Centrifugal compressor

Abstract

In this centrifugal compressor, a plurality of impellers have a first impeller group into which a working fluid flows from a first side in the axial direction, and a second impeller group into which the working fluid flows from a second side in the axial direction, which is the opposite side. A casing has a first suction nozzle, a first discharge nozzle, a second suction nozzle, a second discharge nozzle, an intermediate nozzle located between the second suction nozzle and the second discharge nozzle in the axial direction, a diaphragm covering the impellers, an outer casing covering the diaphragm, a first discharge scroll that guides the working fluid to the first discharge nozzle, and a second discharge scroll that guides the working fluid to the second discharge nozzle. The first discharge scroll and the second discharge scroll are disposed radially outside the diaphragm.

Description

Centrifugal compressor

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[0006] ,

[0001] The present disclosure relates to a centrifugal compressor. This application claims priority to Japanese Patent Application No. 2024-229702 filed in Japan on December 26, 2024, and incorporates the content thereof herein.

[0002] As a type of centrifugal rotating machine, a multistage centrifugal compressor having a plurality of stages of impellers for compressing gas is known. The multistage centrifugal compressor successively compresses the gas sucked into the casing with a plurality of stages of impellers and discharges it outside the casing. The compressed gas is discharged from the impeller through a diffuser flow path and further discharged through a discharge scroll that guides the gas flow to a discharge nozzle.

[0003] In addition, as described in Patent Document 1, there is a back-to-back type centrifugal compressor in which impellers are arranged back-to-back. In such a centrifugal compressor, a seal structure is arranged between the first compression stage and the second compression stage, and the impellers are arranged in opposite directions in the first compression stage and the second compression stage.

[0004] Japanese Patent Publication No. 2017-507281

[0005] By the way, in a centrifugal compressor having a plurality of impellers in different directions like the above-described back-to-back type centrifugal compressor, the axial length of the rotor becomes longer as the number of impellers increases. Further, when an intermediate nozzle, which is another opening for allowing fluid to flow in or out between the suction nozzle and the discharge nozzle, is formed, the axial length of the rotor becomes even longer. When the axial length becomes longer, the vibration generated in the rotor becomes larger. Therefore, even in a centrifugal compressor having a plurality of impellers in different directions and an intermediate nozzle, a structure that suppresses the axial length is desired.

[0006] The present disclosure provides a centrifugal compressor capable of suppressing the axial length even in a centrifugal compressor having a plurality of impellers in different directions and an intermediate nozzle.

[0007] The centrifugal compressor according to this disclosure comprises a rotor having a rotating shaft extending in the axial direction over which a central axis extends, and a plurality of impellers fixed to the rotating shaft, and a casing covering the rotor from the radially outer side with respect to the central axis, wherein the plurality of impellers have a first impeller group into which working fluid flows from a first side in the axial direction, and a second impeller group into which working fluid flows from a second side in the axial direction opposite to the first side in the axial direction, and the casing has a first suction nozzle into which the working fluid supplied to the first impeller group flows, a first discharge nozzle into which the working fluid discharged from the first impeller group flows out, a second suction nozzle into which the working fluid discharged from the first discharge nozzle and supplied to the second impeller group flows out, and the working fluid discharged from the second impeller group The impeller comprises a second discharge nozzle from which the working fluid flows, an intermediate nozzle positioned in the axial direction between the first suction nozzle and the first discharge nozzle, or between the second suction nozzle and the second discharge nozzle, through which the working fluid can flow, a diaphragm formed in a cylindrical shape extending in the axial direction to cover the impeller, an external casing formed in a cylindrical shape extending in the axial direction to cover the diaphragm, a first discharge scroll that guides the working fluid discharged from the first impeller group to the first discharge nozzle, and a second discharge scroll that guides the working fluid discharged from the second impeller group to the second discharge nozzle, wherein the first discharge scroll and the second discharge scroll are positioned radially outward from the diaphragm.

[0008] According to the centrifugal compressor of this disclosure, the axial length can be reduced even in a centrifugal compressor having multiple impellers and intermediate nozzles oriented in different directions.

[0009] This is a cross-sectional view of a centrifugal compressor according to the first embodiment of this disclosure. This is an enlarged cross-sectional view showing the configuration around the discharge scroll of the centrifugal compressor of the first embodiment. This is an enlarged cross-sectional view showing the configuration around the discharge scroll of the centrifugal compressor of the second embodiment. This is a side view showing the configuration around the discharge scroll of a modified centrifugal compressor.

[0010] <First Embodiment> Hereinafter, an embodiment for implementing the centrifugal compressor 1 according to the present invention will be described with reference to the attached drawings. However, the present invention is not limited to this embodiment.

[0011] (Configuration of the centrifugal compressor) As shown in Figure 1, the centrifugal compressor 1 in this embodiment is a single-shaft multi-stage centrifugal compressor. The centrifugal compressor 1 constitutes part of a compressor system 100 installed in, for example, a chemical plant. Therefore, ammonia, for example, flows through the centrifugal compressor 1 as a working fluid. The centrifugal compressor 1 mainly comprises a rotor 2 that rotates around a central axis O and a casing 10 formed to surround the rotor 2.

[0012] (Configuration of rotor 2) The rotor 2 extends in the axial direction Da. The rotor 2 extends through the inside of the casing 10 along the central axis O. The rotor 2 has a rotating shaft 21 and an impeller 22.

[0013] In this embodiment, the direction in which the central axis O extends is defined as the axial direction Da. The axial direction Da of the rotor 2 lies along the horizontal plane. That is, the central axis O extends horizontally. In the centrifugal compressor 1, the position where one end is located in the axial direction Da is referred to as the first side Da1. In the centrifugal compressor 1, the position where the end opposite to the end of the first side Da1 is located in the axial direction Da is referred to as the second side Da2, which is on the opposite side of the axial direction Da from the first side Da1. The radial direction of the rotor 2 with respect to the central axis O is simply referred to as the radial direction Dr. The direction around the rotor 2 with respect to the central axis O is referred to as the circumferential direction Dc.

[0014] The rotating shaft 21 is formed in a cylindrical shape extending in the axial direction Da. The first end Da1 of the rotating shaft 21 in the axial direction Da is supported by the casing 10 so as to be rotatable around the central axis O by a journal bearing 32A and a thrust bearing 31. The second end Da2 of the rotating shaft 21 in the axial direction Da is supported by the casing 10 so as to be rotatable around the central axis O by a journal bearing 32B.

[0015] The impeller 22 is positioned on the outer side Dr in the radial direction Dr with respect to the central axis O relative to the rotation axis 21. Multiple impellers 22 are arranged separately in the axial direction Da within the casing 10. These impellers 22 constitute two sets of multi-stage first impeller group 22A and second impeller group 22B, facing opposite directions from each other in the axial direction Da. Thus, the centrifugal compressor 1 of this embodiment is a so-called back-to-back single-shaft multi-stage centrifugal compressor. The first impeller group 22A is positioned on the first side Da1 relative to the second impeller group 22B in the axial direction Da. The second impeller group 22B is positioned on the second side Da2, which is opposite to the first side Da1 in the axial direction Da relative to the first impeller group 22A. Therefore, the orientation of the impellers 22 is different in the first impeller group 22A and the second impeller group 22B. Furthermore, in this embodiment, the first impeller group 22A has, for example, two impellers 22 spaced apart in the axial direction Da. The second impeller group 22B has, for example, five impellers 22 spaced apart in the axial direction Da. In other words, the first impeller group 22A and the second impeller group 22B have different numbers of impellers 22.

[0016] The centrifugal compressor 1 has a first compression section 20A having a first impeller group 22A and a second compression section 20B having a second impeller group 22B. In the centrifugal compressor 1, the working fluid compressed in the first compression section 20A is further compressed in the second compression section 20B. Therefore, the pressure range of the working fluid compressed by the first impeller group 22A of the first compression section 20A and the second impeller group 22B of the second compression section 20B are different.

