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System Introduction
   Home | System Introduction | Selective catalyst reduction denitrification (SCR)
 
Selective Catalyst Reduction Denitrification (SCR)


​SCR for the use of catalyst to reduce the pollutants and NO and other pollutants to N2 and H2O, reducing agent 20% to 25% of ammonia for its treatment than pure ammonia safety, and for the production of pure ammonia by-products (N2 + H2 to Hubble Method of ammonia synthesis of water to absorb NH3, NH3 distillation of the distillation column of the substrate), the price is not used, SCR reaction is:


          4NO + 4NH3 + O2 → 4N2 + 6H2O
          2NO2 + 4NH3 + O2 → 3N2 + 6H2O
          NO + NO2 + 2NH3 → 2N2 + 3H2O

Its side products are:

          2SO2 + O2 → 2SO3
          2NH3 + SO3 + H2O → (NH4)2SO4
          NH3 + SO3 + H2O → NH4HSO4

NH4HSO4, produced by the side reactions, is called ABS (Ammonia Bisulfide). ABS is a black viscous liquid at 320oC, which will fail. It is generally required to ensure that SO2 oxidation SO3 side reaction conversion rate to a certain extent.
(Catalyst: SCR catalyst to TiO2 as a monomer, the active material for the vanadium, molybdenum, tungsten metal oxide)




The figure shows a typical high-temperature SCR for the catalyst to have a suitable reaction temperature (typically 350oC), set between the economizer (Economizer) and APH.

SCR反應器
 


As shown above, the exhaust gas and dilution air are injected from the bottom AIG (Ammonia Injection Grid) in conjunction with NH3. For the NH3 concentration evenly distributed, AIG is usually composed of multiple NH3 nozzles, supplemented by dilution air to make the exhaust gas more homogeneous with NH3 Mixing, gas injection after the spoiler stirring, and then flow through the rectifier, and finally through the rectifier screen into the catalyst area.           SCR catalyst life of 16,000 Hr (two years), but this life refers to the catalytic activity degradation to the emission of NO concentration exceeds the emission standards, not complete loss of activity. So the SCR reactor will generally be more than a set of media placed in the discharge standards, more than the discharge standard is not replaced, but more place a layer of new catalyst to reduce NO emissions, and the original activity of the catalyst to continue to use, Media replacement cycle as shown below. This picture shows a three-year (24000 Hr) catalyst replacement cycle, since 24,000 hours to add new catalyst after the next replacement time of 77,000 hours; 107,000; 143,000 hours and so on.