High-temperature low-cost ternary mixed molten salt heat transfer and storage medium as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of solar energy utilization, and particularly discloses a high-temperature low-cost ternary mixed molten salt heat transfer and storage medium and a preparation method and application thereof, and the ternary mixed molten salt heat transfer and storage medium is composed of 30-37.5 wt% of sodium carbonate, 30-37.5 wt% of potassium carbonate and 25-40 wt% of potassium chloride. According to the ternary mixed molten salt heat transfer and storage medium, potassium chloride is added into carbonate, the content of potassium chloride is optimized, the mixed molten salt with good thermophysical properties can be obtained while the production cost is effectively reduced, the ternary mixed molten salt heat transfer and storage medium is applied to an S-CO2 solar thermal power generation system, the power cycle and overall system efficiency can be effectively improved, and the energy consumption is reduced. And the method has the advantages of low production cost and low heat storage cost.

Description

Technical Field

[0001] This application belongs to the technical field of solar energy utilization, and more specifically, relates to a high-temperature and low-cost ternary hybrid molten salt heat transfer and energy storage medium, a preparation method thereof, and an application thereof. Background Art

[0002] In recent decades, with the aggravation of environmental pollution and the demand for sustainable development, vigorously developing renewable energy sources such as solar energy and wind energy is an important means of energy structure transformation. Concentrating solar power generation technology integrated with energy storage can convert intermittent and fluctuating solar energy into electric energy controllably, and it is a clean power generation and peak shaving technology friendly to grid connection. Among them, the energy storage device can alleviate the adverse effects of the intermittency and volatility of solar energy resources on power supply reliability. Therefore, the energy storage device plays an important role in concentrating solar power plants. Nitrate, namely solar salt, has been widely used in tower-type and trough-type solar demonstration power plants.

[0003] At present, the power generation cost of concentrating solar power technology is high. To further improve efficiency and reduce costs, in 2017, the National Renewable Energy Laboratory of the United States proposed to replace the steam Rankine cycle with a supercritical carbon dioxide (S-CO2) Brayton cycle. Since the S-CO2 Brayton cycle provides a higher power cycle efficiency, it can effectively reduce the scale and cost of the solar field. At a temperature close to 700 °C, the efficiency of the S-CO2 cycle will reach more than 50%, and it is expected to achieve the power generation target of 5.9 cents per kilowatt-hour for solar thermal power plants. The highest working temperature of the most commonly used nitrate (solar salt) in current solar thermal power plants is 565 °C, which cannot meet the needs of S-CO2 Brayton cycle power generation. Chloride salts and carbonate salts have high working temperatures and can work stably in a higher temperature range of 600 - 800 °C, and are more suitable as heat storage media for high-temperature S-CO2 cycle solar thermal power generation systems.

[0004] Compared with the commercial application of nitrates, the research on chloride salts and carbonate salts mostly remains at the laboratory level, mainly focusing on exploring their feasibility of use. The cost of mixed chloride salts is extremely low, but their specific heat capacity is also relatively low (<1.15 kJ·kg -1 ·K -1),(resulting in a lower volumetric heat capacity and heat storage density compared to nitrates, which increases the amount of molten salt used in the heat storage system and the scale of heat storage, and the economic advantage is limited. At the same time, the high corrosivity of chloride salts at high temperatures also poses great challenges to the material properties of storage tanks, instruments, and pipelines, which largely limits their application in engineering practice. The corrosivity of mixed carbonates is relatively low, and among carbonates, the ternary carbonate Na2CO3-K2CO3-Li2CO3 has relatively prominent thermal properties and a suitable working temperature, and it has more advantages compared to nitrates. However, the high market price of Li2CO3 makes the ternary carbonate unsuitable as an economic choice for large-scale heat storage. At the same time, the high viscosity of mixed carbonates also limits their engineering application to a certain extent.

