Gas supply system for high- and low-pressure gas-consuming devices and method for controlling such a system

Abstract

The present invention relates to a supply system (1) for supplying a high-pressure gas-consuming device (4) and a low-pressure gas-consuming device (5) of a floating structure comprising a tank (8), the supply system (1) comprising: a first supply circuit (2), a second supply circuit (3), a return line (14), a first heat exchanger (6) and a second heat exchanger (7), the supply system (1) comprising at least one branch (40) for cooling the gas withdrawn in the vapour state from the tank (8), connected to the second supply circuit (3) upstream of the compression device (13), the supply system (1) comprising at least one heat exchanger (41) configured to operate a heat exchange between the vapour-state gas flowing through the cooling branch (40) and the liquid-state gas flowing through the first supply circuit (2).

Description

[0001] DESCRIPTION

[0002] Title of the invention: Gas supply system for high and low pressure gas consuming appliances and method for controlling such a system

[0003] The present invention relates to the field of vessels for storing and / or transporting gas in the liquid state and more particularly concerns a gas supply system for consumer devices included within such vessels, as well as a method for controlling such a system.

[0004] During a journey made by a vessel comprising a tank of gas in the liquid state intended to be consumed and / or delivered to a destination point, said vessel may be able to use at least part of said gas in the liquid state in order to supply at least one of its engines, via a gas supply system. This is the case for vessels equipped with a high-pressure propulsion engine of the ME-GI type. In order to supply this type of engine, the gas must be compressed to very high pressure by special compression devices capable of compressing the gas up to 300 bars absolute, but such compression devices are expensive, generate significant maintenance costs and induce vibrations within the vessel.

[0005] An alternative to installing these high-pressure compression devices is to vaporize the gas into liquid form at 300 bars absolute, in particular using a high-pressure pump, before it is sent to the propulsion engine. Since such a solution does not allow the removal of the gas in vapor form (or BOG, which in English stands for "Boil-Off Gas") naturally forming within a tank containing at least part of the cargo, a low-pressure compression means can be installed to supply an auxiliary engine, capable of consuming the gas in vapor form at low pressure. The excess gas in vapor form can also be recirculated to the tank by being recondensed.

[0006] The efficiency achieved by such a system is already high, but it is still possible to increase the overall efficiency of this system. Indeed, a disadvantage of this system lies in the variations in the temperature of the gas in vapor form taken from the tank. There are cases where this temperature exceeds a threshold which ultimately causes an increase in the consumption of the low-pressure compression means, in particular an increase in its electricity consumption.

[0007] Another disadvantage is the large amount of energy required to vaporize the gas into liquid form to reach 300 bars absolute.

[0008] The present invention aims to solve such problems by proposing a gas supply system for at least one high-pressure gas-consuming device and at least one low-pressure gas-consuming device of a floating structure which comprises at least one tank configured to contain the gas at least in the liquid state, the supply system comprising: at least one first gas supply circuit for the high-pressure gas-consuming device, at least one high-pressure evaporator configured to evaporate the gas circulating in the first supply circuit, at least one second gas supply circuit for the low-pressure gas-consuming device, comprising at least one compression device configured to compress gas taken in the vapor state from the tank to a pressure compatible with the needs of the low-pressure gas-consuming device,at least one gas return line connected to the second supply circuit downstream of the compression device and extending to the tank, at least one first heat exchanger and one second heat exchanger, each configured to carry out a heat exchange between the gas circulating in the return line and the gas in the liquid state circulating in the first supply circuit.,

[0009] The feed system is innovative in that it comprises at least one branch for cooling the gas taken in the vapor state from the tank connected to the second feed circuit upstream of the compression device, the feed system comprising at least one heat exchanger which comprises at least a first pass installed on the first feed circuit between the second heat exchanger and the high-pressure evaporator as well as a second pass installed on the cooling branch.

