Galvanic coatings suppress the formation of rust. However, the reddish-brown iron oxide can play a decisive role in the energy transition. In a cycle of oxidation and reduction, rust could become a crucial building block for so-called metal power plants that generate and store energy. Scientists at TU Darmstadt are currently testing the technology and plan to convert a coal-fired power plant in Berlin in the near future.
Protection against corrosion or rust is the most important purpose of electroplating technology. The German Paint Institute recently reported that 16 tons of steel disappear every day in Germany due to corrosion. An almost revolutionary discovery has now shed new light on the supposedly invariably harmful corrosion process: rust can contribute to theCO2-free generation and storage of energy in a cycle of oxidation and reduction. Using this technology, which Dr. Andreas Dietz from the Fraunhofer Institute for Surface Engineering and Thin Films IST already described in his presentation at the last Ulm Dialogue, researchers at TU Darmstadt now want to pave the way for so-called metal power plants in the "Clean Circles" project (Fig. 1).
Fig. 1: View into a pulverized combustion chamber. This plant at TU Darmstadt will burn iron dust with an output of 1 MW
Iron and rust as energy storage
The concept behind "Clean Circles" sounds simple at first: iron is burned to generate heat. Iron powder has combustible properties, similar to coal, but with a decisive ecological advantage: as iron is carbon-free, no climate-damaging carbon dioxide (CO2) is produced during combustion. The researchers (Fig. 2) want to make targeted use of this advantage for a sustainable energy supply.
The central element of the process is rust - which is known to consist of iron and oxygen. By using hydrogen from renewable energies, this oxygen can be removed from the rust and the iron regenerated. This continuous cycle of oxidation and reduction enables long-term storage of energy from renewable sources.
Fig. 2: Marius Schmidt, Christian Hasse, Andreas Dreizler and Rainer Hofmann from the Darmstadt Clean Circles team. In the background, the tower of TUDa's own demonstration power plant
"Rust is therefore no longer just a by-product, but is becoming a valuable component of a sustainable energy storage system," explains Prof. Andreas Dreizler, an expert in reactive flows and co-leader of the project at TU Darmstadt. The energy stored in iron can be used in the long term and can be easily transported in a functioning infrastructure, which gives the concept global significance. Millions of tons of iron and rust are already transported by rail or ship every year.
Energy storage for a reliable future
Storing energy efficiently, especially overnight or during the winter months, is a key challenge of the energy transition. Iron offers a promising solution for this, as it can be repeatedly regenerated - similar to a battery. In addition, noCO2 is produced in the process.
Scientists are currently testing the implementation on a larger scale in an experimental power plant on the TU Darmstadt campus. This power plant, which has previously been used to research biomass and waste materials, is now set to supply one megawatt of "iron energy". If the concept proves successful, the researchers are already planning an even more ambitious step: the conversion of a Berlin coal-fired power plant to iron combustion in order to enable a sustainable local heating supply.
New prospects for coal-fired power plants
The "Clean Circles" research team sees the future of energy supply in a mix of different technologies. In particular, the long-term storage of renewable energy could experience a decisive further development thanks to iron.
"Enormous amounts of energy can be stored in iron over long periods of time," emphasizes Professor Christian Hasse, an expert in thermo-fluid systems and co-leader of the project. This is an essential solution, especially for the European winter with its long dark doldrums. The first conversions from coal-fired power plants to iron as an energy source could start as early as 2030. "Iron should definitely be included as a promising technology for the energy transition," said Hasse. He is convinced that storage technology would also bring us much closer to the required energy security. This is good news for energy-intensive industries such as electroplating, among others. Furthermore, this approach could have a sustainable effect in the construction industry: Former coal-fired power plants would not have to be demolished, but could be converted to climate-friendly energy production with minimal intervention.
Fig. 3: A clean cycle: green electricity - also via the hydrogen storage stage - reduces the metal-oxygen compound to pure metal. Burning it releases heat, but also storable hydrogen. These energies can be used for production or stored
Generating heat and hydrogen with iron combustion
The team from TU Darmstadt recently won two prizes in an ideas competition with an additional utilization idea: the iron energy store can not only supply a lot of heat, but also the coveted hydrogen (Fig. 3). When iron is oxidized with water vapour - i.e. H2O - hydrogen (H2) is produced in addition to iron oxide. The team gave this research idea the name "MetalH2eat" for metal to H2 and heat. The team, led by Marius Schmidt, a doctor of engineering from TU Darmstadt and Managing Director of Clean Circles, impressed the jury with their sustainable idea. According to Schmidt, this could be another building block for the energy transition and hydrogen strategy - "for example, for a glassworks in the deep Black Forest that can use energy in the form of hydrogen and heat but is not connected to appropriate grids". Such companies could use decentralized energy from iron.
Photos: TU Darmstadt/ Anja Störiko
