What is SCR?

Selective Catalytic Reduction (SCR) is an advanced emission control technology used primarily to reduce nitrogen oxides (NOx) from diesel engine exhaust. It's widely employed in industries such as automotive, power generation, and marine transportation to meet stringent emissions regulations. Diesel engines equipped with SCR systems often exhibit improved fuel efficiency compared to older emission control technologies.

How SCR Works

• Injection of Reducing Agent:
  1. A liquid reductant, typically urea-based Diesel Exhaust Fluid (DEF), is injected into the exhaust stream upstream of a catalyst.
  2. The urea decomposes into ammonia (NH3) at high temperatures.
• Catalytic Reaction:
  1. The exhaust gases mixed with ammonia pass through a specialized SCR catalyst.
  2. The catalyst facilitates a chemical reaction between NOx in the exhaust and the ammonia, converting NOx into harmless nitrogen (N2) and water (H2O).
• Key Reactions:
  1. 4NO+4NH3+O2→4N2+6H2O
  2. 2NO2+4NH3+O2→3N2+6H2O

The process significantly reduces NOx emissions, often achieving up to a 90% reduction.

Applications

• Automotive: Heavy-duty trucks, buses, passenger cars with diesel engines.
• Power Plants: To reduce NOx emissions from combustion processes.
• Marine Engines: Complies with IMO (International Maritime Organization) Tier III standards.