Low-melting-point binary molten salt heat storage material and preparation method thereof

Abstract

The invention discloses a low-melting-point binary molten salt heat storage material and a preparation method thereof, the low-melting-point binary molten salt heat storage material comprises NaNOx and KNOy, x is 2 and 3, y is 2 and 3, and x is not equal to y. When x is 2 and y is 3, the mass percent of NaNO2 is 30%-40%, and the mass percent of KNO3 is 60%-70%. When x is 3 and y is 2, the mass percentages of NaNO3 and KNO2 are 50%-60% and 40%-50% respectively. Compared with the final melting temperature of 249 DEG C and the decomposition temperature of 586 DEG C of the most common fused salt material solar salt (60wt% of NaNO3 and 40wt% of KNO3) at present, the prepared fused salt material has the advantages of low melting point and wide operating temperature range, can be used in the field of recycling medium-high temperature heat transfer and storage, and is beneficial to popularization of the application in the field of medium-high temperature energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of medium and high temperature energy storage, and specifically relates to a low-melting-point binary molten salt heat storage material and a preparation method thereof. Background Art

[0002] As a renewable energy source, solar energy has numerous remarkable advantages. First of all, solar energy resources are abundant and inexhaustible. The solar energy received by the Earth every day far exceeds the daily needs of humans. As long as it is effectively utilized, it can meet the global energy demand. Secondly, no greenhouse gases, wastewater or waste are produced during the utilization of solar energy, making it a clean and environmentally friendly energy form. Compared with traditional fossil fuels, its negative impact on the environment is minimal, contributing to slowing down global climate change and environmental pollution problems. In addition, the solar energy system operates quietly without noise, making it suitable for use in places such as residential areas and schools that require a quiet environment.

[0003] As one of the main technologies for solar energy utilization, solar thermal power generation technology has a large-scale heat storage system, making its power generation quality comparable to that of traditional thermal power generation. Currently, solar thermal power generation technology mainly includes tower type, trough type, dish type and linear Fresnel type, and the commonly used heat storage medium is molten salt. Molten salt has become the most widely used energy storage material in this technical field due to its high specific heat, high heat transfer coefficient, excellent thermal stability, high working temperature, as well as low saturated vapor pressure, low viscosity and low cost.

[0004] The most widely used molten salt material at home and abroad currently is solar salt, which is prepared by mixing and melting 60wt% NaNO3 and 40wt% KNO3. The end melting temperature of solar salt is 249°C, the decomposition temperature is 586°C, and the normal operating temperature range is 264 - 556°C. The problems existing in the current use of solar salt are relatively high melting point and narrow operating temperature range, which result in a large risk of freezing and blockage during the operation of the system, and the improvement of power generation efficiency is limited. Currently, a large amount of research work has been carried out on low-melting-point molten salts. Patents with publication numbers CN111040739A, CN117417730A, CN118206960A, CN101050355A, CN103992775A, CN117417730A, CN105018045A, CN104610927A and CN116355597A disclose ternary and above multi-component low-melting-point mixed molten salts. Although these molten salts have the advantage of low crystallization temperature, they usually have complex compositions. Although the patent with publication number CN105524596A discloses a binary molten salt formula with a low crystallization temperature, this formula contains calcium salts, and calcium salts are prone to deliquescence and have a relatively high viscosity.

[0005] In summary, developing a molten salt material formulation with a low crystallization temperature, a high upper temperature limit for use, a simple formulation, and low deliquescence is of great significance for medium- and high-temperature molten salt thermal energy storage systems. Summary of the Invention

[0006] To address the deficiencies of existing commercial molten salts, such as complex formulations, relatively high melting points, or low upper temperature limits for use, the present invention proposes a low-melting-point binary molten salt thermal energy storage material and its preparation method. The formulation is simple, significantly reducing the melting point of the molten salt while further increasing the upper temperature limit for use, thereby broadening the operating temperature range of the molten salt and enhancing the variable operating condition adjustment ability of the system.

