U.S. patent application number 13/409722 was filed with the patent office on 2012-06-28 for system and method for fuel and air mixing in a gas turbine.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Samuel David Draper, Hassan Ul Karim, Christopher John Mordaunt, James Anthony West.
Application Number | 20120159959 13/409722 |
Document ID | / |
Family ID | 40299355 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120159959 |
Kind Code |
A1 |
West; James Anthony ; et
al. |
June 28, 2012 |
System and Method for Fuel and Air Mixing in a Gas Turbine
Abstract
A gas turbine system including a source of gas coupled to a
source of fuel wherein the gas and the fuel are combined to form a
mixture of gas and fuel prior to the mixture being introduced to a
fuel nozzle of the gas turbine system.
Inventors: |
West; James Anthony;
(Simpsonville, SC) ; Draper; Samuel David;
(Simpsonville, SC) ; Karim; Hassan Ul;
(Simpsonville, SC) ; Mordaunt; Christopher John;
(Mifflinburg, PA) |
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
40299355 |
Appl. No.: |
13/409722 |
Filed: |
March 1, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11846209 |
Aug 28, 2007 |
8171716 |
|
|
13409722 |
|
|
|
|
Current U.S.
Class: |
60/772 |
Current CPC
Class: |
F23K 2400/201 20200501;
F23N 1/022 20130101; F23D 14/62 20130101; F23R 3/286 20130101; Y02E
20/16 20130101 |
Class at
Publication: |
60/772 |
International
Class: |
F02C 9/40 20060101
F02C009/40 |
Claims
1. A method for operating a gas turbine, the method comprising:
receiving gas from a source of gas; receiving fuel from a source of
fuel; and mixing the gas with the fuel to form a mixture of gas and
fuel prior to the mixture being introduced to a fuel nozzle of the
gas turbine.
2. The method of claim 1, wherein the mixture is
non-combustible.
3. The method of claim 1, wherein the method is implemented by a
computer program product stored on machine-readable media and
comprising machine executable instructions for operating a gas
turbine, the product comprising instructions for: receiving the gas
from the source of gas; receiving the fuel from the source of fuel;
and mixing the gas with the fuel to form a mixture of gas and fuel
prior to the mixture being introduced to a fuel nozzle of the gas
turbine.
4. The method of claim 1, wherein the gas includes air.
5. A method for operating a gas turbine system, the method
comprising: receiving gas from a source of gas; receiving fuel from
a source of fuel; and combining the gas and the fuel in a portion
of a fuel line connected to fuel nozzle of the gas turbine system
to form a mixture of gas and fuel prior to the mixture being
introduced to the fuel nozzle of the gas turbine system.
6. The method of claim 5, further comprising: measuring a rate of
flow of the fuel in the fuel line; and regulating a flow of the gas
from the source of gas responsive to the measured rate of flow of
the fuel in the fuel line.
7. The method of claim 5, wherein the rate of flow of the fuel in
the fuel line is measured with a sensor.
8. The method of claim 5, wherein the flow of the gas from the
source of gas is regulated with a control valve.
9. The method of claim 5, wherein the gas includes air.
10. The method of claim 5, wherein the gas includes air and at
least one of carbon dioxide, additional nitrogen, and steam.
11. The method of claim 5, wherein the fuel is in at least one of a
gaseous state and a liquid state.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of application Ser. No.
11/846,209, filed Aug. 28, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention disclosed herein relates to the field of gas
turbines and, in particular, to increasing the efficiency and
limiting the emissions of lean premixed gas turbines.
[0004] 2. Description of the Related Art
[0005] Gas turbines are used to generate a significant portion of
electricity to the public and industry. It is important for the gas
turbines to operate efficiently and with low emissions. Several
operating factors can influence efficiency and emissions.
[0006] Combustion temperature in a combustion chamber of a gas
turbine is one factor that can influence efficiency. Generally, an
increase in the combustion temperature results in an increase in
efficiency.
[0007] The amount of mixing of fuel and air prior to combustion can
influence emissions. During lean premixed combustion, if the fuel
and air are not properly mixed, then local areas in the combustion
chamber can have mixtures that are either richer or leaner than the
surrounding mixture. These richer mixtures burn at higher
temperatures than the average combustion temperature and create
what are known as "hot zones." The hot zones generally contribute
to larger rates of production of nitrous oxides (NO.sub.x).
