JPWO2016199454A1 - Molten salt heat medium, method of using molten salt heat medium, and solar heat utilization system - Google Patents

Abstract

It is an object of the present invention to provide a molten salt heat medium having a high heat-resistant temperature and a wide usable temperature range, a method for using the molten salt heat medium, and a solar heat utilization system using the molten salt heat medium. The molten salt type heat medium contains 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent lithium carbonate. Contains carbonate mixture. The method of using the molten salt type heat medium includes heating the molten salt type heat medium described above, supplying the molten salt type heat medium to the heat using part through a pipe line in fluid communication with the heating part, and Using the heat provided by the molten salt type heat medium in the heat use section.

Description

  The present invention relates to a molten salt heat medium, a method of using the molten salt heat medium, and a solar heat utilization system.

  In recent years, the use of solar thermal energy has attracted worldwide attention as a renewable energy that can be used permanently. Solar thermal power generation systems and the like are known as devices using solar thermal energy, and molten salt heat media that can be used at high temperatures are widely used. Among these, a nitrate mixture in which potassium nitrate and sodium nitrate are mixed is known as a molten salt type heat medium having high heat resistance.

  On the other hand, it is said that the solar thermal power generation system can generate heat of about 1000 ° C. by sunlight, and by increasing the steam temperature accordingly, the power generation efficiency of the solar thermal power generation system can be increased. It has been demanded. A hydrogen production system using solar heat is also known, but a high-temperature process exceeding about 800 ° C. is required for the hydrothermal decomposition reaction, and a method of directly heating the reaction tank with solar heat or the like is used. . However, in the method of directly heating the reaction vessel, it is difficult to control the reaction temperature, and in order to control the reaction temperature more easily and stably, it is required to heat with a heat-resistant heat medium.

  However, even with a molten salt type heat medium in which potassium nitrate and sodium nitrate are mixed, the heat resistance temperature is about 560 ° C., and thus the above-mentioned requirement cannot be met. That is, in the solar thermal power generation system, power generation efficiency cannot be increased due to the low heat-resistant temperature of the heat medium that mediates solar heat. Similarly, even in a hydrogen production apparatus that requires a high-temperature process, since there is no heat medium that can be used, the reaction temperature cannot be easily and stably controlled. Furthermore, since the molten salt type heat medium in which potassium nitrate and sodium nitrate are mixed has a melting point of 220 ° C. and a heat-resistant temperature of about 560 ° C., the practically usable temperature range is as narrow as 220 ° C. to 560 ° C. In order to reduce the amount of heat medium used, the appearance of a heat medium having a wide usable temperature range has been desired.

  Therefore, the inventor has reported use as a heat storage material for solar power generation described in Patent Document 1 and use as an electrolyte for fuel cells described in Patent Document 2, but use as a heat medium is not possible. As a result of diligent research focusing on unreported carbonates, the present invention has been achieved.

International Publication No. 2012/130285 Japanese Patent Publication No. 7-54710

  Accordingly, an object of the present invention is to provide a molten salt type heat medium having a high heat-resistant temperature and a wide practical temperature range, a method for using the molten salt type heat medium, and the molten salt type heat medium. To provide a solar heat utilization system.

(1) The molten salt type heat medium according to an embodiment of the present invention includes 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent. And a carbonate mixture containing no more than a percent lithium carbonate.
(2) The method of using the molten salt type heat medium according to another embodiment of the present invention includes 12 mol percent or more and 40 mol percent or less of potassium carbonate, 20 mol percent or more and 40 mol percent or less of sodium carbonate, and 25 mol percent. The molten salt type heat medium containing a carbonate mixture containing 55 mol% or less of lithium carbonate is heated in the heating unit, and the molten salt type heat medium is supplied by a pipe line in fluid communication with the heating unit. Feeding to the heat using part, and using the heat provided by the molten salt type heat medium in the heat using part.
(3) A solar thermal utilization system according to another embodiment of the present invention includes 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent. A molten salt-type heat medium containing a carbonate mixture containing lithium carbonate, a solar heating section for heating the molten salt-type heat medium with sunlight, and heat provided by the molten salt-type heat medium. A heat use part to be used; and a pipe that is in fluid communication with the solar heating part and the heat use part to feed the heated molten salt type heat medium to the heat use part. Features.

  The molten salt type heat medium of the present invention has high heat resistance and can widen the usable temperature range. For this reason, the molten salt type heat medium of the present invention can be applied, for example, to a process requiring high temperature such as hydrogen production by increasing the power generation efficiency of the solar thermal power generation system. Moreover, the usage method and solar heat utilization system of the molten salt type heat medium of the present invention can downsize equipment and reduce costs by using this molten salt type heat medium.

