U.S. patent application number 14/337765 was filed with the patent office on 2015-01-29 for axial compressor.
The applicant listed for this patent is Mitsubishi Hitachi Power Systems, Ltd.. Invention is credited to Kohta KAWAMURA, Chihiro MYOREN, Yasuo TAKAHASHI.
Application Number | 20150030438 14/337765 |
Document ID | / |
Family ID | 51224753 |
Filed Date | 2015-01-29 |
United States Patent
Application |
20150030438 |
Kind Code |
A1 |
TAKAHASHI; Yasuo ; et
al. |
January 29, 2015 |
Axial Compressor
Abstract
An axial compressor includes: a spray nozzle (32) that supplies
droplets to a working fluid before compression or being compressed;
a variable stator vane (56) having a stem section (94) inserted in
an insertion hole (73) in a casing (54), the variable stator vane
(56) having an angle of attack varied through sliding motion
relative to the casing caused by rotation of the stem section; a
sealing groove (93) provided in a sliding portion between a thrust
washer (82) slid relative to the casing during rotation of the stem
section and the casing; and a sealing member (92) housed in the
sealing groove.
Inventors: |
TAKAHASHI; Yasuo; (Yokohama,
JP) ; MYOREN; Chihiro; (Yokohama, JP) ;
KAWAMURA; Kohta; (Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Hitachi Power Systems, Ltd. |
Yokohama |
|
JP |
|
|
Family ID: |
51224753 |
Appl. No.: |
14/337765 |
Filed: |
July 22, 2014 |
Current U.S.
Class: |
415/159 |
Current CPC
Class: |
Y02T 50/60 20130101;
F04D 29/563 20130101; Y02T 50/675 20130101; F04D 29/582 20130101;
F04D 29/083 20130101; F04D 19/028 20130101; F01D 11/003 20130101;
F04D 29/5846 20130101; F01D 17/162 20130101; F02C 7/1435 20130101;
F04D 29/705 20130101 |
Class at
Publication: |
415/159 |
International
Class: |
F04D 29/56 20060101
F04D029/56; F04D 29/08 20060101 F04D029/08; F04D 19/02 20060101
F04D019/02; F04D 29/58 20060101 F04D029/58 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2013 |
JP |
2013-152807 |
Claims
1. An axial compressor comprising: a droplet supply unit that
supplies droplets to a working fluid before compression or being
compressed; a variable stator vane having a rotational shaft
inserted in a hole in a casing, the variable stator vane having an
angle of attack varied through sliding motion relative to the
casing caused by rotation of the rotational shaft; and a sealing
structure provided in a sliding portion between the casing and a
member slid relative to the casing during rotation of the
rotational shaft.
2. The axial compressor of claim 1, further comprising: a stator
vane base provided in the variable stator vane so as to be
positioned between the rotational shaft and a vane section of the
variable stator vane, the stator vane base being disposed to face
an inner peripheral surface of the casing, wherein the sealing
structure is provided in a sliding portion between the stator vane
base and the casing.
3. The axial compressor of claim 1, further comprising: a stator
vane base provided in the variable stator vane so as to be
positioned between the rotational shaft and a vane section of the
variable stator vane, the stator vane base being disposed on a side
of an inner peripheral surface of the casing; and a washer inserted
over the rotational shaft so as to be positioned between the stator
vane base and the inner peripheral surface of the casing, wherein
the sealing structure is provided in the casing, at a site that
faces a surface of the washer on an outside in a rotor radial
direction.
4. The axial compressor of claim 1, further comprising: a stator
vane base provided in the variable stator vane so as to be
positioned between the rotational shaft and a vane section of the
variable stator vane, the stator vane base being disposed on a side
of an inner peripheral surface of the casing; and a washer inserted
over the rotational shaft so as to be positioned between the stator
vane base and the inner peripheral surface of the casing, wherein
the sealing structure is provided in the stator vane base, at a
site that faces a surface of the washer on an inside in the rotor
radial direction.
5. The axial compressor of claim 1, further comprising: a
counterbored groove formed around the rotational shaft in an outer
peripheral surface of the casing; and a flange portion housed in
the counterbored groove, wherein the sealing structure is provided
at a sliding portion at which the flange portion slides relative to
the rotational shaft.
6. The axial compressor of claim 1, wherein the sealing structure
is provided in a sliding portion between the member slid relative
to the casing and a lower half side of the casing.
7. The axial compressor of claim 1, wherein the sealing structure
is provided in a portion having pressure of a working medium higher
than atmospheric pressure near the casing.
8. An axial compressor comprising: a variable stator vane having a
rotational shaft inserted in a hole in a casing, the variable
stator vane having an angle of attack varied through sliding motion
relative to the casing caused by rotation of the rotational shaft;
and a sealing structure provided in a sliding portion between the
variable stator vane and the casing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an axial compressor for a
gas turbine or an industrial use.
[0003] 2. Description of the Related Art
[0004] Operating a gas turbine in, for example, summer results in a
reduced gas turbine output due to a drop in inlet air density at a
high atmospheric temperature. To solve this problem of the reduced
output, a known method sprays water or other fluid droplets over
inlet air of the compressor using a spray nozzle to thereby
increase the inlet air density, thus improving the gas turbine
output through an effect of inlet air cooling. In addition, with
the droplets introduced into an inside of the compressor by
increasing an amount of sprayed droplets, an effect of intermediate
cooling reduces compressor work to thereby improve gas turbine
efficiency. The fine droplets conveyed with an airflow into the
inside of the compressor vaporize up to a saturation temperature of
a stage while passing through rotor blade cascades and stator vane
cascades, and reduce the temperature of a working fluid through
latent heat of vaporization.
