How a Dutch brewery is using iron powder as fuel
What if we could curb the fossil fuel-fed climate change nightmare and burn something else for fuel? What if this something else is also one of the most common elements of Earth? There is a simple answer to this question: burning iron.
While setting fire to an iron ingot may appear troublesome, fine iron mixed with air is highly combustible. Burning this mixture means oxidising iron. While carbon fuel oxidises into CO2, an iron fuel produces Fe2O3, which is nothing but rust. The best thing about rust is that it can be turned into a solid form that can be captured post-combustion. And that is not the only by-product that can be used. The iron powder comes out in the form of heat and rust powder. Iron, which has an energy density of about 11.3 kWh/L is so much better than gasoline. Although its specific energy is relatively poor, which is 1.4 kWh/kg, meaning that for a given amount of energy, the iron powder will take up a little bit less space than gasoline, but it will be almost ten times heavier. In other words, it can easily power a car. Perhaps it cannot heat a house, but it sure can be an ideal fuel replacement.
A research study at the TU Eindhoven University in the Netherlands showed that scientists have been developing iron powder as a practical fuel substance for the last couple of years. They installed an iron powder heating system at a brewery in the Netherlands, which is turning all the stored energy into beer. Since electricity cannot efficiently produce the kind of heat required for many industrial applications, iron powder proves to be a valuable zero-carbon option, with only leaves rust as a by-product.
So, what happens with all the rust then? Because iron is not just the fuel that is consumed, the energy stored can be easily recharged. And to recharge it, all that oxygen from FeO can be stripped out, and turned back into Fe, ready to be burned again. It might not be easy to do this, but much of the energy and work consists of prying that oxygen away from all the iron, which gets returned to when burning the iron, the next time. The idea is to use the same iron repeatedly, discharging it, and recharging it every time – just like a battery.
In order to maintain the “zero-carbon” nature of the iron fuel, the recharging process must be zero-carbon too. There exists a variety of ways of using electricity to turn rust back into iron – and a consortium led by the TU researchers explored three different technologies based on hot hydrogen reduction. First is the mesh belt furnace method, where the iron oxide is first transported onto a conveyor belt through a furnace. Then, hydrogen is added at about 800-1000°C. The iron oxide is further reduced to iron that holds together because of heat, resulting in the formation of another layer of iron. This can then be ground up to obtain an iron powder. The second method is the fluidized bed reactor – this is a conventional reactor type, but its use in hydrogen reduction of iron oxide is new. In the fluidized bed reactor, the reaction is carried out at lower temperatures around 600°c, avoiding sticking, but taking longer. The last is the entrained flow reactor. The entrained flow reactor is an attempt to implement flash ironmaking technology. This very method performs the reaction at high temperatures, 1100- 1400°C, by blowing the iron oxide through a reaction chamber together with the hydrogen flow to avoid sticking. It might be a good solution, but it is a new technology and has yet to be proven. Both production of the hydrogen and the heat necessary to run the furnace or the reactors require energy, of course, but it is grid energy that can come from renewable sources.
An obvious question here is if renewing the iron fuel requires hydrogen, why not just use hydrogen as a zero-carbon fuel in the first place? The problem is simple -using hydrogen as an energy storage medium is tremendously difficult because it involves high pressure and extreme cold. In a localised industrial setting, this might not be as big of a deal, but distributing it is a hassle. Iron powder, on the other hand, is safe to handle, stores indefinitely and can be easily moved with existing bulk carriers like rail. Therefore, its future looks to be in applications where weight is not a primary concern and collection of the rust is feasible. In addition to industrial heat generation, scientists are also exploring whether iron powder could be used as fuel for large cargo ships, which are extraordinarily dirty carbon emitters that are also designed to carry a lot of weight.
Philip de Goey, a professor of combustion technology said that he hopes to be able to deploy 10 MW iron powder high-temperature heat systems for industry within the next four years, with 10 years to the first coal power plant conversion. There are still challenges, de Goey says: “the technology needs refinement and development, the market for metal powders needs to be scaled up, and metal powders have to be part of the future energy system and regarded as a safe and clean alternative.” De Goey’s view is that iron powder has a significant but well-constrained role in energy storage, transport, and production that complements other zero-carbon sources like hydrogen. For a zero-carbon energy future, de Goey says, “there is no winner or loser— we need them all.”
Running iron powder through existing power generation infrastructure that may simply need retrofitting to deal with a different combustion process, would enable a very clean, load-responsive power grid. This means it could operate on an easily stored stash of raw material trucked in either from clean, renewable energy regeneration operations as described above, or from any number of industrial manufacturing operations.
“Iron is one of the most common elements in the Earth’s crust – there’s a lot of it and it’s really cheap, which is really what you need in an energy carrier that you’re going to use everywhere,” says Vincent van der Schaft from the student-led metal fuel research group Solid, based at the Eindhoven University of Technology in the Netherlands. “And there are a few other nice properties – an important one is that iron actually burns at a temperature that’s very close to the temperature of a gas flame.” He explains that this helps to avoid some difficult engineering challenges when retrofitting old installations or industrial processes to run on a new fuel.
This technology has the potential to become an important element in the future energy system. Excess renewable energy, generated for example by solar panels on sunny days, can be stored compactly in iron by converting rust (iron oxide) into iron. The iron can later be used as fuel when energy is needed. The iron oxide resulting from the combustion is collected and reused. The use of iron in this system is circular, generating no waste and most importantly, no carbon dioxide. In the coming days, economics and market dynamics will eventually determine how far this idea gets, and that remains in question at this early stage. But the idea certainly seems to have a mighty potential; at least it has some major advantages over hydrogen, pumped hydro, batteries, or kinetic energy storage, depending on what it may be used for, and it is something that industries should be keeping their eyes on.