Liquid gas transfer and gravity discharge systems

Abstract

The present invention relates to a transmission system (1) for transmitting liquid gas (31) between two liquid gas units, comprising a main pipeline (6), which is configured to transmit the liquid gas (31) from a source tank (4) of a liquid gas source unit (2) to a receiving tank (5) of a liquid gas receiving unit (3), wherein the main pipeline (6) comprises at least a first part (7) and a flexible second part (8), and is characterized in that the transmission system (1) comprises at least one return pipeline (18), which is configured to transmit the liquid gas (31) present in the main pipeline (6) toward the source tank (4), and the transmission system (1) is configured to discharge the liquid gas (31) under the action of gravity.

Description

Technical Field

[0001] The present invention relates to the field of liquid gas transportation and / or storage, and more particularly to a system for transferring liquid gas from one liquid gas transportation and / or storage entity to another. Background Art

[0002] Liquid gas is typically transported from one location to another by sea. This transport begins with loading a seagoing vessel with the liquid gas. Vessels suitable for this type of transport, such as methane tankers or barges, can then collect the liquid gas cargo from liquid gas storage platforms, such as floating reliquefaction units (FRUs), shore-based storage tanks, or gravity platforms or GBSs (gravity-based structures).

[0003] It is a known practice to load liquid gas according to a specific loading method, which includes connecting a pipeline that provides a fluid connection between a liquid gas storage unit and a liquid gas carrier or a ship propelled by liquid gas. Thus, liquid gas transport tanks present in the carrier, or fuel tanks in the case of a ship propelled by liquid gas, are filled with liquid gas by means of pumping means until the carrier or ship propelled by liquid gas is fully loaded.

[0004] Once the liquefied gas has been transferred, the pipeline must be disconnected from the receiving vessel. This disconnection carries risks, primarily due to the fact that the liquefied gas is at a cryogenic temperature, on the order of -160°C, and potentially at a pressure above atmospheric pressure. Therefore, if liquefied gas remains in the pipeline after the transfer is complete, it could flow out of the pipe ends released during disconnection, or even erupt. Due to the cryogenic temperature of the liquefied gas, escaping from the storage unit or transport vessel could result in personal injury and / or material damage. If this outflow were to flow directly into the sea, it could also pollute the environment.

[0005] One solution to mitigate this risk is to vaporize the liquid gas by spraying the length of the pipeline with seawater, which can be done before disconnecting the transmission line. The seawater raises the temperature of the liquid gas remaining in the pipeline, causing it to evaporate. However, this solution is laborious and time-consuming, as the pipeline must be sprayed for several hours during the operation, extending the time the ship is out of service. Summary of the Invention

[0006] The present invention simplifies and shortens the operation by proposing a transmission system for transmitting liquid gas between two liquid gas units. The transmission system includes a main pipeline, which is constructed to transmit liquid gas from a source tank of a liquid gas source unit to a receiving tank of a liquid gas receiving unit. The main pipeline includes at least a first part and a flexible second part. The transmission system includes an articulated support device for supporting the main pipeline, the first part is fixed to the articulated support device and is constructed to extract the liquid gas contained in the source tank. It is characterized in that the transmission system includes at least one return pipeline, which is constructed to transmit the liquid gas present in the main pipeline toward the source tank. The transmission system for transmitting liquid gas is constructed to discharge the liquid gas present in the main pipeline toward the source tank via the return pipeline under the action of gravity.

[0007] Gravity discharge ensures a simplified return of the liquid gas to the source tank, requiring only a return line connected to the main pipeline. Furthermore, the transfer system according to the present invention accelerates the discharge process, as liquid gas can be removed from the main pipeline more quickly than by forced evaporation. Furthermore, the return of the discharged liquid gas to the source tank limits overall energy losses compared to operations involving vaporized liquid gas, which would require reliquefaction or combustion by a liquid gas unit.

[0008] The liquid gas unit is a floating structure, such as a barge, a methane tanker, a platform of the offshore platform type, or an onshore structure, such as an onshore reservoir, a pier in a port area, or a gravity platform. The liquid gas can thus be transferred from one floating structure to another, from an onshore structure to a floating structure, or from a floating structure to an onshore structure. Typically, the liquid gas is transferred from a liquid gas source unit to a liquid gas receiving unit. The following table provides a non-exhaustive list of source units and their corresponding receiving unit(s):

[0009] [Table 1]

[0010]

[0011] A first section of the main conduit leads to the source tank, allowing the liquid gas contained therein to circulate within the first section for the purpose of the transfer operation. The first section can be rigid or flexible and extends primarily along an articulated support device that supports the main conduit. For example, the articulated support device can be a crane comprising a mast and a boom. The articulated support device supports the first section of the main conduit and can be remotely controlled to extend it, thereby facilitating connection of the main conduit to the liquid gas receiving unit.

[0012] The flexible second portion is positioned continuously with the first portion and is connected to the first portion. The flexibility of the flexible second portion ensures freedom of movement of the flexible second portion, thereby allowing relative movement between the liquid gas source unit and the liquid gas receiving unit, particularly relative movement caused by expansion. Once the connection between the main pipeline and the liquid gas receiving unit is established, liquid gas transfer can proceed.

[0013] Once the liquid gas transfer is complete, the return line is connected to the main line. Alternatively, the return line is connected to the main line from the moment the main line is connected to the liquid gas receiving unit. In the latter case, the return line is closed so that liquid gas does not flow through it during the liquid gas transfer operation. Preferably, the return line is flexible to facilitate connection to the main line and the source tank. Furthermore, the flexibility of the return line allows for relative movement between the liquid gas source unit and the liquid gas receiving unit, particularly relative movement caused by expansion.

[0014] A return line extends from the main line to the source tank of the liquid gas source unit. Thus, any liquid gas remaining in the main line after a liquid gas transfer operation can be returned to the source tank via the return line. This ensures that no liquid gas remains in the main line and the return line, which can then be disconnected from the main line. The main line can then be disconnected from the liquid gas receiving unit in complete safety, without risk to the environment.

