US3171369A

US3171369A - Combustion of carbonaceous solids

Info

Publication number: US3171369A
Application number: US248082A
Authority: US
Inventors: Jr Frank M Stephens; William M Goldberger
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1962-12-28
Filing date: 1962-12-28
Publication date: 1965-03-02
Anticipated expiration: 1982-03-02
Also published as: AT250742B; JPS5131372B1; SE334970B

Description

March 2, 1965 F. M. STEPHENS, JR. arm. 3,171,369

COMBUSTIQN 0F CARBONACEOUS SOLIDS Filed Dec. 28, 1962 3 Sheets-Sheet 1 Combustion Gass '.Z 2 so 2 g 70- b g 60- p 3 somvmons 8 4 r l l FRANK. M STEPHENS, JR.

l ooo' I200 I400 I000 mm 2000 2200 WILLIAM TEMPERATURQF I M. so pnaaaesn:

ATTORNEY March 1965 F. M. STEPHENS, JR.. ETAL 3,171,359

COMBUSTION OF CARBONACEOUS SOLIDS Filed Dec. 28, 1962 3 Sheets-Sheet 2 7.0 t 0.0 r u 5.0 U Q u STABLE (L FLUIDIZATION H so u E h. E, 20 o. 3 UNSTABLE 0 Le FLUIDIZATION 0 I900 I950 2000 2050 2:00 2l50 BED TEMPERATURE, F

O m D 83A @2 1 5 f 2 d] 75 m S I 2 9 2? Ld 50' a v POUNDS-BED G SCFM INVENTORS FRANK M. STEPHENS, JR. WILLIAM M. GOLDBERGER ATTORNEY March 1965 F. M. STEPHENS, Jli. ETAL 3,171,359

COMBUSTION OF CARBONACEOUS SOLIDS Filed Dec. 28, 1962 3 Sheets-Sheet 3 Combustion Gases Ash Removal IN VENTORS FRANK M. STEPHENS, JR.

WILLIAM M. GOLDBERGER A T TORNEY United States Patent The present invention relates to a process of burning carbonaceous fuels and is particularly related to the burning of carbonaceous solids by means of fluidized solid process to produce hot, pressurized and dust-free gas suitable as a working fluid for gas turbines.

The use of coal for industrial power generation has received considerable commercial consideration in recent years. Most industrial plants use lump coal on mechanically operated grates and stokers, but some burn coal in powdered or pulverized form. Grate-type burners do not have as high a thermal efficiency and are more costly to operate than powdered coal burners. Burners for pulverized coal are more flexible and can handle coals having widely different characteristics including the easily fused or caking coals which are troublesome when burned on grates. However, a serious disadvantage of pulverized coal burners in the past has been the fact that finely divided ash (hereafter referred to as fly-ash), which is produced during the combustion process, is carried away from the burner with the exhaust gas. The ash materials in the gas are erosive and prevent the use of the gas in open-cycle turbines. Also, the ash-containing gas cannot be used efficiently as a heat exchange medium because the ash materials deposit on the interior sur-' faces of the heat exchanger and reduce its heat transferability. Furthermore, the coal burning efficiencies of these burners are usually lowered due to the fact that some carbon particles become surrounded by the ash materials in the burner and are carried away by the combustion gas without undergoing complete combustion. Fly-ash materials in the gas are also undesirable from the standpoint of air pollution.

Auxiliary gas cleaning equipment such as cyclones have been employed but complete dependence thereon to remove suspended solids from the gas has not proved economically practical. The major difficulty is that the ash particles entrained in the combustion gas are extremely small and difficult to remove unless a plurality of gas cleaning equipment are employed. To maintain a competitive position with other combustion processes using more convenient fuels, such as natural gas or fuel oil, coal-burning devices must provide for continuous operation with a minimum of labor or auxiliary mechanical equipment.

