JP5896469B2 - Gas hydrate storage method and gas hydrate storage device - Google Patents

Description

  The present invention relates to a gas hydrate storage method and gas hydrate storage device which are clathrate hydrates of hydrate-forming substances such as methane, natural gas, carbon dioxide and water.

  The gas hydrate is generated by reacting a hydrate-forming substance such as methane, natural gas, carbon dioxide or the like with water under a predetermined temperature and pressure as conditions for generating the gas hydrate. And the produced | generated gas hydrate is decomposed | disassembled into a hydrate formation substance and water by changing at least any one of temperature and pressure, and setting it as the decomposition conditions of gas hydrate.

Gas hydrate production conditions vary depending on the type of hydrate-forming substance, but are generally high pressure and low temperature conditions. For example, when the hydrate-forming substance is methane (CH ₄ ), a temperature of about 1 ° C. to 11 ° C. corresponds to a pressure of about 4 MPa to 8 MPa. When the hydrate-forming substance is natural gas (NG), a temperature of about 1 ° C. to 17 ° C. corresponds to a pressure of about 5 MPa to 6 MPa. When the hydrate-forming substance is carbon dioxide (CO ₂ ), a temperature of about 1 ° C. to 10 ° C. corresponds to a pressure of about 2 MPa to 6 MPa.

When the generated gas hydrate is transferred or stored, it is desirable to store it at a temperature close to normal temperature and atmospheric pressure from the viewpoints of economy such as equipment costs and operation costs and safety.
However, such a condition is generally a gas hydrate decomposition condition. For this reason, the gas hydrate is allowed to contain a decomposition inhibitor of the gas hydrate. For example, Patent Document 1 discloses that a gas hydrate is stored under such conditions by containing an electrolyte in the gas hydrate and allowing ions generated by dissociation of the electrolyte to function as a decomposition inhibitor of gas hydrate. It is disclosed to enhance the performance. Patent Document 2 discloses a gas hydrate containing a predetermined amount of sodium chloride and calcium chloride as a gas hydrate decomposition inhibitor.

JP 2004-2754 A JP 2011-52155 A

However, Patent Document 1 does not discuss storage temperature conditions according to the type of gas hydrate decomposition inhibitor. Patent Document 2 only describes a preferable storage temperature from the viewpoint of operating energy of the gas hydrate storage facility. Conventionally, only substances containing less than about 10 mol / m ³ of electrolyte as gas hydrate decomposition inhibiting substances have been disclosed. In such gas hydrates, the self-preserving effect of gas hydrate (gas hydrate It was generally stored at about −20 ° C., which is believed to have the highest effect of suppressing metathesis of the product to become a metastable state. In addition, a preferred storage temperature range is not disclosed for a gas hydrate containing 10 mol / m ³ or more of an electrolyte as a gas hydrate decomposition inhibitor.

The present inventors have conducted intensive studies on the assumption that the decomposition rate of the gas hydrate changes depending on the type and concentration of the gas hydrate decomposition inhibitor contained therein and the storage temperature of the gas hydrate corresponding to the type. As a result, the present inventors have found that there is a tendency specific to temperature conditions suitable for storage depending on the type of decomposition inhibitor of gas hydrate contained, that is, the difference in electrolyte contained as the decomposition inhibitor. .
Accordingly, the present invention provides a gas hydrate storage method and a gas hydrate storage device capable of improving the storage stability of the gas hydrate and suppressing the decomposition of the gas hydrate during transfer or storage based on such knowledge. The purpose is to do.

  The method for storing a gas hydrate according to the first aspect of the present invention for solving the above problem includes a gas hydrate containing at least one of an electrolyte and ions generated by dissociation of the electrolyte (electrolyte, etc.) It is stored at a temperature below the freezing point and at or near the eutectic point of the electrolyte and water.

  Here, “containing at least one of an electrolyte and ions generated by dissociation of the electrolyte” may be any form such as salt (crystal) or ion as the form contained in the gas hydrate. It means that various forms may be mixed. For this reason, when the said gas hydrate contains the anionic component and cationic component which can comprise electrolyte, it is contained in this aspect. Further, “near the eutectic point” means, for example, a temperature range determined according to the electrolyte at a temperature that is 10 ° C. lower than the eutectic point and lower than a temperature that is 10 ° C. higher than the eutectic point. This is a temperature range in which the decomposition inhibiting effect is as high as the eutectic point.

