Abstract: A process and apparatus are disclosed for achieving turbulent or fast fluidized bed regeneration of spent FCC catalyst in a bubbling bed regenerator having a stripper mounted over the regenerator and a stripped catalyst standpipe within the regenerator. A coke combustor vessel is immersed in, and in open fluid communication with, the bubbling dense bed of the existing regenerator vessel. Spent catalyst is discharged into the coke combustor, mixes with hot regenerated catalyst which flows into the coke combustor, and regenerated with combustion air in a turbulent or fast fluidized bed. Catalyst and flue gas are discharged up into a dilute phase transport riser, preferably into cyclone which separate hot regenerated catalyst from flue gas. Regenerated catalyst is collected in the bubbling dense bed surrounding the coke combustor, and some is recycled by flowing into the coke combustor for direct contact heat exchange.