System for managing a gas contained in a floating structure

Abstract

The present invention relates to a system (1) for managing a gas contained in a tank (2) comprising: - at least one supply circuit (6), - at least one heat treatment circuit (8), - at least one first heat exchanger (13), - at least one cooling circuit (17), - at least one second heat exchanger (16), characterised in that the heat treatment circuit (8) comprises at least one first branch (9) connected to a first compression stage (11) of the compression device (7) and a second branch (10) connected to a second compression stage (12) of the compression device (7), the first branch (9) and the second branch (10) meeting at a convergence point (14) in the heat treatment circuit (8).

Description

[0001] DESCRIPTION

[0002] Title of the invention: System for managing a gas contained in 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] However, it happens that certain floating structures, and more particularly the tank(s) they contain, are authorized to store and / or transport different types of gas in the liquid state. Said floating structures may, for example, contain a cargo of liquefied natural gas, consisting almost exclusively of methane, or a cargo of ethane, which may contain a tiny proportion of methane.

[0007] These different types of gas have different chemical structures. Due to this difference in structure, other characteristics vary from one gas to another, such as the evaporation temperature or compatibility with at least one device integrated into the floating structure and capable of consuming gas, such as an engine.

[0008] It can thus be complicated to use the gas contained in the tank as fuel or to reliquefy it depending on the nature of said gas because depending on the different parameters of these, some may not be optimally compatible with the system used, and this can harm the efficiency of the reliquefaction of the gas. The present invention allows adaptation to different types of gas stored and / or transported and therefore proposes a system for managing a gas contained in at least one tank of a floating structure which comprises at least one gas-consuming device, the management system comprising:

[0009] - at least one gas supply circuit for the gas-consuming appliance, the supply circuit comprising at least one compression device comprising at least two compression stages and configured to compress gas taken in the vapor state from the tank to a pressure compatible with the needs of the gas-consuming appliance,

[0010] - at least one circuit for thermal treatment of the gas in the vapor state compressed by at least one compression stage of the compression device,

[0011] - 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,

[0012] - at least one cooling circuit comprising at least one pump configured to draw the gas in the liquid state from the tank,

[0013] - at least one 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 circulating in the cooling circuit, characterized in that the heat treatment circuit comprises at least a first branch connected to a first compression stage of the compression device and a second branch connected to a second compression stage of the compression device, the second compression stage being arranged downstream of the first compression stage, the first branch and the second branch joining at a convergence point of the heat treatment circuit. Thanks to this management system, the gas in the vapor state contained in the tank can be consumed and also reliquefied optimally, regardless of its nature.Depending on the characteristics of the gas stored and / or transported, but also depending on the compatibility of said gas with the gas-consuming device, the management system can adapt for systematically efficient gas treatment. A compression stage as described in the invention can correspond to several compressors.

[0014] The feed circuit allows the gas in the vapor state forming at the level of a tank head to be sampled. This gas in the vapor state is due to the evaporation of a part of the cargo of gas in the liquid state contained in the tank. Such evaporation can occur naturally or forced by any device integrated into the floating structure. The gas in the vapor state can therefore be consumed or reliquefied, but must generally be evacuated in order to regulate the pressure of the tank.

[0015] The compression device therefore ensures the suction of the gas in the vapor state out of the tank and compresses it. The compression device can, for example, be a plurality of compressors arranged in series with one another, or a single compressor with multiple compression stages. The more compression stages the gas in the vapor state passes through, the higher the pressure the gas in the vapor state is put under. The gas compressed by the entire compression device can reach a pressure of between 250 and 400 bars. The pressure applied to the gas in the vapor state is important to supply the gas-consuming device because the latter can only consume the gas in the vapor state if it is at a compatible pressure. Furthermore, the gas-consuming device may not be able to consume the gas contained in the tank depending on the chemical structure of the gas.In such a configuration, the gas in the vapor state is then not evacuated from the tank for supply purposes.

[0016] If the gas vapor is not compatible with the gas-consuming device or if the gas-consuming device does not require supply, the gas vapor circulates in the heat treatment circuit. If the gas-consuming device only requires a fraction of the gas vapor to be supplied, the remainder of the gas vapor also circulates in the heat treatment circuit. One of the functions of this heat treatment circuit is to participate in the reliquefaction of the compressed gas vapor.

[0017] The first heat exchanger allows the compressed gas to be pre-cooled in the vapor state on the one hand and the gas to be reheated in the vapor state at the tank outlet on the other hand. Pre-cooling the compressed gas facilitates its subsequent thermal treatment, in particular its reliquefaction for example. The first heat exchanger thus improves the overall efficiency of the management system because the low temperature of the gas in the vapor state at the tank outlet indirectly contributes to the reliquefaction of the compressed gas in the vapor state, via the heat exchange taking place in the first heat exchanger.

[0018] The cooling circuit can have several functions such as participating in the reliquefaction of the gas in the vapor state circulating in the heat treatment circuit, or even managing the pressure of the tank. To do this, the gas in the liquid state of the tank is taken by the pump, the latter being able for example to be submerged at the bottom of the tank, and circulates within the cooling circuit.

[0019] By circulating in the cooling circuit, the gas in the liquid state can pass through the second heat exchanger, which is also crossed by the gas in the vapor state circulating in the heat treatment circuit. This heat exchange thus makes it possible to reliquefy the gas in the vapor state without leading to the evaporation of the gas in the liquid state circulating in the cooling circuit. Once the gas in the vapor state has been reliquefied, it can return to the tank, just like the gas in the liquid state used for reliquefaction by circulating within the cooling circuit.

