Promoted conversion of a carbon free fuel: NH3 (NH3PROM)

The present project addresses the study of the use of promoters to facilitate the combustion of ammonia and, therefore, its use as fuel in the context of a free, or at least low, carbon economy. Ammonia, when used as a fuel, can be burned, ideally producing water and nitrogen, which is an important advantage over conventional fuels. The main disadvantage of using ammonia as fuel is its difficulty in self-ignition. In this project, the possibility of using combustion promoters is explored. Combustion promoters selected are dimethoxymethane (DMM) and diethyl ether (DEE), which would be added in small amounts to ammonia in order to promote its ignition. The aforementioned organic compounds have been used previously as combustion additives in internal combustion diesel engines, together with diesel fuel, favoring the clean combustion of this fuel.

In this context, the overall objective of this project is the knowledge of the oxidation of ammonia mixtures with the mentioned combustion promoters, both from the point of view of the conversion of reactants in the mixture and the formation of products, specifically pollutant emissions. In practice, the combustion of NH3 can generate nitrogen oxides, and thus, the nitric oxide reduction capacity of the mixtures considered will be evaluated, since synergies that lead to the minimization of this pollutant may be produced. The optimal conditions for NO reduction, through two mechanisms that can be produced jointly will be evaluated: reburning by the action of hydrocarbon radicals generated from the promoters considered, and Non-Catalytic Selective Reduction (SNCR) of NO by the action of ammonia present in the mixtures. A good optimization of the operating conditions that favors these synergies could lead to a maximum reduction of NO.

An extensive experimental study of the conversion of NH3 mixtures with the selected promoters (DMM and DEE) will be carried out considering the influence of different operating variables, such as temperature, oxygen stoichiometry, pressure (from atmospheric pressure up to 60 bar), the residence time of the gas, and the composition of the mixtures considered. Likewise, the impact of the presence of NO on the oxidation regime of the mixtures will be determined, and the optimal conditions that allow reaching a minimum emission of NO will be determined. The studies carried out, both from experimental and kinetic modeling points of view, will allow us to determine the mechanisms through which the oxidation of the mixtures under consideration takes place, as well as the maximum reduction of NO that can be achieved for the different conditions considered. In this sense, the reaction mechanisms, developed and validated for the different mixtures in this project, will be very useful as a simulation tool of the ammonia conversion process in the presence of promoters, in representative cases for industrial application under conditions real that occur in combustion chambers.