One-axis multi-stage telecentric fluid machinery

Abstract

The present invention provides 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, and can provide sufficient pre-swirl throughout the entire upstream and downstream side of the compressor. [Solution] The single-axis multi-stage centrifugal fluid machine 100 of the present invention has a first suction passage 7 that allows fluid to flow into the first-stage centrifugal impeller 1 during rated flow rate operation, and a second suction passage 8 that allows fluid to flow into the first-stage centrifugal impeller 1 to impart pre-swirl during low flow rate operation, and the cross-sectional area A1 of the first suction passage 7 at 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 is smaller than the cross-sectional area A2 of the second suction passage 8 at the confluence position 8a.

Description

[Technical Field]

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

[0002] Conventionally, a single-axis 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). This single-shaft multi-stage centrifugal compressor controls the angle of the inlet guide vanes 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. In addition, this compressor imparts a pre-swirling motion to the suction flow to the intermediate-stage impellers using fixed guide vanes. This allows the compressor to regulate the flow rate of the working fluid to the downstream compression stages, including the intermediate stages. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2007-309154 [Overview of the project] [Problems that the invention aims to solve]

[0004] In general, single-shaft multi-stage centrifugal compressors are used in various plants, and depending on the type of plant, frequent and repeated operation at rated flow rates and at flow rates 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. By the way, in conventional single-axis 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 applying pre-swirl and the state of applying pre-swirl are repeated. However, while the conventional single-shaft multi-stage centrifugal compressor requires high-frequency operation of the inlet guide vanes, it has not been sufficiently considered to ensure high reliability for its angle control. In addition, the pre-whirl imparting structure by the fixed guide vanes in the conventional single-shaft multi-stage centrifugal compressor is for adjusting the flow rate of the working fluid to the downstream compression stage, and cannot be used for low-flow operation of the entire compressor including the upstream side.

[0005] An object of the present invention is to provide a single-shaft multi-stage centrifugal fluid machine that can switch between rated flow operation and low-flow operation with a highly reliable configuration, can impart sufficient pre-whirl over the entire upstream and downstream sides of the compressor, and can further improve the compressor efficiency.

Means for Solving the Problems

[0006] The single-shaft multi-stage centrifugal fluid machine of the present invention that solves the above problems includes a plurality of centrifugal impellers mounted so as to be arranged in the axial direction of the rotating shaft, a casing that houses the plurality of centrifugal impellers, an inlet nozzle provided in the casing for introducing fluid into the first-stage centrifugal impeller among the plurality of centrifugal impellers, and a discharge nozzle provided in the casing for discharging the fluid sent out from the last-stage centrifugal impeller among the plurality of centrifugal impellers. The inlet nozzle has a first inlet nozzle used during rated flow operation and a second inlet nozzle used during low-flow operation with a flow rate less than the rated flow rate. The casing has a first suction passage for flowing fluid from the first inlet nozzle into the first-stage centrifugal impeller and a second suction passage for flowing fluid from the second inlet nozzle into the first-stage centrifugal impeller. The fluid machine further includes a flow path switching device for switching the flow path of the fluid introduced into the inlet nozzle to the first suction passage or the second suction passage. The cross-sectional area of the flow path at the confluence position of the first suction passage in the confluence portion of the first suction passage and the second suction passage is smaller than the cross-sectional area of the flow path at the confluence position of the second suction passage.

