Multistage centrifugal compressor for hydrogen

Abstract

This technology enables stable, high-speed rotation of the impeller in multi-stage centrifugal compressors for hydrogen applications. [Solution] The multi-stage centrifugal compressor for hydrogen comprises a rotating shaft, a plurality of impellers through which the rotating shaft is inserted and which rotate integrally with the rotating shaft, a casing housing the rotating shaft and the plurality of impellers, and journal bearings positioned at both ends of the rotating shaft to support the rotating shaft in the casing, and compresses hydrogen gas in multiple stages with the plurality of impellers. The plurality of impellers are closed impellers made of aluminum alloy with hydrogen embrittlement resistance. The journal bearing is a squeeze film damper bearing having a bearing portion that supports the rotating shaft and a squeeze film damper portion positioned between the bearing portion and the casing.

Description

Technical Field

[0001] The present disclosure relates to a multi-stage centrifugal compressor for compressing hydrogen gas.

Background Art

[0002] A centrifugal compressor gives centrifugal force to a working fluid by passing the working fluid through a rotating impeller to compress the working fluid. In a centrifugal compressor for compressing a low molecular weight gas with a small gas density such as hydrogen or helium, in order to achieve a high compression ratio, multi-staging and high-speed rotation of the impeller have been proposed. For example, Patent Document 1 discloses this type of multi-stage centrifugal compressor.

[0003] The multi-stage centrifugal compressor disclosed in Patent Document 1 includes a hollow cylindrical casing, a rotating shaft assembly housed in the casing, and a plurality of fiber reinforced plastic impellers fixed to the rotating shaft assembly. In the casing, a journal bearing that rotatably supports the rotating shaft assembly and a thrust bearing that receives an axial thrust force are provided. The journal bearing and the thrust bearing are fluid bearings or magnetic bearings, and are designed to support the shaft flexibly with a small rigidity compared to rolling bearings and sliding bearings.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a multi-stage centrifugal compressor as described above, with the high-speed rotation of the impeller, the vibration of the rotating shaft that rotates integrally with the impeller may increase, and the rotation may become unstable. In addition, there is a risk that the impeller expanded by heat may collide with the stationary flow path due to vibration.

[0006] This disclosure is made in view of the above circumstances, and its purpose is to achieve stable high-speed rotation of the impeller in a multi-stage centrifugal compressor for hydrogen. [Means for solving the problem]

[0007] To solve the above problems, a multi-stage centrifugal compressor for hydrogen according to one aspect of this disclosure is provided. The axis of rotation and Multiple impellers through which the aforementioned rotating shaft is inserted and which rotate integrally with the aforementioned rotating shaft, The casing housing the rotating shaft and the plurality of impellers, A multi-stage centrifugal compressor for hydrogen, comprising journal bearings positioned at both ends of the rotating shaft and supporting the rotating shaft in the casing, wherein the plurality of impellers compress hydrogen gas in multiple stages, The aforementioned plurality of impellers are closed impellers made of an aluminum alloy that has resistance to hydrogen embrittlement. The journal bearing is a squeeze film damper bearing having a bearing portion that supports the rotating shaft and a squeeze film damper portion disposed between the bearing portion and the casing. [Effects of the Invention]

[0008] According to this disclosure, stable high-speed rotation of the impeller can be achieved in a multi-stage centrifugal compressor for hydrogen. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a meridional view of a multi-stage centrifugal compressor according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a cross-sectional view of the impeller of the multi-stage centrifugal compressor shown in Figure 1. [Figure 3] Figure 3 is a perspective view of the impeller. [Figure 4] Figure 4 is a cross-sectional view of the journal bearing of the multi-stage centrifugal compressor shown in Figure 1. [Modes for carrying out the invention]

[0010] Next, embodiments of the present disclosure will be described with reference to the drawings. Figure 1 is a meridional view of a multistage centrifugal compressor 1 according to one embodiment of the present disclosure. The multistage centrifugal compressor 1 shown in Figure 1 compresses hydrogen gas, which is the working fluid. However, the multistage centrifugal compressor 1 can also be applied to compress low molecular weight gases other than hydrogen, such as helium.

