U.S. patent application number 11/745266 was filed with the patent office on 2008-11-13 for low swirl injector and method for low-nox combustor.
This patent application is currently assigned to Caterpillar Inc.. Invention is credited to Waseem A. Nazeer, Frank J. Ritz, Kenneth O. Smith.
Application Number | 20080280238 11/745266 |
Document ID | / |
Family ID | 39969862 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080280238 |
Kind Code |
A1 |
Smith; Kenneth O. ; et
al. |
November 13, 2008 |
LOW SWIRL INJECTOR AND METHOD FOR LOW-NOX COMBUSTOR
Abstract
A fuel injector and a combustor including a fuel injector that
enables a combustor to burn a lean fuel/oxider gas mixture while
providing low emissions of oxides of nitrogen (NO.sub.x), and a
method of combustion. The fuel injector includes three fuel/oxider
flow path channels. The first channel includes a flow balancing
insert and provides a relatively straight flow. The second channel
includes at least one angled vane that imparts a swirl to the flow.
The third channel is a central tube, the first channel annularly
surrounding the third channel, the second channel annularly
surrounding the first channel.
Inventors: |
Smith; Kenneth O.; (San
Diego, CA) ; Nazeer; Waseem A.; (San Diego, CA)
; Ritz; Frank J.; (San Diego, CA) |
Correspondence
Address: |
LEYDIG, VOIT & MAYER, LTD
TWO PRUDENTIAL PLAZA SUITE 4900, 180 N. STETSON AVE
CHICAGO
IL
60601
US
|
Assignee: |
Caterpillar Inc.
Peoria
IL
|
Family ID: |
39969862 |
Appl. No.: |
11/745266 |
Filed: |
May 7, 2007 |
Current U.S.
Class: |
431/9 ;
431/8 |
Current CPC
Class: |
F23D 2900/00008
20130101; F23R 3/286 20130101; F23D 2900/14003 20130101; F23D
2900/14004 20130101; F23R 3/14 20130101; F23D 2900/14701 20130101;
F23D 2900/00015 20130101 |
Class at
Publication: |
431/9 ;
431/8 |
International
Class: |
F23C 5/00 20060101
F23C005/00; F23M 9/00 20060101 F23M009/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND
DEVELOPMENT
[0001] This invention was made in part with Government support
under Grant Number DE-AC03-76SF00098 awarded by the Department of
Energy to the University of California, Lawrence Berkeley National
Laboratory. The Government may have certain rights in this
invention.
Claims
1. A low swirl injector for use with a combustor, the low swirl
injector comprising: at least one passage adapted to provide a fuel
gas and an oxidant gas, at least one of said fuel gas and said
oxidant gas establishing an axial gas flow through said injector, a
first channel adapted for passage of said gas flow, said first
channel disposed to direct said gas flow to the combustor, a flow
balancing insert disposed within said gas flow through said first
channel, said flow balancing insert introducing additional pressure
drop beyond that occurring in the first channel without said flow
balancing insert, a second channel disposed annularly about said
first channel and adapted for passage of said gas flow, said second
channel including at least one vane oriented to impart angular
momentum to the gas flow exiting said second channel, and a third
channel having an inlet disposed to receive a feed gas, and an
outlet aligned to direct said feed gas to said combustor.
2. The low swirl injector of claim 1 wherein the first channel is
disposed annularly about the third channel.
3. The low swirl injector of claim 1 wherein the feed gas includes
at least one of the following: pure fuel or a premix of fuel and a
second oxidant gas.
4. The low swirl injector of claim 1 wherein said feed gas and fuel
gas include a same fuel.
5. The low swirl injector of claim 1 wherein said at least one
passage including at least one passage adapted to provide said fuel
gas and at least one passage adapted to provide said oxidant
gas.
6. The low swirl injector of claim 5 said at least one passage
adapted to provide said fuel gas includes a plurality of passages
including a hollow interior and at least orifice opening from the
hollow interior into at least one of said first or second
channels.
