Method for managing a fluid in liquid form contained in a container

Abstract

The invention relates to a method (64) for managing the gas phase of a fluid contained in liquid form in a container of a floating structure for transporting the fluid in liquid form, comprising a system for supplying fuel to at least one consumer equipped with the floating structure, the method (64) includes at least three different modes of operation (94, 98 or 100) for condensing a gas phase not consumed by the consumer.

Description

[0001] The present invention relates to the field of floating structures for storing and / or transporting gases in liquid form, in particular liquefied natural gas, and more particularly to the field of managing fluids in liquid form present in the containers of such floating structures.

[0002] To more easily transport and / or store fluids in liquid form, such as natural gas in liquid form, the gas is typically liquefied by cooling it to cryogenic temperatures, for example to -163 °C at atmospheric pressure, in order to obtain liquefied natural gas, more commonly denoted by the abbreviation "LNG", which stands for "Liquefied Natural Gas". This liquefied natural gas is then loaded into dedicated storage containers in a floating structure.

[0003] However, such containers are never perfectly insulated, so natural evaporation of the gas is inevitable, a phenomenon known as BOG (Boil-Off Gas). Thus, the storage containers of the floating structure contain liquefied natural gas and gaseous natural gas, with the gas phase of the natural gas accumulating in the head of the container.

[0004] In a known manner, at least some of the natural gas present in gaseous form in the container can be used to supply at least one consumer designed to meet the energy requirements for the operation of the floating structure, in particular for its propulsion and / or for the production of electricity for on-board equipment. For this purpose, it is particularly known to circulate the gas phase through at least one natural gas treatment system in order to allow it to be reheated and compressed, said system comprising a heat exchanger acting as a superheater and a compressor, both placed upstream of the consumer.

[0005] The natural gas treatment system also has the function of condensing a part of the gas phase after the gas phase has been compressed. Condensation of the natural gas may be required when the pressure in the container is unacceptable, in which case the natural gas treatment system allows the gas phase to be condensed and returned to the container in liquid form. Today, this condensation function is achieved by technical means that consume a large amount of energy, such as electricity.

[0006] In the field of the present invention, when the floating structure arrives at a delivery location to unload the cargo, the state of the natural gas in liquid form must also be taken into account. The ports for unloading natural gas in liquid form have requirements regarding the characteristics of the natural gas in liquid form being transported, such as the temperature or the saturation pressure of the natural gas in liquid form. Then, if the cargo does not meet the characteristics imposed by the delivery location, the cargo can be rejected at the delivery site.

[0007] Thus, the general problem is to maintain the temperature and the saturation pressure of the fluid in liquid form contained in the container at a level below or equal to the maximum temperature permitted upon arrival at the delivery location, while limiting the energy consumption caused by the heat treatment of the boil-off gas.

[0008] Accordingly, the present invention proposes to optimize the use of the re-liquefaction system in order to reduce the overall consumption of the floating structure by proposing different operating modes adapted to the different uses of the re-liquefaction system.

[0009] The present invention includes a method for managing the gas phase of a fluid contained in liquid form in a container of a floating structure, the floating structure including a system for equipping at least one consumer of the floating structure, the supply system including at least one compression device configured to absorb the gas phase in order to convey it to the consumer, the compression device including at least a first outlet, a second outlet, and a third outlet for conveying the gas phase at three different pressure levels, the supply system including a reflux circuit configured to return a portion of the gas phase compressed by the compression device to the container, the reflux circuit being alternately connected to the first outlet or the second outlet of the compression device and including at least a first portion and a second portion provided with an expansion device, the supply system including at least one heat exchanger configured to operate a heat exchange between the gas phase absorbed by the compression device and the gas phase passing through the reflux circuit, the supply system including at least one cooling circuit configured to absorb the fluid in liquid form from the container, the reflux circuit including at least one heat exchanger configured to operate a heat exchange between the gas phase of the fluid flowing in the reflux circuit and the fluid in liquid form flowing in the cooling circuit, the supply system including a cooling circuit participating in the condensation of the gas phase from the compression device, and the method for managing the gas phase includes multiple operating modes, at least including:

[0010] - A first operating mode, in which the reflux circuit is connected to the first outlet of the compression device, and the heat exchanger operates a heat exchange between the fluid in liquid form flowing in the cooling circuit and the gas phase flowing in the reflux circuit;

[0011] - A second operating mode, in which the reflux circuit is connected to the second outlet of the compression device, the heat exchanger operates a heat exchange between the gas phase expanded by the expansion device and the fluid in liquid form flowing in the cooling circuit, and the cooling circuit does not participate in the condensation of the gas phase from the compression device;

[0012] - A third operating mode, in which the reflux circuit is connected to the second outlet of the compression device, the heat exchanger operates a heat exchange between the gas phase expanded by the expansion device and the fluid in liquid form flowing in the cooling circuit, and the cooling circuit participates in the condensation of the gas phase from the compression device.

[0013] A floating structure can be, for example, a carrier capable of storing and / or transporting a fluid in liquid form (such as natural gas in liquid form). The system for supplying a consumer of the floating structure manages the gas phase formed in the container head by using it to supply fuel to the consumer or consumers (such as a propulsion engine or a generator for the floating structure).

[0014] The supply system includes a compression device, the function of which is to raise the pressure of the gas phase to a pressure level compatible with the operation of the consumer or consumers. The compression device is, for example, a multistage compressor or a series of compressors arranged one after another. The compression device includes at least three outlets, including a first outlet arranged between the first compression stage and the second compression stage of the compression device, a second outlet arranged between the second compression stage and the third compression stage of the compression device, and a third outlet forming the outlet of the third compression stage.

