You don’t have to be an expert to realize what a huge energy problem our world is facing, and it’s not a problem that will resolve itself when the war in Ukraine ends. What’s needed is a sustained decarbonization of the energy system – zero-emission fuels. Research on renewable energy sources and green hydrogen continues apace, but doesn’t seem to be enough, so several research teams around the world have been studying another energy source that could help solve the problem – iron. This mineral has been tested as a fuel, and can also be used to store solar or wind energy. Iron is abundant, cheap and easy to transport.
“Burning iron generates the same amount of energy as burning coal, but without a speck of carbon dioxide emission because iron doesn’t contain carbon,” said Carmen Mayoral Gastón, head of Chemical Processes and Nanotechnology at the Spanish National Research Council’s (CSIC) Institute for Carbon Chemistry. “When you burn iron,” says Mayoral, “what you get is a by-product called iron oxide. If you take the oxygen out of that iron oxide, you get iron again. It’s a circular process: you burn iron, you get iron oxide; you remove the oxygen, and you have iron again that’s ready to use as a fuel.”
It not only sounds easy but ideal, and it may become a reality in the near future. Two important research efforts projects are underway in Europe: Iron Fuel in the Netherlands and Clean Circles in Germany. The Dutch project is the most advanced, and its scientific director, Philip de Goey, says: “In 2024, we will be able to regenerate iron powder from iron oxide in a fully circular and emission-free process.” The Iron Fuel team installed such a system for a brewery in the Netherlands. Although it’s a low-power system, it proved that the system really works.
Andreas Dreizler, a spokesperson for the Clean Circles team, believes that we are very close to being able to use iron as a fuel. “We think that we’re only a few years away from using iron as storage for renewable energies. For small-scale industrial processes where heat is needed, we estimate that it will be available in about three to five years. And for the modernization of large-scale systems, such as power plants, it may be about 10 years.” To achieve these deadlines, Germany has launched the ambitious Clean Circles project, with a budget of US$12 million over four years.
“We still don’t fully understand the processes that occur during the oxidation of iron and the reduction of iron oxide,” said Dreizler, citing two areas of focus for the Dutch and German researchers. Their respective projects are also looking at immediate applications of their research in the industrial, social, economic and political sectors.
We think that we’re only a few years away from using iron as storage for renewable energiesAndreas Dreizler, a spokesperson for the Clean Circles team
Because it seems increasingly viable to use iron as a fuel and renewable energy storage medium, it should become an integral part of the overall energy transition strategy. Iron is very abundant and easy to transport. The idea of using it as a fuel is counter-intuitive because most people don’t think you can burn iron. But iron does burn, and it’s not the first solid to be used as fuel. Coal is also a solid fuel, and solids have been used to light matches and propel rockets into space.
“Iron must be in powder form to be used as fuel,” said Carmen Mayoral. “It’s a very fine powder, like flour, similar to the coal powder used in thermal power plants.” It has an energy density of 11.3 KWh/L, which is higher than gasoline, for example. But it also has a few drawbacks, like its weight. To produce an equivalent amount of energy, iron powder takes up less space than gasoline, but weighs almost 10 times as much. This means that it can’t easily be used in automobiles or home heating. But it’s perfect for powering industrial plants and large ships, both of which are heavy polluters.
The cyclical process of using iron as a fuel makes it very valuable for renewable energy storage. Once iron is used to fuel a thermal power plant or factory, the iron oxide residue is transported to a facility where it is converted back to iron. To remove the oxygen from that iron oxide and convert it back to iron, energy must be used. “But if that energy is obtained from renewable hydrogen produced by solar energy, for example, you have completed the circle with zero emissions,” said Carmen Mayoral. And that’s exactly the idea.
“Iron is the best method for storing and transporting large quantities of renewable energy from countries where it can be cheaply produced,” said Dutch scientist Philip de Goey. “In 20 or 30 years, the Netherlands will only be able to produce 20% of the energy it needs from renewable sources, while Spain and other countries may have a surplus.” Iron could be used to transport solar energy produced in Spain to northern countries that can’t produce sufficient sustainable energy on their own. “The important thing,” said Mayoral, “is not to rely on a single solution. Hydrogen, renewable energies, iron... we need to use all the available resources.” And iron increasingly seems to be one of them.