[0017] Each impeller 22 compresses and discharges working fluid (e.g., gas) supplied from one side in the axial direction Da to the outer side Dr in the radial direction Dr. Working fluid flows into the impeller 22 of the first impeller group 22A from the first side Da1 in the axial direction Da. Working fluid flows into the impeller 22 of the second impeller group 22B from the second side Da2 in the axial direction Da. Each impeller 22 has an impeller flow path 23 formed inside. The cross-sectional area of ​​the impeller flow path 23 gradually decreases from the inner side Dri in the radial direction Dr to the outer side Dr in the radial direction Dr. As a result, the working fluid flowing through the impeller flow path 23 while the impeller 22 is rotating is gradually compressed and becomes high pressure. Note that each of the impellers 22 of the first impeller group 22A and the second impeller group 22B may be a closed impeller with a cover or an open impeller without a cover.

[0018] (Casing configuration) The casing 10 is formed to surround the rotating shaft 21 and the plurality of impellers 22 from the outer side Dr in the radial direction Dr. The casing 10 comprises an outer casing 11, a plurality of diaphragms 15, a head 16, a first suction nozzle 121, a first discharge nozzle 122, a second suction nozzle 123, a second discharge nozzle 124, an intermediate suction nozzle 125 (intermediate nozzle), an intermediate scroll 130, an intermediate partition plate 17, a first discharge scroll 18, and a second discharge scroll 19.

[0019] The external casing 11 is formed in a cylindrical shape extending in the axial direction Da. The external casing 11 is formed to cover the rotor 2, the multiple diaphragms 15, and the head 16 from the outside Dr in the radial direction Dr. The external casing 11 is connected to the first suction nozzle 121, the first discharge nozzle 122, the second suction nozzle 123, the second discharge nozzle 124, and the intermediate suction nozzle 125. The external casing 11 is divisible into upper and lower parts in the vertical direction Dv, with the horizontal plane passing through the central axis O serving as the dividing plane. Details of the structure of the external casing 11 in this embodiment will be described later.

[0020] Multiple diaphragms 15 are positioned inside the outer casing 11 in the radial direction Dr. The multiple diaphragms 15 are collectively formed in a cylindrical shape extending in the axial direction Da so as to cover the rotor 2 from the radial direction Dr. outside Dr. The multiple diaphragms 15 cover the periphery of the rotor 2 and form a casing flow path 40 inside that connects the multiple impellers 22.

[0021] Each diaphragm 15 covers the impeller 22 at each stage. Each diaphragm 15 is formed in a disc shape with a central axis O at its center. Multiple diaphragms 15 are stacked in the axial direction Da. Each diaphragm 15 is designed to be separable into upper and lower parts in the vertical direction Dv, with the horizontal plane passing through the central axis O serving as the dividing plane.

[0022] These diaphragms 15 constitute two sets of multi-stage covering diaphragms, a first diaphragm group 15A and a second diaphragm group 15B, separated in the axial direction Da. Thus, in this embodiment, the first compression section 20A has a first diaphragm group 15A that covers the first impeller group 22A, and the second diaphragm group 15B that covers the second impeller group 22B in the second compression section 20B. The first diaphragm group 15A and the second impeller group 22B are separated in the axial direction Da, with an intermediate partition plate 17 placed between them.

[0023] Furthermore, each of the multiple diaphragms 15 has an introduction channel 41, a diffuser channel 42, and a return channel 43 as a casing channel 40. The introduction channel 41, the diffuser channel 42, and the return channel 43 are formed in the first compression section 20A and the second compression section 20B, respectively.

[0024] The introduction channel 41 guides the working fluid from the outer Dr in the radial direction Dr to the inner Dr in the radial direction Dr. The introduction channel 41 changes the flow of the working fluid moving towards the inner Dr in the radial direction Dr to a flow toward the inlet of the impeller 22 in the axial direction Da, and guides it to the impeller 22. In this way, the introduction channel 41 changes the flow direction of the working fluid toward the axial direction Da and guides it to the impeller channel 23 of the impeller 22.

[0025] The diffuser channel 42 extends from the inner Dri to the outer Dr in the radial direction Dr. The inner Dri end of the diffuser channel 42 is in communication with the outer Dr end of the impeller channel 23 in the radial direction Dr. The diffuser channel 42 guides the working fluid compressed by the impeller 22 from the inner Dri to the outer Dr in the radial direction Dr.

[0026] The return channel 43 reverses the flow direction of the working fluid that has flowed from the inner Dr in the radial direction Dr to the outer Dr in the radial direction Dr via the diffuser channel 42. The return channel 43 guides the working fluid flowing towards the outer Dr in the radial direction Dr back to the inner Dr in the radial direction Dr. One end of the return channel 43 (one side in the axial direction Da), which is upstream in the flow direction of the working fluid, is connected to the diffuser channel 42. The other end of the return channel 43 (the opposite side in the axial direction Da), which is downstream in the flow direction of the working fluid, is connected to the next inlet channel 41.

[0027] The heads 16 are arranged in pairs to close the openings at both ends of the cylindrical outer casing 11 in the axial direction Da. They are annular members centered on the central axis O. The pair of heads 16 are arranged inside the outer casing 11. Each head 16 is divisible into upper and lower parts in the vertical direction Dv, with the horizontal plane passing through the central axis O serving as the dividing plane. The head 16 in this embodiment has a first casing head 161 and a second casing head 162.

[0028] The first casing head 161 is positioned to close the opening on the first side Da1 in the axial direction Da of the outer casing 11. In other words, the first casing head 161 is positioned adjacent to the first side Da1 in the axial direction Da of the multiple diaphragms 15. Therefore, the second casing head 162 is adjacent to the first stage diaphragm 15 of the second compression section 20B, which is located at the second side Da2 in the axial direction Da of the multiple diaphragms 15. Between the first casing head 161 and the first stage diaphragm 15 of the first compression section 20A, a first suction scroll 165 is formed to take in external working fluid into the casing passage 40 via a first suction nozzle 121.

[0029] The second casing head 162 is positioned to close the opening on the second side Da2 of the outer casing 11 in the axial direction Da. In other words, the second casing head 162 is positioned adjacent to the second side Da2 in the axial direction Da with respect to the multiple diaphragms 15. Therefore, the second casing head 162 is adjacent to the first stage diaphragm 15 of the second compression section 20B, which is located furthest to the second side Da2 in the axial direction Da among the multiple diaphragms 15. Between the second casing head 162 and the first stage diaphragm 15 of the second compression section 20B, a second suction scroll 166 is formed to take in external working fluid into the casing passage 40 via a second suction nozzle 123.

[0030] The first suction nozzle 121 is located on the first side Da1 in the axial direction Da of the external casing 11. The first suction nozzle 121 allows working fluid to flow into the external casing 11 from the outside. Working fluid supplied to the first impeller group 22A flows into the first suction nozzle 121. The first suction nozzle 121 is connected to the first suction scroll 165, which is connected to the first stage impeller flow path 23 of the first impeller group 22A. The first suction nozzle 121 is positioned to protrude downward in the vertical direction Dv from the lower part of the external casing 11.

[0031] The first discharge nozzle 122 is positioned at a distance of the first suction nozzle 121, on the second side Da2 in the axial direction Da. The first discharge nozzle 122 is positioned near the center of the outer casing 11 in the axial direction Da. Working fluid discharged from the first impeller group 22A flows out from the first discharge nozzle 122. The first discharge nozzle 122 is a discharge nozzle in the first compression section 20A. The first discharge nozzle 122 is connected to the first discharge scroll 18, which is connected to the impeller flow path 23 located on the second side Da2 in the axial direction Da within the first compression section 20A. The first discharge nozzle 122 discharges the working fluid, which has been compressed within the casing 10 through the two impellers 22 of the first compression section 20A, to the outside of the outer casing 11. The first discharge nozzle 122 is positioned to protrude downward in the vertical direction Dv from the bottom of the outer casing 11.

