Liquefied gas pump and method for operating liquefied gas pump

Abstract

This liquefied gas pump comprises a rotary shaft that can rotate around an axis, an impeller that is provided integrally with the rotary shaft and that can pump liquefied gas by rotating together with the rotary shaft, an electric motor that rotationally drives the rotary shaft around the axis, a bearing device that supports the rotary shaft to be rotatable around the axis, a liquefied gas supply source that can supply the liquefied gas to the bearing device at a first pressure, and a switching unit that can switch between a state in which the bearing device communicates with a space having a second pressure lower than the first pressure and a state in which the bearing device does not communicate with the space having the second pressure.

Description

Liquefied Gas Pump and Operating Method of Liquefied Gas Pump

[0007] ,

[0001] The present disclosure relates to a liquefied gas pump and an operating method of a liquefied gas pump. This application claims priority to Japanese Patent Application No. 2024-168184 filed in Japan on September 27, 2024, and incorporates its content herein by reference.

[0002] As a pump for boosting the pressure of a liquid, there is a vertical rotary pump. For example, Patent Document 1 discloses a technique for simplifying the structure, improving the reliability, and enhancing the efficiency of a pump for liquefied gas used in a low-temperature environment.

[0003] Japanese Patent Application Laid-Open No. 2006-170046

[0004] By the way, when a hydrostatic sliding bearing is used as a thrust bearing in a pump whose rotating shaft extends in the vertical direction, some contrivance is required at the time of starting and stopping the pump. That is, when the configuration is such that the hydrostatic pressure is supplied from the impeller to the hydrostatic sliding bearing, the hydrostatic pressure is not supplied at the time of starting and stopping. Therefore, at the location where the rotating shaft is supported in the vertical direction, the hydrostatic pressure is not stably supplied and friction occurs. As a result, the thrust bearing may wear out.

[0005] The present disclosure provides a liquefied gas pump and an operating method of a liquefied gas pump that can suppress wear of the thrust bearing during startup and shutdown.

[0006] The liquefied gas pump according to the present disclosure includes a rotating shaft rotatable about an axis, an impeller provided integrally with the rotating shaft and capable of pumping liquefied gas by rotating together with the rotating shaft, an electric motor that rotationally drives the rotating shaft about the axis, a bearing device that rotatably supports the rotating shaft about the axis, a liquefied gas supply source capable of supplying the liquefied gas to the bearing device at a first pressure, and a switching unit capable of switching between a state in which the bearing device communicates with a space at a second pressure lower than the first pressure and a state in which it does not communicate with the space at the second pressure.

[0007] The method for operating a liquefied gas pump according to the present disclosure is a method for operating a liquefied gas pump, the liquefied gas pump comprising: a rotating shaft rotatable around an axis; an impeller integrally provided with the rotating shaft and capable of pumping liquefied gas by rotating together with the rotating shaft; an electric motor for rotationally driving the rotating shaft around the axis; a bearing device for supporting the rotating shaft so as to be rotatable around the axis; a liquefied gas supply source capable of supplying the liquefied gas to the bearing device at a first pressure; and a switching unit capable of switching the bearing device between a state in which it is in communication with a space at a second pressure lower than the first pressure and a state in which it is not in communication with the space at the second pressure, the method for operating the liquefied gas pump comprising: a pre-cooling step of supplying the liquefied gas to the flow path of the liquefied gas pump at the first pressure; a startup communication step after the pre-cooling step of connecting the bearing device to the space at the second pressure; and a drive step after the startup communication step of rotationally driving the rotating shaft around the axis.

[0008] According to the liquefied gas pump and operating method of the liquefied gas pump described herein, wear of the thrust bearing during starting and stopping can be suppressed.

[0009] This is a schematic diagram showing the entire liquefied gas pump according to the embodiment of this disclosure. This is an enlarged view of the main part showing the flow of liquefied gas in the liquefied gas pump according to the embodiment of this disclosure. This is a cross-sectional view showing the flow of liquefied gas near the thrust bearing of the liquefied gas pump according to the embodiment of this disclosure. This is a flowchart showing an example of how to operate the liquefied gas pump according to the embodiment of this disclosure.

[0010] <Embodiments> Hereinafter, embodiments relating to this disclosure will be described in detail with reference to the drawings.

[0011] <Liquefied Gas Pump> First, the liquefied gas pump 1 will be described with reference to Figures 1 to 3. As shown in Figure 1, the liquefied gas pump 1 is positioned so as to be suspended inside the sump 50. The liquefied gas pump 1 is a device for pressurizing liquefied gas as a fluid. In this embodiment, the liquefied gas pump 1 for pressurizing liquid hydrogen will be described. Note that the fluid is not limited to liquid hydrogen, but may be other liquids or gases. For example, liquefied natural gas (LNG) is one example.

[0012] The sump 50 is capable of storing liquid. In this embodiment, the sump 50 is capable of storing liquid hydrogen. The sump 50 is a vacuum-insulated container. That is, the sump 50 is an insulated structure having a bottomed cylindrical shape. The sump 50 has a liquid storage chamber 53 formed inside it. The liquid storage chamber 53 is capable of storing liquid hydrogen. The sump 50 has an outer peripheral flange 51 provided on its upper vertical side. The sump 50 is installed on a stand (not shown). The sump 50 has an upper flange provided on its upper vertical side. The upper flange is provided vertically above the outer peripheral flange 51. The upper flange and the outer peripheral flange 51 are arranged in contact with each other. The upper flange and the outer peripheral flange 51 are connected, for example, via bolts. The upper flange is positioned to maintain the airtightness of the sump 50. The upper flange can also be installed in a manner that suspends the liquefied gas pump 1.