[0005] In a multistage axial compressor, the droplets are vaporized
from the upstream side of the compressor, resulting in a reduced
temperature of a mainstream. Thus, blade loading decreases on an
upstream side of the compressor and increases on a downstream side
of the compressor, in which a load distribution differs from that
of a normal dry operation relative to a flow direction. To spray a
large amount of droplets in the inside of the compressor, the
foregoing necessitates engineering to increase the blade loading on
the upstream side and reduce the blade loading on the downstream
side in advance. No droplets are sprayed in a low-speed operating
range of a gas turbine engineered as described above, such as
during starting of the gas turbine. Thus, as compared with starting
of an ordinary simple cycle gas turbine, a greater separation range
may result from an unsteady fluid phenomenon in which a flow
through an upstream blade cascade stalls as a result of a flow
through a downstream blade cascade choking, what is called, a
rotating stall.
[0006] To operate the compressor steadily in gas turbines, a stator
vane (a variable stator vane) having a mechanism that varies an
angle of attack (an angle of a blade chord relative to a direction
of flow of the working fluid) is disposed upstream of the
compressor. During an operation at low speeds, such as when
starting the compressor, an inflow angle to the variable stator
vane increases due to a reduced intake flow rate. This makes it
necessary to adjust the angle of attack of the variable stator vane
corresponding to the increased inflow angle by rotating the
variable stator vane in a direction in which the flow is
restricted. In contrast, during a high-speed operation, the
variable stator vane is rotated in a direction in which the flow is
increased to respond to an increased intake flow rate.
[0007] Axial compressors including stator vanes having such a
variable mechanism are disclosed, for example, in JP-1990-294501-A
and JP-2012-72763-A. JP-1990-294501-A discloses a structure having
a reduced gap between taper surfaces of an inner peripheral side
end portion of a variable stator vane and an outer peripheral
portion of a rotor disc. JP-2012-72763-A discloses a structure that
incorporates considerations for wear resistance of a sliding
portion of a variable mechanism.
SUMMARY OF THE INVENTION
[0008] The variable stator vane incorporated in a simple cycle gas
turbine is generally rotated to vary its angle of attack during
starting of the gas turbine or partial loading operation. In
addition, the variable stator vane comprises a plurality of
variable stator vanes disposed in an axial direction and a
circumferential direction of a casing. The angle of attack (angle
of rotation) of these variable stator vanes disposed in the same
circumferential direction needs to be changed simultaneously
according to the flow, which makes highly accurate angle control
important. Techniques are known to improve sliding performance of
the variable stator vane, such as incorporating a metal bushing on
a rotational shaft of the variable stator vane and incorporating a
thrust washer between an end face on the side of a casing and a
casing inner peripheral surface of the variable stator vane.
[0009] Unfortunately, however, considerations are not very much
given to improving sealing performance in the sliding portion
between the variable stator vane and the casing. As a result, when
water or other fluid droplets are to be sprayed inside the
compressor having the variable stator vanes, in particular,
droplets may leak from the variable stator vane mechanism to the
outside of the casing due to a difference in pressure between the
inside and outside of the casing. In addition, on a long-term
perspective, rust may gather as a result of corrosion on the
sliding portion between the rotational shaft of the variable stator
vanes and the casing surface, resulting overall in degraded device
reliability of the variable stator vane.
[0010] It is an object of the present invention to provide an axial
compressor capable of preventing fluid leakage from a sliding
portion between a variable stator vane and a casing.
[0011] To achieve the foregoing object, an aspect of the present
invention provides an axial compressor comprising: a droplet supply
unit that supplies a working fluid before compression or being
compressed with droplets; a variable stator vane having a
rotational shaft inserted in a hole in a casing, the variable
stator vane having an angle of attack varied through sliding motion
relative to the casing caused by rotation of the rotational shaft;
and a sealing structure provided in a sliding portion between a
member slid relative to the casing during rotation of the
rotational shaft and the casing.
[0012] The present invention can prevent leakage of a fluid from
the sliding portion between the variable stator vane and the casing
to thereby improve reliability of the axial compressor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will be described hereinafter with
reference to the accompanying drawings.
[0014] FIG. 1 is a configuration diagram showing a gas turbine
system including an inlet air spray mechanism according to an
embodiment of the present invention;
[0015] FIG. 2 is a meridional cross-sectional view showing an axial
compressor according to an embodiment of the present invention;
[0016] FIG. 3 is a cross-sectional view showing a variable stator
vane structure according an embodiment of the present
invention;
[0017] FIG. 4 is a cross-sectional view showing a variable stator
vane structure according another embodiment of the present
invention; and
[0018] FIG. 5 is a cross-sectional view showing a variable stator
vane structure according still another embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Preferred embodiments of the present invention will be
described below with reference to the accompanying drawings. With
reference to FIG. 1, an exemplary configuration of a gas turbine
system including an inlet air spray mechanism will first be
described. FIG. 1 is a schematic general configuration diagram
showing the gas turbine system including the inlet air spray
mechanism.
[0020] The gas turbine system shown in FIG. 1 includes a compressor
1, a combustor 2, and a turbine 3. The compressor 1 compresses air
to thereby generate high-pressure air. The combustor 2 mixes and
burns compressed air and fuel. The turbine 3 is rotatably driven by
combustion gas at high temperature. The compressor 1 and the
turbine 3 are mechanically connected to a generator 4 via a
rotational shaft.
