US2067670A

US2067670A - Fluid heater

Info

Publication number: US2067670A
Application number: US594175A
Authority: US
Inventors: Howard J Kerr
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1932-02-20
Filing date: 1932-02-20
Publication date: 1937-01-12
Anticipated expiration: 1954-01-12
Also published as: FR751081A

Description

3 Sheets-Sheet l H. J. KERR 'FLUID HEATER Filed Feb. 20, 1932 Jan. 12, 1937.

INVENTOR HowardJ/(err ATTORNEY H. J. KERR FLUID HEATER Jan. 12, 1937.

' Filed Feb. 20, 1932 3 Sheets-Sheet 2 INVENTOR Howarc/J lterr & Fa

ATTORN EY Jan. 12, 1937. H. J. KERR 2,067,670

FLUID HEATER Filed Feb. 20, 1932 3 Sheets-Sheet 3 INVENTOR HowardJ/(err ATTORNEY Patented JI2, 1937 FLUID HEATER Howard J. Kerr, Westfield, N. 1., assil'nor to the Babcock & Wilcox Company, Bayom N. 1., I corporation of New Jersey Application February 20, 1932, sci-m No. 594,115

' 22 Claims.

creased by the high hydraulic head to which it is continuously subjected. The invention is especially useful in high drum water tubeboilers comprising two steam generating stages, a'forced circulation stage through which all of the feed water to the unit is, circulated and heated to a substantialtemperature, and :a natural circulatio'n'stage through which the portion of the water unevaporated in. the forced circulation stage is circulated and evaporated.

The general object of my present invention is the provisionv of a water tube steam boiler having an improved arrangement and construction of the fiuid heating surface thereof. Another object is the provision of ahigh drum water 1 2 tube boiler with an improved arrangement of and supporting means for the auxiliary fluid heating surface included therein.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. 'For a better understanding of the'invention,'itsoperating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred embodiments of my invention.

Of the drawings,v Fig. l is a sectional elevation,

partly broken away, of a high drum water tube boiler constructed in accordance with my inven-' tionyFig. 2 is an enlarged fragmentary view 11- lustrating the arrangement of the superheater and economizer tubes shown in Fig. 1; Fig. 3, is an enlarged end view taken on the line H of Fig. 1; Fig. 4 is a sectional elevation, partly broken away, of a modified construction; Fig. 5,

is an enlarged section on the line 5-5 01' Fig. 4; Fig. 6 is'an enlarged section on the line 86' of Fig.7, and illustrating the economizer-support 'shown .in Fig. 4; Fig. 7 is a section on the line 1-] of Fig. 6; Fig. 8 is a sectional elevation, partly broken away, of a second modification; Fig. 9 is a section on the line 9-9 of Fig. 8; and Fig. 10 .is a section on the line I0ll l of Fig. 9. 5 In the drawings, and particularly in Figs. 1

to 3, I have illustrated my invention'as embodied in a high drum two-stage water tube boiler, which comprises a steam and water drum I having its water space'connected by vertical downtake circulators 2 to vertical downtake headers 5 3 of a bank of superposed horizontally inclined water tubes 4 having their upper ends expanded into vertical uptake headers I. The uptake headers S are connected by a series of uptake circulators 6 to the steam and water drum I m in a manner hereinafter described. The tube bank 4 is positioned in the lower portion of a vertical heating gas pass 1 in communication with a furnace chamber I of any suitable form.

Theheating gas pass illustrated is of taper- 1 ing cross-sectional area in the direction of gas flow, and has a gas exit I at its uppermost end into a flue 9 in which an air preheater ID, of any. suitable form, is positioned to receive the gases after their passage over the tubes of an economizer arranged in the flue adjacent the gas outlet from the boiler. The economizer is formed by horizontal inlet and outlet headers II and i2, respectively, connected by a series of return bend tubes l3 arranged in'parallel therebetween. a

In the boiler illustrated, the gas pass 7 is partly defined by a substantially vertical wall it formed by metallic plates is arranged edge to edge and lined attheir inner sides with a layer of refractory heat insulating material ii. The wall ll '0 is supported by a supporting wall i1 carried by the upper row or rows of steam generating tubes 4. The lowermost portion of that side of the gas pass is defined by the downtake headers 3, and the space between the headers and the wall 35 i1 is closed by an inclined baifle l8 extending along the upper row oi tubes 4. It will be noted that in this embodiment the downtake circulators 2 are outside of and horizontally spaced from the wall II. The space betweenthe upper end of o the wall it and gas exit I is closed by vertical plates IS.

