A Comparative Study of NO_x Emission Characteristics in a Fuel Staging and Air Staging Combustor Fueled with Partially Cracked Ammonia

Recently, ammonia is emerging as a potential source of energy in power generation and industrial sectors. One of the main concerns with ammonia combustion is the large amount of NO emission. Air staging is a conventional method of reducing NO emission which is similar to the Rich-Burn, Quick-Mix, Lean-Burn (RQL) concept. In air-staged combustion, a major reduction of NO emission is based on the near zero NO emission at fuel-rich combustion of NH₃/Air mixture. A secondary air stream is injected for the oxidation of unburned hydrogen and NH_x. On the other hand, in fuel-staged combustion, NO emission is reduced by splitting NH₃ injection, which promotes the thermal DeNO_x process. In this study, NO_x emission characteristics of air-staged and fuel-staged combustion of partially cracked ammonia mixture are numerically investigated. First, the combustion system is modeled by a chemical reactor network of a perfectly stirred reactor and plug flow reactor with a detailed chemistry mechanism. Then, the effects of ammonia cracking, residence time, and staging scheme on NO_x emission are numerically analyzed. Finally, the limitations and optimal conditions of each staging scheme are discussed.