US2639695A - Vapor generator - Google Patents

Description

May 2 59 1953 L. H; CQYKENDALL VAPOR GENERATOR Filed Nov. 5, 1949 s Shets-Sheet 1 Rial-2i 1 iii w h rlxilllllaLllll INVENTOR Leon H Coykendai/ ATTORNEY y 6, 1953 a... H. COYKENDALL 2,639,695

' VAPOR GENERATOR ATTORNEY L. H'. COYKENDALL 2,639,695

May 26, 1953 VAPOR GENERATOR Filed Nov. 5, 1949 5 Sheets-Sheet 3 N M v 3 V? 45v 419 57. i EZg /M INVENTOR L eon H Coykendal/ Patented May 26, 1953 Leon H. Coykendall, w estfielfl, N- L, 'as signor to The'Babcock & Wilcox Company, New York, N. Y., a corporation of NewJersey- Application November 5, 1949, SerialNol 125,756

The present invention relates in general to the construction and operation of vapor generators and more particularly, to fuel-fired steam generators or boilers of the water tube. type having provision for heating air required 'for the com- 2' Claims. 1. 122- 1) bustion of fuel in an associated furnace. In the practice of my invention, I contemplate, among various permissible embodiments, a form of water tube steam boiler having a large proportion of its heating surface in the form of upright steam generating tubes arranged laterallyofthe furnace combustion chamber and disposed in successive gas passes through which'the h'ot gaseous products of combustion are directed in series along a substantially horizontal gas flow path. The complete boiler unit may also include a superheater disposed intermediate groups of boiler tubes in one or more of the passes and, foradequate efiicieney at high ratings, may further'i'nclude additional tubular heating surface in the form of a boiler feed water heater or economizer disposed in the path of the heating gasese'ither before or after the gases are disch'arged'from the boiler setting.

According to customary prior practice, the total quantity of gases generated in the boiler furnace is directed over all boiler, :superheater "and" economizer surface and thereafter, at the resulting reduced temperature, is directed over air heater surface prior to final discharge to the stack.. In conventional forms ofair heaters, wherein heat is transferred from combustion gases to combustion air, the transfer of heatis effected through the medium of metallic heat transfer elements either in the form of spaced tubes or plates.

Each such heat transfer element 135 provides opposite surface areas'which, in the re cuperative type of air heater, arecontactedfby the respective fluids, gas and air, simultaneously,

whereas, in the regenerative type of air heater, for corresponding elements or material, all major-ex terior surface areas thereof are contacted by the gas during one period of operation, and by the air during another period of operation; In either tion' of airflow to gas flow is ordinarily main-'-- type of air heater, generallycounterflow relatained so as to provide the maximum rate of heat transfer from one fluid to the other. I In the operation of an'air heater, .ofbeither of the above mentioned types, it is known that those portions of the heat transfer. elements ad-n jacent the cold air inlet are subject to fairly rapid corrosion unless the air heater is operated so as to maintain all portions of such elements ad-J jacent the-air inlet zone at temperatures high.

enough to prevent the condensation of vapors flowing in contact therewith. The corrosive ef-' fect mentioned is generally the result'of the con-U; densation of water vapor carried by the heating gases flowing. in contact with the metallic heat transfer surfaces, combined with the presence of a gaseous constituent such as sulphur dioxide resulting'from.combustion of thefuel by which.

the gases are generated. Condensation of the aqueous vap'or also maintains the low temperature surfaces in :amoist condition which is conduciveto the collection of dust, particles thereon and tog, a consequent decrease inheat transferyefficiencyr When the gas-flow passages are of relatively small area or width, and, particle carrying gases are directed therethrough, such passages are liable to become plugged and the effectiveness of the heat,

transfer elements thus completely nullified.