[0007] In addition, the single-axis multi-stage centrifugal fluid machine of the present invention that solves the above problems includes a plurality of centrifugal impellers mounted so as to be arranged in the axial direction of the rotating shaft, a casing that houses the plurality of centrifugal impellers, an inlet nozzle provided in the casing for introducing fluid into the first-stage centrifugal impeller among the plurality of centrifugal impellers, and a discharge nozzle provided in the casing for discharging the fluid sent out from the last-stage centrifugal impeller among the plurality of centrifugal impellers. The inlet nozzle has a first inlet nozzle used during rated flow operation and a second inlet nozzle used during low-flow operation with a flow rate less than the rated flow rate. The casing has a first suction passage for allowing fluid to flow into the first-stage centrifugal impeller from the first inlet nozzle and a second suction passage for allowing fluid to flow into the first-stage centrifugal impeller from the second inlet nozzle. The fluid machine further includes a flow path switching device for switching the flow path of the fluid introduced into the inlet nozzle to the first suction passage or the second suction passage. The volume flow rate Q1 of the fluid introduced into the first suction passage during rated flow operation, the volume flow rate Q2 of the fluid introduced into the second suction passage during low-flow operation, the flow path width b1 at the confluence position of the first suction passage at the confluence of the first suction passage and the second suction passage, and the flow path width b2 at the confluence position of the second suction passage at the confluence of the first suction passage and the second suction passage satisfy the relationship of the following formula (3). Q1 / Q2>b1 / b2(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 formula (5), from the confluence position of the first suction channel at the confluence of the first and second suction channels to the position of the suction port of the first stage centrifugal impeller is substantially constant. Ar = A / A1a (5) (However, in formula (5) above, A is the cross-sectional area of ​​the flow path at any position between the confluence of the first suction flow path and the suction port of the first stage centrifugal impeller, and A1a is the cross-sectional area of ​​the flow path at the suction port of the first stage centrifugal impeller.) [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0010] [Figure 1] This is a meridian cross-sectional view of a single-axis multi-stage centrifugal compressor according to a first embodiment of the present invention. [Figure 2]Figure 1 is a magnified view of the area near the confluence of the first and second suction passages of the single-axis multi-stage centrifugal compressor, schematically illustrating the movement of the working fluid during low-flow operation. [Figure 3] Figure 1 is a magnified view of the area near the confluence of the first and second suction passages of the single-axis multi-stage centrifugal compressor, schematically illustrating the movement of the working fluid during rated flow rate operation. [Figure 4] This graph shows the relationship between the total pressure loss in the suction channel of a single-axis multi-stage centrifugal compressor according to the first embodiment and the value of [volume flow rate ratio of the working fluid (Q1 / Q2) / cross-sectional area ratio of the confluence channel (A1 / A2)]. [Figure 5] This is an explanatory diagram of the configuration of a single-axis multi-stage centrifugal compressor according to a second embodiment of the present invention, and is a partially enlarged view corresponding to section V in Figure 1. [Figure 6] Figure 5 is a graph illustrating the distribution of the flow path cross-sectional area from the inside of the first suction flow path to the suction port of the first stage centrifugal impeller of the single-axis multi-stage centrifugal compressor. [Modes for carrying out the invention]

[0011] Embodiments for implementing the single-axis multi-stage centrifugal fluid machine of the present invention will be described in detail with reference to the drawings as appropriate. In the following, the single-axis multi-stage centrifugal fluid machine of the present invention will be described using a single-axis multi-stage centrifugal compressor as an example, but the present invention is not limited to this and can also be applied to single-axis multi-stage centrifugal pumps and the like.

[0012] (First Embodiment) Figure 1 is a meridian cross-sectional view of a single-axis multi-stage centrifugal compressor 100 according to the first embodiment of the present invention. As shown in Figure 1, the single-shaft multi-stage centrifugal compressor 100 is configured in which multiple centrifugal impellers 1, housed in a cylindrical casing 4, are mounted in multiple stages on a single rotating shaft 2. In this embodiment, the centrifugal impeller 1 is a closed-type impeller in which a plurality of blades 1d arranged in the circumferential direction of the rotation axis 2 are sandwiched between a shroud 1b and a hub 1c. However, the centrifugal impeller 1 is not limited to this, and an open-type impeller without a shroud 1b can also be used. The rotating shaft 2 is rotatably supported at both ends by bearings 3b located within the bearing case 3a. The bearing case 3a is either integrally provided with the casing 4 or attached to a separate mounting base (not shown).

[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 last stage centrifugal impeller 1. This casing 4 will be explained in more detail later.

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

[0015] A return channel 10 is provided downstream of the diffuser section 9, forming an intake 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. Furthermore, the return channel 10 is provided with return vanes 10a that rectify the flow of the working fluid. These return vanes 10a are arranged at intervals in the circumferential direction. The diffuser section 9 and the return channel 10 form a stationary fluid passage 11 on the radially outer 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 seal portion 13 is provided in the gap between the centrifugal impeller 1 and the casing 4, and in the gap between the portion of the casing 4 in which 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, the shaft seals 13, 14, and 15 are assumed to consist of labyrinth seals, but are not limited to this.

