GAS SUPPLY SYSTEM FOR HIGH- AND LOW-PRESSURE GAS-CONSUMING APPARATUSES AND METHOD OF CONTROLLING SUCH A SYSTEM

Abstract

A system supplies gas to a high-pressure gas-consuming apparatus and a low-pressure gas-consuming apparatus of a floating structure including a tank. The supply system includes: a first supply circuit, a second supply circuit, a return line, a first heat exchanger and a second heat exchanger. The return line includes a flow-regulating member. The supply system includes a device for managing the supply system which includes a control module to control the flow-regulating member based on the characteristics of the gas.

Claims

1-13. (canceled)

14. A system for supplying gas to at least one high-pressure gas-consuming apparatus and at least one low-pressure gas-consuming apparatus of a floating structure comprising at least one tank configured to contain the gas, the supply system comprising: at least one first circuit supplying gas to the high-pressure gas-consuming apparatus, at least one high-pressure evaporator configured to evaporate the gas circulating in the first gas supply circuit, at least one second circuit supplying gas to the low-pressure gas-consuming apparatus, comprising at least one compressor configured to compress gas taken in a vapor state into the tank to a pressure compatible with the requirements of the low-pressure gas-consuming apparatus, at least one gas return line connected to the second supply circuit downstream of the compressor and extending to the tank, at least one first heat exchanger and one second heat exchanger, each configured to exchange heat between the gas circulating in the return line in the vapor state and the gas circulating in the first supply circuit in a liquid state, the first supply circuit comprising a pump interposed between the first heat exchanger and the second heat exchanger, the return line comprising a flow-regulating member arranged between the first heat exchanger and the tank, and a management device configured to manage said supply system, said management device comprising at least one first sensor and a first detector respectively configured to determine a temperature and pressure of the gas present in the first supply circuit between the first heat exchanger and the pump, a second sensor configured to determine a temperature of the gas present in the first supply circuit between the tank and the first heat exchanger, a third sensor configured to determine a temperature of the gas present in the return line between the first heat exchanger and the flow-regulating member, the management device comprising a control module configured to control the flow-regulating member according to the characteristics of the gas determined by the first sensor, the second sensor, the third sensor and the first detector.

15. The supply system according to claim 14, further comprising a fluid analyzer configured to determine a composition of the gas in the liquid state contained in the tank.

16. The supply system according to claim 14, wherein the management device comprises a second detector configured to determine a pressure of the gas present in the tank, the control module being configured to control the flow-regulating member according to the pressure of the gas determined by the second detector.

17. The supply system according to claim 14, wherein the return line comprises a flowmeter configured to determine the flow rate of gas in the vapor state circulating in the return line, the control module being configured to control the flow-regulating member according to the gas flow rate determined by the flowmeter.

18. The supply system according to claim 14, wherein the first supply circuit comprises at least one pumping member configured to pump the gas taken from the liquid state in the tank.

19. A method for controlling the supply system according to claim 14, comprising: comparing the temperature of the gas present in the first supply circuit between the first heat exchanger and the pump, and a maximum temperature threshold determined as a function of the pressure of the gas present in the first supply circuit between the first heat exchanger and the pump, a composition of the gas circulating in the supply system and a safety margin, reducing, when the temperature of the gas present in the first supply circuit between the first heat exchanger and the pump is greater than the maximum temperature threshold, a passage section of the flow-regulating member, implementing, when the temperature of the gas present in the first supply circuit between the first heat exchanger and the pump is lower than the maximum temperature threshold, a comparison between the temperature of the gas present in the return line between the first heat exchanger and the flow-regulating member and an optimal temperature threshold determined according to the temperature of the gas present in the first supply circuit between the tank and the first heat exchanger and a temperature difference, reducing, when the temperature of the gas present in the return line between the first heat exchanger and the flow-regulating member is greater than the optimal temperature threshold, the passage section of the flow-regulating member, increasing, when the temperature of the gas present in the return line between the first heat exchanger and the flow-regulating member is lower than the optimal temperature threshold, the passage section of the flow-regulating member.

