U.S. patent application number 11/843347 was filed with the patent office on 2009-02-26 for method and apparatus for clearance control of turbine blade tip.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Kenneth Damon Black, Christopher Sean Bowes, Bradley James Miller, Eric Scicchitano, Ian David Wilson.
Application Number | 20090053042 11/843347 |
Document ID | / |
Family ID | 40280464 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090053042 |
Kind Code |
A1 |
Wilson; Ian David ; et
al. |
February 26, 2009 |
METHOD AND APPARATUS FOR CLEARANCE CONTROL OF TURBINE BLADE TIP
Abstract
A gas turbine including a casing and a shroud ring, the gas
turbine including an attachment device rigidly attached to the
casing and at least one of the shroud ring and a duct attached to
the shroud ring, wherein the device allows the shroud ring to
expand and contract independent of the casing and provides limited
net axial growth of the shroud ring.
Inventors: |
Wilson; Ian David;
(Simpsonville, SC) ; Miller; Bradley James;
(Simpsonville, SC) ; Scicchitano; Eric; (Montreal,
CA) ; Bowes; Christopher Sean; (Simpsonville, SC)
; Black; Kenneth Damon; (Travelers Rest, SC) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
40280464 |
Appl. No.: |
11/843347 |
Filed: |
August 22, 2007 |
Current U.S.
Class: |
415/134 ;
415/173.6 |
Current CPC
Class: |
F01D 11/20 20130101;
F05D 2250/70 20130101; F01D 25/246 20130101; F01D 11/24
20130101 |
Class at
Publication: |
415/134 ;
415/173.6 |
International
Class: |
F01D 11/22 20060101
F01D011/22; F01D 25/24 20060101 F01D025/24 |
Claims
1. A gas turbine comprising a casing and a shroud ring, the gas
turbine comprising: an attachment device rigidly attached to the
casing and at least one of the shroud ring and a duct attached to
the shroud ring, wherein the device allows the shroud ring to
expand and contract independent of the casing and provides limited
net axial growth of the shroud ring.
2. The gas turbine as in claim 1, wherein the net axial growth is
about zero.
3. The gas turbine as in claim 1, wherein the device comprises a
spring.
4. The gas turbine as in claim 3, wherein the spring comprises a
general "C" shape.
5. The gas turbine as in claim 3, wherein the spring comprises a
general "W" shape.
6. The gas turbine as in claim 3, wherein the spring comprises a
rail for coupling to the casing.
7. The gas turbine as in claim 1, wherein the device comprises a
360.degree. segment.
8. A gas turbine comprising a casing and a shroud ring, the gas
turbine comprising: a plurality of springs shaped generally as a
"C" rigidly attached to the casing and at least one of the shroud
ring and a duct attached to the shroud ring, wherein the device
allows the shroud ring to expand and contract independent of the
casing and provides limited net axial growth of the shroud
ring.
9. A method for controlling a dimension of a shroud ring in a gas
turbine comprising a casing, the method comprising: establishing
the dimension for the shroud ring; and controlling a size of the
shroud ring to maintain the dimension using an attachment device
rigidly attached to the casing and at least one of the shroud ring
and a duct attached to the shroud ring, wherein the device allows
the shroud ring to expand and contract independent of the casing
and provides limited net axial growth of the shroud ring.
10. The method as in claim 9, wherein the method is implemented by
a computer program product stored on machine-readable media and
comprising machine executable instructions for controlling a
dimension of a shroud ring in a gas turbine comprising a casing,
the product comprising instructions for: establishing the dimension
for the shroud ring; and controlling a size of the shroud ring to
maintain the dimension using an attachment device rigidly attached
to the casing and at least one of the shroud ring and a duct
attached to the shroud ring, wherein the device allows the shroud
ring to expand and contract independent of the casing and provides
limited net axial growth of the shroud ring.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention disclosed herein relates to the field of gas
turbines. In particular, the invention is used to provide control
of turbine blade tip clearance.
[0003] 2. Description of the Related Art
[0004] A gas turbine includes many parts, each of which may expand
or contract as operational conditions change. A turbine interacts
with hot gases emitted from a combustion chamber to turn a shaft.
The shaft is generally coupled to a compressor and, in some
embodiments, a device for receiving energy such as an electric
generator. The turbine is generally adjacent to the combustion
chamber. The turbine uses blades, sometimes referred to as
"buckets," for using energy of the hot gases to turn the shaft.
[0005] The buckets rotate within a shroud ring. As the hot gases
impinge on the buckets, the shaft is turned. The shroud ring is
used to prevent the hot gases from escaping around the buckets and,
therefore, not turning the shaft.
