Multistage centrifugal fluid machine

Abstract

Provided is a multistage centrifugal fluid machine that can achieve both a wide operation range and simplicity in return vane design.　A multistage centrifugal fluid machine 20 comprises: a diffuser 5 in which a stationary flow passage 14 is provided at a radially outer side of an impeller 1; a return flow passage 6 that guides fluid from the diffuser 5 to the impeller 1 at a rear stage; and a plurality of return vanes 8 that are provided in the return flow passage 6 and are arranged at intervals along a circumferential direction. The return flow passage 6 has a return bend 7 that guides, toward a radially inner side, fluid that has passed through the diffuser 5. The return bend 7 has a first curved portion 12 that redirects the fluid from the radially outward direction to the same direction as a rotary shaft 4, and a second curved portion 13 that is positioned on the downstream side of the first curved portion 12 and redirects the fluid from the same direction as the rotary shaft 4 to a radially inward direction. A front edge of the return vane 8 is positioned directly downstream of the outlet of the return bend 7. The diffuser 5 and the return bend 7 are bladeless, and the stationary flow passage 14 has, at an upstream side, a region 21 having a constant flow passage width in which the flow passage width is narrower than an outlet of the impeller 1, and has, at a downstream side, an enlarged flow passage 22 in which the flow passage width is increased to be greater than the outlet of the impeller 1.

Description

Multistage centrifugal fluid machinery

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

[0002] In various plants, single-shaft multi-stage centrifugal compressors with multiple centrifugal impellers arranged in multiple stages on a single rotating shaft are used to pressurize process gas. These single-shaft multi-stage centrifugal compressors are configured to draw process gas through a suction nozzle, introduce it into an annular passage, compress and pressurize the gas sequentially using the centrifugal impellers arranged in multiple stages on the rotating shaft, and then discharge it through a discharge nozzle. These single-shaft multi-stage centrifugal compressors are required to achieve high efficiency and stable operation over a wide flow rate range (hereinafter referred to as a wide operating range). To achieve a wide operating range in single-shaft multi-stage centrifugal compressors, it is necessary to suppress flow instabilities such as flow separation and stall caused by changes in the flow angle of the gas flow inside the compressor due to changes in the flow rate of the process gas. To suppress flow instabilities such as flow separation and stall, vaneless (VL) design is known to be effective for the suppression of flow instabilities. The vaneless design is used for the diffuser and bend passages that constitute part of the stationary passages inside the compressor.

[0003] Patent Document 1 describes a conventional single-shaft multi-stage centrifugal compressor with a VL-type diffuser passage. In this document, the compressor includes a VL-type diffuser and a return passage, which is located downstream of the diffuser and guides the flow discharged from the diffuser radially outward inward, and a return vane section that guides the flow from the return bend to the next impeller while removing the swirl component. The return bend also includes an axis-parallel passage, and a vane is provided in part of this axis-parallel passage to remove the swirl component. This configuration reduces the flow path length in the meridian plane of the return bend and the vane provided in the axis-parallel passage redirects the flow, reducing the swirl component of the flow. This reduces the three-dimensional flow path length, increases the flow angle, and accelerates the flow deceleration, thereby reducing wall friction loss in the return bend. Furthermore, by providing vanes in a portion of the axis-parallel flow passage of the return bend section to redirect the flow toward the meridian plane, the inflow angle of the flow toward the leading edge of the return vane becomes larger. This reduces the amount of swirl component of the flow that needs to be removed between the return vane inlet and outlet, thereby reducing the blade angle difference between the return vane inlet and outlet, i.e., the blade loading. This simplifies the design of the return vane and improves the performance of the next-stage compressor.

[0004] Furthermore, in Patent Document 1, an axially parallel portion is provided on either the inner or outer flow path wall of the bend, and vanes are provided in this portion to eliminate flow swirl, and the flow path width is configured to increase downstream. This configuration can further increase the deceleration of the flow in the return bend, thereby reducing wall friction loss in the return bend.

