U.S. patent application number 11/631335 was filed with the patent office on 2008-10-23 for turbine nozzle support device and steam turbine.
This patent application is currently assigned to Kabushiki Kaiisha Toshiba. Invention is credited to Hiroshi Kawakami.
Application Number | 20080260529 11/631335 |
Document ID | / |
Family ID | 35782719 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080260529 |
Kind Code |
A1 |
Kawakami; Hiroshi |
October 23, 2008 |
Turbine Nozzle Support Device and Steam Turbine
Abstract
A steam turbine includes a turbine casing, a turbine rotor
disposed in the turbine casing, a plurality of turbine stages, a
cylinder substantially coaxial with the turbine casing, and a
fixing partition plate having an outer edge fixed to the turbine
casing and an inner edge fixed to an outer circumferential portion
of the cylinder. In a turbine nozzle support holder of such the
steam turbine, the turbine stages each includes turbine movable
blades disposed circumferentially around the turbine rotor and
turbine nozzles paired with the turbine movable blades and disposed
upstream of the turbine movable blades. The turbine nozzles of the
turbine stages are arranged inside the cylinder in an axial
direction and are engaged with and fixed to the cylinder. The
fixing partition plate is disposed downstream of the center of the
cylinder in the axial direction to separate an upstream atmosphere
and a downstream atmosphere.
Inventors: |
Kawakami; Hiroshi;
(Kanagawa-Ken, JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
Kabushiki Kaiisha Toshiba
|
Family ID: |
35782719 |
Appl. No.: |
11/631335 |
Filed: |
June 29, 2005 |
PCT Filed: |
June 29, 2005 |
PCT NO: |
PCT/JP05/11908 |
371 Date: |
April 8, 2008 |
Current U.S.
Class: |
415/209.3 |
Current CPC
Class: |
F01D 25/246 20130101;
F01D 25/24 20130101; F01D 25/26 20130101; F05D 2220/31 20130101;
F01D 11/025 20130101; F01D 9/02 20130101; F05D 2230/642
20130101 |
Class at
Publication: |
415/209.3 |
International
Class: |
F04D 29/54 20060101
F04D029/54 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2004 |
JP |
2004-192692 |
Claims
1. A turbine nozzle holder for a steam turbine which comprises: a
turbine casing; a turbine rotor disposed in the turbine casing; a
plurality of turbine stages, each including turbine movable blades
disposed circumferentially around the turbine rotor and turbine
nozzles paired with the turbine movable blades and disposed on an
upstream side of the turbine movable blades; a cylinder
substantially coaxial with the turbine casing, the turbine nozzles
of the turbine stages being arranged inside the cylinder in an
axial direction and being engaged with and fixed to the cylinder;
and a fixing partition plate having an outer edge fixed to the
turbine casing and an inner edge fixed to an outer circumferential
portion of the cylinder, wherein the fixing partition plate is
disposed on a downstream side of the center of the cylinder in the
axial direction in a manner such that one fixing partition plate is
provided for one cylinder so as to separate an upstream atmosphere
and a downstream atmosphere with respect to the fixing partition
plate.
2. The turbine nozzle holder according to claim 1, wherein the
cylinder is separated in two portions in the axial direction.
3. The turbine nozzle holder according to claim 1, wherein the
cylinder is separated in two portions in the axial direction, and
the turbine nozzle holder further includes joint flanges disposed
along opposing separate surfaces and fastening bolts fastening the
joint flanges.
4. The turbine nozzle holder according to claim 3, further
comprising dummy flanges protruding from the outer circumferential
portion of the cylinder in addition to the joint flanges disposed
along the separate surfaces.
5. The turbine nozzle holder according to claim 4, wherein the
dummy flanges are regularly arranged between the two joint flanges
disposed on the cylinder.
6. The turbine nozzle holder according to claim 5, wherein the
dummy flanges are regularly arranged at intervals of 45.degree.
between the two joint flanges disposed on the cylinder.
7. The turbine nozzle holder according to claim 5, wherein the
dummy flanges are regularly arranged at intervals of 60.degree.
between the two joint flanges disposed on the cylinder.
8. The turbine nozzle holder according to claim 4, wherein the
dummy flanges have substantially the same shape as that of the
joint flanges.
9. The turbine nozzle holder according to claim 8, wherein the
cylinder has a cross-sectional shape symmetrical with respect to
the axis thereof.
