Interactions of Flow and Reaction in Fluid Catalytic Cracking Risers

Fluid catalytic cracking (FCC) is the primary conversion process in oil refining. The performance of an FCC riser strongly depends on the interactions between oil/catalyst flow and cracking kinetics, but most FCC riser models do not consider such interactions. Accordingly, this work develops a computationally simple model capturing the dominant features of flow-reaction coupling in the riser's dense phase and acceleration zones. Specifically, the particle-particle collision force and the particle-fluid interfacial force are considered. With a four-lump kinetic model, the riser model predicts conversion and selectivity from the axial profile of the catalyst-to-oil ratio resulting from particle-fluid interfacial momentum transfer. The cracking intensity in the riser bottom zone is much greater than that calculated from conventional riser models, which neglects oil-catalyst hydrodynamic coupling and catalyst dilution due to volume expansion. The present model compares well with published data and predicts conversion-selectivity patterns that are qualitatively different from those obtained from conventional models. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 3122-3131, 2011