7. The low swirl injector of claim 6 further including at least one
valve adapted to control flow of fuel gas to said first channel and
at least one valve adapted to control flow of fuel gas to said
second channel.
8. The low swirl injector of claim 1 wherein said at least one
passage adapted to provide the fuel gas and the oxidant gas
provides a premix of fuel gas and oxidant gas.
9. The low swirl injector of claim 1 wherein the flow balancing
insert comprises at least one of a porous material, a perforated
screen, a wire mesh, a porous ceramic material, a porous polymeric
material, a porous metallic material, or a plate comprising at
least one opening therethrough.
10. The low swirl injector of claim 2 including a passage adapted
to provide oxidant gas to the first and second channels, and a
plurality of passages adapted to provide said fuel gas to the first
and second channels, said plurality of passages including a hollow
interior and at least one orifice opening from the hollow interior
into at least one of said first or second channels, said plurality
of passages being substantially radially disposed, and wherein the
flow balancing insert comprises a plate having a plurality of
openings therethrough.
11. A combustor comprising: a combustion zone, a mix zone opening
to said combustion zone, a low swirl injector including at least
one passage adapted to provide a fuel gas and an oxidant gas, at
least one of said fuel gas and said oxidant gas establishing an
axial gas flow, a first channel having an entrance disposed to
accept said gas flow, and an exit aligned to direct said gas flow
into the mix zone, a flow balancing insert disposed within said gas
flow through said first channel, said flow balancing insert
introducing additional pressure drop beyond that occurring in the
first channel without said flow balancing insert, a second channel
disposed annularly about said first channel to accept said gas flow
and direct said gas flow to said mix zone, said second channel
including at least one vane oriented to impart angular momentum to
the gas flow exiting said second channel, a third channel having an
inlet disposed to receive a feed gas, and an outlet aligned to
direct said feed gas into said mix zone, and said gas flow from
said first channel, said gas flow from said second channel, and
said feed gas from said third channel interacting in said mix zone
prior to the combustion zone.
12. The combustor of claim 11 wherein the first channel is disposed
annularly about the third channel.
13. The combustor of claim 11 said at least one passage including
at least one passage adapted to provide said oxidant gas to the
first and second channels, and a plurality of passages adapted to
provide fuel gas to the first and second channels, said plurality
of passages including a hollow interior and at least one aperture
opening from the hollow interior into at least one of said first or
second channels.
14. The combustor of claim 13 further including at least one valve
adapted to selectively provide fuel gas to said first channel and
at least one valve adapted to selectively provide fuel gas to said
second channel.
15. The combustor of claim 13 wherein the at least one passage
adapted to provide oxidant gas comprises a restriction.
16. The combustor of claim 11 wherein the flow balancing insert
comprises at least one of a porous material, a perforated screen, a
wire mesh, a porous ceramic material, a porous polymeric material,
a porous metallic material, or a plate comprising at least one
opening therethrough.
17. A method of combustion comprising the steps of: establishing an
axial gas flow of a fuel gas and an oxidant gas through a first
channel, through a flow balancing insert, and into a mix zone, said
flow balancing insert introducing additional pressure drop beyond
that occurring in the first channel without said flow balancing
insert, establishing an axial gas flow of said fuel gas and said
oxidant gas through a second channel and into the mix zone, passing
said axial gas flow through said second channel along at least one
vane disposed within the second channel and oriented to impart an
angular momentum to said gas flow through the second channel,
directing a feed gas into a third channel having an outlet aligned
to direct said feed gas into said mix zone, allowing said gas flow
from said first channel, said gas flow from said second channel,
and said feed gas from said third channel to interact in said mix
zone, and opening said mix zone into a combustion zone.
18. The method of claim 17 wherein the step of establishing an
axial gas flow through said first channel includes steps of
providing a flow of fuel gas to said first channel and providing a
flow of oxidant gas to said first channel, and the step of
establishing an axial gas flow through said second channel includes
steps of providing a flow of fuel gas to said second channel and
providing a flow of oxidant gas to said second channel.
