Near-seabed methane gas collection device

Abstract

The near-seabed methane gas collection device is characterized in that a floating platform is arranged on the sea surface and carries a gas-liquid separation device, a suction pipe extending into the seabed is arranged in the middle of the floating platform, a liquid discharge pipe is arranged at the bottom of the floating platform, and a methane collection opening is formed in the top of the floating platform; a suction power device is arranged in the suction pipe, a collecting cover is arranged at the bottom end of the suction pipe, and a plurality of screen pipes can be arranged on the seabed within the horizontal projection range of the collecting cover. The suction power device can be an electric pump or a bubble pump. When the methane concentration of seawater is high, the tube bundle liquid extraction tube can be adopted to replace the collection cover. The collecting device can collect and extract high-concentration methane solution close to the seabed and seawater containing methane bubbles, collection of combustible ice methane gas under the non-excavation condition is achieved, mining of methane gas is achieved, the amount of methane reaching the sea surface is reduced, and greenhouse gas emission is reduced.

Description

Technical Field

[0001] This application belongs to the technical field of combustible ice exploitation, and particularly relates to a near-seabed methane gas collection device. Background Art

[0002] Combustible ice, also known as natural gas hydrate, has hydrocarbon molecules mainly composed of methane, so it is also called methane hydrate. One cubic meter of combustible ice can release 160 - 170 cubic meters of natural gas, which is a new energy source with great prospects. However, at present, the technical level cannot achieve commercial direct exploitation of combustible ice, and directly excavating combustible ice under the seabed may also face the risk of destroying the seabed geological balance, resulting in a burst release of methane, bringing an unbearable disaster to the marine ecosystem and the atmospheric environment. With global warming and more frequent earth activities, the release amount of combustible ice under the seabed increases. The methane gas released by combustible ice passes through the seabed sediment layer and enters the sea water. Part of it dissolves in the sea water to form a methane dissolved solution, and part rises in the form of bubbles. After the methane gas entering the sea water is consumed by the marine system, there is still residual gas reaching the shallow sea water and entering the atmosphere through sea-air exchange. This part of methane can contribute 2 - 4% to the atmospheric methane. Therefore, whether from the perspective of exploiting green energy or reducing atmospheric greenhouse gas emissions, non-invasive collection of near-seabed dissolved methane in the ocean is of great significance. Summary of the Invention

[0003] This application proposes a near-seabed methane gas collection device, which can collect and extract the methane dissolved solution formed by the methane released from seabed combustible ice and ejected to the seabed surface and the escaped methane bubbles, realizing the collection of combustible ice methane gas without excavation. It not only realizes the exploitation of methane gas but also reduces the amount of methane reaching the sea surface, reduces the methane sea-air exchange amount, and reduces greenhouse gas emissions.

[0004] To achieve the above object, this application proposes the following technical solutions:

[0005] The near-seabed methane gas collection device described in this application includes a floating platform, a gas-liquid separator, a suction pipe, a drain pipe, a collection hood, an anchor rope, an anchor, and a suction power device. The gas-liquid separator is placed on the floating platform. The top of the gas-liquid separator is provided with an air outlet, and the bottom is provided with a drain pipe. The lower end of the drain pipe extends away from the floating platform.

[0006] In a seabed area with a relatively high dissolved methane concentration, a collection hood is set within a height not greater than 20 m vertically upward from the seabed. The distance between the lower edge of the outer periphery of the collection hood and the seabed is not greater than 1 m. A main suction pipe is set at the center of the collection hood. The lower end opening of the main suction pipe communicates with the top of the collection hood, and the upper end opening of the suction pipe communicates with the middle part of the gas-liquid separator. A suction power device is set inside the suction pipe. The suction power device can pump the high-concentration methane-dissolved liquid near the seabed and the seawater containing methane bubbles to the gas-liquid separator on the floating platform on the sea surface. After gas-liquid separation, methane gas is obtained.

[0007] Further, the suction power device can be a bubble pump, an electric pump, or a combination of a bubble pump and an electric pump. The bubble pump is equipped with a methane pressurization device.

[0008] The collection hood is in an umbrella shape and is an N-sided membrane structure. Along the radial direction, a PE rod is used as a framework as a floating body, and a PVC rod or a metal part is used as a support rod at the outer edge periphery as a counterweight. A film is covered on the framework, and the film is an airtight material.

[0009] When the dissolved methane concentration near the seabed is relatively low, M fully buried sieve tubes or semi-buried sieve tubes can be set within the horizontal projection area of the collection hood. Both the fully buried sieve tube and the semi-buried sieve tube are composed of a porous tube with a piercing cone at the front end and a limiting plate. The limiting plate of the fully buried sieve tube is close to the rear end, and the limiting plate of the semi-buried sieve tube is located in the middle of the porous tube. The rear end opening of the porous tube of the fully buried sieve tube, and a transition tube is set at the rear end of the semi-buried sieve tube to communicate with the suction pipe.

