U.S. patent application number 13/213433 was filed with the patent office on 2013-02-21 for system and method for operating a combustor.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is Gilbert Otto Kraemer, Andrew Mitchell Rodwell, Matthew M. Scheid, Robert Thomas Thatcher. Invention is credited to Gilbert Otto Kraemer, Andrew Mitchell Rodwell, Matthew M. Scheid, Robert Thomas Thatcher.
Application Number | 20130045449 13/213433 |
Document ID | / |
Family ID | 47172238 |
Filed Date | 2013-02-21 |
United States Patent
Application |
20130045449 |
Kind Code |
A1 |
Thatcher; Robert Thomas ; et
al. |
February 21, 2013 |
SYSTEM AND METHOD FOR OPERATING A COMBUSTOR
Abstract
A system for operating a combustor includes a sensor that
measures an operating parameter associated with the combustor and
generates a signal reflective of the operating parameter. The
operating parameter is reflective of an ash deposition rate or an
accumulated ash buildup. A controller receives the signal, compares
the signal to a predetermined limit, and generates a control
signal. A method for operating a combustor includes operating the
combustor at a first power level that produces a first temperature
that is less than or equal to a first predetermined temperature and
creating a layer of ash. The method further includes measuring an
operating parameter reflective of an ash deposition rate or an
accumulated ash buildup, comparing the operating parameter to a
limit, and operating the combustor at a second power level that
produces a second temperature that is greater than or equal to the
first predetermined temperature.
Inventors: |
Thatcher; Robert Thomas;
(Greer, SC) ; Kraemer; Gilbert Otto; (Greer,
SC) ; Rodwell; Andrew Mitchell; (Greenville, SC)
; Scheid; Matthew M.; (Marietta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thatcher; Robert Thomas
Kraemer; Gilbert Otto
Rodwell; Andrew Mitchell
Scheid; Matthew M. |
Greer
Greer
Greenville
Marietta |
SC
SC
SC
GA |
US
US
US
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
47172238 |
Appl. No.: |
13/213433 |
Filed: |
August 19, 2011 |
Current U.S.
Class: |
431/2 ;
431/75 |
Current CPC
Class: |
F23N 2241/20 20200101;
F02C 7/30 20130101; F23R 2900/00004 20130101; F23J 3/00 20130101;
F02C 9/28 20130101; F23N 1/002 20130101 |
Class at
Publication: |
431/2 ;
431/75 |
International
Class: |
F23N 5/00 20060101
F23N005/00 |
Claims
1. A system for operating a combustor, comprising: a. a sensor that
measures an operating parameter associated with the combustor and
generates a signal reflective of the operating parameter, wherein
the operating parameter is reflective of at least one of an ash
deposition rate or an accumulated ash buildup in a hot gas path; b.
a controller in communication with said sensor to receive said
signal reflective of the operating parameter, wherein said
controller compares said signal reflective of the operating
parameter to a predetermined limit and generates a control signal
for operating the combustor; and c. wherein said control signal
comprises at least one of a signal that permits the combustor to
operate at an increased temperature or a signal that permits the
combustor to operate using fuel containing vanadium.
2. The system as in claim 1, wherein the operating parameter
comprises at least one of a fuel content, a fuel flow rate, a
temperature, a time, or an efficiency associated with the
combustor.
3. The system as in claim 1, wherein the operating parameter is
reflective of at least one of a deposition rate or an accumulated
buildup of a soluble ash in the hot gas path.
4. The system as in claim 1, wherein the operating parameter is
reflective of at least one of a deposition rate or an accumulated
buildup of an insoluble ash in the hot gas path.
5. The system as in claim 1, wherein said control signal includes
at least one of maintenance scheduling information, permitted fuel
content, or permitted operating levels associated with the
combustor.
6. The system as in claim 1, further comprising an input device in
communication with said controller, wherein said input device
generates an input signal to said controller.
7. The system as in claim 6, wherein said controller adjusts said
control signal based on said input signal.