19. The method of claim 18 wherein the steps of providing the flow
of fuel gas to said first channel, providing the flow of oxidant
gas to said first channel, providing the flow of fuel gas to said
second channel and providing the flow of oxidant gas to said second
channel, further comprise the step of establishing different fuel
gas/oxidant gas ratios through the first and second channels.
20. The method of claim 16 wherein the step of establishing an
axial flow through said flow balancing insert includes the step of
establishing an axial flow through a plurality of openings in the
flow balancing insert.
Description
TECHNICAL FIELD
[0002] This patent disclosure relates generally to combustors and
burners, and, more particularly to low swirl injectors for use in a
combustor or burner.
BACKGROUND
[0003] Combustion is a major source of a class of pollutants
including oxides of nitrogen, or NO.sub.x, (NO or nitric oxide, and
NO.sub.2 or nitrogen dioxide), which may contribute to acid rain,
smog, and ozone depletion. NO.sub.x emissions from combustion
sources primarily consist of nitric oxide produced during
combustion. When utilizing gaseous fuels, combustion processes that
decrease the combustion temperature can greatly reduce the
production of NO, and, accordingly, can have a large effect on the
overall production of NO.sub.x.
[0004] Various attempts have been made to re-engineer conventional
non-premixed combustion systems to reduce emissions of oxides of
nitrogen (NO.sub.x). Flames in non-premixed combustion, that is,
the combustion process wherein fuel and oxidizer (typically air)
mix and burn concurrently, generally emit unacceptable levels of
NO.sub.x, over 200 parts-per-million (ppm), substantially higher
than regulations allow for certain applications. The heating and
power generation industries have recognized the need to develop
cleaner, premixed combustion systems in which gaseous fuel and
oxidizer (typically air) mix prior to burning.
[0005] Although separation of the mixing and burning processes
provides the opportunity to control the fuel-to-air ratio delivered
to the reaction zone, differences in flame dynamics between
non-premixed and premixed arrangements do not typically allow the
direct application of non-premixed technology to premixed systems.
For example, although maintenance of a stable flame in the zone
where the fuel and air are mixed is the important design criterion
in non-premixed burners, the design requirements are different
relative to mixing in premixed systems, that is, prior to the
burning processes. In premixed systems, the flame propagates
through the feed gas, which is a premix of fuel and air. The flame
speed, or the speed at which a premixed flame propagates through
the mixture, is a function of the fuel air equivalence ratio and
turbulence intensities. In order to prevent "flash-back," or
propagation of the flame upstream against the premixed feed gas
stream and into the body of the premixed burner, the velocity of
the premixed feed gas in the burner has to be greater than the
flame speed.
[0006] To maintain a stable flame, an obstacle may be placed in the
premixed feed gas to "anchor" the flame. The size of the flame
anchor and their aerodynamic shapes can be optimized for given
operating ranges and burner considerations. The anchor generates a
zone of zero axial flow on its upstream side and turbulent flow on
its downstream side. As the fuel flows around the obstruction, the
flow becomes turbulent, creating several regions of reverse flow
where the fuel flow is actually circling back in a direction
opposite to the original flow. This pattern or "recirculation" is
relatively stable and generally prevents blowout when the operating
conditions of the burner are appropriately set. Blowout, or an
extinguishing of the flame, may occur when the velocity of the fuel
mixture is greater than the speed of the flame. Although these
anchors can help to prevent flash-back, a flame can become unstable
and "blow-off" the anchor if the velocities are too high. This is
particularly true for lean flames, as they tend to blow-off easily
due to the excess air in the feed gas. In premixed burners that
support lean flame conditions, it is a challenge to design burners
robust enough to eliminate both flash-back and blow-off
occurrences.