[0021] A flow of a working fluid in the gas turbine system shown in
FIG. 1 will be described below. Air 11 as the working fluid flows
into the compressor 1 and, while being compressed by the compressor
1, flows as high-pressure air 12 into the combustor 2. The
combustor 2 mixes the high-pressure air 12 with fuel 13 to burn a
resultant mixture and thereby generates high-temperature combustion
gas 14. The combustion gas 14 rotates the turbine 3 before being
released to an outside of the system as exhaust gas 15. The
generator 4 is driven by turbine rotating power transmitted via a
rotational shaft 5 that connects the compressor 1 to the turbine
3.
[0022] In a constant speed compressor with a constant volumetric
flow rate commonly used in the gas turbine system, an increased
inlet air temperature in summer lowers air density, resulting in a
reduced mass flow rate of the inlet air. This necessitates
reduction in a fuel flow rate in the combustor accordingly.
Specifically, the higher the inlet air temperature of the
compressor, the lower the output of the gas turbine.
[0023] Thus, a known method sprays water or other fluid droplets
over the inlet air of the compressor to thereby improve the gas
turbine output through an effect of inlet air cooling. One known
method for inlet air cooling incorporates a medium-based inlet air
cooler disposed in an air intake duct, inlet air passing through
the inlet air cooler to reduce the inlet air temperature.
[0024] Another known method for inlet air cooling incorporates a
droplet spray nozzle (droplet supply unit) 32 disposed in an air
intake duct 31 as shown in FIG. 1. The method sprays fine droplets
over air drawn into the air intake duct 31 before compression to
thereby vaporize the droplets in the airflow. Latent heat of
vaporization of the droplets is thereby utilized to reduce the
inlet air temperature. From the method of spraying droplets, an
intermediate cooling effect can also be expected.
[0025] Specifically, an increase in the amount of droplets results
in not only an inlet air cooling effect vaporizing droplets inside
the air intake duct being achieved, but also the droplets being
supplied into, and vaporized in, the inside of the compressor to
achieve the intermediate cooling effect. This contributes to
greater gas turbine efficiency thanks to the improved gas turbine
output and reduced compression work.
[0026] The example shown in FIG. 1 includes the droplet spray
nozzle 32 disposed at only one place in the air intake duct 31. The
droplet spray nozzle 32 may nonetheless be disposed at any other
place than the air intake duct 31 or at two or more places. For
example, two droplet spray nozzles 32 are disposed, one in the air
intake duct 31 and the other in an air inlet plenum 33 at an
entrance of the compressor, so that inlet air spraying can be
performed in two stages. Furthermore, the droplet spray nozzle may
be disposed inside the compressor 1 and the droplet spraying may be
performed not only over the working fluid before compression, but
also the working fluid being compressed.
[0027] A detailed structure of the compressor 1 will be described
below with reference to FIG. 2 that schematically shows a
meridional cross-sectional view of the compressor 1. As shown in
FIG. 2, the axial compressor 1 includes a rotor 52 and a casing 54.
A plurality of rotor blade cascades 51, 57 is mounted on the rotor
52 that is rotated by an axial driving force given by a drive
source (turbine 3). A plurality of stator vane cascades 56, 53 is
mounted on an inner peripheral surface of the casing 54. An outer
peripheral surface of the rotor 52 and the inner peripheral surface
of the casing 54 form an annular flow path.
[0028] The rotor blade cascades 51, 57 and the stator vane cascades
56, 53 are alternately arranged along a rotor shaft direction, one
set of a rotor blade cascade and a stator vane cascade constituting
a stage. An inlet guide vane (IGV) 55 that controls the intake flow
rate to thereby adjust gas turbine load is disposed upstream of the
first-stage rotor blade 51. A variable mechanism 71 for varying the
angle of attack of the inlet guide vane 55 is mounted on the inlet
guide vane 55. The variable mechanism 71 is connected to a control
ring 91 via a thin-plate lever 85. Rotating the control ring 91
rotates the inlet guide vane 55, which results in the angle of
attack being varied.
[0029] The front-stage stator vane cascade (first-stage stator vane
cascade) 56 disposed between the first-stage rotor blade cascade 51
and the second-stage rotor blade cascade 51 is a variable stator
vane cascade, each of the vanes having a variable mechanism 70 for
varying the angle of attack while, for example, the gas turbine is
being started. For example, varying the angle of attack of the
variable stator vane 56 during starting of the gas turbine allows a
rotating stall to be prevented. Similarly to the variable mechanism
71, the variable mechanism 70 to be described in detail later is
connected to a control ring 91 via a thin-plate lever 85.
[0030] In the compressor 1 shown in FIG. 2, of the stator vane
cascades 56, 53 spaced apart from each other in the rotor shaft
direction, only the first-stage stator vane cascade 56 has the
variable mechanism 70. Nonetheless, any stator vane cascade on the
second stage onward (e.g. the second-stage stator vane cascade 53)
may have the variable mechanism 70. Especially with an inlet air
spray compressor having a droplet spray nozzle, blade loading on
the front-stage side increases, so that having variable stator
vanes over a plurality of stages is advantageous for ensuring
steady starting.
[0031] The air 11 that has flowed in from the air intake duct (not
shown) has a circulation direction turned 90 degrees at the air
inlet plenum 33 disposed upstream of the compressor 1 and is
supplied into the compressor 1. Water or other fluid droplets are
jetted from the droplet spray nozzle 32 disposed inside the air
intake duct. Fine droplets are vaporized in the airflow and the
latent heat of vaporization of the droplets reduces the temperature
of gas flowing into the compressor 1, and at the same time,
increases the inlet air density.
