HYDRODYNAMIC CHARACTERISTICS OF FLUIDIZATION IN LIQUID-SOLID TAPERED BEDS

Hydrodynamic characteristics of fluidization in conical or tapered bed s differ from those in columnar beds due to the variation of superfici al velocity in the axial direction of the beds. In the former, fixed a nd fluidized regions could coexist and the sharp peaking of the pressu re drop could occur, thereby giving rise to a remarkable pressure drop -flow rate hysteresis loop at incipient fluidization. To explore these unique properties, a series of experiments was carried out in liquid- solid tapered fluidized beds with various tapering angles. Detailed vi sual observations of fluid and particle behavior and measurements of t he pressure drops have led to the identification of five flow regimes. The tapering angle of the beds has been found to dramatically affect the beds' behavior. Other hydrodynamic characteristics determined expe rimentally included the maximum pressure drop, minimum velocity of par tial fluidization, minimum velocity of full fluidization, maximum velo city of partial defluidization, and maximum velocity of full defluidiz ation. Models have been proposed to quantify the hydrodynamic characte ristics of liquid-solid tapered fluidized beds. The results predicted by the models compare favorably with experimental data. Naturally, the models are applicable to liquid-solid columnar fluidized beds corresp onding to the tapered beds with a tapering angle of zero. (C) 1997 Els evier Science Ltd. All rights reserved.