In the receiver, sodium has a distinct performance advantage compared to baseline molten salts, due to its excellent conductivity, resulting in \~8% higher annual solar-to-electric efficiency. Nitrate molten salt concentrating solar power (CSP) systems are currently deployed globally and are considered to be state-of the art heat transfer fluids (HTFs) for present day high-temperature operation. However, decomposition challenges occur with these salts for operation beyond 600 ℃. Although slightly higher limits may be possible with molten salt, to fully realize SunShot efficiency goals of \$15/kWh~th~ HTFs and an LCOE of 6¢/kWh, HTF technologies working at higher temperatures (e.g., 650 °C to 750 °C) will require an alternative to molten salts, such as with alkali metal systems. The poor HTF characteristics of molten salts can lead to excessive tube temperatures not well accommodated with the mechanical strength of existing alloys to achieve a 30-year design life. Further, there is freezing risk of salt in narrow receiver tubes where Sodium’s melting point of approximately 98 ℃ make it an attractive candidate for generation 3 CSP systems. Although chloride salts may present a viable cost TES option, their corrosion well beyond 30 µm/yr. present a cost challenge for two-tank TES whereas the corrosion challenges and vapor pressures found with sodium are substantially less. Additionally, with sodium’s thermal conductivity being approximately two orders of magnitude higher, substantially increased CSP receiver efficiencies may also be possible. This investigation explores the development of a 2.0 MW~th~ sodium receiver system that employs a sodium receiver as the HTF, as well as with a ternary chloride (20%NaCl/40%MgCl/40%KCl) salt as a thermal energy storage (TES) medium to facilitate a 6 hr. storage duration. A sodium-to-salt heat exchanger model as well as a salt-to-sCO2 primary heat exchanger model are employed and evaluated in this investigation. A thermodynamic system design model was developed using Engineering Equation Solver (EES) where state properties were calculated at inlets and outlets along both hot and cold legs of the pilot-scale plant. This investigation assesses receiver performance as well as system efficiency studies for the pump and system operational ranges. Preliminary comparisons are made between a sodium and salt receiver where results using a developed computational thermodynamic model has found improvement with the use of sodium as high as 5.7%. Additionally, current system modelling results indicate a minimum *C*v of 60 required for both cold and hot-side throttle recirculation valves for the operational pump operating between speeds of 1800 and 2400 RPM.


Operational Modes and System Design of a 2.0 Mwth Sodium Molten Salt Pilot System

Division / Sponsor:
Advanced Energy Systems Division (AESD) & Solar Energy Division (SED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ES/ES2020/volume/83631

ES2020 - Virtual Conference 

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.