Selective Catalytic Reduction (Selective Non - Catalytic Reduction, the following abbreviations for SNCR) technology is a mature commercial NOx control processing technology. SNCR method mainly in 850 ~ 1100 ℃, the chemical of nitrogen injection lean combustion flue gas, will be NO reduction, generated nitrogen and water. And Selective Catalytic Reduction (Selective Catalytic Reduction, SCR), due to the use of the catalyst, thus under the temperature of 300-400 ℃ removal of NOx. Both methods use the selective reduction of NOx by reducing agent to effectively avoid the reaction between reducing agent and a large amount of oxygen in lean combustion flue gas, so they are called selective reduction methods. The chemical reaction principles of the two methods are the same. But SCR technology system investment is larger.

In SNCR denitrification, ammonia or urea is sprayed into the furnace in the presence of no catalyst to reduce NOx to N2 and H2O. Reducing agent is sprayed into the furnace (850 ℃ ~ 1000 ℃), denitration efficiency 30% ~ 60%. At about 950 ℃ temperature range, the equation is:

4 nh3 + 4 no + O2 - > 4 n2 + 6 h2o

When the temperature is too high, the following side reactions will occur, and NO will be generated:

4 nh3 + 5 o2 - > 4 no + 6 h2o

Compared with other denitrification technologies, SNCR technology has the following advantages:

Satisfactory denitrification effect: the long-term field application of SNCR technology in CFB boiler can generally achieve 30 ~ 70% NOx removal rate.

Reducing agents are diverse and easy to obtain: in SNCR technology, reducing agents removing NOx are generally nitrogen-containing substances, including ammonia, urea, cyanuric acid and various ammonium salts (ammonium acetate, ammonium bicarbonate, ammonium chloride, ammonium oxalate, ammonium citrate, etc.). But the most effective, the most widely used are ammonia and urea.

No secondary pollution: SNCR technology is a clean technology, without any solid or liquid pollutants or by-products, no secondary pollution.

Good economy: because the reaction of SNCR is driven by the high temperature in the boiler, no expensive catalyst system is needed, so the investment cost and operation cost are low.

Simple system and short construction time: the main system of SNCR technology is the reducing agent storage system and injection system, the main equipment is tanks, pumps, spray guns and necessary pipelines, measurement and control equipment. Due to the simple equipment, the installation period of SNCR technology is short, only 2 days or so of furnace shutdown time is needed, and the furnace construction can be completed during minor repair.

Easy to operate: the SNCR technology does not need to change the boiler, nor does it need to change the boiler's conventional operation mode, and has no significant impact on the main operating parameters of the boiler.