[0007] Swirling flows have also been used to stabilize combustion
in a variety of burners, both premixed and non-premixed. Swirl in
such burners is generally created either by generating tangential
flow motion in a cylindrical chamber, as in cyclone combustion
chambers, or swirling a co-axial air flow. In both cases, the
function of the swirl is to create a torroidal recirculation zone.
For non-premixed combustion, the role of the torroidal
recirculation zone is to mix the fuel and air to allow for complete
combustion, to stabilize the combustion process, to recirculate
some fraction of the products, and to dictate the physical shape
and length of the flame in these burners. In premixed burners, the
torroidal recirculation zone created by the strong swirl creates a
zone where the combustion zone is "anchored" due to an area of low
flow velocities found within the torroidal recirculation zone.
[0008] Many attempts have been made to reduce NO.sub.x emissions
from combustion sources in hopes of reducing the air pollution
associated with the burning of hydrocarbon fuels. Pollution
reduction methods generally fall into two categories. One category
of reduction methods involves post-combustion remediation
technologies, such as Selective Catalytic Reduction (SCR) or
Selective Non-Catalytic Reduction (SNCR), to reduce pollution after
it has been generated in the combustion zone. A second category of
pollution reduction technologies concentrates on combustion
modifications through burner design changes, such as burning lean,
fuel-air staging, or flue gas recirculation, to reduce pollutant
formation in the reaction zone. Taking into account tradeoffs with
engineering considerations and other pollutants, low NO.sub.x
burners generally burn with as much excess air (i.e. "lean") as
possible, as this will reduce combustion temperatures and minimize
thermal NO.sub.x production, although some NO.sub.x may still be
produced by virtue other mechanisms.
[0009] U.S. Pat. No. 5,879,148 to Cheng, et al., discloses a lean
premixed burner which generates a stable flame by providing
parallel flows of a thoroughly mixed fuel-oxidant mixture or feed
gas through a central passage and an annular passage about the
central passage. The central passage includes a flow balancing
insert that introduces an additional pressure drop beyond that
which would occur in the central passage absent the flow balancing
insert. The annular passage includes one or more vanes oriented to
impart angular momentum to feed gas exiting the annular passage.
The low swirl creates a divergent flow pattern that stabilizes lean
combustion, allowing for lower production of pollutants,
particularly oxides of nitrogen.
[0010] The swirl requirement of a weak-swirl burner (WSB) is
different from that of other burners since the feed gas is premixed
and flame stabilization is achieved through use of a divergent flow
field instead of a torroidal recirculation zone. Due to the
propagating nature of pre-mixed flames and the deceleration of the
flow as it moves away from its source, the flame is able to
aero-dynamically stabilize itself at the position where the local
mass velocity balances the flame propagation speed. The weak-swirl
stabilization mechanism does not apply to diffusion flames (not
pre-mixed) because they do not propagate, but rather burn at the
boundary where the air and fuel flows have diffused to the
appropriate ratios for sustaining the combustion reaction.
[0011] Industrial gas turbine manufacturers rely primarily on
lean-premixed combustion technology to meet current engine
emissions regulations. Lean-premixed combustion systems premix fuel
and air prior to injection to prevent stoichiometric burning
locally within the flame. This results in a more spatially uniform
flame temperature that reduces the conversion of atmospheric
nitrogen to oxides of nitrogen (NO.sub.x). Operating at lean
conditions, however, may result in increased carbon monoxide (CO)
and unburned hydrocarbon emissions. Consequently, the combustion
system must operate within a narrow flame temperature range to
maintain NO.sub.x, CO and unburned hydrocarbon emissions at
acceptable levels. The window of low emissions operability is close
to the lean extinction limit, which can lead to high amplitude
combustion pressure oscillations that may damage the combustor
hardware.
[0012] Lean premixed combustion systems first entered the gas
turbine market in the early 1990's. Typically, NO.sub.x levels were
reduced to 25 to 42 ppm range on natural gas fuel. As air quality
regulations continue to tighten, however, manufacturers are
actively pursuing technologies that can meet customer demands of
the future. In some parts of the United States, gas turbines must
already meet regulations as low as 2.5 ppm NO.sub.x. To date,
lean-premixed combustion systems have not been able to achieve
these ultra-low levels. Rather, operators must rely on costly
exhaust clean up technologies such as selective catalytic
reduction.
