Technical application of SNCR denitration technology in boiler denitration

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As providers of steam and hot water for industrial production, industrial boilers are essential consumables for industrial development and daily life. In the application of industrial boilers, those that burn coal, as well as power plant boilers, produce large amounts of nitrogen oxides, which cause severe air pollution; therefore, boiler denitration has also become an issue that cannot be ignored. In boiler denitration technologies, SNCR denitration technology has become the preferred choice for denitration in many small and medium-sized boilers. SNCR stands for Selective Non-Catalytic Reduction denitration technology, and it is currently the second-most widely used denitration technique in China, after SCR. Compared with the SCR denitration technology, the SNCR denitration technology does not require a catalyst; in addition to ammonia, urea can also be used as the reducing agent in this process. It features low investment costs, low operating expenses, and short implementation times. However, the larger the boiler, the lower the denitration efficiency, which is why SNCR technology is more suitable for small and medium-sized boilers. As SNCR technology becomes more mature, it is gradually being applied to large boilers. The SNCR denitration technology involves injecting reducers such as NH3 and urea into the boiler to undergo a selective reaction with NOx; since no catalyst is used, it is necessary to add the reducers in the high-temperature area. The reducing agent is injected into the furnace chamber at a temperature of 850–1100°C, where it rapidly thermally decomposes into NH3, which then reacts with NOx in the flue gas to produce N2 and water; this technology uses the furnace chamber as a reactor. The denitration efficiency of the SNCR flue gas denitration technology is generally between 30% and 80%, and it is greatly influenced by the structural dimensions of the boiler. With SNCR technology, the current trend is to use urea instead of ammonia as a reducing agent. In the range of 850–1100°C, the main reactions for the reduction of NOx using NH3 or urea are as follows: when NH3 is used as a reducing agent, 4 NH3 + 4NO + O2 → 4N2 + 6H2O; when urea is used as a reducing agent, NO + CO(NH2)2 + 1/2O2 → 2N2 + CO2 + H2O