JPH0719005A - Labyrinth seal device - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress the generation of steam whirl and prevent self-excited vibration of the turbine shaft system. [Structure] A seal fin 21 is embedded in an annular seal ring 22. The seal fin 21 is attached to the seal ring 22.
A through hole 25 for communicating the chamber 24 between the first row and the second row on the upstream side with the outer region of the seal ring 22 is bored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial flow type steam turbine, and more particularly to a labyrinth seal device suitable for preventing automatic vibration of a turbine shaft system to improve safety in operation.

[0002]

2. Description of the Related Art There is a type of steam turbine called an axial flow type. In this type, a large number of paragraphs including moving blades and stationary blades are provided along the turbine axis, and it has long been established as a mainstream type suitable for large capacity. FIG. 6 shows a typical axial flow steam turbine.

A large number of moving blades 2 are arranged vertically to the axial center of the rotor 1, and these moving blades 2 are bound by a shroud 3 in the circumferential direction. The rotor blades 2 that form a paragraph along the axial center of the rotor 1 have different lengths in each stage, and are short in a high pressure paragraph, while long in a low pressure paragraph.

On the other hand, a large number of stationary blades 5 are arranged on the inner peripheral surface of the casing 4 at positions facing the moving blades 2 at each stage. These stationary blades 5 are supported by a nozzle diaphragm 7 composed of an outer ring 6a fitted to the casing 4 in the circumferential direction and an inner ring 6b close to the rotor 1. The length of each stage of the stationary blade 5 also follows the moving blade 2 and varies according to the pressure in the paragraph.

In addition to the above paragraph components, axial flow steam turbines use sealing means between shaft seals and paragraphs.
The sealing means is a high pressure gland packing 8a incorporated in the high pressure side casing 4, a low pressure gland packing 8b incorporated in the low pressure side casing 4, a nozzle root packing 9 incorporated in the inner ring 6b, and a nozzle tip packing 10 incorporated in the outer ring 6a. Note that reference numerals 11a and 11 in the figure
Reference numeral b is a bearing, which supports both ends of the rotor 1.

Since these sealing means minimize the increase of steam that does not participate in work and leaks when the steam flows from the high pressure side paragraph to the low pressure side paragraph, the packing is composed of a large number of fins. Labyrinth packing is used.

Hereinafter, the above-mentioned sealing means will be collectively referred to as a labyrinth seal.

The details of the labyrinth seal are shown in FIG.

The seal fin 21 is an annular seal ring 2.
2, the tip of which extends toward the rotor 1, for example. The seal ring 22 is fitted in, for example, a groove 23 formed in the casing 4 so as not to fall off.

The steam enters the labyrinth as shown by the arrow S and flows into a space 24 (referred to as a chamber) between the seal fins 21 and 21. The pressure of the steam continues to drop while passing through the continuous chamber 24 from the upstream side to the downstream side, and finally the leakage stops. At this time, the larger the pressure drop is, the less the leakage is. Therefore, the number of the chambers 24 normally ranges from several to ten and more (particularly, the high pressure portion).

[0011]

The above-described labyrinth seal has a structure in which an annular seal ring 22 surrounds the entire circumference of the rotor 1, seal fins 21 extend toward the rotor 1, and a chamber 24 is formed therebetween. in this case,
The pressure distribution of steam becomes non-uniform in the circumferential direction in the chamber 24, and this tendency is strong especially in a large-capacity steam turbine in which the temperature and pressure are significantly increased. This non-uniform circumferential pressure distribution causes an unstable phenomenon in which the turbine shaft system oscillates at the natural frequency of the shaft system. This phenomenon is generally called steam whirl and exhibits a property that depends on the turbine load. Therefore, the excitation force tends to increase as the turbine load increases.

The state when the steam whirl occurs will be described with reference to the schematic diagram of FIG.

Generally, when the center o of the rotor 1 is displaced by the eccentric amount e with respect to the labyrinth seal (represented by the seal ring 22), the circumferential pressure distribution in each chamber 24 shows the highest pressure in the eccentric direction. It has a symmetrical distribution. If this is integrated in the circumferential direction, a vertically downward force P is obtained. This force P causes the acting direction to be downward, thus increasing the bearing load. This force P also has an effect of suppressing the steam whirl phenomenon.

