Fluidization behavior of particles under agglomerating conditions

Abstract

To obtain fundamental information on the fluidization behavior of sticky particles, a visually observable fluidized bed, which can be operated under conditions in which agglomeration of the bed materials occurs, was designed and constructed. Polyethylene particles and silica sand coated with a thin layer of low melting point polymer were chosen as bed materials. Two types of fluidizing gas distributors were used: a porous plate and a porous plate with an independently fed jet at the center. Our fluidized bed was operated in continuous-feed mode and in batch mode. The weight percentage of the aggomerates was measured at different residence times, jet air velocities, and jet and auxiliary air temperatures, using different particle sizes, coating thicknesses, and concentrations of coated particles in the fluidized bed. In the case of polyethylene particles as bed material in the batch system, the amount of agglomerates generated increased linearly with residence time and increased exponentially with either auxiliary air or jet air temperatures. Within the operating conditions of our study, the amount of agglomerates generated increased with jet nozzle size at the constant jet air flow rate. Under conditions of high temperature, a low jet velocity resulted in excessive agglomeration, which led to catastrophic sintering and defluidization. In the case of coated particles as bed materials in our batch fluidized bed, the amount of agglomerates generated increased with residence time and then leveled off. It increased sharply with jet air temperature, coating thickness, concentration of coated particles and decreasing particle sizes in the range of our experimental conditions.