Experimental Investigation of Chloride Molten Salts for Thermal Energy Storage Applications

Abstract

Due to their physicochemical and thermal properties, molten halide salt mixtures are potential liquids to be used for sensible thermal energy storage (TES) in Concentrating Solar Power (CSP) plants. Their high thermal stability makes them appropriate candidates to replace the currently used nitrate salts (stable up to 560 °C) when higher operating temperatures are required (up to 700 °C). However, the application of molten halides in CSP causes additional challenges such as increased corrosiveness. In the present work, we focus on the molten salts purity, because it has a direct influence on the corrosion rate of metals. Some halide salts are hygroscopic and heating in presence of water induces hydrolysis of the salt and formation of oxides/hydroxides compounds. First tests using simple heating procedures showed unacceptable salt decomposition and corrosion rates. An advanced process technology and purification approach has been developed yielding improved salt quality and thus reduced corrosion rates. In this paper the optimized process technology for the dehydration of the salt and simultaneously investigation of the corrosion rate depending on the salt impurities is presented. This is an important step for a better utilization of molten halides as liquid media for solar and other application requiring molten salt operation in contact with structural metallic components.