BACKGROUND Selective non-catalytic reduction (SNCR) is a proven technique to lessen nitric oxide (NO) emissions from stationary sources. However, the process using ammonia or urea as a reducing agent is only effective in a narrow and high temperature window, with the maximum NO abatement declining when increasing the oxygen (O-2) content. Large industrial boilers may be often under a variable load and an excess of O-2, which could decrease the effectiveness of the de-NOx process. This study investigated hydrazine (N2H4) as a reagent to improve SNCR performance. RESULTS NO reduction by N2H4 was experimentally investigated in a pilot-scale flow reactor. The effect of reaction temperature, molar ratio of NH2 to NO (normalized stoichiometric ratio, NSR), initial NO level and O-2 concentration on the NO reduction in flue gas containing 7.4-17.4% (v/v) O-2 at temperatures between 450 and 1100 degrees C was determined. The experimental results indicated that NO reduction by N2H4 was possible in dual temperature ranges, and the optimum reaction temperatures were about 580 and 1060 degrees C at NSR = 2.0. Moreover, the N2H4-NO reaction is less O-2-sensitive. A chemical kinetic model was developed to correctly describe the non-catalytic reduction of NO by N2H4 in the presence of O-2. CONCLUSION Hydrazine-based SNCR is an alternative method for NO reduction occurring in dual temperature ranges and excess O-2. The present model provided a satisfactory prediction of the experimental results, offering an effective tool for process simulation over a wide range of operating conditions. (c) 2019 Society of Chemical Industry