The first tests on reducing NOx emi

The first tests on reducing NOx emission by means of combustion modification were performed in the late 1950s (Muzio and Quartucy, 1997). In 1959 the influence of O2 level on nitrogen oxides emission as well as fuel type was assessed in Southern California Edison's El Segundo Generating Station (Muzio and Quartucy, 1997). It is well known that main factors influencing the formation of nitrogen oxides in combustion processes are combustion temperature (the higher the temperature the higher the NOx formation), proportion between the amount of air and fuel, mixing degree of air, fuel and incineration products distribution. Hence, the main target of combustion modification techniques is to create oxygen deficient stoichiometric conditions, reduce flame temperature or to vary the residence time within different parts of the combustion zone (Gomez-Garcia et al.,2005; Javed et al., 2007). This can be achieved through the application of various technologies presented in Table 3.