Concentrated solar power system, more commonly referred to as CSP, is unique among renewable energy generators because even though it is variable, like solar photovoltaic and wind, it can be easily coupled with thermal energy storage as well as conventional fuels, making it highly dispatchable. In these systems molten salts, specifically molten halides, are widely applied as the heat transfer medium due to their good thermal conductivity and relatively good chemical inertness [1]. However, the molten halide salts are highly corrosive, especially at high temperatures (700-1000 °C) [2]. Although superalloys have been developed for high-temperature applications, they are not able to meet both the high-temperature strength and the high-temperature corrosion resistance simultaneously. As a result, the challenge with CSP systems is the potential corrosion of the superalloys in the receivers and heat exchangers at high-temperature operational conditions, which leads to a reduction of heat transfer efficiency and impacts the systems durability [3]. In this work a comprehensive mathematical model has been developed to predict the rates and mechanisms for the corrosion of superalloys that are in contact with a molten salt heat transfer system. Coupled with computational fluid dynamics (CFD), the local electrochemical environment and corrosion rates in a high temperature molten salt system can be predicted. The corrosion model has been designed and benchmarked against a thermosiphon reactor. This thermosiphon reactor exposed alloy coupons to the non-isothermal conditions expected in CSP plants. Cathodic protection was also added to the model as a mitigation strategy for corrosion of metal surfaces. The model compared the corrosion rates for the cases with and without cathodic protection under different operating conditions for different superalloys. Results were in good agreement with the experimental values for the cases with and without the cathodic protection and at isothermal and non-isothermal conditions.

Acknowledgements

The authors gratefully acknowledge the financial support for this work from the DOE EERE SunShot Initiative (DE-AC36-08GO28308) under a subcontract from SRNL to the University of South Carolina. The authors also thank the University of South Carolina Center for Fuel Cells and the CD-adapco group for their support.

References

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2. Y. L. Wang, H. J. Liu, G. J. Yu, J. Hou and C. L. Zeng, J. Fluorine Chem., 178, 14 (2015).

3. H. Cho, J. W. Van Zee, S. Shimpalee, B. A. Tavakoli, J. W. Weidner, B. L. Garcia-Diaz, M. J. Martinez-Rodriguez, L. Olson and J. Gray, Corrosion, 72(6), 742 (2016).