Preparation method of anhydrous ternary nitric acid molten salt heat storage material

Abstract

The application discloses a preparation method of anhydrous ternary nitric acid molten salt heat storage material, which comprises the following steps: (1) taking Mg(NO3)2.6H2O, grinding the Mg(NO3)2.6H2O into 100-200 mesh particles, and then placing the particles into a first container; (2) mechanically blending NaNO3 and KNO3 fine particles, and then placing the NaNO3 and KNO3 fine particles into a second container; (3) combining the first container and the second container to obtain a nitrate molten salt base body preparation device, and then placing the device into a muffle furnace to be calcined in stages to obtain the ternary nitric acid molten salt heat storage material. The method can remove the crystal water of Mg(NO3)2.6H2O in one step and simultaneously prepare high-purity Mg(NO3)2-NaNO3-KNO3 ternary molten salt heat storage material, and solves the problems that Mg(NO3)2.6H2O is difficult to dehydrate and is easy to decompose.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of nitric acid molten salt, in particular to a preparation method of anhydrous ternary nitric acid molten salt heat storage material. BACKGROUND

[0002] The molten salt has excellent thermal physical properties and is an important solar thermal power generation heat storage medium, in a trough-type solar thermal power generation system, nitric acid molten salt is used to replace traditional heat-conducting oil as a heat transfer fluid and heat storage medium, so that the safety and heat utilization rate of the system can be improved. However, the melting point of the widely used SolarSalt molten salt (60wt% NaNO3-40wt% KNO3) is relatively high (223 DEG C) and the low-temperature fluidity is poor, the molten salt is prone to solidification and crystallization to block the pipeline at night, on cloudy days or in winter, and a heating device is needed to heat the molten salt to maintain the smooth operation of the system. Therefore, development of a multi-component nitric acid molten salt heat storage material with good fluidity and low melting point is conducive to improving the safety of the trough-type solar thermal power generation system and reducing the heating energy consumption.

[0003] In recent years, Mg(NO3)2-based multi-component molten salt has attracted much attention due to its high-temperature fluidity, heat storage and heat conduction. However, due to the fact that Mg(NO3)2 exists in the form of Mg(NO3)2·6H2O in the natural environment and is prone to water absorption, it is difficult to prepare large-scale high-purity Mg(NO3)2-based multi-component molten salt, and the thermal physical properties, stability and fluidity of the molten salt are seriously affected, which restricts the development of Mg(NO3)2-based multi-component molten salt. SUMMARY

[0004] Therefore, the application provides a method for removing the crystal water of Mg(NO3)2·6H2O and preparing high-purity Mg(NO3)2-NaNO3-KNO3 ternary molten salt heat storage material in one step, which solves the problems of difficulty in dehydration and easy decomposition of Mg(NO3)2·6H2O. The influence of one-step dehydration on the melting point, decomposition temperature and thermal stability of high-purity Mg(NO3)2-NaNO3-KNO3 ternary molten salt is shown.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] A preparation method of anhydrous ternary nitric acid molten salt heat storage material, comprising the following steps:

[0007] (1) Mg(NO3)2·6H2O is weighed and ground to 100-200 mesh particles and then put into a first container;

[0008] (2) NaNO3 and KNO3 fine particles are mechanically blended and put into a second container;

[0009] (3) combine the first container and the second container to obtain a nitrate molten salt matrix preparation device, and then put it into a muffle furnace to obtain a ternary nitrate molten salt heat storage material through staged calcination.

[0010] Preferably, the mass ratio of Mg(NO3)2·6H2O, NaNO3 and KNO3 is:

[0011] 20% Mg(NO3)2-48% NaNO3-32% KNO3

[0012] Preferably, the staged calcination includes three stages, the first stage is to heat from room temperature to 120-170℃ at a heating rate of 5℃·min-1, and melt-calcine for 1-1.5h; the second stage is to continue heating to 230-270℃ at a heating rate of 5℃·min-1, and melt-calcine for 2-3h; the third stage is to continue heating to 280-450℃ at a heating rate of 5℃·min-1, and melt-calcine for 2-3h. 1 1 1

[0013] According to the technical solution, compared with the prior art, the application has the following beneficial effects:

[0014] (1) The problem of difficulty in dehydration of Mg(NO3)2·6H2O and easy decomposition is solved.

