SCR (Selective Catalytic Reduction) is a selective catalytic reduction technology. Catalytic reduction using ammonia is the most widely used system. It has no by-products, no secondary pollution, simple device structure, high cleaning efficiency (up to 88%), reliable operation and easy maintenance. Selectivity means that oxygen to NH3 undergoes a reduction and removal reaction with NOx, which is preferential to form nitrogen and water without being oxidized by oxygen in the flue gas.
Main Reaction Formula
4NO + 4NH3 + O2 → 4N2 + 6H2O
2NO2 + 4NH3 + O2 → 3N2 + 6H2O
The above-mentioned chemical reaction without the use of 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 the catalyst temperature caused by the reaction can be ignored.
(Selective Non-Catalytic Reduction) is a selective non-catalytic reduction method. It is an economical and practical NOx removal technology. Its principle is based on the use of NH3, urea [CO (NH2) 2], aqueous solutions. Before the boiler is atomized or injected into the boiler, it is atomized by the heat in the furnace. Sprayed into the furnace temperature range of 800 -1000 degrees, the reducing agent is quickly thermally decomposed into NH3 and other by-products, and then the NOx in the flue gas enters the SNCR reaction to produce N2. Therefore, it can be regarded as a selective chemical process. The reduction performance varies according to the flue gas temperature range, dosing points, nozzle placement and angles.