8. The system as in claim 6, wherein said input device comprises a
database of parameter information associated with comparable
combustors.
9. A system for operating a combustor in a gas turbine, comprising:
a. a compressor; b. a combustor downstream from said compressor; c.
a fuel supply in fluid communication with said combustor; d. a
turbine downstream from said combustor; e. a signal reflective of
at least one of an ash deposition rate or an accumulated ash
buildup in said turbine; f. a controller that receives said signal,
compares said signal to a predetermined limit, and generates a
control signal for operating the gas turbine; and g. wherein said
control signal comprises at least one of a signal that permits the
combustor to operate at an increased temperature or a signal that
permits the combustor to operate using fuel containing
vanadium.
10. The system as in claim 9, wherein said signal is reflective of
at least one of a deposition rate or an accumulated buildup of a
soluble ash in said turbine.
11. The system as in claim 9, wherein said signal is reflective of
at least one of a deposition rate or an accumulated buildup of an
insoluble ash in said turbine.
12. The system as in claim 9, wherein said control signal includes
at least one of maintenance scheduling information, permitted fuel
content, or permitted operating levels for the gas turbine.
13. The system as in claim 9, further comprising an input device in
communication with said controller, wherein said input device
generates an input signal to said controller.
14. The system as in claim 13, wherein said controller adjusts said
control signal based on said input signal.
15. The system as in claim 13, wherein said input device comprises
a database of parameter information from comparable gas
turbines.
16. A method for operating a combustor, comprising: a. operating
the combustor at a first power level that produces a first
temperature in a hot gas path that is less than or equal to a first
predetermined temperature; b. creating a layer of ash over at least
a portion of the hot gas path; c. measuring an operating parameter
associated with the combustor, wherein the operating parameter is
reflective of at least one of an ash deposition rate or an
accumulated ash buildup in the hot gas path; d. comparing the
operating parameter to a first predetermined limit; and e. when the
operating parameter exceeds the first predetermined limit,
permitting the combustor to operate at a second power level that
produces a second temperature in the hot gas path that is greater
than or equal to the first predetermined temperature.
17. The method as in claim 16, further comprising comparing the
operating parameter to a second predetermined limit.
18. The method as in claim 16, wherein creating the layer of ash
comprises creating a layer of soluble ash over at least a portion
of the hot gas path.
19. The method as in claim 16, wherein creating the layer of ash
comprises creating a layer of insoluble ash over at least a portion
of the hot gas path.
20. The method as in claim 16, further comprising removing the
layer of ash over at least a portion of the hot gas path.
21. The method as in claim 16, further comprising generating a
control signal containing at least one of maintenance scheduling
information, permitted fuel content, or permitted operating levels
for the combustor.
22. A method for operating a combustor, comprising: a. operating
the combustor using a vanadium-free fuel; b. creating a layer of
ash over at least a portion of the hot gas path; c. measuring an
operating parameter associated with the combustor, wherein the
operating parameter is reflective of at least one of an ash
deposition rate or an accumulated ash buildup in the hot gas path;
d. comparing the operating parameter to a first predetermined
limit; and e. when the operating parameter exceeds the first
predetermined limit, permitting the combustor to operate using fuel
containing vanadium.
23. The method as in claim 22, further comprising comparing the
operating parameter to a second predetermined limit.
24. The method as in claim 22, wherein creating the layer of ash
comprises creating a layer of soluble ash over at least a portion
of the hot gas path.
25. The method as in claim 22, wherein creating the layer of ash
comprises creating a layer of insoluble ash over at least a portion
of the hot gas path.
26. The method as in claim 22, further comprising removing the
layer of ash over at least a portion of the hot gas path.
27. The method as in claim 22, further comprising generating a
control signal containing at least one of maintenance scheduling
information, permitted fuel content, or permitted operating levels
for the combustor.
