JP7330463B2 - Gas transportation method and gas transportation system - Google Patents

Description

The present invention relates to a gas transport method and a gas transport system for transporting gas recovered from a gas-liquid mixture.

When the gas recovered from the gas-liquid mixture is transported through the transport pipe, gas transport may be hindered if gas hydrate is generated in the transport pipe and the pressure loss increases. In Patent Documents 1 and 2 below, a hydrate inhibitor is used to suppress the generation of gas hydrate.

JP-A-2003-336084 Japanese Patent Application Laid-Open No. 2000-356088

When a hydrate inhibitor is used as in Patent Documents 1 and 2, installation of a hydrate inhibitor addition device and recovery device is costly. It is required to prevent the increase of pressure loss due to gas hydrate and to transport gas stably by a cheaper method.

The present invention has been made in view of the circumstances described above, and provides a gas transportation method and a gas transportation system capable of stably transporting gas while preventing an increase in pressure loss due to gas hydrate. for the purpose.

In order to solve the above problems, the present invention proposes the following means.
A gas transport method according to the present invention is a gas transport method for transporting a gas recovered from a gas-liquid mixture, wherein a fluid containing the gas as a main component is separated from the gas-liquid mixture by a separation device. and a second step of transporting the fluid separated by the separation device through a transport pipe, wherein at least part of the droplets contained in the fluid is converted to gas hydrate in the second step. A management section is provided in the transport pipe, and in a region of the transport pipe located downstream with respect to the management section, the surface of the droplet is covered with the gas hydrate, or the entire droplet is covered. It is characterized by using the gas hydrate.

A gas transportation system according to the present invention is a gas transportation system for transporting a gas recovered from a gas-liquid mixture, comprising: a separation device for separating a fluid containing the gas as a main component from the gas-liquid mixture; a transport pipe for transporting the fluid separated by the separation device, wherein the transport pipe is provided with a management section in which at least part of droplets contained in the fluid is gas hydrate, and the transport pipe Among them, in a region located downstream with respect to the management section, the surface of the droplet is covered with the gas hydrate, or the entire droplet is made of the gas hydrate. do.

A management section in which at least part of the droplets contained in the fluid is gas hydrate is provided in the transport pipe, and in a region of the transportation pipe located downstream of the management section, the surface of the droplet is gas hydrate. Either the droplet is covered by the rate, or the entire droplet is gas hydrate. As a result, droplets (free water) that are not covered with gas hydrate can be eliminated or minimized in the area of the transport pipe located downstream of the management section. Here, gas hydrate is present in the fluid, but if droplets (free water) not covered by the gas hydrate are not present, the gas hydrate adheres to the inner surface of the transport tube. and formation of gas hydrate agglomerations can be prevented. Therefore, it is possible to prevent adhesion and agglomeration of gas hydrate in a region of the transport pipe located downstream of the management section, and to prevent an increase in pressure loss due to gas hydrate. As a result, the gas recovered from the gas-liquid mixture can be stably transported.

Moreover, the gas transportation system according to the present invention may further include a temperature control device that makes the temperature of the management section relatively lower than the temperature of the separation device.

Moreover, in the gas transport system according to the present invention, the temperature control device may be a heating device that heats the separation device.

Moreover, the gas transportation system which concerns on this invention WHEREIN: The cooling device which cools the said management area may be sufficient as the said temperature control apparatus.

Moreover, in the gas transportation system according to the present invention, the management section may include a large-diameter portion having an inner diameter larger than that of other portions of the transportation pipe.

Further, in the gas transportation system according to the present invention, the management section may be provided with a flow velocity adjusting member that narrows the cross-sectional area of the flow path in the management section to increase the flow velocity of the fluid in the management section.

Moreover, in the gas transportation system according to the present invention, a water-repellent layer may be provided on the inner surface of the management section.

Moreover, the gas transportation system according to the present invention may further include a removal device provided in the management section for removing methane hydrate adhering to the inner surface of the management section.

Further, in the gas transportation system according to the present invention, the transportation pipe includes a main pipe and a management pipe connected to the main pipe and forming the management section, and the management pipe communicates with the main pipe. A plurality of management pipes may be provided switchably, and the transport pipe may be formed by connecting one of the plurality of management pipes to the main pipe.

According to the present invention, an increase in pressure loss due to gas hydrate can be prevented, and gas can be stably transported.

1 is an overall view of a gas transportation system according to a first embodiment of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is an enlarged view which shows the principal part of the gas transportation system which concerns on 1st Embodiment of this invention. It is a figure which shows the transport pipe which concerns on 1st Embodiment of this invention. 4 is a graph showing a phase equilibrium curve of methane gas; FIG. 4 is a diagram for explaining an increase in pressure loss due to adhesion of methane hydrate to the inner surface of a transport pipe; FIG. 4 is a diagram for explaining an increase in pressure loss due to agglomeration of methane hydrate; FIG. 4 is a diagram for explaining the relationship between the contact angle θ with water and wettability; It is a figure which shows the management piping which concerns on 2nd Embodiment of this invention. It is a figure which shows the management piping which concerns on 3rd Embodiment of this invention. (a) cross-sectional view of the management pipe and first main pipe according to the fourth embodiment of the present invention, (b) (a) AA line sectional view, and (c) (a) BB line It is a cross-sectional view. FIG. 10A is a lateral cross-sectional view of a management pipe and a first main pipe according to a first modification of the fourth embodiment of the present invention, and FIG. FIG. 10A is a cross-sectional view of a management pipe and a first main pipe according to a second modification of the fourth embodiment of the present invention, and FIG. It is the (a) top view of the transport pipe which concerns on 5th Embodiment of this invention, and (b) It is a side view.

(First embodiment)
A gas transport system 100 according to a first embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. FIG. 1 is an overall view of a gas transportation system 100. As shown in FIG. FIG. 2 is an enlarged view showing the essential parts of the gas transportation system 100. As shown in FIG. FIG. 3 is a diagram showing the transport pipe 2 of the gas transport system 100. As shown in FIG.

