Refrigeration unit and system

Description

[0001] The invention relates to a refrigeration device and installation.

[0002] The invention relates more particularly to a low-temperature refrigeration device, i.e., at a temperature between -100 degrees Celsius and -273 degrees Celsius, the device being arranged in a frame and comprising a working circuit forming a loop and containing a working fluid, the working circuit forming a cycle comprising in series: a working fluid compression mechanism, a working fluid cooling mechanism, a working fluid expansion mechanism and a working fluid heating mechanism, the device comprising a refrigeration heat exchanger intended to extract heat from at least one component by heat exchange with the working fluid circulating in the working circuit,The working fluid cooling and heating mechanisms include a common heat exchanger in which the working fluid flows counter-currently through two separate transit portions of the working circuit depending on whether it is being cooled or heated; the compression mechanism includes at least two compressors and at least one compressor drive motor; the working fluid expansion mechanism includes at least one rotary turbine; the device includes at least one drive motor comprising a drive shaft, one end of which drives at least one compressor and the other end of which is coupled to a turbine, said motor being fixed to the frame at at least one fixed point; the common heat exchanger is fixed to the frame at at least one fixed point; the two counter-current transit portions of the common heat exchanger are oriented along a longitudinal direction of the frame.

[0003] Low temperature refrigeration devices are defined as refrigeration devices operating at a temperature between -100 degrees Celsius and -273 degrees Celsius, in particular between -100 degrees Celsius and -253 degrees Celsius.

[0004] The invention relates in particular to cryogenic refrigerators and / or liquefiers, for example of the "Turbo Brayton" cycle type or "Turbo Brayton coolers" in which a working gas, also called cycle gas (helium, nitrogen, hydrogen or other pure gas or mixture), undergoes a thermodynamic cycle producing cold which can be transferred to an organ or gas to be cooled.

[0005] These devices are used in a wide variety of applications, including cooling natural gas from a tank (for example, in ships). Liquefied natural gas is, for instance, subcooled to prevent vaporization, or the gaseous portion is cooled to facilitate liquefaction.

[0006] For example, a natural gas stream can be circulated in a heat exchanger cooled by the cycle gas from the refrigerator / liquefier.

[0007] These systems may include several heat exchangers positioned at the outlet of the compression stages. These systems are integrated into a frame or structure with limited volume. This makes integrating these various exchangers and their associated piping difficult. Cooling the working gas can also be problematic in some cases.

[0008] Furthermore, the various components of the device can be subjected to significant temperature variations between ambient temperature and cryogenic temperatures (up to 25K). These temperature variations can cause dimensional changes that may compromise the device's stability.

[0009] A low-temperature refrigeration device similar to the device according to claim 1 is known from XP001277379 ("BRAYTON CLOSED CYCLE GAS TURBINE STUDY FOR LNG RELICIFACTION SYSTEM", SHIPPING WORLD & SHIPBUILDER, vol. 166, no. 3887 (1973-11-01), pp. 1199-1200; in particular figure 3 ).

[0010] One aim of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

[0011] To that end, un device according to the invention, which also conforms to the generic definition given in the preamble above, is defined by claim 1.