1 is an overall schematic diagram of a solar heat utilization system using a molten salt type heat medium according to an embodiment of the present invention. It is the elements on larger scale which expanded the condensing element of the solar thermal utilization system of FIG. It is the graph which plotted the weight decreasing rate of the molten salt type heat medium of an Example with respect to heating temperature, (a) is Example 1, (b) is Example 4, (c) is Example 7, (d ) Shows the weight reduction rate of the molten salt type heat medium of Example 10. It is the graph which plotted the weight decreasing rate of the molten salt type heat medium of the comparative example with respect to heating temperature. It is the graph which plotted the weight decreasing rate of the molten salt type heat medium of Example 10 with respect to heating temperature, (a) is a carbon dioxide atmosphere, (b) is a nitrogen atmosphere, (c) is an air atmosphere. The measured weight loss rate of the molten salt type heat medium is shown. It is the graph which plotted the weight decreasing rate of the molten salt type heat carrier which concerns on Example 11 which is one Example of this invention with respect to heating temperature. It is the graph which plotted the weight decreasing rate of the molten salt type heat medium which concerns on Example 8 which is one Example of this invention with respect to heating temperature. It is the graph which plotted the weight decreasing rate of the molten salt type heat carrier which concerns on Example 5 which is one Example of this invention with respect to heating temperature. It is the graph which plotted the weight decreasing rate of the molten salt type heat carrier which concerns on Example 2 which is one Example of this invention with respect to heating temperature.

  With reference to FIGS. 1 to 2, a molten salt heat medium 10, a method of using the molten salt heat medium 10, and a solar heat utilization system 1 using the molten salt heat medium 10 according to the embodiment of the present invention are described. explain. FIG. 1 is an overall schematic diagram of a solar heat utilization system 1 using a molten salt type heat medium 10, and FIG. 2 is a partially enlarged view in which the condensing element 110 of the solar heat utilization system 1 in FIG. 1 is enlarged. In addition, in this specification, each component ratio of the component of the molten salt type heat medium 10 is shown by mole percentage. That is, each component ratio of the molten salt type heat medium 10 represents the number of moles of each component with respect to the total number of moles of all the components of the molten salt type heat medium 10 as a percentage. The number of moles of each component) × 100 / (total number of moles of all components of the molten salt type heat medium 10) [mole percent]. Also, in this specification, fluid communication means that the same fluid is connected so that it can flow, and includes both cases of direct connection and indirect connection. . Moreover, although this specification demonstrates using the solar-heat utilization system 1, the molten salt type heat medium 10 can be utilized for various uses which need to take out heat from a heat source not only in it, for example, thermal power It can also be used for power generation systems.

[Molten salt type heat medium]
With reference to FIG. 1 and FIG. 2, the molten salt type heat medium 10 which concerns on embodiment of this invention is demonstrated. The molten salt type heat medium 10 according to the embodiment of the present invention heats or cools an object in a heat use unit 300 including a power generation device such as thermal power generation and solar thermal power generation, a reaction device that produces hydrogen by hydrothermal decomposition reaction, and the like. In order to achieve the target temperature, it is used to transfer heat between the heating unit 100 and the heat using unit 300 of the molten salt heat medium 10. For example, in a power generation device, a gas generation product for rotating a gas turbine such as steam or combustion gas is an object, and in a reaction device for producing hydrogen, a reaction object such as water vapor or a metal oxide is an object. It becomes a thing.

The molten salt type heat medium 10 includes at least 12 mole percent to 40 mole percent potassium carbonate (K ₂ CO ₃ ), 20 mole percent to 40 mole percent sodium carbonate (Na ₂ CO ₃ ), and 25 moles. And a carbonate mixture containing lithium carbonate (Li ₂ CO ₃ ) in a range of not less than 55 percent and not more than 55 mole percent. That is, the molten salt heat medium 10 contains the above-described three components at a relatively high ratio. According to this, since the heat resistance of the molten salt heat medium 10 can be increased, the molten salt heat medium 10 is heated between the heating unit 100 and the heat using unit 300 of the molten salt heat medium 10. Exchange efficiency can be improved. Further, the molten salt type heat medium 10 enables the use of a heat medium in a high temperature process that could not be conventionally used, facilitates and stabilizes the temperature control of the high temperature process in the heat using part 300. Can do. In addition, the molten salt type heat medium 10 may be comprised only from the carbonate mixture from a viewpoint of controlling a physical property favorably.

As described above, since the molten salt type heat medium 10 has heat resistance, that is, the heat resistance temperature Th is high and the melting point Tm is low, the normal use temperature range ΔT that is the temperature difference between the heat resistance temperature Th and the melting point Tm is It is wide. Therefore, according to the molten salt heat medium 10, it is possible to reduce the size of the equipment and reduce the amount of heat medium used. In addition, since the molten salt type heat medium 10 has a relatively low viscosity, the molten salt type heat medium 10 can flow smoothly in the pipe 410 and does not contain or contain a metal halide based molten salt such as a metal chloride. Since the amount is small, it can be said that it has excellent physical properties as a heat medium in that corrosion of equipment can be suppressed.
As will be described in detail later, the “heat-resistant temperature” in the present invention means that when the molten salt heat medium is heated to 500 ° C. or higher, the first nonlinear weight loss of the molten salt heat medium is reduced. It shall refer to the starting temperature. Therefore, the “heat-resistant temperature” is usually lower than the practical use temperature range as the molten salt type heat medium. That is, the molten salt heat medium of the present invention has a sufficiently high “heat-resistant temperature”, but the “practical heat-resistant temperature” may be higher than the “heat-resistant temperature”. Furthermore, the “normal use temperature” refers to a temperature range in which there is no fear of thermal decomposition from the melting point of the molten salt type heat medium.

