The hydrodynamic behavior of a cocurrent gas-liquid-solid semifluidized bed was investigated. A separate investigation was performed on a packed bed and a fluidized bed under gas-liquid flow conditions similar to that for the semifluidized bed, Parameters of the semifluidized bed under extensive study include pressure drop, gas holdup, onset liquid velocity for semifluidization, and the height of the packed bed section and the fluidized section. The pressure drop of the semi-fluidized bed obtained experimentally was compared favorably with that predicted by the model equations.
SCOPEA semifluidized bed is formed when a mass of fluidized particles is compressed by fluids with a porous retaining grid. This gives rise to the creation of a fluidized bed and a fixed bed in series within a single containing vessel. Studies of semifluidization have been limited to the gas-solid or liquid-solid systems (e.g., Fan and Wen, 1961). Only until recently has semifluidization in the gas-liquid-solid system been explored by Chern et al. (1981). Their investigation was concerned with the hydrodynamic behavior of inverse semifluidization in which countercurrent flow of a gas and a liquid takes place in a bed of particles with the density lower than that of a liquid.In this study, hydrodynamic behavior of semifluidization in which cocurrent flow of a gas and a liquid takes place in a bed of particles with the density higher than that of a liquid was investigated. Various parameters under extensive analysis include pressure drop, gas holdup, onset liquid velocity for semifluidization, and the height of the packed section and fluidized section. Separate experiments on the packed bed were performed to simulate the flow behavior in the packed section of the semifluidized bed.
CONCLUSIONS AND SIGNIFICANCEThe separated flow concept was adopted satisfactorily in this study to describe the pressure drop behavior in the cocurrent gas-liquid upward flow in a packed bed. The friction factor between the liquid and the solid in the packed bed was defined and empirically correlated as a function of the liquid Reynolds number. The gas holdup in the packed bed was shown to increase with the decrease of the liquid velocity and the increase of the gas velocity.The simplified generalized wake model, more specifically, the solid-free wake model, was utilized to account for the bed expansion behavior in the gas-liquid-solid fluidized bed. With modification, Nicklin's theory for the two-phase bubble flow and the slug flow elucidates well the gas holdup in the dispersed bubble flow regime and the slug flow regime for the gas-liquid-solid fluidized bed.Based on the bed expansion characteristics of the fluidized bed, the onset liquid velocity for gas-liquid-solid semifluidization was established. The height of the packed section in the semifluidized bed was found to be predictable directly from a simple material balance equation for the solid particles in the bed. Following the model equations developed in this study the pressure drop in the semifluidized ...