[0010] The cooling branch branches the gas in the vapor state taken from the tank in relation to a portion of the second supply circuit. In doing so, the gas is brought to the heat exchanger which implements a cooling of the gas circulating in the cooling branch by means of the gas in the liquid state which passes through the first supply circuit. The heat exchange is all the more efficient as it is carried out between a fluid in the liquid state and a fluid in the gaseous state. The cooling branch and its heat exchanger are therefore interesting in the case where the consumer device is supplied at low pressure or in the case where the aim is to liquefy the excess gas present in the tank headspace.The densification of the gas in the value state after passing through the heat exchanger makes it possible to reduce the electrical consumption of the compression device by up to 30% when the gas in the vapor state circulates in the return line for condensing. This reduction in the electrical consumption of the compression device can reach 45% when the gas in the vapor state circulates in the second supply circuit for supply to the low-pressure gas-consuming device.

[0011] The first gas supply circuit is used to meet the fuel requirements of the high-pressure gas-consuming device. This may, for example, be the means of propulsion for the floating structure, such as a ME-GI engine. The first supply circuit extends from the tank to the high-pressure gas-consuming device. The pump is installed at the bottom of the tank and pumps the gas in liquid form so that it can circulate in the first supply circuit.

[0012] Since the gas must be in the vapor state to be able to supply the high-pressure gas-consuming device, the high-pressure evaporator ensures the evaporation of the gas before it is supplied to the high-pressure gas-consuming device. The high-pressure evaporator is the site of an exchange of calories between the gas in the liquid state circulating in the first supply circuit and a heat transfer fluid, for example glycolated water, sea water or water vapor. This heat transfer fluid, whatever its form, must be at a sufficiently high temperature to create a change of state of the gas so that the latter passes into the vapor or supercritical state and supplies the high-pressure gas-consuming device.

[0013] The second supply circuit extends from the tank to the low-pressure gas-consuming device. The latter may, for example, be an auxiliary engine such as an internal combustion engine of an electric generator. The compression device arranged on the second supply circuit is responsible for sucking the gas present in the tank's headspace in order to be able to both supply the low-pressure gas-consuming device and regulate the pressure within the tank.

[0014] At the outlet of the compression device, the gas in vapor state can supply the low-pressure gas-consuming device, and / or circulate through the return line if the low-pressure gas-consuming device requires little or no fuel supply. Since the return line is connected downstream of the compression device, the gas in vapor state drawn in by the compression device can therefore circulate through it.

[0015] The gas in the vapor state circulating in the return line first passes through the second heat exchanger, then the first heat exchanger, before returning to the tank. According to this configuration, thanks to the exchange of calories taking place between the gas in the liquid state circulating in the first supply circuit and the gas in the vapor state circulating in the return line, the temperature of the gas in the vapor state decreases while passing through the two heat exchangers, until said gas condenses and returns to the liquid state substantially downstream of the first heat exchanger. The gas thus condensed, that is to say in the liquid state, then circulates to the tank.

[0016] According to a characteristic of the invention, the heat exchanger comprises at least a first pass installed on the first supply circuit upstream of the high-pressure evaporator, as well as a second pass installed on the cooling branch. The gas in the liquid state which passes through the first supply circuit therefore first passes through the heat exchanger, then passes through the first pass of the high-pressure evaporator. According to another refinement, the first pass of the heat exchanger is installed between the second heat exchanger and the high-pressure evaporator. It is understood here that the gas in the liquid state which circulates in the first supply circuit first passes through the first pass of the first exchanger, then passes through the first pass of the heat exchanger and finally passes through the first pass of the high-pressure evaporator.

[0017] The successions of heat exchange implemented by the above variants make it possible to take advantage of the calories of one and / or the other of the fluids concerned, in an order which increases the efficiency of the system.

[0018] According to another characteristic of the invention, the second pass of the heat exchanger is upstream of the compression device, according to the direction of circulation of the gas within the second supply circuit. The gas in the vapor state thus enters the compression device at a lower temperature, which makes it possible to increase the density of the gas and thus reduce the volume flow rate of the compression device.

[0019] According to yet another feature, the power supply system comprises a point of divergence where the cooling branch and the second power supply circuit separate and a point of convergence where the cooling branch and the second power supply circuit join, the cooling branch extending between the point of divergence and the point of convergence. The point of divergence and the point of convergence delimit a portion of the second power supply circuit and the cooling branch is thus in parallel with this portion.

