US2871004A - Process for heat treating heat sensitive solid particles - Google Patents

Description

E. GORIN PROCESS FOR HEAT TREATING HEAT SENSITIVE SOLID PARTICLES Filed Feb. 29, 1956 2 Sheets-Shee't 1 INVENTOR.

EVERETT GOR/IV Jan. 27, 1959 E. GORIN 2,

PROCESS FOR HEAT TREATING HEAT SENSITIVE SOLID PARTICLES Filed Feb. 29, 1956 22 Sheets-Sheet 2 INVENTOR. EVE/P677 GOR/IV U d States PatdlfO PROCESS FOR HEAT TREATING HEAT SENSITIVE SOLID PARTICLES Everett Gorin, Pittsburgh, Pa., assignor to Consolidation Coal Company, Pittsburgh, Pa., a corporation of 1 Pennsylvania Application February 29, 1956, Serial No. 568,594

13 Claims. (Cl. 263--52) This invention relates to a method of heat treating heat sensitive solid particles and more particularly to a method of heat treating coal having agglomerating properties at elevated temperatures.

In the preparation of coal for either chemical treatment or combustion it has been found economically advantageous to both dry and preheat the coal to an elevated temperature before subjecting it to further treatment. This heat treating of coal lowers the heat require ments in further chemical treatment and increases the yield of desired chemical product obtained there'from..

A readily available source of heat for the heat treating of coal is the sensible heat of waste flue gas obtained either from the combustion of coal or from an allied thermal process. Depending on its source, the flue gas may have a temperature between 1l00 and 2500 F.

which can be utilized in heat treating the coal. Several the temperature above which the coal becomes plastic due to the pressure of confined gases causing surface flow on each particle. When the coal is heated above its plastic temperature there is both a swelling of the particles and formation of a film of viscous material surrounding each particle. into a solid mass and adhere both to each other and to the surrounding apparatus, thus making the heat exchange operation inoperable.

, The recent development of the fluidized bed type exchanger ofiered what was thought to be a solution to this agglomerating problem. The fluidized bed heatexchanger may be defined as a vessel having an inventory of particulate solid particles suspended therein by means of a fluidizing gas passing upwardly therethrough. The particulate solid particles so suspended define a fluidized bed which exhibits many characteristic properties of a liquid confined in a heat exchange vessel. The fluidized bed acts as a heat reservoir and exhibits a rapid rate of heat transfer. Because of this rapid rate of heat transfer The particles of coal then agglomerate cles.

and the almost instantaneous dispersion of heat throughv out the entire bed, it was believed that the heat of the hot gas introduced into the fluidized bed would immediately disperse throughout the entire bed and by regulating either gas flow or coal feed and withdrawal thetemperature of the bed could be maintained below the plastic the-plastic temperatureof the coal and "the rate of heat transfer within the fluidized bed was practically instanized bed defines three distinct zones.

r i Ice 87100 taneous, agglomerating difficulties within the bed were not expected. After several runs difliculty and inoperability of the process resulted. Two principal causes were attributed to the inoperability of the fluidized bed type heat exchanger. One of the difliculties was in the coal adjacent the gas inlet becoming overheated, i. e., being heated above the plastic temperature, and agglomerating. The heavy agglomerates, due to their increased size, would progress to the bottom of the fluidized bed where they constricted the gas distributor plate. Another difliculty encountered was the distributor plate adjacent the gas inlet being heated above the plastic temperature of the coal due to the elevated temperature of the inlet flue gas. The coal particles adjacent the overheated plate would adhere to it and form a layer of agglomerated coal. This layer of agglomerated coal would restrict the gas flow until the fluidized bed heat exchanger became inoperable.

This invention eliminates the above difliculties encountered in a fluidized bed heat exchanger and now presents an operable method of heat treating coal having agglomerating properties in a fluidized bed with a gas having a temperature above the plastic temperature of the coal.