[0020] The advantage of the heat treatment system according to the invention is the presence of several branches within the heat treatment circuit, at the outlet of the compression device. Thus, regardless of the nature of the gas contained in the tank, it can be systematically consumed and / or reliquefied in an optimal manner. For example, a gas intended to be consumed at low pressure and whose reliquefaction is more efficient at low pressure can exit the compression device at the first compression stage, while a gas intended to be consumed at high pressure and whose reliquefaction is more efficient at high pressure can exit the compression device at the second compression stage. The same applies to a gas intended to be consumed at high pressure and whose reliquefaction is more efficient at low pressure or vice versa.

[0021] By connection to the first compression stage and the second compression stage, it is understood that the first branch is connected to an outlet of the first compression stage and the second branch is connected to an outlet of the second compression stage. In other words, the first compression stage is the last stage to compress the gas in the vapor state flowing in the first branch, and the second compression stage is the last stage to compress the gas in the vapor state flowing in the second branch.

[0022] The gas compressed by the compression device up to the first compression stage has a pressure between 7 and 20 bars. The gas compressed by the compression device up to the second compression stage has a pressure between 120 and 150 bars. In this configuration, the gas can exit the compression device at two different compression stages. The two branches then join so that the compressed gas is treated within the heat treatment circuit, regardless of the pressure to which the gas was compressed.

[0023] As mentioned previously, the management system can be adapted with respect to the nature and / or composition of the gas contained in the tank. Thus, in the case where the floating structure and its tank are configured to transport and / or store methane-type gas or ethane-type gas, the management system is then configured to authorize the circulation of the gas in the first branch and / or in the second branch if the gas contained in the tank is methane, and only in the first branch if the gas contained in the tank is ethane. Such a configuration makes it possible to best treat each of the types of gas in terms of supply and / or reliquefaction.

[0024] According to a feature of the invention, the convergence point is arranged between the compression device and the first heat exchanger. It is particularly advantageous to pre-cool the compressed gas, regardless of the pressure to which it was compressed. The convergence point is therefore preferably positioned upstream of the first heat exchanger relative to the direction of circulation of the compressed gas.

[0025] According to a characteristic of the invention, the heat treatment circuit comprises at least one expansion member arranged downstream of the first heat exchanger. After being pre-cooled, the gas in the vapor state is expanded in order to lower its pressure and temperature, in particular with the aim of further cooling the gas, or even reliquefying it. Expansion can also be carried out, for example, in the case where the gas is ethane and the objective is to create a two-phase mixture in order to extract the fraction of methane contained in the ethane by maintaining it in the gaseous state while the ethane is reliquefied. Expansion can help to form this two-phase mixture by modifying the point of change of state of the gas by lowering its pressure.

[0026] According to a characteristic of the invention, the expansion member is arranged between the first heat exchanger and the second heat exchanger. This particular arrangement makes it possible to prepare the gas in the vapor state for reliquefaction, in particular thanks to the second heat exchanger.

[0027] According to a feature of the invention, the second branch of the heat treatment circuit comprises a control member. The second branch is connected to the second compression stage, i.e. to the compression stage where the gas is most compressed. The control member arranged on the second branch thus makes it possible to control the flow rate of gas in the vapor state of the second branch. The control member may optionally be capable of expanding the gas in the vapor state circulating in the second branch in addition to ensuring the regulation of the flow rate. An expansion of this gas may be advantageous before its cooling within the first heat exchanger so that the gas pressure is compatible with the technology of the first heat exchanger.

[0028] According to a characteristic of the invention, the first branch is devoid of a control member. It is not necessary to expand the gas when it is compressed only up to the first compression stage. According to a characteristic of the invention, the gas consuming device is a high-pressure gas consuming device, the supply circuit being configured to supply the high-pressure gas consuming device and / or a low-pressure gas consuming device. In other words, there are at least two gas consuming devices that can be supplied by the gas in the vapor state contained in the tank. For example, the high-pressure gas consuming device may be an engine ensuring the propulsion of the floating structure while the low-pressure gas consuming device may be an electricity generator for the floating structure.These two examples of gas-consuming devices may or may not be compatible with the gas stored and / or transported in the tank, and at a particular pressure range in the event of compatibility.

[0029] According to a feature of the invention, a supply to the low-pressure gas-consuming device via the supply circuit passes at least partially through the first branch. As mentioned previously, the first branch is connected to the first compression stage of the compression device, to the stage where the gas is compressed to low pressure. The first compression stage is therefore adapted to compress the gas in the vapor state to a pressure compatible with the needs of the low-pressure gas-consuming device, provided that the latter can consume the type of gas contained in the tank. As a result, the supply to the low-pressure gas-consuming device is therefore partially merged with the first branch.

[0030] According to a characteristic of the invention, the heat treatment circuit comprises a separation device, an inlet of which is arranged downstream of the second heat exchanger. The separation device makes it possible to separate the gaseous phase from the liquid phase of the gas circulating in the heat treatment circuit, after said gas has passed through the second heat exchanger. The separation device can be used in the event of partial reliquefaction of the gas circulating in the heat treatment circuit in order to retain the fraction of gas which has not reliquefied. According to a characteristic of the invention, the separation device comprises a first outlet configured to allow the gas in the vapor state to exit the separation device, the heat treatment circuit comprising a third branch connecting the first outlet of the separation device to the supply circuit of the low-pressure gas-consuming device.As mentioned above, if the gas contained in the tank is ethane, the thermal treatment of said gas can be carried out so as to reliquefy the ethane while retaining the methane in the vapor state, the methane being present in minimal proportion in the ethane. The methane can then subsequently circulate out of the separation device via the first outlet, then within the third branch in order to supply the low-pressure gas-consuming device. Since the latter is not capable of consuming ethane, the only way to supply it with gas in the vapor state is to isolate the methane contained in the ethane and to supply said methane.