[0020] Advantageously, the second supply circuit comprises at least one member for controlling the circulation of gas within said second supply circuit, the cooling branch being arranged in parallel with the member for controlling the circulation of gas within said second supply circuit. The control member is thus arranged on the portion of the second supply circuit.

[0021] The point of divergence is then upstream of the gas circulation control member within said second supply circuit and the point of convergence is downstream of said control member, depending on the direction of circulation of the gas within said second supply circuit. In a further advantageous manner, the cooling branch comprises at least one valve for controlling the circulation of the gas within said cooling branch. The flow of gas passing through the heat exchanger, in particular its second pass, is thus controlled.

[0022] The control organ and / or the control valve can for example be an on / off valve.

[0023] The supply system which is the subject of the invention may also comprise at least one means for determining the temperature of the gas in the vapor state taken from the tank and a management device which controls at least the member for controlling the circulation of the gas within said second supply circuit and the valve for controlling the circulation of the gas within said cooling branch. The determination means evaluates or measures, directly or indirectly, the temperature of the gas in the vapor state taken from the tank.

[0024] The management device is capable of authorizing the circulation of gas within the cooling branch when the temperature determined by the determination means is higher than a reference threshold. Furthermore, the management device is capable of prohibiting the circulation of gas within the cooling branch when the temperature determined by the determination means is lower than the reference threshold.

[0025] Interestingly, the first supply circuit comprises a pump interposed between the first heat exchanger and the second heat exchanger. It is the pump, called the high-pressure pump, which makes it possible to increase the pressure of the gas in the liquid state circulating in the first supply circuit, so that it has a gas pressure compatible with the supply of the high-pressure gas-consuming device.

[0026] According to a first example of implementation, the high-pressure evaporator and the heat exchanger form a unitary heat exchange module. Alternatively, the second heat exchanger and the heat exchanger form a unitary heat exchange module. In combination, at least the high-pressure evaporator, the second heat exchanger and the heat exchanger form a unitary heat exchange module. This unitary heat exchange module is a single exchanger provided with at least three, four or five fluidically distinct passes from one another.

[0027] According to a characteristic of the invention, the supply system comprises a branch for heat treatment of the gas in the vapor state circulating in the return line, the heat treatment branch being connected to the second supply circuit upstream of the compression device, the supply system comprising a third heat exchanger configured to carry out a heat exchange between the gas in the vapor state circulating in the heat treatment branch and the gas in the vapor state circulating in the return line. The heat treatment branch and the third heat exchanger make it possible to exploit the cold contained in the gas in the vapor state taken from the tank to transfer it to the gas in the vapor state circulating in the return line, so as to promote the liquefaction of this gas.

[0028] According to a characteristic of the invention, the first supply circuit comprises at least one pump configured to pump the gas taken in the liquid state from the tank. The pump is advantageously submerged while being arranged at the bottom of the tank in order to take the gas in the liquid state to circulate it within the first supply circuit. When the gas in the liquid state is pumped by the pump, the pressure thereof is high between 6 and 17 bars absolute.

[0029] The invention also relates to a method for controlling a supply system as described in the present document, during which: in a determination step, the temperature of the gas in the vapor state taken from the tank is determined, then the gas in the vapor state is circulated within the cooling branch if the temperature of the gas in the vapor state determined in the determination step is higher than a reference threshold or, the gas in the vapor state is circulated within the second supply circuit if the temperature of the gas in the vapor state determined in the determination step is lower than the reference threshold.

[0030] In other words, if the temperature of the gas taken in the vapor state from the tank is higher than the reference threshold, the valve controlling the circulation of the gas within the cooling branch authorizes circulation of the gas within said cooling branch. If the temperature of the gas taken in the vapor state from the tank is lower than the reference threshold, the valve controlling the circulation of the gas within the cooling branch prohibits circulation of the gas within said cooling branch. Depending on the selected reference threshold, the method authorizes circulation of the gas within said second supply circuit by opening a member controlling the circulation of the gas within the second supply circuit and prohibits circulation within the return line, for example by closing the flow regulating member.

[0031] The determination step is implemented by the means of determining the temperature of the gas in the vapor state taken from the tank. The comparison between this temperature thus determined and the reference threshold, as well as the resulting choice, are implemented by the management device.

