AN INVESTIGATION OF THE CLEANING OF BITUMINOUS COAL REFUSE FINES BY AN EXPERIMENTAL HYDROCYCLONE

Special Research Report SR-58 The reduction of ash and sulfur in bituminous coal refuse fines by an experimental 15-inch hydrocyclone, operated at low inlet pressures, was investigated. The two objectives of the investigation were (1) to determine by statistical methods the combination of hydrocyclone dimensional parameters that together yield the optimum rejection of ash and sulfur constituents to the underflow product and (2) to analyze the relative contributions made by three different cone angles to the rejection of ash and sulfur constituents to the underflow product. A total of 36 tests were conducted in which the cone angleJ vortex finder lengthJ vortex finder diameter, and apex diameter were varied. To determine the optimum combination of dimensional parametersJ the Gaudin selectivity index formula was used to calculate two measures of performance for each hydrocyclone testJ based upon the rejections of ash and sulfur to the underflow product. Factorial design analyses were used to determine those dimensional parameters which caused significant changes in selectivity index values from test to test. Size distribution curves for all tests were plotted. The optimum combination of dimensi.onal parameters was found to be a 60 degree cone angleJ 15-inch long vortex finder having a diameter of 4-1/16 inchesJ and a 2-1/4 inch diameter apex. With this combination, 94.1 percent of the ash and 90.2 percent of the sulfur present in the plus 200 mesh feed solids were rejected to the underflow product. Recovery of plus 200 mesh non-ash clean coal was 33.7 percent and recovery of plus 200 mesh non-sulfur clean coal was 28.0 percent. The clean coal contained 5.1 percent ash and 1.8 percent sulfur. The relative effects of three cone angles were determined from size and specific gravity distribution curves obtained from three tests in which all dimensional parameters except for the cone angle remained constant. It was determined that both the specific gravity of separation and the size of separation of plus 200 mesh material increased in the order of 45, 60, and 95 degree cone angles. The size separation efficiency decreased with increasing cone angle. Rejection of ash and sulfur to the underflow increased when the cone angle was increased from 45 to 60 degrees, but decreased when the cone angle was further increased from 60 to 95 degrees.