U.S. patent application number 11/280664 was filed with the patent office on 2007-05-17 for low emission combustion and method of operation.
Invention is credited to Andrei Tristan Evulet, Jassin Marcel Fritz, Balachandar Varatharajan.
Application Number | 20070107437 11/280664 |
Document ID | / |
Family ID | 37594788 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070107437 |
Kind Code |
A1 |
Evulet; Andrei Tristan ; et
al. |
May 17, 2007 |
Low emission combustion and method of operation
Abstract
A combustor is provided. The combustor includes a combustor
liner and a swirl premixer disposed on a head end of the combustor
liner and configured to provide a fuel-air mixture to the
combustor. The combustor also includes a plurality of tangentially
staged injectors disposed downstream of the swirl premixer on the
combustor liner, wherein each of the plurality of injectors is
configured to introduce the fuel-air mixture in a transverse
direction to a longitudinal axis of the combustor and to
sequentially ignite the fuel-air mixtures from adjacent tangential
injectors.
Inventors: |
Evulet; Andrei Tristan;
(Clifton Park, NY) ; Varatharajan; Balachandar;
(Clifton Park, NY) ; Fritz; Jassin Marcel;
(Muenchen, DE) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Family ID: |
37594788 |
Appl. No.: |
11/280664 |
Filed: |
November 15, 2005 |
Current U.S.
Class: |
60/776 ;
60/748 |
Current CPC
Class: |
F23R 3/286 20130101;
Y02T 50/60 20130101; F23R 3/346 20130101; F23R 3/06 20130101; F23R
3/16 20130101; F23R 3/58 20130101 |
Class at
Publication: |
060/776 ;
060/748 |
International
Class: |
F23R 3/14 20060101
F23R003/14 |
Claims
1. A combustor, comprising: a combustor liner; a swirl premixer
disposed on a head end of the combustor liner and configured to
provide a fuel-air mixture to the combustor; and a plurality of
tangentially staged injectors disposed downstream of the swirl
premixer on the combustor liner; wherein each of the plurality of
injectors is configured to introduce the fuel-air mixture in a
transverse direction to a longitudinal axis of the combustor and to
sequentially ignite the fuel-air mixtures from adjacent tangential
injectors.
2. The combustor of claim 1, wherein the combustor comprises a can
combustor, or a can-annular combustor.
3. The combustor of claim 1, wherein the fuel mixtures introduced
through the plurality of injectors are ignited by utilizing heat
from previous burnt gases from the injectors.
4. The combustor of claim 1, wherein the plurality of injectors are
configured to induce a torroidal momentum inside the combustor to
facilitate flame stabilization.
5. The combustor of claim 1, wherein the swirl premixer is
configured to induce a core swirl of the fuel-air mixture within
the combustor during a startup, or an acceleration, or a turndown
condition of the combustor.
6. The combustor of claim 1, wherein the combustor comprises a Dry
Low Emission (DLE) combustor.
7. The combustor of claim 1, wherein the plurality of injectors are
configured to introduce the fuel-air mixture in a direction at an
angle to the axis of the combustor.
8. The combustor of claim 1, wherein the fuel comprises a natural
gas, or hydrogen, or syngas, or a hydrocarbon, or carbon monoxide,
or a distillate fuel or combinations thereof.
9. The combustor of claim 1, further comprising a plurality of
dilution holes disposed downstream of the injectors for introducing
dilution air to facilitate cooling of combustor walls.
10. The combustor of claim 1, further comprising an igniter to
ignite the fuel-air mixture during the startup condition of the
combustor.
11. The combustor of claim 1, wherein the plurality of injectors
are arranged in a staggered configuration on the combustor liner to
achieve fuel staging within the combustor.
12. The combustor of claim 11, wherein the plurality of injectors
may be staggered axially or tangentially to achieve dynamics
reduction.