[0015] (2) The technology not only can improve the decomposition temperature (increase by 13%±2.5) and the latent heat of phase change (increase by 33%±4.1) of the ternary nitrate molten salt MNK, but also can reduce the melting point (decrease by 5.9%±1.7) of the ternary nitrate molten salt MNK, thereby expanding the working temperature range of high-temperature molten salt and reducing the burden of the external heat insulation system of the molten salt operation.

[0016] (3) The technology makes the ternary mixed molten salt MNK have no decomposition after 720h of 450℃ circulation, has better chemical stability, and has stable thermal properties with a floating rate of less than 1%.

[0017] The technology makes the thermal weight loss of the ternary nitrate molten salt MNK in different use temperature ranges be less than 3%, and the stability be better. The thermal stability is obviously increased, and the mass loss is greatly reduced under the same conditions. This is consistent with the above TG test results.

[0018] (4) The technology reduces the decomposition rate of the ternary nitrate molten salt MNK, can delay the time of molten salt deterioration, and is conducive to prolonging the service life of the molten salt. BRIEF DESCRIPTION OF DRAWINGS

[0019] ​​​In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are only part of the embodiments of the present application, and not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0020] Figure 1 Process flow diagram of the mixed molten salt of the present application;

[0021] Figure 2 Raman spectrum of the product obtained by the stepwise dehydration of Mg(NO3)2·6H2O in the present application;

[0022] Figure 3 XRD of the dehydrated ternary nitric salt MNK after 300h of circulation in the present application;

[0023] Figure 4 TG-DGC curve of the dehydrated and non-dehydrated ternary nitric salt MNK in the present application;

[0024] Figure 5 Melting point, phase change enthalpy and decomposition temperature diagram of the ternary nitric salt MNK after 720h of circulation in the present application, a-melting point, b-phase change enthalpy, c-decomposition temperature;

[0025] Figure 6 Mass loss versus temperature diagram of the dehydrated and non-dehydrated ternary nitric salt MNK in the present application;

[0026] Figure 7 NO2- content versus temperature diagram of the dehydrated and non-dehydrated ternary nitric salt MNK in the present application;

[0027] Figure 8 XRD spectrum of the product obtained by the stepwise vacuum calcination of Mg(NO3)2·6H2O under the same conditions in the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, and not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0029] Example 1

[0030] Reagents used in the examples

[0031] NaNO3, KNO3, Mg(NO3)2·6H2O were all taken from Qinghai Salt Lake, which produced the abundant glauber's salt, by-product potassium chloride and bischofite (MgCl2·6H2O).

[0032] Instruments used in the examples

[0033] Vacuum muffle furnace (ZSX-6-14, Xinnite Technology Co., Ltd.), electronic balance (S201, Sartorius, Germany), constant temperature drying oven (DHG-9023, Jinan Hibo Instrument Co., Ltd.), simultaneous differential scanning calorimetry-thermal gravimetric analyzer (SDTQ600, TA Instruments), inductively coupled plasma spectrometer (ICAP6500DUO, TA Instruments), comprehensive property tester for molten salt, high-temperature thermal conductivity tester and molten salt viscosity tester (Shanghai Institute of Applied Physics).

[0034] Dehydration of Mg(NO3)2·6H2O

[0035] About 10 g of Mg(NO3)2·6H2O was weighed into a No. 2 special corundum crucible, and the No. 1 and No. 2 special corundum crucibles were combined as Figure 1 follows and placed in the muffle furnace, and a staged heating program was set for dehydration. First, the temperature was raised from room temperature to 150°C at a rate of 5°C·min- 1 , and the Mg(NO3)2·2H2O was crystallized by evaporation and dehydration after melting and calcination for 1 h; the second stage was to prevent the decomposition of Mg(NO3)2·2H2O, and vacuum calcination was used to continue the temperature rise from 150°C to 230°C at a rate of 5°C·min- 1 , and the product was completely dehydrated to anhydrous Mg(NO3)2 after melting and calcination for 2 h. The product in the No. 1 crucible was quickly transferred to the glove box for cooling, ground to powder, and sample preparation and characterization;

