Low-NOx conversion of pure ammonia in a cyclonic burner under locally diluted and preheated conditions

Chemical storage in suitable energy carriers is a requirement for any renewable source-based energy supply system. In this framework, owing to its very high hydrogen density and long established production processes, ammonia appears to be a very promising carrier. Furthermore, it is not necessary to use hydrogen extraction processes because ammonia can be directly used as a fuel in combustion systems. Nevertheless, there is a notable gap between the rising interest in ammonia-based power technologies and the actual knowledge and understanding of the physical and chemical underpinnings of its reactivity features. In particular, the viability of ammonia as an energy vector relies on the global process conversion efficiency, including the possibility of obtaining the required power levels at consumption points with minimal environmental impact. Therefore, this study is aimed at bridging the gap between the fundamental research and the development and implementation of ammonia-fueled combustion technologies in the context of eco-friendly, safe, and sustainable energy systems. The combination of high preheating and dilution levels, which are realized by means of a strong internal recirculation, leads to a very peculiar combustion regime. The potential of this oxidation mode, as realized in a cyclonic flow burner, to achieve stable ammonia combustion is explored to determine the influence of the operational parameters. The dependence of the process stability and NOx emissions on the equivalence ratio, inlet preheating level, and thermal load of the inflow mixture was studied by monitoring the temperatures and species concentrations to identify the optimal burner operating conditions.