US2087800A - Furnace - Google Patents

Description

July 20, 1937 E. G. BAILEY ET AL 2,087,800

FURNACE Filed Nov. 16, 1934 I 3 Sheets-Sheet 1 Fig- I 20 EINVIIEN gi /e I V O O O O 51 MO 0 E g]: MfHardg npve B Howard J. Kefh AT ORNEY July 20, 1937 G, BNLEY ET AL 2,087,800

FURNACE Filed Nov. 16, 1954 s Sheets-Sheet 2 IN VENTOR.S E'r n G. Bailey Ra ph M; Hardgro/g Hoya'raj Kerr Aho NEY July 20, 1937 E. G. BAILEY ET AL 2,087,300

FURNACE Filed Nov. 16, 1954 '5 Sheets-Sheet 5 Fly. 4

INYENTORS Ervm G. Baildy e Ralph M. Har grave Howa JKerr E A fioRl lEY Patented July 20, 1937 UNITED STATES PATENT OFFICE FURNACE Ervin G. Bailey, Easton, Pa., Ralph M. Hardgrove and Howard J. Kerr, Westfield, N. J., assignors to The Babcock & Wilcox Company, Newark, N. J., a corporation of New Jersey Application November 16, 1934, Serial No. 753,272

18 Claims.

means is provided for controlling the mean temperature of the furnace and for disposing of the ash resulting from the combustion of a slagforming fuel in suspension in a furnace chamber.

A further object of the invention is to provide an improved method of burning a slag-forming fuel in a furnace chamber.

These and other objects are elfected by our invention, as will be apparent from an examination of the following description and claims, taken in connection with the accompanying drawings, in which:

Fig. 1 is a vertical sectional view of a boiler furnace constructed in accordance with the present invention;

Fig. 2 is a transverse section taken on the line 2-2 of Fig. 1 and illustrating one preferred arrangement of tubes which form the pervious water-cooled screen through which the furnace gases flow;

Fig. 3 is a view similar to Fig. 1 illustrating a slightly modified furnace arrangement;

Fig. 4 is a view also similar to Fig. 1 illustrating a further modification of our invention;

Fig. 5 is a fragmentary section of the front wall of the furnace and is taken on the line 5-5 of Fig. 1; and

Fig. 6 is a fragmentary section of the rear wall taken on the line 66 of Fig. 1.

According to one embodiment of our invention, we provide a plurality of furnace walls which define a chamber for the combustion of a slagforming fuel; the slag-forming fuel being introduced downwardly and along one side of the a chamber and an outlet being provided in the upper portion of the chamber and at the side opposite the point of introduction of the fuel, whereby the stream of burning fuel and gaseous products of combustion follows a U-shaped flow path with the bottom of the U along thebottom of the chamber and the legs at opposite sides of the chamber.

That portion of the bottom of the combustion chamber which is at theside adjacent the fuel inlet is formed to collect molten ash or slag in a pool, and that portion of the bottom which is adjacent the other 'or gas outlet side of the chamber is formed to collect chilled-or dry ash particles. Molten ash is released in the downwardly moving stream by combustion at a, sufiiciently 'high temperature and the change in direction of flow of the stream of burning fuel from downward to sidewise results in the separation out. of the stream of the molten ash, which collects on that portion of the bottom of the furnace constructed to receive it.

A pervious water-cooled screen is disposed between the two portions of the bottom and across the flow path of the burning fuel stream, and functions to catch at least a portion of the molten ash in the stream which has not been previously separated out by the change of direction of flow,

and causes such ash to gravitate to that portion of the bottom which-is formed to receive the molten ash. The screen also functions to mix the remaining combustible matter and air in the stream and thereby promotes the combustion of such combustible matter. to retard or prevent the transmission of radiant heat from the hotter side of the chamber adjacent the fuel inlet to the colder side of the chamber adjacent the gas outlet. The amount of heat released by combustion in relation to cold wall heat receiving surface is greater in the former part of the chamber than in the latter, so the mean temperature of the former is higher, and the temperature of both parts of the chamber is different than if the screen were not provided, especially as the load changes.