Further, the molten salt type heat medium 10 further includes 1.0 to 20 mole percent of barium carbonate (BaCO ₃ ), and 1.0 to 15 mole percent of calcium carbonate (CaCO ₃ ), A carbonate mixture further containing at least one of the above may be included. By containing at least one of barium carbonate and calcium carbonate in the above range with respect to the three components described above, the melting point Tm of the molten salt heat medium 10 can be greatly reduced, and the normal use temperature range ΔT is expanded. It is something that can be done.

  In particular, the molten salt heating medium 10 further contains a carbonate mixture containing both 1.0 mole percent and 20 mole percent of barium carbonate and 1.0 mole percent and 15 mole percent of calcium carbonate. May be. The molten salt type heat medium 10 including at least five components obtained by adding barium carbonate and calcium carbonate to the three components described above has a melting point Tm of 15 ° C. or higher as compared with the molten salt type heat medium 10 including only the above three components. This is because the normal operating temperature range ΔT can be expanded to about 400 ° C.

And it cannot be overemphasized that molten salt type heat carrier 10 may contain other ingredients other than potassium carbonate, sodium carbonate, lithium carbonate, barium carbonate, and calcium carbonate. Other components of the molten salt type heat medium 10 include carbonates of alkali metals or alkaline earth metals other than the above, such as strontium carbonate (SrCO ₃ ), cesium carbonate (Cs ₂ CO ₃ ), and magnesium carbonate (MgCO ₃ ). Examples include alkali metal or alkaline earth metal nitrates, sulfates, acetates and phosphates, alkali metal or alkaline earth metal halides, and other molten salts.

  As described above, when the molten salt type heat medium 10 contains other components, it is desirable to select other components from the viewpoint of lowering the melting point and viscosity of the molten salt type heat medium 10. Further, in this case, the other components of the molten salt heat transfer medium 10 are greater than 0 mole percent and less than or equal to 20 mole percent, preferably greater than 0 mole percent and less than or equal to 10 mole percent, more preferably greater than 0 mole percent and 5 mole percent. It is contained in the molten salt type heat medium 10 at a mole percent or less.

  When the metal halide is contained as the other component, the content of the metal halide contained in the molten salt type heat medium 10 is changed from that of the molten salt type heat medium 10 due to the necessity of preventing the corrosion of the equipment. Of the total amount of 100 mole percent, it is preferably 0.1 mole percent or less, more preferably 0.05 mole percent or less, and still more preferably not blended at all.

Further, in the molten salt type heat medium 10, each carbonate contained in the molten salt type heat medium 10 may exist separately, but a plurality of types of carbonates are combined to form, for example, sodium potassium carbonate. It may exist as a carbonate containing a plurality of metal ions such as sodium and potassium such as (NaKCO ₃ ).

  Since it is as above-mentioned, the molten salt type heat medium which concerns on embodiment of this invention can raise the electric power generation efficiency of a solar thermal power generation system, and can be applied also for the heating of the reactor which requires high temperature processes, such as hydrogen production. .

[Solar heat utilization system]
Next, with reference to FIG. 1 and FIG. 2, the solar-heat utilization system 1 which concerns on embodiment of this invention is demonstrated. The solar heat utilization system 1 uses a molten salt type heat medium 10, and includes a molten salt type heat medium 10, a solar heating unit 100 that heats the molten salt type heat medium 10 with sunlight, and a molten salt type heat medium. In order to supply the heat using part 300 using the heat provided by the medium 10 and the heated molten salt type heat medium 10 to the heat using part 300, the solar heating part 100 and the heat using part 300 are in fluid communication. A pipe line 410 to be provided.

  The solar heating unit 100 includes a light collecting element 110, and the light collecting element 110 may include a light collecting tube 112 and a light collecting mirror 114 through which the molten salt heat medium 10 passes. As shown in the figure, the light collecting element 110 may be a trough-type light collecting device in which a plurality of curved reflecting mirrors are arranged along a plurality of light collecting tubes 112 arranged in parallel. It may be a Fresnel type, a dish type, or other known light collecting device. Needless to say, the condensing element 110 may include components (not shown) such as a heliostat as necessary.

  The solar heat utilization system 1 may further include at least one of the heat medium containers 210, 220, and 230 that are in fluid communication with the pipe line 410. That is, the heat medium containers 210, 220, and 230 are containers that temporarily store the molten salt type heat medium 10 temporarily. For example, the heat medium containers 210, 220, and 230 are provided with the high temperature heat medium container 210 that can store the high temperature molten salt type heat medium 10 heated by the solar heating unit 100 and the heat using unit 300 after supplying heat. They are a low-temperature heat medium container 220 that can store a low-temperature molten salt heat medium 10 and an expansion tank 230 for the molten salt heat medium 10.

