U.S. patent application number 13/680379 was filed with the patent office on 2014-05-22 for system and method for reducing modal coupling of combustion dynamics.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Sarah Lori Crothers, Christian Xavier Stevenson, Willy Steve Ziminsky.
Application Number | 20140137561 13/680379 |
Document ID | / |
Family ID | 49596124 |
Filed Date | 2014-05-22 |
United States Patent
Application |
20140137561 |
Kind Code |
A1 |
Crothers; Sarah Lori ; et
al. |
May 22, 2014 |
SYSTEM AND METHOD FOR REDUCING MODAL COUPLING OF COMBUSTION
DYNAMICS
Abstract
A system for reducing modal coupling of combustion dynamics
includes a plurality of combustors, and at least one fuel injector
in each of the plurality of combustors. The system also includes
structure for dithering a combustion instability frequency in at
least one combustor in the plurality of combustors. A method for
reducing modal coupling of combustion dynamics includes flowing a
compressed working fluid at a temperature to a plurality of
combustors and flowing a fuel to at least one fuel injector in each
of the plurality of combustors. The method further includes
dithering at least one of the temperature of the compressed working
fluid flowing to the plurality of combustors or the fuel flow to
the at least one fuel injector in at least one combustor in the
plurality of combustors.
Inventors: |
Crothers; Sarah Lori;
(Greenville, SC) ; Ziminsky; Willy Steve;
(Simpsonville, SC) ; Stevenson; Christian Xavier;
(Inman, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
49596124 |
Appl. No.: |
13/680379 |
Filed: |
November 19, 2012 |
Current U.S.
Class: |
60/772 ;
60/740 |
Current CPC
Class: |
F02C 9/28 20130101; F23R
3/28 20130101 |
Class at
Publication: |
60/772 ;
60/740 |
International
Class: |
F23R 3/28 20060101
F23R003/28 |
Claims
1. A system for reducing modal coupling of combustion dynamics,
comprising: a. a plurality of combustors; b. at least one fuel
injector in each of the plurality of combustors; and c. means for
dithering a combustion instability frequency in at least one
combustor in the plurality of combustors.
2. The system as in claim 1, wherein the means for dithering the
combustion instability frequency in at least one combustor in the
plurality of combustors dithers a fuel flow to at least one fuel
injector in at least one combustor in the plurality of
combustors.
3. The system as in claim 1, wherein the means for dithering the
combustion instability frequency in at least one combustor in the
plurality of combustors dithers a temperature of a fuel flow to at
least one fuel injector in at least one combustor in the plurality
of combustors.
4. The system as in claim 1, wherein the means for dithering the
combustion instability frequency in at least one combustor in the
plurality of combustors dithers a Wobbe index of a fuel flow to at
least one fuel injector in at least one combustor in the plurality
of combustors.
5. The system as in claim 1, wherein the means for dithering the
combustion instability frequency in at least one combustor in the
plurality of combustors comprises a processor configured to execute
logic stored in a memory that causes the processor to dither at
least one of a fuel flow, a temperature of the fuel flow, or a
Wobbe index of the fuel flow to at least one fuel injector in at
least one combustor in the plurality of combustors.
6. The system as in claim 1, further comprising a compressor
section upstream from the plurality of combustors configured to
produce a compressed working fluid at a temperature and the means
for dithering the combustion instability frequency in at least one
combustor in the plurality of combustors dithers a temperature of a
working fluid entering the compressor section.
7. The system as in claim 1, further comprising a compressor
section upstream from the plurality of combustors configured to
produce a compressed working fluid at a temperature and the means
for dithering the combustion instability frequency in at least one
combustor in the plurality of combustors dithers a flow rate of a
working fluid entering the compressor section.
8. The system as in claim 1, further comprising a compressor
section upstream from the plurality of combustors configured to
produce a compressed working fluid at a temperature and the means
for dithering the combustion instability frequency in at least one
combustor in the plurality of combustors dithers a flow rate of the
compressed working fluid recirculated through the compressor
section.
9. A gas turbine comprising: a. a compressor section configured to
produce a compressed working fluid at a temperature; b. a plurality
of combustors downstream from the compressor section, wherein each
combustor comprises a fuel injector; c. a turbine section
downstream from the plurality of combustors; and d. means for
dithering the temperature of the compressed working fluid produced
by the compressor section.
10. The gas turbine as in claim 9, wherein the means for dithering
the temperature of the compressed working fluid produced by the
compressor section dithers a temperature of a working fluid
entering the compressor section.