[0007] To achieve the above object, the present invention provides the following technical solution: A low-melting-point binary molten salt thermal energy storage material, comprising NaNO x and KNO y , x Take 2, 3, y Take 2, 3, and x ≠ y .

[0008] Further, when x takes 2, y takes 3, the mass percentages of NaNO2 and KNO3 are 30% - 40% and 60% - 70% respectively.

[0009] Further, the end melting temperature of the binary molten salt thermal energy storage material prepared from NaNO2 and KNO3 is 150°C - 165°C, and the decomposition temperature is 600°C - 640°C.

[0010] Further, when x takes 3, y takes 2, the mass percentages of NaNO3 and KNO2 are 50% - 60% and 40% - 50% respectively.

[0011] Further, the end melting temperature of the binary molten salt thermal energy storage material prepared from NaNO3 and KNO2 is 150°C - 165°C, and the decomposition temperature is 600°C - 640°C.

[0012] The present invention also provides a preparation method for a low-melting-point binary molten salt thermal energy storage material, and the specific steps are as follows: Mix and grind the dried NaNO x and KNO y to obtain a mixed salt; Perform two-stage heating on the mixed salt to obtain a molten salt material; The molten salt material crystallizes at room temperature, is crushed, and dried to obtain a low-melting-point binary molten salt thermal energy storage material.

[0013] Further, the step of mixing and grinding the dried NaNOx Mix with KNO y In the step of mixing and grinding to obtain the mixed salt: NaNO x Mix with KNO y The purity of is greater than 99.5%, and NaNO x Mix with KNO y in x Take 2 and 3, y Take 2 and 3, and x ≠ y ; When x Take 2, y Take 3, the mass percentages of NaNO2 and KNO3 are 30% - 40% and 60% - 70% respectively; When x Take 3, y Take 2, the mass percentages of NaNO3 and KNO2 are 50% - 60% and 40% - 50% respectively.

[0014] Furthermore, in the step of subjecting the mixed salt to two-stage heating to obtain the molten salt material: The first-stage heating is to heat at a heating rate of 10°C / min - 20°C / min to 150°C, and the holding time is 2h - 4h; The second-stage heating is to heat at a heating rate of 10°C / min - 20°C / min to 350°C, and the holding time is 12h - 24h.

[0015] Furthermore, in the step of subjecting the molten salt material to room-temperature crystallization, pulverizing, and drying to obtain the low-melting-point binary molten salt heat storage material: The particle size of the obtained low-melting-point binary molten salt heat storage material after pulverization is 50 mesh - 200 mesh.

[0016] The present invention also provides a heat storage device, and the heat storage material is the above-mentioned low-melting-point binary molten salt heat storage material; or a low-melting-point binary molten salt heat storage material prepared by the above-mentioned preparation method.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a low-melting-point binary molten salt heat storage material. By adjusting NaNO x and KNO y in x , yThe value range and the ratio of the two salts can achieve a low melting point and a high upper limit temperature of the molten salt material, thus meeting the low-temperature and high-temperature requirements of the new energy system for the heat transfer and heat storage medium; the melting point of the low-melting binary molten salt heat storage material of the present invention is as low as 150°C to 165°C, and the decomposition temperature is as high as 600°C to 640°C, with a wide normal liquid temperature range, which can meet the temperature range requirements of the new energy system for the heat transfer and heat storage medium; this low-melting binary molten salt heat storage material uses NaNO x and KNO y two single-component salts, with simple components, no other metal ions, low corrosion, and no "salt creeping" phenomenon during long-term use, and stable use performance, effectively solving the problem of the relatively high melting point of existing commercial molten salts, enabling the molten salt to start melting at a lower temperature, thus reducing the start-up temperature of the heat storage system and improving the response speed and flexibility of the system.