[0031] According to a characteristic of the invention, the heat treatment circuit comprises a fourth branch connecting the first outlet of the separation device to the supply circuit at a point located between the tank and the first heat exchanger. The fourth branch is for example used in the case of partial reliquefaction without the objective of separating components of the gas. The gas remaining in the vapor state after passing through the second exchanger is then isolated within the separation device and then circulates in the fourth branch in order to recirculate within the supply circuit in order to be consumed or to cause a new attempt at reliquefaction.

[0032] According to a characteristic of the invention, the separation device comprises a second outlet configured to allow the gas in the liquid state to exit the separation device, the heat treatment circuit comprising a fifth branch connecting the second outlet of the separation device to the cooling circuit. The reliquefied gas therefore leaves the separation device in the liquid state and circulates in the fifth branch in order to return to the tank by joining the cooling circuit. According to a characteristic of the invention, the heat treatment circuit comprises a sixth branch connecting an outlet of a pass of the second heat exchanger constituting the heat treatment circuit to the fifth branch. In other words, the sixth branch bypasses the separation device and directly joins the cooling circuit via the fifth branch.When it is certain that reliquefaction is complete after the gas has passed through the second heat exchanger, it is advantageous to bypass the separation device in order to avoid unnecessary heat inputs.

[0033] According to a feature of the invention, the management system comprises a third heat exchanger configured to carry out a heat exchange between the gas in the liquid state circulating in the cooling circuit and a refrigerant circulating in a cooling loop. This third heat exchanger makes it possible to subcool the gas in the liquid state, for example in order to improve the reliquefaction of the gas in the vapor state circulating through the second heat exchanger by circulating the subcooled gas in the liquid state within this same second heat exchanger. The subcooled gas in the liquid state can also return to the tank in order to lower the overall temperature thereof and thus reduce the pressure of the tank. The refrigerant circulating in the cooling loop used to subcool the gas in the liquid state can for example be nitrogen.

[0034] According to a characteristic of the invention, the management system comprises an additional branch connecting the first compression stage of the compression device to the tank, the management system further comprising a heat exchanger configured to carry out a heat exchange between the gas in the vapor state circulating in the additional branch and a refrigerant fluid circulating in a reliquefaction loop. This is an alternative embodiment that can be implemented for example in the absence of the third heat exchanger mentioned above or to treat a large quantity of gas in the vapor state.

[0035] The presence of the additional branch and the heat exchanger can be useful, for example, in the case where there is too little gas in the vapor state circulating from the tank to the compression device to carry out effective pre-cooling. The heat exchanger can also be used when the gas in the liquid state contained in the tank is at a temperature too high to properly reliquefy the gas in the vapor state circulating in the heat treatment circuit and said gas in the liquid state cannot otherwise be sub-cooled.

[0036] In this configuration, at least part of the gas in the compressed vapor state and intended to be reliquefied can circulate in the additional branch and be reliquefied separately thanks to the heat exchange carried out within the heat exchanger. Just like the cooling loop mentioned above, the reliquefaction loop can be traversed by a refrigerant fluid, for example nitrogen.

[0037] The additional branch extends to the tank so that the gas, once reliquefied within the heat exchanger, can circulate in liquid state to the tank.

[0038] According to a characteristic of the invention, the cooling circuit comprises at least one termination opening into the tank, the termination being a spray member and / or an orifice arranged in a lower part of the tank.

[0039] The cooling circuit, in addition to participating in the reliquefaction of the gas in the vapor state, can also participate in the management of the pressure of the tank and the overall temperature of the gas contained in the tank.

[0040] The management system may include a single termination which may be the orifice or the spray member, or may include two terminations including an orifice and a spray member.

[0041] To participate in the cooling of the tank, the gas in the liquid state can circulate in the cooling circuit, be subcooled thanks to the third heat exchanger, then return to the tank via the orifice and / or the spraying member. The orifice ensures a return within the tank in order to lower the overall temperature of the gas in the liquid state of the tank. The spraying member allows a projection of gas in the liquid state at the level of the tank crown, which promotes the condensation of the gas in the vapor state present in the tank crown in order to lower the pressure of the tank. The invention also covers a floating structure comprising at least one tank and a management system as described above, the tank containing liquefied natural gas.

[0042] According to a characteristic of the invention, the floating structure comprises at least one tank and a management system as described previously, the tank containing ethane.

[0043] As described above, the nature of the gas contained in the tank will determine the operation of the management system, how the gas-consuming device is supplied and how the gas in vapor state is reliquefied.

[0044] The invention also covers a method for managing a gas contained in at least one tank of a floating structure, implemented by a management system as described previously, during which:

[0045] - the gas is circulated in the first branch and / or in the second branch of the heat treatment circuit if the gas contained in the tank is liquefied natural gas, or,

[0046] - the gas is circulated in the first branch of the heat treatment circuit if the gas contained in the tank is ethane, the circulation of the gas being prevented in the second branch.

[0047] The management process thus makes it possible to adapt the management system, whether in terms of gas consumption or reliquefaction, regardless of whether the gas contained in the tank is liquefied natural gas or ethane.