The gas transportation system 100 according to this embodiment is used, for example, in methane hydrate development to transport methane gas (gas) produced from a production well E2 dug on the seabed E1 to a land facility 200.

As shown in FIG. 2, a production well E2 is drilled downward from the seabed E1 to reach a methane hydrate layer E3. The depth of the seabed E1 is, for example, about 1000 m, and the pressure near the seabed E1 is, for example, about 10 MPa. The depth of the production well E2 is, for example, about 300 m, and the pressure near the bottom of the production well E2 is, for example, about 13 MPa.
The production fluid A1 is produced from the production well E2 by decomposing the methane hydrate (gas hydrate) in the methane hydrate layer E3 by a decompression method. The production fluid A1 is a gas-liquid mixture mainly composed of methane gas (gas) and water (liquid).

The gas transportation system 100 includes a separation device 1 that separates a separation fluid (fluid) A2 mainly composed of methane gas (gas) from a production fluid (gas-liquid mixture) A1 produced from a production well E2; A transportation pipe 2 that connects with the land facility 200 is provided.

The separation device 1 includes a separator 10 , a drain pipe 11 and a pump 12 . The separation device 1 is a submarine facility arranged on the seabed E1.

The production fluid A1 flows into the separator 10 through the inflow pipe 13 . The separator 10 separates the production fluid A1 into a separation fluid A2 containing methane gas as a main component and water A3. The separation fluid A2 is discharged to the transport pipe 2 from a discharge port provided in the upper part of the separator 10. As shown in FIG.

The separator 10 is provided with a heating device (temperature control device) (not shown) for heating the separator 10 . By heating the separators 10 with the heating device, the temperature of the separators 10 is relatively high with respect to the temperature of the management pipe 21 of the transport pipe 2, which will be described later. By heating the separator 10 with the heating device, generation of methane hydrate in the separator 10 can be prevented.
For example, when the pressure of the production fluid A1 flowing into the separator 10 from the production well E2 is about 4 MPaA or more, if the temperature inside the separator 10 is about 4° C., methane hydrate may be generated. There is By raising the temperature inside the separator 10 to a temperature higher than the temperature at which methane hydrate is produced by the heating device, the production of methane hydrate inside the separator 10 can be prevented. Note that the separator 10 may be provided with a heat insulating material (heat retaining device) for keeping the temperature inside the separator 10 raised.

By separating the production fluid A1 into the separation fluid A2 and water A3 by the separator 10, the amount of water contained in the separation fluid A2 can be reduced. However, droplets (water) that could not be completely separated by the separator 10 also exist in the separated fluid A2 together with the methane gas.
It is preferable that the size of the droplets contained in the separation fluid A2 be reduced by the separator 10 (for example, droplets having a maximum particle size of about several tens of μm).
For example, when a gravity separation type separator provided with a baffle is used as the separator 10, the size of the droplets contained in the separation fluid A2 depends on the flow velocity of the airflow in which the separation fluid A2 moves toward the outlet in the separator 10. do. Specifically, the faster the airflow, the larger the droplets, but the slower the airflow, the smaller the droplets. Therefore, the particle diameter of the droplets can be reduced by adjusting (reducing) the flow velocity of the airflow in which the separation fluid A2 is directed to the outlet.
Alternatively, when a mechanism is used as the separator 10 to remove water masses from the production fluid A1 by swirl flow and then remove water droplets from the production fluid A1 by centrifugal separation, the design of the centrifugal separation mechanism allows the maximum droplet size Diameter can be controlled.

A drain pipe 11 is connected to the bottom of the separator 10 . A pump 12 is connected to the drain pipe 11 . The water A3 separated from the production fluid A1 is discharged to the outside of the separation device 1 via the drain pipe 11 and the pump 12 .

One end of the transport pipe 2 is connected to the outlet of the separator 10 . The separation fluid A2 discharged from the separator 10 flows into the transport pipe 2. As shown in FIG. The other end of the transport pipe 2 is connected to land facilities 200 . The methane gas in the separation fluid A2 is transported to the land facility 200 through the transport pipe 2.

In this embodiment, the transport pipe 2 is provided with a management section in which at least part of the liquid droplets (water) contained in the separation fluid A2 is gas hydrate. That is, the transport pipe 2 includes a management pipe 21 forming a management section, a first main pipe 22 connecting the separator 10 and the management pipe 21, and a second main pipe 23 connecting the management pipe 21 and the land facility 200. and

The separation fluid A2 discharged from the separator 10 first flows into the first main tube 22 . In order to prevent the formation of methane hydrate inside the first main pipe 22, the first main pipe 22 is covered with a heat insulating material (heat retaining device). As a result, the separated fluid A2 is maintained in a temperature-increased state by the heating device of the separator 10 (that is, while the temperature of the separated fluid A2 is maintained at or above the temperature at which methane hydrate is generated), It flows through the tube 22 . The separation fluid A2 flows into the management pipe 21 from the first main pipe 22 .
A heating device that heats the first main tube 22 may be provided. In this case, for example, a double pipe is used as the first main pipe 22, and the first main pipe 22 is heated by flowing warm water through the outer pipe or the inner pipe.

In this embodiment, in the management pipe 21 (management section), the droplets contained in the separation fluid A2 are actively hydrated to cover the surface of the droplets with methane hydrate, or Let the whole be methane hydrate.

Now, with reference to FIG. 4, the methane hydrate generation environment will be described.
FIG. 4 shows a phase equilibrium curve for methane gas. In FIG. 4, the horizontal axis represents the temperature of methane gas and water, and the vertical axis represents the pressure of methane gas and water.
In FIG. 4, the region where the pressure is higher and/or the temperature is lower than the phase equilibrium curve L1 is an environment in which methane hydrate is generated. For example, the seabed E1 at a depth of 1000 m is in a state R3 where the temperature is about 4° C. (277 K) and the pressure is about 10.1 MPa, and is within the region R1. In this state R3, when methane and water are present, methane exists as a hydrate, not as a gas. Further, for example, when the temperature inside the transport pipe 2 is 4° C. (277 K), when the pressure inside the transport pipe 2 rises to about 4 MPa, the environment is such that methane hydrate is generated. That is, when the temperature in the transport pipe 2 is 4° C. (277 K) and the pressure is about 4 MPa, methane gas and water are present in the separated fluid A2 to produce methane hydrate.
On the other hand, no methane hydrate is produced in the region where the pressure is lower and/or the temperature is higher than the phase equilibrium curve L1. Moreover, even if methane hydrate exists in the separated fluid A2, the methane hydrate is decomposed into methane gas and water.

