Materials selection of steam-phase change material (PCM) heat exchanger for thermal energy storage systems in direct steam generation facilities

- A516 Gr70, A316L and Inconel 625 corrosion by LiOH-KOH mixture has been evaluated.
- Tests performed in closed autoclaves under N2 atmosphere. LiOH-KOH mixture at 360 °C.
- A516 Gr70 does not offer long term corrosion resistance.
- Inconel 625 shows good corrosion performance but is discarded due to high cost.
- A316L selected as potential candidate for the design of steam-PCM heat exchanger.

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 °C 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 h. Finally, A316L stainless steel was selected as potential candidate for the construction of the steam-PCM heat exchanger considering cost and thermal efficiency optimization.

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