Low-melting-point fused salt as well as preparation method and application thereof

Abstract

The invention relates to the technical field of molten salt preparation, in particular to low-melting-point molten salt and a preparation method and application thereof. Comprising the following raw materials in percentage by mass: 10-30% of sodium nitrate, 5-30% of potassium nitrate, 5-50% of sodium nitrite, 1-5% of aluminum nitrate and 1-10% of calcium carbonate. According to the invention, the sodium nitrate, the potassium nitrate, the sodium nitrite, the aluminum nitrate and the calcium carbonate are selected as raw materials to prepare the molten salt, and each component has a lower melting point, so that the crystallization temperature of the molten salt is reduced, the melting point range is 100-130 DEG C, the heat storage temperature interval of the molten salt is widened, and the crystallization risk of the molten salt is reduced; meanwhile, due to the fact that sodium nitrite exists in the molten salt, metal materials can be corroded, a proper amount of aluminum nitrate is added to serve as a corrosion inhibitor, and a passive film is formed to protect the metal surface in the system.

Description

Technical Field

[0001] The present invention relates to the technical field of molten salt preparation, and in particular to a low-melting-point molten salt and a preparation method and application thereof. Background Art

[0002] Molten salt is a mixture of multiple chemical components in a certain proportion, in which the main component is a low-melting-point inorganic salt and the secondary component is a high-melting-point inorganic salt. When the low-melting-point inorganic salt of the main component melts, the high-melting-point inorganic salt of the secondary component is still in a solid state. At this time, the solution is in an ionic state, so it is also called a molten liquid.

[0003] Normally, molten salt is composed of two or more chemical substances, such as binary molten salt, ternary molten salt, etc. Molten salt has a wide range of uses and can be used as a neutron moderator in nuclear reactors; a carrier of catalysts in the petroleum industry; a chemical reaction medium in the chemical industry; a conductive liquid in the electric power industry, etc. At present, molten salt heat storage is widely used in the fields of solar thermal power generation, clean heating, and thermal power plant transformation, which can improve energy utilization and system stability. However, due to the high crystallization temperature of commonly used molten salts, a certain risk of pipeline crystallization is caused, and low-melting-point molten salts need to be developed. Therefore, the present invention is proposed. Summary of the invention

[0004] The first object of the present invention is to provide a low melting point molten salt, which has the advantages of a wide melting point range and a low crystallization temperature. The second object of the present invention is to provide a preparation method and application of a low melting point molten salt.

[0005] The invention provides a low melting point molten salt, which comprises the following raw materials in percentage by mass: 10-30% of sodium nitrate, 5-20% of potassium nitrate, 5-50% of sodium nitrite, 1-5% of aluminum nitrate and 1-10% of calcium carbonate.

[0006] Preferably, the raw materials are included in the following mass percentages: 25-30% sodium nitrate, 15-30% potassium nitrate, 25-40% sodium nitrite, 5% aluminum nitrate, and 5-10% calcium carbonate.

[0007] The present invention provides a method for preparing the above-mentioned low melting point molten salt, comprising the following steps:

[0008] S1. Mixing sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate to obtain a mixture;

[0009] S2. The mixture is heated under vacuum conditions, and when the mixture is heated to 200 ° C, the slag is removed, and after the slag is removed, it is cooled to room temperature and then ground;

[0010] S3. The ground mixture is heated again under vacuum conditions to completely melt it, kept warm, and cooled to room temperature to obtain a low melting point molten salt.

[0011] Preferably, the crystal particles of the low melting point molten salt obtained in step S3 are 190-210 μm.

[0012] Preferably, the temperature in step S3 is raised to 200-300°C.

[0013] Preferably, the temperature is raised to 250° C. in step S3.

[0014] Preferably, the insulation time in step S3 is 30-35 minutes.

[0015] The present invention provides an application of the low-melting-point molten salt as a heat storage medium for molten salt energy storage.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The present invention uses five substances, sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate, and calcium carbonate, as raw materials to prepare molten salt. Each component has a low melting point, which reduces the crystallization temperature of the molten salt. The melting point range is 100-130°C, which is conducive to widening the molten salt heat storage temperature range and reducing the risk of molten salt crystallization. At the same time, the presence of sodium nitrite in the molten salt may cause corrosion of metal materials. An appropriate amount of aluminum nitrate is added as a corrosion inhibitor to protect the metal surface in the system by forming a passivation film. DETAILED DESCRIPTION

[0018] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0019] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this description, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example 1

[0022] A low melting point molten salt is composed of the following raw materials in percentage by mass: 30% sodium nitrate, 20% potassium nitrate, 35% sodium nitrite, 5% aluminum nitrate and 10% calcium carbonate.

