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.

Ammonia Injection Grid

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.

SCR machine

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.

When is SCR applicable?

SCR system has the highest level of efficiency for NOx reduction and can reach performance up to 98% reduction with less than 2 ppmvd of NH3 slip.  

An SCR system is recommended when the following conditions are met: 

  • The temperature of the flue gas shall be between 180 °C and 450 °C 
  • Limited presence of catalyst poisons in the flue gas 
  • Available space to install the AIG and Catalyst 

Why choose Yara?

With near 300 references in green field and retrofits SCR installation globally, we can meet your needs from design and fabrication to installation and commissioning. YARA SCR systems are capable of reaching the most stringent requirements and are present in all major industries: Coal, Oil and Gas fired Power plants, Waste to Energy, Biomass, Petrochemicals and various industrial applications. 

 Additional links: 

Do you have an upcoming project for SCR system: here are the basic info we need to start a quotation.  Adding link to download form. 

Are you interested to review our detailed reference list. Please contact us for additional info:  

Contact us

Wolfgang Kurka
Wolfgang Kurka
Sales Department – Global

SCR Industrial

Profile Picture Christian Lechner
Christian Lechner
Head of Global Sales – SCR Coal Fired Plants


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