WO2018006820A1 - Low melting point heat transfer and heat storage molten salt, preparation method and use thereof - Google Patents

Abstract

Provided are a low melting point heat transfer and heat storage molten salt, a preparation method and a use thereof. The molten salt is prepared by the following steps: (1) four monomer molten salts Ca(NO₃)₂•4H₂O, KNO₃, NaNO₃ and LiNO₃ are placed in a corundum crucible, and mixed with stirring; (2) the mixed molten salts are placed in an oven, heated incrementally from 50ºC for 24 to 36 hours, and finally heated at 150ºC and stirred until the composite molten salt becomes a homogeneous solution system; (3) the composite molten salt is placed in a muffle furnace at 200ºC-250ºC, maintained at the temperature for 8 to 12 hours to remove the crystal water in Ca(NO₃)₂•4H₂O; and after the crystal water is evaporated, the temperature is raised to 350ºC, the moisture in the molten salt is completely removed, and after cooling, a solid homogeneous composite molten salt system is obtained. The low melting point molten salt obtained runs stably in a temperature range of 150-550 degrees Celsius, and the viscosity is not higher than 5.5 cp. The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the risk of pipeline blockage is reduced, the safety stability of the whole system is improved, and the lifetime is increased.

Description

Low melting point heat transfer and heat storage molten salt, preparation method and application thereof Technical field

The invention relates to a low melting point heat transfer and heat storage molten salt, in particular to a low melting point heat transfer and heat storage molten salt, a preparation method and application thereof.

Background technique

At present, in the field of industrial energy storage and solar high-temperature heat utilization, the nitrate molten salt system for heat transfer and heat storage medium mainly includes binary Solar Salt molten salt (60wt% NaNO ₃ + 40wt% KNO ₃ ) and ternary Hitec Molten salt system 7 wt% NaNO ₃ + 53 wt% KNO ₃ + 40 wt% NaNO ₂ . Among the two molten salt systems, the binary nitrate system is heat stable and low in cost, but its melting point is as high as 220 ° C, which requires high safety and stability of the system, and the working temperature range is narrow, and the unit is cold. The startup process is complicated, the heat consumption is large, and the system maintenance cost is high. The ternary nitrate system has a relatively low melting point of about 140 ° C, but the upper limit is also lower in temperature, has thermal stability below 450 ° C, can be operated at 538 ° C for a short period of time, has poor thermal stability, and is in use. An inert gas such as nitrogen is required to protect the system from oxidative deterioration.

In the prior art, attempts have been made to add other components to the nitrate molten salt system to solve the above problems, but the upper limit temperature of the improved molten salt system is increased, and the lower limit operating temperature is also increased, resulting in cloud cover insulation. Increased maintenance costs also exacerbate the safety and stability of the system. For example, Ding Jing et al. invented a quaternary molten salt, that is, LiNO ₃ -KNO ₃ -NaNO ₃ -NaNO ₂ was obtained by adding LiNO ₃ to the ternary molten salt system _{, and} the optimum temperature range was 250-550 ° C. . The upper working temperature of this system is improved compared with the ternary nitrate molten salt system, reaching 550 ° C, but the lower limit working temperature is also improved, and it is necessary to use an inert gas to protect the system from stability and prevent oxidative deterioration. Therefore, the quaternary system is used as a heat transfer and heat storage medium for solar thermal power generation, and improvement is still needed.

The present invention has been made accordingly.

Summary of the invention

In order to overcome the problems of high melting point, high maintenance cost, low specific heat capacity, low thermal conductivity and the like of the conventional molten salt, the present invention provides a new low melting point composite molten salt, and the technical scheme is as follows:

A low melting point heat transfer and heat storage molten salt characterized by: Ca(NO ₃ ) ₂ ·4H ₂ O, KNO ₃ , NaNO ₃ , LiNO ₃ as raw materials, comprising the following preparation steps:

(1) Put four kinds of raw materials Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ and LiNO ₃ into corundum crucible, and mix and stir;

(2) placing the mixed molten salt in an oven, heating at an increasing temperature from 50 ° C for 24-36 hours, and finally heating and stirring at 150 ° C until the composite molten salt becomes a uniform solution system;

