Influence of water addition on MILD ammonia combustion performances and emissions

The global energy shift towards the exploitation of renewable energy sources requires the development of proper energy storage and back-up technologies to deal with their intermittency and seasonality. Renewable energy chemical storage offers the possibility of efficiently storing large amounts of energy for long time. Ammonia is increasingly considered a feasible alternative to the use of hydrogen, due to the existence of already well assessed production technologies and transport infrastructures. However, it presents some challenges and the most relevant of these concern combustion stability and NO emissions when ammonia is burned in traditional conditions. A promising approach to ensure combustion stability while containing NO emissions relies on the shift from traditional to new combustion modes. MILD combustion has been proven as a reliable alternative to reach these targets. At the same time, water addition to reactants is a well-known strategy that promote DeNO routes in fossil fuel combustion. In this study, the influence of water addition to ammonia-air mixtures in a cyclonic flow burner was investigated to exploit the possible benefits of the simultaneous application of MILD combustion conditions and water addition. The experimental analyses were performed in premixed and non-premixed feeding conditions. Results indicated that water addition to the reactant mixture may represent a very simple and efficient solution in determining the reduction of NO emissions in ammonia combustion, especially in fuel-lean conditions. Moreover, the comparison between premixed and non-premixed configuration showed that it is possible to enhance the process performance through a simultaneous optimization of the burner internal flow-field and reactants injection strategies.