13. A gas turbine system, comprising: a compressor configured to
compress ambient air; a combustor in flow communication with the
compressor, the combustor being configured to receive compressed
air from the compressor and to combust a fuel stream to generate a
combustor exit gas stream; wherein the combustor comprises: a swirl
premixer disposed on a head end of the combustor to induce a core
swirl of a fuel-air mixture within the combustor; and a plurality
of tangential injectors disposed downstream of the swirl premixer;
wherein each of the tangential injectors is configured to introduce
fuel-air mixtures in a transverse direction to a longitudinal axis
of the combustor to facilitate sequential ignition of the fuel-air
mixtures through the injector; and a turbine located downstream of
the combustor and configured to expand the combustor exit gas
stream.
14. The gas turbine system of claim 13, wherein the combustor
comprises a can combustor, or a can-annular combustor.
15. The gas turbine system of claim 13, wherein the plurality of
injectors is configured to induce a torroidal movement of the
fuel-air mixture inside the combustor to facilitate flame
stabilization.
16. The gas turbine system of claim 15, wherein the swirl premixer
and the plurality of injectors are configured to substantially
reduce pollutant emissions from the combustor.
17. The gas turbine system of claim 16, wherein the swirl premixer
and the plurality of injectors are configured to facilitate a
turndown capability of the combustor and to facilitate mode
switching to move from a 0% load to about 100% load.
18. The gas turbine system of claim 15, wherein the core swirl of
the fuel-air mixture generated by the swirl premixer facilitates
ignition propagation from the swirl premixer to the plurality of
injectors.
19. The gas turbine system of claim 15, wherein each of the
plurality of injectors is configured to facilitate self-ignition of
the fuel-air mixture through previous burnt gases from an adjacent
injector.
20. The gas turbine system of claim 15, wherein the plurality of
injectors are configured to introduce the fuel-air mixture in a
direction at an angle to the longitudinal axis of the
combustor.
21. The gas turbine system of claim 15, wherein the fuel comprises
a natural gas, or hydrogen, or syngas, or a hydrocarbon, or
combinations thereof.
22. A method of operating a combustor, comprising: generating a
core swirl flow of a fuel-air mixture within the combustor through
a swirl premixer disposed at a head end of the combustor;
transversely introducing fuel-air mixtures downstream of the swirl
premixer through a plurality of injectors; and sequentially
igniting the fuel-air mixtures introduced through each of the
injectors by utilizing heat from previous burnt gases from an
adjacent injector.
23. The method of claim 22, comprising substantially reducing
pollutant emissions generated from the combustor via fuel staging
achieved through the swirl premixer and the plurality of
injectors.
24. The method of claim 22, comprising inducing a toroidal movement
of the fuel-air mixture within the combustor to facilitate flame
stabilization.
25. The method of claim 22, further comprising introducing fuel-air
mixtures in a direction at an angle to a longitudinal axis of
combustor through the plurality of injectors.
26. The method of claim 22, comprising achieving flame
stabilization within the combustor through the swirl premixer
during startup of the combustor and subsequently by self-sustaining
ignition of the fuel-air mixtures through the plurality of
injectors.
27. A method of reducing emissions from a combustor, comprising:
disposing a swirler premixer at a head end of the combustor to
provide a core swirl flow of a fuel-air mixture to the combustor;
and coupling a plurality of tangentially staged injectors
downstream of the swirler premixer to introduce fuel-air mixtures
in a transverse direction to a longitudinal axis of the combustor
and to facilitate sequential ignition of the fuel-air mixtures
through the injectors.
28. The method of claim 27, wherein the core swirl flow of the
fuel-air mixture generated by the swirl premixer facilitates
ignition propagation from the swirl premixer to the plurality of
injectors.
29. The method of claim 28, wherein ignition propagation from the
swirl premixer to the plurality of injectors facilitates flame
stabilization via recirculation of previous burnt gases within the
combustor.
30. A combustor, comprising: a combustor housing; a swirl premixer
disposed on a head end of the combustor housing and configured to
provide a fuel-air mixture to the combustor; and a plurality of
tangentially staged injectors disposed downstream of the swirl
premixer on the combustor housing; wherein each of the plurality of
injectors is configured to introduce the fuel-air mixture in a
transverse direction to a longitudinal axis of the combustor and to
sequentially ignite the fuel-air mixtures from adjacent tangential
injectors.