[0032] Of the fine droplets conveyed with the airflow, droplets
that have not been vaporized until saturation flow into the inside
of the compressor 1 as droplets. The droplets, while passing
through the rotor blade cascades and the stator vane cascades
inside the compressor 1, vaporize until reaching a saturation
temperature and decrease the temperature of the working fluid being
compressed. This intermediate cooling effect causes compression
characteristics to approach isothermal compression, which reduces
work of the compressor 1. Preferably, all droplets introduced into
the compressor 1 vaporize completely in the airflow before a
discharge port of the compressor 1.
[0033] Part of the droplets jetted from the droplet spray nozzle 32
may not contribute to cooling of the mainstream air and may thus be
deposited as liquid film on different parts inside the compressor
1, forming drain.
[0034] Behavior of the droplets that do not contribute to cooling
of the mainstream air of the compressor 1 will here be described.
Part of the droplets sprayed by the droplet spray nozzle 32
collides with a wall surface of the air inlet plenum 33 to be
deposited as liquid film. When sprayed droplets interfere with each
other to form droplets with large particle diameters, such droplets
are not conveyed with the airflow and collide with the wall surface
to be deposited as liquid film. In addition, the droplets with
large particle diameters collide with a strut 58 and the IGV 55 at
the entrance of the compressor 1 with part thereof sticking to a
blade surface to form liquid film.
[0035] Part of the liquid film affixed to the blade surface is
split into secondary droplets with large particle diameters and the
secondary droplets flow into the inside of the compressor 1.
Droplets with large particle diameters collide with the rotor
blades 51, 57 inside the compressor 1, are blown outwardly in a
rotor radial direction by a centrifugal force of the rotor 52, and
are deposited as liquid film on the inner peripheral surface of a
casing 54.
[0036] Part of the liquid film on the inner peripheral surface of
the casing 54 partly vaporizes by thermal conduction of the casing
54 and is partly split into secondary droplets, flying toward a
downstream stage. The secondary droplets have large particle
diameters and thus are more likely to collide with downstream rotor
blades and stator vanes, forming liquid film.
[0037] The range over which the liquid film such as that described
above exists extends from the first stage of the axial compressor 1
to a stage in which droplets vaporize completely inside the
compressor (hereinafter, vaporization completion stage). The
inventors confirmed that the liquid film occurs particularly in
upstream to intermediate stages. Additionally, the mainstream
temperature in an area near the vaporization completion stage is
300.degree. C. or higher and droplets, should they collide with the
inner peripheral surface of the casing 54, are considered to
vaporize instantaneously.
[0038] A schematic structure of the variable stator vane 56 will be
described below with reference to FIG. 2. A plurality of variable
stator vanes 56, being spaced at predetermined interval, is
disposed circumferentially of the casing 54 in a particular stage
of the compressor 1 (the first-stage stator vane in the example
shown in FIG. 2).
[0039] The variable stator vane 56 includes a vane section 72, a
stem section 94, and a stator vane base 81. The stem section 94
having a substantially cylindrical shape assumes a rotational shaft
of the variable stator vane 56. The stator vane base 81 having a
substantially disc shape is disposed in the variable stator vane 56
so as to be disposed between the stem section 94 and the vane
section 72. The stator vane base 81 is disposed on, and to face,
the inner peripheral surface of the casing 54. The thin-plate lever
85 has a first end connected to the stem section 94 and a second
end connected rotatably to the control ring 91. It is noted that
FIG. 2 shows only part of a cross section of the control ring
91.
[0040] The control ring 91 is formed into an annular shape and
supported so that a central axis thereof coincides with a central
axis of the rotor 52. One example of supporting the control ring 91
is to have the control ring 91 in contact with the casing 54 at a
plurality of places (not shown). An actuator (not shown) is mounted
on the control ring 91. The actuator rotates the control ring 91
about the central axis of the rotor 52. When the actuator is
driven, the control ring 91 is rotated clockwise or
counterclockwise circumferentially about the rotor 52. Rotating the
control ring 91 circumferentially about the rotor 52 moves with the
control ring 91 the second end of the thin-plate lever 85 on the
side of the control ring 91 and causes the first end of the
thin-plate lever 85 to rotate the stem section 94. This results in
the angle of attack of the variable stator vane 56 being
varied.
[0041] A detailed structure of the variable stator vane 56 in the
compressor according to a first embodiment of the present invention
will be described below with reference to FIG. 3. In FIG. 3, the
variable stator vane 56 includes the vane section 72, the stator
vane base 81, the stem section 94, and a bolted stem section 89.
Preferably, the vane section 72, the stator vane base 81, the stem
section 94, and the bolted stem section 89 are integrally molded
using, for example, casting.
[0042] The stem section 94 has a cylindrical shape and is inserted
in a cylindrical through hole 73 formed radially relative to the
casing 54. The stem section 94 assumes a rotational shaft of the
variable stator vane 56. Rotating the stem section 94 about an
axial center thereof varies the angle of attack of the vane section
72.
[0043] In the example shown in FIG. 3, the stem section 94 is
inserted in the through hole 73 in the casing 54 after a thrust
washer 82 is inserted. The thrust washer 82 is disposed between the
stator vane base 81 and the inner peripheral surface of the casing
54. The thrust washer 82, having a low coefficient of friction and
offering wear resistance, can slide the variable stator vane 56 and
the casing 54 without requiring any lubrication.