  According to this aspect, the storage temperature is set to a temperature at which the electrolyte or the like can sufficiently function as the gas hydrate decomposition inhibitor. For this reason, the gas hydrate has a high self-preserving effect and can be stored in a state where decomposition is suppressed. When the temperature range near the eutectic point includes a temperature range above the freezing point, the temperature range near the eutectic point is limited to a temperature range below the freezing point.

The gas hydrate storage method according to a second aspect of the present invention is the gas hydrate storage method according to the first aspect, comprising a gas hydrate containing less than 10 mol / m ³ in total of the electrolyte and ions generated by dissociation of the electrolyte. It is stored at a temperature equal to or higher than the eutectic point and equal to or lower than a temperature Tu determined according to the electrolyte.

Here, “containing the electrolyte and ions generated by dissociation of the electrolyte in a total of less than 10 mol / m ³ ” means that the electrolyte is contained, and the electrolyte is converted into an electrolyte as a whole. It means that the total amount of the electrolyte and the like is less than 10 mol / m ³ . Further, the “temperature Tu” is an upper limit temperature that is equal to or higher than the eutectic point and is capable of producing an effect of suppressing the decomposition of the gas hydrate, for example, the gas hydrate. Is the upper limit temperature at which the decomposition rate can be suppressed to 10% / day or less or 5% / day or less.

According to this aspect, it becomes possible to store the gas hydrate containing the electrolyte and the like at a low concentration of less than 10 mol / m ³ in a state where decomposition is suppressed with higher accuracy. In addition, since the storage temperature of the gas hydrate is a temperature equal to or higher than the eutectic point, it is possible to improve economics and safety such as equipment costs and operation costs.

A gas hydrate storage method according to a third aspect of the present invention is the gas hydrate containing a total of 10 mol / m ³ or more of the electrolyte and ions generated by dissociation of the electrolyte in the first aspect. It is stored at a temperature Te or lower corresponding to the eutectic point.

Here, “containing the electrolyte and ions generated by dissociation of the electrolyte in a total of 10 mol / m ³ or more” means that when the electrolyte and the like are all present as an electrolyte, the electrolyte and the like are added in a total of 10 mol / m 2. It means containing m ³ or more. In addition, “below the temperature Te corresponding to the eutectic point” is different depending on the type of the electrolyte and the like, but means the temperature below the upper limit temperature at which the gas hydrate decomposition suppressing effect can be produced. It is below the temperature of the eutectic point or below 1 ° C to 2 ° C below the temperature of the eutectic point.

The gas hydrate containing the electrolyte and the like at a high concentration has a narrower range of the optimum temperature stored in a state where decomposition is suppressed compared to the gas hydrate containing the electrolyte and the like at a low concentration on the high temperature side. Tend to be.
According to this aspect, it becomes possible to store the gas hydrate containing the electrolyte and the like at a high concentration of 10 mol / m ³ or more in a state where decomposition is suppressed with higher accuracy.

  A gas hydrate storage device according to a fourth aspect of the present invention is contained in a gas hydrate storage unit, a temperature adjusting unit for adjusting a storage temperature of the gas hydrate in the storage unit, and a gas hydrate. Accepting means for accepting selection of electrolyte type and concentration, storing means for storing gas hydrate storage temperature information corresponding to the electrolyte type and concentration, and storing in the storing means in accordance with the selection accepted by the accepting means And a controller that reads the stored storage temperature information and controls the temperature adjustment unit so that the storage unit reaches the storage temperature.

According to this aspect, when gas hydrate containing a total of less than 10 mol / m ^{3 of the} electrolyte and the like is stored by appropriately selecting the type and concentration of the electrolyte, the conventional general storage temperature condition (about −20 It becomes possible to store at a higher temperature than Further, even when gas hydrate containing a total of 10 mol / m ³ or more of the electrolyte and the like is stored, such as when there is a restriction on the raw material water that can be used, the gas hydrate can be stably stored.

It is a figure which shows the measurement result of the methane residual rate of the gas hydrate in Test 1. It is a figure which shows the measurement result of the methane residual rate of the gas hydrate in Test 2. 3 is a table summarizing temperatures at which decomposition is suppressed from Test 1 and Test 2. It is a figure which shows the measurement result of the methane residual rate of the gas hydrate in Test 3. It is a block diagram which shows one Example of the storage apparatus of the gas hydrate of this invention.

