U.S. patent application number 13/684906 was filed with the patent office on 2014-05-29 for premixer with diluent fluid and fuel tubes having chevron outlets.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Thomas Edward Johnson, Christian Xavier Stevenson, Jong Ho Uhm, Baifang Zuo.
Application Number | 20140144141 13/684906 |
Document ID | / |
Family ID | 50772058 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140144141 |
Kind Code |
A1 |
Uhm; Jong Ho ; et
al. |
May 29, 2014 |
PREMIXER WITH DILUENT FLUID AND FUEL TUBES HAVING CHEVRON
OUTLETS
Abstract
A premixer includes an air tube formed in a burner tube defining
a longitudinal axis, and a coaxially disposed fuel tube with a
turbulence enhancing chevron outlet. The fuel tube may include an
exterior tube and an interior tube with the interior tube, the
exterior tube or both having chevron outlets. The chevron outlets
may be tapered and notched.
Inventors: |
Uhm; Jong Ho; (Simpsonville,
SC) ; Johnson; Thomas Edward; (Greer, SC) ;
Zuo; Baifang; (Simpsonville, SC) ; Stevenson;
Christian Xavier; (Inman, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
50772058 |
Appl. No.: |
13/684906 |
Filed: |
November 26, 2012 |
Current U.S.
Class: |
60/737 |
Current CPC
Class: |
F23C 2202/10 20130101;
F23L 7/00 20130101; F23R 3/286 20130101; F23L 2900/07002
20130101 |
Class at
Publication: |
60/737 |
International
Class: |
F23R 3/28 20060101
F23R003/28 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] This invention was made with Government support under
contract number DE-FC26-05NT42643 awarded by the Department of
Energy. The Government has certain rights in this invention.
Claims
1. A premixer, comprising: a fuel plenum; a burner tube; an air
tube formed in the burner tube; a first tube disposed coaxially
inside the air tube; a second tube disposed coaxially inside the
first tube at least one of the first tube and second tube having a
chevron outlet, at least one of the first tube and second tube
coupled to the fuel plenum, and disposed coaxially inside the air
tube; an air source coupled to the air tube; and a bell mouth
disposed at least partially about the burner tube and coupled to
the air source, the bell mouth adapted to direct air into the air
tube.
2. The premixer of claim 1, wherein the chevron outlet comprises a
notch at a downstream end of the second tube.
3. The premixer of claim 2 wherein the notch comprises a notch
selected from among a group consisting of a V shaped notch, a U
shaped notch and a straight notch.
4. The premixer of claim 1, wherein at least one of the first tube
and second tube having a tapered downstream end.
5. The premixer of claim 1, wherein the first tube has a chevron
outlet and the second tube does not have a chevron outlet.
6. The premixer of claim 1, wherein the second tube has a chevron
outlet and the first tube does not have a chevron outlet.
7. The premixer of claim 5, further comprising a source of diluent
fluid coupled to one of the first tube and second tube.
8. A combustor, comprising: a fuel source; an air source; and a
plurality of premixers comprising: a burner tube; an air tube
formed in the burner tube and coupled to the air source; a first
tube disposed coaxially inside the air tube; a second tube disposed
coaxially inside the first tube; at least one of the first tube and
second tube having a turbulence enhancing chevron outlet; and at
least one of the first tube and second tube coupled to the fuel
source.
9. The combustor of claim 8 each premixer further comprises a bell
mouth disposed at least partially about the burner tube and coupled
to the air source the bell mouth adapted to direct air into the air
tube.
10. The combustor of claim 8, wherein the turbulence enhancing
chevron outlet comprises a notch at a downstream end of the first
tube.
11. The combustor of claim 8, wherein the turbulence enhancing
chevron outlet comprises a notch at a downstream end of the second
tube.
12. The combustor of claim 8 wherein the first tube comprises a
tube with a tapered downstream end and a notch on the tapered
downstream end.
13. The combustor of claim 8 wherein the second tube comprises a
tube with a tapered downstream end and a notch on the tapered
downstream end.
14. The combustor of claim 12, wherein at least one of the first
tube or the second tube is tapered.