20. The control method according to claim 19, wherein the control method is repeated over time.

21. The control method according to claim 19, wherein the supply system further comprises a fluid analyzer configured to determine a composition of the gas in the liquid state contained in the tank, and the composition of the gas is determined by the fluid analyzer.

22. The control method according to claim 19, wherein the composition of the gas is determined by technical documentation.

23. The control method according to claim 19, wherein the maximum temperature threshold is determined by virtue of a data table of several types of gas.

24. The control method according to claim 19, wherein the safety margin and the temperature difference correspond to a value between 1° C. and 3° C.

25. The control method according to claim 19, wherein the management device comprises a second detector configured to determine a pressure of the gas present in the tank, the control module being configured to control the flow-regulating member according to the pressure of the gas determined by the second detector, and the pressure of the gas determined by the second detector is compared to a pressure threshold.

26. The control method according to claim 25, further comprising interrupting the gas flow within the return line when the pressure of the gas determined by the second detector is lower than the pressure threshold.

Description

[0058] Other features and advantages of the invention will appear both from the description which follows and from several exemplary embodiments, which are given for illustrative purposes and without limitation with reference to the appended schematic drawings, in which:

[0059] FIG. 1 is a schematic representation of a supply system according to the invention,

[0060] FIG. 2 is a flowchart of a control method according to the invention, of the supply system,

[0061] FIG. 3 is a flowchart of a part of the control method monitoring an amount of gas in the vapor state,

[0062] FIG. 4 is an example of a data table of several types of gas, usable for the implementation of the control method,

[0063] FIG. 5 is a cut-away schematic illustration of a tank of a floating structure and of a terminal for loading and/or unloading this tank.

[0064] The terms “upstream” and “downstream” employed in the following description are used to express positions of elements within gas circuits in the liquid state or in the vapor state and refer to the direction of circulation of said gas within said circuit.

[0065] FIG. 1 shows a gas supply system 1 arranged on a floating structure. The supply system 1 makes it possible to circulate gas that can be in the liquid state, in the vapor state, in the two-phase state or in the supercritical state, from a storage and/or transport tank 8, to a high-pressure gas-consuming apparatus 4 and to a low-pressure gas-consuming apparatus 5, in order to supply the latter with fuel.

[0066] Said floating structure may for example be a ship that can store and/or transport gas in the liquid state, in particular natural gas. In this case, the supply system 1 is capable of using the gas in the liquid state that the floating structure stores and/or transports to supply the high-pressure gas-consuming apparatus 4, which may for example be a propulsion engine, and the low-pressure gas-consuming apparatus 5, which may for example be an electric generator supplying the floating structure with electricity.

[0067] In order to ensure the circulation of the gas contained in the tank 8 to the high-pressure gas-consuming apparatus 4, the supply system 1 is provided with a first gas supply circuit 2. The first supply circuit 2 comprises a pumping member 9, advantageously a submerged pump 9 arranged within the tank 8. The submerged pump 9 makes it possible to pump the gas in the liquid state and to circulate it in particular within the first supply circuit 2. By drawing the gas in the liquid state, the pumping member 9 raises the pressure thereof to a value of between 6 and 17 bar absolute.

[0068] The gas in the liquid state, in a direction of circulation from the tank 8 to the high-pressure gas-consuming apparatus 4, passes through a first heat exchanger 6 and is pressurized by a pump 10. Subsequently, the gas in the liquid state passes through a single heat exchanger 21, combining a second heat exchanger 7 and a high-pressure evaporator 11. However, it is possible for the second heat exchanger 7 and the high-pressure evaporator 11 to be distinct from one another. The details concerning heat exchangers will be described below.

[0069] The single heat exchanger 21, via the high-pressure evaporator 11, makes it possible to modify the state of the gas circulating in the first supply circuit 2 in order to change it to the vapor or supercritical state. Such a state allows the gas to be compatible to supply the high-pressure gas-consuming apparatus 4. The evaporation of the gas in the liquid state can for example be carried out by heat exchange with a heat transfer fluid at a temperature high enough to evaporate the gas in the liquid state, in this case glycol water, seawater or water vapor.

