US2112202A

US2112202A - Steam boiler

Info

Publication number: US2112202A
Application number: US43321A
Authority: US
Inventors: Charles E Lucke
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1935-10-03
Filing date: 1935-10-03
Publication date: 1938-03-22
Anticipated expiration: 1955-03-22

Description

C. E. LUCKE March 22, 1938.

STEAM BOILER Filed Oct. 5, 1935 4 Sheets-Sheet l INVENTOR. A Char/e5 E. VLuc/fe March 22, 1938. C. E. LUCKE STEAM BOILER Filed oct. 3. 19:55

4 sheets-sheet 3 00,0000 J O/amo INVENTOR. Char/es E. Lacke R ATTORNEY.

March 22, 1938. C, E, LUCKE 2,112,202

STEAM BOILER r Filed Oct. 3, 1935 l 4 Sheets-Sheet 4 INVENT OR.

Char/g5 E, [uc/( ATTORNEY.

I. Patented Mar. 22, 1,938u

UNITE-o STATES PA'rENTtoFFIcE STEAM BOILER Charles E. Lucke, New York, N. Y., Aassigner to The Babcock & Wilcox Company, Newark, N. J.. a corporationof New Jersey Application October 3,

7.1'1 Y Claims.

This invention..relates in general to the construction of steam generating umts, and more particularly tosteam generating units in which a water cooled furnace is located wholly at one side of the main tube bank of a two-drum steam boiler. Steam generating units of this type are i mainly characterized by their relatively low cost of manufacture and maintenance, small lfloor space and headroom requirements, and relatively wide range of capacity operation at high' emciencies.

A main object ofmy invention is the provision of a steam `generating unit of the character described with an improved location of the fuel burning means in one of the furnace walls -extending longitudinally of the main tube bank with the fueli discharged having a length oi'- travel in the furnace through a path directed so as to cause .substantially the entire furnace volume to be filled with fuel burning in suspension at various stages of combustion` and the initial portionv of the path to receive asubstantial amount of heat radiation from the, higher temperature.

section of 4the path, thus insuring complete combustion of the fuel in suspension in the furnacel at a high rateof heatfrelease. Anotherl mai'n object of my invention is the provision in a steam generating unit of the character described of -a baille systemA for the tube bank which will cause a heating gas ow relative to the tubes of the tube bank isuch as to effect a high rate of heat `wanner throughout the tube bank, a 10W draft, loss inthe unit, and a rapid rate of fluid circula-4 tion through the tubes, whereby a relatively high steaming capacity and generating efciency can be easily maintained in operation. f

The various features of novelty which characterize my invention are pointed out with pary ticularity in4 the claims annexed to and forming a.

part of this speciiication. For a better understanding oflv the invention, its operating advantages and specific objects attained by its use,

reference should be had tothe accompanying' 1935, serial No. 43,321 (ci. 122-336) Fig. 4 is a view similar to Fig. 1 of a modi; flcation;

Fig. 5 is a horizontal section taken on the line 5-5 of'Fig. 4; and

Figs. 6 and '7 are views similar to Fig. k1 of two other modifications.

In the embodiments of my invention illustrated in the drawings, the boiler settings are substantially rectangular in horizontal and vertical cross-section, being formed by vertical side walls Ill and I2, end walls II and I3, a top wall or roof I4, and a bottom wall or floor I5, hereinafter, specincally described. In the unit shown in Fig'. 2, the horizontal distance between the side Walls Ill-and I2l is substantially greater, than between the end walls. II and I3, but this ratio will vary with thefsize of the unit'.

