Refrigeration and / or liquefaction method, device and system

Abstract

Disclosed is a refrigeration and / or liquefaction method using a system comprising a cryogenic refrigeration device (1), the refrigeration device comprising a working circuit (10) which forms a loop and is filled with a working fluid, the working circuit (10) forming a cycle which includes in series: a compression mechanism (2, 3), a cooling mechanism (6), an expansion mechanism (7), and a heating mechanism (6, 8), the refrigeration device (1) further comprising a cooling exchanger (8) for extracting heat from a useful fluid stream by heat exchange with the working fluid flowing in the working circuit (10), the system comprising a pipe (15) through which the useful fluid stream flows in the cooling exchanger (8), the method comprising a cooling step in which the refrigeration device (1) is in a first operating mode of cooling the cooling exchanger (8) while the useful fluid flows in the cooling exchanger (8), the method comprising, after the cooling step, a step of cleaning impurities that have solidified in the cooling exchanger (8), characterized in that, during the cleaning step, the refrigeration device (1) is in a second operating mode in which the working gas flows in the working circuit (10), but in the second operating mode, the cooling intensity of the cooling exchanger (8) is lower than that in the first operating mode.

Description

[0001] The present invention relates to a method, device and system for refrigeration and / or liquefaction.

[0002] The present invention more particularly relates to a method for refrigerating and / or liquefying a user fluid stream, in particular a natural gas stream, the method using a cooling and / or liquefaction system which comprises a cryogenic refrigeration device for refrigeration at a temperature between -100 °C and -273 °C, and in particular between -100 °C and -253 °C, the refrigeration device comprising a working circuit which forms a loop and is filled with a working fluid, the working circuit forming a cycle which serially comprises: means for compressing the working fluid; means for cooling the working fluid; means for expanding the working fluid; and means for heating the working fluid, the refrigeration device comprising a cooling exchanger which is intended to extract heat from the user fluid stream by heat exchange with the working fluid circulating in the working circuit, the system comprising pipes for the circulation of the said user fluid stream in the cooling exchanger, the method comprising a cooling step in which the refrigeration device is in a first cooling operation mode of the cooling exchanger while causing the user fluid stream to circulate in this cooling exchanger, the method comprising, after this cooling step, a step of removing solidified impurities from the cooling exchanger.

[0003] The present invention particularly relates to cryogenic refrigerators or liquefiers, for example of the type having a "turbo-Brayton" cycle or a "turbo-Brayton cooler", in which a cycle gas (helium, nitrogen, hydrogen or another pure gas or mixture) undergoes a thermodynamic cycle for generating cold which can be transferred to a member or gas to be cooled.

[0004] These devices are used for a wide variety of applications, in particular for cooling natural gas in storage tanks (for example in ships). Liquefied natural gas is for example supercooled to avoid its vaporization, or the gaseous fraction is cooled in order to be re-liquefied.

[0005] For example, it is possible to cause a natural gas stream to circulate in a heat exchanger cooled by the cycle gas of a refrigerator / liquefier.

[0006] The gas cooled in this exchanger may contain impurities (such as carbon dioxide) which may solidify at the low temperatures reached by the exchanger. This can block the heat exchanger and affect the efficiency of the system.

[0007] A solution may consist in actively heating the heat exchanger with an electric heater. However, this is energy-expensive and is generally not suitable for explosive environments.

[0008] The object of the present invention is to overcome all or part of the above-mentioned drawbacks of the prior art.

[0009] To this end, the essential feature of the method according to the invention, which in other respects also conforms to its general definition given in the preamble above, lies in that during the cleaning step, the refrigeration device is in a second operating mode in which the working gas circulates in the working circuit, but in this second operating mode, the cooling of the cooling exchanger is reduced compared to the first operating mode.

[0010] Furthermore, embodiments of the present invention may include one or more of the following features:

[0011] - During the cleaning step, the refrigeration device achieves zero cooling or heating of the cooling exchanger.

[0012] - During the cleaning step, a user fluid flow is circulated in the cooling exchanger and heated by it.

[0013] - The compression mechanism includes one or more compressors and at least one drive motor for rotating the compressor(s). The refrigeration capacity of the refrigeration device is variable and is controlled by adjusting the rotational speed of the drive motor(s). In the second operating mode, the rotational speed of at least one drive motor is between 1% and 60% of the maximum or nominal rotational speed of the motor, preferably between 10% and 50%, and particularly between 20% and 30%.

