JP5031012B2 - Compressor and operation control method thereof - Google Patents

Description

  The present invention can be applied to a centrifugal compressor, a mixed flow compressor, or the like that compresses a fluid by the rotational force of an impeller, and particularly relates to a compressor capable of suppressing a rotating stall in these compressors and an operation control method thereof.

Conventionally, high-pressure industrial centrifugal compressors are used in petrochemical plants and natural gas plants. In this centrifugal compressor, an impeller is rotatably supported on a rotating shaft in a housing, and by rotating the impeller, a fluid such as air or gas is sucked from a fluid inlet of the housing to apply a centrifugal force. The kinetic energy is converted into pressure energy by the diffuser and the scroll unit, and is sent from the compressed fluid outlet of the housing through the discharge pipe.
FIG. 11 is a cross-sectional view of an essential part of the centrifugal compressor. The centrifugal compressor includes a rotating shaft 01 and an impeller 02 that rotates integrally with the rotating shaft 01. On the outlet side of the impeller 02, a vaneless diffuser 03 serving as a fluid flow path to which centrifugal force is applied by the impeller 02 is provided. A labyrinth 06 is provided between the shroud disk 04 and the shroud casing 05 of the impeller 02, and a labyrinth 08 is provided between the rotating shaft 01 and the hub casing 07.

In an industrial centrifugal compressor that requires high performance and high reliability as described above, if the structure is simple and the flow angle is appropriate, the loss is small, the operating range is wide, and the fluid applied to the impeller 02 Since no exciting force is generated, the vaneless diffuser 03 is widely adopted as the most suitable diffuser type. However, when the flow angle is increased, loss is increased and a rotational stall is generated in which the flow in the circumferential direction is non-uniform, and pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like, which are considered to be caused by this, occur.
It is known that this rotating stall occurs particularly when the centrifugal compressor is operated in a low flow rate region. FIG. 12 shows the relationship between the flow rate Q at which turning stall occurs, the outlet pressure (head pressure) H of the compressor, and the efficiency η. The flow rate Q1 is the turning stall occurrence point, and the flow rate range at a lower flow rate than that. Is the turning stall generation region W1.

When the rotating stall occurs, the above-described problems are caused, and it is difficult to continuously operate the centrifugal compressor stably. Therefore, the centrifugal compressor cannot be continuously operated in a low flow rate region below the turning stall occurrence point, and the range in which the centrifugal compressor can be stably operated is reduced accordingly.
Therefore, there has been proposed a high-pressure fluid having a pressure higher than its internal pressure introduced into the diffuser for the purpose of preventing the occurrence of turning stall (see Patent Document 1).

Japanese Patent Laid-Open No. 2003-13895

However, what is described in Patent Document 1 is such that a high-pressure fluid higher than the internal pressure of the diffuser is directly ejected from the diffuser wall surface, so that when the fluid merges with the main fluid flow of the diffuser, the main fluid flow is disturbed. However, there is a problem of increasing the pressure loss due to flow shear.
Also, in order to eject a high-pressure fluid higher than the internal pressure of the diffuser, when the compressed fluid is introduced and accumulated in the chamber through the intake pipe from the impeller outlet, the flow rate drops to the swirl stall generation region, A configuration for jetting into the diffuser via a jet pipe, a configuration for taking in high-pressure compressed fluid from the final compression stage via a communication pipe, or a configuration for supplying high-pressure fluid from a separately installed high-pressure fluid supply unit, etc. However, this complicates the structure around the diffuser and detracts from the advantage of the vaneless diffuser that the structure is simple.

  The present invention has been made in view of such circumstances, and is capable of suppressing turning stall in the vaneless diffuser, has almost no power loss or pressure loss, and has a simple structure. It is an object of the present invention to provide a compressor capable of maintaining the advantages of a diffuser and an operation control method thereof.

In order to solve the above problems, the compressor and the operation control method thereof of the present invention employ the following means.
That is, the compressor according to the present invention includes a vaneless diffuser that converts kinetic energy given to the fluid by the impeller into pressure energy on the outlet side of the impeller, and is provided on the outlet side of the vaneless diffuser. The inlet has an opening, and the outlet has a fluid circulation channel that is opened in a casing wall surface facing the rear surface of the hub disk of the impeller, and the inlet is opened in the hub casing wall surface at the return vane inlet position to the downstream compression stage. The fluid circulation channel is configured by a plurality of communication holes or one or a plurality of slits , and the fluid taken in from the inlet is ejected from the outlet toward the back surface of the hub disk of the impeller, A circumferential flow velocity is applied to the rear surface of the hub disk so that the vaneless diffuser inlet Wherein the recycle stream is merged with the primary fluid flow from Npera it is possible form.