11. The gas turbine as in claim 9, wherein the means for dithering
the temperature of the compressed working fluid produced by the
compressor section dithers a flow rate of a working fluid entering
the compressor section.
12. The gas turbine as in claim 9, wherein the means for dithering
the temperature of the compressed working fluid produced by the
compressor section dithers a flow rate of the compressed working
fluid recirculated through the compressor section.
13. The gas turbine as in claim 9, wherein the means for dithering
the temperature of the compressed working fluid produced by the
compressor section comprises a processor configured to execute
logic stored in a memory that causes the processor to dither at
least one of a temperature of a working fluid entering the
compressor section, a flow rate of the working fluid entering the
compressor section, or a flow rate of the compressed working fluid
recirculated through the compressor section.
14. The gas turbine as in claim 9, further comprising means for
dithering a fuel flow to at least one fuel injector in at least one
combustor in the plurality of combustors.
15. The gas turbine as in claim 14, wherein the means for dithering
the fuel flow to at least one fuel injector in at least one
combustor in the plurality of combustors dithers the fuel flow to
each fuel injector in the plurality of combustors.
16. A method for reducing modal coupling of combustion dynamics,
comprising: a. flowing a compressed working fluid at a temperature
to a plurality of combustors; b. flowing a fuel to at least one
fuel injector in each of the plurality of combustors; and c.
dithering at least one of the temperature of the compressed working
fluid flowing to the plurality of combustors or the fuel flow to
the at least one fuel injector in at least one combustor in the
plurality of combustors.
17. The method as in claim 16, further comprising dithering a
temperature of the fuel flow to at least one fuel injector in at
least one combustor in the plurality of combustors.
18. The method as in claim 16, further comprising dithering a Wobbe
index of the fuel flow to at least one fuel injector in at least
one combustor in the plurality of combustors.
19. The method as in claim 16, dithering a flow rate of the
compressed working recirculated through a compressor.
20. The method as in claim 16, further comprising compressing a
working fluid to produce the compressed working fluid and dithering
at least one of a temperature or flow rate of the working fluid.
Description
FIELD OF THE INVENTION
[0001] The present invention generally involves a system and method
for reducing modal coupling of combustion dynamics. In particular
embodiments, the system and method may be incorporated into a gas
turbine or other turbomachine.
BACKGROUND OF THE INVENTION
[0002] Combustors are commonly used in industrial and commercial
operations to ignite fuel to produce combustion gases having a high
temperature and pressure. For example, gas turbines and other
turbomachines typically include one or more combustors to generate
power or thrust. A typical gas turbine used to generate electrical
power includes an axial compressor at the front, multiple
combustors around the middle, and a turbine at the rear. Ambient
air enters the compressor as a working fluid, and the compressor
progressively imparts kinetic energy to the working fluid to
produce a compressed working fluid at a highly energized state. The
compressed working fluid exits the compressor and flows through one
or more fuel injectors in the combustors where the compressed
working fluid mixes with fuel before igniting to generate
combustion gases having a high temperature and pressure. The
combustion gases flow to the turbine where they expand to produce
work. For example, expansion of the combustion gases in the turbine
may rotate a shaft connected to a generator to produce
electricity.
[0003] Various factors influence the design and operation of the
combustors. For example, higher combustion gas temperatures
generally improve the thermodynamic efficiency of the combustors.
However, higher combustion gas temperatures also promote flame
holding conditions in which the combustion flame migrates toward
the fuel being supplied by the fuel injectors, possibly causing
accelerated wear to the fuel injectors in a relatively short amount
of time. In addition, higher combustion gas temperatures generally
increase the disassociation rate of diatomic nitrogen, increasing
the production of nitrogen oxides (NO.sub.x). Conversely, a lower
combustion gas temperature associated with reduced fuel flow and/or
part load operation (turndown) generally reduces the chemical
reaction rates of the combustion gases, increasing the production
of carbon monoxide and unburned hydrocarbons.
[0004] At particular operating conditions, combustion dynamics at
specific frequencies and with sufficient amplitudes, which are
in-phase and coherent, may produce undesirable sympathetic
vibrations in the turbine and/or other downstream components.
Typically, this problem is managed by combustor tuning Combustor
tuning to protect the turbine buckets, however, may impose severe
restrictions on the function and operability of the combustor.
