Controlling particle size in fluid coking

Claim 1

A PROCESS FOR FLUID COKING HYDROCARBON OILS INCLUDING A REACTION ZONE AND A BURNER ZONE WHEREIN COKE PARTICLES ARE MEAINTAINED IN A DENSE FLUIDIZED CONDITION AND ARE CIRCULATED BETWEEN SAID REACTION ZONE AND SAID BURNER ZONE AND COARSE PRODUCT COKE IS WITHDRAWN AS PRODUCT, THE IMPROVEMENT WHICH COMPRISES PROVIDING SAID BURNER ZONE WITH A CONTINUOUS VERTICAL SERIES OF SECTIONS OF INCREASING CROSS-SECTIONAL AREA INCREASING FROM THE BOTTOM TO THE TOP, PROVIDING IN SAID BURNER ZONE A SINGLE DENSE FLUIDIZED BED CONSISTING ESSENTIALLY OF COKE PARTICLES EXTENDING AS A CONTINUOUS FLUIED BED THROUGH SAID SECTIONS INTRODUCING AN OXYGEN-CONTAINING GAS INTO THE LOWER PORTION OF EACH SECTION AND ADJUSTING THE GAS FLOW RATES TO THE VARIOUS SECTIONS TO EFFECT DENSE PHASE ELUTRIATION OF FINE COKE PARTICLES FROM THE PRODUCT COKE STREAM AND BURNING OF COKE PARTICLES TO PROVIDE HEAT OF COKING FOR SAID REACTION ZONE.