15. The combustor of claim 12, further comprising a source of
diluent fluid coupled to the first tube and wherein the fuel source
is coupled to the second tube.
16. The combustor of claim 12, further comprising a source of
diluent fluid coupled to the second tube and wherein the fuel
source is coupled to the first tube.
17. An apparatus, comprising: a fuel source; a first tube; a second
tube disposed within the first tube; wherein one of the first tube
or second tube is coupled to the fuel source and at least one of
the first tube or second tube has a chevron outlet for enhancing
turbulence; an air tube surrounding the first tube; an air source;
and an air directing component coupled to the air source and
adapted to direct air into the air tube.
18. The apparatus of claim 17, wherein the chevron outlet comprises
one selected from among a group consisting of a V-shaped notch on
the first tube, a U shaped notch on the first tube, and a straight
notch on the first tube.
19. The apparatus of claim 17, wherein at least one of the first
tube or second tube is tapered.
20. The apparatus of claim 17, further comprising: a diluent
source; and wherein the first tube is coupled to the fuel source
and the second tube is coupled to the diluent source.
21. The apparatus of claim 17, further comprising: a diluent
source; and wherein the second tube is coupled to the fuel source
and the first tube is coupled to the diluent source.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to co-pending U.S. patent
applications entitled "PREMIXER WITH FUEL TUBES HAVING CHEVRON
OUTLETS", Ser. No. ______, filed concurrently herewith.
TECHNICAL FIELD
[0003] The subject matter disclosed herein relates to premixing
devices for injection nozzles and more particularly to a premixer
having coaxial fuel tube for enhanced mixing, flame holding and
flashback resistance.
BACKGROUND
[0004] Gas turbine manufacturers are continuously improving the
emission performance of gas turbines. The primary pollutant
produced by gas turbines are oxides of nitrogen (NOx), carbon
monoxide (CO) and unburned hydrocarbons. NOx emissions depend upon
the maximum temperature in the combustor and the residence time for
the reactants. One known method of controlling the temperature in
the combustor is to premix fuel and air to a lean mixture prior to
combustion. Such premixing tends to reduce combustion temperatures
and undesirable NOx emissions. In these systems fuel is mixed with
air using a premixing device that is upstream of a combustion zone
for creating a premixed flame at lean conditions to reduce
emissions from the combustor. Ideally, the flame should be
contained inside of the combustor downstream of the fuel/air
premixing passages. However, premixing devices are susceptible to
flashback. During flashback, the fuel and air mixture in the
premixing passages combusts. The flashback condition generally
occurs when a flame travels upstream from the main burning zone
into the premixing zone. Serious damage may occur to the combustion
system when flame holding or flashback occurs. Similarly, the flame
may develop on or near surfaces, which can also result in damage
due to the heat of combustion. This phenomenon is generally
referred to as flame holding. For example, the flame holding may
occur on or near a fuel nozzle in a low velocity region. In
particular, an injection of a fuel flow into an air flow may cause
a low velocity region near the injection point of the fuel flow,
which can lead to flame holding.
[0005] Typically, it is difficult to control flame holding in
premixing devices. In some combustors, the average velocity of
fuel/air mixture may be increased within a mixing region of the
premixing device for enhancing the flame holding margins in such
devices. However, this results in a relatively high pressure drop
across the combustor, thereby decreasing the combustor
efficiency.
BRIEF DESCRIPTION OF THE INVENTION
[0006] In accordance with one exemplary non-limiting embodiment,
the invention relates to a premixer having a fuel plenum, a burner
tube, and an air tube formed in the burner tube. A fuel tube having
a chevron outlet is coaxially disposed inside the air tube. An air
source is coupled to the air tube. The premixer includes a bell
mouth disposed at least partially about the burner tube and coupled
to the air source, the bell mouth adapted to direct air into the
air tube.
[0007] In another embodiment, the invention relates to a combustor
with a fuel source, an air source, and a premixer. The premixer
includes a burner tube and an air tube formed in the burner tube
and coupled to the air source, and a fuel tube with a turbulence
enhancing chevron outlet disposed inside the air tube and coupled
to the fuel source. The premixer also includes a bell mouth
disposed at least partially about the burner tube and coupled to
the air source the bell mouth adapted to direct air into the at
least one air tube.
