JP2009264205A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal compressor, capable of reducing the vibration of an impeller by restraining pressure fluctuation of peripheral fluid, and capable of attaining safe operation. <P>SOLUTION: The centrifugal compressor is equipped with a casing 1, a rotor, disposed rotatably in the casing and having at least one stage impeller 3, and a diffuser 7 located downstream of the impeller of the casing, and compresses gas by rotation of the rotor. A noise reduction means is disposed, on at least one of a casing surface 9 confronting an impeller main plate and a casing surface 10 confronting a side plate. Preferably, the predominant frequency of the noise reduction means is set, based on a blade passing frequency, calculated by the product of a number of blades of the impeller and the rotor rotational frequency, or a frequency in an integral multiple thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a centrifugal compressor, and more particularly, to a centrifugal compressor that can be operated safely by preventing the vibration of the impeller by suppressing the pressure fluctuation of the fluid around the impeller.

  For example, a single-shaft multi-stage centrifugal compressor includes a casing, a rotary shaft rotatably provided in the casing, and a rotor having a plurality of impellers mounted on the rotary shaft, and gas is generated by the rotation of the rotor. Compress. The casing is often provided with a diffuser downstream of the impeller, and the diffuser is often provided with guide vanes to improve the efficiency of the compressor. When the blades of the impeller pass in the vicinity of the guide blades of the diffuser, pressure fluctuations of the blade passage frequency determined by the product of the number of blades and the rotor rotation frequency occur. If the frequency of this pressure fluctuation matches the natural frequency of the impeller, the impeller may be damaged by resonance. In order to prevent the impeller from being damaged due to resonance, an avoidance resonance design is performed in which the excitation frequency and the natural frequency are detuned.

  As a technique for reducing the vibration of a structure, a dynamic vibration absorber is generally known in which a secondary vibration system with a natural frequency tuned to an excitation frequency is attached. A silencer is generally known as a technique for reducing fluid pulsation. A single or concentrated expansion silencer that uses a resonance in the cavity and an expansion silencer that produces a sound reduction effect by causing sound interference by rapid expansion and contraction of the conduit connecting the entrance and exit of the silencer There is a resonant silencer that cancels the sound in the hole. Both inflatable and resonant silencers exhibit frequency-dependent sound reduction characteristics depending on their shape and size, but inflatable silencers can reduce a relatively wide frequency range. On the other hand, the resonance silencer has a narrow frequency range with a sound reduction effect, but exhibits a high sound reduction effect at the resonance frequency expressed by the following equation (1).

  Where f is the resonance frequency, c is the speed of sound of the working fluid, S is the hole cross-sectional area, l is the hole length (including the corrected opening end), and V is the cavity volume.

  On the other hand, Japanese Patent Application Laid-Open No. 2002-161897 discloses a technique for suppressing a resonance phenomenon in a gap and reducing noise by providing a sound absorbing material on a casing surface facing an impeller main plate and a casing surface facing a side plate. is there.

JP 2002-161897 A

  When the compressed gas becomes a high pressure of, for example, 10 MPa or more, the fluid excitation force tends to increase. Furthermore, since the natural frequency of the impeller changes due to the coupling effect between the fluid and the impeller, the design for avoiding resonance becomes difficult. In the centrifugal compressor, since the impeller rotates at high speed, it is difficult to attach the dynamic vibration absorber to the impeller.

  In addition, providing the sound absorbing material has an effect of adding damping to the coupled vibration of the impeller and the surrounding fluid, but it cannot be said that the effect of preventing resonance and reducing the vibration of the impeller is sufficient.

  An object of the present invention is to provide a centrifugal compressor capable of safe operation by suppressing pressure fluctuations of the surrounding fluid and reducing the vibration of the impeller.

  To achieve the above object, the present invention comprises a casing, a rotor rotatably provided in the casing and having at least one impeller, and a diffuser downstream of the impeller of the casing, In the centrifugal compressor that compresses gas by the rotation of the rotor, a silencer is provided on at least one of the surfaces of the casing facing the main plate or the side plate of the impeller.

  In the above (1), preferably, the dominant frequency of the silencer is set based on the blade passing frequency determined by the product of the number of impeller blades and the rotor rotational frequency, or an integer multiple thereof.