Referring now in detail to the construction illustrated and particularly to Figs. 1 and 2, the reference number 9 indicates, in its entirety, a boiler furnace constructed in accordance with the present invention. The furnace 9 comprises a combustion chamber l0 defined by front and rear walls I I and. I2 respectively, side walls 3 (only one side wall being shown), and a botto n,

' l4 divided into a portion l5 constructed to retain a pool of molten ash or slag and a portion l6 constructed to collect and remove chilled or dry ash particles.

A roof or arch portion I1 is provided in the upper portion of the combustion chamber l0 and at one side thereof. Burners l8 are provided for introducing through the roof portion, a stream of slag-forming fuel and air more or less vertically downward into the combustion chamber. If desired, the fuel used may be coal which is pulverized to a degree of fineness sufficient to permit its being burned in suspension in the combustion chamber.

The combustion chamber [0 is provided at the side opposite the roof portion H with an outlet IQ for the furnace gases, a steam boiler 20, here shown to be of the horizontally inclined water tube type being disposed across the outlet and The screen also serves absorbing heat derived from the combustion of the fuel in the combustion chamber. Preferably the front and rear walls II and I2,

the side walls i3, and the roof portion I! are of the water cooled type and are composed of spaced tubes 2| with closure members for the spaces. While any of the conventional types of closure members or coverings may be used for the tubes without departing from certain aspects of our invention, we have shown. the spaces between the tubes as closed and the tubes covered by heat-resistant blocks 22 secured to the tubes and providing the interior surface of the combustion chamber In. Opposite the burners l8 the heatresistant blocks 22 are omitted to permit the introduction of the fuel and air into the chamber through the spaces between tubes.

The tubes 2| forming the walls of the furnace are connected into the boiler circulation system so as to assure circulation of water through the tubes for cooling the latter and so that the heat from the combustion chamber may be utilized in making steam. The front wall ii is provided with an inlet header 23 and an outlet header 24 connected respectively to the ends of the tubes forming the wall. Similarly, the rear wall is provided with inlet and outlet headers 25 and 26 respectively, the side wall with inlet headers 21 and outlet headers 28 and 29, and the roof portion with inlet and outlet headers 30 and 3| respectively. The inlet headers 25, 21 and 30 may be each connected by downcomers 32 with the water space of the boiler. The inlet header 23 is connected to the upper end of a row of horizontally-inclined spaced tubes 33 embedded in the portion l5 of the bottom. The lower ends of the tubes 33 are connected to a header 34 to which downcomers 35 are in turn connected. The outlet headers 24, 26, 28, 29 and 3| are connected by upcomers or risers 36 with the steam and water drum of the boiler. In order to promote local circulation in the rows of wall tubes, recirculating tubes 31 may be provided to connect any or all of the pairs of inlet and outlet headers.

As previously stated, the portion i5 of the furnace bottom is constructed to provide for the collection thereon of the molten ash or slag and for the removal of the slag from the furnace. In Fig. 1 the portion i5 is illustrated as being water cooled and comprising the tubes 33 with suitable means for closing the spaces between the tubes, for example, heat-resistant blocks 38 secured to the tubes. The portion |5 may be suitably supported by structural members 39. We prefer to maintain a pool of molten ash or slag on the portion l5 of the furnace floor, as indicated at 40 in Fi 1.

During furnace operation, the heat from the burning fuel willmaintain at least the surface of the slag pool in a fluid or molten condition by reason of the large amount of heat released by combustion per unit area of cold absorbing wall of the space above they pool, and at lightloads the combustion may be wholly completed in this 1 space. .However, the portion of the slag in the ber bottom is constructed to provide for the colbottom which contacts with the heat-resistant blocks may become chilled, thereby providing a solidified layer of slag which aidsin protecting the portion l5 of the floor from the heat of the furnace and from the destructive action of. the molten slag above. We have indicated at 4| a slag-tap opening through which the slag may be either periodically or-continuously tapped.