[0005] Altering the frequency relationship between two or more
combustors may reduce the coherence of the combustion system as a
whole, diminishing any combustor-to-combustor coupling. In the
context of this invention, coherence refers to the strength of the
linear relationship between two (or more) dynamic signals, which is
strongly influenced by the degree of frequency overlap between
them. As the combustion dynamics frequency in one combustor is
driven away from that of the other combustors, modal coupling of
combustion dynamics is reduced, which, in turn, reduces the ability
of the combustor tone to cause a vibratory response in downstream
components. Therefore, a system and method that reduces the modal
coupling of combustion dynamics by altering the frequency
difference between two or more combustors would be useful for
enhancing the thermodynamic efficiency of the combustors,
protecting against accelerated wear, promoting flame stability,
and/or reducing undesirable emissions over a wide range of
operating levels, without detrimentally impacting the life of the
downstream hot gas path components.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Aspects and advantages of the invention are set forth below
in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0007] One embodiment of the present invention is a system for
reducing modal coupling of combustion dynamics. The system includes
a plurality of combustors, and at least one fuel injector in each
of the plurality of combustors. The system also includes means for
dithering a combustion instability frequency in at least one
combustor in the plurality of combustors.
[0008] Another embodiment of the present invention is a gas turbine
that includes a compressor section configured to produce a
compressed working fluid at a temperature, a plurality of
combustors downstream from the compressor section, wherein each
combustor comprises a fuel injector, and a turbine section
downstream from the plurality of combustors. The gas turbine
further includes means for dithering the temperature of the
compressed working fluid produced by the compressor section.
[0009] The present invention may also include a method for reducing
modal coupling of combustion dynamics that includes flowing a
compressed working fluid at a temperature to a plurality of
combustors and flowing a fuel to at least one fuel injector in each
of the plurality of combustors. The method further includes
dithering at least one of the temperature of the compressed working
fluid flowing to the plurality of combustors or the fuel flow to
the at least one fuel injector in at least one combustor in the
plurality of combustors.
[0010] Those of ordinary skill in the art will better appreciate
the features and aspects of such embodiments, and others, upon
review of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A full and enabling disclosure of the present invention,
including the best mode thereof to one skilled in the art, is set
forth more particularly in the remainder of the specification,
including reference to the accompanying figures, in which:
[0012] FIG. 1 is a simplified side cross-section view of an
exemplary gas turbine according to various embodiments of the
present invention;
[0013] FIG. 2 is a simplified side cross-section view of an
exemplary combustor according to various embodiments of the present
invention;
[0014] FIG. 3 is an upstream plan view of the cap assembly shown in
FIG. 2 according to an embodiment of the present invention;
[0015] FIG. 4 is an upstream plan view of the cap assembly shown in
FIG. 2 according to an alternate embodiment of the present
invention;
[0016] FIG. 5 is a simplified side cross-section view of a system
for dithering the compressor discharge temperature according to
various embodiments of the present invention;
[0017] FIG. 6 is a diagram of a system for dithering fuel to the
combustors according to alternate embodiments of the present
invention; and
[0018] FIG. 7 is an exemplary flow diagram of a method for
preventing modal coupling of the combustion system, according to
various embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Reference will now be made in detail to present embodiments
of the invention, one or more examples of which are illustrated in
the accompanying drawings. The detailed description uses numerical
and letter designations to refer to features in the drawings. Like
or similar designations in the drawings and description have been
used to refer to like or similar parts of the invention. As used
herein, the terms "first", "second", and "third" may be used
interchangeably to distinguish one component from another and are
not intended to signify location or importance of the individual
components. The terms "upstream," "downstream," "radially," and
"axially" refer to the relative direction with respect to fluid
flow in a fluid pathway. For example, "upstream" refers to the
direction from which the fluid flows, and "downstream" refers to
the direction to which the fluid flows. Similarly, "radially"
refers to the relative direction substantially perpendicular to the
fluid flow, and "axially" refers to the relative direction
substantially parallel to the fluid flow.
[0020] Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that modifications and
variations can be made in the present invention without departing
from the scope or spirit thereof. For instance, features
illustrated or described as part of one embodiment may be used on
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0021] Various embodiments of the present invention include a
system and method for reducing modal coupling of combustion
dynamics. The system and method generally include multiple
combustors, and each combustor includes one or more fuel injectors
for mixing fuel with a compressed working fluid prior to
combustion. The system and method may further include means for
dithering a combustion instability frequency in at least one
combustor. In particular embodiments, the means for dithering the
combustion instability frequency in at least one combustor may
dither a temperature of the compressed working fluid and/or dither
a fuel flow to one or more fuel injectors. As used herein, the term
"dithering" means modulating or oscillating, and the timing and
amount of the dithering may be random, scheduled, and/or in
response to one or more of the amplitude, phase, coherence, and/or
frequencies of combustion instabilities in two or more combustors.