[0015] When the storage devices are at substantially equal pressure, the transfer system further includes a return gas pipeline (not mentioned) between the liquid gas source unit and the liquid gas receiving unit. The gas pipeline allows gas to return from the liquid gas receiving unit to the liquid gas source unit, so as to balance the pressure between the tanks of the liquid gas receiving unit and the liquid gas source unit during the transfer of liquid gas.

[0016] According to a feature of the present invention, the return pipe includes a first end connected to the main pipe and a second end configured to lead to a source tank of the liquid gas source unit, and the second end of the return pipe is lower vertically downward than the first end of the return pipe. In order to perform gravity discharge, the liquid gas needs to flow naturally in the return pipe, flowing from the main pipe to the source tank. To achieve this, the first end of the return pipe connected to the main pipe is positioned at a higher altitude than the second end of the return pipe connected to the source tank. This height difference can be determined relative to a horizontal or substantially horizontal reference (such as sea level). Therefore, when the liquid gas circulates in the return pipe, the gas will flow to the second end of the return pipe without additional effects other than gravity. The greater the height difference between the two ends of the return pipe, the more rapid and efficient the flow of liquid gas. Therefore, it is advantageous that the height difference between the two ends of the return pipe is at least three to four meters in order to optimize the operation of discharging the liquid gas.

[0017] According to one feature of the present invention, the flexible second portion of the main conduit comprises a first end and a second end, the first end of the flexible second portion being fixed to an articulated support device. As previously described, the flexible second portion is continuous with the first portion by a direct connection between the first portion and the first end of the flexible second portion, and the connection between the first portion of the main conduit and the flexible second portion may include, for example, a safety member. When the articulated support device supports the first portion, it also indirectly supports the flexible second portion. Once the liquid gas transfer has been performed and before the liquid gas remaining in the main conduit is discharged, the articulated support device can be moved in such a way as to raise the first end of the flexible second portion so that the first end is vertically higher than the second end of the flexible second portion. The purpose of this operation is to form a downward slope between the first end of the flexible second portion and the second end of the flexible second portion so as to collect any liquid gas remaining in the main conduit in a region of the main conduit, preferably located near the first end of the return conduit, in order to optimize the discharge of the liquid gas.

[0018] According to one feature of the present invention, a first end of the return line is connected to the main line via a first connecting / disconnecting device. This connecting / disconnecting device allows for quick connection and disconnection of the return line and ensures an optimal seal during connection. The main line is designed to allow connection of the return line using the first connecting / disconnecting device.

[0019] According to one feature of the present invention, the discharge of the liquid gas is initiated by at least one flow controller located in the return pipeline. In other words, the flow controller allows and blocks the flow of liquid gas in the return pipeline. Therefore, during the liquid gas transfer operation, the flow controller is logically closed, allowing the liquid gas to flow from the source tank to the receiving tank through the main pipeline. Once the liquid gas transfer operation is completed, the flow controller is opened, allowing the liquid gas to flow in the return pipeline. The flow controller remains open throughout the liquid gas discharge operation. Once the liquid gas discharge operation is completed, the flow controller is closed again.

[0020] According to one feature of the invention, the return line can be connected simultaneously with the main line, either during the liquid gas transfer or at the end of the liquid gas transfer.

[0021] According to a feature of the invention, the first end of the return pipe comprises a first flow controller and a second flow controller, and the second end of the return pipe comprises a third flow controller and a fourth flow controller. The plurality of flow controllers at the ends of the return pipe make it possible to adjust the flow rate of the liquid gas flowing in the return pipe. Advantageously, when the discharge operation is started, at least one flow controller located at the first end of the return pipe is gradually opened so that too large a quantity of liquid gas does not circulate at once. Thus, gradually opening at least one flow controller of the return pipe makes it possible to avoid damage to the return pipe due to a too high flow rate of the liquid gas circulating in the return pipe or a too sudden pressure difference, which would result in a two-phase flow in the pipe.

[0022] According to one feature of the invention, the return pipeline includes an emergency disconnect device. If, for some reason, such as a change in the distance between the two liquid gas units caused by sea waves, excessive mechanical stress is applied to the return pipeline, there is a risk of the return pipeline being damaged. In order to alleviate this disadvantage, the emergency disconnect device is able to separate the return pipeline from the main pipeline before the mechanical stress applied to the return pipeline irreversibly damages the return pipeline. When the main pipeline and the return pipeline are disconnected in an emergency, their ends are equipped with automatic closing devices to prevent the liquid gas from flowing out. The emergency disconnect device and the first connecting / disconnecting device can be a separate device. In this case, the return pipeline is disconnected at the connection with the main pipeline. The emergency disconnect device can also be independent of the first connecting / disconnecting device and be located between the first end of the return pipeline and the second end of the return pipeline. Therefore, in the event of excessive mechanical stress, the return pipeline will be divided into two parts.

[0023] According to one feature of the present invention, the return pipeline includes at least one pressure sensor and at least one temperature sensor for sensing the pressure and temperature of the return pipeline. The pressure sensor and the temperature sensor can be located between the first end and the second end of the return pipeline and measure the pressure and temperature in the return pipeline, respectively. The pressure measurement makes it possible to determine at what moment the operation of pressurizing the main pipeline and the return pipeline can be performed in order to drive the liquid gas that remains in the main pipeline and cannot yet be discharged under the action of gravity. Inert gases such as molecular nitrogen can be used for pressurization. The gas phase of the liquid gas can also be used for pressurization, which is taken from the source tank itself. However, if the pressure in the return pipeline is too high, this pressurization operation is impossible. Excessive pressure can easily cause liquid gas to flow into the pressurization pipeline. Therefore, the pressure sensor makes it possible to check whether the pressure in the return pipeline is low enough to start the pressurization operation in complete safety.

[0024] The temperature sensor measures the temperature in the return line. This temperature measurement allows checking whether any liquid gas remains in the return line. A very low temperature recorded by the temperature sensor indicates the presence of liquid gas in the return line. A minimum temperature threshold can be defined, above which the measured temperature indicates the absence of liquid gas in the return line.