[0036] A certain proportion of pretreated high-purity sodium nitrate and potassium nitrate was ground in a mortar, and then poured into a No. 1 corundum crucible. About 10 g of Mg(NO3)2·6H2O was weighed into a No. 2 special corundum crucible, and a staged heating program was set for dehydration, melting and blending according to the above dehydration process to prepare a 20% Mg(NO3)2-48% NaNO3-32% KNO3 ternary nitric acid molten salt. The temperature rise program of the third stage was set as follows: after the Mg(NO3)2·6H2O was completely dehydrated to anhydrous Mg(NO3)2, the temperature was continuously raised to 280°C at a rate of 5°C·min- 1 , and after 2 h the ternary molten salt was completely mixed and homogeneous, the product was quickly transferred to the glove box for cooling, ground to powder, and sample preparation and characterization. The process flow is as Figure 1 .

[0037] Detection method and characterization

[0038] Thermophysical properties of molten salt were analyzed using a simultaneous differential scanning calorimetry-thermogravimetric analyzer (DSC-TG) at a heating rate of 5 °C / min, collecting experimental data between 100 and 600 °C. The contents of various ions in the raw materials were determined using ion chromatography and chemical analysis. The calcined products were characterized using Raman spectroscopy at frequencies ranging from 100 to 2000 cm⁻¹. 1 The samples were tested using XRD with a scan step of 0.0167°.

[0039] Results and Discussion

[0040] Raman

[0041] Raman analysis curves of Mg(NO3)2·6H2O before and after dehydration are shown below. Figure 2 As shown, after calcination for half an hour, the Raman curve shows a value of 1061.31 cm⁻¹. 1 The characteristic peaks of Mg(NO3)2·6H2O and the dehydration intermediates are observed at 1097.78 cm⁻¹. 1 The characteristic peak of Mg(NO3)2·2H2O was observed. After dehydration using the above-mentioned segmented calcination dehydration method for 2 hours, the characteristic peak of Mg(NO3)2·6H2O gradually disappeared with increasing calcination time. When the second stage of calcination time exceeded 2 hours, the characteristic peak disappeared completely, and a peak at 1099.78 cm⁻¹ appeared. 1 and 1107.318cm- 1 The characteristic peak of Mg(NO3)2 indicates that Mg(NO3)2·6H2O is completely dehydrated to Mg(NO3)2.

[0042] XRD

[0043] The ternary nitrate molten salt MNK prepared by one-step dehydration was characterized by XRD as follows: Figure 3 As shown in the figure, only NaNO3, KNO3, and Mg(NO3)2 diffraction peaks were detected in the diffraction patterns of the samples obtained from the three-stage sintering process. No nitrite or Mg(NO3)2·6H2O decomposition products were detected, indicating that the sample is an anhydrous NaNO3-KNO3-Mg(NO3)2 ternary molten salt. After cycling the molten salt at 450°C for 300 hours, the diffraction peaks remained stable, and no other diffraction peaks were detected, indicating that the sintering temperature and time were suitable and the raw materials did not decompose. This shows that NaNO3 did not undergo any decomposition reaction at 450°C and still possesses good chemical stability.

[0044] Thermophysical advantages of one-step dehydration of ternary nitrate molten salt MNK

[0045] The TG-DSC analysis curves of the ternary nitrate molten salt MNK before and after dehydration are shown below. Figure 4As shown by the DSC curve, the sharp endothermic peak of the non-dehydrated MNK at 127°C is the melting endothermic peak of Mg(N03)2-2H20, and the corresponding TG curve also has a mutation. The DSC and TG curves of the MNK molten salt synthesized by the dehydration one-step method have no heat absorption peak and no thermal weight loss at this point. The decomposition temperature (the thermal decomposition temperature is determined according to the extrapolated initial temperature of the TG curve) is greatly improved, which is 53.5°C higher than that of the non-dehydrated MNK molten salt, i.e., 457.6°C. At the same time, compared with the non-dehydrated MNK, the melting point of the MNK is reduced from 157.5°C to 148.2°C, and the latent heat of phase change is increased from 66.61 J / g to 88.71 J / g. It is shown that the dehydration and vacuum isolation one-step method can not only improve the decomposition temperature and latent heat of phase change of the ternary nitric acid molten salt MNK, but also reduce the melting point of the ternary nitric acid molten salt MNK, expand the working temperature range of the high-temperature molten salt, and reduce the burden of the external heat insulation system of the molten salt operation.