[0013] Accordingly, there exists a need for alternative designs for
low NO.sub.x emission weak swirl burners, particularly designs that
are easily adaptable to a broad range of applications, including,
for example, designs that meet the need for ultra-low NO.sub.x
emissions in mid-range industrial gas turbines without selective
catalytic reduction. Such designs would be particularly
advantageous if they were relatively simple and economical to
scale, manufacture and operate.
BRIEF SUMMARY OF THE INVENTION
[0014] The disclosure describes, in one aspect, a low swirl
injector for use with a combustor and a combustor including a low
swirl injector that includes three different channels for providing
fuel gas and oxidant gas to a flame zone of the combustor. The
first channel provides a straight flow of fuel/oxidant gasses; a
flow balancing insert, which is of a porous material or includes a
number of openings therethrough, is disposed within the first
channel and introduces an additional pressure drop beyond that
which would occur in the first channel absent the insert. The
second channel is disposed annularly about the first channel and
includes at least one vane that imparts an angular momentum to the
gas flow exiting the second channel. The third channel provides a
feed gas that may be a fuel gas, such as the fuel gas of the first
and second channels, or a premix of fuel gas and oxidant gas; the
third channel may be disposed along the central axis of the
injector, the first channel being annularly disposed about the
third channel. A premix of fuel gas and oxidant gas may be provided
to the first and second channels. Alternately, oxidant gas and fuel
gas may be separately provided to the first and/or second channels,
for example, the fuel gas being provided by one or more generally
radially extending spokes that include at least one injector
orifice; mixing of the fuel and oxidant gasses then occurs within
the separate first and second channels.
[0015] Also disclosed is a method of combustion comprising the
steps of establishing an axial gas flow of a fuel gas and an
oxidant gas through a first channel and a flow balancing insert to
establish a straight flow, establishing an axial gas flow of said
fuel gas and said oxidant gas through a second channel and past at
least one vane disposed within the second channel to impart an
angular momentum to said gas flow, and directing a feed gas into a
third channel having an outlet aligned to direct said feed gas into
a mix zone, allowing said gas flow from the channels to interact in
the mix zone, and opening said mix zone into a combustion zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross-sectional view of an embodiment of
injector according to the disclosure.
[0017] FIG. 2 is a fragmentary view of the injector of FIG. 1 taken
along line 2-2 in FIG. 1.
[0018] FIG. 3 is an isometric view of the injector of FIG. 1.
[0019] FIG. 4 is a partially cross-sectioned plan view of an
exemplary combustor including the injector of FIG. 1.
DETAILED DESCRIPTION
[0020] Turning now to the drawings, there is shown a cross-section
of a fuel injector assembly 10 including a low-swirl injector 12.
In the illustrated embodiment, the injector 12 includes three gas
flow channels 14, 16, 18 adapted to supply gas flow to a flame zone
20. The gas flow channels 14, 16, 18 are disposed within a housing
22 that includes an upstream opening 24 and a downstream mix zone
26 prior to an outlet 28 at the flame zone 20, the channels 14, 16,
18 opening to provide gas flow to the mix zone 26. The axial gas
flow through the injector 12 is indicated generally by arrow
21.
[0021] The first channel 14 is defined by an elongated tubular
structure 30 and provides a relatively straight gas flow profile
that includes no swirl component. While the illustrated elongated
tubular structure 30 is of a generally circular cross-section, the
structure 30 may be of any cross-section, including, by way of
example only, oval or octagonal. Gas flow enters the channel 14
through opening 32, and exits the channel 14 at end 34, the fuel
gas and the oxidant gas of the gas flow being thoroughly mixed as
the gas flow proceeds through the first channel 14.
