JPH0979192A - Multistage centrifugal compressor and its inter-stage injection flow passage structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multistage centrifugal compressor and its inter-stage injection passage structure by which a loss by mixing and collision of injection gas and pressure increased gas is reduced and which have high performance. SOLUTION: As a means to reduce a collision loss of an injection flow 18 and a main flow, plural plate-like nozzle guide blades 12 are installed in an annular nozzle 11 to inject gas from outside into main flow gas of a return passage to form a stage space of a multistage centrifugal compressor so as to become almost equal to an angle of a speed vector of a main flow in a merging part 13. Therefore, speed vectors of a branch flow and the main flow in the merging part are made to coincide with each other, and a mixing loss is reduced, and performance of the multistage centrifugal compressor is significantly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal compressor used for pressurization in a refrigeration process or the like, and more particularly to a high performance multistage centrifugal compressor in which injection is performed between stages and an interstage injection flow channel structure thereof. .

[0002]

2. Description of the Related Art Generally, in a multi-stage centrifugal compressor that sequentially increases the pressure to a high pressure by a plurality of stages, each stage is composed of an impeller, a diffuser arranged downstream of the impeller, a return passage, and the like. This return flow path is composed of a so-called bend section and blade section (channel section). Further, when injection is performed between these plural stages, conventionally, for example, Japanese Patent Publication No. 6-6957, As disclosed in JP-A-57-206800 or JP-B-59-30240, the outlet portion of the bend portion and the blade portion (channel portion)
Gas is injected in the middle of the. The interstage injection flow path (nozzle) that is the gas injection flow path is generally composed of a tubular suction nozzle, a scroll (collector), and an annular nozzle.

Further, according to Japanese Patent Application Laid-Open No. 6-257590, an interstage suction nozzle structure of a multistage centrifugal compressor that enables reduction of loss due to interstage mixing is provided. It is already known that guide vanes are provided in the circumferential direction, and an annular partition plate of a predetermined length is provided between each guide vane and a stationary vane provided in the return passage (main flow passage). Are known.

[0004]

However, in the above-mentioned conventional multistage centrifugal compressor for interstage injection, generally, the annular nozzle for interstage injection is not provided with guide vanes, Therefore, there is a problem that the main stream and the tributary stream (injection flow) in the injecting portion (merging portion) have different speed magnitudes and directions, a large collision loss occurs, and the performance of the compressor deteriorates.

Further, by adjusting the area of the suction port in the conventional injection flow path constituted by the suction nozzle, the collector and the gas suction port as shown in Japanese Utility Model Publication No. Sho 59-30240, Although it is possible to match the speeds of the main stream and the tributary (injection), however, the gas flow direction of the main stream is different from that of the tributary, so that the collision loss increases and the compressor performance decreases. was there.

Further, in the gas injection flow channel structure known from Japanese Patent Laid-Open No. 6-257590, no measures are taken to positively match the directions of the mainstream gas and the tributary gases, and the collision loss increases. There is a problem that the compressor performance is reduced.

Therefore, an object of the present invention is to provide a high-performance multi-stage centrifugal compressor in a multi-stage centrifugal compressor in which the pressure is sequentially increased to a high pressure by a plurality of stages by reducing the mixing loss of the main stream gas and the tributary gas in the inter-stage injection passage. It is to provide a compressor and its interstage injection flow channel structure.

[0008]

In order to achieve the above object, according to the present invention, a diffuser is arranged on the radial outer periphery of a rotating centrifugal impeller, and a return flow passage provided downstream of the diffuser is provided. A multi-stage centrifugal compressor for guiding the gas pressurized by the centrifugal impeller to the centrifugal impeller of the next stage via an annular shape for injecting the gas between the stages to the pressurized gas guided through the return flow path. In the one provided with a nozzle, the annular nozzle is provided with a means for reducing a collision loss between a flow of gas injected between the stages and a flow of the pressurized gas guided through the return passage. Multistage centrifugal compressors have been proposed.

Further, according to the present invention, also in order to achieve the above-mentioned object, a diffuser is arranged on the outer circumference of the rotating centrifugal impeller in the radial direction, and a return passage is provided downstream of the diffuser. In a multi-stage centrifugal compressor that guides the gas pressurized by the centrifugal impeller to the centrifugal impeller of the next stage, interstage injection for injecting gas between the stages into the pressurized gas guided through the return flow path. A flow channel structure, comprising an annular nozzle in a part of the return flow channel,
Between the stages of the multi-stage centrifugal compressor, the annular nozzle is provided with means for reducing a collision loss between the flow of the gas injected between the stages and the flow of the pressurized gas introduced through the return passage. Injection flow channel structures have been proposed.

