Segregation and attrition of polydisperse solids in a circulating fluidized bed

Fluidization of polydisperse mixtures of solids differing in size and/or density in a cold model CFB is studied. The attention has been focused on segregation and attrition phenomena with specific reference to conditions establishing in the primary zone of a CFB combustor. A purposely developed experimental apparatus is presented. Two bidisperse mixtures of granular solids were tested: a mixture of glass beads of different size and a mixture of silica sand and lime. Operating conditions (gas superficial velocities, solids mass fluxes) were such that hydrodynamic regimes ranging from dilute to dense bottom bed established in the riser. Segregation was assessed by periodic sampling of solids from the riser and the standpipe. Attrition by abrasion during tests carried on the sand-lime mixture was assessed by continuous collection of elutriated fines at the exhaust.