METHOD FOR MANAGING A FLUID IN LIQUID FORM CONTAINED IN A TANK

Abstract

Title of the invention: Method for managing a fluid in liquid form contained in a tank The invention relates to a method 64 for managing a gaseous phase of a fluid in liquid form contained in a tank of a floating structure intended to transport the fluid in liquid form, the floating structure comprising a system for supplying fuel to at least one consumer equipping the floating structure, the method 64 implementing at least three different operating modes 94, 98 or 100 to condense the gaseous phase not consumed by the consumer. Figure 3

Description

Title of the invention: Method for managing a fluid in liquid form contained in a tank

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

[0002] In order to more easily transport and / or store fluid in liquid form, such as natural gas in liquid form, the gas is generally liquefied by cooling it to cryogenic temperatures, for example -163°C at atmospheric pressure, in order to obtain liquefied natural gas, more commonly known by the acronym "LNG" or "LNG" which means "Liquefied Natural Gas". This liquefied natural gas is then loaded into specialized storage tanks of the floating structure.

[0003] Such tanks are nevertheless never perfectly thermally insulated so that natural evaporation of the gas is inevitable, this phenomenon being called BOG, acronym for "Boil-Off Gas". The storage tanks of the floating structure thus comprise both natural gas in liquid form and natural gas in gaseous form, the gaseous phase of the natural gas accumulating in a headspace of the tank.

[0004] In a known manner, at least a portion of the natural gas present in the tank in gaseous form can be used to supply at least one consumer intended to meet the operating energy needs of the floating structure, in particular for its propulsion and / or its production of electricity for the equipment on board. For this purpose, it is in particular known to circulate the gaseous phase through at least one natural gas treatment system, so as to allow its heating and compression, said system comprising a heat exchanger used as a superheater and a compressor, both placed upstream of the consumer.

[0005] The natural gas treatment system also has a function of condensing a portion of the gaseous phase, after its compression. The condensation of natural gas may in particular be required when the pressure in the tank is unacceptable, the natural gas treatment system then making it possible to condense this gaseous phase in order to return it to the tank in the liquid state. This condensation function is currently implemented by technical means which consume a significant amount of energy, for example electricity.

[0006] In the field of the invention, it is also essential to take into account the state of the liquid natural gas when the floating structure arrives at the delivery location to unload the cargo. Indeed, ports for unloading liquid natural gas have requirements regarding the characteristics of the delivered liquid natural gas, such as the temperature or saturation pressure of the liquid natural gas. The cargo may then be refused at the delivery location if it does not meet the characteristics imposed by the delivery location.

[0007] The general problem is therefore to succeed in maintaining the temperature and saturation pressure of the fluid in liquid form contained in the tank at a level lower than or equal to the maximum temperature authorized on arrival at the delivery location, while limiting the energy consumption resulting from the thermal treatment of the evaporated gas.

[0008] The present invention therefore proposes to optimize the use of a reliquefaction system so as to reduce the overall consumption of the floating structure by proposing different operating modes adapted to different uses of the reliquefaction system.

[0009] The invention consists of a method for managing a gaseous phase of a fluid contained in liquid form in a tank of a floating structure, the floating structure comprising a system for supplying fuel to at least one consumer equipping the floating structure, the supply system comprising at least one compression device intended to take the gaseous phase to deliver it to the consumer, the compression device comprising at least a first outlet, a second outlet and a third outlet configured to deliver the gaseous phase at three different pressure levels, the supply system comprising a return circuit intended to return to the tank a portion of the gaseous phase compressed by the compression device, the return circuit being alternately connected to the first outlet or to the second outlet of the compression device and comprising at least a first portion,as well as a second portion provided with an expansion means, the supply system comprising at least one heat exchanger configured to carry out a heat exchange between the vapor phase taken by the compression device and the gaseous phase which flows through the return circuit, the supply system comprising at least one cooling circuit configured to take the fluid in the liquid state from the tank, the return circuit comprising at least one heat exchanger configured to carry out a heat exchange between the gaseous phase of the fluid circulating in the return circuit and the fluid in the liquid state circulating in the cooling circuit, the supply system comprising a cooling loop participating in the condensation of the gaseous phase coming from the compression device, the method for managing the gaseous phase, comprising a plurality of operating modes, among which there are at least: - a first operating mode where the return circuit is connected to the first outlet of the compression device, the heat exchanger carrying out a heat exchange between the fluid in liquid form circulating in the cooling circuit and the gaseous phase circulating in the return circuit; - a second mode of operation where the return circuit is connected to the second outlet of the compression device, the heat exchanger carrying out a heat exchange between the gaseous phase expanded by the expansion means and the fluid in liquid form circulating in the cooling circuit, the cooling loop not participating in the condensation of the gaseous phase coming from the compression device; - a third mode of operation where the return circuit is connected to the second outlet of the compression device, the heat exchanger carrying out a heat exchange between the gas phase expanded by the expansion means and the fluid in liquid form circulating in the cooling circuit, the cooling loop participating in the condensation of the gas phase coming from the compression device.

[0010] The floating structure may for example be a transport vessel capable of storing and / or transporting fluid in liquid form, for example natural gas in liquid form. The supply system of a consumer of the floating structure ensures the management of the gaseous phase forming in the tank ceiling by using it for supplying as fuel the consumer(s) such as a propulsion engine of the floating structure, or an electric generator.