Accordingly this invention contemplates burning carbonaceous solids by means of a fluidized solids process to produce a hot, pressurized gas which is essentially completely dust-free. By the term dust-free it is meant that the gas is essentially free from solid particles smaller than about 10 microns. These solid particles are extremely difiicult to remove by means of ordinary gas cleaning equipment, such as a cyclone. The gas, however, may contain solid particles larger than about 10 microns, but these particles are readily removable by ordinary gascleaning equipment. A minor amount of solid particles of less than 10 microns in size may be present in the gas, but their amount and concentration is too low to cause erosion of the turbine blades or fouling of the interior surfaces of heat exchangers. This invention is accordingly directed to burning carbonaceous solid particles with oxygen or air, in a combustion zone, under such operative conditions that the carbonaceous solid particles burn substantially instantly as they are introduced into the combustion zone. The temperature in the combustion zone is maintained at or slightly below tthe temperature of incipient fusion of the ash produced during the combustion reaction. Thus, the ash particles soften, become tacky, stick together upon collision with other ash particles and agglomerate into larger particles which are eventually withdrawn from the combustion zone. Since, as was previously mentioned, the carbon particles burn rapidly and instantly as they enter the combustion zone, the agglomerated ash which is withdrawn from the combustion zone is essentially completely carbon-free. This permits operation at nearly percent combustion efiiciency since all the carbonaceous solids feed can be burned with essentially no carbon losses from the combustion zone. For example, ignition tests made on these agglomerated ash particles when burning a bituminous coal at about 1975 F. showed that the carbon level of the bed, determined as the percent loss on ignition was 0.70 percent. At 2100 F., however, the carbon level was found to be 0.55 percent. Similar results were found when burning sub-bituminous coal. The rapid burning of the carbonaceous solid particles releases enormous quantities of heat which can be recovered and utilized as will hereinafter be described. The combustion gases which are thus produced are essentially completely free from fly-ash and fine suspended solids.

The novel process will be more clearly understood with reference to the attached drawings wherein:

FIGURE 1 is a schematic flow diagram of a process of burning carbonaceous solids in a fluidized combustion zone.

FIGURE 2 is a plot of combustion efficiency as a function of bed temperature in the combustion zone for one type of carbonaceous solid materials, i.e., powerhouse coal.

FIGURE 3 is a plot of superficial gas velocity versus bed temperature in the combustion zone using powerhouse coal.

FIGURE 4 is a curve representing the relationship between percent ash removed in the fluid-bed and W/ G, wherein W is the bed weight in pounds per square foot of cross-sectional area of the bed and G is the gas rate in standard cubic feet per minute per square foot of bed area, using powerhouse coal.

FIGURE 5 is a schematic flow diagram of a process of burning carbonaceous solids in a combustion zone, operating in conjunction with gasification of carbonaceous solids in a gasification zone.

Referring to FIGURE 1, coal particles 1 are fed from a storage vessel 3 through a metering valve 5 and feed pipe 7. Air is supplied from an air supply source (not shown) into feed pipe 7 to carry coal particles 1 into combustion zone 9. Air is employed both for fiuidizing and for burning said coal particles. Combustion zone 9 is provided with an overhead line 11 to remove the combustion gases, discharge pipe 13 and meter valve 15 for the withdrawal and metering of the solids from said zone 9. Make-up coal may be introduced into the combustion zone via make-up line 17, if necessary. The make-up coal particles are preferably introduced at a point below the surface of the bed to avoid elutriation. Other auxiliary equipment not shown in the drawing may form part of the apparatus employed in carrying out the novel process. For example, the combustion gases may pass through a cyclone to insure complete removal of solid particles from the gas, if necessary.

The operation of this invention can be illustrated using pulverized coal as the carbonaceous solids feed to the combustion zone. However, other carbonaceous sol-ids such as, for example, coke, slack, anthracite, asphalt, pitch, etc., or ash-containing liquid carbonaceous fuels such as liquid asphalt, liquid petroleum residues, fuel oils, gas oils, etc. can be also employed with efiicacious results.

period of about several .hours,: the .bed temperature in: the combustion. zone reaches the incipient'fusion tem@ perature of the ash materials. produced during the com- Cit bustion:reaction, causing the ashiparticles to become tacky and agglomerate upon collisioniwith other particlesin the bed.- j

The temperature in the combustion zone can be con trolled by providing. saidizone. with. external cooling coils or a cooling jacket, or by adjusting the coal feed rate, or oxygen or air rate to the combustion zone. A particularly advantageous method of controlling the bedtemperature in the combustion zone can be accomplished by feeding water slurry of coal, or by introducting water separately into-the combustion zone by means of'line 17a. Water thus vaporizes in the combustion zone, absorbing large quantities of heat (heat of vaporization) which serves to control the temperature in the combustion zone. The quantity of water which is necessary to achieve the desired degree of temperature control may, of course, bedetermined by those skilled in the art. Coal slurry feeding is particularly advantageous economically in commercial operations as the coal is often available in slurry form andcan therefore be pumped directly into the combustion zone without the necessity of drying and storing the coal.