In particular embodiments, the system and method may dither at
least one of a temperature of a working fluid entering a compressor
section, a flow rate of the working fluid entering the compressor
section, or a flow rate of the compressed working fluid
recirculated through the compressor section. Alternately or in
addition, the system and method may dither at least one of the fuel
flow, a temperature of the fuel flow, or a Wobbe index of the fuel
flow to one or more of the fuel injectors in one or more of the
combustors. As a result, various embodiments of the present
invention may dither the frequency relationship between two or more
combustors to reduce the coherence of the combustion system as a
whole and diminish any combustor-to-combustor coupling. This may
reduce the ability of the combustor tone to cause a vibratory
response in downstream components. Although exemplary embodiments
of the present invention will be described generally in the context
of combustion dynamics in a gas turbine for purposes of
illustration, one of ordinary skill in the art will readily
appreciate that embodiments of the present invention may be applied
to any combustion dynamics and are not limited to a gas turbine
unless specifically recited in the claims.
[0022] Referring now to the drawings, wherein identical numerals
indicate the same elements throughout the figures, FIG. 1 provides
a simplified side cross-section view of an exemplary gas turbine 10
that may incorporate various embodiments of the present invention.
As shown, the gas turbine 10 may generally include an inlet section
12, a compressor section 14, a combustion section 16, a turbine
section 18, and an exhaust section 20. The inlet section 12 may
include a series of filters 22 and one or more fluid conditioning
devices 24 to clean, heat, cool, moisturize, demoisturize, and/or
otherwise condition a working fluid (e.g., air) 28 entering the gas
turbine 10. The cleaned and conditioned working fluid 28 flows to a
compressor 30 in the compressor section 14. A compressor casing 32
contains the working fluid 28 as alternating stages of rotating
blades 34 and stationary vanes 36 progressively accelerate and
redirect the working fluid 28 to produce a continuous flow of
compressed working fluid 38 at a higher temperature and
pressure.
[0023] The majority of the compressed working fluid 38 flows
through a compressor discharge plenum 40 to one or more combustors
42 in the combustion section 16. A fuel supply 44 in fluid
communication with each combustor 42 supplies a fuel to each
combustor 42. Possible fuels may include, for example, blast
furnace gas, coke oven gas, natural gas, methane, vaporized
liquefied natural gas (LNG), hydrogen, syngas, butane, propane,
olefins, diesel, petroleum distillates, and combinations thereof.
The compressed working fluid 38 mixes with the fuel and ignites to
generate combustion gases 46 having a high temperature and
pressure.
[0024] The combustion gases 46 flow along a hot gas path through a
turbine 48 in the turbine section 18 where they expand to produce
work. Specifically, the combustion gases 46 may flow across
alternating stages of stationary nozzles 50 and rotating buckets 52
in the turbine 48. The stationary nozzles 50 redirect the
combustion gases 46 onto the next stage of rotating buckets 52, and
the combustion gases 46 expand as they pass over the rotating
buckets 52, causing the rotating buckets 44 to rotate. The rotating
buckets 52 may connect to a shaft 54 that is coupled to the
compressor 30 so that rotation of the shaft 54 drives the
compressor 30 to produce the compressed working fluid 46.
Alternately or in addition, the shaft 54 may connect to a generator
56 for producing electricity. Exhaust gases 58 from the turbine
section 18 flow through the exhaust section 20 prior to release to
the environment.
[0025] The combustors 42 may be any type of combustor known in the
art, and the present invention is not limited to any particular
combustor design unless specifically recited in the claims. FIG. 2
provides a simplified side cross-section view of an exemplary
combustor 42 according to various embodiments of the present
invention. As shown in FIG. 2, a combustor casing 60 and an end
cover 62 may combine to contain the compressed working fluid 38
flowing to the combustor 42. A cap assembly 64 may extend radially
across at least a portion of the combustor 42, and one or more fuel
injectors 66 may be radially arranged across the cap assembly 64 to
supply fuel to a combustion chamber 70 downstream from the cap
assembly 64. A liner 72 may circumferentially surround at least a
portion of the combustion chamber 70, and a transition duct 74
downstream from the liner 72 may connect the combustion chamber 70
to the inlet of the turbine 48. An impingement sleeve 76 with flow
holes 78 may circumferentially surround the transition duct 74, and
a flow sleeve 88 may circumferentially surround the liner 72. In
this manner, the compressed working fluid 38 may pass through the
flow holes 78 in the impingement sleeve 76 to flow through an
annular passage 80 outside of the transition duct 74 and liner 72.
