CN112143463A - Nitric acid nano molten salt heat transfer and storage medium and preparation method thereof - Google Patents
Nitric acid nano molten salt heat transfer and storage medium and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a nitric acid NaNO molten salt heat transfer and storage medium and a preparation method thereof, wherein the nitric acid NaNO molten salt heat transfer and storage medium comprises NaNO2、LiNO3、KNO2And nanoparticles comprising metal oxide nanoparticles and/or non-metal nanoparticles. The nitric acid nano molten salt heat transfer and storage medium provided by the embodiment of the invention can widen the working temperature range, and can be widely applied to the technical fields of compressed air energy storage systems and solar photo-thermal power generation.
Description
Technical Field
The invention belongs to the technical field of compressed air energy storage and industrial energy storage, and particularly relates to a nitric acid nano molten salt heat transfer and storage medium and a preparation method thereof.
Background
China is a country with large energy consumption, the development of economy is gradually restricted by energy problems, and the vigorous development of new energy and renewable resources is an important measure for ensuring the sustainable development of the economy of China. However, renewable energy is rapidly developing and many problems are exposed. The peak regulation means of the Chinese power grid is very limited, and a large amount of unstable renewable energy sources such as wind power and the like are difficult to accept for power generation. In recent years, the phenomenon of wind abandon and electricity limiting caused by the fact that China wind power generation cannot be connected to a power grid is more and more serious.
At present, the research on molten salt is mostly concentrated in the field of solar heat storage power generation, the application of the molten salt in a compressed air energy storage project is less, heat conduction oil is mostly used as fuel in the compressed air energy storage project, and it is worth mentioning that the heat conduction oil with the working online temperature of about 320 ℃ has the price of about 20000 plus 30000 yuan per ton, and the price of the heat conduction oil is greatly reduced when the working online temperature of the heat conduction oil is reduced by 20-30 ℃. Molten salt has been a potential heat transfer and storage medium due to its characteristics of wide application temperature range, low vapor pressure, low viscosity, good stability, low cost, etc., and at present, high temperature molten salt mainly includes nitric acid series, carbonate series, sulfate series, fluoride, chloride series, etc.
The nitrate-based molten salt has the advantages of wide raw material sources, low price and low corrosion performance, and compared with other molten salts, the nitrate-based molten salt has the problems of low solution heat and low thermal conductivity.
The majority of the heat-storage and heat-storage materials typically used are Solar Salt (60% KNO)3+40％NaNO3) And Hitech (53% KNO)3+7％NaNO3+40％NaNO2) The application temperature ranges of 220-: high melting point, easy solidification and easy pipeline blockage. A great deal of research is done in the aspect of nitric acid series molten salt in China, and the common ternary nitric acid series molten salt system is easy to cause waste in the using process due to factors such as volatilization, wall adhering devices and the like in the using process. The quaternary nitric acid system molten salt formula (LiNO) disclosed in Chinese patent 00111406.93-KNO3-NaNO3-NaNO2) The use temperature range is between 250 ℃ and 550 ℃, although the upper limit temperature range is increased compared with that of Solar Salt and Hitech, the lower limit temperature range is also increased, and the melting point is too high, thus being not beneficial to industrial application. KNO proposed in Chinese patent 201110425668.73-NaNO3-Ca(NO3)2System, melting point120 ℃ and an upper temperature limit of 550 ℃ was used, except that Ca (NO)3)2The high viscosity of the molten salt can affect the viscosity of the mixed molten salt, so that the resistance is increased in the pipeline circulation process, and the heat transfer performance is reduced. Therefore, lowering the melting point, raising the upper limit of the operating temperature, and raising the heat of solution and thermal conductivity are problems to be solved by the ternary nitric acid molten salt. It is necessary to develop a ternary nitric acid series nano molten salt heat transfer and storage material meeting the requirements.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art.
Therefore, the invention provides a nitric acid nano molten salt heat transfer and storage medium which can lower the melting point of molten salt, improve the upper limit temperature in use, improve the heat of solution and the heat conductivity and is beneficial to application in a compressed air energy storage project. The medium can also avoid the defect of local overheating when the ternary nitrate fused salt is used, can also ensure lower limit working temperature while ensuring that the upper limit working temperature of the whole system is higher than that of a common ternary nitrate system fused salt system, greatly widens the working temperature range of the ternary nitrate system fused salt, and can be widely used in compressed air energy storage projects and the technical field of solar photo-thermal power generation.
