The effects of urea molar ratio (1.0–2.0), reaction temperature and additives on NO reduction in flue gas have been determined in a pilot-scale flow reactor. A kinetic model is proposed for NO reduction rate with -NH and -CN in selective reducing agents (urea, cyanuric acid, ammonia). Two primary reactions can be expressed kinetically in the DeNO_x process as:

N.S. (nitrogenous species) + O_x (oxidants) → NO + … (k_f; rate constant for NO formation)

N.S. + NO → N₂ + … (k_r; rate constant for NO reduction)

in which the rate constants of k_f and k_r in the model are determined from the experimental data in the temperature range 1173 K–1373 K as:

k_f = 4.01 × 10¹¹ exp(–267/RT)

k_r = 7.24 × 10¹¹ exp(–230/RT)

The proposed model can predict the lowered activation energies caused by the addition of different species and molar ratio to NO.