According to the present invention, an inlet is opened on the outlet side of the vaneless diffuser, and the outlet has a fluid circulation channel opened on a casing wall surface facing the back surface of the hub disk of the impeller, and the inlet is a downstream compression stage. Opened to the wall surface of the hub casing at the return vane inlet position, and the fluid circulation flow path is constituted by a plurality of communication holes, or one or a plurality of slits, and the hub disk of the impeller receives the fluid taken in from the inlet from the outlet It is possible to form a circulating flow that is ejected toward the rear surface and a circumferential flow velocity is given by the rear surface of the hub disk to join the main fluid from the impeller at the vaneless diffuser inlet. A part of the high-pressure fluid is circulated to the inlet side of the vaneless diffuser to increase the flow rate of the fluid flowing through the vaneless diffuser. It can be. For this reason, the turning stall occurrence point can be shifted to the low flow rate side by the increased flow rate ratio, and the occurrence of turning stall can be suppressed. Accordingly, it is possible to suppress pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall, and to expand the range in which the compressor can be stably operated.
Further, since the inlet of the fluid circulation channel is opened in the hub casing wall surface at the return vane inlet position to the downstream compression stage, the fluid circulation channel can be provided in one hub casing. Therefore, the fluid circulation channel that can suppress the rotation stall can be easily configured, and the flow of the fluid flowing into the fluid circulation channel from the return vane inlet position can cause the main fluid flow at the return vane inlet position. Since peeling can be suppressed, the flow rate characteristic can be improved.
In addition, since the outlet of the fluid circulation passage is opened in the casing wall surface facing the rear surface of the hub disk, the main fluid flowing through the impeller is not disturbed by the circulation flow ejected from the outlet of the fluid circulation passage. . Moreover, when this circulating flow merges with the main fluid at the vaneless diffuser inlet, the circumferential flow velocity is approximately the same as that of the main fluid. Therefore, an increase in pressure loss due to flow shear can also be suppressed.
Furthermore, since the fluid circulation channel is composed of a plurality of communication holes, or one or a plurality of slits, by appropriately selecting the number and hole diameter of the communication holes, or the number, width and length of the slits, It is possible to appropriately set a fluid circulation channel that can obtain a required circulation flow rate.
In the present invention, when the compression stage is the final compression stage, the outlet side of the vaneless diffuser means a high-pressure flow path from the vaneless diffuser outlet of the compression stage to the scroll, and the downstream side is the final compression stage. When it is not a stage, it means a high-pressure flow path not only from the vaneless diffuser outlet of the compression stage to the return vane inlet of the downstream compression stage but also to the return vane outlet.

Furthermore, the compressor according to the present invention is characterized in that, in the above-described compressor, the outlet is directed obliquely in a turning direction of the impeller.

  According to the present invention, since the outlet of the fluid circulation channel is oriented obliquely in the impeller turning direction, the circulating flow ejected from the fluid circulation channel outlet is ejected along the impeller turning direction. . Accordingly, it is possible to suppress friction loss due to the circulation flow being ejected to the hub disk on the back surface of the impeller.

  Furthermore, the compressor of the present invention is characterized in that, in any of the above-described compressors, the outlet is opened in the casing wall surface at a position equal to or less than half of the outer diameter of the impeller.

  According to the present invention, since the outlet of the fluid circulation channel is opened to the casing wall surface at a position that is less than half the outer diameter of the impeller, the circumferential velocity component of the circulation flow is sufficiently developed at the outlet position of the impeller. The necessary distance can be secured. For this reason, when the circulating flow joins the fluid main flow at the vaneless diffuser inlet, the flow velocity can be set to a circumferential flow velocity substantially the same as the fluid main flow. Accordingly, an increase in pressure loss due to flow shear in the vaneless diffuser can be suppressed.

  The compressor of the present invention is characterized in that, in any of the compressors described above, the fluid circulation flow rate of the fluid circulation channel is set to about 10% of the main fluid flowing through the impeller.

  According to the present invention, since the fluid circulation flow rate of the fluid circulation channel is set to about 10% of the fluid main flow that flows through the impeller, power loss hardly occurs. That is, since the fluid circulation by the fluid circulation channel of the present invention is circulation between the vaneless diffuser inlet / outlet without passing through the impeller, almost no power loss occurs. Therefore, it is possible to suppress the occurrence of turning stall and to suppress the efficiency of the compressor to a slight decrease of about 1% at most.

  The compressor of the present invention is characterized in that, in any of the compressors described above, an opening / closing means for opening and closing the fluid circulation channel is provided in the fluid circulation channel.

