U.S. patent application number 12/713818 was filed with the patent office on 2010-09-02 for steam turbine and method for extracting moisture from a steam turbine.
This patent application is currently assigned to ALSTOM Technology Ltd. Invention is credited to Said Havakechian, Sergey KOSTYUCHENKO, Benjamin Megerle, Thomas Mokulys.
Application Number | 20100221095 12/713818 |
Document ID | / |
Family ID | 40673661 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100221095 |
Kind Code |
A1 |
KOSTYUCHENKO; Sergey ; et
al. |
September 2, 2010 |
STEAM TURBINE AND METHOD FOR EXTRACTING MOISTURE FROM A STEAM
TURBINE
Abstract
A steam turbine is disclosed which includes a casing containing
a plurality of expansion stages, each including stator and rotor
airfoils. Downstream of the stator airfoils of one or more
expansion stages, the casing includes a slot arranged to receive
moisture that concentrates on an end wall of the stator airfoils
and discharge it to the outside. Each end wall has a side portion
facing the slot having a variable radial obstruction in a
tangential direction, in order to define with the slot a passage
through which the moisture may pass that is smaller or closed at
the suction side and larger at the pressure side of the stator
blades, to at least partially prevent the dry steam from entering
the slot at the suction side of the blade.
Inventors: |
KOSTYUCHENKO; Sergey;
(Neuenhof, CH) ; Megerle; Benjamin; (Baden,
CH) ; Mokulys; Thomas; (Wuerenlingen, CH) ;
Havakechian; Said; (Baden, CH) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
40673661 |
Appl. No.: |
12/713818 |
Filed: |
February 26, 2010 |
Current U.S.
Class: |
415/1 ;
415/169.2 |
Current CPC
Class: |
F01D 25/32 20130101;
F05D 2220/31 20130101; F01D 5/143 20130101 |
Class at
Publication: |
415/1 ;
415/169.2 |
International
Class: |
F01D 25/32 20060101
F01D025/32 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2009 |
EP |
09153874.4 |
Claims
1. Steam turbine comprising: a casing having plural expansion
stages, each including stator and rotor airfoils, a slot arranged
in the casing downstream of the stator air foils of at least one
expansion stage for receiving moisture that concentrates on an end
wall of the stator airfoils and for discharging the moisture,
wherein each end wall includes a side portion facing the slot,
which has a variable radial obstruction in a tangential direction
to define, with the slot, a passage for the moisture that is
smaller or closed at a suction side of stator blade and larger at a
pressure side of the stator blade, to at least partially prevent
the dry steam from entering the slot at the suction side.
2. Steam turbine as claimed in claim 1, wherein said slot is a
circumferential slot.
3. Steam turbine as claimed in claim 1, wherein the side portion
facing the slot of the end wall comprises: at the suction side, a
thick zone located adjacent to the stator blade and at least
partially obstructs the slot.
4. Steam turbine as claimed in claim 3, wherein said thick portion
completely obstructs the slot.
5. Steam turbine as claimed in claim 3, wherein said thick portion
is adjacent to each of plural stator blades at the suction
side.
6. Steam turbine as claimed in claim 3, wherein, the side portion
facing the slot of the end wall comprises: a thin zone adjacent to
the thick zone in a tangential direction.
7. Steam turbine as claimed in claim 6, wherein, in a tangential
direction, said thin zone has a thickness that continuously
decreases from that of the thick portion toward the side of the end
wall.
8. Steam turbine as claimed in claim 6, wherein, in an axial
direction, the thin zone has a thickness that continuously
decreases in a direction from opposite the slot towards the
slot.
9. Steam turbine as claimed in claim 1, wherein the variable radial
obstruction comprises a slope at the end wall.
10. Steam turbine as claimed in claim 6, comprising: a step between
the thick zone and the thin zone.
11. Steam turbine as claimed in claim 10, wherein said step
comprises: a wall perpendicular to surfaces of the thick zone and
thin zone.
