Disclosed is an apparatus and process for prolonging the residence time of catalyst in a chamber for regenerating catalyst. Spent catalyst, perhaps from an FCC reactor, is introduced into a chamber of a regeneration vessel between lower and higher combustion gas distributors. The velocity of gas from the lower distributor is insufficient to entrain catalyst from the bed, and gas from the higher distributor when combined with gas rising from the lower distributor is sufficient to generate a fast fluidized flow condition. The second distributor elevates the location of the transition from turbulent bed to fast fluidized conditions.