Single-shaft multistage centrifugal fluid machine

Abstract

A single-shaft multistage centrifugal fluid machine (100) according to the present invention has: a first suction flow passage (7) that causes a fluid to flow into a first-stage centrifugal impeller (1) during rated flow rate operation; and a second suction flow passage (8) that causes a fluid which imparts prerotation to flow into the first-stage centrifugal impeller (1) during small flow rate operation, wherein the flow passage cross-sectional area (A1) at a merging location (7a) of the first suction flow passage (7) in a merging section (Cf) of the first suction flow passage (7) and the second suction flow passage (8) is smaller than the flow passage cross-sectional area (A2) at a merging location (8a) of the second suction flow passage (8).

Description

Single-axis multi-stage centrifugal fluid machine

[0001] This invention relates to a single-axis, multi-stage centrifugal fluid machine.

[0002] Conventionally, a single-shaft multi-stage centrifugal fluid machine (compressor) is known that has a movable inlet guide vane upstream of the first-stage impeller and a fixed guide vane upstream of the intermediate-stage impeller (see, for example, Patent Document 1). In this single-shaft multi-stage centrifugal compressor, the angle of the inlet guide vane is controlled to impart a pre-swirling motion to the suction flow to the first-stage impeller. This allows the compressor to regulate the flow rate of the working fluid to the upstream compression stages, including the first stage. Furthermore, this compressor imparts a pre-swirling motion to the suction flow to the intermediate-stage impeller using the fixed guide vane. This allows the compressor to regulate the flow rate of the working fluid to the downstream compression stages, including the intermediate stage.

[0003] Japanese Patent Publication No. 2007-309154

[0004] In general, single-shaft multi-stage centrifugal compressors are used in various plants, and depending on the type of plant, frequent repeated operation at rated flow rate and low flow rate at a flow rate lower than the rated flow rate may be required while maintaining the rated discharge pressure. That is, in a single-shaft multi-stage centrifugal compressor, the working fluid is introduced without pre-swirl during rated flow rate operation, while the working fluid is introduced with pre-swirl during low flow rate operation. However, in conventional single-shaft multi-stage centrifugal compressors (for example, Patent Document 1), it is necessary to control the angle of the movable inlet guide vanes each time the state of not having pre-swirl and the state of having pre-swirl are repeated. However, while conventional single-shaft multi-stage centrifugal compressors require operation with a high frequency of driving the inlet guide vanes, sufficient consideration has been given to ensuring high reliability of the angle control. Furthermore, the pre-swirl structure using fixed guide vanes in conventional single-shaft multi-stage centrifugal compressors adjusts the flow rate of the working fluid to the downstream compression stage and cannot be used for low flow rate operation of the entire compressor, including the upstream side.

[0005] The present invention aims to provide a single-axis multi-stage centrifugal fluid machine that can switch between rated flow rate operation and low flow rate operation with a highly reliable configuration, can provide sufficient pre-swirl throughout the entire upstream and downstream side of the compressor, and can also improve compressor efficiency.

[0006] The single-axis multi-stage centrifugal fluid machine of the present invention, which solves the above problems, comprises: a plurality of centrifugal impellers mounted in line in the axial direction of the rotating shaft; a casing housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers; and a discharge nozzle provided in the casing for discharging fluid delivered from the final stage centrifugal impeller among the plurality of centrifugal impellers, wherein the introduction nozzle is a first introduction nozzle used during rated flow rate operation and a discharge nozzle used during low flow rate operation below the rated flow rate. The casing comprises a second introduction nozzle and a casing having a first suction passage for introducing fluid from the first introduction nozzle to the first stage centrifugal impeller, and a second suction passage for introducing fluid from the second introduction nozzle to the first stage centrifugal impeller, and further comprises a flow path switching device for switching the flow path of the fluid introduced to the introduction nozzle between the first suction passage and the second suction passage, wherein the flow path cross-sectional area of ​​the first suction passage at the confluence of the first and second suction passages is smaller than the flow path cross-sectional area of ​​the second suction passage at the confluence of the first and second suction passages.

[0007] Furthermore, the single-axis multi-stage centrifugal fluid machine of the present invention, which solves the above problems, comprises a plurality of centrifugal impellers mounted so as to be aligned in the axial direction of the rotating shaft, a casing housing the plurality of centrifugal impellers, an introduction nozzle provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers, and a discharge nozzle provided in the casing for discharging fluid delivered from the last stage centrifugal impeller among the plurality of centrifugal impellers, wherein the introduction nozzle is a first guide used during rated flow rate operation. The casing comprises an inlet nozzle and a second inlet nozzle used during low-flow operation below the rated flow rate, and the casing comprises a first suction passage for introducing fluid from the first inlet nozzle to the first stage centrifugal impeller, and a second suction passage for introducing fluid from the second inlet nozzle to the first stage centrifugal impeller, and further comprises a flow path switching device for switching the fluid flow path introduced to the inlet nozzle between the first suction passage and the second suction passage, and the volumetric flow rate Q of the fluid introduced into the first suction passage during rated flow rate operation １ The volumetric flow rate Q of the fluid introduced into the second suction channel during the low-flow operation is ２ The flow path width b at the confluence point of the first suction flow path and the second suction flow path. １ The flow path width b at the confluence point of the second suction flow path at the junction of the first suction flow path and the second suction flow path. ２ This satisfies the relationship in equation (3) below. Q １ / Q ２ >b １ / b ２ (3)

[0008] Furthermore, the single-axis multi-stage centrifugal fluid machine of the present invention, which solves the above problems, comprises: a plurality of centrifugal impellers mounted so as to be aligned in the axial direction of the rotating shaft; a casing housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers; and a discharge nozzle provided in the casing for discharging fluid delivered from the last stage centrifugal impeller among the plurality of centrifugal impellers, wherein the introduction nozzle is a first introduction nozzle used during rated flow rate operation and a second introduction nozzle used during low flow rate operation below the rated flow rate The casing comprises an introduction nozzle and a first suction channel for introducing fluid from the first introduction nozzle to the first stage centrifugal impeller, and a second suction channel for introducing fluid from the second introduction nozzle to the first stage centrifugal impeller. The casing further comprises a channel switching device for switching the fluid flow path introduced to the introduction nozzle between the first suction channel and the second suction channel, wherein the cross-sectional area ratio Ar, shown by the following equation (5), from the confluence position of the first suction channel to the suction port of the first stage centrifugal impeller at the confluence of the first and second suction channels, is substantially constant. Ar = A / A1a (5) (wherein in equation (5), A is the cross-sectional area of ​​the channel at any position between the confluence position of the first suction channel and the suction port of the first stage centrifugal impeller, and A1a is the cross-sectional area of ​​the channel at the suction port of the first stage centrifugal impeller)

[0009] According to the present invention, it is possible to provide a single-axis multi-stage centrifugal fluid machine that can switch between rated flow rate operation and low flow rate operation with a highly reliable configuration, can provide sufficient pre-swirl throughout the entire upstream and downstream side of the compressor, and can further improve compressor efficiency.