Although not necessarily limited to the following mechanisms, the agglomeration of fly ash may occur in the following manner; As the coal particles enter the fluidized combustion zone, they quickly reach their ig nition temperature and begin to burn. Combustion is rapid because the dispersed coal particles in the fluilized state present a large surface area for the combustion reaction. In addition the high rate of agitationwithin the bed reduces the resistance-to heat and mass transfer and permits rapid burning.- As the coal particles burn, localized temperatureswithin the particles exceed the ash softening temperature and the ash contained in the coal particles becomes sticky. The burning coal particles, upon contact with the bed particles containing the softened ash, adherethereto and continue to burn. In this manner combustion proceeds and, at the same time, the flyashmaterials are removed by agglomeration with the burning bed particles. The bed particles in the combustion zone also agglomerate by another yet similar mechanism. Many of these bed particles have adhering on their surfaces the burning coal particles just described. These particles" present sticky exterior surfaces which are effective for collecting the fiy-ash materials from the combustion gases. In this manner fly-ash can be removed from the combustion gases even though the ash itself is below its incipient fusion temperature. A third mechanism by which'fiy-ashmaterials are removed from the combustion zone is as follows: Many of the bed particles become partially'coated'with the softened and sticky ash materials, and will agglomerate upon collision with eachother.

At temperatures considerably below the incipient fusion temperature of 'the'ash, the agglomeration and re-' :moval. of fly-ash is predominantly by the first of the foregoing mechanisms. Thus, some fly-ash is removed even at fluidized-bed temperatures far below the incipient fusion temperature of the ash'materials, but the relative quantity of fly-ash removed in this manner is usually very small. As the bed temperature is raised, the flyash. materials are agglomerated and removed from the combustion gases by a combinationof the first two mech anisms hereinbefore described. The ash collection efficiency increases with increased bed temperatures as will hereinafter be discussed. As the bed temperature is further raised so that itis slightly below the incipient fusion temperature of the .ash. materials, agglomeration by the thirdrnechanism begins'to occur.-.

It should be 'empha'siz'ed' lthat the carbon particles quickly reach their ignition temperature and burn almost instantly as they are introduced into the combustion zone. Thus, carbon particles are present in the combustion zone for an extremely shortresidence time and are converted to combustionproductswithout the danger of elutriation. The instantaneous and complete burning of the carbon particles therefor permit operation at near ly 100 percent combustioneificiency sincethe entire carbon feed can be rapidly burned with substantially no carbon losses from'thecombustion zone.

Theefficiency of the combustion reaction depends upon the'bed temperature and the particle sizes of the 'coal. Since, as it was previously pointed'out, the coal particles burn almost instantly as they are introduced into the combustion zone-extremely small coal particles can be fed into the combustion zone without the danger of elutriation therefrom. The smaller the particles, the greater the area available for combustion, hence the more rapid and efiicient the combustion reaction. Coal particles of the order of less than about 1 micron can be satisfactorily employed for-the combustion reaction herein without the danger of elutriation. The'relationship between combustion efficiency and bed temperature is shown by the plot in FIGURE 2 for powerhouse coal. Efficiencies upwards of 90'percentior' better were obtained for bed temperatures of the order of about 1550 F. and higher, and an efliciency of nearly '100 percent was obtained at a bed temperature of about 1950" F. Similar plots can be'prepared to determine the optimum bed temperature corresponding to a desired combustion efficiency, or vice versa, for othercarbonaceous solids.

It should also be pointed out that there is a practical upper limit of temperature. beyond which the bed cannot be maintained in fluidized conditions. This temperature is the incipient fusion temperature of theash materials producedduringtthe combustion reaction. At temperatures above the incipient fusion temperature, the agglomerated ash particles tend to fuse together, therefore causing the bed'to d'efluidize and collapse. The incipient fusion temperature of the ash, of course, varies depending upon the composition thereof, and is therefore different for different carbonaceous solids.

The tendency'of'the bed to defluidize has been found to be directly related to the adhesive forces on the surface of the bed particles and on the surface area available for particle contact. Adhesion of particles is also inversely proportional to the particle momentum. As the temperature is raised, the adhesive characteristics of the surface of the particles are increased and the agglomerating action is therefore enhanced. However, the increased adhesiveness tends .to increase the defluidization tendency of the bed. This phenomenon can be compensated for by increasing the. velocity ofthe fluidizing gas which tends'to increase the momentum of the fluidized particles, hence decreasing the. tendency toward defiuidization.

