Centrifugal compressor

Abstract

A compressor according to one embodiment of the present disclosure is provided with a first discharge flow path that is partitioned by a first diaphragm and a second diaphragm and that connects an outer-diameter end of a first impeller and an inner-diameter end of a volute, and a plurality of spacer vanes disposed in the first discharge flow path. The volute includes a first portion that is in contact with a radially outer edge part of the diaphragm, a second portion that is connected to the downstream end of the first portion and does not contact the radially outer edge part of the diaphragm, and a second discharge flow path that is connected to the downstream end of the first discharge flow path inside both the first portion and the second portion. A first gap between spacer vanes that are adjacent via a first region containing a tongue part to which the first portion and the second portion are connected is wider than a second gap between spacer vanes that are adjacent via a second region not containing a tongue part.

Description

centrifugal compressor

[0001] The present disclosure relates to centrifugal compressors.

[0002] Patent Document 1 describes a centrifugal compressor. The centrifugal compressor includes a rotating shaft, a plurality of impellers that rotate around the rotating shaft and are arranged in parallel in the axial direction of the rotating shaft, and a plurality of diaphragms that cover the impellers and are arranged in parallel in the axial direction. The diaphragms include a first diaphragm and a second diaphragm adjacent to the first diaphragm. Four spacers are arranged between the first diaphragm and the second diaphragm to connect the first diaphragm and the second diaphragm. The four spacers are arranged at equal intervals on the same circumference centered on the rotating shaft.

[0003] Japanese Patent Application Laid-Open No. 2019-44659

[0004] In Patent Document 1, four spacers connect two adjacent diaphragms to each other, but Patent Document 1 does not take into consideration improving the compression efficiency of the fluid while ensuring the connection strength of the two diaphragms.

[0005] Therefore, an object of the present disclosure is to improve the fluid compression efficiency in a centrifugal compressor while ensuring the connection strength between two adjacent diaphragms.

[0006] A centrifugal compressor according to one aspect of the present disclosure includes a rotating shaft, a plurality of impellers that rotate around the rotating shaft and are arranged in parallel in an axial direction of the rotating shaft, a plurality of diaphragms that cover the plurality of impellers and are arranged in parallel in the axial direction, a volute connected to radially outer edge portions of first and second diaphragms that are adjacent to each other among the plurality of diaphragms and are perpendicular to the axial direction, and a first surface of the first diaphragm that faces the second diaphragm in the axial direction and a second surface of the second diaphragm that faces the first diaphragm in the axial direction and faces the first surface, the volute connecting an outer diameter end of a first impeller of the plurality of impellers that is arranged between the first diaphragm and the second diaphragm in the axial direction to an inner diameter end of the volute. a first discharge flow path; and a plurality of spacer vanes at a downstream end of the first discharge flow path, the spacer vanes being arranged on the same circumference centered on the rotary shaft and spaced apart from each other in the circumferential direction of the rotary shaft, wherein the volute includes a first portion in contact with the radial outer edge portion, a second portion connected to the downstream end of the first portion and not in contact with the radial outer edge portion, and second discharge flow paths connected to the downstream ends of the first discharge flow path within each of the first portion and the second portion, and a first spacing between two of the spacer vanes adjacent to each other across a first circumferential region in the first discharge flow path where a tongue portion connecting the first portion and the second portion is present is wider than a second spacing between two of the spacer vanes adjacent to each other across a second circumferential region in the first discharge flow path where the tongue portion is not present.

[0007] According to one aspect of the present disclosure, in a centrifugal compressor, the fluid compression efficiency can be improved while ensuring the connection strength between two adjacent diaphragms.

[0008] Fig. 1 is a cross-sectional view of a main part of a centrifugal compressor according to an embodiment. Fig. 2 is a schematic view of the entire first discharge flow path and a part of the second discharge flow path in Fig. 1 when viewed from the axial direction. Fig. 3 is an enlarged view showing a spacer vane in Fig. 2. Fig. 4 is an enlarged view of the spacer vane and the surrounding area of ​​the spacer vane in Fig. 1. Fig. 5A is a schematic view corresponding to Fig. 2 of a centrifugal compressor according to a first modified example. Fig. 5B is a schematic view corresponding to Figs. 2 and 5A of a centrifugal compressor according to a second modified example.

[0009] Hereinafter, an embodiment will be described with reference to the drawings. In the following description, the axial direction of the rotating shaft 2 will be simply referred to as the "axial direction," the radial direction of the rotating shaft 2 perpendicular to the axial direction will be simply referred to as the "radial direction," and the circumferential direction of the rotating shaft 2 will be simply referred to as the "circumferential direction."