[0070] The increase in gas pressure is ensured by the pump 10 when the latter pumps the gas in the liquid state. The pump 10 makes it possible to raise the pressure of the gas in the liquid state to a value of between 30 and 400 bar absolute, in particular for use with ammonia or hydrogen, between 30 and 70 bar absolute for use with liquefied petroleum gas, and preferably between 150 and 400 bar absolute for use with ethane, ethylene or else liquefied natural gas consisting mainly of methane.

[0071] By virtue of the combination of the pump 10 and the single heat exchanger 21, the gas is at a pressure and in a compatible state for the supply of the high-pressure consuming apparatus 4. Such a configuration makes it possible to avoid the installation of high-pressure compressors on the first supply circuit 2 which have cost constraints and generate strong vibrations.

[0072] Within the tank 8, a part of the gas cargo can naturally change to the vapor state and diffuse into a space of the tank 12. In order to avoid overpressure within the tank 8, the gas in the vapor state contained in the tank space 12 must be discharged.

[0073] The supply system 1 therefore comprises a second gas supply circuit 3, which uses the gas in the vapor state to supply the low-pressure gas-consuming apparatus 5. The second supply circuit 3 extends between the tank space 12 and the low-pressure gas-consuming apparatus 5. In order to suck the gas in the vapor state contained in the tank space 12, the second supply circuit 3 comprises a compressor 13. In addition to sucking the gas in the vapor state, the compressor 13 also makes it possible to compress the gas in the vapor state circulating in the second supply circuit 3 to a pressure of between 6 and 20 bar absolute, so that the gas in the vapor state is at a compatible pressure for the supply of the low-pressure gas-consuming apparatus 5. The second supply circuit 3 thus makes it possible to supply the low-pressure gas-consuming apparatus 5, while regulating the pressure within the tank 8 by sucking the gas in the vapor state present in the tank space 12.

[0074] The presence of the gas in the vapor state in excess quantity within the tank space 12 causes an overpressure within the tank 8. It is therefore necessary to evacuate the gas in the vapor state in order to lower the pressure within the tank 8. The excess gas in the vapor state can then for example be eliminated by a burner 18 or, in a manner not shown, discharged into the atmosphere and thus generate a loss of cargo. However, the supply system 1 according to the invention comprises a return line 14 which extends from the second supply circuit 3 to the tank 8.

[0075] The return line 14 is connected to the second supply circuit 3 downstream of the compressor 13 relative to a direction of circulation of the gas in the vapor state circulating in the second supply circuit 3. The return line 14 passes through the single heat exchanger 21 in a first step. As such, the single heat exchanger 21 therefore comprises a first pass 24 within which the gas in the liquid state circulates from the first supply circuit 2, a second pass 28 within which the gas in the vapor state circulates from the return line 14 and a third pass 29 within which the heat transfer fluid circulates evaporating the gas in the liquid state circulating in the first pass 24.

[0076] At the outlet of the second pass 28 of the single heat exchanger 21, the gas in the vapor state circulates until it passes through the first heat exchanger 6. The inlet of the first heat exchanger 6 is where the gas in the liquid state of the first supply circuit 2 has the lowest temperature. Consequently, it is therefore after having passed through the first heat exchanger 6 that the gas circulating in the return line 14 is condensed. The gas from the return line 14 is therefore in the vapor state at the inlet of the first heat exchanger 6 and exits in the liquid state following the exchange of calories taking place within the first heat exchanger 6.

[0077] The return line 14 also comprises a flow-regulating member 15 which controls the flow rate of the fluid circulating in the return line 14. This flow-regulating member 15 has a passage section that can be modified. Once the gas is condensed, it circulates to the tank 8. The first heat exchanger 6 therefore acts as a condenser, while the flow-regulating member 15 controls the heat exchange that takes place in the first heat exchanger 6 and in the single heat exchanger 21.

