US1999985A - Steam boiler - Google Patents

Description

April 30, 1935. T. B. sTlLLMAN STEAM BOILER 5 Sheets-Sheet Filed June 50, 1953 INVENTOR hama/s B. Sti/Iman ATORNEY N A M L H. T. S B. T.

STEAM BOILER Filed June 30, 1953 3 Shee'ts-Sh'e'e't 2 0 0000 0 0 0 0 0 00000000000000000000000000 000000000000 00000000 0000O000000000000900O000000000000050OQOMMw .H\\\. oooooo 000000000000000000000.0000000000000000000000000 000000000000 00000000000000000000 00000000000000000 000000000000000000000 00000000000000000000 00000000000000000# 00000000000000000000 0 00 00000000000000000 0O0000O00OQ000-00O 00000 0000000000000 OOD 000000000000000000 00000000000000000 00000000000000000 D00 0 OOOOAOOOOOOOOQOOOOD OOOOOOOOOOOOOOOQOO 0 000000000000000000 INVENTOR hamas Silzm'zrz ATTORNEY April 30, 1935. T. B. STILLMAN STEAM BOILR Filed June 30, 1933 5 Sheets-Sheet I5 odMHf/oooooooooooocoooooo o o o o o o /ofdowomomooooooomomooo o .2.... ooooooooo c O00 00000 OOOOOOOOOOOO Hv/0O0000O0000000 -A INVENTOR B(Lh0mas ,B Stillman YDH-Q-XK A ATTORNEY Patented Apr. 30, 1935 UNrrlaDv STATI-:fsr PATENT OFFICE f Thomas B. Stillman, South Orange, NkJ., as-

signor to The Babcock & Wilcox Company, Newark, N. J., a corporation of New Jersey Application .lune 30, 1933, Serial No. 678,343 18 Claims. (Cl. 122-336) My present invention relatesto the construction and operation of water tube boilers in which the steam generating surface is mainly concentrated in a single vertical bank of bent tubes ex- 5 tending between a lower water drum and an upper steam and water drum and receiving heating gases from an integral fiuid cooled furnace laterally adjoining the tube bank. 'Boilers of this type have been recently developed for industrial plants having low head room requirements and small steaming capacities.

The main object of my invention is an improved constructionxof a two-drum steam boiler of the type described which, is characterized by an arrangement of fuel burning provisions and a furnace construction permitting the burning of fuel at extremely high rates of heat release per unit of furnace volume, a superheater location in which ther superheater tube temperatures will be maintained within safe limits, and the superheater tubes readily accessible for cleaning and replacement with a minimum lof external space requirements for that purpose, and an improved construction and location of a water screen for the superheater. A further and more speciiic object is the provision of a two-drum boiler of the characterspecied above which is especially adapted for marine use due to its particular form,

limited 'space requirements, light weight and weight distribution, capacity for operation hat high ratings, and relatively lowcost ,of construction.

The various features of novelty which characterize my invention are pointed out with par- 35 'ticularity in the claims annexedto and forming a part of this specification. For a better understanding of the invention, its operating 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 a preferred embodiment of my invention.

Of the drawings:

Fig. l is a sectional elevation of a steam boiler embodying my invention, taken on the line I-i of Fig. 2;

Fig. 2 is a horizontal section taken on the line 2--2 of Fig. i;

Fig. 3 is a vertical section taken on the line 3 3 of Fig. 2;

Fig. 4 is a diagrammatic View of two such boilers as arranged in a marine installation; and

Fig. 5 is a somewhat diagrammatic sectional elevation iilustrating the Water tube screen.

