Prediction of Pressure Drop and Top Packed Bed Height in Three-Phase Semi-fluidized Bed with Cylindrical Particles

Abstract

The phenomenon of semi-fluidization can be visualized as a combination of fluidized bed at the bottom and a fixed bed at the top. Such a reactor bed can be used in the bio-oxidation process for wastewater treatment in which various low-moderate density solid particles of different shape and size can be 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, formation of top packed bed and phase hold up of a co-current gas-liquid-solid three-phase semi-fluidized bed are 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 semi-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 semi-fluidization velocity and variation of pressure drop with the top packed bed. By keeping gas velocity at a fixed value, the liquid velocity is varied and its effect on minimum liquid fluidization velocity, pressure drop and the expansion ratio is studied for different particle size and static bed height, expansion ratio and gas velocities