[0022] Gas flow through the channel 14 is at least partially
controlled by a flow balancing insert 36, here disposed at
downstream end 34. The flow balancing insert 36 includes at least
one opening 38 through which the gas flow proceeds from the first
channel 14. As gas flow exits the first channel 14 through the
restriction of the openings 38 at the downstream end 34, the gas
flow exhibits a higher velocity than the gas flow entering the
first channel 14 through opening 32. It will be appreciated that
the flow balancing insert 36 introduces an additional pressure drop
across the tubular structure 30 than would occur absent the
inclusion of the flow balancing insert 36.
[0023] The flow balancing insert 36 may be formed of any
appropriate design and of any appropriate material. For example,
the flow balancing insert 36 may be constructed from metal, or
other rigid material in which one or more openings may be placed,
and the insert may be in the form of a perforated or porous plate,
a screen, a mesh, or a wire cloth.
[0024] While the openings 38 may be of any appropriate size, shape,
and configuration, in the illustrated embodiment, the openings 38
are generally round, and distributed uniformly about the insert 36,
as may be seen most readily in FIG. 2. As also shown in FIG. 2, the
flow balancing insert 36 further includes an opening 39, the
significance of which will be apparent upon reading the disclosure
with regard to the third channel 18, below.
[0025] As shown in FIGS. 1 and 2, the second channel 16 is provided
annularly about the first channel 14. The second channel 16 is
defined by the elongated tubular structure 30 and an outer annular
wall 40, and includes an upstream entry 42, and a downstream exit
44. The outer annular wall 40 is formed, in part, by an annular
sleeve 46, the inner surface 48 of the annular sleeve 46 being
continuous with the remainder of the outer annular wall 40.
[0026] In order to impart an angular momentum or swirl to the gas
flow exiting the second channel 16, at least one vane 50 is
disposed within the second channel 16. In the illustrated
embodiment, a plurality of such vanes 50 is provided with the
elongated tubular structure 30 acting as a hub and the vanes 50
extending outward to the outer annular wall 40. In an embodiment,
the vanes 50 extend between the elongated tubular structure 30 and
the annular sleeve 46. In this way, the elongated tubular structure
30 with the flow balancing insert 36, the annular sleeve 46, and
the vanes 50 extending between the structure 30 and the annular
sleeve 46 may fabricated as a subassembly that may be disposed
within a combustor 10 during assembly.
[0027] Any appropriate number of vanes 50 may be provided, and the
vanes 50 may have any appropriate structure and be disposed at any
appropriate angle, so long as the vanes impart the desired angular
momentum to the gas as it flows from the downstream exit 44. In the
embodiment illustrated in FIGS. 1 and 2, sixteen axial curved vanes
50 are disposed between a tubular structure 30 having a diameter on
the order of 1.5 inches and an annular sleeve 46 having a diameter
on the order of 2.75 inches. The vanes 50 present a vane angle on
the order of 40.degree. to 60.degree., here, 46.degree. to
48.degree.. Typical swirl numbers for gas flow exiting the second
channel 16 are between 0.6 and 1.2, although alternate swirl levels
may be provided, depending upon the gas flow and the design of the
vane 50 arrangement. The non-dimensional swirl number, S, is
defined as the ratio of axial flux of angular momentum to axial
flux of linear momentum.
[0028] The gas flow may be provided to the first and second
channels 14, 16 by any appropriate arrangement. For example, a
premix of fuel gas and oxidant gas may be provided to the upstream
inlet 24 to the housing 22. Alternately, separate fuel gas and
oxidant gas may be provided to the housing 22. In an embodiment,
oxidant gas, typically air, is supplied to the housing 22 through
upstream opening 24. Fuel gas may be introduced at any appropriate
opening or location to mix with the oxidant gas, so long as
adequate residence time is provided within the injector 12 for
efficient and effective oxidant gas/fuel gas mixing. Fuel gas may
be provided through one or more passages 52 into the housing
22.
