Uniaxial multistage centrifugal fluid machine

Abstract

This uniaxial multistage centrifugal fluid machine is provided with: a rotary shaft; a plurality of centrifugal impellers; a casing; an introduction nozzle provided in the casing to introduce fluid to the centrifugal impeller of the first stage; and a discharge nozzle for discharging the fluid discharged from the centrifugal impeller of the final stage. The introduction nozzle is provided with: a first introduction nozzle used during rated flow rate operation; and a second introduction nozzle used during low flow rate operation. The uniaxial multistage centrifugal fluid machine has: a first suction flow path in which fluid flows from the first introduction nozzle to the centrifugal impeller of the first stage; and a second suction flow path in which fluid flows from the second introduction nozzle to the centrifugal impeller of the first stage. The second suction flow path is configured to impart a swirling component to a flow that causes fluid to flow to the centrifugal impeller of the first stage. The uniaxial multistage centrifugal fluid machine is provided with a switching device that switches a flow of fluid introduced to the introduction nozzle between the first suction flow path and the second suction flow path. As a result, the rated flow rate operation and the low flow rate operation can be switched with a highly reliable configuration, and the compressor efficiency can be improved.

Description

Technical Field

[0001] The present invention relates to a uniaxial multistage centrifugal fluid machine provided with a large number of centrifugal impellers on a single shaft, particularly with respect to a shape of its suction flow paths. The present invention is particularly suitable for a uniaxial multistage centrifugal compressor.Background Art

[0002] In various plants, a uniaxial multistage centrifugal compressor that is provided with a plurality of centrifugal impellers in multiple stages on a single rotary shaft is used to increase a pressure of a process gas. The uniaxial multistage centrifugal compressor is configured to draw in the process gas through a suction nozzle that forms a suction flow path, introduce it to an annular flow path portion, sequentially compress it with the centrifugal impellers provided in multiple stages on the rotary shaft to increase its pressure, and then discharge it through a discharge nozzle.

[0003] Such a uniaxial multistage centrifugal compressor is described in Japanese Unexamined Patent Application Publication No. 2007-309154 (Patent Literature 1). The uniaxial multistage centrifugal compressor described in Patent Literature 1 is provided with a movable inlet guide vane whose mounting angle is variable upstream of the impeller of a first stage and adjusts a flow rate of a compression stage of a first group on an upstream side in the uniaxial multistage centrifugal compressor by controlling the movable inlet guide vane. In the compression stage of a second group on a downstream side of the uniaxial multistage centrifugal compressor, a preswirl means is provided on the upstream side of the impeller for imparting preswirl to a flow that flows to the impeller. The preswirl means, which is configured with an introduction flow path portion for introducing a gas from outside to an introduction nozzle and a guide vane flow path portion having a plurality of fixed guide vanes arranged at an interval in a circumferential direction on the downstream side of the introduction flow path portion, mixes a flow passing through the introduction flow path portion and the guide vane flow path portion with a flow of a gas drawn in through the suction nozzle and imparts preswirl to a suction flow of the impeller of the second group to adjust the flow rate.Citation ListPatent Literature

[0004] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2007-309154Summary of InventionTechnical Problem

[0005] For a uniaxial multistage centrifugal compressor to be installed, depending on plant types, a rated flow rate operation and a low flow rate operation at a flow rate lower than a rated flow rate may be required to be switched repeatedly, for example, every day while maintaining a rated discharge pressure. In this case, while working fluid is introduced to the compressor with no preswirl during the rated flow rate operation, the working fluid is introduced to the compressor with preswirl being imparted during the low flow rate operation in which an operation at a low flow rate is required. The operation with no preswirl and the operation with preswirl need to be switched on a daily basis.

[0006] The uniaxial multistage centrifugal compressor described in Patent Literature 1 described above is provided with a movable inlet guide vane whose mounting angle is variable upstream of an impeller of a first stage and enables a flow rate to be controlled in an upstream side compression stage including the first stage by driving the vane to impart preswirl to the impeller of the first stage. However, controlling the flow rate requires repeatedly driving the inlet guide vane, and a state with no preswirl and a state with preswirl are switched by repeatedly driving the inlet guide vane every day. Even in such a case in which the operation with high-frequency driving of the movable inlet guide vane is required, sufficient consideration has not been given to ensuring high reliability.

[0007] The uniaxial multistage centrifugal compressor described in Patent Literature 1 is provided with an introduction flow path portion for introducing a gas from outside and a preswirl means that is configured with a guide vane flow path portion having a plurality of fixed guide vanes arranged at an interval in a circumferential direction on a downstream side of the introduction flow path portion on an upstream side of the impeller of an arbitrary intermediate stage. Meanwhile, a flow that has been drawn in through a suction nozzle and has passed through the upstream side compression stage including the impeller of the first stage is directed to pass through a plurality of return vanes (vanes) arranged at an interval in the circumferential direction in a return flow path immediately upstream side of the impeller of the intermediate stage, thereby forming a flow of the working fluid with a swirling component removed. By mixing the working fluid with the swirling component removed and the flow with preswirl imparted by the preswirl means at an inlet side of the impeller of the intermediate stage, the amount of preswirl of an inflow to the impeller of the intermediate stage is adjusted without a movable guide vane to control the flow rate.

[0008] However, since the preswirl means is provided upstream of the impeller of the intermediate stage, the flow rate can only be controlled in a compression stage on the downstream side of the impeller of the intermediate stage, making the low flow rate operation impossible for the entire compressor. The flow with the swirling component removed by the return vane and the flow with the swirling component imparted by the preswirl means converge at an inlet of the impeller of the intermediate stage, resulting in additional problems such as increased mixing losses at a confluence and reduced compressor efficiency.

[0009] The objective of the present invention is to provide a uniaxial multistage centrifugal fluid machine capable of switching between the rated flow rate operation and the low flow rate operation at a flow rate lower than the rated flow rate with a highly reliable configuration to improve the compressor efficiency even when preswirl is imparted. Solution to Problem

[0010] To achieve the objective described above, the present invention is a uniaxial multistage centrifugal fluid machine including: a rotary shaft; a plurality of centrifugal impellers mounted on the rotary shaft; a casing for housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid to the centrifugal impeller of a first stage from among the plurality of centrifugal impellers; and a discharge nozzle provided in the casing for discharging fluid discharged from the centrifugal impeller of a final stage from among the plurality of centrifugal impellers. The introduction nozzle includes: a first introduction nozzle used during rated flow rate operation, and a second introduction nozzle used during low flow rate operation at a flow rate lower than a rated flow rate. The uniaxial multistage centrifugal fluid machine includes: a first suction flow path in which fluid flows from the first introduction nozzle to the centrifugal impeller of the first stage; and a second suction flow path in which fluid flows from the second introduction nozzle to the centrifugal impeller of the first stage. The second suction flow path is configured to impart a swirling component to a flow that causes fluid to flow to the centrifugal impeller of the first stage. The uniaxial multistage centrifugal fluid machine further includes a switching device that switches a flow of fluid introduced to the introduction nozzle between the first suction flow path and the second suction flow path.Advantageous Effects of Invention

[0011] According to the present invention, a uniaxial multistage centrifugal fluid machine capable of switching between the rated flow rate operation and the low flow rate operation at a flow rate lower than the rated flow rate with a highly reliable configuration to improve the compressor efficiency even when preswirl is imparted can be provided.Brief Description of Drawings

[0012] FIG. 1 is a longitudinal cross-sectional view illustrating a first embodiment of a uniaxial multistage centrifugal fluid machine according to the present invention. FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1. FIG. 5 is a diagram illustrating a modification example of the first embodiment of the present invention, which corresponds to FIG. 1. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 5. FIG. 7 is a diagram illustrating a second embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention, which corresponds to FIG. 2. FIG. 8 is a cross-sectional view illustrating a flow path shape of a second suction flow path in the second embodiment in FIG. 7, which corresponds to FIG. 4. FIG. 9 is a diagram illustrating a modification example of the second embodiment according to the present invention, which corresponds to FIG. 8. Description of Embodiments

[0013] A specific example of a uniaxial multistage centrifugal fluid machine according to the present invention is described below with reference to the drawings. In each of the figures, a portion marked with the same reference numeral indicates an identical or corresponding portion. Although the following embodiments describe a uniaxial multistage centrifugal compressor as an example of the uniaxial multistage centrifugal fluid machine, the present invention is similarly applicable to a uniaxial multistage centrifugal pump or the like.First Embodiment

[0014] A first embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 1 through 4. FIG. 1 is a longitudinal cross-sectional view illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the first embodiment, FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, and FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1.

[0015] As shown in FIG. 1, the uniaxial multistage centrifugal compressor 100 of the present embodiment as the uniaxial multistage centrifugal fluid machine is provided with a plurality of centrifugal impellers (hereinafter simply referred to as impellers) 1 mounted in multiple stages on a single rotary shaft 2. Both end portions of the rotary shaft 2 are rotatably supported by bearings 3b provided inside bearing cases 3a. The reference numeral 4 denotes a cylindrical casing that houses the plurality of centrifugal impellers 1, and the casing 4 includes an introduction nozzle 5 for introducing fluid (hereinafter also referred to as working fluid or a working gas) to the centrifugal impeller of a first stage from among the plurality of centrifugal impellers 1 and a discharge nozzle 6 provided on the casing 4 for discharging fluid discharged from the centrifugal impeller of a final stage from among the plurality of centrifugal impellers 1.

[0016] The introduction nozzle 5 is configured with a first introduction nozzle 5a that is used during a rated flow rate operation and a second introduction nozzle 5b that is used during a low flow rate operation at a flow rate lower than the rated flow rate. The reference numeral 5aa denotes an inlet flange portion of the first introduction nozzle 5a, and the reference numeral 5ba denotes the inlet flange portion of the second introduction nozzle 5b. The reference numeral 7 denotes a first suction flow path that causes fluid drawn in through the first introduction nozzle 5a to flow to the centrifugal impeller 1 of the first stage, and the reference numeral 8 denotes a second suction flow path that causes fluid drawn in through the second introduction nozzle 5b to flow to the centrifugal impeller 1 of the first stage.

[0017] The first suction flow path 7 includes a nozzle flow path portion 7a, which is a flow path formed inside the first introduction nozzle 5a, an annular flow path portion 7b annularly provided around the rotary shaft 2 for causing the working fluid to flow circumferentially, and an L-shaped bend flow path portion 7c provided on an inner circumferential side of the annular flow path portion 7b for directing a flow passing through the annular flow path portion 7b to the centrifugal impeller 1 of the first stage by redirecting it from a radially inward direction to a downstream side direction of the rotary shaft 2.

