Process for expansion and storage of a flow of liquefied natural gas from a natural gas liquefaction plant, and associated plant

Abstract

The process includes the following steps: - mixing a flash gas stream (48) and an evaporation gas stream (52) to form a mixed gas stream (54); - compressing the mixed gas stream (54) in at least one compression unit (30) to form a compressed fuel gas stream (32); - taking a bypass stream (36) from the compressed fuel gas stream (32); - compressing the bypass stream (36) in at least one downstream compressor (34); - cooling and expanding the compressed bypass stream (66); - reheating at least one first stream (68; 70) from the expanded bypass stream (68) in at least one downstream heat exchanger (40); - reintroducing the reheated first stream (68; 70) into the mixed gas stream (54) upstream of the compression unit (30).

Description

[0001] The present invention relates to a method for expanding and storing a stream of liquefied natural gas from a natural gas liquefaction installation, comprising the following steps: flash expansion of the liquefied natural gas stream in an expansion device to form a stream of expanded liquefied natural gas; supplying the expanded liquefied natural gas stream into an end-of-flash capacity; recovering, at the foot of the end-of-flash capacity, a liquid stream of liquefied natural gas; conveying the liquid stream of liquefied natural gas into at least one liquefied natural gas tank; withdrawing, at the head of the end-of-flash capacity, a gaseous stream of flash gas; recovering, at the head of the liquefied natural gas tank, a gaseous stream of evaporation gas; mixing the gaseous stream of flash gas and the gaseous stream of evaporation gas to form a mixed gas stream; compressing the mixed gas stream in at least one compression device to form a compressed combustible gas stream.

[0002] Such a process is intended in particular to be implemented in floating installations for the production of liquefied natural gas, or in land-based liquefaction installations, with reduced space requirements.

[0003] In currently operating liquefied natural gas production plants, natural gas is condensed and subcooled at high pressure before undergoing flash expansion to atmospheric pressure. The resulting liquefied natural gas can be stored at atmospheric pressure and at 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 combustible gas stream, or to be recycled within the liquefaction train.

[0006] Furthermore, another stream of vapour 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 flow of evaporation gas from the tank is therefore recovered and compressed in another dedicated compressor, to form a stream of combustible gas or to be recycled within the unit, particularly when the unit is a floating unit.

[0008] This method is not entirely satisfactory, especially in a floating environment. Implementing the method requires several separate compressors, often at least three, which is particularly bulky and 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 boil-off gas stream are mixed and then jointly compressed in a common compressor to form the fuel gas stream.

[0010] Such a process reduces the footprint of the installation and reduces implementation costs. However, the process is not fully optimized in terms of yield and recovery of liquefied natural gas.

[0011] An 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 installation by using one or more compressors dedicated to the two functions.

[0012] To this end, the invention relates to a method of the aforementioned type comprising the following steps: taking a bypass stream from the compressed fuel gas stream; compressing the bypass stream in at least one downstream compressor to form a compressed bypass stream; cooling the compressed bypass stream; expanding the compressed bypass stream to form an expanded bypass stream; reheating at least a first stream from the expanded bypass stream in at least one downstream heat exchanger, reintroducing the heated first stream into the mixed gas stream and / or into at least one of the evaporation gas stream and the flash gas stream, upstream of the compression apparatus.

[0013] According to particular embodiments, the method according to the invention comprises one or more of the following characteristics, taken in isolation or in any technically possible combination: the at least partially liquid expanded bypass stream is introduced into a downstream separator tank, the method comprising the following steps: sampling, at the top of the downstream separator tank, the first stream in gaseous form, and reintroducing the first stream into the mixed gas stream and / or into at least one of the evaporation gas stream and the flash gas stream, upstream of the compression apparatus; recovering, at the bottom of the downstream separator tank, a second liquid bypass stream, and introducing the liquid bypass stream into the expanded liquefied natural gas stream, upstream of the end-of-flash capacity; the entire expanded bypass stream constitutes the first stream; the compressed bypass stream from the downstream compressor is introduced into the downstream heat exchanger to be put into heat exchange relation with the first stream;the evaporation gas flow is introduced into the downstream heat exchanger to be put into heat exchange relation with the first flow; it comprises the following steps: - supplying a treated natural gas stream intended to be liquefied; - introducing at least a first part of the treated natural gas stream into the downstream heat exchanger to be put into heat exchange relation with the first flow; - at least partial liquefaction of the first part of the treated natural gas stream in the downstream heat exchanger by heat exchange with the first flow; it comprises the introduction of the first part of the liquefied treated natural gas stream into the expanded liquefied natural gas stream from the expansion device, upstream of an end-of-flash capacity;it comprises the following steps: - separation of the treated natural gas stream into the first part of the treated natural gas stream and a second part of the treated natural gas stream; - introduction of the second part of the treated natural gas stream into an additional heat exchanger, to be put into heat exchange relation with the flash gas flow; - liquefaction of the second part of the treated natural gas stream in the additional heat exchanger by reheating the flash gas flow; - introduction of the second part of the liquefied treated natural gas stream into the expanded liquefied natural gas stream from the expansion device, upstream of the end-of-flash capacity; it also comprises the following steps: diversion of a recirculation stream into the compressed diversion stream; liquefaction of at least part of the recirculation stream in the downstream heat exchanger by heat exchange with the first stream;the end-of-flash capacity is an end-of-flash drum or an end-of-flash distillation column; the expansion device comprises a dynamic expansion turbine; the molar flow rate of the first portion of the treated natural gas stream is less than 10% of the molar flow rate of the expanded liquefied natural gas stream from the expansion device.;