10. A steam turbine comprising: a turbine casing; a turbine rotor
disposed in the turbine casing; a plurality of turbine stages, each
including turbine movable blades disposed circumferentially around
the turbine rotor and turbine nozzles paired with the turbine
movable blades and disposed upstream of the turbine movable blades;
a cylinder substantially coaxial with the turbine casing, the
turbine nozzles of the turbine stages being arranged inside the
cylinder in an axial direction and being engaged with and fixed to
the cylinder; and a fixing partition plate having an outer edge
fixed to the turbine casing and an inner edge fixed to an outer
circumferential portion of the cylinder, the fixing partition plate
being disposed downstream of the center of the cylinder in the
axial direction in a manner such that one fixing partition plate is
provided for one cylinder so as to separate an upstream atmosphere
and a downstream atmosphere with respect to the fixing partition
plate.
Description
TECHNICAL FIELD
[0001] The present invention relates to a turbine nozzle
(stationary blade) holder for a steam turbine and a steam turbine
which include the holder, and particularly relates to a turbine
nozzle holder having a structure for supporting the turbine nozzle
and fixing a turbine casing.
BACKGROUND ART
[0002] A steam turbine has turbine stages, each including turbine
movable blades (turbine buckets) and turbine nozzles (stationary
blades) paired with the turbine movable blades. The turbine movable
blades are disposed circumferentially around a turbine rotor
(rotating shaft) inside a turbine casing. The turbine nozzles are
disposed upstream of the turbine movable blades in the
circumferential direction of the turbine rotor.
[0003] The turbine nozzles (stationary blades) are held between
inner and outer nozzle diaphragm rings. The outer nozzle diaphragm
ring is supported by the turbine casing so as to fix the turbine
nozzles inside the casing.
[0004] In addition, a support structure is used in which turbine
nozzles of turbine pressure stages are supported by a single
holder, called a turbine nozzle holder, which is supported by a
turbine casing.
[0005] An example of a known turbine nozzle holder will be
described hereunder with reference to FIG. 11.
[0006] FIG. 11 is a sectional view of the upper half part of the
known turbine nozzle holder. In FIG. 11, a turbine nozzle holder 57
includes a cylinder 56 extending axially substantially in parallel
with a turbine rotor 52 and a support flange 58 engaged with a
turbine casing 51 to support the cylinder 56. An outer nozzle
diaphragm ring, not shown, is engaged with grooves provided in an
inner surface of the cylinder 56. The number of grooves corresponds
to the number of nozzle plates 53 supported (four grooves in the
example of FIG. 11). The cylinder 56 has a separate structure
including two semicylindrical portions for ease of assembly. These
semicylindrical portions are mechanically joined at joint portions,
such as flanges, disposed along separate surfaces by means of
bolts, for example.
[0007] The turbine nozzle holder 57 having the structure described
above is engaged and supported at a relatively upstream position on
the turbine casing 51 for easy assembling, for example, for easy
positioning of the support flange 58 and the turbine casing 51.
[0008] A high-temperature, high-pressure steam passing through
pressure stages 55 in the turbine nozzle holder 57 feeds a torque
to movable blades 54 and flows toward the downstream side while
decreasing in pressure and temperature. The upstream side of a
space defined between the turbine casing 51 and the turbine nozzle
holder 57 (outside the cylinder 56) is filled with the
high-pressure steam to be supplied to the turbine stages while the
downstream side of the space is filled with the low-pressure steam
that has lost its pressure after passing through all stages. The
support flange 58 also serves as a pressure barrier to prevent
communication between the steams with different pressures.
[0009] FIG. 12 shows pressure distribution inside and outside the
turbine nozzle holder 57 and on the front and rear sides of the
support flange 58. A curve indicated by the dotted line P1
represents the pressure distribution of the steam passing through
the pressure stages inside the turbine nozzle holder 57. This curve
shows that the pressure decreases gradually as the steam passes
through the pressure stages. The solid line P2a represents the
pressure of an atmosphere 59 upstream of the support flange 58,
which also serves as a pressure barrier. The solid line P2b
represents the pressure of an atmosphere 60 downstream of the
support flange 58. The hatched parts (areas) represent pressures
applied to the turbine nozzle holder 57 (cylinder 56) as a result
of a pressure difference between the inside and outside of the
turbine nozzle holder 57. In the hatched area A1, the pressure
outside the cylinder 56 is larger than the pressure inside the
cylinder 56, and thus, the cylinder 56 receives an external
pressure. In the hatched area A2, on the other hand, the pressure
inside the cylinder 56 is larger than the pressure outside the
cylinder 56, and thus, the cylinder 56 receives an internal
pressure. In this case, the turbine nozzle holder 57 is required to
support a net internal pressure because the hatched area A2 is much
larger than the hatched area A1.
