US2697422A

US2697422A - Boiler furnace

Info

Publication number: US2697422A
Application number: US149972A
Authority: US
Inventors: Wilbur H Armacost
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1950-03-16
Filing date: 1950-03-16
Publication date: 1954-12-21
Anticipated expiration: 1971-12-21

Description

Dec. 21, 1954 w. H."ARMACOST 2,697,422

I BOILER FURNACE Filed March 16. 1950 s Sheets-Sheet 1 wmip ii mm ATTORNEY 8 Sheets-Sheet 2 BOILER FURNACE W. H. ARMACOST l INVE OR I /Mw ATTORNEYS Filed March 16, 1950 Dec. 21, 1954 Dec. 21, 1954 w. H. ARMACOST BOILER FURNACE 8 Sheets-Sheet 3 Filed March 16. 1950 i6, wad," j ,LTZF/ ATTORNEYS Dec. 21, 1954 w. H. ARMACOST 2,697,422

BOILER FURNACE Filed March 16. 1950 8 Sheets-Sheet 4 ATTORNEY Dec. 21, 1954 w. H. ARMACOST BOILER FURNACE 8 Sheets-Sheet 5 Filed March 16. 1950 BY Z a ATTORNEY:

Dec. 21, 1954 w. H. ARMACOST 2,697,422

BOILER FURNACE FiledMarch 16, 195O 8 Sheets-Sheet 6 g ,2 T 3 g 1 if 3 J4 ail 35.24 j ilhzlfiw ATTO R N 5Y Dec. 21, 1954 w. H. ARMACOST 2,697,422

BOILER FURNACE Filed March 16, 1950 8 Sheets-Sheet 7 g I I u I I I I M; l I

I I I I I 3% I I I I I I I I I 1 I I I I I l I I "A -L I a REAR WALL TUBES27 5/05 mu megs Z? lizalN Toz A BY ZMml L ATTORNEY? w. H. ARMACOST 2,697,422

BOILER FURNACE 8 Sheets-Sheet 8 Dec. 21, 1954 Filed March 16. 1950 ATTORNEYS 7 s't'antially': on the line 5-. -5: of

United States Patent BOILER FURNACE j Wilbur H; Armacost, Scarsdale, N. Y.,1assignor'to Combustion Engineering,.Inc.,-:New York, N. Y., a corporation of Delaware Application ;March 16, 1950,. Serial No; 149,972 1-0 Claim'sf (Cl. up-33s This invention relates to steam, generating boiler furnaces in which the stearngeneratingsurfaces are largely subject to radiant ,heat and in which so-called tangential firing of the fuel is employed.

7 The primary object of my invention is the provision of a high capacity steamflgenerating installation employing afurnaceor combustion chamber lined with radiant heat tubesfin which Wideflexibilityjof flame control and wide angle of flame adjustment tomeetvarying operating ;conditions may be procured. withoutjencountering objectionable fuel and flame: impingement on the tubular walls'of the furnace and OtherdifiicuIties and while lsecuring superheat temperature control and other ad- ;vantages hereinafter set forth.

How the foregoing,'jtogetherfwithj'suchother objects .and advantages as may herinaftepflPPBfiI, ,or, are incident to my invention, are;.realized.is jllhstratedjin the following drawings, Lin which- Fig. l is ,azbroken out 'ver'tic l iseetional,,view of a steam; generating boiler fui'naceconstructed; in accordance with rny-invention; A Fig.2 is 'an' enlargedfhrokenf out vertical elevational Lviewfwith the right hand half of the. viewllookingfin the direction of the arrows.,2-J-2 [of Fig. l'andiwith. the

, left hand half of the view beingja section taken; subv sta'ntially on the, line lit- 12a of Fig. 1;

Fig.j 3.is anen-l'a'r'ged horizontal section taken sub- .jstantiallylon the linel33 offlFig ljbutjwithfcj rtain burner and air casing, parts infull view;

' Fig. 4 is an enlarged vertical sectional viewofra portion of, one of the burners, taken. ,substantially on the line .44 of Fig. 1; .7 Fig. 5 is'Ja fragmentary :horizon1tal.- .se'c'tion taken sub- Eig.

