US2754808A - Fluid heater furnace - Google Patents

Description

July 17, 1956 Filed Feb. 26, 1952 B. SILK FLUID HEATER FURNACE 4 Sheets-Sheet 1 a 32 35 y f/ INVENTOR.

July 17, 1956 P. B. SILK 2,754,808

FLUID HEATER FURNACE Filed Feb. 26, 1952 Sheet s-Sheet 2 2 g k 84 74 .M. I-- /6 4 73 a Z 75 32 g 80 7/ A, 76 22 /7 75 79 FIG. 3 E /6 97 25 19 6? 2/ 26 6 76 34 7: k o0 IN V EN TOR.

July 17, 1956 P. B. SILK FLUID HEATER FURNACE 4 Sheets-Sheet 3 Filed Feb. 26, 1952 INVENTOR. BY fizz/1p 5 iii/r ATTORNEY United States Patent FLUID HEATER FURNACE Philip B. Silk, Burstead Close, Cobham, England, assignor to The Babcock & Wilcox Company, Jersey City, N. 3., a corporation of New Jersey Application February 26, 1952, Serial No. 273,425 8 Claims. (Cl. 122-235) This invention relates to tubular fluid heaters, or fluid heating units, having furnaces fired by pulverized fuel. In such pulverized fuel fired units, the furnace combustion chambers frequently are formed with hopper-like bottoms providing narrow outlets for the passage of ash into subjacent ash collecting chambers. In tubular fluid heaters operating as vapor generating units, the walls of such combustion chambers are normally provided with vaporizing tubes and these tubes may be bare, or may be partly or wholly covered with, for example, cast iron blocks. The nature of the ash, that is, whether it is in the form of dust or whether it contains clinker, is influenced by the nature of the Wall surface of the combustion chamber and by the nature of the fuel supplied to the chamber. Unfortunately the origin and character of the coal available for use may be unpredictable and this un- 9 certainty is liable to lead to diificulties in handling ash evacuated from an ash collecting chamber, since a system, such as a pneumatic conveying system, suitable for dealing with dust, may be rendered inoperative by large pieces of clinker, while an hydraulic system, utilizing a storage bunker and adapted to deal with ash in the form of clinker, is unsuited for dealing with ash largely in the form of fine dust. Large pieces of clinker can be reduced to such a size that they may be handled by the pneumatic system, but the reduction necessitates the provision and upkeep of a clinker grinder and the power for operating the grinder.

Another problem that has arisen in connection with such ash collecting chambers is that, due to after-burning of the ash during its stay in the ash collecting chamber, there is a danger of the formation of large masses of clinker therein, which masses are difficult to remove. In addition, the refractory lining of the chamber attains a relatively high temperature with the result that each time the ash is removed from the chamber if, for example, a high velocity jet of water is used for the removal, the refractory lining is rapidly and considerably cooled and as a result tends to deteriorate. Heretofore in order to limit the temperature in the chamber and so overcome these ditficulties, continuously operated quencher sprays have been fitted inside the ash chamber, or the chamber has been maintained full of water. However, the possibility of handling the ash pneumatically is then ruled out and evaporation of the cooling water represents a loss of efficiency. An advantage would be gained if heat carried into the collecting chamber by the ash and transmitted into the chamber by radiation were recovered.

The present invention is therefore directed particularly to an improved form of fluid heater furnace having its combustion chamber arranged to be fired by pulverized fuel and formed with a bottom outlet for the discharge of ash into a subjacent ash collecting chamber. The last named chamber includes fluid cooled walls which are formed as continuations of walls associated with the upper furnace structure. The ash collecting chamber is suitably arranged for the convenient evacuation of ash and slag therefrom and further provides for separation from the incoming ashes of particles of ash in the form of dust or relatively small pieces of clinker, whereby such separated particles may be evacuated separately from the remainder of the ashes.

