Experimental investigation of NOx emissions in oxycoal combustion

Abstract This work presents the results of an experimental investigation on NO x emissions from coal combustion in a pilot scale test facility. Three oxidiser atmospheres have been compared, namely air, CO 2 /O 2 , and O 2 enriched recirculated flue gas. NO x emissions from two different combustion modes have been studied, swirl flame and flameless combustion. The influence of the burner oxygen ratio and the oxidiser O 2 concentration on NO x formation and reduction have been analysed. With increasing burner oxygen ratio, an increase of NO x emissions has been obtained for air and CO 2 /O 2 in both, swirl flame and flameless combustion. In case of the swirl flame, flue gas recirculation leads to a reduction of NO x emissions up to 50%, whereas in case of flameless combustion this reduction is around 40% compared to CO 2 /O 2 . No significant impact of the oxidiser O 2 concentration in the CO 2 /O 2 mixture on NO x emissions is observed in the range between 18 and 27 vol.% in swirl flames. An analysis of NO x formation and reduction mechanisms showed, that the observed reduction of NO x emissions by flue gas recirculation cannot be attributed to the reduction of recirculated NO x alone, but also to a reduced conversion of fuel-N to NO.

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