JP7176202B2 - Composition, production method and use thereof - Google Patents

Description

_The present invention relates to compositions containing NaCl, KCl, MgCl2 and _ZnCl2 . It also relates to a heat medium and a heat storage material using the composition. Furthermore, the present invention relates to a heat medium and a heat storage material with a low solidification temperature and high heat resistance that can be used for transportation and storage technology of renewable energy such as solar heat.

Plants using renewable energy such as sunlight are attracting attention as next-generation energy plants to replace plants using fossil fuels. Thermal power generation using fossil fuels has problems such as depletion of resources and emission of greenhouse gases that cause global warming, and conversion to renewable energy is an urgent issue.

In recent years, a concentrator solar power plant has been developed in which sunlight is collected by a large mirror, etc., converted into heat in a light collecting part, a heat medium is passed through the light collecting part, and the heat medium is used to generate power in a boiler/turbine. Introduction is in progress. At this time, if a substance with high heat resistance is used as a heat medium, it is possible to raise the temperature to 500° C. or higher. In boiler/turbine power generation, generally, operating at a higher temperature increases the power generation efficiency, so there is a demand for the development of a heat medium that does not deteriorate even in the above-mentioned high-temperature environment and has high heat resistance.

Moreover, this is the same for wind thermal power generation. That is, in wind thermal power generation, the rotational force of a windmill is converted into heat, and this heat is used to generate power. In this application as well, since power generation efficiency and heat storage efficiency are improved by operating at a higher temperature, the development of a heat medium with high heat resistance is required.

Furthermore, a technique for producing hydrogen by water electrolysis using electricity obtained by concentrating solar power generation or the like has also been developed. Especially in high-temperature steam electrolysis technology, although low-temperature operation technology has been studied through the development of solid electrolytes, high-temperature operation at about 600°C to 700°C is still required.

In addition, a technology for chemically producing hydrogen by using solar heat as it is for a thermochemical reaction has also been developed. For this thermochemical reaction as well, attempts have been made to reduce the reaction temperature by improving the catalyst, but a high temperature of 600° C. or higher is required.

As an organic heat transfer medium generally used at present, a eutectic mixture of biphenyl and diphenyl oxide [for example, Dow Thermo A (registered trademark) of Dow Chemical Co.] is known. Furthermore, as an inorganic heat medium that can be used in a higher temperature range, a nitrate heat medium such as a mixture of potassium nitrate and sodium nitrate (for example, Solar Salt: Non-Patent Document 1) is known. Furthermore, a heating medium that can be used in a wider temperature range by adding chloride to nitrate to lower the melting point (Patent Document 1) is disclosed. In recent years, a chloride-based inorganic composition of Li—Na—K—Cs—Sr—Cl has been disclosed as an inorganic heat medium that can be used at higher temperatures (Patent Document 2).

In addition, as an inorganic heat medium with a low melting point, 7.5NaCl-23.9KCl-68.6ZnCl ₂ [wt%], which is a NaCl-KCl-ZnCl ₂ system eutectic composition, is a low-cost inorganic heat medium. As a heat medium, 62.5KCl-37.5MgCl ₂ [wt %], which is a KCl-MgCl ₂ eutectic composition, is disclosed (Non-Patent Document 2).

In addition, Patent Document 3 discloses the relationship between the composition and the melting point of a NaCl--KCl--ZnCl.sub.2 _- based heat transfer medium.

JP 2015-67670 US2013/0180520 A1 US2015/0010875 A1

N. Boerema, G.; Morrison, R.; Taylor, G.; Rosengarten, Solar Energy, 86 (2012) (2294 pages) M. Mehos, C.; Turchi, J.; Vidal, M.; Wagner, Z.; Ma, C.I. Ho, W.; Kolb, C.; Andraka, A.; Kruizenga, NREL Technical Report (NREL/TP-5500-67464) (2017) (25 pages)

However, the organic heat transfer medium has the danger of decomposition, ignition, etc. at high temperatures, and the upper temperature limit that can be used is limited to about 400.degree. Even with a nitrate-based heat transfer medium having higher heat resistance, the thermal decomposition reaction of nitrate proceeds as the temperature rises, so the upper limit temperature that can be used is limited to about 580°C.

