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

Abstract

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

Description

[0001] DESCRIPTION

[0002] Title of the invention: System for managing a gas in the liquid state transported and / or stored by a floating structure

[0003] The present invention relates to the field of floating structures for storing and / or transporting gas in the liquid state and more particularly concerns a system for managing a gas stored and / or transported within such vessels.

[0004] During a journey made by a floating structure comprising a tank of gas in the liquid state intended to be consumed and / or to be delivered to a destination point, said floating structure may be able to use the gas which has evaporated within the tank, then to compress it in order to supply the engine(s) of the floating structure.

[0005] It is also known, in the event of excess gas evaporating within the tank, to reliquefy the gas not used to power the motor(s) of the floating structure by circulating it through one or more heat exchangers, then returning it to the tank.

[0006] Finally, it is known to thermally treat the gas in the liquid state contained in the tank by sub-cooling the gas in the liquid state contained in the tank using a refrigerant loop traversed by a refrigerant fluid.

[0007] This subcooling operation can be problematic depending on the composition of the gas contained in the tank. Indeed, some of these gases may contain heavy components, as is the case for natural gas from shale gas. These heavy components have a higher frosting temperature than methane, the main constituent of natural gas. Since the subcooling operation is capable of subcooling the gas in the liquid state to a temperature of up to approximately -172°C, the heavy components can frost within a heat exchanger ensuring the heat exchange between the gas in the liquid state intended to be subcooled and the refrigerant circulating in the refrigerant loop. This thus causes a malfunction of said heat exchanger, and can impair the circulation as well as the good cooling capacity of the gas in the liquid state. The present invention makes it possible to avoid these frosting phenomena,and proposes as such a system for managing a gas in the liquid state transported and / or stored by a floating structure comprising at least one tank configured to contain the gas and at least one gas-consuming device, the management system comprising: at least one supply circuit configured to supply gas to the gas-consuming device, the supply circuit comprising at least one compression device, at least one circuit for heat treatment of the gas in the vapor state compressed by the compression device, at least one first heat exchanger configured to carry out a heat exchange between the gas in the vapor state circulating in the supply circuit between the tank and the compression device and the gas in the vapor state circulating in the heat treatment circuit, at least one cooling circuit comprising at least one pumping device configured to take the gas in the liquid state from the tank,characterized in that the cooling circuit comprises a reliquefaction section, a subcooling section and a bypass device configured to circulate the gas in the liquid state to the reliquefaction section or to the subcooling section, the management system comprising: a second heat exchanger configured to carry out a heat exchange between the gas in the vapor state circulating in the heat treatment circuit downstream of the first heat exchanger and the gas in the liquid state circulating in the reliquefaction section, a third heat exchanger and a refrigerant loop, the third heat exchanger being configured to carry out a heat exchange between the gas in the liquid state circulating in the subcooling section and a refrigerant fluid circulating within the refrigerant loop,a connecting line configured to fluidically connect the second heat exchanger and the third heat exchanger in series so that the liquid gas having circulated in the second heat exchanger subsequently circulates within the third heat exchanger.,

[0008] The management system according to the invention can thus manage the supply of a gas-consuming device by using the gas in the vapor state as fuel and / or reliquefying said gas in the vapor state. Subcooling of the tank is also possible but, when the gas contained in the tank contains too large a quantity of heavy hydrocarbons, it is the gas in the liquid state resulting from the reliquefaction and / or participating in the reliquefaction of the gas in the vapor state which is cooled within the third heat exchanger. Given that the gas in the liquid state having circulated within the second heat exchanger has a higher overall temperature than the gas in the liquid state contained in the tank, its temperature at the outlet of the third heat exchanger after cooling is higher than an outlet temperature of the gas coming directly from the tank and subcooled within the third heat exchanger.This prevents the heavy hydrocarbons from freezing within the latter, while still providing significant cooling of the tank if necessary.

[0009] The supply circuit allows the gas in the vapor state forming in the tank to be taken and used as fuel for the gas-consuming device. Although the tank has properties ensuring thermal insulation, the gas in the vapor state forms naturally over time and must be treated in some way to limit the increase in pressure in the tank. The compression device, in addition to ensuring the suction of the gas in the vapor state out of the tank, allows it to be raised to a pressure compatible with the gas-consuming device.

[0010] The gas-consuming device may, for example, be an engine providing propulsion for the floating structure or an electrical generator supplying the floating structure with electricity. It is also possible for the management system to be able to supply a plurality of gas-consuming devices, in which case the supply circuit is adapted accordingly in order to be able to supply each of them with gas in the vapor state. The heat treatment circuit is connected to the supply circuit downstream of the compression device and allows the circulation of the gas in the vapor state present in excess of the supply requirement of the gas-consuming device. Instead of wasting this excess gas in the vapor state, it circulates in the heat treatment circuit in order to be able to return to the tank.The first heat exchanger allows the return gas to be pre-cooled by exchanging heat with the vaporous gas leaving the tank and circulating in the supply circuit. The excess vaporous gas is therefore retained by returning to the tank instead of being burned or released into the atmosphere.

[0011] The cooling circuit is configured to ensure the circulation of the gas in the liquid state in one way or another depending on the function that must be implemented within the management system. The pumping device ensuring the collection of the gas in the liquid state is advantageously arranged at the bottom of the tank in order to pump the gas in the liquid state at the lowest possible temperature.

[0012] From the pumping device, the liquid gas from the tank can flow either to the reliquefaction section or to the subcooling section. The circulation of the liquid gas to the reliquefaction section makes it possible to reliquefy the vapor gas circulating in the heat treatment circuit, via the second heat exchanger. During the heat exchange, the low temperature of the liquid gas causes the vapor gas temperature to drop until it reliquefies. Advantageously, all of the vapor gas entering the second heat exchanger leaves reliquefied.

[0013] Furthermore, preferably, the reliquefied gas within the second heat exchanger and the liquid gas from the tank and used for reliquefaction meet at a junction point arranged at the outlet of the second heat exchanger. More specifically, the junction point is arranged at the reliquefaction section of the cooling circuit, and the heat treatment circuit is connected to the reliquefaction section at this junction point. It is therefore a mixture of liquid gas that is formed at this junction point. Due to the reliquefaction operation taking place in the second heat exchanger, the liquid gas mixture forming at the junction point is at a higher temperature than the liquid gas contained in the tank.

[0014] From the pumping device, the liquid gas can be sent to the subcooling section, with the aim of subcooling a fraction of the liquid gas contained in the tank and then returning it to the tank in order to lower the overall temperature of the liquid gas contained in said tank. In compliance with the resolution of the technical problem of the invention, such an operation can only be carried out if the composition of the liquid gas contained in the tank is limited in heavy hydrocarbons. It is the third heat exchanger which ensures the subcooling of the liquid gas via the refrigerant loop.The refrigerant circulating in the refrigerant loop has a lower temperature than the liquid gas in the tank when it passes through the third heat exchanger, thus lowering the temperature of the liquid gas circulating in the subcooling section. The refrigerant can, for example, be nitrogen.

[0015] The bypass device controls the flow of liquid gas contained in the tank and circulating in the cooling circuit. The bypass device is configured to allow the flow of liquid gas to the reliquefaction section while preventing the flow of liquid gas to the subcooling section or vice versa.