According to the present invention, since the opening / closing means for opening / closing the fluid circulation flow path is provided in the fluid circulation flow path, the fluid circulation flow path is closed by the opening / closing means in an area where the rotation stall is not likely to occur. Therefore, the compressor can be operated with the same efficiency as a compressor that does not include a fluid circulation channel. Also, in the turning stall region, the opening of the fluid circulation channel by the opening / closing means can shift the turning stall occurrence point to the low flow rate side to suppress the turning stall and expand the range in which the compressor can be stably operated. it can.
In this case, it is only necessary to circulate the fluid through the fluid circulation channel only when suppressing the rotating stall, and there is almost no need to worry about the decrease in efficiency. can do.

  A compressor operation control method according to the present invention is a compressor operation control method for controlling the operation of the above-described compressor, and detects the flow rate of fluid flowing through the vane-less diffuser, and the flow rate is in the turning stall region. When this happens, the fluid circulation flow path is opened by the opening / closing means.

According to the present invention, when the flow rate of the fluid flowing through the vaneless diffuser is detected and the flow rate is in the rotating stall region, the fluid circulation channel is opened by the opening / closing means, and a part of the high-pressure fluid is introduced into the inlet of the vaneless diffuser. The flow rate of fluid flowing through the vaneless diffuser can be increased. For this reason, the turning stall occurrence point can be shifted to the low flow rate side by the increased flow rate ratio to suppress the occurrence of turning stall. Accordingly, it is possible to suppress pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall, and to expand the range in which the compressor can be stably operated.
Further, in the region where there is no possibility of causing the rotation stall, the fluid circulation channel can be stopped by closing the fluid circulation channel by the opening / closing means. Therefore, similarly to the compressor not having the fluid circulation channel. , Driving with priority on efficiency can be performed.

  Furthermore, the compressor operation control method of the present invention is characterized in that, in the compressor operation control method, the opening / closing means is opened during a partial load operation of a predetermined load or less.

  According to the present invention, the opening / closing means for opening and closing the fluid circulation flow path is opened during partial load operation below a predetermined load, so that part of the high-pressure fluid is vane-less during low flow operation at partial load. Circulating to the inlet side of the diffuser, the flow rate of the fluid flowing through the vaneless diffuser can be increased. For this reason, the turning stall occurrence point can be shifted to the low flow rate side by the increased flow rate ratio to suppress the occurrence of turning stall. Therefore, pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall can be suppressed, and the range in which the compressor can be stably operated and the operation range by partial load can be expanded.

According to the compressor of the present invention, a part of the high-pressure fluid is circulated to the inlet side of the vaneless diffuser by the fluid circulation passage, and the flow rate of the fluid flowing through the vaneless diffuser is increased, thereby reducing the turning stall occurrence point. Shifting to the flow rate side can suppress the occurrence of turning stall. Accordingly, it is possible to suppress pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall, and to expand the range in which the compressor can be stably operated. In addition, since the inlet of the fluid circulation channel is opened in the hub casing wall surface at the return vane inlet position to the downstream compression stage, the rotation stall can be suppressed by providing the fluid circulation channel in one hub casing. The fluid circulation flow path can be easily configured, and the flow of the fluid flowing into the fluid circulation flow path from the return vane inlet position can suppress separation of the fluid main flow at the return vane inlet position. The flow characteristics can be improved.

In addition, since the outlet of the fluid circulation channel is opened in the casing wall surface facing the rear surface of the hub disk, the main flow of fluid flowing through the impeller is not disturbed by the circulating flow ejected from the outlet, and this When the circulating flow joins the main fluid at the vaneless diffuser inlet, the circumferential flow velocity is approximately the same as that of the main fluid. Therefore, an increase in pressure loss due to flow shear can also be suppressed.
Furthermore, since the fluid circulation channel can be provided in one casing, the fluid circulation channel that can suppress the rotation stall can be easily configured. Therefore, the advantage of the vaneless diffuser that the structure is simple can be maintained as it is. In addition, since the fluid circulation channel is composed of a plurality of communication holes, or one or a plurality of slits, by appropriately selecting the number and hole diameter of the communication holes, or the number, width and length of the slits, It is possible to appropriately set a fluid circulation channel that can obtain a required circulation flow rate.