Description
FIELD OF THE INVENTION
[0001] The present invention generally involves a system and method
for operating a combustor. More specifically, the present invention
describes a system and method that controls, limits, or adjusts
operating levels of the combustor to facilitate the use of ash
bearing fuels.
BACKGROUND OF THE INVENTION
[0002] Combustors are commonly used to ignite fuel to produce
combustion gases having a high temperature and pressure. For
example, a typical gas turbine used to generate electrical power
includes an axial compressor at the front, one or more combustors
around the middle, and a turbine at the rear. Ambient air may be
supplied to the compressor, and rotating blades and stationary
vanes in the compressor progressively impart kinetic energy to the
working fluid (air) to produce a compressed working fluid at a
highly energized state. The compressed working fluid exits the
compressor and flows through one or more nozzles into a combustion
chamber in each combustor where the compressed working fluid mixes
with fuel and ignites to generate combustion gases having a high
temperature and pressure. The combustion gases flow along a hot gas
path through 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] The fuel supplied to the combustors may vary according to
several factors. For example, fuel costs and available supplies may
make it desirable to supply the combustor with certain low-value
petroleum fractions, such as very heavy crude oils, heavy
distillates, distillation residues from atmospheric or vacuum
distillation, by-products resulting from deep conversion of oils,
high cycle oils, and slurries derived from fluid catalytic cracking
units. These low-value fuels often contain contaminants and other
impurities, such as oil soluble vanadium, which, when combusted,
produces very corrosive byproducts having a low melting point. For
example, the byproduct vanadium pentoxide V.sub.2O.sub.5,
particularly in association with alkali metals such as sodium or
potassium, is corrosive to metal alloys, ceramics, and thermal
barrier coatings that may line a hot gas path from the combustor
through the turbine.
[0004] Vanadium inhibitors such as calcium, iron, aluminum, and
magnesium oxides or salts or nickel compounds may be added to the
fuel or injected into the combustors. These vanadium inhibitors
react with the vanadium compounds to produce orthovanadate
compounds generally in the general form M.sub.3(VO.sub.4).sub.2, in
which M denotes the vanadium inhibitor. For example, in the
particular case of using magnesium as an inhibitor, a magnesium
orthovanadate Mg.sub.3(VO.sub.4).sub.2 is formed according to the
following reaction:
V.sub.2O.sub.5+3MgO.fwdarw.Mg.sub.3(VO.sub.4).sub.2
In the presence of sulphur oxides, the magnesium orthovanadate
partially decomposes to produce water-soluble magnesium sulphate
MgSO.sub.4 and magnesium pyrovanadate Mg.sub.2V.sub.2O.sub.7
according the following reaction:
Mg.sub.3(VO.sub.4).sub.2+SO.sub.3.fwdarw.Mg.sub.2V.sub.2O.sub.7+MgSO.sub-
.4
At surface temperatures above approximately 1650.degree. F.,
corresponding to a combustor firing temperature of approximately
2000.degree. F., the water-soluble magnesium sulfate decomposes
into a higher density and insoluble magnesium oxide MgO according
to the following reaction:
MgSO.sub.4.fwdarw.MgO+SO.sub.3
[0005] The reaction between the vanadium inhibitors and the
vanadium compounds is thus effective at isolating the vanadium to
protect metal alloys, ceramics, and thermal barrier coatings from
corrosion. However, the orthovanadate compounds
M.sub.3(VO.sub.4).sub.2 and the magnesium sulfate MgSO.sub.4 and
magnesium oxide MgO byproducts also precipitate as ash along the
hot gas path. The ash deposits along the hot gas path progressively
interfere with the aerodynamic and thermal properties of the
surfaces along the hot gas path, reducing the efficiency and/or
power output of the gas turbine.