When the compressed working fluid 38 reaches the end cover 62, the
compressed working fluid 38 reverses direction to flow through the
fuel injectors 66 into the combustion chamber 70.
[0026] Although generally shown as cylindrical, the radial
cross-section of the fuel injectors 66 may be any geometric shape,
and the present invention is not limited to any particular radial
cross-section unless specifically recited in the claims. In
addition, various embodiments of the combustor 42 may include
different numbers and arrangements of fuel injectors 66 in the cap
assembly 64.
[0027] FIGS. 3 and 4 provide upstream plan views of exemplary
arrangements of the fuel injectors 66 in the cap assembly 64 within
the scope of the present invention. As shown in FIG. 3, for
example, multiple fuel injectors 66 may be radially arranged around
a single fuel injector 66. Alternatively, a plurality of
non-circular pie-shaped fuel injectors 68 may circumferentially
surround a single fuel injector 66, as shown in FIG. 4. One of
ordinary skill in the art will readily appreciate multiple other
shapes and arrangements for the fuel injectors 66, 68 from the
teachings herein, and the particular shape and arrangement of the
fuel injectors 66, 68 are not limitations of the present invention
unless specifically recited in the claims.
[0028] The fuel injectors 66, 68 may be divided into various groups
or circuits to facilitate multiple fueling regimes over the range
of operations. For example, in the exemplary arrangements shown in
FIGS. 3 and 4, the center fuel injector 66 and/or one of the outer
fuel injectors 66, 68 may receive fuel from a first fuel circuit
82, while one or more of the surrounding fuel injectors 66, 68 may
be grouped to receive the same or a different fuel from a second
and/or third fuel circuit 84, 86. During base load operations, fuel
may be supplied to each fuel injector 66, 68 shown in FIGS. 3 and 4
through all three fuel circuits 82, 84, 86, while fuel flow may be
reduced or completely eliminated from one or more of the fuel
injectors 66, 68 during reduced or turndown operations.
[0029] An overlap between the combustion instability frequency and
the downstream component resonant frequency may result in unwanted
vibration of the downstream components. Alternately or in addition,
a coherent relationship between the frequencies of two or more
combustors 42 may exacerbate the vibratory response of the
downstream components. Various embodiments of the present invention
seek to vary or oscillate the frequency in the combustors such that
there is a timing delay in the frequency variation between two or
more combustors 42 by dithering the temperature of the compressed
working fluid 38 and/or the fuel flow supplied to the combustors
42. The timing and amount of the dithering may be random,
scheduled, and/or in response to one or more of the amplitude,
phase, coherence and/or frequency of the combustion instabilities.
In this manner, the embodiments of the present invention may
produce a combustion instability frequency in a first combustor
that is different from the combustion instability frequency in a
second combustor, reducing the modal coupling of combustion
dynamics and/or coherence of the combustion system.
[0030] FIG. 5 provides a simplified cross-section view of a system
90 for dithering the combustion instability frequency by dithering
the compressor 30 discharge temperature according to various
embodiments of the present invention. A change in the temperature
of the compressed working fluid 38 produced by the compressor
section 14 directly affects the combustion instability frequency of
each combustor 42. As shown in FIG. 5, the system 90 may be
incorporated into the gas turbine 10 previously described with
respect to FIG. 1 and may include various means for dithering the
temperature of the compressed working fluid 38 produced by the
compressor section 14. The function of the means is to modulate or
oscillate the temperature of the compressed working fluid 38
produced by the compressor section 14, and the timing and amount of
the dithering may be random, scheduled, and/or in response to one
or more of the amplitude, phase, coherence, and/or frequency of the
combustion instabilities.
[0031] In one particular embodiment shown in FIG. 5, the means may
accomplish this function by dithering a temperature of the working
fluid 28 entering the compressor section 14 using evaporative
cooling, heat exchangers, or other temperature-altering devices
known in the art. As shown in FIG. 5, the structure associated with
dithering the temperature of the working fluid 28 entering the
compressor section 14 may include a control valve 92, throttle
valve, thermostatic expansion valve, or other suitable flow control
device operably connected to the one or more temperature-altering
devices 24, such as heat exchangers or evaporative coolers, in the
inlet section 12. The control valve 92 may be manually and/or
remotely repositioned randomly or at desired intervals to
alternately increase or decrease heating or cooling provided to the
working fluid 28 flowing through the inlet section 12. In this
manner, the means may vary or oscillate the temperature of the
working fluid 28 entering the compressor section 14, which in turn
will vary or oscillate the temperature of the compressed working
fluid 38 produced by the compressor section 14.