The invention also provides a preparation method of the nitric acid nano molten salt heat transfer and storage medium, and the preparation method has the advantages of strong universality, good use effect, simplicity and convenience in operation, convenience in implementation and the like.
The nitric acid NaNO molten salt heat transfer and storage medium comprises NaNO2、LiNO3、 KNO2And nanoparticles comprising metal oxide nanoparticles and/or non-metal nanoparticles.
The nitric acid nano molten salt heat transfer and storage medium provided by the embodiment of the invention has the advantages of wide working temperature, uniform temperature and good heat conduction effect when in use, and low corrosivity on equipment.
According to one embodiment of the invention, the nanoparticles comprise a material selected from SiO2Nanoparticles and ZnO nanoparticles、Al2O3Nanoparticles, TiO2One or more of nano particles, MgO nano particles and carbon nano tubes.
According to one embodiment of the invention, the nanoparticles have an average particle size of 10nm to 30 nm.
According to one embodiment of the invention, the weight ratio of each component is as follows: 40-65 parts of potassium nitrite; 20-45 parts of lithium nitrate; 10-35 parts of sodium nitrite; 1-5 parts of nano particles.
According to one embodiment of the invention, the weight ratio of the components is as follows: 15-30 parts of potassium nitrite; 25-40 parts of lithium nitrate; 15-30 parts of sodium nitrite; 2-5 parts of nano particles.
According to one embodiment of the invention, the nitric acid nano molten salt heat transfer and storage medium is applied to industrial energy storage and solar power generation.
According to one embodiment of the invention, the industrial energy storage is a compressed air energy storage system comprising: a gas storage chamber in which high pressure gas can be stored; the low-temperature molten salt tank is internally limited with a low-temperature molten salt accommodating cavity, and molten salt can be stored in the low-temperature molten salt accommodating cavity; the high-temperature molten salt tank is internally limited with a high-temperature molten salt accommodating cavity, molten salt can be stored in the high-temperature molten salt accommodating cavity, the high-temperature molten salt accommodating cavity is communicated with the low-temperature molten salt accommodating cavity, and the molten salt in the high-temperature molten salt tank and/or the low-temperature molten salt tank is the nitric acid nano molten salt heat transfer and storage medium; the molten salt electric heater is connected with the low-temperature molten salt tank and can heat the molten salt in the low-temperature molten salt accommodating cavity to a high temperature and be in a flowing state, and the molten salt in the low-temperature molten salt accommodating cavity flows to the high-temperature molten salt accommodating cavity to store heat energy; and the turbine assembly is respectively connected with the air storage chamber and the high-temperature molten salt tank, and the high-pressure gas is expanded to generate power to release energy after being released from the air storage chamber.
According to one embodiment of the invention, the turbine assembly is a compressor.
According to one embodiment of the invention, the turbine assembly comprises a first-stage turbine and a second-stage turbine, wherein N is not less than 2, and the high-pressure gas after the work of the N-1 stage turbine enters the N stage turbine to be expanded and does work after being heated by molten salt again.
The preparation method of the nitric acid nano molten salt heat transfer and storage medium comprises the following steps: s1, preparing the nano particles; s2, preparing a ternary nitrate molten salt system, wherein the ternary nitrate molten salt system is NaNO2-LiNO3-KNO2(ii) a S3, mixing the nano particles obtained in the step S1 with the ternary nitrate molten salt system obtained in the step S2 to obtain mixed molten salt.
According to an embodiment of the present invention, the nanoparticles are prepared in step S1 by using a physical method, a gas phase method or a chemical method.
According to one embodiment of the present invention, step S2 includes: s21, taking NaNO2、LiNO3、KNO2Mixing the raw materials in proportion to obtain a mixture; s22, putting the mixture obtained in the step S21 into a mortar, uniformly stirring, and grinding until no obvious particles exist; s23, heating the mixture obtained in the step S22 until the mixture is completely melted, cooling and taking out; and S24, grinding the cooled mixture obtained in the step S23 into powder to obtain the ternary nitrate molten salt system.
According to one embodiment of the present invention, the heating temperature in step S22 is 400 deg.C-450 deg.C.
According to one embodiment of the present invention, the mixture is heated to be completely melted in step S23, and then cooled to room temperature after heat preservation.