[0006] The ash deposits may be periodically removed to restore the
efficiency and/or power output of the gas turbine using various
cleaning procedures. For example, a "dry cleaning" procedure may be
performed while the gas turbine is operating at a reduced load by
injecting projectiles, such as nut shell fragments of a calibrated
size, through the combustor. The combustor sinters the projectiles
to produce a slightly abrasive, ash-free material that impinges on
the hot gas path surfaces to erode the ash deposits. Alternately,
or in addition, a "water washing" procedure may be performed while
the gas turbine is off-line by injecting water through the turbine
to dissolve and carry away the ash deposits. However, the water
washing procedure generally requires that the gas turbine be
shutdown and cooled for several hours beforehand to reduce thermal
stresses in the turbine. In addition, both the dry cleaning and
water washing procedures have limited effectiveness at removing the
more dense and insoluble magnesium oxide ash, especially compared
to the effectiveness at removing the magnesium sulfate ash.
[0007] As a result, combustors operating on low-value fuels
containing oil soluble vanadium are generally limited to firing
temperatures of less than 2000.degree. F. to reduce or prevent the
formation of the more dense and insoluble magnesium oxide ash. This
reduced firing temperature produces a corresponding reduction in
the maximum power level and efficiency of the gas turbine.
Therefore, an improved system and method for operating a combustor
that allows the combustor to operate using low value fuels
containing oil soluble vanadium without unduly sacrificing
efficiency, power output, and/or availability would be useful.
BRIEF DESCRIPTION OF THE INVENTION
[0008] 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.
[0009] One embodiment of the present invention is a system for
operating a combustor. The system includes a sensor that measures
an operating parameter associated with the combustor and generates
a signal reflective of the operating parameter. The operating
parameter is reflective of at least one of an ash deposition rate
or an accumulated ash buildup in a hot gas path. A controller in
communication with the sensor receives the signal reflective of the
operating parameter, compares the signal reflective of the
operating parameter to a predetermined limit, and generates a
control signal for operating the combustor.
[0010] Another embodiment of the present invention is a system for
operating a combustor in a gas turbine. The system includes a
compressor, a combustor downstream from the compressor, a fuel
supply in fluid communication with the combustor, and a turbine
downstream from the combustor. A signal is reflective of at least
one of an ash deposition rate or an accumulated ash buildup in the
turbine, and a controller receives the signal, compares the signal
to a predetermined limit, and generates a control signal for
operating the gas turbine.
[0011] The present invention may also include a method for
operating a combustor that includes operating the combustor at a
first power level that produces a first temperature in a hot gas
path that is less than or equal to a first predetermined
temperature, creating a layer of ash over at least a portion of the
hot gas path, and measuring an operating parameter associated with
the combustor, wherein the operating parameter is reflective of at
least one of an ash deposition rate or an accumulated ash buildup
in the hot gas path. The method further includes comparing the
operating parameter to a first predetermined limit and, when the
operating parameter exceeds the first predetermined limit,
permitting the combustor to operate at a second power level that
produces a second temperature in the hot gas path that is greater
than or equal to the first predetermined temperature.
[0012] In yet another embodiment, a method for operating a
combustor includes operating the combustor using a vanadium-free
fuel, creating a layer of ash over at least a portion of the hot
gas path, and measuring an operating parameter associated with the
combustor, wherein the operating parameter is reflective of at
least one of an ash deposition rate or an accumulated ash buildup
in the hot gas path. The method further includes comparing the
operating parameter to a first predetermined limit and, when the
operating parameter exceeds the first predetermined limit,
permitting the combustor to operate using fuel containing
vanadium.
[0013] 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
[0014] 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:
[0015] FIG. 1 is a simplified diagram of an exemplary embodiment of
the present invention incorporated into a gas turbine;
[0016] FIG. 2 is a graph of firing temperature over time according
to one embodiment of the present invention; and
[0017] FIG. 3 is a enlarged view of an airfoil in the turbine shown
in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0018] 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.
[0019] 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.
