Stabilizing Molten Salts Through Additives for High Temperature CSP Applications

Solar salt, an equimolar concentration of KNO3 and NaNO3 is currently being used as the heat transfer fluid in concentrating solar power plants. It decomposes around 600 °C. Hitec® salt, another potential salt mixture, is not stable beyond 538 °C. There has been work directed toward improving its high temperature stability of Hitec® salt by adding a chloride component. It was observed that the stability of the mixture increased by 50 °C enabling its use at temperatures above 600 °C. A new ternary mixture comprising of Ca(NO3)2–KNO3–NaNO3 termed as “Base salt” was prepared in the lab which has a significantly lower freezing temperature (145 °C), and the high temperature stability is above 600 °C. In the current work, additions of other components like NaCl, KCl, LiCl, and CaCl2 in various proportions were done to the Base salt and the thermogravimetric studies were carried out in a custom-made TGA set up to analyze any further improvement in high temperature stability of the mixture. Among all the chloride additions, 5% sodium chloride (NaCl) and 5% NaCl + 5% KCl addition by weight to the Base salt proved to be most promising.