Liquefaction system for a gas intended for a transport and / or storage tank for said gas.

Abstract

Liquefaction system for a gas intended for a transport and / or storage tank for said gas.The invention relates to a gas liquefaction system (1) for a gas intended for a tank (2) for transporting and / or storing said gas and comprising a main line (12) connecting the tank (2) to a gas / liquid separator (14), said main line (12) carrying a first compression device (24), a second compression device (26), and a first expansion device (36), the liquefaction system (1) comprising a return line (20) connecting the separator (14) to the tank (2) and comprising a heat exchanger (38) through which a first part (41) and a second part (42) of the main line (12) pass, characterized in that the liquefaction system (1) comprises a branch line (44) comprising a second expansion device (50) and of which a first section (52) passes through the heat exchanger (38), and of which a second section (54) passes through the heat exchanger (38). (Figure 3).

Description

Title of the invention: Gas liquefaction system intended for a transport and / or storage tank for said gas.

[0001] The present invention relates to the field of transport and storage of a liquefied gas, for example dihydrogen. It relates more particularly to installations for a sealed and thermally insulated tank for the storage and / or transport of the liquefied gas.

[0002] The liquefied gas is transported by sea in sealed, thermally insulated storage tanks installed on transport vessels. The gas is kept in liquid form to increase the quantity of gas transported per tank, as the volume occupied by one kilogram of gas in liquid form is much smaller than the volume occupied by one kilogram of gas in gaseous form. These tanks maintain the liquefied gas at very low temperatures, and more specifically for dihydrogen, at a temperature below -250°C, the temperature at which dihydrogen is in liquid form at atmospheric pressure.

[0003] The tank has a sealed wall that delimits the liquefied gas storage volume. This wall is subject to a heat flux that tends to warm the tank's contents, resulting in the evaporation of the liquefied gas. The tank is said to be thermally insulating insofar as the structure of the sealed wall is configured to minimize this heat flux and the vaporization of the liquefied gas.

[0004] The liquefied gas is thus present in the tank in a two-phase liquid-vapor equilibrium state. Part of the liquefied gas is in the vapor phase, thus forming a boiled-off gas (BOG) in a larger volume of the tank, the liquefied gas being mainly in the liquid phase, this liquid phase extending into a smaller volume of the tank.

[0005] It is desirable to minimize the presence of evaporation gas in the storage tank. Several systems are therefore designed to condense this evaporation gas. Reliquefaction systems, for example, draw the evaporation gas out of the tank, cool it using heat exchangers before reintroducing it into the tank.

[0006] There are also subcooling systems, which operate by recovering liquid gas from the tank, subcooling it, and then spraying it onto the evaporation gas inside the tank to cool and liquefy this evaporation gas. For example, the liquefied gas in liquid phase is pumped from the bottom of the tank, subcooled out of the tank, then directed to spray booms located against the upper wall, which spray the gas into the upper volume of the tank where the evaporation gas resides.

[0007] In these prior art systems, when it comes to cooling dihydrogen, a gas with a boiling point lower than that of dihydrogen is used as a cooling source, for example, helium. The use of this gas requires a specific cooling system to maintain it at a low temperature and allow its circulation within the vessel. These reliquefaction and subcooling systems are therefore bulky, energy-intensive, and expensive to install and maintain.

[0008] The invention falls within this context and aims to offer an alternative to these systems by presenting a gas liquefaction system for a transport and / or storage tank. This liquefaction system uses the evaporation gas from the tank as a cooling source, thereby reducing the number of machines installed and consequently lowering energy, installation, and maintenance costs.

[0009] The present invention thus has as its main object a gas liquefaction system intended for a transport and / or storage tank of said gas, the liquefaction system comprising a main line fluidly connecting an upper volume of the tank to a gas / liquid separator and comprising a first compression device and a second compression device arranged successively between the tank and the separator, the liquefaction system comprising a return line from the tank fluidly connecting the separator to a lower volume of the tank, the main line comprising a first expansion member arranged between the second compression device and the separator,said liquefaction system comprising a heat exchanger through which passes a first part of the main line disposed between the tank and the first compression device and through which passes a second part of the main line disposed between the second compression device and the first expansion device, characterized in that the main line comprises a branch line comprising an inlet, an outlet and a second expansion device, the inlet being fluidly connected to the main line between the second compression device and the first expansion device, the outlet being fluidly connected to the main line between the first compression device and the second compression device, a first section of the branch line disposed between the inlet and the second expansion device passing through the heat exchanger,and a second section of the bypass line arranged between the second expansion valve and the outlet passing through the heat exchanger.

[0010] The gas transported and / or stored in the tank may, in particular, be a gas with a very low boiling point, often at temperatures expressed in negative degrees Celsius, such as dihydrogen. During transport and / or storage, This gas is mostly in liquid form within a compartment of the tank. However, heat transfer occurs through a tank wall, which can heat the gas and cause it to partially vaporize.

[0011] It should therefore be noted that inside the tank housing, the gas exists in both liquid and gaseous form. The gas in liquid form, due to gravity, remains at the bottom of the housing, referred to as the lower volume of the housing, while the gas in gaseous form occupies the top of the tank, designated as the upper volume of the housing.

[0012] It is understood that, depending on the quantity of gas in gaseous and liquid form, the lower and upper volumes fluctuate. As will become apparent from the description, the present invention makes it possible to control the pressure rise of the tank, which cannot reach a high pressure (typically a maximum pressure of around 2 bar) by liquefying the evaporation gas or by consuming it, while limiting the energy consumption associated with managing the evaporation gas, i.e., the gas in its gaseous form. In other words, the invention allows for the delivery of a maximum of gas in liquid form while ensuring minimal energy consumption for processing the gas in its gaseous form.

[0013] The main line, being fluidly connected to the upper volume of the tank, is configured to draw the gas in vapor form from the tank. This gas is then compressed first by the first compression device, then a second time by the second compression device, before flowing within the second part of the main line, where it is cooled by the heat exchanger.

[0014] Alternatively, the liquefaction system may comprise a single compression device performing both compressions, with the outlet of the bypass line positioned at an intermediate point between the two compressions of said compression device.

[0015] The gas, exiting the second part of the main pipeline, is then expanded, which further lowers its temperature and causes it to liquefy. This liquefied gas then reaches the separator, where the remaining vaporized gas is separated from the liquefied gas. The liquefied gas is then returned to the tank, specifically to its lower section.

[0016] To cool the gas flowing in the second part of the main line, the heat exchanger uses a cold source. In this invention, the cold source is the gas itself, in particular that flowing in the bypass line.