12. Steam turbine as claimed in claim 10, wherein said step
comprises: a wall tilted with respect to surfaces of at least one
of the thick zone and thin zone.
13. Method for extracting moisture from a steam turbine including a
casing containing plural expansion stages each including stator and
rotor airfoils, the method comprising: providing, downstream of the
stator airfoils of at least one of the plural expansion stages, the
casing with a slot arranged to receive moisture that concentrates
on an end wall of the stator airfoils; discharging said moisture;
and at least partially preventing dry steam from entering the slot
at a suction side of a blade of the steam turbine by using any end
wall of the stator airfoils.
14. Method as claimed in claim 13, comprising: arranging the end
wall of the stator airfoils to drive the moisture away from the
suction side.
Description
RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
to European Patent Application No. 09153874.4 filed in Europe on
Feb. 27, 2009, the entire content of which is hereby incorporated
by reference in its entirety.
FIELD
[0002] The present disclosure relates to a steam turbine and a
method for extracting moisture from a steam turbine.
BACKGROUND INFORMATION
[0003] Steam turbine plants, such as plants for electricity
generation are known to include a steam generator that feeds a
turbine. The turbine expands the steam to operate an electrical
generator and then discharges the exhausted steam in a
condenser.
[0004] In order to extract high power from the steam, it is known
to expand steam far into the wet steam region.
[0005] Even though this allows power to be increased, this may
cause the generation of moisture within the steam that may have a
number of negative effects.
[0006] Because of their high momentum of inertia, moisture
droplets, such as droplets which exceed a certain size, cannot
follow the turning of the steam flow. Thus, they impinge on the
following blade surface causing the so called wet steam
erosion.
[0007] This can be particularly relevant in low pressure turbines
where expansion in the wet steam region takes place and often the
amount of moisture may be large.
[0008] Steam turbines, such as low pressure stages of steam
turbines, can be provided with devices that extract the moisture
and discharge it to the outside.
[0009] With reference to the stator blades, such devices can be
provided upstream of the stator blades and/or downstream of the
stator blades.
[0010] In the following, the extraction devices downstream of the
stator blades will be discussed in detail.
[0011] Steam turbines have a casing that carries the stator
airfoils.
[0012] Each stator airfoil has an end wall that may be connected to
the casing and from which a stator blade extends.
[0013] Downstream of the stator airfoil, the casing may be provided
with a circumferential slot arranged to receive the moisture that
during operation concentrates near the end wall of the airfoils
(due to the centrifugal forces caused by the swirling steam flow
and the rotating parts).
[0014] In order to protect the blades from erosion, the amount of
moisture that is extracted trough the slot should be as high as
possible. Thus, the slot can be as large as possible to let a large
amount of moisture be seized therein.
[0015] Nevertheless, a large slot (in addition to a large amount of
moisture) may also seize a large amount of dry steam.
[0016] This may cause a loss in performance.
SUMMARY
[0017] A steam turbine includes a casing having plural expansion
stages, each including stator and rotor airfoils. A slot is
arranged in the casing downstream of the stator air foils of at
least one expansion stage for receiving moisture that concentrates
on an end wall of the stator airfoils and for discharging the
moisture. Each end wall includes a side portion facing the slot,
which has a variable radial obstruction in a tangential direction
to define, with the slot, a passage for the moisture that is
smaller or closed at a suction side of stator blade and larger at a
pressure side of the stator blade, to at least partially prevent
the dry steam from entering the slot at the suction side.
[0018] A method for extracting moisture from a steam turbine
includes a casing containing plural expansion stages each including
stator and rotor airfoils. The method includes providing,
downstream of the stator airfoils of at least one of the plural
expansion stages, the casing with a slot arranged to receive
moisture that concentrates on an end wall of the stator airfoils;
discharging said moisture; and at least partially preventing dry
steam from entering the slot at a suction side of a blade of the
steam turbine by using any end wall of the stator airfoils.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Further characteristics and advantages of the disclosure
will be more apparent from the description of a preferred but
non-exclusive embodiment of the steam turbine and the method
according to the disclosure, illustrated by way of non-limiting
example in the accompanying drawings, in which:
[0020] FIG. 1 is a schematic perspective view of three exemplary
stator airfoils according to the disclosure associated with a slot
of the casing (the slot is shown in dashed line).