[0011] The supply system comprises a compression device whose role is to raise the pressure of this gaseous phase to a pressure level compatible with the operation of the consumer(s). The compression device is for example a multi-stage compressor or a series of compressors arranged one after the other. This compression device comprises at least three outlets, including a first outlet arranged between a first compression stage and a second compression stage of the compression device, a second outlet arranged between the second compression stage and a third compression stage of the compression device, and a third outlet forming the outlet of the third compression stage.

[0012] The compression device is configured so that the pressure of the gas phase at the first outlet is lower than the pressure of the gas phase taken at the second outlet, the latter being lower than the pressure of the gas phase taken at the third outlet.

[0013] The power supply system also includes a return circuit whose role is to return to the tank a portion of the gaseous phase compressed by the compression device, after having condensed it. This return circuit can be connected to the first outlet of the compression device or to the second outlet of this compression device. The return circuit comprises at least two portions of circulation of the gaseous phase which are parallel to each other. A first portion is without an expansion member and it is traversed by the gaseous phase when the return circuit is connected to the first outlet of the compression device. A second portion is provided with an expansion means, for example a Thomson Joule valve, the role of which is to lower the pressure of the gaseous phase. This second portion is traversed by the gaseous phase when the return circuit is connected to the second outlet of the compression device.In other words, the use of the first portion is carried out in combination with the use of the first output of the compression device, while the use of the second portion and its expansion means is carried out in combination with the use of the second output of the compression device.

[0014] The supply system comprises a cooling circuit provided with at least one pump configured to draw the fluid in the liquid state from the tank. This cooling circuit is used to exploit the frigories present in the fluid in the liquid state and deliver them to the gaseous phase which circulates in the return circuit, so as to condense this gaseous phase.

[0015] The return circuit also comprises at least one heat exchanger whose role is to condense the gaseous phase of the fluid circulating in the return circuit by heat exchange between this gaseous phase and the fluid in the liquid state circulating in the cooling circuit.

[0016] The supply system also comprises a cooling loop which ensures all or part of the condensation of the gaseous phase of the fluid which comes from the compression device. This cooling loop can take at least two forms: a first form where it is integrated into the cooling circuit. In such a case, the cooling loop lowers the temperature of the fluid in the liquid state which circulates in the cooling circuit and it is in this that this cooling loop participates indirectly in the condensation of the gaseous phase which leaves the first outlet or the second outlet of the compression device. According to a second form of the cooling loop, it is installed on a return line connected at the inlet to the first outlet of the compression device and which opens into the tank. This cooling loop directly liquefies the gaseous phase which comes from the compression device.

[0017] The first mode of operation implements an extraction of the gas phase through the first outlet of the compression device. According to one option, this gas phase is cooled within the heat exchanger which implements a heat exchange between the compressed gas phase and the gas phase from the tank head before its compression.

[0018] According to this first mode of operation, the gaseous phase passes through the first portion, then passes through the heat exchanger where this gaseous phase is condensed by heat exchange with the fluid in the liquid state which comes from the tank via the cooling circuit. The gaseous phase circulating in the heat exchanger is then condensed and returned to the bottom of the tank. In such a situation, the cooling loop, whatever its form, is inactive, which makes it possible to reduce the overall consumption of the system.

[0019] The second mode of operation implements an extraction of the gaseous phase through the second outlet of the compression device. The first valve being closed, the gaseous phase circulates in the return circuit. According to one option, this gaseous phase is cooled within the heat exchanger which implements a heat exchange between the compressed gaseous phase and the gaseous phase coming from the tank headspace before its compression.

[0020] According to this second mode of operation, the first valve is closed and the gaseous phase passes through the second portion where it is expanded by passing through the expansion means that this second portion comprises. Once expanded, this gaseous phase passes through the heat exchanger where this gaseous phase is condensed by heat exchange with the fluid in the liquid state which comes from the tank via the cooling circuit.

[0021] The second portion of the return circuit comprises the expansion means for reducing the pressure of the gaseous phase circulating in the second portion of the return circuit. Within the heat exchanger, the expanded gaseous phase carries out a heat exchange with the cooling circuit and therefore with the fluid in liquid form coming from the tank. In this mode of operation, the cooling loop, whatever its form, is inactive, which makes it possible to reduce the overall consumption of the system. The gaseous phase circulating in this heat exchanger is then reliquefied and returned to the bottom of the tank.

[0022] The third mode of operation implements an extraction of the gaseous phase through the second outlet of the compression device. The first valve being closed, the gaseous phase circulates in the return circuit. According to one option, this gaseous phase is cooled within the heat exchanger which implements a heat exchange between the compressed gaseous phase and the gaseous phase coming from the tank headspace before its compression.

[0023] According to this third mode of operation, the first valve is closed and the gas phase passes through the second portion where it is expanded by passing through the means of expansion that this second portion includes. Once expanded, this gaseous phase passes through the heat exchanger where this gaseous phase is condensed by heat exchange with the fluid in the liquid state which comes from the tank via the cooling circuit.

[0024] Within the heat exchanger, the gaseous phase which has passed through the second portion of the return circuit carries out a heat exchange with the cooling circuit. According to this third mode of operation, the cooling loop is active in the sense that it participates in the liquefaction of the gaseous phase which comes from the compression device. According to one example, the cooling loop subcools the fluid in the liquid state which comes from the tank and which circulates within the cooling circuit. According to another example, the cooling loop is part of a liquefaction line which takes the gaseous phase at the first outlet of the compression device, liquefies it via the cooling loop, then injects it at the bottom of the tank.

