A nanofluid quaternary nitric acid molten salt heat storage medium, a preparation method and application thereof

Abstract

The application provides a kind of nanofluid quaternary nitric acid molten salt heat storage medium and its preparation method and application, belong to molten salt technical field.The nanofluid quaternary nitric acid molten salt heat storage medium of the application includes quaternary nitric acid molten salt system, in the quaternary nitric acid molten salt system, the mass percentage content of each component is 4% to 6% of sodium nitrate, 39% to 44% of potassium nitrate, 42% to 45% of calcium nitrate, 5% to 15% of aluminum nitrate;And functionalized modified nanoparticles, the addition amount of the functionalized modified nanoparticles is 0.2% to 2% of the total mass of the nanofluid quaternary nitric acid molten salt heat storage medium.The nanofluid quaternary nitric acid molten salt prepared by the application has low melting point, large heat capacity, stable thermal physical properties in heat storage cycle, and is very suitable for thermal power-molten salt energy storage coupling system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of molten salt, and particularly relates to a kind of nanofluid quaternary nitric acid molten salt heat storage medium and its preparation method and application. BACKGROUND

[0002] Molten salt has the advantages of wide use temperature range, low working pressure, good economy, strong heat transfer and storage performance, and stable chemical performance, and is widely used in the fields of solar heat utilization, renewable energy storage, high-temperature hydrogen production by hydrolysis, and molten salt reactor as an ideal medium for high-temperature heat transfer and storage.

[0003] The fire power-molten salt energy storage coupling technology uses the technical advantages of large-capacity molten salt energy storage to make up for the defects of insufficient stability of deep peak regulation of the fire power unit, and at the same time improves the steam and heat supply efficiency of the unit, and promotes the green and low-carbon development of the fire power unit. However, the fire power-molten salt energy storage coupling technology has operating parameters that are clearly different from the photothermal molten salt power generation system, and therefore special requirements are put forward for the performance of the molten salt medium, especially in terms of melting point control. Commercial molten salt products cannot meet the special requirements of the technology in terms of ultra-low melting point and high specific heat capacity.

[0004] The current commercial molten salt products are still concentrated on eutectic nitrate. The outstanding advantages of nitric acid molten salt system are wide raw material sources, low price, and small corrosion, so compared with other molten salts, nitric acid molten salt has great advantages. However, the multi-component nitric acid molten salt system has the disadvantages of high melting point, small specific heat capacity, and low thermal conductivity, and is difficult to meet the requirements of the fire power-molten salt energy storage coupling technology.

[0005] The patent application with the application number CN201510233093.7 discloses a kind of low melting point nanometer molten salt heat transfer and storage medium and preparation method, and adopts metal oxide nanoparticles to modify the mixed molten salt of potassium nitrate, sodium nitrate, calcium nitrate and lithium nitrate, and the melting point of the molten salt is reduced to 80-130 DEG C.

[0006] The patent application with the application number CN201310029569.6 discloses a kind of ternary nitric acid nanometer molten salt heat transfer and storage medium and its preparation method and application, and the nanoparticles are selected from one or more of SiO2 nanoparticles, ZnO nanoparticles, Al2O3 nanoparticles, TiO2 nanoparticles and MgO nanoparticles.

[0007] The patent application with the application number CN20131005397.1 discloses a kind of multi-component nitric acid nanometer molten salt heat transfer and storage medium and its preparation method and application, and adopts metal oxide or non-metal oxide nanoparticles to modify the mixed molten salt of potassium nitrate, sodium nitrate, sodium nitrite and cesium nitrate, and the thermal conductivity is greatly enhanced.

[0008] However, the nanofluid composite molten salt has the defect that solid particle agglomeration leads to solid / liquid separation and loss of heat transfer enhancement characteristics during long-term operation, which seriously reduces the enhancement effect on the molten salt; in addition, the solid particle agglomeration settles in the flow dead zone of the pipeline loop, which may cause local overheating or heat exchanger heat exchange efficiency reduction or even risk of blocking the pipeline. SUMMARY

[0009] To solve the defects in the prior art, the application provides a nanofluid quaternary nitric acid molten salt heat storage medium and a preparation method and application thereof. The heat storage medium provided by the application can greatly improve the operation stability of the existing nanofluid molten salt, avoid heat performance decline, and reduce the risk of local overheating or heat exchanger heat exchange efficiency reduction or even blocking the pipeline caused by agglomeration settlement, and can be widely used in the field of thermal power-molten salt energy storage coupling technology.