[0017] More specifically, the bypass line draws compressed gas from the outlet of the second compression device via its inlet. This gas is cooled in the first section of the bypass line by the heat exchanger, and then expanded by the second expansion device, thus significantly reducing the gas temperature. This gas then flows into the second section of the bypass line, and thus through a new pass of the heat exchanger, where it is used as a source of cold for the gas flowing in the second part of the main line, as well as for the gas flowing in the first section of the bypass line.

[0018] The second section of the bypass line is particularly effective as a cooling source, thanks to the expansion that occurs between the first and second sections of this line via the second expansion valve. In this configuration, the liquefaction efficiency is very high, making it possible to liquefy all of the excess evaporation gas, even when the evaporation gas is not very cold.

[0019] The liquefaction system also uses another source of cold, which is the first section of the main pipe located between the tank and the first compression device and passing through the heat exchanger. Indeed, as it passes through the heat exchanger, the gas flowing in the first section of the main pipe is heated by absorbing heat from contact with the gas flowing in other sections of the exchanger, before continuing its path towards the first compression device.

[0020] It is therefore understood that the sources of cold are the gas in vapor form exiting the tank, that is to say that circulating in the first part of the main pipe, as well as the gas circulating in the second section of the bypass line.

[0021] The first part of the main line allows all of the gas in the form of vapor exiting the tank to recover heat, thus helping to cool the gas circulating in the second part of the main line before its return to the tank.

[0022] The combination of these two cold sources therefore makes it possible to efficiently cool the gas in the second part of the main line as well as that circulating in the first section of the bypass line.

[0023] It is therefore understood that the heat exchanger here is an exchanger with at least four passes, among which the pass relating to the second part of the main pipe, the pass relating to the first part of the main pipe, the pass relating to the first section of the bypass line and the pass relating to the second section of the bypass line.

[0024] It should be noted that the gas liquefaction is achieved by actuating the first expansion device. Thanks to the system of the invention, and in particular to the bypass line and the first section of the main pipe, the energy required for gas liquefaction can be reduced, since the gas circulating in the second section, i.e., one pass of the heat exchanger, is cooled in the heat exchanger by the second section of the bypass line and by the first section of the main pipe, i.e., two other passes of the heat exchanger. which limits the energy required to implement the expansion by the first expansion organ.

[0025] In other words, the gas flow in the bypass line provides additional cooling to that already present in the pass related to the first section of the main pipeline. This additional cooling helps to reduce the temperature before the first expansion stage, which improves gas liquefaction and reduces the amount of steam generated after expansion by the first expansion stage.

[0026] The gas flowing in the bypass line is, after passing through the heat exchanger via the pass relating to the second section of the bypass line, mixed with the gas flowing in the main line between the first compression device and the second compression device, via the outlet of said bypass line.

[0027] According to an optional feature of the invention, the bypass line includes at least one control valve configured to regulate the flow of gas circulating within said bypass line.

[0028] By regulating the gas flow in the bypass line, this control valve helps to control the amount of gas taken by the bypass line from the main line via the bypass line inlet.

[0029] The control valve can be an on / off valve or a proportional valve, capable of positioning itself at various degrees between a fully open and a fully closed position. By controlling the amount of gas drawn from the bypass line, the liquefaction efficiency is indirectly influenced. Indeed, since the gas liquefaction is achieved by actuation of the first expansion device, the energy required for this expansion can be reduced by cooling the gas in the heat exchanger via the second section of the bypass line.

[0030] It should be noted that the temperature levels at the inlet of the pass for the first section of the main pipeline and at the inlet of the second section of the bypass line differ, with a generally lower temperature at the pass for the first section of the main pipeline. As a result, heat exchange always occurs between the pass for the first section of the main pipeline and the pass for the second section of the main pipeline.

[0031] Thus, the control valve can be controlled in particular according to the temperature at the inlet of the pass relative to the first part of the main pipe which corresponds to the temperature of the gas in gaseous form within the tank.

[0032] Indeed, the higher the temperature at the inlet of the pass relative to the first part of the main line, the more relevant it is to increase the quantity of gas circulating in the bypass line, in particular by means of the control valve.

[0033] According to an optional feature of the invention, the bypass line includes a first control valve disposed between the inlet of the bypass line and the first section.

[0034] According to an optional feature of the invention, the bypass line includes a second control valve disposed between the second section and the outlet of the bypass line.

[0035] According to an optional feature of the invention, the main line includes a control valve configured to regulate the flow of gas circulating within said main line, the control valve being disposed between the inlet of the bypass line and the second part of the main line.

[0036] Like the control valve, the regulating valve can be an on / off valve or a proportional valve. By being positioned between the inlet of the branch line and the second part of the main pipeline, the regulating valve helps to control the gas flow to the second part of the main pipeline.

[0037] Thus, if this regulating valve is closed, and the first and second control valves are open, no more gas flows in the second part of the main line, and all the gas is diverted through the bypass line.

[0038] It is therefore understood that by closing the regulating valve, all the gas is redirected to the bypass line, thus creating a loop circulation where the gas flows in the bypass line, returns to the main line, and then returns again to the bypass line. This loop allows for several expansion stages via the second expansion device, which generates pre-cooling of the gas that can be advantageous for cooling and / or maintaining the cooling of the liquefaction system.

[0039] On the contrary, in a normal operating mode, the traffic in the bypass line is generally associated with the traffic in the main pipe.

[0040] Alternatively, the main line can be equipped with a three-way valve at the inlet of the branch line. In this case, this three-way valve replaces the functions of the first control valve and the regulating valve.

[0041] According to an optional feature of the invention, the liquefaction system includes a gas recirculation line from the separator, the recirculation line extending between the separator and a convergence point disposed on the main line between the tank and the first compression device.

[0042] At the separator, as mentioned previously, the liquefied gas is separated from the remaining vapor gas. The liquefied gas is then returned to the tank via the return line, while the gas in vapor form accumulates in a separator sky and is then reintroduced into the main line via the recirculation line.

[0043] Thus, the gas in vapor form from the separator is mixed with the gas in vapor form from the tank and circulating in the main line, at the point where the recirculation line converges. As a result, this portion of the gas that is reinjected into the main line is intended to be at least partially reliquefied.

[0044] It should be noted that, since the circulation of the gas in the bypass line brings additional cold to that already present in the pass relating to the first part of the main line and thus reduces the amount of steam generated after expansion by the first expansion member, less gas in gaseous form then recirculates in the recirculation line, which reduces the work of the first compression member as well as the second compression member.