[0018] Compared with the most widely used molten salt material solar salt (60wt% NaNO3 + 40wt% KNO3) at present, the melting point of the low-melting binary molten salt heat storage material of the present invention has been significantly reduced. The end melting temperature of solar salt is 249°C, while the molten salt material of the present invention can achieve a lower melting point through formula optimization, which means that under the same operating conditions, the molten salt material of the present invention can enter the working state earlier, improving the overall efficiency of the heat storage system. At the same time, the molten salt material of the present invention further increases the upper limit of the use temperature, enabling the molten salt material to have higher thermal stability while maintaining a low melting point, and being able to operate stably at a higher temperature, thus broadening the use temperature range of the molten salt. This advantage makes the molten salt material of the present invention have a wider application prospect in medium and high temperature heat storage and heat transfer fields such as solar thermal power generation and metallurgical waste heat recovery.

[0019] The preparation method of the low-melting binary molten salt heat storage material of the present invention has simple steps and convenient operation, reducing the preparation cost and improving the preparation efficiency. The purity requirements of NaNO x and KNO y are greater than 99.5%, which ensures the purity and quality of the molten salt material. At the same time, during the mixing and grinding process, by precisely controlling the mixing ratio and grinding time, the mixed salt has uniform particle size and composition, providing a good basis for subsequent heating treatment.

[0020] Preferably, during the two-stage heating process, the present invention adopts precise heating rates and holding times. In the first-stage heating, the temperature is raised to 150°C at a heating rate of 10°C / min to 20°C / min, and the holding time is 2 h to 4 h; in the second-stage heating, the temperature is raised to 350°C at a heating rate of 10°C / min to 20°C / min, and the holding time is 12 h to 24 h. The precise control of the heating rate and holding time enables the molten salt material to fully react and crystallize during the heating process, forming a molten salt material with a low melting point and good thermal stability.

[0021] Preferably, the particle size of the low-melting-point binary molten salt heat storage material of the present invention is 50 mesh to 200 mesh. The molten salt material with such a particle size has good fluidity and filling properties, and can be conveniently applied to the heat storage system.

[0022] The heat storage material of the present invention is applicable to medium- and high-temperature heat storage and heat transfer fields such as solar thermal power generation and metallurgical waste heat recovery. In these fields, the heat storage material needs to have good thermal stability, thermal conductivity, and variable operating condition adjustment capabilities. By optimizing the formula and preparation process, the heat storage material of the present invention has successfully achieved the improvement of these properties, enabling it to operate stably under medium- and high-temperature conditions and quickly respond to changes in operating conditions. The heat storage material of the present invention has a significantly reduced melting point and an increased upper limit of the use temperature. This advantage enables the heat storage system to start at a lower temperature and operate stably at a higher temperature, thereby broadening the use temperature range of the heat storage system. This not only improves the overall efficiency of the heat storage system but also enables the heat storage system to more flexibly adapt to different operating condition requirements.

[0023] Generally speaking, the low-melting-point binary molten salt heat storage material of the present invention has significant advantages in the application of heat storage materials, and can provide an efficient, stable, and low-cost heat storage solution for medium- and high-temperature heat storage and heat transfer fields such as solar thermal power generation and metallurgical waste heat recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following further describes the binary mixed molten salt of the present invention in conjunction with two embodiments and the drawings. In the drawings: Figure 1 is the DSC curve of the mixed molten salt sample of Embodiment 1 of the present invention; Figure 2 is the TG curve of the mixed molten salt sample of Embodiment 1 of the present invention; Figure 3 is the DSC curve of the mixed molten salt sample of Embodiment 2 of the present invention; Figure 4 is the TG curve of the mixed molten salt sample of Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The following will further clearly and completely elaborate on the objectives, technical solutions, and advantages in the embodiments of the present invention in combination with specific embodiments and the accompanying drawings. According to the following description and claims, the advantages and features of the present invention will become clearer. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0026] The present invention proposes a low-melting-point binary molten salt heat storage material, specifically including two formulations: The first one is: composed of a mixture of NaNO3 and KNO2, and the mass percentages of NaNO3 and KNO2 are 50% - 60% and 40% - 50% respectively; the termination melting temperature of the obtained molten salt material is 150°C - 165°C, and the decomposition temperature is 600°C - 640°C; The second one is: composed of a mixture of KNO3 and NaNO2, and the mass percentages of NaNO2 and KNO3 are 30% - 40% and 60% - 70% respectively; the termination melting temperature of the obtained molten salt material is 150°C - 165°C, and the decomposition temperature is 600°C - 640°C.

