JP2007309154A - Single-shaft multi-stage centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-shaft multi-stage centrifugal compressor controlling flow with a simple construction even in an intermediate stage. <P>SOLUTION: The single-shaft multi-stage centrifugal compressor 50 has a plurality of impellers 4a-4e on the same rotary shaft 2. The impellers are received in a casing 1 having a suction nozzle 5 and a discharge nozzle 8. On an upstream side of the impeller in at least any stage except the first stage, a pre-swirl means is provided for giving pre-swirl to a flow entering the impeller. The pre-swirl means has an introductory flow passage 12 section for introducing gas from the outside and an guide vane flow passage section which has a plurality of fixed guide vanes 14a arranged on a downstream side of the introductory flow passage section at intervals in a circumferential direction. A flow from the introductory flow passage section through the guide vane flow passage section and a gas flow sucked through the suction nozzle are mixed and supplied to the impeller 14c. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a single-shaft multistage centrifugal compressor in which a number of centrifugal impellers are attached to the same shaft.

  An example of a conventional single-shaft multi-stage centrifugal compressor is described in Patent Document 1. In the centrifugal compressor described in this publication, in order to improve the efficiency at the time of partial load, in the single-shaft multistage centrifugal compressor having a diffuser with guide vanes, the return vane and the guide vanes of the diffuser are simultaneously associated and returned. It corresponds to the change in the incident angle of the flow flowing into the guide vanes.

  Another example of a conventional uniaxial centrifugal compressor is described in Patent Document 2. In the centrifugal compressor described in this publication, in order to control the suction flow rate of the fluid without increasing the size of the centrifugal compressor, in the two-stage centrifugal compressor, a variable inlet normally used on the upstream side of the first stage impeller Vane is arranged. In addition, a movable vane capable of changing the installation angle with respect to the fluid flow direction is provided on the upstream side of the two-stage impeller.

  Another method for controlling the flow rate of the multistage centrifugal compressor is described in Patent Document 3. In the multistage centrifugal compressor described in this publication, a part of the gas flow sucked into the centrifugal compressor is bypassed without flowing to the impeller, and the bypassed gas flow is ejected to the suction pipe to the impeller. The flow rate is controlled by giving a pre-turn to the inflow gas.

Japanese Patent Publication No. 60-27840 JP 2003-307197 A JP 2003-328996 A

  In the single-shaft multistage centrifugal compressor described in Patent Document 1, since the diff user and the return channel vane are simultaneously rotated for each stage, the flow rate can be controlled while maintaining high compressor efficiency. However, since the vane is rotated at each stage, the driving mechanism for moving the vane at each stage becomes complicated. Therefore, if a problem occurs in the drive system during operation, the flow rate cannot be controlled. Since the multistage centrifugal compressor for a process occupies an important part of the plant and requires extremely high reliability, it is difficult to use such a compressor as a process gas compressor.

  Since the centrifugal compressor described in Patent Document 2 is a compressor for a refrigerator, it is unlikely to be a severe use condition like a process gas compressor. Therefore, even if a movable part is provided between the suction port and the discharge port of the centrifugal compressor, the use conditions are not as high as those of the process gas compressor, and thus reliability can be ensured. However, in order to use this compressor as a process gas compressor, it must satisfy various conditions of temperature conditions and gaseous examination, and the compressor described in Patent Document 2 having a movable part is Such conditions are not fully considered.

  Furthermore, in the compressor described in Patent Document 3, instead of the conventional inlet guide vane, the suction flow into the first stage impeller is constituted by the axial flow and the swirl flow, and the flow rate ratio of each flow is changed to change the swirl flow. The flow rate is controlled by changing the strength. However, the pre-swivel imparting method described in Patent Document 3 controls the flow of the first stage of the multistage compressor and does not consider application to the intermediate stage. Therefore, if it is applied to the intermediate stage as it is, the mechanism configuration becomes complicated and the reliability of the compressor may be lowered.

  The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to make it possible to control the flow with a simple configuration without a movable mechanism even in an intermediate stage in a single-shaft multistage centrifugal compressor. Another object of the present invention is to realize a single-shaft multistage centrifugal compressor having high reliability and high efficiency and a wide operating range. Still another object of the present invention is to enable control of the flow inside the centrifugal compressor without increasing the size of the centrifugal compressor.