[0045] According to an optional feature of the invention, the recirculation line includes a valve for managing the flow of gas circulating within said recirculation line.

[0046] This control valve makes it possible in particular to maintain a pressure in the separator higher than the pressure in the tank, thus facilitating the filling of the tank with the liquid gas from the liquefaction system via the return line.

[0047] According to an optional feature of the invention, the convergence point is disposed between the heat exchanger and the first compression device, a portion of the recirculation line passing within the heat exchanger.

[0048] The gas circulating in this portion of the recirculation line is thus heated within the heat exchanger until it reaches an ambient temperature, before being mixed with the gas circulating in the main line, between the heat exchanger and the first compression device.

[0049] It is therefore understood that, when heated, the gas circulating in the portion of the recirculation line acts as an additional source of cooling, contributing to the cooling of the gas circulating in the second part of the main line and in the first section of the bypass line. Thus, when the sources of cooling include the gas circulating in the portion of the recirculation line, in the first part of the main line, and in the second section of the bypass line, the heat exchanger is a 5-pass heat exchanger.

[0050] The advantage of having this fifth pass related to the portion of the recirculation line lies in the fact that the temperature at the inlet of this pass is colder than that at the inlet of the pass related to the first part of the main pipe. Thus, in By adding the pass relating to the portion of the recirculation line in the exchanger, we make use of the very low temperature cold coming from the separator.

[0051] For example, when the heat exchanger has five passes and the gas is dihydrogen, it is possible to liquefy all of the excess evaporation gas, even when the temperature of the evaporation gas at the outlet of the tank is about -220 °C.

[0052] According to an alternative embodiment of the invention, the convergence point is located between the tank and the heat exchanger. In other words, the convergence point is located on the main line upstream of the heat exchanger, which allows the gas passing through the heat exchanger to be cooled by the first part of the main line upstream of said heat exchanger.

[0053] According to an optional feature of the invention, the liquefaction system includes a consumption line extending between a divergence point and consumers of said gas, the divergence point being disposed on the main line between the first compression device and the second compression device.

[0054] By being positioned on the main line between the first and second compression devices, the divergence point allows the gas flowing at that point to be drawn off, that is, the gas already compressed by the first compression device. It is thus understood that this makes it possible to recover the compressed gas to meet consumer needs.

[0055] It should also be noted that the first compression device can be adjusted to compress the gas to a pressure acceptable to consumers.

[0056] Alternatively, when a single compression device is used in the liquefaction system to perform both compressions, the divergence point could be positioned at an intermediate point between the two compressions of this compression device.

[0057] According to an optional feature of the invention, the consumption line includes a modulating valve configured to regulate the flow of gas circulating within said consumption line.

[0058] The modulating valve can be either an on / off valve or a proportional valve, thus allowing precise control of the gas flow rate. By regulating the gas flow rate in the consumption line, the quantity of gas drawn from the main line is controlled.

[0059] It should be noted that the quantity of gas withdrawn depends on consumer needs. For example, if gas demand is high and all the evaporation gas from the tank is required, the modulating valve can be fully opened while the control valves and the regulating valve are closed. In this case, all the gas flowing in the main pipe is directed to the consumption line.

[0060] It is understood that in this way, the regulating valve, the modulating valve, and the control valves can be controlled simultaneously or independently of each other according to various parameters, such as consumer needs, pressure in the tank, or the level of liquid gas in the tank.

[0061] Controlling the flow rate in the bypass line depends primarily on controlling the regulating valve, the modulating valve, and the control valves. This control of the various valves can be based, firstly, on the temperature at the inlet of the bypass relative to the first section of the main line, which corresponds to the temperature of the gas in gaseous form in the tank, and secondly, on the flow rate sent to the consumers via the consumption line. For this purpose, there can be at least one temperature sensor in the tank and at least one flow sensor in the consumption line.

[0062] Thus, the higher the temperature at the inlet of the bypass in the first section of the main line, the more advantageous it becomes to increase the quantity of gas flowing in the bypass line by controlling all these valves. Conversely, the lower the flow rate in the consumption line, the more advantageous it becomes to increase the quantity of gas flowing in the bypass line, also by controlling all these valves.

[0063] According to an optional feature of the invention, the first compression device is configured to compress the gas from a pressure between 1 and 2.5 absolute bars to a pressure between 5 and 15 absolute bars.

[0064] By compressing it to a pressure between 5 and 15 bar absolute, the gas is compressed to a pressure acceptable to consumers. It is understood that the pressure of the gas flowing in the main line between the tank and the first compression device is between 1 and 2.5 bar absolute, while the pressure of the gas flowing in the main line between the first and second compression devices is between 5 and 15 bar absolute.

[0065] According to an optional feature of the invention, the second compression device is configured to compress the gas from a pressure between 5 and 15 absolute bars to a pressure between 20 and 40 absolute bars.

[0066] The gas pressure in the main line between the second compression device and the first expansion device is therefore between 20 and 40 absolute bars, and the gas pressure in the bypass line between the second compression device and the second expansion device is between 20 and 40 absolute bars.

[0067] Alternatively, when there is a single compression device playing the role of both the first and second compression device, this device unique is capable of performing a first compression, going from a pressure of 1 to 2.5 absolute bars to a pressure of 5 to 15 absolute bars, and of performing a second compression, going from 5 to 15 absolute bars to a pressure of 20 to 40 absolute bars.

[0068] According to an optional feature of the invention, the first expansion member is configured to expand the gas from a pressure between 20 and 40 absolute bars to a pressure between 1 and 2.5 absolute bars.

[0069] The gas pressure in the main line between the first expansion device and the separator is therefore 1 to 2.5 bar absolute, so that the pressure within the separator, the recirculation line and the return line is also 1 to 2.5 bar absolute.

[0070] According to an optional feature of the invention, the second expansion member is configured to expand the gas from a pressure between 20 and 40 absolute bars to a pressure between 5 and 15 absolute bars.

[0071] The gas pressure in the main line between the first expansion device and the separator is therefore 1 to 2.5 bar absolute; the pressure within the separator, the recirculation line and the return line is also between 1 and 2.5 bar absolute.

[0072] According to an optional feature of the invention, the gas is dihydrogen. Indeed, the liquefaction system is particularly efficient for liquefying dihydrogen, because the bypass line ensures complete liquefaction at very low temperatures, while avoiding excessive energy consumption at the first expansion valve of the main line. This is true even when the temperature of the vaporized gas at the tank outlet is significantly higher than its liquefaction temperature.

[0073] The invention also covers a gas transport and / or storage tank comprising a gas liquefaction system as described above.