The condensation is promoted when the metal of certain portions of the heat transfer elements is compelled to operate continuously at relatively low temperatures; for example, in an air heater of therecuperative type, those portions ofthe tubes or plates adjacent the cooler gas exit end, due to the continuous contact of cold inlet air with one surface, and to the continuous contact of cooled gases with the opposite surface. Similarly, in anair heater of the'regenerative type, those portions of the heat transfer elements or material most susceptible to corrosion due to low temperature operation'are the portions which, during alternate periods of operation are adjacent the-gas Outlet zone and thus swept throughout by cooled outgoing gases,'and' during the remain- I ing alternate periods'of operation are adjacent the'air inlet, zone and thus similarly swept by the cold entering, air. 1

My invention is therefore concerned with an improved form of vapor generator or boiler wherebycombustion gases of adequately high temperature are made available for use as the heating fluid in a heat exchanger located exteriorly of the boilersetting; the purpose being to maintain the metal of the heattransfer elements above the temperature at which condensation of vapor carried by the gases takes, place. vAs will be understood from preceding remarks, the maintenance of the heat transfer metal at relatively high temperatures is of particular importance in .heat

exchangers of 'thetype wherein, as. 'in. an air heater, the fluid to be heated is continuously ad-* mittedatrelatively low-ambient temperatures; In. accordance with my invention, .1 therefore proposela form of vapor generator in which provision". is madesfor 1 the withdrawal of heating gases, under suitable regulation, from an inter mediate point in the gas flow path throughout the boiler where such gases are at an appreciably higher temperature than the gases normally deiivered to the air heater from the usual gas outlet. The gases thus withdrawn are then directed to the gas inlet of the air heater for mingling with the main heating gas supply soas to result in an increase in the initial temperature of the total entering gas stream. Such an arrangement is effective in maintaining temperatures of all portions of the metallic heat transfer elements above the temperature of vapor condensation and is therefore advantageous when the'boil'er being operated at low capacities, particularly under conditions of low capacity operation over an extended period when the heating gases discharged from the usual boiler outlet are continuously at temperatures too low to prevent condensation of vapor on air heater element portions adjacent the cold 'air'inl'et; Aspecific il'lustra tionof the necessity oflow' capacity boiler operation over extended periods. found in \hydroe electricplants where auzi-iliary steam turbine-- driven electric generators are customarily mainttained in operation as a: so -called spinningrep serve" so as to be available for operation; at greatly increased load whenever thes-demandi 00-. ours.

The various features :of"novelty-- which 161131 36." terize my invention are 'pointed outwithuparticularity in the claims annexed; to and forming a part of this specification. For a better-under standing of theinvention; its operating ash/ans tages and specific objects attainedby its use, ret-' erence should" be had to the accompanying drawings and descriptive matter in I'have ill ustrated and described a preferred embodiment of my -invention.

Of the drawings: 40

Fig. 1 is a front'elevation vie-w, partly broken away, of a vapor generatoror boiler representinga structural embodiment of myinvent'i'on';

Fig. 2 is a sectional planview, partly broken away, of the boilerillustrateddn Fig.- 1; taken it along line 2'--2; and

Fig. 3 is sideel'evational view, partly broken away, of the boiler illustra'ted -in Figsr 1- and- 2;"

As illustratedherein; theselected embodiment" of my invention comprisesa-vapor-generatoror boiler having aconvectionboiler tube section iZ- disposed in laterally adjacent relation to the furnace combustion chamber I3; within-a common setting of substantiallyrectangular her izontal cross-section, thesettingbein -definedin 5,

part by'fl'uid cooled upright front and 'rear Walls M and I5, and by fluid cooled upright boiler and furnace side walls- It and!!! The-combustionchamber-is formedwith ahopperbottom-portion Ithaving a lower ashdischarge-throat I92 Provision is made for discharging fuelinto' the-com bustion chamber through the-front wall l i 'by burners, not shown, grouped-withinthe-windbox- 2! at locations indicated bythe burnensuppor-t' plates 23-.

The boiler section t2 occupies a' boiler: tube space 2:? which lies adjacent theupperm'ost por tion of combustion chamber is and which is par titioned therefrom by an. upright fluid cooled wall ZEjformingan uppercontinuation of adower side wall'boundarytt offch-am-ber It;.thepartition wall 25- extending from. front-wallxito' a point: forwardly spaced from therearwall' 15 so as to define. therewith a: common gas-outlet and gas-inlet 27: through which heating gases flow:

from chamber I3 into the boiler section space 2%. Boiler section I2 comprises an upper steam and Water drum 28 and a lower water drum 25, horizontally disposed and arranged in substantially vertical alignment. Horizontally spaced upright boiler tubes 3| extend between the drums Z8 and 29 to which the upper and lower ends of tubes 3! areiconnected substantially throughout the length of boiler tube space 24' between the front and rear walls I l and I5.

gas pass intermediate: fron-t ancl rear rows of tubes of-theboiler :tube group 3 I a.

