WO2018088053A1

WO2018088053A1 - Gas hydrate recovery method and gas hydrate recovery device

Info

Publication number: WO2018088053A1
Application number: PCT/JP2017/035138
Authority: WO
Inventors: 寿仁加藤
Original assignee: 三井造船株式会社
Priority date: 2016-11-11
Filing date: 2017-09-28
Publication date: 2018-05-17
Also published as: CN109661501B; JP2018076743A; JP6713405B2; CN109661501A

Abstract

The purpose of the invention is to provide a gas hydrate recovery method and a gas hydrate recovery device that can suppress changes in an underwater environment caused by gas hydrate recovery. Provided is a gas hydrate recovery method in which a riser pipe 4 is extended from a gas separation tank 5 down toward the water bottom 2 and in which a gas hydrate aggregation m is suctioned and lifted along with water from the water bottom 2 from a recovery opening 4a on the bottom of the riser pipe 4 to the gas separation tank 5, wherein a discharge pipe 9 is extended from the gas separation tank 5 toward the water bottom 2, and all of the water from the water bottom 2 taken up from the recovery opening 4a is discharged to the water bottom 2 from a discharge opening 9a on the bottom of the discharge pipe 9.

Description

Gas hydrate recovery method and gas hydrate recovery device

The present invention relates to a gas hydrate recovery method and a gas hydrate recovery device for collecting and recovering a massive gas hydrate from the bottom of the water together with the water at the bottom of the water, and more specifically, an underwater environment accompanying the recovery of the gas hydrate. The present invention relates to a gas hydrate recovery method and a gas hydrate recovery device that can suppress the change of the gas.

Various gas hydrate recovery devices for recovering methane gas hydrate present at the bottom of the sea or lake (hereinafter sometimes referred to as water bottom) have been proposed (see, for example, Patent Document 1).

Patent Document 1 proposes a gas hydrate recovery device that collects massive gas hydrate together with water at the bottom of the water and collects the generated gas by melting the massive gas hydrate. The water at the bottom after the gas is recovered is drained to the surface layer near the water surface.

Since the water bottom where gas hydrate is buried is about 400 m or deeper, the properties of the water near the water bottom and the surface water near the water surface are different. Specifically, the types and amounts of microorganisms contained in each water are different, the types and concentrations of salts and trace metals are different, and the types and concentrations of dissolved gases such as nitrogen and oxygen are different.

Therefore, if the water at the bottom of the water is drained to the surface layer near the water surface, the underwater environment on the surface layer changes. This change in the aquatic environment may be undesirable from an environmental protection standpoint or from a biological standpoint.

Japanese Unexamined Patent Publication No. 2015-31097

The present invention has been made in view of the above problems, and an object thereof is to provide a gas hydrate recovery method and a gas hydrate recovery device capable of suppressing changes in the underwater environment due to the recovery of gas hydrate. It is.

A gas hydrate recovery method for achieving the above-mentioned object is that a riser pipe is extended from a gas separation tank toward a lower water bottom, and a lump of gas is collected together with the water at the bottom from a recovery port at the lower end of the riser pipe. In the gas hydrate recovery method of sucking up hydrate and collecting it in the gas separation tank, a drain pipe is extended from the gas separation tank toward the bottom of the water, and the water in the bottom of the water is collected from the recovery port. All of the above is returned to the water bottom from the discharge port at the lower end of the discharge pipe.

A gas hydrate recovery device for achieving the above object includes a riser pipe that extends upward from a bottom of the water and sucks up the massive gas hydrate recovered at the bottom of the water together with the water in the bottom, and the riser pipe And a gas separation tank connected to the upper end of the gas separation tank into which the massive gas hydrate sucked up flows, and includes a discharge pipe extending from the gas separation tank toward the water bottom. The bottom water collected from the lower end of the riser pipe is returned to the bottom from the lower end of the discharge pipe.

According to the gas hydrate recovery method and the gas hydrate recovery apparatus of the present invention, all the water recovered at the bottom of the water is returned to the bottom without flowing out to other areas, so the environment in water accompanying the recovery of the gas hydrate. It is advantageous to suppress the change of.

FIG. 1 is an explanatory view illustrating a gas hydrate recovery apparatus of the present invention. FIG. 2 is an explanatory view illustrating the configuration of the gas hydrate recovery apparatus of FIG. FIG. 3 is an explanatory view illustrating a modification of the gas hydrate recovery apparatus of FIG. FIG. 4 is an explanatory view illustrating a modification of the gas hydrate recovery apparatus of FIG. FIG. 5 is an explanatory view illustrating a modification of the gas hydrate recovery apparatus of FIG.

Hereinafter, a gas hydrate recovery method and a gas hydrate recovery apparatus of the present invention will be described based on the embodiments shown in the drawings.