Conversely, leaner mixtures burn at temperatures lower than the
average combustion temperature. Combustion of the lean mixtures
generally can result in the formation of additional carbon monoxide
(CO).
[0008] The degree of mixing of the fuel and air in the gas turbine
is important to controlling emissions. In addition, if the
emissions can be held constant with an increase in combustion
temperature, then the gas turbine can be operated with increased
efficiency.
[0009] Fuel and air mixing is generally performed in the combustion
chamber or in the mixing section of a fuel nozzle. The fuel nozzle
is used to inject fuel into the incoming airstream, provide a
mixing region, and then direct the fuel/air mixture into the
combustion chamber. In general, the fuel and the air are each
provided by a stream. Improvements to the fuel and air mixing have
been handled by modifying or adjusting at least one of generation
of air swirl, the type of fuel nozzles, and locations of the fuel
nozzles relative to the stream of air. For example, the use of
vanes in the stream of air is one way to increase swirl. Even with
the improvements described above, some degree of uneven mixing
still occurs.
[0010] Therefore, what are needed are techniques to improve the
mixing of fuel and air for combustion in a gas turbine.
BRIEF DESCRIPTION OF THE INVENTION
[0011] Disclosed is a gas turbine system including a source of gas
coupled to a source of fuel wherein the gas and the fuel are
combined to form a mixture of gas and fuel prior to the mixture
being introduced to a fuel nozzle of the gas turbine system.
[0012] Also disclosed is a gas turbine including an air-line
comprising air, the air-line coupled to a fuel-line comprising a
gas wherein the air and the gas are combined to form a mixture of
air and gas prior to the mixture being introduced to a fuel nozzle
of the gas turbine; and a control system for controlling a ratio of
air and gas in the mixture.
[0013] Also disclosed is a method for operating a gas turbine, the
method including receiving air from a source of air; receiving fuel
from a source of fuel; and mixing the air with the fuel to form a
mixture of air and fuel prior to the mixture being introduced to a
fuel nozzle of the gas turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] 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:
[0015] FIG. 1 illustrates an exemplary embodiment of a gas
turbine;
[0016] FIG. 2 illustrates an exemplary embodiment of a control
system for pre-mixing air and fuel;
[0017] FIGS. 3A and 3B, collectively referred to as FIG. 3,
illustrate another exemplary embodiment of the gas turbine with
premixing of fuel and air;
[0018] FIG. 4 illustrates an exemplary graph of nitrous oxide
emissions versus flame temperature; and
[0019] FIG. 5 presents an exemplary method for operating the gas
turbine.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The teachings provide embodiments of apparatus and methods
for mixing fuel and air prior to combustion in a gas turbine. In
particular, the apparatus and methods provide for more even mixing
of the fuel and the air than the mixing performed in the prior art.
In one embodiment of the prior art, the fuel and the air are
injected separately towards the head-end of a combustion chamber in
the gas turbine. The fuel is injected using a fuel nozzle supplied
by a fuel line. In the combustion chamber, the fuel and the air are
mixed using swirl among other features prior to combustion. The
teachings provide for pre-mixing the fuel with an amount of air
prior to the mixture entering the fuel nozzle. In a non-limiting
embodiment, the fuel is mixed with the amount of air in the fuel
line. The amount of air is selected to preclude combustion prior to
entering the fuel nozzle. In the embodiments presented below,
natural gas is used as the fuel. Using natural gas as the fuel,
mixtures of about fifty percent natural gas and about fifty percent
air by volume at 2.758 MPa (400 psia) will generally preclude
combustion as is known to those skilled in the art of natural gas
combustion.
[0021] For convenience, certain definitions are provided before the
teachings are discussed in detail. The term "gas turbine" relates
to a continuous combustion engine. The gas turbine generally
includes a compressor, a combustion chamber and a turbine. The
compressor compresses air for combustion in a combustion chamber.