[0015] The compression device is configured such that the pressure of the gas phase at the first outlet is lower than the pressure of the gas phase obtained at the second outlet, and the latter is lower than the pressure of the gas phase obtained at the third outlet.

[0016] The supply system further includes a reflux circuit, the purpose of which is to return a part of the gas phase to the container after the gas phase compressed by the compression device has condensed. The return circuit can be connected to the first outlet of the compression device or the second outlet of the compression device. The reflux circuit includes at least two gas-phase flow-through parts arranged in parallel. The first part has no expansion member, and when the reflux circuit is connected to the first outlet of the compression device, the gas phase flows through the first part. The second part is provided with an expansion device, such as a Thomson-Joule valve, the purpose of which is to reduce the pressure of the gas phase. When the reflux circuit is connected to the second outlet of the compression device, the gas phase flows through the second part. In other words, the use of the first part is combined with the use of the first outlet of the compression device, while the use of the second part and its expansion device is combined with the use of the second outlet of the compression device.

[0017] The supply system includes a cooling circuit provided with at least one pump configured to extract a fluid in liquid form from the container. The cooling circuit is used to utilize the refrigerant present in the fluid in liquid form and transport it to the gas phase flowing in the reflux circuit in order to condense the gas phase.

[0018] The reflux circuit further includes at least one heat exchanger, the function of which is to condense the gas phase by heat exchange between the gas phase of the fluid flowing in the reflux circuit and the fluid in liquid form flowing in the cooling circuit.

[0019] The supply system also includes a cooling circuit that ensures the condensation of all or part of the gaseous fluid from the compression device. This cooling circuit can take at least two forms: in a first form, it is integrated into the cooling circuit. In this case, the cooling circuit reduces the temperature of the fluid in liquid form circulating in the cooling circuit, and in this way, the cooling circuit indirectly participates in the condensation of the gas phase leaving the first or second outlet of the compression device. In a second form of the cooling circuit, it is installed on a return pipeline that is connected to the first outlet of the compression device at the input and leads to the container. This cooling circuit directly liquefies the gas phase from the compression device.

[0020] A first operating mode enables the extraction of the gas phase via the first outlet of the compression device. Optionally, the gas phase is cooled in a heat exchanger that effects a heat exchange between the compressed gas phase and the gas phase from the head of the container before its compression.

[0021] According to this first operating mode, the gas phase passes through a first section and then through the heat exchanger, where the gas phase is condensed by heat exchange with the fluid in liquid form from the container via the cooling circuit. The gas phase circulating in the heat exchanger is then condensed and returned to the bottom of the container. In this case, the cooling circuit, regardless of its form, is inactive, which allows for a reduction in the total consumption of the system.

[0022] A second operating mode enables the extraction of the gas phase via the second outlet of the compression device. With the first valve closed, the gas phase circulates in the return circuit. Optionally, the gas phase is cooled in a heat exchanger that effects a heat exchange between the compressed gas phase and the gas phase from the head of the container before its compression.

[0023] According to this second operating mode, the first valve is closed, and the gas phase passes through a second section, where the gas phase expands through an expansion device included in this second section. Once expanded, the gas phase passes through the heat exchanger, where the phase is condensed by heat exchange with the fluid in liquid form from the container via the cooling circuit.

[0024] The second section of the return circuit includes an expansion device that allows the pressure of the gas phase circulating in the second section of the return circuit to be reduced. Inside the heat exchanger, the expanded gas phase exchanges heat with the cooling circuit and thus with the fluid in liquid form from the container. In this operating mode, the cooling circuit, regardless of its form, is inactive, which allows for a reduction in the total consumption of the system. The gas phase circulating in this heat exchanger is then re-liquefied and returned to the bottom of the container.

[0025] The third operating mode enables the extraction of the gas phase via the second outlet of the compression device. With the first valve closed, the gas phase circulates in the reflux circuit. Optionally, the gas phase is cooled in a heat exchanger that effects heat exchange between the compressed gas phase and the gas phase before compression from the vessel headspace.

[0026] According to this third operating mode, the first valve is closed and the gas phase passes through a second section where the gas phase expands through an expansion device included in this second section. Once expanded, the gas phase passes through a heat exchanger where the phase condenses via heat exchange with a liquid fluid from the vessel through a cooling circuit.

[0027] Inside the heat exchanger, the gas phase that has passed through the second section of the reflux circuit effects heat exchange with the cooling circuit. According to this third operating mode, the cooling circuit is active in the sense that it participates in the liquefaction of the gas phase from the compression device. In one example, the cooling circuit subcools a fluid in liquid form coming from the vessel and circulating within the cooling circuit. In another example, the cooling circuit forms part of a liquefaction line that receives the gas phase from the first outlet of the compression device, liquefies it via the cooling circuit, and then injects it into the bottom of the vessel.

[0028] According to one aspect, the management method includes a step of pre-cooling the gas phase, which is implemented by means of a heat exchanger.

[0029] According to another feature of the invention, the operating mode is implemented as a function of parameters that at least include the amount of vapor gas present in the vessel, the maximum temperature allowed upon arrival at the delivery location, and / or the temperature of the fluid in liquid form contained in the vessel.

[0030] Some of these parameters relate to the gas contained in the vessel, while other parameters depend on constraints external to the vessel.

