JP5190620B2 - Gas hydrate storage method and storage facility - Google Patents

Description

  The present invention relates to a gas hydrate storage method and storage for storing a gas hydrate that is an inclusion compound of water and a gaseous gas hydrate forming substance that forms a gas hydrate such as natural gas, methane, ethane, and propane. It relates to equipment.

  Gas hydrate is an ice-like solid crystal consisting of water molecules and gas molecules, and clathrate hydrates in which gas molecules are interspersed inside the cage of the three-dimensional structure constructed by water molecules. (Hydrate) is a general term.

Natural gas hydrate contains about 165 Nm ^{3 of} natural gas in 1 m ³ of gas hydrate. For this reason, research and development using gas hydrate as a means for transporting and storing natural gas has been actively conducted.

  Advantages of hydrating natural gas include: (a) the natural gas hydrate has an equilibrium temperature condition under atmospheric pressure of −80 ° C. (193 K) or less, so that liquefied natural gas (LNG) that has already been put into practical use is used. ) Under atmospheric pressure storage and transportation temperature (-163 ° C. (110 K)), storage and transportation are possible, (b) In addition, as described above, large natural gas hydrate Since the equilibrium temperature condition under atmospheric pressure is −80 ° C. (193 K) or less, the durability and heat insulation of storage and transportation facilities can be greatly simplified.

  Natural gas hydrate is known to exist in a relatively stable state even outside equilibrium conditions because it has a special performance called a self-preservation effect. A transparent ice film is formed on the surface of natural gas hydrate in a self-preserving state, and it is becoming clear that this ice film expresses self-preserving properties.

According to this self-preserving effect, the amount of natural hydrate decomposed at around -23 ° C. (250 K) is the smallest. By utilizing this phenomenon, natural gas hydrate can be stored in a relatively stable state (for example, Patent Documents). 1).
JP 2003-287199 A

  Conventionally, the storage of natural gas hydrate has been devised to improve the storage stability by controlling the temperature and pressure.

  However, even at -23 ° C. (250 K), which is an appropriate temperature at which a self-preserving effect is exhibited, the decomposition of natural gas hydrate proceeds, and the influence becomes even greater particularly in long-term storage such as long-distance transportation. . Here, the cause of the progress of the decomposition of the natural gas hydrate is caused by the ice film formed on the surface of the natural gas hydrate, which is self-preserving, and even under the temperature condition where the ice film does not melt. Investigated.

  As a result of repeating all the experiments, it was found that the point at which the self-preserving effect of natural gas hydrate is exhibited is an ice film formed on the surface of natural gas hydrate, which is natural even at −23 ° C. (250 K). It was discovered that the cause of gas hydrate decomposition is that the ice film was destroyed, and one of the causes was the humidity around the natural gas hydrate.

  Even if it is -23 degreeC (250K), when the humidity in a storage is low, ice will sublimate and become water vapor | steam and will be discharge | released in the air, and the self-preservation property of natural gas hydrate is expressed. This is because the decomposition of natural gas hydrate proceeds by the ice film being decomposed by the sublimation. Conventionally, humidity has not been noticed in a low temperature state of −23 ° C. (250 K).

  It was discovered that the above phenomenon occurred in natural gas hydrate stored at −23 ° C. (250 K), and this phenomenon is outlined below.

  FIG. 4 is a schematic view simply showing a state where gas hydrate pellets are stored in the gas hydrate storage. The gas hydrate pellet 2 is stored in the gas hydrate storage 41, and the state where the water vapor 24 is scattered in the space is schematically shown. FIG. 4B schematically shows a state where the amount of water vapor is large and the humidity is high compared to FIG. When the humidity in the storage is lower than the equilibrium state as shown in FIG. 4A, the reaction proceeds in the direction of maintaining the equilibrium state by the decomposition of the gas hydrate ice film.

  FIG. 5 schematically shows how the gas hydrate pellets are decomposed. The gas hydrate pellet 2 of FIG. 5A is formed of a gas 21, a water molecule cage 22 and an ice film 23. When the temperature of the gas hydrate 2 exceeds the solid-gas equilibrium temperature condition under atmospheric pressure, for example, in the case of natural gas hydrate above -80 ° C (193K), the surface of the gas hydrate decomposes, By forming the ice film 23, the self-preserving property of gas hydrate is expressed. This is the self-preserving effect of gas hydrate, and it is most important that the ice film is formed.