[0027] The preparation method of the above-mentioned low-melting-point binary molten salt heat storage material specifically includes the following steps: Step 1: First, place the single-component salts to be mixed in a constant-temperature drying oven for drying, the drying temperature is 120 °C, and the drying time is not less than 2h; Step 2: Take out the dried single-component salts, weigh each single-component salt using a high-precision balance according to the mass ratio, and then pour them into a crucible for mixing and grinding; Step 3: Put the mixed salts obtained in Step 2 into a high-temperature muffle furnace and raise the temperature to 150°C at a certain constant heating rate, and keep it warm for a period of time; Step 4: Further raise the temperature of the mixed salts obtained in Step 3 to 350°C at a certain constant heating rate, and keep it warm for a period of time. The single-component salts will undergo eutectic melting to form a new molten salt material; Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling crystallization, and put the obtained solid molten salt into a pulverizer for ultrafine pulverization. Finally, place the pulverized molten salt powder in a constant-temperature drying oven at a temperature of 120°C for drying and storage for subsequent physical property measurement and analysis.

[0028] Preferably, the heating rate in Step 3 is 10°C / min - 20°C / min, and the holding time is 2h - 4h.

[0029] Preferably, the heating rate in Step 4 is 10°C / min to 20°C / min, and the heat preservation time is 12 h to 24 h.

[0030] Preferably, the particle size of the molten salt powder in Step 5 is 50 mesh to 200 mesh.

[0031] The following will, with reference to the drawings, elaborate on some embodiments of the present invention. Without conflict, the following embodiments and the features in the embodiments may be combined with each other.

[0032] Example 1 A low-melting-point binary molten salt heat storage material, with a specific composition of: 55 wt% NaNO3 and 45 wt% KNO2. The preparation method is as follows: Step 1: First, put NaNO3 and KNO2 with a purity greater than 99.5% to be mixed into a constant-temperature drying oven for drying. The drying temperature is 120°C, and the drying time is 2 h. Step 2: Take out the dried NaNO3 and KNO2, weigh each single-component salt according to the mass ratio using a high-precision balance, and then pour it into a crucible for mixing and grinding. Step 3: Put the mixed salt obtained in Step 2 into a high-temperature muffle furnace, and raise the temperature to 150°C at a constant heating rate of 10°C / min, and keep it warm for 2 h. Step 4: Further raise the temperature of the mixed salt obtained in Step 3 to 350°C at a constant heating rate of 10°C / min, and keep it warm for 24 h. The single-component salts will undergo eutectic melting to form a new molten salt material. Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling and crystallization, put the obtained solid molten salt into a pulverizer for ultrafine pulverization to 150 mesh, and finally place the pulverized molten salt powder in a constant-temperature drying oven at 120°C for drying and storage for subsequent physical property measurement and analysis.