[0010] Fig. 1 is a cross-sectional view of a main part of a centrifugal compressor 1 according to an embodiment. As shown in Fig. 1, the centrifugal compressor 1 includes a rotating shaft 2, six impellers I1 to I6 that rotate around the rotating shaft 2 and are arranged in parallel in the axial direction, four diaphragms D1 to D4 that cover the impellers I1 to I6 and are arranged in parallel in the axial direction, and a casing 3 that houses the rotating shaft 2, the impellers I1 to I6, and the diaphragms D1 to D4. The centrifugal compressor 1 further includes bolts 4 that connect the diaphragms D1 to D4 to one another. The centrifugal compressor 1 may be used, for example, to compress hydrogen gas.

[0011] The rotating shaft 2 extends horizontally along the length of the casing 3. Seal structures 5 and 6 are arranged on the rotating shaft 2 in the axial direction outside the impellers I1 to I6, diaphragms D1 to D4, and volutes V1 to V3 (described later). The seal structure 5 isolates the impellers I1 to I6, diaphragms D1 to D4, and volutes V1 to V3 (described later) from bearings arranged at one axial end of the rotating shaft 2, while the seal structure 6 isolates the impellers I1 to I6, diaphragms D1 to D4, and volutes V1 to V3 (described later) from bearings arranged at the other axial end of the rotating shaft 2. The seal structures 5 and 6 may be, for example, dry gas seal structures.

[0012] Impeller I1 is covered by diaphragm D1. Impeller I2 is axially disposed between and covered by diaphragms D1 and D2. Impeller I3 is axially disposed between and covered by diaphragms D2 and D3. Impeller I4 is covered by diaphragm D3. Impeller I5 is axially disposed between and covered by diaphragms D3 and D4. Impeller I6 is covered by diaphragm D4.

[0013] The diaphragm D1 includes an intake passage DFa connecting the downstream end of the intake nozzle F1 (described later) to the radial center of the impeller I1, and a central passage DFb extending through the impellers I1 and I2 to the outer diameter end of the impeller I2. The diaphragm D1 further includes a first surface DSa facing the diaphragm D2 in the axial direction, and a first insertion hole DHa extending in the axial direction and through which a bolt 4 is inserted. The first insertion hole DHa communicates with first insertion holes DHb to DHd (described later). In this embodiment, the diaphragm D1 includes four first insertion holes DHa.

[0014] The diaphragm D2 includes a second surface DSb that faces the diaphragm D1 in the axial direction and faces the first surface DSa of the diaphragm D1, a first surface DSc that faces the diaphragm D3 in the axial direction, and first insertion holes DHb that extend in the axial direction and through which the bolts 4 are inserted. In the present embodiment, the diaphragm D2 includes four first insertion holes DHb.

[0015] The centrifugal compressor 1 further includes a first discharge flow path DFc that is defined by a first surface DSa of the diaphragm D1 and a second surface DSb of the diaphragm D2 and that connects an outer diameter end of the impeller I2 to an inner diameter end of a volute V1 (described later). That is, in this embodiment, the impeller I2 can be the first impeller.

[0016] The diaphragm D3 includes an intake passage DFg connecting the downstream end of a intake nozzle F3 (described later) to the radial center of the impeller I4, and a central passage DFh extending through the impellers I4 and I3 to the outer diameter end of the impeller I3. The diaphragm D3 further includes a second surface DSd facing the diaphragm D2 in the axial direction and opposing the first surface DSc of the diaphragm D2, a first surface DSe facing the diaphragm D4 in the axial direction, and first insertion holes DHc extending in the axial direction and through which the bolts 4 are inserted. In this embodiment, the diaphragm D3 includes four first insertion holes DHc.

[0017] The centrifugal compressor 1 further includes a first discharge flow path DFi that is defined by the first surface DSc of the diaphragm D2 and the second surface DSd of the diaphragm D3 and that connects the outer diameter end of the impeller I3 to the inner diameter end of a volute V3 (described later). That is, in this embodiment, in addition to the impeller I2, the impeller I3 can also be the first impeller.

[0018] The diaphragm D4 includes an intake passage DFd connecting the downstream end of the intake nozzle F2 (described later) to the radial center of the impeller I6, and a central passage DFe extending through the impellers I6 and I5 to the outer diameter end of the impeller I5. The diaphragm D4 further includes a second surface DSf facing the diaphragm D3 in the axial direction and opposing the first surface DSe of the diaphragm D3, and first insertion holes DHd extending in the axial direction and through which the bolts 4 are inserted. In this embodiment, the diaphragm D4 includes four first insertion holes DHd.

