Assessment and development of molten salt storage and heat transfer fluids for solar thermal power plants and industrial processes.

Abstract

For solar power plants the use of molten salt as a thermal storage material or heat transfer fluid is one of the key technologies. Due to their very low vapour pressure and comparatively high thermal stability, molten salts are promising heat transfer and storage media. At present, the two-tank molten salt storage is the most developed concept. Commercial examples of two-tank storages and current research developments such as the single-tank thermocline storage with filler material are presented. Nitrate molten salts are the first choice in solar thermal power plants due to several advantages in comparison with other molten salts. However, the binary salt mixture NaNO3-KNO3, which is currently used in commercial storage systems, has some disadvantages that have led to further research. Different known salt mixtures and results of molten quartenary salt investigations carried out at DLR are presented and compared with results in literature. The results of the measurements on liquidus lines on the quaternary system K,Li,Na // NO2,NO3 showed similar results with those found in literature. In addition, stability measurements by thermogravimetry were conducted. These measurements, all in a nitrogen atmosphere, show that the stability of this novel mixture is similar to that of NaNO3.