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Show control systems such as Selective Catalytic Reduction. Thus, the StAR technology offers industrial furnace owners and operators a cost-effective compliance solution. Industrial Burner Design Following the prototype testing, a field demonstration model of the StAR burner, designated StAR II, was designed and constructed [Ref. 3]. This burner, shown in Figure 3, includes many refmements engineered by Hauck to produce an attractive commercial product. It was sized specifically for use in a forge furnace owned by Schlosser Forge in Cucamonga, California This burner has a design firing rate of 2 MMBtuIhr and uses combustion air preheated to 700 - 755 K (800 - 900~. The StAR II burner is equipped with an internal jet pump, driven by the primary fueVair mixture, which provides recirculation of about 30% of the total flue gas to the primary zone of the flame. All internal surfaces of the burner are made of high temperature refractory material, compatible with the service requirements. Final Optimization Testing and final optimization of the StAR II burner was conducted at the GRIIDOE Burner Engineering Research Laboratory [Ref. 4]. The StAR II burner was installed in the BERL furnace, a 0.9 x 2.1 m (3' x 7') vertical furnace with an octagonal cross section, where extensive parametric studies were carried out to optimize performance. These data were collected at furnace temperatures of 1505 - 1560 K (2250 - 2350r). To provide insights on flame structure and NOx formation, spatially detailed flame characterizations were carried out for several operating conditions. Through these measurements, regions of NOx formation and high radical concentration were identified. Strategies were then developed to reduce the NOx fonnation, which was most significant at the interface of the primary combustion zone and the secondary air jets. After optimization of the burner geometry, parametric studies were carried out to characterize the effects of flue gas recirculation (FGR) rate, air preheat temperature, excess air level and turndown on NOx emissions. As was shown in the MIT tests, the operating parameter with the strongest influence on NOx emissions was the FGR rate (Figure 5). Besides its effect on NOx emissions, the FGR caused the flame to become transparent, although the ultra-violet flame scanner was still able to detect a strong signal. Although this mode of combustion differs from a normal, luminous diffusion flame, it is also distinctly different from "flameless oxidation" [Ref. 5] in which the flame is lifted from the burner. For most metals processing applications, a stable, attached flame is desirable for safe operation and to prevent hot-spots in the furnace. The amount of recirculated flue gas that can be accepted by the StAR burner is limited by the jet-pump capacity and by flame stability at low air temperatures. The effect that high levels of air preheat would have on NOx formation in conventional burner systems is offset in the StAR burner by the high recirculated flue 9 |