[0074] The gas transport and / or storage tank then allows precise and efficient control of the quantity of liquid gas and evaporation gas present in the tank thanks to this liquefaction system.

[0075] The invention also relates to a method for controlling a liquefaction system as described above, in which the gas flow rate in the bypass line is regulated according to the temperature of the gas in gaseous form present in the tank and / or according to the gas flow rate circulating in the consumption line. Based on these parameters, it is determined whether it is necessary to recirculate the gas in the bypass line and to activate an additional pressure reducing device, the second pressure reducing device, in order to liquefy the gas more efficiently.

[0076] For this purpose, the control process can in particular act on the control valves of the bypass line, on the regulating valve of the main line and on the modulation valve of the consumption line.

[0077] More specifically, when the temperature of the gas in gaseous form in the tank, and therefore the temperature at the inlet of the pass relative to the first section of the main line, is high, this first section becomes less effective as a cooling source. It then becomes relevant to increase the quantity of gas circulating in the bypass line by controlling the modulating valves, the control valves, and the regulating valve, in order to also use the second section of the bypass line as a cooling source, thereby achieving more efficient liquefaction.

[0078] On the other hand, when the flow rate in the consumption line is low, this means that consumers are using less gas, thus requiring the liquefaction of more gas. In this case, it is also relevant to increase the amount of gas flowing in the bypass line in order to improve the efficiency of the liquefaction.

[0079] Thus, it is understood that the control of all the valves, as well as the piloting of the compression devices, makes it possible to direct the appropriate flow rates to the desired circuits according to the quantity of gas to be liquefied. The action of the valves can therefore be coordinated to direct the flow rates optimally; for example, the first control valve and the regulating valve can have the following control logic: when the first control valve is fully open, the regulating valve is fully closed.

[0080] It should be noted that, thanks to this control method, the liquefaction system can operate in different modes. These operating modes depend in particular on the opening or closing of the control valves, the regulating valve, and the modulating valve.

[0081] For example, in an operating mode where consumers require a large quantity of gas, the modulating valve can be fully open while the control valve(s) and the regulating valve are closed. Conversely, in another operating mode where consumers have no identified gas demand and the pressure in the tank (i.e., the quantity of gas in vapor form) is too high, the consumption line is closed by the modulating valve, while the control valves and the regulating valve are open, thus allowing efficient liquefaction of the vaporized gas to reduce the pressure in the tank.

[0082] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and the illustrative and non-limiting examples of embodiments given with reference to the accompanying drawings on the other hand, in which:

[0083] [Fig-1] is a schematic representation of a first embodiment of a gas liquefaction system installed on a transport and / or storage tank for said gas;

[0084] [Fig.2] is a schematic representation of a first mode of operation of the liquefaction system of the first embodiment of [Fig.1];

[0085] [Fig.3] is a schematic representation of a second mode of operation of the liquefaction system of the first embodiment of [Fig.1];

[0086] [Fig.4] is a schematic representation of a third mode of operation of the liquefaction system of the first embodiment of [Fig.1];

[0087] [Fig.5] is a schematic representation of a second embodiment of the liquefaction system.

[0088] The features and variants of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0089] In the figures, the elements common to several figures retain the same reference.

[0090] Figures 2 to 4 each illustrate a specific operating mode of the liquefaction system. The list of these operating modes is not exhaustive, and a plurality of other operating modes not illustrated may be implemented within the liquefaction system.

[0091] Fig. 1 is a schematic representation of a first embodiment of a gas liquefaction system 1 installed on a tank 2 for transporting and / or storing said gas.

[0092] The gas can be of any type that exists in gaseous and liquid forms. Dihydrogen is particularly used as a gas, notably because the system according to the invention allows for the cost-effective reliquefaction of this gas, which requires a very low liquefaction temperature. Other applications of the tank 2, for example with liquefied natural gas, are nevertheless conceivable.

[0093] It should be noted that the invention also covers the case of several tanks 2 mounted in parallel, with a liquefaction system 1 for all the tanks 2 mounted in parallel or a liquefaction system 1 for each tank 2.

[0094] The tank 2 includes a wall 4 which delimits a housing 6. It should be understood that the housing 6 corresponds to an internal empty space of the tank 2, designed to contain the gas. Wall 4 therefore serves to form this internal void space by delimiting housing 6.

[0095] Within this housing 6, the gas can be present in different states. It is originally stored in the tank 2 in liquid form, but due to a heat flow at the wall 4 which tends to cause the evaporation of the gas, the gas is present in housing 6 in both liquid and gaseous form.

[0096] Housing 6 thus comprises a lower volume 8, where the gas is in liquid form, and an upper volume 10, where the gas is in gaseous form. Indeed, under the effect of gravity, the gas in liquid form naturally remains in the lower volume 8, which can be considered the lower part of housing 6. At the same time, the gas in gaseous form will occupy the part of housing 6 not filled by the liquid gas and therefore naturally remains in the upper volume 10, which can be considered the upper part of housing 6.

[0097] The dimensions, and in particular the height of each volume, vary according to the quantity of gas in liquid form and therefore the additional quantity of gas in vapor form.

[0098] The gas in liquid form is loaded or unloaded into the tank 2 via one or more loading and / or unloading lines 11 of said gas.

[0099] The liquefaction system 1 is installed on said tank 2, more specifically so as to be in fluidic communication, on the one hand, with the upper volume 10 of the housing 6 of the tank 2 and, on the other hand, with the lower volume 8 of the housing 6 of the tank 2. The liquefaction system 1 is thus capable of drawing gas in the form of vapor from the upper volume 10 of the housing 6 of the tank 2 and of injecting gas in the form of liquid into the lower volume 8 of the housing 6 of the tank 2.

[0100] For this purpose, the liquefaction system 1 includes a main line 12. This main line 12 extends between the tank 2 and a gas / liquid separator 14, and includes in particular an extraction end 16 for the gas and a reinjection end 18 for said gas.

[0101] It should be noted that in order to facilitate reading, in [Fig. 1] and in the following figures, the main pipe 12 is represented in bolder lines than the other lines through which the gas flows. The extraction end 16 of the main line 12 is positioned in the housing 6 of the tank 2, in particular in the upper volume 10 of the housing 6. Thus, the extraction end 16 is configured to draw the gas in the form of vapor contained in the tank 2. The gas can then flow within the main line 12, in particular from the extraction end 16 to the reinjection end 18.

[0102] The reinjection end 18 of the main line 12 is fluidly connected to the separator 14 of the liquefaction system 1. The gas flowing within the main line 12 can be discharged via this reinjection end 18 into the separator 14.