Theshotheatingcgases resulting from the combustion of. fuel in: chambenI-S .thus' enter-the tube space 24' through thezin'let? passage 21 and new in: r

a generally horizontal directionthroughout the' successive gasipasseswiifia 36z.-and: 31", wherein the gases-are directed transverselyof all boiler and superheater: surface contained in the respective:-

A main heatingi gasioutlet this provided i passes. at the bottom'odthet final gas pass 31' through which heating; gases. are! discharged from the boilersetting;

li -gas outlet duct figzhavinga ges flow connec tionwith the/boiler gas'outlet 435; provides a; flue through which-thexgasesiare directed downward-1y" over a; boiler feedswazteif 'liieateror" economizei 5 5' located: thereim: the; economi'zer being formed:-

with a bank :ofztubestt 'i" extending: throughout the horizontalxcrosssection of-thesfiue andarrang'ed in continuous-coils'ror platens; asindicateclin Fig.

1; the tubestth having oppositeends connected F to inlet and outlet headers 48 and m respectively theinlet head'enfi' 418": having a connection to a source; of feed:v water: supply; and" the outletheader 19! havinga connection tattle-upper boiler druntZil; neither of."which connections is illustrated. Gases: leaving theieconomizer tube 4 t arer discharged from duct through aside outlet 51-; under: regulation: 1 of a" multi-leaf damper 522',v having: arr exterior operating mechanism 53:

Upon discharge from the ec'onom'izer duct" 45; the'heatingcgases-pass which-y; inv the-term hereinrindicated i's' o'f' the regenerative; indirect heat transfe'rtype andwhich;

for-the purposes 'of-thi's disclosure maybe of the samegeneral; construction as the" regenerative heating device ill'ustrated 'in" U1 S. Patent No: issuednOctober 20; 1925'. Accordingly, theaair heater 54 as shown; comprises a stationarycasing: 56 i-having an intermediate cylindrical section. 51? which contains a' rotor; to he later described;andcpposite end sectionsfili and 59 of whichieachis.horizontally divided by adiaphra-gm 6 I so: as to: formupper and-lower compartments 58a, 58b and 5902591); at the respective ends. The

Z'OtOIyflIlOtE' showm. which provides the: metallic heat:- transferrelements; is suitably mounted for rotationaboutz'azcentral horizontal axis 'coincid ing. withxthe-z plane of 'the diapliragms 6 I at op-'-- positea ends. The 'heat transfer elements which constitut'eithe regenerativem'aterial may be providedin the formzof closely spacedmetallic plates which extend axially of the rotor so as to de fine a multiplicity of axially extending channels or passages which, during rotation of the rotor, provide fluid flow paths connecting opposite end compartments 58a and 59a, above partitions 6i, and other fluid flow paths connecting opposite end compartments and 5%, below the partitions.

Gases discharging from the economizer duct 45 are thus directed into the upper, gas inlet compartment 58a of air heater 54,. and are then conducted through the connecting rotor channels into the upper gas outlet compartment 55a from which the gases are discharged through the gas outlet duct 62, under the influence of suitable induced draft fan means, not shown. Air is supplied to the air heater, suitably by means of a forced draft fan 63, and is directed into the lower, air inlet compartment 5% from which it is conducted through the connecting rotor channels into the lower, air outlet compartment 58b from which the air passes into suitable conduit means comprising an air delivery duct 65 by which the heated air is supplied to the burner windbox 2|.

During operation of air heater 54, gas flow is confined to passages at the upper side of diaphragms 6i, and is countercurrent to air flow which is confined to passages at the lower side of the diaphragms. Continuous rotation of the rotor in one direction results in each axial rotor channel serving as a gas conducting channel during one-half of each revolution and the same channel serving as an air conducting channel during the remaining half revolution. Thus, the radially extending metal plates which provide the walls of the channels are swept by heating gases during the upper half of each revolution and by air to be heated during the remaining lower half revolution. These metal plates which constitute the regenerative material thus present end portions toward the gas outlet-air inlet end of the air heater and consequently are alternately swept by cooled gases and by the cold entering air whereby the mean temperature of the metal of such end portions remains relatively low throughout operation. During extended periods of low capacity operation of the associated boiler, these low temperature portions of the metallic regenerative material are therefore subject to corrosion as the result of condensation of vapor thereon. It will be understood, of course, that if such plates were made of a noncorrosive metal, the cost of the air heater might be prohibitive commercially. Furthermore, the substitution of a non-corrosive metal would in itself not prevent condensation and the resulting collection of ash particles on the heat transfer surfaces.