This invention accomplishes the above by carrying out the heat treating process in a fluidized bed in the presence of an inert material which functions as an insulator and absorbs the initial heat shock of the flue gas. By inert material I mean any material that does not react chemically with flue gas and does not agglomerate at temperatures up to 2500 F. The inert material, which may be sand, quartz, or the like may be 8 x 14 mesh in size, that is, all of the sand particles will pass through an 8 mesh Tyler standard screen and will be retained on a 14 mesh Tyler standard screen. An inventory of this inert material is maintained in the heat treating vessel. Coal that is crushed to a size capable of passing through a 14 mesh Tyler standard screen is introduced into the heat treating vessel and an inventory of the coal particles is maintained therein. Flue gas having a temperature range between ll0O F. and 2500 F. is introduced into the bottom of the heat treating vessel at a velocity suflicient to maintain both the inert particles and the coal particles in a fluidized condition so that all of the particles define a single fluidized bed. Since the fluidized density and size of the inert particles is greater than that of the coal particles the fluid- The upper zone of the fluidized bed consists essentially of coal particles. The intermediate zone of the fluidized bed consists of a mixture of inert particles and coal particles. This zone iscalled the zone of interpenetration. The lower zone of the fluidized bed consists essentially of the inert parti- The hot flue gas enters the heat treating vessel through the bottom and first contacts the inert material. The initial heat shock of the hot flue gas is absorbed by the inert material and the flue gas is tempered to a lower temperature. As the gas progresses upwardly through the fluidized bed it contacts the coal particles in the upper zone of the bed and transfers heat thereto. Also, because of the mixing action in the fluidized bed and the temperature differential between the incoming coal particles and the inert particles in the bed, heat is transferred from the inert particles to the coal particles. In this manner the coal is heated to a temperature below its plastic temperature with a gas having a temperature above the plastic temperature of the coal, without the accompanying undesirable agglomeration of the coal particles being heated.

Throughout this specification the term fluidized density relates to the density of the material under fluidizing conditions. fined as having a particle size of 8 x 1-4 mesh it should be understood that theinert material may be of any size fluidizable.

Patented Jan. 27, 1959 I Also, although the inert material has been de The raw coal introduced into the heat treating vessel may be introduced into the intermediate zone of the fluidized bed so that a more effective heat transfer may occur. Also, a second inert gas at a temperature below the plastic temperature of the coal may be introduced into the heat treating vessel adjacent the lower portion of the upper fluidized bed zone to assist in maintaining the fluidized density differential between the coal particles and the inert particles.

A recycle leg may be provided on the heat treating vessel to aid in the recirculation of the inert material and act as a means to mix and smooth out the temperature of the inert material. This mixing prevents hot spots in the lower portion of the vessel where agglomeration of stray coal particles could occur. Air may also be introduced into the bottom of the fluidized bed to burn any of the coal particles which may have progressed into the lower zone of the fluidized bed. The combustion of coal in this lower zone does not elevate the temperature of the coal in the upper zone of the fluidized bed above the plastic temperature because the heat generated by this combustion is immediately dispersed throughout the entire fluidized bed. As an alternative, the mixture of inert particles and coal particles may be withdrawn from the heat treating vessel and introduced into a combustion vessel where the coal particles may be burned in the presence of air. The inert material remaining in the combustion zone may be withdrawn and recycled to the heat treating vessel.

For installations where a source of waste flue gas is not available the above described process may be practiced using air as the fluidizing media and burning a portion of the coal to supply the necessary heat to perform the drying and preheating function.

It is therefore a principal object of this invention to provide an improved method for heat treating a heat sensitive solid material.

Another object of this invention is to provide a method of heat treating coal having agglomcrating properties with a gas in a fluidized bed.

Another object of this invention is to provide a method of heat treating coal having agglomerating properties with a gas heated by means of combustion of a portion of the coal being treated.

These and other objects and advantages will become apparent from the specification and claims.

In the drawings:

Fig. 1 is a semi-diagrammatic view of a preferred cmbedirnent of a system for carrying out the present in.- vention.

Fig; 2 is a semi-diagrammatic view of another embodiment of my invention showing a combustion means external to the heat treating vessel.

Fig. 3 is a semi-diagrammatic view of another embodiment of my invention showing a combustion means using a portion of the coal being treated to elevate the temperature of the fluidizing and treating gas.