[0032] A good level of efficiency is obtained from the system when the reference threshold is equal to - 90°C, in particular + / - 10%, the process then comprising a step of condensation of the gas in the vapor state circulating in the return line.

[0033] According to one aspect of the invention, when the reference threshold is greater than or equal to - 150°C, the method comprises a step of supplying the gas-consuming device at low pressure via the second supply circuit.

[0034] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several exemplary embodiments given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which: [fig 1] is a schematic representation of a power supply system according to the invention, [fig 2] is a schematic representation of a power supply system of figure 1 in a first operating state,

[0035] [fig 3] is a schematic representation of a power supply system of figures 1 and 2 in a second operating state,

[0036] [fig 4] is a schematic representation of a power supply system according to the invention, according to another embodiment.

[0037] The terms "upstream" and "downstream" used 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.

[0038] Identical elements retain the same reference regardless of the figures in which they appear.

[0039] Figure 1 represents a gas supply system 1 on board a floating structure. The supply system 1 makes it possible to circulate gas which may be in the liquid state, in the vapor state, in the two-phase state or in the supercritical state, and this from a storage and / or transport tank 8, and to a high-pressure gas-consuming device 4 and to a low-pressure gas-consuming device 5, in order to supply the latter with fuel.

[0040] Said floating structure may for example be a vessel of the LNG carrier type capable of storing and / or transporting gas in the liquid state, in particular natural gas. The supply system 1 is in this case capable of using the gas in the liquid state that the floating structure stores and / or transports to supply the high-pressure gas-consuming device 4, which may for example be a propulsion engine, and the low-pressure gas-consuming device 5, which may for example be an electric generator supplying the floating structure with electricity.

[0041] In order to ensure the circulation of the gas contained in the tank 8 to the high-pressure gas-consuming device 4, the supply system 1 is provided with a first gas supply circuit 2. The first supply circuit 2 comprises a submersible pump 9 arranged within the tank 8. The submersible 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 sucking in the gas in the liquid state, the submersible pump 9 raises the pressure thereof to a value of between 6 and 17 bars absolute.

[0042] The gas in the liquid state, in a direction of circulation going from the tank 8 to the high-pressure gas-consuming device 4, passes through a first heat exchanger 6 and is pressurized by a pump 10, otherwise called a high-pressure pump. Subsequently, the gas in the liquid state passes through a second heat exchanger 7, then a high-pressure evaporator 11 before reaching the high-pressure engine 4. The pump 10 is advantageously arranged between the first heat exchanger 6 and the second heat exchanger 7.

[0043] 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 is a state compatible with supplying the high-pressure gas-consuming device 4. The evaporation of the gas to the liquid state can, for example, be done by heat exchange between the gas in the liquid state which enters the high-pressure evaporator 11 and a heat transfer fluid at a temperature high enough to evaporate the gas to the liquid state, here glycolated water, sea water or water vapor.

[0044] The increase in gas pressure is ensured by the pump 10 when it 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 between 30 and 400 bars absolute, in particular for use with ammonia or hydrogen, between 30 and 70 bars absolute for use with liquefied petroleum gas, and preferably between 150 and 400 bars absolute for use with ethane, ethylene or even with liquefied natural gas consisting mainly of methane.

[0045] Thanks to the combination of the pump 10 and the high-pressure evaporator 11, the gas is at a pressure and in a state compatible for supplying the high-pressure consumer device 4. Such a configuration makes it possible to avoid the installation of high-pressure compression devices on the first supply circuit 2 which present cost constraints and generate strong vibrations.

[0046] Within the tank 8, part of the gas cargo can naturally pass into the vapor state and be contained in a tank headspace 12. In order to avoid overpressure within the tank 8, the gas in the vapor state contained in the tank headspace 12 must be evacuated.

[0047] 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 device 5. The second supply circuit 3 extends between the tank canopy 12 and the low-pressure gas-consuming device 5. In order to suck in the gas in the vapor state contained in the tank canopy 12, the second supply circuit 3 comprises a compression device 13, in particular a compressor. In addition to sucking in the gas in the vapor state, the compression device 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 bars absolute, so that the gas in the vapor state is at a pressure compatible with supplying the low-pressure gas-consuming device 5.The second supply circuit 3 thus makes it possible to supply the low-pressure gas-consuming device 5, while regulating the pressure within the tank 8 by sucking in the gas in the vapor state present in the tank ceiling 12.

