In this study, group C powder in Geldart's classification was added to a circulating fluidized bed or a fluid bed of group A particles. We define this system as a circulating powder-particle fluidized bed (CPPFB). The separation rate of fine powders from a CPPFB was investigated using two different types of solid collectors. A cyclone or a settling chamber was used as a solid collector. The effects of the superficial gas velocity (0.65-1.0 m/s), the holdup of fine powders in the bed (0-5 wt.%), and the size of fine powders (0.5-15 mum) on the separation rate of fine powders from the system were investigated. The separation rate increased with the increases in the holdup of fine powders in the bed and the superficial gas velocity. Irrespective of the type of the solid collector, the separation rate of fines was strongly influenced by the fine powder size and reached the maximum at a fine powder size around 3.5 mum. However, operation with a settling chamber causes a threshold of holdup of fine powders in the bed, below which the separation of fine powders did not occur. An empirical equation for the separation rates of fine powders of 0.5-3.0 mum in size from the CPPFB was obtained. (C) 2004 Elsevier B.V. All rights reserved.