Modelling and Simulation of Riser Reactor of a Commercial Fluid Catalytic Cracking Unit Using 6-Lump Kinetics of Vacuum Gas Oil

This work presents a one-dimensional adiabatic mathematical model for the riser reactor of a commercial fluid catalytic cracking unit, FCCU. The cracking reactions in the riser reactor were based on six-lump kinetics of the catalytic cracking of vacuum gas oil, taking cognizance of diffusion resistance, which is a departure from the general norm in the literature. Moreover, two-phase hydrodynamic model for the riser reactor, coke-on-catalyst deactivation model as well as heat transfer resistance between the fluid and solid phases were considered. Two vaporization approaches (the instantaneous and one-dimensional vaporization) of the feedstock were investigated. The developed model was a set of eleven highly non-linear, coupled and stiff ordinary differential equations, ODEs, which was numerically solved with an implicit MATLAB built-in solver, ode23tb, designed deliberately for handling stiff differential equations to circumvent the problem of instability associated with explicit methods. The industrial plant data of China National Petroleum Corporation (CNPC) were used to validate the simulated results of this study. Moreover, our simulated results revealed that the mode of vaporization of the feedstock had influence on the conversion, yield and other process parameters at the riser reactor outlet. Excellent agreements were achieved between the CNPC FCCU plant data and the simulated results of this study for instantaneous vaporization of feedstock, with AAD being <  5% in all cases investigated, where the optimal yields of the cracked products needed to meet market demands and ensuring maximum profit were achieved