U.S. patent application number 12/534407 was filed with the patent office on 2010-02-11 for centrifugal compressor.
This patent application is currently assigned to HITACHI PLANT TECHNOLOGIES, LTD.. Invention is credited to Tetsuya KUWANO, Yohei MAGARA, Haruo MIURA, Naohiko TAKAHASHI, Kazuyuki YAMAGUCHI.
Application Number | 20100034646 12/534407 |
Document ID | / |
Family ID | 41137382 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100034646 |
Kind Code |
A1 |
MAGARA; Yohei ; et
al. |
February 11, 2010 |
CENTRIFUGAL COMPRESSOR
Abstract
The present invention provides a centrifugal compressor that
inhibits possible leakage while reducing a destabilizing fluid
force generated in a seal to prevent the possible instable
vibration of a rotor. The centrifugal compressor includes a casing,
a rotor rotatably installed in the casing and having an impeller,
and seals provided in the clearance between the casing and the
rotor to prevent a fluid from leaking through the clearance from a
high pressure side to a low pressure side. The rotor rotates to
compress gas. For example, the balance piston seal is composed of a
damper seal with a plurality of holes and a labyrinth seal with an
annular parallel groove; the damper seal and the labyrinth seal are
continuously provided. The damper seal is disposed on the high
pressure side in a leakage flow direction. The labyrinth seal is
disposed on the low pressure side in the leakage flow
direction.
Inventors: |
MAGARA; Yohei; (Mito,
JP) ; YAMAGUCHI; Kazuyuki; (Kasumigaura, JP) ;
KUWANO; Tetsuya; (Tsuchiura, JP) ; MIURA; Haruo;
(Kasumigaura, JP) ; TAKAHASHI; Naohiko;
(Tsuchiura, JP) |
Correspondence
Address: |
MATTINGLY & MALUR, P.C.
1800 DIAGONAL ROAD, SUITE 370
ALEXANDRIA
VA
22314
US
|
Assignee: |
HITACHI PLANT TECHNOLOGIES,
LTD.
Tokyo
JP
|
Family ID: |
41137382 |
Appl. No.: |
12/534407 |
Filed: |
August 3, 2009 |
Current U.S.
Class: |
415/173.5 ;
415/173.1 |
Current CPC
Class: |
F04D 29/102 20130101;
F16J 15/4472 20130101; F04D 29/0516 20130101 |
Class at
Publication: |
415/173.5 ;
415/173.1 |
International
Class: |
F04D 29/08 20060101
F04D029/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2008 |
JP |
2008-204570 |
Claims
1. A centrifugal compressor comprising a casing, a rotor comprising
a rotating shaft rotatably installed in said casing and an impeller
installed on said rotating shaft, and a seal preventing a fluid
from leaking between said casing and said rotor from a high
pressure side to a low pressure side, wherein said seal has a
damper seal with a plurality of cavity formed on a seal surface and
a labyrinth seal with a plurality of annular grooves.
2. The centrifugal compressor according to claim 1, wherein said
labyrinth seal is provided juxtaposed to said damper seal.
3. The centrifugal compressor according to claim 2, wherein said
damper seal is disposed on a high pressure side in a leakage flow
of said seal, and said labyrinth seal is disposed on a low pressure
side in the leakage flow of said seal.
4. The centrifugal compressor according to claim 3, wherein a
length of said damper seal in a leakage flow direction is set to at
most half of that of said seal.
5. The centrifugal compressor according to claim 4, wherein a
length of said damper seal in a leakage flow direction is set to or
larger than a length of said seal multiplied by 0.05.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a seal structure for a
centrifugal compressor, and is suitable particularly for preventing
unstable vibration of a rotor during a high-speed, high-pressure
operation.
[0002] Centrifugal compressors compressing gas such as air are
widely utilized for various machines. Inside of a casing of a
centrifugal compressor, a rotating shaft with an impeller installed
thereon is rotatably supported by bearings. Gas sucked through a
suction port is compressed by rotation of the impeller and
discharged through a discharge port. The gas compressed by the
impeller is sealed by an impeller eye seal of an impeller eye, an
inter-stage seal between stages of the impeller, and a balance
piston seal provided in a last stage.
