Fine coal preparation using novel tribo-electrostatic separator

Dry coal beneficiation has been examined by tribo-electrostatic method using Indian thermal coal sample from Ramagundam coal mines. The process of tribo-electric coal/ash cleaning is carried out with a newly built cylindrical fluidised bed tribo-charger with internal baffles, made up of copper metal. The charge transfer in coal maceral and mineral particles after repeated contact with copper plate tribo-charger is measured. Separation of particles in an electrostatic separator according to the polarity of particle charge generated during tribo-electrification is discussed with respect to gas flow rate and residence time in fluidised bed tribo-charger and the applied electric field. The coal and mineral particles charge with positive and negative polarities respectively. The magnitude of particles charge found to be relatively high illustrating greater efficiency of contact electrification in fluidised bed tribo-charger. The separation results with −300 μm size fraction of coal containing 43% ash showed that the ash content can be reduced to 18% and 33% with an yield of about 30% and 67%, respectively. These results are comparable to the maximum separation efficiency curve of washability studies on this coal sample. Since the ash percentage of coal particles collected in the bins close to positive and negative electrodes are about 70% and 20%, a better yield with low ash content can be accomplished on recycling the material.