The opposite side wall of the gas pass is defined by the uptake headers 5 and uptake circulators 6. As shown, each uptake clrculator i has 45 an' inwardly inclined lower section 6a, horizontal upper portion 6b extending across the gas exit 1', and an intermediate inwardly inclined vertical section 60. The uptake circulators are supported from a top supporting structural member I9 through rods "connected to lugs 2i welded on the cir'culators. This wall of the heating gas pass is partly closed by plates 22 conforming to the curvature of the circulators 8. A bofler casing 23 encloses all of the boiler parts heretofore 66 described and with those parts is supported from below on I-beams 24.

To adequately screen the heat'absorbingfele ments hereinafter described from exposure to' the radiant heat of the furnace, and to prevent the passage of molten slag particles when pulverized coal is burned in the furnace chamber, the upper screen, while the lower rows of tubes are more a widely spaced to provide an effective slag screen.

,The transversely arranged steam and water 'drum l,

circulators

2 and 6, and the tube bank 4, combine to form the natural circulation steam generating stage of the boiler. In view of the high rate of heat transfer present in the tube bank 4, due to the exposure of the tubes to the radiant heat of the furnace and to the heating gases while at their highest temperaturein the: gas pass, it is highly desirable to provide a rapid circulation of the water to be evaporated through the tube bank to prevent the tubes from overheating. For this purpose, the steam and water drum I is located a substantial vertical distance above the tube bank and the circulators are made long, providing in operation a considerable static head on the fluid in the bank.

It has heretofore been proposed in designing high drum water tube boilers to locate the auxiliary fluid heating surface of the boiler in por tions of the boiler other than the first vertical pass in which the natural circulation tube bankwas located. Such constructions would have many practical disadvantagesin operation. For example, the surface area exposed to external radiation would be undesirably large and the amount of expensive insulating material required commercially prohibitive. Furthermore, the horizontal portions 6b of the uptake circulators containing steam and water passing to the steam and water drum would be liable to overheating on exposure to high temperature gases, due to the steam and water separating action occurring therein. By utilizing the portion of the gas pass of a high drum boiler bounded by the natural circulation tube bank, steam and water drum, and the uptake and downtake circulators, for the location of part or all of the remaining boiler heating surface, it is possible to increase the thermal eificiency of the unit, while the radiation losses, cost of construction and floor space occupied by the unit are sub stantially decreased. The temperature of the heating gases would also be reduced sufficiently to permit the horizontal portions-of the uptake circulators to be safely exposed thereto. The absence of flow directing baflles and changes in direction of the heating gas flow will provide an effective flow of the heating gases with a low draft loss and fan power consumption.

In the high drum water tube boiler illustrated, the portion of the gas pass between the natural circulation tube bank and the horizontal portions of the uptake circulators is utilized effectively by the arrangement in successive upper portions thereof of a superheater and an economizer, although other types of heating surface, such as a steam reheater or air preheater, could be used in lieu of or in conjunction with the foregoing apparatus.

As shownythe superheater isformed by horizontal inlet and

outlet headers

25 and 26 rethe heating gas pass. The

headers

25 and 26 are preferably located at the outer side of the gas ;pass -wall l4,=the header 15' being connected to -j the steam space'of the steam and water drum .fl1by-steam pipes 28,and the return bends of the superheater tubes at that side of the pass being formed in Y formations 29 having shank pore tions 30 extending through the wall l4; The outer end of each tube shank hasa collar 3| welded thereon in contact with the outer side of the wall plate l5, and a removable cap 32 to facilitate cleaning of the tubes. The inner portions of the superheater tubes are supported by a vertical plate member 33 carried by the upper row of tubes 4. The superheater so constructed is adequately protected from radiant heat'and slagging by the tube bank 4 andin operation absorbs a limited amount of heat from the hot gases leaving that bank. Inthe} boiler-1 illustrated the heating gases vleaving the supe'rheater would normally be at a temperature substantially above the saturated steam temperature and could be used for thegeneration-orreheatmg of steam in any heat transferelem'en'ts'that may be exposed thereto. 1

