Construction And Development Of High-performance Nitrate Molten Salt System

As energy and electrical power are crucial contents to achieve carbon peak and neutrality targets,the development of clean energy for new electrical system has become the main direction of energy transformation in the world today.Concentrated solar thermal power generation system(Concentrated Solar Power,CSP)shows a huge low-carbon advantage,which is undoubtedly one of the most important components of renewable energy power generation.Due to introduction of the heat storage system,CSP has a better peak regulation function than coal power,and its power quality is similar to the coal-fired generator.Energy storage system is the key part of CSP.Energy storage medium is an important factor of energy storage system.Therefore,the key to the popularization and application of solar thermal power generation lies in the construction and development of energy storage medium.Molten salt is the most widely used and mature heat storage medium in solar-thermal power generation.Due to its advantages of low melting point,wide use temperature range,weak corrosive nature and small steam pressure,nitrate molten salt is the dominated energy storage medium for solar-thermal power station.Now,two main commercial materials used in CSP are the binary nitrate molten salt(60wt.%Na NO₃+40 wt.%KNO₃,Solar Salt)and the ternary nitrate/nitrite molten salt(53wt.%KNO₃+40 wt.%Na NO₂+7 wt.%Na NO₃,Hitec).However,the two salts still have bottlenecks of small specific heat capacity and low thermal conductivity,which cannot meet the needs of advanced high-parameter CSP.Therefore,the construction of high-performance molten nitrate salt system is of great significance for the power generation efficiency and operating cost of solar thermal power station.Based on this background,this paper focuses on the construction and development of wider working temperature range,higher thermal conductivity,larger specific heat capacity and other excellent heat storage properties of nitrate molten salt systems.The main research contents are as follows:1.Construction and development of carbon-based nanomaterials doped Solar Salt composites.To further increase the heat transfer performance and heat storage performance of Solar Salt,the doping of nanomaterials was employed.With Solar Salt as the base salt and carbon-based nanomaterials of different scales,structures and shapes as additives,the composite systems of Solar Salt doped with different carbon-based nanomaterials was obtained.Firstly,the preparation methods for different molten salt carbon-based nanocomposites were developed.Then the type and content of carbon-based nanomaterials on the properties of composites were compared and analyzed.Lastly,the structure-activity relationship of different composites was analyzed by various means of characterization and computational simulation.Based on this,the interaction between different carbon-based nanomaterials and Solar salt was speculated and the mechanism of Solar Salt with different carbon-based nanomaterials was constructed.(1)Construction and development of one-dimensional doped Solar Salt composite system with single-walled carbon nanotubes.Solar Salt was doped by two kinds of single-wall carbon nanotubes with the same diameter and different length(SSCNT and LSCNT),the SSCNT-Solar salt composite series and LSCNT-Solar salt composite series were developted.Various thermal properties of the two series composites were investigated and the effects of different lengths and fractions of single-walled carbon nanotubes on the composites were analyzed.(2)Construction and development of one-dimensional doped Solar Salt composite system with two-dimensional graphene served as additives.The GO-Solar Salt composite series were obtained by static melting,and then the RGO-Solar Salt composite series were obtained by in situ reduction of GO-Solar Salt composite series.Various thermal properties of the two series composites were investigated and the effects of different forms and fractions of graphene on the composites were analyzed.(3)Construction and development of one-dimensional doped Solar Salt composite system with quasi-two-dimensional graphite oxide served as additives.Graphite oxide(G1)was prepared by Hummers method and graphite oxide(G2)was prepared Brodie.G1 and G2 doped respectively in Solar Salt,and then G1-Solar Salt composite series and G2-Solar Salt composite series were prepared by static melting method.Various thermal properties of the two series composites were investigated and the effects of different types and fractions of graphite oxide on the composites were analyzed.2.In view of the low heat storage capacity of Hitec,a new ternary nitrate molten salt(KNK)with high specific heat is constructed,and the various thermoproperty parameters and energy storage density of Hitec and KNK are compared,explaining the differences of the structure on the performance through various characterization,especially the molecular dynamics simulation was employed to further explain the microstructural parameters such as radial distribution function,coordination number and angular distribution function.