US2713853A - Apparatus for burning fuel - Google Patents

Description

July 26, 1955 R. M. HARDGROVE APPARATUS FOR BURNING FUEL 2 Sheets-Sheet 1 Filed Dec. 50, 1949 FIG] INVENTOR Mflam'grore Fag/z ATTO R N EY y 6, 1955 R. M. HARDGROVE APPARATUS FOR BURNING FUEL 2 Sheets-Sheet 2 Filed Dec. 30, 1949 INVENTOR 1? 0 5 flff/amgm Ve ATTORNEY United States Patent APPARATUS FOR BURNING FUEL Ralph M. Hardgrove, Canton, Babcock & Wilcox Company, poration of New Jersey Ohio, assignor to The Rockleigh, N. L, a cor- The present invention relates in general to an apparatus for burning fuels, and more particularly to an apparatus for burning ash-containing particle form solid fuels at least partially in suspension under furnace conditions insuring a high combustion efficiency and permitting the separation and removal of the fuel ash constituents from the combustion zone in a molten condition.

In the burning of an ash-containing fuel in suspension in the furnace of a fluid heating unit containing convection heated fluid heating tubes, for example, it is important from both the standpoint of thermal efliciency and unit availability that combustion of the combustible constituents be completed before the gaseous products of combustion reach any relatively closely spaced convection heated fluid heating tubes. This is especially important when the mean or average furnace temperature exceeds the initial deformation temperature of the ash constituents of the fuel. Under such conditions ash particles suspended in the gaseous products of combustion are likely to be in a sticky condition when reaching such cooler heat transfer tubes and to deposit thereon to such an extent as to restrict and even close the intertube gas flow passages. Ash particles which are solidified before reaching such heat transfer tubes, or solidified in the intertube passages, are either deposited on subsequent heat transfer tubes in an easily removable condition or are carried out of the fluid heating unit and unless collected by expensive dust collecting equipment, will foul the atmosphere. In view of the increasing efforts to minimize atmospheric pollution, there has been a constant trend to separate and recover as much as possible of the recoverable ash content within the combustion zone in a molten condition and or zig-zag flow path, stratification of the gases therein is minimized, and a highly effective turbulent mixing of the fuel particles and oxygen-containing gas will occur, while maintaining a relatively low gaseous pressure drop between the furnace entrance and exit. A high thermal eificiency is insured and ash separation facilitated by the maintenance of furnace temperatures in the fusing temperature range of the fuel ash sufficient to render the ash particles in a fluid or molten condition. Under these conditions, the successive relatively abrupt changes in direction of the stream of burning fuel, oxygen-containing gas and products of combustion cause agglomeration of the tiny particles of ash and successive separation of the resultant heavier ash particles from the stream. The successive changes in direction cause the agglomerated ash particles to deposit on the wall surfaces defining the gas flow path, while retaining the gaseous pressure drop within practical operating limits. As a consequence, the ash particles coming into contact with the confining walls of the combustion zone are in a condition suitable for adher ing thereto and forming a sticky film or layer of downwardly flowing molten ash. With the gaseous flow path thus mainly defined by surfaces having a sticky film of ash thereon, unburned large or heavy fuel particles coming into contact therewith are entrapped thereon and burned in situ by the scrubbing contact of the high velocity oxygen-containing gases. Thus the fuel particles entrapped on the molten ash film are not only provided with the necessary oxygen for their combustion, but are also retained within the combustion zone long enough to complete their combustion. Under such furnace temperature conditions in a tortuous combustion zone, any purely refractory wall surface defining the same would be rapidly eroded and be commercially impracticable. Such erosion is avoided, in accordance with the present invention, and