[0014] The invention also relates to an installation for expanding and storing a stream of liquefied natural gas from a natural gas liquefaction installation, comprising: an expansion device capable of performing a flash expansion of the liquefied natural gas stream to form a stream of expanded liquefied natural gas; an end-of-flash capacity capable of receiving the expanded liquefied natural gas stream from the expansion device; a recovery assembly, at the foot of the end-of-flash capacity, of a liquid stream of liquefied natural gas; at least one liquefied natural gas tank and an assembly for conveying the liquid stream of liquefied natural gas into the liquefied natural gas tank; a collection assembly, at the head of the end-of-flash capacity, of a gaseous stream of flash gas; a recovery assembly, at the head of the liquefied natural gas tank, of a gaseous stream of evaporation gas; an assembly for mixing the gaseous stream of flash gas and the gaseous stream of evaporation gas to form a mixed gaseous stream;at least one compression device capable of compressing the mixed gas stream to form a compressed combustible gas stream; characterized by: an assembly for drawing a bypass stream from the compressed combustible gas stream; at least one downstream compressor for compressing the bypass stream and forming a compressed bypass stream; a downstream heat exchanger for cooling the compressed bypass stream to form an expanded bypass stream; a device for expanding and at least partially liquefying the compressed bypass stream; an assembly for introducing at least a first flow from the expanded bypass stream into the downstream heat exchanger, to allow the first flow to be heated, an assembly for reintroducing the first flow into the mixed gas stream and / or into at least one of the evaporation gas flow and the flash gas flow, upstream of the compression apparatus.

[0015] According to particular embodiments, the installation according to the invention comprises one or more of the following characteristics, taken in isolation or in any technically possible combination: the first flow is made up of the entire expanded bypass stream; it comprises: - a downstream separator tank, - a collection assembly, at the top of the downstream separator tank, of the first flow in gaseous form, and of reintroduction of the first flow into the mixed gas stream and / or into at least one of the evaporation gas stream and the flash gas stream, upstream of the compression apparatus; - a recovery assembly, at the bottom of the downstream separator tank, of a second liquid bypass stream, and of introduction of the liquid bypass stream into the expanded liquefied natural gas stream, upstream of the end-of-flash tank; the downstream heat exchanger is capable of putting the first flow and at least part of a treated gas stream intended to be liquefied into heat exchange relation; it comprises: a diversion assembly of a recirculation stream from the compressed bypass stream;an assembly for introducing at least part of the recirculation stream into the downstream heat exchanger to liquefy it at least partially in the downstream heat exchanger.;

[0016] The invention will be better understood from reading the following description, given solely by way of example, and made with reference to the appended drawings, in which: there figure 1 is a block diagram of a first installation intended for the implementation of a first method according to the invention; the figures 2 à 6 are block diagrams of installation variants intended for the implementation of process variants according to the invention.

[0017] In all that follows, the same references will be used to designate a current flowing in a pipe and the pipe that transports it. The terms "upstream" and "downstream" generally extend in relation to the normal direction of circulation of a fluid.

[0018] Furthermore, unless otherwise stated, percentages quoted are molar percentages, and pressures are given in absolute bars.

[0019] The additional turbines described drive compressors, but can also drive variable frequency electric generators whose electricity can be used in the network via a frequency converter.

[0020] Streams with a temperature above ambient are described as being cooled by air coolers. Alternatively, water exchangers, such as fresh water or sea water, can be used.