That is, according to the multistage centrifugal compressor and the interstage injection flow channel structure thereof according to the present invention described above, the multistage centrifugal compressor is provided in a part of the return flow channel which constitutes the multistage centrifugal compressor, and the return flow channel is used. In the structure of injecting the gas into the flow of the pressurized gas guided by the injecting flow path formed by the annular nozzle, the annular nozzle includes guide vanes and the like, and the flow of the gas injected between the stages is By providing means for reducing the collision loss with the flow of the boosted gas guided through the return flow path, the confluence portion of the boosted gas flow and the interstage injected gas flow guided through these return flow paths. It becomes possible to make the respective speed vectors in the two mutually coincident with each other, thereby significantly reducing the mixing loss (collision loss), and thereby realizing a high-performance multistage centrifugal compressor.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, FIG. 2 attached herewith shows a longitudinal section showing an internal structure of a first embodiment of a multistage centrifugal compressor adopting an interstage injection flow channel structure of the present invention. In this figure, a rotary sleeve 3 and centrifugal impellers 4 and 4a are fixed to a rotary shaft 1, and the gas sucked from a suction part 2 is compressed by the impeller 4 rotating at a high speed by its rotation. A diffuser 5 is arranged radially outward of the centrifugal impeller 4, a bend portion 6 curved in a “U” shape is arranged downstream of the diffuser, and further, a circular blade row shape. The return flow path 15 is formed by the channel portion 7 provided with the guide vanes 14 of FIG. Then, the impeller 4 a of the next stage is provided downstream of the return flow path 15.

At the connecting portion between the bend portion 6 and the channel portion 7, an annular nozzle 11 for injecting gas into the return flow passage 15 is provided between stages of multistage compression by a plurality of impellers. The cross section from the cross section line AA indicated by the alternate long and short dash line in the figure is shown in FIG. 1 (however, the central portion thereof is not shown). As is clear from FIG. 1, the injection port of the injection channel to the compressor has an injection nozzle 1 through which the interstage injected gas is injected.
6, a scroll 10 whose cross-sectional area changes (gradually decreases) along the circumferential direction, and an annular nozzle 11. The inlet of the injection channel to the compressor, that is, the outlet of the annular nozzle is the outlet of the bend section 6,
That is, it is provided upstream of the inlet of the channel section 7. The annular nozzle 11 is provided with a plurality of flat plate-shaped guide blades 12, 12 ... In the form of a circular blade row, and the outlet blade angle βa (angle measured from the tangential direction) of these guide blades 12, 12 ... ) Is set to an angle substantially equal to the flow angle αa of the main flow at the confluence of the main flow of gas from the bend section 6 and the tributary that is the injected gas (circle 13 in the figure, outlet of the annular nozzle). The flow width of the annular nozzle 11 is selected so that the radial velocity of the tributary at the outlet of the annular nozzle is equal to the radial velocity of the main flow at the confluence 13. Furthermore, the flat plate-shaped guide vanes 12 described above are used.
Has a curved surface at the end portion thereof and has a circular cross section.

Next, when the multistage centrifugal compressor whose detailed structure has been described above is operated, the gas sucked from the suction portion 2 is compressed by the impeller 4 rotating at a high speed by the rotating shaft 1, that is, the main flow. The impeller 17 is pressurized by the impeller 4 and decelerated by the diffuser 5, and then passes through the bend portion 6 to reach its exit. On the other hand, an injection flow (tributary flow) 18, which is a gas injected from the injection nozzle 16 of FIG. 1, enters the scroll 10 and is accelerated by the annular nozzle 11 to reach the injection port (that is, the nozzle outlet). These mainstream 17 and tributaries 1
8 merges at the merging section 13 which is the exit of the bend 6,
It flows into the channel portion 7 and is further sucked into the impeller 4a of the next stage. Generally, in the structure of the conventional annular nozzle portion 11, the mainstream 17 and the tributary 18 have different velocity vectors, and therefore, in the joining portion 13, the tributary 18 and the mainstream 1 are formed.
It is difficult to match the velocity vectors of 7 with each other, which causes a large mixing loss (collision loss).