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

Of the drawings:

Fig. 1 is a sectional side elevation through the lower part of a hopper-bottomed pulverized-fuel-fired top suspended combustion chamber forming part of a vapor generating unit and through an associated ash collecting chamber, some details remote from the section plane being omitted;

Figs. 2, 3, 4 and 5 are sectional side elevations similar to Fig. 1 showing alternative constructions of the ash collecting chamber;

Fig. 6 is a view of part of a tubular sifting device shown in Fig. 1, looking in the direction of the arrows 6-6;

Fig. 7 is a sectional view taken on the plane 77 of Fig. 6 looking in the direction indicated by the arrows;

Fig. 8 is a View, similar to that shown in Fig. 6, of part of an alternative sifting device; and

Figs. 9 and 10 are sectional views taken on the planes 99 and iii-4i? respectively of Fig. 8 looking in the direction indicated by the arrows.

Referring generally to the various embodiments of the invention illustrated in Figs. 1 to 5 of the drawings, the lower part of the rectangular combustion chamber of a pulverized-fuel-fired tubular vapor generator is formed in known manner with a hopper-like bottom part 1 including a refractory layer 2 and an outer layer of heat insulating material 3 and providing a transversely extending slot-like outlet or throat 5 for the passage of ash resulting from combustion of fuel in the combustion chamber into an ash collecting chamber 6 disposed below the combustion chamber. 7

The four walls of the combustion chamber which, for convenience, are termed the front, rear and side walls, are lined with fluid cooled tubes, the tubes in the upper upright parts of the front and rear walls being continued downward in the inclined walls 7 and 8 respectively of the hopper-like bottom part 1, and tubes of the side walls being continued downwardly to form the other two walls (e. g. the wall 9) of the lower part of the combustion chamber. In each of the embodiments shown, some at least of the combustion chamber wall tubes extend below the outlet 5 to provide ash cooling surfaces in the ash collecting chamber 6, as will be described in detail later.

In each of the embodiments, a tubular sifting device 11, for example, extends across the ash collecting chamber and, at least below the outlet 5, is arranged at a steep inclination, it being shown in the drawings as being of approximately the same inclination as the hopper-bottom rear wall 8. The actual arrangement of this sifting device varies in the different embodiments, but in each case it is formed by spaced parallel tube lengths 12 (see Fig. 6) arranged with their axes parallel to the side wall 9 of the combustion chamber. Each of these tube lengths is provided with two diametrically opposite rows of equally spaced radially extending studs 13 fusion welded to the tube (see Figs. 6 and 7). The studs on adjacent tubes project into the intertube space in staggered relationship, the studs on one tube being midway between the studs on the other tube. It will be seen that by using studs of appropriate length and spacing, it is possible to control the size of body which may pass freely through the sifting device.

In each embodiment, the sifting device 11 or 11a divides the ash collecting chamber into two compartments, namely, an upper or clinker collecting compartment 14, and a lower or fine ash collecting compartment 15.

The clinker collecting compartment 14, at a location adjacent the lower end of the sitting device, is provided with a clinker removal door 16 having a frame 17 arranged to be fluid cooled, the door being operable remotely by means including an hydraulic cylinder 13 and being arranged to close wall opening 19.

The fine ash collecting compartment 15 is provided with a fine ash removal door 20 adjacent its lowest level, this door having a frame 21 arranged to be fluid cooled and operable remotely by means including a second hydraulic cylinder 22. At the outer side of door 20 is arranged a fine ash chute 23 from which fine ash may be removed pneumatically by suction through a pipe 24 connected to the bottom of the chute, the chute being enclosed by a casing 25 in order to prevent fine ash passing through the chute from creating a dust nuisance about the vapor generator. The casing 25 is provided with an access door 26 and with suitable expansion joints (not shown) to allow for downward movement of the top suspended combustion chamber and ash collecting compartment due to thermal expansion. As will be understood, a similar downward movement of the ash collecting compartment 6 will occur, although in a lesser degree, when top suspension is provided intermediate the total height of the combustion chamber, for example, at or adjacent the upper limit of the hopper-like bottom portion 1.

