is a marked tendency towardscale formation, the interest and depreciation on the added boiler unitsnecessary to allow for the systematic cleaning of certain units must betaken into consideration. Again there is a considerable loss in takingboilers off for cleaning and replacing them on the line. On the otherhand, the decrease in capacity and efficiency accompanying an increasedincrustation of boilers in use has been too generally discussed to needrepetition here. Many experiments have been made and actual figuresreported as to this decrease, but in general, such figures apply only tothe particular set of conditions found in the plant where the boiler inquestion was tested. So many factors enter into the effect of scale oncapacity and economy that it is impossible to give any accurate figureson such decrease that will serve all cases, but that it is large hasbeen thoroughly proven. While it is almost invariably true that practically any cost oftreatment will pay a return on the investment of the apparatus, the factmust not be overlooked that there are certain waters which should neverbe used for boiler feed purposes and which no treatment can rendersuitable for such purpose. In such cases, the only remedy is thesecuring of other feed supply or the employment of evaporators fordistilling the feed water as in marine service. TABLE 14 APPROXIMATE CLASSIFICATION OF IMPURITIES FOUND IN FEED WATERS THEIR EFFECT AND ORDINARY METHODS OF RELIEF +-----------------------+--------------+-----------------------------+| Difficulty Resulting | Nature of | Ordinary Method of || from Presence of | Difficulty | Overcoming or Relieving |+-----------------------+--------------+-----------------------------+| Sediment, Mud, etc. | Incrustation | Settling tanks, filtration, || | | blowing down. || | | || Readily Soluble Salts | Incrustation | Blowing down. || | | || Bicarbonates of Lime, | Incrustation | Heating feed. Treatment by || Magnesia, etc. | | addition of lime or of lime || | | and soda. Barium carbonate. || | | || Sulphate of Lime | Incrustation | Treatment by addition of || | | soda. Barium carbonate. || | | || Chloride and Sulphate | Corrosion | Treatment by addition of || of Magnesium | | carbonate of soda. || | | || Acid | Corrosion | Alkali. || | | || Dissolved Carbonic | Corrosion | Heating feed. Keeping air || Acid and Oxygen | | from feed. Addition of || | | caustic soda or slacked || | | lime. || | | || Grease | Corrosion | Filter. Iron alum as || | | coagulent. Neutralization || | | by carbonate of soda. Use || | | of best hydrocarbon oils. || | | || Organic Matter | Corrosion | Filter. Use of coagulent. || | | || Organic Matter | Priming | Settling tanks. Filter in || (Sewage) | | connection with coagulent. || | | || Carbonate of Soda in | Priming | Barium carbonate. New feed || large quantities | | supply. If from treatment, || | | change. |+-----------------------+--------------+-----------------------------+ It is evident that the whole subject of boiler feed waters and theirtreatment is one for the chemist rather than for the engineer. A briefoutline of the difficulties that may be experienced from the use of poorfeed water and a suggestion as to a method of overcoming certain ofthese difficulties is all that will be attempted here. Such a briefoutline of the subject, however, will indicate the necessity for achemical analysis of any water before a treatment is tried and thenecessity of adapting the treatment in each case to the nature of thedifficulties that may be experienced. Table 14 gives a list of impurities which may be found in boiler feedwater, grouped according to their effect on boiler operation and givingthe customary method used for overcoming difficulty to which they lead. Scale--Scale is formed on boiler heating surfaces by the depositing ofimpurities in the feed water in the form of a more or less hard adherentcrust. Such deposits are due to the fact that water loses its solublepower at high temperatures or because the concentration becomes so high, due to evaporation, that the impurities crystallize and adhere to theboiler surfaces. The opportunity for formation of scale in a boiler willbe apparent when it is realized that during a month's operation of a 100horse-power boiler, 300 pounds of solid matter may be deposited fromwater containing only 7 grains per gallon, while some spring and wellwaters contain sufficient to cause a deposit of as high as 2000 pounds. The salts usually responsible for such incrustation are the carbonatesand sulphates of lime and magnesia, and boiler feed treatment in generaldeals with the getting rid of these salts more or less completely. TABLE 15 SOLUBILITY OF MINERAL SALTS IN WATER (SPARKS)IN GRAINS PER U. S. GALLON (58, 381 GRAINS), EXCEPT AS NOTED +------------------------------+------------+-------------+|Temperature Degrees Fahrenheit| 60 Degrees | 212 Degrees |+------------------------------+------------+-------------+|Calcium Carbonate | 2. 5 | 1. 5 ||Calcium Sulphate | 140. 0 | 125. 0 ||Magnesium Carbonate | 1. 0 | 1. 8 ||Magnesium Sulphate | 3. 0 pounds | 12. 0 pounds ||Sodium Chloride | 3. 5 pounds | 4. 0 pounds ||Sodium Sulphate | 1. 1 pounds | 5. 0 pounds |+------------------------------+------------+-------------+ CALCIUM SULPHATE AT TEMPERATURE ABOVE 212 DEGREES (CHRISTIE) +------------------------------+----+----+-------+----+---+|Temperature degrees Fahrenheit|284 |329 |347-365| 464|482||Corresponding gauge pressure | 38 | 87 |115-149| 469|561||Grains per gallon |45. 5|32. 7| 15. 7 |10. 5|9. 3|+------------------------------+----+----+-------+----+---+ Table 15 gives the solubility of these mineral salts in water at varioustemperatures in grains per U. S. Gallon (58, 381 grains). It will be seenfrom this table that the carbonates of lime and magnesium are notsoluble above 212 degrees, and calcium sulphate while somewhat insolubleabove 212 degrees becomes more greatly so as the temperature increases. Scale is also formed by the settling of mud and sediment carried insuspension in water. This may bake or be cemented to a hard scale whenmixed with other scale-forming ingredients. Corrosion--Corrosion, or a chemical action leading to the actualdestruction of the boiler metal, is due to the solvent or oxidizingproperties of the feed water. It results from the presence of acid, either free or developed[15] in the feed, the admixture of air with thefeed water, or as a result of a galvanic action. In boilers it takesseveral forms: 1st. Pitting, which consists of isolated spots of active corrosion whichdoes not attack the boiler as a whole. 2nd. General corrosion, produced by naturally acid waters and where theamount is so even and continuous that no accurate estimate of the metaleaten away may be made. 3rd. Grooving, which, while largely a mechanical action which may occurin neutral waters, is intensified by acidity. Foaming--This phenomenon, which ordinarily occurs with waterscontaminated with sewage or organic growths, is due to the fact that thesuspended particles collect on the surface of the water in the boilerand render difficult the liberation of steam bubbles arising to thatsurface. It sometimes occurs with water containing carbonates insolution in which a light flocculent precipitate will be formed on thesurface of the water. Again, it is the result of an excess of sodiumcarbonate used in treatment for some other difficulty where animal orvegetable oil finds its way into the boiler. Priming--Priming, or the passing off of steam from a boiler in belches, is caused by the concentration of sodium carbonate, sodium sulphate orsodium chloride in solution. Sodium sulphate is found in many southernwaters and also where calcium or magnesium sulphate is precipitated withsoda ash. Treatment of Feed Water--For scale formation. The treatment of feedwater, carrying scale-forming ingredients, is along two main lines: 1st, by chemical means by which such impurities as are carried by the waterare caused to precipitate; and 2nd, by the means of heat, which resultsin the reduction of the power of water to hold certain salts insolution. The latter method alone is sufficient in the case of certaintemporarily hard waters, but the heat treatment, in general, is used inconnection with a chemical treatment to assist the latter. Before going further into detail as to the treatment of water, it may bewell to define certain terms used. _Hardness_, which is the most widely known evidence of the presence inwater of scale-forming matter, is that quality, the variation of whichmakes it more difficult to obtain a lather or suds from soap in onewater than in another. This action is made use of in the soap test forhardness described later. Hardness is ordinarily classed as eithertemporary or permanent. Temporarily hard waters are those containingcarbonates of lime and magnesium, which may be precipitated by boilingat 212 degrees and which, if they contain no other scale-formingingredients, become "soft" under such treatment. Permanently hard watersare those containing mainly calcium sulphate, which is only precipitatedat the high temperatures found in the boiler itself, 300 degreesFahrenheit or more. The scale of hardness is an arbitrary one, based onthe number of grains of solids per gallon and waters may be classed onsuch a basis as follows: 1-10 grain per gallon, soft water; 10-20 grainper gallon, moderately hard water; above 25 grains per gallon, very hardwater. _Alkalinity_ is a general term used for waters containing compounds withthe power of neutralizing acids. _Causticity_, as used in water treatment, is a term coined by A. McGill, indicating the presence of an excess of lime added during treatment. Though such presence would also indicate alkalinity, the term isarbitrarily used to apply to those hydrates whose presence is indicatedby phenolphthalein. Of the chemical methods of water treatment, there are three generalprocesses: 1st. Lime Process. The lime process is used for waters containingbicarbonates of lime and magnesia. Slacked lime in solution, as limewater, is the reagent used. This combines with the carbonic acid whichis present, either free or as carbonates, to form an insolublemonocarbonate of lime. The soluble bicarbonates of lime and magnesia, losing their carbonic acid, thereby become insoluble and precipitate. 2nd. Soda Process. The soda process is used for waters containingsulphates of lime and magnesia. Carbonate of soda and hydrate of soda(caustic soda) are used either alone or together as the reagents. Carbonate of soda, added to water containing little or no carbonic acidor bicarbonates, decomposes the sulphates to form insoluble carbonate oflime or magnesia which precipitate, the neutral soda remaining insolution. If free carbonic acid or bicarbonates are present, bicarbonateof lime is formed and remains in solution, though under the action ofheat, the carbon dioxide will be driven off and insoluble monocarbonateswill be formed. Caustic soda used in this process causes a moreenergetic action, it being presumed that the caustic soda absorbs thecarbonic acid, becomes carbonate of soda and acts as above. 3rd. Lime and Soda Process. This process, which is the combination ofthe first two, is by far the most generally used in water purification. Such a method is used where sulphates of lime and magnesia are containedin the water, together with such quantity of carbonic acid orbicarbonates as to impair the action of the soda. Sufficient soda isused to break down the sulphates of lime and magnesia and as much limeadded as is required to absorb the carbonic acid not taken up in thesoda reaction. All of the apparatus for effecting such treatment of feed waters isapproximately the same in its chemical action, the numerous systemsdiffering in the methods of introduction and handling of the reagents. The methods of testing water treated by an apparatus of this descriptionfollow. When properly treated, alkalinity, hardness and causticity should be inthe approximate relation of 6, 5 and 4. When too much lime is used inthe treatment, the causticity in the purified water, as indicated by theacid test, will be nearly equal to the alkalinity. If too little lime isused, the causticity will fall to approximately half the alkalinity. Thehardness should not be in excess of two points less than the alkalinity. Where too great a quantity of soda is used, the hardness is lowered andthe alkalinity raised. If too little soda, the hardness is raised andthe alkalinity lowered. Alkalinity and causticity are tested with a standard solution ofsulphuric acid. A standard soap solution is used for testing forhardness and a silver nitrate solution may also be used for determiningwhether an excess of lime has been used in the treatment. Alkalinity: To 50 cubic centimeters of treated water, to which there hasbeen added sufficient methylorange to color it, add the acid solution, drop by drop, until the mixture is on the point of turning red. As theacid solution is first added, the red color, which shows quickly, disappears on shaking the mixture, and this color disappears more slowlyas the critical point is approached. One-tenth cubic centimeter of thestandard acid solution corresponds to one degree of alkalinity. [Illustration: 2640 Horse-power Installation of Babcock & Wilcox Boilersat the Botany Worsted Mills, Passaic, N. J. ] Causticity: To 50 cubic centimeters of treated water, to which there hasbeen added one drop of phenolphthalein dissolved in alcohol to give thewater a pinkish color, add the acid solution, drop by drop, shakingafter each addition, until the color entirely disappears. One-tenthcubic centimeter of acid solution corresponds to one degree ofcausticity. The alkalinity may be determined from the same sample tested forcausticity by the coloring with methylorange and adding the acid untilthe sample is on the point of turning red. The total acid added indetermining both causticity and alkalinity in this case is the measureof the alkalinity. Hardness: 100 cubic centimeters of the treated water is used for thistest, one cubic centimeter of the soap solution corresponding to onedegree of hardness. The soap solution is added a very little at a timeand the whole violently shaken. Enough of the solution must be added tomake a permanent lather or foam, that is, the soap bubbles must notdisappear after the shaking is stopped. Excess of lime as determined by nitrate of silver: If there is an excessof lime used in the treatment, a sample will become a dark brown by theaddition of a small quantity of silver nitrate, otherwise a milky whitesolution will be formed. Combined Heat and Chemical Treatment: Heat is used in many systems offeed treatment apparatus as an adjunct to the chemical process. Heatalone will remove temporary hardness by the precipitation of carbonatesof lime and magnesia and, when used in connection with the chemicalprocess, leaves only the permanent hardness or the sulphates of lime tobe taken care of by chemical treatment. TABLE 16 REAGENTS REQUIRED IN LIME AND SODA PROCESS FOR TREATING 1000 U. S. GALLONS OF WATER PER GRAIN PER GALLON OF CONTAINED IMPURITIES[16] +-----------------------+-----------+-----------+| | Lime[17] | Soda[18] || | Pounds | Pounds |+-----------------------+-----------+-----------+| Calcium Carbonate | 0. 098 | . .. || Calcium Sulphate | . .. | 0. 124 || Calcium Chloride | . .. | 0. 151 || Calcium Nitrate | . .. | 0. 104 || Magnesium Carbonate | 0. 234 | . .. || Magnesium Sulphate | 0. 079 | 0. 141 || Magnesium Chloride | 0. 103 | 0. 177 || Magnesium Nitrate | 0. 067 | 0. 115 || Ferrous Carbonate | 0. 169 | . .. || Ferrous Sulphate | 0. 070 | 0. 110 || Ferric Sulphate | 0. 074 | 0. 126 || Aluminum Sulphate | 0. 087 | 0. 147 || Free Sulphuric Acid | 0. 100 | 0. 171 || Sodium Carbonate | 0. 093 | . .. || Free Carbon Dioxide | 0. 223 | . .. || Hydrogen Sulphite | 0. 288 | . .. |+-----------------------+-----------+-----------+ The chemicals used in the ordinary lime and soda process of feed watertreatment are common lime and soda. The efficiency of such apparatuswill depend wholly upon the amount and character of the impurities inthe water to be treated. Table 16 gives the amount of lime and sodarequired per 1000 gallons for each grain per gallon of the variousimpurities found in the water. This table is based on lime containing 90per cent calcium oxide and soda containing 58 per cent sodium oxide, which correspond to the commercial quality ordinarily purchasable. Fromthis table and the cost of the lime and soda, the cost of treating anywater per 1000 gallons may be readily computed. Less Usual Reagents--Barium hydrate is sometimes used to reducepermanent hardness or the calcium sulphate component. Until recently, the high cost of barium hydrate has rendered its use prohibitive but atthe present it is obtained as a by-product in cement manufacture and itmay be purchased at a more reasonable figure than heretofore. It actsdirectly on the soluble sulphates to form barium sulphate which isinsoluble and may be precipitated. Where this reagent is used, it isdesirable that the reaction be allowed to take place outside of theboiler, though there are certain cases where its internal use ispermissible. Barium carbonate is sometimes used in removing calcium sulphate, theproducts of the reaction being barium sulphate and calcium carbonate, both of which are insoluble and may be precipitated. As barium carbonatein itself is insoluble, it cannot be added to water as a solution andits use should, therefore, be confined to treatment outside of theboiler. Silicate of soda will precipitate calcium carbonate with the formationof a gelatinous silicate of lime and carbonate of soda. If calciumsulphate is also present, carbonate of soda is formed in the abovereaction, which in turn will break down the sulphate. Oxalate of soda is an expensive but efficient reagent which forms aprecipitate of calcium oxalate of a particularly insoluble nature. Alum and iron alum will act as efficient coagulents where organic matteris present in the water. Iron alum has not only this property but alsothat of reducing oil discharged from surface condensers to a conditionin which it may be readily removed by filtration. Corrosion--Where there is a corrosive action because of the presence ofacid in the water or of oil containing fatty acids which will decomposeand cause pitting wherever the sludge can find a resting place, it maybe overcome by the neutralization of the water by carbonate of soda. Such neutralization should be carried to the point where the water willjust turn red litmus paper blue. As a preventative of such actionarising from the presence of the oil, only the highest grades ofhydrocarbon oils should be used. Acidity will occur where sea water is present in a boiler. There is thepossibility of such an occurrence in marine practice and in stationaryplants using sea water for condensing, due to leaky condenser tubes, priming in the evaporators, etc. Such acidity is caused through thedissociation of magnesium chloride into hydrochloride acid and magnesiaunder high temperatures. The acid in contact with the metal forms aniron salt which immediately upon its formation is neutralized by thefree magnesia in the water, thereby precipitating iron oxide andreforming magnesium chloride. The preventive for corrosion arising fromsuch acidity is the keeping tight of the condenser. Where it isunavoidable that some sea water should find its way into a boiler, theacidity resulting should be neutralized by soda ash. This will convertthe magnesium chloride into magnesium carbonate and sodium chloride, neither of which is corrosive but both of which are scale-forming. The presence of air in the feed water which is sucked in by the feedpump is a well recognized cause of corrosion. Air bubbles form below thewater line and attack the metal of the boiler, the oxygen of the aircausing oxidization of the boiler metal and the formation of rust. Theparticle of rust thus formed is swept away by the circulation or isdislodged by expansion and the minute pit thus left forms an idealresting place for other air bubbles and the continuation of theoxidization process. The prevention is, of course, the removing of theair from the feed water. In marine practice, where there has beenexperienced the most difficulty from this source, it has been found tobe advantageous to pump the water from the hot well to a filter tankplaced above the feed pump suction valves. In this way the air isliberated from the surface of the tank and a head is assured for thesuction end of the pump. In this same class of work, the corrosiveaction of air is reduced by introducing the feed through a spray nozzleinto the steam space above the water line. Galvanic action, resulting in the eating away of the boiler metalthrough electrolysis was formerly considered practically the sole causeof corrosion. But little is known of such action aside from the factthat it does take place in certain instances. The means adopted as aremedy is usually the installation of zinc plates within the boiler, which must have positive metallic contact with the boiler metal. In thisway, local electrolytic effects are overcome by a still greaterelectrolytic action at the expense of the more positive zinc. Thepositive contact necessary is difficult to maintain and it isquestionable just what efficacy such plates have except for a shortperiod after their installation when the contact is known to bepositive. Aside from protection from such electrolytic action, however, the zinc plates have a distinct use where there is the liability of airin the feed, as they offer a substance much more readily oxidized bysuch air than the metal of the boiler. Foaming--Where foaming is caused by organic matter in suspension, it maybe largely overcome by filtration or by the use of a coagulent inconnection with filtration, the latter combination having come recentlyinto considerable favor. Alum, or potash alum, and iron alum, which inreality contains no alumina and should rather be called potassia-ferric, are the coagulents generally used in connection with filtration. Suchmatter as is not removed by filtration may, under certain conditions, behandled by surface blowing. In some instances, settling tanks are usedfor the removal of matter in suspension, but where large quantities ofwater are required, filtration is ordinarily substituted on account ofthe time element and the large area necessary in settling tanks. Where foaming occurs as the result of overtreatment of the feed water, the obvious remedy is a change in such treatment. Priming--Where priming is caused by excessive concentration of saltswithin a boiler, it may be overcome largely by frequent blowing down. The degree of concentration allowable before priming will take placevaries widely with conditions of operation and may be definitelydetermined only by experience with each individual set of conditions. Itis the presence of the salts that cause priming that may result in theabsolute unfitness of water for boiler feed purposes. Where these saltsexist in such quantities that the amount of blowing down necessary tokeep the degree of concentration below the priming point results inexcessive losses, the only remedy is the securing of another supply offeed, and the results will warrant the change almost regardless of theexpense. In some few instances, the impurities may be taken care of bysome method of water treatment but such water should be submitted to anauthority on the subject before any treatment apparatus is installed. [Illustration: 3000 Horse-power Installation of Cross Drum Babcock &Wilcox Boilers and Superheaters Equipped with Babcock & Wilcox ChainGrate Stokers at the Washington Terminal Co. , Washington, D. C. ] Boiler Compounds--The method of treatment of feed water by far the mostgenerally used is by the use of some of the so-called boiler compounds. There are many reliable concerns handling such compounds whounquestionably secure the promised results, but there is a greattendency toward looking on the compound as a "cure all" for any waterdifficulties and care should be taken to deal only with reputableconcerns. The composition of these compounds is almost invariably based on sodawith certain tannic substances and in some instances a gelatinoussubstance which is presumed to encircle scale particles and preventtheir adhering to the boiler surfaces. The action of these compounds isordinarily to reduce the calcium sulphate in the water by means ofcarbonate of soda and to precipitate it as a muddy form of calciumcarbonate which may be blown off. The tannic compounds are used inconnection with the soda with the idea of introducing organic matterinto any scale already formed. When it has penetrated to the boilermetal, decomposition of the scale sets in, causing a disruptive effectwhich breaks the scale from the metal sometimes in large slabs. It isthis effect of boiler compounds that is to be most carefully guardedagainst or inevitable trouble will result from the presence of loosescale with the consequent danger of tube losses through burning. When proper care is taken to suit the compound to the water in use, theresults secured are fairly effective. In general, however, the use ofcompounds may only be recommended for the prevention of scale ratherthan with the view to removing scale which has already formed, that is, the compounds should be introduced with the feed water only when theboiler has been thoroughly cleaned. FEED WATER HEATING AND METHODS OF FEEDING Before water fed into a boiler can be converted into steam, it must befirst heated to a temperature corresponding to the pressure within theboiler. Steam at 160 pounds gauge pressure has a temperature ofapproximately 371 degrees Fahrenheit. If water is fed to the boiler at60 degrees Fahrenheit, each pound must have 311 B. T. U. Added to it toincrease its temperature 371 degrees, which increase must take placebefore the water can be converted into steam. As it requires 1167. 8B. T. U. To raise one pound of water from 60 to 371 degrees and toconvert it into steam at 160 pounds gauge pressure, the 311 degreesrequired simply to raise the temperature of the water from 60 to 371degrees will be approximately 27 per cent of the total. If, therefore, the temperature of the water can be increased from 60 to 371 degreesbefore it is introduced into a boiler by the utilization of heat fromsome source that would otherwise be wasted, there will be a saving inthe fuel required of 311 ÷ 1167. 8 = 27 per cent, and there will be a netsaving, provided the cost of maintaining and operating the apparatus forsecuring this saving is less than the value of the heat thus saved. The saving in the fuel due to the heating of feed water by means of heatthat would otherwise be wasted may be computed from the formula: 100 (t - t_{i})Fuel saving per cent = --------------- (1) H + 32 - t_{i} where, t = temperature of feed water after heating, t_{i} = temperatureof feed water before heating, and H = total heat above 32 degrees perpound of steam at the boiler pressure. Values of H may be found in Table23. Table 17 has been computed from this formula to show the fuel savingunder the conditions assumed with the boiler operating at 180 poundsgauge pressure. TABLE 17 SAVING IN FUEL, IN PER CENT, BY HEATING FEED WATER GAUGE PRESSURE 180 POUNDS +-----------+-----------------------------------------+| Initial | Final Temperature--Degrees Fahrenheit ||Temperature|-----+-----+-----+-----+-----+-----+-----|| Fahrenheit| 120 | 140 | 160 | 180 | 200 | 250 | 300 |+-----------+-----+-----+-----+-----+-----+-----+-----+| 32 | 7. 35| 9. 02|10. 69|12. 36|14. 04|18. 20|22. 38|| 35 | 7. 12| 8. 79|10. 46|12. 14|13. 82|18. 00|22. 18|| 40 | 6. 72| 8. 41|10. 09|11. 77|13. 45|17. 65|21. 86|| 45 | 6. 33| 8. 02| 9. 71|11. 40|13. 08|17. 30|21. 52|| 50 | 5. 93| 7. 63| 9. 32|11. 02|12. 72|16. 95|21. 19|| 55 | 5. 53| 7. 24| 8. 94|10. 64|12. 34|16. 60|20. 86|| 60 | 5. 13| 6. 84| 8. 55|10. 27|11. 97|16. 24|20. 52|| 65 | 4. 72| 6. 44| 8. 16| 9. 87|11. 59|15. 88|20. 18|| 70 | 4. 31| 6. 04| 7. 77| 9. 48|11. 21|15. 52|19. 83|| 75 | 3. 90| 5. 64| 7. 36| 9. 09|10. 82|15. 16|19. 48|| 80 | 3. 48| 5. 22| 6. 96| 8. 70|10. 44|14. 79|19. 13|| 85 | 3. 06| 4. 80| 6. 55| 8. 30|10. 05|14. 41|18. 78|| 90 | 2. 63| 4. 39| 6. 14| 7. 89| 9. 65|14. 04|18. 43|| 95 | 2. 20| 3. 97| 5. 73| 7. 49| 9. 25|13. 66|18. 07|| 100 | 1. 77| 3. 54| 5. 31| 7. 08| 8. 85|13. 28|17. 70|| 110 | . 89| 2. 68| 4. 47| 6. 25| 8. 04|12. 50|16. 97|| 120 | . 00| 1. 80| 3. 61| 5. 41| 7. 21|11. 71|16. 22|| 130 | | . 91| 2. 73| 4. 55| 6. 37|10. 91|15. 46|| 140 | | . 00| 1. 84| 3. 67| 5. 51|10. 09|14. 68|| 150 | | | . 93| 2. 78| 4. 63| 9. 26|13. 89|| 160 | | | . 00| 1. 87| 3. 74| 8. 41|13. 09|| 170 | | | | . 94| 2. 83| 7. 55|12. 27|| 180 | | | | . 00| 1. 91| 6. 67|11. 43|| 190 | | | | | . 96| 5. 77|10. 58|| 200 | | | | | . 00| 4. 86| 9. 71|| 210 | | | | | | 3. 92| 8. 82|+-----------+-----+-----+-----+-----+-----+-----+-----+ Besides the saving in fuel effected by the use of feed water heaters, other advantages are secured. The time required for the conversion ofwater into steam is diminished and the steam capacity of the boilerthereby increased. Further, the feeding of cold water into a boiler hasa tendency toward the setting up of temperature strains, which arediminished in proportion as the temperature of the feed approaches thatof the steam. An important additional advantage of heating feed water isthat in certain types of heaters a large portion of the scale formingingredients are precipitated before entering the boiler, with aconsequent saving in cleaning and losses through decreased efficiencyand capacity. In general, feed water heaters may be divided into closed heaters, openheaters and economizers; the first two depend for their heat uponexhaust, or in some cases live steam, while the last class utilizes theheat of the waste flue gases to secure the same result. The question ofthe type of apparatus to be installed is dependent upon the conditionsattached to each individual case. In closed heaters the feed water and the exhaust steam do not come intoactual contact with each other. Either the steam or the water passesthrough tubes surrounded by the other medium, as the heater is of thesteam-tube or water-tube type. A closed heater is best suited for waterfree from scale-forming matter, as such matter soon clogs the passages. Cleaning such heaters is costly and the efficiency drops off rapidly asscale forms. A closed heater is not advisable where the engines workintermittently, as is the case with mine hoisting engines. In this classof work the frequent coolings between operating periods and the suddenheatings when operation commences will tend to loosen the tubes or evenpull them apart. For this reason, an open heater, or economizer, willgive more satisfactory service with intermittently operating apparatus. Open heaters are best suited for waters containing scale-forming matter. Much of the temporary hardness may be precipitated in the heater and thesediment easily removed. Such heaters are frequently used with a reagentfor precipitating permanent hardness in the combined heat and chemicaltreatment of feed water. The so-called live steam purifiers are openheaters, the water being raised to the boiling temperature and thecarbonates and a portion of the sulphates being precipitated. Thedisadvantage of this class of apparatus is that some of the sulphatesremain in solution to be precipitated as scale when concentrated in theboiler. Sufficient concentration to have such an effect, however, mayoften be prevented by frequent blowing down. Economizers find their largest field where the design of the boiler issuch that the maximum possible amount of heat is not extracted from thegases of combustion. The more wasteful the boiler, the greater thesaving effected by the use of the economizer, and it is sometimespossible to raise the temperature of the feed water to that of highpressure steam by the installation of such an apparatus, the savingamounting in some cases to as much as 20 per cent. The fuel used bearsdirectly on the question of the advisability of an economizerinstallation, for when oil is the fuel a boiler efficiency of 80 percent or over is frequently realized, an efficiency which would leave asmall opportunity for a commercial gain through the addition of aneconomizer. From the standpoint of space requirements, economizers are at adisadvantage in that they are bulky and require a considerable increaseover space occupied by a heater of the exhaust type. They also requireadditional brickwork or a metal casing, which increases the cost. Sometimes, too, the frictional resistance of the gases through aneconomizer make its adaptability questionable because of the draftconditions. When figuring the net return on economizer investment, allof these factors must be considered. When the feed water is such that scale will quickly encrust theeconomizer and throw it out of service for cleaning during an excessiveportion of the time, it will be necessary to purify water beforeintroducing it into an economizer to make it earn a profit on theinvestment. From the foregoing, it is clearly indicated that it is impossible tomake a definite statement as to the relative saving by heating feedwater in any of the three types. Each case must be worked outindependently and a decision can be reached only after an exhaustivestudy of all the conditions affecting the case, including the time theplant will be in service and probable growth of the plant. When, as aresult of such study, the possible methods for handling the problem havebeen determined, the solution of the best apparatus can be made easilyby the balancing of the saving possible by each method against its firstcost, depreciation, maintenance and cost of operation. Feeding of Water--The choice of methods to be used in introducing feedwater into a boiler lies between an injector and a pump. In most plants, an injector would not be economical, as the water fed by such means mustbe cold, a fact which makes impossible the use of a heater before thewater enters the injector. Such a heater might be installed between theinjector and the boiler but as heat is added to the water in theinjector, the heater could not properly fulfill its function. TABLE 18 COMPARISON OF PUMPS AND INJECTORS _________________________________________________________________________| | | || Method of Supplying | | || Feed-water to Boiler | Relative amount of | Saving of fuel over|| Temperature of feed-water as | coal required per | the amount required|| delivered to the pump or to | unit of time, the | when the boiler is || injector, 60 degrees Fahren- | amount for a direct-| fed by a direct- || heit. Rate of evaporation of | acting pump, feeding| acting pump without|| boiler, to pounds of water | water at 60 degrees | heater || per pound of coal from and | without a heater, | Per Cent || at 212 degrees Fahrenheit | being taken as unity| ||______________________________|_____________________|____________________|| | | || Direct-acting Pump feeding | | || water at 60 degrees without | | || a heater | 1. 000 | . 0 || | | || Injector feeding water at | | || 150 degrees without a heater | . 985 | 1. 5 || Injector feeding through a | | || heater in which the water is | | || heated from 150 to 200 | | || degrees | . 938 | 6. 2 || | | || Direct-acting Pump feeding | | || water through a heater in | | || which it is heated from 60 | | || to 200 degrees | . 879 | 12. 1 || | | || Geared Pump run from the | | || engine, feeding water | | || through a heater in which it | | || is heated from 60 to 200 | | || degrees | . 868 | 13. 2 ||______________________________|_____________________|____________________| The injector, considered only in the light of a combined heater andpump, is claimed to have a thermal efficiency of 100 per cent, since allof the heat in the steam used is returned to the boiler with the water. This claim leads to an erroneous idea. If a pump is used in feeding thewater to a boiler and the heat in the exhaust from the pump is impartedto the feed water, the pump has as high a thermal efficiency as theinjector. The pump has the further advantage that it uses so much lesssteam for the forcing of a given quantity of water into the boiler thatit makes possible a greater saving through the use of the exhaust fromother auxiliaries for heating the feed, which exhaust, if an injectorwere used, would be wasted, as has been pointed out. In locomotive practice, injectors are used because there is no exhauststeam available for heating the feed, this being utilized in producing aforced draft, and because of space requirements. In power plant work, however, pumps are universally used for regular operation, thoughinjectors are sometimes installed as an auxiliary method of feeding. Table 18 shows the relative value of injectors, direct-acting steampumps and pumps driven from the engine, the data having been obtainedfrom actual experiment. It will be noted that when feeding cold waterdirect to the boilers, the injector has a slightly greater economy butwhen feeding through a heater, the pump is by far the more economical. Auxiliaries--It is the general impression that auxiliaries will takeless steam if the exhaust is turned into the condensers, in this wayreducing the back pressure. As a matter of fact, vacuum is rarelyregistered on an indicator card taken from the cylinders of certaintypes of auxiliaries unless the exhaust connection is short and withoutbends, as long pipes and many angles offset the effect of the condenser. On the other hand, if the exhaust steam from the auxiliaries can be usedfor heating the feed water, all of the latent heat less only the lossdue to radiation is returned to the boiler and is saved instead of beinglost in the condensing water or wasted with the free exhaust. Takinginto consideration the plant as a whole, it would appear that theauxiliary machinery, under such conditions, is more efficient than themain engines. [Illustration: Portion of 4160 Horse-power Installation of Babcock &Wilcox Boilers at the Prudential Life Insurance Co. Building, Newark, N. J. ] STEAM When a given weight of a perfect gas is compressed or expanded at aconstant temperature, the product of the pressure and volume is aconstant. Vapors, which are liquids in aeriform condition, on the otherhand, can exist only at a definite pressure corresponding to eachtemperature if in the saturated state, that is, the pressure is afunction of the temperature only. Steam is water vapor, and at apressure of, say, 150 pounds absolute per square inch saturated steamcan exist only at a temperature 358 degrees Fahrenheit. Hence if thepressure of saturated steam be fixed, its temperature is also fixed, and_vice versa_. Saturated steam is water vapor in the condition in which it is generatedfrom water with which it is in contact. Or it is steam which is at themaximum pressure and density possible at its temperature. If any changebe made in the temperature or pressure of steam, there will be acorresponding change in its condition. If the pressure be increased orthe temperature decreased, a portion of the steam will be condensed. Ifthe temperature be increased or the pressure decreased, a portion of thewater with which the steam is in contact will be evaporated into steam. Steam will remain saturated just so long as it is of the same pressureand temperature as the water with which it can remain in contact withouta gain or loss of heat. Moreover, saturated steam cannot have itstemperature lowered without a lowering of its pressure, any loss of heatbeing made up by the latent heat of such portion as will be condensed. Nor can the temperature of saturated steam be increased except whenaccompanied by a corresponding increase in pressure, any added heatbeing expended in the evaporation into steam of a portion of the waterwith which it is in contact. Dry saturated steam contains no water. In some cases, saturated steam isaccompanied by water which is carried along with it, either in the formof a spray or is blown along the surface of the piping, and the steam isthen said to be wet. The percentage weight of the steam in a mixture ofsteam and water is called the quality of the steam. Thus, if in amixture of 100 pounds of steam and water there is three-quarters of apound of water, the quality of the steam will be 99. 25. Heat may be added to steam not in contact with water, such an additionof heat resulting in an increase of temperature and pressure if thevolume be kept constant, or an increase in temperature and volume if thepressure remain constant. Steam whose temperature thus exceeds that ofsaturated steam at a corresponding pressure is said to be superheatedand its properties approximate those of a perfect gas. As pointed out in the chapter on heat, the heat necessary to raise onepound of water from 32 degrees Fahrenheit to the point of ebullition iscalled the _heat of the liquid_. The heat absorbed during ebullitionconsists of that necessary to dissociate the molecules, or the _innerlatent heat_, and that necessary to overcome the resistance to theincrease in volume, or the _outer latent heat_. These two make up the_latent heat of evaporation_ and the sum of this latent heat ofevaporation and the heat of the liquid make the _total heat_ of thesteam. These values for various pressures are given in the steam tables, pages 122 to 127. The specific volume of saturated steam at any pressure is the volume incubic feet of one pound of steam at that pressure. The density of saturated steam, that is, its weight per cubic foot, isobviously the reciprocal of the specific volume. This density varies asthe 16/17 power over the ordinary range of pressures used in steamboiler work and may be found by the formula, D = . 003027p^{. 941}, whichis correct within 0. 15 per cent up to 250 pounds pressure. The relative volume of steam is the ratio of the volume of a givenweight to the volume of the same weight of water at 39. 2 degreesFahrenheit and is equal to the specific volume times 62. 427. As vapors are liquids in their gaseous form and the boiling point is thepoint of change in this condition, it is clear that this point isdependent upon the pressure under which the liquid exists. This fact isof great practical importance in steam condenser work and in manyoperations involving boiling in an open vessel, since in the latter caseits altitude will have considerable influence. The relation betweenaltitude and boiling point of water is shown in Table 12. The conditions of feed temperature and steam pressure in boiler tests, fuel performances and the like, will be found to vary widely indifferent trials. In order to secure a means for comparison of differenttrials, it is necessary to reduce all results to some common basis. Themethod which has been adopted for the reduction to a comparable basis isto transform the evaporation under actual conditions of steam pressureand feed temperature which exist in the trial to an equivalentevaporation under a set of standard conditions. These standardconditions presuppose a feed water temperature of 212 degrees Fahrenheitand a steam pressure equal to the normal atmospheric pressure at sealevel, 14. 7 pounds absolute. Under such conditions steam would begenerated _at_ a temperature of 212 degrees, the temperaturecorresponding to atmospheric pressure at sea level, _from_ water at 212degrees. The weight of water which _would_ be evaporated under theassumed standard conditions by exactly the amount of heat absorbed bythe boiler under actual conditions existing in the trial, is, therefore, called the equivalent evaporation "from and at 212 degrees. " The factor for reducing the weight of water actually converted intosteam from the temperature of the feed, at the steam pressure existingin the trial, to the equivalent evaporation under standard conditions iscalled the _factor of evaporation. _ This factor is the ratio of thetotal heat added to one pound of steam under the standard conditions tothe heat added to each pound of steam in heating the water from thetemperature of the feed in the trial to the temperature corresponding tothe pressure existing in the trial. This heat added is obviously thedifference between the total heat of evaporation of the steam at thepressure existing in the trial and the heat of the liquid in the waterat the temperature at which it was fed in the trial. To illustrate by anexample: In a boiler trial the temperature of the feed water is 60 degreesFahrenheit and the pressure under which steam is delivered is 160. 3pounds gauge pressure or 175 pounds absolute pressure. The total heat ofone pound of steam at 175 pounds pressure is 1195. 9 B. T. U. Measuredabove the standard temperature of 32 degrees Fahrenheit. But the waterfed to the boiler contained 28. 08 B. T. U. As the heat of the liquidmeasured above 32 degrees Fahrenheit. Therefore, to each pound of steamthere has been added 1167. 82 B. T. U. To evaporate one pound of waterunder standard conditions would, on the other hand, have required but970. 4 B. T. U. , which, as described, is the latent heat of evaporationat 212 degrees Fahrenheit. Expressed differently, the total heat of onepound of steam at the pressure corresponding to a temperature of 212degrees is 1150. 4 B. T. U. One pound of water at 212 degrees contains180 B. T. U. Of sensible heat above 32 degrees Fahrenheit. Hence, understandard conditions, 1150. 4 - 180 = 970. 4 B. T. U. Is added in thechanging of one pound of water into steam at atmospheric pressure and atemperature of 212 degrees. This is in effect the definition of thelatent heat of evaporation. Hence, if conditions of the trial had been standard, only 970. 4 B. T. U. Would be required and the ratio of 1167. 82 to 970. 4 B. T. U. Is theratio determining the factor of evaporation. The factor in the assumedcase is 1167. 82 ÷ 970. 4 = 1. 2034 and if the same amount of heat had beenabsorbed under standard conditions as was absorbed in the trialcondition, 1. 2034 times the amount of steam would have been generated. Expressed as a formula for use with any set of conditions, the factoris, H - hF = ----- (2) 970. 4 Where H = the total heat of steam above 32 degrees Fahrenheit from steam tables, h = sensible heat of feed water above 32 degrees Fahrenheit from Table 22. In the form above, the factor may be determined with either saturated orsuperheated steam, provided that in the latter case values of H areavailable for varying degrees of superheat and pressures. Where such values are not available, the form becomes, H - h + s(t_{sup} - t_{sat})F = ---------------------------- (3) 970. 4 Where s = mean specific heat of superheated steam at the pressure existing in the trial from saturated steam to the temperature existing in the trial, t_{sup} = final temperature of steam, t_{sat} = temperature of saturated steam, corresponding to pressure existing, (t_{sup} - t_{sat}) = degrees of superheat. The specific heat of superheated steam will be taken up later. Table 19 gives factors of evaporation for saturated steam boiler trialsto cover a large range of conditions. Except for the most refined work, intermediate values may be determined by interpolation. Steam gauges indicate the pressure above the atmosphere. As has beenpointed out, the atmospheric pressure changes according to the altitudeand the variation in the barometer. Hence, calculations involving theproperties of steam are based on _absolute_ pressures, which are equalto the gauge pressure plus the atmospheric pressure in pounds to thesquare inch. This latter is generally assumed to be 14. 7 pounds persquare inch at sea level, but for other levels it must be determinedfrom the barometric reading at that place. Vacuum gauges indicate the difference, expressed in inches of mercury, between atmospheric pressure and the pressure within the vessel to whichthe gauge is attached. For approximate purposes, 2. 04 inches height ofmercury may be considered equal to a pressure of one pound per squareinch at the ordinary temperatures at which mercury gauges are used. Hence for any reading of the vacuum gauge in inches, G, the absolutepressure for any barometer reading in inches, B, will be (B - G) ÷ 2. 04. If the barometer is 30 inches measured at ordinary temperatures and notcorrected to 32 degrees Fahrenheit and the vacuum gauge 24 inches, theabsolute pressure will be (30 - 24) ÷ 2. 04 = 2. 9 pounds per square inch. TABLE 19 FACTORS OF EVAPORATION CALCULATED FROM MARKS AND DAVIS TABLES ______________________________________________________________________| | ||Feed | ||Temp- | ||erature| ||Degrees| Steam Pressure by Gauge ||Fahren-| ||heit | ||_______|______________________________________________________________|| | | | | | | | || | 50 | 60 | 70 | 80 | 90 | 100 | 110 ||_______|________|________|________|________|________|________|________|| | | | | | | | || 32 | 1. 2143 | 1. 2170 | 1. 2194 | 1. 2215 | 1. 2233 | 1. 2233 | 1. 2265 || 40 | 1. 2060 | 1. 2087 | 1. 2111 | 1. 2131 | 1. 2150 | 1. 2168 | 1. 2181 || 50 | 1. 1957 | 1. 1984 | 1. 2008 | 1. 2028 | 1. 2047 | 1. 2065 | 1. 2079 || 60 | 1. 1854 | 1. 1881 | 1. 1905 | 1. 1925 | 1. 1944 | 1. 1961 | 1. 1976 || 70 | 1. 1750 | 1. 1778 | 1. 1802 | 1. 1822 | 1. 1841 | 1. 1859 | 1. 1873 || 80 | 1. 1649 | 1. 1675 | 1. 1699 | 1. 1720 | 1. 1738 | 1. 1756 | 1. 1770 || 90 | 1. 1545 | 1. 1572 | 1. 1596 | 1. 1617 | 1. 1636 | 1. 1653 | 1. 1668 || 100 | 1. 1443 | 1. 1470 | 1. 1493 | 1. 1514 | 1. 1533 | 1. 1550 | 1. 1565 || 110 | 1. 1340 | 1. 1367 | 1. 1391 | 1. 1411 | 1. 1430 | 1. 1448 | 1. 1462 || 120 | 1. 1237 | 1. 1264 | 1. 1288 | 1. 1309 | 1. 1327 | 1. 1345 | 1. 1359 || 130 | 1. 1134 | 1. 1161 | 1. 1185 | 1. 1206 | 1. 1225 | 1. 1242 | 1. 1257 || 140 | 1. 1031 | 1. 1058 | 1. 1082 | 1. 1103 | 1. 1122 | 1. 1139 | 1. 1154 || 150 | 1. 0928 | 1. 0955 | 1. 0979 | 1. 1000 | 1. 1019 | 1. 1036 | 1. 1051 || 160 | 1. 0825 | 1. 0852 | 1. 0876 | 1. 0897 | 1. 0916 | 1. 0933 | 1. 0948 || 170 | 1. 0722 | 1. 0749 | 1. 0773 | 1. 0794 | 1. 0813 | 1. 0830 | 1. 0845 || 180 | 1. 0619 | 1. 0646 | 1. 0670 | 1. 0691 | 1. 0709 | 1. 0727 | 1. 0741 || 190 | 1. 0516 | 1. 0543 | 1. 0567 | 1. 0587 | 1. 0606 | 1. 0624 | 1. 0638 || 200 | 1. 0412 | 1. 0439 | 1. 0463 | 1. 0484 | 1. 0503 | 1. 0520 | 1. 0535 || 210 | 1. 0309 | 1. 0336 | 1. 0360 | 1. 0380 | 1. 0399 | 1. 0417 | 1. 0432 ||_______|________|________|________|________|________|________|________| ______________________________________________________________________| | ||Feed | ||Temp- | ||erature| ||Degrees| Steam Pressure by Gauge ||Fahren-| ||heit | ||_______|______________________________________________________________|| | | | | | | | || | 120 | 130 | 140 | 150 | 160 | 170 | 180 ||_______|________|________|________|________|________|________|________|| | | | | | | | || 32 | 1. 2280 | 1. 2292 | 1. 2304 | 1. 2314 | 1. 2323 | 1. 2333 | 1. 2342 || 40 | 1. 2196 | 1. 2209 | 1. 2221 | 1. 2231 | 1. 2241 | 1. 2250 | 1. 2259 || 50 | 1. 2093 | 1. 2106 | 1. 2117 | 1. 2128 | 1. 2137 | 1. 2147 | 1. 2156 || 60 | 1. 1990 | 1. 2003 | 1. 2014 | 1. 2025 | 1. 2034 | 1. 2044 | 1. 2053 || 70 | 1. 1887 | 1. 1900 | 1. 1911 | 1. 1922 | 1. 1931 | 1. 1941 | 1. 1950 || 80 | 1. 1785 | 1. 1797 | 1. 1809 | 1. 1819 | 1. 1828 | 1. 1838 | 1. 1847 || 90 | 1. 1682 | 1. 1695 | 1. 1706 | 1. 1717 | 1. 1725 | 1. 1735 | 1. 1744 || 100 | 1. 1579 | 1. 1592 | 1. 1603 | 1. 1614 | 1. 1623 | 1. 1633 | 1. 1642 || 110 | 1. 1477 | 1. 1489 | 1. 1500 | 1. 1511 | 1. 1520 | 1. 1530 | 1. 1539 || 120 | 1. 1374 | 1. 1386 | 1. 1398 | 1. 1408 | 1. 1418 | 1. 1427 | 1. 1436 || 130 | 1. 1271 | 1. 1284 | 1. 1295 | 1. 1305 | 1. 1315 | 1. 1324 | 1. 1333 || 140 | 1. 1168 | 1. 1181 | 1. 1192 | 1. 1203 | 1. 1212 | 1. 1221 | 1. 1230 || 150 | 1. 1065 | 1. 1078 | 1. 1089 | 1. 1099 | 1. 1109 | 1. 1118 | 1. 1127 || 160 | 1. 0962 | 1. 0975 | 1. 0986 | 1. 0997 | 1. 1006 | 1. 1015 | 1. 1024 || 170 | 1. 0859 | 1. 0872 | 1. 0883 | 1. 0893 | 1. 0903 | 1. 0912 | 1. 0921 || 180 | 1. 0756 | 1. 0768 | 1. 0780 | 1. 0790 | 1. 0800 | 1. 0809 | 1. 0818 || 190 | 1. 0653 | 1. 0665 | 1. 0676 | 1. 0687 | 1. 0696 | 1. 0706 | 1. 0715 || 200 | 1. 0549 | 1. 0562 | 1. 0573 | 1. 0584 | 1. 0593 | 1. 0602 | 1. 0611 || 210 | 1. 0446 | 1. 0458 | 1. 0469 | 1. 0480 | 1. 0489 | 1. 0499 | 1. 0508 ||_______|________|________|________|________|________|________|________| ______________________________________________________________________| | ||Feed | ||Temp- | ||erature| ||Degrees| Steam Pressure by Gauge ||Fahren-| ||heit | ||_______|______________________________________________________________|| | | | | | | | || | 190 | 200 | 210 | 220 | 230 | 240 | 250 ||_______|________|________|________|________|________|________|________|| | | | | | | | || 32 | 1. 2350 | 1. 2357 | 1. 2364 | 1. 2372 | 1. 2378 | 1. 2384 | 1. 2390 || 40 | 1. 2267 | 1. 2274 | 1. 2282 | 1. 2289 | 1. 2295 | 1. 2301 | 1. 2307 || 50 | 1. 2164 | 1. 2171 | 1. 2178 | 1. 2186 | 1. 2192 | 1. 2198 | 1. 2204 || 60 | 1. 2061 | 1. 2068 | 1. 2075 | 1. 2083 | 1. 2089 | 1. 2095 | 1. 2101 || 70 | 1. 1958 | 1. 1965 | 1. 1972 | 1. 1980 | 1. 1986 | 1. 1992 | 1. 1998 || 80 | 1. 1855 | 1. 1863 | 1. 1869 | 1. 1877 | 1. 1883 | 1. 1889 | 1. 1895 || 90 | 1. 1750 | 1. 1760 | 1. 1766 | 1. 1774 | 1. 1780 | 1. 1786 | 1. 1792 || 100 | 1. 1650 | 1. 1657 | 1. 1664 | 1. 1671 | 1. 1678 | 1. 1684 | 1. 1690 || 110 | 1. 1547 | 1. 1554 | 1. 1562 | 1. 1569 | 1. 1575 | 1. 1581 | 1. 1587 || 120 | 1. 1444 | 1. 1452 | 1. 1459 | 1. 1466 | 1. 1472 | 1. 1478 | 1. 1484 || 130 | 1. 1341 | 1. 1349 | 1. 1356 | 1. 1363 | 1. 1369 | 1. 1375 | 1. 1381 || 140 | 1. 1239 | 1. 1246 | 1. 1253 | 1. 1260 | 1. 1266 | 1. 1272 | 1. 1278 || 150 | 1. 1136 | 1. 1143 | 1. 1150 | 1. 1157 | 1. 1163 | 1. 1169 | 1. 1176 || 160 | 1. 1033 | 1. 1040 | 1. 1047 | 1. 1054 | 1. 1060 | 1. 1066 | 1. 1073 || 170 | 1. 0930 | 1. 0937 | 1. 0944 | 1. 0951 | 1. 0957 | 1. 0963 | 1. 0969 || 180 | 1. 0826 | 1. 0834 | 1. 0841 | 1. 0848 | 1. 0854 | 1. 0860 | 1. 0866 || 190 | 1. 0723 | 1. 0730 | 1. 0737 | 1. 0745 | 1. 0751 | 1. 0757 | 1. 0763 || 200 | 1. 0620 | 1. 0627 | 1. 0634 | 1. 0641 | 1. 0647 | 1. 0653 | 1. 0660 || 210 | 1. 0516 | 1. 0523 | 1. 0530 | 1. 0538 | 1. 0544 | 1. 0550 | 1. 0556 ||_______|________|________|________|________|________|________|________| The temperature, pressure and other properties of steam for varyingamounts of vacuum and the pressure above vacuum corresponding to eachinch of reading of the vacuum gauge are given in Table 20. TABLE 20 PROPERTIES OF SATURATED STEAM FOR VARYING AMOUNTS OF VACUUM CALCULATED FROM MARKS AND DAVIS TABLES ______________________________________________________________________| | | | | | | || | | | Heat of | Latent | Total | || | | Temp- | the Liquid| Heat | Heat | || | | erature | Above | Above | Above |Density or|| | Absolute | Degrees | 32 De- | 32 De- | 32 De- |Weight per|| Vacuum | Pressure | Fahren- | grees | grees | grees |Cubic Foot||Ins. Hg. | Pounds | heit | B. T. U. |B. T. U. |B. T. U. | Pounds ||________|__________|_________|___________|________|________|__________|| | | | | | | || 29. 5 | . 207 | 54. 1 | 22. 18 | 1061. 0 | 1083. 2 | 0. 000678 || 29 | . 452 | 76. 6 | 44. 64 | 1048. 7 | 1093. 3 | 0. 001415 || 28. 5 | . 698 | 90. 1 | 58. 09 | 1041. 1 | 1099. 2 | 0. 002137 || 28 | . 944 | 99. 9 | 67. 87 | 1035. 6 | 1103. 5 | 0. 002843 || 27 | 1. 44 | 112. 5 | 80. 4 | 1028. 6 | 1109. 0 | 0. 00421 || 26 | 1. 93 | 124. 5 | 92. 3 | 1022. 0 | 1114. 3 | 0. 00577 || 25 | 2. 42 | 132. 6 | 100. 5 | 1017. 3 | 1117. 8 | 0. 00689 || 24 | 2. 91 | 140. 1 | 108. 0 | 1013. 1 | 1121. 1 | 0. 00821 || 22 | 3. 89 | 151. 7 | 119. 6 | 1006. 4 | 1126. 0 | 0. 01078 || 20 | 4. 87 | 161. 1 | 128. 9 | 1001. 0 | 1129. 9 | 0. 01331 || 18 | 5. 86 | 168. 9 | 136. 8 | 996. 4 | 1133. 2 | 0. 01581 || 16 | 6. 84 | 175. 8 | 143. 6 | 992. 4 | 1136. 0 | 0. 01827 || 14 | 7. 82 | 181. 8 | 149. 7 | 988. 8 | 1138. 5 | 0. 02070 || 12 | 8. 80 | 187. 2 | 155. 1 | 985. 6 | 1140. 7 | 0. 02312 || 10 | 9. 79 | 192. 2 | 160. 1 | 982. 6 | 1142. 7 | 0. 02554 || 5 | 12. 24 | 202. 9 | 170. 8 | 976. 0 | 1146. 8 | 0. 03148 ||________|__________|_________|___________|________|________|__________| From the steam tables, the condensed Table 21 of the properties of steamat different pressures may be constructed. From such a table there maybe drawn the following conclusions. TABLE 21 VARIATION IN PROPERTIES OF SATURATED STEAM WITH PRESSURE ___________________________________________________| | | | | || Pressure |Temperature | Heat of | Latent | Total || Pounds | Degrees | Liquid | Heat | Heat || Absolute | Fahrenheit |B. T. U. |B. T. U. |B. T. U. ||__________|____________|_________|________|________|| | | | | || 14. 7 | 212. 0 | 180. 0 | 970. 4 | 1150. 4 || 20. 0 | 228. 0 | 196. 1 | 960. 0 | 1156. 2 || 100. 0 | 327. 8 | 298. 3 | 888. 0 | 1186. 3 || 300. 0 | 417. 5 | 392. 7 | 811. 3 | 1204. 1 ||__________|____________|_________|________|________| As the pressure and temperature increase, the latent heat decreases. This decrease, however, is less rapid than the corresponding increase inthe heat of the liquid and hence the total heat increases with anincrease in the pressure and temperature. The percentage increase in thetotal heat is small, being 0. 5, 3. 1, and 4. 7 per cent for 20, 100, and300 pounds absolute pressure respectively above the total heat in onepound of steam at 14. 7 pounds absolute. The temperatures, on the otherhand, increase at the rates of 7. 5, 54. 6, and 96. 9 per cent. Theefficiency of a perfect steam engine is proportional to the expression(t - t_{1})/t in which t and t_{1} are the absolute temperatures of thesaturated steam at admission and exhaust respectively. While actualengines only approximate the ideal engine in efficiency, yet they followthe same general law. Since the exhaust temperature cannot be loweredbeyond present practice, it follows that the only available method ofincreasing the efficiency is by an increase in the temperature of thesteam at admission. How this may be accomplished by an increase ofpressure is clearly shown, for the increase of fuel necessary toincrease the pressure is negligible, as shown by the total heat, whilethe increase in economy, due to the higher pressure, will resultdirectly from the rapid increase of the corresponding temperature. TABLE 22 HEAT UNITS PER POUND AND WEIGHT PER CUBIC FOOT OF WATER BETWEEN 32 DEGREES FAHRENHEIT AND 340 DEGREES FAHRENHEIT _________________________________| | | ||Temperature|Heat Units| Weight || Degrees | per | per || Fahrenheit| Pound |Cubic Foot||___________|__________|__________|| | | || 32 | 0. 00 | 62. 42 || 33 | 1. 01 | 62. 42 || 34 | 2. 01 | 62. 42 || 35 | 3. 02 | 62. 43 || 36 | 4. 03 | 62. 43 || 37 | 5. 04 | 62. 43 || 38 | 6. 04 | 62. 43 || 39 | 7. 05 | 62. 43 || 40 | 8. 05 | 62. 43 || 41 | 9. 05 | 62. 43 || 42 | 10. 06 | 62. 43 || 43 | 11. 06 | 62. 43 || 44 | 12. 06 | 62. 43 || 45 | 13. 07 | 62. 42 || 46 | 14. 07 | 62. 42 || 47 | 15. 07 | 62. 42 || 48 | 16. 07 | 62. 42 || 49 | 17. 08 | 62. 42 || 50 | 18. 08 | 62. 42 || 51 | 19. 08 | 62. 41 || 52 | 20. 08 | 62. 41 || 53 | 21. 08 | 62. 41 || 54 | 22. 08 | 62. 40 || 55 | 23. 08 | 62. 40 || 56 | 24. 08 | 62. 39 || 57 | 25. 08 | 62. 39 || 58 | 26. 08 | 62. 38 || 59 | 27. 08 | 62. 37 || 60 | 28. 08 | 62. 37 || 61 | 29. 08 | 62. 36 || 62 | 30. 08 | 62. 36 || 63 | 31. 07 | 62. 35 || 64 | 32. 07 | 62. 35 || 65 | 33. 07 | 62. 34 || 66 | 34. 07 | 62. 33 || 67 | 35. 07 | 62. 33 || 68 | 36. 07 | 62. 32 || 69 | 37. 06 | 62. 31 || 70 | 38. 06 | 62. 30 || 71 | 39. 06 | 62. 30 || 72 | 40. 05 | 62. 29 || 73 | 41. 05 | 62. 28 || 74 | 42. 05 | 62. 27 || 75 | 42. 05 | 62. 26 || 76 | 44. 04 | 62. 26 || 77 | 45. 04 | 62. 25 || 78 | 46. 04 | 62. 24 || 79 | 47. 04 | 62. 23 || 80 | 48. 03 | 62. 22 || 81 | 49. 03 | 62. 21 || 82 | 50. 03 | 62. 20 || 83 | 51. 02 | 62. 19 || 84 | 52. 02 | 62. 18 || 85 | 53. 02 | 62. 17 || 86 | 54. 01 | 62. 16 || 87 | 55. 01 | 62. 15 || 88 | 56. 01 | 62. 14 || 89 | 57. 00 | 62. 13 || 90 | 58. 00 | 62. 12 || 91 | 59. 00 | 62. 11 || 92 | 60. 00 | 62. 09 || 93 | 60. 99 | 62. 08 || 94 | 61. 99 | 62. 07 || 95 | 62. 99 | 62. 06 || 96 | 63. 98 | 62. 05 || 97 | 64. 98 | 62. 04 || 98 | 65. 98 | 62. 03 || 99 | 66. 97 | 62. 02 || 100 | 67. 97 | 62. 00 || 101 | 68. 97 | 61. 99 || 102 | 69. 96 | 61. 98 || 103 | 70. 96 | 61. 97 || 104 | 71. 96 | 61. 95 || 105 | 72. 95 | 61. 94 || 106 | 73. 95 | 61. 93 || 107 | 74. 95 | 61. 91 || 108 | 75. 95 | 61. 90 || 109 | 76. 94 | 61. 88 || 110 | 77. 94 | 61. 86 || 111 | 78. 94 | 61. 85 || 112 | 79. 93 | 61. 83 || 113 | 80. 93 | 61. 82 || 114 | 81. 93 | 61. 80 || 115 | 82. 92 | 61. 79 || 116 | 83. 92 | 61. 77 || 117 | 84. 92 | 61. 75 || 118 | 85. 92 | 61. 74 || 119 | 86. 91 | 61. 72 || 120 | 87. 91 | 61. 71 || 121 | 88. 91 | 61. 69 || 122 | 89. 91 | 61. 68 || 123 | 90. 90 | 61. 66 || 124 | 91. 90 | 61. 65 || 125 | 92. 90 | 61. 63 || 126 | 93. 90 | 61. 61 || 127 | 94. 89 | 61. 59 || 128 | 95. 89 | 61. 58 || 129 | 96. 89 | 61. 56 || 130 | 97. 89 | 61. 55 || 131 | 98. 89 | 61. 53 || 132 | 99. 88 | 61. 52 || 133 | 100. 88 | 61. 50 || 134 | 101. 88 | 61. 49 || 135 | 102. 88 | 61. 47 || 136 | 103. 88 | 61. 45 || 137 | 104. 87 | 61. 43 || 138 | 105. 87 | 61. 41 || 139 | 106. 87 | 61. 40 || 140 | 107. 87 | 61. 38 || 141 | 108. 87 | 61. 36 || 142 | 109. 87 | 61. 34 || 143 | 110. 87 | 61. 33 || 144 | 111. 87 | 61. 31 || 145 | 112. 86 | 61. 29 || 146 | 113. 86 | 61. 27 || 147 | 114. 86 | 61. 25 || 148 | 115. 86 | 61. 24 || 149 | 116. 86 | 61. 22 || 150 | 117. 86 | 61. 20 || 151 | 118. 86 | 61. 18 || 152 | 119. 86 | 61. 16 || 153 | 120. 86 | 61. 14 || 154 | 121. 86 | 61. 12 || 155 | 122. 86 | 61. 10 || 156 | 123. 86 | 61. 08 || 157 | 124. 86 | 61. 06 || 158 | 125. 86 | 61. 04 || 159 | 126. 86 | 61. 02 || 160 | 127. 86 | 61. 00 || 161 | 128. 86 | 60. 98 || 162 | 129. 86 | 60. 96 || 163 | 130. 86 | 60. 94 || 164 | 131. 86 | 60. 92 || 165 | 132. 86 | 60. 90 || 166 | 133. 86 | 60. 88 || 167 | 134. 86 | 60. 86 || 168 | 135. 86 | 60. 84 || 169 | 136. 86 | 60. 82 || 170 | 137. 87 | 60. 80 || 171 | 138. 87 | 60. 78 || 172 | 139. 87 | 60. 76 || 173 | 140. 87 | 60. 73 || 174 | 141. 87 | 60. 71 || 175 | 142. 87 | 60. 69 || 176 | 143. 87 | 60. 67 || 177 | 144. 88 | 60. 65 || 178 | 145. 88 | 60. 62 || 179 | 146. 88 | 60. 60 || 180 | 147. 88 | 60. 58 || 181 | 148. 88 | 60. 56 || 182 | 149. 89 | 60. 53 || 183 | 150. 89 | 60. 51 || 184 | 151. 89 | 60. 49 || 185 | 152. 89 | 60. 47 || 186 | 153. 89 | 60. 45 || 187 | 154. 90 | 60. 42 || 188 | 155. 90 | 60. 40 || 189 | 156. 90 | 60. 38 || 190 | 157, 91 | 60. 36 || 191 | 158. 91 | 60. 33 || 192 | 159. 91 | 60. 31 || 193 | 160. 91 | 60. 29 || 194 | 161. 92 | 60. 27 || 195 | 162. 92 | 60. 24 || 196 | 163. 92 | 60. 22 || 197 | 164. 93 | 60. 19 || 198 | 165. 93 | 60. 17 || 199 | 166. 94 | 60. 15 || 200 | 167. 94 | 60. 12 || 201 | 168. 94 | 60. 10 || 202 | 169. 95 | 60. 07 || 203 | 170. 95 | 60. 05 || 204 | 171. 96 | 60. 02 || 205 | 172. 96 | 60. 00 || 206 | 173. 97 | 59. 98 || 207 | 174. 97 | 59. 95 || 208 | 175. 98 | 59. 93 || 209 | 176. 98 | 59. 90 || 210 | 177. 99 | 59. 88 || 211 | 178. 99 | 59. 85 || 212 | 180. 00 | 59. 83 || 213 | 181. 0 | 59. 80 || 214 | 182. 0 | 59. 78 || 215 | 183. 0 | 59. 75 || 216 | 184. 0 | 59. 73 || 217 | 185. 0 | 59. 70 || 218 | 186. 1 | 59. 68 || 219 | 187. 1 | 59. 65 || 220 | 188. 1 | 59. 63 || 221 | 189. 1 | 59. 60 || 222 | 190. 1 | 59. 58 || 223 | 191. 1 | 59. 55 || 224 | 192. 1 | 59. 53 || 225 | 193. 1 | 59. 50 || 226 | 194. 1 | 59. 48 || 227 | 195. 2 | 59. 45 || 228 | 196. 2 | 59. 42 || 229 | 197. 2 | 59. 40 || 230 | 198. 2 | 59. 37 || 231 | 199. 2 | 59. 34 || 232 | 200. 2 | 59. 32 || 233 | 201. 2 | 59. 29 || 234 | 202. 2 | 59. 27 || 235 | 203. 2 | 59. 24 || 236 | 204. 2 | 59. 21 || 237 | 205. 3 | 59. 19 || 238 | 206. 3 | 59. 16 || 239 | 207. 3 | 59. 14 || 240 | 208. 3 | 59. 11 || 241 | 209. 3 | 59. 08 || 242 | 210. 3 | 59. 05 || 243 | 211. 4 | 59. 03 || 244 | 212. 4 | 59. 00 || 245 | 213. 4 | 58. 97 || 246 | 214. 4 | 58. 94 || 247 | 215. 4 | 58. 91 || 248 | 216. 4 | 58. 89 || 249 | 217. 4 | 58. 86 || 250 | 218. 5 | 58. 83 || 260 | 228. 6 | 58. 55 || 270 | 238. 8 | 58. 26 || 280 | 249. 0 | 57. 96 || 290 | 259. 3 | 57. 65 || 300 | 269. 6 | 57. 33 || 310 | 279. 9 | 57. 00 || 320 | 290. 2 | 56. 66 || 330 | 300. 6 | 56. 30 || 340 | 311. 0 | 55. 94 ||___________|__________|__________| The gain due to superheat cannot be predicted from the formula for theefficiency of a perfect steam engine given on page 119. This formula isnot applicable in cases where superheat is present since only arelatively small amount of the heat in the steam is imparted at themaximum or superheated temperature. The advantage of the use of high pressure steam may be also indicated byconsidering the question from the aspect of volume. With an increase ofpressure comes a decrease in volume, thus one pound of saturated steamat 100 pounds absolute pressure occupies 4. 43 cubic feet, while at 200pounds pressure it occupies 2. 29 cubic feet. If then, in separatecylinders of the same dimensions, one pound of steam at 100 poundsabsolute pressure and one pound at 200 pounds absolute pressure enterand are allowed to expand to the full volume of each cylinder, thehigh-pressure steam, having more room and a greater range for expansionthan the low-pressure steam, will thus do more work. This increase inthe amount of work, as was the increase in temperature, is largerelative to the additional fuel required as indicated by the total heat. In general, it may be stated that the fuel required to impart a givenamount of heat to a boiler is practically independent of the steampressure, since the temperature of the fire is so high as compared withthe steam temperature that a variation in the steam temperature does notproduce an appreciable effect. The formulae for the algebraic expression of the relation betweensaturated steam pressures, temperatures and steam volumes have been upto the present time empirical. These relations have, however, beendetermined by experiment and, from the experimental data, tables havebeen computed which render unnecessary the use of empirical formulae. Such formulae may be found in any standard work of thermo-dynamics. Thefollowing tables cover all practical cases. Table 22 gives the heat units contained in water above 32 degreesFahrenheit at different temperatures. Table 23 gives the properties of saturated steam for various pressures. Table 24 gives the properties of superheated steam at various pressuresand temperatures. These tables are based on those computed by Lionel S. Marks and HarveyN. Davis, these being generally accepted as being the most correct. TABLE 23 PROPERTIES OF SATURATED STEAM REPRODUCED BY PERMISSION FROM MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" (Copyright, 1909, by Longmans, Green & Co. ) ____________________________________________________________________|Pressure, | Temper- |Specific Vol-|Heat of |Latent Heat|Total Heat|| Pounds |ature De-| ume Cu. Ft. |the Liquid, | of Evap. , |of Steam, ||Absolute |grees F. | per Pound | B. T. U. | B. T. U. | B. T. U. ||_________|_________|_____________|___________|___________|__________|| 1 | 101. 83 | 333. 0 | 69. 8 | 1034. 6 | 1104. 4 || 2 | 126. 15 | 173. 5 | 94. 0 | 1021. 0 | 1115. 0 || 3 | 141. 52 | 118. 5 | 109. 4 | 1012. 3 | 1121. 6 || 4 | 153. 01 | 90. 5 | 120. 9 | 1005. 7 | 1126. 5 || 5 | 162. 28 | 73. 33 | 130. 1 | 1000. 3 | 1130. 5 || 6 | 170. 06 | 61. 89 | 137. 9 | 995. 8 | 1133. 7 || 7 | 176. 85 | 53. 56 | 144. 7 | 991. 8 | 1136. 5 || 8 | 182. 86 | 47. 27 | 150. 8 | 988. 2 | 1139. 0 || 9 | 188. 27 | 42. 36 | 156. 2 | 985. 0 | 1141. 1 || 10 | 193. 22 | 38. 38 | 161. 1 | 982. 0 | 1143. 1 || 11 | 197. 75 | 35. 10 | 165. 7 | 979. 2 | 1144. 9 || 12 | 201. 96 | 32. 36 | 169. 9 | 976. 6 | 1146. 5 || 13 | 205. 87 | 30. 03 | 173. 8 | 974. 2 | 1148. 0 || 14 | 209. 55 | 28. 02 | 177. 5 | 971. 9 | 1149. 4 || 15 | 213. 0 | 26. 27 | 181. 0 | 969. 7 | 1150. 7 || 16 | 216. 3 | 24. 79 | 184. 4 | 967. 6 | 1152. 0 || 17 | 219. 4 | 23. 38 | 187. 5 | 965. 6 | 1153. 1 || 18 | 222. 4 | 22. 16 | 190. 5 | 963. 7 | 1154. 2 || 19 | 225. 2 | 21. 07 | 193. 4 | 961. 8 | 1155. 2 || 20 | 228. 0 | 20. 08 | 196. 1 | 960. 0 | 1156. 2 || 22 | 233. 1 | 18. 37 | 201. 3 | 956. 7 | 1158. 0 || 24 | 237. 8 | 16. 93 | 206. 1 | 953. 5 | 1159. 6 || 26 | 242. 2 | 15. 72 | 210. 6 | 950. 6 | 1161. 2 || 28 | 246. 4 | 14. 67 | 214. 8 | 947. 8 | 1162. 6 || 30 | 250. 3 | 13. 74 | 218. 8 | 945. 1 | 1163. 9 || 32 | 254. 1 | 12. 93 | 222. 6 | 942. 5 | 1165. 1 || 34 | 257. 6 | 12. 22 | 226. 2 | 940. 1 | 1166. 3 || 36 | 261. 0 | 11. 58 | 229. 6 | 937. 7 | 1167. 3 || 38 | 264. 2 | 11. 01 | 232. 9 | 935. 5 | 1168. 4 || 40 | 267. 3 | 10. 49 | 236. 1 | 933. 3 | 1169. 4 || 42 | 270. 2 | 10. 02 | 239. 1 | 931. 2 | 1170. 3 || 44 | 273. 1 | 9. 59 | 242. 0 | 929. 2 | 1171. 2 || 46 | 275. 8 | 9. 20 | 244. 8 | 927. 2 | 1172. 0 || 48 | 278. 5 | 8. 84 | 247. 5 | 925. 3 | 1172. 8 || 50 | 281. 0 | 8. 51 | 250. 1 | 923. 5 | 1173. 6 || 52 | 283. 5 | 8. 20 | 252. 6 | 921. 7 | 1174. 3 || 54 | 285. 9 | 7. 91 | 255. 1 | 919. 9 | 1175. 0 || 56 | 288. 2 | 7. 65 | 257. 5 | 918. 2 | 1175. 7 || 58 | 290. 5 | 7. 40 | 259. 8 | 916. 5 | 1176. 4 || 60 | 292. 7 | 7. 17 | 262. 1 | 914. 9 | 1177. 0 || 62 | 294. 9 | 6. 95 | 264. 3 | 913. 3 | 1177. 6 || 64 | 297. 0 | 6. 75 | 266. 4 | 911. 8 | 1178. 2 || 66 | 299. 0 | 6. 56 | 268. 5 | 910. 2 | 1178. 8 || 68 | 301. 0 | 6. 38 | 270. 6 | 908. 7 | 1179. 3 || 70 | 302. 9 | 6. 20 | 272. 6 | 907. 2 | 1179. 8 || 72 | 304. 8 | 6. 04 | 274. 5 | 905. 8 | 1180. 4 || 74 | 306. 7 | 5. 89 | 276. 5 | 904. 4 | 1180. 9 || 76 | 308. 5 | 5. 74 | 278. 3 | 903. 0 | 1181. 4 || 78 | 310. 3 | 5. 60 | 280. 2 | 901. 7 | 1181. 8 || 80 | 312. 0 | 5. 47 | 282. 0 | 900. 3 | 1182. 3 || 82 | 313. 8 | 5. 34 | 283. 8 | 899. 0 | 1182. 8 || 84 | 315. 4 | 5. 22 | 285. 5 | 897. 7 | 1183. 2 || 86 | 317. 1 | 5. 10 | 287. 2 | 896. 4 | 1183. 6 || 88 | 318. 7 | 5. 00 | 288. 9 | 895. 2 | 1184. 0 || 90 | 320. 3 | 4. 89 | 290. 5 | 893. 9 | 1184. 4 || 92 | 321. 8 | 4. 79 | 292. 1 | 892. 7 | 1184. 8 || 94 | 323. 4 | 4. 69 | 293. 7 | 891. 5 | 1185. 2 || 96 | 324. 9 | 4. 60 | 295. 3 | 890. 3 | 1185. 6 || 98 | 326. 4 | 4. 51 | 296. 8 | 889. 2 | 1186. 0 || 100 | 327. 8 | 4. 429 | 298. 3 | 888. 0 | 1186. 3 || 105 | 331. 4 | 4. 230 | 302. 0 | 885. 2 | 1187. 2 || 110 | 334. 8 | 4. 047 | 305. 5 | 882. 5 | 1188. 0 || 115 | 338. 1 | 3. 880 | 309. 0 | 879. 8 | 1188. 8 || 120 | 341. 3 | 3. 726 | 312. 3 | 877. 2 | 1189. 6 || 125 | 344. 4 | 3. 583 | 315. 5 | 874. 7 | 1190. 3 || 130 | 347. 4 | 3. 452 | 318. 6 | 872. 3 | 1191. 0 || 135 | 350. 3 | 3. 331 | 321. 7 | 869. 9 | 1191. 6 || 140 | 353. 1 | 3. 219 | 324. 6 | 867. 6 | 1192. 2 || 145 | 355. 8 | 3. 112 | 327. 4 | 865. 4 | 1192. 8 || 150 | 358. 5 | 3. 012 | 330. 2 | 863. 2 | 1193. 4 || 155 | 361. 0 | 2. 920 | 332. 9 | 861. 0 | 1194. 0 || 160 | 363. 6 | 2. 834 | 335. 6 | 858. 8 | 1194. 5 || 165 | 366. 0 | 2. 753 | 338. 2 | 856. 8 | 1195. 0 || 170 | 368. 5 | 2. 675 | 340. 7 | 854. 7 | 1195. 4 || 175 | 370. 8 | 2. 602 | 343. 2 | 852. 7 | 1195. 9 || 180 | 373. 1 | 2. 533 | 345. 6 | 850. 8 | 1196. 4 || 185 | 375. 4 | 2. 468 | 348. 0 | 848. 8 | 1196. 8 || 190 | 377. 6 | 2. 406 | 350. 4 | 846. 9 | 1197. 3 || 195 | 379. 8 | 2. 346 | 352. 7 | 845. 0 | 1197. 7 || 200 | 381. 9 | 2. 290 | 354. 9 | 843. 2 | 1198. 1 || 205 | 384. 0 | 2. 237 | 357. 1 | 841. 4 | 1198. 5 || 210 | 386. 0 | 2. 187 | 359. 2 | 839. 6 | 1198. 8 || 215 | 388. 0 | 2. 138 | 361. 4 | 837. 9 | 1199. 2 || 220 | 389. 9 | 2. 091 | 363. 4 | 836. 2 | 1199. 6 || 225 | 391. 9 | 2. 046 | 365. 5 | 834. 4 | 1199. 9 || 230 | 393. 8 | 2. 004 | 367. 5 | 832. 8 | 1200. 2 || 235 | 395. 6 | 1. 964 | 369. 4 | 831. 1 | 1200. 6 || 240 | 397. 4 | 1. 924 | 371. 4 | 829. 5 | 1200. 9 || 245 | 399. 3 | 1. 887 | 373. 3 | 827. 9 | 1201. 2 || 250 | 401. 1 | 1. 850 | 375. 2 | 826. 3 | 1201. 5 ||_________|_________|_____________|___________|___________|__________| [Illustration: Portion of 6100 Horse-power Installation of Babcock &Wilcox Boilers Equipped with Babcock & Wilcox Chain Grate Stokers at theCampbell Street Plant of the Louisville Railway Co. , Louisville, Ky. This Company Operates a Total of 14, 000 Horse Power of Babcock & WilcoxBoilers] TABLE 24 PROPERTIES OF SUPERHEATED STEAM REPRODUCED BY PERMISSION FROM MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" (Copyright, 1909, by Longmans, Green & Co. ) __________________________________________________________________| | | || | | Degrees of Superheat ||Pressure| |_______________________________________________|| Pounds |Saturated| | | | | | ||Absolute| Steam | 50 | 100 | 150 | 200 | 250 | 300 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 162. 3 | 212. 3 | 262. 3 | 312. 3 | 362. 3 | 412. 3 | 462. 3 || 5 v| 73. 3 | 79. 7 | 85. 7 | 91. 8 | 97. 8 | 103. 8 | 109. 8 || h| 1130. 5 |1153. 5 |1176. 4 |1199. 5 |1222. 5 |1245. 6 |1268. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 193. 2 | 243. 2 | 293. 2 | 343. 2 | 393. 2 | 443. 2 | 493. 2 || 10 v| 38. 4 | 41. 5 | 44. 6 | 47. 7 | 50. 7 | 53. 7 | 56. 7 || h| 1143. 1 |1166. 3 |1189. 5 |1212. 7 |1236. 0 |1259. 3 |1282. 5 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 213. 0 | 263. 0 | 313. 0 | 363. 0 | 413. 0 | 463. 0 | 513. 0 || 15 v| 26. 27 | 28. 40| 30. 46| 32. 50| 34. 53| 36. 56| 38. 58|| h| 1150. 7 |1174. 2 |1197. 6 |1221. 0 |1244. 4 |1267. 7 |1291. 1 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 228. 0 | 278. 0 | 328. 0 | 378. 0 | 428. 0 | 478. 0 | 528. 0 || 20 v| 20. 08 | 21. 69| 23. 25| 24. 80| 26. 33| 27. 85| 29. 37|| h| 1156. 2 |1179. 9 |1203. 5 |1227. 1 |1250. 6 |1274. 1 |1297. 6 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 240. 1 | 290. 1 | 340. 1 | 390. 1 | 440. 1 | 490. 1 | 540. 1 || 25 v| 16. 30 | 17. 60| 18. 86| 20. 10| 21. 32| 22. 55| 23. 77|| h| 1160. 4 |1184. 4 |1208. 2 |1231. 9 |1255. 6 |1279. 2 |1302. 8 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 250. 4 | 300. 4 | 350. 4 | 400. 4 | 450. 4 | 500. 4 | 550. 4 || 30 v| 13. 74 | 14. 83| 15. 89| 16. 93| 17. 97| 18. 99| 20. 00|| h| 1163. 9 |1188. 1 |1212. 1 |1236. 0 |1259. 7 |1283. 4 |1307. 1 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 259. 3 | 309. 3 | 359. 3 | 409. 3 | 459. 3 | 509. 3 | 559. 3 || 35 v| 11. 89 | 12. 85| 13. 75| 14. 65| 15. 54| 16. 42| 17. 30|| h| 1166. 8 |1191. 3 |1215. 4 |1239. 4 |1263. 3 |1287. 1 |1310. 8 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 267. 3 | 317. 3 | 367. 3 | 417. 3 | 467. 3 | 517. 3 | 567. 3 || 40 v| 10. 49 | 11. 33| 12. 13| 12. 93| 13. 70| 14. 48| 15. 25|| h| 1169. 4 |1194. 0 |1218. 4 |1242. 4 |1266. 4 |1290. 3 |1314. 1 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 274. 5 | 324. 5 | 374. 5 | 424. 5 | 474. 5 | 524. 5 | 574. 5 || 45 v| 9. 39 | 10. 14| 10. 86| 11. 57| 12. 27| 12. 96| 13. 65|| h| 1171. 6 |1196. 6 |1221. 0 |1245. 2 |1269. 3 |1293. 2 |1317. 0 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 281. 0 | 331. 0 | 381. 0 | 431. 0 | 481. 0 | 531. 0 | 581. 0 || 50 v| 8. 51 | 9. 19| 9. 84| 10. 48| 11. 11| 11. 74| 12. 36|| h| 1173. 6 |1198. 8 |1223. 4 |1247. 7 |1271. 8 |1295. 8 |1319. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 287. 1 | 337. 1 | 387. 1 | 437. 1 | 487. 1 | 537. 1 | 587. 1 || 55 v| 7. 78 | 8. 40| 9. 00| 9. 59| 10. 16| 10. 73| 11. 30|| h| 1175. 4 |1200. 8 |1225. 6 |1250. 0 |1274. 2 |1298. 1 |1322. 0 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 292. 7 | 342. 7 | 392. 7 | 442. 7 | 492. 7 | 542. 7 | 592. 7 || 60 v| 7. 17 | 7. 75| 8. 30| 8. 84| 9. 36| 9. 89| 10. 41|| h| 1177. 0 |1202. 6 |1227. 6 |1252. 1 |1276. 4 |1300. 4 |1324. 3 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 298. 0 | 348. 0 | 398. 0 | 448. 0 | 498. 0 | 548. 0 | 598. 0 || 65 v| 6. 65 | 7. 20| 7. 70| 8. 20| 8. 69| 9. 17| 9. 65|| h| 1178. 5 |1204. 4 |1229. 5 |1254. 0 |1278. 4 |1302. 4 |1326. 4 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 302. 9 | 352. 9 | 402. 9 | 452. 9 | 502. 9 | 552. 9 | 602. 9 || 70 v| 6. 20 | 6. 71| 7. 18| 7. 65| 8. 11| 8. 56| 9. 01|| h| 1179. 8 |1205. 9 |1231. 2 |1255. 8 |1280. 2 |1304. 3 |1328. 3 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 307. 6 | 357. 6 | 407. 6 | 457. 6 | 507. 6 | 557. 6 | 607. 6 || 75 v| 5. 81 | 6. 28| 6. 73| 7. 17| 7. 60| 8. 02| 8. 44|| h| 1181. 1 |1207. 5 |1232. 8 |1257. 5 |1282. 0 |1306. 1 |1330. 1 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 312. 0 | 362. 0 | 412. 0 | 462. 0 | 512. 0 | 562. 0 | 612. 0 || 80 v| 5. 47 | 5. 92| 6. 34| 6. 75| 7. 17| 7. 56| 7. 95|| h| 1182. 3 |1208. 8 |1234. 3 |1259. 0 |1283. 6 |1307. 8 |1331. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 316. 3 | 366. 3 | 416. 3 | 466. 3 | 516. 3 | 566. 3 | 616. 3 || 85 v| 5. 16 | 5. 59| 6. 99| 6. 38| 6. 76| 7. 14| 7. 51|| h| 1183. 4 |1210. 2 |1235. 8 |1260. 6 |1285. 2 |1309. 4 |1333. 5 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 320. 3 | 370. 3 | 420. 3 | 470. 3 | 520. 3 | 570. 3 | 620. 3 || 90 v| 4. 89 | 5. 29| 5. 67| 6. 04| 6. 40| 6. 76| 7. 11|| h| 1184. 4 |1211. 4 |1237. 2 |1262. 0 |1286. 6 |1310. 8 |1334. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 324. 1 | 374. 1 | 424. 1 | 474. 1 | 524. 1 | 574. 1 | 624. 1 || 95 v| 4. 65 | 5. 03| 5. 39| 5. 74| 6. 09| 6. 43| 6. 76|| h| 1185. 4 |1212. 6 |1238. 4 |1263. 4 |1288. 1 |1312. 3 |1336. 4 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 327. 8 | 377. 8 | 427. 8 | 477. 8 | 527. 8 | 577. 8 | 627. 8 || 100 v| 4. 43 | 4. 79| 5. 14| 5. 47| 5. 80| 6. 12| 6. 44|| h| 1186. 3 |1213. 8 |1239. 7 |1264. 7 |1289. 4 |1313. 6 |1337. 8 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 331. 4 | 381. 4 | 431. 4 | 481. 4 | 531. 4 | 581. 4 | 631. 4 || 105 v| 4. 23 | 4. 58| 4. 91| 5. 23| 5. 54| 5. 85| 6. 15|| h| 1187. 2 |1214. 9 |1240. 8 |1265. 9 |1290. 6 |1314. 9 |1339. 1 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 334. 8 | 384. 8 | 434. 8 | 484. 8 | 534. 8 | 584. 8 | 634. 8 || 110 v| 4. 05 | 4. 38| 4. 70| 5. 01| 5. 31| 5. 61| 5. 90|| h| 1188. 0 |1215. 9 |1242. 0 |1267. 1 |1291. 9 |1316. 2 |1340. 4 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 338. 1 | 388. 1 | 438. 1 | 488. 1 | 538. 1 | 588. 1 | 638. 1 || 115 v| 3. 88 | 4. 20| 4. 51| 4. 81| 5. 09| 5. 38| 5. 66|| h| 1188. 8 |1216. 9 |1243. 1 |1268. 2 |1293. 0 |1317. 3 |1341. 5 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 341. 3 | 391. 3 | 441. 3 | 491. 3 | 541. 3 | 591. 3 | 641. 3 || 120 v| 3. 73 | 4. 04| 4. 33| 4. 62| 4. 89| 5. 17| 5. 44|| h| 1189. 6 |1217. 9 |1244. 1 |1269. 3 |1294. 1 |1318. 4 |1342. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 344. 4 | 394. 4 | 444. 4 | 494. 4 | 544. 4 | 594. 4 | 644. 4 || 125 v| 3. 58 | 3. 88| 4. 17| 4. 45| 4. 71| 4. 97| 5. 23|| h| 1190. 3 |1218. 8 |1245. 1 |1270. 4 |1295. 2 |1319. 5 |1343. 8 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 347. 4 | 397. 4 | 447. 4 | 497. 4 | 547. 4 | 597. 4 | 647. 4 || 130 v| 3. 45 | 3. 74| 4. 02| 4. 28| 4. 54| 4. 80| 5. 05|| h| 1191. 0 |1219. 7 |1246. 1 |1271. 4 |1296. 2 |1320. 6 |1344. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 350. 3 | 400. 3 | 450. 3 | 500. 3 | 550. 3 | 600. 3 | 650. 3 || 135 v| 3. 33 | 3. 61| 3. 88| 4. 14| 4. 38| 4. 63| 4. 87|| h| 1191. 6 |1220. 6 |1247. 0 |1272. 3 |1297. 2 |1321. 6 |1345. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 353. 1 | 403. 1 | 453. 1 | 503. 1 | 553. 1 | 603. 1 | 653. 1 || 140 v| 3. 22 | 3. 49| 3. 75| 4. 00| 4. 24| 4. 48| 4. 71|| h| 1192. 2 |1221. 4 |1248. 0 |1273. 3 |1298. 2 |1322. 6 |1346. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 355. 8 | 405. 8 | 455. 8 | 505. 8 | 555. 8 | 605. 8 | 655. 8 || 145 v| 3. 12 | 3. 38| 3. 63| 3. 87| 4. 10| 4. 33| 4. 56|| h| 1192. 8 |1222. 2 |1248. 8 |1274. 2 |1299. 1 |1323. 6 |1347. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 358. 5 | 408. 5 | 458. 5 | 508. 5 | 558. 5 | 608. 5 | 658. 5 || 150 v| 3. 01 | 3. 27| 3. 50| 3. 75| 3. 97| 4. 19| 4. 41|| h| 1193. 4 |1223. 0 |1249. 6 |1275. 1 |1300. 0 |1324. 5 |1348. 8 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 361. 0 | 411. 0 | 461. 0 | 511. 0 | 561. 0 | 611. 0 | 661. 0 || 155 v| 2. 92 | 3. 17| 3. 41| 3. 63| 3. 85| 4. 06| 4. 28|| h| 1194. 0 |1223. 6 |1250. 5 |1276. 0 |1300. 8 |1325. 3 |1349. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 363. 6 | 413. 6 | 463. 6 | 513. 6 | 563. 6 | 613. 6 | 663. 6 || 160 v| 2. 83 | 3. 07| 3. 30| 3. 53| 3. 74| 3. 95| 4. 15|| h| 1194. 5 |1224. 5 |1251. 3 |1276. 8 |1301. 7 |1326. 2 |1350. 6 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 366. 0 | 416. 0 | 466. 0 | 516. 0 | 566. 0 | 616. 0 | 666. 0 || 165 v| 2. 75 | 2. 99| 3. 21| 3. 43| 3. 64| 3. 84| 4. 04|| h| 1195. 0 |1225. 2 |1252. 0 |1277. 6 |1302. 5 |1327. 1 |1351. 5 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 368. 5 | 418. 5 | 468. 5 | 518. 5 | 568. 5 | 618. 5 | 668. 5 || 170 v| 2. 68 | 2. 91| 3. 12| 3. 34| 3. 54| 3. 73| 3. 92|| h| 1195. 4 |1225. 9 |1252. 8 |1278. 4 |1303. 3 |1327. 9 |1352. 3 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 370. 8 | 420. 8 | 470. 8 | 520. 8 | 570. 8 | 620. 8 | 670. 8 || 175 v| 2. 60 | 2. 83| 3. 04| 3. 24| 3. 44| 3. 63| 3. 82|| h| 1195. 9 |1226. 6 |1253. 6 |1279. 1 |1304. 1 |1328. 7 |1353. 2 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 373. 1 | 423. 1 | 473. 1 | 523. 1 | 573. 1 | 623. 1 | 673. 1 || 180 v| 2. 53 | 2. 75| 2. 96| 3. 16| 3. 35| 3. 54| 3. 72|| h| 1196. 4 |1227. 2 |1254. 3 |1279. 9 |1304. 8 |1329. 5 |1353. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 375. 4 | 425. 4 | 475. 4 | 525. 4 | 575. 4 | 625. 4 | 675. 4 || 185 v| 2. 47 | 2. 68| 2. 89| 3. 08| 3. 27| 3. 45| 3. 63|| h| 1196. 8 |1227. 9 |1255. 0 |1280. 6 |1305. 6 |1330. 2 |1354. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 377. 6 | 427. 6 | 477. 6 | 527. 6 | 577. 6 | 627. 6 | 677. 6 || 190 v| 2. 41 | 2. 62| 2. 81| 3. 00| 3. 19| 3. 37| 3. 55|| h| 1197. 3 |1228. 6 |1255. 7 |1281. 3 |1306. 3 |1330. 9 |1355. 5 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 379. 8 | 429. 8 | 479. 8 | 529. 8 | 579. 8 | 629. 8 | 679. 8 || 195 v| 2. 35 | 2. 55| 2. 75| 2. 93| 3. 11| 3. 29| 3. 46|| h| 1197. 7 |1229. 2 |1256. 4 |1282. 0 |1307. 0 |1331. 6 |1356. 2 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 381. 9 | 431. 9 | 481. 9 | 531. 9 | 581. 9 | 631. 9 | 681. 9 || 200 v| 2. 29 | 2. 49| 2. 68| 2. 86| 3. 04| 3. 21| 3. 38|| h| 1198. 1 |1229. 8 |1257. 1 |1282. 6 |1307. 7 |1332. 4 |1357. 0 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 384. 0 | 434. 0 | 484. 0 | 534. 0 | 584. 0 | 634. 0 | 684. 0 || 205 v| 2. 24 | 2. 44| 2. 62| 2. 80| 2. 97| 3. 14| 3. 30|| h| 1198. 5 |1230. 4 |1257. 7 |1283. 3 |1308. 3 |1333. 0 |1357. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 386. 0 | 436. 0 | 486. 0 | 536. 0 | 586. 0 | 636. 0 | 686. 0 || 210 v| 2. 19 | 2. 38| 2. 56| 2. 74| 2. 91| 3. 07| 3. 23|| h| 1198. 8 |1231. 0 |1258. 4 |1284. 0 |1309. 0 |1333. 7 |1358. 4 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 388. 0 | 438. 0 | 488. 0 | 538. 0 | 588. 0 | 638. 0 | 688. 0 || 215 v| 2. 14 | 2. 33| 2. 51| 2. 68| 2. 84| 3. 00| 3. 16|| h| 1199. 2 |1231. 6 |1259. 0 |1284. 6 |1309. 7 |1334. 4 |1359. 1 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 389. 9 | 439. 9 | 489. 9 | 539. 9 | 589. 9 | 639. 9 | 689. 9 || 220 v| 2. 09 | 2. 28| 2. 45| 2. 62| 2. 78| 2. 94| 3. 10|| h| 1199. 6 |1232. 2 |1259. 6 |1285. 2 |1310. 3 |1335. 1 |1359. 8 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 391. 9 | 441. 9 | 491. 9 | 541. 9 | 591. 9 | 641. 9 | 691. 9 || 225 v| 2. 05 | 2. 23| 2. 40| 2. 57| 2. 72| 2. 88| 3. 03|| h| 1199. 9 |1232. 7 |1260. 2 |1285. 9 |1310. 9 |1335. 7 |1360. 3 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 393. 8 | 443. 8 | 493. 8 | 543. 8 | 593. 8 | 643. 8 | 693. 8 || 230 v| 2. 00 | 2. 18| 2. 35| 2. 51| 2. 67| 2. 82| 2. 97|| h| 1200. 2 |1233. 2 |1260. 7 |1286. 5 |1311. 6 |1336. 3 |1361. 0 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 395. 6 | 445. 6 | 495. 6 | 545. 6 | 595. 6 | 645. 6 | 695. 6 || 235 v| 1. 96 | 2. 14| 2. 30| 2. 46| 2. 62| 2. 77| 2. 91|| h| 1200. 6 |1233. 8 |1261. 4 |1287. 1 |1312. 2 |1337. 0 |1361. 7 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 397. 4 | 447. 4 | 497. 4 | 547. 4 | 597. 4 | 647. 4 | 697. 4 || 240 v| 1. 92 | 2. 09| 2. 26| 2. 42| 2. 57| 2. 71| 2. 85|| h| 1200. 9 |1234. 3 |1261. 9 |1287. 6 |1312. 8 |1337. 6 |1362. 3 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 399. 3 | 449. 3 | 499. 3 | 549. 3 | 599. 3 | 649. 3 | 699. 3 || 245 v| 1. 89 | 2. 05| 2. 22| 2. 37| 2. 52| 2. 66| 2. 80|| h| 1201. 2 |1234. 8 |1262. 5 |1288. 2 |1313. 3 |1338. 2 |1362. 9 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 401. 0 | 451. 0 | 501. 0 | 551. 0 | 601. 0 | 651. 0 | 701. 0 || 250 v| 1. 85 | 2. 02| 2. 17| 2. 33| 2. 47| 2. 61| 2. 75|| h| 1201. 5 |1235. 4 |1263. 0 |1288. 8 |1313. 9 |1338. 8 |1363. 5 ||________|_________|_______|_______|_______|_______|_______|_______|| t| 402. 8 | 452. 8 | 502. 8 | 552. 8 | 602. 8 | 652. 8 | 702. 8 || 255 v| 1. 81 | 1. 98| 2. 14| 2. 28| 2. 43| 2. 56| 2. 70|| h| 1201. 8 |1235. 9 |1263. 6 |1289. 3 |1314. 5 |1339. 3 |1364. 