Numerical Simulation Study on the Combustion of Coal Powder in Swirl Burners with Different Ammonia Blending Ratios

To promote carbon reduction in existing coal-fired power units while ensuring stable operation, ammonia–coal co-firing has attracted increasing attention as a promising low-carbon combustion technology. This study developed a three-dimensional numerical model for a single swirl-stabilized pulverized-coal burner to investigate ammonia–coal co-firing under a constant total fuel heating input. The model was validated against reference measurements, with relative deviations of 2.97% for nitrogen oxide concentration and 2.92% for burnout rate. The effects of ammonia co-firing on flame characteristics, combustion performance, and species distribution were then evaluated. As the ammonia blending ratio increased from 0% to 20%, the peak furnace temperature decreased from 1597.35 to 1389.82 K, while the high-temperature region contracted. At the centerline end, the carbon dioxide molar fraction decreased from 16.46% to 12.03%, corresponding to a 26.9% reduction. Nitrogen oxide concentrations were lower near the burner but increased downstream after secondary-air mixing; the highest downstream concentration was 544.86 mg/Nm3 under a 15% ammonia blending condition. The present study clarifies how co-firing of ammonia with pulverized coal affects in-furnace temperature and combustion-species distributions in a swirl pulverized-coal burner, providing an engineering basis for low-carbon retrofits of existing coal-fired power units.