Hydrodynamic Study of Gas-Solid Fluidization of a Ternary Mixture in a Tapered Bed

Abstract

Hydrodynamic characteristics of fluidization in conical or tapered beds differ from those in columnar beds due to the variation of superficial velocity in the axial direction of the beds. In the former, fixed and fluidized regions could coexist and the sharp peaking of the pressure 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 of homogenous well-mixed ternary mixtures of three different particle sizes at varying compositions in gas-solid tapered fluidized beds with various tapering angles. The tapering angle of the beds has been found to dramatically affect the beds' behavior. Other hydrodynamic characteristics determined experimentally included the maximum pressure drop, minimum velocity of fluidization, bed fluctuation ratio and bed expansion ratio. The dependence of these quantities on average particle diameter, mass fraction of the fines in the mixture, bed height and cone angle has been discussed.
Based on dimensional analysis, correlations have been developed with the system parameters viz., geometry of tapered bed, particle diameter, static bed height, density of solid and gas and superficial velocity of the fluidizing medium. Correlations have been also been developed for bed fluctuation ratio and bed expansion ratio in gas-solid tapered fluidized bed of ternary mixture of irregular particles using factorial design method. Experimental values of critical fluidization velocities and maximum bed pressure drops have been compared with the developed correlations in literature.
Keywords: Gas–solid fluidization, homogeneous ternary mixtures, irregular particles, maximum pressure drop, minimum fluidization velocity, bed fluctuation ratio and bed expansion ratio.