[0078] The supply system 1 further comprises an auxiliary supply line 16, extending from the first supply circuit 2, via a tap arranged between the pumping member 9 and the first heat exchanger 6, to the second supply circuit 3, connecting thereto between the compressor 13 and the low-pressure gas-consuming apparatus 5. The auxiliary supply line 16 makes it possible to power the low-pressure gas-consuming apparatus 5 in the event of insufficient flow of gas in the vapor state formed within the tank space 12.

[0079] When the gas in the vapor state is not present in sufficient quantity in the tank space 12, the liquid gas pumped by the submerged pump 9 can then circulate within this auxiliary supply line 16 in order to supply the low-pressure gas-consuming apparatus 5. To do this, the auxiliary supply line 16 passes through a low-pressure evaporator 17 so that the gas in the liquid state circulating in the auxiliary supply line 16 passes to the vapor state. The operation of the low pressure evaporator 17 can for example be identical to that of the high-pressure evaporator 11, that is, the gas is evaporated by heat exchange with a heat transfer fluid at a temperature high enough to boil off the gas in the liquid state. At the outlet of the low pressure evaporator 17, the gas in the vapor state circulates within the auxiliary supply line 16, then joins the second supply circuit 3 in order to supply the low-pressure gas-consuming apparatus 5.

[0080] It is understood from the foregoing that the auxiliary supply line 16 is used only when there is not enough gas in the vapor state within the tank space 12. Thus, the auxiliary supply line 16 comprises a valve 19 controlling the flow of gas within the auxiliary supply line 16 when the use thereof is not necessary.

[0081] The pump 10 is advantageously arranged between the first heat exchanger 6 and the single heat exchanger 21. The pump 10 is only capable of pumping gas in the liquid state. In order not to harm its correct operation, it is important that the gas circulating in the first supply circuit 2 is kept in the liquid state in the outlet of the first heat exchanger 6.

[0082] Furthermore, one of the objectives of the supply system 1 according to the invention is to re-condense a maximum gas in the vapor state formed in the tank space 12 and not consumed by the low-pressure gas-consuming apparatus 5, but without causing the boil-off of the gas circulating in the first supply circuit 2 when the first heat exchanger 6 is passed through.

[0083] To do this, the supply system 1 comprises a management device 80 ensuring the control of the different parameters mentioned above. The management device 80 notably comprises a first sensor 81, a second sensor 82, a third sensor 83, a first detector 84 and a second detector 85. It will subsequently be considered that the sensors 81, 82, 83 determine a temperature of the gas, while the detectors 84, 85 determine a pressure of the gas. The management device 80 also comprises a control module 86 receiving the different data determined by the sensors 81, 82, 83 as well as by the detectors 84, 85. In response to these said data, the control module 86 can act on the flow-regulating member 15 in order to vary the flow rate of gas circulating in the return line 14.

[0084] The first sensor 81 is positioned at the first supply circuit 2 between the first heat exchanger 6 and the pump 10. The second sensor 82 is positioned at the first supply circuit 2 between the tank 8 and the first heat exchanger 6. The third sensor 83 is positioned at the return line 14 between the first heat exchanger 6 and the flow-regulating member 15. Each of the sensors 81, 82, 83 is configured to determine the temperature of the gas circulating at each respective position of said sensors 81, 82, 83. The temperature of the gas circulating in these different sections of the supply system 1 is used to control the flow-regulating member 15. The same applies for the pressures determined by the first detector 84, positioned at the first supply circuit 2 between the first heat exchanger 6 and the pump 10, and for the second detector 85, positioned at the second supply circuit 3 between the tank 8 and the compressor 13.

