System for managing liquid gas transported and / or stored by a floating structure

Abstract

The invention relates to a system (1) for managing a liquid gas, comprising a supply circuit (4), a heat treatment circuit (6), a first heat exchanger (7), a cooling circuit (8), characterized in that the cooling circuit (8) comprises a reliquefaction section (10), a subcooling section (11) and a bypass device (12) configured to circulate the liquid gas either towards the reliquefaction section (10) or towards the subcooling section (11), the management system (1) comprising a second heat exchanger (13), a third heat exchanger (23), a connection line (33) configured to fluidically connect the second heat exchanger (13) and the third heat exchanger (23) in series.

Description

Technical Field

[0001] This invention relates to the field of floating structures for storing and / or transporting liquid gases, and more specifically, to systems for managing such gases stored and / or transported within a vessel. Background Technology

[0002] During the journey of the floating structure, the floating structure includes a tank of liquid gas for consumption and / or delivery to the destination, the floating structure being able to use the gas evaporated within the tank and then compress the latter to supply the floating structure's (multiple) engines.

[0003] In cases of excess vaporized gas in the tank, it is also known to reliquefy the gas by circulating the gas, which has not yet been used to supply the floating structure's (multiple) engines, through one or more heat exchangers, and then return it to the tank.

[0004] Finally, it is known that the liquid gas contained in the tank is heat-treated by subcooling the liquid gas contained in the tank through a refrigerant loop through which the refrigerant fluid flows.

[0005] Depending on the composition of the gas contained in the tank, this subcooling operation can prove problematic. In fact, some of these gases may contain heavy components, such as in the case of natural gas derived from shale gas. These heavy components have a higher freezing point than methane (the main component of natural gas). Because subcooling can subcool a liquid gas to temperatures reaching approximately -172°C, these heavy components can freeze within the heat exchanger, thus hindering heat exchange between the subcooled liquid gas and the refrigerant fluid flowing in the refrigerant loop. Therefore, this can lead to malfunctions of the heat exchanger and can adversely affect the flow of liquid gas and cooling capacity. Summary of the Invention

[0006] This invention allows for the avoidance of these icing phenomena and, for this purpose, provides a management system for managing liquid gases transported and / or stored by a floating structure, the floating structure comprising at least one tank configured to contain the gas and at least one gas consumption device, the management system comprising:

[0007] - At least one supply circuit is configured to supply gas to the gas-consuming device, the supply circuit including at least one compression device.

[0008] - At least one heat treatment circuit for heat treating a vapor-state gas compressed by a compression device.

[0009] - At least one first heat exchanger is configured to exchange heat between a vapor-state gas flowing in the supply loop between the tank and the compression unit and a vapor-state gas flowing in the heat treatment loop.

[0010] - At least one cooling circuit, including at least one pumping device configured to draw liquid gas from a tank.

[0011] The cooling circuit is characterized by comprising a reliquefaction section, a subcooling section, and a bypass device, wherein the bypass device is configured to allow liquid gas to flow toward the reliquefaction section or toward the subcooling section, and the management system includes:

[0012] - A second heat exchanger is configured to exchange heat between a vapor state gas flowing in the heat treatment circuit downstream of the first heat exchanger and a liquid gas flowing in the reliquefaction section.

[0013] - A third heat exchanger and refrigerant loop are configured to exchange heat between the liquid gas flowing in the subcooled section and the refrigerant fluid flowing in the refrigerant loop.

[0014] - A connecting pipeline is configured to fluidly connect the second heat exchanger and the third heat exchanger in series, such that liquid gas already flowing in the second heat exchanger subsequently flows in the third heat exchanger.

[0015] Therefore, the management system according to the invention can manage the supply and / or reliquefaction of gas-consuming equipment using vaporized gas as fuel. Subcooling of the tank is also feasible; however, when the gas contained in the tank contains an excessive amount of heavy hydrocarbons, the liquid gas cooled in the third heat exchanger is from reliquefaction and / or gas that facilitates the reliquefaction of the vaporized gas. Since the liquid gas already circulating in the second heat exchanger has a higher overall temperature than the liquid gas contained in the tank, its temperature at the outlet of the third heat exchanger after cooling is higher than the outlet temperature of the gas directly from the tank and subcooled in the third heat exchanger. Therefore, icing of heavy hydrocarbons in the latter is avoided, while still achieving significant cooling of the tank if necessary.

[0016] The supply loop allows the extraction of vaporized gas formed within the tank and its use as fuel for gas-consuming equipment. Although the tank is designed to ensure insulation, vaporized gas naturally forms over time and should be managed in a way that limits the increase in pressure within the tank. In addition to ensuring the vaporized gas is drawn out of the tank, the compression unit allows it to be increased to a pressure compatible with the gas-consuming equipment.

[0017] For example, gas-consuming devices could be engines that ensure propulsion of the floating structure or generators that power the floating structure. The management system can also supply multiple gas-consuming devices, in which case the supply circuitry is adjusted accordingly to supply vaporized gas to each device.

[0018] The heat treatment loop is connected to the supply loop downstream of the compressor and allows the flow of excess vapor state gas compared to the supply demand of the gas-consuming equipment. Instead of wasting this excess vapor state gas, it flows through the heat treatment loop so that it can be returned to the tank. A first heat exchanger allows for the pre-cooling of this excess vapor state gas during its return due to heat exchange with the vapor state gas exiting the tank and flowing through the supply loop. Thus, the excess vapor state gas is preserved by returning to the tank, rather than being burned or released into the atmosphere.

[0019] The cooling circuit is configured to ensure the flow of liquid gas in one way or another, depending on the functions to be implemented within the management system. Advantageously, the pumping device for extracting the liquid gas is located at the bottom of the tank to pump the liquid gas at the lowest possible temperature.

[0020] From the pumping device, the liquid gas from the tank can flow towards either the reliquefaction section or the subcooling section. The flow of liquid gas towards the reliquefaction section allows for the reliquefaction of the vapor state gas flowing in the heat treatment circuit, and this is carried out by means of a second heat exchanger. During the heat exchange process, the low temperature of the liquid gas causes the temperature of the vapor state gas to decrease until the latter is reliquefied. Advantageously, all vapor state gas entering the second heat exchanger exits in a reliquefied state.

[0021] Furthermore, preferably, the reliquefied gas within the second heat exchanger and the liquid gas from the tank that has already been reliquefied combine at a junction located at the outlet of the second heat exchanger. More specifically, the junction is located at the reliquefaction section of the cooling circuit, and the heat treatment circuit is connected to the reliquefaction section at this junction. Therefore, a mixture of liquid and gas is formed at this junction. Due to the reliquefaction operation occurring in the second heat exchanger, the liquid-gas mixture formed at the junction is at a higher temperature than the liquid gas contained in the tank.

[0022] Liquid gas can be pumped from the pumping unit to the subcooling section to subcool a portion of the liquid gas in the tank, and then returned to the tank to lower the overall temperature of the liquid gas contained in the tank. This operation is only possible when the composition of the liquid gas contained in the tank is limited to heavy hydrocarbons, considering the technical problems of the present invention. A third heat exchanger ensures the subcooling of the liquid gas via the refrigerant loop. The refrigerant fluid flowing in the refrigerant loop has a lower temperature than the liquid gas contained in the tank when passing through the third heat exchanger, thereby lowering the temperature of the liquid gas flowing in the subcooling section. For example, the refrigerant fluid can be nitrogen.

