Hydrodynamics and mass transfer in three-phase fluidized beds with non-Newtonian fluids

Hydrodynamics and gas-liquid mass transfer in three-phase fluidized beds have been investigated. Particular attention has been paid to the influence of non-Newtonian flow behaviors of liquids on hydrodynamic characteristics and mass transfer rates. The minimum fluidization velocity, bed voidage, gas holdup and gas-liquid volumetric mass transfer coefficient were measured in a 0.068 m i.d. fluidized bed. Glass beads of three different sizes (3, 5 and 7 mm) were used. The minimum fluidization velocity decreased with increasing non-Newtonian flow behaviors. We proposed a new theoretical correlation for minimum fluidization velocity with non-Newtonian liquids, which is applicable to two-and three-phase fluidized beds in the whole region of the Reynolds number. It is developed on the basis of the free-surface cell concept. Reasonable agreement between the predictions and the experimental data for liquid-solid two-phase and gas-liquid-solid three-phase systems was obtained. The bed voidage was found to increase due to non-Newtonian anomalies. The gas holdup decreased with increasing non;Newtonian flow behaviors and decreasing particle diameter. It was also found that the gas-liquid volumetric mass transfer coefficients in non-Newtonian liquids are smaller compared with those in water. (C) 1997 Elsevier Science Ltd.