[0014] - The compression mechanism includes a plurality of rotary compressors and at least two drive motors. Each drive motor includes a rotary drive shaft, and these compressors are driven to rotate by the corresponding rotary shaft(s). The mechanism for expanding the working fluid includes at least one rotary turbine, and the at least one rotary turbine rotates together with the shaft of one of the drive motors of at least one compressor.

[0015] - In the second operating mode of the refrigeration device, at least one motor is deactivated. The at least one motor includes a turbine that rotates together with its shaft, and at least one other drive motor of the compressor operates at a rotational speed between 1% and 60% of the maximum or nominal speed of the motor, preferably between 10% and 50%, and particularly between 20% and 30%.

[0016] - The at least one deactivated motor is braked, which means that the rotation of the corresponding shaft and / or compressor and / or turbine is braked or blocked.

[0017] - In the first operating mode of the refrigeration device, the rotating shafts of these drive motors rotate in a respective first rotational direction, and the working fluid circulates in the working circuit in a first circulation direction, and in the second operating mode of the refrigeration device, at least one motor, in particular the motor to whose shaft the turbine is coupled, is set to rotate in the opposite direction, which means that the rotating shaft of this motor rotates in a rotational direction opposite to the first rotational direction.

[0018] - The at least one compressor driven by the motor is centrifugal, the motor includes a turbine rotating with its shaft, and in the second operating mode of the refrigeration device, the working fluid circulates in the working circuit in the first circulation direction.

[0019] - In the second operating mode of the refrigeration device, at least one drive motor is deactivated or operated at a rotational speed between 1% and 60%, and preferably between 10% and 50%, in particular between 20% and 30%, of the maximum or nominal speed of the motor, and this at least one drive motor is separate from the motor set to rotate in the opposite direction.

[0020] - By pumping a user fluid stream from the user fluid reservoir to circulate it in the cooling exchanger and returning the user fluid that has undergone heat exchange with the cooling exchanger to the reservoir.

[0021] - The method includes a step simultaneous with and / or after the cleaning step: purging the cooling exchanger with a purge fluid stream injected into the cooling exchanger to sweep and discharge the impurities shed during the cleaning step from the cooling exchanger.

[0022] - The purging step includes sweeping the exchanger with a neutral gas to discharge it to the discharge area.

[0023] - The purging step includes sweeping the exchanger with the user fluid.

[0024] The present invention also relates to a cryogenic refrigeration device for refrigerating at temperatures between -100 degrees Celsius and -273 degrees Celsius. The refrigeration device includes a working circuit that forms a loop and is filled with a working fluid. The working circuit forms a cycle that serially includes: a mechanism for compressing the working fluid; a mechanism for cooling the working fluid; a mechanism for expanding the working fluid; and a mechanism for heating the working fluid. The device includes a cooling exchanger that is designed to extract heat from at least one component by heat exchange with the working fluid circulating in the working circuit. The refrigeration device includes an electronic controller that is configured to control the refrigeration capacity of the refrigeration device and switch the refrigeration device to a first cooling operation mode of the cooling exchanger to cool the user fluid flow to be circulated in the cooling exchanger, and a cleaning mode for removing solidified impurities in the cooling exchanger. In this cleaning mode, the electronic controller is configured to reduce the refrigeration capacity of the refrigeration device and reduce the cooling of the cooling exchanger compared to the first operation mode.

[0025] According to other possible specific features:

[0026] - The compression mechanism includes one or more compressors and at least one drive motor for rotating the (multiple) compressors. The refrigeration capacity of the refrigeration device is variable and is controlled by adjusting the rotational speed of the (multiple) drive motors. The electronic controller is configured to set the rotational speed of at least one of the drive motors to a value between 2% and 60%, preferably between 10% and 50%, and especially between 20% and 30% of the maximum or nominal speed of the motor in a second operation mode.

[0027] - The compression mechanism includes multiple rotary compressors and at least two drive motors. Each drive motor includes a rotary drive shaft, and these compressors are driven to rotate by the corresponding (multiple) rotary shafts. The mechanism for expanding the working fluid includes at least one rotary turbine that rotates together with the shaft of one of the drive motors of at least one compressor.