Referring now in detail to Fig. 1 the numeral lit designates a coal. storage vessel and the numeral 12 generally designates a heat treating vessel. Conduit M from the coal storage vessel 1! is connected to conduit 16 and conveys coal thereto. Gas is introduced into the heat treating vessel 12 through the conduit 16. Particles of coal from the coal storage vessel 1d are entrained in the gas and conveyed through conduit 16 to the heat treating vessel 12. The heat treating vessel .12 has an upper cylindrical portion 18, an intermediate portion 20 having the shape of a conical segment, and a lower portion 22 of smaller cross section than the upper cylindrical portion 18. The lower cylindrical portion 22 has a conical bottom end portion 24. The heat treating vessel l2 has a coal Withdrawal conduit 26 extending from the upper cylindrical portion 18. A deflector member 28 is provided adjacent the withdrawal conduit 26. A cyclone type separator 30 is positioned within the heat treating vessel 12 and is operable to separate fine particles entrained in the exit gas leaving through the conduit 32. Conduit 34 is connected to the bottom of the conical bottom end portion 24 and is operable to provide flue gas at elevated temperatures and predetermined velocities to the heat treating vessel 12. A second conduit 36 is connected to the bottom of the conical end portion 24 and is operable to convey air or any combustionsupporting gas to the heat treating vessel 12. A recycle leg 38 is provided for the heat treating vessel 12 and is connected to the lower cylindrical portion 22. The recycle leg 38 is interconnected with the tide gas inlet conduit 34 by means of the conduit 40 so that the material within the recycle leg 38 may be conveyed to the heat treating vessel 12 by means of the flue gas flowing through the conduit 34. A valve means 42 is positioned in the conduit 40 to control the recycle rate of inert material from the heat treating vessel 12 and limit the flow of material from the recycle leg in one direction.

An inventory of inert particles having a size consist of approximately 14 x- 8 mesh" is maintained within the heat exchange vessel 12. The inventory of inert particles, when expanded under the influence of a fluidizing gas, should be suflicient to till the lower cylindrical portion 22, the recycle leg 38 and a portion of the intermediate conical segment 20. An inventory of coal particles having' a size consist smaller than that of the above men'- tioned inert particles, for example being capable of passing through a- 14' mesh Tyler standard screen, is maintained within'the heat treating vessel 12. The inventory oi coal particles should be adequate for the upper level of the fluidized bed to extend above the deflector meniber 28. Flue gas atan elevated temperature is introduced into the bottom of the heat treating vessel 12 at a velocity sulficient to maintain all the particles within the heat treating vessel 12 in a fluidized condition. Additional inert gas may bcintroduced through the conduit 16 to assist in maintaining the fluidized density of the particles in the upper cylindrical portion 1.8 below the fluidized density of the particles in the lower cylindrical portion 22;

In Fig. 2 of the drawings similar numerals increased by one hundred designate similar parts as illustrated in Fig. l. The embodiment shown in Fig. 2 includes a combustion vessel 150. A withdrawal conduit 152 extends from the heat treating vessel intermediate portion and with drawal conduit 154 extends from the heat treating vessel lower cylindrical portion 122. Valve means 156 and 158 are positioned in the respective conduits" 152 and 154 to control the rate of withdrawal from the heat treating vessel 112. Both theconduits 152 and 154' join a conduit 160 through which air is conveyed to the combustion vessel 150. The material which is withdrawn from the heat treating vessel 112 is conveyed with the air through the conduit 160 to the combustion vessel 150; The mater'ial-wit'hin the combustion vessel 150 is eleva'tedin tern perature until the coal particles contained therein burn and react exothermically with the air supplied through the conduit 160. The flue gases generated in the vessel 150 are withdrawn therefrom through the conduit 152 andmay be vented to the atmosphere. The combustion vessel 150 has a withdrawal conduit 164' extending therefrom and a deflector plate'166 within the vessel 150. The inert particles remaining after the combustion of the coal particles in the combustion vessel 150 are withdrawn therefrom and conveyed through the conduit .164 to the flue gas conduit 134- where the withdrawn inert particles are entrained in the flue g'as and introduced into the bottom' of the heat treating vessel 112. The withdrawal rate of the inert particles from the combustion vessel 1'50 iscontrolled by means of the valve 168 in the withdrawal conduit 164; A cyclone separator 170 is positioned with in thecombustion vessel 150 to separate entrained fines from the gases withdrawn from the combustion vessel 150.