1 ||________|_________|_______|_______|_______|_______|_______|_______| t = Temperature, degrees Fahrenheit. V = Specific volume, in cubic feet, per pound. H = Total heat from water at 32 degrees, B. T. U. [Graph: Temperature of Steam--Degrees Fahr. Against Temperature in Calorimeter--Degrees Fahr. Fig. 15. Graphic Method of Determining Moisture Contained in Steam fromCalorimeter Readings] MOISTURE IN STEAM The presence of moisture in steam causes a loss, not only in thepractical waste of the heat utilized to raise this moisture from thetemperature of the feed water to the temperature of the steam, but alsothrough the increased initial condensation in an engine cylinder andthrough friction and other actions in a steam turbine. The presence ofsuch moisture also interferes with proper cylinder lubrication, causes aknocking in the engine and a water hammer in the steam pipes. In steamturbines it will cause erosion of the blades. The percentage by weight of steam in a mixture of steam and water iscalled the _quality of the steam_. The apparatus used to determine the moisture content of steam is calleda calorimeter though since it may not measure the heat in the steam, thename is not descriptive of the function of the apparatus. The first formused was the "barrel calorimeter", but the liability of error was sogreat that its use was abandoned. Modern calorimeters are in general ofeither the throttling or separator type. Throttling Calorimeter--Fig. 14 shows a typical form of throttlingcalorimeter. Steam is drawn from a vertical main through the samplingnipple, passes around the first thermometer cup, then through aone-eighth inch orifice in a disk between two flanges, and lastly aroundthe second thermometer cup and to the atmosphere. Thermometers areinserted in the wells, which should be filled with mercury or heavycylinder oil. [Illustration: Fig. 14. Throttling Calorimeter and Sampling Nozzle] The instrument and all pipes and fittings leading to it should bethoroughly insulated to diminish radiation losses. Care must be taken toprevent the orifice from becoming choked with dirt and to see that noleaks occur. The exhaust pipe should be short to prevent back pressurebelow the disk. When steam passes through an orifice from a higher to a lower pressure, as is the case with the throttling calorimeter, no external work has tobe done in overcoming a resistance. Hence, if there is no loss fromradiation, the quantity of heat in the steam will be exactly the sameafter passing the orifice as before passing. If the higher steampressure is 160 pounds gauge and the lower pressure that of theatmosphere, the total heat in a pound of dry steam at the formerpressure is 1195. 9 B. T. U. And at the latter pressure 1150. 4 B. T. U. , a difference of 45. 4 B. T. U. As this heat will still exist in the steamat the lower pressure, since there is no external work done, its effectmust be to superheat the steam. Assuming the specific heat ofsuperheated steam to be 0. 47, each pound passing through will besuperheated 45. 4/0. 47 = 96. 6 degrees. If, however, the steam hadcontained one per cent of moisture, it would have contained less heatunits per pound than if it were dry. Since the latent heat of steam at160 pounds gauge pressure is 852. 8 B. T. U. , it follows that the one percent of moisture would have required 8. 5 B. T. U. To evaporate it, leaving only 45. 4 - 8. 5 = 36. 9 B. T. U. Available for superheating;hence, the superheat would be 36. 9/0. 47 = 78. 5 degrees, as against 96. 6degrees for dry steam. In a similar manner, the degree of superheat forother percentages of moisture may be determined. The action of thethrottling calorimeter is based upon the foregoing facts, as shownbelow. Let H = total heat of one pound of steam at boiler pressure, L = latent heat of steam at boiler pressure, h = total heat of steam at reduced pressure after passing orifice, t_{1} = temperature of saturated steam at the reduced pressure, t_{2} = temperature of steam after expanding through the orifice in the disc, 0. 47 = the specific heat of saturated steam at atmospheric pressure, x = proportion by weight of moisture in steam. The difference in B. T. U. In a pound of steam at the boiler pressureand after passing the orifice is the heat available for evaporating themoisture content and superheating the steam. Therefore, H - h = xL + 0. 47(t_{2} - t_{1}) H - h - 0. 47(t_{2} - t_{1})or x = --------------------------- (4) L Almost invariably the lower pressure is taken as that of the atmosphere. Under such conditions, h = 1150. 4 and t_{1} = 212 degrees. The formulathus becomes: H - 1150. 4 - 0. 47(t_{2} - 212)x = ------------------------------ (5) L For practical work it is more convenient to dispense with the upperthermometer in the calorimeter and to measure the pressure in the steammain by an accurate steam pressure gauge. A chart may be used for determining the value of x for approximate workwithout the necessity for computation. Such a chart is shown in Fig. 15and its use is as follows: Assume a gauge pressure of 180 pounds and athermometer reading of 295 degrees. The intersection of the verticalline from the scale of temperatures as shown by the calorimeterthermometer and the horizontal line from the scale of gauge pressureswill indicate directly the per cent of moisture in the steam as readfrom the diagonal scale. In the present instance, this per cent is 1. 0. Sources of Error in the Apparatus--A slight error may arise from thevalue, 0. 47, used as the specific heat of superheated steam atatmospheric pressure. This value, however is very nearly correct and anyerror resulting from its use will be negligible. There is ordinarily a larger source of error due to the fact that thestem of the thermometer is not heated to its full length, to an initialerror in the thermometer and to radiation losses. With an ordinary thermometer immersed in the well to the 100 degreesmark, the error when registering 300 degrees would be about 3 degreesand the true temperature be 303 degrees. [19] The steam is evidently losing heat through radiation from the moment itenters the sampling nipple. The heat available for evaporating moistureand superheating steam after it has passed through the orifice into thelower pressure will be diminished by just the amount lost throughradiation and the value of t_{2}, as shown by the calorimeterthermometer, will, therefore, be lower than if there were no such loss. The method of correcting for the thermometer and radiation errorrecommended by the Power Test Committee of the American Society ofMechanical Engineers is by referring the readings as found on the boilertrial to a "normal" reading of the thermometer. This normal reading isthe reading of the lower calorimeter thermometer for dry saturatedsteam, and should be determined by attaching the instrument to ahorizontal steam pipe in such a way that the sampling nozzle projectsupward to near the top of the pipe, there being no perforations in thenozzle and the steam taken only through its open upper end. The testshould be made with the steam in a quiescent state and with the steampressure maintained as nearly as possible at the pressure observed inthe main trial, the calorimeter thermometer to be the same as was usedon the trial or one exactly similar. With a normal reading thus obtained for a pressure approximately thesame as existed in the trial, the true percentage of moisture in thesteam, that is, with the proper correction made for radiation, may becalculated as follows: Let T denote the normal reading for the conditions existing in thetrial. The effect of radiation from the instrument as pointed out willbe to lower the temperature of the steam at the lower pressure. Letx_{1} represent the proportion of water in the steam which will lowerits temperature an amount equal to the loss by radiation. Then, H - h - 0. 47(T - t_{1})x_{1} = ----------------------- L This amount of moisture, x_{1} was not in the steam originally but isthe result of condensation in the instrument through radiation. Hence, the true amount of moisture in the steam represented by X is thedifference between the amount as determined in the trial and thatresulting from condensation, or, X = x - x_{1} H - h - 0. 47(t_{2} - t_{1}) H - h - 0. 47(T - t_{1}) = --------------------------- - ----------------------- L L 0. 47(T - t_{2}) = --------------- (6) L As T and t_{2} are taken with the same thermometer under the same set ofconditions, any error in the reading of the thermometers will beapproximately the same for the temperatures T and t_{2} and the abovemethod therefore corrects for both the radiation and thermometer errors. The theoretical readings for dry steam, where there are no losses due toradiation, are obtainable from formula (5) by letting x = 0 and solvingfor t_{2}. The difference between the theoretical reading and the normalreading for no moisture will be the thermometer and radiation correctionto be applied in order that the correct reading of t_{2} may beobtained. For any calorimeter within the range of its ordinary use, such athermometer and radiation correction taken from one normal reading isapproximately correct for any conditions with the same or a duplicatethermometer. The percentage of moisture in the steam, corrected for thermometer errorand radiation and the correction to be applied to the particularcalorimeter used, would be determined as follows: Assume a gaugepressure in the trial to be 180 pounds and the thermometer reading to be295 degrees. A normal reading, taken in the manner described, gives avalue of T = 303 degrees; then, the percentage of moisture corrected forthermometer error and radiation is, 0. 47(303 - 295)x = ---------------- 845. 0 = 0. 45 per cent. The theoretical reading for dry steam will be, 1197. 7 - 1150. 4 - 0. 47(t_{2} - 212) 0 = ------------------------------------ 845. 0 t_{2} = 313 degrees. The thermometer and radiation correction to be applied to the instrumentused, therefore over the ordinary range of pressure is Correction = 313 - 303 = 10 degrees The chart may be used in the determination of the correct reading ofmoisture percentage and the permanent radiation correction for theinstrument used without computation as follows: Assume the same trialpressure, feed temperature and normal reading as above. If the normalreading is found to be 303 degrees, the correction for thermometer andradiation will be the theoretical reading for dry steam as found fromthe chart, less this normal reading, or 10 degrees correction. Thecorrect temperature for the trial in question is, therefore, 305degrees. The moisture corresponding to this temperature and 180 poundsgauge pressure will be found from the chart to be 0. 45 per cent. [Illustration: Fig. 16. Compact Throttling Calorimeter] There are many forms of throttling calorimeter, all of which work uponthe same principle. The simplest one is probably that shown in Fig. 14. An extremely convenient and compact design is shown in Fig. 16. Thiscalorimeter consists of two concentric metal cylinders screwed to a capcontaining a thermometer well. The steam pressure is measured by a gaugeplaced in the supply pipe or other convenient location. Steam passesthrough the orifice A and expands to atmospheric pressure, itstemperature at this pressure being measured by a thermometer placed inthe cup C. To prevent as far as possible radiation losses, the annularspace between the two cylinders is used as a jacket, steam beingsupplied to this space through the hole B. The limits of moisture within which the throttling calorimeter will workare, at sea level, from 2. 88 per cent at 50 pounds gauge pressure and7. 17 per cent moisture at 250 pounds pressure. Separating Calorimeter--The separating calorimeter mechanicallyseparates the entrained water from the steam and collects it in areservoir, where its amount is either indicated by a gauge glass or isdrained off and weighed. Fig. 17 shows a calorimeter of this type. Thesteam passes out of the calorimeter through an orifice of known size sothat its total amount can be calculated or it can be weighed. A gauge isordinarily provided with this type of calorimeter, which shows thepressure in its inner chamber and the flow of steam for a given period, this latter scale being graduated by trial. The instrument, like a throttling calorimeter, should be well insulatedto prevent losses from radiation. While theoretically the separating calorimeter is not limited incapacity, it is well in cases where the percentage of moisture presentin the steam is known to be high, to attach a throttling calorimeter toits exhaust. This, in effect, is the using of the separating calorimeteras a small separator between the sampling nozzle and the throttlinginstrument, and is necessary to insure the determination of the fullpercentage of moisture in the steam. The sum of the percentages shown bythe two instruments is the moisture content of the steam. The steam passing through a separating calorimeter may be calculated byNapier's formula, the size of the orifice being known. There areobjections to such a calculation, however, in that it is difficult toaccurately determine the areas of such small orifices. Further, smallorifices have a tendency to become partly closed by sediment that may becarried by the steam. The more accurate method of determining the amountof steam passing through the instrument is as follows: [Illustration: Fig. 17. Separating Calorimeter] A hose should be attached to the separator outlet leading to a vessel ofwater on a platform scale graduated to 1/100 of a pound. The steamoutlet should be connected to another vessel of water resting on asecond scale. In each case, the weight of each vessel and its contentsshould be noted. When ready for an observation, the instrument should beblown out thoroughly so that there will be no water within theseparator. The separator drip should then be closed and the steam hoseinserted into the vessel of water at the same instant. When theseparator has accumulated a sufficient quantity of water, the valve ofthe instrument should be closed and the hose removed from the vessel ofwater. The separator should be emptied into the vessel on its scale. Thefinal weight of each vessel and its contents are to be noted and thedifferences between the final and original weights will represent theweight of moisture collected by the separator and the weight of steamfrom which the moisture has been taken. The proportion of moisture canthen be calculated from the following formula: 100 wx = ----- (7) W - w Where x = per cent moisture in steam, W = weight of steam condensed, w = weight of moisture as taken out by the separating calorimeter. Sampling Nipple--The principle source of error in steam calorimeterdeterminations is the failure to obtain an average sample of the steamdelivered by the boiler and it is extremely doubtful whether such asample is ever obtained. The two governing features in the obtaining ofsuch a sample are the type of sampling nozzle used and its location. The American Society of Mechanical Engineers recommends a samplingnozzle made of one-half inch iron pipe closed at the inner end and theinterior portion perforated with not less than twenty one-eighth inchholes equally distributed from end to end and preferably drilled inirregular or spiral rows, with the first hole not less than one-halfinch from the wall of the pipe. Many engineers object to the use of aperforated sampling nipple because it ordinarily indicates a higherpercentage of moisture than is actually present in the steam. This isdue to the fact that if the perforations come close to the inner surfaceof the pipe, the moisture, which in many instances clings to thissurface, will flow into the calorimeter and cause a large error. Where aperforated nipple is used, in general it may be said that theperforations should be at least one inch from the inner pipe surface. A sampling nipple, open at the inner end and unperforated, undoubtedlygives as accurate a measure as can be obtained of the moisture in thesteam passing that end. It would appear that a satisfactory method ofobtaining an average sample of the steam would result from the use of anopen end unperforated nipple passing through a stuffing box which wouldallow the end to be placed at any point across the diameter of the steampipe. Incidental to a test of a 15, 000 K. W. Steam engine turbine unit, Mr. H. G. Stott and Mr. R. G. S. Pigott, finding no experimental databearing on the subject of low pressure steam quality determinations, made a investigation of the subject and the sampling nozzle illustratedin Fig. 18 was developed. In speaking of sampling nozzles in thedetermination of the moisture content of low pressure steam, Mr. Pigottsays, "the ordinary standard perforated pipe sampler is absolutelyworthless in giving a true sample and it is vital that the sample beabstracted from the main without changing its direction or velocityuntil it is safely within the sample pipe and entirely isolated from therest of the steam. " [Illustration: Fig. 18. Stott and Pigott Sampling Nozzle] It would appear that the nozzle illustrated is undoubtedly the best thathas been developed for use in the determination of the moisture contentof steam, not only in the case of low, but also in high pressure steam. Location of Sampling Nozzle--The calorimeter should be located as nearas possible to the point from which the steam is taken and the samplingnipple should be placed in a section of the main pipe near the boilerand where there is no chance of moisture pocketing in the pipe. TheAmerican Society of Mechanical Engineers recommends that a samplingnipple, of which a description has been given, should be located in avertical main, rising from the boiler with its closed end extendingnearly across the pipe. Where non-return valves are used, or where thereare horizontal connections leading from the boiler to a vertical outlet, water may collect at the lower end of the uptake pipe and be blownupward in a spray which will not be carried away by the steam owing to alack of velocity. A sample taken from the lower part of this pipe willshow a greater amount of moisture than a true sample. With goose-neckconnections a small amount of water may collect on the bottom of thepipe near the upper end where the inclination is such that the tendencyto flow backward is ordinarily counterbalanced by the flow of steamforward over its surface; but when the velocity momentarily decreasesthe water flows back to the lower end of the goose-neck and increasesthe moisture at that point, making it an undesirable location forsampling. In any case, it should be borne in mind that with lowvelocities the tendency is for drops of entrained water to settle to thebottom of the pipe, and to be temporarily broken up into spray wheneveran abrupt bend or other disturbance is met. [Illustration: Fig. 19. Illustrating the Manner in which ErroneousCalorimeter Readings may be Obtained due to Improper Location of SamplingNozzle Case 1--Horizontal pipe. Water flows at bottom. If perforations in nozzle are too near bottom of pipe, water piles against nozzle, flows into calorimeter and gives false reading. Case 2--If nozzle located too near junction of two horizontal runs, as at a, condensation from vertical pipe which collects at this point will be thrown against the nozzle by the velocity of the steam, resulting in a false reading. Nozzle should be located far enough above junction to be removed from water kept in motion by the steam velocity, as at b. Case 3--Condensation in bend will be held by velocity of the steam as shown. When velocity is diminished during firing intervals and the like moisture flows back against nozzle, a, and false reading is obtained. A true reading will be obtained at b provided condensation is not blown over on nozzle. Case 4--Where non-return valve is placed before a bend, condensation will collect on steam line side and water will be swept by steam velocity against nozzle and false readings result. ] Fig. 19 indicates certain locations of sampling nozzles from whicherroneous results will be obtained, the reasons being obvious from astudy of the cuts. Before taking any calorimeter reading, steam should be allowed to flowthrough the instrument freely until it is thoroughly heated. The methodof using a throttling calorimeter is evident from the description of theinstrument given and the principle upon which it works. [Illustration: Babcock & Wilcox Superheater] SUPERHEATED STEAM Superheated steam, as already stated, is steam the temperature of whichexceeds that of saturated steam at the same pressure. It is produced bythe addition of heat to saturated steam which has been removed fromcontact with the water from which it was generated. The properties ofsuperheated steam approximate those of a perfect gas rather than of avapor. Saturated steam cannot be superheated when it is in contact withwater which is also heated, neither can superheated steam condensewithout first being reduced to the temperature of saturated steam. Justso long as its temperature is above that of saturated steam at acorresponding pressure it is superheated, and before condensation cantake place that superheat must first be lost through radiation or someother means. Table 24[20] gives such properties of superheated steam forvarying pressures as are necessary for use in ordinary engineeringpractice. Specific Heat of Superheated Steam--The specific heat of superheatedsteam at atmospheric pressure and near saturation point was determinedby Regnault, in 1862, who gives it the value of 0. 48. Regnault's valuewas based on four series of experiments, all at atmospheric pressure andwith about the same temperature range, the maximum of which was 231. 1degrees centigrade. For fifty years after Regnault's determination, thisvalue was accepted and applied to higher pressures and temperatures aswell as to the range of his experiments. More recent investigations haveshown that the specific heat is not a constant and varies with bothpressure and the temperature. A number of experiments have been made byvarious investigators and, up to the present, the most reliable appearto be those of Knoblauch and Jacob. Messrs. Marks and Davis have usedthe values as determined by Knoblauch and Jacob with slightmodifications. The first consists in a varying of the curves at lowpressures close to saturation because of thermodynamic evidence and inview of Regnault's determination at atmospheric pressure. The secondmodification is at high degrees of superheat to follow Holborn's andHenning's curve, which is accepted as authentic. For the sake of convenience, the mean specific heat of superheated steamat various pressures and temperatures is given in tabulated form inTable 25. These values have been calculated from Marks and Davis SteamTables by deducting from the total heat of one pound of steam at anypressure for any degree of superheat the total heat of one pound ofsaturated steam at the same pressure and dividing the difference by thenumber of degrees of superheat and, therefore, represent the averagespecific heat starting from that at saturation to the value at theparticular pressure and temperature. [21] Expressed as a formula thiscalculation is represented by H_{sup} - H_{sat}Sp. Ht. = ----------------- (8) S_{sup} - S_{sat} Where H_{sup} = total heat of one pound of superheated steam at any pressure and temperature, H_{sat} = total heat of one pound of saturated steam at same pressure, S_{sup} = temperature of superheated steam taken, S_{sat} = temperature of saturated steam corresponding to the pressure taken. TABLE 25 MEAN SPECIFIC HEAT OF SUPERHEATED STEAM CALCULATED FROM MARKS AND DAVIS TABLES _______________________________________________________________|Gauge | ||Pressure | Degree of Superheat || |_____________________________________________________|| | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 ||_________|_____|_____|_____|_____|_____|_____|_____|_____|_____|| 50 | . 518| . 517| . 514| . 513| . 511| . 510| . 508| . 507| . 505|| 60 | . 528| . 525| . 523| . 521| . 519| . 517| . 515| . 513| . 512|| 70 | . 536| . 534| . 531| . 529| . 527| . 524| . 522| . 520| . 518|| 80 | . 544| . 542| . 539| . 535| . 532| . 530| . 528| . 526| . 524|| 90 | . 553| . 550| . 546| . 543| . 539| . 536| . 534| . 532| . 529|| 100 | . 562| . 557| . 553| . 549| . 544| . 542| . 539| . 536| . 533|| 110 | . 570| . 565| . 560| . 556| . 552| . 548| . 545| . 542| . 539|| 120 | . 578| . 573| . 567| . 561| . 557| . 554| . 550| . 546| . 543|| 130 | . 586| . 580| . 574| . 569| . 564| . 560| . 555| . 552| . 548|| 140 | . 594| . 588| . 581| . 575| . 570| . 565| . 561| . 557| . 553|| 150 | . 604| . 595| . 587| . 581| . 576| . 570| . 566| . 561| . 557|| 160 | . 612| . 603| . 596| . 589| . 582| . 576| . 571| . 566| . 562|| 170 | . 620| . 612| . 603| . 595| . 588| . 582| . 576| . 571| . 566|| 180 | . 628| . 618| . 610| . 601| . 593| . 587| . 581| . 575| . 570|| 190 | . 638| . 627| . 617| . 608| . 599| . 592| . 585| . 579| . 574|| 200 | . 648| . 635| . 624| . 614| . 605| . 597| . 590| . 584| . 578|| 210 | . 656| . 643| . 631| . 620| . 611| . 602| . 595| . 588| . 583|| 220 | . 664| . 650| . 637| . 626| . 616| . 607| . 600| . 592| . 586|| 230 | . 672| . 658| . 644| . 633| . 622| . 613| . 605| . 597| . 591|| 240 | . 684| . 668| . 653| . 640| . 629| . 619| . 610| . 602| . 595|| 250 | . 692| . 675| . 659| . 645| . 633| . 623| . 614| . 606| . 599||_________|_____|_____|_____|_____|_____|_____|_____|_____|_____||Gauge | ||Pressure | Degree of Superheat || |-----------------------------------------------------|| | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 225 | 250 ||---------+-----+-----+-----+-----+-----+-----+-----+-----+-----|| 50 | . 504| . 503| . 502| . 501| . 500| . 500| . 499| . 497| . 496|| 60 | . 511| . 509| . 508| . 507| . 506| . 504| . 504| . 502| . 500|| 70 | . 516| . 515| . 513| . 512| . 511| . 510| . 509| . 506| . 504|| 80 | . 522| . 520| . 518| . 516| . 515| . 514| . 513| . 511| . 508|| 90 | . 527| . 525| . 523| . 521| . 519| . 518| . 517| . 514| . 510|| 100 | . 531| . 529| . 527| . 525| . 523| . 522| . 521| . 517| . 513|| 110 | . 536| . 534| . 532| . 529| . 528| . 526| . 525| . 520| . 517|| 120 | . 540| . 537| . 535| . 533| . 531| . 529| . 528| . 523| . 519|| 130 | . 545| . 542| . 539| . 537| . 535| . 533| . 531| . 527| . 523|| 140 | . 550| . 547| . 544| . 541| . 539| . 536| . 534| . 530| . 526|| 150 | . 554| . 550| . 547| . 544| . 542| . 539| . 537| . 533| . 529|| 160 | . 558| . 554| . 551| . 548| . 545| . 543| . 541| . 536| . 531|| 170 | . 562| . 558| . 555| . 552| . 549| . 546| . 544| . 538| . 533|| 180 | . 566| . 561| . 558| . 555| . 552| . 549| . 546| . 540| . 536|| 190 | . 569| . 565| . 562| . 558| . 555| . 552| . 549| . 543| . 538|| 200 | . 574| . 569| . 566| . 562| . 558| . 555| . 552| . 546| . 541|| 210 | . 578| . 573| . 569| . 565| . 561| . 558| . 555| . 549| . 543|| 220 | . 581| . 577| . 572| . 568| . 564| . 561| . 558| . 551| . 545|| 230 | . 585| . 580| . 575| . 572| . 567| . 564| . 561| . 554| . 548|| 240 | . 589| . 584| . 579| . 575| . 571| . 567| . 564| . 556| . 550|| 250 | . 593| . 587| . 582| . 577| . 574| . 570| . 567| . 559| . 553||_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| Factor of Evaporation with Superheated Steam--When superheat is presentin the steam during a boiler trial, where superheated steam tables areavailable, the formula for determining the factor of evaporation is thatalready given, (2), [22] namely, H - hFactor of evaporation = ----- L Here H = total heat in one pound of superheated steam from the table, h and L having the same values as in (2). Where no such tables are available but the specific heat of superheat isknown, the formula becomes: H - h + Sp. Ht. (T - t)Factor of evaporation = ---------------------- L Where H = total heat in one pound of saturated steam at pressure existing in trial, h = sensible heat above 32 degrees in one pound of water at the temperature entering the boiler, T = temperature of superheated steam as determined in the trial, t = temperature of saturated steam corresponding to the boiler pressure, Sp. Ht. = mean specific heat of superheated steam at the pressure and temperature as found in the trial, L = latent heat of one pound of saturated steam at atmospheric pressure. Advantages of the Use of Superheated Steam--In considering the savingpossible by the use of superheated steam, it is too often assumed thatthere is only a saving in the prime movers, a saving which is at leastpartially offset by an increase in the fuel consumption of the boilersgenerating steam. This misconception is due to the fact that the fuelconsumption of the boiler is only considered in connection with adefinite weight of steam. It is true that where such a definite weightis to be superheated, an added amount of fuel must be burned. With aproperly designed superheater where the combined efficiency of theboiler and superheater will be at least as high as of a boiler alone, the approximate increase in coal consumption for producing a givenweight of steam will be as follows: _Superheat_ _Added Fuel_ _Degrees_ _Per Cent_ 25 1. 59 50 3. 07 75 4. 38 100 5. 69 150 8. 19 200 10. 58 These figures represent the added fuel necessary for superheating adefinite weight of steam to the number of degrees as given. The standardbasis, however, of boiler evaporation is one of heat units and, considered from such a standpoint, again providing the efficiency of theboiler and superheater is as high, as of a boiler alone, there is noadditional fuel required to generate steam containing a definite numberof heat units whether such units be due to superheat or saturation. Thatis, if 6 per cent more fuel is required to generate and superheat to 100degrees, a definite weight of steam, over what would be required toproduce the same weight of saturated steam, that steam when superheated, will contain 6 per cent more heat units above the fuel water temperaturethan if saturated. This holds true if the efficiency of the boiler andsuperheater combined is the same as of the boiler alone. As a matter offact, the efficiency of a boiler and superheater, where the latter isproperly designed and located, will be slightly higher for the same setof furnace conditions than would the efficiency of a boiler in which nosuperheater were installed. A superheater, properly placed within theboiler setting in such way that products of combustion for generatingsaturated steam are utilized as well for superheating that steam, willnot in any way alter furnace conditions. With a given set of suchfurnace conditions for a given amount of coal burned, the fact thatadditional surface, whether as boiler heating or superheating surface, is placed in such a manner that the gases must sweep over it, will tendto lower the temperature of the exit gases. It is such a lowering ofexit gas temperatures that is the ultimate indication of addedefficiency. Though the amount of this added efficiency is difficult todetermine by test, that there is an increase is unquestionable. Where a properly designed superheater is installed in a boiler theheating surface of the boiler proper, in the generation of a definitenumber of heat units, is relieved of a portion of the work which wouldbe required were these heat units delivered in saturated steam. Such asuperheater needs practically no attention, is not subject to a largeupkeep cost or depreciation, and performs its function without in anyway interfering with the operation of the boiler. Its use, thereforefrom the standpoint of the boiler room, results in a saving in wear andtear due to the lower ratings at which the boiler may be run, or its usewill lead to the possibility of obtaining the same number of boilerhorse power from a smaller number of boilers, with the boiler heatingsurface doing exactly the same amount of work as if the superheaterswere not installed. The saving due to the added boiler efficiency thatwill be obtained is obvious. Following the course of the steam in a plant, the next advantage of theuse of superheated steam is the absence of water in the steam pipes. Thethermal conductivity of superheated steam, that is, its power to give upits heat to surrounding bodies, is much lower than that of saturatedsteam and its heat, therefore, will not be transmitted so rapidly to thewalls of the pipes as when saturated steam is flowing through the pipes. The loss of heat radiated from a steam pipe, assuming no loss inpressure, represents the equivalent condensation when the pipe iscarrying saturated steam. In well-covered steam mains, the heat lost byradiation when carrying superheated steam is accompanied only by areduction of the superheat which, if it be sufficiently high at theboiler, will enable a considerable amount of heat to be radiated andstill deliver dry or superheated steam to the prime movers. It is in the prime movers that the advantages of the use of superheatedsteam are most clearly seen. In an engine, steam is admitted into a space that has been cooled by thesteam exhausted during the previous stroke. The heat necessary to warmthe cylinder walls from the temperature of the exhaust to that of theentering steam can be supplied only by the entering steam. If this steambe saturated, such an adding of heat to the walls at the expense of theheat of the entering steam results in the condensation of a portion. This initial condensation is seldom less than from 20 to 30 per cent ofthe total weight of steam entering the cylinder. It is obvious that ifthe steam entering be superheated, it must be reduced to the temperatureof saturated steam at the corresponding pressure before any condensationcan take place. If the steam be superheated sufficiently to allow areduction in temperature equivalent to the quantity of heat that must beimparted to the cylinder walls and still remain superheated, it is clearthat initial condensation is avoided. For example: assume one pound ofsaturated steam at 200 pounds gauge pressure to enter a cylinder whichhas been cooled by the exhaust. Assume the initial condensation to be 20per cent. The latent heat of the steam is given up in condensation;hence, . 20 × 838 = 167. 6 B. T. U. Are given up by the steam. If onepound of superheated steam enters the same cylinder, it would have to besuperheated to a point where its total heat is 1199 + 168 = 1367B. T. U. Or, at 200 pounds gauge pressure, superheated approximately 325degrees if the heat given up to the cylinder walls were the same as forthe saturated steam. As superheated steam conducts heat less rapidlythan saturated steam, the amount of heat imparted will be less than forthe saturated steam and consequently the amount of superheat required toprevent condensation will be less than the above figure. This, ofcourse, is the extreme case of a simple engine with the range oftemperature change a maximum. As cylinders are added, the range in eachis decreased and the condensation is proportionate. The true economy of the use of superheated steam is best shown in acomparison of the "heat consumption" of an engine. This is the number ofheat units required in developing one indicated horse power and themeasure of the relative performance of two engines is based on acomparison of their heat consumption as the measure of a boiler is basedon its evaporation from and at 212 degrees. The water consumption of anengine in pounds per indicated horse power is in no sense a trueindication of its efficiency. The initial pressures and correspondingtemperatures may differ widely and thus make a difference in thetemperature of the exhaust and hence in the temperature of the condensedsteam returned to the boiler. For example: suppose a certain weight ofsteam at 150 pounds absolute pressure and 358 degrees be expanded toatmospheric pressure, the temperature then being 212 degrees. If thesame weight of steam be expanded from an initial pressure of 125 poundsabsolute and 344 degrees, to enable it to do the same amount of work, that is, to give up the same amount of heat, expansion then must becarried to a point below atmospheric pressure to, say, 13 poundsabsolute, the final temperature of the steam then being 206 degrees. Inactual practice, it has been observed that the water consumption of acompound piston engine running on 26-inch vacuum and returning thecondensed steam at 140 degrees was approximately the same as whenrunning on 28-inch vacuum and returning water at 90 degrees. With anequal water consumption for the two sets of conditions, the economy inthe former case would be greater than in the latter, since it would benecessary to add less heat to the water returned to the boiler to raiseit to the steam temperature. The lower the heat consumption of an engine per indicated horse power, the higher its economy and the less the number of heat units must beimparted to the steam generated. This in turn leads to the lowering ofthe amount of fuel that must be burned per indicated horse power. With the saving in fuel by the reduction of heat consumption of anengine indicated, it remains to be shown the effect of the use ofsuperheated steam on such heat consumption. As already explained, theuse of superheated steam reduces condensation not only in the mains butespecially in the steam cylinder, leaving a greater quantity of steamavailable to do the work. Furthermore, a portion of the saturated steamintroduced into a cylinder will condense during adiabatic expansion, this condensation increasing as expansion progresses. Since superheatedsteam cannot condense until it becomes saturated, not only is initialcondensation prevented by its use but also such condensation as wouldoccur during expansion. When superheated sufficiently, steam deliveredby the exhaust will still be dry. In the avoidance of such condensation, there is a direct saving in the heat consumption of an engine, the heatgiven up being utilized in the developing of power and not in changingthe condition of the working fluid. That is, while the number of heatunits lost in overcoming condensation effects would be the same ineither case, when saturated steam is condensed the water of condensationhas no power to do work while the superheated steam, even after it haslost a like number of heat units, still has the power of expansion. Thesaving through the use of superheated steam in the heat consumption ofan engine decreases demands on the boiler and hence the fuel consumptionper unit of power. Superheated Steam for Steam Turbines--Experience in using superheatedsteam in connection with steam turbines has shown that it leads toeconomy and that it undoubtedly pays to use superheated steam in placeof saturated steam. This is so well established that it is standardpractice to use superheated steam in connection with steam turbines. Aside from the economy secured through using superheated steam, there isan important advantage arising through the fact that it materiallyreduces the erosion of the turbine blades by the action of water thatwould be carried by saturated steam. In using saturated steam in a steamturbine or piston engine, the work done on expanding the steam causescondensation of a portion of the steam, so that even were the steam dryon entering the turbine, it would contain water on leaving the turbine. By superheating the steam the water that exists in the low pressurestages of the turbine may be reduced to an amount that will not causetrouble. Again, if saturated steam contains moisture, the effect of this moistureon the economy of a steam turbine is to reduce the economy to a greaterextent than the proportion by weight of water, one per cent of watercausing approximately a falling off of 2 per cent in the economy. The water rate of a large economical steam turbine with superheatedsteam is reduced about one per cent, for every 12 degrees of superheatup to 200 degrees Fahrenheit of superheat. To superheat one pound ofsteam 12 degrees requires about 7 B. T. U. And if 1050 B. T. U. Arerequired at the boiler to evaporate one pound of the saturated steamfrom the temperature of the feed water, the heat required for thesuperheated steam would be 1057 degrees. One per cent of saving, therefore, in the water consumption would correspond to a net saving ofabout one-third of one per cent in the coal consumption. On this basis100 degrees of superheat with an economical steam turbine would resultin somewhat over 3 per cent of saving in the coal for equal boilerefficiencies. As a boiler with a properly designed superheater placedwithin the setting is more economical for a given capacity than a boilerwithout a superheater, the minimum gain in the coal consumption wouldbe, say, 4 or 5 per cent as compared to a plant with the same boilerswithout superheaters. The above estimates are on the basis of a thoroughly dry saturated steamor steam just at the point of being superheated or containing a fewdegrees of superheat. If the saturated steam is moist, the saving due tosuperheat is more and ordinarily the gain in economy due to superheatedsteam, for equal boiler efficiencies, as compared with commercially drysteam is, say, 5 per cent for each 100 degrees of superheat. Aside fromthis gain, as already stated, superheated steam prevents erosion of theturbine buckets that would be caused by water in the steam, and for thereasons enumerated it is standard practice to use superheated steam forturbine work. The less economical the steam motor, the more the gain dueto superheated steam, and where there are a number of auxiliaries thatare run with superheated steam, the percentage of gain will be greaterthan the figures given above, which are the minimum and are for the mosteconomical type of large steam turbines. An example from actual practice will perhaps best illustrate andemphasize the foregoing facts. In October 1909, a series of comparabletests were conducted by The Babcock & Wilcox Co. On the steam yacht"Idalia" to determine the steam consumption both with saturated andsuperheated steam of the main engine on that yacht, including as wellthe feed pump, circulating pump and air pump. These tests are morerepresentative than are most tests of like character in that the savingin the steam consumption of the auxiliaries, which were much morewasteful than the main engine, formed an important factor. A résumé ofthese tests was published in the Journal of the Society of NavalEngineers, November 1909. The main engines of the "Idalia" are four cylinder, triple expansion, 11-1/2 × 19 inches by 22-11/16 × 18 inches stroke. Steam is supplied bya Babcock & Wilcox marine boiler having 2500 square feet of boilerheating surface, 340 square feet of superheating surface and 65 squarefeet of grate surface. The auxiliaries consist of a feed pump 6 × 4 × 6 inches, an independentair pump 6 × 12 × 8 inches, and a centrifugal pump driven by areciprocating engine 5-7/16 × 5 inches. Under ordinary operatingconditions the superheat existing is about 100 degrees Fahrenheit. Tests were made with various degrees of superheat, the amount beingvaried by by-passing the gases and in the tests with the lower amountsof superheat by passing a portion of the steam from the boiler to thesteam main without passing it through the superheater. Steam temperaturereadings were taken at the engine throttle. In the tests with saturatedsteam, the superheater was completely cut out of the system. Carefulcalorimeter measurements were taken, showing that the saturated steamdelivered to the superheater was dry. The weight of steam used was determined from the weight of the condensedsteam discharge from the surface condenser, the water being pumped fromthe hot well into a tank mounted on platform scales. The sameindicators, thermometers and gauges were used in all the tests, so thatthe results are directly comparable. The indicators used were of theoutside spring type so that there was no effect of the temperature ofthe steam. All tests were of sufficient duration to show a uniformity ofresults by hours. A summary of the results secured is given in Table 26, which shows the water rate per indicated horse power and the heatconsumption. The latter figures are computed on the basis of the heatimparted to the steam above the actual temperature of the feed waterand, as stated, these are the results that are directly comparable. TABLE 26 RESULTS OF "IDALIA" TESTS _______________________________________________________________________| | | | | | ||Date 1909 |Oct. 11|Oct. 14|Oct. 14|Oct. 12|Oct. 13||_______________________________|_______|_______|_______|_______|_______||Degrees of superheat Fahrenheit| 0 | 57 | 88 | 96 | 105 ||Pressures, pounds per} Throttle| 190 | 196 | 201 | 198 | 203 ||square inch above } First | | | | | ||Atmospheric Pressure } Receiver| 68. 4 | 66. 0 | 64. 3 | 61. 9 | 63. 0 || } Second | | | | | || } Receiver| 9. 7 | 9. 2 | 8. 7 | 7. 8 | 8. 4 ||Vacuum, inches | 25. 5 | 25. 9 | 25. 9 | 25. 4 | 25. 2 ||Temperature, Degrees Fahrenheit| | | | | || } Feed | 201 | 206 | 205 | 202 | 200 || } Hot Well | 116 | 109. 5 | 115 | 111. 5 | 111 || | | | | | ||Revolutions per minute | | | | | || {Air Pump | 57 | 56 | 53 | 54 | 45 || {Circulating Pump| 196 | 198 | 196 | 198 | 197 || {Main Engine | 194. 3 | 191. 5 | 195. 1 | 191. 5 | 193. 1 ||Indicated Horse Power, | | | | | || Main Engine | 512. 3 | 495. 2 | 521. 1 | 498. 3 | 502. 2 ||Water per hour, total pounds |9397 |8430 |8234 |7902 |7790 ||Water per indicated | | | | | || Horse Power, pounds | 18. 3 | 17. 0 | 15. 8 | 15. 8 | 15. 5 ||B. T. U. Per minute per | | | | | || indicated Horse Power | 314 | 300 | 284 | 286 | 283 ||Per cent Saving of Steam | . .. | 7. 1 | 13. 7 | 13. 7 | 15. 3 ||Percent Saving of Fuel | | | | | || (computed) | . .. | 4. 4 | 9. 5 | 8. 9 | 9. 9 ||_______________________________|_______|_______|_______|_______|_______| The table shows that the saving in steam consumption with 105 degrees ofsuperheat was 15. 3 per cent and in heat consumption about 10 per cent. This may be safely stated to be a conservative representation of thesaving that may be accomplished by the use of superheated steam in aplant as a whole, where superheated steam is furnished not only to themain engine but also to the auxiliaries. The figures may be taken asconservative for the reason that in addition to the saving as shown inthe table, there would be in an ordinary plant a saving much greaterthan is generally realized in the drips, where the loss with saturatedsteam is greatly in excess of that with superheated steam. The most conclusive and most practical evidence that a saving ispossible through the use of superheated steam is in the fact that in thelargest and most economical plants it is used almost without exception. Regardless of any such evidence, however, there is a deep rootedconviction in the minds of certain engineers that the use of superheatedsteam will involve operating difficulties which, with additional firstcost, will more than offset any fuel saving. There are, of course, conditions under which the installation of superheaters would in no waybe advisable. With a poorly designed superheater, no gain would result. In general, it may be stated that in a new plant, properly designed, with a boiler and superheater which will have an efficiency at least ashigh as a boiler without a superheater, a gain is certain. Such a gain is dependent upon the class of engine and the power plantequipment in general. In determining the advisability of making asuperheater installation, all of the factors entering into eachindividual case should be considered and balanced, with a view todetermining the saving in relation to cost, maintenance, depreciationetc. In highly economical plants, where the water consumption for anindicated horse power is low, the gain will be less than would resultfrom the use of superheated steam in less economical plants where thewater consumption is higher. It is impossible to make an accuratestatement as to the saving possible but, broadly, it may vary from 3 to5 per cent for 100 degrees of superheat in the large and economicalplants using turbines or steam engines, in which there is a large ratioof expansion, to from 10 to 25 per cent for 100 degrees of superheat forthe less economical steam motors. Though a properly designed superheater will tend to raise rather than todecrease the boiler efficiency, it does not follow that all superheatersare efficient, for if the gases in passing over the superheater do notfollow the path they would ordinarily take in passing over the boilerheating surface, a loss may result. This is noticeably true where part ofthe gases are passed over the superheater and are allowed to pass overonly a part or in some cases none of the boiler heating surface. With moderate degrees of superheat, from 100 to 200 degrees, where thepiping is properly installed, there will be no greater operatingdifficulties than with saturated steam. Engine and turbine buildersguarantee satisfactory operation with superheated steam. With highdegrees of superheat, say, over 250 degrees, apparatus of a specialnature must be used and it is questionable whether the additional careand liability to operating difficulties will offset any fuel savingaccomplished. It is well established, however, that the operatingdifficulties, with the degrees of superheat to which this article islimited, have been entirely overcome. The use of cast-iron fittings with superheated steam has been widelydiscussed. It is an undoubted fact that while in some instancessuperheated steam has caused deterioration of such fittings, in otherscast-iron fittings have been used with 150 degrees of superheat withoutthe least difficulty. The quality of the cast iron used in such fittingshas doubtless a large bearing on the life of such fittings for thisservice. The difficulties that have been encountered are an increase inthe size of the fittings and eventually a deterioration great enough tolead to serious breakage, the development of cracks, and when flangesare drawn up too tightly, the breaking of a flange from the body of thefitting. The latter difficulty is undoubtedly due, in certain instances, to the form of flange in which the strain of the connecting bolts tendedto distort the metal. The Babcock & Wilcox Co. Have used steel castings in superheated steamwork over a long period and experience has shown that this metal issuitable for the service. There seems to be a general tendency towardthe use of steel fittings. In European practice, until recently, castiron was used with apparently satisfactory results. The claim ofEuropean engineers was to the effect that their cast iron was of betterquality than that found in this country and thus explained the resultssecured. Recently, however, certain difficulties have been encounteredwith such fittings and European engineers are leaning toward the use ofsteel for this work. The degree of superheat produced by a superheater placed within theboiler setting will vary according to the class of fuel used, the formof furnace, the condition of the fire and the rate at which the boileris being operated. This is necessarily true of any superheater swept bythe main body of the products of combustion and is a fact that should beappreciated by the prospective user of superheated steam. With aproperly designed superheater, however, such fluctuations would not beexcessive, provided the boilers are properly operated. As a matter offact the point to be guarded against in the use of superheated steam isthat a maximum should not be exceeded. While, as stated, there may be aconsiderable fluctuation in the temperature of the steam as deliveredfrom individual superheaters, where there are a number of boilers on aline the temperature of the combined flow of steam in the main will befound to be practically a constant, resulting from the offsetting ofvarious furnace conditions of one boiler by another. [Illustration: 8400 Horse-power Installation of Babcock & Wilcox Boilersand Superheaters at the Butler Street Plant of the Georgia Railway andPower Co. , Atlanta, Ga. This Company Operates a Total of 15, 200 HorsePower of Babcock & Wilcox Boilers] PROPERTIES OF AIR Pure air is a mechanical mixture of oxygen and nitrogen. While differentauthorities give slightly varying values for the proportion of oxygenand nitrogen contained, the generally accepted values are: By volume, oxygen 20. 91 per cent, nitrogen 79. 09 per cent. By weight, oxygen 23. 15 per cent, nitrogen 76. 85 per cent. Air in nature always contains other constituents in varying amounts, such as dust, carbon dioxide, ozone and water vapor. Being perfectly elastic, the density or weight per unit of volumedecreases in geometric progression with the altitude. This fact has adirect bearing in the proportioning of furnaces, flues and stacks athigh altitudes, as will be shown later in the discussion of thesesubjects. The atmospheric pressures corresponding to various altitudesare given in Table 12. The weight and volume of air depend upon the pressure and thetemperature, as expressed by the formula: Pv = 53. 33 T (9) Where P = the absolute pressure in pounds per square foot, v = the volume in cubic feet of one pound of air, T = the absolute temperature of the air in degrees Fahrenheit, 53. 33 = a constant for air derived from the ratio of pressure, volume and temperature of a perfect gas. The weight of one cubic foot of air will obviously be the reciprocal ofits volume, that is, 1/v pounds. TABLE 27 VOLUME AND WEIGHT OF AIR AT ATMOSPHERIC PRESSURE AT VARIOUS TEMPERATURES _______________________________________| | | || | Volume | || Temperature | One Pound | Weight One || Degrees | in | Cubic Foot || Fahrenheit | Cubic Feet | in Pounds ||_____________|____________|____________|| | | || 32 | 12. 390 | . 080710 || 50 | 12. 843 | . 077863 || 55 | 12. 969 | . 077107 || 60 | 13. 095 | . 076365 || 65 | 13. 221 | . 075637 || 70 | 13. 347 | . 074923 || 75 | 13. 473 | . 074223 || 80 | 13. 599 | . 073535 || 85 | 13. 725 | . 072860 || 90 | 13. 851 | . 072197 || 95 | 13. 977 | . 071546 || 100 | 14. 103 | . 070907 || 110 | 14. 355 | . 069662 || 120 | 14. 607 | . 068460 || 130 | 14. 859 | . 067299 || 140 | 15. 111 | . 066177 || 150 | 15. 363 | . 065092 || 160 | 15. 615 | . 064041 || 170 | 15. 867 | . 063024 || 180 | 16. 119 | . 062039 || 190 | 16. 371 | . 061084 || 200 | 16. 623 | . 060158 || 210 | 16. 875 | . 059259 || 212 | 16. 925 | . 059084 || 220 | 17. 127 | . 058388 || 230 | 17. 379 | . 057541 || 240 | 17. 631 | . 056718 || 250 | 17. 883 | . 055919 || 260 | 18. 135 | . 055142 || 270 | 18. 387 | . 054386 || 280 | 18. 639 | . 053651 || 290 | 18. 891 | . 052935 || 300 | 19. 143 | . 052238 || 320 | 19. 647 | . 050898 || 340 | 20. 151 | . 049625 || 360 | 20. 655 | . 048414 || 380 | 21. 159 | . 047261 || 400 | 21. 663 | . 046162 || 425 | 22. 293 | . 044857 || 450 | 22. 923 | . 043624 || 475 | 23. 554 | . 042456 || 500 | 24. 184 | . 041350 || 525 | 24. 814 | . 040300 || 550 | 25. 444 | . 039302 || 575 | 26. 074 | . 038352 || 600 | 26. 704 | . 037448 || 650 | 27. 964 | . 035760 || 700 | 29. 224 | . 034219 || 750 | 30. 484 | . 032804 || 800 | 31. 744 | . 031502 || 850 | 33. 004 | . 030299 ||_____________|____________|____________| Example: Required the volume of air in cubic feet under 60. 3 poundsgauge pressure per square inch at 115 degrees Fahrenheit. P = 144 (14. 7 + 60. 3) = 10, 800. T = 115 + 460 = 575 degrees. 53. 33 × 575Hence v = ----------- = 2. 84 cubic feet, and 10, 800 1 1Weight per cubic foot = - = ---- = 0. 352 pounds. V 2. 84 Table 27 gives the weights and volumes of air under atmospheric pressureat varying temperatures. Formula (9) holds good for other gases with the change in the value ofthe constant as follows: For oxygen 48. 24, nitrogen 54. 97, hydrogen 765. 71. The specific heat of air at constant pressure varies with itstemperature. A number of determinations of this value have been made andcertain of those ordinarily accepted as most authentic are given inTable 28. TABLE 28 SPECIFIC HEAT OF AIR AT CONSTANT PRESSURE AND VARIOUS TEMPERATURES ______________________________________________________________| | | || Temperature Range | | ||_________________________|_______________|____________________|| | | | || Degrees | Degrees | Specific Heat | Authority || Centigrade | Fahrenheit | | ||____________|____________|_______________|____________________|| | | | || -30- 10 | -22- 50 | 0. 2377 | Regnault || 0-100 | 32- 212 | 0. 2374 | Regnault || 0-200 | 32- 392 | 0. 2375 | Regnault || 20-440 | 68- 824 | 0. 2366 | Holborn and Curtis || 20-630 | 68-1166 | 0. 2429 | Holborn and Curtis || 20-800 | 68-1472 | 0. 2430 | Holborn and Curtis || 0-200 | 32- 392 | 0. 2389 | Wiedemann ||____________|____________|_______________|____________________| This value is of particular importance in waste heat work and it isregrettable that there is such a variation in the different experiments. Mallard and Le Chatelier determined values considerably higher than anygiven in Table 28. All things considered in view of the discrepancy ofthe values given, there appears to be as much ground for the use of aconstant value for the specific heat of air at any temperature as for avariable value. Where this value is used throughout this book, it hasbeen taken as 0. 24. Air may carry a considerable quantity of water vapor, which isfrequently 3 per cent of the total weight. This fact is of importance inproblems relating to heating drying and the compressing of air. Table 29gives the amount of vapor required to saturate air at differenttemperatures, its weight, expansive force, etc. , and contains sufficientinformation for solving practically all problems of this sort that mayarise. TABLE 29 WEIGHTS OF AIR, VAPOR OF WATER, AND SATURATED MIXTURES OF AIR AND VAPOR AT DIFFERENT TEMPERATURES, UNDER THE ORDINARY ATMOSPHERIC PRESSURE OF 29. 921 INCHES OF MERCURY Column Headings: 1: Temperature Degrees Fahrenheit 2: Volume of Dry Air at Different Temperatures, the Volume at 32 Degrees being 1. 000 3: Weight of Cubic Foot of Dry Air at the Different Temperatures Pounds 4: Elastic Force of Vapor in Inches of Mercury (Regnault) 5: Elastic Force of the Air in the Mixture of Air and Vapor in Inches of Mercury 6: Weight of the Air in Pounds 7: Weight of the Vapor in Pounds 8: Total Weight of Mixture in Pounds 9: Weight of Vapor Mixed with One Pound of Air, in Pounds10: Weight of Dry Air Mixed with One Pound of Vapor, in Pounds11: Cubic Feet of Vapor from One Pound of Water at its own Pressure in Column 4 ____________________________________________________________________________| | | | | | || | | | | Mixtures of Air Saturated | || | | | | with Vapor | ||___|_____|_____|______|______________________________________________|______|| | | | | |Weight of Cubic Foot | | | || | | | | | of the Mixture of | | | || | | | | | Air and Vapor | | | || | | | | |_____________________| | | || | | | | | | | | | | || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 ||___|_____|_____|______|______|_____|_______|_______|________|________|______|| | | | | | | | | | | || 0| . 935|. 0864| . 044|29. 877|. 0863|. 000079|. 086379| . 00092|1092. 4 | || 12| . 960|. 0842| . 074|29. 849|. 0840|. 000130|. 084130| . 00155| 646. 1 | || 22| . 980|. 0824| . 118|29. 803|. 0821|. 000202|. 082302| . 00245| 406. 4 | || 32|1. 000|. 0807| . 181|29. 740|. 0802|. 000304|. 080504| . 00379| 263. 81 |3289 || 42|1. 020|. 0791| . 267|29. 654|. 0784|. 000440|. 078840| . 00561| 178. 18 |2252 || | | | | | | | | | | || 52|1. 041|. 0776| . 388|29. 533|. 0766|. 000627|. 077227| . 00810| 122. 17 |1595 || 62|1. 061|. 0761| . 556|29. 365|. 0747|. 000881|. 075581| . 01179| 84. 79 |1135 || 72|1. 082|. 0747| . 785|29. 136|. 0727|. 001221|. 073921| . 01680| 59. 54 | 819 || 82|1. 102|. 0733| 1. 092|28. 829|. 0706|. 001667|. 072267| . 02361| 42. 35 | 600 || 92|1. 122|. 0720| 1. 501|28. 420|. 0684|. 002250|. 070717| . 03289| 30. 40 | 444 || | | | | | | | | | | ||102|1. 143|. 0707| 2. 036|27. 885|. 0659|. 002997|. 068897| . 04547| 21. 98 | 334 ||112|1. 163|. 0694| 2. 731|27. 190|. 0631|. 003946|. 067046| . 06253| 15. 99 | 253 ||122|1. 184|. 0682| 3. 621|26. 300|. 0599|. 005142|. 065042| . 08584| 11. 65 | 194 ||132|1. 204|. 0671| 4. 752|25. 169|. 0564|. 006639|. 063039| . 11771| 8. 49 | 151 ||142|1. 224|. 0660| 6. 165|23. 756|. 0524|. 008473|. 060873| . 16170| 6. 18 | 118 || | | | | | | | | | | ||152|1. 245|. 0649| 7. 930|21. 991|. 0477|. 010716|. 058416| . 22465| 4. 45 | 93. 3||162|1. 265|. 0638|10. 099|19. 822|. 0423|. 013415|. 055715| . 31713| 3. 15 | 74. 5||172|1. 285|. 0628|12. 758|17. 163|. 0360|. 016682|. 052682| . 46338| 2. 16 | 59. 2||182|1. 306|. 0618|15. 960|13. 961|. 0288|. 020536|. 049336| . 71300| 1. 402| 48. 6||192|1. 326|. 0609|19. 828|10. 093|. 0205|. 025142|. 045642| 1. 22643| . 815| 39. 8|| | | | | | | | | | | ||202|1. 347|. 0600|24. 450| 5. 471|. 0109|. 030545|. 041445| 2. 80230| . 357| 32. 7||212|1. 367|. 0591|29. 921| 0. 000|. 0000|. 036820|. 036820|Infinite| . 000| 27. 1||___|_____|_____|______|______|_____|_______|_______|________|________|______| Column 5 = barometer pressure of 29. 921, minus the proportion of thisdue to vapor pressure from column 4. COMBUSTION Combustion may be defined as the rapid chemical combination of oxygenwith carbon, hydrogen and sulphur, accompanied by the diffusion of heatand light. That portion of the substance thus combined with the oxygenis called combustible. As used in steam engineering practice, however, the term combustible is applied to that portion of the fuel which is dryand free from ash, thus including both oxygen and nitrogen which may beconstituents of the fuel, though not in the true sense of the termcombustible. Combustion is perfect when the combustible unites with the greatestpossible amount of oxygen, as when one atom of carbon unites with twoatoms of oxygen to form carbon dioxide, CO_{2}. The combustion isimperfect when complete oxidation of the combustible does not occur, orwhere the combustible does not unite with the maximum amount of oxygen, as when one atom of carbon unites with one atom of oxygen to form carbonmonoxide, CO, which may be further burned to carbon dioxide. Kindling Point--Before a combustible can unite with oxygen andcombustion takes place, its temperature must first be raised to theignition or kindling point, and a sufficient time must be allowed forthe completion of the combustion before the temperature of the gases islowered below that point. Table 30, by Stromeyer, gives the approximatekindling temperatures of different fuels. TABLE 30 KINDLING TEMPERATURE OF VARIOUS FUELS ____________________________________| | || | Degrees || | Fahrenheit ||_________________|__________________|| | || Lignite Dust | 300 || Dried Peat | 435 || Sulphur | 470 || Anthracite Dust | 570 || Coal | 600 || Coke | Red Heat || Anthracite | Red Heat, 750 || Carbon Monoxide | Red Heat, 1211 || Hydrogen | 1030 or 1290 ||_________________|__________________| Combustibles--The principal combustibles in coal and other fuels arecarbon, hydrogen and sulphur, occurring in varying proportions andcombinations. Carbon is by far the most abundant as is indicated in the chapters onfuels. Hydrogen in a free state occurs in small quantities in some fuels, butis usually found in combination with carbon, in the form ofhydrocarbons. The density of hydrogen is 0. 0696 (Air = 1) and its weightper cubic foot, at 32 degrees Fahrenheit and under atmospheric pressure, is 0. 005621 pounds. Sulphur is found in most coals and some oils. It is usually present incombined form, either as sulphide of iron or sulphate of lime; in thelatter form it has no heat value. Its presence in fuel is objectionablebecause of its tendency to aid in the formation of clinkers, and thegases from its combustion, when in the presence of moisture, may causecorrosion. Nitrogen is drawn into the furnace with the air. Its density is 0. 9673(Air = 1); its weight, at 32 degrees Fahrenheit and under atmosphericpressure, is 0. 07829 pounds per cubic foot; each pound of air atatmospheric pressure contains 0. 7685 pounds of nitrogen, and one poundof nitrogen is contained in 1. 301 pounds of air. Nitrogen performs no useful office in combustion and passes through thefurnace without change. It dilutes the air, absorbs heat, reduces thetemperature of the products of combustion, and is the chief source ofheat losses in furnaces. Calorific Value--Each combustible element of gas will combine withoxygen in certain definite proportions and will generate a definiteamount of heat, measured in B. T. U. This definite amount of heat perpound liberated by perfect combustion is termed the calorific value ofthat substance. Table 31, gives certain data on the reactions andresults of combustion for elementary combustibles and several compounds. TABLE 31 OXYGEN AND AIR REQUIRED FOR COMBUSTION AT 32 DEGREES AND 29. 92 INCHES Column headings: 1: Oxidizable Substance or Combustible 2: Chemical Symbol 3: Atomic or Combining Weight 4: Chemical Reaction 5: Product of Combustion 6: Oxygen per Pound of Column 1 Pounds 7: Nitrogen per Pound of Column 1. 3. 32[23] × O Pounds 8: Air per Pound of Column 1. 4. 32[24] × O Pounds 9: Gaseous Product per Pound of Column 1[25] + Column 8 Pounds10: Heat Value per Pound of Column 1 B. T. U. 11: Volumes of Column 1 Entering Combination Volume12: Volumes of Oxygen Combining with Column 11 Volume13: Volumes of Product Formed Volume14: Volume per Pound of Column 1 in Gaseous Form Cubic Feet15: Volume of Oxygen per Pound of Column 1 Cubic Feet16: Volume of Products of Combustion per Pound of Column 1 Cubic Feet17: Volume of Nitrogen per Pound of Column 1 3. 782[26] × Column 15 Cubic Feet18: Volume of Gas per pound of Column 1 = Column 10 ÷ Column 17 Cubic Feet BY WEIGHT ________________________________________________________________________| | | | | | || 1 | 2 | 3 | 4 | 5 | 6 ||________________|_______|____|________________|_________________|_______|| | | | | | || Carbon | C | 12 | C+2O = CO_{2} | Carbon Dioxide | 2. 667 || Carbon | C | 12 | C+O = CO | Carbon Monoxide | 1. 333 || Carbon Monoxide| CO | 28 | CO+O = CO_{2} | Carbon Dioxide | . 571 || Hydrogen | H | 1 | 2H+O = H_{2}O | Water | 8 || | | / CH_{4}+4O = | Carbon Dioxide \ || Methane | CH_{4}| 16 | | | 4 || | | \ CO_{2}+2H_{2}O | and Water / || Sulphur | S | 32 | S+2O = SO_{2} | Sulphur Dioxide | 1 ||________________|_______|____|________________|_________________|_______| ________________________________________________________| | | | | | || 1 | 2 | 7 | 8 | 9 | 10 ||________________|_______|_______|_______|_______|_______|| | | | | | || Carbon | C | 8. 85 | 11. 52 | 12. 52 | 14600 || Carbon | C | 4. 43 | 5. 76 | 6. 76 | 4450 || Carbon Monoxide| CO | 1. 90 | 2. 47 | 3. 47 | 10150 || Hydrogen | H | 26. 56 | 34. 56 | 35. 56 | 62000 || | | | | | || Methane | CH_{4}| 13. 28 | 17. 28 | 18. 28 | 23550 || | | | | | || Sulphur | S | 3. 32 | 4. 32 | 5. 32 | 4050 ||________________|_______|_______|_______|_______|_______| BY VOLUME ________________________________________________________________| | | | | | || 1 | 2 | 11 | 12 | 13 | 14 ||_________________|________|______|____|________________|________|| | | | | | || Carbon | C | 1C | 2 | 2CO_{2} | 14. 95 || Carbon | C | 1C | 1 | 2CO | 14. 95 || Carbon Monoxide | CO | 2CO | 1 | 2CO_{2} | 12. 80 || Hydrogen | H | 2H | 1 | 2H_{2}O | 179. 32 || Methane | CH_{4} | 1C4H | 4 | 1CO_{2} 2H_{2}O| 22. 41 || Sulphur | S | 1S | 2 | 1SO_{2} | 5. 60 ||_________________|________|______|____|________________|________| _____________________________________________________________| | | | | | || 1 | 2 | 15 | 16 | 17 | 18 ||_________________|________|_______|________|________|________|| | | | | | || Carbon | C | 29. 89 | 29. 89 | 112. 98 | 142. 87 || Carbon | C | 14. 95 | 29. 89 | 56. 49 | 86. 38 || Carbon Monoxide | CO | 6. 40 | 12. 80 | 24. 20 | 37. 00 || Hydrogen | H | 89. 66 | 179. 32 | 339. 09 | 518. 41 || Methane | CH_{4} | 44. 83 | 67. 34 | 169. 55 | 236. 89 || Sulphur | S | 11. 21 | 11. 21 | 42. 39 | 53. 60 ||_________________|________|_______|________|________|________| It will be seen from this table that a pound of carbon will unite with2-2/3 pounds of oxygen to form carbon dioxide, and will evolve 14, 600B. T. U. As an intermediate step, a pound of carbon may unite with 1-1/3pounds of oxygen to form carbon monoxide and evolve 4450 B. T. U. , butin its further conversion to CO_{2} it would unite with an additional1-1/3 times its weight of oxygen and evolve the remaining 10, 150B. T. U. When a pound of CO burns to CO_{2}, however, only 4350 B. T. U. Are evolved since the pound of CO contains but 3/7 pound carbon. Air Required for Combustion--It has already been shown that eachcombustible element in fuel will unite with a definite amount of oxygen. With the ultimate analysis of the fuel known, in connection with Table31, the theoretical amount of air required for combustion may be readilycalculated. Let the ultimate analysis be as follows: _Per Cent_Carbon 74. 79Hydrogen 4. 98Oxygen 6. 42Nitrogen 1. 20Sulphur 3. 24Water 1. 55Ash 7. 82 ------ 100. 00 When complete combustion takes place, as already pointed out, the carbonin the fuel unites with a definite amount of oxygen to form CO_{2}. Thehydrogen, either in a free or combined state, will unite with oxygen toform water vapor, H_{2}O. Not all of the hydrogen shown in a fuelanalysis, however, is available for the production of heat, as a portionof it is already united with the oxygen shown by the analysis in theform of water, H_{2}O. Since the atomic weights of H and O arerespectively 1 and 16, the weight of the combined hydrogen will be 1/8of the weight of the oxygen, and the hydrogen available for combustionwill be H - 1/8 O. In complete combustion of the sulphur, sulphurdioxide SO_{2} is formed, which in solution in water forms sulphuricacid. Expressed numerically, the theoretical amount of air for the aboveanalysis is as follows: 0. 7479 C × 2-2/3 = 1. 9944 O needed( 0. 0642 )( 0. 0498 - -------) H × 8 = 0. 3262 O needed( 8 ) 0. 0324 S × 1 = 0. 0324 O needed ------ Total 2. 3530 O needed One pound of oxygen is contained in 4. 32 pounds of air. The total air needed per pound of coal, therefore, will be 2. 353 × 4. 32= 10. 165. The weight of combustible per pound of fuel is . 7479 + . 0418[27] + . 0324+ . 012 = . 83 pounds, and the air theoretically required per pound ofcombustible is 10. 165 ÷ . 83 = 12. 2 pounds. The above is equivalent to computing the theoretical amount of airrequired per pound of fuel by the formula: ( O)Weight per pound = 11. 52 C + 34. 56 (H - -) + 4. 32 S (10) ( 8) where C, H, O and S are proportional parts by weight of carbon, hydrogen, oxygen and sulphur by ultimate analysis. In practice it is impossible to obtain perfect combustion with thetheoretical amount of air, and an excess may be required, amounting tosometimes double the theoretical supply, depending upon the nature ofthe fuel to be burned and the method of burning it. The reason for thisis that it is impossible to bring each particle of oxygen in the airinto intimate contact with the particles in the fuel that are to beoxidized, due not only to the dilution of the oxygen in the air bynitrogen, but because of such factors as the irregular thickness of thefire, the varying resistance to the passage of the air through the firein separate parts on account of ash, clinker, etc. Where thedifficulties of drawing air uniformly through a fuel bed are eliminated, as in the case of burning oil fuel or gas, the air supply may bematerially less than would be required for coal. Experiment has shownthat coal will usually require 50 per cent more than the theoretical netcalculated amount of air, or about 18 pounds per pound of fuel eitherunder natural or forced draft, though this amount may vary widely withthe type of furnace, the nature of the coal, and the method of firing. If less than this amount of air is supplied, the carbon burns tomonoxide instead of dioxide and its full heat value is not developed. An excess of air is also a source of waste, as the products ofcombustion will be diluted and carry off an excessive amount of heat inthe chimney gases, or the air will so lower the temperature of thefurnace gases as to delay the combustion to an extent that will causecarbon monoxide to pass off unburned from the furnace. A sufficientamount of carbon monoxide in the gases may cause the action known assecondary combustion, by igniting or mingling with air after leaving thefurnace or in the flues or stack. Such secondary combustion which takesplace either within the setting after leaving the furnace or in theflues or stack always leads to a loss of efficiency and, in someinstances, leads to overheating of the flues and stack. Table 32 gives the theoretical amount of air required for various fuelscalculated from formula (10) assuming the analyses of the fuels given inthe table. The process of combustion of different fuels and the effect of variationin the air supply for their combustion is treated in detail in thechapters dealing with the various fuels. TABLE 32 CALCULATED THEORETICAL AMOUNT OF AIR REQUIRED PER POUND OF VARIOUS FUELS ____________________________________________________________| |Weight of Constituents in One |Air Required|| Fuel |Pound Dry Fuel |per Pound || |______________________________|of Fuel || | Carbon | Hydrogen| Oxygen |Pounds || | Per Cent| Per Cent| Per Cent | ||________________|_________|_________|__________|____________||Coke | 94. 0 | . | . | 10. 8 ||Anthracite Coal | 91. 5 | 3. 5 | 2. 6 | 11. 7 ||Bituminous Coal | 87. 0 | 5. 0 | 4. 0 | 11. 6 ||Lignite | 70. 0 | 5. 0 | 20. 0 | 8. 9 ||Wood | 50. 0 | 6. 0 | 43. 5 | 6. 0 ||Oil | 85. 0 | 13. 0 | 1. 0 | 14. 3 ||________________|_________|_________|__________|____________| [Illustration: 4064 HORSE-POWER Installation of Babcock & Wilcox Boilersand Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers, atthe Cosmopolitan Electric Co. , Chicago, Ill. ] ANALYSIS OF FLUE GASES The object of a flue gas analysis is the determination of thecompleteness of the combustion of the carbon in the fuel, and the amountand distribution of the heat losses due to incomplete combustion. Thequantities actually determined by an analysis are the relativeproportions by volume, of carbon dioxide (CO_{2}), oxygen (O), andcarbon monoxide (CO), the determinations being made in this order. The variations of the percentages of these gases in an analysis is bestillustrated in the consideration of the complete combustion of purecarbon, a pound of which requires 2. 67 pounds of oxygen, [28] or 32 cubicfeet at 60 degrees Fahrenheit. The gaseous product of such combustionwill occupy, when cooled, the same volume as the oxygen, namely, 32cubic feet. The air supplied for the combustion is made up of 20. 91 percent oxygen and 79. 09 per cent nitrogen by volume. The carbon unitedwith the oxygen in the form of carbon dioxide will have the same volumeas the oxygen in the air originally supplied. The volume of the nitrogenwhen cooled will be the same as in the air supplied, as it undergoes nochange. Hence for complete combustion of one pound of carbon, where noexcess of air is supplied, an analysis of the products of combustionwill show the following percentages by volume: _Actual Volume_ _for One Pound Carbon_ _Per Cent_ _Cubic Feet_ _by Volume_Carbon Dioxide 32 = 20. 91Oxygen 0 = 0. 00Nitrogen 121 = 79. 09 --- ------Air required for one pound Carbon 153 = 100. 00 For 50 per cent excess air the volume will be as follows: 153 × 1½ = 229. 5 cubic feet of air per pound of carbon. _Actual Volume_ _for One Pound Carbon_ _Per Cent_ _Cubic Feet_ _by Volume_Carbon Dioxide 32 = 13. 91 }Oxygen 16 = 7. 00 } = 20. 91 per centNitrogen 181. 5 = 79. 09 ----- ------ 229. 5 = 100. 00 For 100 per cent excess air the volume will be as follows: 153 × 2 = 306 cubic feet of air per pound of carbon. _Actual Volume_ _for One Pound Carbon_ _Per Cent_ _Cubic Feet_ _by Volume_Carbon Dioxide 32 = 10. 45 }Oxygen 32 = 10. 45 } = 20. 91 per centNitrogen 242 = 79. 09 --- ------ 306 = 100. 00 In each case the volume of oxygen which combines with the carbon isequal to (cubic feet of air × 20. 91 per cent)--32 cubic feet. It will be seen that no matter what the excess of air supplied, theactual amount of carbon dioxide per pound of carbon remains the same, while the percentage by volume decreases as the excess of air increases. The actual volume of oxygen and the percentage by volume increases withthe excess of air, and the percentage of oxygen is, therefore, anindication of the amount of excess air. In each case the sum of thepercentages of CO_{2} and O is the same, 20. 9. Although the volume ofnitrogen increases with the excess of air, its percentage by volumeremains the same as it undergoes no change while combustion takes place;its percentage for any amount of air excess, therefore, will be the sameafter combustion as before, if cooled to the same temperature. It mustbe borne in mind that the above conditions hold only for the perfectcombustion of a pound of pure carbon. Carbon monoxide (CO) produced by the imperfect combustion of carbon, will occupy twice the volume of the oxygen entering into its compositionand will increase the volume of the flue gases over that of the airsupplied for combustion in the proportion of 100 + ½ the per cent CO1 to ----------------------- 100 When pure carbon is the fuel, the sum of the percentages by volume ofcarbon dioxide, oxygen and one-half of the carbon monoxide, must be inthe same ratio to the nitrogen in the flue gases as is the oxygen to thenitrogen in the air supplied, that is, 20. 91 to 79. 09. When burningcoal, however, the percentage of nitrogen is obtained by subtracting thesum of the percentages by volume of the other gases from 100. Thus if ananalysis shows 12. 5 per cent CO_{2}, 6. 5 per cent O, and 0. 6 per centCO, the percentage of nitrogen which ordinarily is the only otherconstituent of the gas which need be considered, is found as follows: 100 - (12. 5 + 6. 5 + 0. 6) = 80. 4 per cent. The action of the hydrogen in the volatile constituents of the fuel isto increase the apparent percentage of the nitrogen in the flue gases. This is due to the fact that the water vapor formed by the combustion ofthe hydrogen will condense at a temperature at which the analysis ismade, while the nitrogen which accompanied the oxygen with which thehydrogen originally combined maintains its gaseous form and passes intothe sampling apparatus with the other gases. For this reason coalscontaining high percentages of volatile matter will produce a largerquantity of water vapor, and thus increase the apparent percentage ofnitrogen. Air Required and Supplied--When the ultimate analysis of a fuel isknown, the air required for complete combustion with no excess can befound as shown in the chapter on combustion, or from the followingapproximate formula: Pounds of air required per pound of fuel = (C O S) 34. 56 (- + (H - -) + -)[29] (11) (3 8 8) where C, H and O equal the percentage by weight of carbon, hydrogen andoxygen in the fuel divided by 100. When the flue gas analysis is known, the total, amount of air suppliedis: Pounds of air supplied per pound of fuel = N 3. 036 (-----------) × C[30] (12) CO_{2} + CO where N, CO_{2} and CO are the percentages by volume of nitrogen, carbondioxide and carbon monoxide in the flue gases, and C the percentage byweight of carbon which is burned from the fuel and passes up the stackas flue gas. This percentage of C which is burned must be distinguishedfrom the percentage of C as found by an ultimate analysis of the fuel. To find the percentage of C which is burned, deduct from the totalpercentage of carbon as found in the ultimate analysis, the percentageof unconsumed carbon found in the ash. This latter quantity is thedifference between the percentage of ash found by an analysis and thatas determined by a boiler test. It is usually assumed that the entirecombustible element in the ash is carbon, which assumption ispractically correct. Thus if the ash in a boiler test were 16 per centand by an analysis contained 25 per cent of carbon, the percentage ofunconsumed carbon would be 16 × . 25 = 4 per cent of the total coalburned. If the coal contained by ultimate analysis 80 per cent of carbonthe percentage burned, and of which the products of combustion pass upthe chimney would be 80 - 4 = 76 per cent, which is the correct figureto use in calculating the total amount of air supplied by formula (12). The weight of flue gases resulting from the combustion of a pound of drycoal will be the sum of the weights of the air per pound of coal and thecombustible per pound of coal, the latter being equal to one minus thepercentage of ash as found in the boiler test. The weight of flue gasesper pound of dry fuel may, however, be computed directly from theanalyses, as shown later, and the direct computation is that ordinarilyused. The ratio of the air actually supplied per pound of fuel to thattheoretically required to burn it is: N3. 036(---------)×C CO_{2}+CO------------------ (13) C O34. 56(- + H - -) 3 8 in which the letters have the same significance as in formulae (11) and(12). The ratio of the air supplied per pound of combustible to the amounttheoretically required is: N------------------ (14)N - 3. 782(O - ½CO) which is derived as follows: The N in the flue gas is the content of nitrogen in the whole amount ofair supplied. The oxygen in the flue gas is that contained in the airsupplied and which was not utilized in combustion. This oxygen wasaccompanied by 3. 782 times its volume of nitrogen. The total amount ofexcess oxygen in the flue gases is (O - ½CO); hence N - 3. 782(O - ½CO)represents the nitrogen content in the air actually required forcombustion and N ÷ (N - 3. 782[O - ½CO]) is the ratio of the air suppliedto that required. This ratio minus one will be the proportion of excessair. The heat lost in the flue gases is L = 0. 24 W (T - t) (15) Where L = B. T. U. Lost per pound of fuel, W = weight of flue gases in pounds per pound of dry coal, T = temperature of flue gases, t = temperature of atmosphere, 0. 24 = specific heat of the flue gases. The weight of flue gases, W, per pound of carbon can be computeddirectly from the flue gas analysis from the formula: 11 CO_{2} + 8 O + 7 (CO + N)---------------------------- (16) 3 (CO_{2} + CO) where CO_{2}, O, CO, and N are the percentages by volume as determinedby the flue gas analysis of carbon dioxide, oxygen, carbon monoxide andnitrogen. The weight of flue gas per pound of dry coal will be the weightdetermined by this formula multiplied by the percentage of carbon in thecoal from an ultimate analysis. [Graph: Temperature of Escaping Gases--Deg. Fahr. Against Heat carried away by Chimney Gases--In B. T. U. Per pound of Carbon burned. [31] Fig. 20. Loss Due to Heat Carried Away by Chimney Gases for VaryingPercentages of Carbon Dioxide. Based on Boiler Room Temperature = 80Degrees Fahrenheit. Nitrogen in Flue Gas = 80. 5 Per Cent. CarbonMonoxide in Flue Gas = 0. Per Cent] Fig. 20 represents graphically the loss due to heat carried away by drychimney gases for varying percentages of CO_{2}, and differenttemperatures of exit gases. The heat lost, due to the fact that the carbon in the fuel is notcompletely burned and carbon monoxide is present in the flue gases, inB. T. U. Per pound of fuel burned is: ( CO )L' = 10, 150 × (-----------) (17) (CO + CO_{2}) where, as before, CO and CO_{2} are the percentages by volume in theflue gases and C is the proportion by weight of carbon which is burnedand passes up the stack. Fig. 21 represents graphically the loss due to such carbon in the fuelas is not completely burned but escapes up the stack in the form ofcarbon monoxide. [Graph: Loss in B. T. U. Per Pound of Carbon Burned[32]against Per Cent CO_{2} in Flue Gas Fig. 21. Loss Due to Unconsumed Carbon Contained in theCO in the Flue Gases] Apparatus for Flue Gas Analysis--The Orsat apparatus, illustrated inFig. 