[0048] 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:

[0049] [fig 1] is a diagram of a system for managing a gas contained in a tank within a floating structure, [fig 2] is a diagram of an example of gas circulation when the gas contained in the tank is liquefied natural gas,

[0050] [fig 3] is a diagram of an example of gas circulation when the gas contained in the tank is ethane,

[0051] [fig 4] represents an alternative embodiment of the management system according to the invention.

[0052] Figure 1 illustrates a management system 1 according to the invention. The management system 1 can be integrated within a floating structure, for example a vessel for storing and / or transporting a gas in the liquid state contained in at least one tank 2. The gas in the liquid state can naturally partially evaporate within a ceiling 3 of the tank 2.

[0053] In order to manage the pressure of the tank 2 which increases due to the presence of gas in the vapor state within the headspace 3, the management system 1 can process this gas so that the latter supplies at least one gas consuming device. In Figure 1, the management system is configured to be able to supply a high-pressure gas consuming device 4 and a low-pressure gas consuming device 5. The high-pressure gas consuming device 4 can for example be an engine ensuring the propulsion of the floating structure. The low-pressure gas consuming device 5 can be a generator supplying the floating structure with electricity. The high-pressure gas consuming device 4 and the low-pressure gas consuming device 5 each have their gas supply conditions, said gas having to be of a particular nature and at a particular pressure to be compatible with the needs of each of the gas consuming devices 4, 5.

[0054] In order to supply the gas-consuming devices 4, 5, the management system 1 comprises a supply circuit 6 extending between the tank 2 and the high-pressure gas-consuming device 4. The supply circuit 6 comprises a compression device 7 for sucking in the gas in the vapor state contained in the headspace 3 and the tank 2 and compressing it to a pressure compatible with the needs of the high-pressure gas-consuming device 4. In Figure 1, the compression device 7 is represented schematically by a series of compressors, but the compression device 7 can also be a single multi-stage compressor. Thus, the compression device 7 has several compression stages in order to compress the gas in the vapor state to a higher or lower pressure. The more compression stages the gas in the vapor state passes through, the higher the pressure it is compressed.The gas in the vapor state must therefore pass through all of the compression stages of the compression device 7 to reach the pressure compatible with supplying the high-pressure gas-consuming device 4. At the outlet of the entire compression device 7, the gas in the vapor state can reach a pressure value of between 250 and 400 bars.

[0055] The management system 1 also comprises a heat treatment circuit 8. The heat treatment circuit 8 is connected to the supply circuit 6, more particularly at the compression device 7. The particularity of the management system 1 according to the invention is that the heat treatment circuit 8 comprises a first branch 9 and a second branch 10, respectively connected to a first compression stage 11, and to a second compression stage 12 arranged downstream of the first compression stage 11. The first branch 9 and the second branch 10 thus make it possible to circulate the gas in the vapor state within the heat treatment circuit 8 at two different pressure levels. Furthermore, a part of the supply circuit 6 is connected to the first branch 9 in order to connect the latter to the low-pressure gas-consuming device 5.Such a connection is implemented because the gas in the vapor state compressed in the first compression stage 11 has a pressure compatible with supplying the low-pressure gas-consuming device 5. The gas in the vapor state compressed up to the first compression stage 11 has a pressure of between 7 and 20 bars while the gas in the vapor state compressed up to the second compression stage 12 has a pressure of between 120 and 150 bars.

[0056] Beyond the connection to a different compression stage, the first branch 9 and the second branch 10 are distinguished from each other by the fact that the second branch 10 comprises a control member 32, while the first branch does not. The control member 32 makes it possible to regulate the flow circulating in the second branch 10, but can also ensure an expansion of the gas circulating in the second branch.

[0057] 10 after compressing it to the second compression stage 12.

[0058] One of the objectives of the heat treatment circuit 8 is to participate in the reliquefaction of the gas in the vapor state not used for supplying the gas consuming devices 4, 5 in order to limit the losses linked to the evaporation of the gas contained in the tank 2. To do this, the management system 1 comprises a first heat exchanger 13 configured to carry out a heat exchange between the gas in the compressed vapor state circulating in the heat treatment circuit 8 and the gas in the vapor state circulating in the supply circuit 6 upstream of the compression device 7.

[0059] The first heat exchanger 13 thus makes it possible to pre-cool the gas in the vapor state circulating in the heat treatment circuit 8 by using the gas in the vapor state at the outlet of the tank 2. The latter is then heated by capturing the calories from the gas in the vapor state circulating in the heat treatment circuit 8.

[0060] 11 It should be noted that the first branch 9 and the second branch 10 join at a convergence point 14. The latter is advantageously arranged upstream of the first heat exchanger 13 so that all of the gas in the vapor state circulating in the heat treatment circuit 8 passes through the first heat exchanger 13 to be pre-cooled. The management system 1 can however be configured, in a manner not illustrated, so that the first branch 9 or the second branch 10 bypasses the first heat exchanger 13. The convergence point 14 is in this case arranged downstream of the first heat exchanger 13.

[0061] At the outlet of the first heat exchanger 13, the pre-cooled gas in the vapor state is expanded by an expansion member 15. The expansion of the gas in the vapor state makes it possible to further lower its pressure and temperature. The expansion member 15 also modifies the temperature at which the gas in the vapor state changes state. The gas in the vapor state then passes through a second heat exchanger 16 in order to be at least partially reliquefied. In FIG. 1, the expansion member 15 is arranged between the first heat exchanger 13 and the second heat exchanger 16, but the expansion member 15 can also be arranged downstream of the second heat exchanger 16.