[0028] - In the second operation mode, the electronic controller is configured to deactivate at least one motor that includes a turbine rotating with its shaft, and operate at least another drive motor of the compressor at a rotational speed between 1% and 60%, preferably between 10% and 50%, and especially between 20% and 30% of the maximum or nominal speed of the motor.

[0029] - The device has a mechanical or electrical or magnetic system for braking the deactivated motor, braking and / or preventing the rotation of the shaft of the deactivated motor and / or the compressor and / or the turbine.

[0030] - In a first operating mode, these drive motors are configured to rotate their axes of rotation in respective first rotational directions, at least one motor being of the type having a reversible direction of rotation, the at least one motor including a turbine rotating with its shaft, and the electronic controller being configured to rotate said motor in a rotational direction opposite to the first rotational direction during a second operating mode of the refrigeration device.

[0031] - In a second operating mode of the refrigeration device, the electronic controller is configured to: deactivate at least one drive motor that is separate from the motor set to rotate in the opposite direction; or limit the rotational speed of this drive motor, which is separate from the motor set to rotate in the opposite direction, to a value between 1% and 60% of the rotational speed of said motor during the first operating mode, and preferably between 10% and 50%, and in particular between 20% and 30%.

[0032] The invention also relates to a system for refrigerating and / or liquefying a user fluid stream, in particular a natural gas stream, the system including a refrigeration device according to any one of the above or below features, the system including at least one user fluid storage tank and pipes for circulating said user fluid in a cooling exchanger.

[0033] The invention can also relate to any alternative device or method including any combination of the above or below features within the scope of the claims.

[0034] Further specific features and advantages will become apparent by reading the description given with reference to the following drawings, in which:

[0035] Figure 1 shows a schematic partial view demonstrating the structure and operation of an example of a device and system in which the invention can be implemented.

[0036] Figure 1 The cooling and / or liquefaction system in [] includes a refrigeration device 1 that supplies cold (cooling capacity) at a cooling exchanger 8. The system includes pipes 25 for circulating a fluid stream to be cooled that is placed in heat exchange with this cooling exchanger 8. For example, the fluid is liquid natural gas that is pumped (e.g., via a pump) from a storage tank 16, then cooled (preferably outside the storage tank 16), and then returned to the storage tank 16 (e.g., dripping in the gas phase of the storage tank 16). This can cool or subcool the contents of the storage tank 16 and limit the occurrence of vaporization. For example, the liquid from the storage tank 16 is subcooled to below its saturation temperature (its temperature drops by several degrees K, in particular 5 to 20 K, and specifically 14 K) before being reinjected into the storage tank 16. In a variant, this refrigeration can be applied to the vaporized gas from the storage tank to re-liquefy it in particular. This means that the refrigeration device 1 generates cold at the cooling exchanger 8. ​​

[0037] The refrigeration device 1 includes a working circuit 10 (preferably a closed circuit), which forms a circulation loop. This working circuit 10 is filled with a working fluid (helium, nitrogen, neon, hydrogen, or another suitable gas or mixture, such as helium and argon, or helium and nitrogen, or helium and neon, or helium, nitrogen, and neon).

[0038] The working circuit 10 forms a cycle, which serially includes: a mechanism for compressing the working fluid; a mechanism for cooling the working fluid; a mechanism for expanding the working fluid; and a mechanism for heating the working fluid.

[0039] The device 1 includes a cooling heat exchanger 8, which is designed to extract heat from at least one component by heat exchange with the working fluid circulating in the working circuit 10.

[0040] The mechanisms for cooling and heating the working fluid generally include a common heat exchanger 6, and the working fluid passes through the common heat exchanger in a countercurrent manner in two separate passage portions of the working circuit 10 depending on whether it is to be cooled or heated.

[0041] The cooling heat exchanger 8 is, for example, located between the expansion mechanism and the common heat exchanger 6. As shown in the figure, the cooling heat exchanger 8 can be a heat exchanger separate from the common heat exchanger 6. However, in a variant, this cooling heat exchanger 8 can be constituted by a part of the common heat exchanger 6 (which means that these two exchangers 6 and 8 can be integrated, that is, they can have separate fluid circuits sharing the same exchange structure).