  The gas hydrate according to the present invention contains at least one of an electrolyte and ions generated by dissociation of the electrolyte as a gas hydrate decomposition inhibitor. The gas hydrate according to the present invention can be obtained by reacting raw material water with a gas hydrate-forming substance in the presence of a decomposition inhibitor.

<Raw material water>
As the raw water, purified water or pure water that does not contain impurities affecting the production of gas hydrate is preferably used. In particular, pure water containing almost no electrolyte is preferably used because it is easy to grasp the electrolyte concentration when producing gas hydrate. The raw water and the gas hydrate forming substance can be reacted in a solution in which an electrolyte is added to the raw water and dissociated to generate ions. In addition, raw material water containing at least one of an electrolyte as a decomposition inhibitor and an ion generated by dissociation of the electrolyte can be used as it is. For example, tap water or industrial water containing ions generated by dissociation of the electrolyte can be used as it is.

<Gas hydrate forming substance>
The gas hydrate-forming substance is not particularly limited as long as it forms a gas hydrate under predetermined pressure and temperature conditions. For example, methane, ethane, propane, butane, natural gas (a mixed gas containing methane as a main component and containing ethane, propane, butane, etc.), a substance that is a gas at normal temperature and normal pressure, such as carbon dioxide.

<Gas hydrate generation conditions>
Gas hydrate generation conditions (temperature and pressure) vary depending on the type of gas hydrate-forming substance, but can be generated under known conditions. For example, in the case of methane, it can be generated at a temperature of about 1 ° C. to 11 ° C. at a pressure of about 4 MPa to 8 MPa. In the case of natural gas, it can be produced at a pressure of about 5 MPa to 6 MPa at a temperature of about 1 ° C. to 17 ° C. In the case of carbon dioxide, it can be produced at a temperature of about 1 ° C. to 10 ° C. at a pressure of about 2 MPa to 6 MPa.
The reaction between the raw material water and the gas hydrate-forming substance can be performed by a known method such as a bubbling method in which fine bubbles are blown into water or a spray method in which water is sprayed into gas.

<Electrolyte>
As the electrolyte, a substance that generates an ion by dissociating the electrolyte in a solution and has an effect of suppressing decomposition of gas hydrate is used. If it is such a substance, there is no restriction in particular, for example, chloride, fluoride, bromide, sulfate, carbonate, acetate, nitrate, sodium salt, potassium salt, magnesium salt, calcium salt, ammonium salt, etc. Used. Of these, chlorides capable of generating chloride ions such as sodium chloride, ammonium chloride, potassium chloride, magnesium chloride, calcium chloride, iron chloride, manganese chloride, and zinc chloride are preferably used in terms of cost and safety. . Sodium chloride is particularly preferably used.

<Gas hydrate storage conditions>
The gas hydrate storage method according to the present invention can be stored under atmospheric pressure, and is preferably stored under atmospheric pressure. This is because the equipment for adjusting the pressure is not necessary and can be stored safely at low cost.

  Further, the gas hydrate storage method according to the present invention stores a gas hydrate containing at least one of an electrolyte and ions generated by dissociation of the electrolyte in a temperature range set according to the type of the electrolyte. To do. Preferably, it is stored at a temperature below the freezing point and near the eutectic point of the electrolyte and water. The vicinity of the eutectic point is, for example, a temperature range determined according to the electrolyte at a temperature lower than the eutectic point by 10 ° C. or higher and lower than the temperature of the eutectic point by 10 ° C. or less. Is a high temperature range.

<Estimated mechanism of self-preserving mechanism>
If the storage temperature of the gas hydrate is higher than a certain level, the decomposition of the gas hydrate becomes remarkable, which is not preferable. However, the lower the gas hydrate storage temperature, the more stable the gas hydrate can be stored. This is because when the gas hydrate is stored in a certain temperature range, the gas hydrate exhibits self-preserving properties. The presumed mechanism about the self-preserving expression mechanism is described below.

  When the gas hydrate is decomposed at a temperature above the freezing point, the gas hydrate is decomposed into a gas hydrate-forming substance and liquid water. It has been confirmed by Melnikov et al. That gas hydrate decomposes into a gas hydrate-forming substance and supercooled water even at temperatures below freezing point. The life of this supercooling water is shortened when the temperature is lowered, and it is said that supercooling water is not confirmed at -24 ° C. or lower in the gas hydrate in which no electrolyte is added to the raw water.