According to one embodiment of the present invention, step S3 includes: s31, adding the nano particles into the ternary molten nitrate salt system to obtain a molten salt mixture; s32, stirring, preserving heat and carrying out ultrasound on the molten salt mixture to obtain the mixed molten salt; and S33, cooling and drying the mixed molten salt to obtain the nitric acid nano molten salt heat transfer and storage medium.
According to one embodiment of the present invention, steps S1, S2, and S3 are performed in an inert gas.
According to one embodiment of the present invention, the moisture-proof treatment is performed in steps S1, S2 and S3, and the moisture-proof treatment includes at least one of temperature and humidity control of the storage environment, removal of moisture by heating, wax sealing, and sealing in a ground bottle.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flow chart of a preparation method of a nitric acid nano molten salt heat transfer and storage medium according to an embodiment of the invention;
FIG. 2 is a DSC curve of the heat transfer and storage medium of the nitrate nano molten salt obtained in example 1 of the invention;
FIG. 3 is a DSC curve of the heat transfer and storage medium of the nitrate nano molten salt obtained in example 2 of the invention;
FIG. 4 is a DSC curve of a nitric acid-based molten salt of comparative example 1;
FIG. 5 is a schematic view of a compressed air energy storage system according to an embodiment of the present invention.
Reference numerals:
a compressed air energy storage system 100;
an air reservoir 10; a low-temperature molten salt tank 20; a high-temperature molten salt tank 30; a molten salt electric heater 40; a first stage turbine 50; a second stage turbine 60; a third stage turbine 70.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention. Furthermore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The following describes a nitrate nano molten salt heat transfer and storage medium and a preparation method thereof according to an embodiment of the invention with reference to the accompanying drawings.
The nitric acid NaNO molten salt heat transfer and storage medium comprises NaNO2、LiNO3、KNO2And nanoparticles comprising metal oxide nanoparticles and/or non-metal nanoparticles, the nanoparticles dispersed in NaNO2、 LiNO3、KNO2Ternary nitrate molten salt systemAnd synthesizing to form ternary nitric acid nano molten salt.
The nitric acid nano molten salt heat transfer and storage medium provided by the embodiment of the invention has the advantages of wide working temperature, uniform temperature, good heat conduction effect and low corrosion to equipment in use.
According to one embodiment of the invention, the nanoparticles comprise a material selected from the group consisting of SiO2Nanoparticles, ZnO nanoparticles, and Al2O3Nanoparticles, TiO2Compared with the nitrate system molten salt in the prior art, the addition of the nano particles reduces the volume shrinkage of the ternary nitric acid system molten salt and improves the latent heat of phase change of the system.
Preferably, the average particle diameter of the nano particles is 10nm-30nm, and the used nano particles meet the requirements, so that the ternary nitric acid system nano molten salt has wider use temperature than the existing molten nitrate salt, and the good heat conduction effect of the ternary nitric acid nano molten salt can be ensured. .
In some specific embodiments of the invention, the mass ratio of each component is as follows: 40-65 parts of potassium nitrite; 20-45 parts of lithium nitrate; 10-35 parts of sodium nitrite; 1-5 parts of nano particles. The lowest melting point of the ternary nitric acid system nano molten salt heat transfer and storage medium prepared according to the proportion is 80-90 ℃, and the melting point is reduced. Compared with the prior art (CN 103881662A), the melting point is obviously reduced, and the working requirement of a low-temperature interval in a compressed air energy storage project can be met.
Further, the weight ratio of each component is as follows: 15-30 parts of potassium nitrite; 25-40 parts of lithium nitrate; 15-30 parts of sodium nitrite; 2-5 parts of nano particles. The lowest melting point temperature of the ternary nitric acid system nano molten salt heat transfer and storage medium is 70-80 ℃, and the ternary nitric acid system nano molten salt has a lower melting point than that of a formula provided in the prior art (CN 103881662A) while keeping a lower limit use temperature of the ternary nitric acid system nano molten salt.
According to one embodiment of the invention, the nitric acid nano molten salt heat transfer and storage medium is applied to industrial energy storage and solar power generation.
Optionally, the industrial energy storage is a compressed air energy storage system, the compressed air energy storage system comprising: a gas storage chamber 10, a low temperature molten salt tank 20, a high temperature molten salt tank 30, a molten salt electric heater 40 and a turbine assembly.