Substantially all of the remaining portion of the heating gas pass is preferably occupied by an economizer. The economizer shownin Fig. 1 is formed by'a series of closely spaced return bend tubes 34 arranged in parallel and similar in form to the superheater tubes 21 previously described. The economizer shown has an .upflow circulation, the lower ends of the tubes being connected to an inlet header 35, which in turn is connected to the outlet header it of the flue economizer by downcomers 36. An alternate arrangement would provide a feed connection direct to header 35. The upper most legs of the tubes 34 are bent inwardly and then horizontally into the adjacent side of the steam and water drum. The return bend portions of the tubes 34 at the downtake circulator side of the gas pass are of Y formation and supported in the wall l4 in the same manner as the corresponding. portions of the superheater tubes. economizer tubes at .the uptake side of the gas pass are supported by the sections 6c of the uptake circulators by spot welding the bend portions of each tube to a narrow vertical plate 37 clamped to one of the uptake circulators'by a cross member 38 secured to the circulators and covering the weld and bend portions with a layer of heat insulating material 39. While the economizer shown is of the upflow type, it is feasible, and within the scope of my invention that the fluid flow therein be downwardly, or partly'downward and partly upward.

In the operation of the two-stage high drum water tube boiler illustrated, heating gases are generated in the furnace and pass upwardly suecessively over the natural circulation stage, superheater, forced flowstage, horizontal portions of the uptake circulators, water economizer and air being proportioned to maintain high mass flow.

The feed water to the unit is delivered by a suitable boiler feed pump (not shown) to the inlet header I I of the flue economizer, and after being heated during its downward passage through the economizer tubes is delivered to the inlet header of the forced flow stage. During its upward flow therethrough, a portion of the water is evaporated, and the steam and water mixture discharged into The return bends of the Y natural circulation stage.

the steam andwaterfdrum, It will'be noted that in the forced flowf stage of the boiler, jail of the flow from the iii-let head'eriizto the steam and water drum-*is'through parallel new. paths, in which the use ofjunction headers between the tube legs isavoided'fii 'I 'he'usejof parallel flow pathsin and after the steam gener'ating zone,

is especially desirable. This arrangementjaffords a low@ fluid head loss and a positive andiuniform f distribution of-the fli' id flow; Theavoidance of V junction" headers renders this construction especially adapted for the generation of steam athighpressures. Y

The portion of'thewater une vaporated in the forcedbirculation stage and delivered to the steam and water drum l passes downwardly through the circulators 2 into the relatively shallow natural circulationtubebank. Due to the high rate of heat absorption present in this portion of the boiler heating surface, the balance of the water will be rapidly evaporated. The

high static head to which the fluid in the tubes tid n bank is' partly limited;

4 is subjected, causes the fluid to circulate rapidly through the tube bank and upwardly through the circulators li into the steam and Jwate'r drum.

' The steamfg'eneratedtin theg'forcedand natural circulation, stages passesfrcrn the steam and water drum iintdtne superheater tubes 21 where it is superheated to. the 'desired. degree before passing to the pointof utilization. H

Q'Ihe tube spacing across thefnaturar'circulaomrnercially by the his w n thick- I v r a ctions intended for highpressures an ns'eq entlythe possible amount'jof"heatingisurfac ,7 thisi type exposed to the'heatingj gases'ain'high essure boilers is limited. In theeconomize a however, the'tubesmay vher: osely spaced in the gas pass and" any g -inc'rease 'in the draft loss fgheader thereby causedkis inbrefthan oil-set by the increased jheat'j absorption attained.v A greater thermakefflcienpy-ls possible with the described arrangement than ifitheforoed flow stage was replaced by a, tube'Iban kof the type used in the The boiler construction illustrated in Figs. 4 to 7 differs from that in Figs. 1 to 3 by the elimination of-the Y formation of the economizer return bands at the downtake side of the gas pass and by the bending of the downtake circulator tubes 2 inwardly from the adjacent wall 23 of the boiler casing to define a portion of the gas pass. In this construction the metal plates 31, cross members 38, spot weld connection and heat insulating materialiiS are; used at both sides of the gas pass forsupporting the economizer tubes.