[0031] According to another feature of the invention, the amount of vapor gas present in the vessel is determined by varying the pressure in the headspace of the vessel over a given time.

[0032] In one example, the pressure in the vessel is measured by a pressure sensor at known intervals.

[0033] According to another feature of the present invention, the amount of vapor gas present in the container is determined by the consumption of the consumer between the loading location and the delivery location and the estimation of the estimated amount of vapor phase generation in the container based on the design features of the container. In other words, the heat entering the container generates the vapor phase. Depending on the characteristics of the container, the amount of vapor gas generated can be determined based on the temperature outside the container and / or the temperature of the water in which the floating structure sails. At the same time, the consumption of the vapor phase by one or more users is known. These two data can be combined to determine the amount of vapor gas present in the head of the container.

[0034] According to another feature of the present invention, when the temperature of the fluid in liquid form contained in the container is less than or equal to the maximum temperature permitted upon arrival at the delivery location and the amount of vapor gas to be re-liquefied is greater than the initial threshold (e.g., equal to 0 kg / h), the first operating mode is implemented.

[0035] The first operating mode is the preferred operating mode, which allows the vapor phase in the head of the container to be re-liquefied using fewer resources than other operating modes. The present invention allows the cold energy stored by the cargo to be used to condense the vapor phase flowing in the reflux circuit via the first part from the first outlet of the compression device.

[0036] According to another feature of the present invention, when the temperature of the fluid in liquid form contained in the container is greater than the maximum temperature permitted upon arrival at the delivery location and the amount of vapor gas to be re-liquefied is less than the first threshold, the second operating mode is implemented by means of an expansion device, the first threshold being greater than the initial threshold, for example between 500 kg / h and 2000 kg / h, advantageously between 500 kg / h and 1250 kg / h, or even more advantageously equal to 750 kg / h.

[0037] The second operating mode allows a limited amount of vapor phase to be condensed without adding heat to the fluid in liquid form in the container.

[0038] According to another feature of the present invention, when the temperature of the fluid in liquid form contained in the container is greater than the maximum temperature permitted upon arrival at the delivery location and the amount of vapor gas to be re-liquefied is greater than the first threshold, the third operating mode is implemented.

[0039] When a large amount of vapor phase must be condensed, the third operating mode is implemented. For this purpose, the cooling circuit is enabled.

[0040] According to another feature of the present invention, a fourth operating mode, in which the container head is sucked in by a compression device until the pressure in the container head is less than the saturation pressure of the fluid in the form of a liquid present in the container, is implemented when the temperature of the fluid in the form of a liquid contained in the container is higher by a value between 0 °C and 1 °C than the maximum temperature permitted upon arrival at the delivery location, and when the amount of evaporated gas is less than the amount of gas consumed by the consumer.

[0041] The fourth operating mode is enabled when the consumer consumes more than the amount of evaporated gas present in the container head. In such a fourth mode, the pressure inside the container is reduced by the compression device, which facilitates the evaporation of the fluid in the form of a liquid, thereby generating the gas phase required to be consumed by the consumer of the floating structure.

[0042] According to another feature of the present invention, the method includes a fifth operating mode during which a cooling circuit is enabled, and the fifth operating mode is implemented when the temperature of the fluid in the form of a liquid contained in the container is higher by a value between 0 °C and 1.5 °C than the maximum temperature permitted upon arrival at the delivery location.

[0043] When the temperature of the fluid in the form of a liquid contained in the container is higher than the maximum temperature permitted upon arrival at the delivery location, the fifth operating mode is executed to reduce the temperature of the fluid in the form of a liquid contained in the container such that the latter is lower than the receiving temperature at the cargo delivery location.

[0044] According to an optional feature of the present invention, the fifth operating mode is implemented simultaneously with any one of the first operating mode, the second operating mode, or the fourth operating mode. It should be understood that the cooling circuit helps to keep the temperature of the cargo below the maximum permitted temperature upon arrival at the delivery location in these modes.

[0045] In certain cases, the floating structure can be referred to as the speed evolution of the crossing speed, which corresponds to the speed at which the entire gas phase is consumed by one or more consumers without the need to generate additional gas phase. When the floating structure moves at the crossing speed, no operating mode is implemented.

[0046] The present invention also relates to a fuel supply system for supplying fuel to at least one consumer equipped with a floating structure, the fuel supply system being configured to implement the management method as described herein.

[0047] The present invention also relates to a floating structure for transporting and / or storing a fluid in the form of a liquid, which includes the supply system according to the foregoing claims.

[0048] Other features, details, and advantages of the present invention will become clearer by reading the following description on the one hand and by referring to the accompanying drawings by way of illustration and not limitation, in which:

[0049] Figure 1 is the first embodiment of a system for supplying a floating structure;

[0050] Figure 2 is the second embodiment of a system for supplying a floating structure;

[0051] Figure 3 is a flowchart representing a method for managing a fluid in liquid form in a container housed in a floating structure;

[0052] Figure 4 shows a cross-sectional view of a floating structure including a supply system including Figure 1 or Figure 2 .

[0053] Figure 1 shows a first embodiment of the supply system 1 according to the present invention. The supply system 1 can be integrated into a floating structure, such as a ship for storing and / or transporting gas in liquid form, which is housed in at least one container 2 equipped to the floating structure. The gas in liquid form can partially evaporate naturally and form a gas phase, or so-called evaporation gas, which is stored in the head 3 of the container 2.

