Experimental and numerical studies on the NO reaction pathways of NH3 cofiring with coal volatile matter
Jingyang Han, Yan Xie, Jun Li, Xin Liu, Wen‐Zhen Zhang, Heyang Wang
Abstract
Ammonia (NH 3 ) cofiring provides a promising solution to carbon reduction of coal-fired boilers, but it may lead to increased NO x emissions. However, many experiments observed that the NO x emissions exhibited an increase-then-decrease trend with the increase of NH 3 cofiring ratio ( R NH3 ), indicating that NO x could be controlled under high R NH3 . To reveal the underlying mechanism, the experiments of NH 3 cofiring with coal volatile were first conducted in a one-dimensional flow reactor to reveal that this trend is primarily attributed to the gaseous reactions of volatile and NH 3 . A chemical reactor network model was then constructed to investigate the influences of R NH3 on the NO reaction pathways of NH 3 . The predicted results replicated the increase and then decrease trend of NO x emissions as R NH3 increased beyond 25 %. It was found that NO formation is primarily controlled by the reactions between HNO/N and OH/H radicals. Under lower R NH3 , the concentrations of HNO/N increase with the increase of R NH3 leading to increased NO formation. Under higher R NH3 , however, much of the OH/H radicals are consumed by the dehydrogenation reactions of NH 3 which consequently inhibits the NO formation reactions. Therefore, the root mechanism of the increase-then-decrease trend of NO x emissions is attributed to the competition for the OH/H radicals between the initial and final steps of the NO formation reaction pathway.