Insights into the NO removal mechanism by hydrazine

Hydrazine (N2H4 ) can be a better reductant than ammonia (NH3 ) for NO removal during the selective non-catalytic reduction (SNCR) process due to its wider temperature window. To better understand the DeNOx chemistry by N2H4 , this study conducted a kinetic modeling study for N2H4 /NO/O-2 based on recent NH3 oxidation models. Compared with previous kinetic models, the present model is more accurate in predicting a four-stage NO removal phenomenon over 673-1,523 K. In Stage I (673-848 K), N2H4 is more favorable to produce NH2 via N1 pathways, which mainly reacts with NO to proceed DeNOx pathways. In Stage II (848-1,048 K), the reaction sequence N2H4 -> N2H3 -> H2NN -> NO2 -> NO prevails, decreasing NOx removal ratios. In Stage III (1,048-1,248 K), the branching fraction of H2NN = N2H2 increases, resulting in less NO2 and more N2H2 being produced. The NO removal efficiency is further increased. When the temperature exceeds 1,248 K, i.e. Stage IV, NH2 is favorable to produce NH via H-abstraction reactions, which can be subsequently oxidized to produce NO. Additionally, the present model is also validated against experimental data at various oxygen contents, suggesting that the NO removal efficiency is less affected by the oxygen concentration