[0029] In the illustrated embodiment, a plurality of generally
radially extending spokes 54 form at least a portion of the passage
52. More specifically, the spokes 54 include a hollow interior 56
and at least one injection orifice 58 through which fuel gas flows
into the housing 22. Although sixteen such spokes 54 and a
plurality of injection orifices 58 are shown, any number of such
spokes 54 and/or orifices 58 may be provided, so long as adequate
fuel gas is provided and distributed to allow for adequate mixing
with the oxidant gas. The spokes 54 may extend into either the
first channel 14 or second channel 16, or both the first and second
channels 14, 16, as illustrated. In this way, the particular design
and distribution of the spokes 54 and injection orifices 58
provides for controlled distribution and flow of fuel gas to the
first and second channels 14, 16. Although the same oxidant
gas/fuel gas ratio or nominal equivalence ratio may be provided in
both the first and second channels 14, 16, the arrangement may be
designed such that varied ratios may be provided between two
channels 14, 16.
[0030] In order to provide fuel gas to the spoke arrangement, an
annular passage 60 fluidly connects a fuel gas supply passage 62 in
a supply line 64 with the spokes 54. Thus, the fuel gas supply
passage 62, the annular passage 60, the hollow interior of the
spokes, and the orifices 58 together form a plurality of passages
52 that supply fuel gas to the interior of the housing 22. Flow of
fuel gas into the supply passage 62 of the supply line 64 may be
provided by a valve 66. Alternate arrangements are within the
purview of the disclosure, however. By way of example only,
although a single such valve 66 is illustrated, should alternate
fuel gas flow passages be provided to first and second channels 14,
16, a plurality of valves may be provided to control the flow of
fuel gas to the various fuel gas flow passages.
[0031] Turning now to the third channel 18, an embodiment may
include a pilot fuel injector 70 which forms the third channel 18.
The pilot injector 70 includes an elongated tubular structure 72
that extends from a source of feed gas to the mix zone 26. Although
the tubular structure 72 may be of any appropriate cross-section
and any appropriate dimension, in an embodiment, the tubular
structure 72 has a substantially annular cross-section with an
interior diameter on the order of 0.5 inches. In an embodiment, the
downstream end 74 of the pilot fuel injector 70 is disposed along
the centerline of the injector 12, although it may be alternately
disposed. Feed gas may be provided to the fuel injector 70 through
line 76 or the like and gas flow controlled by any appropriate
structure, such as the valve 78 illustrated. The feed gas may be in
the form of either pure fuel gas or a premix of fuel gas and
oxidant gas.
[0032] The fuel gas may be any appropriate gas, such as, for
example, natural gas. Likewise, the oxidant gas may be any
appropriate gas, such as, for example, air.
INDUSTRIAL APPLICABILITY
[0033] The industrial applicability of the injector 12 described
herein will be readily appreciated from the foregoing discussion.
The injector 12 may be utilized to achieve ultra-low NO.sub.x
emissions in, for example, an industrial gas turbine without
establishing a strong recirculation region. The injector 12 may
present a low swirl concept that utilizes an aerodynamic flame
stabilization mechanism in a diverging flow field where an
unanchored flame is allowed to freely propagate at ultra-lean
conditions. The lack of a strong recirculation region with a large
recirculated mass of combustion products may also reduce the
residence time in the primary flame zone 20 of the combustor 86.
This stability at very lean conditions and reduced residence time
of the combustion products in the flame zone 20, may contribute to
ultra low NO.sub.x emissions.
[0034] Turning to FIG. 4, the disclosed injector 12 is illustrated
with a combustor 86. The injector 12 is disposed within a combustor
housing 80 to which oxidant or air flow may be provided through an
air inlet 82. In turn, exhaust gas may be expelled to outlet 84. In
use, the gas flow exiting the first and second chambers 14, 16 and
the feed gas 18 exiting the third chamber 18 interact and partially
mix in the downstream, mix zone 26 of the injector 12. As the gas
flow then exits the injector 12, it may expand radially outward
into the combustor 86 in the illustrated embodiment. Upon ignition,
a flame may be stabilized just downstream of the injector exit
plane at the downstream outlet 28 and centered on a central axis of
the injector 12. Inasmuch as the central flow of the injector 12
may have no recirculation zone, the flame is held at the flame zone
20 and does not stabilize within the injector barrel.