[0023] The bypass device ensures control over the flow of liquid gas contained in the tank and circulating in the cooling circuit. The bypass device is configured to allow liquid gas to flow toward the reliquefaction section while preventing liquid gas from flowing toward the subcooling section, and vice versa.

[0024] If the liquid gas contained in the tank has an excessively high proportion of heavy hydrocarbons, direct flow of the liquid gas into the subcooling section should not be considered, as the risk of icing within the third heat exchanger is too high. For heavy hydrocarbons, it should be understood that this corresponds to hydrocarbons with at least six carbon atoms. Therefore, in this case, the liquid gas contained in the tank and flowing through the cooling circuit can be sent only to the reliquefaction section to reliquefy the vaporized gas flowing through the heat treatment circuit. The flow of the liquid gas within the second heat exchanger and its mixture with the reliquefied gas at the latter's outlet causes an increase in the temperature of the liquid gas.

[0025] The flow of liquid gas is then continued using a connecting line. This connecting line allows for fluid connection between the reliquefaction section and the subcooling section, enabling the second and third heat exchangers to be connected in series.

[0026] Advantageously, the connecting pipeline is connected to the reliquefaction section at the aforementioned junction and extends to the subcooling section upstream of the third heat exchanger, so that the liquid gas that has already flowed in the second heat exchanger subsequently flows in the third heat exchanger in this order.

[0027] Because the temperature of the liquid gas from the reliquefaction section is higher than that of the liquid gas contained in the tank, the temperature of the liquid gas is reduced to a sufficiently low temperature by passing through the third heat exchanger to lower the overall temperature of the tank upon return, but also high enough to prevent the heavy hydrocarbons contained in the liquid gas from freezing within the third heat exchanger and causing it to malfunction. Therefore, the management system according to the invention has multiple functions, all of which can be implemented optimally, regardless of the composition of the liquid gas contained in the tank.

[0028] According to the features of the invention, the bypass device includes a first bypass valve disposed on the reliquefaction section and a second bypass valve disposed on the supercooling section. The first and second bypass valves can be switched to an open or closed position to allow or block the flow of liquid gas in the section under consideration, respectively.

[0029] When liquid gas flows in the cooling circuit, it can flow only in the reliquefaction section or in the subcooling section. Therefore, when one valve is in the open position, the other valve must be in the closed position.

[0030] According to features of the invention, the connecting line includes a coupling valve configured to control the series connection of the third heat exchanger with the second heat exchanger. Similar to the first and second bypass valves, the coupling valve can be switched between an open and a closed position to allow for the series connection or non-series connection of the second and third heat exchangers.

[0031] According to the features of the invention, the cooling circuit includes at least one end, to which a reliquefaction section and / or a supercooling section are fluidly connected. The cooling circuit includes a first end and a second end. The first end includes a return port configured to be disposed at the bottom of the tank, and the second end includes a jetting device configured to be disposed in the top space of the tank. Once the liquid gas has passed through one or more heat exchangers, the end allows the liquid gas to return to the tank. Depending on the applied heat treatment, the liquid gas is preferably sent toward either the first end or the second end.

[0032] The return port at the first end is located at the bottom of the tank, allowing the liquid gas to return to the tank at the highest static pressure level. Due to this, the liquid gas returning to the tank remains liquid and does not vaporize. Furthermore, the tank's inertia slows the temperature rise caused by injecting liquid gas at a higher temperature, thus minimizing the effect of the temperature of the liquid gas returning to the tank (if said temperature is higher than the temperature of the gas contained in the tank).

[0033] Accordingly, the injection device is used to inject supercooled gas into the top space of the tank. Injecting supercooled gas allows vaporized gas that may exist at the level of the top space of the tank to condense, thereby reducing the pressure of the tank. Nevertheless, the injection device should be used with caution, that is, only when supercooling liquid gas without passing through a second heat exchanger. In fact, injecting gas at excessively high temperatures through the injection device may partially evaporate the gas during injection and may cause the pressure of the tank to increase rather than decrease. Therefore, to avoid this phenomenon, the gas already circulating in the second heat exchanger should be returned to the tank through a return port at the first end. As with sections or connecting lines of the cooling circuit, the flow within the end can be controlled by a valve.

[0034] According to the features of the invention, the management system includes a separation device disposed downstream of a second heat exchanger on a heat treatment loop, the heat treatment loop extending from the second heat exchanger to the inlet of the separation device and from the liquid outlet of the separation device to a reliquefaction section. It is feasible that the gas flowing in the heat treatment loop is only partially reliquefied upon exiting the second heat exchanger, i.e., in a two-phase state. In this configuration, the separation device allows the separation of the liquid portion and gas portion of the two-phase gas flow, such that only the liquid portion continues to flow within the heat treatment loop until it reaches the reliquefaction section.

[0035] Therefore, the separation unit is located downstream of the second heat exchanger, allowing gas flowing in the heat treatment circuit and exiting the second heat exchanger to directly enter the separation unit via an inlet. Thus, only liquid gas flows within the portion of the heat treatment circuit extending between the liquid outlet of the separation unit and the reliquefaction section. As previously mentioned, the heat treatment circuit is advantageously connected to the reliquefaction section at the aforementioned junction.

[0036] According to features of the invention, the separation device includes a vapor outlet, and the management system includes a recirculation line extending from the vapor outlet of the separation device to a supply loop between the tank and the first heat exchanger. As previously described, the gas flowing in the heat treatment loop can exit from the second heat exchanger in a state of at least partial reliquefaction, and the separation device isolates the vapor portion from the liquid portion. The vapor portion forms a gaseous portion that has not been reliquefied after flowing within the second heat exchanger. This vaporous gaseous portion then exits the separation device through the vapor outlet and flows within the recirculation line until it reaches the supply loop, where it is recirculated to supply gas-consuming equipment or return to the heat treatment loop.

[0037] According to features of the invention, when the management system is configured for a floating structure comprising at least two tanks, the cooling circuit includes at least two pumping devices, each configured to extract liquid gas from one of the tanks. The cooling circuit includes distribution lines that fluidly connect each pumping device to a reliquefaction section and a subcooling section. In practice, the management system according to the invention can be applied to floating structures comprising multiple tanks. Liquid gas can then be drawn into each tank via multiple pumping devices, each pumping device arranged in one tank. The distribution lines allow all pumping devices to be fluidly connected to the reliquefaction section and the subcooling section. Therefore, liquid gas is collected, and can be collected regardless of the original tanks (multiple tanks), and can be later sent to any of the sections.

[0038] According to features of the invention, when the management system is configured for a floating structure comprising at least two tanks, the cooling circuit includes a return line configured to return gas from the reliquefaction section or the supercooling section to one or both tanks. In the same manner as liquid gas can be drawn from any of the tanks, liquid gas can also be returned to any of the tanks as needed after heat treatment. The return line ensures fluid connection between each section of the cooling circuit and each of the tanks, enabling the return of liquid gas toward a specific tank or tanks, regardless of its source. In this respect, the return line may include a valve system to control the delivery of heat-treated liquid gas to the tank(s).