The steam boiler illustrated comprises a horizontally arranged lower water or mud drum II supported on a cradle I2 and connected to a similarly arranged upper steam and water drum I3 by an upright bank of bent tubes I4. Thel axes of the drums are in vertical alignment and the tube bank I4 is preferably symmetrically arranged relative to thedrums Il and I3'. The

weight of the drum I3 is mainly supported by the tube bank I4 and drum II. 'I'he drlmis Hand I3 and tube bank I4 are positioned in a boiler housl0 ing having vertical front and` rear walls I5 and I 5 respectively, and side walls I1 and I8 at opposite sides of the tube bank, the wall I1 ex- I tending adjacent the tube bank and the wall I8 being laterally spaced a considerable distance l5 from the opposite side of the tube bank. The walls I5 and I1 are of firebrick, throughout and the walls I6 and I8 are constructed as hereinafter described. As shown in Fig. 2, the boiler housing is substantiallyrectangular in horizontal crosssection. The housing space between the inner side of the tube bank I4 and the side wall I8 is the boiler furnace or combustion chamber 20, closed at its front end by the wall I5 and substantially coex- 25 tensive with the tube bank. The boiler furnace is separated from the space occupied by the tube bank I t throughout substantially its entire length by a partition or baille wall 2I formed by a row of horizontally spaced vertical bent tubes I4 30 extending between and directlyK connected to the The outer side wall I8 of the furnace is formed 40 by a row of substantially straight stud tubes 23 with the inter-tube spaces closed by'refractory materialA 2t. The tubes and refractory material Aare backed by a layer of insulating material and a sectional metallic casing 26. The"lower ends of the tubes 23 are connected to a horizontally arranged header 2l at substantially the same level as the drum I I and connected into the adjacent side thereof by a row of horizontal longitudinally spaced watery tubes 28. The tubes Ita and 23 in the forward part of the furnace chamber have their inner faces covered by refractory, while the tubes |48' and 23 in the rear part have their inner faces exposed, as shown in.l Fig, 2. The spaces between the tubes 28 are'y 55 rounding the burner ports.

closedn by refractory blocks 29 resting on the tubes, the upper surfaces of which form a flat floor for the furnace chamber. The boiler furnace is supported on I-beams 3D and 3l extending below the floor and header 21.

The upper ends of the tubes 23 are connectedv to a horizontally arranged header 32 having its axis positioned at a level slightly below the axis of the drum I3 and substantially in vertical alignment with the axis of the header 21. The header 32 is connected to the drum I3 by a lower row of straight tubes 33 and an upper row of bent tubes 34, both of which are longitudinally spaced and open intothe drum I3 above the points of connection of the tubes |48. The spaces between the lower row of tubes 33 are closed by tile pieces 35 which define the roof of the furnace chamber.

The metallic outer casing 26 has horizontal sec-V per unit of furnace volume and with high boiler efficiencies. The provisions for supplying fuel to the furnace are mounted in the refractory front wall I5, and consist of a battery of`r'luid` fuel burners 36 having fuel burner ports- 31 symmetrically arranged relative to the furnace chamber side walls, as shown in Figs.v 1 and 2. The 'fuel burners indicated are intended to discharge oil or other hydrocarbons. The fuel burners are arranged to discharge separate streams of fuel horizontally into the furnace chamber, and the great length of travel therein insures complete combustion of the fuel. Air for combustion is supplied in regulable quantities through a casing 38 extending along the front wall I5 and sur- The described arrangement ofthe battery of fuel burners permits the several flame and gas streams to pass through the furnace Achamber without substantial interference with one another and all with the same length of travel or time for combustion. This arrangement contributes to the maintenance of high combustion eiciencies over theentire range of boiler capacities, particularly at high loads, as compared to the drooping character of the efficiency curve in present multi-burner boilers where some of the burners are located nearer the tubes than others and the flame streams are reversed in the furnace. The baille wall 2| is provided with a metallic plate extension 39 beyond therear end of the tube bank I4. The rear wall I6 of the boiler is V-,shaped in horizontal cross-section, and formed by` a plurality of removable panels I6EL andl I6b providing access to the space at the rear end of the boiler. The apex of the rear wall is positioned in line with and spaced from the end of the baille extension 39. With the foregoing arrangement a horizontal flow of combustion gases is provided rearwardly through the furnace charnber, around the end of the baille extension 39 and through the triangular pressure equalization space and then forwardly through the tube space in intimate contact with the tubes therein. The forward end of the. tube space opens into an uptake flue 40 for the exit of the heating gases.

