JP2008190487A - Centrifugal fluid machine - Google Patents

Abstract

In a centrifugal fluid machine, a flow path for injecting a high-pressure fluid to a labyrinth seal can be easily formed, and excitation of a rotating shaft can be reduced.
A centrifugal fluid machine 50 includes a centrifugal impeller 2 that pressurizes a fluid, a rotary shaft 1 that drives the centrifugal impeller 2, and a fluid that has been pressurized by the centrifugal impeller 2 with a rotating portion and a stationary portion. And a labyrinth seal 22 having a plurality of seal fins 22a that suppress passage through the gap. A jet port 22c for jetting high-pressure fluid is provided between adjacent seal fins 22a on the upstream side of the leak flow passing through the labyrinth seal 22, and the high-pressure fluid jetted from the jet port 22c is prevented from flowing in the rotation direction. Thus, the partition wall 22d is provided close to the rotational direction side of the jet nozzle 22c.
[Selection] Figure 2

Description

  The present invention relates to a centrifugal fluid machine provided with a labyrinth seal, and in particular, a centrifugal fluid machine that handles various gases including hydrocarbon gas and carbon dioxide gas, for example, high-pressure applications used in petrochemical and natural gas plants. It is suitable for a multistage centrifugal compressor.

  FIG. 5 shows the structure around the final stage centrifugal impeller of a general multistage centrifugal compressor used in a petrochemical or natural gas plant. This multistage centrifugal compressor is a fluid machine that pressurizes a fluid by centrifugal force caused by rotation.

  When the rotating shaft 1 is rotated by a driving force input from the outside, the centrifugal impeller 2 fixed thereto continuously boosts the fluid. Since the fluid pressurized by the centrifugal impeller 2 tends to flow back to the inlet side of the centrifugal impeller 2, a mouth seal 20 is provided to restrict it. In a multistage centrifugal compressor, the fluid pressure increases from stage to stage, so that a pressure difference occurs between the stages in the axial direction. A stage seal 21 is provided to limit the amount of the pressurized fluid that flows back to the previous stage. A balance piston 3 is fixed to the rotary shaft 1 on the rear surface of the centrifugal impeller 2 at the final stage in order to balance axial thrust. A balance piston seal 22 is provided to limit the amount of fluid pressurized by the final stage centrifugal impeller 2 and flowing out of the balance piston 3 to the low pressure portion. The pressure applied to the balance piston seal 22 is the highest as compared to the pressure applied to the other seals 20, 21 both as an absolute pressure and as a differential pressure. Labyrinth seals are used for these seals 20 to 22 arranged around the centrifugal impeller 2.

  In a multistage centrifugal compressor for high pressure applications, the fluid force by the fluid passing through these seals 20 to 22 is increased, which affects the stability of the rotary shaft 1. This fluid force is greatest at the balance piston seal 22 having the largest absolute pressure and differential pressure. Whether the fluid force in the balance piston seal 22 destabilizes the rotary shaft 1 is largely related to the swirl component of the fluid passing through the balance piston seal 22. That is, the fluid flowing into the balance piston seal 22 from the impeller side has a rotational component in the rotational direction, and this rotational component excites the forward mode of the natural vibration mode of the rotating shaft 1.

  A conventional centrifugal fluid machine that reduces the influence of the swirling component of the fluid passing through the labyrinth seal is disclosed in Japanese Utility Model Publication No. 63-16938 (Patent Document 1). This centrifugal fluid machine has a labyrinth composed of a plurality of seal fins between a peripheral surface of the rotating shaft and a stationary portion adjacent to the rotating shaft so as to prevent fluid leakage from the high pressure portion along the rotating shaft to the low pressure portion. A nozzle hole is provided in the stationary part, the nozzle hole for ejecting the fluid guided from the high pressure part into the seal chamber between adjacent seal fins of the labyrinth seal, and the ejection direction of the nozzle hole is It is formed in the direction opposite to the rotation direction of the rotation shaft.