22, is generally used for analyzing flue gases. The burette A isgraduated in cubic centimeters up to 100, and is surrounded by a waterjacket to prevent any change in temperature from affecting the densityof the gas being analyzed. For accurate work it is advisable to use four pipettes, B, C, D, E, thefirst containing a solution of caustic potash for the absorption ofcarbon dioxide, the second an alkaline solution of pyrogallol for theabsorption of oxygen, and the remaining two an acid solution of cuprouschloride for absorbing the carbon monoxide. Each pipette contains anumber of glass tubes, to which some of the solution clings, thusfacilitating the absorption of the gas. In the pipettes D and E, copperwire is placed in these tubes to re-energize the solution as it becomesweakened. The rear half of each pipette is fitted with a rubber bag, oneof which is shown at K, to protect the solution from the action of theair. The solution in each pipette should be drawn up to the mark on thecapillary tube. The gas is drawn into the burette through the U-tube H, which is filledwith spun glass, or similar material, to clean the gas. To discharge anyair or gas in the apparatus, the cock G is opened to the air and thebottle F is raised until the water in the burette reaches the 100 cubiccentimeters mark. The cock G is then turned so as to close the airopening and allow gas to be drawn through H, the bottle F being loweredfor this purpose. The gas is drawn into the burette to a point below thezero mark, the cock G then being opened to the air and the excess gasexpelled until the level of the water in F and in A are at the zeromark. This operation is necessary in order to obtain the zero reading atatmospheric pressure. The apparatus should be carefully tested for leakage as well as allconnections leading thereto. Simple tests can be made; for example: Ifafter the cock G is closed, the bottle F is placed on top of the framefor a short time and again brought to the zero mark, the level of thewater in A is above the zero mark, a leak is indicated. [Illustration: Fig. 22. Orsat Apparatus] Before taking a final sample for analysis, the burette A should befilled with gas and emptied once or twice, to make sure that all theapparatus is filled with the new gas. The cock G is then closed and thecock I in the pipette B is opened and the gas driven over into B byraising the bottle F. The gas is drawn back into A by lowering F andwhen the solution in B has reached the mark in the capillary tube, thecock I is closed and a reading is taken on the burette, the level of thewater in the bottle F being brought to the same level as the water in A. The operation is repeated until a constant reading is obtained, thenumber of cubic centimeters being the percentage of CO_{2} in the fluegases. The gas is then driven over into the pipette C and a similar operationis carried out. The difference between the resulting reading and thefirst reading gives the percentage of oxygen in the flue gases. The next operation is to drive the gas into the pipette D, the gas beinggiven a final wash in E, and then passed into the pipette C toneutralize any hydrochloric acid fumes which may have been given off bythe cuprous chloride solution, which, especially if it be old, may giveoff such fumes, thus increasing the volume of the gases and making thereading on the burette less than the true amount. The process must be carried out in the order named, as the pyrogallolsolution will also absorb carbon dioxide, while the cuprous chloridesolution will also absorb oxygen. As the pressure of the gases in the flue is less than the atmosphericpressure, they will not of themselves flow through the pipe connectingthe flue to the apparatus. The gas may be drawn into the pipe in the wayalready described for filling the apparatus, but this is a tediousmethod. For rapid work a rubber bulb aspirator connected to the airoutlet of the cock G will enable a new supply of gas to be drawn intothe pipe, the apparatus then being filled as already described. Anotherform of aspirator draws the gas from the flue in a constant stream, thusinsuring a fresh supply for each sample. The analysis made by the Orsat apparatus is volumetric; if the analysisby weight is required, it can be found from the volumetric analysis asfollows: Multiply the percentages by volume by either the densities or themolecular weight of each gas, and divide the products by the sum of allthe products; the quotients will be the percentages by weight. For mostwork sufficient accuracy is secured by using the even values of themolecular weights. The even values of the molecular weights of the gases appearing in ananalysis by an Orsat are: Carbon Dioxide 44Carbon Monoxide 28Oxygen 32Nitrogen 28 Table 33 indicates the method of converting a volumetric flue gasanalysis into an analysis by weight. TABLE 33 CONVERSION OF A FLUE GAS ANALYSIS BY VOLUME TO ONE BY WEIGHT Column Headings: A: Analysis by Volume Per CentB: Molecular WeightC: Volume times Molecular WeightD: Analysis by Weight Per Cent _____________________________________________________________________| | | | | || Gas | A | B | C | D ||________________________|_______|___________|________|_______________|| | | | | || | | | | || | | | | 536. 8 || Carbon Dioxide CO_{2} | 12. 2 | 12+(2×16) | 536. 8 | ------ = 17. 7 || | | | | 3022. 8 || | | | | || | | | | 11. 2 || Carbon Monoxide CO | . 4 | 12+16 | 11. 2 | ------ = . 4 || | | | | 3022. 8 || | | | | || | | | | 220. 8 || Oxygen O | 6. 9 | 2×16 | 220. 8 | ------ = 7. 3 || | | | | 3022. 8 || | | | | || | | | | 2254. 0 || Nitrogen N | 80. 5 | 2×14 | 2254. 0 | ------ = 74. 6 || | | | | 3022. 8 ||________________________|_______|___________|________|_______________|| | | | | || Total | 100. 0 | | 3022. 8 | 100. 0 ||________________________|_______|___________|________|_______________| Application of Formulae and Rules--Pocahontas coal is burned in thefurnace, a partial ultimate analysis being: _Per Cent_Carbon 82. 1Hydrogen 4. 25Oxygen 2. 6Sulphur 1. 6Ash 6. 0B. T. U. , per pound dry 14500 The flue gas analysis shows: _Per Cent_ CO_{2} 10. 7O 9. 0CO 0. 0N (by difference) 80. 3 Determine: The flue gas analysis by weight (see Table 33), the amount ofair required for perfect combustion, the actual weight of air per poundof fuel, the weight of flue gas per pound of coal, the heat lost in thechimney gases if the temperature of these is 500 degrees Fahrenheit, andthe ratio of the air supplied to that theoretically required. Solution: The theoretical weight of air required for perfect combustion, per pound of fuel, from formula (11) will be, (. 821 . 026 . 016)W = 34. 56 (---- + (. 0425 - ----) + ----) = 10. 88 pounds. ( 3 8 8 ) If the amount of carbon which is burned and passes away as flue gas is80 per cent, which would allow for 2. 1 per cent of unburned carbon interms of the total weight of dry fuel burned, the weight of dry gas perpound of carbon burned will be from formula (16): 11 × 10. 7 + 8 × 9. 0 + 7(0 + 80. 3)W = --------------------------------- = 23. 42 pounds 3(10. 7 + 0) and the weight of flue gas per pound of coal burned will be . 80 × 23. 42= 18. 74 pounds. The heat lost in the flue gases per pound of coal burned will be fromformula (15) and the value 18. 74 just determined. Loss = . 24 × 18. 74 × (500 - 60) = 1979 B. T. U. The percentage of heat lost in the flue gases will be 1979 ÷ 14500 =13. 6 per cent. The ratio of air supplied per pound of coal to that theoreticallyrequired will be 18. 74 ÷ 10. 88 = 1. 72 per cent. The ratio of air supplied per pound of combustible to that required willbe from formula (14): . 803------------------------- = 1. 73. 803 - 3. 782(. 09 - ½ × 0) The ratio based on combustible will be greater than the ratio based onfuel if there is unconsumed carbon in the ash. Unreliability of CO_{2} Readings Taken Alone--It is generally assumedthat high CO_{2} readings are indicative of good combustion and hence ofhigh efficiency. This is true only in the sense that such high readingsdo indicate the small amount of excess air that usually accompanies goodcombustion, and for this reason high CO_{2} readings alone are notconsidered entirely reliable. Wherever an automatic CO_{2} recorder isused, it should be checked from time to time and the analysis carriedfurther with a view to ascertaining whether there is CO present. As thepercentage of CO_{2} in these gases increases, there is a tendencytoward the presence of CO, which, of course, cannot be shown by a CO_{2}recorder, and which is often difficult to detect with an Orsatapparatus. The greatest care should be taken in preparing the cuprouschloride solution in making analyses and it must be known to be freshand capable of absorbing CO. In one instance that came to our attention, in using an Orsat apparatus where the cuprous chloride solution wasbelieved to be fresh, no CO was indicated in the flue gases but onpassing the same sample into a Hempel apparatus, a considerablepercentage was found. It is not safe, therefore, to assume withoutquestion from a high CO_{2} reading that the combustion iscorrespondingly good, and the question of excess air alone should bedistinguished from that of good combustion. The effect of a smallquantity of CO, say one per cent, present in the flue gases will have anegligible influence on the quantity of excess air, but the presence ofsuch an amount would mean a loss due to the incomplete combustion of thecarbon in the fuel of possibly 4. 5 per cent of the total heat in thefuel burned. When this is considered, the importance of a complete fluegas analysis is apparent. Table 34 gives the densities of various gases together with other datathat will be of service in gas analysis work. TABLE 34 DENSITY OF GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE ADAPTED FROM SMITHSONIAN TABLES +----------+----------+--------+---------+----------+---------------+| | | | | | Relative || | | | Weight | | Density, || | | | of | Volume | Hydrogen = 1 || | |Specific|One Cubic| of +-------+-------+| Gas | Chemical |Gravity | Foot |One Pound | |Approx-|| | Symbol | Air=1 | Pounds |Cubic Feet| Exact | imate |+----------+----------+--------+---------+----------+-------+-------+|Oxygen | O | 1. 053 | . 08922 | 11. 208 | 15. 87 | 16 ||Nitrogen | N | 0. 9673 | . 07829 | 12. 773 | 13. 92 | 14 ||Hydrogen | H | 0. 0696 | . 005621 | 177. 90 | 1. 00 | 1 ||Carbon | | | | | | || Dioxide | CO_{2} | 1. 5291 | . 12269 | 8. 151 | 21. 83 | 22 ||Carbon | | | | | | || Monoxide | CO | 0. 9672 | . 07807 | 12. 809 | 13. 89 | 14 ||Methane | CH_{4} | 0. 5576 | . 04470 | 22. 371 | 7. 95 | 8 ||Ethane |C_{2}H_{6}| 1. 075 | . 08379 | 11. 935 | 14. 91 | 15 ||Acetylene |C_{2}H_{2}| 0. 920 | . 07254 | 13. 785 | 12. 91 | 13 ||Sulphur | | | | | | || Dioxide | SO_{2} | 2. 2639 | . 17862 | 5. 598 | 31. 96 | 32 ||Air | . .. | 1. 0000 | . 08071 | 12. 390 | . .. | . .. |+----------+----------+--------+---------+----------+-------+-------+ [Illustration: 1942 Horse-power Installation of Babcock & Wilcox Boilersand Superheaters in the Singer Building, New York City] CLASSIFICATION OF FUELS (WITH PARTICULAR REFERENCE TO COAL) Fuels for steam boilers may be classified as solid, liquid or gaseous. Of the solid fuels, anthracite and bituminous coals are the most common, but in this class must also be included lignite, peat, wood, bagasse andthe refuse from certain industrial processes such as sawdust, shavings, tan bark and the like. Straw, corn and coffee husks are utilized inisolated cases. The class of liquid fuels is represented chiefly by petroleum, thoughcoal tar and water-gas tar are used to a limited extent. Gaseous fuels are limited to natural gas, blast furnace gas and cokeoven gas, the first being a natural product and the two latterby-products from industrial processes. Though waste gases from certainprocesses may be considered as gaseous fuels, inasmuch as the questionof combustion does not enter, the methods of utilizing them differ fromthat for combustible gaseous fuel, and the question will be dealt withseparately. Since coal is by far the most generally used of all fuels, this chapterwill be devoted entirely to the formation, composition and distributionof the various grades, from anthracite to peat. The other fuels will bediscussed in succeeding chapters and their combustion dealt with inconnection with their composition. Formation of Coal--All coals are of vegetable origin and are the remainsof prehistoric forests. Destructive distillation due to great pressuresand temperatures, has resolved the organic matter into its invariableultimate constituents, carbon, hydrogen, oxygen and other substances, invarying proportions. The factors of time, depth of beds, disturbance ofbeds and the intrusion of mineral matter resulting from suchdisturbances have produced the variation in the degree of evolution fromvegetable fiber to hard coal. This variation is shown chiefly in thecontent of carbon, and Table 35 shows the steps of such variation. TABLE 35 APPROXIMATE CHEMICAL CHANGES FROM WOOD FIBER TO ANTHRACITE COAL +----------------------+-------+--------+-------+|Substance |Carbon |Hydrogen|Oxygen |+----------------------+-------+--------+-------+|Wood Fiber | 52. 65 | 5. 25 | 42. 10 ||Peat | 59. 57 | 5. 96 | 34. 47 ||Lignite | 66. 04 | 5. 27 | 28. 69 ||Earthy Brown Coal | 73. 18 | 5. 68 | 21. 14 ||Bituminous Coal | 75. 06 | 5. 84 | 19. 10 ||Semi-bituminous Coal | 89. 29 | 5. 05 | 5. 66 ||Anthracite Coal | 91. 58 | 3. 96 | 4. 46 |+----------------------+-------+--------+-------+ Composition of Coal--The uncombined carbon in coal is known as fixedcarbon. Some of the carbon constituent is combined with hydrogen andthis, together with other gaseous substances driven off by theapplication of heat, form that portion of the coal known as volatilematter. The fixed carbon and the volatile matter constitute thecombustible. The oxygen and nitrogen contained in the volatile matterare not combustible, but custom has applied this term to that portion ofthe coal which is dry and free from ash, thus including the oxygen andnitrogen. The other important substances entering into the composition of coal aremoisture and the refractory earths which form the ash. The ash varies indifferent coals from 3 to 30 per cent and the moisture from 0. 75 to 45per cent of the total weight of the coal, depending upon the grade andthe locality in which it is mined. A large percentage of ash isundesirable as it not only reduces the calorific value of the fuel, butchokes up the air passages in the furnace and through the fuel bed, thuspreventing the rapid combustion necessary to high efficiency. If thecoal contains an excessive quantity of sulphur, trouble will result fromits harmful action on the metal of the boiler where moisture is present, and because it unites with the ash to form a fusible slag or clinkerwhich will choke up the grate bars and form a solid mass in which largequantities of unconsumed carbon may be imbedded. Moisture in coal may be more detrimental than ash in reducing thetemperature of a furnace, as it is non-combustible, absorbs heat both inbeing evaporated and superheated to the temperature of the furnacegases. In some instances, however, a certain amount of moisture in abituminous coal produces a mechanical action that assists in thecombustion and makes it possible to develop higher capacities than withdry coal. Classification of Coal--Custom has classified coals in accordance withthe varying content of carbon and volatile matter in the combustible. Table 36 gives the approximate percentages of these constituents for thegeneral classes of coals with the corresponding heat values per pound ofcombustible. TABLE 36 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF GENERAL GRADES OF COAL ON BASIS OF COMBUSTIBLE +-------------------+----------------------------+--------------+| Kind of Coal | Per Cent of Combustible | B. T. U. || +------------+---------------+ Per Pound of || |Fixed Carbon|Volatile Matter| Combustible |+-------------------+------------+---------------+--------------+|Anthracite |97. 0 to 92. 5| 3. 0 to 7. 5 |14600 to 14800||Semi-anthracite |92. 5 to 87. 5| 7. 5 to 12. 5 |14700 to 15500||Semi-bituminous |87. 5 to 75. 0| 12. 5 to 25. 0 |15500 to 16000||Bituminous--Eastern|75. 0 to 60. 0| 25. 0 to 40. 0 |14800 to 15300||Bituminous--Western|65. 0 to 50. 0| 35. 0 to 50. 0 |13500 to 14800||Lignite | Under 50 | Over 50 |11000 to 13500|+-------------------+------------+---------------+--------------+ Anthracite--The name anthracite, or hard coal, is applied to those drycoals containing from 3 to 7 per cent volatile matter and which do notswell when burned. True anthracite is hard, compact, lustrous andsometimes iridescent, and is characterized by few joints and clefts. Itsspecific gravity varies from 1. 4 to 1. 8. In burning, it kindles slowlyand with difficulty, is hard to keep alight, and burns with a short, almost colorless flame, without smoke. Semi-anthracite coal has less density, hardness and luster than trueanthracite, and can be distinguished from it by the fact that when newlyfractured it will soot the hands. Its specific gravity is ordinarilyabout 1. 4. It kindles quite readily and burns more freely than the trueanthracites. Semi-bituminous coal is softer than anthracite, contains more volatilehydrocarbons, kindles more easily and burns more rapidly. It isordinarily free burning, has a high calorific value and is of thehighest order for steam generating purposes. Bituminous coals are still softer than those described and contain stillmore volatile hydrocarbons. The difference between the semi-bituminousand the bituminous coals is an important one, economically. The formerhave an average heating value per pound of combustible about 6 per centhigher than the latter, and they burn with much less smoke in ordinaryfurnaces. The distinctive characteristic of the bituminous coals is theemission of yellow flame and smoke when burning. In color they rangefrom pitch black to dark brown, having a resinous luster in the mostcompact specimens, and a silky luster in such specimens as show tracesof vegetable fiber. The specific gravity is ordinarily about 1. 3. Bituminous coals are either of the caking or non-caking class. Theformer, when heated, fuse and swell in size; the latter burn freely, donot fuse, and are commonly known as free burning coals. Caking coals arerich in volatile hydrocarbons and are valuable in gas manufacture. Bituminous coals absorb moisture from the atmosphere. The surfacemoisture can be removed by ordinary drying, but a portion of the watercan be removed only by heating the coal to a temperature of about 250degrees Fahrenheit. Cannel coal is a variety of bituminous coal, rich in hydrogen andhydrocarbons, and is exceedingly valuable as a gas coal. It has a dullresinous luster and burns with a bright flame without fusing. Cannelcoal is seldom used for steam coal, though it is sometimes mixed withsemi-bituminous coal where an increased economy at high rates ofcombustion is desired. The composition of cannel coal is approximatelyas follows: fixed carbon, 26 to 55 per cent; volatile matter, 42 to 64per cent; earthy matter, 2 to 14 per cent. Its specific gravity isapproximately 1. 24. Lignite is organic matter in the earlier stages of its conversion intocoal, and includes all varieties which are intermediate between peat andcoal of the older formation. Its specific gravity is low, being 1. 2 to1. 23, and when freshly mined it may contain as high as 50 per cent ofmoisture. Its appearance varies from a light brown, showing a distinctlywoody structure, in the poorer varieties, to a black, with a pitchyluster resembling hard coal, in the best varieties. It is non-caking andburns with a bright but slightly smoky flame with moderate heat. It iseasily broken, will not stand much handling in transportation, and ifexposed to the weather will rapidly disintegrate, which will increasethe difficulty of burning it. Its composition varies over wide limits. The ash may run as low as oneper cent and as high as 50 per cent. Its high content of moisture andthe large quantity of air necessary for its combustion cause large stacklosses. It is distinctly a low-grade fuel and is used almost entirely inthe districts where mined, due to its cheapness. Peat is organic matter in the first stages of its conversion into coaland is found in bogs and similar places. Its moisture content when cutis extremely high, averaging 75 or 80 per cent. It is unsuitable forfuel until dried and even then will contain as much as 30 per centmoisture. Its ash content when dry varies from 3 to 12 per cent. In thiscountry, though large deposits of peat have been found, it has not asyet been found practicable to utilize it for steam generating purposesin competition with coal. In some European countries, however, the peatindustry is common. Distribution--The anthracite coals are, with some unimportantexceptions, confined to five small fields in Eastern Pennsylvania, asshown in the following list. These fields are given in the order oftheir hardness. Lehigh or Eastern Middle Field Green Mountain District Black Creek District Hazelton District Beaver Meadow District Panther Creek District[33] Mahanoy or Western Field[34] East Mahanoy District West Mahanoy District Wyoming or Northern Field Carbondale District Scranton District Pittston District Wilkesbarre District Plymouth District Schuylkill or Southern Field East Schuylkill District West Schuylkill District Louberry District Lykens Valley or Southwestern Field Lykens Valley District Shamokin District[35] Anthracite is also found in Pulaski and Wythe Counties, Virginia; alongthe border of Little Walker Mountain, and in Gunnison County, Colorado. The areas in Virginia are limited, however, while in Colorado thequality varies greatly in neighboring beds and even in the same bed. Ananthracite bed in New Mexico was described in 1870 by Dr. R. W. Raymond, formerly United States Mining Commissioner. Semi-anthracite coals are found in a few small areas in the western partof the anthracite field. The largest of these beds is the Bernice inSullivan County, Pennsylvania. Mr. William Kent, in his "Steam BoilerEconomy", describes this as follows: "The Bernice semi-anthracite coalbasin lies between Beech Creek on the north and Loyalsock Creek on thesouth. It is six miles long, east and west, and hardly a third of a mileacross. An 8-foot vein of coal lies in a bed of 12 feet of coal andslate. The coal of this bed is the dividing line between anthracite andsemi-anthracite, and is similar to the coal of the Lykens ValleyDistrict. Mine analyses give a range as follows: moisture, 0. 65 to 1. 97;volatile matter, 3. 56 to 9. 40; fixed carbon, 82. 52 to 89. 39; ash, 3. 27to 9. 34; sulphur, 0. 24 to 1. 04. " Semi-bituminous coals are found on the eastern edge of the greatAppalachian Field. Starting with Tioga and Bradford Counties of northernPennsylvania, the bed runs southwest through Lycoming, Clearfield, Centre, Huntingdon, Cambria, Somerset and Fulton Counties, Pennsylvania;Allegheny County, Maryland; Buchannan, Dickinson, Lee, Russell, Scott, Tazewell and Wise Counties, Virginia; Mercer, McDowell, Fayette, Raleighand Mineral Counties, West Virginia; and ending in northeasternTennessee, where a small amount of semi-bituminous is mined. The largest of the bituminous fields is the Appalachian. Beginning nearthe northern boundary of Pennsylvania, in the western portion of theState, it extends southwestward through West Virginia, touching Marylandand Virginia on their western borders, passing through southeasternOhio, eastern Kentucky and central Tennessee, and ending in westernAlabama, 900 miles from its northern extremity. The next bituminous coal producing region to the west is the NorthernField, in north central Michigan. Still further to the west, and secondin importance to the Appalachian Field, is the Eastern Interior Field. This covers, with the exception of the upper northern portion, nearlythe entire State of Illinois, southwest Indiana and the western portionof Kentucky. The Western Field extends through central and southern Iowa, westernMissouri, southwestern Kansas, eastern Oklahoma and the west centralportion of Arkansas. The Southwestern Field is confined entirely to thenorth central portion of Texas, in which State there are also two smallisolated fields along the Rio Grande River. The remaining bituminous fields are scattered through what may be termedthe Rocky Mountain Region, extending from Montana to New Orleans. Apartial list of these fields and their location follows: Judith Basin Central MontanaBull Mountain Field Central MontanaYellowstone Region Southwestern MontanaBig Horn Basin Region Southern MontanaBig Horn Basin Region Northern WyomingBlack Hills Region Northeastern WyomingHanna Field Southern WyomingGreen River Region Southwestern WyomingYampa Field Northwestern ColoradoNorth Park Field Northern ColoradoDenver Region North Central ColoradoUinta Region Western ColoradoUinta Region Eastern UtahSouthwestern Region Southwestern UtahRaton Mountain Region Southern ColoradoRaton Mountain Region Northern New MexicoSan Juan River Region Northwestern New MexicoCapitan Field Southern New Mexico Along the Pacific Coast a few small fields are scattered in westernCalifornia, southwestern Oregon, western and northwestern Washington. Most of the coals in the above fields are on the border line betweenbituminous and lignite. They are really a low grade of bituminous coaland are known as sub-bituminous or black lignites. Lignites--These resemble the brown coals of Europe and are found in thewestern states, Wyoming, New Mexico, Arizona, Utah, Montana, NorthDakota, Nevada, California, Oregon and Washington. Many of the fieldsgiven as those containing bituminous coals in the western states alsocontain true lignite. Lignite is also found in the eastern part of Texasand in Oklahoma. Alaska Coals--Coal has been found in Alaska and undoubtedly is of greatvalue, though the extent and character of the fields have probably beenexaggerated. Great quantities of lignite are known to exist, and inquality the coal ranges in character from lignite to anthracite. Thereare at present, however, only two fields of high-grade coals known, these being the Bering River Field, near Controllers Bay, and theMatanuska Field, at the head of Cooks Inlet. Both of these fields areknown to contain both anthracite and high-grade bituminous coals, thoughas yet they cannot be said to have been opened up. Weathering of Coal--The storage of coal has become within the last fewyears to a certain extent a necessity due to market conditions, dangerof labor difficulties at the mines and in the railroads, and thecrowding of transportation facilities. The first cause is probably themost important, and this is particularly true of anthracite coals wherea sliding scale of prices is used according to the season of the year. While market conditions serve as one of the principal reasons for coalstorage, most power plants and manufacturing plants feel compelled toprotect their coal supply from the danger of strikes, car shortages andthe like, and it is customary for large power plants, railroads and coalcompanies themselves, to store bituminous coal. Naval coaling stationsare also an example of what is done along these lines. Anthracite is the nearest approach to the ideal coal for storing. It isnot subject to spontaneous ignition, and for this reason is unlimited inthe amount that may be stored in one pile. With bituminous coals, however, the case is different. Most bituminous coals will ignite ifplaced in large enough piles and all suffer more or less fromdisintegration. Coal producers only store such coals as are least liableto ignite, and which will stand rehandling for shipment. The changes which take place in stored coal are of two kinds: 1st, theoxidization of the inorganic matter such as pyrites; and 2nd, the directoxidization of the organic matter of the actual coal. The first change will result in an increased volume of the coal, andsometimes in an increased weight, and a marked disintegration. Thechanges due to direct oxidization of the coal substances usually cannotbe detected by the eye, but as they involve the oxidization of thecarbon and available hydrogen and the absorption of the oxygen byunsaturated hydrocarbons, they are the chief cause of the weatheringlosses in heat value. Numerous experiments have led to the conclusionthat this is also the cause for spontaneous combustion. Experiments to show loss in calorific heat values due to weatheringindicate that such loss may be as high as 10 per cent when the coal isstored in the air, and 8. 75 per cent when stored under water. It wouldappear that the higher the volatile content of the coal, the greaterwill be the loss in calorific value and the more subject to spontaneousignition. Some experiments made by Messrs. S. W. Parr and W. F. Wheeler, publishedin 1909 by the Experiment Station of the University of Illinois, indicate that coals of the nature found in Illinois and neighboringstates are not affected seriously during storage from the standpoint ofweight and heating value, the latter loss averaging about 3½ per centfor the first year of storage. They found that the losses due todisintegration and to spontaneous ignition were of greater importance. Their conclusions agree with those deduced from the other experiments, viz. , that the storing of a larger size coal than that which is to beused, will overcome to a certain extent the objection to disintegration, and that the larger sizes, besides being advantageous in respect todisintegration, are less liable to spontaneous ignition. Storage underwater will, of course, entirely prevent any fire loss and, to a greatextent, will stop disintegration and reduce the calorific losses to aminimum. To minimize the danger of spontaneous ignition in storing coal, thepiles should be thoroughly ventilated. Pulverized Fuels--Considerable experimental work has been done withpulverized coal, utilizing either coal dust or pulverizing such coal asis too small to be burned in other ways. If satisfactorily fed to thefurnace, it would appear to have several advantages. The dust burned insuspension would be more completely consumed than is the case with thesolid coals, the production of smoke would be minimized, and the processwould admit of an adjustment of the air supply to a point very close tothe amount theoretically required. This is due to the fact that inburning there is an intimate mixture of the air and fuel. The principalobjections have been in the inability to introduce the pulverized fuelinto the furnace uniformly, the difficulty of reducing the fuel to thesame degree of fineness, liability of explosion in the furnace due toimproper mixture with the air, and the decreased capacity and efficiencyresulting from the difficulty of keeping tube surfaces clean. Pressed Fuels--In this class are those composed of the dust of somesuitable combustible, pressed and cemented together by a substancepossessing binding and in most cases inflammable properties. Such fuels, known as briquettes, are extensively used in foreign countries andconsist of carbon or soft coal, too small to be burned in the ordinaryway, mixed usually with pitch or coal tar. Much experimenting has beendone in this country in briquetting fuels, the government having takenan active interest in the question, but as yet this class of fuel hasnot come into common use as the cost and difficulty of manufacture andhandling have made it impossible to place it in the market at a price tosuccessfully compete with coal. Coke is a porous product consisting almost entirely of carbon remainingafter certain manufacturing processes have distilled off the hydrocarbongases of the fuel used. It is produced, first, from gas coal distilledin gas retorts; second, from gas or ordinary bituminous coals burned inspecial furnaces called coke ovens; and third, from petroleum bycarrying the distillation of the residuum to a red heat. Coke is a smokeless fuel. It readily absorbs moisture from theatmosphere and if not kept under cover its moisture content may be asmuch as 20 per cent of its own weight. Gas-house coke is generally softer and more porous than oven coke, ignites more readily, and requires less draft for its combustion. [Illustration: 16, 000 Horse-power Installation of Babcock & WilcoxBoilers and Superheaters at the Brunot's Island Plant of the DuquesneLight Co. , Pittsburgh, Pa. ] THE DETERMINATION OF HEATING VALUES OF FUELS The heating value of a fuel may be determined either by a calculationfrom a chemical analysis or by burning a sample in a calorimeter. In the former method the calculation should be based on an ultimateanalysis, which reduces the fuel to its elementary constituents ofcarbon, hydrogen, oxygen, nitrogen, sulphur, ash and moisture, to securea reasonable degree of accuracy. A proximate analysis, which determinesonly the percentage of moisture, fixed carbon, volatile matter and ash, without determining the ultimate composition of the volatile matter, cannot be used for computing the heat of combustion with the same degreeof accuracy as an ultimate analysis, but estimates may be based on theultimate analysis that are fairly correct. An ultimate analysis requires the services of a competent chemist, andthe methods to be employed in such a determination will be found in anystandard book on engineering chemistry. An ultimate analysis, whileresolving the fuel into its elementary constituents, does not reveal howthese may have been combined in the fuel. The manner of theircombination undoubtedly has a direct effect upon their calorific value, as fuels having almost identical ultimate analyses show a difference inheating value when tested in a calorimeter. Such a difference, however, is slight, and very close approximations may be computed from theultimate analysis. Ultimate analyses are given on both a moist and a dry fuel basis. Inasmuch as the latter is the basis generally accepted for thecomparison of data, it would appear that it is the best basis on whichto report such an analysis. When an analysis is given on a moist fuelbasis it may be readily converted to a dry basis by dividing thepercentages of the various constituents by one minus the percentage ofmoisture, reporting the moisture content separately. _Moist Fuel_ _Dry Fuel_ C 83. 95 84. 45H 4. 23 4. 25O 3. 02 3. 04N 1. 27 1. 28S . 91 . 91Ash 6. 03 6. 07 ------ 100. 00 Moisture . 59 . 59 ------ 100. 00 Calculations from an Ultimate Analysis--The first formula for thecalculation of heating values from the composition of a fuel asdetermined from an ultimate analysis is due to Dulong, and this formula, slightly modified, is the most commonly used to-day. Other formulae havebeen proposed, some of which are more accurate for certain specificclasses of fuel, but all have their basis in Dulong's formula, theaccepted modified form of which is: Heat units in B. T. U. Per pound of dry fuel = O14, 600 C + 62, 000(H - -) + 4000 S (18) 8 where C, H, O and S are the proportionate parts by weight of carbon, hydrogen, oxygen and sulphur. Assume a coal of the composition given. Substituting in this formula(18), Heating value per pound of dry coal ( . 0304)= 14, 600 × . 8445 + 62, 000 (. 0425 - -----) + 4000 × . 0091 = 14, 765 B. T. U. ( 8 ) This coal, by a calorimetric test, showed 14, 843 B. T. U. , and from acomparison the degree of accuracy of the formula will be noted. The investigation of Lord and Haas in this country, Mabler in France, and Bunte in Germany, all show that Dulong's formula gives resultsnearly identical with those obtained from calorimetric tests and may besafely applied to all solid fuels except cannel coal, lignite, turf andwood, provided the ultimate analysis is correct. This practically limitsits use to coal. The limiting features are the presence of hydrogen andcarbon united in the form of hydrocarbons. Such hydrocarbons are presentin coals in small quantities, but they have positive and negative heatsof combination, and in coals these appear to offset each other, certainly sufficiently to apply the formula to such fuels. High and Low Heat Value of Fuels--In any fuel containing hydrogen thecalorific value as found by the calorimeter is higher than thatobtainable under most working conditions in boiler practice by an amountequal to the latent heat of the volatilization of water. This heat wouldreappear when the vapor was condensed, though in ordinary practice thevapor passes away uncondensed. This fact gives rise to a distinction inheat values into the so-called "higher" and "lower" calorific values. The higher value, _i. E. _, the one determined by the calorimeter, is theonly scientific unit, is the value which should be used in boilertesting work, and is the one recommended by the American Society ofMechanical Engineers. There is no absolute measure of the lower heat of combustion, and inview of the wide difference in opinion among physicists as to thedeductions to be made from the higher or absolute unit in thisdetermination, the lower value must be considered an artificial unit. The lower value entails the use of an ultimate analysis and involvesassumptions that would make the employment of such a unit impracticablefor commercial work. The use of the low value may also lead to error andis in no way to be recommended for boiler practice. An example of its illogical use may be shown by the consideration of aboiler operated in connection with a special economizer where the vaporproduced by hydrogen is partially condensed by the economizer. If thelow value were used in computing the boiler efficiency, it is obviousthat the total efficiency of the combined boiler and economizer must bein error through crediting the combination with the heat imparted incondensing the vapor and not charging such heat to the heat value of thecoal. Heating Value of Gaseous Fuels--The method of computing calorific valuesfrom an ultimate analysis is particularly adapted to solid fuels, withthe exceptions already noted. The heating value of gaseous fuels may becalculated by Dulong's formula provided another term is added to providefor any carbon monoxide present. Such a method, however, involves theseparating of the constituent gases into their elementary gases, whichis oftentimes difficult and liable to simple arithmetical error. As thecombustible portion of gaseous fuels is ordinarily composed of hydrogen, carbon monoxide and certain hydrocarbons, a determination of thecalorific value is much more readily obtained by a separation into theirconstituent gases and a computation of the calorific value from a tableof such values of the constituents. Table 37 gives the calorific valueof the more common combustible gases, together with the theoreticalamount of air required for their combustion. TABLE 37 WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION +---------------+----------+------+-----+------+----------+-----------+| Gas | Symbol |Cubic |B. T. U|B. T. U. |Cubic Feet|Cubic Feet || | | Feet | per | per | of Air | of Air || | |of Gas|Pound|Cubic | Required | Required || | | per | | Foot |per Pound | Per Cubic || | |Pound | | | of Gas |Foot of Gas|+---------------+----------+------+-----+------+----------+-----------+|Hydrogen | H |177. 90|62000| 349 | 428. 25 | 2. 41 ||Carbon Monoxide| CO | 12. 81| 4450| 347 | 30. 60 | 2. 39 ||Methane |CH_{4} | 22. 37|23550| 1053 | 214. 00 | 9. 57 ||Acetylene |C_{2}H_{2}| 13. 79|21465| 1556 | 164. 87 | 11. 93 ||Olefiant Gas |C_{2}H_{4}| 12. 80|21440| 1675 | 183. 60 | 14. 33 ||Ethane |C_{2}H_{6}| 11. 94|22230| 1862 | 199. 88 | 16. 74 |+---------------+----------+------+-----+------+----------+-----------+ In applying this table, as gas analyses may be reported either by weightor volume, there is given in Table 33[36] a method of changing fromvolumetric analysis to analysis by weight. Examples: 1st. Assume a blast furnace gas, the analysis of which in percentages byweight is, oxygen = 2. 7, carbon monoxide = 19. 5, carbon dioxide = 18. 7, nitrogen = 59. 1. Here the only combustible gas is the carbon monoxide, and the heat value will be, 0. 195 × 4450 = 867. 75 B. T. U. Per pound. The _net_ volume of air required to burn one pound of this gas will be, 0. 195 × 30. 6 = 5. 967 cubic feet. 2nd. Assume a natural gas, the analysis of which in percentages byvolume is oxygen = 0. 40, carbon monoxide = 0. 95, carbon dioxide = 0. 34, olefiant gas (C_{2}H_{4}) = 0. 66, ethane (C_{2}H_{6}) = 3. 55, marsh gas(CH_{4}) = 72. 15 and hydrogen = 21. 95. All but the oxygen and the carbondioxide are combustibles, and the heat per cubic foot will be, From CO = 0. 0095 × 347 = 3. 30 C_{2}H_{4} = 0. 0066 × 1675 = 11. 05 C_{2}H_{6} = 0. 0355 × 1862 = 66. 10 CH_{4} = 0. 7215 × 1050 = 757. 58 H = 0. 2195 × 349 = 76. 61 ------ B. T. U. Per cubic foot 914. 64 The _net_ air required for combustion of one cubic foot of the gas willbe, CO = 0. 0095 × 2. 39 = 0. 02C_{2}H_{4} = 0. 0066 × 14. 33 = 0. 09C_{2}H_{6} = 0. 0355 × 16. 74 = 0. 59CH_{4} = 0. 7215 × 9. 57 = 6. 90H = 0. 2195 × 2. 41 = 0. 53 ---- Total net air per cubic foot 8. 13 Proximate Analysis--The proximate analysis of a fuel gives itsproportions by weight of fixed carbon, volatile combustible matter, moisture and ash. A method of making such an analysis which has beenfound to give eminently satisfactory results is described below. From the coal sample obtained on the boiler trial, an average sample ofapproximately 40 grams is broken up and weighed. A good means ofreducing such a sample is passing it through an ordinary coffee mill. This sample should be placed in a double-walled air bath, which shouldbe kept at an approximately constant temperature of 105 degreescentigrade, the sample being weighed at intervals until a minimum isreached. The percentage of moisture can be calculated from the loss insuch a drying. For the determination of the remainder of the analysis, and the heatingvalue of the fuel, a portion of this dried sample should be thoroughlypulverized, and if it is to be kept, should be placed in an air-tightreceptacle. One gram of the pulverized sample should be weighed into aporcelain crucible equipped with a well fitting lid. This crucibleshould be supported on a platinum triangle and heated for seven minutesover the full flame of a Bunsen burner. At the end of such time thesample should be placed in a desiccator containing calcium chloride, andwhen cooled should be weighed. From the loss the percentage of volatilecombustible matter may be readily calculated. The same sample from which the volatile matter has been driven should beused in the determination of the percentage of ash. This percentage isobtained by burning the fixed carbon over a Bunsen burner or in a mufflefurnace. The burning should be kept up until a constant weight issecured, and it may be assisted by stirring with a platinum rod. Theweight of the residue determines the percentage of ash, and thepercentage of fixed carbon is easily calculated from the loss during thedetermination of ash after the volatile matter has been driven off. Proximate analyses may be made and reported on a moist or dry basis. Thedry basis is that ordinarily accepted, and this is the basis adoptedthroughout this book. The method of converting from a moist to a drybasis is the same as described in the case of an ultimate analysis. Aproximate analysis is easily made, gives information as to the generalcharacteristics of a fuel and of its _relative_ heating value. Table 38 gives the proximate analysis and calorific value of a number ofrepresentative coals found in the United States. TABLE 38 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN COALS ____________________________________________________________________________ | | | | | | | | | | | |No. | State | County | Field, Bed | Mine | Size | | | | or Vein | | | | | | | | | | | | | | |____|_______|________________|________________|_______________|_____________| | | | | | | ANTHRACITES | |____|_______|_________________________________________________|_____________| | | | | | | 1 | Pa. | Carbon | Lehigh | Beaver Meadow | | 2 | Pa. | Dauphin | Schuylkill | | Buckwheat | 3 | Pa. | Lackawanna | Wyoming | Belleview | No. 2 Buck. | 4 | Pa. | Lackawanna | Wyoming | Johnson | Culm. | 5 | Pa. | Luzerne | Wyoming | Pittston | No. 2 Buck. | 6 | Pa. | Luzerne | Wyoming | Mammoth | Large | 7 | Pa. | Luzerne | Wyoming | Exeter | Rice | 8 | Pa. | Northumberland | Schuylkill | Treverton | | 9 | Pa. | Schuylkill | Schuylkill | Buck Mountain | | 10 | Pa. | Schuylkill | | York Farm | Buckwheat | 11 | Pa. | | | Victoria | Buckwheat | 12 | Pa. | Carbon | Lehigh | Lehigh & | Buck. & Pea | | | | | Wilkes C. Co. | | 13 | Pa. | Carbon | Lehigh | | Buckwheat | 14 | Pa. | Lackawanna | |Del. & Hud. Co. | No. 1 Buck. |____|_______|________________|________________|_______________|_____________| | | | | | | SEMI-ANTHRACITES | |____|_______|_________________________________________________|_____________| | | | | | | 15 | Pa. | Lycoming | Loyalsock | | | 16 | Pa. | Sullivan | | Lopez | | 17 | Pa. | Sullivan | Bernice | | |____|_______|________________|________________|_______________|_____________| | | | | | | SEMI-BITUMINOUS | |____|_______|_________________________________________________|_____________| | | | | | | 18 | Md. | Alleghany | Big Vein, | | | | | | George's Crk. | | | 19 | Md. | Alleghany | George's Creek | | | 20 | Md. | Alleghany | George's Creek | | | 21 | Md. | Alleghany | George's Creek | Ocean No. 7 | Mine run | 22 | Md. | Alleghany | Cumberland | | | 23 | Md. | Garrett | | Washington | Mine run | | | | | No. 3 | | 24 | Pa. | Bradford | | Long Valley | | 25 | Pa. | Tioga | | Antrim | | 26 | Pa. | Cambria | "B" or Miller | Soriman Shaft | | | | | | C. Co. | | 27 | Pa. | Cambria | "B" or Miller | Henrietta | | 28 | Pa. | Cambria | "B" or Miller | Penker | | 29 | Pa. | Cambria | "B" or Miller | Lancashire | | 30 | Pa. | Cambria | Lower | Penn. C. & C. | Mine run | | | | Kittanning | Co. No. 3 | | 31 | Pa. | Cambria | Upper | Valley | Mine run | | | | Kittanning | | | 32 | Pa. | Clearfield | Lower | Eureka | Mine run | | | | Kittanning | | | 33 | Pa. | Clearfield | | Ghem | Mine run | 34 | Pa. | Clearfield | | Osceola | | 35 | Pa. | Clearfield | Reynoldsville | | | 36 | Pa. | Clearfield | Atlantic- | | Mine run | | | | Clearfield | | | 37 | Pa. | Huntington | Barnet & Fulton| Carbon | Mine run | 38 | Pa. | Huntington | | Rock Hill | Mine run | 39 | Pa. | Somerset | Lower | Kimmelton | Mine run | | | | Kittanning | | | 40 | Pa. | Somerset | "C" Prime Vein | Jenner | Mine run |____|_______|________________|________________|_______________|_____________| _____________________________________________________________________ | | | | | Proximate Analysis (Dry Coal) |B. T. U. | |No. |________________________________________| Per | | | | | | | Pound | Authority | | Moisture | Volatile | Fixed | Ash | Dry | | | | Matter | Carbon | | Coal | |____|__________|__________|________|_________|________|______________| | | | | | | | | | | | | | |____|__________|__________|________|_________|________|______________| | | | | | | | 1 | 1. 50 | 2. 41 | 90. 30 | 7. 29 | | Gale | 2 | 2. 15 | 12. 88 | 78. 23 | 8. 89 | 13137 | Whitham | 3 | 8. 29 | 7. 81 | 77. 19 | 15. 00 | 12341 | Sadtler | 4 | 13. 90 | 11. 16 | 65. 96 | 22. 88 | 10591 | B. & W. Co. | 5 | 3. 66 | 4. 40 | 78. 96 | 16. 64 | 12865 | B. & W. Co. | 6 | 4. 00 | 3. 44 | 90. 59 | 5. 97 | 13720 | Carpenter | 7 | 0. 25 | 8. 18 | 79. 61 | 12. 21 | 12400 | B. & W. Co. | 8 | 0. 84 | 6. 73 | 86. 39 | 6. 88 | | Isherwood | 9 | | 3. 17 | 92. 41 | 4. 42 | 14220 | Carpenter | 10 | 0. 81 | 5. 51 | 75. 90 | 18. 59 | 11430 | | 11 | 4. 30 | 0. 55 | 86. 73 | 12. 72 | 12642 | B. & W. Co. | 12 | 1. 57 | 6. 27 | 66. 53 | 27. 20 | 12848 | B. & W. Co. | | | | | | | | 13 | | 5. 00 | 81. 00 | 14. 00 | 11800 | Carpenter | 14 | 6. 20 | | | 11. 60 | 12100 | Denton |____|__________|__________|________|_________|________|______________| | | | | | | | | | | | | | |____|__________|__________|________|_________|________|______________| | | | | | | | 15 | 1. 30 | 8. 72 | 84. 44 | 6. 84 | | | 16 | 5. 48 | 7. 53 | 81. 00 | 11. 47 | 13547 | B. & W. Co. | 17 | 1. 29 | 8. 21 | 84. 43 | 7. 36 | | |____|__________|__________|________|_________|________|______________| | | | | | | | | | | | | | |____|__________|__________|________|_________|________|______________| | | | | | | | 18 | 3. 50 | 21. 33 | 72. 47 | 6. 20 | 14682 | B. & W. Co. | | | | | | | | 19 | 3. 63 | 16. 27 | 76. 93 | 6. 80 | 14695 | B. & W. Co. | 20 | 2. 28 | 19. 43 | 77. 44 | 6. 13 | 14793 | B. & W. Co. | 21 | 1. 13 | | | | 14451 | B. & W. Co. | 22 | 1. 50 | 17. 26 | 76. 65 | 6. 09 | 14700 | | 23 | 2. 33 | 14. 38 | 74. 93 | 10. 49 | 14033 | U. S. Geo. S. | | | | | | | [37] | 24 | 1. 55 | 20. 33 | 68. 38 | 11. 29 | 12965 | | 25 | 2. 19 | 18. 43 | 71. 87 | 9. 70 | 13500 | | 26 | 3. 40 | 20. 70 | 71. 84 | 7. 46 | 14484 | N. Y. Ed. Co. | | | | | | | | 27 | 1. 23 | 18. 37 | 75. 28 | 6. 45 | 14770 | So. Eng. Co. | 28 | 3. 64 | 21. 34 | 70. 48 | 8. 18 | 14401 | B. & W. Co. | 29 | 4. 38 | 21. 20 | 70. 27 | 8. 53 | 14453 | B. & W. Co. | 30 | 3. 51 | 17. 43 | 75. 69 | 6. 88 | 14279 | U. S. Geo. S. | | | | | | | | 31 | 3. 40 | 14. 89 | 75. 03 | 10. 08 | 14152 | B. & W. Co. | | | | | | | | 32 | 5. 90 | 16. 71 | 77. 22 | 6. 07 | 14843 | U. S. Geo. S. | | | | | | | | 33 | 3. 43 | 17. 53 | 69. 67 | 12. 80 | 13744 | B. & W. Co. | 34 | 1. 24 | 25. 43 | 68. 56 | 6. 01 | 13589 | B. & W. Co. | 35 | 2. 91 | 21. 55 | 69. 03 | 9. 42 | 14685 | B. & W. Co. | 36 | 1. 55 | 23. 36 | 71. 15 | 5. 94 | 13963 | Whitham | | | | | | | | 37 | 4. 50 | 18. 34 | 73. 06 | 8. 60 | 13770 | B. & W. Co. | 38 | 5. 91 | 17. 58 | 73. 44 | 8. 99 | 14105 | B. & W. Co. | 39 | 3. 09 | 17. 84 | 70. 47 | 11. 69 | 13424 | U. S. Geo. S. | | | | | | | | 40 | 9. 37 | 16. 47 | 75. 76 | 7. 77 | 14507 | P. R. R. |____|__________|__________|________|_________|________|______________| APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICANCOALS--Continued ____________________________________________________________________________ | | | | | | | | | | | |No. | State | County | Field, Bed | Mine | Size | | | | or Vein | | | | | | | | | | | | | | |____|_______|________________|________________|_______________|_____________| | | | | | | 41 | W. Va. | Fayette | New River | Rush Run | Mine run | 42 | W. Va. | Fayette | New River | Loup Creek | | 43 | W. Va. | Fayette | New River | | Slack | 44 | W. Va. | Fayette | New River | | Mine run | 45 | W. Va. | Fayette | New River | Rush Run | Mine run | 46 | W. Va. | McDowell | Pocahontas | Zenith | Mine run | | | | No. 3 | | | 47 | W. Va. | McDowell | Tug River | Big Sandy | Mine run | 48 | W. Va. | Mercer | Pocahontas | Mora | Lump | 49 | W. Va. | Mineral | Elk Garden | | | 50 | W. Va. | McDowell | Pocahontas | Flat Top | Mine run | 51 | W. Va. | McDowell | Pocahontas | Flat Top | Slack | 52 | W. Va. | McDowell | Pocahontas | Flat Top | Lump |____|_______|________________|________________|_______________|_____________| | | | | | | BITUMINOUS | |____|_______|_________________________________________________|_____________| | | | | | | 53 | Ala. | Bibb | Cahaba | Hill Creek | Mine run | 54 | Ala. | Jefferson | Pratt | Pratt No. 13 | | 55 | Ala. | Jefferson | Pratt | Warner | Mine run | 56 | Ala. | Jefferson | | Coalburg | Mine run | 57 | Ala. | Walker | Horse Creek | Ivy C. & I. | Nut | | | | | Co. No. 8 | | 58 | Ala. | Walker | Jagger | Galloway C. | Mine run | | | | | Co. No. 5 | | 59 | Ark. | Franklin | Denning | Western No. 4 | Nut | 60 | Ark. | Sebastian | Jenny Lind | Mine No. 12 | Lump | 61 | Ark. | Sebastian | Huntington | Cherokee | Mine run | 62 | Col. | Boulder | South Platte | Lafayette | Mine run | 63 | Col. | Boulder | Laramie | Simson | Mine run | 64 | Col. | Fremont | Canon City | Chandler | Nut and | | | | | | Slack | 65 | Col. | Las Animas | Trinidad | Hastings | Nut | 66 | Col. | Las Animas | Trinidad | Moreley | Slack | 67 | Col. | Routt | Yampa | Oak Creek | | 68 | Ill. | Christian | Pana | Penwell Col. | Lump | 69 | Ill. | Franklin | No. 6 | Benton | Egg | 70 | Ill. | Franklin | Big Muddy | Zeigler | ¾ inch | 71 | Ill. | Jackson | Big Muddy | | | 72 | Ill. | La Salle | Streator | | | 73 | Ill. | La Salle | Streator | Marseilles | Mine run | 74 | Ill. | Macoupin | Nilwood | Mine No. 2 | Screenings | 75 | Ill. | Macoupin | Mt. Olive | Mine No. 2 | Mine run | 76 | Ill. | Madison | Belleville | Donk Bros. | Lump | 77 | Ill. | Madison | Glen Carbon | | Mine run | 78 | Ill. | Marion | | Odin | Lump | 79 | Ill. | Mercer | Gilchrist | | Screenings | 80 | Ill. | Montgomery | Pana or No. 5 | Coffeen | Mine run | 81 | Ill. | Peoria | No. 5 | Empire | | 82 | Ill. | Perry | Du Quoin | Number 1 | Screenings |____|_______|________________|________________|_______________|_____________| APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICANCOALS--Continued _____________________________________________________________________ | | | | | Proximate Analysis (Dry Coal) |B. T. U. | |No. |________________________________________| Per | | | | | | | Pound | Authority | | Moisture | Volatile | Fixed | Ash | Dry | | | | Matter | Carbon | | Coal | |____|__________|__________|________|_________|________|______________| | | | | | | | 41 | 2. 14 | 22. 87 | 71. 56 | 5. 57 | 14959 | U. S. Geo. S. | 42 | 0. 55 | 19. 36 | 78. 48 | 2. 16 | 14975 | Hill | 43 | 6. 66 | 20. 94 | 73. 16 | 5. 90 | 14412 | B. & W. Co. | 44 | 2. 16 | 17. 82 | 75. 66 | 6. 52 | 14786 | B. & W. Co. | 45 | 0. 94 | 22. 16 | 75. 85 | 1. 99 | 15007 | B. & W. Co. | 46 | 4. 85 | 17. 14 | 76. 54 | 6. 32 | 14480 | U. S. Geo. S. | | | | | | | | 47 | 1. 58 | 18. 55 | 76. 44 | 4. 91 | 15170 | U. S. Geo. S. | 48 | 1. 74 | 18. 55 | 75. 15 | 6. 30 | 15015 | U. S. Geo. S. | 49 | 2. 10 | 15. 70 | 75. 40 | 8. 90 | 14195 | B. & W. Co. | 50 | 0. 52 | 24. 02 | 74. 59 | 1. 39 | 14490 | B. & W. Co. | 51 | 3. 24 | 15. 33 | 77. 60 | 7. 07 | 14653 | B. & W. Co. | 52 | 3. 63 | 16. 03 | 78. 04 | 5. 93 | 14956 | B. & W. Co. |____|__________|__________|________|_________|________|______________| | | | | | | | | | | | | | |____|__________|__________|________|_________|________|______________| | | | | | | | 53 | 6. 19 | 28. 58 | 55. 60 | 15. 82 | 12576 | B. & W. Co. | 54 | 4. 29 | 25. 78 | 67. 68 | 6. 54 | 14482 | B. & W. Co. | 55 | 2. 51 | 27. 80 | 61. 50 | 10. 70 | 13628 | U. S. Geo. S. | 56 | 0. 94 | 31. 34 | 65. 65 | 3. 01 | 14513 | B. & W. Co. | 57 | 2. 56 | 31. 82 | 53. 89 | 14. 29 | 12937 | U. S. Geo. S. | | | | | | | | 58 | 4. 83 | 34. 65 | 51. 12 | 14. 03 | 12976 | U. S. Geo. S. | | | | | | | | 59 | 2. 22 | 12. 83 | 75. 35 | 11. 82 | | U. S. Geo. S. | 60 | 1. 07 | 17. 04 | 74. 45 | 8. 51 | 14252 | U. S. Geo. S. | 61 | 0. 97 | 19. 87 | 70. 30 | 9. 83 | 14159 | U. S. Geo. S. | 62 | 19. 48 | 38. 80 | 49. 00 | 12. 20 | 11939 | B. & W. Co. | 63 | 19. 78 | 44. 69 | 48. 62 | 6. 69 | 12577 | U. S. Geo. S. | 64 | 9. 37 | 38. 10 | 51. 75 | 10. 15 | 11850 | B. & W. Co. | | | | | | | | 65 | 2. 15 | 31. 07 | 53. 40 | 15. 53 | 12547 | B. & W. Co. | 66 | 1. 88 | 28. 47 | 55. 58 | 15. 95 | 12703 | B. & W. Co. | 67 | 6. 67 | 42. 91 | 55. 64 | 1. 45 | | Hill | 68 | 8. 05 | 43. 67 | 49. 97 | 6. 36 | 10900 | Jones | 69 | 8. 31 | 34. 52 | 54. 05 | 11. 43 | 11727 | U. S. Geo. S. | 70 | 13. 28 | 31. 97 | 57. 37 | 10. 66 | 12857 | U. S. Geo. S. | 71 | 4. 85 | 31. 55 | 62. 19 | 6. 26 | 11466 | Breckenridge | 72 | 8. 40 | 41. 76 | 51. 42 | 6. 82 | 11727 | Breckenridge | 73 | 12. 98 | 43. 73 | 49. 13 | 7. 14 | 10899 | B. & W. Co. | 74 | 13. 34 | 34. 75 | 44. 55 | 20. 70 | 10781 | B. & W. Co. | 75 | 13. 54 | 41. 28 | 46. 30 | 12. 42 | 10807 | U. S. Geo. S. | 76 | 13. 47 | 38. 69 | 48. 07 | 13. 24 | 12427 | U. S. Geo. S. | 77 | 9. 78 | 38. 18 | 51. 52 | 10. 30 | 11672 | Bryan | 78 | 6. 20 | 42. 91 | 49. 06 | 8. 03 | 11880 | Breckenridge | 79 | 8. 50 | 36. 17 | 41. 64 | 22. 19 | 10497 | Breckenridge | 80 | 11. 93 | 34. 05 | 49. 85 | 16. 10 | 10303 | U. S. Geo. S. | 81 | 17. 64 | 31. 91 | 46. 17 | 21. 92 | 10705 | B. & W. Co. | 82 | 9. 81 | 33. 67 | 48. 36 | 17. 97 | 11229 | B. & W. Co. |____|__________|__________|________|_________|________|______________| APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICANCOALS--Continued ____________________________________________________________________________ | | | | | | | | | | | |No. | State | County | Field, Bed | Mine | Size | | | | or Vein | | | | | | | | | | | | | | | |_______|________________|________________|_______________|_____________| | | | | | | 83 | Ill. | Perry | Du Quoin | Willis | Mine run | 84 | Ill. | Sangamon | | Pawnee | Slack | 85 | Ill. | St. Clair | Standard | Nigger Hollow | Mine run | 86 | Ill. | St. Clair | Standard | Maryville | Mine run | 87 | Ill. | Williamson | Big Muddy | Daws | Mine run | 88 | Ill. | Williamson | Carterville | Carterville | | | | | or No. 7 | | | 89 | Ill. | Williamson | Carterville | Burr | Nut, Pea | | | | or No. 7 | | and Slack | 90 | Ind. | Brazil | Brazil | Gartside | Block | 91 | Ind. | Clay | | Louise | Block | 92 | Ind. | Green | Island City | | Mine run | 93 | Ind. | Knox | Vein No. 5 | Tecumseh | Mine run | 94 | Ind. | Parke | Vein No. 6 | Parke Coal Co. | Lump | 95 | Ind. | Sullivan | Sullivan No. 6 | Mildred | Washed | 96 | Ind. | Vigo | Number 6 | Fontanet | Mine run | 97 | Ind. | Vigo | Number 7 | Red Bird | Mine run | 98 | Iowa | Appanoose | Mystic | Mine No. 3 | Lump | 99 | Iowa | Lucas | Lucas | Inland No. 1 | Mine run |100 | Iowa | Marion | Big Vein | Liberty No. 5 | Mine run |101 | Iowa | Polk | Third Seam | Altoona No. 4 | Lump |102 | Iowa | Wapello | Wapello | | Lump |103 | Kan. | Cherokee | Weir Pittsburgh| Southwestern | Lump | | | | | Dev. Co. | |104 | Kan. | Cherokee | Cherokee | | Screenings |105 | Kan. | Cherokee | Cherokee | | Lump |106 | Kan. | Linn | Boicourt | | Lump |107 | Ky. | Bell | Straight Creek | Str. Ck. C. & | Mine run | | | | | C. Co. | |108 | Ky. | Hopkins | Bed No. 9 | Earlington | Lump |109 | Ky. | Hopkins | Bed No. 9 | Barnsley | Mine run |110 | Ky. | Hopkins | Vein No. 14 | Nebo |Pea and Slack|111 | Ky. | Johnson | Vein No. 1 | Miller's Creek| Mine run |112 | Ky. | Mulenburg | Bed No. 9 | Pierce |Pea and Slack|113 | Ky. | Pulaski | | Greensburg | |114 | Ky. | Webster | Bed No. 9 | |Pea and Slack|115 | Ky. | Whitley | | Jellico |Nut and Slack|116 | Mo. | Adair | | Danforth | Mine run |117 | Mo. | Bates | Rich Hill | New Home | Mine run |118 | Mo. | Clay | Lexington | Mo. City Coal | | | | | | Co. | |119 | Mo. | Lafayette | Waverly | Buckthorn | |120 | Mo. | Lafayette | Waverly | Higbee | |121 | Mo. | Linn | Bevier | Marceline | |122 | Mo. | Macon | Bevier | Northwest | | | | | | Coal Co. | |123 | Mo. | Morgan | Morgan Co. | Morgan Co. | Mine run | | | | | Coal Co. | |124 | Mo. | Putnam | Mendotta | Mendotta No. 8| |125 | N. Mex. | McKinley | Gallup | Gibson |Pea and Slack|____|_______|________________|________________|_______________|_____________| ______________________________________________________________________ | | | | | Proximate Analysis (Dry Coal) |B. T. U. | |No. |________________________________________| Per | | | | | | | Pound | Authority | | Moisture | Volatile | Fixed | Ash | Dry | | | | Matter | Carbon | | Coal | |____|__________|__________|________|_________|________|______________| | | | | | | | 83 | 7. 22 | 33. 06 | 53. 97 | 12. 97 | 11352 | U. S. Geo. S. | 84 | 4. 81 | 41. 53 | 39. 62 | 18. 85 | 10220 | Jones | 85 | 14. 39 | 32. 90 | 44. 84 | 22. 26 | 11059 | B. & W. Co. | 86 | 15. 71 | 38. 10 | 41. 10 | 20. 80 | 10999 | B. & W. Co. | 87 | 8. 17 | 34. 33 | 52. 50 | 13. 17 | 12643 | U. S. Geo. S. | 88 | 4. 66 | 35. 65 | 56. 86 | 7. 49 | 12286 | Univ. Of Ill. | | | | | | | | 89 | 11. 91 | 33. 70 | 55. 90 | 10. 40 | 12932 | B. & W. Co. | | | | | | | | 90 | 2. 83 | 40. 03 | 51. 97 | 8. 00 | 13375 | Stillman | 91 | 0. 83 | 39. 70 | 52. 28 | 8. 02 | 13248 | Jones | 92 | 6. 17 | 35. 42 | 53. 55 | 11. 03 | 11916 | Dearborn | 93 | 10. 73 | 35. 75 | 54. 46 | 9. 79 | 12911 | B. & W. Co. | 94 | 10. 72 | 44. 02 | 46. 33 | 9. 65 | 11767 | U. S. Geo. S. | 95 | 16. 59 | 42. 17 | 48. 44 | 9. 59 | 13377 | U. S. Geo. S. | 96 | 2. 28 | 34. 95 | 50. 50 | 14. 55 | 11920 | Dearborn | 97 | 11. 62 | 41. 17 | 46. 76 | 12. 07 | 12740 | U. S. Geo. S. | 98 | 13. 48 | 39. 40 | 43. 09 | 17. 51 | 11678 | U. S. Geo. S. | 99 | 16. 01 | 37. 82 | 46. 24 | 15. 94 | 11963 | U. S. Geo. S. |100 | 14. 88 | 41. 53 | 39. 63 | 18. 84 | 11443 | U. S. Geo. S. |101 | 12. 44 | 41. 27 | 40. 86 | 17. 87 | 11671 | U. S. Geo. S. |102 | 8. 69 | 36. 23 | 43. 68 | 20. 09 | 11443 | U. S. Geo. S. |103 | 4. 31 | 33. 88 | 53. 67 | 12. 45 | 13144 | U. S. Geo. S. | | | | | | | |104 | 6. 16 | 35. 56 | 46. 90 | 17. 54 | 10175 | Jones |105 | 1. 81 | 34. 77 | 52. 77 | 12. 46 | 12557 | Jones |106 | 4. 74 | 36. 59 | 47. 07 | 16. 34 | 10392 | Jones |107 | 2. 89 | 36. 67 | 57. 24 | 6. 09 | 14362 | U. S. Geo. S. | | | | | | | |108 | 6. 89 | 40. 30 | 55. 16 | 4. 54 | 13381 | St. Col. Ky. |109 | 7. 92 | 40. 53 | 48. 70 | 10. 77 | 13036 | U. S. Geo. S. |110 | 8. 02 | 31. 91 | 54. 02 | 14. 07 | 12448 | B. & W. Co. |111 | 5. 12 | 38. 46 | 58. 63 | 2. 91 | 13743 | U. S. Geo. S. |112 | 9. 22 | 33. 94 | 52. 18 | 13. 88 | 12229 | B. & W. Co. |113 | 2. 80 | 26. 54 | 63. 58 | 9. 88 | 14095 | N. Y. Ed. Co. |114 | 7. 30 | 31. 08 | 60. 72 | 8. 20 | 13600 | B. & W. Co. |115 | 3. 82 | 31. 82 | 58. 78 | 9. 40 | 13175 | B. & W. Co. |116 | 9. 00 | 30. 55 | 46. 26 | 23. 19 | 9889 | B. & W. Co. |117 | 7. 28 | 37. 62 | 43. 83 | 18. 55 | 12109 | U. S. Geo. S. |118 | 12. 45 | 39. 39 | 48. 47 | 12. 14 | 12875 | Univ. Of Mo. | | | | | | | |119 | 8. 58 | 41. 78 | 45. 99 | 12. 23 | 12735 | Univ. Of Mo. |120 | 10. 84 | 31. 72 | 55. 29 | 12. 99 | 12500 | Univ. Of Mo. |121 | 9. 45 | 36. 72 | 52. 20 | 11. 08 | 13180 | Univ. Of Mo. |122 | 13. 09 | 37. 83 | 42. 95 | 19. 22 | 11500 | U. S. Geo. S. | | | | | | | |123 | 12. 24 | 45. 69 | 47. 98 | 6. 33 | 14197 | U. S. Geo. S. | | | | | | | |124 | 20. 78 | 39. 36 | 50. 00 | 10. 64 | 12602 | U. S. Geo. S. |125 | 12. 17 | 36. 31 | 51. 17 | 12. 52 | 12126 | B. & W. Co. |____|__________|__________|________|_________|________|______________| APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICANCOALS--Continued ____________________________________________________________________________ | | | | | | | | | | | |No. | State | County | Field, Bed | Mine | Size | | | | or Vein | | | | | | | | | | | | | | | |_______|________________|________________|_______________|_____________| | | | | | |126 | Ohio | Athens | Hocking Valley | Sunday Creek | Slack |127 | Ohio | Belmont | Pittsburgh | Neff Coal Co. | Mine run | | | | No. 8 | | |128 | Ohio | Columbiana | Middle | Palestine | | | | | Kittanning | | |129 | Ohio | Coshocton | Middle | Morgan Run | Mine run | | | | Kittanning | | |130 | Ohio | Guernsey | Vein No. 7 | Little Kate | |131 | Ohio | Hocking | Hocking Valley | | Lump |132 | Ohio | Hocking | Hocking Valley | | |133 | Ohio | Jackson | Brookville | Superior | Mine run | | | | | Coal Co. | |134 | Ohio | Jackson | Lower | Superior | Mine run | | | | Kittanning | Coal Co. | |135 | Ohio | Jackson | Quakertown | Wellston | |136 | Ohio | Jefferson | Pittsburgh | Crow Hollow | ¾ inch | | | | or No. 8 | | |137 | Ohio | Jefferson | Pittsburgh | Rush Run No. 1| ¾ inch | | | | or No. 8 | | |138 | Ohio | Perry | Hocking | Congo | |139 | Ohio | Stark | Massillon | | Slack |140 | Ohio | Vinton | Brookville | Clarion | Nut and | | | | or No. 4 | | Slack |141 | Okla. | Choctaw | McAlester | Edwards No. 1 | Mine run |142 | Okla. | Choctaw | McAlester | Adamson | Slack |143 | Okla. | Creek | | Henrietta | Lump and | | | | | | Slack |144 | Pa. | Allegheny | Pittsburgh | | Slack | | | | 3rd Pool | | |145 | Pa. | Allegheny | Monongahela | Turtle Creek | |146 | Pa. | Allegheny | Pittsburgh | Bertha | ¾ inch |147 | Pa. | Cambria | | Beach Creek | Slack |148 | Pa. | Cambria | Miller | Lincoln | Mine run |149 | Pa. | Clarion | Lower Freeport | | |150 | Pa. | Fayette | Connellsville | | Slack |151 | Pa. | Greene | Youghiogheny | | Lump |152 | Pa. | Greene | Westmoreland | | Screenings |153 | Pa. | Indiana | | Iselin | Mine run |154 | Pa. | Jefferson | | Punxsutawney | Mine run |155 | Pa. | Lawrence | Middle | | | | | | Kittanning | | |156 | Pa. | Mercer | Taylor | | |157 | Pa. | Washington | Pittsburgh | Ellsworth | |158 | Pa. | Washington | Youghiogheny | Anderson | ¾ inch |159 | Pa. | Westmoreland | Pittsburgh | Scott Haven | Lump |160 | Tenn. | Campbell | Jellico | | |161 | Tenn. | Claiborne | Mingo | | |162 | Tenn. | Marion | | Etna | |163 | Tenn. | Morgan | Brushy Mt. | | |164 | Tenn. | Scott | Glen Mary No. 4| Glen Mary | |165 | Tex. | Maverick | | Eagle Pass | |166 | Tex. | Paolo Pinto | | Thurber | Mine run |167 | Tex. | Paolo Pinto | | Strawn | Mine run |168 | Va. | Henrico | | Gayton | |____|_______|________________|________________|_______________|_____________| _____________________________________________________________________ | | | | | Proximate Analysis (Dry Coal) |B. T. U. | |No. |________________________________________| Per | | | | | | | Pound | Authority | | Moisture | Volatile | Fixed | Ash | Dry | | | | Matter | Carbon | | Coal | |____|__________|__________|________|_________|________|______________| | | | | | | |126 | 12. 16 | 34. 64 | 53. 10 | 12. 26 | 12214 | |127 | 5. 31 | 38. 78 | 52. 22 | 9. 00 | 12843 | U. S. Geo. S. | | | | | | | |128 | 2. 15 | 37. 57 | 51. 80 | 10. 63 | 13370 | Lord & Haas | | | | | | | |129 | | 41. 76 | 45. 24 | 13. 00 | 13239 | B. & W. Co. | | | | | | | |130 | 6. 19 | 33. 02 | 59. 96 | 7. 02 | 13634 | B. & W. Co. |131 | 6. 45 | 39. 12 | 50. 08 | 10. 80 | 12700 | Lord & Haas |132 | 2. 60 | 40. 80 | 47. 60 | 11. 60 | 12175 | Jones |133 | 7. 59 | 38. 45 | 43. 99 | 17. 56 | 11704 | U. S. Geo. S. | | | | | | | |134 | 8. 99 | 41. 43 | 50. 06 | 8. 51 | 13113 | U. S. Geo. S. | | | | | | | |135 | 3. 38 | 35. 26 | 54. 18 | 7. 56 | 12506 | Hill |136 | 4. 04 | 40. 08 | 52. 27 | 9. 65 | 13374 | U. S. Geo. S. | | | | | | | |137 | 4. 74 | 36. 08 | 54. 81 | 9. 11 | 13532 | U. S. Geo. S. | | | | | | | |138 | 6 41 | 38. 33 | 46. 71 | 14. 96 | 12284 | B. & W. Co. |139 | 6. 67 | 40. 02 | 46. 46 | 13. 52 | 11860 | B. & W. Co. |140 | 2. 47 | 42. 38 | 50. 39 | 6. 23 | 13421 | U. S. Geo. S. | | | | | | | |141 | 4. 79 | 39. 18 | 49. 97 | 10. 85 | 13005 | U. S. Geo. S. |142 | 4. 72 | 28. 54 | 58. 17 | 13. 29 | 12105 | B. & W. Co. |143 | 7. 65 | 36. 77 | 50. 14 | 13. 09 | 12834 | U. S. Geo. S. | | | | | | | |144 | 1. 77 | 32. 06 | 57. 11 | 10. 83 | 13205 | Carpenter | | | | | | | |145 | 1. 75 | 36. 85 | 53. 94 | 9. 21 | 13480 | Lord & Haas |146 | 2. 61 | 35. 86 | 57. 81 | 6. 33 | 13997 | U. S. Geo. S. |147 | 3. 01 | 32. 87 | 55. 86 | 11. 27 | 13755 | B. & W. Co. |148 | 5. 39 | 30. 83 | 61. 05 | 8. 12 | 13600 | B. & W. Co. |149 | 0. 54 | 35. 93 | 57. 66 | 6. 41 | 13547 | |150 | 1. 85 | 28. 73 | 63. 22 | 7. 95 | 13775 | Whitham |151 | 1. 25 | 32. 60 | 54. 70 | 12. 70 | 13100 | B. & W. Co. |152 | 11. 12 | 31. 67 | 55. 61 | 12. 72 | 13100 | P. R. R. |153 | 2. 70 | 29. 33 | 63. 56 | 7. 11 | 14220 | B. & W. Co. |154 | 3. 38 | 29. 33 | 64. 93 | 5. 73 | 14781 | B. & W. Co. |155 | 0. 70 | 37. 06 | 56. 24 | 6. 70 | 13840 | Lord & Haas | | | | | | | |156 | 4. 18 | 32. 19 | 55. 55 | 12. 26 | 12820 | B. & W. Co. |157 | 2. 46 | 35. 35 | 58. 46 | 6. 19 | 14013 | U. S. Geo. S. |158 | 1. 00 | 39. 29 | 54. 80 | 5. 91 | 13729 | Jones |159 | 4. 06 | 32. 91 | 59. 78 | 7. 31 | 13934 | B. & W. Co. |160 | 1. 80 | 37. 76 | 62. 12 | 1. 12 | 13846 | U. S. Navy |161 | 4. 40 | 34. 31 | 59. 22 | 6. 47 | | U. S. Geo. S. |162 | 3. 16 | 32. 98 | 56. 59 | 10. 43 | | |163 | 1. 77 | 33. 46 | 54. 73 | 11. 87 | 13824 | B. & W. Co. |164 | 1. 53 | 40. 80 | 56. 78 | 2. 42 | 14625 |Ky. State Col. |165 | 5. 42 | 33. 73 | 44. 89 | 21. 38 | 10945 | B. & W. Co. |166 | 1. 90 | 36. 01 | 49. 09 | 14. 90 | 12760 | B. & W. Co. |167 | 4. 19 | 35. 40 | 52. 98 | 11. 62 | 13202 | B. & W. Co. |168 | 0. 82 | 17. 14 | 74. 92 | 7. 94 | 14363 | B. & W. Co. |____|__________|__________|________|_________|________|______________| APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICANCOALS--Continued ____________________________________________________________________________ | | | | | | | | | | | |No. | State | County | Field, Bed | Mine | Size | | | | or Vein | | | | | | | | | | | | | | | |_______|________________|________________|_______________|_____________| | | | | | |169 | Va. | Lee | Darby | Darby | 1½ inch |170 | Va. | Lee | McConnel | Wilson | Mine run |171 | Va. | Wise | Upper Banner | Coburn | 3½ inch |172 | Va. | Rockingham | | Clover Hill | |173 | Va. | Russel | Clinchfield | | |174 | Va. | | Monongahela | Bernmont | |175 | W. Va. | Harrison | Pittsburgh | Ocean | Mine run |176 | W. Va. | Harrison | | Girard | Nut, Pea | | | | | | and Slack |177 | W. Va. | Kanawha | Winifrede | Winifrede | |178 | W. Va. | Kanawha | Keystone | Keystone | Mine run |179 | W. Va. | Logan | Island Creek | |Nut and Slack|180 | W. Va. | Marion | Fairmont | Kingmont | |181 | W. Va. | Mingo | Thacker | Maritime | |182 | W. Va. | Mingo | Glen Alum | Glen Alum | Mine run |183 | W. Va. | Preston | Bakerstown | | |184 | W. Va. | Putnam | Pittsburgh | Black Betsy | Bug dust |185 | W. Va. | Randolph | Upper Freeport | Coalton | Lump and Nut|____|_______|________________|________________|_______________|_____________| | | | | | | LIGNITES AND LIGNITIC COALS | |____|_______|_________________________________________________|_____________| | | | | | |186 | Col. | Boulder | | Rex | |187 | Col. | El Paso | | Curtis | |188 | Col. | El Paso | | Pike View | |189 | Col. | Gunnison | South Platte | Mt. Carbon | |190 | Col. | Las Animas | | Acme | |191 | Col. | | Lehigh | | |192 |N. Dak. | McLean | | Eckland | Mine run |193 |N. Dak. | McLean | | Wilton | Lump |194 |N. Dak. | McLean | | Casino | |195 |N. Dak. | Stark | Lehigh | Lehigh | Mine run |196 |N. Dak. | William | Williston | | Mine run |197 |N. Dak. | William | Williston | | Mine run |198 | Tex. | Bastrop | Bastrop | Glenham | |199 | Tex. | Houston | Crockett | | |200 | Tex. | Houston | | Houston C. & | | | | | | C. Co. | |201 | Tex. | Milam | Rockdale | Worley | |202 | Tex. | Robertson | Calvert | Coaling No. 1 | |203 | Tex. | Wood | Hoyt | Consumer's | | | | | | Lig. Co. | |204 | Tex. | Wood | Hoyt | | |205 | Wash. | King | | Black Diamond | |206 | Wyo. | Carbon | Hanna | | Mine run |207 | Wyo. | Crook | Black Hills | Stilwell Coal | | | | | | Co. | |208 | Wyo. | Sheridan | Sheridan | Monarch | |209 | Wyo. | Sweetwater | Rock Spring | | Screenings |210 | Wyo. | Uinta | Adaville | Lazeart | |____|_______|________________|________________|_______________|_____________| _____________________________________________________________________ | | | | | Proximate Analysis (Dry Coal) |B. T. U. | |No. |________________________________________| Per | | | | | | | Pound | Authority | | Moisture | Volatile | Fixed | Ash | Dry | | | | Matter | Carbon | | Coal | |____|__________|__________|________|_________|________|______________| | | | | | | |169 | 4. 35 | 38. 46 | 56. 91 | 4. 63 | 13939 | U. S. Geo. S. |170 | 3. 35 | 36. 35 | 57. 88 | 5. 77 | 13931 | U. S. Geo. S. |171 | 3. 05 | 32. 65 | 62. 73 | 4. 62 | 14470 | U. S. Geo. S. |172 | | 31. 77 | 57. 98 | 10. 25 | 13103 | |173 | 2. 00 | 35. 72 | 56. 12 | 8. 16 | 14200 | |174 | | 32. 00 | 59. 90 | 8. 10 | 13424 | Carpenter |175 | 2. 47 | 39. 35 | 52. 78 | 7. 87 | 14202 | U. S. Geo. S. |176 | | 36. 66 | 57. 49 | 5. 85 | 14548 | B. & W. Co. | | | | | | | |177 | 1. 05 | 32. 74 | 64. 38 | 2. 88 | 14111 | Hill |178 | 2. 21 | 33. 29 | 58. 61 | 8. 10 | 14202 | U. S. Geo. S. |179 | 1. 12 | 38. 61 | 55. 91 | 5. 48 | 14273 | Hill |180 | 1. 90 | 35. 31 | 57. 34 | 7. 35 | 14198 | U. S. Geo. S. |181 | 0. 68 | 31. 89 | 63. 48 | 4. 63 | 14126 | Hill |182 | 3. 02 | 33. 81 | 59. 45 | 6. 74 | 14414 | U. S. Geo. S. |183 | 4. 14 | 29. 09 | 63. 50 | 7. 41 | 14546 | U. S. Geo. S. |184 | 7. 41 | 32. 84 | 53. 96 | 13. 20 | 12568 | B. & W. Co. |185 | 2. 11 | 29. 57 | 59. 93 | 10. 50 | 13854 | U. S. Geo. S. |____|__________|__________|________|_________|________|______________| | | | | | | | | | | | | | |____|__________|__________|________|_________|________|______________| | | | | | | |186 | 16. 05 | 42. 12 | 47. 97 | 9. 91 | 10678 | B. & W. Co. |187 | 23. 25 | 42. 11 | 49. 38 | 8. 51 | 11090 | B. & W. Co. |188 | 23. 77 | 48. 70 | 41. 47 | 9. 83 | 10629 | B. & W. Co. |189 | 20. 38 | 46. 38 | 47. 50 | 6. 12 | | |190 | 16. 74 | 47. 90 | 44. 60 | 7. 50 | |Col. Sc. Of M. |191 | 18. 30 | 45. 29 | 44. 67 | 10. 04 | | |192 | 29. 65 | 45. 56 | 47. 05 | 7. 39 | 10553 | Lord |193 | 35. 96 | 49. 84 | 38. 05 | 12. 11 | 11036 | U. S. Geo. S. |194 | 29. 65 | 46. 56 | 38. 70 | 14. 74 | | Lord |195 | 35. 84 | 43. 84 | 39. 59 | 16. 57 | 10121 | U. S. Geo. S. |196 | 41. 76 | 39. 37 | 48. 09 | 12. 54 | 10121 | B. & W. Co. |197 | 42. 74 | 40. 83 | 47. 79 | 11. 38 | 10271 | B. & W. Co. |198 | 32. 77 | 42. 76 | 36. 88 | 20. 36 | 8958 | B. & W. Co. |199 | 23. 27 | 40. 95 | 38. 37 | 20. 68 | 10886 | U. S. Geo. S. |200 | 31. 48 | 46. 93 | 34. 40 | 18. 87 | 10176 | B. & W. Co. | | | | | | | |201 | 32. 48 | 43. 04 | 41. 14 | 15. 82 | 10021 | B. & W. Co. |202 | 32. 01 | 43. 70 | 43. 08 | 13. 22 | 10753 | B. & W. Co. |203 | 33. 98 | 46. 97 | 41. 40 | 11. 63 | 10600 | U. S. Geo. S. | | | | | | | |204 | 30. 25 | 43. 27 | 41. 46 | 15. 27 | 10597 | |205 | 3. 71 | 48. 72 | 46. 56 | 4. 72 | | Gale |206 | 6. 44 | 51. 32 | 43. 00 | 5. 68 | 11607 | B. & W. Co. |207 | 19. 08 | 45. 21 | 46. 42 | 8. 37 | 12641 | U. S. Geo. S. | | | | | | | |208 | 21. 18 | 51. 87 | 40. 43 | 7. 70 | 12316 | U. S. Geo. S. |209 | 7. 70 | 38. 57 | 56. 99 | 4. 44 | 12534 | B. & W. Co. |210 | 19. 15 | 45. 50 | 48. 11 | 6. 39 | 9868 | U. S. Geo. S. |____|__________|__________|________|_________|________|______________| [Illustration: Portion of 12, 080 Horse-power Installation of Babcock &Wilcox Boilers and Superheaters at the Potomac Electric Co. , Washington, D. C. ] TABLE 39 SHOWING RELATION BETWEEN PROXIMATE AND ULTIMATE ANALYSES OF COAL =========================================================================| | | | Common in || | | |Proximate &|| | Proximate | | Ultimate || | Analysis | Ultimate Analysis | Analysis ||--------------------|-----------|--------------------------|-----------|| | | | V | | | H | | N | | | M || | | | o | | | y | | i | S | | o || | | | l M | C | C | d | O | t | u | | i || S | | | a a | F a | a | r | x | r | l | | s || t | | | t t | i r | r | o | y | o | p | | t || a | Field | | i t | x b | b | g | g | g | h | A | u || t | or | | l e | e o | o | e | e | e | e | s | r || e | Bed | Mine | e r | d n | n | n | n | n | r | h | e ||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|| | |Icy Coal| | | | | | | | | || | | & Iron | | | | | | | | | || | Horse | Co. | | | | | | | | | ||Ala| Creek | No. 8 |31. 81|53. 90|72. 02|4. 78| 6. 45|1. 66| . 80|14. 29| 2. 56||---|----------------|-----|-----|-----|----|-----|----|----|-----|-----|| | |Central | | | | | | | | | || | |C. & C. | | | | | | | | | || | Hunt- | Co. | | | | | | | | | ||Ark|ington | No. 3 |18. 99|67. 71|76. 37|3. 90| 3. 71|1. 49|1. 23|13. 30| 1. 99||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|| | Pana | Clover | | | | | | | | | || | or | Leaf, | | | | | | | | | ||Ill| No. 5 | No. 1 |37. 22|45. 64|63. 04|4. 49|10. 04|1. 28|4. 01|17. 14|13. 19||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|| |No. 5, | | | | | | | | | | || |Warrick| | | | | | | | | | ||Ind| Co. |Electric|41. 85|44. 45|68. 08|4. 78| 7. 56|1. 35|4. 53|13. 70| 9. 11||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|| |No. 11, | St. | | | | | | | | | || |Hopkins|Bernard, | | | | | | | | | ||Ky | Co. | No. 11 |41. 10|49. 60|72. 22|5. 06| 8. 44|1. 33|3. 65| 9. 30| 7. 76||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|| |"B" or | | | | | | | | | | || |Lower | | | | | | | | | | || |Kittan-| Eureka, | | | | | | | | | ||Pa | ning | No. 31 |16. 71|77. 22|84. 45|4. 25| 3. 04|1. 28| . 91| 6. 07| . 56||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|| |Indiana| | | | | | | | | | ||Pa | Co. | |29. 55|62. 64|79. 86|5. 02| 4. 27|1. 86|1. 18| 7. 81| 2. 90||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----||W. | Fire | Rush | | | | | | | | | ||Va | Creek | Run |22. 87|71. 56|83. 71|4. 64| 3. 67|1. 70| . 71| 5. 57| 2. 14|========================================================================= Table 39 gives for comparison the ultimate and proximate analyses ofcertain of the coals with which tests were made in the coal testingplant of the United States Geological Survey at the Louisiana PurchaseExposition at St. Louis. The heating value of a fuel cannot be directly computed from a proximateanalysis, due to the fact that the volatile content varies widely indifferent fuels in composition and in heating value. Some methods have been advanced for estimating the calorific value ofcoals from the proximate analysis. William Kent[38] deducted fromMahler's tests of European coals the approximate heating value dependentupon the content of fixed carbon in the combustible. The relation asdeduced by Kent between the heat and value per pound of combustible andthe per cent of fixed carbon referred to combustible is representedgraphically by Fig. 23. Goutal gives another method of determining the heat value from aproximate analysis, in which the carbon is given a fixed value and theheating value of the volatile matter is considered as a function of itspercentage referred to combustible. Goutal's method checks closely withKent's determinations. All the formulae, however, for computing the calorific value of coalsfrom a proximate analysis are ordinarily limited to certain classes offuels. Mr. Kent, for instance, states that his deductions are correctwithin a close limit for fuels containing more than 60 per cent of fixedcarbon in the combustible, while for those containing a lowerpercentage, the error may be as great as 4 per cent, either high or low. While the use of such computations will serve where approximate resultsonly are required, that they are approximate should be thoroughlyunderstood. Calorimetry--An ultimate or a proximate analysis of a fuel is useful indetermining its general characteristics, and as described on page 183, may be used in the calculation of the approximate heating value. Wherethe efficiency of a boiler is to be computed, however, this heatingvalue should in all instances be determined accurately by means of afuel calorimeter. [Graph: B. T. U. Per Pound of Combustibleagainst Per Cent of Fixed Carbon in Combustible Fig. 23. Graphic Representation of Relation between Heat Value Per Poundof Combustible and Fixed Carbon in Combustible as Deduced by Wm. Kent. ] In such an apparatus the fuel is completely burned and the heatgenerated by such combustion is absorbed by water, the amount of heatbeing calculated from the elevation in the temperature of the water. Acalorimeter which has been accepted as the best for such work is one inwhich the fuel is burned in a steel bomb filled with compressed oxygen. The function of the oxygen, which is ordinarily under a pressure ofabout 25 atmospheres, is to cause the rapid and complete combustion ofthe fuel sample. The fuel is ignited by means of an electric current, allowance being made for the heat produced by such current, and by theburning of the fuse wire. A calorimeter of this type which will be found to give satisfactoryresults is that of M. Pierre Mahler, illustrated in Fig. 24 andconsisting of the following parts: A water jacket A, which maintains constant conditions outside of thecalorimeter proper, and thus makes possible a more accurate computationof radiation losses. The porcelain lined steel bomb B, in which the combustion of the fueltakes place in compressed oxygen. [Illustration: Fig. 24. Mahler Bomb Calorimeter] The platinum pan C, for holding the fuel. The calorimeter proper D, surrounding the bomb and containing a definiteweighed amount of water. An electrode E, connecting with the fuse wire F, for igniting the fuelplaced in the pan C. A support G, for a water agitator. A thermometer I, for temperature determination of the water in thecalorimeter. The thermometer is best supported by a stand independent ofthe calorimeter, so that it may not be moved by tremors in the parts ofthe calorimeter, which would render the making of readings difficult. Toobtain accuracy of readings, they should be made through a telescope oreyeglass. A spring and screw device for revolving the agitator. A lever L, by the movement of which the agitator is revolved. A pressure gauge M, for noting the amount of oxygen admitted to thebomb. Between 20 and 25 atmospheres are ordinarily employed. An oxygen tank O. A battery or batteries P, the current from which heats the fuse wireused to ignite the fuel. This or a similar calorimeter is used in the determination of the heatof combustion of solid or liquid fuels. Whatever the fuel to be tested, too much importance cannot be given to the securing of an averagesample. Where coal is to be tested, tests should be made from a portionof the dried and pulverized laboratory sample, the methods of obtainingwhich have been described. In considering the methods of calorimeterdetermination, the remarks applied to coal are equally applicable to anysolid fuel, and such changes in methods as are necessary for liquidfuels will be self-evident from the same description. Approximately one gram of the pulverized dried coal sample should beplaced directly in the pan of the calorimeter. There is some danger inthe using of a pulverized sample from the fact that some of it may beblown out of the pan when oxygen is admitted. This may be at leastpartially overcome by forming about two grams into a briquette by theuse of a cylinder equipped with a plunger and a screw press. Such abriquette should be broken and approximately one gram used. If apulverized sample is used, care should be taken to admit oxygen slowlyto prevent blowing the coal out of the pan. The weight of the sample islimited to approximately one gram since the calorimeter is proportionedfor the combustion of about this weight when under an oxygen pressure ofabout 25 atmospheres. A piece of fine iron wire is connected to the lower end of the plungerto form a fuse for igniting the sample. The weight of iron wire used isdetermined, and if after combustion a portion has not been burned, theweight of such portion is determined. In placing the sample in the pan, and in adjusting the fuse, the top of the calorimeter is removed. It isthen replaced and carefully screwed into place on the bomb by means of along handled wrench furnished for the purpose. The bomb is then placed in the calorimeter, which has been filled with adefinite amount of water. This weight is the "water equivalent" of theapparatus, _i. E. _, the weight of water, the temperature of which wouldbe increased one degree for an equivalent increase in the temperature ofthe combined apparatus. It may be determined by calculation from theweights and specific heats of the various parts of the apparatus. Such adetermination is liable to error, however, as the weight of the bomblining can only be approximated, and a considerable portion of theapparatus is not submerged. Another method of making such adetermination is by the adding of definite weights of warm water todefinite amounts of cooler water in the calorimeter and taking anaverage of a number of experiments. The best method for the making ofsuch a determination is probably the burning of a definite amount ofresublimed naphthaline whose heat of combustion is known. The temperature of the water in the water jacket of the calorimetershould be approximately that of the surrounding atmosphere. Thetemperature of the weighed amount of water in the calorimeter is made bysome experimenters slightly greater than that of the surrounding air inorder that the initial correction for radiation will be in the samedirection as the final correction. Other experimenters start from atemperature the same or slightly lower than the temperature of the room, on the basis that the temperature after combustion will be slightlyhigher than the room temperature and the radiation correction be eithera minimum or entirely eliminated. While no experiments have been made to show conclusively which of thesemethods is the better, the latter is generally used. After the bomb has been placed in the calorimeter, it is filled withoxygen from a tank until the pressure reaches from 20 to 25 atmospheres. The lower pressure will be sufficient in all but exceptional cases. Connection is then made to a current from the dry batteries in series soarranged as to allow completion of the circuit with a switch. Thecurrent from a lighting system should not be used for ignition, as thereis danger from sparking in burning the fuse, which may effect theresults. The apparatus is then ready for the test. Unquestionably the best method of taking data is by the use ofco-ordinate paper and a plotting of the data with temperatures and timeintervals as ordinates and abscissae. Such a graphic representation isshown in Fig. 25. [Graph: Temperature--° C. Against Time--Hours and Minutes Fig. 25. Graphic Method of Recording Bomb Calorimeter Results] After the bomb is placed in the calorimeter, and before the coal isignited, readings of the temperature of the water should be taken at oneminute intervals for a period long enough to insure a constant rate ofchange, and in this way determine the initial radiation. The coal isthen ignited by completing the circuit, the temperature at the instantthe circuit is closed being considered the temperature at the beginningof the combustion. After ignition the readings should be taken atone-half minute intervals, though because of the rapidity of themercury's rise approximate readings only may be possible for at least aminute after the firing, such readings, however, being sufficientlyaccurate for this period. The one-half minute readings should be takenafter ignition for five minutes, and for, say, five minutes longer atminute intervals to determine accurately the final rate of radiation. Fig. 25 shows the results of such readings, plotted in accordance withthe method suggested. It now remains to compute the results from thisplotted data. The radiation correction is first applied. Probably the most accuratemanner of making such correction is by the use of Pfaundler's method, which is a modification of that of Regnault. This assumes that instarting with an initial rate of radiation, as represented by theinclination of the line AB, Fig. 25, and ending with a final radiationrepresented by the inclination of the line CD, Fig. 25, that the rate ofradiation for the intermediate temperatures between the points B and Care proportional to the initial and final rates. That is, the rate ofradiation at a point midway between B and C will be the mean between theinitial and final rates; the rate of radiation at a point three-quartersof the distance between B and C would be the rate at B plusthree-quarters of the difference in rates at B and C, etc. This methoddiffers from Regnault's in that the radiation was assumed by Regnault tobe in each case proportional to the difference in temperatures betweenthe water of the calorimeter and the surrounding air plus a constantfound for each experiment. Pfaundler's method is more simple than thatof Regnault, and the results by the two methods are in practicalagreement. Expressed as a formula, Pfaundler's method is, though not in form givenby him: _ _ | R' - R |C = N|R + ------ (T" - T)| (19) |_ T' - T _| Where C = correction in degree centigrade, N = number of intervals over which correction is made, R = initial radiation in degrees per interval, R' = final radiation in degrees per interval, T = average temperature for period through which initial radiation is computed, T" = average temperature over period of combustion[39], T' = average temperature over period through which final radiation is computed. [39] The application of this formula to Fig. 25 is as follows: As already stated, the temperature at the beginning of combustion is thereading just before the current is turned on, or B in Fig. 25. The pointC or the temperature at which combustion is presumably completed, shouldbe taken at a point which falls well within the established final rateof radiation, and not at the maximum temperature that the thermometerindicates in the test, unless it lies on the straight line determiningthe final radiation. This is due to the fact that in certain instanceslocal conditions will cause the thermometer to read higher than itshould during the time that the bomb is transmitting heat to the waterrapidly, and at other times the maximum temperature might be lower thanthat which would be indicated were readings to be taken at intervals ofless than one-half minute, _i. E. _, the point of maximum temperaturewill fall below the line determined by the final rate of radiation. Withthis understanding AB, Fig. 25, represents the time of initialradiation, BC the time of combustion, and CD the time of finalradiation. Therefore to apply Pfaundler's correction, formula (19), tothe data as represented by Fig. 25. N = 6, R = 0, R' = . 