Although only one clinker removal door and one fine ash removal door are shown, two or more of each may be provided, suitably spaced along the length of the ash collecting chamber. Preferably some of the fluid heating tubes in the side walls 9 of the combustion chamber are also continued downwardly below the ash outlet to line the corresponding walls of the ash collecting chamber.

The actual shape and arrangement of the compartments of the ash collecting chamber 6 will depend upon the ratio of fine ash to clinker in the ash produced in the combustion chamber under normal operating conditions, and upon the storage capacity for fine ash and clinker which it is desired to provide.

Thus, Figs. 1, 2 and 3 illustrate arrangements in which the ash will normally include substantial amounts of both clinker and fine ash, in which cases it is usually economic to utilize water sluicing for conveyance of the clinker to some convenient point of disposal.

In these three arrangements, a water sluiceway 30 of well known type is arranged close to the clinker removal door 16 for the reception of clinker discharged from the clinker compartment 14, the clinker being swept along the sluiceway by a powerful jet of water discharged by a nozzle (not shown). Entry of oversize pieces of clinker into the sluiceway is prevented by the sizing and breaking grid 31, on which such large pieces are retained until broken up by an attendant. The door 16 and the adjacent part of the sluiceway are enclosed by a casing 32 to prevent fumes resulting from quenching of clinker entering the sluiceway from becoming a nuisance adjacent the vapor generator. The casing 32 is provided with an access door 33.

With the arrangement of sifting device and clinker and fine ash compartments described above, the clinker carries with it into the sluiceway but little fine ash, and no difliculty is experienced due to excessive fine ash in the sluiceway, while on the other hand, the pieces of clinker which do reach the fine ash chute 23 are all of such small size as to be readily handled by the pneumatic fine ash handling plant, as represented in part by suction pipe 24.

Referring now particularly to Fig. 1, all the tubes included in the front wall 7 of the hopper-bottom I extend beyond the throat 5 laterally then downwardly to form first a roof 36 and then a front wall 37 of the ash collecting chamber, and are joined at their lower ends to an inlet header 38 connected by downcomers such as 39 into the circulatory system of the vapor generator. All the tubes included in the rear wall 3 of the hopper-bottom extend downwardly beyond the outlet 5, but at the outlet the alternate tubes are bent downwardly and then laterally to form first, in conjunction with refractory material 40, the rear wall 41 and then, in conjunction with refractory material 42 the bottom 43 of the ash collecting chamber 6, these tubes also terminating in the inlet header 38. The remainder of the tubes included in the wall 8 of the furnace bottom extend across the ash collecting chamber to the header 38 at the same steep slope as wall 8 of the hopper-bottom to form the sifting device 11 which extends from one side of the outlet 5 to a location considerably beyond the vertical plane through the opposite front side 44 of the outlet. The clinker removal door 16 is adjacent the inlet header 38, and the adjacent lower part of the clinker compartment 14 is provided with an inclined refractory floor 45. In the neighborhood of the door, the tubes of the front wall 37 are displaced sidewardly to leave a clear space 47 behind the door. The fine ash door 2%) is arranged in front of an opening 48 in the rear wall 41, the Wall tubes in this vicinity being bent sidewardly to leave the opening 48 for the discharge of fine ash from the lower compartment 15.

With the arrangement set out in Fig. l, clinker collected in the clinker compartment 14 is discharged by gravity into the sluiceway 30 upon opening of the door 16, while most of the fine ash collected in the fine ash compartment 15 is discharged by gravity into the fine ash chute 23 upon opening of the door 20. A relatively small amount of the fine ash will remain on the horizontal bottom 43 and this is removed by raking into the chute 23. The projecting roof 36 of the clinker compartment serves to shield, to a large extent, the clinker collected at the lower end of the sifting device 11 from thermal radiation originating in the combustion chamber, and the sifting device similarly serves to shield the fine ash in the lower compartment 15.

