The research project “Clean Circles” is investigating the potential of iron as a storage medium for renewable energies. If things go well, the Darmstadt University of Applied Sciences, h_da, will be the first University of Applied Sciences to be part of the ‘Exzellenzinitiative’.
By Nico Damm, 8.7.2021
Iron - a word that probably makes most people think of railroad tracks rather than the the energy storage system of the future. Anyone who visits Prof. Dr. Dirk Geyer from the Department of Mechanical Engineering and Plastics Engineering in his laser diagnostic laboratory can get a whole new look at the element iron. All it needs is a Bunsen-burner and some fine iron dust. Geyer takes a spatula and spreads a small amount of the particles into the flame. Immediately, a shower of sparks pours over the metal table. This is because iron particles burn very vell in the micrometer range and release energy. “This produces no CO₂, but iron-oxide, in other words, rust, which can then be reduced back to pure iron using renewable energies”, says Geyer. Making this ‘Clean Circle’ effect reality is the goal of a new joint project, which aims to explore the potential of iron as an energy storage medium.
Europe will import electricity
Why iron? “Europe is getting out of fossil fuels, at the same time, the potential for renewable energy in Central Europe is limited”, says Geyer. In the future, Europe will have to import large amounts of renewable energy. What could happen is: At wind- and sun-rich locations outside Germany, renewable energy is stored in iron, imported to Germany and burned in conventional coal-fired power plants to generate energy. This is since iron is not only favourable for energy use, but also easy to store and transport. From the researchers’ point of view, this makes iron particularly attractive, as the storage of energy can be separated in time and space from its release, i.e. the use for energy. Furthermore: The cycle would be CO₂-free. The Hessian Ministry of Science and Art is funding the joint project with 5.7 million euros as part of the so-called ‘Cluster-projects’, which are intended to help promising initiatives ready to apply for the upcoming round of the Federal State ‘Exzellenzinitiative’. ‘Clean Circles’ is a consortium that includes the h_da and the TU Darmstadt, which is in charge of the project, the Karlsruhe Institute of Technology, the University of Mainz and other partners, such as the ‘Gesellschaft für Internationale Zusammenarbeit’. Two doctoral positions have been created at the h_da for this purpose.
Iron instead of coal?
The chances are good that coal-fired power plants can be converted for iron combustion at moderate cost and thus the infrastructure for the ‘Clean Circle’ initiative is already in place. The rust produced during combustion can be collected and transported to sun- and wind-rich locations such as Southern Spain or Morocco. There, renewable energy could be used to generate hydrogen via electrolysis to reduce the rust back to pure iron. At high temperatures, oxygen bound in the rust would react with hydrogen – creating iron and water. “This keeps the water in circulation and prevents it from being taken from arid regions”, says Geyer. According to Geyer, this cycle can be repeated as often as desired. The technical feasibility of the process has already been demonstrated on a small-scale. However, since so many countries shift towards climate neutrality a consecutively new approach is required.
If only it were that simple, as Dr. Sandra Hartl notes. The mathematician and post-doc graduate engineer supervises one of the new PhD students at the h_da. As a specialist for turbulent combustion processes, she is one of the first two women to receive funding from a combined federal/state program for female post-docs, and now manages one of the two subprojects of ‘Clean Circles’ at the h_da. Her task is to develop thermochemical-mathematical models to mimic the processes of the iron cycle. As she points out “this allows us to reduce complexity and simulate how changes in the basic conditions will affect the system.” The finished models will help to understand sensitivities of the process and figure out how to re-configure coal-fired plants: How high must the temperature be? How can iron be prevented from forming pollutants? All of these aspects can also be explored experimentally, but such efforts cost not only money but also time.