Characteristics of Three-Phase (Gas-Liquid-Solid) Circulating Fluidized Beds

The characteristics of three-phase (gas-liquid-solid) circulating fluidized beds (TPCFBs) are discussed in order to visualize the unique features and advantages thereof due to the intrinsic flow and contacting behaviors of multi-phases, providing a better understanding of the state of art of TPCFBs and their feasible applications as multi-phase reactors and contactors. The hydrodynamics such as individual phase holdups, bubbling flow behaviors, bubble properties and liquid phase dispersions, and heat and mass transfer characteristics in the riser were examined based on the previous investigations. Although the information in the riser of various kinds of TPCFBs deviated from each other depending on the solid circulation modes and experimental conditions, they were summarized and consociated for the elucidation of the present states and views of the investigations. Rational guides to predict the hydrodynamics and heat and mass transfer phenomena in the riser of the TPCFB were possible by analyzing and synthesizing the results reported in the literatures presently available. Especially, the effects of operating variables including gas (U-G) and liquid (U-L) velocities, properties of fluidized solid particles and continuous liquid media, and solid circulation rate (Gs) on the hydrodynamic parameters and the heat and mass transfer characteristics such as heat transfer coefficient (h) and resistance, volumetric mass transfer coefficient (k(L)a), gas-liquid interfacial area (a) and liquid side mass transfer coefficient (k(L)) were determined. The information on the heat and mass transfer, however, were extremely limited comparing with those of hydrodynamics. Some correlations were suggested to predict the hydrodynamic parameters, and the values of h, k(L)a, a, and k(L) in the riser of the TPCFBs to provide insights for the present and future studies. The mechanism of heat and mass transfer and their modeling should be conducted for the better prediction of the performance of the TPCFB-reactors and contactors in the future.