[0046] The melting point, phase change enthalpy and decomposition temperature of the ternary nitric acid molten salt MNK after 720h of cyclic operation are shown in Figure 5 (a-c) As can be seen from the figure, the melting point of the ternary nitric acid molten salt MNK prepared by the dehydration one-step method is lower than that of the non-dehydrated MNK, and the latent heat of phase change and the decomposition temperature are higher than those of the non-dehydrated MNK. As shown in Figure 5 a, the melting points of the MNK ternary mixed molten salt after 0h, 120h, 240h, 360h, 480h and 600h of cyclic operation at 450°C are 10.29%, 10.47%, 6.91%, 7.43%, 3.99% and 4.05% lower than that of the MNK before dehydration, respectively, indicating that the dehydration one-step synthesis method can reduce the melting point of the MNK ternary mixed molten salt. However, the melting point of the non-dehydrated ternary mixed molten salt MNK decreases sharply after 648h of cyclic operation at 450°C, which is considered to be caused by decomposition. However, under the same conditions, the melting point of the dehydrated ternary mixed molten salt MNK remains stable, and the numerical value fluctuates less. The latent heat of phase change of the dehydrated ternary mixed molten salt MNK also has the above trend as shown in Figure 5 b, which further illustrates the advantages of the dehydration one-step method. The decomposition temperatures of the MNK ternary mixed molten salt before and after dehydration are summarized in Figure 5In c, it can be seen from the figure that the decomposition temperature of MNK ternary mixed molten salt after 0h, 120h, 240h, 360h, 480h, 600h and 720h at 450℃ is respectively 9.18%, 9.64%, 10.45%, 12.64%, 13.61%, 15.46% and 20.55% higher than that of MNK before dehydration, and remains stable. It shows that dehydration increases the decomposition temperature of MNK ternary mixed molten salt. Combined with the decrease of the melting point of MNK ternary mixed molten salt by dehydration in 5a, it can be seen that dehydration expands the working temperature range of MNK ternary mixed molten salt (generally, the working temperature range of high-temperature molten salt is melting point + 50℃ to decomposition temperature - 50℃). From the data trend, it can be seen that the melting point and decomposition temperature of the ternary nitric acid molten salt MNK prepared by the dehydration one-step method are more stable and have smaller fluctuations (the fluctuation rate of MNK ternary mixed molten salt after 720h at 450℃ is less than 0.5%), which shows that dehydration makes the ternary nitric acid molten salt MNK more stable.

[0047] Combined with the chemical composition analysis results of the dehydrated ternary nitric acid molten salt MNK after 720h at 450℃, it can be found that the amount of Mg 2 +, Ca 2 +, NH4+, Fe 3 +, Cl-, SO4 2 - and water-insoluble substances in the ternary nitric acid molten salt MNK prepared by the dehydration one-step method is almost unchanged, and NO2- is not detected by ion chromatography. This further shows that the chemical composition of the dehydrated ternary nitric acid molten salt MNK at 450℃ has almost no change and no decomposition, and has good chemical stability.

[0048] Table 1 Chemical composition analysis of ternary nitric acid molten salt MNK

[0049]

[0050] Advantages of thermal stability of the dehydrated one-step ternary nitric acid molten salt MNK

[0051] As Figure 6The graph shows the thermogravimetric analysis (TGA) curves of dehydrated and undehydrated ternary nitrate molten salt (MNK) after 270 hours of cycling. As can be seen from the graph, the TGA of the undehydrated MNK ternary nitrate molten salt gradually increases with increasing firing temperature, exceeding 3% after 270 hours at 400℃ (generally, a TGA of less than 3% is considered a stable state). In contrast, the TGA of the dehydrated MNK ternary nitrate molten salt, at 500℃, is still much less than 3%, at 0.6721%. After 270 hours of cycling, the TGA of the dehydrated MNK ternary nitrate molten salt, when fired at 350℃, 400℃, 450℃, and 500℃, are 0.4152%, 0.7162%, 2.1107%, and 11.5485%, respectively. The weight loss on ignition at 350℃, 400℃, 450℃, and 500℃ was 452.04%, 389.47%, 307.49%, and 32.46% lower than that of undried MNK ternary nitrate molten salt, respectively. This indicates that the dehydrated MNK ternary nitrate molten salt is relatively stable below 450℃, exhibiting significantly higher thermal stability than unpurified SolarSalt molten salt, and a substantial reduction in mass loss under the same conditions. This is consistent with the above TG test results.