As illustrated in FIG. 1 and FIG. 2, the gas hydrate recovery device 1 of the present invention excavates methane gas hydrate m present in the bottom 2 of the sea or lake to collect massive gas hydrate m. And a riser pipe 4 that conveys the gas hydrate m collected by the excavating mechanism 3 upward from the vicinity of the water bottom 2.

The excavation mechanism 3 can be composed of a drill bit or an underwater heavy machine, for example. The configuration of the excavation mechanism 3 is not limited to this, and it is sufficient that the excavation mechanism 3 has a configuration in which the bottom 2 is excavated and the massive gas hydrate m is sent to the recovery port 4 a at the lower end of the riser pipe 4.

The riser tube 4 can be formed of, for example, a cylindrical body extending in the vertical direction. A recovery port 4 a at the lower end of the riser pipe 4 is disposed in the vicinity of the water bottom 2. In the present specification, the vicinity of the bottom means a region from the bottom 2 up to about 10 m. The range in the vicinity of the water bottom is not limited to the above and can be set as appropriate. The range in the vicinity of the water bottom may be, for example, a range from the water bottom 2 up to 2 m, or a range from the water bottom 2 up to 50 m.

The upper end of the riser pipe 4 is directly or indirectly connected to the gas separation tank 5. The gas separation tank 5 is installed in a structure 6 such as a ship or a floating body arranged near the water surface. The structure 6 in which the gas separation tank 5 is installed is not limited to a ship or the like arranged near the water surface, but may be composed of a land structure or a floating body arranged in water.

The gas separation tank 5 has a function of separating the gas generated in the vicinity of the bottom 2, inside the riser pipe 4, and inside the gas separation tank 5 from the water in the bottom 2 by melting the massive gas hydrate. . This gas separation tank 5 may have a function of gasifying the massive gas hydrate m. The gas separation tank 5 includes a gas recovery unit 7 that extracts the internal gas g to the outside, and a gas supply line 8 that is connected to the gas recovery unit 7 at one end. The other end of the gas supply line 8 is connected to a storage tank for storing the gas g and a pipeline for transporting the gas g to a consumption place.

The gas separation tank 5 is connected directly or indirectly to a discharge pipe 9 extending toward the bottom 2. The discharge pipe 9 is formed of, for example, a cylindrical body, and the discharge port 9 a at the lower end is disposed in the vicinity of the water bottom 2.

The massive gas hydrate m excavated and collected by the excavating mechanism 3 at the bottom 2 is sent to the recovery port 4 a at the lower end of the riser pipe 4. Since the gas hydrate m contains a gas resource such as methane gas and has a relatively small specific gravity, the gas hydrate m moves upward in the riser pipe 4 by buoyancy.

Since the water pressure decreases and the temperature increases as it approaches the water surface, the gas hydrate m rising in the riser tube 4 may melt and generate gas g bubbles. Since the amount of bubbles increases as it approaches the upper end of the riser tube 4, the density of the fluid in the riser tube 4 decreases as it approaches the upper end.

Since the specific gravity difference between the recovery port 4a of the riser pipe 4 and the upper end becomes large, an upward flow is generated in the riser pipe 4 due to this specific gravity difference. The same effect as a so-called air lift pump occurs. With this upward flow, water and earth and sand in the vicinity of the bottom 2 together with the massive gas hydrate m are sucked up by the riser pipe 4 and collected in the gas separation tank 5. A power source such as a pump is installed in the riser pipe 4 or a gas is blown into the riser pipe 4 to generate bubbles so that an upward flow is actively generated in the riser pipe 4. Good.

The bottom 2 where the gas hydrate m exists is, for example, a depth of 400 m or more, and the water temperature of the bottom 2 is 5 ° C. or less. On the other hand, the circumference of the gas separation tank 5 installed in the structure 6 such as a ship is about 20 ° C., for example. Since the temperature in the gas separation tank 5 is relatively higher than that of the bottom 2, the gas hydrate m melts in the gas separation tank 5 to generate gas g. Further, the gas g generated by melting the gas hydrate m during the flow through the riser pipe 4 is collected in the gas separation tank 5.

Gas g such as methane gas in the gas separation tank 5 is taken out from the gas recovery unit 7 to the gas supply line 8 outside the gas separation tank 5. The gas recovery unit 7 can be constituted by, for example, a check valve that allows gas to move only from the inside to the outside of the gas separation tank 5.

The gas recovery unit 7 has a configuration in which the gas g such as methane gas is taken out as a resource from the inside of the gas separation tank 5 to the outside and the fluid is prevented from flowing into the inside from the outside of the gas separation tank 5. The gas separation tank 5 can be prevented from flowing a gas such as the atmosphere or a liquid such as seawater. As a result, it is possible to prevent microorganisms and the like existing in the atmosphere and in the surface layer and intermediate layer water from entering the gas separation tank 5.