[0019] The centrifugal compressor 1 further includes a first discharge flow path DFf that is defined by the first surface DSe of the diaphragm D3 and the second surface DSf of the diaphragm D4 and that connects the outer diameter end of the impeller I5 to the inner diameter end of a volute V2 (described later). That is, in this embodiment, in addition to the impellers I2 and I3, the impeller I5 can also be the first impeller.

[0020] The casing 3 includes an intake nozzle F1 connected to the upstream end of the intake flow path DFa of the diaphragm D1, an intake nozzle F2 connected to the upstream end of the intake flow path DFd of the diaphragm D4, and an intake nozzle F3 connected to the upstream end of the intake flow path DFg of the diaphragm D3.

[0021] The casing 3 further includes volutes V1 to V3 adjacent to the diaphragms D1 to D4 on the radial outside. The volute V1 is connected to the radially outer edge of the adjacent diaphragms D1, D2. That is, the diaphragms D1, D2 may be the first diaphragm and the second diaphragm adjacent to each other. The volute V2 is connected to the radially outer edge of the adjacent diaphragms D3, D4. That is, the diaphragms D3, D4 may also be the first diaphragm and the second diaphragm adjacent to each other. The volute V3 is connected to the radially outer edge of the adjacent diaphragms D2, D3. That is, the diaphragms D2, D3 may also be the first diaphragm and the second diaphragm adjacent to each other.

[0022] The casing 3 further includes a discharge nozzle E1 connected to the downstream end of the volute V1, a discharge nozzle E2 connected to the downstream end of the volute V2, and a discharge nozzle E3 connected to the downstream end of the volute V3.

[0023] The centrifugal compressor 1 includes a section SC1 from the suction nozzle F1 to the discharge nozzle E1, a section SC2 from the suction nozzle F2 to the discharge nozzle E2, and a section SC3 from the suction nozzle F3 to the discharge nozzle E3. The centrifugal compressor 1 can compress hydrogen gas, for example, in the following manner.

[0024] First, the centrifugal compressor 1 compresses hydrogen gas in section SC1. Specifically, the centrifugal compressor 1 draws in hydrogen gas through a suction nozzle F1, and while accelerating the drawn-in hydrogen gas using impellers I1 and I2, compresses the drawn hydrogen gas through a suction passage DFa, a central passage DFb, a first discharge passage DFc, and a second discharge passage VFa (described later), and discharges the compressed hydrogen gas from a discharge nozzle E1. The hydrogen gas discharged from the discharge nozzle E1 is cooled by a cooling device disposed outside the centrifugal compressor 1.

[0025] Next, the centrifugal compressor 1 further compresses in section SC2 the hydrogen gas that has been compressed in section SC1 and cooled by the cooling device. Specifically, the centrifugal compressor 1 draws in hydrogen gas through the suction nozzle F2, accelerates the drawn hydrogen gas using impellers I6 and I5, and further compresses the gas through the suction passage DFd, the central passage DFe, the first discharge passage DFf, and a second discharge passage VFb (described later). The compressed hydrogen gas is then discharged from the discharge nozzle E2. The hydrogen gas discharged from the discharge nozzle E2 is cooled again by a cooling device disposed outside the centrifugal compressor 1.

[0026] Finally, the centrifugal compressor 1 further compresses, in section SC3, the hydrogen gas that has been compressed in sections SC1 and SC2 and cooled by the cooling device. Specifically, the centrifugal compressor 1 draws in hydrogen gas through the suction nozzle F3, accelerates the drawn-in hydrogen gas with the impellers I4 and I3, and further compresses the gas through the suction passage DFg, the central passage DFh, the first discharge passage DFi, and a second discharge passage VFc (described later), and then discharges the compressed hydrogen gas from the discharge nozzle E3.

[0027] FIG. 2 is a schematic diagram of the entire first discharge flow path DFf and a portion of the second discharge flow path VFb in FIG. 1 as viewed from the axial direction. The first discharge flow paths DFc and DFi have substantially the same structure as the first discharge flow path DFf, except for the volute incident angle α, which will be described later. The volutes V1 and V3 have substantially the same structure as the volute V2. Therefore, hereinafter, unless otherwise necessary, only the first discharge flow path DFf and the volute V2 will be described, and similar descriptions of the first discharge flow paths DFc and DFi and the volutes V1 and V3 will not be repeated. In FIG. 2, the rotation direction of the rotating shaft 2 is counterclockwise around the rotation axis AR. Hereinafter, unless otherwise necessary, the rotation direction of the rotating shaft 2 will be simply referred to as the "rotation direction."