As shown in fig. 5, specifically, high-pressure gas can be stored in the gas storage chamber 10, a low-temperature molten salt accommodating cavity is defined in the low-temperature molten salt tank 20, molten salt can be stored in the low-temperature molten salt accommodating cavity, a high-temperature molten salt accommodating cavity is defined in the high-temperature molten salt tank 30, molten salt can be stored in the high-temperature molten salt accommodating cavity, the high-temperature molten salt accommodating cavity is communicated with the low-temperature molten salt accommodating cavity, molten salt in the high-temperature molten salt tank 30 and/or the low-temperature molten salt tank 20 is a nitrate-based molten salt heat transfer and storage medium, a molten salt electric heater 40 is connected with the low-temperature molten salt tank 20 and can heat molten salt in the low-temperature molten salt accommodating cavity to a high temperature and in a flowing state, molten salt in the low-temperature molten salt accommodating cavity flows to the high-temperature molten salt accommodating cavity to store heat energy, turbine components are respectively connected with the gas storage chamber.
Further, the turbine assembly is a compressor.
Preferably, the turbine assembly comprises a first stage turbine 50, a second stage turbine 60, an Nth stage turbine, N is not less than 2, and the high-pressure gas after the work of the N-1 stage turbine enters the Nth stage turbine to be expanded and does work after being heated by molten salt again.
By describing that the turbine assembly comprises the first stage turbine 50, the second stage turbine 60 and the third stage turbine 70, the compressed air energy storage system 100 according to the embodiment of the invention couples the molten salt energy storage with the compressed air energy storage, and the air at the inlet of the turbine assembly is heated by using the heat in the molten salt heat storage system, so that the efficient energy storage and power generation are realized. The system comprises two processes of energy storage and energy release when in operation. During energy storage, the compressor is driven by utilizing off-peak electricity, abandoned wind electricity, abandoned light electricity and the like, the ambient atmosphere is compressed to high pressure and stored in the gas storage chamber 10, and the storage of high-pressure gas is completed. At the same time, the molten salt electric heater 40 heats the low-temperature molten salt in the low-temperature molten salt tank 20 to a high temperature by electric energy and stores the heated molten salt in the high-temperature molten salt tank 30, thereby completing the storage of thermal energy.
Wherein, the low ebb electricity: 22: 00-next day 8: the time of 00 hours is 10 hours, which is called as the valley period, the price of the produced electricity is low, and in the compressed air energy storage technology, the valley electricity can be stored for heating in the daytime. Abandoning wind power: the abandoned wind is the phenomenon that partial wind turbines of the wind power plant are suspended due to the self characteristics of insufficient local power grid acceptance capacity, unmatched construction period of the wind power plant, unstable wind power and the like under the normal condition of the wind turbines in the initial development stage of the wind power. Wind power output characteristics are different from those of a conventional power supply, on one hand, wind power prediction precision is low due to the characteristics of randomness and volatility of wind power output, and after wind power reaches a certain scale, if the standby level of a system is not improved, wind is hardly abandoned in scheduling operation; on the other hand, wind power has the characteristic of reverse peak regulation. Abandoning photoelectricity: abandoning light, abandoning the power generated by photovoltaic, generally means that the photovoltaic system is not allowed to be connected to the grid, because the power generated by the photovoltaic system is influenced by the environment and is in continuous change, the power is not a stable power supply, and the power grid management unit refuses the power grid access of the photovoltaic system.
When releasing energy, the high-pressure air is released from the air storage chamber 10, heated by the high-temperature molten salt, and then enters the first-stage turbine 50 to expand and do work. The air after work is discharged from the first stage turbine 50, heated again by high temperature molten salt (i.e. the molten salt releases heat), and then enters the second stage turbine 60 to do work. Similarly, the exhaust gas from the second stage turbine 60 is also heated by the high-temperature molten salt and enters the third stage turbine 70 to perform work. Finally, the exhaust from the third stage turbine 70 is directly vented to ambient atmosphere to complete the expansion power generation process.
The molten salt heat storage system mainly comprises a low-temperature molten salt tank 20, a high-temperature molten salt tank 30, a molten salt electric heater 40, a molten salt pump and the like. In a conventional two-tank arrangement, one each of the low temperature molten salt tank 20 and the high temperature molten salt tank 30 is provided, and molten salt is driven to flow in the system by a molten salt pump. The molten salt electric heater 40 absorbs fluctuating electric energy input, and can convert waste electricity such as waste wind and waste light into high-grade heat energy. Because the fused salt is used for heat storage, the limitation of a high-temperature compressor is eliminated, a conventional indirect cooling type compressor can be used, the compression efficiency of the system is improved, and the compression power consumption is reduced.