[0010] It is a meridian sectional view of a single-shaft multi-stage centrifugal compressor according to the first embodiment of the present invention. It is a partial enlarged view near the confluence of the first suction flow path and the second suction flow path of the single-shaft multi-stage centrifugal compressor shown in FIG. 1, and is a diagram schematically showing the movement of the working fluid during low-flow operation. It is a partial enlarged view near the confluence of the first suction flow path and the second suction flow path of the single-shaft multi-stage centrifugal compressor shown in FIG. 1, and is a diagram schematically showing the movement of the working fluid during rated flow operation. The total pressure loss of the suction flow path in the single-shaft multi-stage centrifugal compressor according to the first embodiment, and [(volume flow rate ratio of the working fluid (Q １ / Q ２ )) / (confluence part flow path cross-sectional area ratio (A １ / A ２ ))] is a graph showing the relationship with the value. It is a configuration explanatory diagram of a single-shaft multi-stage centrifugal compressor according to the second embodiment of the present invention, and is a partial enlarged view corresponding to the V part of FIG. 1. It is a graph explaining the cross-sectional area distribution of the flow path from the inside of the first suction flow path of the single-shaft multi-stage centrifugal compressor shown in FIG. 5 to the suction port of the first-stage centrifugal impeller.

[0011] A mode (embodiment) for implementing the single-shaft multi-stage centrifugal fluid machine of the present invention will be described in detail with reference to the drawings as appropriate. Hereinafter, the single-shaft multi-stage centrifugal fluid machine of the present invention will be described by taking a single-shaft multi-stage centrifugal compressor as an example, but the present invention is not limited to this and can also be applied to a single-shaft multi-stage centrifugal pump or the like.

[0012] (First Embodiment) FIG. 1 is a meridian sectional view of a single-shaft multi-stage centrifugal compressor 100 according to the first embodiment of the present invention. As shown in FIG. 1, the single-shaft multi-stage centrifugal compressor 100 is configured such that a plurality of centrifugal impellers 1 housed in a cylindrical casing 4 are attached to a single rotating shaft 2 in multiple stages. The centrifugal impeller 1 in the present embodiment is a closed-type impeller formed such that a plurality of blades 1d arranged in the circumferential direction of the rotating shaft 2 are sandwiched between a shroud 1b and a hub 1c. However, the centrifugal impeller 1 is not limited to this, and can also be an open-type impeller without a shroud 1b. Both ends of the rotating shaft 2 are rotatably supported by bearings 3b provided in a bearing case 3a. Note that the bearing case 3a is provided integrally with the casing 4 or attached to a mounting base (not shown) provided separately.

[0013] The casing 4 is equipped with an introduction nozzle 5 for introducing fluid (hereinafter sometimes referred to as working fluid) into the first stage centrifugal impeller 1 of the multiple centrifugal impellers 1, and a discharge nozzle 6 for discharging the fluid discharged from the final stage centrifugal impeller 1. This casing 4 will be described in detail later.

[0014] On the radially outer side of each stage of centrifugal impeller 1, a diffuser section 9 is formed, which serves as a flow path for the working fluid discharged from each stage of centrifugal impeller 1, extending almost radially. In this embodiment, the diffuser section 9 is a bladed diffuser having a plurality of blades 9a arranged at intervals in the circumferential direction. However, a bladeless diffuser without any blades 9a can also be used for the diffuser section 9.

[0015] Downstream of the diffuser section 9, a return channel 10 is provided, which forms a suction passage to the next stage centrifugal impeller 1. The return channel 10 changes the radially outward flow of the working fluid to a radially inward flow. The return channel 10 is also provided with return vanes 10a that rectify the flow of the working fluid. These return vanes 10a are spaced apart in the circumferential direction. The diffuser section 9 and the return channel 10 together form a stationary passage 11 for the working fluid on the radially outward side of the rotating centrifugal impeller 1.

[0016] A scroll 12 is formed downstream of the final stage centrifugal impeller 1. The scroll 12 is formed radially outward from the centrifugal impeller 1. The scroll 12 collects the high-pressure working fluid flowing out from the final stage centrifugal impeller 1 and discharges it outside the machine through the discharge nozzle 6.

[0017] Furthermore, the single-shaft multi-stage centrifugal compressor 100 is provided with multiple shaft seals 13. Specifically, as shown in Figure 1, the shaft seals 13 are provided in the gap between the centrifugal impeller 1 and the casing 4, and in the gap between the portion of the casing 4 where the diffuser portion 9 and the return channel 10 are formed and the rotating shaft 2.

[0018] Furthermore, as shown in Figure 1, the single-shaft multi-stage centrifugal compressor 100 further includes a shaft seal 14 and a shaft seal 15. The shaft seal 14 is located in the shaft penetration between the first-stage centrifugal impeller 1 and the bearing 3b. The shaft seal 14 prevents outside air and other elements from flowing into the first-stage centrifugal impeller 1. The shaft seal 15 is located in the shaft penetration between the final-stage centrifugal impeller 1 and the bearing 3b. The shaft seal 15 prevents the working fluid discharged from the final-stage centrifugal impeller 1 from leaking outside the machine. This allows the working fluid to flow efficiently into the scroll 12. In this embodiment, these shaft seals 13, 14, and 15 are assumed to be labyrinth seals, but are not limited to this.

[0019] Next, the casing 4 will be described in more detail. As shown in Figure 1, the outer circumferential surface of the suction side of the casing 4 is provided with a first inlet nozzle 5a and a second inlet nozzle 5b, which constitute the inlet nozzle 5. The casing 4 also has a first suction passage 7 that communicates with the first inlet nozzle 5a. The casing 4 also has a second suction passage 8 that communicates with the second inlet nozzle 5b.

[0020] As shown in Figure 1, the first suction passage 7 and the second suction passage 8 are located at the end of the casing 4 on the side of the first stage centrifugal impeller 1. The second suction passage 8 is formed closer to the first stage centrifugal impeller 1 than the first suction passage 7. The first suction passage 7 and the second suction passage 8 are passages for introducing working fluid from outside the single-shaft multi-stage centrifugal compressor 100 into the compressor.

[0021] Specifically, the first suction channel 7 allows the working fluid drawn in from the first inlet nozzle 5a to flow into the first-stage centrifugal impeller 1. The second suction channel 8 allows the working fluid drawn in from the second inlet nozzle 5b to flow into the first-stage centrifugal impeller 1. At this time, the first suction channel 7 and the second suction channel 8 change the flow of the working fluid flowing into the first-stage centrifugal impeller 1 from the radially outward direction to a suction flow along the axis X. Subsequently, the working fluid flows into the suction port 1a of the first-stage centrifugal impeller 1.

[0022] Of the inlet nozzles 5, the first inlet nozzle 5a and the first suction passage 7 are used during rated flow rate operation. The second inlet nozzle 5b and the second suction passage 8 are used during low flow rate operation below the rated flow rate. The working fluid flowing through the second suction passage 8 merges with the working fluid flowing through the first suction passage 7, thereby imparting a swirling component to the working fluid flowing into the first-stage centrifugal impeller 1. The first suction passage 7 supplies working fluid to the first-stage centrifugal impeller 1 that has less or no swirling component than the working fluid flowing through the second suction passage 8.

[0023] In Figure 1, reference numeral 5aa indicates the inlet flange portion of the first inlet nozzle 5a. Reference numeral 5ba indicates the inlet flange portion of the second inlet nozzle 5b. The cross-sectional shape of the inner flow path in the inlet flange portions 5aa and 5ba is circular. The first suction flow path 7 and the second suction flow path 8 each have an oval shape when viewed in a horizontal cross-sectional view parallel to axis X. The cross-sectional shape of the first suction flow path 7 and the second suction flow path 8 is such that the major axis gradually becomes longer as you move radially inward from the inlet flange portions 5aa and 5ba, and the oval shape becomes flatter.

