WO2019205759A1 - Solar photothermal power generation heat-transfer and heat-storage medium and preparation method therefor - Google Patents

Abstract

A solar photothermal power generation heat-transfer and heat-storage medium, comprising a nitric acid fused salt heat-storage medium and a carbon nanotube composited in the nitric acid fused salt heat-storage medium; in the solar photothermal power generation heat-transfer and heat-storage medium, the mass percent of the carbon nanotube is 0.1%~1%, and the diameter of the carbon nanotube d≥10nm. The heat-transfer and heat-storage medium is prepared by grinding and homogeneously mixing a sodium nitrate and potassium nitrate fused salt with the carbon nanotube to obtain a raw material powder; heating and melting the raw material powder and preserving heat for at least 1h to obtain a molten mixture; and cooling the molten mixture to an indoor temperature and crushing and homogenously mixing the mixture.

Description

Solar thermal power generation heat transfer heat storage medium and preparation method thereof Technical field

The present application relates to the field of solar thermal power generation technology, and in particular to a solar thermal power generation heat transfer heat storage medium and a preparation method thereof.

Background technique

Environmental and energy issues are the two most important issues in the world today, and the effective use of solar energy is an important way to develop new energy, protect the environment and achieve sustainable development, so it is strongly supported by national policies. In recent years, solar thermal power generation has become one of the main ways to develop solar energy on a large scale. The key technology of solar thermal power generation is high temperature heat transfer and heat storage technology, in which heat transfer and heat storage medium is essential for system efficiency and cost reduction.

At present, the commonly used heat transfer and heat storage medium mainly includes high pressure water, steam, heat transfer oil and liquid metal. In contrast, molten salt has wide use temperature, high thermal stability, low viscosity, low saturated vapor pressure and low price. Such advantages have become the first choice for solar thermal power storage media. According to different anions, molten salt heat storage materials used in solar thermal power generation mainly include nitrate molten salt, carbonate molten salt, chlorinated molten salt, fluorinated molten salt, etc.; among them, nitrate has low melting point, low cost and weak corrosiveness. It has become the first choice for molten salt applications.

China's solar energy resources are very rich, especially in the western and southern parts of the Qinghai-Tibet Plateau. The solar energy resources are particularly abundant. At the same time, it has the conditions of grid access, cooling water source and a large amount of desertified land. It is very suitable for the construction of large-scale solar thermal power stations. At the same time, Qinghai Province has a large number of salt lakes, large reserves and abundant salt and mineral resources. It is one of the important production bases of salt lakes and salt chemical industry in China, among which minerals such as sodium chloride, magnesium chloride, potassium salt, lithium mine and thenardite are all in the country. first place. Rich inorganic salts such as potassium salts, sodium salts and magnesium salts are important raw materials for the main components of nitrate storage heat storage medium (potassium nitrate and sodium nitrate). Combining the advantages of local resources, reducing the operating cost of solar thermal utilization system, and solving the problem of low comprehensive utilization rate of salt lake resource development, the high value of salt lake resources is promoted.

Taking Qinghai Zhongkong Delingha 10MW Solar Thermal Power Station and Dunhuang First Aviation Energy Saving 10MW Photothermal Power Plant as examples, they all use binary nitrate molten salt heat storage medium as heat transfer and heat storage medium; the molten salt has good heat. Stability and low cost, but its thermal conductivity is low, only 0.5W·m ^-1 ·K ^-1 , which puts a test on the heat transfer performance of the system.

At present, there are related researches on how to improve the thermal conductivity of molten salt heat storage medium, mainly to add other components to form a multi-component system, such as quartz sand, metal oxide (or non-metal oxide) nanoparticles, water. Although glass and the like have improved in thermal conductivity, in these reports, specific values are not given, and the improvement is mainly for the thermal stability of the molten salt heat storage medium, that is, the decomposition temperature is increased. improve. However, when other components are added to form a polybasic nitrate molten salt, the thermal conductivity is generally lowered while lowering the melting point. Therefore, there is still a great challenge to improve the thermal conductivity of the molten salt heat storage medium of nitric acid, which has important and practical significance.

Summary of the invention

In order to solve the problem that the thermal conductivity of the above-mentioned existing molten salt molten heat transfer medium is low, affecting the heat exchange efficiency of the molten salt heat transfer process in actual operation, thereby affecting the energy utilization and utilization efficiency, the present invention provides a The solar thermal power generation heat transfer heat storage medium and the preparation method thereof, the solar thermal energy storage heat transfer medium through which the carbon nanotubes can effectively improve the thermal conductivity of the nitrate molten salt heat storage medium.