I'he pressure parts of .the steam boilers shown in Figs. 1-5 and 7 include a horizontally elongated upper steam and water dru'm I6 `and a lower water` drum I1 in axial alignment therewith, both of which extend the full distance .between the side wallsII and I3 and adjacent to but spaced from the side wall I2. The drums I6 and I1 are connected by a vertically disposed bank of substantially straight water tubes I8 extending between and `having their ends radially connected to the Y drum walls at both sides of the vertical plane including the longitudinal axes of the drums. As shown in Figs. 1 and 2, the innermost longitudinal tuberowv Iii'l is spaced from the adjacent tube row a substantially greater distance than that between the remaining longitudinal rows of the tube bank. 4 I c A row of water tubes I9 extends laterally from fthe lower drum Il to a longitudinal header 20 at the bottom of the side wallv Il), the spaces be tween the tubes being closed by refractory mav terial 2l constructed to form a floor I5. JA row olv tubes 22 extends upwardly from theheader 2li to a similarly arranged top header 23. The spaces between the tubes 22 are filled with refractory material to form the inner portion of the sidel wall I0. A corresponding row of roof tubes 24 vconnects the header 23 to the upper drum I6, with cated at one side of the tube bank I 8 and between the vertical limits of the drums I3 and I1. 'Ihe construction of the walls I t, II, I3 and I4 with a substantial amount of exposed tube surface permits the ratio of cold surface to total wall surface and to furnace volume to be varied over a relativelydwide range to secure the most effective mean furnace temperature for different operating conditions and for different sizes of furnaces. 4

'I'he boiler furnace shown in Figs. 1-3 is adapted for the burningof various fluid fuels, such as pulverized fuel, oil, or gas, in suspension, and is particularly suitable for the burning of pulverized coal. The provisions for this purpose preferably consist of one or more at ame burners 3 I, such as the multiple outlet pulverized fuel burner shown in a pending application of Ervin G. Bailey, Serial No. 484,739, led Sept. 27, 1930, mounted in corresponding burner ports 32 formed in the roof I4 intermediate the ends of the furnace and adjacent the drum I6. The nozzle outlets of each fuel burner are positioned within an air box 33 opening to the corresponding burner port and the fuel streams pass between corresponding roof tubes 24, to produce a longitudinally elongated stream of mixed pulverized coal and air. Each fuel burner is downwardly directed With its axes of discharge intersecting the side Wall IIl adjacent its lower end, whereby the fuel stream tends to follow a flame path initially directed toward the side wall Ill, but curving downwardly above the iioor I5 towards the tube bank I8, whereby substantially all of the furnace volume will be effectively utilized by the elongated flame path so provided to permit substantially 'complete combustiondof the fuel stream before reaching the tube bank. The fuel stream thus passes through the furnace in a direction transversely of the tubebank, i. e., the fuel burner is located in a furnace wall extending longitudinally of the tube bank with its axis of discharge in a vertical plane transverse to that wall. f

The specific construction of the furnace bottom I 5 will mainly depend upon the mean furnace temperature desired to be maintained and the ash fusion temperature of the pulverized fuel to be used. The furnace shown in Figs. 1 and 2 is designed for dry ash removal. For this reason the furnace bottom is constructed to provide a relatively fiat horizontal floor for receiving the ash separating from the burning fuel. The deposited ash may be periodically removed from the floor by pushing or blowing the same into an ash pit 35, constructed in the ioor adjacent the end wall I I, .as shown in Fig. 2. Clean-out openings 36 are provided in the walls II and I3 at the oor level andin the ash pit to facilitate removal ofthe deposited ash.

The fuel burner arrangement described is especially adapted for an advantageous heating gas flow relative to the tube bank I8. As shown in y Fig. 1, the tube bank I3 is provided with a baille system consisting of a tube baille 40 extending downwardly from the upper drum I6 and formed by providing the upper half of the tubes I8' with studs 4 I, and filling the corresponding intertube spaces with refractory material 42, as shown in Fig. 3. The lower end of the baiiie 40 has a downwardly inclined lateral extension 43 terminating adjacent the outer side of the tube bank.

lThe lower ends of the tubes I8' are also provided with refractory embedded studs to form a short tube baille 44 which protects that side of the lower drum from furnace radiation and forms a pocket aliases for holdingmaterial, such as deposited furnace dust, to protect the upper surface of the drum from the high temperature gases. At the opposite side of the drum I 'I is a dust hopper 45, which receives dust swept oil' the drum by the gases or separated out of the heating gases above the hopper.

