Apparatus, apparatus and method for maintaining liquefied gas reservoir at cryogenic temperature

Abstract

The invention relates to a device for keeping a liquefied gas reservoir (2) at a low temperature, comprising: a cryocooler; a subcooling circuit including a set of lines, the subcooling circuit including a suction end located in the lower portion of the reservoir; a heat exchanger exchanging heat between the fluid drawn by the subcooling circuit and the chiller, the subcooling circuit including an injection end configured to inject the fluid cooled in the heat exchanger into the reservoir, the apparatus further including a boil-off gas recovery line having an upstream end connected to an upper portion of the reservoir to recover boil-off gas, the recovery line includes a downstream end connected to the boil-off gas consuming device, the device includes a bypass line having a first end connected to the recovery line and a second end connected to the subcooling circuit, the second end connected to the subcooling circuit upstream of the heat exchanger, and a set of valves for transferring boil-off gas from the recovery line to the subcooling circuit. The invention also relates to a liquefied gas storage plant and a method for maintaining a liquefied gas reservoir (2) at a low temperature using the device.

Description

Technical Field

[0001] The present invention relates to a device, an apparatus and a method for maintaining a liquefied gas reservoir at low temperature.

[0002] The present invention relates in particular to an apparatus and method for keeping a liquefied gas reservoir, such as a liquefied gas reservoir for liquefied natural gas, cryogenically and / or pressurized.

[0003] More specifically, the present invention relates to a device for keeping a liquefied gas reservoir at low temperature, such as a liquefied gas reservoir for liquefied natural gas, the device comprising: a cryogenic refrigerator; a subcooling circuit comprising a set of pipelines, the subcooling circuit comprising a suction end intended to be located in the lower part of the liquefied gas reservoir and configured to pump liquefied gas; a heat exchanger for exchanging heat between the pumping subcooling circuit and the refrigerator, the subcooling circuit comprising at least one injection end, the at least one injection end being configured to inject a fluid cooled in the heat exchanger injected into the reservoir, the device also includes a recovery line for the boil-off gas, the recovery line having an upstream end intended to be connected to the upper part of the reservoir to recover the boil-off gas, the recovery line including a downstream end intended to be connected to a consumer of the boil-off gas, such as a burner and / or a motor, the device includes a bypass line and a set of valves, the bypass line and the set of valves are configured to enable the boil-off gas to be transferred from the recovery line to the subcooling circuit, the bypass line having a first end connected to the recovery line and a second end connected to the subcooling circuit. Background Art

[0004] The boil-off gases from the cryogenic fluid in the reservoir can be recovered by direct reliquefaction. The scheme consists in cryogenically compressing these boil-off gases, bringing them to ambient temperature and then sending them to a liquefier.

[0005] Another function includes reliquefying the boil-off gas by transferring refrigeration power from the refrigerator to the cryogenic liquid by subcooling the cryogenic liquid, and returning it to the reservoir.

[0006] Document WO2019020742 A1 describes a device for treating boil-off gas or cooling liquefied gas.

[0007] Cooling heat exchangers can clog due to precipitation of the heaviest components (lower solubility at lower temperatures). This is because cryogenic fluids are not necessarily pure components but can also be mixtures. This means that some components of the mixture may become solid / solidified during the supercooling process. These solid particles can clog the exchangers of the chiller, deteriorating the performance of the system.

[0008] There are different known solutions to reduce or limit this clogging. However, these solutions are not satisfactory for handling boil-off gas and / or subcooling stored liquefied gas. Summary of the invention

[0009] It is an object of the present invention to overcome all or some of the above-mentioned disadvantages of the prior art.

[0010] To this end, also according to the general definition given above in the introduction, the device according to the invention is essentially characterized in that the second end of the bypass line is connected to the subcooling circuit upstream of the heat exchanger.

