Natural gas processing system for gas from a floating structure's tank, configured to supply natural gas as fuel to a natural gas-consuming appliance

Abstract

Natural gas processing system from a tank of a floating structure configured to supply natural gas as fuel to a natural gas consuming appliance. The invention relates to a compression system (2) intended to equip a refrigerant circuit (4), comprising at least one compression device (19) configured to compress the refrigerant, the compression device (19) comprising at least one compression member (10) actuated by a drive device (32) connected to each other by at least one bearing (14) configured to be at least partially sealed by the refrigerant, the compression system (2) comprising a refrigerant recovery device (22) present in the drive device (32), the refrigerant recovery device (22) being configured to return the refrigerant recovered in the drive device (32) to the refrigerant circuit (4).Figure from the summary: Fig 1.

Description

Title of the invention: System for treating natural gas from a tank of a floating structure configured to supply natural gas as fuel to a natural gas-consuming device

[0001] The present invention relates to the field of compression systems intended to be installed on floating structures using, storing and / or transporting liquefied natural gas. It relates in particular to a system for treating natural gas used as fuel for at least one consumer device equipping the floating structure.

[0002] In order to transport and / or store natural gas more easily over long distances, natural gas is generally maintained in liquid form at temperatures below -163°C and at atmospheric pressure, in order to obtain liquefied natural gas, commonly known by the acronym "LNG", or "Liquefied Natural Gas". This liquefied natural gas is then loaded or unloaded from dedicated storage tanks of the floating structure.

[0003] Such tanks are never perfectly thermally insulated so that the natural gas evaporates at least partially. Thus, these tanks contain both natural gas in liquid and gaseous form, the latter form of natural gas also being called "BOG" from the English acronym "Boil-Off Gas" and accumulating in the tank ceiling.

[0004] In a known manner, at least a portion of the natural gas present in the tank in gaseous form can be used to power a consumer device, such as an engine, intended to meet the operating energy needs of the floating structure, in particular for its propulsion and / or its production of electricity for the on-board equipment. For this purpose, it is known in particular to circulate the natural gas in the gaseous state through at least one natural gas treatment system so as to allow its compression and heating to a temperature suitable for its use as fuel in the consumer device. Such a treatment system comprises a refrigerant circuit configured to implement at least one heat exchange with the natural gas circulating in the treatment system.

[0005] The known refrigerant circuit uses a compression device. Since such a circuit operates at cryogenic temperatures, it is essential that the sealing of the various rotation bearings of the compression device is achieved by means of gas, for example nitrogen. Indeed, at such temperatures, the use of oil in the compression device(s) is accompanied by a solidification at least partial oil filling which is likely to impair the proper functioning of the treatment system. A disadvantage of using a compression device comprising a nitrogen-sealed bearing is that it is inevitably accompanied by nitrogen leaks into the refrigerant circulating in the circuit, which leads to an alteration of the reference composition of said refrigerant and results in a reduction in the performance of the refrigerant circuit.

[0006] The invention corrects this defect and proposes a compression system intended to equip a refrigerant circuit, comprising at least one compression device configured to compress the refrigerant, the compression device comprising at least one compression member actuated by a drive device connected to each other by at least one bearing configured to be at least partly sealed by the refrigerant, the compression system comprising a device for recovering the refrigerant present in the drive device, the refrigerant recovery device being configured to return the refrigerant recovered in the drive device to the refrigerant circuit.

[0007] In the present invention, the compression device comprises a compression member actuated by a drive device connected to each other by at least one bearing configured to be at least partially sealed by the refrigerant fluid. The integrity of the refrigerant fluid within the refrigerant circuit is maintained since the gas used to seal the bearing is the refrigerant fluid itself and this is returned to the refrigerant circuit. Since the sealing of the bearing is achieved by means of the refrigerant fluid, the refrigerant circuit is not polluted by the presence of an unwanted gas and the circulating mass of refrigerant fluid within the refrigerant circuit is maintained.

