Experimental study on effects of air-staged strategy and NH3 co-firing ratios on NO formation characteristics in ammonia/coal co-firing process

Ammonia/coal co-firing in coal-fired power plants is an effective and promising route to achieve CO2 reduction. This paper studies ammonia/coal co-firing in a 45 kW wall-temperature controlled staged combustion furnace employing overall air-staged combustion technology to meet the goal of low carbon and low NOx emissions. The effect of different burnout air addition positions and combustion environmental temperatures on the NO emissions, as well as the CO and H2S release characteristics of ammonia/coal co-firing was studied for ammonia co-firing ratios ranging from 0 % to 100 % (calorific value), with bituminous coal as the experimental object. To offer a qualitative overview of the experimental results, chemical reaction kinetic calculations were performed. The position of the burnout air addition has significant effects on the ammonia/coal co-firing products. The further the burnout air addition position is from the burner outlet, the lower the NO emission. When the distance is too great, however, the improvement in NO reduction efficiency is limited, which might have a negative impact on combustion efficiency. At 1300 °C, the NO emission concentration is substantially higher due to the deterioration of SNCR (selective non-catalytic reduction) capabilities of NH3 at high temperatures. High temperatures also reduce coal char production, which results in less heterogeneous reduction reactions on char surface. Based on experimental results and chemical kinetic calculations, the release patterns and mechanisms of combustion products during ammonia/coal co-firing under various air-staged strategies were explored in this work, presenting a promising technically achievable solution for reducing CO2 and NOx emissions from the coal-fired power plants.