Sudershan Ganguly

Chemical Leaching of High-Ash Indian Coals for Production of Low-Ash Clean Coal

It is difficult to reduce the ash content in Indian coals below a certain level by conventional physical beneficiation techniques due to their poor washability characteristics. In the present work, the effect of aqueous alkali leaching at elevated temperature, followed by acid washing on the removal of mineral matter, was evaluated for different captive coals of Tata Steel. The research study revealed that the ash content of all these coals could be reduced by more than 50% using this method. The degree of demineralization improved by increasing the reaction time, alkali concentration, and temperature, and by reducing the coal particle size. No significant change was observed in the alkali content, whereas silica, alumina, and phosphorous content reduced significantly after the final acid treatment. The mechanism of demineralization was evaluated by analyzing the coal samples before and after the alkali and acid treatments using X-ray diffraction (XRD) techniques. Overall, this study provides an insight into possible alternative methods of beneficiation for removal of ash from physically beneficiated high-ash Indian coals.

Maximizing Demineralization during Chemical Leaching of Coal through Optimal Reagent Addition Policy

Abstract The main objective of the optimal reagent addition was to maximize the quantity of product with minimal quantity of feed. In the present study, the optimal addition of reagents during the chemical leaching of coal was computed. Chemical leaching of coal was carried out using aqueous solution of caustic to dissolve and remove the mineral matter. Simulation studies were carried out using the optimal reagent addition for chemical leaching of coal in batch reactors. This was experimentally validated, using the bench-scale reactor setup with hierarchical optimization architecture. Chemical leaching experiments were conducted using West Bokaro coal. Samples collected at various time intervals during the experiment were analyzed. Variations in silica (SiO2) and alumina (Al2O3) concentrations, which were main constituents present in coal ash, were evaluated with respect to time for different concentrations of caustic. The simulation studies for optimal addition were carried out at 6, 8 and 10 intervals. An objective function, required for maximum ash removal, was solved, using sequential quadratic programming (SQP) algorithm to find out the optimum sequence for reagent dosing. An improvement of about 1% (wt) ash reduction on an average was observed with implementation of optimal reagent addition.