Solar Carbothermic Reduction of ZnO in a Two-Cavity Reactor: Laboratory Experiments for a Reactor Scale-Up

Solar energy can be stored chemically by using concentrated solar irradiation as an energy source for carbothermic ZnO reduction. The produced Zn might be used for the production of electricity in Zn-air fuel cells or of H2 by splitting water. In either case the product is again ZnO which can be reprocessed in the solar process step. This innovative concept will be scaled up to 300kW solar input power within the so-called SOLZINC-project. In this paper we report on experimental results obtained with a two cavity reactor operated at solar power inputs of 3-8kW in a solar furnace. The objective was to generate input data which are necessary for designing the scaled up reactor, such as the effect of process temperature (1100-1300°C) and carrier gas (N2 and CO) on the overall reaction rate. Furthermore, construction materials were tested and a variety of carbonaceous materials were screened for their use as reducing agents by means of thermogravimetric measurements. As a result, beech charcoal was chosen as the standard reducing agent.