Detailed Description
Hereinafter, a gas hydrate recovery system and a gas hydrate recovery method according to the present invention will be described based on the illustrated embodiments.
As illustrated in fig. 1, a gas hydrate recovery system 1 according to the present invention includes an excavation mechanism 3 and an elevator pipe 4, the excavation mechanism 3 excavates a surface methane gas hydrate m existing on a water bottom 2, which is a bottom of a sea or a lake, to collect a massive gas hydrate m, and the elevator pipe 4 transports the collected gas hydrate m from the vicinity of the water bottom 2 to the water.
The excavating mechanism 3 can be constituted by, for example, heavy equipment or a drill bit in water. The excavation mechanism 3 is not limited to this configuration, and may be configured to excavate the water bottom 2 and send the massive gas hydrate m to the lower end of the ascending/descending pipe 4.
The elevator tube 4 may be formed of, for example, a cylindrical body extending in the vertical direction. The upper end of the elevator tube 4 is connected to the water surface equipment 5. The water craft 5 can be constituted by a ship or a floating body structure, for example. The configuration of the water surface facility 5 is not limited to this, and may be configured to collect the lump gas hydrate m transported by the ascending/descending pipe 4.
The water surface facility 5 includes a discharge mechanism 6, and the discharge mechanism 6 separates water, sand, and the like collected together with the gas hydrate m and discharges the sand, and the like to the vicinity of the water bottom 2. The discharge mechanism 6 can be constituted by a conveying pipe or the like, for example. The discharge mechanism 6 is not limited to this configuration, and may be configured to discharge unnecessary materials such as water and sand from the water surface equipment 5. The discharge means 6 is preferably configured to discharge unnecessary materials such as sand and soil to the vicinity of the water bottom 2 without spreading the unnecessary materials near the water surface.
As illustrated in fig. 2, the water surface facility 5 includes a vaporizing mechanism 7, a compressing mechanism 8, and a buffer tank 9, the vaporizing mechanism 7 is connected to an upper end of the elevating pipe 4 to vaporize the collected massive gas hydrate m, the compressing mechanism 8 compresses the gas g generated in the vaporizing mechanism 7 to increase the pressure, and the buffer tank 9 temporarily stores the gas g compressed by the compressing mechanism 8.
The compression mechanism 8 can be constituted by a turbo compressor, for example. The configuration of the compression mechanism 8 is not limited to this, and may have a function of compressing the gas g. The compression mechanism 8 may be constituted by, for example, a reciprocating compressor, a swash plate compressor, a diaphragm compressor, a single screw compressor, a twin screw compressor, a scroll compressor, a rotary compressor, or the like.
A gas lift mechanism 10 is disposed between the buffer tank 9 and the elevator tube 4, and the gas lift mechanism 10 supplies the compressed gas g from the buffer tank 9 to the elevator tube 4. The gas lift mechanism 10 includes a supply pipe 11, and the supply pipe 11 connects an inlet side end portion 11a to the buffer tank 9 and an outlet side end portion 11b to a middle portion of the ascending/descending tube 4.
The lump gas hydrate m recovered from the riser 4 to the water surface facility 5 is melted by the vaporizing mechanism 7 and separated into gas g and water. The vaporizing unit 7 includes a vessel 12 and a heater 13, the vessel 12 stores gas hydrate m and water associated therewith, and the heater 13 heats the inside of the vessel 12.
The structure of the gasification mechanism 7 is not limited to this, and may be a structure that melts the gas hydrate m. For example, the heat exchanger may be configured to circulate water having a high temperature near the water as a heat medium around the container 12 to heat the inside.
The vaporizing unit 7 may be constituted only by the container 12, and the pressure in the container 12 may be controlled to be lower than the pressure in the vicinity of the water bottom 2 by an opening/closing valve or the like. The gasification means 7 can melt the gas hydrate m by reducing the pressure in the vessel 12, and separate the gas hydrate m into gas g and water. That is, the heater 13 is not an essential feature of the present invention.
