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

Experimental fluidization results were compared for three gas distributors with the same opening ratio but different orifice inclinations (30 degrees, 45 degrees, and 90 degrees). Hydrodynamic studies were conducted with glass beads (diameter 154 mu m) 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 76 mu m), 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 degrees-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 degrees-hole distributor in a shallow bed. (C) 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.