[0085] The management device 80 can also comprise a fluid analyzer 87 able to determine the composition of the gas in the liquid state contained in the tank 8. The fluid analyzer 87 can determine the composition of the gas directly in the liquid state or may require the gas to be vaporized in order to determine the composition thereof. Knowledge of the gas composition is advantageous for determining an boil-off temperature of the gas as will be described in detail below. Like the temperature and pressure values, the composition of the gas determined by the fluid analyzer 87 is also transmitted to the control module 86. The composition of the gas may however also be given via technical documentation relating to the gas cargo or correspond to a type of gas, the characteristics of which are mentioned within a data table, as will be shown below.

[0086] The return line 14 may also comprise a flowmeter 88. The flowmeter is configured to determine the gas flow rate circulating in the return line 14. Advantageously, the gas flow rate is determined between the connection with the second supply circuit 3 and the single heat exchanger 21. The flowmeter 88 is also connected to the control module 86 which can act on the flow-regulating member 15. As such, an operator can act on the flowmeter 88 so that the control member 86 receives the information from the flow meter 88 and acts on the flow-regulating member 15 in response to this information from the flow meter 88.

[0087] FIG. 2 is a flowchart making it possible to describe the various steps of a control method 100 according to the invention, for example when it is implemented by the management device described above.

[0088] The control method 100 begins with a comparison step 101 between the temperature of the gas by the first sensor 81 and a maximum temperature threshold Tmax. The temperature of the gas determined by the first sensor 81 corresponds to the temperature of the gas circulating in the first supply circuit at the outlet of the first heat exchanger. It may in particular be a measurement in-situ, by positioning the first sensor 81 at any location located between an outlet of the pass of the first heat exchanger forming part of the first supply circuit and an inlet of the pump, as shown in FIG. 1. It may also be an estimate or a calculation made from other data of the system.

[0089] Before, simultaneously or successively, determining the temperature of the gas by the first sensor 81, the maximum temperature threshold Tmax is defined from the pressure of the gas determined by the first detector, the composition of the gas, and a safety margin. The pressure of the gas used during the determination of the maximum temperature threshold Tmax corresponds to the pressure of the gas circulating in the first supply circuit, at the outlet of the first heat exchanger.

[0090] As for the first sensor 81, the first detector can measure the pressure in-situ or result from an estimate or a calculation made from other data of the system.

[0091] It is possible to find the boil-off temperature of the gas if its pressure and composition are known. The pressure is determined by the first detector 84, while the composition of the gas can be obtained by virtue of the fluid analyzer 87 shown in FIG. 1. If the supply system does not include a fluid analyzer, the gas composition may be given by the technical documentation of the cargo, in particular communicated at the time of loading the cargo. If neither one nor the other are available, the maximum temperature threshold Tmax can be determined using a data table, shown in FIG. 4, grouping together the different types of gas and having the different boil-off temperatures depending on the pressure of each of the gases. Since the pressure determined by the first detector 84 is known, the data table is therefore read from this pressure by choosing the lowest boil-off temperature in order to ensure that, regardless of the type of gas contained in the tank, that gas has at least this selected temperature as the boil-off temperature.

[0092] The maximum temperature threshold Tmax is finally obtained by subtracting the safety margin from the boil-off temperature of the gas obtained previously. The safety margin depends on the net positive suction height of the pump and a safety threshold. The net positive suction height is specific to the pump used within the first supply circuit and corresponds to a limit at which point the pump risks boiling off the gas in the liquid state by pumping it. The security threshold can be selected by the operator. The safety margin may for example be between 1° C. and 3° C. in order to obtain a maximum temperature threshold Tmax slightly lower than the actual boil-off temperature of the gas.

[0093] Once the maximum temperature threshold has been obtained, the comparison between the latter and the temperature of the gas determined by the first sensor 81 can be implemented.

[0094] If the temperature of the gas determined by the first sensor 81 is greater than the maximum temperature threshold, this means that the gas circulating in the first supply circuit leaves the first heat exchanger at an excessively high temperature, thus risking boiling off at least partially and damaging the pump as a result.

[0095] Too high a gas temperature between the first heat exchanger and the pump means that the heat exchange occurring within the first heat exchanger is too great. In order to reduce this heat exchange, the flow rate of gas circulating in the return line must therefore be reduced.