Hot gasses exit the combustion chamber and turn a turbine. The
turbine is coupled to a shaft, which may also be coupled to an
electric generator. Power generated by the gas turbine can be used
to turn the electric generator to generate electricity. The term
"fuel-line" relates a line for transporting fuel to a fuel nozzle.
The term "fuel nozzle" relates to a nozzle used to inject fuel, and
often air, into the combustion chamber. Fuel nozzles can be of
various designs. In one embodiment, a combustible mixture of fuel
and air is formed at the tip of the fuel nozzle adjacent to the
combustion chamber. The term "equivalence ratio" relates to a
fuel/air ratio divided by the stoichiometric fuel/air ratio. The
term "unmixedness" relates to how well fuel and air are mixed in a
volume. In particular, unmixedness refers to the standard deviation
of equivalence ratios of mixtures throughout the volume divided by
the average of the equivalence ratios. For example, if the standard
deviation of the equivalence ratios of mixtures throughout a volume
is 0.025 and the average equivalence ratio is 0.5, then the
unmixedness of the mixture is five percent (0.05). The term "inlet
bleed-heat air" relates to air extracted from the compressor before
the air is sent to the combustion chamber. The extracted air is
generally heated from the compressing and directed to the inlet of
the compressor.
[0022] 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 shaft 5. In the embodiment of FIG. 1, the shaft 5 is also coupled
to an electric generator 6. The compressor 2 provides compressor
air 14.
[0023] Referring to FIG. 1, a fuel-line 7 is coupled to a fuel
nozzle 8. The fuel nozzle 8 can inject one of fuel and an air-fuel
mixture. Also depicted in FIG. 1 is an air-line 9 coupled on one
end to the compressor 2 and on the other end to the fuel-line 7. In
accordance with the teachings herein, a portion of the compressor
air 14 (referred to herein as "pre-mix air 11") is diverted to the
air-line 9. The air-line 9 provides the pre-mix air 11 to the
fuel-line 7. In the fuel-line 7, the pre-mix air 11 and the fuel 10
are mixed to form an air-fuel mixture 12. The air-fuel mixture 12
is injected via the fuel nozzle 8 into the combustion chamber 3
where the air-fuel mixture 12 is combined with air not diverted
from the compressor air 14 (referred to herein as "direct-air 13")
prior to combustion. The air-fuel mixture 12 and the direct air 13
combine to form a combustible mixture 15 that ignites in the
combustion chamber 3. In one embodiment, the sum of pre-mix air 11
and direct-air 13 is essentially the same as the amount of
combustion air required if there was no pre-mixing of the fuel 10
and the pre-mix air 11. In order to preclude combustion of the
air-fuel mixture 12 in the fuel-line 7, an amount of the pre-mix
air 11 to be pre-mixed with the fuel 10 is controlled by a control
system to provide a safe non-combustible air-fuel mixture 12.
[0024] FIG. 2 illustrates an exemplary embodiment of a control
system 20 for providing the safe air-fuel mixture 12. In the
embodiment of FIG. 2, a flow sensor 21 measures the flow of the
fuel 10 in the fuel-line 7. A controller 22 receives information
related to the flow of the fuel 10 and controls a flow control
valve 23 based on the information. The flow control valve 23
regulates the amount of pre-mix air 11 that is to be pre-mixed with
the fuel 10. An exemplary embodiment of the flow sensor 21 is a
variable orifice as is known to those skilled in the art of flow
sensing.
[0025] FIG. 3 illustrates another exemplary embodiment of the gas
turbine 1. In this embodiment, the gas turbine 1 includes a
plurality of fuel nozzles 8 coupled to a plurality of associated
combustion chambers 3 as depicted in FIG. 3A. In general, the
combustion chambers 3 are disposed circumferentially about a center
axis 30. For teaching purposes, FIG. 3A depicts the control system
20 for one fuel nozzle 8 and associated combustion chamber 3. The
teachings provide the control system 20 to control the air-fuel
mixture 12 delivered to each of the fuel nozzles 8.
[0026] Referring to FIG. 3A, the compressor air 14 enters a plenum
31 where a portion of the compressor air 14 is diverted as the
pre-mix air 11. Flow of the pre-mix air 11 is regulated by the flow
control system 20.
