METHOD FOR EXPANSION AND STORAGE OF A STREAM OF LIQUIDATED NATURAL GAS FROM A NATURAL GAS LIQUIDATION PLANT AND ASSOCIATED PLANT

Description

[0001] The present invention relates to a method for decompression and storage of a stream of liquefied natural gas from a natural gas liquefaction plant, comprising the following steps: flash expansion of the liquefied natural gas stream in an expansion device to form an expanded liquefied natural gas stream; bringing the expanded liquefied natural gas stream into an end-of-flash tank; recovery, at the bottom of the end-of-flash tank, of a liquid stream of liquefied natural gas; conveying the liquid stream of liquefied natural gas into at least one liquefied natural gas tank; withdrawal, at the top of the end-of-flash tank, of a gaseous stream of flash gas; recovery, at the top of the liquefied natural gas tank, of a gaseous stream of evaporation gas; mixing of the gaseous stream of flash gas and the gaseous stream of evaporation gas to form a mixed gas stream; compression of the mixed gas stream in at least one compression unit to form a compressed combustible gas stream.

[0002] Such a process is intended in particular to be implemented in floating liquefied natural gas production facilities, or in land-based liquefaction facilities, with a reduced footprint.

[0003] In currently operating liquefied natural gas (LNG) plants, natural gas is condensed and subcooled at high pressure before undergoing flash expansion to atmospheric pressure. The resulting LNG can then be stored at atmospheric pressure and a cryogenic temperature, typically around -160°C.

[0004] The expansion is carried out either directly at the liquefied natural gas storage tank, or in a dedicated unit, for example a flash gas recovery unit.

[0005] In such a unit, the steam generated by the expansion is recovered, then compressed in a dedicated compressor to form a stream of combustible gas, or to be recycled within the liquefaction train.

[0006] Furthermore, another stream of vapor is generated in the liquefied natural gas storage tank, due to the pressure difference between the liquid directly from the expansion and that present in the storage tank and / or due to the heating of the liquefied natural gas during its transport to the tank.

[0007] A gaseous stream of evaporation gas from the tank is therefore recovered and compressed in another dedicated compressor, to form a combustible gas stream or to be recycled within the unit, particularly when the unit is a floating unit.

[0008] Such a process is not entirely satisfactory, particularly in a floating environment. Indeed, implementing the process requires several separate compressors, often at least three, which is particularly bulky, heavy, and increases the fixed and variable costs of the installation.

[0009] To overcome this problem, DE102010062050 describes a process in which the flash gas stream and the evaporation gas stream are mixed and then jointly compressed in a common compressor to form the combustible gas stream.

[0010] This process reduces the installation's footprint and lowers implementation costs. However, the process is not fully optimized in terms of efficiency and liquefied natural gas recovery.

[0011] US 2008 / 0066493, US 3 690 114, US 4 229 195 and US 2011 / 0094262 describe processes in which an evaporation gas stream from transfer into an LNG tank is recovered.

[0012] US2004 / 0065113 describes a process in which a gaseous stream of flash gas is recovered and undergoes a thermal cycle.

[0013] One aim of the invention is therefore to obtain a particularly compact and economical process for recovering flash gases and evaporation gases from a natural gas liquefaction plant by using one or more compressors dedicated to the two functions.

[0014] For this purpose, the invention relates to a method according to claim 1.

[0015] In particular embodiments, the process according to the invention comprises one or more of the features of claims 2 to 9 or the following feature(s), taken individually or in any technically feasible combination: the molar flow rate of the first part of the treated natural gas stream is less than 10% of the molar flow rate of the de-expanded liquefied natural gas stream from the de-expansion device.

[0016] The invention also relates to a facility for reducing and storing a stream of liquefied natural gas from a natural gas liquefaction facility, according to claim 10.

