Thermodynamic calculations and experimental studies of ternary molten salts for high-temperature thermal energy storage

Abstract

Chloride, fluoride, and carbonate salts act as potentially promising thermal storage media for high-temperature thermal energy storage (TES) systems. In this study, the eutectic components of three ternary molten salts; i.e., NaCl–KCl–LiCl, NaCl–KCl–NaF, and NaCl–KCl–Na2CO3 were first predicted by using thermodynamic calculations and the accuracy was further verified by differential scanning calorimetry. Next, the melting point, thermal conductivity, latent heat, specific heat, and TES density of the three eutectic salts were determined and calculated by thermal analysis methods and compared with those of Solar and Hetic salts. The results show that the eutectic salt NaCl–KCl–Na2CO3 exhibits the highest TES density, which is 1.87 and 1.31 times higher than that of the Solar salt and Hetic salt, respectively. Moreover, the costs of the three eutectic salts were calculated and analyzed herein, and the cost per unit TES density of the eutectic salt NaCl–KCl–Na2CO3 accounted for only 17.01 % and 29.75 % of the cost of the Solar salt and Hetic salt, respectively. The three eutectic salts exhibit good thermal stability even at a high temperature of 700 °C, and thus act as potential candidates for thermal storage materials for the next-generation concentrating solar power plants.