[0019] Next, we will explain casing 4 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 introduction nozzle 5a and a second introduction nozzle 5b, which constitute the introduction nozzle 5. Furthermore, a first suction channel 7 is formed in the casing 4 so as to communicate with the first inlet nozzle 5a. Also, a second suction channel 8 is formed in the casing 4 so as to communicate 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 on the side of 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 the working fluid from outside the single-axis 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, which is less than the rated flow rate. The working fluid flowing through the second suction channel 8 merges with the working fluid flowing through the first suction channel 7, thereby imparting a swirling component to the working fluid that flows into the first-stage centrifugal impeller 1. Furthermore, the first suction passage 7 allows a working fluid with less or no swirling component than the working fluid flowing through the second suction passage 8 to flow into the first stage centrifugal impeller 1.

[0023] In Figure 1, reference numeral 5aa indicates the inlet flange portion of the first introduction nozzle 5a. Reference numeral 5ba indicates the inlet flange portion of the second introduction nozzle 5b. The cross-sectional shape of the inner flow path at the inlet flange portions 5aa and 5ba is circular. The first suction flow path 7 and the second suction flow path 8, respectively, exhibit 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 gradually changes as the length of the major axis increases and the oval shape becomes flatter as you move radially inward from the inlet flange portions 5aa and 5ba.

[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. Furthermore, 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 leads 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 between the first suction flow path 7 and the second suction flow path 8. This flow path switching device 20 includes a main pipe 21 that guides the working fluid to a first inlet nozzle 5a, a secondary pipe 22 that branches off from the main pipe 21 and guides the working fluid to a second inlet nozzle 5b, an on-off valve 21a located in the main pipe 21 downstream of the branching point of the secondary pipe 22, an on-off valve 22a located in the secondary pipe 22, and a control unit 23 for the on-off valves 21a and 22a. The flow path switching device 20 enables rated flow rate operation of the single-shaft 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 rate operation of the single-shaft multi-stage centrifugal compressor 100 by closing the on-off valve 21a and opening the on-off valve 22a based on commands 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-axis multi-stage centrifugal compressor 100 of this embodiment will be explained. Figures 2 and 3 are enlarged views of the area near the confluence Cf of the first suction passage 7 and the second suction passage 8 of the single-axis multi-stage centrifugal compressor 100 shown in Figure 1. Figure 2 schematically shows the movement of the working fluid during low-flow operation, and Figure 3 schematically shows the movement of the working fluid during rated-flow 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 junction position of the first suction channel 7 with respect to the confluence section Cf, and reference numeral 8a indicates the junction position of the second suction channel 8 with respect to the confluence section Cf.

[0027] The confluence position 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 A1 represents the cross-sectional area of ​​the first suction channel 7 at the confluence point 7a, and the symbol b1 represents the width of the first suction channel 7 at the confluence point 7a in a meridian cross-sectional view. Furthermore, the cross-sectional area A1 of the first suction channel 7 at the confluence position 7a facing the annular confluence section Cf is the area of ​​the circumferential surface of a virtual cylindrical body 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, the symbol A2 represents the cross-sectional area of ​​the second suction channel 8 at the confluence point 8a, and the symbol b2 represents the width of the second suction channel 8 at the confluence point 8a in a meridian cross-sectional view. Furthermore, the cross-sectional area A2 of the second suction channel 8 at the confluence position 8a facing the annular confluence section Cf is the area of ​​the circumferential surface of the virtual cylindrical body formed by rotating the line segment consisting of the dotted line shown as the confluence position 8a around the axis X. In addition, in Figures 2 and 3, reference numeral 1a denotes the intake port of the first-stage centrifugal impeller 1 (see Figure 1), reference numeral 13 denotes the shaft seal portion provided in the gap between the casing 4 and the shroud 1b, and reference numeral 1bw denotes 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 A1 of the first suction flow path 7 at the confluence position 7a is set to be relatively smaller than the flow path cross-sectional area A2 of the second suction flow path 8 at the confluence position 8a of the second suction flow path 8.

[0031] Furthermore, in such a single-shaft multi-stage centrifugal compressor 100, specifically, the flow path cross-sectional area A1 of the first suction flow path 7 at the confluence position 7a and the flow path cross-sectional area A2 of the second suction flow path 8 at the confluence position 8a are set to satisfy the following equation (1). Q1 / Q2>A1 / A2(1) (However, in equation (1), Q1 is the volumetric flow rate of the working fluid in the first suction passage 7 during rated flow rate operation, and Q2 is the volumetric flow rate of the working fluid in the second suction passage 8 during low flow rate operation.)

