Study On Properties Of Carbonate-Fluoride High Temperature Molten Salt

In order to maintain the sustainable development of human society, it is indispensable to develop and utilize various renewable energy and green energy. As solar energy is inexhaustible, widespread, clean, economic and safe, it will take a leading role in the future transition of the energy structure, and become the ideal basis of renewable energy. However, the operating temperature of well-developed nitrate system in CSP plants must not exceed600℃, and enhancing molten salt operating temperature and broadening molten salt operating temperature range is an important way to promote the efficiency of solar thermal power generation, so it is of great significance to research the optimum seeking and thermal physical properties of high temperature molten salt.To meet the requirements of solar thermal power generation at high temperature, this paper analyzes the advantages and disadvantages of nitrate, carbonate, chloride, fluoride salts, and determines the carbonate-fluoride high temperature molten salt system as the research object. The composite molten salts are prepared by static melting method. Their melting point, latent heat and solidification/segregation temperature are measured by using of thermal gravimetric and differential scanning calorimetry(TG-DSC), and high temperature molten salts are optimum seeked which have low melting point and broad operating temperature range. The density, viscosity and specific heat capacity of optimum seeked high temperature molten salts are respectively measured by utilizing of CM-1melt tester, RTW-09melt analyzer and differential scanning calorimetry(DSC). Thermal stability of optimum seeked molten salts is investigated under the condition of constant high temperature as well as thermal shock experiment. In addition, the high temperature corrosion of stainless steel in optimum seeked molten salts is also investigated.The experimental results showed that: the advantages of13.04%LiF composite molten salt are low melting point, broad temperature range while the advantages of13.04%NaF composite molten salt are relatively low melting point, relatively broad temperature range and low price. The density of optimum seeked high temperature molten salts decreases with rising temperature, and is in the interests of good linear relationship. The density both ranges from1.94to2.14g·m-3, which is suitable for solar high-temperature thermal power generation applications. The overall trend of the viscosity of optimum seeked high temperature molten salts decreases with rising temperature, which ranges from0.022to0.045Pa·s. Compared with the main salt Na2CO3, the viscosity almost reduced by an order of magnitude, and the size of viscosity is similar to nitrate system, which meet the solar high-temperature thermal power generation requirements well. In the temperature range of450to650℃, the specific heat capacity of13.04%LiF salt ranges from1.47to2.10J·g-1·K-1, which is very suitable for thermal energy storage in CSP. The vapor pressure at high temperature of optimum seeked high temperature molten salts is large, and quality loss is in severe cases, namely the thermal stability of the optimum seeked salts is poor when at constant high temperature, so it is indispensable to pay great attention to sealing measures in molten salt system. The melting points of optimum seeked high temperature molten salts change by less than1%with the increasing times of thermal shock, namely the thermal stability under thermal shock conditions of the optimum seeked high temperature molten salts is very well. The corrosion of304and316L in the optimum seeked high temperature molten salts at800℃is very serious, and the corrosion of304is more serious than316L. Both304and316L can form corrosion layer which combine with substrate closely, and the corrosion products are mainly Fe oxide and Cr oxide.