Experimental Study of the Behaviour of a Three-phase Fluidized Bed with Cylindrical Particles

Three-phase fluidized beds have been applied successfully in the bio-oxidation process for wastewater treatment in which various low-moderate density solid particles of different shape and size are used as cell support. Ceramic raschig ring possess moderate density and high surface area due to its hollow cylindrical structure, thus can be used as solid support for microorganisms, where higher mass transfer rate can be achieved. In this study the hydrodynamic characteristics viz. the pressure drop, bed expansion and phase hold up of a co-current gas-liquid-solid three-phase fluidized bed has been studied using liquid as the continuous phase and gas as the discontinuous phase. These have been done in order to develop a good understanding of each flow regime in gas-liquid and liquid-solid fluidization. Air, water and ceramic raschig rings are used as the gas, liquid and solid phases respectively. The experiments were carried out in a 100 mm ID, 2m-height vertical Plexiglas column. The column consists of three sections, viz., the gas-liquid disengagement section, test section and gas-liquid distributor section. Bed pressure measurements have been made to predict the minimum liquid fluidization velocity. By keeping gas velocity at a fixed value, the liquid velocity is varied and the effect on minimum liquid fluidization velocity, pressure drop and the expansion ratio was studied for different particle size and static bed height.