The side wall I2 is as shown, spaced throughout its'extent from the outer side of the tube bank I8. A baille d6 extends horizontally from the wall I2 across most of the tube bank I8 at a level intermediate the bafiie extension 43 and the upper drum I6, whereby the bailles 4I), 43, and 46 in conjunction with the side walls II, I2, and I3 define three serially connected superposed gas passes 50, 5I, and 52 extending transversely of the tube bank I8, with the passes 50 and 5I progressively tapering and connected by a gas turning and equalizing space 53 between the tube bank I8 and wall I2, and the passes 5I and 52 connected by a gas turning and equalizing space 54 between the tube baille 40 and the main portion of the tube bank. 'At the side of the upper drum I6 opposite the furnace and in communication with the outer end of the gas pass 52 is arranged a heating gas outlet 55 controlled by one or more dampers 56. The heating gases from the furnace will thus flow transversely of the tubes I8 throughout their height through gas passes having flow areas proportioned for a low draft loss. and highly effective heat transfer by reason of the mass ow conditions.A The passage of the hottest gases rst across the lower portions of the tubes effects a rapid iuid circulation in the tubes I8, because the average fluid density in the tubes due to the presence of steam in the water will be reduced over a greater vertical height of tube compared with the water in downcomer tubes.

The steam generated in the boiler passes out of the upper drum I6 through outlet connections 63 leading to a looped tube self-draining superheater formed by a pair of longitudinally extending horizontal headers di and 62 located adjacent the drum I1 and connected by nested rows of looped tubes 63 positioned in the gas pass 50 in the space between the tubes I8' and the adjacent row of tubes I3. The superheater tubes are arranged in position to receive a portion of their heat by radiation from the furnace chamber through the spaces between the tubes I8. The nested superheater tube rows are preferably spaced to provide a uniform transverse spacing of the tube legs and the tubes are bent at theirlower ends to pass between the tubes I8'.

In operation, the streams of pulverized fuel and air are discharged downwardly over a substantial portion of the furnace length in a path initially directed towards the side wall I0 and then curving towards the'lower portion of the tube bank. Combustion of the fuel is substantially completed before the stream reaches the tube bank, and

the ash separated in suspension drops to the furnace floor normally in a dry condition, The portions of the tubes I8 in front oi.' the superheater further cool any ash particles in suspension and also protect the superheater tubes from an excessive amount of radiant heat. The gases then pass over the superheater tubes and the remaining portion of the tube bank and turn upwardly through the space 53 into the gas pass 5I. The space 53 effectively maintains a uniform distribution f the heating gases and permits ash particles separating from the heating gases to drop directly into the ash hopper 45. The gases then pass inwardly through the second pass SI to the ct cially suitable for the collection'of slag deposits furnace side of the superheater. Figs. 4 and 5, the portions of the tubes it bespace t which functions in the same manner as the .space 53. Any ash deposited on the baille l extension 43 can be blown into the ash hopper. The -gases thenl pass outwardly vthrough the top gas pass 53 to the' heating gas outlet 55.

The modification illustrated in Figs. 4 and 5 is primarily distinguished from the form shown'.

in Figs. 1 to 3 by the different provisions for treating the Iincombustible ash residue of the fuel. In Fig. 4 the furnace bottom is shown as designed for thecollection of the ash in a molten condition, the tubes i9 being covered by a layer of slag resistant material B5 shaped to support a pool of molten slag which can be continuously or intermittently tapped through a slag tap opening 66 located in the side wall ii. In view oi the molten condition of the ash particles in suspension the tubes it and the nextadjacent row of tubes i8 of the tube bank have their lower portions bent to form a slag screen at the As shown in low the vertical portion of the baille 40 are alternately bent inwardly to varying extents to form spaced rows of tubes ita and ith. Alternate tubes in the laterally adjacent row of tubes i8,

' toincrease the width of the furnace.

which is alsospaced from the remaining rows, have their `lower portions bent inwardly in front of the superheater to form a third row .of screen tubes isc. The bent portions of this row 'of `tubes aid in supporting and cooling angularly arranged tile pieces 43 forming the inner portion'oi the baille extension 43.

In Fig. 6 I have illustrated another modificationl in which the tube bank it is constructed and arranged similarly to that of Fig.` 4, but in Fig. 6 the Awalls ii, i3, It, and i5 are extended Theiloor tubes `i9 are also bent at their outer ends to provide an elevated portioniof the furnace floor door may be designed for the reception and re-l moval of the'ash therefrom in dry form as shown in Figs. 1 and 2 or in a molten condition as shown in Fig. 4.

