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Show APPLICATION OF PREi\1IX COMBUSTION TO HIGH INPUT BURNER SYSTEMS With the prtmary burner core progressing through testing and dey lopment, we began to address the limitations of high excess air firing. Prototype operation was limited to 35% excess air due to the desired emission p rfornlance goals «20 ppmv NOx). While lean premix is ex eptional at inhibiting NOx fornlation, many applications cannot operate efficiently at these levated excess air levels. Therefore extra fuel nl ust be added to the systenl to bring the overall ratio to - 10% excess air. Control of the fuel supply nli xing and conl bustion is necessary to prevent excessive NOx formation. Since no further air is desired, suppression of the peak flame tenlperature must be acconlplished vvith a thermal ballast. The application environment itself is the best source for this ballast, with a large volume of "low" tenlperature, low oxygen content co nlbustion products already present. When the extra fuel is targeted to entrain cl large volunle of product gases, the resulting flame tenlperature is reduced. Figure 4 shows equilibriunl NOx formation with increasingly dilute mixtures. This dilute jet combustion technique is extrenlely effective at suppressing thernlal NOx production. The combination of a lean premix core with dilute secondary jet onlbustion yields a burner systenl that produces extremely low NOx and CO enl issions. In the prinlary stage roughly 65% of the fuel burns with a NOx nlission rate below 5 ppmv. The dilute jet conlbustion NOx levels are dependent upon furnace tenlperature and oxygen concentration, but vvith a 1600 F chanlber and 2% O2 product gases NOx production will be -20 ppmv for the renlaining 35% of the fuel. Both techniques produce these levels independent of each other, resulting in a final burner emission rate of less than 15 ppnlv. A schematic of the 4211 Magna Flame LE, that incorporates these elements, is shown in Figure 5. The complete control of reaction kineti s in the 4211 burn r s ries nlade it ideal for extension to large burner sizes. Simpl rules vver dey loped for reaction chamber and mi xer sizing ensuring consistent premix enlission perfornlance for the full burner family. Likewise, position and targeting for the |