[0028] As shown in FIG. 2, the centrifugal compressor 1 further includes: 21 diffuser vanes 10 arranged at an upstream end of the first discharge flow path DFf at intervals from one another in the circumferential direction on the same circumference centered on the rotating shaft 2; and 7 spacer vanes 11 arranged at a downstream end of the first discharge flow path DFf at intervals from one another in the circumferential direction on the same circumference centered on the rotating shaft 2.

[0029] The volute V2 includes a first portion Va that contacts the radial outer edge Da of the first discharge flow path DFf, a second portion Vb that is connected to the downstream end of the first portion Va and does not contact the radial outer edge Da, and a second discharge flow path VFb that is connected to the downstream end of the first discharge flow path DFf within each of the first portion Va and the second portion Vb.

[0030] The first spacing SP1 between two adjacent spacer vanes 11 through a first region R1 in the circumferential direction where a tongue portion Vc connecting the first portion Va and the second portion Vb of the first discharge flow path DFf exists is wider than the second spacing SP2 between two adjacent spacer vanes 11 through a second region R2 in the circumferential direction where no tongue portion Vc exists of the first discharge flow path DFf.

[0031] The radial dimension of the first portion Va of the volute V2 increases, for example, from the upstream end where the tongue portion Vc is present toward the downstream end where the volute V2 is connected to the second portion Vb.

[0032] When the first discharge flow path DFf is viewed from the axial direction, seven regions of the first discharge flow path DFf are defined by seven imaginary lines VL connecting the rotation axis AR of the rotating shaft 2 and each spacer vane 11, the inner diameter ends Db of the first discharge flow path DFf, and the outer diameter ends Dc of the first discharge flow path DFf. Here, the first spacing SP1 is the circumferential spacing between the two spacer vanes 11 in the first region R1 where the tongues Vc are present at the outer diameter ends Dc. The second spacing SP2 is the circumferential spacing between the spacer vanes 11 in the second region R2 where the tongues Vc are not present at the outer diameter ends Dc.

[0033] In this embodiment, the centrifugal compressor 1 includes seven spacer vanes 11, the first interval SP1 is 90°, and the second interval SP2 is 45°. Therefore, if one spacer vane 11 is added between two spacer vanes 11 adjacent to each other with the first region R1 interposed therebetween and at a position rotated 45° circumferentially from one of the two spacer vanes 11, eight spacer vanes 11 will be arranged at equal intervals on the same circumference centered on the rotary shaft 2.

[0034] Figure 3 is an enlarged view of a spacer vane 11 in Figure 2. The seven spacer vanes 11 have similar structures and are similarly arranged on the same circumference centered on the rotary shaft 2. Therefore, hereinafter, unless otherwise necessary, only one spacer vane 11 will be described, and similar descriptions of the other six spacer vanes will not be repeated.

[0035] As shown in FIG. 3 , the spacer vane 11 includes a base end 13 in the radial direction, a tip end 14 located radially outward of the base end 13, and a bone line 15 extending along the center of the width direction from the base end 13 to the tip end 14 when viewed in the axial direction. The bone line 15 may be determined, for example, so that the expansion angle θ of the equivalent cross-sectional area in the streamline direction can suppress separation. The expansion angle θ may be, for example, 10° or less. The angle of the leading edge of the base end 13 of the spacer vane 11 in the rotational direction may be the average angle of the airflow that can be discharged from the diffuser vane 10. The angle of the leading edge of the tip end 14 of the spacer vane 11 in the rotational direction may be an angle that can suppress swirling of the fluid within the volute V2.

[0036] At least one of the spacer vanes 11 has a second insertion hole 12, which communicates with the first insertion holes DHa to DHd and through which the bolt 4 is inserted, located in the longitudinal center of the bone line 15. As shown in Fig. 2, in this embodiment, the spacer vane 11 closest to the tongue portion Vc, the spacer vane 11 located 90° counterclockwise from the spacer vane 11 closest to the tongue portion Vc, the spacer vane 11 located 180° counterclockwise from the spacer vane 11 closest to the tongue portion Vc, and the spacer vane 11 located 270° counterclockwise from the spacer vane 11 closest to the tongue portion Vc each have the second insertion hole 12. However, this is not limited to this, and all of the spacer vanes 11 may each have the second insertion hole 12.

