A model proposed for the typical regenerator of a commercial fluid catalytic cracking unit (FCCU) incorporates a fluid-dynamics model for a fluidized bed that takes into account three phases, namely, emulsion, wake-cloud, and bubbles, and is combined with a kinetic coke combustion model. The latter is complemented with a model for the afterburning that may occur in the freeboard. The overall model computes the extent to which coke deposited on the catalyst is burnt, the diameter and rate of ascent of bubbles, the composition and temperature of the combustion gases (O-2, CO2, CO, and H2O) at different heights of the fluidized bed and freeboard in the generator, and the temperature of the cyclones. The regenerator model was written in Visual Basic in order to simulate an actual regenerator unit.