[0103] The gas / liquid separator 14 is configured to separate the gas in vapor form from the gas in liquid form. It is therefore understood that the gas discharged from the reinjection end 18 of the main line 12 is a mixture of gas in vapor form and gas in liquid form. The proportions of gas in vapor form and gas in liquid form depend on the efficiency of the gas liquefaction, which will be detailed later. It should be noted, however, that at this point in the liquefaction system 1, the gas mixture contains a majority of gas in liquid form and a minority of gas in vapor form.

[0104] In order to separate the gas in liquid form from the gas in vapor form, the separator 14 can use any type of technology that enables gas / liquid separation. For example, the separator 14 can be a gravity separator, thus using the effect of gravity to separate the gas in liquid form from the gas in vapor form. In this case, the gas in liquid form is attracted by gravity and accumulates at the bottom of the separator 14, while the gas in vapor form remains suspended and accumulates at the top of the separator 14.

[0105] The liquefaction system 1 also includes a return line 20, configured to inject the gas in liquid form from the liquefaction system 1 into the lower volume 8 of the housing 6 of the tank 2. The return line 20 is thus fluidly connected to the lower volume 8 of the housing 6 of the tank 2 and is also fluidly connected to the bottom of the separator 14. Thus, the gas in liquid form, after being separated from the gas in vapor form within the separator 14, is discharged from the latter by the return line 20 in order to fill the lower volume 8 of the housing 6 of the tank 2 with gas in liquid form.

[0106] The return line 20 includes a valve 22, located on the return line 20 between the separator 14 and the wall 4 of the tank 2. This valve 22 controls the injection of the gas in liquid form into the tank 2 after it exits the separator 14. The valve 22 can be either an on / off valve, switching between an open position, where the gas in liquid form is injected into the lower volume 8 of the tank 2, and a closed position, preventing the injection of the gas in liquid form. The valve 22 can also be a proportional valve, allowing the selection of an intermediate position between fully open and fully closed, in order to regulate the flow rate of gas in liquid form injected into the lower volume 8 of the housing 6 of the tank 2.

[0107] The liquefaction system 1 also includes a plurality of expansion and compression devices, used to compress and expand the circulating gas in the main line 12, in particular to heat or cool the gas by compression and expansion effects.

[0108] More specifically, the main line 12 is equipped with a first compression device 24 and a second compression device 26, arranged successively on the main line 12. By "arranged successively", it is meant that the first compression device 24 is the compression device, among these two compression devices, which is placed closest to the tank 2 if we consider the distance traveled by the gas within the main line 12, and furthest from the separator 14, while the second compression device 26 is the compression device, among these two compression devices, placed closest to the separator 14 and furthest from the tank 2.

[0109] In other words, when the liquefaction system 1 is in operation, the gas flows from the extraction end 16 to the reinjection end 18 of the main line 12, which means that, following the direction of gas flow in the main line 12, the first compression device 24 is upstream of the second compression device 26, and that the latter is therefore downstream of the first compression device 24.

[0110] The first compression device 24 is configured to compress the gas flowing in the main line 12. When the gas flows from the tank 2 to the first compression device 24, it is at a pressure between 1 and 2.5 bar absolute, generally at atmospheric pressure. The first compression device 24 is thus configured to compress this gas, in order to increase the initial pressure of said gas from 1 to 2.5 bar absolute to a final pressure between 5 and 15 bar absolute, for example around 7 bar absolute.

[0111] The second compression device 26, being disposed downstream of the first compression device 24, is therefore configured to compress the gas which has already been compressed by the first compression device 24. The second compression device 26 can thus compress the gas from an initial pressure of between 5 and 15 absolute bars to a final pressure of between 20 and 40 absolute bars.

[0112] In other words, upstream of the first compression device 24, the gas is at a pressure between 1 and 2.5 absolute bars; between the first compression device 24 and the second compression device 26, the gas is at a pressure between 5 and 15 absolute bars; and downstream of the second compression device 26, the gas reaches a pressure between 20 and 40 absolute bars.

[0113] Between these two compression devices 24 and 26, the liquefaction system 1 includes a connection point for a consumption line 28 configured to draw gas flowing in the main line 12. The consumption line 28 extends from this connection point, here a divergence point 30, located on the Main line 12 between the first compression unit 24 and the second compression unit 26, to one or more consumers 32 of this gas. The consumers 32 can be any type of technology using this gas as an energy source. The consumers 32 can also be burners intended to burn excess gas from the tank 2.

[0114] The gas flow rate in the consumption line 28 is regulated by a modulating valve 34, which can, for example, be an on / off valve or a proportional valve. The on / off valve switches between an open and a closed position, while the proportional valve allows for the selection of an intermediate position to adjust the gas flow rate. By regulating the gas flow rate in the consumption line 28, the quantity of gas drawn from the main line 12 to supply the consumption line 28 is thus controlled, this quantity of gas being dependent, in particular, on the needs of the consumers 32.

[0115] It should be noted that, since the divergence point 30 is located between the first compression device 24 and the second compression device 26, the gas drawn from the consumption line 28 is at a pressure between 5 and 15 bar, which also corresponds to the pressure required for the consumers 32.

[0116] The liquefaction system 1 also includes a first expansion device 36, arranged on the main line 12 and configured to expand the gas flowing in the main line 12. The first expansion device 36 is disposed between the second compression device 26 and the separator 14.

[0117] The gas arriving at the first expansion device 36 is therefore at a pressure between 20 and 40 bar. The first expansion device 36 can be, for example, a turbine or any other device allowing expansion close to isentropic expansion. It can also simply be a valve or any other device allowing isenthalpic expansion. The first expansion device 36 is configured to reduce this gas to a pressure between 1 and 2.5 bar absolute, which has the effect of cooling the gas exiting this device. The gas then arriving at the separator 14 is therefore at this pressure, and the gas in liquid form entering the tank 2 via the return line 20 is also at this pressure.

[0118] The operating principle of the liquefaction system 1 is based on the use of the gas withdrawn from tank 2 to cool the same gas in order to liquefy it and reinject it into tank 2. To do this, the liquefaction system 1 includes a heat exchanger 38.

[0119] The heat exchanger 38 is arranged within the liquefaction system 1 in order to carry out a heat exchange between different elements of the system in which the gas circulates.

