Improved NO removal from flue gas by hydrazine and its mechanism analysis

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 (O2) content. Large industrial boilers may be often under a variable load and an excess of O2, 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 O2 concentration on the NO reduction in flue gas containing 7.4–17.4% (v/v) O2 at temperatures between 450 and 1100 °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 °C at NSR = 2.0. Moreover, the N2H4–NO reaction is less O2‐sensitive. A chemical kinetic model was developed to correctly describe the non‐catalytic reduction of NO by N2H4 in the presence of O2. CONCLUSION Hydrazine‐based SNCR is an alternative method for NO reduction occurring in dual temperature ranges and excess O2. 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.