Iron as a Fuel
September 18, 2023 Iron and steel are the least expensive of the metals, and they comprise about 95% of all the metal tonnage produced annually in the world.[1] The August, 2023, price of iron ore is about $105/metric ton, as compared with the price of gold at about $1,950/Troy ounce, a ratio of gold price to iron price of 32,150.[1] The table shows the metric tons of pig iron and raw steel production in the United States for the years 2018-2022.[1]| Year | Pig Iron Million Metric Tons |
Raw Steel Million Metric Tons |
|---|---|---|
| 2018 | 24.1 | 86.6 |
| 2019 | 22.3 | 87.8 |
| 2020 | 18.3 | 72.7 |
| 2021 | 22.2 | 85.8 |
| 2022 | 21.0 | 82.0 |
Iron is inexpensive; but, as the saying goes, "You get what you pay for." The problem with iron and inexpensive alloys of iron, including steel, is their rusting. Rust is the oxidation of iron to produce iron oxide, generally hydrous iron(III) oxides (Fe2O3·nH2O).(Rusted lid of a rain cistern, a Wikimedia Commons image by Agnes Monkelbaan.)
The ancient Greeks understood the advantage of using iron as a structural material, provided that its corrosion could be overcome. In the construction of the Parthenon, they secured its marble blocks with iron H pins in prepared grooves, but they covered the iron with molten lead.[2] The lead protected the iron from environmental water, and the soft lead served also to cushion the joints from seismic tremors.[2] However, an 1898 restoration of the Parthenon by Greek architect, Nikolaos Balanos (1869-1943), used iron pins without a protective coating.[2] Water eventually rusted the iron, which caused its expansion, cracking the marble.[2] Another restoration attempt, started in 1975, is designed to correct these problems and restore nearby buildings in the Athenian Acropolis. Iron releases a lot of energy when forming its oxide, as the following graph shows.
Gibbs free energy of formation of haematite (often called hematite) from the elements as a function of temperature. These data are from the JANAF Thermochemical Tables, available at the NIST Standard Reference Data Website.[3] I prefer kilocalories to joules because of my materials science background, so I converted the tabulated SI units of free energy to kilocalories. Negative energy indicates an exothermic reaction. The graph was produced using Gnumeric. Click for larger image.
As I wrote in an earlier article (Metal Powder Energy, January 18, 2021), a research team from the Eindhoven University of Technology used combustion of iron as a renewable energy source in a pilot operation for beer brewing at a Noord-Brabant brewery.[4-6] Since iron powder combusts without a release of carbon dioxide, its use does not contribute to global warming. The iron powder is used as a circular fuel in which the oxidized iron can be recycled into iron using renewable energy sources. One other advantage of iron fuel is its safety. There is no energy lost during storage, and it can be easily transported. One disadvantage, however, is its low specific energy, just 1.4 kWh/kg, so its energy density is about an order of magnitude less than gasoline.[4] This means it isn't suitable as an automotive fuel; but, fixed applications, such as industrial heating and residential heating, and as an energy storage material for electrical system energy storage, are possible. The circular fuel process involves the conversion of the iron oxide caused by the iron combustion back to elemental iron by reaction with hydrogen. This converts the contained oxygen of the oxide to water, and it can be done in several ways. One of these is just heating the iron oxide in hydrogen at 800-1000°C.[4] There's a more rapid method of blowing the iron powder in a stream of hydrogen at 1100-1400°C, or the use a fluidized bed reactor at the lower temperature of about 600°C for a longer time.[4] Today, two and a half years later, the Dutch brewery's 100 kilowatt pilot plant has now expanded into a one megawatt iron combustion heat generator named IRON+, created in part by Metalot, a startup company spun out of the Eindhoven University of Technology.[7] Another spin-off from Eindhoven, RIFT, for Renewable Iron Fuel Technology, used iron fuel to heat five homes.[7] McGill University pioneered iron fuel technology,[8] and a McGill University startup company, Altiro Energy, created a 10 kilowatt unit that they intend to scale up.[7] Surprisingly, the initial McGill University research was funded by the European Space Agency and the Canadian Space Agency.[7]
An iron fuel demonstration plant running in Budel, near Eindhoven, The Netherlands. This plant can produce one megawatts of steam in a unit that's sited in a warehouse. A plant such as this can be easily scaled to produce much more power.
(European Space Agency image.)
Metalot and the Technical University of Darmstadt (Darmstadt, Germany) have determined that it’s more efficient to produce iron from hydrogen gas than to produce the hydrogen fuel alternative, liquid hydrogen.[7] As work progresses, some technical problems have been mitigated. One problem is that iron does not ignite as easily as hydrocarbon fuels, and its combustion rate is slower, making for unstable burning and easy extinguishing.[7] It was found that the addition of some natural gas assists with initial ignition.[7] Other techniques stabilize the combustion to prevent its extinguishing.[7]
Iron burning has been tested in microgravity aboard European Space Agency sounding rockets by a research team from McGill University and Eindhoven University of Technology.
(European Space Agency image.)
Just as hydrocarbon combustion leads to unwanted carbon soot, iron combustion produces iron oxide nanoparticles that can't be converted into iron. At present, the iron loss is less than 0.3 percent, and these nanoparticles are captured in a HEPA filter.[7] Also, not all of the iron is burned into iron oxide.[7] After some process optimization, it would be possible to use renewable energy to produce iron, store it as long as necessary, and also transport it where power when needed.[7] Jeffrey M. Bergthorson, one of the researchers and an associate professor at McGill University, is quoted in IEEE Spectrum as saying,
"Places that have excess energy could make iron, and others can buy it. This way, you could commodify renewable energy so it can be globally distributed without the need for transmission lines. Metals can solve a big problem in the renewable energy transition: long-duration energy storage."[7]
References:
- Iron and Steel Statistics and Information, National Minerals Information Center, U.S. Geological Survey, U.S. Department of the Interior.
- Evan Hadingham, "Unlocking Mysteries of the Parthenon," Smithsonian Magazine, February, 2008.
- Fe2O23 (Haematite) from the NIST-JANAF Thermochemical Tables, Fourth Edition, Part I and Part II, M.W. Chase, Jr., Editor, found at NIST Standard Reference Data, Hematite (Fe2O3). Earlier data can be found in C. E. Wicks and F. E. Block, "Thermodynamic Properties of 65 Elements - Their Oxides, Halides, Carbides, and Nitrides," U. S. Bureau of Mines Bulletin 605, U. S. Government Printing Office (1963);, with an Online version, via The University of North Texas Library.
- Evan Ackerman, "Iron Powder Passes First Industrial Test as Renewable, Carbon Dioxide-Free Fuel," IEEE Spectrum, November 13, 2020.
- World's first iron-based energy storage system, YouTube Video by Solid, September 6, 2018,
- Iron Powder - the green energy solution, YouTube Video by the Eindhoven University of Technology, October 21, 2020.
- Prachi Patel, "Iron Fuel Shows Its Mettle," IEEE Spectrum, June 22, 2023.
- J.M.Bergthorson, S.Goroshin, M.J.Soo, P.Julien, J.Palecka, D.L.Frost, and D.J.Jarvis, "Direct combustion of recyclable metal fuels for zero-carbon heat and power," Applied Energy, Vol. 160 (December, 2015), pp. 368-382, https://doi.org/10.1016/j.apenergy.2015.09.037.