Development of an Ultra Low NOx Burner with Widened Stability Limits

This paper describes development process of a new ultra low NOx burner for industrial steam generators that targets 5 ppm NOx emissions on natural gas with primary emphasis on the burner operational limits over the turndown range and requirements to the combustion controls. Mixing of air and high percentages of recirculated FGR with fuel gas prior to ignition is used to control thermal and prompt NOx down to a few ppm range. Combustion driven pulsation is viewed as a major problem to be solved by burner design and high dynamic accuracy combustion controls. This paper specifically addresses the flammability and burner stability issues involved with ultra low NOx performance. The need for advanced combustion controls and flame scanners are also discussed. A variable geometry burner, with multiple fuel zones, described showed significant improvements to the stability limits with respect to allowable deviations in the amounts of FGR and excess air over wider turndown. The developed burner has demonstrated the target ultra low NOx levels of less than 5 ppm without air preheat and less than 9 ppm with air preheat up to 600°F.