[0012] Furthermore, embodiments of the invention may include one or more of the following characteristics: When the device is in operation, the temperature of the common heat exchanger varies longitudinally between a cold end and a hot end, the cold end, in particular at a temperature of around 100K, receiving the relatively cold working fluid from the expansion mechanism for heating and expelling the cooled working fluid before it enters the expansion mechanism, the hot end, in particular at a temperature of around 300K, receiving the hot working fluid from the compression mechanism and expelling the heated working fluid before it enters the compression mechanism, the connection of the common heat exchanger to the fixed point of the frame being located at an intermediate longitudinal position of the heat exchanger between its cold and hot ends, in particular at an area with an operating temperature between 200 and 270K, in particular 250K,The fixed fixing points of the engine and the common heat exchanger on the frame are spaced less than 100cm apart along the longitudinal direction (A), in particular less than 50cm apart, and preferably are located at the same level along the longitudinal direction of the frame. The working fluid cooling mechanism comprises two cooling heat exchangers disposed respectively at the outlet of the two compressors and ensuring heat exchange between the working fluid and a cooling fluid. The frame includes a lower base intended to be fixed to a support. The two cooling heat exchangers are located in the frame next to the common heat exchanger in a direction transverse to the longitudinal axis, i.e., the cooling heat exchangers are not located between the common heat exchanger and the lower base of the frame.The two cooling heat exchangers each have an oblong shape extending along respective longitudinal directions parallel to the longitudinal axis; the two cooling heat exchangers are arranged one above the other; each cooling heat exchanger comprises a working gas inlet to be cooled and a cooled working gas outlet, respectively located at two longitudinal ends; each cooling heat exchanger comprises a cooling fluid inlet and a cooling fluid outlet; the two cooling heat exchangers are arranged inverted, i.e., the respective longitudinal directions of the two cooling heat exchangers are parallel or substantially parallel, and the directions of flow of the working fluid in said cooling heat exchangers are opposite.The cooling fluid outlet of one of the two cooling heat exchangers is connected to the cooling fluid inlet of the other cooling heat exchanger, such that some of the cooling fluid flowing through one of the cooling heat exchangers has already circulated through the other cooling heat exchanger. The two cooling heat exchangers are located adjacently, i.e., spaced between 50 and 500 mm apart, specifically between 10 and 300 mm.

[0013] The invention also relates to a refrigeration and / or liquefaction installation for a user fluid stream, in particular natural gas, comprising a refrigeration device according to any one of the characteristics above or below, the installation comprising at least one user fluid tank, a circulation line for said user fluid stream in the cooling exchanger.

[0014] Other features and advantages will become apparent upon reading the description below, which refers to the figures in which: [ Fig. 1 ] represents a schematic and partial top view illustrating the structure and operation of an example device and installation that can implement the invention, [ Fig. 2 ] represents a schematic and partial side view along arrow V of the figure 1 illustrating details of the structure and operation of the device and installation, [ Fig. 3 ] represents a schematic and partial view illustrating a detail of the structure and operation of the device and installation according to a possible variant of the agency of two cooling heat exchangers.

[0015] The cooling and / or liquefaction installation of the [ Fig. 1 ] and the [ Fig. 2 ] includes a refrigeration device 1 providing cold (cooling power) at the level of a refrigeration heat exchanger 8.

[0016] The installation includes a circulation pipe 125 for a flow of fluid to be cooled, which is subjected to heat exchange with this cooling exchanger 8. For example, the fluid is liquid natural gas pumped into a tank 16 (for example, via a pump), then cooled (preferably outside the tank 16) and then returned to the tank 16 (for example, as a spray into the gaseous phase of the tank 16). This allows the contents of the tank 16 to be cooled or subcooled and limits vaporization. For example, the liquid in the tank 16 is subcooled below its saturation temperature (a drop in temperature of several degrees K, in particular 5 to 20 K and especially 14 K) before being reinjected into the tank 16. Alternatively, this cooling can be applied to the vaporized gas in the tank, particularly for the purpose of its reliquefaction.That is to say, the refrigeration device 1 produces a cooling power at the level of the refrigeration heat exchanger 8.

[0017] The refrigeration device 1 includes a working circuit 10 (preferably closed) forming a circulation loop. This working circuit 10 contains a working fluid (helium, nitrogen, neon, hydrogen or other suitable gas or mixture for example helium and argon or helium and nitrogen or helium and neon or helium and argon and nitrogen or helium and nitrogen and argon or helium and neon and argon or helium and nitrogen and argon and neon....).

[0018] The working circuit 10 forms a cycle comprising: a working fluid compression mechanism 2, 3, a working fluid cooling mechanism 4, 5, 6, a working fluid expansion mechanism 7 and a working fluid heating mechanism 6.

[0019] Device 1 includes a refrigeration heat exchanger 8 located downstream of the expansion mechanism 7 and intended to extract heat from at least one component 25 by heat exchange with the cold working fluid circulating in the working circuit 10.

