DeNOx plant with selective catalytic reduction SCR
NOx is a generic term for the nitrogen oxides that are most important for air pollution, namely nitrogen oxide (NO) and nitrogen dioxide (NO2). These gases contribute to the formation of smog and acid rain and affect tropospheric ozone.
There are three main pathways for NOx formation:
- Thermal nitrogen oxides are formed at high temperatures from molecular atmospheric nitrogen and the oxygen in the combustion air.
- Prompt nitrogen oxides are also formed from atmospheric nitrogen and atmospheric oxygen in the presence of hydrocarbon radicals.
- Nitrogen oxides from the nitrogen present in the fuel are formed from chemically bound nitrogen (e.g. in the form of amines).
In combustion reactions, nitrogen oxides are therefore almost always formed.
In the case of NOx, the limits have been significantly reduced in recent years, posing increasingly difficult challenges for plant operators. And this is exactly what P&P uses its DeNOx plants for.
The P&P DeNOx plant enables the removal of these dangerous nitrogen oxides (NOx) by adding ammonia (NH3) or urea ((CO(NH2)2) by using selective catalytic reduction (SCR). The end products of the denitrification process are harmless molecular nitrogen (N2) and water (H2O).
The most important reactions can - exemplary for ammonia - be summarized in simplified form according to the following desired reactions:
4NO + 4NH3 + O2 → 4N2 + 6H2O
2NO2 + 4NH3 + O2 → 3N2 + 6H2O
These reactions are operated slightly overstoichiometrically, whereby the strictest limit values can be adhered to by optimal operating conditions.
Preferably, honeycomb catalysts with square channels are used, which consist of titanium dioxide, vanadium pentoxide and tungsten dioxide. By using a catalyst, the reaction of NOx with the reducing agent in the SCR process is accelerated on the catalyst surface and therefore takes place at much lower temperatures (approx. 250 to 450°C). The catalyst also enables better utilization of the reducing agent and thus permits higher separation efficiencies.
SCR is the most effective method for reducing nitrogen oxides (NOx) in exhaust gases!
It is used for example in:
- Combustion plants
- Waste incineration plants
- Gas Turbines
- Industrial plants
- Combustion engines
The chemical reaction at the SCR catalytic converter is selective, which means that nitrogen oxides (NO, NO2) are reduced preferentially, while undesirable side reactions such as the oxidation of sulphur dioxide to sulphur trioxide are largely suppressed.
The SCR process is extremely versatile and economical in its application.
Selective non-catalytic reduction (SNCR) is a secondary process for flue gas denitrification. By thermolysis, ammonia (NH3) or urea is reacted with the gaseous nitrogen oxides (NOx) to form water vapour and nitrogen.
Ammonia (NH3) or urea (NH2CONH2) is injected as an aqueous solution at temperatures between 850 and 950 °C in several levels directly into the combustion chamber. There it reacts with nitrogen monoxide (NO) to form nitrogen and water vapor. Due to the side reactions that occur, larger quantities of ammonia or urea are required for the SNCR process compared to the SCR process. Shown here as an example for NH3:
4NH3 + 3O2 → 2N2 + 6H2O
Advantages of a P&P - DeNOx plant:
- Versatile in use
- Highly effective in the removal of NOx
- Perfectly adapted to the customer situation
P&P DeNOx plants are offered by us as a complete solution - turnkey plant or as an engineering package. We are happy to assist you with a specific DeNOx plant solution tailored to your needs.
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