[0005] Japanese Patent Application Publication No. 8-193600

[0006] As described above, Patent Document 1 aims to reduce wall friction loss of the fluid in the bend section and reduce the blade loading of the return vane by providing an axis-parallel flow passage in the bend section, installing blades there to eliminate flow swirl, and further expanding the flow passage width near the blade installation. However, this configuration also poses the problem that, when the operating flow rate of the compressor deviates significantly from the rated flow rate, the deviation between the flow angle of the flow entering the blades installed in the bend section and the inlet blade angle of the blade increases, causing separation and other problems on the blade surface, narrowing the stable operating flow rate range of the single-shaft multi-stage centrifugal compressor. To maintain stable operation over a wide flow rate range, the bend section must also be configured as a VL. On the other hand, if both the diffuser section and the bend section are configured as VL sections to expand the operating range, the flow swirl will not be sufficiently eliminated before it enters the leading edge of the return vane. In this case, it is necessary to fully eliminate swirl between the inlet and outlet of the return vane, which necessitates increasing the blade loading of the return vane. The present invention provides a multi-stage centrifugal fluid machine that can achieve both a wide operating range and ease of return vane design, because an increase in the blade loading of the return vane in turn causes flow separation in the inter-blade passage of the return vane, making the design of the return vane difficult.

[0007] In order to solve the above-mentioned problems, 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 on which the plurality of impellers are attached, and a stationary flow path that is provided downstream of the impellers and that guides 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 that are provided in the return flow path and arranged at intervals along a circumferential direction, and the return flow path guides the fluid that has passed through the diffuser toward the radially inward direction. 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 has an upstream region with a constant flow path width that is narrower than the impeller outlet and a downstream region with an expanded flow path width that is wider than the impeller outlet.

[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.

[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 return vane design. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0010] 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. FIG. 2 is a meridian cross-sectional view showing the overall configuration of a single-shaft multi-stage centrifugal compressor as an example of a general multi-stage centrifugal fluid machine including the portion shown in FIG. 1. FIG. 3 is a meridian cross-sectional view showing the vicinity of a return bend of the single-shaft multi-stage centrifugal compressor according to Example 1 of the present invention. FIG. 4 is an explanatory diagram of a velocity triangle of a flow near a side wall of a flow passage whose flow passage width is narrower than that of an impeller outlet, corresponding to the upstream side of a stationary flow passage in the single-shaft multi-stage centrifugal compressor according to Example 1 of the present invention. FIG. 5 is an explanatory diagram of an inflow flow vector into a return vane and a blade cross-sectional shape of the return vane in the single-shaft multi-stage centrifugal compressor according to Example 1 of the present invention. FIG. 6 is a diagram showing an example of the results of an investigation into how much the absolute flow angle changes when the outlet diameter of a flow passage whose flow passage width is narrower than that of the impeller outlet is changed in the single-shaft multi-stage centrifugal compressor according to Example 1 of the present invention. FIG. 7 is a meridian cross-sectional view showing the vicinity of a return bend in the single-shaft multi-stage centrifugal compressor according to Example 1 of the present invention, when a first curved portion of the return bend is not an expanded flow passage. 1 is a meridional cross-sectional view of a return bend and its vicinity in a single-shaft multi-stage centrifugal compressor according to a second embodiment of the present invention; FIG. 2 is a meridional cross-sectional view of a return bend and its vicinity in a modified example of the single-shaft multi-stage centrifugal compressor according to the second embodiment of the present invention; FIG. 3 is a meridional cross-sectional view of a return bend and its vicinity in a single-shaft multi-stage centrifugal compressor according to a third embodiment of the present invention;

[0011] Hereinafter, a single-shaft multi-stage centrifugal compressor will be described as an example of a multi-stage 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. Figure 1 is a meridian cross-sectional view showing a part of a single-shaft multi-stage centrifugal compressor as an example of a general multi-stage centrifugal fluid machine, and Figure 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 part shown in Figure 1.

[0012] First, a single-shaft multi-stage centrifugal compressor 20 will be described as an example of a general multi-stage centrifugal fluid machine using Fig. 1. As shown in Fig. 1, the single-shaft multi-stage centrifugal compressor 20 is roughly 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. In addition, a return flow path 6 is provided downstream of the diffuser 5 to guide the fluid to the centrifugal impeller 1 in the subsequent stage.

