Multistage centrifugal fluid machine

Abstract

To provide a multistage centrifugal fluid machine which can achieve both broadening an operation range and facilitating return vane designing.SOLUTION: A multistage centrifugal fluid machine comprises: a diffuser 5 provided with a stationary flow passage 14 radially outside an impeller 1; a return flow passage 6 guiding fluid from the diffuser 5 to a subsequent-stage impeller 1; and a plurality of return vanes 8 provided in the return flow passage 6 and arranged at intervals along a circumferential direction. The return flow passage 6 has a return bend 7 guiding the fluid having passed through the diffuser 5 radially inward. The return bend 7 has: a first curved part 12 turning the fluid from radially outward to the same direction as a rotation axis; and a second curved part 13 located downstream from the first curved part 12 and turning the fluid from the same direction as the rotation axis to radially inward, wherein a front edge of the return vane 8 is located directly downstream from an exit of the return bend 7, and neither the diffuser 5 nor the return bend 7 has a blade.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a multi-stage centrifugal fluid machine having a plurality of impellers, and particularly relates to the shape of the stationary flow path portion of each stage of the multi-stage centrifugal fluid machine.

Background Art

[0002] In various plants, in order to boost the pressure of a process gas, a single-shaft multi-stage centrifugal compressor in which a plurality of centrifugal impellers are provided in multiple stages on a single rotating shaft is used. This single-shaft multi-stage centrifugal compressor is configured to suck a process gas from a suction nozzle forming a suction flow path, introduce it into the annular flow path portion, then sequentially compress and boost the pressure by centrifugal impellers provided in multiple stages on the rotating shaft, and then discharge it from a discharge nozzle. These single-shaft multi-stage centrifugal compressors are required to achieve high efficiency and ensure stable operation in a wide flow rate range (hereinafter referred to as wide operation range). In order to achieve a wide operation range in a single-shaft multi-stage centrifugal compressor, it is necessary to suppress the occurrence of unstable flows such as flow separation and stall caused by changes in the flow angle of the gas flow inside the compressor accompanying changes in the flow rate of the process gas in a wide flow rate range. To suppress the occurrence of unstable flows such as separation and stall, it is known that it is effective to configure diffusers, bend flow paths, etc., which form part of the stationary flow path inside the compressor, as vaneless flow paths (hereinafter referred to as VL) without installing blades.

[0003] In a single-shaft multi-stage centrifugal compressor, a conventional example in which the diffuser flow path is configured as VL is described in Patent Document 1. In Patent Document 1, the diffuser of the single-shaft multi-stage centrifugal compressor is configured as VL, and a return bend portion that is placed downstream of the diffuser and guides the flow discharged from the diffuser in the radially outward direction to the radially inward direction, and a return vane portion that guides the flow exiting the return bend portion to the impeller of the next stage while removing the swirling component are provided to form a return flow path. Further, an axial parallel flow path is provided in the return bend portion, and blades for removing the swirling of the flow are provided in a part of this axial parallel flow path. By configuring in this way, the flow path length in the meridional plane of the return bend portion becomes small, and the flow is turned by the blades provided in the axial parallel flow path portion, so that the swirling component of the flow becomes small. Therefore, a three-dimensional reduction in flow path length, an increase in flow angle, and an increase in flow deceleration can be achieved, and the wall friction loss in the return bend portion is reduced. Further, by providing blades in a part of the axial parallel flow path of the return bend portion and turning the flow in the meridional plane direction, the inflow angle of the flow to the leading edge of the return vane becomes large. As a result, the swirling component of the flow to be removed between the inlet and outlet of the return vane becomes small, so that the vane angle difference between the inlet and outlet of the return vane, that is, the blade load, can be reduced, the ease of design of the return vane is ensured, and the performance of the next stage compressor can be improved.

[0004] Furthermore, in Patent Document 1, an axial parallel portion is provided on either the inner or outer flow path wall surface of the bend portion, blades for removing the swirling of the flow are provided in this portion, and the flow path width is configured to increase toward the downstream. By configuring in this way, the above-described deceleration of the flow in the return bend portion can be further increased, and it becomes possible to reduce the wall friction loss in the return bend portion.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, in Patent Document 1, aiming at reducing the wall friction loss of the fluid in the bend portion and reducing the blade load of the return vane, an axially parallel flow path is provided in the bend portion, and blades for removing the swirl of the flow are installed therein. Further, the flow path width of the flow path in the vicinity of the blade installation is enlarged. However, with such a configuration, when the deviation between the operating flow rate of the compressor and the rated flow rate becomes large, the deviation between the flow angle of the flow flowing into the blade installed in the bend portion and the inlet blade angle of the blade becomes large, and separation or the like occurs on the blade surface, There was a problem that the stable operating flow rate range of the single-shaft multi-stage centrifugal compressor was narrowed. In order to maintain stable operation in a wide flow rate range, it is necessary to configure the bend portion as a VL. On the other hand, if both the diffuser portion and the bend portion are configured as VLs for widening the operating range, the swirl of the flow will not be sufficiently removed by the time it flows into the leading edge of the return vane. At this time, it is necessary to completely remove the swirl between the inlet and outlet of the return vane, and it becomes necessary to increase the blade load of the return vane. Increasing the blade load of the return vane in turn causes flow separation in the flow path between the blades of the return vane, and there is also a problem that the design of the return vane becomes difficult. Therefore, the present invention provides a multi-stage centrifugal fluid machine capable of achieving both a wide operating range and ease of return vane design.

