System for processing natural gas arranged to supply natural gas as fuel coming from a tank of a floating structure to a natural gas consumer

Abstract

The present invention relates to a compression system (2) intended to comprise a refrigerant circuit (4), comprising at least one compression device (19) configured to compress a refrigerant, the compression device (19) comprising at least one compression member (10) actuated by a drive device (32), the compression member (10) and the drive device (32) being connected to each other by at least one support (14) configured to be at least partially sealed by the refrigerant, the compression system (2) comprising a device (22) for collecting refrigerant present in the drive device (32), the device (22) for collecting refrigerant being configured to send the collected refrigerant from the drive device (32) to the refrigerant circuit (4).

Description

[Technical field]

[0001] The present invention relates to the field of compression systems designed to be installed on floating structures that use, store and / or transport liquefied natural gas, in particular to a system for treating natural gas as fuel for at least one natural gas consumer included on the floating structure. [Background technology]

[0002] To more easily transport and / or store natural gas over long distances, it is typically maintained in a liquid state at temperatures below -163°C under ambient pressure, resulting in a liquefied gas, commonly referred to as "GNL" or "LNG" (liquefied natural gas), which is then loaded into or unloaded from dedicated storage tanks located on floating structures.

[0003] Such tanks are not fully insulated, and therefore the natural gas at least partially evaporates. Thus, these tanks contain natural gas both as a liquid and as a gas. The gaseous form of natural gas, also known as "BOG" (boil off gas), accumulates in the tank blanket.

[0004] It is known that at least a part of the natural gas in the vapour state in the tanks can be used to feed consumers, such as prime movers, provided to meet the power requirements of the floating installation, in particular for the propulsion of the installation and / or for the generation of electricity for the installation's on-board equipment. To do so, it is known in particular to circulate the natural gas in the vapour state at least through a natural gas processing system, making it possible to compress and heat the natural gas to a temperature suitable for use as fuel in the consumer. Such a processing system comprises a refrigerant circuit arranged to carry out at least a heat exchange between the natural gas flowing through the processing system.

[0005] Known refrigerant circuits implement a compression device. Such circuits work at very low temperatures, which makes it essential that the various rotating supports of the compression device are made watertight by a gas, for example dinitrogen. Indeed, at such temperatures, the use of any oil in the compression device would result in at least a part of this oil solidifying, which would impair the functioning of the treatment system. A drawback of using a compression device based on dinitrogen-sealed supports is the inevitable leakage of dinitrogen into the refrigerant flowing through the circuit, which would change the nominal composition of said refrigerant and therefore reduce the performance of the refrigerant circuit. Summary of the Invention [Means for solving the problem]

[0006] The present invention remedies this deficiency and proposes a compression system designed with a refrigerant circuit, comprising at least a compression device configured to compress a refrigerant, said compression device comprising at least a compression mechanism driven by a drive device, said compression mechanism and said drive device being connected to each other by at least one support configured to be at least partially sealed by the refrigerant, said compression system comprising a recirculation device for the refrigerant in the drive device, said refrigerant recirculation device being configured to return the refrigerant recirculated through the drive device to the refrigerant circuit.

[0007] According to the invention, the compression device comprises a compression mechanism driven by a drive device, the compression mechanism and the drive device being connected to each other by at least one support arranged to be at least partially sealed by the refrigerant. The consistency of the refrigerant in the refrigerant circuit is maintained, since the gas sealing the support is the refrigerant itself and is recirculated back into the refrigerant circuit. The watertightness of the support is ensured by the refrigerant, so that the refrigerant circuit is not contaminated by undesired gases and the flow mass of the refrigerant through the refrigerant circuit is maintained.

[0008] The support is configured to be sealed at least by the refrigerant, so that one part of the support cannot have a sealing system, while another part is sealed by the refrigerant, i.e. by the same fluid compressed by the compression mechanism when the compression system is assembled in the refrigerant circuit. The water-tightness in the part of the support configured to seal by the refrigerant is provided exclusively by the refrigerant. Therefore, no separate gas is required for water-tightness.

[0009] Thus, for example, the recirculation device makes it possible to draw the refrigerant from the transmission of the drive unit through the compression device and then separate it from the lubricant coming from the transmission by means of a filtering mechanism.

[0010] According to a feature of the invention, the recirculation device comprises at least one compression mechanism and at least a pipe in which the compression mechanism is located, the pipe extending from the drive device to an injection point configured to be located in the low pressure portion of the refrigerant circuit.