  Further, according to the compressor operation control method of the present invention, when the flow rate of the fluid flowing through the vaneless diffuser is detected and is in the rotating stall region, the fluid circulation channel is opened by the opening / closing means, By circulating the part to the inlet side of the vaneless diffuser and increasing the flow rate of the fluid flowing through the vaneless diffuser, the turning stall generation point can be moved to the low flow rate side to suppress the occurrence of the turning stall. Accordingly, it is possible to suppress pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall, and to expand the range in which the compressor can be stably operated. Further, in the region where there is no possibility of causing the rotation stall, the fluid circulation channel can be stopped by closing the fluid circulation channel by the opening / closing means, and therefore, similarly to the compressor not provided with the fluid circulation channel. , Driving with priority on efficiency can be performed.

1 is a longitudinal sectional view of a two-stage centrifugal compressor according to a first embodiment of the present invention. It is principal part sectional drawing of the two-stage centrifugal compressor shown in FIG. It is a performance curve figure which shows the turning stall generation | occurrence | production point of the two-stage centrifugal compressor shown in FIG. It is principal part sectional drawing of the two-stage centrifugal compressor which concerns on the 1st reference example of this invention. It is principal part sectional drawing of the two-stage centrifugal compressor which concerns on the 2nd reference example of this invention. It is principal part sectional drawing of the two-stage centrifugal compressor which concerns on the 3rd reference example of this invention. It is a fragmentary cross-sectional view of a two-stage centrifugal compressor according to the second embodiment of the present invention. It is a performance curve figure which shows the turning stall generation | occurrence | production point of the two-stage centrifugal compressor shown in FIG. It is principal part sectional drawing of the two-stage centrifugal compressor which concerns on the 4th reference example of this invention. It is principal part sectional drawing (A) of the two-stage centrifugal compressor which concerns on 3rd Embodiment of this invention, and its AA arrow sectional drawing (B). It is principal part sectional drawing of the two-stage centrifugal compressor of a prior art example. It is a performance curve figure which shows the turning stall generation | occurrence | production point of the two-stage centrifugal compressor of the prior art example shown in FIG.

Embodiments according to the present invention will be described below with reference to the drawings.
[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a longitudinal sectional view of a centrifugal compressor 1 according to the first embodiment of the present invention.
The centrifugal compressor 1 includes a casing 2 configured by combining a plurality of parts, a rotating shaft 4 that is rotatably supported around the axis L in the casing 2 via a bearing (not shown), and the rotating shaft 4. And two closed type or open type impellers 5A and 5B (closed impellers are shown in the present embodiment) provided so as to rotate together.

The centrifugal compressor 1 is driven by a drive device (not shown) and the impellers 5A and 5B are rotated, whereby the gas to be compressed or the compression target gas via the fluid suction port 6 provided in the casing 2 Air or other fluid is inhaled. This fluid is first subjected to centrifugal force by the rotation of the first stage impeller 5A, and its kinetic energy is converted into pressure energy by the first stage vaneless diffuser 7A provided at the outlet of the impeller 5A, and then returned. The bend 8 and the return vane 9 are led to the inlet of the second stage impeller 5B, which is the next stage compression stage.
This compressed fluid is similarly given a centrifugal force by the second stage impeller 5B, and the kinetic energy is converted into pressure energy by the second stage vaneless diffuser 7B, and further becomes a high-pressure compressed fluid to the scroll 10. Discharged. And it is sent from the scroll 10 to the discharge piping not shown through the fluid outlet 11 provided in the casing 2. Thus, in this embodiment, the two-stage centrifugal compressor 1 is illustrated.

The vaneless diffusers 7A and 7B are provided in communication with the exit side of the space in which the impellers 5A and 5B rotate, respectively, and convert the kinetic energy of the fluid given centrifugal force by the impellers 5A and 5B into pressure energy and send it out. This constitutes a flow path.
In the vaneless diffusers 7A and 7B, as described above, when the centrifugal compressor 1 is operated in a low flow rate region, a rotating stall that causes uneven flow in the circumferential direction occurs.
In order to suppress the occurrence of the turning stall, the present embodiment employs the following configuration.

FIG. 2 is a cross-sectional view of the main part showing the configuration of the vaneless diffuser 7A.
The vaneless diffuser 7A is formed by a shroud casing 2A and a hub casing 2B constituting the housing 2. An inlet 12A is opened on the wall surface of the hub casing 2B at the inlet position of the return vane 9 to the downstream compression stage on the outlet side of the vaneless diffuser 7A, that is, the compression stage of the second stage (the final stage in this embodiment), A fluid circulation hole 12 having an outlet 12B opened in the wall surface of the hub casing 2B facing the back surface of the hub disk 5C constituting the impeller 5A is provided in the hub casing 2B.