[0011] Additionally, embodiments of the present invention may include one or more of the following features:

[0012] - said set of valves comprises a flow control valve on said bypass line;

[0013] - the flow control valve is a controlled valve configured to transmit the boil-off gas flow to the subcooling circuit to increase the temperature of the fluid entering the heat exchanger by a given value, for example in the range of 5° C. to 25° C.;

[0014] - the flow control valve is a controlled valve configured to transmit the boil-off gas flow to the subcooling circuit to maintain the temperature of the fluid entering the heat exchanger below the saturation temperature of the liquefied gas;

[0015] - the flow control valve is a controlled valve configured to convey the boil-off gas flow to the subcooling circuit to keep the temperature of the fluid flowing out of the heat exchanger above a given value, for example above -160° C., and / or at a value equal to the temperature of the liquefied gas in the reservoir, and / or at a value equal to the temperature of the liquefied gas drawn at the suction end;

[0016] - the recovery line comprises at least one compressor, the first end of the bypass line being connected to the recovery line downstream of the compressor;

[0017] - the recovery line comprises a plurality of compressors connected in series, the first end of the bypass line being connected to the recovery line downstream of an intermediate compressor, i.e. upstream of the last compressor of the plurality of compressors connected in series;

[0018] - the compressor is configured to supply a gas flow to the bypass line at a pressure greater than the pressure of the liquid sucked at the suction end and supplied to the subcooling circuit;

[0019] - the device comprises a mixing unit for mixing the boil-off gas into the subcooling circuit, the mixing unit being located, for example, at the junction between the second end of the bypass line and the subcooling circuit, the mixing unit comprising at least one of the following: an indirect heat exchanger with an injection portion, a gas injector for injecting into a liquid, a static mixer, an upstream injector, a filtering system, a condensation tank with random packing or structured packing;

[0020] - the bypass line comprises a precooling unit exchanging heat with the boil-off gas being conveyed towards the subcooling circuit, the precooling unit being configured, for example, to cool the conveyed boil-off gas flow to an intermediate temperature between the temperature of the boil-off gas in the recovery line and the temperature of the liquefied gas;

[0021] - the recovery line comprises a heat exchanger capable of exchanging heat between boil-off gas in the recovery line and boil-off gas in the bypass line;

[0022] - the bypass line comprises a bypass line and a set of valves for controlling the flow rate of boil-off gas in the bypass line that is allowed to flow through the heat exchanger on the recovery line;

[0023] - The suction end comprises a suction pump.

[0024] The present invention also relates to a liquefied gas storage device, such as a liquefied gas storage device for liquefied natural gas, such as a ship carrying liquefied gas, the liquefied gas storage device comprising at least one liquefied gas tank and a device for keeping the fluid contained in the tank at a low temperature, the low temperature maintaining device having any of the above or following characteristics.

[0025] The present invention also relates to a method for maintaining a liquefied gas reservoir at a low temperature using an apparatus according to any of the preceding items, the method comprising pumping liquefied gas from a low-temperature reservoir, cooling the pumped liquefied gas, and reinjecting the cooled liquefied gas into the reservoir, the method comprising the steps of recovering boil-off gas from the reservoir and injecting and mixing the boil-off gas into the pumped liquefied gas before cooling the pumped liquefied gas.

[0026] Since the subcooler (refrigerator) is preferably configured so that the temperature of the fluid to be cooled never falls below the initial temperature of the subcooled liquid, this makes it possible to increase the temperature of the fluid at the input of the subcooling circuit by injecting boil-off gas to prevent heavy hydrocarbons from crystallizing in the heat exchanger 6 .

[0027] According to other possible features, the injection and mixing steps are configured to increase the temperature of the pumped liquefied gas by a given value before cooling and / or to keep the temperature of the cooled liquefied gas below a given threshold and / or to maintain the temperature of the stored or pumped liquefied gas.

[0028] The invention may also relate to any alternative device or method comprising any combination of the above or below features falling within the scope of the claims.

[0029] Other particular features and advantages will become apparent from a reading of the following description provided with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention will be better understood by reading the following description, which is given by way of example only and with reference to the accompanying drawings, in which:

[0031] Figure 1 is a schematic diagram showing an example of the structure and operation of the device according to the first embodiment of the present invention;

[0032] Figure 2 is a schematic diagram showing an example of the structure and operation of an apparatus according to a second embodiment of the present invention;

[0033] Figure 3 is a schematic diagram showing an example of the structure and operation of an apparatus according to a third embodiment of the present invention;

[0034] Figure 4 is a schematic diagram showing an example of the structure and operation of an apparatus according to a fourth embodiment of the present invention.

[0035] The same reference numerals refer to the same elements throughout the drawings. DETAILED DESCRIPTION

[0036] In this detailed description, the following embodiments are examples. Although the description relates to one or more embodiments, this does not mean that these features are only applicable to a single embodiment. The various features of different embodiments may also be combined and / or interchanged to provide other embodiments.

[0037] As shown, the device 1 for keeping a liquefied gas reservoir 2 at low temperature may be used, for example, for keeping a liquefied natural gas tank, for example on board a ship, at low temperature and / or pressurized.