Means for Solving the Problems

[0007] In order to solve the above problems, the multistage centrifugal fluid machine according to the present invention includes a plurality of impellers, a rotating shaft to which the plurality of impellers are attached, and a stationary flow path provided on the downstream side of the impeller and guiding the fluid that has passed through the outlet of the impeller to the impeller in the subsequent stage. The stationary flow path includes a diffuser provided on the radially outer side of the impeller, a return flow path that guides the fluid from the diffuser to the impeller in the subsequent stage, and a plurality of return vanes provided in the return flow path and arranged at intervals along the circumferential direction. The return flow path has a return bend that guides the fluid passing through the diffuser toward the radially inner side. The return bend has a first curved portion that turns the fluid from the radially outward direction to the same direction as the rotation axis, and a second curved portion that is located on the downstream side of the first curved portion and turns the fluid from the same direction as the rotation axis to the radially inward direction. The leading edge of the return vane is located immediately downstream of the outlet of the return bend. The diffuser and the return bend have no blades, and the stationary flow path has a region with a constant flow path width that is narrower than the outlet of the impeller on the upstream side and a divergent flow path with a flow path width that is increased compared to the outlet of the impeller on the downstream side.

[0008] Furthermore, a multi-stage centrifugal fluid machine according to the present invention is a multi-stage centrifugal fluid machine having a plurality of impellers, a rotary shaft to which the plurality of impellers are attached, and a stationary flow path provided downstream of the impellers to guide fluid that has passed through an outlet of the impeller to the impeller of a subsequent stage, wherein the stationary flow path comprises a diffuser provided radially outside the impeller, a return flow path that guides fluid from the diffuser to the impeller of the subsequent stage, and a plurality of return vanes provided in the return flow path and arranged at intervals along the circumferential direction, and the return flow path includes a return vane that guides the fluid that has passed through the diffuser radially inward. the return bend has a first curved portion that turns the fluid from a radially outward direction to the same direction as the rotation axis, and a second curved portion located downstream of the first curved portion that turns the fluid from the same direction as the rotation axis to a radially inward direction; the leading edge of the return vane is located immediately downstream of an outlet of the return bend; the diffuser and the return bend are bladeless; and the stationary flow path from the inlet of the diffuser to the outlet of the return bend has a flow path with increased wall roughness on the upstream side and an enlarged flow path with an increased flow path width on the downstream side. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a multi-stage centrifugal fluid machine that can achieve both a wide operating range and ease of design of the return vanes. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a meridional cross-sectional view showing a part of a single-shaft multistage centrifugal compressor as an example of a general multistage centrifugal fluid machine. [Diagram 2] FIG. 2 is a meridional cross-sectional view showing the overall configuration of a single-shaft multistage centrifugal compressor as an example of a general multistage centrifugal fluid machine including the portion shown in FIG. [Figure 3] 1 is a meridional cross-sectional view of a single-shaft multi-stage centrifugal compressor in the vicinity of a return bend according to a first embodiment of the present invention. FIG. [Figure 4] FIG. 2 is an explanatory diagram of a velocity triangle of a flow near a side wall of a flow path whose width is narrower than that of an impeller outlet, which corresponds to the upstream side of a stationary flow path in the single-shaft multi-stage centrifugal compressor according to the first embodiment of the present invention. [Figure 5] FIG. 2 is an explanatory diagram of an inflow flow vector to a return vane and a blade cross-sectional shape of the return vane in the single-shaft multi-stage centrifugal compressor according to the first embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing an example of the results of a study on how much the absolute flow angle changes when the outlet diameter of a flow path having a flow path width narrower than that of the impeller outlet is changed in the single-shaft multi-stage centrifugal compressor according to the first embodiment of the present invention. [Figure 7] 1 is a meridional cross-sectional view of the vicinity of a return bend in a single-shaft multi-stage centrifugal compressor according to a first embodiment of the present invention, in which a first curved portion of the return bend is not formed as an expanded flow passage. FIG. [Figure 8] FIG. 6 is a meridional cross-sectional view of a single-shaft multi-stage centrifugal compressor in the vicinity of a return bend according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a meridional cross-sectional view of a modified example of a single-shaft multi-stage centrifugal compressor according to a second embodiment of the present invention, in the vicinity of a return bend. [Figure 10] FIG. 10 is a meridional cross-sectional view of a single-shaft multi-stage centrifugal compressor in the vicinity of a return bend according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a single-shaft multistage centrifugal compressor will be described as an example of a multistage centrifugal fluid machine according to an embodiment of the present invention based on the illustrated embodiments. Note that the same reference numerals are used for the same components in each drawing. FIG. 1 is a meridian cross-sectional view showing a portion of a single-shaft multi-stage centrifugal compressor as an example of a general multi-stage centrifugal fluid machine, and FIG. 2 is a meridian cross-sectional view showing the overall configuration of a single-shaft multi-stage centrifugal compressor 20 as an example of a general multi-stage centrifugal fluid machine including the portion shown in FIG. 1.

