S3K SCR Systems

A selective catalytic reduction (SCR) system is an emissions-control technology that converts harmful nitrogen oxides (NOx) in exhaust gas into harmless nitrogen and water vapor.

It works by injecting a reducing agent, typically ammonia or a urea solution (such as diesel exhaust fluid, or DEF), into the exhaust stream upstream of a catalyst. As the exhaust and reductant pass over the catalyst, which is commonly made from materials like vanadium, tungsten, or zeolites, the NOx reacts with the ammonia and breaks down into nitrogen (N₂) and water (H₂O). The process is “selective” because the ammonia reacts preferentially with NOx rather than with the oxygen also present in the exhaust.

SCR systems are widely used in off road applications, locomotives, ships, power plants, and industrial boilers. They can cut NOx emissions by 90% or more, which helps reduce smog, acid rain, and respiratory health problems. The main tradeoffs are the need to periodically refill the reductant tank in vehicles, added system cost, and the need to keep the catalyst within an effective temperature range, generally around 200–400°C.