[0003] A labyrinth seal and a damper seal are known as conventional
seal structures. As shown in a sectional view of any impeller stage
in a centrifugal compressor in FIG. 1 of JP Published Patent
Application No. 6-249186, the labyrinth seal structure has a large
number of annular fins in the clearance between a rotor and a
stator. Thus, a pressure loss in a fluid flowing through the top
clearance between the fins and the rotor reduces the leakage of the
fluid.
[0004] The damper seal has a seal structure with a plurality of
holes formed in a seal stator surface and is classified into a hole
pattern seal, a honeycomb seal, and the like. The hole pattern seal
structure has a large number of holes in the seal stator surface as
shown in JP Published Patent Application No. 6-249186, for example.
Thus, a pressure loss in a fluid flowing through the clearance
between the uneven seal stator surface and the rotor reduces the
leakage of the fluid. Furthermore, the honeycomb seal is disclosed
in, for example, JP Published Patent Application Nos. 11-44201 and
2007-113458. In particular, FIG. 1(b) of JP Published Patent
Application No. 11-44201 clearly shows a honeycomb seal structure.
The seal stator surface shown in FIG. 1(b) has a honeycomb
structure with a large number of hexagonal shaped holes. Thus, a
pressure loss in a fluid flowing by the uneven seal stator surface
reduces the leakage of the fluid.
[0005] In the above-described seals, when the shaft is displaced in
a radial direction with the leakage flow velocity of the seal
having a circumferential component, the circumferential pressure
distribution in the seal becomes asymmetrical. This results in a
fluid force (hereinafter referred to as a "destabilizing fluid
force) destabilizing the rotor. In the worst case, the
destabilizing fluid force causes the rotor to vibrate unstably. In
particular, if the rotor rotates at high speed or there is a high
differential pressure between the seal inlet and outlet, the
destabilizing fluid force is increased. As is well known, if the
damper seal such as the hole pattern seal or the honeycomb seal is
used instead of the labyrinth seal, the unstable vibration of the
rotor caused by the destabilizing fluid force can be stabilized
because the damper seal exerts a higher damping effect than the
labyrinth seal.
[0006] The labyrinth seal is excellent in the leakage prevention
property. However, the increased discharge pressure of the
centrifugal compressor increases the destabilizing fluid force,
thus reducing the vibration stability of the rotor. The damper seal
exerts a higher damping effect than the labyrinth seal, thus
stabilizing the vibration of the rotor. However, the damper seal is
inferior in the leakage prevention property, thus reducing the
efficiency of the compressor.
BRIEF SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a
centrifugal compressor that can be stably operated under a
high-speed and high-pressure condition, with possible leakage from
a seal prevented.
[0008] To accomplish the object, the present invention provides a
centrifugal compressor comprising a casing, a rotor comprising a
rotating shaft rotatably installed in the casing and an impeller
installed on the rotating shaft, and a seal preventing a fluid from
flowing between a stator and the rotor in the casing from a high
pressure side to a low pressure side, the impeller rotating to
compress gas, wherein in the seal, a damper seal with a plurality
of holes and a labyrinth seal with an annular parallel groove are
continuously provided on a stator surface.
[0009] Furthermore, preferably, in the seal, the damper seal is
disposed on the high pressure side in a leakage flow direction of
the seal, and the labyrinth seal is disposed on a low pressure side
in the leakage flow direction of the seal.
[0010] Furthermore, preferably, in the seal, length of the damper
seal in the leakage flow direction is set to at most half of that
of the entire seal.
[0011] Furthermore, preferably, in the seal, the length of the
damper seal in the leakage flow direction is set equal to or larger
than the length of the entire seal multiplied by 0.05.
[0012] According to the present invention, the damper seal and the
labyrinth seal are continuously provided. Thus, the labyrinth seal
can inhibit possible leakage, while the damper seal can stabilize
the rotor. Moreover, the damper seal is disposed on the high
pressure side of the seal, whereas the labyrinth seal is disposed
on the low pressure side. Thus, on the high pressure side, where a
relatively strong destabilizing fluid force may be generated, the
damper seal can exert a damping effect. Furthermore, on the high
pressure side, corresponding to a leakage flow upstream side, the
circumferential component of the leakage flow velocity can be
reduced. This enables the rotor to be further stabilized.
