Hydrodynamic study of three phase fluidized bed with moderately viscous solutions-CFD analysis

Abstract

Fluidization basically refers to the process of passing a fluid upwards through a packed bed of solid particles resulting in a pressure drop due to the drag force of fluid. If the fluid velocity is gradually increased then the pressure drop increases as well as the drag force on the particles and after some time the particles will no longer be in a state of rest but will start to move and will
remain suspended in the fluid. This condition represents fluidization. Three-phase fluidized beds or slurry bubble columns have gained considerable importance because of the good heat and mass transfer characteristics in their applications in physical, chemical, petrochemical, and
biochemical processing. They are operated by a number of industries around the world for carrying out various reactions and for them to be successful their hydrodynamics (phase holdups, bed expansion, pressure drop etc) have to be studied.
To understand better the bed complexities while designing and carrying out reactions CFD-Computational
Fluid Dynamics is promoted as a useful tool. The potential of CFD for describing the hydrodynamics and heat and mass transfer of multiphase fluidized beds has been established
by several publications. CFD predicts the flow characteristics, bed hydrodynamics, phase
holdups and heat and mass transfer happening inside the bed qualitatively.
In the current work an attempt has been made to study the hydrodynamics of three phase fluidized bed with moderately viscous solutions. The simulation is done for a column of 1.88m height and 0.1m diameter filled with 4mm glass beads till a certain height. GAMBIT 2.2.30 is used to develop the computational grid of 0.01m and FLUENT 6.3.26 is used to carry out the simulation. It is observed that the bed expands considerably with increase in glycerol concentration for a constant inlet gas and liquid velocity. The gas holdups as well as liquid holdups are found to increase with glycerol concentrations for constant inlet velocities whereas solid holdup decreases.