Fig.v 6 isfa fragmentary'l horizontal section'-.taken substan'tially on the line 6 6--illustrating the cornertube arrangement;

2,697,422 Batented Dec. 21, 1954 Lboiler furnace, as viewed infigs. 3,f5, 6-and 7 are cut walls of the" furnace flQl'rlfedgd to edge 'of th 'ICllt-o'fi s.- i pl ty of. co nec in be 19,: e' dp.

the headers 18 tolatsteamflandwaterdrum 20. o, ,The front'wall 2 1 of the, furnace is lined jwjthi closely space p gh a ant. heatfiwa l't bes un onne te at .their lower ends into a j bottom.he ader 23]; and atjtheir upper ends, after inclining qupwardly Tat .24.,across the top of the furnace,,into thel steam' and'water'drurn 20. The lower portionof these front wall tubes "incline'doWnwardly and inwardly at ,to,forrn the. front of. a basketbottom for thefurnace, j Itis to be. noted thatkafgroup of the front Wall; tubes 22a, see Figsgl and..3,Q at-each end are arranged to line thecornerjsurfaces114 of the cut-off corners. The tubes of' these, groups. ,have,,th'eir lower end portions bent. downwardly, and inwardly to line up with thetube portions 25fabove mentioned so as to complete the 'front of the .basket bottom from; side wall ,to side wall of the furnace, Atfltheir lowerfierids these tubes connect into 'thebottorn 'head'er'23, which extends for the fullwidthof the furnace. -AttheiruDPer end portions thetub'es ofthese groups are b'entto 'in- -cline,-upwardly in line-with the upperportions 24 of the front wall tubes'22 forconnectioniinto the drum 20. Certainof-Jhese cornerftubes areib'enholt.bowed to provide openings 32' for the burners D, while "the reeause of the. diagonal 'widthof the corner surfaces 14,

a; space developsb'e'tween the tubes, and in. ordeptopro- 'v de-a. complete metalliclsurface atltheselcornerst'longr "tudinally extending fins 33 areuprovided on thektubes as shown in Fig. 6' for example.

\ The rearwall 26.:of thefurnace.islinedwithidoselv spacedupright radiant heat. tubes -27. connected at ;their lower ends into a bottom header 128- and;- at their. upper ends (after inclining: upwardly and inwardly-to formf'an arch 29; then upwardlv, and-rearwardly to form the bottom of a. sunerheater. space 30a, andthen up- Fig. 7 is aview similar; to' 'Fig; 6 hut showing the-tube arrangement at the burner opening. and. taken -substan Fig. 8 is a fragmentary v'e'rti'callface, viewilooking togard a corner.burnergtasaindieated :by 'the'IineES S' of 1g. 5; Fig. 9 isa fragmentary' sectioiial-lview'similari to Fig.

"5; and p Fig. 10 is a view, similar to Fig. 9.

The boiler. furnace is. rectangular in cross section and ing 9, andan upper throatportion Q havingan outlet fporti'o'n 10. -Hot' gaseous products of. combustion pass downwardly from the outlet'portio'n 10andj finallyto the stack (not shownlw .Superheaters andieheaters 11,

11a, 12 and- 12a"a're desirably locatedjasdndicated in Figure 1. The combustion chamberfis lined withnradiant heat tubes and is provided with burrtersD'atthe corners artionof the combustion chamber, combined with vadiustableburners, enables me to obtain, 'int'er'alia," wide latitude of flame control without. flame impingement "on the 4 walls; and enables the positioning of structural work "si1 ch'- as-columlns close to the installationfat the corners without interference with the-*burners,-all-as will appear herern after.

' Before describing the invention '-in detail; particular 'attention is ealledto the fact-that the l corners -,-13-of the wardlv again) into the pooch-steam andwater. drum 20. The lower 1 portion ofthese rear, wall tubes inclines downwardly and inwardlvf'at'31 torform the rear of 'the basket-bottom for the furnace. -ln a manner similar to that described-above in -connection with thefront wall.

a grou of the rear wall tubes 22! (see-Fi s. 1,3, 6,

7, and .8) at each end arearr'anged to. line the-co ner surfaces 14 of the cut-off corners. Thetubes ofth se groups have their lower end portions bent-downwardlv andin ardlv to line-u with thetubeportions 31 so as to com lete the rear of the basket-bottom of the furna e 1 comprises, in 7 general, a combustion chamber- A' having v.abasket-bottom portion-B with a bottomdi'scharge' openfromsidewall to side' wall of the-furnacea A..t tl1eir lower ends these-tubesconnectinto the-bottom header 28 which extends for the full width f the-furnace. At

their upper endportion the-tubesofthese r ups,hend ,in the same manner as the rear wall-tubes 26 andthen co nect into the drum;20.

ranged for tangential firing; The particular construe Referring'to Fins. 5-7 and 8 -which;show thet be arran ement at the burner-o enin s; it will be seen th t the howedportions -34 of-several of the-tubesateach' side of the o ening-c me intoclose'contact and that-several f the tubes are bowed rearwardlv at the openin2 --as at 35. The wall tubes are desir blv lined on the ou sidei h refractorv material 36: and refractory materi l 37 and 38 isorovided on the ro f and arch portionsof thet'ubes.

