Refrigerator, facility including such a refrigerator, and refrigeration method

Abstract

The invention relates to a refrigerator comprising, in a cycle circuit (60), a compression system (16), a cooling system (3, 4) and an expansion system (26) with at least one turbine (26) coupled to a compressor (26) of the refrigerator on either side of a common shaft (20), wherein a casing (19) houses a first chamber (15) for the compressor (16), a second, intermediate chamber for the shaft (20) mounted on a set of bearings, and a third chamber (24) for the turbine (26), wherein the refrigerator (6) comprises a set of pressurised fluid circuits (11, 14) in communication with at least two cavities (14, 18) located in the second chamber in order to attenuate or cancel the axial force on the shaft (20), wherein the end of the shaft (20) carrying the compressor (16) is provided with a recess (30) in which one end of a fixed support (130) is received, wherein the shaft (20) is rotatably mounted relative to the support (130), wherein the recess (30) and the end of the support (130) together define, with the bottom of the recess (30), a volume separate from the first chamber (15), configured to maintain in the recess (30) a pressure that is distinct from and lower than the pressure of the first chamber (15), and wherein the shaft comprises an inner channel (120) having a first end opening into the recess (30) and a second end opening into a first cavity (11) at an offset position along the shaft (20).

Description

Refrigerator, installation including such a refrigerator and refrigeration process

[0001] The invention relates to a refrigerator, an installation comprising such a refrigerator and a refrigeration process.

[0002] The invention relates more particularly to a gas cycle refrigerator comprising, in a cycle circuit, a compression system, a cooling system and an expansion system for subjecting the cycle gas to a thermodynamic cycle to produce cold, the expansion system comprising at least one expansion turbine coupled to a compressor of the refrigerator and, for example, a compressor of the gas cycle compression system, the expansion turbine and the compressor being coupled on either side of a common shaft, the expansion turbine, the compressor and the shaft being housed in a casing enclosing a first chamber in which the compressor is rotatably mounted, a second intermediate chamber in which the shaft is rotatably mounted on a set of bearings, and a third chamber in which the turbine is rotatably mounted.the refrigerator comprising a set of pressurized fluid circuits communicating with at least two cavities located in the second chamber, the pressurized fluid circuits being configured to supply determined pressurized gas flows into the cavities to mitigate or cancel the axial force on the shaft caused by the pressure difference between the pressures prevailing in the first chamber (at the compressor inlet) and the pressure in the third chamber.

[0003] In refrigeration cycle refrigerators using turbines, energy recovery on cryogenic turbines is important to increase energy efficiency.

[0004] This is particularly important for high-power hydrogen liquefiers (e.g., 60 to 300 tonnes per day) using such refrigerators.

[0005] One solution adopted is the recovery of work via a compressor coupled to the shaft of the cryogenic turbine in order to increase the high compression pressure at the main compression station.

[0006] For specific volumetric flow rate constraints, these coupled compressors are those installed at the outlet of the compression station, therefore at the highest pressure (above 20 bar abs). On the cryogenic turbine side, the optimal arrangement involves staggering the turbines in series from the highest pressure (for example, between 30 and 50 bar abs) down to the lowest pressure (between 1 and 10 bar abs, for example).

[0007] The pressure differences between the coupled turbine and compressor sections become significant. This pressure differential generates axial loads that must be partially compensated by the selected bearings supporting the shaft and by an appropriate distribution of pressures on the rotating surfaces involved, via the turbomachine's sealing systems.

[0008] On a turbomachine, the load-bearing capacity of the bearings is, as a first approximation, proportional to the size of the machine. Indeed, the larger the turbomachine, the greater the surface area over which pressure forces are applied. With such pressure differentials at the shaft ends, the axial loads are greater than or very close to the maximum capacity of the bearings (magnetic, gas, rolling, or other).

[0009] One known solution is a thrust equalizing mechanism (or "TEM").

[0010] Another solution is to include a balancing piston on the centrifugal compressor.

[0011] Another solution involves a wheel balancing hole, which is a cavity at the rear of the wheel maintained at a medium pressure or one adapted to cancel the residual axial forces related to the pressure differential on the wheel blades. However, this does not eliminate the piston effect up to the diameter of the labyrinth seal on the shaft.

[0012] One aim of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

[0013] To this end, the refrigerator according to the invention, which also conforms to the generic definition given in the preamble above, is essentially characterized in that the end of the shaft carrying the compressor is provided with a housing in which one end of a fixed support is received, the shaft being mounted in rotation relative to the support, the housing, the end of the support delimiting with the bottom of the housing a volume separated from the first chamber by a set of seal(s) configured to maintain in the housing a distinct pressure lower than the pressure of the first chamber, the shaft comprising an internal channel having a first end opening into the housing and a second end opening into a first cavity in an offset manner along the shaft.