31. The combustor of claim 30, wherein the fuel mixtures introduced
through the plurality of injectors are ignited by utilizing heat
from previous burnt gases from the injectors.
32. The combustor of claim 30, wherein the plurality of injectors
are configured to induce a torroidal momentum inside the combustor
to facilitate flame stabilization.
33. The combustor of claim 30, wherein the swirl premixer is
configured to induce a core swirl of the fuel-air mixture within
the combustor during a startup, or an acceleration, or a turndown
condition of the combustor.
Description
BACKGROUND
[0001] The invention relates generally to combustors, and more
particularly, to a low emission combustor and method of
operation.
[0002] Various types of gas turbine systems are known and are in
use. For example, aeroderivative gas turbines are employed for
applications such as power generation, marine propulsion, gas
compression, cogeneration, offshore platform power and so forth.
Typically, a gas turbine includes a compressor for compressing an
air flow and a combustor that combines the compressed air with fuel
and ignites the mixture to generate a working gas. Further, the
working gas is expanded through a turbine for power generation.
Typically, the combustor section is arranged coaxially with the
compressor and turbine sections. Further, the design of the
combustor section may be selected based upon the operational layout
of the gas turbine. For example, the combustor employed in a
particular gas turbine may be a can combustor, an annular combustor
or a can-annular combustor.
[0003] Moreover, the combustors for the gas turbines are designed
to minimize emissions such as NO.sub.x and carbon monoxide
emissions. In certain systems, lean premixed combustion technology
is employed to reduce the emissions from such systems. Typically,
NO.sub.x emissions are controlled by reducing the flame temperature
in the reaction zone of the combustor. In operation, low flame
temperature is achieved by premixing fuel and air prior to
combustion. Unfortunately, the window of operability becomes very
small for such combustors and the combustors are required to be
operated away from the lean blow out limit. As a result, it is
difficult to operate the premixers employed in the combustors
outside of their design space. Moreover, when sufficiently lean
flames are subjected to power setting changes, flow disturbances,
or variations in fuel composition, the resulting equivalence ratio
perturbations may cause loss of combustion. Such a blowout may
cause loss of power and expensive down times in stationary
turbines.
[0004] Furthermore, lean premixed combustion may cause fluctuations
in the position of the heat release zone leading to high
fluctuations in pressure. Such fluctuations may reach high
amplitudes and result in substantially higher NO.sub.x emissions
that may damage the combustor hardware.
[0005] Accordingly, there is a need for a combustor that has
reduced NO.sub.x emissions while operating at full power. It would
also be advantageous to provide a combustor for a gas turbine that
will work on a variety of fuels, while maintaining acceptable
levels of pressure fluctuations across the turbine load.
BRIEF DESCRIPTION
[0006] Briefly, according to one embodiment a combustor is
provided. The combustor includes a combustor liner and a swirl
premixer disposed on a head end of the combustor liner and
configured to provide a fuel-air mixture to the combustor. The
combustor also includes a plurality of tangentially staged
injectors disposed downstream of the swirl premixer on the
combustor liner; wherein each of the plurality of injectors is
configured to introduce the fuel-air mixture in a transverse
direction to a longitudinal axis of the combustor and to
sequentially ignite the fuel-air mixtures from adjacent tangential
injectors.
[0007] In another embodiment, a gas turbine system is provided. The
gas turbine system includes a compressor configured to compress
ambient air and a combustor in flow communication with the
compressor, the combustor being configured to receive compressed
air from the compressor and to combust a fuel stream to generate a
combustor exit gas stream. The gas turbine system also includes a
turbine located downstream of the combustor and configured to
expand the combustor exit gas stream. The combustor includes a
swirl premixer disposed on a head end of the combustor to induce a
core swirl of a fuel-air mixture within the combustor and a
plurality of tangential injectors disposed downstream of the swirl
premixer; wherein each of the tangential injectors is configured to
introduce fuel-air mixtures in a transverse direction to a
longitudinal axis of the combustor to facilitate sequential
ignition of the fuel-air mixtures through the injector.