[0021] FIGS. 2-4 are schematic cross section through lines II-II,
III-III and IV-IV of FIG. 1, wherein a part of the casing defining
the slot is also shown.
[0022] FIG. 5 is a further schematic prospective view of three
exemplary stator airfoils according to the disclosure; wherein the
slot is shown in dashed line.
[0023] FIG. 5A is a schematic prospective view of three exemplary
stator airfoils according to the disclosure in different
embodiments; wherein the slot is shown in dashed line.
[0024] FIG. 6 is a schematic longitudinal section of a portion of
an exemplary turbine according to the disclosure.
[0025] FIG. 7 is a perspective view of an exemplary stator airfoil
row according to the disclosure.
[0026] FIGS. 8 and 9 are exemplary details of FIG. 7, which for
sake of clarity show only some of the stator airfoils.
DETAILED DESCRIPTION
[0027] A steam turbine and a method are disclosed for extracting
moisture from a steam turbine.
[0028] A steam turbine and a method as disclosed can let a large
amount of moisture be extracted from low pressure expansion stages
with respect to known steam turbines, but at the same time that may
cause only a small extraction of dry steam.
[0029] A steam turbine and a method are also disclosed that can
increase both performance and reliability with respect to known
steam turbines.
[0030] An exemplary steam turbine of FIG. 11 includes a casing 1
that contains a plurality of expansion stages.
[0031] Each expansion stage includes a plurality of stator airfoils
2 downstream of which a plurality of rotor airfoils 5 are provided.
For example, each stator airfoil 2 includes an end wall 3 that is
connected to the casing 1 and from which a stator blade 4
extends.
[0032] In order to extract moisture from the steam turbine,
downstream of the stator airfoils 2 of one or all the expansion
stages (the enclosed figures show only one exemplary stage), the
casing 1 can include a circumferential slot 7 that is arranged to
receive the moisture that concentrates on the end wall 3 of the
stator airfoils 2 and discharge it to the outside of the steam
turbine, for example via holes 8.
[0033] Each stator airfoil 2 can have the end wall 3 define, with
the slot 7, a passage 10 through which the moisture may pass.
[0034] This passage 10 can be smaller or closed at the suction side
12 and may be larger at the pressure side 13 of each stator blade
4, to at least partially prevent the dry steam from entering the
slot 7 at the suction side 12 of the blades 4.
[0035] In order to define a smaller or closed passage 10 at the
suction side 12 of the stator blades 4, each end wall 3 may have a
portion facing the slot 7 having a variable radial obstruction in a
tangential direction.
[0036] In this respect, the portion facing the slot 7 of the end
wall 3 may have at the suction side 12 a thick zone 15 that is
located adjacent to the stator blade 4 and partially or completely
obstructs the slot 7.
[0037] Moreover, the portion facing the slot 7 of the end wall 3
may have a thin zone 17 that is adjacent to the thick zone 15 in a
tangential direction.
[0038] Advantageously, the thin zone 17 may have a thickness that,
in a tangential direction, continuously decreases from that of the
thick zone 15 towards the side of the end wall 3.
[0039] The thin zone 17 also may have a thickness that, in an axial
direction, continuously decreases from its portion opposite the
portion facing the slot 7 toward the portion facing the slot 7.
[0040] The operation of the steam turbine of the disclosure will be
apparent to those skilled in the art from the description and
drawings, and may, for example, be substantially as follows:
[0041] Steam flow flows in an axial direction (as shown by arrows
F) and, when passing through the stator and rotor blades 4, 5, can
turn to follow the curved channels.