The cross members '38 are clamped to the circulatcrs by clamping members 40 and bolts 4|,

as shown-inl igs. 6 and 7. Each clamping member- 40 preferably extends between the outer sides of a pair of circulators, and is provided with end flanges- 4,2 for connection to the end flanges of adjacent clamping members by bolts 43. The cross members36'are additionally supported on the circulator tubes by lugs 44 welded on the tubes at the lower sides of the cross members;

In the construction illustrated in Figs. 8 to 10, the economizertubes are supported on the uptake '1 and downtake circulatorsby adifferent arrange ment which consists of a triangular spacer block H 45 positioned between each circulator tube and? an adjacent pair of parallel economizer tube ire turn bends, and arranging U-shaped bolts 46 about the combined'tube structure with their ruction shown culators from'the wall plate 48,, tofwhich the bolts are secured. It willbe understood" that the upends extendingthro' ate nalism; the cirtake circulators' in f the modified constructions 5 maybe supported 'in' 'a manner-- similar to that described inconnection with thefembodiment illustrated in Fig, 1. The downtake'"circulators '2 in the constructions.jshown-tinJ'igsz} to might well be straiglitas in land the economizer. tubes extended 1' and I connected thereto in that location. In such a construction, the bafiles I8 and I9 would not be require d.f=.;-, I

While in accordance with the provisions, of the statutes I have illustrated and described herein the best forms 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 coveredby 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 water tube boiler comprising in combination a furnace chamber, a vertical heating gas pass communicating with said chamber, a naturalcirculation bank of steam generating tubular-elements extending across said gas pass, a stea'm'and water drum positioned a substantial distance above said tube bank and providing a considerable static head on the fluid in said tube bank, spaced rows of downtake and uptake circulators extending along opposite sides of said gas pass for aconsiderable height and connecting said tube bankwith said steam and water drum, a plurality .of fluid heating elements exposed tothe heating gases in the portion of said gas pass bounded by said uptake and downtake circulators, tubebank and steam and water drum,

and means for supporting said fluid heating elements from one of said rows of circulators.

2. A high drum water tube boilery comprising in combination a furnace chamber, aestack. a

single vertical heating gas jifpassg extending between said chamberandstack, a5 natural circulation bank of steam-generating tubular elements extending across said gas pass, a steam jand water drum positioned {a substantial distance above said tube bank and providing a considerable static head on the fluid in said tube bank. spaced'downtake and uptake circulators defining; opposite sides of said gas pass and connecting said tube bank with said steam andwater drum, asuper- 1 heater and an economizer both arranged'in' the portion of said gas pass bounded by-isa'id uptake and downtake c'irculators; tube' bankand'steam uptake circulators connected to the other end' of v said tube-bank and having substantially horizontal portions extending across said gas pass and connected to said steam and water drum, ysaid downtake and uptake cir'culators defining opposite sides of said gas pass, a plurality of fluid heating tubular elements horizontally arranged in said gas pass above said tube bank and in the space bounded by said uptake and downtake circulators, tube bank and steam and water drum, and means for supporting said fluid heating elements from said uptake and downtake circulators.

4. A water tube boiler comprising in combination a furnace chamber, a vertical heating gas pass communicating with said chamber, a natural circulation stage including a bank of horizontally inclined water tubes in said gas pass, a steam and water drum positioned above said tube bank, downtake circulators connecting one end of said tube bank with said steam and water drum, and uptake circulators connected to'the other end of saidtube bank and having substantially horizon-- talportions extending across said gas pass and connected to said steam and water drum, and a forced flow stage including a plurality of multiple loop return bend water tubes arranged in parallel in said gas pass above said tube bank and in the space bounded-by said uptake and downtake circulators, tube bank and steam and water drum, and having their upper ends connected to said steam and water drum, and means for supplying feed water to the lower'ends of said rei turn bend water tubes.

5. A water tube boiler comprising in combination a furnace chamber, a stack, a single vertical heating gas pass of progressivelydecreasing flow area extending between said chamber and stack, a natural circulation steam generating stage including a bank of horizontally inclined water tubes in said gas pass, a steam and water drum positioned-a substantial'distance above said tube bank and at' one side of said gas pass, downtake circulators connecting one end of said tube bank with said steam and water drum, and uptake circulators connected to the other end of said tube bank and having substantially horizontal portions extending across said gas pass adjacent the level of said steam and water drum, and a forced flow steam generating stage including a'plurality of upfiow return bend water tubes arranged in parallel in said gas pass above said tube bank and in the space defined by said uptake and downtake circulators, tube bank and steam and water drum, and having their upper outlet ends connected to said steam and water drum, and means for supplying all of the feed water for said boiler to thelower inlet ends of said return bend water tubes.

