SCR (Selective Catalytic Reduction) is a selective catalytic reduction technology. At present, ammonia catalytic reduction method is the most widely used technology. It has no by-products, no secondary pollution, simple device structure, high removal efficiency (up to 90%), reliable operation, and easy maintenance. Selectivity means that in the presence of oxygen and in the presence of oxygen, NH3 preferentially undergoes a reduction and removal reaction with NOx to form nitrogen and water, without oxidizing with the oxygen in the flue gas.

Its main reaction formula is:

(1) 4NO + 4NH3 + O2 → 4N2 + 6H2O

(2) 2NO2 + 4NH3 + O2 → 3N2 + 6H2O

In the absence of a catalyst, the above-mentioned chemical reaction is only carried out in a very narrow temperature range (about 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 pre-conditioning. 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 can be ignored.