[0020] The working fluid cooling and heating mechanisms classically include a common heat exchanger 6 in which the working fluid flows counter-currently in two separate transit portions of the working circuit 10 depending on whether it is being cooled or heated in the cycle.

[0021] The cooling heat exchanger 8 is located, for example, between the expansion mechanism 7 and the common heat exchanger 6. As illustrated, this cooling heat exchanger 8 can be integrated with the common heat exchanger 6 (i.e., the two exchangers 6 and 8 can be monobloc, meaning they can have separate fluid circuits that share the same heat exchange structure). Alternatively, the cooling heat exchanger 8 can be a separate heat exchanger from the common heat exchanger 6.

[0022] Thus, the working fluid which exits relatively hot from the compression mechanism 2, 3 is cooled in the common heat exchanger 6 before entering the expansion mechanism 7. The working fluid which exits relatively cold from the expansion mechanism 7 and the cooling heat exchanger 8 is, in turn, heated in the common heat exchanger 6 before returning to the compression mechanism 2 3 in order to start a new cycle.

[0023] The compression mechanism 2, 3 may include at least two compressors and at least one motor 14, 15 for driving the compressors 2, 3. Furthermore, preferably the cooling capacity of the device is variable and can be controlled by regulating the rotational speed of the drive motor(s) 14, 15 (cycle speed). Preferably, the cooling capacity produced by the device 1 can be adjusted from 0 to 100% of a rated or maximum capacity by changing the rotational speed of the motor(s) 14, 15 between zero and a maximum or rated speed. Such an architecture makes it possible to maintain high efficiency over a wide operating range (e.g., 97% of rated efficiency at 50% of rated cooling capacity).

[0024] In the non-limiting example shown, the refrigeration device 1 comprises two compressors 2, 3 in series. These two compressors 2, 3 can be driven respectively by two separate motors 14, 15. A turbine 7 is coupled to the drive shaft of one 14 of the two motors. For example, a first motor 14 drives a compressor 2 and is coupled to a turbine 7 (motor-turbocharger), while the other motor 15 drives only a compressor 3 (motor-compressor). The order of these two motor-turbochargers and motor-compressors can be reversed in the working circuit 10 (i.e., the first compressor in series can be driven by a motor whose shaft is not coupled to a turbine, while the second compressor in series is driven by a motor whose shaft is also coupled to a turbine).

[0025] For example, device 1 includes two high-speed motors 14, 15 (e.g. 10,000 revolutions per minute or several tens of thousands of revolutions per minute) for driving the respective compression stages 2, 3. The turbine 7 can be coupled to the motor 15 of one of the compression stages 2, 3, i.e. the device can have a turbine 7 constituting the expansion mechanism which is coupled to the motor 15 driving one compression stage (the first or the second).

[0026] Thus, the power of turbine(s) 7 can be advantageously recovered and used to reduce the fuel consumption of the motor(s). By increasing the motor speed (and therefore the flow rate in the working gas cycle), the refrigeration power produced is increased, and consequently, so is the electrical consumption of the liquefier (and vice versa). Compressors 2, 3 and turbine(s) 7 are preferably directly coupled to an output shaft of the relevant motor (without a gear-driven transmission mechanism).

[0027] The output shafts of the motors are preferably mounted on magnetic or gas-charged dynamic bearings. These bearings are used to support the compressors and turbines.

[0028] In the example shown, the refrigeration device 1 comprises two compressors 2, 3 forming two compression stages and an expansion turbine 7. That is to say, the compression mechanism comprises two compressors 2, 3 in series, preferably of the centrifugal type, and the expansion mechanism comprises a single turbine 7, preferably centripetal. Of course, any other number and arrangement of compressor(s), turbine(s), and motor(s) can be considered, for example: three compressors driven respectively by three separate motors, the turbine being, for example, coupled to one end of the drive shaft of one of these motors; or three compressors and two turbines... Other architectures can be considered, in particular three compressors and one turbine; or three compressors; or two; or three turbines; or two compressors and two turbines...Each motor may include a rotating drive shaft, one end of which drives a compressor and possibly another wheel, and the other end of which is free (no wheel mounted on the end) or possibly drives at least one other wheel (compressor or turbine).