[0054] To manage the pressure in the container 2, which increases due to the presence of the gas phase in the head 3, the supply system 1 can use this gas phase to supply fuel to at least one gas-consuming appliance. In Figure 1 , the supply system 1 is configured to supply a high-pressure gas-consuming appliance 4 and a low-pressure gas-consuming appliance 5. The high-pressure gas-consuming appliance 4 can be, for example, a motor for propelling the floating structure. The low-pressure gas-consuming appliance 5 can be a generator for powering the floating structure.

[0055] To supply the gas-consuming appliances 4, 5, the supply system 1 includes a supply circuit extending between the container 2 and the gas-consuming appliances 4, 5. The supply circuit 6 includes a compression device 7, which allows the gas phase housed in the head 3 and the container 2 to be sucked in and compressed to a pressure compatible with the requirements of the high-pressure gas-consuming appliance 4, for example higher than 250 bar, or to a pressure compatible with the requirements of the low-pressure gas-consuming appliance 5, especially between 7 bar and 20 bar.

[0056] In Figure 1 , the compression device 7 is shown by a series of compressors, but the compression device 7 can also be a single multi-stage compressor.

[0057] Therefore, the compression device 7 has multiple compression stages in order to compress the gas to a higher or lower pressure. Such a compression device 7 includes at least three outlets, wherein at least two outlets are arranged between two compression stages. The more compression stages the gas passes through, the higher the pressure. ​​​​

[0058] Therefore, Figure 1 The compression device 7 shown in Figure 1 includes at least a first compression stage 11, a second compression stage 12, and a third compression stage 13. The compression device 7 further includes a first outlet 56 disposed between the first compression stage 11 and the second compression stage 12, a second outlet 57 disposed between the second compression stage 12 and the third compression stage 13, and a third outlet 58 after the third compression stage 13.

[0059] These three outlets 56, 57, 58 respectively ensure that the gas phase leaves the compression device 7. The gas phase passes through the entire compression device 7 and leaves via the third outlet 58 to reach a pressure compatible with the supply to the high-pressure gas-consuming appliance 4. At the outlet of the third compression stage 13 of the compression device 7, the gas phase can reach a pressure between 250 bar and 400 bar.

[0060] The gas phase compressed by the first compression stage 11 has a pressure between 7 bar and 20 bar, while the gas phase compressed by the second compression stage 12 has a pressure between 70 bar and 150 bar. The first compression stage 11 also raises the pressure of the gas phase to a value compatible with the supply to the low-pressure gas-consuming appliance 5.

[0061] The supply system 1 further includes a reflux circuit 8. The reflux circuit 8 is connected to the supply circuit 6, more specifically at the compression device 7. According to the first embodiment of the supply system 1, the reflux circuit 8 includes a first branch 9 and a second branch 10. The first branch 9 and the second branch 10 are respectively connected to the first outlet 56 of the compression device 7 disposed downstream of the first compression stage 11 and upstream of the second compression stage 12, and the second outlet 57 of the compression device 7 disposed downstream of the second compression stage 12 and upstream of the third compression stage 13.

[0062] The first branch 9 and the second branch 10 allow the gas phase to flow within the reflux circuit 8 at two different pressure levels.

[0063] The first branch 9 and the second branch 10 converge at the convergence point 53. Preferably, the gas phase only flows within one of the two branches 9, 10. To control the flow within the branches 9, 10, the first branch 9 includes a first valve 43, and the second branch 10 includes a second valve 44.

[0064] One of the purposes of the reflux circuit 8 is to assist in the condensation of the gas phase not used for supplying fuel to the gas-consuming appliances 4, 5. For this purpose, the supply system 1 includes a heat exchanger 14, which is configured to operate a heat exchange between the compressed gas phase flowing in the reflux circuit 8 and the gas phase flowing in the supply circuit 6, which is upstream of the compression device 7 and from the head of the container.

[0065] Thus, the heat exchanger 14 allows the gas phase flowing in the reflux circuit 8 to be pre-cooled by the gas phase leaving the container 2 before it is compressed. The latter is then heated by capturing the calories from the gas phase flowing in the reflux circuit 8.

[0066] The gas phase flowing in the reflux circuit 8 is pre-cooled in the heat exchanger 14, regardless of the use of the branch 9 or 10. Advantageously, the confluence point 53 is located upstream of the heat exchanger 14 so that all the gas phases flowing in the reflux circuit 8 pass through the heat exchanger 14 to be pre-cooled.

[0067] According to such a configuration, after the first branch 9 and the second branch 10 have converged at the confluence point 53, the heat exchanger 14 includes two passages, one of which allows the gas phase flowing in the supply circuit 6 upstream of the compression device 7 to flow through, and the other of which allows the compressed gas phase flowing in the reflux circuit 8 to flow through.

[0068] The reflux circuit 8 includes a first part 51 and a second part 52, each part being adapted to allow the gas phase previously compressed by the first compression stage 11 or by the second compression stage 12 to flow through.

[0069] Figure 1 It is shown that the second part 52 includes an expansion device 15 while the first part 51 does not. Therefore, it should be understood that the first part 51 is dedicated to the flow of the gas phase compressed only by the first compression stage 11, while the second part 52 is dedicated to the flow of the gas phase compressed by the second compression stage 12. The pressurization by the second compression stage 12 requires subsequent expansion, which is provided by the expansion device 15.