[0020] Various embodiments of the present invention include a
system and method for operating a combustor. In particular
embodiments, a controls solution may operate the combustor at an
initial firing temperature to produce a soft and water-soluble ash
coating in or along a hot gas path. As used herein, the term
"firing temperature" refers to the temperature of the combustion
gases exiting the combustor. The controls solution may monitor one
or more operating parameters reflective of a thickness of the soft
and water-soluble ash coating, and when the operating parameter(s)
indicates that a sufficient thickness has been achieved, the
controls solution may allow the use of low-value fuels containing
oil soluble vanadium and/or combustor operations at higher firing
temperatures, either of which may produce a more dense and
insoluble ash coating on top of the previously deposited
water-soluble ash coating. The controls solution may continue to
monitor the one or more operating parameters to determine
appropriate intervals between cleaning procedures to reduce
operational limitations and/or shutdowns of the combustor for these
procedures while enhancing the overall efficiency of the combustor.
Although exemplary embodiments of the present invention will be
described generally in the context of a combustor incorporated into
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 combustor and are not limited to a
gas turbine combustor unless specifically recited in the
claims.
[0021] FIG. 1 provides a simplified diagram of an exemplary
embodiment of the present invention incorporated, for example, into
a gas turbine 10 used to produce electricity. As shown, the gas
turbine 10 generally includes an axial compressor 12 at the front,
one or more combustors 14 downstream from the compressor 12, and a
turbine 16 downstream from the combustors 14. As used herein, the
terms "upstream" and "downstream" refer to the relative location of
components in a fluid pathway. For example, component A is upstream
of component B if a fluid flows from component A to component B.
Conversely, component B is downstream of component A if component B
receives a fluid flow from component A.
[0022] Ambient air may be supplied to the compressor 12, and
rotating blades 18 and stationary vanes 20 in the compressor 12
progressively impart kinetic energy to the working fluid (air) to
produce a compressed working fluid at a highly energized state. The
compressed working fluid exits the compressor 12 and flows into a
combustion chamber 22 in each combustor 14. A fuel supply 24 in
fluid communication with each combustor 14 supplies a fuel to each
combustion chamber 22, and the compressed working fluid mixes with
the fuel and ignites to generate combustion gases having a high
temperature and pressure. The combustion gases flow along a hot gas
path 26 through the turbine 16 where they expand to produce work.
Specifically, the combustion gases may flow across alternating
stages of stationary nozzles 28 and rotating buckets 30 in the hot
gas path 26 to rotate a shaft 32 connected to a generator (not
shown) to produce electricity.
[0023] As previously described, various fuels supplied to the
combustors 14 may include contaminants and other impurities, such
as oil soluble vanadium, which, when combusted, produces very
corrosive byproducts having a low melting point. As a result,
additives, such as calcium, iron, aluminum, and magnesium oxides or
salts or nickel compounds, may be added to the fuel or injected
into the combustors 14 to react with and/or stabilize the corrosive
byproducts. Although effective at isolating the corrosive
byproducts, the additives also produce substantial amounts of ash
which precipitates along the hot gas path 26. For example, when
added to a more pure, vanadium-free fuel, the additives tend to
produce a soft, water-soluble ash across a broad range of firing
temperatures. However, when added to a less pure,
vanadium-containing fuel, especially in the presence of sulfur
oxides, the additives tend to produce a soft, water-soluble ash at
firing temperatures below approximately 2000.degree. F. and a
higher density and insoluble ash at firing temperatures above
approximately 2000.degree. F.