[0029] As illustrated, a cooling heat exchanger 4, 5 can be provided at the outlet of each of the two compressors 2, 3 (for example, cooling by heat exchange with water at ambient temperature or any other fluid or cooling agent from a refrigerant circuit 26). Cf. [ Fig. 2 ].

[0030] This allows for isentropic, isothermal, or nearly isothermal compression. Similarly, a heat exchanger may or may not be included at the outlet of all or part of the expansion turbines 7 to achieve isentropic or isothermal expansion. Preferably, the heating and cooling of the working fluid are also isobaric, although this is not a limitation.

[0031] The device is housed in a frame 100, for example, a parallelepiped. The frame 100 includes a lower base 101. Unlike the representation of the figure 2 The upper end of the frame does not necessarily have a structure above the device but could only have peripheral posts located vertically above the base 101 at or below the highest point of the device. In other words, the frame can form lateral protection all around the device while leaving the upper part uncovered.

[0032] The motor 14, equipped with a compressor 2 and a turbine, is fixed to the frame 100 at a fixed point 104. For example, the frame 100 comprises a parallelepiped-shaped structure or frame made of rigid beams or uprights. For example, this motor 14 is fixed to a peripheral longitudinal upright, for example by screwing and / or riveting and / or welding.

[0033] Similarly, the common heat exchanger 6 is fixed to the frame 100 at a fixed point 106. For example, this heat exchanger 6 is fixed to a central longitudinal support, for example, by screwing and / or riveting and / or welding

[0034] The two counter-current transit portions of the common heat exchanger 6 are oriented along a longitudinal direction A of the frame 100. That is to say, the common heat exchanger 6 is oriented along a longitudinal direction A and the working gas flows within it progress essentially parallel along this direction.

[0035] As can be seen in the [ Fig. 1 ], the drive shaft of the motor 14, 15 equipped with a compressor 2 and a turbine 7 is also oriented in a direction parallel or substantially parallel to this longitudinal direction A.

[0036] Furthermore, the turbine 7 and the compressor 2 are arranged relatively longitudinally so that the turbine 7 is located longitudinally on the side corresponding to the relatively cold end of the common heat exchanger 6 when the device is in operation (on the right of the [ Fig. 1 ]) and the compressor (2) is located longitudinally on the side corresponding to the relatively hot end of the common heat exchanger 6 when the device is in operation (on the left of the [ Fig. 1 ]).

[0037] This allows: to have the same side of the device (here longitudinal and on the right of the [ Fig. 1 ]) the elements (portion to be exchanged, 6, turbian 7 and associated piping) susceptible to dimensional shrinkage when passing from the hot to the cold operating state, to have on the same side of the device (here longitudinal and on the left of the [ Fig. 1 ]) the elements (portion of exchange, 6, compressor 2 and associated piping) likely to undergo dimensional shrinkage when moving from the hot operating state.

[0038] These elements located on either side of the fixed point 104 106 of fixation can thus be free to retract / expand without constraint.

[0039] The "cold" elements (turbine 7, cold end of the heat exchanger and associated piping) are free to contract in the same direction while (to the left on [ Fig. 1 ]). The "hot" elements (compressor 2, hot end of heat exchanger 6 and associated piping) are free to expand in the same direction (also to the left on [ Fig. 1 ]). This helps to avoid or limit parasitic stresses on the device, which better absorbs dimensional variations due to temperature changes within it.

[0040] Indeed, typically when the device is operating (particularly during nominal operation), the temperature of the heat exchanger 6 equilibrates along a longitudinal gradient between a cold end and a hot end. The cold end, for example at a temperature of around 100 K, is the end of the heat exchanger 6 that receives the relatively cold working fluid from the expansion mechanism 7 for heating and discharges the cooled working fluid in the opposite direction before it enters the expansion mechanism 7. The hot end, for example at a temperature of around 300 K, is the end of the common heat exchanger 6 that receives the hot working fluid from the compression mechanism and discharges the heated working fluid in the opposite direction before it enters the compression mechanism.

