Elutriation of very fine particles from fluidized bed - Effect of mean diameter of bed particles

The elutriation of fine powders (group C or group A powders in Geldart's cl assification) from a fluidized bed of fine-coarse particle mixtures in a st eady state is investigated. FCC and alumina particles of 12 mum to 91 mum i n diameter (group C and group A powders) were used as fines. Alumina partic les of 69 mum to 650 mum in diameter (group A and group B particles) were u sed as coarse particles. The effects of the weight fraction of powder in th e bed, superficial gas velocity, size of fine powder, size of coarse partic le, and mean diameter of bed particles on the elutriation rate constant wer e investigated. The following results are obtained. The elutriation rate constant of group A particles is affected by the properties of the elutriated particles and g as and by operating conditions such as gas velocity. However, the elutriati on rate constant of group C powders is not only affected by the above condi tions, but also by the weight fraction of the elutriated powder in the bed and sizes of both coarse particles and elutriated powder in the bed, that i s, the mean diameter of the bed particles. The elutriation rate constant of group C powders decreases with increases in the mean diameter of bed parti cles and with decreases in the size of group C powders under the condition of a constant superficial gas velocity. This finding Is quite different fro m that of elutriation of group A or group B particles.