U.S. patent number 3,826,078 [Application Number 05/238,318] was granted by the patent office on 1974-07-30 for combustion process with selective heating of combustion and quench air.
This patent grant is currently assigned to Phillips Petroleum Company. Invention is credited to Harold T. Quigg.
United States Patent |
3,826,078 |
Quigg |
July 30, 1974 |
COMBUSTION PROCESS WITH SELECTIVE HEATING OF COMBUSTION AND QUENCH
AIR
Abstract
A new combustion process wherein combustion efficiency is
retained while reducing inlet air temperature to the combustor so
as to obtain reduced nitrogen oxides emissions. A new combustor,
and a new combination of combustion apparatus and heat utilization
apparatus are also provided.
Inventors: |
Quigg; Harold T. (Bartlesville,
OK) |
Assignee: |
Phillips Petroleum Company
(Bartlesville, OK)
|
Family
ID: |
26903033 |
Appl.
No.: |
05/238,318 |
Filed: |
March 27, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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208245 |
Dec 15, 1971 |
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Current U.S.
Class: |
60/776;
60/39.511; 60/732; 431/10 |
Current CPC
Class: |
F23R
3/02 (20130101); F02C 7/08 (20130101); F02C
3/36 (20130101); F23C 6/045 (20130101) |
Current International
Class: |
F23C
6/04 (20060101); F23C 6/00 (20060101); F23R
3/02 (20060101); F02C 3/00 (20060101); F02C
7/08 (20060101); F02C 3/36 (20060101); F02c
001/04 () |
Field of
Search: |
;60/39.02,39.06,39.51,39.65 ;431/10 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Engineering Knowhow in Engine Design part 19, Sae Publication SP
365 HS-010922, pg. 7..
|
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Olsen; Warren
Parent Case Text
This application is a continuation-in-part of copending application
Ser. No. 208,245, filed Dec. 15, 1971, now abandoned.
Claims
I claim:
1. In a method wherein a stream of air and a stream of fuel are
passed to a combustion zone comprising a primary combustion region,
a secondary combustion region located downstream from said primary
combustion region, and a quench region located downstream from said
secondary combustion region, said fuel and said air are at least
partially mixed to form a combustible mixture which is burned to
produce hot combustion gases containing heat energy, and said hot
combustion gases are passed to a heat energy utilization zone to
utilize a portion of said heat energy, the improvement
comprising:
dividing said stream of air into a first stream of air and a second
stream of air;
further dividing said first stream of air into a stream comprising
primary air and another stream comprising secondary air;
introducing a stream of said fuel into said primary combustion
region;
introducing said stream comprising primary air into said primary
combustion region;
burning said fuel;
introducing said stream comprising secondary air into said
secondary combustion region at a temperature within the range of
from about 100.degree. to about 500.degree. F. greater than the
temperature of said primary air;
passing said second stream of air in heat exchange relationship
with an exhaust stream from said heat energy utilization zone to
heat said second stream of air and thereby utilize an additional
portion of said energy; and
passing at least a portion of said heated second stream of air into
said quench region of said combustion zone.
2. A method according to claim 1 wherein the temperature of said
primary air is not greater than about 700.degree. F.
3. A method according to claim 2 wherein the equivalence ratio in
said primary combustion region is greater than stoichiometric and
is adjusted to a value such that the NO.sub.x emissions value in
the exhaust gases from said combustion zone is not greater than
about 5 pounds per 1,000 pounds of fuel burned in said combustion
zone.
4. A method according to claim 3 wherein the CO emissions value in
the exhaust gases from said combustion zone is not greater than
about 25 pounds per 1,000 pounds of fuel burned in said combustion
zone.
5. A method according to claim 4 wherein the equivalence ratio in
said primary combustion region is at least about 3.5.
6. A method for forming and burning a combustible mixture of a fuel
and air in a combustion zone having a primary combustion region, a
secondary combustion region located downstream from said primary
combustion region, and a quench region located downstream from said
secondary combustion region, to produce hot combustion gases
containing heat energy which are passed to a heat energy
utilization zone to utilize a portion of said heat energy, which
method comprises:
dividing a stream of air into a first stream of air and a second
stream of air;
further dividing said first stream of air into a stream comprising
primary combustion air and another stream comprising secondary
combustion air;
introducing a stream of fuel into said primary combustion
region;
introducing said stream comprising primary combustion air into said
primary combustion region at a temperature not greater than about
700.degree. F.;
burning said fuel;
introducing said stream comprising secondary combustion air into
said secondary region at a temperature within the range of from
about 100.degree. to about 500.degree. F. greater than the
temperature of said primary air;
passing said second stream of air in heat exchange relationship
with an exhaust stream from said heat energy utilization zone to
heat said second stream of air; and
introducing at least a portion of said heated second stream of air
into said quench region of said combustion zone.