[0039] The present invention also relates to a floating structure comprising at least one tank configured to contain liquid gas, at least one gas consumption device, and a management system as described above.

[0040] The present invention also relates to a management method for managing liquid gas contained in at least one tank of a floating structure as described above before traveling toward a destination, during which:

[0041] -Consider the composition of the liquid gas contained in the tank,

[0042] - Measure the temperature of the liquid gas contained in the container and compare the measured temperature with a temperature threshold for the gas.

[0043] - If the level of hydrocarbons having at least six carbon atoms is below the hydrocarbon threshold and if the temperature is below the temperature threshold, then allow the liquid gas to flow only in the reliquefaction section.

[0044] - If the level of hydrocarbons having at least six carbon atoms is below the hydrocarbon threshold and if the temperature is above the temperature threshold, then allow the liquid gas to circulate at least in the supercooled section.

[0045] - If the level of hydrocarbons having at least six carbon atoms is above the hydrocarbon threshold and if the temperature is below the temperature threshold, then allow the liquid gas to flow only in the reliquefaction section.

[0046] - If the level of hydrocarbons having at least six carbon atoms is above the hydrocarbon threshold, and if the temperature is above the temperature threshold, then liquid gas is allowed to flow in the reliquefaction section, and gas is allowed to flow in the connecting pipeline so that the second heat exchanger is fluidly connected in series to the third heat exchanger.

[0047] This management method is implemented to prevent icing in the third heat exchanger when transporting liquid gas containing excessive amounts of heavy hydrocarbons. Therefore, the composition of the liquid gas is first considered and compared to hydrocarbon thresholds to determine if there is a risk of icing. As previously mentioned, heavy hydrocarbons with an icing risk are hydrocarbons containing at least six carbon atoms. The heavy hydrocarbon threshold that leads to an icing risk can include between 80 and 150 parts per million (ppm), for example, 100 ppm. Below this threshold, although heavy hydrocarbons are present in the liquid gas, the latter is negligible and sufficient to be considered sufficient for the liquid gas to be supercooled without any risk of icing.

[0048] The temperature of one or more tanks is also measured to compare it to a temperature threshold. This threshold can be a fixed value or can be defined, for example, by the unloading conditions at the destination. In practice, each destination capable of unloading liquefied gases has its own requirements for liquefied gas cargo. If the threshold is exceeded, the destination's management can refuse unloading, resulting in heavy time and cost constraints. Therefore, the management system should be used in conjunction with the temperature threshold to determine whether the cargo temperature can be increased without fear of exceeding the threshold, or conversely, whether the cargo should be cooled if the temperature threshold is exceeded.

[0049] In the absence of a risk of icing, the liquid gas can be subcooled without concern by directly feeding it into the subcooling section, and this is done to cool the cargo if the temperature exceeds a certain threshold. Conversely, if the tank temperature is below the threshold, a reliquefaction operation can be performed separately to save energy required for operating the refrigerant loop. Nevertheless, since reliquefaction inevitably leads to a gradual increase in cargo temperature, the cargo temperature should be controlled periodically.

[0050] In cases where there is a risk of liquefied gas freezing within the third heat exchanger, a separate overcooling operation should not be considered. If the tank temperature is below a certain threshold, a separate reliquefaction operation is feasible. Conversely, if the temperature exceeds this threshold, the cargo should be cooled. In this configuration, and to avoid any risk of freezing, the connecting lines are then opened to connect the second and third heat exchangers in series. The liquefied gas then passes sequentially through the two heat exchangers to reach a temperature sufficient to cool the cargo, but the heavy hydrocarbons contained in the liquefied gas will not freeze in the third heat exchanger.

[0051] Based on the characteristics of this method:

[0052] - If the level of hydrocarbons with at least six carbon atoms is below the hydrocarbon threshold and if the temperature is above the temperature threshold, then determine the surplus of vapor state gas exceeding the supply demand of the gas-consuming equipment, and compare this surplus with the subcooling capacity of the third heat exchanger.

[0053] -If the surplus of vapor gas is less than the subcooling capacity of the third heat exchanger, then liquid gas will only flow in the subcooling section.

[0054] If the surplus of vapor gas exceeds the subcooling capacity of the third heat exchanger, liquid gas flows in the reliquefaction section, and gas flow in the connecting lines is permitted to fluidly connect the second heat exchanger of the reliquefaction section to the third heat exchanger of the subcooling section in series.

[0055] In cases where there is no risk of icing and the temperature threshold is exceeded, the management method may implement an additional comparison step before selecting the operating mode. Surplus vapor state gas corresponds to the total amount of vapor state gas contained in the tank minus the portion of the vapor state gas required by the supply gas consumption equipment.

[0056] If the excess vapor state gas is excessive compared to the subcooling capacity of the third heat exchanger, then circulating liquid gas only in the subcooling section (e.g., so that the subcooled gas can be injected into the top space of the tank later) is counterproductive. The amount of excess vapor state gas is excessive for sufficiently influencing the subcooling of the liquid gas.

[0057] In this situation, it is more efficient to discharge the surplus gas from the tank rather than attempting to condense it in the space at the top of the tank. Therefore, it is advantageous to allow the surplus vapor state gas to circulate in the supply loop and then in the heat treatment loop to reliquefy it. Thus, the liquefied gas is sent toward the reliquefaction section to reliquefy the surplus vapor state gas.

[0058] However, it should be remembered that the tank temperature also needs to be reduced, as it is too high compared to the temperature threshold. Therefore, returning gas directly from the reliquefaction section to the tank is not recommended, as this would instead increase the tank temperature. Thus, the only suitable configuration for this situation is to allow the liquid gas from the second heat exchanger to circulate in the connecting line so that it is cooled in the third heat exchanger before being returned to the tank, as in cases where there is a risk of icing due to the gas composition. Preferably, this results in a reduction in the tank temperature, which is theoretically less effective than circulating liquid gas only in the supercooling section, but in practice, it is more effective than cases where there is an excessive amount of excess vapor state gas in the tank. Alternatively, this at least allows for a substantial limitation on the temperature rise of the liquid gas contained in the tank. Depending on the course of the floating structure, once the course of the floating structure has been completed, the limitation on the temperature rise of the liquid gas may be sufficient to keep the cargo below the temperature threshold. In this respect, the temperature threshold can be specifically selected to provide this configuration.

[0059] If the subcooling capacity of the third heat exchanger is sufficient compared to the amount of surplus vapor state gas contained in the tank, then liquid gas is separately fed into the subcooling section to condense the surplus in the tank.

[0060] Based on the characteristics of this method, a fluid analyzer can be used to consider the composition of the gas contained in the tank. The fluid analyzer can determine the amount of heavy hydrocarbons contained in the transported gas, in parts per million.

[0061] Based on the characteristics of this method, technical documentation can be used to consider the composition of the gas contained in the tank. This is an alternative solution to determination using a fluid analyzer. The technical document provides for cargoes containing liquid gases and includes several characteristics associated with liquid gases, such as the amount of heavy hydrocarbons in parts per million.

