Medium-low melting point phase change molten salt heat storage material and preparation method thereof

Abstract

The invention discloses a medium-low melting point phase change molten salt heat storage material and a preparation method thereof. The medium-low melting point phase change molten salt heat storage material comprises the following components: 30-80 wt% of NaNO3; 5 to 40 wt% of KNO3; 5 to 55 wt% of ZnCl2; 0 to 2 weight percent of MgO; when the mass ratio of NaNO3 to KNO3 to ZnCl2 to MgO is 7: 1: 1: 0.1, the melting point is 200.1 DEG C, the decomposition point is 638.3 DEG C, the phase change latent heat is 138.3 J / g, and the specific heat capacity is 1.94 J / (g.K). The fused salt material has the beneficial effects that the fused salt material has relatively high specific heat capacity and is low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of heat storage molten salt materials, and in particular to medium-low melting point phase change molten salt heat storage materials and preparation methods thereof. Background Art

[0002] In solar thermal power generation systems, the heat storage system is the most critical part of the entire system, and the energy storage material is the core factor affecting the heat storage system. The energy storage materials currently used mainly include air, water, thermal oil, liquid metal and molten salt. Compared with other energy storage materials, molten salt has the advantages of "four highs and three lows" of high specific heat capacity, high heat transfer coefficient, high thermal stability, high temperature, low saturated vapor pressure, low viscosity and low price, making it the most widely used energy storage material in solar thermal power generation technology. Traditional phase change heat storage materials have problems such as high melting point, low phase change latent heat, and poor thermal stability, which limit their application in medium and low temperature energy storage systems.

[0003] In the prior art, a large number of scholars have improved the specific heat capacity of materials by modifying molten salts with nanoparticles. However, the synthesis cost of nanoparticles is relatively high and they cannot be used in large-scale industrial applications. The improved specific heat capacity is not very high. The solid-state specific heat capacity of ordinary NaNO3 is around 1.3 J / (g℃), and the addition of nanoparticles generally only increases it by around 10%-20%. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present application proposes a medium-low melting point phase change molten salt heat storage material and a preparation method thereof. The molten salt material has a high specific heat capacity and low cost.

[0005] The following is the technical solution of the present invention, the medium-low melting point phase change molten salt heat storage material comprises the following components: NaNO3: 30-80wt%; KNO3: 5-40wt%; ZnCl2: 5-55wt%; MgO: 0-2wt%.

[0006] Preferably, when the mass ratio of NaNO3, KNO3, ZnCl2 and MgO is 7:1:1:0.1, the melting point is 200.1°C, the decomposition point is 638.3°C, the latent heat of phase change is 138.3J / g, and the specific heat capacity is 1.94J / (g·K).

[0007] Preferably, when the mass ratio of NaNO3, KNO3, ZnCl2 and MgO is 7:2:1:0.1, the melting point is 220.9°C, the decomposition point is 638.7°C, the latent heat of phase change is 116.0J / g, and the specific heat capacity is 2.48J / (g·K).

[0008] Preferably, when the mass ratio of NaNO3, KNO3, ZnCl2 and MgO is 6:3:2:0.1, the melting point is 212.0°C, the decomposition point is 658.1°C, the latent heat of phase change is 126.9 J / g, and the specific heat capacity is 2.49 J / (g·K).

[0009] Preferably, when the mass ratio of NaNO3, KNO3, ZnCl2 and MgO is 6:4:1:0.2, the melting point is 302.3°C, the decomposition point is 636.7°C, the latent heat of phase change is 158.4J / g, and the specific heat capacity is 2.53J / (g·K).

[0010] Preferably, when the mass ratio of NaNO3, KNO3, ZnCl2 and MgO is 5:5:5:0.2, the melting point is 316.5°C, the decomposition point is 598.2°C, the latent heat of phase change is 144.3J / g, and the specific heat capacity is 1.86J / (g·K).

[0011] Preferably, when the mass ratio of NaNO3, KNO3, ZnCl2 and MgO is 4:1:6:0.2, the melting point is 354.6°C, the decomposition point is 632.2°C, the latent heat of phase change is 182.7J / g, and the specific heat capacity is 2.51J / (g·K).

[0012] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S1. Mixing NaNO3, KNO3, ZnCl2 and MgO in a certain mass ratio to obtain a mixed raw material; S2, the mixed raw material is dried at 150 ° C for 72 hours to obtain a dried raw material after removing moisture; S3, grinding the dried raw material to obtain a uniform raw material; S4. Place the uniform raw material in a heating device, heat it at 450°C for 24 hours, and crush it after cooling to obtain a molten salt material.

