Mass transfer and phase holdup characteristics in three-phase fluidized beds

The effects of liquid surface tension (42.6 — 72.4 mN/m) and viscosity (1 —214 mPa • s”), liquid (0.01—0.12 m/s) and gas (0.01 — 0.20 m/s) velocities and particle sizes (1—8 mm) on phase holdup and mass transfer coefficient (kLa) have been determined in a 0.142 m-I.D. X2.0m-high Plexiglas column. The gas phase holdup increases with liquid velocity, and the rate of increase in gas phase holdup sharply increases with gas velocity in the bed of surfactant solutions. In the beds of 1.0 and 1.7 mm glass beads, the bed contraction occurs whereas in the beds of 2.3 mm glass beads the bed contraction does not occur with an aqueous soltuion of ethanol (o = 50.4 mN/m). The value of kLa increases with decreasing surface tension (a) but it decreases exponentially with increasing liquid viscosity in continuous bubble columns and three-phase fluidized beds. In three-phase fluidized beds with surfactant solutions, kLa increases with gas and liquid velocities and particle size. In three-phase fluidized beds of viscous or surfactant soltuions, kLa can be estimated in terms of the energy dissipation rate based on the isotropic turbulence theory and a flow regime map is proposed based on the drift flux theory.