As stated, the portion l6 .of thefurnace chamlection and removal of chilled or dry ash or slag particles and this chilling is the resu t of a s i ciently low average temperature resulting from the relatively large amount of cold heat absorbingwall surface of this part of the chamber in which the heat released is less than in the other and at light loads there may be little combus tion here. In the embodiment of our invention, illustrated in Fig. 1, we have shown the portion l6-as comprising a hopper 42 disposed beneath an opening 43, ,the latter being defined by the lower end of the water-cooled rear wall l2, the lower ends of the side walls l3, and a water cooled wall 44 adjacent the side of the portion |5 supporting the slag pool. The dry or chi led ash may be removed from the hopper 40 in any suitable manner, for example, through a door controlled opening 45.

A short partition wall 46 extends downwardly and diagonally from the upper portion of the combustion chamber and in conjunction with the side walls l3, the front wall H and rear wall I2, defines a downflow passage 41 and an up-flow passage 48 connected at their lower ends to pr" vide a U-shaped flow path for the burningfuel and gaseous products of combustion.

The partition wall 46 is composed of spaced water tubes 49 with means closing the spaces between tubes, for example, heat-resistant blocks 50 secured to each side of the tubes. The tubes 49 extend upwardly from the partition wall 46 and are connected at their upper ends to the outlet header 3| previously described. We have shown the portion of the tubes 49 above the wall 46 as not being provided with the heat-resistant blocks 50.

The tubes 43 extend downwardly from the partition wall 46 and are arranged in groups 5| and 52, which groups may be arranged as indicated in Fig. 2 to provide a pervious water-cooled screen 53 extending across the U-shaped flow path of the burning stream. The lower ends of the tubes 49 may be covered by heat-resistant blocks 54 and thus form the water cooled wall 44 which was previously described as defining in part the opening 43 and hopper 42. An inlet header 55 is connected to the lower ends of the tubes 49, and a downcomer 56 is connected to the header 55 to supply the latter with water from the water space of the boiler.

It is to be observed that while we have shown in Fig. 2 a particular form and position of screen, our invention in its broader aspects is not so limited, for other structures may be used without departing from its intended scope. For example, screen structures like those shown in our Patents Nos. 2,002,463 and 2,002,464, may be used if the proper conditions exist; or, if desired, a structure like thatshown in the co-pending application of Rolfe Shellenberger, Ser. No. 750,342, filed Dec. 27, 1934,; may be used. Furthermore, with any form of screen, the division of the chamber and other factors are to be such that the meantem perature of the down-flow passage shall be normally above slag fusion temperature and that of the up-flow passage 'normally below ash fusion temperature. v

The diagonally disposed partition wall 46 and I an inclined lower portion 51 of the rear wall l2,

in conjunctionwith the front and side walls and|3 respectively, and the remaining portions of the rearwall I2,,provide a downward div'ergence, to the down-flow passage 41 and an upward divergence to the up -fiow passage 48. The purmoves downwardly along its flow path and the temperature thereof becomes higher and to assist in the combustion of enough of the fuel to make the mean temperature of the space higher than ash fusion temperature. The purpose of the divergence in the up-fiow passage is to equalize the distribution of the gases across the outlet and to effect a reduction in fiow velocity of the stream after it passes through the screen 53 so as to permit the dry ash particles to settle out of the stream into the hopper 42. The flow path of the burning stream is changed in direction and is somewhat restricted by the screen 53, as a result of which the velocity of the stream is increased at this point, the purpose of which will presently appear.

