JPH05248548A - Labyrinth seal - Google Patents

Abstract

PURPOSE:To stabilize a rotating shaft system by eliminating the turning component of a leakage flow in a rotating direction from the labyrinth seal of a rotary fluid machine with a simple means. CONSTITUTION:Fluid is flowed from a high pressure side chamber communicated with an outlet for an impeller 3 to the chamber 23 of one or more fins at a low pressure side, via space 22 behind a labyrinth 21 and a port 23. A flow having a turning component coming through a high pressure side fin gap is thus destroyed, thereby eliminating the turning component of a labyrinth leakage flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a labyrinth seal for shaft-sealing turbo-type rotary fluid machines such as centrifugal compressors and centrifugal pumps, and more particularly to a labyrinth seal suitable for shaft-sealing high-pressure high-speed process centrifugal compressors. Regarding

[0002]

2. Description of the Related Art An example of a conventional turbo type fluid machine provided with a labyrinth seal will be described with reference to FIG. FIG. 6 is a schematic structural vertical sectional view showing an example of a conventional process centrifugal compressor. In FIG. 6, an impeller 3 is attached to a rotating shaft 2 inside a casing 1. The gas fluid sucked from the suction nozzle 6 is boosted by the impeller 3, is sucked into the next-stage impeller through the stationary flow path constituted by the diaphragm 5, is sequentially boosted, and is finally discharged from the discharge nozzle 7. Is ejected. The rotating shaft 2 is supported by bearings 9 at both ends and rotates. The seal between the impellers is made by a mouth labyrinth 11 and a stage labyrinth 12. The balance labyrinth 13 is located after the final impeller. A balance drum 14 is provided on the rotary shaft side opposite to the balance labyrinth 13. The shaft end side (secondary side) chamber of the balance labyrinth 13 is generally connected to the compressor suction line and used for adjusting the thrust force of the rotary shaft.

The rotary shaft 2 of this centrifugal compressor rotates by being supported by the bearings 9 at both ends as described above. However, even in the labyrinth portion, there is some bearing effect in the narrow gap portion, which is the high pressure and high speed of the compressor. In some cases, it cannot be ignored. Generally, a process centrifugal compressor has an operating speed at a position higher than the primary bending natural frequency of the shaft-bearing system. In such a case, if the bearing oil film has a characteristic that an oil film reaction force is generated in a direction orthogonal to the shaft displacement direction, the shaft vibration may become unstable. That is, it is a self-excited vibration that vibrates with the primary bending natural frequency component of the shaft-bearing system. Therefore, in the process centrifugal compressor in which the operating speed is higher than the primary bending natural frequency, the tilting pad bearing without the above characteristics is used.

However, the labyrinth and the shaft have the same structure as that of a true circular bearing, and the reaction force (in this case, the reaction force due to gas pressure) generated in the narrow gap portion acts in the direction orthogonal to the displacement direction of the shaft. There is a reaction force. Normally, the reaction force generated in the labyrinth portion does not pose a problem as compared with the stability force of the bearing. However, when the compressor is operated at high pressure and high speed, the spring force of the labyrinth part increases and the vibration (displacement) of the shaft of the labyrinth part increases, so this unstable force cannot be ignored and unstable vibration (self-excited vibration) ). If the unstable vibration becomes large, it becomes difficult to operate the compressor.

The reason why the above unstable force is generated in the labyrinth portion is that the leak flow flowing through the gap between the labyrinth and the shaft has a swirling component in the same direction as the rotation direction of the shaft. That is, part of the flow having the swirl component at the outlet of the impeller is the leak flow at the labyrinth portion. As a means for removing this turning component, there has been one in which a turning prevention component such as a bar is attached between the impeller and the diaphragm. Further, as described in JP-A-59-226299 and JP-A-59-226300, there has been one in which a plurality of radial radial fins are projected on the casing surface facing the impeller.

[0006]

SUMMARY OF THE INVENTION The above-mentioned prior art is related to the rotation of the shaft caused by the leakage flow flowing through the gap between the labyrinth and the shaft, which causes unstable vibration of the rotary shaft of a turbo rotary fluid machine such as a centrifugal compressor. In order to remove the swirl component in the direction, the radial direction of the leakage fluid from the outlet of the impeller to the inlet of the labyrinth seal is set by projecting multiple radial radial fins on the casing surface facing the impeller. I was trying to regulate it. However, in the conventional method,
There is a problem that the swirl component of the leakage flow that flows through the gap between the labyrinth and the shaft cannot be completely removed. Further, there is a problem that the structure is not simple due to the means such as providing a plurality of radially extending fins on the casing surface facing the impeller.

According to the present invention, the swirl component of the leak flow flowing through the gap between the labyrinth and the shaft in a turbo rotary fluid machine such as a centrifugal compressor, which causes an instability in the gap, can be completely removed by a simple means. It is an object to provide a labyrinth seal having a removable structure.