The upper drum 20a interconnected with a rear drum 39 bv means of a luralitv ,ofcircnlat-ingtuhes. 40 anclfto a lowerdrum 41-bv a pluralityof circulating tubes 42. The drums 39 and 41 are,connected'bv'meanslofa plurality of circulatingtubes 43. A plur li y, f d wnco'mer ,tubes 44 lead from the lower. drum 41'to fthe lower por tion of the installation and frorn the lower portion of these tubes a pluralitv'of downcomentubes 45" arrdi46 lead to Reverting now to the tubular wall construction, it is to be noted that by employing the cut-off corner arrangement described I am enabled, inter alia, to reduce the number of tubes in the side walls by grouping the corner tubes with the tubes of the front and rear walls, thus enabling the use of short headers for the side walls as contrastedwith the longer headers for the front and rear walls.

The burners D, of which there is one for each corner of the installation, comprise in general a plurality of tiltable air nozzles and a plurality of tiltable fuel nozzles arranged alternately in vertically spaced relation, the number of nozzles employed being determined by the size of the installation. In this particular instance, I employ a plurality of fuel nozzles 47 for burning pulverized fuel and a plurality of fuel nozzles 48 for burning oil, and upon inspection of Fig. 1 it will be seen that each burner has four pulverized fuel nozzles 47 and three oil nozzles 48. At the bottom and top of the burner, tiltable air nozzles 49 are provided. Each pulverized fuel nozzle 47 has air nozzles 50 in the nozzle tip and movable therewith; and the oil nozzles 48 each have tiltable air nozzles 51 associated and movable therewith as clearly shown in Fig. 4.

All of the nozzles are supported in a burner casing 52, the outlet ends of which register with the burner openings 32 in the angular corner surfaces 14 of the furnace. The casings 52 and fuel nozzles are so positioned that tangential firing is obtained as clearly indicated by the dot and dash lines in Figure 3.

The burner casings 52 are housed in air casings or wind boxes 53 which have connection by means of conduits 54 with air ducts 55 leading from a source of preheated air such as a regenerative air heater located in the furnace off-take. Suitable dampers indicated at 56 in Fig. 3 are associated with each wind box to provide for air control.

Control and latitude of firing is obtained by employing the tiltable nozzles above described, the construction and operation of which are as follows:

The nozzle tips 47a of the pulverized fuel nozzles 47 have pivotal connection with the nozzles at 57 so that they can be tilted through the range indicated by the dot and dash positions 47b and 47c. Adjustment to the desired position of tilt is obtained by means of an operating bar 58 connected to a bell crank 59 which in turn is connected to a link 60 having connection with the nozzle tip 47a at 61.

The oil burner nozzles 48 are pivotally mounted at 62 i and the air nozzles 51 associated therewith are pivotally mounted at 63 so that they can be tilted through the ranges indicated by the dot and dash

position

62a and 62b and 63a and 63b. Adjustment to the desired position of tilt is obtained by means of the operating bar 58 connected to the bell crank 64 which in turn is connected to a link 65 having connection with the air nozzle 51 at 66. The two air nozzles 51 and the oil burner nozzle 48 are interconnected by means of a link 67 and levers 68.

The air nozzles 49 are pivotally mounted at 69 so that they can be tilted through the range indicated by the dot and dash

position

49a and 49b. Adjustment to the desired position of tilt is obtained by means of the operating bar 58 connected to the bell crank 70 which in turn is connected to a'link 71 having connection with the upper air nozzle 49 at 72. This upper air nozzle 49 is connected to the lower nozzle 49 by means of a link 73 and levers 74.

It is to be observed that by mounting the burners D in the set-in angular corner wall portions 14 of the combustion chamber, see particularly Figs. and 9, the burner tips extend well into the combustion chamber with the result that the fuel streams discharging'therefrom are spaced from the adjacent walls of the chamber. This is very advantageous from the standpoint of flexibility of firing because I am thus enabled to employ a flame ranging from a narrow to a very wide angle without flame impingement on the walls.

