CFD Simulation of Hydrodynamics of Three Phase Fluidized Bed

Abstract

The gas-liquid-solid fluidized bed has emerged in recent years as one of the most promising devices for three-phase operation. Such a device is of considerable industrial importance as evident from its wide application in chemical, refining, petrochemical, biochemical processing, pharmaceutical and food industries. Selection and design is one of the main parameter in the performance of three phase system. Success is dependent on the effective contact between the phases. Even though a large number of experimental studies have been done in different process parameters and physical properties, the complex hydrodynamics of three phase fluidized bed reactors are not well understood due to complicated phenomena such as particle–particle, liquid–particle and particle–bubble interactions. For this reason, computational fluid dynamics (CFD) has been promoted as a useful tool for understanding multiphase reactors for precise design and scale up. In the present work three different configuration of cylindrical column has been taken for studying co-current gas-liquid-solid fluidization with the help of commercial CFD codes as FLUENT. The main focus for analyzing the results is on the column with 1.88 m height and diameter of 0.1 m containing solid particles as glass beads of size 2.18 mm and 4.05 mm. In the present study of three phase fluidized simulation the hydrodynamic parameters investigated includes phase hold up, velocity profiles of all phases, bed expansion, bed voidage, static pressure drop, frictional pressure drop at wall, and energy flows. The operating variables varied includes liquid and air inlet velocity, initial solid static bed height and particle size. The dynamic characteristics obtained from CFD simulation have been validated with the experimental results and a good agreement has been observed. Eulerian-Eulerian granular multiphase flow approach is capable of predicting the overall performance of gas–liquid–solid fluidized bed. The expanded bed height is strong function of liquid velocity, it increases with liquid velocity. Velocity of the phases has been observed more in center region than near at wall in fluidized bed. Bed voidage increases with the liquid velocity and depending on the particle size. Axial velocity in small diameter column is more than the large diameter column. Frictional pressure drop at wall has been found to decrease with increase in the bed height.