[0017] According to particular embodiments, the installation according to the invention comprises one or more of the features of claims 11 to 14, taken individually or in any technically possible combination. The first flow consists of the entire expanded bypass stream; it includes: a downstream separator tank, a sampling assembly, at the head of the downstream separator tank, for the first flow in gaseous form, and for reintroducing the first flow into the mixing gas stream and / or into at least one of the evaporation gas streams and the flash gas streams, upstream of the compressor; a recovery assembly, at the foot of the downstream separator tank, for a second liquid bypass stream, and for introducing the liquid bypass stream into the expanded liquefied natural gas stream, upstream of the end-of-flash tank; the downstream heat exchanger is suitable for heat exchange between the first flow and at least part of a treated gas stream intended for liquefaction; it includes: a bypass assembly for a recirculation stream from the compressed bypass stream; The invention will be better understood upon reading the following description, given solely by way of example, and made with reference to the attached drawings, in which: there figure 1 is a synoptic diagram of a first installation intended for the implementation of a first process according to the invention; the figures 2 , 4 And 6 These are synoptic diagrams of variant installations intended for implementing variant processes according to the invention. figures 3 And 5 are synoptic diagrams of variant installations which are not processes according to the invention.

[0018] Throughout this text, the same references will be used to refer to a current flowing in a pipe and the pipe that carries it. The terms "upstream" and "downstream" generally extend from the normal direction of fluid flow.

[0019] Furthermore, unless otherwise stated, the percentages quoted are molar percentages, and the pressures are given in absolute bars.

[0020] The additional turbines described drive compressors, but can also drive variable frequency electric generators whose electricity produced can be used in the grid via a frequency converter.

[0021] Air currents with a temperature above ambient are described as being cooled by air-cooled condensers. Alternatively, water-based heat exchangers, for example using fresh water or seawater, can be used.

[0022] The ambient temperature around the installation is not significant with regard to the invention and can be between 15°C and 35°C.

[0023] A first installation 10 for the pressure reduction and storage of liquefied natural gas from a natural gas liquefaction installation 12 is schematically illustrated by the figure 1 .

[0024] The installations 10, 12 are advantageously supported by a structure 14 located on the surface of a body of water, such as a sea, a lake, an ocean, or a river. The structure 14 is, for example, a floating barge and constitutes a floating natural gas liquefaction unit (FLNG).

[0025] The liquefaction installation 12 is not described here in detail. It includes, as is known, a natural gas processing unit 16, suitable for producing a treated gas free from compounds capable of solidifying during liquefaction, and a treated gas liquefaction unit 18, comprising at least one system (not shown) for cooling, liquefying, and subcooling the treated gas 20, suitable for producing a stream 22 of liquefied natural gas under pressure.

[0026] The pressure reduction and storage installation 10 includes a pressure reduction device 24 for the pressurized liquefied natural gas stream 22, comprising here a dynamic expansion turbine 25 and a flash-off capacity, in this particular example a flash-off tank 26. It also includes at least one liquefied natural gas recovery tank 28, and a compression unit 30, suitable for recovering and compressing both the flash gas from the tank 26 and the vaporization gas from the tank(s) 28, to form a compressed combustible gas stream 32.

[0027] According to the invention, the installation 10 further comprises, a downstream compressor 34, intended to compress a bypass stream 36 taken from the compressed fuel gas stream 32, and at least one dynamic expansion turbine 38, suitable for expanding the bypass stream 36.

[0028] In the example shown on the figure 1 , the installation 10 further includes a downstream heat exchanger 40 and an additional heat exchanger 41 intended for the liquefaction of at least part of the treated gas 20, using the cold produced during the dynamic expansion of the bypass stream 36 in the turbine 38.

[0029] As an alternative or supplement, as described below on the figure 3 , the exchangers 40 and 41 are intended for the cooling and at least partial liquefaction of a portion of the bypass stream 36, when an excess of flash gas and / or evaporation gas is present in the compressed combustible gas stream 32.

[0030] A first method according to the invention for the decompression and storage of the liquefied natural gas stream 22, implemented in the installation 10, will now be described.

[0031] Initially, a stream of liquefied natural gas 22 under pressure is produced by the installation 12.

[0032] The liquefied natural gas stream 22 has a pressure, for example, greater than 60 bar, and can be between 40 bar and 80 bar.

[0033] The 22 stream is subcooled. The temperature of the liquefied natural gas 22 stream is typically below -150 °C but can range between -140 °C and -160 °C.

[0034] Current 22 advantageously has a methane molar content greater than 80%, and a C4+ molar content less than 5%.