[0033] Experiment: The end melting temperature and the primary crystallization temperature of the mixed molten salt were measured by a differential scanning calorimeter (DSC). The results are as Figure 1 shown. The decomposition temperature of the mixed molten salt was measured by a thermogravimetric analyzer (TG). The results are as Figure 2As shown. The test results show that the termination melting temperature of the mixed molten salt prepared in Example 1 is 162 °C, the primary crystallization temperature is 152 °C, and the decomposition temperature is 636 °C. According to relevant national standards: 15 °C above the primary crystallization temperature is used as the lowest lower limit temperature for molten salt use, and 30 °C below the decomposition temperature is used as the highest upper limit temperature for molten salt use. Thus, it can be known that the operating temperature range of the mixed molten salt obtained in Example 1 of the present invention is 167 °C to 606 °C, which greatly broadens the use temperature range compared with the operating temperature range of solar salt of 264 °C to 556 °C. Thus, it can be known that compared with the molten salt thermal energy storage system using solar salt, the heat preservation energy consumption required for the molten salt thermal energy storage system using the present invention is smaller, thereby reducing the risk of freezing and blocking; and the steam temperature obtained by heat exchange of this molten salt will be higher, thereby improving the steam turbine power generation efficiency.

[0034] Example 2 A low-melting-point binary molten salt heat storage material, with a specific composition of: 62 wt% KNO3 and 38 wt% NaNO2. The preparation method is as follows: Step 1: First, put KNO3 and NaNO2 with a purity greater than 99.5% to be mixed into a constant-temperature drying oven for drying. The drying temperature is 120 °C and the drying time is 2 h; Step 2: Take out the dried KNO3 and NaNO2, weigh each single-component salt according to the mass ratio using a high-precision balance, and then pour them into a crucible for mixing and grinding; Step 3: Put the mixed salt obtained in Step 2 into a high-temperature muffle furnace and raise the temperature to 150 °C at a constant heating rate of 15 °C / min, and keep it warm for 2 h; Step 4: Further raise the temperature of the mixed salt obtained in Step 3 to 350 °C at a constant heating rate of 15 °C / min and keep it warm for 24 h. The single-component salts will undergo eutectic melting to form a new molten salt material; Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling and crystallization, put the obtained solid molten salt into a pulverizer for ultrafine pulverization to 100 mesh, and finally place the pulverized molten salt powder in a constant-temperature drying oven at a temperature of 120 °C for drying and storage for subsequent physical property measurement and analysis.

[0035] Experiment: The termination melting temperature and primary crystallization temperature of the mixed molten salt were measured by a differential scanning calorimeter (DSC). The results are as Figure 3 shown. The decomposition temperature of the mixed molten salt was measured by a thermogravimetric analyzer (TG). The results are as Figure 4As shown. The test results show that the termination melting temperature of the mixed molten salt prepared in Example 2 is 160 °C, the primary crystallization temperature is 151 °C, and the decomposition temperature is 630 °C. According to relevant national standards: 15 °C above the primary crystallization temperature is taken as the lowest lower limit temperature for the use of molten salt, and 30 °C below the decomposition temperature is taken as the highest upper limit temperature for the use of molten salt. Thus, it can be known that the operating temperature range of the mixed molten salt obtained in Example 2 of the present invention is 166 °C to 600 °C. Compared with the operating temperature range of solar salt, which is 264 °C to 556 °C, the use temperature range is greatly broadened. Thus, it can be known that compared with the molten salt thermal energy storage system using solar salt, the heat preservation energy consumption required for the molten salt thermal energy storage system of the present invention is smaller, thereby reducing the risk of freezing and blocking; and the steam temperature obtained by heat exchange of this molten salt will be higher, thereby improving the steam turbine power generation efficiency.

[0036] Example 3 A low-melting-point binary molten salt heat storage material, with a specific composition of: 50 wt% NaNO3 and 50 wt% KNO2. The preparation method is as follows: Step 1: First, put the NaNO3 and KNO2 with a purity greater than 99.5% to be mixed into a constant-temperature drying oven for drying. The drying temperature is 120 °C, and the drying time is 2 h; Step 2: Take out the dried NaNO3 and KNO2, weigh each single-component salt according to the mass ratio using a high-precision balance, and then pour them into a crucible for mixing and grinding; Step 3: Put the mixed salt obtained in Step 2 into a high-temperature muffle furnace, and raise the temperature to 150 °C at a constant heating rate of 20 °C / min, and keep it warm for 4 h; Step 4: Further raise the temperature of the mixed salt obtained in Step 3 to 350 °C at a constant heating rate of 20 °C / min, and keep it warm for 12 h. The single-component salts will undergo eutectic melting to form a new type of molten salt material; Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling and crystallization, put the obtained solid molten salt into a pulverizer for ultrafine pulverization to 200 meshes, and finally place the pulverized molten salt powder in a constant-temperature drying oven at a temperature of 120 °C for drying and storage; After testing, the termination melting temperature of the prepared low-melting-point binary molten salt heat storage material is 165 °C, and the decomposition temperature is 640 °C.