[0120] The main conduit 12 comprises at least a first part 41 and a second part 42 arranged respectively within the heat exchanger to perform heat exchange. Thus, the first part 41 of the main conduit 12 and the second part 42 of the main conduit 12 are passes of the heat exchanger 38. The first part 41 is located between the tank 2 and the first compression device 24, more precisely between the extraction end 16 and the first compression device 24, and the second part 42 is located between the second compression device 26 and the first expansion member 36.

[0121] It should therefore be noted that the gas circulating in the second part 42 is at a pressure between 20 and 40 bar, since this part is located between the second compression device 26 and the first expansion device 36. On the other hand, the gas circulating in the first part 41 is at a pressure between 1 and 2.5 bar absolute, because this part is located between the tank 2 and the first compression device 24, and therefore contains the gas in the form of vapor from the upper volume 10 of the housing 6 of the tank 2. The gas circulating in the second part 42 is thus at a higher temperature than the gas circulating in the first part 41. It follows that the gas circulating in the second part 42 is capable of releasing heat, while the gas circulating in the first part 41 is capable of recovering heat.

[0122] According to the invention, the liquefaction system 1 comprises a bypass line 44, configured to pass through the heat exchanger 38 in order to form a complementary pass to at least the second part 42 of the circulation line 12, with the aim of improving the liquefaction performance of said system.

[0123] Thus, in certain particular embodiments of the invention, it is understood that the heat exchanger 38 could comprise only one pass formed by the second part 42 of the circulation pipe 12 and another pass formed by the bypass line 44.

[0124] The bypass line 44 extends between an inlet 46 and an outlet 48. The inlet 46 is located on the main line 12 between the second compression device 26 and the first expansion device 36, more precisely between the second compression device 26 and the second part 42 of the main line 12, in order to draw the gas circulating in the main line 12 upstream of the heat exchanger 38. The outlet 48 is located on the main line 12 between the first compression device 24 and the second compression device 26, more precisely between the divergence point 30 and the second compression device 26, in order to reinject the gas circulating in the bypass line 44 into the main line 12.

[0125] The bypass line 44 includes a second expansion device 50, arranged on this line and configured to expand the gas flowing within it. The second expansion device 50 can allow a gas expansion close to isentropic expansion, and This could be, for example, a turbine. It allows the gas to be reduced from a pressure between 20 and 40 bar absolute to a pressure between 5 and 15 bar. It is thus understood that, since the inlet 46 is positioned between the second compression device 26 and the first expansion device 36, the gas flowing between the inlet 46 and the second expansion device 50 is at a pressure between 20 and 40 bar. The gas flowing after the second expansion device 50 is, on the other hand, at a pressure between 5 and 15 bar. Therefore, when the gas flowing in the bypass line 44 is mixed with that flowing in the main line 12, between the first compression device 24 and the second compression device 26, the two gases are at a substantially similar pressure.

[0126] In order to participate in the liquefaction of the gas, the bypass line 44 comprises a first section 52 and a second section 54, both passing through the heat exchanger 38. The first section 52 is positioned between the inlet 46 and the second expansion member 50, while the second section 54 is positioned between the second expansion member 50 and the outlet 48. It is thus understood that, in the first section 52, the gas pressure is between 20 and 40 bar, and in the second section 54, it is between 5 and 15 bar. The gas flowing in the first section 52 is thus at a higher temperature than that flowing in the second section 54, in particular thanks to the expansion of the gas in the bypass line by the second expansion device 50. It results in the gas flowing in the first section 52 being able to give up heat, while that flowing in the second section 54 is able to recover heat.In other words, the pass formed by the first section 52 allows the gas flowing in the bypass line 44 to be cooled before it passes into the second expansion device, so that this gas after expansion is very cold and cold enough to liquefy the gas flowing in the pass formed by the second part 42.

[0127] To control the flow of gas drawn from the bypass line 44, the liquefaction system 1 includes a set of control valves and a regulating valve. On the one hand, the branch line 44 includes at least one control valve, more specifically in the illustrated example a first control valve 56 and a second control valve 58, and on the other hand, the main line 12 includes a regulating valve 60. The first control valve 56 is located on the branch line 44 between the inlet 46 and the first section 52 of the branch line 44, while the second control valve 58 is located between the second section 54 and the outlet 48 of the branch line 44. The regulating valve 60, for its part, is located on the main line 12 between the inlet 46 of the branch line 44 and the second section 42 of the main line 12.

[0128] It should be noted that, depending on whether the control valve 60 is open or closed, the quantity of gas passing through the second section 42 of the main line 12 downstream of said control valve 60 is regulated. Similarly, depending on whether the first control valve 56 and the second control valve 58 are open or closed, the flow rate in the bypass line 44 is regulated, which makes it possible to control whether the gas passes mainly through the second section 42 of the main line 12 or through the first section 52 and the second section 54 of the bypass line 44. Further details on these features will be provided in connection with the following figures, which represent different operating modes of the liquefaction system 1.

[0129] The liquefaction system 1 is also equipped, in this first embodiment, with a recirculation line 62 extending between the separator 14 and a convergence point 64. This recirculation line 62 is configured to recirculate the gas in vapor form separated in the separator 14 within the main line 12. For this purpose, the recirculation line 62 extends between the top of the separator 14, where the gas in vapor form accumulates, and the convergence point 64, located on the main line 12.

[0130] It should be noted that the gas circulating within the recirculation line 62 is at a pressure between 1 and 2.5 bar absolute, because it comes from the separator 14, itself located downstream of the first expansion device 36.

[0131] The recirculation line 62 may include a control valve 63 for the flow of gas circulating within said recirculation line 62.

[0132] The convergence point 64 is positioned between the tank 2 and the first compression device 24, so that the gas in vapor form from the separator 14 joins the gas drawn from the tank 2 before its compression by the first compression device 24. The convergence point 64 is, in this first embodiment, more precisely located between the first part 41 of the main line 12 and the first compression device 24. It is thus understood that, being arranged in this way, a portion 66 of the recirculation line 62 passes through the heat exchanger 38.

[0133] The heat exchanger 38 is therefore, in this first embodiment, a five-pass heat exchanger, where the second part 42 of the main pipe 12, the first part 41 of the main pipe 12, the first section 52 of the bypass line 44, the second section 54 of the bypass line 44, as well as the portion 66 of the recirculation line 62 pass inside the heat exchanger 38. Details concerning the heat exchanges taking place within this heat exchanger 38 will be given in relation to the description of the operating modes illustrated in the following figures.