01, T = 20. 29, T' = 22. 83, 20. 29 + 22. 54 + 22. 84 + 22. 88 + 22. 87 + 22. 86T" = --------------------------------------------- = 22. 36 6 _ _ | . 01 - 0 |C = 6|0 + -------------(22. 36 - 20. 29)| |_ 22. 85 - 20. 29 _| = 6 × . 008 = . 048 Pfaundler's formula while simple is rather long. Mr. E. H. Peabody hasdevised a simpler formula with which, under proper conditions, thevariation from correction as found by Pfaundler's method is negligible. It was noted throughout an extended series of calorimeter tests that themaximum temperature was reached by the thermometer slightly over oneminute after the time of firing. If this period between the time offiring and the maximum temperature reported was exactly one minute, theradiation through this period would equal the radiation per one-halfminute _before firing_ plus the radiation per one-half minute _after themaximum temperature is reached_; or, the radiation through the oneminute interval would be the average of the radiation per minute beforefiring and the radiation per minute after the maximum. A plotted chartof temperatures would take the form of a curve of three straight lines(B, C', D) in Fig. 25. Under such conditions, using the notation as informula (19) the correction would become, 2R + 2R'C = ------- + (N - 2)R', or R + (N - 1)R' (20) 2 This formula may be generalized for conditions where the maximumtemperature is reached after a period of more than one minute asfollows: Let M = the number of intervals between the time of firing and themaximum temperature. Then the radiation through this period will be anaverage of the radiation for M intervals before firing and for Mintervals after the maximum is recorded, or MR + MR' M MC = ------- + (N - M)R' = - R + (N - -)R' (21) 2 2 2 In the case of Mr. Peabody's deductions M was found to be approximately2 and formula (21) becomes directly, C = R + (N - 1)R' or formula (20). The corrections to be made, as secured by the use of this formula, arevery close to those secured by Pfaundler's method, where the point ofmaximum temperature is not more than five intervals later than the pointof firing. Where a longer period than this is indicated in the chart ofplotted temperatures, the approximate formula should not be used. As theperiod between firing and the maximum temperature is increased, theplotted results are further and further away from the theoreticalstraight line curve. Where this period is not over five intervals, ortwo and a half minutes, an approximation of the straight line curve maybe plotted by eye, and ordinarily the radiation correction to be appliedmay be determined very closely from such an approximated curve. Peabody's approximate formula has been found from a number of tests togive results within . 003 degrees Fahrenheit for the limits within whichits application holds good as described. The value of M, which is notnecessarily a whole number, should be determined for each test, thoughin all probability such a value is a constant for any individualcalorimeter which is properly operated. The correction for radiation as found on page 188 is in all instances tobe added to the range of temperature between the firing point and thepoint chosen from which the final radiation is calculated. Thiscorrected range multiplied by the water equivalent of the calorimetergives the heat of combustion in calories of the coal burned in thecalorimeter together with that evolved by the burning of the fuse wire. The heat evolved by the burning of the fuse wire is found from thedetermination of the actual weight of wire burned and the heat ofcombustion of one milligram of the wire (1. 7 calories), _i. E. _, multiply the weight of wire used by 1. 7, the result being in gramcalories or the heat required to raise one gram of water one degreecentigrade. Other small corrections to be made are those for the formation of nitricacid and for the combustion of sulphur to sulphuric acid instead ofsulphur dioxide, due to the more complete combustion in the presence ofoxygen than would be possible in the atmosphere. To make these corrections the bomb of the calorimeter is carefullywashed out with water after each test and the amount of acid determinedfrom titrating this water with a standard solution of ammonia or ofcaustic soda, all of the acid being assumed to be nitric acid. Eachcubic centimeter of the ammonia titrating solution used is equivalent toa correction of 2. 65 calories. As part of acidity is due to the formation of sulphuric acid, a furthercorrection is necessary. In burning sulphuric acid the heat evolved pergram of sulphur is 2230 calories in excess of the heat which would beevolved if the sulphur burned to sulphur dioxide, or 22. 3 calories foreach per cent of sulphur in the coal. One cubic centimeter of theammonia solution is equivalent to 0. 00286 grams of sulphur as sulphuricacid, or to 0. 286 × 22. 3 = 6. 38 calories. It is evident therefore thatafter multiplying the number of cubic centimeters used in titrating bythe heat factor for nitric acid (2. 65) a further correction of6. 38 - 2. 65 = 3. 73 is necessary for each cubic centimeter used intitrating sulphuric instead of nitric acid. This correction will be3. 73/0. 297 = 13 units for each 0. 01 gram of sulphur in the coal. The total correction therefore for the aqueous nitric and sulphuric acidis found by multiplying the ammonia by 2. 65 and adding 13 calories foreach 0. 01 gram of sulphur in the coal. This total correction is to bededucted from the heat value as found from the corrected range and theamount equivalent to the calorimeter. After each test the pan in which the coal has been burned must becarefully examined to make sure that all of the sample has undergonecomplete combustion. The presence of black specks ordinarily indicatesunburned coal, and often will be found where the coal contains bone orslate. Where such specks are found the tests should be repeated. Intesting any fuel where it is found difficult to completely consume asample, a weighed amount of naphthaline may be added, the total weightof fuel and naphthaline being approximately one gram. The naphthalinehas a known heat of combustion, samples for this purpose beingobtainable from the United States Bureau of Standards, and from thecombined heat of combustion of the fuel and naphthaline that of theformer may be readily computed. The heat evolved in burning of a definite weight of standard naphthalinemay also be used as a means of calibrating the calorimeter as a whole. COMBUSTION OF COAL The composition of coal varies over such a wide range, and the methodsof firing have to be altered so greatly to suit the various coals andthe innumerable types of furnaces in which they are burned, that anyinstructions given for the handling of different fuels must of necessitybe of the most general character. For each kind of coal there is somemethod of firing which will give the best results for each individualset of conditions. General rules can be suggested, but the best resultscan be obtained only by following such methods as experience andpractice show to be the best suited to the specific conditions. The question of draft is an all important factor. If this beinsufficient, proper combustion is impossible, as the suction in thefurnace will not be great enough to draw the necessary amount of airthrough the fuel bed, and the gases may pass off only partiallyconsumed. On the other hand, an excessive draft may cause losses due tothe excess quantities of air drawn through holes in the fire. Where coalis burned however, there are rarely complaints from excessive draft, asthis can be and should be regulated by the boiler damper to give onlythe draft necessary for the particular rate of combustion desired. Thedraft required for various kinds of fuel is treated in detail in thechapter on "Chimneys and Draft". In this chapter it will be assumed thatthe draft is at all times ample and that it is regulated to give thebest results for each kind of coal. TABLE 40 ANTHRACITE COAL SIZES _________________________________________________________________| | | || | | Testing Segments || | Round Mesh | Standard Square || | | Mesh || Trade Name |__________________|__________________|| | | | | || | Through | Over | Through | Over || | Inches | Inches | Inches | Inches ||___________________________|_________|________|_________|________|| | | | | || Broken | 4-1/2 | 3-1/4 | 4 | 2-3/4 || Egg | 3-1/4 | 2-3/8 | 2-3/4 | 2 || Stove | 2-3/8 | 1-5/8 | 2 | 1-3/8 || Chestnut | 1-5/8 | 7/8 | 1-3/8 | 3/4 || Pea | 7/8 | 5/8 | 3/4 | 1/2 || No. 1 Buckwheat | 5/8 | 3/8 | 1/2 | 1/4 || No. 2 Buckwheat or Rice | 3/8 | 3/16 | 1/4 | 1/8 || No. 3 Buckwheat or Barley | 3/16 | 3/32 | 1/8 | 1/16 ||___________________________|_________|________|_________|________| Anthracite--Anthracite coal is ordinarily marketed under the names andsizes given in Table 40. The larger sizes of anthracite are rarely used for commercial steamgenerating purposes as the demand for domestic use now limits thesupply. In commercial plants the sizes generally found are Nos. 1, 2 and3 buckwheat. In some plants where the finer sizes are used, a smallpercentage of bituminous coal, say, 10 per cent, is sometimes mixed withthe anthracite and beneficial results secured both in economy andcapacity. Anthracite coal should be fired evenly, in small quantities and atfrequent intervals. If this method is not followed, dead spots willappear in the fire, and if the fire gets too irregular through burningin patches, nothing can be done to remedy it until the fire is cleanedas a whole. After this grade of fuel has been fired it should be leftalone, and the fire tools used as little as possible. Owing to thedifficulty of igniting this fuel, care must be taken in cleaning fires. The intervals of cleaning will, of course, depend upon the nature of thecoal and the rate of combustion. With the small sizes and moderatelyhigh combustion rates, fires will have to be cleaned twice on eacheight-hour shift. As the fires become dirty the thickness of the fuelbed will increase, until this depth may be 12 or 14 inches just before acleaning period. In cleaning, the following practice is usuallyfollowed: The good coal on the forward half of the grate is pushed tothe rear half, and the refuse on the front portion either pulled out ordumped. The good coal is then pulled forward onto the front part of thegrate and the refuse on the rear section dumped. The remaining good coalis then spread evenly over the whole grate surface and the fire built upwith fresh coal. A ratio of grate surface to heating surface of 1 to from 35 to 40 willunder ordinary conditions develop the rated capacity of a boiler whenburning anthracite buckwheat. Where the finer sizes are used, or whereoverloads are desirable, however, this ratio should preferably be 1 to25 and a forced blast should be used. Grates 10 feet deep with a slopeof 1½ inches to the foot can be handled comfortably with this class offuel, and grates 12 feet deep with the same slope can be successfullyhandled. Where grates over 8 feet in depth are necessary, shaking gratesor overlapping dumping grates should be used. Dumping grates may beapplied either for the whole grate surface or to the rear section. Airopenings in the grate bars should be made from 3/16 inch in width forNo. 3 buckwheat to 5/16 inch for No. 1 buckwheat. It is important thatthese air openings be uniformly distributed over the whole surface toavoid blowing holes in the fire, and it is for this reason thatoverlapping grates are recommended. No air should be admitted over the fire. Steam is sometimes introducedinto the ashpit to soften any clinker that may form, but the quantity ofsteam should be limited to that required for this purpose. The steamthat may be used in a steam jet blower for securing blast will incertain instances assist in softening the clinker, but a much greaterquantity may be used by such an apparatus than is required for thispurpose. Combustion arches sprung above the grates have proved ofadvantage in maintaining a high furnace temperature and in assisting inthe ignition of fresh coal. Stacks used with forced blast should be of such size as to insure aslight suction in the furnace under any conditions of operation. A blastup to 3 inches of water should be available for the finer sizes suppliedby engine driven fans, automatically controlled by the boiler pressure. The blast required will increase as the depth of the fuel bed increases, and the slight suction should be maintained in the furnace by damperregulation. The use of blast with the finer sizes causes rapid fouling of theheating surfaces of the boiler, the dust often amounting to over 10 percent of the total fuel fired. Economical disposal of dust and ashes isof the utmost importance in burning fuel of this nature. Provisionshould be made in the baffling of the boiler to accommodate and disposeof this dust. Whenever conditions permit, the ashes can be economicallydisposed of by flushing them out with water. Bituminous Coals--There is no classification of bituminous coal as tosize that holds good in all localities. The American Society ofMechanical Engineers suggests the following grading: _Eastern Bituminous Coals_-- (A) Run of mine coal; the unscreened coal taken from the mine. (B) Lump coal; that which passes over a bar-screen with openings 1¼ inches wide. (C) Nut coal; that which passes through a bar-screen with 1¼-inch openings and over one with ¾-inch openings. (D) Slack coal; that which passes through a bar-screen with ¾-inch openings. _Western Bituminous Coals_-- (E) Run of mine coal; the unscreened coal taken from the mine. (F) Lump coal; divided into 6-inch, 3-inch and 1¼-inch lump, according to the diameter of the circular openings over which the respective grades pass; also 6 × 3-inch lump and 3 × 1¼-inch lump, according as the coal passes through a circular opening having the diameter of the larger figure and over that of the smaller diameter. (G) Nut coal; divided into 3-inch steam nut, which passes through an opening 3 inches diameter and over 1¼ inches; 1¼ inch nut, which passes through a 1¼-inch diameter opening and over a ¾-inch diameter opening; ¾-inch nut, which passes through a ¾-inch diameter opening and over a 5/8-inch diameter opening. (H) Screenings; that which passes through a 1¼-inch diameter opening. As the variation in character of bituminous coals is much greater thanin the anthracites, any rules set down for their handling must be themore general. The difficulties in burning bituminous coals with economyand with little or no smoke increases as the content of fixed carbon inthe coal decreases. It is their volatile content which causes thedifficulties and it is essential that the furnaces be designed toproperly handle this portion of the coal. The fixed carbon will takecare of itself, provided the volatile matter is properly burned. Mr. Kent, in his "Steam Boiler Economy", described the action ofbituminous coal after it is fired as follows: "The first thing that thefine fresh coal does is to choke the air spaces existing through the bedof coke, thus shutting off the air supply which is needed to burn thegases produced from the fresh coal. The next thing is a very rapidevaporation of moisture from the coal, a chilling process, which robsthe furnace of heat. Next is the formation of water-gas by the chemicalreaction, C + H_{2}O = CO + 2H, the steam being decomposed, its oxygenburning the carbon of the coal to carbonic oxide, and the hydrogen beingliberated. This reaction takes place when steam is brought in contactwith highly heated carbon. This also is a chilling process, absorbingheat from the furnaces. The two valuable fuel gases thus generated wouldgive back all the heat absorbed in their formation if they could beburned, but there is not enough air in the furnace to burn them. Admitting extra air through the fire door at this time will be of noservice, for the gases being comparatively cool cannot be burned unlessthe air is highly heated. After all the moisture has been driven offfrom the coal, the distillation of hydrocarbons begins, and aconsiderable portion of them escapes unburned, owing to the deficiencyof hot air, and to their being chilled by the relatively cool heatingsurfaces of the boiler. During all this time great volumes of smoke areescaping from the chimney, together with unburned hydrogen, hydrocarbons, and carbonic oxide, all fuel gases, while at the same timesoot is being deposited on the heating surface, diminishing itsefficiency in transmitting heat to the water. " To burn these gases distilled from the coal, it is necessary that theybe brought into contact with air sufficiently heated to cause them toignite, that sufficient space be allowed for their mixture with the air, and that sufficient time be allowed for their complete combustion beforethey strike the boiler heating surfaces, since these surfaces arecomparatively cool and will lower the temperature of the gases belowtheir ignition point. The air drawn through the fire by the draftsuction is heated in its passage and heat is added by radiation from thehot brick surfaces of the furnace, the air and volatile gases mixing asthis increase in temperature is taking place. Thus in most instances isthe first requirement fulfilled. The element of space for the propermixture of the gases with the air, and of time in which combustion is totake place, should be taken care of by sufficiently large combustionchambers. Certain bituminous coals, owing to their high volatile content, requirethat the air be heated to a higher temperature than it is possible forit to attain simply in its passage through the fire and by absorptionfrom the side walls of the furnace. Such coals can be burned with thebest results under fire brick arches. Such arches increase thetemperature of the furnace and in this way maintain the heat that mustbe present for ignition and complete combustion of the fuels inquestion. These fuels too, sometimes require additional combustionspace, and an extension furnace will give this in addition to therequired arches. As stated, the difficulty of burning bituminous coals successfully willincrease with the increase in volatile matter. This percentage ofvolatile will affect directly the depth of coal bed to be carried andthe intervals of firing for the most satisfactory results. The variationin the fuel over such wide ranges makes it impossible to definitelystate the thickness of fires for all classes, and experiment with theclass of fuel in use is the best method of determining how thatparticular fuel should be handled. The following suggestions, which arenot to be considered in any sense hard and fast rules, may be of servicefor general operating conditions for hand firing: Semi-bituminous coals, such as Pocahontas, New River, Clearfield, etc. , require fires from 10 to 14 inches thick; fresh coal should be fired atintervals of 10 to 20 minutes and sufficient coal charged at each firingto maintain a uniform thickness. Bituminous coals from Pittsburgh Regionrequire fires from 4 to 6 inches thick, and should be fired often incomparatively small charges. Kentucky, Tennessee, Ohio and Illinoiscoals require a thickness from 4 to 6 inches. Free burning coals fromRock Springs, Wyoming, require from 6 to 8 inches, while the poorergrades of Montana, Utah and Washington bituminous coals require a depthof about 4 inches. In general as thin fires are found necessary, the intervals of firingshould be made more frequent and the quantity of coal fired at eachinterval smaller. As thin fires become necessary due to the character ofthe coal, the tendency to clinker will increase if the thickness beincreased over that found to give the best results. There are two general methods of hand firing: 1st, the spreading method;and 2nd, the coking method. [Illustration: Babcock & Wilcox Chain Grate Stoker] In the spreading method but little fuel is fired at one time, and isspread evenly over the fuel bed from front to rear. Where there is morethan one firing door the doors should be fired alternately. Theadvantage of alternate firing is the whole surface of the fire is notblanketed with green coal, and steam is generated more uniformly than ifall doors were fired at one time. Again, a better combustion results dueto the burning of more of the volatile matter directly after firing thanwhere all doors are fired at one time. In the coking method, fresh coal is fired at considerable depth at thefront of the grate and after it is partially coked it is pushed backinto the furnace. The object of such a method is the preserving of a bedof carbon at the rear of the grate, in passing over which the volatilegases driven off from the green coal will be burned. This method isparticularly adaptable to a grate in which the gases are made to passhorizontally over the fire. Modern practice for hand firing leans moreand more toward the spread firing method. Again the tendency is to workbituminous coal fires less than formerly. A certain amount of slicingand raking may be necessary with either method of firing, but ingeneral, the less the fire is worked the better the results. Lignites--As the content of volatile matter and moisture in lignite ishigher than in bituminous coal, the difficulties encountered in burningthem are greater. A large combustion space is required and the bestresults are obtained where a furnace of the reverberatory type is used, giving the gases a long travel before meeting the tube surfaces. A fuelbed from 4 to 6 inches in depth can be maintained, and the coal shouldbe fired in small quantities by the alternate method. Above certainrates of combustion clinker forms rapidly, and a steam jet in the ashpitfor softening this clinker is often desirable. A considerable draftshould be available, but it should be carefully regulated by the boilerdamper to suit the condition of the fire. Smokelessness with hand firingwith this class of fuel is a practical impossibility. It has a strongtendency to foul the heating surfaces rapidly and these surfaces shouldbe cleaned frequently. Shaking grates, intelligently handled, aid incleaning the fires, but their manipulation must be carefully watched toprevent good coal being lost in the ashpit. Stokers--The term "automatic stoker" oftentimes conveys the erroneousimpression that such an apparatus takes care of itself, and it must bethoroughly understood that any stoker requires expert attention to ashigh if not higher degree than do hand-fired furnaces. Stoker-fired furnaces have many advantages over hand firing, but where astoker installation is contemplated there are many factors to beconsidered. It is true that stokers feed coal to the fire automatically, but if the coal has first to be fed to the stoker hopper by hand, itsautomatic advantage is lost. This is as true of the removal of ash froma stoker. In a general way, it may be stated that a stoker installationis not advantageous except possibly for diminishing smoke, unless theautomatic feature is carried to the handling of the coal and ash, aswhere coal and ash handling apparatus is not installed there is nosaving in labor. In large plants, however, stokers used in conjunctionwith the modern methods of coal storage and coal and ash handling, makepossible a large labor saving. In small plants the labor saving forstokers over hand-fired furnaces is negligible, and the expense of theinstallation no less proportionately than in large plants. Stokers are, therefore, advisable in small plants only where the saving in fuel willbe large, or where the smoke question is important. Interest on investment, repairs, depreciation and steam required forblast and stoker drive must all be considered. The upkeep cost will, ingeneral, be higher than for hand-fired furnaces. Stokers, however, makepossible the use of cheaper fuels with as high or higher economy than isobtainable under operating conditions in hand-fired furnaces with abetter grade of fuel. The better efficiency obtainable with a goodstoker is due to more even and continuous firing as against theintermittent firing of hand-fired furnaces; constant air supply asagainst a variation in this supply to meet varying furnace conditions inhand-fired furnaces; and the doing away to a great extent with thenecessity of working the fires. Stokers under ordinary operating conditions will give more nearlysmokeless combustion than will hand-fired furnaces and for this reasonmust often be installed regardless of other considerations. While aconstant air supply for a given power is theoretically secured by theuse of a stoker, and in many instances the draft is automaticallygoverned, the air supply should, nevertheless, be as carefully watchedand checked by flue gas analyses as in the case of hand-fired furnaces. There is a tendency in all stokers to cause the loss of some good fuelor siftings in the ashpit, but suitable arrangements may be made toreclaim this. In respect to efficiency of combustion, other conditions being equal, there will be no appreciable difference with the different types ofstokers, provided that the proper type is used for the grade of fuel tobe burned and the conditions of operation to be fulfilled. No stokerwill satisfactorily handle all classes of fuel, and in making aselection, care should be taken that the type is suited to the fuel andthe operating conditions. A cheap stoker is a poor investment. Only thebest stoker suited to the conditions which are to be met should beadopted, for if there is to be a saving, it will more than cover thecost of the best over the cheaper stoker. Mechanical Stokers are of three general types: 1st, overfeed; 2nd, underfeed; and 3rd, traveling grate. The traveling grate stokers aresometimes classed as overfeed but properly should be classed bythemselves as under certain conditions they are of the underfeed ratherthan the overfeed type. Overfeed Stokers in general may be divided into two classes, thedistinction being in the direction in which the coal is fed relative tothe furnaces. In one class the coal is fed into hoppers at the front endof the furnace onto grates with an inclination downward toward the rearof about 45 degrees. These grates are reciprocated, being made to takealternately level and inclined positions and this motion graduallycarries the fuel as it is burned toward the rear and bottom of thefurnace. At the bottom of the grates flat dumping sections are suppliedfor completing the combustion and for cleaning. The fuel is partlyburned or coked on the upper portion of the grates, the volatile gasesdriven off in this process for a perfect action being ignited and burnedin their passage over the bed of burning carbon lower on the grates, oron becoming mixed with the hot gases in the furnace chamber. In thesecond class the fuel is fed from the sides of the furnace for its fulldepth from front to rear onto grates inclined toward the center of thefurnace. It is moved by rocking bars and is gradually carried to thebottom and center of the furnace as combustion advances. Here some typeof a so-called clinker breaker removes the refuse. Underfeed Stokers are either horizontal or inclined. The fuel is fedfrom underneath, either continuously by a screw, or intermittently byplungers. The principle upon which these stokers base their claims forefficiency and smokelessness is that the green fuel is fed under thecoked and burning coal, the volatile gases from this fresh fuel beingheated and ignited in their passage through the hottest portion of thefire on the top. In the horizontal classes of underfeed stokers, theaction of a screw carries the fuel back through a retort from which itpasses upward, as the fuel above is consumed, the ash being finallydeposited on dead plates on either side of the retort, from which it canbe removed. In the inclined class, the refuse is carried downward to therear of the furnace where there are dumping plates, as in some of theoverfeed types. Underfeed stokers are ordinarily operated with a forced blast, this insome cases being operated by the same mechanism as the stoker drive, thus automatically meeting the requirements of various combustion rates. Traveling Grates are of the class best illustrated by chain gratestokers. As implied by the name these consist of endless grates composedof short sections of bars, passing over sprockets at the front and rearof the furnace. Coal is fed by gravity onto the forward end of thegrates through suitable hoppers, is ignited under ignition arches and iscarried with the grate toward the rear of the furnace as its combustionprogresses. When operated properly, the combustion is completed as thefire reaches the end of the grate and the refuse is carried over thisrear end by the grate in making the turn over the rear sprocket. In somecases auxiliary dumping grates at the rear of the chain grates are usedwith success. Chain grate stokers in general produce less smoke than either overfeedor underfeed types, due to the fact that there are no cleaning periodsnecessary. Such periods occur with the latter types of stokers atintervals depending upon the character of the fuel used and the rate ofcombustion. With chain grate stokers the cleaning is continuous andautomatic, and no periods occur when smoke will necessarily be produced. In the earlier forms, chain grates had an objectionable feature in thatthe admission of large amounts of excess air at the rear of the furnacethrough the grates was possible. This objection has been largelyovercome in recent models by the use of some such device as the bridgewall water box and suitable dampers. A distinct advantage of chaingrates over other types is that they can be withdrawn from the furnacefor inspection or repairs without interfering in any way with the boilersetting. This class of stoker is particularly successful in burning low grades ofcoal running high in ash and volatile matter which can only be burnedwith difficulty on the other types. The cost of up-keep in a chaingrate, properly constructed and operated, is low in comparison with thesame cost for other stokers. The Babcock & Wilcox chain grate is representative of this design ofstoker. Smoke--The question of smoke and smokelessness in burning fuels hasrecently become a very important factor of the problem of combustion. Cities and communities throughout the country have passed ordinancesrelative to the quantities of smoke that may be emitted from a stack, and the failure of operators to live up to the requirements of suchordinances, resulting as it does in fines and annoyance, has broughttheir attention forcibly to the matter. The whole question of smoke and smokelessness is to a large extent acomparative one. There are any number of plants burning a wide varietyof fuels in ordinary hand-fired furnaces, in extension furnaces and onautomatic stokers that are operating under service conditions, practically without smoke. It is safe to say, however, that no plantwill operate smokelessly under any and all conditions of service, nor isthere a plant in which the degree of smokelessness does not dependlargely upon the intelligence of the operating force. [Illustration: Fig. 26. Babcock & Wilcox Boiler and Superheater Equippedwith Babcock & Wilcox Chain Grate Stoker. This Setting has beenParticularly Successful in Minimizing Smoke] When a condition arises in a boiler room requiring the fires to bebrought up quickly, the operatives in handling certain types of stokerswill use their slice bars freely to break up the green portion of thefire over the bed of partially burned coal. In fact, when a load issuddenly thrown on a station the steam pressure can often be maintainedonly in this way, and such use of the slice bar will cause smoke withthe very best type of stoker. In a certain plant using a highly volatilecoal and operating boilers equipped with ordinary hand-fired furnaces, extension hand-fired furnaces and stokers, in which the boilers with thedifferent types of furnaces were on separate stacks, a difference insmoke from the different types of furnaces was apparent at light loads, but when a heavy load was thrown on the plant, all three stacks wouldsmoke to the same extent, and it was impossible to judge which type offurnace was on one or the other of the stacks. In hand-fired furnaces much can be accomplished by proper firing. Acombination of the alternate and spreading methods should be used, thecoal being fired evenly, quickly, lightly and often, and the firesworked as little as possible. Smoke can be diminished by giving thegases a long travel under the action of heated brickwork before theystrike the boiler heating surfaces. Air introduced over the fires andthe use of heated arches, etc. , for mingling the air with the gasesdistilled from the coal will also diminish smoke. Extension furnaceswill undoubtedly lessen smoke where hand firing is used, due to theincrease in length of gas travel and the fact that this travel ispartially under heated brickwork. Where hand-fired grates areimmediately under the boiler tubes, and a high volatile coal is used, ifsufficient combustion space is not provided the volatile gases, distilled as soon as the coal is thrown on the fire, strike the tubesurfaces and are cooled below the burning point before they are whollyconsumed and pass through as smoke. With an extension furnace, thesevolatile gases are acted upon by the radiant heat from the extensionfurnace arch and this heat, together with the added length of travelcauses their more complete combustion before striking the heatingsurfaces than in the former case. Smoke may be diminished by employing a baffle arrangement which givesthe gases a fairly long travel under heated brickwork and by introducingair above the fire. In many cases, however, special furnaces for smokereduction are installed at the expense of capacity and economy. From the standpoint of smokelessness, undoubtedly the best results areobtained with a good stoker, properly operated. As stated above, thebest stoker will cause smoke under certain conditions. Intelligentlyhandled, however, under ordinary operating conditions, stoker-firedfurnaces are much more nearly smokeless than those which are hand fired, and are, to all intents and purposes, smokeless. In practically allstoker installations there enters the element of time for combustion, the volatile gases as they are distilled being acted upon by ignition orother arches before they strike the heating surfaces. In many instancestoo, stokers are installed with an extension beyond the boiler front, which gives an added length of travel during which, the gases are actedupon by the radiant heat from the ignition or supplementary arches, andhere again we see the long travel giving time for the volatile gases tobe properly consumed. To repeat, it must be emphatically borne in mind that the question ofsmokelessness is largely one of degree, and dependent to an extent muchgreater than is ordinarily appreciated upon the handling of the fuel andthe furnaces by the operators, be these furnaces hand fired orautomatically fired. [Illustration: 3520 Horse-power Installation of Babcock & Wilcox Boilersat the Portland Railway, Light and Power Co. , Portland, Ore. TheseBoilers are Equipped with Wood Refuse Extension Furnaces at the Frontand Oil Burning Furnaces at the Mud Drum End] SOLID FUELS OTHER THAN COAL AND THEIR COMBUSTION Wood--Wood is vegetable tissue which has undergone no geological change. Usually the term is used to designate those compact substancesfamiliarly known as tree trunks and limbs. When newly cut, wood containsmoisture varying from 30 per cent to 50 per cent. When dried for aperiod of about a year in the atmosphere, the moisture content will bereduced to 18 or 20 per cent. TABLE 41 ULTIMATE ANALYSES AND CALORIFIC VALUES OF DRY WOOD (GOTTLIEB) _______________________________________________________| | | | | | | || Kind | | | | | | B. T. U. || of | C | H | N | O | Ash | per || Wood | | | | | | Pound ||________|_______|______|______|_______|______|_________|| | | | | | | || Oak | 50. 16 | 6. 02 | 0. 09 | 43. 36 | 0. 37 | 8316 || Ash | 49. 18 | 6. 27 | 0. 07 | 43. 91 | 0. 57 | 8480 || Elm | 48. 99 | 6. 20 | 0. 06 | 44. 25 | 0. 50 | 8510 || Beech | 49. 06 | 6. 11 | 0. 09 | 44. 17 | 0. 57 | 8391 || Birch | 48. 88 | 6. 06 | 0. 10 | 44. 67 | 0. 29 | 8586 || Fir | 50. 36 | 5. 92 | 0. 05 | 43. 39 | 0. 28 | 9063 || Pine | 50. 31 | 6. 20 | 0. 04 | 43. 08 | 0. 37 | 9153 || Poplar | 49. 37 | 6. 21 | 0. 96 | 41. 60 | 1. 86 | 7834[40]|| Willow | 49. 96 | 5. 96 | 0. 96 | 39. 56 | 3. 37 | 7926[40]||________|_______|______|______|_______|______|_________| Wood is usually classified as hard wood, including oak, maple, hickory, birch, walnut and beech; and soft wood, including pine, fir, spruce, elm, chestnut, poplar and willow. Contrary to general opinion, the heatvalue per pound of soft wood is slightly greater than the same value perpound of hard wood. Table 41 gives the chemical composition and the heatvalues of the common woods. Ordinarily the heating value of wood isconsidered equivalent to 0. 4 that of bituminous coal. In considering thecalorific value of wood as given in this table, it is to be rememberedthat while this value is based on air-dried wood, the moisture contentis still about 20 per cent of the whole, and the heat produced inburning it will be diminished by this amount and by the heat required toevaporate the moisture and superheat it to the temperature of the gases. The heat so absorbed may be calculated by the formula giving the lossdue to moisture in the fuel, and the net calorific value determined. In designing furnaces for burning wood, the question resolves itselfinto: 1st, the essential elements to give maximum capacity andefficiency with this class of fuel; and 2nd, the construction which willentail the least labor in handling and feeding the fuel and removing therefuse after combustion. Wood, as used commercially for steam generating purposes, is usually awaste product from some industrial process. At the present time refusefrom lumber and sawmills forms by far the greater part of this class offuel. In such refuse the moisture may run as high as 60 per cent and thecomposition of the fuel may vary over wide ranges during differentportions of the mill operation. The fuel consists of sawdust, "hogged"wood and slabs, and the percentage of each of these constituents mayvary greatly. Hogged wood is mill refuse and logs that have been passedthrough a "hogging machine" or macerator. This machine, through theaction of revolving knives, cuts or shreds the wood into a state inwhich it may readily be handled as fuel. Table 42 gives the moisture content and heat value of typical sawmillrefuse from various woods. TABLE 42 MOISTURE AND CALORIFIC VALUE OF SAWMILL REFUSE _____________________________________________________________________| | | | || | | Per Cent | B. T. U. || Kind of Wood | Nature of Refuse | Moisture | per Pound || | | | Dry Fuel ||_____________________|_______________________|__________|____________|| | | | || Mexican White Pine | Sawdust and Hog Chips | 51. 90 | 9020 || Yosemite Sugar Pine | Sawdust and Hog Chips | 62. 85 | 9010 || Redwood 75%, | Sawdust, Box Mill | | || Douglas Fir 25% | Refuse and Hog | 42. 20 | 8977[41] || Redwood | Sawdust and Hog Chips | 52. 98 | 9040[41] || Redwood | Sawdust and Hog Chips | 49. 11 | 9204[41] || Fir, Hemlock, | | | || Spruce and Cedar | Sawdust | 42. 06 | 8949[41] ||_____________________|_______________________|__________|____________| It is essential in the burning of this class of fuel that a largecombustion space be supplied, and on account of the usually highmoisture content there should be much heated brickwork to radiate heatto the fuel bed and thus evaporate the moisture. Extension furnaces ofthe proper size are usually essential for good results and when thisfuel is used alone, grates dropped to the floor line with an ashpitbelow give additional volume for combustion and space for maintaining athick fuel bed. A thick fuel bed is necessary in order to avoidexcessive quantities of air passing through the boiler. Where the fuelconsists of hogged wood and sawdust alone, it is best to feed itautomatically into the furnace through chutes on the top of theextension. The best results are secured when the fuel is allowed to pileup in the furnace to a height of 3 or 4 feet in the form of a cone undereach chute. The fuel burns best when not disturbed in the furnace. Eachfuel chute, when a proper distance from the grates and with the pilesmaintained at their proper height, will supply about 30 or 35 squarefeet of grate surface. While large quantities of air are required forburning this fuel, excess air is as harmful as with coal, and care mustbe taken that such an excess is not admitted through fire doors or fuelchutes. A strong natural draft usually is preferable to a blast withthis fuel. The action of blast is to make the regulation of the furnaceconditions more difficult and to blow over unconsumed fuel on theheating surfaces and into the stack. This unconsumed fuel settling inportions of the setting out of the direct path of the gases will have atendency to ignite provided any air reaches it, with results harmful tothe setting and breeching connection. This action is particularlyobjectionable if these particles are carried over into the base of astack, where they will settle below the point at which the flue entersand if ignited may cause the stack to become overheated and buckle. Whether natural draft or blast is used, much of the fuel is carried ontothe heating surfaces and these should be cleaned regularly to maintain agood efficiency. Collecting chambers in various portions of the settingshould be provided for this unconsumed fuel, and these should be keptclean. With proper draft conditions, 150 pounds of this fuel containing about30 to 40 per cent of moisture can be burned per square foot of gratesurface per hour, and in a properly designed furnace one square foot ofgrate surface can develop from 5 to 6 boiler horse power. Where the woodcontains 50 per cent of moisture or over, it is not usually safe tofigure on obtaining more than 3 to 4 horse power per square foot ofgrate surface. Dry sawdust, chips and blocks are also used as fuel in many wood-workingindustries. Here, as with the wet wood, ample combustion space should besupplied, but as this fuel is ordinarily kiln dried, large brickworksurfaces in the furnace are not necessary for the evaporation ofmoisture in the fuel. This fuel may be burned in extension furnacesthough these are not required unless they are necessary to secure anadded furnace volume, to get in sufficient grate surface, or where suchan arrangement must be used to allow for a fuel bed of sufficientthickness. Depth of fuel bed with the dry fuel is as important as withthe moist fuel. If extension furnaces are used with this dry wood, caremust be taken in their design that there is no excessive throttling ofthe gases in the furnace, or brickwork trouble will result. In Babcock &Wilcox boilers this fuel may be burned without extension furnaces, provided that the boilers are set at a sufficient height to provideample combustion space and to allow for proper depth of fuel bed. Sometimes this is gained by lowering the grates to the floor line andexcavating for an ashpit. Where the fuel is largely sawdust, it may beintroduced over the fire doors through inclined chutes. The old methodsof handling and collecting sawdust by means of air suction and blastwere such that the amount of air admitted through such chutes wasexcessive, but with improved methods the amount of air so admitted maybe reduced to a negligible quantity. The blocks and refuse which cannotbe handled through chutes may be fired through fire doors in the frontof the boiler, which should be made sufficiently large to accommodatethe larger sizes of fuel. As with wet fuel, there will be a quantity ofunconsumed wood carried over and the heating surfaces must be keptclean. In a few localities cord wood is burned. With this as with other classesof wood fuel, a large combustion space is an essential feature. Thepercentage of moisture in cord wood may make it necessary to use anextension furnace, but ordinarily this is not required. Ample combustionspace is in most cases secured by dropping the grates to the floor line, large double-deck fire doors being supplied at the usual fire door levelthrough which the wood is thrown by hand. Air is admitted under thegrates through an excavated ashpit. The side, front and rear walls ofthe furnace should be corbelled out to cover about one-third of thetotal grate surface. This prevents cold air from laneing up the sides ofthe furnace and also reduces the grate surface. Cord wood and slabs forman open fire through which the frictional loss of the air is much lessthan in the case of sawdust or hogged material. The combustion rate withcord wood is, therefore, higher and the grate surface may beconsiderably reduced. Such wood is usually cut in lengths of 4 feet or 4feet 6 inches, and the depth of the grates should be kept approximately5 feet to get the best results. Bagasse--Bagasse is the refuse of sugar cane from which the juice hasbeen extracted by pressure between the rolls of the mill. From the startof the sugar industry bagasse has been considered the natural fuel forsugar plantations, and in view of the importance of the industry a wordof history relative to the use of this fuel is not out of place. When the manufacture of sugar was in its infancy the cane was passedthrough but a single mill and the defecation and concentration of thesaccharine juice took place in a series of vessels mounted one afteranother over a common fire at one end and connected to a stack at theopposite end. This primitive method was known in the English colonies asthe "Open Wall" and in the Spanish-American countries as the "JamaicaTrain". The evaporation and concentration of the juice in the open air and overa direct fire required such quantities of fuel, and the bagasse, infact, played such an important part in the manufacture of sugar, thatoftentimes the degree of extraction, which was already low, would besacrificed to the necessity of obtaining a bagasse that might be readilyburned. The furnaces in use with these methods were as primitive as the rest ofthe apparatus, and the bagasse could be burned in them only by firstdrying it. This naturally required an enormous quantity of handling ofthe fuel in spreading and collecting and frequently entailed a shuttingdown of the mill, because a shower would spoil the supply which had beendried. The difficulties arising from the necessity of drying this fuel caused awidespread attempt on the part of inventors to the turning out of afurnace which would successfully burn green bagasse. Some of the designswere more or less clever, and about the year 1880 several such greenbagasse furnaces were installed. These did not come up to expectations, however, and almost invariably they were abandoned and recourse had tobe taken to the old method of drying in the sun. From 1880 the new era in the sugar industry may be dated. Slavery wasalmost universally abolished and it became necessary to pay for labor. The cost of production was thus increased, while growing competition ofEuropean beet sugar lowered the prices. The only remedy for the newstate of affairs was the cheapening of the production by the increase ofextraction and improvement in manufacture. The double mill took theplace of the single, the open wall method of extraction was replaced byvacuum evaporative apparatus and centrifugal machines were introduced todo the work of the great curing houses. As opposed to theseimprovements, however, the steam plants remained as they started, consisting of double flue boilers externally fired with dry bagasse. On several of the plantations horizontal multitubular boilers externallyfired were installed and at the time were considered the acme ofperfection. Numerous attempts were made to burn the bagasse green, amongothers the step grates imported from Louisiana and known as the LeonMarie furnaces, but satisfactory results were obtained in none of theappliances tried. The Babcock & Wilcox Co. At this time turned their attention to theproblem with the results which ultimately led to its solution. Their NewOrleans representative, Mr. Frederick Cook, invented a hot forced blastbagasse furnace and conveyed the patent rights to this company. Thisfurnace while not as efficient as the standard of to-day, and expensivein its construction, did, nevertheless, burn the bagasse green andenabled the boilers to develop their normal rated capacity. The firstfurnace of this type was installed at the Southwood and Mt. Houmasplantations and on a small plantation in Florida. About the year 1888two furnaces were erected in Cuba, one on the plantation Senado and theother at the Central Hormiguero. The results obtained with thesefurnaces were so remarkable in comparison with what had previously beenaccomplished that the company was overwhelmed with orders. The expenseof auxiliary fuel, usually wood, which was costly and indispensable inrainy weather, was done away with and as the mill could be operated onbagasse alone, the steam production and the factory work could beregulated with natural increase in daily output. Progress and improvement in the manufacture itself was going on at aremarkable rate, the single grinding had been replaced by a doublegrinding, this in turn by a third grinding, and finally the macerationand dilution of the bagasse was carried to the extraction of practicallythe last trace of sugar contained in it. The quantity of juice to betreated was increased in this way 20 or 30 per cent but was accompaniedby the reduction to a minimum of the bagasse available as a fuel, andled to demands upon the furnace beyond its capacity. With the improvements in the manufacture, planters had been compelled tomake enormous sacrifices to change radically their systems, and theheavy disbursement necessary for mill apparatus left few in a financialposition to make costly installations of good furnaces. The necessity ofturning to something cheap in furnace construction but which wasnevertheless better than the early method of burning the fuel dry led tothe invention of numerous furnaces by all classes of engineersregardless of their knowledge of the subject and based upon noexperience. None of the furnaces thus produced were in any senseinventions but were more or less barefaced infringements of the patentsof The Babcock & Wilcox Co. As the company could not protect its rightswithout hurting its clients, who in many cases against their own willwere infringing upon these patents, and as on the other hand they wereanxious to do something to meet the wants of the planters, a series ofexperiments were started, at their own rather than at their customers'expense, with a view to developing a furnace which, without being asexpensive, would still fulfill all the requirements of the manufacturer. The result was the cold blast green bagasse furnace which is nowoffered, and it has been adopted as standard for this class of workafter years of study and observation in our installations in the sugarcountries of the world. Such a furnace is described later in consideringthe combustion of bagasse. Composition and Calorific Value of Bagasse--The proportion of fibercontained in the cane and density of the juice are important factors inthe relation the bagasse fuel will have to the total fuel necessary togenerate the steam required in a mill's operation. A cane rich in woodfiber produces more bagasse than a poor one and a thicker juice issubject to a higher degree of dilution than one not so rich. Besides the percentage of bagasse in the cane, its physical conditionhas a bearing on its calorific value. The factors here entering are theage at which the cane must be cut, the locality in which it is grown, etc. From the analysis of any sample of bagasse its approximatecalorific value may be calculated from the formula, 8550F + 7119S + 6750G - 972WB. T. U. Per pound bagasse = ---------------------------- (22) 100 Where F = per cent of fiber in cane, S = per cent sucrose, G = per centglucose, W = per cent water. This formula gives the total available heat per pound of bagasse, thatis, the heat generated per pound less the heat required to evaporate itsmoisture and superheat the steam thus formed to the temperature of thestack gases. Three samples of bagasse in which the ash is assumed to be 3 per centgive from the formula: F = 50 S and G = 4. 5 W = 42. 5 B. T. U. = 4183F = 40 S and G = 6. 0 W = 51. 0 B. T. U. = 3351F = 33. 3 S and G = 7. 0 W = 56. 7 B. T. U. = 2797 A sample of Java bagasse having F = 46. 5, S = 4. 50, G = 0. 5, W = 47. 5gives B. T. U. 3868. These figures show that the dryer the bagasse is crushed, the higher thecalorific value, though this is accompanied by a decrease in sucrose. The explanation lies in the fact that the presence of sucrose in ananalysis is accompanied by a definite amount of water, and that theresidual juice contains sufficient organic substance to evaporate thewater present when a fuel is burned in a furnace. For example, assumethe residual juice (100 per cent) to contain 12 per cent organic matter. From the constant in formula, 12×7119 (100-12)×972------- = 854. 3 and ------------ = 855. 4. 100 100 That is, the moisture in a juice containing 12 per cent of sugar will beevaporated by the heat developed by the combustion of the containedsugar. It would, therefore, appear that a bagasse containing such juicehas a calorific value due only to its fiber content. This is, of course, true only where the highest products of oxidization are formed duringthe combustion of the organic matter. This is not strictly the case, especially with a bagasse of a high moisture content which will not burnproperly but which smoulders and produces a large quantity of productsof destructive distillation, chiefly heavy hydrocarbons, which escapeunburnt. The reasoning, however, is sufficient to explain the steammaking properties of bagasse of a low sucrose content, such as aresecured in Java, as when the sucrose content is lower, the heat value isincreased by extracting more juice, and hence more sugar from it. Thesugar operations in Java exemplify this and show that with a highdilution by maceration and heavy pressure the bagasse meets all of thesteam requirements of the mills without auxiliary fuel. A high percentage of silica or salts in bagasse has sometimes beenascribed as the reason for the tendency to smoulder in certain cases ofsoft fiber bagasse. This, however, is due to the large moisture contentof the sample resulting directly from the nature of the cane. Solublesalts in the bagasse has also been given as the explanation of suchsmouldering action of the fire, but here too the explanation lies solelyin the high moisture content, this resulting in the development of onlysufficient heat to evaporate the moisture. TABLE 43 ANALYSES AND CALORIFIC VALUES OF BAGASSE+---------------------------------------------------------------------+|+----------+--------+-------+-------+-------+-------+-------+-------+||| | | | | | | |B. T. U. |||| | | | | | | | per |||| Source |Moisture| C | H | O | N | Ash | Pound |||| | | | | | | | Dry |||| | | | | | | |Bagasse|||+----------+--------+-------+-------+-------+-------+-------+-------+|||Cuba | 51. 50 | 43. 15 | 6. 00 | 47. 95 | | 2. 90 | 7985 ||||Cuba | 49. 10 | 43. 74 | 6. 08 | 48. 61 | | 1. 57 | 8300 ||||Cuba | 42. 50 | 43. 61 | 6. 06 | 48. 45 | | 1. 88 | 8240 ||||Cuba | 51. 61 | 46. 80 | 5. 34 | 46. 35 | | 1. 51 | ||||Cuba | 52. 80 | 46. 78 | 5. 74 | 45. 38 | | 2. 10 | ||||Porto Rico| 41. 60 | 44. 28 | 6. 66 | 47. 10 | 0. 41 | 1. 35 | 8359 ||||Porto Rico| 43. 50 | 44. 21 | 6. 31 | 47. 72 | 0. 41 | 1. 35 | 8386 ||||Porto Rico| 44. 20 | 44. 92 | 6. 27 | 46. 50 | 0. 41 | 1. 90 | 8380 ||||Louisiana | 52. 10 | | | | | 2. 27 | 8230 ||||Louisiana | 54. 00 | | | | | | 8370 ||||Louisiana | 51. 80 | | | | | | 8371 ||||Java | | 46. 03 | 6. 56 | 45. 55 | 0. 18 | 1. 68 | 8681 |||+----------+--------+-------+-------+-------+-------+-------+-------+|+---------------------------------------------------------------------+ Table 43 gives the analyses and heat values of bagasse from variouslocalities. Table 44 gives the value of mill bagasse at differentextractions, which data may be of service in making approximations as toits fuel value as compared with that of other fuels. TABLE 44 VALUE OF ONE POUND OF MILL BAGASSE AT DIFFERENT EXTRACTIONS 1: Per Cent Extraction of Weight of Cane 2: Per Cent Moisture in Bagasse 3: Per Cent in Bagasse 4: Fuel Value, B. T. U. 5: Per Cent in Bagasse 6: Fuel Value, B. T. U. 7: Per Cent in Bagasse 8: Fuel Value, B. T. U. 9: Total Heat Developed per Pound of Bagasse10: Heat Required to Evaporate Moisture[42]11: Heat Available for Steam Generation12: Pounds of Bagasse Equivalent to one Pound of Coal of 14, 000 B. T. U. +----------------------------------------------------------------+|+---+-----+----------+---------+---------+----------------+----+||| | | | | |B. T. U. Value per| |||| | | Fiber | Sugar |Molasses |Pound of Bagasse| |||| | +-----+----+----+----+----+----+-----+----+-----+ |||| | | | | | | | | | | | |||| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+||| BASED UPON CANE OF 12 PER CENT FIBER AND JUICE CONTAINING ||||18 PER CENT OF SOLID MATTER. REPRESENTING TROPICAL CONDITIONS |||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+|||75 |42. 64|48. 00|3996|6. 24|451 |3. 12|217 |4664 |525 |4139 |3. 38||||77 |39. 22|52. 17|4343|5. 74|414 |2. 87|200 |4958 |483 |4475 |3. 13||||79 |35. 15|57. 14|4757|5. 14|371 |2. 57|179 |5307 |433 |4874 |2. 87||||81 |30. 21|63. 16|5258|4. 42|319 |2. 21|154 |5731 |372 |5359 |2. 61||||83 |24. 12|70. 59|5877|3. 53|256 |1. 76|122 |6255 |297 |5958 |2. 35||||85 |16. 20|80. 00|6660|2. 40|173 |1. 20| 83 |6916 |200 |6716 |2. 08|||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+||| BASED UPON CANE OF 10 PER CENT FIBER AND JUICE CONTAINING ||||15 PER CENT OF SOLID MATTER. REPRESENTING LOUISIANA CONDITIONS|||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+|||75 |51. 00|40. 00|3330|6. 00|433 |3. 00|209 |3972 |678 |3294 |4. 25||||77 |48. 07|43. 45|3617|5. 66|409 |2. 82|196 |4222 |592 |3630 |3. 86||||79 |44. 52|47. 62|3964|5. 24|378 |2. 62|182 |4524 |548 |3976 |3. 52||||81 |40. 18|52. 63|4381|4. 73|342 |2. 36|164 |4887 |495 |4392 |3. 19||||83 |35. 00|58. 82|4897|4. 12|298 |2. 06|143 |5436 |431 |5005 |2. 80||||85 |28. 33|66. 67|5550|3. 33|241 |1. 67|116 |5907 |349 |5558 |2. 52|||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+|+----------------------------------------------------------------+ Furnace Design and the Combustion of Bagasse--With the advance in sugarmanufacture there came, as described, a decrease in the amount ofbagasse available for fuel. As the general efficiency of a plant of thisdescription is measured by the amount of auxiliary fuel required per tonof cane, the relative importance of the furnace design for the burningof this fuel is apparent. In modern practice, under certain conditions of mill operation, and withbagasse of certain physical properties, the bagasse available from thecane ground will meet the total steam requirements of the plant as awhole; such conditions prevail, as described, in Java. In the UnitedStates, Cuba, Porto Rico and like countries, however, auxiliary fuel isalmost universally a necessity. The amount will vary, depending to agreat extent upon the proportion of fiber in the cane, which varieswidely with the locality and with the age at which it is cut, and to alesser extent upon the degree of purity of the manufactured sugar, theuse of the maceration water and the efficiency of the mill apparatus asa whole. [Illustration: Fig. 27. Babcock & Wilcox Boiler Set with Green BagasseFurnace] Experience has shown that this fuel may be burned with the best resultsin large quantities. A given amount of bagasse burned in one furnacebetween two boilers will give better results than the same quantityburned in a number of smaller furnaces. An objection has been raisedagainst such practice on the grounds that the necessity of shutting downtwo boiler units when it is necessary for any reason to take off afurnace, requires a larger combined boiler capacity to insure continuityof service. As a matter of fact, several small furnaces will costconsiderably more than one large furnace, and the saving in originalfurnace cost by such an installation, taken in conjunction with theadded efficiency of the larger furnace over the small, will probablymore than offset the cost of additional boiler units for spares. The essential features in furnace design for this class of fuel areample combustion space and a length of gas travel sufficient to enablethe gases to be completely burned before the boiler heating surfaces areencountered. Experience has shown that better results are secured wherethe fuel is burned on a hearth rather than on grates, the objection tothe latter method being that the air for combustion enters largelyaround the edges, where the fuel pile is thinnest. When burned on ahearth the air for combustion is introduced into the furnace throughseveral rows of tuyeres placed above and symmetrically around thehearth. An arrangement of such tuyeres over a grate, and a propermanipulation of the ashpit doors, will overcome largely the objection togrates and at the same time enable other fuel to be burned in thefurnace when necessary. This arrangement of grates and tuyeres isprobably the better from a commercially efficient standpoint. Where theair is admitted through tuyeres over the grate or hearth line, itimpinges on the fuel pile as a whole and causes a uniform combustion. Such tuyeres connect with an annular space in which, where a blast isused, the air pressure is controlled by a blower. All experience with this class of fuel indicates that the best resultsare secured with high combustion rates. With a natural draft in thefurnace of, say, three-tenths inch of water, a combustion rate of from250 to 300 pounds per square foot of grate surface per hour may beobtained. With a blast of, say, five-tenths inch of water, this rate canbe increased to 450 pounds per square foot of grate surface per hour. These rates apply to bagasse as fired containing approximately 50 percent of moisture. It would appear that the most economical results aresecured with a combustion rate of approximately 300 pounds per squarefoot per hour which, as stated, may be obtained with natural draft. Where a natural draft is available sufficient to give such a rate, it isin general to be preferred to a blast. Fig. 27 shows a typical bagasse furnace with which very satisfactoryresults have been obtained. The design of this furnace may be altered tosuit the boilers to which it is connected. It may be changed slightly inits proportions and in certain instances in its position relative to theboiler. The furnace as shown is essentially a bagasse furnace and may bemodified somewhat to accommodate auxiliary fuel. The fuel is ignited in a pit A on a hearth which is ordinarilyelliptical in shape. Air for combustion is admitted through the tuyeresB connected to an annular space C through which the amount of air iscontrolled. Above the pit the furnace widens out to form a combustionspace D which has a cylindrical or spherical roof with its topordinarily from 11 to 13 feet above the floor. The gases pass from thisspace horizontally to a second combustion chamber E from which they areled through arches F to the boiler. The arrangement of such arches ismodified to suit the boiler or boilers with which the furnace isoperated. A furnace of such design embodies the essential features ofample combustion space and long gas travel. The fuel should be fed to the furnace through an opening in the roofabove the pit by some mechanical means which will insure a constant fuelfeed and at the same time prevent the inrush of cold air into thefurnace. This class of fuel deposits a considerable quantity of dust, which ifnot removed promptly will fuse into a hard glass-like clinker. Ampleprovision should be made for the removal of such dust from the furnace, the gas ducts and the boiler setting, and these should be thoroughlycleaned once in 24 hours. Table 45 gives the results of several tests on Babcock & Wilcox boilersusing fuel of this character. TABLE 45 TESTS OF BABCOCK & WILCOX BOILERS WITH GREEN BAGASSE ____________________________________________________________________| Duration of Test | Hours | 12 | 10 | 10 | 10 || Rated Capacity of Boiler |Horse Power| 319 | 319 | 319 | 319 || Grate Surface |Square Feet| 33 | 33 | 16. 5 | 16. 5 || Draft in Furnace | Inches | . 30 | . 28 | . 29 | . 27 || Draft at Damper | Inches | . 47 | . 45 | . 46 | . 48 || Blast under Grates | Inches | . .. | . .. | . .. | . 34 || Temperature of Exit Gases | Degrees F. | 536 | 541 | 522 | 547 || /CO_{2} | Per Cent | 13. 8 | 12. 6 | 11. 7 | 12. 8 || Flue Gas Analysis { O | Per Cent | 5. 9 | 7. 6 | 8. 2 | 6. 9 || \CO | Per Cent | 0. 0 | 0. 0 | 0. 0 | 0. 0 || Bagasse per Hour as Fired | Pounds | 4980 | 4479 | 5040 | 5586 || Moisture in Bagasse | Per Cent |52. 39 |52. 93 |51. 84 |51. 71 || Dry Bagasse per Hour | Pounds | 2371 | 2108 | 2427 | 2697 || Dry Bagasse per Square Foot| | | | | || of Grate Surface per Hour| Pounds | 71. 9 | 63. 9 |147. 1 |163. 4 || Water per Hour from and at | | | | | || 212 Degrees | Pounds |10141 | 9850 |10430 |11229 || Per Cent of Rated Capacity | | | | | || Developed | Per Cent | 92. 1 | 89. 2 | 94. 7 |102. 0 ||____________________________|___________|______|______|______|______| Tan Bark--Tan bark, or spent tan, is the fibrous portion of barkremaining after use in the tanning industry. It is usually very high inits moisture content, a number of samples giving an average of 65 percent or about two-thirds of the total weight of the fuel. The weight ofthe spent tan is about 2. 13 times as great as the weight of the barkground. In calorific value an average of 10 samples gives 9500 B. T. U. Per pound dry. [43] The available heat per pound as fired, owing to thegreat percentage of moisture usually found, will be approximately 2700B. T. U. Since the weight of the spent tan as fired is 2. 13 as great asthe weight of the bark as ground at the mill, one pound of ground barkproduces an available heat of approximately 5700 B. T. U. Relative tobituminous coal, a ton of bark is equivalent to 0. 4 ton of coal. Anaverage chemical analysis of the bark is, carbon 51. 8 per cent, hydrogen6. 04, oxygen 40. 74, ash 1. 42. Tan bark is burned in isolated cases and in general the remarks onburning wet wood fuel apply to its combustion. The essential featuresare a large combustion space, large areas of heated brickwork radiatingto the fuel bed, and draft sufficient for high combustion rates. Theratings obtainable with this class of fuel will not be as high as withwet wood fuel, because of the heat value and the excessive moisturecontent. Mr. D. M. Meyers found in a series of experiments that anaverage of from 1. 5 to 2. 08 horse power could be developed per squarefoot of grate surface with horizontal return tubular boilers. This horsepower would vary considerably with the method in which the spent tan wasfired. [Illustration: 686 Horse-power Babcock & Wilcox Boiler and Superheaterin Course of Erection at the Quincy, Mass. , Station of the Bay StateStreet Railway Co. ] LIQUID FUELS AND THEIR COMBUSTION Petroleum is practically the only liquid fuel sufficiently abundant andcheap to be used for the generation of steam. It possesses manyadvantages over coal and is extensively used in many localities. There are three kinds of petroleum in use, namely those yielding ondistillation: 1st, paraffin; 2nd, asphalt; 3rd, olefine. To the firstgroup belong the oils of the Appalachian Range and the Middle West ofthe United States. These are a dark brown in color with a greenishtinge. Upon their distillation such a variety of valuable light oils areobtained that their use as fuel is prohibitive because of price. To the second group belong the oils found in Texas and California. Thesevary in color from a reddish brown to a jet black and are used verylargely as fuel. The third group comprises the oils from Russia, which, like the second, are used largely for fuel purposes. The light and easily ignited constituents of petroleum, such as naphtha, gasolene and kerosene, are oftentimes driven off by a partialdistillation, these products being of greater value for other purposesthan for use as fuel. This partial distillation does not decrease thevalue of petroleum as a fuel; in fact, the residuum known in trade as"fuel oil" has a slightly higher calorific value than petroleum andbecause of its higher flash point, it may be more safely handled. Statements made with reference to petroleum apply as well to fuel oil. In general crude oil consists of carbon and hydrogen, though it alsocontains varying quantities of moisture, sulphur, nitrogen, arsenic, phosphorus and silt. The moisture contained may vary from less than 1 toover 30 per cent, depending upon the care taken to separate the waterfrom the oil in pumping from the well. As in any fuel, this moistureaffects the available heat of the oil, and in contracting for thepurchase of fuel of this nature it is well to limit the per cent ofmoisture it may contain. A large portion of any contained moisture canbe separated by settling and for this reason sufficient storage capacityshould be supplied to provide time for such action. A method of obtaining approximately the percentage of moisture in crudeoil which may be used successfully, particularly with lighter oils, isas follows. A burette graduated into 200 divisions is filled to the 100mark with gasolene, and the remaining 100 divisions with the oil, whichshould be slightly warmed before mixing. The two are then shakentogether and any shrinkage below the 200 mark filled up with oil. Themixture should then be allowed to stand in a warm place for 24 hours, during which the water and silt will settle to the bottom. Theirpercentage by volume can then be correctly read on the burettedivisions, and the percentage by weight calculated from the specificgravities. This method is exceedingly approximate and where accurateresults are required it should not be used. For such work, thedistillation method should be used as follows: Gradually heat 100 cubic centimeters of the oil in a distillation flaskto a temperature of 150 degrees centigrade; collect the distillate in agraduated tube and measure the resulting water. Such a method insurescomplete removal of water and reduces the error arising from the slightsolubility of the water in gasolene. Two samples checked by the twomethods for the amount of moisture present gave, _Distillation_ _Dilution_ _Per Cent_ _Per Cent_ 8. 71 6. 25 8. 82 6. 26 TABLE 46 COMPOSITION AND CALORIFIC VALUE OF VARIOUS OILS +-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+| Kind of Oil | %C | %H | %S | %O |S. G. |FP | %H2O |Btu |Authority |+-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+|California, Coaling | | | | |. 927|134| |17117|Babcock & Wilcox Co. ||California, Bakersfield | | | | |. 975| | |17600|Wade ||California, Bakersfield | | |1. 30| |. 992| | |18257|Wade ||California, Kern River | | | | |. 950|140| |18845|Babcock & Wilcox Co. ||California, Los Angeles | | |2. 56| | | | |18328|Babcock & Wilcox Co. ||California, Los Angeles | | | | |. 957|196| |18855|Babcock & Wilcox Co. ||California, Los Angeles | | | | |. 977| | . 40 |18280|Babcock & Wilcox Co. ||California, Monte Christo| | | | |. 966|205| |18878|Babcock & Wilcox Co. ||California, Whittier | | | . 98| |. 944| |1. 06 |18507|Wade ||California, Whittier | | | . 72| |. 936| |1. 06 |18240|Wade ||California |85. 04|11. 52|2. 45| . 99[44]| | |1. 40 |17871|Babcock & Wilcox Co. ||California |81. 52|11. 51| . 55|6. 92[44]| |230| |18667|U. S. N. Liquid Fuel Board||California | | | . 87| | | | . 95 |18533|Blasdale ||California | | | | |. 891|257| |18655|Babcock & Wilcox Co. ||California | | |2. 45| |. 973| |1. 50[45]|17976|O'Neill ||California | | |2. 46| |. 975| |1. 32 |18104|Shepherd ||Texas, Beaumont |84. 6 |10. 9 |1. 63|2. 87 |. 924|180| |19060|U. S. N. Liquid Fuel Board||Texas, Beaumont |83. 3 |12. 4 | . 50|3. 83 |. 926|216| |19481|U. S. N. Liquid Fuel Board||Texas, Beaumont |85. 0 |12. 3 |1. 75| . 92[44]| | | |19060|Denton ||Texas, Beaumont |86. 1 |12. 3 |1. 60| |. 942| | |20152|Sparkes ||Texas, Beaumont | | | | |. 903|222| |19349|Babcock & Wilcox Co. ||Texas, Sabine | | | | |. 937|143| |18662|Babcock & Wilcox Co. ||Texas |87. 15|12. 33|0. 32| |. 908|370| |19338|U. S. N. ||Texas |87. 29|12. 32|0. 43| |. 910|375| |19659|U. S. N. ||Ohio |83. 4 |14. 7 |0. 6 |1. 3 | | | |19580| ||Pennsylvania |84. 9 |13. 7 | |1. 4 |. 886| | |19210|Booth ||West Virginia |84. 3 |14. 1 | |1. 6 |. 841| | |21240| ||Mexico | | | | |. 921|162| |18840|Babcock & Wilcox Co. ||Russia, Baku |86. 7 |12. 9 | | |. 884| | |20691|Booth ||Russia, Novorossick |84. 9 |11. 6 | |3. 46 | | | |19452|Booth ||Russia, Caucasus |86. 6 |12. 3 | |1. 10 |. 938| | |20138| ||Java |87. 1 |12. 0 | | . 9 |. 923| | |21163| ||Austria, Galicia |82. 2 |12. 1 |5. 7 | |. 870| | |18416| ||Italy, Parma |84. 0 |13. 4 |1. 8 | |. 786| | | | ||Borneo |85. 7 |11. 0 | |3. 31 | | | |19240|Orde |+-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ %C = Per Cent Carbon%H = Per Cent Hydrogen%S = Per Cent Sulphur%O = Per Cent OxygenS. G. = Specific GravityFP = Degrees Flash Point%H_{2}O = Per Cent MoistureBtu = B. T. U. Per Pound Calorific Value--A pound of petroleum usually has a calorific value offrom 18, 000 to 22, 000 B. T. U. If an ultimate analysis of an averagesample be, carbon 84 per cent, hydrogen 14 per cent, oxygen 2 per cent, and assuming that the oxygen is combined with its equivalent of hydrogenas water, the analysis would become, carbon 84 per cent, hydrogen 13. 75per cent, water 2. 25 per cent, and the heat value per pound includingits contained water would be, Carbon . 8400 × 14, 600 = 12, 264 B. T. U. Hydrogen . 1375 × 62, 100 = 8, 625 B. T. U. ------[**Should be . 1375 x 62, 000 = 8, 525] Total 20, 889 B. T. U. [**Would be Total = 20, 789] The nitrogen in petroleum varies from 0. 008 to 1. 0 per cent, while thesulphur varies from 0. 07 to 3. 0 per cent. Table 46, compiled from various sources, gives the composition, calorific value and other data relative to oil from differentlocalities. The flash point of crude oil is the temperature at which it gives offinflammable gases. While information on the actual flash points of thevarious oils is meager, it is, nevertheless, a question of importance indetermining their availability as fuels. In general it may be statedthat the light oils have a low, and the heavy oils a much higher flashpoint. A division is sometimes made at oils having a specific gravity of0. 85, with a statement that where the specific gravity is below thispoint the flash point is below 60 degrees Fahrenheit, and where it isabove, the flash point is above 60 degrees Fahrenheit. There are, however, many exceptions to this rule. As the flash point is lower thedanger of ignition or explosion becomes greater, and the utmost careshould be taken in handling the oils with a low flash point to avoidthis danger. On the other hand, because the flash point is high is nojustification for carelessness in handling those fuels. With properprecautions taken, in general, the use of oil as fuel is practically assafe as the use of coal. Gravity of Oils--Oils are frequently classified according to theirgravity as indicated by the Beaume hydrometer scale. Such aclassification is by no means an accurate measure of their relativecalorific values. Petroleum as Compared with Coal--The advantages of the use of oil fuelover coal may be summarized as follows: 1st. The cost of handling is much lower, the oil being fed by simplemechanical means, resulting in, 2nd. A general labor saving throughout the plant in the elimination ofstokers, coal passers, ash handlers, etc. 3rd. For equal heat value, oil occupies very much less space than coal. This storage space may be at a distance from the boiler withoutdetriment. 4th. Higher efficiencies and capacities are obtainable with oil thanwith coal. The combustion is more perfect as the excess air is reducedto a minimum; the furnace temperature may be kept practically constantas the furnace doors need not be opened for cleaning or working fires;smoke may be eliminated with the consequent increased cleanliness of theheating surfaces. 5th. The intensity of the fire can be almost instantaneously regulatedto meet load fluctuations. 6th. Oil when stored does not lose in calorific value as does coal, norare there any difficulties arising from disintegration, such as may befound when coal is stored. 7th. Cleanliness and freedom from dust and ashes in the boiler room witha consequent saving in wear and tear on machinery; little or no damageto surrounding property due to such dust. The disadvantages of oil are: 1st. The necessity that the oil have a reasonably high flash point tominimize the danger of explosions. 2nd. City or town ordinances may impose burdensome conditions relativeto location and isolation of storage tanks, which in the case of a plantsituated in a congested portion of the city, might make use of this fuelprohibitive. 3rd. Unless the boilers and furnaces are especially adapted for the useof this fuel, the boiler upkeep cost will be higher than if coal wereused. This objection can be entirely obviated, however, if theinstallation is entrusted to those who have had experience in the work, and the operation of a properly designed plant is placed in the hands ofintelligent labor. TABLE 47 RELATIVE VALUE OF COAL AND OIL FUEL +------+--------+-------+-----------------------------------------------+|Gross | Net | Net | Water Evaporated from and at ||Boiler| Boiler |Evap- | 212 Degrees Fahrenheit per Pound of Coal ||Effic-|Effici- |oration+-----+-----+-----+-----+-----+-----+-----+-----+| iency|ency[46]| from | | | | | | | | || with | with |and at | | | | | | | | || Oil | Oil | 212 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 || Fuel | Fuel |Degrees| | | | | | | | || | |Fahren-| | | | | | | | || | | heit +-----+-----+-----+-----+-----+-----+-----+-----+| | | per | || | | Pound | Pounds of Oil Equal to One Pound of Coal || | |of Oil | |+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+| 73 | 71 | 13. 54 |. 3693|. 4431|. 5170|. 5909|. 6647|. 7386|. 8124|. 8863|| 74 | 72 | 13. 73 |. 3642|. 4370|. 5099|. 5827|. 6556|. 7283|. 8011|. 8740|| 75 | 73 | 13. 92 |. 3592|. 4310|. 5029|. 5747|. 6466|. 7184|. 7903|. 8621|| 76 | 74 | 14. 11 |. 3544|. 4253|. 4961|. 5670|. 6378|. 7087|. 7796|. 8505|| 77 | 75 | 14. 30 |. 3497|. 4196|. 4895|. 5594|. 6294|. 6993|. 7692|. 8392|| 78 | 76 | 14. 49 |. 3451|. 4141|. 4831|. 5521|. 6211|. 6901|. 7591|. 8281|| 79 | 77 | 14. 68 |. 3406|. 4087|. 4768|. 5450|. 6131|. 6812|. 7493|. 8174|| 80 | 78 | 14. 87 |. 3363|. 4035|. 4708|. 5380|. 6053|. 6725|. 7398|. 8070|| 81 | 79 | 15. 06 |. 3320|. 3984|. 4648|. 5312|. 5976|. 6640|. 7304|. 7968|| 82 | 80 | 15. 25 |. 3279|. 3934|. 4590|. 5246|. 5902|. 6557|. 7213|. 7869|| 83 | 81 | 15. 44 |. 3238|. 3886|. 4534|. 5181|. 5829|. 6447|. 7125|. 7772|+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+| | | Net | || | |Evap- | || | |oration| || | | from | || | |and at | || | | 212 | Barrels of Oil Equal to One Ton of Coal || | |Degrees| || | |Fahren-| || | | heit | || | | per | || | |Barrel | || | |of Oil | |+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+| 73 | 71 | 4549 |2. 198|2. 638|3. 077|3. 516|3. 955|4. 395|4. 835|5. 275|| 74 | 72 | 4613 |2. 168|2. 601|3. 035|3. 468|3. 902|4. 335|4. 769|5. 202|| 75 | 73 | 4677 |2. 138|2. 565|2. 993|3. 420|3. 848|4. 275|4. 703|5. 131|| 76 | 74 | 4741 |2. 110|2. 532|2. 954|3. 376|3. 798|4. 220|4. 642|5. 063|| 77 | 75 | 4807 |2. 082|2. 498|2. 914|3. 330|3. 746|4. 162|4. 578|4. 994|| 78 | 76 | 4869 |2. 054|2. 465|2. 876|3. 286|3. 697|4. 108|4. 518|4. 929|| 79 | 77 | 4932 |2. 027|2. 433|2. 838|3. 243|3. 649|4. 054|4. 460|4. 865|| 80 | 78 | 4996 |2. 002|2. 402|2. 802|3. 202|3. 602|4. 003|4. 403|4. 803|| 81 | 79 | 5060 |1. 976|2. 371|2. 767|3. 162|3. 557|3. 952|4. 348|4. 743|| 82 | 80 | 5124 |1. 952|2. 342|2. 732|3. 122|3. 513|3. 903|4. 293|4. 683|| 83 | 81 | 5187 |1. 927|2. 313|2. 699|3. 085|3. 470|3. 856|4. 241|4. 627|+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ [Illustration: City of San Francisco, Cal. , Fire Fighting Station. No. 1. 2800 Horse Power of Babcock & Wilcox Boilers, Equipped for BurningOil Fuel] Many tables have been published with a view to comparing the two fuels. Such of these as are based solely on the relative calorific values ofoil and coal are of limited value, inasmuch as the efficiencies to beobtained with oil are higher than that obtainable with coal. Table 47takes into consideration the variation in efficiency with the two fuels, but is based on a constant calorific value for oil and coal. This table, like others of a similar nature, while useful as a rough guide, cannotbe considered as an accurate basis for comparison. This is due to thefact that there are numerous factors entering into the problem whichaffect the saving possible to a much greater extent than do the relativecalorific values of two fuels. Some of the features to be considered inarriving at the true basis for comparison are the labor saving possible, the space available for fuel storage, the facilities for conveying theoil by pipe lines, the hours during which a plant is in operation, theload factor, the quantity of coal required for banking fires, etc. , etc. The only exact method of estimating the relative advantages and costs ofthe two fuels is by considering the operating expenses of the plant witheach in turn, including the costs of every item entering into theproblem. Burning Oil Fuel--The requirements for burning petroleum are as follows: 1st. Its atomization must be thorough. 2nd. When atomized it must be brought into contact with the requisitequantity of air for its combustion, and this quantity must be at thesame time a minimum to obviate loss in stack gases. 3rd. The mixture must be burned in a furnace where a refractory materialradiates heat to assist in the combustion, and the furnace must stand upunder the high temperatures developed. 4th. The combustion must be completed before the gases come into contactwith the heating surfaces or otherwise the flame will be extinguished, possibly to ignite later in the flue connection or in the stack. 