  A feature of the present invention that achieves the above object is that, in a single-shaft multi-stage centrifugal compressor in which a plurality of impellers provided on the same rotating shaft are accommodated in a casing having a suction nozzle and a discharge nozzle, at least any of the first stage except the first stage A pre-swirl means for pre-swirling the flow flowing into the impeller is provided on the upstream side of the impeller of the stage, and the pre-swirl means has an introduction flow path portion for introducing gas from the outside, and the introduction flow path A guide vane channel section having a plurality of fixed guide vanes arranged at intervals in the circumferential direction on the downstream side of the section, and a flow from the introduction channel section through the guide vane channel section and a suction nozzle It is to mix the flow of the gas sucked from and supply it to the impeller.

  And in this feature, any one of the impeller in which the flow guided from the introduction flow path section gives the pre-swirling flow to the introduction flow path portion of the pre-swirling means and the impeller disposed downstream of the impeller. It is preferable to connect a pipe that guides the discharge gas discharged from the pipe, and to interpose a valve in this pipe, and this compressor can be connected to one of the impellers excluding the first stage among the multistage impellers formed in the casing. An intermediate stage suction nozzle for injecting gas from the outside may be provided, a pipe for guiding a part of the injection gas supplied to the intermediate stage suction nozzle to the introduction flow path section may be provided, and a valve may be interposed in the pipe.

  Further, a spiral channel portion whose channel cross-sectional area gradually decreases in the circumferential direction is connected to the downstream side of the introduction channel portion, and the spiral channel portion may be connected to the guide vane channel portion. There may be two spiral channel portions. In addition, the meridian cross-sectional shape having the same axial depth at the same radial position may have a trapezoidal annular flow path portion on the inner diameter side of the introduction flow path portion. May have a shape in which a substantially radial direction is peeled on the outer diameter side, a circumferential direction is laid on the inner diameter side, and an intermediate portion thereof is connected by a smooth curve.

  Further, the casing is provided with an intermediate stage suction nozzle for injecting gas from the outside of the compressor in one of the impellers formed in multiple stages except the first stage, and the gas sucked from the intermediate stage suction nozzle May be formed in the casing so as to be injected into the inlet side of the return channel provided downstream of the intermediate stage impeller.

  According to the present invention, in the single-shaft multi-stage centrifugal compressor, the flow path for imparting the swirl flow is formed on the suction side of the intermediate stage, and the vanes for imparting swirl are provided to the flow path. The flow can be controlled with simple configuration. Further, since the blade provided in the swirl flow imparting channel is a fixed blade, there is no movable mechanism, and a high operating range can be obtained with high reliability. Furthermore, since only a simple sub-channel and blades are added, the flow inside the centrifugal compressor can be controlled without increasing the size of the centrifugal compressor.

  Several embodiments of the single-shaft multistage centrifugal compressor according to the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of a single-shaft multistage centrifugal compressor 50. In the single-shaft multistage centrifugal compressor 50, a large number of centrifugal impellers, in this FIG. 1, five centrifugal impellers 4a to 4e are fixedly arranged at intervals in the axial direction. Yes. At both ends of the rotary shaft 2, radial bearings 3a and 3b for supporting the rotary shaft so as to be rotatable in the radial direction and a thrust bearing 3b for supporting a load acting on the rotary shaft 2 from the axial direction are arranged. .

  Between the leftmost impeller 4a and the radial bearing 3a in the axial direction, there is provided a shaft sealing means 21a for preventing the gas inside the machine from leaking out of the machine. Similarly, the rightmost impeller 4e is provided. A shaft sealing means 21b is provided at an axially intermediate portion between the radial bearing 3b and the radial bearing 3b. The shaft sealing means 21a and 21b, the bearings 3a to 3c, and the impellers 4a to 4e of each stage are accommodated in the casing 1.

  The impellers 4a to 4e of each stage form a compression stage, and each has a suction channel and a discharge channel. A suction nozzle 5 for sucking gas into the multistage centrifugal compressor 50 from the outside of the machine is formed on the outer peripheral portion on the left end side of the casing 1. A suction passage of the first stage compression stage is formed radially inward from the suction nozzle 5. A movable vane type inlet guide vane device is provided in the middle of the suction flow path of the first stage compression stage.