[0032] In a second embodiment shown in FIG. 5, the means may
accomplish the function of varying or oscillating the temperature
of the compressed working fluid 38 produced by the compressor
section 14 by dithering a flow rate of the working fluid 28
entering the compressor section 14. As shown in FIG. 5, the
structure associated with dithering the flow rate of the working
fluid 28 entering the compressor section 14 may include an actuator
94 or other operator operably connected to one or more inlet guide
vanes 96 installed in the compressor 30. The actuator 94 or other
operator may be manually and/or remotely repositioned at random or
periodic intervals to alternately open or close the inlet guide
vanes 96, thereby increasing or decreasing the flow rate of the
working fluid 28 entering the compressor section 14. In alternate
embodiments, the structure associated with dithering the flow rate
of the working fluid 28 entering the compressor section 14 may
include one or more sets of stationary vanes 36 having variable
positions, also known as variable stator vanes, to vary or
oscillate the flow rate of the working fluid 28 through the
compressor 30. In this manner, the means may vary or oscillate the
flow rate of the working fluid 28 through the compressor 30, which
in turn will vary or oscillate the temperature of the compressed
working fluid 38 produced by the compressor section 14.
[0033] FIG. 5 provides a third example of suitable structure for
dithering the temperature of the compressed working fluid 38
produced by the compressor section 14. Specifically, the means may
accomplish the function of varying or oscillating the temperature
of the compressed working fluid 38 produced by the compressor
section 14 by dithering a flow rate of the compressed working fluid
38 recirculated through the compressor section 14. As shown in FIG.
5, the structure associated with dithering the flow rate of the
compressed working fluid 38 recirculated through the compressor
section 14 may include a conduit 98, pipe, or other fluid
connection between a downstream portion of the compressor 30 and
the inlet of the compressor 30. A control valve 100, throttle
valve, thermostatic expansion valve, or other suitable flow control
device may be manually and/or remotely repositioned at random or
periodic intervals to alternately increase or decrease the flow
rate of the compressed working fluid 38 diverted through the
conduit 98 to recirculate through the compressor section 14. In
alternate embodiments, the means may include an additional heat
exchanger (not shown) operably connected to the conduit 98 to
alternately heat or cool the compressed working fluid 38
recirculated through the compressor section 14. In this manner, the
means may vary or oscillate the flow rate and/or temperature of the
compressed working fluid 38 recirculated through the compressor
section 14, which in turn will vary or oscillate the temperature of
the compressed working fluid 38 produced by the compressor section
14.
[0034] In each embodiment shown in FIG. 5, the system 90 may
optionally include a processor 102 to remotely and/or automatically
control the dithering of the temperature of the compressed working
fluid 38 produced by the compressor section 14. The processor 102
may generally be any suitable processing device known in the art
and may include a memory 104 for storing logic 106 executable by
the processor 102. The memory 104 may generally be any suitable
computer-readable medium or media, including, but not limited to,
RAM, ROM, hard drives, flash drives, or other memory devices. As is
generally understood, the memory 104 may be configured to store
information accessible by the processor 102, including instructions
or logic 106 that can be executed by the processor 102. The
instructions or logic 106 may be any set of instructions that when
executed by the processor 102 cause the processor 102 to provide
the desired functionality. For instance, the instructions or logic
106 can be software instructions rendered in a computer-readable
form. When software is used, any suitable programming, scripting,
or other type of language or combinations of languages may be used
to implement the teachings contained herein. Alternatively, the
instructions can be implemented by hard-wired logic or other
circuitry, including, but not limited to application-specific
circuits.
[0035] The technical effect of the processor 102 is to execute the
logic 106 stored in the memory 104 to cause the processor 102 to
dither at least one of the temperature of the working fluid 28
entering the compressor section 14, the flow rate of the working
fluid 28 entering the compressor section 14, or the flow rate of
the compressed working fluid 38 recirculated through the compressor
section 14. As shown in FIG. 5, the processor 102 may be operably
connected to one or more of the control valves 92, 100 and/or the
actuator 94 to vary or oscillate the position or operation of these
components. In particular embodiments, the processor 102 may be
programmed to continuously dither the various control valves 92,
100 and/or the actuator 94, while in other particular embodiments,
the processor 102 may be programmed to dither the various control
valves 92, 100 and/or the actuator 94 randomly, when manually
instructed do so, or in response to a sensed combustor instability
that exceeds or drops below a predetermined limit, in terms of
amplitude, frequency, phase, and/or coherence.