However, in general, the steam flowing into the labyrinth seal becomes a circumferential swirl flow due to the rotation of the rotor 1, and as shown in FIG. 9, a swirl flow (direction T) in the same direction as the rotational direction of the rotor 1 (arrow T). Due to the inflow of steam that causes the arrow W), the pressure distribution is such that the peak point of the pressure deviates from the minimum gap point in the direction opposite to the rotor rotation direction in the eccentric direction of the rotor 1. When this pressure distribution is integrated in the circumferential direction, a vertically downward force P and a horizontal force Q are obtained. As described above, the vertically downward force P causes an increase in bearing load. The horizontal force Q does not increase the bearing load.

FIG. 10 is a schematic diagram showing the influence of the force Q in the horizontal direction. The center o of the rotor 1 whirls in the direction of the arrow U, and if a horizontal force Q acts on the rotor 1 at this time, the horizontal force Q acts in the same direction as the whirling direction U of the rotor 1. Then, the whirling of the turbine shaft system is promoted, and the shaft system becomes more unstable.

It is an object of the present invention to provide a labyrinth seal device which effectively suppresses the generation of steam whirl to prevent self-excited vibration of a turbine shaft system.

[0017]

In order to achieve the above object, the present invention maintains a minute gap in the radial direction between the rotor and the rotor.
Also, in a labyrinth seal device having a large number of fins provided in a plurality of rows in the axial direction, a stationary portion supporting the fins is communicated with the fins in the first row and the second row on the upstream side from the area outside the stationary portion, and each of them rotates. A plurality of through holes are provided so as to maintain a fixed angle with respect to the tangential direction of the body, and extraction steam from the outer region of the stationary part flows between the fins in the direction opposite to the swirling flow around the rotating body through the through holes. It is characterized in that it is configured to.

[0018]

The operation of the present invention will be described with reference to FIG. Figure 3
In (a), the steam that has flowed into the labyrinth seal follows the arrow W in the chamber in the rotational direction of the rotor 1 shown by the arrow.
It becomes a swirling flow in the direction indicated by a. Extracted steam flows into this chamber through a through hole formed in the seal ring 22 on the upstream side of the labyrinth seal. The direction of the through hole is in the tangential direction of the rotor 1, and the extracted steam flows into the chamber from the direction indicated by the arrow Wb opposite to the rotating direction of the rotor 1. The swirling flow and the extracted steam flow collide with each other in the chamber, and vortices are generated there as shown in FIG. For this reason, the swirling flow flowing along the rotor 1 is disturbed, and the motion component in the rotation direction is lost.

The degree to which the rotational motion component is lost from this swirling flow is greatly influenced by the inflow angle of the axial vapor flowing through the through hole. FIG. 4 shows the relationship between the inflow angle and the rotational motion component reduction rate. In FIG. 4A, the inflow angle (0 °) that is correctly oriented in the tangential direction of the rotor 1,
Inflow angle θ ₁ (+ side) with an inclination to the tangential direction, θ
₂ There is a significant difference in the degree of reduction of the motor component from the (-) side.

As shown in FIG. 4B, the decrease rate is highest when the inflow angle is 0 °, and the range of the inflow angle θ ₁ = + 5 ° and the inflow angle θ ₂ = −5 ° is approximate to 0 °. Although it shows a high reduction rate, if the inflow angle is inclined more than that, the desired reduction rate cannot be obtained. Therefore, the deviation from the tangential direction of the rotor 1 is ± 5 as the range of the desired inflow angle.
It should be within °.

Thus, by reducing the motion component of the swirling flow, a pressure distribution in which only the downward force P in the vertical direction acts can be formed, and the steam whirl phenomenon can be suppressed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, the seal fin 21 is embedded in an annular seal ring 22, and its tip extends straight toward the rotor 1. In this embodiment, the seal ring 22 is provided with a through hole 25 for communicating the chamber 24 formed between the first row and the second row on the upstream side of the seal fin 21 and the outer region of the seal ring 22.

