How did iron work before electricity?
Heat from iron: the element can be used to store energy
A commonplace element could help solve the electricity storage problem and give coal-fired power plants a future.
Hydrogen is often traded as a miracle drug for the energy transition. Generated with climate-friendly electricity, the energy source can be transported and stored so that it can be used when required. But the gas is highly volatile and flammable, which makes it difficult to handle.
An alternative could be iron. Several research teams are exploring how the fourth most common element on earth could be used to store energy. Initial attempts, including in a brewery, are promising. In the end, it could even enable a renaissance for the outlawed coal-fired power plants, albeit as a climate-friendly variant.
"Iron fuel", as it is called in the technical jargon, is based on the chemical reactions of oxidation and reduction. The former is nothing more than combustion: iron powder is mixed with oxygen and ignited. In contrast to a lump of iron, the innumerable particles of the powder have a much larger surface on which the reaction can take place in a stable manner. This releases a lot of heat that can be used. What remains is iron oxide, i.e. rust.
In order to make fresh iron particles from it again, the reduction is necessary. To do this, hydrogen is passed through the iron oxide. It reacts with the oxygen atoms in iron oxide and combines with them to form water. What remains is iron powder that can be burned again.
If the hydrogen is produced using “green” electricity, a cycle is created in which the iron acts as an energy store. In this way, the electricity and heat demand could be met on a large scale without using fossil raw materials, said Jeffrey Bergthorson from McGill University in Montreal in a 2018 article. However, he emphasizes that there are still numerous details to be clarified.
Researchers and the student team “Solid” at the TU Eindhoven in the Netherlands are working on this. After numerous laboratory tests, they started the first system in an industrial environment: in the Bavaria brewery in Lieshout. Brewing requires a lot of heat, some of which comes from the burning of iron. It is a fine powder, the grains are only 40 micrometers in size on average, explains Sofie Scheij from the Solid team. "It is stored in bulk and is easy to handle."
The system consumes around 60 kilograms of iron per hour and supplies up to 100 kilowatts of thermal energy. "We want to further increase the output and are already planning a plant with one megawatt," says Scheij. In four years, the team wants to exceed the 10 megawatt limit. "We also want to get away from the experimental setup and design a system that can be marketed." The researchers are supported by industrial partners who work together in the Metal Power Consortium.
“The technology is very promising and definitely worth researching more closely,” says Uwe Riedel, who runs the Institute for CO2-leading poor industrial processes at the German Aerospace Center (DLR). He trusts her a lot more. Iron could therefore play a key role in the energy supply - wherever coal-fired power plants emit climate-damaging carbon dioxide. "Instead of the fossil raw material, iron would be burned and thus generated electricity whenever it is needed to close the gaps in renewables," he says. The warmth that the Eindhoven researchers are aiming for would only be a by-product, for example for neighboring residential areas.
While hydrogen requires special pressure vessels and cooling technology, iron powder can be transported in large bags.
It is crucial that “green” hydrogen is used to reduce iron, says the researcher. "This is best done in southern countries, where there is a lot of inexpensive solar power for electrolysis." Grate down, fresh iron powder back.
It remains to be seen whether this will all work as hoped. It is true that the quantities of raw materials would be sufficient for such an iron cycle, as estimates suggest. But in detail, there are many questions that the researchers are working on: From reliable transport routes in politically difficult regions to combustion technology that runs effectively in large power plants.
Even then, it is estimated that the overall efficiency for power generation would only be around 35 percent. Most of the energy is lost in electrolysis, iron reduction and combustion. If you rely on hydrogen, the losses up to the power plant are similar, says Riedel. "But it can be burned in a gas and steam turbine power plant that works more efficiently." In the end, the hydrogen path is around 38 percent efficient. In addition, hydrogen is more flexible. It can also release its energy in fuel cells to power cars, trains and, in the future, also small aircraft.
Alternative for China and India
“It is not just the degree of efficiency that decides whether a technology will prevail, but rather the costs,” says Uwe Riedel. They are likely to be lower for iron. While hydrogen requires special pressure vessels and cooling technology, iron powder can be transported in big bags.
At least for stationary applications, the metal could prove to be the more economical fuel. Especially when existing coal-fired power plants can be converted and used further with relatively little effort. “You shouldn't just think of the power plants in Central Europe,” says Riedel. China and India have built hundreds and are planning more. "If we convert this to a climate-neutral fuel, a lot would be achieved."
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