In this specification, the surface layer means, for example, a region from a depth of 10 m to the water surface. Further, the intermediate layer refers to a region sandwiched between the surface layer and the vicinity of the water bottom. The range of the surface layer is not limited to the above and can be set as appropriate. The range of the surface layer may be, for example, a range from the water surface to a water depth of 2 m, or a range from the water surface to a water depth of 50 m.

The gas recovery unit 7 may be configured by a pump or the like that moves the gas only in the direction in which the gas separation tank 5 flows from the inside to the outside.

Water and earth and sand collected in the gas separation tank 5 together with the gas hydrate m are all collected from the bottom 2. The water generated as the gas hydrate m is melted is also recovered from the bottom 2. All of these are returned to the bottom 2 by the discharge pipe 9.

The mass gas hydrate m collected in the gas separation tank 5 may be collected in a storage tank or the like as a lump without being melted and transported to a consumption area. In this case, a part of the water constituting the gas hydrate m is taken out from the inside of the gas separation tank 5. Even in this case, all the water in the bottom 2 collected from the recovery port 4a of the riser pipe 4 together with the gas hydrate m is returned to the bottom 2 by the discharge pipe 9.

A power source such as a pump may be installed in the discharge pipe 9 to return the water collected from the bottom 2 and earth and sand from the gas separation tank 5 to the bottom 2.

In this embodiment, the rise of the gas hydrate m by the riser pipe 4 is continuously performed, and the discharge by the discharge pipe 9 is continuously performed in parallel with the gasification in the gas separation tank 5. That is, the recovery of the gas hydrate m is continuously performed.

As illustrated in FIG. 2, the gas hydrate recovery device 1 is configured so that the water in the bottom 2 recovered from the recovery port 4 a is route c in the path c from the recovery port 4 a of the riser tube 4 to the discharge port 9 a of the discharge tube 9. It has the structure which circulates in the state which does not flow outside from the inside.

Also, it is desirable that all of the substances recovered from the bottom 2 are exhausted from the outlet 9a to the bottom 2 in a state where they do not flow out of the path c except for gas recovered as resources. In this configuration, all solids such as earth and sand collected from the bottom 2 are also returned to the bottom 2 from the discharge port 9a. Further, water generated by melting the gas hydrate m is also returned to the bottom 2.

According to the above configuration, microorganisms and the like contained in the water at the bottom 2 and earth and sand do not flow out to other regions such as the surface layer and the intermediate layer. This is advantageous for suppressing changes in the underwater environment such as the surface layer and intermediate layer.

・ Water and earth and sand etc. in the bottom 2 with different types and amounts of salts and trace metals are not discharged to other areas such as the surface layer. It is advantageous to suppress changes in the underwater environment such as the surface layer by mixing water with different components.

水 Water, earth and sand, etc. in the bottom 2 with different types and concentrations of dissolved nitrogen, oxygen, methane, and other gases are not discharged to other areas such as the surface layer. It is advantageous for suppressing changes in the underwater environment such as the surface layer.

The gas hydrate recovery apparatus 1 may be configured such that surrounding water or the like does not flow from the outside to the inside of the path c in the path c from the recovery port 4a of the riser pipe 4 to the discharge port 9a of the discharge pipe 9. it can. That is, no liquid other than water generated as the gas hydrate m melts and water in the bottom 2 flows into the path c. Thereby, it can suppress that the water of other area | regions, such as a surface layer, mixes with the water of the bottom 2 etc. which flow the inside of the path | route c. This is advantageous for suppressing changes in the underwater environment of the bottom 2.

In the present specification, the path c indicates a path through which water collected from the bottom 2 passes before returning to the bottom 2, and specifically includes, for example, a riser pipe 4, a gas separation tank 5, and a discharge pipe 9. Show the route.

Further, a configuration in which a gas such as ambient air does not flow from the outside to the inside of the path c may be adopted. That is, no gas other than the gas generated as the gas hydrate m melts flows into the path c. Thereby, it can suppress that air | atmosphere mixes in the water of the bottom 2 etc. which flow through the inside of the path | route c. Since it is possible to avoid the problem that microorganisms and the like contained in the atmosphere are transported to the bottom 2 together with the water in the bottom 2 flowing through the path c, it is advantageous for suppressing changes in the underwater environment of the bottom 2.

The farther the disposition position of the discharge port 9a is from the recovery port 4a, the more advantageous it is to suppress unnecessarily sucking up earth and sand discharged from the discharge port 9a from the recovery port 4a. The smaller the ratio of earth and sand in the fluid conveyed by the riser pipe 4, the smaller the density ρ 1, which is advantageous for improving the conveyance efficiency of the riser pipe 4.