[0038] The device 1 comprises a low temperature refrigerator 3 and subcooling circuits 4, 5, wherein the subcooling circuits 4, 5 comprise a set of pipelines.

[0039] The subcooling circuit 4, 5 comprises at least one suction end 4, which is intended to be located in the lower part of the liquefied gas reservoir 2 and is configured to suck the liquefied gas. As shown in the figure, the suction end 4 preferably comprises a suction pump 17.

[0040] The subcooling circuit 4, 5 further comprises a heat exchanger 6 which exchanges heat between the suction subcooling circuit 4, 5 and the refrigerator 3. The heat exchanger 6 is preferably located outside the reservoir 2.

[0041] The refrigerator may in particular comprise or consist of a cryogenic liquefier or refrigerator in which a circulating gas (helium, nitrogen or any other pure gas or mixture) undergoes a thermodynamic cycle (compression, cooling, expansion, heating) so as to generate a cooling power at at least one end that can be transferred by heat exchange. For example, the refrigerator is a reverse Brayton cycle refrigerator, more specifically a turbo-Brayton refrigerator, which uses a turbine (connecting at least one compressor on a single shaft and at least one turbine on bearings and a magnetic motor). The subcooling circuit 4, 5 comprises at least one injection end 5, 7 configured to inject the fluid cooled in the heat exchanger 6 into the reservoir 2.

[0042] In the example shown, the subcooling circuit 4, 5 comprises two injection ends 5, 7. The first end opens into the upper part of the reservoir in the form of one or more nozzles to enable the cooled fluid to be injected into the gas phase of the reservoir 2, thereby recondensing the vapor and controlling the pressure in the reservoir 2.

[0043] The second end opens, for example, into the lower part of the reservoir 2 to cool the liquid phase.

[0044] According to the invention, an ejector (injector) at the bottom of the reservoir 2 preferably returns the liquefied gas and mixes it in the liquid phase. The injected liquid is no longer subcooled but is at the same temperature as the liquid in the reservoir 2.

[0045] The device 1 also includes a boil-off gas recovery line 8, the upstream end of which is connected to the upper part of the reservoir 2 and is configured to recover the boil-off gas. The recovery line 8 preferably includes at least one compression unit 11 (usually at least one compressor) for the recovered boil-off gas. The recovery line 8 includes at least one downstream end 18 located downstream, and the downstream end 18 is intended to be connected to a consumer of the boil-off gas, such as a burner and / or a motor. This compression 11 makes it possible to maintain a constant pressure in the reservoir 2 and supply gas to the motor. For example, excess combustible boil-off gas can be delivered to a combustion torch.

[0046] The device 1 comprises a bypass line 9 and a set of valves 10 configured to enable the transfer of boil-off gas from the recovery line 8 to the subcooling circuits 4, 5. The bypass line 9 has a first end connected to the recovery line 8, preferably downstream of the compression unit 11, and a second downstream end connected to the subcooling circuits 4, 5 upstream of the heat exchanger 6. The set of valves comprises, for example, a flow control valve 10 on the bypass line 9.

[0047] This makes it possible to avoid clogging by injecting the extracted boil-off gas, for example after compression, for example at ambient temperature.

[0048] This makes it possible to inject relatively hot gas upstream of cooling by the refrigerator / liquefier. This gas brought by the bypass line 9 can be mixed with the cryogenic liquid stream drawn from the reservoir via the suction line 4 of the subcooling circuit.

[0049] The pressure of the extracted gas mixed with the liquid flow is preferably at least greater than the delivery pressure of the liquid suction pump 17 located at the bottom of the cryogenic fluid reservoir 2 .

[0050] As shown, the device 1 may include a mixing unit 12 for vaporizing gas in the subcooling circuit 4, 5. The mixing unit 12 is configured to partially or completely mix the gas into the liquid, and for example, the mixing unit is located at the junction between the downstream end of the bypass line 9 and the subcooling circuit 4, 5. The mixing unit 12 includes, for example, at least one of the following: an indirect heat exchanger with an injection portion, a gas injector injected into the liquid, a static mixer, an upstream injector, a filtration system, a condensation tank with random packing or structured packing, or any other suitable unit or a combination of several of these technologies.

[0051] The flow control valve 10 is, for example, a controlled valve which may be configured to transmit the boil-off gas flow to the subcooling circuit 4, 5 to increase the temperature of the fluid entering the heat exchanger 6 by a given value, for example in the range of 5 to 25°C.

