Numerical Analysis of Combustion Performance and Emission Characteristics of Co-Firing Coal–Gamal (Gliricidia sepium) in a Pulverized Coal Boiler

Co-firing biomass with low-rank coal (LRC) is a strategic approach to optimizing combustion and reducing emissions in pulverized coal (PC) boilers. This study utilizes three-dimensional Computational Fluid Dynamics (CFD) to investigate the co-firing of LRC with Gliricidia sepium (GML) in a 315 MW PC boiler. Four scenarios were evaluated: 100% LRC and GML blending ratios of 10%, 20%, and 30%. Results indicate that increasing GML fractions intensifies combustion and shifts heat release toward the lower furnace, improving temperature uniformity and lowering the Furnace Exit Gas Temperature (FEGT). Analysis of O2 and H2O distributions confirms that GML mitigates LRC moisture effects and enhances oxygen utilization. While biomass integration generally promotes carbon oxidation – reducing outlet CO2 – it also influences NOx formation. Notably, NOx emissions exhibit a non-linear trend, with the 20% GML ratio achieving an optimal equilibrium between high combustion intensity and emission control. Mechanistically, at lower GML ratios, dilution of fuel-bound nitrogen and moderate flame temperatures suppress both fuel-NOx and thermal-NOx. At 30% GML, intensified lower-furnace combustion raises local temperatures, promoting thermal-NOx formation. Overall, the 20% GML blend represents the most favorable configuration, significantly improving thermal performance and reducing environmental impact without inducing significant thermal non-uniformity. These findings suggest that moderate GML co-firing is a viable strategy for enhancing large-scale utility boilers.