[0048] The presence of gas in the vapor state in excessive quantity within the tank head 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 illustrated, released into the atmosphere. These solutions cause a loss of cargo. This is why 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.

[0049] The return line 14 is connected to the second supply circuit 3 downstream of the compression device 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 initially passes through the second heat exchanger 7, then continues its path by passing through the first heat exchanger 6.

[0050] The first heat exchanger 6 comprises a first pass 6a which is part of the first supply circuit 2. This first heat exchanger 6 comprises a second pass 6b which is part of the return line 14. The direction of circulation within the first pass 6a is opposite to the direction of circulation within the second pass 6b of the first heat exchanger 6.

[0051] The second heat exchanger 7 is installed between the first heat exchanger 6 and the high pressure evaporator 11, on the first supply circuit 2.

[0052] The second heat exchanger 7 comprises a first pass 7a which is part of the first supply circuit 2. This second heat exchanger 7 comprises a second pass 7b which is part of the return line 14. The direction of circulation within the first pass 7a is opposite to the direction of circulation within the second pass 7b of the second heat exchanger 7.

[0053] It is at the inlet of the first pass 6a of the first heat exchanger 6 that the gas in the liquid state of the first supply circuit 2 has the lowest temperature. Therefore, it is after passing through the first heat exchanger 6 that the gas circulating in the return line 14 is condensed. The fluid circulating in the return line 14 is therefore in the vapor state at the inlet of the second pass 6b of the first heat exchanger 6 and leaves in the liquid state following the exchange of calories taking place within the first heat exchanger 6.

[0054] The return line 14 further 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 which 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 taking place in the first heat exchanger 6, in the second heat exchanger 7 and in the high pressure evaporator 11. The supply system 1 also comprises an auxiliary supply line 16, extending from the first supply circuit 2, via a tapping arranged between the submerged pump 9 and the first heat exchanger 6, to the second supply circuit 3, connecting to it between the compression device 13 and the low pressure gas consuming device 5.The auxiliary supply line 16 makes it possible to supply the low-pressure gas-consuming device 5 in the event of insufficient flow of gas in the vapor state formed within the tank ceiling 12.

[0055] When the gas in the vapor state is not present in sufficient quantity in the tank head 12, the gas in the liquid state pumped by the submerged pump 9 can then circulate within this auxiliary supply line 16 in order to supply the low-pressure gas-consuming device 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 changes 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 to say that the gas is evaporated by heat exchange with a heat transfer fluid at a temperature high enough to evaporate 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 device 5.

[0056] It is understood from the above that the auxiliary supply line 16 is only used in the absence of gas in the vapor state in sufficient quantity within the tank head 12. Thus, the auxiliary supply line 16 comprises a valve 19 controlling the circulation of gas within the auxiliary supply line 16 when the use thereof is not necessary.

[0057] According to the invention, the supply system 1 comprises at least one cooling branch 40 for the gas taken in the vapor state from the tank. Such a branch makes it possible to circulate the gas taken in the vapor state from the tank 8 in order to cool it.

[0058] The cooling branch 40 is fluidically connected to the second supply circuit 3, at a position located upstream of the compression device 13. Thus, the supply system comprises a divergence point 44 arranged on the second supply circuit 3 and at which the cooling branch 40 begins. The supply system 3 further comprises a convergence point 45, where the second supply circuit 3 and the cooling branch 40 join. The divergence point 44 and the convergence point 45 are both placed on the second supply circuit 3, before the compression device 13.

[0059] The feed system 1 also comprises a heat exchanger 41 responsible for cooling the gas taken in the vapor state from the tank by exchanging calories with the gas in the liquid state which circulates in the first feed circuit 2.

[0060] This heat exchanger 41 comprises a first pass 42 which exchanges calories with a second pass 43 constituting this heat exchanger 41. The first pass 42 of the heat exchanger 41 is part of the first supply circuit 2 and is traversed by the gas in the liquid state, while the second pass 43 of the heat exchanger 41 is part of the cooling branch 40 and is traversed by the gas in the vapor state taken from the tank 8.