[0025] According to one aspect, the management method comprises a step of pre-cooling the vapor phase and which is implemented by means of the heat exchanger.

[0026] According to another characteristic of the invention, the operating modes are implemented as a function of parameters among which there is at least a quantity of evaporated gas present in the tank, a maximum temperature authorized on arrival at a delivery location and / or a temperature of the fluid in liquid form contained in the tank.

[0027] Some of these parameters are relative to the gas contained in the tank while others depend on constraints external to the tank.

[0028] According to another characteristic of the invention, the quantity of evaporated gas present in the tank is determined by variation of a pressure in the top of the tank over a given time.

[0029] According to one example, the pressure in the tank is measured via a pressure sensor and at known intervals.

[0030] According to another characteristic of the invention, the quantity of evaporated gas present in the tank is determined by the consumption of the consumer between the loading location and the delivery location and by an estimation of the generation of the gaseous phase of the tank as a function of the design characteristics of the tank. In other words, the heat inputs into the tank generate the gaseous phase. Depending on the characteristics of the tank, it is possible to determine the quantity of evaporated gas generated as a function of the temperature outside the tank and / or as a function of the temperature of the water in which the floating structure is sailing. At the same time, the consumption of the gaseous phase by the consumer(s) is known. The combination of these two data makes it possible to determine the quantity of evaporated gas present in the sky of the tank.

[0031] According to another characteristic of the invention, the first mode of operation is implemented when the temperature of the fluid in liquid form contained in the tank is less than or equal to the maximum temperature authorized on arrival at the delivery location and the quantity of evaporated gas to be reliquefied is greater than an initial threshold, for example equal to 0 kg / h.

[0032] The first mode of operation is the preferred mode of operation, this mode of operation makes it possible to reliquefy the gaseous phase of the tank top using fewer resources than the other modes of operation. The invention makes it possible to use the cold stored by the cargo to condense the gaseous phase which circulates in the return circuit coming from the first outlet of the compression device via the first portion.

[0033] According to another characteristic of the invention, the second mode of operation is implemented by means of expansion the temperature of the fluid in liquid form contained in the tank is higher than the maximum temperature authorized on arrival at the delivery location and the quantity of evaporated gas to be reliquefied is lower than a first threshold, said first threshold being higher than the initial threshold, for example being between 500 kg / h and 2000 kg / h, advantageously between 500 kg / h and 1250 kg / h or even more advantageously equal to 750 kg / h.

[0034] The second mode of operation allows the condensation of a limited quantity of gaseous phase, without however adding heat to the fluid in liquid form contained in the tank.

[0035] According to another characteristic of the invention, the third mode of operation is implemented when the temperature of the fluid in liquid form contained in the tank is higher than the maximum temperature authorized on arrival at the delivery location and the quantity of evaporated gas to be reliquefied is higher than the first threshold.

[0036] The third mode of operation is implemented when a significant amount of gas phase needs to be condensed. To do this, the cooling loop is activated.

[0037] According to another characteristic of the invention, a fourth mode of operation where the tank head is sucked by the compression device until the pressure in the tank head is lower than a saturation pressure of the fluid in liquid form present in the tank, this fourth mode of operation being implemented when the temperature of the fluid in liquid form contained in the tank is higher than the maximum temperature authorized on arrival at the delivery location by a value between 0°C and 1°C and the quantity of evaporated gas is lower than the quantity of gas consumed by the consumer.

[0038] The fourth mode of operation is activated when the consumer consumes more than the quantity of evaporated gas present in the tank ceiling. In such a fourth mode, the pressure within the tank is lowered by the compression device, which promotes vaporization of the fluid in the liquid state, thus creating the gaseous phase necessary for the consumption of the consumer of the floating structure.

[0039] According to another characteristic of the invention, the method comprises a fifth mode of operation during which the cooling loop is activated, this fifth mode of operation being implemented when the temperature of the fluid in liquid form contained in the tank is higher than the maximum temperature authorized on arrival at the delivery location by a value between 0°C and 1.5°C.

[0040] When the temperature of the fluid in liquid form contained in the tank is higher than the maximum temperature authorized on arrival at the delivery location, the fifth mode of operation is implemented to reduce the temperature of the fluid in liquid form contained in the tank, so that the latter is below the acceptance temperature of the cargo delivery location.

[0041] According to an optional feature of the invention, the fifth mode of operation is implemented simultaneously with any of the first mode of operation, the second mode of operation or the fourth mode of operation. It is understood here that the cooling loop contributes with these modes to bringing the temperature of the cargo below the maximum temperature authorized on arrival at the delivery location.

[0042] The floating structure may, in certain situations, operate at a speed called crossover speed which corresponds to the speed where the entire gas phase is consumed by the consumer(s), without requiring the generation of additional gas phase. When the floating structure operates at crossover speed, none of the operating modes are implemented.

[0043] The invention also relates to a system for supplying fuel to at least one consumer equipping a floating structure, configured to implement the management method as described in the present document.

[0044] The invention also relates to a floating structure for transporting and / or storing fluid in liquid form comprising a supply system according to the preceding claim.

[0045] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and examples of embodiment given for informational and non-limiting purposes with reference to the appended drawings on the other hand, in which:

[0046] [Fig-1] is a first embodiment of a system for supplying a floating structure;

[0047] [Fig.2] is a second embodiment of a power supply system for a floating structure;

[0048] [Fig.3] is a flowchart representing the process for managing a fluid in liquid form contained in a tank of a floating structure;

[0049] [Fig.4] represents, according to a cutaway view, a floating structure comprising the supply system of figures 1 or 2.