  The heat medium containers 210, 220, and 230 may be configured to seal the molten salt type heat medium 10 with carbon dioxide by being filled with the molten salt type heat medium 10 and carbon dioxide. According to this, the heat resistance of the molten salt heat medium 10 can be further improved, and the practical heat resistant temperature can be increased to about 1000 ° C. In addition, the liquid containing the molten salt type heat medium 10 can be put in the heat medium containers 210, 220, and 230, and the empty area can be filled with only carbon dioxide.

The heat use unit 300 is not particularly limited as long as it uses solar heat, and may include a heat use element 310 such as a power generation device including a gas turbine and a reaction device that produces hydrogen by a hydrothermal decomposition reaction. Examples of the gas turbine include a steam turbine and a combustion gas turbine. For example, as the hydrothermal decomposition reaction, a two-stage hydrothermal decomposition reaction using a metal oxide such as iron oxide or cerium oxide is exemplified. The two-stage hydrothermal decomposition reaction includes an oxygen generation reaction in which oxygen is released from the metal oxide at a high temperature of 800 ° C. or higher in a low oxygen partial pressure gas atmosphere such as nitrogen, and the metal oxide after releasing oxygen is heated to 800 ° C. This is performed by alternately repeating two reactions of hydrogen generation reaction in which water vapor (H ₂ O) is brought into contact with each other at a low temperature to generate hydrogen.

  The heat use unit 300 may further include a cooling element 320 that cools a heat medium different from the molten salt heat medium 10, which will be described later, after the heat use element 310. In addition, in the heat use part 300, the molten salt type heat medium 10 supplied from the pipe line 410 may be directly circulated. The heat use part 300 further includes a heat exchanger 330, and in the heat use part 300, Alternatively, another heat medium different from the molten salt type heat medium 10 that has exchanged heat with the molten salt type heat medium 10 may be circulated.

  The pipe line 410 is in fluid communication with the piping of the solar heating unit 100 such as the condenser tube 112 and the piping of the heat using unit 300, for example, so Circulate between. For this reason, the pipe line 410 may be provided with one or more pumps 420 and one or more valves 461 and 462.

  Moreover, since solar heat utilization efficiency fluctuates according to the amount of solar radiation, in order to stabilize the solar heat utilization efficiency of the solar heat utilization system 1, the solar heat utilization system 1 may further include a heat storage unit (not shown). That is, the solar heat utilization system 1 may store solar heat in the heat storage unit during daytime or when the weather is good, and take out solar heat from the heat storage unit and use it at night or when the weather is bad.

  Since it is as above-mentioned, the solar-heat utilization system which concerns on embodiment of this invention can make a solar-heat utilization system more efficient by using the molten salt type heat medium 10 with high heat resistance. For example, the solar heat utilization system can be improved in efficiency because power generation efficiency can be increased and a heat medium can be used for a process requiring high temperature such as hydrogen production. Further, the use of the molten salt type heat medium 10 is suitable for downsizing the equipment and reducing the operation cost because the normal use temperature range ΔT is wide.

[How to use molten salt type heat medium]
Next, with reference to FIG. 1 and FIG. 2, the usage method of the molten salt type heat medium 10 which concerns on embodiment of this invention is demonstrated. The molten salt type heat medium 10 is used by heating the molten salt type heat medium 10 with sunlight in the solar heating unit 100 and by using a pipe 410 in fluid communication with the solar heating unit 100. Supplying the medium 10 to the heat using unit 300 and using the heat provided by the molten salt type heat medium 10 in the heat using unit 300.

  Specifically, in the heating step of the molten salt heat medium 10, the sunlight collected by the condensing element 110 is converted into heat in the solar light heating unit 100, and the molten salt heat medium 10 is heated. For example, when passing through the condenser tube 112 of the solar heat utilization system 1, heating is performed by sunlight collected by the condenser mirror 114 on the condenser tube 112. And the molten salt type heat medium 10 transfers solar heat from the solar heating part 100 to the heat using part 300, and uses the solar heat in the heat using part 300 to perform hydrogen generation by power generation or hydrothermal decomposition reaction. .

  The method of using the molten salt heat medium 10 may further include a storage step of the molten salt heat medium 10. In the storage step of the molten salt type heat medium 10, the molten salt type heat medium 10 is supplied to the heat medium containers 210, 220, 230, and the molten salt type heat medium 10 is stored in the heat medium containers 210, 220, 230. It is. In this case, a carbon dioxide filling step of filling the heat medium containers 210, 220, and 230 with carbon dioxide may be included before or after the storage step of the molten salt heat medium 10. According to this, since the inside of the heat medium container 210, 220, 230 can be a carbon dioxide atmosphere, the reduction of the heated molten salt type heat medium 10 can be suppressed in the heat medium container 210, 220, 230. . Thus, the heat resistance of the molten salt heat medium 10 can be further improved.