5th. There must be no localization of the heat on certain portions ofthe heating surfaces or trouble will result from overheating andblistering. The first requirement is met by the selection of a proper burner. The second requirement is fulfilled by properly introducing the air intothe furnace, either through checkerwork under the burners or throughopenings around them, and by controlling the quantity of air to meetvariations in furnace conditions. The third requirement is provided for by installing a furnace sodesigned as to give a sufficient area of heated brickwork to radiate theheat required to maintain a proper furnace temperature. The fourth requirement is provided for by giving ample space for thecombustion of the mixture of atomized oil and air, and a gas travel ofsufficient length to insure that this combustion be completed before thegases strike the heating surfaces. The fifth requirement is fulfilled by the adoption of a suitable burnerin connection with the furnace meeting the other requirements. A burnermust be used from which the flame will not impinge directly on theheating surface and must be located where such action cannot take place. If suitable burners properly located are not used, not only is the heatlocalized with disastrous results, but the efficiency is lowered by thecooling of the gases before combustion is completed. Oil Burners--The functions of an oil burner is to atomize or vaporizethe fuel so that it may be burned like a gas. All burners may beclassified under three general types: 1st, spray burners, in which theoil is atomized by steam or compressed air; 2nd, vapor burners, in whichthe oil is converted into vapor and then passed into the furnace; 3rd, mechanical burners, in which the oil is atomized by submitting it to ahigh pressure and passing it through a small orifice. Vapor burners have never been in general use and will not be discussed. Spray burners are almost universally used for land practice and thesimplicity of the steam atomizer and the excellent economy of the bettertypes, together with the low oil pressure and temperature required makesthis type a favorite for stationary plants, where the loss of freshwater is not a vital consideration. In marine work, or in any case whereit is advisable to save feed water that otherwise would have to be addedin the form of "make-up", either compressed air or mechanical means areused for atomization. Spray burners using compressed air as theatomizing agent are in satisfactory operation in some plants, but theiruse is not general. Where there is no necessity of saving raw feedwater, the greater simplicity and economy of the steam spray atomizer isgenerally the most satisfactory. The air burners require blowers, compressors or other apparatus which occupy space that might beotherwise utilized and require attention that is not necessary wheresteam is used. Steam spray burners of the older types had disadvantages in that theywere so designed that there was a tendency for the nozzle to clog withsludge or coke formed from the oil by the heat, without means of beingreadily cleaned. This has been overcome in the more modern types. Steam spray burners, as now used, may be divided into two classes: 1st, inside mixers; and 2nd, outside mixers. In the former the steam and oilcome into contact within the burner and the mixture is atomized inpassing through the orifice of the burner nozzle. [Illustration: Fig. 28. Peabody Oil Burner] In the outside mixing class the steam flows through a narrow slot orhorizontal row of small holes in the burner nozzle; the oil flowsthrough a similar slot or hole above the steam orifice, and is picked upby the steam outside of the burner and is atomized. Fig. 28 shows a typeof the Peabody burner of this class, which has given eminentsatisfaction. The construction is evident from the cut. It will be notedthat the portions of the burner forming the orifice may be readilyreplaced in case of wear, or if it is desired to alter the form of theflame. Where burners of the spray type are used, heating the oil is ofadvantage not only in causing it to be atomized more easily, but inaiding economical combustion. The temperature is, of course, limited bythe flash point of the oil used, but within the limit of thistemperature there is no danger of decomposition or of carbon deposits onthe supply pipes. Such heating should be done close to the boiler tominimize radiation loss. If the temperature is raised to a point wherean appreciable vaporization occurs, the oil will flow irregularly fromthe burner and cause the flame to sputter. On both steam and air atomizing types, a by-pass should be installedbetween the steam or air and the oil pipes to provide for the blowingout of the oil duct. Strainers should be provided for removing sludgefrom the fuel and should be so located as to allow for rapid removal, cleaning and replacing. Mechanical burners have been in use for some time in European countries, but their introduction and use has been of only recent occurrence in theUnited States. Here as already stated, the means for atomization arepurely mechanical. The most successful of the mechanical atomizers up tothe present have been of the round flame type, and only these will beconsidered. Experiments have been made with flat flame mechanicalburners, but their satisfactory action has been confined to instanceswhere it is only necessary to burn a small quantity of oil through eachindividual burner. This system of oil burning is especially adapted for marine work as thequantity of steam for putting pressure on the oil is small and thecondensed steam may be returned to the system. The only method by which successful mechanical atomization has beenaccomplished is one by which the oil is given a whirling motion withinthe burner tip. This is done either by forcing the oil through a passageof helical form or by delivering it tangentially to a circular chamberfrom which there is a central outlet. The oil is fed to these burnersunder a pressure which varies with the make of the burner and the ratesat which individual burners are using oil. The oil particles fly offfrom such a burner in straight lines in the form of a cone rather thanin the form of a spiral spray, as might be supposed. With burners of the mechanical atomizing design, the method ofintroducing air for combustion and the velocity of this air are of thegreatest importance in securing good combustion and in the effects onthe character and shape of the flame. Such burners are located at thefront of the furnace and various methods have been tried for introducingthe air for combustion. Where, in the spray burners, air is ordinarilyadmitted through a checkerwork under the burner proper, with themechanical burner, it is almost universally admitted around the burner. Early experiments with these air distributors were confined largely tosingle or duplicate cones used with the idea of directing the air to theaxis of the burner. A highly successful method of such air introduction, developed by Messrs. Peabody and Irish of The Babcock & Wilcox Co. , isby means of what they term an "impeller plate". This consists of acircular metal disk with an opening at the center for the oil burner andwith radial metal strips from the center to the periphery turned at anangle which in the later designs may be altered to give the air supplydemanded by the rate of combustion. The air so admitted does not necessarily require a whirling motion, butexperiments show that where the air is brought into contact with the oilspray with the right "twist", better combustion is secured and lower airpressures and less refinement of adjustment of individual burners arerequired. Mechanical burners have a distinct advantage over those in which steamis used as the atomizing agent in that they lend themselves more readilyto adjustment under wider variations of load. For a given horse powerthere will ordinarily be installed a much greater number of mechanicalthan steam atomizing burners. This in itself is a means to betterregulation, for with the steam atomizing burner, if one of a number isshut off, there is a marked decrease in efficiency. This is due to thefact that with the air admitted under the burner, it is ordinarilypassing through the checkerwork regardless of whether it is beingutilized for combustion or not. With a mechanical burner, on the otherhand, where individual burners are shut off, air that would be admittedfor such burner, were it in operation, may also be shut off and therewill be no undue loss from excess air. Further adjustment to meet load conditions is possible by a change inthe oil pressure acting on all burners at once. A good burner willatomize moderately heavy oil with an oil pressure as low as 30 poundsper square inch and from that point up to 200 pounds or above. Theheating of the oil also has an effect on the capacity of individualburners and in this way a third method of adjustment is given. Underworking conditions, the oil pressure remaining constant, the capacity ofeach burner will decrease as the temperature of the oil is increasedthough at low temperatures the reverse is the case. Some experimentswith a Texas crude oil having a flash point of 210 degrees showed thatthe capacity of a mechanical atomizing burner of the Peabody typeincreased from 80 degrees Fahrenheit to 110 degrees Fahrenheit, fromwhich point it fell off rapidly to 140 degrees and then more slowly tothe flash point. The above methods, together with the regulation possible throughmanipulation of the boiler dampers, indicate the wide range of loadconditions that may be handled with an installation of this class ofburners. As has already been stated, results with mechanical atomizing burnersthat may be considered very successful have been limited almost entirelyto cases where forced blast of some description has been used, the highvelocity of the air entering being of material assistance in securingthe proper mixture of air with the oil spray. Much has been done and isbeing done in the way of experiment with this class of apparatus towarddeveloping a successful mechanical atomizing burner for use with naturaldraft, and there appears to be no reason why such experiments should noteventually produce satisfactory results. Steam Consumption of Burners--The Bureau of Steam Engineering, U. S. Navy, made in 1901 an exhaustive series of tests of various oil burnersthat may be considered as representing, in so far as the performance ofthe burners themselves is concerned, the practice of that time. Thesetests showed that a burner utilizing air as an atomizing agent, requiredfor compressing the air from 1. 06 to 7. 45 per cent of the total steamgenerated, the average being 3. 18 per cent. Four tests of steamatomizing burners showed a consumption of 3. 98 to 5. 77 per cent of thetotal steam, the average being 4. 8 per cent. Improvement in burner design has largely reduced the steam consumption, though to a greater degree in steam than in air atomizing burners. Recent experiments show that a good steam atomizing burner will requireapproximately 2 per cent of the total steam generated by the boileroperated at or about its rated capacity. This figure will decrease asthe capacity is increased and is so low as to be practically negligible, except in cases where the question of loss of feed water is allimportant. There are no figures available as to the actual steamconsumption of mechanical atomizing burners but apparently this is smallif the requirement is understood to be entirely apart from the steamconsumption of the apparatus producing the forced blast. Capacity of Burners--A good steam atomizing burner properly located in awell-designed oil furnace has a capacity of somewhat over 400 horsepower. This question of capacity of individual burners is largely one ofthe proper relation between the number of burners used and the furnacevolume. In some recent tests with a Babcock & Wilcox boiler of 640 ratedhorse power, equipped with three burners, approximately 1350 horse powerwas developed with an available draft of . 55 inch at the damper or 450horse power per burner. Four burners were also tried in the same furnacebut the total steam generated did not exceed 1350 horse power or in thisinstance 338 horse power per burner. From the nature of mechanical atomizing burners, individual burners havenot as large a capacity as the steam atomizing class. In some tests on aBabcock & Wilcox marine boiler, equipped with mechanical atomizingburners, the maximum horse power developed per burner was approximately105. Here again the burner capacity is largely one of proper relationbetween furnace volume and number of burners. Furnace Design--Too much stress cannot be laid on the importance offurnace design for the use of this class of fuel. Provided a good typeof burner is adopted the furnace arrangement and the method ofintroducing air for combustion into the furnace are the all importantfactors. No matter what the type of burner, satisfactory results cannotbe secured in a furnace not suited to the fuel. The Babcock & Wilcox Co. Has had much experience with the burning of oilas fuel and an extended series of experiments by Mr. E. H. Peabody ledto the development and adoption of the Peabody furnace as being mosteminently suited for this class of work. Fig. 29 shows such a furnaceapplied to a Babcock & Wilcox boiler, and with slight modification itcan be as readily applied to any boiler of The Babcock & Wilcox Co. Manufacture. In the description of this furnace, its points of advantagecover the requirements of oil-burning furnaces in general. The atomized oil is introduced into the furnace in the direction inwhich it increases in height. This increase in furnace volume in thedirection of the flame insures free expansion and a thorough mixture ofthe oil with the air, and the consequent complete combustion of thegases before they come into contact with the tube heating surfaces. Insuch a furnace flat flame burners should be used, preferably of thePeabody type, in which the flame spreads outward toward the sides in theform of a fan. There is no tendency of the flames to impinge directly onthe heating surfaces, and the furnace can handle any quantity of flamewithout danger of tube difficulties. The burners should be so locatedthat the flames from individual burners do not interfere nor impinge toany extent on the side walls of the furnace, an even distribution ofheat being secured in this manner. The burners are operated from theboiler front and peepholes are supplied through which the operator maywatch the flame while regulating the burners. The burners can beremoved, inspected, or cleaned and replaced in a few minutes. Air isadmitted through a checkerwork of fire brick supported on the furnacefloor, the openings in the checkerwork being so arranged as to give thebest economic results in combustion. [Illustration: Fig. 29. Babcock & Wilcox Boiler, Equipped with a PeabodyOil Furnace] With steam atomizing burners introduced through the front of the boilerin stationary practice, it is usually in the direction in which thefurnace decreases in height and it is with such an arrangement thatdifficulties through the loss of tubes may be expected. With such anarrangement, the flame may impinge directly upon the tube surfaces andtube troubles from this source may arise, particularly where the feedwater has a tendency toward rapid scale formation. Such difficulties maybe the result of a blowpipe action on the part of the burner, the overheating of the tube due to oil or scale within, or the actual erosion ofthe metal by particles of oil improperly atomized. Such action need notbe anticipated, provided the oil is burned with a short flame. Theflames from mechanical atomizing burners have a less velocity ofprojection than those from steam atomizing burners and if introducedinto the higher end of the furnace, should not lead to tube difficultiesprovided they are properly located and operated. This class of burneralso will give the most satisfactory results if introduced so that theflames travel in the direction of increase in furnace volume. This isperhaps best exemplified by the very good results secured withmechanical atomizing burners and Babcock & Wilcox marine boilers inwhich, due to the fact that the boilers are fired from the low end, theflames from burners introduced through the front are in this direction. Operation of Burners--When burners are not in use, or when they arebeing started up, care must be taken to prevent oil from flowing andcollecting on the floor of the furnace before it is ignited. In startinga burner, the atomized fuel may be ignited by a burning wad of oil-soakedwaste held before it on an iron rod. To insure quick ignition, the steamsupply should be cut down. But little practice is required to become anadept at lighting an oil fire. When ignition has taken place and thefurnace brought to an even heat, the steam should be cut down to theminimum amount required for atomization. This amount can be determinedfrom the appearance of the flame. If sufficient steam is not supplied, particles of burning oil will drop to the furnace floor, giving ascintillating appearance to the flame. The steam valves should be openedjust sufficiently to overcome this scintillating action. Air Supply--From the nature of the fuel and the method of burning, thequantity of air for combustion may be minimized. As with other fuels, when the amount of air admitted is the minimum which will completelyconsume the oil, the results are the best. The excess or deficiency ofair can be judged by the appearance of the stack or by observing thegases passing through the boiler settings. A perfectly clear stackindicates excess air, whereas smoke indicates a deficiency. Withproperly designed furnaces the best results are secured by running nearthe smoking point with a slight haze in the gases. A slight variation inthe air supply will affect the furnace conditions in an oil burningboiler more than the same variation where coal is used, and for thisreason it is of the utmost importance that flue gas analysis be madefrequently on oil-burning boilers. With the air for combustion properlyregulated by adjustment of any checkerwork or any other device which maybe used, and the dampers carefully set, the flue gas analysis shouldshow, for good furnace conditions, a percentage of CO_{2} between 13 and14 per cent, with either no CO or but a trace. In boiler plant operation it is difficult to regulate the steam supplyto the burners and the damper position to meet sudden and repeatedvariations in the load. A device has been patented which automaticallyregulates by means of the boiler pressure the pressure of the steam tothe burners, the oil to the burners and the position of the boilerdamper. Such a device has been shown to give good results in plantoperation where hand regulation is difficult at best, and in manyinstances is unfortunately not even attempted. Efficiency with Oil--As pointed out in enumerating the advantages of oilfuel over coal, higher efficiencies are obtainable with the former. Withboilers of approximately 500 horse power equipped with properly designedfurnaces and burners, an efficiency of 83 per cent is possible or makingan allowance of 2 per cent for steam used by burners, a net efficiencyof 81 per cent. The conditions under which such efficiencies are to besecured are distinctly test conditions in which careful operation is aprime requisite. With furnace conditions that are not conductive to thebest combustion, this figure may be decreased by from 5 to 10 per cent. In large properly designed plants, however, the first named efficiencymay be approached for uniform running conditions, the nearness to whichit is reached depending on the intelligence of the operating crew. Itmust be remembered that the use of oil fuel presents to the carelessoperator possibilities for wastefulness much greater than in plantswhere coal is fired, and it therefore pays to go carefully into thisfeature. Table 48 gives some representative tests with oil fuel. TABLE 48 TESTS OF BABCOCK AND WILCOX BOILERS WITH OIL FUEL _______________________________________________________________________| | | | || |Pacific Light|Pacific Light|Miami Copper || | and Power | and Power | Company || Plant | Company | Company | || |Los Angeles, | | Miami, || | Cal. |Redondo, Cal. | Arizona ||_____________________________|_____________|_____________|_____________|| | | | | || Rated Capacity | Horse | | | || of Boiler | Power | 467 | 604 | 600 ||__________________|__________|_____________|_____________|_____________|| | | | | | | | || Duration of Test | Hours | 10 | 10 | 7 | 7 | 10 | 4 || | | | | | | | || Steam Pressure | | | | | | | || by Gauge | Pounds | 156. 4| 156. 9| 184. 7| 184. 9| 183. 4| 189. 5|| | | | | | | | || Temperature of | Degrees | | | | | | || Feed Water | F. | 62. 6| 61. 1| 93. 4| 101. 2| 157. 7| 156. 6|| | | | | | | | || Degrees of | Degrees | | | | | | || Superheat | F. | | | 83. 7| 144. 3| 103. 4| 139. 6|| | | | | | | | || Factor of | | | | | | | || Evaporation | |1. 2004|1. 2020|1. 2227|1. 2475|1. 1676|1. 1886|| | | | | | | | || Draft in Furnace | Inches | . 02 | . 05 | . 014| . 19 | . 12 | . 22 || | | | | | | | || Draft at Damper | Inches | . 08 | . 15 | . 046| . 47 | . 19 | . 67 || | | | | | | | || Temperature of | Degrees | | | | | | || Exit Gases | F. | 438 | 525 | 406 | 537 | 430 | 612 || _ | | | | | | | || Flue | CO_{2} | Per Cent | | | 14. 3 | 12. 1 | | || Gas | O | Per Cent | | | 3. 8 | 6. 8 | | || Analysis|_CO | Per Cent | | | 0. 0 | 0. 0 | | || | | | | | | | || Oil Burned | | | | | | | || per Hour | Pounds | 1147 | 1837 | 1439 | 2869 | 1404 | 3214 || | | | | | | | || Water Evaporated | | | | | | | || per Hour from | | | | | | | || from and at | Pounds | 18310| 27855| 22639| 40375| 21720| 42863|| 212 Degrees | | | | | | | || | | | | | | | || Evaporation from | | | | | | | || and at 212 | | | | | | | || Degrees per | Pounds | 15. 96| 15. 16| 15. 73| 14. 07| 15. 47| 13. 34|| Pound of Oil | | | | | | | || | | | | | | | || Per Cent of | | | | | | | || Rated Capacity | Pounds | 113. 6| 172. 9| 108. 6| 193. 8| 104. 9| 207. 1|| Developed | | | | | | | || | | | | | | | || B. T. U. Per | | | | | | | || Pound of Oil | B. T. U. | 18626| 18518| 18326| 18096| 18600| 18600|| | | | | | | | || Efficiency | Per Cent | 83. 15| 79. 46| 83. 29| 76. 02| 80. 70| 69. 6 ||__________________|__________|______|______|______|______|______|______| Burning Oil in Connection with Other Fuels--Considerable attention hasbeen recently given to the burning of oil in connection with otherfuels, and a combination of this sort may be advisable either with theview to increasing the boiler capacity to assist over peak loads, or tokeep the boiler in operation where there is the possibility of atemporary failure of the primary fuel. It would appear from experimentsthat such a combination gives satisfactory results from the standpointof both capacity and efficiency, if the two fuels are burned in separatefurnaces. Satisfactory results cannot ordinarily be obtained when it isattempted to burn oil fuel in the same furnace as the primary fuel, asit is practically impossible to admit the proper amount of air forcombustion for each of the two fuels simultaneously. The Babcock &Wilcox boiler lends itself readily to a double furnace arrangement andFig. 30 shows an installation where oil fuel is burned as an auxiliaryto wood. [Illustration: Fig. 30. Babcock & Wilcox Boiler Set with Combination Oiland Wood-burning Furnace] Water-gas Tar--Water-gas tar, or gas-house tar, is a by-product of thecoal used in the manufacture of water gas. It is slightly heavier thancrude oil and has a comparatively low flash point. In burning, it shouldbe heated only to a temperature which makes it sufficiently fluid, andany furnace suitable for crude oil is in general suitable for water-gastar. Care should be taken where this fuel is used to install a suitableapparatus for straining it before it is fed to the burner. [Illustration: Babcock & Wilcox Boilers Fired with Blast Furnace Gas atthe Bethlehem Steel Co. , Bethlehem, Pa. This Company Operates 12, 900Horse Power of Babcock & Wilcox Boilers] GASEOUS FUELS AND THEIR COMBUSTION Of the gaseous fuels available for steam generating purposes, the mostcommon are blast furnace gas, natural gas and by-product coke oven gas. Blast furnace gas, as implied by its name, is a by-product from theblast furnace of the iron industry. This gasification of the solid fuelin a blast furnace results, 1st, through combustion by the oxygen of theblast; 2nd, through contact with the incandescent ore (Fe_{2}O_{3} + C= 2 FeO + CO and FeO + C = Fe + CO); and 3rd, through the agency ofCO_{2} either formed in the process of reduction or driven from thecarbonates charged either as ore or flux. Approximately 90 per cent of the fuel consumed in all of the blastfurnaces of the United States is coke. The consumption of coke per tonof iron made varies from 1600 to 3600 pounds per ton of 2240 pounds ofiron. This consumption depends upon the quality of the coal, the natureof the ore, the quality of the pig iron produced and the equipment andmanagement of the plant. The average consumption, and one which isapproximately correct for ordinary conditions, is 2000 pounds of cokeper gross ton (2240 pounds) of pig iron. The gas produced in a gasfurnace per ton of pig iron is obtained from the weight of fixed carbongasified, the weight of the oxygen combined with the material of chargereduced, the weight of the gaseous constituents of the flux and theweight of air delivered by the blowing engine and the weight of volatilecombustible contained in the coke. Ordinarily, this weight of gas willbe found to be approximately five times the weight of the coke burned, or 10, 000 pounds per ton of pig iron produced. With the exception of the small amount of carbon in combination withhydrogen as methane, and a very small percentage of free hydrogen, ordinarily less than 0. 1 per cent, the calorific value of blast furnacegas is due to the CO content which when united with sufficient oxygenwhen burned under a boiler, burns further to CO_{2}. The heat value ofsuch gas will vary in most cases from 85 to 100 B. T. U. Per cubic footunder standard conditions. In modern practice, where the blast is heatedby hot blast stoves, approximately 15 per cent of the total amount ofgas is used for this purpose, leaving 85 per cent of the total for useunder boilers or in gas engines, that is, approximately 8500 pounds ofgas per ton of pig iron produced. In a modern blast furnace plant, thegas serves ordinarily as the only fuel required. Table 49 gives theanalyses of several samples of blast furnace gas. TABLE 49 TYPICAL ANALYSES OF BLAST FURNACE GAS +----------------------------------------------------------------+|+-----------------------+------+----+-----+----+------+--------+||| |CO_{2}| O | CO | H |CH_{4}| N |||+-----------------------+------+----+-----+----+------+--------+|||Bessemer Furnace | 9. 85|0. 36|32. 73|3. 14| . . |53. 92 ||||Bessemer Furnace | 11. 4 | . . |27. 7 |1. 9 | 0. 3 |58. 7 ||||Bessemer Furnace | 10. 0 | . . |26. 2 |3. 1 | 0. 2 |60. 5 ||||Bessemer Furnace | 9. 1 | . . |28. 7 |2. 7 | 0. 2 |59. 3 ||||Bessemer Furnace | 13. 5 | . . |25. 2 |1. 43| . . |59. 87 ||||Bessemer Furnace[47] | 10. 9 | . . |27. 8 |2. 8 | 0. 2 |58. 3 ||||Ferro Manganese Furnace| 7. 1 | . . |30. 1 | . . | . . |62. 8[48]||||Basic Ore Furnace | 16. 0 |0. 2 |23. 6 | . . | . . |60. 2[48]|||+-----------------------+------+----+-----+----+------+--------+|+----------------------------------------------------------------+ Until recently, the important consideration in the burning of blastfurnace gas has been the capacity that can be developed with practicallyno attention given to the aspect of efficiency. This phase of thequestion is now drawing attention and furnaces especially designed forgood efficiency with this class of fuel are demanded. The essentialfeature is ample combustion space, in which the combustion of gases maybe practically completed before striking the heating surfaces. The gaseshave the power of burning out completely after striking the heatingsurfaces, provided the initial temperature is sufficiently high, butwhere the combustion is completed before such time, the results securedare more satisfactory. A furnace volume of approximately 1 to 1. 5 cubicfeet per rated boiler horse power will give a combustion space that isample. Where there is the possibility of a failure of the gas supply, or wheresteam is required when the blast furnace is shut down, coal fired gratesof sufficient size to get the required capacity should be installed. Where grates of full size are not required, ignition grates should beinstalled, which need be only large enough to carry a fire for ignitingthe gas or for generating a small quantity of steam when the blastfurnace is shut down. The area of such grates has no direct bearing onthe size of the boiler. The grates may be placed directly under the gasburners in a standard position or may be placed between two bridge wallsback of the gas furnace and fired from the side of the boiler. Anadvantage is claimed for the standard grate position that it minimizesthe danger of explosion on the re-ignition of gas after a temporarystoppage of the supply and also that a considerable amount of dirt, ofwhich there is a good deal with this class of fuel and which isdifficult to remove, deposits on the fire and is taken out when thefires are cleaned. In any event, regardless of the location of thegrates, ample provision should be made for removing this dust, not onlyfrom the furnace but from the setting as a whole. Blast furnace gas burners are of two general types: Those in which theair for combustion is admitted around the burner proper, and those inwhich this air is admitted through the burner. Whatever the design ofburner, provision should be made for the regulation of both the air andthe gas supply independently. A gas opening of . 8 square inch per ratedhorse power will enable a boiler to develop its nominal rating with agas pressure in the main of about 2 inches. This pressure is ordinarilyfrom 6 to 8 inches and in this way openings of the above size will begood for ordinary overloads. The air openings should be from . 75 to . 85square inch per rated horse power. Good results are secured by incliningthe gas burners slightly downward toward the rear of the furnace. Wherethe burners are introduced over coal fired grates, they should be sethigh enough to give headroom for hand firing. Ordinarily, individual stacks of 130 feet high with diameters as givenin Kent's table for corresponding horse power are large enough for thisclass of work. Such a stack will give a draft sufficient to allow aboiler to be operated at 175 per cent of its rated capacity, and beyondthis point the capacity will not increase proportionately with thedraft. When more than one boiler is connected with a stack, the draftavailable at the damper should be equivalent to that which an individualstack of 130 feet high would give. The draft from such a stack isnecessary to maintain a suction under all conditions throughout allparts of the setting. If the draft is increased above that which such astack will give, difficulties arise from excess air for combustion withconsequent loss in efficiency. A poor mixing or laneing action in the furnace may result in a pulsatingeffect of the gases in the setting. This action may at times be remediedby admitting more air to the furnace. On account of the possibility of apulsating action of the gases under certain conditions and the puffs orexplosions, settings for this class of work should be carefullyconstructed and thoroughly buckstayed and tied. Natural Gas--Natural gas from different localities varies considerablyin composition and heating value. In Table 50 there is given a number ofanalyses and heat values for natural gas from various localities. This fuel is used for steam generating purposes to a considerable extentin some localities, though such use is apparently decreasing. It is bestburned by employing a large number of small burners, each being capableof handling 30 nominal rated horse power. The use of a large number ofburners obviates the danger of any laneing or blowpipe action, whichmight be present where large burners are used. Ordinarily, such a gas, as it enters the burners, is under a pressure of about 8 ounces. For thepurpose of comparison, all observations should be based on gas reducedto the standard conditions of temperature and pressure, namely 32degrees Fahrenheit and 14. 7 pounds per square inch. When the temperatureand pressure corresponding to meter readings are known, the volume ofgas under standard conditions may be obtained by multiplying the meterreadings in cubic feet by 33. 54 P/T, in which P equals the absolutepressure in pounds per square inch and T equals the absolute temperatureof the gas at the meter. In boiler testing work, the evaporation shouldalways be reduced to that per cubic foot of gas under standardconditions. TABLE 50 TYPICAL ANALYSES (BY VOLUME) AND CALORIFIC VALUES OF NATURAL GAS FROM VARIOUS LOCALITIES +----------------+-----+-----+-----+-----+-----+----+-------+------+--------+|Locality of Well| H |CH_{4}| CO |CO_{2}| N | O | Heavy |H_{2}S|B. T. U. || | | | | | | |Hydro- | | per || | | | | | | |carbons| | Cubic || | | | | | | | | | Foot || | | | | | | | | |Calcul- || | | | | | | | | |ated[49]||----------------+-----+-----+-----+-----+-----+----+-------+------+--------+|Anderson, Ind. | 1. 86|93. 07| 0. 73| 0. 26| 3. 02|0. 42| 0. 47 | 0. 15 | 1017 ||Marion, Ind. | 1. 20|93. 16| 0. 60| 0. 30| 3. 43|0. 55| 0. 15 | 0. 20 | 1009 ||Muncie, Ind. | 2. 35|92. 67| 0. 45| 0. 25| 3. 53|0. 35| 0. 25 | 0. 15 | 1004 ||Olean, N. Y. | |96. 50| 0. 50| | |2. 00| 1. 00 | | 1018 ||Findlay, O. | 1. 64|93. 35| 0. 41| 0. 25| 3. 41|0. 39| 0. 35 | 0. 20 | 1011 ||St. Ive, Pa. | 6. 10|75. 54|Trace| 0. 34| | | 18. 12 | | 1117 ||Cherry Tree, Pa. |22. 50|60. 27| | 2. 28| 7. 32|0. 83| 6. 80 | | 842 ||Grapeville, Pa. |24. 56|14. 93|Trace|Trace|18. 69|1. 22| 40. 60 | | 925 ||Harvey Well, | | | | | | | | | || Butler Co. , Pa. |13. 50|80. 00|Trace| 0. 66| | | 5. 72 | | 998 ||Pittsburgh, Pa. | 9. 64|57. 85| 1. 00| |23. 41|2. 10| 6. 00 | | 748 ||Pittsburgh, Pa. |20. 02|72. 18| 1. 00| 0. 80| |1. 10| 4. 30 | | 917 ||Pittsburgh, Pa. |26. 16|65. 25| 0. 80| 0. 60| |0. 80| 6. 30 | | 899 |+----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ [Illustration: 1600 Horse-power Installation of Babcock & Wilcox Boilersand Superheaters at the Carnegie Natural Gas Co. , Underwood, W. Va. Natural Gas is the Fuel Burned under these Boilers] When natural gas is the only fuel, the burners should be evenlydistributed over the lower portion of the boiler front. If the fuel isused as an auxiliary to coal, the burners may be placed through the firefront. A large combustion space is essential and a volume of . 75 cubicfeet per rated horse power will be found to give good results. Theburners should be of a design which give the gas and air a rotary motionto insure a proper mixture. A checkerwork wall is sometimes placed inthe furnace about 3 feet from the burners to break up the flame, butwith a good design of burner this is unnecessary. Where the gas isburned alone and no grates are furnished, good results are secured byinclining the burner downward to the rear at a slight angle. By-product Coke Oven Gas--By-product coke oven gas is a product of thedestructive distillation of coal in a distilling or by-product cokeoven. In this class of apparatus the gases, instead of being burned atthe point of their origin, as in a beehive or retort coke oven, aretaken from the oven through an uptake pipe, cooled and yield asby-products tar, ammonia, illuminating and fuel gas. A certain portionof the gas product is burned in the ovens and the remainder used or soldfor illuminating or fuel purposes, the methods of utilizing the gasvarying with plant operation and locality. Table 51 gives the analyses and heat value of certain samples ofby-product coke oven gas utilized for fuel purposes. This gas is nearer to natural gas in its heat value than is blastfurnace gas, and in general the remarks as to the proper methods ofburning natural gas and the features to be followed in furnace designhold as well for by-product coke oven gas. TABLE 51 TYPICAL ANALYSES OF BY-PRODUCT COKE OVEN GAS +----------------------------------------------+|+------+-------------------------------------+|||CO_{2}| O |CO |CH_{4}| H | N |B. T. U. Per|||| | | | | | |Cubic Foot|||+------+-----+---+------+----+----+----------+||| 0. 75 |Trace|6. 0|28. 15 |53. 0|12. 1| 505 |||| 2. 00 |Trace|3. 2|18. 80 |57. 2|18. 0| 399 |||| 3. 20 | 0. 4 |6. 3|29. 60 |41. 6|16. 1| 551 |||| 0. 80 | 1. 6 |4. 9|28. 40 |54. 2|10. 1| 460 |||+------+-----+---+------+----+----+----------+|+----------------------------------------------+ The essential difference in burning the two fuels is the pressure underwhich it reaches the gas burner. Where this is ordinarily from 4 to 8ounces in the case of natural gas, it is approximately 4 inches of waterin the case of by-product coke oven gas. This necessitates the use oflarger gas openings in the burners for the latter class of fuel than forthe former. By-product coke oven gas comes to the burners saturated with moistureand provision should be made for the blowing out of water ofcondensation. This gas too, carries a large proportion of tar andhydrocarbons which form a deposit in the burners and provision should bemade for cleaning this out. This is best accomplished by an attachmentwhich permits the blowing out of the burners by steam. UTILIZATION OF WASTE HEAT While it has been long recognized that the reclamation of heat from thewaste gases of various industrial processes would lead to a great savingin fuel and labor, the problem has, until recently, never been given theattention that its importance merits. It is true that installations havebeen made for the utilization of such gases, but in general they haveconsisted simply in the placing of a given amount of boiler heatingsurface in the path of the gases and those making the installations havebeen satisfied with whatever power has been generated, no attentionbeing given to the proportioning of either the heating surface or thegas passages to meet the peculiar characteristics of the particularclass of waste gas available. The Babcock & Wilcox Co. Has recently goneinto the question of the utilization of what has been known as wasteheat with great thoroughness, and the results secured by theirinstallations with practically all operations yielding such gases areeminently successful. TABLE 52 TEMPERATURE OF WASTE GASES FROM VARIOUS INDUSTRIAL PROCESSES +-----------------------------------------------------+|+-----------------------------------+---------------+|||Waste Heat From |Temperature[50]|||| | Degrees |||+-----------------------------------+---------------+|||Brick Kilns | 2000-2300 ||||Zinc Furnaces | 2000-2300 ||||Copper Matte Reverberatory Furnaces| 2000-2200 ||||Beehive Coke Ovens | 1800-2000 ||||Cement Kilns | 1200-1600[51]||||Nickel Refining Furnaces | 1500-1750 ||||Open Hearth Steel Furnaces | 1100-1400 |||+-----------------------------------+---------------+|+-----------------------------------------------------+ The power that can be obtained from waste gases depends upon theirtemperature and weight, and both of these factors vary widely indifferent commercial operations. Table 52 gives a list of certainprocesses yielding waste gases the heat of which is available for thegeneration of steam and the approximate temperature of such gases. Itshould be understood that the temperatures in the table are the averageof the range of a complete cycle of the operation and that the minimumand maximum temperatures may vary largely from the figures given. The maximum available horse power that may be secured from such gases isrepresented by the formula: W(T-t)sH. P. = ------- (23) 33, 479 Where W = the weight of gases passing per hour, T = temperature of gases entering heating surface, t = temperature leaving heating surface, s = specific heat of gases. The initial temperature and the weight or volume of gas will depend, asstated, upon the process involved. The exit temperature will depend, toa certain extent, upon the temperature of the entering gases, but willbe governed mainly by the efficiency of the heating surfaces installedfor the absorption of the heat. Where the temperature of the gas available is high, approaching thatfound in direct fired boiler practice, the problem is simple and thequestion of design of boiler becomes one of adapting the proper amountof heating surface to the volume of gas to be handled. With suchtemperatures, and a volume of gas available approximately in accordancewith that found in direct fired boiler practice, a standard boiler orone but slightly modified from the standard will serve the purposesatisfactorily. As the temperatures become lower, however, the problemis more difficult and the departure from standard practice more radical. With low temperature gases, to obtain a heat transfer rate at allcomparable with that found in ordinary boiler practice, the lack oftemperature must be offset by an added velocity of the gases in theirpassage over the heating surfaces. In securing the velocity necessary togive a heat transfer rate with low temperature gases sufficient to makethe installation of waste heat boilers show a reasonable return on theinvestment, the frictional resistance to the gases through the boilerbecomes greatly in excess of what would be considered good practice indirect fired boilers. Practically all operations yielding waste gasesrequire that nothing be done in the way of impairing the draft at thefurnace outlet, as this might interfere with the operation of theprimary furnace. The installation of a waste heat boiler, therefore, very frequently necessitates providing sufficient mechanical draft toovercome the frictional resistance of the gases through the heatingsurfaces and still leave ample draft available to meet the maximumrequirements of the primary furnace. Where the temperature and volume of the gases are in line with what arefound in ordinary direct fired practice, the area of the gas passagesmay be practically standard. With the volume of gas known, the draftloss through the heating surfaces may be obtained from experimental dataand this additional draft requirement met by the installation of a stacksufficient to take care of this draft loss and still leave draft enoughfor operating the furnace at its maximum capacity. Where the temperatures are low, the added frictional resistance willordinarily be too great to allow the draft required to be secured byadditional stack height and the installation of a fan is necessary. Sucha fan should be capable of handling the maximum volume of gas that thefurnace may produce, and of maintaining a suction equivalent to themaximum frictional resistance of such volume through the boiler plus themaximum draft requirement at the furnace outlet. Stacks and fans forthis class of work should be figured on the safe side. Where a faninstallation is necessary, the loss of draft in the fan connectionsshould be considered, and in figuring conservatively it should beremembered that a fan of ample size may be run as economically as asmaller fan, whereas the smaller fan, if overloaded, is operated with alarge loss in efficiency. In practically any installation where lowtemperature gas requires a fan to give the proper heat transfer from thegases, the cost of the fan and of the energy to drive it will be morethan offset by the added power from the boiler secured by its use. Furthermore, the installation of such a fan will frequently increase thecapacity of the industrial furnace, in connection with which the wasteheat boilers are installed. In proportioning heating surfaces and gas passages for waste heat workthere are so many factors bearing directly on what constitutes theproper installation that it is impossible to set any fixed rules. Eachindividual installation must be considered by itself as well as theparticular characteristics of the gases available, such as theirtemperature and volume, and the presence of dust or tar-like substances, and all must be given the proper weight in the determination of thedesign of the heating surfaces and gas passages for the specific set ofconditions. [Graph: Per Cent of Water Heating Surface passed over by Gases/Per Centof the Total Amount of Steam Generated in the Boileragainst Temperature in Degrees Fahrenheit of Hot Gases Sweeping HeatingSurface Fig. 31. Curve Showing Relation Between Gas Temperature, Heating Surfacepassed over, and Amount of Steam Generated. Ten Square Feet of HeatingSurface are Assumed as Equivalent to One Boiler Horse Power] Fig. 31 shows the relation of gas temperatures, heating surface passedover and work done by such surface for use in cases where thetemperatures approach those found in direct fired practice and where thevolume of gas available is approximately that with which one horse powermay be developed on 10 square feet of heating surface. The curve assumeswhat may be considered standard gas passage areas, and further, thatthere is no heat absorbed by direct radiation from the fire. Experiments have shown that this curve is very nearly correct for theconditions assumed. Such being the case, its application in waste heatwork is clear. Decreasing or increasing the velocity of the gases overthe heating surfaces from what might be considered normal direct firedpractice, that is, decreasing or increasing the frictional loss throughthe boiler will increase or decrease the amount of heating surfacenecessary to develop one boiler horse power. The application of Fig. 31to such use may best be seen by an example: Assume the entering gas temperatures to be 1470 degrees and that thegases are cooled to 570 degrees. From the curve, under what are assumedto be standard conditions, the gases have passed over 19 per cent ofthe heating surface by the time they have been cooled 1470 degrees. When cooled to 570 degrees, 78 per cent of the heating surface has beenpassed over. The work done in relation to the standard of the curve isrepresented by (1470 - 570) ÷ (2500 - 500) = 45 per cent. (Thesefigures may also be read from the curve in terms of the per cent of thework done by different parts of the heating surfaces. ) That is, 78 percent - 19 per cent = 59 per cent of the standard heating surface hasdone 45 per cent of the standard amount of work. 59 ÷ 45 = 1. 31, whichis the ratio of surface of the assumed case to the standard case of thecurve. Expressed differently, there will be required 13. 1 square feetof heating surface in the assumed case to develop a horse power asagainst 10 square feet in the standard case. The gases available for this class of work are almost invariably verydirty. It is essential for the successful operation of waste-heatboilers that ample provision be made for cleaning by the installation ofaccess doors through which all parts of the setting may be reached. Inmany instances, such as waste-heat boilers set in connection with cementkilns, settling chambers are provided for the dust before the gasesreach the boiler. By-passes for the gases should in all cases be provided to enable theboiler to be shut down for cleaning and repairs without interfering withthe operation of the primary furnace. All connections from furnace toboilers should be kept tight to prevent the infiltration of air, withthe consequent lowering of gas temperatures. Auxiliary gas or coal fired grates must be installed to insurecontinuity in the operation of the boiler where the operation of thefurnace is intermittent or where it may be desired to run the boilerwith the primary furnace not in operation. Such grates are sometimesused continuously where the gases available are not sufficient todevelop the required horse power from a given amount of heating surface. Fear has at times been expressed that certain waste gases, such as thosecontaining sulphur fumes, will have a deleterious action on the heatingsurface of the boiler. This feature has been carefully watched, however, and from plants in operation it would appear that in the absence ofwater or steam leaks within the setting, there is no such harmfulaction. [Illustration: Fig. 32. Babcock & Wilcox Boiler Arranged for UtilizingWaste Heat from Open Hearth Furnace. This Setting may be Modified toTake Care of Practically any Kind of Waste Gas] CHIMNEYS AND DRAFT The height and diameter of a properly designed chimney depend upon theamount of fuel to be burned, its nature, the design of the flue, withits arrangement relative to the boiler or boilers, and the altitude ofthe plant above sea level. There are so many factors involved that asyet there has been produced no formula which is satisfactory in takingthem all into consideration, and the methods used for determining stacksizes are largely empirical. In this chapter a method sufficientlycomprehensive and accurate to cover all practical cases will bedeveloped and illustrated. Draft is the difference in pressure available for producing a flow ofthe gases. If the gases within a stack be heated, each cubic foot willexpand, and the weight of the expanded gas per cubic foot will be lessthan that of a cubic foot of the cold air outside the chimney. Therefore, the unit pressure at the stack base due to the weight of thecolumn of heated gas will be less than that due to a column of cold air. This difference in pressure, like the difference in head of water, willcause a flow of the gases into the base of the stack. In its passage tothe stack the cold air must pass through the furnace or furnaces of theboilers connected to it, and it in turn becomes heated. This newlyheated gas will also rise in the stack and the action will becontinuous. The intensity of the draft, or difference in pressure, is usuallymeasured in inches of water. Assuming an atmospheric temperature of 62degrees Fahrenheit and the temperature of the gases in the chimney as500 degrees Fahrenheit, and, neglecting for the moment the difference indensity between the chimney gases and the air, the difference betweenthe weights of the external air and the internal flue gases per cubicfoot is . 0347 pound, obtained as follows: Weight of a cubic foot of air at 62 degrees Fahrenheit = . 0761 poundWeight of a cubic foot of air at 500 degrees Fahrenheit = . 0414 pound ------------------------ Difference = . 0347 pound Therefore, a chimney 100 feet high, assumed for the purpose ofillustration to be suspended in the air, would have a pressure exertedon each square foot of its cross sectional area at its base of . 0347 ×100 = 3. 47 pounds. As a cubic foot of water at 62 degrees Fahrenheitweighs 62. 32 pounds, an inch of water would exert a pressure of 62. 32 ÷12 = 5. 193 pounds per square foot. The 100-foot stack would, therefore, under the above temperature conditions, show a draft of 3. 47 ÷ 5. 193 orapproximately 0. 67 inches of water. The method best suited for determining the proper proportion of stacksand flues is dependent upon the principle that if the cross sectionalarea of the stack is sufficiently large for the volume of gases to behandled, the intensity of the draft will depend directly upon theheight; therefore, the method of procedure is as follows: 1st. Select a stack of such height as will produce the draft required bythe particular character of the fuel and the amount to be burned persquare foot of grate surface. 2nd. Determine the cross sectional area necessary to handle the gaseswithout undue frictional losses. The application of these rules follows: Draft Formula--The force or intensity of the draft, not allowing for thedifference in the density of the air and of the flue gases, is given bythe formula: / 1 1 \D = 0. 52 H × P |--- - -----| (24) \ T T_{1}/ in which D = draft produced, measured in inches of water, H = height of top of stack above grate bars in feet, P = atmospheric pressure in pounds per square inch, T = absolute atmospheric temperature, T_{1} = absolute temperature of stack gases. In this formula no account is taken of the density of the flue gases, itbeing assumed that it is the same as that of air. Any error arising fromthis assumption is negligible in practice as a factor of correction isapplied in using the formula to cover the difference between thetheoretical figures and those corresponding to actual operatingconditions. The force of draft at sea level (which corresponds to an atmosphericpressure of 14. 7 pounds per square inch) produced by a chimney 100 feethigh with the temperature of the air at 60 degrees Fahrenheit and thatof the flue gases at 500 degrees Fahrenheit is, / 1 1 \D = 0. 52 × 100 × 14. 7 | --- - --- | = 0. 67 \ 521 961 / Under the same temperature conditions this chimney at an atmosphericpressure of 10 pounds per square inch (which corresponds to an altitudeof about 10, 000 feet above sea level) would produce a draft of, / 1 1 \D = 0. 52 × 100 × 10 | --- - --- | = 0. 45 \ 521 961 / For use in applying this formula it is convenient to tabulate values ofthe product / 1 1 \ 0. 52 × 14. 7|--- - -----| \ T T_{1}/ which we will call K, for various values of T_{1}. With these valuescalculated for assumed atmospheric temperature and pressure (24) becomes D = KH. (25) For average conditions the atmospheric pressure may be considered 14. 7pounds per square inch, and the temperature 60 degrees Fahrenheit. Forthese values and various stack temperatures K becomes: _Temperature Stack Gases_ _Constant K_ 750 . 0084 700 . 0081 650 . 0078 600 . 0075 550 . 0071 500 . 0067 450 . 0063 400 . 0058 350 . 0053 Draft Losses--The intensity of the draft as determined by the aboveformula is theoretical and can never be observed with a draft gauge orany recording device. However, if the ashpit doors of the boiler areclosed and there is no perceptible leakage of air through the boilersetting or flue, the draft measured at the stack base will beapproximately the same as the theoretical draft. The difference existingat other times represents the pressure necessary to force the gasesthrough the stack against their own inertia and the friction against thesides. This difference will increase with the velocity of the gases. With the ashpit doors closed the volume of gases passing to the stackare a minimum and the maximum force of draft will be shown by a gauge. As draft measurements are taken along the path of the gases, thereadings grow less as the points at which they are taken are fartherfrom the stack, until in the boiler ashpit, with the ashpit doors openfor freely admitting the air, there is little or no perceptible rise inthe water of the gauge. The breeching, the boiler damper, the bafflesand the tubes, and the coal on the grates all retard the passage of thegases, and the draft from the chimney is required to overcome theresistance offered by the various factors. The draft at the rear of theboiler setting where connection is made to the stack or flue may be 0. 5inch, while in the furnace directly over the fire it may not be over, say, 0. 15 inch, the difference being the draft required to overcome theresistance offered in forcing the gases through the tubes and around thebaffling. One of the most important factors to be considered in designing a stackis the pressure required to force the air for combustion through the bedof fuel on the grates. This pressure will vary with the nature of thefuel used, and in many instances will be a large percentage of the totaldraft. In the case of natural draft, its measure is found directly bynoting the draft in the furnace, for with properly designed ashpit doorsit is evident that the pressure under the grates will not differsensibly from atmospheric pressure. Loss in Stack--The difference between the theoretical draft asdetermined by formula (24) and the amount lost by friction in the stackproper is the available draft, or that which the draft gauge indicateswhen connected to the base of the stack. The sum of the losses of draftin the flue, boiler and furnace must be equivalent to the availabledraft, and as these quantities can be determined from record ofexperiments, the problem of designing a stack becomes one ofproportioning it to produce a certain available draft. The loss in the stack due to friction of the gases can be calculatedfrom the following formula: f W² C H[Delta]D = -------- (26) A³ in which [Delta]D = draft loss in inches of water, W = weight of gas in pounds passing per second, C = perimeter of stack in feet, H = height of stack in feet, f = a constant with the following values at sea level: . 0015 for steel stacks, temperature of gases 600 degrees Fahrenheit. . 0011 for steel stacks, temperature of gases 350 degrees Fahrenheit. . 0020 for brick or brick-lined stacks, temperature of gases 600 degrees Fahrenheit. . 0015 for brick or brick-lined stacks, temperature of gases 350 degrees Fahrenheit. A = Area of stack in square feet. [Illustration: 24, 420 Horse-power Installation of Babcock & WilcoxBoilers and Superheaters, Equipped with Babcock & Wilcox Chain GrateStokers in the Quarry Street Station of the Commonwealth Edison Co. , Chicago, Ill. ] This formula can also be used for calculating the frictional losses forflues, in which case, C = the perimeter of the flue in feet, H = thelength of the flue in feet, the other values being the same as forstacks. The available draft is equal to the difference between the theoreticaldraft from formula (25) and the loss from formula (26), hence: f W² C Hd^{1} = available draft = KH - -------- (27) A³ Table 53 gives the available draft in inches that a stack 100 feet highwill produce when serving different horse powers of boilers with themethods of calculation for other heights. TABLE 53 AVAILABLE DRAFT CALCULATED FOR 100-FOOT STACK OF DIFFERENT DIAMETERS ASSUMING STACKTEMPERATURE OF 500 DEGREES FAHRENHEIT AND 100 POUNDS OF GAS PER HORSE POWER FOR OTHER HEIGHTS OF STACK MULTIPLY DRAFT BY HEIGHT ÷ 100 +-----+-------------------------------------------------------------------+|Horse| ||Power| Diameter of Stack in Inches |+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+| |36 |42 |48 |54 |60 |66 |72 |78 |84 |90 |96 |102|108|114|120|132|144|+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+| 100 |. 64| | | | | | | | | | | | | | | | || 200 |. 55|. 62| | | | | | | | | | | | | | | || 300 |. 41|. 55|. 61| | | | | | | | | | | | | | || 400 |. 21|. 46|. 56|. 61| | | | | | | | | | | | | || 500 | |. 34|. 50|. 57|. 61| | | | | | | | | | | | || 600 | |. 19|. 42|. 53|. 59| | | | | | | | | | | | || 700 | | |. 34|. 48|. 56|. 60|. 63| | | | | | | | | | || 800 | | |. 23|. 43|. 52|. 58|. 61|. 63| | | | | | | | | || 900 | | | |. 36|. 49|. 56|. 60|. 62|. 64| | | | | | | | ||1000 | | | |. 29|. 45|. 53|. 58|. 61|. 63|. 64| | | | | | | ||1100 | | | | |. 40|. 50|. 56|. 60|. 62|. 63|. 64| | | | | | ||1200 | | | | |. 35|. 47|. 54|. 58|. 61|. 63|. 64|. 65| | | | | ||1300 | | | | |. 29|. 44|. 52|. 57|. 60|. 62|. 63|. 64|. 65| | | | ||1400 | | | | | |. 40|. 49|. 55|. 59|. 61|. 63|. 64|. 65|. 65| | | ||1500 | | | | | |. 36|. 47|. 53|. 58|. 60|. 62|. 63|. 64|. 65|. 65| | ||1600 | | | | | |. 31|. 43|. 52|. 56|. 59|. 62|. 63|. 64|. 65|. 65| | ||1700 | | | | | | |. 41|. 50|. 55|. 58|. 61|. 62|. 64|. 64|. 65| | ||1800 | | | | | | |. 37|. 47|. 54|. 57|. 60|. 62|. 63|. 64|. 65| | ||1900 | | | | | | |. 34|. 45|. 52|. 56|. 59|. 61|. 63|. 64|. 64| | ||2000 | | | | | | | |. 43|. 50|. 55|. 59|. 61|. 62|. 63|. 64| | ||2100 | | | | | | | |. 40|. 49|. 54|. 58|. 60|. 62|. 63|. 64| | ||2200 | | | | | | | |. 38|. 47|. 53|. 57|. 59|. 61|. 62|. 64| | ||2300 | | | | | | | |. 35|. 45|. 52|. 56|. 59|. 61|. 62|. 63| | ||2400 | | | | | | | |. 32|. 43|. 50|. 55|. 58|. 60|. 62|. 63| | ||2500 | | | | | | | | |. 41|. 49|. 54|. 57|. 60|. 61|. 63| | ||2600 | | | | | | | | | |. 47|. 53|. 56|. 59|. 61|. 62|. 64|. 65||2700 | | | | | | | | | |. 45|. 52|. 55|. 58|. 60|. 62|. 64|. 65||2800 | | | | | | | | | |. 44|. 59|. 55|. 58|. 60|. 61|. 64|. 65||2900 | | | | | | | | | |. 42|. 49|. 54|. 57|. 59|. 61|. 63|. 65||3000 | | | | | | | | | |. 40|. 48|. 53|. 56|. 59|. 61|. 63|. 64||3100 | | | | | | | | | |. 38|. 47|. 52|. 56|. 58|. 60|. 63|. 64||3200 | | | | | | | | | | |. 45|. 51|. 55|. 58|. 60|. 63|. 64||3300 | | | | | | | | | | |. 44|. 50|. 54|. 57|. 59|. 62|. 64||3400 | | | | | | | | | | |. 42|. 49|. 53|. 56|. 59|. 62|. 64||3500 | | | | | | | | | | |. 40|. 48|. 52|. 56|. 58|. 62|. 64||3600 | | | | | | | | | | | |. 47|. 52|. 55|. 58|. 61|. 63||3700 | | | | | | | | | | | |. 45|. 51|. 55|. 57|. 61|. 63||3800 | | | | | | | | | | | |. 44|. 50|. 54|. 57|. 61|. 63||3900 | | | | | | | | | | | |. 43|. 49|. 53|. 56|. 60|. 63||4000 | | | | | | | | | | | |. 42|. 48|. 52|. 56|. 60|. 62||4100 | | | | | | | | | | | |. 40|. 47|. 52|. 55|. 60|. 62||4200 | | | | | | | | | | | |. 39|. 46|. 51|. 55|. 59|. 62||4300 | | | | | | | | | | | | |. 45|. 50|. 54|. 59|. 62||4400 | | | | | | | | | | | | |. 44|. 49|. 53|. 59|. 62||4500 | | | | | | | | | | | | |. 43|. 49|. 53|. 58|. 61||4600 | | | | | | | | | | | | |. 42|. 48|. 52|. 58|. 61||4700 | | | | | | | | | | | | |. 41|. 47|. 51|. 57|. 61||4800 | | | | | | | | | | | | |. 40|. 46|. 51|. 57|. 60||4900 | | | | | | | | | | | | | |. 45|. 50|. 57|. 60||5000 | | | | | | | | | | | | | |. 44|. 49|. 56|. 60|+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ FOR OTHER STACK TEMPERATURES ADD OR DEDUCT BEFORE MULTIPLYING BYHEIGHT ÷ 100 AS FOLLOWS[52] For 750 Degrees F. Add . 17 inch. For 700 Degrees F. Add . 14 inch. For 650 Degrees F. Add . 11 inch. For 600 Degrees F. Add . 08 inch. For 550 Degrees F. Add . 04 inch. For 450 Degrees F. Deduct . 04 inch. For 400 Degrees F. Deduct . 09 inch. For 350 Degrees F. Deduct . 14 inch. [Graph: Horse Power of Boilers against Diameter of Stack in Inches Fig. 33. Diameter of Stacks and Horse Power they will Serve Computed from Formula (28). For brick or brick-lined stacks, increasethe diameter 6 per cent] Height and Diameter of Stacks--From this formula (27) it becomes evidentthat a stack of certain diameter, if it be increased in height, willproduce the same available draft as one of larger diameter, theadditional height being required to overcome the added frictional loss. It follows that among the various stacks that would meet therequirements of a particular case there must be one which can beconstructed more cheaply than the others. It has been determined fromthe relation of the cost of stacks to their diameters and heights, inconnection with the formula for available draft, that the minimum coststack has a diameter dependent solely upon the horse power of theboilers it serves, and a height proportional to the available draftrequired. Assuming 120 pounds of flue gas per hour for each boiler horse power, which provides for ordinary overloads and the use of poor coal, themethod above stated gives: For an unlined steel stack-- diameter in inches = 4. 68 (H. P. )^{2/5} (28) For a stack lined with masonry-- diameter in inches = 4. 92 (H. P. )^{2/5} (29) In both of these formulae H. P. = the rated horse power of the boiler. From this formula the curve, Fig. 33, has been calculated and from itthe stack diameter for any boiler horse power can be selected. For stoker practice where a large stack serves a number of boilers, thearea is usually made about one-third more than the above rules call for, which allows for leakage of air through the setting of any idle boilers, irregularities in operating conditions, etc. Stacks with diameters determined as above will give an available draftwhich bears a constant ratio of the theoretical draft, and allowing forthe cooling of the gases in their passage upward through the stack, thisratio is 8. Using this factor in formula (25), and transposing, theheight of the chimney becomes, d^{1}H = ----- (30) . 8 K Where H = height of stack in feet above the level of the grates, d^{1} = available draft required, K = constant as in formula. Losses in Flues--The loss of draft in straight flues due to friction andinertia can be calculated approximately from formula (26), which wasgiven for loss in stacks. It is to be borne in mind that C in thisformula is the actual perimeter of the flue and is least, relative tothe cross sectional area, when the section is a circle, is greater for asquare section, and greatest for a rectangular section. The retardingeffect of a square flue is 12 per cent greater than that of a circularflue of the same area and that of a rectangular with sides as 1 and 1½, 15 per cent greater. The greater resistance of the more or less unevenbrick or concrete flue is provided for in the value of the constantsgiven for formula (26). Both steel and brick flues should be short andshould have as near a circular or square cross section as possible. Abrupt turns are to be avoided, but as long easy sweeps require valuablespace, it is often desirable to increase the height of the stack ratherthan to take up added space in the boiler room. Short right-angle turnsreduce the draft by an amount which can be roughly approximated as equalto 0. 05 inch for each turn. The turns which the gases make in leavingthe damper box of a boiler, in entering a horizontal flue and in turningup into a stack should always be considered. The cross sectional areasof the passages leading from the boilers to the stack should be of amplesize to provide against undue frictional loss. It is poor economy torestrict the size of the flue and thus make additional stack heightnecessary to overcome the added friction. The general practice is tomake flue areas the same or slightly larger than that of the stack;these should be, preferably, at least 20 per cent greater, and a saferule to follow in figuring flue areas is to allow 35 square feet per1000 horse power. It is unnecessary to maintain the same size of fluethe entire distance behind a row of boilers, and the areas at any pointmay be made proportional to the volume of gases that will pass thatpoint. That is, the areas may be reduced as connections to variousboilers are passed. [Illustration: 6000 Horse-power Installation of Babcock & Wilcox Boilersat the United States Navy Yard, Washington, D. C. ] With circular steel flues of approximately the same size as the stacks, or reduced proportionally to the volume of gases they will handle, aconvenient rule is to allow 0. 1 inch draft loss per 100 feet of fluelength and 0. 05 inch for each right-angle turn. These figures are alsogood for square or rectangular steel flues with areas sufficiently largeto provide against excessive frictional loss. For losses in brick orconcrete flues, these figures should be doubled. Underground flues are less desirable than overhead or rear flues for thereason that in most instances the gases will have to make more turnswhere underground flues are used and because the cross sectional area ofsuch flues will oftentimes be decreased on account of an accumulation ofdirt or water which it may be impossible to remove. In tall buildings, such as office buildings, it is frequently necessaryin order to carry spent gases above the roofs, to install a stack theheight of which is out of all proportion to the requirements of theboilers. In such cases it is permissible to decrease the diameter of astack, but care must be taken that this decrease is not sufficient tocause a frictional loss in the stack as great as the added draftintensity due to the increase in height, which local conditions makenecessary. In such cases also the fact that the stack diameter is permissiblydecreased is no reason why flue sizes connecting to the stack should bedecreased. These should still be figured in proportion to the area ofthe stack that would be furnished under ordinary conditions or with anallowance of 35 square feet per 1000 horse power, even though the crosssectional area appears out of proportion to the stack area. Loss in Boiler--In calculating the available draft of a chimney 120pounds per hour has been used as the weight of the gases per boilerhorse power. This covers an overload of the boiler to an extent of 50per cent and provides for the use of poor coal. The loss in draftthrough a boiler proper will depend upon its type and baffling and willincrease with the per cent of rating at which it is run. No figures canbe given which will cover all conditions, but for approximate use infiguring the available draft necessary it may be assumed that the lossthrough a boiler will be 0. 25 inch where the boiler is run at rating, 0. 40 inch where it is run at 150 per cent of its rated capacity, and0. 70 inch where it is run at 200 per cent of its rated capacity. Loss in Furnace--The draft loss in the furnace or through the fuel bedvaries between wide limits. The air necessary for combustion must passthrough the interstices of the coal on the grate. Where these are large, as is the case with broken coal, but little pressure is required toforce the air through the bed; but if they are small, as with bituminousslack or small sizes of anthracite, a much greater pressure is needed. If the draft is insufficient the coal will accumulate on the grates anda dead smoky fire will result with the accompanying poor combustion; ifthe draft is too great, the coal may be rapidly consumed on certainportions of the grate, leaving the fire thin in spots and a portion ofthe grates uncovered with the resulting losses due to an excessiveamount of air. [Graph: Force of Draft between Furnace and Ash Pit--Inches of Wateragainst Pounds of Coal burned per Square Foot of Grate Surface per Hour Fig. 34. Draft Required at Different Combustion Rates for Various Kindsof Coal] Draft Required for Different Fuels--For every kind of fuel and rate ofcombustion there is a certain draft with which the best general resultsare obtained. A comparatively light draft is best with the free burningbituminous coals and the amount to use increases as the percentage ofvolatile matter diminishes and the fixed carbon increases, being highestfor the small sizes of anthracites. Numerous other factors such as thethickness of fires, the percentage of ash and the air spaces in thegrates bear directly on this question of the draft best suited to agiven combustion rate. The effect of these factors can only be found byexperiment. It is almost impossible to show by one set of curves thefurnace draft required at various rates of combustion for all of thedifferent conditions of fuel, etc. , that may be met. The curves in Fig. 34, however, give the furnace draft necessary to burn various kinds ofcoal at the combustion rates indicated by the abscissae, for a generalset of conditions. These curves have been plotted from the records ofnumerous tests and allow a safe margin for economically burning coals ofthe kinds noted. Rate of Combustion--The amount of coal which can be burned per hour persquare foot of grate surface is governed by the character of the coaland the draft available. When the boiler and grate are properlyproportioned, the efficiency will be practically the same, withinreasonable limits, for different rates of combustion. The area of thegrate, and the ratio of this area to the boiler heating surface willdepend upon the nature of the fuel to be burned, and the stack should beso designed as to give a draft sufficient to burn the maximum amount offuel per square foot of grate surface corresponding to the maximumevaporative requirements of the boiler. Solution of a Problem--The stack diameter can be determined from thecurve, Fig. 33. The height can be determined by adding the draft lossesin the furnace, through the boiler and flues, and computing from formula(30) the height necessary to give this draft. Example: Proportion a stack for boilers rated at 2000 horse power, equipped with stokers, and burning bituminous coal that will evaporate 8pounds of water from and at 212 degrees Fahrenheit per pound of fuel;the ratio of boiler heating surface to grate surface being 50:1; theflues being 100 feet long and containing two right-angle turns; thestack to be able to handle overloads of 50 per cent; and the rated horsepower of the boilers based on 10 square feet of heating surface perhorse power. The atmospheric temperature may be assumed as 60 degrees Fahrenheit andthe flue temperatures at the maximum overload as 550 degrees Fahrenheit. The grate surface equals 400 square feet. 2000 × 34½The total coal burned at rating = ---------- = 8624 pounds. 8 The coal per square foot of grate surface per hour at rating = 8624---- = 22 pounds. 400 For 50 per cent overload the combustion rate will be approximately 60per cent greater than this or 1. 60 × 22 = 35 pounds per square foot ofgrate surface per hour. The furnace draft required for the combustionrate, from the curve, Fig. 34, is 0. 6 inch. The loss in the boiler willbe 0. 4 inch, in the flue 0. 1 inch, and in the turns 2 × 0. 05 = 0. 1 inch. The available draft required at the base of the stack is, therefore, _Inches_Boiler 0. 4Furnace 0. 6Flues 0. 1Turns 0. 1 --- Total 1. 2 Since the available draft is 80 per cent of the theoretical draft, thisdraft due to the height required is 1. 2 ÷ . 8 = 1. 5 inch. The chimney constant for temperatures of 60 degrees Fahrenheit and 550degrees Fahrenheit is . 0071 and from formula (30), 1. 5H = ----- = 211 feet. . 0071 Its diameter from curve in Fig. 33 is 96 inches if unlined, and 102inches inside if lined with masonry. The cross sectional area of theflue should be approximately 70 square feet at the point where the totalamount of gas is to be handled, tapering to the boiler farthest from thestack to a size which will depend upon the size of the boiler unitsused. Correction in Stack Sizes for Altitudes--It has ordinarily been assumedthat a stack height for altitude will be increased inversely as theratio of the barometric pressure at the altitude to that at sea level, and that the stack diameter will increase inversely as the two-fifthspower of this ratio. Such a relation has been based on the assumption ofconstant draft measured in inches of water at the base of the stack fora given rate of operation of the boilers, regardless of altitude. If the assumption be made that boilers, flues and furnace remain thesame, and further that the increased velocity of a given weight of airpassing through the furnace at a higher altitude would have no effect onthe combustion, the theory has been advanced[53] that a different lawapplies. Under the above assumptions, whenever a stack is working at its maximumcapacity at any altitude, the entire draft is utilized in overcoming thevarious resistances, each of which is proportional to the square of thevelocity of the gases. Since boiler areas are fixed, all velocities maybe related to a common velocity, say, that within the stack, and allresistances may, therefore, be expressed as proportional to the squareof the chimney velocity. The total resistance to flow, in terms ofvelocity head, may be expressed in terms of weight of a column ofexternal air, the numerical value of such head being independent of thebarometric pressure. Likewise the draft of a stack, expressed in heightof column of external air, will be numerically independent of thebarometric pressure. It is evident, therefore, that if a given boilerplant, with its stack operated with a fixed fuel, be transplanted fromsea level to an altitude, assuming the temperatures remain constant, thetotal draft head measured in height of column of external air will benumerically constant. The velocity of chimney gases will, therefore, remain the same at altitude as at sea level and the weight of gasesflowing per second with a fixed velocity will be proportional to theatmospheric density or inversely proportional to the normal barometricpressure. To develop a given horse power requires a constant weight of chimney gasand air for combustion. Hence, as the altitude is increased, the densityis decreased and, for the assumptions given above, the velocity throughthe furnace, the boiler passes, breeching and flues must becorrespondingly greater at altitude than at sea level. The meanvelocity, therefore, for a given boiler horse power and constant weightof gases will be inversely proportional to the barometric pressure andthe velocity head measured in column of external air will be inverselyproportional to the square of the barometric pressure. For stacks operating at altitude it is necessary not only to increasethe height but also the diameter, as there is an added resistance withinthe stack due to the added friction from the additional height. Thisfrictional loss can be compensated by a suitable increase in thediameter and when so compensated, it is evident that on the assumptionsas given, the chimney height would have to be increased at a ratioinversely proportional to the square of the normal barometric pressure. In designing a boiler for high altitudes, as already stated, theassumption is usually made that a given grade of fuel will require thesame draft measured in inches of water at the boiler damper as at sealevel, and this leads to making the stack height inversely as thebarometric pressures, instead of inversely as the square of thebarometric pressures. The correct height, no doubt, falls somewherebetween the two values as larger flues are usually used at the higheraltitudes, whereas to obtain the ratio of the squares, the flues must bethe same size in each case, and again the effect of an increasedvelocity of a given weight of air through the fire at a high altitude, on the combustion, must be neglected. In making capacity tests with coalfuel, no difference has been noted in the rates of combustion for agiven draft suction measured by a water column at high and lowaltitudes, and this would make it appear that the correct height to useis more nearly that obtained by the inverse ratio of the barometricreadings than by the inverse ratio of the squares of the barometricreadings. If the assumption is made that the value falls midway betweenthe two formulae, the error in using a stack figured in the ordinary wayby making the height inversely proportional to the barometric readingswould differ about 10 per cent in capacity at an altitude of 10, 000feet, which difference is well within the probable variation of the sizedetermined by different methods. It would, therefore, appear that ampleaccuracy is obtained in all cases by simply making the height inverselyproportional to the barometric readings and increasing the diameter sothat the stacks used at high altitudes have the same frictionalresistance as those used at low altitudes, although, if desired, thestack may be made somewhat higher at high altitudes than this rule callsfor in order to be on the safe side. The increase of stack diameter necessary to maintain the same frictionloss is inversely as the two-fifths power of the barometric pressure. Table 54 gives the ratio of barometric readings of various altitudes tosea level, values for the square of this ratio and values of thetwo-fifths power of this ratio. TABLE 54 STACK CAPACITIES, CORRECTION FACTORS FOR ALTITUDES _______________________________________________________________________| | | | | || Altitude | | R | | R^{2/5} || Height in Feet | Normal | Ratio Barometer | | Ratio Increase || Above | Barometer | Reading | R² | in Stack || Sea Level | | Sea Level to | | Diameter || | | Altitude | | ||________________|___________|_________________|_______|________________|| | | | | || 0 | 30. 00 | 1. 000 | 1. 000 | 1. 000 || 1000 | 28. 88 | 1. 039 | 1. 079 | 1. 015 || 2000 | 27. 80 | 1. 079 | 1. 064 | 1. 030 || 3000 | 26. 76 | 1. 121 | 1. 257 | 1. 047 || 4000 | 25. 76 | 1. 165 | 1. 356 | 1. 063 || 5000 | 24. 79 | 1. 210 | 1. 464 | 1. 079 || 6000 | 23. 87 | 1. 257 | 1. 580 | 1. 096 || 7000 | 22. 97 | 1. 306 | 1. 706 | 1. 113 || 8000 | 22. 11 | 1. 357 | 1. 841 | 1. 130 || 9000 | 21. 28 | 1. 410 | 1. 988 | 1. 147 || 10000 | 20. 49 | 1. 464 | 2. 144 | 1. 165 ||________________|___________|_________________|_______|________________| These figures show that the altitude affects the height to a muchgreater extent than the diameter and that practically no increase indiameter is necessary for altitudes up to 3000 feet. For high altitudes the increase in stack height necessary is, in somecases, such as to make the proportion of height to diameterimpracticable. The method to be recommended in overcoming, at leastpartially, the great increase in height necessary at high altitudes isan increase in the grate surface of the boilers which the stack serves, in this way reducing the combustion rate necessary to develop a givenpower and hence the draft required for such combustion rate. TABLE 55 STACK SIZES BY KENT'S FORMULA ASSUMING 5 POUNDS OF COAL PER HORSE POWER ____________________________________________________________________| | | | || | | Height of Stack in Feet |Side of|| | |______________________________________________|Equiva-|| Dia- | Area | | | | | | | | | | | lent || meter|Square| 50| 60| 70| 80 | 90 | 100| 110| 125| 150| 175|Square ||Inches| Feet |___|___|___|____|____|____|____|____|____|____| Stack || | | |Inches || | | Commercial Horse Power | ||______|______|______________________________________________|_______|| | | | | | | | | | | | | || 33 | 5. 94|106|115|125| 133| 141| 149| | | | | 30 || 36 | 7. 07|129|141|152| 163| 173| 182| | | | | 32 || 39 | 8. 30|155|169|183| 196| 208| 219| 229| 245| | | 35 || 42 | 9. 62|183|200|216| 231| 245| 258| 271| 289| 316| | 38 || 48 | 12. 57|246|269|290| 311| 330| 348| 365| 389| 426| 460| 43 || 54 | 15. 90|318|348|376| 402| 427| 449| 472| 503| 551| 595| 48 || 60 | 19. 64|400|437|473| 505| 536| 565| 593| 632| 692| 748| 54 || 66 | 23. 76|490|537|580| 620| 658| 694| 728| 776| 849| 918| 59 || 72 | 28. 27|591|646|698| 747| 792| 835| 876| 934|1023|1105| 64 || 78 | 33. 18|700|766|828| 885| 939| 990|1038|1107|1212|1310| 70 || 84 | 38. 48|818|896|968|1035|1098|1157|1214|1294|1418|1531| 75 ||______|______|___|___|___|____|____|____|____|____|____|____|_______|| | | | || | | Height of Stack in Feet |Side of|| | |______________________________________________|Equiva-|| Dia- | Area | | | | | | | | | lent || meter|Square| 100| 110 | 125 | 150 | 175 | 200 | 225 | 250 |Square ||Inches| Feet |____|_____|_____|_____|_____|_____|_____|_____| Stack || | | |Inches || | | Commercial Horse Power | ||______|______|______________________________________________|_______|| | | | | | | | | | | || 90 | 44. 18|1338| 1403| 1496| 1639| 1770| 1893| 2008| 2116| 80 || 96 | 50. 27|1532| 1606| 1713| 1876| 2027| 2167| 2298| 2423| 86 || 102 | 56. 75|1739| 1824| 1944| 2130| 2300| 2459| 2609| 2750| 91 || 108 | 63. 62|1959| 2054| 2190| 2392| 2592| 2770| 2939| 3098| 98 || 114 | 70. 88|2192| 2299| 2451| 2685| 2900| 3100| 3288| 3466| 101 || 120 | 78. 54|2438| 2557| 2726| 2986| 3226| 3448| 3657| 3855| 107 || 126 | 86. 59|2697| 2829| 3016| 3303| 3568| 3814| 4046| 4265| 112 || 132 | 95. 03|2970| 3114| 3321| 3637| 3929| 4200| 4455| 4696| 117 || 144 |113. 10|3554| 3726| 3973| 4352| 4701| 5026| 5331| 5618| 128 || 156 |132. 73|4190| 4393| 4684| 5131| 5542| 5925| 6285| 6624| 138 || 168 |153. 94|4878| 5115| 5454| 5974| 6454| 6899| 7318| 7713| 150 ||______|______|____|_____|_____|_____|_____|_____|_____|_____|_______| Kent's Stack Tables--Table 55 gives, in convenient form for approximatework, the sizes of stacks and the horse power of boilers which they willserve. This table is a modification of Mr. William Kent's stack tableand is calculated from his formula. Provided no unusual conditions areencountered, it is reliable for the ordinary rates of combustion withbituminous coals. It is figured on a consumption of 5 pounds of coalburned per hour per boiler horse power developed, this figure giving afairly liberal allowance for the use of poor coal and for a reasonableoverload. When the coal used is a low grade bituminous of the Middle orWestern States, it is strongly recommended that these sizes be increasedmaterially, such an increase being from 25 to 60 per cent, dependingupon the nature of the coal and the capacity desired. For the coalburned per hour for any size stack given in the table, the values shouldbe multiplied by 5. A convenient rule for large stacks, 200 feet high and over, is toprovide 30 square feet of cross sectional area per 1000 rated horsepower. Stacks for Oil Fuel--The requirements of stacks connected to boilersunder which oil fuel is burned are entirely different from those wherecoal is used. While more attention has been paid to the matter of stacksizes for oil fuel in recent years, there has not as yet been gatheredthe large amount of experimental data available for use in designingcoal stacks. In the case of oil-fired boilers the loss of draft through the fuel bedis partially eliminated. While there may be practically no loss throughany checkerwork admitting air to the furnace when a boiler is new, theareas for the air passage in this checkerwork will in a short time bedecreased, due to the silt which is present in practically all fuel oil. The loss in draft through the boiler proper at a given rating will beless than in the case of coal-fired boilers, this being due to adecrease in the volume of the gases. Further, the action of the oilburner itself is to a certain extent that of a forced draft. To offsetthis decrease in draft requirement, the temperature of the gasesentering the stack will be somewhat lower where oil is used than wherecoal is used, and the draft that a stack of a given height would give, therefore, decreases. The factors as given above, affecting as they dothe intensity of the draft, affect directly the height of the stack tobe used. As already stated, the volume of gases from oil-fired boilers being lessthan in the case of coal, makes it evident that the area of stacks foroil fuel will be less than for coal. It is assumed that these areas willvary directly as the volume of the gases to be handled, and this volumefor oil may be taken as approximately 60 per cent of that for coal. In designing stacks for oil fuel there are two features which must notbe overlooked. In coal-firing practice there is rarely danger of toomuch draft. In the burning of oil, however, this may play an importantpart in the reduction of plant economy, the influence of excessive draftbeing more apparent where the load on the plant may be reduced atintervals. The reason for this is that, aside from a slight decrease intemperature at reduced loads, the tendency, due to careless firing, istoward a constant gas flow through the boiler regardless of the rate ofoperation, with the corresponding increase of excess air at light loads. With excessive stack height, economical operation at varying loads isalmost impossible with hand control. With automatic control, however, where stacks are necessarily high to take care of known peaks, underlighter loads this economical operation becomes less difficult. For thisreason the question of designing a stack for a plant where the load isknown to be nearly a constant is easier than for a plant where the loadwill vary over a wide range. While great care must be taken to avoidexcessive draft, still more care must be taken to assure a draft suctionwithin all parts of the setting under any and all conditions ofoperation. It is very easily possible to more than offset the economygained through low draft, by the losses due to setting deterioration, resulting from such lack of suction. Under conditions where the suctionis not sufficient to carry off the products of combustion, the action ofthe heat on the setting brickwork will cause its rapid failure. [Illustration: 7800 Horse-power Installation of Babcock & WilcoxBoilers, Equipped with Babcock & Wilcox Chain Grate Stokers at theMetropolitan West Side Elevated Ry. Co. , Chicago, Ill. ] It becomes evident, therefore, that the question of stack height foroil-fired boilers is one which must be considered with the greatest ofcare. The designer, on the one hand, must guard against the evils ofexcessive draft with the view to plant economy, and, on the other, against the evils of lack of draft from the viewpoint of upkeep cost. Stacks for this work should be proportioned to give ample draft for themaximum overload that a plant will be called upon to carry, allconditions of overload carefully considered. At the same time, wherethis maximum overload is figured liberally enough to insure a draftsuction within the setting under all conditions, care must be takenagainst the installation of a stack which would give more than thismaximum draft. TABLE 56 STACK SIZES FOR OIL FUEL ADAPTED FROM C. R. WEYMOUTH'S TABLE (TRANS. A. S. M. E. VOL. 34) +----------------------------------------------------+|+--------+-----------------------------------------+||| | Height in Feet Above Boiler Room Floor ||||Diameter+------+------+------+-----+--------------+||| Inches | 80 | 90 | 100 | 120 | 140 | 160 |||+--------+------+------+------+------+------+------+||| 33 | 161 | 206 | 233 | 270 | 306 | 315 |||| 36 | 208 | 253 | 295 | 331 | 363 | 387 |||| 39 | 251 | 303 | 343 | 399 | 488 | 467 |||| 42 | 295 | 359 | 403 | 474 | 521 | 557 |||| 48 | 399 | 486 | 551 | 645 | 713 | 760 |||| 54 | 519 | 634 | 720 | 847 | 933 | 1000 |||| 60 | 657 | 800 | 913 | 1073 | 1193 | 1280 |||| 66 | 813 | 993 | 1133 | 1333 | 1480 | 1593 |||| 72 | 980 | 1206 | 1373 | 1620 | 1807 | 1940 |||| 84 | 1373 | 1587 | 1933 | 2293 | 2560 | 2767 |||| 96 | 1833 | 2260 | 2587 | 3087 | 3453 | 3740 |||| 108 | 2367 | 2920 | 3347 | 4000 | 4483 | 4867 |||| 120 | 3060 | 3660 | 4207 | 5040 | 5660 | 6160 |||+--------+------+------+------+------+------+------+|+----------------------------------------------------+ Figures represent nominal rated horse power. Sizes as given good for 50per cent overloads. Based on centrally located stacks, short direct flues and ordinaryoperating efficiencies. Table 56 gives the sizes of stacks, and horse power which they willserve for oil fuel. This table is, in modified form, one calculated byMr. C. R. Weymouth after an exhaustive study of data pertaining to thesubject, and will ordinarily give satisfactory results. Stacks for Blast Furnace Gas Work--For boilers burning blast furnacegas, as in the case of oil-fired boilers, stack sizes as suited for coalfiring will have to be modified. The diameter of stacks for this workshould be approximately the same as for coal-fired boilers. The volumeof gases would be slightly greater than from a coal fire and woulddecrease the draft with a given stack, but such a decrease due to volumeis about offset by an increase due to somewhat higher temperatures inthe case of the blast furnace gases. Records show that with this class of fuel 175 per cent of the ratedcapacity of a boiler can be developed with a draft at the boiler damperof from 0. 