. the heat recovery efficiency of the associated fluid heating unit increased, by the provision of fluid heating tubes in the wall surfaces lining the flow'path within the combustion zone. Advantageously, the combustion zone shape is such that relatively simple formations of fluid heating tubes can be used to define the same, and the tubes covered with a refractory layer proportioned to facilitate solidify the remainder before the gaseous products of k combustion reach any closely spaced heat transfer tubes. For the burning of pulverized bituminous coal, for example, wet bottom or slag tap furnaces have been developed in which the fuel is burned in suspension under furnace temperatures such that ash collecting in the combustion zone can be removed in a fluid or molten condition. Approximately of the recoverable ash content of the fuel can be recovered in the combustion zone under these conditions. However, the ash remaining in the a better understanding of the invention, its operating a'dgases leaving the combustion zone is still sufficient in amount to present a considerable operating problem in maintaining the heat transfer surface in an eflicient heat absorbing condition, and also to cause a considerable amount of atmospheric pollution unless collected extershaped combustion zone through which the fuel and an oxygen-containing gas, such as air, are passed under high velocity turbulent flow conditions, resulting in an intimate mixing of the oxygen-containing gas and the combustible fuel constituents and rapid and complete combustion thereof. With such a high velocity flow through a sinuous the maintenance of the deposited ash particles in a fluid or molten condition within the combustion zone and to permit their flow under the action of gravity through the combustion zone, and the collection and removal of the separated ash in a molten condition, i. e. as molten slag, at a point outside of the main gas flow path. Substantially all of the recoverable ash constituents are thus recovered and the gaseous products of combustion are discharged from the combustion zone substantially free of entrained ash particles. I

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For

vantages and specific objects attained by its use, reference should be had to the accompanying drawings and descrip tive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is an elevation, partly in section, of a vapor generating unit having an experimental type furnace constructed in accordance with the present invention;

Fig. 2 is an enlarged horizontal section taken on the line 22 of Fig. l;

Fig. 3 is an enlarged elevation of the burner nozzles viewed from the inside of the furnace along the line 33 of Fig. 1; and

Fig. 4 is an enlarged transverse line 4-4 of Fig. 1.

As shown in Fig. l, the furnace 10 of the present invensection taken on the tion is associated with a well known type of steam generating unit 14. When applied to this form of heat user, the furnace is symmetrically arranged relative to the width of the unit and advantageously formed by boundary walls which are defined by spaced tubes connected into the circulatory system of the steam generating unit 14. The tubes are studded in a known manner and coated with an initially plastic refractory material, such as plastic chrome ore, to provide a refractory lining for the furnace and supporting surfaces for the film of molten noncombustible matter deposited thereon.

In the embodiment illustrated, the front and rear walls of the furnace are defined by rows of refractory-faced studded upright tubes and 16, respectively, shaped to define the front and rear sides, roof and floor of an upper fuel ignition chamber 11, the flow directing walls of a zig-zag or sinuous passageway in the intermediate portion 12 thereof, and the front and rear sides, roof and bottom of a lower ash receiving and heating gas outlet chamber 13. The opposite side walls of the furnace 1 are also defined by rows of refractory faced studded upright tubes 18 and 20 extending the full height of the furnace 10 between pairs of upper headers 21 and lower headers 22 arranged at opposite sides of the furnace.

The upper ignition chamber 11 is bounded by the upper portions of the rows of tubes 15 and 16 to define a chamber of rectangular horizontal and vertical cross-section. The furnace roof 23 is formed by the inclined upper end portions of the front wall tubes 15, the upper ends of which are connected with the front upper drum 24 of the steam generating unit 14. The rear tubes 16 extend downwardly from an upper end connection with the drum 24 to a spaced position below the roof 23 where they slope downwardly toward the front wall tubes 15 to form the floor 25 of the chamber 11. The floor 25 ends at a position transversely spaced from the front wall tubes 15 to define an outlet opening 26, as shown in Fig. 2, of generally rectangular cross-section. Below the opening 26, the rear wall tubes 16 have an irregular sinuosity in vertical plane, being rearwardly and downwardly bent at an inclination of, for example, approximately 15 to the horizontal, to a position generally in vertical alignment with the rear wall of the ignition chamber. The tubes 16 are then bent vertically downward and then sloped downwardly and forwardly to a position generally in vertical alignment with the rear edge of the opening 26, and then sloped rearwardly and downwardly to substantially duplicate the described shape of the superjacent projecting portion. The tubes 16 are again bent vertically downward and then forwardly and downwardly at the bottom of the intermediate portion 12 of the furnace to a position spaced from the front wall tubes 15 to provide a bottom outlet 27 of larger rectangular crosssectional area than the outlet 26, opening into the lower ash-receiving chamber 13.