[0013] Preferably, in S4, the heating device is a muffle furnace.

[0014] The beneficial effects of the present invention are: 1. Molten salt materials have a higher specific heat capacity; 2. Compared with the conventional method of adding nanoparticles to modify the specific heat capacity of heat storage materials, this method is simple, low-cost, and can be widely used in industrial use; 3. Molten salt materials have a lower melting point, higher decomposition temperature and greater latent heat of phase change, making them suitable for medium and low temperature energy storage systems, improving the energy storage efficiency and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a flow chart of the preparation method. DETAILED DESCRIPTION

[0016] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0017] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0018] Embodiment 1: A medium-low melting point phase change molten salt heat storage material, comprising: sodium nitrate (NaNO3), potassium nitrate (KNO3), zinc chloride (ZnCl2) and magnesium oxide (MgO); Among them, the mass ratio of the ingredients is: sodium nitrate, 7; potassium nitrate, 1; zinc chloride, 1; magnesium oxide, 0.1.

[0019] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S11, mixing sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide in a ratio of 7:1:1:0.1; S12, drying the mixed raw materials at 150°C for 72 hours to remove moisture; S13, grinding the dried raw materials to ensure uniformity of the raw materials; S14. The ground raw material is heated in a muffle furnace at 450°C for 24 hours, then cooled, crushed and bottled.

[0020] Embodiment 2: A medium-low melting point phase change molten salt heat storage material, comprising: sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide; Among them, the mass ratio of the ingredients is: sodium nitrate, 7; potassium nitrate, 2; zinc chloride, 1; magnesium oxide, 0.1.

[0021] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S21, mixing sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide in a ratio of 7:2:1:0.1; S22, drying the mixed raw materials at 150°C for 72 hours to remove moisture; S23, grinding the dried raw materials to ensure uniformity of the raw materials; S24. The ground raw material is heated in a muffle furnace at 450°C for 24 hours, then cooled, crushed and bottled.

[0022] Embodiment 3: A medium-low melting point phase change molten salt heat storage material, comprising: sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide; Among them, the mass ratio of the ingredients is: sodium nitrate, 6; potassium nitrate, 3; zinc chloride, 2; magnesium oxide, 0.1.

[0023] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S31, mixing sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide in a ratio of 6:3:2:0.1; S32, drying the mixed raw materials at 150°C for 72 hours to remove moisture; S33, grinding the dried raw materials to ensure uniformity of the raw materials; S34. The ground raw material is heated in a muffle furnace at 450°C for 24 hours, then cooled, crushed and bottled.

[0024] Embodiment 4: A medium-low melting point phase change molten salt heat storage material, comprising: sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide; Among them, the mass ratio of the ingredients is: sodium nitrate, 6; potassium nitrate, 4; zinc chloride, 1; magnesium oxide, 0.2.

[0025] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S41, mixing sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide in a ratio of 6:4:1:0.2; S42, drying the mixed raw materials at 150°C for 72 hours to remove moisture; S43, grinding the dried raw materials to ensure uniformity of the raw materials; S44. The ground raw material is heated in a muffle furnace at 450°C for 24 hours, then cooled, crushed and bottled.

[0026] Embodiment 5: A medium-low melting point phase change molten salt heat storage material, comprising: sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide; Among them, the mass ratio of the ingredients is: sodium nitrate, 5; potassium nitrate, 5; zinc chloride, 5; magnesium oxide, 0.2.

[0027] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S51, mixing sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide in a ratio of 5:5:5:0.2; S52, drying the mixed raw materials at 150°C for 72 hours to remove moisture; S53, grinding the dried raw materials to ensure uniformity of the raw materials; S54. The ground raw material is heated in a muffle furnace at 450°C for 24 hours, then cooled, crushed and bottled.

[0028] Embodiment 6: A medium-low melting point phase change molten salt heat storage material, comprising: sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide; Among them, the mass ratio of the ingredients is: sodium nitrate, 4; potassium nitrate, 1; zinc chloride, 6; magnesium oxide, 0.2.

