What is SCR denitration technology?

Release time:

2022-08-09

SCR denitrification is selective catalytic reduction denitrification technology, sometimes called ammonia catalytic reduction denitrification, is in the upstream of the catalyst to inject ammonia or other appropriate reducing agent into the flue gas, using the catalyst (iron, vanadium, chromium, cobalt or molybdenum and other alkali metals) at 200-450℃ will be NOx in the flue gas into nitrogen and water. In common designs, liquid pure ammonia or ammonia water is used as SCR denitrification agent. Whatever form of ammonia is used, the ammonia must be vaporized and then mixed with diluted air or flue gas to be sprayed into the flue gas upstream of the SCR reactor using an ammonia injection grate. SCR denitration has been widely used at home and abroad.

SCR denitrification process has some obvious shortcomings: the composition of flue gas is often complex, some pollutants will make denitrification catalyst poisoning; Highly dispersed dust particles can coat the surface of the catalyst, reducing its activity. In SCR denitration system, there are some unreacted NH3 and SO2 in flue gas. Ammonium sulfate (NH4)2SO4 and ammonium bisulfate NH4HSO4 are generated. It is easy to corrode and clog denitration equipment, and reduce the utilization rate of ammonia. SCR denitrification equipment investment and operation costs are high, SCR denitrification system investment scale and operation costs are much higher than SNCR denitrification system. Liquid ammonia, as a SCR reducing agent, is a dangerous chemical, which has some hidden dangers in storage and use.

SCR denitration system uses liquid ammonia or ammonia water as denitration agent (reducing agent), which may cause secondary pollution due to ammonia escape; SCR denitration equipment must use expensive catalyst, denitration catalyst must be returned to the plant after a certain period of time for regeneration or scrap; Compared with SNCR and oxidation, the structure of SCR denitration device is more complex. However, SCR catalytic reduction denitrification technology has been widely used in large boilers or furnaces in recent ten years. This is partly due to the low denitrification efficiency (only 30% to 50%) of the traditional SNCR denitrification technology used in large boilers and furnaces, which cannot meet customer emission requirements.

SCR denitrification has a high removal efficiency of nitrogen oxides (up to 90%), and the temperature window is in the middle (relative to the high temperature and oxidation of SNCR). When the flue gas temperature is not suitable for other denitrification processes, SCR may be the ideal choice. The use of SCR for denitration in some furnace types has unique advantages. In some cases, a single denitrification technology cannot meet the emission standards, and SNCR/SCR mixed flue gas denitrification technology, oxidation /SCR mixed flue gas denitrification technology, or oxidation /SNCR mixed flue gas denitrification technology can also be used.

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