[0042] Due to centrifugal forces and inertia, the moisture can be
forced to concentrate on the end walls 3 of the stator airfoils 2,
at the pressure side 13 of their blades 4.
[0043] In addition, the particular shape of the end walls 3 can
force the moisture to run towards the zone of the end walls 3 at
the pressure side 13 of the blades 4 (see arrows M).
[0044] From this zone the moisture can pass through the passages 10
and enters the slot 7 to be discharged to the outside of the steam
turbine.
[0045] In addition to the moisture, dry steam may also be
discharged through the passages 10.
[0046] Nevertheless, as the zones close to the suction sides 12 of
the stator blades 4 are not provided with passages 10 (or, in any
case, these passages are smaller than that at the pressure sides
13) neither moisture nor dry steam may be discharged through these
zones (or, for example, only limited amounts are discharged).
[0047] Because the moisture is concentrated in the zones close to
the pressure sides 13 of the blades 4, whereas the dry steam can be
almost uniformly distributed in the channels defined between two
adjacent stator blades 4, in an exemplary steam turbine as
disclosed herein the amount of moisture discharged can be increased
and/or the amount of dry steam discharged can be reduced with
respect to known steam turbines.
[0048] FIG. 5A shows a different exemplary embodiment of the
disclosure. In this embodiment the same reference numbers are used
for elements already described.
[0049] In this embodiment the variable radial obstruction may be
defined by a slope at the end wall.
[0050] Moreover, between the thick zone 15 and the thin zone 17
there may be provided a step. The step can have a wall 20
perpendicular to the surfaces of the thick zone 15 and thin zone 17
or, alternatively, tilted with respect to them (or at least one of
them).
[0051] FIGS. 7-9 show a further exemplary embodiment of the
disclosure. In this embodiment the same reference numbers are used
for elements already described.
[0052] In this embodiment, the variable radial obstruction may also
be defined by a slope at the end wall. The slope projects inwardly
from the leading edge 18 of each stator blade 4 to the trailing
edge 19 of the same stator blade 4. Moreover the slope may be
adjacent to each stator blade 4 at its suction side 12.
[0053] The present disclosure also relates to a method for
extracting moisture from a steam turbine that includes a casing 1
containing a plurality of expansion stages each including stator
and rotor airfoils. Downstream of the stator airfoils of at least a
stage, the casing 1 is provided with a circumferential slot 7
arranged to receive the moisture that concentrates on an end wall 3
of the stator airfoils 2 and discharge it to the outside.
[0054] According to an exemplary method of the disclosure, the end
wall 3 of the stator airfoils 2 drives the moisture away from the
suction side 12 of its blade and at least partially prevents the
dry steam from entering the slot 7 at the suction side 12 of the
blade 4.
[0055] A steam turbine and the method as disclosed herein can be
implemented with numerous modifications and variants, all falling
within the scope of the inventive concept. Moreover all details can
be replaced by technically equivalent elements.
[0056] In practice, the materials used and the dimensions can be
chosen at will according to a desired application and the state of
the art.
[0057] Thus, it will be appreciated by those skilled in the art
that the present invention can be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The presently disclosed embodiments are therefore
considered in all respects to be illustrative and not restricted.
The scope of the invention is indicated by the appended claims
rather than the foregoing description and all changes that come
within the meaning and range and equivalence thereof are intended
to be embraced therein.
REFERENCE NUMBERS
[0058] 1 casing [0059] 2 stator airfoil [0060] 3 end wall [0061] 4
stator blade [0062] 5 rotor blades [0063] 7 slot [0064] 8 holes
[0065] 10 passage [0066] 12 suction side of the blades [0067] 13
pressure side of the blades [0068] 15 thick zone of the end wall
[0069] 17 thin zone of the end wall [0070] 18 leading edge of the
stator blade [0071] 19 trailing edge of the stator blade [0072] 20
wall of the step [0073] F steam flow [0074] M moisture
* * * * *