[0010] An example of a steam turbine includes a turbine nozzle
holder supported on a casing by a pressure difference between the
upstream and downstream sides of the turbine nozzle holder (for
example, see Japanese Unexamined Patent Application Publication No.
10-103009). According to this publication, the turbine nozzle
holder is supported by fitting or engaging a rib protruding from an
inner surface of the turbine casing to a groove provided on an
outer circumferential portion of the turbine nozzle holder. A side
surface of the groove of the turbine nozzle holder is pressed
against and fixed to a side surface of the rib of the turbine
casing by a thrust force resulting from a pressure difference
between the front and rear sides of the rib.
[0011] With reference to FIG. 11, the turbine nozzle holder 57,
specifically, the cylinder 56, involves several matters to be
solved, including leakage of steam passing through the cylinder
(i.e., through the stages).
[0012] As described above, the turbine nozzle holder 57 (cylinder
56) constantly supports an internal pressure. This pressure is
generally supported by the fastening bolts attached to the joint
portions point flanges) provided along the joint surfaces of the
cylinder 56, which has a separate structure. During the operation
of the steam turbine, the temperature of the fastening bolts
reaches substantially the same temperature as that of the steam
passing through the turbine stages. For the latest models of steam
turbines, the steam temperature (entrance temperature) reaches
about 600.degree. C. After extended operation, therefore, the
fastening bolts undergo gradual creep deformation. Such fastening
bolts fail to maintain the initial fastening force and thus cause
steam leakage.
[0013] In addition, the turbine nozzle holder 57 becomes longer in
the axial direction if the number of the turbine nozzles 53
supported by the turbine nozzle holder 57 is increased. In that
case, a uniform fastening force is difficult to achieve over the
entire joint surfaces of the cylinder 56 because of complicated
factors, including the creep deformation of the fastening bolts,
the thermal expansion and the deformation of the turbine nozzle
holder 57 due to the temperature distribution thereof, the pressure
distribution of the steam passing through the turbine stages 55,
and the number of fastening bolts. As a result, the turbine nozzle
holder 57 cannot avoid slight steam leakage.
[0014] One of the possible measures to avoid such leakage is to
increase the diameter of the fastening bolts or the area of the
joint portions joint flanges) of the cylinder 56. Such measures,
however, contribute to an increase in the size of the turbine
nozzle holder 57 and thus to an increase in the volume of the
turbine casing 51. This undesirably causes problems such as
increases in the cost and installation area of the steam
turbine.
[0015] Furthermore, many fastening bolts are firmly fixed only to
the joint portions joint flanges) of the cylinder 56, and thus, for
example, deformation due to internal pressure and thermal expansion
can be concentrated in the portions of the cylinder 56 other than
the joint portions, that is, in less rigid portions. Such uneven
deformation varies, for example, gaps between seal fins provided on
a ground portion of the turbine casing 51, gaps between seal fins
provided between the turbine nozzles 53 and the turbine rotor 52,
and gaps between seal fins provided between the leading ends of the
turbine movable blades 54 and the turbine nozzle holder 57. If the
gaps are narrowed, rubbing (contact) occurs and the operation must
be stopped. If, on the other hand, the gaps are widened, steam
leakage occurs more significantly and the internal efficiency of
the turbine decreases.
[0016] As described above, steam leakage due to the deformation of
a turbine nozzle holder decreases the internal efficiency of the
turbine. On the other hand, the above measures for preventing the
steam leakage involve an increase in the size of the fastening
bolts and cause a problem such as an increase in the size of a
turbine casing engaged with the turbine nozzle holder.
DISCLOSURE OF THE INVENTION
[0017] An object of the present invention is to eliminate the
defects of the known art described above by providing a turbine
nozzle holder having joint portions (joint flanges) closely
fastened without depending on the fastening force of fastening
bolts to reduce steam leakage and achieve uniform rigidity in a
circumferential direction and by providing a steam turbine
including the holder.
[0018] To achieve the above object, a turbine nozzle holder for a
steam turbine according to the present invention which includes a
turbine casing, a turbine rotor disposed in the turbine casing, a
plurality of turbine stages, a cylinder substantially coaxial with
the turbine casing, and a fixing partition plate having an outer
edge fixed to the turbine casing and an inner edge fixed to an
outer circumferential portion of the cylinder, wherein the turbine
stages each includes turbine movable blades disposed
circumferentially around the turbine rotor and turbine nozzles
paired with the turbine movable blades and disposed upstream of the
turbine movable blades. The turbine nozzles of the turbine stages
are arranged inside the cylinder in an axial direction and are
engaged with and fixed to the cylinder. The fixing partition is
disposed downstream of the center of the cylinder in the axial
direction to separate an upstream atmosphere and a downstream
atmosphere with respect to the partition plate.
