Hydrodynamics-reaction-coupled simulations in a low-scale batch FCC regenerator: Comparison between an annular and a free-bubbling fluidized beds

Abstract

Although annular fluidized beds (AFB) has been widely studied, a direct comparative evaluation of its reactive performance with bubbling fluidized beds (BFB) under similar operating conditions is still lacking. In this study, a comparative simulation using Euler–Lagrange MP-PIC method is performed under varying superficial gas velocities to assess their chemical reaction performance in relation to coke combustion rate, flue gas and temperature profiles in both reactors. The macroscale hydrodynamics of transport phenomenon, pressure fluctuation, solids holdup, slip velocity, and radial nonuniformity index (RNI) are also evaluated in detail. The results show, compared to BFB, the AFB shows big hydrodynamic differences, as indicated by the stronger cross-flow of solids, higher pressure fluctuation magnitudes, nonuniform lateral solids distribution, higher slip velocity and RNIs. However, reaction performance in relation to coke burning pattern and rates, flue gas distribution and temperature profile in the two beds are close. Under the constant bed inventory and air flowrate criteria, bigger changes in hydrodynamics are needed to affect the reaction performance significantly in the two small reactors due to the batch operation mode and the slow coke burning rate.