The portions of the front wall tubes 15 in the intermediate section 12 of the furnace are bent in substantially parallel relationship to the rear wall tubes 16 to define the flow-directing walls of a sinuous passageway 28 of substantially uniform cross-sectional flow area throughout the intermediate portion 12 of the furnace. The flow passageway 28 is formed by a plurality of straight passageway sections 28A, 28B, 28C and 28D connected in substantially end to end angular relationship, e. g, angles of 30, so as to form a flow path having a series of relatively abrupt changes in flow direction. With this arrangement, the tubes 16 will define the inclined roof portions of the sections 28A and 28C and the inclined floor or hearth portions of the sections 283 and 28D, while the successive sections of the tubes 15 form the floor portions of the sections 28A and 28C and roof portions of the sections 283 and 28D. In operation, the section 28A will receive a substantially vertical flow of burning fuel and ash in suspension from the ignition chamber outlet 26 and directs the fiow in a rearwardly direction to the adjoining section 28B. In entering and passing through the section 28B, the stream of burning fuel and gaseous products of combustion makes a short radius turn through an angle of approximately substantially reversing the direction of the stream. This abrupt reversal of stream fiow is repeated in successively opposite directions in entering and passing through each of the adjoining passageway sections 28C and 28D, discharging at the end of the latter section downwardly through the outlet 27 into the chamber 13.

From the outlet 27 at the top of the ash-receiving chamber 13 the front wall tubes 15 extend downwardly to a connection in a horizontal header 3i which is connected to the lower drurn 31 of the generator 14 as hereinafter described. The front and side walls of the ashreceiving chamber 13 are defined by upright lower portions of the rows of tubes 15, 1S and 20. The rear wall tubes 16 are alternately bent to different degrees to form two rows of bare tubes which slope downwardly and rearwardly from the opening 27 to a spaced position above the fioor of the chamber 13 to provide an inclined slag screen 32 through which the heating gases pass in leaving the chamber 13. Beneath the lower end of the slag screen 52, the lower portions of the tubes 16 define an upright rear wall and the inclined floor of the chamber 33, with the lower ends of the tubes opening into the header 30. A row of tubes 33 are inclined downwardly from the drum 31 to merge into the tube row 16 at the lower end of the slag screen 32 and to connect with the header 30. The floor of the chamber 13 is provided with a slag tap hole 34 near its lower end formed by bending the forward portions of some of the floor tubes. A plug 35 is mounted on an arm 36 so that the tap hole 34 may be closed or opened by raising and lowering the plug, respectively. The arm is moved by means of a hydraulic piston 37 which can be manually regulated or arranged for periodic movement in response to impulses transmitted by a suitable timing device (not shown). The molten ash or slag dropping through the slag hole falls into a tank 38 of water and is removed from the tank or slag pit by an upwardly inclined screw conveyor 40 for suitable disposal.