[0024] The combustors 14 and/or associated components such as the
compressor 12 and/or turbine 16 have various operating parameters
that are indicative of or reflective of the ash deposition rate
and/or the accumulated ash buildup in the hot gas path 26. For
example, the concentration of vanadium in the fuel directly affects
the rate at which the ash deposits and/or accumulates in the hot
gas path 26, and the firing temperature of the combustors 14 may be
used to characterize the ash formation as being primarily either
magnesium sulfate or magnesium oxide. Therefore, the vanadium
content of the fuel, the fuel flow rate, the operating time, and/or
the firing temperature of the combustors 14 are examples of
operating parameters associated with the combustors 14 that may
indicate and/or reflect the type, rate, and/or accumulated ash
buildup in the hot gas path 26. The ash deposition rate and/or the
accumulated ash buildup in the hot gas path 26 progressively
interferes with the aerodynamic and thermal properties of the
surfaces along the hot gas path 26, which in turn directly affects
the heat transfer characteristics and/or overall thermodynamic
efficiency of the gas turbine 10, compressor 12, combustors 14,
and/or turbine 16. As a result, various pressures, temperatures,
power levels, and/or efficiency calculations associated with the
gas turbine 10, compressor 12, combustors 14, and/or turbine 16
provide alternate or additional operating parameters that may
indicate and/or reflect the ash deposition rate and/or the
accumulated ash buildup in the hot gas path 26. For example, the
accumulation of ash in the hot gas path 26 directly affects the
pressure ratio of the compressor 12 and/or the overall efficiency
of the gas turbine 10. As yet another example, the accumulation of
ash in the hot gas path 26 generally causes a corresponding
increase in the differential pressures and/or temperatures along
the hot gas path 26. One of ordinary skill in the art can readily
appreciate that the preceding examples are only a few of the
operating parameters associated with the combustors 14 that are
indicative or reflective of the ash deposition rate and/or the
accumulated ash buildup in the hot gas path 26, and the various
embodiments of the present invention are not limited to any
particular operating parameter unless specifically recited in the
claims.
[0025] As shown in FIG. 1, a system 40 for operating the combustor
14 may include one or more sensors 42, a controller 44, and an
input device 46. Each sensor 42 measures one or more of the
operating parameters associated with the combustors 14 that
indicate or reflect at least one of the ash deposition rate or
accumulated ash buildup in the hot gas path 26. The sensors 42 may
comprise, for example, any combination of fuel sensors, pressure
sensors, flow sensors, temperature sensors, and other sensors
commonly associated with combustor and/or gas turbine operations.
For example, as shown in FIG. 1, a first sensor 48 may measure the
temperature or pressure of the compressor 12 inlet, a second sensor
50 may measure the fuel content or flow rate, a third sensor 52 may
measure the firing temperature or pressure, and/or a fourth sensor
54 may measure the temperature or pressure of the turbine 16
exhaust. Each sensor 42 generates one or more signals 56 reflective
of the operating parameter being monitored, which in turn indicates
or reflects the ash deposition rate and/or the accumulated ash
buildup in the hot gas path 26 and/or turbine 16.
[0026] The controller 44 is in communication with the one or more
sensors 42 to receive the signals 56 reflective of the operating
parameter. The technical effect of the controller 44 is to compare
the signal(s) 56 reflective of the operating parameter to a
predetermined limit and generate a control signal 62 for operating
the combustor. As used herein, the controller 44 may comprise any
combination of microprocessors, circuitry, or other programmed
logic circuit and is not limited to any particular hardware
architecture or configuration. Embodiments of the systems and
methods set forth herein may be implemented by one or more
general-purpose or customized controllers 44 adapted in any
suitable manner to provide the desired functionality. The
controller 44 may be adapted to provide additional functionality,
either complementary or unrelated to the present subject matter.
For instance, one or more controllers 44 may be adapted to provide
the described functionality by accessing 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. However, software need not be used exclusively,
or at all. For example, as will be understood by those of ordinary
skill in the art without required additional detailed discussion,
some embodiments of the systems and methods set forth and disclosed
herein may also be implemented by hard-wired logic or other
circuitry, including, but not limited to application-specific
circuits. Of course, various combinations of computer-executed
software and hard-wired logic or other circuitry may be suitable,
as well.
