CFD Analysis of Phase Holdup Behaviour in a Three Phase Fluidized Bed

Abstract

Fluidized beds are used extensively in various fields of engineering since they have the potential to promote high levels of contact between gases, liquids and solids. A characteristic set of basic properties of a fluidized bed can be practically used which is absolutely essential for the modern process and chemical engineering. Knowledge of the onset of fluidization is highly relevant and it serves as the key to three-phase fluidized-bed reactors design and safe operation. In a Three-phase fluidization the particulate solid is suspended in an upward co-current flow of gas and liquid. Three phase fluidized beds also commonly referred to as Gas-Liquid-Solid fluidized beds are used extensively in petrochemical, refining and food processing industries. The most important industrial application of the process is the heterogeneous catalytic hydrogenation of residual oils or coal slurry for the removal of sulfur and the production of hydrocarbon distillates by hydrocracking. Keeping in view the complexity of the hydrodynamic behavior of gas-liquid-solid fluidized, CFD analysis is used to predict the various characteristics.
In the present work FLUENT 6.3.26 has been used to study co-current gas-liquid-solid fluidization. CFD simulations have been done for a column of height 1.88 m and diameter 0.1 m containing glass beads as solid particles of size 2.18 mm. In the present work, involving three phase fluidized bed, CFD analysis of phase holdup behavior is studied. GAMBIT 2.3.16 has been used to generate a 2D coarse grid. Individual phase holdup have been determined in this present work. CFD results indicate that the gas as well as solid holdup increases with increasing gas velocity and decreasing liquid velocity. Liquid holdup increases with increasing liquid velocity and decreasing air velocity. The results have been compared with those calculated from the experimental work and have been found to agree well.

Keywords: Three phase fluidized bed, phase holdup, CFD