It should be noted that, in the process of compressing the ambient atmosphere to high pressure and storing the ambient atmosphere in the air storage chamber 10, the ambient atmosphere needs to be compressed layer by the compressor, and after the temperature becomes high, the ambient atmosphere needs to be cooled and then enters the air storage chamber 10, and the air storage chamber 10 may be a salt cavern.
As shown in fig. 1, the preparation method of the nitric acid nano molten salt heat transfer and storage medium according to the embodiment of the invention comprises the following steps: s1, preparing nanoparticles; s2, preparing a ternary nitrate molten salt system, wherein the ternary nitrate molten salt system is NaNO2-LiNO3-KNO2(ii) a S3, mixing the nanoparticles obtained in the step S1 with the ternary nitrate molten salt system obtained in the step S2 to obtain mixed molten salt. The preparation method has good use effect and strong universality.
Alternatively, the nanoparticles are prepared in step S1 by a physical method, a gas phase method or a chemical method, wherein the physical method is a physical pulverization method or a mechanical ball milling method. The gas phase method is to absorb and cool the material forming gas under certain conditions. The chemical method is obtained by chemical reaction of two or more substances at a certain temperature and pressure, and by extraction, distillation and drying.
Further, step S2 includes: s21, taking NaNO2、LiNO3、KNO2Mixing the raw materials in proportion to obtain a mixture; s22, putting the mixture obtained in the step S21 into a mortar, uniformly stirring, and grinding until no obvious particles exist; s23, heating the mixture obtained in the step S22 until the mixture is completely melted, cooling and taking out; and S24, grinding the cooled mixture obtained in the step S23 into powder to obtain a ternary nitrate molten salt system.
According to one embodiment of the present invention, the heating temperature in step S22 is 400 deg.C-450 deg.C.
In some embodiments of the present invention, after the mixture is heated to be completely melted, the mixture is kept at the temperature and then cooled to room temperature in step S23, and the holding time may be set to 2 hours.
Optionally, step S3 includes: s31, adding the nano particles into a ternary nitrate molten salt system to obtain a molten salt mixture; s32, stirring, preserving heat and performing ultrasound on the molten salt mixture, wherein the stirring time can be 0.5h-1h, and the heat preservation ultrasound time can be 0.5h-1h, so as to obtain mixed molten salt; and S33, cooling and drying the mixed molten salt to obtain the uniform and stable nitric acid nano molten salt heat transfer and storage medium.
Further, the steps S1, S2 and S3 are performed in an inert gas, which can effectively prevent the oxidation of nitrite.
According to an embodiment of the present invention, the moisture-proof treatment is performed in steps S1, S2 and S3, and the moisture-proof treatment includes at least one of temperature and humidity control of the storage environment, removal of moisture by heating, wax sealing, and sealing in a ground bottle. It should be noted that since sodium nitrite readily adsorbs water vapor in the air, attention should be paid to the moisture-proof treatment to reduce the influence on the results.
The following specifically describes the nitric acid nano molten salt heat transfer and storage medium and the preparation method thereof according to the embodiment of the present invention.
Example 1
The preparation method of the nitric acid nano molten salt heat transfer and storage medium (ternary nitric acid system molten salt) comprises the following steps:
mixing 14% of sodium nitrite, 20% of lithium nitrate, 65% of potassium nitrite and nano particles of SiO21 percent of the components are mixed in a corundum crucible and stirred evenly to obtain a mixture.
And (3) heating the mixture in a muffle furnace to melt the mixture, preserving the heat for 2 hours, cooling to room temperature, taking out, and crushing to powder to obtain the prepared ternary nitric acid system molten salt.
Melting point tests were carried out on the molten nitric acid-based salts prepared in this example by TG-DSC, and the obtained curves are shown in FIG. 2. The test results showed that the melting point of the molten salt was 91.08 ℃.
Example 2
The preparation method of the nitric acid nano molten salt heat transfer and storage medium (ternary nitric acid system molten salt) comprises the following steps:
20% of sodium nitrite, 23% of lithium nitrate, 55% of potassium nitrite, nano-particle ZnO: 2 percent of the mixture is mixed in a corundum crucible and stirred evenly to obtain a mixture.