[0062] Based on the characteristics of this method, it is repeatable over time. Although the composition of the transported gas does not change over time, it is necessary to implement the management method periodically throughout the journey because the tank temperature varies over time, and the temperature variation is even greater if the management system is being configured specifically. Therefore, the comparison between the measured tank temperature and the temperature threshold should be verified periodically to determine whether the configuration of the management system should be changed or should remain unchanged. Attached Figure Description

[0063] Other features and advantages of the invention will become more apparent, both in the description which follows and from several embodiments given with reference to the accompanying schematic diagrams for illustrative and non-limiting purposes, wherein:

[0064] [ Figure 1 [Illustration] is a schematic diagram of a gas management system according to the present invention.

[0065] [ Figure 2 This illustrates the flow of gas within the management system according to the first operating mode.

[0066] [ Figure 3 This illustrates the gas flow within the management system according to the second operating mode.

[0067] [ Figure 4 This illustrates the gas flow within the management system according to the third operating mode.

[0068] [ Figure 5 This is a schematic diagram of a gas management system applicable to a floating structure comprising multiple tanks.

[0069] [ Figure 6 [A flowchart of a gas management method implemented by a management system according to the present invention]

[0070] [ Figure 7 [ ] is a flowchart of a variation of a gas management method implemented by a management system according to the present invention. Detailed Implementation

[0071] Figure 1 This is a schematic diagram of a gas management system 1 according to the present invention. For example, such a management system 1 can be integrated into a floating structure for transporting and / or storing liquid gases. Typically, such a floating structure includes at least one tank 2 to ensure the transport and / or storage of liquid gases, but according to… Figure 1 The configuration shown indicates that the floating structure includes a single tank 2. This floating structure also includes at least one gas-consuming device 3, which may be, for example, an engine ensuring propulsion of the floating structure or a generator ensuring power supply to the floating structure. The management system can supply the single gas-consuming device 3, but in… Figures 1 to 5 In this design, the floating structure includes a first gas-consuming device 3a and a second gas-consuming device 3b. For example, the first gas-consuming device 3a may be an engine that ensures the propulsion of the floating structure, while the second gas-consuming device 3b may be a generator that ensures the supply of power to the floating structure.

[0072] Tank 2 is constructed to ensure a tight seal and insulation for the liquid gas contained therein. Nevertheless, over time, some of the liquid gas present in tank 2 evaporates, causing an increase in pressure within tank 2. Therefore, management system 1 allows for the prevention of potential overpressure within tank 2 by venting the vaporized gas from tank 2.

[0073] For this purpose, the management system 1 includes a supply loop 4 extending between the tank 2 and the gas consuming device 3. The supply loop 4 includes at least one compression device 5 configured to draw in vapor-state gas present in the tank 2. Figures 1 to 5 In the system, the management system 1 includes a first compression device 5a and a second compression device 5b, thereby allowing redundancy to be ensured so that even if one of the compression devices 5 fails, the gas consumption device 3 can be continuously supplied.

[0074] Each compression unit 5 is configured to increase the pressure of the vapor state gas so that it is compatible with the pressure required by one or both of the gas consuming devices 3. Therefore, the supply circuit 4 allows for both pressure regulation of the tank 2 and supply of fuel to the gas consuming devices 3.

[0075] The management system 1 also includes a heat treatment circuit 6, which is connected downstream of the compression unit 5 to the supply circuit 4. This is a flow of vaporized gas circulating in the heat treatment circuit 6, corresponding to a surplus of vaporized gas exceeding the supply demand of the gas-consuming devices(s)3. Therefore, the heat treatment circuit 6 facilitates the return of the surplus vaporized gas towards the tank 2. One objective of the management system 1 according to the invention is to reliquefy the surplus vaporized gas before returning it to the tank 2.

[0076] In this respect, the management system 1 includes a first heat exchanger 7 configured to exchange heat between the vapor state gas flowing in the supply circuit 4 and the vapor state gas flowing in the heat treatment circuit 6 to precool the latter. This precooling then facilitates the reliquefaction of the vapor state gas intended to be returned to the tank 2. In some configurations, such as when there is no vapor state gas flowing in the heat treatment circuit 6, the vapor state gas flowing in the supply circuit 4 can bypass the first heat exchanger 7 using a bypass line 35 to limit any pressure drop in the vapor state gas. The flow of vapor state gas within the bypass line 35 is managed by a bypass valve 36.

[0077] The management system 1 also includes a cooling circuit 8, which can operate in different ways to perform various operating modes, which will be described in detail later. The cooling circuit 8 includes a pumping device 9 configured to draw liquid gas from the tank 2. From this pumping device 9, the cooling circuit 8 is divided into two sections: a reliquefaction section 10 and a supercooling section 11. Therefore, liquid gas from the tank 2 and pumped by the pumping device 9 can flow within the reliquefaction section 10 or within the supercooling section 11.

[0078] In this respect, the cooling circuit 8 includes a bypass device 12, which is provided with a first bypass valve 12a located at the reliquefaction section 10 and a second bypass valve 12b located at the subcooling section 11. The bypass valves are configured to alternate between an open position that allows the flow of liquid gas and a closed position that prevents the flow of liquid gas. Liquid gas can flow from the pumping device 9 only toward either the reliquefaction section 10 or the subcooling section 11, and when one bypass valve is open, the other bypass valve must be closed.

[0079] The management system 1 also includes a second heat exchanger 13 configured to exchange heat between a vapor state gas flowing in the heat treatment circuit 6 downstream of the first heat exchanger 7 and a liquid gas flowing in the reliquefaction section 10. After being pre-cooled in the first heat exchanger 7, the vapor state gas flowing in the heat treatment circuit 6 then passes through the second heat exchanger 13 and is at least partially reliquefied due to heat exchange with the liquid gas from the tank 2 flowing in the reliquefaction section 10.

[0080] In the event that the vapor-state gas flowing in the heat treatment circuit 6 is partially reliquefied, the management system 1 includes a separation device 14 disposed downstream of the second heat exchanger 13 in the heat treatment circuit 6. At the outlet of the second heat exchanger 13, the at least partially reliquefied gas enters the separation device 14 via inlet 15. If the gas is in a two-phase state at the outlet of the second heat exchanger 13, the separation device 14 separates the liquid portion from the gas portion. The liquid portion exits the separation device 14 via liquid outlet 16 and continues its flow in the heat treatment circuit 6 until it reaches the reliquefaction section 10 of the cooling circuit 8, advantageously at the junction 17.

[0081] The separation device 14 also includes a vapor outlet 18 through which the vapor portion of the gas in a potential two-phase state is discharged at the outlet of the second heat exchanger 13. Therefore, the management system 1 includes a recirculation line 19 extending from the vapor outlet 18 of the separation device 14 to the supply circuit 4, so as to recirculate the unreliquefied gas toward the gas consumption device 3 or recirculate it again in the heat treatment circuit 6.

[0082] To improve the thermodynamic properties of the gas, the heat treatment circuit 6 may be provided with a first expansion member 20 between the second heat exchanger 13 and the inlet 15 of the separation device 14, and a second expansion member 21 may be provided between the liquid outlet 16 of the separation device 14 and the junction 17. Correspondingly, the recirculation line 19 may be provided with a third expansion member 22.