[0005] Currently, in most studies of high-temperature mixed molten salts, chloride salts have a suitable use temperature, but low heat storage density, high corrosivity, and are difficult to apply in engineering; carbonates have good thermal properties and low corrosivity, but lithium-containing carbonates (Li2CO3-Na2CO3-K2CO3) are too costly, and lithium-free carbonates (Na2CO3-K2CO3) have too high a melting point temperature (710 °C), and neither can meet the temperature and use requirements of S-CO2 solar thermal power plants. Summary of the Invention

[0006] Aiming at the defects of the prior art, the present application provides a high-temperature low-cost ternary mixed molten salt heat transfer and heat storage medium, its preparation method and application, aiming to solve the problem that existing mixed molten salts cannot simultaneously meet the requirements of low cost and good thermal properties.

[0007] According to one aspect of the present application, a high-temperature low-cost ternary mixed molten salt heat transfer and heat storage medium is provided. The ternary mixed molten salt heat transfer and heat storage medium is composed of 30 wt% - 37.5 wt% sodium carbonate, 30 wt% - 37.5 wt% potassium carbonate, and 25 wt% - 40 wt% potassium chloride.

[0008] Through the above technical solution conceived by the present application, compared with the prior art, since the present application proposes to add only potassium chloride to carbonates and optimize its content, good thermal properties can be obtained while reducing costs.

[0009] As a further preference, the ternary mixed molten salt heat transfer and heat storage medium is composed of 35 wt% - 37.5 wt% sodium carbonate, 35 wt% - 37.5 wt% potassium carbonate, and 25 wt% - 30 wt% potassium chloride.

[0010] As a further preference, the ternary mixed molten salt heat transfer and heat storage medium is composed of 37.5 wt% sodium carbonate, 37.5 wt% potassium carbonate, and 25 wt% potassium chloride.

[0011] As a further preference, the specific heat capacity of the ternary mixed molten salt heat transfer and heat storage medium is 1.22 kJ·kg -1 ·K -1 ~1.77 kJ·kg -1 ·K -1 within the temperature range of 600°C to 800°C, and the thermal conductivity is 0.42 W·m -1 ·K -1 ~0.54W·m -1 ·K -1 .

[0012] According to another aspect of the present application, a preparation method of the above-mentioned ternary mixed molten salt heat transfer and heat storage medium is provided, specifically: mixing sodium carbonate, potassium carbonate and potassium chloride in proportion and drying them at a constant temperature to obtain a mixed molten salt; heating the mixed molten salt to the melting temperature and keeping it warm for a preset time, so that the mixed molten salt melts and mixes evenly, and finally cooling it to room temperature and crushing it to a preset particle size to obtain the ternary mixed molten salt heat transfer and heat storage medium.

[0013] As a further preference, the temperature for drying at a constant temperature is 105°C to 120°C, and the time for drying at a constant temperature is more than 24 hours.

[0014] As a further preference, the melting temperature is 600°C to 650°C, and the melting time is 2 hours to 4 hours.

[0015] As a further preference, the crushing particle size is 50 mesh to 300 mesh.

[0016] According to yet another aspect of the present application, an application of the above-mentioned ternary mixed molten salt heat transfer and heat storage medium in a supercritical carbon dioxide solar power generation system is provided.