And (3) heating the mixture in a muffle furnace to melt the mixture, preserving the heat for 2 hours, cooling to room temperature, taking out, and crushing to powder to obtain the prepared ternary nitric acid system molten salt.
Melting point test of the molten nitric acid salt prepared in this example was carried out by TG-DSC, and the obtained curve is shown in FIG. 3. The test results show that the melting point of the molten salt is 82.86 ℃, which is lower than that of example 1.
Example 3
The preparation method of the nitric acid nano molten salt heat transfer and storage medium (ternary nitric acid system molten salt) comprises the following steps:
20% of sodium nitrite, 23% of lithium nitrate, 55% of potassium nitrite, nano-particle MgO: 2 percent of the mixture is mixed in a corundum crucible and stirred evenly to obtain a mixture.
And (3) heating the mixture in a muffle furnace to melt the mixture, preserving the heat for 2 hours, cooling to room temperature, taking out, and crushing to powder to obtain the prepared ternary nitric acid system molten salt.
The melting point of the molten nitric acid-based salt prepared in this example was measured by TG-DSC. The test results show that the melting point of the molten salt is 74.6 ℃, which is lower than that of example 1.
Example 4
The preparation method of the nitric acid nano molten salt heat transfer and storage medium (ternary nitric acid system molten salt) comprises the following steps:
20 percent of sodium nitrite, 23 percent of lithium nitrate, 55 percent of potassium nitrite and nano particlesMgO: 1%, nanoparticles: SiO 22:1 percent, and evenly stirring in a corundum crucible to obtain a mixture.
And (3) heating the mixture in a muffle furnace to melt the mixture, preserving the heat for 2 hours, cooling to room temperature, taking out, and crushing to powder to obtain the prepared ternary nitric acid system molten salt.
The melting point of the molten nitric acid-based salt prepared in this example was measured by TG-DSC. The test results show that the melting point of the molten salt is 71.2 ℃, which is lower than that of example 1.
Comparative example 1
A method for preparing ternary nitric acid system molten salt comprises the following steps:
mixing 14% of sodium nitrite, 20% of lithium nitrate and 65% of potassium nitrite in a corundum crucible, and uniformly stirring to obtain a mixture.
And (3) heating the mixture in a muffle furnace to melt the mixture, preserving the heat for 2 hours, cooling to room temperature, taking out, and crushing to powder to obtain the prepared ternary nitric acid system molten salt.
Melting point tests were carried out on the nitric acid molten salt prepared in this comparative example by DSC, and the obtained curve is shown in fig. 4. The test results showed that the melting point of the molten salt was 85.95 ℃.
From the above data, it can be known that the melting point of the ternary nitric acid system molten nano salt prepared in examples 1 to 4 is not significantly improved compared with that of the ternary nitric acid system molten salt prepared in comparative example 1, and the low-melting-point property of the ternary nitric acid molten salt system is maintained.
Thermal stability Performance test of examples 1 to 4, comparative example 1
The test was carried out by gravimetric method: adding a molten salt sample to be tested into an unnecessary nickel crucible, putting the crucible into a temperature control furnace for heating, weighing by using an analytical balance, carrying out an experiment from the normal temperature, then statically heating until the solid is completely molten, naturally cooling to the room temperature at intervals, taking out the experimental crucible, and weighing by using the analytical balance. If the weight of the sample is not reduced within a certain temperature range, the temperature of the temperature-controlled oven is increased. Then taken out at intervals and weighed by an analytical balance until the temperature rises after another steady state. And circulating the steps until the temperature reaches 600 ℃, recording the specific heat preservation temperature and the heat preservation time, and calculating the residual rate corresponding to the specific heat preservation temperature and the heat preservation time. The examples were tested using the methods described above, respectively, and table 1 was obtained from the test data.
TABLE 1
It can be seen from table 1 that the ternary nitric acid based molten salt media in examples 1 to 4 of the present invention melts at about 70 ℃, and the loss of components is less, and the ternary nitric acid based molten salt media can basically stably operate at 120 ℃ to 600 ℃. In the case where comparative example 1 is a ternary nitric acid-based molten salt to which no nanoparticles were added, it was found that the component was remarkably lost as compared with examples 1 to 4. From the data, the stability of the molten salt at 600 ℃ can be effectively improved and the component loss can be reduced due to the addition of the specific nanoparticles in the ternary nitric acid system molten salt.