[0032] The second suction nozzle 123 is located on the second side Da2 in the axial direction Da of the external casing 11. The second suction nozzle 123 is located away from the first discharge nozzle 122 on the second side Da2 in the axial direction Da. Working fluid flowing out from the first discharge nozzle 122 and supplied to the second impeller group 22B flows into the second suction nozzle 123. The second suction nozzle 123 is a suction nozzle in the second compression section 20B. The second suction nozzle 123 is connected to the impeller 22 located on the second side Da2 in the axial direction Da within the second compression section 20B. The second suction nozzle 123 is connected to the second suction scroll 166, which is connected to the first stage impeller flow path 23 of the second impeller group 22B. The second suction nozzle 123 directs the working fluid, which has been discharged from the first discharge nozzle 122 through the two impellers 22 of the first compression section 20A within the external casing 11, into the second suction scroll 166. The second suction nozzle 123 is positioned to protrude downward in the vertical direction Dv from the lower part of the external casing 11.

[0033] The second discharge nozzle 124 is located near the center of the outer casing 11 in the axial direction Da. The second discharge nozzle 124 is located a distance of Da2 on the second side of the axial direction Da relative to the first discharge nozzle 122. Also, the second discharge nozzle 124 is located a distance of Da1 on the first side of the axial direction Da relative to the second suction nozzle 123. Working fluid discharged from the second impeller group 22B flows out from the second discharge nozzle 124. The second discharge nozzle 124 is connected to the second discharge scroll 19, which is connected to the impeller flow path 23 located at the first side Da1 in the axial direction Da within the second compression section 20B. Therefore, the second discharge nozzle 124 discharges the working fluid, which has been compressed through all the impellers 22 within the outer casing 11, to the outside of the outer casing 11. The second discharge nozzle 124 is located so as to protrude downward in the vertical direction Dv from the bottom of the outer casing 11.

[0034] The intermediate suction nozzle 125 is formed at a distance of Da1 on the first side in the axial direction Da from the second suction nozzle 123. The intermediate suction nozzle 125 is formed at a distance of Da2 on the second side in the axial direction Da from the second discharge nozzle 124. In other words, the intermediate suction nozzle 125 is positioned between the second suction nozzle 123 and the second discharge nozzle 124 in the axial direction Da. The intermediate suction nozzle 125 circulates the working fluid inside and outside the external casing 11. The intermediate suction nozzle 125 circulates the working fluid that is not circulating in the first compression section 20A and the second compression section 20B. In this embodiment, the intermediate suction nozzle 125 introduces the working fluid into the middle of the second impeller group 22B. The intermediate suction nozzle 125 is connected to the intermediate scroll 130. Furthermore, the intermediate suction nozzle 125, for example, directs the working fluid supplied from a device other than the centrifugal compressor 1 in the compressor system into the third stage impeller 22 of the second compression section 20B. The intermediate suction nozzle 125 is positioned to protrude vertically downward from the lower part of the external casing 11.

[0035] The intermediate scroll 130 is connected to the impeller flow path 23 of an impeller 22 (for example, the third stage impeller 22) located midway in the axial direction Da within the second compression section 20B. More specifically, the intermediate scroll 130 is connected to the impeller flow path 23 by merging with an introduction flow path 41 midway through the second compression section 20B. Therefore, in the second impeller group 22B of the second compression section 20B, the pressure range of the working fluid being compressed differs between the upstream and downstream positions relative to the position where the working fluid is supplied from the intermediate scroll 130.

[0036] The intermediate partition plate 17 is positioned to separate the first compression section 20A and the second compression section 20B. The intermediate partition plate 17 is positioned between the first diaphragm group 15A and the second diaphragm group 15B in the axial direction Da. The intermediate partition plate 17 covers the main body of the rotating shaft 21. The intermediate partition plate 17 seals the space between itself and the outer circumferential surface of the rotating shaft 21. The intermediate partition plate 17 has a first surface 171 facing the first side Da1 in the axial direction Da, and a second surface 172 facing the second side Da2. That is, the intermediate partition plate 17 faces the first diaphragm group 15A with its first surface 171. It also faces the second diaphragm group 15B with its second surface 172. The intermediate partition plate 17 is designed to be divisible into upper and lower sections in the vertical direction Dv, with a horizontal plane passing through the central axis O serving as the dividing surface.

[0037] (Detailed configuration of the external casing) The external casing 11 of the first embodiment also has a casing body 111 and a casing projection 112.

[0038] The casing body 111 is formed in a cylindrical shape with a central axis O at its center. The casing body 111 has a constant outer diameter. The casing body 111 has a constant outer diameter in all areas covering the first compression section 20A and the second compression section 20B. The inner circumferential surface of the casing body 111 faces the outer circumferential surface of the diaphragm 15 so as to be in contact with it. The outer circumferential surface of the casing body 111 forms the outer shape of the casing body 111. The inner and outer circumferential surfaces of the casing body 111 are formed in a perfect circle shape with a constant radial distance Dr from the central axis O along the axial direction Da. In the radial direction Dr, the casing body 111 and the outer circumferential surface are formed smaller than the outer diameter of the intermediate partition plate 17. Also, in the radial direction Dr, the inner circumferential surface of the casing body 111 is formed larger than the outer diameter of the diaphragm 15. The casing body 111 is connected to a first suction nozzle 121, a second suction nozzle 123, and an intermediate suction nozzle 125. Therefore, the casing body 111 has open nozzles that communicate with the first suction nozzle 121, the second suction nozzle 123, and the intermediate suction nozzle 125, respectively. The first suction nozzle 121, the second suction nozzle 123, and the intermediate suction nozzle 125 are connected to the external casing 11 so as to protrude radially outward from the outer circumferential surface of the casing body 111 toward Dr. In other words, the first suction nozzle 121, the second suction nozzle 123, and the intermediate suction nozzle 125 are arranged to protrude downward from the lower part of the casing body 111 toward the vertical direction Dv. In addition, the casing body 111 has an opening that communicates with the inside of the casing projection 112 at a position that overlaps with the casing projection 112 in the axial direction Da.

[0039] The casing projection 112 is formed in the middle of the casing body 111 in the axial direction Da. The casing projection 112 has a larger outer diameter than the casing body 111. In other words, the casing projection 112 is formed to protrude outward from the casing body 111 in the radial direction Dr. Furthermore, in the radial direction Dr, the outer diameter of the casing projection 112 is formed to change in the circumferential direction Dc. The casing projection 112 has an opening formed in the axial direction Da into which the intermediate partition plate 17 is fitted so as to penetrate in the radial direction Dr. The casing projection 112 is fixed to the first surface 171 and the second surface 172 by welding or by detachable fastening members with the intermediate partition plate 17 fitted inside. In other words, the casing projection 112 is formed integrally with the intermediate partition plate 17. Furthermore, a space is formed inside the casing projection 112 that defines the first discharge scroll 18 and the second discharge scroll 19, which will be described later. In other words, the casing projection 112 is formed in a position that overlaps with the first discharge scroll 18 and the second discharge scroll 19 in the axial direction Da. The casing projection 112 is connected to the first discharge nozzle 122 and the second discharge nozzle 124.