-In Fig. 'I I have illustrated another form of my invention in which the drums it and i'i are laterally oiiset and the tube bank it correspondingly inclined, leaving the furnace 3b substan-l tially trapezoidal in vertical cross-section as distinguished from the rectangular formation in Figs. 1, 4, and 6. In this form, the upper header `28 is eliminated and the portion ofthe top wall it above the furnace is relatively short. The fuel burner Sie. is rarranged to discharge vertically downward through a burner port`32El in the top wall. 'I'his furnace construction is espein a molten condition on the bottom and their removal 'through a slag tap opening 66a. The baille system for the tube bank is arranged substlntially as shown in Figs. 1, 4, and 6 to prof Avide a similar fiow of heatinggases relative to the tube bank. 'I'he baiiie extension 43a is arranged horizontally instead of inclined, while the superposed baille 46 is downwardly inclined across the tube bank and providedswith a horizontal extension 46h between the tube bank and side wall I2,the baille system thus defining three superposed serially connected gas passes 50', 5I', and 52'. `'I'he setting space made available above the baille extension 46h and'below the top wall iii at the outer side of the gas pass 52 .is advantageouslyv utilized for an auxiliary uid heater 10, such as an economizer or lair heater. The steam boiler construction illustrated in Fig. ,7, like those shown in Figs. 1-6, provides a rela- 'tively long flame path in the fluid cooled furnace in a direction transversely of the tube bank and effects a .passage of the heating gases transversely of the tubes in the tube bank for substantially their entire length. Alb of the described forms of my-invention are adapted for manufacturing in arange of sizes having substantially the same overall eiiiciency.

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 covered byvmy claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

I claim: i

1. A two-drum steam boiler comprising substantially parallel upper and lower horizontal drums, a bank of' vertically disposed water tubes connecting said drums, side, top and bottom walls defining a furnace Wholly at one side 01 and open along its length to said tube bank and closed at its lower end, a heating gas outlet at the opposite side of, said tube bank, cooling tubes extending from said lower drum to the outer side wall of said furnace and along said outer side wall and top wall to said upper drum, fuel burner means mounted in one of said furnace walls in position to discharge a stream of fuel in a direction transversely of said tube bank and to cause the gases of combustion to approach said tube bank substantially throughout the length thereof,a baille system for said tube bank arranged to form a plurality of serially connected superposed gas passes providing a generally vertical flow of gases relative to said tube bank and a substantially transverse ilow oi'gases over the tubes of said tube bank throughout their lengths, and a group of looped superheater tubes arranged within and substantially parallel to the tubes of said tube bank across the first gas pass traversed by the combustion gases.

2. A two-drum steam boiler comprising substantially parallel upper and lower horizontal drums, a bank of vertically disposed water tubes connecting said drums and arranged at both sides of the plane including the longitudinal axes of a .furnace wholly at one side of and open alo-ng its length to said tube bank and closed at its lower end, a heating gas outlet along the opposite side of said tube bank, cooling tubes extending from said lower drum to the outer side wall of 'said furnace and` along` said outer side wall and top wall to said upper drum, fuel burner means mounted in one of said furnace walls at a point intermediate the length of vsaid drums and arranged to discharge a stream of fuel in a direction transversely 'of said tube bank' and to cause the gases ofA combustion to approach said tube bank substantially throughout the length thereof and adjacent one of said drums, Maille system.

for said tube bank arranged to form a plurality of serially connected superposed gas passes providing a generally verticalJ flow of gases relative to said tube bank and a substantially transverse flow of gases overfthe tubes of said tube bank .throughout their lengths, and a group of looped superheater tubes arranged within and substantially parallel Ato the tubes of said. tube bank across the first gas pass traversed by the combustion gases.

3. A two-drum steam boiler comprisingsubstantially parallel upper and lower horizontal drums with their axes in vertical alignment, a bank of vertically disposed water tubes connecting said drums and arranged at both sides of the plane including the longitudinal axes of said drums, side, top and bottom walls defining a furf nace wholly at one side of and open along its length to said tube bank and closedl at its lower end, a heating gas outlet along the opposite side of said tube bank adjacent said upper drum, cooling tubes extending from said lower drum to the outer side wall of said furnace and along said outer side wall and top wally to said upper drum, fuel burner means mounted in one of said furnace walls at a point intermediate the length of said drums and arranged to discharge a stream of fuel in a direction transversely of said tube bank and to cause the gases of combustion to approach said tube bank substantially throughout the length thereof and adjacent one of said drums, a baille system lfor said tube bank arranged to form three serially connected superposed gas passes providing a generally vertical flow of gases relative to said tube bank and a substantially transverse flow of gases over the tubes of said tube bank throughout their lengths, said baille system including means forming a vertical baille extending from one of said drums to a level intermediate the height 0f said tube bank, a rearward extension on said baille separating the first and second gas passes; and a horizontally arranged baille extending inwardly from the outer side of said tube bank intermediate the height of said vertical baffle and separating the second and third gas passes, and a group of looped superheater tubes arranged substantially parallel to the tubes of said tube bank across the first gas pass.

