SNCR (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 at 800 -1000 degrees, the reducing agent rapidly thermally decomposes into NH3 and other by-products, and then NOx in the flue gas enters the SNCR reaction to produce N2. Therefore, it can be considered a selective chemical process. Reduction performance varies according to flue gas temperature range, dosing points, nozzle placement and angles.