[0013] The sump 50 has a supply pipe 60 and a gas discharge pipe 61 connected to its side. The supply pipe 60 is a pipe that allows liquid hydrogen to be supplied to the liquid storage chamber 53 from an external source. The gas discharge pipe 61 is a pipe that allows vaporized hydrogen from the liquid storage chamber 53 to be discharged to the outside of the sump 50. The gas discharge pipe 61 is located vertically above the supply pipe 60. The gas discharge pipe 61 may also be capable of discharging liquid hydrogen to the outside of the sump 50, as well as vaporized hydrogen.

[0014] The liquefied gas pump 1 comprises a liquefied gas supply source 2, an external sump 3, a communication passage 4, a switching unit 5, and a pump body 6. The liquefied gas supply source 2 is capable of circulating liquefied gas. In this embodiment, the liquefied gas supply source 2 is capable of circulating liquid hydrogen. The liquefied gas supply source 2 is capable of supplying liquid hydrogen to the bearing device 40 at a first pressure. The first pressure is an arbitrarily determined pressure value. The first pressure is, for example, the pressure inside the liquefied gas pump 1, i.e., the internal pressure. As shown in Figure 2, the liquefied gas supply source 2 in this embodiment is provided separately from the supply pipe 60. However, it is not limited to this, and for example, a branch from the supply pipe 60 may be provided as the liquefied gas supply source 2. The liquefied gas supply source 2 is in communication with the supply passage 80 (described later). That is, the liquefied gas supply source 2 is capable of supplying liquid hydrogen to the bearing device 40 through the supply passage 80.

[0015] The external sump 3 is separate from the sump 50 and is located outside the sump 50. The interior of the external sump 3 is a space 3A with a second pressure. The second pressure is a pressure value lower than the first pressure. The second pressure is also an arbitrarily determined pressure value. In this embodiment, the second pressure is atmospheric pressure, but is not limited to this. For example, the second pressure may be set to atmospheric pressure or lower by evacuating the external sump 3. Furthermore, the external sump 3 is capable of communicating with the bearing device 40, which will be described later. That is, the space 3A with the second pressure is capable of communicating with the bearing device 40. The external sump 3 and the bearing device 40 are capable of communicating with each other via a communication channel 4.

[0016] The communication passage 4 is provided to connect the external sump 3 and the bearing device 40. The communication passage 4 is a pipe through which liquid hydrogen can flow. The communication passage 4 has a communication passage 4A that communicates with the thrust bearing 44, and communication passages 4B and 4C that communicate with the radial bearing 41. However, the communication passage 4 is not limited to this configuration. The communication passage 4 may also be capable of facilitating the flow of gas. Furthermore, the communication passage 4 may be provided to communicate with locations other than the bearing device 40 of the pump body 6.

[0017] The switching unit 5 is capable of switching between a state in which the external sump 3 and the bearing device 40 are in communication and a state in which they are not. In other words, the switching unit 5 is capable of switching between a state in which the bearing device 40 is in communication with the second pressure space 3A and a state in which it is not in communication with the second pressure space 3A. The switching unit 5 is provided so as to be sandwiched between the communication passage 4. Furthermore, the switching unit 5 is located outside the sump 50. However, the location of the switching unit 5 is not limited to this. For example, the switching unit 5 may be provided so as to connect the external sump 3 and the communication passage 4. Also, for example, the switching unit 5 may be provided inside the sump 50.

[0018] The pump body is located inside the sump 50. The pump body comprises a casing 10, a rotating shaft 20, an electric motor 30, an inducer 24, an impeller 25, a bearing device 40, and a supply passage 80. In the following, when simply referred to as a flow path, it refers to the part of the liquefied gas pump 1 through which liquid hydrogen flows.

[0019] <Casing> The casing 10 forms the outer shell of the liquefied gas pump 1. The casing 10 has a hollow shape. The casing 10 may be composed of a single component or may be composed of multiple components assembled together. The casing 10 is capable of housing the electric motor 30, inducer 24, impeller 25, and bearing device 40 inside. The upper end of the casing 10 is connected to the upper flange and suspended and supported inside the sump 50. The casing 10 has a cylindrical shape centered on an axis O that extends in the vertical direction, but is not limited to this. In addition, although both the sump 50 and the casing 10 spread out from the axis O, the centers of the sump 50 and the casing 10 may be offset from each other.

[0020] The casing 10 has a suction section 11 at its lower end. The suction section 11 is formed to communicate with the liquid storage chamber 53. Liquid hydrogen stored in the liquid storage chamber 53 can flow through the suction section 11. The casing 10 also has a discharge section 12 at its upper end. The discharge section 12 is connected to a discharge pipe 62 that extends to the outside of the sump 50. The suction section 11 may also be directly connected to piping extended from the supply pipe 60 or the like. In other words, liquid hydrogen may be introduced directly from the piping to the suction section 11 without first being stored in the liquid storage chamber 53.