7. A method for forming and burning a combustible mixture of a fuel
and air in a combustion zone having a primary combustion region, a
secondary combustion region located downstream from said primary
combustion region, and a quench region located downstream from said
secondary combustion region, to produce hot combustion gases
containing heat energy which are passed to a heat energy
utilization zone to utilize a portion of said heat energy, which
method comprises:
dividing a stream of air into a first stream of air and a second
stream of air;
further dividing said first stream of air into a stream comprising
primary combustion air and another stream comprising secondary
combustion air;
introducing a stream of fuel into said primary combustion
region;
introducing said stream comprising primary combustion air into said
primary combustion region at a temperature not greater than about
700.degree. F. and in an amount relative to said fuel sufficient to
provide a fuel-rich mixture having an equivalence ratio in said
primary combustion region greater than stoichiometric;
burning said fuel;
introducing said stream comprising secondary combustion air into
said secondary region, in an amount sufficient to provide a
fuel-lean mixture in said secondary region with respect to any
unburned fuel entering said secondary region from said primary
region, and at a temperature within the range of from about
100.degree. to about 500.degree. F. greater than the temperature of
said introduced primary air;
passing said second stream of air in heat exchange relationship
with an exhaust stream from said heat energy utilization zone to
heat said second stream of air; and
introducing at least a portion of said heated second stream of air
into said quench region of said combustion zone at a temperature
greater than the temperature of said secondary air.
8. A method according to claim 7 wherein said stream of air
comprising primary combustion air is not more than about 25 percent
of the total air introduced into said combustion zone.
9. A method according to claim 8 wherein said stream of air
comprising primary combustion air is not more than about 5.6
percent of the total air introduced into said combustion zone.
10. A method according to claim 7 wherein said equivalence ratio is
adjusted to a value such that the NO.sub.x emissions value in the
exhaust gases from said combustion zone is not greater than about 5
pounds per 1,000 pounds of fuel burned in said combustion zone.
11. A method according to claim 10 wherein said equivalence ratio
is at least about 1.5.
12. A method according to claim 10 wherein said equivalence ratio
is at least about 3.5.
13. A method according to claim 7 wherein the equivalence ratio in
said primary combustion region is greater than stoichiometric and
is adjusted to a value such that the NO.sub.x emissions value in
the exhaust gases from said combustion zone is not greater than
about 5 pounds per 1,000 pounds of fuel burned in said combustion
zone.
14. A method according to claim 13 wherein the CO emissions value
in the exhaust gases from said combustion zone is not greater than
about 25 pounds per 1,000 pounds of fuel burned in said combustion
zone.
15. A method according to claim 14 wherein said equivalence ratio
is at least about 1.5.
16. A method according to claim 14 wherein said equivalence ratio
is at least about 3.5.
17. A method for forming and burning a combustible mixture of a
fuel and air in a combustion zone having a primary combustion
region, a secondary combustion region located downstream from said
primary combustion region, and a quench region located downstream
from said secondary combustion region, to produce hot combustion
gases containing heat energy which are passed to a heat energy
utilization zone to utilize a portion of said heat energy, which
method comprises:
dividing a stream of air into a first stream of air and a second
stream of air;
further dividing said first stream of air into a stream comprising
primary combustion air and another stream comprising secondary
combustion air;
introducing a stream of fuel into said primary combustion
region;
introducing said stream comprising primary combustion air into said
primary combustion region;
burning said fuel;
introducing said stream comprising secondary combustion air into
said secondary region at a temperature at least 100.degree. F.
greater than the temperature of said primary combustion air;
passing said second stream of air in heat exchange relationship
with an exhaust stream from said heat energy utilization zone to
heat said second stream of air; and
introducing at least a portion of said heated second stream of air
into said quench region of said combustion zone.
18. A method according to claim 17 wherein said heated second
stream of air is passed in heat exchange with an outer wall of said
primary combustion region so as to remove heat from the interior of
said primary combustion region and further heat said air, and is
then introduced into said quench region.
19. A method according to claim 17 wherein:
said heated second stream of air is passed in a first annular
stream surrounding an outer wall of said primary combustion region
and a portion of said secondary combustion region, and is then
introduced into said quench region; and
said secondary air is passed in a second annular stream surrounding
but separated from said first annular stream, and is then
introduced into said secondary combustion region.
20. A method according to claim 17 wherein the temperature of said
first stream of air is not greater than about 700.degree. F.
21. A method according to claim 17 wherein a portion of said heated
second stream of air is mixed with said secondary air so as to
increase the temperature of said secondary air.