In order that the advantages to be realized through the practice of my invention may be better understood, I have illustrated, more or less diagrammatically, a comparison of my arrangement, see Fig. 9, with the usual arrangement of corner firing, see Fig. 10.

In Figs. 9 and I have illustrated burners D having nozzle tips 75 which, in addition to being adjustable up and down on pivots 76, are also adjustable from side to side on pivots 77, thus enabling universal adjustment of the tips. In Fig. 9 I have indicated at 78 the distance that the center of discharge of the burners is from the furnace wall in my arrangement, while in Fig. 10 I have indicated at 79 the distance that the center of discharge of the burners could be from the furnace walls when employing the usual arrangement of burners for corner firing. It will thus be observed that with my arrangement it is possible to employ an adjustable burner to produce a wide angle of flame without flame impingement on the walls, while with the previous arrangement as exemplified in Fig. 10, adjustment of the burner for a wide angle of flame would cause flame impingement on the walls.

Another advantage of my arrangement resides in the fact that, by employing the flatted corners, I eliminate the relatively cold or dead areas of the conventional sharp V corners, such as are present at 80 in the arrangement of Fig. 10. Thus the collecting of coked unburned fuel on the corner surfaces, which is an incident to the arrangement of Fig. 10, is avoided.

My arrangement is also advantageous in that by employing cut-off corners, the burners and associated casings can be set in close to the furnace, thus giving ample clearance on the outside for the location of structural columns and beams close to the sides of the furnace without interfering with the burners as clearly shown at 81 in Fig. 3.

The provision of the flatted corners and the location of the burner tips closely adjacent thereto shortens the distance from the burner tips to the center of the furnace. This ensures turbulence of the fuel and flame streams in all positions of burner adjustment. With the burners in mid position, vertically and laterally, the turbulence will be at a maximum for any given velocity of fuel and air admission, and will be reduced somewhat as the burners are shifted from such position, sidewise or up and down.

With turbulence at the maximum, the intensity of the flame and therefore its temperature is at the greatest, decreasing as adjustment is made of the burners from said position. By vertical adjustment, the body of flame is lowered or raised as the case may be. Thus, by virtue of the flexibility of flame control and flame location, a variety of operating conditions may be met while ensuring effective combustion and control of superheat temperatures, and without encountering the difiiculties which would be encountered if the wall tubes were substantially impinged by the fuel and flame streams.

While the invention has been described in connection with an installation using pulverized fuel as the primary fuel, it is to be understood that the advantages to be realized through the practice of the invention will be realized when other fuels are used, such as oil or gas.

I claim:

1. In a steam generating boiler furnace, the combination of an interiorly unobstructed combustion chamber having its walls lined with closely spaced upright radiant heat tubes, said combustion chamber being generally rec tangular in cross section with its four corners cut at an angle to provide substantially cut-off corner wall portions set in a substantial distance from the theoretical, projected corners of the combustion chamber, radiant heat tubes lining said corner wall portions, said corner wall portions having burner openings therein, and fuel burners for introducing fuel into said combustion chamber through said openings to provide tangential firing, said fuel burners comprising casing structure mounted in said corner wall portions at said openings, fuel and air nozzles mounted in said casing structure with their discharge ends extending well into said openings, and adjustable tips for said nozzles for controlling fuel and air admission into the combustion chamber, the extent of the cut off at the corners and the location of the adjustable burner tips being such that in no position of adjustment of the tips will there be impingement of the fuel and flame stream of the radiant heat wall tubes.

2. In a steam generating boiler furnace, the combination of a combustion chamber generally rectangular in cross section and having its walls lined with closely spaced upright radiant heat tubes, substantial cut-off wall portions at the corners of said combustion chamber having burner openings therein, upright radiant heat tubes lining said angular wall portions, and fuel burners mounted at said openings and extending well thereinto for introducing fuel into said combustion chamber to provide tangential firing, said fuel burners comprising air and fuel nozzles mounted with their discharge ends at said fuel openings, and adjustable tips for said nozzles for controlling fuel and air admission into the combustion chamber, the extent of the cut off at the corners and the location of the adjustable burner tips being such that in no position of -adjustment-of the tipswilltherei-be impingementfof' the 'fuel and flame stream of the radiant-heat-wall-*tubes.