(3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. °C, completely remove the water in the molten salt, after cooling, to obtain a solid homogeneous composite molten salt;

The weight percentages of the molten salts of Ca(NO ₃ ) ₂ , KNO ₃ , NaNO ₃ and LiNO _{3 in the prepared} molten salt are as follows:

10-16% calcium nitrate, 38-50% potassium nitrate, 23.5-35% sodium nitrate, 3-9% lithium nitrate;

Calcium nitrate 15-40%, potassium nitrate 35-60%, sodium nitrate 6-30%, lithium nitrate 3-18%;

15-40% calcium nitrate, 35-60% potassium nitrate, 6-30% sodium nitrate, 9% lithium nitrate; or

Calcium nitrate is 29-40%, potassium nitrate is 35-60%, sodium nitrate is 6-30%, and lithium nitrate is 3-18%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate is 29-40%, potassium nitrate is 35-60%, sodium nitrate is 6-30%, and lithium nitrate is 3-18%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate is 29-40%, potassium nitrate is 35-60%, sodium nitrate is 15-30%, and lithium nitrate is 3-18%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate is 29-40%, potassium nitrate is 40-52%, sodium nitrate is 6-12%, and lithium nitrate is 3-14%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate is 29-40%, potassium nitrate is 40-49.5%, sodium nitrate is 6-12%, and lithium nitrate is 3-14%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate 29-40%, potassium nitrate 38-50%, sodium nitrate 6-30%, lithium nitrate 3-9%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate 22-30%, potassium nitrate 38-55%, sodium nitrate 6-30%, lithium nitrate 3-9%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate 22-30%, potassium nitrate 38-49%, sodium nitrate 8-30%, lithium nitrate 3-9%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate 22-28%, potassium nitrate 38-50%, sodium nitrate 6-30%, lithium nitrate 3-9%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

17-20% calcium nitrate, 36-54% potassium nitrate, 15-30% sodium nitrate, and 1-14% lithium nitrate.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate 15-28%, potassium nitrate 35-55%, sodium nitrate 21-30%, lithium nitrate 3-9%.

Preferably, the weight percentages of the four monomer molten salts are as follows:

Calcium nitrate is 15-35%, potassium nitrate is 35-55.5%, sodium nitrate is 15-30%, and lithium nitrate is 14.5-18%.

Preferably, the weight percentages of the four monomer molten salts are as shown in any of the following formulations:

Preferably, any of the above molten salts may further comprise 0.5-2% by weight of CsNO ₃ and/or Sr(NO ₃ ) _{2 .}

In any of the above molten salts, preferably, the temperature is gradually heated from 50 ° C for 24-36 hours, which means heating and stirring at 50 ° C for 8-12 hours, heating at 80 ° C and stirring for 8-12 hours, heating at 120 ° C and Stir for 8-12 hours.

Preferably, the four monomer molten salt raw materials of Ca(NO ₃ ) ₂ ·4H ₂ O, KNO ₃ , NaNO ₃ and LiNO ₃ are monomer molten salts subjected to recrystallization purification treatment. The experimental data show that the molten salt of the present invention obtained by recombining the recrystallized and purified monomeric nitric acid molten salt has a markedly improved thermal stability as compared with the molten salt of the industrial pure grade monomeric nitrate molten salt.

Any of the low melting point heat transfer and heat storage molten salts described herein for use in solar thermal power generation, energy storage peaking, clean energy station systems, and other heat and heat storage fields.

The invention also provides a preparation process of any of the above low melting point heat transfer and heat storage molten salts:

(1) The four monomer molten salt raw materials Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ , and LiNO _{3 are} placed in a corundum crucible, and mixed and stirred;

(2) placing the mixed molten salt in an oven, heating at an increasing temperature from 50 ° C for 24-36 hours, and finally heating and stirring at 150 ° C until the composite molten salt becomes a uniform solution system;

(3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. At °C, the water in the molten salt is completely removed, and after cooling, a solid homogeneous composite molten salt is obtained.

