A new study in the United States aims to study how to mitigate corrosion in concentrated solar power (CSP) plants.
The next generation of CSP plants requires high-temperature fluids (such as molten salts) at 550 to 750 degrees Celsius to store heat and generate electricity. However, in this high temperature environment, common alloys used in heat exchangers, pipes and storage vessels of CSP systems will be corroded by molten salts.
The latest research from the National Renewable Energy Laboratory of the U.S. Department of Energy (NREL) aims to mitigate corrosion in CSP plants through nickel-based coatings.
The next generation of CSP plants uses low-cost thermal storage facilities to provide electricity whenever it is needed, helping to support the reliability of the power grid. Molten salts are commonly used for heat transfer fluids and thermal energy storage because they can withstand high temperatures and retain the collected solar heat for hours. In order to ensure that the corrosion rate in the tanks of commercial CSP plants using a molten salt mixture containing sodium chloride, potassium chloride and magnesium chloride can reach a 30-year service life, the corrosion rate must be controlled - less than 20 microns per year.
Current bare stainless steel alloys tested in molten chloride have an annual corrosion rate of up to 4500 microns. To this end, NREL's Judith Gomez-Vidal studied MCrAlX coatings to combat molten chloride corrosion in concentrated solar power applications.
Gomez-Vidal applied different types of nickel-based coatings, commonly used to reduce oxidation and corrosion, to stainless steel. One coating studied, with the chemical formula NiCoCrAlYTa, showed the best performance, limiting the corrosion rate to 190 microns per year, a 96% improvement over uncoated steel. The coating forms a uniform, dense aluminum oxide layer during a 24-hour pre-oxidation period that can be used to further protect the stainless steel from corrosion.
According to Dr. Gomez-Vidal, "Surface protection using the newly studied coatings is very promising for mitigating corrosion in molten salts, especially for substrate surfaces exposed to chlorine-containing vapors in metallurgy and materials engineering. However, corrosion rates in CSP remain quite high, and current efforts have only addressed the relevance of testing material durability in solar applications. More research and development is needed to achieve the desired target corrosion protection level, which may include synergistic effects combining surface protection with chemical control of the molten salt and surrounding environment."