[0040] (Configuration of the First Discharge Scroll) As shown in Figures 1 and 2, the first discharge scroll 18 guides the working fluid discharged from the impeller 22 to the first discharge nozzle 122. The first discharge scroll 18 is compressed in the first compression section 20A and guides the working fluid discharged from the final stage impeller 22 of the first compression section 20A to the first discharge nozzle 122. The first discharge scroll 18 is connected to the final stage diffuser flow path 42 of the first compression section 20A at an outer diameter Dr. The first discharge scroll 18 is positioned at an outer diameter Dr. relative to the diaphragm 15. The first discharge scroll 18 is a space formed inside the casing projection 112. The first discharge scroll 18 extends in the circumferential direction Dc around the central axis O. The first discharge scroll 18 is a flow path formed in a spiral shape over a full rotation in the circumferential direction Dc around the central axis O. The first discharge scroll 18 is connected to the diffuser flow path of the final stage of the first compression section 20A by an inner Dri in the radial direction Dr over its entire circumference. The first discharge scroll 18 is connected to the first discharge nozzle 122 by an outer Dr in the radial direction Dr over a portion of the circumferential direction Dc. The first discharge scroll 18 is formed such that the flow path area changes in the circumferential direction Dc so that the pressure distribution of the working fluid flowing inside is uniform. Specifically, the first discharge scroll 18 is formed such that the flow path area as viewed from the circumferential direction Dc decreases as it moves away from the first discharge nozzle 122 in the circumferential direction Dc. In the first embodiment, the first discharge scroll 18 is formed such that the axial spacing Da as viewed from the circumferential direction Dc is constant, and only the radial spacing Dr changes. In the first embodiment, the first discharge scroll 18 is formed such that as it moves away from the first discharge nozzle 122 in the circumferential direction Dc, the axial spacing Da remains constant, while only the radial spacing Dr approaches. In other words, the first discharge scroll 18 has the widest radial spacing Dr at the position closest to the first discharge nozzle 122 in the circumferential direction Dc. The radial spacing Dr of the first discharge scroll 18 gradually narrows in the circumferential direction Dc to reduce pressure loss of the working fluid flowing inside and to ensure a uniform pressure distribution.

[0041] Furthermore, the first discharge scroll 18 is formed by the space formed in the diaphragm 15 of the final stage of the first compression section 20A, the outer casing 11, and the intermediate partition plate 17. The first discharge scroll 18 is surrounded by the first scroll inner circumferential surface 181 on the inner side Dri in the radial direction Dr, the first scroll outer circumferential surface 182 on the outer side Dr in the radial direction Dr, the first surface 171 located on the second side Da2 in the axial direction Da, and the first scroll side surface 183 located on the first side Da1 in the axial direction Da.

[0042] The first scroll inner surface 181 is located at the innermost Dri in the radial direction Dr on the first discharge scroll 18. The first scroll inner surface 181 is a surface facing the outer Dr in the radial direction Dr. The first scroll inner surface 181 is formed by the outer surface of the final stage diaphragm 15 of the first diaphragm group 15A. When viewed from the circumferential direction Dc, the first scroll inner surface 181 is positioned at the outer Dri in the radial direction Dr with respect to the diffuser flow path. When viewed from the circumferential direction Dc, the first scroll inner surface 181 is positioned at the inner Dri in the radial direction Dr with respect to the casing projection 112. When viewed from the circumferential direction Dc, the first scroll inner surface 181 is positioned at the inner Dri in the radial direction Dr with respect to the inner surface of the casing body 111.

[0043] The first scroll outer circumferential surface 182 is located at the outermost radial Dr of the first discharge scroll 18. The first scroll outer circumferential surface 182 is a surface facing the inner radial Dr. The first scroll outer circumferential surface 182 is separated from the first scroll inner circumferential surface 181 in the radial Dr. The first scroll outer circumferential surface 182 is formed by the inner circumferential surface of the casing projection 112 facing the inner radial Dr. The first scroll outer circumferential surface 182 is positioned radially outward relative to the casing body 111 in the radial Dr. The first scroll outer circumferential surface 182 is formed such that the radial Dr distance from the first scroll inner circumferential surface 181 decreases as it moves away from the first discharge nozzle 122 in the circumferential Dc.

[0044] The first surface 171 is located on the second side Da2 in the axial direction Da that is the most in the first discharge scroll 18. As described above, the first surface 171 is the surface facing the first side Da1 in the axial direction Da in the intermediate partition plate 17. The first surface 171 forms a part of the diffuser flow path of the final stage of the first compression part 20A in the axial direction Da and also forms a part of the first discharge scroll 18.

[0045] The first scroll side surface 183 is located on the first side Da1 in the axial direction Da that is the most in the first discharge scroll 18. The first scroll side surface 183 is the surface facing the second side Da2 in the axial direction Da. The first scroll side surface 183 is formed by the casing protrusion 112. The first scroll side surface 183 extends from the first scroll outer peripheral surface 182 to the inner side Dri in the radial direction Dr. The first scroll side surface 183 faces the first surface 171 in the axial direction Da. The distance between the first scroll side surface 183 and the first surface 171 in the axial direction Da is constant at any position in the circumferential direction Dc. The first scroll side surface 183 is arranged at a position overlapping with the return flow path 43 connected to the impeller 22 of the final stage of the first compression part 20A in the axial direction Da when viewed from the circumferential direction Dc.

[0046] (Configuration of the second discharge scroll) The second discharge scroll 19 guides the working fluid discharged from the impeller 22 to the second discharge nozzle 124. The second discharge scroll 19 is compressed in the second compression section 20B and guides the working fluid discharged from the final stage impeller 22 of the second compression section 20B to the second discharge nozzle 124. The second discharge scroll 19 is connected to the final stage diffuser flow path of the second compression section 20B at an outer diameter Dr. The second discharge scroll 19 is positioned at an outer diameter Dr. relative to the diaphragm 15. The second discharge scroll 19 is a space formed inside the casing projection 112. The second discharge scroll 19 is formed inside the casing projection 112, with an intermediate partition plate 17 in between, on the second side Da2 in the axial direction Da relative to the first discharge scroll 18. In other words, the second discharge scroll 19 is formed as a space independently of the first discharge scroll 18. The second discharge scroll 19 extends in the circumferential direction Dc around the central axis O. The second discharge scroll 19 is a flow path formed in a spiral shape over a full circumference in the circumferential direction Dc around the central axis O. The second discharge scroll 19 is connected to the diffuser flow path of the final stage of the second compression section 20B at the inner Dri in the radial direction Dr over its entire circumference. The second discharge scroll 19 is connected to the second discharge nozzle 124 at the outer Dr in the radial direction Dr in a part of the circumferential direction Dc. The second discharge scroll 19 is formed so that the flow path area changes in the circumferential direction Dc so that the pressure distribution of the working fluid flowing inside is uniform. Specifically, the second discharge scroll 19 is formed so that the flow path area as viewed from the circumferential direction Dc decreases as it moves away from the second discharge nozzle 124 in the circumferential direction Dc. In the first embodiment, the second discharge scroll 19 is formed so that the spacing in the axial direction Da as viewed from the circumferential direction Dc is constant, and only the spacing in the radial direction Dr changes. The second discharge scroll 19 is formed such that, as it moves away from the second discharge nozzle 124 in the circumferential direction Dc, the axial distance Da remains constant while only the radial distance Dr decreases. In other words, the radial distance Dr of the second discharge scroll 19 is widest at the position closest to the second discharge nozzle 124 in the circumferential direction Dc.The second discharge scroll 19 has a gradually narrowing interval in the radial direction Dr so as to reduce the pressure loss of the working fluid flowing through the inside in the circumferential direction Dc and make the pressure distribution uniform. The second discharge scroll 19 is formed such that the size in the radial direction Dr is the same as that of the first discharge scroll 18, while the size in the axial direction Da is larger.

[0047] Further, the second discharge scroll 19 is formed by the space formed by the diaphragm 15 at the final stage of the second compression section 20B, the outer casing 11, and the intermediate partition plate 17. The second discharge scroll 19 is surrounded by a second scroll inner peripheral surface 191 on the inner side Dri in the radial direction Dr, a second scroll outer peripheral surface 192 on the outer side Dro in the radial direction Dr, a second surface 172 disposed on the first side Da1 in the axial direction Da, and a second scroll side surface 193 disposed on the second side Da2 in the axial direction Da.

[0048] The second scroll inner peripheral surface 191 is located at the innermost position in the radial direction Dr in the second discharge scroll 19. The second scroll inner peripheral surface 191 is a surface facing the outer side Dro in the radial direction Dr. The second scroll inner peripheral surface 191 is formed by the outer peripheral surface of the diaphragm 15 at the final stage of the second diaphragm group 15B. When viewed from the circumferential direction Dc, the second scroll inner peripheral surface 191 is disposed on the outer side Dro in the radial direction Dr with respect to the diffuser flow path. When viewed from the circumferential direction Dc, the second scroll inner peripheral surface 191 is disposed on the inner side Dri in the radial direction Dr with respect to the casing protrusion 112. When viewed from the circumferential direction Dc, the second scroll inner peripheral surface 191 is disposed on the inner side Dri in the radial direction Dr with respect to the inner peripheral surface of the casing body 111. The second scroll inner peripheral surface 191 is formed at the same position as the first scroll inner peripheral surface 181 in the radial direction Dr.

[0049] The second scroll outer circumferential surface 192 is located at the outermost radial Dr of the second discharge scroll 19. The second scroll outer circumferential surface 192 is a surface facing the inner radial Dr. The second scroll outer circumferential surface 192 is separated from the second scroll inner circumferential surface 191 in the radial Dr. The second scroll outer circumferential surface 192 is formed by the inner circumferential surface of the casing projection 112 facing the inner radial Dr. The second scroll outer circumferential surface 192 is located radially outward relative to the casing body 111 in the radial Dr. The second scroll outer circumferential surface 192 is formed such that the radial Dr distance from the second scroll inner circumferential surface 191 decreases as it moves away from the second discharge nozzle 124 in the circumferential Dc. The second scroll outer circumferential surface 192 is formed at the same radial Dr as the first scroll outer circumferential surface 182.

[0050] The second surface 172 is located on the first side Da1 in the axial direction Da of the second discharge scroll 19. As mentioned above, the second surface 172 is the surface of the intermediate partition plate 17 that faces the second side Da2 in the axial direction Da. In the axial direction Da, the second surface 172 forms part of the diffuser flow path of the final stage of the second compression section 20B, and also forms part of the second discharge scroll 19.

[0051] The second scroll side surface 193 is located on the second side Da2 in the axial direction Da of the second discharge scroll 19. The second scroll side surface 193 is the surface facing the first side Da1 in the axial direction Da. The second scroll side surface 193 is formed by the casing projection 112. The second scroll side surface 193 extends from the outer peripheral surface 192 of the second scroll to the inner side Dri in the radial direction Dr. The second scroll side surface 193 faces the second surface 172 in the axial direction Da. The distance between the second scroll side surface 193 and the second surface 172 in the axial direction Da is constant at any position in the circumferential direction Dc. When viewed from the circumferential direction Dc, the second scroll side surface 193 is positioned in the axial direction Da to overlap with the return flow path 43 connected to the final stage impeller 22 of the second compression section 20B.

[0052] (Effects) The centrifugal compressor 1 with the above configuration has a first impeller group 22A of the first compression section 20A and a second impeller group 22B of the second compression section 20B which faces in the opposite direction in the axial direction Da. As a result, the number of impellers 22 arranged in the centrifugal compressor 1 is large. In this embodiment as well, the first impeller group 22A is composed of two impellers 22, and the second impeller group 22B is composed of five impellers 22. As a result, the length of the rotor 2 in the axial direction Da becomes longer in order to arrange multiple impellers 22. Furthermore, it has a first suction nozzle 121 and a first discharge nozzle 122 connected to the first impeller group 22A of the first compression section 20A, a second suction nozzle 123 and a second discharge nozzle 124 connected to the second impeller group 22B of the second compression section 20B, and an intermediate suction nozzle 125 arranged between the second suction nozzle 123 and the second discharge nozzle 124 in the axial direction Da. Therefore, because the intermediate suction nozzle 125 is positioned between the second suction nozzle 123 and the second discharge nozzle 124, the axial length Da of the rotor 2 is longer compared to a structure in which the intermediate suction nozzle 125 is not positioned.

[0053] In contrast, in this embodiment, the first discharge scroll 18 and the second discharge scroll 19 are positioned radially outward (Dr) relative to the diaphragm 15. Therefore, the first discharge scroll 18 and the second discharge scroll 19 are not formed inside the diaphragm 15 by cutting away a portion of the diaphragm 15. As a result, the axial length Da of the diaphragm 15 can be shortened compared to the case where the first discharge scroll 18 and the second discharge scroll 19 are formed to bite into the diaphragm 15. This makes it possible to reduce the axial length of the rotor 2 even in a centrifugal compressor 1 having multiple impellers 22 and intermediate nozzles facing different directions.

[0054] Furthermore, the centrifugal compressor 1 of this embodiment is a back-to-back type single-shaft multi-stage centrifugal compressor in which the first impeller group 22A and the second impeller group 22B are arranged in opposite directions in the axial direction Da. In this configuration, the axial thrust force Da acting on the first impeller group 22A is generated in the direction of the first side Da1 in the axial direction Da. Conversely, the axial thrust force Da acting on the second impeller group 22B is generated in the direction of the second side Da2 in the axial direction Da. As a result, the thrust force acting on the first impeller group 22A and the thrust force acting on the second impeller group 22B cancel each other out. This makes it possible to suppress the thrust force acting on the rotor 2. As a result, the size of the thrust bearing 31 can be reduced. As a result, the axial length of the rotor 2 can be reduced by the amount by which the thrust bearing 31 is reduced, compared to a straight-type single-shaft multi-stage centrifugal compressor in which all impellers 22 are oriented in the same direction in the axial direction Da.

[0055] Furthermore, the working fluid discharged from the final stage impeller 22 of the first compression section 20A flows through the final stage diffuser passage and into the first discharge scroll 18. Similarly, the working fluid discharged from the final stage impeller 22 of the second compression section 20B flows through the final stage diffuser passage and into the second discharge scroll 19. The first discharge scroll 18 and the second discharge scroll 19 are connected to the diffuser passage radially outward (Dr). Therefore, the direction of flow of the working fluid does not change when it flows from the diffuser passage into the first discharge scroll 18 and the second discharge scroll 19. As a result, separation of the working fluid when it flows from the diffuser passage into the first discharge scroll 18 and the second discharge scroll 19 can be suppressed.

[0056] Furthermore, the first discharge scroll 18 and the second discharge scroll 19 have a constant distance between them in the axial direction Da when viewed from the circumferential direction Dc. In other words, the distance between the first discharge scroll 18 and the second discharge scroll 19 in the axial direction Da is constant regardless of the position in the circumferential direction Dc. In addition, the first discharge scroll 18 and the second discharge scroll 19 can secure a flow path area for the working fluid by changing the distance between them in the radial direction Dr. As a result, the necessary performance can be ensured for the first discharge scroll 18 and the second discharge scroll 19 while suppressing the expansion of the area in the axial direction Da where the first discharge scroll 18 and the second discharge scroll 19 are formed. In this way, the first discharge scroll 18 and the second discharge scroll 19 can be formed compactly while suppressing flow separation when the working fluid flows in.

[0057] Furthermore, the first discharge scroll 18 and the second discharge scroll 19 have a gradually narrowing radial distance Dr to reduce pressure loss of the working fluid flowing inside them in the circumferential direction Dc, thereby ensuring a uniform pressure distribution. As a result, while suppressing expansion of the first discharge scroll 18 and the second discharge scroll 19 in the axial direction Da, stall and pressure loss of the working fluid flowing through the first discharge scroll 18 and the second discharge scroll 19 can be reduced. In this way, stable performance can be ensured even with compact first discharge scroll 18 and second discharge scroll 19.

[0058] Furthermore, the inner surface 181 of the first scroll and the inner surface 191 of the second scroll are formed by the outer surface of the diaphragm 15. Therefore, the first discharge scroll 18 and the second discharge scroll 19 can be formed without interfering with the diaphragm 15 in the radial direction Dr. Moreover, since the outer surface of the diaphragm 15 that is exposed to the outside becomes the inner surface 181 of the first scroll and the inner surface 191 of the second scroll, the workability when forming the inner surface 181 of the first scroll and the inner surface 191 of the second scroll is improved.

[0059] Furthermore, a casing projection 112, which has a larger outer diameter than the casing body 111, is formed in the axial direction Da at a position that overlaps with the first discharge scroll 18 and the second discharge scroll 19. In other words, the first discharge scroll 18 and the second discharge scroll 19 can be formed inside the casing projection 112. Therefore, even if the first discharge scroll 18 and the second discharge scroll 19 are formed on the outside Dr of the diaphragm 15, it is possible to minimize the impact on the shape of the casing body 111. This makes it possible to simplify the shape of the external casing 11.

[0060] Furthermore, the first suction nozzle 121, the second suction nozzle 123, and the intermediate suction nozzle 125 are connected to the external casing 11 so as to protrude radially outward from the outer circumferential surface of the casing body 111. On the other hand, the first discharge nozzle 122 and the second discharge nozzle 124 are connected to the external casing 11 so as to protrude radially outward from the outer circumferential surface of the casing projection 112. Therefore, the first discharge nozzle 122 connected to the first discharge scroll 18 and the second discharge nozzle 124 connected to the second discharge scroll 19 can be formed without affecting the shape of the casing body 111. This simplifies the shape of the external casing 11.

[0061] Furthermore, the intermediate partition plate 17 is positioned to separate the first compression section 20A and the second compression section 20B. In addition, one side of the first discharge scroll 18 and the second discharge scroll 19 in the axial direction Da is formed by the intermediate partition plate 17. Therefore, when forming the first discharge scroll 18 and the second discharge scroll 19, one side of the axial direction Da can be formed by processing the intermediate partition plate 17. As a result, the workability when forming the inner surface 181 of the first scroll and the inner surface 191 of the second scroll is improved.

[0062] Furthermore, the casing body 111 has a constant outer diameter in all areas covering the first compression section 20A and the second compression section 20B. Therefore, the external shape of the casing body 111 can be simplified. As a result, even when the outer casing 11 is formed by welding thin metal such as steel plates, the number of welds can be reduced. This reduces the manufacturing cost of the centrifugal compressor 1 and shortens the manufacturing period. In addition, the overall manufacturing accuracy of the centrifugal compressor 1 can be improved.

[0063] <Second Embodiment> Next, a centrifugal compressor 1A of the second embodiment according to the present disclosure will be described. In the second embodiment described below, components common to the first embodiment are denoted by the same reference numerals in the figures and their descriptions are omitted. The centrifugal compressor 1A of the second embodiment differs from the first embodiment in that the shapes of the first discharge scroll 18A and the second discharge scroll 19A are further different.

[0064] The first discharge scroll 18A and the second discharge scroll 19A are not limited to a structure in which the size of the radial Dr changes, as in the first embodiment, as long as they are formed such that the flow path area decreases as they move away from the first discharge nozzle 122 or the second discharge nozzle 124 in the circumferential direction Dc.

[0065] As shown in Figure 3, in the second embodiment, the first discharge scroll 18A is formed such that the flow path area as viewed from the circumferential direction Dc decreases as it moves away from the first discharge nozzle 122 in the circumferential direction Dc. In this embodiment, the first discharge scroll 18A is formed such that the radial distance Dr as viewed from the circumferential direction Dc is constant, and only the axial distance Da changes. In the first discharge scroll 18A, as it moves away from the first discharge nozzle 122 in the circumferential direction Dc, the radial distance Dr remains constant, while only the axial distance Da decreases. In other words, in the first discharge scroll 18A, the axial distance Da is widest at the position closest to the first discharge nozzle 122 in the circumferential direction Dc. In the first discharge scroll 18A, the axial distance Da gradually narrows in the circumferential direction Dc to reduce pressure loss of the working fluid flowing inside and to make the pressure distribution uniform.

[0066] Therefore, in the second embodiment, the distance between the first scroll outer circumferential surface 182A and the first scroll inner circumferential surface 181 in the radial direction Dr is constant at any position in the circumferential direction Dc. Furthermore, in the second embodiment, the first scroll side surface 183A is formed such that the distance from the first surface 171 in the axial direction Da decreases as it moves away from the first discharge nozzle 122 in the circumferential direction Dc.

[0067] Furthermore, the second discharge scroll 19A is formed such that the flow path area, as viewed from the circumferential direction Dc, decreases as it moves away from the second discharge nozzle 124 in the circumferential direction Dc. In this embodiment, the second discharge scroll 19A is formed such that the radial distance Dr, as viewed from the circumferential direction Dc, remains constant, and only the axial distance Da changes. The second discharge scroll 19A is formed such that, as it moves away from the second discharge nozzle 124 in the circumferential direction Dc, the radial distance Dr remains constant, while only the axial distance Da decreases. In other words, the axial distance Da of the second discharge scroll 19A is widest at the position closest to the second discharge nozzle 124 in the circumferential direction Dc. The axial distance Da of the second discharge scroll 19A gradually narrows in the circumferential direction Dc to reduce pressure loss of the working fluid flowing inside and to make the pressure distribution uniform.

[0068] Therefore, in the second embodiment, the distance between the outer circumferential surface 192A and the inner circumferential surface 191 of the second scroll in the radial direction Dr is constant at any position in the circumferential direction Dc. Furthermore, in the second embodiment, the side surface 193A of the second scroll is formed such that the distance in the axial direction Da from the second surface 172 decreases as it moves away from the second discharge nozzle 124 in the circumferential direction Dc.

[0069] Therefore, in the radial direction Dr, the outer diameter of the casing projection 112A in the second embodiment is formed such that it does not change in the circumferential direction Dc, but the length in the axial direction Da changes.

[0070] (Effects) In the second embodiment, the first discharge scroll 18A and the second discharge scroll 19A have a gradually narrowing distance in the axial direction Da, rather than in the radial direction Dr, to reduce pressure loss of the working fluid flowing inside in the circumferential direction Dc and to ensure a uniform pressure distribution. Even with this structure, stall and pressure loss of the working fluid flowing through the first discharge scroll 18A and the second discharge scroll 19A can be reduced, similar to the first embodiment. Therefore, stable performance can be ensured even with the centrifugal compressor 1A of the second embodiment.

[0071] <Modification> Furthermore, the first discharge scroll and the second discharge scroll are not limited to being formed such that only the radial Dr spacing or the axial Da spacing decreases in the circumferential direction Dc, as in the first and second embodiments. The first discharge scroll and the second discharge scroll are formed such that at least one of the radial Dr spacing and the axial Da spacing decreases as they move away from the first discharge nozzle 122 or the second discharge nozzle 124 in the circumferential direction Dc. For example, in the modified centrifugal compressor 1B, as shown in Figure 4, both the radial Dr spacing and the axial Da spacing of the first discharge scroll 18B and the second discharge scroll 19B change. Specifically, the axial Da spacing of the first discharge scroll 18B and the second discharge scroll 19B changes above the vertical Dv direction with respect to the central axis O, and the radial Dr spacing changes below the vertical Dv direction with respect to the central axis O. In other words, the modified first discharge scroll 18B and second discharge scroll 19B are formed in the same shape as the second embodiment, above the vertical direction Dv with respect to the central axis O. Furthermore, the first discharge scroll 18B and second discharge scroll 19B are formed in the same shape as the first embodiment, below the vertical direction Dv with respect to the central axis O.

[0072] Therefore, the outer diameter of the modified casing projection 112A is formed such that, above the vertical direction Dv with respect to the central axis O, the length of the radial direction Dr remains unchanged in the circumferential direction Dc while the length of the axial direction Da changes. Also, the outer diameter of the modified casing projection 112A is formed such that, below the vertical direction Dv with respect to the central axis O, the length of the radial direction Dr remains unchanged in the circumferential direction Dc while the length of the axial direction Da changes.

[0073] Even with this structure, stall and pressure loss of the working fluid flowing through the first discharge scroll 18B and the second discharge scroll 19B can be reduced, similar to the first and second embodiments. Therefore, even with the modified centrifugal compressor 1B, stable performance can be ensured.

[0074] (Other Embodiments) Although embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of the present disclosure.

[0075] In this embodiment, an intermediate suction nozzle 125 is described as being positioned between the second suction nozzle 123 and the second discharge nozzle 124 in the axial direction Da. However, the intermediate nozzle is not limited to this configuration. For example, the intermediate nozzle is not limited to a structure that allows working fluid to flow in, as is the case with the intermediate suction nozzle 125. For example, the intermediate nozzle may be an intermediate discharge nozzle that allows working fluid flowing through the second impeller group 22B to flow out midway. Furthermore, the intermediate nozzle is not limited to a structure that is positioned in the second compression section 20B to allow working fluid flowing through the second impeller group 22B to flow. Therefore, the intermediate nozzle may be positioned in the first compression section 20A to allow working fluid flowing through the first impeller group 22A to flow. In other words, the intermediate nozzle may be positioned between the first suction nozzle 121 and the first discharge nozzle 122 in the axial direction Da. Therefore, the intermediate nozzle may be, for example, an intermediate discharge nozzle that allows working fluid flowing through the first impeller group 22A to flow out. Furthermore, the intermediate nozzle may be an intermediate suction nozzle 125 that supplies working fluid to the first impeller group 22A midway, or an intermediate discharge nozzle that causes the working fluid flowing through the first impeller group 22A to flow out midway.

[0076] Furthermore, the centrifugal compressor 1 may have impellers 22 other than the first impeller group 22A and the second impeller group 22B. In other words, the centrifugal compressor 1 may have a third or further compression section. To put it another way, the centrifugal compressor 1 according to this embodiment is not limited in the number of compression sections formed.

[0077] <Note> The centrifugal compressor 1 described in the embodiment can be understood, for example, as follows.

[0078] (1) The centrifugal compressor 1 according to the first embodiment comprises a rotor 2 having a rotating shaft 21 extending in the axial direction Da of the central axis O, and a plurality of impellers 22 fixed to the rotating shaft 21, and a casing 10 covering the rotor 2 from the outside Dr in the radial direction Dr with respect to the central axis O, wherein the plurality of impellers 22 include a first impeller group 22A into which working fluid flows from the first side Da1 in the axial direction Da, and the axial direction on the opposite side of the first side Da1 in the axial direction Da The casing 10 has a second impeller group 22B into which working fluid flows from the second side Da2 of direction Da, and the casing 10 has a first suction nozzle 121 into which the working fluid supplied to the first impeller group 22A flows, a first discharge nozzle 122 into which the working fluid discharged from the first impeller group 22A flows out, a second suction nozzle 123 into which the working fluid that flows out from the first discharge nozzle 122 and is supplied to the second impeller group 22B flows, and the second impeller group 22 The impeller 22 has a second discharge nozzle 124 through which the working fluid discharged from B flows out, an intermediate nozzle positioned between the first suction nozzle 121 and the first discharge nozzle 122 in the axial direction Da, or between the second suction nozzle 123 and the second discharge nozzle 124 in the axial direction Da, through which the working fluid can flow, a diaphragm 15 formed in the shape of a cylinder extending in the axial direction Da to cover the impeller 22, an external casing 11 formed in the shape of a cylinder extending in the axial direction Da to cover the diaphragm 15, a first discharge scroll 18 that guides the working fluid discharged from the first impeller group 22A to the first discharge nozzle 122, and a second discharge scroll 19 that guides the working fluid discharged from the second impeller group 22B to the second discharge nozzle 124, wherein the first discharge scroll 18 and the second discharge scroll 19 are positioned outside Dr in the radial direction Dr relative to the diaphragm 15.

[0079] With this configuration, the first discharge scroll 18 and the second discharge scroll 19 are positioned radially outward (Dr) relative to the diaphragm 15. Therefore, the first discharge scroll 18 and the second discharge scroll 19 are not formed inside the diaphragm 15 by cutting away a portion of it. As a result, the axial length Da of the diaphragm 15 can be shortened compared to the case where the first discharge scroll 18 and the second discharge scroll 19 are formed to bite into the diaphragm 15. This makes it possible to reduce the axial length of the rotor 2 even in a centrifugal compressor 1 having multiple impellers 22 and intermediate nozzles oriented in different directions.

[0080] Furthermore, the axial thrust force Da acting on the first impeller group 22A is generated in the direction of the first side Da1 in the axial direction Da. Conversely, the axial thrust force Da acting on the second impeller group 22B is generated in the direction of the second side Da2 in the axial direction Da. As a result, the thrust force acting on the first impeller group 22A and the thrust force acting on the second impeller group 22B cancel each other out. This reduces the thrust force acting on the rotor 2. As a result, the size of the thrust bearing 31 can be reduced. This reduces the axial length of the rotor 2 compared to a straight-type single-shaft multi-stage centrifugal compressor in which all impellers 22 face the same direction in the axial direction Da.

[0081] (2) The centrifugal compressor 1 according to the second embodiment is the centrifugal compressor 1 of (1), wherein the first discharge scroll 18 and the second discharge scroll 19 have inner scroll surfaces in the radial direction Dr in the inner Dri direction formed by the outer surface of the diaphragm 15.

[0082] With this configuration, the first discharge scroll 18 and the second discharge scroll 19 can be formed without interfering with the diaphragm 15 in the radial direction Dr. Furthermore, since the outer peripheral surface of the diaphragm 15 that is exposed to the outside becomes the inner peripheral surface of the scroll, the workability when forming the inner peripheral surface of the scroll is improved.

[0083] (3) The centrifugal compressor 1 according to the third embodiment is any one of the centrifugal compressors 1 of (1) to (3), wherein the external casing 11 has a casing body 111 formed in a cylindrical shape with a constant outer diameter and centered on the central axis O, and a casing projection 112 formed in the axial direction Da at a position overlapping with the first discharge scroll 18 and the second discharge scroll 19 and having a larger outer diameter than the casing body 111.

[0084] With this configuration, the first discharge scroll 18 and the second discharge scroll 19 can be formed inside the casing projection 112. Therefore, even if the first discharge scroll 18 and the second discharge scroll 19 are formed on the outside of the diaphragm 15, it is possible to minimize the impact on the shape of the casing body 111. As a result, the shape of the external casing 11 can be simplified.

[0085] (4) The centrifugal compressor 1 according to the fourth embodiment is the centrifugal compressor 1 of (3), wherein the first suction nozzle 121, the second suction nozzle 123, and the intermediate nozzle are connected to the external casing 11 so as to protrude outward in the radial direction Dr from the outer circumferential surface of the casing body 111, and the first discharge nozzle 122 and the second discharge nozzle 124 are connected to the external casing 11 so as to protrude outward in the radial direction Dr from the outer circumferential surface of the casing protrusion 112.