[0041] According to the invention, the connection of the common heat exchanger 6 to the fixed point 106 of the frame 100 is located at an intermediate longitudinal position of the heat exchanger 6 between its cold and hot ends, in particular at the level of an area with an operating temperature between 200 and 270K, in particular 250K.

[0042] The connection of the common heat exchanger 6 to the fixed point of the frame 100 is located at a longitudinal position of the heat exchanger 6 situated between its relatively hot and cold ends when the device is in operation, and in particular at the portion of the heat exchanger 6 separating the cold end of the heat exchanger 6 which is capable of contracting (differential contraction due to cooling to low temperatures) and the hot end of the heat exchanger 6 which is capable of expanding (differential expansion due to relative heating to higher temperatures).

[0043] This allows the cold parts of the common heat exchanger 6 and associated cold piping to retract freely (to the left in the example of the [ Fig. 1 ]) and for the warm parts to expand freely (to the left in the example of the [ Fig. 1 ]).

[0044] This reduces harmful mechanical stresses within the device.

[0045] Preferably, the fixed points 104, 106 for fixing respectively the motor 14 and the common heat exchanger 6 on the frame 100 are located at the same longitudinal level on the frame or spaced along this longitudinal direction A by a distance of less than 100cm, in particular less than 50cm.

[0046] By arranging the fixed points in this way, we position relatively the cold elements likely to contract and, on the other hand, the relatively hot elements likely to expand, so as to allow movements of the same nature without inducing or limiting opposing antagonistic forces.

[0047] The frame 100 includes a lower base 101 intended to be fixed to a support (for example, the ground or a boat floor or the top of a tank 16 of liquid to be cooled, for example). This base can be formed of rigid uprights delimiting a rectangle with longitudinal or transverse uprights.

[0048] As illustrated [ Fig. 1 ] at least part of the elements of the device can be fixed on this base 101, in particular a box housing the common heat exchanger 6 and the refrigeration exchanger 8.

[0049] The two cooling heat exchangers 4 and 5 can be arranged in the frame 100 next to the common heat exchanger 6 in a direction transverse to the longitudinal axis A. That is to say, the cooling heat exchangers 4 and 5 are not located between the common heat exchanger 6 and the lower base 101 of the frame 100. The inventors have found that this arrangement ensures a mass distribution that improves the device's resistance to stress, particularly when the device is mounted on a boat.

[0050] As illustrated, the two cooling heat exchangers 4, 5 can each have an oblong shape extending along respective longitudinal directions that are parallel to the longitudinal axis A. The two cooling heat exchangers 4, 5 can be arranged one above the other.

[0051] Each cooling heat exchanger 4, 5 comprises a cooling fluid inlet 24, 25 and a cooling fluid outlet 34, 35. According to an advantageous feature, the cooling fluid outlet 34 of one of the two cooling heat exchangers 4, 5 can be connected to the cooling fluid inlet 25 of the other cooling heat exchanger 5 so that some of the cooling fluid flowing through one 5 of the cooling heat exchangers has already flowed through the other cooling heat exchanger 4 (cf. [ Fig. 3 ]).

[0052] This allows the two cooling heat exchangers 4, 5 to receive 100% of a cooling fluid flow (instead of subdividing this flow into two halves distributed respectively in the two exchangers 4, 5).

[0053] This relative increase in the cooling fluid flow rate thus increases the heat transfer coefficient and therefore improves the quality and reliability of the cooling. Furthermore, this solution avoids problems inherent in the known solution where two flow rates can diverge within the two heat exchangers (due in particular to pressure losses that can vary from one circuit or exchanger to another).

[0054] As explained in more detail below, this arrangement also simplifies the network of cooling fluid and working gas lines to and from heat exchangers 4, 5. In particular, this arrangement makes it easier to arrange the fluid circulation circuits (cooling and working) in a small space by allowing counter-current circulation between the working fluid and the cooling fluid, thereby reducing the number and / or length of the lines carrying these fluids.

[0055] As depicted in the [ Fig. 3 ], for example, the refrigerant circuit 26 supplies cooling fluid first to the second cooling heat exchanger 5 and then to the first cooling heat exchanger 8 (the qualifiers "first" and "second" referring to the first and second compression stage in the direction of flow of the working fluid).