[0052] Combining the ion chromatography analysis results of dehydrated and undehydrated ternary nitrate molten salt MNK after 270 hours of cyclic firing at different temperatures, as follows: Figure 7 As shown, the NO2- content in the ternary nitrate molten salt MNK prepared by the one-step dehydration method remained undetectable below 450℃, while the NO2- content in the undehydrated MNK molten salt remained undetectable below 400℃, consistent with the conclusions of the aforementioned thermogravimetric analysis. Furthermore, the NO2- content detected by ion chromatography increased with increasing temperature, indicating decreased thermal stability. At a firing temperature of 475℃ and a cycle time of 270 hours, the NO2- content in the dehydrated MNK molten salt was 0.0189%, while the NO2- content in the undehydrated MNK molten salt was 0.6976%, showing signs of deterioration. At 500℃, the NO2- content in the undehydrated MNK molten salt exceeded 1%, while the NO2- content in the dehydrated MNK molten salt, after cycling at the same temperature for 270 hours, was only 0.0417%, 2748.2% lower than that in the undehydrated MNK molten salt. This indicates that, under the same conditions, the decomposition rate of the ternary nitrate molten salt MNK prepared by the one-step dehydration method is reduced, suggesting that dehydration can delay the deterioration of molten salt and help extend its service life.

[0053] in conclusion

[0054] A one-step method for removing the water of crystallization from Mg(NO3)2·6H2O and simultaneously preparing high-purity Mg(NO3)2·6H2O

[0055] The method of preparing Mg(NO3)2-NaNO3-KNO3 ternary molten salt heat storage material can greatly improve the decomposition temperature of molten salt and reduce the melting point of the material. The method solves the problem of hydrolysis of magnesium nitrate hexahydrate to form basic magnesium nitrate when preparing Mg(NO3)2-NaNO3-KNO3 ternary molten salt by direct melting and blending. The melting point of the molten salt is 148.2℃, the phase change enthalpy is 88.71J / g, and the decomposition temperature is 457.6℃. The decomposition temperature of the ternary nitric acid molten salt MNK prepared by this method is above 450℃, and it remains stable during the 720h operation, which is much higher than the thermal stability of the non-dehydrated MNK mixed molten salt. At the same time, the phase change enthalpy is also improved. The EDS line scanning is used to observe the uniformity of the material mixture, and no agglomeration of single elements is found, and the mixture is uniform. After firing at 450℃ for 720h, no NO2- is detected in the ternary mixed molten salt MNK by ion chromatography, indicating that the molten salt has no decomposition at 450℃, and has good chemical stability.

[0056] Preparation method of non-dehydrated MNK:

[0057] The laboratory self-made sodium nitrate, potassium nitrate and magnesium nitrate hexahydrate are put into a mortar in a certain proportion (20% Mg(NO3)2-48% NaNO3-32% KNO3), ground, and then poured into a corundum crucible. The sample is heated in a muffle furnace at a temperature of 300-400℃. After a certain temperature, it is kept at a constant temperature for 2-3h. After cooling, the sample is taken out and placed in a desiccator to cool to room temperature. Then it is ground to obtain the non-dehydrated MNK molten salt sample.

[0058] Preparation method of dehydrated MNK:

[0059] Because magnesium nitrate absorbs water seriously and easily forms crystals, it usually exists in the form of Mg(NO3)2·6H2O in the atmospheric environment. However, the conventional preparation method of MNK ternary nitric acid molten salt makes the thermal properties of the product extremely unstable. Through research, it is found that during the direct calcination of Mg(NO3)2·6H2O, XRD shows the existence of Mg(NO3)2 hydrolysis product, basic magnesium nitrate (Mg3(OH)(NO3)), which is consistent with the research of Gabdulli et al. The above-mentioned step-by-step vacuum dehydration method and one-step method are used to synthesize anhydrous MNK ternary nitric acid molten salt. The method can avoid the existing problem of hydrolysis of magnesium-based molten salt. At the same time, it solves the problem that nitrate is easy to absorb moisture in the air, and the free water is easy to remove, but the crystal water is difficult to remove.