By the way, in the present embodiment, as described above, the annular nozzle 11 is provided with the guide vanes 12, 12, ... whose outlet vane angle βa is substantially equal to the mainstream flow angle αa in the merging portion 13. Therefore, the tributary is guided by these guide vanes 12, 12, ..., At the merging portion 13, the flow angle of the tributary 18 substantially matches the flow angle of the main flow 17. The flow width of the annular nozzle 11 is selected so that the radial velocity of the tributary 18 at the nozzle outlet is equal to the radial velocity of the main flow 17 at the confluence 13, so that the velocity vector 22 of the tributary 17 and the main flow The velocity vectors 21 of 18 almost coincide with each other, whereby the tributary 17 and the mainstream 1
The collision loss with 8 is significantly reduced, and as a result, the compressor performance can be significantly improved.

FIG. 3 shows a second embodiment of the multi-stage centrifugal compressor according to the present invention by the sectional structure of its annular nozzle, as in FIG. In this second embodiment, the injection flow path for the injection gas is also the injection nozzle 16,
It consists of a collector 19 and an annular nozzle 11,
Unlike the embodiment shown in FIG. 1, the collector 19 has a constant cross-sectional area in the circumferential direction. In addition,
The inlet to the compressor is provided at the outlet of the bend portion 6, that is, upstream of the inlet of the channel portion 7, and the annular nozzle 11 is provided with a plurality of flat plate-shaped guide blades 12, 12 ... And the outlet blade angle βa of these guide blades 12
Is set to be substantially equal to the flow angle αa of the main flow in the merging portion 13, as in the embodiment of FIG.

Also in this second embodiment, the annular nozzle 11 has a plurality of guide vanes 12, 1 whose outlet vane angle βa is substantially equal to the mainstream flow angle αa at the confluence 13.
2 are provided, these guide blades 12, 12
The tributary 18 is guided by the action of ...
The flow angle of the tributary stream 18 in 3 is almost the same as the flow angle of the main stream 17. When a collector 19 having a constant cross-sectional area along the circumferential direction is used in the injection flow channel as in this embodiment, the flow rate decreases in the circumferential direction, so that the tributary stream 18 in the vicinity of the merging portion 13 is formed. Since the velocity vector 22 changes according to the position in the circumferential direction, it is difficult to match the velocity vector with the mainstream 17 over the entire circumference.
(The velocity vector 22 shown in the figure gradually decreases in size counterclockwise from the top of the confluence portion 13.) However, at least the flow directions thereof match,
Collision loss will be greatly reduced compared to the past, and as a result, compressor performance will also be significantly improved.

FIG. 4 shows a third embodiment of the multi-stage centrifugal compressor according to the present invention, similarly to FIG. 1, by the sectional structure of the annular nozzle which is the characteristic point thereof. In the third embodiment, the plurality of guide blades 20, 20 ... Provided in the annular nozzle 11 of the injection flow passage are different from the above-mentioned flat plate-shaped guide blade 12 and extend from the front edge to the rear edge. A blade-shaped guide blade 20 having a reduced blade thickness is provided. The outlet vane angle βa of the plurality of guide vanes 20, 20 ... Is approximately equal to the flow angle αa of the main flow in the confluence portion 13, and the flow width of the annular nozzle 11 is the radial direction of the tributary flow at the nozzle outlet. Similar to the above embodiment, the velocity is selected to be equal to the radial velocity of the mainstream of the confluence.

Also in the multi-stage centrifugal compressor having such a structure, as in the above embodiment, the guide vane 20 has an outlet vane angle βa in the annular nozzle 11 at an angle substantially equal to the mainstream flow angle αa in the confluence 13. Are provided, the tributary stream 18 is guided by these guide vanes 20, 20 ... And the flow angle of the tributary stream 18 at the confluence 13 is substantially equal to the flow angle of the main stream 17. The flow width of the annular nozzle 11 is selected so that the radial velocity of the tributary 18 at the nozzle outlet is equal to the radial velocity of the main flow 17 at the confluence 13, so that the velocity vectors of the tributary 18 and the main flow 17 are calculated. Are similar to each other, and the collision loss is greatly reduced, as described above.