  The first-stage suction flow path has a flow path section extending in the radial direction from the suction nozzle 5 and an annular flow path section extending in front of the first-stage impeller 4a. A plurality of inlet guide vanes 15 are arranged at intervals. Each inlet guide vane 15 is provided with a rotating shaft 16a on the end face on the side opposite to the impeller 4a. All the rotating shafts 16a are connected to the output shaft 17a of one motor 17b by a guide blade driving mechanism 17 including gears and the like.

  A discharge nozzle 8 for guiding the compressed gas generated by the multistage centrifugal compressor 50 to the outside of the casing 1 is formed on the outer peripheral portion on the right end side of the casing 1. The discharge nozzle 5 communicates with a spiral scroll 8a formed in the discharge flow path of the final compression stage, and communicates with a flow path extending inward in the radial direction. In the final discharge channel, a plurality of blades are arranged at intervals in the circumferential direction to form a vaned diffuser.

  The discharge flow path of each compression stage except the final stage is a vaneless diffuser part and a downstream side of the vaneless diffuser part, and has a U-shaped cross section that changes the gas flow from radially outward to radially inward It has a flow path part and a return flow path part downstream of the U-shaped flow path part and having a plurality of blades arranged at intervals in the circumferential direction. The vaneless diffuser portion has a parallel wall surface portion. Between the back side of each stage impeller 4a-4d and the next stage impeller 4b-4e, the sealing means which prevents the flow of the front stage impeller 4a-4d from leaking to the next stage impeller 4b-4e is provided. Is provided.

  Here, details of the control means for controlling the flow of the intermediate stage, which is a feature of the present invention, will be described below. In the discharge channel 22 of the second-stage compression stage, it extends to the outer diameter side of the return channel portion 22b to which the U-shaped channel portion 22a is connected, separately from the U-shaped channel 22a. An annular channel 6b is connected. The annular flow path 6b is connected to a ring-shaped collecting portion 6a, and an intermediate stage injection nozzle 6 is connected to the ring-shaped collecting portion 6a.

  In the vicinity of the inner diameter side end of the return flow path portion 22b of the second stage compression stage and on the suction side of the third stage compression stage, the discharge gas of the compressor 50 is passed through the valve 11 to the third stage compression stage. A flow path communicating with the pipe 10 for injecting into the pipe is formed. That is, an extraction gas introduction nozzle 7 to which a pipe 10 is connected is formed on the outer periphery of the casing 1 adjacent to the intermediate stage injection nozzle 6, and the upstream introduction flow is directed radially inward from the extraction gas introduction nozzle 7. A path 12 is formed.

On the inner diameter side of the upstream side introduction flow path 12, an inner circumferential side introduction flow path 13 formed in a spiral shape is provided. An annular blowing channel 14 in which a plurality of fixed guide vanes 14 a are arranged at intervals in the circumferential direction is formed on the inner diameter side of the inner circumferential side introducing channel 13. The outlet of the outlet channel 14 is near the outer periphery of the inlet of the third stage impeller 4c.

  The operation of the single-shaft multistage centrifugal compressor 50 configured in this manner will be described below. The working gas sucked in from the suction nozzle 5 flows in the compressor 50 as a radially inward flow 9, passes through the inlet guide vane 15 provided in the suction channel of the first stage compression stage, and passes through the first stage impeller. 4a. The working gas compressed and pressurized by the first stage impeller 4a and the second stage impeller 4b passes through the U-shaped section 22a provided downstream of the second stage compression stage, and is injected from the intermediate stage injection nozzle 6 into the intermediate stage injection. It merges with the flow 9a and flows in the return flow path portion 22b inward in the radial direction.

  The working gas merged with the intermediate stage injection flow becomes a flow 9b from the radially inward to the axial direction and is guided to the suction side of the three-stage impeller 4c. On the other hand, a part of the discharge flow 9c of the compressed gas discharged from the discharge nozzle 8 is guided to the extraction gas introduction nozzle 7 and then passed through the blowout flow path 14 to the blow flow 9f into the suction flow path of the three-stage impeller. As blown out.

  Here, the compressed gas that has flowed in from the extraction gas introduction nozzle 7 becomes a flow 9d that travels inward in the radial direction through the introduction flow path 12, and turns around the spiral inner introduction flow path 13 to become a swirl flow 9e. Thereafter, the gas flows inward in the radial direction little by little and is guided to the blowout flow path 14. Details will be described with reference to FIG. FIG. 2 is an AA arrow view of FIG.