[0035] The molar flow rate of the liquefied natural gas stream 22 is, for example, greater than 10000 kmol / h.

[0036] The liquefied natural gas stream 22 is conveyed to the dynamic expansion turbine 25 of the expansion device 24 to undergo a flash expansion and form a stream 42 of expanded liquefied natural gas.

[0037] The pressure of the de-expanded liquefied natural gas stream 42 is for example less than 7 bar, in particular between 6 bar and 12 bar.

[0038] The expansion of stream 22 results in the formation of residual flash gas in stream 42 downstream of the final expansion valve. The molar content of flash gas in stream 42 is, for example, greater than 5% and is typically between 4% and 10%.

[0039] The current 42 is then introduced into the end-of-flash balloon 26, to recover, at the foot of the balloon 26, a liquid flow 46 of liquefied natural gas, and at the top of the balloon 26, a gaseous flow 48 of flash gas.

[0040] The liquid flow 46 is then conveyed to a storage tank 28. In the example shown on the figure 1 , the flow 46 is pumped through a pump 50. Alternatively, it flows by gravity into the reservoir 28, without being pumped.

[0041] During its transport and introduction into the tank 28, a residual evaporation gas ("boil off gas" in English) is formed from the liquid stream 46, notably by heating the liquid stream 46 in the transport lines, by heat inputs from the tank(s) 28 and / or under the effect of a pressure difference between the tank 26 and the tank 28.

[0042] A gaseous stream 52 of evaporation gas is recovered at the head of the tank 28. The gaseous stream of evaporation gas 52 is heated in the downstream heat exchanger 40, for example to a temperature above -60 °C.

[0043] The flash gas stream 48 is heated in the additional heat exchanger 41, for example to a temperature above -60°C.

[0044] It is then mixed with the evaporation gas stream 52 to form a mixed gas stream 54.

[0045] The gas flow 48 represents between 30 molar percent and 80 molar percent of the mixed gas stream 54.

[0046] The mixed gas stream 54 is then introduced into the compression device 30 to form a compressed combustible gas stream 32.

[0047] In the example shown on the figure 1 , the current 54 passes successively through a first compressor 56, a first air-cooled heat exchanger or a water heat exchanger 58 to be cooled to ambient temperature, a second compressor 60, then a second heat exchanger 62 to be cooled again to ambient temperature or water temperature.

[0048] The pressure of the compressed combustible gas stream 32 is for example greater than 25 bar and is in particular between 5 bar and 70 bar.

[0049] In one particular example, the composition of stream 32 is typically made up of 15 molar percent nitrogen and 85 molar percent methane.

[0050] The compressed combustible gas stream 32 is then recovered for use as fuel in the installation 12, or as a make-up fluid in this installation 12.

[0051] A bypass stream 36 is taken from the fuel gas stream 32. The molar flow rate of the bypass stream 36 is, for example, greater than 10% of the molar flow rate of the fuel gas stream 32 from the compression device 30, and is in particular between 10% and 100% of this flow rate.

[0052] The bypass stream 36 is then compressed in the compressor 34, then cooled to ambient temperature in the air-cooled heat exchanger or water heat exchanger 64, to form a compressed bypass stream 66.

[0053] The pressure of the compressed bypass stream 66 is, for example, 30 bar higher than the pressure of the stream 32.

[0054] The current 66 is then introduced into the downstream heat exchanger 40 to be cooled to a temperature advantageously below -50 °C.

[0055] It is then expanded in the dynamic expansion turbine 38, down to a pressure below 2 bar and is in particular between 1.1 bar and 3 bar, to form an expanded bypass stream 68.

[0056] The temperature of current 68 is preferably below -150 °C and is in particular between -140° C and -160° C.

[0057] The relaxed bypass stream 68 is possibly at least partially liquid. In this case, the liquid content in the stream 68 is typically less than 15 mol%. Alternatively, the stream 68 remains entirely gaseous.

[0058] In this example, the entire relaxed bypass stream 68 forms a first flow 70 which is then introduced into the downstream heat exchanger 40 to be heated. The temperature of the first heated flow 71 is advantageously greater than -60 °C.

[0059] The first heated stream 71 is then reintroduced into the mixing stream 54, downstream of the end-of-flash balloon 26, and upstream of the compression device 30.

