Fluidization characteristics and charging behavior of fly ash in a vibro-fluidized bed

Fluidization characteristics of fly ash were investigated in a fluidized bed subjected to mechanical vibrations. In the presence of mechanical vibrations, the minimum fluidization velocity decreased from 4.0 to 1.0 mm/s, and the pressure drop increased slightly. The charge-to-mass ratios of fly ash along the fluidized column revealed that charging behavior of fly ash in the freeboard region significantly differed from that in the dense bed region. In the dense bed region, the net charges of fly ash were slightly negative or almost neutral, whereas fly ash in the freeboard region tended to carry positive charges. Loss-on-ignition (LOI) of fly ash was examined in different regions of the fluidized bed, and the results showed that LOI varied considerably inside the column, generally being lower in the freeboard than in the dense bed since finer particles were entrained into the freeboard. In the dense bed, particle-wall collisions resulted in positively charged carbon and negatively charged ash particles, whereas carbon particles in the freeboard region tended to carry negative charges. The findings demonstrate the potential for separating unburned carbon from fly ash by utilizing a vibro-fluidized bed as a tribocharger. (C) 2011 Elsevier B.V. All rights reserved.