[0083] The liquid gas portion exiting the separation device 14 and the liquid gas flowing in the reliquefaction section 10 from the second heat exchanger 13 merge at junction 17. From the latter, the liquid gas can continue its flow in the reliquefaction section 10 to return to tank 2. This flow is managed by return valve 37. Due to the reliquefaction operation that occurs in the second heat exchanger 13, the liquid gas flowing through junction 17 is necessarily at a higher temperature than the liquid gas contained in tank 2.

[0084] Regarding the subcooling section 11, the management system 1 includes a third heat exchanger 23 configured to exchange heat between the liquid gas flowing in the subcooling section 11 and the refrigerant fluid flowing in a refrigerant loop 24 (not described in detail). The refrigerant loop 24 is configured to allow the refrigerant fluid (e.g., nitrogen) to flow through while simultaneously heat-treating it, such that the refrigerant fluid cools the liquid gas within the third heat exchanger 23 despite the low temperature of the liquid gas. Subcooling the liquid gas from tank 2 then lowers the temperature of tank 2 and the liquid gas it contains.

[0085] The reliquefaction section 10 and the supercooling section 11 extend downstream of the junction 17 and the third heat exchanger 23, respectively, until they join together at the confluence 25 before returning to the tank 2. To optimize the return to the tank 2 based on the prior heat treatment of the liquefied gas, the cooling circuit 8 includes a first end 26 and a second end 27.

[0086] The first end 26 extends to the tank 2 and includes a return port 28 advantageously disposed at the bottom of the tank 2. Returning the liquid gas to the bottom of the tank 2 limits its effect on temperature, which may be higher than the temperature of the gas contained in the tank 2, and also prevents undesirable evaporation of the liquid gas as it exits through the return port 28.

[0087] For example, the return port 28 is a calibration port, meaning it has a smaller cross-section than the cross-section of the first end 26 measured just before the return port 28. The cross-section of the return port 28 is between 5% and 30% of the cross-section of the first end 26. This has the effect of keeping the pressure inside the first end 26 higher than the pressure at the bottom of the tank 2.

[0088] The second end 27 also extends into the tank 2 and includes an injection device 29 disposed at the level of the top space 30 of the tank 2. The injection device 29 allows supercooled gas to be injected into the top space 30 to recondense the vapor-state gas present therein. This recondensation allows for a reduction in the pressure and temperature of the tank 2. Flow within the first end 26 and the second end 27 is controlled by a first end valve 31 and a second end valve 32, respectively.

[0089] As can be understood from the foregoing, the management system allows for the reliquefaction of the vaporized gas contained in tank 2, and also lowers the temperature of tank 2 by subcooling a portion of the liquid gas therein and returning it to the tank. Nevertheless, depending on the composition of the liquid gas contained in tank 2, this subcooling operation can be risky.

[0090] In reality, some types of gases, such as natural gas from shale gas, may contain a significant amount of heavy hydrocarbons, i.e., hydrocarbons containing at least six carbon atoms. Heavy hydrocarbons have a higher solidification temperature than light hydrocarbons. However, the supercooling of the liquid gas significantly lowers the already very low temperature of the liquid gas contained in tank 2. If the latter contains an excessive amount of hydrocarbons, these hydrocarbons may freeze within the third heat exchanger 23 and cause a malfunction in the management system 1.

[0091] To overcome this, the management system 1 according to the invention includes a connecting line 33 extending between the reliquefaction section 10 (advantageously at the junction 17) and the subcooling section 11. The connecting line 33 allows fluid connection between the second heat exchanger 13 and the third heat exchanger 23. Control of flow within the connecting line 33 is ensured by a connection valve 34.

[0092] As previously described, due to the heat exchange occurring within the second heat exchanger 13, the temperature of the liquid gas flowing to the junction 17 of the reliquefaction section 10 is higher than that of the liquid gas contained in tank 2. If the liquid gas then flows to the third heat exchanger 23 via the connecting line 33, the liquid gas is then cooled due to the refrigerant fluid in the refrigerant loop 24. Nevertheless, since the temperature of the liquid gas is higher than that of the liquid gas contained in tank 2, the cooling occurring within the third heat exchanger 23 does not lower the temperature of the liquid gas sufficiently to cause the heavy hydrocarbons to freeze within the third heat exchanger 33. Nevertheless, the temperature of the liquid gas passing sequentially through the second heat exchanger 13 and the third heat exchanger 23 is low enough to reduce the temperature of tank 2 during the liquid gas return.

[0093] Therefore, it can be understood that the management system 1 according to the present invention can ensure all the functions previously described, while adjusting according to the composition of the liquid gas contained in the tank 2, and there is no risk of the management system 1 failing due to the freezing of heavy hydrocarbons in the third heat exchanger 23.

[0094] Figures 2 to 4 The diagram illustrates fluid flow within a management system according to three operating modes. For each of these diagrams, lines and loops shown as solid lines correspond to fluid flow, while dashed lines and loops indicate the absence of fluid flow.

[0095] Figure 2 A first operating mode is illustrated, during which only reliquefaction is performed. In this mode, the vaporized gas contained in the top space 30 of tank 2 is drawn in by at least one of the compression devices 5 within the supply circuit 4. The vaporized gas passes through a first heat exchanger 7 and is then compressed by at least one of the compression devices 5 to a pressure compatible with the gas-consuming devices 3. If this proves necessary, at least a portion of the vaporized gas is sent to at least one of the gas-consuming devices 3 to supply the latter or these gas-consuming devices.

[0096] Accordingly, the vapor state gas representing the surplus vapor state gas flows within the heat treatment circuit 6 and passes through the first heat exchanger 7 so as to be pre-cooled by the vapor state gas flowing in the supply circuit 4.

[0097] At the outlet of the first heat exchanger 7, the vaporized gas continues to flow in the heat treatment circuit 6 until it passes through the second heat exchanger 13. Simultaneously, the liquid gas contained in the tank 2 is pumped by the pumping device 9 to flow in the cooling circuit 8. To reliquefy the vaporized gas passing through the second heat exchanger 13, the bypass device 12 is configured to send the liquid gas toward the reliquefaction section 10. Therefore, the first bypass valve 12a is open, while the second bypass valve 12b is closed.

[0098] Therefore, the liquid gas also passes through the second heat exchanger 13, and the resulting heat exchange ensures at least partial reliquefaction of the vapor state gas flowing through the heat treatment circuit 6 and passing through the second heat exchanger 13.

[0099] At the outlet of the second heat exchanger 13, the at least partially reliquefied gas expands through the first expansion member 20 and enters the separation device 14 via the inlet 15. If the gas that has entered the separation device 14 is in a two-phase state, the separation device 14 separates the liquid portion from the vapor portion. The potential vapor portion exits the separation device 14 through the vapor outlet 18 and flows within the recirculation line 19 to reach the supply loop 4 again.

[0100] Accordingly, the liquid portion exits from the separation device 14 through the liquid outlet 16 and continues to flow in the heat treatment circuit 6 until it reaches the reliquefaction section 10 through the junction 17, where the liquid gas from the tank 2 also flows and is aided in the reliquefaction of the vapor state gas by passing through the second heat exchanger 13.