[0014] Furthermore, embodiments of the invention may include one or more of the following features: the first cavity is located on the turbine side; the first cavity is delimited between two labyrinth-type seal(s); the first cavity is maintained at a pressure equal to or close to the pressure of the third chamber; the refrigerator includes a circuit connected to the first cavity equipped with a pressure regulating device, such as a valve, and configured to regulate the pressure in the first cavity and optionally in the housing; the refrigerator includes a second cavity located between the first chamber and the first cavity; the second cavity is connected to a pressurized fluid circuit configured to maintain the second cavity at a pressure level intermediate between the pressure in the first chamber and the pressure in the first cavity; the shaft includes a collar projecting on a portion of its external surface.The collar is located in the second cavity, for example in the central part of the tree.

[0015] The invention also relates to a liquefaction plant for a feed fluid at a cryogenic temperature, for example hydrogen, comprising a feed circuit for the feed fluid, a set of heat exchanger(s) in heat exchange with the feed circuit, a cooling device in heat exchange with at least part of the set of heat exchanger(s) configured to cool the feed fluid to a determined target temperature, the cooling device comprising a refrigerator according to any one of the above or below characteristics.

[0016] The invention also relates to a refrigeration method using a refrigerator according to any one of the above or below characteristics, or an installation according to any one of the above or below characteristics, the method comprising a cold power production during which the expansion turbine expands the cycle gas and the compressor compresses gas by generating a pressure difference between the pressures prevailing in the first chamber and in the third chamber, this pressure difference producing a longitudinal force along the shaft, the method comprising a pressure regulation step in the bottom of the housing and the cavities to generate an opposing longitudinal counter-force of the same or substantially equal intensity to limit the resulting axial force on the shaft.

[0017] According to one possible feature, the process includes a step of maintaining, in the housing, a pressure lower than the pressure in the first chamber.

[0018] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0019] Other features and advantages will become apparent upon reading the description below, which refers to the figures in which: Brief description of the figures

[0020] The invention will be better understood upon reading the following description, given solely by way of example and made with reference to the accompanying drawings in which:

[0021] is a schematic and partial view illustrating an example of the structure and operation of an installation comprising a refrigerator according to one possible embodiment of the invention,

[0022] is a schematic longitudinal cross-sectional view of a detail of the arrangement of the wheels (turbine and compressor) on a refrigerator shaft according to one possible embodiment. Detailed description

[0023] In all the figures, the same references refer to the same elements.

[0024] In this detailed description, the following embodiments are examples. Although the description refers to one or more embodiments, this does not mean that the features apply only to a single embodiment. Simple features from different embodiments can also be combined and / or interchanged to provide other embodiments.

[0025] Installation 1, illustrated as an example, is a liquefier for a feed fluid at a cryogenic temperature, for example, hydrogen. This installation 1 includes a feed circuit 2 for the feed fluid and a set of heat exchanger(s) 3, 4 in heat exchange with the feed circuit. A cooling device 6 is in heat exchange with at least part of the heat exchanger(s) configured to cool the feed fluid to a predetermined target temperature, for example, for liquefaction. As illustrated, the installation optionally includes a pre-cooling device 23 in heat exchange with at least part of the heat exchanger(s).

[0026] The 6-unit cooling system includes a cycle refrigerator.

[0027] The gas cycle refrigerator 6 includes, in a cycle circuit 60, a compression system 16, a cooling system 3, 4 and an expansion system 26 to subject the cycle gas to a thermodynamic cycle to produce cold.

[0028] The expansion system includes at least one expansion turbine 26 coupled to a refrigerator compressor 26.

[0029] The heat exchanger assembly 3, 4 may include at least one counter-current exchanger simultaneously providing heating and cooling of the cycle fluid at two points in the cycle (cooling after compression and heating after expansion before returning to compression).

[0030] In this example, the expansion turbine 26 is coupled to a compressor of the cycle gas compression system 16.

[0031] The expansion turbine 26 and the compressor 16 are coupled on either side of a common shaft 20. As illustrated in the figure, the expansion turbine 26, the compressor and the shaft 20 can be housed in a casing 19 defining a first chamber 15 (or volume) in which the compressor 16 is mounted for rotation, a second intermediate chamber in which the shaft 20 is mounted for rotation on a set of bearings (not shown) and a third chamber 24 in which the turbine 26 is mounted for rotation.

