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Està subjecte a una llicència de Reconeixement-NoComercial-SenseObraDerivada 4.

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Phase change materials (PCM) is one of the most interesting solutions to be used in thermal energy storage (TES) systems for direct steam generation (DSG) thermosolar facilities. Properties such as high energy density and energy storing/delivery at constant temperature bring PCM based systems in excellent candidates for DSG facility storage units. Accordingly, LiOH-KOH peritectic mixture, with a melting point of 315 ºC and an enthalpy change of 535 kJ/kg, has been reported as attractive solution for the saturated storage module in DSG plants. A steam-PCM heat exchanger is the critical component to carry out the thermal transference between both substances. Although materials selection to be applied for steam applications is well known, lack of knowledge is detected in the field of high temperature hydroxides corrosion. Therefore, three metallic materials, A516 Gr70 carbon steel, A316L stainless steel and Inconel 625 Ni-base alloy, have been evaluated to determine their corrosion performance after hydroxides exposure. While A516 Gr70 was discarded for this application due to high corrosion rates, A316L and Inconel 625 displayed good corrosion resistance after 2640 hours. Finally, A316L stainless steel was selected as potential candidate for the construction of the steam-PCM heat exchanger considering cost and thermal efficiency optimization.

When a system for thermal energy storage (TES) is designed, many factors must be considered: storage time, dimensions, material to store heat, etc. Usually, molten salts are selected as TES materials because of their great thermal properties at high temperatures. When the whole TES system is going to be built, the material to be used for containing the thermal storage material becomes an important issue. It must have proper mechanical properties, withstand high temperatures and, above all, resist corrosion due to storage material, being in most of the cases, highly corrosive molten salt mixtures. To determine the corrosion on a metal plate, ASTM Standard-G1-03 procedure is usually applied, in which the corroded metal sample is submitted to several cycles including: attack by a chemical solution, washing, cleaning, drying, and weighing. In order to minimize the handling of the sample, a new methodology (Dynamic Gravimetric Analysis, DGA) has been developed and used to determine the corrosion produced in carbon steel A516Gr70 samples induced by different salt mixtures commonly used as molten salts containing different amounts of chloride, at working temperatures conditions. The results show that the higher is the content of chloride in molten salts the greater is the steel loss produced by corrosion and makes the corrosive kinetics to be highly increased when it is overtaken.