  The method for using the molten salt type heat medium 10 further includes a step of supplying the molten salt type heat medium 10 to the solar heating unit 100, and the molten salt type heat medium 10 is circulated in the solar heat utilization system 1 for use. It is preferable. In this case, maintenance such as replacement of the molten salt heat medium 10 is required as the molten salt heat medium 10 deteriorates. Although the usage method of the molten salt type heat medium 10 which concerns on embodiment of this invention demonstrated using the solar-heat utilization system 1, it is not limited to this, You may use in a thermal power generation system etc. In this case, the solar heating unit 100 is replaced with a heating unit 100a including a heating medium heater such as a heating medium boiler (not shown).

  Next, the molten salt type heat medium according to Examples 1 to 23 that further embodies the molten salt type heat medium 10 according to the present embodiment will be described. First, a method for preparing a molten salt heat medium and a method for measuring physical properties according to Examples and Comparative Examples will be described in detail.

<Method for preparing molten salt type heat medium>
(Examples 1, 2, and 3)
A method for preparing a molten salt heat medium according to Examples 1, 2, and 3 will be described. The molten salt type heat medium according to Example 1 is a carbonic acid obtained by mixing potassium carbonate, lithium carbonate, sodium carbonate, barium carbonate, and calcium carbonate in the ratios described in the component columns of Examples 1, 2, and 3 in Table 1. After the salt mixture was pulverized for 1 hour in an automatic mortar, it was dehydrated by heating at 300 ° C. for 2 hours using a dryer. The mixture was uniformly mixed for 5 minutes by a rocking mill at the ratio described in the component column of Examples 1, 2 and 3 in Table 1, and used as the molten salt type heat medium according to Examples 1, 2 and 3.

(Examples 4, 5, and 6)
In the molten salt type heat medium according to Examples 4, 5, and 6, potassium carbonate, lithium carbonate, sodium carbonate, and barium carbonate were mixed in the ratios described in the component columns of Examples 4, 5, and 6 in Table 1. A sample prepared in the same manner as the molten salt type heat medium according to Examples 1, 2, and 3 except that the carbonate mixture was used was used as the molten salt type heat medium according to Examples 4, 5, and 6.

(Examples 7, 8, and 9)
In the molten salt type heat medium according to Examples 7, 8, and 9, potassium carbonate, lithium carbonate, sodium carbonate, and calcium carbonate were mixed in the ratios described in the component columns of Examples 7, 8, and 9 in Table 1. A sample prepared in the same manner as the molten salt type heat medium according to Examples 1, 2, and 3 except that the carbonate mixture was used was used as the molten salt type heat medium according to Examples 7, 8, and 9.

(Examples 10, 11, and 12)
The molten salt type heat medium according to Examples 10, 11, and 12 is a carbonate mixture in which potassium carbonate, lithium carbonate, and sodium carbonate are mixed in the ratios described in the component columns of Examples 10, 11, and 12 in Table 1. A sample prepared in the same manner as the molten salt type heat medium according to Examples 1, 2, and 3 was used as the molten salt type heat medium according to Examples 10, 11, and 12 except that was used.

(Examples 13, 14, 15, 16, 17)
The molten salt type heat medium according to Examples 13, 14, 15, 16, and 17 is obtained by combining potassium carbonate, lithium carbonate, sodium carbonate, barium carbonate, and calcium carbonate with Examples 13, 14, 15, 16, and Samples prepared in the same manner as the molten salt-type heat medium according to Examples 1, 2, and 3 except that the carbonate mixture mixed at the ratio described in the 17 component column was used. 16 and 17 were used as the molten salt type heat medium.

(Examples 18, 19, and 20)
In the molten salt type heat medium according to Examples 18, 19, and 20, potassium carbonate, lithium carbonate, sodium carbonate, and barium carbonate were mixed in the ratios described in the component columns of Examples 18, 19, and 20 in Table 2. A sample prepared in the same manner as the molten salt type heat medium according to Examples 1, 2, and 3 except that the carbonate mixture was used was used as the molten salt type heat medium according to Examples 18, 19, and 20.

(Examples 21, 22, and 23)
In the molten salt type heat medium according to Examples 21, 22, and 23, potassium carbonate, lithium carbonate, sodium carbonate, and calcium carbonate were mixed in the ratios described in the component columns of Examples 21, 22, and 23 in Table 2. A sample prepared in the same manner as the molten salt type heat medium according to Examples 1, 2, and 3 except that the carbonate mixture was used was used as the molten salt type heat medium according to Examples 21, 22, and 23.

(Comparative Example 1)
The molten salt type heat medium according to Comparative Example 1 was a molten salt according to Example 1 except that a nitrate mixture in which potassium nitrate and sodium nitrate were mixed at a ratio described in the component column of Comparative Example 1 in Table 1 was used. A sample prepared in the same manner as the mold heat medium was used as the molten salt heat medium of Comparative Example 1.