3.-In a steam :generating'boiler furnace, the-combination-ofa combustion-chamber"generally-rectangular in cross-section with its corners-formed to provide substantial cut-off corner wall-portionsy upright radiant heat tubes lining the walls of said combustion chamber including said eut-off'corner wall portions; said fiatted-corner wall portions having burner openings therein; and burners for introducing fuel through said openings into the combustion chamber to provide tangential firing, said burners includingadjustablenozzles the discharge-ends of which lie closely adjacent the plane of said fuel openings for introducing fuel-with wide-"latitude of flame adjustment, the extent of the cut-otfat thecorners and :the positionof the adjustable burner nozzles being such that in 'no position of adjustment of the*latter will there be impingement of the fuel and flame stream" on the radiant heat tubes.

'4. .In 'a steam generating boiler furnace, the combina- --tion of a'combustion chamber generally rectangular incross section, fuel burners mountedzat the corners of said combustion chamber for introducing fuel tangentially intosaid chamber, said burners having nozzles extending well into-the combustion chamber at said corners',*substantial cut-off corner wall portions for said combustion chamber cutting the corners thereof and having fuel openings in registry with said nozzles, upright radiant heat tubes lining the walls of the combustion chamber including said corner wall portions, and means for adjusting said nozzles for flame control, the extent of the cutoff at the corners and the position of the burner nozzles being such that in no position of adjustment of the burner nozzles will there be impingement of the fuel and flame stream on the radiant heat tubes.

5. A steam generating boiler furnace comprising in combination a combustion chamber generally rectangular in cross section having side walls, a front wall, a rear wall, and substantial corner wall portions cutting its corners, upright radiant heat tubes lining said side walls, lower headers into which the lower ends of the side wall tubes are connected. upper headers into which the upper ends of the side wall tubes are connected, upright radiant heat tubes lining said front and rear walls, upright radiant heat tubes lining said corner wall portions. a lower header into which the lower ends of the front wall tubes are connected and into which the lower ends of the corner wall tubes adjacent the front wall tubes are connected, a lower header into which the lower ends of the rear wall tubes are connected and into which the lower ends of the corner wall tubes adjacent the rear wall tubes are connected. an u er rum into which the upper ends of said front, rear, and corner tubes are connected, and burner means mounted in said corner wall portions extending well Within the theoretical projected corners formed by the walls of the combustion chamber for introducing fuel into said combustion chamber tangentially, said burner means being adjustable to alter the delivery of fuel therefrom, the extent to which the corner wall portions cut the corners of the combustion chamber and the location of the adjustable burner means being such that in no position of adjustment of the latter will there be impingement of the fuel and flame stream on the radiant heat tubes.

6. A steam generating boiler furnace comprising in combination a combustion chamber generally rectangular in cross section having side walls. a front wall, a rear wall, and substantial corner wall portions cutting its corners. upright radiant heat tubes lining said side walls, lower headers into which the lower ends of the side wall tubes are connected, upper headers into which the upper ends of the side wall tubes are connected, upright radiant heat tubes lining said front and rear Walls, and upright radiant heat tubes lining said corner wall portions, a lower header into which the lower ends of the front wall tubes are connected and into which the lower ends of the corner wall tubes adjacent the front wall tubes are connected, a lower header into which the lower ends of the rear wall tubes are connected and into which the lower ends of the corner wall tubes adjacent the rear wall tubes are connected, an upper drum into which the upper ends of said front, rear, and corner tubes are connected, and burner means mounted in said corner wall portions for introducing fuel into said combustion chamber tangentially at a point Well within the theoretical projected corners formed by the walls of the combustion chamber, certain tubes of said corner wall tubes being bowed to ,the adjustable burner means being such that in no position of adjustment of-the latter 'will-there be impingement of the fuela'nd flameas'tream -'on the radial -=heat tubes.

7; A steam 'generating boiler furnace comprising in combination a combustion chambergenerally-rectangular in -cross=-section= having side walls, a front 'wall,--:a rear *wall, and substantial corner wall 1 portions "-cuttlng its corners, uprightradiant'heat-tubes lining-said-side walls,

--upright radiantheat tubes lining said front wallsJup'right radiant heat-tubes grouped' withsaid-front wall-'-tubes lining the; cornerwall portions adjacent said =-fr'ont -wall, upright radiant-"heattubes lining said rear wall, upr1g'ht 'radia-nt heattubes grouped with said rearwall' tube's lining the'angular-wall portions adjacent said 'rearwall,'= lower -'headers for said side wall-tubes-,-a lowerheadebcommon to said front wall tubes-and the corner wall tubesgrouped therewith,- a -lower-header common to said rear walltubes and the "corner wall -tubes-grouped-- therewith-,- and adjustable burner means at=the corners the discharge; ends of which extend well within the theoretical projectedcorne'rs formed by the walls of the combustion chambers, the extent to which the corner wall portions cut the corners of the combustion chamber and the location of the adjustable burner means being such that in no position of adjustment of the latter will there be impingement of the fuel and flame stream on the radiant heat tubes.