[0052] For example, the flow control valve 10 can be configured to transfer the boil-off gas flow to the subcooling circuit 4, 5 to keep the temperature of the fluid entering the heat exchanger 6 below the saturation temperature of the liquefied gas. This keeps the mixture in the liquid phase. A temperature margin can be provided, for example 2°C below the saturation temperature, to ensure that no gas bubbles enter the heat exchanger 6.

[0053] For example, the gas flows mixed upstream of the heat exchanger 6 can be controlled by calculating the saturation temperature of the fluid (the bubble point temperature is the temperature at which the first vapor bubble is generated).

[0054] The saturation temperature may be based on the typical composition of the stored fluid.

[0055] The saturation temperature can be adjusted according to a correlation, for example, via a pressure parameter. This makes it possible to control the injection of the vaporized gas via the flow control valve 10 until the output temperature of the mixer 12 is a temperature with a safety margin relative to the saturation temperature (the output temperature of the mixer 12 is equal to the saturation temperature of the fluid minus the safety margin).

[0056] Alternatively or in combination, the flow control valve 10 may be controlled to keep the temperature of the fluid flowing out of the heat exchanger 6 above a given value, for example above -160°C, and / or at a value equal to the temperature of the liquefied gas in the reservoir, and / or at a value equal to the temperature of the liquefied gas pumped at the suction end 4.

[0057] For example, the temperature of the fluid may be measured at the output of the pump 17 and / or in the reservoir 2. The flow rate may be regulated by the flow control valve 10 to ensure that the temperature of the fluid at the output of the cooling heat exchanger 6 is equal to the temperature of the liquid in the reservoir 2.

[0058] The pressure increase in the pumped liquid raises its saturation point. This enables the gas to fully or partially dissolve in the cryogenic liquid upstream of the liquefier.

[0059] This dissolution of the vaporized gas in the liquid is caused by the increase in temperature of the cryogenic liquid.

[0060] The amount of gas injected via the bypass line 9 makes it possible to selectively control the temperature at the input and / or output of the chiller (the input and / or output of the heat exchanger 6). This control can be achieved by a single flow control valve 10. Thus, the temperature of the fluid to be cooled can be measured at the input and / or output of the heat exchanger 6 by one or more suitable temperature sensors 19.

[0061] The refrigerator 3 reduces the temperature of the liquid or the resulting gas / liquid mixture and then returns it to the reservoir 2 (either at the reservoir bottom and / or in the upper part via one or more spray bars or nozzles).

[0062] The temperature of the fluid at the output of the cooling heat exchanger 6 is thus controlled so that no or less solidification occurs in the heat exchanger 6. The temperature is therefore at least equal to the initial temperature of the cryogenic liquid pumped from the reservoir 2. The amount of gas injected via the bypass line 9 can also regulate the pressure drop inside the heat exchanger 6.

[0063] The device 1 can also be used in a “hybrid” mode, ie combining, on the one hand, liquefaction of the boil-off gas for recovery, compression and reinjection, and, on the other hand, partial subcooling of the cryogenic liquid before its return to the reservoir 2 .

[0064] Alternatively, the device 1 can be operated in a subcooling mode, in which the injection of relatively hot boil-off gas via the bypass line 9 is stopped (valve 10 closed), or in a liquefaction mode by injecting boil-off gas via the bypass line 9 (valve 10 open).

[0065] This provides a flexible system that offers two operating modes. Switching from one mode to the other can be arbitrarily decided by the operator, for example, according to the risk of blockage of the heat exchanger 6 and / or automatically decided by detection or prediction (intelligence) by detecting blockage (increase in terminal pressure difference of the heat exchanger 6, temperature drop, etc.).

[0066] Figure 2 The examples in Figure 1 The embodiment in FIG. 4 differs in that the bypass line 9 comprises a precooling unit 13 which exchanges heat with the boil-off gas being conveyed towards the subcooling circuit 4, 5. The precooling unit 13 may, for example, be configured to cool the conveyed boil-off gas flow to an intermediate temperature between the temperature of the boil-off gas in the recovery line 8 and the temperature of the liquefied gas pumped from the reservoir 2.

