centrifugal compressor

Abstract

To downsize a casing while reducing pressure loss in an intermediate scroll.SOLUTION: A centrifugal compressor comprises a rotating shaft comprising a plurality of impellers, and a casing comprising a suction port, a discharge port, and an intermediate discharge port. The casing comprises a plurality of diaphragms, an outer casing formed in a cylindrical shape, a return flow passage for guiding a flow direction of working fluid discharged from the impellers to the inside in a radial direction, and an intermediate scroll for guiding a portion of the working fluid discharged from the impellers in an intermediate stage to the intermediate discharge port. The intermediate scroll comprises a scroll flow passage formed on a second side in an axial direction with respect to the return flow passage, and an introduction part connecting the return flow passage and the scroll flow passage. An outside flow passage formation surface of the scroll flow passage is formed by a casing inner peripheral surface facing the inside in the radial direction in the outer casing.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to centrifugal compressors. [Background technology]

[0002] A multi-stage centrifugal compressor, which has multiple stages of impellers that compress gas, is known as a type of centrifugal rotating machine. In a multi-stage centrifugal compressor, gas is drawn into a casing through a suction port, compressed sequentially by multiple stages of impellers, and then discharged out of the casing through a discharge port.

[0003] Among such multi-stage centrifugal compressors, a structure having an intermediate discharge port between an inlet port and a discharge port is known. For example, Patent Document 1 discloses a multi-stage centrifugal compressor including: a casing having an inlet port, a discharge port, and an intermediate discharge port; a rotating shaft disposed within the casing and extending in the axial direction; multiple impellers fixed to the rotating shaft; diffusers disposed radially outward of each impeller; and a return passage disposed downstream of the diffusers. This multi-stage centrifugal compressor includes an annular extraction port that extracts a portion of the gas pressurized by the intermediate-stage impeller; and an intermediate scroll (collecting pipe) that collects the extracted gas flow and guides it to the intermediate discharge port. The intermediate scroll is disposed radially outward of a bend at which the diffuser transitions to the return passage, and is located axially between the return passage and the diffuser. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3432674 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the configuration described in Patent Document 1, the intermediate scroll is located radially outward of the bend where the diffuser transitions to the return passage. This leads to an increase in the diameter of the casing, which hinders the miniaturization of the multi-stage centrifugal compressor. On the other hand, if the intermediate scroll is located radially inward of the bend in the return passage, depending on its position, the flow direction of the working fluid discharged from the diffuser may be significantly deflected, resulting in increased pressure loss.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a centrifugal compressor that can reduce the diameter of the casing while suppressing pressure loss in the intermediate scroll. [Means for solving the problem]

[0007] In order to solve the above-described problems, a centrifugal compressor according to the present disclosure includes a rotating shaft extending in an axial direction in which a central axis extends, and a casing having an inlet port formed on a first side in the axial direction, an outlet port formed on a second side in the axial direction, and an intermediate outlet port formed between the inlet port and the outlet port in the axial direction, wherein the rotating shaft has a plurality of impellers arranged apart from each other in the axial direction within the casing, the impellers compressing and discharging a working fluid supplied from the first side in the axial direction toward the outside in a radial direction based on the central axis, the casing including a plurality of diaphragms formed in a cylindrical shape extending in the axial direction so as to cover the impeller, an outer casing formed in a cylindrical shape extending in the axial direction so as to cover the plurality of diaphragms, and a flow direction of the working fluid discharged from the impeller and flowing toward the outside in the radial direction being determined by the radial direction. and an intermediate scroll that guides a portion of the working fluid discharged from an intermediate-stage impeller of the plurality of impellers that is arranged midway in the axial direction to the intermediate discharge port, wherein the intermediate scroll has a scroll passage that is formed on a second side of the return passage in the axial direction, extends in a circumferential direction around the central axis, and is connected to the intermediate discharge port at a portion of the circumferential direction, and an introduction section that connects the return passage and the scroll passage and introduces a portion of the working fluid flowing through the return passage into the scroll passage, wherein an outer passage forming surface located at the outermost side in the radial direction of the scroll passage faces inward in the radial direction of the outer casing and is formed by a casing inner peripheral surface that faces an outer peripheral surface of the diaphragm that faces outward in the radial direction of the diaphragm. the plurality of diaphragms include a first diaphragm arranged on a first side in the axial direction, and a second diaphragm arranged on a second side in the axial direction with respect to the first diaphragm and having a smaller outer diameter in the radial direction than the first diaphragm; the outer casing includes a first cylindrical portion covering the first diaphragm, a second cylindrical portion covering the second diaphragm and having a smaller inner diameter in the radial direction than the first cylindrical portion, and a connecting wall portion formed between the first cylindrical portion and the second cylindrical portion, extending in a direction intersecting the axial direction to connect the first cylindrical portion and the second cylindrical portion; and a second-side flow path forming surface located on the second side in the axial direction in the scroll flow path is formed by an inner wall surface of the connecting wall portion facing the first side in the axial direction. are. [Effects of the Invention]

[0008] According to the centrifugal compressor of the present disclosure, it is possible to reduce the diameter of the casing while suppressing pressure loss in the intermediate scroll. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a centrifugal compressor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the configuration of the periphery of an intermediate scroll of the centrifugal compressor. [Figure 3] FIG. 2 is a cross-sectional view taken along the arrow II in FIG. [Figure 4] FIG. 10 is a cross-sectional view showing a modified example of the introduction portion of the intermediate scroll. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of a centrifugal compressor according to the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to this embodiment.