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

[0014] The diffuser 5 refers to the region of radially outward flow immediately downstream of the outlet 1B of the centrifugal impeller 1. The diffuser 5 may be either a vaned diffuser having multiple blades arranged at approximately equal intervals in the circumferential direction, or a vaneless diffuser (not shown in Fig. 1) without blades. The return flow passage 6 is composed of a return bend 7 and return vanes 8, and the return bend 7 redirects the fluid that has passed through the diffuser 5 from an outward to an inward radial direction, and the return vanes 8 remove the swirling component of the fluid, 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 passage in the meridional plane surrounded by surrounding structures, with its return bend inlet 9 defined by a substantially cylindrical surface corresponding to the outlet of the diffuser 5, and its return bend outlet 10 defined as a section from the return bend inlet 9 to the return bend outlet 10, with the substantially cylindrical surface corresponding to the end of the meridional curved passage located immediately upstream of the return vane leading edge 11. The return bend 7 further includes a return bend first curved portion 12 located upstream of the return bend 7 and redirecting the working gas (fluid) from a radially outward direction to the same direction as the rotational axis 4, and a return bend second curved portion 13 located downstream of the return bend first curved portion 12 and redirecting the working gas (fluid) from the same direction as the rotational axis 4 to a radially inward direction. The return vane 8 is composed of a plurality of blades arranged at substantially equal pitches in the circumferential direction around the rotational axis 4. The above-mentioned diffuser 5 and the return flow passage 6 consisting of the return bend 7 and the return vane 8 are collectively referred to as the stationary flow passage 14 .

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

[0017] 3 is a meridional cross section of the vicinity of the return bend of the single-shaft multi-stage centrifugal compressor according to the first embodiment of the present invention. That is, Fig. 3 is a meridional cross section of the single-shaft multi-stage centrifugal compressor 20 according to the present embodiment, taken from the vicinity of the outlet 1B of the centrifugal impeller 1 to the diffuser 5 and return bend 7 downstream thereof, and the vicinity of the leading edge 11 of the return vane 8.

[0018] As shown in FIG. 3, in this embodiment, the diffuser 5 and the return bend 7 of the stationary flow passage 14 are configured with VL, and further, the stationary flow passage 14 between the inlet of the diffuser 5 and the outlet 10 of the return bend 7 has a flow passage width b ２ The flow path width narrower than b ３ The flow path 21 has a constant width, and downstream of the flow path 21, the flow path 22 has an expanded width.

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

[0020] FIG. 4 shows the flow path width b at the outlet of the centrifugal impeller 1, which corresponds to the upstream side of the stationary flow path 14 (FIG. 3) when this embodiment is applied. ２ The flow path width is narrower than ３ The solid arrows indicate the velocity triangle of the flow near the side wall 23 of the flow path 21 (FIG. 3) with a constant width b. The dashed arrows in the figure indicate the velocity triangle of the flow near the side wall 23 of the flow path 21 (FIG. 3) with a constant width b. ２The figure shows a velocity triangle near the side wall 23 when the flow path width is not reduced relative to the stationary flow path 14. As shown in Figure 4, when a constant flow path width region 21 is provided upstream of the stationary flow path 14, narrowing the flow path width relative to 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 Figure 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 flow path width is reduced upstream of the stationary flow path 14 as in this embodiment, the velocity gradient in the direction perpendicular to the wall surface of the side wall 23 increases, thereby increasing the wall friction acting on the working fluid (fluid) from the side wall 23. With this increase in wall friction, the angular momentum significantly decreases, 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 swirl component of the flow. Furthermore, the increase in the Cm component and the decrease in the Cu component described above also increase the absolute flow angle α.

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

[0022] 5 shows the inlet velocity triangle of the return vane 8 and the blade cross section of the return vane when this embodiment is applied. In this embodiment, a constant flow path width region 21, whose flow path width is narrower than the impeller outlet, is provided upstream of the stationary flow path 14 (FIG. 3), thereby significantly reducing the swirl component of the working gas (fluid) and increasing α in the region 21. Therefore, even if the meridional velocity Cm at the leading edge 11 of the return vane 8 decreases by making the flow path from the outlet of the constant flow path width region 21, whose flow path width is narrower than the impeller outlet on the upstream side of the stationary flow path, to the return bend outlet 10 into an expanded flow path, the inflow angle α of the working gas (fluid) in the velocity triangle at the leading edge 11 of the return vane 8 becomes large. Therefore, the inlet angle βb of the return vane 8, which is set to match the inflow angle α of the fluid into the return vane 8, is set to ５ On the other hand, the return vane trailing edge 8TE is generally set to face the direction of the rotation axis 4 in order to eliminate swirling 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 the extent to which 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 R at the outlet 1B of the centrifugal impeller 1. ２ 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, is R ３４ The radius ratio R ３４ / R ２ The VL diffuser 5 has a flow path width b at the impeller outlet 1B. ２ The radius R of the return bend inlet 9 when the flow path is configured as a constant flow path portion without narrowing the flow path width ４ and R ２ The radius ratio R ４ / R ２ The vertical axis represents the ratio of 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, at each value on the horizontal axis.３４ The absolute flow angle α at the return bend inlet 9 when the flow path width is narrowed to the position and then widened downstream. ４ and the VL diffuser 5 is connected to the impeller outlet 1B with a flow passage width b ２ Absolute flow angle α at the return bend inlet 9 when the flow path is configured as a constant flow path portion without narrowing the flow path width ４ The difference between ' and Δα (= α ４ -α ４ The area where the vertical axis is greater than 0° is the area 21 where the flow path width is constant and is narrower than the impeller outlet flow path width b ２ The example shown in Figure 6 is a region where the flow path width b in the constant flow path width region 21 is narrower than the impeller outlet on the upstream side of the stationary flow path. ３ The width of the flow path at the impeller outlet is b ２ 70% of the width of the diffuser inlet, and ３ As shown in FIG. 6, the horizontal axis increases, that is, 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. ３４ It can be seen that the larger the value of Δα, the greater the effect of increasing the absolute flow angle. Here, the flow turning angle by the vanes installed in the diffuser 5 or return bend 7 is generally set to about several degrees. In FIG. 6, the insufficiency in the 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 insufficiency in the 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. That is, in this case, the radius R of the return bend inlet 9 is ４ If the flow path width is narrowed to 88% of the radius of the diffuser 5 and return bend 7, the lack of turning angle due to the VL configuration can be fully compensated for. ３４ / R ４ The range of R was approximately 0.5 or more and 1.0 or less.３４ / R ４ It is preferable to set it within this range.