[0012] First, a single-shaft multi-stage centrifugal compressor 20 as an example of a general multi-stage centrifugal fluid machine will be described with reference to FIG. 1. As shown in FIG. 1, the single-shaft multi-stage centrifugal compressor 20 is schematically composed of a centrifugal impeller 1 that imparts rotational energy to a fluid, a rotating shaft 4 to which the centrifugal impeller 1 is attached, and a diffuser 5 that is located radially outside the centrifugal impeller 1 and converts the dynamic pressure of the fluid flowing out from the centrifugal impeller 1 into static pressure. Further, a return flow path 6 for guiding the fluid to the centrifugal impeller 1 in the subsequent stage is provided downstream of the diffuser 5.

[0013] The centrifugal impeller 1 has a disk (hub) 2 fastened to the rotating shaft 4, a side plate (shroud) 3 arranged opposite to the hub 2, and a plurality of blades 1A located between the hub 2 and the shroud 3 and spaced apart in the circumferential direction (perpendicular to the plane of FIG. 1). Note that FIG. 1 shows the case of a closed impeller having a shroud 3, but an open impeller without a shroud 3 may be used instead.

[0014] The diffuser 5 refers to the radially outward flow region immediately downstream of the outlet 1B of the centrifugal impeller 1. Either a vaned diffuser having a plurality of vanes arranged at substantially equal pitches in the circumferential direction or a vaneless diffuser (not shown in FIG. 1) without vanes is used for the diffuser 5. The return flow path 6 is composed of a return bend 7 and a return vane 8. The return bend 7 turns the fluid that has passed through the diffuser 5 from radially outward to inward, and further, the return vane 8 removes the swirling component of the fluid and plays a role of rectifying the fluid and allowing it to flow into the centrifugal impeller 1 in the next stage.

[0015] The return bend 7 is formed as a U-shaped curved flow path surrounded by surrounding structures in the meridional plane. The return bend inlet 9 is defined by a substantially cylindrical surface corresponding to the outlet of the diffuser 5, and the return bend outlet 10 is defined by a substantially cylindrical surface corresponding to the end of the meridional curved flow path located immediately upstream of the leading edge 11 of the return vane. It is defined as the section from the return bend inlet 9 to the return bend outlet 10. Further, the return bend 7 includes a first return bend curved portion 12 located on the upstream side of the return bend 7 that turns the working gas (fluid) from the radially outward direction to the same direction as the rotation axis 4, and a second return bend curved portion 13 located on the downstream side of the first return bend curved portion 12 that turns the working gas (fluid) from the same direction as the rotation axis 4 to the radially inward direction. The return vane 8 is composed of a plurality of vanes arranged at substantially equal pitches in the circumferential direction around the rotation axis 4. The above-mentioned diffuser 5 and the return flow path 6 composed of the return bend 7 and the return vane 8 are collectively referred to as the stationary flow path 14.

[0016] FIG. 2 shows a single-shaft multi-stage centrifugal compressor 20 in which the compression stages shown in FIG. 1 are stacked in the axial direction in multiple stages. As shown in FIG. 2, radial bearings 17 that rotatably support the rotation axis 4 are arranged on both ends of the rotation axis 4, and a thrust bearing 18 that axially supports the rotation axis 4 is arranged at one end of the rotation axis 4. Further, a multi-stage centrifugal impeller (five centrifugal impellers in FIG. 2) 1 is fixedly attached to the rotation axis 4, and a diffuser 5 and a return flow path 6 are provided on the downstream side of each centrifugal impeller 1 in the same manner as shown in FIG. 1. These centrifugal impellers 1, the diffuser 5, and the return flow path 6 are housed in a casing 19. Further, a suction flow path 15 is provided on the suction side of the casing 19, and a discharge flow path 16 is provided on the discharge side of the casing 19. In the multi-stage centrifugal fluid machine 20 configured as described above, the fluid (working gas) sucked from the suction flow path 15 is pressurized each time it passes through the centrifugal impellers 1, the diffuser 5, and the return flow path 6 of each stage, and finally reaches a predetermined pressure and is discharged from the discharge flow path 16. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example

[0017] FIG. 3 is a meridional sectional view near the return bend of the single-shaft multi-stage centrifugal compressor according to Embodiment 1 of the present invention. That is, FIG. 3 is a meridional sectional view showing, in the single-shaft multi-stage centrifugal compressor 20 in this embodiment, from near the outlet 1B of the centrifugal impeller 1 to near the leading edge 11 of the diffuser 5, the return bend 7, and the return vane 8 downstream thereof.

[0018] As shown in FIG. 3, in this embodiment, the diffuser 5 and the return bend 7 in the stationary flow path 14 are formed of VL. Further, the stationary flow path 14 between the inlet of the diffuser 5 and the outlet 10 of the return bend 7 is configured such that, on the upstream side, the flow path width is made narrower than the flow path width b2 at the outlet of the centrifugal impeller 1, and the flow path width is a constant region 21 with a flow path width of b3, and on the downstream side, it is configured as a divergent flow path 22 with a larger flow path width than that.

[0019] The effects of the structure of the stationary flow path 14 in this embodiment will be described below. First, it is obvious that by forming the diffuser 5 and the return bend 7 of VL, the wide operating range of the single-shaft multi-stage centrifugal compressor 20 can be achieved.