[0021] <Rotational Shaft> The rotational shaft 20 is a rod-shaped member extending along the axis O. The rotational shaft 20 and the casing 10 are arranged concentrically with respect to the axis O. The rotational shaft 20 is supported by a bearing device 40 so as to be rotatable around the axis O relative to the casing 10. Hereinafter, the radial direction of the rotational shaft 20 will be simply referred to as the radial direction, and the circumferential direction of the rotational shaft 20 will be simply referred to as the circumferential direction. The direction in which the axis O extends will be referred to as the axial direction. The inducer 24, the impeller 25, and the rotor 36 of the electric motor 30 are fixed to the rotational shaft 20. The rotational shaft 20 also has a rotational shaft body 21 and a thrust collar 22.

[0022] The rotating shaft body 21 is a rod-shaped member extending along the axis O. The rotating shaft body 21 is fixed to the thrust collar 22, which is fixed to the outer circumference of the rotating shaft body 21. The thrust collar 22 is disc-shaped and is provided to expand the diameter of the rotating shaft body 21 in the radial direction while fixed to the rotating shaft body 21. In other words, the thrust collar 22 is provided to protrude outward from the rotating shaft body 21. The thrust collar 22 is rotatable together with the rotating shaft body 21. The thrust collar 22 is also movable together with the rotating shaft body 21 in the axial direction. The thrust collar 22 has an upper surface 22A facing upward in the axial direction and a lower surface 22B facing downward. The rotating shaft body 21 and the thrust collar 22 may be molded as a single unit or molded separately and then connected.

[0023] <Bearing Device> The bearing device 40 is a component that supports the rotating shaft 20 so that it can rotate around axis O relative to the casing 10. The bearing device 40 is fixedly installed inside the casing 10. The bearing device 40 is installed so that liquid hydrogen can be supplied at a first pressure. The bearing device 40 is also installed so that it can communicate with a second pressure space 3A. The bearing device 40 has a radial bearing 41 and a thrust bearing 44.

[0024] The radial bearing 41 is positioned to receive the radial load of the rotating shaft 20. That is, the radial bearing 41 is positioned concentrically with the rotating shaft 20 and is provided to cover the rotating shaft 20 from its outer circumferential surface. Multiple radial bearings 41 are provided. In this embodiment, a first radial bearing 42 and a second radial bearing 43 are provided. The first radial bearing 42 is positioned vertically above the casing 10. The second radial bearing 43 is positioned vertically below the casing 10. The radial bearing 41 in this embodiment is a sliding bearing, but the type is not limited. For example, the radial bearing 41 may be a rolling bearing. Also, the first radial bearing 42 and the second radial bearing 43 may be bearings of the same type, or they may be bearings of different types.

[0025] The thrust bearing 44 is positioned to receive the axial load of the rotating shaft 20. The thrust bearing 44 is provided to sandwich the thrust collar 22 in the axial direction. The thrust bearing 44 is a hydrostatic bearing. The thrust bearing 44 is provided to support the thrust collar 22 in the axial direction via fluid pressure. The thrust bearing 44 is provided to contact the lower surface 22B of the thrust collar 22 when the liquefied gas pump 1 is stopped. Also, as shown in Figure 2, the thrust bearing 44 is capable of supplying liquid hydrogen from the liquefied gas supply source 2 at a first pressure. Figure 3 shows a cross-sectional view of the main part of the thrust bearing 44. The thrust bearing 44 has an upper bearing body 45 and a lower bearing body 46. The upper bearing body 45 and the lower bearing body 46 are ring-shaped. The upper bearing body 45 and the lower bearing body 46 are fixed to the casing 10.

[0026] The upper bearing body 45 is positioned opposite the upper surface 22A of the thrust collar 22 with a gap in the axial direction. The upper bearing body 45 has an upper pocket 45A, an upper manifold 45B, and an upper connecting passage 45C. The upper pocket 45A is formed at a position opposite the upper surface 22A of the thrust collar 22. The upper pocket 45A is formed such that the upper bearing body 45 is recessed upward in the axial direction. Multiple upper pockets 45A are provided at intervals in the circumferential direction. Liquid hydrogen is allowed to flow through the upper pockets 45A.

[0027] The upper manifold 45B is formed axially on the opposite side of the thrust collar 22 from the upper pocket 45A. The upper manifold 45B is formed such that the upper bearing body 45 protrudes upward in the axial direction. The upper manifold 45B has an annular shape along the circumferential direction. Liquid hydrogen is allowed to flow through the upper manifold 45B. The upper pocket 45A and the upper manifold 45B are connected by an upper connecting passage 45C. Liquid hydrogen is allowed to flow through the upper connecting passage 45C.

[0028] The lower bearing body 46 is positioned opposite the lower surface 22B of the thrust collar 22 with a gap in the axial direction. The lower bearing body 46 has a lower pocket 46A, a lower manifold 46B, and a lower connecting passage 46C. The lower pocket 46A is formed at a position opposite the lower surface 22B of the thrust collar 22. The lower pocket 46A is formed such that the lower bearing body 46 is recessed downward in the axial direction. Multiple lower pockets 46A are provided at intervals in the circumferential direction. Liquid hydrogen is allowed to flow through the lower pockets 46A.