[0027] FIG. 3B illustrates a more detailed view of the flow nozzle
8 and the associated combustion chamber 3. Referring to the
embodiment of FIG. 3B, the direct air 13 from the plenum 31 enters
an annulus of the combustion chamber 3 and flows towards the flow
nozzle 8. At the flow nozzle 8, the direct air 13 combines with the
air-fuel mixture 12 to form the combustible mixture 15. The
combustible mixture 15 is ignited in each combustion chamber 3.
[0028] The use of the teachings herein provide at least one of a
decrease in emissions of nitrous oxides (NO.sub.X) and an increase
in efficiency of the gas turbine 1. FIG. 4 presents an exemplary
graph depicting the effects of unmixedness on emissions of
NO.sub.X. The graph illustrates plots of NO.sub.X emissions versus
flame temperature in the combustion chamber 3 for different
percentages of unmixedness. As seen in FIG. 4 with respect to the
plot of ten percent unmixedness (S=10%), at a constant level of
NO.sub.X emissions, a one percent improvement in unmixedness allows
for an increase in the flame temperature of approximately
8.33.degree. C. (15.degree. F.). The increase in temperature can
relate to an increase in efficiency of the gas turbine 1. In
combined cycle applications of the gas turbine 1, the 8.33.degree.
C. (15.degree. F.) increase in flame temperature can result in
about a 0.1% increase in combined cycle efficiency. Alternatively,
at a constant flame temperature, the NO.sub.X emissions decrease
approximately two ppm with a one percent improvement in
umixedness.
[0029] FIG. 5 presents an exemplary method 50 for operating the gas
turbine 1. The method 50 calls for receiving 51 pre-mix air 11 from
a source of air. Further, the method 50 calls for receiving 52 the
fuel 10 from a source of fuel. Further, the method 50 calls for
mixing 53 the pre-mix air 11 with the fuel 10 to provide a mixture
of air and fuel to the fuel nozzle 8.
[0030] The embodiments presented above are not intended to be
limiting. The teachings provide for pre-mixing the pre-mix air 11
with the fuel 10 prior to the air-fuel mixture 12 being combined
with the direct air 13. In certain embodiments, the pre-mixing may
be performed in at least one of the fuel line 7, the fuel nozzle 8,
a mixing chamber, and in suitable components known to those skilled
in the art of gas turbines. Mixing of the air-fuel mixture 12 with
the direct air 13 may be performed in at least one of the fuel
nozzle 8, the combustion chamber 3, and in suitable components
known to those skilled in the art of gas turbines. In certain
embodiments, the pre-mix air 11 may be obtained from at least one
of the compressor 2, inlet bleed-heat air, and any suitable source
of air known to those skilled in the art of gas turbines.
[0031] While the discussion above is with respect to using natural
gas as the fuel 10, other fuels, such as gasified coal, or a
combination of fuels and inerts in at least one of a gaseous state
and a liquid state may be used. The teachings provide that the
air-fuel mixture 12 preclude combustion prior to combining with the
direct air 13 to form the combustible mixture 15. A ratio of fuel
10 and pre-mix air 11 that precludes combustion may be determined
by those skilled in the art of combustion of the type of fuel 10
selected.
[0032] In the embodiments presented above, air is used as the gas
that is input to the compressor 2. In other embodiments of the
teachings herein, other gases may be included with the air.
Examples of the other gases include carbon dioxide, steam, and
additional nitrogen over the concentration of nitrogen in air.
[0033] Various components may be included and called upon for
providing for aspects of the teachings herein. For example, the
control system 20 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, a computer
program product stored on machine-readable media and including
machine executable instructions can be input to the digital system.
The computer program product may include instructions that can be
executed by the processor for pre-mixing the pre-mix air 11 with
the fuel 10 at a ratio that precludes combustion of the air-fuel
mixture 12 prior to the air-fuel mixture 12 being introduced to the
fuel nozzle 8. The various components may be included in support of
the various aspects discussed herein or in support of other
functions beyond this disclosure. The technical effect of the
computer program product is to increase the efficiency and limit
the emissions of the gas turbine 1.
[0034] 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.
[0035] 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 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.
* * * * *