[0020] FIG. 4 shows, with solid arrows, a velocity triangle of the flow near the side wall 23 of the flow passage 21 (FIG. 3) with a constant flow passage width b3, which is narrower than the flow passage width b2 at the outlet of the centrifugal impeller 1, corresponding to the upstream side of the stationary flow passage 14 (FIG. 3) when this embodiment is applied. The dashed arrow in the figure indicates the velocity triangle near the side wall 23 when the flow passage width is not reduced compared to the flow passage width b2 at the outlet 1B of the centrifugal impeller 1, shown for comparison. As shown in FIG. 4, when a constant flow passage width region 21 is provided upstream of the stationary flow passage 14, where the flow passage width is narrower than the flow passage width b2 at the outlet 1B of the centrifugal impeller, as in this embodiment, the meridional velocity Cm in the velocity triangle near the side wall 23 in this region 21 increases. On the other hand, as shown in FIG. 4, near the inlet of the diffuser 5 of the single-shaft multi-stage centrifugal compressor 20, the magnitude of the circumferential velocity Cu is overwhelmingly larger than the magnitude of Cm. Here, when the channel width is reduced upstream of the stationary channel 14 as in this embodiment, the velocity gradient in the direction normal to the wall surface of the side wall 23 increases, and the wall friction acting on the working fluid (fluid) from the side wall 23 increases. With this increase in wall friction, the angular momentum decreases significantly, particularly near the inlet of the diffuser 5 where the magnitude of Cu is larger, making it possible to efficiently reduce the circumferential component Cu, i.e., the swirling component of the flow. Furthermore, the absolute flow angle α also increases due to the increase in the Cm component and the decrease in the Cu component described above.

[0021] However, if left as is, the efficiency of the single-shaft multi-stage centrifugal compressor 20 will decrease due to an increase in wall friction caused by the provision of the constant passage width region 21, which has a narrower passage width than the impeller outlet, on the upstream side of the stationary passage 14. Therefore, in this embodiment, the passage between the outlet downstream of the constant passage width region 21, which has a narrower passage width than the impeller outlet, on the upstream side of the above-mentioned stationary passage 14, and the return bend outlet 10 is made into an expanded passage region 22, which has an increased passage width along the downstream flow direction. This reduces the flow velocity of the working gas (fluid) downstream of the constant passage width region 21, which has a narrower passage width than the impeller outlet, on the upstream side of the stationary passage, and offsets the effect of increased loss caused by the reduced passage width on the upstream side of the stationary passage 14, making it possible to maintain or improve the stage efficiency.

[0022] FIG. 5 shows the inlet velocity triangle of the return vane 8 and the blade cross-sectional shape of the return vane when this embodiment is applied. In this embodiment, a constant-width region 21, whose width is narrower than the impeller outlet, is provided upstream of the stationary passage 14 (FIG. 3). This significantly reduces the swirl component of the working gas (fluid) and increases α in the region 21. Therefore, even if the meridional velocity Cm at the leading edge 11 of the return vane 8 decreases because the passage between the outlet of the constant-width region 21, whose width is narrower than the impeller outlet on the upstream side of the stationary passage, and the return bend outlet 10 is an expanded passage, the inflow angle α of the working gas (fluid) in the velocity triangle at the leading edge 11 of the return vane 8 increases. Therefore, the inlet angle βb5 of the return vane 8, which is set to match the inflow angle α of the fluid into the return vane 8, can be increased. Meanwhile, the trailing edge 8TE of the return vane is generally set to face the direction of the rotation axis 4 in order to eliminate swirl of the working gas (fluid). As described above, the turning of the fluid from the return vane leading edge 11 to the return vane trailing edge 8TE can be reduced, so that the ease of design of the return vane 8 can be maintained.

[0023] 6 shows an example of the results of a study conducted in this embodiment on how the absolute flow angle α changes when the outlet diameter of the constant flow path width region 21, which is narrower than the impeller outlet on the upstream side of the stationary flow path, is changed. The horizontal axis represents the radius at the outlet 1B of the centrifugal impeller 1, R2, and the outlet radius of the constant flow path width region 21, which is narrower than the impeller outlet on the upstream side of the stationary flow path, R 34 The radius ratio R 34 The vertical axis shows the ratio of the radius R4 / R2 of the radius R4 of the return bend inlet 9 to the radius ratio R2 when the VL diffuser 5 is configured as a constant flow passage section that does not narrow the flow passage width compared to the flow passage width b2 of the impeller outlet 1B. The vertical axis shows the ratio of the outlet radius R4 of the constant flow passage width region 21, which has a narrower flow passage width than the impeller outlet on the upstream side of the stationary flow passage, for each value on the horizontal axis. 34This figure shows the difference Δα (=α4 - α4') between the absolute flow angle α4 at the return bend inlet 9 when the flow path width is narrowed up to the position and expanded downstream, and the absolute flow angle α4' at the return bend inlet 9 when the VL diffuser 5 is configured as a constant flow path section where the flow path width is not narrowed relative to the flow path width b2 at the impeller outlet 1B. The region where the vertical axis is greater than 0° is the region where the flow path width is narrower than the impeller outlet on the upstream side of the stationary flow path, and the flow path width is increased by narrowing the flow path width relative to the impeller outlet flow path width b2. Note that the example shown in Figure 6 is a case where the flow path width b3 in the constant flow path width region 21, where the flow path width is narrower than the impeller outlet on the upstream side of the stationary flow path, is set to 70% of the flow path width b2 at the impeller outlet, and the flow path width is increased downstream to 1.2 times the flow path width b3 at the diffuser inlet. As shown in FIG. 6, the outlet radius R of the constant flow path width region 21, which is narrower than the impeller outlet on the upstream side of the stationary flow path 14, increases as the horizontal axis increases, i.e., the outlet radius R of the constant flow path width region 21 increases as the horizontal axis increases. 34 It can be seen that the larger the value, the larger Δα becomes, and the greater the effect of increasing the absolute flow angle. Here, the flow turning angle by the vanes installed in the diffuser 5 and return bend 7 is generally set to about several degrees. In Figure 6, the insufficient turning angle due to the absence of the vanes (vaneless: VL) is set to 5°, and the horizontal axis position (approximately 0.88) at which this insufficient turning angle can be compensated for by reducing the flow path width in the constant flow path width region 21, which is narrower than the impeller outlet on the upstream side of the stationary flow path, is shown by a vertical dotted line. In other words, in this case, if the flow path width is narrowed to a position of 88% of the radius R4 of the return bend inlet 9, the insufficient turning angle due to the diffuser 5 and return bend 7 being configured as VL can be fully compensated for. Similar studies were conducted on other specifications, and it was found that R 34 The range of / R4 was approximately 0.5 or more and 1.0 or less. 34 It is preferable to set / R4 within this range.