  In the above (2), preferably, the silencer is an expansion-type silencer comprising a plurality of holes or slits and a cavity communicating therewith.

  In the above (2), preferably, the silencer is a resonance-type silencer comprising a cavity independent of a hole.

  In the above (3) or (4), preferably, a sound absorbing member is attached or filled inside the cavity.

  In the above (3) or (4), preferably, the hole or the slit is provided on the same circumference centering on the rotation center of the rotor, and the circumference is a main plate of the impeller. And the fluid existing in the gap between the casing facing the main plate (hereinafter referred to as the main plate side gap) or the gap between the side plate of the impeller and the casing facing the side plate (hereinafter referred to as the side plate side gap) Of the natural vibration modes of the coupled vibration system including the impeller, the same radius as the antinodes of pressure fluctuations in the vibration modes excited during operation is used.

  In the above (6), preferably, the number of holes is four times or more the number of node diameters of the excited vibration mode.

  According to the present invention, by providing a silencing means on at least one of the casing surface facing the main plate or the side plate, the pressure fluctuation of the surrounding fluid coupled with the impeller is suppressed, and as a result, the vibration of the impeller Therefore, safe operation is possible even under high pressure conditions in which the fluid excitation force becomes large.

  In addition, by setting the dominant frequency of the silencer based on the blade passing frequency or an integer multiple thereof, it is the same as installing a dynamic vibration absorber for the coupled vibration system of the impeller and the surrounding fluid. Thus, the impeller can be prevented from resonating and safe operation is possible.

  Moreover, the vibration reduction effect in a wide frequency range is acquired by forming a silencer by a some hole or slit and the cavity which connects them.

  Further, by forming the silencer by the hole and the independent cavity, a greater vibration reduction effect can be obtained at the resonance frequency.

  Furthermore, by attaching or filling a sound absorbing member inside the cavity, energy of pressure fluctuation can be consumed by the sound absorbing member, and attenuation can be added to the fluid in the silencer, reducing vibration. Increases effectiveness.

  Furthermore, the effect of reducing the vibration is increased by arranging the hole or the slit on the antinode of the pressure fluctuation.

  Embodiments of the present invention will be described below with reference to the drawings. In the second and subsequent embodiments, the description overlapping that of the first embodiment is omitted.

  FIG. 1 is a cross-sectional view showing a detailed structure around the impeller of one impeller stage in the first embodiment of the centrifugal compressor of the present invention, and FIG. 2 is a cross-sectional view showing the entire structure.

  2, the centrifugal compressor includes a casing 1 (stationary body), a rotary shaft 2 rotatably provided in the casing 1, and, for example, a plurality of stages (seven stages in FIG. 2) attached to the rotary shaft 2. And a rotor 15 (rotary body) having the impeller 3. In the casing 1, a suction flow path 16 that introduces gas into the first stage impeller 3, a diffuser 7 that converts kinetic energy of the gas emitted from each stage impeller 3 into pressure energy, and the diffuser 7 The return flow path 17 for introducing the compressed gas into the next stage impeller 3 and the discharge flow path 18 for discharging the gas discharged from the final stage impeller 3 are formed.

  The rotating shaft 2 of the rotor 15 is rotatably supported via a radial bearing 19 provided at the suction side (left side in FIG. 2) end and the discharge side (right side in FIG. 2) end. A thrust bearing 20 that receives a thrust load is provided at the suction side end of the rotary shaft 2, and a balance piston 21 that cancels the thrust load is provided at the discharge side end. Further, a driving machine (not shown) such as a motor is connected to the discharge side end of the rotating shaft 2, and the rotor 15 is rotated by driving of this driving machine. The rotation of the rotor 15 causes the gas to be sucked from the suction flow path 16, sequentially compressed by the plurality of impellers 3, and finally discharged from the discharge flow path 18.

  In FIG. 1, the impeller 3 is mounted on the rotary shaft 2, and a plurality of blades 6 are installed in the circumferential direction. A diffuser 7 is provided over the entire circumference in the outer circumferential direction downstream of the impeller, and guide vanes 8 are installed. A plurality of guide blades 8 are installed in a circular blade row shape.

  Around the impeller 3, there are a main plate side gap 11 and a side plate side gap 12 surrounded by the main plate 4 and the side plate 5 of the impeller and the main plate side casing surface 9 and the side plate side casing surface 10 facing each other. In the present invention, a main plate side silencer 13 and a side plate side silencer 14 are provided to suppress pressure fluctuations occurring in the gaps 11 and 12, respectively.

