Process for burning retorted oil shale and improved combustor

Claim 1

In a process for retorting oil shale using a heat transfer material heated by burning retorted oil shale containing residual carbonaceous material, wherein said retorted oil shale contains both fine and coarse grained material and at least part of said fine grained material is contained in a separate feedstream from the coarse grained material, an improved process for burning the oil shale comprising: (a) burning at least part of the residual carbonaceous material in the fine grained material present in said separate feedstream in a fine preburner by entraining said fine particles in first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the fine particles; (b) burning part of the carbonaceous residue in the coarse grained material in a coarse preburner containing less than a stoichiometric amount of oxygen; (c) mixing the entrained partially burned fine grained material from the fine preburner and the partially burned coarse grained material from the coarse preburner in a second entraining gas stream having a velocity greater than the terminal velocity of the mixture of fine and coarse particles and containing at least a stoichiometric amount of oxygen; and (d) burning the carbonaceous residue remaining in the entrained fine and coarse grained material in a vertical combustion zone through which the entraining gas is directed.