You don’t have to be a lynx to realize the enormous energy problem that our civilization has. It is not just about the freezing winter that awaits us Europeans. The problem is prior and is not temporary, it is not related to the war in Ukraine, but is due to the necessary decarbonization of energy. Humanity needs zero-emission fuels. Research on renewable energies or green hydrogen is advancing, but it does not seem to be enough. For a few years, several research groups in various countries have been studying another possibility that, apparently, could solve many of the current problems. That possibility is iron: it could be used as fuel (in fact it has already started to be used) and to store solar or wind energy. And iron is plentiful, cheap, and easy to transport.
“When you burn iron you get the same amount of energy as if you burn coal, but without a drop of carbon dioxide emission, because iron does not contain carbon,” explains Carmen Mayoral Gastón, head of the Chemical Processes and Nanotechnology Department at the Institute of Carbochemistry of the CSIC. “What you get when you burn iron,” Mayoral continues, “is a by-product, iron oxide. You can remove the oxygen from that iron oxide and you have iron again. It’s a circular process: you burn iron, you get iron oxide, you take the oxygen out of it, and you have iron ready again to use as fuel.”
It looks not only easy but perfect. And it is possible that at some point in the fairly near future it will be. To achieve this, there are various research teams working on it. Two of the most important projects are in Europe: Iron Fuel (iron fuel, in its Spanish translation) in the Netherlands and Clean Circles (clean circles, in Spanish) in Germany. The Dutch project is the most advanced. According to its scientific director, researcher Philip de Goey: “In 2024 we will be ready for the regeneration of iron powder from iron oxide in a completely circular and emission-free process.” The Iron Fuel scientific team has managed to install a technology for the use of iron as fuel in a brewery in the Netherlands. It is a low power system, but they have shown that it works. For his part, Andreas Dreizler, spokesperson for the Clean Circles team, estimates that the periods of time necessary for iron as fuel to be a fact are very close: “We believe that there are a couple of years left before iron is used as storage of renewable energies. For small-scale industrial processes where heat is needed, we estimate it will be available in about three to five years, and for retrofitting large-scale systems like power plants, it may be 10 years away.” In order to meet these deadlines, Germany has embarked on the ambitious Clean Circles scientific project, which has a budget of twelve million euros for four years.
“We still don’t fully understand the processes that take place neither during the oxidation of iron nor in the reduction of iron oxide,” explains Dreizler. Advancing that knowledge is what both Dutch and German researchers are dedicated to. But his projects are not nourished only by science. Both are interdisciplinary and include industrial, social, economic and political aspects that help their discoveries have an immediate application.
“We believe that there are a couple of years left before iron is used as storage for renewable energies”
Because the theory of using iron as a fuel and renewable energy reserve appears more and more as a complementary but necessary solution for the energy transition. To begin with because iron is very abundant and easy to transport. The idea of using it as fuel is counterintuitive because iron is, for non-experts, what doesn’t burn. But iron does burn. And it is not the first solid fuel to be used or studied either. Coal, for example, is also a solid fuel. As are the ones used to drive space rockets or the one that allows us to light a match.
“The iron for its use as fuel must be in powder —explains Carmen Mayoral—. It is like iron flour, just like the coal used in thermal power plants, which is also powdered”. It has an energy density of 11.3 KWh/L which is higher than, for example, that of gasoline. But he also has some problems, like his weight. To obtain a given amount of energy, the iron powder needed takes up less space than gasoline, but weighs almost 10 times more. This impediment means that its use for automobiles or home heating is not considered. But it does make it perfect for industry or also to power large ships that are currently very polluting.
In addition, the cyclical process of using iron as fuel is considered a very valuable resource for renewable energy storage. The idea is that the iron is used as fuel in a thermal power plant or an industry. Once used, the residue, which is iron oxide, will have to be transported to a facility where it is converted back into iron. To remove the oxygen from that oxide and transform it back into iron, you have to use energy. “But if that energy is obtained from renewable hydrogen, that is, obtained with solar energy, for example, you have completed the circle with zero emissions,” says Carmen Mayoral. And that is exactly what is intended.
“Iron is the best method for storing and transporting large amounts of renewable energy from countries where it is cheap to produce,” says Dutch scientist Philip de Goey. “In 20 or 30 years, in the Netherlands we will only be able to produce 20% of what we will need with renewable energy, while Spain and other countries may have a surplus,” he adds. Iron may be used to bring the sun’s energy produced in Spain to northern countries with difficulties in obtaining sufficient sustainable energy resources in their own territory. “The important issue”, concludes Carmen Mayoral, “is that there is no single solution: hydrogen, renewable energies, iron… The energy solution is that we use all available resources”. And iron seems to be among them more and more every day.
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