<Measuring method of melting point>
10 mg of the molten salt type heat medium of Examples 1 to 23 and Comparative Example 1 was placed in a platinum sample dish, precisely weighed, and then set in a differential thermothermal gravimetric simultaneous measurement apparatus (TG / DTA, manufactured by Hitachi High-Tech Science Co., Ltd.). . Then, the molten salt type heat medium of Examples 1 to 23 and Comparative Example 1 was heated from 23 ° C. to 700 ° C. at a rate of 40 ° C./min and held at 700 ° C. for 10 minutes to melt the molten salt type heat medium. Thereafter, the temperature is lowered to 150 ° C. at 40 ° C./min to solidify, and the temperature at the endothermic peak of each molten salt heat medium during the temperature increase to 500 ° C. at 10 ° C./min is defined as the melting point Tm of the molten salt heat medium. . The measurement was performed in carbon dioxide. Tables 1 and 2 show the melting points of the measured molten salt type heat media of Examples 1 to 23 and Comparative Example 1.

<Method for measuring weight loss rate>
After putting 10 mg of molten salt type heat media of Examples 1 to 23 and Comparative Example 1 into a platinum sample dish and precisely weighing them, using a differential thermothermal gravimetric simultaneous measurement device (TG / DTA, manufactured by Hitachi High-Tech Science Co., Ltd.) The mixture was heated from room temperature to 1400 ° C., and the initial weight of the molten salt heat medium at room temperature before heating and the weight of the molten salt heat medium at each heating temperature were measured. And the weight change rate of each molten salt type heat carrier which decreases by heating was made into the weight reduction rate of a molten salt type heat medium. That is, the weight reduction rate of the molten salt heat medium is expressed as (weight of molten salt heat medium at each measurement temperature [g] −initial weight of molten salt heat medium [g] / initial weight of molten salt heat medium [ g]) × 100 [%]. FIG. 3 is a graph in which the weight reduction rate of the molten salt type heat medium of Examples 1, 4, 7, and 10 is plotted against the heating temperature, and the weight reduction rate of the molten salt type heat medium of Comparative Example 1 with respect to the heating temperature. The plotted graph is shown in FIG. In FIG. 3, line (a) represents the weight of the molten salt heat medium of Example 1, line (b) represents Example 4, line (c) represents Example 7, and line (d) represents the weight reduction of the molten salt heat medium of Example 10. Shows the rate. The weight reduction ratios according to Table 1, FIG. 3, FIG. 4 and FIGS. 6 to 9 were measured by heating the sample in a carbon dioxide atmosphere in Examples 1 to 23 and in a nitrogen atmosphere in Comparative Example 1. Furthermore, FIG. 5 shows the weight of the molten salt type heat medium when heated in the (a) carbon dioxide atmosphere, (b) air, and (c) nitrogen atmosphere for the molten salt type heat medium of Example 10. The graph which plotted the decreasing rate with respect to temperature is shown. In FIG. 5, the line (a) shows the weight reduction rate of the molten salt type heat medium measured in a carbon dioxide atmosphere, the line (b) in the air, and the line (c) in the nitrogen atmosphere. And the graph which plotted the weight reduction rate of the molten salt type heat medium which concerns on Example 11 with respect to heating temperature is plotted with FIG. 6, The weight reduction rate of the molten salt type heat medium which concerns on Example 8 is plotted with respect to heating temperature FIG. 8 is a graph obtained by plotting the weight reduction rate of the molten salt type heat medium according to Example 5 with respect to the heating temperature, and FIG. 8 is the weight reduction rate of the molten salt type heat medium according to Example 2. A graph plotted against the heating temperature is shown in FIG.

<Method for measuring heat-resistant temperature>
When the molten salt type heat mediums of Examples 1 to 23 and Comparative Example 1 were heated to 500 ° C. or higher, the temperature at which the first nonlinear weight loss of the molten salt type heat medium started was reduced. The temperature was Th. Tables 1 and 2 show the measured heat resistance temperature Th of the molten salt type heat medium of Examples 1 to 23 and Comparative Example 1 of the molten salt type heat medium.

<Normal operating temperature range calculation method>
For the molten salt type heat mediums of Examples 1 to 23 and Comparative Example 1, the difference between the heat resistance temperature Th and the melting point Tm (= heat resistance temperature Th [° C.] − Melting point Tm [° C.]) is calculated as a normal use temperature range ΔT. did. Tables 1 and 2 show the normal operating temperature range ΔT of the calculated molten salt type heat transfer media of Examples 1 to 23 and Comparative Example 1.

  As shown in Table 1 and FIG. 4, the molten salt type heat medium composed of potassium nitrate and sodium nitrate of Comparative Example 1 rapidly decomposes from 560 ° C., and when the temperature exceeds 560 ° C., the weight of the molten salt type heat medium decreases. Was remarkable. That is, the heat resistance temperature of the molten salt type heat medium composed of potassium nitrate and sodium nitrate was 560 ° C.