The fuel is ignited as it enters the combustion chamber under conditions that cause it to burn rapidly. Before the fuel reaches the bottom, combustion has proceeded far enough to have released a large portion of the ash which is separated out of the stream in a molten form due to the high temperature of this space. The separated molten ash collccts on the portion l5 of the bottom due to the change in direction of flow of the stream. Such ash or slag as has not been previously separated passes through the screen which serves to catch at least a substantial portion of the slag, the collected slag dropping from or running down the screen into the pool. Combustion conditions in the down-flow passage in relation to the cooling of its walls are such as to not only keep the mean temperature higher than the ash fusion point, but to be actually hottest near the pool of molten slag. The ash in the fuel is liberated in the down-flow passage wholly or substantially becauseof the substantial completion of combustion of the fuel therein and as stated, is separated out of the stream due to the change in direction of fiow .of the stream and also to the slag catching func-- tion of the screen 53.

In addition to the slag catching function just described, the screen 53 serves to mix theconstituents of the stream passing therethrough,

and thereby promotes the completion of combustion of the combustible matter therein. As stated previously, the mixing function of the screen is aided by the fact that the fiow area through.

tributing to the chilling or solidifying of the molten ash carried over from the down-flow passage to the cooler chamber beyond so that such ash may settle out of the stream in the up-flow passage;

A further function of the screen is to reduce the transmission of radiant heat from the'relatively higher temperature space'ofthe 'downfiow passage 41 to the cooler space of the up-flow passage 48, thereby aiding insustaining the desired temperature difference. The chilling of the ash in the up-fiow passage tends to reduce or prevent the harmful deposition of slag on the boiler tubes. N

As the up-fiow passage 48 diverges upwardly, and the passage is defined by Water-cooled walls of suificient area, and as a relatively small amount of heat is released in the passage, the temperature of the stream is lowered to a degree s'ufficient to promote the effective chilling of the molten ash or slag remaining in the stream; the reduction in velocity of the stream serving to promote the settlingout of the stream of the chilled ash particles into the hopper 42.

From the above, it will be apparent that the temperature within the down-flow passage 47 is maintained relatively higher than the temperature within the up-fiow' passage 48. As stated previously, one purpose of the difference in temperature between the two passages is to efiect early ignition and combustion of the fuel in the down-flow passage so that the ash may be liberated and separated out'of the stream and collected in the pool, and to effect a cooling of the stream in the up-flow passage so that remaining ash may be chilled and separated out in the up-fiow passage. Atlight loads all of the combustion may be completed in the down-flow passage and the pool kept molten when it might freeze if the screen were removed because the flame gases could then radiate to a larger area, that of the whole furnace boundary.

It is within the scope of the present invention to provide a furnace wall structure defining the passages 41 and 48 which aids in pro viding the desired high temperature condition in the passage 41 for accelerating the combusi-' tion process therein and the desired relatively low temperature condition inthe passage 48 for aid ng in the chilling of the remaining ash in the stream. This may be accomplished in a num-- ber of ways, for example, the blocks 22 covering the tubes 2| and the blocks 50 covering the tubes 49 which provide the wall structure for the passage 41 may be formed in whole or in part with a ceramic refractory material and the blocks 22 .and 50 defining the passage 48 may be formed of a metallic refractory. Fig. 5 is a fragmentary section through the front wall H and illustrates the blocks as being formed of cast metal with a ceramic refractory facing. Fig. 6 is a fragmentary section through the rear wall l2 and illustrates a bare metal refractory block. .The ceramic material has relatively higher insulatingqualities than the bare metal refractory and slag-tap bottom l5a forthe down-flow passage 41a. The bottom I5o is composed of layers BI' hence a higher temperature will be had in the of suitable refractory, for example, dolomita,

supported by a plate structure 62 which is in turn supported by structural members 63. The portion 16a of the furnace bottom which is constructed to collect and remove the chilled slag from the passage 48a is also slightly different, in that we .have shown a horizontallymovable ash gate ,64. v

The construction shown. in Fig.' 3 occupies a smaller cross-sectional area of the boiler room than the structure of Fig. '1. Because the rear wall I2a is disposed vertically instead of having a bend in the lower end like Fig. 1, the front walllla. may be arranged more nearly beneath theboiler and the same furnace chamber area obtained. A further feature of the structure shown in Fig; 3 is that the wall tube arrangement is somewhat simplified and there are fewer bends in the tubes, viz: the tubes 2la forming the rear wall l2a are straight; the front wall Ha and the roof portion l'la are formed of the same tubes, thereby reducing the number of headers required; and the tubes forming the partition 46a and the screen 53a extend diagonally downward from the front of the boiler and thereby require fewer bends.