[0017] Generally speaking, compared with the prior art through the above technical solutions conceived by the present application, the following technical advantages are mainly possessed: By adding potassium chloride to the carbonate and optimizing its content, the present application can obtain a mixed molten salt with good thermal properties while effectively reducing the production cost. Among them, the use temperature range of the ternary mixed molten salt heat transfer and heat storage medium is 600°C to 800°C, the melting point temperature range is 558.1°C to 559.1ºC, and the decomposition temperature range is 844.6°C to 863.9ºC, which can meet the temperature and use requirements of the S-CO2 solar thermal power generation station. At the same time, the specific heat capacity of the ternary mixed molten salt heat transfer and heat storage medium is 1.22 kJ·kg -1 ·K -1 ~1.77 kJ·kg -1 ·K -1 , and the thermal conductivity is 0.42 W·m -1 ·K -1 ~0.54W·m-1 ·K -1 , with a density of about 1.79 g·cm -3 ~1.96 g·cm -3 , having good thermal properties and a relatively high density. Applying this ternary mixed molten salt heat transfer and energy storage medium to an S-CO2 solar thermal power generation system can effectively improve the power cycle and overall system efficiency. And the viscosity of this ternary mixed molten salt heat transfer and energy storage medium is about 0.77 cp to 18.09 cp in the temperature range of 600°C to 800°C, and the viscosity is significantly lower than that of common carbonate energy storage materials, which is beneficial to reducing the resistance and cost of the molten salt heat transfer pipeline system in solar thermal power generation. In addition, the cost of the energy storage material of this ternary mixed molten salt heat transfer and energy storage medium is about 3.58 yuan / kg -1 ~3.79 yuan·kg -1 , and the sensible heat energy storage cost is about 39.97 yuan·kW -1 ·h -1 ~49.42 yuan·kW -1 ·h -1 , having the advantages of low production cost and energy storage cost, and can achieve large-scale engineering applications in the S-CO2 solar thermal power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the DSC curve of the ternary mixed molten salt heat transfer and energy storage medium prepared in Examples 1 to 4 of the present application; Figure 2 is the TG curve of the ternary mixed molten salt heat transfer and energy storage medium prepared in Examples 1 to 4 of the present application; Figure 3 is the specific heat capacity test result of the ternary mixed molten salt heat transfer and energy storage medium prepared in Examples 1 to 4 of the present application; Figure 4 is the density measurement and calculation result of the ternary mixed molten salt heat transfer and energy storage medium prepared in Examples 1 to 4 of the present application; Figure 5 is the viscosity measurement result of the ternary mixed molten salt heat transfer and energy storage medium prepared in Examples 1 to 4 of the present application; Figure 6 is the thermal conductivity measurement result of the ternary mixed molten salt heat transfer and energy storage medium prepared in Examples 1 to 4 of the present application; Figure 7 is the DSC thermal analysis test result of the mixed molten salt with KCl added to carbonate; Figure 8 is the DSC thermal analysis test result of the mixed molten salt with NaCl added to carbonate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] To make the objectives, technical solutions and advantages of this application more clear and understandable, the following further details this application in combination with the attached drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0020] According to one aspect of this application, a high-temperature and low-cost ternary mixed molten salt heat transfer and heat storage medium is provided. The ternary mixed molten salt heat transfer and heat storage medium is composed of 30 wt% - 37.5 wt% sodium carbonate, 30 wt% - 37.5 wt% potassium carbonate, and 25 wt% - 40 wt% potassium chloride.

[0021] By adding potassium chloride to the carbonate and optimizing its content, this application can obtain a mixed molten salt with good thermal properties while effectively reducing production costs. Among them, the operating temperature range of the ternary mixed molten salt heat transfer and heat storage medium is 600°C - 800°C, the melting point temperature range is 558.1°C - 559.1°C, and the decomposition temperature range is 844.6°C - 863.9°C, which can meet the temperature and usage requirements of the S-CO2 solar thermal power generation station.

[0022] At the same time, the specific heat capacity of the ternary mixed molten salt heat transfer and heat storage medium provided by this application is 1.22 kJ·kg -1 ·K -1 ~1.77 kJ·kg -1 ·K -1 , the thermal conductivity is 0.42 W·m -1 ·K -1 ~0.54 W·m -1 ·K -1 , the density is about 1.79 g·cm -3 ~1.96 g·cm -3 . It has good thermal properties and a relatively high density. Applying the ternary mixed molten salt heat transfer and heat storage medium to the S-CO2 solar thermal power generation system can effectively improve the power cycle and the overall system efficiency. And the viscosity of the ternary mixed molten salt heat transfer and heat storage medium is about 0.77 cp - 18.09 cp in the temperature range of 600°C - 800°C, and the viscosity is significantly lower than that of common carbonate heat storage materials, which is beneficial to reducing the resistance and cost of the molten salt heat transfer pipeline system in solar thermal power generation.

[0023] In addition, the cost of the heat storage material of the ternary mixed molten salt heat transfer and heat storage medium is about 3.58 yuan·kg -1 ~3.79 yuan·kg -1 , and the heat storage cost is about 39.97 yuan·kW -1 ·h -1 ~49.42 yuan·kW -1 ·h -1, with the advantages of low production cost and low heat storage cost, can achieve large-scale engineering applications in the S-CO2 solar thermal power generation system.