On the other hand, generation of an ice film covering the surface of the gas hydrate can be considered as a cause of the self-preserving property of the gas hydrate. It is considered that the formation of the ice film suppresses the permeation of the gas that is a gas hydrate forming substance generated by the decomposition of the gas hydrate, and as a result, suppresses the decomposition of the gas hydrate. The self-preserving property of gas hydrate has temperature dependence. The present inventors consider the cause of this temperature dependence as follows.
The water produced by the decomposition of the gas hydrate freezes on the surface of the gas hydrate and the like, and ice is produced. However, the ice immediately after the production has many defects and the gas permeation cannot be sufficiently suppressed. However, the ice is reduced in defects by gradually sintering and the like, and the permeation of gas can be sufficiently suppressed. That is, the decomposition of the gas hydrate can be sufficiently suppressed. When the temperature is high, the speed of sintering is increased and self-preserving properties are easily developed. For this reason, the self-preserving property is more easily exhibited when the temperature is not too low than when the temperature is too low.

Further, the present inventors consider the cause of temperature dependence as follows.
The gas hydrate according to the present invention contains an electrolyte and the like. This is because a gas hydrate containing an electrolyte or the like is excellent in storage stability because the electrolyte or the like functions as a decomposition inhibitor. The inventors of the present invention are concerned with a sintering mechanism via supercooled water as a cause of self-preservation in gas hydrates containing electrolytes, etc. thinking.

  When an electrolyte or the like is contained in the gas hydrate, the periphery of the electrolyte crystal melts at a temperature equal to or higher than the eutectic point, and a stable aqueous solution is formed around the electrolyte crystal. Even at a temperature equal to or lower than the eutectic point, in a certain temperature range, the periphery of the electrolyte crystal becomes supercooled water in which the electrolyte or ions from which the electrolyte is dissociated is dissolved. Supercooled water can exist as long as ice nuclei are not generated, but freezes as soon as it comes into contact with ice. If the life of the supercooling water is long, the supercooling water moves to the surface of the gas hydrate and can exist as supercooling water until it comes into contact with ice. For this reason, when the lifetime of the supercooling water is long, the ice film generated by the supercooling water can sufficiently cover the surface of the gas hydrate. That is, the decomposition of the gas hydrate can be sufficiently suppressed.

  The life of the supercooling water tends to be longer at higher temperatures than at lower temperatures. Further, when the life of the supercooling water is prolonged, the ice generated on the surface of the gas hydrate is easily sintered with the help of the supercooling water. For this reason, the ice film covering the surface of the gas hydrate becomes more effective for improving the self-preserving property of the gas hydrate. That is, the self-preserving property is more easily exhibited when the temperature is not too low than when the temperature is too low.

[Example]
Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to these examples.

<Test 1>
Methane hydrate was produced from water and methane gas containing 1 mol / m ³ of sodium chloride (NaCl), sodium nitrate (NaNO ₃ ), ammonium chloride (NH ₄ Cl), and potassium chloride (KCl) as electrolytes. These methane hydrates are crushed to about 0.5 mm to 1 mm and heated from −40 ° C. to 0 ° C. at 0.2 ° C./hr, and the methane residual rate (methane inclusion rate α _H / initial methane inclusion rate for each hour) (Α _H ) ₀ ) was measured using a gas flow meter.

The result is shown in FIG. The vertical axis in the figure is the methane residual rate (α _H / (α _H ) ₀ ), the upper horizontal axis is temperature (° C.), and the lower horizontal axis indicates time (hr).
In FIG. 1, a portion with a steep slope corresponds to a portion where the decomposition rate of methane hydrate is fast, and a portion where the slope is gentle corresponds to a portion where the decomposition rate of methane hydrate is slow.
As is clear from FIG. 1, any methane hydrate containing sodium chloride, sodium nitrate, ammonium chloride, or potassium chloride as an electrolyte has a temperature range where the decomposition rate of methane hydrate is slow (location where the slope is gentle). doing.