[0050] [Fig.l] illustrates a first embodiment of a supply system 1 according to the invention. The supply 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 which equips the floating structure. The gas in the liquid state can naturally evaporate partially and form a gaseous phase, otherwise called evaporated gas, which is stored within a ceiling 3 of the tank 2.

[0051] In order to manage the pressure in the tank 2 which increases due to the presence of the gaseous phase within the sky 3, the supply system 1 can use this gaseous phase to supply fuel to at least one gas-consuming device. In [Fig.l], the supply system 1 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.

[0052] In order to ensure a supply of the gas consuming devices 4, 5, the supply system 1 comprises a supply circuit extending between the tank 2 and the gas consuming devices 4, 5. The supply circuit 6 comprises a compression device 7 making it possible to suck in the gaseous phase contained in the headspace 3 and the tank 2 and to compress it to a pressure compatible with the needs of the high-pressure gas consuming device 4, for example above 250 bars, or of the low-pressure gas consuming device 5, in particular between 7 and 20 bars.

[0053] In [Fig.l], the compression device 7 is illustrated 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 to a higher or lower pressure, such a compression device 7 comprising at least three outlets, at least two of which are arranged between two compression stages. The more compression stages the gas passes through, the more its pressure is increased.

[0054] The compression device 7 shown in [Fig.l] thus comprises at least a first compression stage 11, a second compression stage 12 and a third compression stage 13. The compression device 7 also comprises a first outlet 56 arranged between the first compression stage 11 and the second compression stage 12, a second outlet 57 arranged between the second compression stage 12 and the third compression stage 13 and a third outlet 58 after the third compression stage 13.

[0055] These three outlets 56, 57, 58 each provide an outlet for the gas phase from the compression device 7. This gas phase passes through the entire compression device 7 and exits through the third outlet 58 to reach the pressure compatible with supplying the high-pressure gas-consuming device 4. At the outlet of the third compression stage 13 of the compression device 7, the gas phase can reach a pressure of between 250 and 400 bars.

[0056] The gaseous phase compressed by the first compression stage 11 has a pressure of between 7 and 20 bars, while the gaseous phase compressed by the second compression stage 12 has a pressure of between 70 and 150 bars. The first compression stage 11 also makes it possible to raise the pressure of the gaseous phase to a value compatible with the supply of the low-pressure gas-consuming device 5.

[0057] The supply system 1 also comprises a return circuit 8. The return circuit 8 is connected to the supply circuit 6, more particularly at the compression device 7. According to the first embodiment of the supply system 1, the return circuit 8 comprises a first branch 9 and a second branch 10, respectively connected to the first outlet 56 of the compression device 7 arranged downstream of the first compression stage 11 and upstream of the second compression stage 12, and to the second outlet 57 of the compression device 7 arranged downstream of the second compression stage 12 and upstream of the third compression stage 13. The first branch 9 and the second branch 10 make it possible to circulate the gas phase within the return circuit 8 at two different pressure levels.

[0058] The first branch 9 and the second branch 10 join at a junction point 53. Preferably, the gas phase only circulates within one of the two branches 9, 10. In order to control the circulation within said branches 9, 10, the first branch 9 comprises a first valve 43 and the second branch 10 comprises a second valve 44.

[0059] One of the objectives of the return circuit 8 is to participate in the condensation of the gaseous phase not used for supplying fuel to the gas-consuming devices 4, 5. To do this, the supply system 1 comprises a heat exchanger 14 configured to carry out a heat exchange between the compressed gaseous phase circulating in the return circuit 8 and the gaseous phase circulating in the supply circuit 6, upstream of the compression device 7 and in origin of the tank sky.

[0060] The heat exchanger 14 thus makes it possible to pre-cool the gaseous phase circulating in the return circuit 8 by using the gaseous phase at the outlet of the tank 2, before its compression. The latter is then heated by capturing the calories from the gaseous phase circulating in the return circuit 8.

[0061] The gaseous phase circulating in the return circuit 8 is pre-cooled within the heat exchanger 14, regardless of the branch 9 or 10 used. Thus, the junction point 53 is advantageously arranged upstream of the heat exchanger 14 so that the entire gaseous phase circulating in the return circuit 8 passes through the heat exchanger 14 to be pre-cooled there.

[0062] According to such a configuration, the heat exchanger 14 comprises two passes, one of which is where the gaseous phase circulating in the supply circuit 6 upstream of the compression device 7 circulates and the other where the compressed gaseous phase circulating in the return circuit 8 circulates, after the first branch 9 and the second branch 10 have joined at the junction point 53.

[0063] The return circuit 8 comprises a first portion 51 and a second portion 52, each being adapted to the circulation of the gaseous phase previously compressed by the first compression stage 11 or by the second compression stage 12.

[0064] In [Fig. 1], it can be seen that the second portion 52 comprises an expansion means 15, while the first portion 51 does not. It can thus be understood that the first portion 51 is specific to the circulation of the gas phase compressed only by the first compression stage 11, while the second portion 52 is specific to the circulation of the gas phase compressed by the second compression stage 12. Pressurization by the second compression stage 12 requires subsequent expansion, which is ensured by the expansion means 15.

