Molten chloride salt technology for next-generation Thermal Energy Storage (TES): Corrosion control of Fe based alloy at 800°C

Abstract

In this work, the corrosion mitigation strategy by prior thermal purification of ternary chloride salt mixture MgCl2–KCl–NaCl and addition of Magnesium corrosion inhibitor was investigated. Corrosion rates of commercial steel DMV 310N at 800°C under inert argon atmosphere for 200h and 500h in the molten salt phase, vapor phase and interphase were studied. Since during heating to high temperatures the water in hydrated salts decomposes to corrosive impurities like MgOHCl and HCl. The water content of the hydrated salt has a significant effect on the purification process. Coulometric Karl fischer titration was studied to measure the water content to low ppm levels. Moreover, the acid-base titration developed in our group previously was used to measure the MgOHCl corrosive impurity in the molten salt. During the immersion test, the vapor phase impurities like HCl, H2O, O2 and Cl2 were quantitatively analyzed with the installed gas analyzers. After the corrosion tests, the steel samples were characterized by macrostructure and microstructure analysis. The macrostructure analysis was done by descaling using acid wash and microstructure analysis for surface and cross section of steel samples was done by Scanning electron microscopy with electron dispersive X-ray spectroscopy (SEM-EDX). The corrosion rates of alloy DMV 310N are 73 µm/year and 18.6 µm/year after 200h and 500h in molten salt at 800°C respectively. In vapor phase, the corrosion rates are 2.7 µm/year after 500h. The low corrosion rates show the selected affordable Fe based alloy DMV 310N (not Ni based alloy) is corrosion resistant to the purified molten chloride salt and the vapor above the molten salt at 800°C. The corrosion mitigation strategy investigated in this work can successfully control the corrosion of molten chlorides at up to 800°C.