[0008] In another embodiment, an apparatus is provided that
includes a fuel source, a first fuel tube coupled to the fuel
source and a chevron outlet for enhancing turbulence of fuel
flowing through the first fuel tube. The apparatus also includes an
air tube surrounding the first fuel tube an air source, and an air
directing component coupled to the air source and adapted to direct
air into the air tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings which illustrate, by way of example, the principles of
certain aspects of the invention.
[0010] FIG. 1 is a perspective view of an embodiment of a
premixer.
[0011] FIG. 2 is a cross-sectional view of an embodiment of a
premixer.
[0012] FIG. 3 is a cross-sectional view of an embodiment of a
premixer.
[0013] FIG. 4 is a perspective view of an embodiment of a fuel
tube.
[0014] FIG. 5 is a cross-sectional view of an embodiment of a fuel
tube.
[0015] FIG. 6 is a cross-sectional view of an embodiment of a fuel
tube.
[0016] FIG. 7 is a cross-sectional view of an embodiment of a fuel
tube.
[0017] FIG. 8 is a perspective view of an embodiment of a fuel
tube.
[0018] FIG. 9 is a cross-sectional view of an embodiment of a fuel
tube.
[0019] FIG. 10 is a perspective view of an embodiment of a fuel
tube.
[0020] FIG. 11 is a cross-sectional view of an embodiment of a fuel
tube.
[0021] FIG. 12 a perspective view of an alternate embodiment of a
premixer.
[0022] FIG. 13 is a cross-sectional view of an embodiment of a
premixer.
[0023] FIG. 14 is a cross-sectional view of an embodiment of a fuel
tube.
[0024] FIG. 15 is a cross-sectional view of an embodiment of a fuel
tube.
[0025] FIG. 16 is a cross-sectional view of an embodiment of a fuel
tube.
[0026] FIG. 17 is a cross-sectional view of an embodiment of a fuel
tube.
[0027] FIG. 18 is a cross-sectional view of an embodiment of a fuel
tube.
[0028] FIG. 19 is a cross-sectional view of an embodiment of a fuel
tube.
[0029] FIG. 20 is a cross-sectional view of an embodiment of a
nozzle assembly.
[0030] FIG. 21 is a cross-sectional view of an embodiment of a
nozzle assembly.
[0031] FIG. 22 is a schematic of an embodiment of a turbine system
with a nozzle assembly.
DETAILED DESCRIPTION OF THE INVENTION
[0032] FIG. 1 shows a premixer 10 as may be described herein. The
premixer 10 may be used in a combustor (not shown) and in similar
devices. The premixer 10 may include a fuel conduit 11 coupled to a
fuel plenum 12. The fuel plenum 12 is in fluid communication with
one or more fuel tubes 13. The fuel plenum 12 may have any desired
size or configuration. Any number of fuel tubes 13 may be used
herein. The fuel tubes 13 may have any desired size or
configuration.
[0033] The premixer 10 also may include a burner tube 14. The
burner tube 14 may include one or more air tubes 15 extending
through the burner tube 14. Any number of the air tubes 15 may be
used. The air tubes 15 may have any desired size or configuration.
The air tubes 15 may extend from a bell mouth 16 facing the fuel
plenum 12 to an opposite burner tube 14. The air tubes 15 may have
a larger diameter as compared to the fuel tubes 13.
[0034] The fuel plenum 12 and the burner tube 14 may be separated
by a number of spacers 18. Any number of spacers 18 may be used.
The spacers 18 may have any desired size or configuration. The
spacers 18 may be attached to a burner tube flange 20 on one end
and a fuel plenum flange 22 on the other. The fuel plenum flange 22
and the burner tube flange 20 may have any desired size or
configuration. Other types of connection means may be used herein.
The spacing between the fuel plenum 12 and the burner tube 14 may
vary.
