NH3 co-firing strategy in 500 MW tangential utility boiler: Impact of blending methods

Abstract

Ammonia co-firing is increasingly regarded as an effective strategy to reduce CO₂ emissions in coal-fired boilers. In this study, we introduce and evaluate two innovative fuel blending methods for ammonia-coal co-firing in a commercial 500 MW utility boiler: burner blending and in-boiler blending. Using computational fluid dynamics simulations, we investigated the effects of 20 % ammonia co-firing on heat transfer efficiency, fuel burnout rate, and pollutant emissions. The results show that while ammonia co-firing effectively reduces CO₂ emissions, it also leads to decreases in the furnace and furnace exit-gas temperatures due to the lower flame temperature and increased moisture production. Specifically, the total heat absorption by the water walls and heat exchangers decreased by 4.58 % in the burner blending method and 2.27 % in the in-boiler blending method compared to that with pure coal combustion. Although ammonia co-firing suppresses the generation of thermal NO, overall NO emissions increase significantly due to the substantial release of fuel NO. However, the in-boiler blending method demonstrated superior NO reduction, reducing NO emissions by 13.48 ppm compared to the burner blending method. In addition, the in-boiler blending method showed better combustion stability, achieving faster ignition and reducing the amount of unburned carbon in fly ash by 0.97 %, compared to that with the burner blending method. This is likely due to the higher concentration of combustible gases near the burner in the in-boiler blending system. These findings indicate that the in-boiler blending method is more effective than the burner blending method for ammonia-coal co-firing in a 500 MW utility boiler. This provides valuable insights into the implementation of ammonia co-firing in commercial boilers as part of efforts to achieve carbon neutrality.