Regenerating cracking catalyst contaminated with coke - by burning off coke in two stages

摘要

In fluidised cracking, the spent catalyst is regenerated by (a) charging the catalyst downward into a vertical, cylindrical lower regeneration zone, (b) feeding an O2-contg. prim. regeneration gas under turbulent flow, to give 25-40% of the stoichiometric amt. of O2 needed to burn the coke on the catalyst to CO2 and water, (c) flowing the mixt. of catalyst and prim. gas up through the lower regeneration zone at 4.5-8 ft/second and residence time 1-60 seconds, into the bottom of a vertical, cylindrical, upper regeneration zone, (d) feeding an O2-contg. sec. regeneration gas radially into the bottom of this upper zone to provide 60-85% of the stoichiometric amt. of O2 needed to burn the coke, so that the total O2 supplied is 100-110% of the stoichiometric amt., (e) maintaning in the upper zone a fluidised dense bed of catalyst under going regeneration having an upper surface, a regeneration gas velocity of 2.5-6 ft/second, residence time 3-20 mins., press. at the upper surface of 6-50 psig, and temp. 1150-1350 degrees F, to burn off coke at 0.05-1 lb coke/hr./lb. catalyst, (f) withdrawing hot regenerated catalyst for recycling to the reaction, (g) removing regeneration gas, contg. CO2, CO and entrained catalyst, from the upper surface, (h) passing the prod. from (g) into a frusto-conical transition zone in which the vapour velocity decreases from 2.5-6 ft./second at the bottom to 1.2.2 ft/second at the top, when most of the entrained catalyst returns to the fluidised dense bed under the influence of gravity and a dil. phase of catalyst suspended in spent regeneration gas forms, (i) passing this dil. phase from the top of the transition zone to the bottom of a cylindrical regeneration zone at 1-2 ft/second and 1150-1450 degrees F (j) sepg. the dil. phase into a catalyst phase and spent gas free from catalyst, (k) transferring the sepd. catalyst to the lower regeneration zone, and (l) venting the catalyst-free spent regeneration gas as flue gas. The regenerated catalyst contains is not >0.1 (is not >0.05) wt. % residual C. CO is converted almost completely to CO2.