[0011] The multi-stage centrifugal compressor 1 comprises a casing 12, a rotating shaft 3 rotatably supported by the casing 12, a plurality of impellers 4 arranged inside the casing 12 and fixed to the rotating shaft 3, and a drive device for rotating the rotating shaft 3. The plurality of impellers 4 are arranged in the axial direction X of the rotating shaft 3. The plurality of impellers 4 arranged in the axial direction X is also called an impeller stack 40, and the multi-stage rotor 2 consisting of the rotating shaft 3 and the impeller stack 40 is also called a stacked rotor. Here, the direction in which the rotation axis A of the rotating shaft 3 extends is called the "axial direction X", the radial direction centered on the rotation axis A is called the "radial direction", the direction approaching the rotation axis A in this radial direction is called the "radial inward direction", the direction moving away from the rotation axis A in the radial direction is called the "radial outward direction", and the circumferential direction centered on the rotation axis A is called the "circumferential direction".

[0012] The rotating shaft 3 is inserted through the impeller stack 40. Each of the impellers 4 that make up the impeller stack 40 is made of an aluminum alloy that has excellent high-temperature strength above 100°C and resistance to hydrogen embrittlement. Examples of such aluminum alloys include Al-Cu-Mg alloys such as A2618 (JIS) and KS2000 (Kobe Steel, Ltd.).

[0013] Figure 2 is a cross-sectional view of the impeller 4. As shown in Figure 2, the impeller 4 is a closed impeller and has a hub 41 through which the rotating shaft 3 is inserted, a disc 42 fixed to the hub 41, a plurality of blades 43 arranged circumferentially on the disc 42, and a shroud 44 covering the plurality of blades 43. All constituent impellers 4 of the impeller stack 40 may be closed impellers. By making the constituent impellers 4 of the impeller stack 40 closed impellers in this way, the amount of working fluid leakage from the impeller tip side can be reduced. In addition, all constituent impellers 4 of the impeller stack 40 may have substantially the same diameter and shape without applying impeller cuts. By making all constituent impellers 4 the same shape in this way, cost reduction and lead time reduction can be achieved.

[0014] The impeller 4 has an impeller channel 45 through which the working fluid passes between adjacent blades 43 in the circumferential direction. In each impeller channel 45, the inlet is located radially inside the impeller 4, and the outlet 45out is located radially outside the impeller 4. The working fluid passes radially through the impeller channel 45 of the rotating impeller 4 from the inlet to the outlet 45out, and the centrifugal force generated at that time imparts kinetic energy to the working fluid. This kinetic energy is converted into positive pressure in the stationary channel 21, thereby increasing the pressure of the working fluid. Figure 3 is a perspective view of the impeller 4. As shown in Figure 3, from the viewpoint of suppressing centrifugal stress generated in the blades 43 of the impeller 4, the outlet angle θ of the impeller channel 45 is preferably about 90°. The outlet angle θ of the impeller channel 45 is the angle formed by the tangent 47 of the blade centerline and the tangent 48 of the outer diameter circle at the intersection of the outer diameter circle and the blade centerline. In other words, the outlet 45out of the impeller flow path 45 discharges hydrogen gas radially outward from the rotation axis A, and approximately parallel to the radial direction.

[0015] Returning to Figure 1, both end faces of the hub 41 of the impeller 4 in the axial direction X are toothed flanges with teeth formed in the circumferential direction. Adjacent impellers 4 in the axial direction X are connected in a way that allows power to be transmitted by a mechanical coupling in which the toothed flanges mesh with each other. The mechanical coupling may be a Curvic coupling or a Haas coupling.

[0016] The impeller stack 40 may include at least one balance piston 57. The balance piston 57 autonomously adjusts the axial thrust of the rotating multi-stage rotor 2. The balance piston 57 is fitted onto the rotating shaft 3, similar to the impeller 4. The impellers 4 and balance pistons 57 adjacent to each other in the axial direction X are connected in a power-transmitting manner by a mechanical coupling through meshing.