[0018] The second suction flow path 8 similarly includes a nozzle flow path portion 8a, which is a flow path formed inside the second introduction nozzle 5b, an annular flow path portion 8b annularly provided around the rotary shaft 2 for causing the working fluid to flow circumferentially, and an L-shaped bend flow path portion 8c provided on an inner circumferential side of the annular flow path portion 8b for directing a flow passing through the annular flow path portion 8b to the centrifugal impeller 1 of the first stage by redirecting it from the radially inward direction to the downstream side direction of the rotary shaft 2.

[0019] The second suction flow path 8 is configured to impart a swirling component to a flow that causes the fluid to flow to the centrifugal impeller 1 of the first stage. The first suction flow path 7 is configured to either cause the fluid to flow to the centrifugal impeller 1 of the first stage as a flow with a swirling component smaller than that of the second suction flow path 8, or cause the fluid to flow to the centrifugal impeller 1 of the first stage as a flow with no swirling component being imparted.

[0020] On a radially outer side of the centrifugal impeller 1 of each stage, a diffuser portion 9 that serves as a flow path for the working gas discharged from the impeller of each stage is formed approximately radially. In the present embodiment, the diffuser portion 9 is configured as a vaned diffuser having a plurality of vanes 9a that are arranged at an interval in a circumferential direction. Note that a vaneless diffuser provided with no vanes at all may be used for the diffuser portion 9.

[0021] On the downstream side of the diffuser portion 9, a return channel 10 is provided to convert the flow of the working gas from a radially outward flow into a radially inward flow to form a suction flow path to the centrifugal impeller 1 of the next stage. Return vanes 10a are arranged at an interval in the circumferential direction on the return channel 10 to rectify the flow of the working gas. The diffuser portion 9 and the return channel 10 form a stationary flow path 11.

[0022] A scroll 12 is formed on the radially outer side on the downstream side of the centrifugal impeller 1 of the final stage, configured to collect a high-pressure working gas flowing out from the centrifugal impeller 1 of the final stage and discharge it outside the machine through the discharge nozzle 6.

[0023] A shaft seal portion 13 is provided to seal a gap between the rotary shaft 2 and the casing 4 in a portion between the diffuser portion 9 and the return channel 10. The shaft seal portion 13 is configured with a labyrinth seal in the present embodiment, in which the labyrinth seal is mounted on an inner circumferential surface of a shaft penetration portion of the casing 4 and arranged with a small gap with the rotary shaft 2. The shaft seal portion 13 prevents the working gas discharged from the centrifugal impeller 1 of the preceding stage from flowing to the centrifugal impeller 1 of the subsequent stage through the gap.

[0024] In addition, shaft seal portions 14 and 15, which are configured with a labyrinth seal, are provided at the shaft penetration portion between the centrifugal impeller 1 of the first stage and the bearings 3b, and at the shaft penetration portion between the centrifugal impeller 1 of the final stage and the bearing 3b, respectively. The shaft seal portion 14 is provided to prevent air outside the machine or the like from flowing to the centrifugal impeller 1 of the first stage, and the shaft seal portion 15 is provided to prevent the working gas discharged from the centrifugal impeller 1 of the final stage from leaking directly outside the machine without flowing to the scroll 12.

[0025] Note that the bearing cases 3a are provided integrally with the casing 4, or alternatively, the bearing cases 3a are mounted with a mounting platform provided separately.

[0026] The suction flow paths are formed at an end portion on a side of the centrifugal impeller 1 of the first stage in the cylindrical casing 4 that houses the plurality of centrifugal impellers 1 and the rotary shaft 2, and in the present embodiment, the suction flow paths are composed of the first suction flow path 7 described above and the second suction flow path 8 that is provided at a position closer to the centrifugal impeller 1 of the first stage than the first suction flow path 7. The first suction flow path 7 and the second suction flow path 8 serve as flow paths for introducing the working gas from outside the uniaxial multistage centrifugal compressor 100 to the inside of the compressor, configured to convert a flow flowing from a radial direction to the centrifugal impeller 1 of the first stage into a suction flow in an axial direction.

[0027] The first introduction nozzle 5a and the second introduction nozzle 5b are provided on a cylindrical outer peripheral surface on a suction side of the casing 4, and their inlet portions form the inlet flange portions 5aa and 5ba. The inlet flange portions 5aa and 5ba have a circular cross-sectional shape, and each of the introduction nozzles 5a and 5b is configured such that its cross-sectional shape becomes oval (highly flattened) and plane-symmetric with respect to a center cross-section of the compressor shown in FIG. 1 toward a radially inner side.

[0028] The working gas drawn in through the first introduction nozzle 5a or the second introduction nozzle 5b is directed radially inward via the first suction flow path 7 or the second suction flow path 8 and flows to a suction port 1a of the centrifugal impeller 1 of the first stage. Here, a flow path from the inlet flange portion 5aa of the first introduction nozzle 5a to the suction port 1a of the centrifugal impeller 1 of the first stage is the first suction flow path 7, and a flow path from the inlet flange portion 5ba of the second introduction nozzle 5b to the suction port 1a of the centrifugal impeller 1 of the first stage is the second suction flow path 8.

[0029] Each of the suction flow paths 7 and 8 is configured, as described above, with the nozzle flow path portions 7a and 8a, the annular flow path portions 7b and 8b, and the L-shaped bend flow path portions 7c and 8c, respectively, and the annular flow path portions 7b and 8b are connected to radially inner sides of the nozzle flow path portions 7a and 8a, respectively, causing a flow introduced through each of the introduction nozzles 5a and 5b to flow in the circumferential direction. The L-shaped bend flow path portions 7c and 8c are connected to radially inner sides 7ba and 8ba of the annular flow path portions 7b and 8b, respectively, to redirect the working gas from the radially inward direction to the downstream side direction of an axis line X of the rotary shaft 2.

[0030] A plurality of fixed fluid guides 17 are provided in the L-shaped bend flow path portion 8c of the second suction flow path 8, arranged annularly at an interval in the circumferential direction. The fixed fluid guides 17 are for imparting a stable, uniform swirling flow to the fluid flowing through the second suction flow path 8.

[0031] The first suction flow path 7 and the second suction flow path 8 are separated by a partition wall 18 that forms part of the casing 4, and the L-shaped bend flow path portion 7c and the L-shaped bend flow path portion 8c are configured to converge on the downstream side of a radially inner-side end portion 18a of the partition wall 18 and be connected to the suction port 1a of the centrifugal impeller 1 of the first stage.

[0032] In the present embodiment, a switching device (inflow control device) that switches the flow of fluid introduced to the introduction nozzle 5 between the first suction flow path 7 and the second suction flow path 8 is provided.

[0033] The switching device is described below.

[0034] As shown in FIG. 1, in the present embodiment, a main pipe 21 for directing the working fluid to the first introduction nozzle 5a that forms the first suction flow path 7 of the uniaxial multistage centrifugal compressor 100, an opening / closing valve 21a provided on the main pipe 21, a sub-pipe 22 that branches from an upstream side of the opening / closing valve 21a in the main pipe 21 for directing the working fluid to the second introduction nozzle 5b that forms the second suction flow path 8, and an opening / closing valve 22a provided in the sub-pipe 22 are provided. The switching device controls whether a flow of the working fluid from the main pipe 21 is directed to the first suction flow path 7 or to the second suction flow path 8 by controlling opening and closing of the opening / closing valves 21a and 22a.

[0035] Although an example of the switching device configured with opening / closing valves 21a and 22a that allow or block inflow of the working fluid has been described in the present embodiment, a flow regulating valve capable of regulating the amount of inflow may configure the device instead of the opening / closing valves 21a and 22a. The flow regulating valve enables a change in the amount of inflow to the centrifugal impeller 1 when switching between the first suction flow path 7 and the second suction flow path 8 for the working fluid to be smoothly controlled to avoid a sudden change in flow rate, thereby ensuring stable operation even when switching the flow.

[0036] Next, the configuration of the introduction nozzles 5 (the first introduction nozzle 5a and the second introduction nozzle 5b) and the suction flow paths (the first suction flow path 7 and the second suction flow path 8) for introducing the working gas to the centrifugal impeller 1 of the first stage in the uniaxial multistage centrifugal compressor 100 of the present embodiment and a flow state of the working gas passing through the suction flow paths are described also with reference to FIGS. 2 through 4.

[0037] FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1, illustrating the uniaxial multistage centrifugal compressor 100 as viewed from the upstream side in the direction of the axis line X of the rotary shaft 2, and arrangement positions of the first introduction nozzle 5a and the second introduction nozzle 5b are described with reference to FIG. 2. As shown in FIG. 2, the first introduction nozzle 5a that forms the first suction flow path 7 in the present embodiment is arranged toward a direction of the rotary shaft 2. In contrast, the second introduction nozzle 5b that forms the second suction flow path 8 is arranged toward a direction offset from the direction of the rotary shaft 2. The second introduction nozzle 5b that forms the second suction flow path 8 is provided at a position that precedes the first introduction nozzle 5a that forms the first suction flow path 7 in rotational direction A of the centrifugal impeller 1 and the rotary shaft 2 as viewed from an upstream direction of the rotary shaft 2.

[0038] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, illustrating a flow path shape of the first suction flow path 7 and a flow direction of the working gas in the first embodiment. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1, illustrating the flow path shape of the second suction flow path 8 and the flow direction of the working gas.

[0039] As shown in FIG. 3, in the present embodiment, the annular flow path portion 7b in the first suction flow path 7 is configured such that its flow path cross-sectional shape is approximately unchanged along the circumferential direction of the rotary shaft 2. FIG. 3 illustrates not only the flow path shape of the first suction flow path 7 but also the flow of the working gas when only the opening / closing valve 21a is open and the opening / closing valve 22a is closed, which are both shown in FIGS. 1 and 2.

[0040] The flow (flow direction) of the working gas introduced to the first suction flow path 7 from the inlet flange portion 5aa of the first introduction nozzle 5a is indicated by arrow B. The working gas introduced to the first suction flow path 7 from the inlet flange portion 5aa of the first introduction nozzle 5a passes through the nozzle flow path portion 7a and flows into the annular flow path portion 7b. The working gas, while flowing to the annular flow path portion 7b that extends around the entire circumference on the left and right sides and flowing in with the flow direction at each circumferential position toward the axis line X of the rotary shaft 2 as indicated by arrow B, in other words, toward a flow direction with no swirling component, forms a left-right symmetric flow field and flows to the L-shaped bend flow path portion 7c. The working gas flowing to the L-shaped bend flow path portion 7c changes its flow direction toward the downstream side of the axis line X to flow to the suction port 1a of the centrifugal impeller 1 of the first stage.

[0041] Note that in the present embodiment, as shown in FIG. 3, a swirl prevention plate 23 is provided inside the flow path from the annular flow path portion 7b to the L-shaped bend flow path portion 7c in the first suction flow path 7 that is on an opposite side of a position where the first introduction nozzle 5a is provided with the aim of eliminating swirl in the flow of the working gas and ensuring left-right symmetry of the flow.