The fluid circulation hole 12 takes in a part of the high-pressure compressed fluid that has passed through the vaneless diffuser 7A from the inlet 12A, and ejects it from the outlet 12B, and part of the compressed fluid between the inlet and outlet of the vaneless diffuser 7A. Is configured to be circulated. A plurality of fluid circulation holes 12 are provided, and the outlet 12B is opened on the wall surface of the hub casing 2B at a position equal to or less than half the outer diameter of the impeller 5A. As a result, the fluid jetted from the outlet 12B is configured to be given a circumferential flow velocity by the back surface of the hub disk 5C.
In addition, since the circumferential direction flow velocity of the circumferential speed x 0.5 is given to the jetting fluid by the back surface of the hub disk 5C, the jetting fluid from the outlet 12B causes the impeller 5A to enter the inlet of the vaneless diffuser 7A. The circumferential flow velocity at the time of merging with the flowing fluid main flow can be set to a circumferential flow velocity substantially equal to the fluid main flow.

Further, the fluid circulation hole 12 is selected so that the total flow rate of the fluid circulating through all the fluid circulation holes 12 is about 10% of the flow rate of the main fluid flowing through the impeller 5A. Or it is set as the structure which provided the appropriate orifice in either the inside of a hole, the inlet_port | entrance 12A, and the exit 12B.
In FIG. 2, reference numeral 13 denotes a labyrinth provided between the shroud casing 2A and the shroud disk 5D, and reference numeral 14 denotes a labyrinth provided between the rotary shaft 4 and the hub casing 2B. It is installed for the purpose of preventing fluid from leaking through the gap.

With the configuration described above, according to the present embodiment, the following operational effects can be obtained.
Even when the centrifugal compressor 1 is operated in a low flow rate region, since the fluid circulation hole 12 is provided as described above, the outlet position of the vaneless diffuser 7A is caused by the pressure difference between the inlet and outlet of the fluid circulation hole 12. A part of the high-pressure compressed fluid is circulated through the fluid circulation hole 12 to the rear surface of the hub disk 5C of the impeller 5A. Then, in a state where a circumferential flow velocity is applied by the rear surface of the hub disk 5C, the main fluid flowing through the impeller 5A and its outlet, that is, the inlet of the vaneless diffuser 7A are merged, and again flowed into the vaneless diffuser 7A. . Thus, by circulating a part of high-pressure fluid (about 10% of the main fluid flow) between the inlet and outlet of the vaneless diffuser 7A, the flow rate of the fluid flowing through the vaneless diffuser 7A can be increased.

For this reason, as shown in FIG. 3, the turning stall occurrence point Q2 can be moved to the low flow rate side by the increased flow rate ratio, thereby suppressing the occurrence of turning stall. Accordingly, it is possible to suppress pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall, and to expand the range in which the compressor can be stably operated.
In FIG. 3, the flow rate Q2 is the turning stall occurrence point, and the flow rate range lower than that is the turning stall occurrence region W2, and the swirl is compared with the case where the fluid circulation hole 12 shown in FIG. It is understood that the stall generation point Q2 is shifted to the low flow rate region side, the turning stall generation region W2 is significantly narrowed, and the range in which the centrifugal compressor 1 can be stably operated is expanded.

  Further, since the outlet 12B of the fluid circulation hole 12 is opened in the wall surface of the hub casing 2B facing the rear surface of the hub disk 5C, the main fluid flowing through the impeller 5A is disturbed by the circulating flow ejected from here. Moreover, since the jet flow is not circulated to the impeller 5A, no power loss occurs. Further, this circulating flow is given a circumferential flow velocity by the back surface of the hub disk 5C, and has a circumferential flow velocity substantially equal to that of the fluid main flow when joining with the fluid main flow at the inlet of the vaneless diffuser 7A. Therefore, it is possible to suppress an increase in pressure loss due to shearing of the flow, and even if about 10% of the fluid main flow is a circulating flow, a reduction in the efficiency of the compressor can be suppressed to a slight decrease of about 1% at most.

In addition, since a plurality of fluid circulation holes 12 are provided in one hub casing 2B, a means for enabling suppression of turning stall is only provided in the plurality of fluid circulation holes 12 in one casing. This can be realized with a simple configuration. Therefore, it is possible to maintain the feature of the vaneless diffuser 7A that the structure is simple as it is.
In addition, the surging generation point is shifted to the low flow rate side by increasing the flow rate of the fluid flowing through the vaneless diffuser 7A and shifting the rotation stall generation point Q2 to the low flow rate side to suppress the generation of the rotation stall. There is also a possibility.

