Multidimensional Modeling of Nickel Alloy Corrosion inside High Temperature Molten Salt Systems

Concentrated solar power (CSP) systems in the presence of high operating temperature heat transfer fluids for power production processes has attracted more attention in recent years. The challenge with these systems is the corrosion of alloys at high-temperature (700-1000°C) in receivers and heat exchangers causing a reduction in heat transfer efficiency and influencing the apparent durability [1-3]. In this work, a corrosion model that includes thermal gradients and fluid flow is developed to predict corrosion rates and mechanisms observed in a nickel base alloy in contact with a molten salt heat transfer system.

     The model takes into account the electrochemical kinetics in addition to mass transfer-limited corrosion coupled with a computational fluid dynamic (CFD) model that can predict the local electrochemical environment and corrosion rates in a system with temperature and fluid flows. The kinetic and mass transfer parameters used in the model are based on the experimental coupon studies were conducted between 700-1000 °C within molten salt in a thermosiphon reactor that designed to allow exposure the coupons to the non-isothermal condition.  The thermal gradients between top and bottom of the reactor could induce natural convection of the salts [4-5].

     Fig. 1 shows an example of the model prediction of corrosion rate distribution, i (A/cm²) at coupon surfaces at both hot and cold zones in addition to the temperature gradient near the wall and streamlines that show the flow pattern of molten salt inside the thermosiphon. the This corrosion model accounts for the effects of different operational conditions such as temperature and component concentrations in addition to the alloy surface properties on the corrosion rate.

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 Alabama and 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

1. C. Forsberg, P.F. Peterson, and H.H. Zhao, J. Sol. Energy Eng. Trans.-ASME, 129, 141-146, 2007.
2. C. Forsberg, Progress in Nuclear Energy, 47, 32-43, 2005.
3. D. Ludwig, L. Olson, K. Sridahran, M. Anderson, and T. Allen, Corrosion Engineering Science and Technology, 46, 360-364, 2011.
4. B. L. Garcia-Diaz, L. Olson, M. Martinez-Rodriguez, R. Fuentens, J. Gray. paper #741, 2014 ECS and SMEQ Joint International Meeting, Cancun, Mexico, Oct. 08, 2014.
5. R. Fuentens, L. Olson, M. Martinez-Rodriguez, J. Gray, B. L. Garcia-Diaz. paper #743, 2014 ECS and SMEQ Joint International Meeting, Cancun, Mexico, Oct. 08, 2014.

Figure 1. Corrosion rate distribution, i (A/cm²) at coupon surfaces at both hot and cold zones in addition to the temperature gradient near the wall and streamlines inside the thermosiphon.