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Show 4.4.1 T in Near-Burner Region In the near-burner region, the characteristic mean temperature (T)c IS taken to scale with the adiabatic flame temperature as (T)c = 0'. Tadiabatic (34) The proportionality constant 0' is obtained from the in-flame temperature measurements at baseline condi tions as 0' = (T)c Tadiabatic ba3eline (35) with data showing 0'1,2 ~ 0.88 for all scales. The adiabatic equilibrium temperature is computed by the STANJAN chemical equilibrium code [18] for the given combustion air temperature and the effective air-fuel equivalence ratio A' in (29). The temperature scaling thus reflects the effects of overall fuel-air ratio, staging, and combustion air preheating. The rms temperature fluctuation level in the near-burner region is taken as a = 0.25(T)c. 4.4.2 T in Flame-sheet Region In the flame-sheet region, (T)c is set to the adiabatic equilibrium value corresponding to a stoichiometric air-fuel mixture, as computed by the STANJAN equilibrium chemistry code [18]. As a result, (T)c in this region varies only with combustion air preheating. Temperature fluctuations are assumed to be insignificant within the flame-sheet, and consequently the NOx production in this region does not require the pdf approach described above. 4.4.3 T in Furnace Region The characteristic mean temperature (T)c in the furnace region scales with the effective air-fuel ratio )..' and the combustion air temperature in the same way as shown in equations (34) and (35), with the baseline (T)c set to the flue gas temperature at baseline conditions. The rms temperature fluctuation level in the furnace region can be expected to be significantly lower than that in the near-burner region, and thus is set to a = 0.1 (T)c. This also accounts for the measured spatial variations in temperature wi thin the furnace. The temperature in the furnace is affected by turndown, as evidenced by the flue gas temperature data. However the temperature at the end of the near-burner zone is independent of turndown. As a consequence, the high temperature volume in the furnace decreases with turndown. Results show that the contribution to total EINOx from the furnace region is comparatively small, nevertheless in the scaling model this effective reduction in volume is accounted for, and taken to scale the same way as in (11), namely V:j jeetive Vjurna ce . Q Q full-l oad (36) w~e~e Q is the actual the~'m~l i~put- an~ Q full-load is the design thermal input. 13 |