[0070] The supply system 1 allows the condensation of the gas phase to be optimized by saving as much energy as possible and by keeping the temperature of the fluid cargo in liquid form below a given threshold, which can be the maximum temperature allowed at the location where the container 2 is unloaded or transported.

[0071] This optimization is achieved by favoring the use of the first branch 9 in combination with the first part 51 over the use of the second branch 10 in combination with the second part 52 (possibly in combination with the implementation of the cooling loops 20, 50).

[0072] Figure 1 The shown reflux circuit 8 includes a splitting point 54 and a converging point 55, where the first part 51 and the second part 52 start and end respectively. These valves also include a first valve 41 and a second valve 42 that control the gas flow within the respective parts. Finally, the reflux circuit 8 includes a flow rate regulating member 40 located downstream of the converging point 55 between the first part 51 and the second part 52. The flow rate regulating member 40 adjusts the pressure and flow rate within the reflux circuit 8 so that the pressure is closer to the main pressure within the container 2.

[0073] The flow rate regulating member 40 is located downstream of the branch of the return circuit 8 passing through the heat exchanger 16 and upstream of the mixing point 39 between the return circuit 8 and the cooling circuit 17.

[0074] After flowing through the first part 51 or the second part 52, the gas phase then passes through the heat exchanger 16 in order to be at least partially (if not completely) condensed. The convergence point 55 is located upstream of the heat exchanger 16. Like the heat exchanger 14, the heat exchanger 16 includes two channels.

[0075] To achieve efficient condensation, the supply system 1 includes a cooling circuit 17 through which a fluid in liquid form obtained from the container 2 flows. The cooling circuit 17 includes a pump 18 which is advantageously immersed in the bottom of the container 2 and which causes the fluid in liquid form to flow within the cooling circuit 17. One of the various functions of the cooling circuit 17 is to participate in the condensation of the gas in vapor form flowing in the return circuit 8. Thus, the fluid in liquid form flowing in the cooling circuit 17 can pass through the heat exchanger 16 and effect a heat exchange within the heat exchanger 16 with the gas phase flowing in the return circuit 8. The gas phase is then condensed. This is advantageous because the calories contained in the gas in liquid form contained in the container are used to operate the re-liquefaction.

[0076] To optimize the condensation of the gas phase flowing in the heat exchanger 16, the supply system 1 includes another heat exchanger, hereinafter referred to as the second heat exchanger 19, through which or around which the fluid in liquid form flowing in the cooling circuit 17 can pass.

[0077] The second heat exchanger 19 allows the fluid in liquid form to be sub-cooled in order to compensate for the calories captured by the fluid in liquid form during the heat exchange occurring within the heat exchanger 16 (also referred to as the first heat exchanger 16 when the system includes a plurality of heat exchangers).

[0078] To sub-cool the fluid in liquid form, the supply system 1 includes a cooling loop 20 passing through the second heat exchanger 19 through which a refrigerant fluid passes, thereby ensuring the sub-cooling of the fluid in liquid form. The refrigerant fluid flowing in the cooling loop 20 can be, for example, nitrogen.

[0079] At the outlet of the first heat exchanger 16, the gas phase condensed in this way also enters the cooling circuit 17 at the outlet of the first heat exchanger 16 and is mixed at the mixing point 39. The cooling circuit 17 extends up to the container 2 such that the fluid can return to liquid form within the container. The cooling circuit 17 includes at least one terminal 29 which can be an orifice 30 arranged at the bottom of the container 2.

[0080] When the amount of gas evaporated in the head 3 of the container 2 is not sufficient to meet the consumption of the high-pressure gas-consuming appliance 4, the supply system 1 can be configured to supply this gas phase to the high-pressure gas-consuming appliance 4. In this way, the supply system 1 can include an additional supply circuit 33. The additional supply circuit 33 includes an additional pump 35, a high-pressure pump 36, and an evaporator 37. The additional pump 35 allows a fluid in liquid form to be obtained from the container 2, and then the high-pressure pump 36 pumps the fluid in liquid form to a pressure compatible with the pressure required by the high-pressure gas-consuming appliance 4. The vaporizer 37 allows the fluid in liquid form to be evaporated under high pressure so that the fluid becomes in vapor form and can be consumed by the high-pressure gas-consuming appliance 4.

[0081] As Figure 1 and Figure 2 shown, the additional pump 35 and the pump 18 of the cooling circuit 17 are separate and different pumps. Alternatively, the system does not have an additional pump dedicated to the additional supply circuit 33. In this case, the additional supply circuit 33 is connected to the cooling circuit 17 between the output port of the pump 18 and the input port of the heat exchanger 16, and in addition to the initial function of the pump 18, the pump 18 also obtains the gas in liquid form from the container 2 to supply it to the high-pressure pump 36.

[0082] Figure 2 Shows Figure 1 a variant of the supply system shown in Figure 1 .

[0083] Figure 2 Differing from the previous figure, it does not include a second heat exchanger that allows the fluid in liquid form flowing in the cooling circuit 17 to be supercooled.

[0084] Alternatively, the supply system 1 includes an additional branch 48 that is connected to the first output port 56 of the compression device 7, is in parallel with the first branch 9, and the additional branch 48 extends to the container 2.

[0085] The supply system 1 includes a cooling circuit 50 that can be enabled or disabled according to the selected operating mode. This additional branch 48 guides the gas phase through the second heat exchanger 49, which is configured to operate the heat exchange between the gas phase from the compression device 7 and the refrigerant fluid flowing in the cooling circuit 50. At the output port of the second heat exchanger 49, the condensed gas phase flows in the additional branch 48 until it returns to the container 2.

