Fluidized catalytic cracking regeneration process

In a fluidized cracking catalyst regeneration process wherein a spent, coke-contaminated cracking catalyst is contacted with a molecular oxygen containing regeneration gas, in a single regeneration vessel, at catalyst regeneration conditions, for burning substantially all the coke from said spent catalyst, producing a spent regeneration gas comprising carbon dioxide and carbon monoxide and substantially depleted in oxygen, and a hot regenerated catalyst substantially reduced in residual carbon suitable for cracking a hydrocarbon charge;

• the improvement which comprises:
• a. contacting, in the bottom of a frustoconical first regeneration zone, having a closed bottom and an open top spent catalyst with an amount of molecular oxygen containing primary regeneration gas sufficient to provide about the stoichometric amount of oxygen for complete combustion of coke under turbulent flow conditions for forming an intimate mixture of spent catalyst and primary regeneration gas;
• b. flowing said mixture of spent catalyst and primary regeneration gas upward, at catalyst regeneration conditions, at superficial vapor velocities of about 5-8 ft/sec near the bottom decreasing to about 2.5-4.5 ft/sec at the top of said first regeneration zone, for forming a fluidized dense phase bed of catalyst having an upper surface within said first regeneration zone;
• c. withdrawing hot, regenerated catalyst from the upper portion of said fluidized dense phase catalyst bed for use in cracking hydrocarbon charge stock;
• d. disengaging spent regeneration gas containing entrained catalyst from the upper surface of said fluidized dense phase catalyst bed;
• e. flowing said spent regeneration gas and entrained catalyst from the open top of said first regeneration zone into the bottom of a frusto-conical second regeneration zone, having an open top and open bottom in open communication with the top of said first regeneration zone, at a superficial vapor velocity in the range of about 2.5-4.5 ft/sec at the bottom decreasing to about 1.0-2.2 ft/sec at the top of said second regeneration zone such that a major portion of the entrained catalyst returns under the influence of gravity to the upper surface of said fluidized dense phase catalyst bed, and a dilute phase of catalyst suspended in spent regeneration gas exits the top of said second regeneration zone;
• f. radially distributing a molecular oxygen containing secondary regeneration gas into said second regeneration zone in an amount to provide the equivalent of about 1-10 percent of the oxygen in said primary regeneration gas for combusting substantially all the carbon monoxide in said spent regeneration gas to carbon dioxide;
• g. separating, in a separation zone, said dilute phase into a hot catalyst fraction and a flue gas fraction essentially free of entrained catalyst;
• h. venting said flue gas fraction from the regeneration process;
• i. flowing said hot, separated catalyst fraction from the separation zone to the bottom of the first regeneration zone for contact with additional spent catalyst and primary regeneration gas.