[0008] In another embodiment, a method of operating a combustor is
provided. The method includes generating a core swirl flow of a
fuel-air mixture within the combustor through a swirl premixer
disposed at a head end of the combustor and transversely
introducing fuel-air mixtures downstream of the swirl premixer
through a plurality of injectors. The method also includes
sequentially igniting the fuel-air mixtures introduced through each
of the injectors by utilizing heat from previous burnt gases from
an adjacent injector.
DRAWINGS
[0009] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0010] FIG. 1 is a diagrammatical illustration of a gas turbine
having a low emission combustor in accordance with aspects of the
present technique;
[0011] FIG. 2 is a diagrammatical illustration of the process of
operation of the gas turbine of FIG. 1 in accordance with aspects
of the present technique;
[0012] FIG. 3 is a diagrammatical illustration of the low emission
combustor of FIG. 1 in accordance with aspects of the present
technique;
[0013] FIG. 4 is a diagrammatical illustration of a configuration
of tangential injectors and the axial swirl premixer at head end
employed in the combustor of FIG. 3 in accordance with aspects of
the present technique;
[0014] FIG. 5 is a cross-sectional view of another exemplary
combustor in accordance with aspects of the present technique;
and
[0015] FIG. 6 is a diagrammatical illustration of zones of fuel
staging and sequential ignition achieved through the tangential
injectors and the head end swirl premixer of FIG. 3 in accordance
with aspects of the present technique.
DETAILED DESCRIPTION
[0016] As discussed in detail below, embodiments of the present
technique function to reduce emissions in combustors such as in can
combustors and can-annular combustors employed in gas turbines. In
particular, the present technique includes employing lean premixed
fuel staging and flue gas recirculation within the combustor to
enable a lean operation of the combustor with homogenous combustion
to minimize emissions such as NO.sub.x emissions. In a present
embodiment, the lean premixed fuel staging enables a stable
combustion with a substantially low flame temperature in the
combustor to minimize emissions. Turning now to the drawings and
referring first to FIG. 1 a gas turbine 10 having a low emission
combustor 12 is illustrated. The gas turbine 10 includes a
compressor 14 configured to compress ambient air. The combustor 12
is in flow communication with the compressor 14 and is configured
to receive compressed air from the compressor 14 and to combust a
fuel stream to generate a combustor exit gas stream. In addition,
the gas turbine 10 includes a turbine 16 located downstream of the
combustor 12. The turbine 16 is configured to expand the combustor
exit gas stream to drive an external load. In the illustrated
embodiment, the compressor 16 is driven by the power generated by
the turbine 16 via a shaft 18.
[0017] FIG. 2 illustrates the process of operation of the gas
turbine 10 of FIG. 1. In operation, the compressor 14 receives a
flow of ambient air 20 and compresses the flow of ambient air 20 to
produce a flow of compressed air 22. In certain embodiments, a
boost compressor may be employed to receive and compress the flow
of ambient air 20. Further, this flow of compressed air from the
boost compressor is channeled towards the compressor 14 for further
compression. As will be appreciated by one skilled in the art,
depending on the operational layout, the compressor 14 may include
a plurality of compressors for increasing the power output of the
gas turbine 10. For example, the gas turbine 10 may include a
low-pressure compressor and a high-pressure compressor.
Alternatively, the gas turbine 10 may include a low-pressure
compressor, a medium-pressure compressor and a high-pressure
compressor.
[0018] The compressed air flow 22 from the compressor 14 is then
directed towards the combustor 12 for mixing and combustion with a
fuel stream 24 and to generate a combustor exit gas stream 26. In
one embodiment, the combustor 12 includes a can combustor. In
another embodiment, the combustor 12 includes a can-annular
combustor. Further, the combustor exit gas stream 26 is expanded
through the turbine 16 for driving an external load. In the
illustrated embodiment, the combustor 12 employs fuel staging of
the fuel stream 24 via a plurality of transverse injectors that
will be described in detail below with reference to FIGS. 3-6. As
used herein, the term "fuel staging" refers to ignition of the
fuel-air mixture at different points as it travels through the
combustor 12.