FIG. 2 shows the arrangement of the through holes 25 in detail, and four through holes 25 are provided so as to coincide with the tangential direction of the rotor 1. The through holes 25 must be large enough to deliver the proper amount of bleed air into the chamber 24. The pressure in the chamber 24 is lower than that in the outer region of the seal ring 22 due to the first-row seal fins 21. However, when the swirling flow indicated by the arrow Wa and the extraction steam flow indicated by the arrow Wb collide with each other, It is necessary to equally damp the motion component in the rotation direction, and at least four, and possibly more, through holes are provided.

In the above structure, a swirling flow is generated in the chamber 24 by the rotation of the rotor 1 in the direction of the arrow Wa. When the extracted steam extracted in the outer region of the seal ring 22 flows through the through hole 25 into the chamber 24 in the direction of the arrow Wb, the extracted steam flow and the swirling flow in opposite directions collide with each other, and a vortex is generated there. As a result, the flow is disturbed. Therefore, the swirling flow loses the motion component in the rotation direction, and it becomes possible to form a pressure distribution (see FIG. 8) in which only the downward force P in the vertical direction acts.

Therefore, an exciting force that promotes whirling is not applied to the turbine shaft system, so that the shaft system is kept stable,
The occurrence of steam whirl can be prevented.

In particular, the uneven pressure distribution in which the peak points of the pressure are displaced in the rotor rotation direction shown in FIG.
Since it appears remarkably in the seal fins 21 of the row, suppressing the generation of the swirling flow in this part is effective in preventing the generation of steam whirls.

That is, the pressure drop in each chamber 24 is, as shown in FIG. 3, the chamber 2 between the first and second rows.
It is most desirable to form the through hole 25 in the upstream chamber 24 having a large absolute value, which gradually decreases from ΔP _{1 in} 4 to ΔP ₂ and ΔP ₃ .

The chamber 24 between the first and second rows
As shown by ΔP ₁ ′ in FIG. 3, the non-uniform pressure distribution of is a substantially uniform pressure distribution, and the point showing the highest pressure can be shifted to around 180 °, that is, right above.

[0030]

As described above, in the present invention, a plurality of through holes communicating from the stationary portion outer region to the upstream first and second row fins are provided to extract air from the stationary portion outer region. Since the steam flows between the fins in the direction opposite to the swirling flow around the rotating body, steam whirl can be effectively suppressed, the turbine shaft system can be kept stable, and the steam turbine does not cause self-excited vibration. It is possible to maintain safe driving.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a labyrinth seal device according to the present invention.

2 is a cross-sectional view of the labyrinth seal device shown in FIG.

FIG. 3 is a diagram for explaining a pressure drop in each chamber of the labyrinth seal device.

FIG. 4 is a view for explaining the operation of the labyrinth seal device according to the present invention.

FIG. 5 is a diagram showing a relationship between an inflow angle and a rotational direction motion component reduction rate.

FIG. 6 is a sectional view showing a conventional axial flow steam turbine.

FIG. 7 is a sectional view showing a conventional labyrinth seal device.

FIG. 8 is a schematic diagram showing a pressure distribution in a chamber.

FIG. 9 is a schematic diagram showing a pressure distribution in a chamber.

FIG. 10 is a diagram for explaining the influence of a horizontal force.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Rotor 21 ... Seal fin 22 ... Seal ring 24 ... Chamber 25 ... Through hole T ... Rotation direction of rotor W, Wa ... Direction of swirling flow Wb ... Direction of extraction steam flow U ... Whirling direction of rotor

Claims (1)

[Claims] 1. A labyrinth seal device having a large number of fins arranged in a plurality of rows in the axial direction while maintaining a small radial gap between the stationary part and the stationary part in the stationary part supporting the fins. A plurality of through holes are provided so as to communicate between the fins in the first row and the second row on the upstream side from the outer area, and each of them has a plurality of through holes so as to maintain a predetermined angle with respect to the tangential direction of the rotating body. The labyrinth seal device is characterized in that the extracted steam from the above flows into the space between the fins in a direction opposite to the swirling flow around the rotating body through the through hole.