75 inch to 1. 0 inch, and it is well to limit the height ofstacks to one which will give this draft as a maximum. A stack of properdiameter, 130 feet high above the ground, will produce such a draft andthis height should ordinarily not be exceeded. Until recently thequestion of economy in boilers fired with blast furnace gas has not beenconsidered, but, aside from the economical standpoint, excessive draftshould be guarded against in order to lower the upkeep cost. Stacks should be made of sufficient height to produce a draft that willdevelop the maximum capacity required, and this draft decreasedproportionately for loads under the maximum by damper regulation. Theamount of gas fed to a boiler for any given rating is a fixed quantityand if a draft in excess of that required for that particular rate ofoperation is supplied, economy is decreased and the wear and tear on thesetting is materially increased. Excess air which is drawn in, eitherthrough or around the gas burners by an excessive draft, will decreaseeconomy, as in any other class of work. Again, as in oil-fired practice, it is essential on the other hand that a suction be maintained withinall parts of the setting, in this case not only to provide againstsetting deterioration but to protect the operators from leakage of gaswhich is disagreeable and may be dangerous. Aside from the intensity ofthe draft, a poor mixture of the gas and air or a "laneing" action maylead to secondary combustion with the possibility of dangerousexplosions within the setting, may cause a pulsating action within thesetting, may increase the exit temperatures to a point where there isdanger of burning out damper boxes, and, in general, is hard on thesetting. It is highly essential, therefore, that the furnace be properlyconstructed to meet the draft which will be available. Stacks for Wood-fired Boilers--For boilers using wood as fuel, there isbut little data upon which to base stack sizes. The loss of draftthrough the bed of fuel will vary over limits even wider than in thecase of coal, for in this class of fuel the moisture may run frompractically 0. 0 per cent to over 60 per cent, and the methods ofhandling and firing are radically different for the different classes ofwood (see chapter on Wood-burning Furnaces). As economy is ordinarily oflittle importance, high stack temperatures may be expected, and oftenunavoidably large quantities of excess air are supplied due to themethod of firing. In general, it may be stated that for this class offuel the diameter of stacks should be at least as great as for coal-firedboilers, while the height may be slightly decreased. It is far the bestplan in designing a stack for boilers using wood fuel to consider eachindividual set of conditions that exist, rather than try to follow anygeneral rule. One factor not to be overlooked in stacks for wood burning is theirlocation. The fine particles of this fuel are often carried unconsumedthrough the boiler, and where the stack is not on top of the boiler, these particles may accumulate in the base of the stack below the pointat which the flue enters. Where there is any air leakage through thebase of such a stack, this fuel may become ignited and the stack burned. Where there is a possibility of such action taking place, it is well toline the stack with fire brick for a portion of its height. Draft Gauges--The ordinary form of draft gauge, Fig. 35, which consistsof a U-tube, containing water, lacks sensitiveness in measuring suchslight pressure differences as usually exist, and for that reason gaugeswhich multiply the draft indications are more convenient and are muchused. [Illustration: Fig. 35. U-tube Draft Gauge] [Illustration: Fig. 36. Barrus Draft Gauge] An instrument which has given excellent results is one introduced by Mr. G. H. Barrus, which multiplies the ordinary indications as many times asdesired. This is illustrated in Fig. 36, and consists of a U-tube madeof one-half inch glass, surmounted by two larger tubes, or chambers, each having a diameter of 2½ inches. Two different liquids which willnot mix, and which are of different color, are used, usually alcoholcolored red and a certain grade of lubricating oil. The movement of theline of demarcation is proportional to the difference in the areas ofthe chambers and the U-tube connecting them. The instrument iscalibrated by comparison with the ordinary U-tube gauge. In the Ellison form of gauge the lower portion of the ordinary U-tubehas been replaced by a tube slightly inclined to the horizontal, asshown in Fig. 37. By this arrangement any vertical motion in theright-hand upright tube causes a very much greater travel of the liquidin the inclined tube, thus permitting extremely small variation in theintensity of the draft to be read with facility. [Illustration: Fig. 37. Ellison Draft Gauge] The gauge is first leveled by means of the small level attached to it, both legs being open to the atmosphere. The liquid is then adjusteduntil its meniscus rests at the zero point on the left. The right-handleg is then connected to the source of draft by means of a piece ofrubber tubing. Under these circumstances, a rise of level of one inch inthe right-hand vertical tube causes the meniscus in the inclined tube topass from the point 0 to 1. 0. The scale is divided into tenths of aninch, and the sub-divisions are hundredths of an inch. The makers furnish a non-drying oil for the liquid, usually a 300degrees test refined petroleum. A very convenient form of the ordinary U-tube gauge is known as thePeabody gauge, and it is shown in Fig. 38. This is a small modifiedU-tube with a sliding scale between the two legs of the U and withconnections such that either a draft suction or a draft pressure may betaken. The tops of the sliding pieces extending across the tubes areplaced at the bottom of the meniscus and accurate readings in hundredthsof an inch are obtained by a vernier. [Illustration: Fig. 38. Peabody Draft Gauge] EFFICIENCY AND CAPACITY OF BOILERS Two of the most important operating factors entering into theconsideration of what constitutes a satisfactory boiler are itsefficiency and capacity. The relation of these factors to one anotherwill be considered later under the selection of boilers with referenceto the work they are to accomplish. The present chapter deals with theefficiency and capacity only with a view to making clear exactly what ismeant by these terms as applied to steam generating apparatus, togetherwith the methods of determining these factors by tests. Efficiency--The term "efficiency", specifically applied to a steamboiler, is the ratio of heat absorbed by the boiler in the generation ofsteam to the total amount of heat available in the medium utilized insecuring such generation. When this medium is a solid fuel, such ascoal, it is impossible to secure the complete combustion of the totalamount fed to the boiler. A portion is bound to drop through the grateswhere it becomes mixed with the ash and, remaining unburned, produces noheat. Obviously, it is unfair to charge the boiler with the failure toabsorb the portion of available heat in the fuel that is wasted in thisway. On the other hand, the boiler user must pay for such waste and isjustified in charging it against the combined boiler and furnace. Due tothis fact, the efficiency of a boiler, as ordinarily stated, is inreality the combined efficiency of the boiler, furnace and grate, and Efficiency of boiler, } Heat absorbed per pound of fuel furnace and grate } = ------------------------------- (31) Heat value per pound of fuel The efficiency will be the same whether based on dry fuel or on fuel asfired, including its content of moisture. For example: If the coalcontained 3 per cent of moisture, the efficiency would be Heat absorbed per pound of dry coal × 0. 97 ------------------------------------------ Heat value per pound of dry coal × 0. 97 where 0. 97 cancels and the formula becomes (31). The heat supplied to the boiler is due to the combustible portion offuel which is actually burned, irrespective of what proportion of thetotal combustible fired may be. [54] This fact has led to the use of asecond efficiency basis on combustible and which is called theefficiency of boiler and furnace[55], namely, Efficiency of boiler and furnace[55] Heat absorbed per pound of combustible[56] = -------------------------------------- (32) Heat value per pound of combustible The efficiency so determined is used in comparing the relativeperformance of boilers, irrespective of the type of grates used underthem. If the loss of fuel through the grates could be entirely overcome, the efficiencies obtained by (31) and (32) would obviously be the same. Hence, in the case of liquid and gaseous fuels, where there ispractically no waste, these efficiencies are almost identical. As a matter of fact, it is extremely difficult, if not impossible, todetermine the actual efficiency of a boiler alone, as distinguished fromthe combined efficiency of boiler, grate and furnace. This is due to thefact that the losses due to excess air cannot be correctly attributed toeither the boiler or the furnace, but only to a combination of thecomplete apparatus. Attempts have been made to devise methods fordividing the losses proportionately between the furnace and the boiler, but such attempts are unsatisfactory and it is impossible to determinethe efficiency of a boiler apart from that of a furnace in such a way asto make such determination of any practical value or in a way that mightnot lead to endless dispute, were the question to arise in the case of aguaranteed efficiency. From the boiler manufacturer's standpoint, theonly way of establishing an efficiency that has any value whenguarantees are to be met, is to require the grate or stoker manufacturerto make certain guarantees as to minimum CO_{2}, maximum CO, and thatthe amount of combustible in the ash and blown away with the flue gasesdoes not exceed a certain percentage. With such a guarantee, theefficiency should be based on the combined furnace and boiler. General practice, however, has established the use of the efficiencybased upon combustible as representing the efficiency of the boileralone. When such an efficiency is used, its exact meaning, as pointedout on opposite page, should be realized. The computation of the efficiencies described on opposite page is bestillustrated by example. Assume the following data to be determined from an actual boiler trial. Steam pressure by gauge, 200 pounds. Feed temperature, 180 degrees. Total weight of coal fired, 17, 500 pounds. Percentage of moisture in coal, 3 per cent. Total ash and refuse, 2396 pounds. Total water evaporated, 153, 543 pounds. Per cent of moisture in steam, 0. 5 per cent. Heat value per pound of dry coal, 13, 516. Heat value per pound of combustible, 15, 359. The factor of evaporation for such a set of conditions is 1. 0834. Theactual evaporation corrected for moisture in the steam is 152, 775 andthe equivalent evaporation from and at 212 degrees is, therefore, 165, 516 pounds. The total dry fuel will be 17, 500 × . 97 = 16, 975, and the evaporationper pound of dry fuel from and at 212 degrees will be 165, 516 ÷ 16, 975 =9. 75 pounds. The heat absorbed per pound of dry fuel will, therefore, be9. 75 × 970. 4 = 9461 B. T. U. Hence, the efficiency by (31) will be 9461÷ 13, 516 = 70. 0 per cent. The total combustible burned will be 16, 975- 2396 = 14, 579, and the evaporation from and at 212 degrees per poundof combustible will be 165, 516 ÷ 14, 579 = 11. 35 pounds. Hence, theefficiency based on combustible from (32) will be (11. 35 × 97. 04) ÷15, 359 = 71. 79. [**should be 71. 71] For approximate results, a chart may be used to take the place of acomputation of efficiency. Fig. 39 shows such a chart based on theevaporation per pound of dry fuel and the heat value per pound of dryfuel, from which efficiencies may be read directly to within one-half ofone per cent. It is used as follows: From the intersection of thehorizontal line, representing the evaporation per pound of fuel, withthe vertical line, representing the heat value per pound, the efficiencyis read directly from the diagonal scale of efficiencies. This chart mayalso be used for efficiency based upon combustible when the evaporationfrom and at 212 degrees and the heat values are both given in terms ofcombustible. [Graph: Evaporation from and at 212° per Pound of Dry Fuelagainst B. T. U. Per Pound of Dry Fuel Fig. 39. Efficiency Chart. Calculated from Marks and Davis Tables Diagonal Lines Represent Per Cent Efficiency] Boiler efficiencies will vary over a wide range, depending on a greatvariety of factors and conditions. The highest efficiencies that havebeen secured with coal are in the neighborhood of 82 per cent and fromthat point efficiencies are found all the way down to below 50 per cent. Table 59[57] of tests of Babcock & Wilcox boilers under varyingconditions of fuel and operation will give an idea of what may beobtained with proper operating conditions. The difference between the efficiency secured in any boiler trial andthe perfect efficiency, 100 per cent, includes the losses, some of whichare unavoidable in the present state of the art, arising in theconversion of the heat energy of the coal to the heat energy in thesteam. These losses may be classified as follows: 1st. Loss due to fuel dropped through the grate. 2nd. Loss due to unburned fuel which is carried by the draft, as smallparticles, beyond the bridge wall into the setting or up the stack. 3rd. Loss due to the utilization of a portion of the heat in heating themoisture contained in the fuel from the temperature of the atmosphere to212 degrees; to evaporate it at that temperature and to superheat thesteam thus formed to the temperature of the flue gases. This steam, ofcourse, is first heated to the temperature of the furnace but as itgives up a portion of this heat in passing through the boiler, thesuperheating to the temperature of the exit gases is the correct degreeto be considered. 4th. Loss due to the water formed and by the burning of the hydrogen inthe fuel which must be evaporated and superheated as in item 3. 5th. Loss due to the superheating of the moisture in the air suppliedfrom the atmospheric temperature to the temperature of the flue gases. 6th. Loss due to the heating of the dry products of combustion to thetemperature of the flue gases. 7th. Loss due to the incomplete combustion of the fuel when the carbonis not completely consumed but burns to CO instead of CO_{2}. The COpasses out of the stack unburned as a volatile gas capable of furthercombustion. 8th. Loss due to radiation of heat from the boiler and furnace settings. Obviously a very elaborate test would have to be made were all of theabove items to be determined accurately. In ordinary practice it hasbecome customary to summarize these losses as follows, the methods ofcomputing the losses being given in each instance by a typical example: (A) Loss due to the heating of moisture in the fuel from the atmospherictemperature to 212 degrees, evaporate it at that temperature andsuperheat it to the temperature of the flue gases. This in reality isthe total heat above the temperature of the air in the boiler room, inone pound of superheated steam at atmospheric pressure at thetemperature of the flue gases, multiplied by the percentage of moisturein the fuel. As the total heat above the temperature of the air wouldhave to be computed in each instance, this loss is best expressed by: Loss in B. T. U. Per pound = W(212-t+970. 4+. 47(T-212)) (33) Where W = per cent of moisture in coal, t = the temperature of air in the boiler room, T = temperature of the flue gases, . 47 = the specific heat of superheated steam at the atmospheric pressure and at the flue gas temperature, (212-t) = B. T. U. Necessary to heat one pound of water from the temperature of the boiler room to 212 degrees, 970. 4 = B. T. U. Necessary to evaporate one pound of water at 212 degrees to steam at atmospheric pressure, . 47(T-212) = B. T. U. Necessary to superheat one pound of steam at atmospheric pressure from 212 degrees to temperature T. [Illustration: Portion of 15, 000 Horse-power Installation of Babcock &Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers atthe Northumberland, Pa. , Plant of the Atlas Portland Cement Co. ThisCompany Operates a Total of 24, 000 Horse Power of Babcock & WilcoxBoilers in its Various Plants] (B) Loss due to heat carried away in the steam produced by the burningof the hydrogen component of the fuel. In burning, one pound of hydrogenunites with 8 pounds of oxygen to form 9 pounds of steam. Following thereasoning of item (A), therefore, this loss will be: Loss in B. T. U. Per pound = 9H((212-t)+970. 4+. 47(T-212)) (34) where H = the percentage by weight of hydrogen. This item is frequently considered as a part of the unaccounted forloss, where an ultimate analysis of the fuel is not given. (C) Loss due to heat carried away by dry chimney gases. This isdependent upon the weight of gas per pound of coal which may bedetermined by formula (16), page 158. Loss in B. T. U. Per pound = (T-t)×. 24×W. Where T and t have values as in (33), . 24 = specific heat of chimney gases, W = weight of dry chimney gas per pound of coal. (D) Loss due to incomplete combustion of the carbon content of the fuel, that is, the burning of the carbon to CO instead of CO_{2}. 10, 150 COLoss in B. T. U. Per pound = C×--------- (35) CO_{2}+CO C = per cent of carbon in coal by ultimate analysis, CO and CO_{2} = per cent of CO and CO_{2} by volume from flue gasanalysis. 10, 150 = the number of heat units generated by burning to CO_{2} onepound of carbon contained in carbon monoxide. (E) Loss due to unconsumed carbon in the ash (it being usually assumedthat all the combustible in the ash is carbon). Loss in B. T. U. Per pound =per cent C × per cent ash × B. T. U. Per pound of combustible in the ash(usually taken as 14, 600 B. T. U. ) (36) The loss incurred in this way is, directly, the carbon in the ash inpercentage terms of the total dry coal fired, multiplied by the heatvalue of carbon. To compute this item, which is of great importance in comparing therelative performances of different designs of grates, an analysis of theash must be available. The other losses, namely, items 2, 5 and 8 of the first classification, are ordinarily grouped under one item, as unaccounted for losses, andare obviously the difference between 100 per cent and the sum of theheat utilized and the losses accounted for as given above. Item 5, orthe loss due to the moisture in the air, may be readily computed, themoisture being determined from wet and dry bulb thermometer readings, but it is usually disregarded as it is relatively small, averaging, say, one-fifth to one-half of one per cent. Lack of data may, of course, makeit necessary to include certain items of the second and ordinaryclassification in this unaccounted for group. TABLE 57 DATA FROM WHICH HEAT BALANCE (TABLE 58) IS COMPUTED +------------------------------------------------------+|+----------------------------------------------------+|||Steam Pressure by Gauge, Pounds | 192 ||||Temperature of Feed, Degrees Fahrenheit | 180 ||||Degrees of Superheat, Degrees Fahrenheit |115. 2||||Temperature of Boiler Room, Degrees Fahrenheit| 81 ||||Temperature of Exit Gases, Degrees Fahrenheit | 480 ||||Weight of Coal Used per Hour, Pounds | 5714||||Moisture, Per Cent | 1. 83||||Dry Coal Per Hour, Pounds | 5609||||Ash and Refuse per Hour, Pounds | 561||||Ash and Refuse (of Dry Coal), Per Cent |10. 00||||Actual Evaporation per Hour, Pounds |57036|||| . - C, Per Cent |78. 57|||| | H, Per Cent | 5. 60||||Ultimate | O, Per Cent | 7. 02||||Analysis -+ N, Per Cent | 1. 11||||Dry Coal | Ash, Per Cent | 6. 52|||| '- Sulphur, Per Cent | 1. 18||||Heat Value per Pound Dry Coal, B. T. U. |14225||||Heat Value per Pound Combustible, B. T. U. |15217||||Combustible in Ash by Analysis, Per Cent | 17. 9|||| . - CO_{2}, Per Cent |14. 33||||Flue Gas -+ O, Per Cent | 4. 54||||Analysis | CO, Per Cent | 0. 11|||| '- N, Per Cent |81. 02|||+----------------------------------------------+-----+|+------------------------------------------------------+ A schedule of the losses as outlined, requires an evaporative test ofthe boiler, an analysis of the flue gases, an ultimate analysis of thefuel, and either an ultimate or proximate analysis of the ash. As theamount of unaccounted for losses forms a basis on which to judge theaccuracy of a test, such a schedule is called a "heat balance". A heat balance is best illustrated by an example: Assume the data asgiven in Table 57 to be secured in an actual boiler test. From this data the factor of evaporation is 1. 1514 and the evaporationper hour from and at 212 degrees is 65, 671 pounds. Hence the evaporationfrom and at 212 degrees per pound of dry coal is 65, 671÷5609 = 11. 71pounds. The efficiency of boiler, furnace and grate is: (11. 71×970. 4)÷14, 225 = 79. 88 per cent. The heat losses are: (A) Loss due to moisture in coal, = . 01831 ((212-81)+970. 4+. 47(480-212))= 22. B. T. U. , = 0. 15 per cent. (B) The loss due to the burning of hydrogen: = 9×. 0560((212-81)+970. 4+. 47(480-212))= 618 B. T. U. , = 4. 34 per cent. (C) To compute the loss in the heat carried away by dry chimney gasesper pound of coal the weight of such gases must be first determined. This weight per pound of coal is: (11CO_{2}+8O+7(CO+N))(-------------------)C( 3(CO_{2}+CO) ) where CO_{2}, O, CO and H are the percentage by volume as determined bythe flue gas analysis and C is the percentage by weight of carbon in thedry fuel. Hence the weight of gas per pound of coal will be, (11×14. 33+8×4. 54+7(0. 11+81. 02))(-----------------------------)×78. 57 = 13. 7 pounds. ( 3(14. 33+0. 11) ) Therefore the loss of heat in the dry gases carried up the chimney = 13. 7×0. 24(480-81) = 1311 B. T. U. , = 9. 22 per cent. (D) The loss due to incomplete combustion as evidenced by the presenceof CO in the flue gas analysis is: 0. 11----------×. 7857×10, 150 = 61. B. T. U. , 14. 33+0. 11 = . 43 per cent. (E) The loss due to unconsumed carbon in the ash: The analysis of the ash showed 17. 9 per cent to be combustible matter, all of which is assumed to be carbon. The test showed 10. 00 of the totaldry fuel fired to be ash. Hence 10. 00×. 179 = 1. 79 per cent of the totalfuel represents the proportion of this total unconsumed in the ash andthe loss due to this cause is 1. 79 per cent × 14, 600 = 261 B. T. U. , = 1. 83 per cent. The heat absorbed by the boilers per pound of dry fuel is 11. 71×970. 4 =11, 363 B. T. U. This quantity plus losses (A), (B), (C), (D) and (E), or11, 363+22+618+1311+61+261 = 13, 636 B. T. U. Accounted for. The heatvalue of the coal, 14, 225 B. T. U. , less 13, 636 B. T. U. , leaves 589B. T. U. , unaccounted for losses, or 4. 15 per cent. The heat balance should be arranged in the form indicated by Table 58. TABLE 58 HEAT BALANCE B. T. U. PER POUND DRY COAL 14, 225 +----------------------------------------------------------------------+|+--------------------------------------------------------------------+||| |B. T. U. |Per Cent|||+--------------------------------------------------+--------+--------+|||Heat absorbed by Boiler | 11, 363 | 79. 88 ||||Loss due to Evaporation of Moisture in Fuel | 22 | 0. 15 ||||Loss due to Moisture formed by Burning of Hydrogen| 618 | 4. 34 ||||Loss due to Heat carried away in Dry Chimney Gases| 1311 | 9. 22 ||||Loss due to Incomplete Combustion of Carbon | 61 | 0. 43 ||||Loss due to Unconsumed Carbon in the Ash | 261 | 1. 83 ||||Loss due to Radiation and Unaccounted Losses | 589 | 4. 15 |||+--------------------------------------------------+--------+--------+|||Total | 14, 225 | 100. 00 |||+--------------------------------------------------+--------+--------+|+----------------------------------------------------------------------+ Application of Heat Balance--A heat balance should be made in connectionwith any boiler trial on which sufficient data for its computation hasbeen obtained. This is particularly true where the boiler performancehas been considered unsatisfactory. The distribution of the heat is thusdetermined and any extraordinary loss may be detected. Where accuratedata for computing such a heat balance is not available, such acalculation based on certain assumptions is sometimes sufficient toindicate unusual losses. The largest loss is ordinarily due to the chimney gases, which dependsdirectly upon the weight of the gas and its temperature leaving theboiler. As pointed out in the chapter on flue gas analysis, the lowerlimit of the weight of gas is fixed by the minimum air supplied withwhich complete combustion may be obtained. As shown, where this supplyis unduly small, the loss caused by burning the carbon to CO instead ofto CO_{2} more than offsets the gain in decreasing the weight of gas. The lower limit of the stack temperature, as has been shown in thechapter on draft, is more or less fixed by the temperature necessary tocreate sufficient draft suction for good combustion. With natural draft, this lower limit is probably between 400 and 450 degrees. Capacity--Before the capacity of a boiler is considered, it is necessaryto define the basis to which such a term may be referred. Such a basisis the so-called boiler horse power. The unit of motive power in general use among steam engineers is the"horse power" which is equivalent to 33, 000 foot pounds per minute. Stationary boilers are at the present time rated in horse power, thoughsuch a basis of rating may lead and has often led to a misunderstanding. _Work_, as the term is used in mechanics, is the overcoming ofresistance through space, while _power_ is the _rate_ of work or theamount done per unit of time. As the operation of a boiler in serviceimplies no motion, it can produce no power in the sense of the term asunderstood in mechanics. Its operation is the generation of steam, whichacts as a medium to convey the energy of the fuel which is in the formof heat to a prime mover in which that heat energy is converted intoenergy of motion or work, and power is developed. If all engines developed the same amount of power from an equal amountof heat, a boiler might be designated as one having a definite horsepower, dependent upon the amount of engine horse power its steam woulddevelop. Such a statement of the rating of boilers, though it wouldstill be inaccurate, if the term is considered in its mechanical sense, could, through custom, be interpreted to indicate that a boiler was ofthe exact capacity required to generate the steam necessary to develop adefinite amount of horse power in an engine. Such a basis of rating, however, is obviously impossible when the fact is considered that theamount of steam necessary to produce the same power in prime movers ofdifferent types and sizes varies over very wide limits. To do away with the confusion resulting from an indefinite meaning ofthe term boiler horse power, the Committee of Judges in charge of theboiler trials at the Centennial Exposition, 1876, at Philadelphia, ascertained that a good engine of the type prevailing at the timerequired approximately 30 pounds of steam per hour per horse powerdeveloped. In order to establish a relation between the engine power andthe size of a boiler required to develop that power, they recommendedthat an evaporation of 30 pounds of water from an initial temperature of100 degrees Fahrenheit to steam at 70 pounds gauge pressure beconsidered as _one boiler horse power_. This recommendation has beengenerally accepted by American engineers as a standard, and when theterm boiler horse power is used in connection with stationaryboilers[58] throughout this country, [59] without special definition, itis understood to have this meaning. Inasmuch as an equivalent evaporation from and at 212 degrees Fahrenheitis the generally accepted basis of comparison[60], it is now customaryto consider the standard boiler horse power as recommended by theCentennial Exposition Committee, in terms of equivalent evaporation fromand at 212 degrees. This will be 30 pounds multiplied by the factor ofevaporation for 70 pounds gauge pressure and 100 degrees feedtemperature, or 1. 1494. 30 × 1. 1494 = 34. 482, or approximately 34. 5pounds. Hence, _one boiler horse power is equal to an evaporation of34. 5 pounds of water per hour from and at 212 degrees Fahrenheit_. Theterm boiler horse power, therefore, is clearly a measure of evaporationand not of power. A method of basing the horse power rating of a boiler adopted by boilermanufacturers is that of heating surfaces. Such a method is absolutelyarbitrary and changes in no way the definition of a boiler horse powerjust given. It is simply a statement by the manufacturer that hisproduct, under ordinary operating conditions or conditions which may bespecified, will evaporate 34. 5 pounds of water from and at 212 degreesper definite amount of heating surface provided. The amount of heatingsurface that has been considered by manufacturers capable of evaporating34. 5 pounds from and at 212 degrees per hour has changed from time totime as the art has progressed. At the present time 10 square feet ofheating surface is ordinarily considered the equivalent of one boilerhorse power among manufacturers of stationary boilers. In view of thearbitrary nature of such rating and of the widely varying rates ofevaporation possible per square foot of heating surface with differentboilers and different operating conditions, such a basis of rating hasin reality no particular bearing on the question of horse power andshould be considered merely as a convenience. The whole question of a unit of boiler capacity has been widelydiscussed with a view to the adoption of a standard to which there wouldappear to be a more rational and definite basis. Many suggestions havebeen offered as to such a basis but up to the present time there hasbeen none which has met with universal approval or which would appearlikely to be generally adopted. With the meaning of boiler horse power as given above, that is, ameasure of evaporation, it is evident that the capacity of a boiler is ameasure of the power it can develop expressed in boiler horse power. Since it is necessary, as stated, for boiler manufacturers to adopt astandard for reasons of convenience in selling, the horse power forwhich a boiler is sold is known as its normal rated capacity. The efficiency of a boiler and the maximum capacity it will develop canbe determined accurately only by a boiler test. The standard methods ofconducting such tests are given on the following pages, these methodsbeing the recommendations of the Power Test Committee of the AmericanSociety of Mechanical Engineers brought out in 1913. [61] Certain changeshave been made to incorporate in the boiler code such portions of the"Instructions Regarding Tests in General" as apply to boiler testing. Methods of calculation and such matter as are treated in other portionsof the book have been omitted from the code as noted. [Illustration: Portion of 2600 Horse-power Installation of Babcock &Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers atthe Peter Schoenhofen Brewing Co. , Chicago, Ill. ] 1. OBJECT Ascertain the specific object of the test, and keep this in view notonly in the work of preparation, but also during the progress of thetest, and do not let it be obscured by devoting too close attention tomatters of minor importance. Whatever the object of the test may be, accuracy and reliability must underlie the work from beginning to end. If questions of fulfillment of contract are involved, there should be aclear understanding between all the parties, preferably in writing, asto the operating conditions which should obtain during the trial, and asto the methods of testing to be followed, unless these are alreadyexpressed in the contract itself. Among the many objects of performance tests, the following may be noted: Determination of capacity and efficiency, and how these compare with standard or guaranteed results. Comparison of different conditions or methods of operation. Determination of the cause of either inferior or superior results. Comparison of different kinds of fuel. Determination of the effect of changes of design or proportion upon capacity or efficiency, etc. 2. PREPARATIONS _(A) Dimensions:_ Measure the dimensions of the principal parts of the apparatus to betested, so far as they bear on the objects in view, or determine thesefrom correct working drawings. Notice the general features of the same, both exterior and interior, and make sketches, if needed, to showunusual points of design. The dimensions of the heating surfaces of boilers and superheaters to be found are those of surfaces in contact with the fire or hot gases. The submerged surfaces in boilers at the mean water level should be considered as water-heating surfaces, and other surfaces which are exposed to the gases as superheating surfaces. _(B) Examination of Plant:_ Make a thorough examination of the physical condition of all parts ofthe plant or apparatus which concern the object in view, and record theconditions found, together with any points in the matter of operationwhich bear thereon. In boilers, examine for leakage of tubes and riveted or other metal joints. Note the condition of brick furnaces, grates and baffles. Examine brick walls and cleaning doors for air leaks, either by shutting the damper and observing the escaping smoke or by candle-flame test. Determine the condition of heating surfaces with reference to exterior deposits of soot and interior deposits of mud or scale. See that the steam main is so arranged that condensed and entrained water cannot flow back into the boiler. If the object of the test is to determine the highest efficiency orcapacity obtainable, any physical defects, or defects of operation, tending to make the result unfavorable should first be remedied; allfoul parts being cleaned, and the whole put in first-class condition. If, on the other hand, the object is to ascertain the performance underexisting conditions, no such preparation is either required or desired. _(C) General Precautions against Leakage:_ In steam tests make sure that there is no leakage through blow-offs, drips, etc. , or any steam or water connections of the plant or apparatusundergoing test, which would in any way affect the results. All suchconnections should be blanked off, or satisfactory assurance should beobtained that there is leakage neither out nor in. This is a mostimportant matter, and no assurance should be considered satisfactoryunless it is susceptible of absolute demonstration. 3. FUEL Determine the character of fuel to be used. [62] For tests of maximumefficiency or capacity of the boiler to compare with other boilers, thecoal should be of some kind which is commercially regarded as a standardfor the locality where the test is made. In the Eastern States the standards thus regarded for semi-bituminous coals are Pocahontas (Va. And W. Va. ) and New River (W. Va. ); for anthracite coals those of the No. 1 buckwheat size, fresh-mined, containing not over 13 per cent ash by analysis; and for bituminous coals, Youghiogheny and Pittsburgh coals. In some sections east of the Allegheny Mountains the semi-bituminous Clearfield (Pa. ) and Cumberland (Md. ) are also considered as standards. These coals when of good quality possess the essentials of excellence, adaptability to various kinds of furnaces, grates, boilers, and methods of firing required, besides being widely distributed and generally accessible in the Eastern market. There are no special grades of coal mined in the Western States which are widely and generally considered as standards for testing purposes; the best coal obtainable in any particular locality being regarded as the standard of comparison. A coal selected for maximum efficiency and capacity tests, should be thebest of its class, and especially free from slagging and unusualclinker-forming impurities. For guarantee and other tests with a specified coal containing not morethan a certain amount of ash and moisture, the coal selected should notbe higher in ash and in moisture than the stated amounts, because anyincrease is liable to reduce the efficiency and capacity more than theequivalent proportion of such increase. The size of the coal, especially where it is of the anthracite class, should be determined by screening a suitable sample. 4. APPARATUS AND INSTRUMENTS[63] The apparatus and instruments required for boiler tests are: (A) Platform scales for weighing coal and ashes. (B) Graduated scales attached to the water glasses. (C) Tanks and platform scales for weighing water (or water meters calibrated in place). Wherever practicable the feed water should be weighed, especially for guarantee tests. The most satisfactory and reliable apparatus for this purpose consists of one or more tanks each placed on platform scales, these being elevated a sufficient distance above the floor to empty into a receiving tank placed below, the latter being connected to the feed pump. Where only one weighing tank is used the receiving tank should be of larger size than the weighing tank, to afford sufficient reserve supply to the pump while the upper tank is filling. If a single weighing tank is used it should preferably be of such capacity as to require emptying not oftener than every 5 minutes. If two or more are used the intervals between successive emptyings should not be less than 3 minutes. (D) Pressure gauges, thermometers, and draft gauges. (E) Calorimeters for determining the calorific value of fuel and the quality of steam. (F) Furnaces pyrometers. (G) Gas analyzing apparatus. 5. OPERATING CONDITIONS Determine what the operating conditions and method of firing should beto conform to the object in view, and see that they prevail throughoutthe trial, as nearly as possible. Where uniformity in the rate of evaporation is required, arrangement can be usually made to dispose of the steam so that this result can be attained. In a single boiler it may be accomplished by discharging steam through a waste pipe and regulating the amount by means of a valve. In a battery of boilers, in which only one is tested, the draft may be regulated on the remaining boilers to meet the varying demands for steam, leaving the test boiler to work under a steady rate of evaporation. 6. DURATION The duration of tests to determine the efficiency of a hand-firedboiler, should be 10 hours of continuous running, or such time as may berequired to burn a total of 250 pounds of coal per square foot of grate. In the case of a boiler using a mechanical stoker, the duration, wherepracticable, should be at least 24 hours. If the stoker is of a typethat permits the quantity and condition of the fuel bed at beginning andend of the test to be accurately estimated, the duration may be reducedto 10 hours, or such time as may be required to burn the above notedtotal of 250 pounds per square foot. In commercial tests where the service requires continuous operation night and day, with frequent shifts of firemen, the duration of the test, whether the boilers are hand fired or stoker fired, should be at least 24 hours. Likewise in commercial tests, either of a single boiler or of a plant of several boilers, which operate regularly a certain number of hours and during the balance of the day the fires are banked, the duration should not be less than 24 hours. The duration of tests to determine the maximum evaporative capacity of a boiler, without determining the efficiency, should not be less than 3 hours. 7. STARTING AND STOPPING The conditions regarding the temperature of the furnace and boiler, thequantity and quality of the live coal and ash on the grates, the waterlevel, and the steam pressure, should be as nearly as possible the sameat the end as at the beginning of the test. To secure the desired equality of conditions with hand-fired boilers, the following method should be employed: The furnace being well heated by a preliminary run, burn the fire low, and thoroughly clean it, leaving enough live coal spread evenly over the grate (say 2 to 4 inches), [64] to serve as a foundation for the new fire. Note quickly the thickness of the coal bed as nearly as it can be estimated or measured; also the water level, [65] the steam pressure, and the time, and record the latter as the starting time. Fresh coal should then be fired from that weighed for the test, the ashpit throughly cleaned, and the regular work of the test proceeded with. Before the end of the test the fire should again be burned low and cleaned in such a manner as to leave the same amount of live coal on the grate as at the start. When this condition is reached, observe quickly the water level, [65] the steam pressure, and the time, and record the latter as the stopping time. If the water level is not the same as at the beginning a correction should be made by computation, rather than by feeding additional water after the final readings are taken. Finally remove the ashes and refuse from the ashpit. In a plant containing several boilers where it is not practicable to clean them simultaneously, the fires should be cleaned one after the other as rapidly as may be, and each one after cleaning charged with enough coal to maintain a thin fire in good working condition. After the last fire is cleaned and in working condition, burn all the fires low (say 4 to 6 inches), note quickly the thickness of each, also the water levels, steam pressure, and time, which last is taken as the starting time. Likewise when the time arrives for closing the test, the fires should be quickly cleaned one by one, and when this work is completed they should all be burned low the same as the start, and the various observations made as noted. In the case of a large boiler having several furnace doors requiring the fire to be cleaned in sections one after the other, the above directions pertaining to starting and stopping in a plant of several boilers may be followed. To obtain the desired equality of conditions of the fire when amechanical stoker other than a chain grate is used, the procedure shouldbe modified where practicable as follows: Regulate the coal feed so as to burn the fire to the low condition required for cleaning. Shut off the coal-feeding mechanism and fill the hoppers level full. Clean the ash or dump plate, note quickly the depth and condition of the coal on the grate, the water level, [66] the steam pressure, and the time, and record the latter as the starting time. Then start the coal-feeding mechanism, clean the ashpit, and proceed with the regular work of the test. When the time arrives for the close of the test, shut off the coal-feeding mechanism, fill the hoppers and burn the fire to the same low point as at the beginning. When this condition is reached, note the water level, the steam pressure, and the time, and record the latter as the stopping time. Finally clean the ashplate and haul the ashes. In the case of chain grate stokers, the desired operating conditions should be maintained for half an hour before starting a test and for a like period before its close, the height of the throat plate and the speed of the grate being the same during both of these periods. 8. RECORDS A log of the data should be entered in notebooks or on blank sheetssuitably prepared in advance. This should be done in such manner thatthe test may be divided into hourly periods, or if necessary, periods ofless duration, and the leading data obtained for any one or more periodsas desired, thereby showing the degree of uniformity obtained. Half-hourly readings of the instruments are usually sufficient. If thereare sudden and wide fluctuations, the readings in such cases should betaken every 15 minutes, and in some instances oftener. The coal should be weighed and delivered to the firemen in portions sufficient for one hour's run, thereby ascertaining the degree of uniformity of firing. An ample supply of coal should be maintained at all times, but the quantity on the floor at the end of each hour should be as small as practicable, so that the same may be readily estimated and deducted from the total weight. The records should be such as to ascertain also the consumption of feed water each hour and thereby determine the degree of uniformity of evaporation. 9. QUALITY OF STEAM[67] If the boiler does not produce superheated steam the percentage ofmoisture in the steam should be determined by the use of a throttling orseparating calorimeter. If the boiler has superheating surface, thetemperature of the steam should be determined by the use of athermometer inserted in a thermometer well. For saturated steam construct a sampling pipe or nozzle made of one-halfinch iron pipe and insert it in the steam main at a point where theentrained moisture is likely to be most thoroughly mixed. The inner endof the pipe, which should extend nearly across to the opposite side ofthe main, should be closed and interior portion perforated with not lessthan twenty one-eighth inch holes equally distributed from end to endand preferably drilled in irregular or spiral rows, with the first holenot less than half an inch from the wall of the pipe. The sampling pipe should not be placed near a point where water may pocket or where such water may effect the amount of moisture contained in the sample. Where non-return valves are used, or there are horizontal connections leading from the boiler to a vertical outlet, water may collect at the lower end of the uptake pipe and be blown upward in a spray which will not be carried away by the steam owing to a lack of velocity. A sample taken from the lower part of this pipe will show a greater amount of moisture than a true sample. With goose-neck connections a small amount of water may collect on the bottom of the pipe near the upper end where the inclination is such that the tendency to flow backward is ordinarily counterbalanced by the flow of steam forward over its surface; but when the velocity momentarily decreases the water flows back to the lower end of the goose-neck and increases the moisture at that point, making it an undesirable location for sampling. In any case it must be borne in mind that with low velocities the tendency is for drops of entrained water to settle to the bottom of the pipe, and to be temporarily broken up into spray whenever an abrupt bend or other disturbance is met. If it is necessary to attach the sampling nozzle at a point near the endof a long horizontal run, a drip pipe should be provided a shortdistance in front of the nozzle, preferably at a pocket formed by somefitting and the water running along the bottom of the main drawn off, weighed, and added to the moisture shown by the calorimeter; or, better, a steam separator should be installed at the point noted. In testing a stationary boiler the sampling pipe should be located asnear as practicable to the boiler, and the same is true as regards thethermometer well when the steam is superheated. In an engine or turbinetest these locations should be as near as practicable to throttle valve. In the test of a plant where it is desired to get complete information, especially where the steam main is unusually long, sampling nozzles orthermometer wells should be provided at both points, so as to obtaindata at either point as may be required. 10. SAMPLING AND DRYING COAL During the progress of test the coal should be regularly sampled for thepurpose of analysis and determination of moisture. Select a representative shovelful from each barrow-load as it is drawnfrom the coal pile or other source of supply, and store the samples in acool place in a covered metal receptacle. When all the coal has thusbeen sampled, break up the lumps, thoroughly mix the whole quantity, andfinally reduce it by the process of repeated quartering and crushing toa sample weighing about 5 pounds, the largest pieces being about thesize of a pea. From this sample two one-quart air-tight glass fruitjars, or other air-tight vessels, are to be promptly filled andpreserved for subsequent determinations of moisture, calorific value, and chemical composition. These operations should be conducted where theair is cool and free from drafts. [Illustration: 3460 Horse-power Installation of Babcock & Wilcox Boilersat the Chicago, Ill. , Shops of the Chicago and Northwestern Ry. Co. ] When the sample lot of coal has been reduced by quartering to, say, 100pounds, a portion weighing, say, 15 to 20 pounds should be withdrawn forthe purpose of immediate moisture determination. This is placed in ashallow iron pan and dried on the hot iron boiler flue for at least 12hours, being weighed before and after drying on scales reading toquarter ounces. The moisture thus determined is approximately reliable for anthraciteand semi-bituminous coals, but not for coals containing much inherentmoisture. For such coals, and for all absolutely reliable determinationsthe method to be pursued is as follows: Take one of the samples contained in the glass jars, and subject it to a thorough air drying, by spreading it in a thin layer and exposing it for several hours to the atmosphere of a warm room, weighing it before and after, thereby determining the quantity of surface moisture it contains. [68] Then crush the whole of it by running it through an ordinary coffee mill or other suitable crusher adjusted so as to produce somewhat coarse grains (less than 1/16 inch), thoroughly mix the crushed sample, select from it a portion of from 10 to 50 grams, [69] weigh it in a balance which will easily show a variation as small as 1 part in 1000, and dry it for one hour in an air or sand bath at a temperature between 240 and 280 degrees Fahrenheit. Weigh it and record the loss, then heat and weigh again until the minimum weight has been reached. The difference between the original and the minimum weight is the moisture in the air-dried coal. The sum of the moisture thus found and that of the surface moisture is the total moisture. 11. ASHES AND REFUSE The ashes and refuse withdrawn from the furnace and ashpit during theprogress of the test and at its close should be weighed so far aspossible in a dry state. If wet the amount of moisture should beascertained and allowed for, a sample being taken and dried for thispurpose. This sample may serve also for analysis and the determinationof unburned carbon and fusing temperature. The method above described for sampling coal may also be followed forobtaining a sample of the ashes and refuse. 12. CALORIFIC TESTS AND ANALYSES OF COAL The quality of the fuel should be determined by calorific tests andanalysis of the coal sample above referred to. [70] 13. ANALYSES OF FLUE GASES For approximate determinations of the composition of the flue gases, theOrsat apparatus, or some modification thereof, should be employed. Ifmomentary samples are obtained the analyses should be made as frequentlyas possible, say, every 15 to 30 minutes, depending on the skill of theoperator, noting at the time the sample is drawn the furnace and firingconditions. If the sample drawn is a continuous one, the intervals maybe made longer. 14. SMOKE OBSERVATIONS[71] In tests of bituminous coals requiring a determination of the amount ofsmoke produced, observations should be made regularly throughout thetrial at intervals of 5 minutes (or if necessary every minute), notingat the same time the furnace and firing conditions. 15. CALCULATION OF RESULTS The methods to be followed in expressing and calculating those resultswhich are not self-evident are explained as follows: (A) _Efficiency. _ The "efficiency of boiler, furnace and grate" is the relation between the heat absorbed per pound of coal fired, and the calorific value of one pound of coal. The "efficiency of boiler and furnace" is the relation between the heat absorbed per pound of combustible burned, and the calorific value of one pound of combustible. This expression of efficiency furnishes a means for comparing one boiler and furnace with another, when the losses of unburned coal due to grates, cleanings, etc. , are eliminated. The "combustible burned" is determined by subtracting from the weight of coal supplied to the boiler, the moisture in the coal, the weight of ash and unburned coal withdrawn from the furnace and ashpit, and the weight of dust, soot, and refuse, if any, withdrawn from the tubes, flues, and combustion chambers, including ash carried away in the gases, if any, determined from the analysis of coal and ash. The "combustible" used for determining the calorific value is the weight of coal less the moisture and ash found by analysis. The "heat absorbed" per pound of coal, or combustible, is calculated by multiplying the equivalent evaporation from and at 212 degrees per pound of coal or combustible by 970. 4. Other items in this section which have been treated elsewhere are: (B) Corrections for moisture in steam. (C) Correction for live steam used. (D) Equivalent evaporation. (E) Heat balance. (F) Total heat of combustion of coal. (G) Air for combustion and the methods recommended for calculating these results are in accordance with those described in different portions of this book. 16. DATA AND RESULTS The data and results should be reported in accordance with either theshort form or the complete form, adding lines for data not provided for, or omitting those not required, as may conform to the object in view. 17. CHART In trials having for an object the determination and exposition of thecomplete boiler performance, the entire log of readings and data shouldbe plotted on a chart and represented graphically. 18. TESTS WITH OIL AND GAS FUELS Tests of boilers using oil or gas for fuel should accord with the ruleshere given, excepting as they are varied to conform to the particularcharacteristics of the fuel. The duration in such cases may be reduced, and the "flying" method of starting and stopping employed. The table of data and results should contain items stating character of furnace and burner, quality and composition of oil or gas, temperature of oil, pressure of steam used for vaporizing and quantity of steam used for both vaporizing and for heating. TABLE DATA AND RESULTS OF EVAPORATIVE TEST SHORT FORM, CODE OF 1912 1 Test of. .. .. .. .. .. .. .. .. Boiler located at. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . To determine. .. .. .. .. .. .. .. Conducted by. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 2 Kind of furnace. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 3 Grate surface. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Square feet 4 Water-heating surface. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Square feet 5 Superheating surface. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Square feet 6 Date. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 7 Duration. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Hours 8 Kind and size of coal. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . AVERAGE PRESSURES, TEMPERATURES, ETC. 9 Steam pressure by gauge. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Pounds10 Temperature of feed water entering boiler. .. .. .. .. .. .. .. .. .. .. .. .. Degrees11 Temperature of escaping gases leaving boiler. .. .. .. .. .. .. .. .. .. .. . Degrees12 Force of draft between damper and boiler. .. .. .. .. .. .. .. .. .. .. .. .. .. Inches13 Percentage of moisture in steam, or number degrees of superheating. .. .. .. .. .. .. .. .. . Per cent or degrees TOTAL QUANTITIES 14 Weight of coal as fired[72]. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Pounds15 Percentage of moisture in coal. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Per cent16 Total weight of dry coal consumed. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Pounds17 Total ash and refuse. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Pounds18 Percentage of ash and refuse in dry coal. .. .. .. .. .. .. .. .. .. .. .. .. Per cent19 Total weight of water fed to the boiler[73]. .. .. .. .. .. .. .. .. .. .. .. . Pounds20 Total water evaporated, corrected for moisture in steam. .. .. .. .. .. . Pounds21 Total equivalent evaporation from and at 212 degrees. .. .. .. .. .. .. .. Pounds HOURLY QUANTITIES AND RATES 22 Dry coal consumed per hour. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Pounds23 Dry coal per square feet of grate surface per hour. .. .. .. .. .. .. .. .. Pounds24 Water evaporated per hour corrected for quality of steam. .. .. .. .. .. Pounds25 Equivalent evaporation per hour from and at 212 degrees. .. .. .. .. .. . Pounds26 Equivalent evaporation per hour from and at 212 degrees per square foot of water-heating surface. .. .. .. .. .. .. .. .. .. .. .. . Pounds CAPACITY 27 Evaporation per hour from and at 212 degrees (same as Line 25). .. .. Pounds28 Boiler horse power developed (Item 27÷34½). .. .. .. .. .. .. Boiler horse power29 Rated capacity, in evaporation from and at 212 degrees per hour. .. . Pounds30 Rated boiler horse power. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Boiler horse power31 Percentage of rated capacity developed. .. .. .. .. .. .. .. .. .. .. .. .. .. Per cent ECONOMY RESULTS 32 Water fed per pound of coal fired (Item 19÷Item 14). .. .. .. .. .. .. .. . Pounds33 Water evaporated per pound of dry coal (Item 20÷Item 16). .. .. .. .. .. Pounds34 Equivalent evaporation from and at 212 degrees per pound of dry coal (Item 21÷Item 16). .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Pounds35 Equivalent evaporation from and at 212 degrees per pound of combustible [Item 21÷(Item 16-Item 17)]. .. .. .. .. .. .. .. .. .. .. . Pounds EFFICIENCY 36 Calorific value of one pound of dry coal. .. .. .. .. .. .. .. .. .. .. .. .. B. T. U. 37 Calorific value of one pound of combustible. .. .. .. .. .. .. .. .. .. .. . B. T. U. ( Item 34×970. 4)38 Efficiency of boiler, furnace and grate (100 × -------------). .. . Per cent ( Item 36 ) ( Item 35×970. 4)39 Efficiency of boiler and furnace (100 × -------------). .. .. .. .. .. Per cent ( Item 37 ) COST OF EVAPORATION 40 Cost of coal per ton of. .. .. . Pounds delivered in boiler room. .. .. . Dollars41 Cost of coal required for evaporating 1000 pounds of water from and at 212 degrees. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Dollars [Illustration: Portion of 3600 Horse-power Installation of Babcock &Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers atthe Loomis Street Plant of the Peoples Gas Light & Coke Co. , Chicago, Ill. This Company has Installed 7780 Horse Power of Babcock & WilcoxBoilers] THE SELECTION OF BOILERS WITH A CONSIDERATION OF THE FACTORS DETERMININGSUCH SELECTION The selection of steam boilers is a matter to which the most carefulthought and attention may be well given. Within the last twenty years, radical changes have taken place in the methods and appliances for thegeneration and distribution of power. These changes have been madelargely in the prime movers, both as to type and size, and are bestillustrated by the changes in central station power-plant practice. Itis hardly within the scope of this work to treat of power-plant designand the discussion will be limited to a consideration of the boiler endof the power plant. As stated, the changes have been largely in prime movers, the steamgenerating equipment having been considered more or less of a standardpiece of apparatus whose sole function is the transfer of the heatliberated from the fuel by combustion to the steam stored or circulatedin such apparatus. When the fact is considered that the cost of steamgeneration is roughly from 65 to 80 per cent of the total cost of powerproduction, it may be readily understood that the most fruitful fieldfor improvement exists in the boiler end of the power plant. Theefficiency of the plant as a whole will vary with the load it carriesand it is in the boiler room where such variation is largest and mostsubject to control. The improvements to be secured in the boiler room results are not simplya matter of dictation of operating methods. The securing of perfectcombustion, with the accompanying efficiency of heat transfer, whilecomparatively simple in theory, is difficult to obtain in practicaloperation. This fact is perhaps best exemplified by the differencebetween test results and those obtained in daily operation even underthe most careful supervision. This difference makes it necessary toestablish a standard by which operating results may be judged, astandard not necessarily that which might be possible under testconditions but one which experiment shows can be secured under the verybest operating conditions. The study of the theory of combustion, draft, etc. , as already given, will indicate that the question of efficiency is largely a matter ofproper relation between fuel, furnace and generator. While thepossibility of a substantial saving through added efficiency cannot beoverlooked, the boiler design of the future must, even more than in thepast, be considered particularly from the aspect of reliability andsimplicity. A flexibility of operation is necessary as a guarantee ofcontinuity of service. In view of the above, before the question of the selection of boilerscan be taken up intelligently, it is necessary to consider the subjectsof boiler efficiency and boiler capacity, together with their relationto each other. The criterion by which the efficiency of a boiler plant is to be judgedis the cost of the production of a definite amount of steam. Consideredin this sense, there must be included in the efficiency of a boilerplant the simplicity of operation, flexibility and reliability of theboiler used. The items of repair and upkeep cost are often high becauseof the nature of the service. The governing factor in these items isunquestionably the type of boiler selected. The features entering into the plant efficiency are so numerous that itis impossible to make a statement as to a means of securing the highestefficiency which will apply to all cases. Such efficiency is to besecured by the proper relation of fuel, furnace and boiler heatingsurface, actual operating conditions, which allow the approaching of thepotential efficiencies made possible by the refinement of design, and asystematic supervision of the operation assisted by a detailed record ofperformances and conditions. The question of supervision will be takenup later in the chapter on "Operation and Care of Boilers". The efficiencies that may be expected from the combination ofwell-designed boilers and furnaces are indicated in Table 59 in whichare given a number of tests with various fuels and under widelydifferent operating conditions. It is to be appreciated that the results obtained as given in this tableare practically all under test conditions. The nearness with whichpractical operating conditions can approach these figures will dependupon the character of the supervision of the boiler room and theintelligence of the operating crew. The size of the plant willordinarily govern the expense warranted in securing the right sort ofsupervision. The bearing that the type of boiler has on the efficiency to be expectedcan only be realized from a study of the foregoing chapters. Capacity--Capacity, as already defined, is the ability of a definiteamount of boiler-heating surface to generate steam. Boilers areordinarily purchased under a manufacturer's specification, which rates aboiler at a nominal rated horse power, usually based on 10 square feetof heating surface per horse power. Such a builders' rating isabsolutely arbitrary and implies nothing as to the limiting amount ofwater that this amount of heating surface will evaporate. It does notimply that the evaporation of 34. 5 pounds of water from and at 212degrees with 10 square feet of heating surface is the limit of thecapacity of the boiler. Further, from a statement that a boiler is of acertain horse power on the manufacturer's basis, it is not to beunderstood that the boiler is in any state of strain when developingmore than its rated capacity. Broadly stated, the evaporative capacity of a certain amount of heatingsurface in a well-designed boiler, that is, the boiler horse power it iscapable of producing, is limited only by the amount of fuel that can beburned under the boiler. While such a statement would imply that thequestion of capacity to be secured was simply one of making anarrangement by which sufficient fuel could be burned under a definiteamount of heating surface to generate the required amount of steam, there are limiting features that must be weighed against the advantagesof high capacity developed from small heating surfaces. Briefly stated, these factors are as follows: 1st. Efficiency. As the capacity increases, there will in general be adecrease in efficiency, this loss above a certain point making itinadvisable to try to secure more than a definite horse power from agiven boiler. This loss of efficiency with increased capacity is treatedbelow in detail, in considering the relation of efficiency to capacity. 2nd. Grate Ratio Possible or Practicable. All fuels have a maximum rateof combustion, beyond which satisfactory results cannot be obtained, regardless of draft available or which may be secured by mechanicalmeans. Such being the case, it is evident that with this maximumcombustion rate secured, the only method of obtaining added capacitywill be through the addition of grate surface. There is obviously apoint beyond which the grate surface for a given boiler cannot beincreased. This is due to the impracticability of handling grates abovea certain maximum size, to the enormous loss in draft pressure through aboiler resulting from an attempt to force an abnormal quantity of gasthrough the heating surface and to innumerable details of design andmaintenance that would make such an arrangement wholly unfeasible. 3rd. Feed Water. The difficulties that may arise through the use of poorfeed water or that are liable to happen through the use of practicallyany feed water have already been pointed out. This question of feed isfrequently the limiting factor in the capacity obtainable, for with anincrease in such capacity comes an added concentration of suchingredients in the feed water as will cause priming, foaming or rapidscale formation. Certain waters which will give no trouble that cannotbe readily overcome with the boiler run at ordinary ratings will causedifficulties at higher ratings entirely out of proportion to anyadvantage secured by an increase in the power that a definite amount ofheating surface may be made to produce. Where capacity in the sense of overload is desired, the type of boilerselected will play a large part in the successful operation through suchperiods. A boiler must be selected with which there is possible afurnace arrangement that will give flexibility without undue loss inefficiency over the range of capacity desired. The heating surface mustbe so arranged that it will be possible to install in a practicalmanner, sufficient grate surface at or below the maximum combustion rateto develop the amount of power required. The design of boiler must besuch that there will be no priming or foaming at high overloads and thatany added scale formation due to such overloads may be easily removed. Certain boilers which deliver commercially dry steam when operated atabout their normal rated capacity will prime badly when run at overloadsand this action may take place with a water that should be easilyhandled by a properly designed boiler at any reasonable load. Suchaction is ordinarily produced by the lack of a well defined, positivecirculation. Relation of Efficiency and Capacity--The statement has been made that ingeneral the efficiency of a boiler will decrease as the capacity isincreased. Considering the boiler alone, apart from the furnace, thisstatement may be readily explained. Presupposing a constant furnace temperature, regardless of the capacityat which a given boiler is run; to assure equal efficiencies at low andhigh ratings, the exit temperature in the two instances wouldnecessarily be the same. For this temperature at the high rating, to beidentical with that at the low rating, the rate of heat transfer fromthe gases to the heating surfaces would have to vary directly as theweight or volume of such gases. Experiment has shown, however, that thisis not true but that this rate of transfer varies as some power of thevolume of gas less than one. As the heat transfer does not, therefore, increase proportionately with the volume of gases, the exit temperaturefor a given furnace temperature will be increased as the volume of gasesincreases. As this is the measure of the efficiency of the heatingsurface, the boiler efficiency will, therefore, decrease as the volumeof gases increases or the capacity at which the boiler is operatedincreases. Further, a certain portion of the heat absorbed by the heating surfaceis through direct radiation from the fire. Again, presupposing aconstant furnace temperature; the heat absorbed through radiation issolely a function of the amount of surface exposed to such radiation. Hence, for the conditions assumed, the amount of heat absorbed byradiation at the higher ratings will be the same as at the lower ratingsbut in proportion to the total absorption will be less. As the addedvolume of gas does not increase the rate of heat transfer, there aretherefore two factors acting toward the decrease in the efficiency of aboiler with an increase in the capacity. TABLE 59 TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS ______________________________________________________________________|Number| | | | Rated || of | Name and Location | Kind of Coal | Kind of | Horse || Test | of Plant | | Furnace |Power of|| | | | | Boiler || | | | | ||______|___________________________|________________|_________|________|| |Susquehanna Coal Co. , |No. 1 Anthracite|Hand | || 1 |Shenandoah, Pa. |Buckwheat |Fired | 300 ||______|___________________________|________________|_________|________|| |Balbach Smelting & |No. 2 Buckwheat |Wilkenson| || 2 |Refining Co. , Newark, N. J. |and Bird's-eye | Stoker | 218 ||______|___________________________|________________|_________|________|| |H. R. Worthington, |No. 2 Anthracite|Hand | || 3 |Harrison N. J. |Buckwheat |Fired | 300 ||______|___________________________|________________|_________|________|| |Raymond Street Jail, |Anthracite Pea |Hand | || 4 |Brooklyn, N. Y. | |Fired | 155 ||______|___________________________|________________|_________|________|| |R. H. Macy & Co. , |No. 3 Anthracite|Hand | || 5 |New York, N. Y. |Buckwheat |Fired | 293 ||______|___________________________|________________|_________|________|| |National Bureau of |Anthracite Egg |Hand | || 6 |Standards, Washington, D. C. | |Fired | 119 ||______|___________________________|________________|_________|________|| |Fred. Loeser & Co. , |No. 1 Anthracite|Hand | || 7 |Brooklyn, N. Y. |Buckwheat |Fired | 300 ||______|___________________________|________________|_________|________|| |New York Edison Co. , |No. 2 Anthracite|Hand | || 8 |New York City |Buckwheat |Fired | 374 ||______|___________________________|________________|_________|________|| |Sewage Pumping Station, |Hocking Valley |Hand | || 9 |Cleveland, O. |Lump, O. |Fired | 150 ||______|___________________________|________________|_________|________|| |Scioto River Pumping Sta. , |Hocking Valley, |Hand | || 10 |Cleveland, O. |O. |Fired | 300 ||______|___________________________|________________|_________|________|| |Consolidated Gas & Electric|Somerset, Pa. |Hand | || 11 |Co. , Baltimore, Md. | |Fired | 640 ||______|___________________________|________________|_________|________|| |Consolidated Gas & Electric|Somerset, Pa. |Hand | || 12 |Co. , Baltimore, Md. | |Fired | 640 ||______|___________________________|________________|_________|________|| |Merrimac Mfg. Co. , |Georges Creek, |Hand | || 13 |Lowell, Mass. |Md. |Fired | 321 ||______|___________________________|________________|_________|________|| |Great West'n Sugar Co. , |Lafayette, Col. , |HandFired| || 14 |Ft. Collins, Col. |Mine Run |Extension| 351 ||______|___________________________|________________|_________|________|| |Baltimore Sewage Pumping |New River |Hand | || 15 | Station | |Fired | 266 ||______|___________________________|________________|_________|________|| |Tennessee State Prison, |Brushy Mountain, |Hand | || 16 |Nashville, Tenn. |Tenn. |Fired | 300 ||______|___________________________|________________|_________|________|| |Pine Bluff Corporation, |Arkansas Slack |Hand | || 17 |Pine Bluff, Ark. | |Fired | 298 ||______|___________________________|________________|_________|________|| |Pub. Serv. Corporation |Valley, Pa. , |Roney | || 18 |of N. J. , Hoboken |Mine Run |Stoker | 520 ||______|___________________________|________________|_________|________|| |Pub. Serv. Corporation |Valley, Pa. , |Roney | || 19 |of N. J. , Hoboken |Mine Run |Stoker | 520 ||______|___________________________|________________|_________|________|| |Frick Building, |Pittsburgh Nut |American | || 20 |Pittsburgh, Pa. |and Slack |Stoker | 300 ||______|___________________________|________________|_________|________|| |New York Edison Co. , |Loyal Hanna, Pa. |Taylor | || 21 |New York City | |Stoker | 604 ||______|___________________________|________________|_________|________|| |City of Columbus, O. , |Hocking Valley, |Detroit | || 22 |Dept. Lighting |O. |Stoker | 300 ||______|___________________________|________________|_________|________|| |Edison Elec. Illum. Co. , |New River |Murphy | || 23 |Boston, Mass. | |Stoker | 508 ||______|___________________________|________________|_________|________|| |Colorado Springs & |Pike View, Col. , |Green Chn| || 24 |Interurban Ry. , Col. |Mine Run |Grate | 400 ||______|___________________________|________________|_________|________|| |Pub. Serv. Corporation |Lancashire, Pa. |B&W. Chain| || 25 |of N. J. , Marion | |Grate | 600 ||______|___________________________|________________|_________|________|| |Pub. Serv. Corporation |Lancashire, Pa. |B&W. Chain| || 26 |of N. J. , Marion | |Grate | 600 ||______|___________________________|________________|_________|________|| |Erie County Electric Co. , |Mercer County, |B&W. Chain| || 27 |Erie, Pa. |Pa. |Grate | 508 ||______|___________________________|________________|_________|________|| |Union Elec. Lt. & Pr. Co. , |Mascouth, Ill. |B&W. Chain| || 28 |St. Louis, Mo. | |Grate | 508 ||______|___________________________|________________|_________|________|| |Union Elec. Lt. & Pr. Co. , |St. Clair |B&W. Chain| || 29 |St. Louis, Mo. |County, Ill. |Grate | 508 ||______|___________________________|________________|_________|________|| |Commonwealth Edison Co. , |Carterville, |B&W. Chain| || 30 |Chicago, Ill. |Ill. , Screenings|Grate | 508 ||______|___________________________|________________|_________|________| ________________________________________________________________|Number|Grate |Dura-|Steam |Temper-|Degrees|Factor| Draft || of |Surf. | tion|Pres. | ature | Super | of | In | At || Test |Square|Test | By | Water | -heat |Evapo-|Furnace|Boiler|| | Feet |Hours|Gauge |Degrees|Degrees|ration|Inches |Damper|| | | |Pounds| Fahr. | Fahr. | |Upr/Lwr|Inches||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 1 | 84 | 8 | 68 | 53. 9 | |1. 1965| +. 41 | . 21 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | +. 65 | || 2 | 51. 6 | 7 | 136. 3| 203 | 150 |1. 1480| . 47 | . 56 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 3 | 67. 6 | 8 | 139 | 139. 6 | 139 |1. 1984| . 70 | . 96 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 4 | 40 | 8 | 110. 2| 137 | |1. 1185| . 33 | . 43 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 5 | 59. 5 | 10 | 133. 2| 75. 2 | |1. 1849| . 19 | . 40 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 6 | 26. 5 | 18 | 132. 1| 70. 5 | |1. 1897| . 33 | ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | +. 51 | || 7 | 48. 9 | 7 | 101. | 121. 3 | |1. 1333| -. 20 | . 30 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 8 | 59. 5 | 6 | 191. 8| 88. 3 | |1. 1771| . 50 | ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 9 | 27 | 24 | 156. 3| 58 | |1. 2051| . 10 | . 24 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 10 | | 24 | 145 | 75 | |1. 1866| . 26 | . 46 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 11 | 118 | 8 | 170 | 186. 1 | 66. 7 |1. 1162| . 34 | . 42 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 12 | 118 | 7. 92| 173 | 180. 2 | 75. 2 |1. 1276| . 44 | . 58 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 13 | 52 | 24 | 75 | 53. 3 | |1. 1987| . 25 | . 35 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 14 | 59. 5 | 8 | 105 | 35. 8 | |1. 2219| . 17 | . 38 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 15 | 59. 5 | 24 | 170. 1| 133 | |1. 1293| . 12 | . 43 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 16 | 51. 3 | 10 | 105 | 75. 1 | |1. 1814| . 21 | . 42 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 17 | 59. 5 | 8 | 149. 2| 71 | |1. 1910| . 35 | . 59 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 18 | 103. 2| 10 | 133. 2| 65. 3 | 65. 9 |1. 2346| . 05 | . 49 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 19 | 103. 2| 9 | 139 | 64 | 80. 2 |1. 2358| . 18 | . 57 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 20 | 53 | 9 | 125 | 76. 6 | |1. 1826| +1. 64 | . 64 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 21 | 75 | 8 | 198. 5| 165. 1 | 104 |1. 1662| +3. 05 | . 60 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 22 | | 9 | 140 | 67 | 180 |1. 2942| . 22 | . 35 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 23 | 90 |16. 25| 199 | 48. 4 | 136. 5 |1. 2996| . 23 | 1. 27 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 24 | 103 | 8 | 129 | 56 | |1. 2002| . 23 | . 30 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | +. 52 | || 25 | 132 | 8 | 200 | 57. 2 | 280. 4 |1. 3909| +. 19 | . 52 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | +. 15 | || 26 | 132 | 8 | 199 | 60. 7 | 171. 0 |1. 3191| . 04 | . 52 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 27 | 90 | 8 | 120 | 69. 9 | |1. 1888| . 31 | . 58 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 28 | 103. 5| 8 | 180 | 46 | 113 |1. 2871| . 62 | 1. 24 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 29 | 103. 5| 8 | 183 | 53. 1 | 104 |1. 2725| . 60 | 1. 26 ||______|______|_____|______|_______|_______|______|_______|______|| | | | | | | | | || 30 | 90 | 7 | 184 | 127. 1 | 180 |1. 2393| . 68 | 1. 15 ||______|______|_____|______|_______|_______|______|_______|______| ______________________________________________________________|Number|Temper-| Coal || of | ature | Total | Moist-| Total |Ash and| Total |DryCoal|| Test |FlueGas|Weight:| ure | dry | Refuse|Combus-|/sq. Ft. || |Degrees| Fired | Per | Coal | Per | tible | Grate || | Fahr. |Pounds | Cent | Pounds| Cent | Pounds|/Hr. Lb. ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 1 | | 11670 | 4. 45 | 11151 | 26. 05 | 8248 | 16. 6 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 2 | 487 | 8800 | 7. 62 | 8129 | 29. 82 | 5705 | 19. 71 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 3 | 559 | 10799 | 6. 42 | 10106 | 20. 02 | 8081 | 21. 77 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 4 | 427 | 5088 | 4. 00 | 4884 | 19. 35 | 3939 | 15. 26 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 5 | 414 | 9440 | 2. 14 | 9238 | 11. 19 | 8204 | 15. 52 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 6 | 410 | 8555 | 3. 62 | 8245 | 15. 73 | 6948 | 17. 28 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 7 | 480 | 7130 | 7. 38 | 6604 | 18. 35 | 5392 | 19. 29 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 8 | 449 | 7500 | 2. 70 | 7298 | 27. 94 | 5259 | 14. 73 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 9 | 410 | 15087 | 7. 50 | 13956 | 11. 30 | 12379 | 21. 5 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 10 | 503 | 29528 | 7. 72 | 27248 | | | 24. 7 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 11 | 487 | 20400 | 2. 84 | 19821 | 7. 83 | 18269 | 21. 00 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 12 | 494 | 21332 | 2. 29 | 20843 | 8. 23 | 19127 | 22. 31 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 13 | 516 | 24584 | 4. 29 | 23529 | 7. 63 | 21883 | 18. 85 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 14 | 523 | 15540 | 18. 64 | 12643 | | | 28. 59 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 15 | 474 | 18330 | 2. 03 | 17958 | 16. 36 | 16096 | 12. 57 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 16 | 536 | 12243 | 2. 14 | 11981 | | | 23. 40 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 17 | 534 | 10500 | 3. 04 | 10181 | | | 21. 40 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 18 | 458 | 18600 | 3. 40 | 17968 | 18. 38 | 14665 | 17. 41 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 19 | 609 | 23400 | 2. 56 | 22801 | 16. 89 | 18951 | 24. 55 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 20 | 518 | 10500 | 1. 83 | 10308 | 12. 22 | 9048 | 21. 56 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 21 | 536 | 25296 | 2. 20 | 24736 | | | 41. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 22 | 511 | 14263 | 8. 63 | 13032 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 23 | 560 | 39670 | 4. 22 | 37996 | 4. 32 | 36355 | 25. 98 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 24 | 538 | 23000 | 23. 73 | 17542 | | | 21. 36 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 25 | 590 | 32205 | 4. 03 | 30907 | 15. 65 | 26070 | 29. 26 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 26 | 529 | 24243 | 4. 09 | 23251 | 12. 33 | 20385 | 22. 01 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 27 | 533 | 22328 | 4. 42 | 21341 | 16. 88 | 17739 | 29. 64 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 28 | 523 | 32163 | 13. 74 | 27744 | | | 33. 50 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 29 | 567 | 36150 | 14. 62 | 30865 | | | 37. 28 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 30 | | 30610 | 11. 12 | 27206 | 14. 70 | 23198 | 43. 20 ||______|_______|_______|_______|_______|_______|_______|_______| ______________________________________________________________|Number| Water | | Flue Gas Analysis || of |Actual | Equiv. |ditto /|% Rated|CO_{2} | O | CO || Test |Evapor-|Evap. @|sq. Ft. |Cap'ty. | Per | Per | Per || | ation |>=212° |Heating|Develpd| Cent | Cent | Cent || |/Hr. Lb. |/Hr. Lb. |Surface|PerCent| | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 1 | 10268 | 12286 | 4. 