[0044] A gap is formed between an outer periphery of the stem
section 94 inserted in the through hole 73 in the casing 54 and the
through hole 73 in the casing 54. Metal bushings 83 exhibiting
outstanding slidability requiring no lubrication are disposed on
both ends in the rotor radial direction in the gap so as to be
positioned on the outer periphery of the stem section 94. A tube 84
is inserted over the stem section 94 so as to be disposed between
the two metal bushings 83. The tube 84 supports the two metal
bushings 83. While the two metal bushings 83 are disposed in the
gap to surround the stem section 94 in the example shown in FIG. 3,
one metal bushing 83 may be disposed around the stem section
94.
[0045] The bolted stem section 89 is provided at an end portion
outside in the rotor radial direction in the stem section 94. The
bolted stem section 89 protrudes on the outside of the casing 54
when the stem section 94 is inserted in the through hole 73 in the
casing 54 and is inserted into a through hole (not shown) formed in
the thin-plate lever 85. The portion of the bolted stem section 89
protruding on the outside of the casing 54 has screw threads
thereon for engaging a nut 90. The bolted stem section 89 shown in
FIG. 3 has a diameter smaller than diameters of other parts of the
stem section 94.
[0046] In the example shown in FIG. 3, a disc spring 86, a lower
washer 88, the thin-plate lever 85, and an upper washer 87 are
inserted in sequence over the bolted stem section 89. Then, the nut
90 is finally threaded over the bolted stem section 89 to thereby
connect the stem section (the bolted stem section 89) to the
thin-plate lever 85. This causes the upper washer 87 and the lower
washer 88 to clamp the thin-plate lever 85 therebetween, thereby
connecting the stem section 94 to the thin-plate lever 85.
[0047] Referring to FIG. 3, the disc spring 86 is disposed between
the lower washer 88 and the casing 54 in the rotor radial
direction. The disc spring 86 functions as follows. When the
variable stator vane 56 is pushed down toward the inside in the
rotor radial direction by stiffness of the thin-plate lever 85
while the control ring 91 is rotating, the disc spring 86, with its
reaction, pushes up the variable stator vane 56 toward the outside
in the rotor radial direction. The disc spring 86 thereby prevents
the outer peripheral surface of the rotor 52 from interfering with
a top end (tip) of the variable stator vane 56.
[0048] The stator vane base 81 having a substantially disc shape
connects between the vane section 72 and the stem section 94. The
stator vane base 81 is housed in a casing groove 98 that is a
substantially disc-shaped recess (a countersunk hole) provided on
the inner peripheral surface of the casing 54. The casing groove 98
has a diameter greater than a diameter of the through hole 73 in
which the stem section 94 is inserted. The vane section 72
protrudes toward the inside in the rotor radial direction from a
surface of the stator vane base 81 on the inside in the rotor
radial direction. The stem section 94 protrudes toward the outside
in the rotor radial direction from a surface of the stator vane
base 81 on the outside in the rotor radial direction.
[0049] A sealing structure (sealing device) is provided between a
member slid relative to the casing 54 as the stem section 94
rotates (part of the variable stator vane 56 or elements associated
therewith; e.g. the stator vane base 81, the stem section 94, and
the washer 81) and a portion over which the casing 54 relatively
slides (a sliding portion). In the present embodiment, the sealing
structure is provided at a portion at which the thrust washer 82
slides relative to the casing 54. The sealing structure is provided
at a site in the casing 54 at which the surface of the thrust
washer 82 on the outside in the rotor radial direction faces. The
sealing structure includes a ring-shaped sealing groove 93 provided
in a bottom of the casing groove 98 in the casing 54 and a
ring-shaped sealing member 92 (e.g. an O-ring) housed in the
sealing groove 93. It is noted that the sealing groove 93 shown in
FIG. 3 is formed into a ring shape concentric with a central axis
of the stem section 94 and the casing groove 98 and has an outside
diameter smaller than a diameter of the casing groove 98.
[0050] Additionally, the variable stator vane 56 is pushed to the
outside in the rotor radial direction by the disc spring 86
disposed on the outer peripheral surface of the casing 54. Thus,
having the sealing structure on the outside in the rotor radial
direction of the thrust washer 82 as in the present embodiment
enables sealing performance to be improved.
[0051] The following describes a problem that can occur when the
droplet spray nozzle 32 supplies droplets into the inside of the
compressor 1 in a configuration having no sealing structures as
described above (the sealing groove 93 and the sealing member 92).
In this case, droplets having large particle diameters collide with
the rotor blade 51 inside the compressor 1 and are blown toward the
outside in the rotor radial direction by a centrifugal force
generated by the rotation of the rotor blade 51, thus forming
liquid film on the inner wall surface of the casing 54. Droplets
deposited on the inner wall surface of the casing 54 flow into a
gap between the casing groove 98 and the thrust washer 82, travel
along the gap between the through hole 73 in the casing 54 and the
stem section 94 past the metal bushings 83 and the like, and may be
discharged outside the casing 54 as drain.
[0052] The droplets flowing into the gap between the casing groove
98 and the thrust washer 82 are considered to come both from the
upstream and downstream sides on the basis of the flow of the
working fluid. It is nonetheless considered that the inflow of the
droplets (drain) from the downstream side is more noticeable than
that from the upstream side. This is because of the following
reason. Specifically, the flow through the stator vanes including
the variable stator vane 56 is decelerated to boost static
pressure, resulting in a tendency toward a greater difference
between pressure downstream of the stator vane and pressure outside
the casing 54 (atmospheric pressure).