22. A method for forming and burning a combustible mixture of a
fuel and air in a combustion zone having a primary combustion
region, a secondary combustion region located downstream from said
primary combustion region, and a quench region located downstream
from said secondary combustion region, to produce hot combustion
gases containing heat energy which are passed to a heat energy
utilization zone to utilize a portion of said heat energy, which
method comprises:
dividing a stream of air into a first stream of air and a second
stream of air;
further dividing said first stream of air into a stream comprising
primary combustion air and another stream comprising secondary
combustion air;
introducing a stream of fuel into said primary combustion
region;
introducing said stream comprising primary combustion air into said
primary combustion region in an amount relative to said fuel
sufficient to provide a fuel-rich mixture having an equivalence
ratio in said primary combustion region greater than
stoichiometric;
burning said fuel;
introducing said stream comprising secondary combustion air into
said secondary region, in an amount sufficient to provide a
fuel-lean mixture in said secondary region with respect to any
unburned fuel entering said secondary region from said primary
region, and at a temperature at least 100.degree. F. greater than
the temperature of said introduced primary air;
passing said second stream of air in heat exchange relationship
with an exhaust stream from said heat energy utilization zone to
heat said second stream of air; and
introducing at least a portion of said heated second stream of air
into said quench region of said combustion zone at a temperature
greater than the temperature of said secondary air.
Description
This invention relates to improved combustion processes, improved
combustors which can be employed in said processes, and an improved
combination of combustion apparatus and heat utilization
apparatus.
Air pollution has become a major problem in the United States and
other highly industrialized countries of the world. Consequently,
the control and/or reduction of said pollution has become the
object of major research and development effort by both
governmental and nongovernmental agencies. Combustion of fossil
fuel is a primary source of said pollution. It has been alleged,
and there is supporting evidence, that the automobiles employing
conventional piston-type engines burning hydrocarbon fuels are a
major contributor to said pollution. Vehicle emission standards
have been set by the United States Environmental Protection Agency
which are sufficiently restrictive to cause automobile
manufacturers to consider employing alternate engines instead of
the conventional piston engine.
The gas turbine engine is being given serious consideration as an
alternate engine. However, insofar as is presently known, there is
no published information disclosing realistic and/or practical
combustion processes or combustors which can be operated at
conditions typical of those existing in high performance engines,
and which will have emission levels meeting or reasonably
approaching the standard set by said United States Environmental
Protection Agency. This is particularly true with respect to
nitrogen oxides emissions. Thus, there is a need for a combustion
process, and a combustor of practical and/or realistic design,
which can be operated in a manner such that the emissions therefrom
will meet said standards. Even a process and/or a combustor giving
reduced emissions approaching said standards would be a great
advance in the art. Such a process or combustor would have great
potential value because it is possible the presently very
restrictive standards may be reduced.
In the operation of combustion processes, conservation of the
thermal energy produced is essential for efficiency. For example,
in current gas turbine engines being proposed for automotive
service, the turbine exhaust gases are heat exchanged with the
inlet air to the primary combustion zone of the combustor so as to
recover heat from said exhaust gases and improve overall
efficiency. However, these engines will not meet the emission
standards set by said Environmental Protection Agency.
The present invention solves the above-described problems by
heatexchanging the turbine exhaust gases with another air stream to
the combustor, e.g., the dilution or quench air, instead of the
primary inlet air. The method of the invention thus provides for
reducing the temperature of the primary inlet air to the combustor.
This reduces the temperature in the combustor which results in
reduced nitrogen oxides emissions. Thus, the overall advantageous
result of the invention includes (1) reduction of nitrogen oxide
emissions from the combustor while (2) maintaining thermal
efficiency by returning the recovered heat to the process at a
point where it has no effect on nitrogen oxides production. The
invention also provides novel combustors, and a novel combination
of combustion apparatus and heat utilization apparatus.
Thus, according to the invention there is provided in a method
wherein a stream of air and a stream of fuel are passed to a
combustion zone, at least partially mixed to form a combustible
mixture which is burned to produce hot combustion gases containing
heat energy, and said hot combustion gases are passed to a heat
energy utilization zone to utilize a portion of said heat energy,
the improvement comprising: dividing said stream of air into a
first stream of air and a second stream of air; passing at least a
portion of said first stream of air to said combustion zone;
passing said second stream of air in heat exchange relationship
with an exhaust stream from said heat energy utilization zone to
heat said second stream of air and thereby utilize an additional
portion of said energy; and passing at least a portion of said
heated second stream of air into a quench region of said combustion
zone.