Examples 1 to 4 and comparative example 1 latent heat of phase transition test
The samples were tested for latent heat of phase change using TG-DSC and DSC, and the results are shown in Table 2.
TABLE 2
The results show that the ternary nitric acid system nano molten salt prepared in the embodiments 1 to 4 of the invention has higher latent heat of phase change compared with the comparative example 1 without the nano material, so that the invention can maintain a lower limit use temperature, improve the safe upper limit use temperature and widen the working temperature of the invention.
Compared with the ternary nitric acid-based molten salt, the ternary nitric acid-based nano molten salt prepared in the embodiments 1 to 4 of the invention has the advantages of reduced phase change volume shrinkage and improved thermal conductivity. In general, the nitric acid-based nano molten salt prepared in examples 1 to 4 of the present invention is superior to the ternary nitric acid-based molten salt prepared in comparative example 1 in performance.
In summary, according to the nitric acid nano molten salt heat transfer and storage medium and the preparation method thereof provided by the embodiment of the invention, metal nanoparticles and/or non-metal particles with high thermal conductivity are added into ternary nitric acid molten salt to prepare the composite phase-change molten salt. The invention not only reduces the volume shrinkage ratio of the high-temperature phase-change heat storage material, but also improves the phase-change latent heat of the phase-change material, improves the heat conductivity of the heat transfer and heat storage medium, and improves the use temperature of the heat transfer and heat storage medium while ensuring the low melting point of the heat transfer and heat storage medium, so that the working temperature range is widened.
The invention solves the technical problem that the existing ternary nitrate system molten salt can not simultaneously give consideration to lower operating temperature and higher upper limit operating temperature by adding the nano particles into the ternary nitrate molten salt system, widens the operating temperature range of the ternary nitrate system molten salt, and can be used for the technical fields of compressed air energy storage projects and solar photo-thermal power generation. The invention can overcome the defects of small solution heat and low thermal conductivity of the ternary molten nitrate salt and avoid the defect of local overheating of the ternary molten nitrate salt during use.
The invention overcomes the KNO provided by the Chinese patent 201110425668.73-NaNO3-Ca(NO3)2The problem of poor thermal stability of calcium nitrate in the system, Ca (NO)3)2The high viscosity of the molten salt can affect the viscosity of the mixed molten salt, so that the resistance is increased in the pipeline circulation process, and the heat transfer performance is reduced. The problem that the application of compressed air energy storage in a low-temperature range cannot be met due to high melting point in the Chinese patent CN 103881662A is solved. The ternary nitric acid system nano molten salt has low melting point and is suitable for compressed air energy storage projects and heat storage and heat transfer systems of solar thermal power generation.
The ternary nitric acid system nano molten salt has a low melting point and good thermal stability, can be applied to compressed air energy storage projects, and meets the requirements of low-temperature working intervals.
The ternary nitric acid system nano molten salt disclosed by the invention is good in heat transfer and heat storage capacity, improved in heat conductivity coefficient and increased in heat conductivity, overcomes the defects of poor heat conductivity and local overheating of the ternary nitric acid system molten salt, and can be widely applied to compressed air energy storage projects and heat storage and heat transfer systems of solar thermal power generation.
The invention overcomes the defect that the molten salt can not be used for working in a low-temperature range of compressed air energy storage, is cleaner than the traditional working method using heat conducting oil, and reduces the operation cost.
The ternary nitric acid system molten salt prepared by the invention expands the application of the nitrate to the fields of new energy and industrial waste heat, and improves the added value and the development and utilization value of the nitrate.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples" or the like mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
Claims (17)
1. The heat transfer and storage medium for the nitric acid NaNO molten salt is characterized by comprising NaNO2、LiNO3、KNO2And nanoparticles comprising metal oxide nanoparticles and/or non-metal nanoparticles.
2. The molten nitrate nano-salt heat transfer and storage medium of claim 1, wherein the nano-particles comprise a material selected from SiO2Nanoparticles, ZnO nanoparticles, and Al2O3Nanoparticles, TiO2One or more of nano particles, MgO nano particles and carbon nano tubes.
3. The molten nitrate nano-salt heat transfer and storage medium of claim 1, wherein the average particle size of the nano-particles is 10nm to 30 nm.
4. The nitric acid nano molten salt heat transfer and storage medium according to claim 1, wherein the mass ratio of each component is as follows:
40-65 parts of potassium nitrite;
20-45 parts of lithium nitrate;
10-35 parts of sodium nitrite;
1-5 parts of nano particles.