As illustrated in FIG. 3, a buffer tank 5 a can be installed between the upper end of the riser pipe 4 and the gas separation tank 5. In this embodiment, the riser pipe 4 and the gas separation tank 5 are indirectly connected. The buffer tank 5a temporarily stores the massive gas hydrate m that is collected together with the water in the bottom 2. The buffer tank 5a has a configuration in which the gas hydrate m floating in the water is moved to the gas separation tank 5 and water that does not contain the gas hydrate m is drained from the vicinity of the bottom of the buffer tank 5a to the discharge pipe 9. is doing.

At this time, there are two paths c: a path from the riser pipe 4 to the discharge pipe 9 via the buffer tank 5a and the gas separation tank 5, and a path c from the riser pipe 4 to the discharge pipe 9 via the buffer tank 5a. Exists.

As illustrated in FIG. 4, the gas hydrate recovery device 1 measures the density of the fluid passing through the inside of the riser pipe 4 and the pressure measuring mechanism 11 that measures the pressure inside the gas separation tank 5. It can be set as the structure provided with. The density measuring mechanism 10 is installed on the inside or outside of the riser pipe 4. The density measuring mechanism 10 is preferably located near the upper end of the riser pipe 4 and close to the gas separation tank 5. The pressure measuring mechanism 11 is disposed on the upper side inside the gas separation tank 5 and has a configuration for measuring the pressure in the gas phase portion.

The density measuring mechanism 10 and the pressure measuring mechanism 11 are connected to the control mechanism 12 by wired or wireless signal lines, respectively. The control mechanism 12 can be disposed in the vicinity of the gas separation tank 5, for example. The control mechanism 12 has a configuration that controls the flow rate of the gas g that passes through the gas recovery unit 7 and is extracted to the outside according to the values acquired from the density measurement mechanism 10 and the pressure measurement mechanism 11. In this embodiment, the gas recovery unit 7 is arranged in the middle of a pipe extending from the gas separation tank 5 toward the gas supply line 8.

The heating mechanism 13 for supplying heat to the water inside the gas separation tank 5 may be installed in the gas separation tank 5. The heating mechanism 13 can be composed of, for example, a heater that generates heat when supplied with electricity. This heater is disposed inside the gas separation tank 5.

The heating mechanism 13 forms, for example, a pipe that circulates the water inside the gas separation tank 5 to the outside, and contacts the outside of this pipe with water having a relatively high temperature, for example, surface water as a heat medium. It can be set as the structure which performs heat exchange. Since only heat transfer is performed in the pipeline, the water in the gas separation tank 5 does not directly contact the surface water or the atmosphere.

The heating mechanism 13 can be configured such that a pipe line for circulating a heat medium such as surface water is disposed inside the gas separation tank 5. The water in the gas separation tank 5 is in contact with the wall surface of the pipe to exchange heat. Only heat is transferred in the pipe, and the water inside the gas separation tank 5 and the heat medium do not come into direct contact with each other.

In the present invention, the heating mechanism 13 is not an essential requirement. In the case where the heating mechanism 13 is installed, it is desirable to connect the control mechanism 12 with a signal line. With this configuration, the control mechanism 12 can control the amount of heat supplied to the water inside the gas separation tank 5 by the heating mechanism 13.

A gas lift mechanism 14 that blows gas such as methane gas taken out from the gas recovery unit 7 to the gas supply line 8 outside from the middle part of the riser pipe 4 may be installed. The flow rate of the upward flow generated in the riser pipe 4 can be increased by the gas lift mechanism 14. Since the gas g recovered from the gas hydrate m rather than air in the atmosphere is blown into the riser pipe 4, it is possible to avoid a problem that microorganisms in the atmosphere are mixed into the fluid flowing through the riser pipe 4.

Since the gas g used in the gas lift mechanism 14 is taken out from the gas supply line 8, it is possible to prevent the pressure in the gas separation tank 5 from fluctuating due to the operation of the gas lift mechanism 14. The gas g used in the gas lift mechanism 14 may be removed from the gas separation tank 5.

In the present invention, the gas lift mechanism 14 is not an essential requirement. When the gas lift mechanism 14 is installed, it is desirable to install a pump 15 in the middle of the flow path through which the gas passes and to connect the pump 15 to the control mechanism 12 through a signal line. With this configuration, the control mechanism 12 can control the flow rate of the gas supplied into the riser pipe 4 by the gas lift mechanism 14.

In the gas lift mechanism 14, a dehumidifying mechanism 16 that removes moisture contained in the gas may be installed in the middle of the flow path through which the gas passes. This is advantageous in avoiding a problem that the gas g reacts with moisture in the flow path of the gas lift mechanism 14 to generate a gas hydrate m and closes the flow path.