[0021] The ambient temperature around the installation is not significant for the purposes of the invention and may be between 15°C and 35°C.

[0022] A first installation 10 for the expansion and storage of liquefied natural gas from a natural gas liquefaction installation 12 is schematically illustrated by the figure 1 .

[0023] The installations 10, 12 are advantageously carried by a support 14 located on the surface of a body of water, such as a sea, a lake, an ocean or a river. The support 14 is for example a floating barge and constitutes a floating natural gas liquefaction unit (FLNG).

[0024] The liquefaction installation 12 is not described here in detail. It comprises, in a known manner, a natural gas treatment unit 16, capable of producing a treated gas free of compounds capable of solidifying during liquefaction, and a unit 18 for liquefying the treated gas, comprising at least one system (not shown) for cooling, liquefying, and sub-cooling the treated gas 20, capable of producing a stream 22 of liquefied natural gas under pressure.

[0025] The expansion and storage installation 10 comprises a device 24 for expanding the stream of pressurized liquefied natural gas 22, here comprising a dynamic expansion turbine 25 and an end-of-flash capacity, in this particular example an end-of-flash tank 26. It also comprises at least one tank 28 for recovering liquefied natural gas, and a compression device 30, capable of recovering and compressing both the flash gas from the tank 26 and the evaporation gas from the or each tank 28, to form a compressed stream of combustible gas 32.

[0026] According to the invention, the installation 10 further comprises a downstream compressor 34, intended to compress a bypass stream 36 taken from the compressed combustible gas stream 32, and at least one dynamic expansion turbine 38, capable of expanding the bypass stream 36.

[0027] In the example shown in the figure 1 , the installation 10 further comprises 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 current 36 in the turbine 38.

[0028] Alternatively or in addition, as described below on the figure 3 , the exchangers 40 and 41 are intended for the cooling and at least partial liquefaction of a part of the bypass stream 36, when an excess of flash gas and / or evaporation gas is present in the compressed combustible gas stream 32.

[0029] A first method according to the invention for expanding and storing the liquefied natural gas stream 22, implemented in the installation 10, will now be described.

[0030] Initially, a stream of pressurized liquefied natural gas 22 is produced by the installation 12.

[0031] The liquefied natural gas stream 22 has a pressure for example greater than 60 bar, and can be between 40 bar and 80 bar.

[0032] Stream 22 is subcooled. The temperature of liquefied natural gas stream 22 is typically below -150°C but can be between -140°C and -160°C.

[0033] Stream 22 advantageously has a molar methane content greater than 80%, and a molar C 4 +< content less than 5%.

[0034] The molar flow rate of the liquefied natural gas stream 22 is, for example, greater than 10,000 kmol / h.

[0035] The stream of liquefied natural gas 22 is conveyed to the dynamic expansion turbine 25 of the expansion device 24 to undergo flash expansion and form a stream 42 of expanded liquefied natural gas.

[0036] The pressure of the expanded liquefied natural gas stream 42 is, for example, less than 7 bar, in particular between 6 bar and 12 bar.

[0037] The expansion of stream 22 causes the formation in stream 42 of a residual flash gas downstream of the final expansion valve. The molar content of flash gas in stream 42 is for example greater than 5% and is in particular between 4% and 10%.

[0038] The stream 42 is then introduced into the end-of-flash tank 26, to recover, at the foot of the tank 26, a liquid flow 46 of liquefied natural gas, and at the head of the tank 26, a gaseous flow 48 of flash gas.

[0039] The liquid flow 46 is then conveyed to a storage tank 28. In the example shown in the figure 1 , the flow 46 is pumped through a pump 50. Alternatively, it flows by gravity into the reservoir 28, without being pumped.

[0040] During its transport, and its introduction into the tank 28, a residual evaporation gas (“boil off gas” in English) is formed from the liquid flow 46, in particular by reheating the liquid flow 46 in the transport pipes, by the heat inputs of the tank(s) 28 and / or under the effect of a pressure difference between the tank 26 and the tank 28.

[0041] A gaseous flow 52 of evaporation gas is recovered at the top of the tank 28. The gaseous flow of evaporation gas 52 is heated in the downstream heat exchanger 40, for example to a temperature above -60°C.

[0042] The gas flow 48 of flash gas is heated in the additional heat exchanger 41, for example to a temperature above -60°C.

[0043] It is then mixed with the gas stream 52 of boil-off gas to form a mixture gas stream 54.

[0044] The gas stream 48 represents between 30 mol% and 80 mol% of the mixing gas stream 54.