The embodiment shown in Fig. 4 is also similar in structure and operation to that of Fig. 1. The principal distinguishing feature of Fig. 4 is the relatively high furnace and the vertical arrangement of the partition wall D. The sides of the tubes 4% forming the partition wall 46b which are adjacent the up-fiow passage 481) are bare, which aids in the cooling of the stream in the up-fiow passage. The rear wall I2!) is formed of straight tubes as was the case in Fig. 3. In Fig. 4, the down-flow passage 41b and the up-fiow passage 48b do not increase in crosssectional area in the direction of stream fiow. The up-flow passage is relatively large,'-and the hopper 42b for chilled ash is also large. The walls of the hopper 42b are formed of water tubes 10 and refractory blocks ll secured to the tubes.

From the above description, it will be apparent that in each of the modifications we have provided a furnace which is of improved construction and arrangement of parts. In each of the structures the division of the furnace chamber into a relatively hot down-flow passage and a relatively cool up-fiow passage with the molten ash collection at the bottom of the down-fiow passage and the dry ash removal at the bottom of the up-flow passage in conjunction with the screen, provides a furnace which operates effectively and efficiently and a furnace having an improved means for disposing of the ash.

While we have shown our invention in three forms. it will be obvious to those skilled in the art that it is 'not so limited but is susceptible of various other changes and modifications without departing from the spirit thereof, and we desire, therefore,, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

We claim:

1. In a furnace for burning a slag-forming fuel, the combination of means defining a combustion chamber including a floor portion, one part of which is constructed to support and provide for the removal of molten slag and another part of whichis constructed to collect chilled slag particles; means providing for the introduction of a stream of slag-forming fuel with air for supporting combustion chamber; means providing for the movement of the stream first over the part of the floor supporting the molten slag and then over the part where the chilled slag is collected; and means for chilling the slag in the stream after the latter passes over the part supporting the molten slag.

2. A method of operating a furnace which comprises introducing into the furnace chamber a stream of slag-forming fuel and air; effecting movement'of such stream in a predetermined path through the furnace chamber; igniting and effecting combustion of the fuel while in suspension; removing from the stream a portion of the ash resulting from combustion while the ash is in a molten form and collecting the molten ash in a pool in the lower portion of the furnace; chilling the remaining ash in the stream; and

thereof into the combustion collecting the chilled ash in the lower portion of the furnace and at points spaced from the slag pool.

3. In a furnace for burning slag-forming fuel, the combination of means defining a combustion chamber; means delineating a down-flow and an up-fiow passage in the combustion chamber intercommunicating at their lower ends; means providing for the introduction of a stream of slagforming fuel and air for supporting the combustion thereof into the upper end of the down-fiow passage; means at the lower end of the downfiow passage providing for the collection of molten slag resulting from combustion; means at the lower end of the up-fiow passage providing for the separate collection and removal of chilled slag particles; and means providing a cooling surface over which the stream fiows in passing from the down-flow to the up-fiow passage so as to lower the temperature of the stream and chill the remaining slag particles therein.

' 4. In a furnace for burning a slag-forming fuel, the combination of means defining a combustion chamber; means delineating a down-flow and an up-fiow passage in the combustion chamber intercommunicating at their lower ends; means providing for the introduction of a stream of slagforming fuel and air for supporting the combustion thereof into the upper end of the downfiow passage; means at the lower end of the down-flow passage providing for the collection of molten slag resulting from combustion; means at the lower end of the up-flow passage providing for the collection and removal of chilled slag particles; said delineating means including a row of spaced water cooled surfaces through which the stream passes in flowing from the down-flow passage to the up-fiow passage; the row of tubes extending downwardly to that edge of the molten slag collecting means which is adjacent the lower end of the up-fiow passage.