The gas g taken out from the gas separation tank 5 may be pressurized by a compression mechanism 17 such as a pump and supplied into the gas separation tank 5. Specifically, for example, the gas supply line 8 and the gas separation tank 5 can be communicated with each other through the reflux line 18, and the compression mechanism 17 can be installed in the middle of the reflux line 18. With the configuration in which the gas g is pressurized and supplied to the gasification separation tank 5, it is possible to control to increase the pressure inside the gas separation tank 5.

In the present invention, the configuration for supplying the gas g into the gas separation tank 5 is not an essential requirement. When the compression mechanism 17 and the reflux line 18 are installed, it is desirable that the compression mechanism 17 is connected to the control mechanism 12 through a signal line. With this configuration, the control mechanism 12 can easily control the pressure inside the gas separation tank 5 by the compression mechanism 17.

When the gas hydrate m is collected by the gas hydrate collecting device 1, first, the density ρ 1 (kg / m ³ ) of the fluid flowing inside the riser pipe 4 is measured by the density measuring mechanism 10. The fluid flowing inside the riser pipe 4 includes earth and sand, but also includes bubbles of gas g generated by melting the gas hydrate m or supplied from the gas lift mechanism 14. Therefore, the density is relatively smaller than the water outside the riser pipe 4. This density ρ1 is, for example, about 900 kg / m ³ . When the gas lift mechanism 14 is provided, the density ρ1 can be lowered by increasing the flow rate of the gas supplied into the riser pipe 4.

Since the density ρ0 of the water outside the riser tube 4 hardly changes throughout the year, it can be regarded as a fixed value. This density ρ0 is, for example, about 1000 kg / m ³ .

On the other hand, the pressure P1 (kg / m ² ) inside the gas separation tank 5 is measured by the pressure measuring mechanism 11. Here, the pressure P1 represents a gauge pressure. Inside the gas separation tank 5, the pressure P 1 increases due to the generation of gas g accompanying the melting of the massive gas hydrate m. By taking out the gas g from the gas recovery unit 7, the pressure P1 decreases. Further, the pressure P 1 increases due to inflow of fluid such as water in the bottom 2 from the riser pipe 4 to the gas separation tank 5, and decreases due to discharge to the discharge pipe 9.

The force pushed by the water pressure from the recovery port 4a acts as an upward force on the fluid in the riser pipe 4. The mass of the fluid in the riser tube 4 acts as a downward force. Further, the pressure P1 inside the gas separation tank 5 acts as a downward force. Therefore, in order for the fluid in the riser pipe 4 to be withdrawn, the following formula 1 needs to be satisfied.

Here, H represents the water depth (m) where the recovery port 4a of the riser pipe 4 is disposed. The following formula 2 is obtained by modifying the above formula 1.

Here, ρ0-ρ1 indicates the difference in fluid density between the inside and outside of the riser tube 4. From Equation 2, it can be seen that the lower the pressure P1 inside the gas separation tank 5, the easier it is to maintain the uplift by the riser pipe 4. The control mechanism 12 controls the pressure P1 in the gas separation tank 5 so that the gas g in the gas separation tank 5 is taken out by the operation of the gas recovery unit 7 and the pressure P1 satisfies Equation 1. When the gas recovery unit 7 is configured by a check valve, the pressure P1 of the gas separation tank 5 can be reduced by opening the check valve.

When the gas hydrate recovery device 1 includes the gas lift mechanism 14, the control mechanism 12 may be configured to control the amount of gas g supplied into the riser pipe 4 by the control of the pump 15. Since the density ρ1 of the fluid in the riser pipe 4 decreases as the supply amount of the gas g increases, the upward flow in the riser pipe 4 is easily maintained.

This control may be performed together with the control of the gas recovery unit 7 described above. That is, the pressure P1 inside the gas separation tank 5 may be lowered and the density ρ1 of the fluid in the riser pipe 4 may be reduced.

If the water depth H for excavating the gas hydrate m does not change, the value on the left side of Equation 1 hardly changes and can be regarded as a constant. Accordingly, the control mechanism 12 controls the product so that a value obtained by adding the pressure P1 inside the gas separation tank 5 to the product of the density ρ1 of the fluid inside the riser pipe 4 and the water depth H is within a predetermined range. Also good.

The force pushed by the water pressure from the discharge port 9a acts as an upward force on the fluid in the discharge pipe 9. The mass of the fluid in the discharge pipe 9 acts as a downward force. Further, the pressure P1 inside the gas separation tank 5 acts as a downward force. Therefore, in order for the fluid in the discharge pipe 9 to be discharged to the bottom 2, the following formula 3 needs to be satisfied.

Here, ρ2 represents the density (kg / m ³ ) of the fluid remaining in the gas separation tank 5. Since the gas g is separated inside the gas separation tank 5, the density ρ2 of the fluid remaining inside the gas separation tank 5 increases. This fluid includes water in the bottom 2 and earth and sand, and the density ρ2 is, for example, about 1100 kg / m ³ .