[0042] In this way, the first suction flow path 7 serves as a suction flow path for introducing the working gas to the suction port 1a of the centrifugal impeller 1 of the first stage with no swirling component.

[0043] In contrast, as shown in FIG. 4, the annular flow path portion 8b in the second suction flow path 8 is configured such that its flow path cross-sectional shape has a spiral shape in which a flow path cross-sectional area gradually narrows along the circumferential direction of the rotary shaft 2 from confluence portion C of the nozzle flow path portion 8a of the second introduction nozzle 5b and the annular flow path portion 8b. FIG. 4 illustrates not only the flow path shape of the second suction flow path 8 but also the flow of the working gas when only the opening / closing valve 22a is open and the opening / closing valve 21a is closed, which are both shown in FIGS. 1 and 2.

[0044] The flow (flow direction) of the working gas introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b is indicated by arrow B in this figure as well. The working gas introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b passes through the nozzle flow path portion 8a and flows into the annular flow path portion 8b.

[0045] The working gas introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b flows into the annular flow path portion 8b after passing through the nozzle flow path portion 8a, as indicated by arrow B. In the present embodiment, the second introduction nozzle 5b is provided in a direction that is offset from the direction of a shaft center X of the rotary shaft 2 and precedes the first introduction nozzle 5a in rotational direction A of the rotary shaft 2.

[0046] Therefore, the working gas flowing into the annular flow path portion 8b flows gradually toward the inner circumference side in the annular flow path portion 8b while swirling in a specific direction, that is, in the same direction as rotational direction A of the rotary shaft 2 and the centrifugal impeller 1 in the case shown in FIG. 4, and then flows to the L-shaped bend flow path portion 8c.

[0047] A volume flow rate of the working gas flowing through the annular flow path portion 8b is highest at the circumferential position in the vicinity of confluence portion C of the second introduction nozzle 5b and the annular flow path portion 8b, and gradually decreases toward the direction of rotational direction A of the impeller. The annular flow path portion 8b in the present embodiment is configured such that its flow path cross-sectional shape has a spiral shape in which the flow path cross-sectional area gradually narrows along the circumferential direction from confluence portion C of the second introduction nozzle 5b and the annular flow path portion 8b. Therefore, even in a case in which the working gas flowing through the annular flow path portion 8b has a circumferential distribution of volume flow rate, a swirling flow velocity of the working gas can be maintained constant regardless of the circumferential position, thereby improving a uniformity of flow when the gas flows to the L-shaped bend flow path portion 8c.

[0048] The plurality of fixed fluid guides 17 are provided annularly in the L-shaped bend flow path portion 8c at a specific interval in the circumferential direction with respect to the axis line X as a rotational center. Thus, the working gas is rectified by the fixed fluid guides 17 to have a desired swirling angle. Although the fixed fluid guides 17 are configured as straight vanes with a constant vane thickness in FIG. 4, they may be configured as airfoils having a distribution of vane thickness and a cambered cross-sectional shape.

[0049] The working gas flowing to the L-shaped bend flow path portion 8c changes its flow direction toward the downstream side of the axis line X while swirling to flow to the suction port 1a of the centrifugal impeller 1 of the first stage. In this way, the second suction flow path 8 can introduce the working gas to the suction port 1a of the centrifugal impeller 1 of the first stage with a swirling flow that is rectified to the desired swirling angle to the flow of the working gas being imparted by the fixed fluid guides 17.

[0050] Next, effects of the present embodiment are described.

[0051] The uniaxial multistage centrifugal compressor 100 of the present embodiment, by being configured as described above, has a relatively simple configuration that merely switches the opening and closing of the opening / closing valve 21a provided in the main pipe 21 and the opening / closing valve 22a provided in the sub-pipe 22 to make it possible to switch between a state in which the working fluid is allowed to flow to the centrifugal impeller 1 of the first stage with no preswirl and a state in which the working fluid is allowed to flow to the centrifugal impeller 1 of the first stage with preswirl being imparted. Therefore, there is no need to provide any driving mechanism for controlling the flow rate, such as movable inlet guide vanes inside the uniaxial multistage centrifugal compressor 100, as in the prior art. As a result, according to the present embodiment, high product reliability can be maintained even in a case in which the compressor is required to switch highly frequently between a rated flow rate operation mode and a low flow rate operation mode.

[0052] In addition, the first suction flow path 7 for introducing the working gas to the suction port 1a of the centrifugal impeller 1 of the first stage with no preswirl is not provided with a fixed fluid guide, thus inhibiting a pressure loss due to the installation of fixed fluid guides from occurring.

[0053] Furthermore, a configuration of introducing the working gas with preswirl imparted to the centrifugal impeller 1 of the first stage for controlling the flow rate provides the effect of enabling the flow rate to be controlled for the entire uniaxial multistage centrifugal compressor 100. The second suction flow path 8 for introducing the working gas with preswirl imparted to the suction port 1a of the centrifugal impeller 1 of the first stage is configured as a flow path separate from the first suction flow path 7 for introducing the working fluid with no preswirl. Therefore, when introducing the working gas only from the second suction flow path 8 that causes the working fluid to flow to the centrifugal impeller 1 of the first stage with preswirl imparted, a flow with no swirl and a swirling flow do not converge. This inhibits a mixing loss from occurring, enabling the compressor efficiency to be improved when imparting preswirl.

[0054] In the present embodiment, the first introduction nozzle 5a is arranged in the direction of the rotary shaft 2, while the second introduction nozzle 5b is arranged at a position in a direction that is offset from the direction of the rotary shaft 2 and precedes the first introduction nozzle 5a in rotational direction A of the rotary shaft 2. As a result, the first introduction nozzle 5a and the second introduction nozzle 5b are arranged at positions in the casing 4 that are circumferentially offset from each other, allowing these two introduction nozzles 5a and 5b to be provided without interference. Therefore, a thickness in an axial direction of the partition wall 18 does not need to be increased to prevent the interference between the introduction nozzles 5a and 5b, minimizing a distance in the axial direction between the first suction flow path 7 and the second suction flow path 8. As a result, a distance between the two bearings 3b provided at both ends of the rotary shaft 2 can be maintained short, enabling a rotational speed of the rotary shaft 2 (rotational speed of the compressor) to be higher.

[0055] Next, a modification example of the first embodiment of the present invention is described with reference to FIGS. 5 and 6. FIGS. 5 and 6 correspond to FIGS. 1 and 4, respectively, with FIG. 5 being a longitudinal cross-sectional view of the uniaxial multistage centrifugal compressor of the present modification example, and FIG. 6 being a cross-sectional view taken along line VI-VI in FIG. 5, illustrating the flow path shape of the second suction flow path and the flow direction of the working gas in the present modification example.

[0056] In the modification examples shown in FIGS. 5 and 6, the annular flow path portion 8b in the second suction flow path 8 is configured such that its flow path cross-sectional shape is approximately unchanged along the circumferential direction of the rotary shaft 2. Other configurations are the same as those in the first embodiment shown in FIGS. 1 through 4 described above.

[0057] The configuration of the present modification example simplifies the shape of the annular flow path portion 8b, thereby reducing the cost of manufacturing the annular flow path portion 8b.

[0058] Note that in the first embodiment and the modification example described above, as shown in FIGS. 1 and 5, the first suction flow path 7 is arranged on the upstream side in a longitudinal direction of the rotary shaft 2 relative to the second suction flow path 8. The fixed fluid guides 17 can be provided most simply by forming the fixed fluid guides 17 in a radial direction area where two opposing flow path wall surfaces in the L-shaped bend flow path portion 8c form flat planes in a vertical direction (direction perpendicular to the axis line X). In the present embodiment, the second suction flow path 8 is arranged on the downstream side in the longitudinal direction of the rotary shaft 2, thus enabling a length in a radial direction of the area where the fixed fluid guides 17 can be easily provided as described above to be increased. Therefore, the length in the radial direction of the fixed fluid guides 17 can also be increased, enabling the flow of the working gas to be easily rectified by allowing the flow of the working gas toward the centrifugal impeller 1 to have the desired swirling angle.

[0059] In the uniaxial multistage centrifugal compressor 100 of the first embodiment and the modification example described above, the working gas passes through the first introduction nozzle 5a in the rated flow rate operation mode, in which the gas flow rate is higher, or through the second introduction nozzle 5b in the low flow rate operation mode, in which the gas flow rate is lower. Therefore, a nozzle size of the second introduction nozzle 5b is preferably smaller than that of the first introduction nozzle 5a.

[0060] The uniaxial multistage centrifugal compressor 100 described in the present embodiment described above can be applied to various plants and is significantly effective, in particular, when applied to uniaxial multistage centrifugal compressors for which stable operation is required over a wide range of flow rates from the rated flow rate to the low flow rate while maintaining a rated discharge pressure. Uniaxial multistage centrifugal compressors of this type include those for synthesis plants of ammonia, methanol, and the like. For synthesis gas compressors used in these synthesis plants, stable operation is required across a wide range of flow rates from the rated flow rate to the low flow rate in accordance with a desired amount of gas synthesis while maintaining a gas pressure necessary for synthesizing ammonia or methanol. The amount of gas synthesis needs to be switched between the rated flow rate (daytime) and the low flow rate (nighttime) in accordance with a significant fluctuation in power generation between day and night, particularly in plants where electricity generated from solar power is used as driving power for the synthesis gas compressor.

[0061] Therefore, by applying the present embodiment to a synthesis gas compressor used in such a plant, with regard to the working gas flowing to the centrifugal impeller 1 of the first stage, the operation can be performed by switching so that the working gas (working fluid) is introduced through the first suction flow path 7 with no preswirl imparted for operation during daytime and the working gas with preswirl imparted is introduced through the second suction flow path for operation during nighttime. As a result, the uniaxial multistage centrifugal compressor can be operated stably across a wide range of flow rates from the rated flow rate to the low flow rate.Second Embodiment

[0062] A second embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 7 and 8. FIG. 7 is a diagram illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the present invention, which corresponds to FIG. 2, and FIG. 8 is a cross-sectional view illustrating the flow path shape of the second suction flow path in the second embodiment in FIG. 7, which corresponds to FIG. 4. In the description of the second embodiment, descriptions of parts similar to those in the first embodiment described above are omitted to focus on the parts that are different from the first embodiment.

[0063] FIG. 7 is a diagram of the uniaxial multistage centrifugal compressor as viewed from the upstream direction of the rotary shaft, illustrating arrangement positions and orientations of the first suction flow path and the second suction flow path. In the first embodiment described above, as shown in FIG. 2, the first introduction nozzle 5a is arranged toward the direction of the rotary shaft 2, while the second introduction nozzle 5b is arranged in the direction offset from the direction of the rotary shaft 2. In contrast, in the second embodiment shown in FIG. 7, the configuration of the first introduction nozzle 5a that forms the first suction flow path 7 and the second introduction nozzle 5b that forms the second suction flow path 8 differs from that of the first embodiment in that both are arranged toward the direction of the rotary shaft 2.

