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In order to produce coal containing less than 2% ash using a physical cleaning process, the coal must initially be ground to liberate the mineral matter. The result is a micronized feed material that cannot be efficiently treated using the commercial methods currently available. Therefore, an advanced physical cleaning technique for ultrafine coal, called"selective-shear coagulation", is presently being investigated. The process utilizes high shear conditions to overcome the strong electrostatic repulsive force between particles. The attractive hydrophobic interaction and van der Waals forces control the coagulation of the coal particles. The effects of various chemical parameters, such as pH and ion concentration, were studied. An optimum pH range was established for tap water and distilled water media. The presence of multivalent cations in the system increased coal recovery, but decreased selectivity. Physical parameters of the selective coagulation process, such as particle size, percent solids, and specific energy input, were studied. It was found that separation efficiency improved with decreasing particle size. An optimum feed percent solids was found by maximizing separation efficiency. In the case of distilled water, test results revealed that additional specific energy provided by mechanical agitation was required to induce coagulation after grinding. However, additional mixing was found unnecessary in the case of tap water. A continuous selective-shear coagulation process using an elutriation column as the separator was designed and characterized. A steady-state population balance model of the elutriation column was developed. The predictions were found to be in good agreement with experimental results. / Master of Science

Korean coals are typically high rank anthracite characterized by high ash content and difficult cleaning characteristics. The main objective of the study was to evaluate the feasibility of treating various size fractions within the coal using an assortment of physical coal cleaning technologies. Dry cleaning is preferred due to the friability of the coal. As such, three pneumatic processes were tested including Ore Sorting for the plus 10 mm material, Air Table Separation for 10 x 1 mm fraction and Tribo-electric Separator for - 1 mm fraction. The Dense Medium Cyclone is known to be one of the most efficient separation processes and thus was evaluated for the cleaning of 10 x 1 mm coal. To realize the optimum performances from the Air Table and Rotary Tribo-electric Separator, their operational variables were systematically studied using a parametric experimental design. In addition, the dense medium cyclone and X-ray Transmission Sorting trials were performed under various medium densities and separation settings, respectively. A comparison of the cleaning performance revealed that the Dense Medium Cyclone and X-ray Transmission Sorting proved to provide the most effective results with maximum ash rejection and combustible recovery. The tribo-electric separation process was ineffective while the air table provided modest ash reduction potential.