The SCR dosing system injects the necessary volume of gaseous reducing agent (ammonia (NH3)) into the exhaust gas flow at the start of the mixing section.
The ammonia is stored as a pressurised liquid in industrial compressed gas cylinders. The ammonia is removed through extraction valves and evaporates during this process. A mixer with controlled flow regulators is used to introduce the volume of NH3 required for reduction into the exhaust gas flow.
Catalyst elements are fitted in the SCR reactor, on the active surfaces of which the NH3 then reacts with the components of the nitrogen oxides NOx – mainly in the form of nitrogen monoxide (NO) and nitrogen dioxide (NO2). These reactions reduce NO and NO2 to nitrogen N2. Water vapour H2O forms as a by-product. Depending on the application, the degree of NOx reduction to N2 ranges between 50% and more than 90%.
We can also design our SCR reactor so that it simultaneously acts as a silencer, removing the need for an additional exhaust silencer in some applications. If an additional silencer is used, please note that absorptive silencers in particular should only be placed downstream of the SCR catalyst; otherwise, any insulation wool that comes loose from the silencer may cause irreparable damage to the catalyst.