Effect of ammonia blending on the emission behavior of NOx during coal combustion: A global meta-analysis

Abstract

Utilizing ammonia energy and fuels is crucial for advancing low-carbon power development and achieving carbon peaking and neutrality in the power sector. However, ammonia blending with pulverized coal increases NO_x emissions, and the specific contributions of various factors and their mechanisms in influencing NO_x generation are not well known. In this meta-analysis, 771 paired observations from 13 peer-reviewed articles were used to assess the effects of feeding properties and operating parameters of the ammonia-coal blending process on NO_x formation. The results showed that the application of ammonia fuel could increase NO_x emission during coal combustion, and the total emission was increased by 25.14 % compared with that of single coal combustion. Ammonia fuel's combustion ratio is the direct driver of emissions. Similarly, volatility and particle size of coal significantly affected NO_x emissions. Gaseous ammonia injection, compared to liquid, typically reduced NO_x due to quicker reactions and enhanced mixing. In terms of experimental scale, larger scale ammonia-coal blending tended to meet more technical challenges and thus affected the amount of NO_x being produced. Simulation tests could often achieve more accurate condition control and effectively control NO_x generation. CFB and BFB usually have better NO_x emission control effects than PC. In addition, the air staging and excess air ratio directly affected the temperature and oxygen concentration of the combustion area, thus controlling the redox reaction during the process, but the excess air coefficient was not the greater the better. This research is expected to provide new insights for reducing carbon emissions in coal-fired power plants and promoting clean co-combustion of ammonia coal.