[0010] When the dissolved methane concentration near the seabed is high enough, the collection hood can be not used, and a suction pipe bundle composed of multiple suction branch pipes is used to replace the suction pipe. The lower pipe orifices of the suction branch pipes are close to the seabed and are evenly distributed along the circumference with the floating platform as the center. The distance between the suction openings and the seabed in the vertical direction is not greater than 20 m, preferably 1 - 10 m.

[0011] Further, the methane pressurization device is composed of a liquid nitrogen tank, a cryogenic fluid pump, a shell-and-tube heat exchanger, a dryer, and supporting connecting pipes. The gas source of the bubble pump is high-pressure methane gas, and this high-pressure methane gas is obtained by liquefying normal-pressure methane gas with liquid nitrogen and then gasifying and pressurizing it.

[0012] Further, the normal-pressure methane gas is obtained by separating, drying, and purifying the methane gas extracted near the seabed.

[0013] Compared with the prior art, the beneficial effects of the near-seabed methane gas collection device described in this application are:

[0014] The piercing cone of the fully buried sieve tube or the semi-buried sieve tube can pierce the soft sediment covering the surface of the combustible ice under the seabed, open the channel between the seabed and the combustible ice, and enable the combustible ice to release methane gas or high-concentration methane dissolved liquid along the inner cavity of the sieve tube in a directional manner.

[0015] The collection hood can collect the methane hydrate released from the sediment layer under the seabed and dissipated into the methane gas near the seabed, and effectively isolate the high-concentration methane seawater dissolved with methane gas from the low-concentration methane seawater and oxygen-containing substances, reducing the consumption of methane gas in the seawater, thereby increasing the effective content of methane extracted from the seawater, including the number of methane bubbles and the dissolved methane concentration.

[0016] The suction power device can be a bubble pump, an electric pump, or a combination of the two. When a bubble pump is used as the power source, the introduced gas is high-pressure methane gas. While providing lift for the extracted high-concentration methane-dissolved seawater, this high-pressure methane gas also provides a large number of bubble nuclei, prompting more dissolved methane gas in the seawater to form bubbles and release, forming a greater lift, making the entire extraction process self-consistent, achieving twice the result with half the effort, and greatly reducing the extraction energy consumption; at the same time, using methane gas as the power gas does not introduce impurity gases, ensuring the high purity of methane gas.

[0017] The wire mesh demister in the gas-liquid separator can reduce the liquid carry-over of the product methane gas, and the tetrafluoro Pall rings expand the surface area of the gas-liquid mixture to be separated, improving the separation efficiency.

[0018] The drain pipe at the lower end of the gas-liquid separator transports the separated low-concentration seawater to a farther sea area, dispersing the residual methane gas as much as possible.

[0019] The near-seabed methane gas collection device can collect and extract the methane-dissolved liquid formed by the methane released from the methane hydrate and ejected to the seabed surface and dissolved in the seawater, as well as the escaped methane bubbles, realizing the collection of methane hydrate methane gas without excavation, which not only realizes the extraction of methane gas but also reduces the amount of methane reaching the sea surface, reduces the methane-air exchange amount in the sea, and reduces greenhouse gas emissions. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the near-seabed methane gas collection device described in this application, showing the positional relationship between the device and the sea level and the seabed, and annotating the names and flow directions of relevant fluids;

[0021] Figure 2 It is a schematic diagram of the near-seabed methane gas collection device described in this application when the suction power device uses a bubble pump, and a methane pressurization device is provided;

[0022] Figure 3 It is a schematic diagram of the methane pressurization device described in this application;

[0023] Figure 4 It is a schematic diagram of the collection hood described in this application;

[0024] Figure 5 It is an application schematic diagram when using a fully buried screen pipe in this application;

[0025] Figure 6 Schematic diagram of the application when using a semi-buried screen pipe in this application;

[0026] Figure 7 Schematic diagram of the full-buried screen pipe and semi-buried screen pipe in this application;

[0027] Figure 8 Schematic diagram of using a suction pipe bundle to replace the collection hood in this application.

[0028] The markings in the above-mentioned drawings are explained as follows:

[0029] 1 - Gas-liquid separator, 13 - Drain pipe, 2 - Floating platform, 21 - Anchor rope, 22 - Anchor, 3 - Suction pipe, 4 - Suction power device, 5 - Collection hood, 51 - Membrane, 52 - Skeleton, 53 - Support rod, 6 - Full-buried screen pipe, 61 - Porous pipe, 62 - Limiting plate, 63 - Penetrating cone, 7 - Transition pipe, 8 - Suction pipe bundle, 81 - Suction branch pipe, 9 - Methane booster device, 91 - Liquid nitrogen tank, 92 - Cryogenic fluid pump, 93 - Shell-and-tube heat exchanger, 10 - Semi-buried screen pipe.