[0037] When viewed from the axial direction, the radial outer edge 16 of each spacer vane 11 includes a shape that follows a first circle C centered on the rotation axis 2. The volute incidence angle α formed by a first straight line L extending outward from the tip of the bone line 15 and a first tangent line TL to the first circle C at an intersection P between the bone line 15 and the first circle C may be approximately 31°. The volute incidence angle α of each spacer vane 11 disposed in the first discharge flow path DFc of section SC1 may be approximately 36°. The volute incidence angle α of each spacer vane 11 disposed in the first discharge flow path DFi of section SC3 may be approximately 23°. The volute incidence angle α is preferably 15° or greater and 45° or less. The volute incidence angle α is more preferably 20° or greater and 40° or less.

[0038] Fig. 4 is an enlarged view of the spacer vane 11 of section SC2 in Fig. 1 and the surrounding area of ​​the spacer vane 11. As shown in Fig. 4, the dimension of the spacer vane 11 in the axial direction increases as it moves radially outward.

[0039] Some conventional centrifugal compressors have multiple spacer vanes arranged at equal intervals in the circumferential direction of the rotating shaft. In such conventional centrifugal compressors, the first interval between two spacer vanes adjacent to each other across a first circumferential region where the tongues are present is equal to the second interval between two spacer vanes adjacent to each other across a second circumferential region where the tongues are not present. As a result, in conventional centrifugal compressors, for example, fluid that is influenced by a spacer vane located clockwise from the tongues in FIG. 2 among two spacer vanes adjacent to each other across the first region and flows out radially outward from the spacer vane is further influenced by the tongues. The fluid that flows into the second portion of the volute after being influenced by both the spacer vane and the tongues may swirl within the second portion, adversely affecting compression efficiency. On the other hand, in the centrifugal compressor 1 described above, the first spacing SP1 between two adjacent spacer vanes 11 across a first circumferential region R1 where the tongue portion Vc is present is wider than the second spacing SP2 between two adjacent spacer vanes 11 across a second circumferential region R2 where the tongue portion Vc is not present. Therefore, the fluid accelerated by the impeller I5 can flow from the first discharge flow path DFf to the second discharge flow path VFb of the volute V2 without interference from the spacer vanes 11 arranged in the first discharge flow path DFf. This improves the fluid compression efficiency. Even with this structure, the second spacing SP2 is narrower than the first spacing SP1, ensuring the strength of connection between the two adjacent diaphragms D3 and D4. As described above, the centrifugal compressor 1 can improve the fluid compression efficiency while ensuring the strength of connection between the two adjacent diaphragms D3 and D4. The same effect can be obtained with two adjacent diaphragms D1 and D2 and two adjacent diaphragms D2 and D3.

[0040] The centrifugal compressor 1 includes seven spacer vanes 11, the first spacing SP1 is 90° or more, and the second spacing SP2 is 45° or less, so that the effect of improving the fluid compression efficiency while ensuring the connection strength of the two adjacent diaphragms D3, D4 can be more pronounced. Note that the same effect can be obtained for the two adjacent diaphragms D1, D2 and the two adjacent diaphragms D2, D3.

[0041] The spacer vanes 11 each have an axial dimension that increases radially outward, thereby suppressing acceleration of the fluid when it flows from the first discharge flow path DFf to the second discharge flow path VFb. This improves the efficiency of converting kinetic energy into pressure energy. The same effect is achieved when the fluid flows from the first discharge flow path DFc to the second discharge flow path VFa and when the fluid flows from the first discharge flow path DFi to the second discharge flow path VFc.

[0042] The diaphragms D1 to D4 include first insertion holes DHa to DHd through which bolts 4 are inserted to connect the diaphragms D1 to D4 to one another, and the spacer vanes 11 each have second insertion holes 12 that communicate with the first insertion holes DHa to DHd and through which the bolts 4 are inserted. This allows the fluid accelerated by the impeller I5 to flow from the first discharge flow path DFf to the second discharge flow path VFb of the volute V2 without interference from the bolts 4 located in the first discharge flow path DFf. This allows the fluid compression efficiency to be improved while ensuring the connection strength of the two adjacent diaphragms D3 and D4 with a simple structure. Similar effects can be achieved with the two adjacent diaphragms D1 and D2 and the two adjacent diaphragms D2 and D3.

[0043] Since the volute incidence angle α of each spacer vane 11 is between 15° and 45°, the compression efficiency of the fluid can be further improved. If the volute incidence angle α is less than 15°, the fluid accelerated by the impeller I5 will be excessively decelerated by the spacer vanes 11. This will cause the fluid to swirl easily before flowing into the volute V2, reducing the compression efficiency. On the other hand, if the volute incidence angle α is greater than 45°, the fluid accelerated by the impeller I5 will hardly be decelerated by the spacer vanes 11. This will cause the fluid to swirl easily within the volute V2, reducing the compression efficiency.