5. In a furnace for burning a slag-forming fuel, the combination of means defining a combustion chamber; means delineating a down-flow and an up-fiow passage in the combustion chamber intercommunicating at their lower ends; means providing for the introduction of a stream of slag-forming fuel and air for supporting the combustion thereof into the upper end of the down-flow passage; means at the lower end of the down-flow passage providing for the collection of molten slag resulting from combustion; means at the lower end of the up-fiow passage providing for the collection and removal of chilled slag particles; the delineating means including a water-cooled screen comprising a row of spaced water-cooled tubes extending across the fiow path of the stream and to the lower portion of the furnace and between the molten slag collecting means and the chilled slag collecting means.

6. In a furnace for burning slag-forming fuel, the combination of means defining a combustion chamber; means delineating a down-flow and an up-flow passage in the combustion chamber intercommunicating at their lower ends; means providing for the introduction of a stream of slagforming fuel and air for supporting the combustion thereof into the upper end of the downfiow-passage; means at the lower end of the down-flow passage providing for the collection of molten slag resulting from combustion; means at the lower end of the up-fiow passage providing for the collection and removal of chilled slag particles; the delineating means including a water-cooled screen comprising a plurality of rows of spaced water-cooled tubes extending across the flow path 'of the stream and to the lower portion of the furnace chamber and bebeing arranged in staggered relation with respect to the tubes of an adjacent row so as to provide a multitude. of tortuous paths for the stream flowing through the screen.

7. In a furnace for burning a slag-forming fuel, the combination of means defining a combustion chamber including upright side walls; a partition wall extending downwardly from the upper portion of the chamber and terminating short of the lower portion of the chamber to divide the latter into first and second substantially vertical passages connected at their lower ends to provide a U-shaped flow path for the fuel undergoing combustion; means for cooling the side wall structure of the furnace chamber; means providing for the introduction of a stream of slag-forming fuel and air for supporting combustion thereof into the upper end of the first passage; means at the lower end of the first passage providing for the collection of molten slag resulting from the combustion of the fuel; means providing a posi-- tively cooled screen through which the stream flows in passing from the first to the second passage so as to lower the temperature of the stream and chill the remaining slag particles; and means in the lower portion of the second passage providing for the separate collection and removal of slag chilled while passing through said screen and by the action of the cooled walls of the second passage.

8. In a furnace for the combustion of a slagforming fuel, the combination of wall means dedownflow passage and having its surface constructed to maintain fining a Ushaped passage for the flow of fuel undergoing combustion; the construction and arrangement of the passage-defining wall means being such that the legs of the U extend upwardly and the'base of the U extends along the bottom of the furnace; means for introducing a slagforming fuel and air into the upper end of one of the legs of the U-shaped passage; an outlet for the furnace gases at the upper end of the other leg of the U-shaped passage; means beneath said one leg and a portion of the base of the U-shaped passage for collecting molten slag in a pool;

.Ineans beyond the last mentioned means, considered in the direction of fuel travel, for chilling fuel comprising front, rear and side walls defining a combustion chamber, means extending downwardly across the furnace intermediate the ends thereof for defining a front downflow passage and a rear up-flow passage communicating at their lower ends, means for introductingslagforming fuel into the upper end of and burning the same in suspension in said downflow passage, heat absorbing means lining the walls of said heat absorbing a normal mean temperature in. said downflow passage higher than the ash fusion temperature of the fuel burned therein, heat absorbing means lining the walls of said up-fiow passage and having its heat absorbing surface constructed to maintain a normal mean temperature in said upfiow passage lower than the ash fusion temperature of the fuel burned in said downflow passage, the portion of said furnace bottom directly below said downflow passage of said furnace bottom directly below said upfiow passage being constructed as a hopper extending below the level of said floor.