[0101] The two liquid gas streams then continue to circulate within the reliquefaction section 10 until they converge at point 25. According to this first operating mode, return valve 37 opens while engagement valve 34 closes. Finally, the liquid gas flows to the first end 26 and returns to tank 2 through return port 28 located at the bottom of tank 2.

[0102] According to this first operating mode, the liquid gas returns to tank 2 at a higher temperature than the liquid gas contained in tank 2. Therefore, it is understood that injecting it into the top space 30 of tank 2 would be counterproductive, causing the liquid gas to return to tank 2 via the first end 26. Consequently, the first end valve 31 opens, while the second end valve 32 closes.

[0103] This first operating mode allows the vaporized gas contained in tank 2 to be reliquefied, but because the temperature of the liquid gas returning to tank 2 is high, the temperature of the vaporized gas contained in tank 2 gradually increases. Since the refrigerant loop 24 is not activated, this first operating mode also allows for energy savings.

[0104] Figure 3 A second operating mode of the management system 1 according to the invention is shown. This second operating mode allows for the supercooling of a portion of the liquid gas contained in the tank 2 to reduce the overall temperature of the latter and / or to recondense the vapor state gas present in the top space 30 of the tank 2.

[0105] Therefore, vaporized gas can flow in supply circuit 4, but only in sufficient quantity to supply gas-consuming equipment 3, without allowing surplus vaporized gas to flow in heat treatment circuit 6. The first heat exchanger 7 is not required; bypass valve 36 is opened, and the vaporized gas flowing in supply circuit 4 passes through bypass line 35 instead of unnecessarily passing through the first heat exchanger 7.

[0106] Accordingly, a portion of the liquid gas contained in tank 2 is pumped by pumping device 9 to circulate in cooling circuit 8. To lower the temperature of tank 2, bypass device 12 is configured to direct the liquid gas toward subcooled section 11. Therefore, first bypass valve 12a is closed, while second bypass valve 12b is open.

[0107] Then, the liquid gas flows to the third heat exchanger 23. At the same time, the refrigerant loop 24 is activated to allow the refrigerant fluid to flow within the third heat exchanger 23, thereby ensuring the subcooling of the liquid gas flowing in the subcooling section 11.

[0108] At the outlet of the third heat exchanger 23, the supercooled liquid gas continues its flow in the supercooled section 11 until it reaches the confluence point 25. The liquid gas then returns to tank 2. When there is excessive vapor state gas in the top space 30 of tank 2, the supercooled liquid gas flows through the second end 27 and is injected into the top space 30 of tank 2 via the injection device 29 to recondense the vapor state gas therein. However, the supercooled liquid gas can also return to tank 2 via the first end 26 and through the return port 28. This alternative also helps to lower the temperature of tank 2. Depending on one or the other of the feasible options, either end valve 31, 32 is open while the other is closed.

[0109] As mentioned earlier, if the gas contained in tank 2 has an excessive amount of heavy hydrocarbons, the second operating mode cannot be used because they may freeze in the third heat exchanger 23.

[0110] In this situation, the only means to reduce the temperature of tank 2 is to use Figure 4 The third operating mode of the management system is shown.

[0111] According to the third operating mode, the vapor state gas contained in the top space 30 of the tank 2 flows in the supply circuit 4, passes through the first heat exchanger 7, and is then compressed by at least one of the compression devices 5 to a pressure compatible with the gas consumption device 3 in order to supply at least one of them.

[0112] The surplus vapor state gas flows within the heat treatment circuit 6, is pre-cooled by passing through the first heat exchanger 7, and then passes through the second heat exchanger 13.

[0113] Accordingly, the liquid gas contained in tank 2 is pumped by pumping device 9 to flow in cooling circuit 8, and more specifically in reliquefaction section 10. For this purpose, first bypass valve 12a is opened, while second bypass valve 12b is closed.

[0114] Therefore, the liquid gas also passes through the second heat exchanger 13, and the resulting heat exchange ensures at least partial reliquefaction of the vapor state gas flowing through the heat treatment circuit 6 and passing through the second heat exchanger 13.

[0115] At the outlet of the second heat exchanger 13, at least partially reliquefied gas enters the separation device 14, and the liquid portion exits the separation device 14 through the liquid outlet 16 and continues to flow in the heat treatment circuit 6 until it reaches the reliquefaction section 10 through the junction 17, where the liquid gas from the tank 2 also flows and is aided in the reliquefaction of the vapor state gas by passing through the second heat exchanger 13.

[0116] The purpose here is to lower the temperature of tank 2, so that the liquid gas passing through junction 17 cannot... Figure 2 The solution is returned directly to tank 2, as this would, conversely, increase the temperature of tank 2.

[0117] Therefore, in this configuration, the return valve 37 is closed, while the connection valve 34 is open, allowing the liquid gas to flow through the connection line 33 and connect to the subcooling section 11 to pass through the third heat exchanger 23, which is connected in series with the second heat exchanger 13. The refrigerant loop 24 is activated to cool the liquid gas flowing within the third heat exchanger 23. Because its temperature is higher than that of the liquid gas contained in tank 2, the liquid gas flowing through the connection line 33 in the subcooling section 11 is cooled within the third heat exchanger 23, but not to a temperature low enough to cause the heavy hydrocarbons to freeze within the third heat exchanger 23. However, the cooling is sufficient to lower the temperature of tank 2 later.

[0118] The liquefied gas cooled in the third heat exchanger 23 then continues to flow in the supercooled section 11 until it reaches the confluence point 25 and returns to the tank 2 via the first end 26 and the return port 28. In fact, returning the cooled liquefied gas to the tank 2 by injection via the injection device 29 is counterproductive. According to this third operating mode, although the liquefied gas is cooled, it is not cooled sufficiently to effectively inject it into the top space of the tank 30. In fact, there is a risk of gas evaporation during injection, which increases rather than decreases the amount of vaporized gas in the top space 30 of the tank 2.

[0119] Therefore, according to this third operating mode, the liquid gas can only return to the tank 2 through the first end 26, but the temperature of the tank 2 is still allowed to be reduced, and there is no risk of heavy hydrocarbons contained in the liquid gas in the third heat exchanger 23 freezing.

[0120] Figure 5 A gas management system 1 according to the present invention is shown, but this is applicable to a floating structure comprising a plurality of tanks 2 intended to store the liquid gas. Figure 5 The diagram shows two tanks 2a and 2b, but the management system 1 can be adapted to interact with more tanks 2.

[0121] In the case of a floating structure comprising two tanks 2a and 2b, at least a portion of the loops and pipelines of the management system 1 that directly interact with said tanks 2a and 2b are replicated in order to ensure gas management with respect to all of these tanks.

[0122] Therefore, the vaporized gas from both tanks 2 can be drawn in by the compression device and circulated within the supply circuit 4. Conversely, liquid gas can be drawn out from one or both tanks 2 and circulated within the cooling circuit 8. Figure 5 The management system 1 shown includes a first pumping device 9a disposed in a first tank 2a and a second pumping device 9b disposed in a second tank 2b.

