Comparative study on high temperature thermal stability of quaternary nitrate-nitrite mixed salt and Solar salt

Abstract

Molten salts are applied in solar thermal power plant as heat transfer and heat storage medium. In this work, the thermal stability of quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are studied under three constant temperature conditions (500 °C, 565 °C, 600 °C) for 1008h. The results show that the mass ratio of N O 2 − 1 / N O 3 − 1 plays an important role in the thermal physical properties of nitrite/nitrate molten salt. The mass ratio of N O 2 − 1 / N O 3 − 1 in Solar salt increases with the increasing of working temperature, which results in the decreasing of melting point and initial crystal temperature and the increasing of decomposition temperature. The average values of melting point and initial crystal temperature of QNN mixed salt are maximum 119 °C and 24 °C lower than that of Solar salt. Meanwhile, the maximum increase of average values of specific heat and thermal conductivity of QNN mixed salt are 14.26%, 8.18% compared with its base salt, respectively. When the working temperature is higher than decomposition temperature, average values of specific heat and thermal conductivity of Solar salt decrease because of the acceleration of nitrite formation. The viscosity values of QNN mixed salt and Solar salt decrease with the increasing of temperature. Based on the comparative analysis, QNN mixed salt has good application value in practical engineering applications. • The long-time thermal stability of QNN mixed salt and Solar salt are studied. • Nitrite/nitrate ratio plays an vital role in molten salt thermal physical property. • The thermal physical performance of QNN mixed salt is better than Solar salt.