Solar Salt above 600 °C: Impact of Experimental Design on Thermodynamic Stability Results
Julian Steinbrecher, Markus Braun, Thomas Bauer, Sebastian Kunkel, Alexander Bonk
Abstract
Thermal energy storage (TES) based on molten salts has been identified as a key player in the transition from fossil fuels to renewable energy sources. Solar Salt, a mixture of NaNO3 (60 wt%) and KNO3 (40 wt%), is currently the most advanced heat transfer and storage material used in concentrating solar power (CSP) plants. Here, it is utilized to produce electricity via a Rankine cycle, with steam temperatures reaching 550 °C. The goal of this study is to increase the operating temperature of solar salt to over 600 °C, allowing it to be adapted for use in high-temperature Rankine cycles with steam temperatures greater than 600 °C. Yet, this goal is impaired by the lack of available thermodynamic data given the salt’s complex high-temperature decomposition and corrosion chemistry. The study explores the thermodynamics of the decomposition reactions in solar salt, with a focus on suppressing decomposition into corrosive oxide ions up to a temperature of 620 °C. The results provide a new understanding of the stabilization of solar salt at previously unexplored temperatures with effective utilization of gas management techniques.