Hydrodynamics of three-phase fluidized beds

Abstract

The hydrodynamics of three-phase (gas-liquid-solid) fluidized beds has been studied in two columns with inside diameters of 7.62 and 15.2 cm respectively. The minimum gas and liquid velocities necessary to fluidize various types of solids were determined and correlated as a function of the particle size and density and the liquid viscosity; no effect of the initial bed height or column diameter was found. Overall phase holdups, or volume fractions, determined from a homogeneous bed model were combined with similar literature data to yield correlations for the overall gas and solid phase holdups. The overall gas holdup increased as the gas velocity was increased, while the overall solid holdup was decreased by increased liquid velocity and was increased by increased particle diameter or solid/liquid density difference. An electroconductivity technique was developed for use in the three-phase fluidized beds which allowed each of the phase holdups to be determined at any point in the column. The technique has shown the existence of a transition region as the bed goes from a three-phase to a two-phase system. The holdup profiles were fitted using the error function, and the mean and standard deviation of the solid holdup profile, along with the gas andmore » solid holdups in the regions where they were constant, were measured for each set of run conditions. Use of these five parameters, which were correlated with the physical pxrameters of the systems studied, permits each of the three phase holdup profiles to be predicted. This gives the reactor designer more information concerning phase distributions than was available previously; thus it will aid in the design of reactors where local conditions throughout the bed must be considered. « less

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