Catalyst regenerators and methods for regenerating catalysts

A method of regenerating a catalyst comprising the steps of:

• combusting coke from the catalyst in a second stage regenerator to produce a second flue gas, wherein the second stage regenerator comprises a second combustion chamber and a top with a top cross-sectional area;
• partially combusting the coke from the catalyst in a first stage regenerator to produce a first flue gas, wherein the first stage regenerator comprises a first combustion chamber, wherein the first stage regenerator is positioned above the second stage regenerator with the top positioned between the first combustion chamber and the second combustion chamber;
• separating the catalyst from the first flue gas in a cylindrical cyclone positioned over the top and within the first stage regenerator;
• separating the catalyst from the first flue gas in an annular cyclone positioned within the first stage regenerator beyond the area directly over the top;
• and
• venting the second flue gas into the first combustion chamber through a vent tube such that a superficial gas velocity at the cylindrical cyclone is about one to about one and a half times the superficial gas velocity at the annular cyclone.

A catalyst regenerator comprising:

• a first stage regenerator comprising a first combustion chamber having a first combustion chamber cross-sectional area;
• a second stage regenerator comprising a second combustion chamber with a top having a top cross-sectional area less than the first combustion chamber cross-sectional area, wherein the first stage regenerator is positioned over the second stage regenerator such that a cylindrical section of the first combustion chamber is over the top, and an annular section of the first combustion chamber surrounds the cylindrical section;
• and
• a plurality of vent tubes extending from the second combustion chamber into the first combustion chamber through the top, wherein a portion of the plurality of vent tubes comprise a discharge point within the annular section.