Method for controlling regenerator temperature in a fluidized catalytic

Abstract

An improved method for controlling the fluidized dense catalyst phase temperature in the regeneration zone of a fluid catalytic cracking unit. In this method, the level of the fluidized catalyst bed above the riser discharge in the reaction vessel is adjusted in response to a change detected in the temperature of the fluidized dense catalyst phase of the regeneration zone. Adjustment of the catalyst bed level in the reaction zone affects the coke laydown on the catalyst in the reactor and, consequently, the amount of heat liberated in the regeneration zone upon combustion of the coke contained in the partially deactivated catalyst. A reactor bed level is attained where the resulting coke laydown on the catalyst is sufficient to maintain the desired temperature in the fluidized dense catalyst phase. Also, as a part of this improved method, the amount of oxygen-containing regeneration gas supplied to the regeneration zone is adjusted to provide sufficient oxygen to effect substantially complete combustion of the coke to carbon dioxide and to maintain the oxygen content of the flue gas at a desired level within the range of from about 1 to about 10 mol %. Maintaining the oxygen content of the flue gas within this range provides a flue gas having a carbon monoxide content of from 0 to 500 ppm. The residence time of catalyst in the regeneration zone fluidized dense catalyst phase is adjusted to provide a regenerated catalyst with a low level of residual carbon-on-regenerated-catalyst.