[0045] The mixture gas stream 54 is then introduced into the compression apparatus 30 to form a compressed combustible gas stream 32.

[0046] In the example shown in the figure 1 , the stream 54 passes successively through a first compressor 56, a first air-cooling exchanger or a water exchanger 58 to be cooled to ambient temperature, a second compressor 60, then a second exchanger 62 to be cooled again to ambient temperature or water temperature.

[0047] 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.

[0048] In a particular example, the composition of stream 32 is typically 15 mol% nitrogen and 85 mol% methane.

[0049] The compressed combustible gas stream 32 is then recovered to be used as fuel in the installation 12, or as a make-up fluid in this installation 12.

[0050] A bypass stream 36 is taken from the combustible 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 combustible gas stream 32 coming from the compression device 30, and is in particular between 10% and 100% of this flow rate.

[0051] The bypass stream 36 is then compressed in the compressor 34, and is then cooled to room temperature in the air-cooling exchanger or the water exchanger 64, to form a compressed bypass stream 66.

[0052] The pressure of the compressed bypass stream 66 is for example 30 bar higher than the pressure of the stream 32.

[0053] The stream 66 is then introduced into the downstream heat exchanger 40 to be cooled there to a temperature advantageously below -50°C.

[0054] It is then expanded in the dynamic expansion turbine 38, to a pressure less than 2 bar and in particular between 1.1 bar and 3 bar, to form an expanded bypass stream 68.

[0055] The temperature of the stream 68 is preferably less than -150°C and is in particular between -140°C and -160°C.

[0056] The expanded bypass stream 68 is optionally at least partially liquid. In this case, the molar liquid content in stream 68 is typically less than 15 mol%. Alternatively, stream 68 remains completely gaseous.

[0057] In this example, the entire expanded bypass stream 68 forms a first flow 70 which is then introduced into the downstream heat exchanger 40 to be reheated there. The temperature of the first reheated flow 71 is advantageously greater than -60°C.

[0058] The first reheated flow 71 is then reintroduced into the mixing stream 54, downstream of the end-of-flash tank 26, and upstream of the compression device 30.

[0059] In this embodiment, at least one gaseous stream of treated gas 72 from the installation 12 is diverted to the installation 10.

[0060] The gas stream 72 has a pressure for example greater than 60 bar, and in particular between 40 bar and 90 bar. The temperature of the gas stream is typically equal to ambient or pre-cooled temperature.

[0061] Gas stream 72 has a molar methane content greater than 80%, and a molar C 4 +< content less than 5%.

[0062] The molar flow rate of the gas stream 72 can represent up to 10% of the flow rate of the initial charge of natural gas introduced into the liquefaction installation 12.

[0063] The gas stream 72 is then separated into a first part 74 and a second part 76.

[0064] 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.

[0065] 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 expanded bypass stream 68, to a temperature advantageously lower than -150°C.

[0066] The first portion 74 then passes through a control valve 78, before being mixed with the expanded liquefied natural gas stream 42 from the expansion device 24.

[0067] 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 gas stream of flash gas 48, down to a temperature advantageously lower than - 150°C.

[0068] The second part 76 then passes through a control valve 80, before being mixed with the expanded liquefied natural gas stream 42 from the expansion device 24.

[0069] The implementation of the method according to the invention is therefore particularly simple since it reduces the number of equipment required to flash liquefied natural gas for storage, and to advantageously recover the flash gases and evaporation gases produced.

[0070] In particular, a single compression apparatus 30 is used to compress a mixture stream 54 formed from the flash gases and the boil-off gases.

[0071] 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 very efficient thermal integration, and to take advantage of the available frigories to at least partially liquefy the gas treated in the installation 12.

[0072] The thermal integration of the bypass current 36 makes it possible to adjust the frigories between the different operating modes of the installation 10, between the phases of filling the tanks, and the phases of loading a methane carrier.

[0073] The method according to the invention and the installation 10 allowing its implementation are therefore particularly suitable for a floating unit such as an FLNG.

[0074] In a variant, shown schematically on the figure 1 , a portion 90 of the gaseous flow of boil-off gas is sent to other liquefaction trains. Conversely, a stream of liquefied natural gas 92 from other liquefaction trains is introduced into the tank 28.

[0075] 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 the sense that it comprises a downstream tank 112, placed at the outlet of the dynamic expansion turbine 38.

[0076] The expanded bypass stream 68 is introduced into the downstream tank 112 to recover, at the top, the first flow 70 in gaseous form, and at the bottom, a second liquid flow 114.

