Control of coke particle size in fluid coking process

Claim 1

IN A PROCESS FOR COKING HEAVY HYDROCARBINACEOUS MATERIAL WHEREIN THE HYDROCARBONACEOUS MATERIAL IS FED INTO A DENSE TURBULENT FLUIDIZED BED OF FINELY DIVIDED ESSENTIALLY INERT REFRACTORY SOLIDS MAINTAINED IN A COKING ZONE AT COKING TEMPERATURE TO PRODUCE LOWER BOILING HYDROCARBON VAPORS WHICH ARE REMOVED OVERHEAD AND A COKE-LIKE DEPOSIT WHICH REMAINS ON THE FLUIDIZED SOLIDS, AND THE COKE-CONTAINING SOLIDS ARE WITHDRAWN FROM SAID FLUIDIZED BED, HEATED TO A TEMPERATURE OF AT LEAST 1000*F. AND RETURNED TO SAID COKING ZONE TO MAINTAIN SAID FLUIDIZED BED AT COKING TEMPERATURE, THE IMPROVEMENT WHICH COMPRISES PASSING THE SOLIDS WITHDRAWN FROM SAID COKING ZONE TO A DILUTE PHASE ELUTRIATION ZONE, PASSING AN INERT GAS UPWARDLY THROUGH THE SOLIDS IN A DILUTE PHASE IN THE ELUTRIATION ZONE AT A VELOCITY OF AT LEAST 1.5 TO 3 TIMES THE FREE FALL VELOCITY OF THE LARGEST PARTICLES TO BE ENTRAINED, SUFFICIENT TO ENTRAIN PARTICLES SMALLER THAN ABOUT 175 MICRONS REMOVING THE INERT GAS AND ENTRAINED PARTICLES UPWARDLY FROM THE ELUTRIATION ZONE AND PASSING THEM DIRECTLY INTO THE AFORESAID FLUIDIZED BED IN SAID COKING ZONE, WITHDRAWING RELATIVELY COARSE PARTICLES DOWNWARDLY FROM THE ELUTRIATION ZONE, GRINDING THE RELATIVELY COARSE PARTICLES, AND RETURNING THE GROUND PARTICLES TO THE AFORESAID ELUTRIATION ZONE.