The invention forms a eutectic composite molten salt through a plurality of monomer molten salts, reduces the melting point thereof, increases the specific heat capacity and thermal conductivity, and obtains a minimum by reducing the content of LiNO ₃ in the composite molten salt and introducing multiple components to reduce the cost. A low melting point heat transfer and heat storage composite molten salt which is inexpensive, has a low viscosity, and has a wide use temperature and excellent performance.

Specifically, by adjusting the respective specific gravity of the calcium nitrate, potassium nitrate, sodium nitrate and lithium nitrate and the preparation process, one is obtained. The series melting point is as low as 80 ° C, the decomposition temperature can be as high as 670 ° C, and the thermal conductivity can reach 0.57 W (m·K), and the specific heat capacity can reach 1.75 ~ 1.9 KJ / (kg · K). The molten salt has many advantages in preparation and use:

On the one hand, compared with the current high cost consumption of the construction and operation of the solar thermal power station, the molten salt provided by the invention is used, because the content of lithium nitrate is low, the raw material cost is relatively low; and the molten salt of the invention is increased from 50 degrees Celsius. The heating method is not only able to completely remove water molecules, but more importantly, the calcium nitrate does not substantially decompose during the preparation process, and does not produce calcium nitrite and oxygen, so that the nitrite ion content in the system is extremely low, almost no And the obtained low melting point quaternary nitric acid composite molten salt of the invention has better thermal stability, and is not easy to produce corrosive nitrite during use, therefore, it is not necessary to add nitrogen to prevent oxidative deterioration during preparation and use. It is less corrosive to the system; in addition, the low chloride ion content further ensures its low corrosivity to the system; the above characteristics make the molten salt of the invention, whether prepared or used, greatly reduce the operating cost.

In the second aspect, it has been found that the saturated vapor pressure of the molten salt of the present invention is low, not higher than 2 atm, so that the safety and reliability of the solar thermal power generation system is improved.

In the third aspect, it is found that the molten salt of the present invention operates stably in a temperature range of 150-550 degrees Celsius, and the viscosity is not more than 5.5 cp, and the viscosity is low, which can ensure good heat transfer efficiency, power generation efficiency, and reduced risk of pipeline blockage. The safety and stability of the entire system is improved and the life is increased.

Therefore, the present invention provides a low-cost clean energy medium with significantly improved comprehensive performance, which is particularly suitable as a heat transfer and heat storage medium in a clean energy boiler, and can also be used in the field of solar thermal power generation and other heat and heat storage.

DRAWINGS

Figure 1 is a mixed nitrate DTA curve of the number 15 of the present invention;

Figure 2 is a mixed nitrate TG curve of the number 15 of the present invention.

detailed description

raw material:

Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ , and LiNO _{3 are} industrial grades, which are available from general chemical companies.

Recrystallized and purified Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ , LiNO ₃ monomer salts: The preparation process is as follows:

Various industrial pure grade monomer salts slowly dissolve the single product salt solution at low temperature (50-100 degrees Celsius), adsorbed by adsorption resin, and then filtered through a filter press, and then the single product salt solution is cooled and recrystallized. The recrystallized single product salt is washed with pure water, and the washed single product salt is placed in an electric heating reaction kettle, and after adding pure water, heating is performed, and the electric heating is reversed. The single product salt solution in the kettle is placed in a cooler to cool the crystal, and the crystallized single product salt is dehydrated by a centrifuge, and then the dehydrated single product salt is washed with pure water, and the single product salt is again centrifuged by washing. The machine is dehydrated and then dried to obtain a high purity single product salt.

Example 1. The first group of composite molten salts

Step 1. Prepare the composite molten salt:

(1) the composition of Table 1-1 composite weighed molten _{KNO 3, NaNO 3, LiNO 3} , and in accordance with the Ca (NO _{3) 2} Weigh ratio required for _{Ca (NO 3) 2 · 4H} 2 O Put into a corundum crucible and mix and stir;

(2) The mixed molten salt is placed in an oven, heated and stirred at 50 ° C for 12 hours, heated at 80 ° C for 10 hours, heated at 120 ° C for 8 hours, heated at 150 ° C and stirred until the composite molten salt becomes a homogeneous solution. system;

(3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. °C, the water in the molten salt is completely removed, and after cooling, a solid homogeneous system composite molten salt is obtained.