[0024] Furthermore, the single-axis multi-stage centrifugal compressor 100 of this embodiment has a fixed fluid guide 17, as shown in Figure 1. The fixed fluid guide 17 provides a stable and uniform swirling flow (swirling component) to the working fluid flowing inside the second suction passage 8. The first suction passage 7 and the second suction passage 8 are separated by a partition wall 18 that forms part of the casing 4. The first suction passage 7 and the second suction passage 8 merge at the inner diameter end 18a of the partition wall 18, and the merged passage is connected to the suction port 1a of the first-stage centrifugal impeller 1.

[0025] Furthermore, the single-axis multi-stage centrifugal compressor 100 of this embodiment is equipped with a flow path switching device 20 that switches the flow path of the introduced working fluid to either the first suction flow path 7 or the second suction flow path 8. This flow path switching device 20 includes a main pipe 21 that guides the working fluid to the first inlet nozzle 5a, a sub-pipe 22 that branches off from the main pipe 21 and guides the working fluid to the second inlet nozzle 5b, an on-off valve 21a located in the main pipe 21 downstream of the branching point of the sub-pipe 22, an on-off valve 22a located in the sub-pipe 22, and a control unit 23 for the on-off valves 21a and 22a. This flow path switching device 20 realizes rated flow rate operation of the single-axis multi-stage centrifugal compressor 100 by opening the on-off valve 21a and closing the on-off valve 22a based on commands from the control unit 23, which is equipped with a CPU (central processing unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. Furthermore, the flow path switching device 20 enables low-flow operation of the single-shaft multi-stage centrifugal compressor 100 by closing the on-off valve 21a and opening the on-off valve 22a in response to a command from the control unit 23.

[0026] Next, the relationship between the cross-sectional area of ​​the first suction passage 7 and the cross-sectional area of ​​the second suction passage 8 in the single-shaft multi-stage centrifugal compressor 100 of this embodiment will be explained. Figures 2 and 3 are enlarged views of the vicinity of the confluence Cf of the first suction passage 7 and the second suction passage 8 of the single-shaft multi-stage centrifugal compressor 100 shown in Figure 1. Figure 2 is a schematic diagram showing the movement of the working fluid during low-flow rate operation, and Figure 3 is a schematic diagram showing the movement of the working fluid during rated flow rate operation. The confluence Cf shown in Figures 2 and 3 is formed in an annular space formed around the axis X. In Figures 2 and 3, reference numeral 7a indicates the confluence position of the first suction passage 7 with respect to the confluence Cf, and reference numeral 8a indicates the confluence position of the second suction passage 8 with respect to the confluence Cf.

[0027] The confluence point 7a of the first suction channel 7 is shown by a dotted line in Figures 2 and 3, and represents the channel cross-sectional position where, in a meridian cross-sectional view, the distance from the radially inward tip 18a of the partition wall 18 to the wall surface of the first suction channel 7 facing the wall surface of the first suction channel 7 on the side where this tip 18a is formed is the shortest. In Figures 2 and 3, the symbol is A. １This is the cross-sectional area of ​​the first suction channel 7 at the confluence point 7a, and is denoted by the symbol b. １ This is the width of the first suction channel 7 at the confluence point 7a in a meridian cross-sectional view. Note that A is the cross-sectional area of ​​the first suction channel 7 at the confluence point 7a facing the annular confluence section Cf. １ This is the area of ​​the circumferential surface of the virtual cylinder formed by rotating the line segment consisting of the dotted line shown as the confluence position 7a around the axis X.

[0028] Furthermore, the confluence position 8a of the second suction channel 8 is shown by a dotted line in Figures 2 and 3, and represents the channel cross-sectional position where, in a meridian cross-sectional view, the distance from the radially inward tip 18a of the partition wall 18 to the wall surface of the second suction channel 8 facing the wall surface of the second suction channel 8 on the side where this tip 18a is formed is the shortest.

[0029] In Figures 2 and 3, reference numeral A ２ This is the cross-sectional area of ​​the flow path of the second suction flow path 8 at the confluence position 8a, and is denoted by the symbol b. ２ This is the channel width of the second suction channel 8 at the confluence point 8a in a meridian cross-sectional view. Note that A is the channel cross-sectional area of ​​the second suction channel 8 at the confluence point 8a facing the annular confluence section Cf. ２ This is the area of ​​the circumferential surface of the virtual cylinder formed by rotating the line segment consisting of the dotted line shown as the confluence position 8a around the axis X. Also, in Figures 2 and 3, reference numeral 1a is the intake port of the first stage centrifugal impeller 1 (see Figure 1), reference numeral 13 is the shaft seal portion provided in the gap between the casing 4 and the shroud 1b, and reference numeral 1bw is the inlet flow path surface on the shroud 1b side that forms the intake port 1a.

[0030] In this embodiment of the single-axis multi-stage centrifugal compressor 100, the flow path cross-sectional area A of the first suction flow path 7 at the confluence position 7a １ This is the cross-sectional area A of the second suction passage 8 at the confluence point 8a of the second suction passage 8. ２ It is set to be relatively small in relation to [another value].

[0031] Furthermore, in such a single-shaft multi-stage centrifugal compressor 100, specifically, the flow path cross-sectional area A of the first suction flow path 7 at the confluence position 7a １ And the cross-sectional area of ​​the flow path A of the second suction flow path 8 at the confluence point 8a ２The following equation (1) is satisfied. １ / Q ２ > A １ / A ２ (1) (However, in equation (1), Q １ Q is the volumetric flow rate of the working fluid in the first suction passage 7 during rated flow rate operation. ２ (This is the volumetric flow rate of the working fluid in the second suction channel 8 during low-flow operation.)

[0032] Furthermore, in such a single-axis multi-stage centrifugal compressor 100, Q １ / Q ２ and A １ / A ２ As will be explained in detail later, it is desirable to set it so that the following relationship (2) is satisfied: 1.5 × A １ / A ２ ≦Q １ / Q ２ ≤3.0 × A １ / A ２ (2)

[0033] Furthermore, in such a single-axis multi-stage centrifugal compressor 100, as shown in Figure 3, the tangent 18w of the radially inward tip 18a of the partition wall 18 to the wall surface of the first suction passage 7 is in contact with the inlet passage surface 1bw of the shroud 1b of the first-stage centrifugal impeller 1 (see Figure 1) on the downstream extension line.

[0034] Furthermore, in such a single-axis multi-stage centrifugal compressor 100, the A in equations (1) and (2) １ / A ２ Instead of the area ratio shown, the flow path width b at the confluence position 7a of the first suction flow path 7 in the confluence Cf of the first suction flow path 7 and the second suction flow path 8 is used. １ And the flow path width b at the confluence position 8a of the second suction flow path 8 in the confluence section Cf. ２ The ratio of b １ / b ２ The following can also be applied: that is, the volumetric flow rate Q of the working fluid in the first suction passage 7 during rated flow rate operation satisfies equation (3) below and equation (4) below. １The volumetric flow rate Q of the working fluid in the second suction channel 8 during low-flow operation. ２ And the flow path width b １ And the flow path width b ２ You can also set this. Q １ / Q ２ >b １ / b ２ (3) 1.5 × b １ / b ２ ≦Q １ / Q ２ ≤ 3.0 × b １ / b ２ (4)

[0035] ≪Effects≫ Next, we will explain the effects of the single-shaft multi-stage centrifugal compressor 100 (see Figure 1) while describing its operation. The single-shaft multi-stage centrifugal compressor 100 operates at a low flow rate when the on-off valve 21a (see Figure 1) is closed and the on-off valve 22a (see Figure 1) is opened by the flow path switching device 20 (see Figure 1). During this low flow rate operation, as shown in Figure 2, the volumetric flow rate Q of the working fluid in the first suction flow path 7 becomes zero (Q = 0), and the volumetric flow rate Q of the working fluid in the second suction flow path 8 becomes Q ２ Set to (Q = Q ２ ).

