Fluidized catalytic cracking regeneration process

In a fluidized catalytic cracking process wherein a hydrocarbon charge is cracked, in a reaction zone, in the presence of hot, regenerated cracking catalyst, for conversion of the hydrocarbon charge into lower boiling hydrocarbon product, wherein catalyst, spent by the accumulation of coke thereon is separated from the hydrocarbon product at a temperature in the range of about 750.degree.-1100.degree. F, and wherein the spent catalyst is regenerated, in a regeneration zone, by burning coke therefrom;

• the improvement which comprises:
• a. charging spent catalyst substantially vertically downward into a vertical, cylindrical lower regeneration zone;
• b. charging an oxygen containing primary regeneration gas, under turbulent flow conditions, at a flow rate sufficient to provide about 25 to 40 percent of the stoichometric amount of oxygen required for combusting the coke on spent catalyst to carbon dioxide and water, for forming an intimate mixture of spent catalyst and primary regeneration gas;
• c. flowing the catalyst-primary regeneration gas mixture upward through said lower regeneration zone at a superficial vapor velocity in the range of about 4.5-8 ft/sec, and a catalyst residence time in the range of about 1.0 seconds to 1 minute into the bottom of a vertical, cylindrical upper regeneration zone for catalyst regeneration;
• d. radially distributing an oxygen containing secondary regeneration gas into the bottom of the upper regeneration zone at a flow rate sufficient to provide about 60 to 85 percent of the stoichometric amount of oxygen required for combustion of the coke to carbon dioxide and water such that about 100 to 110 percent of the stoichometric amount oxygen required for combustion of coke to carbon dioxide and water is supplied to the upper and lower regeneration zone;
• e. maintaining, in said upper regeneration zone, a fluidized dense phase bed of catalyst undergoing regeneration, having an upper surface, a regeneration gas superficial vapor velocity in the range of about 2.5-6.0 ft/sec, a catalyst residence time in the range of about 3-20 minutes, a pressure at the upper surface in the range of 6-50 psig, an a temperature in the range of about 1150.degree.-1350.degree. F, for burning coke from the catalyst undergoing regeneration at a specific coke burning rate in the range of about 0.05 to 1.0 pounds of coke per hour per pound of catalyst;
• f. withdrawing hot regenerated catalyst from the upper portion of the fluidized dense phase catalyst bed for contact with additional hydrocarbon charge in the reaction zone;
• g. disengaging regeneration gas, comprising carbon dioxide and carbon monoxide, substantially spent in oxygen, and containing entrained catalyst from the upper surface of the fluidized dense phase catalyst bed;
• h. flowing the spent regeneration gas and entrained catalyst from the top of the upper regeneration zone into a frusto-conic transition zone wherein the spent regeneration gas superficial vapor velocity decreases from about 2.5-6 ft/sec at the bottom, to about 1.0-2.2 ft/sec at the top of the transition zone, wherein a major portion of the entrained catalyst disengages the spent regeneration gas and returns to the fluidized dense phase bed under the influence of gravity, and wherein a dilute phase of catalyst suspended in spent regeneration gas is formed;
• i. flowing the dilute phase from the top of the transition zone into the bottom of a cylindrical dilute phase regeneration zone at a superficial vapor velocity in the range of about 1.0-2.0 ft/sec and a temperature in the range of about 1150 .degree. to 1450.degree. F;
• j. separating, in a separation zone, the dilute phase into a catalyst phase and spent regeneration gas phase essentially free of entrained catalyst;
• k. transferring the separated catalyst from the separation zone to the lower regeneration zone for contact with additional spent catalyst and primary regeneration gas;
• and
• l. venting the spent regeneration gas essentially free of entrained catalyst from the separation zone as a flue gas.