[0035] A number of the fuel tubes 13 may extend from the fuel
plenum 12 into a number of the air tubes 15 within the burner tube
14. The fuel tubes 13 have a downstream end portion 17 (shown in
FIG. 2) that may be provided with a variety of geometries. Fuel
thus may enter the fuel plenum 12 via fuel conduit 11 and may be
distributed to the fuel tubes 13. The fuel may then be injected
from the downstream end portion 17 (shown in FIG. 2) of the fuel
tube 13 into an air stream in each of the air tubes 15 so as to mix
the fuel and air. Likewise, the air flow may be guided between the
fuel plenum 12 and the bell mouth 16 and into the air tubes 15.
Some or all of the air tubes 15 may have one of the fuel tubes 13
positioned therein. The premixer 10 thus may use a plurality of air
tubes 15 with a plurality of fuel tubes 13 so as to create multiple
co-flow jets of air and fuel. As used herein, the term "co-flow"
means the fuel and air flow in the same direction at the point of
injection of the fuel. The size and number of the fuel tubes 13,
and air tubes 15 may vary. Other configurations of the premixer 10
may be used herein.
[0036] Illustrated in FIG. 2 is an embodiment of a premixer 10
having a fuel conduit 11, a fuel plenum 12, and a plurality of fuel
tubes 13 coupled to the fuel plenum 12. A plurality of air tubes 15
are formed in the burner tube 14. A bell mouth 16 is disposed
around the burner tube 14 and functions to force air into the
plurality of air tubes 15. One of the plurality of fuel tubes 13
may be disposed coaxially within one of the plurality of air tubes
15 which feed fuel and air into a mixing portion 25 of air tubes 15
wherein the air and fuel are mixed. As used herein, the terms
"coaxial" and "coaxially" means that the fuel tubes 13 and the air
tubes 15 substantially share a common longitudinal axis or have
longitudinal axes that are substantially parallel to each other.
The terms "coaxial" and "coaxially" are intended to be interpreted
broadly and include small variations in the angles formed by the
respective longitudinal axes of the air tubes 15 and the fuel tubes
13 and minor offsets between the longitudinal axes. The arrangement
of the fuel tubes 13 and the air tubes 15 enable the creation of a
flow jet of air and fuel within the mixing portion 25. Multiple
flow jets of air and fuel may be obtained using multiple pairs of
fuel tubes 13 and air tubes 15.
[0037] Illustrated in FIG. 3 is an embodiment of a premixer 10
wherein the air tubes 15 are provided with a tapered upstream
section 27. The term "tapered", as used herein means a structure
that is not uniform in dimension. For example, the tapered upstream
section 27 of one of the air tubes 15 may have a larger diameter
than the diameter of the downstream section of the air tubes 15.
This configuration helps to accelerate the airflow for better fuel
and air mixing in the mixing portion 25 of the air tubes 15 and to
obtain an enhanced margin of flashback/flame holding and faster
fuel/air mixing that can shorten the length of the body of the air
tubes 15 and result in reduced NOx.
[0038] In operation, fuel enters the fuel plenum 12, and is
conveyed into the fuel tubes 13. Air is entrained by bell mouth 16
and is conveyed to the air tubes 15. The fuel and air mix in the
mixing portion 25 of the air tubes 15. The fuel exiting the fuel
tubes 13 is provided with enhanced turbulence resulting from the
various chevron configurations of the downstream end portion 17 of
the fuel tubes 13 (described in detail below) thereby shortening
the length required to achieve adequate mixing in the mixing
portion 25 of the air tubes 15.
[0039] FIGS. 4 and 5 illustrate the downstream end portion 17 of
one of the fuel tubes 13. As used herein, the term "downstream"
means in the direction of flow of the fuel/air mixture. The fuel
tubes 13 may have a cylindrical end 31 that is provided with a
V-shaped notch 33. The V-shaped notch 33 induces and enhances the
turbulence of the fuel/air flow beyond the downstream end portion
17 of the fuel tubes 13 to enable the mixing of fuel and air in the
mixing portion 25 of the air tubes 15 within a shorter interval and
shorter length along the air tubes 15. The V-shaped notch 33
defines a turbulence enhancing chevron outlet 34 that increases the
turbulence intensity of the fuel/air mixture and widens the mixing
layer beyond the point of the fuel injection. The configuration of
the downstream end portion 17 of the fuel tubes 13 may vary as
shown from the following examples.