[0077] The molar flow rate of the second stream 114 constitutes, for example, between 10% and 15% of the molar flow rate of the expanded bypass stream 68.

[0078] As previously, 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.

[0079] The second flow 114 is reintroduced into the expanded liquefied natural gas stream 42 coming from the expansion device 24, upstream of the end-of-flash tank 26.

[0080] The second method according to the invention optimizes the distribution of the liquid in the downstream heat exchanger 40.

[0081] A third installation 120, intended for the implementation of a third method according to the invention, is illustrated by the figure 3 .

[0082] Unlike the first method implemented in the installation 10 described in the figure 1 , a recirculation stream 122 is taken from the compressed bypass stream 66.

[0083] The recirculation stream 122 represents, for example, between 30% and 80% molar of the compressed bypass stream 66 from the compressor 34.

[0084] The recirculation stream 122 is then separated into a first portion 124 and a second portion 126.

[0085] The molar flow rate of the first part 124 of the recirculation stream 122 constitutes for example between 20% and 50% molar of the recirculation stream 122 and the molar flow rate of the second part 126 of the recirculation stream 122 constitutes for example between 50% and 80% of the molar flow rate of the recirculation stream 122.

[0086] The first part 124 of the recirculation stream 122 is introduced into the downstream heat exchanger 40 to be cooled there, and possibly at least partially liquefied, by heat exchange in particular with the expanded bypass stream 68, down to a temperature advantageously lower than -150°C.

[0087] The first portion 124 then passes through a control valve 128, before being mixed with the expanded liquefied natural gas stream 42 from the expansion device 24.

[0088] The second part 126 of the bypass stream 122 is introduced into the additional heat exchanger 41, to be cooled there and possibly at least partially liquefied by heat exchange with the gaseous flow of flash gas 48, down to a temperature advantageously lower than -150°C.

[0089] The second part 126 then passes through a control valve 130, before being mixed with the expanded liquefied natural gas stream 42 from the expansion device 24.

[0090] The use of a bypass stream 36 taken from the fuel stream 32 formed at the outlet of the compression apparatus 30 makes it possible to obtain very efficient thermal integration, and to take advantage of the available frigories to at least partially liquefy a recirculation stream 122 from the bypass stream, when an excess of flash gas and / or evaporation gas occurs.

[0091] In a variant shown in dotted lines on the figure 3 , at least a portion 76 of the gaseous stream of treated gas 72 from the installation 12 is also introduced into the additional heat exchanger 41, as described above for the figure 2 .

[0092] A fourth installation 130, intended for the implementation of a fourth method according to the invention, is illustrated by the figure 4 .

[0093] This installation 130 differs from the 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.

[0094] A reboiling exchanger 134 is arranged upstream of the expansion device 24 to put the liquefied natural gas stream 22 into heat exchange relation with a reboiling stream 136 coming from the column 132.

[0095] The implementation of the fourth method according to the invention is otherwise similar to that of the first method according to the invention.

[0096] A fifth installation 140, intended for the implementation of a fifth method according to the invention, is illustrated by the figure 5 .

[0097] 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.

[0098] The implementation of the fifth method according to the invention is also similar to that of the third method according to the invention.

[0099] A sixth installation 150, intended for the implementation of a sixth method according to the invention, is illustrated by the figure 6 .

[0100] 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.

[0101] The intermediate tank 152 receives the expanded liquefied natural gas stream 42 and separates it into a head stream 154, mixed with the gaseous stream 48 of flash gas, and into a bottom stream 156, introduced into the reboiling exchanger 134 before reaching the distillation column 132.

[0102] This installation 150 is beneficial for the recovery of helium in the case where the gaseous stream 154 is rich in helium, typically consisting of at least 25% helium, and can therefore be advantageously sent to a helium purification installation.

[0103] In variants of each of the installations 120 to 150, a downstream tank 112 is provided to separate the expanded bypass stream 68, as described in the second method according to the invention.

[0104] 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 stream of liquefied natural gas then undergoes static and not dynamic expansion in the expansion device 24.

[0105] The method 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 coming from the tank 28 between the phases of loading a methane carrier by emptying the tank and the phases of filling the tank.

[0106] As indicated above, thermal integration of the bypass stream 36 with the boil-off gas stream 52 is used to adjust the required frigories, and vary the relative flow rates of the fuel gas stream 32 and the bypass stream 36.

[0107] This is achieved without having to modify operating parameters for the liquefaction of natural gas, particularly at the level of the main liquefaction cycles.