[0053] In addition, the variable stator vane 56 is disposed to
extend throughout the entire circumference in the circumferential
direction of the casing 54. The droplets introduced into the
compressor 1 tend to be deposited on a lower half side of the
casing 54 by gravitational influence. Specifically, occurrence of
drain from the variable stator vane mechanism 56 on the lower half
side of the casing 54 is noticeable, so that degraded device
reliability can result due to drain deposited on the base of the
gas turbine during operation of the gas turbine. The "lower half
side of the casing 54", as used herein, refers to a lower-half
portion of the casing 54 when the casing 54 is split into two along
a horizontal plane passing through the central axis of the rotor
52, while an upper half side of the casing 54 is an upper-half
portion above the lower half side.
[0054] The drain arising from the droplets spayed from the droplet
spray nozzle not only degrades the device reliability of the gas
turbine. On a short-term perspective, the inflow of drain mixed
with dust into the sliding portion of the variable stator vane may
also reduce control accuracy of the variable stator vane as
affected by the dust. For example, a large difference in an opening
degree may be produced among different variable stator vanes
disposed in the rotor circumferential direction, resulting in
separation occurring in part of the stator vanes disposed on an
identical circumference. If this happens, separation of the stator
vane cascade in the upstream stage in a multistage axial compressor
greatly affects the stator vane cascade in the downstream stage,
causing efficiency to be reduced. In addition, partial separation
in the upstream stage degrades reliability of the compressor blade
due to an unsteady phenomenon of flow such as a rotating stall and
surging. On a long-term perspective, rust gathers as a result of
corrosion on the sliding portion of the variable stator vane, which
can degrade accuracy in the opening degree of the variable stator
vane. For example, in the variable stator vane or a transonic
airfoil profile, a difference of about .+-.5.degree. relative to a
design value of an incidence angle that represents a difference
between a vane inlet metal angle and an inflow angle substantially
doubles profile loss, which is highly likely to make noticeable the
separation on the blade surface. It is thus important in terms of
both performance and reliability to ensure that the incidence angle
is free of deviation from the design value.
[0055] As described above, when droplets are supplied into the
inside of the compressor, droplets that enter through the sliding
portion of the variable stator vane is discharged out of the casing
as drain, affecting performance and reliability of the compressor
and gas turbine. A certain amount of a working medium is considered
to escape from of the casing even with no droplets sprayed. Because
the variable stator vane is disposed in an upstream stage in the
compressor, the temperature of the working medium is low and only a
very small amount of air flows out, so that the effect on device
reliability in gas turbine operation is smaller than in drain
discharge. Additionally, the sliding portion of the variable stator
vane is unlikely to corrode, which eliminates the likelihood that
device reliability will be degraded.
[0056] To solve the foregoing problem, the embodiment of the
present invention provides the sealing structure comprising the
sealing groove 93 and the sealing member 92. Even when drain
arising from the droplet spraying is deposited on the inner wall
surface of the casing 54 in the variable stator vane 56, the
sealing structure thus configured prevents, through an effect of
the sealing member 92, entry of droplets in the gap between the
stem section 94 and the through hole 73. Leak of drain to the
outside of the casing 54 can thereby be prevented, so that device
reliability can be improved.
[0057] Coating with considerations given to sliding performance and
wear resistance has been applied to a surface of the thrust washer
82 on the inside in the rotor radial direction, specifically, the
surface adjacent to the stator vane base 81. A surface of the
thrust washer 82 on the outside in the rotor radial direction has
not been subjected to coating. Thus, the thrust washer 82 has a
larger contact area on its coated surface (the surface on the
inside). A comparison of an amount of drain leak (an amount of
drain leaking into the gap between the stem section 94 and the
through hole 73) made in the thrust washer 82 between the outside
surface and the inside surface in the rotor radial direction
suggests that a less amount of drain leaks to the inside surface
than to the outside surface. The present embodiment in which the
sealing structure is provided on the outside surface of the thrust
washer 82 therefore achieves a particularly noticeable drain leak
prevention effect.
[0058] The angle of attack of the variable stator vane 56 is
frequently changed by rotating the stem section 94 at such timing
as, for example, during starting of the gas turbine and partial
loading operation. Thus, sliding between the thrust washer 82 and
the sealing member 92 may cause the end face of the thrust washer
82 to wear, resulting in degraded sliding performance. However,
coating with considerations given to sliding performance and wear
resistance has been applied to the surface of the thrust washer 82
on the side adjacent to the stator vane base 81, but not to the
surface on the side of the inner peripheral surface of the casing.
The sealing member 92 disposed on the side of the thrust washer 82
adjacent to the inner peripheral surface side of the casing 54
therefore does not affect the coated surface of the thrust washer
82. This allows reliability of the thrust washer 82 to be
maintained and occurrence of drain to be prevented.
[0059] The sealing member 92 may be a metal seal. In addition, an
identical effect can be achieved by using a resin sealing member to
ensure sliding performance. In this case, however, the sealing
member needs to be replaced with a new one at regular intervals in
terms of long-term reliability of the sealing member. Because the
variable stator vane 56 is disposed in a stage upstream of the
compressor 1, the temperature of the working fluid remains low when
the droplets are not sprayed, which allows the resin sealing member
to be applied.
