Seal for a joint or juncture – Seal between relatively movable parts – Close proximity seal
Reexamination Certificate
1998-12-30
2001-02-20
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Close proximity seal
C277S419000
Reexamination Certificate
active
06189892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotational seal device applicable mainly as a gas turbine end rotor seal having a structure that provides an enhanced sealing performance and facilitates assembly or replacement of the seal portion.
2. Description of the Prior Art
FIG. 8
is a cross sectional side view showing one example of a seal structure of a gas turbine rotor end portion which has been developed by the inventors for use together with a steam cooled system of the rotor. In
FIG. 8
, numeral
11
designates a rotor comprising an inner rotor
11
a
and an outer rotor
11
b
. A cooling medium, or steam
20
, is supplied between the inner rotor
11
a
and the outer rotor
11
b
via a steam inlet
14
. The steam, after having cooled the rotor, passes through the inner rotor
11
a
and flows out of a steam outlet
15
to be recovered. Numeral
16
designates a bearing portion and a labyrinth seal
13
is provided between the outer rotor
11
b
and a stator
12
for sealing to prevent the steam from leaking outside.
In the above-mentioned end rotor seal, because the end rotor overhangs beyond the bearing portion
16
as shown in
FIG. 8
, there is a limitation in a rotor axial directional length of the seal portion by which the seal portion cannot be further elongated. Also, because there is a large difference in the thermal elongation between the rotor side and the stator side, there is also a limitation in the length from this point of view. Due to these limitations, if a steam cooled system is to be used for the rotor, the seal length is limited to about 270 mm at most and if a labyrinth seal is employed therefor, the number of stages (number of fins) is limited to about ten (10).
FIGS.
7
(
a
)-
7
(
b
) are an explanatory views showing examples of prior art seal structures applied for the end rotor seal described above, wherein FIG.
7
(
a
) is a double strip seal and FIG.
7
(
b
) is a labyrinth seal. In the double strip seal of FIG.
7
(
a
), there are provided fins
32
on the stator side
31
and fins
34
on the rotor side
33
, disposed such that the fins
32
are opposed to the fins
34
with a predetermined clearance C in a rotor radial direction being maintained therebetween and also with a fin to fin pitch P in a rotor axial direction with respect to the fins
32
and the fins
34
, respectively. If the double strip seal is used for the end rotor seal of a gas turbine, the length L thereof is about 270 mm as mentioned above and when the pitch P=3 mm, the number of fins is 90, when P=6 mm, the number of fins is 45 and when P=10 mm, the number of fins is 27.
In the labyrinth seal of FIG.
7
(
b
), there are provided fins
42
, projection portions
43
and fins
44
on the projection portion
43
on the stator side
41
and projection portions
46
on the rotor side
45
, disposed such that the fins
42
are opposed to the projection portions
46
with a predetermined clearance C′ in the rotor radial direction being maintained therebetween. If this labyrinth seal is used for the end rotor seal of a gas turbine, because there occurs a thermal elongation of about ±20 mm in the rotor axial direction, the number of the fins is limited to about ten (10) due to the arrangement of the fins
44
and the projection portions
46
.
FIG. 6
is a detailed cross sectional view showing one example of the end rotor seal portion shown in FIG.
8
.
In
FIG. 6
, the interior of the rotor
11
is made in a double structure, wherein numeral
53
designates an outer cooling passage and numeral
54
designates a central cooling passage. A cooling medium, shown by arrow
20
a
, which is for example a cooling air or the steam
20
, as shown in
FIG. 8
, is led into the outer cooling passage
53
for cooling of the rotor
11
and, after having been used for the cooling, flows in the central cooling passage
54
, as shown by arrow
20
b
, to flow outside of the rotor
11
. There are provided a multiplicity of the fins
34
in the rotor axial direction on a rotor outer circumferential surface so as to form a seal portion of the rotor side.
As a seal portion of the stator side, there are provided a multiplicity of the fins
32
in the rotor axial direction, like the fins
34
on the rotor
11
, and the fins
32
are disposed close to the fins
34
in an opposing relationship along a rotor circumferential direction. Thus, a double strip seal is formed by the fins
34
on the rotor side and the fins
32
on the stator side.
The fins
34
on the rotor side, as described above, are formed by cutting the outer circumferential surface of the rotor
11
, or are buried fixedly therein if the pitch between the fins is comparatively large, so that the rotor
11
and the fins
34
are made integrally in one unit.
In the present state gas turbine, a large amount of cooling air is introduced in the rotor and the blade continuously and thus, a considerable amount of power is consumed for a compressor or a cooler thereof for producing high pressure air therefor, which is an obstacle in enhancing the gas turbine performance. Also, in the recent combined cycle power plant having an enhanced power generation efficiency due to the use of the combination of a gas turbine and a steam turbine, trials are being conducted so that, in place of using air for cooling the rotor or the blade, a portion of steam from the steam turbine is extracted and led into the rotor or the blade for cooling thereof, but this steam cooled system is still being developed.
The seal structure of the prior art gas turbine rotor is formed in one unit of the rotor and the fins as mentioned above, and in case the fins of the rotor have worn out after long hours of use, it is necessary to change the entire rotor along with the fins. Even if only the fins have worn out and there is nothing unusual in the rotor itself, the rotor must be changed, which is very economically inefficient. Also, in the case where the seal is formed by the fins being buried one by one, a long period of time is required in order to perform the difficult task of replacing the fins.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention, in the case of a steam cooled system for a gas turbine rotor or blade, to provide a high differential pressure type end rotor seal which is applicable as an end rotor rotational seal and in which a fin-to-fin pitch in a rotor axial direction and a clearance in a rotor radial direction between fins have been designed optimally as the result of repeated experiments carried out so as to reduce leakage of cooling medium to a minimum in consideration of the influence of a thermal elongation.
Also, it is an object of the present invention to provide a high differential pressure type end rotor seal, in addition to that having the minimum leakage as mentioned above, in which a fin portion of the rotor is made and assembled separately from the rotor and is then fitted to the rotor so that, when only the fins have worn out, it is not necessary to replace the entire rotor but only the fin portion can be changed.
In order to achieve said object, the present invention provides the following means:
(1) A high differential pressure type end rotor seal, applicable as a seal for a rotor end portion of a turbine, made as a double strip seal type having fins spaced with a predetermined fin-to-fin pitch in a rotor axial direction on a rotor side and a stator side, respectively. The fins on the rotor side and those on the stator side are disposed so as to be opposed to each other with a predetermined clearance in a rotor radial direction maintained between apexes of the respective fins. The seal is characterized in that the fin-to-fin pitch is set in a range of 2 to 6 mm and the clearance is set in a range of 0.3 to 1.0 mm.
(2) A high differential pressure type end rotor seal as mentioned in (1) above, characterized in that the fins on the rotor side are provided on a sleeve and the sleeve is detachably fitted around the rotor end portion.
(3) A high differe
Chikami Rintaro
Hirokawa Kazuharu
Uematsu Kazuo
Knight Anthony
Mitsubishi Heavy Industries Ltd.
Pickard Alison K.
Wenderoth , Lind & Ponack, L.L.P.
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