The water, sand, soil, and the like separated by the gasifying means 7 are discharged to the outside through the discharging means 6 constituted by a conveying pipe or the like communicating with the container 12. The gas g separated by the vaporizing unit 7 is sent to the compressing unit 8 and pressurized. The pressurized gas g is sent to the buffer tank 9. Most of the high-pressure gas g in the buffer tank 9 is sent to a pipeline for consuming and supplying the gas g from the buffer tank 9, a tank for consuming and transporting the gas g from the buffer tank 9, and the like, and a part of the gas g is sent to the gas lift mechanism 10.
The pressure of the gas g pressurized by the compression mechanism 8 can be set according to the depth of the water in the outlet-side end 11b of the supply pipe 11 connected to the ascending/descending pipe 4. For example, the compression mechanism 8 pressurizes the gas g to 5MPa or more when the water depth of the outlet-side end 11b is 500m, to 10MPa or more when the water depth is 1000m, and to about 15MPa or more when the water depth is 1500 m. By setting the pressure of the gas g higher than the water pressure of the water flowing in the elevator tube 4 in the vicinity of the outlet-side end 11b, the gas lift mechanism 10 can efficiently supply the gas g into the elevator tube 4.
In the recovery system described in patent document 1, the following structure is adopted: the gas g is pressurized by a blowing mechanism provided at the outlet end 11b and blown into the elevator tube 4. In contrast, in the present invention, since the gas g pressurized by the marine facility 5 is sent to the elevator tube 4, it is not necessary to provide a blowing mechanism for pressurizing the gas g at the outlet-side end portion 11 b. Since there is no complicated device such as a blowing mechanism provided at the outlet-side end portion 11b, there is no problem in the present invention that these devices are clogged by rehydration.
Since the temperature of the gas g compressed by the compression mechanism 8 increases with the compression, it is difficult to rehydrate the gas g when the gas g passes through the supply pipe 11 of the gas lift mechanism 10. For example, to rehydrate a gas g of about 5MPa, it is necessary to cool it to a temperature lower than about 5 ℃ together with the water associated with the gas g.
The temperature of the gas g compressed to about 5MPa by the compression mechanism 8 rises to about 80 ℃, and therefore the possibility that the gas g passes through the supply pipe 11 at a temperature lower than about 5 ℃ is very low. That is, the possibility of rehydration of the gas g in the supply pipe 11 can be reduced. When the gas g is compressed to a high pressure higher than 5MPa, the temperature of the gas g is further increased, and therefore, the possibility of rehydration of the gas g in the supply pipe 11 can be further reduced.
Since the gas lift mechanism 10 is less likely to be clogged by rehydration, the stability of operation can be improved. Since the failure of the gas lift mechanism 10 hardly occurs, the gas hydrate recovery system 1 can be continuously operated for a long time. Since the recovery amount per unit time of the gas hydrate m increases, cost reduction in recovering the gas hydrate m is advantageous.
In the present embodiment, the supply pipe 11 constituting the gas lift mechanism 10 is connected to the middle portion of the elevator tube 4, but the supply pipe 11 may be connected to a position lower than the middle portion in the extending direction of the elevator tube 4 or may be connected to a position upper than the middle portion. When the elevator tube 4 is bent in water, it is desirable that the supply tube 11 is connected to the vicinity of the position where the flow velocity in the elevator tube 4 is decreased. The gas lift mechanism 10 may be configured by a plurality of supply pipes 11, and configured to supply the gas g into the elevator tube 4 from a plurality of locations.
Since the gas hydrate m moves inside the elevator tube 4, the gas hydrate m is cooled by water. Therefore, the temperature of the water on the outer side is higher than that on the inner side of the elevator tube 4. Since the supply pipe 11 is disposed outside the elevator tube 4, the rate of cooling of the gas g passing through the supply pipe 11 by the surrounding water can be suppressed. When the gas g is sufficiently heated by the compression mechanism 8, the supply pipe 11 may be disposed inside the elevator tube 4.
