Synergistic Preheating Combustion of Low-Grade Coal Gangue and Salix: Burnout, NO x Emissions, and Submicron Particulate Matter Formation

The co-processing of coal gangue and locally sourced biomass enables energy recovery while enhancing the resource utilization potential of ash residues, resulting in significant economic and environmental benefits. The application of preheating combustion facilitates the disposal of low-grade coal gangue, which is otherwise difficult to combust, thereby improving the overall disposal efficiency. In this study, the synergistic disposal potential of low-grade coal gangue (CG) and Salix (SA) through preheating combustion was evaluated, with particular focus on burnout performance, NOx emission characteristics, and submicron particulate matter (PM1) formation. The results show that blending 30% SA reduces the unburned carbon content by 41.4%. At a preheating temperature of 900°C, the unburned carbon content decreases by 36.3% for pure CG and by 58.4% for the CG/30%SA blend, while NOx emissions decrease by 36.8 ppm and 43.9 ppm, respectively. Increasing the SA blending ratio from 10% to 30% initially increases the total yield of submicron particulate matter to 3.45 mg/g fuel, then decreases it to 3.02 mg/g fuel. Submicron particulate matter generated during preheating co-combustion of CG and SA was primarily composed of sulfur and aluminum. The formation of submicron particulate matter is a result of both combustion intensity and the original inorganic element content in the fuel.