4NO + 4NH3 + O2 → 4N2 + 6H2O
2NO2 + 4NH3 + O2 → 3N2 + 6H2O
The above-mentioned chemical reaction without the use of a catalyst is carried out in a certain temperature range (about 970 980 °C). When the catalyst is used, the reaction temperature can be controlled at 300-400°C, which is equivalent to the boiler economizer and air preconditioning. The temperature of the flue gas between the heaters is exothermic. Due to the low concentration of NOx in the flue gas, the increase in catalyst temperature caused by the reaction is negligible.