Researchers at the TU/e present evidence that iron powder can be used as an alternative fuel. When talking about energy carriers many people think of molecules such as hydrogen or ethanol. But there is a whole different class of substances that can store a lot of energy: metals. In the future these so-called metal fuels will provide our coal-fired power stations and cars with the energy they need. That is indeed the conviction of researchers at TU/e.
‘The volumetric energy density of iron powder is at least three times higher than that of hydrogen’, says Philip de Goey, combustion technology lecturer at the TU/e. ‘And you do not have to transport this powder under high pressure or extremely low temperatures.’ De Goey and his colleagues have been looking into the possibilities of using iron powder as a fuel for two years now. For example, by burning it to rust powder in an external combustion engine. You can also use it to store solar energy, according to postdoc Yuriy Shoshin. ‘We can already convert solar energy into hydrogen. Then we use the hydrogen to reduce rust powder to iron powder.’ This approach has many advantages: iron is cheap, easily manageable and reusable. Shoshin: ‘We still have to adjust the reduction techniques to the process, but the reactions are known.’
De Goey is optimistic and thinks that it is going to work. ‘We expect to be able to reuse the iron for about a hundred times.’ But how can you derive energy from iron powder? ‘You burn it’, says Shoshin. First you distribute the iron powder in the air by means of an electrical field. Then a small spark activates the reaction of oxygen and iron in the air. The iron oxidizes into iron oxide. That reaction warms up the environment, which causes other iron particles to oxidize. ‘This reaction is similar to what happens in coal-fired power stations’, says Shoshin. ‘The only difference is they use finely ground coal instead of iron powder.’ The researcher are still looking for a way to collect the rust particles after use, otherwise it will be difficult to reuse them. The Goey is now considering filtering, because with sizes of 1 µm the particles are quite easy to catch.
In order to make the combustion easier Shoshin wants to use iron particles in the shape of a sponge in the future. ‘This morphology is generated during the reduction of iron and creates a larger surface. This makes the iron more reactive. We have not got round to testing this iron shape, because we first want to optimise the process.’ The researchers do have to find a way of converting the energy into electrical energy or motion. Pouring this fuel into a normal combustion engine does not seem to be an option. The powder would get caught between the cylinder and the piston and this friction would cause the engine to break. De Goey: ‘We are looking for a closed system, where the small particles cannot cause any harm. At this time we are considering an external combustion engine or some kind of steam system similar to those used in the coal-fired power stations.’
Even though the technique still needs to overcome some obstacles, metal fuels are already drawing the attention of companies. De Goey is in contact with a coal-fired power station willing to test whether iron can replace coal. The people from Eindhoven think metal fuels will become indispensable in a few years time. ‘We really have to get rid of the coal, and metals are a good alternative’, De Goey pleas. Shoshin agrees: ‘Metal fuels will certainly find their way to the market.’
Renée Moezelaar, C2W Magazine, year 113, edition 8