[0025] According to one feature of the invention, the return pipe has a 2 and 2000mm 2 In other words, if the return line is circular, the diameter of the return line is approximately between 20 mm and 50 mm. It has been shown that a return line with such a hole cross-section can avoid potential boiling of the liquid gas when the liquid gas circulates in the return line.

[0026] According to one feature of the present invention, the flow of liquid gas within the main pipeline is activated by at least one first valve located on the main pipeline. In other words, the first valve allows or disallows the flow of liquid gas within the main pipeline. Thus, during a transfer operation, the first valve is open, allowing liquid gas to flow from the source tank to the receiving tank via the main pipeline. Once the transfer operation is complete, the first valve can be closed again to isolate any liquid gas remaining in the main pipeline, which will then flow through the return pipeline.

[0027] According to one feature of the present invention, the transfer system includes a flow member for circulating liquid gas, which transfers the liquid gas from the source tank to the receiving tank via the main pipeline. The flow member for circulating liquid gas allows the liquid gas to flow through the main pipeline during the transfer operation. Advantageously, the flow member takes the form of a liquid gas pump. Once the main pipeline is connected to the liquid gas receiving unit, the flow member for circulating liquid gas begins to operate.

[0028] According to one feature of the invention, the transmission system comprises a pressurized pipeline connected to the main pipeline and configured to remove the liquid gas present in the main pipeline and the return pipeline. The pressurized pipeline allows the introduction of a fluid, for example an inert gas such as nitrogen. Once this gas enters the main pipeline, it drives the liquid gas therein and then enters the return pipeline. In order to evaporate the liquid gas, nitrogen can also be introduced at ambient temperature. The pressurized pipeline thus allows traces of liquid gas that are not discharged under the action of gravity to be removed, thereby ensuring the complete removal of the liquid gas. The fluid thus drives the liquid gas to the source tank. If the fluid is at ambient temperature, it evaporates the remaining liquid gas.

[0029] According to one feature of the present invention, the main pipeline includes a third section comprising a first terminal end provided with a header and a second terminal configured to lead to a receiving tank. The third section of the main pipeline is located at the liquid gas receiving unit, allowing the second terminal end to lead to the receiving tank. At the first terminal, the header facilitates the loading and / or unloading of liquid gas by providing a connection between the two sections of the pipeline used to transport liquid gas. Thus, the third section allows liquid gas to flow from the header to the receiving tank.

[0030] According to one feature of the present invention, the third section includes at least one second valve located between the third section's header and the third section's second terminal. In other words, the second valve facilitates the passage of liquid gas through the main pipeline, either allowing or preventing it. Thus, the second valve is open during transfer operations, much like the aforementioned first valve. Once the transfer is complete, the second valve closes, isolating the receiving tank from the return pipeline. Closing the second valve prevents liquid gas contained in the receiving tank from returning to the return pipeline during discharge operations.

[0031] According to one feature of the present invention, the flexible second portion is configured to be connected to the manifold of the third portion via a second connecting / disconnecting device. Thus, the connection between the flexible second portion and the third portion forms the connection between the source tank and the receiving tank. Thus, during a transfer operation, the liquid gas contained in the source tank can flow to the receiving tank via the main pipeline. To this end, the second connecting / disconnecting device is designed to connect to the manifold of the third portion. The second connecting / disconnecting device can be similar to the first connecting / disconnecting device installed on the return pipeline mentioned above.

[0032] According to one feature of the invention, the return line can be connected to the main line in a flexible second portion of the main line, upstream of the header. The terms upstream and downstream, with respect to the main line, are defined with reference to the direction of circulation of the liquid gas in the main line, that is, from the source tank toward the receiving tank. This connection of the return line constitutes a first embodiment of the transfer system according to the invention.

[0033] According to one feature of the present invention, the return line can be connected to the main pipeline in the third section of the main pipeline, downstream of the header and upstream of the second valve in the third section. This is a second embodiment of the transmission system according to the present invention. However, the connection of the return line to the third section of the main pipeline must be made upstream of the second valve so that closing the second valve can isolate the receiving tank from the return line. Therefore, the embodiment according to the present invention is defined by the location of the connection between the return line and the main pipeline.

[0034] The present invention also includes a method for discharging liquid gas, the method being implemented by the transmission system for transmitting liquid gas as described above, the method comprising:

[0035] - a first step in which the second valve of at least the third section of the main pipeline is closed,

[0036] - a second step, in which the articulated support means supporting the main conduit is raised so as to position the first end of the flexible second part vertically above the second end of the flexible second part,

[0037] - A third step in which at least the flow controller of the return line is opened.

[0038] Once the transfer of liquid gas from the source tank to the receiving tank via the main pipeline is complete, the draining process is initiated. As previously mentioned, the draining operation involves clearing the liquid gas remaining in the main pipeline after the transfer operation. The second valve in the third section is closed, isolating the receiving tank from the return pipeline. Naturally, the return pipeline is connected to the main pipeline upstream of the second valve.

[0039] The second step of the discharge method consists in raising the articulated support device. Since the first end of the second part is fixed to the articulated support device, it is also raised. The purpose of this step is to create a height difference between the first end of the flexible second part and the second end of the flexible second part connected to the manifold of the third part. As a result, the liquid gas retained in the flexible second part is guided towards the second end of the flexible second part under the action of gravity. The flexible second part thus presents a continuous slope. This operation makes it possible to avoid the creation of gas pockets of liquid gas in the flexible second part of the main pipeline. Such gas pockets of liquid gas tend to be located at a certain distance from the return pipeline and run the risk of not being discharged during the discharge method. Raising the articulated support device makes it possible to alleviate this problem by creating a height difference between the first end of the flexible second part and the second end of the flexible second part, so that the liquid gas contained in the flexible second part is visibly concentrated near the return pipeline.

[0040] Once this second step has been performed, the flow controller of the return line can be opened so that the liquid gas can flow into the return line.

