Axial pressure profiles and solids concentration distributions in the CFB bottom zone

The solids concentration distribution in the bottom zone of a cold model CF B unit was measured with fiber-optical probes and by gamma-ray absorption. A higher solids concentration at the wall and a lower concentration in the center of the riser was found. Starting at the distributor, the time and cr oss-sectional average solids volume concentration increases slightly or rem ains constant with height up to a height H-b from where it drops off. H-b m ay be defined as the height of a bottom zone. The comparison with the axial pressure profile indicates the presence of strong local acceleration effec ts in the bottom zone. A core-annulus approach is presented to model the co ntribution of acceleration to the axial pressure drop. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.