<Test 2>
Methane hydrate was generated from methane gas and water containing 34 mol / m ³ of sodium chloride (NaCl), ammonium chloride (NH ₄ Cl), and potassium chloride (KCl) as electrolytes. These methane hydrates are crushed to about 0.5 mm to 1 mm and heated from −40 ° C. to 0 ° C. at 0.2 ° C./hr, and the methane residual rate (methane inclusion rate α _H / initial methane inclusion rate for each hour) (Α _H ) ₀ ) was measured using a gas flow meter.

The result is shown in FIG. The vertical axis in the figure is the methane residual rate (α _H / (α _H ) ₀ ), the upper horizontal axis is temperature (° C.), and the lower horizontal axis indicates time (hr).
In FIG. 2, a portion with a steep slope corresponds to a portion where the decomposition rate of methane hydrate is fast, and a portion where the slope is gentle corresponds to a portion where the decomposition rate of methane hydrate is slow.
As is apparent from FIG. 2, any methane hydrate containing sodium chloride, ammonium chloride, or potassium chloride as an electrolyte has an inflection point (a point at which the slope changes suddenly) of the decomposition rate of methane hydrate.

<Discussion 1>
The decomposition rate of methane hydrate was calculated from the measurement results of the methane residual rate in Test 1 and Test 2, and the temperature at which the decomposition rate of methane hydrate was slow, that is, the temperature at which decomposition of methane hydrate was suppressed was determined.
FIG. 3 is a table summarizing temperatures at which decomposition is suppressed from Test 1 and Test 2. The temperature at which decomposition is suppressed can be controlled within a temperature range that can be suppressed to 5% / day or less for NaCl, which has a particularly high decomposition suppressing effect, and can be suppressed to 10% / day or less for other electrolytes. Temperature range.

As shown in FIG. 3, the range of temperature at which decomposition is suppressed differs depending on the type of electrolyte. For this reason, when storing gas hydrate, it is preferable to set the temperature range for storing gas hydrate according to the type of electrolyte.
Further, the methane hydrate and methane hydrate the electrolyte containing 34 mol / m ³ containing 1 mol / m ³ the electrolyte, the temperature decomposition inhibition against eutectic point is the temperature near the eutectic point. Specifically, the temperature is generally about 10 ° C. lower than the eutectic point and lower than 10 ° C. higher than the eutectic point.

In the case of methane hydrate having a low electrolyte content, that is, containing 1 mol / m ^{3 of} electrolyte, the upper limit temperature Tu at which the gas hydrate decomposition suppressing effect can be produced is −13 ° C. for NaCl and ₋₃ for NaNO ₃ . 12 ° C., NH ₄ Cl at −11 ° C., KCl at −11 ° C. That is, it was found that the product can be stored at a temperature about 7 to 9 ° C. higher than the conventional general storage temperature condition (about −20 ° C.).
The temperature Tu is a temperature that is equal to or higher than the eutectic point of the electrolyte, and is an upper limit temperature at which the gas hydrate decomposition suppression effect determined according to the electrolyte can be produced. In this example, the decomposition rate of gas hydrate is set to an upper limit temperature that can be suppressed to 5% / day or less for NaCl, which has a particularly high decomposition suppressing effect, and is suppressed to 10% / day or less for other electrolytes. The upper limit temperature that can be used. However, even when the upper limit temperature at which the decomposition rate of gas hydrate in NaCl was able to be suppressed to 10% / day or less was set, the temperature Tu was −13 ° C. That is, the temperature Tu in the present embodiment is a temperature that is equal to or higher than the eutectic point of the electrolyte and is the upper limit that can suppress the decomposition rate of the gas hydrate to 10% / day or less. Temperature.

Further, if the electrolyte content is high, that is, limited to methane hydrate containing 34 mol / m ^{3 of} electrolyte, the temperature range in which decomposition is suppressed is the temperature Te corresponding to the eutectic point (in NaCl, the eutectic point is − 2 ° C., NH ₄ Cl and KCl are limited to a temperature of −1 ° C. or less with respect to the eutectic point. In methane hydrate containing 34 mol / m ^{3 of} electrolyte, the eutectic point corresponds to the inflection point of the decomposition rate of methane hydrate shown in FIG. These eutectic points are −21 ° C. for NaCl, −15 ° C. for NH ₄ Cl, and −11 ° C. for KCl. Conventionally, in a gas hydrate containing a large amount of an electrolyte containing 10 mol / m ³ or more of an electrolyte, a preferable storage temperature range has not been disclosed, but a preferable storage temperature range in such a gas hydrate is not It was found that the temperature was equal to or lower than the temperature Te corresponding to the eutectic point.

