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Show • further optimize the existing burner geometry (FGR rates and air staging ratio) with respect to emissions, with both preheated and cold combustion air and at turn-down • perform a spatially detailed characterization of the burner so that regions of NO x formation and high flame radical concentrations can be identified, this information is essential for the rational further optimization and scale-up of the burner. This paper discusses the results of both the parametric burner optimization as well as the detailed burner characterization. 2 Experimental and Equipment 2.1 StAR Burner To achieve low NOx and CO emissions in applications with furnace temperatures up to 1650 K (-2500 OF), with combustion air preheat temperatures up to 1100 K (-1500 OF), the StAR concept embodies staged air supply and flue gas recirculation to the fuel rich zone of the flame (Figure 1). The combination of these two approaches enables three NOx reduction mechanisms. The concept provides a low temperature (due to FGR), fuel rich primary zone, reducing the formation of prompt and thermal NO, followed by a lean secondary zone. In addition, part of the NOx present in the recirculated flue gas is "reburned" in the primary zone, leading to further reduction in the NOx emissions. The StAR burner is equipped with an internal jet pump, driven by the primary fuel/air mixture, which provides recirculation of about 30% of the total flue gas to the primary zone of the flame. Due to the inherent self-proportioning entrainment of the jet pump, the FGR fraction is maintained substantially constant over the entire firing range, without the help of external controls. The initial prototype tests at MIT clearly demonstrated the potential of the burner to achieve low emissions «50 ppm) at air preheat temperatures as high as 1100 K (1500 ° F). At moderate preheat temperatures (530 K or 500 OF), NOx emission levels below 20 ppm were achieved (Figure 2). Based on this success, the 0.6 MW (2 MM Btulln) StAR II burners were designed and constructed (Figure 3). In October 1993, two burners were installed in a forge furnace at Schlosser Forge Company (Cucamonga, Ca), as part of a field experiment. The burners were proven to have good operating characteristics, providing excellent furnace temperature uniformity and efficiency, while achieving NOx emission levels ranging from 25 to 40 ppm (depending on operating conditions) during nomial operation; a 60-85% reduction compared to state of the art burner technology used under the same conditions. CO emission levels remained below 30 ppm under all operating conditions. Since then, the burners have been operated for normal production, to the satisfaction of Schlosser Forg . Nevertheless, further optimization of the burners, to allow even lower NOx emissions, and to improve the turn-down and start-up performance, were warranted. Additionally, a version of the StAR burner that operates with ambient air is planned for 1994-1995. For this new version, the perfonnance of the burner with cold air needed to be assessed. The optimization of the burner geometry S~. C~ \ |