[0065] The supply system 1 makes it possible to optimize the condensation of the gas phase by saving a maximum amount of energy and by maintaining the temperature of the cargo of fluid in the liquid state below a determined threshold, such a threshold being able to be a maximum temperature authorized at a place of unloading or delivery of the tank 2. This optimization is obtained by favoring the use of the first branch 9 combined with the use of the first portion 51, compared to the use of the second branch 10 combined with the use of the second portion 52, possibly combined with the implementation of a cooling loop 20, 50.

[0066] The return circuit 8 illustrated in [Fig. 1] comprises a divergence point 54 and a convergence point 55, respectively where the first portion 51 and the second portion 52 begin and end. The latter also comprise respectively a first valve 41 and a second valve 42 which control the circulation of gas within the respective portions. Finally, the return circuit 8 comprises a flow regulating member 40 arranged downstream of the point of convergence 55 between the first portion 51 and the second portion 52. This flow regulating member 40 adapts the pressure and the flow rate within the return circuit 8 so as to bring this pressure closer to the pressure which prevails within the tank 2.

[0067] This flow regulating member 40 is arranged downstream of the branch of the return circuit 8 which passes through a heat exchanger 16, and upstream of a mixing point 39 between the return circuit 8 and a cooling circuit 17.

[0068] After having circulated within the first portion 51 or the second portion 52, the gaseous phase then passes through the heat exchanger 16 in order to be at least partially, or even totally, condensed. The convergence point 55 is arranged upstream of the heat exchanger 16. Thus, just as for the heat exchanger 14, the heat exchanger 16 comprises two passes.

[0069] In order to carry out efficient condensation, the supply system 1 comprises the cooling circuit 17 within which circulates fluid in the liquid state taken from the tank 2. The cooling circuit 17 comprises a pump 18, advantageously immersed at the bottom of the tank 2 and which circulates the fluid 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 condensation of the gas in the vapor state circulating in the return circuit 8. The fluid in the liquid state circulating in the cooling circuit 17 can thus pass through the heat exchanger 16 within which a heat exchange takes place with the gaseous phase circulating in the return circuit 8. The gaseous phase is then condensed. This is advantageous in that the frigories contained in the liquid gas in the tank are used to carry out the reliquefaction.

[0070] In order to optimize the condensation of the gaseous phase circulating in the heat exchanger 16, the supply system 1 comprises another heat exchanger hereinafter called second heat exchanger 19, which the fluid in the liquid state circulating in the cooling circuit 17 can pass through or bypass.

[0071] The second heat exchanger 19 makes it possible to sub-cool the fluid in the liquid state in order to compensate for the calories captured by the fluid in the liquid state during the heat exchange occurring within the heat exchanger 16, otherwise called the first heat exchanger 16 when the system comprises several heat exchangers.

[0072] In order to subcool the fluid in the liquid state, the supply system 1 comprises a cooling loop 20 which passes through the second heat exchanger 19, such a cooling loop 20 being traversed by a refrigerant fluid ensuring the subcooling of the fluid in the liquid state. The refrigerant fluid circulating in the cooling loop 20 may for example be nitrogen.

[0073] At the outlet of the first heat exchanger 16, the gaseous phase thus condensed joins the cooling circuit 17, also at the outlet of the first heat exchanger 16, mixing at the mixing point 39. The cooling circuit 17 extends to the tank 2 so that the return of the fluid to the liquid state can take place within the latter. The cooling circuit 17 therefore comprises at least one termination 29 which may be an orifice 30 arranged at the bottom of the tank 2.

[0074] When the quantity of gas evaporated in the ceiling 3 of the tank 2 is not sufficient to satisfy the consumption of the high-pressure gas-consuming device 4, the supply system 1 can be configured to supply this gaseous phase to the latter. Thus, the supply system 1 can comprise an additional supply circuit 33. The additional supply circuit 33 comprises an additional pump 35, a high-pressure pump 36 and a vaporizer 37. The additional pump 35 makes it possible to take the fluid in the liquid state from the tank 2, then the high-pressure pump 36 pumps the fluid in the liquid state up to a pressure compatible with the pressure required by the high-pressure gas-consuming device 4. The vaporizer 37 makes it possible to evaporate the fluid in the liquid state put under high pressure so that this fluid passes into the vapor state and can be consumed by the high-pressure gas-consuming device 4.

[0075] As illustrated in Figures 1 or 2, the additional pump 35 and the pump 18 of the cooling circuit 17 are separate and distinct pumps. According to an alternative, the system is devoid of an additional pump dedicated to the additional supply circuit 33. In such a case, the additional supply circuit 33 is connected to the cooling circuit 17, between an outlet of the pump 18 and an inlet of the heat exchanger 16 and it is the pump 18 which, in addition to its initial function, takes gas in the liquid state from the tank 2 to supply it to the high-pressure pump 36.

[0076] [Fig. 2] represents a variant of the power supply system illustrated in [Fig. 1]. Only the structural and functional differences from what has been previously discussed will be described. Reference will therefore be made to the description in [Fig. 1] for all features not detailed below.

[0077] [Fig. 2] differs from what has been described previously in particular by the absence of the second heat exchanger making it possible to sub-cool the fluid in the liquid state circulating in the cooling circuit 17.

[0078] Instead, the feed system 1 comprises an additional branch 48 connected to the first output 56 of the compression device 7, in parallel with the first branch 9, and which extends to the tank 2.