  From the measurement results of Test 1 and Test 2, when storing the gas hydrate, it is stored at a temperature near the eutectic point, which is the temperature at which the gas hydrate is inhibited from being decomposed, thereby improving the preservability of the gas hydrate. It has been found that the decomposition of the gas hydrate during transfer or storage can be suppressed. Thus, it was found that by selecting the type and concentration of the electrolyte well, the electrolyte can be stored at a temperature higher than that of a conventional general storage temperature condition (about −20 ° C.).

<Test 3>
Sodium chloride as an electrolyte (NaCl) and ^{0.034mol / m 3, 1mol / m} 3, 10mol / m 3, to produce a methane hydrate containing 34 mol / ^{m 3.} These methane hydrates were heated from −40 ° C. to 0 ° C. at 0.034 mol / m ³ , 1 mol / m ³ , 34 mol / m ³ at 0.2 ° C./hr, and 10 mol / m ³ at 1 ° C./hr. The methane residual rate (the methane occlusion rate α _H / the initial methane occlusion rate (α _H ) ₀ ) for each hour was measured using a gas flow meter.

The result is shown in FIG. The vertical axis in the figure is the methane residual rate (α _H / (α _H ) ₀ ), and the horizontal axis indicates the temperature (° C.).
In FIG. 4, a portion with a steep slope corresponds to a portion where the decomposition rate of methane hydrate is fast, and a portion where the slope is gentle corresponds to a portion where the decomposition rate of methane hydrate is slow.

<Discussion 2>
As shown in FIG. 4, a small content of the electrolyte, methane hydrate sodium chloride containing ³ 0.034 mol / ^{m 3} and 1 mol / ^m is the slope in the range of about -23 ° C. to about -13 ° C. Is moderate. That is, the decomposition of the gas hydrate can be more effectively suppressed by storing at a temperature of about −13 ° C. or less, which is the upper limit temperature Tu that can cause the gas hydrate decomposition suppressing effect. . In general terms, a gas hydrate containing less than 10 mol / m ^{3 of} electrolyte is more effectively stored at a temperature equal to or higher than the eutectic point and equal to or lower than a temperature Tu determined according to the electrolyte. It was found that the decomposition of gas hydrate can be suppressed.

On the other hand, the high content of the electrolyte, methane hydrate which sodium chloride containing 10 mol / ^{m 3} and 34 mol / ^{m 3,} the temperature in the boundary of -21 ° C. which is the eutectic point of the sodium chloride and water exceeds this The slope is steep at That is, in the methane hydrate containing 10 mol / m ³ or more of sodium chloride, the eutectic point corresponds to the inflection point of the decomposition rate of methane hydrate. In general terms, a gas hydrate containing 10 mol / m ³ or more of an electrolyte can be more effectively suppressed from decomposition of the gas hydrate by storing it at a temperature Te or less corresponding to the eutectic point. I found out that

The present inventors consider the reason why the decomposition rate of the gas hydrate increases at a temperature exceeding the eutectic point only in the gas hydrate having a high electrolyte content as follows.
When the content of the electrolyte is small, the number of places where a stable aqueous solution is formed around the electrolyte is reduced. In addition, supercooled water is generated in the decomposition of the gas hydrate at a place other than around the electrolyte. There are few places where the stable aqueous solution is formed, and the effect of dissolving the surrounding gas hydrate is small, so that the supercooled water forms an ice film and suppresses the decomposition of the gas hydrate compared to the effect. Is bigger. For this reason, when the content of the electrolyte is low, the decomposition rate of the gas hydrate can be suppressed in a certain temperature range even at a temperature exceeding the eutectic point.

  On the other hand, when the content of the electrolyte is large, there are many places where a stable aqueous solution is formed around the electrolyte. If there are many places where the stable aqueous solution is formed, the effect of dissolving the gas hydrate around the solution is increased, and the supercooled water forms an ice film and suppresses the decomposition of the gas hydrate. When the content of the electrolyte is large, the stable aqueous solution is formed at once when the eutectic point temperature is exceeded. Therefore, when the eutectic point temperature is exceeded, the decomposition rate of the gas hydrate increases.

