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Air Quality Control Systems (AQCS)Selective Catalytic Reduction (SCR) System

  • Maximum Capacity

    1,050 MW

  • Max. NOx Removal Efficiency


  • Low Environmental Impact

    Slip NH3 < 2ppm

  • SCR Catalyst

    High Reliability
    High Durability

The selective catalytic reduction (SCR) removes nitrogen oxides (NOx) from flue gas emitted by power plant boilers and other combustion sources, and the catalyst is the key component of this system. Mitsubishi Hitachi Power Systems (MHPS) has compiled more than 40 years of experience in the supply of highly reliable SCR catalyst for its sophisticated flue gas treatment systems, contributing to the prevention of air pollution.

Special Features

We have supplied more than 1,400 SCR plants and catalyst units worldwide and have gained a larger market share with systems offering the following features:

  • High NOx reduction meeting required emission standards for all kinds of fossil fuels
  • Integrated NOx reduction linked with boilers/HRSGs
  • Best optimization of catalysts for customers‘ requirements
  • Multiple pollutant control to include mercury and low sulfur trioxide
  • High reliability
  • Long-term catalyst maintenance

Basic Principle of NOx Reduction

The basic principle of SCR is simple. Ammonia is injected into the flue gas and NOx is decomposed into N2 and H2O vapor. The SCR catalyst efficiently facilitates ammonia and NOx reactions. The process forms no harmful by-products. Also plants using the SCR catalyst are easy to maintain and are capable of stable operation.

Chemical Reactions

  • 4NO + 4NH3 + O2 → 4N2 + 6H2O
  • 6NO2 + 8NH3 → 7N2 + 12H2O

The SCR catalyst serves as the heart of the SCR system, and we provide both a plate-type catalyst and a honeycomb-type catalyst based on fuel type, system configuration, clients' needs, and other considerations.

Plate-type Catalyst
Honeycomb-type Catalyst

Our SCR system has been applied to many types of boilers, HRSGs, and heaters that burn various fuels. We are one of the original developers of SCR systems and has over 40 years of experience, dating back to the 1970s.

Conventional Boiler Application

SCR System Flow Diagram of Conventional Boiler
  • Application Range

NOx Removal Efficiency: Max. 95%
Treated Gas Flow Rate : 3,140,000 Nm3/h, wet
Fuel : Coal, Oil, Gas, Residual Oil Fuel, etc.

Gas Turbine Simple Cycle (GTSC) Application

SCR System Flow Diagram of GTSC
  • Application Range

NOx Removal Efficiency: Max. 95%
Treated Gas Flow Rate: 1,560,000 Nm3/h, wet
Fuel : Gas, Oil

Gas Turbine Combined Cycle (GTCC) Application

SCR System Flow Diagram of GTCC/HRSG
  • Application Range

NOx Removal Efficiency : Max. 95%
Treated Gas Flow Rate : 2,820,000 Nm3/h, wet
Fuel : Gas, Oil

Inquiries Regarding Air Quality Control Systems (AQCS)