[0036] In this process, the working fluid flowing into the second suction channel 8 is given a swirling component by the stationary fluid guide 17 (see Figure 1). The working fluid that has passed through the stationary fluid guide 17 (see Figure 1) then flows from the confluence point 8a towards the suction port 1a, as shown in Figure 2. In Figure 2, the symbol S Ｍ This indicates the main flow of the working fluid, and is denoted by the symbol S. Ｌ This indicates leakage flow that detours towards the confluence point 7a of the first suction passage 7. Incidentally, during low-flow operation, the confluence point 7a of the first suction passage 7 is in a stagnant state with no working fluid flow.

[0037] Volumetric flow rate Q of the working fluid flowing into the compressor during low-flow operation. ２All of this flows into the second suction channel 8. At this time, the working fluid passes through the stationary fluid guide 17 and is given a large swirling component, so the working fluid at the confluence point 8a has a flow velocity component in the direction perpendicular to the cross-section of the flow path, as well as a flow velocity component in the direction of the swirling motion. As a result, the absolute flow velocity of the working fluid at the confluence point 8a becomes very large.

[0038] Furthermore, as shown in Figure 2, the working fluid flowing inside the second suction passage 8 flows radially inward along the flow path wall surface of the partition wall 18 up to the confluence point 8a of the second suction passage 8. However, radially inward from the tip 18a of the partition wall 18 is the confluence point Cf, so the flow path rapidly expands towards the first suction passage 7. The working fluid is indicated by the symbol S in Figure 2. Ｌ As indicated by the dotted arrow, the fluid flows backward from the confluence point 8a on the second suction passage 8 side toward the upstream side of the first suction passage 7, and then detours back to the confluence point Cf. This is the leakage flow S of the working fluid. Ｌ The main working fluid S Ｍ It merges with the other flow and flows towards the suction port 1a. This is the leakage flow S. Ｌ This can generally lead to a decrease in the pre-swirl of the working fluid introduced from the second suction passage 8, as well as an increase in deceleration losses and mixing losses.

[0039] Although not shown in the diagram here, a general pre-swirl structure is assumed as a comparative example of this embodiment. In this pre-swirl structure, the volumetric flow rate of the introduced working fluid is Q X Therefore, the channel cross-sectional area is A X The first channel is defined as the first channel, and the volumetric flow rate of the working fluid introduced is Q. Y Therefore, the channel cross-sectional area is A Y The second channel, which is configured to merge with the first channel, is configured to satisfy the following equation (m), Q X Q Y A X , and A Y This will be set. Q X / Q Y = A X / A Y (m) (However, in equation (m), Q X Q is the volumetric flow rate of the working fluid during rated flow rate operation. Yis the volume flow rate of the working fluid during low-flow operation, where Q X / Q Y > 1)

[0040] That is, the volume flow rate ratio of the working fluid flowing through the first flow path and the second flow path (Q X / Q Y ) and the confluence flow path cross-sectional area of each flow path (A X / A Y ) are made to match, and the confluence flow path cross-sectional areas A X and A Y of each flow path are set. As a result, the confluence flow path cross-sectional area A X of the first flow path into which the working fluid is introduced during rated flow operation is larger than the confluence flow path cross-sectional area A Y of the second flow path into which the working fluid is introduced during low-flow operation. Incidentally, the confluence flow path cross-sectional area A X corresponds to the flow path cross-sectional area A １ at the confluence position 7a of the first suction flow path 7 shown in FIG. 2.

[0041] Therefore, in the flow path portion having a confluence flow path cross-sectional area A Y larger than the confluence flow path cross-sectional area A X , the flow resistance of the working fluid becomes small, and the leakage flow S Ｌ of the working fluid shown in FIG. 2 is likely to occur. Therefore, in the pre-whirl imparting structure described as a comparative example of the present embodiment, it will cause a decrease in the pre-whirl of the introduced working fluid, an increase in deceleration loss, and an increase in mixing loss.

[0042] In contrast, the single-shaft multi-stage centrifugal compressor 100 of the present embodiment includes a plurality of centrifugal impellers 1 mounted so as to be arranged in the axial direction of the rotating shaft 2 (axis X direction), a casing 4 that houses the plurality of centrifugal impellers 1, an inlet nozzle 5 provided in the casing 4 for introducing fluid into the first-stage centrifugal impeller 1 among the plurality of centrifugal impellers 1, and a discharge nozzle 6 provided in the casing 4 for discharging the fluid sent out from the final-stage centrifugal impeller 1 among the plurality of centrifugal impellers 1. The inlet nozzle 5 has a first inlet nozzle 5a used during rated flow operation and a second inlet nozzle 5b used during low-flow operation with a flow rate less than the rated flow rate. The casing 4 has a first suction flow path 7 for allowing fluid to flow into the first-stage centrifugal impeller 1 from the first inlet nozzle 5a and a second suction flow path 8 for allowing fluid to flow into the first-stage centrifugal impeller 1 from the second inlet nozzle 5b. The one-axis multi-stage centrifugal compressor 100 further includes a flow path switching device 20 for switching the flow path of the fluid introduced into the inlet nozzle 5 to the first suction flow path 7 or the second suction flow path 8. The flow path cross-sectional area A at the confluence position 7a of the first suction flow path 7 in the confluence portion Cf of the first suction flow path 7 and the second suction flow path 8 １ is smaller than the flow path cross-sectional area A at the confluence position 8a of the second suction flow path 8. ２ Specifically, in order for the single-shaft multi-stage centrifugal compressor 100 to more reliably achieve the relationship of "flow path cross-sectional area A

[0043] < flow path cross-sectional area A １ <", the volume flow rate Q of the fluid introduced into the first suction flow path during rated flow operation ２ and the volume flow rate Q of the fluid introduced into the second suction flow path during low-flow operation １ and the flow path cross-sectional area A at the confluence position 7a of the first suction flow path 7 in the confluence portion Cf of the first suction flow path 7 and the second suction flow path 8 ２ and the flow path cross-sectional area A at the confluence position 8a of the second suction flow path 8 in the confluence portion Cf of the first suction flow path 7 and the second suction flow path 8 １ satisfy the following relationship of formula (1). Q ２ / Q １ > A １ / A ２ (1)

[0044] According to such a single-shaft multi-stage centrifugal compressor 100, the flow path cross-sectional area A １ １ １At the confluence point 7a, the flow resistance of the first suction channel 7 increases, resulting in the leakage flow S of the working fluid shown in Figure 2. Ｌ This makes it less likely for problems to occur. With such a single-shaft multi-stage centrifugal compressor 100, it is possible to prevent a decrease in the pre-swirl of the working fluid introduced into the first-stage centrifugal impeller 1, thereby suppressing deceleration losses and reducing mixing losses. The single-shaft multi-stage centrifugal compressor 100 can switch between rated flow rate operation and low flow rate operation with a relatively simple and reliable configuration using a flow path switching device 20, and can provide sufficient pre-swirl throughout the entire upstream and downstream side of the compressor. Furthermore, the single-shaft multi-stage centrifugal compressor 100 can also improve compressor efficiency by preventing a decrease in pre-swirl.