8. A steam generating boiler furnace comprising in combination a combustion chamber generally rectangular in cross section having side walls, a front wall, a rear wall, substantial corner wall portions cutting its corners, and a basket-bottom, upright radiant heat tubes lining said side walls, upright radiant heat tubes lining said front wall, upright radiant heat tubes grouped with said front wall tubes lining the corner Wall portions adjacent said front wall, said front wall tubes and the corner wall tubes grouped therewith being bent downwardly and inwardly at their lower portions to form the front of said basketbottom from side wall to side wall of the combustion chamber, upright radiant heat tubes lining said rear wall, upright radiant heat tubes grouped with said rear wall tubes lining the corner wall portions adjacent said rear wall, said rear wall tubes and the corner wall tubes grouped therewith being bent downwardly and inwardly at their lower portions to form the rear of said basketbottom from side wall to side wall of the combustion chamber, upper and lower headers into which the side wall tubes are connected, lower headers into which the front and rear wall tubes and their grouped corner tubes are connected, an upper drum into which said front, rear and grouped tubes are connected, and adjustable burner means at the corners the discharge ends of which extend well within the theoretical projected corners formed by the walls of the combustion chamber, the extent to which the corner wall portions cut the corners of the combustion chamber and the location of the adjustable burner means being such that in no position of adjustment of the latter will there be impingement of the fuel and flame stream on the radiant heat tubes.

9. A steam generating boiler furnace comprising in combination a combustion chamber generally rectangular in cross section having side Walls, a front wall, a rear wall, substantial corner wall portions cutting its corners, and a basket-bottom, and a top wall, upright radiant heat tubes lining said side walls, upright radiant heat tubes lining said front wall, upright radiant heat tubes grouped with said front wall tubes lining the angular wall portions adjacent said front wall, said front wall tubes and the corner Wall tubes grouped therewith being bent upwardly and rearwardly at their upper portions to line said top wall from side to side wall of the combustion chamber, upright radiant heat tubes lining said rear wall, upright radiant heat tubes grouped with said rear wall tubes lining the corner wall portion adjacent said rear wall, upper and lower headers into which the side wall tubes are connected, lower headers into which the front and rear wall tubes and their grouped corner tubes are connected, an upper drum into which said front, rear and grouped tubes are connected, and adjustable burner means at the corners the discharge ends of which extend well within the theoretical projected corners formed by the walls of the combustion chamber, the extent to which the comer wall portions cut ,the corners of the combustion chamber and the location of the adjustable burner means being such that in no position of adjustment of the latter will there be impingemgnt of the fuel and flame stream on the radiant heat tu es.

10. A steam generating boiler furnace comprising in combination a combustion chamber generally rectangular in cross section having side walls, .a front wall, a rear wall, substantial corner wall portions cutting its corners, upright radiant heat tubes lining said side walls, upright radiant heat tubes lining said front walls, upright radiant heat tubes grouped with said front wall tubes lining the corner wall portions adjacent said front wall, upright radiant heat tubes lining said rear wall, upright radiant heat tubes grouped with said rear wall tubes lining the corner wall portions adjacent said rear wall, said rear wall tubes and the corner wall tube grouped therewith being bent upwardly and forwardly at their upper portions to provide an arch for said combustion chambers from side wall to side wall thereof, downcomer connections to all of said upright tubes, an upper drum with which all of said tubes have upcomer connection, and adjustable burner means at the corners the discharge ends of which extend well within the theoretical projected corners formed by the walls of the combustion chamber, the extent to which the corner wall portions cut the corners of the combustion chamber and the location of the adjustable burner means being such that in no position of adjustment of the latter will there be impingement of the fuel and flame stream on the radiant heat tubes.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,766,989 Forssblad June 24, 1930 1,866,404 Frisch et al July 5, 1932 1,905,283 Heaton Apr. 25, 1933 1,992,953 Kerr Mar. 5, 1935 1,994,447 Bailey et a1 Mar. 12, 1935 2,011,026 Bailey et al Aug. 13, 1935 2,243,909 Kruger June 5, 1941 2,363,875 Kreisinger et al Nov. 28, 1944 2,608,168 Jackson Aug. 26, 1952 FOREIGN PATENTS Number Country Date 71,857 Switzerland May 19, 1931