Further according to the invention, there is provided an apparatus
for producing and utilizing heat energy, comprising, in
combination: an air supply conduit; a combustion means for burning
a fuel to produce hot combustion gases containing heat energy; a
fuel inlet means for introducing a fuel into said combustion means;
a primary air conduit means connected to said air supply conduit
and said combustion means for introducing a stream of air
comprising primary air into said combustion means; a heat exchange
means; a quench air conduit means connected to said air supply
conduit, said heat exchange means, and said combustion means for
delivering a stream of air comprising quench air from said air
supply conduit, through said heat exchange means, and into said
combustion means; a heat energy utilization means for utilizing a
portion of said heat energy; an effluent conduit means for passing
said hot combustion gases from said combustion means to said heat
energy utilization means; and an exhaust conduit means connecting
said heat energy utilization means and said heat exchange means for
passing said hot combustion gases from said heat utilization means
and into heat exchange relationship with said stream of quench air
to heat said quench air and thereby utilize an additional portion
of said heat energy.
Still further according to the invention, there is provided a
combustor comprising, in combination: an outer tubular casing; a
flame tube disposed concentrically within said casing and spaced
apart therefrom to form a first annular chamber between said flame
tube and said casing; an air inlet means for introducing a stream
of air comprising primary air into the upstream end portion of said
flame tube; a fuel inlet means for introducing fuel into the
upstream end portion of said flame tube; an imperforate sleeve
surrounding an upstream portion of said flame tube and spaced apart
therefrom to longitudinally enclose an upstream portion of said
first annular chamber and define a second annular chamber between
said sleeve and said outer casing; a wall member closing the
downstream end of said second annular chamber; a baffle member
closing the upstream end of said enclosed portion of said first
annular chamber; at least one opening provided in the wall of said
flame tube at a first station located intermediate the upstream and
downstream ends thereof; a first conduit means extending from said
second annular chamber into communication with said opening located
at said first station for admitting a second stream of air from
said second annular chamber into the interior of said flame tube;
at least one other opening provided in the wall of said flame tube
at a second station located downstream from said first station for
admitting a third stream of air from said first annular chamber
into the interior of said flame tube; and a second conduit means
extending through said outer casing, said second annular chamber,
said sleeve, and into communication with said enclosed portion of
said first annular chamber for admitting a stream of air
thereto.
FIG. 1 is a diagrammatic flow sheet illustrating methods of
producing and utilizing heat energy in accordance with the
invention.
FIG. 2 is a diagrammatic illustration of methods and apparatus in
accordance with the invention.
FIG. 3 is a view in cross section of a combustor in accordance with
the invention.
FIG. 4, 5, 6, and 7 are views in cross section taken along the
lines 4--4, 5--5, 6--6, and 7--7, respectively, of FIG. 3.
FIG. 8 is a fragmentary perspective view of a combustor flame tube
illustrating another type of fin or extended surface which can be
employed thereon.
FIG. 9 is a partial view in cross section of another combustor in
accordance with the invention.
FIG. 10 is a front elevation view taken along the lines 10--10 of
FIG. 9.
FIG. 11 is a cross section view in elevation of the swirl plate of
the dome or closure member in the combustor of FIG. 9.
FIG. 12 is a diagrammatic view, partially in cross section of
another combustor in accordance with the invention.
Referring now to the drawings, wherein like reference numerals are
employed to denote like elements, the invention will be more fully
explained. In FIG. 1 a stream of air from an air supply conduit 10
is divided into a first stream of air in conduit 12 and a second
stream of air in conduit 14. In one embodiment, at least a portion
of said first stream of air 12 is passed into combustion zone 16. A
stream of fuel is introduced into said combustion zone via conduit
18. Said combustion zone can comprise any suitable type of
combustion zone for burning a mixture of fuel and air to produce
hot combustion gases containing heat energy. For example, said
combustion zone can be a combustor in a gas turbine engine, a
combustor in an aircraft jet engine, a combustor or other furnace
employed in a boiler for generating steam, or other types of
stationary power plant, etc.
Said fuel and said first stream of air are at least partially mixed
to form a combustible mixture which is burned to produce hot
combustion gases containing heat energy. Said hot combustion gases
are passed via conduit 20 to heat energy utilization zone 22 so as
to utilize a portion of the heat energy in said gases. Said heat
energy utilization zone can comprise any suitable method and/or
means for utilizing or putting to use the heat energy contained in
said hot combustion gases. For example, a turbine in a gas turbine
engine wherein heat energy is converted to mechanical energy, or
the heat exchange tubes in a boiler where water is connected to
steam, etc.
Said second stream of air in conduit 14 is passed through heat
exchange zone 24 in heat exchange relationship with an exhaust
stream in conduit 26 from heat energy utilization zone 22 so as to
heat said air and thereby utilize an additional portion of said
heat energy. Said heat exchange zone can comprise any suitable
method and/or means for effecting heat exchange between two
separate streams of fluids, e.g., indirect heat exchange. The
heated second stream of air is passed from said heat exchange zone
via conduit 15 and returned to said combustion zone 16, preferably
at a downstream location therein, to serve as a diluent or quench
medium to lower the temperature of the effluent gases in conduit 20
before they are passed to the heat energy utilization zone 22.
