EP3344936A1

EP3344936A1 - System and method for treating gas resulting from the evaporation of a cryogenic liquid

Info

Publication number: EP3344936A1
Application number: EP16775768.1A
Authority: EP
Inventors: Mathias Ragot
Original assignee: Cryostar SAS
Current assignee: Cryostar SAS
Priority date: 2015-09-03
Filing date: 2016-09-02
Publication date: 2018-07-11
Also published as: JP6766135B2; RU2719258C2; RU2018110349A3; RU2018110349A; KR102514327B1; CN108369058B; KR20180050345A; FR3040773A1; FR3040773B1; US20180245843A1; CN108369058A; JP2018526595A; WO2017037400A1

Abstract

The invention relates to a system comprising a power supply line for at least one motor, on which line a first unit (3) for compressing said gas is located, and a bypass to a return line on which cooling means (10) and reliquefaction means (30) are located in series. The cooling means comprise a second compression unit (11, 12, 13) and a heat exchanger (17) in series. Downstream of the second compression unit (11, 12, 13), a bypass to a loop (18, 20, 21) comprises first decompression means (14). The loop joins up with the return line upstream of the second compression unit (11, 12, 13) after passing through the heat exchanger (17) in the opposite direction to the gas fraction which has not been diverted by the loop.

Description

SYSTEM AND METHOD FOR TREATING GAS FROM

EVAPORATION OF A CRYOGENIC LIQUID

The present invention relates to a system and a method for treating gas resulting from the evaporation of a cryogenic liquid.

The field of the present invention is more particularly the maritime transport of cryogenic liquids and even more particularly of Liquefied Natural Gas (LNG). However, the systems and processes that will be proposed later could also find applications in terrestrial installations.

If we consider the liquefied natural gas, it has, at room temperature, a temperature of about -1 63 ° C (or less). When shipping LNG, the latter is put in tanks on a ship. Although these tanks are thermally insulated, thermal leaks exist and the external environment brings heat to the liquid contained in the tanks. The liquid heats up and evaporates. Given the size of the tanks on an LNG carrier, depending on the thermal insulation conditions and external conditions, several tons of gas can evaporate per hour.

It is not possible to maintain the evaporated gas in the tanks of the ship for safety reasons. The pressure in the tanks would increase dangerously. So let the evaporating gas escape from the tanks. The regulations prohibit the discharge of this gas (if it is natural gas) into the atmosphere as it is. It must be burned.

To avoid losing this evaporating gas, it is also known, on the one hand, to use it as a fuel for the engines on board the ship carrying it and, on the other hand, to reliquefy it to put it back in. the reservoirs from which it comes.

The object of the present invention relates to the supply of the engines on board the ship from the gas which evaporates. When the consumption of the engines is greater than the "natural" evaporation of the gas from the tanks, it is known to take gas to vaporize it and then supply the engines. The present invention, however, relates more particularly to reliquefaction of gas which has evaporated in tanks or tanks of cryogenic liquid, and more particularly in tanks or tanks of LNG tankers, when the evaporation of the gas is greater than the consumption of the engines of the ship.

EP-2 933 183 relates to a liquefied gas treatment system for a vessel which comprises a storage tank which stores a liquefied natural gas, and an engine which uses the liquefied natural gas stored in the storage tank as a fuel. The liquefied gas processing system disclosed herein includes: a storage tank that stores a liquefied gas, an engine that uses the liquefied gas stored in the storage tank as fuel, and a fuel supply line that can vaporize the liquefied gas; liquefied gas and supply the gas generated to the engine as fuel. The engine receives a fuel gas supply that is pressurized to a low pressure.

In all the embodiments proposed herein, the gas to be reliqued is cooled before reliquefaction by the gas stream leaving the tanks before it is compressed and led to the engine (s). There is then in each case an exchanger which has the reference 21 in Figures 1 to 17.