Japanese Utility Model Publication No. 63-16938

  However, in the centrifugal fluid machine of Patent Document 1, it is necessary to form a flow path that faces a tangential direction with respect to the inner peripheral surface of the labyrinth seal, and the formation of the flow path is troublesome, and in the tangential direction. In order to obtain the necessary injection force, it is necessary to secure a sufficient flow path length, and it is sometimes difficult to ensure the flow path length.

  An object of the present invention is to provide a centrifugal fluid machine that can easily form a flow path for injecting a high-pressure fluid to a labyrinth seal and can reduce excitation of a rotating shaft.

  In order to achieve the above-described object, the present invention provides a centrifugal impeller that pressurizes a fluid, a rotating shaft that drives the centrifugal impeller, and a fluid pressurized by the centrifugal impeller includes a rotating portion and a stationary portion. A labyrinth seal having a plurality of seal fins that suppress passage through the gap, and provided with a jet port for ejecting high-pressure fluid between the adjacent seal fins on the upstream side of the leakage flow passing through the labyrinth seal In the centrifugal fluid machine, a partition wall is provided adjacent to the rotation direction side of the jet port so as to prevent the high-pressure fluid jetted from the jet port from flowing in the rotation direction.

A more preferable specific configuration example of the present invention is as follows.
(1) The high-pressure fluid jets and the partition walls are provided evenly at a plurality of locations in the circumferential direction.
(2) The centrifugal impeller is provided in a plurality of stages in the axial direction of the rotating shaft, and a high-pressure fluid extracted from an outlet or a scroll portion of a diffuser provided in the final stage of the centrifugal impeller is used as the high-pressure fluid.
(3) A balance piston for balancing axial thrust is provided on the back surface of the final stage centrifugal impeller, and the labyrinth seal is mounted on the inner peripheral surface of the casing facing the outer peripheral surface of the balance piston. The high pressure fluid extracted from the outlet of the diffuser provided at the last stage and the scroll portion is sprayed through a linear flow path toward the center of the casing and the labyrinth seal.

  According to the centrifugal fluid machine of the present invention having such a configuration, a flow path for injecting high-pressure fluid to the labyrinth seal can be easily formed, and excitation of the rotating shaft can be reduced.

  Hereinafter, an embodiment of a centrifugal fluid machine according to the present invention will be described with reference to FIGS. 1 to 4. 1 to 4 and FIG. 5 indicate the same or equivalent components.

  First, the centrifugal fluid machine 50 of the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view around the final stage centrifugal impeller of the multistage centrifugal compressor 50 of the present embodiment. The multistage centrifugal compressor 50 of this embodiment is a multistage centrifugal compressor for high pressure used in petrochemical and natural gas plants.

  The rotating shaft 1 is rotated by a driving force input from the outside. When the rotary shaft 1 rotates, the centrifugal impeller 2 fixed to the rotary shaft continuously pressurizes the fluid. The centrifugal impeller 2 is mounted in multiple stages on the rotary shaft 1 and is rotated together with the rotary shaft 1. The centrifugal impeller 2 sucks and pressurizes the fluid from the side surface of the central part and discharges it from the outer periphery. A sleeve 4 is interposed between the centrifugal impellers 2 of each stage.

  Since the fluid pressurized by the centrifugal impeller 2 tends to flow backward to the inlet side of the centrifugal impeller 2, a mouth seal 20 is provided to limit this. The mouth seal 20 is attached to the inner peripheral surface of the casing suction portion 30 a and seals the gap between the casing suction portion 30 a and the suction portion 2 a of the centrifugal impeller 2. As the mouth seal 20, a labyrinth seal in which a plurality of seal fins 20a are formed in the axial direction is used.

  In a multistage centrifugal compressor, the fluid pressure increases from stage to stage, so that a pressure difference occurs between the stages in the axial direction. A stage seal 21 is provided to limit the amount of the pressurized fluid that flows back to the previous stage. The stage seal 21 is attached to the inner peripheral surface of the partition part 30b that partitions each stage of the casing, and seals the gap between the partition part 30b of the casing and the sleeve 4. As the stage seal 21, a labyrinth seal in which a plurality of seal fins 21a are formed in the axial direction is used.