[0016] If the liquid gas in the tank contains too high a proportion of heavy hydrocarbons, circulating the liquid gas in the tank directly into the subcooling section is not feasible because the risk of icing within the third heat exchanger is too high. Heavy hydrocarbons are understood to mean hydrocarbons containing at least six carbon atoms. In this situation, the liquid gas in the tank and circulating in the cooling circuit can therefore only be sent to the reliquefaction section in order to reliquefy the vapor gas circulating in the heat treatment circuit. The circulation of the liquid gas within the second heat exchanger and the mixing with the reliquefied gas at its outlet then leads to an increase in the temperature of the liquid gas.

[0017] The connecting line is then used to continue the circulation of the gas in the liquid state. This connecting line provides a fluid connection between the reliquefaction section and the subcooling section in order to connect the second heat exchanger and the third heat exchanger in series.

[0018] The junction line is advantageously connected to the reliquefaction section at the junction point mentioned above and extends to the subcooling section upstream of the third heat exchanger so that the gas in the liquid state having circulated in the second heat exchanger subsequently circulates within the third heat exchanger, in this order.

[0019] Since the liquid gas from the reliquefaction section is at a higher temperature than the liquid gas contained in the tank, passing through the third heat exchanger causes the temperature of the liquid gas to decrease to a temperature low enough to be able to reduce the overall temperature of the tank after return to it, 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. The management system according to the invention therefore has a plurality of functions that can all be implemented optimally regardless of the composition of the liquid gas contained in the tank.

[0020] According to a feature of the invention, the bypass device comprises a first bypass valve arranged on the reliquefaction section and a second bypass valve arranged on the subcooling section. The first bypass valve and the second bypass valve can switch to the open position or the closed position in order to respectively authorize or prohibit the circulation of the gas in the liquid state in the section in question. When the gas in the liquid state circulates in the cooling circuit, it can only circulate in the reliquefaction section or in the subcooling section. Thus, when one of the valves is in the open position, the other valve is necessarily in the closed position.

[0021] According to a feature of the invention, the junction line comprises a junction valve configured to control the series connection of the third heat exchanger to the second heat exchanger. Just like the first bypass valve and the second bypass valve, the junction valve can switch between an open position and a closed position in order to connect or not connect the second heat exchanger and the third heat exchanger in series.

[0022] According to a characteristic of the invention, the cooling circuit comprises at least one termination to which the reliquefaction section and / or the subcooling section are fluidically connected, the cooling circuit comprising a first termination comprising a return orifice configured to be arranged at a bottom of the tank and a second termination comprising a projection device configured to be arranged at a tank top. The terminations allow the gas in the liquid state to return to the tank once it has passed through one or more heat exchangers. Depending on the heat treatment applied, the gas in the liquid state is preferentially sent to the first termination or to the second termination.

[0023] The return port of the first termination is positioned at the bottom of the tank so that the liquid gas returns to the tank at the level where the static pressure is highest. Thanks to the latter, the liquid gas returning to the tank is maintained in the liquid state without generating vapor. In addition, the inertia of the tank is such that the temperature rise caused by the injection of liquid gas at a higher temperature is slowed down, thus minimizing the impact 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. The projection device is used to project subcooled gas into the tank headspace. The projection of subcooled gas makes it possible to condense the vapor gas that may be present at the tank headspace and thus lower the tank pressure.The spraying device should, however, be used with caution, i.e. only in the case of subcooling the gas to the liquid state without passing through the second heat exchanger. Indeed, spraying gas at too high a temperature via the spraying device risks partially evaporating it at the time of spraying and can cause the tank pressure to rise instead of lowering it. Therefore, to avoid such a phenomenon, the gas having circulated within the second heat exchanger must be returned to the tank via the return port via the first termination. Just as for the sections of the cooling circuit or for the junction line, the circulation within the terminations can be controlled by valves.

[0024] According to a feature of the invention, the management system comprises a separation device arranged on the heat treatment circuit downstream of the second heat exchanger, the heat treatment circuit extending from the second heat exchanger to an inlet of the separation device, and from a liquid outlet of the separation device to the reliquefaction section. It is possible for the gas circulating in the heat treatment circuit to leave the second heat exchanger only partially reliquefied, i.e. in a two-phase state. In such a configuration, the separation device makes it possible to separate a liquid fraction from a gaseous fraction of a gas flow in the two-phase state, so that only the liquid fraction continues to circulate within the heat treatment circuit until it reaches the reliquefaction section.

[0025] The separation device is therefore positioned downstream of the second heat exchanger, so that the gas circulating in the heat treatment circuit and leaving the second heat exchanger enters directly into the separation device via the inlet. There is therefore only gas in the liquid state circulating within the portion of the heat treatment circuit extending between the liquid outlet of the separation device and the reliquefaction section. As previously described, the heat treatment circuit is advantageously connected to the reliquefaction section at the previously mentioned junction point.

[0026] According to a feature of the invention, the separation device comprises a steam outlet, the management system comprising a recirculation line extending from the steam outlet of the separation device to the supply circuit between the tank and the first heat exchanger. As mentioned previously, the gas circulating in the heat treatment circuit can exit the second heat exchanger at least partially reliquefied, and the separation device isolates the vapor fraction from the liquid fraction. The vapor fraction constitutes the gas fraction that has not reliquefied after circulation within the second heat exchanger.This fraction of gas in the vapor state then leaves the separation device through the vapor outlet and circulates within the recirculation line until it reaches the supply circuit in order to recirculate there to supply the gas-consuming device or to return to the heat treatment circuit.

[0027] According to a feature of the invention, when the management system is configured for a floating structure comprising at least two tanks, the cooling circuit comprises at least two pumping devices, each pumping device being configured to take the gas in the liquid state from one of the tanks, the cooling circuit comprising a distribution line fluidly connecting each of the pumping devices to the reliquefaction section and to the subcooling section. The management system according to the invention can in fact be adapted for a floating structure comprising a plurality of tanks. The gas in the liquid state can then be taken from each of the tanks via a plurality of pumping devices, each being arranged in one of the tanks. The distribution line allows the fluidic connection of all of the pumping devices to the reliquefaction section and to the subcooling section.Thus, the gas in the liquid state is collected, regardless of the tank(s) of origin, and can subsequently be sent to one or other of the sections. According to a characteristic of the invention, when the management system is configured for a floating structure comprising at least two tanks, the cooling circuit comprises a return line configured to return the gas from the reliquefaction section or the sub-cooling section to one and / or other of the tanks. In the same way that the gas in the liquid state can be taken from one or other of the tanks, the gas in the liquid state can also, after heat treatment, be returned to one or other of the tanks as required.The return line provides a fluid connection between each section of the cooling circuit and each of the tanks, in order to be able to return the gas in the liquid state to a particular tank or a plurality of tanks, regardless of its origin. The return line may therefore include a system of valves to control to which tank(s) the heat-treated gas in the liquid state is sent.

[0028] The invention also covers a floating structure comprising at least one tank configured to contain gas in the liquid state, at least one gas-consuming device and a management system as described previously.

