Magnetite has proven to be the ideal mineral for energy storage. In cooperation with the University of Barcelona and the international research institute CIC Energigune, LKAB Minerals researches how magnetite can be effectively used as thermal energy storage material. The first results from a Moroccan pilot plant with thermal energy storage (TES) tanks show that high efficiency of energy storage is possible. “Energy storage in magnetite is remarkably applicable in industries worldwide”, says Leon Hendriks, Business Development Manager Magnetite at LKAB.
Nowadays, the industry pays more attention to efficient and sustainable thermal energy. The mineral magnetite (Fe304) is very suitable to store energy sustainably. LKAB mines their Magnetite (an iron ore) in the northern part of Sweden at a depth of over 1000 meters. It is an inert and environmentally-friendly material, which the construction industry uses a lot to create high density concrete.
European subsidies for heat storage with magnetite
Recently the ORC-PLUS project was executed as part of the ‘Horizon 2020’-project (a European subsidy scheme). The purpose of this project was to extend the solar power plant with heat storage. First, scientific research has been done to find the most suitable mineral. From this in-depth investigation, resulted that magnetite is the most appropriate because of:
- Heat capacity; 0.89kJ/kg*K
- Good thermal conductivity; 3.4W/m*K
- Density; 4.8 t/m3 (volumetric storage capacity 4272 kJ/m3*K
- Thermal stability at high temperatures (1000˚C no problem)
- Thermal-mechanical stability (very little loss after many cycles)
- Availability and price
High temperatures for more efficient storage
The density of magnetite creates a volumetric storage capacity which is equal to the one for water, which is one of the highest. However, the biggest advantage of magnetite compared to water is its ability to store heat up to 1000˚C, where water can only do this at 90˚C. “Because of this, the heat stored in magnetite is an ideal energy source in high-temperature systems”, says Ana Inés Fernández researcher and professor at the Materials Science & Physical Chemistry faculty at the University of Barcelona. Magnetite also conducts heat, which can, therefore, be used again immediately. “Thermal conductivity is an important feature to maintain the heat storage at the same level, independent of peaks and dips in the energy supply. Especially the antiferromagnetic values of magnetite allow for a speedy conductivity at high temperatures”, Fernández explains.
“Currently, most solar power plants store their heat in molten salts. One of the disadvantages of these molten salts is that they can’t work at temperatures above 565°C, and solutions above this limit temperature are being researched. Because the higher the storage temperature the more efficient you can generate the electricity”, explains Fernández.
The economic value of heat storage
The energy plant related to the ORC-PLUS project is situated in Ben Guerir (Morocco) where heat storage in magnetite is tested. The Concentrated Solar Power (CSP) plant uses mirrors to reflect the sun heat, which heats organic oil. Next, the oil transports this heat to a turbine that generates electricity. The oil is guided through a large storage tank filled with magnetite which allows the magnetite to heat up during the day. Thanks to this heat storage, the installation can run another four hours at full capacity after sunset. The search for new heat storage concepts for sustainable energy was the reason for this research.
From research to practice
“We apply LKAB Minerals’ magnetite for this pilot project. In our research, we have tested with temperatures up to 1000 oC. During these tests, we identified how much heat we stored over a period of 21 days”, explains Dr Abdessamad Faik, project manager for the pilot project in Morocco and researcher at CIC Energigune. “We have determined that magnetite remains thermally stable at these high temperatures. Besides, we have confirmed that we can store heat at high temperatures for a longer period. This allows for a stable heat source, with which we can generate electricity continuously. Also at night, when there is no sunshine, the energy plant can still run”, says Faik.
Industrial heat storage
LKAB Minerals supplied the mineral for this pilot project. According to Leon Hendriks of LKAB Minerals, there are also industrial applications for heat storage possible. “Magnetite can also perfectly store heat from other energy sources than concentrated solar plants”, says Hendriks. This feature is of particular interest for companies using lots of heat; they can store and reuse residual later. Next to that, the application potential is much broader thanks to the fact that the conversion of electricity into heat is very efficient and hardly gives any loss of energy. As a result, companies that buy electricity to produce heat for their processes can create flexibility in the procurement of power, enabling them to buy at the most convenient (cheap) moment. Further magnetite can be the solution to store the temporary overcapacity of green energy from solar panels and windmills.
Abundantly available mineral
“Magnetite is an environmental-friendly, cheap and abundantly available mineral”, explains Hendriks. “Applications of magnetite for heat storage is little known at this moment. That is why we are looking for partners and specialist that can develop applications, with which the stored heat from magnetite can be re-used sustainably”, Hendriks finishes.