[0041] According to one feature of the present invention, the evacuation method includes an additional step after the first step, during which at least the first valve of the main pipeline is closed. This additional step can be performed at any time during the method, once the first step has been performed. This additional step constitutes a first variation of the evacuation method, in which the first valve is closed to isolate the liquid gas remaining in the main pipeline. When the second valve is also closed, the liquid gas remaining in the main pipeline remains in the portion of the main pipeline extending between the first and second valves.

[0042] According to one characteristic of the invention, during the discharge method, a fluid other than the liquid gas is injected in order to expel the liquid gas present in the main pipe. This fluid injection takes place after an additional step during which the first valve is closed and corresponds to a second variant of the discharge method. The fluid corresponds to the fluid coming from the aforementioned pressurized pipeline. This fluid thus allows the removal of traces of liquid gas that do not flow out under gravity discharge. The fluid can be an inert gas, such as molecular nitrogen. If the pressure in the return pipe is too high, the fluid cannot be introduced. The pressure sensor for the return pipe, as described above, thus makes it possible to determine whether the pressure is low enough to carry out this additional step. Once this has been done, and once the return pipe is opened during the third step of the discharge method, there is no longer any liquid gas in the main pipe and the return pipe. They can then be disconnected in complete safety.

[0043] According to one feature of the invention, the discharge method includes an additional step after the first step, and during this additional step, the gas valve is opened so as to connect the head space of the source tank to the first part of the main pipeline. This is a third variant of the discharge method. Unlike the first and second variants, the first valve remains open here. The gas valve is located on the gas line extending between the head space of the source tank and the first part of the main pipeline. Opening this gas valve allows the gas phase of the liquid gas to circulate in the main pipeline. Therefore, in the third variant, the gas phase of the liquid gas will drive the liquid gas remaining in the main pipeline. Once this is done, and once the return pipeline is opened during the third step of the discharge method, there will be no liquid gas left in the main pipeline and the return pipeline. Molecular nitrogen can then be injected into these pipelines before being completely and safely disconnected.

[0044] According to one feature of the present invention, the discharge method includes a fourth step, subsequent to the third step, of heating the main pipeline. It should be understood that heating the main pipeline can be any means that readily increases the temperature of the liquid gas remaining in the main pipeline. Heating the main pipeline can, for example, include flushing the main pipeline with seawater. This fourth step increases the pressure, thereby promoting the flow of the liquid gas within the return pipeline. This fourth step can be performed using any variation of the discharge method. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Other characteristics and advantages of the invention will become more apparent on reading the following description, on the one hand, and on reference to a number of exemplary embodiments given by way of non-limiting indication with reference to the attached schematic drawings, on the other hand, in which:

[0046] [ Figure 1 ] is a schematic diagram of the first embodiment of the liquid gas transmission system according to the present invention during liquid gas transmission operation;

[0047] [ Figure 2] is a schematic diagram of the first embodiment of the transmission system during a liquid gas discharge operation;

[0048] [ Figure 3 ] is a schematic diagram of the second embodiment of the transfer system during liquid gas transfer operation;

[0049] [ Figure 4 ] is a schematic diagram of a second embodiment of a transfer system during a liquid gas discharge operation;

[0050] [ Figure 5 ] is a flow chart of the liquid gas discharge method according to the present invention;

[0051] [ Figure 6 ] is a cross-sectional schematic diagram of a tank of a transport ship and a marine terminal for loading the tank. DETAILED DESCRIPTION

[0052] During the course of this description, the terms "upstream" and "downstream" will refer to the positioning of an element relative to the direction of circulation of the liquid gas in said conduit.

[0053] Figure 1 A first embodiment of a liquid gas transfer system 1 is depicted. Transfer system 1 transfers liquid gas 31 from a liquid gas source unit 2 to a liquid gas receiving unit 3. Liquid gas source unit 2 includes a source tank 4, and liquid gas receiving unit 3 includes a receiving tank 5. It will be appreciated that transfer system 1 collects liquid gas 31 contained in source tank 4 in order to transfer it to receiving tank 5, thereby filling the latter. By way of example, liquid gas source unit 2 and its associated liquid gas receiving unit 3 may correspond to the various examples listed in the following table:

[0054] [Table 2]

[0055]

[0056]

[0057] exist Figure 1 In the embodiment, the liquid gas source unit 2 may be, for example, a loading barge or a dock area for loading liquid gas. Figure 1 The illustrated liquid gas receiving unit 3 corresponds to a ship that transports liquid gas, such as a methane tanker.

[0058] In order to transfer the liquid gas 31 from the source tank 4 to the receiving tank 5, the transfer system 1 comprises a main pipeline 6 participating in the operation of transferring the liquid gas 31. The transfer system 1 also comprises a return pipeline 18 which at least partially contributes to the operation of discharging the liquid gas 31 once the transfer operation is completed.

[0059] The main pipeline 6 generally extends from the source tank 4 to a point where the main pipeline 6 collects the liquid gas at the source tank 4 and leads to the receiving tank 5 at this point. In this case, the main pipeline 6 includes a first portion 7, a flexible second portion 8 and a third portion 9. The first portion 7 is partially immersed in the liquid gas 31 of the source tank 4. Therefore, the liquid gas 31 of the source tank 4 can circulate in the main pipeline 6 by passing through the first portion 7. The first portion 7 includes a pump 32, the purpose of which is to pump the liquid gas 31 from the source tank 4 into the main pipeline 6. Therefore, the transfer operation is started by starting the pump 32 of the first portion 7. The first portion 7 outside the source tank 4 is supported by an articulated support device 26. The articulated support device 26 can, for example, be a crane located at the liquid gas source unit 2. The articulated support device 26 includes a mast 27, a cantilever 29 and a pivot 28 connecting the cantilever 29 to the mast 27. The pivot 28 is therefore able to cause the cantilever 29 to pivot relative to the mast 27. The mast 27 extends primarily vertically, and the first portion 7 extends along the mast 27, for example, being secured thereto by any securing means. The first portion 7 also extends along a cantilever 29, where it is supported, for example, by at least one bracket 30. Thus, when the cantilever 29 is articulated via the pivot 28, the first portion 7 is driven by the cantilever 29 via the bracket 30. The first portion 7 also includes a first valve 11. The first valve 11 can be opened or closed manually or remotely. The first valve 11 allows or disallows the flow of liquid gas 31 within the main pipeline 6.

