Multi-Dimensional Optimization of Coal–RDF–Ammonia Fuel Blends: Exergetic Efficiency and Environmental Impact

Coal-fired power generation remains a major source of anthropogenic greenhouse-gas emissions, motivating low-carbon co-firing strategies compatible with existing infrastructure. This study presents an integrated thermodynamic and environmental assessment of a ternary coal–RDF–ammonia co-firing system, combining Aspen Plus equilibrium simulation, second-law exergy analysis based on the Szargut–Styrylska correlation, and Response Surface Methodology (RSM) optimization. Twelve blend compositions spanning a wide range of coal, refuse-derived fuel (RDF), and ammonia fractions were evaluated. A validated optimum blend was identified that simultaneously maximizes combustion-chamber exergetic efficiency and minimizes equilibrium CO2, SOx, and NOx emissions relative to a pure-coal baseline. The RSM model achieved excellent statistical fit and identified the directional sensitivity of efficiency to the RDF and ammonia content. A key trade-off is identified between thermodynamic performance and kinetic NOx risk: ammonia-rich blends improve equilibrium-based efficiency but may increase real kinetic NOx formation, requiring advanced combustion control for safe industrial deployment. These findings position ternary co-firing as a promising transitional decarbonization pathway for the existing coal fleet.