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Show -11- 100.0..------------------, 99.5 99.0 g "5 98.5 o E ::J II) 98.0 97.5 o + o + • gbbase o gbng + gbgb 97.0 L....---'------'-_....&......-.-..L.._'---"-----"-_..L-.--'------L_....I...---I o 200 400 600 800 1000 1200 NO x [ppm, dry @ 3% 02 ) Figure 10 Burnout vs NOx - GB (primary) : baseline and with NG or GB as reburn fuel El Cerej on as primary fuel: Natural Gas or EI Cerej on as reburn fuel Burnout with the baseline flames using EI Cerejon coal, shows similar levels to those with Gottelborn coal (Tx > 99.5 %). Reburning with natural gas or coal (EI Cerejon) again shows very little difference in burnout although data with coal/ coal interaction was limited. It is significant that for the cases investigated, and particularly those with natural gas rebuming, that there are very few conditions at which NOx is less than 300 ppm. This is attributed to the natural gas which consumes all available O2 from the primary combustion zone, and thus forces the char from the primary fuel to bum in a lower oxygen environment. The case where burnout was less than 98 %, was with a Rff of 35 % and the tertiary air introduced as overfired air , i.e. position 4. With this condition, the natural gas impairs char combustion and burnout falls to an unexceptable level. Middleburg as primary fuel: Natural Gas or Middleburg as reburn fuel Baseline burnout results with Middleburg coal, are lower when compared to both the Gottelborn and EI Cerejon coal, and can be directly correlated to the volatile matter content. Although the data is limited with this coal, and all data was taken with the tertiary air through the annulus (position 1), a trend was observed with NOx levels increasing and burnout decreasing. 'Best' performance was obtained with natural gas as the reburn fuel, which highlights the importance of reburning with a high volatile fuel, in the presence of a lower volatile primary fuel. It is also important to note that even with natural gas as the reburn fuel, NOx levels cannot be reduced below 400 ppm as a result of the lower reactivity and volatile content matter of the coal. The low burnout values , |