This heat exchanger 21 creates significant pressure drops in the gas stream that evaporates from the tanks. Under certain operating conditions, the evaporated gas can therefore arrive at the compressor at a pressure below atmospheric pressure. Air can then be sucked in and mixed with the gas.

Another disadvantage of the system presented in this document of the prior art is that it does not allow to balance the production and consumption of cold. The amount of gas consumed by the engine (s) is to a large extent independent of the amount of gas that evaporates. Thus the exchange in the exchanger 21 is not adjustable depending in particular cold requirements for reliquefaction.

To reliquefier the gas that has evaporated, it is known to cool this gas to bring it back into conditions of temperature and pressure allowing it to return to the liquid phase. This intake of cold is the most often performed by heat exchange with a refrigerant circuit comprising for example a refrigerant loop such as nitrogen.

Thus, EP 1 120 615 discloses an apparatus for use on ships for recompressing pressurized steam. The recompression is performed in a closed cycle in which a working fluid is compressed in at least one compressor, is cooled in a first heat exchanger, is expanded in a turbine and is heated in a second heat exchanger, in which the compressed steam is at least partially condensed. The apparatus comprises a first subassembly comprising the second heat exchanger and a second subassembly including the first heat exchanger, the compressor and the expansion turbine. The two subsets are placed on two platforms respectively.

In WO 2014/095877, natural gas evaporating from liquefied natural gas storage tanks, typically located aboard an ocean going vessel, is compressed in a multi-stage compressor comprising compression stages . At least a portion of the stream of compressed natural gas is sent to a liquefier, typically operating in a Brayton cycle, to be reliqued. The temperature of the compressed natural gas from the final stage is reduced to less than 0 ° C by passing through a heat exchanger. The first compression stage operates as a low temperature compressor, and the resulting cold compressed natural gas is employed in the heat exchanger to effect the necessary cooling of the stream from the compression stage. Downstream of its passage through the heat exchanger, the cold compressed natural gas flows through the remaining stages of the compressor. If desired, a portion of the compressed natural gas can be used as fuel and feed the engines of the ocean-going vessel.

The presence of a refrigerant loop with nitrogen, or any other refrigerant gas distinct from the fluid to be refrigerated, involves providing specific equipment for the refrigerant. Thus, for example when a nitrogen refrigerant circuit is provided on board a ship (or elsewhere), a unit for treating (purifying) nitrogen is necessary to allow its use in the cryogenic field. It is also necessary to provide a specific tank, valves and other devices for regulating the flow of nitrogen.

The purpose of the present invention is therefore to provide an optimized system enabling a ship carrying liquefied natural gas to carry out the gas supply of an engine from natural gas evaporating from the ship's storage tanks and to reliquefy the gas that evaporated and that was not consumed in the engine. This system will not present any coolant of a nature other than that of the gas used for the motor supply and limit the pressure drop upstream of the compressor used to supply the engine. Advantageously, the cold production may be adapted to the amount of gas to reliquefier.

For this purpose, the present invention proposes a feed system from a gas resulting from the evaporation of a cryogenic liquid and from reliquefaction of this gas, said system comprising a feed line for at least one engine on which is a first compression unit of said gas and a bypass to a return line on which are successively cooling means and first expansion means.

According to the present invention, the cooling means comprise successively a second compression unit and a heat exchanger and downstream of the second compression unit a branch to a loop comprising second expansion means, and the loop joining the line back upstream of the second compression unit after having passed through the heat exchanger in the opposite direction to the gas fraction not derived by the loop.

Thus, it is proposed a mechanical cooling loop that avoids using gas evaporates tanks as a source of cold to cool a portion of the gas before liquefaction. In this way, the evaporated gas tanks can be sent directly into the first compression unit without experiencing losses (or limiting the maximum pressure losses). The operation of this cooling loop is moreover independent of the other systems around and can thus operate almost as a closed loop of another refrigerant. The expansion means make it possible to rapidly pass the fluid from a high pressure to a lower pressure and it may be each time an expansion turbine, or an expansion valve, or an orifice or any other equivalent system.