Table 1-1 Composition of low temperature molten salt 1-5

Note: The %wt of calcium nitrate indicates the ratio of Ca(NO ₃ ) ₂ in the finally obtained low-temperature molten salt. The raw material of molten salt is Ca(NO ₃ ) ₂ ·4H ₂ O, according to the specific gravity of Ca(NO ₃ ) ₂ Calculate and weigh the amount of Ca(NO ₃ ) ₂ · 4H ₂ O. For example, in the molten salt No. 1, 11 g of Ca(NO ₃ ) ₂ is contained per 100 g of the low-temperature molten salt _, since Ca(NO ₃ ) _{2 is} in Ca ( The content of NO ₃ ) ₂ · 4H ₂ O is about 70%, so the amount of Ca(NO ₃ ) ₂ · 4H ₂ O is 11/0.7 = 15.7 g. Thus obtained as an example of the weight percentage of anhydrous calcium nitrate in the composite molten salt listed in 1.

Step 2. Measure the thermal conductivity

Method: The liquid thermal conductivity tester was used (tested under a nitrogen atmosphere), and each molten salt was tested in triplicate. The test results were averaged at 300 ° C. The test results are shown in Table 1-3:

Step 3. Measuring specific heat capacity

Method: Using a universal differential thermal scanner DSC (scanning under normal pressure), each molten salt was taken in three portions. Test, the test results are taken at 300 ° C and / or 400 ° C average, the test results are shown in Table 1-3:

Step 4. Determine the melting point

Method: Using a universal differential thermal scanner DSC (scanning under normal pressure), each molten salt was taken in three parts for testing, and the test results were averaged. The test results are shown in Table 1-3:

Step 5. Determine the decomposition temperature

Method: The general thermogravimetric analyzer TGA was used (scanning under normal pressure), and each molten salt was taken in three parts for testing. The test results were averaged. The test results are shown in Table 1-3:

Step 6 saturated vapor pressure

Test instrument: Using a saturated vapor pressure tester, each molten salt was taken in three parts for testing, and the test results were averaged. The test results are shown in Table 1-2.

Step 7. Measuring viscosity

Test instrument: using a rotary rheometer (passing protective gas), each molten salt is tested in triplicate, and the test results are taken at 300 ° C and / or 400 ° C average, the results are shown in Table 1-3

Table 1-2 Commonly used molten salt test results in the prior art

Table 1-3 Physical properties test results of low temperature molten salt 1-5

It can be seen from Table 1-3 and Table 1-2 that the melting point of the molten salt of this group of formulas is basically below about 100 degrees Celsius, and the decomposition temperature is higher than 580 degrees Celsius, which has an ideal temperature range of use, which can correspondingly increase The power generation efficiency of molten salt; specific heat capacity, thermal conductivity and viscosity are significantly better than those commonly used in the prior art.

In addition, the molten salt test before use, the results show that the low-temperature molten salt provided by the invention is substantially free of nitrite ions, indicating that the calcium nitrate does not substantially decompose during the preparation process, and the resulting low-temperature molten salt is most likely to be reduced. Corrosion of the system container.

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat transfer capacity is improved, the specific heat capacity and the use temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 1

The only difference from Example 1 is the use of four molten salt monomers after recrystallization purification. The test result data is similar to Table 1-3. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 2. The second group of composite molten salts

Step 1. Prepare the composite molten salt:

(1) The composite molten salt composition according to Table 2-1 purpose weighed _{KNO 3, NaNO 3, LiNO 3} , and in accordance with said ratio Ca (NO _{3) 2} taken desired _{Ca (NO 3) 2 · 4H} 2 O is placed in corundum crucible and mixed;

(2) The mixed molten salt is placed in an oven, heated and stirred at 50 ° C for 12 hours, heated at 80 ° C for 12 hours, heated at 120 ° C for 12 hours, heated at 150 ° C and stirred until the composite molten salt becomes a homogeneous solution. system;

(3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. °C, the water in the molten salt is completely removed, and after cooling, a solid homogeneous system composite molten salt is obtained.

