Study on high-temperature carbonate-chloride molten salt applied to supercritical CO2 concentrated solar power plant

Mixed chloride salts and mixed carbonates are ideal thermal storage materials for future high-temperature concentrated solar power (CSP) plants. However, due to the strong corrosiveness and poor thermal capacity of chloride salts as well as high material costs of carbonates, these two types of molten salts are not suitable for large-scale thermal energy storage (TES) engineering applications. By using chloride salt instead of lithium carbonate in carbonates, the economic benefits and thermal storage potential of high-temperature molten salt can be effectively improved. In this paper, the preparation and optimization, physical property measurement, economic evaluation and corrosivity characterization of carbonate-chloride molten salt are analyzed. Results show that Na2CO3-K2CO3-KCl salts with four different composition ratios have suitable operating temperatures and stable thermophysical properties in the mixed carbonate-chloride molten salt system. The preferred Na2CO3-K2CO3-KCl (37.5%-37.5%-25% wt%) with a melting point of 558.2 °C, a decomposition temperature of 855.2 °C, a specific heat capacity of 1.59–1.77 kJ·kg−1·K−1, a density of 1.85–1.95 g·cm−3, a viscosity of 4.25–13.03 mPa·s, and a thermal conductivity of 0.46–0.53 W·m−1·K−1 is selected to be compared with common chloride salt and carbonate. It has better compatibility with CSP plants based on supercritical CO2 cycle, exhibiting excellent thermophysical properties, lower storage costs, and weaker corrosiveness at storage temperatures of 600–800 °C. Compared with chloride salt, its specific heat capacity is about 1.4 times higher, and the corrosivity is only about 5%. Compared with carbonate, its material cost is only about 25%. This salt will have certain application prospects in high-temperature TES systems.