[0036] FIG. 6 provides a diagram of a system 110 for dithering the
combustion instability frequency by dithering the fuel flow to one
or more of the combustors 42 according to alternate embodiments of
the present invention. Dithering the fuel flow to one or more of
the fuel circuits supplying one or more of the combustors 42 may
vary or oscillate the frequency of each combustor 42 differently
due to a change in the fuel pressure ratio (i.e., combustor
pressure : fuel pressure) and/or equivalence ratio resulting from
the differences in the fuel flow rate, temperature, and/or energy
content or Wobbe index. The temperature and/or Wobbe index of the
fuel may be oscillated by pulsing the fuel flow with an additional
fuel stream of a different temperature and/or Wobbe index into that
supplying the one or more fuel injectors in one or more
combustors.
[0037] As shown in FIG. 6, the system 110 may be incorporated into
the gas turbine 10 previously described with respect to FIG. 1 and
may include various means for dithering the combustion instability
frequency by dithering the fuel flow to one or more of the fuel
circuits 82, 84, 86 in one or more combustors 42. Although only
three combustors 42 are shown in FIG. 7, the present invention is
not limited to any specific number of combustors 42 unless
specifically recited in the claims. The function of the means is to
modulate or oscillate the fuel flow to one or more of the fuel
circuits 82, 84, 86 supplying one or more of the combustors 42, and
the timing and amount of the dithering may be random, scheduled,
and/or in response to one or more of the amplitude, phase,
coherence and/or frequency of the combustion instabilities.
[0038] In one particular embodiment shown in FIG. 6, the structure
associated with dithering the fuel flow to one or more of the
combustors 42 may include a control valve 112, throttle valve, or
other suitable flow control device operably connected to one or
more of the fuel circuits 82, 84, 86 that supply fuel to one or
more of the combustors 42. Each control valve 112 in the respective
fuel circuits 82, 84, 86 may be manually and/or remotely
repositioned randomly or at desired intervals to alternately
increase or decrease the fuel flow into one more of the fuel
circuits 82, 84, 86.
[0039] In other particular embodiments, the means for dithering the
fuel flow to one or more of the combustors 42 may accomplish this
function by dithering the fuel flow to one or more fuel injectors
66 in one or more of the combustors 42. In still further particular
embodiments, the means may accomplish this function by dithering a
Wobbe index by pulsing fuel of a different Wobbe index into the
fuel flow supplying one or more of the fuel injectors 66 in one or
more of the combustors 42. The structure associated with varying or
oscillating the fuel flow to one or more fuel injectors 66 or the
Wobbe index of the fuel flow to one or more of the combustors 42
may include individual control valves 114, throttle valves, or
other suitable flow control devices operably connected between an
alternate fuel supply and/or a heat exchanger and one or more fuel
circuits 82, 84, 86 supplying one or more fuel injectors 66 in one
or more combustors 42. Each individual control valve 114 may be
manually and/or remotely repositioned randomly or at desired
intervals to change the fuel flow supplied to one or more fuel
circuits of one or more combustors 42, thus changing the fuel flow
and/or Wobbe index of the fuel flow to the fuel injectors 66 and/or
combustors 42. One of ordinary skill in the art will readily
appreciate from the teachings herein that the individual control
valves 114 between one or more fuel circuits 82, 84, 86 and one or
more fuel injectors 66 may be present in addition to, or in place
of, the control valves 112 in the respective fuel circuits 82, 84,
86. In this manner, the fuel flow from one or more fuel circuit 82,
84, 86 may be varied or oscillated to one or more fuel injectors 66
and/or combustors 42 to vary or oscillate the frequency of one or
more combustors 42.
[0040] In yet another particular embodiment shown in FIG. 6, the
means may accomplish the function of varying or oscillating the
fuel flow to the combustors 42 by dithering a temperature of the
fuel flow to the combustors 42. As shown in FIG. 6, the structure
associated with dithering the temperature of the fuel flow to the
combustors 42 may further include a control valve 116, throttle
valve, thermostatic expansion valve, or other suitable flow control
device operably connected to one or more heat exchangers 118 used
to adjust the temperature of the fuel in one or more of the fuel
circuits 82, 84, 86. One or more of the control valves 112, 114
previously described may permit pulsing of the fuel from the heat
exchanger and into one or more of the fuel injectors 66 in one or
more of the combustors 42. In this manner, the means may vary or
oscillate the temperature of the fuel flow to the combustors 42,
which in turn will vary or oscillate the fuel flow to the
combustors 42.