[0010] To achieve the above purpose, the application adopts the following technical scheme:

[0011] A nanofluid quaternary nitric acid molten salt heat storage medium comprises:

[0012] The quaternary nitric acid molten salt system, wherein the mass percentage content of each component is 4-6% of sodium nitrate, 39-44% of potassium nitrate, 42-45% of calcium nitrate, and 5-15% of aluminum nitrate;

[0013] and functionalized modified nanoparticles, wherein the addition amount of the functionalized modified nanoparticles is 0.2-2% of the total mass of the nanofluid quaternary nitric acid molten salt heat storage medium.

[0014] As a further improvement of the application, the nanoparticles are metal oxide nanometer ions or non-metal oxide nanoparticles.

[0015] As a further improvement of the application, the nanoparticles are one or more of SiO2, Al2O3, TiO2, CeO2, and La2O3.

[0016] The average particle size of the nanoparticles is 10-60 nm.

[0017] As a further improvement of the application, the functionalized modified nanoparticles are obtained by treating and modifying the nanoparticles with a silane coupling agent.

[0018] The silane coupling agent is one or more of 2-[methoxy(polyethylene oxide)propyl]trimethoxysilane, (3-ethoxypropyl)trimethylsilane, 3-aminopropyltrimethoxysilane, and vinyltris(beta-methoxyethoxy)silane.

[0019] As a further improvement of the application, the addition amount of the silane coupling agent is 5-50% of the mass of the nanoparticles.

[0020] A preparation method of a nanofluid quaternary nitric acid molten salt heat storage medium, comprising the following steps:

[0021] Proportionally grind the quaternary nitric acid molten salt system and the functionalized modified nanoparticles uniformly, and heat to a molten state;

[0022] After uniform stirring, ultrasonic preservation for a predetermined time; naturally cool to obtain the nanofluid quaternary nitric acid molten salt heat storage medium.

[0023] As a further improvement of the present application, the heating temperature for heating to a molten state is 200-250 DEG C.

[0024] As a further improvement of the present application, after uniform stirring, ultrasonic preservation for a predetermined time refers to magnetic stirring for 1-2 h, and ultrasonic preservation for 1-2 h.

[0025] As a further improvement of the present application, the preparation method of the functionalized modified nanoparticles comprises:

[0026] Stirring uniformly dispersing the nanoparticles in deionized water, and dropping a silane coupling agent solution;

[0027] Heating to 60-80 DEG C, and continuously stirring for 48-72 h;

[0028] After filtration separation, freeze-drying the nanoparticles to obtain the functionalized modified nanoparticles.

[0029] A nanofluid quaternary nitric acid molten salt heat storage medium is applied in a thermal power-molten salt energy storage coupling system.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] The functionalized nanoparticles prepared by the present application reduce the surface energy of the nanopowder particles, and improve the dispersion stability of the nanoparticles in the molten salt. The silane coupling agent is grafted to the surface of the nanoparticles to reduce the surface energy of the nanopowder particles and improve the dispersion stability of the nanoparticles in the molten salt, because the high specific surface energy of the nanopowder particles and the mutual attraction between the particles cause the agglomeration of the nanopowder. The nanofluid quaternary nitric acid molten salt heat storage medium prepared by the present application has a low melting point, a high specific heat capacity, and stable thermal properties in a heat storage cycle, and can be widely used in the field of thermal power-molten salt energy storage coupling technology.

[0032] Further, the silane coupling agent is used to functionalize and modify the metal oxide or non-metal oxide nanoparticles, and the nanofluid quaternary nitric acid molten salt heat storage medium is prepared by compounding the functionalized and modified nanoparticles with the quaternary nitric acid molten salt. DETAILED DESCRIPTION

[0033] To enable persons skilled in the art to understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings to those skilled in the art of the present application, and in the event of conflict, the definitions in the specification shall prevail.