[0060] The composition of the product is determined by XRD Figure 8It can be seen from the figure that the product obtained after direct calcination at 300-400℃ for 2-3h is Mg(NO3)2, Mg(OH)(NO3), Mg(NO3)2·2H2O and incompletely dehydrated Mg(NO3)2·6H2O. The diffraction peaks of basic magnesium nitrate Mg(OH)(NO3) exist in the spectrum, indicating that hydrolysis reaction of Mg(NO3)2·6H2O occurs to generate Mg(OH)(NO3) during the dehydration process. The product obtained by the vacuum dehydration method proposed in this study is Mg(NO3)2 and Mg(NO3)2·2H2O after 2h of dehydration. The characteristic peaks of Mg(NO3)2·2H2O disappear after 3h, and the product obtained is mainly anhydrous Mg(NO3)2. Part of the residual Mg(NO3)2·2H2O is due to the atmospheric environment during the XRD test process, and Mg(NO3)2 will inevitably absorb moisture in the atmosphere to generate Mg(NO3)2·2H2O.

[0061] Determination of the content of Mg(OH)(NO3) in dehydrated and non-dehydrated ternary nitrate molten salt MNK

[0062] Table 2

[0063]

[0064] The dehydrated and non-dehydrated ternary nitrate molten salt MNK prepared under the same conditions was dissolved in deionized water, and the insoluble substance was Mg(OH)2 generated by the hydrolysis product of Mg(NO3)2·6H2O during calcination. As can be seen from Table 2, within the temperature range of the upper and lower lines of the molten salt, the content of Mg(OH)(NO3) in the non-dehydrated ternary nitrate molten salt MNK fluctuates with the increase of the calcination temperature, and the content of the hydrolysis product is the lowest at 300-400℃, but it is also above 2%, indicating that Mg(NO3)2·6H2O in the non-dehydrated ternary nitrate molten salt MNK is easy to hydrolyze during the calcination process and combine with water in the air to generate Mg(OH)(NO3); the hydrolysis rule of Mg(NO3)2 in the segmented vacuum environment is the same as that in the normal pressure environment, but there is no Mg(OH)(NO3) detected in the dehydrated ternary nitrate molten salt MNK under certain conditions (calcination time 2-3h, calcination temperature 300-450℃), indicating that Mg(NO3)2·6H2O does not hydrolyze during the segmented vacuum calcination process. It can be analyzed that the vacuum extraction can improve the dehydration rate of Mg(NO3)2·2H2O and reduce the calcination temperature required for complete dehydration of Mg(NO3)2·2H2O, thereby reducing the content of the hydrolysis product in anhydrous Mg(OH)2.

[0065] The various embodiments described in this specification are implemented in a progressive manner, each embodiment focusing on the differences from other embodiments, and the same or similar parts between embodiments can be mutually referred to. For the apparatus disclosed by the embodiments, since it corresponds to the method disclosed by the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0066] The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing anhydrous ternary nitrate molten salt heat storage material, characterized in that, It comprises the following steps: (1) Take Mg(NO3)2·6H2O and grind it to 100-200 mesh particles, and then put it into a first container; (2) Put NaNO3 and KNO3 fine particles into a second container through mechanical blending; (3) Put the first container on the top of the second container, and get a nitrate molten salt matrix preparation device, and then put it into a muffle furnace to obtain a ternary nitrate molten salt heat storage material through staged calcination; The ternary nitrate molten salt heat storage material comprises, by mass ratio: 20% Mg(NO3)2-48% NaNO3-32% KNO3; The segmental calcination includes three stages, the first stage is 5℃·min -1 from room temperature to 120-170℃, melt calcination 1-1.5h; the second stage is to continue to heat up to 230-270℃ at a heating rate of 5℃·min -1 , melt calcination 2-3h; the third stage is to continue to heat up to 280-450℃ at a heating rate of 5℃·min -1 , melt calcination 2-3h.

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