Selective catalytic reduction (SCR) is a means of converting nitrogen oxides, also referred to as nitrogen oxides (NOx). When burning coal, petroleum products, natural gas as well as domestic and hazardous waste for industrial production pollutions are created, that are emitted with off gas. Thus, significant amounts of NOx, one of the main pollutants, forms despite optimized combustion. Through the reaction of nitrogen oxides with other atmospheric constituents, ozone is created and leads to the so-called summer smog. Other reaction products such as nitric acid, reach the water and soil with the precipitation in the form of acid rain. The resulting nitrate accumulation has a negative impact on human, plants and animals.
For these reasons almost all industrialized countries have adopted laws to strict nitrogen oxide emissions. GEA is a leader in DeNOx plants worldwide and develops and manufactures highly-efficient denitrification systems, individually tailored for different customer needs. Aqueous ammonia solution or urea is injected into the ductwork upstream of the SCR and evaporates immediately. Two-fluid nozzles (ammonia and compressed air) are used for the injection of the ammonia solution. A system of static mixers installed in the ductwork downstream of the ammonia injection points ensure adequate mixing of ammonia. The gas and ammonia mixture enters the unit from the top and exits horizontally at the bottom. A gas distribution system (swirl breaker) ensures adequate gas distribution over the entire cross-section of the unit. The reaction between ammonia and NOX is enhanced by the presence of the catalyst bed located at the bottom of the unit.
The reduction occurs in the presence of the catalyst at a temperature range between 250°C to 380°C (570°F to 716°F).
The main chemical reactions are:
4 NO + 4 NH3 + O2 -> 4 N2 + 6 H2O (1)
6 NO2 + 8 NH3 -> 7 N2 + 12 H2O (2)
NOx - Removal / Flow Sheet SCR - DeNOx
Different types of catalyst modules can be selected
The reduction occurs in the presence of the catalyst at a temperature range between 250°C to 380° C (570°F to 716°F).The catalyst bed is cleaned in an intermittent fashion (once or more per 24 hours) with compressed air and steam. A raking arm travels slowly over the catalyst, ensuring efficient cleaning of the top surface and inside the channels.
The catalyst bed is cleaned in an intermittent fashion (once or more per 24 hours) with compressed air and steam. A raking arm travels slowly over the catalyst, ensuring efficient cleaning of the top surface and inside the channels.
The ammonia feed rate is controlled by the NOX outlet concentration of the gas. The resulting products from chemical reactions are nitrogen and water vapor, which constitute the natural components of ambient air, and can be discharged to atmosphere.
Main Benefits
- Provide highest SCR performance efficiency with minimized ammonia slip
- Proven reliability over extended years of operation
- Reduced overall SCR pressure drop
- Ability to mitigate poisoning of the catalyst and extend the life of catalyst
Soot Blower System
There are sealing profiles in order to secure low ammonia slip.
Testmodule for analyzing activity losses
These modules are developed to analyze the module life-time on a regular basis.
Source: GEA Group Aktiengesellschaft
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