[0067] This makes it possible to optimize or increase the amount of compressed gas that can be injected at an intermediate temperature between the temperature of the cryogenic liquid and the ambient temperature via the external pre-cooling unit 13. For example, the pre-cooling unit 13 may comprise or consist of at least one of the following: a refrigeration cycle using a refrigerant fluid, a compression system and an expansion system based on a valve, an orifice or a turbine.

[0068] Figure 3 The examples in Figure 1 The embodiment in FIG. 1 is different in that the recovery line 8 includes a heat exchanger 16 that enables heat exchange between the boil-off gas in the recovery line 8 and the boil-off gas in the bypass line 9. For example, the bypass line 9 includes a bypass line 14 and a set of valves 15 for controlling the flow rate of the boil-off gas in the bypass line 9 that is allowed to flow through the heat exchanger 16 on the recovery line 8.

[0069] This makes it possible to precool the boil-off gas by recovering cooling power from the boil-off gas extracted from the reservoir 2 upstream of the compression.

[0070] One or more control valves may be used to selectively control the temperature of the gas at the input of the compression unit, the temperature of the fluid at the input of the chiller (entering the heat exchanger 6), or the temperature of the fluid at the output of the heat exchanger 6. Such control may be used to maximize the recovered cooling power while ensuring proper operation of the compressor 11 and preventing the formation of solids in the heat exchanger 6 of the chiller 3. This makes it possible to optimize / increase the amount of compressed boil-off gas that can be injected through the bypass line 9.

[0071] Figure 4 The examples in Figure 1 The embodiment in FIG. 2 is different in that the recovery line 8 comprises a plurality of compressors 11 connected in series, and a first upstream end of the bypass line 9 is connected to the recovery line 8 downstream of the intermediate compressor 11, ie upstream of the last compressor in the series.

[0072] This means that the boil-off gas is recovered at the output of the first or subsequent compression stage, rather than at the output of the last compressor. However, the pressure of the recovered gas is preferably greater than the pressure of the liquid pumped from the reservoir with which it is mixed. The temperature of the boil-off gas at the intermediate compression stage is relatively lower than the temperature at the output of the last compressor. The amount of boil-off gas that can be mixed with the liquid can be greater than Figure 1 The amount in the embodiment in the embodiment. This embodiment can also replace Figure 2 The pre-cooling unit 13 of the embodiment.

[0073] The device thus enables optimized management of boil-off gas and cryogenic maintenance (particularly subcooling) of liquefied gas reservoirs, for example for methane, without generating solid deposits in the cooling heat exchanger 6. The invention makes it possible to avoid or limit performance degradation in the device.

[0074] The boil-off gas injected upstream of the heat exchanger 6 of the refrigerator 3 heats the liquid before it cools. The refrigerator 3 then brings the mixture to the temperature of the fluid in the reservoir 2, for example.

[0075] The extracted and mixed boil-off gases 9 are fully or partially liquefied when they are returned to the reservoir 2. The lowest temperature reached by the fluid in the heat exchanger 6 does not allow the freezing conditions to be reached.

[0076] The described solution enables conversion by changing a conventional subcooling system to a direct reliquefier in the presence of heavy hydrocarbon contaminants. The solution prevents the heavy hydrocarbons from crystallizing during the cooling process.

Claims

1. A device for keeping a liquefied gas tank (2) at low temperature, the liquefied gas tank being, for example, a liquefied gas tank for liquefied natural gas, the device comprising: A cryogenic refrigerator (3); a subcooling circuit (4, 5) comprising a set of pipelines, the subcooling circuit (4, 5) comprising a suction end (4) intended to be located in the lower part of a liquefied gas reservoir (2) and configured to pump liquefied gas; a heat exchanger (6) for exchanging heat between the fluid pumped by the subcooling circuit (4, 5) and the refrigerator (3), the subcooling circuit (4, 5) comprising at least one injection end (5, 7), the at least one injection end configured to inject the fluid cooled in the heat exchanger (6) into the reservoir (2), the device (1) also comprising a recovery line (8) of the boiled gas, the recovery line having a nozzle intended to be connected to the reservoir (2) The upper part is to recover the upstream end of the boil-off gas, the recovery line (8) includes a downstream end (18) intended to be connected to a consumer of the boil-off gas, such as a burner and / or a motor, the device (1) includes a bypass line (9) and a set of valves (10), the bypass line and the set of valves are configured to enable the boil-off gas to be transferred from the recovery line (8) to the subcooling circuit (4, 5), the bypass line (9) having a first end connected to the recovery line (8) and a second end connected to the subcooling circuit (4, 5), characterized in that the second end of the bypass line (9) is connected to the subcooling circuit (4, 5) upstream of the heat exchanger (6).