  A fixed guide vane 14a is provided in the blowing channel 14, and this guide vane 14a imparts a predetermined swirl to the blowing flow 9f. The blowing flow 9f provided with the swirling is mixed with the working gas flow 9b flowing from the second compression stage. Then, a swirl component is given to the flow 9b of the working gas flowing in from the second stage compression stage. The strength of the swirl flow applied to the working gas flow 9b depends on the swirl magnitude of the blown flow 9f, and the swirl magnitude of the blown flow 9f depends on the flow rate of the flow 9d flowing from the extraction gas introduction nozzle 7. Dependent. The amount of compressed gas introduced to the extracted gas introduction nozzle 7 is easily controlled using a valve 11 interposed in the pipe 10.

The compressed gas introduced into the compressor 50 from the extraction gas introduction nozzle 7 and the working gas introduced into the compressor 50 from the suction nozzle 5 are mixed on the suction side of the three-stage impeller 4c to be mixed into the four-stage impeller 4d. The pressure is further increased by the 5-stage impeller 4e. Thereafter, it flows out of the machine from the discharge nozzle 8. As described above, a part of the compressed gas discharged from the discharge nozzle 8 is returned from the extraction gas introduction nozzle 7 into the apparatus. Since the means for controlling the flow on the suction side of the intermediate stage, specifically the three-stage compression stage, is provided on the upstream side of the three-stage compression stage, the single-shaft multistage compressor 50 is connected to the first group G ₁ on the upstream side. The second group G ₂ on the downstream side is formed. The upstream side is a low pressure stage, and the downstream side is a high pressure stage.

In this embodiment, the flow rate of the compression stage of the first group G ₁ on the upstream side is controlled using the inlet guide vanes 15, and the flow rate of the compression stage of the second group G ₂ on the downstream side is controlled by the swirl flow. Yes. Thus, by dividing the multistage compressor 50 into a plurality of groups and including one or a plurality of compression stages in each group, the control method and means can be appropriately set for each group, and the following advantages are obtained.

Since the inlet guide vane 15 included in the first group G ₁ is provided in the first stage compression stage, the first group G ₁ is in a position close to the shaft end side of the rotary shaft 2. Therefore, the inlet guide vane drive 17 that drives the inlet guide vane 15 can of course be arranged outside the compressor 50, and the drive mechanism 16 that connects the inlet guide vane drive 17 and the inlet guide vane 15 is provided in the casing. Since it can be arranged near the end of 1, even if a mechanical failure occurs, it can be easily repaired and maintained.

  Further, the driving mechanism for connecting the motor 17b outside the machine and the inlet guide vane 15 inside the machine is simpler than that provided in the intermediate stage. Further, when the centrifugal compressor 50 is started, if the inlet guide vanes 15 provided on the upstream side of the first stage impeller 4a are almost fully closed, the starting load can be reduced.

If the second group G ₂ , which is an intermediate stage, is provided with a drive mechanism such as that provided in the first group G ₁ described above, not only the structure becomes complicated but also a large space in the axial direction is required. As a result, the rotor dynamics of the centrifugal compressor 50 may be adversely affected, making it difficult to design a centrifugal compressor that requires high reliability.

  On the other hand, according to the present embodiment, the swirl flow imparting device provided in the intermediate stage has no movable part, and has a simple configuration, improving the reliability. Further, since the axial length of the rotating shaft is not so long, the rotor dynamics are not adversely affected. Furthermore, guide vanes are provided in the swirling flow blowout flow path, and a uniform swirling flow can be blown out in the circumferential direction, so that a uniform swirling flow can be imparted to the gas flow sucked from the first stage compression stage, effectively Can be controlled.

  FIG. 3 shows a modification of the embodiment shown in FIG. This embodiment is different from the embodiment shown in FIG. 2 in that the compressed gas introduction flow path 12 sucked from the extraction gas introduction nozzle 7 is divided into two swirl flow paths 13a and 13b using a branch wall 13c. It is in dividing. Since the compressed gas flow 9d is branched into two swirl flows 9e at the branch wall 13c, the swirl flow 9e flows into the flow path formed by the fixed guide vanes 14a from the circumferential direction with a uniform flow rate. Finally, the flow 9f blown out to the gas flow 9b sucked from the suction nozzle 5 is made uniform in the circumferential direction, and a uniform pre-swirl is given to the suction flow of the impeller 4c.