[0017] The impeller stack 40 according to this embodiment has a so-called back-to-back arrangement in which the impellers 4 located on the non-load side and the impellers 4 located on the load side have different orientations via a balance piston 57 located midway along the axial direction X. However, the arrangement of the impellers 4 in the impeller stack 40 is not limited to this, and it may also have a straight-type arrangement in which all the impellers 4 are aligned in the same direction.

[0018] Of the plurality of impellers 4 that make up the impeller stack 40, the leading impeller 4 disposed at the tip is in contact with a stepped surface 36 formed on the rotating shaft 3 in the axial direction X. The leading impeller 4L and the stepped surface 36 are coupled by friction, and power can be transmitted from the rotating shaft 3 to the leading impeller 4L. Of the plurality of impellers 4 that make up the impeller stack 40, the trailing impeller 4T disposed at the rear end is in contact with a balance piston 56 fitted on the rotating shaft 3. The trailing impeller 4T and the balance piston 56 are coupled by a mechanical coupling by meshing. A lock nut 6 is screwed onto the rotating shaft 3, and the impeller stack 40 and the balance piston 56 are disposed between the stepped surface 36 of the rotating shaft 3 and the lock nut 6 in the axial direction X. Due to the axial force of the rotating shaft 3, the impeller stack 40 and the balance piston 56 are sandwiched in a state of being axially pressurized between the stepped surface 36 and the lock nut 6.

[0019] On the shaft end side of the impeller stack 40 of the rotating shaft 3, dry gas seals 54, 55 for sealing between the casing 12 and the rotating shaft 3 are disposed. The dry gas seals 54, 55 prevent leakage of the working fluid compressed by the multi-stage rotor 2 to a high pressure to the outside. Seal gas is supplied to the dry gas seals 54, 55 from the outside.

[0020] At least one of both ends of the rotating shaft 3 is rotatably supported by the casing 12 via a thrust bearing 51. Also, both ends of the rotating shaft 3 are supported by the casing 12 via journal bearings 52, 53. The journal bearings 52, 53 are disposed on the shaft end side of the dry gas seals 54, 55.

[0021] Journal bearings 52 and 53 are squeeze film damper bearings that offer excellent vibration stability in high-speed rotational regions. Journal bearings 52 and 53 have substantially the same configuration. Figure 4 is a cross-sectional view of journal bearings 52 and 53. As shown in Figure 4, the squeeze film damper bearings, which are journal bearings 52 and 53, consist of a bearing portion 69, a damper portion 70, and a bearing casing 68 that houses the bearing portion 69 and the damper portion 70. The bearing portion 69 is fitted onto the rotating shaft 3 and supports the rotating shaft 3. The bearing portion 69 may be a rolling bearing or a sliding bearing. If the bearing portion 69 is a sliding bearing, the bearing portion 69 may be a so-called tilting pad bearing, which consists of a plurality of bearing pads arranged in the circumferential direction.

[0022] The damper section 70 is interposed between the bearing section 69 and the casing 12 in the radial direction to dampen vibrations. The damper section 70 consists of an inner ring 71, an outer ring 72, and viscous granules filling the gap between the outer circumferential surface of the inner ring 71 and the inner circumferential surface of the outer ring 72. The inner ring 71 is a cylindrical member having a predetermined width in the axial direction X. The inner ring 71 supports the bearing section 69 from the radial outside and is movable in the radial direction. The outer ring 72 is a cylindrical member having a predetermined width in the axial direction X. The outer ring 72 is fitted into the casing 12. The outer ring 72 is positioned radially outward from the inner ring 71 at a predetermined distance, thereby creating a gap between the outer circumferential surface of the inner ring 71 and the inner circumferential surface of the outer ring 72. A squeeze film 73 (fluid film) is formed by the viscous fluid filling this gap. When the bearing section 69 and the inner ring 71 supporting it vibrate in conjunction with the vibration of the rotating shaft 3, the viscous fluid forming the squeeze film 73 flows, and pressure is generated due to the so-called squeeze film effect caused by the viscous resistance of the viscous fluid as a result of this fluid flow. This pressure dampens the vibration of the bearing section 69, thereby suppressing the vibration of the rotating shaft 3. The rigidity and vibration damping capacity of the damper section 70 can be adjusted by the viscosity of the viscous particles, etc., and are appropriately adjusted for each multi-stage centrifugal compressor 1.