  FIG. 3 is a cross-sectional perspective view showing the detailed structure of the main plate-side silencer 13 in the first embodiment. The side plate side silencer 14 has the same structure.

  The main plate-side silencer 13 includes a plurality of holes 22 that communicate with the main plate-side casing surface 9 and a silencer cavity 23 that communicates the holes 22 in the circumferential direction. An effect is obtained. At this time, the shape and size of the hole 22 and the silencer cavity 23 are adjusted so that the frequency having a particularly high silencing effect is the blade passing frequency or an integral multiple of the blade passing frequency.

  Assume that the vibration mode excited during operation is, for example, a vibration mode having a two-node diameter. FIG. 4 is an example of a contour map of the pressure distribution on the main plate-side casing surface 9 in the two-node diameter mode, which is obtained by the fluid-impeller coupled vibration analysis by the finite element method. The black-colored portion is the portion with the largest pressure fluctuation amplitude (pressure fluctuation antinode 29), and the pressure fluctuation antinode 29 is on the reference circle (circumference) 24 including the maximum point of pressure fluctuation. In this vibration mode, there is also a multiple root mode in which the antinode 29 and the node 30 in FIG. 4 are interchanged.

  FIG. 5 is a plan view showing the main plate side casing surface 9 in the present embodiment. A plurality of holes 22 are provided on the reference circle 24. In such a structure, since the hole 22 that is the inlet of the silencer can be arranged on the same circumference as the antinode of pressure fluctuation, the pressure fluctuation generated in the main plate side gap 11 can be effectively suppressed. In addition, by setting the number of holes 22 to eight, which is four times the number of node diameters 2, the holes 22 can be arranged at the antinodes of pressure fluctuations even in the multiple root mode of FIG. Variations can be reliably suppressed. As a result, the vibration of the impeller can be reduced, and the centrifugal compressor can be safely operated even under high pressure conditions.

  In the above-described embodiment, the silencer cavity 23 is described as being communicated with the entire circumference. However, for example, a partition may be provided in the middle to divide the cavity into a plurality of cavities. Further, in the above-described embodiment, the example in which the silencer is disposed only on one circumference has been described. However, for example, the silencer may be provided on two circumferences having different radii. Further, the cavities of the silencers on two circumferences having different radii may be partially or entirely communicated with each other. An example of the silencer having such a structure will be described with reference to a cross-sectional perspective view shown in FIG. A plurality of holes 22 serving as inlets of the main plate side silencer 13 are provided on two circumferences of the second outer circumference side reference circle 24 a and the second inner circumference side reference circle 24 b, and are communicated by the silencer cavity 23. . The silencer cavity 23 is divided into a plurality of spaces by a partition 25. In such a structure in which the partition is provided, the volume of the cavity can be controlled to some extent, so that the dominant frequency of the silencer can be set to the blade passing frequency or an integer multiple thereof. Further, by arranging a plurality of silencer groups in the radial direction, for example, it is possible to cope with a vibration mode in which an antinode of pressure fluctuation is located on the second inner peripheral side reference circle 24b.

  Moreover, the vibration damping effect is increased by attaching or filling the sound absorbing member inside the silencer cavity 23.

  Further, in order to reduce the vibration in the vibration mode having the node diameter, the silencers may be distributed in the circumferential direction, and are not necessarily arranged on the concentric circumference.

  Furthermore, even in the case of an open impeller without a side plate, the same effect can be obtained by providing a silencer on the main plate side.

  FIG. 7 is a cross-sectional perspective view showing the detailed structure of the silencer cavity 23 in the second embodiment of the present invention. The main plate-side silencer 13 includes a circular slit 26 that communicates with the main plate-side casing surface 9 and a silencer cavity 27 that communicates with the slit 26. As an expansion-type silencer, a silencing effect in a wide frequency range is obtained. . At this time, the shape and size of the slit 26 and the silencer cavity 27 are adjusted so that the frequency with a particularly high silencing effect is the blade passing frequency or an integer multiple thereof.

  FIG. 8 is a plan view showing the main plate side casing surface 9 in the present embodiment. The reference circle of the slit 26 is made to coincide with the reference circle (circumference) 24 including the maximum point of pressure fluctuation.