On the other hand, the chloride-based heat transfer medium of Patent Document 2 uses chloride having a relatively high thermal decomposition temperature, and therefore has high heat resistance. However, there is a problem that the cost is high because there are resource restrictions and it contains expensive Li, Cs, and Sr.

The NaCl-KCl-ZnCl ₂ eutectic composition described in Non-Patent Document 2 also has a low melting point of 204 ° C. and can be used in a low temperature range, but 68.6 wt% (52.9 mol%) of expensive ZnCl ₂ ) and a large amount, there is a problem that the cost is high. Moreover, since ZnCl ₂ is highly volatile, there is also a problem that the amount of volatilization of the heat medium is large in a high temperature range.

Regarding the NaCl--KCl--ZnCl.sub.2 _- based heat medium described in Patent Document 3, the melting point is disclosed only in the composition range where the _ZnCl.sub.2 content is 28.9 mol % or more.

The KCl-MgCl ₂ eutectic composition described in Non-Patent Document 2 uses relatively inexpensive KCl and MgCl ₂ , so it is advantageous in terms of cost. Therefore, it is not suitable as a heat medium for use in renewable energy plants such as solar thermal plants.

An object of the present invention is to provide a heat medium having high heat resistance, low cost and a low melting point. Another object of the present invention is to provide a heat transfer system and a heat storage system using these molten salts, as well as a renewable energy plant and a chemical plant equipped with these.

_In order to solve this problem, the authors conducted extensive studies and found that a composition containing NaCl, KCl, MgCl2 and _ZnCl2 can be used as a heat transfer medium at a temperature of 450°C or higher and 800°C or lower. , can be suitably used as a heat medium.

That is, the gist of the present invention is to provide a composition comprising NaCl, KCl, _MgCl2 and _ZnCl2 .

The composition of the present invention is described below.

The present invention is a composition comprising NaCl, KCl, MgCl2 and _{ZnCl2 (} hereinafter referred to as "the composition of the present invention"). As a result, it has excellent heat resistance and can be suitably used as a heat medium over a wide temperature range.

Also preferably, the composition of the present invention has the following composition.
NaCl: 10 mol% or more and 40 mol% or less KCl: 10 mol% or more and 50 mol%
MgCl ₂ : 20 mol % or more and 50 mol % or less ZnCl ₂ : 3 mol % or more and 30 mol % or less By this, the solidification temperature of the present composition can be suppressed to approximately 420° C. or less.

Furthermore, the composition of the present invention contains ZnCl ₂ from 10 mol % to 25 mol %. As a result, the solidification temperature of the present composition can be suppressed to approximately 400° C. or lower.

Still more preferably, the composition of the present invention has the following composition.
NaCl: 20 mol% or more and 35 mol% or less KCl: 12 mol% or more and 27 mol%
MgCl ₂ : 20 mol % or more and 42 mol % or less ZnCl ₂ : 12 mol % or more and 25 mol % or less By this, the solidification temperature of the present composition can be suppressed to 350° C. or less.

Particularly preferably, the composition of the invention has the following composition.
NaCl: 20 mol% or more and 27 mol% or less KCl: 12 mol% or more and 20 mol%
MgCl ₂ : 35 mol % or more and 42 mol % or less ZnCl ₂ : 18 mol % or more and 25 mol % or less By this, the solidification temperature of the present composition can be suppressed to approximately 300° C. or less.

The compositions of the present invention can contain elements other _than NaCl, KCl, MgCl2 and _ZnCl2 , which result in undesirable effects such as decreased heat resistance, increased solidification temperature, increased corrosion rate, and the like. It is preferable to keep the content of unavoidable impurities low when there is an influence. The amount of unavoidable impurities is preferably 0.1 mol % or less.

The solidification temperature of the composition of the present invention refers to the point at which the output suddenly changes at the peak edge of the thermal output during the cooling process when the composition is subjected to differential thermal analysis (DTA). More specifically, in the DTA curve, a tangent line is obtained from the flat portion to the low temperature side, and an approximate tangent line is obtained at a portion where the thermal output rapidly changes from the flat portion to the heat generation side, and the intersection of these two tangent lines is obtained. The point where the value of the temperature directly below is read.

The composition of the invention can be used as a heat carrier. The heat medium can be suitably used in a heat transfer system.

The composition of the invention can be used as a heat reservoir. The heat storage medium can be suitably used in a heat storage system.