The relationship between the gas velocity in the combustion 'zoneto the bed temperature, other. conditions being constant, is illustratedbythe curve in FIGURE 3. for a-particular type of coal,.i.e., powerhouse coal. The unshaded area above the curve indicates the area of stable fluid-bed operation whereas the area below the curve indicatesthe area of unstable fluid-bed operation. Thus, at a temperature of, say, about 2000 F., the velocity required for stable fiuidizationis determined by projecting a vertical line from the abscissa corresponding to 2000" F. in FIGURE 3, and determining .the point of intersection of said line with the curve (corresponding to an-ordinate of about 1.4feet per second). The velocity of the fiuidizing gas is then chosen at slightly above the value of the velocity so determined to insure operation within the area of stable fiuidization.

The collection efliciency of fly-ash particles is also related to the conditions of operation in the combustion zone. Although some fly-ash is collected on the bed particles at all bed temperatures above the ignition temperature of the coal particles, collection efliciency is best when the bed temperature approaches the incipient fusion temperature of the ash produced during the combustion process. The collection efliciency of fly-ash is dependent on such variables as bed-depth, fluid-bed density, the velocity of the fiuidizing gas and the bed temperatures. FIGURE 4 illustrates the relationship between percent ash removal from the fluidized bed with W/ G as hereinbefore described. FIGURE 4 was prepared for a particular type coal, i.e., powerhouse coal of certain particle size, at three diflerent temperatures. It will be noticed from FIGURE 4 that the collection efficiency at a bed temperature of, say 2050" F. is increased by increasing W or by decreasing G. Thus, the collection efficiency at a given bed temperature, and for a certain type and size coal, increases with increase in bed depth and bed density and is lowered by higher fiuidizing velocities. The effect of the velocity of the fiuidizing medium on the collection efiiciency, however, is less pronounced than the effect of bed depth and bed density. It should also be pointed out that the collection efiiciency is not particularly effected by changes in coal feed rates to the combustion zone. In some studies, for example, the coal feed rate was increased by a factor of about 29 percent without noticeable change in collection efiiciency, the bed depth and bed temperature being constant.

Any oxygen-containing gas, preferably air, can be employed to fluidize the bed in the combustion zone and to support the combustion of carbonaceous solid particles. Since the bed in the combustion zone consists mainly of agglomerated ash particles, relatively high velocities of air can be employed through the combustion zone, if desired.

The pressure in the combustion zone can be atmosphenic or superatmospheric. Since the combustion gases are extremely useful as working fluids for driving gas turbines, from the standpoint of energy recovery in the turbine it is desirable to employ a pressurized gas therein. The combustion zone is, therefore, preferably maintained at superatmospheric pressures, most preferably in the range of from about 20 p.s.i.g. to about 150 p.s.i.g. Accordingly, the fiuidizing medium (air) must be compressed prior to its introduction into the combustion zone.

The dust loading of the combustion gas which is produced by the process of this invention is extremely low, of the order of about 5 grains per 100 cubic feet of the combustion gases or less. The extremely low dust loading of gas is related to the conditions maintained in the combustion zone.

The agglomerated ash particles which are withdrawn from the combustion zone are extremely valuable as high level heat exchange media. For example, they can be used to supply the heat of reaction to endothermic processes. In addition to serving as high level heat source, the withdrawal of the agglomerated ash particles serves to control the temperature in the combustion zone. Furthermore, the Withdrawal of oversized agglomerated ash particles is necessary to maintain the bed fluidized throughout the entire operation. One particularly advantageous application of these hot agglomerated ash particles is to supply heat for the gasification of carbonaceous solids as illustrated and described in details in FIGURE 5.

