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The mineral magnetite appears to be ideal for storing energy. In cooperation with the University of Barcelona and international research institute CIC EnergiGUNE, LKAB Minerals in Moerdijk is investigating how magnetite can be effectively used for thermal energy storage. Initial results from a pilot plant with thermal energy storage (TES) tanks in Morocco show that high efficiency energy storage can be achieved with magnetite. "Energy storage in magnetite is also extremely applicable in the Netherlands," says Leon Hendriks, Business Development Manager Magnetite at LKAB.
Efficient and sustainable thermal energy storage is receiving increasing attention. The mineral magnetite (Fe304) is very suitable for storing energy in a sustainable way. Magnetite (a form of iron ore) is mined in northern Sweden at a depth of more than a thousand meters. It is an inert and environmentally friendly material, widely used in construction to produce heavy concrete.
Recently, the ORC-PLUS project was conducted under the 'Horizon 2020' flag (European funding scheme). This project aims to equip a solar power plant with thermal storage. First of all, there is a scientific research conducted on the most suitable mineral. This showed that magnetite is the most suitable because of:
The density of magnetite ensures that its volumic heat capacity is similar to that of water (>4 MJ/m3*K). However, the major advantage of magnetite over water is that it can easily store heat at temperatures up to 1000˚C, where water is limited to 90˚C. "This makes the heat stored in magnetite an ideal source of energy in high-temperature systems," said Ana Inés Fernández researcher and lecturer in the Faculty of Materials Science & Physical Chemistry at the University of Barcelona. Magnetite easily conducts heat, so it can be used again immediately. "Thermal conduction plays an important role in keeping heat storage at the same level continuously, even during peaks and troughs in energy supply. In particular, the anti-ferromagnetic values of magnetite ensure that magnetite conducts heat quickly at high temperatures," Fernández explained. "Currently, solar power plants store heat in liquid salts. One of the disadvantages of liquid salts is that they do not work above temperatures of 565 ˚C while solutions that can do this have been sought. Because the higher the temperature the more efficiently electricity can be generated," Fernández explains.
The power plant of the ORC-PLUS project is in Ben Guerir, Morocco, testing heat storage in magnetite. The solar power plant uses mirrors to reflect the solar heat with which organic oil is heated. Then that oil transports the heat to a turbine that generates electricity. The oil first flows through a large storage vessel containing magnetite pellets, causing the magnetite to heat up during the day. This heat storage allows the plant to continue running at full capacity for four hours after sunset. The search for new concepts for heat storage for renewable energy prompted this research.
"For this pilot project, magnetite from LKAB Minerals was used. With this mineral, tests were done with heating up to 1000 oC where we looked at how much heat was retained over a 21-day period," explained Dr. Abdessamad Faik, Project Manager of the pilot project and Group Leader at CIC EnergiGUNE. "We found that magnetite remains thermally stable under these higher temperatures. Moreover, it turns out that high temperatures can be stored for a longer period of time. This provides a stable heat source, which can be used to generate electricity continuously. Even at night when the sun is not shining, the power plant can continue to run," Faik said.
LKAB Minerals provided the mineral for this pilot. According to Leon Hendriks of LKAB Minerals, several industrial applications for heat storage are possible. "Heat from energy sources other than solar power plants can also be excellently stored in magnetite," says Hendriks. This is particularly interesting for companies that consume heat; Residual heat can be stored for reuse later. In addition, because virtually no losses occur in the conversion of electricity to heat, the usability is even greater. Companies can therefore use the heat battery to flexibly purchase power for their industrial heating. It also makes it possible to store temporary excess capacity of green energy from solar panels or wind turbines. "The mineral magnetite is environmentally friendly, cheap and in plentiful supply," says Hendriks. "Application of magnetite as heat storage is still little known. That is why we are looking for partners and specialists who can develop applications, with which the heat stored in magnetite can be sustainably reused," Hendriks said.
Because of price differences for day and night power, there is a desire to use electricity when costs are low (i.e., at night) and power is converted to heat and stored in a heat storage heater. During the day, the heat stored in the blocks of magnetite is slowly released. People then use the heat during the day that they took at a cheap rate at night. We see this application particularly in countries where there is a large cost difference between peak and off-peak rates. LKAB Minerals has been supplying magnetite for this application for more than 25 years.
Energy company Enerray (part of Maccaferri Group) has set up a pilot solar power plant at Ben Guerir in Morocco. They are now testing the use of magnetite in a Thermal Energy Storage Tank (TES). When the sun shines, heat transfer fluid (oil) is passed through the TES and the magnetite stores the energy as heat. After sunset, the magnetite releases the heat and the turbine continues to produce power. Detailed information can be found at: https://www.enerray.com/solar-services/epc/case-studies/csp-iresen-morocco/
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