In the illustrated embodiment of the invention, an ashbearing particle form fuel, such as pulverized coal, is delivered to the ignition chamber 11 in a carrier or primary air stream through a feed pipe 41. Raw coal from an overhead bin 42 is drawn through the feed spout 43 into a unit pulverizer 4'4, with the air-borne pulverized coal discharging therefrom into the pipe 41. The upper end of the feed pipe 41 is divided into a plurality of horizontally elongated nozzles 46 which are arranged in a spaced horizontal row to discharge the air-borne fuel through corresponding burner ports in the front wall of the chamber 11. The burner ports are formed o5- setting a portion of alternate front wall tubes 15 and omitting the studs and refractory therefrom, as shown in Fig. 3, to provide a plurality of vertically elongated intertube burner ports 47 in the chamber front wall. The nozzles 46 have their inner ends terminating at the center line of the tube row 15 and in contact with the adjacent tubes. The nozzles 46 and ports 47 are generally centered horizontally of the upper part of the chamber 11, so that the fuel and air streams discharged therefrom are initially directed substantially horizontally toward the upper rear wall of the ignition chamber 11. An external air housing 48 encloses the ports 47 and sur rounds the nozzles 46 so that superatrnospheric pressurc air delivered to the housing from an external source will pass through the ports 47 both above and below the nozzles 46 to provide secondary combustion air for the fuel. Under certain conditions of operation, it may be desirable to divide the required amount of secondary air to the furnace. For this purpose, one or more valved air conduits 49 extend from the bottom of the air housing 48 and discharge between adjacent tubes into the passageway section 2813, as shown in Fig. l.

Preheating of the secondary combustion air for the furnace of the present invention is desirable, although not essential. As shown in Fig. 1, thesecondary air delivered to the burner ports 47 is preheated to a high temperature in a recuperative type air heater 50 mounted above the steam generator. High temperature combustion gases are withdrawn from the generator setting before they enter the tube banks through a duct 51 and passed through a plurality of groups of tubes 52 within the heater to discharge into the stack 53. Air is delivered to the heater 50 through the air duct 54 from a forced draft fan 55, passed over the tubes 52 of the air heater and delivered through the discharge duct 56 to the air housing 48. With the described arrangement, air temperatures as high as 870 F. have been obtained and the preheated air used for combustion purposes in the described process. A valved by-pass connection 57 between the air inlet portion of the heater and the discharge duct 56 permits a proportioning of cold and hot air to regulate the secondary air temperature delivered to the air housing 48.

In starting up, a torch 17, for example, an oil burner, is used to preheat the chamber 11. Thereafter the pulverized coal is delivered with its carrier air through the pipe 41 and the nozzles 46 to the ignition chamber 11 where it is ignited from the torch flame. When the coal flame has become stabilized, the use of the torch 17 is discontinued.

The pulverized coal-primary air streams entering the ignition chamber 11 rapidly mix with the superjacent and subjacent secondary combustion air streams, with most of the finer coal particles burning during their movement through the U-shaped path in the ignition chamber leading to the outlet 26. The ash residue of the burned coal particles is initially released in a substantially molten state, and some of the globules of ash and other suspended solids are forced outwardly of the stream of burning fuel and gases largely by reason of the reversal in the direction of flow thereof in the ignition chamber due to the relative position of the burner nozzles 46 and the outlet 26. The fuel and air are normally supplied in sufiicient quantity to maintain the ignition chamber at a temperature in excess of the ash fluid temperature, so that the globules of molten ash contacting the chamber walls will tend to adhere thereto to form a downwardly moving film of sticky ash thereon.

The burning mass or stream of gaseous products of combustion, burning combustible matter and heated air, with its suspended globules of ash, passes through an abrupt change in flow direction ,in leaving the chamber 11 and entering the passageway 28A through the outlet 26. The substantial change in flow direction intimately remixes the constituents of the burning stream, causing agglomeration of suspended molten ashparticles and a further separation of the ash by the inertia effect on the particles and their adhesion to the walls of the passageway. The separated molten ash flows down the side walls and floor of the corresponding floor or hearth por tion and either drops to the floor of the subjacent section or is swept around the rounded nose at the fioor end and partly down the roof section of the subjacent section before the gravitational effect causes it to drop. The straight portion of each passageway section causes an acceleration of any solid or liquid particles in suspension in the burning stream, so that as the stream turns in passing from one passageway section to the subjacent section, the momentum of the particle tends to force it outwardly into contact with the confining wall of the passageway turn. The repeated turns through the described reversals in direction of the flow path of the burning stream continue the ash agglomerating and separating effect of the furnace. It is believed that high gas velocities through the sinuous section of the furnace of the order of those indicated herein are essential to an effective ag glomeration of the fine molten ash particles released in the burning of a pulverized ash-bearing solid fuel suf ficient to cause their separation from the burning stream under the successive inertia eifects imposed thereon by the successive reversals of flow direction.