[0123] The cooling circuit 8 also includes a distribution line 38 that can collect the liquid gas from each tank 2 and send all the collected liquid gas to the reliquefaction section 10 and / or the supercooling section 11.

[0124] Once the heat treatment of the liquid gas has been performed, the liquid gas can also be returned to one or both of the tanks 2 as needed. In this regard, the cooling circuit includes a return line 39 to ensure that the liquid gas from the reliquefaction section 10 or the supercooling section 11 is distributed to one or both tanks 2. The return line 39 includes a first return valve 40a and a second return valve 40b, which allow or prevent the flow of liquid gas to one or both of the tanks 2.

[0125] To ensure optimal return of liquid gas to each tank 2, for each tank 2, the cooling circuit 8 includes first ends 26a, 26b having first end valves 31a, 31b and return orifices 28a, 28b, and second ends 27a, 27b having second end valves 32a, 32b and injection devices 29a, 29b. Each of these elements is configured to return liquid gas to one or both of the tanks 2a, 2b in one manner or another, depending on the specific circumstances. Figures 2 to 4 The operating mode described in the document is the one that is enabled.

[0126] Return line 39 allows selection of tank 2 to return liquid gas, or return of liquid gas to two tanks 2 by distributing liquid gas in a defined manner. For example, gas from only the reliquefaction operation can be preferentially returned to the coldest tank 2, while gas from only the supercooling operation can be preferentially returned to the hottest tank 2.

[0127] Figure 5 The undescribed structural and functional elements of management system 1 are the same as those previously described, and will be referred to... Figures 1 to 4 About Figures 1 to 5 Description of all common components.

[0128] Figure 6 A flowchart of a management method 100 implemented by a management system according to the present invention is shown. Management method 100 allows determining which method should be used based on previously verified conditions. Figures 2 to 4 Which of the operating modes described herein. Preferably, management method 100 is implemented during the journey of the floating structure designed to transport a liquid gaseous cargo contained in a tank. Management method 100 begins with initiation step 101.

[0129] Next, consider the composition of the liquid gas contained in the tank. More specifically, verify whether the level of hydrocarbons with at least six carbon atoms (C6) is below or above the hydrocarbon threshold Sh. If it is above this threshold Sh, the risk of freezing is too high to proceed. Figure 3 The second operating mode 103 shown is supercooling only. Therefore, considering this composition is necessary to determine which configuration to implement within the management system. For example, the composition of the liquid gas can be measured by a fluid analyzer that can be arranged in the tank. Such a fluid analyzer is capable of measuring the level of hydrocarbons with at least six carbon atoms (C6) in parts per million (ppm). The hydrocarbon threshold Sh that leads to the risk of icing can include between 80 and 150 ppm, for example, 100 ppm. According to another example, when liquid gas is loaded in a floating structure, the level of hydrocarbons with at least six carbon atoms (C6) can be read from the provided technical documentation.

[0130] Regardless of the level of hydrocarbons (C6) with at least six carbon atoms in the liquid gas, another step should be performed before determining which operating mode should be implemented. The temperature T of the liquid gas cargo is measured and compared to a temperature threshold Ts. For example, the temperature threshold Ts can be a fixed value or can be defined by the unloading conditions at the destination point (i.e., the point where the liquid gas cargo should be transported). Therefore, the threshold Ts may vary from destination point to destination and should be adhered to, as exceeding the threshold Ts may result in the destination point's management rejecting the cargo, leading to time and financial losses. Therefore, it is necessary to periodically verify that the cargo temperature T is below the temperature threshold Ts, and if not, to cool the cargo.

[0131] If the cargo temperature T is below the temperature threshold Ts, it means the cargo temperature can be increased. In this case, and regardless of the gas composition, [further action is taken]. Figure 2 The first operating mode 102 is shown, and the liquid gas flows only in the reliquefaction section. Furthermore, this allows for the avoidance of unnecessary use of the previously described cooling loop, and thus saves energy by keeping it inactive.

[0132] If the level of hydrocarbons (C6) with at least six carbon atoms is below the hydrocarbon threshold Sh and the cargo temperature T is above the temperature threshold TS, then the cargo should be cooled, but there is no risk of heavy hydrocarbons freezing in the third heat exchanger. This can be implemented. Figure 3 The second operating mode 103 is shown, and liquid gas flows in the supercooled section to cool the temperature of the tank.

[0133] If the level of hydrocarbons (C6) with at least six carbon atoms is above the hydrocarbon threshold Sh and the cargo temperature T is above the temperature threshold Ts, the cargo should be cooled; however, there is a risk that heavy hydrocarbons may freeze in the third heat exchanger. Therefore, in this case, a cooling method should be used. Figure 4 The third operating mode 104 shown in the diagram involves the liquid gas passing through a second heat exchanger and then through a third heat exchanger in series, in order to reach a temperature low enough to cool the cargo but high enough to prevent the heavy hydrocarbons from freezing in the third heat exchanger.

[0134] Management method 100 can be repeated over time. It may even need to be iterated throughout the entire journey, as the operating mode affects the cargo temperature T over time, and it is likely that the operating mode must be changed once or more over time. The composition of the liquid gas does not necessarily need to be considered in every iteration; management method 100 can take it into account during its first iteration and then retain it in memory.

[0135] Figure 7A variation of management method 100 is shown, which allows for optimized heat treatment of liquid gas cargoes when the level of hydrocarbons C6, which have at least six carbon atoms, is below the hydrocarbon threshold Sh and the cargo temperature T is above the temperature threshold Ts. Therefore, the situation here is to cool the cargo without concern about icing within the third heat exchanger.

[0136] According to this variation of management method 100, the amount of surplus vapor state gas Sbog is measured and compared with the subcooling capacity Cs of the third heat exchanger. The purpose of this paper is to determine whether injecting subcooled gas into the tank top space is effective for the amount of vapor state gas to be recondensed.

[0137] If the supercooling capacity Cs is sufficient to heat-treat the surplus vapor state gas Sbog in the tank top space, then the second operating mode 103 is implemented to allow liquid gas to circulate only in the supercooling section, to inject supercooled liquid gas, and to recondense all surplus vapor state gas Sbog in the tank top space.

[0138] If the excess vapor state gas Sbog in the tank top space is excessive compared to the subcooling capacity Cs of the third heat exchanger, it is more efficient to remove the excess Sbog from the tank to reliquefy it than to attempt to recondense it in the tank top space by injecting subcooled liquid gas. In this case, implementation should be optimized. Figure 4 The third operating mode shown in the diagram is 104, not... Figure 3 The second operating mode 103 illustrated in the diagram is more suitable. This allows for faster removal of excess vapor-state gas Sbog contained in the top space of the tank. Furthermore, this allows for a reduction in the tank temperature, where the cargo temperature T is above a temperature threshold Ts. Therefore, this variation of the management method 100 allows for further optimization of the heat treatment of the gas contained in the tank, regardless of whether the gas is in a liquid or gaseous state.

[0139] Of course, the present invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the present invention.

[0140] As just described, the present invention achieves its intended purpose and allows for the provision of a system for managing gases contained in a tank, ensuring gas supply, reliquefaction of surplus vapor state gases, and / or management of the tank temperature, all in an optimal manner regardless of the composition of the gas contained in the tank. Variations not described herein may be implemented without departing from the context of the invention, provided they include the management system according to the invention.