An example of a heat transfer/storage system utilizing the composition of the present invention is shown in FIG.

A renewable energy plant including at least one of the heat transfer system and the heat storage system has excellent energy use efficiency.

A chemical plant including at least one of the heat transfer system and the heat storage system has excellent energy use efficiency.

More specifically, the composition of the present invention can be used in various applications for transferring and storing heat, and is particularly suitable for use as a heat medium and heat storage material for renewable energy plants and chemical plants. can be done. As renewable energy plants, it can be suitably used in solar thermal power plants, solar thermal chemical hydrogen production plants, wind thermal power plants, wind thermal hydrogen production plants, and the like.

Since the composition of the present invention has high heat resistance, for example, when it is used in a power plant, it is possible to use steam of a higher temperature. I can. In addition, when it is used in a hydrogen production plant or a chemical plant, the reaction temperature can be raised, so an improvement in the reaction rate and reaction yield can be expected.

Since the composition of the present invention has a low solidification temperature, it is possible to reduce the electric power of the heater to prevent the solidification of the heat medium, especially when the temperature drops at night in a solar thermal plant, etc., and the heat medium can be melted and started. It has many advantages, such as being able to reduce heater power consumption at times, and reducing energy consumption by reducing pump power due to reduced viscosity.

Furthermore, since ΔT, which is the difference between the maximum use temperature and the minimum use temperature, can be made large, it is possible to transfer and store a larger amount of heat when compared with the same volume of heat medium, which is preferable. Electric power leveling in renewable energy is one of the major challenges in the introduction of renewable energy, and the ability to store more heat means that it can be leveled with a smaller amount of heat storage material, or it can be used for a longer time. It means that the leveling of

In addition, since the composition of the present invention is composed of relatively inexpensive elements with few resource restrictions, the piping of the heat collecting part is very long, especially in trough-type solar thermal plants, and even nighttime operation is realized. Therefore, it can be suitably used for applications that use a large amount of heat medium, such as plants equipped with large-sized heat storage tanks.

Since the composition of the present invention has high hygroscopicity, it is desirable to handle, store, and transport the composition in a low-humidity environment. Moreover, before being melted and used as a heat medium, it is also possible to preheat at a temperature of about 200° C. and dehydrate sufficiently before use.

The method for producing the composition of the present invention is described below.

The method for producing the composition of the present invention has a mixing step of mixing raw materials containing Na, K, Mg, Zn and Cl.

The raw materials for the composition of the present invention are not particularly limited as long as the desired composition can be achieved, and chlorides of constituent metals can be used. Specifically, NaCl, KCl, MgCl ₂ , ZnCl ₂ and the like can be used.

These chlorides can also be obtained by concentrating and drying after neutralizing the constituent metal hydroxides with hydrochloric acid. Alternatively, a chloride can be obtained by reacting the constituent metal as it is with hydrochloric acid.

There are no particular restrictions on the form of the raw material, and various forms such as powder, chunk, massive raw material, and melt can be used. In the case of powder, it is sufficient to weigh the material as it is in the case of chunks or lumps, or to obtain a pulverized material so as to obtain a desired composition ratio. .

The composition of the present invention may be obtained by putting the above-mentioned mixture into a heat-resistant container such as a crucible, melting it at a temperature of about 500° C. to 600° C., and solidifying it again. That is, the method for producing the composition of the present invention preferably has a melting step of melting the mixture obtained in the mixing step at a temperature of 550°C or higher and 750°C or lower. In this case, the melt may be pulverized.

In the melting step, the raw materials described above are weighed to a desired composition ratio and put into a heat-resistant container, heated and melted at a temperature of 550° C. or higher and 750° C. or lower, and mixed by a stirring mechanism such as a propeller. However, a similar composition can be obtained. At this time, a mixing effect can also be obtained by circulating the heated and melted liquid in the piping by means of a pump or the like, and the composition can be similarly obtained.

According to the present invention, it can be used as a heat medium at a temperature of 450 ° C. or higher and 800 ° C. or lower, and has low corrosiveness to iron-based materials in this temperature range, so it is suitable as a heat medium in renewable energy plants or chemical plants. To provide a composition that can be used for

1 is an example of a heat transfer/storage system utilizing the composition of the present invention.