[0062] In order to carry out efficient reliquefaction, the management system 1 comprises a cooling circuit 17 within which circulates gas in the liquid state taken from the tank 2. The cooling circuit 17 comprises a pump 18, advantageously submerged at the bottom of the tank 2 and which circulates gas in the liquid state within the cooling circuit 17. Among the different functions of the cooling circuit 17, one of them is to participate in the reliquefaction of the gas in the vapor state circulating in the heat treatment circuit 8. The gas in the liquid state circulating in the cooling circuit 17 can thus pass through the second heat exchanger 16 within which the heat exchange takes place with the gas in the vapor state circulating in the heat treatment circuit 8. The gas in the vapor state is then reliquefied.

[0063] In order to improve the reliquefaction of the gas in the vapor state circulating in the second heat exchanger 16, the management system 1 comprises a third heat exchanger 19, through which the gas in the liquid state circulating in the cooling circuit 17 can pass.

[0064] The third heat exchanger 19 makes it possible to subcool the gas in the liquid state in order to compensate for the calories captured by the gas in the liquid state during the heat exchange occurring within the second heat exchanger 16. In order to subcool the gas in the liquid state, the third heat exchanger 19 is also crossed by a cooling loop 20 within which a refrigerant circulates ensuring the subcooling of the gas in the liquid state. The refrigerant circulating in the cooling loop 20 may for example be nitrogen.

[0065] Once the gas circulating in the heat treatment circuit 8 has been at least partially reliquefied, it can circulate to a separation device 21 comprising an inlet 22 through which the gas flows at the outlet of the second heat exchanger 16. The separation device 21 makes it possible to separate a liquid fraction from a vapor fraction of the gas if the latter is not entirely reliquefied. The separation device 21 comprises a first outlet 23 allowing the vapor fraction to exit the separation device 21 and a second outlet 24 allowing the liquid fraction to exit the separation device 21.

[0066] The vapor fraction, if it is present in the separation device 21, can exit via the first outlet 23 and circulate within a third branch 25 or a fourth branch 26. The third branch 25 is connected to the low-pressure gas-consuming device 5 so that the vapor fraction can supply the latter if the gas in question is consumable by the low-pressure gas-consuming device 5. The fourth branch is connected to the supply circuit 6 and allows the recirculation of the gas in the non-reliquefied vapor state within said supply circuit 6 so that said gas is consumed or reliquefied.

[0067] The liquid fraction present in the separation device 21 can exit through the second outlet 24 and circulate within a fifth branch 27 which connects the separation device 21 to the cooling circuit 17. After joining the latter, the reliquefied gas then circulates to the tank 2. In Figure 1, the fifth branch 27 is connected to the cooling circuit 17, but the fifth branch 27 can just as easily extend directly to the tank 2.

[0068] The heat treatment circuit 8 also comprises a sixth branch 28 starting at an outlet of the second heat exchanger 16, upstream of the separation device 21, and extending to the fifth branch 27. The sixth branch 28 allows the reliquefied gas to return directly to the tank 2 by bypassing the separation device 21. Such a bypass makes it possible to avoid unnecessary heat inputs due to the passage of the gas through the separation device 21. The sixth branch 28 is therefore used when all of the gas in the vapor state circulating in the heat treatment circuit 8 is reliquefied by passing through the second heat exchanger 16.

[0069] After having circulated in the cooling circuit 17 or having been reliquefied in the heat treatment circuit 8, the gas in the liquid state returns to the tank 2 via at least one termination 29. The termination 29 can allow regulation of the temperature of the gas contained in the tank 2 and / or of the pressure of said tank 2. The termination 29 can thus be an orifice 30 or a spraying member 31. The orifice 30 can be arranged at the bottom of the tank 2.

[0070] It is possible to lower the temperature of the gas in the liquid state contained in the tank 2 thanks to the third heat exchanger 19 mentioned above. The gas in the liquid state is thus taken from the tank 2, is sub-cooled by passing through the third heat exchanger 19, and returns sub-cooled to the tank 2 via the orifice 30. The overall temperature of the gas in the liquid state contained in the tank 2 can thus decrease over time.

[0071] The pressure of the tank 2 can be lowered in the case where the termination 29, or at least one of them, is a spraying member 31. The latter makes it possible to spray gas in the liquid state into the headspace 3 of the tank 2 in order to condense the gas in the vapor state present in the headspace 3 and thus to lower the pressure of the tank 2. The spraying member 31 can also spray gas in the liquid state previously sub-cooled via the third heat exchanger 19 in order to promote the condensation of the gas in the vapor state of the headspace 3 of the tank 2.

[0072] When the generation of gas in the vapor state in the headspace 3 of the tank 2 is not sufficient to satisfy the consumption of the high-pressure gas-consuming device 4 and / or the low-pressure gas-consuming device 5, the management system 1 can be configured to supply the gas in the liquid state to the latter. Thus, the management system can comprise an additional supply circuit 33. This can for example be connected to the cooling circuit 17 in order to take advantage of the pump 18 to ensure circulation within the additional supply circuit 33.

