CLUSTER STRUCTURE IN A CIRCULATING FLUIDIZED-BED

Micrographs in a 10-m high and 90-mm ID fluidized catalytic cracking ( FCC) catalyst-air fast fluidized bed were taken by a video camera prov ided with an optical fiber probe inserted radially into the bed to stu dy cluster size and shape in gas-solid suspension. A computer aided (C A) particle image processing system was used to analyze images which w ere obtained under different superficial gas velocities and solid circ ulating rates at different radial positions. Cluster size and its prob ability density distribution were investigated and a simple model was established. A roundness factor was put forward to describe the shape of the cluster. We also discovered that clusters assembled by particle s show evident fractal character both in 'shape' and 'fragmentation'. The fractal dimension of clusters at different flow patterns was found to be a function of position.