Methane-assisted iron oxides chemical looping in a solar concentrator: tests in real conditions on the Energy Center rooftop

Recent interest in hydrogen as an alternative fuel for lowering carbon emissions is funding the exploration of new ways for producing this molecule in a clean way. Iron oxides can be used within a process of chemical looping to produce hydrogen when switching from an oxidation state to another one. More specifically, they can lose oxygens at extremely high temperature in an inert atmosphere. The reaction can be helped by adding a gas to the reactor, so that it can happen at a temperature level reachable in a solar dish concentrator. The optimization and well-functioning of the solar facility is key for running the reaction. The materials used for the reactor and its shape highly influence the results. After a deep literature review about the technology and the chemical reaction, several tests with 35% methane feed were performed. Testing a pipe placed horizontally in the focus, alumina could not stand the extreme thermal stress, while steel (AISI 316 and Inconel Hastelloy c-276) lasted enough for the reaction to start, but eventually experienced melting. Operating at a temperature level above 1000 K helped the reaction to switch from methane chemical looping combustion to chemical looping reforming, thus favouring hydrogen and carbon monoxide yields. The gas flow outlet from the reactor reached a percentage up to 45% of hydrogen and 10% of carbon monoxide. Carbon dioxide instead reached very low concentrations. While carbon monoxide and carbon dioxide reached a peak at the beginning of the experiment and then decreased, hydrogen was oscillating around a stable value. Unreacted methane was detected. The temperatures recorded in the reactor and the gas mixture obtained were performed with the outputs of two different simulations studying the heat transfer and the chemistry of the experiment. Matching results highlighted the goodness and reliability of the models built.