[0086] With this configuration, the first discharge nozzle 122 connected to the first discharge scroll 18 and the second discharge nozzle 124 connected to the second discharge scroll 19 can be formed without affecting the shape of the casing body 111. This simplifies the shape of the external casing 11.

[0087] (5) The centrifugal compressor 1 according to the fifth embodiment is any one of the centrifugal compressors 1, 1A, 1B described in (1) to (4), wherein the first discharge scrolls 18, 18A, 18B and the second discharge scrolls 19, 19A, 19B are formed such that the flow area decreases as they move away from the first discharge nozzle 122 or the second discharge nozzle 124 in the circumferential direction Dc, so that the pressure distribution of the working fluid flowing inside them is uniform in the circumferential direction Dc.

[0088] With this configuration, it is possible to reduce stall and pressure loss of the working fluid flowing through the first discharge scrolls 18, 18A, 18B and the second discharge scrolls 19, 19A, 19B while suppressing the expansion of the first discharge scrolls 18, 18A, 18B and the second discharge scrolls 19, 19A, 19B in the axial direction Da. In this way, stable performance can be ensured even with compact first discharge scrolls 18, 18A, 18B and second discharge scrolls 19, 19A, 19B.

[0089] (6) The centrifugal compressor 1 according to the sixth embodiment is the centrifugal compressor 1, 1A, 1B of (5), wherein the first discharge scrolls 18, 18A, 18B and the second discharge scrolls 19, 19A, 19B are formed such that at least one of the distance in the radial direction Dr and the distance in the axial direction Da decreases as they move away from the first discharge nozzle 122 or the second discharge nozzle 124 in the circumferential direction Dc.

[0090] (7) The centrifugal compressor 1 according to the seventh embodiment is any one of the centrifugal compressors 1 of (1) to (6), comprising: a first compression section 20A which compresses the working fluid flowing in from the first suction nozzle 121 and discharges it to the first discharge nozzle 122 using the first impeller group 22A; and a second compression section 20B which compresses the working fluid flowing in from the second suction nozzle 123 at a higher pressure than the first compression section 20A and discharges it to the second discharge nozzle 124 using the second impeller group 22B, wherein the casing 10 further comprises an intermediate partition plate 17 which is positioned between the first compression section 20A and the second compression section 20B in the axial direction Da so as to separate the first compression section 20A and the second compression section 20B and covers the rotating shaft 21, and the first discharge scroll 18 and the second discharge scroll 19 have one side in the axial direction Da formed by the intermediate partition plate 17.

[0091] With this configuration, when forming the first discharge scroll 18 and the second discharge scroll 19, one side of the axial direction Da can be formed by machining the intermediate partition plate 17. Therefore, the workability when forming the inner surface 181 of the first scroll and the inner surface 191 of the second scroll is improved.

[0092] According to the centrifugal compressor of this disclosure, the axial length can be reduced even in a centrifugal compressor having multiple impellers and intermediate nozzles oriented in different directions.

[0093] 1, 1A, 1B Centrifugal compressor 100 Compressor system 20A First compression section 20B Second compression section 0 Central shaft 2 Rotor 21 Rotating shaft 22 Impeller 22A First impeller group 22B Second impeller group 23 Impeller flow path 10 Casing 11 External casing 111 Casing body 112, 112A, 112B Casing protrusions 121 First suction nozzle 122 First discharge nozzle 123 Second suction nozzle 124 Second discharge nozzle 125 Intermediate suction nozzle 130 Intermediate scroll 15 Diaphragm 15A First diaphragm group 15B Second diaphragm group 40 Casing flow path 41 Inlet flow path 42 Diffuser flow path 43 Return flow path 16 Head 161 First casing head 162 Second casing head 165 First suction scroll 166 Second suction scroll 17 Intermediate partition plate 171 First surface 172 Second surface 18, 18A, 18B First discharge scroll 181 First scroll inner surface 182, 182A First scroll outer surface 183, 183A First scroll side surface 19, 19A, 19B Second discharge scroll 191 Second scroll inner surface 192, 192A Second scroll outer surface 193, 193A Second scroll side surface 31 Thrust bearing 32A, 32B Journal bearing Da Axial Da1 First side Da2 Second side Dr Radial Dr Outer Dri Inner Dc Circumferential Dv Vertical

Claims

1. A rotor having a rotating shaft extending in the axial direction from which a central axis extends, and a plurality of impellers fixed to the rotating shaft; a casing covering the rotor from the radially outer side with respect to the central axis, wherein the plurality of impellers include a first impeller group from which working fluid flows in from a first side in the axial direction, and a second impeller group from which working fluid flows in from a second side in the axial direction opposite to the first side in the axial direction; the casing includes a first suction nozzle from which the working fluid supplied to the first impeller group flows; a first discharge nozzle from which the working fluid discharged from the first impeller group flows out; a second suction nozzle from which the working fluid discharged from the first discharge nozzle and supplied to the second impeller group flows in; a second discharge nozzle from which the working fluid discharged from the second impeller group flows out; and an intermediate nozzle positioned in the axial direction between the first suction nozzle and the first discharge nozzle, or between the second suction nozzle and the second discharge nozzle, through which the working fluid can flow. A centrifugal compressor comprising: a diaphragm formed in a cylindrical shape extending in the axial direction so as to cover the impeller; an external casing formed in a cylindrical shape extending in the axial direction so as to cover the diaphragm; a first discharge scroll that guides the working fluid discharged from the first impeller group to the first discharge nozzle; and a second discharge scroll that guides the working fluid discharged from the second impeller group to the second discharge nozzle, wherein the first discharge scroll and the second discharge scroll are arranged radially outward from the diaphragm.

2. The centrifugal compressor according to claim 1, wherein the inner surface of the radially inner scroll of the first discharge scroll and the second discharge scroll is formed by the outer surface of the diaphragm.

3. The centrifugal compressor according to claim 1 or 2, wherein the external casing comprises a casing body formed in a cylindrical shape with a constant outer diameter and centered on the central axis, and a casing projection formed in the axial direction at a position overlapping with the first discharge scroll and the second discharge scroll, and having a larger outer diameter than the casing body.

4. The centrifugal compressor according to claim 3, wherein the first suction nozzle, the second suction nozzle, and the intermediate nozzle are connected to the external casing so as to protrude radially outward from the outer circumferential surface of the casing body, and the first discharge nozzle and the second discharge nozzle are connected to the external casing so as to protrude radially outward from the outer circumferential surface of the casing protrusion.

5. The centrifugal compressor according to claim 1 or 2, wherein the first discharge scroll and the second discharge scroll are formed such that the flow path area decreases as they move away from the first discharge nozzle or the second discharge nozzle in the circumferential direction, so that the pressure distribution of the working fluid flowing inside them is uniform in the circumferential direction around the rotor with respect to the central axis.

6. The centrifugal compressor according to claim 5, wherein the first discharge scroll and the second discharge scroll are formed such that at least one of the radial spacing and the axial spacing decreases as they move away from the first discharge nozzle or the second discharge nozzle in the circumferential direction.

7. The centrifugal compressor according to claim 1 or 2, comprising: a first compression section that compresses the working fluid flowing in from the first suction nozzle and discharges it to the first discharge nozzle using the first impeller group; and a second compression section that compresses the working fluid flowing in from the second suction nozzle at a higher pressure than the first compression section and discharges it to the second discharge nozzle using the second impeller group, wherein the casing further has an intermediate partition plate that is positioned between the first compression section and the second compression section in the axial direction to separate the first compression section and the second compression section and covers the rotating shaft, and one side of the first discharge scroll and the second discharge scroll in the axial direction is formed by the intermediate partition plate.

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