  In such a structure, the slit 26 which is the inlet of the silencer can always be disposed at the antinode position of the pressure fluctuation, so that vibration can be effectively and reliably reduced.

  As in the first embodiment, a part of the silencer cavity 27 may be provided with a partition, or a plurality of silencer groups may be provided in the radial direction.

  FIG. 9 is a cross-sectional perspective view showing the detailed structure of the main plate-side silencer 13 in the third embodiment of the present invention.

  The main plate-side silencer 13 is composed of a hole 22 conducting to the main plate-side casing surface 9 and a silencer cavity 28, and one hole is provided in one cavity. At this time, the main plate side silencer 13 functions as a resonance type silencer, and a large silencing effect is obtained around a specific resonance frequency.

  In the present embodiment, the resonance frequency of the silencer is set so as to match the blade passing frequency determined by the product of the number of impeller blades and the number of rotor rotations, or an integer multiple thereof.

  As in the first embodiment, a plurality of silencer groups may be provided in the radial direction. Moreover, although the shape of the silencer cavity 28 has been described by taking a cylindrical shape as an example, for example, an elliptical column shape extending in the radial direction or a rectangular column shape may be used.

It is sectional drawing showing the detailed structure of the impeller vicinity in embodiment of the centrifugal compressor of this invention. It is sectional drawing showing the whole structure of embodiment of the centrifugal compressor of this invention. It is a section perspective view showing detailed structure of main plate side silencer 13 in a 1st embodiment of a centrifugal compressor of the present invention. It is the example of the contour map of the pressure distribution of the main-plate side casing surface 9 in the two-node diameter mode calculated | required by the coupled vibration analysis of the fluid and the impeller by the finite element method. It is a top view which shows the main plate side casing surface 9 in 1st Embodiment of the centrifugal compressor of this invention. It is a cross-sectional perspective view showing the detailed structure of the main board side silencer 13 by another example of 1st Embodiment of the centrifugal compressor of this invention. It is a cross-sectional perspective view showing the detailed structure of the main plate side silencer 13 in 2nd Embodiment of the centrifugal compressor of this invention. It is a top view which shows the casing surface 9 in 2nd Embodiment of the centrifugal compressor of this invention. It is a cross-sectional perspective view showing the detailed structure of the main plate side silencer 13 in 3rd Embodiment of the centrifugal compressor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Casing 2 Rotating shaft 3 Impeller 4 Impeller main plate 5 Impeller side plate 6 Impeller blade 7 Diffuser 8 Diffuser guide vane 9 Casing surface 10 facing the impeller main plate Casing surface 11 facing the impeller side plate 11 Main plate of the impeller Gap between the casing facing the main plate (gap on the main plate)
12 Gap between the side plate of the impeller and the casing facing the side plate (side plate side gap)
13 Main plate side silencer 14 Side plate side silencer 15 Rotor 16 Suction flow path 17 Return flow path 18 Discharge flow path 19 Bearing 20 Thrust bearing 21 Balance piston 22 Holes 23, 27, 28 Silencer cavity 24 Reference circle 24a Second outer circumference Side reference circle 24b Second inner circumference reference circle 25 Partition 26 Slit 29 Pressure fluctuation belly 30 Pressure fluctuation node

Claims (5)

A centrifugal compressor that includes a casing, a rotor that is rotatably provided in the casing and includes at least one impeller, and a diffuser downstream of the impeller of the casing, and compresses gas by the rotation of the rotor In
A centrifugal compressor characterized in that a silencer is provided on at least one of the surfaces of the casing facing the main plate or side plate of the impeller. The centrifugal compressor according to claim 1,
The silencer comprises a plurality of holes formed on the surface and cavities formed on a lower surface of the plurality of holes. The centrifugal compressor according to claim 1,
The silencer comprises a slit formed on the surface and a cavity formed on the lower surface of the slit. The centrifugal compressor according to claim 2 or 3,
A centrifugal compressor characterized in that a sound absorbing member is provided inside the cavity. The centrifugal compressor according to claim 1,
The centrifugal compressor is characterized in that the dominant frequency of the silencer is set based on a blade passing frequency determined by a product of the number of impeller blades and a rotor rotational frequency, or an integer multiple of the blade passing frequency.

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