Corrosion inhibitors for TES material at high temperature for CSP plants

Abstract

Molten salt technology using nitrate salts as thermal energy storage material is the current state-of-the-art of concentrated solar power technology and power tower central receivers are currently limited by the maximum operating temperature of their working fluid. The limit of solar salt (60wt.%NaNO3 + 40wt.%KNO3) thermal stability is around 565°C with ambient air as the cover gas. In order to obtain higher efficiency goals using molten salt technologies working at higher temperatures (e.g., 650°C to 750°C), a different salt chemistry is required for new generation of CSP plants and chlorides molten salts could be a feasible option. Corrosion mitigation could solve the current issues related with the use of chloride salt at high temperature. In this work, the proposal of different corrosion mitigation strategies has been evaluated, as well as the identification of the most corrosive impurities present in the ternary chloride salt composed by MgCl2/KCl/NaCl (60/20/20 mol%). For this purpose, electrochemical impedance spectroscopy tests were carried out at 700°C on austenitic stainless steel (AISI 304) and a Ni base alloy (Inconel 702) during 100 hours. In this case, MgOHCl was identified as the main important corrosive impurity, present in the chloride salt, to control in the storage system. Regarding the materials tested, Ni base alloy (Inconel 702) showed the most promising results for their use as container material.

The research leading to these results has received funding from Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group GREiA (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. Angel G. Fernández wants to acknowledge the financial support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant No 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme.