WO2023218724A1 - Multistage centrifugal compressor, and multistage centrifugal compressor adjustment method - Google Patents

Abstract

This multistage centrifugal compressor comprises a plurality of impellers, and a casing. The plurality of impellers include a first impeller and a second impeller positioned in a subsequent stage of the first impeller. The casing forms a diffuser flow passage that leads a fluid exiting the first impeller to the outside in the radial direction of a rotation shaft, a fold-back flow passage that is connected to a downstream side of the diffuser flow passage, and a return flow passage that is connected to a downstream side of the fold-back flow passage. The casing includes: an annular partition wall member that partitions the diffuser flow passage and the return flow passage; and a ring-shaped member that forms, together with the partition wall member, a hub-side wall surface among a pair of wall surfaces which form the diffuser flow passage. The partition wall member and the ring-shaped member are constituted by separate bodies.

Description

Multi-stage centrifugal compressor and adjustment method for multi-stage centrifugal compressor

The present disclosure relates to a multi-stage centrifugal compressor and a method for adjusting a multi-stage centrifugal compressor.
This application claims priority based on Japanese Patent Application No. 2022-078130 filed with the Japan Patent Office on May 11, 2022, the contents of which are incorporated herein.

Patent Document 1 discloses a multistage centrifugal compressor that includes a rotating shaft, multiple stages of impellers provided on the rotating shaft, and a casing that accommodates the multiple stages of impellers.

The casing of a multistage centrifugal compressor is connected to a diffuser passage that guides the fluid exiting the impeller to the outside in the radial direction of the rotating shaft, and is connected to the downstream side of the diffuser passage, so that the direction in which the fluid that has passed through the diffuser passage is radially A return flow path that is connected to the downstream side of the return flow path and guides the fluid that has passed through the return flow path inward in the radial direction, and a return flow path that is connected to the downstream side of the return flow path. , and an introduction channel for introducing the fluid that has passed through the return channel into the impeller of the next stage. The casing also includes an annular partition wall member that partitions the diffuser flow path and the return flow path.

Patent No. 3488718

Incidentally, the pressure head of the compressor changes depending on the usage conditions of the compressor (for example, the region where the compressor is installed, the temperature, etc.). One way to achieve the desired pressure head under the operating conditions of the compressor is to change the outer diameter of the impeller, but in conventional multi-stage centrifugal compressors, when changing the outer diameter of the impeller, It is necessary to process or replace the annular partition wall member so that a gap of an appropriate size is formed between the radially outer end surface of the hub and the above-mentioned annular partition member. Since this annular partition wall member is a large-sized structure, it requires a great deal of effort to process or replace the annular partition wall member for each usage condition of the compressor. For this reason, in conventional multistage centrifugal compressors, it is not easy to change the outer diameter of the impeller.

In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a multistage centrifugal compressor and a method for adjusting the multistage centrifugal compressor that can easily change the outer diameter of the impeller.

In order to achieve the above object, a multistage centrifugal compressor according to at least one embodiment of the present disclosure includes:
a rotating shaft; a multi-stage impeller provided on the rotating shaft;
a casing that accommodates the multiple stages of impellers;
A multistage centrifugal compressor comprising:
The multi-stage impeller includes a first impeller and a second impeller located at the next stage of the first impeller,
The casing is connected to a diffuser passage that guides the fluid exiting the first impeller to the outside in the radial direction of the rotating shaft, and a downstream side of the diffuser passage, and is connected to a downstream side of the diffuser passage, so that the fluid that has passed through the diffuser passage flows. A return flow path that turns the direction inward in the radial direction, and a return flow path that is connected to the downstream side of the return flow path and guides the fluid that has passed through the return flow path inward in the radial direction. and
The casing is
A casing body;
an annular partition wall member that partitions the diffuser flow path and the return flow path;
A wall surface on the hub side of a pair of wall surfaces forming the diffuser flow path, which is provided between the radially outer end surface of the hub of the first impeller and the partition wall member so as to face the end surface. a ring-shaped member formed together with the partition wall member;
including;
The partition wall member and the ring-shaped member are configured separately.

In order to achieve the above object, in a method for adjusting a multistage centrifugal compressor according to at least one embodiment of the present disclosure,
The multistage centrifugal compressor includes:
a rotating shaft; a multi-stage impeller provided on the rotating shaft;
a casing that accommodates the multiple stages of impellers;
A multistage centrifugal compressor comprising:
The multi-stage impeller includes a first impeller and a second impeller located at the next stage of the first impeller,
The casing is connected to a diffuser passage that guides the fluid exiting the first impeller to the outside in the radial direction of the rotating shaft, and a downstream side of the diffuser passage, and is connected to a downstream side of the diffuser passage, so that the fluid that has passed through the diffuser passage flows. A return flow path that turns the direction inward in the radial direction, and a return flow path that is connected to the downstream side of the return flow path and guides the fluid that has passed through the return flow path inward in the radial direction. and
The casing is
A casing body;
an annular partition wall member that partitions the diffuser flow path and the return flow path;
A wall surface on the hub side of a pair of wall surfaces forming the diffuser flow path, which is provided between the radially outer end surface of the hub of the first impeller and the partition wall member so as to face the end surface. a ring-shaped member formed together with the partition wall member;
including;
The partition wall member and the ring-shaped member are configured separately, and the adjustment method includes:
changing the outer diameter of the first impeller;
changing the inner diameter of the ring-shaped member;
including.

According to at least one embodiment of the present disclosure, a multi-stage centrifugal compressor and a method for adjusting the multi-stage centrifugal compressor are provided that can easily change the outer diameter of an impeller.

1 is a schematic cross-sectional view including a rotation axis O of a multistage centrifugal compressor 2 according to an embodiment. 2 is an enlarged sectional view showing an example of a detailed configuration of the multistage centrifugal compressor 2 shown in FIG. 1. FIG. 2 is an enlarged sectional view showing an example of a detailed configuration of the multistage centrifugal compressor 2 shown in FIG. 1. FIG. FIG. 2 is a flow diagram showing an example of a method for adjusting the pressure head in the multistage centrifugal compressor 2. FIG. 1 is a schematic cross-sectional view including a rotation axis O of a multistage centrifugal compressor 2 according to an embodiment. 1 is a schematic cross-sectional view including a rotation axis O of a multistage centrifugal compressor 2 according to an embodiment. 2 is a pressure head-flow characteristic diagram showing the relationship between the pressure head and the volumetric flow rate in the multistage centrifugal compressor 2. FIG. It is a figure which shows an example of the arrangement|positioning of the ring-shaped member fixing bolt 36 and the vane fixing bolt 42 in the circumferential direction. 2 is an enlarged sectional view showing another example of the detailed configuration of the multistage centrifugal compressor 2 shown in FIG. 1. FIG. FIG. 3 is a diagram for explaining the arrangement of a plurality of divided bodies divided in the circumferential direction.

Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangement, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the invention thereto, and are merely illustrative examples. .
For example, expressions expressing relative or absolute positioning such as "in a certain direction,""along a certain direction,""parallel,""orthogonal,""centered,""concentric," or "coaxial" are strictly In addition to representing such an arrangement, it also represents a state in which they are relatively displaced with a tolerance or an angle or distance that allows the same function to be obtained.
For example, expressions such as "same,""equal," and "homogeneous" that indicate that things are in an equal state do not only mean that things are exactly equal, but also have tolerances or differences in the degree to which the same function can be obtained. It also represents the existing state.
For example, expressions expressing shapes such as squares and cylinders do not only refer to shapes such as squares and cylinders in a strict geometric sense, but also include uneven parts and chamfers to the extent that the same effect can be obtained. Shapes including parts, etc. shall also be expressed.
On the other hand, the expressions "comprising,""comprising,""comprising,""containing," or "having" one component are not exclusive expressions that exclude the presence of other components.

(Configuration of multistage centrifugal compressor)
FIG. 1 is a schematic cross-sectional view including a rotation axis O of a multistage centrifugal compressor 2 according to an embodiment. The use of the multistage compressor 2 is not particularly limited, but it may be applied to, for example, a turbo refrigerator.
As shown in FIG. 1, the multistage centrifugal compressor 2 includes a rotating shaft 4 (shaft), multiple stages of impellers 6 provided on the rotating shaft 4, and a casing 8 that accommodates the multiple stages of impellers 6. . Hereinafter, "axial direction" means the axial direction of the rotating shaft 4, that is, the axial direction of the impeller 6, unless otherwise specified, and "radial direction" means the radial direction of the rotating shaft 4, that is, the radial direction of the impeller 6, unless otherwise specified. "Circumferential direction" means the circumferential direction of the rotating shaft 4, that is, the circumferential direction of the impeller 6, unless otherwise specified. Moreover, "fluid" means a fluid to be compressed (pressurized) by the multistage centrifugal compressor 2 unless otherwise specified.

The multiple stages of impellers 6 are arranged along the axial direction and include an impeller 6A (first impeller) and an impeller 6B (second impeller) located at the next stage of the impeller 6A. Although FIG. 1 shows only two-stage impellers for ease of explanation, the number of impellers 6 provided in the multi-stage centrifugal compressor 2 is not limited to two stages, but may be three or more stages. Further, the impeller 6A may be a first-stage impeller, or may be a second-stage or subsequent stage impeller.

The impeller 6A includes a hub 22 and a plurality of blades 26 provided on the outer peripheral surface 24 of the hub 22 at intervals in the circumferential direction. The hub 22 includes an outer peripheral surface 24 and a back surface 28 facing the impeller 6B side in the axial direction. The outer circumferential surface 24 includes a hub surface 30 whose distance from the rotational axis O of the rotating shaft 4 increases as it goes downstream in the axial direction, and an outer end surface 32 of the hub 22 in the radial direction. The plurality of wings 26 are provided on the hub surface 30, and the end surface 32 faces outward in the radial direction and is formed in an annular shape so as to connect the hub surface 30 and the back surface 28.

The casing 8 (stationary member) forms a compression flow path 9 between it and the hub surface 30 of the impeller 6A. Further, the casing 8 is connected to a diffuser flow path 10 that guides the fluid exiting the impeller 6A to the outside in the radial direction, and to the downstream side of the diffuser flow path 10, so that the flow direction of the fluid that has passed through the diffuser flow path 10 is radially A return flow path 14 is formed, which is connected to the downstream side of the return flow path 12 and which guides the fluid that has passed through the return flow path 12 inward in the radial direction. The fluid that has passed through the return flow path 14 is diverted to the downstream side in the axial direction, flows into the impeller 6B, and is further pressurized.

In the illustrated example, the casing 8 includes a casing body 16, a partition wall member 18, a ring-shaped member 20, and a plurality of return vanes 23.

The casing body 16 accommodates multiple stages of impellers 6, a partition wall member 18, a ring-shaped member 20, and a plurality of return vanes 23. The casing main body 16 forms a shroud 21 facing the hub surface 30, and a wall surface 33 on the shroud 21 side among a pair of wall surfaces 33, 34 forming the diffuser flow path 10 (a later stage of the wall surfaces forming the diffuser flow path 10). (the wall surface on the side far from the impeller 6B).

The partition wall member 18 is formed in an annular shape around the rotating shaft 4 and partitions the diffuser flow path 10 and the return flow path 14. The partition wall member 18 forms a diffuser channel 10, a folded channel 12, and a return channel 14 between the partition wall member 18 and the casing body 16. A gap between the partition wall member 18 and the rotating shaft 4 is sealed by a seal member 19 for suppressing fluid leakage.

The ring-shaped member 20 is located between the end surface 32 of the hub 22 of the impeller 6A and the partition wall member 18, and is provided along the circumferential direction around the end surface 32 of the hub 22 so as to face the end surface 32. The ring-shaped member 20 includes a wall surface 34 on the hub 22 side among the pair of wall surfaces 33 and 34 forming the diffuser flow path 10 (a side closer to the rear impeller 6B among the pair of wall surfaces 33 and 34 forming the diffuser flow path 10). wall surface) is formed together with the partition wall member 18. The partition wall member 18 and the ring-shaped member 20 are constructed separately. That is, the partition wall member 18 and the ring-shaped member 20 are molded as separate parts that can be separated from each other. In the illustrated example, the outer diameter of the ring-shaped member 20 is smaller than the outer diameter of the partition wall member 18, and the inner diameter of the ring-shaped member 20 is larger than the inner diameter of the partition wall member 18.

The partition wall member 18 forms a wall surface portion 34a on the outer peripheral side of the wall surface 34, and the ring-shaped member 20 forms a wall surface portion 34b on the inner peripheral side of the wall surface 34. The wall portion 34b is located on the inner side of the wall portion 34a in the radial direction, and is adjacent to the wall portion 34a in the radial direction.

The plurality of return vanes 23 are provided in the return flow path 14 at intervals in the circumferential direction. Each of the plurality of return vanes 23 is supported by the casing body 16 on one side (downstream side) in the axial direction, and supported by the partition wall member 18 on the other side (upstream side) in the axial direction. The plurality of return vanes 23 may be configured integrally with the partition wall member 18, for example. In other words, the plurality of return vanes 23 and the partition wall member 18 may be configured as one piece as a whole, or may be integrally molded. The plurality of return vanes 23 may have the same shape, for example, and may be arranged rotationally symmetrically around the rotation axis O. In the illustrated example, the flow path width of the return flow path 14 in the axial direction becomes smaller toward the inside in the radial direction in the section from the front edge 38 to the rear edge 40 of the return vane 23 in the return flow path 14. ing.

FIG. 2 is an enlarged sectional view showing an example of a detailed configuration of the multistage centrifugal compressor 2 shown in FIG. 1. As shown in FIG.
In the example shown in FIG. 2, the multistage centrifugal compressor 2 includes a plurality of ring-shaped member fixing bolts 36 for fixing the ring-shaped member 20 to the partition wall member 18. Each of the ring-shaped member fixing bolts 36 is located inside the front edge 38 of each return vane 23 in the radial direction, and located outside the rear edge 40 of each return vane 23 in the radial direction. Further, each of the ring-shaped member fixing bolts 36 passes through the ring-shaped member 20 and the partition wall member 18, and reaches the inside of the corresponding return vane 23. Further, the outer end 25 of the ring-shaped member 20 in the radial direction (the outer peripheral surface of the ring-shaped member 20) is located inside the front edge 38 of each return vane 23 in the radial direction, and the rear edge 40 of each return vane 23 It is located on the outer side in the radial direction.

Furthermore, in the example shown in FIG. 2, the multistage centrifugal compressor 2 includes a plurality of vane fixing bolts 42 for fixing the plurality of return vanes 23 to the casing body 16. Each of the ring-shaped member fixing bolts 36 is located inside of each of the vane fixing bolts 42 in the radial direction. Further, the ring-shaped member fixing bolt 36 and the vane fixing bolt 42 are fixed to the same return vane 23. Further, the outer end 25 of the ring-shaped member 20 in the radial direction (the outer circumferential surface of the ring-shaped member 20) is located inside each of the vane fixing bolts 42 in the radial direction.

In the example shown in FIG. 2, the top surface 36a of the ring-shaped member fixing bolt 36 and the surface 34b of the ring-shaped member 20 on the side of the diffuser flow path 10 are flush with each other.

In the example shown in FIG. 2, the surface 44 of the partition wall member 18 on the diffuser flow path 10 side includes a recess 46 that is recessed toward the return flow path 14 side (downstream side in the axial direction). A surface 49 of the ring-shaped member 20 on the side opposite to the diffuser flow path 10 includes a convex portion 50 as an engaging portion that engages with the partition wall member 18 . The convex portion 50 fits into the concave portion 46 and restricts movement of the ring-shaped member 20 in the radial direction. The ring-shaped member 20 includes a ring-shaped plate portion 48 provided along the surface 44, and the convex portion 50 extends from the ring-shaped plate portion 48 toward the return flow path 14 side (downstream side in the axial direction). It stands out. Each of the recess 46 and the projection 50 may be formed in an annular shape extending along the circumferential direction, and in this case, the recess 46 and the projection 50 may constitute a spigot structure. Each of the ring-shaped member fixing bolts 36 passes through the convex portion 50 in the axial direction and is fixed to the partition wall member 18 and the corresponding return vane 23.

FIG. 3 is an enlarged sectional view showing an example of a detailed configuration of the multistage centrifugal compressor 2 shown in FIG. 1. As shown in FIG.
In the example shown in FIG. 3, the trailing edge 52 of the blade 26 of the impeller 6A is inclined outward in the radial direction as it moves away from the hub 22 (as it approaches the shroud 21). Further, the end surface 32 of the hub 22 is inclined along the direction of inclination of the rear edge 52, and is inclined inward in the radial direction as it approaches the return flow path 14 (see FIG. 1 or 2). . Further, a surface 54 of the ring-shaped member 20 that faces the end surface 32 of the hub 22 is inclined inward in the radial direction as it approaches the return flow path 14 . End surface 32 and surface 54 may be parallel.

In the example shown in FIG. 3, the outermost position P1 of the impeller 6A is located outside the innermost position P2 of the ring-shaped member 20 in the radial direction. Further, assuming that the position where the surface 54 of the ring-shaped member 20 that faces the end surface 32 of the hub 22 and the wall surface portion 34b connect is P3, the outermost position P1 of the impeller 6A is radially smaller than the position P3 in the radial direction. Located on the outside in the direction. In the illustrated example, the position of the tip 56 of the trailing edge 52 is the outermost position P1 of the impeller 6A in the radial direction, and the position closest to the return flow path 14 on the surface 54 is the position of the ring-shaped member 20 in the radial direction. This is the innermost position P2.

(Adjustment method for multistage centrifugal compressor)
FIG. 4 is a flowchart showing an example of a method for adjusting the pressure head in the multistage centrifugal compressor 2. As shown in FIG. This adjustment method may be implemented, for example, when manufacturing a new multistage centrifugal compressor 2, or after disassembling the multistage centrifugal compressor 2 that has already started operation.

As shown in FIG. 4, in S11, the outer diameter of the impeller 6A is changed. In S11, for example, the impeller 6A may be replaced so that the outer diameter of the impeller 6A becomes larger, or the impeller 6A may be processed (for example, by cutting) or replaced so that the outer diameter of the impeller 6A becomes smaller. good.

In S12, the inner diameter of the ring-shaped member 20 is changed. Specifically, the impeller after being changed in S11 so that an appropriate gap is formed between the radially outer end surface 32 of the hub 22 of the impeller 6A and the inner peripheral surface 54 of the ring-shaped member 20. The inner diameter of the ring-shaped member 20 is changed according to the outer diameter of 6A. For example, when increasing the outer diameter of the impeller 6A in S11, the inner peripheral surface 54 of the ring-shaped member 20 may be processed (for example, by cutting) in S12 so that the inner diameter of the ring-shaped member 20 is increased. However, the ring-shaped member 20 may be replaced so that the inner diameter of the ring-shaped member 20 becomes larger. ). Moreover, when reducing the outer diameter of the impeller 6B in S12, the ring-shaped member 20 may be replaced so that the inner diameter of the ring-shaped member 20 becomes smaller (in FIG. 6, the outlet part 53 of the impeller 6A and the ring-shaped member This corresponds to changing the inner circumferential surface 54 of the member 20 from the position indicated by the solid line to the position indicated by the broken line).

In S13, the multistage centrifugal compressor 2 is assembled, including the impeller 6A whose outer diameter has been changed in S11 and the ring-shaped member 20 whose inner diameter has been changed in S12.

(Effects of multistage centrifugal compressor)
The effects of the multistage centrifugal compressor 2 will be described below.
As explained using FIG. 1 etc., in the multistage centrifugal compressor 2, of the pair of wall surfaces 33 and 34 forming the diffuser flow path 10, the wall surface 34 on the hub 22 side of the impeller 6A is annular with the ring-shaped member 20. A ring-shaped member 20 facing the radially outer end surface 32 of the hub 22 is formed separately from the partition wall member 18 . Therefore, when processing or replacing the impeller 6A to change the outer diameter of the impeller 6A, there is a gap between the radially outer end surface 32 of the hub 22 of the impeller 6A and the inner peripheral surface 54 of the ring-shaped member 20. The ring-shaped member 20 can be processed or replaced depending on the outer diameter of the hub 22 of the impeller 6A so that an appropriate gap is formed. Therefore, compared to the case where the wall surface 34 on the hub 22 side of the diffuser flow path 10 is formed only by the annular partition wall member 18, the partition wall member 18 is processed to change the outer diameter of the impeller 6A. Alternatively, there is no need to replace it, and the ring-shaped member 20, which has an outer diameter smaller than that of the partition wall member 18, can be processed or replaced, making it possible to easily change the outer diameter of the impeller 6A. Therefore, the pressure head of the multistage centrifugal compressor 2 can be easily changed to a desired pressure head according to the usage conditions (region, temperature, etc.) of the multistage centrifugal compressor 2.

FIG. 7 is a pressure head-flow characteristic diagram showing the relationship between the pressure head and the volumetric flow rate in the multistage centrifugal compressor 2. In FIG. 7, the broken line graph shows the case where the rotational speed of the multistage centrifugal compressor 2 is changed to α times, β times, and γ times by the speed increasing gear while maintaining the outer diameter D of the impeller 6A at a constant value _D0 . The solid line graph shows the case where the outer diameter D of the impeller 6A is changed from _D0 to _D1 , _D2 , _D3 while maintaining the rotational speed N of the multistage centrifugal compressor 2 at a constant value _N0. ing. Note that D ₀ to D ₃ satisfy D ₃ <D ₀ <D ₁ <D ₂ . In the illustrated example, α<1<β<γ is satisfied.

As shown in FIG. 7, by changing the outer diameter D of the impeller 6A, the pressure characteristics can be changed in the same way as changing the rotation speed N of the multistage centrifugal compressor 2 using a speed increasing gear. In addition, the desired pressure head can be quickly achieved according to the usage conditions (region, temperature, etc.) of the multistage centrifugal compressor 2 without procuring a speed increasing gear to change the rotation speed of the multistage centrifugal compressor 2. This makes it possible to avoid increased costs and longer delivery times due to the procurement of speed increasing gears.

Furthermore, as explained using FIG. 2 and the like, the multistage centrifugal compressor 2 includes the ring-shaped member fixing bolt 36 that fixes the ring-shaped member 20 to the partition wall member 18. It is possible to suppress the shaped member 20 from shifting in the axial direction. Thereby, it is possible to suppress the occurrence of a step on the wall surface 34 on the hub 22 side in the diffuser flow path 10, and to suppress pressure loss caused by the step.

Moreover, as explained using FIG. 2 etc., in the multistage centrifugal compressor 2, the outer end 25 of the ring-shaped member 20 in the radial direction is located inside the front edge 38 of the return vane 23 in the radial direction. Therefore, the outer diameter of the ring-shaped member 20 is smaller compared to the case where the outer end 25 of the ring-shaped member 20 in the radial direction is located on the outer side in the radial direction than the front edge 38 of the return vane 23. 20 can be easily processed or replaced.

Moreover, as explained using FIG. 2 etc., the wall thickness of the partition wall member 18 is not large enough to properly fix the ring-shaped member 20 to the partition wall member 18 using the ring-shaped member fixing bolt 36. Even if the ring-shaped member fixing bolt 36 reaches the inside of the return vane 23, the ring-shaped member 20 can be firmly fixed to the partition wall member 18 and the return vane 23, and the ring-shaped member 20 It is possible to suppress displacement and falling off.

Further, as explained using FIG. 2 and the like, since the surface 34b of the ring-shaped member 20 on the diffuser flow path 10 side and the top surface 36a of the ring-shaped member fixing bolt 36 are flush with each other, the ring-shaped member 20 Compared to the case where a step is provided between the surface 34b on the side of the diffuser flow path 10 and the top surface 36a of the ring-shaped member fixing bolt 36, pressure loss caused by the step can be reduced.

Further, as described using FIG. 2 and the like, the convex portion 50 formed on the surface 49 of the ring-shaped member 20 on the opposite side to the diffuser flow path 10 is connected to the surface 49 of the partition wall member 18 on the side of the diffuser flow path 10. By engaging with the recess 46 formed in the partition wall member, movement of the ring-shaped member 20 in the radial direction is restricted. 18 and from falling off.

Further, as explained using FIG. 2 and the like, by providing the ring-shaped member fixing bolt 36 so as to axially pass through the convex portion 50 that easily ensures a relatively large wall thickness in the ring-shaped member 20, the ring-shaped member Damage to the ring-shaped member 20 caused by the ring-shaped member fixing bolt 36 can be suppressed.

Further, as described using FIG. 3 and the like, the surface 54 of the ring-shaped member 20 that faces the end surface 32 of the hub 22 and the end surface 32 of the hub 22 move inward in the radial direction as they approach the return flow path 14. Since it is inclined toward the front, the distance between the surface 54 and the end surface 32 can be reduced at each position in the axial direction, and pressure loss caused by leakage flow from the gap between the hub 22 and the ring-shaped member 20 can be reduced. The increase can be suppressed.

(Modified example)
The present disclosure is not limited to the embodiments described above, and also includes forms in which modifications are added to the embodiments described above, and forms in which these forms are appropriately combined.
For example, in the example shown in FIG. 2 etc., the ring-shaped member fixing bolt 36 and the vane fixing bolt 42 are fixed to the same return vane 23, but each of the ring-shaped member fixing bolts 36 has a plurality of The vane fixing bolt 42 may be fixed to a return vane 23 among the return vanes 23 in which the vane fixing bolt 42 is not provided. In this case, in the casing 8 shown in FIG. 2, each of the ring-shaped member fixing bolts 36 passes through each of the ring-shaped member 20 and the partition wall member 18, and a plurality of vane fixing bolts 42 among the plurality of return vanes 23 It may also reach the inside of the return vane 23 that is not provided. For example, as shown in FIG. 8, ring-shaped member fixing bolts 36 and vane fixing bolts 42 may be provided alternately on the plurality of return vanes 23 in the circumferential direction. As a result, compared to the case where the ring-shaped member fixing bolt 36 and the vane fixing bolt 42 are provided on the same return vane 23, each bolt is placed around each of the ring-shaped member fixing bolt 36 and the vane fixing bolt 42. It becomes easy to ensure the wall thickness for fixing 36 and 42.

Further, in the example shown in FIG. 2 etc., the top surface 36a of the ring-shaped member fixing bolt 36 and the surface 34b of the ring-shaped member 20 on the side of the diffuser flow path 10 are flush with each other. For example, as shown in FIG. 9, a step g may be formed between the top surface 36a of the ring-shaped member fixing bolt 36 and the surface 34b of the ring-shaped member 20 on the diffuser flow path 10 side. In this case, the multistage centrifugal compressor 2 may include a cover portion 58 that covers the top surface 36a so as to fill at least a portion of the step g. Moreover, the surface 60 of the cover part 58 on the side of the diffuser flow path 10 and the surface 34b of the ring-shaped member 20 on the side of the diffuser flow path 10 may be flush with each other. The cover portion 58 may be, for example, a cap or putty that covers the top surface 36a of the ring-shaped member fixing bolt 36.

Furthermore, each of the casing body 16, the partition wall member 18, and the ring-shaped member 20 may be constituted by a plurality of circumferentially divided bodies (a plurality of circumferentially divided parts). For example, as shown in FIG. 10, the casing body 16 is constructed by connecting a plurality of circumferentially divided bodies (in the illustrated example, two circumferentially divided bodies 16A and 16B). You can leave it there. For example, as shown in FIG. 10, the partition wall member 18 connects a plurality of circumferentially divided bodies (in the illustrated example, two circumferentially divided bodies 18A and 18B). It may be configured by Further, as shown in FIG. 10, for example, the ring-shaped member 20 connects a plurality of divided bodies divided in the circumferential direction (in the illustrated example, two divided bodies 20A and 20B divided in the circumferential direction). It may be configured by In addition, each of the casing main body 16, the partition wall member 18, and the ring-shaped member 20 can be divided into any direction and any number of parts.

Further, in the configuration shown in FIG. 2 and the like, a convex portion 50 is provided on a surface 49 of the ring-shaped member opposite to the diffuser flow path 10, and a convex portion 50 is provided on the surface 44 of the partition wall member 18 on the diffuser flow path 10 side. Although the engaging recesses 46 were provided, the relationship between these recesses and recesses may be reversed. That is, a recess is provided on the surface 49 of the ring-shaped member opposite to the diffuser flow path 10, and a convex portion that engages (fits) with the recess is provided on the surface 44 of the partition wall member 18 on the diffuser flow path 10 side. It may be. This restricts the movement of the ring-shaped member 20 in the radial direction, enables positioning of the ring-shaped member in the radial direction, and suppresses the ring-shaped member 20 from shifting or falling off from the partition wall member 18. Can be done.

Further, in the configuration shown in FIG. 2 etc., the ring-shaped member 20 is fixed to the partition wall member 18 by a plurality of ring-shaped member fixing bolts 36, but the number of ring-shaped member fixing bolts 36 is one. The number may be 2 or more, preferably 2 or more. The multistage centrifugal compressor 2 may not include the ring-shaped member fixing bolts 36, and the ring-shaped member 20 may be fixed to the partition wall member 18 by fixing means other than bolts (for example, welding or press-fitting). .

The contents described in each of the above embodiments can be understood as follows, for example.

(1) A multistage centrifugal compressor (for example, the above-mentioned multistage centrifugal compressor 2) according to at least one embodiment of the present disclosure,
a rotating shaft (for example, the above-mentioned rotating shaft 4); a multi-stage impeller (for example, the above-mentioned multi-stage impeller 6) provided on the rotating shaft;
A casing (for example, the above-mentioned casing 8) that accommodates the multiple stages of impellers;
A multistage centrifugal compressor comprising:
The multi-stage impeller includes a first impeller (for example, the above-mentioned impeller 6A) and a second impeller located at the next stage of the first impeller (for example, the above-mentioned impeller 6B),
The casing is connected to a diffuser flow path (for example, the above-described diffuser flow path 10) that guides the fluid exiting the first impeller to the outside in the radial direction of the rotating shaft, and the diffuser flow path is connected to the downstream side of the diffuser flow path. A folded passageway (for example, the above-mentioned folded passageway 12) that turns the flow direction of the fluid that has passed through the passageway inward in the radial direction; and a folded passageway connected to the downstream side of the folded passageway; forming a return flow path (for example, the above-mentioned return flow path 14) that guides the passed fluid to the inside in the radial direction,
The casing is
a casing body (for example, the casing body 16 described above);
an annular partition wall member (for example, the above-mentioned partition wall member 18) that partitions the diffuser flow path and the return flow path;
It is provided between the radially outer end surface (for example, the above-mentioned end surface 32) of the hub of the first impeller (for example, the above-mentioned hub 22) and the partition wall member so as to face the end surface, and the diffuser flow A ring-shaped member (for example, the above-mentioned ring-shaped member) that forms the hub-side wall surface (for example, the above-mentioned wall surface 34) of the pair of wall surfaces forming the path (for example, the above-mentioned pair of wall surfaces 33 and 34) together with the partition wall member. 20) and
including;
The partition wall member and the ring-shaped member are configured separately.

According to the multistage centrifugal compressor described in (1) above, of the pair of wall surfaces forming the diffuser flow path, the wall surface on the hub side of the first impeller is formed by the ring-shaped member and the annular partition wall member. The ring-shaped member facing the radially outer end surface of the hub is constructed separately from the partition wall member. Therefore, when processing or replacing the first impeller to change the outer diameter of the first impeller, there is an appropriate gap between the radially outer end surface of the hub of the first impeller and the inner peripheral surface of the ring-shaped member. The ring-shaped member can be machined or replaced depending on the outer diameter of the hub of the first impeller so that a suitable gap is formed. For this reason, compared to a case where the wall surface on the hub side of the diffuser flow path is formed only by an annular partition wall member, it is necessary to process or replace the partition wall member in order to change the outer diameter of the first impeller. Since there is no need to process or replace a ring-shaped member having an outer diameter smaller than that of the partition wall member, it becomes possible to easily change the outer diameter of the impeller. Therefore, the pressure head of the multistage centrifugal compressor can be easily changed to a desired pressure head depending on the usage conditions (region, temperature, etc.) of the multistage centrifugal compressor.

(2) In some embodiments, in the multistage centrifugal compressor described in (1) above,
The apparatus further includes a ring-shaped member fixing bolt (for example, the above-mentioned ring-shaped member fixing bolt 36) for fixing the ring-shaped member to the partition wall member.

According to the multistage centrifugal compressor described in (2) above, it is possible to suppress the ring-shaped member from shifting in the axial direction of the rotating shaft with respect to the partition wall member. Thereby, it is possible to suppress the occurrence of a step on the wall surface on the hub side of the diffuser flow path, and to suppress pressure loss caused by the step.

(3) In some embodiments, in the multistage centrifugal compressor described in (1) or (2) above,
Further comprising a return vane (for example, the above-mentioned return vane 23) provided in the return flow path,
The outer end (for example, the above-mentioned outer end 25) of the ring-shaped member in the radial direction is located inside the front edge (for example, the above-mentioned front edge 38) of the return vane in the radial direction.

According to the multistage centrifugal compressor described in (3) above, the outer end of the ring-shaped member in the radial direction is located inside the front edge of the return vane in the radial direction, so that the outer end of the ring-shaped member in the radial direction The outer diameter of the ring-shaped member can be made smaller compared to the case where the end is located radially outward from the front edge of the return vane, so the ring-shaped member can be easily processed or replaced. Can be done.

(4) In some embodiments, in the multistage centrifugal compressor described in (3) above,
a ring-shaped member fixing bolt (for example, the ring-shaped member fixing bolt 36 described above) that fixes the ring-shaped member to the partition wall member;
A vane fixing bolt (for example, the vane fixing bolt 42 described above) fixing the return vane to the casing body,
The ring-shaped member fixing bolt is located inside the vane fixing bolt in the radial direction.

According to the multistage centrifugal compressor described in (4) above, the ring-shaped member can be easily processed or replaced, and interference between the ring-shaped member fixing bolt and the vane fixing bolt can be avoided.

(5) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (4) above,
a ring-shaped member fixing bolt (for example, the ring-shaped member fixing bolt 36 described above) that fixes the ring-shaped member to the partition wall member;
A return vane (for example, the above-mentioned return vane 23) provided in the return flow path,
The ring-shaped member fixing bolt passes through the ring-shaped member and the partition wall member to reach the inside of the return vane.

According to the multi-stage centrifugal compressor described in (5) above, even if the wall thickness of the partition wall member is insufficient to properly fix the ring-shaped member, the ring-shaped member fixing bolt is attached to the return vane. Since the ring-shaped member reaches the inside of the partition wall member and the return vane, the ring-shaped member can be firmly fixed to the partition wall member and the return vane, and falling off of the ring-shaped member can be suppressed.

(6) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (5) above,
A ring-shaped member fixing bolt (for example, the ring-shaped member fixing bolt 36 described above) for fixing the ring-shaped member to the partition wall member,
The surface of the ring-shaped member on the diffuser flow path side (for example, the above-mentioned surface 34b) and the top surface of the ring-shaped member fixing bolt (for example, the above-mentioned top surface 36a) are flush with each other.

According to the multistage centrifugal compressor described in (6) above, compared to the case where a step is provided between the surface of the ring-shaped member on the diffuser flow path side and the top surface of the ring-shaped member fixing bolt, the step is The resulting pressure loss can be reduced.

(7) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (5) above,
A ring-shaped member fixing bolt (for example, the ring-shaped member fixing bolt 36 described above) for fixing the ring-shaped member to the partition wall member,
There is a step (for example, the above-mentioned step g) between the surface of the ring-shaped member on the diffuser flow path side (for example, the above-mentioned surface 34b) and the top surface of the ring-shaped member fixing bolt (for example, the above-mentioned top surface 36a). is formed,
The multistage centrifugal compressor includes a cover portion (for example, the above-mentioned cover portion 58) that covers the top surface so as to fill at least a portion of the step.

According to the multistage centrifugal compressor described in (7) above, the cover portion is provided so as to fill at least a portion of the step between the surface of the ring-shaped member on the diffuser flow path side and the top surface of the ring-shaped member fixing bolt. Therefore, pressure loss caused by the step can be reduced.

(8) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (7) above,
A surface of the ring-shaped member opposite to the diffuser flow path (for example, the above-mentioned surface 49) is an engagement portion that engages with the partition wall member so as to restrict movement of the ring-shaped member in the radial direction. (for example, the above-mentioned convex portion 50).

According to the multistage centrifugal compressor described in (8) above, the engagement portion of the ring-shaped member engages with the partition wall member, thereby enabling positioning of the ring-shaped member in the radial direction and Falling off from the partition wall member can be suppressed.

(9) In some embodiments, in the multistage centrifugal compressor described in (8) above,
The surface of the partition wall member on the diffuser flow path side (for example, the above-mentioned surface 44) includes a recess (for example, the above-mentioned recess 46),
The engaging portion is a protrusion (for example, the above-mentioned protrusion 50) that fits into the recess.

According to the multistage centrifugal compressor described in (9) above, the convex portion formed on the surface of the ring-shaped member opposite to the diffuser flow path is the recess formed on the surface of the partition wall member on the diffuser flow path side. By fitting into the partition wall member, it is possible to suppress the ring-shaped member from falling off from the partition wall member.

(10) In some embodiments, in the multistage centrifugal compressor described in (9) above,
Each of the concave portion and the convex portion is formed in an annular shape so as to extend along the circumferential direction of the rotating shaft.

According to the multistage centrifugal compressor described in (10) above, the annular convex portion formed on the surface of the ring-shaped member opposite to the diffuser flow path is formed on the surface of the partition wall member on the diffuser flow path side. By fitting the ring-shaped member into the annular recess, it is possible to effectively prevent the ring-shaped member from falling off from the partition wall member.

(11) In some embodiments, in the multistage centrifugal compressor described in (9) or (10) above,
A ring-shaped member fixing bolt (for example, the ring-shaped member fixing bolt 36 described above) for fixing the ring-shaped member to the partition wall member,
The ring-shaped member fixing bolt passes through the convex portion in the axial direction of the rotating shaft.

According to the multi-stage centrifugal compressor described in (11) above, the ring-shaped member fixing bolt is provided so as to axially pass through the convex portion where it is easy to ensure a relatively large wall thickness in the ring-shaped member. Damage to the ring-shaped member due to the member fixing bolt can be suppressed.

(12) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (11) above,
In the radial direction, the outermost position (for example, the above-mentioned position P1) of the blades of the impeller (for example, the above-mentioned blade 26) is further outward than the innermost position (for example, the above-mentioned position P2) of the ring-shaped member. To position.

According to the multistage centrifugal compressor described in (12) above, compared to the case where the outermost position of the blade in the radial direction of the impeller is located radially inward than the innermost position of the ring-shaped member, the impeller can increase the outlet pressure.

(13) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (12) above,
A surface of the ring-shaped member that faces the end surface (for example, the inner circumferential surface 54 described above) is inclined inward in the radial direction as it approaches the return flow path.

According to the multistage centrifugal compressor described in (13) above, when the radially outer end face of the hub is similarly inclined (the end face is inclined radially inward as it approaches the return flow path) In this case, the gap between the end face and the surface facing the end face can be reduced at each position in the axial direction, and an increase in pressure loss caused by leakage flow from the gap can be suppressed.

(14) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (13) above,
a plurality of ring-shaped member fixing bolts (for example, the plurality of ring-shaped member fixing bolts 36 described above) that are provided at intervals in the circumferential direction of the rotating shaft and fix the ring-shaped member to the partition wall member;
a plurality of return vanes (for example, the plurality of return vanes 23 described above) provided in the return flow path at intervals in the circumferential direction;
a plurality of vane fixing bolts (for example, the plurality of vane fixing bolts 42 described above) for fixing the plurality of return vanes to the casing body;
Equipped with
Each of the plurality of ring-shaped member fixing bolts passes through the partition wall member and reaches the inside of the return vane where the plurality of vane fixing bolts are not provided among the plurality of return vanes.

According to the multistage centrifugal compressor described in (14) above, compared to the case where the ring-shaped member fixing bolt and the vane fixing bolt are provided on the same return vane, the ring-shaped member fixing bolt and the vane fixing bolt are It is easy to secure enough wall thickness around each bolt to secure each bolt.

(15) In some embodiments, in the multistage centrifugal compressor according to any one of (1) to (14) above,
The ring-shaped member includes a plurality of divided bodies (for example, the plurality of divided bodies described above (for example, the plurality of divided bodies 20A and 20B described above) divided in the circumferential direction of the rotating shaft.

According to the multistage centrifugal compressor described in (15) above, the size of the ring-shaped member can be made smaller compared to the case where the ring-shaped member is integrally formed (one piece). Therefore, the work of attaching the ring-shaped member to the partition wall member and the work of removing the ring-shaped member from the partition wall member are facilitated.

(16) In a method for adjusting a multistage centrifugal compressor (for example, the above-mentioned multistage centrifugal compressor 2) according to at least one embodiment of the present disclosure,
The multistage centrifugal compressor includes:
a rotating shaft (for example, the above-mentioned rotating shaft 4); a multi-stage impeller (for example, the above-mentioned multi-stage impeller 6) provided on the rotating shaft;
A casing (for example, the above-mentioned casing 8) that accommodates the multiple stages of impellers;
A multistage centrifugal compressor comprising:
The multi-stage impeller includes a first impeller (for example, the above-mentioned impeller 6A) and a second impeller located at the next stage of the first impeller (for example, the above-mentioned impeller 6B),
The casing is connected to a diffuser flow path (for example, the above-described diffuser flow path 10) that guides the fluid exiting the first impeller to the outside in the radial direction of the rotating shaft, and the diffuser flow path is connected to the downstream side of the diffuser flow path. A folded passageway (for example, the above-mentioned folded passageway 12) that turns the flow direction of the fluid that has passed through the passageway inward in the radial direction; and a folded passageway connected to the downstream side of the folded passageway; forming a return flow path (for example, the above-mentioned return flow path 14) that guides the passed fluid to the inside in the radial direction,
The casing is
a casing body (for example, the casing body 16 described above);
an annular partition wall member (for example, the above-mentioned partition wall member 18) that partitions the diffuser flow path and the return flow path;
It is provided between the radially outer end surface (for example, the above-mentioned end surface 32) of the hub of the first impeller (for example, the above-mentioned hub 22) and the partition wall member so as to face the end surface, and the diffuser flow A ring-shaped member (for example, the above-mentioned ring-shaped member) that forms the hub-side wall surface (for example, the above-mentioned wall surface 34) of the pair of wall surfaces forming the path (for example, the above-mentioned pair of wall surfaces 33 and 34) together with the partition wall member. 20) and
including;
The partition wall member and the ring-shaped member are configured separately, and the adjustment method includes:
changing the outer diameter of the first impeller;
changing the inner diameter of the ring-shaped member;
including.

In a multistage centrifugal compressor to which the method for adjusting a multistage centrifugal compressor described in (16) above is applied, the wall surface on the hub side of the first impeller among the pair of walls forming the diffuser flow path is connected to the ring-shaped member and the annular member. A ring-shaped member facing the radially outer end surface of the hub is formed separately from the partition wall member. Therefore, when changing the outer diameter of the first impeller by processing or replacing the first impeller, by processing or replacing the ring-shaped member, the inner diameter of the ring-shaped member can be changed according to the outer diameter of the first impeller. By changing, an appropriate gap can be formed between the radially outer end surface of the hub of the first impeller and the inner peripheral surface of the ring-shaped member. For this reason, it is only necessary to process or replace the ring-shaped member with an outer diameter smaller than that of the partition wall member, compared to the case where the wall surface on the hub side of the diffuser flow path is formed only by the annular partition wall member. It becomes possible to easily change the outer diameter of the impeller. Therefore, the pressure head of the multistage centrifugal compressor can be easily changed to a desired pressure head depending on the usage conditions (region, temperature, etc.) of the multistage centrifugal compressor.

2 Multistage centrifugal compressor 4 Rotating shaft 6 (6A, 6B) Impeller 8 Casing 9 Compression channel 10 Diffuser channel 12 Turning channel 14 Return channel 16 Casing body 16A, 16B, 18A, 18B, 20A, 20B Divided body 18 Partition wall member 19 Seal member 20 Ring-shaped member 21 Shroud 22 Hub 23 Return vane 24 Outer circumferential surface 25 Outer end 26 Wing 28 Back surface 30 Hub surface 32 End surface 33, 34, 34b Wall surface 34a, 34b Wall surface portion 44, 49, 54, 60 Surface 36 Ring-shaped member fixing bolt 36a Top surface 38 Front edge 42 Vane fixing bolt 46 Concave portion 48 Plate portion 50 Convex portion 52 Rear edge 53 Outlet portion 54 Inner peripheral surface 56 Tip 58 Cover member 72 Processor 74 RAM
76 ROM
78 HDD
80 Input I/F
82 Output I/F
84 bus

Claims (16)

1. a rotating shaft; a multi-stage impeller provided on the rotating shaft;
   a casing that accommodates the multiple stages of impellers;
   A multistage centrifugal compressor comprising:
   The multi-stage impeller includes a first impeller and a second impeller located at the next stage of the first impeller,
   The casing is connected to a diffuser passage that guides the fluid exiting the first impeller to the outside in the radial direction of the rotating shaft, and a downstream side of the diffuser passage, and is connected to a downstream side of the diffuser passage, so that the fluid that has passed through the diffuser passage flows. A return flow path that turns the direction inward in the radial direction, and a return flow path that is connected to the downstream side of the return flow path and guides the fluid that has passed through the return flow path inward in the radial direction. and
   The casing is
   A casing body;
   an annular partition wall member that partitions the diffuser flow path and the return flow path;
   A wall surface on the hub side of a pair of wall surfaces forming the diffuser flow path, which is provided between the radially outer end surface of the hub of the first impeller and the partition wall member so as to face the end surface. a ring-shaped member formed together with the partition wall member;
   including;
   A multistage centrifugal compressor in which the partition wall member and the ring-shaped member are constructed separately.
2. The multistage centrifugal compressor according to claim 1, further comprising a ring-shaped member fixing bolt that fixes the ring-shaped member to the partition wall member.
3. Further comprising a return vane provided in the return flow path,
   The multistage centrifugal compressor according to claim 1, wherein an outer end of the ring-shaped member in the radial direction is located inside a leading edge of the return vane in the radial direction.
4. a ring-shaped member fixing bolt that fixes the ring-shaped member to the partition wall member;
   Further comprising a vane fixing bolt that fixes the return vane to the casing body,
   The multistage centrifugal compressor according to claim 3, wherein the ring-shaped member fixing bolt is located inside the vane fixing bolt in the radial direction.
5. a ring-shaped member fixing bolt that fixes the ring-shaped member to the partition wall member;
   Further comprising a return vane provided in the return flow path,
   The multistage centrifugal compressor according to claim 1, wherein the ring-shaped member fixing bolt passes through the ring-shaped member and the partition wall member to reach the inside of the return vane.
6. further comprising a ring-shaped member fixing bolt for fixing the ring-shaped member to the partition wall member,
   The multistage centrifugal compressor according to claim 1, wherein a top surface of the ring-shaped member fixing bolt and a surface of the ring-shaped member on the diffuser flow path side are flush with each other.
7. further comprising a ring-shaped member fixing bolt for fixing the ring-shaped member to the partition wall member,
   A step is formed between the surface of the ring-shaped member on the diffuser flow path side and the top surface of the ring-shaped member fixing bolt,
   The multistage centrifugal compressor according to claim 1, further comprising a cover portion that covers the top surface so as to fill at least a portion of the step.
8. According to claim 1, the surface of the ring-shaped member opposite to the diffuser flow path includes an engaging portion that engages with the partition wall member so as to restrict movement of the ring-shaped member in the radial direction. Multi-stage centrifugal compressor as described.
9. A surface of the partition wall member on the diffuser flow path side includes a recess,
   The multistage centrifugal compressor according to claim 8, wherein the engaging portion is a convex portion that fits into the recess.
10. The multistage centrifugal compressor according to claim 9, wherein each of the recessed portion and the convex portion is formed in an annular shape so as to extend along the circumferential direction of the rotating shaft.
11. comprising a ring-shaped member fixing bolt for fixing the ring-shaped member to the partition wall member,
    The multistage centrifugal compressor according to claim 9 or 10, wherein the ring-shaped member fixing bolt passes through the convex portion in the axial direction of the rotating shaft.
12. The multistage centrifugal compressor according to claim 1, wherein in the radial direction, the outermost position of the impeller is located outside the innermost position of the ring-shaped member.
13. The multistage centrifugal compressor according to claim 12, wherein a surface of the ring-shaped member facing the end surface is inclined inward in the radial direction as it approaches the return flow path.
14. a plurality of ring-shaped member fixing bolts that are provided at intervals in the circumferential direction of the rotating shaft and fix the ring-shaped member to the partition wall member;
    a plurality of return vanes provided in the return flow path at intervals in the circumferential direction;
    a plurality of vane fixing bolts for fixing the plurality of return vanes to the casing body;
    Equipped with
    Each of the plurality of ring-shaped member fixing bolts passes through the partition wall member and reaches the inside of the return vane where the plurality of vane fixing bolts are not provided among the plurality of return vanes. The multistage centrifugal compressor according to claim 1.
15. The multistage centrifugal compressor according to claim 1, wherein the ring-shaped member includes a plurality of divided bodies divided in the circumferential direction of the rotating shaft.
16. A method for adjusting a multistage centrifugal compressor, the method comprising:
    The multistage centrifugal compressor includes:
    a rotating shaft; a multi-stage impeller provided on the rotating shaft;
    a casing that accommodates the multiple stages of impellers;
    A multistage centrifugal compressor comprising:
    The multi-stage impeller includes a first impeller and a second impeller located at the next stage of the first impeller,
    The casing is connected to a diffuser passage that guides the fluid exiting the first impeller to the outside in the radial direction of the rotating shaft, and a downstream side of the diffuser passage, and is connected to a downstream side of the diffuser passage, so that the fluid that has passed through the diffuser passage flows. A return flow path that turns the direction inward in the radial direction, and a return flow path that is connected to the downstream side of the return flow path and guides the fluid that has passed through the return flow path inward in the radial direction. and
    The casing is
    A casing body;
    an annular partition wall member that partitions the diffuser flow path and the return flow path;
    A wall surface on the hub side of a pair of wall surfaces forming the diffuser flow path, which is provided between the radially outer end surface of the hub of the first impeller and the partition wall member so as to face the end surface. a ring-shaped member formed together with the partition wall member;
    including;
    The partition wall member and the ring-shaped member are configured separately, and the adjustment method includes:
    changing the outer diameter of the first impeller;
    changing the inner diameter of the ring-shaped member;
    A method of adjusting a multi-stage centrifugal compressor, including:

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