Materials Performance

NOV 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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36 NOVEMBER 2018 W W W.MATERIALSPERFORMANCE.COM CHEMICAL TREATMENT T Concentrating solar power (CSP) is an efficient way of providing renewable energy but it is still cost-prohibitive. Molten chloride salts can lower the cost of these power plants by push- ing their operating temperature ≥720 °C, thereby increasing their effi- ciency. However, these salts are very corrosive toward the steel alloys used in CSP. An inhibitor package was developed that when added to these salt blends can protect the steel sur- faces by formation of a crystalline perovskite layer. Experiments showed that these chloride salt blends had favorable thermo-physical properties at high temperature. Successful for- mation of the perovskite layer was confirmed by various analytical techniques. The largest source of greenhouse gas emissions in the United States is from burning fossil fuels for electricity, heat, and transportation. Electricity generated from fossil fuels alone contributed to ~20% of t o t a l g re e n h o u s e e m i ssi o n s i n 2 0 1 5 . 1 A l t h o u g h e l e c t r i c i ty f r o m re n e w a b l e sources, such as solar and wind, are becom- ing more abundant, it is still a small frac- tion (~10%) of the total energy demand of the country. Solar is a clean and ubiquitous Corrosion Prevention of Stainless Steel in Molten Chloride Sre Y a Dutta, Dynalene, Inc., Whitehall, Pennsylvania, USA a nime S h Kun D u, Lehigh University, Bethlehem, Pennsylvania, USA form of energy harnessed using different methods such as photovoltaics (PV), con- centrating solar power (CSP), etc. A power tower is a type of CSP plant that uses mir- rors to focus and concentrate sunlight onto a receiver, where the heat is absorbed by a heat transfer fluid that is then converted by a turbine to generate electricity. The high capital and maintenance cost of CSP plants has caused their limited deployment com- pared to the cheaper PV solar option. But one big advantage of CSP plants is that they can provide dispatchable electricity on demand by storing thermal energy in low- cost, stable materials in storage tanks. Molten salts such as nitrate are used as thermal energy storage in the state-of-the art C SP plants, but the temperature of operation is limited to around 550 °C as the molten nitrate salts degrade at tempera- tures ~565 °C. 2-4 A roadmap to Generation 3 CSP plants 5 proposed that by elevating the temperature of operation to >700 °C, the solar to electric efficiency can be increased from 40 to ~50%. Molten chloride salts, which are cheaper and have excellent ther- mal stability >1,000 °C, would be suitable replacements for the molten nitrate salts by pushing the operating temperature from 565 °C to >700 °C. But the molten chloride salts are extremely corrosive at high tem- peratures and attack stainless steel (SS) alloys, causing depletion of the protective chromium oxide (CrO) and making the steel vulnerable to failure. 6

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