Shaft seal and turbine using the same

Details Shaft seal and turbine using the same Shaft seal and turbine using the same

2000-03-13

2002-02-05

Knight, Anthony (Department: 3626)

Seal for a joint or juncture

Seal between relatively movable parts

Brush seal

C277S345000

Reexamination Certificate

active

06343792

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a shaft sealing structure applicable to a rotation shaft of a large fluid machine such as various kinds of turbines, compressors, water turbines or wheels, refrigerating machines, and pumps, and in particular, to a gas or steam turbine to which a shaft seal is applied.
BACKGROUND ART
A typical gas turbine generates power by introducing a high-temperature and high-pressure gas into a turbine so as to expand the gas, and converting the thermal energy of the gas into mechanical rotational energy. Such a gas turbine has a seal mechanism (i.e., shaft seal), arranged between stationary blades and -the rotation shaft, for reducing the leakage of the combustion gas, that is, the amount of gas which leaks from the high-pressure side to the low-pressure side. Conventionally, a non-contact labyrinth seal is widely known and used as such a sealing structure. When the labyrinth seal is employed, it is necessary to have a relatively large gap at the end of each fin so as to prevent the fin from contacting the face which faces the fin even if the shaft is vibrated during a transitional period of the rotation, or if the relevant portion is thermally and transitionally deformed. Therefore, the leakage is relatively large in the labyrinth seal. As a substitute for the labyrinth seal, a brush seal has been developed so as to reduce the leakage.
FIGS. 37A and 37B
show a general structure of the brush seal. In the figures, reference numeral
1
indicates a rotation shaft, reference numeral
2
indicates a casing, reference numeral
3
indicates a low-pressure side end plate, reference numeral
4
indicates a high-pressure side end plate, reference numeral
5
indicates a brazed portion, and reference numeral
6
indicates a wire bundle. The wire bundle
6
, having a width of 1 to 3 mm, consists of filaments closely arranged with no gap between each other, and each filament has a diameter of 50 to 100 &mgr;m and suitable rigidity by which eccentricity due to vibration or thermal deformation of the rotation shaft
1
or the like can be absorbed. In addition, the wire bundle
6
is inclined with respect to the rotation direction so as to make an acute angle between the wire bundle and the outer-peripheral surface of the rotation shaft
1
. The end of the wire bundle
6
contacts the outer-peripheral surface of the rotation shaft
1
via a specific pre-load, thereby reducing the leakage in the axial direction of the shaft.
The wire bundle
6
slides on the rotation shaft
1
in contact with the shaft. This sliding motion may heat the wire bundle
6
and make the bundle red, according to the environmental conditions or the rotation speed. Therefore, the wire bundle
6
may be made of a heat-resisting material such as inconel or hastelloy according to the usage condition. In addition, the sliding surface, that is, the outer-peripheral surface of the rotation shaft
1
, is also subject to abrasion, as in the wire bundle
6
; thus, the relevant surface of the rotation shaft
1
is coated with an abrasion resistant material. Furthermore, the wire bundle
6
has smaller rigidity in the axial direction of the rotation shaft
1
; thus, the inner diameter of the low-pressure side end plate is made approximately the same as the diameter of the circumference of the rotation shaft
1
, thereby preventing breakage of the wire bundle
6
.
The above brush seal has the following problems.
In the brush seal, leakage through gaps between the wires of the bundle
6
or gaps near the end of the bundle, or around the sliding portion (i.e., face) contacting the outer-peripheral surface of the rotation shaft
1
is a typical problem. If the differential pressure of the seal exceeds a permissible value which is determined based on the diameter of each wire of bundle
6
, the structure or arrangement of the low-pressure side end plate, and the like, the wire bundle
6
is deformed towards the low-pressure side, so that the area between the wire bundle
6
and the rotation shaft
1
is not sealed and thus the sealing effect cannot be obtained.
The rigidity of the wire bundle
6
as a constituent of the brush seal is determined according to the following capability of the wire bundle
6
with respect to the vibration of the rotation shaft
1
, or to a suitable pre-load between the wire bundle
6
and the rotation shaft
1
. The rigidity can be increased by using a thicker wire, but this has limits. That is, the maximum differential pressure for sealing in the axial direction of the rotation shaft
1
, dependent on the rigidity of wire bundle
6
, is approximately 5 kgf/cm
2
, and a much larger differential pressure cannot be maintained using a seal. Generally, the diameter of each wire is approximately 50 to 100 &mgr;m, that is, very thin. Therefore, when such thin wires contact and slide on the peripheral surface of the rotation shaft
1
, the wire bundle
6
may be broken and come off, and this is a serious problem when the relevant gas turbine is operated for a long time.
The leakage around the end portion of the wire bundle
6
is much smaller than that of the labyrinth seal or the like, because the wire bundle
6
contacts the peripheral surface of the rotation shaft
1
when it slides on the surface. However, it is difficult to reliably maintain a smaller leakage between the wires of the wire bundle
6
.
In addition, the peripheral surface of the rotation shaft
1
must be coated with an abrasion resistant material because the wire bundle
6
and the peripheral surface contact each other during the sliding motion. However, a technique for making an anti-abrasion coating C which suits a rotation shaft having a large diameter and lasts for a long time has not yet been established, and the wire bundle
6
and rotation shaft
1
suffer considerable abrasion. Therefore, the brush seal has a short lifetime and must be frequently replaced.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a shaft seal which has a high sealing capability and by which leakage can be reduced. Another object of the present invention is to provide a turbine using the above shaft seal, in particular, a gas turbine which has a high abrasion resistance in the seal structure, and can reduce the gas leakage from the high-pressure side to the low-pressure side.
Therefore, the present invention provides a shaft seal having flexible leafs (i.e.,) which are multi-layered to form a ring shape. Typically, one side of the multi-layered leaves is fixed to a fixing member having a cylindrical shape, and the shaft seal is arranged around a predetermined shaft (mainly, a rotation shaft).
According to the leaves employed as a sealing component, the area fixed to the casing is larger in comparison with the conventional wires; thus, the leaves are firmly fixed to the casing, thereby preventing the leaves from falling off from the casing, as observed in the conventional brush seal.
In addition, the top ends of the leaves have flexibility in the circumferential direction of the rotation shaft, and have high rigidity in the axial direction of the rotation shaft. Therefore, the leaves are not easily deformed in the direction of the differential pressure; and thus the permissible value of the differential pressure to be sealed can be increased.
When the vibration of the rotation shaft is large near the resonance point or the like, the leaves are deformed and the contact state with the rotation shaft is eased. In addition, under the rated conditions, the ends of the leaves separate from the surface of the shaft due to the dynamic pressure generated by the rotation of the rotation shaft. Therefore, it is possible to prevent excessive heating and abrasion caused by the contact of the leaves and the rotation shaft. Furthermore, according to the prevention of the heating due to the contact between the leaves and the rotation shaft, vibration generated depending on the thermal balance in the rotation shaft can also be prevented.
In the above structure, each leaf may be inclined with respect to the radial

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