CFD modelling of three-phase fluidized bed with low density solid particles

Abstract

Three-phase fluidization is defined as an operation in which a bed of solid particles is suspended in gas and liquid media due to net drag force of the gas and/or liquid flowing opposite to the net gravitational force (or buoyancy force) on the particles. Such an operation generates considerable, intimate contact among the gas, liquid and the solid in the system and provides substantial advantages for application in physical, chemical or biochemical processing involving gas, liquid and solid phases. Among all the types of three-phase fluidized beds, three-phase concurrent gas-liquid-solid fluidized beds are used in a wide range of applications including hydro-treating and conversation of heavy petroleum and synthetic crude, coal liquefaction, methanol production, sand filter cleaning, electrolytic timing, conversion of glucose to ethanol, aerobic waste water treatment, and various other hydrogenation and oxidation reactions. The recent fluidized bed bioreactors are superior in performance due to immobilization of cells on solid particles reducing the time of treatment, volume of reactor is extremely small, lack of clogging of bio-mass and removal of pollutant like phenol even at lower concentrations. In the fluidized bed system used in waste water treatment, low density solid matrix is used to immobilize the microbes as the system operates at low water and air velocities to avoid transportation of the particles from the bed. Hydrodynamics study of three-phase fluidized bed with low density particles are rarely seen in literature although a tremendous work is seen for moderate or high density solid particles. In the present work, the computational studies have been carried out on two dimensional fluidized beds to characterize there hydrodynamic behavior. Air, water and low density solid particles have been used as the gas, liquid and solid phase to analyze the system behaviors.