[0032] Furthermore, in such a single-axis multi-stage centrifugal compressor 100, it is desirable that Q1 / Q2 and A1 / A2 be set to satisfy the relationship shown in equation (2) below, as will be explained in detail later. 1.5×A1 / A2≦Q1 / Q2≦3.0×A1 / A2(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-shaft multi-stage centrifugal compressor 100, instead of the area ratio A1 / A2 in equations (1) and (2), the ratio b1 / b2 of the flow path width b1 of the first suction flow path 7 at the confluence position 7a of the first suction flow path 7 and the second suction flow path 8 at the confluence position 8a of the second suction flow path 8 at the confluence Cf can also be applied. In other words, the volumetric flow rate Q1 of the working fluid in the first suction passage 7 during rated flow rate operation, the volumetric flow rate Q2 of the working fluid in the second suction passage 8 during low flow rate operation, the passage width b1, and the passage width b2 can be set so as to satisfy equation (3) and equation (4) below. Q1 / Q2>b1 / b2(3) 1.5×b1 / b2≦Q1 / Q2≦3.0×b1 / b2(4)

[0035] <Effects> Next, we will explain the operation of such a single-shaft multi-stage centrifugal compressor 100 (see Figure 1) and the effects it provides. The single-shaft multi-stage centrifugal compressor 100 operates at a low flow rate when the flow path switching device 20 (see Figure 1) closes the on-off valve 21a (see Figure 1) and opens the on-off valve 22a (see Figure 1). During this low-flow operation, as shown in Figure 2, the volumetric flow rate Q of the working fluid in the first suction passage 7 becomes zero (Q=0), and the volumetric flow rate Q of the working fluid in the second suction passage 8 is set to Q2 (Q=Q2).

[0036] At this time, the working fluid flowing into the second suction channel 8 is given a swirling component by the stationary fluid guide 17 (see Figure 1). Then, as shown in Figure 2, the working fluid that has passed through the stationary fluid guide 17 (see Figure 1) flows from the confluence point 8a toward the suction port 1a. 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 a leakage flow that detours towards the confluence point 7a of the first suction channel 7. Incidentally, during low-flow operation, the confluence point 7a of the first suction channel 7 is in a stagnant state with no working fluid flow.

[0037] During low-flow operation, the volumetric flow rate Q2 of the working fluid flowing into the compressor flows entirely into the second suction passage 8. In this process, the working fluid passes through the stationary fluid guide 17 and is given a large swirling component. As a result, at the confluence point 8a, the working fluid has a large swirling velocity component in addition to a velocity component perpendicular to the flow path cross-section. Consequently, the absolute 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 channel 8 flows radially inward along the channel wall surface of the partition wall 18 until it reaches the confluence point 8a of the second suction channel 8. However, since the area radially inward from the tip 18a of the partition wall 18 is a confluence Cf, the flow path rapidly expands towards the first suction flow path 7. The working fluid is indicated by the symbol S in Figure 2. L As indicated by the dotted arrow, the working fluid bypasses the confluence point 8a on the second suction channel 8 side, flows backward towards the upstream side of the first suction channel 7, and then returns 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 into the suction port 1a. Such leakage 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 here, a general pre-whirl imparting structure as a comparative example of this embodiment is assumed. The volume flow rate of the working fluid introduced into this pre-whirl imparting structure is Q X and the cross-sectional area of the flow path is A X for the first flow path, and the volume flow rate of the working fluid introduced is Q Y and the cross-sectional area of the flow path is A Y for the second flow path. The structure is configured such that the two flow paths merge, and Q X , Q Y , A X , and A Y are set to satisfy the following formula (m). Q X / Q Y =A X / A Y (m) (However, in formula (m), Q X is the volume flow rate of the working fluid during rated flow rate operation, Q Y is the volume flow rate of the working fluid during low flow rate operation, and Q X / Q Y > 1)

[0040] That is, the volume flow rate ratio (Q X / Q Y ) of the working fluid flowing through the first and second flow paths and the cross-sectional area of the confluence portion of each flow path (A X / A Y ) are made to match, and the cross-sectional areas A X and A Y of the confluence portion of each flow path are set. As a result, the cross-sectional area A​​​​​​​​​​​​​​​In the flow channel section having this feature, the flow resistance of the working fluid decreases, resulting in the leakage flow S of the working fluid shown in Figure 2. L This makes it easier for this to occur. Therefore, in the pre-swirl imparting structure mentioned as a comparative example of this embodiment, a decrease in the pre-swirl of the introduced working fluid, as well as an increase in deceleration losses and mixing losses, occurs.