In order to achieve the above object, the present application adopts the following technical solutions:

The embodiment of the present application provides a solar thermal power generation heat transfer heat storage medium, comprising a nitrate molten salt heat storage medium and carbon nanotubes composited in the nitrate molten salt heat storage medium; wherein, the solar heat is In the power generation heat transfer heat storage medium, the mass percentage of the carbon nanotubes is 0.1% to 1%, and the diameter of the carbon nanotubes is d≥10 nm.

Further, the carbon nanotubes have a diameter of 10 nm ≤ d ≤ 20 nm.

Further, the nitrate molten salt heat storage medium comprises uniformly mixed sodium nitrate and potassium nitrate.

Further, in the solar thermal power generation heat transfer heat storage medium, the mass percentage of sodium nitrate is 59% to 60%, and the mass percentage of potassium nitrate is 39% to 40%.

Another object of the present application is to provide a method for preparing a solar thermal power generation heat transfer heat storage medium, comprising the steps of:

S1, the nitrate molten salt heat storage medium and the carbon nanotubes are ground and uniformly mixed to obtain a raw material powder, wherein, in the raw material powder, the mass percentage of the carbon nanotubes is 0.1% to 1%, The diameter of the carbon nanotubes is d≥10 nm;

S2, heating and melting the raw material powder for at least 1 h to obtain a molten mixture;

S3. The molten mixture is cooled to room temperature and pulverized to obtain a solar thermal power generation heat transfer heat storage medium.

Further, the carbon nanotubes have a diameter of 10 nm ≤ d ≤ 20 nm.

Further, the nitrate molten salt heat storage medium comprises uniformly mixed sodium nitrate and potassium nitrate.

Further, in the raw material powder, the mass percentage of sodium nitrate is 59% to 60%, and the mass percentage of potassium nitrate is 39% to 40%.

Further, in the step S2, the holding time is 1 h to 3 h.

Further, in the step S2, the raw material powder is melted at 300 ° C to 400 ° C.

Compared with the prior art, the beneficial effects of the present application are:

In the present application, a carbon nanotubes having a diameter d≥10 nm are added to a molten salt heat storage medium, and a solar thermal power generation heat storage medium is obtained by controlling the addition amount of the carbon nanotubes; Compared with the molten salt storage medium of the nitric acid, the heat transfer and heat storage medium of the power generation obviously increases the thermal conductivity under the premise of ensuring the decomposition temperature is equivalent, and the thermal conductivity is as high as 1.7 W·m ^-1 ·K ^-1 , thereby making the When the solar thermal power generation heat transfer storage medium is applied to solar thermal power generation, the utilization efficiency of solar energy is improved. Moreover, the solar thermal power generation heat transfer heat storage medium of the present invention has better compatibility with other added components than the other similar media materials in the prior art, in which the nitrate molten heat storage medium and the carbon nanotubes have compatibility with other added components. better.

DRAWINGS

The above and other aspects, features and advantages of the embodiments of the present invention will become more apparent from

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the comparison of thermal conductivity of solar thermal power generation heat transfer heat storage media according to Examples 1 to 5 and Comparative Example 1 at different temperatures.

detailed description

Hereinafter, embodiments of the present invention will be described in detail in the future. However, the invention may be embodied in many different forms and the invention should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and the application of the invention, and the various embodiments of the invention can be understood.

The invention provides a solar thermal power generation heat transfer heat storage medium, which comprises a nitrate molten salt heat storage medium and carbon nanotubes compounded in the nitrate molten salt heat storage medium.

Specifically, in the solar thermal power generation heat transfer heat storage medium, the mass percentage of the carbon nanotubes is 0.1% to 1%, and the diameter of the carbon nanotubes is d ≥ 10 nm, preferably 10 nm to 20 nm.

Further, in the solar thermal power generation heat transfer heat storage medium, the mass percentage of the carbon nanotubes is 0.1% to 0.5%.

More specifically, the nitrate molten salt heat storage medium comprises uniformly mixed sodium nitrate and potassium nitrate; generally, in the solar thermal power generation heat transfer heat storage medium, the mass percentage of sodium nitrate is controlled to be 59% to 60%, The mass percentage of potassium nitrate is controlled to be 39% to 40%.

The solar thermal power generation heat transfer and heat storage medium provided by the invention can significantly improve the thermal conductivity under the premise of maintaining the decomposition temperature of the nitrate molten heat storage medium by using the carbon nanotubes therein.

