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Learn more about our air quality control systems

For the denitrification of flue gases – i.e. the separation of NOx emissions – we offer you customised solutions depending on the required emission limits. Our portfolio includes systems integrated into the combustion process (primary measures for nitrogen oxide reduction) and separate (secondary) applications.

Selective Non-Catalytic Reduction (SNCR)

The selective non-catalytic reduction (SNCR) process separates NOx emissions by injecting a reagent into the first pass of the boiler. The reducing agent can be either ammonia water or urea (NH2CONH2), which reacts with the nitrogen oxides (NO, NO2) to form nitrogen (N2) and water.
The SNCR process reduces the NOx¬ emissions in the flue gas to values in the upper range of the BREF requirements.

Selective Catalytic Reduction (SCR)

If your project requires compliance with stricter NOx emission limits, we can offer a separate selective catalytic reduction (SCR) system to help you achieve NOx limits in the lower range of the BREF documents.

The SCR system essentially consists of the reducing agent injection, a metering and mixing section, and the catalytic reactor, which, depending on the requirements, is equipped with several honeycomb catalyst layers. The layers are made up of individual catalyst modules.
Before the flue gas enters the upper section of the SCR reactor, the reducing agent (either NH3 produced from urea or ammonia water) is finely atomised and evaporated in the flue gas channel. To optimise the reaction conditions, a static mixer is installed downstream of the ammonia water injection. This improves the mixing of the reducing agent with the hot flue gas. The amount of ammonia water to be injected depends on the quantity and NOx content of the flue gas.

While ensuring a low NH3 slip, the NOx emissions are separated in the reactor. Selective reduction at the catalyst produces nitrogen (N2) and water vapour (H2O) from the nitrogen oxides (NO and NO2) by adding ammonia water (NH4OH). To control the intensity of the reactions, the catalyst used is specially tailored to the requirements of your process in terms of its chemical, physical, and geometric properties.

Depending on the project-specific conditions, the SCR can be designed as a High-Dust, Low-Dust or Low-Temperature application. The High-Dust SCR is integrated directly into the boiler passes, where the flue gases still have the temperature of about 300-400 C° required for the catalytic reaction. In the Low-Dust variant, the SCR is installed downstream of the flue gas cleaning system. Pollutants such as SOx or dust are already removed from the gas, which has a positive effect on the service lifetime of the catalytic converter. In order to reach the temperature required for denitrification, the flue gas is (re)heated e.g. with a gas/gas heat exchanger, steam heat exchanger or gas burner. The design of a Low-Temperature application also provides for the integration of the SCR downstream of the flue gas cleaning system, but without the installation of heat exchangers.

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