10. A furnace for the burning of slag-forming fuel comprising front, rear and side walls defining a combustion chamber, an arch extending over the front upper portion of said combustion chamber, a heating gas outlet between the rear end of said arch and said rear wall, means including a group of water screen tubes extending downwardly across the furnace from said arch to the combustion chamber bottom intermediate the ends thereof for defining a front downflow passage and arear up-flow passage communicating at their lower ends, means in said arch for introducing slag-forming fuel into the upper end of and burning the same in suspension in said downflow passage, fluid heating surface lin-' ing the walls of said downflow passage and con structed to maintain a normal mean temperature in said downflow passage higher than the ash fusion temperature of the fuel burned therein, fluid heating surface lining the walls of said upflow passage and constructed to maintain a normal mean temperature in said upfiow passage lower than the ash fusion temperature of the fuel burned in said downflow passage, the portion of said furnace bottom below said downflow passage being constructed to receive slag particles in a molten condition, andthe portion of said furnace bottom below said upfiow passage being constructed to receive condition. l

11. A furnace for burning finely divided solid fuel comprising vertically disposed front, rear and side walls defining a furnace chamber, means forming a transverse baffle extending downwardly and terminating above the bottom of said furnace chamber to separate a front downflow passage and a rear upfiow passage communicating at their lower ends, means for burning finely divided solid fuel in suspension in said downflow passage, means arranged to form a pervious fluid cooled screen between the lower end of said baflie and an intermediate portion of the furnace bottom, a floor forming the furnace bottom at the front sideof said screen, and a hopper forming the furnace bottom at the rear side of said screen. 12. A furnace for burning finely divided solid fuel comprising vertically disposed front, rear and side walls defining a furnace chamber, an' arch extending .rearwardly from said front wall over the front portion of said furnace chamber, means forming a transverse baflle extending downwardly from said arch. and terminating above the bottom of said furnace chamber to separate a front downflow passage and a rear upfiow passage communicating at their lower ends, means in said arch for introducing finely divided solid fuel into the upper end of and burning the same in suspension in said downflow passage, water tubes arranged to form a pervious fluid cooled screen between the lower end of said baflle and an intermediate portion of the furnace bottom, a forwardly inclined floor forming the furnace bottom at the front side of said screen, a row of inclined water tubes arranged along and cooling said floor, and a hopper forming the furnace bottom at the rear side of said screen and arranged to directly receive ash particles separated in said upfiow passage.

ash particles in a dry 13. A furnace for burning finely divided solid fuel comprising vertically disposed front, rear and side walls defining a furnace chamber, means forming a transverse baflle extending downwardly and terminating above the bottom of said furnace chamber to separate a front downfiow passage and a rear upfiow passage communicating at their lower ends, means for burning finely divided solid fuel in suspension in said downfiow passage, heat absorbing surface lining the sides of said downfiow passage and constructed to maintain a normal mean temperature therein higher than the fuel ash fusion temperature, heat absorbing surface lining the sides of said upfiow passage and constructed to maintain a normal mean temperature therein lower than the fuel ash fusion temperature, and means arranged to form a pervious fluid cooled screen between the lower end of said baflle and an intermediate portion of the furnace bottom.

14. A furnace for burning finely divided solid fuel comprising vertically disposed front, rear and side walls defining a furnace chamber, an arch extending rearwardly from said'front wall over the front portion of said furnace chamber, means forming a transverse bafile extending downwardly from said arch and terminating above the bottom of said furnace chamber to separate a front downfiow passage and a rear upfiow passage communicating at their lower ends, means for burning finely divided solid fuel in suspension in said downfiow passage, heat absorbing surface lining the sides of said downfiow passage and constructed to maintain a normal mean temperature therein higher than the fuel ash fusion temperature, heat absorbing surface lining the sides of said upfiow passage and constructed to maintain a normal mean temperature therein lower than the fuel ash fusion temperature, a floor forming the furnace bottom below said downfiow passage and constructed to receive ash particlesin a molten condition, and a hopper forming the furnace bottom below said upfiow passage and constructed to receive ash particles in a dry condition.