[0042] In contrast, the single-shaft multi-stage centrifugal compressor 100 of this embodiment comprises 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 a first introduction nozzle 5a used during rated flow rate operation and a second introduction nozzle 5a used during low flow rate operation below the rated flow rate The casing 4 has a second introduction nozzle 5b used for the first stage of the centrifugal impeller 1, and a first suction passage 7 that allows fluid to flow from the first introduction nozzle 5a to the first stage of the centrifugal impeller 1, and a second suction passage 8 that allows fluid to flow from the second introduction nozzle 5b to the first stage of the centrifugal impeller 1, and further comprises a flow path switching device 20 that switches the flow path of the fluid introduced into the introduction nozzle 5 to either the first suction passage 7 or the second suction passage 8, wherein the flow path cross-sectional area A1 at 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 is smaller than the flow path cross-sectional area A2 at the confluence position 8a of the second suction passage 8.

[0043] More specifically, in order to more reliably achieve the relationship "flow path cross-sectional area A1 < flow path cross-sectional area A2", the single-axis multi-stage centrifugal compressor 100 satisfies the following relationship (1): the volumetric flow rate Q1 of the fluid introduced into the first suction flow path during rated flow rate operation, the volumetric flow rate Q2 of the fluid introduced into the second suction flow path during low flow rate operation, the flow path cross-sectional area A1 at the confluence position 7a of the first suction flow path 7 at the confluence Cf of the first suction flow path 7 and the second suction flow path 8, and the flow path cross-sectional area A2 at the confluence position 8a of the second suction flow path 8 at the confluence Cf of the first suction flow path 7 and the second suction flow path 8. Q1 / Q2>A1 / A2(1)

[0044] With such a single-axis multi-stage centrifugal compressor 100, the flow resistance of the first suction flow path 7 at the confluence position 7a, which has a flow path cross-sectional area A1, increases, resulting in the leakage flow S of the working fluid shown in Figure 2. L This makes it less likely for this to occur. With such a single-axis 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, it is desirable that the relationship between Q1 / Q2 and A1 / A2 satisfies the following equation (2). 1.5×A1 / A2≦Q1 / Q2≦3.0×A1 / A2(2) In this embodiment, when the relationship between the volumetric flow rate ratio Q1 / Q2 of the working fluid flowing through each channel and the channel cross-sectional area A1 / A2 at the confluence of each channel is set as shown in equation (1), a trade-off may occur between the performance during rated flow rate operation and low flow rate operation.

[0046] Next, we will explain the relationship between equation (2) and trade-offs. The single-shaft multi-stage centrifugal compressor 100 operates at its rated flow rate when the flow path switching device 20 (see Figure 1) opens the on-off valve 21a (see Figure 1) and closes the on-off valve 22a (see Figure 1). During operation at the rated flow rate, as shown in Figure 3, the volumetric flow rate Q of the working fluid in the second suction passage 8 becomes zero (Q=0), and the volumetric flow rate Q of the working fluid in the first suction passage 7 is set to Q1 (Q=Q1). In Figure 3, symbol M M This indicates the main flow of the working fluid, and the symbol M LThis indicates a leakage flow that detours towards the confluence point 8a of the second suction channel 8. Incidentally, during rated flow rate operation, the confluence point 8a of the second suction channel 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 turning component. Furthermore, the flow path cross-sectional area A2 at the confluence point 8a of the second suction flow path 8 is set to match the small volumetric flow rate Q2 during low-flow operation. Therefore, leakage flow M L The flow rate is small, and the leakage flow M L The resulting pressure loss is also small. Therefore, the leakage flow M during rated flow rate operation. 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 A1 of the flow path at the confluence point 7a of the first suction flow path 7 is smaller than the cross-sectional area A2 of the flow path at the confluence point 8a of the second suction flow path 8. Therefore, when operating at the rated flow rate, the flow velocity of the working fluid increases near the confluence point 7a of the first suction passage 7, and frictional losses at the passage wall near the confluence point 7a increase. In this case, if we apply formula (m) from the comparative example above and assume that the flow channel cross-sectional area A1 is set to half, for example, the flow velocity at the confluence point 7a will be doubled. 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, when the relationship between the volumetric flow rate ratio Q1 / Q2 of the working fluid flowing through each channel and the channel cross-sectional area ratio A1 / A2 at the confluence of each channel is set as in equation (1) in this embodiment, a trade-off may occur regarding the performance during rated flow rate operation and low flow rate operation. On the other hand, in the single-shaft multi-stage centrifugal compressor 100 of this embodiment, there is an appropriate range for the value of the confluence flow area ratio A1 / A2 with respect to the volume flow rate ratio Q1 / Q2, from the viewpoint of balancing performance during rated flow rate operation and low flow rate operation. In this embodiment, the range of A1 / A2 with respect to Q1 / Q2 that provides a good performance balance is defined as shown in equation (2) above.