[0086] As Figure 3As shown in the flowchart, the method 64 for managing the gas phase begins with the recovery 68 of the navigation parameters of the floating structure 70. These parameters can be used to select a preferred operating mode for condensing the evaporated gas present in the head 3 of the container 2.

[0087] According to the present invention, the method implements at least three operating modes of the supply system 1, and the purpose of implementing these modes is to reduce the total consumption of the floating structure.

[0088] The first operating mode, indicated by the reference numeral 94, corresponds to connecting the reflux circuit 8 to the first outlet 56 of the compression device 7 and the circulation of the gas phase through the first section 51. The heat exchanger 16 operates in heat exchange between the fluid in the form of a liquid flowing in the cooling circuit 17 and the gas phase flowing in the reflux circuit 8, and the cooling circuit 17 is not overcooled. In this case, the first valve 43 is open and the second valve 44 is closed, so the gas phase starts its journey in the reflux circuit 8 via the first branch 9. After the heat exchanger 14, the gas phase continues to flow in the reflux circuit 8 via the first branch 51 (i.e., the branch without an expansion device). For this purpose, the first valve 41 is opened and the second valve 42 is closed.

[0089] When it is determined in step 84 that the amount of gas evaporated in the container head is greater than an initial threshold (e.g., equal to 0 kg / h), and when it is determined in step 82 that the temperature of the fluid in the form of a liquid present in the container is less than the maximum temperature of the fluid in the form of a liquid permitted at the delivery location, the first operating mode 94 is implemented. The first operating mode 94 is the operating mode that consumes the least energy to condense the gas phase passing through the reflux circuit, and the present invention is conducive to implementing this first operating mode compared with the second mode 100 or the third operating mode 98.

[0090] The second operating mode, indicated by the reference numeral 100, corresponds to connecting the reflux circuit 8 to the second outlet 57 of the compression device 7 and corresponds to passing the gas phase through the second section 52 and through the expansion device 15. The heat exchanger 16 operates in heat exchange between the fluid in the form of a liquid flowing in the cooling circuit 17 and the gas phase flowing in the reflux circuit 8 after its expansion, and the cooling circuit 17 is not overcooled. In this case, the first valve 43 is closed and the second valve 44 is open, so the gas phase starts its journey in the reflux circuit 8 via the second branch 10. After the heat exchanger 14, the gas phase continues to flow in the reflux circuit 8 via the second branch 52 (i.e., the branch provided with the expansion device 15). For this purpose, the first valve 41 is closed and the second valve 42 is opened.

[0091] When it is determined in step 96 that the amount of gas evaporated in the container head is between the initial threshold and the first threshold, and when it is determined in step 82 that the temperature of the fluid in liquid form in the container is higher than the maximum temperature permitted at the delivery location, the second operating mode 100 is implemented, where the first threshold can take any value between 1 kg / h and 750 kg / h. In this case, the first valve 43 is closed and the second valve 44 is opened, so that the gas phase starts its journey in the reflux loop 8 via the second branch 10. After the heat exchanger 14, the gas phase continues to flow in the reflux loop 8 via the second branch 52 (i.e., the branch provided with the expansion device 15). For this purpose, the first valve 41 is closed and the second valve 42 is opened. This second operating mode 100 consumes less energy to condense the gas phase passing through the reflux loop than the third operating mode 98, because the cooling loop is inactive regardless of its embodiment.

[0092] The third operating mode 98 shown by the reference numeral 98 corresponds to the connection of the reflux loop 8 to the second outlet 57 of the compression device 7 and the flow of the gas phase through the second part 52 and through the expansion device 15, and the heat exchanger 16 operates the heat exchange between the fluid in liquid form flowing in the cooling loop 17 and the gas phase flowing in the reflux loop 8 after expansion in the reflux loop 8. In this mode, the cooling loop is active, thus allowing the overcooling of the fluid in liquid form flowing in the cooling loop 17 or the liquefaction of the gas phase flowing in the additional branch 48.

[0093] When it is determined in step 96 that the amount of gas evaporated in the container head is greater than the above-mentioned first threshold (e.g., 750 kg / h), and when it is determined in step 82 that the temperature of the fluid in liquid form present in the container is greater than the maximum temperature permitted at the delivery location, the third operating mode 98 is implemented. This third operating mode reduces the temperature of the fluid in liquid form present in the container so that the latter is lower than the maximum temperature permitted at the delivery location.

[0094] In step 84, it is determined whether the amount of gas evaporated in the container head is equal to the initial threshold, e.g., 0 kg / h. This is especially the case when the consumption of the gas phase by the consumer corresponds to the estimated amount of gas phase generated in the container head. If this amount is equal to 0 kg / h, the method does not implement any operating mode related to the condensation of the gas phase.

[0095] If it is determined in step 84 that the amount of gas evaporated in the container head is less than the initial threshold, and it is determined in step 92 that the temperature of the fluid in liquid form is between 0 °C and 1 °C higher than the maximum temperature permitted at the delivery location, the fourth operating mode 104 is implemented.

[0096] This fourth operating mode 104 consists in creating a vacuum inside the container 2. This vacuum is achieved by a compression device 7 or any other suction device which sucks in the gas phase present in the container head until the pressure in the head 3 of the container 2 is lower than the saturation pressure of the fluid in liquid form present in the container 2. In doing so, the fluid in liquid form evaporates into the container head, thus creating a gas phase.

