Study on Mechanisms of NOx Formation and Inhibition during the Combustion of NH3/CH4 and NH3/CO Mixtures

Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NOx) emissions. Co-firing ammonia with an industrial by-product gas (with CH4 and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NOx generation. Currently, the research on NOx formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NOx formation and inhibition mechanisms during the combustion of NH3/CH4 and NH3/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (alpha), temperature, residence time, and fuel concentration, the key factors influencing NOx generation and inhibition were further analyzed. The results showed that when alpha was no less than 1, the production of NOx initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 degrees C to 1500 degrees C, the amount of NOx generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH3/CH4 and NH3/CO, the emissions of NOx were higher than those during pure ammonia combustion.

Automated summary

Ammonia is an ideal renewable fuel and hydrogen carrier, but it has low reactivity, slow flame-propagation speed, and high nitrogen oxide emissions risks. Co-firing ammonia with industrial by-product gases is a cost-effective method to improve its combustion characteristics, but NOx generation needs attention. This study investigated the factors influencing NOx formation during the combustion of NH3/CH4 and NH3/CO mixtures and found that the proportion of ammonia and temperature played significant roles.