[0019] In the turbine nozzle holder for a steam turbine, the
cylinder may be separated in two portions in the axial direction,
and the turbine nozzle holder further includes joint flanges
disposed along opposing separate surfaces and fastening bolts
fastening the joint flanges.
[0020] The turbine nozzle holder may further include dummy flanges
protruding from the outer circumferential portion of the cylinder
in addition to the joint flanges disposed along the separate
surfaces.
[0021] The dummy flanges may be preferably regularly arranged
between the two joint flanges disposed on the cylinder. In
particular, the dummy flanges are preferably regularly arranged at
intervals of 45.degree. or 60.degree. between the two joint flanges
disposed on the cylinder.
[0022] The dummy flanges preferably have substantially the same
shape as the joint flanges.
[0023] The cylinder preferably may have a cross-sectional shape
symmetrical with respect to the axis thereof.
[0024] To achieve the above object, additionally, there is also
provided a steam turbine according to the present invention
comprising a turbine casing, a turbine rotor disposed in the
turbine casing, a plurality of turbine stages, a cylinder
substantially coaxial with the turbine casing, and a fixing
partition plate having an outer edge fixed to the turbine casing
and an inner edge fixed to an outer circumferential portion of the
cylinder, wherein the turbine stages each includes turbine movable
blades disposed circumferentially around the turbine rotor and
turbine nozzles paired with the turbine movable blades and disposed
upstream of the turbine movable blades, the turbine nozzles of the
turbine stages are arranged inside the cylinder in an axial
direction and are engaged with and fixed to the cylinder, and the
fixing partition plate is disposed downstream of the center of the
cylinder in the axial direction to separate an upstream atmosphere
and a downstream atmosphere with respect to the partition
plate.
[0025] For the turbine nozzle holder and the steam turbine having
the features described above according to the present invention,
the size or number of fastening bolts used to fasten the separate
surfaces can be reduced, and the separate surfaces are firmly
fastened by a steam pressure difference between the inside and
outside of the turbine nozzle holder. The turbine nozzle holder and
the steam turbine can therefore reduce leakage of steam passing
through the stages to further enhance the internal efficiency of
the turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic partial sectional view of a turbine
nozzle holder and a steam turbine according to a first embodiment
of the present invention.
[0027] FIG. 2 is a graph showing pressure distribution inside and
outside the turbine nozzle holder according to the first embodiment
of the present invention.
[0028] FIG. 3A is a front vertical sectional view of a known
turbine nozzle holder and steam turbine for comparison with the
turbine nozzle holder and the steam turbine according to the
present invention.
[0029] FIG. 3B is a front vertical sectional view of the turbine
nozzle holder and the steam turbine according to the present
invention.
[0030] FIG. 4 is a schematic sectional view of a turbine nozzle
holder according to a modification of the first embodiment of the
present invention.
[0031] FIG. 5 is a schematic sectional view of a turbine nozzle
holder according to a second embodiment of the present
invention.
[0032] FIG. 6 is a sectional view taken along line VI-VI of FIG.
5.
[0033] FIG. 7 is a sectional view of a turbine nozzle holder having
no dummy flanges and a steam turbine.
[0034] FIG. 8 is a sectional view of a turbine nozzle holder having
dummy flanges and a steam turbine.
[0035] FIG. 9 is a schematic sectional view of a turbine nozzle
holder and a steam turbine according to a modification of the
second embodiment of the present invention.
[0036] FIG. 10 is a schematic sectional view of a turbine nozzle
holder and a steam turbine according to another modification of the
second embodiment of the present invention.
[0037] FIG. 11 is a schematic partial sectional view of a known
turbine nozzle holder and steam turbine.
[0038] FIG. 12 is a graph showing pressure distribution inside and
outside the known turbine nozzle holder.
[0039] FIG. 13 is a schematic axial sectional view of a steam
turbine according to the present invention, and a circled portion
thereof corresponds to the view of FIG. 1 in an enlarged scale.
BEST MODE FOR EMBODYING THE INVENTION
[0040] A turbine nozzle holder and a steam turbine according to an
embodiment of the present invention will be described hereunder
with reference to the accompanying drawings and the reference
numerals used therein.