The invention also provides a preparation method of the above solar thermal power generation heat transfer heat storage medium, in particular, the preparation method comprises the following steps:

In step S1, the nitrate molten salt heat storage medium and the carbon nanotubes are ground and uniformly mixed to obtain a raw material powder.

Specifically, in the raw material powder, the mass percentage of the controlled carbon nanotubes is 0.1% to 1%, and the diameter of the carbon nanotubes is controlled to be d ≥ 10 nm, preferably 10 nm to 20 nm.

Further, in the raw material powder, the mass percentage of the carbon nanotubes is from 0.1% to 0.5%.

Further, the nitrate molten salt heat storage medium comprises uniformly mixed sodium nitrate and potassium nitrate; and, the mass percentage of sodium nitrate in the raw material powder is controlled to be 59% to 60%, and the mass percentage of potassium nitrate is 39% to 40%.

In step S2, the raw material powder is heated and melted and kept for at least 1 hour to obtain a molten mixture.

Specifically, the raw material powder can be heated and melted in a temperature range not lower than the melting temperature and not higher than the decomposition temperature, and at the same time, considering the energy consumption factor, the heating temperature is generally controlled to be 300 ° C to 400 °C can be.

Further, after the raw material powder is melted, in order to further mix it uniformly, it is necessary to carry out heat preservation for a certain period of time, and it is preferably controlled to be 1 h to 3 h.

In step S3, the molten mixture is cooled to room temperature and pulverized to obtain a solar thermal power generation heat transfer heat storage medium.

Hereinafter, the above-mentioned solar thermal power generation heat transfer heat storage medium of the present invention and its preparation method and performance will be described by way of specific embodiments, but the present invention is not limited to the following embodiments, and the following embodiments are merely the present invention. Specific example.

Example 1

The embodiment provides a method for preparing a solar thermal power generation heat storage heat storage medium, the specific method is: first, mixing 59.94% sodium nitrate, 39.96% potassium nitrate, and 0.10% carbon nanotubes in a crucible Uniformly, a mixed powder is obtained; wherein, sodium nitrate and potassium nitrate are collectively referred to as a molten salt heat storage medium; then, the mixed powder is heated and melted in a muffle furnace at 400 ° C, and after being completely melted, the temperature is constant. The mixture was kept for 60 minutes to obtain a molten mixture. Finally, the molten mixture was cooled to room temperature and mechanically pulverized to obtain a carbon nanotube doped composite nitrate molten salt heat storage medium, that is, a solar thermal power generation heat storage medium.

Thus, in this embodiment, a solar thermal power generation heat transfer heat storage medium is obtained by the above preparation method, which is composed of 99.90% nitrate molten salt heat storage medium and 0.10% carbon nanotube composite; wherein the nitric acid The molten salt heat storage medium consists of 59.94% sodium nitrate and 39.96% potassium nitrate.

Specifically, the diameter d of the carbon nanotubes is from 10 nm to 20 nm.

The melting point and the decomposition temperature of the solar thermal power generation heat storage medium of the present embodiment were tested by synchronous thermal analysis. The test results are shown in Table 1. Meanwhile, the solar energy of the present embodiment was applied at 300 ° C using a transient planar heat source method. The photothermal power generation heat transfer heat storage medium was used to measure the thermal conductivity, and the test results are shown in Fig. 1.

Example 2

In the description of the second embodiment, the same points as those of the embodiment 1 will not be described again, and only the differences from the embodiment 1 will be described. Example 2 differs from Example 1 in that, in the preparation method of Example 2, 59.88% of sodium nitrate, 39.92% of potassium nitrate, and 0.20% of carbon nanotubes (d=10-20 nm) were placed in the crucible. The mixture was uniformly mixed to obtain a mixed powder; at the same time, the mixed powder was heated and melted in a muffle furnace at 340 ° C, and after being completely melted, the mixture was kept at a constant temperature for 150 minutes to obtain a molten mixture; the rest was obtained as described in Example 1. Solar thermal power generation heat transfer heat storage medium.

As described above, in the solar thermal power generation heat storage medium of the present embodiment, the difference from the solar thermal power generation heat storage medium in the first embodiment lies in the solar thermal power generation heat storage of the present embodiment. The heat medium is composed of 99.8% nitrate molten salt heat storage medium and 0.20% carbon nanotubes; wherein the nitrate molten salt heat storage medium is composed of 59.88% sodium nitrate and 39.92% potassium nitrate.

