HYDRODYNAMIC BEHAVIOR OF CIRCULATING FLUIDIZED-BED WITH POLYMERIC PARTICLES

A systematic study conducted explores the hydrodynamics of a circulating fluidized bed with polymeric particles employing polyethylene resins with a particle density of 660 kg/m3 and size ranging from 90 to 500 mum. The study indicates that polyethylene resins can be fluidized smoothly in the fast fluidization regime. However, the operating range of the fast fluidization regime for these particles is smaller than that for FCC particles. The deviation of the fluidization behavior of polyethylene particles from that of common Group-A particles is explained considering the interparticle forces. Experiments with fine polyethylene particles are also conducted with coarse particles added in a circulating fluidized bed. Axial profiles of solid holdups in a bed with and without coarse particles, as well as overall fine particle holdup, are studied. The results show a significantly wider operating range of the fast fluidization regime and enhancement of fine particle holdups in a bed with the presence of coarse particles. For comparison, fluidization with FCC particles is also conducted. A mechanistic model considering particle-particle collision is proposed. The model accounts for the momentum exchange rate between a coarse particle and a cloud of fine particles, which explains the enhancement of fine particle holdups observed experimentally.