Hydrodynamics and solids mixing in fluidized beds with inclined-hole distributors

Abstract

Experimental fluidization results were compared for three gas distributors with the same opening ratio but different orifice inclinations (30°, 45°, and 90°). Hydrodynamic studies were conducted with glass beads (diameter 154μm) to evaluate the impacts of orifice inclination and static bed depth on pressure drop, pressure drop fluctuations, bed expansion, and minimum fluidization velocity. Solids residence time distributions were determined using phosphorescent tracer particles (mean diameter 76μm), activated by ultraviolet light. The bed pressure drop was higher with the inclined-hole distributors and increased with static bed height. In a shallow bed, the inclined-hole distributors gave less expansion; however, in deep beds, the orifice angle had negligible influence on bed expansion. The minimum fluidization velocity varied with static bed height for the inclined-hole distributors and was higher for steeper angles. The turnover time estimated using bubbling-bed equations matched the experimental results well for vertical mixing. Probes and ports at the walls of the fluidization column reduced the dense-phase downward velocity by up to 40%. The tangential particle velocity was highest for the 30°-hole distributor and decreased with increasing orifice angle. Tangential mixing was described by a dispersion model; the dispersion coefficient for the inclined-hole distributors was approximately twice that for the 90°-hole distributor in a shallow bed.