Additionally, the length of the damper seal in the leakage flow
direction is set to at most half of that of the entire seal. This
allows the rotor to be effectively stabilized, with possible
leakage from the seal inhibited.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0013] FIG. 1 is a perspective view showing, in detail, the
structure of a stator side of a balance piston seal according to an
embodiment of a centrifugal compressor according to the present
invention;
[0014] FIG. 2 is a sectional view showing the general structure of
an embodiment of the centrifugal compressor according to the
present invention;
[0015] FIG. 3 is an enlarged partially sectional view showing the
inside of an area A in FIG. 2;
[0016] FIG. 4 is a diagram showing the relationship between a seal
structure ratio (the rate of the entire seal length accounted for
by the length of a hole pattern seal) and a seal instability
indicator according to the embodiment of the centrifugal compressor
according to the present invention;
[0017] FIG. 5 is a diagram showing the relationship between the
rate of the entire seal length accounted for by the length of the
hole pattern seal and the leakage flow rate of the entire seal
according to the embodiment of the centrifugal compressor according
to the present invention; and
[0018] FIG. 6 is a sectional perspective view showing a variation
of the structure of the stator side of the balance piston seal
according to the embodiment of the centrifugal compressor according
to the present invention;
DETAILED DESCRIPTION OF THE INVENTION
[0019] An embodiment of the present invention will be described
below with reference to the drawings.
[0020] FIG. 1 is a perspective view showing, in detail, the
structure of a balance piston seal 14 in an embodiment of a
centrifugal compressor 20 according to the present invention. An
illustrated damper seal is a hole pattern seal 15 made up of a
large number of holes 16. FIG. 2 shows the general structure of a
centrifugal compressor 20 according to the present invention. FIG.
3 is a diagram showing an area A in FIG. 2.
[0021] In FIG. 2, the centrifugal compressor 20 includes a casing 1
(stationary member), a rotating shaft 2 rotatably provided in the
casing 1, and a rotor 4 having a multi-stage (in FIG. 2,
seven-stage) impeller 3 installed on the rotating shaft 2. The
casing 1 includes a suction channel 5 through which gas is
introduced into a first stage of the impeller 3, a diffuser 6 that
converts kinetic energy from each stage of the impeller 3 into
pressure energy, a return channel 7 through which compressed gas
from the diffuser 6 is introduced into the following stage of the
impeller 3, and a discharge channel 8 through which gas from the
final stage of the impeller 3 is discharged.
[0022] The rotating shaft 2 of the rotor 4 is rotatably supported
by radial bearings 9 provided at a suction-side (the left side of
FIG. 2) end and a discharge-side (the right side of FIG. 2) end. A
thrust bearing 10 is also provided at the suction-side end of the
rotating shaft 2 to receive a thrust load. A balance piston 11 is
provided at the discharge-side end to offset the thrust load.
Additionally, a driver such as a motor (not shown in the drawings)
is coupled to the discharge-side end of the rotating shaft 2. The
driver drives the rotor 4, which is thus rotated. The rotation of
the rotor 4 allows gas to be sucked through the suction channel 5,
sequentially compressed by the multi-stage impeller 3, and finally
discharged through the discharge channel 8.
[0023] An impeller eye seal 12 is provided in the clearance between
each stage of the impeller 3 and the impeller eye 21. The impeller
eye seal 12 inhibits gas from the impeller 3 from passing through
the clearance and back to the inlet of the impeller 3 (see FIG. 3).
Furthermore, an inter-stage seal 13 is provided between each stage
of the impeller 3 and the succeeding stage of the impeller 3 in the
clearance between the inter-stage 22 of the rotor 4 and the casing
1. The inter-stage seal 13 inhibits gas from the return channel 7
from passing through the clearance and back to the outlet of the
preceding stage of the impeller 3. Additionally, as shown in FIG.
3, a balance piston seal 14 is provided in the clearance between
the balance piston 11 of the rotor 4 and the casing 1. The balance
piston seal 14 inhibits high-pressure gas from the final stage of
the impeller 3 from leaking to a low pressure portion.
[0024] The balance piston seal 14 is composed of two parts shaped
like the two halves of a cylinder. FIG. 1 shows one of the halves.
