Investigation of KNO2-KNO3-K2CO3 mixed molten salts with higher working temperature for supercritical CO2 concentrated solar power application

Abstract

In the present work, the new eutectic composition of KNO2-KNO3-K2CO3 ternary salt for sCO2 solar thermal power generation is predicted by thermodynamic calculation, then the thermophysical properties of the eutectic salt are investigated by experiments combined with theoretical calculation, further studies are focused on its corrosivity. The results show that the predicted ternary molten salt is confirmed as 0.259KNO2–0.687KNO3–0.054K2CO3. Due to mixing a small amount of K2CO3, the upper limit of the operating temperature of the eutectic salt can reach 750.1 °C, and the melting point and the freezing point have a good thermal stability in the heating-cooling cycles. The calculated specific heat is lower than the measured one which can maintain at 1.407 J/(g·K) in the range of 400–450 °C. With the increase of temperature, the density decreases linearly and the thermal diffusivity tends to increase, thus there is a slight growing in thermal conductivity with an average value of 0.3 W/(m·K). The novel eutectic salt has an energy storage density of 865 MJ/m3. Although containing a low concentration of K2CO3, the eutectic salt shows low corrosion to 310S stainless steel. After the corrosion test of 240 h at 600 °C, the mass loss of stainless steel maintains a constant at 0.067 mg/cm2. The above results indicate that 0.259KNO2–0.687KNO3–0.054K2CO3 eutectic salt is a promising high-temperature thermal storage material for solar thermal power generation.