[0029] The invention also covers a method for managing a gas in the liquid state contained in at least one tank of a floating structure as described above traveling towards a destination point, during which: a composition of the gas in the liquid state contained in the tank is taken into account, a temperature of the gas in the liquid state contained in the tank is measured and the measured temperature is compared to a temperature threshold of the gas, if the rate of hydrocarbons with at least six carbons is lower than a hydrocarbon threshold and if the temperature is lower than the temperature threshold, the gas in the liquid state is circulated only in the reliquefaction section, if the rate of hydrocarbons with at least six carbons is lower than the hydrocarbon threshold and if the temperature is higher than the temperature threshold, the gas in the liquid state is circulated at least in the sub-cooling section,if the hydrocarbon content of at least six carbons is higher than the hydrocarbon threshold and if the temperature is lower than the temperature threshold, the gas is circulated in the liquid state only in the reliquefaction section, if the hydrocarbon content of at least six carbons is higher than the hydrocarbon threshold and if the temperature is higher than the temperature threshold, the gas is circulated in the liquid state in the reliquefaction section and the gas is allowed to circulate in the junction line in order to fluidically connect the second heat exchanger to the third heat exchanger in series.,

[0030] This management method is implemented to prevent the formation of frost in the third heat exchanger in the event of transport of gas in the liquid state containing too high a quantity of heavy hydrocarbons. The composition of the gas in the liquid state is therefore initially taken into account and compared to the hydrocarbon threshold in order to determine whether or not a risk of frosting is present. As mentioned previously, heavy hydrocarbons presenting a risk of frosting are hydrocarbons comprising at least six carbon atoms. The limit threshold of heavy hydrocarbons leading to a risk of frosting can be between 80 and 150 parts per million, for example 100 parts per million. Below the hydrocarbon threshold, although there is a presence of heavy hydrocarbons in the gas in the liquid state, this is sufficiently negligible to consider that the gas in the liquid state can be subcooled without risk of frosting.

[0031] The temperature of the tank(s) is also measured to compare it to the temperature threshold. The temperature threshold can be a fixed value or can, for example, be defined by the unloading conditions of the destination point. Indeed, each destination point authorized for unloading gas in a liquid state has its own requirements for a cargo of gas in a liquid state. If this threshold is exceeded, the administration of the destination point may refuse to unload the cargo, which leads to significant time and cost constraints. The management system must therefore be used taking into account the temperature threshold to determine whether the cargo temperature can be increased without fear of exceeding this threshold, or on the contrary, whether it must be cooled because the temperature threshold is exceeded.

[0032] In the case where there is no risk of icing, subcooling the gas to the liquid state by sending it directly into the subcooling section can be implemented without fear, in order to cool the temperature of the cargo if the temperature threshold is exceeded. If, on the other hand, the tank temperature is below the temperature threshold, a reliquefaction operation can be implemented alone, in order to save the energy necessary for the operation of the refrigeration loop. The temperature of the cargo must, however, be monitored regularly over time because the reliquefaction operation necessarily leads to a gradual increase in the temperature of the cargo.

[0033] If there is a risk of icing of the liquid gas in the third heat exchanger, there is no question of implementing a subcooling operation alone. A reliquefaction operation alone is possible if the tank temperature is below the temperature threshold. However, if this temperature threshold is exceeded, the cargo must be cooled. In this configuration and to avoid any risk of icing, the junction line is then opened in order to connect the second heat exchanger and the third heat exchanger in series. The liquid gas then passes through the two heat exchangers one after the other in order to reach a temperature suitable for cooling the cargo but without the heavy hydrocarbons contained in the liquid gas icing in the third heat exchanger.

[0034] According to a characteristic of the method: if the rate of hydrocarbons with at least six carbons is lower than the hydrocarbon threshold and if the temperature is higher than the temperature threshold, a surplus of gas in the vapor state in excess of a supply requirement of the gas-consuming device is determined and this surplus is compared to a subcooling capacity of the third heat exchanger, if the quantity of surplus gas in the vapor state is lower than the subcooling capacity of the third heat exchanger, the gas in the liquid state is circulated only in the subcooling section, if the quantity of surplus gas in the vapor state is higher than the subcooling capacity of the third heat exchanger,the gas in the liquid state is circulated in the reliquefaction section and the gas is allowed to circulate in the junction line in order to fluidically connect in series the second heat exchanger of the reliquefaction section to the third heat exchanger of the subcooling section.,

[0035] In the situation where there is no risk of icing and the temperature threshold is exceeded, the management method can implement an additional comparison step before an operating mode is selected. The surplus gas in the vapor state corresponds to the total quantity of gas in the vapor state contained in the tank, from which a fraction of gas in the vapor state necessary for supplying the gas-consuming device is subtracted.

[0036] If this excess vapor gas is too large compared to the subcooling capacity of the third heat exchanger, it means that it is counterproductive to circulate the liquid gas in the subcooling section alone in order, for example, to spray the subcooled gas into the vessel headspace afterwards. The amount of excess vapor gas is too large for subcooling of the liquid gas to have sufficient impact.

[0037] In such a situation, it is more efficient to evacuate the excess gas from the tank rather than trying to condense it in the tank headspace. It is therefore advantageous to circulate the excess gas in the vapor state in the feed circuit and then in the heat treatment circuit in order to reliquefy it. The gas in the liquid state is therefore sent to the reliquefaction section to reliquefy the excess gas in the vapor state. However, as a reminder of the situation, it is also necessary to reduce the tank temperature because it is too high compared to the temperature threshold. Returning the gas to the tank directly from the reliquefaction section is therefore prohibited because this tends to increase the said tank temperature.The only configuration suitable for the situation is therefore to circulate the liquid gas from the second heat exchanger in the junction line in order to cool it within the third heat exchanger before returning it to the tank, just as when there is a risk of icing due to the composition of the gas. This preferentially leads to a decrease in the tank temperature, which is theoretically less efficient than circulating the liquid gas in the subcooling section alone, but in practice more efficient compared to the situation due to the excessive quantity of surplus gas in the vapor state in the tank. Alternatively, this at least makes it possible to greatly limit the increase in temperature of the liquid gas contained in the tank.Depending on the journey of the floating structure, limiting the temperature increase of the gas in the liquid state may be sufficient to keep the cargo below the temperature threshold once the journey of the floating structure is completed. The temperature threshold may therefore be specifically chosen to provide for such a configuration.

[0038] If the subcooling capacities of the third heat exchanger are sufficient in relation to the quantity of surplus gas in the vapor state contained in the tank, then the gas in the liquid state is sent to the subcooling section alone in order to condense said surplus in the tank.

[0039] According to a feature of the process, the composition of the gas contained in the tank can be taken into account using a fluid analyzer. The fluid analyzer can determine the quantity of heavy hydrocarbons in parts per million contained in the transported gas.

[0040] According to a feature of the process, the composition of the gas contained in the tank can be taken into account using technical documentation. This is an alternative solution to determination via the fluid analyzer. The technical documentation is supplied with the gas cargo in liquid state and contains a plurality of characteristics relating to it, such as the quantity of heavy hydrocarbons in parts per million.

[0041] According to a characteristic of the process, it is repeatable over time. Although the composition of the transported gas does not vary over time, it is important to implement the management process regularly during the journey because the temperature of the tank changes over time, and changes even more if the management system is implementing a particular configuration. The comparison between the measured tank temperature and the temperature threshold must therefore be checked regularly to determine whether the configuration of the management system must be changed or whether it must be maintained as is.