2. The device according to claim 1, characterized in that The set of valves (10) includes a flow control valve on the bypass line (9).

3. The device according to claim 2, characterized in that The flow control valve (10) is a controlled valve configured to transmit the boil-off gas flow to the subcooling circuit (4, 5) to increase the temperature of the fluid entering the heat exchanger (6) by a given value, for example in the range of 5°C to 25°C.

4. The device according to claim 2 or 3, characterized in that The flow control valve (10) is a controlled valve configured to transmit the boil-off gas flow to the subcooling circuit (4, 5) to maintain the temperature of the fluid entering the heat exchanger (6) below the saturation temperature of the liquefied gas.

5. The device according to any one of claims 2 to 4, characterized in that The flow control valve (10) is a controlled valve configured to transmit the boil-off gas flow to the subcooling circuit (4, 5) to keep the temperature of the fluid flowing out of the heat exchanger (6) above a given value, for example above -160°C, and / or at a value equal to the temperature of the liquefied gas in the reservoir, and / or at a value equal to the temperature of the liquefied gas sucked at the suction end (4).

6. The device according to any one of claims 1 to 5, characterized in that The recovery line (8) comprises at least one compressor (11), and a first end of the bypass line (9) is connected to the recovery line (8) downstream of the compressor (11).

7. The device according to claim 6, characterized in that The recovery line (8) includes a plurality of compressors (11) connected in series, and a first end of the bypass line (9) is connected to the recovery line (8) downstream of the intermediate compressor (11), that is, upstream of the last compressor among the plurality of compressors connected in series.

8. The device according to claim 6 or 7, characterized in that The compressor (11) is configured to supply a gas flow to the bypass line (9) at a pressure greater than the pressure of the liquid sucked at the suction end (4) and delivered to the subcooling circuit (4, 5).

9. The device according to any one of claims 1 to 8, characterized in that The device comprises a mixing unit (12) for mixing the boil-off gas into the subcooling circuit (4, 5), the mixing unit (12) being located, for example, at the junction between the second end of the bypass line (9) and the subcooling circuit (4, 5), the mixing unit (12) comprising at least one of the following: an indirect heat exchanger with an injection portion, a gas injector for injecting into a liquid, a static mixer, an upstream injector, a filtering system, a condensation tank with random packing or structured packing.

10. The device according to any one of claims 1 to 9, characterized in that The bypass line (9) comprises a pre-cooling unit (13) which exchanges heat with the boil-off gas being transported towards the subcooling circuit (4, 5), the pre-cooling unit (13) being configured, for example, to cool the transported boil-off gas flow to an intermediate temperature between the temperature of the boil-off gas in the recovery line (8) and the temperature of the liquefied gas.

11. The device according to any one of claims 1 to 10, characterized in that The recovery line (8) includes a heat exchanger (16) capable of exchanging heat between the boil-off gas in the recovery line (8) and the boil-off gas in the bypass line (9).

12. The device according to claim 11, characterized in that The bypass line (9) comprises a bypass line (14) and a set of valves (15) for controlling the flow rate of boil-off gas in the bypass line (9) that is allowed to flow through the heat exchanger (16) on the recovery line (8).

13. The device according to any one of claims 1 to 12, characterized in that The suction end (4) comprises a suction pump (17).

14. A liquefied gas storage device, such as a liquefied gas storage device for liquefied natural gas, such as a ship carrying liquefied gas, the liquefied gas storage device comprising at least one liquefied gas tank (2) and a device for keeping the fluid contained in the tank at a low temperature, the device (1) for keeping the low temperature being a device according to any one of the preceding claims.

15. A method for maintaining a liquefied gas reservoir (2) at a low temperature using an apparatus according to any one of claims 1 to 13, the method comprising pumping liquefied gas from a low-temperature reservoir, cooling the pumped liquefied gas, and reinjecting the cooled liquefied gas into the reservoir, the method comprising the steps of recovering boil-off gas from the reservoir and injecting and mixing the boil-off gas into the pumped liquefied gas before cooling the pumped liquefied gas.

16. The method according to claim 15, characterized in that The steps of injecting and mixing are configured to increase the temperature of the pumped liquefied gas by a given value before cooling and / or to maintain the temperature of the cooled liquefied gas below a given threshold and / or to maintain the temperature of the stored or pumped liquefied gas.

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