[0108] Clause 1. Method for expanding and storing a stream of liquefied natural gas (22) from a natural gas liquefaction installation (12), comprising the following steps: flash expansion of the liquefied natural gas stream (22) in an expansion device (24) to form a stream of expanded liquefied natural gas (42); supplying the expanded liquefied natural gas stream (42) into an end-of-flash capacity (26; 132); recovering, at the foot of the end-of-flash capacity (26; 132), a liquid stream of liquefied natural gas (46); conveying the liquid stream of liquefied natural gas (46) into at least one liquefied natural gas tank (28); withdrawing, at the head of the end-of-flash capacity (26; 132), a gaseous stream of flash gas (48); recovering, at the head of the liquefied natural gas tank (28), a gaseous stream of evaporation gas (52); mixing the flash gas stream (48) and the boil-off gas stream (52) to form a mixed gas stream (54); compressing the mixed gas stream (54) in at least one compression apparatus (30) to form a compressed combustible gas stream (32); characterized by the following steps: taking a bypass stream (36) from the compressed fuel gas stream (32); 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 stream (68; 70) from the expanded bypass stream (68) in at least one downstream heat exchanger (40), reintroducing the heated first stream (68; 70) into the mixed gas stream (54) and / or into at least one of the evaporation gas stream (52) and the flash gas stream (48), upstream of the compression apparatus (30).

[0109] Clause 2. - Method according to clause 1, in which the at least partially liquid expanded bypass stream (68) is introduced into a downstream separator tank (112), the method comprising the following steps: collection, at the top of the downstream separator tank (112), of the first flow (70) in gaseous form, and reintroduction of the first flow (70) into the gaseous mixture stream (54) and / or into at least one of the gaseous flow of evaporation gas (52) and the gaseous flow of flash gas (48), upstream of the compression apparatus (30); recovery, at the bottom of the downstream separator tank (112), of a second liquid bypass flow (114), and introduction of the liquid bypass flow (114) into the flow (42) of expanded liquefied natural gas, upstream of the end-of-flash capacity (26; 132).

[0110] Clause 3. - A method according to clause 1, wherein the entire expanded bypass stream (68) constitutes the first stream (70).

[0111] Clause 4. - Method according to any one of clauses 1 to 3, in which the compressed bypass stream (66) from the downstream compressor (34) is introduced into the downstream heat exchanger (40) to be put into heat exchange relation with the first flow (70).

[0112] Clause 5. - Method according to any one of clauses 1 to 4, in which the evaporation gas stream (52) is introduced into the downstream heat exchanger (40) to be put into heat exchange relation with the first stream (70).

[0113] Clause 6. - A method according to any one of clauses 1 to 5, comprising the following steps: supplying a treated natural gas stream (72) intended to be liquefied; introducing at least a first portion (74) of the treated natural gas stream (72) into the downstream heat exchanger (40) to be placed in heat exchange relationship with the first flow (70); at least partial liquefaction of the first portion (74) of the treated natural gas stream (72) in the downstream heat exchanger (40) by heat exchange with the first flow (68; 70).

[0114] Clause 7. - Method according to clause 6, comprising introducing the first part (74) of the liquefied treated natural gas stream (72) into the expanded liquefied natural gas stream (42) from the expansion device (24), upstream of an end-of-flash capacity (26; 132).

[0115] Clause 8. - Method according to clause 6 or 7, comprising the following steps: separation of the treated natural gas stream into the first part (74) of the treated natural gas stream (72) and a second part (76) of the treated natural gas stream (72); introduction of the second part (76) of the treated natural gas stream (72) into an additional heat exchanger (41), to be put into heat exchange relation with the flash gas flow (48); liquefaction of the second part (76) of the treated natural gas stream (72) in the additional heat exchanger (41) by reheating the flash gas flow (48); introduction of the second part (76) of the liquefied treated natural gas stream (72) into the expanded liquefied natural gas stream (42) from the expansion device (24), upstream of the end-of-flash capacity (26; 132).

[0116] Clause 9.- A method according to any one of clauses 1 to 8, comprising the following steps: bypassing a recirculation stream (122) into the compressed bypass stream (66); liquefying at least a portion (124) of the recirculation stream (122) in the downstream heat exchanger (40) by heat exchange with the first stream (68; 70).

[0117] Clause 10. - A method according to any one of clauses 1 to 9, wherein the end-flash capacity (26; 132) is an end-flash drum (26) or an end-flash distillation column (132).

[0118] Clause 11. - A method according to any one of clauses 1 to 10, wherein the expansion device (24) comprises a dynamic expansion turbine (25).