The density ρ2 of the fluid in the discharge pipe 9 is larger than the density ρ0 of the external water. Therefore, if the pressure P1 inside the gas separation tank 5 becomes smaller than the atmospheric pressure and the value does not become negative, the fluid in the discharge pipe 9 can move to the bottom 2 under its own weight. From Equation 3, it can be seen that the larger the pressure P1 in the gas separation tank 5 is, the more efficiently the discharge by the discharge pipe 9 can be performed.

The control mechanism 12 controls the pressure P 1 by the operation of the gas recovery unit 7. When the gas recovery unit 7 is configured by a check valve, the pressure P1 of the gas separation tank 5 can be increased by preventing the check valve from being opened.

When the gas hydrate recovery device 1 includes the heating mechanism 13, the control mechanism 12 may be configured to control the amount of heat supplied into the gas separation tank 5 by the control of the heating mechanism 13. As the amount of heat supplied increases, the massive gas hydrate m melts to generate gas g, and the pressure P1 inside the gas separation tank 5 increases.

This control may be performed together with the control of the gas recovery unit 7 described above. That is, the control of increasing the pressure P1 in the gas separation tank 5 by stopping the extraction of the gas g from the gas separation tank 5 or suppressing the amount of the gas g to be extracted and increasing the generation amount of the gas g is performed. May be.

When the gas hydrate recovery apparatus 1 includes the compression mechanism 17 and the reflux line 18, the control mechanism 12 controls the compression mechanism 17 to pressurize the gas g in the gas separation tank 5 to flow back. You may make it the structure which controls. As the flow rate of the supplied gas g increases, the pressure P1 inside the gas separation tank 5 increases.

This control may be performed together with the control of the gas recovery unit 7 and the heating mechanism 13 described above. The control of the pressure P 1 by the gas recovery unit 7, the heating mechanism 13, and the compression mechanism 17 may be performed by only one, or may be performed by appropriately combining a plurality.

From the

above formulas

2 and 3, the smaller the pressure P1 inside the gas separation tank 5 is, the more advantageous is the lifting by the riser pipe 4, and the larger the pressure P1 is, the more advantageous is the discharging by the discharge pipe 9. The control mechanism 12 performs control to adjust the balance between the picking up and discharging. For example, by controlling the pressure P1 in the gas separation tank 5 to be maintained at about atmospheric pressure, the riser pipe 4 and the discharge pipe 9 can be discharged simultaneously and continuously.

In this embodiment, the control mechanism 12 adjusts the balance of pressure at various points in the path c, so that the water in the bottom 2 is returned to the bottom 2 again from the bottom 2 via the riser pipe 4 and the discharge pipe 9. Water can be circulated with little use of power such as a pump. Since the energy consumption in the gas hydrate recovery apparatus 1 is suppressed, it is advantageous for improving the energy efficiency in resource recovery.

Since the fluid can be continuously circulated in the path c, it is advantageous to maintain the circulation of the fluid with relatively small energy. Further, the configuration in which the fluid is continuously circulated in the path c is advantageous in increasing the amount of the gas hydrate m recovered per unit time in the gas separation tank 5.

The circulation of the fluid in the path c is not limited to the continuous type as described above, and may be a batch type. In the case of the batch type, a process for lifting the gas hydrate m (hereinafter sometimes referred to as a lifting process), a process for gasifying the gas hydrate m (hereinafter sometimes referred to as a gasification process), and a discharge pipe 9 is performed separately from the step of discharging water or the like to the bottom 2 (hereinafter also referred to as a discharge step).

In the lifting process, gas hydrate m is first lifted by the riser pipe 4 and collected in the gas separation tank 5. When the gas hydrate m includes the heating mechanism 13, the heating mechanism 13 is not operated. The gas g generated when the gas hydrate m naturally melts in the riser tube 4 or the gas separation tank 5 is sequentially recovered from the gas recovery unit 7.

Since the gas g is sequentially discharged from the gas separation tank 5 to the outside, it is advantageous to keep the pressure P1 in the gas separation tank 5 relatively small. By keeping the pressure in the gas separation tank 5 small, the yield efficiency by the riser pipe 4 can be improved.

In the lifting process, the discharge pipe 9 can be opened without being closed by a valve or the like. Since the pressure P1 in the gas separation tank 5 is kept relatively small, the flow rate of the fluid flowing toward the bottom 2 is not so large even when the discharge pipe 9 is open. Further, since the specific gravity of the massive gas hydrate m is relatively smaller than that of water or the like in the gas separation tank 5, there is almost no possibility that the gas hydrate m flows out from the discharge pipe 9 to the bottom 2. Therefore, the ratio of the massive gas hydrate m in the gas separation tank 5 increases.

On the other hand, the discharge pipe 9 may be closed with a valve or the like so that the water in the gas separation tank 5 is not discharged from the discharge pipe 9 to the bottom 2.