[0050] Next, we will explain the specific basis for the inequality shown in equation (2) above. Figure 4 is a graph showing the relationship between the value of (Q1 / Q2) / (A1 / A2) and the total pressure loss in the suction channel obtained by computational fluid dynamics simulation. In Figure 4, the series plotted with circles represents the total pressure loss for the working fluid with a volumetric flow rate Q1 (see Figure 3) flowing through the first suction channel 7 (see Figure 3) during rated flow rate operation, from just 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). Also in Figure 4, the series plotted with squares represents the total pressure loss for the working fluid with a volumetric flow rate Q2 (see Figure 2) flowing through the second suction channel 8 (see Figure 2) during low flow rate operation, from just 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 represent the total pressure loss 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), assuming that (Q1 / Q2) / (A1 / A2) ≈ 3.5 for the series marked with a square (low flow rate operation), and all values ​​have been made dimensionless. That is, for the horizontal axis value (Q1 / Q2) / (A1 / A2) ≈ 3.5 for the series marked with a square (low flow rate operation), the value of the 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, it is appropriate to determine the range of the value of (Q1 / Q2) / (A1 / A2) 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), the total pressure loss gradually decreases as (Q1 / Q2) / (A1 / A2) increases. However, the rate of decrease in total pressure loss gradually decreases as we move to the right of the graph. Therefore, to the right of (Q1 / Q2) / (A1 / A2) = 3.0, the total pressure loss remains almost constant even if (Q1 / Q2) / (A1 / A2) is increased further.

[0054] In contrast, the total pressure loss in the series marked with a circle (rated flow rate operation) increases as the value of (Q1 / Q2) / (A1 / A2) increases. That is, considering that the total pressure loss in the series marked with a square (low flow rate operation) is approximately constant when (Q1 / Q2) / (A1 / A2) is 3.0 or higher, in the single-shaft multi-stage centrifugal compressor 100 of this embodiment (see Figure 1), in the range where (Q1 / Q2) / (A1 / A2) > 3.0, only the total pressure loss in the series marked with a circle (rated flow rate operation) increases. Therefore, in the single-axis multi-stage centrifugal compressor 100 of this embodiment (see Figure 1), (Q1 / Q2) and (A1 / A2) are set to satisfy the inequality (Q1 / Q2) / (A1 / A2)≦3.0, that is, (Q1 / Q2)≦3.0×(A1 / A2).

[0055] Furthermore, as shown in Figure 4, when (Q1 / Q2) / (A1 / A2) < 3.0, the total pressure loss value in the series marked with a square (low flow rate operation) becomes large. Specifically, the rate of increase in total pressure loss becomes large from around (Q1 / Q2) / (A1 / A2) = 2.0, and in the range of (Q1 / Q2) / (A1 / A2) < 1.5, 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 more than 1.5 times the total pressure loss at (Q1 / Q2) / (A1 / A2) ≈ 3.5. Therefore, in the single-axis multi-stage centrifugal compressor 100 of this embodiment (see Figure 1), (Q1 / Q2) and (A1 / A2) are set so as to satisfy the inequality (Q1 / Q2) / (A1 / A2)≧1.5, i.e., 1.5×(A1 / A2)≦(Q1 / Q2), which means that the total pressure loss does not exceed 1.5 times when (Q1 / Q2) / (A1 / A2) ≈ 3.5.