[0042] Therefore, the working fluid leaving the compression mechanism in a relatively hot state is cooled in the common heat exchanger 6 before entering the expansion mechanism. The working fluid leaving the expansion mechanism and the cooling heat exchanger 8 in a relatively cold state is itself heated in the common heat exchanger 6 before returning to the compression mechanism to start a new cycle.

[0043] Generally, in the normal operating mode (hereinafter referred to as the "first operating mode"), the working gas undergoes a cycle of compression, cooling, expansion, and heating and generates cold at the cooling exchanger 8. Generally, an equal or substantially equal mass flow circulates in the two passage portions of the common heat exchanger 6.

[0044] As shown in the figure, in the normal operating mode, a fluid stream (for example, liquefied natural gas) can be cooled in the cooling exchanger 8. In the event that this fluid contains impurities (such as carbon dioxide), these impurities may solidify when cooled, and blockage 17 or obstruction may occur in the cooling exchanger 8.

[0045] This blockage can be eliminated by a cleaning step carried out by the refrigeration device 1 itself in a second operating mode, in which the working gas still circulates in the working circuit 10 as described above, but in the second operating mode, the cooling of the cooling exchanger 8 is reduced compared to the first operating mode.

[0046] For example, the refrigeration device 1 periodically achieves zero cooling or heating of the cooling exchanger 8.

[0047] During this cleaning, a user fluid flow can be circulated in the cooling exchanger 8 to carry away impurities heated by the cooling exchanger. In particular, the user fluid flow can be heated during this second operating mode.

[0048] The compression mechanism can include one or more compressors and at least one drive motor 14, 15 for rotating the compressor(s) 2, 3. Furthermore, preferably, the refrigerating capacity of the device is variable and can be controlled by adjusting the rotational speed (cycle speed) of the drive motor(s) 14, 15. Preferably, the cooling capacity generated by the device 1 can be adapted to 0% to 100% of the nominal or maximum capacity by varying the rotational speed of the motor(s) 14, 15 between zero rotational speed and the maximum or nominal speed. Such an architecture can maintain a high performance level over a wide operating range (e.g., maintaining 97% of the nominal performance at 50% of the nominal cooling capacity).

[0049] For example, in the second operating mode, the rotational speed of at least one of the motors 14, 15 is reduced to a value between 1% and 60%, preferably between 10% and 50%, and particularly between 20% and 30% of the rotational speed of the motors 14, 15 during the first cooling operating mode. For example, this reduced rotational speed corresponds to 1% to 60%, preferably between 10% and 50%, and particularly between 20% and 30% of the nominal or maximum speed of the motors 14, 15.

[0050] In this configuration, the refrigerating capacity (or heat generated here) generated at the cooling exchanger 8 is reduced or eliminated. In this way, the heating exchanger 8 will warm up, causing the solidified impurities to melt and then vaporize. This heating (optionally associated with the user fluid flow in the cooling heat exchanger 8) carries these impurities out of the exchanger 8, for example towards the user fluid reservoir 16.

[0051] In the non - limiting example depicted, the refrigeration device 1 includes two compressors 2, 3 in series, which are respectively driven by two separate motors 14, 15; and a turbine 7 coupled to the drive shaft of one of the two motors 15.

[0052] This means that one motor 14 drives only one compressor 3 (motor-compressor), while the other motor 15 drives compressor 2 and is coupled to turbine 7 (motor-turbine-compressor).

[0053] For example, in the second operating mode of the refrigeration device (1), motor 15 is deactivated, which has a drive shaft to which turbine 7 is coupled, and the other motor 14 (which only drives compressor 3) operates at a rotational speed between 1% and 60% of the maximum rotational speed or the nominal rotational speed of this motor, and preferably between 10% and 50%, especially between 20% and 30%. The nominal rotational speed or the maximum rotational speed of the motor refers to the maximum speed that the motor can generate in the case of maximum refrigeration capacity. This maximum or nominal rotational speed is the maximum speed recommended for operating the refrigeration device 1 and can be lower than the maximum speed that the motor itself can achieve if required.

[0054] In this configuration, turbine 7 and compressor 2 (both of which are coupled to the drive shaft of the deactivated motor 15) can rotate freely.