After a predetermined amount of gas hydrate m is collected in the gas separation tank 5, a gasification step is performed. In the gasification step, the riser pipe 4 and the gas separation tank 5 are closed by a valve or the like. Thereafter, the gas hydrate m in the gas separation tank 5 is melted to generate gas g. At this time, it is desirable that the gas recovery unit 7 is closed and the pressure P1 in the gas separation tank 5 is kept relatively large. When the gas hydrate recovery apparatus 1 includes the heating mechanism 13, the heating mechanism 13 is operated to promote melting of the gas hydrate m.

In the gasification step, control for taking out the gas g from the gas separation tank 5 may be performed while maintaining the state where the pressure P1 inside the gas separation tank 5 is equal to or higher than a predetermined value. At this time, the control mechanism 12 may control the opening / closing of the gas recovery unit 7 and the amount of heat supplied from the heating mechanism 13.

The discharge process is performed in parallel with the gasification process. In the discharge process, water, earth and sand separated from the gas g in the gas separation tank 5 are sent to the bottom 2 through the discharge pipe 9. At this time, since the pressure P1 in the gas separation tank 5 is relatively high, water or the like can be efficiently discharged from the discharge pipe 9 to the bottom 2.

When the gas hydrate recovery device 1 includes the compression mechanism 17 and the reflux line 18, the pressure P 1 in the gas separation tank 5 can be increased by operating the compression mechanism 17. Thereby, water etc. can be discharged | emitted from the discharge pipe 9 to the bottom 2 in a short time.

In the gasification step and the discharge step, the gap between the gas separation tank 5 and the riser pipe 4 is closed by a valve or the like. Therefore, even if the pressure P1 in the gas separation tank 5 increases, the fluid remains in the riser pipe 4. There is no possibility of backflow toward the recovery port 4a. Since the massive gas hydrate m that floats up in the riser pipe 4 by buoyancy is not returned to the bottom 2, it is advantageous for improving the recovery efficiency of the gas hydrate m.

As illustrated in FIG. 5, the gas hydrate recovery apparatus 1 may include two gas separation tanks 5. The riser pipe 4 includes a switching valve 19 disposed at the upper end, and a branch pipe portion 4 b that communicates between the switching valve 19 and each gas separation tank 5. Similarly, the discharge pipe 9 includes a switching valve 20 disposed at the upper end, and a branch pipe portion 9 b that communicates between the switching valve 20 and each gas separation tank 5. The gas separation tank 5 connected to the riser pipe 4 and the discharge pipe 9 can be switched by the switching

valves

19 and 20. In this embodiment, the above-described batch method is adopted.

The operation of the switching valve 19 causes the one gas separation tank 5 and the riser pipe 4 to communicate with each other to perform the lifting process. The gas separation tank 5 performing the lifting process is not in communication with the discharge pipe 9 due to the operation of the switching valve 20.

After a predetermined amount of gas hydrate m has been collected in the gas separation tank 5, the communication with the riser pipe 4 is released by the operation of the switching valve 19 and the communication with the discharge pipe 9 is performed by the operation of the switching valve 20. . Thereafter, the gasification step and the discharge step are simultaneously performed in the gas separation tank 5. The pressure P 1 in the gas separation tank 5 increases and water and the like are discharged from the discharge pipe 9 to the bottom 2.

When the gasification process and the discharge process are performed in one gas separation tank 5, the lifting process is performed with the other gas separation tank 5 in communication with the riser pipe 4. That is, one of the two gas separation tanks 5 performs a lifting process, and the other performs a gasification process and a discharge process. By the operation of the switching

valves

19 and 18, the work performed in each gas separation tank 5 is switched every predetermined time.

Since the two gas separation tanks 5 are switched and used, the fluid flowing through the riser pipe 4 and the discharge pipe 9 can be continuously flowed while adopting a batch type. Once the flow of fluid inside the riser pipe 4 and the discharge pipe 9 is stopped, a relatively large amount of energy is required to flow again as the total length of the riser pipe 4 and the discharge pipe 9 increases. According to this embodiment, the efficiency of energy required for resource recovery can be improved.

Further, since the excavation work by the excavation mechanism 3 and the movement of the fluid by the riser pipe 4 and the discharge pipe 9 can be continuously performed on the bottom 2, it is advantageous for improving the efficiency of resource recovery.

The number of gas separation tanks 5 is not limited to two, and three or more gas separation tanks may be installed and switched for use. For example, the first gas separation tank 5 can perform a lifting process, the second gas separation tank 5 can perform a gasification process, and the third gas separation tank 5 can perform a discharge process. . Further, a plurality of gas separation tanks 5 may be assigned to a process that requires a relatively long working time such as a gasification process.