[0045] Furthermore, in this single-axis multi-stage centrifugal compressor 100, Q １ / Q ２ and A １ / A ２ It is desirable that the following relationship (2) is satisfied: 1.5 × A １ / A ２ ≦Q １ / Q ２ ≤3.0 × A １ / A ２ (2) In the single-axis multi-stage centrifugal compressor 100 of this embodiment, the volume flow rate ratio Q of the working fluid flowing through each flow path is as shown in formula (1) above. １ / Q ２ and the cross-sectional area of ​​the channel at the confluence of each channel A １ / A ２ When setting the relationship between these two factors, a trade-off may occur between performance during rated flow rate operation and performance during low flow rate operation.

[0046] Next, the relationship between equation (2) and the trade-off will be explained. The single-axis multi-stage centrifugal compressor 100 operates at its rated flow rate when the on-off valve 21a (see Figure 1) is opened and the on-off valve 22a (see Figure 1) is closed by the flow path switching device 20 (see Figure 1). During this rated flow rate operation, as shown in Figure 3, the volumetric flow rate Q of the working fluid in the second suction flow path 8 becomes zero (Q = 0), and the volumetric flow rate Q of the working fluid in the first suction flow path 7 becomes Q １ Set to (Q = Q １). In Figure 3, symbol M Ｍ This indicates the main flow of the working fluid, and the symbol M represents this. Ｌ This indicates leakage flow that detours towards the confluence point 8a of the second suction passage 8. Incidentally, during rated flow rate operation, the confluence point 8a of the second suction passage 8 is in a stagnant state with no working fluid flow.

[0047] As shown in Figure 3, during rated flow rate operation, leakage flow M from the first suction passage 7 to the second suction passage 8. Ｌ This occurs. However, this leakage flow M Ｌ This refers to the leakage flow S during low-flow operation. Ｌ Unlike (see Figure 2), it does not have a swirling component. Also, the flow path cross-sectional area A at the confluence position 8a of the second suction flow path 8. ２ This refers to the small volumetric flow rate Q during low-flow operation. ２ It is set accordingly. Therefore, the leakage flow M Ｌ The flow rate is small, and the leakage flow M Ｌ The pressure loss due to this is also small. Therefore, the leakage flow M during rated flow rate operation is small. Ｌ This does not constitute a major cause of loss in the first suction channel 7.

[0048] On the other hand, as described above, the cross-sectional area of ​​the flow path A at the confluence point 7a of the first suction flow path 7. １ This is the cross-sectional area of ​​the flow path A at the confluence point 8a of the second suction flow path 8. ２ It is smaller than. Therefore, the flow velocity of the working fluid near the confluence point 7a of the first suction passage 7 increases during rated flow rate operation, and the friction loss at the passage wall near the confluence point 7a increases. In this case, applying the formula (m) from the comparative example, for example, the cross-sectional area A of the passage １ Assuming that the value is set to be halved, the flow velocity at the confluence point 7a will double. Since wall friction loss basically increases in proportion to the square of the flow velocity, the wall friction loss in this case will increase fourfold when the general formula (m) is applied.

[0049] As described above, the volumetric flow rate ratio Q of the working fluid flowing through each channel is as shown in equation (1) in this embodiment. １ / Q ２ and the ratio of the cross-sectional area of ​​the confluence of each channel A１ / A ２ When the relationship is set, a trade-off may occur regarding the performance during rated flow rate operation and low flow rate operation. On the other hand, the single-shaft multi-stage centrifugal compressor 100 of this embodiment has a volume flow rate ratio Q １ / Q ２ Ratio A of confluence channel area １ / A ２ Regarding the value of Q, there is an appropriate range from the perspective of balancing performance during rated flow rate operation and low flow rate operation. １ / Q ２ A １ / A ２ In this embodiment, the range is defined as shown in formula (2) above.

[0050] Next, we will explain the specific basis for the inequality shown in equation (2) above. Figure 4 shows (Q １ / Q ２ ) / (A １ / A ２ This graph shows the relationship between the value of and the total pressure loss in the suction channel, which was obtained by simulation using numerical fluid analysis. In Figure 4, the series plotted with circles represents the volumetric flow rate Q flowing through the first suction channel 7 (see Figure 3) during rated flow rate operation. １ Regarding the working fluid (see Figure 3), the total pressure loss occurring from directly upstream of the confluence point 7a (see Figure 3) to the suction port 1a (see Figure 1) of the first-stage centrifugal impeller 1 (see Figure 1) is shown. Also, in Figure 4, the series plotted with squares represents the volumetric flow rate Q flowing through the second suction channel 8 (see Figure 2) during low-flow operation. ２ The total pressure loss for the working fluid (see Figure 2) is shown from directly upstream of the confluence point 8a to the suction port 1a (see Figure 1) of the first-stage centrifugal impeller 1 (see Figure 1).

[0051] Note that the values ​​on the vertical axis of Figure 4 are the series marked with a square (low flow rate operation), as described later (Q １ / Q ２ ) / (A １ / A ２When ) ≈ 3.5, the total pressure loss value that occurs from directly upstream of the confluence position 8a (see Figure 2) to the suction port 1a (see Figure 1) of the first stage centrifugal impeller 1 (see Figure 1) is entirely dimensionless. That is, the value on the horizontal axis of the series marked with a square (low flow rate operation) (Q) １ / Q ２ ) / (A １ / A ２ For a value of approximately 3.5, the value of total pressure loss on the vertical axis is 1.0.

[0052] As shown in Figure 4, the total pressure loss in the series marked with a square (low flow rate operation) is generally larger than the total pressure loss in the series marked with a circle (rated flow rate operation). Therefore, (Q １ / Q ２ ) / (A １ / A ２ It is appropriate to determine the range of the value of ) based on the total pressure loss value that occurs from directly upstream of the confluence point 8a (see Figure 2) to the suction port 1a (see Figure 1) of the first stage centrifugal impeller 1 (see Figure 1) during low flow rate operation.

[0053] As shown in Figure 4, when we look at the change in total pressure loss in the series marked with a square (low flow rate operation), (Q １ / Q ２ ) / (A １ / A ２ As (Q) increases, the total pressure loss gradually decreases. However, the rate of decrease in total pressure loss gradually decreases as you move to the right of the graph. Therefore, (Q) １ / Q ２ ) / (A １ / A ２ ) = 3.0 or to the right of that, anything above (Q １ / Q ２ ) / (A １ / A ２ Even when the ) is increased, the total pressure loss remains approximately constant.

[0054] In contrast, the total pressure loss in the circled series (rated flow rate operation) is (Q １ / Q ２ ) / (A １ / A ２ The larger the value of (Q), the larger it becomes. In other words, the series of square marks (low flow rate operation) １ / Q ２ ) / (A１ / A ２ Considering that the total pressure loss becomes approximately constant when ) is 3.0 or higher, in the single-shaft multi-stage centrifugal compressor 100 of this embodiment (see Figure 1), (Q １ / Q ２ ) / (A １ / A ２ In the range where ) > 3.0, only the total pressure loss of the circled series (rated flow rate operation) becomes large. Therefore, in the single-shaft multi-stage centrifugal compressor 100 of this embodiment (see Figure 1), (Q １ / Q ２ ) / (A １ / A ２ ) ≤ 3.0, that is, (Q １ / Q ２ ) ≤ 3.0 × (A １ / A ２ (Q) １ / Q ２ ) and (A １ / A ２ ) is set.