[0064] The second introduction nozzle 5b is provided in the same manner as in the first embodiment at a position that precedes the first introduction nozzle 5a in rotational direction A of the centrifugal impeller 1 and the rotary shaft 2 as viewed from the upstream direction of the rotary shaft 2. However, since the configuration of the second suction flow path 8 is as shown in FIG. 8 in the second embodiment, the relative positions of the first introduction nozzle 5a and the second introduction nozzle 5b are not limited to those shown in FIG. 7. Specifically, the second introduction nozzle 5b may be arranged at the same position in rotational direction A relative to the first introduction nozzle 5a, or the second introduction nozzle 5b may be arranged at a position on a delaying side in rotational direction A relative to the first introduction nozzle 5a. Therefore, according to the second embodiment, restriction on the position of providing the second introduction nozzle 5b is reduced, increasing the degree of freedom in arranging the second introduction nozzle 5b in the casing 4.

[0065] The flow path shape of the second suction flow path 8 in the second embodiment, is described with reference to FIG. 8. FIG. 8 also illustrates flow direction B of the working gas when the working gas is introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b, with the opening / closing valve 21a closed and only the opening / closing valve 22a open, which are both shown in FIG. 7. Note that FIG. 8 is an illustration with the drawing direction adjusted such that the inlet flange portion 5ba shown in FIG. 7 faces vertically upward.

[0066] In the present embodiment, the second introduction nozzle 5b is arranged toward the axis line X of the rotary shaft 2, in which the flow path shape differs from that of the second suction flow path of the first embodiment described with reference to FIG. 4. The present embodiment employs the following configuration to ensure that the working gas flowing in from the second introduction nozzle 5b flows through the annular flow path portion 8b while swirling in the same direction as rotational direction A of the impeller in spite of the arrangement of the second introduction nozzle 5b in such a manner. Specifically, an outlet side of the nozzle flow path portion 8a is bent such that the nozzle flow path portion 8a is directed toward a tangential direction of the annular flow path portion 8b to allow the working gas to flow out toward the tangential direction of the annular flow path portion 8b in the vicinity of confluence portion C of the nozzle flow path portion 8a of the second introduction nozzle 5b and the annular flow path portion 8b.

[0067] In the present embodiment as well, similar to the first embodiment shown in FIG. 4, the annular flow path portion 8b is configured such that its flow path cross-sectional shape has a spiral shape in which the flow path cross-sectional area gradually narrows along the circumferential direction from confluence portion C of the nozzle flow path portion 8a of the second introduction nozzle 5b and the annular flow path portion 8b. Therefore, it is configured to be capable of improving the uniformity of the flow when the gas flows to the L-shaped bend flow path portion 8c as well.

[0068] Next, a modification example of the second embodiment is described with reference to FIG. 9. FIG. 9 is a diagram corresponding to FIG. 8, illustrating the flow path shape of the second suction flow path and the flow direction of the working gas in the present modification example. The modification example shown in FIG. 9 simplifies the shape of the second suction flow path 8 to allow for cost reduction. Specifically, the nozzle flow path portion 8a converges with the annular flow path portion 8b in the vicinity of confluence portion C without being bent in the tangential direction of the annular flow path portion 8b as shown in FIG. 8. The annular flow path portion 8b is configured such that its flow path cross-sectional shape is approximately unchanged along the circumferential direction of the rotary shaft 2.

[0069] When configured in this manner, although the shape of the second suction flow path 8 is simplified, the working gas does not flow in a specific direction identical to rotational direction A of the impeller, preventing the working gas from flowing in along the plurality of fixed fluid guides 17 arranged annularly at an interval in the circumferential direction. As a result, the flow separates from the fixed fluid guides 17, reducing the compressor efficiency. The deviation of an inflow direction of the working gas relative to the fixed fluid guides 17 is greater in an area to the right side of the annular flow path portion 8b in FIG. 9.

[0070] Thus, in the present modification example, as shown in FIG. 9, the shape of the fixed fluid guides 17b that are provided on the right side of a center of the nozzle flow path portion 8a is oriented approximately radially on an outer surface side and lies in the circumferential direction on an inner surface side, with a smooth curve connecting intermediate portions thereof. Other configurations are the same as those in the second embodiment shown in FIGS. 7 and 8 described above.

[0071] The deviation of the inflow direction of the working gas, which is indicated by arrow B, relative to the fixed fluid guides 17 (17a and 17b) is reduced by being configured as described above, suppressing flow separation on the fixed fluid guides 17 (17a and 17b) and thereby suppressing a decrease in compressor efficiency.

[0072] Note that in the second embodiment as well, similar to the first embodiment described above, the first suction flow path 7 is arranged on the upstream side in the longitudinal direction of the rotary shaft 2 relative to the second suction flow path 8. The nozzle size of the second introduction nozzle 5b is preferably smaller than that of the first introduction nozzle 5a.

[0073] According to each of the embodiments of the present invention described above, with a simple configuration without a drive device inside the compressor capable of switching between the state in which the working fluid is allowed to flow to the centrifugal impeller of the first stage with no preswirl and the state in which the working fluid is allowed to flow to the centrifugal impeller of the first stage with preswirl being imparted, it is possible to switch between the rated flow rate operation and the low flow rate operation of the compressor with high reliability. In addition, a uniaxial multistage centrifugal compressor capable of improving the compressor efficiency when imparting preswirl can be provided.

[0074] It should be noted that the present invention is not limited to the embodiments described above, and includes various modification examples. For example, although the embodiments described above describe a case in which the present invention is applied to a uniaxial multistage centrifugal compressor, the present invention is not limited to uniaxial multistage centrifugal compressors but can similarly be applied to uniaxial multistage centrifugal machines such as a uniaxial multistage centrifugal pump, as long as they include a suction flow path that causes the working fluid to flow to the centrifugal impeller by introducing it from the radial direction of the rotary shaft. In addition, the present invention is not limited to synthesis gas compressors used in synthesis plants of ammonia, methanol, or the like but can be applied as a compressor for various other plants.

[0075] The embodiments described above have been described in detail to simply describe the present invention, and it is not necessarily limited to those including all the described configurations. In addition, part of the configuration of each of the embodiments can be subjected to addition, deletion and replacement with respect to other configurations.Reference Signs List

[0076] 1: centrifugal impeller 1a: suction port 2: rotary shaft 3a: bearing case 3b: bearing 4: casing 5: introduction nozzle 5a: first introduction nozzle 5aa: inlet flange portion 5b: second introduction nozzle 5ba: inlet flange portion 6: discharge nozzle 7: first suction flow path 7a: nozzle flow path portion 7b: annular flow path portion 7ba: inner surface side of annular flow path portion 7c: L-shaped bend flow path portion 8: second suction flow path 8a: nozzle flow path portion 8b: annular flow path portion 8ba: inner surface side of annular flow path portion 8c: L-shaped bend flow path portion 9: diffuser portion 9a: vane 10: return channel 10a: return vane 11: stationary flow path 12: scroll 13 to 15: shaft seal portion 17, 17a, 17b: fixed fluid guide 18: partition wall between first suction flow path and second suction flow path 18a: radially inner-side end portion of partition wall between first suction flow path and second suction flow path 21: main pipe 21a: opening / closing valve 22: sub-pipe 22a: opening / closing valve 23: swirl prevention plate 100: uniaxial multistage centrifugal compressor A: rotational direction of impeller B: arrow indicating flow of working gas C: confluence portion X: axis line

Examples

first embodiment

[0014]A first embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 1 through 4. FIG. 1 is a longitudinal cross-sectional view illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the first embodiment, FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, and FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1.

[0015]As shown in FIG. 1, the uniaxial multistage centrifugal compressor 100 of the present embodiment as the uniaxial multistage centrifugal fluid machine is provided with a plurality of centrifugal impellers (hereinafter simply referred to as impellers) 1 mounted in multiple stages on a single rotary shaft 2. Both end portions of the rotary shaft 2 are rotatably supported by bearings 3b provided inside bearing cases 3a. The referen...

second embodiment

[0062] A second embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 7 and 8. FIG. 7 is a diagram illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the present invention, which corresponds to FIG. 2, and FIG. 8 is a cross-sectional view illustrating the flow path shape of the second suction flow path in the second embodiment in FIG. 7, which corresponds to FIG. 4. In the description of the second embodiment, descriptions of parts similar to those in the first embodiment described above are omitted to focus on the parts that are different from the first embodiment.

[0063]FIG. 7 is a diagram of the uniaxial multistage centrifugal compressor as viewed from the upstream direction of the rotary shaft, illustrating arrangement positions and orientations of the first suction flow path and the second suction flow path. In the first embod...

Technical Field

[0001] The present invention relates to a uniaxial multistage centrifugal fluid machine provided with a large number of centrifugal impellers on a single shaft, particularly with respect to a shape of its suction flow paths. The present invention is particularly suitable for a uniaxial multistage centrifugal compressor.Background Art

[0002] In various plants, a uniaxial multistage centrifugal compressor that is provided with a plurality of centrifugal impellers in multiple stages on a single rotary shaft is used to increase a pressure of a process gas. The uniaxial multistage centrifugal compressor is configured to draw in the process gas through a suction nozzle that forms a suction flow path, introduce it to an annular flow path portion, sequentially compress it with the centrifugal impellers provided in multiple stages on the rotary shaft to increase its pressure, and then discharge it through a discharge nozzle.

[0003] Such a uniaxial multistage centrifugal compressor is described in Japanese Unexamined Patent Application Publication No. 2007-309154 (Patent Literature 1). The uniaxial multistage centrifugal compressor described in Patent Literature 1 is provided with a movable inlet guide vane whose mounting angle is variable upstream of the impeller of a first stage and adjusts a flow rate of a compression stage of a first group on an upstream side in the uniaxial multistage centrifugal compressor by controlling the movable inlet guide vane. In the compression stage of a second group on a downstream side of the uniaxial multistage centrifugal compressor, a preswirl means is provided on the upstream side of the impeller for imparting preswirl to a flow that flows to the impeller. The preswirl means, which is configured with an introduction flow path portion for introducing a gas from outside to an introduction nozzle and a guide vane flow path portion having a plurality of fixed guide vanes arranged at an interval in a circumferential direction on the downstream side of the introduction flow path portion, mixes a flow passing through the introduction flow path portion and the guide vane flow path portion with a flow of a gas drawn in through the suction nozzle and imparts preswirl to a suction flow of the impeller of the second group to adjust the flow rate.Citation ListPatent Literature

[0004] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2007-309154Summary of InventionTechnical Problem

[0005] For a uniaxial multistage centrifugal compressor to be installed, depending on plant types, a rated flow rate operation and a low flow rate operation at a flow rate lower than a rated flow rate may be required to be switched repeatedly, for example, every day while maintaining a rated discharge pressure. In this case, while working fluid is introduced to the compressor with no preswirl during the rated flow rate operation, the working fluid is introduced to the compressor with preswirl being imparted during the low flow rate operation in which an operation at a low flow rate is required. The operation with no preswirl and the operation with preswirl need to be switched on a daily basis.

[0006] The uniaxial multistage centrifugal compressor described in Patent Literature 1 described above is provided with a movable inlet guide vane whose mounting angle is variable upstream of an impeller of a first stage and enables a flow rate to be controlled in an upstream side compression stage including the first stage by driving the vane to impart preswirl to the impeller of the first stage. However, controlling the flow rate requires repeatedly driving the inlet guide vane, and a state with no preswirl and a state with preswirl are switched by repeatedly driving the inlet guide vane every day. Even in such a case in which the operation with high-frequency driving of the movable inlet guide vane is required, sufficient consideration has not been given to ensuring high reliability.

[0007] The uniaxial multistage centrifugal compressor described in Patent Literature 1 is provided with an introduction flow path portion for introducing a gas from outside and a preswirl means that is configured with a guide vane flow path portion having a plurality of fixed guide vanes arranged at an interval in a circumferential direction on a downstream side of the introduction flow path portion on an upstream side of the impeller of an arbitrary intermediate stage. Meanwhile, a flow that has been drawn in through a suction nozzle and has passed through the upstream side compression stage including the impeller of the first stage is directed to pass through a plurality of return vanes (vanes) arranged at an interval in the circumferential direction in a return flow path immediately upstream side of the impeller of the intermediate stage, thereby forming a flow of the working fluid with a swirling component removed. By mixing the working fluid with the swirling component removed and the flow with preswirl imparted by the preswirl means at an inlet side of the impeller of the intermediate stage, the amount of preswirl of an inflow to the impeller of the intermediate stage is adjusted without a movable guide vane to control the flow rate.

[0008] However, since the preswirl means is provided upstream of the impeller of the intermediate stage, the flow rate can only be controlled in a compression stage on the downstream side of the impeller of the intermediate stage, making the low flow rate operation impossible for the entire compressor. The flow with the swirling component removed by the return vane and the flow with the swirling component imparted by the preswirl means converge at an inlet of the impeller of the intermediate stage, resulting in additional problems such as increased mixing losses at a confluence and reduced compressor efficiency.

[0009] The objective of the present invention is to provide a uniaxial multistage centrifugal fluid machine capable of switching between the rated flow rate operation and the low flow rate operation at a flow rate lower than the rated flow rate with a highly reliable configuration to improve the compressor efficiency even when preswirl is imparted. Solution to Problem

[0010] To achieve the objective described above, the present invention is a uniaxial multistage centrifugal fluid machine including: a rotary shaft; a plurality of centrifugal impellers mounted on the rotary shaft; a casing for housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid to the centrifugal impeller of a first stage from among the plurality of centrifugal impellers; and a discharge nozzle provided in the casing for discharging fluid discharged from the centrifugal impeller of a final stage from among the plurality of centrifugal impellers. The introduction nozzle includes: a first introduction nozzle used during rated flow rate operation, and a second introduction nozzle used during low flow rate operation at a flow rate lower than a rated flow rate. The uniaxial multistage centrifugal fluid machine includes: a first suction flow path in which fluid flows from the first introduction nozzle to the centrifugal impeller of the first stage; and a second suction flow path in which fluid flows from the second introduction nozzle to the centrifugal impeller of the first stage. The second suction flow path is configured to impart a swirling component to a flow that causes fluid to flow to the centrifugal impeller of the first stage. The uniaxial multistage centrifugal fluid machine further includes a switching device that switches a flow of fluid introduced to the introduction nozzle between the first suction flow path and the second suction flow path.Advantageous Effects of Invention

[0011] According to the present invention, a uniaxial multistage centrifugal fluid machine capable of switching between the rated flow rate operation and the low flow rate operation at a flow rate lower than the rated flow rate with a highly reliable configuration to improve the compressor efficiency even when preswirl is imparted can be provided.Brief Description of Drawings

[0012] FIG. 1 is a longitudinal cross-sectional view illustrating a first embodiment of a uniaxial multistage centrifugal fluid machine according to the present invention. FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1. FIG. 5 is a diagram illustrating a modification example of the first embodiment of the present invention, which corresponds to FIG. 1. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 5. FIG. 7 is a diagram illustrating a second embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention, which corresponds to FIG. 2. FIG. 8 is a cross-sectional view illustrating a flow path shape of a second suction flow path in the second embodiment in FIG. 7, which corresponds to FIG. 4. FIG. 9 is a diagram illustrating a modification example of the second embodiment according to the present invention, which corresponds to FIG. 8. Description of Embodiments

[0013] A specific example of a uniaxial multistage centrifugal fluid machine according to the present invention is described below with reference to the drawings. In each of the figures, a portion marked with the same reference numeral indicates an identical or corresponding portion. Although the following embodiments describe a uniaxial multistage centrifugal compressor as an example of the uniaxial multistage centrifugal fluid machine, the present invention is similarly applicable to a uniaxial multistage centrifugal pump or the like.First Embodiment

[0014] A first embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 1 through 4. FIG. 1 is a longitudinal cross-sectional view illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the first embodiment, FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, and FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1.

[0015] As shown in FIG. 1, the uniaxial multistage centrifugal compressor 100 of the present embodiment as the uniaxial multistage centrifugal fluid machine is provided with a plurality of centrifugal impellers (hereinafter simply referred to as impellers) 1 mounted in multiple stages on a single rotary shaft 2. Both end portions of the rotary shaft 2 are rotatably supported by bearings 3b provided inside bearing cases 3a. The reference numeral 4 denotes a cylindrical casing that houses the plurality of centrifugal impellers 1, and the casing 4 includes an introduction nozzle 5 for introducing fluid (hereinafter also referred to as working fluid or a working gas) to the centrifugal impeller of a first stage from among the plurality of centrifugal impellers 1 and a discharge nozzle 6 provided on the casing 4 for discharging fluid discharged from the centrifugal impeller of a final stage from among the plurality of centrifugal impellers 1.

[0016] The introduction nozzle 5 is configured with a first introduction nozzle 5a that is used during a rated flow rate operation and a second introduction nozzle 5b that is used during a low flow rate operation at a flow rate lower than the rated flow rate. The reference numeral 5aa denotes an inlet flange portion of the first introduction nozzle 5a, and the reference numeral 5ba denotes the inlet flange portion of the second introduction nozzle 5b. The reference numeral 7 denotes a first suction flow path that causes fluid drawn in through the first introduction nozzle 5a to flow to the centrifugal impeller 1 of the first stage, and the reference numeral 8 denotes a second suction flow path that causes fluid drawn in through the second introduction nozzle 5b to flow to the centrifugal impeller 1 of the first stage.

[0017] The first suction flow path 7 includes a nozzle flow path portion 7a, which is a flow path formed inside the first introduction nozzle 5a, an annular flow path portion 7b annularly provided around the rotary shaft 2 for causing the working fluid to flow circumferentially, and an L-shaped bend flow path portion 7c provided on an inner circumferential side of the annular flow path portion 7b for directing a flow passing through the annular flow path portion 7b to the centrifugal impeller 1 of the first stage by redirecting it from a radially inward direction to a downstream side direction of the rotary shaft 2.

[0018] The second suction flow path 8 similarly includes a nozzle flow path portion 8a, which is a flow path formed inside the second introduction nozzle 5b, an annular flow path portion 8b annularly provided around the rotary shaft 2 for causing the working fluid to flow circumferentially, and an L-shaped bend flow path portion 8c provided on an inner circumferential side of the annular flow path portion 8b for directing a flow passing through the annular flow path portion 8b to the centrifugal impeller 1 of the first stage by redirecting it from the radially inward direction to the downstream side direction of the rotary shaft 2.

[0019] The second suction flow path 8 is configured to impart a swirling component to a flow that causes the fluid to flow to the centrifugal impeller 1 of the first stage. The first suction flow path 7 is configured to either cause the fluid to flow to the centrifugal impeller 1 of the first stage as a flow with a swirling component smaller than that of the second suction flow path 8, or cause the fluid to flow to the centrifugal impeller 1 of the first stage as a flow with no swirling component being imparted.

[0020] On a radially outer side of the centrifugal impeller 1 of each stage, a diffuser portion 9 that serves as a flow path for the working gas discharged from the impeller of each stage is formed approximately radially. In the present embodiment, the diffuser portion 9 is configured as a vaned diffuser having a plurality of vanes 9a that are arranged at an interval in a circumferential direction. Note that a vaneless diffuser provided with no vanes at all may be used for the diffuser portion 9.

[0021] On the downstream side of the diffuser portion 9, a return channel 10 is provided to convert the flow of the working gas from a radially outward flow into a radially inward flow to form a suction flow path to the centrifugal impeller 1 of the next stage. Return vanes 10a are arranged at an interval in the circumferential direction on the return channel 10 to rectify the flow of the working gas. The diffuser portion 9 and the return channel 10 form a stationary flow path 11.

[0022] A scroll 12 is formed on the radially outer side on the downstream side of the centrifugal impeller 1 of the final stage, configured to collect a high-pressure working gas flowing out from the centrifugal impeller 1 of the final stage and discharge it outside the machine through the discharge nozzle 6.

[0023] A shaft seal portion 13 is provided to seal a gap between the rotary shaft 2 and the casing 4 in a portion between the diffuser portion 9 and the return channel 10. The shaft seal portion 13 is configured with a labyrinth seal in the present embodiment, in which the labyrinth seal is mounted on an inner circumferential surface of a shaft penetration portion of the casing 4 and arranged with a small gap with the rotary shaft 2. The shaft seal portion 13 prevents the working gas discharged from the centrifugal impeller 1 of the preceding stage from flowing to the centrifugal impeller 1 of the subsequent stage through the gap.

[0024] In addition, shaft seal portions 14 and 15, which are configured with a labyrinth seal, are provided at the shaft penetration portion between the centrifugal impeller 1 of the first stage and the bearings 3b, and at the shaft penetration portion between the centrifugal impeller 1 of the final stage and the bearing 3b, respectively. The shaft seal portion 14 is provided to prevent air outside the machine or the like from flowing to the centrifugal impeller 1 of the first stage, and the shaft seal portion 15 is provided to prevent the working gas discharged from the centrifugal impeller 1 of the final stage from leaking directly outside the machine without flowing to the scroll 12.

[0025] Note that the bearing cases 3a are provided integrally with the casing 4, or alternatively, the bearing cases 3a are mounted with a mounting platform provided separately.

