Experimental study of a two‐stage thermochemical cycle for hydrogen production

Abstract

The use of renewable energy sources is the main strategy toward a low-carbon society. A promising alternative for the production of hydrogen gas is the water-splitting thermochemical cycles activated by solar energy. This work presents an experimental study of a two-stage thermochemical cycle for hydrogen production. It is based on the carbothermic reduction of iron ore (Fe2O3) and the re-oxidation of it with steam can be powered by concentrated solar energy. Samples studied were self-reducing pellets. The first stage of the proposed cycle consists in the reduction of hematitic iron oxide into its own metal at temperatures above 1173 K. The second phase of the cycle consists of iron metal oxidation by steam, which produces hydrogen gas. Sponge iron samples obtained in this work had a specific surface area of 35.05 m2/g measured by the BET method, which is a high value compared to specific surface areas obtained from conventional processes. It was shown that at 973 K the hydrogen gas production rate is slower, whereas at 1073 K and at 1173 K the sample reached 63% of its maximum oxygen gain between 2 and 7.5 minutes, respectively. As the hydrogen gas production rate is also proportional to the iron oxidation rate, it was shown to be very important to balance out the hydrogen gas production over the entire cycle time as a function of temperature. Finally, the analyzed thermochemical cycle can also operate with any other renewable carbon source.