[0055] Also, as shown in Figure 4, (Q １ / Q ２ ) / (A １ / A ２ ) < 3.0 means that the total pressure loss value in the series marked with a square (low flow rate operation) increases. Specifically, the rate of increase in total pressure loss is (Q １ / Q ２ ) / (A １ / A ２ )=2.0 and then it gets bigger, (Q １ / Q ２ ) / (A １ / A ２ ) < 1.5 is when the value of the total pressure loss on the vertical axis exceeds 1.5. This value of the total pressure loss on the vertical axis is (Q １ / Q ２ ) / (A １ / A ２ ) ≈ 3.5 is 1.5 times or more the total pressure loss. Therefore, in the single-shaft multi-stage centrifugal compressor 100 of this embodiment (see Figure 1), (Q １ / Q ２ ) / (A １ / A ２ ) ≈ 3.5 does not exceed 1.5 times the total pressure loss, (Q１ / Q ２ ) / (A １ / A ２ ) ≥ 1.5, that is, 1.5 × (A １ / A ２ )≦(Q １ / Q ２ (Q) １ / Q ２ ) and (A １ / A ２ ) is set.

[0056] Furthermore, in the single-shaft multi-stage centrifugal compressor 100, the second suction passage 8 is configured to impart a swirling component to the fluid (working fluid) that flows into the first-stage centrifugal impeller 1. With such a single-shaft multi-stage centrifugal compressor 100, the introduction of the working fluid into the second suction passage 8 by the flow path switching device 20 (see Figure 1) can more reliably prevent a decrease in the pre-swirling of the working fluid introduced into the first-stage centrifugal impeller 1.

[0057] Furthermore, in the single-shaft multi-stage centrifugal compressor 100, the casing 4 is equipped with a partition wall 18 separating the first suction passage 7 and the second suction passage 8. In a meridional cross-sectional view of the single-shaft multi-stage centrifugal compressor 100, the tangent 18w of the radially inward tip 18a of the partition wall 18 to the wall surface of the first suction passage 7 is in contact with the inlet passage surface 1bw of the shroud 1b of the first-stage centrifugal impeller 1 on the downstream extension. With such a single-shaft multi-stage centrifugal compressor 100, as shown in Figure 3, the main flow M passing through the first suction passage 7 during rated flow rate operation... Ｍ However, it flows smoothly into the first stage centrifugal impeller 1. As a result, the single-shaft multi-stage centrifugal compressor 100 has a leak flow M Ｌ The mainstream M Ｍ This can be prevented. The single-axis multi-stage centrifugal compressor 100 can suppress the increase in pressure loss caused by the first suction passage 7 during rated flow rate operation.

[0058] Furthermore, the single-shaft multi-stage centrifugal compressor 100 includes a plurality of centrifugal impellers 1 mounted in the axial direction (axis X direction) of the rotating shaft 2, a casing 4 housing the plurality of centrifugal impellers 1, an introduction nozzle 5 provided in the casing 4 for introducing fluid to the first stage centrifugal impeller 1 of the plurality of centrifugal impellers 1, and a discharge nozzle 6 provided in the casing 4 for discharging fluid delivered from the final stage centrifugal impeller 1 of the plurality of centrifugal impellers 1, wherein the introduction nozzle 5 is the first introduction nozzle used during rated flow rate operation. The casing 4 has an inlet nozzle 5a and a second inlet nozzle 5b used during low-flow operation below the rated flow rate. The casing 4 has a first suction passage 7 through which fluid flows from the first inlet nozzle 5a to the first stage centrifugal impeller 1, and a second suction passage 8 through which fluid flows from the second inlet nozzle 5b to the first stage centrifugal impeller 1. The casing 4 further includes a flow path switching device 20 that switches the fluid flow path introduced into the inlet nozzle 5 between the first suction passage 7 and the second suction passage 8, and the volumetric flow rate Q of the fluid introduced into the first suction passage 7 during rated flow rate operation. １ The volumetric flow rate Q of the fluid introduced into the second suction channel 8 during low-flow operation. ２ The flow path width b at the confluence position 7a of the first suction flow path 7 in the confluence section Cf of the first suction flow path 7 and the second suction flow path 8. １ And the flow path width b at the confluence position 8a of the second suction flow path 8 in the confluence section Cf of the first suction flow path 7 and the second suction flow path 8. ２ This satisfies the relationship in equation (3) below. Q １ / Q ２ >b １ / b ２ (3)

[0059] According to such a single-axis multi-stage centrifugal compressor 100, the flow path width b １ At the confluence point 7a, the flow resistance of the first suction channel 7 increases, resulting in the leakage flow S of the working fluid shown in Figure 2. ＬThis makes it less likely for problems to occur. With such a single-shaft multi-stage centrifugal compressor 100, it is possible to prevent a decrease in the pre-swirl of the working fluid introduced into the first-stage centrifugal impeller 1, thereby suppressing deceleration losses and reducing mixing losses. The single-shaft multi-stage centrifugal compressor 100 can switch between rated flow rate operation and low flow rate operation with a highly reliable configuration using a flow path switching device 20, and can provide sufficient pre-swirl throughout the entire upstream and downstream side of the compressor. Furthermore, the single-shaft multi-stage centrifugal compressor 100 can also improve compressor efficiency by preventing a decrease in pre-swirl.

[0060] Furthermore, in this single-axis multi-stage centrifugal compressor 100, Q １ / Q ２ and the aforementioned b １ / b ２ This satisfies the relationship in equation (4) below: 1.5 × b １ / b ２ ≦Q １ / Q ２ ≤ 3.0 × b １ / b ２ (4) With such a single-shaft multi-stage centrifugal compressor 100, even considering the trade-off between performance during rated flow rate operation and low flow rate operation as described above, the effect of suppressing performance degradation during low flow rate operation is sufficiently outstanding.

[0061] Furthermore, in this single-shaft multi-stage centrifugal compressor 100, the second suction passage 8 is configured to impart a swirling component to the fluid flowing into the first-stage centrifugal impeller 1. With such a single-shaft multi-stage centrifugal compressor 100, the introduction of the working fluid into the second suction passage 8 by the aforementioned flow path switching device 20 (see Figure 1) makes it possible to more reliably prevent a decrease in the pre-swirling of the working fluid introduced into the first-stage centrifugal impeller 1.

[0062] Furthermore, in this single-shaft multi-stage centrifugal compressor 100, the casing 4 is equipped with a partition wall 18 separating the first suction passage 7 and the second suction passage 8, and in a meridional cross-sectional view of the single-shaft multi-stage centrifugal compressor 100, the tangent 18w of the radially inward tip 18a of the partition wall 18 to the wall surface of the first suction passage 7 is in contact with the inlet passage surface 1bw of the shroud 1b of the first-stage centrifugal impeller 1 on the downstream extension line. With such a single-shaft multi-stage centrifugal compressor 100, as described above, the main flow M passing through the first suction passage 7 during rated flow rate operation Ｍ However, it flows smoothly into the first stage centrifugal impeller 1. As a result, the single-shaft multi-stage centrifugal compressor 100 has a leak flow M Ｌ The mainstream M Ｍ This can be prevented. The single-axis multi-stage centrifugal compressor 100 can suppress the increase in pressure loss caused by the first suction passage 7 during rated flow rate operation.

[0063] (Second Embodiment) Next, a single-shaft multi-stage centrifugal compressor 100 according to a second embodiment of the present invention will be described. In this second embodiment, the same reference numerals are used for the same components as in the first embodiment, and their detailed descriptions are omitted. Figure 5 is an explanatory diagram of the configuration of the single-shaft multi-stage centrifugal compressor 100 of this embodiment, and corresponds to section V in Figure 1. In Figure 5, reference numeral 1a is the suction port of the first-stage centrifugal impeller 1, and reference numeral 7a is the merging position of the first suction passage 7 at the merging section Cf of the first suction passage 7 and the second suction passage 8.