[0026] The suction flow paths are formed at an end portion on a side of the centrifugal impeller 1 of the first stage in the cylindrical casing 4 that houses the plurality of centrifugal impellers 1 and the rotary shaft 2, and in the present embodiment, the suction flow paths are composed of the first suction flow path 7 described above and the second suction flow path 8 that is provided at a position closer to the centrifugal impeller 1 of the first stage than the first suction flow path 7. The first suction flow path 7 and the second suction flow path 8 serve as flow paths for introducing the working gas from outside the uniaxial multistage centrifugal compressor 100 to the inside of the compressor, configured to convert a flow flowing from a radial direction to the centrifugal impeller 1 of the first stage into a suction flow in an axial direction.

[0027] The first introduction nozzle 5a and the second introduction nozzle 5b are provided on a cylindrical outer peripheral surface on a suction side of the casing 4, and their inlet portions form the inlet flange portions 5aa and 5ba. The inlet flange portions 5aa and 5ba have a circular cross-sectional shape, and each of the introduction nozzles 5a and 5b is configured such that its cross-sectional shape becomes oval (highly flattened) and plane-symmetric with respect to a center cross-section of the compressor shown in FIG. 1 toward a radially inner side.

[0028] The working gas drawn in through the first introduction nozzle 5a or the second introduction nozzle 5b is directed radially inward via the first suction flow path 7 or the second suction flow path 8 and flows to a suction port 1a of the centrifugal impeller 1 of the first stage. Here, a flow path from the inlet flange portion 5aa of the first introduction nozzle 5a to the suction port 1a of the centrifugal impeller 1 of the first stage is the first suction flow path 7, and a flow path from the inlet flange portion 5ba of the second introduction nozzle 5b to the suction port 1a of the centrifugal impeller 1 of the first stage is the second suction flow path 8.

[0029] Each of the suction flow paths 7 and 8 is configured, as described above, with the nozzle flow path portions 7a and 8a, the annular flow path portions 7b and 8b, and the L-shaped bend flow path portions 7c and 8c, respectively, and the annular flow path portions 7b and 8b are connected to radially inner sides of the nozzle flow path portions 7a and 8a, respectively, causing a flow introduced through each of the introduction nozzles 5a and 5b to flow in the circumferential direction. The L-shaped bend flow path portions 7c and 8c are connected to radially inner sides 7ba and 8ba of the annular flow path portions 7b and 8b, respectively, to redirect the working gas from the radially inward direction to the downstream side direction of an axis line X of the rotary shaft 2.

[0030] A plurality of fixed fluid guides 17 are provided in the L-shaped bend flow path portion 8c of the second suction flow path 8, arranged annularly at an interval in the circumferential direction. The fixed fluid guides 17 are for imparting a stable, uniform swirling flow to the fluid flowing through the second suction flow path 8.

[0031] The first suction flow path 7 and the second suction flow path 8 are separated by a partition wall 18 that forms part of the casing 4, and the L-shaped bend flow path portion 7c and the L-shaped bend flow path portion 8c are configured to converge on the downstream side of a radially inner-side end portion 18a of the partition wall 18 and be connected to the suction port 1a of the centrifugal impeller 1 of the first stage.

[0032] In the present embodiment, a switching device (inflow control device) that switches the flow of fluid introduced to the introduction nozzle 5 between the first suction flow path 7 and the second suction flow path 8 is provided.

[0033] The switching device is described below.

[0034] As shown in FIG. 1, in the present embodiment, a main pipe 21 for directing the working fluid to the first introduction nozzle 5a that forms the first suction flow path 7 of the uniaxial multistage centrifugal compressor 100, an opening / closing valve 21a provided on the main pipe 21, a sub-pipe 22 that branches from an upstream side of the opening / closing valve 21a in the main pipe 21 for directing the working fluid to the second introduction nozzle 5b that forms the second suction flow path 8, and an opening / closing valve 22a provided in the sub-pipe 22 are provided. The switching device controls whether a flow of the working fluid from the main pipe 21 is directed to the first suction flow path 7 or to the second suction flow path 8 by controlling opening and closing of the opening / closing valves 21a and 22a.

[0035] Although an example of the switching device configured with opening / closing valves 21a and 22a that allow or block inflow of the working fluid has been described in the present embodiment, a flow regulating valve capable of regulating the amount of inflow may configure the device instead of the opening / closing valves 21a and 22a. The flow regulating valve enables a change in the amount of inflow to the centrifugal impeller 1 when switching between the first suction flow path 7 and the second suction flow path 8 for the working fluid to be smoothly controlled to avoid a sudden change in flow rate, thereby ensuring stable operation even when switching the flow.

[0036] Next, the configuration of the introduction nozzles 5 (the first introduction nozzle 5a and the second introduction nozzle 5b) and the suction flow paths (the first suction flow path 7 and the second suction flow path 8) for introducing the working gas to the centrifugal impeller 1 of the first stage in the uniaxial multistage centrifugal compressor 100 of the present embodiment and a flow state of the working gas passing through the suction flow paths are described also with reference to FIGS. 2 through 4.

[0037] FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1, illustrating the uniaxial multistage centrifugal compressor 100 as viewed from the upstream side in the direction of the axis line X of the rotary shaft 2, and arrangement positions of the first introduction nozzle 5a and the second introduction nozzle 5b are described with reference to FIG. 2. As shown in FIG. 2, the first introduction nozzle 5a that forms the first suction flow path 7 in the present embodiment is arranged toward a direction of the rotary shaft 2. In contrast, the second introduction nozzle 5b that forms the second suction flow path 8 is arranged toward a direction offset from the direction of the rotary shaft 2. The second introduction nozzle 5b that forms the second suction flow path 8 is provided at a position that precedes the first introduction nozzle 5a that forms the first suction flow path 7 in rotational direction A of the centrifugal impeller 1 and the rotary shaft 2 as viewed from an upstream direction of the rotary shaft 2.

[0038] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, illustrating a flow path shape of the first suction flow path 7 and a flow direction of the working gas in the first embodiment. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1, illustrating the flow path shape of the second suction flow path 8 and the flow direction of the working gas.

[0039] As shown in FIG. 3, in the present embodiment, the annular flow path portion 7b in the first suction flow path 7 is configured such that its flow path cross-sectional shape is approximately unchanged along the circumferential direction of the rotary shaft 2. FIG. 3 illustrates not only the flow path shape of the first suction flow path 7 but also the flow of the working gas when only the opening / closing valve 21a is open and the opening / closing valve 22a is closed, which are both shown in FIGS. 1 and 2.

[0040] The flow (flow direction) of the working gas introduced to the first suction flow path 7 from the inlet flange portion 5aa of the first introduction nozzle 5a is indicated by arrow B. The working gas introduced to the first suction flow path 7 from the inlet flange portion 5aa of the first introduction nozzle 5a passes through the nozzle flow path portion 7a and flows into the annular flow path portion 7b. The working gas, while flowing to the annular flow path portion 7b that extends around the entire circumference on the left and right sides and flowing in with the flow direction at each circumferential position toward the axis line X of the rotary shaft 2 as indicated by arrow B, in other words, toward a flow direction with no swirling component, forms a left-right symmetric flow field and flows to the L-shaped bend flow path portion 7c. The working gas flowing to the L-shaped bend flow path portion 7c changes its flow direction toward the downstream side of the axis line X to flow to the suction port 1a of the centrifugal impeller 1 of the first stage.

[0041] Note that in the present embodiment, as shown in FIG. 3, a swirl prevention plate 23 is provided inside the flow path from the annular flow path portion 7b to the L-shaped bend flow path portion 7c in the first suction flow path 7 that is on an opposite side of a position where the first introduction nozzle 5a is provided with the aim of eliminating swirl in the flow of the working gas and ensuring left-right symmetry of the flow.

[0042] In this way, the first suction flow path 7 serves as a suction flow path for introducing the working gas to the suction port 1a of the centrifugal impeller 1 of the first stage with no swirling component.

[0043] In contrast, as shown in FIG. 4, the annular flow path portion 8b in the second suction flow path 8 is configured such that its flow path cross-sectional shape has a spiral shape in which a flow path cross-sectional area gradually narrows along the circumferential direction of the rotary shaft 2 from confluence portion C of the nozzle flow path portion 8a of the second introduction nozzle 5b and the annular flow path portion 8b. FIG. 4 illustrates not only the flow path shape of the second suction flow path 8 but also the flow of the working gas when only the opening / closing valve 22a is open and the opening / closing valve 21a is closed, which are both shown in FIGS. 1 and 2.

[0044] The flow (flow direction) of the working gas introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b is indicated by arrow B in this figure as well. The working gas introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b passes through the nozzle flow path portion 8a and flows into the annular flow path portion 8b.

[0045] The working gas introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b flows into the annular flow path portion 8b after passing through the nozzle flow path portion 8a, as indicated by arrow B. In the present embodiment, the second introduction nozzle 5b is provided in a direction that is offset from the direction of a shaft center X of the rotary shaft 2 and precedes the first introduction nozzle 5a in rotational direction A of the rotary shaft 2.

[0046] Therefore, the working gas flowing into the annular flow path portion 8b flows gradually toward the inner circumference side in the annular flow path portion 8b while swirling in a specific direction, that is, in the same direction as rotational direction A of the rotary shaft 2 and the centrifugal impeller 1 in the case shown in FIG. 4, and then flows to the L-shaped bend flow path portion 8c.

[0047] A volume flow rate of the working gas flowing through the annular flow path portion 8b is highest at the circumferential position in the vicinity of confluence portion C of the second introduction nozzle 5b and the annular flow path portion 8b, and gradually decreases toward the direction of rotational direction A of the impeller. The annular flow path portion 8b in the present embodiment is configured such that its flow path cross-sectional shape has a spiral shape in which the flow path cross-sectional area gradually narrows along the circumferential direction from confluence portion C of the second introduction nozzle 5b and the annular flow path portion 8b. Therefore, even in a case in which the working gas flowing through the annular flow path portion 8b has a circumferential distribution of volume flow rate, a swirling flow velocity of the working gas can be maintained constant regardless of the circumferential position, thereby improving a uniformity of flow when the gas flows to the L-shaped bend flow path portion 8c.

[0048] The plurality of fixed fluid guides 17 are provided annularly in the L-shaped bend flow path portion 8c at a specific interval in the circumferential direction with respect to the axis line X as a rotational center. Thus, the working gas is rectified by the fixed fluid guides 17 to have a desired swirling angle. Although the fixed fluid guides 17 are configured as straight vanes with a constant vane thickness in FIG. 4, they may be configured as airfoils having a distribution of vane thickness and a cambered cross-sectional shape.

[0049] The working gas flowing to the L-shaped bend flow path portion 8c changes its flow direction toward the downstream side of the axis line X while swirling to flow to the suction port 1a of the centrifugal impeller 1 of the first stage. In this way, the second suction flow path 8 can introduce the working gas to the suction port 1a of the centrifugal impeller 1 of the first stage with a swirling flow that is rectified to the desired swirling angle to the flow of the working gas being imparted by the fixed fluid guides 17.