[0024] In this embodiment, as shown in FIG. 3, the flow path from the downstream of the outlet of the region 21 with a constant flow path width, where the flow path width is narrower than the impeller outlet on the upstream side of the stationary flow path, to the return bend outlet 10 is set as a diverging flow path whose flow path width gradually increases in the downward flow direction. However, in the bent portion of the flow path, the acceleration and deceleration of the flow caused by the influence of the flow path curvature occur. Therefore, compared with the case of a flow path without a bend, separation is likely to occur when the flow path is made into a diverging flow path. In particular, in the first return bend portion 12 of the return bend 7 where the flow velocity is still high, separation due to the diverging flow path is likely to occur. Therefore, in this embodiment, as shown in FIG. 7, for the first return bend portion 12 of the return bend 7, it is also possible to adopt a configuration in which the flow path is not made into a diverging flow path but has a constant flow path width (constant at the flow path width b4 in FIG. 7).

[0025] As application destinations of the single-shaft multi-stage centrifugal compressor 20 described in this embodiment, various plants are assumed. Among them, as a case where it is required to ensure stable operation in a wide flow rate range from the rated flow rate to the small flow rate side while maintaining the rated discharge pressure for the installed single-shaft multi-stage centrifugal compressor 20, synthesis plants such as ammonia and methanol plants can be mentioned. For the synthesis gas compressors used in these plants, while maintaining the gas pressure required for the synthesis of ammonia and methanol, it is required to stably operate in a wide flow rate range from the rated flow rate to the small flow rate side according to the desired gas synthesis amount. By applying the structure of this embodiment to the synthesis gas compressor used in such a plant, it is possible to suppress an increase in wall surface friction loss while maintaining the ease of return vane design, and to provide a single-shaft multi-stage centrifugal compressor having a wider operating range.

[0026] As described above, according to this embodiment, it is possible to provide a multi-stage centrifugal fluid machine that can achieve both a widened operating range and ease of return vane design. Also, according to this embodiment, it is possible to suppress an increase in wall surface friction loss.

Embodiment

[0027] FIG. 8 is a meridional cross-sectional view near the return bend of the single-shaft multi-stage centrifugal compressor according to Embodiment 2 of the present invention. FIG. 9 is a meridional cross-sectional view near the return bend showing a modified example of the single-shaft multi-stage centrifugal compressor according to Embodiment 2 of the present invention. In the present embodiment, a region 21 with a constant flow path width, in which the flow path width is narrower than the outlet of the impeller on the upstream side of the stationary flow path, includes, in addition to the diffuser 5, the first curved portion 12 of the return bend 7 and a part of the return bend 7, which is different from Embodiment 1. The same reference numerals are given to the same configurations as those in Embodiment 1. Specifically, FIG. 8 is a meridional cross-sectional view taken out from near the outlet 1B of the centrifugal impeller 1 in the single-shaft multi-stage centrifugal compressor 20 according to the present embodiment to near the leading edge 11 of the diffuser 5, the return bend 7, and the return vane 8 downstream thereof.

[0028] As shown in Fig. 8, in this embodiment, similar to the above-described first embodiment, the diffuser 5 and the return bend 7 in the stationary flow path 14 are composed of VL. Further, the stationary flow path 14 between the inlet of the diffuser 5 and the outlet 10 of the return bend 7 has a flow path width b3 that is constant and narrower than the flow path width b2 at the outlet 1B of the centrifugal impeller 1 on the upstream side, and is configured as a flow path 21. On the downstream side thereof, it is configured as a diffuser flow path 22 with an increased flow path width. Further, in this embodiment, at least a part of the meridian shape of the flow path on the inner diameter side or the outer diameter side between the outlet 12B of the first bending portion 12 and the inlet 13A of the second bending portion 13 of the return bend 7 is an axial flow path portion 24 in the return bend extending in the same direction as the extending direction of the rotation axis 4. Also, the outlet 21B of the region 21 with a constant flow path width b3 that is narrower than the flow path width b2 at the outlet 1B of the centrifugal impeller 1 is configured to be located within the return bend 7 between the outlet 12B of the first bending portion 12 of the return bend 7 and the inlet 13A of the second bending portion 13 of the return bend 7. In other words, within the return bend 7 between the outlet 12B of the first bending portion 12 of the return bend 7 and the inlet 13A of the second bending portion 13 of the return bend 7, the outlet 21B of the region 21 with a constant flow path width b3 that is narrower than the flow path width b2 at the outlet 1B of the centrifugal impeller 1 is located. As shown in Fig. 8, in this embodiment, the region 21 with a constant flow path width b3 that is narrower than the flow path width b2 at the outlet 1B of the centrifugal impeller 1 includes the diffuser 5, the first bending portion 12 of the return bend 7, and a part of the return bend 7.