Referring now to FIGURE 5, there are shown two interconnected fiuidizing zones, one, a combustion zone 9, and the other, a gasification zone 19. Like numerals in FIGURES 1 and 5 indicate like parts. The operation of the combustion zone is essentially as described in connection with the detailed description of FIGURE 1. Coal particles from storage vessel 21 are conveyed through feed line 23 and metering valve 25 into gasification zone 19. The coal particles can fall into gasification zone 19 either by gravity or conveyed by some inert gas or by the fluidizing medium itself. The fiuidizing medium in gasification zone 19 is usually steam, which is also the gasifying agent employed for the gasification reaction. Steam is introduced into gasification zone 19 via conduit 27. The hot agglomerated ash from combustion zone 9 enters gasification zone 19 through discharge line 13. It should be pointed out that the temperature in the combustion zone is usually considerably higher than the temperature in the gasification zone. In addition, the sizes of the agglomerated ash from the combustion zone are preferably considerably :larger than the sizes of the coal particles in the gasification zone. Hence, the agglomerated ash particles progress downward in the gasification zone and after transferring their sensible heat to the reactants in the gasification zone they are withdrawn via line 29 and may be metered through meter valve 31 if desired. Gasification zone 19 may also be provided with another discharge line 33 to permit withdrawal of ash-like materials therefrom and to maintain a balance ofnon-combustibles within the system. Some of the agglomerated ash materials is withdrawn via lines 35, metered through meter valve 37 and recycled by means of a carrier gas, such as air, through line 39 to combustion zone 9. Product gases from gasification zone 19 are moved by line 41 and may be introduced into a cyclone or any other gas cleaning equipment (not shown) if necessary.

It should be pointed out that the velocity of the fluidizing medium in the gasification zone is considerably lower than the Velocity required to maintain the agglomerated ash particles in fluidized condition. Consequently, it is possible to gasify the coal particles in the gasification zone under fluidized conditions and at the same time utilize the sensible heat of the descending agglomerated ash particles from the combustion zone.

The apparatus employed in the novel process can be constructed of materials ordinarily employed for hightemperature fluid-bed operations. For example, the combustion zone may be lined with refractory materials capable of withstanding the high temperatures and the erosive action of the fluidized bed.

Many modifications and revisions can be made both with regard to the apparatus employed in the novel process and in the details of operation without substantial departure from the scope of this invention. Also, the novel process is flexible and can be used with coals having Widely different characteristics, and with other carbonaceous solids such as coke, slack, anthracite, pitches, asphalts, etc.

Studies were made using a bituminous coal and a subbituminous coal. The bituminous coal has a high heating value but is readily fusible and troublesome to burn on grates. The sub-bituminous coal is noncaking, contains considerable moisture and volatiles, and has a low heating value. The studies were made in a 6-inch diameter fluidized coal burner in the manner hereinbefore described in connection with FIGURE 1 and the detailed description of the operation of the novel process. The results are summarized in Table 1 below.

Table 1 Type of Coal Bitumi- Sub-bitunous minous Temperature of Fludizcd Bed, F 2, 050 2, 050 Bed Weight, lb 45 45 Goal Rate, lb./hr 7.00 8. 37 Air Rate, 1b./hr 104. 3 85. 4 Ash In, lb./hr 1. O5 0. 79 Ash Collected, lb./hr 0.87 0.71 Ash Out, lb./hr O. 18 0.08 Ash Collection Efficiency of Fluidized Bed,

Percent 82. 7 90. 0 Ash Collection Efficieney of Bed and Cyclone,

Percent 97. 7 99. 0

Z It has also been found that certain additives can be mixed with'the coal feed'to' promote the ash collection efiiciency in the combustion zone. For example the -addition of soda ash has been shown" to flux the: coal ash to forma lower meltingmixture. A uniform mixture of soda ash in the coal feed'wasprepared by tumblingthe mixture-for 24 hours. A soda ash content of'2'.0 percent was used. Theash collection efiiciency of the bed was found to increase considerably over the range ofbed temperature from about170 F. to about 1900 F. and higher.

Nonfluxing agents orinert diluents such as'silica can be used to permit higher temperature operation, when this is desirable, by retarding the rate of agglomera tion.

What is claimed isz 1. A process for burning carbonaceous fuel" to produce dust-free combustion gas which process comprises thev (e) withdrawing. essentially carbon-free agglomerated ash particles from said combustion zone and' (f) withdrawingthe dust-free gas fromasaid combustion zone. 2. The process of claim 1 wherein the bed temperature in the combustion zone is-maintained at'about the=temperature of incipient fusion of the ash produced from' burning said carbonaceous fuel. 7 o

3. A process for burning carbonaceous solid'particles to produce dust-free combustion gas which process comprises the steps of:

(a) introducing said carbonaceous solid particles into a combustion zone, 7 1 (b) burning said carbonaceous solid particles with air instantly as they are introduced into said com bustion zone, (-0) maintaining in said combustion zone a bed of fluidized ash particles which are produced from'the.

combustion of said carbonaceous solid particles, (d) controlling the bed temperature in said combustion zone so as to cause the ash particles to become tacky and to agglomerate, (e) withdrawing'essentially carbon-free agglomerated ash particles from said combustion zone, and I (f) withdrawing the dust-free gas from said combustion zone. 4. The process of claim 3 wherein said carbonaceous solid particles are pulverized coal. I

5. The process ofclaim 4 wherein the .bed temperature in said combustion zone isfroin about 1900. F. to about 2100 F. 5 6. The process of claim 3 wherein the bedv temperature is maintained at about the incipient fusion temperature of the ash particles produced. during the combustion reaction.