Furthermore, the third embodiment also exhibits the following effects. That is, in the structure of the embodiment of FIG. 1, since the leading edge radius of the plate-shaped guide blade 12 is small, when the angle of the flow of gas flowing from the scroll 10 and the inlet blade angle of the guide blade 12 are different from each other. , This gas flow is separated from the front edge of the guide vane 12,
The loss will increase. On the other hand, in the third embodiment, the leading edge radius ρ of the guide blade 20 is larger than the leading edge radius of the guide blade 12 in FIG. Even if the inlet blade angles are different, the gas flow is less likely to separate from its leading edge, and therefore the loss in the injection flow path is smaller than in the first embodiment. As a result, the performance of the multi-stage compressor according to this embodiment is further improved as compared with the case of FIG.

FIG. 5 shows a fourth embodiment of the multistage centrifugal compressor according to the present invention, centering on the annular nozzle 11 portion which is the characteristic point. In this multi-stage centrifugal compressor,
Similar to the first embodiment shown in FIG. 2, the annular nozzle 11 is provided with the flat guide blades 12 in a circular blade row, and although not shown, the outlet blade angle of the guide blades 12 is not shown. βa is set to be substantially equal to the flow angle αa of the main flow at the confluence 13. However, as is clear from the figure, the flow passage width W of the annular nozzle 11 gradually decreases toward the downstream side. The outlet channel width of the annular nozzle 11 is selected so that the radial velocity of the tributary at the nozzle outlet is equal to the radial velocity of the main stream 17 at the confluence 13, and the inlet channel width is determined by the guide vane 12 The flow angle at the inlet of the is selected to match the vane angle, and thus this fourth embodiment provides a shape of the annular nozzle 11 which is suitable especially when the cross-sectional area of the scroll 10 is relatively large. Has become.

Also in the fourth embodiment, since the velocity vectors of the tributary stream 17 and the main stream 18 at the merging portion 13 are almost the same, the collision loss is greatly reduced. Furthermore, since the flow angle at the inlet of the guide vane 12 matches the vane angle, flow separation at the leading edge of the guide vane 12 is prevented and the loss of the annular nozzle 11 is reduced, and as a result, the compressor performance is This is an improvement over that shown in FIGS. 1 and 2 above.

FIG. 6 shows a fifth embodiment of the multi-stage centrifugal compressor according to the present invention, focusing on the characteristic feature of the annular nozzle 11 portion. Even with this multi-stage centrifugal compressor,
The annular nozzle 11 is provided with flat guide blades 12 in a circular blade row, and the outlet blade angle βa of the guide blades 12 is
The flow angle αa of the main flow 17 in the merging portion 13 is set to be substantially equal. However, in the multistage centrifugal compressor according to the fifth embodiment, as is clear from the figure, the flow passage width W of the annular nozzle 11 gradually increases toward the downstream side. Also, the outlet channel width of the annular nozzle 11 is chosen so that the radial velocity of the tributary at the nozzle outlet is equal to the radial velocity of the confluent mainstream, while its inlet channel width is at the inlet of the guide vane 12. The flow angle is selected so as to match the blade angle, and the present embodiment has a shape suitable especially when the cross-sectional area of the scroll 10 is relatively small.

In the fifth embodiment as well, the velocity vectors of the tributary stream 17 and the main stream 18 at the merging portion 13 substantially coincide with each other, so that the collision loss can be greatly reduced, and further, the guide vane 12 can be reduced. Since the flow angle at the inlet of the guide vane coincides with the vane angle, separation of the flow at the leading edge of the guide vane 12 is prevented, and the loss of the annular nozzle 11 is reduced. As a result, the compressor performance is further improved as compared with the first embodiment shown in FIGS. 1 and 2 as in the above embodiment.

FIG. 7 shows a sixth embodiment of a multistage centrifugal compressor according to the present invention, focusing on the annular nozzle 11 portion which is the characteristic point. Also in the multi-stage centrifugal compressor according to the sixth embodiment, the injection flow path is the injection nozzle 16, the scroll 10, and the annular nozzle 11 in which the guide vanes 12 are provided in a circular blade row, as in the above. However, in this embodiment, the inlet of the injection channel to the compressor is provided in the return channel 15 in the middle of the guide vane 14 (downstream from the front edge). The outlet blade angle βa of the guide blade 12 (angle measured from the tangential direction)
Is almost equal to the blade angle of the confluence portion 23 of the guide vanes 14 of the return flow passage 15, and the flow passage width of the annular nozzle 11 is such that the radial velocity of the tributary 18 at the nozzle outlet is the main flow at the confluence portion 23. As before, it is chosen to be equal to the radial velocity of 17.