[0097] If it is determined in step 84 that the amount of gas evaporated in the container head is less than an initial threshold, for example 0 kg / h, and it is determined in step 92 that the temperature of the fluid in liquid form is higher by a value between 0 °C and 1.5 °C than the maximum temperature permitted at the delivery location, then the fifth operating mode 102 is implemented.

[0098] During this fifth operating mode 102, a fluid in liquid form is obtained from the container 2 by means of an additional supply circuit 33, and this fluid in liquid form is evaporated in the evaporator 37 in order to supply a gas phase to the consumer 4 or 8. A part of the gas phase not consumed by the consumer is condensed directly in an additional branch 48 including a dedicated cooling circuit 50 via a cooling circuit by the cooling loop 20.

[0099] The above-mentioned amount of evaporated gas can be determined, for example, by monitoring the variation of the pressure in the head 3 of the container 2 over a given period of time. If the pressure increases rapidly, this means that the amount of evaporated gas is significant. On the contrary, if the pressure does not increase or increases slowly, this means that the amount of evaporated gas is stable or even low.

[0100] Alternatively or additionally, the amount of evaporated gas present in the container can be determined by comparing the estimated consumption of the consumer between the location where the fluid is loaded into the container and the delivery location of this fluid with the estimated amount of gas phase generation estimated inside the container, this estimation depending on the design characteristics of the container, such as its insulation. If the estimated amount of gas phase generation estimated is greater than the estimated consumption of the consumer, this indicates the presence of a large amount of evaporated gas. On the other hand, if the estimated amount of gas phase generation estimated is less than or equal to the estimated consumer of the consumer, this indicates a stable or even decreasing amount of evaporated gas.

[0101] Figure 4 A floating structure 70 including a container 2 is shown, the container 2 being watertight and insulated. It is generally prismatic and is installed in the double hull 5 of the floating structure 70, which can be a ship or a floating platform. The walls of the container 2 include a main impermeable barrier configured to be in contact with the fluid in liquid form contained in the container 2, a secondary impermeable barrier provided between the main impermeable barrier and the double hull 5 of the ship, and two thermal insulation barriers respectively provided between the main impermeable barrier and the secondary impermeable barrier and between the secondary impermeable barrier and the double hull 5. In a simplified version, the floating structure 70 includes a simple hull.

[0102] The loading / unloading pipeline 73 arranged on the upper deck of the floating structure 70 can be connected to a seaport or a port terminal through appropriate connectors to convey fluid cargo in liquid form from or to the container 2.

[0103] Figure 4 An example of a seaport terminal is also shown, which includes a loading and / or unloading station 75, a subsea pipeline 76, and onshore facilities 77. The loading and / or unloading station 75 is a fixed offshore facility that includes a movable arm 74 and a tower 78 that supports the movable arm 74. The movable arm 74 carries a bundle of insulated flexible hoses 79, which can be connected to the loading / unloading pipeline 73. The movable arm 74 can be oriented to accommodate floating structures 70 of any size. Connecting pipes (not shown) extend inside the tower 78. The loading / unloading station 75 allows the floating structure 70 to load from and / or unload to the onshore facilities 77. This includes a container 80 for storing fluid in liquid form and a connecting pipe 81 that is connected to the loading and / or unloading station 75 through the subsea pipeline 76. The subsea pipeline 76 is used to convey fluid in liquid form over a long distance (e.g., five kilometers) between the loading and / or unloading station 75 and the onshore facilities 77, thereby keeping the floating structure 70 at a great distance from the shore during the loading and / or unloading operations.

[0104] To generate the pressure required to convey fluid in liquid form, pumps on the floating structure 70 and / or pumps equipped to the onshore facilities 77 and / or pumps equipped to the loading and unloading station 75 are implemented.

[0105] Examples have been described for the floating structure 70; however, they are also applicable to structures on land.

[0106] Therefore, the present invention proposes a method for managing the gas phase in a container, which allows the gas phase to be condensed using as little energy as possible. The supply system is equipped with a cooling circuit that, in some cases, allows the temperature of the fluid in liquid form to be lower than a threshold temperature, such as the temperature acceptable at the conveying terminal.

[0107] However, the present invention is not limited to the means and configurations described herein and also extends to any equivalent means and configurations and any technically operable combinations of these means.