[0029] The effects of adopting the structure in this embodiment will be described below. First, similar to Embodiment 1, by configuring the diffuser 5 and the return bend 7 with VL, the operating range of the single-stage multi-stage centrifugal compressor 20 can be widened. Also, the wall friction acting on the working fluid (fluid) from the side wall 23 increases. As a result, it becomes possible to efficiently reduce the swirling component of the flow. The absolute flow angle α can also be increased due to the increase in the Cm component and the decrease in the Cu component, ensuring the ease of designing the return vane 8. By providing the diffuser passage portion 22, the influence of the increased loss caused by the reduction of the passage width in the region 21 with a constant passage width where the passage width is narrower than the impeller outlet on the upstream side of the stationary passage is canceled, and it is also possible to maintain and improve the stage efficiency.

[0030] Furthermore, in this embodiment, an axial flow passage portion 24 is provided in a portion of the return bend 7, and the outlet of a constant flow passage width region 21, which has a narrower flow passage width than the impeller outlet on the upstream side of the stationary flow passage, is provided between the outlet 12B of the first curved portion 12 of the return bend 7 and the inlet 13A of the second curved portion 13 of the return bend 7. In other words, the constant flow passage width region 21, which has a narrower flow passage width than the impeller outlet on the upstream side of the stationary flow passage, includes the diffuser 5, the first curved portion 12 of the return bend 7, and a portion of the return bend 7. As a result, the outlet position of the constant flow passage width region 21, which has a narrower flow passage width than the impeller outlet on the upstream side of the stationary flow passage and has a constant flow passage width b3, is located downstream of the outlet 12B of the first curved portion 12 of the return bend 7, and the flow passage width does not expand within the first curved portion 12 of the return bend 7. As shown in FIG. 8 , in the return bend 7 between the outlet 12B of the first return bend curved section 12 and the inlet 13A of the second return bend curved section 13, both the inner and outer meridional flow passage shapes form an axial flow passage section 24, where the cross-sectional area of the flow passage does not expand radially or axially. As a result, flow separation can be suppressed in the flow passage inside the first return bend curved section 12 and downstream thereof, where the flow velocity of the working gas (fluid) is high. Flow separation occurring inside the diffuser 5 and at the sidewall immediately downstream thereof can cause shaft vibration and limit the stable operation of the single-shaft multi-stage centrifugal compressor 20, resulting in rotating stall, in which a stall / backflow region propagates circumferentially. The structure of this embodiment can also suppress the occurrence of such rotating stall. Furthermore, in this embodiment, an expanded flow path region 22 is provided on the downstream side of the stationary flow path from the exit of a constant flow path width region 21, which has a narrower flow path width than the impeller exit on the upstream side of the stationary flow path and is provided between the exit 12B of the first curved portion 12 of the return bend 7 and the inlet 13A of the second curved portion 13 of the return bend 7, to the exit 10 of the return bend 7. In this region 22, the flow path cross-sectional area in the radial direction relative to the downstream flow direction of the working gas (fluid) is gradually or continuously enlarged. This makes it possible to avoid a sudden increase in the flow path cross-sectional area (abrupt increase in the flow path cross-sectional area), and to decelerate the working gas (fluid) while suppressing flow separation.

[0031] Further, Fig. 8 also shows a diaphragm 19A, which is shown as a gray-filled part in the figure and is one of the two members forming the flow path wall surface of the stationary flow path 14, and an inner casing 19B, which is shown as a hatched part with diagonal lines in the figure. The diaphragm 19A is formed integrally with a member surrounded by the diffusers 5 of each stage, the return bend 7 and the return vane 8, and a member surrounded by the return vane 8 and the return vane 8, the centrifugal impeller 1 of the next stage and the diffuser 5. On the other hand, the inner casing 19B is also formed as an integral part. Therefore, with the configuration as in this embodiment, since the installation part of the radially outer inclined flow path wall surface newly provided to form the enlarged flow path 22 is limited only to the inner peripheral side wall surface part of the inner casing 19B, the structure is simplified and an increase in the processing time compared to the conventional structure can be suppressed.

[0032] In this embodiment, as shown in Fig. 9, further, a flow path width constant region in which both the inner diameter side and the outer diameter side meridian plane flow path shapes become the axial flow path part 24 can also be provided between the outlet 25B of the enlarged flow path part 25 in the return bend 7 and the inlet 13A of the second curved part 13 of the return bend 7. Thereby, since a flow path without an increase in the flow path cross-sectional area is formed also downstream of the outlet 25B of the enlarged flow path part 25 in the return bend 7, it is possible to suppress the separation of the flow in the second curved part 13 of the return bend where the flow path width expands in the flow-down direction.

