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

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. •The additive reduced UBC by approximately 50%.•The additive reduced NOx emissions by approximately 15%.•The additive reduced NOx emissions by approximately 6%.•The additive increased methane conversion by nearly 20%.