[0044] Since the volute incidence angle α of each spacer vane 11 is equal to or greater than 20° and equal to or less than 40°, the compression efficiency of the fluid can be further improved.

[0045] It should be noted that the technology of the present disclosure is not limited to the above-described configuration.

[0046] In the above embodiment, the centrifugal compressor 1 is described as having four diaphragms D1 to D4. However, the present invention is not limited to this, and the centrifugal compressor 1 may have two, three, five or more diaphragms. In this case, the number of the three sections SC1 to SC3 may be changed as appropriate.

[0047] In the above embodiment, the centrifugal compressor 1 includes seven spacer vanes 11 in each of the first discharge flow paths DFc, DFf, and DFi, the first spacing SP1 is 90°, and each of the plurality of second spacings SP2 is 45°. However, the present invention is not limited to this. The centrifugal compressor 1 may include, for example, five, six, or eight or more spacer vanes 11 in each of the first discharge flow paths DFc, DFf, and DFi, and the first spacing SP1 and the second spacing SP2 may be appropriately changed depending on the number of spacer vanes 11. Preferably, the centrifugal compressor 1 includes N (N≧5) spacer vanes 11 in each of the first discharge flow paths DFc, DFf, and DFi, and the N−1 second spacings SP2 may be the same, the first spacing SP1 may be 2×360° / (N+1) or more, and the N−1 second spacings SP2 may be 360° / (N+1) or less. This structure significantly improves the fluid compression efficiency while ensuring the strength of the connection between the two adjacent diaphragms. More preferably, the centrifugal compressor 1 includes seven spacer vanes 11 in each of the first discharge flow paths DFc, DFf, and DFi, and the first spacing SP1 may be 90° or more, and the N-1 second spacings SP2 may be 45° or less. This structure significantly improves the fluid compression efficiency while ensuring the strength of the connection between the two adjacent diaphragms.

[0048] The N-1 second intervals SP2 may be different from one another. For example, the first interval SP1 may be equal to or greater than 2×360° / (N+1), and at least one of the N-1 second intervals SP2 may be equal to or less than 360° / (N+1). For example, in FIG. 2, the second interval SP2 between the spacer vane 11 closest to the tongue portion Vc and the spacer vane 11 adjacent to that spacer vane 11 on the circumferential left side may be 50°, the second interval SP2 between the spacer vane 11 adjacent to that spacer vane 11 on the circumferential left side may be 40°, and the other four second intervals SP2 may each be 45°.

[0049] For example, in the circumferential direction, a region SP3 extending from a location of the first discharge flow path DFf corresponding to the tongue portion Vc and corresponding to the downstream end of the first portion Va of the volute V2 to the upstream side of the first portion Va at an angle of 60° to 120°, in other words, a region SP3 in the circumferential direction of the first discharge flow path DFf that is 60° to 120° clockwise from the tongue portion Vc in Fig. 2, may not include the spacer vane 11. This region SP3 will be described in detail with reference to Figs. 5A and 5B.

[0050] Figure 5A is a schematic diagram of a centrifugal compressor 20 according to a first modified example, corresponding to Figure 2. The centrifugal compressor 20 has the same structure as the centrifugal compressor 1 described with reference to Figures 1 to 4, except for the number and arrangement of the diffuser vanes 10 and spacer vanes 11. Therefore, the same reference numerals are used for the same parts, and similar descriptions will not be repeated. In Figure 5A, the second insertion holes 12 of the spacer vanes 11 described with reference to Figure 3 are omitted to avoid visual complication.

[0051] As shown in FIG. 5A , in this first modification, seven diffuser vanes 10 are arranged at intervals from one another in the circumferential direction at the upstream end of the first discharge flow path DFf on the same circumference centered on the rotary shaft 2. In this first modification, the region SPmin3 of the region SP3 has a lower limit of 60°, and no spacer vanes 11 are arranged in this region SPmin3. Eleven spacer vanes 11 are arranged at intervals of approximately 30° from one another in a 300° circumferential region of the first discharge flow path DFf excluding the region SPmin3. The radial base end of the spacer vane 11 closest to the tongue portion Vc is located at the same position as the tongue portion Vc in the circumferential direction. By arranging the spacer vanes 11 as described above, for the same reasons as in the centrifugal compressor 1 according to the above embodiment, the coupling strength between the two adjacent diaphragms D3, D4 can be further ensured, while improving the fluid compression efficiency.