[0008] The recovery device thus makes it possible to suck up the refrigerant fluid present in a gearbox of the drive device via a compression element, to then be separated from the lubricant coming from the gearbox, using a filtration member, for example.

[0009] According to a characteristic of the invention, the recovery device comprises at least one compression element and at least one pipe on which the compression element is arranged, the pipe extending from the drive device to an injection point configured to be arranged on a low pressure portion of the refrigerant circuit.

[0010] The recovery device comprises a compression element which takes the form, for example, of a diaphragm compressor, as well as a pipe arranged between the gearbox and the injection point present on the closed refrigerant circuit.

[0011] According to another characteristic of the invention, the recovery device comprises at least one filtration member. The filtration member captures the lubricant present in the pipe, before the introduction of the refrigerant into the refrigerant circuit. The filtration member can be placed upstream of the compression element, in order to remove the lubricant before it enters the compression element. Under these conditions, the compression element admits gas recovered into the gearbox and freed from the lubricant present therein.

[0012] Alternatively, the filtration member is located downstream of the compression element.

[0013] According to another feature of the invention, the drive device comprises a gearbox and an actuator which rotates at least one gear of the gearbox, the recovery device being fluidically connected to an upper part of the gearbox. The actuator rotates a plurality of gears constituting the gearbox. The actuator is for example electric, pneumatic or hydraulic. According to a preferred example, the actuator is an electric motor.

[0014] The recovery device is connected to the upper part of the gearbox so as to ensure the recovery of refrigerant in the gaseous state, the refrigerant in the gaseous form being concentrated in an upper part of the gearbox. The position of the recovery device relative to the gearbox also makes it possible to reduce the quantity of lubricant captured by the recovery device.

[0015] According to a feature of the invention, the compression system comprises a pipe connected to the bearing and configured to be fluidically connected to a high-pressure portion of the refrigerant circuit. The pipe connected to the bearing allows the supply of refrigerant under high pressure in order to seal the rotation bearing disposed between the gearbox and the compression device.

[0016] According to another aspect, the invention covers a refrigerant circuit comprising at least two heat exchangers, an expansion member and a compression system as described in the present document.

[0017] Advantageously, the refrigerant fluid present in the refrigerant fluid circuit comprises:

[0018] - 20 to 35 mol% of dinitrogen or 30 to 50 mol% of argon or 35 to 50 mol% of a mixture of nitrogen and argon and,

[0019] - 35 to 55 mol% of methane,

[0020] said refrigerant fluid having a proportion of methane and dinitrogen and / or argon of between 70 and 85 mol% of the refrigerant fluid, the remainder comprising a mixture of hydrocarbons composed of at least ethane and / or propane and / or butane and / or ethylene and / or propylene. Such a composition of the refrigerant fluid is particularly suitable for carrying out a heat exchange with a natural gas used as fuel to supply a consumer device of a natural gas treatment system which equips a floating structure.

[0021] According to a characteristic of this invention, the injection point is arranged on the refrigerant circuit between an outlet of the expansion member and an inlet of the compression member, delimiting the low pressure portion of the refrigerant circuit. The high pressure portion of the refrigerant circuit begins at the outlet of the compression member and ends at the inlet of the expansion member.

[0022] According to a characteristic of the invention, the pipe is connected to the refrigerant circuit at a point located between the outlet of the compression member and the inlet of the expansion member, forming the high pressure portion of the refrigerant circuit.

[0023] The pipe allows the admission of refrigerant fluid into the bearing placed between the compression device and the gearbox. This pipe is supplied by the high pressure portion of the refrigerant circuit.

[0024] According to another aspect, the invention covers a system for treating natural gas stored in a floating structure, comprising at least one tank intended for the transport and / or storage of natural gas in the liquid state, a supply system intended to supply natural gas to a consumer device of the floating structure and a refrigerant fluid circuit as described in the present document.

[0025] According to a feature of this invention, the treatment system comprises at least one device consuming natural gas as fuel. This consumer device uses as fuel the natural gas which passes through the supply system, from the tank.