In the sixth embodiment having the above structure,
Since the annular vane 11 is provided with the guide vanes 12 at an outlet vane angle βa substantially equal to the vane angle of the guide vanes 14 of the return flow passage 15 in the confluence portion 23, the guide vanes 12 cause the tributary stream 18 to flow. Are guided, and the tributaries 18 smoothly flow into the guide vanes 14 at the confluence 23.
Further, the flow width of the annular nozzle 11 is selected so that the radial velocity of the tributary 18 at the nozzle outlet is equal to the radial velocity of the main flow 17 at the confluence 23, so that the tributary 1
The velocity vectors of 7 and the mainstream 18 substantially match, and the collision loss is greatly reduced. As a result, the compressor performance is also significantly improved. Further, the sixth embodiment has an advantage that the outer diameter of the compressor can be made smaller than that of the embodiment of FIG.

Finally, FIG. 8 shows a seventh embodiment of the multi-stage centrifugal compressor according to the present invention, and like the above embodiment, the annular nozzle 11 has a flat guide vane. 24 are provided in the shape of a circular blade, and the mounting angle of the guide vane 24 is adjustable by, for example, an adjusting shaft member indicated by reference numeral 25 in the drawing.

That is, according to the structure in which the mounting angle of the guide blade 24 can be adjusted, the following effects can be obtained. That is, when the annular nozzle 11 having the fixed guide vanes 12 is used as in the embodiment shown in FIGS. 1 and 2, for example, the confluence portion 1 is used except at the design flow point.
The velocity vectors of the main flow 17 and the tributary 18 in No. 3 do not match, and the collision loss tends to increase. On the other hand, as shown in the present embodiment, the mounting angle of the guide blade 24 provided in the annular nozzle 11, that is, the outlet blade angle βa can be changed by the flow rate, so that at a flow rate other than the design flow rate point. The tributary 18 and the main stream 1 at the confluence 13
7 can be made to coincide with each other, thereby making it possible to further reduce the collision loss, and as a result, it is possible to improve the compressor performance in a wider flow range as compared with the conventional case.

[0028]

As is apparent from the above detailed description, according to the multistage centrifugal compressor of the present invention and the interstage injection flow passage structure thereof, it is provided in a part of the return flow passage in the multistage centrifugal compressor. The annular nozzle for injecting the gas from the injection flow path into the pressurized gas flow guided through the return flow path is composed of guide vanes and the like, and the flow of the gas injected between the stages and the return flow path are By providing means for reducing the collision loss with the flow of the boosted gas guided via these, the respective velocities at the confluence of the boosted gas flow and the interstage injected gas flow guided through these return flow paths. It becomes possible to match the vectors with each other, which significantly reduces the mixing loss (collision loss), and thus it is possible to realize a multi-stage centrifugal compressor with significantly improved performance compared to the conventional injection with interstage injection. It will be possible Say, to exert an extremely excellent effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view taken along the line AA in FIG. 2 showing an internal structure of a first embodiment of a multistage centrifugal compressor that employs an interstage injection flow channel structure of the present invention.

FIG. 2 is a vertical sectional view showing the internal structure of the first embodiment of the multi-stage centrifugal compressor shown in FIG.

FIG. 3 is a sectional view showing an internal structure of a second embodiment of a multi-stage centrifugal compressor according to the present invention.

FIG. 4 is a partially enlarged sectional view showing the internal structure of a third embodiment of a multi-stage centrifugal compressor according to the present invention.

FIG. 5 is a partially enlarged vertical sectional view showing the internal structure of a fourth embodiment of the multi-stage centrifugal compressor according to the present invention.

FIG. 6 is a partially enlarged vertical sectional view showing the internal structure of a fifth embodiment of a multi-stage centrifugal compressor according to the present invention.

FIG. 7 is a partially enlarged vertical sectional view showing the internal structure of a sixth embodiment of the multi-stage centrifugal compressor according to the present invention.