[0042] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0043] [fig 1] is a schematic representation of a gas management system according to the invention,

[0044] [fig 2] represents a circulation of gas within the management system according to a first operating mode,

[0045] [fig 3] represents a circulation of gas within the management system according to a second operating mode,

[0046] [fig 4] represents a circulation of gas within the management system according to a third operating mode,

[0047] [fig 5] is a schematic representation of the gas management system adapted to a floating structure comprising a plurality of tanks,

[0048] [fig 6] is a flowchart of a gas management method implemented by the management system according to the invention, [fig 7] is a flowchart of a variant of the gas management method implemented by the management system according to the invention.

[0049] Figure 1 is a schematic representation of a gas management system 1 according to the invention. Such a management system 1 may for example be integrated into a floating structure for transporting and / or storing gas in the liquid state. Generally, such a floating structure comprises at least one tank 2 ensuring the transport and / or storage of gas in the liquid state, but according to the configuration illustrated in Figure 1, said floating structure comprises a single tank 2. Such a floating structure also comprises at least one gas-consuming device 3, which may be for example a motor ensuring the propulsion of the floating structure or an electric generator ensuring the supply of electricity to the floating structure. The management system may supply a single gas-consuming device 3, but in Figures 1 to 5, the floating structure comprises a first gas-consuming device 3a and a second gas-consuming device 3b.The first gas-consuming device 3a may, for example, be a motor providing propulsion for the floating structure, while the second gas-consuming device 3b may be an electric generator providing electricity to the floating structure.

[0050] The tank 2 is configured to ensure sealing and thermal insulation with respect to the gas in the liquid state that it contains. However, over time, the gas in the liquid state present in the tank 2 partially evaporates, leading to an increase in the pressure of the tank 2. The management system 1 therefore makes it possible to prevent a potential overpressure within the tank 2 by evacuating the gas in the vapor state from it.

[0051] To do this, the management system 1 comprises a supply circuit 4 extending between the tank 2 and the gas-consuming devices 3. The supply circuit 4 comprises at least one compression device 5 configured to suck the gas in the vapor state present in the tank 2. In Figures 1 to 5, the management system 1 comprises a first compression device 5a and a second compression device 5b, making it possible to ensure redundancy so that the gas-consuming devices 3 can be constantly supplied, even in the event of a breakdown of one of the compression devices 5.

[0052] Each of the compression devices 5 is configured to raise the pressure of the gas in the vapor state so that the latter has a pressure compatible with the needs of one of the gas-consuming devices 3 or of the two gas-consuming devices 3. The supply circuit 4 thus makes it possible on the one hand to regulate the pressure of the tank 2 and on the other hand to supply fuel to the gas-consuming devices 3.

[0053] The management system 1 also comprises a heat treatment circuit 6 connected to the supply circuit 4 downstream of the compression devices 5. It is a flow of gas in the vapor state which circulates in the heat treatment circuit 6, said flow corresponding to a surplus of gas in the vapor state in excess of the supply requirements of one or more gas consuming devices 3. The heat treatment circuit 6 thus participates in a return of the surplus gas in the vapor state to the tank 2. One of the objectives of the management system 1 according to the invention is to reliquefy the surplus gas in the vapor state before returning it to the tank 2.

[0054] In this respect, the management system 1 comprises a first heat exchanger 7 configured to carry out a heat exchange between the gas in the vapor state circulating in the supply circuit 4 and the gas in the vapor state circulating in the heat treatment circuit 6 in order to precool the latter. Implementing such precooling subsequently makes it possible to facilitate the reliquefaction of the gas in the vapor state intended to return to the tank 2. In certain configurations, for example when there is no gas in the vapor state circulating in the heat treatment circuit 6, the gas in the vapor state circulating in the supply circuit 4 can bypass the first heat exchanger 7 using a bypass line 35 in order to limit any pressure drop of the gas in the vapor state. The circulation of gas in the vapor state within the bypass line 35 is managed by a bypass valve 36.

[0055] The management system 1 also comprises a cooling circuit 8 which can be operated in different ways in order to carry out a plurality of operating modes which will be described in detail later. The cooling circuit 8 comprises a pumping device 9 configured to take the gas in the liquid state from the tank 2. From this pumping device 9, the cooling circuit 8 is split into two sections: a reliquefaction section 10 and a sub-cooling section 11. The gas in the liquid state coming from the tank 2 and pumped by the pumping device

[0056] 9 can therefore circulate either within the reliquefaction section 10 or within the sub-cooling section 11.

[0057] The cooling circuit 8 therefore comprises a bypass device 12 provided with a first bypass valve 12a arranged at the reliquefaction section 10 and a second bypass valve 12b arranged at the subcooling section 11. The bypass valves are configured to alternate between an open position allowing the circulation of the gas in the liquid state and a closed position preventing the circulation of the gas in the liquid state. The gas in the liquid state can only circulate from the pumping device 9 to the reliquefaction section

[0058] 10 or to the subcooling section 11, when one of the bypass valves is open, the other bypass valve is necessarily closed.

[0059] The management system 1 also comprises a second heat exchanger 13 configured to carry out a heat exchange between the gas in the vapor state circulating in the heat treatment circuit 6 downstream of the first heat exchanger 7 and the gas in the liquid state circulating in the reliquefaction section 10. After having been precooled within the first heat exchanger 7, the gas in the vapor state circulating in the heat treatment circuit 6 then passes through the second heat exchanger 13 and is at least partially reliquefied thanks to the heat exchange taking place with the gas in the liquid state coming from the tank 2 and circulating in the reliquefaction section 10.

[0060] In the event of partial reliquefaction of the gas in the vapor state circulating in the heat treatment circuit 6, the management system 1 comprises a separation device 14 arranged at the level of the heat treatment circuit 6 downstream of the second heat exchanger 13. At the outlet of the second heat exchanger 13, the at least partially reliquefied gas enters the separation device 14 via an 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 a liquid fraction from a gaseous fraction. The liquid fraction leaves the separation device 14 via a liquid outlet 16 and continues its circulation in the heat treatment circuit 6 until it reaches the reliquefaction section 10 of the cooling circuit 8, advantageously at a junction point 17.

[0061] The separation device 14 also comprises a steam outlet 18 through which the steam fraction of the gas in the potentially two-phase state exits at the outlet of the second heat exchanger 13. The management system 1 therefore comprises a recirculation line 19 extending from the steam outlet 18 of the separation device 14 to the supply circuit 4 in order to recirculate the gas which has not reliquefied to the gas-consuming devices 3 or again within the heat treatment circuit 6.

[0062] In order to improve the thermodynamic performance of the gas, the heat treatment circuit 6 can be provided with a first expansion member 20 between the second heat exchanger 13 and the inlet 15 of the separation device 14, and with a second expansion member 21 between the liquid outlet 16 of the separation device 14 and the junction point 17. The recirculation line 19 can be provided with a third expansion member 22.

[0063] The fraction of gas in the liquid state leaving the separation device 14 and the gas in the liquid state circulating in the reliquefaction section 10 leaving the second heat exchanger 13 meet at the junction point 17. From the latter, the gas in the liquid state can continue its circulation in the reliquefaction section 10 in order to return to the tank 2. Such circulation is managed by a return valve 37. Due to the reliquefaction operation taking place in the second heat exchanger 13, the gas in the liquid state circulating via the junction point 17 is necessarily at a higher temperature than the gas in the liquid state contained in the tank 2.

