SCRSystems

SCRSystems are selective catalytic reduction systems designed to reduce nitrogen oxide (NOx) emissions from combustion engines and industrial exhaust streams. They achieve emissions reductions by converting NOx into benign nitrogen and water in the presence of a reductant and a catalyst.

Operation: In a typical diesel SCR arrangement, a urea-based reductant (DEF or AdBlue) is injected into the exhaust. The urea decomposes to ammonia, which chemically reduces NOx on a solid catalyst substrate, usually located in a downstream module. The result is nitrogen and water vapor. Catalysts are commonly based on vanadium, copper-zeolite, or iron-zeolite chemistries, selected to match engine exhaust composition and temperature window. Some systems incorporate ammonia slip controls to minimize excess ammonia in the exhaust.

System components: The SCR system comprises a reductant storage and dosing system (tank, pump, lines, injector), an SCR catalyst module, a mixing/retrofit section, and a control unit. Sensors monitor NOx, ammonia slip, and catalyst pressure drop to manage dosing and diagnose faults. The system is designed to operate within a prescribed temperature range to maintain high conversion efficiency.

Applications: SCRSystems are used on highway and off-road diesel vehicles, heavy equipment, marine vessels, and stationary power generators to meet stringent NOx standards. They are often integrated with other aftertreatment devices, such as diesel particulate filters, in modular emissions control architectures.

Benefits and limitations: SCR systems offer substantial NOx reductions, enabling compliance with modern emissions standards without excessively increasing exhaust backpressure. They require a continuous supply of reductant and proper maintenance. Potential issues include ammonia slip, sensitivity to sulfur-containing fuels, catalyst aging, and cold-start limitations.