The space at the rear of the boiler is. advantageously occupied by al draining steam superheater consisting of vertically arranged inlet and outlet headers 4I and 42, respectively, arranged side-by-side in the side wall I1 and connected-by a bank of looped superheater tubes -43 extending horizontally across the rear portions of the tube space and furnace chamber to the side wall I8 of the boiler. are supported by the baiile extension 38, the latter beingI advantageously of sectional formation to facilitate superheater tube removal, as indicated in Fig. 3. A conduit 44 connects the steam and water drum I3 to the upper end of the header 4I and the header 42 is provided with a superheated steam outlet 45 at an intermediate point. In removing any of the superheater tubes, the tubes are cut free from the headers 4I and 42 and with the corresponding portions of the baffle extension 39 withdrawn through the space occupied by the panel IGH. The headers have bottom drain connections (not shown). y

To lessen the amount of radiant heat absorbed by the loopedend portions of the superheater tubes from the furnace chamber, a water tube screen is arranged in the rear portion of the combustion chamber forwardly of the looped end y portions of the superheater' tubes. The water tube screen consists of a horizontal lower header 46 and an inclined upper header 41 connected by staggered rows of bent tubes 48, extending vertically across the width of the furnace chamber. To insure 'a rapid circulation through the Water screen tubes, as shown in Fig. 5, the inner end of the lower header 46 is connected to the lower drum II by a nipple 49 and the inner end of the upper header connected to the upper drum I3 by a-nipple 50. The outer ends of the headers 46 and 41 are connected into the end portions'of.

The tubes 43 extend through and the headers 21 and 32 by nipples 5I and 52 respectively, to structurally reinforce the water screen and improve the uid circulation through the tubes 28 and 23.

Thedescribed boiler construction is especially adaptedl for. marine installations. As diagrammatically illustrated in Fig. 4, the boiler formation lends itself to a twinarrangement in a ship hull. As shown, the major portion of the boiler weight will be concentrated adjacent the center line of the hull; AA common gas exit flue 40 can beused for each pair of boilers. The superheater location and rear wall formation minimize the space required between adjacent pairs of boilers for tube removal. The light weight, low head- ,room requirements, efficient operation over a wide capacity range, and low cost of construction are further characteristics oi this boiler which indicate its f'ltness for marine use. V

While i'n 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: A

1. A steam boiler having an upper'steam and water drum, a lower water drum, a vertically ldisposed convection heated bank of steam generating tubes extending between and connected to saidy drums along the length thereof, a partition defining the inner side wall of a combustion f chamber laterally adjoining the space containing said tube bank and communicating therewith at terial carried by the rear tubes of said row being arranged to leave the inner faces of said tubes exposed to the combustion chamber, headers connected to the lower and upper ends of said water tubes, a row of tubes connecting said lower header to-said lower drum, a row of tubes connecting said upper header to said steam and water drum, and means for burning fuel in suspension in said combustion chamber and' effecting a substantially horizontal ow of heating gases longitudinally through said combustion chamber and reversely through said tube space and in thermal contact with the tubes "therein 2. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a partition defining the inner side wall of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at onegend, a row of vertically disposed water tubes laterally spaced from said tube bank, refractory material carried by said water tubes and defining the outer side wall of said combustion'chamber,

headers connected to the lower and upper ends of said water tubes, a row of tubes connecting said lower header to said lower drum; means closing the spaces between said last named tubes and defining the 'floor of said combustion chamber, a row of tubes connecting said upper header to'said steam and water drum, a superheater positioned in said combustion chamber at the end thereof communicating with said tube space, and means for burning fuel in suspension in said combustion chamber and effecting a substantially horizontal flow -of heating gases longitudinally through said combustion chamber and reversely through said tube space and in thermal contact with the tubes therein.