Claims

1. A management system (1) for managing liquid gases transported and / or stored by a floating structure, the floating structure comprising at least one tank (2, 2a, 2b) configured to contain the gas and at least one gas consumption device (3, 3a, 3b), the management system (1) comprising: - At least one supply circuit (4) configured to supply gas to the gas consuming devices (3, 3a, 3b), the supply circuit (4) including at least one compression device (5). - At least one heat treatment circuit (6) for heat treatment of the vapor state gas compressed by the compression device (5), - At least one first heat exchanger (7) is configured to exchange heat between the vapor state gas flowing in the supply circuit (4) and the vapor state gas flowing in the heat treatment circuit (6) between the tanks (2, 2a, 2b) and the compression device (5). - At least one cooling circuit (8) includes at least one pumping device (9, 9a, 9b), said at least one pumping device (9, 9a, 9b) configured to draw liquid gas from the tanks (2, 2a, 2b), The cooling circuit (8) is characterized in that it includes a reliquefaction section (10), a supercooling section (11), and a bypass device (12), the bypass device (12) being configured to allow liquid gas to flow toward the reliquefaction section (10) or toward the supercooling section (11), and the management system (1) includes: - A second heat exchanger (13) is configured to exchange heat between the vapor state gas flowing in the heat treatment circuit (6) downstream of the first heat exchanger (13) and the liquid gas flowing in the reliquefaction section (10). - A third heat exchanger (23) and a refrigerant loop (24), wherein the third heat exchanger (23) is configured to exchange heat between the liquid gas flowing in the subcooled section (11) and the refrigerant fluid flowing in the refrigerant loop (24). - Connecting line (33) configured to fluidly connect the second heat exchanger (13) and the third heat exchanger (23) in series, such that liquid gas already flowing in the second heat exchanger (13) subsequently flows in the third heat exchanger (23).

2. The management system (1) according to claim 1, wherein, The bypass device (12) includes a first bypass valve (12a) disposed on the reliquefaction section (10) and a second bypass valve (12b) disposed on the subcooling section (11).

3. The management system (1) according to claim 1 or 2, wherein, The connecting line (33) includes a connection valve (34) configured to control the series connection of the third heat exchanger (23) with the second heat exchanger (13).

4. The management system (1) according to any one of the preceding claims, wherein, The cooling circuit (8) includes at least one end, to which the reliquefaction section (10) and / or the supercooling section (11) are fluidly connected. The cooling circuit (8) includes a first end (26, 26a, 26b) and a second end (27, 27a, 27b). The first end includes a return port (28, 28a, 28b) configured to be disposed at the bottom of the tank (2, 2a, 2b). The second end includes a spray device (29, 29a, 29b) configured to be disposed at the top space (30) of the tank (2, 2a, 2b).

5. The management system (1) according to any one of the preceding claims includes a separation device (14) disposed downstream of the second heat exchanger (13) on the heat treatment circuit (6), the heat treatment circuit (6) extending from the second heat exchanger (13) to the inlet (15) of the separation device (14) and from the liquid outlet (16) of the separation device (14) to the reliquefaction section (10).

6. The management system (1) according to claim 5, wherein, The separation device (14) includes a steam outlet (18), and the management system (1) includes a recirculation line (19) extending from the steam outlet (18) of the separation device (14) to the supply loop (4) between the tanks (2, 2a, 2b) and the first heat exchanger (7).

7. The management system (1) according to any one of the preceding claims, the management system being configured for a floating structure comprising at least two tanks (2, 2a, 2b), wherein the cooling circuit (8) comprises at least two pumping devices (9, 9a, 9b), each pumping device (9, 9a, 9b) being configured to pump liquid gas from one of the tanks (2, 2a, 2b), the cooling circuit (8) comprising a distribution line (38) fluidly connecting each of the pumping devices (9, 9a, 9b) to the reliquefaction section (10) and the supercooling section (11).

8. The management system (1) according to claim 7 is configured for a floating structure comprising at least two tanks (2, 2a, 2b), wherein the cooling circuit (8) includes a return line (39) configured to return gas from the reliquefaction section (10) or from the supercooling section (11) toward any one or both of the tanks (2, 2a, 2b).

9. A floating structure comprising at least one tank (2, 2a, 2b) configured to contain liquid gas, at least one gas consumption device (3, 3a, 3b), and a management system (1) according to any one of the preceding claims.

10. A management method (100) for managing liquid gas contained in at least one tank (2, 2a, 2b) of a floating structure according to claim 9, said floating structure traveling toward a destination, during which: Considering the composition of the liquid gas contained in the tanks (2, 2a, 2b), The temperature (T) of the liquid gas contained in the tanks (2, 2a, 2b) is measured and compared with the gas temperature threshold (Ts). If the level of hydrocarbons (C6) with at least six carbon atoms is below the hydrocarbon threshold (Sh) and if the temperature (T) is below the temperature threshold (Ts), then the liquid gas flows only in the reliquefaction section (10). If the level of hydrocarbons (C6) having at least six carbon atoms is below the hydrocarbon threshold (Sh) and if the temperature (T) is above the temperature threshold (Ts), then the liquid gas flows at least in the supercooled section (11). If the level of hydrocarbons (C6) with at least six carbon atoms is above the hydrocarbon threshold (Sh) and if the temperature (T) is below the temperature threshold (Ts), then the liquid gas flows only in the reliquefaction section (10). If the level of hydrocarbons (C6) having at least six carbon atoms is above the hydrocarbon threshold (Sh), and if the temperature (T) is above the temperature threshold (Ts), then liquid gas flows in the reliquefaction section (10) and is allowed to flow in the connecting line (33) so as to fluidly connect the second heat exchanger (13) in series to the third heat exchanger (23).

11. The management method (100) according to claim 10, wherein: If the level of hydrocarbons (C6) with at least six carbon atoms is below the hydrocarbon threshold (Sh) and if the temperature (T) is above the temperature threshold (Ts), then a surplus vapor state gas (Sbog) exceeding the supply demand of the gas-consuming equipment (3, 3a, 3b) is determined, and this surplus (Sbog) is compared with the subcooling capacity (Cs) of the third heat exchanger (23). If the amount of the surplus vapor state gas (Sbog) is less than the subcooling capacity (Cs) of the third heat exchanger (23), then the liquid gas only flows in the subcooling section (11). If the excess vapor state gas (Sbog) is greater than the subcooling capacity (Cs) of the third heat exchanger, then liquid gas is allowed to flow in the reliquefaction section (10) and gas is allowed to flow in the connecting line (33) so that the second heat exchanger (13) of the reliquefaction section (10) is connected in series to the third heat exchanger (23) of the subcooling section (11).

12. The management method (100) according to claim 10 or 11, wherein during the management method, a fluid analyzer is used to take into account the composition of the gas contained in the tank.

13. The management method (100) according to claim 10 or 11, wherein during the management method, technical documentation is used to consider the composition of the gas contained in the tank.

14. The management method (100) according to any one of claims 10 to 13 is iterative over time.

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