[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 this single-axis multi-stage centrifugal compressor 100, the introduction of the working fluid into the second suction channel 8 by the flow path switching device 20 (see Figure 1) makes it possible to more reliably prevent a decrease in the pre-swirl 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 provided 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 line 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-axis multi-stage centrifugal compressor 100, as shown in Figure 3, the main stream M passes 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 MThis 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. The introduction nozzle 5 has a first introduction nozzle 5a used during rated flow rate operation and a second introduction nozzle 5b used during low flow rate operation below the rated flow rate, and the casing 4 is configured to introduce fluid from the first introduction nozzle 5a to the first stage centrifugal impeller 1. The system includes a first suction channel 7 into which fluid flows, and a second suction channel 8 into which fluid flows from the second inlet nozzle 5b to the first stage centrifugal impeller 1. The system further includes a flow path switching device 20 that switches the flow path of the fluid introduced into the inlet nozzle 5 between the first suction channel 7 and the second suction channel 8. The volumetric flow rate Q1 of the fluid introduced into the first suction channel 7 during rated flow rate operation, the volumetric flow rate Q2 of the fluid introduced into the second suction channel 8 during low flow rate operation, the flow path width b1 at the confluence position 7a of the first suction channel 7 at the confluence Cf of the first suction channel 7 and the second suction channel 8, and the flow path width b2 at the confluence position 8a of the second suction channel 8 at the confluence Cf of the first suction channel 7 and the second suction channel 8 satisfy the relationship given by equation (3) below. Q1 / Q2>b1 / b2(3)

[0059] With such a single-axis multi-stage centrifugal compressor 100, the flow resistance of the first suction flow path 7 at the confluence position 7a, which has a flow path width b1, increases, resulting in the leakage flow S of the working fluid shown in Figure 2. L This makes it less likely for this to occur. With such a single-axis 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, the relationship between Q1 / Q2 and b1 / b2 satisfies the following equation (4). 1.5×b1 / b2≦Q1 / Q2≦3.0×b1 / b2(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-axis 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) makes it possible to more reliably prevent a decrease in the pre-swirl 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 that separates 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 line 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-axis 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 MThis 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-axis 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 components that are the same as those in the first embodiment, and their detailed descriptions are omitted. Figure 5 is an explanatory diagram of the configuration of the single-axis multi-stage centrifugal compressor 100 of this embodiment, and corresponds to section V in Figure 1. In Figure 5, reference numeral 1a denotes the suction port of the first stage centrifugal impeller 1, and reference numeral 7a denotes the merging position of the first suction passage 7 at the merging point 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-axis 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 interior of the first suction flow path 7 (see Figure 5) and the position of 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 interior of the first suction flow path 7 (see Figure 5) and the position of the suction port 1 (see Figure 5) by the flow path cross-sectional area A1a at the suction port 1a. 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 section Cf (see Figure 5) are calculated using the tangent line 18w shown in Figure 3 as the boundary.

[0065] In this embodiment, the single-axis multi-stage centrifugal compressor 100 maintains a substantially constant cross-sectional area ratio Ar, shown 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) (However, in formula (5) above, A and A1a are synonymous with A and A1a above.)

[0066] In this single-axis multi-stage centrifugal compressor 100, the flow of working fluid from the first suction channel 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-axis multi-stage centrifugal compressor 100 is approximately constant from the confluence position 7a to the position of the suction port 1a. Specifically, the single-shaft multi-stage centrifugal compressor 100 is configured such that the cross-sectional area of ​​the flow path at the confluence point 7a is approximately the same as the cross-sectional area of ​​the flow path A1a, by increasing the reduction rate of the flow path cross-sectional area from the inside of the upstream side of the first suction flow path 7 to the confluence point 7a.

[0067] Furthermore, in such a single-shaft 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> A single-shaft multi-stage centrifugal compressor 100 according to a 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 a 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) (However, in formula (5) above, 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 the above 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-axis 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-axis 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) makes it possible to more reliably prevent a decrease in the pre-swirl 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 line 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-axis 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-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.

