Review on Thermophysical Properties and Corrosion Performance of Molten Salt in High Temperature Thermal Energy Storage

Abstract

Molten salt is a type of material for high temperature thermal energy storage. The thermophysical property, thermostability, and corrosion performance of molten salt are the main points of interest in thermal energy storage field. How to further broaden the usage temperature range of molten salt, develop more molten salts with low melting points, and optimize the thermal conductivity and viscosity of materials has been widely concerned by researchers. Recently, thermal storage technology of molten salt has been applied to the field of concentrating solar power. The thermophysical property, and corrosive performance of molten salt are very important for the large-scale preparation and application of molten salt materials. Based on the classification of molten salt materials, this paper reviews the thermophysical properties of some common molten salts (carbonate, chloride, nitrate, polybasic salt, etc.), and summarizes the current research progress of improving its thermophysical properties. Moreover, the corrosive performance of several types of commonly used molten salts in thermal energy storage applications is analyzed. Besides, some corrosion protection technologies are proposed according to the current application of molten salt and the corrosion mechanism. Finally, the development trend of the application of molten salt in the field of heat storage is prospected.

The Potential Environmental and Social Influence of the Inorganic Salt Hydrates Used as a Phase Change Material for Thermal Energy Storage in Solar Installations

“…The TCM material should have a specified lifetime of 15-20 years, during which the substance used must retain its properties, and the rate of its decomposition should be as long as possible [71]. Hydrates are also chemically inert towards other construction materials (they cause corrosion) and have a low thermal conductivity [12,72]. Song et al [12] believe that the corrosiveness of molten salts affects molten salt tanks, pumps, electric heaters, molten salt piping, valves, heat sinks, connecting hoses, flanges, etc.…”

“…One of the most promising trends is nanoencapsulation, which improves their structural properties and reduces costs and increases the potential of their applications [4,9,10]. Research is still being undertaken to create mixtures of salt hydrates that will lower their corrosiveness, as well as reduce or stabilize supercooling and volume changes [9][10][11][12]. Researchers are working on improving the environmental properties of PCMs.…”

“…The article reviews, from the point of view of environmental risks, the eight considered to be the most promising inorganic salt hydrates used in solar installations [8][9][10][11][12]. They are magnesium chloride hexahydrate, magnesium nitrate hexahydrate, sodium sulfate decahydrate, sodium acetate trihydrate, sodium carbonate decahydrate, calcium chloride hexahydrate, disodium hydrogen phosphate dodecahydrate, and barium hydroxide octahydrate.…”

Molten salts: Potential candidates for thermal energy storage applications

“…Therefore, before a salt hydrate can be employed as a PCM, fundamental study into its thermal characteristics, such as phase change temperature, sub‐cooling behavior, nucleation rate, and enthalpy curve, is required. High freezing points of molten salts constitute one of the major issues as it results in freeze protection issues in the solar field. For instance, freezing points of synthetic oil, ternary, and binary molten salts are 15°C, 120°C, and 220°C respectively, necessitating the use of novel freeze protection technologies and high construction and maintaining costs. The most serious issue is their highly corrosive nature toward metals 220,221 . Preventing corrosion is important for the design of the system and reducing the overall cost of operation.…”

“…• The most serious issue is their highly corrosive nature toward metals. 220,221 Preventing corrosion is important for the design of the system and reducing the overall cost of operation. All these have been already discussed in detail in Section 8.…”