Table 2-1 Formulation of low temperature molten salt 6-10

Note: The %wt of calcium nitrate indicates the ratio of Ca(NO ₃ ) ₂ in the finally obtained low-temperature molten salt. The raw material of molten salt is Ca(NO ₃ ) ₂ ·4H ₂ O, according to the specific gravity of Ca(NO ₃ ) ₂ Calculate and weigh the amount of Ca(NO ₃ ) ₂ · 4H ₂ O. For example, in the molten salt No. 1, 11 g of Ca(NO ₃ ) ₂ is contained per 100 g of the low-temperature molten salt _, since Ca(NO ₃ ) _{2 is} in Ca ( The content of NO ₃ ) ₂ · 4H ₂ O is about 70%, so the amount of Ca(NO ₃ ) ₂ · 4H ₂ O is 11/0.7 = 15.7 g.

Step 2-7. Same as Example 1, the test results are shown in 2-2.

Table 2-2 Physical property test results of low temperature molten salt 6-10

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system. Overall performance is significantly higher than existing

Parallel embodiment of embodiment 2:

The only difference from Example 2 is that the four molten salt monomers after recrystallization purification are used. The test result data is similar to that shown in Table 2-2. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 3 The third group of composite molten salt

Step 1. Prepare the composite molten salt:

(1) the composition of Table 3-1 composite weighed molten _{KNO 3, NaNO 3, LiNO 3} , and in accordance with the Ca (NO _{3) 2} Weigh ratio required for _{Ca (NO 3) 2 · 4H} 2 O Put into a corundum crucible and mix and stir;

(2) The mixed molten salt is placed in an oven, heated and stirred at 50 ° C for 10 hours, heated at 80 ° C for 8 hours, heated at 120 ° C for 12 hours, heated at 150 ° C and stirred until the composite molten salt becomes a homogeneous solution. system;

(3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. °C, the water in the molten salt is completely removed, and after cooling, a solid homogeneous system composite molten salt is obtained.

Table 3-1 Formulation of low temperature molten salt 11-15

Step 2-7. Same as Example 1, the test results are shown in 2-2.

Table 3-2 Physical property test results of low temperature molten salt 11-15

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 3:

The only difference from Example 3 is the use of four molten salt monomers after recrystallization purification. The test result data is similar to that shown in Table 3-2. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 4 fourth group of composite molten salt

Step 1. Prepare the composite molten salt:

(1) a composite molten salt composition according to Table 4-1 weighed _{KNO 3, NaNO 3, LiNO 3} , and in accordance with the Ca (NO _{3) 2} Weigh ratio required for _{Ca (NO 3) 2 · 4H} 2 O Put into a corundum crucible and mix and stir;

(2) The mixed molten salt is placed in an oven, heated and stirred at 50 ° C for 12 hours, heated at 80 ° C for 10 hours, heated at 120 ° C for 8 hours, heated at 150 ° C and stirred until the composite molten salt becomes a homogeneous solution. system;

(3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. °C, the water in the molten salt is completely removed, and after cooling, a solid homogeneous system composite molten salt is obtained.

Table 4-1 Formulation of low temperature molten salt 16-20

Step 2-7. Same as Embodiment 1, the test result is shown in 4-2.

Table 4-2 Physical property test results of low temperature molten salt 16-20

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 4:

The only difference from Example 4 is the use of four molten salt monomers after recrystallization purification. The test result data is similar to that shown in Table 4-2. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 5. The fifth group of composite molten salts

Step 1. The molten salt was prepared in the same manner as in Example 1.

Table 5-1 Formulation of low temperature molten salt 21-26

Step 2-7. Same as Embodiment 1, the test result is shown in 5-2.

Table 5-2 Physical property test results of low temperature molten salt 21-26

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 5:

The only difference from Example 5 is that the four molten salt monomers after recrystallization purification are used. The test result data is similar to that shown in Table 2-2. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 6. The sixth group of composite molten salts

Step 1. The molten salt was prepared in the same manner as in Example 1.

Table 6-1 Formulation of low temperature molten salt 27-31

Step 2-7. Same as Embodiment 1, the test result is shown in 6-2.