The described successive reversals in direction of the stream of burning fuel, combustion air and products of combustion are highly effective in promoting further mixing of the partially burned and unburned fuel particles with the combustion air in the stream, due to the turbulent flow conditions existing in the gas turning portions. The repeated intimate mixing of unburned fuel and air during the passage of the stream through the sinuous section of the furnace contributes to highly efficient combustion conditions, permitting the burning of low volatile pulverized solid fuels, such as pulverized petroleum coke, heretofore found difficult to burn in suspension without the aid of an auxiliary fuel.

The maintenance in operation of a film or layer of molten ash on the boundary walls of the ignition chamber 11 and sinuous passageway 28, and particularly on the Wall areas in and adjacent to the gas turning portions of the sinuous passageway, also contributes to the fuel burning efiiciency of the furnace, particularly when the maximum particle size of the fuel exceeds that normally present in pulverized bituminous coal as is the case when a crushed or screened coal is being burned. In such cases, the larger fuel particles tend to separate from the stream in the ignition chamber and gas turning sections and to be entrapped in the film of molten ash on the walls of those sections. The scrubbing action of the high velocity oxygen-containing stream relative thereto causes the entrapped fuel particles to burn rapidly in situ, and the ash residue joins with the ash in the molten film on those surfaces.

The combustion gases entering the ash-receiving chamber 13 of the furnace are subjected to a final reversal in flow direction in order to reach the gas outlet from the chamber 13 across which the slag screen 32 extends. This abrupt change in direction affords a final opportunity for molten ash particles to separate in the furnace. Any fine ash particles remaining in the exiting hot gases are cooled below the fusing temperature range of the ash as the gases pass through the slag screen 32 at the rear side of the furnace 10.

In the arrangement described, the direction of gas flow through the furnace and the flow of the molten ash wall film are generally in parallel, although relative cross-flow occurs in some parts of the apparatus. Parallel fiow is the preferred relationship of gas and ash flow direction, but the furnace may be arranged and/ or the fuel inlet and slag chamber gas and slag outlets located so that the flow relationship will be primarily of a cross-flow nature, or primarily of a counter-current flow nature, while retaining desirable ash separating and removal and fuel burning advantages of the present invention.

By way of example and not of limitation, an experimental furnace constructed substantially as disclosed was operated at firing rates of from 3000 to 6000 lbs. of pulverized bituminous coal per hour. The bituminous coals used included a range of ash contents between 9.6 and 24% volatile contents from 18 to 42%, and ash fluid temperatures under oxidizing conditions of between 2490" F. and 2700 F. In this range of capacities, the furnace temperatures maintained were such that molten ash was continuously tapped from the tap hole 34. The nozzle tip velocity of the air-borne pulverized coal was from 4000 to 6000 feet per minute, while the velocity of the burning stream passing through the passageway 28 was of the order of 5000-8000 feet per minute. With a pulverized coal fineness of 70 to passing through a 200 mesh screen, 94 to 99% through a 100 mesh screen, and 99.8% through a 50 mesh screen, and with excess air of the order of 10 to 20%, the dust loading of the gases leaving the furnace was found to be less than 1 pound per 1000 pounds of flue gas. As a further and more specific example, pulverized Fairmont coal having a volatile content of 41.9%, and an ash content of 9.6% was delivered to the furnace at a rate of 5980 pounds per hour. This coal had an ash fluid temperature under oxidizing conditions of 2590 F, and was pulverized to a fineness of 70.4% passing through a 200 mesh screen, 94.4% through a 100 mesh screen, and 99.8% through a 50 mesh screen, for delivery to the furnace. At this capacity with a secondary air temperature of 725 F, and with 125% total air, as measured at the air heater outlet, the dust loading at the stack was found to be .68 pound of dust per 1000 pounds of flue gases.