[0041] FIG. 13 is a schematic longitudinal sectional view of the
steam turbine according to this embodiment. The steam turbine
generally includes three pressure sections of a high-pressure
turbine, an intermediate pressure turbine, and a low-pressure
turbine. Among the three pressure sections, FIG. 13 illustrates the
high-pressure turbine section and the intermediate pressure turbine
section. In FIG. 13, the high-pressure turbine and the intermediate
pressure turbine are integrally provided inside a single turbine
casing 1 among the pressure sections of the steam turbine. The
high-pressure turbine and the intermediate pressure turbine each
have turbine stages 5, each including turbine movable blades
(buckets) 3 and turbine nozzles (stationary blades) 4 paired with
the turbine movable blades 3. The turbine movable blades 3 are
disposed circumferentially around a turbine rotor (rotating shaft)
2. The turbine nozzles 4 are disposed upstream of the turbine
movable blades 3 in the circumferential direction of the turbine
rotor 2.
[0042] In FIG. 13, reference numerals 1' to 14' denote the
individual stages of the high-pressure turbine. A main steam flows
in the order of the stages 1' to 14' to rotate the movable blades
before being discharged. Reference numerals 15' to 22' denote the
individual stages of the intermediate pressure turbine. A boiler,
not shown, reheats the steam discharged from the high-pressure
turbine, and the reheated steam flows in the order of the stages
15' to 22' to rotate the movable blades before being
discharged.
[0043] The turbine nozzles 4 of, for example, the turbine stages of
the intermediate pressure turbine are held between inner and outer
nozzle diaphragm rings. The outer nozzle diaphragm ring is
supported by the turbine casing 1 to fix the turbine nozzles inside
the casing 1.
[0044] The high-pressure turbine has a support structure,
particularly on the downstream side thereof, in which the turbine
nozzles 4 of the turbine stages are supported by a single holder,
called a turbine nozzle holder, which is supported by the turbine
casing 1.
[0045] FIG. 1 is a schematic diagram of the turbine nozzle holder
according to the first embodiment of the present invention, showing
an enlarged view of the circled portion of the steam turbine shown
in FIG. 13. FIG. 1 illustrates the upper half of the turbine nozzle
holder and the steam turbine along a horizontal plane in the axial
direction.
[0046] It should be noted in the description of embodiments of the
present invention that terms relating to directions and positions,
such as "upper", "lower", "left", and "right", are based on the
drawings or the horizontal plane in the axial direction of the
steam turbine.
[0047] As described with reference to FIG. 13, the steam turbine
includes the pressure sections (generally, a high-pressure section,
an intermediate pressure section, and/or a low-pressure section).
These pressure sections each has the turbine stages 5 inside the
turbine casing 1, each including the turbine movable blades 4 and
the turbine nozzles (stationary blades) 3 paired with the turbine
movable blades 4. The turbine movable blades 4 are disposed
circumferentially around the turbine rotor (rotating shaft) 2. The
turbine nozzles are disposed upstream of the turbine movable blades
4 in the circumferential direction of the turbine rotor 2.
[0048] In FIG. 1, a turbine nozzle holder 7 according to this
embodiment includes a cylinder 6 extending axially substantially in
parallel with the turbine rotor 2 and a fixing partition 8 engaged
with the turbine casing 1 so as to support the cylinder 6. The
fixing partition 8 also serves to divide the atmosphere of a space
defined between the turbine casing 1 and the cylinder 6 into an
upstream atmosphere 9 and a downstream atmosphere 10. Grooves (not
shown) for engagement with the turbine nozzles 3 are formed in an
inner surface of the cylinder 6. The number of grooves corresponds
to the number of the turbine nozzles 3 supported (four grooves in
the example of FIG. 1).
[0049] A high-temperature and high-pressure steam passes through
the stages 5 from the upstream side to the downstream side in the
axial direction of the steam turbine (that is, in the direction
from right (IN) to left (EX) in FIG. 1 and from 1' to 14' in FIG.
13). The movable blades convert the energy of the steam into
rotational energy as the steam passes through the stages 5. The
steam itself is discharged from the steam turbine with decreased
pressure and temperature.
[0050] In the steam turbine having the structure described above
according to this embodiment, as shown in FIG. 1, the fixing
partition 8 is engaged with the turbine casing 1 so as to fix and,
support the turbine nozzle holder 7. The fixing partition 8 is
positioned downstream of the central position C of the turbine
nozzle holder 7 (cylinder 6) in the axial direction (a position
corresponding to a length of L/2 where L is the full length of the
turbine nozzle holder 7). More specifically, as shown in FIG. 1, a
rear joint end 11 of a portion of the fixing partition 8 joined to
the cylinder 6 on the downstream side is positioned downstream of
the central position C of the turbine nozzle holder 7 (cylinder 6)
in the axial direction.