  On the back surface of the centrifugal impeller 2 at the final stage, a balance piston 3 is fixed to the rotary shaft 1 in order to balance axial thrust. The low pressure side of the balance piston 3 is connected to the suction portion of the first stage centrifugal impeller in the case of the straight-through type, and to the final stage centrifugal impeller outlet of the low pressure group in the case of the back-to-back type. Therefore, a large differential pressure acts on the seal portion of the balance piston 3. A balance piston seal 22 is provided to limit the amount of fluid pressurized by the final stage centrifugal impeller 2 and flowing out of the balance piston 3 to the low pressure portion. The balance piston seal 22 is attached to the inner peripheral surface of the final stage back surface portion 30c of the casing, and seals the gap between the final stage back surface portion 30c of the casing and the balance piston 3. The balance piston seal 22 is a labyrinth seal in which a plurality of seal fins 22a are formed in the axial direction. The pressure applied to the balance piston seal 22 is the highest as compared with the pressure applied to the other seals 20 and 21 in terms of absolute pressure and differential pressure.

  Next, the injection of high-pressure fluid onto the balance piston seal 22 will be described with reference to FIGS. 2 is a cross-sectional view taken along the line AA in FIG. 1, FIG. 3 is a cross-sectional view taken along the line BB in FIG. 2, and FIG. In FIG. 2 to FIG. 4, some of the constituent elements are omitted, and the flow of the high-pressure fluid is indicated by solid arrows.

  Between the adjacent seal fins 22a on the upstream side of the leakage flow passing through the balance piston seal 22, a jet outlet 22c for jetting high-pressure fluid is provided. The interval between the adjacent seal fins 22a is larger than the interval between the other seal fins 22a. As a result, the function of preventing excitation by the high-pressure fluid can be exhibited more effectively. Moreover, the jet nozzles 22b are equally provided at a plurality of locations in the circumferential direction.

  The high pressure fluid extracted from the outlet of the diffuser provided at the final stage of the centrifugal impeller 2 and the scroll portion is ejected through the high pressure fluid passage 30d of the rear portion 30c of the final stage of the casing and the high pressure fluid passage 22b of the balance piston seal 22. 22c. As a result, the high-pressure fluid can be easily ejected from the ejection port 22c.

  The high-pressure fluid passages 30 d and 22 b are formed by linear flow passages in the central direction of the back surface portion 30 c of the final stage of the casing and the balance piston seal 22. Thereby, the high-pressure fluid passages 30d and 22b can be easily formed. Moreover, the partition wall 22c is equally provided in several places of the circumferential direction similarly to the jet nozzle 22b. As a result, the function of preventing excitation by the high-pressure fluid can be exhibited more effectively. The partition wall 22 c is integrally provided on the inner peripheral surface of the balance piston seal 22.

  A partition wall 22d is provided adjacent to the rotational direction side of the ejection port 22c so as to prevent the high-pressure fluid ejected from the ejection port 22c from flowing in the rotational direction. As a result, the high-pressure fluid ejected from the ejection port 22c collides with the outer peripheral surface of the balance piston 3 and flows in the rotation direction of the balance piston 3 through the partition wall 22d, as indicated by solid arrows in FIGS. This prevents the balance piston 3 from flowing in the direction opposite to the rotation direction. The reverse swirling flow gradually passes through the seal fins 22a due to the seal differential pressure and flows toward the low pressure side.

  Most of the high-pressure fluid flows to the low-pressure side, but a part flows to the impeller side in order to suppress the flow entering the seal portion from the impeller side. In order for the high pressure fluid to overcome the flow from the impeller side and flow to the impeller side, the pressure of the high pressure fluid must be higher than the outlet pressure of the final stage centrifugal impeller 1. Therefore, as described above, the fluid used for the high-pressure fluid is extracted from the final stage differential user outlet, the scroll unit, or the like.

