Effect of a Mechanical Vibration on Particle Migration Behavior in a Gas-Solid Fluidized Bed for Fine Cohesive Powders

This study aimed to investigate the particle migration behavior under mechanical bed vibration in a gas-solid fluidized bed for fine cohesive powders. In this study, the vertical vibration was added to the particle bed, and the characteristics of the pressure drop curve, particle flow patterns, and the migration velocity on the bed surface were examined under various vibration parameters (vibration frequency and vibration amplitude). The powders used in this study were spherical shaped powders of silica, copper dioxide, zirconia, and alumina. The primary size and density were ranged from 6 to 20µm and from 2500 to 6040 kg/m3 , respectively. When the vibration amplitude was lower than a certain critical value (vibration frequency was constant), the dominant particle flow pattern changed from the formation of the stable gas channels to the bubble formation with continuously channel breakage as the gas velocity increased. In such vibration conditions, the pressure drop curve against the gas velocity was a common pressure drop curve that consists of the fixed bed and fluidized bed (the value of the bed pressure is almost constant) was obtained. However, when the vibration amplitude was larger than a certain critical value, vigorous particle migration appeared in the whole bed. From the observation of the vigorous particle migration behavior, the particles and/or agglomerates had a regular migration direction, hence it is considered that a high particle mixing state was achieved under such a vigorous particle migration behavior. This vigorous particle migration behavior was observed between the fixed static state and the bubble formation with channel breakage state. Furthermore, we found that the bed pressure drop became lower while the vigorous particle motion occurred, and the degree of the reduction of the bed pressure drop became larger as the particle migration became vigorous. The experimental result of the particle migration velocity had a strong interrelation with the reduction degree of the bed pressure drop, i.e., as the vibration amplitude increased the particle migration velocity increased while the bed pressure drop was decreased.