15. A furnace for burning finely divided solid fuel comprising vertically disposed front, rear and side walls defining a furnace chamber, means forming a transverse bafile extending downwardly and terminating above the bottom of said furnace chamber to separate a front downfiow passage and a rear upfiow passage communicating at their lower ends, means for burning finely divided solid fuel in suspension in said downfiow passage, heat absorbing surface lining the sides of said downfiow passage and constructed to maintain a normal mean temperature therein higher than the fuel ash fusion temperature, heat absorbing surface lining the sides of said upfiow passage and constructed to maintain a normal mean temperature therein lower than the fuel ash fusion temperature, and means arranged to form a pervious fluid cooled screen between the lower end of said bafile and an intermediate portion of the furnace bottom, said furnace bottom being constructed at the front side of said screen to receive ash particles in a molten condition from said downfiow passage and at the rear side of said screen to receive ash particles in a dry condition from said upfiow passage.

16. A furnace for burning finely divided solid fuel comprising vertically disposed front, rear and side walls defining a furnace chamber, an arch whereby ash separating extending rearwardly from said front wall'over the front portion of said furnace chamber, means forming a transverse baffle extending downwardly from said arch and terminating above the bottom of said furnace chamber to separate a front downfiow passage and a rear upfiow passage communicating at their lower ends, means for burning finely divided solid fuel in suspension in said downfiow passage, heat absorbing surface lining the sides of said downfiow passage and constructed to maintain a normal mean temperature therein higher than the fuel ash fusion temperature, heat absorbing surface lining the sides of said upfiow passage and constructed to maintain a normal mean temperature therein lower than the fuel ash fusion temperature, means arranged to form a pervious fiuid cooled screen between the lower end of said baflle and an intermediate portion of the furnace bottom, a; fioor forming the furnace bottom at the front side of said screen, and a hopper forming the furnace bottom at the rear side of said screen.

17. In a furnace having a furnace chamber divided into a downfiow passage and an upfiow passage communicating at their lower ends, the method of burning finely divided solid fuel and recovering ash constituents of the fuel in the furnace which comprises introducing a stream of finely divided solid fuel into the upper end of and burning the, fuel in suspension in said downfiow passage, maintaining a normal mean temperature in said downfiow passage above the-fuel ash fusion temperature, in said downfiow passage will be in a molten condition, molten ash on the portion of the furnace bottom below said downfiow passage, maintaining a. normal mean temperature in said upfiow passage below the fuel ash fusion temperature, whereby ash separating out in said upfiow passage will be in a dry condition, and collecting ash separating in said upfiow passage in a portion of the furnace bottom below said upfiow passage and separate from the bottom portion supporting the layer of molten ash.

18. In a furnace having a furnace chamber divided into a downfiow passage and an upfiow passage communicating at their lower ends, the method of burning finely divided solid fuel and recovering ash constituents of the fuel in the furnace which comprises introducing a stream of, finely divided solid fuel and air for combustion collecting and maintaining a layer of :1

whereby ash separating out into the upper end of and burning the fuel in sus/- pension in said downfiow passage, maintaining a normal mean temperature in said downfiow passage above the fuel ash fusion temperature, out in said downfiow passage will be in a molten condition, collecting and maintaining a layer of molten ash on the portion of the furnace bottom below said downflow passage, maintaining a normal mean temperature in said upfiow passage below the fuel ash fusion temperature, whereby ash separating out in said upfiow passage will be in a dry condition, collecting ash separating in said upfiow passage in a portion of the furnace bottom below said upfiow passage and separate from the bottom portion supporting the layer of molten ash, and separately removing the molten and dry ash from the furnace chamber.

ERVIN G. BAILEY. RALPH M. HARDGROVE. HOWARD J. KERR.

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