[0023] Returning to Figure 1, the casing 12 is provided with an intake passage 22 that draws in fluid and sends it to the first stage impeller 4, and a discharge passage 23 that discharges fluid from the final stage impeller 4 to the outside. The casing 12 is also provided with a stationary passage 21 that sends the fluid from the impeller 4 to the next stage impeller 4. The stationary passage 21 connects the outlet 45out of the impeller passage 45 to the inlet of the next stage impeller passage 45. The working fluid compressed by a certain stage impeller 4 is discharged into the stationary passage 21 and flows through the stationary passage 21 into the impeller passage 45 of the next stage impeller 4. The combination of the impeller 4 and the stationary passage 21 constitutes a stage that forms a pressurization unit of the multi-stage centrifugal compressor 1. The fluid drawn into the intake passage 22 is pressurized by compression each time it passes through a stage consisting of an impeller 4 and a stationary passage 21. As described above, in the multi-stage centrifugal compressor 1 according to this embodiment, a series of compression passages are formed by the casing 12 and the impellers 4, through which the working fluid drawn in from the suction passage 22 is compressed stepwise through multiple stages of impellers 4 and then discharged to the outside from the discharge passage 23. However, the flow paths for the working fluid and the number of stages of the impellers 4 in the multi-stage centrifugal compressor 1 are merely illustrative examples.

[0024] Furthermore, the casing 12 is provided with an intermediate discharge port 27 for temporarily removing the working fluid from the intermediate stages of the multiple impellers 4 to the outside of the machine, and an intermediate intake port 28 for returning it to the inside of the machine. The working fluid removed from the intermediate discharge port 27 is cooled by an intermediate cooler 65 provided outside the casing 12, and then returned to the inside of the casing 12 through the intermediate intake port 28. In other words, the intermediate cooler 65 cools the working fluid that is removed from the intermediate stage impellers 4 among the multiple impellers 4 and returned to the inlet of the next stage impeller 4. The intermediate cooler 65 is a heat exchanger that cools the working fluid by heat exchange. Thus, in the multi-stage centrifugal compressor 1 according to this embodiment, the working fluid flowing through the compression passage is temporarily removed from the machine through the intermediate discharge port 27 provided between stages, cooled, and then returned to the inside of the machine through the intermediate intake port 28, and is further compressed through the multiple impellers 4. Thus, the compression passage of the multi-stage centrifugal compressor 1 according to this embodiment has an intermediate cooling structure at least at one location in the compression passage, which cools the working fluid that is guided outside the machine from the intermediate discharge port 27 in an intermediate cooler 65 before returning it to the intermediate intake port 28. Since the work required to compress the gas increases in proportion to the inlet temperature of the impeller passage 45, the multi-stage centrifugal compressor 1 can reduce the power required to compress the working fluid by lowering the inlet temperature of the impeller passage 45 with the intermediate cooling structure.

[0025] [Summary] The multi-stage centrifugal compressor 1 relating to the first item of this disclosure is Rotation axis 3 and A rotating shaft 3 is inserted through it, and multiple impellers 4 rotate integrally with the rotating shaft 3, A casing 12 housing a rotating shaft 3 and multiple impellers 4, A multi-stage centrifugal compressor 1 for hydrogen, comprising journal bearings 52 and 53 positioned at both ends of a rotating shaft 3 and supporting the rotating shaft 3 in a casing 12, and compressing hydrogen gas in multiple stages with multiple impellers 4, Multiple impellers 4 are closed impellers made of hydrogen-brittle aluminum alloy. Journal bearings 52 and 53 are characterized by being squeeze film damper bearings having a bearing portion 69 that supports the rotating shaft 3 and a squeeze film damper portion 70 positioned between the bearing portion 69 and the casing 12.