EXAMPLES The present invention will be specifically described below with reference to examples. However, the invention is not limited to these examples.

The measurement methods used in Examples and Comparative Examples are as follows.

Examples 1-40
Predetermined amounts of each reagent of NaCl, KCl, MgCl ₂ , and ZnCl ₂ (all special grades manufactured by Wako Pure Chemical Industries) are weighed so as to achieve the composition ratio shown in Table 1, mixed in a mortar, and then put into a porcelain crucible. After dehydration treatment at 200° C. for 10 hours, it was melted in air at 500° C. to 600° C. for 1 hour. The obtained melt was taken out from the crucible and pulverized with a mortar to obtain a sample for evaluation.

(Measurement of solidification temperature)
Weigh the sample in a platinum sample pan, and use Rigaku TG-DTA device TG8120 or Hitachi High Technology TG-DTA device STA7200RV in an inert gas (Ar or N ₂ ) at a flow rate of 200 ml / min. The first peak (primary crystal peak) that appears when the temperature is raised to 600 ° C. at a rate of ° C./min and held for 30 minutes, and then the temperature is lowered at a rate of 10 ° C./min is extrapolated from the high temperature side of the peak. The temperature was taken as the freezing temperature.

Solidification temperatures for Examples 1-40 are shown in Table 1. The solidification temperature was 420° C. or less in all compositions. Furthermore, for compositions with a _ZnCl2 content of 10 mol% or more, all exhibited solidification temperatures below 400 °C.

Comparative Examples 1-8
Reagents of NaCl, KCl, and MgCl ₂ (all special grades manufactured by Wako Pure Chemical Industries, Ltd.) were prepared in the same manner as in Examples 1 to 40 so as to have composition ratios shown in Table 2 to prepare compositions. Next, the solidification temperature of the composition was obtained in the same manner as in Examples 1-40. Here, "-" indicates no addition.

Table 2 shows the solidification temperatures of Comparative Examples 1-8. All compositions had a solidification temperature of 430° C. or higher.

The composition of the present invention can be used as a heat medium or heat storage material for renewable energy plants and chemical plants.

Claims (11)

A heat carrier consisting of a melt containing NaCl, KCl, MgCl ₂ and ZnCl ₂ and having the following composition:
NaCl: 15 mol% or more and 38 mol% or less
KCl: 15 mol% or more and 47.5 mol% or less
MgCl2: 22.5 mol% or _more and 47.5 mol% or less
_ZnCl2 : 5 mol% or more and 25 mol% or less 2. The heat transfer medium according to claim 1, comprising a melt containing _ZnCl2 in an amount of 10 mol % to 25 mol %. 3. The heat transfer medium according to claim 1 or 2, comprising a melt having the following composition.
NaCl: 20 mol% or more and 35 mol% or less
KCl: 15 mol% or more and 27 mol% or less
MgCl2: 22.5 mol% or _more and 42 mol% or less
_ZnCl2 : 18 mol% or more and 25 mol% or less 4. The heat transfer medium according to any one of claims 1 to 3, comprising a melt having the following composition.
NaCl: 20 mol% or more and 27 mol% or less
KCl: 15 mol% or more and 20 mol% or less
MgCl2: 35 mol% or _more and 42 mol% or less
_ZnCl2 : 18 mol% or more and 25 mol% or less 5. The method for producing a heat transfer medium comprising a melt according to any one of claims 1 to 4, comprising a mixing step of mixing raw materials containing Na, K, Mg, Zn and Cl. The manufacturing method according to claim 5, further comprising a melting step of melting the mixture obtained in the mixing step at a temperature of 550°C or higher and 750°C or lower. A heat transfer system using the heat medium according to claim 6. Heat store consisting of a melt containing NaCl, KCl, MgCl ₂ and ZnCl ₂ and having the following composition:
NaCl: 15 mol% or more and 38 mol% or less
KCl: 15 mol% or more and 47.5 mol% or less
MgCl2: 22.5 mol% or _more and 47.5 mol% or less
_ZnCl2 : 5 mol% or more and 25 mol% or less A heat storage system using the heat storage medium according to claim 8 . A renewable energy plant comprising at least one of the heat transfer system according to claim 7 or the heat storage system according to claim 9. A chemical plant comprising at least one of the heat transfer system according to claim 7 or the heat storage system according to claim 9 .

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