Charging of glass powder in a circulating fluidized bed

A laboratory scale circulating fluidized bed of 2.54 cm internal diameter was experimentally studied for the triboelectric charging of glass powder. Both copper and Plexiglas bed risers were investigated. The particle charge was measured by a sampling probe Faraday cage positioned at the exit of the freeboard with a second Faraday cage used to sample particles from the bottom of the bed itself. The rate of charge generation was inferred by current-to-ground measurements along the bed riser and also by a current ball probe at the top of the riser. In a related experiment, the particles were charged down a pipe chute. The charging magnitudes in the circulating bed were typically of the order 10/sup -10/ to 10/sup -9/ C/g with currents measured of the order 10/sup -9/ to 10/sup -8/ A. The variables investigated included particle diameter (5-44, 44-74, and 74-104 /spl mu/m), and superficial air velocity (56 to 116 cm/s). The variables affecting charging in the circulating bed were particle flow rate, particle diameter, superficial velocity, bed depth of particles and sampling height above the distributor. An anomaly was the sign reversal of the powder for particular operating conditions of the bed.