[0023] The preparation process of the above-mentioned low melting point molten salt is as follows:

[0024] S1. Mixing sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate to obtain a mixture;

[0025] S2. The mixture is placed in a Cezanne vacuum melting furnace and heated under vacuum conditions. When the mixture is heated to 200°C, slag removal is performed. After slag removal, the mixture is cooled to room temperature and then ground. The Cezanne vacuum melting furnace uses a Cezanne vacuum melting furnace with high-purity argon added.

[0026] S3. The ground mixture is heated to 250°C under vacuum conditions to completely melt it, kept at this temperature for 30 minutes, and cooled to room temperature to obtain a low-melting-point molten salt.

[0027] The crystal particle size of the low melting point molten salt prepared in this embodiment is 200 μm. Its melting point is 101° C. through DSC (differential scanning calorimetry) analysis, and its decomposition temperature is 492° C. through TG (thermogravimetric analysis).

[0028] Example 2

[0029] A low melting point molten salt is composed of the following raw materials in percentage by mass: 25% sodium nitrate, 25% potassium nitrate, 40% sodium nitrite, 1% aluminum nitrate and 9% calcium carbonate.

[0030] The preparation process of the above-mentioned low melting point molten salt is as follows:

[0031] S1. Mixing sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate to obtain a mixture;

[0032] S2. The mixture is placed in a vacuum melting furnace and heated under vacuum conditions. When the mixture is heated to 200°C, the mixture is deslagging, and after deslagging, the mixture is cooled to room temperature and then ground;

[0033] S3. The ground mixture is heated to 300°C under vacuum conditions to completely melt it, kept at this temperature for 30 minutes, and cooled to room temperature to obtain a low-melting-point molten salt.

[0034] The crystal particle size of the low melting point molten salt prepared in this embodiment is 200 μm. The melting point is 123° C. through DSC analysis, and the decomposition temperature is 411° C. through TG analysis.

[0035] Example 3

[0036] A low melting point molten salt is composed of the following raw materials in percentage by mass: 28% sodium nitrate, 27% potassium nitrate, 35% sodium nitrite, 3% aluminum nitrate and 7% calcium carbonate.

[0037] The preparation process of the above-mentioned low melting point molten salt is as follows:

[0038] S1. Mixing sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate to obtain a mixture;

[0039] S2. The mixture is placed in a vacuum melting furnace and heated under vacuum conditions. When the mixture is heated to 200°C, the mixture is deslagging, and after deslagging, the mixture is cooled to room temperature and then ground;

[0040] S3. The ground mixture is heated to 250°C under vacuum conditions to completely melt it, kept at this temperature for 30 minutes, and cooled to room temperature to obtain a low-melting-point molten salt.

[0041] The crystal particle size of the low melting point molten salt prepared in this embodiment is 200 μm. The melting point is 114° C. through DSC analysis, and the decomposition temperature is 463° C. through TG analysis.

[0042] Example 4

[0043] A low melting point molten salt is composed of the following raw materials in percentage by mass: 30% sodium nitrate, 30% potassium nitrate, 25% sodium nitrite, 5% aluminum nitrate and 10% calcium carbonate.

[0044] The preparation process of the above-mentioned low melting point molten salt is as follows:

[0045] S1. Mixing sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate to obtain a mixture;

[0046] S2. The mixture is placed in a vacuum melting furnace and heated under vacuum conditions. When the mixture is heated to 200°C, the mixture is deslagging, and after deslagging, the mixture is cooled to room temperature and then ground;

[0047] S3. The ground mixture is heated to 300°C under vacuum conditions to completely melt it, kept at this temperature for 35 minutes, and cooled to room temperature to obtain a low-melting-point molten salt.

[0048] The crystal particle size of the low melting point molten salt prepared in this embodiment is 200 μm. The melting point is 130° C. through DSC analysis, and the decomposition temperature is 478° C. through TG analysis.

[0049] Comparative Example 1

[0050] A molten salt is composed of the following raw materials in percentage by mass: 30% sodium nitrate, 20% potassium nitrate, 35% sodium nitrite, 5% lithium nitrate, and 10% calcium carbonate. The preparation method is consistent with the preparation method in Example 1. The melting point is 131° C. through DSC test analysis; the decomposition temperature is 452° C. through TG analysis.

[0051] Comparative Example 2

[0052] A molten salt is composed of the following raw materials in mass percentage: 30% sodium nitrate, 20% potassium nitrate, 35% sodium nitrite, 5% aluminum nitrate, and 10% calcium nitrate. The melting point is 142°C as determined by DSC testing, and the decomposition temperature is 497°C as determined by TG analysis.