[0050] Next, effects of the present embodiment are described.

[0051] The uniaxial multistage centrifugal compressor 100 of the present embodiment, by being configured as described above, has a relatively simple configuration that merely switches the opening and closing of the opening / closing valve 21a provided in the main pipe 21 and the opening / closing valve 22a provided in the sub-pipe 22 to make it possible to switch between a state in which the working fluid is allowed to flow to the centrifugal impeller 1 of the first stage with no preswirl and a state in which the working fluid is allowed to flow to the centrifugal impeller 1 of the first stage with preswirl being imparted. Therefore, there is no need to provide any driving mechanism for controlling the flow rate, such as movable inlet guide vanes inside the uniaxial multistage centrifugal compressor 100, as in the prior art. As a result, according to the present embodiment, high product reliability can be maintained even in a case in which the compressor is required to switch highly frequently between a rated flow rate operation mode and a low flow rate operation mode.

[0052] In addition, the first suction flow path 7 for introducing the working gas to the suction port 1a of the centrifugal impeller 1 of the first stage with no preswirl is not provided with a fixed fluid guide, thus inhibiting a pressure loss due to the installation of fixed fluid guides from occurring.

[0053] Furthermore, a configuration of introducing the working gas with preswirl imparted to the centrifugal impeller 1 of the first stage for controlling the flow rate provides the effect of enabling the flow rate to be controlled for the entire uniaxial multistage centrifugal compressor 100. The second suction flow path 8 for introducing the working gas with preswirl imparted to the suction port 1a of the centrifugal impeller 1 of the first stage is configured as a flow path separate from the first suction flow path 7 for introducing the working fluid with no preswirl. Therefore, when introducing the working gas only from the second suction flow path 8 that causes the working fluid to flow to the centrifugal impeller 1 of the first stage with preswirl imparted, a flow with no swirl and a swirling flow do not converge. This inhibits a mixing loss from occurring, enabling the compressor efficiency to be improved when imparting preswirl.

[0054] In the present embodiment, the first introduction nozzle 5a is arranged in the direction of the rotary shaft 2, while the second introduction nozzle 5b is arranged at a position in a direction that is offset from the direction of the rotary shaft 2 and precedes the first introduction nozzle 5a in rotational direction A of the rotary shaft 2. As a result, the first introduction nozzle 5a and the second introduction nozzle 5b are arranged at positions in the casing 4 that are circumferentially offset from each other, allowing these two introduction nozzles 5a and 5b to be provided without interference. Therefore, a thickness in an axial direction of the partition wall 18 does not need to be increased to prevent the interference between the introduction nozzles 5a and 5b, minimizing a distance in the axial direction between the first suction flow path 7 and the second suction flow path 8. As a result, a distance between the two bearings 3b provided at both ends of the rotary shaft 2 can be maintained short, enabling a rotational speed of the rotary shaft 2 (rotational speed of the compressor) to be higher.

[0055] Next, a modification example of the first embodiment of the present invention is described with reference to FIGS. 5 and 6. FIGS. 5 and 6 correspond to FIGS. 1 and 4, respectively, with FIG. 5 being a longitudinal cross-sectional view of the uniaxial multistage centrifugal compressor of the present modification example, and FIG. 6 being a cross-sectional view taken along line VI-VI in FIG. 5, illustrating the flow path shape of the second suction flow path and the flow direction of the working gas in the present modification example.

[0056] In the modification examples shown in FIGS. 5 and 6, the annular flow path portion 8b in the second suction flow path 8 is configured such that its flow path cross-sectional shape is approximately unchanged along the circumferential direction of the rotary shaft 2. Other configurations are the same as those in the first embodiment shown in FIGS. 1 through 4 described above.

[0057] The configuration of the present modification example simplifies the shape of the annular flow path portion 8b, thereby reducing the cost of manufacturing the annular flow path portion 8b.

[0058] Note that in the first embodiment and the modification example described above, as shown in FIGS. 1 and 5, the first suction flow path 7 is arranged on the upstream side in a longitudinal direction of the rotary shaft 2 relative to the second suction flow path 8. The fixed fluid guides 17 can be provided most simply by forming the fixed fluid guides 17 in a radial direction area where two opposing flow path wall surfaces in the L-shaped bend flow path portion 8c form flat planes in a vertical direction (direction perpendicular to the axis line X). In the present embodiment, the second suction flow path 8 is arranged on the downstream side in the longitudinal direction of the rotary shaft 2, thus enabling a length in a radial direction of the area where the fixed fluid guides 17 can be easily provided as described above to be increased. Therefore, the length in the radial direction of the fixed fluid guides 17 can also be increased, enabling the flow of the working gas to be easily rectified by allowing the flow of the working gas toward the centrifugal impeller 1 to have the desired swirling angle.

[0059] In the uniaxial multistage centrifugal compressor 100 of the first embodiment and the modification example described above, the working gas passes through the first introduction nozzle 5a in the rated flow rate operation mode, in which the gas flow rate is higher, or through the second introduction nozzle 5b in the low flow rate operation mode, in which the gas flow rate is lower. Therefore, a nozzle size of the second introduction nozzle 5b is preferably smaller than that of the first introduction nozzle 5a.

[0060] The uniaxial multistage centrifugal compressor 100 described in the present embodiment described above can be applied to various plants and is significantly effective, in particular, when applied to uniaxial multistage centrifugal compressors for which stable operation is required over a wide range of flow rates from the rated flow rate to the low flow rate while maintaining a rated discharge pressure. Uniaxial multistage centrifugal compressors of this type include those for synthesis plants of ammonia, methanol, and the like. For synthesis gas compressors used in these synthesis plants, stable operation is required across a wide range of flow rates from the rated flow rate to the low flow rate in accordance with a desired amount of gas synthesis while maintaining a gas pressure necessary for synthesizing ammonia or methanol. The amount of gas synthesis needs to be switched between the rated flow rate (daytime) and the low flow rate (nighttime) in accordance with a significant fluctuation in power generation between day and night, particularly in plants where electricity generated from solar power is used as driving power for the synthesis gas compressor.

[0061] Therefore, by applying the present embodiment to a synthesis gas compressor used in such a plant, with regard to the working gas flowing to the centrifugal impeller 1 of the first stage, the operation can be performed by switching so that the working gas (working fluid) is introduced through the first suction flow path 7 with no preswirl imparted for operation during daytime and the working gas with preswirl imparted is introduced through the second suction flow path for operation during nighttime. As a result, the uniaxial multistage centrifugal compressor can be operated stably across a wide range of flow rates from the rated flow rate to the low flow rate.Second Embodiment

[0062] A second embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 7 and 8. FIG. 7 is a diagram illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the present invention, which corresponds to FIG. 2, and FIG. 8 is a cross-sectional view illustrating the flow path shape of the second suction flow path in the second embodiment in FIG. 7, which corresponds to FIG. 4. In the description of the second embodiment, descriptions of parts similar to those in the first embodiment described above are omitted to focus on the parts that are different from the first embodiment.

[0063] FIG. 7 is a diagram of the uniaxial multistage centrifugal compressor as viewed from the upstream direction of the rotary shaft, illustrating arrangement positions and orientations of the first suction flow path and the second suction flow path. In the first embodiment described above, as shown in FIG. 2, the first introduction nozzle 5a is arranged toward the direction of the rotary shaft 2, while the second introduction nozzle 5b is arranged in the direction offset from the direction of the rotary shaft 2. In contrast, in the second embodiment shown in FIG. 7, the configuration of the first introduction nozzle 5a that forms the first suction flow path 7 and the second introduction nozzle 5b that forms the second suction flow path 8 differs from that of the first embodiment in that both are arranged toward the direction of the rotary shaft 2.

[0064] The second introduction nozzle 5b is provided in the same manner as in the first embodiment at a position that precedes the first introduction nozzle 5a in rotational direction A of the centrifugal impeller 1 and the rotary shaft 2 as viewed from the upstream direction of the rotary shaft 2. However, since the configuration of the second suction flow path 8 is as shown in FIG. 8 in the second embodiment, the relative positions of the first introduction nozzle 5a and the second introduction nozzle 5b are not limited to those shown in FIG. 7. Specifically, the second introduction nozzle 5b may be arranged at the same position in rotational direction A relative to the first introduction nozzle 5a, or the second introduction nozzle 5b may be arranged at a position on a delaying side in rotational direction A relative to the first introduction nozzle 5a. Therefore, according to the second embodiment, restriction on the position of providing the second introduction nozzle 5b is reduced, increasing the degree of freedom in arranging the second introduction nozzle 5b in the casing 4.

[0065] The flow path shape of the second suction flow path 8 in the second embodiment, is described with reference to FIG. 8. FIG. 8 also illustrates flow direction B of the working gas when the working gas is introduced to the second suction flow path 8 from the inlet flange portion 5ba of the second introduction nozzle 5b, with the opening / closing valve 21a closed and only the opening / closing valve 22a open, which are both shown in FIG. 7. Note that FIG. 8 is an illustration with the drawing direction adjusted such that the inlet flange portion 5ba shown in FIG. 7 faces vertically upward.

[0066] In the present embodiment, the second introduction nozzle 5b is arranged toward the axis line X of the rotary shaft 2, in which the flow path shape differs from that of the second suction flow path of the first embodiment described with reference to FIG. 4. The present embodiment employs the following configuration to ensure that the working gas flowing in from the second introduction nozzle 5b flows through the annular flow path portion 8b while swirling in the same direction as rotational direction A of the impeller in spite of the arrangement of the second introduction nozzle 5b in such a manner. Specifically, an outlet side of the nozzle flow path portion 8a is bent such that the nozzle flow path portion 8a is directed toward a tangential direction of the annular flow path portion 8b to allow the working gas to flow out toward the tangential direction of the annular flow path portion 8b in the vicinity of confluence portion C of the nozzle flow path portion 8a of the second introduction nozzle 5b and the annular flow path portion 8b.

[0067] In the present embodiment as well, similar to the first embodiment shown in FIG. 4, the annular flow path portion 8b is configured such that its flow path cross-sectional shape has a spiral shape in which the flow path cross-sectional area gradually narrows along the circumferential direction from confluence portion C of the nozzle flow path portion 8a of the second introduction nozzle 5b and the annular flow path portion 8b. Therefore, it is configured to be capable of improving the uniformity of the flow when the gas flows to the L-shaped bend flow path portion 8c as well.

[0068] Next, a modification example of the second embodiment is described with reference to FIG. 9. FIG. 9 is a diagram corresponding to FIG. 8, illustrating the flow path shape of the second suction flow path and the flow direction of the working gas in the present modification example. The modification example shown in FIG. 9 simplifies the shape of the second suction flow path 8 to allow for cost reduction. Specifically, the nozzle flow path portion 8a converges with the annular flow path portion 8b in the vicinity of confluence portion C without being bent in the tangential direction of the annular flow path portion 8b as shown in FIG. 8. The annular flow path portion 8b is configured such that its flow path cross-sectional shape is approximately unchanged along the circumferential direction of the rotary shaft 2.

