Abstract: In a two stage catalytic cracking process a heavy cycle gas oil fraction (HCGO) nominal boiling range 600.degree. F. to 1050.degree. F., API gravity of -10.degree. to +10.degree. and 65 to 95 vol % aromatics is recycled to extinction between an ebullated bed hydrocracking zone and fluidized catalytic cracking zone to yield a liquid fuel and lighter boiling range fraction as the light fraction from each zone.The catalyst in the fluidized catalytic cracking zone is maintained at a micro activity 68 to 72 while cracking a virgin gas oil to HCGO. HCGO is then mixed with vacuum residuum and hydrocracked in an ebullated bed reactor. The mid range fraction is recycled to the fluidized catalytic cracking zone. The 1000.degree. F..sup.+ fraction is blended with a fuel oil.

Abstract: A method has been discovered for controlling catalytic reactor bed temperature in an ebullated bed process. A sour, aromatic feedstock is mixed with a conventional ebullated bed residual oil feedstock in a controlled ratio. The aromatic feedstock is catalytically cracked and thereby releases heat. The flow rate of the aromatic feedstock is controlled to maintain the reactor bed at a selected catalytic reaction temperature.Both feedstocks are upgraded to a fuel boiling range fraction and the fired heater is eliminated for the conventional feedstock and optionally for the hydrogen-containing gas feed stream as well.

Abstract: In an ebullated bed process, it has been found that in switching from one sediment yielding feedstock to a second sediment yielding feedstock that the transient sediment concentration is 5 to 8 times the steady state concentration. Such transients have caused unit shutdowns with lost production time.A method has been found which avoids these high transient sediment concentrations. Second feedstock is added incrementally (1 vol % to 2 vol % of the final rate) over the period of a week or more and sediment in the product analyzed. After full second feedstock rate is achieved, first feedstock is reduced incrementally with sediment analysis. Higher unit utilization is achieved with the corresponding increased yearly production.