10 | 118. 7 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 2 | 8246 | 9466 | 4. 34 | 125. 7 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 3 | 9145 | 10959 | 3. 65 | 105. 9 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 4 | 5006 | 5599 | 3. 61 | 104. 7 | 12. 26 | 7. 88 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 5 | 7434 | 8809 | 3. 06 | 87. 2 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 6 | 2903 | 3454 | 2. 91 | 84. 4 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 7 | 7464 | 8459 | 2. 82 | 81. 7 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 8 | 9164 | 10787 | 2. 88 | 83. 5 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 9 | 4374 | 5271 | 3. 51 | 101. 8 | 11. 7 | 7. 3 | 0. 07 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 10 | 8688 | 10309 | 3. 44 | 99. 6 | 12. 9 | 5. 0 | 0. 2 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 11 | 24036 | 26829 | 4. 19 | 121. 5 | 12. 5 | 6. 4 | 0. 5 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 12 | 25313 | 28544 | 4. 46 | 129. 3 | 13. 3 | 5. 1 | 0. 5 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 13 | 9168 | 10990 | 3. 42 | 99. 3 | 9. 6 | 8. 8 | 0. 4 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 14 | 11202 | 13689 | 3. 91 | 113. 5 | 9. 1 | 9. 9 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 15 | 7565 | 8543 | 3. 21 | 93. 1 | 10. 71 | 9. 10 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 16 | 9512 | 11237 | 3. 74 | 108. 6 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 17 | 9257 | 11025 | 3. 70 | 107. 2 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 18 | 15887 | 19614 | 3. 77 | 108. 7 | 11. 7 | 7. 7 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 19 | 21320 | 26347 | 5. 06 | 146. 7 | 11. 9 | 7. 8 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 20 | 9976 | 11978 | 3. 93 | 112. 0 | 11. 3 | 7. 5 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 21 | 28451 | 33066 | 5. 47 | 158. 6 | 12. 3 | 6. 4 | 0. 7 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 22 | 10467 | 13526 | 4. 51 | 130. 7 | 11. 9 | 7. 2 | 0. 04 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 23 | 20700 | 26902 | 5. 30 | 153. 5 | 11. 1 | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 24 | 14650 | 17583 | 4. 40 | 127. 4 | | | ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 25 | 28906 | 40205 | 6. 70 | 194. 2 | 10. 5 | 8. 3 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 26 | 23074 | 30437 | 5. 07 | 147. 0 | 10. 1 | 9. 0 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 27 | 20759 | 24678 | 4. 85 | 140. 8 | 10. 1 | 9. 1 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 28 | 21998 | 28314 | 5. 67 | 161. 5 | 8. 7 | 10. 6 | 0. 0 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 29 | 24386 | 31031 | 6. 11 | 177. 1 | 8. 9 | 10. 7 | 0. 2 ||______|_______|_______|_______|_______|_______|_______|_______|| | | | | | | | || 30 | 30505 | 37805 | 7. 43 | 215. 7 | 10. 4 | 9. 4 | 0. 2 ||______|_______|_______|_______|_______|_______|_______|_______| _______________________________________________________|Number| Proximate Analysis Dry Coal | Equiv. |Combnd. || of |Volatl. | Fixed | Ash |B. T. U. /|Evap. @|Efficy. || Test |Matter |Carbon | Per | Pound |>=212°/|Boiler || | Per | Per | Cent | Dry | Pound |& Grate|| | Cent | Cent | | Coal |DryCoal|PerCent||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 1 | | | 26. 05 | 11913 | 8. 81 | 71. 8 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 2 | | | | 11104 | 8. 15 | 72. 1 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 3 | 5. 55 | 80. 60 | 13. 87 | 12300 | 8. 67 | 68. 4 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 4 | 7. 74 | 77. 48 | 14. 78 | 12851 | 9. 17 | 69. 2 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 5 | | | | 13138 | 9. 53 | 69. 6 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 6 | 6. 13 | 84. 86 | 9. 01 | 13454 | 9. 57 | 69. 0 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 7 | | | | 12224 | 8. 97 | 71. 2 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 8 | 0. 55 | 86. 73 | 12. 72 | 12642 | 8. 87 | 68. 1 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 9 | 39. 01 | 48. 08 | 12. 91 | 12292 | 9. 06 | 71. 5 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 10 | 38. 33 | 46. 71 | 14. 96 | 12284 | 9. 08 | 71. 7 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 11 | 19. 86 | 73. 02 | 7. 12 | 14602 | 10. 83 | 72. 0 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 12 | 20. 24 | 72. 26 | 7. 50 | 14381 | 10. 84 | 73. 2 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 13 | | | | 14955 | 11. 21 | 72. 7 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 14 | 39. 60 | 54. 46 | 5. 94 | 11585 | 8. 66 | 72. 5 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 15 | 17. 44 | 76. 42 | 5. 84 | 15379 | 11. 42 | 72. 1 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 16 | 33. 40 | 54. 73 | 11. 87 | 12751 | 9. 38 | 71. 4 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 17 | 15. 42 | 62. 48 | 22. 10 | 12060 | 8. 66 | 69. 6 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 18 | 14. 99 | 75. 13 | 9. 88 | 14152 | 10. 92 | 74. 88 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 19 | 14. 40 | 74. 33 | 11. 27 | 14022 | 10. 40 | 71. 97 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 20 | 32. 44 | 56. 71 | 10. 85 | 13510 | 10. 30 | 74. 6 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 21 | 19. 02 | 72. 09 | 8. 89 | 14105 | 10. 69 | 73. 5 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 22 | 32. 11 | 53. 93 | 13. 96 | 12435 | 9. 41 | 73. 4 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 23 | 19. 66 | 75. 41 | 4. 93 | 14910 | 11. 51 | 74. 9 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 24 | 43. 57 | 46. 22 | 10. 21 | 11160 | 8. 02 | 69. 7 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 25 | 22. 84 | 69. 91 | 7. 25 | 13840 | 10. 41 | 72. 6 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 26 | 32. 36 | 60. 67 | 6. 97 | 14027 | 10. 47 | 72. 1 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 27 | 33. 26 | 54. 03 | 12. 71 | 12742 | 9. 25 | 70. 4 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 28 | 28. 96 | 46. 88 | 24. 16 | 10576 | 8. 16 | 74. 9 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 29 | 36. 50 | 41. 20 | 22. 30 | 10849 | 8. 04 | 71. 9 ||______|_______|_______|_______|_______|_______|_______|| | | | | | | || 30 | | | 10. 24 | 13126 | 9. 73 | 71. 9 ||______|_______|_______|_______|_______|_______|_______| [Illustration: 15400 Horse-power Installation of Babcock & WilcoxBoilers and Superheaters, Equipped with Babcock & Wilcox Chain GrateStokers at the Plant of the Twin City Rapid Transit Co. , Minneapolis, Minn. ] This increase in the efficiency of the boiler alone with the decrease inthe rate at which it is operated, will hold to a point where theradiation of heat from the boiler setting is proportionately largeenough to be a governing factor in the total amount of heat absorbed. The second reason given above for a decrease of boiler efficiency withincrease of capacity, viz. , the effect of radiant heat, is to a greaterextent than the first reason dependent upon a constant furnacetemperature. Any increase in this temperature will affect enormously theamount of heat absorbed by radiation, as this absorption will vary asthe fourth power of the temperature of the radiating body. In this wayit is seen that but a slight increase in furnace temperature will benecessary to bring the proportional part, due to absorption byradiation, of the total heat absorbed, up to its proper proportion atthe higher ratings. This factor of furnace temperature more properlybelongs to the consideration of furnace efficiency than of boilerefficiency. There is a point, however, in any furnace above which thecombustion will be so poor as to actually reduce the furnace temperatureand, therefore, the proportion of heat absorbed through radiation by agiven amount of exposed heating surface. Since it is thus true that the efficiency of the boiler considered alonewill increase with a decreased capacity, it is evident that if thefurnace conditions are constant regardless of the load, that thecombined efficiency of boiler and furnace will also decrease withincreasing loads. This fact was clearly proven in the tests of theboilers at the Detroit Edison Company. [74] The furnace arrangement ofthese boilers and the great care with which the tests were run made itpossible to secure uniformly good furnace conditions irrespective ofload, and here the maximum efficiency was obtained at a point somewhatless than the rated capacity of the boilers. In some cases, however, and especially in the ordinary operation of theplant, the furnace efficiency will, up to a certain point, increase withan increase in power. This increase in furnace efficiency is ordinarilyat a greater rate as the capacity increases than is the decrease inboiler efficiency, with the result that the combined efficiency ofboiler and furnace will to a certain point increase with an increase incapacity. This makes the ordinary point of maximum combined efficiencysomewhat above the rated capacity of the boiler and in many cases thecombined efficiency will be practically a constant over a considerablerange of ratings. The features limiting the establishing of the point ofmaximum efficiency at a high rating are the same as those limiting theamount of grate surface that can be installed under a boiler. Therelative efficiency of different combinations of boilers and furnaces atdifferent ratings depends so largely upon the furnace conditions thatwhat might hold for one combination would not for another. In view of the above, it is impossible to make a statement of theefficiency at different capacities of a boiler and furnace which willhold for any and all conditions. Fig. 40 shows in a general form therelation of efficiency to capacity. This curve has been plotted from agreat number of tests, all of which were corrected to bring them toapproximately the same conditions. The curve represents test conditions. The efficiencies represented are those which may be secured only undersuch conditions. The general direction of the curve, however, will befound to hold approximately correct for operating conditions when usedonly as a guide to what may be expected. [Graph: Combined Efficiency of Boiler and Furnace Per Centagainst Per Cent of Boiler's Rated Capacity Developed Fig. 40. Approximate Variation of Efficiency with Capacity under TestConditions] Economical Loads--With the effect of capacity on economy in mind, thequestion arises as to what constitutes the economical load to becarried. In figuring on the economical load for an individual plant, thebroader economy is to be considered, that in which, against the boilerefficiency, there is to be weighed the plant first cost, returns on suchinvestment, fuel cost, labor, capacity, etc. , etc. This matter has beenwidely discussed, but unfortunately such discussion has been largelylimited to central power station practice. The power generated in suchstations, while representing an enormous total, is by no means thelarger proportion of the total power generated throughout the country. The factors determining the economic load for the small plant, however, are the same as in a large, and in general the statements made relativeto the question are equally applicable. The economical rating at which a boiler plant should be run is dependentsolely upon the load to be carried by that individual plant and thenature of such load. The economical load for each individual plant canbe determined only from the careful study of each individual set ofconditions or by actual trial. The controlling factor in the cost of the plant, regardless of thenature of the load, is the capacity to carry the maximum peak load thatmay be thrown on the plant under any conditions. While load conditions, do, as stated, vary in every individual plant, ina broad sense all loads may be grouped in three classes: 1st, theapproximately constant 24-hour load; 2nd, the steady 10 or 12-hour loadusually with a noonday period of no load; 3rd, the 24-hour variableload, found in central station practice. The economical load at whichthe boiler may be run will vary with these groups: 1st. For a constant load, 24 hours in the day, it will be found in mostcases that, when all features are considered, the most economical loador that at which a given amount of steam can be produced the mostcheaply will be considerably over the rated horse power of the boiler. How much above the rated capacity this most economic load will be, isdependent largely upon the cost of coal at the plant, but under ordinaryconditions, the point of maximum economy will probably be found to besomewhere between 25 and 50 per cent above the rated capacity of theboilers. The capital investment must be weighed against the coal savingthrough increased thermal efficiency and the labor account, whichincreases with the number of units, must be given proper consideration. When the question is considered in connection with a plant alreadyinstalled, the conditions are different from where a new plant iscontemplated. In an old plant, where there are enough boilers to operateat low rates of capacity, the capital investment leads to a fixedcharge, and it will be found that the most economical load at whichboilers may be operated will be lower than where a new plant is underconsideration. 2nd. For a load of 10 or 12 hours a day, either an approximately steadyload or one in which there is a peak, where the boilers have been bankedover night, the capacity at which they may be run with the best economywill be found to be higher than for uniform 24-hour load conditions. This is obviously due to original investment, that is, a given amount ofinvested capital can be made to earn a larger return through the higheroverload, and this will hold true to a point where the added return morethan offsets the decrease in actual boiler efficiency. Here again thedetermining factors of what is the economical load are the fuel andlabor cost balanced against the thermal efficiency. With a load of thischaracter, there is another factor which may affect the economical plantoperating load. This is from the viewpoint of spare boilers. That suchadded capacity in the way of spares is necessary is unquestionable. Since they must be installed, therefore, their presence leads to a fixedcharge and it is probable that for the plant, as a whole, the economicalload will be somewhat lower than if the boilers were considered only asspares. That is, it may be found best to operate these spares as a partof the regular equipment at all times except when other boilers are offfor cleaning and repairs, thus reducing the load on the individualboilers and increasing the efficiency. Under such conditions, the addedboiler units can be considered as spares only during such time as someof the boilers are not in operation. Due to the operating difficulties that may be encountered at the higheroverloads, it will ordinarily be found that the most economical ratingsat which to run boilers for such load conditions will be between 150 and175 per cent of rating. Here again the maximum capacity at which theboilers may be run for the best plant economy is limited by the point atwhich the efficiency drops below what is warranted in view of the firstcost of the apparatus. 3rd. The 24-hour variable load. This is a class of load carried by thecentral power station, a load constant only in the sense that there areno periods of no load and which varies widely with different portions ofthe 24 hours. With such a load it is particularly difficult to make anyassertion as to the point of maximum economy that will hold for anystation, as this point is more than with any other class of loaddependent upon the factors entering into the operation of eachindividual plant. The methods of handling a load of this description vary probably morethan with any other kind of load, dependent upon fuel, labor, type ofstoker, flexibility of combined furnace and boiler etc. , etc. In general, under ordinary conditions such as appear in city centralpower station work where the maximum peaks occur but a few times a year, the plant should be made of such size as to enable it to carry thesepeaks at the maximum possible overload on the boilers, sufficient marginof course being allowed for insurance against interruption of service. With the boilers operating at this maximum overload through the peaks alarge sacrifice in boiler efficiency is allowable, provided that by suchsacrifice the overload expected is secured. [Illustration: Portion of 4890 Horse-power Installation of Babcock &Wilcox Boilers at the Billings Sugar Co. , Billings, Mont. 694 HorsePower of these Boilers are Equipped with Babcock and Wilcox Chain GrateStokers] Some methods of handling a load of this nature are given below: Certain plant operating conditions make it advisable, from thestandpoint of plant economy, to carry whatever load is on the plant atany time on only such boilers as will furnish the power required whenoperating at ratings of, say, 150 to 200 per cent. That is, all boilerswhich are in service are operated at such ratings at all times, thevariation in load being taken care of by the number of boilers on theline. Banked boilers are cut in to take care of increasing loads andpeaks and placed again on bank when the peak periods have passed. It isprobable that this method of handling central station load is to-day themost generally used. Other conditions of operation make it advisable to carry the load on adefinite number of boiler units, operating these at slightly below theirrated capacity during periods of light or low loads and securing theoverload capacity during peaks by operating the same boilers at highratings. In this method there are no boilers kept on banked fires, thespares being spares in every sense of the word. A third method of handling widely varying loads which is coming somewhatinto vogue is that of considering the plant as divided, one part to takecare of what may be considered the constant plant load, the other totake care of the floating or variable load. With such a method thatportion of the plant carrying the steady load is so proportioned thatthe boilers may be operated at the point of maximum efficiency, thispoint being raised to a maximum through the use of economizers and thegeneral installation of any apparatus leading to such results. Thevariable load will be carried on the remaining boilers of the plantunder either of the methods just given, that is, at the high ratings ofall boilers in service and banking others, or a variable capacity fromall boilers in service. The opportunity is again taken to indicate the very general character ofany statements made relative to the economical load for any plant and toemphasize the fact that each individual case must be consideredindependently, with the conditions of operations applicable thereto. With a thorough understanding of the meaning of boiler efficiency andcapacity and their relation to each other, it is possible to considermore specifically the selection of boilers. The foremost consideration is, without question, the adaptability of thedesign selected to the nature of the work to be done. An installationwhich is only temporary in its nature would obviously not warrant thefirst cost that a permanent plant would. If boilers are to carry anintermittent and suddenly fluctuating load, such as a hoisting load or areversing mill load, a design would have to be selected that would nottend to prime with the fluctuations and sudden demand for steam. Aboiler that would give the highest possible efficiency with fuel of onedescription, would not of necessity give such efficiency with adifferent fuel. A boiler of a certain design which might be good forsmall plant practice would not, because of the limitations inpracticable size of units, be suitable for large installations. Adiscussion of the relative value of designs can be carried on almostindefinitely but enough has been said to indicate that a given designwill not serve satisfactorily under all conditions and that theadaptability to the service required will be dependent upon the fuelavailable, the class of labor procurable, the feed water that must beused, the nature of the plant's load, the size of the plant and thefirst cost warranted by the service the boiler is to fulfill. TABLE 60 ACTUAL EVAPORATION FOR DIFFERENT PRESSURES AND TEMPERATURES OF FEED WATER CORRESPONDING TO ONE HORSE POWER (34½ POUNDS PER HOUR FROM AND AT 212 DEGREES FAHRENHEIT) -----------------------------------------------------------------------------------------------------------------------------------------Temperature| | of | Pressure by Gauge--Pounds per Square Inch | Feed | | Degrees | |Fahrenheit | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 210 | 220 | 230 | 240 | 250 |-----------+-----------------------------------------------------------------------------------------------------------------------------| 32 |28. 41|28. 36|28. 29|28. 24|28. 20|28. 16|28. 13|28. 09|28. 07|28. 04|28. 02|27. 99|27. 97|27. 95|27. 94|27. 92|27. 90|27. 89|27. 87|27. 86|27. 83| 40 |28. 61|28. 54|28. 49|28. 44|28. 40|28. 35|28. 32|28. 29|28. 26|28. 23|28. 21|28. 18|28. 16|28. 14|28. 12|28. 11|28. 09|28. 07|28. 06|28. 05|28. 03| 50 |28. 85|28. 79|28. 73|28. 68|28. 64|28. 60|28. 56|28. 53|28. 50|28. 47|28. 45|28. 43|28. 40|28. 38|28. 36|28. 35|28. 33|28. 31|28. 30|28. 28|28. 27| 60 |29. 10|29. 04|28. 98|28. 93|28. 88|28. 84|28. 81|28. 77|28. 74|28. 72|28. 69|28. 67|28. 65|28. 62|28. 60|28. 59|28. 57|28. 55|28. 54|28. 52|28. 51| 70 |29. 36|29. 29|29. 23|29. 18|29. 14|29. 09|29. 06|29. 02|28. 99|28. 96|28. 94|28. 92|28. 89|28. 87|28. 85|28. 83|28. 82|28. 80|28. 78|28. 77|28. 76| 80 |29. 62|29. 55|29. 49|29. 44|29. 39|29. 35|29. 31|29. 27|29. 24|29. 22|29. 19|29. 17|29. 14|29. 12|29. 10|29. 08|29. 07|29. 05|29. 03|29. 02|29. 00| 90 |29. 88|29. 81|29. 75|29. 70|29. 65|29. 61|29. 57|29. 53|29. 50|29. 47|29. 45|29. 42|29. 40|29. 38|29. 36|29. 34|29. 32|29. 30|29. 29|29. 27|29. 25|100 |30. 15|30. 08|30. 02|29. 96|29. 91|29. 87|29. 83|29. 80|29. 76|29. 73|29. 71|29. 68|29. 66|29. 63|29. 61|29. 60|29. 58|29. 56|29. 54|29. 53|29. 51|110 |30. 42|30. 35|30. 29|30. 23|30. 18|30. 14|30. 10|30. 06|30. 03|30. 00|29. 97|29. 95|29. 92|29. 90|29. 88|29. 86|29. 84|29. 82|29. 81|29. 79|29. 77|120 |30. 70|30. 63|30. 56|30. 51|30. 46|30. 41|30. 37|30. 33|30. 30|30. 27|30. 24|30. 22|30. 19|30. 17|30. 15|30. 13|30. 11|30. 09|30. 07|30. 06|30. 04|130 |30. 99|30. 91|30. 84|30. 79|30. 73|30. 69|30. 65|30. 61|30. 57|30. 54|30. 52|30. 49|30. 47|30. 44|30. 42|30. 40|30. 38|30. 36|30. 35|30. 33|30. 31|140 |31. 28|31. 20|31. 13|31. 07|31. 02|30. 97|30. 93|30. 89|30. 86|30. 83|30. 80|30. 77|30. 75|30. 72|30. 70|30. 68|30. 66|30. 64|30. 62|30. 61|30. 59|150 |31. 58|31. 49|31. 42|31. 36|31. 31|31. 26|31. 22|31. 18|31. 14|31. 11|31. 08|31. 06|31. 03|31. 01|30. 98|30. 96|30. 94|30. 92|30. 91|30. 89|30. 87|160 |31. 87|31. 79|31. 72|31. 66|31. 61|31. 56|31. 51|31. 47|31. 44|31. 40|31. 37|31. 35|31. 32|31. 29|31. 27|31. 25|31. 23|31. 21|31. 19|31. 18|31. 16|170 |32. 18|32. 10|32. 02|31. 96|31. 91|31. 86|31. 81|31. 77|31. 73|31. 70|31. 67|31. 64|31. 62|31. 59|31. 57|31. 54|31. 52|31. 50|31. 49|31. 47|31. 46|180 |32. 49|32. 41|32. 33|32. 27|32. 22|32. 16|32. 12|32. 08|32. 04|32. 00|31. 97|31. 95|31. 92|31. 89|31. 87|31. 84|31. 82|31. 80|31. 79|31. 77|31. 75|190 |32. 81|32. 72|32. 65|32. 59|32. 53|32. 47|32. 43|32. 38|32. 35|32. 32|32. 29|32. 26|32. 23|32. 20|32. 17|32. 15|32. 13|32. 11|32. 09|32. 07|32. 05|200 |33. 13|33. 05|32. 97|32. 91|32. 85|32. 79|32. 75|32. 70|32. 66|32. 63|32. 60|32. 57|32. 54|32. 51|32. 49|32. 46|32. 44|32. 42|32. 40|32. 38|32. 36|210 |33. 47|33. 38|33. 30|33. 24|33. 18|33. 13|33. 08|33. 03|32. 99|32. 95|32. 92|32. 89|32. 86|32. 83|32. 81|32. 79|32. 76|32. 74|32. 72|32. 70|32. 68|----------------------------------------------------------------------------------------------------------------------------------------- The proper consideration can be given to the adaptability of any boilerfor the service in view only after a thorough understanding of therequirements of a good steam boiler, with the application of what hasbeen said on the proper operation to the special requirements of eachcase. Of almost equal importance to the factors mentioned are theexperience, the skill and responsibility of the manufacturer. With the design of boiler selected that is best adapted to the servicerequired, the next step is the determination of the boiler powerrequirements. The amount of steam that must be generated is determined from the steamconsumption of the prime movers. It has already been indicated that suchconsumption can vary over wide limits with the size and type of theapparatus used, but fortunately all types have been so tested thatmanufacturers are enabled to state within very close limits the actualconsumption under any given set of conditions. It is obvious thatconditions of operation will have a bearing on the steam consumptionthat is as important as the type and size of the apparatus itself. Thisbeing the case, any tabular information that can be given on such steamconsumption, unless it be extended to an impracticable size, is only ofuse for the most approximate work and more definite figures on thisconsumption should in all cases be obtained from the manufacturer of theapparatus to be used for the conditions under which it will operate. To the steam consumption of the main prime movers, there is to be addedthat of the auxiliaries. Again it is impossible to make a definitestatement of what this allowance should be, the figure depending whollyupon the type and the number of such auxiliaries. For approximate work, it is perhaps best to allow 15 or 20 per cent of the steam requirementsof the main engines, for that of auxiliaries. Whatever figure is usedshould be taken high enough to be on the conservative side. When any such figures are based on the actual weight of steam required, Table 60, which gives the actual evaporation for various pressures andtemperatures of feed corresponding to one boiler horse power (34. 5pounds of water per hour from and at 212 degrees), may be of service. With the steam requirements known, the next step is the determination ofthe number and size of boiler units to be installed. This is directlyaffected by the capacity at which a consideration of the economical loadindicates is the best for the operating conditions which will exist. Theother factors entering into such determination are the size of the plantand the character of the feed water. The size of the plant has its bearing on the question from the fact thathigher efficiencies are in general obtained from large units, that laborcost decreases with the number of units, the first cost of brickwork islower for large than for small size units, a general decrease in thecomplication of piping, etc. , and in general the cost per horse power ofany design of boiler decreases with the size of units. To illustratethis, it is only necessary to consider a plant of, say, 10, 000 boilerhorse power, consisting of 40-250 horse-power units or 17-600horse-power units. The feed water available has its bearing on the subject from the otherside, for it has already been shown that very large units are notadvisable where the feed water is not of the best. The character of an installment is also a factor. Where, say, 1000 horsepower is installed in a plant where it is known what the ultimatecapacity is to be, the size of units should be selected with the idea ofthis ultimate capacity in mind rather than the amount of the firstinstallation. Boiler service, from its nature, is severe. All boilers have to becleaned from time to time and certain repairs to settings, etc. , are anecessity. This makes it necessary, in determining the number of boilersto be installed, to allow a certain number of units or spares to beoperated when any of the regular boilers must be taken off the line. With the steam requirements determined for a plant of moderate size anda reasonably constant load, it is highly advisable to install at leasttwo spare boilers where a continuity of service is essential. Thispermits the taking off of one boiler for cleaning or repairs and stillallows a spare boiler in the event of some unforeseen occurrence, suchas the blowing out of a tube or the like. Investment in such spareapparatus is nothing more nor less than insurance on the necessarycontinuity of service. In small plants of, say, 500 or 600 horse power, two spares are not usually warranted in view of the cost of suchinsurance. A large plant is ordinarily laid out in a number of sectionsor panels and each section should have its spare boiler or boilers eventhough the sections are cross connected. In central station work, wherethe peaks are carried on the boilers brought up from the bank, suchspares are, of course, in addition to these banked boilers. From theaspect of cleaning boilers alone, the number of spare boilers isdetermined by the nature of any scale that may be formed. If scale isformed so rapidly that the boilers cannot be kept clean enough for goodoperating results, by cleaning in rotation, one at a time, the number ofspares to take care of such proper cleaning will naturally increase. In view of the above, it is evident that only a suggestion can be madeas to the number and size of units, as no recommendation will hold forall cases. In general, it will be found best to install units of thelargest possible size compatible with the size of the plant andoperating conditions, with the total power requirements divided amongsuch a number of units as will give proper flexibility of load, withsuch additional units for spares as conditions of cleaning and insuranceagainst interruption of service warrant. In closing the subject of the selection of boilers, it may not be out ofplace to refer to the effect of the builder's guarantee upon thedetermination of design to be used. Here in one of its most importantaspects appears the responsibility of the manufacturer. Emphasis hasbeen laid on the difference between test results and those secured inordinary operating practice. That such a difference exists is well knownand it is now pretty generally realized that it is the responsiblemanufacturer who, where guarantees are necessary, submits theconservative figures, figures which may readily be exceeded under testconditions and which may be closely approached under the ordinary plantconditions that will be met in daily operation. OPERATION AND CARE OF BOILERS The general subject of boiler room practice may be considered from twoaspects. The first is that of the broad plant economy, with a suggestionas to the methods to be followed in securing the best economical resultswith the apparatus at hand and procurable. The second deals rather withspecific recommendations which should be followed in plant practice, recommendations leading not only to economy but also to safety andcontinuity of service. Such recommendations are dictated from anunderstanding of the nature of steam generating apparatus and itsoperation, as covered previously in this book. It has already been pointed out that the attention given in recent yearsto steam generating practice has come with a realization of the widedifference existing between the results being obtained in every-dayoperation and those theoretically possible. The amount of such attentionand regulation given to the steam generating end of a power plant, however, is comparatively small in relation to that given to the balanceof the plant, but it may be safely stated that it is here that there isthe greatest assurance of a return for the attention given. In the endeavor to increase boiler room efficiency, it is of the utmostimportance that a standard basis be set by which average results are tobe judged. With the theoretical efficiency obtainable varying so widely, this standard cannot be placed at the highest efficiency that has beenobtained regardless of operating conditions. It is better set at thebest obtainable results for each individual plant under its conditionsof installation and daily operation. With an individual standard so set, present practice can only beimproved by a systematic effort to approach this standard. The degreewith which operating results will approximate such a standard will befound to be directly proportional to the amount of intelligentsupervision given the operation. For such supervision to be given, it isnecessary to have not only a full realization of what the plant can dounder the best operating conditions but also a full and completeknowledge of what it is doing under all of the different conditions thatmay arise. What the plant is doing should be made a matter of continuousrecord so arranged that the results may be directly compared for anyperiod or set of conditions, and where such results vary from thestandard set, steps must be taken immediately to remedy the causes ofsuch failings. Such a record is an important check in the losses in theplant. As the size of the plant and the fuel consumption increase, such a checkof losses and recording of results becomes a necessity. In the largerplants, the saving of but a fraction of one per cent in the fuel billrepresents an amount running into thousands of dollars annually, whilethe expense of the proper supervision to secure such saving is small. The methods of supervision followed in the large plants are necessarilyelaborate and complete. In the smaller plants the same methods may befollowed on a more moderate scale with a corresponding saving in fueland an inappreciable increase in either plant organization or expense. There has been within the last few years a great increase in thepracticability and reliability of the various types of apparatus bywhich the records of plant operation may be secured. Much of thisapparatus is ingenious and, considering the work to be done, isremarkably accurate. From the delicate nature of some of the apparatus, the liability to error necessitates frequent calibration but even wherethe accuracy is known to be only within limits of, say, 5 per centeither way, the records obtained are of the greatest service inconsidering relative results. Some of the records desirable and theapparatus for securing them are given below. [Illustration: 2400 Horse-power Installation of Cross Drum Babcock &Wilcox Boilers and Superheaters at the Westinghouse Electric andManufacturing Co. , East Pittsburgh, Pa. ] Inasmuch as the ultimate measure of the efficiency of the boiler plantis the cost of steam generation, the important records are those ofsteam generated and fuel consumed Records of temperature, analyses, draft and the like, serve as a check on this consumption, indicating thedistribution of the losses and affording a means of remedying conditionswhere improvement is possible. Coal Records--There are many devices on the market for convenientlyweighing the coal used. These are ordinarily accurate within closelimits, and where the size or nature of the plant warrants theinvestment in such a device, its use is to be recommended. The coalconsumption should be recorded by some other method than from theweights of coal purchased. The total weight gives no way of dividing theconsumption into periods and it will unquestionably be found to beprofitable to put into operation some scheme by which the coal isweighed as it is used. In this way, the coal consumption, during anyspecific period of the plant's operation, can be readily seen. Thesimplest of such methods which may be used in small plants is the actualweighing on scales of the fuel as it is brought into the fire room andthe recording of such weights. Aside from the actual weight of the fuel used, it is often advisable tokeep other coal records, coal and ash analyses and the like, for theevaporation to be expected will be dependent upon the grade of fuel usedand its calorific value, fusibility of its ash, and like factors. The highest calorific value for unit cost is not necessarily theindication of the best commercial results. The cost of fuel is governedby this calorific value only when such value is modified by localconditions of capacity, labor and commercial efficiency. One of theimportant factors entering into fuel cost is the consideration of thecost of ash handling and the maintenance of ash handling apparatus ifsuch be installed. The value of a fuel, regardless of its calorificvalue, is to be based only on the results obtained in every-day plantoperation. Coal and ash analyses used in connection with the amount of fuelconsumed, are a direct indication of the relation between the resultsbeing secured and the standard of results which has been set for theplant. The methods of such analyses have already been described. Theapparatus is simple and the degree of scientific knowledge necessary isonly such as may be readily mastered by plant operatives. The ash content of a fuel, as indicated from a coal analysis checkedagainst ash weights as actually found in plant operation, acts as acheck on grate efficiency. The effect of any saving in the ashes, thatis, the permissible ash to be allowed in the fuel purchased, isdetermined by the point at which the cost of handling, combined with thefalling off in the evaporation, exceeds the saving of fuel cost throughthe use of poorer coal. Water Records--Water records with the coal consumption, form the basisfor judging the economic production of steam. The methods of securingsuch records are of later introduction than for coal, but great advanceshave been made in the apparatus to be used. Here possibly, to a greaterextent than in any recording device, are the records of value indetermining relative evaporation, that is, an error is rather allowableprovided such an error be reasonably constant. The apparatus for recording such evaporation is of two general classes:Those measuring water before it is fed to the boiler and those measuringthe steam as it leaves. Of the first, the venturi meter is perhaps thebest known, though recently there has come into considerable vogue anapparatus utilizing a weir notch for the measuring of such water. Bothmethods are reasonably accurate and apparatus of this description has anadvantage over one measuring steam in that it may be calibrated muchmore readily. Of the steam measuring devices, the one in most common useis the steam flow meter. Provided the instruments are selected for aproper flow, etc. , they are of inestimable value in indicating the steamconsumption. Where such instruments are placed on the various engineroom lines, they will immediately indicate an excessive consumption forany one of the units. With a steam flow meter placed on each boiler, itis possible to fix relatively the amount produced by each boiler and, considered in connection with some of the "check" records describedbelow, clearly indicate whether its portion of the total steam producedis up to the standard set for the over-all boiler room efficiency. Flue Gas Analysis--The value of a flue gas analysis as a measure offurnace efficiency has already been indicated. There are on the market anumber of instruments by which a continuous record of the carbon dioxidein the flue gases may be secured and in general the results so recordedare accurate. The limitations of an analysis showing only CO_{2} and thenecessity of completing such an analysis with an Orsat, or likeapparatus, and in this way checking the automatic device, have alreadybeen pointed out, but where such records are properly checked from timeto time and are used in conjunction with a record of flue temperatures, the losses due to excess air or incomplete combustion and the like maybe directly compared for any period. Such records act as a means forcontrolling excess air and also as a check on individual firemen. Where the size of a plant will not warrant the purchase of an expensivecontinuous CO_{2} recorder, it is advisable to make analyses of samplesfor various conditions of firing and to install an apparatus whereby asample of flue gas covering a period of, say, eight hours, may beobtained and such a sample afterwards analyzed. Temperature Records--Flue gas temperatures, feed water temperatures andsteam temperatures are all taken with recording thermometers, any numberof which will, when properly calibrated, give accurate results. A record of flue temperatures is serviceable in checking stack lossesand, in general, the cleanliness of the boiler. A record of steamtemperatures, where superheaters are used, will indicate excessivefluctuations and lead to an investigation of their cause. Feedtemperatures are valuable in showing that the full benefit of theexhaust steam is being derived. Draft Regulation--As the capacity of a boiler varies with the combustionrate and this rate with the draft, an automatic apparatus satisfactorilyvarying this draft with the capacity demands on the boiler willobviously be advantageous. As has been pointed out, any fuel has some rate of combustion at whichthe best results will be obtained. In a properly designed plant wherethe load is reasonably steady, the draft necessary to secure such a ratemay be regulated automatically. Automatic apparatus for the regulation of draft has recently reached astage of perfection which in the larger plants at any rate makes itsinstallation advisable. The installation of a draft gauge or gauges isstrongly to be recommended and a record of such drafts should be kept asbeing a check on the combustion rates. An important feature to be considered in the installing of all recordingapparatus is its location. Thermometers, draft gauges and flue gassampling pipes should be so located as to give as nearly as possible anaverage of the conditions, the gases flowing freely over the ends of thethermometers, couples and sampling pipes. With the location permanent, there is no security that the samples may be considered an average butin any event comparative results will be secured which will be useful inplant operation. The best permanent location of apparatus will varyconsiderably with the design of the boiler. It may not be out of place to refer briefly to some of the shortcomingsfound in boiler room practice, with a suggestion as to a means ofovercoming them. 1st. It is sometimes found that the operating force is not fullyacquainted with the boilers and apparatus. Probably the most general ofsuch shortcomings is the fixed idea in the heads of the operatives thatboilers run above their rated capacity are operating under a state ofstrain and that by operating at less than their rated capacity the mosteconomical service is assured, whereas, by determining what a boilerwill do, it may be found that the most economical rating under theconditions of the plant will be considerably in excess of the builder'srating. Such ideas can be dislodged only by demonstrating to theoperatives what maximum load the boilers can carry, showing how theeconomy will vary with the load and the determining of the economicalload for the individual plant in question. 2nd. Stokers. With stoker-fired boilers, it is essential that theoperators know the limitations of their stokers as determined by theirindividual installation. A thorough understanding of the requirements ofefficient handling must be insisted upon. The operatives must realizethat smokeless stacks are not necessarily the indication of goodcombustion for, as has been pointed out, absolute smokelessness isoftentimes secured at an enormous loss in efficiency through excess air. Another feature in stoker-fired plants is in the cleaning of fires. Itmust be impressed upon the operatives that before the fires are cleanedthey should be put into condition for such cleaning. If this cleaning isdone at a definite time, regardless of whether the fires are in the bestcondition for cleaning, there will be a great loss of good fuel with theashes. 3rd. It is necessary that in each individual plant there be a basis onwhich to judge the cleanliness of a boiler. From the operative'sstandpoint, it is probably more necessary that there be a thoroughunderstanding of the relation between scale and tube difficulties thanbetween scale and efficiency. It is, of course, impossible to keepboilers absolutely free from scale at all times, but experience in eachindividual plant determines the limit to which scale can be allowed toform before tube difficulties will begin or a perceptible falling off inefficiency will take place. With such a limit of scale formation fixed, the operatives should be impressed with the danger of allowing it to beexceeded. 4th. The operatives should be instructed as to the losses resulting fromexcess air due to leaks in the setting and as to losses in efficiencyand capacity due to the by-passing of gases through the setting, thatis, not following the path of the baffles as originally installed. Inreplacing tubes and in cleaning the heating surfaces, care must be takennot to dislodge baffle brick or tile. [Illustration: 2000 Horse-power Installation of Babcock & WilcoxBoilers, Equipped with Babcock & Wilcox Chain Grate Stokers at theSunnyside Plant of the Pennsylvania Tunnel and Terminal Railroad Co. , Long Island City, N. Y. ] 5th. That an increase in the temperature of the feed reduces the amountof work demanded from the boiler has been shown. The necessity ofkeeping the feed temperature as high as the quantity of exhaust steamwill allow should be thoroughly understood. As an example of this, therewas a case brought to our attention where a large amount of exhauststeam was wasted simply because the feed pump showed a tendency to leakif the temperature of feed water was increased above 140 degrees. Theamount wasted was sufficient to increase the temperature to 180 degreesbut was not utilized simply because of the slight expense necessary tooverhaul the feed pump. The highest return will be obtained when the speed of the feed pumps ismaintained reasonably constant for should the pumps run very slowly attimes, there may be a loss of the steam from other auxiliaries byblowing off from the heaters. 6th. With a view to checking steam losses through the useless blowing ofsafety valves, the operative should be made to realize the great amountof steam that it is possible to get through a pipe of a given size. Oftentimes the fireman feels a sense of security from objections to adrop in steam simply because of the blowing of safety valves, notconsidering the losses due to such a cause and makes no effort to checkthis flow either by manipulation of dampers or regulation of fires. The few of the numerous shortcomings outlined above, which may be foundin many plants, are almost entirely due to lack of knowledge on the partof the operating crew as to the conditions existing in their own plantsand the better performances being secured in others. Such shortcomingscan be overcome only by the education of the operatives, the showing ofthe defects of present methods, and instruction in better methods. Wheresuch instruction is necessary, the value of records is obvious. There isfortunately a tendency toward the employment of a better class of laborin the boiler room, a tendency which is becoming more and more marked asthe realization of the possible saving in this end of the plantincreases. The second aspect of boiler room management, dealing with specificrecommendations as to the care and operation of the boilers, is dictatedlargely by the nature of the apparatus. Some of the features to bewatched in considering this aspect follow. Before placing a new boiler in service, a careful and thoroughexamination should be made of the pressure parts and the setting. Theboiler as erected should correspond in its baffle openings, wherebaffles are adjustable, with the prints furnished for its erection, andsuch baffles should be tight. The setting should be so constructed thatthe boiler is free to expand without interfering with the brickwork. This ability to expand applies also to blow-off and other piping. Aftererection all mortar and chips of brick should be cleaned from thepressure parts. The tie rods should be set up snug and then slackedslightly until the setting has become thoroughly warm after the firstfiring. The boiler should be examined internally before starting toinsure the absence of dirt, any foreign material such as waste, andtools. Oil and paint are sometimes found in the interior of a new boilerand where such is the case, a quantity of soda ash should be placedwithin it, the boiler filled with water to its normal level and a slowfire started. After twelve hours of slow simmering, the fire should beallowed to die out, the boiler cooled slowly and then opened and washedout thoroughly. Such a proceeding will remove all oil and grease fromthe interior and prevent the possibility of foaming and tubedifficulties when the boiler is placed in service. The water column piping should be examined and known to be free andclear. The water level, as indicated by the gauge glass, should bechecked by opening the gauge cocks. The method of drying out a brick setting before placing a boiler inoperation is described later in the discussion of boiler settings. A boiler should not be cut into the line with other boilers until thepressure within it is approximately that in the steam main. The boilerstop valve should be opened very slowly until it is fully opened. Thearrangement of piping should be such that there can be no possibility ofwater collecting in a pocket between the boiler and the main, from whichit can be carried over into the steam line when a boiler is cut in. In regular operation the safety valve and steam gauge should be checkeddaily. In small plants the steam pressure should be raised sufficientlyto cause the safety valves to blow, at which time the steam gauge shouldindicate the pressure at which the valve is known to be set. If it doesnot, one is in error and the gauge should be compared with one of knownaccuracy and any error at once rectified. In large plants such a method of checking would result in losses toogreat to be allowed. Here the gauges and valves are ordinarily checkedat the time a boiler is cut out, the valves being assured of notsticking by daily instantaneous opening through manipulation by hand ofthe valve lever. The daily blowing of the safety valve acts not only asa check on the gauge but insures the valve against sticking. The water column should be blown down thoroughly at least once on everyshift and the height of water indicated by the glass checked by thegauge cocks. The bottom blow-offs should be kept tight. These should beopened at least once daily to blow from the mud drum any sediment thatmay have collected and to reduce the concentration. The amount ofblowing down and the frequency is, of course, determined by the natureof the feed water used. In case of low water, resulting either from carelessness or from someunforeseen condition of operation, the essential object to be obtainedis the extinguishing of the fire in the quickest possible manner. Wherepracticable, this is best accomplished by the playing of a heavy streamof water from a hose on the fire. Another method, perhaps not soefficient, but more generally recommended, is the covering of the firewith wet ashes or fresh fuel. A boiler so treated should be cut out ofline after such an occurrence and a thorough inspection made toascertain what damage, if any, has been done before it is again placedin service. The efficiency and capacity depend to an extent very much greater thanis ordinarily realized upon the cleanliness of the heating surfaces, both externally and internally, and too much stress cannot be put uponthe necessity for systematic cleaning as a regular feature in the plantoperation. The outer surfaces of the tubes should be blown free from soot atregular intervals, the frequency of such cleaning periods beingdependent upon the class of fuel used. The most efficient way of blowingsoot from the tubes is by means of a steam lance with which all parts ofthe surfaces are reached and swept clean. There are numerous sootblowing devices on the market which are designed to be permanently fixedwithin the boiler setting. Where such devices are installed, there arecertain features that must be watched to avoid trouble. If there is anyleakage of water of condensation within the setting coming into contactwith the boiler tubes, it will tend toward corrosion, or if in contactwith the heated brickwork will cause rapid disintegration of thesetting. If the steam jets are so placed that they impinge directlyagainst the tubes, erosion may take place. Where such permanent sootblowers are installed, too much care cannot be taken to guard againstthese possibilities. Internally, the tubes must be kept free from scale, the ingredients ofwhich a study of the chapter on the impurities of water indicates arepresent in varying quantities in all feed waters. Not only has thepresence of scale a direct bearing on the efficiency and capacity to beobtained from a boiler but its absence is an assurance against theburning out of tubes. In the absence of a blow-pipe action of the flames, it is impossible toburn a metal surface where water is in intimate contact with thatsurface. In stoker-fired plants where a blast is used, and the furnace is notproperly designed, there is a danger of a blow-pipe action if the firesare allowed to get too thin. The rapid formation of steam at such pointsof localized heat may lead to the burning of the metal of the tubes. Any formation of scale on the interior surface of a boiler keeps thewater from such a surface and increases its tendency to burn. Particlesof loose scale that may become detached will lodge at certain points inthe tubes and localize this tendency at such points. It is because ofthe danger of detaching scale and causing loose flakes to be presentthat the use of a boiler compound is not recommended for the removal ofscale that has already formed in a boiler. This question is covered inthe treatment of feed waters. If oil is allowed to enter a boiler, itsaction is the same as that of scale in keeping the water away from themetal surfaces. [Illustration: Fig. 41] It has been proven beyond a doubt that a very large percentage of tubelosses is due directly to the presence of scale which, in manyinstances, has been so thin as to be considered of no moment, and theimportance of maintaining the boiler heating surfaces in a cleancondition cannot be emphasized too strongly. The internal cleaning can best be accomplished by means of an air orwater-driven turbine, the cutter heads of which may be changed to handlevarious thicknesses of scale. Fig. 41 shows a turbine cleaner withvarious cutting heads, which has been found to give satisfactoryservice. Where a water-driven turbine is used, it should be connected to a pumpwhich will deliver at least 120 gallons per minute per cleaner at 150pounds pressure. This pressure should never be less than 90 pounds ifsatisfactory results are desired. Where an air-driven turbine is used, the pressure should be at least 100 pounds, though 150 pounds ispreferable, and sufficient water should be introduced into the tube tokeep the cutting head cool and assist in washing down the scale as it ischipped off. Where scale has been allowed to accumulate to an excessive thickness, the work of removal is difficult and tedious. Where such a heavy scaleis of sulphate formation, its removal may be assisted by filling theboiler with water to which there has been added a quantity of soda ash, a bucketful to each drum, starting a low fire and allowing the water toboil for twenty-four hours with no pressure on the boiler. It should becooled slowly, drained, and the turbine cleaner used immediately, as thescale will tend to harden rapidly under the action of the air. Where oil has been allowed to get into a boiler, it should be removedbefore placing the boiler in service, as described previously wherereference is made to its removal by boiling out with soda ash. Where pitting or corrosion is noted, the parts affected should becarefully cleaned and the interior of the drums should be painted withwhite zinc if the boiler is to remain idle. The cause of such actionshould be immediately ascertained and steps taken to apply the properremedy. When making an internal inspection of a boiler or when cleaning theinterior heating surfaces, great care must be taken to guard against thepossibility of steam entering the boiler in question from other boilerson the same line either through the careless opening of the boiler stopvalve or some auxiliary valve or from an open blow-off. Bad accidentsthrough scalding have resulted from the neglect of this precaution. Boiler brickwork should be kept pointed up and all cracks filled. Theboiler baffles should be kept tight to prevent by-passing of any gasesthrough the heating surfaces. Boilers should be taken out of service at regular intervals for cleaningand repairs. When this is done, the boiler should be cooled slowly, andwhen possible, be allowed to stand for twenty-four hours after the fireis drawn before opening. The cooling process should not be hurried byallowing cold air to rush through the setting as this will invariablycause trouble with the brickwork. When a boiler is off for cleaning, acareful examination should be made of its condition, both external andinternal, and all leaks of steam, water and air through the settingstopped. If water is allowed to come into contact with brickwork that isheated, rapid disintegration will take place. If water is allowed tocome into contact with the metal of the boiler when out of service, there is a likelihood of corrosion. If a boiler is to remain idle for some time, its deterioration may bemuch more rapid than when in service. If the period for which it is tobe laid off is not to exceed three months, it may be filled with waterwhile out of service. The boiler should first be cleaned thoroughly, internally and externally, all soot and ashes being removed from theexterior of the pressure parts and any accumulation of scale removedfrom the interior surfaces. It should then be filled with water, towhich five or six pails of soda ash have been added, a slow fire startedto drive the air from the boiler, the fire drawn and the boiler pumpedfull. In this condition it may be kept for some time without badeffects. If the boiler is to be out of service for more than three months, itshould be emptied, drained and thoroughly dried after being cleaned. Atray of quick lime should be placed in each drum, the boiler closed, thegrates covered and a quantity of quick lime placed on top of thecovering. Special care should be taken to prevent air, steam or waterleaks into the boiler or onto the pressure parts to obviate danger ofcorrosion. [Illustration: 3000 Horse-power Installation of Babcock & Wilcox Boilersin the Main Power Plant, Chicago & Northwestern Ry. Depot, Chicago, Ill. ] BRICKWORK BOILER SETTINGS A consideration of the losses in boiler efficiency, due to the effectsof excess air, clearly indicates the necessity of maintaining the bricksetting of a boiler tight and free from air leaks. In view of thetemperatures to which certain portions of such a setting are subjected, the material to be used in its construction must be of the bestprocurable. Boiler settings to-day consist almost universally of brickwork--twokinds being used, namely, red brick and fire brick. The red brick should only be used in such portions of the setting as arewell protected from the heat. In such location, their service is not sosevere as that of fire brick and ordinarily, if such red brick aresound, hard, well burned and uniform, they will serve their purpose. The fire brick should be selected with the greatest care, as it is thisportion of the setting that has to endure the high temperatures nowdeveloped in boiler practice. To a great extent, the life of a boilersetting is dependent upon the quality of the fire brick used and thecare exercised in its laying. The best fire brick are manufactured from the fire clays ofPennsylvania. South and west from this locality the quality of fire claybecomes poorer as the distance increases, some of the southern fireclays containing a considerable percentage of iron oxide. Until very recently, the important characteristic on which to base ajudgment of the suitability of fire brick for use in connection withboiler settings has been considered the melting point, or thetemperature at which the brick will liquify and run. Experience hasshown, however, that this point is only important within certain limitsand that the real basis on which to judge material of this descriptionis, from the boiler man's standpoint, the quality of plasticity under agiven load. This tendency of a brick to become plastic occurs at atemperature much below the melting point and to a degree that may causethe brick to become deformed under the stress to which it is subjected. The allowable plastic or softening temperature will naturally berelative and dependent upon the stress to be endured. With the plasticity the determining factor, the perfect fire brick isone whose critical point of plasticity lies well above the workingtemperature of the fire. It is probable that there are but few brick onthe market which would not show, if tested, this critical temperature atthe stress met with in arch construction at a point less than 2400degrees. The fact that an arch will stand for a long period underfurnace temperatures considerably above this point is due entirely tothe fact that its temperature as a whole is far below the furnacetemperature and only about 10 per cent of its cross section nearest thefire approaches the furnace temperature. This is borne out by the factthat arches which are heated on both sides to the full temperature of anordinary furnace will first bow down in the middle and eventually fall. A method of testing brick for this characteristic is given in theTechnologic Paper No. 7 of the Bureau of Standards dealing with "Thetesting of clay refractories with special reference to their loadcarrying capacity at furnace temperatures. " Referring to the test forthis specific characteristic, this publication recommends the following:"When subjected to the load test in a manner substantially as describedin this bulletin, at 1350 degrees centigrade (2462 degrees Fahrenheit), and under a load of 50 pounds per square inch, a standard fire bricktested on end should show no serious deformation and should not becompressed more than one inch, referred to the standard length of nineinches. " In the Bureau of Standards test for softening temperature, or criticaltemperature of plasticity under the specified load, the brick are testedon end. In testing fire brick for boiler purposes such a method might becriticised, because such a test is a compression test and subject toerrors from unequal bearing surfaces causing shear. Furthermore, aseries of samples, presumably duplicates, will not fail in the same way, due to the mechanical variation in the manufacture of the brick. Archesthat fail through plasticity show that the tensile strength of the brickis important, this being evidenced by the fact that the bottom of awedge brick in an arch that has failed is usually found to be wider thanthe top and the adjacent bricks are firmly cemented together. A better method of testing is that of testing the brick as a beamsubjected to its own weight and not on end. This method has been usedfor years in Germany and is recommended by the highest authorities inceramics. It takes into account the failure by tension in the brick aswell as by compression and thus covers the tension element which isimportant in arch construction. The plastic point under a unit stress of 100 pounds per square inch, which may be taken as the average maximum arch stress, should be above2800 degrees to give perfect results and should be above 2400 degrees toenable the brick to be used with any degree of satisfaction. The other characteristics by which the quality of a fire brick is to bejudged are: Fusion point. In view of the fact that the critical temperature ofplasticity is below the fusion point, this is only important as anindication from high fusion point of a high temperature of plasticity. Hardness. This is a relative quality based on an arbitrary scale of 10and is an indication of probable cracking and spalling. Expansion. The lineal expansion per brick in inches. This characteristicin conjunction with hardness is a measure of the physical movement ofthe brick as affecting a mass of brickwork, such movement resulting incracked walls, etc. The expansion will vary between wide limits indifferent brick and provided such expansion is not in excess of, say, . 05 inch in a 9-inch brick, when measured at 2600 degrees, it is notparticularly important in a properly designed furnace, though in generalthe smaller the expansion the better. Compression. The strength necessary to cause crushing of the brick atthe center of the 4½ inch face by a steel block one inch square. Thecompression should ordinarily be low, a suggested standard being that abrick show signs of crushing at 7500 pounds. Size of Nodules. The average size of flint grains when the brick iscarefully crushed. The scale of these sizes may be considered: Small, size of anthracite rice; large, size of anthracite pea. Ratio of Nodules. The percentage of a given volume occupied by the flintgrains. This scale may be considered: High, 90 to 100 per cent; medium, 50 to 90 per cent; low, 10 to 50 per cent. The statement of characteristics suggested as desirable, are for archpurposes where the hardest service is met. For side wall purposes thecompression and hardness limit may be raised considerably and theplastic point lowered. Aside from the physical properties by which a fire brick is judged, itis sometimes customary to require a chemical analysis of the brick. Suchan analysis is only necessary as determining the amount of total basicfluxes (K_{2}O, Na_{2}O, CaO, MgO and FeO). These fluxes are ordinarilycombined into one expression, indicated by the symbol RO. This totalbecomes important only above 0. 2 molecular equivalent as expressed inceramic empirical formulae, and this limit should not be exceeded. [75] From the nature of fire brick, their value can only be considered from arelative standpoint. Generally speaking, what are known as first-gradefire brick may be divided into three classes, suitable for variousconditions of operation, as follows: Class A. For stoker-fired furnaces where high overloads are to beexpected or where other extreme conditions of service are apt to occur. Class B. For ordinary stoker settings where there will be no excessiveoverloads required from the boiler or any hand-fired furnaces where therates of driving will be high for such practice. Class C. For ordinary hand-fired settings where the presumption is thatthe boilers will not be overloaded except at rare intervals and forshort periods only. Table 61 gives the characteristics of these three classes according tothe features determining the quality. This table indicates that thehardness of the brick in general increases with the poorer qualities. Provided the hardness is sufficient to enable the brick to withstand itsload, additional hardness is a detriment rather than an advantage. TABLE 61 APPROXIMATE CLASSIFICATION OF FIRE BRICK ________________________________________________________________________| | | | || Characteristics | Class A | Class B | Class C ||_____________________|________________|________________|________________|| | | | || Fuse Point, Degrees | Safe at Degrees| Safe at Degrees| Safe at Degrees|| Fahrenheit | 3200-3300 | 2900-3200 | 2900-3000 || | | | || Compression Pounds | 6500-7500 | 7500-11, 000 | 8500-15, 000 || | | | || Hardness Relative | 1-2 | 2-4 | 4-6 || | | | || Size of Nodules | Medium | Medium to |Medium to Large || | | Medium Large | || | | | || Ratio of Nodules | High | Medium to High | Medium Low || | | | to Medium ||_____________________|________________|________________|________________| An approximate determination of the quality of a fire brick may be madefrom the appearance of a fracture. Where such a fracture is open, clean, white and flinty, the brick in all probability is of a good quality. Ifthis fracture has the fine uniform texture of bread, the brick isprobably poor. In considering the heavy duty of brick in boiler furnaces, experienceshows that arches are the only part that ordinarily give trouble. Thesefail from the following causes: Bad workmanship in laying up of brick. This feature is treated below. The tendency of a brick to become plastic at a temperature below thefusing point. The limits of allowable plastic temperature have alreadybeen pointed out. Spalling. This action occurs on the inner ends of combustion archeswhere they are swept by gases at a high velocity at the full furnacetemperature. The most troublesome spalling arises through cold airstriking the heated brickwork. Failure from this cause is becoming rare, due to the large increase in number of stoker installations in whichrapid temperature changes are to a great degree eliminated. Furthermore, there are a number of brick on the market practically free from suchdefects and where a new brick is considered, it can be tried out and ifthe defect exists, can be readily detected and the brick discarded. Failures of arches from the expansive power of brick are also rare, dueto the fact that there are a number of brick in which the expansion iswell within the allowable limits and the ease with which such defectsmay be determined before a brick is used. Failures through chemical disintegration. Failure through this cause isfound only occasionally in brick containing a high percentage of ironoxide. With the grade of brick selected best suited to the service of theboiler to be set, the other factor affecting the life of the setting isthe laying. It is probable that more setting difficulties arise from theimproper workmanship in the laying up of brick than from poor material, and to insure a setting which will remain tight it is necessary that themasonry work be done most carefully. This is particularly true where theboiler is of such a type as to require combustion arches in the furnace. Red brick should be laid in a thoroughly mixed mortar composed of onevolume of Portland cement, 3 volumes of unslacked lime and 16 volumes ofclear sharp sand. Not less than 2½ bushels of lime should be used in thelaying up of 1000 brick. Each brick should be thoroughly embedded andall joints filled. Where red brick and fire brick are both used in thesame wall, they should be carried up at the same time and thoroughlybonded to each other. All fire brick should be dry when used and protected from moisture untilused. Each brick should be dipped in a thin fire clay wash, "rubbed andshoved" into place, and tapped with a wooden mallet until it touches thebrick next below it. It must be recognized that fire clay is not acement and that it has little or no holding power. Its action is that ofa filler rather than a binder and no fire-clay wash should be used whichhas a consistency sufficient to permit the use of a trowel. All fire-brick linings should be laid up four courses of headers and onestretcher. Furnace center walls should be entirely of fire brick. If thecenter of such walls are built of red brick, they will melt down andcause the failure of the wall as a whole. Fire-brick arches should be constructed of selected brick which aresmooth, straight and uniform. The frames on which such arches are built, called arch centers, should be constructed of batten strips not over 2inches wide. The brick should be laid on these centers in courses, notin rings, each joint being broken with a bond equal to the length ofhalf a brick. Each course should be first tried in place dry, andchecked with a straight edge to insure a uniform thickness of jointbetween courses. Each brick should be dipped on one side and two edgesonly and tapped into place with a mallet. Wedge brick courses should beused only where necessary to keep the bottom faces of the straight brickcourse in even contact with the centers. When such contact cannot beexactly secured by the use of wedge brick, the straight brick shouldlean away from the center of the arch rather than toward it. When thearch is approximately two-thirds completed, a trial ring should be laidto determine whether the key course will fit. When some cutting isnecessary to secure such a fit, it should be done on the two adjacentcourses on the side of the brick away from the key. It is necessary thatthe keying course be a true fit from top to bottom, and after it hasbeen dipped and driven it should not extend below the surface of thearch, but preferably should have its lower ledge one-quarter inch abovethis surface. After fitting, the keys should be dipped, replacedloosely, and the whole course driven uniformly into place by means of aheavy hammer and a piece of wood extending the full length of the keyingcourse. Such a driving in of this course should raise the arch as awhole from the center. The center should be so constructed that it maybe dropped free of the arch when the key course is in place and removedfrom the furnace without being burned out. [Illustration: A Typical Steel Casing for a Babcock & Wilcox BoilerBuilt by The Babcock & Wilcox Co. ] Care of Brickwork--Before a boiler is placed in service, it is essentialthat the brickwork setting be thoroughly and properly dried, orotherwise the setting will invariably crack. The best method of startingsuch a process is to block open the boiler damper and the ashpit doorsas soon as the brickwork is completed and in this way maintain a freecirculation of air through the setting. If possible, such preliminarydrying should be continued for several days before any fire is placed inthe furnace. When ready for the drying out fire, wood should be used atthe start in a light fire which may be gradually built up as the wallsbecome warm. After the walls have become thoroughly heated, coal may befired and the boiler placed in service. As already stated, the life of a boiler setting is dependent to a largeextent upon the material entering into its construction and the carewith which such material is laid. A third and equally important factorin the determining of such life is the care given to the maintaining ofthe setting in good condition after the boiler is placed in operation. This feature is discussed more fully in the chapter dealing with generalboiler room management. Steel Casings--In the chapter dealing with the losses operating againsthigh efficiencies as indicated by the heat balance, it has been shownthat a considerable portion of such losses is due to radiation and toair infiltration into the boiler setting. These losses have beenvariously estimated from 2 to 10 per cent, depending upon the conditionof the setting and the amount of radiation surface, the latter in turnbeing dependent upon the size of the boiler used. In the modern effortsafter the highest obtainable plant efficiencies much has been done toreduce such losses by the use of an insulated steel casing covering thebrickwork. In an average size boiler unit the use of such casing, whenproperly installed, will reduce radiation losses from one to two percent. , over what can be accomplished with the best brick setting withoutsuch casing and, in addition, prevent the loss due to the infiltrationof air, which may amount to an additional five per cent. , as comparedwith brick settings that are not maintained in good order. Steel plate, or steel plate backed by asbestos mill-board, while acting as apreventative against the infiltration of air through the boiler setting, is not as effective from the standpoint of decreasing radiation lossesas a casing properly insulated from the brick portion of the setting bymagnesia block and asbestos mill-board. A casing which has been found togive excellent results in eliminating air leakage and in the reductionof radiation losses is clearly illustrated on page 306. Many attempts have been made to use some material other than brick forboiler settings but up to the present nothing has been found that may beconsidered successful or which will give as satisfactory service undersevere conditions as properly laid brickwork. BOILER ROOM PIPING In the design of a steam plant, the piping system should receive themost careful consideration. Aside from the constructive details, goodpractice in which is fairly well established, the important factors arethe size of the piping to be employed and the methods utilized inavoiding difficulties from the presence in the system of water ofcondensation and the means employed toward reducing radiation losses. Engineering opinion varies considerably on the question of material ofpipes and fittings for different classes of work, and the following isoffered simply as a suggestion of what constitutes good representativepractice. All pipe should be of wrought iron or soft steel. Pipe at present ismade in "standard", "extra strong"[76] and "double extra strong"weights. Until recently, a fourth weight approximately 10 per centlighter than standard and known as "Merchants" was built but the use ofthis pipe has largely gone out of practice. Pipe sizes, unless otherwisestated, are given in terms of nominal internal diameter. Table 62 givesthe dimensions and some general data on standard and extra strongwrought-iron pipe. TABLE 62 DIMENSIONS OF STANDARD AND EXTRA STRONG[76] WROUGHT-IRON AND STEEL PIPE _______________________________________________________________| | | || | Diameter | Circumference || |__________________________|__________________________|| | | | | || |External| Internal |External| Internal || |Standard|_________________|Standard|_________________|| | and | | | and | | || Nominal | Extra |Standard| Extra | Extra |Standard| Extra || Size | Strong | | Strong | Strong | | Strong ||_________|________|________|________|________|________|________|| | | | | | | || 1/8 | . 405 | . 269 | . 215 | 1. 272 | . 848 | . 675 || 1/4 | . 540 | . 364 | . 302 | 1. 696 | 1. 144 | . 949 || 3/8 | . 675 | . 493 | . 423 | 2. 121 | 1. 552 | 1. 329 || 1/2 | . 840 | . 622 | . 546 | 2. 639 | 1. 957 | 1. 715 || 3/4 | 1. 050 | . 824 | . 742 | 3. 299 | 2. 589 | 2. 331 || 1 | 1. 315 | 1. 049 | . 957 | 4. 131 | 3. 292 | 3. 007 || 1-1/4 | 1. 660 | 1. 380 | 1. 278 | 5. 215 | 4. 335 | 4. 015 || 1-1/2 | 1. 900 | 1. 610 | 1. 500 | 5. 969 | 5. 061 | 4. 712 || 2 | 2. 375 | 2. 067 | 1. 939 | 7. 461 | 6. 494 | 6. 092 || 2-1/2 | 2. 875 | 2. 469 | 2. 323 | 9. 032 | 7. 753 | 7. 298 || 3 | 3. 500 | 3. 068 | 2. 900 | 10. 996 | 9. 636 | 9. 111 || 3-1/2 | 4. 000 | 3. 548 | 3. 364 | 12. 566 | 11. 146 | 10. 568 || 4 | 4. 500 | 4. 026 | 3. 826 | 14. 137 | 12. 648 | 12. 020 || 4-1/2 | 5. 000 | 4. 506 | 4. 290 | 15. 708 | 14. 162 | 13. 477 || 5 | 5. 563 | 5. 047 | 4. 813 | 17. 477 | 15. 849 | 15. 121 || 6 | 6. 625 | 6. 065 | 5. 761 | 20. 813 | 19. 054 | 18. 099 || 7 | 7. 625 | 7. 023 | 6. 625 | 23. 955 | 22. 063 | 20. 813 || 8 | 8. 625 | 7. 981 | 7. 625 | 27. 096 | 25. 076 | 23. 955 || 9 | 9. 625 | 8. 941 | 8. 625 | 30. 238 | 28. 089 | 27. 096 || 10 | 10. 750 | 10. 020 | 9. 750 | 33. 772 | 31. 477 | 30. 631 || 11 | 11. 750 | 11. 000 | 10. 750 | 36. 914 | 34. 558 | 33. 772 || 12 | 12. 750 | 12. 000 | 11. 750 | 40. 055 | 37. 700 | 36. 914 ||_________|________|________|________|________|________|________| __________________________________________________________| | | | || | | Length | || | Internal | of | Nominal Weight || | Transverse |Pipe in | Pounds per || | Area |Feet per| Foot || |_____________________| Square |_________________|| | | |Foot of | | || Nominal | Standard | Extra |External|Standard| Extra || Size | | Strong |Surface | | Strong ||_________|__________|__________|________|________|________|| | | | | | || 1/8 | . 0573 | . 0363 | 9. 440 | . 244 | . 314 || 1/4 | . 1041 | . 0716 | 7. 075 | . 424 | . 535 || 3/8 | . 1917 | . 1405 | 5. 657 | . 567 | . 738 || 1/2 | . 3048 | . 2341 | 4. 547 | . 850 | 1. 087 || 3/4 | . 5333 | . 4324 | 3. 637 | 1. 130 | 1. 473 || 1 | . 8626 | . 7193 | 2. 904 | 1. 678 | 2. 171 || 1-1/4 | 1. 496 | 1. 287 | 2. 301 | 2. 272 | 2. 996 || 1-1/2 | 2. 038 | 1. 767 | 2. 010 | 2. 717 | 3. 631 || 2 | 3. 356 | 2. 953 | 1. 608 | 3. 652 | 5. 022 || 2-1/2 | 4. 784 | 4. 238 | 1. 328 | 5. 793 | 7. 661 || 3 | 7. 388 | 6. 605 | 1. 091 | 7. 575 | 10. 252 || 3-1/2 | 9. 887 | 8. 888 | . 955 | 9. 109 | 12. 505 || 4 | 12. 730 | 11. 497 | . 849 | 10. 790 | 14. 983 || 4-1/2 | 15. 961 | 14. 454 | . 764 | 12. 538 | 17. 611 || 5 | 19. 990 | 18. 194 | . 687 | 14. 617 | 20. 778 || 6 | 28. 888 | 26. 067 | . 577 | 18. 974 | 28. 573 || 7 | 38. 738 | 34. 472 | . 501 | 23. 544 | 38. 048 || 8 | 50. 040 | 45. 664 | . 443 | 28. 544 | 43. 388 || 9 | 62. 776 | 58. 426 | . 397 | 33. 907 | 48. 728 || 10 | 78. 839 | 74. 662 | . 355 | 40. 483 | 54. 735 || 11 | 95. 033 | 90. 763 | . 325 | 45. 557 | 60. 075 || 12 | 113. 098 | 108. 43 | . 299 | 49. 562 | 65. 415 ||_________|__________|__________|________|________|________| Dimensions are nominal and except where noted are in inches. In connection with pipe sizes, Table 63, giving certain tube data may befound to be of service. TABLE 63 TUBE DATA, STANDARD OPEN HEARTH OR LAP WELDED STEEL TUBES +-----+--+----+-----+------+------+------+------+-------+-------+-------+|S E D|B | T | I D |Circumference| Transverse |Square |Length |Nominal||i x i|. | h | n i | | Area | Feet |in Feet|Weight ||z t a|W | i | t a | |Square Inches| of | per |Pounds ||e e m|. | c | e m +------+------+------+------+ Exter |Square | per || r e| | k | r e |Exter-|Inter-|Exter-|Inter-| -nal |Foot of| Foot || n t|G | n | n t | nal | nal | nal | nal |Surface| Exter | || a e|a | e | a e | | | | | per | -nal | || l r|u | s | l r | | | | |Foot of|Surface| || |g | s | | | | | |Length | | || |e | | | | | | | | | |+-----+--+----+-----+------+------+------+------+-------+-------+-------+|1-1/2|10|. 134|1. 232| 4. 712| 3. 870|1. 7671|1. 1921| . 392 | 2. 546 | 1. 955 ||1-1/2| 9|. 148|1. 204| 4. 712| 3. 782|1. 7671|1. 1385| . 392 | 2. 546 | 2. 137 ||1-1/2| 8|. 165|1. 170| 4. 712| 3. 676|1. 7671|1. 0751| . 392 | 2. 546 | 2. 353 || 2 |10|. 134|1. 732| 6. 283| 5. 441|3. 1416|2. 3560| . 523 | 1. 909 | 2. 670 || 2 | 9|. 148|1. 704| 6. 283| 5. 353|3. 1416|2. 2778| . 523 | 1. 909 | 2. 927 || 2 | 8|. 165|1. 670| 6. 283| 5. 246|3. 1416|2. 1904| . 523 | 1. 909 | 3. 234 ||3-1/4|11|. 120|3. 010|10. 210| 9. 456|8. 2958|7. 1157| . 850 | 1. 175 | 4. 011 ||3-1/4|10|. 134|2. 982|10. 210| 9. 368|8. 2958|6. 9840| . 850 | 1. 175 | 4. 459 ||3-1/4| 9|. 148|2. 954|10. 210| 9. 280|8. 2958|6. 8535| . 850 | 1. 175 | 4. 903 || 4 |10|. 134|3. 732|12. 566|11. 724|12. 566|10. 939| 1. 047 | . 954 | 5. 532 || 4 | 9|. 148|3. 704|12. 566|11. 636|12. 566|10. 775| 1. 047 | . 954 | 6. 000 || 4 | 8|. 165|3. 670|12. 566|11. 530|12. 566|10. 578| 1. 047 | . 954 | 6. 