[0006] The distance between the end of one bucket and the shroud
ring is referred to as "clearance." As the clearance increases,
efficiency of the turbine decreases as hot gases escape through the
clearance. Therefore, an amount of clearance can affect the overall
efficiency of the gas turbine.
[0007] If the amount of clearance is too small, then thermal
properties of the buckets, the shroud ring, and other components
can cause the buckets to rub the shroud ring. When the buckets rub
the shroud ring, damage to the buckets, the shroud ring and the
turbine may occur. It is important, therefore, to maintain a
minimal clearance during a variety of operational conditions.
[0008] Therefore, what are needed are techniques to reduce
clearance between buckets and a shroud ring in a gas turbine. The
techniques should be useful for a variety of operational
conditions.
BRIEF DESCRIPTION OF THE INVENTION
[0009] Disclosed is one embodiment of a gas turbine including a
casing and a shroud ring, the gas turbine including an attachment
device rigidly attached to the casing and at least one of the
shroud ring and a duct attached to the shroud ring, wherein the
device allows the shroud ring to expand and contract independent of
the casing and provides limited net axial growth of the shroud
ring.
[0010] Also disclosed is one embodiment of a gas turbine including
a casing and a shroud ring, the gas turbine including a plurality
of springs shaped generally as a "C" rigidly attached to the casing
and at least one of the shroud ring and a duct attached to the
shroud ring, wherein the device allows the shroud ring to expand
and contract independent of the casing and provides limited net
axial growth of the shroud ring.
[0011] Further disclosed is one example of a method for controlling
a dimension of a shroud ring in a gas turbine including a casing,
the method including establishing the dimension for the shroud
ring; and controlling a size of the shroud ring to maintain the
dimension using an attachment device rigidly attached to the casing
and at least one of the shroud ring and a duct attached to the
shroud ring, wherein the device allows the shroud ring to expand
and contract independent of the casing and provides limited net
axial growth of the shroud ring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0013] FIG. 1 illustrates an exemplary embodiment of a gas
turbine;
[0014] FIG. 2 is an end view of an exemplary embodiment of a
turbine stage;
[0015] FIG. 3A and FIG. 3B, collectively referred to as FIG. 3,
illustrate an exemplary embodiment of a duct system coupled to a
shroud ring;
[0016] FIG. 4A and FIG. 4B, collectively referred to as FIG. 4,
illustrate another exemplary embodiment of the duct system;
[0017] FIG. 5 illustrates an exemplary embodiment of a control
system; and
[0018] FIG. 6 presents an exemplary method for controlling a
dimension of the shroud ring.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The teachings provide embodiments of apparatus and methods
for controlling a clearance between a plurality of buckets and a
shroud ring in a gas turbine. The teachings provide for controlling
a temperature of the shroud ring to maintain a proper amount of
clearance. In general, the shroud ring may be made from a metal.
The metal may expand and contract in accordance with its thermal
coefficient of expansion. An attachment device is provided to allow
the shroud ring to expand and contract with respect to a casing of
the gas turbine. Before the embodiments are discussed in detail,
certain definitions are provided.
[0020] The term "gas turbine" relates to a continuous combustion
engine. The gas turbine generally includes a compressor, a
combustion chamber and a turbine. The combustion chamber emits hot
gases that are directed to the turbine. The term "bucket" relates
to a blade included in the turbine. Each bucket generally has an
airfoil shape to provide for converting the hot gases impinging on
the bucket into rotational work. The term "turbine stage" relates
to a plurality of buckets circumferentially disposed about a
section of a turbine shaft. The buckets of the turbine stage are
arranged in a circular pattern about the shaft. The term "shroud
ring" relates to a structure for preventing the hot gases from
escaping, unimpeded, around the buckets of the turbine stage. The
structure may be at least one of cylindrical and conical. In
general, there is one shroud ring for each turbine stage. The term
"clearance" relates to an amount of distance between a tip of the
bucket and the shroud ring. The term "casing" relates to a
structure for supporting the shroud ring. The term "attachment
device" relates to a device used to support the shroud ring from
the casing. The term "rigidly attached" relates to a type of
connection to the attachment device. The attachment device that is
rigidly attached to a structure will not move or slide at the point
of attachment to the structure. The term "net axial growth" relates
to displacement of the shroud ring along the longitudinal axis of
the gas turbine. The term "rubbing" relates to at least one bucket
making contact with the shroud ring. Rubbing generally causes
damage to the gas turbine. The term "bleed-heat" relates to air
extracted from the compressor before the air is sent to the
combustion chamber.