[0037] Example 4 A low-melting-point binary molten salt heat storage material, with a specific composition of: 60 wt% NaNO3 and 40 wt% KNO2. The preparation method is as follows: Step 1: First, put the NaNO3 and KNO2 with a purity greater than 99.5% to be mixed into a constant-temperature drying oven for drying. The drying temperature is 120 °C, and the drying time is 2 h; Step 2: Take out the dried NaNO3 and KNO2, weigh each single-component salt using a high-precision balance according to the mass ratio, and then pour them into a crucible for mixing and grinding; Step 3: Put the mixed salt obtained in Step 2 into a high-temperature muffle furnace, and raise the temperature to 150 °C at a constant heating rate of 15 °C / min, and keep it at this temperature for 3 h; Step 4: Further raise the temperature of the mixed salt obtained in Step 3 to 350 °C at a constant heating rate of 15 °C / min, and keep it at this temperature for 20 h. The single-component salts will undergo eutectic melting to form a new molten salt material; Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling and crystallization, put the obtained solid molten salt into a pulverizer for ultrafine grinding to 50 mesh, and finally place the pulverized molten salt powder in a constant-temperature drying oven at 120 °C for drying and storage; After testing, the termination melting temperature of the prepared low-melting-point binary molten salt heat storage material is 150 °C, and the decomposition temperature is 600 °C.

[0038] Example 5 A low-melting-point binary molten salt heat storage material, with a specific composition of: 70 wt% KNO3 and 30 wt% NaNO2. The preparation method is as follows: Step 1: First, put the KNO3 and NaNO2 with a purity greater than 99.5% to be mixed into a constant-temperature drying oven for drying. The drying temperature is 120 °C, and the drying time is 2 h; Step 2: Take out the dried KNO3 and NaNO2, weigh each single-component salt using a high-precision balance according to the mass ratio, and then pour them into a crucible for mixing and grinding; Step 3: Put the mixed salt obtained in Step 2 into a high-temperature muffle furnace, and raise the temperature to 150 °C at a constant heating rate of 10 °C / min, and keep it at this temperature for 4 h; Step 4: Further raise the temperature of the mixed salt obtained in Step 3 to 350 °C at a constant heating rate of 10 °C / min, and keep it at this temperature for 12 h. The single-component salts will undergo eutectic melting to form a new molten salt material; Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling and crystallization, put the obtained solid molten salt into a pulverizer for ultrafine grinding to 50 mesh, and finally place the pulverized molten salt powder in a constant-temperature drying oven at 120 °C for drying and storage; After testing, the termination melting temperature of the prepared low-melting-point binary molten salt heat storage material is 150 °C, and the decomposition temperature is 640 °C.

