Metal Powder Energy
January 18, 2021 I occasionally author circuit construction articles in hobby electronics magazines. When I publish a circuit, I'm always careful to assure that all the components are available for purchase at the time of my writing; otherwise, the circuit would be nearly worthless as published or need tedious revision. Scientific experiments have a similar problem, and it's solved by freely sharing unique reagents, software, etc., so that experiments can be reproduced. Books and magazines were the only resources available to me as an elementary school experimenter in the dark days before the Internet. I would gleefully buy one book or another about kitchen experiments for children, only to find that most of the chemicals and equipment weren't accessible to me. I had baking soda and vinegar, but no lycopodium powder. In retrospect, it was probably good that I didn't have lycopodium powder, since the stuff is dangerous.
A Lycopodium cernuum var. dussii plant (Scientific classification: Plantae, Tracheophyta, Lycopodiopsida, Lycopodiales, Lycopodiaceae, Palhinhaea, Lycopodium cernuum dussii), native to Guadeloupe.
Lycopodiopsida (clubmoss) plants produce spores that are the source of lycopodium powder
(Wikimedia Commons image by Patrice78500)
Lycopodium powder is a fine powder which is the dried spores of clubmoss plants. Its attraction is its high flammability, a consequence of the material's having a high surface area in contact with air. Lycopodium powder is used to create theatrical explosions and special effects; and, in the past, it was used as a flash powder by early photographers. Because of the small particle size, lycopodium powder can be used to demonstrate Brownian motion, and it's much easier to obtain than the pollen grains of Robert Brown's discovery experiment. Lycopodium powder was a useful technological material, and its utility was facilitated by its extreme hydrophobic nature that keeps the powder dry. Lycopodium powder was used by Chester Carlson (1906-1968) in some of his xerography experiments. I wrote about Carlson in an earlier article (Larry Tesler (1945-2020), March 30, 2020). French inventor, Nicéphore Niépce (1765-1833), who created the first photograph in 1822, also invented the first internal combustion engine, which he called the Pyréolophore, in 1807. This engine was fueled by lycopodium powder. The same principle behind the rapid combustion of lycopodium powder is responsible for many industrial dust explosions. The following table lists a few of the more significant of these.
| Name | Date | Place | Material | Fatalities |
|---|---|---|---|---|
| Washburn "A" Mill explosion | May 2, 1878 | Minneapolis, Minnesota | flour dust | 22 |
| Douglas Starch Works explosion | May 22, 1919 | Cedar Rapids, Iowa | corn starch | 43 |
| Mount Mulligan mine disaster | September 19, 1921 | Mount Mulligan, Australia | coal dust | 75 |
| Benxihu Colliery explosion | April 26, 1942 | Benxi, China | coal dust and gas | 1,549 |
| Harbin textile factory explosion | March 17, 1987 | Harbin, China | flax dust | 58 |
| Imperial Sugar explosion | February 7, 2008 | Port Wentworth, Georgia | sugar dust | 14 |
| 2014 Kunshan explosion | August 2, 2014 | Kunshan,China | metal powder | 146 |
Not so sweet - Aftermath of the Imperial Sugar refinery dust explosion of 2008.
This dust explosion on February 7, 2008, at the sugar refinery at Port Wentworth, Georgia, killed 14 people.
(Wikimedia Commons image from the U.S. Chemical Safety and Hazard Investigation Board.)
The last incident listed in the table is significant, since it shows that metals, not just coal and organic materials, will quickly combust when in powder form. Even a common and inexpensive metal like 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.[1] 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.
Researchers from the Eindhoven University of Technology have used this energy conversion reaction as a renewable energy source in heat-intensive processes at a local brewery, the Swinkels Family Brewers, Noord-Brabant, in a pilot operation for brewing 15 million glasses of beer.[2-5]. The research was undertaken by SOLID, a multidisciplinary team of about 30 students from Eindhoven University of Technology that's been active since 2016.[6] Also participating is Metal Power, a consortium of Noord-Brabant companies.[2] Heat-intensive industries are responsible for a large portion of global carbon dioxide emissions, but the iron powder combusts without a release of carbon dioxide.[2] The iron powder is used as a circular fuel; that is, the oxidized iron can be recycled into iron, and this can be done using renewable energy sources.[2] Says Philip de Goey, a professor at the Eindhoven University of Technology,
"The beauty of iron fuel is that you can release the energy stored in iron fuel when and where you need it... If you grind iron into a powder, it becomes highly flammable and this combustion releases a lot of energy in the form of heat. This heat can meet the industry's energy demand... No CO2 is produced during combustion and only rust remains... It's a circular process: you capture this rust powder and sustainably convert it back into iron powder."[2]There as other advantages to iron fuel. It's safe, no energy is lost during during storage, and it can be easily transported.[2] 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.[3] This means it isn't suitable for automotive fuel, but industrial applications, such as the brewery demonstration, are possible. The combustion heat can be used also for industrial, or residential heating.[3,7]
Combustion of iron in a combustion tube.
Since I've done experiments with molten metals, my calibrated eye sees a temperature of about 1000°C.
(Eindhoven University of Technology image by Bart van Overbeeke.)
The conversion of the iron oxide to elemental iron is by its reaction with hydrogen to convert the contained oxygen to water. This can be done in several ways, one of which is just heating the iron oxide in a hydrogen atmosphere at 800-1000°C.[3] Other methods are using a fluidized bed reactor at the lower temperature of about 600°C for a longer time; or, a rapid method of blowing the iron powder in a stream of hydrogen at 1100-1400°C.[3] Hydrogen is thus used in a stored energy process without the problems of transporting the hydrogen itself.[3] Plans are in place for a 10 MW system in 2024.[2]
References:
- Fe2O3 (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.
- TU/e demonstrates iron fuel at brewery Bavaria: a new circular and CO2-free fuel for the industry, Eindhoven University of Technology Press Release, October 29, 2020.
- 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.
- Team Solid Website, https://teamsolid.org.
- 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.