[0024] In this embodiment, as shown in FIG. 3, the flow path from downstream of the outlet of the constant flow path width region 21, which has a narrower flow path width than the impeller outlet on the upstream side of the stationary flow path, to the return bend outlet 10 is an expanded flow path with a gradually increasing flow path width in the downstream direction. However, since the flow is accelerated or decelerated at the bend in the flow path due to the influence of the flow path curvature, separation is more likely to occur when the flow path is expanded than in a flow path without a bend. In particular, separation is more likely to occur at the return bend first curved portion 12 in the return bend 7, where the flow velocity is still high. Therefore, in this embodiment, as shown in FIG. 7, the return bend first curved portion 12 in the return bend 7 is not an expanded flow path, but is a constant flow path width (flow path width b ４ It may be configured such that the temperature is constant.

[0025] The single-shaft multi-stage centrifugal compressor 20 described in this embodiment is expected to be applied to various plants. Among these, a synthesis plant for ammonia, methanol, etc. is one example where the single-shaft multi-stage centrifugal compressor 20 is required to maintain a rated discharge pressure while ensuring stable operation over a wide flow rate range from the rated flow rate to the low flow rate side. The synthesis gas compressors used in these plants are required to maintain the gas pressure required for the synthesis of ammonia or methanol and to operate stably over a wide flow rate range from the rated flow rate to the low flow rate side in accordance with 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 maintain the ease of return vane design while suppressing an increase in wall friction loss, and to provide a single-shaft multi-stage centrifugal compressor having a wide 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 wide operating range and easy return vane design. Furthermore, according to this embodiment, it is possible to suppress an increase in wall friction loss.

[0027] Second Embodiment Fig. 8 is a meridional cross section near a return bend of a single-shaft multi-stage centrifugal compressor according to a second embodiment of the present invention. Fig. 9 is a meridional cross section near a return bend showing a modified example of the single-shaft multi-stage centrifugal compressor according to the second embodiment of the present invention. This embodiment differs from the first embodiment in that a constant flow path width region 21, which has a flow path width narrower than that of the impeller outlet on the upstream side of the stationary flow path, includes a first curved portion 12 of the return bend 7 and a part of the return bend 7 in addition to the diffuser 5. The same components as those in the first embodiment are denoted by the same reference numerals. Specifically, Fig. 8 is a meridional cross section taken from near the outlet 1B of the centrifugal impeller 1 to the diffuser 5 and return bend 7 downstream thereof, and near the leading edge 11 of the return vane 8 in a single-shaft multi-stage centrifugal compressor 20 according to this embodiment.