[0053] Comparative Example 3

[0054] A molten salt is composed of the following raw materials in percentage by mass: 30% sodium nitrate, 20% potassium nitrate, 35% sodium nitrite, and 15% calcium nitrate. The melting point is 129°C as determined by DSC testing, and the decomposition temperature is 435°C as determined by TG analysis.

[0055] The molten salts prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention were subjected to metal corrosion tests, and the specific test process is as follows:

[0056] (1) Stainless steel plates commonly used in molten salt storage tanks were used as samples. The size of each stainless steel plate was 20 mm × 20 mm × 3 mm. The stainless steel plates were pretreated by first grinding the surface of the stainless steel plates with sandpaper until smooth, then cleaning with acetone and anhydrous ethanol in turn to remove surface oil and impurities, then drying with a hair dryer, measuring the mass of the stainless steel plates, and then placing them in a drying container for later use;

[0057] (2) Put an appropriate amount of molten salt into a crucible, put the crucible into a high-temperature furnace, and heat it at a heating rate of 50°C / min until the molten salt is completely melted and the temperature is stabilized at 400°C;

[0058] (3) Hang the prepared sample with a thin wire or ceramic bracket and slowly place it into the melted salt to ensure that the sample is completely immersed. Cover the crucible with a lid and soak it. The high-temperature furnace should maintain a stable temperature at 400°C for 10 days. Set up 3 parallel tests for each molten salt.

[0059] (4) After immersion, use tweezers to take the sample out of the molten salt, wash it with deionized water to remove the molten salt attached to the surface of the sample, then wash it again with anhydrous ethanol, blow dry it with a hair dryer, and measure the mass of the sample.

[0060] Recording quality changes △ m = m0-m1, where m0 is the mass of the sample before immersion and m1 is the mass of the sample after immersion; calculate the corrosion rate v of the sample =△ m / (st), where s is the surface area of ​​the sample and t is the test immersion time. The test results are shown in Table 1.

[0061] Table 1 Corrosion rate of stainless steel plates in different molten salts

[0062] Group Corrosion rate (mm / d) Example 1 0.093 Example 2 0.15 Example 3 0.102 Example 4 0.076 Comparative Example 1 0.290 Comparative Example 2 0.265 Comparative Example 3 0.392

[0063] It can be seen from Table 1 that the corrosion rate of the low melting point molten salt prepared in Examples 1-4 of the present invention on the stainless steel plate is significantly lower than that of the molten salt prepared in Comparative Examples 1-3. The presence of sodium nitrite in the molten salt can cause corrosion of metal materials. The present invention adds an appropriate amount of aluminum nitrate as a corrosion inhibitor to protect the metal surface by forming a passivation film, thereby delaying metal corrosion.

[0064] The molten salt product prepared by the present invention is pure and uniform, has low requirements on equipment, and is simple and easy to operate. Five substances, namely sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate, are selected as raw materials to prepare the molten salt. Each component in the five-element system has a low melting point of 100-130°C, which reduces the crystallization temperature of the molten salt, is beneficial to widening the molten salt heat storage temperature range, and reduces the risk of molten salt crystallization. In addition, the added aluminum nitrate cooperates with the other components to inhibit metal corrosion.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low melting point molten salt, characterized in that: The invention comprises the following raw materials in percentage by mass: 10-30% of sodium nitrate, 5-30% of potassium nitrate, 5-50% of sodium nitrite, 1-5% of aluminum nitrate and 1-10% of calcium carbonate.

2. The low melting point molten salt according to claim 1, characterized in that: The invention comprises the following raw materials in percentage by mass: 25-30% of sodium nitrate, 15-30% of potassium nitrate, 25-40% of sodium nitrite, 5% of aluminum nitrate and 5-10% of calcium carbonate.

3. A method for preparing a low melting point molten salt according to claim 1 or 2, characterized in that: The following steps are involved: S1. Mixing sodium nitrate, potassium nitrate, sodium nitrite, aluminum nitrate and calcium carbonate to obtain a mixture; S2. The mixture is heated under vacuum conditions, and when the mixture is heated to 200 ° C, the slag is removed, and after the slag is removed, it is cooled to room temperature and then ground; S3. The ground mixture is heated again under vacuum conditions to completely melt it, kept warm, and cooled to room temperature to obtain a low melting point molten salt.

4. The preparation method according to claim 3, characterized in that: The crystal particles of the low melting point molten salt obtained in step S3 are 190-210 μm.

5. The preparation method according to claim 3, characterized in that: In step S3, the temperature is raised to 200-300°C.

6. The preparation method according to claim 5, characterized in that: In the step S3, the temperature is raised to 250°C.

7. The preparation method according to claim 5, characterized in that: The insulation time in step S3 is 30-35 minutes.

8. Use of the low melting point molten salt according to claim 1 or 2 as a heat storage medium for molten salt energy storage.