[0055] As previously mentioned, the operation of the other motor 14 at a reduced speed will cause the working fluid to circulate in the working circuit 10 with low efficiency. The freely rotating turbine 7 and compressor 2 also increase the pressure drop in the working circuit 10 of the working gas. This will increase the relative heating at the cooling exchanger 8 in order to discharge impurities, without increasing the power consumption of the already reduced device 1.

[0056] To further increase this heating and the speed of removing impurities, an additional pressure drop can be increased in this operating mode. For example, the deactivated motor 15 is braked. For example, its shaft and / or the corresponding compressor 2 and / or turbine 7 can be braked or prevented from rotating. This braking 20 or prevention can be a mechanical operation obtained via a moving and / or electrical and / or magnetic stop. For example, the (multiple) motors are electric motors, especially of the synchronous type. The braking of the motor can be carried out by providing a braking resistor in the control circuit of the motor for this operating mode. Similarly, such an electric motor can have a three-phase circuit diagram, which can be temporarily short-circuited to ensure this braking. Motor 15 can especially be reversible, and braking can be obtained by switching it to its reverse generator mode, in which the motor generates current and brakes its drive shaft instead of generating torque.

[0057] These braking modes can be used for the control circuit (inverter) of such electric motors. Thus, simple software control can implement these braking modes without modifying the existing structure of the motor.

[0058] In yet another embodiment variant, in the second operating mode, at least one motor 15 (for example, the motor including turbine 7 rotating with its shaft) is set to rotate in the opposite direction.

[0059] This means that in the first operating mode of the refrigeration device 1, the rotating shafts of the drive motors 14, 15 rotate in the respective first rotation directions, and the working fluid circulates in the working circuit 10 in the first circulation direction, and in the second operating mode of the refrigeration device 1, at least one motor, preferably the motor 15 to whose shaft the turbine 7 is coupled, is set to rotate in the opposite direction, which means that the rotating shaft of this motor rotates in a rotation direction opposite to the first rotation direction.

[0060] The working fluid continues to circulate in the working circuit 10 in the first circulation direction, but the opposite rotation of the turbine 7 (not optimized for this direction) will in particular provide mechanical work to the working gas and thus heat it up, without extracting mechanical work (expansion) from the working gas. This is in particular carried out using turbine technology with a centripetal turbine. And preferably, the compressor(s) is / are centrifugal.

[0061] When this motor 15 is set to rotate in the opposite direction (reverse), the other motor 14 (or other motors, if there are several) can be deactivated, but in particular idles, and preferably the other motor 14 (or other motors) is / are operated at a reduced rotational speed. For example, this other motor 14 (or at least one of the other motors) is set to rotate at a speed of 1% to 60%, and preferably between 10% and 50%, in particular between 20% and 30%, of the maximum or nominal speed of the motor 14.

[0062] This reduced speed of the motor(s) increases the heating efficiency and allows the refrigeration device to be restarted more quickly and efficiently in the first cooling operating mode.

[0063] Preferably, the motor(s) 14 set to rotate in the opposite direction is / are set to rotate at a reduced speed (for example at a speed of 1% to 60%, and preferably between 10% and 50%, in particular between 20% and 30%, of the maximum or nominal speed of the motor).

[0064] However, in a possible variant, the rotational speed in the opposite direction can be higher and can reach the nominal or maximum speed of the motor.

[0065] The device can include at least one electronic controller 12, which is connected to all or part of the components (motors, valves, pumps, etc.) of the system. The electronic controller 12 can include a microprocessor or a computer and can be configured to dynamically control all or part of the components of the system and in particular to implement the above operating modes (automatically and / or in response to a command from the user in particular).

[0066] For example, the refrigeration device 1 switches to the second operating mode to effect cleaning of the cooling exchanger 8 can be achieved by a user command and / or in response to detecting an impurity blockage in the cooling exchanger 8 (such as a pressure sensor in the circuit).

[0067] In addition, the electronic controller 12 can be configured (programmed or commanded) to dynamically control the heating of the cooling exchanger 8 in the second operating mode. For example, such control (the relative heating capacity with respect to the first operating mode) can depend on the rate of increase of the temperature of the common heat exchanger 6 according to a given curve, and / or keeping the rate of increase of the temperature of the common heat exchanger 6 below a given threshold. This can prevent the common heat exchanger 6 and / or the cooling exchanger 8 from heating up too quickly, which is advantageous in the case of an exchanger having an aluminum plate, for example.