[0060] In this embodiment, at least one treated gas stream 72 from installation 12 is diverted to installation 10.

[0061] The gas stream 72 has a pressure, for example, greater than 60 bar, and specifically between 40 bar and 90 bar. The temperature of the gas stream is typically equal to the ambient temperature or pre-cooled.

[0062] The gas stream 72 has a methane molar content greater than 80%, and a C4+ molar content less than 5%.

[0063] The molar flow rate of the gas stream 72 can represent up to 10% of the flow rate of the initial natural gas charge introduced into the liquefaction plant 12.

[0064] The gas stream 72 is then separated into a first part 74 and a second part 76.

[0065] The molar flow rate of the first part 74 of the gas stream 72 constitutes, for example, between 20% and 50% molar of the gas stream 72 and the molar flow rate of the second part 76 of the gas stream 72 constitutes, for example, between 50% and 80% of the molar flow rate of the gas stream 72.

[0066] The first part 74 of the gas stream 72 is then introduced into the downstream heat exchanger 40 to be cooled and liquefied by heat exchange in particular with the relaxed bypass stream 68, to a temperature advantageously below -150 °C.

[0067] The first part 74 then passes through a control valve 78, before being mixed with the stream of de-expanded liquefied natural gas 42 from the de-expansion device 24.

[0068] The second part 76 of the gas stream 72 is introduced into the additional heat exchanger 41 to be cooled and liquefied by heat exchange with the flash gas stream 48, to a temperature advantageously below -150 °C.

[0069] The second part 76 then passes through a control valve 80, before being mixed with the stream of de-expanded liquefied natural gas 42 from the de-expansion device 24.

[0070] The implementation of the process according to the invention is therefore particularly simple since it reduces the number of pieces of equipment needed to perform a flash of the liquefied natural gas for the purpose of its storage, and to recover advantageously the flash gases and the evaporation gases produced.

[0071] In particular, a unique compression device 30 is used to compress a mixture stream 54 formed from flash gases and evaporation gases.

[0072] The use of a bypass stream 36 taken from the fuel stream 32 formed at the outlet of the compression device 30 makes it possible to obtain a very efficient thermal integration, and to take advantage of the available cooling to liquefy at least partially the gas treated in the installation 12.

[0073] The thermal integration of the bypass current 36 allows for the adjustment of cooling capacity between the different operating modes of the installation 10, between the tank filling phases and the LNG carrier loading phases.

[0074] The process according to the invention and the installation 10 enabling its implementation are therefore particularly suitable for a floating unit such as an FLNG.

[0075] In one variant, schematically represented on the figure 1 , part 90 of the evaporation gas stream is sent to other liquefaction trains. Conversely, a stream of liquefied natural gas 92 from other liquefaction trains is introduced into tank 28.

[0076] A second installation 110 according to the invention is illustrated by the figure 2 The second installation 110 differs from the first installation 10 in that it includes a downstream balloon 112, placed at the outlet of the dynamic expansion turbine 38.

[0077] The relaxed bypass stream 68 is introduced into the downstream balloon 112 to recover, at the top, the first flow 70 in gaseous form, and at the bottom, a second flow 114 in liquid form.

[0078] The molar flow rate of the second flow 114 constitutes, for example, between 10% and 15% of the molar flow rate of the relaxed bypass current 68.

[0079] As before, the first flow 70 is introduced into the downstream heat exchanger 40 to be heated by heat exchange in particular with the first part 74 of the gaseous stream 72 of treated gas.

[0080] The second stream 114 is reintroduced into the stream of de-expanded liquefied natural gas 42 coming from the expansion device 24, upstream of the end-of-flash balloon 26.

[0081] The second method according to the invention optimizes the distribution of the liquid in the downstream heat exchanger 40.

[0082] A third installation 120, intended for the implementation of a third process which is not a process according to the invention, is illustrated by the figure 3 .

[0083] Unlike the first process implemented in installation 10 described on the figure 1 , a recirculation current 122 is taken from the compressed bypass current 66.

[0084] The recirculation current 122 represents, for example, between 30% and 80% molar of the compressed bypass current 66 from the compressor 34.

[0085] The recirculation current 122 is then separated into a first part 124 and a second part 126.