In order to maintain the temperature of the gas g passing through the supply pipe 11, a heat insulator may be disposed in the supply pipe 11. This is advantageous in suppressing the possibility of rehydration occurring in the supply pipe 11. Since the gas g having a relatively high temperature can be supplied into the elevator tube 4 by disposing the heat insulator, the melting of the gas hydrate m in the elevator tube 4 can be promoted. Since bubbles are generated along with the melting of the gas hydrate m, the difference in specific gravity in the ascending/descending tube 4 can be increased, and the velocity of the ascending flow can be increased.
A valve 14 for controlling the supply amount of the gas g may be provided in a middle portion of the supply pipe 11. Since the flow rate of the gas g supplied from the supply pipe 11 into the elevator tube 4 can be controlled by the valve 14, the velocity of the rising flow generated in the elevator tube 4 can be controlled.
When the flow velocity is increased, the conveyance time for conveying the massive gas hydrate m to the water surface facility 5 can be shortened. When the flow velocity is reduced, the sand in the elevator pipe 4 is likely to settle, and therefore the amount of the sand conveyed to the water surface equipment 5 by the ascending flow can be suppressed. That is, by controlling the velocity of the upward flow, the recovery rate of the massive gas hydrate m of the water plant 5 can be adjusted, and the amount of the sandy soil recovered along with the gas hydrate m can be adjusted.
The valve 14 may be an on-off valve that closes or opens the supply pipe 11 by opening or closing, or a flow rate regulating valve that precisely controls the flow rate of the gas g by adjusting the opening degree.
The valve 14 is preferably provided in the vicinity of the inlet-side end portion 11a of the supply pipe 11. According to this configuration, it is possible to avoid a problem that the valve 14 cannot be opened or closed due to the fact that the rehydration is frozen due to a high temperature of the gas g passing through the valve 14. Further, when the valve 14 fails, the valve 14 can be replaced without pulling up the entire supply pipe 11 to the marine installation 5, which is advantageous in improving the operation efficiency of the gas hydrate recovery system 1.
As illustrated by a dotted line in fig. 2, a dehumidifying mechanism 15 may be provided between the vaporizing mechanism 7 and the compressing mechanism 8. The dehumidifying mechanism 15 has a function of removing moisture from the passing gas g. The dehumidifying means 15 may be constituted by, for example, a compression type dehumidifier that cools the gas g passing therethrough to condense water and dehumidifies the gas g, and a desiccant type dehumidifier that adsorbs water in the gas g by a desiccant such as zeolite. The structure of the dehumidifying mechanism 15 is not limited to this, and may be another structure as long as it has a function of removing moisture from the gas g.
Since the moisture contained in the gas g can be reduced by the dehumidifying means 15, the gas g can be inhibited from being rehydrated even if the gas g is cooled in the supply pipe 11. Even if the conditions for generating gas hydrate such as temperature and pressure are satisfied, gas g is not rehydrated unless water is bonded to gas g. This is advantageous in improving the stability of the operation of the gas lift mechanism 10.
As illustrated in fig. 3, the compression mechanism 8 may be configured by a multistage compression mechanism 8 including a first compression unit 16, a cooling unit 17, and a second compression unit 18, the first compression unit 16 compressing the gas g supplied from the gasification mechanism 7, the cooling unit 17 cooling the gas g compressed by the first compression unit 16 and having an increased temperature, and the second compression unit 18 further compressing the gas g cooled by the cooling unit 17.
The cooling unit 17 includes a jacket 17a through which a refrigerant circulates and a passage 17b through which the gas g passes, and has a structure for cooling the gas g passing through the passage 17 b. The jacket 17a may be disposed outside the passage 17b through which the gas g passes, or may be disposed inside the passage 17 b. The structure of the cooling unit 17 is not limited to this, and the gas g that has passed through may be cooled. The cooling portion 17 may be constituted by, for example, a peltier element.
