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Show 9 emissions decreasing at a steep rate at low FGR levels and then gradually leveling off at high FGR rates. These figures also show that increasing the rate of FIR consistently reduces NOx emissions across the fu 11 range of FGR. FIR provided about the same percentage reductions of NOx at high FGR rates as with no FGR. NOx reductions with FGR only ranged from 63 percent at 25 11W to 74 percent at 15 MW with high excess O2• Maximum, FGR rates were generally limited by flame stability . NO,. reductions with FIR only were 48 percent at 25 MW and 68 percent at 15 MW, high 02. Maximum FIR injection rates were limited by maximum allowable burner fuel gas pressure. and not by flame stability. NOx reductions with FGR combined with FIR ranged from 79 percent at 25 1v.fW to 89 percent at 15 MW, high O2• Figure 6 presents the same test results as Figure 5, with NOx shown as a function of the relative heat capacity of FGR or FIR, expressed as Btu/hr°F. This allows the effectiveness of FGR and FIR to be directly compared. This figure shows that, on a heat capacity basis, the use of FIR only is much more effective than FGR only in reducing NOx emissions. Also the use of FIR in combination with FGR provides NOx reductions that are additive to those achieved with FGR only. Figure 6 also provides a relative comparison of the results obtained at Highgrove with FIR with results previously obtained with water injection at Haynes Units 3 and 6 and at the Onnond Beach Station. At the Haynes Units, water was injected using atomizers inserted through the oil gun passages. At Onnond Beach, water was injected into the heated combustion air. As shown in the figure, the FIR using steam injection appears to be more effective than water injection when compared on a heat capacity basis. These results indicate that NOx can be more effectively controlled by more intimately mixing the diluent with the reacting species in the flame zone. These results provide some indication that injection of steam into the fuel would be expected to be more effective than injection of steam through the oil gun passage. Operational Impacts. No adverse impacts of the FIR system on boiler operability were observed during the tests at Highgrove. No difficulties were encountered in operating the steam injection system. Flame stability was acceptable and no condensate was collected in the fuel system. Steam injection did not adversely affect flame stability even at the high FIR rates. The rate of FIR injection was limited by the high burner gas pressure, not by flame stability. CO emissions were essentially zero throughout the test, with no increase observed with FIR. Applicability of FIR Process to Utility and Industrial Boilers Possible techniques to implement FIR on a pennanent basis on utility and industrial boilers include: • Direct injection of steam into the fuel, • Modified burner nozzle to mix flue gas with the fuel at low pressure, A054E562.T |