For centuries, combustion reactions have been an efficient means for creating electricity fit to power anything. They also create a considerable amount of NOx, or nitrogen oxide, which harms the environment because it contributes to the proliferation of acid rain and smog. There is a human cost to this. In 2012, the World Health Organization estimated seven million people died prematurely due to air pollution partially made up of NOx.

To retain the efficiency of gas-based processes without emitting significant NOx, many power plants implement Selective Catalytic Reduction systems, or SCR. These systems initiate a secondary reaction downstream from combustion that neutralizes nitrogen oxides before they leave the facility. To better understand how Selective Catalytic Reduction systems work, read this helpful guide to the process’s stages and its chemical underpinnings.

The Path of SCR

First, the downstream combustion exhaust gases deliver nitrogen oxides to an SCR reaction chamber. In this space, the exhaust gases encounter ammonia (NH3), the reactant that neutralizes NOx. The two substances thoroughly diffuse together so there is optimal contact between them. Then, the two contact a catalyst, usually consisting of vanadium or tungsten oxide.

This catalyst sets off a reaction between NOx and NH3 in the presence of oxygen gas (O2) that yields harmless N2 gas and water vapor (H2O), beautiful in its simplicity and effectiveness. From there, the gases are ready for emission. See Figure 1

Figure 1 – Basic SCR Process

The Role of a Catalyst

Another element of how Selective Catalytic Reduction systems work involves the work of a catalyst. Technically, catalysts lower the activation energy necessary for a reaction to occur. Catalysts are not reactants themselves, but rather facilitate the process between two or more react-able substances. Throughout their life, these catalysts require consistent maintenance to ensure the catalytic surface remains available as reactants proceed past.

Retrofitting or building in SCR systems requires a knowledgeable and capable partner. Contact SVI Dynamics for information about how we can help you specifically.