Effect of Biomass Char Injection Position on Combustion and NO Formation in a Tangentially Fired Boiler

To clarify the effects of biomass char injection position on combustion characteristics and NO formation, a three-dimensional CFD model of a 300 MW tangentially fired pulverized coal boiler was developed using ANSYS Fluent. The Realizable k-ε model, discrete phase model, species transport model, and P-1 radiation model were employed to describe the flow, combustion, heat transfer, and NO formation processes. The model was validated against field measurements under pure pulverized coal combustion conditions. Based on the validated model, five co-firing cases were designed by injecting biomass char through primary air nozzles located at five different elevations in the burner zone. The results show that biomass char injection position significantly affects furnace flow organization, heat release distribution, carbon conversion, and NO formation, while maintaining the overall tangential swirling structure. Case C achieved the highest outlet velocity of 10.42 m/s, which was 9.1% higher than that of Case E, and exhibited the lowest CO concentration, indicating improved carbon conversion performance. However, the intensified oxidation environment in Case C promoted fuel-N conversion and resulted in the highest NO concentration of 313 ppm. Case B achieved the highest outlet temperature of 1429 K, which was 6.8% higher than that of Case E. In comparison, Case D maintained a similar CO2 mole fraction of 0.1546 to Case C, which was 0.1545, while reducing the NO concentration from 313 ppm in Case C to 145 ppm, corresponding to a reduction of 53.7%. Therefore, Case D achieved the most favorable balance between carbon conversion and NO emission control under the investigated conditions. This study demonstrates that biomass char injection position is an important operational parameter for optimizing biomass utilization and reducing NO emissions in tangentially fired pulverized coal boilers.