[0068] In the depicted example, the refrigeration device 1 includes an expansion turbine 7 and two compressors 2, 3 forming two compression stages. This means that the compression mechanism includes two compressors 2, 3 in series, preferably centrifugal, and the expansion mechanism includes a single turbine 7, preferably a radial inflow turbine. Of course, any other number and arrangement of (multiple) compressors and turbines can be envisaged, such as three compressors in series and one turbine, or three compressors and two or three turbines, or two compressors and two turbines, etc.

[0069] In the example shown, cooling exchangers 4, 5 are provided at the outlet of each compressor 2, 3 (for example, cooled by heat exchange with water or any other coolant or fluid at ambient temperature).

[0070] This can achieve isentropic or isothermal or substantially isothermal compression. Of course, any other arrangement can be envisaged (for example, without cooling exchangers 4, 5 having one or more compression stages). Similarly, a heating exchanger can be provided or not provided at the outlet of all or part of the expansion turbine 7 to achieve isentropic or isothermal expansion. Also preferably, the heating and cooling of the working fluid is preferably isobaric, but is not limited thereto.

[0071] For example, the device 1 includes two high-speed motors 14, 15 (for example, 10,000 revolutions per minute or tens of thousands of revolutions per minute) to drive the compression stages respectively. The turbine 7 can be coupled to the motor of one of the compression stages, which means that the device can have a turbine to form an expansion mechanism that is coupled to the drive motor of the compression stage (specifically the first).

[0072] Thus, the power of the turbine(s) 7 can be advantageously recovered and used to reduce the consumption of the motor(s). Thus, by increasing the speed of the motor (and thus the flow rate in the working gas cycle), the refrigeration capacity produced is increased and thus the electrical consumption of the liquefier is increased (and vice versa). The compressors 2, 3 and the turbine(s) 7 are preferably directly coupled to the output shaft of the motor(s) (without a gear mechanism).

[0073] The output shaft of the motor is preferably mounted on bearings of the magnetic type or the dynamic gas type. These bearings are used to support the compressor and the turbine.

[0074] Furthermore, all or part of the device, in particular its cold components, can be housed in a thermally insulated sealed enclosure (in particular a vacuum chamber including a common countercurrent heat exchanger).

[0075] To further improve the efficiency and speed of the process, the cooling exchanger 8 can be purged with a purge fluid stream injected into the cooling exchanger 8 simultaneously with and / or after the cleaning step, in order to sweep out and discharge the impurities detached during the cleaning step from the cooling exchanger 8.

[0076] For example, a circuit 18 for a neutral gas etc. (such as nitrogen) can be provided to purge the heated impurities. If necessary, such a purge can replace the circulation of the user fluid stream during heating. The mixture obtained can be discharged to a discharge area (such as to the atmosphere).

[0077] Alternatively, such a purge can be achieved with the user fluid stream. For example, a portion of the user fluid is withdrawn from the circulation pipe (for example via a bypass provided with a valve). The purge user fluid can vaporize in the cooling exchanger 8 and detach the impurities. The mixture obtained can be sent back to the external or collection area and in particular can be reinjected into the user fluid reservoir 16.

[0078] The present invention can be applied to a method for cooling and / or liquefying another fluid or mixture, in particular hydrogen.