[0134] Figure 2 is a schematic representation of a first operating mode of the liquefaction system 1 of the first embodiment of Figure 1. It should also be noted that for each of Figures 2 to 4, the direction of fluid flow is represented by arrows. In this first mode of operation, as well as in the other modes of operation presented here, the gas in gaseous form from the upper volume 10 of the tank 2 is drawn off through the main line 12 via the extraction end 16. This gas is at a very low temperature. The gas, in its gaseous form, then flows from the extraction end 16 to the first compression device 24 via the heat exchanger 38, where it serves as a cooling source. Thus, at the outlet of the first section 41, the gas, in its gaseous form, is brought back to ambient temperature after having recovered heat within the heat exchanger 38.

[0135] The gas, now at room temperature, is then compressed by the first compression device 24 to a pressure between 5 and 15 bar, then it flows to the second compression device 26, where it is compressed again, this time between 20 and 40 bar.

[0136] Part of the gas in gaseous form circulating between the first compression device 24 and the second compression device 26 can be withdrawn by the consumption line 28 according to the needs of the consumers 32. The opening of the modulation valve 34 is managed according to these needs, in order to withdraw a variable quantity of the gas circulating in gaseous form between the two compression devices.

[0137] At the outlet of the second compression device 26, the gas, compressed between 20 and 40 absolute bars and at ambient temperature, continues its path to the inlet 46 of the bypass line 44.

[0138] In this first operating mode, the first control valve 56 and the second control valve 58 of the bypass line 44 are closed, while the regulating valve 60 of the main line 12 is open. This means that the gas is prevented from being diverted through the bypass line 44, and that it continues its path in the main line 12 without being drawn off at the inlet 46 of the bypass line 44.

[0139] The gas then passes through the heat exchanger 38 via the second section 42 of the main line, where it releases its heat and cools down. Here, the gas flowing in the second section 42 of the main line 12 therefore undergoes a heat exchange with the gas flowing in the first section 41 of the main line 12. This heat exchange through the heat exchanger 38 thus makes it possible to use the cold gas in gaseous form exiting the tank 2 and flowing in the first section 41 to cool the compressed gas in the second part 42. At the outlet of the heat exchanger 38, the gas circulating in the main pipe 12 is therefore cold, and ready to be expanded under conditions requiring less energy power.

[0140] The gas from the second part 42 then flows to the first expansion valve 36, where it is reduced from 20-40 bar absolute to 1-2.5 bar absolute. This significant expansion cools the gas even further upon exiting the first expansion valve 36 and reaches its liquefaction temperature.

[0141] The gas, now in liquid form, then reaches the separator 14 at a pressure between 1 and 2.5 bar absolute. The small percentage of gas remaining in gaseous form is separated from the liquid gas, which is returned to the lower volume 8 of the tank 2 via the return line 20, in order to fill the tank 2. This return is controlled by the valve 22.

[0142] The gas in gaseous form, separated in the separator 14, then flows in the recirculation line 62 and passes through the heat exchanger 38 before mixing with the gas in gaseous form flowing in the main line 12, between the first part 41 of the main line 12 and the first compression device 24, via the convergence point 64.

[0143] As it passes through the heat exchanger 38, the gas in gaseous form, separated in the separator 14, releases cold because it is at a temperature close to that of the gas's liquefaction. This contributes to the cooling of the high-pressure gas circulating in the second part 42 of the main line 12.

[0144] In other words, in this first operating mode, since the first control valve 56 and the second control valve 58 of the bypass line 44 are closed, the gas flows mainly in the main line 12, the recirculation line 62, the return line 20, and, if necessary, in the consumption line 28 when the consumers 32 require gas. It should be noted that, in this first operating mode, the gas flowing in the second section 42 is cooled by the gas flowing in the first section 41 of the main line 12 and by the gas flowing in the portion 66 of the recirculation line 62; it is then suitable for expansion under conditions requiring less energy. It is then further cooled and liquefied by the decompression process of the first expansion device 36.

[0145] This first mode of operation is, however, limited in terms of efficiency, since it allows for the reliquefaction of approximately 50% of the excess gas in gaseous form. Furthermore, it only operates when the gas in vapor form, recovered in the upper volume 10 of the housing 6 of the tank 2, is at a temperature below -240°C.

[0146] However, it can be advantageous to use this first operating mode when the gas demand of consumers 32 is relatively high and the pressure within the tank is not too high. Indeed, by closing the first control valve 56 and the second control valve 58, the energy that would have been allocated to the operation of the second pressure-reducing device 50 in the bypass line 44 is saved, while also allowing partial reliquefaction of the excess gas in gaseous form.

[0147] The [Fig.3] is a schematic representation of a second mode of operation of the liquefaction system 1 of the first embodiment of the [Fig.1].

[0148] In this second operating mode, the first control valve 56 and the second control valve 58 are open, allowing gas to circulate within the bypass line 44. Furthermore, the regulating valve 60 of the main line 12 is also open. It should be noted that the gas circulation in the main line 12 remains similar to that of the first operating mode, from the extraction end 16 to the inlet 46. At this inlet 46, the gas from the second compression device 26 is then divided into a first flow portion and a second flow portion.

[0149] The first portion of the flow continues its path in the main line 12, following the same path as that described previously in the first operating mode. Thus, the first portion of the flow is cooled in the second part 42 of the line, then expanded by the first expansion device 36. Next, the gas in vapor form is separated from the gas in liquid form within the separator 14. The gas in liquid form is returned to the tank 2 via the return line 20, while the gas in vapor form returns to the main line 12 via the recirculation line 62.

[0150] The second portion of the flow, meanwhile, flows from the inlet 46 and passes into the bypass line 44. Passing through the first section 52, the gas, which was at ambient temperature, is then cooled to a very low temperature; for example, the second portion of the flow can be cooled to about -210°C for dihydrogen.

[0151] The second portion of the flow then continues to the second expansion valve 50, where it is expanded from 20-40 bar absolute to 5-15 bar absolute, generating even more cold and resulting in an even colder second portion of the flow. This second portion of the flow then circulates in the second section 54 of the bypass line 44, where it acts as a cooling source and warms up, reaching ambient temperature at the outlet of this second section 54.

[0152] The second portion of the flow then mixes with the gas circulating between the first compression device 24 and the second compression device 26 via the outlet 48 of the bypass line 44. This mixture is then compressed by the second compression device 26 and is again divided into a first and second portion of flow at the inlet 46 of the recirculation line 62, as long as the first control valve 56, the second control valve 58 and the regulating valve 60 remain open.

[0153] In this second mode of operation, the heat exchanger 38 therefore uses as cold sources the gas circulating in the first part 41 of the main line 12, the gas circulating in the portion 66 of the recirculation line 62, as well as the second portion of gas flow circulating in the second section 54. This makes it possible to cool the first portion of gas flow in the second part 42 of the main line 12 and the second portion of flow in the bypass line 44.