[0073] The additional supply circuit 33 is divided into a high-pressure path 34 and a low-pressure path 35, respectively intended to supply the high-pressure gas-consuming device 4 and the low-pressure gas-consuming device 5. The high-pressure path 34 comprises a high-pressure pump 36 and a high-pressure evaporator 37. The high-pressure pump 36 pumps the gas in the liquid state up to a pressure compatible with the high-pressure gas-consuming device 4. The high-pressure evaporator 37 makes it possible to evaporate the gas in the liquid state placed under high pressure so that the gas passes into the vapor state and can be consumed by the high-pressure gas-consuming device 4.

[0074] The low pressure channel 35 comprises a low pressure evaporator 38 which evaporates the gas in the liquid state so that the low pressure gas consuming device 5 can consume said gas, if the latter is capable of supplying the low pressure gas consuming device 5. The low pressure channel 35 does not include a pump like the high pressure channel 34 because the circulation of the gas in the liquid state by the pump 18 is sufficient to pressurize the gas in the liquid state to a pressure compatible with the low pressure gas consuming device 5.

[0075] The management system 1 may also comprise an evacuation path 39 connected to the supply circuit 6 and extending to a burner 40. The evacuation path 39 makes it possible to eliminate the gas in the vapor state in the ceiling 3 of the tank 2 in order to avoid overpressure within the tank 2 and so that the gas in the vapor state cannot be consumed or reliquefied.

[0076] In order to determine a path and a pressure of the gas within the management system 1, the latter comprises a plurality of expansion elements and valves in addition to the expansion member 15 and the control member 32 mentioned previously. The heat treatment circuit 8 thus comprises a first regulation element 41 upstream of the separation device 21 and a second regulation element 42 arranged on the sixth branch 28. The first regulation element 41 and the second regulation element 42 control the flow rate of gas circulating within the branches or portions of the circuit considered, and also control the pressure of the gas to a lesser extent.

[0077] The valves can be in the open or closed position depending on the nature of the gas contained in the tank 2 and how said gas is to be used, as will be described in detail later. The first branch 9 thus comprises a first valve 43 and the second branch 10, in addition to the control member 32, can comprise a second valve 44 if the control member 32 does not allow regulation of the flow rate of the gas in the vapor state. Furthermore, the third branch 25 comprises a third valve 45 and the fourth branch 26 comprises a fourth valve 46. The cooling circuit 17 further comprises a fifth valve 47 allowing the gas in the liquid state to pass through the second heat exchanger 16.

[0078] Finally, the part of the supply circuit 6 connecting the first branch 9 to the low-pressure gas-consuming device 5 comprises a sixth valve 51.

[0079] Figures 2 and 3 illustrate an example of gas circulation within the management system 1 according to the nature of the gas. In Figure 2, the gas contained in tank 2 is methane while Figure 3 is an example of circulation when the gas contained in tank 2 is ethane. For each figure, the solid lines correspond to lines where the gas circulates or can circulate, while the dotted lines correspond to lines where the gas does not circulate.

[0080] For Figure 2, the gas contained in the tank 2 and which can circulate in the management system 1 is therefore methane, more precisely natural gas which is largely composed of methane. The methane can be consumed by the high-pressure gas-consuming device 4 and by the low-pressure gas-consuming device 5, provided that it is put at a pressure compatible with them.

[0081] Thus, if natural gas is in the vapor state in the top 3 of the tank 2, it can be sucked into the supply circuit 6. The natural gas in the vapor state then passes through the first heat exchanger 13 to capture the calories released by the gas circulating in the heat treatment circuit 8, then is compressed by the compression device 7.

[0082] If the objective is to supply the high-pressure gas-consuming device 4, the natural gas in the vapor state is compressed by the compression device 7 in its entirety before circulating to the high-pressure gas-consuming device 4 to supply it.

[0083] If the objective is to supply the low-pressure gas-consuming device 5, the natural gas in the vapor state is compressed by the compression device 7 to the first compression stage 11, where the natural gas in the vapor state is then at a pressure compatible with the low-pressure gas-consuming device 5, before partially circulating in the first branch 9, then again in the supply circuit 6 to the low-pressure gas-consuming device 5 to supply it.

[0084] If the objective is to reliquefy the natural gas in the vapor state, it is compressed up to the second compression stage 12, circulates within the second branch 10 and is expanded by the control member 32.

[0085] The natural gas in the vapor state then passes through the first heat exchanger 13 to be pre-cooled and can be further expanded by the expansion member 15 before passing through the second heat exchanger 16. In parallel with this, the natural gas in the liquid state circulates in the cooling circuit 17 and can also pass through the second heat exchanger 16 in order to at least partially reliquefy the natural gas in the vapor state. In order to promote the reliquefaction of the natural gas in the vapor state, the natural gas in the liquid state can be sub-cooled by passing through the third heat exchanger 19 before passing through the second heat exchanger 16. The sub-cooled natural gas can also be used to lower the overall temperature of the natural gas in the liquid state by circulating to the orifice 30 or reduce the pressure of the tank 2 by recondensing the natural gas in the vapor state by projecting the sub-cooled gas via the projection member 31.

[0086] At the outlet of the second heat exchanger 16, if the natural gas is completely reliquefied, it can circulate in the sixth branch 28 in order to return to the tank 2 via the cooling circuit 17 and without passing through the separation device 21 in order to avoid unnecessary heat inputs.

