THE ENTRAPMENT OF SOLID PARTICLES FROM A GAS-SOLID FLUIDIZED BED

Abstract

Entrainment of solid particles (Glass beads, d_p=300-600 μm, U_mf=14 cm/s) from a gassolid fluidized bed was studied experimentally by following the rise of bubbles and measuring the velocity of particles leaving the bed surface. Photographs of the freeboard were taken continually to follow the particle movement in it.
Based on analysis of these data, it was found that the particles in the wake for an isolated bubble scarcely contributed to entrainment but that bubble coalescence near the bed surface was the key factor in entrainment. Bubble bursting behavior was classified into four patterns:
(I) Isolated bubble
(II) Successively rising bubbles
(III) Coalescent bubble
(IV) Successively coalescent bubbles
For the first two groups, the particle velocity leaving the bed surface was usually less than the bubble rising velocity and for the latter two, it exceeded the bubble rising velocity.