[0040] FIGS. 6 and 7 illustrate alternate embodiments of the
downstream end portion 17 of one of the fuel tubes 13. In both
embodiments, a straight notch 35 with a straight inboard portion 36
is provided. The circumferential dimensions of the straight notch
35 may vary as shown.
[0041] It should be noted that the illustrated embodiments of the
turbulence enhancing chevron outlet 34 represent general examples
and are not intended to be limiting. For example, other shapes of a
turbulence enhancing chevron outlet 34 may be used. Similarly the
dimensions of the turbulence enhancing chevron outlet 34 may be
varied without departing from the spirit and scope of the invention
as described and claimed herein. Other geometries and means for
enhancing the turbulence of the fuel exiting the fuel tube 13 may
be used as may be apparent to one of ordinary skill in the art in
light of the teachings herein.
[0042] FIGS. 8 and 9 illustrate the downstream end portion 17 of
one of the fuel tubes 13 that is provided with a downstream end 43
that is tapered (tapered end 37). The tapered end 37 may be
provided with a V-shaped notch 33.
[0043] FIGS. 10 and 11 illustrate the downstream end of one of the
fuel tubes 13 that is provided with a tapered end 37 and with a
U-shaped notch 38.
[0044] As one of ordinary skill in the art will appreciate,
different numbers and shapes of notches (chevrons) and different
angles and lengths of taper for the downstream end portion 17 of
fuel tubes 13 may be selectively applied to form other possible
embodiments of the present invention.
[0045] FIGS. 12 and 13 show an alternative embodiment of a premixer
39 as is described herein. In this embodiment, the premixer 39
includes a downstream plenum 40 and an upstream plenum 41. The
downstream plenum 40 and the upstream plenum 41 may have any
desired size or configuration. In one embodiment, the upstream
plenum 41 is used as a plenum for fuel and the downstream plenum 40
is used as a plenum for diluent. The premixer 39 includes one or
more coaxial tube assemblies 42. Each of the one or more coaxial
tube assemblies 42 includes an interior tube 44 (shown in FIG. 13)
that may extend from the upstream plenum 41 and pass through the
downstream plenum 40. Likewise, an exterior tube 45 may extend from
the downstream plenum 40. The exterior tube 45 may surround the
interior tube 44. The size and number of coaxial tube assemblies 42
may vary. Other configurations may be used herein.
[0046] The premixer 39 also includes a burner tube 14 coupled to a
combustion chamber (not shown). As above, the burner tube 14
includes a number of air tubes 15 extending through the burner tube
14. The size and number of the air tubes 15 may vary. The air tubes
15 may extend from the bell mouth 16 to a downstream end 46 of
burner tube 14. Some of the air tubes 15 may have interior tube 44
extending therein while others may have exterior tube 45 extending
therein. The air tubes 15 may have a larger diameter as compared to
the coaxial tube assemblies 42.
[0047] The premixer 39 also may include a number of spacers 18 that
separate the downstream plenum 40 and the burner tube 14. Any
number of spacers 18 may be used. The spacers 18 may have any
desired size or configuration. The downstream plenum 40 may have a
fuel plenum flange 22 while the burner tube 14 may have a burner
tube flange 20. Fuel plenum flange 22 and burner tube flange 20 may
have any desired size or configuration. Other types of connection
means may be used herein. The spacing between the downstream plenum
40 and the burner tube 14 may vary.
[0048] Fuel or other types of flows thus may flow from the upstream
plenum 41 and the downstream plenum 40 through the coaxial tube
assemblies 42, and mix with the air in the air tubes 15. The
upstream plenum 41 and downstream plenum 40 may be used with
different arrangements of fuel, air, and diluents. For example, the
downstream plenum 40 may be used with a diluent such as nitrogen
(N.sub.2) while the upstream plenum 41 may be used with a fuel such
as hydrogen (H.sub.2), or methane CH.sub.4), or a combination of
both. Alternatively, the diluent flow may be or include a less
reactive fuel. This arrangement of diluent and fuel may create a
diluent inert sheath surrounding the flow of fuel. Such a diluent
inert sheath passing through the air tubes 15 may prevent flame
holding inside air tubes 15.