[0064] Concerning the subcooling section 11, the management system 1 comprises a third heat exchanger 23 configured to carry out a heat exchange between the gas in the liquid state circulating in the subcooling section 11 and a refrigerant circulating in a refrigerant loop 24 not detailed. The refrigerant loop 24 is configured to circulate the refrigerant, which may for example be nitrogen, while thermally treating it so that the latter cools the gas in the liquid state within the third heat exchanger 23 despite the low temperature of said gas in the liquid state. Carrying out a subcooling of the gas in the liquid state coming from the tank 2 subsequently makes it possible to lower the temperature of the tank 2 and of the gas in the liquid state contained therein.

[0065] Respectively downstream of the junction point 17 and the third heat exchanger 23, the reliquefaction section 10 and the sub-cooling section 11 extend until they meet at a convergence point 25 to return to the tank 2. In order to optimize the return to the tank 2 as a function of the prior thermal treatment of the gas in the liquid state, the cooling circuit 8 comprises a first termination 26 and a second termination 27.

[0066] The first termination 26 extends to the tank 2 and comprises a return orifice 28 advantageously arranged at the bottom of the tank 2. Returning the gas in the liquid state to the bottom of the tank 2 makes it possible to limit the impact of its temperature, which is potentially higher than that of the gas contained in the tank 2, and also to avoid unwanted evaporation when the gas in the liquid state leaves the return orifice 28.

[0067] The return orifice 28 is for example a calibrated orifice, in the sense that it has a smaller section than a section of the first termination 26 measured just before the return orifice 28. The section of the return orifice 28 is between 5% and 30% of the section of the first termination 26. This has the effect of maintaining a pressure within the first termination 26 higher than that at the bottom of the tank 2.

[0068] The second termination 27 also extends to the tank 2 and comprises a projection device 29 arranged at a ceiling 30 of the tank 2. The projection device 29 makes it possible to project subcooled gas into the ceiling 30 in order to recondense the gas in the vapor state present therein. Such recondensation makes it possible to lower the pressure and the temperature of the tank 2. The circulation within the first termination 26 and the second termination 27 is respectively controlled by a first termination valve 31 and by a second termination valve 32.

[0069] It is understood from the above that the management system allows the reliquefaction of the gas in the vapor state contained in the tank 2, but also to lower the temperature of the tank 2 by subcooling a part of the gas in the liquid state which is there and by returning it there. Such a subcooling operation can however be risky depending on the composition of the gas in the liquid state contained in the tank 2.

[0070] Indeed, certain types of gas, for example natural gas from shale gas, may contain a significant quantity of heavy hydrocarbons, i.e. hydrocarbons containing at least six carbon atoms. Heavy hydrocarbons have a higher solidification temperature than lighter hydrocarbons. However, the subcooling of the gas in the liquid state greatly lowers the already very low temperature of the gas in the liquid state contained in the tank 2. If the latter contains too large a quantity of hydrocarbons, these may freeze within the third heat exchanger 23 and cause a malfunction of the management system 1.

[0071] To overcome this, the management system 1 according to the invention comprises a junction line 33 extending between the reliquefaction section 10, advantageously at the junction point 17, and the sub-cooling section 11. The junction line 33 makes it possible to fluidically connect the second heat exchanger 13 and the third heat exchanger 23. The circulation within the junction line 33 is controlled by a junction valve 34.

[0072] As previously described, the liquid gas flowing to the junction point 17 of the reliquefaction section 10 is at a higher temperature than the liquid gas contained in the tank 2 due to the heat exchange carried out within the second heat exchanger 13. If subsequently the liquid gas flows to the third heat exchanger 23 via the junction line 33, it is then cooled by the refrigerant fluid of the refrigerant loop 24. However, since the liquid gas is at a higher temperature than the liquid gas contained in the tank 2, the cooling carried out within the third heat exchanger 23 does not lower the temperature of the liquid gas sufficiently for the heavy hydrocarbons to freeze within the third heat exchanger 33.The temperature of the gas in the liquid state having passed in series through the second heat exchanger 13 then the third heat exchanger 23 is however sufficiently low to lower the temperature of the tank 2 when the gas returns to the liquid state.

[0073] It is thus understood that the management system 1 according to the invention is capable of ensuring all of the functions described previously while adapting according to the composition of the gas in the liquid state contained in the tank 2, and this without risk of malfunction of the management system 1 due to icing of the heavy hydrocarbons within the third heat exchanger 23.

[0074] Figures 2 to 4 illustrate fluid circulation within the management system according to three operating modes. For each of these figures, the lines and circuits illustrated in solid lines correspond to fluid circulation while the dotted lines and circuits illustrate an absence of fluid circulation.

[0075] Figure 2 illustrates a first mode of operation, during which a reliquefaction operation alone is carried out. In this situation, the gas in the vapor state contained in the headspace 30 of the tank 2 is sucked by at least one of the compression devices 5 within the supply circuit 4. The gas in the vapor state 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-consuming devices 3. If this proves necessary, at least a portion of the gas in the vapor state is sent to at least one of the gas-consuming devices 3 to supply it or them.

[0076] The gas in the vapor state representing the surplus gas in the vapor state circulates within the heat treatment circuit 6 and passes through the first heat exchanger 7 in order to be pre-cooled by the gas in the vapor state circulating in the supply circuit 4.

[0077] At the outlet of the first heat exchanger 7, the gas in the vapor state continues its circulation in the heat treatment circuit 6 until it passes through the second heat exchanger 13. Simultaneously, gas in the liquid state contained in the tank 2 is pumped by the pumping device 9 in order to circulate in the cooling circuit 8. In order to reliquefy the gas in the vapor state passing through the second heat exchanger 13, the bypass device 12 is configured to send the gas in the liquid state to the reliquefaction section 10. As a result, the first bypass valve 12a is open while the second bypass valve 12b is closed.

[0078] The gas in the liquid state therefore also passes through the second heat exchanger 13, and the heat exchange generated guarantees at least partial reliquefaction of the gas in the vapor state circulating in the heat treatment circuit 6 and passing through the second heat exchanger 13.

[0079] At the outlet of the second heat exchanger 13, the at least partially reliquefied gas is expanded by the first expansion member 20 and enters the separation device 14 via the inlet 15. If the gas entering the separation device 14 is in the two-phase state, the separation device 14 separates the liquid fraction from the vapor fraction. The potential vapor fraction leaves the separation device 14 via the vapor outlet 18 and circulates within the recirculation line 19 to return to the supply circuit 4.

[0080] The liquid fraction leaves the separation device 14 via the liquid outlet 16 and continues its circulation in the heat treatment circuit 6 until it reaches the reliquefaction section 10 via the junction point 17, at which the gas in the liquid state coming from the tank 2 and having participated in the reliquefaction of the gas in the vapor state also circulates by passing through the second heat exchanger 13.

[0081] The two liquid gas flows then continue their circulation within the reliquefaction section 10 up to the convergence point 25. According to this first mode of operation, the return valve 37 is open while the junction valve 34 is closed. Finally, the liquid gas circulates to the first termination 26 and returns to the tank 2 thanks to the return orifice 28 placed at the bottom thereof.

[0082] According to this first mode of operation, the gas in the liquid state returns to the tank 2 at a higher temperature than the gas in the liquid state contained in the tank 2. It is therefore understood that it is counterproductive to project it into the sky 30 of the tank 2, hence the fact that the gas in the liquid state returns to the tank 2 via the first termination 26. As a result, the first termination valve 31 is open while the second termination valve 32 is closed.

[0083] This first mode of operation allows the reliquefaction of the gas in the vapor state contained in the tank 2, but nevertheless leads to a progressive increase in the temperature of the latter due to the high temperature of the gas in the liquid state returning to the tank 2. This first mode of operation also allows energy savings due to the inactivity of the refrigerant loop 24.

[0084] Figure 3 represents a second mode of operation of the management system 1 according to the invention. This second mode of operation makes it possible to sub-cool a portion of the gas in the liquid state contained in the tank 2 in order to lower the overall temperature thereof and / or to recondense the gas in the vapor state present in the headspace 30 of the tank 2.

[0085] As a result, the gas in the vapor state can circulate in the supply circuit 4 but in sufficient quantity to only supply the gas-consuming devices 3 and not to circulate excess gas in the vapor state in the heat treatment circuit 6. Since the use of the first heat exchanger 7 is not necessary, the bypass valve 36 is open and the gas in the vapor state circulating in the supply circuit 4 passes through the bypass line 35 instead of unnecessarily passing through the first heat exchanger 7.

[0086] The gas in the liquid state contained in the tank 2 is partly pumped by the pumping device 9 in order to circulate in the cooling circuit 8. In order to lower the temperature of the tank 2, the bypass device 12 is configured to send the gas in the liquid state to the sub-cooling section 11. As a result, the first bypass valve 12a is closed while the second bypass valve 12b is open.

[0087] The gas in the liquid state then circulates to the third heat exchanger 23. Simultaneously, the refrigerant loop 24 is activated in order to circulate the refrigerant fluid within the third heat exchanger 23, thus ensuring the subcooling of the gas in the liquid state circulating in the subcooling section 11.

[0088] At the outlet of the third heat exchanger 23, the subcooled liquid gas continues its circulation in the subcooling section 11 until it reaches the convergence point 25. The liquid gas is then returned to the tank 2. If the presence of too much vapor gas in the headspace 30 of the tank 2 is too high, the subcooled liquid gas circulates in the second termination 27 and is projected into the headspace 30 of the tank 2 by the projection device 29 in order to recondense the vapor gas present therein. However, the subcooled liquid gas can also return to the tank 2 via the first termination 26 and being returned to the tank 2 via the return port 28. Such an alternative also helps to lower the temperature of the tank 2. Depending on either possibility, one or the other of the termination valves 31, 32 is open while the other is closed.

[0089] As described above, this second mode of operation cannot be used if the gas contained in tank 2 contains too high a quantity of heavy hydrocarbons because they risk freezing within the third heat exchanger 23.

[0090] In this situation, the only way to lower the temperature of tank 2 is to use a third operating mode of the management system illustrated in Figure 4.

[0091] According to this third mode of operation, the gas in the vapor state contained in the ceiling 30 of the tank 2 circulates within 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-consuming devices 3 to supply at least one of them.

[0092] The surplus gas in the vapor state circulates within the heat treatment circuit 6, is precooled by passing through the first heat exchanger 7 and then passes through the second heat exchanger 13. The gas in the liquid state contained in the tank 2 is pumped by the pumping device 9 in order to circulate in the cooling circuit 8, more particularly in the reliquefaction section 10. For this, the first bypass valve 12a is open while the second bypass valve 12b is closed.

[0093] The gas in the liquid state therefore also passes through the second heat exchanger 13, and the heat exchange generated guarantees at least partial reliquefaction of the gas in the vapor state circulating in the heat treatment circuit 6 and passing through the second heat exchanger 13.

[0094] At the outlet of the second heat exchanger 13, the at least partially reliquefied gas enters the separation device 14 and the liquid fraction leaves the separation device 14 via the liquid outlet 16 and continues its circulation in the heat treatment circuit 6 until it reaches the reliquefaction section 10 via the junction point 17, at the level of which also circulates the gas in the liquid state coming from the tank 2 and having participated in the reliquefaction of the gas in the vapor state by passing through the second heat exchanger 13.

[0095] The objective here being to lower the temperature of tank 2, the gas in the liquid state passing through the junction point 17 cannot return directly into tank 2 as illustrated in figure 2 because this would on the contrary increase the temperature of tank 2.

[0096] In this configuration, the return valve 37 is therefore closed while the junction valve 34 is open so that the gas in the liquid state circulates in the junction line 33 and joins the subcooling section 11 to pass through the third heat exchanger 23 in series with the second heat exchanger 13. The refrigerant loop 24 is active in order to cool the gas in the liquid state circulating within the third heat exchanger 23. Due to its higher temperature than the gas in the liquid state contained in the tank 2, the gas in the liquid state circulating in the subcooling section 11 via the junction line 33 is cooled within the third heat exchanger 23 but not to a temperature low enough for the hydrocarbons to freeze within the latter. The cooling is however sufficient to lower the temperature of the tank 2 thereafter.The gas in the liquid state cooled within the third heat exchanger 23 then continues its circulation within the subcooling section 11 until it reaches the convergence point 25 and returns to the tank 2 via the first termination 26 and the return orifice 28. Indeed, it is counterproductive to return the gas in the liquid state cooled to the tank 2 by projecting it via the projection device 29. According to this third mode of operation, although the gas in the liquid state is cooled, it is not cooled sufficiently to carry out an effective projection into the top of the tank 30. There are indeed risks of evaporation of the gas at the time of projection, which increases the quantity of gas in the vapor state in the top 30 of the tank 2 instead of decreasing it.

[0097] According to this third mode of operation, the gas in the liquid state can therefore only return to the tank 2 via the first termination 26, but still allows the temperature of the tank 2 to be lowered without the risk of icing of the heavy hydrocarbons contained in the gas in the liquid state within the third heat exchanger 23.

[0098] Figure 5 represents the gas management system 1 according to the invention, but this time adapted to a floating structure comprising a plurality of tanks 2 intended to store said gas in the liquid state. In Figure 5, two tanks 2a, 2b are represented but the management system 1 can be adapted to interact with more tanks 2.

[0099] When the floating structure comprises two tanks 2a, 2b, at least a portion of the circuits and lines of the management system 1 interacting directly with said tanks 2a, 2b are duplicated in order to ensure gas management with respect to all of the latter.

[0100] Thus, the gas in the vapor state from the two tanks 2 can be sucked in by the compression device and circulate within the supply circuit 4. The gas in the liquid state can circulate in the cooling circuit 8 by being taken from one and / or the other of the tanks 2. As a result, the management system 1 illustrated in FIG. 5 comprises a first pumping device 9a arranged within a first tank 2a and a second pumping device 9b arranged within a second tank 2b.

[0101] The cooling circuit 8 also comprises a distribution line 38 capable of collecting the gas in the liquid state from each of the tanks 2 and of sending all of the collected gas in the liquid state to the reliquefaction section 10 and / or to the sub-cooling section 11.

[0102] Once the thermal treatment of the gas in the liquid state has been carried out, it can also be returned to one and / or the other of the tanks 2 depending on the need. The cooling circuit therefore comprises a return line 39 ensuring the distribution of the gas in the liquid state coming from the reliquefaction section 10 or from the sub-cooling section 11 to one and / or the other of the tanks 2. The return line 39 comprises a first return valve 40a and a second return valve 40b authorizing or prohibiting the circulation of the gas in the liquid state to one and / or the other of the tanks 2.

[0103] In order for the gas in the liquid state to be able to be returned to each of the tanks 2 in an optimal manner, the cooling circuit 8 comprises for each of the tanks 2 a first termination 26a, 26b with a first termination valve 31a, 31b and a return orifice 28a, 28b, and a second termination 27a, 27b with a second termination valve 32a, 32b and a projection device 29a, 29b. Each of these elements is implemented to return the gas in the liquid state to one and / or the other of the tanks 2a, 2b in one way or another depending on the active operating mode among those described in FIGS. 2 to 4.

[0104] The return line 39 makes it possible to select a tank 2 to which to return the gas in the liquid state, or to return the gas in the liquid state to both tanks 2 by distributing it in a defined manner. For example, the gas from a reliquefaction operation alone can be returned as a priority to the coldest tank 2, and conversely, the gas from a subcooling operation alone can be returned as a priority to the hottest tank 2.

[0105] The structural and functional elements not described in the management system 1 of figure 5 being identical to those described previously, reference will be made to the description of figures 1 to 4 concerning the elements common to all of figures 1 to 5.

[0106] Figure 6 represents a flowchart of a management method 100 implemented by the management system according to the invention. The management method 100 makes it possible to determine which operating mode must be used among those described in Figures 2 to 4 according to previously verified conditions. The management method 100 is preferably implemented during a journey of the floating structure whose purpose is to deliver a cargo of gas in the liquid state, said cargo being contained in the tank. The management method 100 begins with an initiation step 101.

[0107] A composition of the gas in the liquid state contained in the tank is then taken into account, more particularly it is checked whether the rate of hydrocarbons with at least six C6 carbons is lower or higher than a hydrocarbon threshold Sh, above which the risk of icing is too high to be able to implement the second operating mode 103 illustrated in FIG. 3, i.e. the subcooling operation alone. Taking this composition into account is therefore essential to determine which configuration to implement within the management system. The composition of the gas in the liquid state can for example be measured by a fluid analyzer that can be arranged in the tank. Such a fluid analyzer is capable of measuring the rate of hydrocarbons with at least six C6 carbons in parts per million. The hydrocarbon threshold Sh leading to a risk of icing can be between 80 and 150 parts per million, for example 100 parts per million.According to another example, the rate of hydrocarbons with at least six C6 carbons can be read on technical documentation provided when loading the gas in liquid state into the floating structure.

[0108] Regardless of the hydrocarbon content of at least six C6 carbons in the liquid gas, another step must be taken before determining which operating mode should be implemented. A temperature T of the liquid gas cargo is measured and compared to a temperature threshold Ts. The temperature threshold Ts can, for example, be a fixed value or can be defined by the unloading conditions of the destination point, i.e. the point where the liquid gas cargo is to be delivered. The threshold Ts can therefore differ depending on each destination point and must be respected, because if the threshold Ts is exceeded, the administration of the destination point may refuse the cargo, resulting in a loss of time and financial loss. It is therefore important to regularly check whether the temperature T of the cargo is below the temperature threshold Ts and to cool the cargo if this is not the case.

[0109] If the temperature T of the cargo is lower than the temperature threshold Ts, this means that it is permitted to increase the temperature of the cargo. In this case, and regardless of the composition of the gas, the first operating mode 102 illustrated in FIG. 2 is implemented and the gas in the liquid state circulates only in the reliquefaction section. This also makes it possible to avoid unnecessarily using the refrigerant loop described above and therefore to save energy by leaving it inactive.

[0110] If the hydrocarbon content with at least six C6 carbons is lower than the hydrocarbon threshold Sh and the temperature T of the cargo is higher than the temperature threshold Ts, this means that the cargo must be cooled but that there is no risk of heavy hydrocarbon icing in the third heat exchanger. The second operating mode 103 illustrated in FIG. 3 can be implemented and the gas in the liquid state is circulated within the subcooling section in order to cool the temperature of the tank.

[0111] If the hydrocarbon content with at least six C6 carbons is higher than the hydrocarbon threshold Sh and the cargo temperature T is higher than the temperature threshold Ts, the cargo must be cooled but there is a risk of icing of the heavy hydrocarbons in the third heat exchanger. In this case, the third operating mode 104 illustrated in Figure 4 must be used, during which the gas in the liquid state passes through the second heat exchanger and then the third heat exchanger in series in order to reach a temperature low enough to cool the cargo but high enough so that the heavy hydrocarbons do not ice in the third heat exchanger.

[0112] The management method 100 can be repeated over time. It is even essential to repeat it during the journey because the operating modes influence the temperature T of the cargo over time and it is likely that the operating mode must be changed one or more times over time. The composition of the gas in the liquid state is not necessarily taken into account at each iteration, the management method 100 being able to keep it in memory after having taken it into account during its first iteration.

[0113] Figure 7 represents a variant of the management method 100 making it possible to optimize the thermal treatment of the gas cargo in the liquid state in the case where the rate of hydrocarbons with at least six C6 carbons is lower than the hydrocarbon threshold Sh and where the temperature T of the cargo is higher than the temperature threshold Ts. The situation here is therefore to cool the cargo without fear of icing within the third heat exchanger

[0114] According to this variant of the management method 100, a quantity of surplus Sbog of gas in the vapor state is measured and compared to a subcooling capacity Cs of the third heat exchanger. The objective here is to determine whether a projection of subcooled gas into the tank headspace is effective in relation to the quantity of gas in the vapor state to be recondensed.

[0115] If the subcooling capacity Cs is sufficient to thermally treat the surplus Sbog of gas in the vapor state of the tank headspace, then the second operating mode 103 is implemented to circulate the gas in the liquid state only in the subcooling section, implement a projection of gas in the subcooled liquid state and recondense all of the surplus Sbog of gas in the vapor state of the tank headspace.

[0116] If the excess Sbog of gas in the vapor state of the tank head is in too large a quantity compared to the subcooling capacity Cs of the third heat exchanger, it is more efficient to evacuate said excess Sbog from the tank in order to reliquefy it rather than to seek to recondense it in the tank head by projection of gas in the subcooled liquid state. In this case, in an optimized manner, it is more judicious to implement the third operating mode 104 illustrated in figure 4 rather than the second operating mode 103 illustrated in figure 3. This makes it possible to eliminate more quickly the excess Sbog of gas in the vapor state contained in the tank head. Furthermore, this also makes it possible to lower the temperature of the tank, the temperature T of the cargo being higher than the temperature threshold Ts.The variant of the management process 100 therefore makes it possible to further optimize the thermal treatment of the gas contained in the tank, whether it is in the liquid state or in the vapor state.