[0030] It should be noted that for the convenience of description and clear expression, the directions or orientations such as "up, down, left, right, front, back, center" in this application are all referenced based on the above-mentioned drawings, and are not limited thereby. Detailed implementation manners

[0031] Combined with the above drawings, the detailed implementation manners of this application are described as follows:

[0032] Compare Figure 1 , select a sea area with exploitable value of combustible ice reserves under the explored seabed, set a floating platform 2 on the sea surface as the carrier and working platform for equipment such as the gas-liquid separator 1, in the seabed area with a relatively high methane dissolution concentration, set a collection hood 5 within a height not greater than 20 m vertically upward from the seabed, the distance between the lower edge of the outer circumference of the collection hood 5 and the seabed is not greater than 1 m, a suction pipe 3 is arranged above the collection hood 5, the lower port of the suction pipe 3 is communicated with the center of the top of the collection hood 5, the upper port of the suction pipe 3 is communicated with the middle part of the gas-liquid separator 1, and a suction power device 4 is arranged inside the suction pipe 3.

[0033] The gas-liquid separator 1 is placed on the floating platform 2, an air outlet is arranged at the top of the inner cavity of the gas-liquid separator 1, a wire mesh demister is arranged in the upper middle part, a liquid storage space is arranged at the lower part, tetrafluoro packing rings are arranged to float on the liquid surface, and a drain pipe 13 is arranged at the bottom, and the lower end of the drain pipe 13 extends in a direction away from the floating platform 2.

[0034] Compare Figure 2, the suction power device 4 can be a bubble pump, an electric pump, or a combination of a bubble pump and an electric pump. The bubble pump is equipped with a methane pressurization device (9). The gas source of the bubble pump is high-pressure methane gas, which is obtained by liquefying normal-pressure methane gas with liquid nitrogen and then gasifying and pressurizing it. The normal-pressure methane gas is obtained by separating, drying, and purifying the methane gas extracted near the seabed.

[0035] Control Figure 3 , the methane pressurization device 9 is composed of a liquid nitrogen tank 91, a cryogenic fluid pump 92, a shell-and-tube heat exchanger 93, and a dryer 94. The normal-pressure methane gas collected from the seabed and separated by the gas-liquid separator 1 is sent to the coil of the liquid nitrogen tank 91 after being processed by the dryer 94. The methane gas in the pipe exchanges heat with the liquid nitrogen outside the pipe and condenses into liquid methane, which is sent out by the cryogenic fluid pump 92. It exchanges heat with the normal-pressure methane gas in the shell-and-tube heat exchanger 93, absorbs heat and evaporates to form high-pressure methane gas, and then is transported to the bubble pump as the gas source. In the shell-and-tube heat exchanger 93, the normal-temperature methane gas is precooled by the liquid methane, realizing cold recovery.

[0036] Control Figure 4 , the N-sided collection cover 5 is composed of a membrane 51, a skeleton 52, and a support rod 53, forming an umbrella shape. The materials of the membrane 51 and the skeleton 52 are preferably PE and are used as floating bodies. The material of the support rod 53 is preferably PVC or 304 pipe and is used as a counterweight. The collection cover 5 is first laid flat on the sea surface and then slowly sinks to the seabed under the guidance of a heavy hammer. Since the density of the materials of the membrane 51 and the skeleton 52 is less than that of seawater, while the density of the outer peripheral support rod 53 is greater than that of seawater, the collection cover 5 will form an umbrella-shaped structure with a high center and low surrounding on the seabed, accumulating methane gas and seawater with a high methane concentration. In the implementation case, N = 24 is taken.

[0037] Control Figure 5 , Figure 6 , when the dissolved methane concentration near the seabed is low, multiple fully buried sieve tubes 6 or semi-buried sieve tubes 10 can be arranged within the horizontal projection area of the collection cover 5. As shown in Figure 7 , a is a fully buried sieve tube 6, b is a semi-buried sieve tube 10. Both the fully buried sieve tube 6 and the semi-buried sieve tube 10 are composed of a porous tube 61 with a piercing cone 63 at the front end and a limiting plate 62. The limiting plate 62 of the fully buried sieve tube 6 is close to the rear end, and the limiting plate 62 of the semi-buried sieve tube 10 is located in the middle of the porous tube 61. The rear end of the porous tube 61 of the fully buried sieve tube 6 is open, and the rear end of the semi-buried sieve tube 10 is as shown in Figure 7 , provided with a transition pipe 7 communicating with the suction pipe 3, which can directly transport the methane gas and high-concentration methane dissolved liquid released by the seabed combustible ice to the suction pipe 3; the piercing cone 63 of the fully buried sieve tube 6 or the semi-buried sieve tube 10 can pierce the soft sediment covering the surface of the seabed combustible ice to form a channel, connecting the seabed with the combustible ice, so that the combustible ice can release methane gas or high-concentration methane dissolved liquid along the inner cavity of the sieve tube.