[0019] FIG. 3 is a diagrammatical illustration of a low emission
combustor 30 of FIG. 1. In the illustrated embodiment, the
combustor 30 includes a combustor liner 32 and a swirl premixer 34
disposed on a head end of the combustor liner 32. The swirl
premixer 34 is configured to provide a fuel-air mixture to the
combustor 30 and to induce a core swirl of the fuel-air mixture
within the combustor 30. In one embodiment, the combustor 30
includes a Dry Low NO, (DLN) combustor. In certain embodiments, the
swirl premixer 34 is operated to induce the core swirl of the
fuel-air mixture within the combustor 30 during a start-up, or
acceleration, or a turndown condition of the combustor 30.
[0020] Further, the combustor 30 includes a plurality of
tangentially staged injectors such as represented by reference
numerals 36, 38, 40 and 42. In the illustrated embodiment, the
combustor 30 includes four tangentially staged injectors 36, 38, 40
and 42. However, a lesser or greater number of injectors may be
employed in the combustor 30. Further, the plurality of injectors
36, 38, 40 and 42 are arranged in a circumferentially staggered
configuration on the combustor liner 32 to achieve the fuel staging
within the combustor 30. In one embodiment, the plurality of
injectors 36, 38, 40 and 42 are staggered axially to achieve axial
fuel staging within the combustor 30. In the illustrated
embodiment, each of the plurality of injectors 36, 38, 40 and 42 is
configured to introduce fresh fuel-air mixture in a transverse
direction to a longitudinal axis 44 of the combustor 30 and to
sequentially ignite the fuel-air mixture. As used herein, the term
"transverse" refers to a direction at right angles to the
longitudinal axis 44 of the combustor 30 but off centerline of the
combustor 30. In certain embodiments, the injectors 36, 38, 40 and
42 may introduce the fuel-air mixtures in a direction at an angle
to the longitudinal axis. The fuel injected through the plurality
of injectors 36, 38, 40 and 42 includes natural gas, or hydrogen,
or syngas, or a hydrocarbon, carbon monoxide, or combinations
thereof. However, a variety of other fuels may be envisaged. In
some embodiments, each of the injectors 36, 38, 40 and 42 have a
dual or multiple fuel capability and employs the
premixed-prevaporize feature for the fuel. Advantageously, the
multiple fuel capability facilitates a backup fuel capability,
particularly for liquid fuels such as distillates.
[0021] In the illustrated embodiment, each of the tangential
injectors 36, 38, 40 and 42 include fuel inlets 46, 48, 50 and 52
for supplying the fuel-air mixtures to respective tangential
injectors 36, 38, 40 and 42. In addition, the injectors 36, 38, 40
and 42 may include associated valving to control the fuel supply to
the injectors 36, 38, 40 and 42. In certain embodiments, the
injectors 36, 38, 40 and 42 may generate a swirling flow to
accelerate the premixing process. In operation, the fuel-air
mixtures introduced through the injectors 36, 38, 40 and 42 are
ignited by utilizing heat from previous burnt gases from the
injectors 36, 38, 40 and 42 and the heat released by the reaction
of the swirl stabilized flame of the head end swirler.
[0022] Further, the plurality of injectors 36, 38, 40 and 42 are
configured to induce a tangential momentum inside the combustor 30
to facilitate flame stabilization within the combustor 30 and
supplementing the swirling flow that is generated by the head end
swirler 34. Thus, the core of the combustor 30 maintains a swirling
movement and fresh lean mixtures are supplied perpendicular to the
axis 44 of the combustor 30. Additionally, the low swirl and
tangential momentum of this fresh mixture of fuel and air induces a
velocity substantially high enough to prevent flame holding on the
combustor liner 32 or the tangential injectors 36, 38, 40 and 42
and to facilitate ignition of the fresh lean mixtures supplied
through the injectors 36, 38, 40 and 42. In the illustrated
embodiment, the combustor 30 includes a plurality of dilution holes
54 disposed downstream of the injectors 36, 38, 40 and 42 for
introducing dilution air to facilitate cooling of walls of the
combustor liner 32. The sequential ignition of the fuel-air
mixtures supplied through the injectors 36, 38, 40 and 42 will be
described below with reference to FIGS. 4-6.