[0029] The lower manifold 46B is formed on the opposite side of the thrust collar 22 from the lower pocket 46A in the axial direction. The lower manifold 46B is formed such that the lower bearing body 46 protrudes downward in the axial direction. The lower manifold 46B has an annular shape along the circumferential direction. Liquid hydrogen is allowed to flow through the lower manifold 46B. The lower pocket 46A and the lower manifold 46B are connected by a lower connecting passage 46C. Liquid hydrogen is allowed to flow through the lower connecting passage 46C.

[0030] Furthermore, the thrust bearing 44 is positioned vertically above the first radial bearing 42 and the second radial bearing 43. However, the position of the thrust bearing 44 is not limited to this. The thrust bearing 44 may be positioned between the first radial bearing 42 and the second radial bearing 43, or vertically below the first radial bearing 42 and the second radial bearing 43.

[0031] <Supply Passage> The supply passage 80 is provided to connect the liquefied gas supply source 2 and the bearing device 40. The supply passage 80 is a pipe through which liquid hydrogen can flow. The supply passage 80 is connected to the bearing device 40 as follows: The supply passage 80 has a first supply passage 81, a second supply passage 82, a third supply passage 83, and a fourth supply passage 84. The first supply passage 81 is provided to communicate with the upper bearing body 45, specifically the upper manifold 45B. The second supply passage 82 is provided to communicate with the lower bearing body 46, specifically the lower manifold 46B. The third supply passage 83 is provided to communicate with the first radial bearing 42. The fourth supply passage 84 is provided to communicate with the second radial bearing 43.

[0032] The supply passage 80 may also be a passage formed in the casing 10. In other words, the supply passage 80 is not limited to being a pipe. Furthermore, the supply piping may be provided to communicate not only with the liquefied gas supply source 2 and the bearing device 40, but also with other parts. In this embodiment, the supply passage 80 is provided to communicate with the second stage impeller 27 (described later).

[0033] <Inducer and Impeller> The inducer 24 and impeller 25 are provided so as to be able to pump liquid hydrogen as the rotating shaft 20 rotates. The inducer 24 and impeller 25 are fixed to the rotating shaft 20 and are provided as a single unit. The inducer 24 and impeller 25 are rotatable together with the rotating shaft 20. In addition, the inducer 24 and impeller 25 are movable together with the rotating shaft 20 in the axial direction. Multiple impellers 25 are provided and are spaced apart in the axial direction. The impeller 25 includes a first-stage impeller 26, a second-stage impeller 27, and a third-stage impeller 28. Note that the number of impellers 25 is not limited to three. The number of impellers 25 may be two or fewer, or four or more.

[0034] The inducer 24 is located at the lower end of the rotating shaft 20. The first stage impeller 26 is provided integrally with the inducer 24. Specifically, the first stage impeller 26 is located axially above the inducer 24. The inducer 24 and the first stage impeller 26 are located in the suction section 11 of the casing 10. The second stage impeller 27 and the third stage impeller 28 are located axially above the first stage impeller 26. Specifically, the second stage impeller 27 and the third stage impeller 28 are located axially above the first stage impeller 26, sandwiching the second radial bearing 43. Note that the inducer 24 is not required.

[0035] <Electric Motor> The electric motor 30 is a component for rotating the rotating shaft 20 around its axis. The electric motor 30 is installed inside the casing 10. The electric motor 30 has a rotor 36 and a stator 31.

[0036] The rotor 36 is a component that receives power to rotate the rotating shaft 20 around its axis and rotates the rotating shaft 20. The rotor 36 is integrally fixed to the rotating shaft 20. Specifically, the rotor 36 is fixed to the outer circumferential surface of the rotating shaft 20. The rotor 36 has a rotor core 38 and permanent magnets.

[0037] The rotor core 38 is arranged concentrically with the rotating shaft 20. The rotor core 38 is provided inside the stator 31, with a clearance between it and the stator 31. The rotor core 38 has an overall cylindrical shape that extends in the axial direction. The rotor core 38 is fixedly provided on the outer circumferential surface of the rotating shaft body 21. The rotor core 38 is made of multiple layers of electromagnetic steel sheets stacked in the axial direction. Multiple permanent magnets are provided inside the rotor core 38, spaced apart in the circumferential direction. In addition, the rotor core 38 may have a support member provided on its outer circumferential surface.

[0038] The stator 31 is fixed to the inner circumferential surface of the casing 10. The stator 31 is arranged concentrically with the rotating shaft 20 and the rotor 36. The stator 31 is cylindrical in shape. The stator 31 is arranged to surround the rotating shaft 20 and the rotor 36 from the radially outer side. In other words, the stator 31 is facing the rotor 36 with a radial gap between them. The stator 31 has a stator core 32 and a coil 35.

[0039] The stator core 32 has a yoke and teeth. The yoke is cylindrical with an axis O. The yoke is fixed to the inner surface of the casing 10 with its outer surface fixed thereto. The teeth are provided so as to protrude from the inner surface of the yoke. Multiple teeth are formed, spaced apart from each other in the circumferential direction. Multiple coils 35 are provided, corresponding to each tooth. The coils 35 are wound around each tooth. Therefore, multiple coils 35 are provided, spaced apart in the circumferential direction.