In one preferred embodiment of the invention, said combustion zone
16 can comprise a primary combustion region, a secondary combustion
region located downstream from said primary combustion region, and
a quench or dilution region located downstream from said secondary
combustion region. In this and other embodiments, said first stream
of air in conduit 12 is further divided into a stream comprising
primary air and another stream comprising secondary air. Said
primary air is introduced into said primary combustion region and
said secondary air is introduced into said secondary region via
conduit 30. At least a portion of said heated second stream of air
is introduced into said quench or dilution region via conduit 15,
as before.
In another preferred embodiment of the invention, a portion of said
heated second stream of air in conduit 15 can be passed via conduit
31 into conduit 30 for mixing with and increasing the temperature
of the secondary air therein. The valves in said conduits 30 and 31
can be employed to regulate the relative proportions of the two
streams of air.
FIG. 2 illustrates one embodiment of the invention wherein the
effluent gases from combustor 16 are passed via conduit 20 to a
turbine 25. In turbine 25 a portion of the heat energy in said
gases is converted to mechanical energy to drive shaft 28 which can
be connected to any suitable load. Exhaust gases from turbine 25
are passed via conduit 26 to heat exchanger 24 and exhausted
therefrom via conduit 27.
In FIG. 3 there is illustrated a combustor in accordance with the
invention, denoted generally by the reference numeral 40, which
comprises an elongated flame tube 42. Said flame tube 42 is open at
its downstream end, as shown, for communication with a conduit
leading to a turbine or other utilization of the combustion gases.
A closure or dome member, designated generally by the reference
numeral 44, is provided for closing the upstream end of said flame
tube, except for the openings in said dome member. An outer housing
or casing 46 is disposed concentrically around said flame tube 42
and spaced apart therefrom to form a first annular chamber 48
around said flame tube and said dome or closure member 44. Said
annular chamber 48 is closed at its downstream end by any suitable
means such as that illustrated. Suitable flange members, as
illustrated, are provided at the downstream end of said flame tube
42 and outer housing 46 for mounting same and connecting same to a
conduit leading to a turbine or other utilization of the combustion
gases from the combustor. Similarly, suitable flange members 50 and
52 are provided at the upstream end of said flame tube 42 and said
outer housing 46 for mounting same and connecting same to a
suitable conduit means which leads from a compressor or other
source of air. As illustrated in the drawing, said upstream flange
members comprise a portion of said outer housing or casing 46 which
encloses dome member 44 and forms the upstream end portion of said
first annular chamber 48. It will be understood that outer housing
or casing 46 can be extended, if desired, to enclose dome 44 and
said upstream flanges then relocated on the upstream end thereof.
While not shown in the drawing, it will be understood that suitable
support members are employed for supporting said flame tube 42 and
said closure member 44 in the outer housing 46 and said flange
members. Said supporting members have been omitted so as to
simplify the drawing.
An air inlet means is provided for introducing a swirling mass or
stream of air into the upstream end portion of flame tube 42. As
illustrated in FIGS. 3 and 6, said air inlet means comprises a
generally cylindrical swirl chamber 54 formed in said dome member
44. The downstream end of swirl chamber 54 is in open communication
with the upstream end of flame tube 42. A plurality of air conduits
56 extend from said first annular chamber 48, or other suitable
source of air, into swirl chamber 54 tangentially with respect to
the inner wall thereof.
A fuel inlet means is provided for introducing a stream of fuel
into the upstream end portion of flame tube 42. As illustrated in
FIG. 3, said fuel inlet means comprises a hollow conduit 58 for
introducing a stream of fuel into the upstream end of swirl chamber
54 and axially with respect to said swirling stream of air. Any
other suitable fuel inlet means can be employed.
A flared expansion passageway 60 is formed in the downstream end
portion of dome or closure member 44. Said flared passageway flares
outwardly from the downstream end of swirl chamber 54 to a point on
the inner wall of flame tube 42.
