Selective catalytic reducer (SCR)

Selective Catalytic Reduction (SCR) is an advanced emissions control technology designed to significantly reduce nitrogen oxides (NOx) in exhaust gases generated by industrial processes, among others.

How does an SCR work?
The operation of the SCR is based on the selective chemical conversion of NOx into nitrogen (N2) and water (H2O) through a catalytic reaction. 

It generally works by injecting a reducing agent and mixing it into the SCR reactor: In the SCR process, a reducing agent is injected into the exhaust gases, which can commonly be ammonia (NH3) or urea (CO(NH2)2) depending on the application and specific conditions. The gases with the reducing agent are mixed in an SCR reactor. It is important to achieve a uniform mixture of the reducing agent with the polluting gases.

In the presence of a specific catalyst, which is usually a zeolite or a metal-based material, a chemical reaction is initiated. The catalyst accelerates the selective conversion of NOx into nitrogen (N2) and water (H2O) through the following chemical reaction:

4NO + 4NH3 → 4N2 + 6H2O

As a result of the catalytic reaction, NOx is converted into nitrogen and water, which significantly reduces NOx emissions in the exhaust gases. Nitrogen and water are harmless products that can be safely released into the environment.

An SCR can operate in a wide temperature range, between 200 ºC and 450 ºC, and achieve reduction efficiencies that can exceed 90%.