[0087] If the natural gas is only partially reliquefied, it circulates to the separation device 21. The liquid fraction circulates in the fifth branch 27 via the second outlet 24 to reach the tank 2 via the cooling circuit 17, then the orifice 30. The vapor fraction circulates in the fourth branch 26 via the first outlet 23 of the separation device 21 in order to reach the supply circuit 6 upstream of the first heat exchanger 13 in order to be consumed or reliquefied. The natural gas can be consumed by the two gas-consuming devices 4, 5, so the gas in the liquid state can also circulate within the additional supply circuit 33, and in particular via the high-pressure route 34 and / or the low-pressure route 35 in the event of insufficient presence of gas in the vapor state in the headspace 3 of the tank 2.

[0088] For Figure 3, the gas in tank 2 is ethane. Ethane contains a fraction of methane, but this fraction is minimal. High-pressure gas-consuming device 4 can consume ethane, but this is not the case for low-pressure gas-consuming device 5, even at a compatible pressure.

[0089] The ethane can be sucked into the supply circuit 6. The ethane in vapor state then passes through the first heat exchanger 13 to capture the calories released by the gas circulating in the heat treatment circuit 8, then is compressed by the compression device 7.

[0090] If the objective is to supply the high-pressure gas-consuming device 4, the ethane in the vapor state is compressed by the compression device 7 in its entirety before circulating to the high-pressure gas-consuming device 4 to supply it.

[0091] If the objective is to supply the low-pressure gas-consuming device 5, the vaporous ethane cannot supply it directly as mentioned previously. For this, the vaporous ethane must first pass through the heat treatment circuit 8.

[0092] If the objective is to reliquefy the ethane in the vapor state or to supply the low-pressure gas-consuming device 5 indirectly, the ethane in the vapor state is compressed up to the first compression stage 11 and circulates within the first branch 9 to the first heat exchanger 13 to be pre-cooled and can be further expanded by the expansion member 15 before passing through the second heat exchanger 16. In parallel with this, the ethane in the liquid state circulates in the cooling circuit 17 and can also pass through the second heat exchanger 16 in order to at least partially reliquefy the ethane in the vapor state. In order to promote the reliquefaction of the ethane in the vapor state, the ethane in the liquid state can be sub-cooled by passing through the third heat exchanger 19 before passing through the second heat exchanger 16.

[0093] If the objective is to supply the low-pressure gas-consuming device 5, the expansion member 15 can be configured to expand the ethane to the vapor state so that, when passing through the second heat exchanger 16, the ethane leaves the latter mainly in the liquid state but with the previously mentioned methane fraction maintained in the vapor state. Since methane has a reliquefaction temperature lower than that of ethane, the gas thus leaves the second heat exchanger 16 at a temperature between the two reliquefaction points of the two types of gas.

[0094] The partially reliquefied ethane then circulates to the separation device 21, and the gaseous fraction, namely the methane, can then supply the low-pressure gas-consuming device 5 by exiting via the first outlet 23 and circulating in the third branch 25 to the low-pressure gas-consuming device 5.

[0095] Ethane can return to the tank in the same way as described above.

[0096] If the objective is to completely reliquefy the ethane in the vapor state, the reliquefied ethane can reach the tank 2 directly via the sixth branch 28 and the fifth branch 27 without passing through the separation device 21.

[0097] If the ethane is only partially reliquefied, it circulates to the separation device 21. The liquid fraction circulates in the fifth branch 27 via the second outlet 24 to reach the tank 2 via the cooling circuit 17, then the orifice 30. The vapor fraction, if there is no objective of supplying the low-pressure gas-consuming device 5, circulates in the fourth branch 26 via the first outlet 23 of the separation device 21 in order to reach the supply circuit 6 upstream of the first heat exchanger 13 in order to be consumed or reliquefied.

[0098] Just as described in Figure 2, the subcooled ethane circulating in the cooling circuit 17 can also be used to lower the overall temperature of the ethane in the liquid state by circulating to the orifice 30 or reduce the pressure of the tank 2 by recondensing the ethane in the vapor state by projecting the subcooled gas via the spraying member 31.

[0099] Concerning the additional supply circuit 33, only the high pressure line 34 can be used for supply, the ethane not being able to be consumed by the low pressure gas consuming device 5.

[0100] Figure 4 represents an alternative embodiment of the management system 1 according to the invention. Only the differences with what has been described previously will be discussed and reference will be made to the description of Figures 1 to 3 for the structural and functional characteristics common to both embodiments.

[0101] The management system 1 illustrated in Figure 4 differs from what was previously described by the absence of the third heat exchanger allowing the gas in the liquid state circulating in the cooling circuit 17 to be subcooled.

[0102] Instead, the alternative embodiment of the management system 1 according to the invention comprises an additional branch 48 connected to the first compression stage 11 in parallel with the first branch 9, and which extends to the tank 2. This additional branch 48 passes the gas in the vapor state through a heat exchanger 49, which is configured to carry out a heat exchange between the gas in the vapor state and a refrigerant circulating in a reliquefaction loop 50. At the outlet of the heat exchanger 49, the reliquefied gas circulates in the additional branch 48 until it returns to the tank 2.

[0103] The additional branch 48 and the heat exchanger 49 can thus be used when it is not possible to sub-cool the gas in the liquid state within the cooling circuit 17, which can lead to poor reliquefaction of the gas in the vapor state passing through the second heat exchanger 16, for example in the event of a temperature differential that is too low or in the event of gas in the vapor state in too large a quantity.

[0104] In such a situation, it may be advisable to distribute the gas in the compressed vapor state between the heat treatment circuit 8 and the additional branch 48 so that all of said gas in the vapor state is efficiently reliquefied. The efficiency is thus identical compared to the management system described in Figures 1 to 3. Reference will be made to the description of Figures 2 and 3 with regard to the path of the gas within the management system, depending on its nature. 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.

