Effect of fines hold-up in the freeboard on elutriation from a fluidized bed

Elutriation of fines within a bubbling fluidized bed of a two-particle system was investigated. The coarse particles were glass beads with a mean size of 545 μm. The fine particles with mean sizes of 81, 97, 115, 137 and 163 μm were used, respectively. Fines elutriated from the fluidized-bed column were weighted continually by an electronic balance (OHAUS TP4KD). Weight of fines hold-up in the freeboard was measured by the method of the pressure drop.The first-order equation was used to determine the elutriation rate of fines. Weight of fines hold-up in the freeboard was removed from the bed weight. The results show that the elutriation rate constant increases with superficial gas velocity. Also it was found that the elutriation rate constant decreases with increasing fine particle size and the freeboard height. In this study, the elutriation rate constant is lower than that from the first-order equation which does not consider fines hold-up in the freeboard indicating that the previous researchers overestimate the elutriation rate constant. Moreover, a generalized correlation was proposed correlating with superficial gas velocity, fine particle size and the freeboard height.