The arrangement of Fig. 2 is directed to the provision of increased storage capacity in the ash collecting chamber. In this arrangement, all the tubes included in the front wall 7 of the hopper-bottom extend, beyond the outlet 5, downwardly in the same direction as the opposite wall 3 of the hopper-bottom to form a front wall 50 of the ash collecting chamber, these tubes being connected at their lower ends to an inlet header 51 connected by downcomers such as 52 into the circulatory system of the vapor generating unit. All the tubes included in the rear Wall 8 of the hopper-bottom extend downwardly beyond the outlet 5, but at the outlet the alternate tubes are bent first downwardly and then forwardly to form first, in conjunction with refractory material 53, the rear wall 54 and then, in conjunction with refractory material 55, the bottom 56 of the ash collecting chamber, the lower ends 57 of these tubes being curved downwardly to connect to the inlet header 51. The remainder of the tubes included in wall 8 of the hopper-bottom I extend downwardly in the same general direction as the wall 3 across the ash collecting chamber 6, in which they are parallel to, but spaced from, the tubes of front wall 50, to form the ash sifting device 11, these tubes being curved forwardly and also terminating in the inlet header 51. In this arrangement, the clinker collecting compartment 14 is provided with a lateral extension 58 connecting the lower part of the compartment to the clinker removal opening 1.9, which is positioned adjacent the header 51, while the refractory floor 59 of the clinker compartment is built-up to the level of the top of the inlet header 51 and, in the neighborhood of the door 16, the tubes of the front wall 50 are displaced sidewardly to leave a clear space 61 behind the door. The wall tubes in the vicinity of the fine ash door 20 are bent sidewardly to leave the wall opening 62 for the discharge of fine ash from the compartment 15. Additionally, the floor 56 of the ash collecting chamber is extended as indicated at 63 to the frame 21 of door 20.

With the arrangement of Fig. 2, not only are the capacities of the clinker compartment and the fine ash compartment increased, but the fabrication of the tubes is simplified by the reduction of the number of bends required. On the other hand, hand removal of both fine ash and clinker by raking is necessary.

Referring now to Fig. 3, all the tubes included in the front wall 7 of the hopper extend forwardly then downwardly beyond the outlet to form first a roof section 70 and then a front wall 71 of the ash collecting chamber, and are joined at their lower ends to an inlet header 72 connected by downcomers (not shown) into the circulatory system of the vapor generating unit. All the tubes included in the rear wall 8 of the hopper-bottom extend rearwardly beyond the outlet 5 to form a second roof section 73 at the outward edge of which they are all connected into a second inlet header 74 also connected into the circulatory system of the vapor generating unit. The sifting device 11 comprises a plurality of spaced tubes '75 arranged with their axes parallel to the side wall 9 of the combustion chamber and extending upwardly at a steep inclination from adjacent the door 16 to a region adjacent the outlet 5, thelower and upper ends of these tubes being curved away from the wall 71 and being joined respectively to an inlet header 76 and an outlet header 77. The rear wall 78 of the ash collecting chamber is formed by a plurality of spaced fluid cooled tubes 79 extending upwardly at a steep inclination from the inlet header 76, in conjunction with refractory material 80, the upper ends of these tubes being bent rearwardly away from the wall 71 and connected to the outlet header 77. The two headers 76 and 77 are appropriately connected for fluid flow therethrough; for example, into the economizer system (not shown) of the associated vapor generator, by inlet and outlet pipes 81 and 82 respectively. At the lower end of the wall 78, the wall tubes 79 in the vicinity of the fine ash door are bent sidewardly to leave the wall opening 83 for the discharge of fine ash from the compartment 15. A gas tight expansion seal 34 is provided, adjacent the header 74, between the lower parts of the tubes included in wall 8 of the hopper-bottom and the upper parts of tubes 75 and 79. The lower parts of those of the tubes forming the front wall 71 which are adjacent the clinker removal door 16 are bent sidewardly so as to form the wall opening 19 for the outflow of clinker, the lower part of this opening being formed by a steeply inclined refractory floor 86. The intertube spaces of the lower parts 87 of the tubes 75 are closed by refractory material (not shown) to form a sloping floor for the fine ash compartment 15.