7. The process of claim 3 wherein solid particles are introduced into said combustion zone as a slurry of said carbonaceous solid particles in water.

8. The process of claim B'Wherein water is introduced separately into the comb st on zone.

the carbonaceous 9. The process of claim 3 wherein a fluxing agent is added-to said carbonaceous solid particles.

10. The process-of claim 3 wherein the hot agglomerated ash particles withdrawn from said combustion zone are utilized as heat-supply source and-to effect temperature control in the combustion zone.

11. A process for burning and gasifying carbonaceous solid particles in two separate and inter-connected zones, which process comprises the steps of (a) introducing carbonaceous solid particles into a combustion zone, 7

(b) burning said carbonaceous-solid particles with air instantly upon their introduction into said combustion zone,

(0) maintaining in said combustion zone a bed of fluidized ashparticles which areproduced from the combustion of said carbonaceous solid particles,

(d) controlling the-bed temperature in said combustion zone so as to cause the ash particles to become tacky and to agglomerate,

(e) withdrawing an essentially carbon-free heated agglomerated ash from said combustion zone and conveying same into a gasification zone,

(f) withdrawing the dust-free .gas from said combustion zone,

(g) introducing carbonaceous solid particles and steam into said gasification zone and supporting said carbonaceous solid particles in fluidized conditions in said gasification zone by means'of the introduced steam,

(h) causing said heated agglomerated ash particles to descend in said gasification zone and transferring the sensible heat of said heated agglomerated ash particles to the fluidized bed'carbonaceous particles and to thesteam in said, gasification zone to thereby supply the beat required to efiect a gasification reaction,

(i) removing. the gasesproduced in the gasification zone therefrom, and

(j) withdrawing agglomerated ash particles from said gasification zone.

, 12. The process of claim 11 wherein said carbonaceous solid particles are pulverized coal.

13. The process of claim 11 wherein said carbonaceous solid particles areintroduced as a slurry of carbonaceous solid particles in water.

14. Theprocess of claim 11 wherein water is introduced separately into said combustion zone.

15. The process of claim 11 wherein the temperature in the combustion zone is maintained at about the incipient fusion temperature of the ash particles produced during the combustion reaction.

16'. The process of claim 11 wherein the temperature in the combustion zone is from about 1900 F. to about 2100 F. andthe temperature in the gasification zone is from about 1500" F. to 1700 F.

17. The process of claim 11 wherein the carbonaceous solid particles from the gasification zone are recycled to the combustion zone.

References Cited by the Examiner UNITED STATES PATENTS 2,357,303 9/44 Kerr et al 1l028 2,729,428 l/ 5 6 Milmore 28 2,741,549 4/56 Russell 110-28 2,868,631 1/59 Woebcke -Q 48-206 2,958,298 11/60 Mayers 1l0,28

JAMES W. WESTHAVER, Primary Examiner. FREDERICK L. MATTESON, JR., Examiner.

Claims

1. A PROCESS FOR BURNING CARBONACEOUS FUEL TO PRODUCE DUST-FREE COMBUSTION GAS WHICH PROCESS COMPRIES THE STEPS OF: (A) INTRODUCING SAID CARBONACEOUS FUEL INTO A COMBUTION ZONE, (B) BURNING SAID CARBONACEOUS FUEL WITH AIR INSTANTLY AS SAID FUEL ENTERS THE COMBUSTION ZONE, (C) MAINTAINING IN SAID COMBUSTION ZONE A BED OF FLUIDIZED ASH PARTICLES WHICH ARE PRODUCED FROM THE (D) CONTROLLING THE BED TEMPERATURE IN SAID COMBUSTION ZONE AS TO CAUSE THE ASH PARTICLES TO BECOME TACKY AND TO AGGLOMERATE, (E) WITHDRAWING ESSENTIALLY CARBON-FREE AGGLOMERATED ASH PARTICLES FROM SAID COMBUSTION ZONE, AND (F) WITHDRAWING THE DUST-FREE GAS FROM SAID COMBUSTION ZONE.