[0021] FIG. 1 illustrates an exemplary embodiment of a gas turbine
1. The gas turbine 1 includes a compressor 2, a combustion chamber
3, and a turbine 4. The compressor 2 is coupled to the turbine 4 by
a turbine shaft 5. In the embodiment of FIG. 1, the turbine shaft 5
is also coupled to an electric generator 6. The turbine 4 includes
turbine stages 7, respective shroud rings 8, and a casing 9. The
turbine 4 is described in more detail next. Also depicted in FIG. 1
is an axial direction 11 parallel to the shaft 5 and a radial
direction 12 representative of radial directions normal to the
shaft 5.
[0022] FIG. 2 illustrates an end view of an exemplary embodiment of
one turbine stage 7 of the turbine 4. Referring to FIG. 2, a
clearance 20 is illustrated. The shroud ring 8 shown in FIG. 2
encloses a plurality of buckets 27 by about 360 degrees. In some
embodiments, the shroud ring 8 is built from a plurality of shroud
ring segments that include a plurality of arc segments, each
segment less than 360 degrees. By controlling the temperature of
the shroud ring 8, the clearance 20 can be minimized without an
increase in a risk of rubbing. The shroud ring 8 is supported by a
plurality of attachment devices.
[0023] Referring to FIG. 2, the shroud ring 8 is shown supported
from the casing 9 by a plurality of devices 22. One end of each
attachment device 22 is rigidly attached to the shroud ring 8. The
other end of the attachment device 22 is rigidly attached to the
casing 9. The attachment devices 22 provide for supporting the
shroud ring 8 and allowing the shroud ring 8 to thermally expand
and contract while maintaining roundness independent of the casing
9. The plurality of attachment devices 22 is generally disposed
circumferentially about the shroud ring 8. One exemplary embodiment
of the attachment device 22 is a spring. A duct system may be used
to provide air for at least one of cooling and heating the shroud
ring 8 to control the clearance 20.
[0024] FIG. 3 illustrates an exemplary embodiment of the shroud
ring 8 coupled to a duct system 30. In the embodiment of FIG. 3,
the duct system 30 is supported from the casing 9 by a plurality of
attachment devices 22. Referring to FIG. 3A, the duct system 30
includes an inlet 33 for providing air into the duct system 30.
Similarly, the duct system 30 includes an outlet 34 for removing
the air. The duct system 21 can conduct one of heated air for
heating and cooled air for cooling. Because of heat transfer
between the air in the duct system 30 and the shroud ring 8, the
temperature of the air at the inlet 33 may be different from the
temperature of the air at the outlet 34. Different temperatures of
air at the inlet 33 and the outlet 34 may lead to warping of the
shroud ring 8.
[0025] Warping of the shroud ring 8 can lead to out-of-roundness.
When the shroud ring 8 is out-of-round, the clearance 20 can vary
about a circumference of the shroud ring 8. As warping increases, a
point will be reached when rubbing will occur. To limit warping,
two flow paths are provided in the duct system 30.
[0026] A first flow path 31 and a second flow path 32 are
illustrated in FIG. 3B. To minimize temperature variations about
the shroud ring 8, the air in the second flow path 32 flows in a
direction 37 opposite to the direction 36 of the air flowing in the
first flow path 31. Also, a conduction plate 35 as shown in FIG. 3B
is used to transfer heat between the first flow path 31 and the
second flow path 32. The use of counter-flow and the conduction
plate 35 acts to minimize any temperature variations about the
shroud ring 8. While the embodiment of FIG. 3B illustrates two flow
paths, more flow paths can be used. The first flow path 31 and the
second flow path 32 are generally normal to the shaft 5. The duct
system 30 of FIG. 3 is referred to as a "dual cross-conduction
counter-flow duct system."
[0027] FIG. 4 illustrates another exemplary embodiment of the duct
system 30. Referring to FIG. 4A and FIG. 4B, the duct system 30
includes notches 40 for coupling to the segments used to build the
shroud ring 8. In the embodiment of FIG. 4, the attachment devices
22 are springs. Referring to FIG. 4A, each attachment device 22
includes an attachment rail 41 for rigidly attaching each
attachment device 22 to the casing 9. Each attachment device 22 is
also rigidly attached to the duct system 30. A closed loop control
system is generally used to control a dimension of the shroud ring
8. For the embodiments of FIGS. 3 and 4, airflow to each of the
first flow path 31 and the second flow path 32 is controlled by an
associated closed loop flow control system.