[0011] The recirculation system includes a compression mechanism, for example a diaphragm compressor, and piping located between the transmission and an injection point in the refrigerant loop.

[0012] According to another feature of the invention, the recirculation device comprises at least one filtering mechanism that captures the lubricant from the pipes before the refrigerant is introduced into the refrigerant circuit. The filtering mechanism may be located upstream of the compression mechanism in order to remove the lubricant before it enters the compression mechanism. In this state, the compression mechanism receives gases recovered from the transmission and from which the lubricant content has been removed.

[0013] Alternatively, the filtration mechanism may be located downstream from the compression mechanism.

[0014] According to another feature of the invention, the drive device comprises a transmission and an actuator for driving in rotation at least one gear of the transmission, the recirculation device being in fluid communication with an upper part of the transmission. The actuator rotates the gears forming the transmission. For example, the actuator may be electric, pneumatic or hydraulic. According to a preferred embodiment, the actuator is an electric motor.

[0015] The recirculation device is connected to the upper part of the transmission to ensure recovery of the refrigerant as a gas, in which case the refrigerant in the gas phase accumulates in the upper part of the transmission, and the position of the recirculation device relative to the transmission makes it possible to reduce the amount of lubricant that it picks up.

[0016] According to a feature of the invention, the compression system comprises a pipe connected to the support and configured to be in fluid communication with a high pressure portion of the refrigerant circuit, the pipe connected to the support making it possible to provide refrigerant under high pressure for sealing the rotating supports between the transmission and the compression device.

[0017] According to another aspect, the invention relates to a refrigerant circuit comprising at least two heat exchangers, an expansion device, and a compression system as described herein.

[0018] Advantageously, the refrigerant in the cooling circuit is - 20-35% mol of dinitrogen or 30-50% mol of argon or a 35-50% mol mixture of dinitrogen and argon, - 35-55% mol of methane Contains The refrigerant contains a portion of methane and dinitrogen and / or argon in 70-85% mol of the refrigerant, the remaining portion comprising a mixture of hydrocarbons consisting of at least ethane and / or propane and / or butane and / or ethylene and / or propylene. Such a composition of the refrigerant is particularly suitable for heat exchange with natural gas used as fuel for supplying consumers of a natural gas processing system installed on a floating structure.

[0019] In accordance with a feature of the invention, an injection point is located in the refrigerant circuit between the outlet of the expansion device and the inlet of the compression mechanism which defines a low pressure portion of the refrigerant circuit beginning at the outlet of the compression mechanism and ending at the inlet of the expansion device.

[0020] In accordance with a feature of the invention, a pipe is connected to the refrigerant circuit at a point located between the outlet of the compression mechanism and the inlet of the expansion device, thereby forming a high pressure portion of the refrigerant circuit.

[0021] A pipe allows the refrigerant to be received in a support between the compression mechanism and the transmission, said pipe being fed by the high pressure part of the refrigerant circuit.

[0022] According to another aspect, the present invention relates to a system for processing natural gas stored in a floating structure, comprising at least a tank designed to transport and / or store natural gas in liquid state, a supply system designed to provide natural gas to consumers of the floating structure, and a refrigerant circuit as described herein.

[0023] According to a feature of the invention, the treatment system comprises at least one consumer of natural gas as fuel, which consumer uses as fuel the natural gas flowing from the tank through the supply system.

[0024] The natural gas in the tank blanket flows into a first heat exchanger, which allows the natural gas to be heated when the refrigerant circuit is in operation, and then flows into a compression mechanism to increase the pressure and temperature of the natural gas in the vapor state, which is then used as fuel for the floating structure's consumers.

[0025] Further characteristics, details and advantages of the invention will become more apparent, on the one hand, from the following description and, on the other hand, from the numerous embodiments thereof, which are produced as a guide and non-limiting example with reference to the attached schematic drawings, in which: [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is a diagram showing a compression mechanism according to the present invention. [Diagram 2] 1 is a schematic diagram of a compression system according to the present invention incorporated within a natural gas supply system; [Diagram 3] FIG. 1 is a schematic diagram of a processing system for liquefied natural gas stored in tanks of a floating structure for transporting and / or storing said natural gas. [Figure 4] FIG. 2 is a schematic cutaway view of a tank of a floating structure and a loading and / or unloading terminal for said tank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] 1 shows a compression mechanism 2 arranged to compress a refrigerant in a refrigerant circuit 4. The refrigerant circuit 4 comprises two parts, a high pressure part 13 and a low pressure part 30. The high pressure part 13 is located downstream from the compression system 2, whereas the low pressure part 30 is the part of the refrigerant circuit upstream from the compression system 2 in the direction of refrigerant flow through the refrigerant circuit.