In Fig; 3 of the drawings similar numerals increased by two" hundred designate similar parts as illustrated in Figs.

l' and 2. The embodiment shown in Fig. 3 includes a heat treating vessel 212 superimposed verticallyon a combustion vessel 250. The heat treating vessel 212 and combustion vessel 250 are interconnected by means of a conduit 254. The coal withdrawal conduit 226 has a conduit 236 connected thereto. The conduit 236 is connected to the gas inlet conduit 234 so that portions of the withdrawn coal may be conveyed from the conduit 226 through the conduit 236 to the gas inlet conduit 234. A valve means 246 positioned in the conduit 236 controls the rate of flow therethrough. A conduit 238 is connected at one end to the heat treating vessel lower portion 222 and at the other end to the gas inlet conduit 234. A valve means 242 is positioned in the conduit 238 to regulate the withdrawal rate of inert material and coal from the heat treating vessel lower portion 222.

Although not shown in Figs. 1, 2 and 3, means may be provided to add inert particles, either continuously or intermittently, to compensate for processing losses that may occur.

Operation For purposes of illustration only the operation of the apparatus shown in Figs. 1, 2 and 3 will be described in connection with the heat treating of bituminous coal. However, it should be understood that not only is the method hereindescribed applicable to the treatment of coal generally,,but also to any system wherein it is desired to contact heat sensitive solids with a gas above the heat sensitive temperature of the solids.

1 Referring to Fig. l the coal is introduced from the coal storage vessel through the conduits 14 and 16 into the heat treating vessel 12. The coal should have a particle size consist in relation to the particle size consist of the inert material within the heat treating'vessel12 so that the fluidized density of the coal particles within the heat treating vessel 12 will be lower than the fluidized density of the inert particles therein. For example the coal may have a particle size consist capable of passing through a 14 mesh Tyler standard screen and the inert material may have a size consist that will pass through an 8 mesh Tyle'r standard screen and be retained on a 14 mesh Tyler standard screen. i

The inventory of inert particles within the heat treat ing vessel 12 should be adequate to maintain the upper level of the inert particles, when fluidized, in the heat treating vessel intermediate portion 20. The temperature ofthe incoming coal is room temperature i. e., 6080 F;, and may contain in excess of 10 weight percent moisture. In fact, the upper moisture limitation of incoming raw coal is only dependent upon the ability of the conveying means to introduce the coal into the heat treating vessel 12. With flue gas passing upwardly through the heat treating vessel 12 at a velocity suflicient to maintain both the inert particles and the coal particles in a fluidized condition a single fluidized bed will result. This bed, due to particle size and fluidized density of the coal and inert material, will separate into three zones. The upper zone indicated by the letter A consists essentially of coal particles and may be confined within the upper cylindrical portion 18. The intermediate zone indicated by theletter B contains a mixture of both inert particles and" 'coal particles which have substantially the same fluidized density. The lower zone indicated by the letter Ccohsists essentially of inert particles and may extend from the conical bottom 24 through the cylindrical section 22 into the conical segment 20. p,

i "As-an example, whereit is desired to heat agglomerati rlfg coal to a temperature between 450 andSSOP-F. a flue gasjhavin-g a temperature between 1100" F. and 2500 Fl is conveyed through the bottom of the heat treating vessel 12 at a velocity suflicient to maintain all the solid particles therein in a fluidized condition and sufficient to maintain the solids in the lower zone C at a temperature between 650 and 700 F. This zone of inert material 6 tempers the hot flue gas and prevents the hot gas'from contacting the coal particles at the incoming elevated temperature. As the flue gas progresses upwardly through zone. C it tends to equalize in temperature with the inert material. Thus, as the gas passes through zone B into zone A the gas is at a lower temperature. The inventory of coal within. the heat treating vessel is maintained at a temperature between 450 and 500 P. which is well below the plastic temperature of 700 F. The temperature of the coal within the heat exchange vessel may also be controlled by controlling the rate of feed and withdrawal of the coal from the heat treating vessel 12 through the outlet conduit 26.

