Upgrading low-rank coal using a dry, density-based separator technology

Low-rank coal such as the coal in the Powder River Basin (PRB) is typically direct shipped without any need for upgrading. Due to the lack of on-site processing capabilities, coal that is mixed with out-of-seam dilution during the mining process is typically left in the mine pit. In some cases, the loss could amount to 5% of the total reserve. Research conducted on laboratory and pilot-scale pneumatic air table separators indicates that sufficient upgrading can be achieved on the +1 mm fraction of the reject material to meet typical end-user specifications. Low-rank coals are especially susceptible to upgrading by density-based processes due its naturally lower density relative to higher rank coals. For example, a PRB coal containing 26% feed ash was reduced to 7% ash content with a combustible recovery of 83% on a dry basis from a coal source that was reject from the mining process. Partition curve data revealed the achievement of relatively low Ep values in the range of 0.12 to 0.22 with separation densities between 1.58 and 1.88 gm/cm³, respectively. Effective separations were achieved using air table separators for particle sizes larger than 1 mm.