[0027] The input device 46 allows a user to communicate with the
controller 44 and may include any structure for providing an
interface between the user and the controller 44. For example, the
input device 46 may comprise a keyboard, computer, terminal, tape
drive, and/or any other device for receiving input from a user and
generating an input signal 58 to the controller 44. In particular
embodiments, the input device 46 may further include a database 60
of operating parameter information associated with comparable
combustors and/or gas turbines. In this manner, the input device 46
may access the database 60 to manually or automatically establish
one or more predetermined limits associated with a desired ash
deposition rate and/or a desired accumulated ash buildup in the hot
gas path 26. The one or more predetermined limits may be included
in the input signal 58, and the controller 44 may compare the one
or more signals 56 reflective of the operating parameter(s) to the
input signal 58 to generate the control signal 62 for operating the
combustor 14. The control signal 62 generated by the controller 44
may include, for example, maintenance scheduling information,
permitted fuel purity, and/or permitted operating levels for the
combustors 14 and/or gas turbine 10. For example, in particular
embodiments, the control signal may include a signal that permits
the combustor to operate at an increased temperature or power
level, while in other particular embodiments, the control signal
may include a signal that permits the combustor to operate using
fuel containing vanadium.
[0028] In a particular embodiment of the present invention using
magnesium as a vanadium inhibitor, for example, a first
predetermined limit may reflect a desired deposition rate and/or
desired accumulated buildup of water-soluble magnesium sulfate in
the hot gas path 26. As the combustor 14 and/or gas turbine 10
initially operates, the control signal 62 generated by the
controller 44 may include permitted operating levels for the
combustor 14 and/or gas turbine 10 that limit the firing
temperature of the combustors 14 to less than approximately
2000.degree. F. to promote the deposition and buildup of
water-soluble magnesium sulfate in the hot gas path 26. When the
signals 56 exceed the first predetermined limit, indicating a
desired accumulation of water-soluble magnesium sulfate in the hot
gas path 26, the control signal 62 generated by the controller 44
may permit the firing temperature of the combustors 14 to exceed
approximately 2000.degree. F., allowing the combustors 14 and thus
the gas turbine 10 to operate at higher power levels and/or higher
firing temperatures to increase the overall thermodynamic
efficiency of the combustors 14 and/or gas turbine 10.
[0029] As the combustors 14 and/or gas turbine 10 operate at higher
power levels and/or firing temperatures greater than approximately
2000.degree. F., higher density and insoluble ash in the form of
magnesium oxide deposits and builds up on top of the previously
accumulated water-soluble magnesium sulfate. A second predetermined
limit may reflect a desired deposition rate and/or desired
accumulated buildup of insoluble magnesium oxide in the hot gas
path 26. As the insoluble magnesium oxide ash builds up in the hot
gas path 26, the signals 56 will eventually indicate that the
second predetermined limit has been met or exceeded, and the
control signal 62 generated by the controller 44 may again limit
the firing temperature of the combustors 14 to less than
approximately 2000.degree. F. to prevent the additional deposition
and buildup of insoluble magnesium oxide ash in the hot gas path
26.
[0030] In another particular embodiment of the present invention,
the combustor 14 may be first operated using a more pure,
vanadium-free fuel, with one or more additives to supplement the
production of the soft, water-soluble ash. As the combustor 14
and/or gas turbine 10 initially operates, the control signal 62
generated by the controller 44 may allow the combustor 14 to
operate across a broad range of firing temperatures but may
restrict or limit the fuel to vanadium-free fuel. The first
predetermined limit may again reflect a desired deposition rate
and/or desired accumulated buildup of water-soluble ash in the hot
gas path 26. When the signals 56 exceed the first predetermined
limit, indicating a desired accumulation of water-soluble ash in
the hot gas path 26, the control signal 62 generated by the
controller 44 may remove the fuel limitation, allowing the
combustors 14 and thus the gas turbine 10 to operate at higher
power levels and/or higher firing temperatures on the less
expensive fuel.
