Optimised NH3 injection in CFB boilers

A commonly used method to reduce the emissions of NOx in CFBC boilers is to add NH3 (SNCR) in the cyclone inlet. However, experience shows that the co nversion of NOx is sometimes ineffective, In this work, it was found that u nder conditions in which combustion occurs in the cyclone, the reduction of NOx 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 c ombustion occurs in the cyclone, the CO emission was found to be decreased by 60% by taking the same measures, without any significant change in NOx r eduction and NH3 slip. The decrease in CO is explained by competition for O H radicals between NH3 decomposition and CO oxidation. The position for amm onia addition in the cyclone was found from laboratory experiments of the m ixing characteristics of such cyclones and modelling of the SNCR reaction u nder well-stirred conditions. (C) 2001 Elsevier Science B.V. All rights res erved.