[0011] (Configuration of centrifugal compressor) 1, the centrifugal compressor 1 in this embodiment is a single-shaft multi-stage centrifugal compressor. The centrifugal compressor 1 mainly includes a rotating shaft 2 that rotates around a central axis O, and a casing 10 formed to surround the rotating shaft 2.

[0012] The rotating shaft 2 extends in the axial direction Da along the central axis O. The rotating shaft 2 extends so as to penetrate the inside of the casing 10 along the central axis O. The rotating shaft 2 has a rotating shaft main body 2A and an impeller 3.

[0013] The rotating shaft body 2A is formed in a cylindrical shape extending in the axial direction Da. An end portion of the rotating shaft body 2A on a first side Da1 in the axial direction Da is supported by a casing 10 by a journal bearing 4A and a thrust bearing 5 so as to be rotatable about a central axis O. An end portion of the rotating shaft body 2A on a second side Da2 in the axial direction Da is supported by a journal bearing 4B so as to be rotatable about the central axis O.

[0014] The impeller 3 is disposed outside the rotating shaft body 2A in a radial direction Dr based on the central axis O. A plurality of impellers 3 are disposed apart from each other in the axial direction Da inside the casing 10. In this embodiment, for example, six impellers 3 are disposed at intervals in the axial direction Da.

[0015] Each impeller 3 includes a disk 3a having a substantially circular cross section when viewed in the axial direction Da, a plurality of blades 3b extending from a first side Da1 of the disk 3a in the axial direction Da, and a shroud 3c covering the plurality of blades 3b from the first side Da1 in the axial direction Da. Each impeller 3 compresses and discharges the working fluid G supplied from the first side Da1 in the axial direction Da to an outer side Dro in the radial direction Dr. As shown in FIG. 2 , each impeller 3 has a compression flow passage 33 formed therein. The compression flow passage 33 is surrounded by the surface of the first side Da1 of the disk 3a in the axial direction Da, the surface of the second side Da2 of the shroud 3c in the axial direction Da, and a pair of circumferentially adjacent blades 3b. The cross-sectional area of ​​the compression flow passage 33 gradually decreases from the inner side Dri in the radial direction Dr to the outer side Dro in the radial direction Dr. As a result, while the impeller 3 is rotating, the working fluid G flowing through the compression passage 33 is gradually compressed to a high pressure. As shown in Fig. 1, each impeller 3 constitutes a compression stage in the centrifugal compressor 1. The centrifugal compressor 1 has a total of six stages, namely, a first compression stage P1 to a sixth compression stage P6. Note that each impeller 3 may be an open impeller without a shroud.

[0016] The casing 10 is formed to surround the rotating shaft main body 2A and the multiple impellers 3 from the outer side Dro in the radial direction Dr. The casing 10 includes an outer casing 11, a suction port 12, a discharge port 13, an intermediate discharge port 14, multiple diaphragms 20, a first casing head 7A, and a second casing head 7B.

[0017] The outer casing 11 is formed in a cylindrical shape extending in the axial direction Da. The outer casing 11 is formed to cover the rotating shaft 2 and the plurality of diaphragms 20 from the outer side Dro in the radial direction Dr. The outer casing 11 forms an intake port 12, a discharge port 13, and an intermediate discharge port 14.

[0018] The suction port 12 is formed on a first side Da1 in the axial direction Da of the outer casing 11. The suction port 12 allows the working fluid G to flow into the outer casing 11 from the outside.

[0019] The discharge port 13 is formed on the second side Da2 in the axial direction Da of the outer casing 11. The discharge port 13 discharges the working fluid G compressed through the impellers 3 of all of the compression stages P1 to P6 inside the outer casing 11 to the outside of the outer casing 11. In other words, the discharge port 13 is disposed away from the suction port 12 on the second side Da2 in the axial direction Da.

[0020] The intermediate discharge port 14 is formed between the suction port 12 and the discharge port 13 in the axial direction Da. The intermediate discharge port 14 is formed at a position separated in the axial direction Da from the suction port 12 and the discharge port 13. As will be described in detail later, the intermediate discharge port 14 discharges the working fluid G compressed through the impellers 3 of some of the compression stages P1 to P6 out of the outer casing 11. The intermediate discharge port 14 of this embodiment discharges the working fluid G compressed through the impellers 3 of some of the compression stages P1 to P3 on the first side Da1 in the axial direction Da out of the outer casing 11. The pressure of the working fluid G discharged from the intermediate discharge port 14 is lower than the pressure of the working fluid G compressed by all of the impellers 3 and discharged from the discharge port 13.

[0021] The multiple diaphragms 20 are arranged on the inner side Dri in the radial direction Dr of the outer casing 11. The multiple diaphragms 20 are formed as a whole in a cylindrical shape extending in the axial direction Da so as to cover the impellers 3 of each stage. Each diaphragm 20 is formed in a disk shape centered on the central axis O. The multiple diaphragms 20 cover the periphery of the rotary shaft 2 to form a casing flow path 30 connecting the multiple impellers 3.

[0022] In this embodiment, the plurality of diaphragms 20 includes a first diaphragm 21 disposed on a first side Da1 in the axial direction Da, and a second diaphragm 22 disposed on a second side Da2 in the axial direction Da relative to the first diaphragm 21. The second diaphragm 22 has a smaller outer diameter in the radial direction Dr than the first diaphragm 21. In this embodiment, of the six compression stages P1 to P6, the plurality (three) of diaphragms 20 covering the impellers 3 of the first compression stage P1 to the third compression stage P3 are constituted by at least the first diaphragm 21. The plurality (two) of diaphragms covering the impellers 3 of the fifth compression stage P5 to the sixth compression stage P6 are constituted by at least the second diaphragm 22.

[0023] In each of the compression stages P1 to P6, the diaphragms 20 have, as the casing flow passage 30, an introduction flow passage 31, a curved flow passage 32, a diffuser flow passage 34, and a return flow passage 35, as shown in FIG.

[0024] The introduction flow path 31 guides the working fluid G from the outer side Dro in the radial direction Dr toward the inner side Dri in the radial direction Dr. The introduction flow path 31 guides the working fluid G toward the inner side Dri in the radial direction Dr to the impeller 3 via the curved flow path 32.

[0025] The curved passage 32 is connected to an inner side Dri in the radial direction Dr, which is the downstream side of the inlet passage 31. The curved passage 32 extends from a position where it connects with the inlet passage 31 so as to curve toward the second side Da2 in the axial direction Da. This changes the flow of the working fluid G from the inlet passage 31 toward the inner side Dri in the radial direction Dr to a flow toward the second side Da2 in the axial direction Da. In this way, the curved passage 32 deflects the working fluid G flowing from the inlet passage 31 toward the second side Da2 in the axial direction Da and guides it to the compression passage 33 of the impeller 3. In other words, the curved passage 32 is connected to the compression passage 33. The compression passage 33 is connected to the second side Da2 in the axial direction Da, which is the downstream side of the curved passage 32. The compression passage 33 extends from a position where it connects with the curved passage 32 so as to curve toward an outer side Dro in the radial direction Dr.

[0026] The diffuser passage 34 extends from the inner side Dri to the outer side Dro in the radial direction Dr. An end of the diffuser passage 34 on the inner side Dri in the radial direction Dr is connected to an end of the compression passage 33 on the outer side Dro in the radial direction Dr. The diffuser passage 34 guides the working fluid G compressed by the impeller 3 from the inner side Dri in the radial direction Dr to the outer side Dro in the radial direction Dr.

[0027] The return flow passage 35 reverses the flow direction of the working fluid G that has passed through the diffuser flow passage 34 and flowed from the inner side Dri in the radial direction Dr to the outer side Dro in the radial direction Dr. The return flow passage 35 guides the working fluid G flowing toward the outer side Dro in the radial direction Dr to the inner side Dri in the radial direction Dr. One end of the return flow passage 35 (a first side Da1 in the axial direction Da) that is upstream in the flow direction of the working fluid G is connected to the diffuser flow passage 34. The other end of the return flow passage 35 (a second side Da2 in the axial direction Da) that is downstream in the flow direction of the working fluid G is connected to the subsequent introduction flow passage 31.

[0028] Furthermore, the outer casing 11 has a first cylindrical portion 111 , a second cylindrical portion 112 , and a connecting wall portion 113 .

[0029] The first cylindrical portion 111 forms a region of a first side Da1 in the axial direction Da of the outer casing 11. The first cylindrical portion 111 is formed so as to cover the first diaphragm 21 from the outer side Dro in the radial direction Dr. The first cylindrical portion 111 extends in the axial direction Da while maintaining a constant inner diameter.

[0030] The second cylindrical portion 112 is formed on the second side Da2 in the axial direction Da with respect to the first cylindrical portion 111. That is, the second cylindrical portion 112 forms a region of the outer casing 11 on the second side Da2 in the axial direction Da. The second cylindrical portion 112 is formed so as to cover the second diaphragm 22 from the outside Dro in the radial direction Dr. The second cylindrical portion 112 has a smaller inner diameter in the radial direction Dr than the first cylindrical portion 111. The second cylindrical portion 112 extends in the axial direction Da while maintaining a constant inner diameter.

[0031] The connecting wall 113 is formed between the first cylindrical portion 111 and the second cylindrical portion 112. The connecting wall 113 connects the first cylindrical portion 111 and the second cylindrical portion 112 in the radial direction Dr. The connecting wall 113 expands so as to extend in a direction perpendicular to (intersecting with) the axial direction Da. When viewed from the axial direction Da, the connecting wall 113 of this embodiment is formed in the shape of a disk expanding in the radial direction Dr perpendicular to the axial direction Da.

[0032] As shown in FIG. 1 , the first casing head 7A is disposed so as to close an opening on a first side Da1 in the axial direction Da of the outer casing 11. That is, the first casing head 7A is disposed adjacent to the first side Da1 of the multiple diaphragms 20 in the axial direction Da. An suction scroll 9A that takes in an external working fluid G into a casing flow path 30 through an suction port 12 is formed between the first casing head 7A and a diaphragm 20A, which is disposed furthest to the first side Da1 in the axial direction Da, among the multiple diaphragms 20. The suction scroll 9A connects the suction port 12 and the casing flow path 30. The suction scroll 9A is continuous in the circumferential direction Dc and has a spiral shape whose cross-sectional area gradually decreases from the suction port 12 toward the casing flow path 30.

[0033] The second casing head 7B is disposed so as to close an opening on the second side Da2 in the axial direction Da of the outer casing 11. That is, the second casing head 7B is disposed adjacent to the second side Da2 in the axial direction Da with respect to the plurality of diaphragms 20. A discharge scroll 9B that discharges the working fluid G to the outside through a discharge port 13 is formed between the second casing head 7B and a diaphragm 20B, among the plurality of diaphragms 20, that is disposed furthest to the second side Da2 in the axial direction Da. The discharge scroll 9B connects the discharge port 13 to the casing flow path 30. The discharge scroll 9B is formed in a spiral shape that is continuous in the circumferential direction Dc and whose cross-sectional area gradually expands from the casing flow path 30 toward the discharge port 13.

[0034] Furthermore, the centrifugal compressor 1 has an intermediate scroll 50 in a middle portion in the axial direction Da. The intermediate scroll 50 guides a portion of the working fluid G discharged from an intermediate-stage impeller 3, among the multiple impellers 3, arranged midway in the axial direction Da, to the intermediate discharge port 14. In this embodiment, the intermediate scroll 50 is arranged between the third compression stage P3 and the fourth compression stage P4. That is, the intermediate scroll 50 guides a portion of the working fluid G discharged from the impeller 3 of the third compression stage P3 to the intermediate discharge port 14. The intermediate scroll 50 is arranged on the inner side Dri in the radial direction Dr of the first cylindrical portion 111 of the outer casing 11. The intermediate scroll 50 includes a scroll flow path 51 and an introduction portion 52.

[0035] As shown in FIG. 2, the scroll passage 51 is formed on a second side Da2 in the axial direction Da with respect to the return passage 35C. The scroll passage 51 is disposed on the inner side Dri in the radial direction Dr with respect to an end 111s of the first cylindrical portion 111 on the second side Da2 in the axial direction Da. As shown in FIG. 3, the scroll passage 51 is formed in a spiral shape in a circumferential direction Dc about the central axis O. The scroll passage 51 is formed so that its cross-sectional area gradually increases toward one side Dc1 in the circumferential direction Dc. The scroll passage 51 is connected to the intermediate discharge port 14 at a portion in the circumferential direction Dc.

[0036] The scroll passage 51 is formed on the outer side in the radial direction Dr of the diaphragm 20C arranged between the third compression stage P3 and the fourth compression stage P4. In the scroll passage 51, an inner passage-forming surface 514 located at the innermost position in the radial direction Dr is formed by the diaphragm outer peripheral surface 20f of the diaphragm 20C facing the outer side Dro in the radial direction Dr. The inner passage-forming surface 514 is the surface of the scroll passage 51 facing the outer side Dro in the radial direction Dr.

[0037] In the scroll flow passage 51, an outer flow-passage-forming surface 512 located outermost in the radial direction Dr is formed by a casing inner circumferential surface 108 facing the inner side Dri in the radial direction Dr in the first cylindrical portion 111 of the outer casing 11. The casing inner circumferential surface 108 faces the diaphragm outer circumferential surface 20f of the diaphragm 20C in the radial direction Dr. The outer flow-passage-forming surface 512 is a surface in the scroll flow passage 51 facing the inner side Dri in the radial direction Dr.

[0038] 2, a second-side flow-path forming surface 516 located on the second side Da2 in the axial direction Da in the scroll flow path 51 is formed by an inner wall surface 113f facing the first side Da1 in the axial direction Da in the connecting wall portion 113. The second-side flow-path forming surface 516 is a surface of the scroll flow path 51 facing the first side Da1 in the axial direction Da.

[0039] The diaphragm 20C forming the scroll passage 51 includes an extension portion 205 that separates the scroll passage 51 from the return passage 35C in the axial direction Da. The extension portion 205 extends from a first side Da1 in the axial direction Da of the inner passage-forming surface 514 to an outer side Dro in the radial direction Dr. In the scroll passage 51, a first-side passage-forming surface 518 located on the first side Da1 in the axial direction Da is formed by an extension wall surface 205f in the extension portion 205 that faces a second side Da2 in the axial direction Da. The first-side passage-forming surface 518 is a surface of the scroll passage 51 that faces the second side Da2 in the axial direction Da.

[0040] The introduction section 52 connects the return passage 35C and the scroll passage 51. The introduction section 52 introduces a portion of the working fluid G flowing through the return passage 35C into the scroll passage 51. The introduction section 52 extends straight in the axial direction Da from the maximum diameter portion 35m, which is the outermost portion in the radial direction Dr, in the return passage 35C. The introduction section 52 is formed on the outer side Dro in the radial direction Dr of the extension section 205. In this embodiment, at least a portion of an introduction section outer passage forming surface 521, which is located outermost in the radial direction Dr in the introduction section 52, is formed by the casing inner circumferential surface 108.

[0041] The flow path cross-sectional area of ​​the introduction section 52 when viewed from the axial direction Da (or the flow path width in the radial direction Dr of the introduction section 52 when viewed from the circumferential direction Dc) may be appropriately set based on the ratio between the flow rate of the working fluid G to be supplied to the scroll flow path 51 and the flow rate supplied from the return flow path 35 to the next introduction flow path 31 (supplied to the next impeller 3).

[0042] At least a part of a flow passage inner surface 351 that forms the maximum diameter portion 35m of the return flow passage 35 is formed by the casing inner circumferential surface 108. That is, the position of the maximum diameter portion 35m of the return flow passage 35 in the radial direction Dr is the same as the position of the outer flow passage forming surface 512 that is the outermost part Dro in the radial direction Dr of the scroll flow passage 51.

[0043] In the intermediate scroll 50, a portion of the working fluid G, the pressure of which has increased by passing through the first compression stage P1 to the third compression stage P3, flows from the return passage 35C through the introduction section 52 into the scroll passage 51. The working fluid G flows along the scroll passage 51 toward one side Dc1 in the circumferential direction Dc and is discharged from the intermediate discharge port 14 to the outside.

[0044] (Action and effect) The centrifugal compressor 1 having the above configuration includes an intermediate scroll 50 that guides a portion of the working fluid G discharged from the intermediate-stage impeller 3 to the intermediate discharge port 14. In the scroll passage 51 of the intermediate scroll 50, an outer passage-forming surface 512 located outermost in the radial direction Dr is formed by the casing inner circumferential surface 108. Furthermore, the casing inner circumferential surface 108 faces the inner side Dri in the radial direction Dr of the outer casing 11 so as to face the diaphragm outer circumferential surface 20f of the diaphragm 20 that faces the outer side Dro in the radial direction Dr. In other words, the region of the scroll passage 51 on the outer side Dro in the radial direction Dr is formed by the outer casing 11, not the diaphragm 20. Therefore, it is not necessary to increase the size of the diaphragm 20 in the radial direction Dr just to form the scroll passage 51, and the size of the diaphragm 20 can be reduced. Furthermore, because the outer flow passage forming surface 512 is the casing inner peripheral surface 108 facing the diaphragm outer peripheral surface 20f, the outer flow passage forming surface 512 is formed at the innermost portion Dri in the radial direction Dr of the outer casing 11 that is closest to the diaphragm 20. Therefore, the scroll flow passage 51 can be formed as large as possible in the radial direction Dr while reducing the size of the diaphragm 20. Therefore, the diameter of the casing 10 can be reduced while ensuring the performance of the intermediate scroll 50. Furthermore, the outer casing 11 can sufficiently ensure the pressure resistance of the scroll flow passage 51.

[0045] Furthermore, the scroll passage 51 is formed on the second side Da2 in the axial direction Da with respect to the return passage 35C. Therefore, the introduction portion 52 discharges the working fluid G from the return passage 35C toward the second side Da2 in the axial direction Da toward the scroll passage 51. Therefore, by utilizing the inertia of the flow of the working fluid G flowing through the return passage 35C, the working fluid G can be smoothly flowed from the introduction portion 52 into the scroll passage 51. This makes it possible to reduce the pressure loss of the working fluid G when it flows into the intermediate scroll 50. Therefore, it is possible to reduce the diameter of the casing 10 while reducing the pressure loss in the intermediate scroll 50.

[0046] The outer casing 11 includes a first cylindrical portion 111 that covers the first diaphragm 21 and a second cylindrical portion 112 that covers the second diaphragm 22, which has a smaller outer diameter in the radial direction Dr than the first diaphragm 21. A connecting wall portion 113 is formed between the first cylindrical portion 111 and the second cylindrical portion 112. Furthermore, a second-side passage-forming surface 516 of the scroll passage 51 is formed by an inner wall surface 113f of the connecting wall portion 113 that faces the first side Da1 in the axial direction Da. That is, the region of the second side Da2 in the axial direction Da of the scroll passage 51 is formed not by the diaphragm 20 but by the connecting wall portion 113, which is a part of the outer casing 11. Therefore, it is not necessary to increase the size of the diaphragm 20 in the axial direction Da just to form the scroll passage 51, and the size of the diaphragm 20 can be reduced. This allows the casing 10 to be made smaller in the axial direction Da.

[0047] Furthermore, the introduction portion 52 of the intermediate scroll 50 extends in the axial direction Da from the maximum diameter portion 35m of the return passage 35. The working fluid G flowing through the return passage 35 flows to gather at the outer side Dro in the radial direction Dr due to centrifugal force. However, in this embodiment, the introduction portion 52 extends in the axial direction Da from the maximum diameter portion 35m of the return passage 35. As a result, the working fluid G flowing along the outer side Dro in the radial direction Dr of the return passage 35 flows from the maximum diameter portion 35m of the return passage 35 into the introduction portion 52 while maintaining the momentum of the working fluid G flowing through the return passage 35. This reduces the dynamic pressure of the working fluid G when it flows into the introduction portion 52. Furthermore, at least a portion of the introduction portion outer flow-path forming surface 521 of the introduction portion 52 is formed by the casing inner peripheral surface 108. As a result, the surface of the outer side Dro in the radial direction Dr that defines the introduction portion 52 extends straight in the axial direction Da. Therefore, it is possible to suppress the dynamic pressure of the working fluid G flowing inside the introduction portion 52. Therefore, it is possible to suppress the pressure loss in the introduction portion 52 and reduce the pressure loss in the intermediate scroll 50.

[0048] Furthermore, at least a portion of the flow passage inner surface 351 of the maximum diameter portion 35m of the return flow passage 35 is formed by the casing inner circumferential surface 108. In other words, the flow passage inner surface 351 of the maximum diameter portion 35m of the return flow passage 35 and the introduction-portion-outer flow passage forming surface 521 of the introduction portion 52 are formed by the same surface. This further reduces the dynamic pressure of the working fluid G when it flows from the return flow passage 35 into the introduction portion 52. Therefore, pressure loss in the introduction portion 52 can be reduced, and pressure loss in the intermediate scroll 50 can be further reduced.

[0049] Furthermore, the scroll passage 51 has an inner passage-forming surface 514 formed by the diaphragm outer peripheral surface 20f of the diaphragm 20C. Therefore, in a region overlapping with the position where the scroll passage 51 is formed in the axial direction Da, the diaphragm 20C does not need to expand in the radial direction Dr to the same position as the casing inner peripheral surface 108, as long as it has an outer diameter in the radial direction Dr that corresponds to the position where the inner passage-forming surface 514 of the scroll passage 51 is formed. Therefore, the size of the radial direction Dr of the diaphragm 20C at the position where the scroll passage 51 is formed can be reduced.

[0050] (Modification of the first embodiment) In the first embodiment, the introduction section 52 is provided, but the introduction section 52 can also be configured as shown below, for example.

[0051] As shown in Fig. 4, the introduction portion 52B of the intermediate scroll 50B is formed between a tip end 205s of an extension portion 205 formed in the diaphragm 20C and the casing inner circumferential surface 108 of the first cylindrical portion 111 of the outer casing 11. In this modification, the tip end 205s of the extension portion 205 is formed to have a shorter length in the axial direction Da than the configuration in Fig. 2 of the above embodiment. In this modification, the tip end 205s is formed only by a curved surface 205w that protrudes toward the outer side Dro in the radial direction Dr.

[0052] In this case, an inlet-portion-inner-flow-path-forming surface 524 located at the innermost position in the radial direction Dr in the inlet portion 52B is a curved surface 205w formed at the tip end 205s of the extension portion 205 when viewed from the circumferential direction Dc.

[0053] Even in this configuration, the curved surface 205w can form the introduction-portion-inner-flow-path-forming surface 524 of the introduction portion 52B. This allows the working fluid G introduced from the return flow path 35 to the scroll flow path 51 to flow smoothly along the curved surface 205w, thereby reducing pressure loss at the inner side Dri of the introduction portion 52B in the radial direction Dr.

[0054] (Other embodiments) The above describes in detail the embodiments of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure.

[0055] In the above embodiment, the outer casing 11 includes the first cylindrical portion 111, the second cylindrical portion 112, and the connecting wall portion 113, and the second-side passage-forming surface 516 of the scroll passage 51 is formed by the inner wall surface 113f of the connecting wall portion 113, but the present invention is not limited to this. For example, if the outer casing 11 is formed to have a constant outer diameter over the entire length in the axial direction Da, the second-side passage-forming surface 516 of the scroll passage 51 may be formed by another diaphragm located on the second side Da2 in the axial direction Da.

[0056] <Additional Notes> The centrifugal compressor 1 described in each embodiment can be understood, for example, as follows.

[0057] (1) A centrifugal compressor 1 according to a first aspect includes a rotating shaft 2 extending in an axial direction Da in which a central axis O extends, and a casing 10 having an intake port 12 formed on a first side Da1 in the axial direction Da, an exhaust port 13 formed on a second side Da2 in the axial direction Da, and an intermediate exhaust port 14 formed between the intake port 12 and the exhaust port 13 in the axial direction Da, and the rotating shaft 2 is arranged in the casing 10 at a distance from each other in the axial direction Da, and a flow of air is supplied from the first side Da1 in the axial direction Da. The casing 10 includes an impeller 3 that compresses and discharges the working fluid G discharged from the impeller 3 toward the outside Dro in a radial direction Dr based on the central axis O, and the casing 10 includes a plurality of diaphragms 20 formed in a cylindrical shape extending in the axial direction Da so as to cover the impeller 3, an outer casing 11 formed in a cylindrical shape extending in the axial direction Da so as to cover the plurality of diaphragms 20, and a casing 11 that controls the flow direction of the working fluid G discharged from the impeller 3 and flowing toward the outside Dro in the radial direction Dr from the inside Dro in the radial direction Dr. and an intermediate scroll 50 that guides a part of the working fluid G discharged from an intermediate-stage impeller 3 of the plurality of impellers 3 that is arranged midway in the axial direction Da to the intermediate discharge port 14, the intermediate scroll 50 having a scroll passage 51 that is formed on a second side Da2 in the axial direction Da with respect to the return passage 35, extends in a circumferential direction Dc around the central axis O, and is connected to the intermediate discharge port 14 at a part of the circumferential direction Dc. and an inlet portion 52 that connects the scroll flow path 51 to the scroll flow path 51 and introduces a portion of the working fluid G flowing through the return flow path 35 into the scroll flow path 51, and in the scroll flow path 51, an outer flow path forming surface 512 located outermost in the radial direction Dr is formed by a casing inner peripheral surface 108 that faces the inner side Dri of the radial direction Dr in the outer casing 11 and faces the outer side Dro of the radial direction Dr in the diaphragm 20C.

[0058] As a result, the outer region Dro of the scroll passage 51 in the radial direction Dr is formed by the outer casing 11, not the diaphragm 20. Therefore, it is not necessary to increase the size of the diaphragm 20 in the radial direction Dr just to form the scroll passage 51, and the size of the diaphragm 20 can be reduced. Furthermore, because the outer passage-forming surface 512 is the casing inner peripheral surface 108 facing the diaphragm outer peripheral surface 20f, the outer passage-forming surface 512 is formed at the innermost portion Dri in the radial direction Dr of the outer casing 11 that is closest to the diaphragm 20. Therefore, it is possible to reduce the size of the diaphragm 20 and maximize the size of the scroll passage 51 in the radial direction Dr. This allows the diameter of the casing 10 to be reduced while ensuring the performance of the intermediate scroll 50. Furthermore, the outer casing 11 allows the pressure-resistant performance of the scroll passage 51 to be sufficiently ensured.

[0059] Furthermore, the scroll passage 51 is formed on the second side Da2 in the axial direction Da with respect to the return passage 35C. Therefore, the introduction portion 52 discharges the working fluid G from the return passage 35C toward the second side Da2 in the axial direction Da toward the scroll passage 51. Therefore, by utilizing the inertia of the flow of the working fluid G flowing through the return passage 35C, the working fluid G can be smoothly flowed from the introduction portion 52 into the scroll passage 51. This makes it possible to reduce the pressure loss of the working fluid G when it flows into the intermediate scroll 50. Therefore, it is possible to reduce the diameter of the casing 10 while reducing the pressure loss in the intermediate scroll 50.

[0060] (2) A centrifugal compressor 1 according to a second aspect is the centrifugal compressor 1 of (1), wherein the plurality of diaphragms 20 include a first diaphragm 21 arranged on a first side Da1 in the axial direction Da and a second diaphragm 22 arranged on a second side Da2 in the axial direction Da relative to the first diaphragm 21 and having a smaller outer diameter in the radial direction Dr than the first diaphragm 21, and the casing 10 includes a first cylindrical portion 111 covering the first diaphragm 21 and a second cylindrical portion 112 covering the second diaphragm 22 and The scroll flow passage 51 has a second cylindrical portion 112 having an inner diameter in the radial direction Dr smaller than that of the first cylindrical portion 111, and a connecting wall portion 113 formed between the first cylindrical portion 111 and the second cylindrical portion 112, extending in a direction intersecting the axial direction Da to connect the first cylindrical portion 111 and the second cylindrical portion 112, and a second side flow passage forming surface 516 located on the second side Da2 in the axial direction Da in the scroll flow passage 51 is formed by an inner wall surface 113f of the connecting wall portion 113 facing the first side Da1 in the axial direction Da.

[0061] As a result, the region of the second side Da2 in the axial direction Da of the scroll passage 51 is formed not by the diaphragm 20 but by the connecting wall portion 113 that is part of the outer casing 11. Therefore, it is not necessary to increase the size of the diaphragm 20 in the axial direction Da just to form the scroll passage 51, and it is possible to reduce the size of the diaphragm 20. This makes it possible to reduce the size of the casing 10 in the axial direction Da.

[0062] (3) A centrifugal compressor 1 according to a third aspect is the centrifugal compressor 1 of (1) or (2), wherein the inlet portion 52 extends in the axial direction Da from the outermost maximum diameter portion 35m in the radial direction Dr in the return flow passage 35, and at least a portion of the inlet portion outer flow passage forming surface 521 located outermost in the radial direction Dr is formed by the casing inner peripheral surface 108.

[0063] The working fluid G flowing through the return passage 35 flows to gather at the outer side Dro in the radial direction Dr due to centrifugal force. However, the introduction section 52 extends in the axial direction Da from the maximum diameter portion 35m of the return passage 35. As a result, the working fluid G flowing at the outer side Dro in the radial direction Dr of the return passage 35 flows from the maximum diameter portion 35m of the return passage 35 into the introduction section 52 while maintaining the momentum of the working fluid G flowing through the return passage 35. Therefore, the dynamic pressure of the working fluid G when it flows into the introduction section 52 is suppressed. Furthermore, at least a portion of the introduction section outer flow-path forming surface 521 of the introduction section 52 is formed by the casing inner peripheral surface 108. As a result, the surface of the outer side Dro in the radial direction Dr that defines the introduction section 52 extends straight in the axial direction Da. Therefore, the dynamic pressure of the working fluid G flowing through the introduction section 52 can be suppressed. Therefore, the pressure loss in the introduction section 52 can be suppressed, and the pressure loss in the intermediate scroll 50 can be reduced.

[0064] (4) The centrifugal compressor 1 according to the fourth aspect is the centrifugal compressor 1 of (3), in which at least a portion of the flow path inner surface 351 of the maximum diameter portion 35m of the return flow path 35 is formed by the casing inner surface 108.

[0065] As a result, the flow passage inner surface 351 of the maximum diameter portion 35m of the return flow passage 35 and the introduction portion outer flow passage forming surface 521 of the introduction portion 52 are formed by the same surface. This further reduces the dynamic pressure of the working fluid G when it flows from the return flow passage 35 into the introduction portion 52. Therefore, the pressure loss in the introduction portion 52 can be reduced, and the pressure loss in the intermediate scroll 50 can be further reduced.

[0066] (5) The centrifugal compressor 1 according to the fifth aspect is any one of the centrifugal compressors 1 according to (1) to (4), in which the inner flow path forming surface 514 located at the innermost position in the radial direction Dr in the scroll flow path 51 is formed by the diaphragm 20C.

[0067] As a result, in a region of the diaphragm 20C that overlaps with the position where the scroll flow passage 51 is formed in the axial direction Da, the diaphragm 20C does not need to expand in the radial direction Dr to the same position as the casing inner circumferential surface 108, as long as it has an outer diameter in the radial direction Dr that corresponds to the position where the inner flow-passage forming surface 514 of the scroll flow passage 51 is formed. Therefore, the size of the radial direction Dr of the diaphragm 20C at the position where the scroll flow passage 51 is formed can be reduced.

[0068] (6) A centrifugal compressor 1 according to a sixth aspect is any one of the centrifugal compressors 1 of (1) to (5), wherein the diaphragm 20C has an extension portion 205 that extends on a first side Da1 in the axial direction Da with respect to the scroll passage 51 to an outer side Dro in the radial direction Dr and separates the return passage 35 from the scroll passage 51 in the axial direction Da, and an inlet-portion-inner-passage-forming surface 524 that is located at the innermost position in the radial direction Dr in the inlet portion 52B is a curved surface 205w that is formed at a tip end 205s of the outer side Dro in the radial direction Dr of the extension portion 205 when viewed from the circumferential direction Dc and that protrudes toward the outer side Dro in the radial direction Dr.