[0026] The natural gas present in the tank's overhead passes into the first exchanger, which allows it to be heated when the refrigerant circuit is in operation. The gas thus heated then passes into a compression device in order to increase the pressure and temperature of the natural gas in the gaseous state. Subsequently, the natural gas serves as fuel for the consuming device of the floating structure.

[0027] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and several exemplary embodiments given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

[0028] [Fig.l] represents the compression system according to the invention;

[0029] [Fig.2] is a schematic representation of the compression system according to the invention integrated into a natural gas supply system;

[0030] [Fig.3] schematically represents a system for treating natural gas liquefied, stored in a tank of a floating transport and / or storage structure said natural gas;

[0031] [Fig.4] is a schematic cutaway representation of the tank of a floating structure and of a terminal for loading and / or unloading this tank.

[0032] [Fig. 1] represents a compression system 2 configured to compress the refrigerant present in a refrigerant circuit 4. The refrigerant circuit 4 comprises two portions: a so-called high pressure portion 13 and a so-called low pressure portion 30. The low pressure portion 30 is a part of the refrigerant circuit arranged upstream of the compression system 2, while the high pressure portion 13 is located downstream of the compression system 2, according to the direction of circulation of the refrigerant within the refrigerant circuit.

[0033] This compression system 2 comprises at least one compression device 19 responsible for compressing the refrigerant fluid. The compression device 19 comprises a compression member 10 and a drive device 32 whose role is to set in motion, in particular to rotate the compression member 10. The compression member 10 is the part of the compression device 19 which carries out the compression work. It may in particular be a centrifugal, screw or vane compressor.

[0034] The drive device 32 is an assembly which comprises an actuator 34, in particular an electric, pneumatic or hydraulic motor, as well as a gearbox 16 installed kinematically between the actuator 34 and the compression member 10. The role of the gearbox 16 is to adapt the torque and the speed between the actuator 34 and the compression member 10. Such a gearbox 16 comprises a housing inside which a plurality of gears and shafts rotate.

[0035] A first of these shafts is disposed between the actuator 34 and an input gear of the gearbox 16. Another shaft is an output shaft which extends from inside the gearbox housing to inside the compression member 10.

[0036] A bearing 14 is arranged between the gearbox 16 and the compression member 10 and this bearing 14 forms the element which carries in rotation the output shaft of the gearbox 16. The sealing of such a bearing 14 is achieved by injecting the refrigerant fluid from the refrigerant circuit 4 into the bearing 14, at a pressure higher than that which prevails at the inlet of the compression member 10.

[0037] To do this, the compression system 2 comprises a pipe 6 which extends between the bearing 14 and a point 8 located on the refrigerant circuit 4, downstream of the compression member 10 and in the high-pressure portion of this circuit. The pipe 6 is configured to channel refrigerant coming from the refrigerant circuit to the bearing 14. The latter is however not completely sealed and a first fraction of the refrigerant spreads towards the inside of the compression member pressure 10, while a second fraction of refrigerant fluid flows to the gearbox 16 and fills it. These fractions of refrigerant fluid are represented by a dotted arrow referenced 18 in [Fig.l].

[0038] The compression system 2 according to the invention also comprises a device 22 for recovering the refrigerant fluid present in the drive device 32, in particular present in the gearbox 16, due to the fraction 18 of refrigerant fluid which passes through the bearing 14 and enters the gearbox 16. The role of the recovery device 22 is to capture the refrigerant fluid present in the gearbox 16 and to return it to the refrigerant fluid circuit, so as to maintain a circulating mass of refrigerant fluid in the refrigerant fluid circuit 4 in accordance with the original prescriptions.

[0039] The recovery device 22 extends from the gearbox 16 to an injection point 33 located on the refrigerant circuit 4, in the low pressure portion 30 of this circuit.