[0117] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0118] The invention, as just described, achieves the aim it set itself, and makes it possible to propose a system for managing gas contained in a tank, guaranteeing gas supply, reliquefaction of surplus gas in the vapor state and / or management of the temperature of the tank, and this in an optimal manner whatever the composition of the gas contained in the tank. Variants not described here could be implemented without departing from the context of the invention, provided that, in accordance with the invention, they comprise a management system in accordance with the invention.

Claims

CLAIMS 1- Management system (1) of a gas in the liquid state transported and / or stored by a floating structure comprising at least one tank (2, 2a, 2b) configured to contain the gas and at least one gas consuming device (3, 3a, 3b), the management system (1) comprising: at least one supply circuit (4) configured to supply gas to the gas consuming device (3, 3a, 3b), the supply circuit (4) comprising at least one compression device (5), at least one heat treatment circuit (6) for the gas in the vapor state compressed by the compression device (5), at least one first heat exchanger (7) configured to carry out a heat exchange between the gas in the vapor state circulating in the supply circuit (4) between the tank (2, 2a, 2b) and the compression device (5) and the gas in the vapor state circulating in the heat treatment circuit (6), at least one cooling circuit (8) comprising at least one pumping device (9, 9a,9b) configured to take the gas in the liquid state from the tank (2, 2a, 2b), characterized in that the cooling circuit (8) comprises a reliquefaction section (10), a sub-cooling section (11) and a bypass device (12) configured to circulate the gas in the liquid state to the reliquefaction section (10) or to the sub-cooling section (11), the management system (1) comprising: a second heat exchanger (13) configured to carry out a heat exchange between the gas in the vapor state circulating in the heat treatment circuit (6) downstream of the first heat exchanger (13) and the gas in the liquid state circulating in the reliquefaction section (10), a third heat exchanger (23) and a refrigerant loop (24), the third heat exchanger (23) being configured to carry out a heat exchange, between the gas in the liquid state circulating in the sub-cooling section (11) and a refrigerant circulating within the refrigerant loop (24), a junction line (33) configured to fluidically connect in series the second heat exchanger (13) and the third heat exchanger (23) so that the gas in the liquid state having circulated in the second heat exchanger (13) subsequently circulates within the third heat exchanger (23). 2- Management system (1) according to claim 1, wherein the bypass device (12) comprises a first bypass valve (12a) arranged on the reliquefaction section (10) and a second bypass valve (12b) arranged on the subcooling section (11). 3- Management system (1) according to claim 1 or 2, wherein the junction line (33) comprises a junction valve (34) configured to control the series connection of the third heat exchanger (23) to the second heat exchanger (13). 4- Management system (1) according to any one of the preceding claims, wherein the cooling circuit (8) comprises at least one termination to which the reliquefaction section (10) and / or the sub-cooling section (11) are fluidically connected, the cooling circuit (8) comprising a first termination (26, 26a, 26b) comprising a return orifice (28, 28a, 28b) configured to be arranged at a bottom of the tank (2, 2a, 2b) and a second termination (27, 27a, 27b) comprising a projection device (29, 29a, 29b) configured to be arranged at a top (30) of the tank (2, 2a, 2b). 5- Management system (1) according to any one of the preceding claims, comprising a separation device (14) arranged on the heat treatment circuit (6) downstream of the second heat exchanger (13), the heat treatment circuit (6) extending from the second heat exchanger (13) to an inlet (15) of the separation device (14), and from a liquid outlet (16) of the separation device (14) to the reliquefaction section (10). 6- Management system (1) according to the preceding claim, in which the separation device (14) comprises a steam outlet (18), the management system (1) comprising a recirculation line (19) extending from the steam outlet (18) of the separation device (14) to the supply circuit (4) between the tank (2, 2a, 2b) and the first heat exchanger (7). 7- Management system (1) according to any one of the preceding claims, configured for a floating structure comprising at least two tanks (2, 2a, 2b), in which the cooling circuit (8) comprises at least two pumping devices (9, 9a, 9b), each pumping device (9, 9a, 9b) being configured to take the gas in the liquid state 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 to the sub-cooling section (11). 8- Management system (1) according to the preceding claim, configured for a floating structure comprising at least two tanks, (2, 2a, 2b), in which the cooling circuit (8) comprises a return line (39) configured to return the gas from the reliquefaction section (10) or from the sub-cooling section (11) to one and / or the other of the tanks (2, 2a, 2b). 9- Floating structure comprising at least one tank (2, 2a, 2b) configured to contain gas in the liquid state, at least one gas-consuming device (3, 3a, 3b) and a management system (1) according to any one of the preceding claims. 10- Method (100) for managing a gas in the liquid state contained in at least one tank (2, 2a, 2b) of a floating structure according to the preceding claim making a journey towards a destination point, during which: a composition of the gas in the liquid state contained in the tank (2, 2a, 2b) is taken into account, a temperature (T) of the gas in the liquid state contained in the tank (2, 2a, 2b) and we compare the measured temperature (T) to a temperature threshold (s) of the gas, if the rate of hydrocarbons with at least six carbons (C6) is lower than a hydrocarbon threshold (Sh) and if the temperature (T) is lower than the temperature threshold (Ts), the gas is circulated in the liquid state only in the reliquefaction section (10), if the rate of hydrocarbons with at least six carbons (C6) is lower than the hydrocarbon threshold (Sh) and if the temperature (T) is higher than the temperature threshold (s), the gas is circulated in the liquid state at least in the subcooling section (H), if the rate of hydrocarbons with at least six carbons (C6) is higher than the hydrocarbon threshold (Sh) and if the temperature (T) is lower than the temperature threshold (s), the gas is circulated in the liquid state only in the reliquefaction section (10), if the rate of hydrocarbons with at least six carbons (C6) is higher than the hydrocarbon threshold (Sh) and if the temperature (T) is higher at the temperature threshold (Ts),the gas in the liquid state is circulated in the reliquefaction section (10) and the gas is allowed to circulate in the junction line (33) in order to fluidically connect in series the second heat exchanger (13) to the third heat exchanger (23)., 11- Management method (100) according to the preceding claim, during which: if the rate of hydrocarbons with at least six carbons (C6) is lower than the hydrocarbon threshold (Sh) and if the temperature (T) is higher than the temperature threshold (Ts), a surplus (Sbog) of gas in the vapor state in excess of a supply requirement of the gas-consuming device (3, 3a, 3b) is determined and this surplus (Sbog) is compared to a subcooling capacity (Cs) of the third heat exchanger (23), if the quantity of surplus (Sbog) of gas in the vapor state is lower than the subcooling capacity (Cs) of the third heat exchanger (23), the gas in the liquid state is circulated only in the subcooling section (11), if the quantity of surplus (Sbog) of gas in the vapor state is higher than the subcooling capacity (Cs) of the third heat exchanger,the gas is circulated in the liquid state in the reliquefaction section (10) and the gas is allowed to circulate, in the junction line (33) in order to fluidically connect in series the second heat exchanger (13) of the reliquefaction section (10) to the third heat exchanger (23) of the subcooling section (11). 12- Management method (100) according to claim 10 or 11, during which the composition of the gas contained in the tank is taken into account using a fluid analyzer. 13- Management method (100) according to claim 10 or 11, during which the composition of the gas contained in the tank is taken into account using technical documentation. 14- Management method (100) according to any one of claims 10 to 13, repeatable over time.

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