[0033] Also, in this embodiment, the expansion rate of the flow path width between the outlet 12B of the first curved part 12 of the return bend 7 and the inlet 13A of the second curved part 13 of the return bend 7 may be set larger than the expansion rate of the flow path width between the inlet 13A of the second curved part 13 of the return bend 7 and the return bend outlet 10. This aims to decelerate the working gas (fluid) as much as possible on the upstream side while preventing swirl stall, and to reduce the deceleration amount in the curved flow path part where separation and the like are likely to occur when the flow path is enlarged, and to decelerate the working gas (fluid) in the region including the axial flow path part 24 as much as possible.

[0034] Needless to say, the single-shaft multi-stage centrifugal compressor 20 described in this embodiment can also be used as a synthesis gas compressor used in a synthesis plant for ammonia, methanol, etc.

[0035] As described above, according to this embodiment, in addition to the effects of the first embodiment, it is possible to suppress the occurrence of flow separation in the return bend first curved portion 12 and in the flow path downstream thereof where the flow velocity of the working gas (fluid) is high. Furthermore, according to this embodiment, the installation location of the radially outer inclined flow path wall surface newly provided to form the expanded flow path 22 is limited to only the inner peripheral wall surface portion of the inner casing 19B, which simplifies the structure and also makes it possible to suppress an increase in processing time compared to the conventional structure. [Example]

[0036] FIG. 10 is a meridional cross section of a single-shaft multi-stage centrifugal compressor according to a third embodiment of the present invention, near a return bend. Specifically, the meridional cross section is taken from near the outlet 1B of the centrifugal impeller 1 to the downstream diffuser 5, the return bend 7, and the vicinity of the leading edge 11 of the return vane 8 in a single-shaft multi-stage centrifugal compressor 20 according to this embodiment. In the first and second embodiments, a method for reducing the gas swirling component to ensure ease of design of the return vane 8 was to increase wall friction by providing a region 21 upstream of the stationary flow passage 14 whose flow passage width is narrower than the flow passage width at the outlet of the centrifugal impeller 1. In contrast, this embodiment differs from the first and second embodiments in that, instead of increasing wall friction by providing the region 21, an increased flow passage wall roughness region 26 having a sidewall 27 with increased wall roughness is provided upstream of the stationary flow passage 14. The same reference numerals are used to design components similar to those in the first and second embodiments.

[0037] As shown in Figure 10, increased wall roughness on the sidewall 27 in the increased wall roughness region on the upstream side of the stationary channel increases wall friction and reduces the swirling component of the flow. Furthermore, downstream of the increased wall roughness region 26 on the upstream side of the stationary channel, an expanded channel 22 is installed, which has a wider channel width than this region 26. This cancels out the effect of increased wall friction loss in the increased wall roughness region 26 on the upstream side of the stationary channel.

[0038] Regarding wall surface roughness, for example, the arithmetic mean roughness (roughness) Ra of the machined flow channel wall surface is generally about 3.2 μm or more and 6.3 μm or less. In contrast, the flow channel wall surface roughness (roughness) Ra that can sufficiently reduce the swirling component of the flow in the flow channel wall surface increased roughness region 26 is preferably about 50 μm or more and 100 μm or less. Such an increased flow channel wall surface roughness region can be realized by subjecting the flow channel wall surface to a blasting process such as shot blasting.

[0039] Needless to say, the single-shaft multi-stage centrifugal compressor 20 described in this embodiment can also be used as a synthesis gas compressor used in a synthesis plant for ammonia, methanol, etc.

[0040] As described above, according to this embodiment, it is possible to provide a multi-stage centrifugal fluid machine that can easily achieve both a wide operating range and ease of return vane design simply by forming an increased flow path wall surface roughness region 26 having a side wall 27 with increased wall surface roughness on the upstream side of the stationary flow path 14.

[0041] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. [Explanation of symbols]

[0042] 1…Centrifugal impeller 1A…Blades of the centrifugal impeller 1B…Outlet of the centrifugal impeller 2…Hub 3…Shroud 4…Rotating shaft 5…Diffuser 5B…Diffuser outlet 6…Return flow path 7…Return bend 8…Return vane 8TE…Trailing edge of the return vane 9…Return bend inlet 10…Return bend outlet 11…Leading edge of the return vane 12…First bending part of the return bend 12B…Outlet of the first bending part of the return bend 13…Second bending part of the return bend 13A…Inlet of the second bending part of the return bend 14…Stationary flow path 15…Suction flow path 16…Discharge flow path 17…Radial bearing 18…Thrust bearing 19…Casing 19A…Diaphragm 19B…Inner casing 20…Single-shaft multi-stage centrifugal compressor 21…Region with a constant flow path width where the flow path width is narrower than the impeller outlet on the upstream side of the stationary flow path 22…Diverging flow path region on the downstream side of the stationary flow path 23…Side wall of the region with a constant flow path width where the flow path width is narrower than the impeller outlet on the upstream side of the stationary flow path 24…Axial flow path part inside the return bend 25…Diverging flow path part inside the return bend 25B…Outlet of the diverging flow path part inside the return bend 26…Wall roughness increasing region on the upstream side of the stationary flow path 27…Side wall in the wall roughness increasing region on the upstream side of the stationary flow path b2…Flow path width at the impeller outlet b3: Diffuser inlet flow path width b4: Diffuser outlet flow passage width (= return bend first curved section inlet flow passage width) C: Absolute flow velocity Cm…Meridional flow velocity Cu: Circumferential component of absolute velocity R2: Impeller outlet radius R 34 ...Outlet radius of the constant flow passage width area, which is narrower than the impeller outlet on the upstream side of the stationary flow passage R4: Return bend entrance radius α...Absolute flow angle