[0079] The power supply system 1 comprises a cooling loop 50 which can be activated or deactivated depending on the selected operating mode. This branch additional branch 48 conducts the gaseous phase through a second heat exchanger 49, which is configured to carry out a heat exchange between the gaseous phase which comes from the compression device 7 and a refrigerant circulating in the cooling loop 50. At the outlet of the second heat exchanger 49, the condensed gaseous phase circulates in the additional branch 48 until it returns to the tank 2.

[0080] As illustrated in the flowchart present in [Fig.3], the gas phase management method 64 begins with a recovery 68 of the navigation parameters of the floating structure 70. These parameters can be involved in the choice of the preferable operating mode for the condensation of the evaporated gas present in the ceiling 3 of the tank 2.

[0081] According to the invention, the method implements at least three operating modes of the power supply system 1, these modes being implemented with the aim of reducing the overall consumption of the floating structure.

[0082] A first mode of operation illustrated by the reference 94 corresponds to a connection of the return circuit 8 to the first outlet 56 of the compression device 7 and to a circulation of the gaseous phase through the first portion 51, the heat exchanger 16 carrying out a heat exchange between the fluid in liquid form circulating in the cooling circuit 17, without the latter being sub-cooled, and the gaseous phase circulating in the return circuit 8. In such a case, the first valve 43 is open and the second valve 44 is closed, the gaseous phase thus beginning its journey in the return circuit 8 via the first branch 9. After the heat exchanger 14, the circulation of the gaseous phase continues in the return circuit 8 via the first branch 51, i.e. the one which is devoid of expansion means. To do this, the first valve 41 is opened and the second valve 42 is closed.

[0083] This first mode of operation 94 is implemented when it is determined in step 84 that the quantity of gas evaporated in the top of the tank is greater than an initial threshold, for example equal to 0 kg / h, and it is determined in step 82 that the temperature of the fluid in liquid form present in the tank is lower than a maximum temperature of the fluid in the liquid state authorized at the delivery location. This first mode of operation 94 is the one that consumes the least energy to condense the gaseous phase which passes through the return circuit, and the invention favors the implementation of this first mode of operation compared to the second mode 100 or the third mode of operation 98.

[0084] The second mode of operation illustrated by the reference 100 corresponds to a connection of the return circuit 8 to the second outlet 57 of the compression device 7 and to a circulation of the gas phase through the second portion 52 and to the through the expansion means 15, the heat exchanger 16 carrying out a heat exchange between the fluid in liquid form circulating in the cooling circuit 17, without the latter being sub-cooled, and the gaseous phase circulating in the return circuit 8 after expansion thereof. In such a case, the first valve 43 is closed and the second valve 44 is open, the gaseous phase thus beginning its journey in the return circuit 8 via the second branch 10. After the heat exchanger 14, the circulation of the gaseous phase continues in the return circuit 8 via the second branch 52, that is to say the one provided with the expansion means 15. To do this, the first valve 41 is closed and the second valve 42 is open.

[0085] This second mode of operation 100 is implemented when it is determined in step 96 that the quantity of gas evaporated in the top of the tank is between the initial threshold and a first threshold, the first threshold being able to take any value between 1 kg / h and 750 kg / h, and when it is determined in step 82 that the temperature of the fluid in liquid form present in the tank is higher than the maximum temperature authorized at the delivery location. In such a case, the first valve 43 is closed and the second valve 44 is open, the gas phase thus beginning its journey in the return circuit 8 via the second branch 10. After the heat exchanger 14, the circulation of the gas phase continues in the return circuit 8 via the second branch 52, i.e. the one provided with expansion means 15. To do this, the first valve 41 is closed and the second valve 42 is open.This second mode of operation 100 consumes less energy to condense the gaseous phase which passes through the return circuit than the third mode of operation 98 because the cooling loop, whatever its embodiment, is inactive.

[0086] The third mode of operation illustrated by the reference 98 corresponds to a connection of the return circuit 8 to the second outlet 57 of the compression device 7 and to a circulation of the gaseous phase through the second portion 52 and through the expansion means 15, the heat exchanger 16 carrying out a heat exchange between the fluid in liquid form circulating in the cooling circuit 17 and the gaseous phase circulating in the return circuit 8 after expansion thereof. In this mode, the cooling loop is active, which makes it possible either to sub-cool the fluid in the liquid state which circulates in the cooling circuit 17, or to liquefy the gaseous phase which circulates in the additional branch 48.

[0087] This third mode of operation 98 is implemented when it is determined in step 96 that the quantity of gas evaporated in the top of the tank is greater than the first threshold mentioned above, for example 750 kg / h, and it is determined in step 82 that the temperature of the fluid in liquid form present in the tank is greater than the maximum temperature authorized at the delivery location. This third mode of operation lowers the temperature of the fluid in the liquid state present in the tank so as to bring the latter below the maximum temperature authorized at the delivery point.

[0088] In step 84, it is determined whether the quantity of gas evaporated in the tank headspace is equal to the initial threshold, for example 0 kg / h. This is particularly the case when the consumption of the gas phase by the consumer corresponds to the generation of gas phase in the tank headspace. If this quantity is equal to 0 kg / h, the method does not implement any operating mode related to the condensation of the gas phase.

[0089] If it is determined in step 84 that the quantity of gas evaporated in the tank ceiling is lower than the initial threshold, and it is determined in a step 92 that the temperature of the fluid in the liquid state is higher than the maximum temperature authorized at the delivery location by a value between 0°C and 1°C, a fourth operating mode 104 is implemented.