An imperforate sleeve 62 surrounds an upstream portion of said
flame tube 42. The outer wall of said sleeve can be insulated if
desired and thus increase its effectiveness as a heat shield. Said
sleeve 62 is spaced apart from flame tube 42 so as to
longitudinally enclose an upstream portion 48' of said first
annular chamber 48 and define a second annular chamber 64 between
said sleeve 62 and outer casing 46. An annular wall member 66,
secured to the inner periphery of casing 46, is provided for
closing the downstream end of said second annular chamber 64. An
annular baffle member 68, secured to the outer wall of flame tube
42 and the inner wall of sleeve 62, is provided for closing the
upstream end of said enclosed portion 48' of first annular space
48. At least one opening 70 is provided in the wall of flame tube
42 at a first station located intermediate the ends of said flame
tube. In most instances, it will be preferred to provide a
plurality of openings 70, as illustrated. A generally tubular
conduit means 72 extends from said second annular chamber 64 into
communication with said opening 70 for admitting a second stream of
air from said second annular chamber 64 into the interior of flame
tube 42. When a plurality of openings 70 are provided, a plurality
of said tubular conduits 72 are also provided, with each individual
conduit 72 being individually connected to an individual opening
70. The above-described structure thus provides an imperforate
conduit means comprising second annular chamber 64 and tubular
conduit(s) 72 for admitting a second straam of air into the
interior of flame tube 42.
At least one other opening 74 is provided in the wall of flame tube
42 at a second station located downstream and spaced apart from
said first station for admitting a third stream of air from first
annular chamber 48 into the interior of flame tube 42. In most
instances, it will be preferred to provide a plurality of openings
74 spaced around the periphery of said flame tube, similarly as
illustrated. A second conduit means 15 extends through said outer
casing 46, said second annular chamber 64, said sleeve 62, and into
communication with said enclosed portion 48' of first annular
chamber 48 for admitting a stream of air thereto. If desired, said
conduit 15 can communicate with the nonenclosed portion of annular
chamber 48.
Preferably, the outer wall surface of flame tube 42 is provided
with an extended surface in the form of fins or tabs mounted
thereon in the region surrounded by sleeve 62, and which extend
into the portion 48' of said first annular chamber which is
enclosed by said sleeve. As illustrated in FIGS. 3, 4, and 5, said
fins or tabs 76 and 78 can be arranged in rows which extend around
the periphery of the flame tube 42, and which are spaced apart
longitudinally on said flame tube. The fins or tabs 76, in each row
thereof, can be spaced apart circumferentially to provide
passageways 77 therebetween. See FIG. 4. Similarly, passageways 79
can be provided between the circumferentially spaced apart fins or
tabs 42. See FIG. 5. FIG. 8 illustrates another type of fin which
can be employed. In FIG. 8 the fins 80 extend longitudinally of
flame tube 42. Said fins 76, 78, and 80 can extend into enclosed
portion 48' any desired distance.
FIG. 7 illustrates one type of structure which can be employed to
provide tubular conduits 72. A plurality of boss members 82, spaced
apart circumferentially in a row around the periphery of flame tube
42, is provided downstream from the last row of fins 78. Said boss
members 82 have the general shape of fins 76 and 78 and passageways
83 are provided therebetween, similarly as for passageways 77 and
79 in the rows of fins 76 and 78. Said imperforate sleeve 62
extends over boss members 82, similarly as for fins 76 and 78, and
said conduits 72 can be formed by cutting through said sleeve 62
and said boss members 80 into communication with openings 70 in
flame tube 42. Said passageways 77, 79 and 83 thus provide
communication through enclosed portion 48', around tubular conduits
72, and into the downstream portion of first annular chamber
48.
Referring now to FIG. 9, there is illustrated the upstream portion
of another combustor in accordance with the invention. The
downstream portion of the combustor of FIG. 9 is like the combustor
of FIG. 3. A closure member or dome, designated generally by the
reference numeral 85, is mounted in the upstream end of flame tube
42 so as to close the upstream end of said flame tube except for
the openings provided in said closure member. Said closure member
can be fabricated integrally, i.e., as one element. However, in
most instances it will be preferred to fabricate said closure
member in a plurality of pieces, e.g., an upstream element 86, a
swirl plate 87 (see FIG. 11), and a downstream element or radiation
shield 88. An air inlet means is provided for introducing a
swirling mass of air into swirl chamber 89 which is formed between
swirl plate 87 and radiation shield 88, and then into the upstream
end of flame tube 42. As illustrated in FIGS. 9, 10, and 11, said
air inlet means comprises a plurality of air conduits 90 and 90'
extending through said upstream member 86 and said swirl plate 87,
respectively. A plurality of angularly disposed baffles 91, one for
each of said air conduits 90, are formed on the downstream side of
said swirl plate adjacent the outlets of said air conduits.
A fuel inlet means is provided for introducing a stream of fuel
into the upstream end of flame tube 42. As illustrated in FIG. 9,
said fuel inlet means comprises a fuel conduit 92 leading from a
source of fuel, communicating with a passageway 93 formed in
upstream element 86, which in turn communicates with chamber 94,
also formed in element 86. A spray nozzle 95 is mounted in a
suitable opening in the downstream side of said element 86 and is
in communication with said chamber 94. Any other suitable type of
spray nozzle and fuel inlet means can be employed, including other
air assist atomization nozzles. For example, it is within the scope
of the invention to employ other nozzle types for atomizing
normally liquid fuels such as nozzles wherein a stream of air is
passed through the nozzle along with the fuel.
