Mixing and dispersion behaviours of ellipsoid particles in a bubbling fluidized bed

Abstract

Fluidization of non-spherical particles is widely practised in chemical engineering processes. In this work, the mixing and dispersion behaviours of non-spherical particles in a bubbling fluidized bed (BFB) are explored by a computational fluid dynamics-discrete element method (CFD-DEM) featuring a super-quadric model to describe particle morphology. After model validation, the general flow patterns, solid mixing, and solid dispersion of ellipsoid particles are studied, together with the discussion of the effect of aspect ratio (AR) on fluidization behaviours. The results show that minimum fluidization velocity increases with the aspect ratio. Bed permeability depends on bed porosity and particle shape. Bubbles place a significant role in determining flow patterns, which induce a double-recirculation pattern where particles mainly move from the wall region to the central region in the lower bed and oppositely in the upper bed. Ellipsoid particles with higher sphericity (e.g., AR = 0.75 and 1.5) show a smaller mixing index in the bed. The magnitudes of solid dispersion coefficients in x, y, and z directions are about ~10−3 m2/s, ~10−5 m2/s, and ~ 10−2 m2/s, respectively. Ellipsoid particles with higher sphericity show larger solid dispersion intensity. These findings shed light on the fundamental understanding of the particle shape on fluidization dynamics.