[0049] Other fuel and air mixing mechanisms may be used herein. For
example, the upstream plenum 41 may be arranged with air while the
downstream plenum 40 may have a mixture of hydrogen and nitrogen.
Likewise, the upstream plenum 41 may use nitrogen while the
downstream plenum 40 may use combinations of hydrogen and nitrogen.
Other arrangements and different types and combinations of air,
fuel, and diluent may be used herein.
[0050] The premixer 10, and premixer 39 described herein (in FIGS.
2 and 13 respectively) thus may use multiple fuel and air tubes 15
to create multiple co-flow jets of air and fuel. Fuel and air
mixing may be enhanced due to the length versus the diameter of the
air tubes 15. The premixer 10 and the premixer 39 also may use jets
of fuel in combination with a sheath of diluent and/or diluent and
air. The multiple jets also provide an increased flame holding
margin due to the increased axial component of the fuel flow to air
flow and by compartmentalizing the conventional burner tube into
the multiple tubes. Local quenching also may be induced by the
inert nitrogen, other diluents, and/or a high flow of air so as to
limit flame holding. Very low emissions thus may be achieved by the
good mixing caused by injecting the fuel into each air tube 15.
[0051] Illustrated in FIG. 13 is a cross-section of premixer 39. As
with the previous embodiment discussed with regard to FIG. 1, the
premixer 39 includes an upstream plenum 41 and a downstream plenum
40 with associated fuel conduits 11 and diluent fluid conduits 47,
respectively. The premixer 39 may include one or more coaxial tube
assemblies 42 having an interior tube 44 and an exterior tube 45.
In one embodiment, the interior tube 44 may be coupled to the
upstream plenum 41. Bell mouth 16 forces air into a plurality of
air tubes 15. The interior tube 44 and exterior tube 45 are
disposed coaxially within air tubes 15. The air and fuel are mixed
in mixing portion 25 of the air tubes 15. In one embodiment, the
exterior tube 45 may be coupled to downstream plenum 40 which is in
turn coupled to the diluent fluid conduit 47 that provides diluent
fluid such as air or an inert fluid such as N.sub.2. In another
embodiment, the interior tube 44 may be coupled to the downstream
plenum 40 as a plenum for diluent fluid and the exterior tube 45
may be coupled to the upstream plenum 41 as a plenum for fuel.
[0052] In the premixer 39 illustrated in FIG. 13, fuel enters the
upstream plenum 41 through the fuel conduit 11. A diluent fluid is
provided to the downstream plenum 40 through the diluent fluid
conduit 47. The interior tube 44 of the coaxial tube assemblies 42
may be coupled to the upstream plenum 41, and the exterior tube 45
may be coupled to the downstream plenum 40. The fuel and diluent
fluid exiting the coaxial tube assemblies 42 may be provided with
enhanced turbulence resulting from the various configurations of
the downstream end 48 of the coaxial tube assemblies 42, thereby
shortening the length of air tubes 15 required to achieve adequate
mixing. As one of ordinary skill in the art will appreciate, the
fuel may also be transported through exterior tube 45, and the
diluent fluid may be transported through the interior tube 44.
[0053] The downstream end 48 of the coaxial tube assemblies 42 may
have one of a variety of configurations as illustrated in FIGS.