[0040] The recovery device 22 is connected to an upper part of the gearbox 16, so as to recover the refrigerant in its gaseous phase. The refrigerant present in the gearbox 16 circulates in a pipe 26 which, at one end, is connected to the upper part of the housing of the gearbox 16 and, at the other end, is connected to the refrigerant circuit 4, upstream of the compression member 10, at the injection point 33.

[0041] The recovery device 22 comprises a compression element 24 which may, for example, take the form of a diaphragm compressor. The compression element 24 is configured to extract the refrigerant present in the gearbox 16 and return it to the low-pressure portion of the refrigerant circuit 4. This is how this compression element 24 raises the pressure of the refrigerant recovered in the gearbox 16 above the pressure of the refrigerant within the refrigerant circuit, upstream of the compression member 10, that is to say in the low-pressure portion of this circuit.

[0042] Optionally, the recovery system 22 comprises a filtration member 28 which can be positioned on the pipe 26 upstream or downstream of the compression element 24, depending on the direction of circulation of the refrigerant fluid within the pipe 26.

[0043] When the filtration member 28 is placed upstream of the compression element 24, this makes it possible to separate the lubricant coming from the gearbox 16 from the refrigerant fluid, before this refrigerant fluid enters the compression element 24. In another case of use, the filtration member 28 is located downstream of the compression element 24. The refrigerant fluid in the gaseous state and the lubricant are then separated by the filtration member 28, so as not to return it to the refrigerant circuit. refrigerant 4 than the refrigerant fluid, i.e. without lubricant.

[0044] [Fig. 2] illustrates a system 38 for supplying fuel to consumer devices 46 installed on a floating structure equipped with such a supply system 38. The fuel here is a liquefied natural gas which is stored in a tank 20 which equips the floating structure. This supply system 38 integrates the compression system described in [Fig. 1].

[0045] The supply system 38 thus comprises at least one tank 20 intended to contain liquefied natural gas, as well as an intake circuit 40 configured to recover the natural gas in the vapor state present in a canopy 42 of the tank 20 and to supply it to one or more consumers 46. This natural gas present in the canopy 42 of the tank 20 results from the natural evaporation of the natural gas stored in the liquid state in the tank 20.

[0046] The intake circuit 40 comprises a compressor 44 configured to raise the temperature and pressure of the natural gas in the vapor state, so as to place this natural gas in pressure and temperature conditions compatible with the need of the fuel-consuming device(s) 46 present on the floating structure. For example, at least one fuel-consuming device 46 may be an electric motor-generator of the DFDE (Dual Fuel Diesel Electric) type, that is to say a gas-consuming device configured to provide the electrical power supply to the floating structure, or a propulsion engine of the ship, such as an ME-GI or XDF engine. It is understood that this is only an exemplary embodiment of the present invention and that the installation of different gas-consuming devices may be provided without departing from the context of the present invention.

[0047] The compressor 44 is redundant with the compression member 10, so that the latter can compensate for a breakdown of the compressor 44, so as to maintain operational the gas supply to the consumer device(s) 46, in particular the ship's propulsion engine.

[0048] Such redundancy also results from the use of valves such as a first stop valve 50 placed on the low pressure portion 30 of the refrigerant circuit 4. This first stop valve 50 is configured to block the arrival of refrigerant to the compression member 10. Similarly, the refrigerant circuit comprises a second stop valve 51 installed on the high pressure portion 13 of the refrigerant circuit 4 and whose function is to isolate the compression member 10 from the rest of the refrigerant circuit when the latter is used within the intake circuit 40, that is to say to supply fuel to the consumer device(s) 46 of the floating structure.

[0049] The intake circuit 40 also comprises valves 52 arranged downstream and upstream of a group formed by the compressor 44 and the compression member 10. These valves 52 have the role of managing the supply of gas coming from the top 42 of the tank 20 either to the compressor 44, or to the compression member 10, so that the compressor 44 is assigned to the intake circuit 40, while the compression element 10 is assigned to the refrigerant circuit 4. These valves 52 and pipes 53 make it possible to use the compression member 10 within the supply circuit 40 when the compressor 44 is faulty, as mentioned above.