[0034] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting on the scope of the present application, i.e., the present application can be implemented without regard to any particular theory or mechanism.

[0035] Herein, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, amounts, contents and concentrations, are for the sake of brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0036] Herein, unless otherwise specified, "comprise", "include", "contain", "have" or similar words encompass the meaning of "consist of" and "consist essentially of", for example, "A comprises a" encompasses the meaning of "A comprises a and other" and "A comprises only a".

[0037] Herein, for the sake of brevity, all possible combinations of the various technical features in the various embodiments or examples are not described. Therefore, as long as the combinations of the technical features do not contradict each other, the various technical features in the various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered as within the scope of the present specification.

[0038] The present application will be described in detail below with reference to specific embodiments.

[0039] The present application provides a nanofluid quaternary nitrate molten salt heat storage medium, which contains a quaternary nitrate molten salt system composed of sodium nitrate, potassium nitrate, calcium nitrate and aluminum nitrate, and further comprises functionalized metal oxide nano-ions or non-metal oxide nanoparticles;

[0040] The nanoparticles are dispersed into the quaternary nitrate molten salt system after functionalization to form the nanofluid quaternary nitrate molten salt heat storage medium; the nanoparticles are one or more of SiO2, Al2O3, TiO2, CeO2 and La2O3;

[0041] In the quaternary nitrate molten salt system, the mass percentage content of each component is 4% to 6% of sodium nitrate, 39% to 44% of potassium nitrate, 42% to 45% of calcium nitrate and 5% to 15% of aluminum nitrate;

[0042] The average particle size of the nanoparticles is 10-60 nm.

[0043] The adding amount of the nanoparticles is 0.2-2% of the total mass of the nanofluid quaternary nitric acid molten salt.

[0044] The preparation method of the functionalized modified nanoparticles comprises the following steps:

[0045] (1) dispersing the nanoparticles in deionized water and stirring vigorously, and adding a silane coupling agent solution dropwise;

[0046] (2) heating to 60-80℃ and continuously stirring for 48-72h;

[0047] (3) freeze-drying the nanoparticles after filtration and separation;

[0048] The silane coupling agent in step (1) is one or more of 2-[methoxy(polyethylene oxide)propyl]trimethoxysilane, (3-ethoxypropyl)trimethylsilane, 3-aminopropyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane;

[0049] The silane coupling agent in step (1) is added in a proportion of 5-50% of the mass of the nanoparticles;

[0050] The application also provides a preparation method of a nanofluid quaternary nitric acid molten salt heat storage medium, comprising the following steps:

[0051] (1) uniformly grinding the molten salt and the functionalized modified nanoparticles in a proportion, and then heating them in a heating furnace to a molten state;

[0052] (2) uniformly stirring by magnetic stirring and ultrasonic incubation;

[0053] (3) naturally cooling the high-temperature molten salt to obtain the nanofluid quaternary nitric acid molten salt heat storage medium;

[0054] The heating temperature in step (1) is 200-250℃;

[0055] The magnetic stirring in step (2) is performed for 1-2h, and the ultrasonic incubation is performed for 1-2h;

[0056] The application of the nanofluid quaternary nitric acid molten salt heat storage medium in a thermal power-molten salt energy storage coupling system also belongs to the protection scope of the application.

[0057] Preparation and performance test of the nanofluid quaternary nitric acid molten salt heat storage medium

[0058] The materials used are SiO2, TiO2, and CeO2 nanoparticles, and the nanoparticles are functionalized by using a silane coupling agent.

[0059] The preparation steps of the nanofluid quaternary nitric acid molten salt heat storage medium are as follows:

[0060] (1) Disperse the nanoparticles in deionized water and stir vigorously, and drop the silane coupling agent solution at a proportion of 5% to 50% of the mass of the nanoparticles;

[0061] (2) Heat to 60-80°C, continuously stir for 48-72 hours, filter and separate, and freeze-dry the nanoparticles;

[0062] (3) Grind the sodium nitrate, potassium nitrate, calcium nitrate, and aluminum nitrate molten salt and the functionalized modified nanoparticles uniformly at a proportion, and place them in a heating furnace and heat to 200-250°C to make them into a molten state;

[0063] (4) After magnetic stirring for 1-2 hours, ultrasonic incubation for 1-2 hours;

[0064] (5) Naturally cool the high-temperature molten salt to obtain the nanofluid quaternary nitric acid molten salt heat storage medium.

