Size separation of oil shale particles for efficient retorting

Claim 1

In a process for retorting oil shale which includes the steps of feeding particulate oil shale containing both fine- and coarse-grained material into the upper part of a retorting vessel, heating the oil shale as it moves downward by mixing therewith a particulate hot heat transfer material to pyrolyze the volatile hydrocarbons, introducing a non-oxidizing stripping gas into the bottom of the retorting vessel at a velocity sufficient to partially fluidize the particles in the retort and entrain the fine-grained particles of oil shale causing an upward flow of gas countercurrent to the movement of the descending oil shale to carry away the volatile hydrocarbons, removing the retorted oil shale particles from the bottom of the retort, and recovering the volatile hydrocarbons from the stripping gas, wherein the improvement comprises separating prior to retorting a fine shale fraction containing particles smaller than a preselected particle size from the oil shale feed stream entering the retorting vessel and introducing said fine oil shale fraction as a separate feedstream into the retorting vessel at a position below the top of the bed of downward moving shale.