Next, the relationship between the production of methane hydrate and pressure loss will be described with reference to FIGS. 5 and 6. FIG.

FIG. 5 is a diagram for explaining an increase in pressure loss due to adhesion of methane hydrate to the inner surface of the methane gas transport pipe 300. As shown in FIG.
FIG. 5( a ) shows a state in which methane hydrate does not adhere to the inner surface of the transport pipe 300 . In FIG. 5(a), although methane hydrate exists within the transport pipe 300, the methane hydrate does not adhere to the inner surface of the transport pipe 300, and therefore the methane gas is transported normally. FIG. 5(b) shows a state in which methane hydrate adheres to the inner surface of the transport pipe 300. FIG. In this state, the adhesion of methane hydrate to the inner surface of transport pipe 300 increases the friction generated between the transported methane gas and the inner surface of transport pipe 300 . Therefore, pressure loss is generated due to methane hydrate. FIG. 5(c) shows a state in which the constriction in the transport pipe 300 progresses due to adhesion of methane hydrate to the inner surface of the transport pipe 300. FIG. In this state, the pressure loss increases further because the ventilation cross-section in the transport tube 300 becomes smaller.

FIG. 6 is a diagram for explaining an increase in pressure loss due to agglomeration of methane hydrate. A methane hydrate agglomerate is generated by combining methane hydrates with each other. Also, if the methane hydrate deposited on the inner surface of the transport pipe 400 is blown off by the gas flow, there is a possibility that a large agglomerate of methane hydrate that is transported together with the gas will be generated.
In FIG. 6( a ), although there is a methane hydrate agglomerate in the transport pipe 400 , the methane hydrate agglomerate is small and has a low concentration, so it flows through the transport pipe 400 together with the methane gas. Therefore, methane gas is being transported as usual. FIG. 6(b) shows a state in which a large agglomeration of methane hydrate is generated or the concentration of the agglomeration transported together with the gas is high, and the inside of the transport pipe 400 is clogged by this agglomeration. In this state, the pressure loss increases because the ventilation cross-section in the transport tube 400 becomes smaller.

Here, recent studies have revealed that methane hydrate itself has no adhesive force. That is, methane gas contains methane hydrate and/or water covered with methane hydrate (hereinafter also simply referred to as methane hydrate), but water not covered with methane hydrate (hereinafter referred to as If free water is not present, methane hydrate will neither adhere to the inner surface of the transport pipe nor form methane hydrate agglomerates. On the other hand, if both methane hydrate and free water are present in the methane gas, the surface tension of the free water acts as a bridging force, and adhesion and aggregation of methane hydrate are thought to occur.

In this embodiment, droplets contained in the separation fluid A2 are actively hydrated in the management section (management pipe 21). As a result, in the second main pipe 23 located downstream of the management section (management pipe 21) in the transport pipe 2, the surface of the droplet is covered with methane hydrate, or the entire droplet is covered with methane hydrate. Methane hydrate. That is, free water can be eliminated or minimized in the second main pipe 23 positioned downstream with respect to the management section (management pipe 21). Therefore, adhesion and agglomeration of methane hydrate in the second main pipe 23 can be prevented, and an increase in pressure loss due to methane hydrate can be prevented.

The management section (management pipe 21) is preferably installed in the most upstream section of the transportation pipe 2 where methane hydrate may be generated. For example, in a submarine pipeline or a buried pipeline, the temperature of the surrounding environment is substantially constant along the transport pipe 2, and near the entrance of the transport pipe 2 (that is, near the discharge port of the separator 10), pressure is the highest. That is, there is a high possibility that methane hydrate will be generated near the entrance of the transport pipe 2 . Therefore, it is preferable that the management pipe 21 be provided at a position as close as possible to the outlet of the separator 10 .

Returning to FIG. 3, the management pipe 21 will be described. The management pipe 21 includes a large diameter portion 31 and a pair of tapered portions 32 connecting the large diameter portion 31 to the first main pipe 22 and the second main pipe 23, respectively.

The large-diameter portion 31 has an inner diameter larger than that of the other portion of the transport pipe 2 . The other portion of the transport pipe 2 includes a portion of the management pipe 21 other than the large diameter portion 31, and a predetermined portion of the first main pipe 22 and the second main pipe 23 adjacent to the management pipe 21. It means a portion having a length (for example, a length equivalent to that of the management pipe 21). In the large-diameter portion 31, the flow velocity of the separation fluid A2 is reduced because the cross-sectional area of the flow path is increased.

The management pipe 21 is provided with a cooling device (temperature control device) for cooling the management pipe 21 . By cooling the management pipe 21 with the cooling device, the temperature of the management pipe 21 is kept relatively low with respect to the temperature of the separator 10 . As the cooling device, for example, a mechanism that cools the separated fluid A2 in the management pipe 21 by heat exchange between the management pipe 21 and surrounding seawater is employed. In this embodiment, fins 33 are provided on the outer surface of the management pipe 21 as one of the cooling devices in order to increase the efficiency of heat exchange between the management pipe 21 and surrounding seawater. The fins 33 can also prevent the management pipe 21 from buckling due to external pressure. Moreover, in order to cool the management pipe 21 efficiently, a steel pipe with no external coating may be used as the management pipe 21 .