  Further, by opening the inlet 12A of the fluid circulation hole 12 at the inlet position of the return vane 9 to the downstream compression stage, it is possible to prevent separation of the boundary layer through the return bend 8 to the inlet position of the return vane 9. it can. That is, with respect to boundary layer separation occurring near the inlet of the return vane 9, the separation is controlled by opening the inlet 12 </ b> A of the fluid circulation hole 12 at the inlet position of the return vane 9 and taking in part of the high-pressure fluid therefrom. In addition, it is possible to suppress the separation of the main fluid that occurs near the inlet of the return vane 9. Thereby, the flow rate characteristic can be improved.

[ First Reference Example ]
Next, a first reference example of the present invention will be described with reference to FIG.
This reference example differs from the above-described first embodiment in the opening position of the inlet 12A of the fluid circulation hole 12. Since other points are the same as those in the first embodiment, description thereof will be omitted.
In this reference example , as shown in FIG. 4, the inlet 12A of the fluid circulation hole 12 has a hub at the top position of the return bend 8 to the downstream compression stage, that is, the compression stage of the second stage (the final stage in this reference example ). Opened on the wall surface of the casing 2B.

  By opening the inlet 12 </ b> A of the fluid circulation hole 12 at the above position, the same effect as that of the first embodiment can be obtained, and separation of the boundary layer occurring near the top of the return bend 8 can be prevented. it can. That is, with respect to boundary layer separation occurring near the top of the return bend 8, the inlet 12A of the fluid circulation hole 12 is opened at the top position of the return bend 8, and separation is controlled by taking a part of the high-pressure fluid therefrom. In addition, it is possible to suppress separation of the main fluid that occurs near the top of the return bend 8. Thereby, the flow rate characteristic can be improved.

[ Second Reference Example ]
Next, a second reference example of the present invention will be described with reference to FIG.
This reference example differs from the first embodiment and the first reference example described above in the position where the fluid circulation hole 12 is provided (compression stage) and the opening position of its inlet 12A. Since other points are the same as those in the first embodiment and the first reference example , the description thereof is omitted.
As shown in FIG. 5, this reference example shows a final compression stage (in the case of a single-stage compressor, the compression stage thereof, and in the case of a multistage compressor of two or more stages, the second and subsequent stages of compression stages). ) Is provided with a fluid circulation hole 12. In this case, the fluid circulation hole 12 can be provided in the discharge casing 2C constituting the final compression stage, and the inlet 12A can open to the bottom surface position of the scroll 10 of the final compression stage. Further, the outlet 12B of the fluid circulation hole 12 is opened in the wall surface of the discharge casing 2C facing the back surface of the hub disk 5E constituting the impeller 5B.
In addition, the code | symbol 15 in FIG. 6 is the balance piston provided in order to adjust the thrust of an impeller, and 16 is the balance piston labyrinth provided between the balance piston 15 and the discharge casing 2C.

Also according to this reference example, capture a portion of the high pressure fluid in the scroll 10 through the fluid circulating holes 12 provided in the discharge casing 2C, it is circulated to the inlet side of the second-stage vane-less diffuser 7B Therefore, the flow rate of the fluid flowing through the vaneless diffuser 7B can be increased.
Therefore, also in this reference example , the same operational effects as those of the first embodiment described above can be obtained.

[ Third reference example ]
Next, a third reference example of the present invention will be described with reference to FIG.
This reference example is different from the above-described second reference example in the opening position of the inlet 12A of the fluid circulation hole 12. The other points are the same as in the second reference example, and thus the description thereof is omitted.
In the centrifugal compressor, as shown in FIG. 6, one end is opened at the bottom surface of the scroll 10 in order to alleviate the swirling flow flowing into the labyrinth 16 of the balance piston 15 and reduce unstable vibration. Some have a shunt hole 17 for a swirl canceller whose end communicates with the balance piston labyrinth 16. In this reference example , the inlet 12 </ b> A of the fluid circulation hole 12 is opened in the middle of the shunt hole 17.

The flow rate of the fluid flowing through the vaneless diffuser 7B can also be increased by branching and taking a part of the high-pressure fluid from the middle position of the shunt hole 17 and circulating it to the inlet side of the vaneless diffuser 7B. .
Therefore, also in this reference example , the same operational effects as those of the first embodiment described above can be obtained. Further, in the present reference example , the fluid circulation hole 12 can be configured using the existing shunt hole 17, and therefore the fluid circulation hole 12 can be configured more simply.
In this case, it is necessary to set the hole diameter, the number of holes, and the like of the shunt hole 17 in accordance with the increase in the flow rate of the high-pressure fluid so as not to hinder the swirl canceller effect.

[ Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.
This embodiment is different from the first embodiment and the first to third reference examples described above in that an opening / closing means 18 for opening and closing the fluid circulation hole 12 is provided in the fluid circulation hole 12. . The other points are the same as those in the first embodiment and the first to third reference examples, and thus the description thereof is omitted.
In the present embodiment, as shown in FIG. 7, an opening / closing means 18 constituted by an electromagnetic valve or the like for opening and closing the fluid circulation hole 12 is provided in the middle of the fluid circulation hole 12.

Thus, by providing the opening / closing means 18 in the fluid circulation hole 12, the fluid circulation hole 12 is closed by the opening / closing means 18 during operation in a high flow rate region where there is no risk of turning stall. The same operation as that of the centrifugal compressor not provided with the fluid circulation hole 12 is possible. For this reason, as shown in FIG. 8, it can drive | operate in a state without an efficiency fall at all.
Further, during operation in a low flow rate region that is a turning stall region, the fluid circulation hole 12 is opened by the opening / closing means 18 to increase the flow rate of the fluid flowing through the vaneless diffuser 7A as described above, and the turning stall occurrence point Q2 Can be shifted to the low flow rate side to suppress turning stall, and the range in which the compressor can be stably operated can be expanded.

Therefore, according to this embodiment, the same operational effects as those of the first embodiment and the first to third reference examples can be obtained. In the case of this embodiment, it is only necessary to open the fluid circulation hole 12 and circulate the high-pressure fluid only at the time of suppressing the turning stall, and there is almost no need to worry about the decrease in efficiency. Can do. Accordingly, the circulation flow rate ratio of the high-pressure fluid can be set to be larger than 10% as described above, and the operation in the lower flow rate region can be performed. Therefore, as shown in FIG. be able to.

Below, the operation control method of the centrifugal compressor 1 concerning this embodiment is demonstrated.
The opening / closing means 18 may be configured to detect the flow rate of the fluid flowing through the vaneless diffuser 7A by a sensor (not shown), and to open the opening / closing means 18 when the flow rate is in a preset turning stall generation region.

  According to this configuration, the flow rate of the fluid flowing through the vaneless diffuser 7A is monitored by the sensor, and when the flow rate is in a region where there is no possibility of causing a stall, the fluid circulation hole 12 is closed by the opening / closing means 18. Since the circulation of the fluid by 12 can be stopped, the efficiency-priority operation can be performed as in the compressor not having the fluid circulation hole 12. When the flow rate of the fluid flowing through the vaneless diffuser 7A is detected by the sensor to be in the swirling stall region, the fluid circulation hole 12 is opened by the opening / closing means 18 so that a part of the high-pressure fluid enters the inlet of the vaneless diffuser 7A. The flow rate of the fluid flowing through the vaneless diffuser 7A can be increased.

  Therefore, according to the operation control method of the centrifugal compressor 1 described above, it is possible to detect whether or not the operation region is a turning stall generation region and to reliably suppress the occurrence of the turning stall. For this reason, it is possible to prevent pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall, and to expand the stable operation range of the compressor.

The opening / closing means 18 may detect the operating load of the centrifugal compressor 1 and may be controlled to be opened when the operating load becomes a partial load equal to or lower than a predetermined load set in advance.
That is, when the centrifugal compressor 1 is partially loaded, the flow rate of the fluid flowing through the vane-less diffuser 7A is also reduced, so that the operation may be performed in a low flow rate region, and there is a possibility that rotation stall will occur. Therefore, when the operating load becomes a predetermined load or less, the opening / closing means 18 is opened, and a part of the high-pressure fluid is circulated to the inlet side of the vaneless diffuser 7A through the fluid circulation hole 12, thereby flowing through the vaneless diffuser 7A. The fluid flow rate can be increased.
As a result, it is possible to suppress the occurrence of turning stall during partial load operation, and to expand the range in which the compressor can be stably operated and the operation range due to the partial load.

[ Fourth Reference Example ]
Next, a fourth reference example of the present invention will be described with reference to FIG.
This reference example is different from the first and second embodiments and the first to third reference examples described above in the opening position of the inlet 12A of the fluid circulation hole 12. Since the other points are the same as those in the first and second embodiments and the first to third reference examples , the description thereof is omitted.
In this reference example , as shown in FIG. 9, the inlet 12A of the fluid circulation hole 12 is located at the outlet position of the return vane 9 of the downstream compression stage, that is, the compression stage of the second stage (the final stage in this reference example ). Opened on the wall surface of 2B.

