Fluidization of cryogels in a conical column

Abstract

Hydrodynamic studies of NiO/Al 2O 3 cryogels (Group-C particles) with varying Ni contents in a cylindrical column indicated poor gas fluidizability, characteristic of cohesive powders. In order to improve the fluidizability of a 14% NiO/Al 2O 3 cryogel, a conical column was designed and employed. Experiments showed that above a critical inlet gas velocity (0.44 m/s), the entire bed fluidized in a state of perfect mixing. Reduction of the gas velocity down to a value of 0.33 m/s caused a segregated bed containing agglomerates (2 mm diameter) in a cylindrical core and clusters (0.33 mm diameter) in the surrounding annulus. A modified Ergun equation was developed to predict the packed bed pressure drop and the minimum fluidization velocity at the inlet of the conical bed. Both correlations were applied to the conical packed bed using a proposed core-annulus model which characterizes the bed composed of the binary particle mixture. The model correlations were validated using experimental data. Analysis of kinetic data supports conclusions made from the hydrodynamic study.