While the present invention is particularly effective in the combustion of, and molten ash separation in the combustion zone from, a pulverized bituminous coal, the process and furnace disclosed can also be used to advantage with other fuels. Relatively coarsely sized ash-bearing solid fuels can be efficiently burned with an effective ash separation in the furnace described, whether the fuel is prepared by crushing or screening. Such coarse particle form fuel should, however, be supplied with its sizing selected in view of its grindability and volatile content. For example, a high volatile bituminous coal which has been prepared by crushing or screening to a A. inch top size and approximately 10% through 200 mesh, will ordinarily contain sufficient fines for use in the furnace. A lower volatile coal should, however, be prepared with a greater percentage of fines, as for example with a maximum size of the order of /4 inch and through 200 mesh. When utilizing such relatively coarse particle form fuels, the molten film of ash on the walls of the combustion zone is particularly effective in entrapping coarse fuel particles so that the particles will be retained in scrubbing contact with the oxygen containing gases to completely consume the combustible content of the fuel particles within the furnace. A fluxing material, such as limestone and/or soda ash, may be added to any of the fuels described to increase the fluidity of the ash and to lower its fusing temperature range. Similar effects can also be obtained with some ash-bearing fuels by operating the ignition chamber under a reducing atmosphere and supplying the remainder of the secondary air required through the pipes 49. The mixing and remixing effect of the high velocity flow through the tortuous refractory faced passageway of the furnace is effective for the combustion of low volatile low ash fuels, such as petroleum coke. The described results are accomplished with a relatively low pressure drop through the furnace, e. g. pressure drops ranging from 2 to 8 in. H2O for a load range of 30006000 lbs. of coal per hour, and therefore a correspondingly low required capacity and power consumption for the forced draft fan 55.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation 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 and in the fuel burning process disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features. For example, changing the cross-sectional shape of the passageway to reduce the ratio of furnace volume to furnace periphery will permit the use of fuels in a wider range of ash fusing temperature ranges.

I claim:

1. Apparatus for burning an ash-bearing fuel comprising reversely bent refractory coated fluid heating tubes cooperating to define a vertically elongated tortuous passageway of substantialy uniform flow area having successive reversals in flow direction and a series of inclined molten ash-supporting surfaces, means for introducing a burning stream of fuel in gaseous suspension into the upper end of said tortuous passageway, and

means for collecting molten ash at the lower end of said tortuous passageway substantially out of entraining contact with the discharging gaseous products of combustion.

2. Apparatus for burning an ash-bearing fuel with combustion temperatures above the ash fusion temperature of said fuel comprising refractory covered fluid heating tubes cooperating to define the walls of a vertically elongated furnace chamber, an ignition section at one end of said elongated chamber, means for introducing a combustible mixture of fuel in suspension and air into said igition chamber, said elongated chamber having a tortuous passageway portion in communication with said ignition chamber and having successive reversals in flow direction therein, the walls of said elongated chamber having a series of inclined ash supporting surfaces, and means for collecting molten ash at a point substantially out of entraining contact with the discharging stream of gaseous products of combustion leaving said tortuous passageway.

3. Apparatus for burning an ash-bearing fuel with combustion temperatures above the ash fusion temperature of said fuel comprising refractory covered fluid heating tubes cooperating to define the walls of a vertically elongated combustion chamber having an ignition section, means for introducing air-borne ash-bearing fuel and combustion air to said ignition section, a molten slag receiving section of said chamber spaced from said ignition section, and walls defining a plurality of passageways of reduced flow area arranged in end to end angular relationship and extending downwardly from said igni tion section to said slag receiving section, said walls having a series of inclined ash supporting surfaces.

