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Molten chloride salts are promising advanced high-temperature (400-800°C) thermal energy storage (TES) and heat transfer fluid (HTF) materials in next generation concentrated solar power (CSP) plants for higher energy conversion efficiencies. However, severe corrosion of structural materials in contact with molten chloride salts is one of the most critical challenges limiting their applications at elevated temperatures. In this work, two corrosion mitigation strategies are investigated to alleviate the hot corrosion of structural materials in molten chloride salts: (1) adding corrosion inhibitor and (2) using a Fe-Cr-Al alloy with a protective alumina layer on the surface after pre-oxidation. Three commercial high temperature Fe-Cr-Ni alloys (SS 310, Incoloy ® 800 H and Hastelloy ® C-276) were exposed to molten MgCl 2 -NaCl-KCl (60-20-20 mole.-%) mixed salts with 1 wt.-% Mg as corrosion inhibitor, for 500h at 700°C under inert atmosphere. By addition of the Mg inhibitor, the corrosion rates of the studied alloys were found to be significantly reduced, more precisely by ~83 % for SS 310, ~70 % for In 800 H and ~94 % for Ha C-276 compared with the exposure tests without Mg addition. To assess the second mitigation strategy two pre-oxidized alumina forming Fe-Cr-Al alloys were exposed to the same molten chloride salts without Mg corrosion inhibitor under the same conditions. It is observed that the adherent alumina scales can effectively inhibit the dissolution of Cr and Fe and the bulk penetration of corrosive impurities. Overall, both strategies offer enormous potential for enhancing the expected lifetime of commercial alloys in molten chloride salts. Highlights  By Mg-addition the corrosion rates of alloy SS 310, In 800 H and Ha C-276 are significantly reduced. 2  Adding Mg inhibitor not only mitigates the corrosion caused by impurities, but also promotes the formation of protective MgO layer on metal surfaces.  The corrosion mitigation mechanism of Fe-Cr-Ni based alloys in molten chloride salts by adding Mg is discussed. Pre-oxidized alumina forming Fe-Cr-Al alloys show promising corrosion resistance and stability in molten chloride salts at 700°C for 500h exposure.

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Methane pyrolysis experiments using a quartz glass-steel bubble column reactor filled with liquid tin and cylindrical quartz glass rings serving as a packed bed were conducted at various liquid metal temperature levels in the range of 930 °C to 1175 °C. Besides the liquid metal temperature, special attention was paid to the influence of the feed gas volume flow rate in the range of 50-200 mln/min and the inlet feed gas dilution with nitrogen. Increasing liquid metal temperatures resulted in increasing hydrogen yields, leading to a maximum hydrogen yield of 78 % at 1175 °C and 50 mln/min methane volume flow rate. Within all experimental runs, less than 1.5 mol-% intermediate products were detected in the product gas. The produced carbon appeared as a powder consisting of flake shaped agglomerations in the size range of 15 µm to 20 µm, wherein the particle size varied from 40 nm to 100 nm. During the experiments, the produced carbon was completely separated and accumulated at the top surface of the liquid metal. Only minor quantities were transported with the off gas stream. Within the liquid metal inventory, a thin carbon layer of about 10 µm, probably partly showing the formation of nanotubes, in the hot reaction zone, had been deposited on the quartz glass reactor wall.

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