[0154] The presence of this cold source, generated by the expansion of the gas already cooled during a first pass through the heat exchanger 38 thanks to the first section 52, is very advantageous and makes it possible to considerably increase the efficiency of the liquefaction of the gas in the form of excess vapor coming from the tank 2. Indeed, this second mode of operation makes it possible to treat all of the gas in the form of excess vapor, and can even be used when the gas in the form of vapor is not very cold at the outlet of the tank 2, for example at -220°C for dihydrogen.

[0155] Thus, this second mode of operation is particularly effective when it is necessary to liquefy a large quantity of gas, for example due to excessive pressure in the tank 2, and also when the consumers 32 cannot sufficiently burn the excess gas in vapor form.

[0156] The invention therefore also relates to a method in which the gas flow in the bypass line 44 is regulated according to the quantity of liquid gas present in the tank 2 and therefore the pressure within the housing 6 of the tank 2. This flow can in particular be controlled by the management of the first control valve 56, the second control valve 58, as well as the regulating valve 60.

[0157] The [Fig.4] is a schematic representation of a third mode of operation of the liquefaction system 1 of the first embodiment of the [Fig.1].

[0158] In this third mode of operation, the first control valve 56, the second control valve 58 and the regulating valve 60 are closed, while the modulation valve 34 of the consumption line 28 is simultaneously open, which notably prevents the circulation of gas within the bypass line 44 as well as in the main line 12 downstream of the regulating valve 60, while allowing circulation within the consumption line 28.

[0159] It should be noted that the gas flow in the main line 12 remains similar to that of the first and second operating modes of the extraction end 16 up to the divergence point 30.

[0160] At this divergence point 30, all the gas flowing in the main line 12 is drawn off by the consumption line 28, since the modulating valve 34 is open, while the first control valve 56, the second control valve 58 and the regulating valve 60 are closed and thus prevent the circulation of gas in the main line 12 downstream of the divergence point 30.

[0161] It is therefore understood that in this third mode of operation, the liquefaction system 1 does not liquefy the excess gas in gaseous form from the tank 2. All of this gas is sent to the consumers 32. This mode of operation is particularly advantageous when the gas requirements of the consumers 32 are high and they can treat all the excess gas in gaseous form without requiring additional liquefaction.

[0162] The [Fig.5] is a schematic representation of a second embodiment of the liquefaction system.

[0163] This second embodiment differs from the first embodiment in only one aspect: in this second embodiment, the convergence point 64 is positioned at a different location on the main conduit 12 compared to the first embodiment.

[0164] More specifically, the convergence point 64 is positioned between the tank 2 and the first part 41 of the main pipe 12, that is to say between the tank 2 and the heat exchanger 38.

[0165] In other words, the convergence point 64 is located upstream of the heat exchanger, so that the gas circulating in the recirculation line joins the gas exiting the tank 2 before passing into the heat exchanger 38. As described above, the present invention achieves its stated objectives, namely reducing the number of machines dedicated to liquefying excess vapor from a transport and / or storage tank of said gas in order to decrease energy, installation, and maintenance costs. To this end, the invention proposes a gas liquefaction system for the transport and / or storage tank, using the excess gas in gaseous form from the tank as a cooling source via a bypass line.

[0166] The present invention is not limited to the means and configurations described and illustrated herein and extends also to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Demands

1. Liquefaction system (1) for a gas intended for a tank (2) for the transport and / or storage of said gas, the liquefaction system (1) comprising a main line (12) fluidly connecting an upper volume (10) of the tank (2) to a gas / liquid separator (14) and comprising a first compression device (24) and a second compression device (26) disposed successively between the tank (2) and the separator (14), the liquefaction system (1) comprising a return line (20) of the tank (2) fluidly connecting the separator (14) to a lower volume (8) of the tank (2), the main line (12) comprising a first expansion device (36) disposed between the second compression device and the separator (14),said liquefaction system (1) comprising a heat exchanger (38) through which passes a first part (41) of the main line (12) disposed between the tank (2) and the first compression device (24) and through which passes a second part (42) of the main line (12) disposed between the second compression device (26) and the first expansion device (36), characterized in that the main line (12) comprises a branch line (44) comprising an inlet (46), an outlet (48) and a second expansion device (50), the inlet (46) being fluidly connected to the main line (12) between the second compression device (26) and the first expansion device (36), the outlet (48) being fluidly connected to the main line (12) between the first compression device (24) and the second compression device (26),a first section (52) of the bypass line (44) disposed between the inlet (46) and the second expansion member (50) passing within the heat exchanger (38), and a second section (54) of the bypass line (44) disposed between the second expansion member (50) and the outlet (48) passing within the heat exchanger (38).

2. Liquefaction system (1) according to claim 1, wherein the bypass line (44) includes at least one control valve (56, 58) configured to regulate the flow of gas circulating within said bypass line (44).

3. Liquefaction system (1) according to claim 2, wherein the bypass line (44) comprises a first control valve (56) arranged between the inlet (46) of the branch line (44) and the first section (52).

4. Liquefaction system (1) according to any one of claims 1 to 3, wherein the main line (12) includes a control valve (60) configured to regulate the flow of gas circulating within said main line (12), the control valve (60) being disposed between the inlet (46) of the bypass line (44) and the second part (42) of the main line (12).

5. Liquefaction system (1) according to any one of claims 1 to 4, comprising a recirculation line (62) for the gas from the separator (14), the recirculation line (62) extending between the separator (14) and a convergence point (64) disposed on the main line (12) between the tank (2) and the first compression device (24).

6. Liquefaction system (1) according to claim 5, wherein the recirculation line (62) includes a control valve (63) for the flow of gas circulating within said recirculation line (62).

7. Liquefaction system (1) according to claim 5 or 6, wherein the convergence point (64) is disposed between the heat exchanger (38) and the first compression device (24), a portion (66) of the recirculation line (62) passing within the heat exchanger (38).

8. Liquefaction system (1) according to claim 5 or 6, wherein the convergence point (64) is disposed between the tank (2) and the heat exchanger (38).

9. Liquefaction system (1) according to any one of claims 1 to 8, comprising a consumption line (28) extending between a divergence point (30) and consumers (32) of said gas, the divergence point (30) being disposed on the main line (12) between the first compression device (24) and the second compression device (26).

10. Liquefaction system (1) according to claim 9, wherein the consumption line (28) includes a modulating valve (34) configured to regulate the flow of gas circulating within said consumption line (28).

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