The melting point and decomposition temperature of the solar thermal power generation heat transfer heat storage medium in this example were measured in the same manner as in Example 1. The test results are shown in Table 1. Meanwhile, the transient planar heat source method was used at 300 ° C. The thermal conductivity of the solar thermal power generation heat storage medium of the present embodiment was measured, and the test results are shown in FIG.

Example 3

In the description of Embodiment 3, the same points as Embodiment 1 will not be described again, and only differences from Embodiment 1 will be described. This embodiment differs from Example 1 in that, in the preparation method of the present embodiment, 59.82% of sodium nitrate, 39.88% of potassium nitrate, and 0.30% of carbon nanotubes (d=10 to 20 nm) are placed in the crucible. The mixture was uniformly mixed to obtain a mixed powder; at the same time, the mixed powder was heated and melted in a muffle furnace at 340 ° C, and after being completely melted, the mixture was kept at a constant temperature for 150 minutes to obtain a molten mixture; the rest was obtained as described in Example 1. Solar thermal power generation heat transfer heat storage medium.

As described above, in the solar thermal power generation heat storage medium of the present embodiment, the difference from the solar thermal power generation heat storage medium in the first embodiment lies in the solar thermal power generation heat storage of the present embodiment. The heat medium is composed of 99.70% nitrate molten salt heat storage medium and 0.30% carbon nanotube composite; wherein the nitrate molten salt heat storage medium is composed of 59.82% sodium nitrate and 39.88% potassium nitrate.

The melting point and decomposition temperature of the solar thermal power generation heat transfer heat storage medium in this example were measured in the same manner as in Example 1. The test results are shown in Table 1. Meanwhile, the transient planar heat source method was used at 300 ° C. The thermal conductivity of the solar thermal power generation heat storage medium of the present embodiment was measured, and the test results are shown in FIG.

Example 4

In the description of the embodiment 4, the same points as those of the embodiment 1 will not be described again, and only the differences from the embodiment 1 will be described. This embodiment differs from Example 1 in that, in the preparation method of the present embodiment, 59.76% of sodium nitrate, 39.84% of potassium nitrate, and 0.40% of carbon nanotubes (d=10-20 nm) are placed in the crucible. The mixture was uniformly mixed to obtain a mixed powder; at the same time, the mixed powder was heated and melted in a muffle furnace at 300 ° C, and after being completely melted, the mixture was kept at a constant temperature for 180 minutes to obtain a molten mixture; the rest was obtained as described in Example 1. Solar thermal power generation heat transfer heat storage medium.

As described above, in the solar thermal power generation heat storage medium of the present embodiment, the difference from the solar thermal power generation heat storage medium in the first embodiment lies in the solar thermal power generation heat storage of the present embodiment. The heat medium is composed of 99.60% nitrate molten salt heat storage medium and 0.40% carbon nanotube composite; wherein the nitrate molten salt heat storage medium is composed of 59.76% sodium nitrate and 39.84% potassium nitrate.

The melting point and decomposition temperature of the solar thermal power generation heat transfer heat storage medium in this example were measured in the same manner as in Example 1. The test results are shown in Table 1. Meanwhile, the transient planar heat source method was used at 300 ° C. The thermal conductivity of the solar thermal power generation heat storage medium of the present embodiment was measured, and the test results are shown in FIG.

Example 5

In the description of the embodiment 5, the same points as those of the embodiment 1 will not be described again, and only the differences from the embodiment 1 will be described. This embodiment differs from Example 1 in that in the preparation method of the present embodiment, 59.70% of sodium nitrate, 39.80% of potassium nitrate, and 0.50% of carbon nanotubes (d=10-20 nm) are placed in the crucible. The mixture was uniformly mixed to obtain a mixed powder; at the same time, the mixed powder was heated and melted in a muffle furnace at 300 ° C, and after being completely melted, the mixture was kept at a constant temperature for 180 minutes to obtain a molten mixture; the rest was obtained as described in Example 1. Solar thermal power generation heat transfer heat storage medium.

As described above, in the solar thermal power generation heat storage medium of the present embodiment, the difference from the solar thermal power generation heat storage medium in the first embodiment lies in the solar thermal power generation heat storage of the present embodiment. The heat medium is composed of 99.50% nitrate molten salt heat storage medium and 0.50% carbon nanotubes; wherein the nitrate molten salt heat storage medium is composed of 59.70% sodium nitrate and 39.80% potassium nitrate.

The melting point and decomposition temperature of the solar thermal power generation heat transfer heat storage medium in this example were measured in the same manner as in Example 1. The test results are shown in Table 1. Meanwhile, the transient planar heat source method was used at 300 ° C. The thermal conductivity of the solar thermal power generation heat storage medium of the present embodiment was measured, and the test results are shown in FIG.