As a cooling device, a mechanism for cooling the management pipe 21 from the outside may be provided.
As a cooling device, a structure may be provided in which at least a part of the management pipe 21 is made of a double pipe, and cold water is passed through the outer pipe or the inner pipe to cool the management pipe 21 .
A pressure control valve may be provided upstream of the management pipe 21 as a cooling device. In this case, the methane gas contained in the separation fluid A2 is adiabatically expanded by lowering the pressure in the management pipe 21 on the downstream side of the pressure control valve with the pressure control valve. This cools the separation fluid A2.

A water-repellent layer is provided on the inner surface of the management pipe 21 . As the water-repellent layer, for example, a fluororesin coating such as polytetrafluoroethylene (so-called Teflon (registered trademark)) is used.

In the second main pipe 23 positioned downstream with respect to the management pipe 21, droplets contained in the separation fluid A2 need to be covered with methane hydrate having a sufficient thickness. The methane hydrate having a sufficient thickness means that the methane hydrate covering the droplet has grown sufficiently so as not to break while being transported together with the methane gas. That is, the separation fluid A2 needs to stay in the management pipe 21 for a period of time for the methane hydrate covering the droplets contained in the separation fluid A2 to grow sufficiently. For example, when the inside of the management pipe 21 is in a methane hydrate production environment, the methane hydrate covering the surface of the droplet is produced in several seconds. Note that when the methane hydrate grows to the center of the droplet, the entire droplet becomes methane hydrate.

The length of the management pipe 21 is set in consideration of the time for the separation fluid A2 to stay in the management pipe 21 (that is, the time for the methane hydrate that covers the droplets contained in the separation fluid A2 to grow sufficiently). .
On the other hand, from an economical point of view, it is preferable to shorten the length of the management pipe 21 . In order to shorten the length of the management pipe 21, the following three measures are conceivable.

First, it is possible to lower the temperature of the management pipe 21 . In this embodiment, the management pipe 21 is provided with a cooling device for cooling the management pipe 21 . This promotes the generation and growth of methane hydrate, and shortens the time required for sufficient growth of methane hydrate. Therefore, the time during which the separation fluid A2 stays in the management pipe 21 can be shortened, and the length of the management pipe 21 can be shortened.

Secondly, reducing the size of droplets contained in the separation fluid A2 can be considered. In this embodiment, the separator 10 reduces the size of the droplets contained in the separation fluid A2 (for example, the maximum particle size of the droplets is about several tens of μm).
Since the methane hydrate generated on the surface of the droplet reaches several to several tens of μm in one second, when the maximum particle size of the droplet contained in the separation fluid A2 is, for example, 20 μm, almost the entire droplet is removed in several seconds. It can be methane hydrate. By reducing the size of the droplets contained in the separation fluid A2 in this way, the methane hydrate can be sufficiently grown in a shorter period of time. Therefore, the time during which the separation fluid A2 stays in the management pipe 21 can be shortened, and the length of the management pipe 21 can be shortened.

The droplets contained in the separation fluid A2 flow through the management pipe 21 along with the flow of the separation fluid A2. easier to gather. In this case, the water concentration at the bottom of the management pipe 21 is higher than that at the top, and at the bottom of the management pipe 21 where the water concentration is high, droplets collide with each other to form methane hydrate agglomerates. more likely to get lost. On the other hand, when the size of the droplets is small, the droplets are stirred by the flow of the separation fluid A2, so that the moisture concentration inside the management pipe 21 can be made uniform. Therefore, by reducing the size of the droplets contained in the separation fluid A2, it is also possible to prevent the formation of methane hydrate agglomerates.

Thirdly, by slowing down the flow velocity of the separation fluid A2, it is conceivable that the time for the separation fluid A2 to stay in the management pipe 21 is obtained. In this embodiment, the management pipe 21 is provided with a large diameter portion 31 .
For example, assuming that the rate of methane gas produced from one production well E2 is 100,000 Sm ³ /day, the pipe diameter of the control pipe 21 is 4 inches, and the plate thickness of the control pipe 21 is 10 mm. When the pressure in the management pipe 21 is 5 MPaA, the flow velocity of the separation fluid A2 in the management pipe 21 is 4.24 m/s. Assuming that the separation fluid A2 stays in the management pipe 21 for 5 seconds, and the flow velocity of the separation fluid A2 is 4.24 m/s, the length of the management pipe 21 is required to be 22 m. On the other hand, when the pipe diameter of the management pipe 21 is increased to 5 inches (plate thickness of 10 mm), the flow velocity of the separation fluid A2 in the management pipe 21 slows down to 2.47 m/s. If the separation fluid A2 stays in the management pipe 21 for 5 seconds and the flow velocity of the separation fluid A2 is 2.47 m/s, the length of the management pipe 21 can be shortened to 13 m.

In the management section (management pipe 21), there are methane hydrate and/or droplets covered with methane hydrate as well as droplets not yet covered with methane hydrate (free water). Therefore, the surface tension of free water acts as a bridging force, and methane hydrate and/or droplets covered with methane hydrate may adhere to the inner surface of the management pipe 21 .
Measures for preventing methane hydrate and/or droplets covered with methane hydrate from adhering to the inner surface of the control pipe 21 will be described below.

In this embodiment, the inner surface of the management pipe 21 is provided with a water-repellent layer. As the water-repellent layer, for example, polytetrafluoroethylene (so-called Teflon (registered trademark)) coating is used. Polytetrafluoroethylene is a material with a large contact angle of 114 degrees with respect to water.
FIG. 7 is a diagram for explaining the relationship between the contact angle θ with respect to water and wettability. As shown in FIG. 7, when the contact angle .theta. with respect to water is small, the wettability (poor repellency) is obtained. On the other hand, when the contact angle θ to water is large, the wettability is poor (repellence is good). By applying a water-repellent layer having a large contact angle θ to water on the inner surface of the management pipe 21, free water that tries to adhere to the inner surface of the management pipe 21 can be repelled and blown away by the flow of the separation fluid A2. As a result, adhesion of methane hydrate and/or droplets covered with methane hydrate to the inner surface of the management pipe 21 can be prevented.