As a means of maintaining higher metal temperatures throughout air heater 54, particularly at the cold air inlet end, the boiler is provided with a secondary gas outlet 68 formed in the boiler side wall H3 adjacent the lower end of the second transverse gas pass 36 and thus at a location downstream of the superheater 4| with respect to heating gas flow thereover. A gas bypass duct 69, exteriorly of the setting, extends from the gas outlet 58 to the air heater 54 where connection is made through opening H with the gas inlet compartment 58a. Gas flow into and through the bypass duct is regulated by means of a damper means 12 disposed across the gas outlet 68. As a result of providing the gas bypass connection to the air heater, hotter gases are directed into the gas inlet compartment 58:). than are delivered thereto from the eccnomizer duct 45. The two gas streams become mingled in the gas inlet compartment 58a and thereby provide, for passage through the rotor chan nels, a body of heating gases of considerably higher temperature than the gases available from a single gas outlet in the usual boiler construction. If gases of the maximum available temperature are to be directed through air heater 54, the damper 52 may be closed entirely, and the bypass damper l'l left open, so as to cause substantially the total quantity of gases to pass through the bypass duct 69, while only a negligible proportion is permitted to pass over the economizer. The arrangement herein disclosed is of particular utility, during extended periods of low capacity boiler operation, due to the fact that under such conditions, the economizer may be operated-at correspondingly reduced capacity so that no disadvantage results from the reduction of gas flow over the economizer.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. A vapor generator comprising horizontally disposed upper and lower drums, vapor generating tubes extending upright between said drums and connected thereto along the length thereof, an upright partition forming the inner side wall boundary of a combustion chamber laterally adjoining the space containing said tubes and separated therefrom except at one end by said partition so as to provide a heating gas entrance to said space, upright baffie means extending transversely of said partition and arranged to divide said space into a plurality of serially connected gas passes throughout-which said tubes are distributed, means for burning fuel in said chamber and effecting a flow of heating gases through said entrance and successively through said passes in contact with said tubes, said space having a main gas outlet discharging a main gas stream from the pass farthest from said entrance and having a secondary gas outlet discharging a secondary gas stream from a preceding gas pass, an air heater disposed externally of said space and having a heating gas inlet and a heated air outlet, dampered conduit means separately connecting said main and secondary gas outlets to said air heater gas inlet, an economizer for heating vaporizable liquid to be fed to one of said drums, said economizer being positioned in said conduit means conducting said main gas stream to said air heater gas inlet, and conduit means conducting heated air from said air heater air outlet to said fuel burning means.

2. A vapor generator comprising horizontally disposed upper and lower drums, vapor generating tubes extending upright between said drumsand connected thereto along the length thereof, an upright partition forming the inner side wall boundary of a combustion chamber laterally adjoining the space containing said tubes and separated therefrom except at one end by said partition so as to provide a heating gas entrance to said space, said combustion chamber extending see -eels downwalidlyrpastsaid 'lower drum so as .to form an exterior :recess ibetwreen an outer side wall boundary of said chamber and 'the lower ;;boundary 10f said space, upright aha-file means extending transversely of :said partition and arranged :to divide said space into'a plurality of serially connected ygas passes throughout Which said tubes are distributed, -means :for burning :fuel in said chamber and 'efiecting a flow of heating gases through said entrance and successively through Said passes in contact withsaid tubes, said space having-a main gas outlet discharging a main gas stream from the lower 'end portion of the pass farthest ,from'said entranceand having asecondary gas outlet discharging a secondary gas stream.

from the lower end :portion of ;a preceding one of saidpasses, an air heater disposed within-said recess and having a heating gas inlet and :a heated air :outlet, dampered conduit means :separately connecting said main and secondary :gas outlets to said air heater'gas inlet, an economizer for heating vaporizable liquid to be fed to one of 8 aid :drums, said :econcmizer ibein :positioned in said conduit means rconducting said main :gas stream to said ;air theater gas inlet, and conduit means conducting heated; air from-said :air Eheater air outiet to said :fuel, burning; means.

LEON 'I-I. OOYKENDALL.

References Cited in the file of this patent UNITED STATES PATENTS

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