In the event particles of coal progress downwardly through the intermediate zone of penetration, i. e. zone B, to the lowerzone; i. e. zone C, air may be introduced through theco nduit 36 to react exothermically with these coal particles. The exothermic reaction should take place adjacent the conical bottom portion 24 to isolate the elevated temperatureof combustion from the coal particles in zone A. The added elevation in temperature of the surrounding inert material due to the combustion of these coal particles in the conical bottom portion 24 would immediately be dispersed throughout the entire fluidized bed and would not elevate the temperature of the coal particles in zone A above the plastic temperature. The recycle leg 38 is provided in the heat treating vessel lower portion 22 as a means to mix the inert material and smooth out any hot spots in the heat treating vessel 22. Thus when the coal which has progressed into zone C is exothermically reacted with the air entering through conduit 36 the inert material will recycle through the recycle leg 38 and thus mix the inert material which has been subjected to the elevated combustion temperature with the remainder of the inert material in zone C. A valve means 42 in the conduit 40 controls the recycle rate of the inert material in zone C.

In Fig. 2 the withdrawal conduits 152 and 154 are operatively associated with the heat treating vessel 112 to withdrawjthe coal-inert mixture from the intermediate zone B and from the lower zone C. The purging of zone C may eventually. be necessary to remove any coal particles which may have progressed down the bed to zone C where they would eventually agglomerate upon being subjected to the hot flue gas. The withdrawn mixtures are conveyed to the combustion vessel .150 in a stream of air or other combustion supporting gas through the conduit 1 60 and the coal is reacted exothermically in the combustion vessel 150, The valves 156 and 158 regulate the ,rate of withdrawal from the intermediate zone B and the lower zone C. The gases of combustion are withdrawn from the combustion zone through the conduit 162 and are vented to the atmosphere. The inert particles are withdrawn from the combustion vessel 150 through the conduit 164 and are recycled to the heat treating vessel 112 with the incoming flue gases through the conduit 134. The valve 168 controls the rate of withdrawal of inert material from the combustion vessel 150. It should beunderstood that although-fine gas was used as the heat treating gas in Figs. 1 and 2 it is. within the scope of this invention to use any inert gas which does not react with the coal particles as the heat treating gas.

In Fig. 3 air or any combustion supporting gas enters the combustion vessel 250 through the conduit 234. Coal withdrawn from the heat treating vessel 212 through the conduit 226 is conveyed through conduit 236 to the air. inlet conduit 234 where it is picked up by the air and conveyed to the combustion vessel 250. The coal is reacted exothermically with the air in the combustion vessel 250 and generates an exhaust gas at an elevated temperature. The hot exhaust gas or flue gas leaves the combustion vessel 250 through the conduit 254 at a velocity adequatcto maintain the coal particlesand inert particles in the heat treating vessel 212 in a fluidized condition. Inert material and any coal which may have progressed into zone C are withdrawn through conduit 238' and conveyed by means of the air passing through conduit 234 to the commerce" vessel 250. The incoming coal particles and inert particles are intermixed in the combustion vessel 250 and the inert particles are heated by means of the coal combustion therein. The heated inert particles are entrained in the exhaust gas and are conveyed from the combustion vessel 250 through the conduit 254 to the heat treating vessel 212 where the inert particles are in heat exchange relationship with the coal particles and transfer'he'at thereto.

