SCR technology for reducing NOx emissions

Selective catalytic reduction (SCR) is a technology used to reduce the level of nitrogen oxides (NOx) in the presence of a catalyst. Vaporized reagent (Ammonia or Urea) is injected into flue gas and reacts with NOx on the SCR catalyst resulting in nitrogen (N2) and water (H2O).

NO2 + NO + 2 NH3 ↔ 2 N2 + 3 H2O

4 NO + 4 NH3 + O2 ↔ 4 N2 + 6 H2O

2 NO2 + 4 NH3 + O2 ↔ 3 N2 + 6 H2O

The catalyst is made from Titanium, Vanadium and Tungsten. It increases the reaction efficiency but does not deteriorate during the process. Over time the catalyst deactivates and will eventually require replacement or rejuvenating.

To inject and distribute the reagent into the flue gas flow, Yara uses an ammonia injection grid with patented designs that achieves very high mixing rates in a confined space. The result is an almost full NOx conversion at minimum ammonia slip.

The AFCU both vaporizes the reagent and regulates the flow of reagent to be injected for proper performance of the SCR. All necessary components (valves, instruments, vaporizers etc.) are assembled on a metal frame skid. The skid is connected, wired and tested by YARA prior to delivery.