[0064] Figure 6 is a graph illustrating the distribution of the flow path cross-sectional area from the inside of the first suction flow path 7 (see Figure 5) to the suction port 1a (see Figure 5) of the single-shaft multi-stage centrifugal compressor 100 (see Figure 5). The horizontal axis of Figure 6 shows the radius ratio R / R1a, obtained by non-dimensionalizing the flow path radius R (see Figure 5) at any position between the inside of the first suction flow path 7 (see Figure 5) and the suction port 1a by the flow path radius R1a (see Figure 5) at the suction port 1a. The vertical axis of Figure 6 shows the cross-sectional area ratio A / A1a, obtained by non-dimensionalizing the flow path cross-sectional area A at any position between the inside of the first suction flow path 7 (see Figure 5) and the suction port 1 (see Figure 5) by the flow path cross-sectional area A1a at the suction port 1a. Note that the flow path cross-sectional area A and flow path radius R of the first suction flow path 7 (see Figure 5) at the confluence Cf (see Figure 5) are calculated using the tangent line 18w shown in Figure 3 as the boundary.

[0065] In this embodiment, the single-shaft multi-stage centrifugal compressor 100 maintains a substantially constant cross-sectional area ratio Ar, expressed by the following equation (5), from the confluence position 7a of the first suction passage 7 at the confluence Cf of the first suction passage 7 and the second suction passage 8 shown in Figure 5, to the position of the suction port 1a of the first-stage centrifugal impeller 1. Ar = A / A1a (5) (wherein A and A1a in equation (5) are the same as A and A1a described above.)

[0066] In this single-shaft multi-stage centrifugal compressor 100, the flow of working fluid from the first suction passage 7 is in the direction from right to left on the horizontal axis of the graph in Figure 6. As shown in Figure 6, the dimensionless flow path cross-sectional area A / A1a in the single-shaft multi-stage centrifugal compressor 100 is approximately constant from the confluence point 7a to the suction port 1a. Specifically, the single-shaft multi-stage centrifugal compressor 100 is configured such that the flow path cross-sectional area at the confluence point 7a is approximately the same as the flow path cross-sectional area A1a by increasing the reduction rate of the flow path cross-sectional area from the inside of the upstream side of the first suction passage 7 to the confluence point 7a.

[0067] Furthermore, in such a single-axis multi-stage centrifugal compressor 100, it is desirable that the second suction passage 8 be configured to impart a swirling component to the fluid flowing into the first-stage centrifugal impeller 1.

[0068] Furthermore, in such a single-shaft multi-stage centrifugal compressor 100, the casing 4 is provided with a partition wall 18 separating the first suction passage 7 and the second suction passage 8, and it is desirable that, in a meridional cross-sectional view of the single-shaft multi-stage centrifugal compressor 100, the tangent line 18w of the radially inward tip 18a of the partition wall 18 to the wall surface of the first suction passage 7 is configured to be in contact with the inlet passage surface 1bw of the shroud 1b of the first-stage centrifugal impeller 1 on the downstream extension line.

[0069] ≪Effects≫ The single-shaft multi-stage centrifugal compressor 100 according to the second embodiment of the present invention comprises a plurality of centrifugal impellers 1 mounted so as to be aligned in the axial direction (axis X direction) of the rotating shaft 2, a casing 4 housing the plurality of centrifugal impellers 1, an introduction nozzle 5 provided in the casing 4 for introducing fluid to the first stage centrifugal impeller 1 of the plurality of centrifugal impellers 1, and a discharge nozzle 6 provided in the casing 4 for discharging fluid delivered from the final stage centrifugal impeller 1 of the plurality of centrifugal impellers 1, wherein the introduction nozzle 5 is a first introduction nozzle 5a used during rated flow rate operation and a discharge nozzle 6 used during low flow rate operation below the rated flow rate The casing 4 has a second introduction nozzle 5b and a first suction passage 7 that allows fluid to flow from the first introduction nozzle 5a to the first stage centrifugal impeller 1, and a second suction passage 8 that allows fluid to flow from the second introduction nozzle 5b to the first stage centrifugal impeller 1. The casing 4 further includes a flow path switching device 20 that switches the flow path of the fluid introduced into the introduction nozzle 5 between the first suction passage 7 and the second suction passage 8, and the cross-sectional area ratio Ar shown by the following formula (5) from the confluence position 7a of the first suction passage 7 to the position of the suction port 1a of the first stage centrifugal impeller 1 at the confluence Cf of the first suction passage 7 and the second suction passage 8 is substantially constant. Ar = A / A1a (5) (wherein in equation (5), A is the cross-sectional area of ​​the flow path at any position between the confluence point 7a of the first suction flow path 7 and the suction port 1a of the first stage centrifugal impeller 1, and A1a is the cross-sectional area of ​​the flow path at the suction port 1a of the first stage centrifugal impeller 1)

[0070] With such a single-axis multi-stage centrifugal compressor 100, the leakage flow S leaks to the upstream side of the first suction passage 7 during low-flow operation. Ｌ(See Figure 2) This makes it less likely for this to occur, reducing the leakage flow rate of the working fluid and suppressing increases in pressure loss and decreases in the pre-swirl angle.

[0071] Furthermore, in this single-shaft multi-stage centrifugal compressor 100, the second suction passage 8 can be configured to impart a swirling component to the fluid flowing into the first-stage centrifugal impeller 1. With such a single-shaft multi-stage centrifugal compressor 100, the introduction of the working fluid into the second suction passage 8 by the aforementioned flow path switching device 20 (see Figure 1) makes it possible to more reliably prevent a decrease in the pre-swirling of the working fluid introduced into the first-stage centrifugal impeller 1.

[0072] Furthermore, in this single-shaft multi-stage centrifugal compressor 100, the casing 4 is provided with a partition wall 18 separating the first suction passage 7 and the second suction passage 8, and in a meridional cross-sectional view of the single-shaft multi-stage centrifugal compressor 100, the tangent 18w of the radially inward tip 18a of the partition wall 18 to the wall surface of the first suction passage 7 can be configured to contact the inlet passage surface 1bw of the shroud 1b of the first-stage centrifugal impeller 1 on the downstream extension line. With such a single-shaft multi-stage centrifugal compressor 100, as described above, the main flow M passing through the first suction passage 7 during rated flow rate operation Ｍ (See Figure 3) The flow (M) flows smoothly into the first stage centrifugal impeller 1. As a result, the single-shaft multi-stage centrifugal compressor 100 has a leak flow M Ｌ (See Figure 3) The main current M leaks into the suction port 1a. Ｍ This can be prevented by (see Figure 3). The single-shaft multi-stage centrifugal compressor 100 can suppress the increase in pressure loss caused by the first suction passage 7 during rated flow rate operation.

[0073] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. The flow path switching device 20 in the first and second embodiments is assumed to use on-off valves 21a and 22a. However, the single-shaft multi-stage centrifugal compressor 100 can also be configured to use flow control valves instead of on-off valves 21a and 22a. With such a single-shaft multi-stage centrifugal compressor 100, when switching the flow path of the working fluid to the first suction flow path 7 or the second suction flow path 8, the change in the amount of working fluid flowing into the centrifugal impeller 1 can be smoothly controlled, enabling more stable operation.