4. Apparatus for burning an ash-bearing fuel substantially in suspension with temperatures in excess of ash fusion and separating the molten ash from the gases of combustion comprising an ignition chamber defined by refractory lined fluid cooled walls having an outlet in the lower end thereof, a multiple tip burner arranged to discharge ash-bearing fuel in air suspension through a wall of said chamber upwardly adjacent said outlet, a slag receiving chamber spaced downwardly from said ignition chamber, refractory lined fluid cooled walls defining a plurality of passageways arranged in series staggered relationship and extending from the outlet of said ignition chamber to said slag receiving chamber, said refractory lined fluid cooled walls having a series of inclined ash supporting surfaces and being spaced to define a flow passageway having a substantially uniform cross-sectional area less than the cross-sectional area of said ignition chamber.

5. Apparatus for the suspension burning of particle form ash-bearing fuel with combustion zone mean temperatures above the ash fluid temperature and agglomerating and separating the resulting ash in a molten condition therein comprising refractory lined fluid cooled walls defining an elongated chamber having a fuel ignition section in one end thereof and a heating gas outlet at its opposite end, fluid cooled tubes covered by refractory material cooperating to define a substantially unobstructed zig-zag gas passageway and inclined molten ash receiving surfaces between said ignition section and heating gas outlet, the cross-sectional area of said zig-zag gas passageway being approximately 20 to per cent of the cross-sectional area of said fuel ignition section, means for introducing a combustible mixture of airborne ash-bearing fuel and combustion air into said ignition section, and means for collecting separated ash in a molten condition from said ash receiving surfaces at the lower end of said chamber.

6. Apparatus for burning particle form ash-bearing fuel at least partially in suspension with combustion zone mean temperatures above the ash fusion temperature and separating the resulting ash in a molten condition therein comprising walls formed by rows of refractory covered vapor generating tubes defining a vertically elongated chamber having a fuel ignition section in one end thereof and a heating gas outlet at its opposite end, said refractory covered fluid cooled tubes spaced to define a substantially unobstructed high velocity zig-zag gas passageway and having inclined molten ash receiving surfaces between said ignition section and heating gas outlet, a burner arranged for introducing a combustible mixture of air-borne ash-bearing fuel and air into said ignition section, the burner and the gas inlet end of said zig-zag gas passageway being positioned to cause the flow of fuel and air through said ignition section to move through a U-shaped path, and means for collecting separated ash in a molten condition from said ash receiving surfaces at the lower end of said chamber.

7. Apparatus for burning particle form ash-bearing fuel in suspension and agglomerating and separating the ash residue in a molten condition in the combustion Zone comprising walls defining a vertically elongated chamber having a fuel ignition section in the upper end thereof and a heating gas outlet at its lower end, sinuous refractory covered fluid cooled tubes cooperating to form a series of oppositely inclined molten ash-receiving surfaces projecting from opposite sides of said chamber and arranged to define a substantially unobstructed vertical zig-zag gas passageway therein between said ignition 10 chamber and heating gas outlet, means for introducing a combustible mixture of particle form ash-bearing fuel and air into said ignition section and burning the same while in said zig-zag gas passageway, and means for collecting ash deposited on said ash-receiving surfaces in a molten condition at the lower end of said chamber.

References Cited in the file of this patent UNlTED STATES PATENTS 608,161 De Sotolongo July 26, 1898 698,190 Fenner Apr. 22, 1902 1,095,489 Alford May 5, 1914 1,294,730 Von Porat Feb. 18, 1919 1,651,646 Trasenster Dec. 6, 1927 1,791,836 Cannon et a1. Feb. 12, 1929 1,930,566 Sanders Oct. 17, 1933 2,031,551 Sorensen Feb. 18, 1936 2,128,177 Carter Aug. 23, 1938 2,268,559 Bailey Jan. 6, 1942 2,275,394 Hardgrove Mar. 3, 1942 2,357,303 Kerr et a1. Sept 5, 1944 FOREIGN PATENTS 518,517 Germany Feb. 17, 1931

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