[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 described above is assumed to use on-off valves 21a and 22a. However, the single-axis 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 between the first suction flow path 7 and 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 described above, 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 leakage flow S can be controlled by setting the volume flow rate ratio Q1 / Q2 of the working fluid and the cross-sectional area ratio A1 / A2 (or flow width ratio b1 / b2) of the confluence section. L This can also suppress performance degradation caused by (see Figure 2). [Explanation of Symbols]

[0075] 1. Centrifugal impeller 1a Inlet 1b Shroud 1bw Inlet flow path surface 2 rotation axes 4. Casing 5. Introduction nozzle 5a First introduction nozzle 5b Second introduction nozzle 6. Discharge nozzle 7. First suction channel 7a Merging position 8. Second suction channel 8a Merging position 18 Bulkhead 18a Tip 18W tangent 20 flow path switching device Cf confluence

Claims

1. Multiple centrifugal impellers are mounted so as to be aligned along the axis of rotation, A casing housing the plurality of centrifugal impellers, An introduction nozzle is provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers, A discharge nozzle is provided in the casing and discharges the fluid sent from the final stage centrifugal impeller among the plurality of centrifugal impellers, Equipped with, The aforementioned introduction nozzle comprises 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 channel for introducing fluid from the first inlet nozzle to the first stage centrifugal impeller, and a second suction channel for introducing fluid from the second inlet nozzle to the first stage centrifugal impeller. The system further includes a flow path switching device that switches the fluid flow path to be introduced into the introduction nozzle to the first suction flow path or the second suction flow path, 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 and, The volumetric flow rate Q of the fluid introduced into the second suction channel during the low-flow operation described above. ２ and, 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 and, 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 The single-axis multi-stage centrifugal fluid machine according to claim 1, characterized in that it satisfies the relationship shown in equation (1) below. Q １ / Q ２ >A １ / A ２ (1)

3. Said Q １ / Q ２ and said A １ / A ２ The single-shaft multi-stage centrifugal fluid machine according to claim 2, characterized in that they satisfy the relationship of the following formula (2). 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 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, as described in claim 2.

6. Multiple centrifugal impellers are mounted so as to be aligned along the axis of rotation, A casing housing the plurality of centrifugal impellers, An introduction nozzle is provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers, A discharge nozzle is provided in the casing and discharges the fluid sent from the final stage centrifugal impeller among the plurality of centrifugal impellers, Equipped with, The aforementioned introduction nozzle comprises 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 channel for introducing fluid from the first inlet nozzle to the first stage centrifugal impeller, and a second suction channel for introducing fluid from the second inlet nozzle to the first stage centrifugal impeller. The system further includes a flow path switching device that switches the fluid flow path to be introduced into the introduction nozzle to the first suction flow path or the second suction flow path, The volumetric flow rate Q of the fluid introduced into the first suction channel during the rated flow rate operation. １ and, The volumetric flow rate Q of the fluid introduced into the second suction channel during the low-flow operation described above. ２ and, The width of the first suction channel at the confluence point of the first suction channel and the second suction channel. １ and, The width of the second suction channel at the confluence point of the first suction channel and the second suction channel. ２ This refers to a single-axis multi-stage centrifugal fluid machine that satisfies the relationship shown in equation (3) below. Q １ / Q ２ >b １ / b ２ (3)

7. The aforementioned 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 shown in equation (4) below. 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 claim 6.

10. Multiple centrifugal impellers are mounted so as to be aligned along the axis of rotation, A casing housing the plurality of centrifugal impellers, An introduction nozzle is provided in the casing for introducing fluid to the first stage centrifugal impeller among the plurality of centrifugal impellers, A discharge nozzle is provided in the casing and discharges the fluid sent from the final stage centrifugal impeller among the plurality of centrifugal impellers, Equipped with, The aforementioned introduction nozzle comprises 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 channel for introducing fluid from the first inlet nozzle to the first stage centrifugal impeller, and a second suction channel for introducing fluid from the second inlet nozzle to the first stage centrifugal impeller. The system further includes a flow path switching device that switches the fluid flow path to be introduced into the introduction nozzle to the first suction flow path or the second suction flow path, A single-axis multi-stage centrifugal fluid machine in which the cross-sectional area ratio Ar, shown by the following formula (5), from the confluence position of the first suction passage at the confluence of the first suction passage and the second suction passage to the position of the suction port of the first stage centrifugal impeller is substantially constant. Ar=A / A1a (5) (However, in formula (5) above, A is the cross-sectional area of ​​the flow path at any position between the confluence point of the first suction flow path and the suction port of the first stage centrifugal impeller, and A1a is the cross-sectional area of ​​the flow path at 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 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 10.

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