(123c) DEM Simulation of Cylinders and Capsules in a Fluidized Bed

Fluidization of non-spherical particles of cylindrical or
close to cylindrical shape is part of many industrial processes, especially in
relation to biomass fuel production, fluidized bed gasifiers and pharmaceutical
tablet coating processes. In these applications accurately accounting for the
details of particle shape is important for safe and efficient design of
industrial equipment. In this work the numerical model based on the Discrete
Element Method (DEM) fully coupled with CFD is used to predict the effect of
particle aspect ratio and presence of sharp edges in the particle’s shape on
the fluidized bed hydrodynamics. The model is implemented within commercial
software STAR-CCM+ version 12.06 developed by Siemens PLM. The model assumes
particles are cylinders or spherocylinders
(capsules). It accurately resolves the collisions between cylindrical particles
or between capsules without employing conventional method of “spheres glued
together” for non-spherical particles.

The model is then used to simulate cylindrical particles or
capsules of the same volume, mass, aspect ratio, and frictional properties in a
cylindrical container with air inlet at the bottom and pressure outlet boundary
at the top with the range of inlet velocities both below and above minimum
fluidization velocity. The results for pressure drop, particle packing and
particle preferred orientation are analyzed for both cylinders and capsules and
compared to the correlations reported in the literature. The results for the
percentage of particles aligned with fluid flow direction in bubbling flow
regime indicate the presence of surprisingly longer timescale for establishing
steady state preferred orientation of particles. The effect of the absence of
the sharp edges in capsules compared to cylinders on the hydrodynamics of the
fluidized bed is discussed in details.