[0029] A method for preparing a medium-low melting point phase change molten salt heat storage material comprises the following steps: S61, mixing sodium nitrate, potassium nitrate, zinc chloride and magnesium oxide in a ratio of 4:1:6:0.2; S62, drying the mixed raw materials at 150°C for 72 hours to remove moisture; S63, grinding the dried raw materials to ensure uniformity of the raw materials; S64. Heat the ground raw material in a muffle furnace at 450°C for 24 hours, then cool, crush and bottle.

[0030] Comparative Example 1: Different from Examples 1 to 6, the ingredients in Comparative Example 1 include sodium nitrate and potassium nitrate, and the mass ratio of the ingredients is: sodium nitrate, 7; potassium nitrate, 2.

[0031] Comparative Example 2: Different from Examples 1 to 6, the ingredients in Comparative Example 2 include sodium nitrate and potassium nitrate, and the mass ratio of the ingredients is: sodium nitrate, 6; potassium nitrate, 4.

[0032] Comparative Example 3: Different from Examples 1 to 6, the ingredients in Comparative Example 3 include sodium nitrate, potassium nitrate and zinc chloride, and the mass ratio of the ingredients is: sodium nitrate, 7; potassium nitrate, 2; zinc chloride, 1.

[0033] Comparative Example 4: Different from Examples 1 to 6, the ingredients in Comparative Example 4 include sodium nitrate, potassium nitrate and zinc chloride, and the mass ratio of the ingredients is: sodium nitrate, 6; potassium nitrate, 4; zinc chloride, 1.

[0034] Comparative Example 5: Different from Examples 1 to 6, the ingredients in Comparative Example 5 include sodium nitrate, potassium nitrate and magnesium oxide, and the mass ratio of the ingredients is: sodium nitrate, 7; potassium nitrate, 2; magnesium oxide, 0.1.

[0035] Comparative Example 6: Different from Examples 1 to 6, the ingredients in Comparative Example 6 include sodium nitrate, potassium nitrate and magnesium oxide, and the mass ratio of the ingredients is: sodium nitrate, 6; potassium nitrate, 4; magnesium oxide, 0.2.

[0036] Comparative Example 7: Different from Example 2, in Comparative Example 7, zinc chloride is replaced by sodium chloride (NaCl), and the ingredients include sodium nitrate, potassium nitrate, sodium chloride and magnesium oxide, and the mass ratio of the ingredients is: sodium nitrate, 7; potassium nitrate, 2; sodium chloride, 1; magnesium oxide, 0.1.

[0037] In Examples 1 to 6 and Comparative Examples 1 to 6, the names of the molten salts and the composition weight ratios are shown in Table 1.

[0038] Table 1 Mass ratios of various molten salt materials.

[0039]

[0040] The performance test of the molten salt material was carried out on Examples 1 to 6 and Comparative Examples 1 to 7 of the present invention, and the test parameters included: melting point, decomposition point, latent heat of phase change, specific heat capacity, thermal conductivity and viscosity; Among them, the melting point, decomposition point and latent heat of phase change were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods, the specific heat capacity was measured by a synchronous thermal analyzer, the thermal conductivity was measured by a thermal conductivity meter, and the viscosity was measured by a rheometer.

[0041] In Examples 1 to 6 and Comparative Examples 1 to 7, the test parameter values ​​of the molten salt materials are shown in Table 2.

[0042] Table 2. Table of test parameter values ​​of molten salt materials.

[0043]

[0044] In this technical solution, nitrates are considered to be excellent heat storage materials due to their low cost, low corrosion and excellent heat storage performance. The thermal stability of nitrates is mainly determined by metal cations, and usually decreases with the increase of cation polarization force. Generally speaking, as the atomic radius increases, the cation polarization force decreases, while as the outer electron charge increases, the cation polarization force increases. Therefore, in the same element group, the stability of molten salts increases with the increase of the period number. In the same period element, the stability of molten salts decreases with the increase of the main group number. For example, the thermal stability of alkaline earth metal nitrates is lower than that of alkali metal nitrates. The order of thermal stability of nitrates is: KNO3>NaNO3>Ca(NO3)2>LiNO3. In addition, the addition of chloride can effectively increase the decomposition point and specific heat capacity of the mixed molten salt, and can improve stability. Compared with other metal oxides, MgO requires higher heat to increase the temperature of nano salt per unit mass due to its stable physicochemical properties and the ability to effectively increase the specific heat capacity, which greatly increases the specific heat capacity of the molten salt.