[0090] This fourth mode of operation 104 consists of generating a depression within the tank 2. Such a depression is implemented by the compression device 7, or by any other suction means, which sucks the gaseous phase present in the tank headspace until the pressure in this headspace 3 of the tank 2 is lower than a saturation pressure of the fluid in liquid form present in the tank 2. In doing so, the fluid in the liquid state evaporates in the tank headspace and thus generates a gaseous phase.

[0091] If it is determined in step 84 that the quantity of gas evaporated in the tank ceiling is lower than the initial threshold, for example 0 kg / h, and it is determined in step 92 that the temperature of the fluid in the liquid state is higher than the maximum temperature authorized at the delivery location by a value between 0°C and 1.5°C, a fifth operating mode 102 is implemented.

[0092] During this fifth mode of operation 102, fluid in liquid form is taken from the tank 2 by means of the additional supply circuit 33, this fluid is evaporated in liquid form within a vaporizer 37 to supply the consumer 4 or 8 in gaseous phase. A portion of the gaseous phase not consumed by the consumer is condensed by the cooling loop 20 via the cooling circuit, or directly within the additional branch 48 which comprises a dedicated cooling loop 50.

[0093] The quantities of evaporated gas described above can be determined for example by monitoring a variation in the pressure in the ceiling 3 of the tank 2 over a given time. If the pressure increases rapidly, this means that the quantity of evaporated gas is significant. Conversely, if the pressure does not increase, or increases slowly, this means that the quantity of evaporated gas is stable, or even low.

[0094] Alternatively or additionally, the quantity of evaporated gas present in the tank can be determined by comparing an estimated consumer consumption between the place of loading the fluid into the tank and the place of delivery of this fluid and an estimate of the generation of the gaseous phase within the tank, such an estimate depending on design characteristics of the tank, such as for example its thermal insulation. If the estimated generation of the gaseous phase is higher than the estimated consumer consumption, this reflects the presence of a significant quantity of evaporated gas. If, on the other hand, the estimated generation of the gaseous phase is lower than or equal to the estimated consumer consumption, this reflects a stable or even decreasing quantity of evaporated gas.

[0095] [Fig.4] represents the floating structure 70 comprising the tank 2, which is watertight and thermally insulated. It is generally prismatic in shape and is mounted in a double hull 5 of the floating structure 70, which may be a ship or a floating platform. A wall of the tank 2 comprises a primary watertight barrier intended to be in contact with the fluid in liquid form contained in the tank 2, a secondary watertight barrier arranged between the primary watertight barrier and the double hull 5 of the ship, and two thermally insulated barriers arranged respectively between the primary watertight barrier and the secondary watertight barrier and between the secondary watertight barrier and the double hull 5. In a simplified version, the floating structure 70 comprises a single hull.

[0096] Loading / unloading pipelines 73 arranged on an upper deck of the floating structure 70 can be connected, by means of appropriate connectors, to a maritime or port terminal to transfer a cargo of fluid in liquid form from or to the tank 2.

[0097] [Fig.4] also illustrates an example of a maritime terminal comprising a post loading and / or unloading station 75, an underwater pipe 76 and a land-based installation 77. The loading and / or unloading station 75 is a fixed offshore installation comprising a mobile arm 74 and a tower 78 which supports the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible pipes 79 which can be connected to the loading / unloading pipes 73. The mobile arm 74 is orientable and adapts to all sizes of floating structure 70. A connecting pipe (not shown) extends inside the tower 78. The loading / unloading station 75 allows the loading and / or unloading of the floating structure 70 from or to the land-based installation 77. The latter comprises storage tanks 80 for fluid in liquid form and connecting pipes 81 connected by the underwater pipe 76 to the loading and / or unloading station 75. unloading 75.The underwater pipe 76 allows the transfer of the fluid in liquid form between the loading and / or unloading station 75 and the onshore installation 77 over a long distance, for example five kilometers, which makes it possible to keep the floating structure 70 at a great distance from the coast. during loading and / or unloading operations.

[0098] To generate the pressure necessary for transferring the fluid in liquid form, pumps on board the floating structure 70 and / or pumps equipping the land-based installation 77 and / or pumps equipping the loading and unloading station 75 are used.

[0099] The examples have been described for a floating structure 70; however, they are also applicable to a land-based structure.

[0100] The present invention thus proposes a method for managing a gaseous phase within a tank which makes it possible to condense this gaseous phase using the least possible energy, this supply system being equipped with a cooling loop when in certain situations it makes it possible to bring the temperature of the fluid to the liquid state below a threshold temperature, for example the temperature accepted by a delivery terminal.