3. A steam boiler having an upper steam and water drum', a lower waterdrum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a partition defining the inner ,side wall of a iiuid cooled combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at one end, a row of vertically disposed water tubes laterally spaced from said tube bank,

refractory material carried by said water tubes and defining the outer side wall of said combustion chamber, headers connected to the lower and upper ends of said watertubes, a row of Atubes connecting said lower header to said lower drum. means closing the spaces between said last named Jtubes and defining the floor of ^said combustion chamber, a plurality of vertically spaced rows of tubes connecting said upper header to said steam and water drum, means closing the spaces between theA lowermost row of said last named tubes and defining the roof of said combustion chamber, and means for burning fuel in suspension in `said combustion chamber and effecting a substantially 'horizontal iiow of heating gases longitudinally through said combustion vchamber and reversely through said tube space and in thermal contact with the tubes therein.

4. A steam boiler having an upper steam and water drum, a lower water druma` verticallyl disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, means delining a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith only at the rear end of said boiler, means for burning fuel in said combustion chamber and effecting a substantially horizontal ow of heating gasesprearwardly through said lcombustion chamber and forwardly through said tube space and in thermal contact with the tubes therein, and a group of superheater tubes positioned in and extending across the rear portions of said combustion chamber and tube space.

5. A steam boiler having an pper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to saiddrums along the length thereof, means defining a combustion chamber laterallyadjoining the space containing said tube bank and communicating therewith only at the. rear end of said boiler, me'ans for burning fuel i'n said combustion chamber and effecting a substantially horizontal iiow of heating gases rearwardly through said combustion chamber and forwardly through said tube space and in thermal contact with the tubes therein, a superheater extending across the rear portion lof said combustion chamber, and a group of tubes in the rear portion of said combustion chamber between said superheater and said fuel burning means and arranged to form a radiant heat screen for said superheater.

6. A steam boiler having an upper steam and` water drum, a lower water drum,a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a partition defining the inner side wall of a combustion charn-- ber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed water tubes laterally spaced from said tube bank and having their upper and lower ends connected to said upper and lower drums respectively, re-

wardly -through said 'combustion chamber and forwardly through said tube space and in thermal contact with the tubes therein, and a super- `heater extending across the rear portions of said combustion chamber and tube space.

7. A steam boiler having an upper steam and water drum, a lower water drum, a verticallydisposed convection heated bank of steam generating tubes extendingo between and connected to said drums along the length thereof, a partition defining the inner side Wall vof 'a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith Atubes and defining the` cuter' side wall of saidv combustion chamber, means for burning fuel in suspension in said combustion chamber land effecting a substantially horizontal flow of heating gases rearwardly through said combustiony P chamber and forwardly through said tube space and in thermal contact with the tubes therein, a bank of superheater tubes extending across the rearportion of said combustion chamber, and a group of tubes in the rear portion of said combustion chamber between said superheater and said fuel burning means and forming a water screen for said superheater.

8. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a partition defining the inner side wall of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed water tubes laterally spaced from said tube bank and having their upper and lower ends connected to said upper and lower drums respectively, refractory material carried by said water tubes and dening the outer side wall of said combustion chamber, means for burning -fuel in suspension in said combustion chamber and effecting a substantially horizontal flow of heating gases rearwardly through said combustion chamber and forwardly through said tube space and 'in thermal contact with the tubes therein, a

bank of U-shaped superheater tubes extending horizontally across the rear portions of said combustion chambervand tube space, a baiile forming an extension of the inner side wall of said combustion chamber andV arranged to support said superheater tubes, and a group of tubes in the rear portion of said combustion chamber between said superheater and said' fuel burning means and forming a water screen for said superheater.

9. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generatingtubes extending between and connected to said drums along the length thereof, a partition defining the inner side wall, of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed water tubes laterally spaced from said tube bank and having their upper and lower ends connected to said upper and lower drums respectively, refractory material carried by said water tubes and defining the outer sidewall of said combustion chamber, means for burning fuel in suspension in said combustion chamber and effecting a substantially horizontal flow of heating gasesrearwardly through said combustion chamber and forwardly through said tube space and in thermal contact with the tubes therein, a bank of U-shaped superheater tubes extending across the rear portions of said combustion chamf ber and tube space, and a group of vertically arranged tubes in the rear portion of said combus-V tion chamber between said superheater and said fuel vburning means and forming a water screen for said superheater.

l0. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, means defining a combustion chamber laterally adjoining the space containing said tube-bank and communicating therewith only at the rear end of said boiler, means for burning fuel in said combustion chamber and effecting a substantially horizontal flow of heating gases rearwardly through said combustion chamber and forwardly through said tube space and in thermal contact with the tubes therein, a water screen extending across the rear portion of said combustion chamber comprising upper and lower transverse headers, vertically extending tubes connecting said headers, and nipples connecting the ends of said upper and lower screen headers to said upper and lower drums respectively.

1l. A steam boiler having an upper steam and water drum, a lower water drum, a. vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a partition defining the inner side wall of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed water tubes laterally spaced from said tube bank and vextending along the outer side wall of said combustion chamber, headers connected to the lower and upper ends of said water tubes, a row of tubes connecting said lower header to said lower drum, a row of tubes connecting said upper header to said steam and water drum, means for burning fuel in said combustion chamber and effecting a substantially horizontal flow of heating gases rearwardly through said combustion chamber and .forwardly through said tube space and in thermal contact lwith the tubes therein, and a water screen extending across the rear portion of said combustion chamber comprising upper and lower transscreen headers to said side wall headers for holdf ing said screen in position.

l2. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a partition defining the inner side wall of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, ak row of vertically disposed water tubes laterally spaced from said tube bank and extending along the outer side wall of said combustion chamber, headers connected to the lower and upper ends of said water tubes, a row of tubes connecting said lower headers to said lower drum, a row of tubes con,

necting said upper header to said steam and water drum, means for burning fuel in said combustion chamber and effecting a substantially horizontal flow of heating gases rearwardly throughV said combustion chamber and forwardly through said tube space and in thermal contact with the tubes therein, and a' water screen extending across the rear portion of said combustion chamber comprising upper and lower transverse headers, vertically extending tubes connecting said headers, and nipples connecting said upper screen header to said upper side wall header and said upper water drum.

13. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convection heated bank of steam generating tubes extending between and connected to said drums along the length thereof, a -partition defining the inner side wall of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed water tubes laterally spaced from said tube bank and extending along theouter side of said combustion chamber, headers connected to.

tube space and in thermal contact with the tubes therein, a water screen extending Vacross the real" portion of said combustion chamber comprising upper and lower transverse headers,l vertically "extending tubes connecting said headers, tubes connecting said upper screen header to said upper drum, and nipples connecting said lower screen header to said lower side wall header and said lower drum.

14. A steam boiler having an upper steam and water drum, a lower water drum, a vertically" disposed convection heated bank of steam generating tubes extending between and connected to said drums alongthe length thereof, a partition dening the `inner side wall of a combustion chamber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed wa.- rter tubes laterally spaced from said tube bank and extending along the outer side wall of said combustion chamber, headers connected to the lower and upper ends of said water tubes, a row of tubes connecting said lower header .to said lower drum, a row of tubes connecting said upper header to ,said steam and water drum, meansl for burning fuel in suspension in said combustion chamber and effecting a substantially horizontal ow of heating gases rearwardly through said-combustion chamber and forwardly through said tube space and in thermal contact with the tubes theren, and a water screen extending across the rear portion of said combustion chamber comprising upper and lower transposed convection heated bank of .steam genera rftubes extending between and connected to said drums along the length thereof, apartition de- `v l ning the inner side wall of a combustion cham-i l ber laterally adjoining the space containing said tube bank and communicating therewith at the rear end of said boiler, a row of vertically disposed water tubes laterally spaced from said tube bank,

