Investigating the potential of a waste-derived additive for enhancing coal combustion efficiency and environmental sustainability in a circular economy

Abstract

This study examines the impact of a waste-derived additive from alumina and shale oil production on the performance of coal combustion. The effects of individual additive components were investigated under oxidant-limited and oxidizing conditions using the isothermal flow reactor (IFR) equipped with gas analysers. The raw materials, as well as fly chars/ashes derived from the IFR, were characterized using standard physicochemical analysis, oxide analysis, oxygen functional group determination, the ash fusion test, thermogravimetry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Results from experiments conducted under oxidant-limited conditions demonstrated that the analysed additive, at a 1% share, increased hydrogen content in char by over 3.5 times (from 600 ppm to 2160 ppm) and enhanced methane conversion by nearly 20%. Under oxidizing conditions, the additive reduced unburned carbon loss by approximately 50%, emissions of NOx from 400-460 ppm to 340–390 ppm and SO2 from 1410-1475 ppm to 1325–1410 ppm. The study emphasized the influence of moisture on thermochemical processes, confirming that a certain amount of water vapour accelerates the conversion of H2, SO2, and NOX. The analysis supported the commercial utilization of the additive from economic, environmental, and operational standpoints.