[0060] The flexible second portion 8 is positioned to be continuous with the first portion 7. The flexible second portion 8 is connected to the first portion 7 via the first end 81 of the flexible second portion 8. As a result, due to the connection between the first portion 7 and the first end 81 of the flexible second portion 8, and because the first portion 7 is supported by the bracket 30 of the hinged support device 26, the flexible second portion 8 is fixed to the hinged support device 26.

[0061] The third part 9 is present at the liquid gas receiving unit 3 and includes a first terminal 91 equipped with a manifold 15 and a second terminal 92 leading to the receiving tank 5. The manifold 15 allows the connection of the main pipeline 6 so that the main pipeline 6 can connect the source tank 4 to the receiving tank 5, thereby allowing a transfer operation to take place. The second terminal 92 of the third part 9 is at least partially inserted into the internal volume of the receiving tank 5 so that the receiving tank 5 can receive the liquid gas 31 from the source tank 4 during the transfer operation. The third part 9 includes a second valve 12 located between the manifold 15 and the second terminal 92 of the third part 9. Like the first valve 11, the second valve 12 allows or prevents the liquid gas 31 from being transferred from the source tank 4 to the receiving tank 5. Therefore, in order to ensure that the transfer operation occurs, both the first valve 11 and the second valve 12 need to be opened so that the liquid gas 31 can flow from the source tank 4 to the receiving tank 5.

[0062] To enable the transfer operation, the second end 82 of the flexible second portion 8 must be connected to the header 15 of the third portion 9. Therefore, the flexible second portion 8 can be brought closer to the liquid gas receiving unit 3 using the hinged support 26, and then the second end 82 of the flexible second portion 8 is connected to the header 15 of the third portion 9. After this operation, the main pipeline 6 is fully connected, and the transfer operation can begin. The flexibility of the flexible second portion 8 facilitates the connection between the flexible second portion 8 and the third portion 9. The first portion 7 and the third portion 9 can be flexible or rigid.

[0063] Before the transfer system is put in place, the first portion 7 and the flexible second portion 8 are stored on the liquid gas source unit 2, as is the return line 18. The third portion 9 is stored on the liquid gas receiving unit 3.

[0064] The return conduit 18 is connected upstream of the second end 82 of the flexible second portion 8 and thus extends from the main conduit 6 until it opens into the source tank 4. The return conduit 18 includes a first end 181 connected to the main conduit 6 and a second end 182 at least partially inserted into the interior volume of the source tank 4. When the transfer operation is completed and the liquid gas 31 still remains in the main conduit 6, the return conduit 18 allows the liquid gas 31 to return to the source tank 4. Details regarding the discharge operation will be explained below.

[0065] Return pipe 18 includes a first flow controller 19, a second flow controller 20, a third flow controller 21, and a fourth flow controller 22. First and second flow controllers 19 and 20 are located at a first end 181 of the return pipe, while third and fourth flow controllers 21 and 22 are located at a second end 182. From a terminological perspective, the term flow controller differs from the term valve in that the flow controllers are located only on return pipe 18. The four flow controllers allow liquid gas 31 to circulate in return pipe 18 during the discharge operation. Incorporating multiple flow controllers into return pipe 18 allows for the flow rate of liquid gas 31 circulating in return pipe 18 to be adjusted, but there is a risk that a flow rate that is too high and too sudden could damage return pipe 18. During the transfer operation, all flow controllers are closed to prevent the flow of liquid gas 31 in return pipe 18.

[0066] The return pipe 18 comprises an emergency disconnect device 23. The emergency disconnect device 23 allows the return pipe 18 to be disconnected from the main pipe 6 when excessive mechanical stress is applied to the return pipe 18. Such mechanical stress may be caused, for example, by tension in the return pipe 18 due to excessive expansion.

[0067] The return conduit 18 also includes a pressure sensor 24 and a temperature sensor 25, which measure the pressure and temperature, respectively, within the return conduit 18. Such measurements allow the discharge operation to proceed smoothly, as will be described in detail below.

[0068] The return pipe 18 is connected to the main pipe 6 by means of a first connection / disconnection device 16. The flexible second part 8 is connected to the header 15 of the third part 9 by means of a second connection / disconnection device 17. Each of these connection / disconnection devices allows a fluid-tight and safe connection.

[0069] The transfer system 1 further comprises a pressurized line 10 connected to the first portion 7 of the main pipeline 6. The pressurized line 10 is capable of conveying fluid into the main pipeline 6 and the return pipeline 18. This fluid may be, for example, an inert fluid such as molecular nitrogen and may be used to drive the liquid gas 31 in the main pipeline 6 and the return pipeline 18 during a discharge operation. The pressurized line 10 comprises a third valve 13 and a fourth valve 14. If both the third valve 13 and the fourth valve 14 are open, fluid can be drawn from the pressurized line 10.

[0070] The transmission system 1 may further include a gas line 36 that connects the headspace of the source tank 4 to the first portion 7 of the main pipeline 6. A gas valve 37 is located on the gas line 36 and allows or disallows the gas phase of the liquid gas 31 of the source tank 4 to circulate in the main pipeline 6. Just like the pressurized line 10, the gas line 36 may facilitate the operation of venting the liquid gas remaining in the main pipeline 6. Various variations of the venting operation will be described in detail below.

[0071] Therefore, during a transfer operation, once the flexible second section 8 has been connected to the manifold 15 of the third section 9, the flow controller of the return line 18 is closed, and the first and second valves 11, 12 are opened. The third and fourth valves 13, 14 are also closed. The pump 32 located on the main line 6 begins operating and draws in liquid gas 31 from the source tank 4. Liquid gas 31 thus circulates through the first section 7, the flexible second section 8, and the third section 9 until it flows out into the receiving tank 5. The transfer operation continues until the receiving tank 5 is full, or until it reaches a level corresponding to the demand from the liquid gas receiving unit 3. Once this occurs, the pump 32 is stopped, and the discharge operation can then begin.

