Elutriation of fines from gas fluidized beds: mechanisms of elutriation and effect of freeboard geometry

Abstract

Experimental work on the entrainment of Geldart group A and C powders was conducted in an 8.2 cm diameter column, fluidized batchwise with air at superficial velocities between 0.1 and 0.8 m/s. The effect of the freeboard geometry was also studied. The entrainment rate at low air velocities is strongly reduced by interparticle adhesion forces. For larger group A particles, gravitational forces dominate. At higher air velocities the hydrodynamic forces overrule adhesion effects. Experimental results are used (i) to define the critical particle size at which interparticle adhesion forces become significant, (ii) to check the applicability of established correlations for the elutriation rate constant K i ∗ in estimating the entrainment rates, (iii) to develop a mdel that relates entrainment to a monolayer of particles carried in the roof and/ or wake zone of erupting bubbles and (iv) to predict the effect of the freeboard diameter on the amount of powder carried over from the fluidized bed.