[0028] As shown in FIG. 8, in this embodiment, the diffuser 5 and the return bend 7 of the stationary flow passage 14 are configured as VL, and further, the stationary flow passage 14 between the inlet of the diffuser 5 and the outlet 10 of the return bend 7 has a flow passage width b ２ The flow path width narrower than b ３ The centrifugal impeller 1 has a constant flow path 21 at the outlet 12B of the first curved portion 12 and an expanded flow path 22 downstream of the constant flow path 21, which has an increased flow path width. 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 curved portion 12 of the return bend 7 and the inlet 13A of the second curved portion 13 is an axial flow path portion 24 in the return bend that extends in the same direction as the extending direction of the rotating shaft 4. In addition, the flow path width b ２ The flow path width narrower than b ３ The outlet 21B of the constant region 21 is located within the return bend 7 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 flow path width b at the outlet 1B of the centrifugal impeller 1 is located within the return bend 7 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. ２ The flow path width narrower than b ３In this embodiment, the outlet 21B of the constant region 21 is located at 21. As shown in FIG. 8, the width of the flow passage at the outlet 1B of the centrifugal impeller 1 is b ２ The flow path width narrower than b ３ The constant region 21 includes the diffuser 5, the first curved portion 12 of the return bend 7 and part of the return bend 7.

[0029] The effects of the structure of this embodiment are described below. First, as in the first embodiment, the diffuser 5 and the return bend 7 are configured as VLs, thereby widening the operating range of the single-shaft multi-stage centrifugal compressor 20. Furthermore, the wall friction acting on the working fluid (fluid) from the side wall 23 increases. This makes it possible to efficiently reduce the swirling component of the flow. The absolute flow angle α can be increased by increasing the Cm component and decreasing the Cu component, ensuring ease of design of the return vane 8. The provision of the expanded flow passage section 22 counteracts the effect of increased loss due to the reduction in the flow passage width in the constant flow passage width region 21, which is narrower than the impeller outlet on the upstream side of the stationary flow passage, and also makes it possible to maintain or improve stage efficiency.

[0030] Furthermore, in this embodiment, an axial flow passage portion 24 is provided in a part of the return bend 7, and the outlet of a constant flow passage width region 21, which has a flow passage width narrower 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 flow passage width narrower than the impeller outlet on the upstream side of the stationary flow passage, is configured to include the diffuser 5, the first curved portion 12 of the return bend 7, and a part of the return bend 7. As a result, first, the flow passage width is b ３The outlet position of the constant flow path width region 21, which has a narrower flow path width than the impeller outlet on the upstream side of the stationary flow path where the width is constant, is located downstream of the outlet 12B of the first curved portion 12 of the return bend 7. Therefore, the flow path width does not expand within the first curved portion 12 of the return bend 7. Furthermore, as shown in FIG. 8 , in the region of the return bend 7 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, where both the inner and outer meridional flow path shapes form an axial flow path portion 24, the flow path cross-sectional area does not expand in either the radial or axial direction. As a result, flow separation can be suppressed in the flow path inside the first curved portion 12 of the return bend 7 and downstream thereof, where the flow velocity of the working gas (fluid) is high. Flow separation occurring within the diffuser 5 and at the sidewall immediately downstream thereof may cause shaft vibration and / or other problems, resulting in rotating stall, in which a stall / backflow region propagates in the circumferential direction, limiting the stable operation of the single-shaft multi-stage centrifugal compressor 20. The structure of this embodiment can also suppress the occurrence of such rotating stall. Furthermore, in this embodiment, an expanded flow passage region 22 is provided on the downstream side of the stationary flow passage from the outlet of a constant flow passage width region 21, which is narrower than the impeller outlet on the upstream side of the stationary flow passage and 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, to the outlet 10 of the return bend 7. In this region 22, the flow passage 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 passage cross-sectional area (a steep increase in the flow passage cross-sectional area), and to decelerate the working gas (fluid) while suppressing flow separation.

[0031] 8 also shows two components that form the flow path wall of the stationary flow path 14: a diaphragm 19A shown as a solid gray area in the figure, and an inner casing 19B shown as a hatched area in the figure. The diaphragm 19A is integrally formed with a member surrounded by the diffuser 5, return bend 7, and return vane 8 of each stage, and a member surrounded by the return vane 8, the centrifugal impeller 1, and the diffuser 5 of the next stage. Meanwhile, the inner casing 19B is also formed as an integral part. Therefore, with the configuration of this embodiment, the installation area of ​​the radially outer inclined flow path wall surface newly provided to form the expanded flow path 22 is limited to the inner peripheral wall surface of the inner casing 19B, simplifying the structure and minimizing the increase in processing time compared to conventional structures.

[0032] 9 , a constant flow path width region can also be provided between the outlet 25B of the expanded flow path section 25 in the return bend 7 and the inlet 13A of the second curved section 13 of the return bend 7, where both the inner and outer meridional flow path shapes form the axial flow path section 24. This allows a flow path with no increase in cross-sectional area to be formed downstream of the outlet 25B of the expanded flow path section 25 in the return bend 7, making it possible to suppress flow separation at the second curved section 13 of the return bend, where the flow path width expands in the downstream direction.

