Abstract
A commonly used method to reduce the emissions of NO x in CFBC (circulating fluidised bed combustion) boilers is to add NH 3 (SNCR (selective non-catalytic reduction)) in the cyclone inlet. However, experience shows that the conversion of NO x is sometimes ineffective. In this work, it was found that under conditions in which combustion occurs in the cyclone, the reduction of NO x could be improved by at least 30% by shifting the position of ammonia addition to the inner vortex of the cyclone. Under conditions in which no combustion occurs in the cyclone, the CO emission was found to be decreased by 60% by taking the same measures, without any significant change in NO x reduction and NH 3 slip. The decrease in CO is explained by competition for OH radicals between NH 3 decomposition and CO oxidation. The position for ammonia addition in the cyclone was found from laboratory experiments of the mixing characteristics of such cyclones and modelling of the SNCR reaction under well-stirred conditions.
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