In the three embodiments of the invention so far described in detail, removal of the clinker from the vicinity of the ash collecting chamber to a suitable disposal point has been by means of water sluiceways.

In some cases, more particularly in cases where the ash normally produced consists mainly of fine ash, it may be economical to remove the clinkeLby wheeled trollies. The arrangements of Figs. 4 and 5 are intended for use mainly in such cases.

Referring first to the arrangement shown in Figure 4, alternate tubes lining the wall 8 of the hopper-bottom extend downwardly beyond the outlet 5, first vertically and then at a steep inclination to form, in conjunction with refractory material 90, first a rear wall 91 and then an inclined bottom part 92 of the fine ash compartment 15, these tubes terminating in a lowermost inlet header 93. The remaining tubes of the wall 8 of the hopper bottom extend downwardly as the spaced parallel tube lengths 12 of the sifting device 11, and terminate in an intermediate inlet header 94. The tubes lining the wall 7 of the hopper-bottom extend substantially horizontally from adjacent the outlet 5 to form an arch or roof 95 above the ash collecting chamber and connect with a third and upper inlet header 96, the wall 97 of the ash collecting chamber below the roof 95 being lined with tubes 98 connecting the upper header 96 with the intermediate header 94, and with tubes 99 connecting the intermediate header 94 with the lowermost header 93. Certain of the wall tubes 98 are omitted to provide an opening 100 behind the clinker removal door 16, and the lower part of the clinker collecting compartment 14, adjacent the door 16, is provided with an inclined refractory floor 101. The parts of the tubes lining the bottom part 92 of the fine ash compartment in the vicinity of the fine ash door 2%) are bent sidewardly to leave the wall opening 102 for the discharge of fine ash from the compartment 15. The headers are connected into the circulatory system of the vapor generating unit by means of downcomers such as 103.

The arrangement of clinker collecting compartment and clinker removal door 16 is such that, upon opening of the door, clinker collected in the compartment will discharge under the effect of gravity into a wheeled trolley indicated by 104.

Figure 5 illustrates a modified form of the arrangement shown in Figure 4, the sifting device 11 being formed with a horizontal extension or shelf 105, which provides increased storage capacity both in the clinker collecting compartment 14 and in the fine ash compartment 15. It is necessary, however, with this construction, to resort to hand raking to discharge the clinker into the trolley 164 and to some hand raking to completely empty the fine ash compartment.

Figures 8, 9 and 10 illustrate a second form of sifting device, which may be used with any of the arrangements set out in Figures 1 to 5. The tubular members 12 included in the sifting device 11a serve to support bars extending in the same direction as the tubular members and arranged at the intertube spaces, e. g. at intertube space 111, thus fulfilling the same function as the studs 13 of Figures 6 and 7. Bent metal clips 114, each clamped about one of the tubular members 12 by means including a rod having screw-threaded ends, nuts 116, and a distance piece or sleeve 117, are formed with apertures 118 through which extend rods 119 extending transversely of and below the tubular members 12 and through apertures 120 in the lower parts or the bars 110. The relative spacing of the bars 110 and the clips 114 is maintained by tubular spaces 121 provided on the rods 119. As shown in Figures 9 and 10, the cross-section of the bars 110 tapers downwardly. The spaced relationship of the lower parts of each pair of bars 110 mounted between a pair of adjacent tubular members is maintained by rivets 123 extending through distance pieces 124 arranged as shown, while additional transverse rods 126 provided with tubular spacers 127 maintain the relative spacing of the upper parts of the bars 110 included in the sifting device.

When the form of sifting device illustrated in Figures 6 and 7 is used, in most cases the slope of the sifting device 11 and the dislodging action of the larger lumps of clinker which slide down the sifting device are sufficient to prevent blockage of the gaps between the sifting device studs 13 by pieces of clinker which are just too large to pass between the studs but which lodge deeply between adjacent studs. In some cases, however, it may be necessary to provide means for preventing the continued lodgement of such pieces of clinker, and these means may suitably include normally closed apertures in the upper part of the side wall of the fine ash compartment for the passage of a cleaning tool such as a steam lance adapted to discharge steam upwardly through the gaps between the tubes forming the sifting device.