5. The nitric acid nano molten salt heat transfer and storage medium according to claim 4, which is characterized by comprising the following components in parts by mass:
15-30 parts of potassium nitrite;
25-40 parts of lithium nitrate;
15-30 parts of sodium nitrite;
2-5 parts of nano particles.
6. The nitrate nano molten salt heat transfer and storage medium according to any one of claims 1 to 5, wherein the nitrate nano molten salt heat transfer and storage medium is applied to industrial energy storage and solar power generation.
7. The molten nitrate nano-salt heat transfer and storage medium of claim 6, wherein the industrial energy storage is a compressed air energy storage system, and the compressed air energy storage system comprises:
a gas storage chamber in which high pressure gas can be stored;
the low-temperature molten salt tank is internally limited with a low-temperature molten salt accommodating cavity, and molten salt can be stored in the low-temperature molten salt accommodating cavity;
the high-temperature molten salt tank is internally limited with a high-temperature molten salt accommodating cavity, molten salt can be stored in the high-temperature molten salt accommodating cavity, the high-temperature molten salt accommodating cavity is communicated with the low-temperature molten salt accommodating cavity, and the molten salt in the high-temperature molten salt tank and/or the low-temperature molten salt tank is the nitric acid nano molten salt heat transfer and storage medium;
the molten salt electric heater is connected with the low-temperature molten salt tank and can heat the molten salt in the low-temperature molten salt accommodating cavity to a high temperature and be in a flowing state, and the molten salt in the low-temperature molten salt accommodating cavity flows to the high-temperature molten salt accommodating cavity to store heat energy;
and the turbine assembly is respectively connected with the air storage chamber and the high-temperature molten salt tank, and the high-pressure gas is expanded to generate power to release energy after being released from the air storage chamber.
8. The molten nitrate nano-molten salt heat transfer and storage medium of claim 7, wherein the turbine component is a compressor.
9. The nanometer nitrate molten salt heat transfer and storage medium as claimed in claim 7, wherein the turbine assembly comprises a first-stage turbine, a second-stage turbine, an Nth-stage turbine, N is not less than 2, and the high-pressure gas after being processed by the N-1 th-stage turbine is processed by molten salt again and then enters the Nth-stage turbine to be expanded and processed.
10. The preparation method of the nitric acid nano molten salt heat transfer and storage medium according to any one of claims 1 to 5, wherein the preparation method comprises the following steps:
s1, preparing the nano particles;
S2、preparing a ternary nitrate molten salt system, wherein the ternary nitrate molten salt system is NaNO2-LiNO3-KNO2；
S3, mixing the nano particles obtained in the step S1 with the ternary nitrate molten salt system obtained in the step S2 to obtain mixed molten salt.
11. The method as claimed in claim 10, wherein the nanoparticles are prepared in step S1 by physical, gas phase or chemical methods.
12. The method according to claim 10, wherein step S2 includes:
s21, taking NaNO2、LiNO3、KNO2Mixing the raw materials in proportion to obtain a mixture;
s22, putting the mixture obtained in the step S21 into a mortar, uniformly stirring, and grinding until no obvious particles exist;
s23, heating the mixture obtained in the step S22 until the mixture is completely melted, cooling and taking out;
and S24, grinding the cooled mixture obtained in the step S23 into powder to obtain the ternary nitrate molten salt system.
13. The method according to claim 12, wherein the heating temperature in step S22 is 400 ℃ to 450 ℃.
14. The method according to claim 12, wherein the mixture is heated to be completely melted in step S23, and then cooled to room temperature after the mixture is kept warm.
15. The method according to claim 10, wherein step S3 includes:
s31, adding the nano particles into the ternary molten nitrate salt system to obtain a molten salt mixture;
s32, stirring, preserving heat and carrying out ultrasound on the molten salt mixture to obtain the mixed molten salt;
and S33, cooling and drying the mixed molten salt to obtain the nitric acid nano molten salt heat transfer and storage medium.
16. The method of claim 10, wherein steps S1, S2, and S3 are performed in an inert gas.
17. The method of claim 10, wherein the steps S1, S2 and S3 are performed with moisture-proof treatment, and the moisture-proof treatment comprises at least one of temperature and humidity control of the storage environment, removal of moisture by heating, wax sealing, and sealing in a ground bottle.
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