[0050] The intake circuit 40 also comprises at least one expansion device 15 whose function is to adapt the pressure of the gas sent to the consumer device 46, by lowering it.

[0051] [Fig. 3] represents a system for treating natural gas 52 stored in the liquid state in the tank 20 of a floating structure 48 for transporting and / or storing natural gas, as shown diagrammatically in [Fig. 4].

[0052] The natural gas treatment system 52 comprises the supply system 38 described in [Fig. 2], as well as a compression system 2 according to the invention. [Fig. 3] shows in detail the constitution of the refrigerant circuit 4 which includes such a compression system 2, as well as the interaction which exists between this refrigerant circuit 4 and the intake circuit 40, or even the interaction which exists between the refrigerant circuit 4 and at least one natural gas liquefaction installation 7.

[0053] The refrigerant circuit 4 therefore comprises at least one compression member 10 as described previously, a first heat exchanger 54, an expansion member 12, for example a Joule-Thomson valve, and a second heat exchanger 56.

[0054] The refrigerant fluid which circulates within the refrigerant circuit has the following composition: 20 to 35 mol% of nitrogen or 30 to 50 mol% of argon or 35 to 50 mol% of a mixture of nitrogen and argon and 35 to 55 mol% of methane, this refrigerant fluid having a proportion of methane and nitrogen and / or argon of between 70 and 85 mol% of the refrigerant fluid, the remainder comprising a mixture of hydrocarbons composed of at least ethane and / or propane and / or butane and / or ethylene and / or propylene. This composition allows the change of state of the refrigerant fluid at the temperatures which the natural gas can reach within the treatment device.

[0055] Examples of the composition of this refrigerant fluid and the proportions of its compounds can take the following form:

[0056] [Tables 1] 111111111 5 Components N 2 3 ? 32 ü 20 Ar o 0 V 46 30 45 40 35 35 3. U 12: 10 § 8 15 0 § Ci 7 Û 12 9 10

[0057] The natural gas liquefaction installation 7 ensures, according to the gaseous natural gas requirements of the fuel-consuming devices 46, the liquefaction of at least part of the natural gas taken from the tank 20 and which is not consumed by the consuming device 46.

[0058] The second heat exchanger 56 ensures, for its part, the evaporation of the refrigerant fluid within the refrigerant fluid circuit 4. This second heat exchanger 56 also ensures sub-cooling of natural gas in the liquid state so as to promote the liquefaction of the natural gas which passes through the liquefaction unit 7, the part of sub-cooled liquid natural gas being sent into the liquefaction unit 7 to cool the natural gas in the gaseous state which circulates in the return pipe 84.

[0059] Within the natural gas treatment system 52, the refrigerant circuit 4 consists of a unit capable of exchanging calories with the natural gas, in the liquid state or in the gaseous state. In particular, in the present invention, the natural gas in the liquid state has a liquefaction temperature, at atmospheric pressure, of approximately -163°C. The composition of the refrigerant which circulates in the refrigerant circuit 4 is adapted to this temperature, in order to optimize the efficiency of the heat exchanges which occur at cryogenic temperature between the refrigerant and the natural gas in the liquid state or in the gaseous state coming from the tank 20.

[0060] As described previously, the refrigerant fluid is first compressed by the compression member 10, then circulates within the high pressure portion 13 of the refrigerant fluid circuit 4, up to a first pass 64 of the first heat exchanger 54.

[0061] The first heat exchanger 54 then comprises at least three passes: the first pass 64 traversed by the refrigerant fluid subjected to high pressure, a second pass 66 traversed by the refrigerant fluid subjected to low pressure and a third pass 58 of the first heat exchanger 54 crossed by the natural gas in the gaseous state which comes from the sky 42 of the tank 20.