[0028] The compression system 2 includes at least a compression device 19 having a function of compressing a refrigerant. The compression device 19 includes a compression mechanism 10 and a drive device 32 having a function of driving, particularly rotating, the compression mechanism 10. The compression mechanism 10 is a part of the compression device 19 that performs compression. In particular, the compression mechanism 10 may be a centrifugal compressor, a screw compressor, or a piston compressor.

[0029] The drive unit 32 is a set including an actuator 34, in particular an electric, pneumatic or hydraulic motor, and a transmission 16 kinematically assembled between the actuator 34 and the compression mechanism 10. The function of the transmission 16 is to match the torque and speed between the actuator 34 and the compression mechanism 10. Such a transmission 16 includes a case with a number of gears and shafts rotating inside.

[0030] The first of these shafts is located between the actuator 34 and the input gear of the transmission 16. The other shaft is an output shaft that extends from inside the transmission housing to the inside of the compression mechanism 10.

[0031] A support 14 is arranged between the transmission 16 and the compression mechanism 10, and this support 14 forms an article that rotatably supports the output shaft of the transmission 16. Such a support 14 is made watertight by injecting the refrigerant from the refrigerant circuit 4 into the support 14 at a pressure higher than the pressure at the inlet of the compression mechanism 10.

[0032] To do so, the compression system 2 comprises a pipe 6 extending between the support 14 and a point 8 in the refrigerant circuit 4 downstream of the compression mechanism 10 and situated in the high pressure part of this circuit. This pipe 6 is arranged to allow a portion of the refrigerant to flow from the refrigerant circuit towards the support 14. However, the support 14 is not completely watertight, and a first portion of the refrigerant diffuses into the compression mechanism 10, whilst a second portion of the refrigerant flows to and fills the transmission 16. These portions of the refrigerant are indicated in Figure 1 by dashed arrows 18.

[0033] The compression system 2 according to the invention also comprises a refrigerant recirculation device 22 present in the drive device 32, and in particular in the transmission 16, due to the portion 18 of refrigerant flowing through the support 14 into the transmission 16. The function of this recirculation device 22 is to take refrigerant from the transmission 16 and to return it into the refrigerant circuit 4 in order to maintain the circulating mass of refrigerant through this refrigerant circuit 4 according to the initial requirements.

[0034] The recirculation device 22 extends from the transmission 16 to an injection point 33 located in the low pressure portion 30 of the refrigerant circuit 4 .

[0035] The recirculation device 22 is connected to the upper part of the transmission 16 for recovering the refrigerant in the vapor state. The refrigerant in the transmission 16 flows through a pipe 26 which is connected at one end to the upper part of the housing of the transmission 16 and at the other end to an injection point 33 of the refrigerant circuit 4 upstream of the compression mechanism 10.

[0036] The recirculation device 22 comprises a compression mechanism 24, which may be, for example, a diaphragm compressor, arranged to extract refrigerant from the transmission 16 and return it to the low pressure part of the refrigerant circuit 4. This means that the compression mechanism 24 increases the pressure of the recovered refrigerant in the transmission 16 above the pressure of the refrigerant in the refrigerant circuit upstream of the compression mechanism 10, i.e. in the low pressure part of this circuit.

[0037] Optionally, the recirculation device 22 includes a filtering mechanism 28 that may be located in the pipe 26 upstream or downstream from the compression mechanism 24 relative to the direction of refrigerant flow through the pipe 26 .

[0038] When the filter 28 is arranged upstream of the compression mechanism 24, this means that the lubricant of the transmission 16 is separated from the refrigerant, which then flows into the compression mechanism 24. In another application, the filter 28 is located downstream of the compression mechanism 24. In this case, the refrigerant in the vapor state and the lubricant are separated by the filter 28, so that only the refrigerant is returned to the refrigerant circuit 4, which means that it is lubricant-free.

[0039] Figure 2 shows a fuel supply system 38 for a consumer 46 installed on a floating structure equipped with such a supply system 38. In this case, the fuel is liquefied natural gas stored in a tank 20 installed on the floating structure. This supply system 38 comprises a compression system as described in figure 1.