[0072] Figure 2 Describes the basis and Figure 1 The same embodiment of the transmission system 1. However, Figure 2 The figure shows the position of the transport system 1 when the transport operation is completed and the draining operation has begun. Because the draining is done under the action of gravity, Figure 2A plurality of heights of certain elements of the transmission system 1 are shown. Each of these heights is defined as a function of a height reference H0, which may correspond, for example, to sea level. Three heights are thus shown. A first height H1 corresponds to the height of the second end 182 of the return pipe 18. A second height H2 corresponds to the height of the first end 181 of the return pipe 18 and the height of the second end 82 of the flexible second portion 8 of the main pipe, both of which are located at Figure 2 Finally, a third height H3 corresponds to the height of the first end 81 of the flexible second portion 8 of the main conduit 6 .

[0073] Once the transfer operation is complete, second valve 12 is closed. First valve 11 may also be closed, depending on the method of discharge being used. Thus, a portion of main pipeline 6 upstream of second valve 12 or between first valve 11 and second valve 12 is isolated from receiving tank 5 to prevent potential return of liquid gas in main pipeline 6. During the discharge operation, liquid gas 31 remaining in main pipeline 6 upstream of second valve 12 or between first valve 11 and second valve 12 is discharged.

[0074] Thereafter, boom 29 of articulated support device 26 is lifted upward. To this end, pivot shaft 28 rotates 33 in a counterclockwise direction, causing boom 29 to rise. This movement of articulated support device 26 is intended to increase third height H3, which is associated with the height of first end 81 of flexible second portion 8, so that third height H3 is greater than second height H2, which is associated with the height of second end 82 of flexible second portion 8. Consequently, second end 82 of flexible second portion 8 is positioned vertically downwardly below first end 81 of flexible second portion 8. The fact that third height H3 is greater than second height H2 means that liquid gas 31 already retained in main conduit 6 can flow under the influence of gravity, collecting at second end 82 of flexible second portion 8. This prevents the formation of cavitation of liquid gas 31 in main conduit 6, resulting in optimal discharge operation.

[0075] The first flow regulator 19 of the return pipe 18 is fully opened, the discharge operation continues, and then the second flow regulator 20 is gradually opened, followed by the third and fourth flow regulators 21 and 22. By opening each flow regulator in the return pipe 18, liquid gas 31 will flow therethrough. The flow of liquid gas 31 in the return pipe 18 can be initiated by, for example, flushing the main pipe 6 with a jet of seawater 34. This creates a pressure differential, which encourages the liquid gas 31 to flow in the return pipe 18.

[0076] Liquid gas 31 is discharged under the influence of gravity. In other words, second height H2, which is associated with the height of first end 181 of return pipe 18, is greater than first height H1, which is associated with the height of second end 182 of return pipe 18. Therefore, liquid gas 31 flows naturally in return pipe 18 until it flows out into source tank 4, with second end 182 of return pipe 18 being vertically lower than first end 181 of return pipe 18. Advantageously, the height difference between first height H1 and second height H2 is a minimum of three to four meters to facilitate the flow of liquid gas 31.

[0077] During the discharge operation, the temperature sensor 25 measures the temperature in the return pipe 18. The temperature measurement makes it possible to check whether any liquid gas 31 remains in the return pipe 18. If the temperature is above a determined minimum temperature threshold, this means that there is no longer any liquid gas 31 in the return pipe 18.

[0078] If, despite gravity drainage, the temperature in the return pipe 18 does not increase, this means that some liquid gas 31 still remains in the return pipe 18. There are many possible ways of optimizing drainage.

[0079] For example, if the first valve 11 is open, the first valve 11 can be closed and then the third valve 13 and the fourth valve 14 of the pressurized pipeline 10 can be opened. The latter will then allow fluid to circulate to drive the liquid gas 31 that remains in the main line and / or return line 18 and has not been removed under the action of gravity. The fluid in the pressurized pipeline 10 can be, for example, an inert gas such as molecular nitrogen. The third valve 13 and the fourth valve 14 can only be opened when the pressure in the return line 18 is sufficiently low, for example below 3.5 bar. The pressure in the return line is checked using a pressure sensor 24. Therefore, it is the pressure sensor 24 that determines the moment when the fluid in the pressurized pipeline 10 can be input into the main line 6 and the return line 18. In addition to driving the liquid gas 31, the fluid from the pressurized pipeline 10 can also circulate at ambient temperature to evaporate the liquid gas 31 remaining in the main line 6.

[0080] Alternatively, the discharge can be optimized by opening the gas valve 37, thereby allowing the gaseous phase of the liquid gas 31 to circulate in the gas line 36 and then in the main pipe 6. Thus, the gaseous phase of the liquid gas 31 will drive the liquid gas 31 remaining in the main pipe 6. Obviously, for this alternative working method, it is necessary to open the first valve 11.

[0081] The discharge operation is completed when the temperature measured by the temperature sensor 25 is estimated to be sufficiently high that it can be assumed that there is no longer any liquid gas 31 in the return pipe 18. The flexible second portion 8 of the main pipe 6 can then be disconnected from the header 15 of the third portion 9, and the return pipe 18 can be disconnected from the main pipe 6. The liquid gas receiving unit 3 is thus filled and disconnected and can thus, for example, perform its task of transporting the liquid gas 31 that has just been loaded into the receiving tank 5, or can consume the liquid gas 31 for propulsion.

[0082] Figure 3 and 4 A second embodiment of the transmission system 1 according to the invention is described. For this second embodiment, only the position at which the return pipe 18 is connected to the main pipe 6 differs from that of the embodiment shown in FIG. Figure 1 and 2 Therefore, in the description of the second embodiment only this connection will be discussed and reference will be made to Figure 1 and Figure 2 The common parts of these two embodiments are described below.

[0083] exist Figure 3 and 4 In the embodiment, the connection between the return pipe 18 and the main pipe 6 is made at the third portion 9. More specifically, the first end 181 of the return pipe 18 is located downstream of the header 15 and upstream of the second valve 12. This positioning, which differs from the first embodiment, does not change the operation of transmitting or discharging the liquid gas 31. On the other hand, the first end 181 of the return pipe does need to be located upstream of the second valve 12 so that the second valve can be closed again to isolate the receiving tank 5 from the main pipe 6.