14-19. FIG. 14 illustrates an embodiment of one of the coaxial tube
assemblies 42 where the downstream end 48 of the exterior tube 45
has a tapered end 49, and the interior tube 44 has a protruding
straight end 51 with a V-shaped notch 33. FIG. 15 illustrates an
embodiment where the downstream end 48 of the exterior tube 45 has
a tapered end 49, and the interior tube 44 also has a tapered end
53. FIG. 16 illustrates an embodiment where the downstream end 48
of the exterior tube 45 has a straight end 55, and the interior
tube 44 has a tapered end 53 that protrudes from the downstream end
48 of the exterior tube 45. FIG. 17 illustrates an embodiment where
the downstream end 48 of the exterior tube 45 has a tapered end 49,
and the interior tube 44 has a straight end 57 mounted flush with
the end of exterior tube 45. FIG. 18 illustrates an embodiment
where the downstream end 48 of the exterior tube 45 has a tapered
end 49, and the interior tube 44 has a tapered end 59 mounted flush
with the end of the exterior tube 45. FIG. 19 illustrates an
embodiment where the downstream end 48 of the exterior tube 45 has
a straight end 55, and the interior tube 44 has a tapered end 59
mounted flush with the end of the exterior tube 45. Although the
tapered end 49 and tapered end 59 are shown as a straight taper,
other types of tapers may be used without departing from the spirit
and scope of the invention as described and claimed herein.
[0054] The various embodiments of the downstream end portion 17 of
the fuel tubes 13 (Shown in FIG. 2) and the downstream end portion
48 of the coaxial tube assemblies 42 (shown in FIG. 13) serve to
minimize flame holding/flashback problems. The premixer 10 will
typically use one or more fuel tubes 13 within air tubes 15 to
create multiple co-flow jets of air and fuel to prevent flame
holding at the fuel injection location. The coaxial tube assemblies
42 provide fuel in combination with a sheath of annular diluent
fluid such as N.sub.2 to premix the air and fuel within the air
tubes 15. The mixing lengths can be improved (shortened) by
providing fuel tubes 13 or coaxial tube assemblies 42 with an
enhanced turbulence capability such as, for example, through the
use of chevron outlets such as V-shaped notch 33 (illustrated in
FIG. 5) or U-shaped notch 38 (illustrated in FIG. 11). The enhanced
turbulence capability provides fast mixing within short length in
the air tubes 15.
[0055] Illustrated in FIG. 20 is a combustor 60 having a plurality
of premixers 10 that inject a fuel/air mixture into a combustion
chamber 63 with a combustor liner 64. Each of the premixers 10 may
be coupled to a fuel source 65. Air (shown by dashed arrows) from
air source 67 enters the air tubes 15 and mixes with fuel injected
through the fuel tubes 13 before entering the combustion chamber
63. The premixers 10 may be supported by a housing 71.
[0056] Illustrated in FIG. 21 is a combustor 75 having a liner 73.
The combustor 75 includes a plurality of premixers 39. The
premixers 39 may be coupled to one or more fuel sources 65 and at
least one source of diluent fluid 79. Fuel and diluent fluid are
conveyed through coaxial tube assemblies 42. Air (shown by dashed
arrows) from air source 67 enters the air tubes 15 and mixes with
fuel and diluent fluids injected through the coaxial tube
assemblies 42 before entering the combustion chamber 63.
[0057] FIG. 22 is a schematic illustrating the environment in which
the premixer 10 may be implemented. A gas turbine 81 may include a
compressor 83 coupled to a compressed air conduit 85. The
compressed air conduit 85 supplies compressed air to a combustor 89
coupled to an exhaust conduit 91. Exhaust from exhaust conduit 91
drives a turbine 93 which may drive a shaft 97 providing power to a
load 103. The combustor 89 may include a nozzle assembly 99 with a
premixer 10 (such as illustrated in FIG. 2) coupled to a fuel
source 101. The premixer 10 may be used to provide multiple co-flow
jets of air and fuel. The assemblies may be used for high H.sub.2
combustion to improve the mixing of the high H.sub.2 fuel and air
without the cost of system pressure drop, and to provide reduced
NOx and flashback probability.
[0058] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. Where the definition of terms departs from the
commonly used meaning of the term, applicants intend to utilize the
definitions provided herein, unless specifically indicated. The
singular forms "a", "an" and "the" are intended to include the
plural forms as well, unless the context clearly indicates
otherwise. It will be understood that, although the terms first,
second, etc. may be used to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. The term "and/or"
includes any, and all, combinations of one or more of the
associated listed items. The phrases "coupled to" and "coupled
with" contemplates direct or indirect coupling.
[0059] 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 have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements.
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