[0062] The first heat exchanger 54 operates as a condenser. This first heat exchanger 54 makes it possible to lower the temperature of the refrigerant fluid present in the high-pressure portion 13, before it enters the expansion member 12. This drop in temperature occurs via an exchange of calories between the refrigerant fluid present in the first pass 64 and the third pass 58 of the first heat exchanger 54, this latter pass being traversed by the natural gas in the gaseous state which results from the natural evaporation of the liquid part of the natural gas stored in the tank 20.

[0063] The first heat exchanger 54 is optionally configured to operate at least in part as an internal heat exchanger that implements a heat exchange between the high pressure portion 13 of the refrigerant circuit 4 and the low pressure portion 30 of the refrigerant circuit 4. The refrigerant present in the first pass 64 of the first heat exchanger 54 captures the cold from the refrigerant of the second pass 66, as well as the cold present in the natural gas in the gaseous state that comes from the headspace 42 of the tank 20.

[0064] At the outlet of the first pass 64 of the first heat exchanger 54, the refrigerant circuit 4 continues to the expansion member 12 in which the refrigerant is expanded and its pressure is lowered, so as to reach a temperature between -168 and -180°C.

[0065] The refrigerant circuit 4 then continues to a first pass 68 of the second heat exchanger 56 which exchanges calories with a second pass 70 of the second heat exchanger 56 in which liquefied natural gas circulates in the liquid state at a temperature of approximately -163°C, by means of a pump 29. The natural gas being at a higher temperature than the refrigerant, it gives up calories to the refrigerant and therefore captures cold. The refrigerant fluid leaves the first pass 68 of the second heat exchanger 56 in the gaseous state at a temperature of the order of -162°C, while the natural gas in the liquid state is sub-cooled to a temperature of the order of -172°C, measured at the outlet of the second pass 70 of the second heat exchanger 56. In this situation, the second heat exchanger 56 behaves like an evaporator.

[0066] The refrigerant fluid circuit 4 then continues to the second pass 66 of the first heat exchanger 54 at which, as previously explained, the refrigerant fluid captures the calories released by the refrigerant fluid circulating in the first pass 64 of the first heat exchanger 54.

[0067] Thus, the refrigerant fluid leaves the second pass 66 of the first exchanger 54 in an essentially gaseous state. The refrigerant fluid is then at a temperature between -30°C and 45°C and moves towards the compression member 10.

[0068] Advantageously, the refrigerant circuit 4 may comprise at least one accumulation device 72. The latter, arranged between the second pass 66 of the first heat exchanger 54 and the inlet of the compression member 10, is configured so as to constitute an accumulation zone for refrigerant in the two-phase state 74 or in the gaseous state 76 and to send only refrigerant in the gaseous state 76 to the compression member 10.

[0069] The natural gas in the gaseous state compressed by the compressor 44 can be returned to the tank 20 via a return pipe 84. The return pipe 84 transports the natural gas in the gaseous state to the liquefaction installation 7, the latter comprising a heat exchanger 60 whose role is to cool the natural gas in the gaseous state in order to liquefy it before its return to the tank 20. To do this, this heat exchanger 60 comprises a first pass 86, traversed by the natural gas in the gaseous state coming from the intake circuit 40, which exchanges heat with a second pass 88 which is traversed by the natural gas in the liquid state cooled by the second heat exchanger 56. The natural gas in the gaseous state therefore returns to the liquid state and is then returned to the tank 20.

[0070] Finally, [Fig.4] is a cutaway representation of a floating structure 48 which can carry the compression system 2 according to the invention, alone or in combination with the supply system 38 as described in [Fig.2], or even integrated into a natural gas treatment system 52, as described in [Fig.3].

[0071] The floating structure 48 comprises the natural gas storage tank 20 mounted in a hull 78 of the floating structure 48, this tank 20 being formed by an assembly of at least one primary sealing membrane, one secondary sealing membrane and two thermally insulating barriers, respectively arranged between the primary sealing membrane and the secondary sealing membrane and between the secondary sealing membrane and the hull.