[0084] Figure 4 The second embodiment Figure 2 In other words, Figure 4 The second embodiment of the transfer system 1 is depicted during a draining operation. The draining method is identical to that of the first embodiment. Therefore, the second valve 12 and possibly the first valve 11 are closed, and then the articulated support device 26 raises the cantilever 29, creating a height difference between the second height H2 and the third height H3. The second height H2 is itself greater than the first height H1, ensuring gravity-induced draining. Liquid gas 31 can thus flow into the return pipe 18 after its flow controller is opened.

[0085] Figure 5The flow chart depicts a discharge method 100 for discharging liquid gas according to the present invention. Discharge method 100 begins once the transfer operation is complete. The end of the transfer operation is marked by the cessation of the pump used to circulate the liquid gas from the source tank to the receiving tank. Discharge method 100 begins with the first step 101, during which the second valve of the third section is also closed. Closing the second valve allows the receiving tank to be isolated while liquid gas remaining in the main pipeline circulates in the return pipeline. Specifically, there is a risk that liquid gas from the receiving tank may flow back into the return pipeline, for example due to a pressure differential between the receiving tank and the return pipeline. This situation is particularly prone to occur if the liquid gas transfer system is installed according to the second embodiment, as the first end of the return pipeline is located at the level of the third section and, therefore, closer to the receiving tank than in the first embodiment. Closing the second valve mitigates this disadvantage, which is why, regardless of the embodiment of the transfer system, the second valve is typically located downstream of the return pipeline connection. It should be understood that first step 101 must absolutely be performed before any other steps in discharge method 100 to ensure smooth operation. Therefore, the liquid gas remaining in the portion of the main pipeline upstream of the second valve is the gas to which the discharge method 100 relates.

[0086] Once the first step 101 has been completed, the discharge method 100 proceeds to the second step 102, in which the articulated support device is raised to create a height difference between the first end of the flexible second part and the second end of the flexible second part. Due to its flexibility, the latter is actually prone to creating cavitation of the liquid gas. The potential creation of such cavitations can make it difficult for the liquid gas to flow into the return pipe. Therefore, raising the articulated support device makes it possible to create a significant height difference between the two ends of the flexible second part, thereby collecting all or nearly all of the liquid gas remaining in the main pipe. The liquid gas remaining in the main pipe is thus collected near the first end of the return pipe, so that it can be discharged into the return pipe more easily and efficiently. In order to create an optimal flow of liquid gas in the return pipe, both the first step 101 and the second step 102 need to be performed before the liquid gas is allowed to enter the return pipe.

[0087] All flow controllers on the return line are not opened until the third step 103. In order to avoid damaging the return line by causing too strong or too sudden liquid gas flow in the return line, at least one flow controller may be opened gradually.

[0088] Once the third step 103 has been performed, the discharge method 100 may end directly with an end step 106. However, the discharge method 100 may comprise a fourth step 104 and / or additional steps 105, allowing the discharge operation to be optimized.

[0089] The fourth step 104 allows the flow of liquid gas to be initiated in the return pipe in the event that the pressure in the main pipe and / or the return pipe causes a blockage. Therefore, the fourth step 104 comprises heating the main pipe so that the liquid gas remaining in the main pipe begins to evaporate, thereby generating a pressure difference that causes the liquid gas to flow in the return pipe. Figure 2 and Figure 4 As shown, heating of the main conduit can be achieved, for example, using seawater injection, but any other way of raising the temperature of the liquid gas and suitable in the context of the invention is conceivable.

[0090] like Figure 5 As shown, the additional step 105 may be performed after the first step 101, but the additional step 105 may be performed at any time in the sequence of the discharge method 100, as long as the time is later than the first step 101. The additional step 105 may be performed according to a number of variants.

[0091] A first variant is to close the first valve so as to isolate the portion of the main conduit containing the liquid gas.A fourth step 104 is then sufficient to allow the liquid gas remaining in the tank to drain under gravity, and the discharge method 100 can end.

[0092] If this is not enough, a second variant of the discharge method 100 can be used. The second variant can be used after using the first variant, or it can be used immediately without going through the first variant. The second variant first comprises closing the first valve and then injecting the fluid from the pressurized pipeline into the main pipeline and the return pipeline by opening the third valve and the fourth valve. The purpose of this second variant is to drive the liquid gas that remains in the main pipeline or the return pipeline and is not removed under the action of gravity. Therefore, the fluid drives the liquid gas to flow through the main pipeline and the return pipeline to the source tank. Therefore, the second variant of the additional step 105 makes it possible to complete the discharge operation in a reliable manner, so that it can be determined that there is no longer any liquid gas remaining in the main pipeline and the return pipeline. The implementation of the second variant depends on the pressure in the return pipeline. The pressure needs to be low enough, for example below 3.5 bar, and a pressure sensor present on the return pipeline is used to check whether the second variant can be carried out. In this second variant, the fluid used is different from the liquid gas and can be, for example, molecular nitrogen.

[0093] A third variation, which includes step 105, can also be used. This variation differs from the first and second variations in that the first valve must remain open, allowing it to be applied. The third variation involves opening a gas valve to connect the headspace of the source tank to the main pipeline via a gas line. This allows the gas phase of the liquid gas to circulate in the main pipeline, driving any remaining liquid gas in the main pipeline to the return pipeline.

[0094] To complete the venting method 100 with the end step 106 , it is advantageous to check that no liquid gas remains in the return line. This check is provided, at least in part, by a temperature sensor on the return line. A sufficiently high temperature in the return line, for example, above -85°C, confirms that there is no longer any liquid gas in the return line. The venting method 100 can then end with the end step 106 , marking the point at which the main and return lines can be completely and safely disconnected.