  4 and 5 show another embodiment of the single-shaft multistage centrifugal compressor according to the present invention. 4 is a longitudinal sectional view of the centrifugal compressor 50, and FIG. The present embodiment differs from the above embodiment in that the inner diameter side downstream of the introduction flow path 12 has a collector shape and that the fixed guide vane 14a has a curved shape with a large curve.

  That is, the inner diameter portion on the downstream side of the introduction flow path 12 is an annular flow path 18 having a trapezoidal cross section having the same axial depth at the same radial position. The flow 9d of the injected gas introduced from the introduction flow path 12 circulates in the circumferential direction in the annular flow path 18 from the radially inward flow and flows into the fixed guide vane 9e. A swirl component is imparted by passing through the fixed guide vanes 14a, and is sucked in as a swirl flow from the suction nozzle 5 and blown out to a gas flow 9b compressed by the first stage and second stage impellers 4a and 4b. Here, the fixed guide vane 14a is oriented in the radial direction on the outer diameter side, and has a shape lying in the circumferential direction so as to impart swirl to the flow 9f on the inner diameter side, and is connected with a smooth curve in the middle. It is.

  According to the present embodiment, the annular flow path 18 has the same radial position and the same axial depth, so that the production is easy and the production cost can be reduced. Further, when the cross-sectional area of the annular flow path 18 is sufficiently large, a swirl flow uniform in the circumferential direction can be obtained. Furthermore, if the inner diameter side shape of the fixed guide vane 14a is set based on the amount of gas sucked from the suction nozzle 5, a gas flow having a suitable pre-turn can be supplied to the third stage impeller 4c.

  Still another embodiment of the single-shaft multi-stage centrifugal compressor according to the present invention is shown in a longitudinal sectional view in FIG. This embodiment differs from the embodiment shown in FIG. 1 in that the gas injected from the extraction gas introduction nozzle 7 is not the discharge gas of the compressor 50, but a part of the gas injected into the intermediate stage injection nozzle 6 is taken out. It is in use.

  Specifically, the intermediate stage suction pipe 19 is branched in the middle, and the branched stage 10 is provided with a valve 11a and the branch pipe 10 is provided with a valve 11b. A part of the flow sucked from the intermediate stage suction pipe 19 is led to the swirl flow introduction flow path 12 through the pipe 10. In this case, the strength of the swirling swirl flow 9 f depends on the flow rate of the branch flow passing through the pipe 10. This amount is determined by the opening degree of the valve 11b.

According to the present embodiment, the amount of pre-swirl applied to the main flow 9b, which is the flow of gas sucked from the suction nozzle 5, is controlled by the opening of the valve 11b, so that the flow rate and head of the compressor can be controlled. Further, since the flow flowing into the intermediate stage is used, the fluid loss can be reduced as compared with the case where the discharge gas is branched from the second group G ₂ forming the high pressure stage.

  According to each embodiment and modification of the present invention described above, (1) in the intermediate stage of the multi-stage centrifugal compressor, the pre-swirl is given to the gas flow and the pre-swivel amount is controlled. The compressor can be operated efficiently over a wide operating range. (2) Since the pre-swivel device provided in the intermediate stage has a simple structure and no drive part, it is possible to avoid the occurrence of problems associated with the pre-swivel device and to operate the multistage centrifugal compressor with extremely high reliability. (3) The pre-swivel device provided in the intermediate stage is simple in the device for gas injection, and thus requires only a short axial space, and is advantageous in terms of rotor dynamics.

  Although an intermediate stage injection nozzle is provided to inject gas from the intermediate stage, the intermediate stage injection nozzle is not necessarily required and may be provided as necessary. Moreover, although the number of stages of the multistage centrifugal compressor is five, it is of course not limited to five. Furthermore, although the fixed guide vane for providing the pre-turn is provided in front of the three-stage impeller, this is not limited to the three-stage impeller, and is not limited to being provided only at a specific one stage. If necessary, it may be two or three stages, or may be provided in two consecutive stages or two stages in between. As described above, the installation position of the fixed guide vanes can be appropriately determined according to the specifications of the compressor.

  In the above embodiment, the discharge gas of the multi-stage compressor is used for the swirl flow, but it is not always necessary to use the discharge gas of the final stage, as long as a higher pressure than the suction pressure of the impeller that imparts the pre-turn is obtained. The middle stage discharge gas can also be used.

