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. On the other hand, 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, the exploitation of ammonia as an energy carrier poses some relevant challenges. The most relevant ones concern combustion stability and NO x emissions, when ammonia is burned in traditional conditions. A promising approach to ensure combustion stability while containing NO x 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 x routes in fossil fuel combustion. In this work, combustion of ammonia-air mixtures assisted by water is studied in a cyclonic burner exercised under MILD operative conditions, to evaluate the effect of water addition on NO x emissions and process stability. The analyses were carried out in premixed and non-premixed feeding conditions. Results highlighted that water addition to the reactant mixture may represent a very simple and efficient solution in determining the reduction of NO x emissions in ammonia combustion, especially in fuel-lean conditions. Moreover, the comparison between premixed and non-premixed configuration shows that it is possible to enhance the process performance through a simultaneous optimization of the burner internal flow-field and reactants injection strategies.