MICROVISUALIZATION OF CLUSTERS IN A FAST FLUIDIZED-BED

Micrographs in a 10-m high by 90-mm ID FCC-air fast fluidized bed were taken by using a video camera provided with a special probe, which consists of a set of lenses and an optical fiber flashlight transmitter, inserted radially into the bed. These micrographs, taken at different radial and axial positions, can distinguish two phases in the fast fluidized bed: a dispersed phase and a cluster phase. In the dispersed phase, the solid particles are noted to be present essentially individually, while in the cluster phase the solid particles agglomerate with one another and are enmeshed in the dispersed phase. The shape of clusters is in general irregular, and their size, highly variable. It seems that the clusters transform from strands at the center of the bed into spheres near the wall. The radial distribution of cluster concentration corresponds to that of solids suspension density.