Next, the gas transportation method in this embodiment will be described.
First, the production fluid A1 is produced from the production well E2 by decomposing the methane hydrate in the methane hydrate layer E3 by the decompression method.
The production fluid A1 enters the separation device 1 via the inlet pipe 13 . A separator 10 of the separation device 1 separates the product fluid A1 into a separation fluid A2 and water A3. That is, a separation fluid A2 containing methane gas as a main component is separated from the production fluid A1 by the separator 10 (first step). In the first step, the size of droplets contained in the separation fluid A2 is reduced by the separator 10 (for example, the maximum particle size of the droplets is about several tens of micrometers). The water A3 is discharged to the outside of the separation device 1 via the drain pipe 11 and the pump 12 .
The separation fluid A2 is discharged from the separator 10 to the transport pipe 2. As shown in FIG. The methane gas contained in the separated fluid A2 is transported to the land facility 200 through the transport pipe 2 (second step). In the second step, at least part of the liquid droplets contained in the separation fluid A2 is changed to methane hydrate in the management section (management pipe 21). In the second main pipe 23 located downstream with respect to the management section (management pipe 21) in the transport pipe 2, the surface of the droplet is covered with methane hydrate, or the entire droplet is methane hydrate. It is said that

In the present embodiment, the transport pipe 2 is provided with a management section (management pipe 21) in which at least part of the droplets contained in the separation fluid A2 is methane hydrate. In the second main tube 23 located downstream with respect to 21), the surface of the droplet is covered with methane hydrate, or the entire droplet is methane hydrate. Thereby, free water in the second main tube 23 can be eliminated or minimized. Therefore, aggregation and adhesion of methane hydrate in the second main pipe 23 can be prevented, and an increase in pressure loss due to methane hydrate can be prevented. As a result, methane gas can be stably transported. In addition, in the present embodiment, injection of a hydrate inhibitor or the like is not required, so it is possible to prevent an increase in pressure loss due to methane hydrate while suppressing costs as compared to the conventional art.

Further, in this embodiment, a heating device for heating the separator 10 of the separation device 1 is provided. By raising the temperature in the separator 10 to a temperature higher than the temperature at which methane hydrate is produced by the heating device, the production of methane hydrate in the separator 10 can be prevented.

Further, in this embodiment, a cooling device for cooling the management pipe 21 is provided. By lowering the temperature in the management pipe 21 with the cooling device, the generation and growth of methane hydrate into droplets contained in the separation fluid A2 can be promoted in the management pipe 21 .

Moreover, in this embodiment, the management pipe 21 is provided with the large diameter portion 31 . In the large-diameter portion 31, the flow velocity of the separation fluid A2 is reduced because the cross-sectional area of the flow path is increased. Therefore, it is possible to secure the time for the separation fluid A2 to stay in the management pipe 21 (that is, the time for the methane hydrate that covers the droplets contained in the separation fluid A2 to grow sufficiently).

(Second embodiment)
A second embodiment of the present invention will be described below with reference to FIG. In this embodiment, the same reference numerals are assigned to the same components as those in the first embodiment, the description thereof is omitted, and only the different points will be described. FIG. 8 is a diagram showing a management pipe 21A according to this embodiment.

The management pipe 21A includes a large diameter portion 31, a tapered portion 32, fins 33, and a reduced diameter portion . The inner diameter of the reduced diameter portion 34 is smaller than that of the large diameter portion 31 . Furthermore, the inner diameter of the reduced diameter portion 34 is smaller than that of the first main tube 22 and the second main tube 23 . The tapered portion 32 connects the large diameter portion 31 and the reduced diameter portion 34 . The reduced diameter portion 34 is arranged on the most upstream side in the management pipe 21A. The reduced diameter portion 34 is arranged upstream of the large diameter portion 31 . In the diameter-reduced portion 34, the cross-sectional area of the flow path is narrowed, so the flow velocity of the separation fluid A2 is increased.

Especially in the upstream part of the management pipe 21A, there are droplets not yet covered with methane hydrate (free water) as well as droplets covered with methane hydrate, so methane hydrate and/or methane hydrate There is a possibility that the droplet covered with the rate adheres to the inner surface of the management pipe 21A. By increasing the flow velocity of the separation fluid A2 by the reduced diameter portion 34, the methane hydrate adhering to the inner surface of the management pipe 21A and/or droplets covered with methane hydrate are blown off by the flow of the separation fluid A2. This can prevent methane hydrate and/or droplets covered with methane hydrate from adhering to the inner surface of the management pipe 21A.

(Third embodiment)
A third embodiment of the present invention will be described below with reference to FIG. In this embodiment, the same reference numerals are assigned to the same components as those in the first embodiment, the description thereof is omitted, and only the different points will be described. FIG. 9 is a diagram showing a management pipe 21B according to this embodiment.

In this embodiment, a rectifier (flow velocity adjusting member) 35 is provided upstream of the large diameter portion 31 of the management pipe 21B. The rectifier 35 narrows the cross-sectional area of the flow path in the large-diameter portion 31 to increase the flow velocity of the separation fluid A2 and concentrate the flow of the separation fluid A2 flowing into the management pipe 21B near the inner surface of the management pipe 21B. As a result, the methane hydrate adhering to the inner surface of the management pipe 21B and/or droplets covered with methane hydrate are blown off by the flow of the separation fluid A2. Therefore, it is possible to prevent methane hydrate and/or droplets covered with methane hydrate from adhering to the inner surface of the management pipe 21B.

(Fourth embodiment)
A fourth embodiment of the present invention will be described below with reference to FIG. In the present embodiment, the same reference numerals are assigned to the same components as those in the second embodiment, the description thereof is omitted, and only the different points are described. FIG. 10 shows (a) a cross-sectional view of the management pipe 21A and the first main pipe 22 according to the present embodiment, (b) (a) AA line cross-sectional view, and (c) (a) B- It is a B line sectional view.