In the operation of a vapor generating unit fitted with an ash collecting chamber in accordance with any one of the embodiments of the invention set out above, substantially all the particles of ash in the form of dust or relatively small pieces of clinker that are present in the ash pass through the sifting device while the remainder of the ash slides down the sifting device and accumulates at the lower end thereof adjacent the door 16.

Both the clinker and the fine ash give up heat, mainly by radiation, to the fluid cooled tubes in the ash collecting chamber, and as a result, not only is much of the heat in the ash usefully recovered, but the formation of large masses of clinker due to after-burning in the ash collecting chamber is eliminated.

At appropriate intervals, the lengths of which will depend upon the ash content of the fuel being burned, the rate of firing of the furnace, and the size of the ash collecting chamber compartments, the clinker removal door 16 is opened by means including the hydraulic cylinder 18 and clinker collected in the clinker compartment is discharged from the compartment through the wall opening 19. At suitable intervals, which may or may not coincide with the intervals for removal of the clinker, the fine ash removal door 20 is opened by means including the hydraulic cylinder 22 and ash collected in the fine ash compartment is discharged into the fine ash chute 23 from which it is removed pneumatically by suction through the pipe 24 to some convenient point of disposal.

In the various arrangements shown, a pneumatic or any other material handling system suitable for dealing with dust and small particles may be successfully used to remove the fine ash whatever the nature of the coal supplied to the combustion chamber and any larger particles of clinker may be separately evacuated and removed by the hydraulic conveying system, by the trollies or by any other suitable means.

Loss of efficiency due to evaporation of water in the ash collecting chamber is avoided, the heat in the ash is absorbed to a substantial degree by the wall tubes of the ash collecting chamber and the tubes of the sifting device while thermal radiation transmitted from the combustion chamber into the ash collecting chamber is also largely absorbed by the tubes of the sifting device and by wall tubes of the ash collecting chamber.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed Without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. A furnace having a combustion chamber adapted to be fired with ash-containing solid fuel in suspension and formed with a hopper bottom having downwardly converging walls defining therebetween a lower ash discharge outlet, an ash collecting chamber arranged subjacent said combustion chamber in a position to receive ash discharged through said outlet, said collecting chamber having an upper portion extended laterally beyond one side of said outlet, 21 sifting device in said ash collecting chamber arranged to effect separation from said ash of the smaller ash particles, said sifting device comprising fluid cooled elements having portions inclined downwardly through said collecting chamber from a point adjacent the opposite side of said outlet, and means for separately evacuating from said collecting chamber the separated smaller ash particles and the remainder of the ash; the lower portions of said fluid cooled elements bcing disposed beneath said laterally extended upper portion of said chamber.

2. A fluid heater furnace having a combustion chamber adapted to be fired with ash-containing solid fuel in suspension and formed with a hopper bottom having downwardly converging walls defining therebetween a lower ash discharge outlet, an ash collecting chamber arranged subjacent said combustion chamber in a position to receive ash discharged through said outlet, a sitting device in said ash collecting chamber arranged to effect separation from said ash of the smaller ash particles, said sifting device dividing said ash collecting chamber into intercommunicating ash collecting compartments respectively constituting a lower compartment in which said separated smaller ash particles are collected and an upper compartment in which the remainder of the ash is collected, said sifting device comprising fluid conducting tubes extending from one side of said outlet and continuing across said collecting chamber at an inclination toward the bottom of said chamber at the opposite side of said outlet, and means for separately evacuating the collected ash from each of said compartrnents.

3. A fluid heater furnace as defined in claim 2 wherein the fluid conducting tubes forming the sifting device have upper portions extended along said hopper bottom of said combustion chamber.

