MEASUREMENT AND CONTROL OF ELECTROSTATIC CHARGES ON PULVERIZED COAL IN A PNEUMATIC PIPELINE∗

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Abstract
Pulverized coal particles flowing in a pneumatic pipeline are naturally charged to a detectable level due to collisions with pipe walls. Systematic charge measurements of Anthracite (AN) coals, Medium Volatile Bituminous (MVB) coals and Lignite A (LIGA) coals in a grounded copper pipe have been made with an upgraded charge measuring system. The net particle charges were found to be positive, although both negative and positive charges were detected in all experiments. Effects of air humidity and conveying velocity on particle charges were examined. The mean particle charge was found in the order of 10−12 Coulomb and the charge-to-mass ratio in the order of 10−5 C/kg. Charge elimination techniques by strict humidity control and by introducing neutralizing charge carriers, such as minus 1 μm activated charcoal fines, ammonia, and piezoelectric ionized gas were explored. Effective reduction of 70 % to 85 % of particle charges was achieved. A charge neutralization mechanism was proposed to interpretate the measured results.

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