Three-stage catalyst regeneration

A method for burning nitrogen-containing coke off a coke-containing particulate catalyst, which comprises:

• (a) introducing a major portion of said coke-containing catalyst into a first fluidized bed comprising substantially coke-free catalyst in a lower zone in a vertically extending regeneration vessel;
• (b) passing a regeneration gas comprising free oxygen upwardly through said lower zone, burning substantially all coke off said major portion of coke-containing catalyst in said first bed, and burning substantially all carbon monoxide formed in said first bed within said lower zone, sufficient free oxygen being introduced into said lower zone to provide at least 1 volume percent residual free oxygen in said regeneration gas at the upper end of said lower zone, whereby nitrogen oxides are generated in said lower zone;
• (c) introducing a minor portion of said coke-containing catalyst into a second fluidized bed of catalyst in a vertically intermediate zone in said regeneration vessel, passing nitrogen oxides-containing regeneration gas from said lower zone upwardly through said intermediate zone, forming carbon monoxide and carbon dioxide and generating a substantially oxygen-free atmosphere in said second bed by reacting substantially all said residual free oxygen with coke and carbon monoxide in said second bed, and decreasing the amount of nitrogen oxides in said regeneration gas by reacting at least a portion of said nitrogen oxides in said intermediate zone to form free nitrogen;
• and
• (d) passing carbon monoxide-containing regeneration gas from said intermediate zone upwardly through a third fluidized bed comprising substantially coke-free catalyst in an upper zone in said regeneration vessel, and burning substantially all carbon monoxide introduced into said upper zone with additional free oxygen in contact with said third bed.