[0024] This application carried out DSC thermal analysis tests on the addition of 10%, 20%, 30% and 40% of NaCl or KCl (the specific components are shown in Table 1), and the results are as Figure 7 , 8 shown. The carbonate-chloride mixed molten salt with NaCl as an additive has large fluctuations in the heating curve after melting, resulting in unstable specific heat capacity values and being not conducive to heat storage; while the carbonate-chloride mixed molten salt with KCl as an additive has a stable overall temperature rise trend. Especially when the mass addition ratio of KCl is 30% and 40%, the DSC curve does not show a rapid decline trend, indicating that the specific heat capacity value is stable.

[0025] Table 1 Content of each component in the mixed molten salt

[0026] Further preferably, the ternary mixed molten salt heat transfer and heat storage medium provided by this application is composed of 35 wt% - 37.5 wt% of sodium carbonate, 35 wt% - 37.5 wt% of potassium carbonate and 25 wt% - 30 wt% of potassium chloride. Within this range, the thermal property parameters such as the upper limit of the working temperature, specific heat capacity, density, and thermal conductivity of the mixed molten salt are higher, which is beneficial to the heat storage and heat release process. The specific heat capacity is 1.44 kJ·kg -1 ·K -1 ~1.77 kJ·kg -1 ·K -1 , the thermal conductivity is 0.46 W·m -1 ·K -1 ~0.54 W·m -1 ·K -1 , and the density is about 1.83 g·cm -3 ~1.96 g·cm -3 .

[0027] More preferably, the ternary mixed molten salt heat transfer and heat storage medium is composed of 37.5 wt% of sodium carbonate, 37.5 wt% of potassium carbonate and 25 wt% of potassium chloride. The specific heat capacity of the ternary mixed molten salt heat transfer and heat storage medium with this composition is 1.59 kJ·kg -1 ·K -1 ~1.77 kJ·kg -1 ·K -1 , showing a trend that the specific heat capacity increases with the increase of temperature within the working temperature range. Applying it to heat storage will have greater advantages in scale control and cost reduction and efficiency improvement.

[0028] According to another aspect of the present application, there is provided a method for preparing the above-mentioned high-temperature and low-cost ternary mixed molten salt heat transfer and energy storage medium, specifically as follows: S1 Weigh sodium carbonate, potassium carbonate and potassium chloride according to the mass ratio using a high-precision analytical balance, grind them in a mortar to make them fully mixed, and then place them in a constant-temperature drying oven, and keep them at a constant temperature of 105°C to 120°C for more than 24 hours to obtain the mixed molten salt; S2 Adopt the static melting method, heat the mixed molten salt to the melting temperature and keep it warm for a preset time, so that the mixed molten salt melts and mixes evenly, and take it out after the mixed molten salt cools; S3 Since the mixed molten salt will form hard solid crystalline salt after being melted, it is crushed to 50 to 300 meshes by a crusher to prepare the ternary mixed molten salt heat transfer and energy storage medium. To avoid water absorption and crystallization, the prepared ternary mixed molten salt heat transfer and energy storage medium is placed in a constant-temperature drying oven for standby to avoid moisture crystallization caused by water absorption.

[0029] Furthermore, the melting temperature is 600°C to 650°C, and the melting time is 2 to 4 hours. If the melting temperature is too high or the melting time is too long, it may cause excessive volatilization of the components in the mixed molten salt, while if the melting temperature is too low or the melting time is too short, it may cause the mixed molten salt not to melt and mix evenly, and thus the eutectic salt cannot be obtained.

[0030] According to yet another aspect of the present application, there is provided the application of the above-mentioned high-temperature and low-cost ternary mixed molten salt heat transfer and energy storage medium in a supercritical carbon dioxide solar power generation system.

[0031] The following further illustrates the technical solutions provided by the present application according to specific embodiments.

[0032] Example 1 S1 Weigh 75 g of sodium carbonate, 75 g of potassium carbonate and 50 g of potassium chloride using a high-precision analytical balance, grind them in a mortar to make them fully mixed, and then place them in a constant-temperature drying oven for constant-temperature drying to obtain the mixed molten salt; S2 Adopt the static melting method, heat the mixed molten salt to 650°C and keep it warm for 3 hours, so that the mixed molten salt melts and mixes evenly, and take it out after the mixed molten salt cools; S3 Use a crusher to crush it to 50 to 300 meshes to prepare the ternary mixed molten salt heat transfer and energy storage medium, which is composed of 37.5 wt% of sodium carbonate, 37.5 wt% of potassium carbonate and 25 wt% of potassium chloride.