FIG. 12 is a diagrammatic illustration of another type of combustor
which can be employed in the practice of the invention. This
combustor is similar to the combustor illustrated in FIG. 3. In the
combustor of FIG. 12 the tubular conduits 72' extend transversely
through annular chamber 48' and through outer casing 46'. Said
tubular conduits 72' can extend to the front or upstream end of the
combustor, as illustrated, and be connected to the same source of
air as is supplying chamber 48; or said conduits 72' can be
connected to another source of air. As here illustrated, said
closure member 44' is like closure member 44 in FIG. 3. However, it
is within the scope of the invention to employ any other suitable
type of closure member, such as closure member 85 in FIG. 10.
In a preferred method of operating the combustor of FIG. 3, a
stream of air from a compressor or other source (not shown) is
divided into a first stream of air and a second stream of air, said
first stream of air is passed, via a conduit connected to flange
52, into the upstream end of annular space 48. Said first stream of
air is further divided into a stream comprising primary air and a
stream comprising secondary air. Said primary air is passed from
annular space 48, through tangential conduits 56, and into swirl
chamber 54. Said tangential conduits impart a helical or swirling
motion to the air entering said swirl chamber and exiting
therefrom. This swirling motion creates a strong vortex action
resulting in a reverse circulation of hot gases within flame tube
42.
A stream of fuel, preferably prevaporized, is admitted, via conduit
58, axially of said swirling stream of air. Controlled mixing of
said fuel and said air occurs at the interface therebetween. The
fuel and air exit from swirl chamber 54 via expansion passageway 60
wherein they are expanded in a uniform and graduated manner, during
at least a portion of the mixing thereof, from the volume in the
region of the initial contact therebetween to the volume of the
primary combustion region, i.e., the upstream portion of flame tube
42.
Said secondary air is passed from the upstream end of annular
chamber 48 via second annular chamber 64, tubular conduits 72, and
openings 70 into a second region of the combustor which is located
downstream from said primary combustion region.
The above-mentioned second stream of air, after passing through a
heat exchanger such as heat exchanger 24 in FIG. 1, enters the
combustor via conduit 15 and is passed from the upstream end of the
enclosed portion 48' of annular chamber 48 through the enclosed
portion 48', around tubular conduits 72, into the downstream
portion of annular chamber 48, and then via openings 74 into a
third region of the combustor which is located downstream from said
second region. Said second stream of air comprises and can be
referred to as quench or dilution air. Conduit 15 can communicate
with enclosed portion 48', or the downstream portion of first
annular space or chamber 48, at any desired location. However, the
upstream end of enclosed portion 48' is a preferred location
because the air flowing over the finned wall portion of flame tube
42 serves to cool said wall portion and remove heat from the
interior of said flame tube, and thus cause the primary combustion
region to operate at a lower temperature. This aids further in
reducing nitrogen oxide emissions.
In one preferred method, the operation of the combustor of FIG. 9
is similar to the above-described operation of the combustor of
FIG. 3, and reference is made thereto. The principal difference is
in the operation of closure member 85 (FIG. 9) and closure member
44 (FIG. 3). In FIG. 9, primary air is passed through said openings
90 and 90', strikes said baffles 91, and has a swirling motion
imparted thereto in chamber 89. A swirling stream of air exits from
swirl chamber 89 through the opening in radiation shield 88 which
surrounds nozzle 95. A stream of liquid fuel is passed through
conduit 92, passageway 93, chamber 94, and exits from nozzle 95 in
a generally cone-shaped discharge. Said fuel contacts said stream
of air, with said air stream assisting the action of nozzle 95 in
atomizing said fuel.
The operation of the combustor illustrated in FIG. 12 is similar to
that described above for the combustors of FIGS. 3 and 9, taking
into consideration the type of dome or closure member employed on
the upstream ends of the flame tubes. The combustor of FIG. 12 is
particularly adapted to be employed in those embodiments of the
invention wherein the stream of secondary air admitted through
openings 70' can have a temperature greater than the temperature of
the primary air admitted through dome or closure member 44'. When
tubular conduits 72' are connected to the same source of air as is
supplying chamber 48, the temperature of the secondary air can be
substantially the same as the primary air. Or, the temperature of
the secondary air can be increased to be greater than the
temperature of the primary air by means of a connection between
said conduits 72' and conduit 15', similarly as illustrated in
FIGS. 1 and 2. When conduits 72' are connected to a source of air
other than that supplying chamber 48, the temperature of the
secondary air can be substantially the same as, or greater than,
the temperature of the primary air. Any suitable means can be
employed for heating said secondary air, e.g., a connection to
conduit 15', or a separate heater or heat exchange means for
heating the air passing through said conduits 72'.