[0119] Clause 12. - Installation for the expansion and storage of a stream of liquefied natural gas from a natural gas liquefaction installation (12), comprising an expansion device (24) capable of performing a flash expansion of the liquefied natural gas stream (22) to form a expanded liquefied natural gas stream (42); an end-of-flash capacity (26; 132) capable of receiving the expanded liquefied natural gas stream (42) from the expansion device (24); a recovery assembly, at the foot of the end-of-flash capacity (26; 132), of a liquid flow of liquefied natural gas (46); at least one liquefied natural gas tank (28) and an assembly for conveying the liquid flow of liquefied natural gas (46) into the liquefied natural gas tank (28); a collection assembly, at the head of the end-of-flash capacity (26; 132), of a gaseous flow of flash gas (48); a recovery assembly, at the head of the liquefied natural gas tank (28), of a gaseous flow of evaporation gas (52);a mixing assembly of the flash gas flow (48) and the evaporation gas flow (52) to form a mixed gas stream (54); at least one compression apparatus (30) capable of compressing the mixed gas stream (54) to form a compressed combustible gas stream (32); ; characterized by: an assembly for drawing a bypass stream (36) from the compressed combustible gas stream (32); 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 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 one of the evaporation gas flow (52) and the flash gas flow (48), upstream of the compression apparatus (30);

[0120] Clause 13. - Installation according to clause 12, in which the first flow (68) consists of the entire relaxed bypass current (68).

[0121] Clause 14. - Installation according to clause 12, including: a downstream separator tank (112), a collection assembly, at the top of the downstream separator tank (112), of the first flow (70) in gaseous form, and of reintroduction of the first flow (70) into the gaseous mixture stream (54) and / or into at least one of the gaseous flow of evaporation gas (52) and the gaseous flow of flash gas (48), upstream of the compression apparatus (30); a recovery assembly, at the bottom of the downstream separator tank (112), of a second liquid bypass flow (114), and of introduction of the liquid bypass flow (114) into the stream (42) of expanded liquefied natural gas, upstream of the end-of-flash tank (26; 132).

[0122] Clause 15. - Installation according to any one of clauses 12 to 14, in which the downstream heat exchanger (40) is capable of putting into heat exchange relation the first flow (68; 70), and at least a part (74) of a treated gas stream (72) intended to be liquefied.

[0123] Clause 16. - Installation according to any of clauses 12 to 14, comprising: an assembly for diverting 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).

Claims

1. Method for expanding and storing a stream of liquefied natural gas (22) from a natural gas liquefaction installation (12), comprising the following steps: - flash expansion of the stream of liquefied natural gas (22) in an expansion device (24) to form a stream of expanded liquefied natural gas (42); - supplying the expanded liquefied natural gas stream (42) into an end-of-flash capacity (26; 132); - recovering, at the foot of the end-of-flash capacity (26; 132), a liquid stream of liquefied natural gas (46); - conveying the liquid stream of liquefied natural gas (46) into at least one liquefied natural gas tank (28); - withdrawing, at the head of the end-of-flash capacity (26; 132), a gaseous stream of flash gas (48); - recovery, at the head of the liquefied natural gas reservoir (28), of a gaseous flow of evaporation gas (52);- mixing the flash gas stream (48) and the evaporation gas stream (52) to form a mixed gas stream (54); - compressing the mixed gas stream (54) in at least one compression apparatus (30) to form a compressed combustible gas stream (32); ; characterized bythe following steps: - taking a bypass stream (36) from the compressed fuel gas stream (32); - 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 a first flow (68; 70) from the expanded bypass stream (68) in at least one downstream heat exchanger (40), - reintroducing the first flow (68;70) heated in the mixed gas stream (54) and / or in at least one of the evaporation gas stream (52) and the flash gas stream (48), upstream of the compression apparatus (30), - bypassing a recirculation stream (122) in the compressed bypass stream (66), and - liquefying at least a portion (124) of the recirculation stream (122) in the downstream heat exchanger (40) by heat exchange with the first stream (68; 70).; 2. Method according to claim 1, in which the expanded bypass stream (68) which is at least partially liquid is introduced into a downstream separator tank (112), the method comprising the following steps: - withdrawal, at the top of the downstream separator tank (112), of the first stream (70) in gaseous form, and reintroduction of the first stream (70) into the mixed gas stream (54) and / or into at least one of the evaporation gas stream (52) and the flash gas stream (48), upstream of the compression apparatus (30); - recovery, at the bottom of the downstream separator tank (112), of a second liquid bypass stream (114), and introduction of the liquid bypass stream (114) into the expanded liquefied natural gas stream (42), upstream of the end-of-flash capacity (26; 132).

