Reduction of iron oxides for chemical looping technology through concentrated solar power

Climate change is a crucial challenge for the entire humankind, resulting from too high anthropogenic emissions of greenhouse gases in the atmosphere. The implications of global warming are huge and alarming, requiring us a deep, radical change and a gradual desertion of fossil fuels. The production of syngas and hydrogen, a promising energy vector, is one of the available solutions to mitigate climate change. In particular, hydrogen is able to store and deliever large amounts of energy per unit mass, without releasing carbon dioxide during the combustion. Syngas is a mixture of mainly hydrogen and carbon monoxide, that acts as an intermediate for the generation of other high value products, such as methanol, gasoline, ammonia. Among the several existing methods for the production of these two outputs, chemical looping technology through concentrated solar power (CSP) is definitely a rising star. This technique involves a solid material, commonly called oxygen carrier, that is initially heated to obtain its reduction and the release of oxygen. In a subsequent exothermic process at a lower temperature, the oxygen carrier is re-oxidized by means of H2O or CO2, releasing H2 or CO. Concentrated solar power systems can provide the heat needed in the first step of these thermochemical processes, enabling the intermittent solar energy to be converted and stored into easily transportable and ready to use solar fuels. In this work thesis iron oxides have been chosen as oxygen carriers, since they are characterized by large availability, low cost and environmental safety. An experimental test (i.e. thermogravimetric analysis (TGA)) has been performed to investigate the behaviour of iron oxides undergoing 20 redox cycles at constant temperature (820°C). Thus the efficiency of the two steps (reduction and oxidation) has been evaluated, showing good results. At last a numerical simulation in COMSOL Multiphysics is presented, taking into account an actual solar receiver, belonging to the paraboloidal CSP system, located on the rooftop of the Energy Center, in Turin. The aim was to obtain the temperature distribution of the cylindrical receiver, starting from experimental data about solar radiation and wind speed and a further simulation of the reduction reaction within the cylinder itself.