The management pipe 21A includes a large diameter portion 31, a tapered portion 32, fins 33, and a reduced diameter portion . Methane hydrate covering droplets contained in the separation fluid A2 is generated in the reduced diameter portion 34 of the management pipe 21A. Further, in the management pipe 21A, the methane hydrate covering the liquid droplets contained in the separation fluid A2 grows on the downstream side of the reduced diameter portion 34 (that is, the tapered portion 32 and the large diameter portion 31). stabilizes.
That is, the diameter-reduced portion 34 of the management pipe 21A forms a generation section in which methane hydrate covering droplets contained in the separation fluid A2 is generated. Moreover, the tapered portion 32 and the large diameter portion 31 of the management pipe 21A form a stabilization section in which the methane hydrate covering the liquid droplets contained in the separated fluid A2 is stabilized.

Here, in the generation section, droplets not yet covered with methane hydrate (free water) exist together with droplets covered with methane hydrate. Therefore, in the generation section, methane hydrate and/or droplets covered with methane hydrate are highly likely to adhere to the inner surface of the management pipe 21A.
In this embodiment, a removing device 4 is provided for removing methane hydrate adhering to the inner surface of the management pipe 21A (the inner surface of the reduced diameter portion 34) in the generation section and/or droplets covered with methane hydrate. .

The removing device 4 includes a shaft 41 , an impeller 42 , a bearing 43 , an upstream support portion 44A, a downstream support portion 44B, and a brush (removing member) 45 .

As shown in FIG. 10(a), the shaft 41 is inserted through the first main pipe 22 and the management pipe 21A. The shaft 41 is rotatably supported by an upstream support portion 44A and a downstream support portion 44B. An impeller 42 is attached to one end of the shaft 41 .

As shown in FIGS. 10( a ) and 10 ( b ), the impeller 42 and the upstream support portion 44A are provided inside the first main tube 22 . That is, the impeller 42 and the upstream support portion 44A are arranged upstream of the management section (management pipe 21A) in the transport pipe 2 . The impeller 42 obtains rotational force using the flow of the separation fluid A2 flowing through the first main tube 22 as a power source, and rotates the shaft 41 about its axis.
In addition, since the first main pipe 22 is covered with a heat insulating material (a heat insulating device), generation of methane hydrate inside the first main pipe 22 is prevented. Therefore, it is possible to prevent methane hydrate from adhering to the impeller 42 and the upstream support portion 44A.

The bearing 43 and the downstream support portion 44B are provided inside the large diameter portion 31 . That is, the bearing 43 and the downstream support portion 44B are arranged in the stabilization section of the management pipe 21 located downstream of the generation section (reduced diameter portion 34). In the stabilization section, most of the droplets contained in the separation fluid A2 are covered with methane hydrate, and almost no free water (droplets not yet covered with methane hydrate) exists. Therefore, it is possible to prevent methane hydrate from adhering to the bearing 43 and the downstream support portion 44B.

Note that the bearing 43 and the downstream side support portion 44B may be omitted. For example, by providing a plurality of upstream side support portions 44A in the axial direction of the shaft 41 and creating a state (cantilever structure) in which a moment reaction force can be taken, even if the downstream side support portion 44B is omitted, the upstream side support portion 44A can support the shaft. 41 can be supported.

A brush 45 is attached to the shaft 41 . The brush 45 is provided in the generation section (reduced diameter portion 34) in the management section (management pipe 21A). The brush 45 is provided over the entire area in the axial direction of the shaft 41 in the generation section (reduced diameter portion 34). The brush 45 rotates around the axis of the shaft 41 together with the shaft 41 .

As shown in FIGS. 10(a) and 10(c), a plurality of (two in this embodiment) brushes 45 are arranged at intervals in the circumferential direction (the direction of rotation around the axis of shaft 41). ). Each bristle row of the brush 45 is composed of a large number of bristles arranged in the axial direction of the shaft 41 . The bristles of brush 45 extend from shaft 41 toward the inner surface of reduced diameter portion 34 . A slight gap is formed between the tip of the bristles of the brush 45 and the inner surface of the reduced diameter portion 34 in order to prevent the inner surface of the reduced diameter portion 34 from being worn by the brush 45 . The plurality of bristle rows of the brush 45 are arranged so that the centrifugal forces of the plurality of bristle rows cancel each other. For example, the plurality of bristle rows of the brush 45 are arranged at regular intervals in the circumferential direction. Thereby, it is possible to prevent the eccentric force from acting on the shaft 41 .

Methane hydrate and/or droplets covered with methane hydrate adhere to the inner surface of the diameter-reduced portion 34 and reach a predetermined height (at least the gap between the tip of the bristles of the brush 45 and the inner surface of the diameter-reduced portion 34). height), the brush 45 removes the stacked methane hydrate and/or droplets covered with the methane hydrate.
Note that the tip of the bristles of the brush 45 may be provided so as to contact the inner surface of the reduced diameter portion 34 . In this case, the hardness of the bristles of the brush 45 is preferably adjusted to the extent that the coating on the inner surface of the reduced diameter portion 34 is not worn away.

In this embodiment, the methane hydrate adhering to the inner surface of the management pipe 21 and/or droplets covered with methane hydrate can be removed by the brush 45 of the removing device 4 .

A configuration other than the brush 45 may be used as the removing member.
For example, as shown in FIG. 11 as a first modification of the fourth embodiment, a plurality of poles 46 may be provided as removing members. 11A and 11B are cross-sectional views of the management pipe 21A and the first main pipe 22 according to the first modification, and FIG.

A plurality of (two in this modified example) poles 46 are provided at intervals in the circumferential direction. The pole 46 extends in the axial direction of the shaft 41 within the reduced diameter portion 34 . More specifically, the pole 46 is provided within the reduced diameter portion 34 such that a slight gap is provided between the pole 46 and the inner surface of the reduced diameter portion 34, and is arranged along the inner surface of the reduced diameter portion 34. be. The pole 46 is provided over the entire area in the axial direction of the shaft 41 in the generation section (reduced diameter portion 34). The pole 46 is arranged in the axial direction of the shaft 41 so that its ends approach the shaft 41 on the upstream and downstream sides (ie, inside the first main tube 22 and inside the tapered portion 32) of the reduced diameter portion 34. incline against Both ends of the pole 46 are joined to the shaft 41 on the upstream side and the downstream side with respect to the reduced diameter portion 34 . The pole 46 rotates around the axis of the shaft 41 together with the shaft 41 .