[0069] When configured in this manner, although the shape of the second suction flow path 8 is simplified, the working gas does not flow in a specific direction identical to rotational direction A of the impeller, preventing the working gas from flowing in along the plurality of fixed fluid guides 17 arranged annularly at an interval in the circumferential direction. As a result, the flow separates from the fixed fluid guides 17, reducing the compressor efficiency. The deviation of an inflow direction of the working gas relative to the fixed fluid guides 17 is greater in an area to the right side of the annular flow path portion 8b in FIG. 9.

[0070] Thus, in the present modification example, as shown in FIG. 9, the shape of the fixed fluid guides 17b that are provided on the right side of a center of the nozzle flow path portion 8a is oriented approximately radially on an outer surface side and lies in the circumferential direction on an inner surface side, with a smooth curve connecting intermediate portions thereof. Other configurations are the same as those in the second embodiment shown in FIGS. 7 and 8 described above.

[0071] The deviation of the inflow direction of the working gas, which is indicated by arrow B, relative to the fixed fluid guides 17 (17a and 17b) is reduced by being configured as described above, suppressing flow separation on the fixed fluid guides 17 (17a and 17b) and thereby suppressing a decrease in compressor efficiency.

[0072] Note that in the second embodiment as well, similar to the first embodiment described above, the first suction flow path 7 is arranged on the upstream side in the longitudinal direction of the rotary shaft 2 relative to the second suction flow path 8. The nozzle size of the second introduction nozzle 5b is preferably smaller than that of the first introduction nozzle 5a.

[0073] According to each of the embodiments of the present invention described above, with a simple configuration without a drive device inside the compressor capable of switching between the state in which the working fluid is allowed to flow to the centrifugal impeller of the first stage with no preswirl and the state in which the working fluid is allowed to flow to the centrifugal impeller of the first stage with preswirl being imparted, it is possible to switch between the rated flow rate operation and the low flow rate operation of the compressor with high reliability. In addition, a uniaxial multistage centrifugal compressor capable of improving the compressor efficiency when imparting preswirl can be provided.

[0074] It should be noted that the present invention is not limited to the embodiments described above, and includes various modification examples. For example, although the embodiments described above describe a case in which the present invention is applied to a uniaxial multistage centrifugal compressor, the present invention is not limited to uniaxial multistage centrifugal compressors but can similarly be applied to uniaxial multistage centrifugal machines such as a uniaxial multistage centrifugal pump, as long as they include a suction flow path that causes the working fluid to flow to the centrifugal impeller by introducing it from the radial direction of the rotary shaft. In addition, the present invention is not limited to synthesis gas compressors used in synthesis plants of ammonia, methanol, or the like but can be applied as a compressor for various other plants.

[0075] The embodiments described above have been described in detail to simply describe the present invention, and it is not necessarily limited to those including all the described configurations. In addition, part of the configuration of each of the embodiments can be subjected to addition, deletion and replacement with respect to other configurations.Reference Signs List

[0076] 1: centrifugal impeller 1a: suction port 2: rotary shaft 3a: bearing case 3b: bearing 4: casing 5: introduction nozzle 5a: first introduction nozzle 5aa: inlet flange portion 5b: second introduction nozzle 5ba: inlet flange portion 6: discharge nozzle 7: first suction flow path 7a: nozzle flow path portion 7b: annular flow path portion 7ba: inner surface side of annular flow path portion 7c: L-shaped bend flow path portion 8: second suction flow path 8a: nozzle flow path portion 8b: annular flow path portion 8ba: inner surface side of annular flow path portion 8c: L-shaped bend flow path portion 9: diffuser portion 9a: vane 10: return channel 10a: return vane 11: stationary flow path 12: scroll 13 to 15: shaft seal portion 17, 17a, 17b: fixed fluid guide 18: partition wall between first suction flow path and second suction flow path 18a: radially inner-side end portion of partition wall between first suction flow path and second suction flow path 21: main pipe 21a: opening / closing valve 22: sub-pipe 22a: opening / closing valve 23: swirl prevention plate 100: uniaxial multistage centrifugal compressor A: rotational direction of impeller B: arrow indicating flow of working gas C: confluence portion X: axis line

Examples

first embodiment

[0014]A first embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 1 through 4. FIG. 1 is a longitudinal cross-sectional view illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the first embodiment, FIG. 2 is a view taken in the direction of arrow II-II in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, and FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1.

[0015]As shown in FIG. 1, the uniaxial multistage centrifugal compressor 100 of the present embodiment as the uniaxial multistage centrifugal fluid machine is provided with a plurality of centrifugal impellers (hereinafter simply referred to as impellers) 1 mounted in multiple stages on a single rotary shaft 2. Both end portions of the rotary shaft 2 are rotatably supported by bearings 3b provided inside bearing cases 3a. The referen...

second embodiment

[0062] A second embodiment of the uniaxial multistage centrifugal fluid machine according to the present invention is described with reference to FIGS. 7 and 8. FIG. 7 is a diagram illustrating a uniaxial multistage centrifugal compressor as the uniaxial multistage centrifugal fluid machine according to the present invention, which corresponds to FIG. 2, and FIG. 8 is a cross-sectional view illustrating the flow path shape of the second suction flow path in the second embodiment in FIG. 7, which corresponds to FIG. 4. In the description of the second embodiment, descriptions of parts similar to those in the first embodiment described above are omitted to focus on the parts that are different from the first embodiment.

[0063]FIG. 7 is a diagram of the uniaxial multistage centrifugal compressor as viewed from the upstream direction of the rotary shaft, illustrating arrangement positions and orientations of the first suction flow path and the second suction flow path. In the first embod...

Claims

1. A uniaxial multistage centrifugal fluid machine comprising: a rotary shaft; a plurality of centrifugal impellers mounted on the rotary shaft; a casing for housing the plurality of centrifugal impellers; an introduction nozzle provided in the casing for introducing fluid to the centrifugal impeller of a first stage from among the plurality of centrifugal impellers; and a discharge nozzle provided in the casing for discharging fluid discharged from the centrifugal impeller of a final stage from among the plurality of centrifugal impellers, wherein the introduction nozzle includes: a first introduction nozzle used during rated flow rate operation; and a second introduction nozzle used during low flow rate operation at a flow rate lower than a rated flow rate; the uniaxial multistage centrifugal fluid machine includes: a first suction flow path in which fluid flows from the first introduction nozzle to the centrifugal impeller of the first stage; and a second suction flow path in which fluid flows from the second introduction nozzle to the centrifugal impeller of the first stage, the second suction flow path is configured to impart a swirling component to a flow that causes fluid to flow to the centrifugal impeller of the first stage, and the uniaxial multistage centrifugal fluid machine includes a switching device that switches a flow of fluid introduced to the introduction nozzle between the first suction flow path and the second suction flow path.

2. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein the first suction flow path is configured to cause fluid to flow to the centrifugal impeller of the first stage as a flow with a swirling component smaller than that of the second suction flow path.

3. The uniaxial multistage centrifugal fluid machine according to claim 2, wherein the first suction flow path causes fluid to flow to the centrifugal impeller of the first stage as a flow with no swirling component being imparted.

4. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein the first suction flow path and the second suction flow path each comprise an annular flow path portion annularly provided around the rotary shaft for causing the fluid to flow circumferentially, and an L-shaped bend flow path portion provided on an inner circumferential side of the annular flow path portion for directing a flow passing through the annular flow path portion to the centrifugal impeller of the first stage by redirecting it from a radially inward direction to a downstream side direction of the rotary shaft.

5. The uniaxial multistage centrifugal fluid machine according to claim 4, wherein the L-shaped bend flow path portion of the second suction flow path is provided with a plurality of fixed fluid guides arranged annularly at an interval in a circumferential direction for imparting a swirling component to a flow.

6. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein the switching device comprises: a main pipe for directing fluid to the first introduction nozzle; a first valve provided in the pipe; a sub-pipe that branches from an upstream side of the first valve in the main pipe for directing fluid to the second introduction nozzle; and a second valve provided in the sub-pipe.

7. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein the first introduction nozzle is arranged toward a direction of the rotary shaft, and the second introduction nozzle is arranged in a direction offset from the direction of the rotary shaft and is arranged at a position that precedes the first introduction nozzle in a rotational direction of the rotary shaft.

8. The uniaxial multistage centrifugal fluid machine according to claim 4, wherein a cross-sectional shape of the annular flow path portion in the first suction flow path is configured to be approximately unchanged along a circumferential direction of the rotary shaft.

9. The uniaxial multistage centrifugal fluid machine according to claim 4, wherein a cross-sectional shape of the annular flow path portion in the second suction flow path is configured to have a spiral shape in which a flow path cross-sectional area gradually narrows along a circumferential direction of the rotary shaft from a confluence portion of the annular flow path and the second introduction nozzle.

10. The uniaxial multistage centrifugal fluid machine according to claim 4, wherein a cross-sectional shape of the annular flow path portion in the second suction flow path is configured to be approximately unchanged along a circumferential direction of the rotary shaft.

11. The uniaxial multistage centrifugal fluid machine according to claim 4, wherein both the first introduction nozzle and the second introduction nozzle are arranged toward a direction of the rotary shaft, and a flow from the second introduction nozzle is configured to be oriented toward a tangential direction of the annular flow path portion.

12. The uniaxial multistage centrifugal fluid machine according to claim 11, wherein the first suction flow path and the second suction flow path each comprise: the annular flow path portion annularly provided around the rotary shaft for causing the fluid to flow circumferentially; and the L-shaped bend flow path portion provided on the inner circumferential side of the annular flow path portion for directing a flow passing through the annular flow path portion to the centrifugal impeller of the first stage by redirecting it from the radially inward direction to the downstream side direction of the rotary shaft, the L-shaped bend flow path portion of the second suction flow path is provided with a plurality of fixed fluid guides arranged annularly at an interval in a circumferential direction for imparting a swirling component to a flow, and a shape of the fixed fluid guides that are provided in a counter-rotational direction from a confluence portion of the second introduction nozzle and the annular flow path portion in the second suction flow path is oriented approximately radially on an outer surface side and lies in a circumferential direction on an inner surface side, with a smooth curve connecting intermediate portions thereof.

13. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein the first suction flow path is arranged on an upstream side in a shaft direction relative to the second suction flow path.

14. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein a nozzle size of the second introduction nozzle is smaller than that of the first introduction nozzle.

15. The uniaxial multistage centrifugal fluid machine according to claim 1, wherein the uniaxial multistage centrifugal fluid machine is a uniaxial multistage centrifugal compressor for synthesizing ammonia or methanol.

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