  On the other hand, as shown in Table 1, Table 2, FIG. 3, FIG. 5 and FIGS. 6 to 9, the molten salt type heat mediums of Examples 1 to 23 melted even when the temperature exceeded 560 ° C. It was found that the weight of the salt-type heat medium did not easily decrease, the heat resistance was very high as compared with the comparative example, and the heat resistance was stable even after high-temperature heating for a long time. For example, referring to FIG. 4 and FIG. 5, even when the rate of decrease from the initial weight under a nitrogen atmosphere is compared, the weight loss of the molten salt type heat medium is 200 ° C. or more than the comparative example. It has become clear that it has far better heat resistance in the temperature range and has excellent heat resistance.

  And as shown in FIG. 5, when the molten salt type heat medium of the carbonate mixture of the example is heated in a carbon dioxide atmosphere, it is about 1000 ° C. as compared with a nitrogen atmosphere and an air atmosphere. Since the decrease in the weight of the molten salt type heat medium is less likely to proceed even at high temperatures, the heat resistance is higher. FIG. 3 shows measured values in a carbon dioxide atmosphere. That is, it has been clarified that the molten salt type heat medium containing the carbonate mixture of Example shows extremely excellent heat resistance when sealed with carbon dioxide in a heated state. That is, as described above, in the solar heat utilization system and the method of using the molten salt heat medium, the heat medium container fluidly connected to the pipe through which the molten salt heat medium passes is formed by the molten salt heat medium and carbon dioxide. When the molten salt type heat medium is filled and sealed with carbon dioxide, the heat resistance of the molten salt type heat medium can be further increased.

  The normal use temperature range ΔT of the molten salt type heat medium of Example 1 is 510 ° C., and the normal use temperature range ΔT of the molten salt type heat medium of Comparative Example 1 is 339 ° C. Thus, the molten salt type heat medium according to the example can make the normal use temperature range ΔT of the molten salt type heat medium wider than the conventional one.

Next, to verify the effect of the addition of at least one of barium carbonate and (BaCO ₃₎ and calcium carbonate (CaCO _3). As shown in Table 1, in Examples 10 to 12, potassium carbonate (K ₂ CO ₃ ) of 12 mole percent or more and 40 mole percent or less and sodium carbonate (Na ₂ CO ₃ ) of 20 mole percent or more and 40 mole percent or less are used. And a molten salt type heat medium comprising a three-component carbonate mixture consisting of 25 mol percent to 55 mol percent lithium carbonate (Li ₂ CO ₃ ), the melting point was 396.7 ° C. on average. It was. Further, in Examples 4 to 6 and Examples 18 to 20 in which barium carbonate (BaCO ₃ ) was further added in an amount of 1.0 to 20 mole percent, the average melting point was 382.9 ° C. In Examples 7 to 9 and Examples 21 to 23 in which calcium carbonate (CaCO ₃ ) was added in an amount of 1.0 mole percent to 15 mole percent instead of (BaCO ₃ ), the average melting point was 384.5 ° C. . Furthermore, in Examples 1 to 3 and Examples 13 to 17 in which barium carbonate was added in an amount of 1.0 to 20 mol percent and calcium carbonate was added in an amount of 1.0 to 15 mol percent, the melting point averaged 375. It was 4 ° C. Thus, by including at least one of barium carbonate and calcium carbonate in the three components included in Examples 10 to 12, the melting point Tm of the molten salt heat medium can be greatly reduced.

  And as shown in FIG. 4, the heat resistance of the molten salt type heat medium according to Example 1 does not show a decrease in weight reduction rate even in a high temperature range exceeding 560 ° C., and barium carbonate and calcium carbonate are added. There is no decrease in heat-resistant temperature. For this reason, it can be said that the normal use temperature range ΔT could be further expanded by adding barium carbonate and calcium carbonate.

  As shown in Tables 1 and 2, the molten salt type heat medium of this example had a relatively low melting point Tm. Further, the molten salt type heat medium of this example had a viscosity sufficiently low to pass through the pipe line 410 and the like.

  As mentioned above, although this invention was demonstrated using embodiment and an Example, it cannot be overemphasized that the technical scope of this invention is not limited to the range as described in the said embodiment and Example. It will be apparent to those skilled in the art that various modifications or improvements can be made to the embodiments and examples. Further, it is apparent from the description of the scope of claims that embodiments with such changes or improvements can also be included in the technical scope of the present invention.