[0052] 5B is a schematic diagram of a centrifugal compressor 40 according to a second modification, corresponding to FIGS. 2 and 5A. The centrifugal compressor 40 has the same structure as the centrifugal compressor 20 described based on FIG. 5A, except for the number and arrangement of the spacer vanes 11. Therefore, the same reference numerals are used for the same parts, and similar descriptions will not be repeated. Note that in FIG. 5B, as in FIG. 5A, the second insertion holes 12 of the spacer vanes 11 are omitted to avoid visual clutter.

[0053] As shown in FIG. 5B , in this second modification, the upper limit of the region SPmax3 of the region SP3 is 120°. The spacer vanes 11 are not disposed in this region SPmax3. Furthermore, five spacer vanes 11 are disposed at intervals of approximately 60° from one another in a 240° circumferential region of the first discharge flow path DFf excluding the region SPmax3. The number of spacer vanes 11 is the lower limit of the number N. As in FIG. 5A , the radial base end of the spacer vane 11 closest to the tongue portion Vc is located at the same position as the tongue portion Vc in the circumferential direction. By arranging the spacer vanes 11 as described above, it is possible to obtain the effect of further improving the fluid compression efficiency while ensuring the connection strength between the two adjacent diaphragms D3, D4, for the same reasons as in the centrifugal compressor 1 according to the above embodiment.

[0054] 5A and 5B show a case where the base end of the spacer vane 11 closest to the tongue portion Vc in the radial direction is located at the same position as the tongue portion Vc in the circumferential direction. However, this is not limited to this case, and for example, as long as the region SP3 is between 60° and 120°, the base end of the spacer vane 11 closest to the tongue portion Vc in the radial direction may be located at a different position from the tongue portion Vc in the circumferential direction.

[0055] For example, the first spacing SP1, the second spacing SP2, the shape of each of the spacer vanes 11, and the angle of each of the spacer vanes 11 relative to the same circumference about the rotational axis 2 may be adjusted as appropriate in accordance with the shape, size, and position of the volute V2 so that the leading edge of the spacer vanes 11 in the rotational direction is aligned with the trailing edge of the fluid discharged from the diffuser vane 10. This allows the fluid discharged from the diffuser vane 10 to flow into the volute V2 while being prevented from interfering with the spacer vanes 11, thereby improving the compression efficiency of the fluid.

[0056] In the above embodiment, the case where 21 diffuser vanes 10 are arranged in each of the first discharge flow paths DFc, DFf, and DFi has been described. However, the present invention is not limited to this case, and the number of diffuser vanes 10 may be other than 21.

[0057] In the above embodiment, the centrifugal compressor 1 includes six impellers I1 to I6. However, the present invention is not limited to this, and the centrifugal compressor 1 may include one to five impellers, or seven or more impellers.

[0058] Each of the following aspects is a disclosure of a preferred embodiment. a plurality of diaphragms covering the plurality of impellers and arranged in parallel in the axial direction of the rotary shaft; a volute connected to radially outer edge portions of a first diaphragm and a second diaphragm adjacent to each other among the plurality of diaphragms, the radially outer edge portion being perpendicular to the axial direction; a first discharge flow path defined by a first surface of the first diaphragm facing the second diaphragm in the axial direction and a second surface of the second diaphragm facing the first diaphragm in the axial direction and opposing the first surface, the first discharge flow path connecting an outer diameter end of a first impeller of the plurality of impellers arranged between the first diaphragm and the second diaphragm in the axial direction to an inner diameter end of the volute; and a plurality of spacer vanes arranged at a downstream end of the first discharge flow path on the same circumference centered on the rotary shaft at intervals from each other in the circumferential direction of the rotary shaft, a second discharge passage connected to a downstream end of the first portion and connected to a downstream end of the first discharge passage within the first portion, the second discharge passage being ... [Aspect 3] The centrifugal compressor according to Aspect 2, wherein the first discharge flow path includes seven spacer vanes, the first interval is 90 degrees or more, and the second interval is 45 degrees or less.[Aspect 4] The centrifugal compressor according to any one of Aspects 1 to 3, wherein the dimension of each of the plurality of spacer vanes in the axial direction increases radially outward. [Aspect 5] The centrifugal compressor according to any one of Aspects 1 to 4, further comprising: a bolt connecting the plurality of diaphragms to each other, each of the plurality of diaphragms including a first insertion hole extending in the axial direction and through which the bolt is inserted, and at least one of the plurality of spacer vanes including a second insertion hole communicating with the first insertion hole and through which the bolt is inserted. [Aspect 6] The centrifugal compressor according to any one of Aspects 1 to 5, wherein each of the plurality of spacer vanes includes a base end in the radial direction, a tip end in the radial direction located radially outward from the base end, and a bone line extending through a center portion in the width direction from the base end to the tip end when viewed from the axial direction, wherein the outer edge in the radial direction of each of the plurality of spacer vanes includes a shape along a first circle centered on the rotation axis when viewed from the axial direction, and wherein a volute incident angle formed by a first straight line extending outward from the tip end of the bone line and a first tangent to the first circle at an intersection of the bone line and the first circle is 15° to 45°. [Aspect 7] The centrifugal compressor according to Aspect 6, wherein the volute incident angle is 20° to 40°.