758 |+-----+--+----+-----+------+------+------+------+-------+-------+-------+ Dimensions are nominal and except where noted are in inches. Pipe Material and Thickness--For saturated steam pressures not exceeding160 pounds, all pipe over 14 inches should be 3/8 inch thick O. D. Pipe. All other pipe should be standard full weight, except high pressurefeed[77] and blow-off lines, which should be extra strong. For pressures above 150 pounds up to 200 pounds with superheated steam, all high pressure feed and blow-off lines, high pressure steam lineshaving threaded flanges, and straight runs and bends of high pressuresteam lines 6 inches and under having Van Stone joints should be extrastrong. All piping 7 inches and over having Van Stone joints should befull weight soft flanging pipe of special quality. Pipe 14 inches andover should be 3/8 inch thick O. D. Pipe. All pipes for these pressuresnot specified above should be full weight pipe. Flanges--For saturated steam, 160 pounds working pressure, all flangesfor wrought-iron pipe should be cast-iron threaded. All high pressurethreaded flanges should have the diameter thickness and drilling inaccordance with the "manufacturer's standard" for "extra heavy" flanges. All low pressure flanges should have diameter, thickness and drilling inaccordance with "manufacturer's standard" for "standard flanges. " The flanges on high pressure lines should be counterbored to receivepipe and prevent the threads from shouldering. The pipe should bescrewed through the flange at least 1/16 inch, placed in machine andafter facing off the end one smooth cut should be taken over the face ofthe flange to make it square with the axis of the pipe. [Illustration: 2000 Horse-power Installation of Babcock & Wilcox Boilersand Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers atthe Kentucky Electric Co. , Louisville, Ky. ] For pressures above 160 pounds, where superheated steam is used, allhigh pressure steam lines 4 inches and over should have solid rolledsteel flanges and special upset lapped joints. In the manufacture ofsuch joints, the ends of the pipe are heated and upset against the faceof a holding mandrel conforming to the shape of the flange, the lappedportion of the pipe being flattened out against the face of the mandrel, the upsetting action maintaining the desired thickness of the lap. Whencool, both sides of the lap are faced to form a uniform thickness and aneven bearing against flange and gasket. The joint, therefore, is astrictly metal to metal joint, the flanges merely holding the lappedends of the pipe against the gasket. A special grade of soft flanging pipe is selected to prevent breaking. The bending action is a severe test of the pipe and if it withstands thebending process and the pressure tests, the reliability of the joint isassured. Such a joint is called a Van Stone joint, though manymodifications and improvements have been made since the joint wasoriginally introduced. The diameter and thickness of such flanges should be special extraheavy. Such flanges should be turned to diameter, their fronts faced andthe backs machined in lieu of spot facing. In lines other than given for pressures over 150 pounds, all flanges forwrought-iron pipe should be threaded. All threaded flanges for highpressure superheated lines 3½ inches and under should be "semi-steel"extra heavy. Flanges for other than steam lines should be manufacturer'sstandard extra heavy. Welded flanges are frequently used in place of those described withsatisfactory results. Fittings--For saturated steam under pressures up to 160 pounds, allfittings 3½ inches and under should be screwed. Fittings 4 inches andover should have flanged ends. Fittings for this pressure should be ofcast iron and should have heavy leads and full taper threads. Flangedfittings in high pressure lines should be extra heavy, and in lowpressure lines standard weight. Where possible in high pressure flangesand fittings, bolt surfaces should be spot faced to provide suitablebearing for bolt heads and nuts. Fittings for superheated steam up to 70 degrees at pressures above 160pounds are sometimes of cast iron. [78] For superheat above 70 degreessuch fittings should be "steel castings" and in general these fittingsare recommended for any degree of superheat. Fittings for other thanhigh pressure work may be of cast iron, except where superheated steamis carried, where they should be of "wrought steel" or "hard metal". Fittings 3½ inches and under should be screwed, 4 inches and overflanged. Flanges for pressures up to 160 pounds in pipes and fittings for lowpressure lines, and any fittings for high pressure lines should haveplain faces, smooth tool finish, scored with V-shaped grooves for rubbergaskets. High pressure line flanges should have raised faces, projectingthe full available diameter inside the bolt holes. These faces should besimilarly scored. All pipe ½ inch and under should have ground joint unions suitable forthe pressure required. Pipe ¾ inch and over should have cast-ironflanged unions. Unions are to be preferred to wrought-iron couplingswherever possible to facilitate dismantling. Valves--For 150 pounds working pressure, saturated steam, all valves 2inches and under may have screwed ends; 2½ inches and over should beflanged. All high pressure steam valves 6 inches and over should havesuitable by-passes. All valves for use with superheated steam should beof special construction. For pressures above 160 pounds, where thesuperheat does not exceed 70 degrees, valve bodies, caps and yokes aresometimes made of cast iron, though ordinarily semi-steel will givebetter satisfaction. The spindles of such valves should be of bronze andthere should be special necks with condensing chambers to prevent thesuperheated steam from blowing through the packing. For pressures over160 pounds and degrees of superheat above 70, all valves 3 inches andover should have valve bodies, caps and yokes of steel castings. Spindles should be of some non-corrosive metal, such as "monel metal". Seat rings should be removable of the same non-corrosive metal as shouldthe spindle seats and plug faces. All salt water valves should have bronze spindles, sleeves and packingseats. The suggestions as to flanges for different classes of service made onpage 311 hold as well for valve flanges, except that such flanges arenot scored. Automatic stop and check valves are coming into general use with boilersand such use is compulsory under the boiler regulations of certaincommunities. Where used, they should be preferably placed directly onthe boiler nozzle. Where two or more boilers are on one line, inaddition to the valve at the boiler, whether this be an automatic valveor a gate valve, there should be an additional gate valve on each boilerbranch at the main steam header. Relief valves should be furnished at the discharge side of each feedpump and on the discharge side of each feed heater of the closed type. Feed Lines--Feed lines should in all instances be made of extra strongpipe due to the corrosive action of hot feed water. While it has beensuggested above that cast-iron threaded flanges should be used in suchlines, due to the sudden expansion of such pipe in certain instancescast-iron threaded flanges crack before they become thoroughly heatedand expand, and for this reason cast-steel threaded flanges will givemore satisfactory results. In some instances, wrought-steel and VanStone joints have been used in feed lines and this undoubtedly is betterpractice than the use of cast-steel threaded work, though the additionalcost is not warranted in all stations. Feed valves should always be of the globe pattern. A gate valve cannotbe closely regulated and often clatters owing to the pulsations of thefeed pump. Gaskets--For steam and water lines where the pressure does not exceed160 pounds, wire insertion rubber gaskets 1/16 inch thick will be foundto give good service. For low pressure lines, canvas insertion blackrubber gaskets are ordinarily used. For oil lines special gaskets arenecessary. For pressure above 160 pounds carrying superheated steam, corrugatedsteel gaskets extending the full available diameter inside of the boltholes give good satisfaction. For high pressure water lines wireinserted rubber gaskets are used, and for low pressure flanged jointscanvas inserted rubber gaskets. Size of Steam Lines--The factors affecting the proper size of steamlines are the radiation from such lines and the velocity of steam withinthem. As the size of the steam line increases, there will be an increasein the radiation. [79] As the size decreases, the steam velocity and thepressure drop for a given quantity of steam naturally increases. There is a marked tendency in modern practice toward higher steamvelocities, particularly in the case of superheated steam. It wasformerly considered good practice to limit this velocity to 6000 feetper minute but this figure is to-day considered low. In practice the limiting factor in the velocity advisable is theallowable pressure drop. In the description of the action of thethrottling calorimeter, it has been demonstrated that there is no lossaccompanying a drop in pressure, the difference in energy between thehigher and lower pressures appearing as heat, which, in the case ofsteam flowing through a pipe, may evaporate any condensation present ormay be radiated from the pipe. A decrease in pipe area decreases theradiating surface of the pipe and thus the possible condensation. As theheat liberated by the pressure drop is utilized in overcoming ordiminishing the tendency toward condensation and the heat loss throughradiation, the steam as it enters the prime mover will be drier or morehighly superheated where high steam velocities are used than where theyare lower, and if enough excess pressure is carried at the boilers tomaintain the desired pressure at the prime mover, the pressure dropresults in an actual saving rather than a loss. The whole is analogousto standard practice in electrical distributing systems where generatorvoltage is adjusted to suit the loss in the feeder lines. In modern practice, with superheated steam, velocities of 15, 000 feetper minute are not unusual and this figure is very frequently exceeded. Piping System Design--With the proper size of pipe to be useddetermined, the most important factor is the provision for the removalof water of condensation that will occur in any system. Suchcondensation cannot be wholly overcome and if the water of condensationis carried to the prime mover, difficulties will invariably result. Water is practically incompressible and its effect when traveling athigh velocities differs little from that of a solid body of equalweight, hence impact against elbows, valves or other obstructions, isthe equivalent of a heavy hammer blow that may result in the fracture ofthe pipe. If there is not sufficient water in the system to produce thisresult, it will certainly cause knocking and vibration in the pipe, resulting eventually in leaky joints. Where the water reaches the primemover, its effect will vary from disagreeable knocking to disruption. Too frequently when there are disastrous results from such a cause theboilers are blamed for delivering wet steam when, as a matter of fact, the evil is purely a result of poor piping design, the most common causeof such an action being the pocketing of the water in certain parts ofthe piping from whence it is carried along in slugs by the steam. Theaction is particularly severe if steam is admitted to a cold pipecontaining water, as the water may then form a partial vacuum bycondensing the steam and be projected at a very high velocity throughthe pipes producing a characteristic sharp metallic knock which oftencauses bursting of the pipe or fittings. The amount of water presentthrough condensation may be appreciated when it is considered thatuncovered 6-inch pipe 150 feet long carrying 3600 pounds of highpressure steam per hour will condense approximately 6 per cent of thetotal steam carried through radiation. It follows that efficient meansof removing condensation water are absolutely imperative and thefollowing suggestions as to such means may be of service: The pitch of all pipe should be in the direction of the flow of steam. Wherever a rise is necessary, a drain should be installed. All mainheaders and important branches should end in a drop leg and each suchdrop leg and any low points in the system should be connected to thedrainage pump. A similar connection should be made to every fittingwhere there is danger of a water pocket. Branch lines should never be taken from the bottom of a main header butwhere possible should be taken from the top. Each engine supply pipeshould have its own separator placed as near the throttle as possible. Such separators should be drained to the drainage system. Check valves are frequently placed in drain pipes to prevent steam fromentering any portion of the system that may be shut off. Valves should be so located that they cannot form water pockets wheneither open or closed. Globe valves will form a water pocket in thepiping to which they are connected unless set with the stem horizontal, while gate valves may be set with the spindle vertical or at an angle. Where valves are placed directly on the boiler nozzle, a drain should beprovided above them. High pressure drains should be trapped to both feed heaters and wasteheaders. Traps and meters should be provided with by-passes. Cylinderdrains, heater blow-offs and drains, boiler blow-offs and similar linesshould be led to waste. The ends of cylinder drains should not extendbelow the surface of water, for on starting up or on closing thethrottle valve with the drains open, water may be drawn back into thecylinders. TABLE 64 RADIATION FROM COVERED AND UNCOVERED STEAM PIPES CALCULATED FOR 160 POUNDS PRESSURE AND 60 DEGREES TEMPERATURE +---------------------------------------------------------------------+|+------+---------------------------+----+----+----+-----+-----+-----+||| | | | | | | | |||| Pipe | |1/2 |3/4 | 1 |1-1/4|1-1/2| ||||Inches| Thickness of Covering |inch|inch|inch|inch |inch |Bare |||+------+---------------------------+----+----+----+-----+-----+-----+||| |B. T. U. Per lineal foot | | | | | | |||| | per hour |149 |118 | 99 | 86 | 79 | 597 |||| |B. T. U. Per square foot | | | | | | |||| | per hour |240 |190 |161 | 138 | 127 | 959 |||| 2 |B. T. U. Per square foot | | | | | | |||| | per hour per one degree | | | | | | |||| | difference in temperature|. 770|. 613|. 519|. 445 |. 410 |3. 198|||+------+---------------------------+----+----+----+-----+-----+-----+||| |B. T. U. Per lineal foot | | | | | | |||| | per hour |247 |193 |160 | 139 | 123 |1085 |||| |B. T. U. Per square foot | | | | | | |||| | per hour |210 |164 |136 | 118 | 104 | 921 |||| 4 |B. T. U. Per square foot | | | | | | |||| | per hour per one degree | | | | | | |||| | difference in temperature|. 677|. 592|. 439|. 381 |. 335 |2. 970|||+------+---------------------------+----+----+----+-----+-----+-----+||| |B. T. U. Per lineal foot | | | | | | |||| | per hour |352 |269 |221 | 190 | 167 |1555 |||| |B. T. U. Per square foot | | | | | | |||| | per hour |203 |155 |127 | 110 | 96 | 897 |||| 6 |B. T. U. Per square foot | | | | | | |||| | per hour per one degree | | | | | | |||| | difference in temperature|. 655|. 500|. 410|. 355 |. 310 |2. 89 |||+------+---------------------------+----+----+----+-----+-----+-----+||| |B. T. U. Per lineal foot | | | | | | |||| | per hour |443 |337 |276 | 235 | 207 |1994 |||| |B. T. U. Per square foot | | | | | | |||| | per hour |196 |149 |122 | 104 | 92 | 883 |||| 8 |B. T. U. Per square foot | | | | | | |||| | per hour per one degree | | | | | | |||| | difference in temperature|. 632|. 481|. 394|. 335 |. 297 |2. 85 |||+------+---------------------------+----+----+----+-----+-----+-----+||| |B. T. U. Per lineal foot | | | | | | |||| | per hour |549 |416 |337 | 287 | 250 |2468 |||| |B. T. U. Per square foot | | | | | | |||| | per hour |195 |148 |120 | 102 | 89 | 877 |||| 10 |B. T. U. Per square foot | | | | | | |||| | per hour per one degree | | | | | | |||| | difference in temperature|. 629|. 477|. 387|. 329 |. 287 |2. 83 |||+------+---------------------------+----+----+----+-----+-----+-----+|+---------------------------------------------------------------------+ Covering--Magnesia, canvas covered. For calculating radiation for pressure and temperature other than 160pounds, and 60 degrees, use B. T. U. Figures for one degree difference. Radiation from Pipes--The evils of the presence of condensed steam inpiping systems have been thoroughly discussed above and in some of theprevious articles. Condensation resulting from radiation, while itcannot be wholly obviated, can, by proper installation, be greatlyreduced. Bare pipe will radiate approximately 3 B. T. U. Per hour per square footof exposed surface per one degree of difference in temperature betweenthe steam contained and the external air. This figure may be reduced tofrom 0. 3 to 0. 4 B. T. U. For the same conditions by a 1½ inch insulatingcovering. Table 64 gives the radiation losses for bare and covered pipeswith different thicknesses of magnesia covering. Many experiments have been made as to the relative efficiencies ofdifferent kinds of covering. Table 65 gives some approximately relativefigures based on one inch covering from experiments by Paulding, Jacobus, Brill and others. TABLE 65 APPROXIMATE EFFICIENCIES OF VARIOUS COVERINGS REFERRED TO BARE PIPES+--------------------------------+|+-------------------+----------+||| Covering |Efficiency|||+-------------------+----------+|||Asbestocel | 76. 8 ||||Gast's Air Cell | 74. 4 ||||Asbesto Sponge Felt| 85. 0 ||||Magnesia | 83. 5 ||||Asbestos Navy Brand| 82. 0 ||||Asbesto Sponge Hair| 86. 0 ||||Asbestos Fire Felt | 73. 5 |||+-------------------+----------+|+--------------------------------+ Based on one-inch covering. The following suggestions may be of service: Exposed radiating surfaces of all pipes, all high pressure steamflanges, valve bodies and fittings, heaters and separators, should becovered with non-conducting material wherever such covering will improveplant economy. All main steam lines, engine and boiler branches, shouldbe covered with 2 inches of 85 per cent carbonate of magnesia or theequivalent. Other lines may be covered with one inch of the samematerial. All covering should be sectional in form and large surfacesshould be covered with blocks, except where such material would bedifficult to install, in which case plastic material should be used. Inthe case of flanges the covering should be tapered back from the flangein order that the bolts may be removed. All surfaces should be painted before the covering is applied. Canvas isordinarily placed over the covering, held in place by wrought-iron orbrass bands. Expansion and Support of Pipe--It is highly important that the piping beso run that there will be no undue strains through the action ofexpansion. Certain points are usually securely anchored and theexpansion of the piping at other points taken care of by providingsupports along which the piping will slide or by means of flexiblehangers. Where pipe is supported or anchored, it should be from thebuilding structure and not from boilers or prime movers. Where supportsare furnished, they should in general be of any of the numerous slidingsupports that are available. Expansion is taken care of by such a methodof support and by the providing of large radius bends where necessary. It was formerly believed that piping would actually expand under steamtemperatures about one-half the theoretical amount due to the fact thatthe exterior of the pipe would not reach the full temperature of thesteam contained. It would appear, however from recent experiments thatsuch actual expansion will in the case of well-covered pipe be verynearly the theoretical amount. In one case noted, a steam header 293feet long when heated under a working pressure of 190 pounds, the steamsuperheated approximately 125 degrees, expanded 8¾ inches; thetheoretical amount of expansion under the conditions would beapproximately 9-35/64 inches. [Illustration: Bankers Trust Building, New York City, Operation 900Horse Power of Babcock & Wilcox Boilers] FLOW OF STEAM THROUGH PIPES AND ORIFICES Various formulae for the flow of steam through pipes have been advanced, all having their basis upon Bernoulli's theorem of the flow of waterthrough circular pipes with the proper modifications made for thevariation in constants between steam and water. The loss of energy dueto friction in a pipe is given by Unwin (based upon Weisbach) as f 2 v² W L E_{f} = ---------- (37) gd where E is the energy loss in foot pounds due to the friction of W unitsof weight of steam passing with a velocity of v feet per second througha pipe d feet in diameter and L feet long; g represents the accelerationdue to gravity (32. 2) and f the coefficient of friction. Numerous values have been given for this coefficient of friction, f, which, from experiment, apparently varies with both the diameter of pipeand the velocity of the passing steam. There is no authentic data on therate of this variation with velocity and, as in all experiments, theeffect of change of velocity has seemed less than the unavoidable errorsof observation, the coefficient is assumed to vary only with the size ofthe pipe. Unwin established a relation for this coefficient for steam at avelocity of 100 feet per second, / 3 \ f = K| 1 + --- | (38) \ 10d / where K is a constant experimentally determined, and d the internaldiameter of the pipe in feet. If h represents the loss of head in feet, then f 2 v² W L E_{f} = Wh = ---------- (39) gd f 2 v² L and h = -------- (40) gd If D represents the density of the steam or weight per cubic foot, and pthe loss of pressure due to friction in pounds per square inch, then hD p = --- (41) 144 and from equations (38), (40) and (41), D v² L / 3 \ p = -------- × K | 1 + --- | (42) 72 g d \ 10d / To convert the velocity term and to reduce to units ordinarily used, letd_{1} the diameter of pipe in inches = 12d, and w = the flow in poundsper minute; then [pi] / d_{1}\ w = 60v × --- | ---- |^{2} D 4 \ 12 / 9. 6 w and v = -------------- [pi] d_{1}^2 D Substituting this value and that of d in formula (42) / 3. 6 \ w^{2} L p = 0. 04839 K | 1 + ----- | ----------- (43) \ d_{1} / D d_{1}^{5} Some of the experimental determinations for the value of K are: K = . 005 for water (Unwin). K = . 005 for air (Arson). K = . 0028 for air (St. Gothard tunnel experiments). K = . 0026 for steam (Carpenter at Oriskany). K = . 0027 for steam (G. H. Babcock). The value . 0027 is apparently the most nearly correct, and substitutingin formula (43) gives, / 3. 6 \ w^{2} L p = 0. 000131 | 1 + ---- | ----------- (44) \ d_{1}/ D d_{1}^{5} / pDd_{1}^{5} \ w = 87 | -------------- |^{½} (45) | / 3. 6 \ | | | 1 + ---- | L | \ \ d_{1}/ / Where w = the weight of steam passing in pounds per minute, p = the difference in pressure between the two ends of the pipe in pounds per square inch, D = density of steam or weight per cubic foot, [80] d_{1} = internal diameter of pipe in inches, L = length of pipe in feet. TABLE 66 FLOW OF STEAM THROUGH PIPES+---------------------------------------------------------------------------------------+|Initl|Diameter[81] of Pipe in Inches, Length of Pipe = 240 Diameters ||Gauge|---------------------------------------------------------------------------------+|Press| ¾ | 1 | 1½ | 2 | 2½ | 3 | 4 | 5 | 6 | 8 | 10 | 12 | 15 | 18 ||Pound|---------------------------------------------------------------------------------+|/SqIn| Weight of Steam per Minute, in Pounds, With One Pound Loss of Pressure |+-----+---------------------------------------------------------------------------------+| 1 |1. 16|2. 07| 5. 7|10. 27|15. 45|25. 38| 46. 85| 77. 3|115. 9|211. 4| 341. 1| 502. 4| 804|1177|| 10 |1. 44|2. 57| 7. 1|12. 72|19. 15|31. 45| 58. 05| 95. 8|143. 6|262. 0| 422. 7| 622. 5| 996|1458|| 20 |1. 70|3. 02| 8. 3|14. 94|22. 49|36. 94| 68. 20|112. 6|168. 7|307. 8| 496. 5| 731. 3|1170|1713|| 30 |1. 91|3. 40| 9. 4|16. 84|25. 35|41. 63| 76. 84|126. 9|190. 1|346. 8| 559. 5| 824. 1|1318|1930|| 40 |2. 10|3. 74|10. 3|18. 51|27. 87|45. 77| 84. 49|139. 5|209. 0|381. 3| 615. 3| 906. 0|1450|2122|| 50 |2. 27|4. 04|11. 2|20. 01|30. 13|49. 48| 91. 34|150. 8|226. 0|412. 2| 665. 0| 979. 5|1567|2294|| 60 |2. 43|4. 32|11. 9|21. 38|32. 19|52. 87| 97. 60|161. 1|241. 5|440. 5| 710. 6|1046. 7|1675|2451|| 70 |2. 57|4. 58|12. 6|22. 65|34. 10|56. 00|103. 37|170. 7|255. 8|466. 5| 752. 7|1108. 5|1774|2596|| 80 |2. 71|4. 82|13. 3|23. 82|35. 87|58. 91|108. 74|179. 5|269. 0|490. 7| 791. 7|1166. 1|1866|2731|| 90 |2. 83|5. 04|13. 9|24. 92|37. 52|61. 62|113. 74|187. 8|281. 4|513. 3| 828. 1|1219. 8|1951|2856|| 100 |2. 95|5. 25|14. 5|25. 96|39. 07|64. 18|118. 47|195. 6|293. 1|534. 6| 862. 6|1270. 1|2032|2975|| 120 |3. 16|5. 63|15. 5|27. 85|41. 93|68. 87|127. 12|209. 9|314. 5|573. 7| 925. 6|1363. 3|2181|3193|| 150 |3. 45|6. 14|17. 0|30. 37|45. 72|75. 09|138. 61|228. 8|343. 0|625. 5|1009. 2|1486. 5|2378|3481|+---------------------------------------------------------------------------------------+ This formula is the most generally accepted for the flow of steam inpipes. Table 66 is calculated from this formula and gives the amount ofsteam passing per minute that will flow through straight smooth pipeshaving a length of 240 diameters from various initial pressures with onepound difference between the initial and final pressures. To apply this table for other lengths of pipe and pressure losses otherthan those assumed, let L = the length and d the diameter of the pipe, both in inches; l, the loss in pounds; Q, the weight under theconditions assumed in the table, and Q_{1}, the weight for the changedconditions. For any length of pipe, if the weight of steam passing is the same asgiven in the table, the loss will be, L l = ---- (46) 240d If the pipe length is the same as assumed in the table but the loss isdifferent, the quantity of steam passing per minute will be, Q_{1} = Ql^{½} (47) For any assumed pipe length and loss of pressure, the weight will be, /240dl\ Q_{1} = Q|-----|^{½} (48) \ L / TABLE 67 FLOW OF STEAM THROUGH PIPES LENGTH OF PIPE 1000 FEET +--------------------------------------------------++----------------------------------------+| Discharge in Pounds per Minute corresponding to || Drop in Pressure in || Drop in Pressure on Right for Pipe Diameters || Pounds per Square Inch corresponding || in Inches in Top Line || to Discharge on Left: Densities || || and corresponding Absolute Pressures || || per Square Inch in First Two Lines |+--------------------------------------------------++----------------------------------------+| Diameter[82]--Discharge || Density--Pressure--Drop |+--------------------------------------------------++----------------------------------------+| 12 | 10 | 8 | 6 | 4 | 3 | 2½| 2 | 1½| 1 ||. 208 |. 230|. 284|. 328|. 401|. 443|. 506|. 548|| In | In | In | In | In | In | In | In | In | In || 90 | 100| 125| 150| 180| 200| 230| 250|+--------------------------------------------------++-------+--------------------------------+|2328|1443| 799| 371|123. |55. 9|28. 8|18. 1|6. 81|2. 52||18. 10|16. 4|13. 3|11. 1|9. 39|8. 50|7. 44|6. 87||2165|1341| 742| 344|114. 6|51. 9|27. 6|16. 8|6. 52|2. 34||15. 60|14. 1|11. 4|9. 60|8. 09|7. 33|6. 41|5. 92||1996|1237| 685| 318|106. 0|47. 9|26. 4|15. 5|6. 24|2. 16||13. 3 |12. 0|9. 74|8. 18|6. 90|6. 24|5. 47|5. 05||1830|1134| 628| 292| 97. 0|43. 9|25. 2|14. 2|5. 95|1. 98||11. 1 |10. 0|8. 13|6. 83|5. 76|5. 21|4. 56|4. 21||1663|1031| 571| 265| 88. 2|39. 9|24. 0|12. 9|5. 67|1. 80|| 9. 25|8. 36|6. 78|5. 69|4. 80|4. 34|3. 80|3. 51||1580| 979| 542| 252| 83. 8|37. 9|22. 8|12. 3|5. 29|1. 71|| 8. 33|7. 53|6. 10|5. 13|4. 32|3. 91|3. 42|3. 16||1497| 928| 514| 239| 79. 4|35. 9|21. 6|11. 6|5. 00|1. 62|| 7. 48|6. 76|5. 48|4. 60|3. 88|3. 51|3. 07|2. 84||1414| 876| 485| 226| 75. 0|33. 9|20. 4|10. 9|4. 72|1. 53|| 6. 67|6. 03|4. 88|4. 10|3. 46|3. 13|2. 74|2. 53||1331| 825| 457| 212| 70. 6|31. 9|19. 2|10. 3|4. 43|1. 44|| 5. 91|5. 35|4. 33|3. 64|3. 07|2. 78|2. 43|2. 24||1248| 873| 428| 199| 66. 2|23. 9|18. 0|9. 68|4. 15|1. 35|| 5. 19|4. 69|3. 80|3. 19|2. 69|2. 44|2. 13|1. 97||1164| 722| 400| 186| 61. 7|27. 9|16. 8|9. 03|3. 86|1. 26|| 4. 52|4. 09|3. 31|2. 78|2. 34|2. 12|1. 86|1. 72||1081| 670| 371| 172| 57. 3|25. 9|15. 6|8. 38|3. 68|1. 17|| 3. 90|3. 53|2. 86|2. 40|2. 02|1. 83|1. 60|1. 48|| 998| 619| 343| 159| 52. 9|23. 9|14. 4|7. 74|3. 40|1. 08|| 3. 32|3. 00|2. 43|2. 04|1. 72|1. 56|1. 36|1. 26|| 915| 567| 314| 146| 48. 5|21. 9|13. 2|7. 10|3. 11|0. 99|| 2. 79|2. 52|2. 04|1. 72|1. 45|1. 31|1. 15|1. 06|| 832| 516| 286| 132| 44. 1|20. 0|12. 0|6. 45|2. 83|0. 90|| 2. 31|2. 09|1. 69|1. 42|1. 20|1. 08|. 949|. 877|| 748| 464| 257| 119| 39. 7|18. 0|10. 8|5. 81|2. 55|0. 81|| 1. 87|1. 69|1. 37|1. 15| . 97|. 878|. 769|. 710|| 665| 412| 228| 106| 35. 3|16. 0| 9. 6|5. 16|2. 26|0. 72|| 1. 47|1. 33|1. 08|. 905|. 762|. 690|. 604|. 558|| 582| 361| 200|92. 8| 30. 9|14. 0| 8. 4|4. 52|1. 98|0. 63|| 1. 13|1. 02|. 828|. 695|. 586|. 531|. 456|. 429|+--------------------------------------------------++----------------------------------------+ To get the pressure drop for lengths other than 1000 feet, multiply bylengths in feet ÷ 1000. Example: Find the weight of steam at 100 pounds initial gauge pressure, which will pass through a 6-inch pipe 720 feet long with a pressure dropof 4 pounds. Under the conditions assumed in the table, 293. 1 poundswould flow per minute; hence, Q = 293. 1, and _ _ | 240×6×4 |Q_{1} = 293. 1 | ------- |^{½} = 239. 9 pounds |_ 720×12_| Table 67 may be frequently found to be of service in problems involvingthe flow of steam. This table was calculated by Mr. E. C. Sickles for apipe 1000 feet long from formula (45), except that from the use of avalue of the constant K = . 0026 instead of . 0027, the constant in theformula becomes 87. 45 instead of 87. In using this table, the pressures and densities to be considered, asgiven at the top of the right-hand portion, are the mean of the initialand final pressures and densities. Its use is as follows: Assume anallowable drop of pressure through a given length of pipe. From thevalue as found in the right-hand column under the column of meanpressure, as determined by the initial and final pressures, pass to theleft-hand portion of the table along the same line until the quantity isfound corresponding to the flow required. The size of the pipe at thehead of this column is that which will carry the required amount ofsteam with the assumed pressure drop. The table may be used conversely to determine the pressure drop througha pipe of a given diameter delivering a specified amount of steam bypassing from the known figure in the left to the column on the rightheaded by the pressure which is the mean of the initial and finalpressures corresponding to the drop found and the actual initialpressure present. For a given flow of steam and diameter of pipe, the drop in pressure isproportional to the length and if discharge quantities for other lengthsof pipe than 1000 feet are required, they may be found by proportion. TABLE 68 FLOW OF STEAM INTO THE ATMOSPHERE __________________________________________________________________| | | | | || Absolute | Velocity | Actual | Discharge | Horse Power || Initial | of Outflow | Velocity | per Square | per Square || Pressure | at Constant | of Outflow | Inch of | Inch of || per Square | Density | Expanded | Orifice | Orifice if || Inch | Feet per | Feet per | per Minute | Horse Power || Pounds | Second | Second | Pounds | = 30 Pounds || | | | | per Hour ||____________|_____________|____________|____________|_____________|| | | | | || 25. 37 | 863 | 1401 | 22. 81 | 45. 6 || 30. | 867 | 1408 | 26. 84 | 53. 7 || 40. | 874 | 1419 | 35. 18 | 70. 4 || 50. | 880 | 1429 | 44. 06 | 88. 1 || 60. | 885 | 1437 | 52. 59 | 105. 2 || 70. | 889 | 1444 | 61. 07 | 122. 1 || 75. | 891 | 1447 | 65. 30 | 130. 6 || 90. | 895 | 1454 | 77. 94 | 155. 9 || 100. | 898 | 1459 | 86. 34 | 172. 7 || 115. | 902 | 1466 | 98. 76 | 197. 5 || 135. | 906 | 1472 | 115. 61 | 231. 2 || 155. | 910 | 1478 | 132. 21 | 264. 4 || 165. | 912 | 1481 | 140. 46 | 280. 9 || 215. | 919 | 1493 | 181. 58 | 363. 2 ||____________|_____________|____________|____________|_____________| Elbows, globe valves and a square-ended entrance to pipes all offerresistance to the passage of steam. It is customary to measure theresistance offered by such construction in terms of the diameter of thepipe. Many formulae have been advanced for computing the length of pipein diameters equivalent to such fittings or valves which offerresistance. These formulae, however vary widely and for ordinarypurposes it will be sufficiently accurate to allow for resistance at theentrance of a pipe a length equal to 60 times the diameter; for a rightangle elbow, a length equal to 40 diameters, and for a globe valve alength equal to 60 diameters. The flow of steam of a higher toward a lower pressure increases as thedifference in pressure increases to a point where the external pressurebecomes 58 per cent of the absolute initial pressure. Below this pointthe flow is neither increased nor decreased by a reduction of theexternal pressure, even to the extent of a perfect vacuum. The lowestpressure for which this statement holds when steam is discharged intothe atmosphere is 25. 37 pounds. For any pressure below this figure, theatmospheric pressure, 14. 7 pounds, is greater than 58 per cent of theinitial pressure. Table 68, by D. K. Clark, gives the velocity ofoutflow at constant density, the actual velocity of outflow expanded(the atmospheric pressure being taken as 14. 7 pounds absolute, and theratio of expansion in the nozzle being 1. 624), and the correspondingdischarge per square inch of orifice per minute. Napier deduced an approximate formula for the outflow of steam into theatmosphere which checks closely with the figures just given. Thisformula is: paW = ---- (49) 70 Where W = the pounds of steam flowing per second, p = the absolute pressure in pounds per square inch, and a = the area of the orifice in square inches. In some experiments made by Professor C. H. Peabody, in the flow ofsteam through pipes from ¼ inch to 1½ inches long and ¼ inch indiameter, with rounded entrances, the greatest difference from Napier'sformula was 3. 2 per cent excess of the experimental over the calculatedresults. For steam flowing through an orifice from a higher to a lower pressurewhere the lower pressure is greater than 58 per cent of the higher, theflow per minute may be calculated from the formula: W = 1. 9AK ((P - d)d)^{½} (50) Where W = the weight of steam discharged in pounds per minute, A = area of orifice in square inches, P = the absolute initial pressure in pounds per square inch, d = the difference in pressure between the two sides in pounds per square inch, K = a constant = . 93 for a short pipe, and . 63 for a hole in a thin plate or a safety valve. [Illustration: Vesta Coal Co. , California, Pa. , Operating at this Plant3160 Horse Power of Babcock & Wilcox Boilers] HEAT TRANSFER The rate at which heat is transmitted from a hot gas to a cooler metalsurface over which the gas is flowing has been the subject of a greatdeal of investigation both from the experimental and theoretical side. Amore or less complete explanation of this process is necessary for adetailed analysis of the performance of steam boilers. Such informationat the present is almost entirely lacking and for this reason a boiler, as a physical piece of apparatus, is not as well understood as it mightbe. This, however, has had little effect in its practical developmentand it is hardly possible that a more complete understanding of thephenomena discussed will have any radical effect on the present design. The amount of heat that is transferred across any surface is usuallyexpressed as a product, of which one factor is the slope or linear rateof change in temperature and the other is the amount of heat transferredper unit's difference in temperature in unit's length. In Fourier'sanalytical theory of the conduction of heat, this second factor is takenas a constant and is called the "conductivity" of the substance. Following this practice, the amount of heat absorbed by any surface froma hot gas is usually expressed as a product of the difference intemperature between the gas and the absorbing surface into a factorwhich is commonly designated the "transfer rate". There has beenconsiderable looseness in the writings of even the best authors as tothe way in which the gas temperature difference is to be measured. Ifthe gas varies in temperature across the section of the channel throughwhich it is assumed to flow, and most of them seem to consider that thiswould be the case, there are two mean gas temperatures, one the mean ofthe actual temperatures at any time across the section, and the otherthe mean temperature of the entire volume of the gas passing such asection in any given time. Since the velocity of flow will of acertainty vary across the section, this second mean temperature, whichis one tacitly assumed in most instances, may vary materially from thefirst. The two mean temperatures are only approximately equal when theactual temperature measured across the section is very nearly aconstant. In what follows it will be assumed that the mean temperaturemeasured in the second way is referred to. In English units thetemperature difference is expressed in Fahrenheit degrees and thetransfer rate in B. T. U. 's per hour per square foot of surface. Pecla, who seems to have been one of the first to consider this subjectanalytically, assumed that the transfer rate was constant andindependent both of the temperature differences and the velocity of thegas over the surface. Rankine, on the other hand, assumed that thetransfer rate, while independent of the velocity of the gas, wasproportional to the temperature difference, and expressed the totalamount of heat absorbed as proportional to the square of the differencein temperature. Neither of these assumptions has any warrant in eithertheory or experiment and they are only valuable in so far as their usedetermine formulae that fit experimental results. Of the two, Rankine'sassumption seems to lead to formulae that more nearly represent actualconditions. It has been quite fully developed by William Kent in his"Steam Boiler Economy". Professor Osborne Reynolds, in a short paperreprinted in Volume I of his "Scientific Papers", suggests that thetransfer rate is proportional to the product of the density and velocityof the gas and it is to be assumed that he had in mind the meanvelocity, density and temperature over the section of the channelthrough which the gas was assumed to flow. Contrary to prevalentopinion, Professor Reynolds gave neither a valid experimental nor atheoretical explanation of his formula and the attempts that have beenmade since its first publication to establish it on any theoreticalbasis can hardly be considered of scientific value. Nevertheless, Reynolds' suggestion was really the starting point of the scientificinvestigation of this subject and while his formula cannot in any sensebe held as completely expressing the facts, it is undoubtedly correct toa first approximation for small temperature differences if the additiveconstant, which in his paper he assumed as negligible, is given avalue. [83] Experimental determinations have been made during the last few years ofthe heat transfer rate in cylindrical tubes at comparatively lowtemperatures and small temperature differences. The results at differentvelocities have been plotted and an empirical formula determinedexpressing the transfer rate with the velocity as a factor. The exponentof the power of the velocity appearing in the formula, according toReynolds, would be unity. The most probable value, however, deduced frommost of the experiments makes it less than unity. After consideringexperiments of his own, as well as experiments of others, Dr. WilhelmNusselt[84] concludes that the evidence supports the following formulae: _ _ [lambda]_{w} | w c_{p} [delta] |a = b ------------ | --------------- |^{u} d^{1-u} |_ [lambda] _| Where a is the transfer rate in calories per hour per square meter of surface per degree centigrade difference in temperature, u is a physical constant equal to . 786 from Dr. Nusselt's experiments, b is a constant which, for the units given below, is 15. 90, w is the mean velocity of the gas in meters per second, c_{p} is the specific heat of the gas at its mean temperature and pressure in calories per kilogram, [delta] is the density in kilograms per cubic meter, [lambda] is the conductivity at the mean temperature and pressure in calories per hour per square meter per degree centigrade temperature drop per meter, [lambda]_{w} is the conductivity of the steam at the temperature of the tube wall, d is the diameter of the tube in meters. If the unit of time for the velocity is made the hour, and in the placeof the product of the velocity and density is written its equivalent, the weight of gas flowing per hour divided by the area of the tube, thisequation becomes: _ _ [lambda]_{w} | Wc_{p} |a = . 0255 ------------ | --------- |^{. 786} d^{. 214} |_ A[lambda] _| where the quantities are in the units mentioned, or, since the constantsare absolute constants, in English units, a is the transfer rate in B. T. U. Per hour per square foot of surface per degree difference in temperature, W is the weight in pounds of the gas flowing through the tube per hour, A is the area of the tube in square feet, d is the diameter of the tube in feet, c_{p} is the specific heat of the gas at constant pressure, [lambda] is the conductivity of the gas at the mean temperature and pressure in B. T. U. Per hour per square foot of surface per degree Fahrenheit drop in temperature per foot, [lambda]_{w} is the conductivity of the steam at the temperature of the wall of the tube. The conductivities of air, carbonic acid gas and superheated steam, asaffected by the temperature, in English units, are: Conductivity of air . 0122 (1 + . 00132 T)Conductivity of carbonic acid gas . 0076 (1 + . 00229 T)Conductivity of superheated steam . 0119 (1 + . 00261 T) where T is the temperature in degrees Fahrenheit. Nusselt's formulae can be taken as typical of the number of otherformulae proposed by German, French and English writers. [85] Physicalproperties, in addition to the density, are introduced in the form ofcoefficients from a consideration of the physical dimensions of thevarious units and of the theoretical formulae that are supposed togovern the flow of the gas and the transfer of heat. All assume that thecorrect method of representing the heat transfer rate is by the use ofone term, which seems to be unwarranted and probably has been adopted onaccount of the convenience in working up the results by plotting themlogarithmically. This was the method Professor Reynolds used indetermining his equation for the loss in head in fluids flowing throughcylindrical pipes and it is now known that the derived equation cannotbe considered as anything more than an empirical formula. It, therefore, is well for anyone considering this subject to understand at the outsetthat the formulae discussed are only of an empirical nature andapplicable to limited ranges of temperature under the conditionsapproximately the same as those surrounding the experiments from whichthe constants of the formula were determined. It is not probable that the subject of heat transfer in boilers willever be on any other than an experimental basis until the mathematicalexpression connecting the quantity of fluid which will flow through achannel of any section under a given head has been found and someexplanation of its derivation obtained. Taking the simplest possiblesection, namely, a circle, it is found that at low velocities the lossof head is directly proportional to the velocity and the fluid flows instraight stream lines or the motion is direct. This motion is in exactaccordance with the theoretical equations of the motion of a viscousfluid and constitutes almost a direct proof that the fundamentalassumptions on which these equations are based are correct. When, however, the velocity exceeds a value which is determinable for any sizeof tube, the direct or stream line motion breaks down and is replaced byan eddy or mixing flow. In this flow the head loss by friction isapproximately, although not exactly, proportional to the square of thevelocity. No explanation of this has ever been found in spite of thefact that the subject has been treated by the best mathematicians andphysicists for years back. It is to be assumed that the heat transferredduring the mixing flow would be at a much higher rate than with thedirect or stream line flow, and Professors Croker and Clement[86] havedemonstrated that this is true, the increase in the transfer being somarked as to enable them to determine the point of critical velocityfrom observing the rise in temperature of water flowing through a tubesurrounded by a steam jacket. The formulae given apply only to a mixing flow and inasmuch as, fromwhat has just been stated, this form of motion does not exist from zerovelocity upward, it follows that any expression for the heat transferrate that would make its value zero when the velocity is zero, canhardly be correct. Below the critical velocity, the transfer rate seemsto be little affected by change in velocity and Nusselt, [87] in anotherpaper which mathematically treats the direct or stream line flow, concludes that, while it is approximately constant as far as thevelocity is concerned in a straight cylindrical tube, it would vary frompoint to point of the tube, growing less as the surface passed overincreased. It should further be noted that no account in any of this experimentalwork has been taken of radiation of heat from the gas. Since the commongases absorb very little radiant heat at ordinary temperatures, it hasbeen assumed that they radiate very little at any temperature. This mayor may not be true, but certainly a visible flame must radiate as wellas absorb heat. However this radiation may occur, since it would be avolume phenomenon rather than a surface phenomenon it would beconsidered somewhat differently from ordinary radiation. It might applyas increasing the conductivity of the gas which, however independent ofradiation, is known to increase with the temperature. It is, therefore, to be expected that at high temperatures the rate of transfer will begreater than at low temperatures. The experimental determinations oftransfer rates at high temperatures are lacking. Although comparatively nothing is known concerning the heat radiationfrom gases at high temperatures, there is no question but what a largeproportion of the heat absorbed by a boiler is received direct asradiation from the furnace. Experiments show that the lower row of tubesof a Babcock & Wilcox boiler absorb heat at an average rate per squarefoot of surface between the first baffle and the front headersequivalent to the evaporation of from 50 to 75 pounds of water from andat 212 degrees Fahrenheit per hour. Inasmuch as in these experiments noseparation could be made between the heat absorbed by the bottom of thetube and that absorbed by the top, the average includes both maximum andminimum rates for those particular tubes and it is fair to assume thatthe portion of the tubes actually exposed to the furnace radiationsabsorb heat at a higher rate. Part of this heat was, of course absorbedby actual contact between the hot gases and the boiler heating surface. A large portion of it, however, must have been due to radiation. Whetherthis radiant heat came from the fire surface and the brickwork andpassed through the gases in the furnace with little or no absorption, orwhether, on the other hand, the radiation were absorbed by the furnacegases and the heat received by the boiler was a secondary radiation fromthe gases themselves and at a rate corresponding to the actual gastemperature, is a question. If the radiations are direct, then the term"furnace temperature", as usually used has no scientific meaning, forobviously the temperature of the gas in the furnace would be entirelydifferent from the radiation temperature, even were it possible toattach any significance to the term "radiation temperature", and it isnot possible to do this unless the radiations are what are known as"full radiations" from a so-called "black body". If furnace radiationtakes place in this manner, the indications of a pyrometer placed in afurnace are hard to interpret and such temperature measurements can beof little value. If the furnace gases absorb the radiations from thefire and from the brickwork of the side walls and in their turn radiateheat to the boiler surface, it is scientifically correct to assume thatthe actual or sensible temperature of the gas would be measured by apyrometer and the amount of radiation could be calculated from thistemperature by Stefan's law, which is to the effect that the rate ofradiation is proportional to the fourth power of the absolutetemperature, using the constant with the resulting formula that has beendetermined from direct experiment and other phenomena. With thisunderstanding of the matter, the radiations absorbed by a boiler can betaken as equal to that absorbed by a flat surface, covering the portionof the boiler tubes exposed to the furnace and at the temperature of thetube surface, when completely exposed on one side to the radiations froman atmosphere at the temperature in the furnace. With this assumption, if S^{1} is the area of the surface, T the absolute temperature of thefurnace gases, t the absolute temperature of the tube surface of theboiler, the heat absorbed per hour measured in B. T. U. 's is equal to _ _ | / T \ / t \ |1600 | |----|^{4} - |----|^{4}| S^{1} |_\1000/ \1000/ _| In using this formula, or in any work connected with heat transfer, theexternal temperature of the boiler heating surface can be taken as thatof saturated steam at the pressure under which the boiler is working, with an almost negligible error, since experiments have shown that witha surface clean internally, the external surface is only a few degreeshotter than the water in contact with the inner surface, even at thehighest rates of evaporation. Further than this, it is not conceivablethat in a modern boiler there can be much difference in the temperatureof the boiler in the different parts, or much difference between thetemperature of the water and the temperature of the steam in the drumswhich is in contact with it. If the total evaporation of a boiler measured in B. T. U. 's per hour isrepresented by E, the furnace temperature by T_{1}, the temperature ofthe gas leaving the boiler by T_{2}, the weight of gas leaving thefurnace and passing through the setting per hour by W, the specific heatof the gas by C, it follows from the fact that the total amount of heatabsorbed is equal to the heat received from radiation plus the heatremoved from the gases by cooling from the temperature T_{1} to thetemperature T_{2}, that _ _ | / T \ / t \ |E = 1600 | |----|^{4} - |----|^{4}| S^{1} + WC(T_{1} - T_{2}) |_\1000/ \1000/ _| This formula can be used for calculating the furnace temperature when E, t and T_{2} are known but it must be remembered that an assumptionwhich is probably, in part at least, incorrect is implied in using it orin using any similar formula. Expressed in this way, however, it seemsmore rational than the one proposed a few years ago by Dr. Nicholson[88]where, in place of the surface exposed to radiation, he uses the gratesurface and assumes the furnace gas temperature as equal to the firetemperature. If the heat transfer rate is taken as independent of the gas temperatureand the heat absorbed by an element of the surface in a given time isequated to the heat given out from the gas passing over this surface inthe same time, a single integration gives Rs(T - t) = (T_{1} - t) e^{- --} WC where s is the area of surface passed over by the gases from the furnaceto any point where the gas temperature T is measured, and the rate ofheat transfer is R. As written, this formula could be used forcalculating the temperature of the gas at any point in the boilersetting. Gas temperatures, however, calculated in this way are not to bedepended upon as it is known that the transfer rate is not independentof the temperature. Again, if the transfer rate is assumed as varyingdirectly with the weight of the gases passing, which is Reynolds'suggestion, it is seen that the weight of the gases entirely disappearsfrom the formula and as a consequence if the formula was correct, aslong as the temperature of the gas entering the surface from the furnacewas the same, the temperatures throughout the setting would be the same. This is known also to be incorrect. If, however, in place of T iswritten T_{2} and in place of s is written S, the entire surface of theboiler, and the formula is re-arranged, it becomes: _ _ WC | T_{1} - t |R = --- Log[89]| --------- | S |_ T_{2} - t _| This formula can be considered as giving a way of calculating an averagetransfer rate. It has been used in this way for calculating the averagetransfer rate from boiler tests in which the capacity has varied from anevaporation of a little over 3 pounds per square foot of surface up to15 pounds. When plotted against the gas weights, it was found that thepoints were almost exactly on a line. This line, however, did not passthrough the zero point but started at a point corresponding toapproximately a transfer rate of 2. Checked out against many othertests, the straight line law seems to hold generally and this is trueeven though material changes are made in the method of calculating thefurnace temperature. The inclination of the line, however, variedinversely as the average area for the passage of the gas through theboiler. If A is the average area between all the passes of the boiler, the heat transfer rate in Babcock & Wilcox type boilers with ordinaryclean surfaces can be determined to a rather close approximation fromthe formula: WR = 2. 00 + . 0014 - A The manner in which A appears in this formula is the same as it wouldappear in any formula in which the heat transfer rate was taken asdepending upon the product of the velocity and the density of the gasjointly, since this product, as pointed out above, is equivalent to W/A. Nusselt's experiments, as well as those of others, indicate that theratio appears in the proper way. While the underlying principles from which the formula for this averagetransfer rate was determined are questionable and at best onlyapproximately correct, it nevertheless follows that assuming thetransfer rate as determined experimentally, the formula can be used inan inverse way for calculating the amount of surface required in aboiler for cooling the gases through a range of temperature covered bythe experiments and it has been found that the results bear out thisassumption. The practical application of the theory of heat transfer, asdeveloped at present, seems consequently to rest on these last twoformulae, which from their nature are more or less empirical. Through the range in the production of steam met with in boilers now inservice which in the marine type extends to the average evaporation of12 to 15 pounds of water from and at 212 degrees Fahrenheit per squarefoot of surface, the constant 2 in the approximate formula for theaverage heat transfer rate constitutes quite a large proportion of thetotal. The comparative increase in the transfer rate due to a change inweight of the gases is not as great consequently as it would be if thisconstant were zero. For this reason, with the same temperature of thegases entering the boiler surface, there will be a gradual increase inthe temperature of the gases leaving the surface as the velocity orweight of flow increases and the proportion of the heat contained in thegases entering the boiler which is absorbed by it is gradually reduced. It is, of course, possible that the weight of the gases could beincreased to such an amount or the area for their passage through theboiler reduced by additional baffles until the constant term in the heattransfer formula would be relatively unimportant. Under such conditions, as pointed out previously, the final gas temperature would be unaffectedby a further increase in the velocity of the flow and the fraction ofthe heat carried by the gases removed by the boiler would be constant. Actual tests of waste heat boilers in which the weight of gas per squarefoot of sectional area for its passage is many times more than inordinary installations show, however, that this condition has not beenattained and it will probably never be attained in any practicalinstallation. It is for this reason that the conclusions of Dr. Nicholson in the paper referred to and of Messrs. Kreisinger and Ray inthe pamphlet "The Transmission of Heat into Steam Boilers", published bythe Department of the Interior in 1912, are not applicable withoutmodification to boiler design. In superheaters the heat transfer is effected in two different stages;the first transfer is from the hot gas to the metal of the superheatertube and the second transfer is from the metal of the tube to the steamon the inside. There is, theoretically, an intermediate stage in thetransfer of the heat from the outside to the inside surface of the tube. The conductivity of steel is sufficient, however, to keep thetemperatures of the two sides of the tube very nearly equal to eachother so that the effect of the transfer in the tube itself can beneglected. The transfer from the hot gas to the metal of the tube takesplace in the same way as with the boiler tubes proper, regard being paidto the temperature of the tube which increases as the steam is heated. The transfer from the inside surface of the tube to the steam is theinverse of the process of the transfer of the heat on the outside andseems to follow the same laws. The transfer rate, therefore, willincrease with the velocity of the steam through the tube. For thisreason, internal cores are quite often used in superheaters and actuallyresult in an increase in the amount of superheat obtained from a givensurface. The average transfer rate in superheaters based on a differencein mean temperature between the gas on the outside of the tubes and thesteam on the inside of the tubes is if R is the transfer rate from thegas to the tube and r the rate from the tube to the steam: Rr ----- R + r and is always less than either R or r. This rate is usually greater thanthe average transfer rate for the boiler as computed in the way outlinedin the preceding paragraphs. Since, however, steam cannot, under anyimagined set of conditions, take up more heat from a tube than wouldwater at the same average temperature, this fact supports the contentionmade that the actual transfer rate in a boiler must increase quiterapidly with the temperatures. The actual transfer rates in superheatersare affected by so many conditions that it has not so far been possibleto evolve any formula of practical value. [Illustration: Iron City Brewery of the Pittsburgh Brewing Co. , Pittsburgh, Pa, Operating in this Plant 2000 Horse Power of Babcock &Wilcox Boilers] INDEX PAGE Absolute pressure 117Absolute zero 80Accessibility of Babcock & Wilcox boiler 59Acidity in boiler feed water 106Actual evap. Corresponding to boiler horse power 288Advantages of Babcock & Wilcox boilers 61 Stoker firing 195 Water tube over fire tube boilers 61Air, composition of 147 In boiler feed water 106 Properties of 147 Required for combustion 152, 156 Specific heat of 148 Supplied for combustion 157 Vapor in 149 Volume of 147 Weight of 147Alkalinity in boiler feed water 103 Testing feed for 103Altitude, boiling point of water at 97 Chimney sizes corrected for 248Alum in feed water treatment 106A. S. M. E. Code for boiler testing 267Analyses, comparison of proximate and ultimate 183 Proximate coal, and heating values 177Analysis, coal, proximate, methods of 176 Coal, ultimate 173 Determination of heating value from 173Analysis, Flue gas 155 Flue gas, methods of 160 Flue gas, object of 155Anthracite coal 166 Combustion rates with 246 Distribution of 167 Draft required for 246 Firing 190 Grate ratio for 191 Semi 166 Sizes of 190 Steam as aid to burning 191 Thickness of fires with 191Arches, fire brick, as aid to combustion 190 Fire brick, for 304 Fire brick, laying 305Automatic stokers, advantages of 195 Overfeed 196 Traveling grate 197 Traveling grate, Babcock & Wilcox 194 Underfeed 196Auxiliaries, exhaust from, in heating feed water 113 Superheated steam with 142Auxiliary grates, with blast furnace gas 228 With oil fuel 225 With waste heat 235Babcock, G. H. , lecture on circulation of water in Boilers 28 Lecture on theory of steam making 92Babcock & Wilcox Co. , Works at Barberton, Ohio 7 Works at Bayonne, N. J. 6Babcock & Wilcox boiler, accessibility of 59 Advantages of 61 Circulation of water in 57, 66 Construction of 49 Cross boxes 50 Cross drum 53 Cross drum, dry steam with 71 Drumheads 49 Drums 49 Durability 75 Evolution of 39 Fittings 55 Fixtures 55 Fronts 53 Handhole fittings 50, 51 Headers 50, 51 Inclined header, wrought steel 54 Inspection 75 Life of 76 Materials entering into the construction of 59 Mud drums 51 Path of gases in 57 Path of water in 57 Rear tube doors of 53, 74 Repairs 75 Safety of 66 Sections 50 Set for utilizing waste heat 236 Set with Babcock & Wilcox chain grate stoker 12 Set with bagasse furnace 208 Set with Peabody oil furnace 222 Supports, cross drum 53 Supports, longitudinal drum 52 Tube doors 53 Vertical header, cast iron 58 Vertical header, wrought steel 48Babcock & Wilcox chain grate stoker 194Babcock & Wilcox superheater 136Bagasse, composition of 206 Furnace 209 Heat, value of 206 Tests of Babcock & Wilcox boilers with 210 Value of diffusion 207Barium carbonate in feed water treatment 106Barium hydrate in feed water treatment 106Barrus draft gauge 254Bituminous coal, classification of 167 Combustion rates with 246 Composition of 177 Distribution of 168 Firing methods 193 Semi 166 Sizes of 191 Thickness of fire with 193Blast furnace gas, burners for 228 Combustion of 228 Composition of 227 Stacks for 228Boiler, Blakey's 23 Brickwork, care of 307 Circulation of water in steam 28 Compounds 109 Development of water tube 23 Eve's 24 Evolution of Babcock & Wilcox 39 Fire tube, compared with water tube 61 Guerney's 24 Horse power 263 Loads, economical 283 Perkins' 24 Room piping 108 Room practice 297 Rumsey's 23 Stevens', John 23 Stevens', John Cox 23 Units, number of 289 Units, size of 289 Wilcox's 25 Woolf's 23Boilers, capacity of 278 Care of 291 Efficiency of 256 Horse power of 265 Operation of 291 Requirements of steam 27 Testing 267Boiling point 86 Of various substances 86 Of water as affected by altitude 97Brick, fire 304 Arches 305 Classification of 304 Compression of 303 Expansion of 303 Hardness of 303 Laying up 305 Nodules, ratio of 303 Nodules, size of 303 Plasticity of 302Brick, red 302Brickwork, care of 307British thermal unit 83Burners, blast furnace gas 228 By-product coke oven gas 231 Natural gas 231 Oil 217 Oil, capacity of 221 Oil, mechanical atomizing 219 Oil, operation of 223 Oil, steam atomizing 218 Oil, steam consumption of 220Burning hydrogen, loss due to moisture formed in 261By-product coke oven gas burners 231By-product coke oven gas, combustion of 231By-product coke oven gas, composition and heat value of 231Calorie 83Calorific value (see Heat value). Calorimeter, coal, Mahler bomb 184 Mahler bomb, method of correction 187 Mahler bomb, method of operation of 185Calorimeter, steam, compact type of throttling 132 Correction for 131 Location of nozzles for 134 Normal reading 131 Nozzles 134 Separating 133 Throttling 129Capacity of boilers 264, 278 As affecting economy 276 Economical loads 283 With bagasse 210 With blast furnace gas 228 With coal 280 With oil fuel 224Capacity of natural gas burners 229Capacity of oil burners 221Carbon dioxide in flue gases 154 Unreliability of readings taken alone 162Carbon, fixed 165 Incomplete combustion of, loss due to 158 Monoxide, heat value of 151 Monoxide, in flue gases 155 Unconsumed in ash, loss due to 261Care of boilers when out of service 300Casings, boilers 307Causticity of feed water 103 Testing for 105Celsius thermometer scale 79Centigrade thermometer scale 79Chain grate stoker, Babcock & Wilcox 194Chemicals required in feed water treatment 105Chimney gases, losses in 158, 159Chimneys (see Draft). Correction in dimensions for altitude 248 Diameter of 243 Draft available from 241 Draft loss in 239 For blast furnace gas 253 For oil fuel 251 For wood fuel 254 Height of 243 Horse power they will serve 250Circulation of water in Babcock & Wilcox boilers 57, 66 Of water in steam boilers 28 Results of defective 62, 66, 67Classification of coals 166 Fire brick 304 Feed water difficulties 100 Fuels 165Cleaners, turbine tube 299Cleaning, ease of, Babcock & Wilcox boilers 73Closed feed water heaters 111Coal, Alaska 169 Analyses and heat value 177 Analysis, proximate 176 Analysis, ultimate 173 Anthracite 166 Bituminous 167 Cannel 167 Classification of 165, 166 Combustion of 190 Comparison with oil 214 Consumption, increase due to superheat 139 Distribution of 167 Formation of 165 Lignite 167 Records 293 Semi-anthracite 166 Semi-bituminous 166 Sizes of anthracite 190 Sizes of bituminous 191Code of A. S. M. E. For boiler testing 267Coefficient of expansion of various substances 87Coke 171 Oven gas, by-product, burners 231 Oven gas, by-product, combustion of 231 Oven gas, by-product, composition and heat value of 231Coking method of firing 195Color as indication of temperature 91Combination furnaces 224Combustible in fuels 150Combustion 150 Air required for 152, 156 Air supplied for 157Combustion of coal 190 Of gaseous fuels 227 Of liquid fuels 212 Of solid fuels other than coal 201Composition of bagasse 205 Blast furnace gas 227 By-product coke oven gas 231 Coals 177 Natural gas 229 Oil 213 Wood 201Compounds, boiler 109Compressibility of water 97Compression of fire brick 303Condensation, effect of superheated steam on 140 In steam pipes 313Consumption, heat, of engines 141Correction, stem, for thermometers 80 For normal reading in steam calorimeter 131 For radiation, bomb calorimeter 187Corrosion 101, 106Coverings, pipe 315Cross drum, Babcock & Wilcox boiler 52, 53, 60 Dry steam with 71Draft area as affecting economy in Babcock & Wilcox boilers 70 Available from chimneys 241Draft loss in chimneys 239 Loss in boilers 245 Loss in flues 243 Loss in furnaces 245Draft required for anthracite 246 Required for various fuels 246Drums, Babcock & Wilcox, cross 53 Cross, boxes 50 Heads 49 Longitudinal 49 Manholes 49 Nozzles on 50Dry steam in Babcock & Wilcox boilers 71Density of gases 147 Steam 115Dulong's formula for heating value 173Ebullition, point of 86Economizers 111Efficiency of boilers, chart of 258 Combustible basis 256 Dry coal basis 256 Increase in, due to superheaters 139 Losses in (see Heat balance) 259 Testing 267 Test _vs. _ operating 278 Variation in, with capacity 284 With coal 288 With oil 224Ellison draft gauge 254Engine, Hero's 13Engines, superheated steam with 141Equivalent evaporation from and at 212 degrees 116Eve's boiler 24Evolution of Babcock & Wilcox boiler 39Exhaust steam from auxiliaries 113Expansion, coefficient of 87 Of fire brick 303 Of pipe 315 Pyrometer 89Factor of evaporation 117Fahrenheit thermometer scale 79Fans, use of, in waste heat work 233Feed water, air in 106 As affecting capacity 279 Boiler 100Feed water heaters, closed 111 Economizers 111 Open 111Feed water heating, methods of 111 Saving by 110Feed water, impurities in 100 Lines 312 Method of feeding 110Feed water treatment 102 Chemical 102 Chemical, lime and soda process 102 Chemical, lime process 102 Chemical, soda process 102 Chemicals used in lime and soda process 105 Combined heat and chemical 105 Heat 102 Less usual reagents 106Firing, advantages of stoker 195 Methods for anthracite 190 Bituminous 193 Lignite 195Fittings, handhole in Babcock & Wilcox boilers 50, 51 Pipe 311 Superheated steam 145 With Babcock & Wilcox boilers 55Fixtures with Babcock & Wilcox boilers 55Flanges, pipe 309Flow of steam into pressure above atmosphere 317 Into the atmosphere 328 Through orifices 317 Through pipes 317Flue gas analysis 155 Conversion of volumetric to weight 161 Methods of making 160 Object of 155 Orsat apparatus 159Flue gas, composition of 155 Losses in 158, 159 Weight per pound of carbon in fuel 158 Weight per pound of fuel 158 Weight resulting from combustion 157Foaming 102, 107Fuel analysis, proximate 176 Ultimate 173Fuel calorimeter, Mabler bomb 184Tests, method of making 186Fuels, classification of 165 Gaseous, and their combustion 227Fuels, liquid, and their combustion 212 Solid, coal 190 Solid, other than coal 201Furnace, bagasse 209 Blast furnace gas 228 By-product coke oven gas 231 Combination wood and oil 225 Efficiency of 283 Natural gas 229 Peabody oil 222 Webster 55 Wood burning 201, 202Galvanic action 107Gas, blast furnace, burners 228 Combustion of 228 Composition of 227Gas, by-product coke oven, burners 231 Combustion of 231 Composition of and heat value 231Gas, natural, burners 229 Combustion of 229 Composition and heat value of 229Gases, chimney, losses in 158, 159 Density of 163 Flue (see Flue gases). Path of in Babcock & Wilcox boilers 57 Waste (see Waste heat) 232Gaskets 312Gauges, draft, Barrus 254 Ellison 255 Peabody 255 U-tube 254Gauges, vacuum 117Grate ratio for anthracite 191Gravity of oils 214Grooving 102Guerney's boiler 24Handhole fittings for Babcock & Wilcox boilers 50, 51Handholes in Babcock & Wilcox boilers 50, 51Hardness of boiler feed water 102 Permanent 102 Temporary 102 Testing for 105Hardness of fire brick 303Heat and chemical methods of treating feed water 105 And its measurement 79 Balance 262 Consumption of engines 141 Latent 84 Of liquid 120 Sensible 84 Specific (see Specific heat) 83 Total 86 Transfer 323Heat value of bagasse 205 By-product coke oven gas 231 Coal 177Heat value of fuels, determination of 173 Determination of Kent's approximate method 183 High and low 174Heat value of natural gas 229 Oil 215 Wood 201Heat waste (see Waste heat) 232Heaters, feed water, closed 111 Economizers 111 Open 111Heating feed water, saving by 110Hero's engine 13High and low heat value of fuels 174High pressure steam, advantages of use of 119High temperature measurements, accuracy of 89Horse power, boiler 265 Evaporation (actual) corresponding to 288 Rated boiler 265 Stacks for various, of boilers 250Hydrogen in flue gases 156Ice, specific heat of 99"Idalia", tests with superheated steam on yacht 143Impurities in boiler feed water 100Incomplete combustion of carbon, loss due to 158Injectors, efficiency of 112 Relative efficiency of, and pumps 112Iron alum in feed water treatment 106Kent, Wm. , determination of heat value from analysis 183 Stack table 250Kindling point 150Latent heat 84, 115Laying of fire brick 305 Red brick 305Lignite, analyses of 181 Combustion of 195Lime and soda treatment of boiler feed 102 Used in chemical treatment of feed 105Lime treatment of boiler feed water 102Liquid fuels and their combustion 212Loads, economical boiler 283Losses due to excess air 158 Due to unburned carbon 158 Due to unconsumed carbon in the ash 261Losses in efficiency (see Heat balance). In flue gases 158, 159Low water in boilers 298Melting points of metals 91Mercurial pyrometers 89Moisture in coal, determination of 176 In fuels, losses due to 259 In steam, determination of 129Mud drum of Babcock & Wilcox boiler 51Napier's formula for flow of steam 321Natural gas, burners for 229 Combustion of 229 Composition and heat value of 229Nitrate of silver in testing feed water 105Nitrogen, as indication of excess air 157 In air 147 In flue gases 157Nodules, fire brick, ratio of 303 Size of 303Normal reading, throttling calorimeter 131Nozzles, steam sampling for calorimeter 134 Location of 134Oil fuel, burners (see Burners). Capacity with 224 Combustion of 217 Comparison with coal 214 Composition and heat value of 213 Efficiency with 224 Furnaces for 221 Gravity of 214 In combination with other fuels 224 Stacks for 251 Tests with 224Open hearth furnace, Babcock & Wilcox boiler set for utilizing waste heat from 236Open heaters, feed water 111Operation of boilers 291Optical pyrometers 91Orsat apparatus 160Oxalate of soda in feed water treatment 106Oxygen in air 147 Flue gases 155Peabody draft gauge 255 Formulae for coal calorimeter correction 188 Furnace for oil fuel 221, 222 Oil burner 218Peat 167Perkins' boiler 24Pfaundler's method of coal calorimeter radiation correction 187Pipe coverings 315 Data 308 Expansion of 315Pipe fittings 311 Flanges 309 Flow of steam through 317 Radiation from bare and covered 314 Sizes 312 Supports for 315Piping, boiler room 308Pitting 102Plant records, coal 293 Draft 294 Temperature 294 Water 293Plasticity of fire brick 302Pressed fuels 171Priming in boilers 102 Methods of treating for 107Properties of water 96Proximate analyses of coal 177Proximate analysis 173 Method of making 176Pulverized fuels 170Pump, efficiency of feed 112Pyrometers, expansion 89 Mercurial 89 Optical 91 Radiation 90 Thermo-electric 90Quality of steam 129Radiation correction for coal calorimeter 187, 188 Correction for steam calorimeter 131 Effect of superheated steam on 140 From pipes 314 Losses in efficiency due to 307 Pyrometers 90Ratio of air supplied to that required for combustion 157Reagents, less usual in feed treatment 106Records, plant, coal 293 Draft 294 Temperature 294 Water 293Requirements of steam boilers 27 As indicated by evolution of Babcock & Wilcox 45Rumsey's boiler 23Safety of Babcock & Wilcox boilers 66Salts responsible for scale 101 Solubility of 101Sampling coal 271 Nozzles for steam 134 Nozzles for steam, location of 134 Steam 134 Steam, errors in 135Saturated air 149Saving by heating feed 110 With superheat in "Idalia" tests 143 With superheat in prime movers 140, 142Scale (see Thermometers) 101Sea water, composition of 97Sections, Babcock & Wilcox boiler 50Selection of boilers 277Sensible heat 84Separating steam calorimeter 132Sizes of anthracite coal 190 Bituminous coal 191Smoke, methods of eliminating 197Smokelessness, relative nature of 197 With hand-fired furnaces 199 With stoker-fired furnaces 199Soda, lime and, treatment of feed 103 Oxalate of, in treatment of feed 106 Removal of scale aided by 300 Silicate of, in treatment of feed 106 Treatment of boiler feed 103Space occupied by Babcock & Wilcox boilers 66Specific heat 83Specific heat of air 148 Ice 99 Saturated steam 99Specific heat of superheated steam 137 Various solids, liquids and gases 85 Water 99Spreading method of firing 193Stacks and draft (see Chimneys) 237Stacks for blast furnace gas 228 Oil fuel 251 Wood 202, 254Stayed surfaces, absence of, in Babcock & Wilcox boilers 69 Difficulties arising from use of 67Steam 115 As aid to combustion of anthracite 191 As aid to combustion of lignite 195 Consumption of prime movers 289 Density of 115 Flow of, into atmosphere 320 Flow of, into pressure above atmosphere 318 Flow of, through pipes 317 High pressure, advantage of 119 History of generation and use of 13 Making, theory of 92 Moisture in 129 Properties of, for vacuum 119 Properties of saturated 122 Properties of superheated 125 Quality of 129 Saturated 115 Specific heat of saturated 99 Specific heat of superheated 137 Specific volume of 115 Superheated 137 Superheaters (see Superheated steam). Steaming, quick, with Babcock & Wilcox boilers 73Stem Correction, thermometer 80Stevens, John, boiler 23Stevens, John Cox, boiler 23Stokers, automatic, advantages of 195 Babcock & Wilcox chain grate 194 Overfeed 196 Smokelessness with 199 Traveling grate 197 Underfeed 196Superheated steam 137 Additional fuel for 139 Effect on condensation 140 Effect on radiation 140 Fittings for use with 145 "Idalia" tests with 143 Specific heat of 137 Variation in temperature of 145 With turbines 142Superheater, Babcock & Wilcox 136 Effect of on boiler efficiency 139Supports, Babcock & Wilcox boiler 52, 53Tan bark 210Tar, water gas 225Temperature, accuracy of high, measurements 89 As indicated by color 91 Of waste gases 232 Records 294Test conditions _vs. _ operating conditions 278Testing, boiler, A. S. M. E. Code for 267Tests of Babcock & Wilcox boilers with bagasse 210 Coal 280 Oil 224Theory of steam making 92Thermo-electric pyrometers 90Thermometer scale, celsius 79Thermometer scale, centigrade 76 Fahrenheit 79 Réaumur 79Thermometer scales, comparison of 80 Conversion of 80Thermometer stem correction for 80Thermometers, glass for 79Throttling calorimeter 129Total heat 86, 115Treatment of boiler feed water (see Feed water) 102 Chemicals used in 105 Less usual reagents in 106Tube data 309 Doors in Babcock & Wilcox boilers 53 Tubes in Babcock & Wilcox boilers 50Ultimate analyses of coal 183 Analysis of fuels 173Unaccounted losses in efficiency 261Unconsumed carbon in ash 261Units, boiler, number of 289 Size of 289Units, British thermal 83Unreliability of CO_{2} readings alone 162Vacuum gauges 117 Properties of steam for 119Valves used with superheated steam 312Variation in properties of saturated steam 119 Superheat from boilers 145Volume of air 147 Water 96Volume, specific, of steam 115Waste heat, auxiliary grates with boilers for 235 Babcock & Wilcox boilers set for use with 236 Boiler design for 233 Curve of temperature, heat absorption, and heating surface 235 Draft for 233 Fans for use with 233 Power obtainable from 232 Temperature of, from various processes 232 Utilization of 232Water, air in boiler feed 106 Boiling points of 97 Compressibility of 97Water feed, impurities in 100 Methods of feeding to boiler 132 Saving by heating 110 Treatment (see Feed water). Water-gas tar 225 Heat of the liquid 120 Path of, in Babcock & Wilcox boilers 57 Properties of 96 Records 293 Specific heat of 99 Volume of 96 Weight of 96, 120Watt, James 17Weathering of coal 169Webster furnace 55Weight of air 147Wilcox boiler 25Wood, combustion of dry 202 Wet 203 Composition and heat value of 201 Furnace design for 201 Moisture in 201 Sawmill refuse 202Woolf s boiler 24Zero, absolute 81 FOOTNOTES [Footnote 1: See discussion by George H. Babcock, of Stirling's paper on"Water-tube and Shell Boilers", in Transactions, American Society ofMechanical Engineers, Volume VI. , Page 601. ] [Footnote 2: When one temperature alone is given the "true" specificheat is given; otherwise the value is the "mean" specific heat for therange of temperature given. ] [Footnote 3: For variation, see Table 13. ] [Footnote 4: Where range of temperature is given, coefficient is meanover range. ] [Footnote 5: Coefficient of cubical expansion. ] [Footnote 6: Le Chatelier's Investigations. ] [Footnote 7: Burgess-Le Chatelier. ] [Footnote 8: For accuracy of high temperature measurements, see Table7. ] [Footnote 9: Messrs. White & Taylor Trans. A. S. M. E. , Vol. XXI, 1900. ] [Footnote 10: See Scientific American Supplement, 624, 625, December, 1887. ] [Footnote 11: 460 degrees below the zero of Fahrenheit. This is thenearest approximation in whole degrees to the latest determinations ofthe absolute zero of temperature] [Footnote 12: Marks and Davis] [Footnote 13: See page 120. ] [Footnote 14: See Trans. , A. S. M. E. , Vol. XIV. , Page 79. ] [Footnote 15: Some waters, not naturally acid, become so at hightemperatures, as when chloride of magnesia decomposes with the formationof free hydrochloride acid; such phenomena become more serious with anincrease in pressure and temperature. ] [Footnote 16: L. M. Booth Company. ] [Footnote 17: Based on lime containing 90 per cent calcium oxide. ] [Footnote 18: Based on soda containing 58 per cent sodium oxide. ] [Footnote 19: See Stem Correction, page 80. ] [Footnote 20: See pages 125 to 127. ] [Footnote 21: The actual specific heat at a particular temperature andpressure is that corresponding to a change of one degree one way or theother and differs considerably from the average value for the particulartemperature and pressure given in the table. The mean values given inthe table give correct results when employed to determine the factor ofevaporation whereas the actual values at the particular temperatures andpressures would not. ] [Footnote 22: See page 117. ] [Footnote 23: Ratio by weight of O to N in air. ] [Footnote 24: 4. 32 pounds of air contains one pound of O. ] [Footnote 25: Per pound of C in the CO. ] [Footnote 26: Ratio by volume of O to N in air. ] [Footnote 27: Available hydrogen. ] [Footnote 28: See Table 31, page 151. ] [Footnote 29: This formula is equivalent to (10) given in chapter oncombustion. 34. 56 = theoretical air required for combustion of one poundof H (see Table 31). ] [Footnote 30: For degree of accuracy of this formula, see Transactions, A. S. M. E. , Volume XXI, 1900, page 94. ] [Footnote 31: For loss per pound of coal multiply by per cent of carbonin coal by ultimate analysis. ] [Footnote 32: For loss per pound of coal multiply by per cent of carbonin coal by ultimate analysis. ] [Footnote 33: The Panther Creek District forms a part of what is knownas the Southern Field; in the matter of hardness, however, these coalsare more nearly akin to Lehigh coals. ] [Footnote 34: Sometimes called Western Middle or Northern SchuylkillField. ] [Footnote 35: Geographically, the Shamokin District is part of theWestern Middle Mahanoy Field, but the coals found in this sectionresemble more closely those of the Wyoming Field. ] [Footnote 36: See page 161. ] [Footnote 37: U. S. Geological Survey. ] [Footnote 38: See "Steam Boiler Economy", page 47, First Edition. ] [Footnote 39: To agree with Pfaundler's formula the end ordinates shouldbe given half values in determining T", _i. E. _, T" = ((Temp. At B +Temp. At C) ÷ 2 + Temp. All other ordinates) ÷ N] [Footnote 40: B. T. U. Calculated. ] [Footnote 41: Average of two samples. ] [Footnote 42: Assuming bagasse temperature = 80 degrees Fahrenheit andexit gas temperature = 500 degrees Fahrenheit. ] [Footnote 43: Dr. Henry C. Sherman. Columbia University. ] [Footnote 44: Includes N. ] [Footnote 45: Includes silt. ] [Footnote 46: Net efficiency = gross efficiency less 2 per cent forsteam used in atomizing oil. Heat value of oil = 18500 B. T. U. One ton of coal weighs 2000 pounds. One barrel of oil weighs 336 pounds. One gallon of oil weighs 8 pounds. ] [Footnote 47: Average of 20 samples. ] [Footnote 48: Includes H and CH_{4}. ] [Footnote 49: B. T. U. Approximate. For method of calculation, see page175. ] [Footnote 50: Temperatures are average over one cycle of operation andmay vary widely as to maximum and minimum. ] [Footnote 51: Dependant upon length of kiln. ] [Footnote 52: Results secured by this method will be approximatelycorrect. ] [Footnote 53: See "Chimneys for Crude Oil", C. R. Weymouth, Trans. A. S. M. E. , Dec. 1912. ] [Footnote 54: To determine the portion of the fuel which is actuallyburned, the weight of ashes should be computed from the total weight ofcoal burned and the coal and ash analyses in order to allow for any ashthat may be blown away with the flue gases. In many cases the ash socomputed is considerably higher than that found in the test. ] [Footnote 55: As distinguished from the efficiency of boiler, furnaceand grate. ] [Footnote 56: To obtain the efficiency of the boiler as an absorber ofthe heat contained in the hot gases, this should be the heat generatedper pound of combustible corrected so that any heat lost throughincomplete combustion will not be charged to the boiler. This, however, does not eliminate the furnace as the presence of excess air in thegases lowers the efficiency and the ability to run without excess airdepends on the design and operation of the furnace. The efficiency basedon the total heat value per pound of combustible is, however, ordinarilytaken as the efficiency of the boiler notwithstanding the fact that itnecessarily involves the furnace. ] [Footnote 57: See pages 280 and 281. ] [Footnote 58: Where the horse power of marine boilers is stated, itgenerally refers to and is synonymous with the horse power developed bythe engines which they serve. ] [Footnote 59: In other countries, boilers are ordinarily rated not inhorse power but by specifying the quantity of water they are capable ofevaporating from and at 212 degrees or under other conditions. ] [Footnote 60: See equivalent evaporation from and at 212 degrees, page116. ] [Footnote 61: The recommendations are those made in the preliminaryreport of the Committee on Power Tests and at the time of going to presshave not been finally accepted by the Society as a whole. ] [Footnote 62: This code relates primarily to tests made with coal. ] [Footnote 63: The necessary apparatus and instruments are describedelsewhere. No definite rules can be given for location of instruments. For suggestions on location, see A. S. M. E. Code of 1912, Appendix 24. For calibration of instruments, see Code, Vol. XXXIV, Trans. , A. S. M. E. , pages 1691-1702 and 1713-14. ] [Footnote 64: One to two inches for small anthracite coals. ] [Footnote 65: Do not blow down the water-glass column for at least onehour before these readings are taken. An erroneous indication mayotherwise be caused by a change of temperature and density of the waterwithin the column and connecting pipe. ] [Footnote 66: Do not blow down the water-glass column for at least onehour before these readings are taken. An erroneous indication mayotherwise be caused by a change of temperature and density of the waterwithin the column and connecting pipe. ] [Footnote 67: For calculations relating to quality of steam, see page129. ] [Footnote 68: Where the coal is very moist, a portion of the moisturewill cling to the walls of the jar, and in such case the jar and fueltogether should be dried out in determining the total moisture. ] [Footnote 69: Say ½ ounce to 2 ounces. ] [Footnote 70: For methods of analysis, see page 176. ] [Footnote 71: For suggestions relative to Smoke Observations, seeA. S. M. E. Code of 1912, Appendix 16 and 17. ] [Footnote 72: The term "as fired" means actual condition includingmoisture, corrected for estimated difference in weight of coal on thegrate at beginning and end. ] [Footnote 73: Corrected for inequality of water level and steam pressureat beginning and end. ] [Footnote 74: See Transactions, A. S. M. E. , Volume XXXIII, 1912. ] [Footnote 75: For methods of determining, see Technologic Paper No. 7, Bureau of Standards, page 44. ] [Footnote 76: Often called extra heavy pipe. ] [Footnote 77: See Feed Piping, page 312. ] [Footnote 78: See Superheat Chapter, page 145. ] [Footnote 79: See Radiation from Steam Lines, page 314. ] [Footnote 80: D, the density, is taken as the mean of the density at theinitial and final pressures. ] [Footnote 81: Diameters up to 5 inches, inclusive, are _actual_diameters of standard pipe, see Table 62, page 308. ] [Footnote 82: Diameters up to 4 inches, inclusive, are _actual_ internaldiameters, see Table 62, page 308. ] [Footnote 83: H. P. Jordan, "Proceedings of the Institute of MechanicalEngineers", 1909. ] [Footnote 84: "Zeitschrift des Vereines Deutscher Ingenieur", 1909, page1750. ] [Footnote 85: Heinrich Gröber--Zeit. D. Ver. Ing. , March 1912, December1912. Leprince-Ringuet--Revue de Mecanique. July 1911. John Perry--"TheSteam Engine". T. E. Stanton--Philosophical Transactions, 1897. Dr. J. T. Nicholson--Proceedings Institute of Engineers & Shipbuilders inScotland, 1910. W. E. Dally--Proceedings Institute of MechanicalEngineers, 1909. ] [Footnote 86: Proceedings Royal Society, Vol. LXXI. ] [Footnote 87: Zeitschrift des Vereines Deutscher Ingenieur, 1910, page1154. ] [Footnote 88: Proceedings Institute of Engineers and Shipbuilders, 1910. ] [Footnote 89: Natural or Hyperbolic Logarithm. ]