  Here, when the amount of water vapor 24 in the storage 41 is small as shown in FIG. 4 (A), that is, when the humidity is low, the ice film 23 on the surface of the gas hydrate is formed as shown in FIG. 5 (B). It sublimates and is discharged from the gas hydrate pellet 2 as water vapor 24, and at the same time, the gas 21 is released. As shown in FIG. 5C, the ice film 23 is re-formed at a location where the ice film 23 is sublimated and does not exist. As described above, the decomposition of the gas hydrate 2 proceeds while repeating the sublimation of the ice film 23 until the humidity in the storage reaches an equilibrium state.

  As mentioned above, maintaining the ice film formed on the surface of the gas hydrate is important for the self-preserving effect of the gas hydrate. By maintaining the ice film for a long period of time, the decomposition of the gas hydrate is suppressed. And can be stored for a long time.

  As described above, the object of the present invention is to optimally control the relative humidity in the storage tank where the gas hydrate is stored, thereby suppressing the sublimation of the ice film on the surface of the gas hydrate and reducing the decomposition amount of the gas hydrate. Another object of the present invention is to provide a gas hydrate storage method and storage equipment with improved storage stability.

A gas hydrate storage method according to the present invention for achieving the above-described configuration is a method for storing a bulk or powder gas hydrate stored and transported at 0 ° C. or less, on the surface of the gas hydrate. The gas hydrate is stored in an atmosphere humidified to a relative humidity of 70 percent or more, which is a humidity capable of suppressing decomposition due to sublimation of the formed ice film 23.

In the above gas hydrate storage method, in the gas hydrate storage method, particularly in the natural gas hydrate storage method, the temperature is in the range of −5 ° C. to −25 ° C., and the relative humidity is in the range of 70% to 100%. The natural gas hydrate is stored in an atmosphere controlled and at atmospheric pressure.

The gas hydrate storage facility according to the present invention for achieving the above configuration includes a storage 41 for storing the gas hydrate, a heat exchanger 43 for cooling air in the storage 41, and the heat exchange. A humidifier 11 for humidifying the air cooled by the vessel 43 and a circulator 42 for circulating the air humidified by the humidifier 11 into the storage 41 are provided.

In the gas hydrate storage facility, the humidifier 11 is added in the sprayer for spraying water onto the air cooled by the heat exchanger 43, the spray chamber 12 for spraying water, and the spray chamber 12. And a separation chamber 13 for removing water other than the gas phase.

In the gas hydrate storage facility, a relative humidity measuring device 16 that measures the relative humidity in the spray chamber 12 in the spray chamber 12 and an ice block formed by water sprayed from the sprayer block the spray chamber 12. And a pressure measuring device 14 for monitoring the current situation.

In the gas hydrate storage facility described above , a multilayer plate 15 is provided in the spray chamber 12.

  When storing the gas hydrate, the humidity in the gas hydrate storage, which has not been noticed in the past, is set to 70% or more, thereby sublimating the ice film 23 contributing to the self-preserving effect of the gas hydrate. It is possible to suppress the decrease in storage and transportation efficiency due to the decomposition of the gas hydrate.

  For example, when storing natural gas hydrate, the inside of the storage is cooled from -5 ° C. (268K) to −25 ° C. (248K). If the heat exchanger 43 for cooling is externally circulated, Humidity decreases. This is because moisture in the gas phase is consumed by icing on the cooling surface of the heat exchanger 43. Therefore, the humidity in the natural gas hydrate storage 41 will continue to decrease in conventional equipment.

  Therefore, according to the gas hydrate storage method and apparatus of the present invention, the gas hydrate storage efficiency can be improved under atmospheric pressure because the self-preserving effect of gas hydrate is improved.

  The humidity inside the gas hydrate storage 41 is maintained at 70% or more by adding the humidity adjusting unit 1 having the spray chamber 12 and the separation chamber 13 in which the humidifying device 11 is arranged to the conventional gas hydrate storage facility. It was possible to suppress the sublimation of the ice film 23, which is the key to the preservation effect.

  Here, while the cooling gas sent from the heat exchanger 43 is passed through the spray chamber 12, the humidifier 11 humidifies the water and the spray water accompanying the cooling gas is separated in the separation chamber 13. The separated water freezes in 13 and inhibits the passage of the cooling gas. On the other hand, the frozen state of the separated water is monitored by the pressure measuring device 14.

  For example, when the separation water is frozen and the separation chamber 13 is closed, the pressure in the spray chamber 12 rises. Therefore, the humidifier 11 is stopped and the ice fixed to the separation chamber 13 is used as a humidifying material. After the blockage of the separation chamber 13 is released by sublimation, the humidifier 11 restarts. From the above, it is possible to maintain the humidity in the storage 41 at 70% or more without flowing more than necessary water molecules into the hydrate storage 41.

  Further, the relative humidity measuring device 16 can measure the relative humidity of the cooling gas passing through the humidity adjusting unit 1.