[0026] In the multi-stage centrifugal compressor 1 with the above configuration, the impeller 4 is made of an aluminum alloy with a higher mass-to-strength ratio compared to iron, allowing the rotational speed and peripheral speed of the impeller 4 to be increased to a level suitable for compressing hydrogen gas. As the impeller 4 rotates at high speed, it becomes hotter, but since the impeller 4 is a closed impeller, the possibility of contact between the impeller 4 and the stationary flow path 5 due to thermal expansion and vibration of the rotating shaft 3 can be reduced. Furthermore, as the rotational speed of the impeller 4 increases, the vibration of the rotating shaft 3 increases, but since the rotating shaft 3 is supported by the casing 12 via a squeeze film damper bearing, the vibration of the rotating shaft 3 is suppressed by the squeeze film damper bearing, improving the rotational stability of the rotating shaft 3. As a result, the multi-stage centrifugal compressor 1 can achieve stable high-speed rotation of the impeller 4.

[0027] The multi-stage centrifugal compressor 1 according to the second item of this disclosure is a multi-stage centrifugal compressor 1 according to the first item, wherein each of the plurality of impellers 4 has an impeller passage 45 through which hydrogen gas flows, and the impeller passage 45 has an outlet 45out that discharges hydrogen gas radially outward from the rotation axis 3 and substantially parallel to the radial direction.

[0028] This reduces the centrifugal stress generated in the impeller 4 when it rotates at high speed, and suppresses the load on the blades 43 of the impeller 4.

[0029] The multi-stage centrifugal compressor 1 according to the third item of this disclosure is a multi-stage centrifugal compressor 1 according to the first or second item, and is equipped with an intermediate cooler 65 which is located outside the casing 12 and cools the hydrogen gas emitted from the intermediate stage impeller 4 among the multiple impellers 4 and returns it to the inlet of the next stage impeller 4 after the intermediate stage impeller 4.

[0030] In a multi-stage centrifugal compressor 1 that compresses low molecular weight gases such as hydrogen gas, more compression work is required compared to compressing high molecular weight gases. However, with the above-mentioned multi-stage centrifugal compressor 1, the inlet temperature of the impeller flow path 45 of the impeller 4 of the stage after the intermediate stage can be lowered, thereby reducing the power required to compress hydrogen gas.

[0031] The foregoing disclosures are presented for illustrative and explanatory purposes only and are not intended to limit the disclosure to the forms disclosed herein. For example, in the above detailed description, various features of the disclosure are grouped into a single embodiment for the purpose of streamlining the disclosure, but some of the features may be combined. Furthermore, some of the features contained herein may be combined into alternative embodiments, configurations, or aspects other than those discussed above. [Explanation of symbols]

[0032] 1: Multistage centrifugal compressor for hydrogen 3: Rotation axis 4: Impeller 12: Casing 45: Impeller flow path 52: Journal bearing 53: Journal bearing 65: Intercooler 69: Bearing part 70: Damper section (squeeze film damper section) 73: Squeeze film

Claims

1. The axis of rotation and Multiple impellers through which the aforementioned rotating shaft is inserted and which rotate integrally with the aforementioned rotating shaft, The casing housing the rotating shaft and the plurality of impellers, A multi-stage centrifugal compressor for hydrogen, comprising journal bearings positioned at both ends of the rotating shaft and supporting the rotating shaft in the casing, wherein the plurality of impellers compress hydrogen gas in multiple stages, The aforementioned plurality of impellers are closed impellers made of an aluminum alloy that has resistance to hydrogen embrittlement. The journal bearing is a squeeze film damper bearing having a bearing portion that supports the rotating shaft and a squeeze film damper portion disposed between the bearing portion and the casing. A multi-stage centrifugal compressor for hydrogen.

2. Each of the plurality of impellers has an impeller passage through which hydrogen gas flows, and the impeller passage has an outlet that discharges the hydrogen gas outward in the radial direction with respect to the axis of rotation, substantially parallel to the radial direction. A multi-stage centrifugal compressor for hydrogen according to claim 1.

3. An intermediate cooler is provided, located outside the casing, which cools the hydrogen gas emitted from the intermediate stage impellers among the plurality of impellers and returns it to the inlet of the next stage impeller. A multi-stage centrifugal compressor for hydrogen according to claim 1 or 2.

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