[0059] 1, 20, 40 Centrifugal compressor 2 Rotating shaft 4 Bolt 11 Spacer vane 12 Second insertion hole 13 Radial base end portion 14 Radial tip portion 15 Bone line 16 Radial outer edge portion α Volute entry angle C First circle L First straight line P Intersection TL First tangent I1 to I6 Impeller D1 to D4 Diaphragm DFc, DFf, DFi First discharge flow path VFa to VFc Second discharge flow path DSa, DSc, DSe First surface DSb, DSd, DSf Second surface DHa to DHd First insertion hole Da Radial outer edge portion V1 to V3 Volute Va First portion Vb Second portion Vc Tongue portion R1 First region R2 Second region SP1 First interval SP2 2nd interval

Claims

1. A centrifugal compressor comprising: a rotating shaft; a plurality of impellers that rotate around the rotating shaft and are arranged in parallel in the axial direction of the rotating shaft; a plurality of diaphragms that cover the plurality of impellers and are arranged in parallel in the axial direction; a volute connected to radially outer edge portions of a first diaphragm and a second diaphragm that are adjacent to each other among the plurality of diaphragms and are perpendicular to the axial direction; a first discharge flow path that is defined by a first surface of the first diaphragm that faces the second diaphragm in the axial direction and a second surface of the second diaphragm that faces the first diaphragm in the axial direction and faces the first surface, and that connects an outer diameter end of a first impeller that is arranged between the first diaphragm and the second diaphragm in the axial direction among the plurality of impellers to an inner diameter end of the volute; and a plurality of spacer vanes that are arranged at a downstream end of the first discharge flow path on the same circumference centered on the rotating shaft and at intervals from each other in the circumferential direction of the rotating shaft, the volute includes a first portion in contact with the radial outer edge portion, a second portion connected to a downstream end of the first portion and not in contact with the radial outer edge portion, and a second discharge passage connected to a downstream end of the first discharge passage within each of the first portion and the second portion, and a first distance between two of the spacer vanes adjacent to each other across a first region in the circumferential direction in which a tongue portion connecting the first portion and the second portion is present is wider than a second distance between two of the spacer vanes adjacent to each other across a second region in the circumferential direction in which the tongue portion is not present in the first discharge passage.

2. The centrifugal compressor according to claim 1, wherein the first discharge flow path comprises N spacer vanes (N≧5), the first interval is 2×360° / (N+1) or greater, and at least one of the N-1 second intervals is 360° / (N+1) or less.

3. The centrifugal compressor according to claim 2, wherein seven spacer vanes are provided in the first discharge flow path, the first interval is 90° or more, and the second interval is 45° or less.

4. A centrifugal compressor according to any one of claims 1 to 3, wherein the dimension of each of the plurality of spacer vanes in the axial direction increases as it moves radially outward.

5. A centrifugal compressor according to any one of claims 1 to 3, further comprising bolts connecting the plurality of diaphragms to one another, each of the plurality of diaphragms including a first insertion hole extending in the axial direction and through which the bolt is inserted, and at least one of the plurality of spacer vanes having a second insertion hole communicating with the first insertion hole and through which the bolt is inserted.

6. A centrifugal compressor according to any one of claims 1 to 3, wherein each of the plurality of spacer vanes includes a base end in the radial direction, a tip end in the radial direction located radially outward of the base end, and a bone line extending through a central portion in the width direction from the base end to the tip end when viewed from the axial direction, wherein the outer edge in the radial direction of each of the plurality of spacer vanes includes a shape that follows a first circle centered on the rotation axis when viewed from the axial direction, and wherein a volute incidence angle formed by a first straight line extending outward from the tip end of the bone line and a first tangent to the first circle at the intersection of the bone line and the first circle is between 15° and 45°.

7. A centrifugal compressor according to claim 6, wherein the volute incidence angle is equal to or greater than 20° and equal to or less than 40°.

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