6. A water tube boiler comprising a plurality of steam generating tubular elements, a steam and water drum positioned above said elements, downtake and uptake circulators connecting said elements with said steam and water drum, a

plurality of tubular fluid heating elements arranged in'the portion of said gas pass between said'uptake and downtake circulators, and a supporting connection between each of said fluid heating elements and one of said circulators.

7. A water tube boiler comprising a plurality of steam generating tubular elements, 'a steam and water drum positioned above said elements,

downtake and uptake circulators connecting said elements with said steam and water drum, a return bend tubular fluid heating element arranged in the portion ofsaid gas pass between said uptake and downtake circulators, and a supporting connection between the returnv bend portion of said fluid heating element and one of said circulators. I

8. A water tube boiler comprising parts defining a heating gas pass, circulator-tubes at oppo' site sides of said gas pass and arranged in subplate and contacting with spacer, block of refractory material between each.

the return bend portions able static head on the fluid in said tube bank.

spaced downtake and uptake circulators connecting said tube bank with, said steam and water drum, a plurality of tubular fluid heating elements arranged in the portion .of said gaspass V bounded by said uptake and downtake circulators, tube bankand steam and water drum, and a supporting connection between said fluid heatingelements and circulators. V

10. A water tube boiler comprising in combination a furnace chamber, a vertical heating gas pass communicating with said chamber, a bank I of steam generating tubular elements, extending across said gas pass, a steam and water drum positioned above said tube bank, spaced downtake and uptake circulators connecting said tube bank with said steam and water drum, a return bend tubular fluid heating element arranged in a portion of said gas passdeflned by said uptake and downtake circulators, and a supporting connection between return bend portions of said fluid heating element and adjacent uptake and downtake circulators. I

11. A water tube boiler comprising in combination a furnace chamber, a vertical-heating gas pass communicating with said chamben'a bank of steam generating tubular elements extending across said gas pass, a steam and water drum.

positioned above said tube bank, spaced downtake and uptake circulators connecting said tube bank with said steam and water drum, a

plurality of return bend tubular fluid heating elements arranged in said gas pass between said uptake and downtake circulators, and a supporting connection betweenreturn bend portions of each of said fluid heatingelements and one of I said circulators comprisingmetallic plates carried by said circulators at the inner side thereof, a layer of heat insulating side of said plates, and the return bend portions of said fluid heating elements being embedded in material at the inner said insulating material and welded to saidwplate.

12. A water tube boiler comprising in combina-c tion a furnace chamber, a vertical heating gas pass communicating with said chamber, a bank of steam generating tubular elements extending across said gas pass, a

one of said circulators comprising a metallic plate at the outer side 01' said circulators, a layer of heat insulating material on the inner side of said 01' said circulators and 'of a pair of adjacent fluid heating elements, and supporting means surrounding and holding said.

steam and water drum positioned above said tube bank, spaced downtake and uptake circulators connecting said tube bank f fluid heating elements said gas pass between said uptake and downtake circulators, and a sup-- tions of each of said fluid heating elements and said circulators, a

fluid heating elements and circulators in a predetermined relation relative to said plate.

13. A water tube boiler comprising in combination a furnace chamber, a vertical heating gas pass communicating with said chamber, a natural circulation stage including uptake and downtake headers, a bank of horizontally inclined water tubes in said gas pass and having their ends connected to said headers, a steam and water drum positioned a substantial distance above said tube bank, and circulators connecting said downtake headers with said steam and water drum, circulators connected to said uptake headers and having horizontal portions extending across said gas pass and connected to said steam and water drum, and a forced flow steam generating stage including a plurality of closely spaced return bend water tubes arranged in parallel in said gas pass in the space bounded by said uptake and downtake circulators, tube bank and steam and water drum, and having their outlet ends connected to said steam and water drum, and a supporting connec-' tion between the return bend portions of each of said water tubes and corresponding uptake and downtake circulators.

