Corrosion evaluation of eutectic chloride molten salt for new generation of CSP plants. Part 1: Thermal treatment assessment

Abstract

The operating temperature of a steam turbine is limited to 565 ºC by the molten nitrate heat-transfer fluid; therefore, a new molten salt chemistry is needed to increase the maximum operating temperature in the new generation of CSP plants and improve the thermal-to-electrical energy conversion efficiency in the turbine block, such as chloride molten salts. Nevertheless, the prevention of high-temperature corrosion on containment materials using chlorides plays a critical role and a corrosion mitigation plan is needed to achieve the target plant lifetime of 30 years. This paper presents a corrosion mitigation strategy focused on different thermal treatments performed in the eutectic ternary chloride molten salt composed by MgCl2/NaCl/KCl (55.1 wt.%/24.5 wt. %/20.4 wt.%). Corrosion rates were obtained through linear polarization resistance technique in a conventional commercial stainless steel (AISI 304) at 720 ºC during 5 h of immersion after the different thermal treatments carried out. Scanning electron microscopy and XRD analysis were used to confirm the corrosion rates and corrosion layer proposed by electrochemical techniques, obtaining a minimum corrosion rate of 6.033 mm/year for the best thermal treatment performed.

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 was partially funded by the Ministerio de Ciencia, Innovación y Universidades de España (RTI2018-093849-B-C31). 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. This work is partially supported by ICREA under the ICREA Academia programme.