Two-dimensional reaction engineering model of the riser section of a fluid catalytic cracking unit

A two-dimensional model that predicts conversion and yield patterns in the riser section of a fluid catalytic cracking unit has been developed. The riser hydrodynamics have been described by the two-dimensional model of Malcus and Pugsley (Circulating Fluidized Bed Technology VII; Grace, J. R., et al., Eds.; Canadian Society of Chemical Engineering: Ottawa, Ontario, Canada, 2002). The hydrodynamic model has been modified to make it predictive by incorporating the slip factor for calculation of the cross-sectionally averaged voidage. The model has been coupled with the four-lump kinetic model of Gianetto et al. (Ind. Eng. Chem. Res. 1994, 33, 3053) to predict how riser operating conditions affect profiles of conversion, yield, temperature, and pressure in the riser. The model was validated against industrial riser data from three literature sources and found to agree within 10-20%. A parametric study of the influence of the liquid feed droplet diameter and feed penetration into the riser was also undertaken. Increasing the droplet size from 50 to 500 mum decreased the gas oil conversion by 4 wt %, while gasoline and light gas yields were both reduced by 1.9 wt %. Increasing the feed penetration distance from the riser wall tended to decrease the gas oil conversion.