[0039] Example 6 A low-melting-point binary molten salt heat storage material, with a specific composition of: 60 wt% KNO3 and 40 wt% NaNO2. The preparation method is as follows: Step 1: First, put KNO3 and NaNO2 with a purity greater than 99.5% to be mixed into a constant-temperature drying oven for drying. The drying temperature is 120 °C and the drying time is 2 h; Step 2: Take out the dried KNO3 and NaNO2, weigh each single-component salt using a high-precision balance according to the mass ratio, and then pour them into a crucible for mixing and grinding; Step 3: Put the mixed salt obtained in Step 2 into a high-temperature muffle furnace and raise the temperature to 150 °C at a constant heating rate of 20 °C / min, and keep it warm for 4 h; Step 4: Further raise the temperature of the mixed salt obtained in Step 3 to 350 °C at a constant heating rate of 20 °C / min, and keep it warm for 20 h. The single-component salts will undergo eutectic melting to form a new molten salt material; Step 5: Place the molten salt obtained in Step 4 at room temperature for cooling and crystallization, put the obtained solid molten salt into a pulverizer for ultrafine grinding to 200 mesh, and finally place the pulverized molten salt powder in a constant-temperature drying oven at 120 °C for drying and storage; After testing, the termination melting temperature of the prepared low-melting-point binary molten salt heat storage material is 153 °C, and the decomposition temperature is 620 °C.

[0040] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A low-melting-point binary molten salt heat storage material, characterized in that, including NaNO x and KNO y , x take 2, 3, y take 2, 3, and x ≠ y .

2. The low-melting binary molten salt heat storage material according to claim 1, characterized in that, When x taking 2, y when taking 3, the mass percentages of NaNO2 and KNO3 are 30% - 40% and 60% - 70% respectively.

3. The low-melting binary molten salt heat storage material according to claim 2, characterized in that, The termination melting temperature of the binary molten salt heat storage material prepared from NaNO2 and KNO3 is 150°C to 165°C, and the decomposition temperature is 600°C to 640°C.

4. The low-melting binary molten salt heat storage material according to claim 1, characterized in that, When x taking 3, y taking 2, the mass percentages of NaNO3 and KNO2 are 50% - 60% and 40% - 50% respectively.

5. A low-melting-point binary molten salt heat storage material according to claim 4, characterized in that The termination melting temperature of the binary molten salt heat storage material prepared from NaNO3 and KNO2 is 150°C to 165°C, and the decomposition temperature is 600°C to 640°C.

6. A preparation method of a low-melting-point binary molten salt heat storage material, characterized in that, The specific steps are as follows: Mix the dry NaNO x with KNO y and grind to obtain a mixed salt; Perform two-stage heating on the mixed salt to obtain a molten salt material; The molten salt material crystallizes at room temperature, is pulverized, and dried to obtain a low-melting-point binary molten salt heat storage material.

7. The preparation method of a low-melting binary molten salt heat storage material according to claim 6, characterized in that, The step of mixing the dried NaNO x with KNO y and grinding to obtain a mixed salt is as follows: NaNO x and KNO y with a purity greater than 99.5%, NaNO x and KNO y in x take 2, 3, y take 2, 3, and x ≠ y ; When x taking 2, y when taking 3, the mass percentages of NaNO2 and KNO3 are 30% - 40% and 60% - 70% respectively; When x taking 3 y and taking 2, the mass percentages of NaNO3 and KNO2 are 50% - 60% and 40% - 50% respectively.

8. The preparation method of a low-melting-point binary molten salt heat storage material according to claim 6, characterized in that, In the step of performing two-stage heating on the mixed salt to obtain a molten salt material: The first-stage heating is to heat at a heating rate of 10°C / min to 20°C / min to 150°C, and the holding time is 2h to 4h; The second-stage heating is to heat at a heating rate of 10°C / min to 20°C / min to 350°C, and the holding time is 12h to 24h.

9. The preparation method of a low-melting-point binary molten salt heat storage material according to claim 6, characterized in that, In the step of the molten salt material crystallizing at room temperature, being pulverized, and dried to obtain a low-melting-point binary molten salt heat storage material: The particle size of the obtained low-melting-point binary molten salt heat storage material after pulverization is 50 mesh to 200 mesh.

10. A heat storage device, characterized in that, The heat storage material is a low-melting-point binary molten salt heat storage material described in claims 1 to 5; or a low-melting-point binary molten salt heat storage material prepared by the preparation method described in claims 6 to 9.

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