97/02575 Fine coal washability-liberation analysis by conebeam X-ray microtomography

Abstract

The performance of an inclined counter-flow settler was examined and found to offer significant cut point control in size classification, and hence a possible alternative to using hydrocyclones A suspension of fine bituminous coal, nominally less than 300μm was fed into the base of a 25 mm diameter tube, 1.4 m long, and inclined at an angle of 45°. The slurry flowed up through the vessel, depositing relatively coarse particles onto the lower portion of the wall of the tube, resulting in the remaining suspension becoming finer and less concentrated. The deposited particles slid down the wall, and were pumped from the base of the tube at an elevated pulp density, while the remaining suspension flowed out through the top of the vessel. Tests were conducted using eight different feed pulp densities, ranging from 2.4 to 21.7% solids. The classification or partitioning of the particles between the underflow (coarse) and overflow (fine) streams was determined for each of the feed pulp densities at six different flow rates. The maximum flow rate, relative to the minimum flow rate, was 4.5. The separation sues, defined by the D50, ranged from about 3 to 116 μm In order to reduce the degrees of freedom in the experiments, the underflow was operated to produce the maximum possible undertow concentration. The subsequent minimization of the water flow in the underfiow also resulted in a minimization of the fines entrainment into the underftow by the water. There was excellent agreement between the reduced partition curves from 38 of the 48 tests, with poor agreement for the experiments conducted at the lowest flow rate and or feed pulp densities. Furthermore, all of the data were found to correlate according to φ0 = 0.44(Vt/Vo) where φo is the volume fraction of the solids in the overflow, Vt is the velocity of the overflow through the tube, and Vt is the terminal velocity of the D50 particle.