Thus inthis embodiment air or any other combustion supporting gas at any temperature is fed into the combustion zone to react exothermically with coal particles therein and generates an exhaust gas at elevated temperatures. This exhaust gas is used to fluidize the partides in the heat treating zone and also to heat the coal particles therein. Simultaneously, inert particles are recyeled from the heat treating vessel 2'12 and heated to an elevated temperature in the combustion vessel 250. The heated inert particles are then entrained in the exhaust gas and conveyed to' the heat treating vessel where the inert particles transfer heat to the coal particles.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

l claim:

1. A method of heat treating a heat sensitive particulate solid material which comprises maintaining an inventory of inert solid particles in a heat treating zone, continuously supplying heat sensitive particles to said heat treating zone, maintaining an inventory of heat sensitive particles in said heat treating zone, passing a treating gas at a temperature above the temperature of said heat treating zone upwardly through said heat treating zone at a velocity suflicient to maintain both said inert particles and said heat sensitive particles in a fluidized condition so that said particles comprise a unitary dense phase fluidized bed, maintaining the fluidized density of said heat sensitive particles below the fluidized density of said inert particles so that the upper portion of said dense phase fluidized bed consists essentially of said heat sensitive particles and the lower portion of said fluidized bed consists essentially of inert particles, said inventory of inert particles in said fluidized bed lower portion serving as a tempering means for said treating gas so that the temperature of said treating gas is reduced prior to contact between said treating gas and said heat sensitive particles, and continuously withdrawing treated heat sensitive particles directly from the top portion of said dense phase fluidized bed. i

2. A method of heat treating a heat sensitive solid material which comprises maintaining a supply of inert solid particles in a heat treating zone, continuously supplying heat sensitive particles to said heat treating zone, maintainingan inventory of heat sensitive particles in said heat treating zone, passing a treating gas at a temperature above the temperature of said heat treating zone upwardly through said heat treating zone at a velocity s'uflicient to maintain both said inert solid particles and said heat sensitive solid particles in a fluidized condition so that all of said particles define a dense phase fluidized bed, the majority of said heat sensitive particles being smaller in size than the majority of said inert particles so that the upper portion of said dense phase fluidized bed consists essentially of said heat sensitive particles and the lower portion of said dense phase fluidized bed con sistsessentially of said inert particles, said supply of inert solid particles in said dense phase fluidized bed lower tive particles, and continuously withdrawing treated heat sensitive particles directly from the upper portion of said dense phase fluidized bed.

3'. The method set forth in claim 2 in which said heat sensitive particles are agglomerative bituminous coal.

4. The method set forth in claim 2 in which said inert particles are sand.

5. The'm'ethod set forth in claim 2 in which a majority of said heat sensitive particles are crushed to a size capable of passing through a 14 mesh Tyler standard screen and a majority of said inert particles are crushed to, a size capable of passing through an 8 mesh Tyler standard screen and being retained on a 14 mesh' Tyler standard screen.

6. The method set forth in claim 2 in which' the temperature of said treating gas entering said heat reatingzone is maintained in the range between 1100' F. to 2500 F.

7. A method of heat treating agglomerative bituminous coal which comprises maintaining a supply of inert solid particles in a heat treating zone, continuously supplying bituminous coal particles to said heat treating zone, main taining an inventory of bituminous coal particles in said heat treating zone, passing a treating gas at a temperature within the range of 1100 F. to 2500 F. upwardly through said heat treating zone at a velocity suflicient to maintain both said inert particles and said bituminous coal particles in a fluidized condition so that all of said particles define a dense phase fluidized bed, a majority of said coal particles being crushed to a size capable of passing through a 14 mesh Tyler standard screen a'nd'a majority of said inert particles being crushed to a size capable of passing through an 8 mesh Tyler standard screen and being retained on a 14 mesh Tyler standard screen so that said dense phase fluidized bed has an upper portion consisting essentially of said bituminous coal particles, an intermediate portion consisting of both bituminous coal particles and said inert solid particles, and a lower portion consisting essentially of said ine'rt particles, said treating gas first passing through the lower portion of said dense phase fluidized bed in order that said inert particles may temper said treating gas prior to contact of said treating gas with said bituminous coal particles, mixing said inert particles by means of withdrawing and recycling a portion of the same, maintaining the temperature of said dense phase fluidized bed lower portion within the range of 600-700 F maintaining the temperature of said dense phase fluidized bed upper portion within the range of 450 to 550 F. and continuously withdrawing treated bituminous coal particles Iitalirgctly from the upper portion of said dense fluidized 8. The method set forth in claim 7 including introducing a combustion supporting gas into said dense phase fluidized bed lower zone and reacting said combustion supporting gas exothermically with the coal particles in said lower zone.