[0051] FIG. 2 shows a graph representing internal and external
steam pressures applied to the turbine nozzle holder 7 with the
fixing partition 8 disposed at the position described above.
[0052] A curve indicated by the dotted line P1 represents the
pressure distribution of the steam passing through the stages
inside the turbine nozzle holder 7. This curve shows the fact that
the pressure decreases gradually as the steam passes through the
stages. The solid lines P2a and P2b represent the pressures of the
upstream atmosphere 9 and the downstream atmosphere 10,
respectively, separated by the fixing partition 8 (rear joint end
11) inside the space defined between the turbine casing 1 and the
cylinder 6. The hatched portions represent pressures applied to the
turbine nozzle holder 7 (cylinder 6) as a result of a pressure
difference between the inside and outside of the turbine nozzle
holder 7.
[0053] In the hatched portion A1 on the upstream side of the fixing
partition 8, more specifically, upstream side of the rear joint end
11, the pressure outside the cylinder 6, represented by the solid
line P2a, is larger than the pressure inside the cylinder 6,
represented by the dotted line. This means that the cylinder 6
receives an external pressure in this portion. In the hatched
portion A2 on the downstream side of the fixing partition 8 (rear
joint end 11), on the other hand, the pressure inside the cylinder
6, represented by the dotted line, is larger than the pressure
outside the cylinder 6, represented by the solid line P2b. This
means that the cylinder 6 receives an internal pressure in this
portion. A comparison of the areas of the upstream hatched portions
A1 and A2 reveals that the turbine nozzle holder 7 receives a net
external pressure because the area of the upstream hatched portion
A1 is larger than that of the downstream hatched portion A2.
[0054] The net external pressure applied to the turbine nozzle
holder 7 eliminates the need to use fasteners, such as bolts, for
fastening the separate structure of the turbine nozzle holder 7 if
the separate surfaces are accurately aligned.
[0055] The embodiment based on the mechanism described above is
specifically illustrated in FIG. 3B, where the cylinder 6 of the
turbine nozzle holder 7 is separated in two parts along a
horizontal plane HL in the axial direction. This structure does not
require, for example, flanges or fastening bolts.
[0056] FIG. 3A illustrates a known turbine nozzle holder 57
including a cylinder 56 having the same diameter as that of the
cylinder 6 of the turbine nozzle holder 7 according to this
embodiment. The cylinder 56 has joint flanges 63a and 63b and
fastening bolts 64 along the horizontal separating plane HL. A
comparison of the turbine nozzle holders 7 and 57 clearly shows
that the turbine casing 51 requires a diameter larger than the
turbine casing 1 according to this embodiment because the turbine
casing 51 accommodates the joint flanges 63a and 63b and the
fastening bolts 64.
[0057] That is, the external pressure is smaller than the internal
pressure in the example of FIG. 3A, while the external pressure is
larger than the internal pressure in the example of FIG. 3B.
[0058] According to this embodiment, as described above, the rear
joint end 11 of the fixing partition 8 is positioned on the
downstream side of the central position C of the turbine nozzle
holder 7 in the axial direction so that the external pressure
applied to the turbine nozzle holder 7 is larger than the internal
pressure applied thereto. This structure eliminates the need to use
flanges or fastening bolts for the separate structure of the
turbine nozzle holder and, because of no fastening bolts used,
prevents steam leakage from the separate surfaces due to the creep
deformation of bolts after extended exposure to elevated
temperature. The steam turbine can therefore constantly maintain
the high internal efficiency over an extended period of time.
[0059] In this embodiment, the cylinder 6 of the turbine nozzle
holder 7 has a separate structure, that is, separated in two parts
along the horizontal plane HL in the axial direction, and no
flanges or fastening bolts are provided along the separate
surfaces. As shown in FIG. 2, the external-pressure region (the
length of the portion of the cylinder 6 upstream of the rear joint
end 11) does not necessarily have a sufficient area. Hence, steam
leakage may be possible from the separate surfaces of the cylinder
6 on the downstream side of the rear joint end 11, at which the
cylinder 6 receives an internal pressure, depending on steam
conditions. Accordingly, a combination of joint flanges and
fastening bolts may be optionally used to prevent leakage as in the
known art. In addition, fixed joint flanges may be coupled to each
other with fastening bolts so as to prevent the misalignment of the
separate surfaces of the cylinder 6 due to, for example, the steam
vibration. In that case, the sizes, diameters, and numbers of joint
flanges and the fastening bolts used may be reduced relative to
those of the known art.