[0072] Loading and / or unloading pipelines 80 arranged on the upper deck of the floating structure 48 can be connected, by means of appropriate connectors, to a maritime or port terminal 82, in order to transfer the cargo of natural gas in the liquid state from or to the tank 20.

[0073] It is understood from reading the above that the present invention proposes a compression system 2 with a bearing sealed against the refrigerant fluid. The leak resulting from this sealing is recovered in the gearbox and then returned to the refrigerant fluid circuit. This compression system is integrated into a supply system for a consumer device, and more generally into a natural gas treatment system fitted to a ship.

[0074] The invention cannot, however, be limited to the means and configurations described and illustrated herein, and it also extends to any equivalent means or configuration and to any technical combination operating such means. In particular, the number of heat exchangers may be modified, the first heat exchanger being able in particular to be divided into a plurality of heat exchangers insofar as the treatment system, ultimately, fulfills the same functionalities as those described in this document.

Claims

Claims

1. Compression system (2) intended to equip a refrigerant circuit (4), comprising at least one compression device (19) configured to compress the refrigerant, the compression device (19) comprising at least one compression member (10) actuated by a drive device (32) connected to each other by at least one bearing (14) configured to be at least partly sealed by the refrigerant, the compression system (2) comprising a device (22) for recovering the refrigerant present in the drive device (32), the refrigerant recovery device (22) being configured to return the refrigerant recovered in the drive device (32) to the refrigerant circuit (4).

2. Compression system (2) according to the preceding claim, wherein the recovery device (22) comprises at least one compression element (24) and at least one pipe (26) on which the compression element (24) is arranged, the pipe (26) extending from the drive device (32) to an injection point (33) configured to be arranged on a low pressure portion (30) of the refrigerant circuit (4).

3. Compression system (2) according to any one of the preceding claims, in which the recovery device (22) comprises at least one filtration member (28).

4. A compression system (2) according to any preceding claim, wherein the drive device (32) comprises a gearbox (16) and an actuator (34) which rotates at least one gear of the gearbox (16), the recovery device (22) being fluidically connected to an upper portion of the gearbox (16).

5. Compression system (2) according to any one of the preceding claims, comprising a conduit (6) connected to the bearing (14) and configured to be fluidically connected to a high pressure portion (13) of the refrigerant circuit (4).

6. Refrigerant fluid circuit (4) comprising at least two heat exchangers (54, 56), an expansion member (12) and a compression system (2) according to any one of the preceding claims.

7. Refrigerant fluid circuit (4) according to the preceding claim, comprising a refrigerant fluid comprising: - 20 to 35 mol% of nitrogen or 30 to 50 mol% of argon or 35 to 50 mol% of a mixture of nitrogen and argon and, - 35 to 55 mol% of methane, said refrigerant fluid having a proportion of methane and nitrogen and / or argon of between 70 and 85 mol% of the refrigerant fluid, the remainder comprising a mixture of hydrocarbons composed of at least ethane and / or propane and / or butane and / or ethylene and / or propylene.

8. Refrigerant circuit (4) according to any one of claims 6 or 7 in combination with claim 2, wherein the injection point (33) is arranged on the refrigerant circuit between an outlet of the expansion member (12) and an inlet of the compression member (10), delimiting the low pressure portion (30) of the refrigerant circuit (4).

9. Refrigerant circuit (4) according to any one of claims 6 to 8, in combination with claim 5, in which the conduit (6) is connected to the refrigerant circuit (4) at a point (8) located between an outlet of the compression member (10) and an inlet of the expansion member (12), forming the high pressure portion (13) of the refrigerant circuit (4).

10. System for treating natural gas (52) stored in a floating structure (48), comprising at least one tank (20) intended for transporting and / or storing natural gas in the liquid state, a supply system (38) intended to supply natural gas to a consumer device (46) of the floating structure (48) and a refrigerant circuit (4) according to any one of claims 6 to 9.

11. System for treating a natural gas (52) according to the preceding claim, comprising at least one appliance consuming (46) natural gas as fuel.

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