<Example of storage device for gas hydrate>
FIG. 5 is a block diagram showing an embodiment of the gas hydrate storage device of the present invention.
The gas hydrate storage device 1 according to this embodiment includes a gas hydrate storage unit 2 and a cooling device 3 as a temperature adjusting unit that adjusts the storage temperature of the gas hydrate in the storage unit 2. In addition, a user interface 4 such as a touch panel as a receiving means for receiving selection of the type and concentration of the electrolyte contained in the gas hydrate, and information on the storage temperature of the gas hydrate corresponding to the type and concentration of the electrolyte are stored. A ROM 5 is provided as storage means. Further, according to the selection received by the user interface 4, the storage unit 2 reads out information on the storage temperature of the gas hydrate stored in the ROM 5, and controls the cooling unit 3 so that the storage unit 2 reaches the storage temperature. I have. The control unit 6 includes a CPU 7, a RAM 8, a system bus 9, and the like.

In the gas hydrate storage device 1 of this embodiment, NaCl, NaNO ₃ , NH ₄ Cl and KCl can be selected as the type of electrolyte, and the concentration of the electrolyte is less than 10 mol / m ³ or 10 mol / m respectively. m ³ or more can be selected. When the electrolyte concentration is less than 10 mol / m ³ , the storage temperature corresponding to the temperature Tu of the selected electrolyte is selected. When the electrolyte concentration is 10 mol / m ³ or more, the selected electrolyte is shared. The control unit 6 is configured to control the cooling device 3 at the storage temperature corresponding to the crystal point. For example, when NaCl is selected as the electrolyte and the electrolyte concentration is less than 10 mol / m ³ , the control unit 6 is configured so that the storage temperature of the gas hydrate in the storage unit 2 is −13 ° C. corresponding to the temperature Tu. Is configured to control the cooling device 3. When NaCl is selected as the electrolyte and the electrolyte concentration is 10 mol / m ³ or more, the storage temperature of the gas hydrate in the storage unit 2 is a temperature Te corresponding to the eutectic point of sodium chloride and water. The control unit 6 is configured to control the cooling device 3 so that the temperature becomes −23 ° C. which is 2 ° C. lower than the eutectic point.

The gas hydrate storage device 1 according to the present embodiment, when storing a gas hydrate containing a total of less than 10 mol / m ^{3 of the} electrolyte and the like by appropriately selecting the type and concentration of the electrolyte, It becomes possible to store at a temperature higher than the storage temperature condition (about -20 ° C). Further, even when gas hydrate containing a total of 10 mol / m ³ or more of the electrolyte and the like is stored, such as when there is a restriction on the raw material water that can be used, the gas hydrate can be stably stored. However, the present invention is not limited to the gas hydrate storage device 1 of this embodiment.

  INDUSTRIAL APPLICABILITY The present invention can be used for a method for storing a gas hydrate which is a clathrate hydrate of a hydrate forming substance such as methane, natural gas, carbon dioxide and water.

Claims (4)

A gas hydrate containing at least one of an electrolyte and ions generated by dissociation of the electrolyte is at a temperature below the freezing point and at a temperature 10 ° C. lower than the eutectic point of the electrolyte and water and at least 10 from the eutectic point. A method for storing a gas hydrate, characterized by storing at a temperature not higher than ° C. 2. The gas hydrate storage method according to claim 1, wherein a gas hydrate containing a total of less than 10 mol / m ^{3 of the} electrolyte and ions generated by dissociation of the electrolyte is at a temperature equal to or higher than the eutectic point. A gas hydrate storage method, wherein the gas hydrate is stored at a temperature equal to or lower than a temperature Tu determined according to the electrolyte. 2. The gas hydrate storage method according to claim 1, wherein a gas hydrate containing a total of 10 mol / m ³ or more of ions generated by dissociation of the electrolyte and the electrolyte is equal to or lower than a temperature Te corresponding to the eutectic point. A method for storing gas hydrate, characterized by being stored in A gas hydrate reservoir,
A temperature adjustment unit for adjusting the storage temperature of the gas hydrate in the storage unit;
Receiving means for receiving selection of the type and concentration of the electrolyte contained in the gas hydrate;
Storage means for storing gas hydrate storage temperature information corresponding to the type and concentration of the electrolyte;
A controller that reads information on the storage temperature stored in the storage unit according to the selection received by the reception unit and controls the temperature adjustment unit so that the storage unit reaches the storage temperature. Gas hydrate storage device.

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