[0061] Ingeniously, the first pass 42 of the heat exchanger 41 is fluidically arranged between the first pass 7a of the second heat exchanger 7 and a first pass 11a of the high-pressure evaporator 11.

[0062] Such a location makes it possible to cool the gas in the vapor state which circulates in the cooling branch 40 by heat exchange with the gas in the liquid state which circulates in the first supply circuit 2, which ultimately makes it possible to reduce the volume flow rate at the inlet of the compression device 13 and thus reduce its consumption, in particular electrical consumption.

[0063] This location also makes it possible to reduce the flow rate of heat transfer fluid which travels through a second pass 11b of the high-pressure evaporator 11 in order to evaporate the gas in the liquid state which comes from the tank 8. Since it is a hot source, the invention makes it possible to reduce the quantity of calories supplied by the heat transfer fluid since a portion of the calories is supplied by the gas in the vapor state which circulates in the cooling branch 40. The circulation of gas in the vapor state within the second supply circuit 3 is placed under the control of a control member 46. The latter is for example a valve. The circulation of gas in the vapor state within the cooling branch 40 is placed under the control of a control valve 47. This control member and / or this control valve is for example a valve or an on / off valve.

[0064] The cooling branch 40 is installed in parallel with this control member 46. In other words, the divergence point 44 is positioned upstream of the control member 46 for controlling the circulation of the gas within the second supply circuit 3, while the convergence point 45 is positioned downstream of this same control member 46.

[0065] The supply system also comprises a management device 49 and at least one means 48 for determining the temperature of the gas in the vapor state taken from the tank 8. The means 48 for determining the temperature is for example a temperature sensor positioned on the second supply circuit 3, between the tank and the point of divergence 44. Alternatively, the sensor can be installed in the tank ceiling 12. This means 48 for determining the temperature is electrically connected to the management device 49 since the information recorded by the determination means 48 is used in a calculation implemented by the management device 49.

[0066] This management device 49 is an electronic control module which receives the information from the determination means 48 and which controls the opening or closing of the control member 46 and / or the control valve 47. The management device 49 implements the method and its various steps, with the exception of the step of determining the temperature of the gas in the value state taken from the tank 8.

[0067] The method which is the subject of the invention is illustrated by Figure 2 and by Figure 3.

[0068] The management device 49 is capable of authorizing the circulation of gas within the cooling branch 40 when the temperature of the gas in the vapor state taken from the tank 8 and determined by the determination means 48 is greater than a reference threshold, such a reference threshold being for example equal to -90°C when the gas in the vapor state flows mainly or exclusively through the return line 14. Alternatively, this reference threshold is greater than or equal to -150°C when the gas in the vapor state is mainly or exclusively sent to the low-pressure gas-consuming appliance 5, via the second supply circuit 3. In such a case, the flow regulating member 15 reduces the flow of gas which circulates in the return line 14, or interrupts it completely if necessary.

[0069] The management device 49 controls an opening of the control valve 47, thus authorizing the gas in the vapor state taken from the tank 8 to reach the heat exchanger 41, in particular its second pass 43. In such a situation, the management device 49 prohibits the passage of gas in the vapor state within a portion 51 of the second supply circuit 3 located between the point of divergence 44 and the point of convergence 45. To do this, the management device 49 controls a closing of the control member 46 installed on this portion 51.

[0070] As shown in Figure 3, the management device 49 is also capable of prohibiting the circulation of gas within the cooling branch 40 when the temperature determined by the determination means 48 is lower than the reference threshold mentioned above. To do this, the management device 49 controls a closing of the control valve 47. In such a case, the management device 49 authorizes the circulation of gas in the vapor state through the portion 51 of the second supply circuit 3, by controlling the opening of the control member 46, thus authorizing the gas in the vapor state taken from the tank 8 to directly reach the compression device 13.

[0071] Of course, the management device 49 can be assigned to other calculation operations necessary for the operation of the supply system 1 according to the invention, such as for example the control of the flow regulating member 15 or the control of the valve 19 controlling the circulation of gas within the auxiliary supply line 16, or even the control of the compression device 13 or the control of the submerged pump 9 or the pump 10.

