FLOW STRUCTURE IN A FAST FLUID-BED

The focus of this work is the determination of the flow structure whic h gives rise to the S-shaped profile of axial pressure gradient charac teristic of a circulating fluidized bed riser operating at fast fluidi zation conditions. The flow structure is characterised by measurement of radial profiles of solids momentum and solids volume fraction in a riser 0.09 m in diameter and 7.2 m high using a momentum probe and cap acitance tomography. The solids used were sand with a Sauter mean diam eter of 100 mu m and particle density of 2650 kg/m(3). The core-annulu s suspension structure typically found in the upper dilute region of t he fast bed is found to extend throughout the S-shaped profile and int o the lower dense region. However, the direction of solids Bow in the annulus changes from downwards in the upper dilute region to upwards i n the lower dense region. The interface between the regions (the middl e of the S) is found to be a region of relatively low axial solids mom entum throughout the riser cross-section. The fast fluidized bed struc ture suggested by these observations is presented in the form of a dia gram. (C) 1998 Elsevier Science S.A. All rights reserved.