[0096] Thus, when the temperature of the gas determined by the first sensor 81 is greater than the maximum temperature threshold, the control method 100 continues with a step of reducing 103 the passage section. During this reduction step 103, the control module described in FIG. 1 acts on the flow-regulating member 15, and decreases its passage section in order to reduce the flow rate of gas circulating in the return line, thus limiting the heat exchange within the first heat exchanger and therefore the rise in temperature of the gas circulating in the first supply circuit. This thus prevents the boil-off of the gas upstream of the pump.

[0097] Once the reduction step 103 has been completed, the control method 100 can be repeated from the comparison step 101, for example in order to verify that the temperature of the gas circulating between the first heat exchanger and the pump has indeed decreased.

[0098] If the temperature of the gas determined by the first sensor 81 is below the maximum temperature threshold Tmax, the control method 100 continues with a comparative step 102.

[0099] The comparative step 102 is done between the temperature of the gas by the third sensor 83, that is, the gas circulating in the return line, after having passed through the first heat exchanger, and an optimal temperature threshold Topt, corresponding to the temperature of the gas determined by the second sensor, that is, the gas circulating in the first supply circuit, upstream of the first heat exchanger, to which a temperature difference is added. That difference, just like for the safety margin, may be between +1° C. and +3° C. This temperature difference is the minimum difference between the temperature of the gas in the liquid state corning from the tank and which enters the first heat exchanger 6, for example measured by the second sensor 82, and the temperature of the gas circulating in the return line 14 measured at the outlet of the first heat exchanger 6, for example measured by the third sensor 83. This temperature difference may correspond to the pinching of the first heat exchanger 6.

[0100] The second sensor and the third sensor 83 can measure the temperature in-situ, that is, at the positions described above, or result from an estimate or a calculation made from other data of the system.

[0101] The comparative step 102 makes it possible to optimize the condensation of the gas circulating in the return line. The objective is to make the value of the temperature of the gas circulating in the return line at the outlet of the first heat exchanger converge to the optimal temperature threshold Topt in order to perform optimum condensation and in maximum quantity. If the gas circulating in the return line leaves the first heat exchanger has too high a temperature, this means that the gas circulates in too great a quantity in order to be condensed effectively. Conversely, if the gas circulating in the return line leaves the first heat exchanger has too low a temperature, this means that the gas flow rate can be increased in order to condense a greater quantity of gas in a given time.

[0102] The temperature of the gas determined by the third sensor 83 is then compared with the optimum temperature threshold Topt. Whether the temperature of the gas determined by the third sensor 83 is greater than or lower than the optimal temperature threshold Topt, the control method 100 continues with a step in which the control module adjusts the passage section of the flow-regulating member. More specifically, the control method 100 continues with the step 103 of reducing the passage section of the flow-regulating member if the temperature of the gas determined by the third sensor 83 is greater than the optimal temperature threshold Topt. This reduction step 103 is similar to that which can result from the comparison step 101. Conversely, the control method 100 continues with the step 104 of reducing the passage section of the flow-regulating member if the temperature of the gas determined by the third sensor 83 is greater than the optimal temperature threshold Topt.

[0103] It should be noted that in FIG. 2, the comparison step 101 and the comparative step 102 are carried out one after the other, the comparison step 101 being carried out first. The control method 100 may however be configured so as to implement the comparison step 101 and the comparative step 102 simultaneously, the comparison step 101 nevertheless taking priority over the comparative step 102.

[0104] Once the reduction step 103 or the increase step 104 is performed according to the comparison step 101 or the comparative step 102, the control method 100 can be reiterated from the comparison step 101 if the steps are successive, or from the two simultaneous steps such as has been described previously. The priority is to ensure that the liquid gas circulating in the first supply circuit does not exit at least partially evaporated. The comparison step 101 therefore has priority on the condensation optimization operation of the gas in the vapor state circulating in the return line, corresponding to the comparative step 102.

