ELUTRIATION OF FINES FROM GAS-FLUIDIZED BEDS OF GELDART A-TYPE POWDERS - EFFECT OF ADDING SUPERFINES

Experimental work on the entrainment of Geldart Group A powders was carried out in a 7.62-cm diameter column fluidized batchwise at velocities between 0.2 and 0.7 m s-1. Group C powders were added to a number of base Group A powders in proportions which ensured that they remained within Group A. The superfines influenced the elutriation rate constant K(i)*; at a given superficial gas velocity, K(i)* increased with decreasing particle size and then levelled off below a critical size. This effect results from interparticle adhesion forces. A method is presented for estimating the critical particle size at which adhesion forces become significant compared with gravitational and hydrodynamic forces, with an empirical equation to predict K(i)* below the critical particle size.