[0105] The invention, as just described, achieves the aim it set for itself, and makes it possible to propose a system for managing a gas ensuring its consumption and / or its reliquefaction, regardless of its nature. 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) for a gas contained in at least one tank (2) of a floating structure which comprises at least one gas-consuming device (4, 5), the management system (1) comprising: at least one gas supply circuit (6) for the gas-consuming device (4, 5), the supply circuit (6) comprising at least one compression device (7) comprising at least two compression stages (11, 12) and configured to compress gas taken in the vapor state from the tank (2) to a pressure compatible with the needs of the gas-consuming device (4, 5), at least one thermal treatment circuit (8) for the gas in the vapor state compressed by at least one compression stage (11, 12) of the compression device (7),at least one first heat exchanger (13) configured to carry out a heat exchange between the gas in the vapor state circulating in the supply circuit (6) between the tank (2) and the compression device (7) and the gas in the vapor state circulating in the heat treatment circuit (8), at least one cooling circuit (17) comprising at least one pump (18) configured to take the gas in the liquid state from the tank (2), at least one second heat exchanger (16) configured to carry out a heat exchange between the gas in the vapor state circulating in the heat treatment circuit (8) downstream of the first heat exchanger (13) and the gas circulating in the cooling circuit (17),characterized in that the heat treatment circuit (8) comprises at least a first branch (9) connected to a first compression stage (11) of the compression device (7) and a second branch (10) connected to a second compression stage (12) of the compression device (7), the second compression stage (12) being arranged downstream of the first compression stage (11), the first branch (9) and the second branch (10) joining at a convergence point (14) of the heat treatment circuit (8)., 2- Management system (1) according to claim 1, wherein the convergence point (14) is arranged between the compression device (7) and the first heat exchanger (13). 3- Management system (1) according to claim 1 or 2, in which the heat treatment circuit (8) comprises at least one expansion member (15) arranged downstream of the first heat exchanger (13). 4- Management system (1) according to the preceding claim, in which the expansion member (15) is arranged between the first heat exchanger (13) and the second heat exchanger (16). 5- Management system (1) according to any one of the preceding claims, in which the second branch (10) of the heat treatment circuit (8) comprises a control member (32). 6- Management system (1) according to any one of the preceding claims, wherein the gas consuming device (4, 5) is a high pressure gas consuming device (4), the supply circuit (6) being configured to supply the high pressure gas consuming device (4) and / or a low pressure gas consuming device (5). 7- Management system (1) according to the preceding claim, in which a supply of the low pressure gas consuming device (5) by the supply circuit (6) passes at least partially through the first branch (9). 8- Management system (1) according to any one of the preceding claims, in which the heat treatment circuit (8) comprises a separation device (21) of which an inlet (22) is arranged downstream of the second heat exchanger (16). 9- Management system (1) according to the preceding claim, in combination with claim 6, in which the separation device (21) comprises a first outlet (23) configured to allow an exit of the gas in the vapor state from the separation device (21), the heat treatment circuit (8) comprising a third Branch (25) connecting the first outlet (23) of the separation device (21) to the supply circuit (6) of the low-pressure gas-consuming device (5). 10- Management system (1) according to the preceding claim, in which the heat treatment circuit (8) comprises a fourth branch (26) connecting the first outlet (23) of the separation device (21) to the supply circuit (6) at a point located between the tank (2) and the first heat exchanger (13). 11- Management system (1) according to the preceding claim, in which the separation device (21) comprises a second outlet (24) configured to allow an outlet of the gas in the liquid state from the separation device (21), the heat treatment circuit (8) comprising a fifth branch (27) connecting the second outlet (24) of the separation device (21) to the cooling circuit (17). 12- Management system (1) according to the preceding claim, in which the heat treatment circuit (8) comprises a sixth branch (28) connecting an outlet of a pass of the second heat exchanger (16) constituting the heat treatment circuit (8) to the fifth branch (27). 13- Management system (1) according to any one of the preceding claims, comprising a third heat exchanger (19) configured to carry out a heat exchange between the gas in the liquid state circulating in the cooling circuit (17) and a refrigerant fluid circulating in a cooling loop (20). 14- Management system (1) according to any one of claims 1 to 12, comprising an additional branch (48) connecting the first compression stage (11) of the compression device (7) to the tank (2), the management system (1) further comprising a heat exchanger (49) configured to carry out a heat exchange between the gas in the vapor state circulating in the additional branch (48) and a refrigerant fluid circulating in a reliquefaction loop (50). 15- Management system (1) according to any one of the preceding claims, in which the cooling circuit (17) comprises at least one termination (29) opening into the tank (2), the termination (29) being a spraying member (31) and / or an orifice (30) arranged in a lower part of the tank (2). 16- Floating structure comprising at least one tank (2) and a management system (1) according to any one of the preceding claims, the tank (2) containing liquefied natural gas. 17- Floating structure comprising at least one tank (2) and a management system (1) according to any one of claims 1 to 15, the tank (2) containing ethane. 18- Method for managing a gas contained in at least one tank (2) of a floating structure, implemented by a management system (1) according to any one of claims 1 to 15, during which: the gas is circulated in the first branch (9) and / or in the second branch (10) of the heat treatment circuit (8) if the gas contained in the tank (2) is liquefied natural gas, or, the gas is circulated in the first branch (9) of the heat treatment circuit (8) if the gas contained in the tank (2) is ethane, the circulation of the gas being prevented in the second branch (10).

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