Minimum fluidization velocities for gas-liquid-solid three-phase systems

Cocurrent upward gas-liquid fluidization of coarse solids is actuated primarily by the motion of the liquid at relatively low gas velocities and by the momentum of the gas at zero or low liquid velocities. Our gas-perturbed Liquid model, which has previously been shown to give good predictions of the minimum liquid fluidization velocity, U-lmf at a fixed low gas velocity, is shown here also to give reasonable agreement with U-lmf measurements for inverse three-phase fluidization at a given upward gas velocity, using the coefficient in the gas hold-up equation of Yang et al. [X.L. Yang, G. Wild, J.P. Euzen, Int. Chem. Eng. 33 ( 1993) 72] as an adjustable parameter. It is further shown that a liquid-buoyed solids/liquid-perturbed gas model can predict with moderate success the minimum gas fluidization velocity, U-gmf, for three-phase cocurrent upward fluidization of coarse solids at zero or low liquid velocities. (C) 1998 Elsevier Science S.A. All rights reserved.