In order to verify the performance of the solar thermal power generation heat transfer heat storage medium of the above embodiment of the present invention, the following comparative experiment was conducted.

Comparative example 1

In this comparative example, the provided solar thermal power generation heat transfer heat storage medium includes only a nitrate molten salt heat storage medium composed of 60% sodium nitrate and 40% potassium nitrate, and no carbon nanotubes are present.

The melting point, decomposition temperature and thermal conductivity of the solar thermal power generation heat storage and heat storage medium in this comparative example were measured in the same manner as in Example 1. The test results are shown in Table 1. Meanwhile, the transient planar heat source method was used. The thermal conductivity of the solar thermal power generation heat storage medium of the present comparative example was measured at 300 ° C, and the test results are shown in FIG. 1 .

Table 1 Comparison of performance test results of Examples 1 to 5 and Comparative Example 1

Sample serial number	Melting point / °C	Decomposition temperature / °C
Comparative example	230.1	568.6
Example 1	226.3	586.2
Example 2	225.2	593.4
Example 3	224.8	586.2
Example 4	224.6	603.0
Example 5	223.3	595.2

It can be seen from Table 1 and FIG. 1 that the solar thermal power generation heat storage heat storage medium of the present invention maintains a relatively high level of melting point and decomposition temperature of the nitrate molten heat storage medium without carbon nanotubes added, but the thermal conductivity has At the same time, it can be seen from the thermal conductivity of Examples 1 to 5 that the change of thermal conductivity does not change linearly with the amount of carbon nanotubes added, and the analysis is a nitrate molten salt heat storage medium and carbon nanotubes. There is a boundary effect between them, and as the amount of carbon nanotubes increases, the thermal conductivity shows a trend of increasing first and then decreasing.

While the invention has been shown and described with respect to the specific embodiments the embodiments of the invention Various changes in details.

Claims (10)

1. A solar thermal power generation heat transfer heat storage medium, comprising: a nitrate molten salt heat storage medium; and a carbon nanotube composited in the nitrate molten salt heat storage medium; wherein, the solar thermal power generation In the heat storage medium, the mass percentage of the carbon nanotubes is 0.1% to 1%, and the diameter of the carbon nanotubes is d≥10 nm.
2. The solar thermal power generation heat transfer heat storage medium according to claim 1, wherein in the solar thermal power generation heat transfer heat storage medium, the mass percentage of the carbon nanotubes is 0.1% to 0.5%; And/or, the carbon nanotubes have a diameter of 10 nm ≤ d ≤ 20 nm.
3. The solar thermal power generation heat transfer heat storage medium according to claim 1, wherein the nitrate molten salt heat storage medium comprises uniformly mixed sodium nitrate and potassium nitrate.
4. The solar thermal power generation heat transfer heat storage medium according to claim 3, wherein in the solar thermal power generation heat transfer heat storage medium, the mass percentage of sodium nitrate is 59% to 60%, and potassium nitrate is used. The mass percentage is 39% to 40%.
5. A method for preparing a solar thermal power generation heat transfer heat storage medium, comprising the steps of:

   S1, the nitrate molten salt heat storage medium and the carbon nanotubes are ground and uniformly mixed to obtain a raw material powder, wherein, in the raw material powder, the mass percentage of the carbon nanotubes is 0.1% to 1%, The diameter of the carbon nanotubes is d≥10 nm;

   S2, heating and melting the raw material powder for at least 1 h to obtain a molten mixture;

   S3. The molten mixture is cooled to room temperature and pulverized to obtain a solar thermal power generation heat transfer heat storage medium.
6. The preparation method according to claim 5, wherein the carbon nanotubes have a diameter of 10 nm ≤ d ≤ 20 nm; and/or, in the raw material powder, the mass percentage of the carbon nanotubes is 0.1%. ~0.5%.
7. The preparation method according to claim 5, wherein the nitrate molten salt heat storage medium comprises uniformly mixed sodium nitrate and potassium nitrate.
8. The preparation method according to claim 7, wherein in the raw material powder, the mass percentage of sodium nitrate is 59% to 60%, and the mass percentage of potassium nitrate is 39% to 40%.
9. The preparation method according to any one of claims 5-8, characterized in that in the step S2, the holding time is from 1 h to 3 h.
10. The production method according to any one of claims 5 to 8, characterized in that in the step S2, the raw material powder is melted at 300 ° C to 400 ° C.

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