[0072] It is noted that each exchanger described in this document may be a two-pass component. The invention also covers the case where certain exchangers are combined to form a single exchanger, for example with three or four passes. Thus, the high-pressure evaporator and the heat exchanger 41, or the second heat exchanger 7 and the heat exchanger 41, or the combination of these three components, may form a unitary heat exchange module 50.

[0073] Figure 4 illustrates the power system shown in Figures 1 to 3 with additional components added.

[0074] The supply system 1 shown in Figure 4 thus further comprises a branch 33 for heat treatment of the gas in the vapor state circulating in the return line 14. This heat treatment branch 33 has the function of participating in the cooling of the gas in the vapor state which circulates in the return line, so as to facilitate its condensation. In this situation, the heat treatment branch 33 makes it possible to collect the cold of the gas in the vapor state taken from the tank 8 and to recover it by transferring it to the return line 14.

[0075] The heat treatment branch 33 is connected to the second supply circuit 3 upstream of the compression device 13, via a divergence zone 52 and a convergence zone 53 specific to the heat treatment branch 33. Alternatively, the heat treatment branch 33 and the cooling branch 40 can both be connected to the divergence point 44 and to the convergence point 45. Whatever the connection method, the heat treatment branch 33 and the cooling branch are in parallel with each other, and with respect to the portion 51 of the second supply circuit 3.

[0076] Figure 4 also shows the presence of a third heat exchanger 36 configured to carry out a heat exchange between the gas in the vapor state circulating in the heat treatment branch 33 and the gas in the vapor state circulating in the return line 14. Such a third heat exchanger 36 comprises a first pass 36a which is part of the return line 14 and which is arranged between the second pass 6b of the first heat exchanger 6 and the second pass 7b of the second heat exchanger 7. This third heat exchanger 36 comprises a second pass 36b which is part of the heat treatment branch 33. The heat treatment branch 33 further comprises a control device 38 configured to control the circulation of gas in the vapor state within the heat treatment branch 33.This control device 38 is placed under the control of the management device 49 and it is in an open position when the temperature of the gas in the vapor state taken from the tank 8 detected by the determination means 48 is lower than a temperature threshold, for example equal to - 110°C.

[0077] When the temperature of the gas in the vapor state determined by the determination means is higher than the temperature threshold, the management device 49 controls the closing of the control device 38 and circulates the gas in the vapor state within the second supply circuit 3.

[0078] According to an interesting aspect of Figure 4, it is appropriate to manage the circulation of the flows between the cooling branch 40 and the heat treatment branch 33. Thus, the method which is the subject of the invention provides in particular that, when the temperature of the gas in the vapor state determined in the determination step by the determination means 48 is lower than the temperature threshold, the gas in the vapor state is circulated exclusively within the heat treatment branch 33. In a complementary manner, when the temperature of the gas in the vapor state determined in the determination step by the determination means 48 is lower than the temperature threshold, the gas in the vapor state is circulated exclusively within the cooling branch 40.Finally, when the temperature of the gas in the vapor state determined in the determination step by the determination means 48 is between the temperature threshold and the reference threshold, the gas in the vapor state is circulated exclusively within the second supply circuit 3.

[0079] In the case of Figure 4, the unitary heat exchange module 50 mentioned above can be completed with the third heat exchanger 36. Such a unitary heat exchange module 50 can then comprise at least five passes fluidically separated from each other. Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0080] The invention, as just described, achieves the aim it set itself, and makes it possible to propose a gas supply system which reduces the energy consumption of the compression device and / or the high-pressure evaporator. Variants not described here could be implemented without departing from the context of the invention, provided that, in accordance with the invention, they comprise a supply system in accordance with the invention.