[0040] <Operation Method of Liquefied Gas Pump> The operation method S1 of the liquefied gas pump in this embodiment will be explained according to the flowchart shown in Figure 4. The operation method S1 of the liquefied gas pump is a method for starting and stopping the liquefied gas pump 1. The operation method S1 of the liquefied gas pump includes a preparation step S11, a pre-cooling step S12, a start-up communication step S13, a drive step S14, a decommunication step S15, a drive stop step S16, and a stop-down communication step S17.

[0041] First, the preparation step S11 is executed. In the preparation step S11, the liquefied gas pump 1 described above is prepared. Also, the switching unit 5 is checked to confirm that the external sample 3 and the bearing device 40 are not in communication.

[0042] After the preparation step S11 is executed, the pre-cooling step S12 is executed. In the pre-cooling step S12, liquid hydrogen is supplied to the flow path of the liquefied gas pump 1 at the first pressure. The liquefied gas pump 1 is cooled by the liquid hydrogen. By the pre-cooling step S12, the internal pressure of the liquefied gas pump 1 is set to the first pressure.

[0043] After the pre-cooling step S12 is executed, the startup communication step S13 is executed. In the startup communication step S13, the switching unit 5 is operated to put the external sample 3 and the bearing device 40 in a communicating state. That is, in the startup communication step S13, the bearing device 40 is communicated with the space 3A at the second pressure. Then, the liquid hydrogen at the first pressure flows toward the space 3A at the second pressure. Specifically, the liquid hydrogen supplied from the liquefied gas supply source 2 to the bearing device 40 flows toward the space 3A at the second pressure. FIG. 3 shows the flow of liquid hydrogen in the thrust bearing 44 in a state where the bearing device 40 is communicated with the space 3A at the second pressure. The liquid hydrogen flows through the upper bearing body 45 and the lower bearing body 46, and then spreads radially between the upper bearing body 45 and the lower bearing body 46 and the thrust collar 22. The liquid hydrogen that has spread radially flows to the external sample 3 through the communication flow path 4. Thus, by communicating the bearing device 40 with the space 3A at the second pressure, a fluid pressure is applied to the bearing device 40, and the bearing device 40 functions as a sliding bearing.

[0044] After the startup communication step S13 is executed, the driving step S14 is executed. In the driving step S14, the electric motor 30 is driven to rotationally drive the rotating shaft 20 around the axis О. When the rotating shaft 20 rotates, the inducer 24 and the impeller 25 fixed to the rotating shaft body 21 rotate, so that the liquefied gas pump 1 operates.

[0045] When the liquefied gas pump 1 is activated, the liquid hydrogen in the liquid storage chamber 53 is drawn into the suction section 11 by the inducer 24. The drawn-in liquid hydrogen is pressurized by one stage by the first-stage impeller 26. The pressurized liquid hydrogen is supplied to the second-stage impeller 27 through the flow path 70 provided in the casing 10. The liquid hydrogen is pressurized by two stages by the second-stage impeller 27. The pressurized liquid hydrogen is supplied to the third-stage impeller 28 through the flow path 71 provided in the casing 10. The liquid hydrogen is pressurized by three stages by the third-stage impeller 28. The pressurized liquid hydrogen is supplied to the discharge section 12 through the flow path 72 provided in the casing 10. The liquid hydrogen supplied to the discharge section 12 is discharged to the outside of the sump 50 from the discharge pipe 62. Furthermore, it is preferable that multiple flow paths 70, 71, and 72 are provided on the radially outer side of the impeller 25, spaced apart in the circumferential direction. In addition, other paths through which liquid hydrogen flows may be provided besides the above-mentioned flow paths 70, 71, and 72.

[0046] Furthermore, the flow paths 70, 71, and 72 in this embodiment may be branched as appropriate. The flow path 71 in this embodiment is provided to communicate with the supply path. That is, two-stage pressurized liquid hydrogen can be supplied to the bearing device 40. However, other branches may be provided as well.

[0047] When the liquefied gas pump 1 is started and the rotating shaft 20 reaches a predetermined rotational speed, the impeller 25 can pressurize the liquid hydrogen to a predetermined pressure. In this state, liquid hydrogen is also supplied to the bearing device 40, stabilizing the position of the rotating shaft 20 in both the axial and radial directions. Liquid hydrogen is supplied to the thrust bearing 44, and the thrust collar 22 is held in a position where it does not come into contact with the thrust bearing 44 in the axial direction via fluid pressure. In other words, by supplying high-pressure liquid hydrogen to the thrust bearing 44, the rotating shaft 20 is supported by the thrust bearing 44 in the axial direction.

[0048] After executing the driving step S14, a non-communication step S15 is executed. In the non-communication step S15, the switching unit 5 is operated to put the external sample 3 and the bearing device 40 in a non-connected state. That is, in the non-communication step S15, the bearing device 40 is put in a non-connected state with the space 3A of the second pressure. The non-communication step S15 is executed after the rotating shaft 20 reaches a predetermined rotational speed. Even if the bearing device 40 is put in a non-connected state with the space 3A of the second pressure, the bearing device 40 is supplied with liquid hydrogen that has been boosted in two stages. Therefore, even if the bearing device 40 is put in a non-connected state with the space 3A of the second pressure, the bearing device 40 functions as a sliding bearing.

