PARTICLE TRIBOCHARGING CHARACTERISTICS RELATING TO ELECTROSTATIC DRY COAL CLEANING

The velocity, number density and size of representative coal mineral matter particles were measured using laser phase Doppler velocimetry subsequent to their triboelectrification and while flowing through a constant electric field. For 60 mum diameter silica particles, the accumulated negative charge, q, could be represented by a normal distribution having an average value which was linearly dependent on the gas velocity in the tribocharger, V, and represented by q(Si) = [2.6V + 4] x 10(-14) C. The width of the distribution increased with increasing gas velocity. Physical mixtures of similar sized silica and glassy carbon, and coal, were also subjected to electrostatic separation while being monitored by the non-intrusive laser optical technique. The purity of the carbon separated from silica was > 90%, and dependent on the accumulation of either positive charge or no charge on the silica. For a high volatile A, Elswick seam, Pike County, Kentucky coal, the removal of mineral matter was comparable to that obtainable by wet processes, decreasing mineral matter content from 6.4% to 3.7% at a 72% combustible recovery.