[0056] Of course, the opposite arrangement can be envisaged (circulation of the cooling fluid first in the first 4 heat exchanger and then in the second 5 heat exchanger).

[0057] As illustrated, in both cases, the directions of flow of the two fluids (working fluid to be cooled and relatively colder cooling fluid) preferably flow in counter-current or opposite directions in each exchanger.

[0058] As illustrated in the [ Fig. 3The fluid connection between the two heat exchangers 4, 5 for cooling, to transfer the cooling fluid, can be simplified and reduced. This transfer of cooling fluid from one heat exchanger 4, 5 to the other can be achieved, in particular, by a short, welded section of tube, or even a simple tube or fitting between the two heat exchangers 4, 5.

[0059] As mentioned above, the two cooling heat exchangers 4 and 5 can be arranged adjacently, in particular side by side. This optimizes the overall footprint of the device.

[0060] If necessary, the two cooling heat exchangers 4, 5 could even be integrated into a single housing or casing comprising two separate working fluid circulation passages, said two passages exchanging heat respectively with two series-connected portions of the same cooling fluid circuit channel. For example, the cooling heat exchangers 4, 5 could each have an oblong shape extending in a respective longitudinal direction. Each cooling heat exchanger 4, 5 comprises a working gas inlet to be cooled and a cooled working gas outlet located respectively at two longitudinal ends.

[0061] The cooling heat exchangers 4 and 5 can be of the shell and tube type, shell and tube type, plate type, or any other suitable technology. The heat exchangers 4 and 5 can be made of aluminum and / or stainless steel.

[0062] Furthermore, the two cooling heat exchangers 4, 5 are preferably arranged in reverse within the device; that is, their respective longitudinal directions are parallel or substantially parallel, and the directions of flow of the working fluid within said cooling heat exchangers 4, 5 are opposite. This arrangement, combined with the arrangement of the cooling fluid circulation, minimizes the complexity of the fluid circuits while ensuring very good performance of the device.

[0063] All or part of the device, in particular its cold components, can be housed in a thermally insulated, sealed casing 11 (in particular a vacuum enclosure containing the common counter-current heat exchanger and the refrigeration exchanger 8).

[0064] A device / installation according to the invention can be applied for a process of cooling and / or liquefying another fluid or mixture, in particular hydrogen.

Claims

1. A low-temperature refrigeration device, that is to say at a temperature comprised between minus 100 degrees centigrade and minus 273 degrees centigrade, the device being arranged in a frame (100) and comprising a working circuit (10) forming a loop and containing a working fluid, the working circuit (10) forming a cycle comprising in series: a mechanism (2, 3) for compressing the working fluid, a mechanism (4, 5, 6) for cooling the working fluid, a mechanism (7) for expanding the working fluid and a mechanism (6, 8) for reheating the working fluid, the device (1) comprising a refrigeration heat exchanger (8) intended to extract heat from at least one member (125) by heat exchange with the working fluid circulating in the working circuit (10), the mechanisms for cooling and reheating the working fluid comprising a common heat exchanger (6) in which the working fluid transits in counter-current in two distinct transit portions of the working circuit (10) depending on whether it is cooled or reheated, the compression mechanism comprising at least two compressors (2, 3) and at least one motor (14, 15) for driving the compressor (2, 3), the mechanism for expanding the working fluid comprising at least one rotary turbine (7), the device comprising at least one drive motor (14, 15) comprising a drive shaft one end of which drives at least one compressor (2) and another end of which is coupled to a turbine (7), said motor (14) being fixed to the frame (100) at at least one fixed point (104), the common heat exchanger (6) being fixed to the frame (100) at at least one fixed point (106), the two counter-current transit portions of the common heat exchanger (6) being oriented along a longitudinal direction (A) of the frame (100), the drive shaft of said motor (14, 15) being oriented along a direction parallel or substantially parallel to the longitudinal direction (A), the turbine (7) and the compressor (2) being arranged relatively longitudinally such that the turbine (7) is situated longitudinally on the side corresponding to the relatively cold end of the common heat exchanger (6) when the device is in operation and the compressor (2) is situated longitudinally on the side corresponding to the relatively hot end of the common heat exchanger (6) when the device is in operation, and the connection of the common heat exchanger (6) to the fixed point of the frame (100) is located at a longitudinal position of the heat exchanger (6) situated between its relatively hot and cold ends when the device is in operation, and in particular at the level of the portion of the heat exchanger (6) separating the cold end of the heat exchanger (6) liable to contract and the hot end of the heat exchanger (6) liable to expand.