4. A fluid heater furnace having upright fluid cooled walls defining a combustion chamber adapted to be fired with ash-containing solid fuel in suspension and having an ash discharge throat formed in the bottom thereof, two of said walls having portions converging downwardly and defining said throat, an ash collecting chamber arranged to receive ash discharged through said throat, said chamber having a roof portion extending laterally of said throat, an ash sifting device inclined downwardly across said ash collecting chamber throughout the greater part of the height thereof and dividing the chamber into intercommunicating ash collecting compartments respectively constituting a lower compartment in which the smaller ash particles are collected and an upper compartment in which the remainder of the ash is collected, said sifting device including steeply inclined horizontally spaced tubes together with means supported on said tubes and partially obstructing the intertube spaces to an extent leaving vertically clear spaces capable of passing only the smaller ash particles into said lower compartment, said tubes of said sifting device having integral upper length portions continuing above said throat along one of said converging wall portions, means for causing fiuid to flow through all said tubes, and means for separately evacuating ash collected in the respective compartments said sifting device extending completely across said throat with its lower end being disposed beneath said roof portion.

5. A fluid heater furnace having a combustion chammer adapted to be fired with pulverized fuel and formed with downwardly converging wall portions defining a bottom outlet through which ash is discharged, an ash collecting chamber arranged subjacent said combustion chamber for receiving said ash and having a lateral extension thereof horizontally displaced from said outlet, said outlet and said ash collecting chamber being horizontally continuous parallel to said wall portions, said ash collecting chamber having opposite end walls each extending downwardly from a side of said outlet and one of said walls having an upper portion formed as an arch above said extension, an ash sifting device extending downwardly across said ash collecting chamber and dividing the chamber into intercommunicating ash collecting compartments respectively constituting a lower compartment in which the smaller ash particles are collected and an upper compartment in which the remainder of the ash is collected, tubes associated with each of said end walls and with said ash sifting device, said tubes of said sifting device being horizontally spaced and arranged to provide vertically clear intertube spaces capable of passing only said smaller ash particles, a header at the bottom of said ash collecting chamber, means including said header for supplying fluid to all of said tubes, and means for separately evacuating the ash collected in each of said compartments, said sifting device extending completely across said throat with its lower end being disposed beneath said arch.

6. In a fluid heater furnace, an ash collecting chamber having an upper portion open to receive ash resulting from the burning of ash-bearing fuel in a region above said chamber, said open upper portion of said chamber being of considerably smaller horizontal cross section than said fuel burning region above said chamber, and an ash sifting device comprising fluid connecting tubes inclined downwardly across said chamber throughout a substantial portion of its height and arranged to efiect separation from said ash of the smaller ash particles, said sifting device dividing said chamber into inter-communieating compartments respectively constituting a lower compartment in which the separated smaller ash particles are collected and an upper compartment in which the remainder of said ash is collected, each of said ash collecting compartments having a closable ash discharge opening leading from a lower portion thereof and directing the collected ash into a separate ash removal means located exteriorly of said chamber; said collecting chamber having a roof portion extending laterally of said 10 outlet, and the lower portions of said fluid conducting tubes being disposed beneath said roof portion.

7. An ash collecting chamber as claimed in claim 2 in which said tubes are spaced laterally, and including, bars extending in the same direction as said tubes and arranged at the spaces between adjacent tubes, and means including said tubes for supporting said bars.

8. In a fluid heater furnace, the combination as defined in claim 7 wherein said bars are arranged at least mainly below the level of said tubes.

References Cited in the file of this patent UNITED STATES PATENTS 47,218 Parker Apr. 11, 1865 890,552 Bibb June 9, 1908 983,741 McDonald Feb. 7, 1911 1,719,874 Chapman July 9, 1929 1,876,623 Daniels Sept. 13, 1932 1,947,460 Coutant Feb. 20, 1934 2,087,800 Bailey et al. July 20, 1937 2,169,848 Murray Aug. 15, 1939 2,299,559 Rehm Oct. 20, 1942 2,551,945 Harvey May 8, 1951

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