9. A method of heat treating agglomerative bituminous coal which comprises maintaining a supply of inert solid particles in a heat treating zone, continuously supplying bituminous coal particles to said heat treating zone, maintaining an inventory of said bituminous coal particles in said. heat treating zone, passing flue gas at a temperahire within the range of ll00 F. to 2500 F. upwardly through said heat treating zone at a velocity suflicient to maintain both said inert particles and said bituminous coal particles in a fluidized condition so that all of said particle's define a dense phase fluidized bed, said bituminous co'al particles being crushed to a size capable of passing through a 14 mesh Tyler standard screen and said inert particles being crushed to a size capable of passing through an 8 mesh Tyler standard screen and being retained on a 14 mesh Tyler standard screen so that said dense phase fluidized bed has an upper portion consisting essentially of bituminous coal particles, an intermediate portion consisting of a mixture of bituminous coal particles and inert particles, and a lower portion consisting essentially of inert particles, said flue gas first passing through said dense phase fluidized bed lower portion in order that said inert particles may temper said flue gas prior to contact of said flue gas with said bituminous coal particles, withdrawing a portion of the mixture of said inert particles and coal particles from said dense phase fluidized bed intermediate portion, introducing said mixture into a combustion zone, passing air through said combustion zone at a velocity sufficient to maintain said mixture within said combustion zone in a fluidized condition, subjecting said mixture to a thermal treatment at an elevated temperature until said air reacts exothermically with said coal particles, withdrawing said inert particles from said combustion zone, introducing said withdrawn particles into said heat treating zone adjacent the bottom of said dense phase fluidized bed, and continuously withdrawing treated bituminous coal particles directly from the upper portion of said dense phase fluidized bed.

10. The method set forth in claim 9 in which said bituminous coal particles are continuously introduced into said intermediate portion of said dense phase fluidized bed within said heat treating zone.

11. The method set forth in claim 9 in which an auxiliary inert gas is introduced into the intermediate portion of said dense phase fluidized bed to assist in maintaining a fluidized density diflferential between said bituminous coal particles and said inert particles.

12. A method of heat treating agglomerative bituminous coal which comprises maintaining a supply of inert solid particles in a heat treating zone, continuously supplying bituminous coal particles to said heat treating zone, maintaining an inventory of said bituminous coal particles in said heat treating zone, passing a treating gas at a temperature above the temperature of said heat treating zone upwardly through said heat treating zone at a velocity sufficient to maintain both said inert solid particles and said coal particles in a fluidized condition so that all of said particles define a dense phase fluidized bed, the majority of said coal particles being smaller in size than the majority of said inert particles so that the upper portion of said dense phase fluidized bed consists essentially of said coal particles and the lower portion of said dense phase fluidized bed consists essentially of said inert particles, said treating gas first passing through the lower portion of said dense phase fluidized bed in order that said inert particles may temper said treating gas prior to contact of said treating gas with said coal particles directly, continuously withdrawing treated coal particles from the upper portion of said dense phase fluidized bed, introducing a portion of said withdrawn coal particles into a combustion zone, introducing a combustion supporting gas into said combustion zone, exothermically reacting said coal particles and said cornbustion supporting gas in said combustion zone to generate a treating gas having a temperature above the temperature of said heat treating zone, and introducing said treating gas into said heat treating zone.

13. The method set forth in claim 12 in which a portion of said inert particles are withdrawn from said heat treating zone, introducing said withdrawn inert particles into said combustion zone, heating said inert particles in said combustion Zone, and introducing said heated inert particles into the lower portion of said heat treating zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,707 Roetheli Oct. 22, 1946 2,638,684 Jukkola May 19, 1953 2,741,549 Russell Apr. 10, 1956 2,774,661 White Dec. 18, 1.956

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