[0035] Beyond merely the provision of fuel gas and oxidant gas
delivered to the injector 12, several design features may provide
design flexibility in establishing optimal performance of the
injector 12. For example, the flow balancing insert 36 and its
openings 38 may be designed to achieve optimal performance in the
form of flame stability and low emissions. The level of open area
provided by the openings 38 through the flow balancing insert 36
within the first channel 14, as well as the level of open area
provided by the upstream opening 24 into the housing 22 may be
adjusted in order to provide a desired gas flow through the first
channel 14, and a desired relationship to the gas flow through the
second channel 16. By way of example only, the extent of open area
provided by the openings 38 through the flow balancing insert 36
may be on the order to 20%-50%, and may be determined based upon
various injector characteristics and dimensions, including, but not
limited to the size and shape of the openings 38 themselves. In an
embodiment, the flow balancing insert 36 includes an open area of
40%-50% of the area covered by the insert 36. The location of the
flow balancing insert 36 with respect to the vanes 50 of the second
chamber 16 may likewise be adjusted to provide desired flow
characteristics. In an embodiment, the flow balancing insert 36 was
disposed on the order of 0.9 to 1.2 inches from the trailing edge
of the swirl vanes, and 2 to 3 inches from the upstream opening 24
into the housing 22.
[0036] Additionally, the arrangement of and/or flow level of fuel
gas through the spokes 54 may be readily adjusted. By way of
example only, spokes 54 may be provided with larger or smaller
hollow interiors 56, and/or larger or smaller injection orifices
58. Alternate arrangements of injection orifices 58 may be
provided, and/or injection orifices 58 may be provided that provide
fuel gas flow to either or both of the first and second channels
14, 16.
[0037] The pilot injector 70 may provide added flame stability
during light off, transients, and off-design operating conditions.
For example, the pilot injector 70 may act as a pilot for ignition
from light-off conditions, it may be utilized to accelerate the
engine to idle speed or full speed in no-load conditions, or it may
be utilized in sudden on-load, or off-load conditions. The pilot
injector 70 may likewise be adjusted for desired injector
characteristics. The size of the tubular structure 72 of the pilot
injector 70 may be adjusted, as well as the flow through the pilot
injector 70. While flame stability may improve with increasing
pilot injector 70 fuel flow rates, higher NO.sub.x emissions may
likewise result, however, low pilot fueling levels may provide a
reasonable operating range with ultra-low NO.sub.x emissions. It is
envisioned that acceptable NO.sub.x and CO emissions may result
with pilot fueling on the order of 5% or less.
[0038] It will be appreciated that the foregoing description
provides examples of the disclosed system and technique. However,
it is contemplated that other implementations of the disclosure may
differ in detail from the foregoing examples. All references to the
invention or examples thereof are intended to reference the
particular example being discussed at that point and are not
intended to imply any limitation as to the scope of the invention
more generally. All language of distinction and disparagement with
respect to certain features is intended to indicate a lack of
preference for those features, but not to exclude such from the
scope of the invention entirely unless otherwise indicated.
[0039] Recitation of ranges of values herein are merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range, unless otherwise indicated
herein, and each separate value is incorporated into the
specification as if it were individually recited herein. All
methods described herein can be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context.
[0040] Accordingly, this invention includes all modifications and
equivalents of the subject matter recited in the claims appended
hereto as permitted by applicable law. Moreover, any combination of
the above-described elements in all possible variations thereof is
encompassed by the invention unless otherwise indicated herein or
otherwise clearly contradicted by context.
* * * * *