Hydrodynamic dependence on riser diameter for different particles in circulating fluidized beds

With two different kinds of particles and three different circulating fluid ized (CFB) bed risers, the riser diameter influences on bed density for dif ferent particles were investigated by measuring the total pressure drop acr oss the whole riser and the axial profile of apparent voidage. The risers h ad the same bed height of 3.0 m but different inner diameters of 66, 97 and 150 mm, respectively. Particles of FCC and silica sand were used, which be long to types A and B of Geldart classification, respectively. It was found that riser diameter has opposite influences for Geldart A and B particles on the total pressure drop across the whole riser and the differential pres sure gradient (apparent solids concentration) at a specified bed elevation. With increasing riser diameter, these two pressure drops increase for grou p B but decrease for group A particles, consistent with several other liter ature measurements in pilot-scale risers. As a result of these different de pendencies of bed density on riser diameter, the saturation-carrying capaci ty, i.e., the solids circulation rate at the dilute suspension collapse, wa s also found to vary differently with riser diameter for different particle s. That is, the increase in riser diameter increases the saturation-carryin g capacity for Geldart A but decreases it for Geldart B particles. (C) 2000 Elsevier Science S.A. All rights reserved.