[0060] The following describes an effect from pressure of the
working medium inside the compressor 1. In general, the
above-described angle-of-attack variable mechanism is applied to
not only the stator vane on the front stage side (the variable
stator vane 56), but also the IGV 55. Unlike the stator vane as a
decelerating cascade, however, the IGV 55 is an accelerating
cascade that accelerates the flow to give the first-stage rotor
blade a swirl, causing negative pressure developing at the inlet
and outlet of the IGV 55. The rotor blade then gives kinetic energy
to the flow to thereby increase total pressure. The first-stage
stator vane downstream thereof then decelerates the flow to thereby
increase static pressure. As such, negative pressure develops in
areas near the IGV 55, so that, in contrast to the case with the
variable stator vane 56, a leak flow occurs from the outside of the
casing 54 toward the inside of the compressor 1 via the through
hole 73. If droplets are supplied into the inside of the compressor
1, this leak flow functions as sealing air against drain outflow,
which prevents drain from occurring. Specifically, there is no need
to install the sealing groove 93 and the sealing member 92 for
drain prevention on the inner peripheral surface of the casing 54
facing a thrust washer (not shown) of the IGV 55.
[0061] When droplets are supplied into the inside of the compressor
1, negative pressure may develop in areas upstream and downstream
of the first-stage stator vane depending of the amount of sprayed
droplets because of small stage loading in the front stage.
Understandably, in this case, there is no need to apply the sealing
groove 93 and the sealing member 92 on the inner peripheral surface
of the casing 54 facing the thrust washer 82 of the first-stage
stator vane. However, even in such a case, preferably, the sealing
groove 93 and the sealing member 92 are applied to a variable
stator vane cascade present downstream of the first-stage stator
vane, when the variable stator vane cascade causes the pressure of
the working fluid to become higher than the atmospheric pressure.
Application of the sealing groove 93 and the sealing member 92, as
described above, only to those portions near the inner peripheral
surface of the casing 54 at which pressure of the working medium is
higher than the atmospheric pressure allows the number of parts
used to be reduced and cost to be reduced. Moreover, the sealing
member needs replacement depending on its service life within a
maintenance period for the gas turbine. Thus, the reduction in the
number of parts used also achieves an effect of reduction in
maintenance cost.
[0062] As described earlier, the occurrence of droplets is
noticeable in the variable stator vane 56 on the lower half side of
the casing 54 by gravitational influence. This gives a good reason
to the adoption of a configuration in which the sealing groove 93
and the sealing member 92 are installed only on the variable stator
vane 56 provided on the lower half side of the casing 54 and none
of the sealing groove 93 and the sealing member 92 are installed on
the upper half side.
[0063] Additionally, various shapes such as an O-shape, a C-shape,
and an E-shape may be applied for the sealing member 92.
Application of the C-shape or E-shape by utilizing differential
pressure between the working medium and the outside of the casing
54 allows the sealing performance against outflow of the drain to
be improved.
[0064] With the IGV 55, the working medium has negative pressure. A
C-shaped or E-shaped sealing member may be applied to the IGV 55 by
utilizing differential pressure relative to the outside of the
casing 54. A leak flow into the inside of the compressor 1 from the
outside can thereby be prevented. This lessens an effect from the
leak flow on the flow inside the compressor 1, thereby improving
performance of the compressor 1.
[0065] A compressor according to a second embodiment of the present
invention will be described below with reference to FIG. 4. FIG. 4
is a cross-sectional view showing schematically a variable stator
vane structure in the compressor according to the second embodiment
of the present invention. Like or corresponding parts are
identified by the same reference numerals as those used for the
first embodiment of the present invention and descriptions for
those parts may be omitted. (The same holds for FIG. 5.)
[0066] The compressor according to the second embodiment differs
from the compressor according to the first embodiment shown in FIG.
3 in that a sealing structure is provided between a surface of the
thrust washer 82 on the inside in the rotor radial direction and a
surface of the stator vane base 81 on the outside in the rotor
radial direction. In the second embodiment of the present
invention, the stator vane base 81 has a ring-shaped sealing groove
93A formed in the surface thereof on the outside in the rotor
radial direction (the surface that faces the surface of the thrust
washer 82 on the inside in the rotor radial direction). The sealing
groove 93A has the rotational shaft of the stem section 94 as a
central axis thereof. In addition, the sealing member 92 capable of
preventing outflow of drain from a gap between the stator vane base
81 and the thrust washer 82 is disposed in the sealing groove
93A.
[0067] Having the sealing groove 93A in the stator vane base 81,
instead of the inner peripheral surface of the casing 54 as in the
first embodiment, is advantageous in machinability of the sealing
groove 93A. Specifically, to machine the sealing groove 93 in the
inner peripheral surface of the casing 54, the casing 54 is first
manufactured by casting and then the sealing groove 93 is cut in
the inner peripheral surface of the casing 54. The number of
variable stator vanes 56 in each stage amounts to several tens
(e.g. about 40 to 50) and machining the sealing grooves 93
throughout entire peripheries of the variable stator vanes takes a
considerable amount of time. In contrast, machining the sealing
groove 93A in the stator vane base 81 as in the second embodiment
involves machining of each individual stator vane. Specifically,
machining the sealing groove in the stator vane base 81 is easy.
This keeps the machining cost low.
[0068] The configuration in the second embodiment results in the
wear-resistant coating surface disposed on the side of the thrust
washer 82 adjacent to the stator vane base 81 being in contact with
the sealing member 92. This reduces the likelihood that the sealing
member 92 will be worn and damaged, so that a risk of occurrence of
drain can be reduced. The configuration also minimizes friction of
the sliding portion between the sealing member 92 and the thrust
washer 82, which allows accuracy in the opening degree of the
variable stator vane to be maintained.