[0031] As previously described, the control signal 62 may thus
alternately limit or permit various power levels, firing
temperatures, and/or fuel content. Alternately or in addition, the
control signal 62 generated by the controller 44 may include
maintenance scheduling information that allows an operator to
schedule a cleaning procedure to remove the accumulated buildup of
magnesium sulfate and/or magnesium oxide ash in the hot gas path
26. For example, the maintenance scheduling information included in
the control signal 62 may allow an operator to schedule a dry
cleaning procedure to coincide with an upcoming anticipated reduced
operating power level and/or firing temperature of the combustor 14
and/or gas turbine 10, such as commonly occurs during nighttime
operations. In other particular embodiments, the operator may use
the maintenance scheduling information to cycle between "lower" and
"higher" firing temperatures to enhance the effectiveness of the
dry cleaning procedure. Alternately, the operator may schedule a
washing procedure to coincide with an upcoming anticipated outage.
The preferential accumulation of the water-soluble ash beneath the
insoluble ash facilitates the removal of the insoluble ash during
the washing procedure. Specifically, it is believed that the
underlying water-soluble ash disrupts the crystal structure of any
insoluble ash coating during cool down of the gas turbine 10,
removing some of the insoluble ash coating and allowing the water
to reach and dissolve the underlying water-soluble ash coating.
During the subsequent start up and heat up of the gas turbine 10,
the residual water vapor further disrupts and removes any insoluble
ash coating remaining in the hot gas path 26.
[0032] FIGS. 2 and 3 illustrate the desired effects of operating
the combustor 14 using the system 40 shown in FIG. 1. Specifically,
FIG. 2 provides a graph of firing temperature versus time, and FIG.
3 provides an enlarged cross-section view of an airfoil 64, such as
may be incorporated into the stationary nozzles 28 and/or rotating
buckets 30 in the turbine 16 shown in FIG. 1. As shown in FIG. 2,
the system 40 provides a method for operating the combustor 14 at a
first power level that produces a first temperature 66 in the hot
gas path 26 that is less than or equal to a first predetermined
temperature 68. As previously described, the first predetermined
temperature 68 may be selected to promote the deposition and
buildup of water-soluble magnesium sulfate in the hot gas path 26.
As a result, the system 40 creates a layer of water-soluble ash 70
over at least a portion of the hot gas path 26, as illustrated on
the airfoil 64 shown in FIG. 3. The system 40 measures one or more
operating parameters associated with the combustor 14 that are
reflective of at least one of the ash deposition rate or the
accumulated ash buildup in the hot gas path 26. The system 40
compares the signals 56 reflective of the operating parameters to
the first predetermined limit, which as previously discussed may
reflect a desired deposition rate and/or desired accumulated
buildup of water-soluble ash in the hot gas path 26. When the
signals 56 meet or exceed the first predetermined limit, the system
40 may operate the combustor at a second power level that produces
a second temperature 72 in the hot gas path 26 that is greater than
or equal to the first predetermined temperature 68. As a result,
the system 40 creates a layer of insoluble ash 74 over at least a
portion of the hot gas path 26, as again illustrated on the airfoil
56 shown in FIG. 3. As previously discussed, the system 40 may
further compare the signals 56 reflective of the operating
parameters to the second predetermined limit, which as previously
discussed may reflect a desired deposition rate and/or desired
accumulated buildup of insoluble ash in the hot gas path 26.
[0033] It is anticipated that the system 40 and methods described
herein may provide several commercial advantages over existing
technologies without requiring the design, purchase, or
installation of any additional hardware. Specifically, the system
40 and methods described herein may allow the use of low value
fuels containing oil soluble vanadium without unduly sacrificing
efficiency, power output, and/or availability of the combustors 14
or gas turbine 10. The establishment of the soft, water-soluble ash
layer allows higher firing temperatures while still allowing water
washing procedures to effectively remove any insoluble ash buildup
in the hot gas path 26. The increased firing temperatures in turn
will increase the available power output and/or overall efficiency
of the combustors 14 and/or gas turbine 10, resulting in
substantial economic benefits.
[0034] 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.
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