The principle of SCR technology technique is adding reducing agent (ammonia or urea) in the flue gas; the reducing agent will react with nitrogen oxides (NOx) to produce harmless nitrogen and water under a certain conditions. In the absence of a catalyst, the denitration reaction will only occur in a very narrow temperature range (800-1200℃). However, the SCR technology is using a catalyst to reduce the activation energy, so that making the reaction can be performed at lower temperatures (320-400℃).

 

The most critical component in SCR system is the denitration catalyst, which typically cost 30%~50% of the total investment denitration unit. SCR denitration catalyst uses titanium dioxide as the carrier, metal oxide such as vanadium pentoxide and tungsten trioxide as the main active ingredient. Cellular, plate and corrugated are the three main structures of SCR catalyst, among them cellular and plate are mainstream products, but the cellular has the highest market share recently. The main active material of cellular SCR denitration catalyst is Ti-W-V, it formed of various materials and then dried, calcined.

 

Under the ideal conditions, SCR denitration catalyst could use for long-term, however, there are varieties of toxic factors affect the active ingredient in the actual operation. In the process SCR denitration catalyst being used, the activity of catalyst will decline because of the active ingredient grain growth or even sintering, namely thermal aging effect; at the same time a number of toxic substances will poison the catalyst, resulting in partial or total loss of activity; Moreover, some contaminants (such as oil, coke etc.) reduce the activity by accumulating on the surface or plugging honeycomb catalyst pores. The SCR catalyst lost activity can be reborn by cleaning, adding the active components vanadium pentoxide, tungsten trioxide and drying to respond the major activity.