[0105] FIG. 3 is a flowchart of a part of the control method monitoring an internal pressure of the tank space. This part of the control method takes place in parallel with what has been described in FIG. 2, and consists in particular of a monitoring step 105 where the determined pressure of the tank space is compared with a pressure threshold Pref. The pressure threshold Pref may for example correspond to a value of −30 mbars or −60 mbars relative to the external pressure. It is the second detector 85 which determines, for example, the pressure of the gas circulating in the second supply circuit between the tank and the compressor, and generally the internal pressure of the tank space.

[0106] This pressure determined by the second detector 85 is then compared with the pressure threshold Pref. Said threshold is fixed and corresponds to a pressure value below which there is a risk of damaging the walls of the tank.

[0107] Thus, if the pressure determined by the second detector 85 is lower than or equal to the pressure threshold Pref, this means that there is a risk of damaging the walls of the tank if the pressure of the tank space decreases further. A step of interruption 110 is implemented, where the control module entirely closes the flow-regulating member. In such a situation, the supply system can be deployed while waiting for the pressure in the tank space to increase. Alternatively, the low-pressure gas-consuming apparatus can be powered by means of the auxiliary supply line 16 shown in FIG. 1.

[0108] If the pressure determined by the second detector 85 is greater than the pressure threshold, the control method can proceed while continuing to monitor the value of the pressure determined by the second detector 85.

[0109] FIG. 4 shows the data table 106 mentioned above making it possible to determine the maximum temperature threshold Tmax mentioned in FIG. 2. This data table 106 represents the boil-off temperature as a function of the pressure determined by the first detector for five different types of gas A, B, C, D and E.

[0110] Thus, if the composition of the gas contained in the tank cannot be known, the data table 106 is used to determine a theoretical boil-off temperature as a function of the pressure determined by the first detector. In order to ensure that the gas contained in the tank is maintained in the liquid state within the first supply circuit at the outlet of the first heat exchanger, rather than the composition of said gas, the chosen boil-off temperature is as low as possible. In FIG. 4, it is therefore the first type of gas A that is chosen. Once the safety margin is applied, the maximum temperature threshold is then determined.

[0111] FIG. 5 is a cutaway view of a floating structure 20 which shows the tank 8 which contains the gas in the liquid state and in the vapor state, this tank 8 having a generally prismatic shape mounted in a double hull 22 of the floating structure 20. The wall of the tank 8 comprises a primary sealing membrane intended to be in contact with the gas in the liquid state contained in the tank 8, a secondary sealing membrane arranged between the primary sealing membrane and the double hull 22 of the floating structure 20, and two thermally insulating barriers respectively arranged between the primary sealing membrane and the secondary sealing membrane and between the secondary sealing membrane and the double hull 22.

[0112] Pipes 23 for loading and/or unloading gas in the liquid state, arranged on the upper deck of the floating structure 20, can be connected, by means of suitable connectors, to a marine or port terminal to transfer the cargo of gas in the liquid state from or to the tank 8.

[0113] FIG. 5 also shows an example of a maritime terminal comprising a port or shipping terminal loading and/or unloading station 25, an underwater duct 26 and an onshore and/or port facility 27. The onshore and/or port facility 27 can for example be arranged on the dock of a port, or according to another example be arranged on a concrete gravity platform. The onshore and/or port facility 27 comprises storage tanks 30 for gas in the liquid state, and connecting pipes 31 that are connected by the underwater pipe 26 to the loading and unloading equipment 25.

[0114] To generate the pressure necessary for the transfer of the gas in the liquid state, pumps equipping the onshore and/or port facility 27 and/or pumps equipping the floating structure 20 are implemented.

[0115] Of course, the invention is not limited to the examples that have just been described, and numerous modifications can be made to these examples without departing from the scope of the invention.

[0116] The invention, as has just been described, clearly achieves its intended goal, and makes it possible to propose a gas supply system comprising a management device ensuring the control of the temperature and the condensation of said gas. Variants not described here could be implemented without departing from the context of the invention, since, in accordance with the invention, they comprise a supply system according to the invention.