[0028] FIG. 5 illustrates an exemplary embodiment of a flow control
system 50. The discussion of the flow control system 50 is with
respect to the first flow path 31. However, the discussion also
applies to the second flow path 32 and any other flow paths. The
flow control system 50 includes a control valve 51 for controlling
the airflow to the first flow path 31. The flow control system 50
also includes a flow controller 52 and at least one sensor 53. The
sensor 53 may be at least one of a flow sensor, a temperature
sensor, a pressure sensor, a distance sensor, and other types of
sensors. For example, the sensor 53 may measure the temperature of
the shroud ring 8. Using the temperature of the shroud ring 8, the
flow controller 52 can regulate airflow through the control valve
51 to control the temperature of the shroud ring 8. A source 54 of
air to the control valve 51 may be at least one of bleed-heat for
heated air, ventilation air for cooled air, and other sources. Air
from the source 54 is generally at a pressure greater than
atmospheric pressure to provide for flow through the first flow
path 31. If the pressure is not great enough to provide the
required flow, a fan may be used to provide the required flow.
While not depicted in FIG. 5, the source 54 may be selected by the
flow controller 52 in order to provide air at a temperature
necessary for controlling the clearance 20. The flow control system
50 also includes the attachment devices 22 to allow the duct system
30 to expand and contract independent of the casing 9.
[0029] In general, detailed analyses and tests are performed to
determine a set point. For example, in situations where the source
54 of air has an approximately constant temperature, the detailed
analyses and tests can determine at least one airflow rate for each
of start-up, shut-down, steady-state operation at full power, and
operation at less than full power. For another example, a sensor
may be use used to measure the clearance 20 while the airflow rate
and the temperature of the source 54 are adjusted to maintain a set
point for the clearance 20.
[0030] FIG. 6 presents an exemplary method 60 for controlling the
clearance 20. The clearance 20 may be controlled by controlling a
dimension, such as a diameter, of the shroud ring 8. The method 60
calls for establishing 61 a dimension of the shroud ring 8.
Further, the method 60 calls for controlling 62 a size of the
shroud ring 8 to maintain the dimension. The method 60 is
implemented using the attachment device 22.
[0031] The method 60 may be implemented by a computer program
product included in the control system 50. The computer program
product is generally stored on machine-readable media and includes
machine executable instructions for controlling a dimension of the
shroud ring 8 in the gas turbine 1.
[0032] The technical effect of the computer program product is to
increase the efficiency of the gas turbine 1 by controlling the
clearance 20.
[0033] The discussion above is with respect to flowing air through
the duct system 30 to transfer heat. It is recognized that other
forms of media such as liquids and gases may also be used to
transfer heat in the duct system 30. Exemplary embodiments of other
media are water and steam. It is also recognized that additives
such as corrosion inhibitors may be added to the media.
[0034] The attachment devices 22 may include various embodiments.
The embodiments allow the shroud ring 8 to expand and contract in
the radial direction 12 independent of the casing 9. The attachment
devices 22 also retain the shroud ring 8 in place in the axial
direction 11. The attachment devices 22 provide for net axial
growth that is at least one of limited and about zero.
[0035] As discussed above, one embodiment of the attachment device
22 is the spring. The spring may include various shapes. One shape
includes a general "C" shape. Another shape may include a general
"W" shape. Another embodiment of the attachment device 22 is a
mechanical linkage. Movement of the mechanical linkage may be
restrained by a spring.
[0036] The teachings provide that the attachment devices 22 may
include various arc segments, which may be measured by a number of
degrees. For example, the gas turbine 1 may include one attachment
device 22 having an arc segment of 360.degree.. As another example,
the gas turbine 1 may include a plurality of attachment devices 22.
Generally, when a plurality of attachment devices 22 is used, each
attachment device 22 has an arc segment less than about
180.degree..
[0037] Various components may be included and called upon for
providing for aspects of the teachings herein. For example, the
flow controller 52 may include at least one of an analog system and
a digital system. The digital system may include at least one of a
processor, memory, storage, input/output interface, input/output
devices, and a communication interface. In general, the computer
program product stored on machine-readable media can be input to
the digital system. The computer program product includes
instructions that can be executed by the processor for controlling
the clearance 20. The various components may be included in support
of the various aspects discussed herein or in support of other
functions beyond this disclosure.
[0038] It will be recognized that the various components or
technologies may provide certain necessary or beneficial
functionality or features. Accordingly, these functions and
features as may be needed in support of the appended claims and
variations thereof, are recognized as being inherently included as
a part of the teachings herein and a part of the invention
disclosed.
[0039] While the invention has been described with reference to
exemplary embodiments, it will be understood that various changes
may be made and equivalents may be substituted for elements thereof
without departing from the scope of the invention. In addition,
many modifications will be appreciated by those skilled in the art
to adapt a particular instrument, situation or material to the
teachings of the invention without departing from the essential
scope thereof. Therefore, it is intended that the invention not be
limited to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims.
* * * * *