Effect of cracking reactions kinetics on the model predictions of an industrial fluid catalytic cracking unit

Fluid catalytic cracking (FCC) is one of the most complex processes in the petroleum industry. The large degree of uncertainty in the kinetics of the cracking reactions and catalyst deactivation by coke deposition in the riser reactor are among several factors that contribute to the process complexity. The model developed by the authors (All and Rohani, 1995) is used to investigate the effect of the three-lumped kinetic scheme (Weekman and Nace, 1970) and the four-lumped scheme (Lee er al., 1989) on the model predictability and reliability. The effect of changes in the catalyst circulation rate, gas oil feed rate, and oxygen feed concentration on various process variables is compared. It is shown that the three-lumped kinetic scheme, despite its extensive use in the literature (McFarlane et al., 1993; Elnashaie and Elshishini, 1993; Theologos and Markatos, 1993; Arandes and de Lasa, 1992; Lopez-Isunza and Ruiz-Martinez, 1991), leads to erroneous results and should not be used in the dynamic simulation of the FCC units.