Non-coking coal preparation by novel tribo-electrostatic method

A new laboratory fluidised bed tribo-electrostatic separator has been assembled and the beneficiation potential of thermal non-coking coal from Hingula block of Talcher coal field, India, is examined on this separator. The uniqueness of the separator originates from the efficient tribo-electrification of coal material in the cylindrical fluidised bed with internal baffle system. The collecting bins of the material underneath the copper plate electrodes are designed to function as Faraday cups such that the charge polarity and magnitude of particles in each bin can be measured directly. The liberation attributes of coal material is assessed by sink and float analysis of various size fractions. The mineral and maceral composition is determined by XRD and petrographic analysis. The separation tests were conducted at different tribo-charging and applied voltage conditions. The material collected in bins close to positive and negative electrodes show an ash content of 61% and 8% respectively, illustrating differential charge acquisition of mineral rich and coal rich particles during tribo-electrification. The charge results are in good agreement with the ash content of the coal material collected in the bins. The results showed that a clean coal of about 15% ash can be obtained from a coal containing 30% ash with about 70% yield. A better separation results can be achieved by recycling the material. The ash content in the clean coal is however limited by the liberation characteristics of the coal, which is evidenced by the SEM analysis of the particles in different bins. Thus, the tribo-electrostatic method observed to be a promising dry coal preparation technique. (C) 2008 Elsevier Ltd. All rights reserved.