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Influence of over fire air system on nox emissions - an experimental case study

In this work, various combinations of the NOx emission influencing factors and their combined effects in air staging combustion on level of furnace, using OFA, were investigated in an experimental lab-scale furnace. At this, process temperature were varied in the range from 950 oC to 1450 oC, excess air ratio in primary zone in the range l1 = 0.9 - 1.2, while distance of OFA nozzles from the burner outlet varied until a given distance of 2/5 of total length of furnace. Basic fuel is brown coal from Middle Bosnia coal basin, mixed in two coal blends and one coal-woody biomass blend, to combine an effect of fuel characteristics variation on NOx emission. Results shows that an average reduction of NOx emission over tested temperature range, when using OFA against conventional air supply with OFA swiched off, is 26.5%. At this, much more NOx emission reduction for two coal blends were occured at higher temperatures - at 1350 oC and above, where an average NOx emission reduction is 32.5%. Furthermore, it was found that the NOx emission decreased with an increase in distance of OFA nozzles from the outlet level of burner until a distance of 1/3 of total furnace lengh; with further increase of the distance, NOx emission is stabilised and no further effect to NOx emission reduction was observed, while CO emission and unburnt increased.
PAPER REVISED: 2018-07-23
PAPER ACCEPTED: 2018-08-08
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