The longitudinal cross-sectional view of one Example of the multistage centrifugal compressor which concerns on this invention. The AA arrow directional view of FIG. The cross-sectional view of the modification of the multistage centrifugal compressor shown in FIG. The longitudinal cross-sectional view of the other Example of the multistage centrifugal compressor which concerns on this invention. The BB arrow line view of FIG. The longitudinal cross-sectional view of the further another Example of the multistage centrifugal compressor which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Casing, 2 ... Rotating shaft, 3 ... Bearing, 4a-4e ... Impeller, 5 ... Suction nozzle, 6 ... Middle stage injection | pouring nozzle, 7 ... Extraction gas introduction nozzle, 8 ... Discharge nozzle, 10 ... Piping, 11 ... Valve 12, upstream introduction flow path 13, inner circumferential introduction flow path 14 blow-out flow path 14 a fixed guide vane 15 inlet guide vane 16 guide vane drive mechanism 17 inlet guide vane drive Machine,
18 ... Introducing flow path (annular flow path), 19 ... Intermediate stage suction pipe, 50 ... Compressor.

Claims (11)

  In a single-shaft multi-stage centrifugal compressor in which a plurality of impellers provided on the same rotating shaft are accommodated in a casing having a suction nozzle and a discharge nozzle, on the upstream side of at least one of the intermediate stage impellers excluding the first stage A pre-turning means for giving a pre-turn to the flow flowing into the impeller is provided, the pre-turning means is for introducing gas from the outside, and on the downstream side of the introduction flow path section in the circumferential direction. A guide vane flow path section having a plurality of fixed guide vanes arranged at intervals, and a flow from the introduction flow path section through the guide vane flow path section and a flow of gas sucked from the suction nozzle A single-shaft multistage centrifugal compressor characterized by mixing and imparting a pre-swirl to the suction flow of the impeller.   The flow introduced from the introduction flow path portion is discharged from either the impeller imparting the pre-swirling flow to the introduction flow path portion of the pre-swirl means or the impeller disposed downstream of the impeller. 2. A single-shaft multistage centrifugal compressor according to claim 1, wherein a pipe for guiding the discharged gas is connected, and a valve is interposed in the pipe.   A spiral channel portion whose channel cross-sectional area gradually decreases in the circumferential direction is connected to the downstream side of the introduction channel portion, and the spiral channel portion is connected to the guide vane channel portion. The single-shaft multistage centrifugal compressor according to claim 2, wherein   4. The single-shaft multistage centrifugal compressor according to claim 3, wherein at least two of the spiral flow passage portions are connected to the downstream side of the introduction flow passage portion.   The casing is provided with an intermediate stage suction nozzle for injecting gas from the outside of the compressor in any one of the impellers formed in multiple stages except the first stage, and an injection gas supplied to the intermediate stage suction nozzle The single-shaft multistage centrifugal compressor according to claim 1, wherein a pipe for guiding a part of the pipe to the introduction flow path portion is provided, and a valve is interposed in the pipe.   A spiral channel portion whose cross-sectional area is gradually narrowed in the circumferential direction is connected to the downstream side of the introduction channel portion, and the spiral channel portion is connected to the guide vane channel portion. The single-shaft multistage centrifugal compressor according to claim 5.   The single-shaft multistage centrifugal compressor according to claim 6, wherein at least two of the spiral flow passage portions are connected to the downstream side of the introduction flow passage portion.   2. The uniaxial multistage according to claim 1, wherein the meridional cross-sectional shape having the same axial depth at the same radial position has a trapezoidal annular flow path portion closer to the inner diameter side than the introduction flow path portion. Shape centrifugal compressor.   9. The fixed guide blade according to claim 8, wherein the fixed guide vane has a shape in which the outer diameter side is almost radially peeled and the inner diameter side is lying in the circumferential direction, and an intermediate portion thereof is connected by a smooth curve. Single-shaft multistage centrifugal compressor.   The casing is provided with an intermediate stage suction nozzle for injecting gas from the outside of the compressor in any one of the impellers formed in multiple stages except the first stage, and the gas sucked from the intermediate stage suction nozzle is supplied to the casing. The single-shaft multistage centrifugal according to any one of claims 1 to 9, wherein an air flow passage is formed in the casing so as to be injected into an inlet side of a return flow passage provided downstream of the intermediate stage impeller. Compressor. The single-shaft multistage centrifugal compressor according to any one of claims 1 to 9, wherein a movable inlet guide vane device is provided upstream of the first stage impeller.

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