14. A steam generator comprising a natural circulation bank of horizontally inclined steam generating tubes extending across a vertical heating gas pass, a steam and water drum above and extending transversely of said tube bank, rows of uptake and downtake fluid conduits connecting the uptake and downtake ends of said tube bank respectively to said drum, a bank of return bend tubular fluid heating elements of substantial length extending across said gas pass above said tube bank and in the space defined by said rows of uptake and downtake fluid conduits, tube bank, and drum, said fluid heating elements having return bend portions adjacent one of said rows of fluid conduits, and means forming a supporting connection between said return bend portions and said last mentioned fluid conduits.

15. A steam generator comprising spaced rows of vertical uptake and downtake headers at opposite sides of a vertical heating gas pass, a natural circulation bank of horizontally inclined steam generating tubes extending across said gas pass and connecting said rows of headers, a steam and water drum above and extending transverselypf said tube bank, rows of uptake and downtake circulators connecting said rows of uptake and downtake headers respectively to said drum, a bank of return bend tubular fluid heating elements of substantial length extending across said gas pass above said tube bank and in the space defined by said rows of uptake and downtake circulators, tube bank, and drum, said fluid heating elements having return bend portions adjacent one of said rows of circulators, and means forming a supporting connection between said return bend portions and said last mentioned circulators.

16. A steam generator comprising spaced rows of vertical uptake and downtake headers at opposite sides of a vertical heating gas pass, a natural circulation bank of horizontally inclined steam generating'tubes extending across said gas pass and connecting said rows of headers, a steam and water drum above and extending transversely oi said tube bank, rows of uptake and downtake circulators connecting said rows 01' uptake and downtake headers respectively to said drum, a bank of return bend tubular fluid heating elements of substantial length extending across said gas 1px;; above said tube bank and in the space defined by said rows of uptake and downtake circulators, tube bank, and drum, said fluid heating elements having return bend portions adjacent said row of uptake circulators, means for supporting said return bend portions from said upsteam and water drum, and a forced flow stage including a plurality of steam generating tubular elements arranged insaid gas pass above said tube bank in the space between said uptake and downtake circulators, means for supplying feed water to said forced flow stage, said forced flow stage steam generating elements being arranged to discharge into said steam and water drum, and

' means for supporting said forced flow stage steam generating elements from said uptake circulators.

18. Fluid heating apparatuscomprising a heating gas pass, vertically extending supporting tubes extending along opposite sides of said gas pass. an auxiliary fluid heater comprising fluid heating tubes each having a series or superposed tube legs extending across said gas pass and serially connected at opposite sides of said gas puss by return bend portions arranged in vertical planes, and means for supporting said auxiliary fluid heater tubes at opposite sides of said gas pass from adjacent supporting tubes independently of subiacent support.

19. Fluid heating apparatus comprising a heating gas pass, vertically extending supporting tubes extending along opposite sides or said gas pass, an auxiliary fluid heater comprising fluid heating tubes each having a series or superposed tube legs extending across said gas pass and serially connected at opposite sides oi. said gas pass'by return bend portions arranged in vertical planes, means forming a supporting connection between adjacent tube legs or each fluid heater tube, and means for supporting said auxiliary fluid heater tubes at opposite sides or said gas pass from adjacent supporting tubes independentlv oi sublecent support.

20. A steam boiler comprising a bank of steam generating tubes, a steam and water drum above said tube bank, groups of tubes spaced longitu dinally oi said tube bank and connecting said tube bank and drum, an auxiliary fluid heater arranged above said tube bank,'and means for sup= porting said fluid heater at spaced points by said spaced groups of tubes and independently of support from said tube bank. 1

21. A steam boiler comprising a. bank of steam generating tubes, a steam and water drum above said tube bank, spaced groups of circulator tubes arranged to connect the opposite ends or said tube bank to said .drum, an auxiliary fluid heater arranged in the space defined by said groups 01' circulator tubes, tube bank, and drum, and means for supporting said fluid heater in its entirety by said spaced groups or circulator tubes independently of said tube bank.

22. A steam boiler comprising a bank of steam generating tubes, a steam and water drum above said tube bank, spaced groups or circulator tubes arranged to connect the opposite ends 01. said tube portions arranged in vertical planes, and means engaging return bend portions or said fluid heating tubes for supporting said fluid heating tubes from said circulator tubes independently or said tube bank.

HOWARD J. KERR.-