Performance and Effectiveness Study of Biomass Pellet Composition and Excess Air Optimization on Emission Reduction and Thermal Efficiency: Application in Coal-Fired co-Firing Systems

This study investigates the impact of excess air levels on pollutant emissions (CO, NO x , SO 2 , and CO 2 ) and thermal efficiency during the co-firing of 95% sub-bituminous coal with 5% biomass pellets of various compositions, including 100% sawdust, 100% rice husk, and blended ratios with cocopeat. Unlike previous studies that typically focused on single biomass feedstocks or limited emission parameters, this research provides a comprehensive evaluation of multi-biomass pellet combinations under varying excess air conditions and links combustion performance to both emission reduction and thermal efficiency. The work also integrates an Analytical Hierarchy Process (AHP) approach to identify the most critical emission parameters influencing environmental performance. The results demonstrate that increasing excess air generally reduces NO x and SO 2 emissions across all biomass types, while the optimal performance—marked by the highest thermal efficiency (74.40%) and the lowest emission indices—was achieved for the sawdust-based configuration. This integrated thermochemical–environmental assessment offers a novel framework for optimizing co-firing operations in existing coal-fired systems to meet low-carbon transition targets. • Impact of excess air on emission and efficiency in coal–biomass co-firing • Multi-biomass pellets: sawdust, rice husk, and cocopeat evaluated • AHP applied to identify key pollutant parameters for optimization • Sawdust-based pellets achieved 74.40% efficiency and lowest emissions • Framework supports low-carbon transition in coal-fired power plants