[0060] FIG. 4 is a schematic sectional view of a turbine nozzle
holder and a steam turbine according to a modification of the first
embodiment of the present invention, in which the same components
as those used in the first embodiment are indicated by the same
reference numerals.
[0061] In FIG. 4, the fixing partition 8 is engaged with the
turbine casing 1 to fix and support the turbine nozzle holder 7. In
this modification, the fixing partition 8 is largely shifted from
the central position C of the turbine nozzle holder 7 (cylinder 6)
in the axial direction (i.e., a position corresponding to a length
of L/2 where L is the full length of the turbine nozzle holder 7)
to the downstream side (to the left in FIG. 4, for example, to a
position corresponding to a length of 3L/4 where L is the full
length of the turbine nozzle holder 7).
[0062] If the fixing partition 8 is disposed at such a position,
the area of the hatched portion A1 on the upstream side of the
fixing partition 8 (rear joint end 11) in FIG. 2 is significantly
increased, and the area of the downstream hatched portion A2 is
decreased accordingly. As a result, the turbine nozzle holder 7
receives a net external pressure larger than that of the first
embodiment. As in the first embodiment, therefore, the net external
pressure eliminates the need to use joint flanges or fastening
bolts for preventing the leakage.
[0063] According to this modification, as described above, the rear
joint end 11 of the fixing partition 8 is largely shifted from the
central position C of the turbine nozzle holder 7 in the axial
direction to the downstream side so that the external pressure
applied to the turbine nozzle holder 7 is larger than the internal
pressure applied thereto. This structure eliminates the need to use
flanges or fastening bolts for the separate structure of the
turbine nozzle holder and, because of no fastening bolts used,
reduces the steam leakage from the separate surfaces due to the
creep deformation of the bolts after the extended exposure to
elevated temperature. The steam turbine can therefore constantly
maintain high internal efficiency over an extended period of
time.
[0064] The position of the fixing partition 8 relative to the
turbine nozzle holder 7 is specifically determined according to,
for example, the steam conditions and operating conditions of the
steam turbine used and the number of turbine nozzles supported by
the turbine nozzle holder 7.
[0065] In this modification, as in the first embodiment, joint
flanges and fastening bolts may be used to prevent misalignment of
the separate surfaces due to, for example, the steam vibration.
[0066] FIGS. 5 and 6 are sectional views of a turbine nozzle holder
and a steam turbine according to a second embodiment of the present
invention.
[0067] In the second embodiment, the turbine nozzles 3 are engaged
with and supported by the cylinder 6, and the turbine nozzle holder
7 has joint flanges 13a and 13b and dummy flanges 15 disposed on
the outer circumferential portion of the cylinder 6 along the
separate surfaces thereof.
[0068] FIGS. 7 and 8 are views for explaining the effect of the
dummy flange 15 of the steam turbine, graphically showing the
amount of deformation. FIG. 7 is a sectional view of a known steam
turbine including a turbine nozzle holder having no dummy flanges.
FIG. 8 is a sectional view of the steam turbine including the
turbine nozzle holder 7 having the dummy flanges according to the
second embodiment. The cylinder 6 shown in FIG. 8 has the same
diameter as that shown in FIG. 7.
[0069] For the known steam turbine shown in FIG. 7, the joint
flanges 13a and 13b are firmly fastened with the fastening bolts
14. For example, an internal pressure tends to expand the cylinder
6 by exerting a uniform force on the entire cylinder 6 in
directions in which the diameter thereof uniformly increases, that
is, perpendicularly to the inner circumferential surface of the
cylinder 6. However, the joint flanges 13a and 13b restrain
deformation of the cylinder 6 in the direction along the joint
surfaces (HL line). Portions of the cylinder 6 around the joint
flanges 13a and 13b have a rigidity higher than other portions
because of the thickness of the joint flanges and the fastening
force of the fastening bolts. Accordingly, the internal pressure
deforms a less rigid portion more significantly, for example, in
the vertical direction of FIG. 7. As a result, the entire cylinder
6 can be deformed to an oval shape.
[0070] According to the embodiment of the present invention shown
in FIG. 8, the dummy flanges 15, which have substantially the same
shape as the joint flanges 13a and 13b, are provided on the less
rigid portion to ensure the rigidity thereof, thus realizing the
substantially uniform amount of deformation.
[0071] That is, the cylinder 6 shown in FIG. 7 is less rigid and
more susceptible to the deformation in the vertical direction and
is more rigid and less susceptible to the deformation in the
horizontal direction, as indicated by the bidirectional arrows. In
contrast, the cylinder 6 shown in FIG. 8 is more rigid and less
susceptible to the deformation in both directions.