[0033] In this embodiment, the expansion rate of the flow passage width from the exit 12B of the first curved portion 12 of the return bend 7 to the entrance 13A of the second curved portion 13 of the return bend 7 may be set to be larger than the expansion rate of the flow passage width from the entrance 13A of the second curved portion 13 of the return bend 7 to the return bend exit 10. This is intended to decelerate the working gas (fluid) as far upstream as possible while preventing rotating stall, and to reduce as much as possible the amount of deceleration in the curved flow passages where separation and the like are likely to occur when the flow passage is expanded, thereby decelerating the working gas (fluid) as much as possible in the region including the axial flow passage 24.

[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 Embodiment 1, it is possible to suppress the occurrence of flow separation in the flow path inside the return bend first curved portion 12 and downstream thereof, where the flow velocity of the working gas (fluid) is high. Furthermore, according to this embodiment, the installation portion 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 suppresses an increase in processing time compared to the conventional structure.

[0036] 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 the vicinity of 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 to 6.3 μm. 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 to 100 μm. Such an increased flow channel wall surface roughness region can be achieved 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.

[0042] DESCRIPTION OF SYMBOLS 1... Centrifugal impeller 1A... Centrifugal impeller blade 1B... Centrifugal impeller outlet 2... Hub 3... Shroud 4... Rotating shaft 5... Diffuser 5B... Diffuser outlet 6... Return flow passage 7... Return bend 8... Return vane 8TE... Return vane trailing edge 9... Return bend inlet 10... Return bend outlet 11... Return vane leading edge 12... Return bend first curved portion 12B... Return bend first curved portion outlet 13... Return bend second curved portion 13A... Return bend second curved portion inlet 14... Stationary flow passage 15... Suction flow passage 16... Discharge flow passage 17... Radial bearing 18... Thrust bearing 19... Casing 19A... Diaphragm 19B... Inner casing 20... Single-shaft multi-stage centrifugal compressor 21...Region of constant flow path width on the upstream side of the stationary flow path where the flow path width is narrower than the impeller outlet 22...Expanded flow path region on the downstream side of the stationary flow path 23...Side wall portion of the region of 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 portion in the return bend 25...Expanded flow path portion in the return bend 25B...Outlet of the expanded flow path portion in the return bend 26...Region of increased wall surface roughness on the upstream side of the stationary flow path 27...Side wall portion in the region of increased wall surface roughness on the upstream side of the stationary flow path b ２ ... width of the flow passage at the impeller outlet b ３ ... Diffuser inlet flow path width b ４ ...flow path width at the diffuser outlet (= inlet flow path width at the first curved portion of the return bend) C...absolute flow velocity Cm...meridional flow velocity Cu...circumferential component of absolute flow velocity R ２ …Impeller outlet radius R ３４ ...Outlet radius R of the constant flow path width area, which is narrower than the impeller outlet on the upstream side of the stationary flow path ４ …Return bend inlet 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 outlets of the impellers to the impellers in the subsequent stage. 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 radially inward. 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.

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

3. The multi-stage centrifugal fluid machine according to claim 2, wherein 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 forms 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 exists at any position within the return bend between the outlet of the first curved portion and the inlet of the second curved portion.

4. The multi-stage centrifugal fluid machine according to claim 2, wherein 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.

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

6. The multi-stage centrifugal fluid machine according to claim 5, wherein the expansion rate 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 rate of the flow path width between the inlet of the second curved portion and the outlet of the return bend.

7. The multi-stage 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 vane of each stage, and a member surrounded by the return vane, the return vane, the impeller of the next stage, and the diffuser.

8. The multi-stage centrifugal fluid machine according to claim 5, wherein a flow path width constant region in which both the inner diameter side and the outer diameter side meridian plane flow path shapes become axial flow path portions is provided 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 impeller and guiding the fluid that has passed through the outlet of the impeller 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 that guides 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 radially outward 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 radially inward, the leading edge of the return vane is located immediately downstream of the outlet of the return bend, the diffuser and the return bend are without blades, and the stationary flow path between the inlet of the diffuser and the outlet of the return bend has a flow path with a larger wall surface 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, wherein the wall surface roughness is 50 μm or more and 100 μm or less. A multistage centrifugal fluid machine characterized by this.

Images