  If the fluid flowing through the seal gap in the balance piston seal 22 has a swirl component in the same direction as the rotation direction of the rotary shaft 1, when the rotary shaft 1 swings, not only in the direction of the swing but also in a direction orthogonal thereto. Fluid force is also generated. This is called cross coupling rigidity, and acts to promote the rotation of the rotating shaft 1 when it is swung forward. Therefore, it is desirable that the fluid flowing through the seal gap in the balance piston seal 22 does not have a swirling component. However, the fluid flowing from the outlet of the centrifugal impeller 2 into the balance piston seal 22 provided outside the balance piston 3 has a swirling component due to the rotation of the centrifugal impeller 2 and flows into the seal as it is. The rotor stiffness causes instability due to the ring rigidity.

  In the present embodiment, the partition wall 22d is provided close to the rotational direction side of the ejection port 22c so as to prevent the high-pressure fluid ejected from the ejection port 22c from flowing in the rotational direction. Inflow of the swirling flow from the centrifugal impeller 2 side to the balance piston seal 22 can be suppressed by the high-pressure fluid, and the cross coupling rigidity can be reduced. Second, the partition wall 22d provided in the vicinity of the high-pressure fluid outlet 22c causes the high-pressure fluid itself to be blown in with a swirling component in the direction opposite to the rotational direction of the rotary shaft 1, and the cross coupling rigidity. It is possible to contribute to further reduction. In the present embodiment, the application of the reverse swirling component to the high-pressure fluid is realized by the partition wall 22d as described above. Therefore, there is no need to incline the high-pressure fluid flow path with respect to the radial direction as in the conventional case, and the length is sufficient. This is applicable even when a high-pressure fluid flow path cannot be secured.

It is sectional drawing around the last stage centrifugal impeller of the multistage centrifugal compressor of one Embodiment of this invention. It is AA sectional drawing of FIG. It is BB sectional drawing of FIG. It is a C direction arrow directional view of FIG. It is sectional drawing around the last stage centrifugal impeller of the conventional multistage centrifugal compressor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Rotating shaft, 2 ... Centrifugal impeller, 3 ... Balance piston, 4 ... Sleeve, 20 ... Mouse seal, 21 ... Stage seal, 22 Balance piston seal (labyrinth seal), 22a ... Seal fin, 22c ... Spout, 30a A suction part of the casing, 30b ... a partition part of the casing, 30c ... a rear face part of the final stage of the casing, 30d ... a high-pressure fluid passage.

Claims (4)

A centrifugal impeller that pressurizes the fluid, a rotating shaft that drives the centrifugal impeller, and a plurality of seal fins that suppress the fluid pressurized by the centrifugal impeller from passing through the gap between the rotating portion and the stationary portion. A centrifugal fluid machine including a labyrinth seal, and provided with an outlet for ejecting a high-pressure fluid between the adjacent seal fins on the upstream side of a leakage flow passing through the labyrinth seal.
A centrifugal fluid machine characterized in that a partition wall is provided adjacent to the rotational direction side of the ejection port so as to prevent the high-pressure fluid ejected from the ejection port from flowing in the rotational direction.   2. The centrifugal fluid machine according to claim 1, wherein the high-pressure fluid jets and the partition walls are provided uniformly at a plurality of locations in a circumferential direction.   In Claim 1, the said centrifugal impeller is provided in multiple stages in the axial direction of the said rotating shaft, and the high pressure fluid extracted from the exit and scroll part of the diffuser provided in the last stage of the said centrifugal impeller is used as said high pressure fluid. A centrifugal fluid machine characterized by that.   2. The balance piston according to claim 1, wherein a balance piston for balancing axial thrust is provided on a back surface of the centrifugal impeller at the final stage, the labyrinth seal is attached to an inner peripheral surface of the casing facing the outer peripheral surface of the balance piston, and the centrifugal A centrifugal fluid machine, wherein a high-pressure fluid extracted from an outlet of a diffuser provided at a final stage of an impeller or a scroll portion is jetted through a linear flow path in a central direction of the casing and the labyrinth seal.

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