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Show - 4 - 2 .1.1 Test Conditions Seven flames (MI-M7), produced from for coal reburning using hvb Saar coal, were studied. One flame (M8), produced with natural gas reburning, was measured. The process conditions are listed in Table 1. The reburn zone stoichiometry, ARB, was set between 0.82 and 0.92 by adjusting the primary zone stoichiometry, Ap, in the range 0.95 to 1.1 and the reburn fuel fraction, iRE, from 10% to 30%. For each flame, the global mixing between the reburn fuel and primary combustion products was varied by adjusting the position of the reburn fuel injectors. Tertiary air was injected through two configurations to determine the influence of staged tertiary air addition on NOx reduction. In the normal air addition pattern, the tertiary air was injected immediately downstream of the reburn zone through Pipes 1 and 2 (Pipes "1,2"), Figure 2. In the delayed air staging configuration, sufficient tertiary air was added through Pipe "2" to raise the stoichiometry to 1.0 and the remaining tertiary air was injected through Pipe "4". Before the experiments were conducted, the degree of mixing between reburn fuel and primary combustion products was estimated. CO2 was injected through the reburn guns to mix with 500°C air flowing through the precombustor. The mixing was calculated from the extent that the CO2 dispersed at the end of the reburn zone. The extent that tertiary air could be recirculated into the reburn zone was also measured before the experiments. Helium was injected through the tertiary air pipes and the concentration measured in the reburn zone. Table 1: Experimental test conditions Flame No. Primary stoich. Reburn Zone Reburn fuel frac.(%) stoich Furnace experiments Ml 0.95 coal 10 0.86 M2 0.95 coal 20 0.78 M3 1.04 coal 10 0.96 M4 1.04 coal 20 0.84 M5 1.10 coal 20 0.89 M6 1.10 coal 30 0.78 M7 1.00 coal 20 0.82 M8 1.00 gas 20 0.80 Reburn zone experiments RBI 1.00 coal 10 0.90 RB2 1.00 coal 20 0.80 RB3 1.05 coal 10 0.93 RB4 1.05 coal 20 0.85 RB5 1.05 coal 30 0.76 RB6 1.05 gas 13 0.92 RB7 1.20 gas 16 1.04 RB8 1.20 gas 25 0.95 |