Claims

1. A multi-stage centrifugal fluid machine including a plurality of impellers, a rotating shaft to which the plurality of impellers are attached, and a stationary flow path provided on the downstream side of the impellers for guiding the fluid that has passed through the outlet of the impellers to the impellers in the subsequent stage, wherein the stationary flow path includes a diffuser provided on the radially outer side of the impeller, a return flow path for guiding the fluid from the diffuser to the impeller in the subsequent stage, and a plurality of return vanes provided in the return flow path and arranged at intervals along the circumferential direction, the return flow path has a return bend for guiding the fluid that has passed through the diffuser toward the radially inner side, the return bend has a first curved portion for turning the fluid from the radially outward direction to the same direction as the rotating shaft, and a second curved portion located on the downstream side of the first curved portion for turning the fluid from the same direction as the rotating shaft to the radially inward direction, the leading edge of the return vane is located immediately downstream of the outlet of the return bend, the diffuser and the return bend have no blades, and the stationary flow path has a region with a constant flow path width that is narrower than the outlet of the impeller on the upstream side and a diverging flow path with a flow path width that is larger than the outlet of the impeller on the downstream side. A multi-stage centrifugal fluid machine characterized by this.

2. The multi-stage centrifugal fluid machine according to Claim 1, wherein the first curved portion has a constant flow path width. A multi-stage centrifugal fluid machine characterized by this.

3. The multi-stage centrifugal fluid machine according to Claim 2, at least a part of the meridian plane shape of the flow path on the inner diameter side or the outer diameter side between the outlet of the first curved portion and the inlet of the second curved portion is an axial flow path portion extending in the same direction as the extending direction of the rotating shaft, and the outlet of the flow path with a constant flow path width that is narrower than the outlet of the impeller in the stationary flow path is present at any position within the return bend between the outlet of the first curved portion and the inlet of the second curved portion. A multi-stage centrifugal fluid machine characterized by this.

4. The multi-stage centrifugal fluid machine according to Claim 2, the region with a constant flow path width that is narrower than the outlet of the impeller includes the diffuser, the first curved portion, and a part of the return bend. A multi-stage centrifugal fluid machine characterized by this.

5. The multi-stage centrifugal fluid machine according to Claim 3, A multistage centrifugal fluid machine, characterized in that an enlarged flow path region is provided on the downstream side of the stationary flow path between the outlet of the flow path with a constant flow path width where the flow path width in the stationary flow path is narrowed and the outlet of the return bend.

6. The multistage centrifugal fluid machine according to claim 5, wherein the expansion ratio of the flow path width between the outlet of the first curved portion and the inlet of the second curved portion is larger than the expansion ratio of the flow path width between the inlet of the second curved portion and the outlet of the return bend.

7. The multistage centrifugal fluid machine according to claim 5, wherein the flow path wall surface of the stationary flow path is formed by a diaphragm and an inner casing, and the diaphragm is integrally formed by a member surrounded by the diffuser, the return bend, and the return vanes of each stage, and a member surrounded by the return vanes and the return vanes, the impeller of the next stage, and the diffuser.

8. The multistage centrifugal fluid machine according to claim 5, characterized in that there is a flow path width constant region where both the inner diameter side and the outer diameter side meridional flow path shapes become axial flow path portions between the outlet of the enlarged flow path region in the return bend and the inlet of the second curved portion.

9. A multistage centrifugal fluid machine having a plurality of impellers, a rotating shaft to which the plurality of impellers are attached, and a stationary flow path provided on the downstream side of the impellers and guiding the fluid that has passed through the outlet of the impellers to the impeller of the subsequent stage, wherein the stationary flow path includes a diffuser provided on the radially outer side of the impeller, a return flow path guiding the fluid from the diffuser to the impeller of the subsequent stage, and a plurality of return vanes provided in the return flow path and arranged at intervals along the circumferential direction. The return flow path has a return bend that guides the fluid that has passed through the diffuser radially inward. The return bend has a first curved portion that turns the fluid from the radially outward direction to the same direction as the rotating shaft, and a second curved portion that is located on the downstream side of the first curved portion and turns the fluid from the same direction as the rotating shaft to the radially inward direction. The leading edge of the return vane is located immediately downstream of the outlet of the return bend, the diffuser and the return bend have no vanes, and the stationary flow path between the inlet of the diffuser and the outlet of the return bend has a flow path with an increased wall roughness on the upstream side and a diffuser flow path with an increased flow path width on the downstream side. A multistage centrifugal fluid machine characterized by this.

10. The multistage centrifugal fluid machine according to Claim 9, A multistage centrifugal fluid machine characterized in that the wall roughness is 50 μm or more and 100 μm or less.

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