In FIG. 1, the balance piston seal 14 has a hole pattern seal 15
located on a stator surface opposite to the balance piston 11 and
on a high pressure side of a leakage flow direction and composed of
a plurality of holes 16, and a labyrinth seal 17 located on a low
pressure side of the leakage flow direction and composed of annular
parallel fins 18 and annular parallel grooves 19. The length of the
hole pattern seal 15 in the leakage flow direction is defined as
Lh. The length of the labyrinth seal 17 in the leakage flow
direction is defined as Ll.
[0025] FIG. 4 is a diagram showing an example of the relationship
between the rate of the length of the hole pattern seal 15 in the
leakage flow direction accounted for by the entire seal length in
the leakage flow direction (the rate is hereinafter referred to as
a seal structure ratio) and a seal instability indicator. The seal
structure ratio is calculated to be Lh/(Lh+Ll) where Lh denotes the
length of hole pattern seal 15 and Ll denotes the length of the
labyrinth seal. The seal instability indicator is calculated to be
Kxy/(Cxx..omega.) that is the ratio of the stiffness coefficient
Kxy of the seal obtained by dividing the destabilizing fluid force
by the radial displacement of the rotating shaft 2 to the product
of the damping coefficient Cxx of the seal for the radial
displacement and the eigen angular frequency .omega. of the rotor
4. A decrease in seal instability indicator improves the stability
of the rotor. FIG. 4 shows that a seal structure ratio of higher
than 0.5 allows the hole pattern seal to exert almost constant
stabilizing effect. Furthermore, a seal structure ratio close to
0.0 rapidly increases the seal instability indicator. Thus, to
ensure the stability of the seal, the seal instability indicator
needs to be kept at 0.6 or less. Desirably, the seal structure
ratio is correspondingly kept at about 0.05 or more.
[0026] FIG. 5 is a diagram showing an example of the relationship
between the seal structure ratio and the leakage flow rate ratio of
the entire seal observed when the entire seal length is constant.
The leakage flow rate ratio is the leakage flow rate expressed in
terms of ratio where the leakage flow rate is set to 1 when the
seal structure ratio is 0. The leakage flow rate increases
consistently with the seal structure ratio, that is, with the rate
of the hole pattern seal. FIGS. 3 and 4 show that the seal
structure ratio may be set to at most 0.5 in order to improve the
stability of the rotor while inhibiting a possible increase in
leakage flow rate.
[0027] At the same seal length, the above-described structure
enables a reduction in leakage flow rate compared to a structure in
which the balance piston seal 14 is entirely composed of the hole
pattern seal 15. Moreover, a stronger destabilizing fluid force is
generated on the high pressure side of the seal. However, in the
present embodiment, the hole pattern seal 15, exerting the damping
effect, is disposed on the high pressure side. This improves the
stability of the rotor. Furthermore, the hole pattern seal 15
disposed on the high pressure side, corresponding to the upstream
side of the leakage flow, enables a reduction in the
circumferential component of the velocity of the leakage flow
toward the labyrinth seal 17, located on the low pressure side,
that is, the downstream side. Thus, the destabilizing fluid force
in the labyrinth seal 17 can be reduced, allowing the possible
unstable vibration of the rotor 4 to be inhibited.
[0028] In the example described in the embodiment, the hole pattern
seal 15 with the circular holes 16 formed therein at equal
intervals is disposed on the high pressure side of the balance
piston seal 14 as a damper seal. However, the present invention is
not limited to this aspect. For example, the damper seal may be a
honeycomb seal composed of hexagonal shaped holes or a seal
composed of triangular or rectangular shaped holes.
[0029] Furthermore, as shown in FIG. 1, the present invention is
not limited to the pattern in which the holes 16 are closely
arranged at equal intervals. For example, as shown in FIG. 6, the
seal may have a portion in which no hole 16 is provided in part of
the axial direction. Moreover, the intervals of the holes may be
varied in the circumferential direction.
[0030] Additionally, in the above-described example, the hole
pattern seal 15 and the labyrinth seal 17 are composed of the
continuous parts. However, the present invention is not limited to
this aspect. For example, the hole pattern seal 15 and the
labyrinth seal 17 may be made of separate parts, which may then be
combined together.
[0031] The balance piston seal 14 has been described by way of
example. However, similar effects can be exerted by applying the
present invention to the impeller eye seal 12 and the inter-stage
seal 13.
* * * * *