Evaluating the potential environmental impact of biomass combustion methods using quantitative universal exergy method

Combustion is one of the most important methods for utilizing biomass energy. However, there is currently a lack of systematic assessment of how different combustion technologies affect the environmental impact of biomass utilization. This study addresses this gap by assessing the potential environmental impact (PEI) of biomass combustion. The biomass combustion methods were divided into open burning, kW-grate, MW-grate, and CFBB (Circulating Fluidized Bed Boiler). Based on the analysis of gaseous pollutants (CO, CO2, NOx) in 31 literature samples, the PEIs of CO and CO2 produced by per kg of C (PEICO-C and PEICO2-C), and the PEI of NOx produced by per kg of N (PEINOx-N) were calculated for each sample. Subsequently, the PEIs of four biomass fuels with different C and N contents were determined. Key findings reveal that open burning yields the highest overall PEI (711.97–1,538.41 kJ/kg), primarily due to its high PEI for CO. While kW-grate combustion shows improvement, its high excess air ratio (1.6–5) limits its cost-effectiveness. In contrast, the CFBB method consistently demonstrates the lowest PEIs (450.25–841.43 kJ/kg) across different biomass fuels, establishing it as a superior technology for minimizing environmental impact. For MW-grate, the reciprocating grate results in a high PEI (515.6 kJ/kg) when the N content in biomass is high (i.e., 2.183%). This study provides a quantitative foundation for selecting environmentally optimal biomass combustion technologies.