[0040] The supply system 38 thus comprises at least one tank 20 designed to contain liquefied natural gas and a supply circuit 40 configured to recover the natural gas in vapour state in the blanket 42 of this tank 20 and to supply this natural gas to at least one consumer 46. This natural gas in the blanket 42 of the tank 20 arises on the basis of the natural evaporation of the natural gas stored in liquid state in the tank 20.

[0041] The supply circuit 40 comprises a compressor 44 arranged to increase the temperature and pressure of the natural gas in the vapour state, thereby bringing it into pressure and temperature conditions complying with the requirements of at least one fuel consuming device 46 arranged on the floating structure. By way of example, the at least one fuel consuming device 46 may be a prime mover generator of the DFDE type (Dual Fuel Diesel Electric), meaning a gas consuming device arranged to transmit power to a propulsion motor of the floating structure or ship, for example an ME-GI or XDF motor. Of course, this is only one embodiment of the invention and different gas consuming devices may be provided without departing from the scope of the invention.

[0042] The compressor 44 is made redundant by the compression mechanism 10, which can compensate for a failure of the compressor 44 and continue to supply gas to at least one consumer 46, in particular the ship's propulsion engine.

[0043] Such redundancy also results in the use of a valve, for example a first shut-off valve 50 located in the low pressure part 30 of the refrigerant circuit 4. This first shut-off valve 50 is arranged to block the entry of refrigerant into the compression mechanism 10. Analogously, the refrigerant circuit comprises a second shut-off valve 51 arranged in the high pressure part 13 of this refrigerant circuit 4. The function of this second shut-off valve 51 is to isolate the compression mechanism 10 from the rest of the refrigerant circuit when it is used in the supply circuit 40, which means to supply fuel to at least one consumer 46 of the floating structure.

[0044] The supply circuit 40 also comprises valves 52 arranged downstream and upstream of the group consisting of the compressor 44 and the compression mechanism 10. These valves 52 are arranged to manage the gas feed from the blanket 42 of the tank 20 to the compressor 44 or to the compression mechanism 10, whereby the compressor 44 is assigned to the supply circuit 40, whereas the compression mechanism 10 is assigned to the refrigerant circuit 4. These valves 52 and pipes 53 make it possible to use the compression mechanism 10 arranged in the supply circuit 40 when the compressor 44 fails, as mentioned above.

[0045] The supply circuit 40 also comprises at least one expansion device 15. The function of this expansion device 15 is to adapt the pressure of the gas sent to the consumer 46 by reducing this pressure.

[0046] FIG. 3 shows a system 52 for processing natural gas stored in a liquid state in a tank 20 of a floating structure 48 for transporting and / or storing natural gas, as shown diagrammatically in FIG. 4.

[0047] The natural gas processing system 52 comprises a supply system 38 as described in Figure 2 and a compression system 2 according to the invention. Figure 3 shows in detail the design of a refrigerant circuit 4 including such a compression system 2 and the interaction between the refrigerant circuit 4 and a supply circuit 40 or between the refrigerant circuit 4 and at least one natural gas liquefaction facility 7.

[0048] The refrigerant circuit 4 therefore comprises at least one compression mechanism 10 as described above, a first heat exchanger 54, an expansion device 12, for example a Joule-Thomson valve, and a second heat exchanger 56.

[0049] The refrigerant passing through the refrigerant circuit has the following composition: 20-35% mol of dinitrogen or 30-50% mol of argon or 35-50% mol of a mixture of dinitrogen and argon and 35-55% mol of methane, the refrigerant containing a portion of methane and dinitrogen and / or argon in 70-85% mol of this refrigerant, the remaining portion containing a mixture of hydrocarbons consisting of at least ethane and / or propane and / or butane and / or ethylene and / or propylene. This composition allows the refrigerant to change state at the temperatures that natural gas can have in the processing equipment.

[0050] An example of the composition of this refrigerant and the proportions of its components can be seen in the following recipe: [Table 1] It may be as follows.

[0051] According to the demand for natural gas in vapor state of the fuel consumer 46 , the natural gas liquefaction unit 7 provides for liquefaction of at least that portion of the natural gas from the tank 20 that has not been consumed by the consumer 46 .

[0052] On the other hand, the second heat exchanger 56 provides evaporation of the refrigerant in the refrigerant circuit 4. This second heat exchanger 56 also provides subcooling of the liquid natural gas in order to make it easier to liquefy the natural gas flowing through the liquefaction unit 7. In this case, a portion of the subcooled liquid natural gas is returned to the liquefaction unit 7 to cool the vapor natural gas flowing through the return pipe 84.