Claims

1. A method (64) for managing the gas phase of a fluid contained in a liquid form in a container (2) of a floating structure (70), the floating structure (70) including a supply system (1) for supplying fuel to at least one consumer (4, 5) equipped with the floating structure (70), the supply system (1) including at least one compression device (7) configured to absorb the gas phase to deliver the gas phase to the consumer (4, 5), the compression device (7) including at least a first outlet (56), a second outlet (57), and a third outlet (58) configured to deliver the gas phase at three different pressure levels, the supply system including a reflux circuit (8) configured to return a part of the gas phase compressed by the compression device (7) to the container (2), the reflux circuit (8) being alternately connected to the first outlet (56) or the second outlet (57) of the compression device (7), and including at least a first part (51) and a second part (52) provided with an expansion device (15), the supply system (1) including at least one heat exchanger (14) configured to operate a heat exchange between the vapor phase absorbed by the compression device (7) and the gas phase passing through the reflux circuit (8), the supply system (1) including at least one cooling circuit (17) configured to absorb the fluid in liquid form from the container (2), the reflux circuit (8) including at least one heat exchanger (16) configured to operate a heat exchange between the gas phase of the fluid flowing in the reflux circuit (8) and the fluid in liquid form flowing in the cooling circuit (17), the supply system (1) including cooling loops (20, 50) participating in the condensation of the gas phase from the compression device (7), the method for managing the gas phase including a plurality of operating modes, at least including: - A first operating mode (94) in which the reflux circuit (8) is connected to the first outlet (56) of the compression device (7), and the heat exchanger (16) operates a heat exchange between the fluid in liquid form flowing in the cooling circuit (17) and the gas phase flowing in the reflux circuit (8); - A second operating mode (100) in which the reflux circuit (8) is connected to the second outlet (57) of the compression device (7), and the heat exchanger (16) operates a heat exchange between the gas phase expanded by the expansion device (15) and the fluid flowing in the cooling circuit (17), and the cooling loops (20, 50) do not participate in the condensation of the gas phase from the compression device (7); - A third operating mode (98), in which the reflux circuit (8) is connected to the second outlet (57) of the compression device (7), and the heat exchanger (16) operates to effect heat exchange between the gaseous phase expanded by the expansion device (15) and the fluid in liquid form flowing in the cooling circuit (17), and the cooling loops (20, 50) are involved in the condensation of the gaseous phase from the compression device (7).

2. The management method (64) according to claim 1, during which the operating mode is implemented according to parameters, the parameters at least including the amount of evaporation gas present in the container, the maximum temperature permitted upon arrival at the delivery location, and / or the temperature of the fluid in liquid form contained in the container.

3. The management method (64) according to claim 2, during which the amount of evaporation gas present in the container (2) is determined by changing the pressure in the top (3) of the container (2) within a given time.

4. The management method (64) according to claim 2, during which the amount of evaporation gas present in the container (2) is determined by the consumption of the consumer (4, 5) between the location for loading the fluid into the container (2) and the delivery location of the fluid, and is determined by estimating the estimated amount of evaporation gas generation in the container (2) according to the design characteristics of the container (2).

5. The management method (64) according to any one of claims 2 to 4, during which, when the temperature of the fluid in liquid form contained in the container (2) is less than or equal to the maximum temperature permitted upon arrival at the delivery location and the amount of evaporation gas to be re-liquefied is greater than an initial threshold, the first operating mode (94) is implemented.

6. The management method (64) according to claim 5, during which, when the temperature of the fluid in liquid form contained in the container (2) is greater than the maximum temperature permitted upon arrival at the delivery location and the amount of evaporation gas to be re-liquefied is less than a first threshold, the second operating mode (95) is implemented, the first threshold being greater than the initial threshold.

7. The management method (64) according to claim 6, during which, when the temperature of the fluid in liquid form contained in the container (2) is greater than the maximum temperature permitted upon arrival at the delivery location and the amount of evaporation gas to be re-liquefied is greater than the first threshold, the third operating mode (100) is implemented.

8. The management method (64) according to any one of claims 2 to 7, including a fourth operating mode (104), wherein, The top (3) of the container (2) is sucked by the compression device (7) until the pressure in the top (3) of the container (2) is less than the saturation pressure of the fluid in liquid form present in the container (2). The fourth operating mode (104) is implemented when the temperature of the fluid in liquid form contained in the container (2) is higher than the maximum temperature allowed when reaching the delivery location by a value between 0 °C and 1 °C and when the amount of evaporated gas is less than the amount of gas consumed by the consumers (4, 5).

9. The management method (64) according to claim 8, comprising a fifth operating mode (102), during which the cooling circuit (20, 50) is enabled. The fifth operating mode (102) is implemented when the temperature of the fluid in liquid form contained in the container (2) is higher than the maximum temperature allowed when reaching the delivery location by a value between 0 °C and 1.5 °C.

10. The management method (64) according to claim 9, during which the fifth operating mode (102) is implemented simultaneously with any one of the first operating mode (94), the second operating mode (100) or the fourth operating mode (104).

11. A fuel supply system (1) for supplying fuel to at least one consumer (4, 5) equipped with a floating structure (70), said fuel supply system (1) comprising at least one compression device (7) configured to absorb a gas phase in order to convey said gas phase to the consumer (4, 5), said compression device (7) comprising at least a first outlet (56), a second outlet (57) and a third outlet (58) configured to convey the gas phase at three different pressure levels, the supply system comprising a reflux circuit (8) configured to return a portion of the gas phase compressed by the compression device (7) to the container (2), the reflux circuit (8) being alternately connected to the first outlet (56) or the second outlet (57) of the compression device (7) and comprising at least a first portion (51) and a second portion (52) provided with an expansion device (15), the supply system (1) comprising at least one heat exchanger (14) configured to operate a heat exchange between the gas phase absorbed by the compression device (7) and the gas phase passing through the reflux circuit (8), the supply system (1) comprising at least one cooling circuit (17) configured to absorb the fluid in liquid form from the container (2), the reflux circuit (8) comprising at least one heat exchanger (16) configured to operate a heat exchange between the gas phase of the fluid flowing in the reflux circuit (8) and the fluid in liquid form flowing in the cooling circuit (17), the supply system (1) comprising cooling loops (20, 50) that participate in the condensation of the fluid in liquid form from the compression device (7), the cooling loops (20, 50) participating in the management method according to any one of claims 1 to 10.

12. A floating structure (70) for transporting and / or storing a fluid in liquid form, comprising the supply system (1) according to claim 11.

Images