The plurality of poles 46 are arranged so that the centrifugal forces of the plurality of poles 46 cancel each other. For example, the plurality of poles 46 are arranged at regular intervals in the circumferential direction. Thereby, it is possible to prevent the eccentric force from acting on the shaft 41 .

Methane hydrate and/or droplets covered with methane hydrate adhere to the inner surface of the diameter-reduced portion 34 and reach a predetermined height (higher than the gap between the pole 46 and the inner surface of the diameter-reduced portion 34). After stacking, the pole 46 removes the stacked methane hydrate and/or droplets covered with the methane hydrate.

Since the poles 46 are arranged away from the shaft 41 , the speed of movement of the poles 46 in the circumferential direction is high when the poles 46 rotate as the shaft 41 rotates. In addition, since the pole 46 has a small diameter and a large curvature, free water and methane hydrate are less likely to adhere to the pole 46 .
Therefore, while preventing the methane hydrate from adhering to the pole 46 itself, the methane hydrate adhering to the inner surface of the control pipe 21 and/or droplets covered with methane hydrate are removed by the pole 46 of the removal device 4. can be removed.

Further, as shown in FIG. 12 as a second modified example of the fourth embodiment, a wire 47 may be provided as a removal member instead of the brush 45 . 12A and 12B are cross-sectional views of the management pipe 21A and the first main pipe 22, and FIG. 12B is a cross-sectional view taken along the line DD of FIG.

In this modified example, two wires 47 are provided at intervals in the circumferential direction. The wire 47 extends in the axial direction of the shaft 41 within the reduced diameter portion 34 . More specifically, the wire 47 is provided inside the diameter-reduced portion 34 so that a slight gap is provided between the wire 47 and the inner surface of the diameter-reduction portion 34 , and is arranged along the inner surface of the diameter-reduction portion 34 . be. The wire 47 is provided over the entire area in the axial direction of the shaft 41 in the generation section (reduced diameter portion 34). The wire 47 is arranged in the axial direction of the shaft 41 so that its ends approach the shaft 41 on the upstream and downstream sides of the reduced diameter portion 34 (that is, inside the first main tube 22 and inside the tapered portion 32). incline against The two wires 47 are joined together at their ends. Thereby, two wires 47 are formed in a loop shape.
The two wires 47 are held by a pair of holding members 48 while maintaining their loop shape. As the holding member 48, for example, a deflecting member that supports the wire 47 at the change point of the extending direction of the wire 47 is used. A holding member 48 is attached to the shaft 41 . The wire 47 and the holding member 48 rotate together with the shaft 41 around the axis of the shaft 41 .

The two wires 47 are arranged so that the centrifugal forces of the two wires 47 cancel each other out. For example, two wires 47 are arranged at regular intervals in the circumferential direction. Thereby, it is possible to prevent the eccentric force from acting on the shaft 41 .

Methane hydrate and/or droplets covered with methane hydrate adhere to the inner surface of the diameter-reduced portion 34 and reach a predetermined height (higher than the gap between the wire 47 and the inner surface of the diameter-reduced portion 34). After stacking, the wire 47 removes the stacked methane hydrate and/or droplets covered with the methane hydrate.

Since the wire 47 is arranged apart from the shaft 41 , the speed of movement of the wire 47 in the circumferential direction is high when the wire 47 rotates as the shaft 41 rotates. Moreover, since the wire 47 has a small diameter and a large curvature, free water and methane hydrate are less likely to adhere to the wire 47 .
Therefore, while preventing methane hydrate from adhering to the wire 47 itself, the methane hydrate adhering to the inner surface of the management pipe 21 and/or droplets covered with methane hydrate are removed by the wire 47 of the removal device 4. can be removed.

In addition, in this modification, at least one of the holding members 48 (the upstream holding member 48 in this modification) has a pulley structure, and a vertical impeller 49 is attached to this holding member 48. there is In addition, it is preferable that the holding member 48 arranged on the upstream side of the reduced diameter portion 34 has a pulley structure. The impeller 49 rotates using the flow of the separation fluid A2 flowing through the first main tube 22 as a power source. By the rotation of the impeller 49, the two looped wires 47 are rotated along the arrows in FIG. 12(a). That is, the two looped wires 47 move from the first main tube 22 side along the inner surface of the reduced diameter portion 34 to reach the tapered portion 32 side, and from the tapered portion 32 side, It circulates so as to move along the inner surface of the reduced diameter portion 34 and reach the first main tube 22 side.
Even if methane hydrate adheres to the wire 47 inside the diameter-reduced portion 34 or inside the tapered portion 32 , when the wire 47 rotates and the portion where the methane hydrate adheres reaches the inside of the first main tube 22 , the wire 47 will adhere. Attached methane hydrate is decomposed. Therefore, deposition of methane hydrate on the wire 47 can be prevented.

(Fifth embodiment)
A fifth embodiment of the present invention will be described below with reference to FIG. In this embodiment, the same reference numerals are assigned to the same components as those in the first embodiment, the description thereof is omitted, and only the different points will be described. FIG. 13 is (a) a plan view and (b) a side view of the transport pipe 2 according to this embodiment.

In this embodiment, a plurality of management pipes 21 are provided, and communication between each management pipe 21 and the first main pipe 22 and the second main pipe 23 can be switched. Also, the transport pipe 2 is formed by connecting one of the plurality of management pipes 21 to the first main pipe 22 and the second main pipe 23 .

As shown in FIG. 13(a), one ends of the plurality of management pipes 21 are connected to each other by header pipes 50A. The other ends of the plurality of management pipes 21 are connected to each other by header pipes 50B.
One ends of the plurality of management pipes 21 are connected to the first main pipe 22 via the header pipe 50A. The other ends of the multiple management pipes 21 are connected to the first main pipe 22 via the header pipe 50B.

