Migration Characteristics of Fine Cohesive Particles in a Vibrating Gas-Solid Fluidized Bed

This study investigated the flow pattern transition for fine cohesive particles in a gas-solid fluidized bed under mechanical vibration. In general, as the particle diameter decreases, the interaction force, such as van der Waals force, acting between particles becomes larger; the bed consists of various sizes and shapes of agglomerates that are not favored for fluidizing gas to flow through evenly. It is well known that mechanical vibration is useful to improve the fluidity of fine cohesive particles due to the breakage of the agglomerates and the stable gas channels by the addition of the vibration. In this study, the migration behavior under vibrating conditions was focused on to examine the interrelation between the vibration-induced particle migration behaviors and bed fluidity. When the vibration intensity was larger than a certain magnitude, the agglomerates started to form convective particle migration (titling or heap types depending on the vibration intensity). Once the agglomerates migrated, the bed pressure drop decreased and its decreasing degree became larger as the migration velocity of agglomerates increased. As the vibration intensity increases, it is considered that the compression by the vibration to the particle bed becomes larger, and the fluidizing gas would be difficult to percolate through the consolidated part. In such situation, the gas flow concentrates to make a preferential flow to migrate the agglomerates to the bed surface. This preferential gas flow induced by the vibration is considered to cause a decrease in the bed pressure drop. In this study, from the interrelation between the particle migration behaviors and the bed pressure drop was experimentally investigated to clarify the fluidization mechanism and the flow pattern transition for fine cohesive particles in a vibrating gas-solid fluidized bed.