[Appendix]
The invention described in the scope of claims attached to the application of this application will be added below. The numbers in parentheses described in the appendix correspond to the item numbers of the claims in the claims attached first to the application of this application.
(1) The molten salt type heat medium according to an embodiment of the present invention includes 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent. And a carbonate mixture containing no more than a percent lithium carbonate.
(2) The molten salt type heat medium according to one embodiment of the present invention is the molten salt type heat medium according to the above (1), wherein the carbonate mixture further includes 1.0 mol percent or more and 20 mol percent. It may be characterized by containing the following barium carbonate.
(3) The molten salt type heat medium according to one embodiment of the present invention is the molten salt type heat medium according to the above (1), wherein the carbonate mixture further includes 1.0 mol percent or more and 15 mol percent. It may be characterized by containing the following calcium carbonate.
(4) The molten salt type heat medium according to one embodiment of the present invention is the molten salt type heat medium according to the above (1), wherein the carbonate mixture further includes 1.0 mol percent or more and 20 mol percent. It may be characterized by containing the following barium carbonate and 1.0 to 15 mol percent of calcium carbonate.
(5) The method of using the molten salt type heat medium according to another embodiment of the present invention includes 12 mol percent or more and 40 mol percent or less of potassium carbonate, 20 mol percent or more and 40 mol percent or less of sodium carbonate, and 25 mol percent. The molten salt type heat medium containing a carbonate mixture containing 55 mol% or less of lithium carbonate is heated in the heating unit, and the molten salt type heat medium is supplied by a pipe line in fluid communication with the heating unit. Supplying to a heat-use part and using the heat provided by the said molten salt type heat medium in the said heat-use part are provided, It is characterized by the above-mentioned.
(6) The method of using the molten salt type heat medium according to another embodiment of the present invention is the method of using the molten salt type heat medium according to (5) above, and further, the heat medium fluidly connected to the pipe line The method further comprises supplying the molten salt heat medium to the container and filling the heat medium container with carbon dioxide before or after the step of supplying the molten salt heat medium.
(7) A solar heat utilization system according to another embodiment of the present invention includes 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent. A molten salt-type heat medium containing a carbonate mixture containing lithium carbonate, a solar heating section for heating the molten salt-type heat medium with sunlight, and heat provided by the molten salt-type heat medium. In order to supply the heat use part to be used and the heated molten salt type heat medium to the heat use part, a pipe line in fluid communication with the solar heating part and the heat use part is provided. Features.
(8) A solar heat utilization system according to another embodiment of the present invention is the solar heat utilization system according to the above (7), further comprising a heat medium container in fluid communication with the pipe line, and the heat medium container, The molten salt heat medium and carbon dioxide may be filled.
(9) The solar-heat utilization system which concerns on other embodiment of this invention is a solar-heat utilization system of the said (7) description, Comprising: The said heat-use part may be characterized by including the electric power generating apparatus containing a gas turbine.
(10) A solar heat utilization system according to another embodiment of the present invention is the solar heat utilization system according to the above (7), wherein the heat using part is a reaction apparatus that produces hydrogen by a hydrothermal decomposition reaction. It may be a feature.

DESCRIPTION OF SYMBOLS 1 Solar heat utilization system 10 Molten salt type heat medium 100 Heating part 112 Condenser pipe 114 Condensing mirror 210 High temperature heat medium container 220 Low temperature heat medium container 230 Expansion tank 300 Heat use part 310 Heat use element 320 Cooling element 410 Pipe line 420 Pump 461,462 Valve Tm Melting point Th Heat resistance temperature ΔT Normal operating temperature range

Claims (10)

  Comprising a carbonate mixture containing 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent lithium carbonate. Molten salt type heat medium. The molten salt type heat medium according to claim 1,
The molten salt type heat medium, wherein the carbonate mixture further contains 1.0 to 20 mole percent of barium carbonate. The molten salt type heat medium according to claim 1,
The molten salt type heat medium, wherein the carbonate mixture further contains 1.0 to 15 mol percent of calcium carbonate. The molten salt type heat medium according to claim 1,
The carbonate mixture further contains 1.0 mol percent or more and 20 mol percent or less of barium carbonate, and 1.0 mol percent or more and 15 mol percent or less of calcium carbonate. Medium. Molten salt form comprising a carbonate mixture containing 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent lithium carbonate Heating the heat medium in the heating section;
Supplying the molten salt type heat medium to the heat using part by a conduit in fluid communication with the heating part; and
The method of using a molten salt type heat medium, comprising: using heat provided by the molten salt type heat medium in the heat using part. A method for using the molten salt heat medium according to claim 5,
Supplying the molten salt heat medium to a heat medium container in fluid communication with the conduit; and
The method for using a molten salt type heat medium, further comprising filling the heat medium container with carbon dioxide before or after the step of supplying the molten salt type heat medium. Molten salt form comprising a carbonate mixture containing 12 to 40 mole percent potassium carbonate, 20 to 40 mole percent sodium carbonate, and 25 to 55 mole percent lithium carbonate A heat medium;
A solar heating section for heating the molten salt heat medium with sunlight,
A heat using part using heat provided by the molten salt type heat medium;
A conduit in fluid communication with the solar heating section and the heat use section for supplying the heated molten salt heat medium to the heat use section;
A solar heat utilization system comprising: The solar heat utilization system according to claim 7,
Furthermore, a heating medium container in fluid communication with the pipe line is provided,
The solar heat utilization system, wherein the heat medium container is filled with the molten salt heat medium and carbon dioxide. The solar heat utilization system according to claim 7,
The said heat utilization part contains the electric power generating apparatus containing a gas turbine, The solar heat utilization system characterized by the above-mentioned. The solar heat utilization system according to claim 7,
The solar heat utilization system, wherein the heat use part is a reaction apparatus for producing hydrogen by a hydrothermal decomposition reaction.

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