Chemical Beneficiation of Physically treated Hingula coal on Laboratory scale

Abstract

Crude oil and coal are the backbone of energy chain for industrial growth, but limited production of oil in India makes coal as the only reliable source of energy. Due to non-availability of good quality coal, supply of high ash (15-55%) coal to power sector has increased over the years. Such coals cause erosion, difficulty in pulverization, low flame temperature and affect efficiency of thermal power station. Although coal is mostly beneficiated by physical method, but combining it with chemical method may improve the quality and efficiency of boilers/plant capacity while reducing the greenhouse gas emissions. This study is based on the treatment of Hingula coal (29.6% ash) obtained from Talcher coal field, Odisha. After physical beneficiation (prox. anal.: 13.3% ash, 49.0% FC, 37.7% VM and 11.8% moisture) material was chemically treated with different alkali and acids to further reduce the ash content. Process parameters such as alkali/acid concentration, time, temperature and pulp density were optimised for de-ashing of coal. Bench scale treatment with Na2CO3 solution for 60 min at 85 oC and 60% pulp density followed by acid wash with dil. HCl, reduced ash content to 9.8%. Similar results were obtained when coal was treated with 10% H2SO4 for 60 min at room temperature and 10% pulp density. Coal before and after chemical beneficiation was characterised by XRD and EPMA. Experiments were carried out on kg scale to validate the bench scale data. When physically beneficiated coal (~1.2 kg) was treated with 0.25N Na2CO3 solution for 60 min at 85 oC and 60% pulp density followed by acid wash with 1% HCl in an agitated reactor, ash content was reduced to 8.98%. The product is being characterised to ascertaining the properties of the demineralised coal.