[0053] In the natural gas processing system 52, the refrigerant circuit 4 consists of units capable of exchanging calories with natural gas in the liquid or vapor state.

[0054] In particular, in the present invention, natural gas in liquid state has a liquefaction temperature at room temperature of approximately −163° C. The composition of the refrigerant circulating in the refrigerant circuit 4 is adapted to this temperature, thereby optimizing the efficiency of the heat exchange that occurs between the refrigerant and the natural gas in liquid or vapour state from the tank 20 at the very low temperatures.

[0055] As described above, the refrigerant is first compressed by the compression mechanism 10 and then flows through the high pressure portion 13 of the refrigerant circuit 4 to the first passage 64 through the first heat exchanger 54.

[0056] In this case, the first heat exchanger 54 has at least three passages: refrigerant under high pressure flows through a first passage 64, refrigerant under low pressure flows through a second passage 66, and natural gas in vapor state from the blanket 42 of the tank 20 flows through a third passage 58 of the first heat exchanger 54.

[0057] The first heat exchanger 54 acts as a condenser and allows the temperature of the refrigerant in the high pressure section 13 to be reduced before it enters the expansion device 12. This reduction in temperature occurs by heat exchange between the refrigerant flowing through the first passage 64 of the first heat exchanger 54 and the refrigerant flowing through the third passage 58 of the first heat exchanger 54. In this case, the natural gas in the vapor state, which is generated due to the natural evaporation of the liquid part of the natural gas stored in the tank 20, travels through the third passage.

[0058] The first heat exchanger 54 is optionally configured to at least partially act as an internal heat exchanger for effecting 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 in the first passage 64 of the first heat exchanger 54 receives cold from the refrigerant in the second passage 66 and cold from the natural gas in a vapor state from the blanket 42 of the tank 20.

[0059] At the outlet of the first passage 64 of the first heat exchanger 54, the refrigerant circuit 4 reaches an expansion device 12. In this expansion device 12, the refrigerant is expanded and its pressure is reduced, whereby its temperature drops to -168°C to -180°C.

[0060] The refrigerant circuit 4 then reaches a first passage 68 of the second heat exchanger 56, which exchanges calories with a second passage 70 of the second heat exchanger 56 through which liquefied natural gas in the liquid state flows at a temperature of about -163°C by the pump 29. Since the natural gas has a higher temperature than the refrigerant, the natural gas provides calories to the refrigerant and therefore captures some cold. The refrigerant leaves the first passage 68 of the second heat exchanger 56 in the vapor state and at a temperature of about -162°C, whereas the natural gas in the liquid state has been subcooled to a temperature of about -172°C, measured at the outlet of the second passage 70 of the second heat exchanger 56. In this situation, the second heat exchanger 56 works as an evaporator.

[0061] The refrigerant circuit 4 then reaches the second passage 66 of the first heat exchanger 54 where, as previously described, the refrigerant picks up calories from the refrigerant flowing through the first passage 64 of the first heat exchanger 54.

[0062] Therefore, the refrigerant flows out of the second passage 66 of the first heat exchanger 54 substantially in a vapor state. The refrigerant then has a temperature of −30° C. to 45° C. and flows toward the compression mechanism 10.

[0063] Advantageously, the refrigerant circuit 4 may comprise at least one accumulator 72 located between the second passage 66 of the first heat exchanger 54 and the inlet of the compression mechanism 10 and configured to provide an accumulation zone for refrigerant in a two-phase state 74 or in a vapor state 76 and to deliver only refrigerant in the vapor state 76 to the compression mechanism 10.

[0064] The natural gas in the vapour state compressed by the compressor 44 may be returned to the tank 20 via a return pipe 84. The return pipe 84 conveys the natural gas in the vapour state to a liquefaction unit 7, which comprises a heat exchanger 60, the function of which is to cool the natural gas in the vapour state and liquefy it before returning it to the tank 20. To do so, the heat exchanger 60 comprises a first passage 86 through which the natural gas in the vapour state flows from the supply circuit 40. The first passage 86 exchanges heat with a second passage 88 through which the natural gas in the liquid state flows after cooling by the second heat exchanger 56. The natural gas in the vapour state is thus returned to the liquid state and returned to the tank 20.

[0065] Finally, FIG. 4 is a cutaway view of a floating structure 48 on which the compression system 2 of the present invention may be shipped, either alone or in combination with a supply system 38 as shown in FIG. 2 or integrated into a system 52 for processing natural gas as shown in FIG. 3.

