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Show thereby likely increasing thermal N O x . The original firing system at Ladyzhin was nominally designed to operate with 10 percent of the total F G R flow to the furnace at the upper F G R position. This capability was retained in the reburn system design. The U.S. team, in the preliminary design analysis, concluded that an upper F G R flow of 8.7 percent effectively controlled furnace horizontal exit gas temperature as well as contributed to controlling N O x (Table 2). Within the operational requirements of the boiler, it is apparent that upper furnace F G R flow should be minimized to minimize NOx. Figure 14 illustrates the relationship between NOx and changes in boiler MWe output (boiler load). As boiler M W e output is reduced, N O x decreases. At lower electrical and steam production rate (and analogously lower fuel consumption rate), furnace gas temperatures typically decrease. Under these conditions, thermal N O x can be reduced significantly, which is consistent with the overall N O x reductions seen in Figure 14. f< o ^5 Co^O-o +* k-k. o O E a. a. 'X**- *' O•? 500 450 400 350 300 250 200 150 100 50 0 Figure 14: Post-Retrofit NOx Emissions vs. Boiler M W e Output Finally, Figure 15 essentially summarizes Ladyzhin reburn system emissions performance, operating in a preliminary optimized condition. Figure 15 plots N O x emissions as a function of percent 0 2 downstream of the economizer (excess air level) both before and after reburn system retrofit. C O emissions are also plotted as a function of percent 0 2 downstream of the economizer. N O x reduction from baseline with reburn is influenced by operating economizer excess air level. Initial parametric test results from this boiler show average N O x reductions of approximately 50 percent from a baseline pre-retrofit level of 600 p p m (0.82 lb/106 Btu). During initial testing, variations in boiler operations and conditions have resulted in a range of N O x reductions from 40 to 60 percent. Additional testing and analysis is currently underway to further define the results and optimize the system performance. It should be noted that these substantial NOx reductions are achievable at CO levels of 250 p p m or less. C O levels could be substantially decreased (to less than 100 p p m ) by 16 11-12 220 240 260 280 300 MWe |
