Thermal and Emission Performance of Fuel-Based Decarbonization Strategies in Coal-Fired Boilers

Coal-fired boilers remain critical for reliable power generation but contribute substantially to anthropogenic CO2 emissions, necessitating practical near-term decarbonization strategies that maintain combustion stability and thermal performance. This study experimentally evaluates the thermal and emission performance of multiple fuel-based decarbonization approaches under controlled combustion conditions representative of pulverized coal-fired systems. Biomass co-firing using Empty Fruit Bunch (EFB), ammonia substitution, coal blending, and coal additive integration were systematically investigated using a pilot-scale combustion test rig. Furnace temperature distribution and gaseous emissions (CO2, CO, NOx) were measured to assess combustion behaviour, emission trade-offs, and thermal stability. In addition, FactSage thermodynamic equilibrium simulations were employed to analyse ash transformation mechanisms, slag viscosity evolution, and mineral phase interactions. Results indicate that low-ratio biomass co-firing reduced CO2 emissions by approximately 9% while maintaining stable combustion characteristics. Coal additives significantly suppressed NOx formation (up to 29%) and improved thermal uniformity, whereas optimized coal blending achieved simultaneous reduction of NOx and CO2 with acceptable combustion performance. Ammonia co-firing demonstrated substantial carbon and sulfur emission reduction but introduced elevated NOx formation due to fuel-nitrogen chemistry. FactSage predictions revealed non-additive ash formation behaviour and highlighted the critical role of mineralogical interactions in governing slagging risk under blended fuel conditions. Overall, the integrated experimental-thermodynamic approach provides insight into fuel-ash-combustion interactions and demonstrates that fuel-based strategies offer a technically viable and scalable pathway for decarbonizing existing coal-fired boilers.