[0049] After executing the non-communication step S15, a driving stop step S16 is executed. In the driving stop step S16, the motor 30 is stopped, and the driving for rotating the rotating shaft 20 around the axis О is stopped. When the driving of the motor 30 is stopped, the rotating shaft 20 is no longer given an external force for rotation. Immediately after the motor 30 is stopped, the rotating shaft 20 continues to rotate around the axis О due to inertia.

[0050] After executing the driving stop step S16, a communication-at-stop step S17 is executed. In the communication-at-stop step S17, the switching unit 5 is operated to put the external sample 3 and the bearing device 40 in a connected state. That is, in the communication-at-stop step S17, the bearing device 40 is connected to the space 3A of the second pressure. The communication-at-stop step S17 is executed after the driving of the motor 30 is stopped and while the rotating shaft 20 continues to rotate. When the driving of the motor 30 is stopped, the rotational speed of the rotating shaft 20 gradually decreases and the rotation is stopped. As the rotational speed of the rotating shaft 20 decreases, the liquid hydrogen supplied to the bearing device 40 by the impeller 25 also decreases. The communication-at-stop step S17 is executed before the thrust collar 22 and the thrust bearing 44 come into contact with each other in the axial direction. By connecting the bearing device 40 to the space 3A of the second pressure, the liquid hydrogen flows toward the space 3A of the second pressure. That is, the liquid hydrogen flows in the same manner as in the communication-at-start step S13, and the bearing device 40 functions as a sliding bearing even after the rotation of the rotating shaft 20 completely stops. When the rotation of the rotating shaft 20 completely stops, the liquefied gas pump 1 stops.

[0051] <Effects> The liquefied gas pump 1 described above is configured by the switching unit 5 to connect the bearing device 40 to the second pressure space 3A. The second pressure is lower than the first pressure. Therefore, liquid hydrogen is drawn in and flows from the liquefied gas supply source 2, which is at the first pressure, to the second pressure space 3A. In other words, by creating a differential pressure so that it passes through the bearing device 40, static pressure is supplied to the bearing device 40. Therefore, by connecting the bearing device 40 to the second pressure space 3A, the bearing device 40 is supplied with static pressure and functions as a sliding bearing. That is, even when the rotating shaft 20 is not rotating around axis O, it is possible to supply static pressure to the bearing device 40. Since the liquefied gas pump 1 can be started and stopped while the thrust bearing 44 is functioning as a sliding bearing, friction between the thrust bearing 44 and the thrust collar 22 due to the rotation of the rotating shaft 20 can be suppressed. Similarly, friction between the radial bearing 41 and the rotating shaft 20 can also be suppressed. Therefore, according to the liquefied gas pump 1 of this embodiment, wear of the bearing device 40 and the rotating shaft 20 during starting and stopping can be suppressed.

[0052] According to the operating method S1 of this embodiment of the liquefied gas pump, the liquefied gas pump 1 is brought to a first pressure by supplying liquid hydrogen in the pre-cooling process S12. In the startup communication process S13, the bearing device 40 is brought into communication with the second pressure space 3A. The second pressure is lower than the first pressure. Therefore, liquefied gas flows from the first pressure space to the second pressure space 3A. Consequently, static pressure is supplied to the bearing device 40 as described above. With static pressure supplied to the bearing device 40, the thrust collar 22 connected to the rotating shaft 20 is separated from the thrust bearing 44. After the startup communication process S13, the drive process S14 is executed to rotate the rotating shaft 20 around the axis O. This makes it possible to suppress friction between the thrust bearing 44 and the thrust collar 22 when the liquefied gas pump 1 is started. Similarly, friction between the radial bearing 41 and the rotating shaft 20 can also be suppressed. Therefore, according to the operating method S1 of the liquefied gas pump of this embodiment, wear of the bearing device 40 and the rotating shaft 20 during startup can be suppressed.

[0053] Furthermore, according to the operating method S1 of the liquefied gas pump of this embodiment, in the non-communication step S15, the bearing device 40 is made non-communicating with the second pressure space 3A. That is, with the liquefied gas pump 1 running, the bearing device 40 is made non-communicating with the second pressure space 3A. With the liquefied gas pump 1 running, pressurized liquid hydrogen is supplied to the bearing device 40. Therefore, even without providing a differential pressure to the bearing device 40, the bearing device 40 functions as a sliding bearing. Thus, by making the bearing device 40 non-communicating with the second pressure space 3A with the liquefied gas pump 1 running, leakage of liquid hydrogen into the second pressure space 3A can be suppressed.

[0054] Furthermore, according to the operating method S1 of the liquefied gas pump of this embodiment, the drive of the rotating shaft 20 is stopped in the drive stop step S16. In the stop communication step S17, the bearing device 40 is connected to the second pressure space 3A. Therefore, even if the drive of the rotating shaft 20 is stopped, liquefied gas flows from the bearing device 40 to the second pressure space 3A. That is, even if the rotational drive of the rotating shaft 20 is stopped, static pressure is supplied to the bearing device 40. Therefore, the rotation of the rotating shaft 20 is stopped while the thrust collar 22 remains axially separated from the thrust bearing 44. Therefore, friction between the thrust bearing 44 and the thrust collar 22 when the liquefied gas pump 1 is stopped can be suppressed. Similarly, friction between the radial bearing 41 and the rotating shaft 20 can also be suppressed. Therefore, according to the operating method S1 of the liquefied gas pump of this embodiment, wear of the bearing device 40 and the rotating shaft 20 when stopped can be suppressed.

[0055] Furthermore, according to the liquefied gas pump 1 and the operating method S1 of this embodiment, wear of the bearing device 40 and the rotating shaft 20 can be suppressed, which also leads to improved maintainability of the liquefied gas pump 1.

[0056] Furthermore, the liquefied gas pump 1 and its operating method S1 are applicable to a variety of fluids. In addition, the liquefied gas pump 1 of this embodiment can pressurize liquid hydrogen. That is, the liquefied gas pump 1 and its operating method S1 of this embodiment are applicable to liquid hydrogen, which is at an even lower temperature than LNG.

[0057] <Other Embodiments> Although embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of the present disclosure.

[0058] For example, the communication passage 4 according to the embodiment may be provided separately in each of the bearing devices 40. Also, the radial bearing 41 does not need to be provided with communication passages 4B and 4C.

[0059] Furthermore, the bearing device 40 does not have to be configured solely to allow liquid hydrogen to be supplied at internal pressure by the liquefied gas supply source 2. That is, the bearing device 40 may also be able to receive liquid hydrogen from sources other than the liquefied gas supply source 2. The liquid hydrogen supplied from sources other than the liquefied gas supply source 2 may be pressurized, for example, rather than at internal pressure.

[0060] Furthermore, the non-communication process S15 may be performed before the rotating shaft 20 reaches a predetermined rotational speed. If the bearing device 40 is supplied with fluid pressure sufficient for it to function as a sliding bearing, the non-communication process S15 may be performed before the rotating shaft 20 reaches a predetermined rotational speed.

[0061] Alternatively, the stop-time communication process S17 may be performed before the drive stop process S16. That is, while the rotating shaft 20 is being driven to rotate by the electric motor 30, the switching unit 5 may be operated to connect the external sump 3 and the bearing device 40. This makes it possible to more reliably connect the bearing device 40 to the second pressure space 3A before the thrust bearing 44 and the thrust collar 22 come into contact.

[0062] <Note> The liquefied gas pump 1 and the operating method S1 of the liquefied gas pump described in each embodiment can be understood, for example, as follows.

[0063] (1) The liquefied gas pump 1 according to the first embodiment comprises a rotating shaft 20 that can rotate around an axis O, an impeller 25 integrally provided with the rotating shaft 20 and capable of pumping liquefied gas by rotating together with the rotating shaft 20, an electric motor 30 that rotates the rotating shaft 20 around the axis O, a bearing device 40 that supports the rotating shaft 20 so as to be rotatable around the axis O, a liquefied gas supply source 2 that can supply the liquefied gas to the bearing device 40 at a first pressure, and a switching unit 5 that can switch the bearing device 40 between a state in which it is in communication with a space 3A at a second pressure lower than the first pressure and a state in which it is not in communication with the space 3A at the second pressure.

[0064] According to the above configuration, the switching unit 5 connects the bearing device 40 to the second pressure space 3A. The second pressure is lower than the first pressure. As a result, liquefied gas is drawn into the second pressure space 3A, and liquefied gas flows from the first pressure liquefied gas supply source 2 to the second pressure space 3A. Therefore, even when the rotating shaft 20 is not rotating around the axis O, it is possible to supply static pressure to the bearing device 40. In this way, wear of the bearing device 40 during starting and stopping can be suppressed.

[0065] (2) The liquefied gas pump 1 relating to the second embodiment is the liquefied gas pump 1 of (1), wherein the liquefied gas is liquid hydrogen.

[0066] (3) The third mode of operation S1 of the liquefied gas pump is a method of operating the liquefied gas pump 1, wherein the liquefied gas pump 1 comprises a rotating shaft 20 rotatable around axis O, an impeller 25 integrally provided on the rotating shaft 20 and capable of pumping liquefied gas by rotating together with the rotating shaft 20, an electric motor 30 that rotates the rotating shaft 20 around axis O, a bearing device 40 that supports the rotating shaft 20 so as to be rotatable around axis O, a liquefied gas supply source 2 capable of supplying the liquefied gas to the bearing device 40 at a first pressure, and the bearing device 40 A method for operating a liquefied gas pump S1, comprising a switching unit 5 capable of switching between a state in which the bearing device 40 is in communication with a space 3A at a second pressure lower than the first pressure and a state in which it is not in communication with the space 3A at the second pressure, includes a pre-cooling step S12 in which the liquefied gas is supplied to the flow path of the liquefied gas pump 1 at the first pressure, a startup communication step S13 in which the bearing device 40 is connected to the space 3A at the second pressure after the pre-cooling step S12, and a drive step S14 in which the rotating shaft 20 is rotated around the axis O after the startup communication step S13.

[0067] According to the above configuration, in the pre-cooling process S12, the liquefied gas pump 1 is brought to a first pressure. In the startup communication process S13, the bearing device 40 is brought into communication with the second pressure space 3A. The second pressure is lower than the first pressure. Therefore, liquefied gas flows from the first pressure space to the second pressure space 3A. Consequently, static pressure is supplied to the bearing device 40, and the bearing device 40 functions as a sliding bearing. After the startup communication process S13, by rotating the rotating shaft 20 around the axis O, wear of the bearing device 40 during the startup of the liquefied gas pump 1 can be suppressed.

[0068] (4) The fourth mode of operation S1 of the liquefied gas pump is the liquefied gas pump operation S1 of (3), further comprising a decommunication step S15 after the drive step S14, which causes the bearing device 40 to be decommunicated with the second pressure space 3A.

[0069] According to the above configuration, in the non-communication process S15, the bearing device 40 is made non-communicating with the second pressure space 3A. That is, while the liquefied gas pump 1 is running, the bearing device 40 is made non-communicating with the second pressure space 3A. Therefore, leakage of liquefied gas into the second pressure space 3A can be suppressed.

[0070] (5) The fifth mode of operation S1 of the liquefied gas pump is the mode of operation S1 of the liquefied gas pump according to (3) or (4), further comprising, after the non-communication step S15, a drive stop step S16 for stopping the drive of the rotating shaft 20, and after the drive stop step S16, a stop-time communication step S17 for connecting the bearing device 40 to the second pressure space 3A.

[0071] According to the above configuration, the drive of the rotating shaft 20 is stopped in the drive stop process S16. In the stop communication process S17, the bearing device 40 is connected to the second pressure space 3A. Therefore, even when the drive of the rotating shaft 20 is stopped, liquefied gas flows from the bearing device 40 to the second pressure space 3A. That is, even when the drive of the rotating shaft 20 is stopped, static pressure is supplied to the bearing device 40. Therefore, the rotation of the rotating shaft 20 is stopped while the thrust collar 22 remains separated from the thrust bearing 44. Thus, wear of the thrust bearing 44 when the liquefied gas pump 1 is stopped can be suppressed.

[0072] According to the liquefied gas pump and operating method of the liquefied gas pump described herein, wear of the thrust bearing during starting and stopping can be suppressed.

[0073] 1 Liquefied gas pump 2 Liquefied gas supply source 3 External sump 3A Second pressure space 4, 4A, 4B, 4C Connecting passages 5 Switching section 6 Pump body 10 Casing 11 Suction section 12 Discharge section 20 Rotating shaft 21 Rotating shaft body 22 Thrust collar 22A Top surface 22B Bottom surface 24 Inducer 25 Impeller 26 First stage impeller 27 Second stage impeller 28 Third stage impeller 30 Electric motor 31 Stator 32 Stator core 35 Coil 36 Rotor 38 Rotor core 40 Bearing device 41 Radial bearing 42 First radial bearing 43 Second radial bearing 44 Thrust bearing 45 Upper bearing body 45A Upper pocket 45B Upper manifold 45C Upper connecting passage 46 Lower bearing body 46A Lower pocket 46B Lower manifold 46C Lower connecting passage 80 Supply passage 81 First supply passage 82 Second supply passage 83 Third supply passage 84 Fourth supply passage 50 Sump 51 Outer flange 53 Liquid storage chamber 60 Supply pipe 61 Gas discharge pipe 62 Discharge pipe O Axis S1 Method of operating the liquefied gas pump S11 Preparation process S12 Pre-cooling process S13 Startup communication process S14 Drive process S15 Decommunication process S16 Drive stop process S17 Stop communication process

Claims

1. A liquefied gas pump comprising: a rotating shaft rotatable about an axis; an impeller integrally provided with the rotating shaft and capable of pumping liquefied gas by rotating together with the rotating shaft; an electric motor for rotationally driving the rotating shaft about the axis; a bearing device for supporting the rotating shaft so as to be rotatable about the axis; a liquefied gas supply source capable of supplying the liquefied gas to the bearing device at a first pressure; and a switching unit capable of switching the bearing device between a state in which it is in communication with a space at a second pressure lower than the first pressure and a state in which it is not in communication with the space at the second pressure.

2. The liquefied gas pump according to claim 1, wherein the liquefied gas is liquid hydrogen.

3. A method for operating a liquefied gas pump, the liquefied gas pump comprising: a rotating shaft rotatable about an axis; an impeller integrally provided with the rotating shaft and capable of pumping liquefied gas by rotating together with the rotating shaft; an electric motor for rotationally driving the rotating shaft about the axis; a bearing device for supporting the rotating shaft so as to be rotatable about the axis; a liquefied gas supply source capable of supplying the liquefied gas to the bearing device at a first pressure; and a switching unit capable of switching the bearing device between a state in which it is in communication with a space at a second pressure lower than the first pressure and a state in which it is not in communication with the space at the second pressure, the method for operating the liquefied gas pump comprising: a pre-cooling step of supplying the liquefied gas to the flow path of the liquefied gas pump at the first pressure; a startup communication step after the pre-cooling step of connecting the bearing device to the space at the second pressure; and a drive step after the startup communication step of rotationally driving the rotating shaft about the axis.

4. The method for operating a liquefied gas pump according to claim 3, further comprising a decommunication step after the driving step, wherein the bearing device is decommunicated with respect to the second pressure space.

5. A method for operating a liquefied gas pump according to claim 4, further comprising: a drive stop step of stopping the drive of the rotating shaft after the non-communication step; and a stop-time communication step of connecting the bearing device to the second pressure space after the drive stop step.

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