[0008]

In order to achieve the above object, the labyrinth seal of the present invention has the following means for removing the swirling component of the leakage flow flowing through the gap between the labyrinth and the shaft. First, the shaft-sealing mechanism of the labyrinth structure creates a fine gap between the labyrinth fin and the shaft to minimize the flow passage area, creates a room between the fins, and adiabatically expands it. Since the differential pressure per fin can be reduced, the amount of leakage is reduced, that is, the pressure between the fins is gradually reduced from the high pressure side to the low pressure side. Therefore, a passage that connects the room between the labyrinth fins relatively close to the high-pressure side chamber with the high-pressure side chamber is provided as follows, which is more than the outside diameter of the room between the high-pressure side end face of the labyrinth and the above labyrinth fin. A space is provided on the outer peripheral side, and a hole is provided to connect the space to the room between the labyrinth fins. The conductive space may be provided on the side of the diaphragm or the casing facing the labyrinth. Further, the area of the conduction path between the chamber between the high pressure side chamber and the labyrinth fin is set to be equal to or larger than the area of the gap between the labyrinth fin on the high pressure side of the chamber and the shaft.

Further, the labyrinth fin is provided on the stationary side. The labyrinth fin may be provided on the rotating side. Further, a projection is provided in the high pressure side chamber from the wall surface of the labyrinth or the diaphragm in the gas intake portion into the communication path (space portion) of the high pressure side chamber to take in the total pressure of the flow between the impeller and the stationary wall surface to take in the labyrinth. It may be blown into the room between the fins.

[0010]

In the labyrinth seal, first, when there is no conduction path from the high pressure side chamber to the room between the labyrinth fins, the flow of the high pressure side chamber having a swirling component flows to the low pressure side in the labyrinth portion, and the labyrinth seal In the room, adiabatic expansion is repeated and the pressure decreases as it goes from the high pressure side to the low pressure side. Therefore, when the gas introduced from the high pressure side chamber to the labyrinth fin and the small passage between the shaft and the conduction path (space) is introduced into the room between the labyrinth fins relatively close to the high pressure side chamber, the flow taken from this high pressure side chamber is The swirl component is removed by blowing out from a plurality of through holes (blowing holes) in the radial direction toward the room from the outer peripheral direction of the room between the labyrinth fins. Further, the area of the conduction path, that is, the area of the intake portion (space portion) from the high-pressure side chamber and the total area of the conduction hole (blowing hole) are both the tip clearance of the labyrinth fin on the high-pressure side of the conduction hole (blowing hole) position. Therefore, the flow from the high-pressure side chamber to the room between the labyrinth fins has a smaller resistance in the flow passage from the high-pressure side chamber to the labyrinth fin than in the labyrinth fin tip gap. Radial flow from the roadside can be supplied to the chamber to remove swirl components of the leaky flow through the labyrinth fin tip gap.

Even if the labyrinth fin is provided on the stationary side or the labyrinth fin is provided on the rotating side, a gap between the labyrinth fin and the shaft is obtained by the same means as above. The swirl component of the leakage flow flowing through the can be easily and completely removed. Further, when the handling gas is taken from the high-pressure side chamber to the above-mentioned communication passage (space portion), if it is taken in from the above-mentioned protruding portion that protrudes into the flow between the impellers, the dynamic pressure of the flow is restored, so a higher pressure is obtained. Thus, it is possible to blow out a flow having no swirl component into the room between the labyrinths.

[0012]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a structural vertical sectional view showing an embodiment of a labyrinth seal according to the present invention. FIG. 1 shows an example of the structure of a balanced labyrinth portion of a centrifugal compressor, in which the labyrinth is at the shaft end. After the final stage of the impeller 3 mounted on the rotary shaft 2 in the casing 1, the balance labyrinth 2
1 is fitted in the casing 1, and a balance drum 14 is provided on the rotary shaft side facing the balance labyrinth portion. The inner side of the balance labyrinth 21, that is, the final impeller outlet side is the high pressure side, and the shaft end side is low pressure, for example, by being connected to a suction nozzle. A space 22 is provided between the balance labyrinth 21 and the inner peripheral surface of the casing on the back surface of the end surface on the high-pressure side, and a radial hole 24 communicating from the space to the chamber 23 between the labyrinth fins is circular. A plurality of them are provided around the circumference. The chamber 23 between the labyrinth fins is arranged so as to have one or more fins between it and the end surface on the high pressure side. Further, the space 2 is larger than the axial area of the gap between the labyrinth fin and the drum 14.
The axial cross-sectional area of 2 and the total area of the conduction holes 24 are larger.