[0065] Example 1

[0066] (1) Disperse the nanoparticles in deionized water and stir vigorously, and drop the silane coupling agent solution at a proportion of 5% of the mass of the nanoparticles;

[0067] (2) Heat to 70°C, continuously stir for 72 hours, filter and separate, and freeze-dry the nanoparticles;

[0068] (3) Grind the sodium nitrate, potassium nitrate, calcium nitrate, and aluminum nitrate molten salt and the functionalized modified nanoparticles uniformly at a proportion, and place them in a heating furnace and heat to 230°C to make them into a molten state;

[0069] (4) After magnetic stirring for 1 hour, ultrasonic incubation for 2 hours;

[0070] (5) naturally cooling the high-temperature molten salt to obtain the nanofluid quaternary nitrate molten salt heat storage medium.

[0071] Example 2

[0072] (1) dispersing the nanoparticles in deionized water and stirring vigorously, and adding a silane coupling agent solution in a proportion of 10% of the mass of the nanoparticles;

[0073] (2) heating to 60°C and continuously stirring for 62h, and freeze-drying the nanoparticles after filtration and separation;

[0074] (3) uniformly grinding the sodium nitrate, potassium nitrate, calcium nitrate, aluminum nitrate molten salt and the functionalized nanoparticles in a proportion and placing them in a heating furnace to heat to 250°C to make them into a molten state;

[0075] (4) magnetically stirring for 2h and ultrasonically incubating for 1h;

[0076] (5) naturally cooling the high-temperature molten salt to obtain the nanofluid quaternary nitrate molten salt heat storage medium.

[0077] Example 3

[0078] (1) dispersing the nanoparticles in deionized water and stirring vigorously, and adding a silane coupling agent solution in a proportion of 5%-50% of the mass of the nanoparticles;

[0079] (2) heating to 80°C and continuously stirring for 48h, and freeze-drying the nanoparticles after filtration and separation;

[0080] (3) uniformly grinding the sodium nitrate, potassium nitrate, calcium nitrate, aluminum nitrate molten salt and the functionalized nanoparticles in a proportion and placing them in a heating furnace to heat to 200°C to make them into a molten state;

[0081] (4) magnetically stirring for 1.5h and ultrasonically incubating for 1.5h;

[0082] (5) naturally cooling the high-temperature molten salt to obtain the nanofluid quaternary nitrate molten salt heat storage medium.

[0083] A series of nanofluid quaternary nitrate molten salts are prepared according to the above steps and the proportions in Table 1 below. Table 1 is the formula of the nanofluid quaternary nitrate molten salts of different numbers in the application, as well as the types of silane coupling agents and the particle sizes of the nanoparticles in the formula, and the formula of the quaternary nitrate molten salt (A) to which the nanoparticles are added and the nanofluid molten salt formula without functionalization treatment (Comparative Examples 1-4).

[0084] Table 1 Nanofluid quaternary nitrate molten salt formula

[0085]

[0086]

[0087] The present application is not limited to the above-mentioned embodiments, and any technical modification made according to the technical principles of the present application falls within the scope of protection of the present application.

[0088] The performance of the prepared nanofluid quaternary nitric acid molten salt was tested as follows:

[0089] Thermal property stability test of heat storage cycle: the molten salt sample was added into an alumina crucible and placed in a temperature-controlled furnace for temperature rising and falling cycle, the temperature range was 200-500°C, the molten salt sample on the surface of the crucible was obtained every different cycle, and the minimum melting temperature and specific heat capacity were measured. The general differential scanning calorimeter (DSC) was used to test the minimum melting temperature and specific heat capacity of the sample molten salt. The molten salt samples shown in Table 1 were tested by the above-mentioned method, and the test results are shown in Table 2.