Claims

DEMANDS 1- Gas supply system (1) for at least one high-pressure gas-consuming appliance (4) and at least one low-pressure gas-consuming appliance (5) of a floating structure which includes at least one tank (8) configured to contain the gas at least in a liquid state, the supply system (1) comprising: at least one first gas supply circuit (2) for the high-pressure gas-consuming appliance (4), at least one high-pressure evaporator (11) configured to evaporate the gas circulating in the first supply circuit (2), at least one second gas supply circuit (3) for the low-pressure gas-consuming appliance (5), comprising at least one compression device (13) configured to compress gas taken in vapor form from the tank (8) to a pressure compatible with the requirements of the low-pressure gas-consuming appliance (5),at least one gas return line (14) connected to the second supply circuit (3) downstream of the compression device (13) and extending to the tank (8), at least one first heat exchanger (6) and one second heat exchanger (7), each configured to perform heat exchange between the gas flowing in the return line (14) and the gas in the liquid state flowing in the first supply circuit (2), characterized in that the supply system (1) comprises at least one cooling branch (40) for the gas taken in the vapor state from the tank (8) connected to the second supply circuit (3) upstream of the compression device (13), the supply system (1) comprising at least one heat exchanger (41) configured to perform heat exchange between the gas in the vapor state flowing in the cooling branch (40) and the gas in the liquid state flowing in the first supply circuit (2). 2- Feeding system (1) according to the preceding claim, wherein the heat exchanger (41) comprises at least one first pass (42) installed on the first supply circuit (2) upstream of the high-pressure evaporator (11), as well as a second pass (43) installed on the cooling branch (40). 3- Supply system (1) according to the preceding claim, in which the first pass (42) of the heat exchanger (41) is installed between the second heat exchanger (7) and the high-pressure evaporator (11). 4- Supply system (1) according to the preceding claim, in which the second pass (43) of the heat exchanger (41) is upstream of the compression device (13), according to the direction of gas flow within the second supply circuit (3). 5- Power supply system (1) according to any one of the preceding claims, comprising a divergence point (44) where the cooling branch (40) and the second power supply circuit (3) separate and a convergence point (45) where the cooling branch (40) and the second power supply circuit (3) rejoin, the cooling branch (40) extending between the divergence point (44) and the convergence point (45). 6- Supply system (1) according to any one of the preceding claims, wherein the second supply circuit (3) comprises at least one control element (46) for the flow of gas within said second supply circuit (3), the cooling branch (40) being arranged in parallel with the control element (46) for the flow of gas within said second supply circuit (3). 7- Supply system (1) according to the preceding claim, wherein the cooling branch (40) includes at least one control valve (47) for the circulation of the gas within said cooling branch (40). 8- Supply system (1) according to the preceding claim, comprising at least one means for determining (48) the temperature of the gas in the vapor state taken from the tank (8) and a management device (49) which controls at least the control element (46) of the gas circulation within said second supply circuit (3) and the control valve (47) of the gas circulation within said cooling branch (40). 9- Supply system (1) according to any one of the preceding claims, wherein the first supply circuit (2) comprises a pump (10) interposed between the first heat exchanger (6) and the second heat exchanger (7). 10- Power supply system (1) according to any one of claims 1 to 9, wherein at least the high-pressure evaporator (11) and the heat exchanger (41) form a unit heat exchange module (50). 11- Power supply system (1) according to any one of claims 1 to 9, wherein at least the high-pressure evaporator (11), the second heat exchanger (7) and the heat exchanger (41) form a unit heat exchange module (50). 12- Feeding system (1) according to any one of the preceding claims, comprising a heat treatment branch (33) of the gas in the vapor state flowing in the return line (14), the heat treatment branch (33) being connected to the second feed circuit (3) upstream of the compression device (13), the feeding system (1) comprising a third heat exchanger (36) configured to operate a heat exchange between the gas in the vapor state flowing in the heat treatment branch (33) and the gas in the vapor state flowing in the return line (14). 13- Method of controlling a supply system (1) according to any one of the preceding claims, during which: at a determination step, the temperature of the gas in the vapor state taken from the tank (8) is determined, then the gas in the vapor state is circulated within the cooling branch (40) if the temperature of the gas in the vapor state determined at the determination step is above a reference threshold or, the gas in the vapor state is circulated within the second supply circuit (3) if the temperature of the gas in the vapor state determined at the determination step is below the reference threshold. 14- Control method according to the preceding claim, wherein the reference threshold is equal to -90°C, the method comprising a step of condensation of the gas in the vapor state circulating in the return line (14). 15- Control method according to the preceding claim, during which the reference threshold is greater than or equal to -150°C, the method comprising a step of supplying the low-pressure gas-consuming device (5) via the second supply circuit (3).

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