Oxygen transfer and hydrodynamics in three-phase inverse fluidized beds

Experiments were performed at ambient temperature and pressure in a 152 mm inner diameter column with air, tap water or 0.5% wt. aqueous ethanol solution, and polypropylene particles. An increase in liquid velocity and solids loading, and the presence of a surfactant reduces the gas velocity required to reach full bed expansion, which is delimited by the gas sparger. With an increase in gas velocity, solids holdups remain constant after full bed expansion, liquid holdups increase to a maximum and then decrease and gas holdups continuously increase. The addition of ethanol greatly increases the gas holdups leading to significant reductions in liquid holdups. The volumetric gas–liquid mass transfer coefficient, kLakLa, increases with increasing gas velocity but does not change significantly with liquid velocity. There are complex interaction effects between solids loading and surfactants as the values of kLakLa in the aqueous ethanol solution were greater than those in water when particles were present and smaller without particles. kLakLa data in water were found to be proportional to gas holdup whereas for the ethanol solution this proportionality constant first decreased with increasing gas velocity to eventually stabilize at a value smaller than for water.