[0090] Table 2: Thermal property test data of molten salt

[0091]

[0092] As can be seen from Table 2, compared with the minimum melting temperature and specific heat capacity of the control comparative example 1, the minimum melting temperature of the nanofluid quaternary nitric acid molten salt prepared by the present application is reduced by 5-8°C, and the initial specific heat capacity is increased by more than 20%. The specific heat capacity of the samples of comparative examples 2-4 is significantly reduced when the cycle number reaches more than 5 times, and is decreased by 13% after 30 cycles. Compared with the molten salt medium of comparative examples 2-4, the specific heat capacity value of the functionalized modified nanofluid quaternary nitric acid molten salt of examples 1-18 prepared by the present application does not decrease significantly with the increase of cycle number. It is shown that by functionalizing the nanoparticles, the surface energy of the nanopowder particles is reduced, the dispersion stability of the nanoparticles in the molten salt is improved, and the strengthening performance of the nanoparticles on the molten salt medium is prolonged.

[0093] As can be seen from the data in Table 2, the nanofluid quaternary nitric acid molten salt of examples 7-9 prepared by the present application has lower minimum melting temperature and higher specific heat capacity value. Overall, the nanofluid quaternary nitric acid molten salt of examples 7-9 prepared by the present application has better performance indicators of heat storage medium.

[0094] The above-mentioned is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should be considered as the protection scope of the present application.

[0095] Finally, it should be noted that the above examples are merely intended to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A nanofluid quaternary nitrate molten salt heat storage medium, characterized in that, Comprise: A quaternary nitric acid molten salt system, wherein the mass percentage of each component is 4-6% of sodium nitrate, 39-44% of potassium nitrate, 42-45% of calcium nitrate, and 5-15% of aluminum nitrate; And functionalized nanoparticles, the addition amount of the functionalized nanoparticles is 0.2-2% of the total mass of the nanofluid quaternary nitric acid molten salt heat storage medium; The nanoparticles are metal oxide nanoparticles or non-metal oxide nanoparticles; The functionalized nanoparticles are obtained by modifying the nanoparticles with a silane coupling agent; The silane coupling agent is one or more of 2-[methoxy(polyethylene oxide)propyl]trimethoxysilane, (3-ethoxypropyl)trimethylsilane, 3-aminopropyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane; The addition amount of the silane coupling agent is 5-50% of the mass of the nanoparticles.

2. The nanofluid quaternary nitrate molten salt heat storage medium according to claim 1, wherein: The nanoparticles are one or more of SiO2, Al2O3, TiO2, CeO2, and La2O3.

3. The nanofluid quaternary nitrate molten salt heat storage medium according to claim 1, wherein: The average particle size of the nanoparticles is 10-60 nm.

4. A preparation method of the nanofluid quaternary nitric acid molten salt heat storage medium according to any one of claims 1-3, comprising the following steps: Grind the quaternary nitric acid molten salt system and the functionalized nanoparticles uniformly in proportion, and heat to a molten state; After uniform stirring, ultrasonically preserve for a predetermined time; naturally cool to obtain the nanofluid quaternary nitric acid molten salt heat storage medium.

5. The preparation method of the nanofluid quaternary nitric acid molten salt heat storage medium according to claim 4, wherein: The heating temperature for heating to a molten state is 200-250°C.

6. The preparation method of the nanofluid quaternary nitric acid molten salt heat storage medium according to claim 4, wherein: After uniform stirring, ultrasonically preserve for a predetermined time, which means magnetic stirring for 1-2 h and ultrasonic preservation for 1-2 h.

7. The method for preparing a nanofluid quaternary nitrate molten salt thermal storage medium according to claim 6, characterized in that: The preparation method of the functionalized nanoparticles comprises: Disperse the nanoparticles in deionized water and stir uniformly, and drop the silane coupling agent solution; Heat to 60-80°C, and continuously stir for 48-72 h; After filtration separation, freeze-dry the nanoparticles to obtain the functionalized nanoparticles.

8. The nanofluid quaternary nitric acid molten salt heat storage medium according to any one of claims 1-3 is applied in a thermal power-molten salt energy storage coupling system.

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