FIG. 8 is a partially enlarged vertical sectional view showing the internal structure of a seventh embodiment of the multi-stage centrifugal compressor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rotary shaft 2 suction part 3 rotary sleeve 4 centrifugal impeller 4a next stage impeller 5 diffuser 6 bend part 7 channel part 8 casing 9 diaphragm 10 scroll 11 annular nozzle 12 nozzle guide vane 13 confluence part 14 guide vane 15 return flow Channel 16 Injection nozzle 17 Main flow 18 Injection flow (tributary) 19 Collector 20 Nozzle guide blade 21 Merging part main flow velocity vector 22 Merging part tributary velocity vector 23 Guide vane Merging part 24 Nozzle guide vane 25 Adjustment shaft member

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Eno Takahisa, Tateura-shi, Ibaraki Prefecture, 603 Kuchitate Factory, Tsuchiura Plant, Ltd. Tsuchiura factory

Claims (14)

[Claims] 1. A diffuser is arranged on the outer circumference in the radial direction of a rotating centrifugal impeller, and a gas boosted by the centrifugal impeller is passed through a return flow passage provided downstream of the diffuser to the centrifugal impeller of the next stage. A multi-stage centrifugal compressor leading to
In the one provided with an annular nozzle for injecting a gas between the stages to the pressurized gas guided through the return flow path, the annular nozzle has a flow of gas to be injected between the stages,
A multistage centrifugal compressor comprising means for reducing collision loss with the pressurized gas flow guided through the return flow path. 2. The multi-stage centrifugal compressor according to claim 1, wherein the collision loss reduction means increases the flow angle of the gas injected between the stages by the pressure-increased gas introduced through the return passage. A multi-stage centrifugal compressor, characterized in that it comprises guide means for making the flow angle of the boosted gas equal to the flow angle at the confluence with the flow. 3. The multistage centrifugal compressor according to claim 2, wherein the guide means is composed of a plurality of plate-shaped guide blades attached so as to form an angle equal to the flow angle of the boosted gas. A multi-stage centrifugal compressor characterized in that 4. The multi-stage centrifugal compressor according to claim 2, wherein the flow width of the annular nozzle is selected so that the flow velocity of the boosted gas and the flow velocity of the injected gas at the merging portion are equal to each other. A multi-stage centrifugal compressor characterized in that 5. The multistage centrifugal compressor according to claim 2, wherein the guide means is composed of a plurality of blade-shaped guide blades whose blade thickness changes from the leading edge to the trailing edge. A multistage centrifugal compressor characterized by. 6. The multi-stage centrifugal compressor according to claim 3 or 5, wherein the guide vanes are attached such that an attachment angle thereof is adjustable. 7. The multistage centrifugal compressor according to claim 3 or 5, wherein a surface of an edge portion of the multistage centrifugal compressor is curved. 8. The multi-stage centrifugal compressor according to claim 4, wherein the flow passage width of the annular nozzle changes from its inlet to its outlet. 9. The multistage centrifugal compressor according to claim 8, wherein the flow passage width of the annular nozzle gradually decreases from the inlet to the outlet thereof. 10. The multistage centrifugal compressor according to claim 8, wherein the flow passage width of the annular nozzle gradually increases from its inlet to its outlet. 11. A diffuser is arranged on the outer circumference in the radial direction of a rotating centrifugal impeller, and a gas boosted by the centrifugal impeller is passed through a return flow passage provided downstream of the diffuser to a centrifugal impeller of the next stage. In a multi-stage centrifugal compressor leading to, an inter-stage injection flow channel structure for injecting a gas between the stages into the pressurized gas guided through the return flow channel, wherein a ring is provided in a part of the return flow channel. Equipped with a nozzle,
The annular nozzle is provided with means for reducing collision loss between the flow of gas injected between the stages and the flow of the pressurized gas introduced through the return flow passage. Interstage injection flow channel structure of the compressor. 12. The interstage injection flow channel structure for a multi-stage centrifugal compressor according to claim 11, wherein the collision loss reducing means determines a flow angle of the gas injected between the stages via the return flow channel. Inter-injection flow channel structure of a multi-stage centrifugal compressor, characterized in that it comprises guide means for making the flow angle of the boosted gas equal to the flow angle of the boosted gas guided by . 13. The interstage injection flow channel structure for a multistage centrifugal compressor according to claim 12, wherein the guide means is a plurality of plate-like members attached so as to form an angle equal to the flow angle of the boosted gas. The inter-stage injection flow channel structure of a multi-stage centrifugal compressor, characterized in that 14. The interstage injection flow channel structure for a multistage centrifugal compressor according to claim 12, wherein a flow channel width of the annular nozzle is a flow velocity of the boosted gas and a flow velocity of the injected gas at the confluence portion. Are selected so that they are equal to each other, an interstage injection flow channel structure of a multistage centrifugal compressor.