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SCR (Selective Catalytic Reduction) NOx Removal System

Nitrogen oxide (NOx) in exhaust fumes from factories and power stations undergoes a photochemical reaction triggered by powerful ultraviolet rays in sunlight to produce toxic photochemical oxidants such as ozone, which are the primary cause of photochemical smog that is harmful to plants and humans alike. NOx also undergoes a chemical reaction in the atmosphere to form nitric acid, which oxidizes water in lakes, rivers and soil and causes acid rain that is harmful to plants and animals. Hitachi Zosen is helping to reduce atmospheric pollution with NOx removal catalysts and denitration systems that render NOx harmless via a decomposition reaction with ammonia.

Denitration system

NOx is present in combustion gases emitted by stationary facilities such as thermal power plants, iron mills and chemical plants. The denitration system separates NOx into harmless nitrogen and water via a reaction with ammonia, thereby reducing overall NOx emissions.

System components

The denitration system consists of a NOx-removal catalyst, denitration reactor, ammonia injection system, ammonia dilution system, and ammonia storage and supply tanks. Hitachi Zosen provides NOx-removal catalysts and SCR systems to a variety of industrial fields including gas turbines, boilers (particularly coal-fired and heavy oil-fired boilers), diesel engines, refuse incinerators, ethylene cracking furnaces, petroleum reforming furnaces, and sintering furnaces.

Typical Flow of SCR System


NOx-removal catalysts

Since we began developing NOx removal catalysts in 1969 and commercialized them in 1973, Hitachi Zosen has implemented many improvements. We began supplying the current product NOXNON700 in 1987 and offer this product to customers not only in Japan but also in the U.S., China, the Middle East, and many other places around the world.


Concept of SCR System

Features of NOXNON700

  • High specific surface area (up to 1,500 m2/m3)
  • Lightweight and compact
  • Low pressure loss
  • Applicable for a wide range of reaction temperatures
  • Applicable for a wide variety of fuels.

Major records of delivery

Starting with the first domestic order in 1974, Hitachi Zosen has delivered over 330 systems to clients in the United States, China, South Korea, Taiwan, Saudi Arabia and Qatar as well as other territories.
Major installations in recent years are listed below.

Country amount of exhaust gas Completed Note
Japan 36,000Nm3/h 1998 For waste incineration plant
Japan 2,690,000Nm3/h 1999 For coal boiler
America 454,000Nm3/h 2005 For coal boiler
Korea 1,576,584Nm3/h 2006  
Saudi Arabia 1,367,135Nm3/h 2009 For gas turbine
China 2,917,036Nm3/h 2011 For boiler
Japan 47,000Nm3/h 2011 For Marine diesel engines
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