refractory material carried by said water tubes.v

and defining the outer side wall of said combustionchamber, headers connected to the lower and upper ends of said water tubes, a row of tubes connecting said lower header to said lower means closing the spaces between said last ed ,tubes and defining the iloor of said combustion chamber, a row of tubes connecting said upper header to said steam and water drum, means closing the spaces between said lasst named tubes and defining the roof of said coinbustion chamber, means for burning fuel in suspension in said combustion chamber and eiecting a substantially horizontal dow of heating gases rearwardly through said combustion chamber and forwardly through said tube space and in thermal contact with the tubes therein', a water screen extending across the rear portion of said combustion cham- Y ber comprising upper and lower transverse headers, verticallyextending tubes connecting said headers, nipples connecting said upper screen header to said upperside wall header and said upper drum, and nipples connecting said lower, screen header to said lower side wall header and said lower drum, and a superheater in the path yoi the heating gases leaving said water screen.

16. A steam boiler having an upper steam and water drum, a lower water drum, a vertically disposed convetion heated bank of steam generating tubes extending between and connected to said drums along the length thereof, means forming a furnace chamber laterally adjoining the space containing saidtube bank and communicating therewith at the rear end of said boiler comprising a row of vertically disposed water tubes forming the innermost row of said tube bank, refractory material carried by said water tubes and dening the inner side wall of said furnace chamber, a second row of radiant heated vertical tubes laterally spaced from said tubebank and having their upper and lower ends connected to said upper and lower drums respectively, and refractory material carried by said' last named tubes and dening the outer side wall of said furnace charnber, the refractory material carried by the forward tubes of said rows being arranged to cover the inner faces of said tubes and the refractory material carried by the rear tubes of said rows being arranged to leave the inner faces of said tubes exposed to the furnace chamber, and means at the Vfront wall for burning fuel in suspension in said furnace chamber and effecting a substantially horizontal flow of heating gases rearwardly through said furnace chamber and forwardly through said tube space and inthermal contact with the tubes therein.

i7. ,d 'f :1 n boiler having a housing enclosing an upper steam and water drum, a lower water mi; .f. a vertically disposed convection heated bank tween and connected to said drums along the llength thereof, a partition defining the inner side wall of a combustion chamber substantially wholly at one side of the plane including the longitu 11:1 axes of said drums and laterally ad-` joining the space containing said tube bank and communicating therewith at 'one end, radiant heated tubes connected to said drums and laterally 'spaced from said partition and extendingl along the outer side wall of said combustion cher,4 means for burning fuel in suspension in said combustion chamber and eecting a substantially horizontal flow of heating gases rearwardly through said c bustion chamber and thence through said tu space ,comprising a group of fluid fuelburners mounted in the front wall of said combustion chamber and symmetri-s cally arranged ln pairs relative to the inner and outer side walls thereof to discharge' parallel streams of fuel substantially horizontally therein,r and a heating gas outlet from said tube space at the sidev Aof said partition opposite said combustion chamber. l v 18. A steam boiler having a setting comprising front, rear and side walls, an upper steam and water drum, a lower water drum, a vertically disconvection heated bank of steam generattubes extending between and connected to ofy steam generating tubes extending betherein, a group of .vertically disposed water tubes arranged to form a. radiant heat screen extending across a. rear portion of said combustion chamber and spaced from said rear wall and having their upper and lower ends connectedv to said upper and lower drums respectively.

THOMAS B. STILLMAN.

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