Table 6-2 Physical property test results of low temperature molten salt 27-31

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 6:

The only difference from Example 6 is that the four molten salt monomers after recrystallization purification are used. The test result data is similar to that shown in Table 6-2. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 7. The seventh group of composite molten salts

Step 1. The molten salt was prepared in the same manner as in Example 1.

Table 7-1 Formulation of low temperature molten salt 32-36

Step 2-7. Same as Embodiment 1, the test result is shown in 7-2.

Table 7-2 Physical property test results of low temperature molten salt 32-36

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 7:

The only difference from Example 7 is that the four molten salt monomers after recrystallization purification are used. The test result data is similar to that shown in Table 7-2. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 8. The eighth group of composite molten salts

Step 1. The molten salt was prepared in the same manner as in Example 1.

Table 8-1 Formulation of low temperature molten salt 37-41

Step 2-7. Same as Embodiment 1, the test result is shown in 8-2.

Table 8-2 Physical property test results of low temperature molten salt 32-31

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 8:

The only difference from Example 8 is the use of four molten salt monomers after recrystallization purification. The test result data is similar to that shown in Table 8-2. However, the upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Example 9 ninth group of composite molten salt

Step 1. The molten salt was prepared in the same manner as in Example 1.

Table 9-1 Formulation of low temperature molten salt 42-49

Step 2-7. Same as Example 1, the test results are shown in 9-2 and 9-3.

Table 9-2 Physical property test results of low temperature molten salt 42-46

Physical properties test results of 9-3 low temperature molten salt 47-49

The saturated vapor pressure measurement results are on average 1.5-1.8 atmospheres, which is less safe and reliable for the pipeline pressure of the system.

The viscosity is low, the heat transfer efficiency is high, the power generation efficiency is high, the pipeline blockage is reduced, the safety and stability of the entire system is improved, and the life is increased.

The thermal conductivity is higher than that of the conventional molten salt, the heat storage capacity is improved, the specific heat capacity and the operating temperature range are better than the conventional molten salt, the heat storage capacity is increased compared with the conventional molten salt, the same amount of the heat storage molten salt, and the heat storage amount of the molten salt of the present invention is used. Significantly higher than conventional Hitec molten salt, which reduces the cost of building a heat storage system.

Parallel embodiment of embodiment 9:

The only difference from Example 9 is the use of four molten salt monomers after recrystallization purification. The test result data is similar to those shown in Tables 9-2 and 9-3. The upper limit use temperature is increased by an average of about 3-5 degrees Celsius.

Claims (18)

1. The invention discloses a low-melting-point heat transfer and heat storage molten salt, which is prepared by using Ca(NO ₃ ) ₂ ·4H ₂ O, KNO ₃ , NaNO ₃ and LiNO ₃ as raw materials, and is prepared by the following preparation steps:

   (1) Put four kinds of raw materials Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ and LiNO ₃ into corundum crucible, and mix and stir;

   (2) placing the mixed molten salt in an oven, heating at an increasing temperature from 50 ° C for 24-36 hours, and finally heating and stirring at 150 ° C until the composite molten salt becomes a uniform solution system;

   (3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. °C, completely remove the water in the molten salt, after cooling, to obtain a solid homogeneous composite molten salt;

   The weight percentages of the molten salts of Ca(NO ₃ ) ₂ , KNO ₃ , NaNO ₃ and LiNO _{3 in the prepared} molten salt are as follows:

   10-16% calcium nitrate, 38-50% potassium nitrate, 23.5-35% sodium nitrate, 3-9% lithium nitrate;

   Calcium nitrate 15-40%, potassium nitrate 35-60%, sodium nitrate 6-30%, lithium nitrate 3-18%;

   15-40% calcium nitrate, 35-60% potassium nitrate, 6-30% sodium nitrate, 9% lithium nitrate; or

