Three-dimensional CFD model of the deaeration rate of FCC particles



Computational fluid dynamics (CFD) has been used to model the deaeration rate for a fluidized bed of fluid catalytic cracking (FCC) catalyst. The Eulerian approach has been used in which the gas and solid phases present in the fluidized bed are treated as interpenetrating continua with constitutive equations obtained from the granular kinetic theory and the interphase drag relationship. Using the CFD code MFIX, transient calculations have been made for a three-dimensional (3-D) cylindrical vessel of 0.104 m diameter. Various cases have been modeled: fluidization at superficial gas velocities of 0.005 and 0.028 m/s followed by deaeration for two catalyst bed masses of 3.17 and 4.05 kg. These have been performed for monosize particles of Sauter mean diameters of 69.8 and 100 microns. The results have been presented in terms of variation of gauge pressure with time at a height of 30 cm above the distributor plate. Comparisons of these predictions with the experimental data show that the deviation between the experimental results and the CFD predictions of deaeration rate is <10%. Based on these results it appears that our CFD modeling approach, which includes the introduction of an empirical correction factor for the gas–solid drag term, can adequately predict the deaeration rate of FCC catalyst using a single mean particle size. © 2006 American Institute of Chemical Engineers AIChE J, 2006