Processes which clean the combustion gas after it has left the combustion space or chamber, by mechanical or chemical means, are referred to as exhaust emission aftertreatment or simply exhaust aftertreatment.

Examples of this are catalysts in passenger cars, or flue-gas desulphurization in thermal power plants.

The technique of selective catalytic reduction of nitrogen oxides in engine exhaust emissions is known as SCR (selective catalytic reduction). This process is also used in firing systems, refuse incinerating plants, gas turbines and industrial facilities.

The chemical reaction in the SCR catalyst is selective, as the nitrogen oxides (NO, NO2) are preferentially reduced, while other undesirable secondary reactions (such as the oxidation of sulfur dioxide to sulfur trioxide, for example) can be largely suppressed. Ammoniac (NH3), which is added to the exhaust gas, is required for this reaction.

The products of the reaction are water (H2O) and nitrogen (N2). From a chemical point of view, the reaction comprises comproportionation of the nitrogen oxides with ammonia to form nitrogen.

The use of SCR catalysts and injection control has become established with almost all major truck manufacturers in order to achieve the Euro 5 emission standard.

Thomas has developed special metering pumps designed for metering and conveying aqueous urea (AdBlue).

Both diaphragm pumps and reciprocating pumps, which are electromagnetically driven, are used. These operate throughout the service life of the vehicle.

In the case of thermal afterburning, the proportion of carbon monoxide (CO) in the exhaust branch can be reduced. Fuel (diesel and petrol) can be specifically injected into the exhaust gas for this purpose. This causes afterburning of the exhaust gases and the conversion of carbon monoxide into carbon dioxide (CO2).

Our proven electromagnetic reciprocating pumps, also successfully used in the field of thermal management in auxiliary heaters and engine-independent heaters, are used for this purpose.