3. The method of claim 1, wherein the entire expanded bypass stream (68) constitutes the first stream (70).

4. Method according to any one of the preceding claims, in which the compressed bypass stream (66) from the downstream compressor (34) is introduced into the downstream heat exchanger (40) to be put into heat exchange relation with the first flow (70).

5. Method according to any one of the preceding claims, in which the evaporation gas flow (52) is introduced into the downstream heat exchanger (40) to be put into heat exchange relation with the first flow (70).

6. Method according to any one of the preceding claims, comprising the following steps: - supplying a treated natural gas stream (72) intended to be liquefied; - introducing at least a first portion (74) of the treated natural gas stream (72) into the downstream heat exchanger (40) to be placed in heat exchange relationship with the first flow (70); - at least partial liquefaction of the first portion (74) of the treated natural gas stream (72) in the downstream heat exchanger (40) by heat exchange with the first flow (68; 70).

7. Method according to claim 6, comprising introducing the first part (74) of the liquefied treated natural gas stream (72) into the expanded liquefied natural gas stream (42) from the expansion device (24), upstream of an end-of-flash capacity (26; 132).

8. Method according to claim 6 or 7, comprising the following steps: - separation of the treated natural gas stream into the first part (74) of the treated natural gas stream (72) and a second part (76) of the treated natural gas stream (72); - introduction of the second part (76) of the treated natural gas stream (72) into an additional heat exchanger (41), to be put into heat exchange relation with the flash gas stream (48); - liquefaction of the second part (76) of the treated natural gas stream (72) in the additional heat exchanger (41) by reheating the flash gas stream (48); - introduction of the second part (76) of the liquefied treated natural gas stream (72) into the expanded liquefied natural gas stream (42) from the expansion device (24), upstream of the end-of-flash capacity (26; 132).

9. A method according to any preceding claim, wherein the end-flash capacity (26; 132) is an end-flash drum (26) or an end-flash distillation column (132).

10. A method according to any preceding claim, wherein the expansion device (24) comprises a dynamic expansion turbine (25).

11. Installation for expanding and storing a stream of liquefied natural gas from a natural gas liquefaction installation (12), comprising - an expansion device (24) capable of performing a flash expansion of the stream of liquefied natural gas (22) to form a stream of expanded liquefied natural gas (42); - an end-of-flash capacity (26; 132) capable of receiving the stream of expanded liquefied natural gas (42) from the expansion device (24); - a recovery assembly, at the foot of the end-of-flash capacity (26; 132), of a liquid stream of liquefied natural gas (46); - at least one liquefied natural gas tank (28) and an assembly for conveying the liquid stream of liquefied natural gas (46) into the liquefied natural gas tank (28); - a collection assembly, at the head of the end-of-flash capacity (26; 132), of a gas flow of flash gas (48);- a recovery assembly, at the head of the liquefied natural gas tank (28), of a gaseous flow of evaporation gas (52); - a mixing assembly of the gaseous flow of flash gas (48) and the gaseous flow of evaporation gas (52) to form a mixed gas stream (54); - at least one compression device (30) capable of compressing the mixed gas stream (54) to form a compressed combustible gas stream (32); ; characterized by: - an assembly for drawing a bypass stream (36) from the compressed combustible gas stream (32); - 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 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 one of the evaporation gas flow (52) and the flash gas flow (48), upstream of the compression apparatus (30);- an assembly for diverting 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 liquefy it at least partially in the downstream heat exchanger (40).; 12. Installation according to claim 11, in which the first flow (68) consists of the entire relaxed bypass current (68).

13. Installation according to claim 11, comprising: - a downstream separator tank (112), - a collection assembly, at the top of the downstream separator tank (112), of the first flow (70) in gaseous form, and of reintroduction of the first flow (70) into the gaseous mixture stream (54) and / or into at least one of the gaseous flow of evaporation gas (52) and the gaseous flow of flash gas (48), upstream of the compression apparatus (30); - a recovery assembly, at the bottom of the downstream separator tank (112), of a second liquid bypass flow (114), and of introduction of the liquid bypass flow (114) into the stream (42) of expanded liquefied natural gas, upstream of the end-of-flash tank (26; 132).

14. Installation according to any one of claims 11 to 13, in which the downstream heat exchanger (40) is capable of putting the first flow (68; 70) into heat exchange relation, and at least a portion (74) of a treated gas stream (72) intended to be liquefied.

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