NO_<i>x</i> Emission and Control in Ammonia Combustion: State-of-the-Art Review and Future Perspectives

Abstract

Global warming as a result of greenhouse gas emissions generated by anthropogenic activities (mainly the combustion of fossil fuels) has become an increasingly more severe challenge for all mankind. As a promising zero-carbon energy carrier toward the transition to a carbon-neutral society, ammonia has drawn broad attention from academia, industry, and government bodies. However, widespread applications of ammonia as a primary fuel in combustion devices require solutions for multiple technical challenges, among which the possibly very high nitrogen oxide (NO x ) emission in the flue gas is the most concerned one. In this regard, extensive research efforts have been devoted over recent years to a deep understanding of the NO x formation mechanisms, which, in turn, result in a number of NO x -inhibiting technologies successfully developed; these include staged combustion, ultra-lean combustion, moderate or intense low oxygen dilution combustion, plasma-assisted combustion, etc. In this review, a brief literature review has been performed on NO x emission from ammonia flames, with the emphasis put on discussions of advances in understanding chemical kinetics related to NO x formation and reduction, effective technologies for NO x abatement, and applications of these technologies in practical ammonia-fired combustion devices. This review can serve as a reference for future studies on NO x emission and control in ammonia flames and the promotion of ammonia as a zero-carbon fuel in practical applications.