[0069] The first and second embodiments have been described with
reference to FIGS. 3 and 4. The sealing groove 93 may still be
formed in both the stator vane base 81 and the inner peripheral
surface of the casing 54 so that the sealing member 92 can be
mounted in both the surface on the inside and the surface on the
outside in the rotor radial direction of the thrust washer 82.
[0070] In the first and second embodiments, the thrust washer 82 is
disposed between the stator vane base 81 and the inner peripheral
surface of the casing 54. Alternatively, the stator vane base 81
may be made to directly slide over the inner peripheral surface of
the casing 54 without having the thrust washer 82 interposed
therebetween and a sealing structure is formed by forming the
sealing groove 93 in, and mounting the sealing member 92 on, the
sliding portion.
[0071] In addition, the sealing structure according to the first
embodiment is preferably used as a sealing structure for the casing
54 on the upper half side thereof. The sealing structure according
to the second embodiment is preferably used as a sealing structure
for the casing 54 on the lower half side thereof. This is because,
under gravitational influence, a gap tends to be formed between the
casing 54 and the thrust washer 82 in the casing 54 on the upper
half side thereof and between the thrust washer 82 and the stator
vane base 81 in the casing 54 on the lower half side thereof.
[0072] A compressor according to a third embodiment of the present
invention will be described below with reference to FIG. 5. FIG. 5
is a cross-sectional view showing schematically a variable stator
vane structure in the compressor according to the third embodiment
of the present invention. The compressor according to the third
embodiment differs from the compressor according to the first
embodiment shown in FIG. 3 in that a sealing groove 93B and a
sealing member 92B are provided on the outside in the rotor radial
direction of, out of the two metal bushings 83 disposed so as to
sandwich the ring-shaped tube 84 therebetween, the metal bushing 83
disposed on the outside in the rotor radial direction.
[0073] The compressor shown in FIG. 5 is characterized by the
following. Specifically, the casing 54 has a counterbored groove
(recess) 101 formed by counterboring a disc concentric with the
central axis of the stem section 94 in the outer peripheral surface
of the casing 54. A ring-shaped flange portion 96 having a hole in
which the stem section 94 is inserted as a center thereof is fitted
in the counterbored groove 101. The flange portion 96 has the
sealing groove 93B that assumes a ring-shaped counterbored groove
formed around the hole therein. The sealing member 92B having a
ring shape is housed in the sealing groove 93B and contacts the
stem section 94. The flange portion 96 is fastened to the casing 54
with a plurality of bolts 102. The counterbored groove 101 is
formed so as to be disposed around the stem section 94 in the outer
peripheral surface of the casing 54. The sealing groove 93B is
disposed at a portion at which the flange portion 96 slides
relative to the stem section 94.
[0074] When the sealing member 92 is to be replaced with a new one
in the compressor shown in FIG. 3 or 4, access to the sealing
member 92 can only be gained after the variable stator vane 56 or
56A is removed from the inner peripheral side of the casing 54,
which makes it necessary to disassemble the casing 54. As a result,
the sealing member 92 is replaced only at a periodic inspection of
the gas turbine. The configuration according to the third
embodiment, however, enables the sealing member 92B to be removed
from the outside of the casing 54. Thus, when the sealing member
92B is worn and damaged, the sealing member 92B can be replaced
with a new one without having to disassemble the casing 54. This
improves maintainability.
[0075] Each of the first to third embodiments of the present
invention described heretofore can prevent leakage of droplets
occurring from the sliding portion of the variable stator vane in
the axial compressor that has the intermediate cooling effect from
spraying of the droplets over the intake air and thus can provide
an axial compressor offering reliability.
[0076] The first to third embodiments described heretofore
introduce a total of three sealing structures. The sealing
structure may nonetheless be provided at any place other than the
above three as long as the places assume a member relatively slid
over the casing 54 during rotation of the stem section 94 and a
sliding portion relative to the casing 54. Specifically, for
example, a sealing structure may be formed by a ring-shaped sealing
groove formed in an outer periphery of the stem section 94 and a
sealing member housed in the sealing groove.
[0077] Each of the first to third embodiments of the present
invention has been exemplified by an axial compressor for a gas
turbine that uses inlet air spraying. The present invention is
nonetheless widely applicable to axial compressors for industrial
use.
[0078] In an axial compressor not performing inlet air spraying,
the variable stator vane is generally incorporated on the upstream
stage side of the compressor in which the operating temperature
remains low. The working fluid that leaks from the variable stator
vane mechanism to the outside of the casing is therefore considered
to be low in temperature and small in quantity and thus not to
affect device reliability. Use of the sealing structure according
to the embodiments of the present invention in the compressor of
this type can, however, prevent leakage of the working fluid from
the inside of the compressor to the outside, so that compressor
efficiency is likely to be increased.
[0079] It should be noted that the present invention is not limited
to the above-described preferred embodiments and various changes
may be made without departing from the true spirit and scope of the
invention. For example, the entire detailed arrangement of the
embodiments described above is not always necessary to embody the
present invention. Part of the arrangement of one embodiment may be
replaced with the arrangement of another embodiment, or the
arrangement of one embodiment may be combined with the arrangement
of another embodiment. The arrangement of each embodiment may
additionally include another arrangement, or part of the
arrangement may be deleted or replaced with another.
* * * * *