[0069] As a result, the curved surface 205w can form an introduction-portion-inside-flow-path-forming surface 524 of the introduction portion 52B. As a result, the working fluid G introduced from the return flow path 35 to the scroll flow path 51 flows smoothly along the curved surface 205w, and pressure loss at the inner side Dri of the introduction portion 52B in the radial direction Dr can be reduced. [Explanation of symbols]

[0070] 1...Centrifugal compressor 2...Rotation axis 2A...Rotating shaft body 3...Impeller 3a...Disc 3b...Blade 3c…Shroud 4A, 4B...Journal bearings 5...Thrust bearing 7A...First casing head 7B...Second casing head 9A...Suction scroll 9B...Discharge scroll 10...Casing 11...Outer casing 111...First cylindrical portion 111s...end 112...Second cylindrical part 113...Connecting wall 113f...inner wall 12...Intake port 13…Discharge port 14…Intermediate discharge port 20, 20A, 20B, 20C...Diaphragm 20f...Outer surface of diaphragm 205...Extension part 205th floor: Extension wall 205s...Tip 205w...curved surface 21...First diaphragm 22...Second diaphragm 30...Casing flow path 31...Inlet channel 32...Bent channel 33...Compression channel 34...Diffuser flow path 35, 35C...Return flow path 351...Inner surface of flow path 35m…Maximum diameter part 50, 50B...Middle scroll 51...Scroll flow path 52, 52B...Introduction 108...Inner surface of casing 512...Outer flow path forming surface 514...Inner flow path forming surface 516…Second side flow path forming surface 518...First side flow path forming surface 521...Introduction part outer flow path forming surface 524…Inner flow path forming surface of introduction part Da…Axis direction Da1…first side Da2…Second side Dc…Circumferential direction Dc1...one side Dr…Radial direction Dri…inside Dro...outside G…Working fluid O…Central axis P1~P6...Compression stage

Claims

1. a rotation axis extending in the axial direction of the central axis; a casing having an intake port formed on a first side in the axial direction, an exhaust port formed on a second side in the axial direction, and an intermediate exhaust port formed between the intake port and the exhaust port in the axial direction, the rotating shaft has a plurality of impellers arranged at intervals in the axial direction within the casing, the impellers compressing and discharging the working fluid supplied from a first side in the axial direction outward in a radial direction relative to the central axis, The casing comprises: a plurality of diaphragms formed in a cylindrical shape extending in the axial direction so as to cover the impeller; an outer casing formed in a cylindrical shape extending in the axial direction so as to cover the plurality of diaphragms; a return flow path that guides the flow direction of the working fluid discharged from the impeller and flowing toward the outside in the radial direction toward the inside in the radial direction; an intermediate scroll that guides a portion of the working fluid discharged from an intermediate stage impeller that is arranged midway in the axial direction among the plurality of impellers to the intermediate discharge port, The intermediate scroll is a scroll flow path formed on a second side in the axial direction with respect to the return flow path, extending in a circumferential direction about the central axis, and connected to the intermediate discharge port at a portion in the circumferential direction; an introduction portion that connects the return passage and the scroll passage and introduces a portion of the working fluid flowing through the return passage into the scroll passage, In the scroll flow path, an outer flow path forming surface located outermost in the radial direction is formed by a casing inner peripheral surface facing inward in the radial direction in the outer casing and opposing a diaphragm outer peripheral surface facing outward in the radial direction in the diaphragm, The plurality of diaphragms include: a first diaphragm disposed on a first side in the axial direction; a second diaphragm disposed on a second side in the axial direction relative to the first diaphragm and having a smaller outer diameter in the radial direction than the first diaphragm, The outer casing comprises: a first cylindrical portion covering the first diaphragm; a second cylindrical portion that covers the second diaphragm and has an inner diameter in the radial direction smaller than that of the first cylindrical portion; a connecting wall portion formed between the first cylindrical portion and the second cylindrical portion, extending in a direction intersecting the axial direction to connect the first cylindrical portion and the second cylindrical portion, a second-side flow-path forming surface located on the second side in the axial direction in the scroll flow path is formed by an inner wall surface of the connecting wall portion facing the first side in the axial direction.

2. 2. The centrifugal compressor according to claim 1, wherein the introduction portion extends in the axial direction from a maximum diameter portion that is the outermost radial portion in the return flow passage, and at least a portion of an introduction portion outer flow passage forming surface that is located outermost in the radial direction is formed by the inner circumferential surface of the casing.

3. 3. The centrifugal compressor according to claim 2, wherein at least a part of the inner surface of the return passage at the maximum diameter portion is formed by the inner peripheral surface of the casing.

4. 4. The centrifugal compressor according to claim 1, wherein an inner flow passage forming surface located at the innermost position in the radial direction of the scroll flow passage is formed by the diaphragm.

5. the diaphragm includes an extension portion that extends radially outward on a first side in the axial direction with respect to the scroll passage and separates the return passage and the scroll passage in the axial direction, 5. The centrifugal compressor according to claim 1, wherein an inlet-portion-inner-flow-path-forming surface located at the radially innermost position in the inlet portion is a curved surface that is formed at a radially outer tip end of the extension portion when viewed from the circumferential direction and that protrudes radially outward.

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