Since the cooling unit 17 cools the gas g compressed by the first compression unit 16 and having an increased temperature, the volume expansion of the gas g accompanying the increase in temperature can be suppressed. This can improve the compression efficiency of the gas g in the second compression part 18. Since the gas g can be compressed to a higher pressure by providing the compression mechanism 8 in a multistage manner, the gas g can be supplied to a position deeper in water by the gas lift mechanism 10.
The compression mechanism 8 includes a temperature monitoring unit 19 and a control unit 20, the temperature monitoring unit 19 monitors the temperature of the gas g compressed by the second compression unit 18 and supplied to the gas lift mechanism 10 via the buffer tank 9, and the control unit 20 receives a signal from the temperature monitoring unit 19. In the figure, signal lines are shown by broken lines.
The temperature monitoring unit 19 may be constituted by a temperature sensor provided in a passage between the compression mechanism 8 and the surge tank 9, for example. The position where the temperature sensor is installed is not limited to this, and the temperature sensor may be disposed in the vicinity of the inlet end 11a, the vicinity of the outlet end 11b, or the buffer tank 9 of the supply pipe 11 constituting the gas lift mechanism 10. The temperature monitoring unit 19 may be constituted by a plurality of temperature sensors.
The control unit 20 controls the flow rate of the refrigerant supplied to the cooling unit 17 based on a signal from the temperature monitoring unit 19. Specifically, the controller 20 controls a pump 21 that supplies the refrigerant to the jacket 17a, for example. The controller 20 controls the flow rate of the refrigerant to be decreased as the temperature of the gas g measured by the temperature sensor of the temperature monitoring unit 19 is decreased. For example, the control unit 20 may control the temperature of the gas g measured by the temperature sensor to be proportional to the flow rate of the refrigerant in the cooling unit 17.
The control of the control unit 20 is not limited to this, and the control of stopping the circulation of the refrigerant in the cooling unit 17 may be performed when the temperature of the gas g measured by the temperature monitoring unit 19 is lower than a predetermined temperature, for example, 100 ℃. The control unit 20 may be configured to control the cooling performance of the cooling unit 17 in a state where the gas g passing through the supply pipe 11 is not at a temperature equal to or lower than the rehydratable temperature.
According to this configuration, the compression mechanism 8 can compress the gas g in multiple stages with high efficiency, and can suppress rehydration of the gas g due to excessive cooling.
Since the temperature of the gas g is the lowest at the outlet-side end 11b of the supply pipe 11, it is desirable to measure the temperature of the gas g at the outlet-side end 11b, but the temperature of the gas g may be measured at the inlet-side end 11 a. When the temperature monitoring unit 19 measures the temperature of the gas g at the inlet end 11a of the supply pipe 11, it is desirable to estimate the temperature of the gas g at the outlet end 11b based on the depth of water at the outlet end 11 b.
When the temperature monitoring unit 19 is configured by a plurality of temperature sensors, the temperature of the gas g can be monitored at a plurality of locations, and therefore, it is advantageous in preventing rehydration. Even if some of the temperature sensors fail, the operation of the gas hydrate recovery system 1 can be continued by using the other temperature sensors, and therefore, it is advantageous in terms of suppressing the recovery cost of the gas hydrate.
Description of the reference numerals
1 gas hydrate recovery system
2 water bottom
3 digging mechanism
4 lifting pipe
5 Water equipment
6 discharge mechanism
7 gasification mechanism
8 compression mechanism
9 buffer tank
10 gas lift mechanism
11 supply pipe
11a inlet side end portion
11b outlet side end portion
12 container
13 heating device
14 valve
15 dehumidifying mechanism
16 first compression part
17 cooling part
17a jacket
17b path
18 second compression part
19 temperature monitoring part
20 control part
21 pump
m gas hydrate
g of gas.