[0066] The floating structure 48 includes a natural gas storage tank 20 mounted within a hull 78 of the floating structure 48. The tank 20 includes at least one primary waterproof membrane, a secondary waterproof membrane, and a set of two insulating barriers located between the primary and secondary waterproof membranes and between the secondary waterproof membrane and the hull, respectively.

[0067] Loading and / or offloading pipes 80 located on the upper deck of the floating structure 48 are connected by suitable connectors to a marine or port terminal 82, by which the natural gas cargo in liquid state can be transferred from or to the tanks 20.

[0068] As is evident from the above, the invention proposes a compression system 2 comprising a support sealed with a refrigerant, leakage from which is collected in the transmission and then returned to the refrigerant circuit, said compression system being integrated into the supply system of the consumer and, more generally, into the natural gas processing system equipped on the ship.

[0069] The present invention is not limited to the means and configurations described and illustrated herein, but must include any equivalent means and configurations, as well as any technically valid combination of such means. In particular, the number of heat exchangers may be varied. In this case, the first heat exchanger may be divided into multiple heat exchangers, as long as the treatment system ultimately performs the same functions as those described herein.

Claims

1. 1. A compression system (2) designed to include a refrigerant circuit (4), the compression system (2) comprising at least a compression device (19) configured to compress a refrigerant, the compression device (19) comprising at least a compression mechanism (10) driven by a drive device (32), the compression mechanism (10) and the drive device (32) being connected to each other by at least one support (14) configured to be at least partially sealed by the refrigerant, the compression system (2) comprising a recirculation device (22) for the refrigerant in the drive device (32), the refrigerant recirculation device (22) being configured to return the refrigerant recirculated through the drive device (32) to the refrigerant circuit (4).

2. 2. The compression system (2) of claim 1, wherein the recirculation device (22) comprises at least one compression mechanism (24) and at least a pipe (26) in which the compression mechanism (24) is located, the pipe (26) extending from the drive device (32) to an injection point (33) configured to be located in the low-pressure portion (30) of the refrigerant circuit (4).

3. The compression system (2) of claim 1 or 2, wherein the recirculation device (22) comprises at least one filtration mechanism (28).

4. 3. The compression system (2) of claim 1 or 2, wherein the drive device (32) comprises a transmission (16) and an actuator (34) that rotationally drives at least one gear of the transmission (16), and the recirculation device (22) is in fluid communication with an upper portion of the transmission (16).

5. 3. The compression system (2) of claim 1 or 2, comprising a conduit (6) connected to the support (14) and configured to be in fluid communication with a high-pressure portion (13) of the refrigerant circuit (4).

6. A refrigerant circuit (4) comprising at least two heat exchangers (54, 56), an expansion device (12), and a compression system (2) according to claim 1.

7. 20-35% mol of dinitrogen or 30-50% mol of argon or a 35-50% mol mixture of dinitrogen and argon, - 35-55% mol methane a refrigerant containing The refrigerant contains 70 to 85 mol% of methane and dinitrogen and / or argon, the remaining portion comprising a mixture of hydrocarbons consisting of at least ethane and / or propane and / or butane and / or ethylene and / or propylene, Refrigerant circuit (4) according to claim 6.

8. A refrigerant circuit (4) as described in claim 6 or 7, wherein the recirculation device (22) comprises at least one compression mechanism (24) and at least a pipe (26) in which the compression mechanism (24) is located, the pipe (26) extending from the drive device (32) to an injection point (33) configured to be located in a low pressure portion (30) of the refrigerant circuit (4), the injection point (33) being located in the refrigerant circuit between the outlet of the expansion device (12) and the inlet of the compression mechanism (10) defining the low pressure portion (30) of the refrigerant circuit (4).

9. A refrigerant circuit (4) as described in claim 8, wherein the compression system (2) comprises a conduit (6) connected to the support (14) and configured to be fluidly connected to a high-pressure portion (13) of the refrigerant circuit (4), the conduit (6) being connected to the refrigerant circuit (4) at a point (8) located between the outlet of the compression mechanism (10) and the inlet of the expansion device (12) forming the high-pressure portion (13) of the refrigerant circuit (4).

10. 8. A system (52) for processing natural gas stored in a floating structure (48), comprising at least a tank (20) designed to transport and / or store natural gas in a liquid state, a supply system (38) designed to deliver natural gas to a consumer (46) of the floating structure (48), and a refrigerant circuit (4) according to claim 6 or 7.

11. The system (52) for processing natural gas according to claim 10, comprising at least one consumer (46) of natural gas as fuel.

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