When deciding how to address NOx emissions in your facility, it might be difficult to pick between Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) systems. The process behind each is similar, but they work differently in several ways. Look through this article to better understand the difference between SNCR and SCR.


Since the underlying reaction is nearly identical, there are of course many similarities between SNCR and SCR. The reagents—ammonia and nitrogen oxide (NOx)—react to form water vapor, nitrogen gas, and trace amounts of carbon dioxide. Both are also relatively simple to install in part because they are post-combustion implements. This means both SNCR and SCR don’t interfere with the actual fuel-burning process, but they react with the burned fuel product. These technologies can even be used in tandem; there are SNCR/SCR hybrid products some use to cut down on ammonia slip, which is the dissipation (waste) of unreacted ammonia.



The biggest contrast between SNCR and SCR is the absence of a catalyst in SNCR systems. Catalysts speed up a chemical reaction, resulting in identical chemical products to an uncatalyzed reaction. To understand SNCR, it’s important to know that a catalyst allows a reaction to take place at a lower temperature because the catalyst lowers the energy needed to begin the reaction. This is called the activation energy, and in SNCR systems it is comparatively high. This means the post-combustion flue gas needs to become quite hot. SNCR technology is typically used in waste management plants for burning waste and biomass, and it can reduce NOx by up to 70%. Reduction rates do vary though—they can be as low as 30%.


Since SCR systems utilize metal catalysts, the reaction activation energy is much lower and the flue gas is much cooler than SNCR. SCR is more efficient, and it reduces up to 90% of NOx without the variability SNCR involves. It is a widely used system especially well-equipped for large-scale facilities, and it even improves diesel fuel efficiency upon installation. If you’re interested in SCR equipment, contact our SVI Dynamics team. We can further explain the differences between SNCR and SCR and discuss the technology we uniquely offer.