MICROSTRUCTURAL ASPECTS OF THE BEHAVIOR OF CIRCULATING FLUIDIZED-BEDS

Local instantaneous and time-averaging suspension densities were determined in a 152 mm diameter by 9.3 m tall circulating fluidized-bed riser using a needle capacitance probe inserted from the side. Radial profiles were obtained at three different heights and for three different solids circulation fluxes for sand particles of mean diameter 148 mum. The results confirm that local densities are greater near the wall than in the interior of the column. The fast-fluidization regime is shown to consist of a developing flow with transfer of particles to and from the wall region. An intermittency index, which would be zero for perfect core-annulus flow and one for perfect cluster flow, is used to characterize the flow; it shows that the behaviour is always between these two limits but tending towards the former with increasing height up the column.