Hydrodynamic studies on three-phase fluidized bed using CFD analysis

Abstract

Three-phase fluidization refers to fluidization of solid particles by co-current, upward flow of gas and liquid-phases for the purpose of bringing three-phases in contact in a single operation. Due to complications in understanding hydrodynamics of three-phase fluidized bed, CFD analysis is used to predict the hydrodynamics of it. In this study, liquid-phase is water which flows continuously, where as the gas phase is air which is distributed discretely throughout the bed. Ceramic particle of 1 mm diameter, density of 2650 kg/m 3 is used as a solid phase. Excellent mixing, heat and mass transfer rates are the unique features of three-phase fluidized bed. The selection of distributor plays an important role in the quality of fluidization [1]. CFD model is created as the realistic representation of actual fluidized bed. The liquid and solid flow is represented by the mixture model. The air is injected from the bottom of the fluidized by means of discrete phase method (DPM). Simulation results are obtained by using porous jump and porous zone model to represent the distributor. It is found that porous zone model is best applicable in the industries, since stability of operating conditions is achieved even with non-uniform air, water flowrates and with different bed heights(100 mm, 200 mm, 300 mm, 400 mm and 500 mm). Simulated Pressure drop values of the fluidized bed have good agreement with the experimental findings. As the gas flowrate increases, the pressure drop in the column is decreases, provided the initial bed height, diameter of the column, and liquid flowrate are constant. This is due to decrease in density of the fluid medium in the bed by means of more gas hold up. The approach of the simulated values to the experimental values can be reduced with better understanding the nature of the fluidized bed.