[0045] At present, mature inorganic high-temperature phase-change materials are missing, so sensible heat commercial molten salt (solar salt) is used for comparison. The melting point of this commercial molten salt is 220°C and the decomposition point is 600°C. Compared with the current commercial molten salt materials, the heat storage density per unit mass is increased by more than 45%; at the same time, the addition of zinc chloride and magnesium oxide improves the thermal stability of nitrate ions. Experimental measurements show that the decomposition amount of the molten salt material developed by the present invention is less than 0.5% after 500 hours at 550°C, which improves the long-term operation stability of the molten salt material; after the molten salt system uses phase-change materials, the system changes from a double tank to a single tank, and the cost is reduced by more than 25%. Since the current commercial molten salt materials are sensible heat, two molten salt tanks, one cold and one hot, are required. After using phase-change molten salt materials, only one molten salt tank is needed, which further optimizes the equipment and cost.

[0046] The molten salt material of the present invention has a lower melting point, a higher decomposition temperature, a larger latent heat of phase change and better thermophysical stability, and is suitable for medium and low temperature energy storage systems, thereby improving the energy storage efficiency and reliability of the system; the molten salt material has a higher specific heat capacity; compared with the conventional method of adding nanoparticles to modify the specific heat capacity of heat storage materials, this method is simple, has a lower cost, and can be widely used in industry.

[0047] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0048] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. Medium and low melting point phase change molten salt heat storage materials, It is characterized in that Includes the following ingredients: NaNO 3 :30-80wt%; KNO 3 :5-40wt%; ZnCl 2 :5-55wt%; MgO: 0-2wt%.

2. The medium-low melting point phase change molten salt heat storage material according to claim 1, It is characterized in that NaNO 3 、KNO 3 、ZnCl 2 When the mass ratio of MgO is 7:1:1:0.1, the melting point is 200.1°C, the decomposition point is 638.3°C, the latent heat of phase change is 138.3J / g, and the specific heat capacity is 1.94J / (g·K).

3. The medium-low melting point phase change molten salt heat storage material according to claim 1, It is characterized in that NaNO 3 、KNO 3 、ZnCl 2 When the mass ratio of MgO is 7:2:1:0.1, the melting point is 220.9°C, the decomposition point is 638.7°C, the latent heat of phase change is 116.0J / g, and the specific heat capacity is 2.48J / (g·K).

4. The medium-low melting point phase change molten salt heat storage material according to claim 1, It is characterized in that NaNO 3 、KNO 3 、ZnCl 2 When the mass ratio of MgO is 6:3:2:0.1, the melting point is 212.0°C, the decomposition point is 658.1°C, the latent heat of phase change is 126.9J / g, and the specific heat capacity is 2.49J / (g·K).

5. The medium-low melting point phase change molten salt heat storage material according to claim 1, It is characterized in that NaNO 3 、KNO 3 、ZnCl 2 When the mass ratio of MgO is 6:4:1:0.2, the melting point is 302.3°C, the decomposition point is 636.7°C, the latent heat of phase change is 158.4J / g, and the specific heat capacity is 2.53J / (g·K).

6. The medium-low melting point phase change molten salt heat storage material according to claim 1, It is characterized in that NaNO 3 、KNO 3 、ZnCl 2 When the mass ratio of MgO is 5:5:5:0.2, the melting point is 316.5°C, the decomposition point is 598.2°C, the latent heat of phase change is 144.3J / g, and the specific heat capacity is 1.86J / (g·K).

7. The medium-low melting point phase change molten salt heat storage material according to claim 1, It is characterized in that NaNO 3 、KNO 3 、ZnCl 2 When the mass ratio of MgO is 4:1:6:0.2, the melting point is 354.6°C, the decomposition point is 632.2°C, the latent heat of phase change is 182.7J / g, and the specific heat capacity is 2.51J / (g·K).

8. A method for preparing a medium-low melting point phase change molten salt heat storage material, applicable to the medium-low melting point phase change molten salt heat storage material as claimed in any one of claims 1 to 7, It is characterized in that The following steps are involved: S1, NaNO 3 、KNO 3 、ZnCl 2 and MgO in a certain mass ratio to obtain a mixed raw material; S2, the mixed raw material is dried at 150 ° C for 72 hours to obtain a dried raw material after removing moisture; S3, grinding the dried raw material to obtain a uniform raw material; S4. Place the uniform raw material in a heating device, heat it at 450°C for 24 hours, and crush it after cooling to obtain a molten salt material.

9. The method for preparing the medium-low melting point phase change molten salt heat storage material according to claim 8, It is characterized in that In S4, the heating device is a muffle furnace.

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