[0032] The refrigerator 6 includes a set of pressurized fluid circuits communicating with at least two cavities 18, 11 located in the second chamber.

[0033] For the sake of simplicity, the fixed part of the stator that surrounds the shaft 20 is not shown.

[0034] As described in more detail below, the pressurized fluid circuits are configured to provide determined pressurized gas flows into the cavities to mitigate or cancel the axial force on the shaft 20 caused by the pressure difference between the pressures prevailing in the first chamber 15 (at the compressor inlet) and the pressure in the third chamber 24. This pressure at the compressor inlet (at the upstream inlet of the compressor wheel) is lower than the pressure at the outlet of the compressor wheel (particularly in the third cavity 14 described below).

[0035] The end of the shaft 20 carrying the compressor 16 is provided with a housing 30 (a hollow) in which is received one end of a fixed support 130 of the installation (for example a fixed shaft).

[0036] The shaft 20 is mounted to rotate relative to the support 130. For example, the compressor wheel 16 rotates on the end of the fixed support 130.

[0037] The end of the support 130 defines with the bottom of the housing 30 a volume (or cavity) which is separated from the first chamber 15 by a set of seal(s) 9 allowing to maintain in this housing 30 a pressure (for example of the order of 10 bar) distinct and lower than the pressure prevailing in the first chamber 15 (for example of the order of 50 bar).

[0038] This arrangement creates a relatively low-pressure cavity on the compressor side 16 (for example, replicating the pressure on the turbine side). This reduces or eliminates the axial forces on the shaft 20.

[0039] This also allows for the formation of a support surface for a balancing piston.

[0040] For example, the end of the support 130 can be positioned at a screw that normally secures the compressor wheel to the shaft. For instance, the screw is drilled to allow for fluid arrangement and transfer. Alternatively, or in combination, a portion of the shaft around the screw or compressor wheel is drilled.

[0041] In addition, the shaft 20 includes an internal channel 120 having a first end opening into the housing 30 and a second end opening into a first cavity 11 located offset along the shaft 20.

[0042] This first cavity 11 can be located on the turbine side 26.

[0043] More specifically, the first cavity 11 opens before the turbine, that is to say that the first cavity 11 opens into the second chamber and not into the third chamber 26 of the turbine 26. That is to say that the internal channel 120 does not pass through to the turbine 26. This avoids the risk of leakage and transfer of fluid between the chambers of the turbine and the compressor.

[0044] As illustrated, the first cavity 11 can be delimited between two labyrinth-type joint(s) 9.

[0045] This first cavity 11 can be maintained at a pressure equal to or close to the pressure of the third chamber 24 (for example, on the order of 10 bar).

[0046] A second cavity 18 can be located between the first chamber 15 and the first cavity 11. This second cavity 18 can be maintained at an intermediate pressure level (for example, on the order of 30 bar) between the pressure in the first chamber 15 and the pressure in the first cavity 11.

[0047] This second cavity 18 can be located in the central part of the shaft 20. The shaft 20 can include a collar 10 projecting on a portion of its external surface, for example in the central part of the shaft 20.

[0048] The arrangement shown further includes a third cavity 14 connected to a high-pressure fluid circuit in communication with a front face of the compressor 16, i.e., a face of the compressor 1 opposite the face of the compressor equipped with blades in the compression chamber. This third cavity 14 is, for example, supplied with pressurized gas compressed by the compressor 16 (at a secondary pressure higher than the initial pressure at the compressor inlet). This generates on the compressor 16 an axial (longitudinal) balancing force opposing the force generated by compression in the compression chamber.

[0049] Pressure regulation in the various cavities makes it possible to generate an overall opposing longitudinal counter-force of the same or nearly equal intensity to limit the resulting axial force on the shaft.

[0050] For example, the resulting axial force is minimized and, for example, less than 10 to 25% of the load capacity of the selected bearings and thrust bearings of the turbomachine. This is achieved without generating significant leaks and without contaminating the relatively cold circuits (turbine side) with relatively hot flows (compressor side).

[0051] For example, the pressure in housing 30 and in the first cavity 11 can be regulated at the outlet of the first cavity 11 by a pressure regulating device 12, for example a valve 12 controlled by the pressure in the cavity 11. Thus, the pressurized gas from the first chamber 15 travels through the housing and then through the internal channel 120 to the first cavity 11. The valve 12 regulates the pressure, for example, according to a pressure measurement 13 in the first cavity 11. The flow downstream of the valve can be supplied to the cycle circuit, for example, at a relatively low pressure level.

