Selective Catalytic Reduction (SCR) technology brings NOx from the flue gas to nitrogen and water using NH3. It works as a reducing agent to specifically react with NOx in flue gas under a catalytic impact. The reactor is placed between the boiler economizer outlet and air preheater inlet, with the temperature ranging from 320℃ to 400℃. The complete process occurs because of the reducing agent, which works as a chemical reactant, ammonia.

With its high potential denitrification efficacy of over 90%, the SCR denitrification catalyst is a mature and reliable technology. The basic to this prevails in controlling the escape rate of NH3 and the conversion rate of SO2 while offering top denitrification efficacy to ensure the SCR system works securely and steadily.

The underlining principle of SCR is simple. Ammonia, when inserted in the flue gas and NOx, is divided into N2 and H20. The SCR denitrification catalyst effectively helps with ammonia and NOx reactions. There are no hazardous byproducts. Also, the SCR catalyst is simple to maintain and allows convenient operation.

Chemical reaction under SCR


The SCR catalyst works efficiently as the core of the SCR system. The plate-type or honeycomb-type catalyst is used depending on fuel type, the configuration of the system, requirements of the clients, and other aspects. The design and selection rely on the condition and ingredients of the flue gas. The design is impacted by several interactional aspects:

  • NOx removal rate
  • Volume of catalyst
  • Escape rate of NH3

The catalyst is majorly available in three forms- corrugated plate, honeycomb, and plate type.

Features of Selective Catalytic Reduction technology for denitrification

  • The SCR technology provides a list of effective catalyst selection processes for major flue gas content and dust composition parameters. Streamlining the selection of catalyst enhances the catalyst’s service life and avoids any collection of dust on the catalyst, thereby lowering system resistance.
  • Several EPC projects use the technology providing immense experience in steel framework design, building, and erection handling.
  • Depending on the streamlined design of the flue arrangement, NH3 homogenization system, deflector arrangement, and ammonia air mixer, you can enhance the system’s reaction efficacy and lower ammonia usage.
  • Long-run catalyst maintenance.
  • Highly reliable
  • Efficient pollutant control
  • Integrated NOx reduction in HRSGs and boilers

The SCR system has been used on different boilers, heaters, and HRSGs, which burn different fuels. Some of its application includes:

  • Conventional Boiler Application: It uses coal, oil, and gas as fuel with a NOx removal efficiency of 95%.
  • Gas Turbine Simple Cycle: It uses gas and oil as fuel and has a NOx removal efficiency of 95%.
  • Gas Turbine Combined Cycle: It uses gas and oil as fuel and has a NOx removal efficiency of 95%.

Major companies use the SCR denitrification catalyst process to avoid waste and residue. It also helps with the easy and convenient working of the system. The specifications and application of various SCR catalysts are assessed and compared for best use.