In this feed and reliquefaction system, a recycling line is advantageously provided for sending a fraction of the non-reliqued gas at the outlet of the first expansion means to the feed line for the engine upstream of the first unit. compression. Advantageously, the recycling line passes through the heat exchanger.

In the cooling unit, the bypass is preferably carried out within the heat exchanger such that the bypass gas stream is already partially cooled to enter the second expansion means thereafter.

In one embodiment of such a supply and reliquefaction system, the first expansion means comprise for example an expansion valve opening into a balloon for separating the formed liquid and the non-liquefied gas fraction. The balloon makes it possible to separate the gas and the liquid and makes it possible to treat the gas and the liquid differently downstream. In such an embodiment, it is proposed that the upper part of the balloon is connected to the heat exchanger so that the gas coming from the balloon enters the exchanger on the same side as the bypass, and that the lower part of the balloon is connected to a cryogenic liquid tank.

A particularly advantageous embodiment of the processing system provides that the second compression unit comprises a plurality of compression stages each with a compression wheel, that the second expansion means comprise an expansion turbine, and that each compression wheel and the turbine are associated with the same mechanical transmission. This embodiment makes it possible to have a compact structure. In addition, the work recovered at the level of the expansion turbine can immediately be transmitted to the compression wheels thus promoting the achievement of energy efficiency for the system. To facilitate the starting of the cooling unit, this system may further comprise means for injecting gas into the loop derived from the cooling unit. In this way, the cooling unit becomes truly autonomous and can be regulated as if it were a closed loop. The means for injecting gas into the derived loop comprise, for example, a pump for cryogenic liquid, a vaporizer and a control valve.

The present invention also relates to:

a supply and reliquefaction system as described above further comprising a collector for the recovery of the evaporated gases from a set of cryogenic liquid tanks, the collector being connected directly, that is to say in particular without intermediate device for heat exchange with another gas pipe, at the first compression unit, and

a cryogenic liquid transport vessel, in particular an LNG carrier, equipped with such a feed and reliquefaction system.

Finally, the invention proposes a method of managing a flow of gas resulting from the evaporation of a cryogenic liquid, in which:

said gas stream being compressed within a first compression unit before being sent either to a motor or to reliquefaction means,

the fraction of gas sent to the reliquefaction means passes through cooling and then expansion means and finally by a separator from which the liquid portion is sent to a cryogenic liquid tank.

According to the present invention, the cooling means are mechanical refrigeration means in which:

a flow of gas is compressed in a second compression unit, then cooled in a heat exchanger before being expanded so that a fraction of gas is reliquified,

after its compression, the gas flow is separated into a first portion of gas flow and a second portion of gas flow,

the first part of the gas flow is cooled and then sent to the relic means to be at least partially liquefied, and the second portion of the gas flow is fed into a loop in which said second gas flow portion is expanded, and then is used to cool the first portion of the gas stream before joining the gas stream to be compressed again in the gas stream; second compression unit.

In such a method of managing a gas flow resulting from the evaporation of a cryogenic liquid, it is advantageously provided that the gas resulting from the evaporation is compressed without prior heat exchange with another gas pipe. This makes it possible to limit the pressure drops before the entry of the gas into the first compression unit.

The non-liquefied gas at the outlet of the first expansion means can be driven by a recycling line upstream of the first compression unit. In this case, for better energy efficiency, the non-liquefied gas output of the first expansion means preferably passes through the heat exchanger before being compressed again in the first compression unit.

Details and advantages of the present invention will become more apparent from the description which follows, given with reference to the appended schematic drawing in which:

FIGS. 1 to 5 are each a schematic view of a cryogenic liquid reservoir associated with a gas recovery system evaporating from said reservoir for, on the one hand, the supply of at least one engine and, on the other hand, the reliquefaction of the gas not consumed by the said engine (s).

In each of the accompanying figures, a reservoir 1 is illustrated. Throughout the remainder of the description, it will be assumed that it is a tank of liquefied natural gas (or LNG) among several other similar tanks aboard an ocean-going vessel of the LNG type.

The numerical values in the description which follows are given as purely numerical examples which are purely illustrative and in no way limitative. They are suitable for handling LNG on board a ship but may vary, especially if the nature of the gas changes.

The tank 1 stores the LNG at a temperature of about -163 ° C which corresponds to the usual storage temperature of the LNG at a pressure close to atmospheric pressure. This temperature depends of course natural gas composition and storage conditions. The atmosphere around the tank 1 being at a much higher temperature than the LNG, although the tank 1 is very well insulated thermally, calories are brought to the liquid that heats and vaporizes. Since the volume of the evaporating gas is much larger than that of the corresponding liquid, the pressure in the tank 1 tends to increase as the time passes and calories are added to the liquid.

To avoid excessive pressures, evaporating gas is withdrawn as the tank 1 (and the other tanks of the vessel) and is collected from several tanks to a main pipe 2.

It is intended in the systems illustrated in the drawing to use the gas that has evaporated to supply at least one engine (not shown) on board the ship and reliquefy the surplus gas. The aim here is to avoid losing the evaporated gas and thus either to use it for the propulsion of the ship, or to recover it and send it back, in the liquid phase, into the tank 1.

To be used in a ship engine, the gas must be compressed first. This compression is then performed within a first compression unit 3 which can be, as illustrated in the drawing, multi-staged. This unit, by way of illustrative numerical example and in no way limiting, carries the pressure of the gas collected in the main pipe 2 by a pressure substantially equal to the atmospheric pressure at a pressure of the order of 15 to 20 bar (1 bar = 10 ⁵ Pa).

After this first compression step, the gas passes into an intercooler 4 in which it is cooled without substantially modifying its pressure. The gas which has been heated during its compression is at a temperature of the order of 40 to 45 ° C at the outlet of the intercooler (these values are given for illustrative purposes only).

The gas thus compressed and cooled can then be sent via an injection line 5 to an engine on board the ship. It can be a motor for the propulsion of the ship or for other uses (auxiliary generator, ...). The main pipe 2 and the injection pipe 5 form a gas supply line of the engine evaporated from the tanks 1. The gas requirements at the engine (s) of the ship are often lower than the "production" of evaporative gas in all the tanks on board the ship. The unused gas in the engine (s) is then sent to a reliquefaction unit comprising in particular a mechanical cooling unit.

The cooling unit 10 comprises at its inlet a valve 6 intended in particular to control the pressure of the gas in the injection line 5, then a main circuit and a loop which will be described below.

The main circuit allows from the gas (which is at a pressure of the order of a few bar to about 50 bar -non-limiting values-) to obtain gas at a temperature such that it goes into the liquid phase before return to the tank 1.

The main circuit of the cooling unit 10 first comprises a multi-stage compressor here comprising three successive stages with the references 1 1, 12 and 13. Each stage is formed by a compression wheel and the three compression wheels are driven by the same transmission 15 to trees and gears. The line between the compression stages in the figures symbolizes the mechanical connection between them.

After this second compression (the gas derived from the feed line having already been compressed in the first compression unit 3), the gas passes into an intercooler 16. Its pressure is then a few tens of bar, for example about 50 bar, and its temperature is again of the order of 40 to 45 ° C.

The gas thus compressed is then cooled in a multiflux exchanger 17. The gas circulates in this exchanger 17 in a first direction. Fluids circulating in the opposite direction (with respect to this first direction) and used to cool it will be described later.

At the outlet of the exchanger 17, the compressed gas cooled to a temperature of the order of -1 10 to -120 ° C. becomes liquid and is sent, always at a pressure of the order of a few tens of bar (for example about 50 bar) through an insulated conduit 22 to expansion means. In the illustrated embodiment corresponding to a preferred embodiment, an expansion valve 30 is used to further cool the reliquefied gas and lower his pressure.

After expansion through the expansion valve 30 is obtained both a methane-rich liquid and a nitrogen-rich gas (because natural gas is not only composed of methane). The separation of this liquid phase and of this gaseous phase is carried out within a balloon 40 in which the pressure is of the order of a few bar, for example between 3 and 5 bar.

The gas of the balloon 40 is preferably returned to the main pipe 2. In this way, it is mixed with the primary flow and will thus be partially used as fuel in the engine (s), or will return to the cooling unit 10. Since the gas coming from the balloon 40 is cold, it can be used to cool the compressed gas in the exchanger 17. It is therefore intended to make it circulate in the opposite direction in this exchanger 17 before returning it to the main pipe 2. by a connecting line 35.

If the gas of the balloon 40 for various reasons, especially during transient phases, can not be recycled to the main pipe 2, it is intended to send it to a flare or a combustion unit. A set of valves 31, 32 controls the delivery of gas from the balloon 40 to the main line 2 via the connecting line 35 or to a combustion unit.

The liquid recovered at the bottom of the flask 40 is for its part intended to return to the tank 1. Depending on the operating conditions, the liquid can be sent directly into the tank 1 (passage controlled by a valve 33), or using a pump 41 (passage controlled by a valve 34).

The return of the liquid from the balloon 40, directly or through the pump 41, to the tank 1 is via an insulated pipe 36.

In the cooling unit 10, as mentioned above, there is also a loop. This loop begins with a bypass line 18 which separates the gas flow downstream of the multi-stage compressor 1 1, 12, 13 into a first flow, or main flow, which corresponds to the main circuit described above, and in a second flow, or derived flow.

The bypass line 18 is preferably connected to the main circuit at the exchanger 17. The gas that enters the pipe of the Bypass 18 is at "high pressure" (about 50 bar in the given numerical example) and at an intermediate temperature between 40 ° C and -1 10 ° C.

The gas taken by the bypass line 18 is expanded within expansion means formed in the preferred embodiment retained in the drawing by an expansion turbine 14. The latter is, in the preferred embodiment illustrated in the drawing, mechanically connected to the three compression wheels corresponding to the stages 1 1, 12 and 13 of the multi-stage compressor of the cooling unit 10. The transmission 15 by shafts and gears connects the expansion turbine 14 and the compressor wheels of the multi compressor -floor. This transmission 15 is symbolized by a line connecting in the figures the expansion turbine 14 to stages 1 1, 12 and 13.

The gas is expanded, for example, to a pressure level which corresponds to its pressure level by entering the cooling unit 10, ie approximately 15 to 20 bar. Its temperature drops below -120 ° C. This flow of gas is then sent into the exchanger 17 in the opposite direction to cool the gas of the main circuit, firstly the portion 19 located downstream of the branch line 18 and then the upstream portion of this branch line 18. At the outlet of the exchanger 17, the gas regains temperatures of the order of 40 ° C. and can be reinjected into the main circuit of the cooling unit, upstream of the multi-stage compressor via a return line. .

This produces an open cooling loop which uses as gas for cooling the same gas that must be liquefied.

In the embodiment of Figure 2, with respect to the embodiment of Figure 1, it is expected to keep the gas exiting the balloon 40 in the cooling unit 10 by injecting into the return line 21 by a connecting pipe 35b rather than sending it to the manifold 2. This embodiment is to be considered in particular in cases where the first compression unit 3 does not have the capacity to treat the nitrogen-rich gas from of the ball 40.

This variant embodiment of FIG. 2 can be combined with one or more of the variants that will be described hereinafter with reference to FIGS. 3 to 5. In FIG. 3, it is planned to modify the configuration of the system downstream of the expansion turbine 14 and the exchanger 17. Instead of sending the expanded gas at the outlet of the exchanger 17 to the inlet of the first stage 1 1 of the multi-stage compressor of the cooling unit 10, it is proposed here to recycle this flow of gas either directly in the main pipe 2, or to enter it at an intermediate level in the first compression unit 3 Valves 23 and 24 make it possible to control the flow of gas which, at the outlet of the exchanger 17, is sent either to the main pipe 2 or to the first compression unit 3.

With this configuration, it is possible to obtain a pressure ratio at the expansion turbine 14 greater than that of the multi-stage compressor of the cooling unit 10.

Figure 4 illustrates the fact that the proposed system allows to power different types of engines. It is possible with the first compression unit 3 to provide different pressure levels to suit different types of engines. If for example the pressure in the injection line 5 is very high, for example greater than 250 bar, to feed a high-pressure gas injection engine, then it is also possible to supply the cooling unit 10 not to from the injection line 5 but from an intermediate stage of the first compression unit 3.

Finally, FIG. 5 illustrates means that can be implemented to facilitate the cooling of the cooling unit 10 and thus its starting. The embodiment shown in FIG. 5 allows such a start without influencing the flow of gas in the injection line 5 supplying an engine or the like. For example, when the cooling unit 10 is cooled down, the valve 6 is closed.

FIG. 5 thus provides for supplying the gas loop directly from the tank 1. For this purpose, a pump 60 makes it possible to take liquid from the reservoir 1 to bring it to an injection system 62 via a feed duct 61. Within the injection system 62, a vaporizer 63 makes it possible to pass the liquid taken from the tank 1 in the gas phase. A valve 64 is then provided to regulate the injection of the gas obtained at the outlet of the vaporizer and to control the quantity of gas injected into the loop and the This is to regulate the cooling of the cooling unit 10. FIG. 5 provides an injection at the return line 21, but another injection point could be chosen.

It may also be provided, if necessary, to take Liquefied Natural Gas (presence of an arrow) on the supply line 61.

The system proposed here thus provides an open loop of refrigerant gas corresponding to the refrigerated gas with a production of cold at two different temperatures, a temperature of about -120 ° C. at the outlet of the expansion turbine and a temperature of about -160 ° C. ° C at the outlet of the expansion valve. The system is independent of the engines on board the ship that are powered by the evaporated gas. Only from the evaporated gas, it allows, independently of any other source of external cold, to achieve liquefaction.

In the loop, the cold production is permanently adapted to the load at the reliquefaction means and can be regulated over a wide range by acting on the second compression unit. It is thus possible to adapt the production of cold necessary for reliquefaction and to achieve the energy balance of the system.

In steady state, no gas discharge, or gas combustion, is expected.

When it starts, cooling down in the cooling loop can be managed as with a closed loop. The cooling unit has no influence on the first compression unit which is also used to power the engines (or other generators). When the loop is cold, it can remain in "standby" and be used in open loop as soon as an excess of evaporated gas has to be liquefied.

The proposed system makes it possible to limit the pressure losses of the gas evaporating from the tank (s). This gas is collected and sent directly to the inlet of the first compression unit. The pressure drop is that inevitable created by the supply of gas through the main pipe. It is limited and avoids in all operating conditions of the system to have an inlet of the first vacuum compression unit.

It is also clear that the proposed system does not require a unity of nitrogen treatment or the like. Its structure is simplified by the use of a refrigerant gas of the same nature as the gas to be refrigerated and liquefied.

Of course, the present invention is not limited to the embodiments of the systems and methods described above by way of non-limiting examples but it also relates to all the variants within the scope of the skilled person within the scope of the present invention. of the claims below.

Claims

1. System for feeding an engine from a gas resulting from the evaporation of a cryogenic liquid and reliquefaction of this gas, said system comprising a supply line for at least one engine on which is located a first compression unit (3) of said gas and a bypass to a return line on which are successively cooling means (10) and first expansion means (30),

characterized in that the cooling means comprise successively a second compression unit (1 1, 12, 13) and a heat exchanger (17) and downstream of the second compression unit (1 1, 12, 13) a branch to a loop (18, 20, 21) having second expansion means (14), the loop joining the return line upstream of the second compression unit (1 1, 12, 13) after passing through the heat exchanger (17) against the non-loop gas fraction.

2. Supply and reliquefaction system according to claim 1, characterized in that it comprises a recycling line (35) for sending a fraction of the unreliquefied gas output of the first expansion means (30) to the supply line (2) for the engine upstream of the first compression unit (3).

3. Supply and reliquefaction system according to claim 2, characterized in that the recycling line (35) passes through the heat exchanger (17).

4. Supply and reliquefaction system according to one of claims 1 to 3, characterized in that the bypass is carried out within the heat exchanger (17).

5. Supply and reliquefaction system according to one of claims 1 to 4, characterized in that the first expansion means comprise an expansion valve (30) opening into a balloon (40) for separating the formed liquid and the fraction of non-liquefied gas.

6. Supply and reliquefaction system according to claim 5, characterized in that the upper part of the balloon (40) is connected to the heat exchanger (17) so that the gas coming from the balloon (40) enters the exchanger (17) on the same side as the bypass, and in that the lower part of the balloon (40) is connected to a reservoir (1) of cryogenic liquid.

7. Supply and reliquefaction system according to one of claims 1 to 6, characterized in that the second compression unit comprises a plurality of compression stages (1 1, 12, 13) each with a compression wheel, in that that the second expansion means comprise an expansion turbine (14), and in that each compression wheel and the expansion turbine (14) are associated with the same mechanical transmission (15).

8. Supply and reliquefaction system according to one of claims 1 to 7, characterized in that it further comprises means

(62) for injecting gas into the loop derived from the circuit.

9. Supply and reliquefaction system according to claim 8, characterized in that the means (62) for injecting gas into the derived loop comprise a pump (60) for cryogenic liquid, a vaporizer

(63) and a control valve (64).

10. Supply and reliquefaction system according to one of claims 1 to 9, characterized in that it further comprises a collector for the recovery of evaporated gases from a set of tanks (1) of cryogenic liquid, and in that the collector is connected directly, that is to say in particular without an intermediate heat exchange device with another gas line, to the first compression unit (3).

11. Cryogenic liquid transport vessel, characterized in that it comprises a feed and reliquefaction system according to one of claims 1 to 10.

12. Ship according to claim 1 1, characterized in that said vessel is a LNG carrier.

13. Process for managing a flow of gas resulting from the evaporation of a cryogenic liquid, in which:

the fraction of gas sent to the reliquefaction means passes through cooling means (10) and then expansion (30) and at the end by a separator (40) from which the liquid part is sent to a reservoir (1) of cryogenic liquid,

characterized in that the cooling means are mechanical refrigeration means in which:

a flow of gas is compressed in a second compression unit (1 1, 12, 13), then cooled in a heat exchanger (17) before being expanded so that a fraction of gas is relieved ,

the first part of the gas flow is cooled and then sent to the relic means to be at least partially liquefied, and

the second portion of the gas flow is fed into a loop (18, 20, 21) in which said second gas flow portion is expanded, and then is used to cool the first portion of the gas flow before joining the gas flow to be compressed again in the second compression unit (1 1, 12, 13).

14. Process for managing a gas flow resulting from the evaporation of a cryogenic liquid according to claim 13, characterized in that the gas resulting from the evaporation is compressed without prior heat exchange with another gas pipe. .

15. A method for managing a gas flow resulting from the evaporation of a cryogenic liquid according to one of claims 13 or 14, characterized in that the non-liquefied gas at the outlet of the first expansion means (30) is driven by a recycling line (35) upstream of the first compression unit (3).

16. A method for managing a gas flow resulting from the evaporation of a cryogenic liquid according to claim 15, characterized in that the non-liquefied gas leaving the first expansion means (30) passes through the exchanger (17). ) of heat before being compressed again in the first compression unit (3).