An anonymous reader quotes a report from IEEE Spectrum: While setting fire to an iron ingot is probably more trouble than it’s worth, fine iron powder mixed with air is highly combustible. When you burn this mixture, you’re oxidizing the iron. Whereas a carbon fuel oxidizes into CO2, an iron fuel oxidizes into Fe2O3, which is just rust. The nice thing about rust is that it’s a solid which can be captured post-combustion. And that’s the only byproduct of the entire business — in goes the iron powder, and out comes energy in the form of heat and rust powder. Iron has an energy density of about 11.3 kWh/L, which is better than gasoline. Although its specific energy is a relatively poor 1.4 kWh/kg, meaning that for a given amount of energy, iron powder will take up a little bit less space than gasoline but it’ll be almost ten times heavier. It might not be suitable for powering your car, in other words. It probably won’t heat your house either. But it could be ideal for industry, which is where it’s being tested right now. Researchers from TU Eindhoven have been developing iron powder as a practical fuel for the past several years, and last month they installed an iron powder heating system at a brewery in the Netherlands, which is turning all that stored up energy into beer. Since electricity can’t efficiently produce the kind of heat required for many industrial applications (brewing included), iron powder is a viable zero-carbon option, with only rust left over. So what happens to all that rust? This is where things get clever, because the iron isn’t just a fuel that’s consumed — it’s energy storage that can be recharged. And to recharge it, you take all that Fe2O3, strip out the oxygen, and turn it back into Fe, ready to be burned again. It’s not easy to do this, but much of the energy and work that it takes to pry those Os away from the Fes get returned to you when you burn the Fe the next time. The idea is that you can use the same iron over and over again, discharging it and recharging it just like you would a battery. To maintain the zero-carbon nature of the iron fuel, the recharging process has to be zero-carbon as well. There are a variety of different ways of using electricity to turn rust back into iron, and the TU/e researchers are exploring three different technologies based on hot hydrogen reduction (which turns iron oxide and hydrogen into iron and water). […] Both production of the hydrogen and the heat necessary to run the furnace or the reactors require energy, of course, but it’s grid energy that can come from renewable sources. […] Philip de Goey, a professor of combustion technology at TU/e, told us 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.

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