[0023] FIG. 4 is a diagrammatical illustration of an exemplary
configuration 56 of tangential injectors employed in the combustor
30 of FIG. 3. As illustrated, the swirl premixer 34 is disposed at
the head end of the combustor 30 (see FIG. 3) and a plurality of
injectors such as 36, 38, 40 and 42 are arranged in a staggered
circumferential or axial configuration to achieve the fuel staging
within the combustor 30. The plurality of injectors 36, 38, 40 and
42 are configured to induce a torroidal movement of the fuel-air
mixture via the fuel staging in addition to the core swirl
generated by the swirl premixer 34. Particularly, such staging is
achieved by tangential injection of fresh fuel-air mixtures through
the injectors 36, 38, 40 and 42. In the illustrated embodiment, the
injectors 36, 38, 40 and 42 introduce the fuel-air mixtures in a
direction perpendicular to the longitudinal axis of the combustor.
Alternatively, the injectors 36, 38, 40 and 42 may introduce the
fuel-air mixtures in a direction at an angle to the longitudinal
axis from about 0 degrees to about 45 degrees. In certain
embodiments, the injectors 36, 38, 40 and 42 may be arranged in a
staggered configuration to enable dynamics reduction within the
combustor 30. In some embodiments, a load staging capability may be
achieved within the combustor 30 by operating a desired number of
injectors 36, 38, 40 and 42. In operation, a selected number of the
injectors 36, 38, 40 and 42 may be turned on while the other
injectors are run cold to facilitate a turndown condition of the
combustor.
[0024] In operation, the core swirl generated by the swirl premixer
34 facilitates flame stabilization in the combustor 30 and enables
start-up of the combustor 30 when the tangential injectors 36, 38,
40 and 42 are not in operation and only air is being supplied to
the latter. Once the flame has been stabilized using the swirl
premixer 34 at the head end of the combustor 30 and possibly a
pilot flame, the swirl premixer 34 facilitates ignition propagation
from the swirl premixer 34 to the injectors 36, 38, 40 and 42 as
described below with reference to FIGS. 5 and 6. Further, once the
ignition is propagated to the injectors 36, 38, 40 and 42 the
combustor head end fuel may be reduced to a minimum thus enabling a
highly premixed operation mode that is close to the lean blow out
point of the premixer, while fuel is being supplied to full
operation via the tangential injectors 36, 38, 40 and 42.
[0025] FIG. 5 is a cross-sectional view 60 of another exemplary
combustor having tangential injection of fuel. As described above,
the combustor 60 receives a core swirl of air 62. In this
embodiment, the premixer 34 is disposed in the center of the
combustor 60 and is aligned with the centerline 44. The premixer 34
is configured to introduce the fuel-air mixture within the
combustor 60. In certain embodiments, the combustor may include an
igniter (not shown) to ignite the fuel-air mixture during the
startup condition of the combustor 60. Additionally, fresh fuel-air
mixtures are introduced in a transverse direction to the axis 44 of
the combustor 60 via a plurality of injectors such as represented
by reference numeral 64 disposed downstream of the swirler premixer
34. In the illustrated embodiment, each of the plurality of
injectors 64 receives fuel and air as represented by reference
numerals 66 and 68 and this premixed mixture is introduced within
the combustor 60 through each of the injectors 64. The injection of
fuel-air mixtures via the plurality of injectors 64 and the head
end swirl premixer 34 introduces a tangential momentum of the
mixture within the core of the combustor 60. In the present
embodiment, the upstream plenum of the combustor 60 functions as a
large premixer and the reaction takes place downstream of the
upstream plenum.