[0038] ControlFigure 8 , when the dissolved methane concentration near the seabed is high, the suction pipe bundle 8 can be used to replace the collection hood 5 and the suction pipe 3. The suction pipe bundle 8 is composed of multiple suction branch pipes 81. In the figure, an example is 4. A set of suction power devices 4 are arranged in each suction branch pipe 81. The lower pipe orifices of the suction branch pipes 81 are evenly distributed along the circumference with the floating platform 2 as the center. The horizontal suction spacing between the lower pipe orifices of the suction branch pipes 81 is not less than 50 meters, and the distance between the suction orifices and the seabed in the vertical direction is not greater than 20 m, preferably 1 - 10 m.

Claims

1. A near-seabed methane gas collection device, characterized in that: It includes a floating platform (2), a gas-liquid separator (1), a suction pipe (3), a drain pipe (13), a collection hood (5), an anchor rope (21), an anchor (22) and a suction power device (4). In the seabed area with a relatively high dissolved methane concentration, a collection hood (5) is arranged within a height not greater than 20 m vertically upward from the seabed. The distance between the lower edge of the outer periphery of the collection hood (5) and the seabed is not greater than 1 m. A suction pipe (3) is arranged at the center of the collection hood (5). The lower end opening of the suction pipe (3) is communicated with the top of the collection hood (5), and the upper end of the suction pipe (3) is communicated with the middle part of the gas-liquid separator (1). A suction power device (4) is arranged inside the suction pipe (3); the gas-liquid separator (1) is placed on the floating platform (2). An air outlet is arranged at the top of the inner cavity of the gas-liquid separator (1), and a drain pipe (13) is arranged at the bottom. The lower end of the drain pipe (13) extends in a direction away from the floating platform (2).

2. The near-seabed methane gas collection device according to claim 1, characterized in that: The suction power device (4) can be a bubble pump, an electric pump or a combination of a bubble pump and an electric pump. The bubble pump is equipped with a methane pressurization device (9), and the methane pressurization device (9) is connected between the bubble pump and the air outlet of the gas-liquid separator (1) through a connecting pipe.

3. The near-seabed methane gas collection device according to claim 1, characterized in that: The collection hood (5) is in an umbrella shape and is an N-sided membrane structure. Its radial direction is framed by a PE rod (52), and the outer edge is supported by a PVC rod or a metal part as a support rod (53). A film (51) is covered on it, and the film (51) is made of an airtight material.

4. The near-seabed methane gas collection device according to claim 1, wherein: When the dissolved methane concentration near the seabed is relatively low, M fully buried sieve pipes (6) or semi-buried sieve pipes (10) can be arranged within the horizontal projection area of the collection hood (5). Both the fully buried sieve pipe (6) and the semi-buried sieve pipe (10) are composed of a porous pipe (61) with a piercing cone (63) at the front end and a limit plate (62). The limit plate (62) of the fully buried sieve pipe (6) is close to the rear end, and the limit plate (62) of the semi-buried sieve pipe (10) is located in the middle of the porous pipe (61). The rear end opening of the porous pipe (61) of the fully buried sieve pipe (6) is open, and a transition pipe (7) is arranged at the rear end of the semi-buried sieve pipe (10) and is communicated with the suction pipe (3).

5. The near-seabed methane gas collection device according to claim 1, characterized in that: When the dissolved methane concentration near the seabed is high, the collection hood (5) can be not used, and a suction pipe bundle (8) composed of multiple suction branch pipes (81) is used to replace the suction pipe (3). The lower pipe orifices of the suction branch pipes (81) are close to the seabed and are evenly distributed along the circumference with the floating platform (2) as the center.

6. The near-seabed methane gas collection device according to claim 2, wherein: The methane pressurization device (9) is composed of a liquid nitrogen tank (91), a cryogenic fluid pump (92), a shell-and-tube heat exchanger (93), a dryer (94) and supporting connecting pipes. The gas source of the bubble pump is high-pressure methane gas, and this high-pressure methane gas is obtained by liquefying atmospheric methane gas with liquid nitrogen and then gasifying and pressurizing it.

7. The near-seabed methane gas collection device according to claim 6, characterized in that: The atmospheric methane gas is obtained by separating, drying and purifying the methane gas extracted near the seabed.

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