[0101] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Claims

1. Method for managing (64) a gaseous phase of a fluid contained in liquid form in a tank (2) of a floating structure (70), the floating structure (70) comprising a system (1) for supplying fuel to at least one consumer (4, 5) equipping the floating structure (70), the supply system (1) comprising at least one compression device (7) intended to take the gaseous phase to deliver it to the consumer (4, 5), the compression device (7) comprising at least a first outlet (56), a second outlet (57) and a third outlet (58) configured to deliver the gaseous phase at three different pressure levels, the supply system (1) comprising a return circuit (8) intended to return to the tank (2) a portion of the gaseous phase compressed by the compression device (7),the return circuit (8) being alternately connected to the first outlet (56) or to the second outlet (57) of the compression device (7) and comprising at least a first portion (51), as well as a second portion (52) provided with an expansion means (15), the supply system (1) comprising at least one heat exchanger (14) configured to carry out a heat exchange between the vapor phase taken by the compression device (7) and the gaseous phase which flows through the return circuit (8), the supply system (1) comprising at least one cooling circuit (17) configured to take the fluid in the liquid state from the tank (2), the return circuit (8) comprising at least one heat exchanger (16) configured to carry out a heat exchange between the gaseous phase of the fluid circulating in the return circuit (8) and the fluid in the liquid state circulating in the cooling circuit (17),the supply system (1) comprising a cooling loop (20, 50) participating in the condensation of the gas phase coming from the compression device (7), the method for managing the gas phase comprising a plurality of operating modes, among which there are at least:, - a first operating mode (94) where the return circuit (8) is connected to the first outlet (56) of the compression device (7), the heat exchanger (16) carrying out a heat exchange between the fluid in liquid form circulating in the cooling circuit (17) and the gaseous phase circulating in the return circuit (8); - a second mode of operation (100) where the return circuit (8) is connected to the second outlet (57) of the compression device (7), the heat exchanger (16) carrying out a heat exchange between the gas phase expanded by the expansion means (15) and the fluid in liquid form circulating in the cooling circuit (17), the cooling loop (20, 50) not participating in the condensation of the gas phase coming from the compression device (7); - a third mode of operation (98) where the return circuit (8) is connected to the second outlet (57) of the compression device (7), the heat exchanger (16) carrying out a heat exchange between the gas phase expanded by the expansion means (15) and the fluid in liquid form circulating in the cooling circuit (17), the cooling loop (20, 50) participating in the condensation of the gas phase coming from the compression device (7).

2. Management method (64) according to claim 1, during which the operating modes are implemented according to parameters including at least a quantity of evaporated gas present in the tank, a maximum temperature authorized on arrival at a delivery location and / or a temperature of the fluid in liquid form contained in the tank.

3. Management method (64) according to claim 2, during which the quantity of evaporated gas present in the tank (2) is determined by variation of a pressure in a ceiling (3) of the tank (2) over a given time.

4. Management method (64) according to claim 2, during which the quantity of evaporated gas present in the tank (2) is determined by the consumption of the consumer (4, 5) between a place of loading of the fluid into the tank (2) and a place of delivery of this fluid and by an estimate of generation of evaporated gas in the tank (2) as a function of design characteristics of the tank (2).

5. Management method (64) according to any one of claims 2 to 4, during which the first mode of operation (94) is implemented when the temperature of the fluid in liquid form contained in the tank (2) is less than or equal to the maximum temperature authorized at arrival at the place of delivery and that the quantity of evaporated gas to be reliquefied is greater than an initial threshold.

6. Management method (64) according to claim 5, during which the second mode of operation (95) is implemented when the temperature of the fluid in liquid form contained in the tank (2) is higher than the maximum temperature authorized on arrival at the delivery location and the quantity of evaporated gas to be reliquefied is lower than a first threshold, said first threshold being higher than the initial threshold.

7. Management method (64) according to claim 6, during which the third mode of operation (100) is implemented when the temperature of the fluid in liquid form contained in the tank (2) is higher than the maximum temperature authorized on arrival at the delivery location and the quantity of evaporated gas to be reliquefied is higher than the first threshold.

8. Management method (64) according to any one of claims 2 to 7, comprising a fourth mode of operation (104) where the sky (3) of the tank (2) is sucked by the compression device (7) until the pressure in this sky (3) of the tank (2) is lower than a saturation pressure of the fluid in liquid form present in the tank (2), this fourth mode of operation (104) being implemented when the temperature of the fluid in liquid form contained in the tank (2) is higher than the maximum temperature authorized on arrival at the delivery location by a value between 0°C and 1°C and the quantity of evaporated gas is lower than the quantity of gas consumed by the consumer (4, 5).

9. Management method (64) according to claim 8, comprising a fifth operating mode (102) during which the cooling loop (20, 50) is activated, this fifth operating mode (102) being implemented when the temperature of the fluid in liquid form contained in the tank (2) is higher than the maximum temperature authorized on arrival at the delivery location by a value between 0°C and 1.5°C.

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

11. Fuel supply system (1) for at least one consumer (4, 5) equipping a floating structure (70), comprising at least one compression device (7) intended to collect the gaseous phase to deliver it to the consumer (4, 5), the compression device (7) comprising at least a first outlet (56), a second outlet (57) and a third outlet (58) configured to deliver the gaseous phase at three different pressure levels, the supply system (1) comprising a return circuit (8) intended to return to the tank (2) a portion of the gaseous phase compressed by the compression device (7), the return circuit (8) being alternately connected to the first outlet (56) or to the second outlet (57) of the compression device (7) and comprising at least a first portion (51), as well as a second portion (52) provided with an expansion means (15),the supply system (1) comprising at least one heat exchanger (14) configured to carry out a heat exchange between the vapor phase taken by the compression device (7) and the gaseous phase which flows through the return circuit (8), the supply system (1) comprising at least one cooling circuit (17) configured to take the fluid in the liquid state from the tank (2), the return circuit (8) comprising at least one heat exchanger (16) configured to carry out a heat exchange between the gaseous phase of the fluid circulating in the return circuit (8) and the fluid in the liquid state circulating in the cooling circuit (17), the supply system (1) comprising a cooling loop (20, 50) participating in the condensation of the gaseous phase coming from the compression device (7), said supply system (1) being configured to implement the management method according to any one of claims 1 to 10.,

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

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