[0072] This embodiment is based on the phenomenon mentioned above,
and as shown in FIG. 6, specifically, the cylinder 6 is separated
along the horizontal plane HL in the axial direction, and the joint
flanges 13a and 13b and the fastening bolts 14 are provided along
the separate surfaces. In addition, the dummy flanges 15 are
provided at the positions farthest away from the joint flanges 13a
and 13b so as to further enhance the rigidity of the turbine nozzle
holder 7 (cylinder 6).
[0073] The turbine nozzle holder 7 including the cylinder 6 having
the dummy flanges 15 can be used for a steam turbine, as shown in
FIG. 5. Gaps 16a between seal fins 16 disposed at the leading ends
of the movable blades 4 and gaps 17a between seal fins 17 disposed
inside the turbine nozzles 4 can be uniformly maintained
irrespective of the operating conditions of the steam turbine (the
extent of variations in pressure difference between the inside and
outside of the turbine nozzle holder).
[0074] According to this embodiment, as described above, the
turbine nozzle holder 7 has the dummy flanges 15 in addition to the
joint flanges 13a and 13b to achieve and realize the rigidity
sufficient to substantially uniformly maintain the distances of the
gaps 16a between the seal fins 16 disposed at the leading ends of
the movable blades 4 and the gaps 17a between the seal fins 17
disposed inside the turbine nozzles 3. The turbine nozzle holder 7
can therefore reduce the steam leakage through the seal fins 16 of
the movable blades 4 and the seal fins 17 of the turbine nozzles 3
to enhance the internal efficiency of the turbine.
[0075] Although it is preferred that the dummy flanges 15 have
substantially the same shape as the joint flanges 13a and 13b, as
described above, the dummy flanges 15 may have any other shape that
allows the cylinder 6 to be deformed uniformly. Such a shape may be
determined by analyzing the deformation of the turbine nozzle
holder 7 (cylinder 6). In addition, the dummy flanges 15 are not
necessarily provided over the full length of the turbine nozzle
holder 7 (cylinder 6) in the axial direction, and may be only
partially provided thereon with consideration given to the amount
of the deformation in the longitudinal direction.
[0076] Although the turbine nozzle holder 7 (cylinder 6) is
separated along the horizontal plane HL in the axial direction with
the joint flanges 13a and 13b disposed along the separate surfaces
in this embodiment, the turbine nozzle holder 7 (cylinder 6) may
also be separated along a vertical plane (perpendicular to the
horizontal plane in the axial direction).
[0077] FIGS. 9 and 10 are schematic views of turbine nozzle holders
and steam turbines according to modifications of the second
embodiment of the present invention.
[0078] In the modification shown in FIG. 9, the turbine nozzle
holder 7 includes the joint flanges 13a and 13b and the fastening
bolts 14 along the separate surfaces in the horizontal plane HL in
the axial direction and dummy flanges 15a, 15b, 15c, . . .
regularly arranged at intervals of 45.degree. from the horizontal
plane HL.
[0079] In this modification, as described above, the turbine nozzle
holder 7 includes the dummy flanges 15a, 15b, 15c, . . . in
addition to the joint flanges 13a and 13b and the fastening bolts
14. The dummy flanges 15a, 15b, 15c, . . . are regularly arranged
at intervals of 45.degree. from the horizontal plane HL to further
reduce the amount of the deformation due to, for example, a
pressure difference between the inside and outside of the turbine
nozzle holder 7. The turbine nozzle holder 7 can therefore inhibit
the steam leakage through, for example, the seal fins of the
movable blades and the turbine nozzles so that the steam turbine
can maintain high internal efficiency.
[0080] In FIG. 10, on the other hand, the turbine nozzle holder 7
is separated along a vertical cross section VL in the axial
direction. The joint flanges 13a and 13b and the fastening bolts 14
are disposed along the separate surfaces of the turbine nozzle
holder 7. The dummy flanges 15a, 15b, 15c, . . . are regularly
arranged at intervals of 60.degree. from the vertical cross section
VL.
[0081] In these modifications, any other structure may be used in
which the dummy flanges 15a, 15b, 15c . . . are arranged so that
the entire cross-sectional shape of the turbine nozzle holder 7
(cylinder 6) is symmetrical with respect to the axis of the
cylinder 6.
[0082] The same advantages as those attained by the embodiments
described hereinbefore can also be achieved in these modifications.
The present invention is not limited to the embodiments described
above, and other embodiments and modifications may be permitted
without departing from the scopes of the appended claims.
* * * * *