[0052] Alternatively, the gas flow could be reversed. That is to say, a flow at relatively low pressure is supplied to the first cavity 11 and circulates to the housing 30 at relatively low pressure.

[0053] Note that for the sake of simplicity, the bearings supporting the shaft in the stator are not shown. These bearings can be magnetic or gas-filled. In the case of gas-filled bearings, the lifting gas can be supplied by all or part of the aforementioned pressurized fluid circuits.

Claims

A gas cycle refrigerator comprising, in a cycle circuit (60), a compression system (16), a cooling system (3, 4), and an expansion system (26) for subjecting the cycle gas to a thermodynamic cycle to produce cold, the expansion system comprising at least one expansion turbine (26) coupled to a compressor (26) of the refrigerator and, for example, a compressor of the cycle gas compression system (16), the expansion turbine (26) and the compressor (16) being coupled on either side of a common shaft (20), the expansion turbine (26), the compressor, and the shaft (20) being housed in a casing (19) containing a first chamber (15) in which the compressor (16) is rotatably mounted, a second intermediate chamber in which the shaft (20) is rotatably mounted on a set of bearings, and a third chamber (24) in which the turbine (26) is rotatably mounted, the refrigerator (6) comprising a set of circuits (11,14) of pressurized fluid communicating at least two cavities (14, 18) located in the second chamber, the pressurized fluid circuits being configured to provide determined pressurized gas flows into the cavities to attenuate or cancel the axial force on the shaft (20) caused by the pressure difference between the pressures prevailing in the first chamber (15) at the compressor inlet and the pressure in the third chamber (24), characterized in that the end of the shaft (20) carrying the compressor (16) is provided with a housing (30) into which is received one end of a fixed support (130), the shaft (20) being mounted to rotate relative to the support (130), the housing (30),the end of the support (130) delimiting with the bottom of the housing (30) a volume separated from the first chamber (15) by a set of seal(s) (9) configured to maintain in the housing (30) a distinct pressure lower than the pressure of the first chamber (15) at the compressor inlet, the shaft (20) comprising an internal channel (120) having a first end opening into the housing (30) and a second end opening into a first cavity (11) offset along the shaft (20), and the first cavity (11) being delimited between two labyrinth-type seal(s) (9), and the first cavity (11) being maintained at a pressure equal to or close to the pressure of the third chamber (24), and the refrigerator comprising a circuit connected to the first cavity (11) equipped with a pressure regulating device, such as a valve (12), and configured to regulate the pressure in the first cavity (11) and optionally in the accommodation (30)., Refrigerator according to claim 1, characterized in that the first cavity (11) is located on the side of the turbine (26). Refrigerator according to claim 1 or 2, characterized in that the first cavity (11) opens along the shaft (20) before the turbine (26), i.e. into the second chamber. Refrigerator according to any one of the preceding claims, characterized in that it comprises a second cavity (18) located between the first chamber (15) and the first cavity (11), the second cavity (18) is connected to a pressurized fluid circuit configured to maintain the second cavity at a pressure level intermediate between the pressure in the first chamber (15) at the compressor inlet and the pressure in the first cavity (11). Refrigerator according to any one of the preceding claims, characterized in that the shaft comprises a collar (10) projecting over a portion of its external surface. Refrigerator according to claims 4 and 5, characterized in that the collar (10) is located in the second cavity (18), for example in the central part of the shaft (20). Installation for liquefying a feed fluid at a cryogenic temperature, for example hydrogen, comprising a feed circuit (2) for the feed fluid, a set of heat exchanger(s) (3, 4) in heat exchange with the feed circuit, a cooling device (6) in heat exchange with at least a part of the set of heat exchanger(s) configured to cool the feed fluid to a determined target temperature, the cooling device (6) comprising a refrigerator according to any one of claims 1 to 6. A refrigeration method using a refrigerator according to any one of claims 1 to 6 or an installation according to claim 7, the method comprising a cold power production in which the expansion turbine (26) expands the cycle gas and the compressor compresses the gas by generating a pressure difference between the pressures prevailing in the first chamber (15) at the inlet of the compressor and the pressure in the third chamber (4), this pressure difference producing a longitudinal force along the shaft (20), the method comprising a pressure regulation step in the bottom of the housing (30) and the cavities to generate an opposing longitudinal counter-force of the same or substantially equal magnitude to limit the resulting axial force on the shaft. Method according to claim 8, characterized in that it comprises a step of maintaining in the housing (30) a pressure lower than the pressure in the first chamber (15) at the inlet of the compressor.

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