Claims

1. A method for refrigerating and / or liquefying a user fluid stream, the method using a refrigeration and / or liquefaction system, the system including a cryogenic refrigeration device for refrigerating at a temperature between -100 degrees Celsius and -273 degrees Celsius, the refrigeration device including a working circuit that forms a loop and is filled with a working fluid, the working circuit forming a cycle that includes in series : means for compressing the working fluid; means for cooling the working fluid; means for expanding the working fluid; and means for heating the working fluid, the refrigeration device including a cooling exchanger that is intended to extract heat from the user fluid stream by heat exchange with the working fluid circulating in the working circuit, the system including pipes for the user fluid stream to circulate in the cooling exchanger, the method including a cooling step in which the refrigeration device is in a first cooling operation mode of the cooling exchanger while causing the user fluid stream to circulate in this cooling exchanger, the method including, after this cooling step, a cleaning step: removing solidified impurities in the cooling exchanger during this cleaning step, the refrigeration device being in a second operation mode in which the working fluid circulates in the working circuit, but in which the cooling of the cooling exchanger is reduced compared to the first cooling operation mode, characterized in that the means for compressing the working fluid includes a plurality of rotary compressors and at least two drive motors, each drive motor including a rotary drive shaft, the compressors being driven to rotate by the respective rotary shafts, the means for expanding the working fluid includes at least one rotary turbine that rotates together with the shaft of one of the drive motors of at least one compressor, and in the first cooling operation mode of the refrigeration device, the rotary shafts of these drive motors rotate in a respective first rotation direction, and the working fluid circulates in the working circuit in a first circulation direction, and in the second operation mode of the refrigeration device, at least one motor to which the turbine is connected to its shaft is set to rotate in the opposite direction, which means that the rotary shaft of the motor rotates in a rotation direction opposite to the first rotation direction.

2. The method according to claim 1, characterized in that the user fluid is natural gas.

3. The method according to claim 1, characterized in that during the cleaning step, the refrigeration device achieves zero cooling or heating of the cooling exchanger.

4. The method according to any one of claims 1 to 3, characterized in that during the cleaning step, the user fluid stream is caused to circulate in the cooling exchanger and is heated by it.

5. The method according to any one of claims 1 to 4, characterized in that The mechanism for compressing the working fluid includes one or more compressors and at least one drive motor for rotating the compressor(s). The refrigerating capacity of the refrigeration device is variable and is controlled by adjusting the rotational speed of the drive motor(s). In the second operating mode, the rotational speed of at least one of the drive motors is between 1% and 60% of the maximum or nominal rotational speed of the motor(s).

6. The method according to claim 5, wherein, the rotational speed of at least one of the drive motors is between 10% and 50% of the maximum or nominal rotational speed of the motor(s).

7. The method according to claim 6, wherein, the rotational speed of at least one of the drive motors is between 20% and 30% of the maximum or nominal rotational speed of the motor(s).

8. The method according to claim 5, wherein, in the second operating mode of the refrigeration device, at least one motor is deactivated. The at least one motor includes a turbine that rotates with its shaft, and at least one other drive motor of the compressor operates at a rotational speed between 1% and 60% of the maximum or nominal speed of the motor(s).

9. The method according to claim 8, wherein, at least one other drive motor of the compressor operates at a rotational speed between 10% and 50% of the maximum or nominal speed of the motor(s).

10. The method according to claim 9, wherein, at least one other drive motor of the compressor operates at a rotational speed between 20% and 30% of the maximum or nominal speed of the motor(s).

11. The method according to claim 8, wherein, the at least one deactivated motor is braked, which means that the rotation of the corresponding shaft and / or compressor and / or turbine is braked or prevented.

12. The method according to any one of claims 1 to 11, wherein, the at least one compressor driven by the motor is centrifugal. The motor includes a turbine that rotates with its shaft, and in the second operating mode of the refrigeration device, the working fluid circulates in the working circuit in the first circulation direction.

13. The method according to any one of claims 1 to 12, wherein, in the second operating mode of the refrigeration device, at least one drive motor is deactivated or operates at a rotational speed between 1% and 60% of the maximum or nominal speed of the motor(s). The at least one drive motor is separate from the motor(s) set to rotate in the opposite direction.

14. The method according to claim 13, wherein, in the second operating mode of the refrigeration device, at least one drive motor operates at a rotational speed between 10% and 50% of the maximum or nominal speed of the motor(s). The at least one drive motor is separate from the motor(s) set to rotate in the opposite direction.

15. The method according to claim 14, wherein, In the second operating mode of the refrigeration device, at least one drive motor operates at a rotational speed between 20% and 30% of the maximum or nominal speed of the motor, and the at least one drive motor is separate from the motor set to rotate in the opposite direction.

16. The method according to any one of claims 1 to 15, characterized in that by pumping a user fluid stream from a user fluid reservoir to circulate it in the cooling exchanger and returning the user fluid that has undergone heat exchange with the cooling exchanger to the reservoir.