By opening the inlet 12A of the fluid circulation hole 12 at the above position, the same effects as the first embodiment can be obtained, and the length of the fluid circulation hole 12 can be set to the length of each of the above embodiments and reference examples. Can be shortened. That is, the outlet 12B of the fluid circulation hole 12 is opened in the wall surface of the hub casing 2B that faces the back surface of the hub disk 5C that constitutes the impeller 5A, and the opposite wall surface of the hub casing 2B with respect to this opening position is the downstream compression stage. Since it substantially corresponds to the return vane 9 outlet position, the fluid circulation hole 12 is penetrated through the hub casing 2B by opening the inlet 12A of the fluid circulation hole 12 in the wall surface of the hub casing 2B at the return vane 9 outlet position of the downstream compression stage. 12 can be drilled, and the length of the fluid circulation hole 12 can be minimized to facilitate drilling.

[ Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIG.
This embodiment differs from the first and second embodiments and the first to fourth reference examples described above in the opening structure of the outlet 12B of the fluid circulation hole 12. Since the other points are the same as those in the first and second embodiments and the first to fourth reference examples , the description is omitted.
In the present embodiment, as shown in FIGS. 10A and 10B, the outlet 12B of the fluid circulation hole 12 is provided so as to be inclined obliquely in the turning direction of the impeller 5A.

By opening the outlet 12B of the fluid circulation hole 12 as described above, the same effects as those of the above embodiments and the reference example can be obtained, and the circulation flow ejected from the outlet 12B of the fluid circulation hole 12 is impeller 5A. Therefore, it is possible to suppress the friction loss caused by the circulation flow being ejected to the hub disk 5C on the back surface of the impeller 5A.
Of course, the opening structure of the outlet 12B can be similarly applied to the first and second embodiments and the first to fourth reference examples .

In each of the above-described embodiments and reference examples , the fluid circulation hole 12 is configured to circulate a part of the high-pressure fluid between the inlet and outlet of the vaneless diffuser 7A. It is good also as a structure which provided the direction slit.
In addition, the fluid circulation hole 12 is not necessarily provided in all the compression stages, and can be provided only in the compression stage that is greatly affected by the rotating stall. In this case, the efficiency reduction amount of the entire compressor can be further reduced. Can do.

In each of the above embodiments and reference examples , a two-stage centrifugal compressor has been described as an example. However, the present invention is not limited to these, and a single-stage or three-stage or more multi-stage centrifugal compressor, It is applicable not only to a centrifugal compressor but also to a mixed flow compressor.

DESCRIPTION OF SYMBOLS 1 Centrifugal compressor 2 Casing 2B Hub casing 2C Discharge casing 5A, 5B Impeller 5C, 5E Hub disk 7A, 7B Vane-less diffuser 8 Return bend 9 Return vane 10 Scroll 12 Fluid circulation hole 12A Fluid circulation hole inlet 12B Fluid circulation hole Outlet 15 Balance piston 16 Balance piston labyrinth 17 Shunt hole 18 Opening / closing means (solenoid valve)

Claims (7)

In a compressor having a vaneless diffuser that converts kinetic energy imparted to a fluid by the impeller into pressure energy on the outlet side of the impeller.
An inlet is opened on the outlet side of the vane-less diffuser, and the outlet has a fluid circulation flow path opened in a casing wall surface facing the rear surface of the hub disk of the impeller.
The inlet is open to the hub casing wall at the return vane inlet position to the downstream compression stage;
The fluid circulation channel is composed of a plurality of communication holes, or one or a plurality of slits ,
The fluid taken in from the inlet is ejected from the outlet toward the rear surface of the hub disk of the impeller, and a circumferential flow velocity is given by the rear surface of the hub disk to join the main fluid from the impeller at the inlet of the vaneless diffuser. A compressor characterized in that a circulating flow can be formed . The compressor according to claim 1 , wherein the outlet is directed obliquely in a turning direction of the impeller. The compressor according to claim 1 or 2 , wherein the outlet is opened in the casing wall surface at a position equal to or less than half of the outer diameter of the impeller. The compressor according to any one of claims 1 to 3 , wherein a fluid circulation flow rate of the fluid circulation channel is set to about 10% of a fluid main flow flowing through the impeller. The compressor according to any one of claims 1 to 4 , wherein opening and closing means for opening and closing the fluid circulation channel is provided in the fluid circulation channel. 6. A compressor operation control method for controlling the operation of the compressor according to claim 5 , wherein the flow rate of fluid flowing through the vaneless diffuser is detected, and when the flow rate is in a rotating stall region, the fluid is controlled by the opening / closing means. An operation control method for a compressor, wherein the circulation flow path is opened. 7. The compressor operation control method according to claim 6 , wherein the opening / closing means is opened during a partial load operation of a predetermined load or less.

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