NaNO3-KNO3-KCl/K2CO3 with the elevated working temperature for CSP application: Phase diagram calculation and machine learning

Abstract

Mixed nitrates with relative low melting point have widely been used as thermal storage medium in the concentrated solar power stations. However, their maximum working temperatures aren’t high enough to integrate with more efficient power generation systems such as the supercritical CO2 cycle. In the present work, mixed nitrates with elevated working temperature were obtained by adding KCl/K2CO3. With the help of FactSage software and back-propagation (BP) algorithm combined with genetic algorithm (GA), the eutectic compositions and melting points of NaNO3-KNO3-KCl and NaNO3-KNO3-K2CO3 were predicted, and the validity of BP algorithm combined with GA was verified. Based on DSC and TG curves, the melting points of the as-prepared NaNO3-KNO3-KCl and NaNO3-KNO3-K2CO3 are 206.12 °C and 207.24 °C, respectively, which are in agreement with predicted values. Moreover, their decomposition temperatures were increased to more than 640 °C. In addition, the specific heat capacity of both mixed molten salts was measured, and it also was calculated by using FactSage software. This work provides two new ternary molten salts based on nitrates with higher working temperature and develops the prediction method on phase diagram calculation and machine learning.