17. A cryogenic refrigeration device for refrigeration at temperatures between -100 degrees Celsius and -273 degrees Celsius, comprising a working circuit that forms a loop and contains a working fluid, the working circuit forming a cycle that is in series including: a mechanism for compressing the working fluid; a mechanism for cooling the working fluid; a mechanism for expanding the working fluid; and a mechanism for heating the working fluid, the refrigeration device including a cooling exchanger configured to extract heat from at least one component by heat exchange with the working fluid circulating in the working circuit, the refrigeration device including an electronic controller configured to control the refrigeration capacity of the refrigeration device and switch the refrigeration device to a first cooling operation mode of the cooling exchanger to cool a user fluid stream to be circulated in the cooling exchanger, and a cleaning mode for removing solidified impurities in the cooling exchanger, in which cleaning mode the electronic controller is configured to reduce the refrigeration capacity of the refrigeration device and reduce the cooling of the cooling exchanger compared to the first cooling operation mode, characterized in that the mechanism for compressing the working fluid includes a plurality of rotary compressors and at least two drive motors, each drive motor including a rotary drive shaft, the compressors being driven to rotate by the respective rotary shafts, the mechanism for expanding the working fluid includes at least one rotary turbine that rotates together with the shaft of one of the drive motors of at least one compressor, and characterized in that in the first cooling operation mode, the drive motors are configured to rotate their rotary shafts in a respective first rotational direction, at least one motor is of the type having a reversible rotational direction, the at least one motor includes a turbine that rotates together with its shaft, and the electronic controller is configured to cause the motors to rotate in a rotational direction opposite to the first rotational direction during a second operating mode of the refrigeration device.

18. The device according to claim 17, characterized in that the mechanism for compressing the working fluid includes one or more compressors and at least one drive motor for rotating the compressors, the refrigeration capacity of the refrigeration device is variable and is controlled by adjusting the rotational speed of the drive motor, and the electronic controller is configured to set the rotational speed of at least one of the drive motors in the second operating mode to a value between 2% and 60% of the maximum or nominal speed of the motor.

19. The device according to claim 18, characterized in that The electronic controller is configured to set the rotational speed of at least one of the drive motors in the second operating mode to a value between 10% and 50% of the maximum or nominal speed of the motor.

20. The device according to claim 19, wherein, the electronic controller is configured to set the rotational speed of at least one of the drive motors in the second operating mode to a value between 20% and 30% of the maximum or nominal speed of the motor.

21. The device according to any one of claims 17 to 20, wherein, in the second operating mode, the electronic controller is configured to deactivate at least one motor, the at least one motor including a turbine that rotates with its shaft, and operate at least another drive motor of the compressor at a rotational speed between 1% and 60% of the maximum or nominal speed of the motor.

22. The device according to claim 21, wherein, operate at least another drive motor of the compressor at a rotational speed between 10% and 50% of the maximum or nominal speed of the motor.

23. The device according to claim 22, wherein, operate at least another drive motor of the compressor at a rotational speed between 20% and 30% of the maximum or nominal speed of the motor.

24. The device according to claim 21, wherein, the device has a mechanical or electrical or magnetic system for braking the deactivated motor, braking and / or preventing the shaft of the deactivated motor and / or the compressor and / or the turbine from rotating.

25. The device according to any one of claims 17 to 24, wherein, in the second operating mode of the refrigeration device, the electronic controller is configured to: deactivate at least one drive motor that is separate from the motor set to rotate in the opposite direction; or limit the rotational speed of this drive motor that is separate from the motor set to rotate in the opposite direction to a value between 1% and 60% of the rotational speed of the motor during the first cooling operation mode.

26. The device according to claim 25, wherein, limit the rotational speed of this drive motor that is separate from the motor set to rotate in the opposite direction to a value between 10% and 50% of the rotational speed of the motor during the first cooling operation mode.

27. The device according to claim 26, wherein, limit the rotational speed of this drive motor that is separate from the motor set to rotate in the opposite direction to a value between 20% and 30% of the rotational speed of the motor during the first cooling operation mode.

28. A system for refrigerating and / or liquefying a user fluid stream, including the refrigeration device according to any one of claims 17 to 25, the system comprises: at least one user fluid storage tank, and pipes for circulating the user fluid stream in the cooling exchanger.

29. The system according to claim 28, wherein, the user fluid is natural gas.

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