[0033] Example 2 S1 Weigh 70 g of sodium carbonate, 70 g of potassium carbonate and 60 g of potassium chloride using a high-precision analytical balance, grind them in a mortar to make them fully mixed, and then place them in a constant-temperature drying oven for constant-temperature drying to obtain the mixed molten salt; In S2, the static melting method is adopted. The mixed molten salt is heated to 650 °C and kept warm for 3 hours, so that the mixed molten salt melts and mixes evenly. After the mixed molten salt cools down, it is taken out. In S3, it is crushed to 50 - 300 meshes by a crusher to obtain the ternary mixed molten salt heat transfer and heat storage medium, which is composed of 35 wt% sodium carbonate, 35 wt% potassium carbonate and 30 wt% potassium chloride.

[0034] Example 3 In S1, 65 g of sodium carbonate, 65 g of potassium carbonate and 70 g of potassium chloride are weighed by a high-precision analytical balance and ground in a mortar to make them fully mixed, and then placed in a constant-temperature drying oven for constant-temperature drying to obtain the mixed molten salt. In S2, the static melting method is adopted. The mixed molten salt is heated to 650 °C and kept warm for 3 hours, so that the mixed molten salt melts and mixes evenly. After the mixed molten salt cools down, it is taken out. In S3, it is crushed to 50 - 300 meshes by a crusher to obtain the ternary mixed molten salt heat transfer and heat storage medium, which is composed of 32.5 wt% sodium carbonate, 32.5 wt% potassium carbonate and 35 wt% potassium chloride.

[0035] Example 4 In S1, 60 g of sodium carbonate, 60 g of potassium carbonate and 80 g of potassium chloride are weighed by a high-precision analytical balance and ground in a mortar to make them fully mixed, and then placed in a constant-temperature drying oven for constant-temperature drying to obtain the mixed molten salt. In S2, the static melting method is adopted. The mixed molten salt is heated to 650 °C and kept warm for 3 hours, so that the mixed molten salt melts and mixes evenly. After the mixed molten salt cools down, it is taken out. In S3, it is crushed to 50 - 300 meshes by a crusher to obtain the ternary mixed molten salt heat transfer and heat storage medium, which is composed of 30 wt% sodium carbonate, 30 wt% potassium carbonate and 40 wt% potassium chloride.

[0036] For the ternary mixed molten salt heat transfer and heat storage media prepared in Examples 1 - 4, a STA449F3 type synchronous thermal analyzer (DSC-TG) is used to test the melting point, decomposition temperature and specific heat capacity of the ternary mixed molten salt heat transfer and heat storage media, a molten salt comprehensive physical property tester is used to test the density of the ternary mixed molten salt heat transfer and heat storage media, a high-temperature viscometer is used to test the viscosity of the ternary mixed molten salt heat transfer and heat storage media, and an LFA 457 type laser thermal conductivity meter is used to test the thermal conductivity of the ternary mixed molten salt heat transfer and heat storage media. The results are shown in Table 2 and Figures 1 - 6 as shown. At the same time, the heat storage material cost and heat storage cost of the ternary mixed molten salt heat transfer and heat storage media prepared in Examples 1 - 4 are shown in Figure 3.

[0037] Table 2 Melting points and decomposition temperatures of the ternary mixed molten salt heat transfer and heat storage mediums prepared in Examples 1-4

[0038] Table 3 Heat storage material costs and heat storage costs of the ternary mixed molten salt heat transfer and heat storage mediums prepared in Examples 1-4

[0039] Figure 1 is the DSC curve of the ternary mixed molten salt heat transfer and heat storage medium, as Figure 2 is the TG curve of the ternary mixed molten salt heat transfer and heat storage medium, Figure 3 is the specific heat capacity test result of the ternary mixed molten salt heat transfer and heat storage medium, Figure 4 is the density measurement and calculation result of the ternary mixed molten salt heat transfer and heat storage medium, Figure 5 is the viscosity measurement result of the ternary mixed molten salt heat transfer and heat storage medium, Figure 6 is the thermal conductivity measurement result of the ternary mixed molten salt heat transfer and heat storage medium. Its specific heat capacity is about 1.59 - 1.77 kJ·kg -1 ·K -1 and its density is about 1.79 - 1.96 g·cm -3 , its viscosity is about 0.77 - 18.09 cp, and its thermal conductivity is about 0.46 - 0.53 W·m -1 ·K -1 , the heat storage material cost is about 3.58 - 3.79 yuan·kg -1 , and the sensible heat storage cost is about 39.97 - 49.42 yuan·kW -1 ·h -1 .