[0095] Figure 6 An example of a marine terminal is shown, in which a transfer system 1 is provided, comprising a main pipeline 6 and a return pipeline 18. The transfer system 1 allows liquid gas to be transferred from a liquid gas source unit 2, which in this case is a fixed offshore installation. The transfer system 1 allows a liquid gas receiving unit 3 to be loaded, which is located at the Figure 6 In the diagram, which is shown as a transport vessel 35 and comprises a receiving tank 5, loading is performed from a liquid gas source unit 2. This unit comprises at least a source tank 4 connected to a transfer system 1.

[0096] Once the liquid gas has been transferred from the source tank 4 to the receiving tank 5 and in order to completely and safely disconnect the main pipeline 6, perform Figure 5 The discharge method described in , allows the liquid gas that has remained in the main pipeline 6 to return to the source tank 4 by traveling along the return pipeline 18.

[0097] Of course, the invention is not limited to the examples that have just been described and various modifications may be made to these examples without departing from the scope of the invention.

[0098] As described above, the present invention achieves its stated objectives and makes it possible to provide a liquid gas transmission system comprising a main pipeline and a return pipeline allowing the liquid gas to return to its starting point by drainage under the action of gravity. Variants not described here may be implemented without departing from the present invention, as long as they include a liquid gas transmission system according to the present invention.

Claims

1. A transmission system (1) for transmitting liquid gas (31) between two liquid gas units, comprising a main pipeline (6), wherein the main pipeline is configured to transmit the liquid gas (31) from a source tank (4) of a liquid gas source unit (2) to a receiving tank (5) of a liquid gas receiving unit (3), wherein the main pipeline (6) comprises at least a first portion (7) and a flexible second portion (8), and the transmission system (1) comprises an articulated support device (26) for supporting the main pipeline (6), wherein the first portion (7) is fixed to the articulated support device (26) and is configured to extract the liquid gas (31) contained in the source tank (4), and is characterized in that The transmission system (1) includes at least one return pipe (18), which is configured to transmit the liquid gas (31) present in the main pipe (6) toward the source tank (4). The transmission system (1) for transmitting the liquid gas (31) is configured to discharge the liquid gas (31) present in the main pipe (6) toward the source tank (4) via the return pipe (18) under the action of gravity.

2. The transmission system (1) according to claim 1, wherein The return pipe (18) includes a first end (181) connected to the main pipe (6) and a second end (182) configured to lead to the source tank (4) of the liquid gas source unit (2), and the second end (182) of the return pipe (18) is vertically lower than the first end (181) of the return pipe (18).

3. The transmission system (1) according to any one of the preceding claims, wherein The flexible second portion (8) of the main pipe (6) comprises a first end (81) and a second end (82), the first end (81) of the flexible second portion (8) being fixed to the hinged support device (26).

4. The transmission system (1) according to claim 2, wherein The first end (181) of the return pipe (18) is connected to the main pipe (6) via a first connecting / disconnecting device (16).

5. The transmission system (1) according to any one of the preceding claims, wherein The discharge of the liquid gas (31) is initiated by at least one flow controller (19, 20, 21, 22) located on the return pipe (18).

6. The transmission system (1) according to any one of the preceding claims, wherein The return pipe (18) comprises an emergency disconnect device (23).

7. The transmission system (1) according to any one of the preceding claims, wherein The return pipe (18) includes at least one pressure sensor (24) and at least one temperature sensor (25) for sensing the pressure and temperature of the return pipe (18).

8. The transmission system (1) according to any one of the preceding claims, wherein The return pipe (18) has a diameter of 300 mm. 2 and 2000mm 2 The hole cross section between.

9. The transmission system (1) according to any one of the preceding claims, wherein The circulation of liquid gas (31) in the main pipe (6) is activated by at least a first valve (11) located on the main pipe (6).

10. The transmission system (1) according to any one of the preceding claims, comprising a pressurizing line (10) connected to the main pipeline (6) and configured to remove liquid gas (31) present in the main pipeline (6) and in the return pipeline (18).

11. The transmission system (1) according to any one of the preceding claims, wherein The main pipeline (6) comprises a third portion (9) comprising a first terminal (91) provided with a header (15) and a second terminal (92) configured to lead to the receiving tank (5).

12. The transmission system (1) according to claim 11, wherein The third section (9) comprises at least one second valve (12) located between the header (15) of the third section (9) and a second terminal (92) of the third section (9).

13. The transmission system (1) according to claim 11 or 12, wherein: The flexible second portion (8) is configured to be connected to the header (15) of the third portion (9) via a second connecting / disconnecting device (17).

14. The transmission system (1) according to claim 13, wherein The return pipe (18) is connected to the main pipe (6) in the flexible second portion (8) of the main pipe (6) upstream of the header (15).

15. The transmission system (1) according to claim 13, wherein The return pipe (18) is connected to the main pipe (6) in its third section (9) downstream of the header (15) of the third section (9) and upstream of the second valve (12) of the third section (9).

16. A method (100) for discharging liquid gas (31), implemented by the transmission system (1) according to claim 12, wherein the flexible second part (8) of the main pipe (6) comprises a first end (81) and a second end (82), the first end (81) of the flexible second part (8) being fixed to the hinged support device (26), and the method comprising: A first step (101) in which at least the second valve (12) of the third portion (9) of the main conduit (6) is closed, a second step (102) in which the hinged support means (26) supporting the main pipe (6) is raised so as to position the first end (81) of the flexible second part (8) vertically higher than the second end (82) of the flexible second part (8), The third step (103) is to open at least the flow controller (19, 20, 21, 22) of the return pipe (18).

17. The discharge method (100) according to claim 16, comprising an additional step (105) after the first step (101), and during which at least the first valve (11) of the main pipe (6) is closed.

18. The discharge method (100) according to claim 17, wherein a fluid different from the liquid gas (31) is injected to drive out the liquid gas (31) present in the main pipe (6).

19. The discharge method (100) according to claim 16 comprises an additional step (105) after the first step (101), and during the additional step, the gas valve is opened to connect the top space of the source tank to the first part (7) of the main pipeline (6).

20. The discharge method (100) according to any one of claims 16 to 19, comprising a fourth step (104) of heating the main pipe (6) subsequent to the third step (103).

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