  Furthermore, by installing the multilayer plate 15 in the spray chamber 12, the opportunity for contact between the cooling gas and water molecules is expanded, and the cooling gas can be efficiently humidified.

  Hereinafter, the present invention will be specifically described with reference to the embodiments shown in the drawings.

  FIG. 1 shows an outline of a gas hydrate storage method and storage apparatus according to the present invention. The gas hydrate storage method and storage apparatus will be described by taking a case of storing natural gas hydrate as an example.

  A storage 41 for storing natural gas hydrate, a circulator 42 for sending air in the storage 41 to the heat exchanger 43, and a heat exchanger 43 for cooling the air sent by the circulator 42. In the gas hydrate storage facility, the humidifier 11 and the spray chamber 12 for humidifying the passing air and the liquid or solid in the air humidified by the humidifier 11 are removed between the heat exchanger 43 and the storage 41. A humidity adjusting unit 1 having a separation chamber 13 is installed.

  When natural gas hydrate is stored under atmospheric pressure, it is said that the self-preserving effect is the highest at -23 ° C (250K). In order to maintain the temperature of −23 ° C. (250 K), the cooling gas cooled by the heat exchanger 43 is sent to the humidity adjusting unit 1 shown in FIG.

  In the humidity adjusting unit 1, water is sprayed by the nozzle 17 installed in the humidifying device 11, and the cooling gas is humidified. FIG. 7 is an enlarged view of the nozzle 17, and the arrows indicate the paths through which water is supplied. In the storage of natural gas hydrate, for example, the nozzle 17 sprays water at a high pressure against a cooling gas of −5 ° C. (278 K) to −25 ° C. (258 K), and supplies it in the form of fine particles. The nozzle 17 includes the heater 18, thereby preventing the water passing through the nozzle 17 from being frozen and blocked due to the low temperature spray chamber 12.

  At this time, the temperature of the water does not freeze in the nozzle 17, but the cooling gas is cooled from −5 ° C. (278K) to −25 ° C. (258K). And a mixture of fine ice. It is humidified by passing a cooling gas through it, and the humidity is increased to 70% or more. The cooling gas containing water and fine ice is divided into a gas and other gas in the separation chamber 13, and only the gas is fed into the storage 41.

  Water and fine ice may freeze in the separation chamber 13, begin to block the passage, and the pressure in the spray chamber 12 may increase. This is measured by the pressure measuring device 14, and when the pressure rises, spraying of water by the humidifying device 11 is stopped, and the ice in the separation chamber 13 is used as a humidifying material. When the ice in the separation chamber 13 is sublimated and the blockage of the passage is resolved, the pressure in the spray chamber 12 is reduced and the spraying of water by the humidifier 11 is started again.

  In addition, the relative humidity measuring device 16 can measure the relative humidity of the cooling gas passing through the humidity adjusting unit 1. The relative humidity measuring device 16 controls to stop spraying when the humidity is within a predetermined range, so that excess ice is not supplied to the storage 41. This means that when gas hydrate is returned to gas at a plant, etc., if there is a large amount of excess ice, energy is required to melt this ice, which increases the cost as the energy efficiency decreases. It is for suppressing.

  By maintaining the humidity in the natural gas hydrate storage 41 at 70% or more as described above, the self-preserving effect of the natural gas hydrate can be increased, and storage and transportation can be performed with almost no decomposition. .

  FIG. 6 shows experimental results for verifying the storage stability of natural gas hydrate at different relative humidities in the natural gas hydrate storage 41. It is the result of having conducted an experiment at a relative humidity of 50%, 60%, and 70%, respectively, with the temperature in the storage 41 being −20 ° C. (253K), the storage period being 200 hours, and so on. When the relative humidity is 50% and 60%, the decomposition of natural gas hydrate proceeds, but when the relative humidity is 70%, the decomposition hardly occurs. This is because the ice film on the surface of the natural gas hydrate is prevented from sublimating by increasing the relative humidity in the storage 41. Furthermore, it was confirmed that even when the storage time was extended, the decomposition of natural gas hydrate hardly progressed at a relative humidity of 70%. It has been confirmed that the effect of the present invention appears more prominently as the storage time becomes longer.

  The present invention can also be applied to storage of gas hydrates other than natural gas. Furthermore, the present invention is applicable not only to gas hydrate pellets but also to powder hydrate powders, compacted blocks, and the like.

  FIG. 3 shows another embodiment of the humidity adjusting unit 1 in which a multilayer plate 15 is provided in the spray chamber 12. In the case of the spray chamber 12 without the multilayer plate 15, water molecules supplied by the humidifier 11 in the spray chamber 12 may freeze and form ice blocks. The larger the ice mass, the smaller the surface area with respect to the water molecular weight, and the smaller the contact area with the cooling gas. As a result, the efficiency of ice sublimation may decrease.