[0040] Compared with common carbonate heat storage materials, the liquid viscosity and heat storage cost of the ternary mixed molten salt heat transfer and heat storage medium provided in this application are significantly reduced, the specific heat capacity and density are slightly reduced, and the thermal conductivity remains the same; compared with common chloride heat storage materials, the specific heat capacity and density of the ternary mixed molten salt heat transfer and heat storage medium provided in this application are higher, the thermal conductivity remains the same, and the liquid viscosity and heat storage cost increase slightly. Generally speaking, the overall performance indicators of the high-temperature and low-cost ternary mixed molten salt heat transfer and heat storage medium provided in this invention are relatively better overall.

[0041] In the description of this application, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality" means two or more unless otherwise specifically defined.

[0042] In addition, references to "one embodiment" throughout this specification; the language such as "one embodiment", "one example", or the like means that the specific features, structures, or characteristics described in connection with that embodiment are included in at least one embodiment of the present application. Thus, the appearances of the phrase "in one embodiment;" and similar language throughout this specification "in one embodiment" may or may not all refer to the same embodiment.

[0043] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application should be included within the protection scope of the present application.

Claims

1. High-temperature and low-cost ternary mixed molten salt heat transfer and heat storage medium, characterized in that: The ternary mixed molten salt heat transfer and heat storage medium consists of 30 wt% to 37.5 wt% of sodium carbonate, 30 wt% to 37.5 wt% of potassium carbonate and 25 wt% to 40 wt% of potassium chloride.

2. The ternary mixed molten salt heat transfer and heat storage medium according to claim 1, characterized in that: The ternary mixed molten salt heat transfer and heat storage medium consists of 35 wt% to 37.5 wt% of sodium carbonate, 35 wt% to 37.5 wt% of potassium carbonate and 25 wt% to 30 wt% of potassium chloride.

3. The ternary mixed molten salt heat transfer and heat storage medium according to claim 1, characterized in that: The ternary mixed molten salt heat transfer and heat storage medium consists of 37.5 wt% of sodium carbonate, 37.5 wt% of potassium carbonate and 25 wt% of potassium chloride.

4. The ternary mixed molten salt heat transfer and heat storage medium according to claim 1, characterized in that: The specific heat capacity of the ternary mixed molten salt heat transfer and heat storage medium is 1.22 kJ·kg in the temperature range of 600℃~800℃ -1 ·K -1 ~1.77 kJ·kg -1 ·K -1 , thermal conductivity is 0.42 W·m -1 ·K -1 ~0.54 W·m -1 ·K -1 .

5. The method for preparing the ternary mixed molten salt heat transfer and heat storage medium according to any one of claims 1 to 4, characterized in that: Specifically, sodium carbonate, potassium carbonate and potassium chloride are mixed in proportion and then dried at a constant temperature to obtain a mixed molten salt; the mixed molten salt is heated to a melting temperature and kept warm for a preset time so that the mixed molten salt is melted and mixed evenly, and finally cooled to room temperature and crushed to a preset particle size to obtain the ternary mixed molten salt heat transfer and heat storage medium.

6. The preparation method according to claim 5, characterized in that: The constant temperature drying temperature is 105°C to 120°C, and the constant temperature drying time is more than 24 hours.

7. The preparation method according to claim 5, characterized in that: The melting temperature is 600°C to 650°C, and the melting time is 2 hours to 4 hours.

8. The preparation method according to claim 5, characterized in that: The crushing particle size is 50 mesh to 300 mesh.

9. Use of the ternary mixed molten salt heat transfer and heat storage medium as claimed in any one of claims 1 to 4 in a supercritical carbon dioxide solar power generation system.

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