2. The device according to claim 1, characterized in that, when the device is in operation, the temperature of the common heat exchanger (6) varies longitudinally between a cold end and a hot end, the cold end, in particular at a temperature of the order of 100K, receiving the relatively cold working fluid coming from the expansion mechanism (7) for its reheating and discharging the cooled working fluid before it enters the expansion mechanism (7), the hot end, in particular at a temperature of the order of 300K, receiving the hot working fluid coming from the compression mechanism and discharging the reheated working fluid before it enters the compression mechanism, in that the connection of the common heat exchanger (6) to the fixed point (106) of the frame (100) is located at an intermediate longitudinal position of the heat exchanger (6) between its cold and hot ends, in particular at the level of a zone at an operating temperature comprised between 200 and 270K, in particular 250K.

3. The device according to any one of claims 1 to 2, characterized in that the fixed points (104, 106) for fixing the motor (14) and the common heat exchanger (6) respectively on the frame (100) are spaced apart along the longitudinal direction (A) by a distance of less than 100cm, in particular less than 50cm and are preferably located at the same level along the longitudinal direction (A) of the frame.

4. The device according to any one of claims 1 to 3, characterized in that the mechanism (4, 5, 6) for cooling the working fluid comprises two cooling heat exchangers (4, 5) arranged respectively at the outlet of the two compressors (2, 3) and ensuring a heat exchange between the working fluid and a cooling fluid, the frame (100) comprising a lower base (101) intended to be fixed on a support, the two cooling heat exchangers (4, 5) being located in the frame (100) next to the common heat exchanger (6) in a direction transverse to the longitudinal axis (A), that is to say that the cooling heat exchangers (4, 5) are not located between the common heat exchanger (6) and the lower base (101) of the frame (100).

5. The device according to claim 4, characterized in that the two cooling heat exchangers (4, 5) each have an oblong shape extending along respective longitudinal directions which are parallel to the longitudinal axis (A).

6. The device according to claim 4 or 5, characterized in that the two cooling heat exchangers (4, 5) are arranged one above the other.

7. The device according to any one of claims 4 to 6, characterized in that each cooling heat exchanger (4, 5) comprises an inlet for working gas to be cooled and an outlet for cooled working gas arranged respectively at two longitudinal ends, each cooling heat exchanger (4, 5) comprising an inlet (24, 25) for cooling fluid and an outlet (34, 35) for cooling fluid, the two cooling heat exchangers (4, 5) being arranged in an inverted manner, that is to say that the respective longitudinal directions of the two cooling exchangers (4, 5) are parallel or substantially parallel and the circulation directions of the working fluid in said cooling exchangers (4, 5) are opposite.

8. The device according to claim 6, characterized in that the outlet (34, 35) for cooling fluid of one of the two cooling exchangers (4, 5) is connected to the inlet (25, 24) for cooling fluid of the other cooling exchanger (5) such that a flow of cooling fluid transiting in one (5, 4) of the cooling heat exchangers has already circulated in the other cooling heat exchanger (4, 5).

9. The device according to any one of claims 4 to 8, characterized in that the two cooling heat exchangers (4, 5) are located adjacently, that is to say spaced apart by a distance comprised between 0 and 500mm, in particular between 10 and 300mm.

10. A refrigeration and / or liquefaction installation for a user fluid stream, in particular natural gas, comprising a refrigeration device (1) according to any one of claims 1 to 9, the installation comprising at least one reservoir (16) of user fluid, a pipe (125) for circulating said user fluid stream in the refrigeration exchanger (8).