With the above structure, the flow of the fluid in the balance labyrinth portion gap is as follows. First, the flow leaving the final impeller 3 flows into the balance labyrinth portion while preserving the angular momentum given by the impeller. Here, although the angular momentum of the flow decreases due to the influence of friction on the casing wall surface and the impeller wall surface, it has a harmful peripheral rotation component in the rotational direction from the dynamic characteristics of the shaft system. This flow tries to flow into the chamber 23 between the labyrinth fins while pressure-dropping through the labyrinth fin tip clearance of the balance labyrinth 21. On the other hand, there is a leakage flow from the back surface of the labyrinth that flows into the chamber 23 between the labyrinth fins through the space 23 and the passage of the through hole 24.
This flow has a swirl component in the rotation direction when flowing into the space 22, but the swirl component is completely removed by passing through the through hole 24 in the radial direction. Moreover, since the passage area to the chamber 23 between the labyrinth fins is larger than the labyrinth fin tip clearance area, the pressure loss is smaller than that of the flow passing through the labyrinth fins. Therefore, the flow flowing into the chamber 23 is dominated by the flow having no swirl component coming through the space portion 22 on the back surface of the labyrinth, so that the swirl component of the flow in the tip clearance of the labyrinth fin from the chamber 23 to the low pressure side chamber is removed. be able to.

FIG. 2 is a structural longitudinal sectional area showing another embodiment of the labyrinth seal according to the present invention. FIG. 2 shows an example in which the balance labyrinth of the centrifugal compressor is located between the impellers. Note that the same reference numerals as those in FIG. 1 denote corresponding parts throughout the drawings. With the configuration of FIG. 2 similar to that of FIG. 1 described above, the swirling component of the flow of the balance labyrinth 21 between the impellers 3 can be eliminated.

FIG. 3 is a structural vertical sectional view showing still another embodiment of the labyrinth seal according to the present invention. 4 is a view taken along the line AA of FIG. 3, and FIG. 5 is a view taken along the line BB of FIG. FIG. 3 shows another example of the structure of the flow intake section of the high pressure side chamber on the back surface of the balance labyrinth. A plurality of projecting portions (flow stop portions) 25 projecting from the labyrinth end surface are provided in this flow intake portion. Spaces (holes) between the plurality of projecting portions 25 and space portions (room) 2 on the low pressure side
2 communicates with the chamber 23 between the labyrinth fins by a through hole 24 in the radial direction, as in FIG. Further, FIG. 4 shows a communication state between the protruding portion (cushion preventing portion) 25 and the space portion (room) 22 of FIG. Further, in FIG. 5, the high pressure side end surface of the projecting portion (cushion preventing portion) 25 in FIG. 4 is inclined in the circumferential direction so that the dynamic pressure of the flow between the impeller 3 and the casing 1 in FIG. 3 can be easily collected. An example is shown. With this configuration, a pressure close to the total pressure at the outlet of the impeller can be guided from the space portion 22, and the room 2 between the labyrinth fins can be
Since the control of the flow having no swirl component from the back surface of the labyrinth through the conduction hole 24 in 3 can be enhanced, the swirl component of the leakage flow in the labyrinth fin tip clearance can be eliminated.

Although the above embodiment shows an example of the labyrinth seal in which the labyrinth fin is provided on the stationary side,
The same applies to a labyrinth seal in which a labyrinth fin is provided on the rotating side. Further, although the through hole 24 is described as a hole in the radial direction, it may be a hole inclined in the direction opposite to the rotation direction, and in this case, the conduction hole 2 is formed.
4, the flow blown into the room 23 between the labyrinth fins has a negative swirl component, so that the control of this flow can be further enhanced.

[0017]

According to the present invention, the rotational component of the flow in the labyrinth portion can be easily and completely eliminated, so that the characteristics of the shaft-bearing system of a rotary fluid machine such as a centrifugal compressor can be stabilized. Therefore, there is an effect that the stability and safety of the plant can be enhanced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

FIG. 2 is a vertical sectional view of another embodiment of the present invention.

FIG. 3 is a vertical sectional view of still another embodiment of the present invention.

FIG. 4 is an AA view of FIG.

5 is a BB view of FIG.

FIG. 6 is a vertical sectional view of an example of a centrifugal compressor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Casing, 2 ... Rotating shaft, 3 ... Impeller, 21 ... Balance labyrinth, 22 ... Space part, 23 ... Room between labyrinth fins, 24 ... Conduction hole, 25 ... Projection part.

Claims (5)

[Claims] 1. A labyrinth seal provided in a shaft penetrating portion of a rotor in a fluid machine for rotating a rotor having an impeller mounted on a rotary shaft, wherein a low pressure side of a labyrinth fin at least one from a high pressure side chamber of the labyrinth seal. The labyrinth seal is characterized in that a gas passage for connecting the high-pressure side chamber is provided in the room. 2. The chamber between the high pressure side chamber and the chamber between the labyrinth fins is larger than the area of the clearance formed between the high pressure side chamber and the chamber between the labyrinth fins communicating with the high pressure side chamber with the rotor. The labyrinth seal according to claim 1, wherein the gas passage area between the two is increased. 3. The labyrinth seal according to claim 1, wherein the labyrinth fin is provided on a stationary side. 4. The labyrinth seal according to claim 1, wherein the labyrinth fin is provided on a rotation side. 5. The labyrinth seal according to claim 1, wherein a protrusion is provided at an inlet of the gas passage from the high-pressure side chamber.