Fuel Staging Burners for NOx Control

Low excess air, flue gas recirculation, air staging and burners-out-of-service have all been utilized extensively to reduce the emissions of NOx from industrial burners and utility boilers. New restrictions in parts of the US and elsewhere, however, have defined levels that are more and more difficult to achieve. Specifications of 75 ppm and even 40 ppm as the maximum allowable concentration are becoming common. Fuel staging has proven to be able to achieve these more restrictive NOx levels in most cases. The results of an extensive research and development program are presented in which the fuel staging technique has been applied to burners for industrial and utility boilers. Burners ranging in size from 25 MMBtu/hr to 100 MMBtu/hr were used in the study. The benefits of combining fuel staging and flue gas recirculation are also presented.