What is the difference between SNCR and SCR denitration technologies?
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I would like to ask the experts: what are the differences between SNCR and SCR denitration technologies? We are a heating company that operates 3 coal-fired chain boilers with a capacity of 45 tons each; we use the magnesium oxide method for desulfurization. The new local standard DB12/151-2016 in Tianjin has tightened the regulations on nitrogen oxide emissions, reducing the allowed level from 400 mg per cubic meter to 200 mg per cubic meter. At present, our actual emission level is around 250–350 mg per cubic meter. What solution can ensure a long service life, minimize the risk of clogging, and reduce the likelihood of tube explosions? Thank you all
The difference is that one has a catalyst and the other doesn’t
Is it better to have a catalyst or not? What are the pros and cons?
Our boss said that one method involves spraying powder, while the other involves spraying liquid. Those that spray liquid have been phased out
SNCR: operating temperature range of 800–1100°C; no catalyst required; low denitration efficiency； SCR, in the medium-temperature range of 300–450°C; requires a catalyst and offers high denitration efficiency.
SNCR: no catalyst required, ammonia water is sprayed; low project investment； There is no elimination of such technologies; they are still widely used. Our factory started using SCR systems only at the beginning of 2015. These systems require catalysts, and the investment in such projects is high; the catalysts themselves are expensive, and they need to be replaced every about 5 years ； The powder spraying method mentioned by your supervisor is likely the technique of injecting lime stone into the furnace to remove sulfur dioxide
The suggestion of using method 7# is reasonable. Generally, SNCR is used first; if the standards are not met, then SCR is considered. In your case, SNCR alone will be sufficient to meet the standards
This post was last edited by hwhk999 on 2017-1-5 at 11:27. SNCR stands for Selective Non-Catalytic Reduction; as the name implies, no catalyst is required in this reaction process. The reducing agent is usually urea or an ammonia solution, which is directly sprayed into the high-temperature area of the furnace at 850–1150°C to react with Nox. The efficiency of SNCR is relatively low; 60%-70% is the maximum achievable level. SCR stands for Selective Catalytic Reduction; a catalyst is required, which means that the reaction temperature remains relatively low. The appropriate temperature range is generally between 320–420°C. The reducing agent is usually ammonia, which can be obtained from the evaporation of ammonia water or the pyrolysis of urea. This ammonia is sprayed into the appropriate temperature zone, typically in the vertical flue area. Using a catalyst installed inside an external reactor yields better results. By installing multiple layers of catalysts in an SCR, the efficiency can reach over 90%.
SNCR, or Selective Non-Catalytic Reduction, means that, as the name suggests, NOx is reduced to N2 using a reducing agent without the need for a catalyst. Generally, ammonia water or urea is used as a SCNR reducer; using ammonia water is simpler, as it can be directly sprayed into the high-temperature area of the furnace, at 850–950℃ ； If urea is used, a urea solution must first be prepared and then sprayed into the furnace, at a temperature of generally 950~1050°C. The SNCR efficiency is generally around 50%, with high ammonia escape. SCR, or Selective Catalytic Reduction, involves the use of a catalyst in addition to what is used in SNCR; typically, vanadium-titanium-based catalysts are employed. The reaction temperature ranges from 350 to 400°C. Many factories in China are now capable of carrying out this process. The reducing agent remains ammonia or urea, although there are slight differences in how they are applied: ammonia needs to be vaporized, while urea requires pyrolysis. SCR has high efficiency, but the catalyst cost is high, and it generally needs to be replaced every 3 years. For a small boiler like this, just installing an SNCR is sufficient; it’s very simple and the investment required is not high.