Entire fluid catalytic cracking (FCC) unit, comprising of a riser and a regenerator, is simulated by integrating FCC riser model presented in our earlier work (Chem. Eng. Sci. 56 (2001) 4489) with an FCC regenerator model. The effect of feed atomization (quantified by average drop size generated by the feed nozzle) on the performance of the unit is evaluated. (C) 2003 Elsevier Ltd. All rights reserved.