[0074] Furthermore, in the first and second embodiments, the working fluid passing through the second suction passage 8 used during low-flow operation is configured to have a swirling component. However, the single-shaft multi-stage centrifugal compressor 100 can also be configured not to impart swirling in the second suction passage 8. That is, in the single-shaft multi-stage centrifugal compressor 100, the volume flow rate ratio Q of the working fluid is... １ / Q ２ And, the cross-sectional area ratio of the confluence channel A １ / A ２ (or flow path width ratio b) １ / b ２ ) With this setting, the leakage flow S Ｌ This also helps to suppress performance degradation caused by (see Figure 2).

[0075] 1 Centrifugal impeller 1a Inlet 1b Shroud 1bw Inlet flow path surface 2 Rotating shaft 4 Casing 5 Inlet nozzle 5a First inlet nozzle 5b Second inlet nozzle 6 Discharge nozzle 7 First suction flow path 7a Confluence point 8 Second suction flow path 8a Confluence point 18 Partition 18a Tip 18w Tangent 20 Flow path switching device Cf Confluence point

Claims

1. A plurality of centrifugal impellers mounted in line along the axial direction of a rotating shaft; a casing housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers; a discharge nozzle provided in the casing for discharging fluid delivered from the last stage centrifugal impeller among the plurality of centrifugal impellers; wherein the introduction nozzle has a first introduction nozzle used during rated flow rate operation and a second introduction nozzle used during low flow rate operation below the rated flow rate; the casing has a first suction passage for introducing fluid from the first introduction nozzle to the first stage centrifugal impeller and a second suction passage for introducing fluid from the second introduction nozzle to the first stage centrifugal impeller; and further comprises a flow path switching device for switching the fluid flow path introduced to the introduction nozzle between the first suction passage and the second suction passage. A single-axis multi-stage centrifugal fluid machine in which the cross-sectional area of ​​the first suction channel at the confluence of the first suction channel and the second suction channel is smaller than the cross-sectional area of ​​the second suction channel at the confluence.

2. The volumetric flow rate Q of the fluid introduced into the first suction channel during the rated flow rate operation. １ The volumetric flow rate Q of the fluid introduced into the second suction channel during the low-flow operation is ２ The cross-sectional area A of the first suction channel at the confluence point of the first suction channel and the second suction channel. １ The cross-sectional area A of the flow path at the confluence point of the second suction flow path at the junction of the first suction flow path and the second suction flow path. ２ This refers to the single-axis multi-stage centrifugal fluid machine according to claim 1, characterized in that it satisfies the relationship in the following formula (1). Q １ / Q ２ > A １ / A ２ (1) 3. The said Q １ / Q ２ and the said A １ / A ２ satisfy the relationship of the following formula (2), and the single-shaft multi-stage centrifugal fluid machine according to claim 2 is characterized in that. 1.5 × A １ / A ２ ≤ Q １ / Q ２ ≤ 3.0 × A １ / A ２ (2) 4. The single-axis multi-stage centrifugal fluid machine according to claim 2, characterized in that the second suction channel is configured to impart a swirling component to the fluid flowing into the first-stage centrifugal impeller.

5. The casing comprises a partition wall separating the first suction passage and the second suction passage, and in a meridional cross-sectional view of the single-axis multi-stage centrifugal fluid machine, the tangent to the wall surface of the first suction passage at the radially inward tip of the partition wall is in contact with the inlet passage surface of the shroud of the first-stage centrifugal impeller on the downstream extension, as described in claim 2.

6. A plurality of centrifugal impellers mounted in line along the axial direction of a rotating shaft; a casing housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid into the first stage centrifugal impeller among the plurality of centrifugal impellers; a discharge nozzle provided in the casing for discharging fluid delivered from the last stage centrifugal impeller among the plurality of centrifugal impellers; the introduction nozzle has a first introduction nozzle used during rated flow rate operation and a second introduction nozzle used during low flow rate operation below the rated flow rate; the casing has a first suction passage for introducing fluid from the first introduction nozzle to the first stage centrifugal impeller and a second suction passage for introducing fluid from the second introduction nozzle to the first stage centrifugal impeller; the device further includes a flow path switching device for switching the fluid flow path introduced into the introduction nozzle between the first suction passage and the second suction passage; and the volumetric flow rate Q of the fluid introduced into the first suction passage during rated flow rate operation. １ The volumetric flow rate Q of the fluid introduced into the second suction channel during the low-flow operation is ２ The flow path width b at the confluence point of the first suction flow path and the second suction flow path at the confluence of the first suction flow path and the second suction flow path. １ And, the flow path width b at the confluence point of the second suction flow path at the confluence of the first suction flow path and the second suction flow path. ２ This refers to a single-axis multi-stage centrifugal fluid machine that satisfies the relationship in equation (3) below. Q １ / Q ２ >b １ / b ２ (3) 7. The above Q １ / Q ２ and the aforementioned b １ / b ２ This refers to the single-axis multi-stage centrifugal fluid machine according to claim 6, characterized in that it satisfies the relationship in the following formula (4). 1.5 × b １ / b ２ ≦Q １ / Q ２ ≤ 3.0 × b １ / b ２ (4) 8. The single-axis multi-stage centrifugal fluid machine according to claim 6, characterized in that the second suction channel is configured to impart a swirling component to the fluid flowing into the first-stage centrifugal impeller.

9. The casing comprises a partition wall separating the first suction passage and the second suction passage, and in a meridional cross-sectional view of the single-axis multi-stage centrifugal fluid machine, the tangent to the wall surface of the first suction passage at the radially inward tip of the partition wall is in contact with the inlet passage surface of the shroud of the first-stage centrifugal impeller on the downstream extension, as described in 6.

10. A plurality of centrifugal impellers mounted in line along the axial direction of a rotating shaft; a casing housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid into the first stage centrifugal impeller among the plurality of centrifugal impellers; a discharge nozzle provided in the casing for discharging fluid delivered from the last stage centrifugal impeller among the plurality of centrifugal impellers; wherein the introduction nozzle has a first introduction nozzle used during rated flow rate operation and a second introduction nozzle used during low flow rate operation below the rated flow rate; the casing has a first suction passage for introducing fluid from the first introduction nozzle to the first stage centrifugal impeller and a second suction passage for introducing fluid from the second introduction nozzle to the first stage centrifugal impeller; and further comprises a flow path switching device for switching the fluid flow path introduced into the introduction nozzle between the first suction passage and the second suction passage. A single-axis multi-stage centrifugal fluid machine in which the cross-sectional area ratio Ar, expressed by the following equation (5), is substantially constant from the confluence position of the first suction passage at the junction of the first suction passage to the position of the suction port of the first-stage centrifugal impeller. Ar = A / A1a (5) (wherein in equation (5), A is the cross-sectional area of ​​the passage at any position between the confluence position of the first suction passage and the position of the suction port of the first-stage centrifugal impeller, and A1a is the cross-sectional area of ​​the passage at the position of the suction port of the first-stage centrifugal impeller) 11. The single-axis multi-stage centrifugal fluid machine according to claim 10, characterized in that the second suction channel is configured to impart a swirling component to the fluid flowing into the first-stage centrifugal impeller.

12. The single-axis multi-stage centrifugal fluid machine according to claim 10, characterized in that the casing is provided with a partition wall separating the first suction passage and the second suction passage, and in a meridional cross-sectional view of the single-axis multi-stage centrifugal fluid machine, the tangent to the wall surface of the first suction passage at the radially inward tip of the partition wall is in contact with the inlet passage surface of the shroud of the first-stage centrifugal impeller on the downstream extension line.

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