[0041] In each embodiment shown in FIG. 6, the system 110 may
optionally include the processor 102, memory 104, and logic 106, as
previously discussed with respect to the embodiment shown in FIG.
5. In this particular embodiment, however, the technical effect of
the processor 102 is to execute the logic 106 stored in the memory
104 to cause the processor 102 to dither at least one of the fuel
flow, the temperature of the fuel flow, or the Wobbe index of the
fuel flow to the combustors 42. As shown in FIG. 6, the processor
102 may be operably connected to one or more of the control valves
112, 114, 116 to vary or oscillate the position or operation of
these components. In particular embodiments, the processor 102 may
be programmed to continuously dither the various control valves
112, 114, 116, while in other particular embodiments, the processor
102 may be programmed to dither the various control valves 112,
114, 116 randomly, when manually instructed do so, or in response
to a sensed combustor instability that exceeds or falls below a
predetermined limit, in terms of amplitude, frequency, phase,
and/or coherence.
[0042] One of ordinary skill in the art will readily appreciate
from the teachings herein that the systems 90, 110 described and
illustrated with respect to FIGS. 5 and 6 may provide various
methods for reducing the coherence of the combustion system, and
FIG. 7 provides an exemplary flow diagram of suitable methods
according to various embodiments of the present invention. The
methods may generally include one or more steps associated with
each section of the gas turbine 10 previously described and
illustrated with respect to FIG. 1. For example, the method may
include filtering and conditioning 120 the working fluid 28 in the
inlet section 12. The method may further include compressing 122
the working fluid 28 to produce the compressed working fluid 38,
and combusting 124 the compressed working fluid 38 with fuel to
produce the combustion gases 46. Lastly, the method may include
flowing the combustion gases 46 through the turbine 48 to generate
126 work and exhausting 128 the exhaust gases 58 to the
environment.
[0043] As described with respect to the particular embodiment shown
in FIG. 5, the method for reducing modal coupling of combustion
dynamics and/or reducing combustion coherence may include dithering
the temperature of the compressed working fluid 38 flowing to the
combustors 42. The method may dither the temperature of the
compressed working fluid 38 flowing to the combustors 42 in one or
more ways. For example, the method may dither the temperature of
the compressed working fluid 38 flowing to the combustors 42 by
dithering the temperature of the working fluid 28 flowing through
the inlet section 12, as indicated by block 130. Alternately, or in
addition, the method may dither the temperature of the compressed
working fluid 38 flowing to the combustors 42 by dithering the flow
rate of the working fluid 38 entering the compressor section 14, as
indicated by block 132. Lastly, the method may dither the
temperature of the compressed working fluid 38 flowing to the
combustors 42 by dithering the flow rate of the compressed working
fluid 38 recirculated in the compressor 30, as indicated by block
134.
[0044] As described with respect to the particular embodiment shown
in FIG. 6, the method for reducing modal coupling of combustion
dynamics and/or reducing combustion coherence may include dithering
the fuel flow to one or more of the fuel injectors 66 of at least
one combustor 42, as indicated by block 136. The method may dither
the fuel flow in one or more ways. For example, the method may
dither the fuel flow to the combustors 42 by dithering the fuel
flow to one or more fuel injectors 66, indicated by block 138.
Alternately, or in addition, the method may dither the fuel flow to
one or more fuel injectors 66 and/or combustors 42 by dithering the
temperature of the fuel flow to one or more fuel injectors 66 in
one or more combustors 42, indicated by block 140. Lastly, the
method may dither the fuel flow to the fuel nozzles 66 and/or
combustors 42 by dithering the Wobbe index of the fuel flow to one
or more of the fuel injectors 66 in one or more of the combustors
42.
[0045] The various embodiments described and illustrated with
respect to FIGS. 1-6 may provide one or more of the following
advantages over existing combustors 42. Specifically, dithering the
temperature of the compressed working fluid 38 and/or the fuel flow
to the combustors 42, alone or in various combinations, may
decouple the combustion dynamics, thereby reducing coherence and/or
modal coupling of combustion dynamics. As a result, the various
embodiments described herein may enhance thermodynamic efficiency,
promote flame stability, and/or reduce undesirable emissions over a
wide range of operating levels, without detrimentally impacting the
life of the downstream hot gas path components.
[0046] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they include structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *