SaltMe

SaltMe: Salt-metal systems as new storage materials with improved thermal conductivity for storing thermal energy

Short description

In solar thermal power plants, solar radiation is bundled and used to heat a heat transfer medium. This is used to generate steam, which is used in a conventional steam turbine generator unit to generate electricity. Salts are increasingly being used as heat carriers, because they can be used both for transporting and storing heat and enable high operating temperatures of currently around 400°C. In order to be able to generate electricity even more efficiently and thus more cost-effectively with solar thermal power plants in the future, the operating temperature must be increased further. However, the nitrate salts used according to the current state of the art are unstable at higher temperatures, which is why other salts, such as chloride salts, have to be used. Pure chloride salts, on the other hand, are unsuitable because they have low thermal conductivity and significantly increase corrosion processes. The idea of ​​this Underlying the project is to add metals to the molten salt. These metal-salt systems are expected to have significantly higher thermal conductivity and at the same time lower corrosiveness. Since there are infinitely many ways of mixing chloride salts with each other and with metals, thermochemical calculations should predict potentially suitable mixtures of substances for use in solar thermal power plants. Unfortunately, there is not enough data available for such material systems, which is why it is first necessary to carry out fundamental investigations in order to determine these material data.

The SaltMe project takes place in cooperation with the Research Center Jülich. There, various salt systems and later metal-salt systems are first produced and thermochemically characterized. The thermal conductivity of their melts is then measured at the TU Dresden using the hot wire method (Transient Hot Wire) in a test stand specially developed for this purpose. The advantage of this method is that only a few parameters have to be measured and a high level of accuracy can be achieved. A schematic test setup is shown in Figure 1. The two heating wires, which are located in the melt, are used both as a heat source and to measure the local temperature. Thus, only the time-dependent change in the electrical voltage is measured at a constant current and the thermal conductivity is calculated from this. The data collected on the investigated salt and metal-salt systems will then be used for simulations in order to find accurate mixtures of substances with the best possible thermal conductivity and high thermal stability. For economic and technical reasons, combined melts of lithium, sodium, potassium, magnesium and calcium chloride and the corresponding metals (Li, Na, K, Mg and Ca) are being investigated.