Although the recovery of the massive gas hydrate m has been described, the gas hydrate recovery device 1 can also be used to recover the gas g generated by melting in the vicinity of the bottom 2. For example, the gas hydrate recovery device 1 of the present invention can be applied even if the excavation mechanism 3 is configured to previously melt and collect the massive gas hydrate m in the bottom 2.

The configuration of the gas hydrate recovery device 1 of the present invention is not limited to the recovery of the gas hydrate m, but can also be used as a recovery device for water resources. For example, it can also be used for recovery of manganese nodules present in the bottom 2 and resource recovery from hydrothermal deposits.

DESCRIPTION OF SYMBOLS 1 Gas hydrate collection | recovery apparatus 2 Water bottom 3 Excavation mechanism 4 Riser pipe 4a Recovery port 4b Branch pipe part 5 Gas separation tank 5a Buffer tank 6 Structure 7 Gas recovery part 8 Gas supply line 9 Exhaust pipe 9a Exhaust port 9b Branch pipe part 10 Density measurement mechanism 11 Pressure measurement mechanism 12 Control mechanism 13 Heating mechanism 14 Gas lift mechanism 15 Pump 16 Dehumidification mechanism 17 Compression mechanism 18 Reflux line 19 Switching valve 20 Switching valve m Gas hydrate g Gas c Path ρ0 Density of fluid outside the riser pipe ρ1 Fluid density inside the riser tube ρ2 Fluid density inside the gas separation tank P1 Pressure inside the gas separation tank

Claims

A gas hydrate that extends a riser pipe from the gas separation tank toward the bottom of the water bottom, sucks up a massive gas hydrate together with the water in the bottom from the recovery port at the lower end of the riser pipe, and collects it in the gas separation tank. In the rate collection method,
A discharge pipe is extended from the gas separation tank toward the bottom of the water, and all the water in the bottom of the water collected from the recovery port is returned to the bottom of the water from the discharge port at the lower end of the discharge pipe. Gas hydrate recovery method.
2. The gas hydrate according to claim 1, wherein water at the bottom of the water is moved from the recovery port to the discharge port without flowing liquid other than water generated at the melting of the massive gas hydrate and water at the bottom of the water. Rate collection method.
A gas recovery unit for extracting the gas inside the gas separation tank to the outside is installed in the gas separation tank, and the gas recovery unit prevents the fluid from flowing into the inside from the outside of the gas separation tank, The gas hydrate recovery method according to claim 1 or 2, wherein the gas is taken out to the outside.
The gas hydrate according to claim 3, wherein the flow rate of the gas taken out through the gas recovery unit is controlled according to the density of the fluid in the riser pipe and the pressure inside the gas separation tank. Collection method.
The gas hydrate recovery according to claim 3 or 4, wherein the amount of heat supplied to the inside of the gas separation tank is controlled according to the density of the fluid in the riser pipe and the pressure inside the gas separation tank. Method.
6. The gas hydrate recovery method according to claim 3, wherein the gas taken out from the inside of the gas separation tank is pressurized and supplied to the gas separation tank.
The gas recovery state is such that the pressure inside the gas separation tank is smaller than the product of the difference in fluid density between the inside and outside of the riser pipe and the water depth at which the recovery port of the riser pipe is located. 4. Controlling at least one of a flow rate of the gas to be taken out through the unit or an amount of heat supplied to the inside of the gas separation tank or a pressure of the gas supplied to the gas separation tank by pressurization. 7. The gas hydrate recovery method according to any one of items 1 to 6.
A riser pipe that extends upward from the bottom of the water and sucks up the massive gas hydrate collected at the bottom of the water together with the water in the bottom of the water, and the massive gas hydrate that is connected to the upper end of the riser pipe and sucked up. In a gas hydrate recovery device comprising a gas separation tank into which a rate flows,
A discharge pipe extending from the gas separation tank toward the water bottom;
A gas hydrate recovery device characterized in that all of the water in the bottom of the water collected from the lower end of the riser pipe is returned to the bottom of the water from the lower end of the discharge pipe.
The gas hydrate recovery device according to claim 8, wherein the gas separation tank includes a gas recovery unit that takes out the gas inside the gas separation tank to the outside and prevents a fluid from flowing into the inside from the outside.
The density measuring mechanism for measuring the density of the fluid in the riser pipe, the pressure measuring mechanism for measuring the pressure inside the gas separation tank, and the density measuring mechanism and the value obtained from the pressure measuring mechanism The gas hydrate recovery apparatus according to claim 9, further comprising a control mechanism that controls a flow rate of the gas that passes through the gas recovery unit and is extracted to the outside.
The compression mechanism which pressurizes the gas taken out outside the gas separation tank via the gas recovery part, and the recirculation line which supplies the gas pressurized by this compression mechanism to the gas separation tank. Or the gas hydrate collection | recovery apparatus of 10.