[0086] The molar flow rate of the first part 124 of the recirculation current 122 constitutes, for example, between 20% and 50% molar of the recirculation current 122 and the molar flow rate of the second part 126 of the recirculation current 122 constitutes, for example, between 50% and 80% of the molar flow rate of the recirculation current 122.

[0087] The first part 124 of the recirculation stream 122 is introduced into the downstream heat exchanger 40 to be cooled, and possibly at least partially liquefied, by heat exchange in particular with the relaxed bypass stream 68, to a temperature advantageously below -150°C.

[0088] The first part 124 then passes through a control valve 128, before being mixed with the stream of de-expanded liquefied natural gas 42 from the de-expansion device 24.

[0089] The second part 126 of the bypass stream 122 is introduced into the additional heat exchanger 41, to be cooled and possibly at least partially liquefied by heat exchange with the flash gas stream 48, to a temperature advantageously below -150°C.

[0090] The second part 126 then passes through a control valve 130, before being mixed with the stream of de-expanded liquefied natural gas 42 from the de-expansion device 24.

[0091] The use of a bypass stream 36 taken from the fuel stream 32 formed at the outlet of the compression device 30 makes it possible to obtain a very efficient thermal integration, and to take advantage of the available cooling to liquefy at least partially a recirculation stream 122 from the bypass stream, when an excess of flash gas and / or evaporation gas occurs.

[0092] In a variant shown in dotted lines on the figure 3 , at least a portion 76 of the treated gas stream 72 from installation 12 is also introduced into the additional heat exchanger 41, as described above for the figure 2 .

[0093] A fourth installation 130, intended for the implementation of a fourth process according to the invention, is illustrated by the figure 4 .

[0094] This installation 130 differs from installation 10 shown on the figure 1 in that the end-of-flash flask 26 is replaced by an end-of-flash distillation column 132.

[0095] A reboiling exchanger 134 is arranged upstream of the expansion device 24 to connect the liquefied natural gas stream 22 with a reboiling stream 136 from the column 132 by heat exchange.

[0096] The implementation of the fourth method according to the invention is also analogous to that of the first method according to the invention.

[0097] A fifth installation 140, intended for the implementation of a fifth process which is not a process according to the invention, is illustrated by the figure 5 .

[0098] This installation 140 differs from the installation 120 shown on the figure 3 in that the end-of-flash flask 26 is replaced by an end-of-flash distillation column 132.

[0099] The implementation of the fifth process is also similar to that of the third process.

[0100] A sixth installation 150, intended for the implementation of a sixth process according to the invention, is illustrated by the figure 6 .

[0101] The sixth installation 150 differs from the fourth installation 130 by the insertion of an intermediate balloon 152 between the outlet of the expansion device 24 and the inlet of the distillation column 132.

[0102] The intermediate flask 152 receives the stream of decompressed liquefied natural gas 42 and separates it into a head stream 154, mixed with the gaseous stream 48 of flash gas, and a foot stream 156, introduced into the reboiling exchanger 134 before reaching the distillation column 132.

[0103] This installation 150 is beneficial for helium recovery in the case where the gas stream 154 is rich in helium, typically consisting of at least 25% helium, and can therefore be advantageously sent to a helium purification installation.

[0104] In variants of each of the installations 120 to 150, a downstream balloon 112 is provided to separate the relaxed bypass current 68, as described in the second method according to the invention.

[0105] In a variant of the installations described above, the dynamic expansion turbine 25 of the expansion device 24 is replaced by a static expansion valve. The liquefied natural gas stream then undergoes static, rather than dynamic, expansion in the expansion device 24.

[0106] The process according to the invention and the corresponding installation are therefore particularly suitable for managing the significant variations in temperature and flow rate of the evaporation gas flow 52 from the tank 28 between the phases of loading a methane tanker by emptying the tank and the phases of filling the tank.

[0107] As mentioned above, the thermal integration of the bypass stream 36 with the evaporation gas stream 52 is used to adjust the required cooling, and to vary the relative flow rates of the fuel gas stream 32 and the bypass stream 36.

[0108] This is achieved without having to modify operating parameters for the liquefaction of natural gas, particularly at the level of the main liquefaction cycles.

