Measurement and Control of Electrostatic Charges on Solids in a Gaseous Suspension. Final Report

摘要

Measurements of mean particle charges and charge distributions on flowing particles in a continuous copper two-phase test loop with a cyclone-venturi configuration have been made under various combinations of air humidities, conveying velocities and particle sizes. Air humidity was shown to have significant effects on particle charges. The charges became effectively below the minimum detectable level (10 sup -15 Coulomb) when the relative humidity exceeded 80%. For glass beads, a linear relationship between mean particle charge and relative humidity was correlated. Large particles carry a large mean charge and a small mean charge-to-mass ratio as expected. A significant finding was that the mean surface charge density remained almost constant over a wide range of particle size. Pulverized coal particles flowing in pneumatic pipeline are naturally charged to a detectable level due to collisions with pipe walls. Systematic charge measurements of Anthracite coals, Medium Volatile Bituminous coals and Lignite A coals in a grounded copper pipe have been made with an upgraded charge measuring system. Both negative and positive charges were found for coal particles in all experiments. Effects of air humidity and conveying velocity on particle charges were examined. In the range of our experiments, the effects of solid loading (concentration) and electric floating of the pipe loop were found of secondary importance compared with the effects of humidity and velocity. Charge elimination techniques by strict humidity control and by introduction of charge carriers, such as minus 1 mu m 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. 35 refs., 41 figs., 8 tabs. (ERA citation 12:003322)