A valve 51A for allowing/blocking communication between the first main pipe 22 and the management pipe 21 is provided for each management pipe 21 in the header pipe 50A. A valve 51B for allowing/blocking communication between the management pipe 21 and the second main pipe 23 is provided for each management pipe 21 in the header pipe 50B. By controlling the opening and closing of the valves 51A and 51B, it is possible to switch the management pipe 21 communicating with the first main pipe 22 and the second main pipe 23 among the plurality of management pipes 21 .

As shown in FIG. 13(b), a pressure release nozzle 52 is provided on the header pipe 50A. The management pipe 21 is arranged inclined with respect to the horizontal direction so as to be lowered from the upstream side to the downstream side. A drain nozzle 53 is provided downstream of the management pipe 21 . A drain nozzle 53 is provided at the bottom of the management pipe 21 .

In this embodiment, when methane hydrate adheres to the inner surface of the management pipe 21, the management pipe 21 to be used can be switched.
In addition, after switching the management pipe 21 to be used, by opening the valve of the pressure release nozzle 52 of the management pipe 21 to which methane hydrate adheres, the pressure in the management pipe 21 is reduced, and the methane hydrate adheres to the inner surface of the management pipe 21. The resulting methane hydrate is decomposed into water and methane gas. As a result, adhesion of methane hydrate to the inner surface of the management pipe 21 can be eliminated, and the management pipe 21 can be reused.
Since the management pipe 21 is inclined so as to become lower from the upstream side to the downstream side, the water generated by the decomposition of methane hydrate flows downstream of the management pipe 21 . By opening the valve of the drain nozzle 53 , the water produced by the decomposition of methane hydrate is drained to the outside of the management pipe 21 through the drain nozzle 53 . Accordingly, it is possible to prevent the water generated by the decomposition of methane hydrate from accumulating in the management pipe 21 and regenerating methane hydrate. In addition, it is possible to prevent water generated by decomposition of methane hydrate from flowing downstream (header pipe 50B and second main pipe 23).

It should be noted that the present invention is not limited to the above-described embodiments described with reference to the drawings, and various modifications are conceivable within its technical scope.
For example, in the above-described embodiments, the gas transportation system and transportation method are used to transport methane gas produced from the production well E2 dug on the seabed E1 to the onshore facility 200. However, the present invention is not limited to this, and the gas transportation system and transportation method of the present invention may be used for transporting gas coming out of a well through a buried pipe in land gas field development.

Further, in this embodiment, a heating device for heating the separator 10 of the separation device 1 is provided. However, if the surrounding environment of the separator 10 is out of the methane hydrate production environment, the heating device may be omitted. Similarly, the heat retaining device provided on the separator 10 and the first main tube 22 may be omitted.

Further, in this embodiment, the management pipe 21 is provided with a cooling device for cooling the management pipe 21 . However, if the surrounding environment of the management pipe 21 is a methane hydrate production environment, the cooling device may be omitted.

Further, in this embodiment, the management pipe 21 has a large diameter portion 31 and a tapered portion 32 . However, the management pipe 21 may not have the large-diameter portion 31 and the tapered portion 32 and may have the same inner diameter as the first main pipe 22 and the second main pipe 23 .

In addition, it is possible to appropriately replace the constituent elements in the above-described embodiment with well-known constituent elements without departing from the spirit of the present invention, and the modifications described above may be combined as appropriate.

REFERENCE SIGNS LIST 1 separation device 2 transport pipe 4 removal device 10 separator 21, 21A, 21B control pipe 22 first main pipe 23 second main pipe 31 large diameter portion 32 Tapered portion 33 Fin (cooling device) 34 Reduced diameter portion 35 Rectifier (flow velocity adjusting member) 100 Gas transport system 200 Land facility A1 Production fluid (gas-liquid mixture) A2 Separation fluid (fluid), A3... Water (liquid)

Claims (10)

A gas transport method for transporting gas recovered from a gas-liquid mixture,
a first step of separating a fluid containing the gas as a main component from the gas-liquid mixture by a separation device;
a second step of transporting the fluid separated by the separation device through a transport pipe;
In the second step, a management section in which at least part of droplets contained in the fluid is gas hydrate is provided in the transport pipe, and a region of the transport pipe located downstream of the management section. Then, the gas transport method characterized by covering the surface of the droplet with the gas hydrate, or converting the entire droplet into the gas hydrate. A gas transportation system for transporting gas recovered from a gas-liquid mixture,
a separation device for separating a fluid containing the gas as a main component from the gas-liquid mixture;
a transport pipe that transports the fluid separated by the separation device;
with
The transport pipe is provided with a management section in which at least part of the droplets contained in the fluid is gas hydrate,
In a region of the transport pipe located downstream of the management section, the surface of the droplet is covered with the gas hydrate, or the entire droplet is made of the gas hydrate. A gas transportation system characterized by: 3. The gas transportation system according to claim 2, further comprising a temperature control device that lowers the temperature of said control section relative to the temperature of said separation device. 4. The gas transport system according to claim 3, wherein the temperature control device is a heating device that heats the separation device. 4. The gas transportation system according to claim 3, wherein the temperature control device is a cooling device that cools the control section. 6. The gas transportation system according to any one of claims 2 to 5, wherein the management section has a large-diameter portion with an inner diameter larger than that of other portions of the transportation pipe. 7. The control section is provided with a flow velocity adjusting member that increases a flow velocity of the fluid in the control section by narrowing a cross-sectional area of the flow path in the control section. The gas transportation system according to . 8. The gas transportation system according to any one of claims 2 to 7, wherein a water-repellent layer is provided on the inner surface of said management section. 9. The gas transportation system according to any one of claims 2 to 8, further comprising a removal device provided in said management section for removing methane hydrate adhering to an inner surface of said management section. The transport pipe includes a main pipe and a management pipe connected to the main pipe and forming the management section,
2. A plurality of said management pipes are provided so as to be able to switch communication with said main pipe, and said transport pipe is formed by one of said plurality of said management pipes communicating with said main pipe. 10. The gas transportation system according to any one of 2 to 9.

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