Claims

1. Method for expanding and storing a stream (22) of liquefied natural gas from a natural gas liquefaction plant (12), comprising the following steps: - flash expanding the stream (22) of liquefied natural gas in an expansion device (24) to form a stream (42) of expanded liquefied natural gas; - bringing the stream (42) of expanded liquefied natural gas into an end-of-flash enclosure (26; 132); - recovering a liquid flow (46) of liquefied natural gas from the bottom of the end-of-flash enclosure (26; 132); - conveying the liquid flow (46) of liquefied natural gas into at least one liquefied natural gas tank (28); - collecting a gaseous flow (48) of flash gas from the top of the end-of-flash enclosure (26; 132); - recovering a gaseous flow (52) of evaporation gas from the top of the liquefied natural gas tank (28); - mixing the gaseous flow (48) of flash gas and the gaseous flow (52) of evaporation gas to form a mixed gas stream (54); - compressing the mixed gas stream (54) in at least one compression apparatus (30) to form a stream (32) of compressed fuel gas; - collecting a bypass stream (36) from the stream (32) of compressed fuel gas; - compressing the bypass stream (36) in at least one downstream compressor (34) to form a compressed bypass stream (66); - cooling the compressed bypass stream (66); - expanding the compressed bypass stream (66) to form an expanded bypass stream (68); - reheating at least one first flow (68; 70) from the expanded bypass stream (68) in at least one downstream heat exchanger (40), - reintroducing the heated first flow (68; 70) into the mixed gas stream (54) and / or into at least either the gaseous flow (52) of evaporation gas or the gaseous flow (48) of flash gas, upstream of the compression apparatus (30); characterized in that the method comprises the following steps: - introducing the gaseous flow (52) of evaporation gas into the downstream heat exchanger (40) so that it is brought into a heat exchange relationship with the first flow (70); - supplying a stream (72) of treated natural gas to be liquefied; - introducing at least a first portion (74) of the stream (72) of treated natural gas into the downstream heat exchanger (40) so that it is brought into a heat exchange relationship with the first flow (70); and - at least partially liquefying the first portion (74) of the stream (72) of treated natural gas in the downstream heat exchanger (40) by heat exchange with the first flow (68; 70).

2. Method according to claim 1, wherein the at least partially liquid expanded bypass stream (68) is introduced into a downstream separator drum (112), the method comprising the following steps: - collecting, from the top of the downstream separator drum (112), the first gaseous flow (70), and reintroducing the first flow (70) into the mixed gas stream (54) and / or into at least either the gaseous flow (52) of evaporation gas or the gaseous flow (48) of flash gas, upstream of the compression apparatus (30); - recovering, from the bottom of the downstream separator drum (112), a second bypass liquid flow (114), and introducing the bypass liquid flow (114) into the stream (42) of expanded liquefied natural gas, upstream of the end-of-flash enclosure (26; 132).

3. Method according to claim 1, wherein the entire expanded bypass stream (68) constitutes the first flow (70).

4. Method according to any of the preceding claims, wherein the compressed bypass stream (66) from the downstream compressor (34) is introduced into the downstream heat exchanger (40) so that it is brought into a heat exchange relationship with the first flow (70).

5. Method according to any of the preceding claims, comprising introducing the first portion (74) of the stream (72) of treated liquefied natural gas into the stream (42) of expanded liquefied natural gas from the flash device (24), upstream of the end-of-flash enclosure (26; 132).

6. Method according to any of the preceding claims, comprising the following steps: - separating the treated natural gas stream into the first portion (74) of the stream (72) of treated natural gas and a second portion (76) of the stream (72) of treated natural gas; - introducing the second portion (76) of the stream (72) of treated natural gas into an additional heat exchanger (41), so that it is brought into a heat exchange relationship with the flow (48) of flash gas; - liquefying the second portion (76) of the stream (72) of treated natural gas in the additional heat exchanger (41) by reheating the flow (48) of flash gas; - introducing the second portion (76) of the stream (72) of liquefied treated natural gas into the stream (42) of expanded liquefied natural gas from the flash device (24), upstream of the end-of-flash enclosure (26; 132).