[0026] Additionally, the fuel-air mixtures are sequentially ignited
by previous burnt gases from an adjacent injector and the heat
released by the reaction of the swirl stabilized flame 70 of the
head end swirl premixer 34. Further, the combustion process is
completed in a burn out zone where any balance combustion air may
be introduced. In the illustrated embodiment, the toroidal movement
of the fuel-air mixture within the combustor facilitates flame
stabilization. In addition, the transverse injection of fuel-air
mixtures facilitates self-sustaining ignition in the combustor 60
that will be described below with reference to FIG. 6.
[0027] FIG. 6 is a diagrammatical illustration of zones 80 of fuel
staging and sequential ignition achieved through the tangential
injectors of FIG. 4. In the illustrated embodiment, the sequential
ignition is achieved through a premix-react-ignite mechanism inside
the combustor. The sequential ignition with the swirl and toroidal
momentum inside the combustor substantially reduces emissions from
the combustor and facilitates operability over a relatively larger
window of temperatures.
[0028] In the illustrated embodiment, for each of the injectors 36,
38, 40 and 42 the ignition can be characterized by four zones 80
that facilitate the flame stabilization and flue gas recirculation
within the combustor. For example, the fuel and air introduced
through the injector 40 is premixed in a premixing zone 82 and then
subsequently in a mixing zone 84. Further, the fuel-air mixtures
are ignited in an ignition zone 86. Once the temperature in the
ignition zone 86 is high enough to sustain combustion, chemical
reactions take place in a reaction zone 88. Subsequently, the gases
emerging from the reaction zone 88 enter a burnout zone 90.
Similarly, for each of injectors 36, 38 and 42 the ignition is
facilitated via the premix-react ignite mechanism as described
above.
[0029] In the illustrated embodiment, the emerging premixed gas and
air velocity out of each of the tangential premixers 36, 38, 40 and
42 is substantially larger than the local flame speed, thus
preventing the flame to flash back into the tangential premixers.
Further, the premixing continues in the premixing zone 82 between
the fuel and air supplied to each of the premixers 36, 38, 40 and
42. Additionally, mixing with hot gases resulted from the
combustion at the core of the combustor develops in the mixing zone
84. As a result, the fresh mixtures are ignited spontaneously upon
reaching the ignition conditions. Further, the momentum carries the
burnt gases and mixes them completely with the core resulting in a
homogeneous and complete reaction in the reaction zone 88, where
the core has a substantially higher axial momentum along the axis
44 (see FIG. 3). This is achieved by inducing a low swirl and large
axial momentum (i.e. low swirl number) in tangential premixing
tubes. It should be noted that the momentum facilitates the
swirling movement in the core and flame is stabilized using this
arrangement. The core flame 70 is thus not scrubbing against the
wall of the liner 42 and thus the walls of the said liner 42 are
kept cooler.
[0030] In the illustrated embodiment, the fuel-air mixtures
introduced at each location are continuously ignited from the
previous burnt gases thus facilitating self-sustaining ignition
within the combustor. Further, the premix-react-ignition mechanism
employed by the injectors 36, 38, 40 and 42 facilitates a
stabilized flame in the center of the combustor or a hot core while
preventing the hot gas scrubbing of the liner and domeplate of the
combustor. The tangential injectors 36, 38, 40 and 42 may be
employed for sequential ignition for various fuel-to-air ratios for
controlling stability, flue gas recirculation of partially or fully
burnt gases. This will achieve lowering of the emissions and
elimination of the aerodynamic flame stabilization requirement by
introducing self-sustaining ignition.
[0031] The various aspects of the method described hereinabove have
utility in different applications such as combustors employed in
gas turbines. As noted above, the fuel staging achieved in a
combustor via transverse introduction of fuel-air mixtures in the
combustor facilitates flame stabilization away from the combustor
walls. Further, the present technique enables reduction of
emissions particularly NOx emissions from such combustors thereby
facilitating the operation of the gas turbine in an environmentally
friendly manner. In addition, the fuel staging described above may
be employed with a variety of fuels thus providing fuel flexibility
of the system while maintaining acceptable levels of pressure
fluctuations across a required turbine load. Moreover, the
technique described above may be employed in the existing can or
can-annular combustors to reduce emissions and achieve a relatively
high stability of the flame.
[0032] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
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