4. A two-drum steam boiler comprising substantially parallel upper and lower horizontal drums, a bank of vertically disposed Water tubes connecting said drums, side, top and bottom walls defining a furnace wholly at one side of said tube bank and closed at its lower end adjoining said lower drum by a fluid cooled floor, a heating gas outlet at the opposite side of said tube bank, cooling tubes extending from said lower drum to the outer side wall of said furnace and along said outer sidewall and top wall to said upper drum, fuel burner means mounted in one of said furnace walls and` arranged to discharge a stream of fuel in a direction transversely of said tube bank causing the gases of combustion to approach therlower portion of said tube bank substantially throughout the length thereof and adjacent said lower drum, and a baiile system for said tube bank arranged to -form a plurality of superposed serially connected gas passes, the lowermost of which opens directly to said furnace throughout the length thereof above said lower drum, whereby a generally upward iiow of gases relative to said tubebank and a substantially transverse ow of gases over `the tubes of said tube .bank throughout their lengths will be effected.

5. A two-drum steam boiler comprising substantially parallel upper and lower horizontal drums, a bank of vertically disposed water tubes connecting said drums, side, top and bottom walls defining a furnace wholly at one side of said tube bank and closed at its lowerend adjoining said lower drum by a fluid cooled floor, a heating gas outlet along the opposite side of said tube bank, cooling tubes extending from said lower drum to the outer side wall of said furnace and along said outer side wall and top wall to said upper drum, fuel burner means mounted in said top wall and arranged to downwardly discharge astream of fuel in a direction transversely of said tube bank and causing the gases of combustion to approach the lower portion of said tube bank substantially throughout the length thereof and adjacent said lower drum, and a baille system for saidl tube bank arranged to form a plurality of superposed serially connected gas passes, the lowermost of which opens directly to said furnace throughout the length thereof above said lower drum, whereby a generally upward flow of gases relative to said tube bank and a substantially transverse flow of gases over the tubes of said tube bank throughout their lengths will be effected.

6. A two-drum steam boiler comprising substantially parallel upper and lower horizontal drums, a bank of water tubes connecting said drums, side, top and bottom walls defining a. furnace wholly at one side of said tube bank and closed at its lower end, a heating gas outlet along the opposite side of said tube bank, cooling tubes extending from said lower drum to the outer side wall of said furnace and along said outer` side wall and top wall to said upper drum, fuel burner means mounted in said bottom wall and arranged to upwardly discharge a stream of fuel between said cooling tubes in a direction transversely of said tube bank and causing the gases of combustion to approach said tube bank throughout the length thereof, and a baiiie system for said tube bank arranged to form a plurality of superposed serially connected gas passes, the lowermost of which opens to said furnace throughout the length thereof, whereby a generally upwardilow of gases relative to said tube bank and a substantially transverse flow of gases over the tubes of said tube bank throughout their lengths willv adjacent said upper drum,icooling tubes extending from said lower drum l)to the outer side wall of said furnace and along said outer side wall and top wall to said upper drum, fuel burner means mounted in one of said furnace walls and arranged to discharge a. stream of fuel in a direction transversely of said tube bank and to cause the gases of combustion to approach said tube A bank substantially throughout the length thereof and adjacent one of said drums, a baille system for said tube bank arranged to form a plu@ rality of superposed gas passes, providing agen-jv Y erally vertical flow ot gases relative to said tubfif bank and a substantially transverse ilow of gases over the tubes of said tube bank throughout their lengths, and the innermost tubes in said bank having portions bent and spaced to form a slag screen for the tubes in the first pass.

8. A two-drum steam boiler comprising substantially parallel upper and lower horizontal drums, a bank of vertically disposed water tubes connecting said drums and arranged at both sides of the plane including the longitudinal axes of said drums, side, top and bottom walls defining a furnace wholly at one side of said tube bank and closed at its lower end, a heating gas outlet along the opposite sideof said tube bank, cooling tubes extending from said lower drum to the outer side wall of said furnace and along said outer side wall and top wall to said upper drum, fuel burner means mounted in said top wall adjacent said upper drum and arranged to discharge a stream of fuel in a direction transversely of said tube bank and to cause the gases of combustion to approach the lower portion of said tube bank substantially throughout the length thereof and adjacent said lower drum, a baiiie system for said tube bank arranged to form a plurality of superposed gas passes providing a generally upward flow of gases through said tube bank and a substantially transverse flow of gases over the tubes of said tube bank throughout their lengths, and the innermost tubes in said bank having their lower ends spaced to form a slag screen for the tubes in the first pass. 'i

9.A A two-drum steam boiler comprising upper and lower horizontal drums, a bank of vertically disposed water tubes connecting said drums and arranged at both sides of the plane including the longitudinal axes of said drums, side, top and bottom walls defining a furnace wholly at one side of said tube bank and closed at its lower end, a heating gas outlet along the opposite side of said tube bank, fuel burner means .mounted in one of said furnace walls and arranged to discharge a stream of fuel in a direction transversely of said tube bank and to cause the gases of combustion to approach said tube bank substantially throughout the length thereof, a baffle system for said tube bank arranged to form three superposed gas passes providing a generally upward flow of gases relative to said tube bank and a substantially transverse ow of gases over the tubes of said tube bank throughout theirlengths, said baiiie system including .a vertical baiiie extending downwardly from said upper.

drum along the inner side of said tube bank,` a lateral extension of said baiile separating the first and second passes, and a horizontally arranged baffle extending inwardly across said tube bank and separating the second and third passes, said Vertical baille being widelyspaced from the main portion of said tube bank to provide a gas turning and equalizing space connecting the second and third gas passes, the outer side of said tube bank being 'spaced from the adjacent wall to form a gas turning and equalizing space therebetween connecting the rst and second gas passes, and an ash hopper below said last mentioned space.

l0. A two-drum steam boiler comprising walls forming a setting of substantially rectangular horizontal cross-section, upper and lower drums adjacent one side of said setting, a bank of vertically disposed water tubes connecting said drums and having transversely spaced inner and outer sections, a group of looped superheater tubes extending vertically within the space between said inner and outer tube bank sections, water tubes extending laterally from said lower drum to the opposite side Wall of said rsetting and upwardly along said side wall and across to said upper drum and defining a uid cooled furnace chamber at one side of and open along its lengthV to said tube bank inner section, a. heating gas outlet at the opposite side of said tube bank, fuel burner meansmounted in one of said setting walls at a point intermediate the ,length of said drums and arranged to discharge a stream of fuel into said furnace chamber in a direction transversely of said tube bank whereby the combustion gases approach said tube bank inner section substantially throughout-the length thereof, the tubes in said tube bank inner section being arrangedto form a protecting screen between said furnace chamber and said superheater tubes, and a baille system for said tube bank arranged to form a plurality of serially connected superposed gas passes across said tube bank outer section providing a substantially transverse flow of gases over the tubes of said outer section substantially throughout their lengths.

11. A two-drum steam boiler comprising walls 4at one side of said setting having their longitudinal axes in vertical alignment, a bank of vertically disposed water tubes connecting said drums and divided into a pair of transversely spaced inner and outer sections, a group of looped superheater tubes extending vertically within the space between said tube bank inner and outer sections, water tubes extending laterally fromv said lower drum to the opposite side wall of said setting and along said side wall and across to said upper drum and dening a 'fluid cooled furnace chamber wholly at one side of said tube bankand open along its length to said tube bank inner. section, a heating gas outlet along the opposite side of said tube bank outer section adjacent said upper drum, fuel burner means arranged to discharge a stream of fuel between said wall water tubes into said furnace at a point intermediate the length of said drums and in a direction transversely of said tube bank and whereby the combustion gases approach said tube bank substantially throughout the length thereof, the tubes in said tube bank inner section being arranged to form a protecting screen between said furnace chamber and said superheater tubes, and a bafrially connected superposed gas passes across said tube bank outer section providing a generally vertical ow of gases relative to said outer section and a substantially transverse flow of gases over the tubes thereof substantially throughout their lengths.

` CHARLES E. LUCKE.