7. Method according to any of the preceding claims, comprising the following steps: - bypassing a recirculation stream (122) into the compressed bypass stream (66); - liquefying at least one portion (124) of the recirculation stream (122) in the downstream heat exchanger (40) by heat exchange with the first flow (68; 70).

8. Method according to any of the preceding claims, wherein the end-of-flash enclosure (26; 132) is an end-of-flash drum (26) or an end-of-flash distillation column (132).

9. Method according to any of the preceding claims, wherein the flash device (24) comprises a dynamic expansion turbine (25).

10. Plant for expanding and storing a stream of liquefied natural gas from a natural gas liquefaction plant (12), comprising - a flash device (24) capable of expanding the stream (22) of liquefied natural gas to form a stream (42) of expanded liquefied natural gas; - an end-of-flash enclosure (26; 132) capable of receiving the stream (42) of expanded liquefied natural gas from the flash device (24); - an assembly for recovering a liquid flow (46) of liquefied natural gas from the top of the end-of-flash enclosure (26; 132); - at least one liquefied natural gas tank (28) and an assembly for conveying the liquid flow (46) of liquefied natural gas into the liquefied natural gas tank (28); - an assembly for collecting a gaseous flow (48) of flash gas from the top of the end-of-flash enclosure (26; 132); - an assembly for recovering a gaseous flow (52) of evaporation gas from the top of the liquefied natural gas tank (28); - an assembly for mixing the gaseous flow (48) of flash gas and the gaseous flow (52) of evaporation gas to form a mixed gas stream (54); - at least one compression apparatus (30) capable of compressing the mixed gas stream (54) to form a stream (32) of compressed fuel gas; - an assembly for collecting a bypass stream (36) from the stream (32) of compressed fuel gas; - at least one downstream compressor (34) for compressing the bypass stream (36) and forming a compressed bypass stream (66); - a downstream heat exchanger (40) for cooling the compressed bypass stream (66) to form an expanded bypass stream (68); - a device for expanding and, if necessary, at least partially liquefying the compressed bypass stream (66); - an assembly for introducing at least a first flow (68; 70) from the expanded bypass stream (68) into the downstream heat exchanger (40), to allow the first flow (68; 70) to be reheated, - an assembly for reintroducing the first flow (68; 70) into the mixed gas stream (54) and / or into at least either the gaseous flow (52) of evaporation gas and the gaseous flow (48) of flash gas, upstream of the compression apparatus (30); characterized in that the plant comprises: - an assembly for introducing the gaseous flow (52) of evaporation gas into the downstream heat exchanger (40) so that it is brought into a heat exchange relationship with the first flow (70); - an assembly for supplying a stream (72) of treated natural gas to be liquefied; - an assembly for introducing at least a first portion (74) of the stream (72) of treated natural gas stream into the downstream heat exchanger (40) so that it is brought into a heat exchange relationship with the first flow (70); - an assembly for at least partially liquefying the first portion (74) of the stream (72) of treated natural gas in the downstream heat exchanger (40) by heat exchange with the first flow (68; 70).

11. Plant according to claim 10, wherein the first flow (68) consists of the entire expanded bypass stream (68).

12. Plant according to claim 10 comprising: - a downstream separator drum (112), - an assembly for collecting the first gaseous flow (70) from the top of the downstream separator drum (112), and for reintroducing the first flow (70) into the mixed gas stream (54) and / or into at least either the gaseous flow (52) of evaporation gas and the gaseous flow (48) of flash gas, upstream of the compression apparatus (30); - an assembly for recovering a second bypass liquid flow (114) from the bottom of the downstream separator drum (112), and for introducing the bypass liquid flow (114) into the stream (42) of expanded liquefied natural gas, upstream of the end-of-flash drum (26; 132).

13. Plant according to any of claims 10 to 12, wherein the downstream heat exchanger (40) is capable of bringing the first flow (68; 70) into a heat exchange relationship with at least a portion (74) of a stream (72) of treated gas to be liquefied.

14. Plant according to any of claims 10 to 12, comprising: - an assembly for bypassing a recirculation stream (122) from the compressed bypass stream (66); - an assembly for introducing at least a portion (124) of the recirculation stream (122) into the downstream heat exchanger (40) to at least partially liquefy it in the downstream heat exchanger (40).