  Therefore, by using the multilayer board 15 as an example shown in FIG. 8, even when water molecules supplied into the spray quality 12 are frozen, the ice blocks are not concentrated and adhered to one place.

  Therefore, by installing the multilayer plate 15, it is possible to keep the size of the ice block small, keep the state dispersed in the spray chamber 12, and maintain the contact area with the cooling gas. Therefore, it is possible to efficiently sublimate ice with respect to the cooling gas.

  As described above, the gas hydrate storage method and storage equipment of the present invention realizes a humidity environment in which the self-preserving property of the gas hydrate can be maximized, and suppresses sublimation of the ice film on the surface of the gas hydrate. As a result, the amount of decomposition of the gas hydrate can be reduced.

  In addition, by controlling the humidity, the amount of decomposition of the gas hydrate was drastically reduced, thereby realizing storage and transportation of gas hydrate with high efficiency and reduced cost.

Schematic showing the gas hydrate storage facility Schematic showing one example of humidity adjustment unit Schematic showing one example of humidity adjustment unit Schematic showing the state of humidity in the gas hydrate storage Schematic showing the decomposition process of gas hydrate pellets A graph showing the relationship between the humidity in the storage and the self-preserving effect of natural gas hydrate pellets Schematic of nozzle installed in humidifier Schematic of multilayer board installed in spray chamber

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Humidity adjustment part 11 Humidifier 14 Pressure measuring device 16 Relative humidity measuring device 2 Gas hydrate pellet 21 Gas 23 Ice film 41 Storage 42 Circulator 43 Heat exchanger

Claims (6)

0 degree Ri gas hydrate storage method der by gas hydrate storage facility for storing bulk or powdery gas hydrate is stored and transported in the following, the gas hydrate storage facilities, for storing a gas hydrate Storage, a heat exchanger for cooling the air in the storage, a humidifier for humidifying the air cooled by the heat exchanger, and a circulator for circulating the air humidified by the humidifier in the storage Have
The humidifier includes a sprayer for spraying water onto the air cooled by the heat exchanger, a spray chamber for spraying water, and a separation chamber for removing water other than the gas phase added in the spray chamber. Have
A relative humidity measuring device for measuring the relative humidity in the spray chamber, and a pressure measuring device for monitoring a situation where ice blocks formed by water sprayed from the sprayer block the spray chamber. In a gas hydrate storage method in a gas hydrate storage facility having
The gas hydrate storage method has a relative humidity of 70% or more in the storage by the humidifier ,
When the separation chamber is closed due to water freezing and the pressure in the spray chamber rises, the control step of stopping spraying of water by the humidifier and using the ice mass in the separation chamber as a humidifying material;
A gas hydrate storage method comprising: a control step of starting spraying of water by the humidifier when the pressure in the spray chamber decreases . 2. The gas hydrate storage method includes a control step of stopping spraying of water by the humidifying device and not supplying excess ice to the storage by the relative humidity measuring device. 2. A gas hydrate storage method according to 1. A gas hydrate storage facility for storing massive or powdered gas hydrate stored and transported at 0 degrees or less, a storage for storing the gas hydrate, and a heat exchanger for cooling the air in the storage A humidifier that humidifies the air cooled by the heat exchanger, and a circulator that circulates the air humidified by the humidifier in the storage ,
The humidifying device sprays water on the air cooled by the heat exchanger, and sprays water.
And a separation chamber for removing other than the gas phase of water added in the spray chamber,
A relative humidity measuring device for measuring the relative humidity in the spray chamber, and a pressure measuring device for monitoring a situation where ice blocks formed by water sprayed from the sprayer block the spray chamber. In a gas hydrate storage facility having
The gas hydrate storage facility has a relative humidity of 70% or more in the storage by the humidifier,
When the separation chamber is closed due to freezing of water and the pressure of the spray chamber rises, spraying of water by the humidifier is stopped, and the ice mass in the separation chamber is used as a humidifying material,
A gas hydrate storage facility characterized by having a configuration in which spraying of water by the humidifier is started when the pressure in the spray chamber decreases . The gas hydrate storage facility according to claim 3, wherein the spray chamber has a multilayer plate . The gas hydrate storage facility has a configuration in which spraying of water by the humidifier is stopped by the relative humidity measuring device and control is performed so as not to supply excess ice to the storage. The gas hydrate storage facility according to claim 3 or 4. The gas hydrate storage facility according to any one of claims 3 to 5, wherein the humidifier includes a nozzle provided with a heater .

Images