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Reduction of NOx emissions in combustion power plants - Expert Paper

The effective reduction of NOx emissions in combustion processes is a key objective for meeting environmental legislation. A generic term for NO and NO2 produced from the reaction of excess nitrogen and oxygen during combustion, especially at high temperatures, NOx is not only subject to legislative requirements for effective control on environmental grounds, but effective management also has important benefits for the effectiveness and efficiency of a combustion process.

In power plants and various other combustion processes waste NOx reduction, referred to as deNOx, is typically achieved by selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR). In SCR process, Ammonia (NH3) is injected into the gas flow from the combustion process; this reacts with NOx in the flue gas, in the presence of a catalyst, to form H2O and N2. The SNCR process requires the introduction and mix of Ammonia or Urea with flue gases in a hotter environment with a temperature optimized to between 800° - 950°C. Temperature control is important in the process, as low temperatures can cause a surplus of unreacted NH3, commonly referred to as Ammonia slip.