   Calcium nitrate is 29-40%, potassium nitrate is 35-60%, sodium nitrate is 6-30%, and lithium nitrate is 3-18%.
2. The low melting point heat transfer and heat storage molten salt according to claim 1, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate is 29-40%, potassium nitrate is 35-60%, sodium nitrate is 6-30%, and lithium nitrate is 3-18%.
3. The low melting point heat transfer and heat storage molten salt according to claim 2, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate is 29-40%, potassium nitrate is 35-60%, sodium nitrate is 15-30%, and lithium nitrate is 3-18%.
4. The low melting point heat transfer and heat storage molten salt according to claim 2, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate is 29-40%, potassium nitrate is 40-52%, sodium nitrate is 6-12%, and lithium nitrate is 3-14%.
5. The low melting point heat transfer and heat storage molten salt according to claim 2, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate is 29-40%, potassium nitrate is 40-49.5%, sodium nitrate is 6-12%, and lithium nitrate is 3-14%.
6. The low melting point heat transfer and heat storage molten salt according to claim 2, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate 29-40%, potassium nitrate 38-50%, sodium nitrate 6-30%, lithium nitrate 3-9%.
7. The low melting point heat transfer and heat storage molten salt according to claim 1, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate 22-30%, potassium nitrate 38-55%, sodium nitrate 6-30%, lithium nitrate 3-9%.
8. The low melting point heat transfer and heat storage molten salt according to claim 7, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate 22-30%, potassium nitrate 38-49%, sodium nitrate 8-30%, lithium nitrate 3-9%.
9. The low melting point heat transfer and heat storage molten salt according to claim 7, wherein the weight percentage of the four monomer molten salts is as follows:

   Calcium nitrate 22-28%, potassium nitrate 38-50%, sodium nitrate 6-30%, lithium nitrate 3-9%.
10. The low melting point heat transfer and heat storage molten salt according to claim 1, wherein the weight percentage of the four monomer molten salts is as follows:

    17-20% calcium nitrate, 36-54% potassium nitrate, 15-30% sodium nitrate, and 1-14% lithium nitrate.
11. The low melting point heat transfer and heat storage molten salt according to claim 1, wherein the weight percentage of the four monomer molten salts is as follows:

    Calcium nitrate 15-28%, potassium nitrate 35-55%, sodium nitrate 21-30%, lithium nitrate 3-9%.
12. The low melting point heat transfer and heat storage molten salt according to claim 1, wherein the weight percentage of the four monomer molten salts is as follows:

    Calcium nitrate is 15-35%, potassium nitrate is 35-55.5%, sodium nitrate is 15-30%, and lithium nitrate is 14.5-18%.
13. The low melting point heat transfer and heat storage molten salt according to claim 1, wherein the weight percentage of the four monomer molten salts is as follows:

    
14. The low melting point heat transfer and heat storage molten salt according to any one of claims 1 to 13, which may further comprise 0.5 to 2% by weight of CsNO ₃ and/or Sr(NO ₃ ) ₂ .
15. The low melting point heat transfer and heat storage molten salt according to any one of claims 1 to 14, wherein the stepwise heating from 50 ° C for 24-36 hours means heating at 50 ° C and stirring for 8-12 hours, heating at 80 ° C and Stir for 8-12 hours, heat and stir at 120 °C 8-12 hours.
16. The low melting point heat transfer and heat storage molten salt according to any one of claims 1 to 15, wherein the molten salts of the four monomers of Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ and LiNO ₃ are heavy A monomer molten salt obtained by crystallization purification treatment.
17. The use of the low melting point heat transfer and heat storage molten salt according to any one of claims 1 to 16 for solar thermal power generation, energy storage peaking, clean energy station systems, and other heat and heat storage fields.
18. The process for preparing a low melting point heat transfer and heat storage molten salt according to any one of claims 1-16:

    (1) The four monomer molten salt raw materials Ca(NO ₃ ) ₂ · 4H ₂ O, KNO ₃ , NaNO ₃ , and LiNO _{3 are} placed in a corundum crucible, and mixed and stirred;

    (2) placing the mixed molten salt in an oven, heating at an increasing temperature from 50 ° C for 24-36 hours, and finally heating and stirring at 150 ° C until the composite molten salt becomes a uniform solution system;

    (3) The composite molten salt is placed in a muffle furnace at 200-250 ° C for 8-12 hours to remove the crystal water in Ca(NO ₃ ) ₂ · 4H ₂ O; after the water of crystallization is evaporated, the temperature is further increased to 350. At °C, the water in the molten salt is completely removed, and after cooling, a solid homogeneous composite molten salt is obtained.

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