It is within the scope of the invention to operate the combustors
or combustion zones employed in the practice of the invention under
any conditions which will give the improved results of the
invention. For example, it is within the scope of the invention to
operate said combustors or combustion zones at pressures within the
range of from about 1 to about 40 atmospheres, or higher; at flow
velocities within the range of from about 1 to about 500 feet per
second, or higher; and at heat input rates within the range of from
about 30 to about 1,200 Btu per pound of air. Since the invention
provides for reducing the temperature of the primary inlet air to
the combustor or combustion zone, to values less than those
normally employed, so as to reduce nitrogen oxides emissions, it is
preferred that the temperature of the inlet primary air be within
the range of from ambient to about 700.degree. F., more preferably
from ambient to about 500.degree. F. In a preferred embodiment of
the invention, the temperature of the secondary air will be about
the same as said primary air. However, it is within the scope of
the invention for the temperature of the secondary air to be
greater, e.g., about 100.degree. to 500.degree. F., preferably
about 100.degree. to 300.degree. F., greater than the temperature
of said primary air, e.g., when the secondary air is passed over a
portion of the flame tube wall or is heated by having a portion of
the heated air in conduit 15 mixed therewith via conduit 31, see
FIGS. 1 and 2. The temperature of the dilution or quench air can be
any suitable temperature depending upon materials of construction
in the equipment employed downstream from the combustor, e.g.,
turbine blades, and how much it is desired to cool the combustor
effluent. Generally speaking, operating conditions in the
combustors employed in the practice of the invention will depend
upon where the combustor is employed. For example, when the
combustor is employed with a high pressure turbine, higher
pressures and higher inlet air temperatures will be employed in the
combustor. Thus, the invention is not limited to any particular
operating conditions.
The relative volumes of the above-described primary, secondary, and
quench or dilution air streams will depend upon the other operating
conditions. Generally speaking, the combined volume of said primary
air and said secondary air will usually be a minor proportion of
the total air to the combustor, e.g., less than about 50 volume
percent, with said primary air being in the range of up to about 25
volume percent and said secondary air being in the range of up to
about 24 volume percent. The volume of said quench or dilution air
will usually be a major portion of the total air to the combustor,
e.g., more than about 50 volume percent. The relative volumes of
said primary, secondary, and quench air streams can be controlled
by varying the sizes of the openings, relative to each other,
through which said streams of air are admitted to the flame tube.
Any other suitable means of controlling said air volumes can be
employed, e.g., flow meters on each air stream.
The term "air" is employed generically herein and in the claims,
for convenience, to include air and other combustion-supporting
gases.
The following examples will serve to further illustrate the
invention.
EXAMPLE I
A series of runs was made in a combustor typical of prior art
combustors. Said combustor basically embodied the principal
features of combustors employed in modern aircraft turbine engines.
The combustor was a straight-through can-type combustor employing
fuel atomization by a single simplex-type nozzle. The combustor
liner (flame tube) was fabricated from 2-inch pipe, with added
internal deflector skirts for air film cooling of surfaces exposed
to the flame. Exhaust emissions from this combustor, when operated
at comparable conditions for combustion, are in general agreement
with measurements presently available from several different gas
turbine engines. A commercial Type A jet fuel was employed in these
test runs. Runs were made at operating conditions simulating idle
conditions and at operating conditions simulating maximum power
conditions. Analyses for content of nitrogen oxides (reported as
NO), carbon monoxide, and hydrocarbons (reported as carbon) in the
combustor exhaust gases were made at each test condition. The
method for measuring nitrogen oxides was based on the Saltzman
technique, "Analytical Chemistry" 26, No. 12, 1954, pages
1,949-1,955. Carbon monoxide was measured by a conventional
chromatographic technique. Hydrocarbon was measured by the
technique described by Lee and Wimmer, SAE Paper 680769. Each
pollutant measured is reported in terms of pounds per 1,000 pounds
of fuel fed to the combustor. The results of these runs were as
follows:
Test Conditions ______________________________________ Combustor
Operating Variables ______________________________________ Idle
Max. Power Temp., Inlet Air, .degree.F. 900 1100 Pressure, in. Hg.
abs. 50 110 Velocity, Cold Flow, ft./sec. 250 250 Heat Input Rate,
Btu/lb. air 200 150 Emissions, lbs./1000 lbs. of fuel
______________________________________ Nitrogen Oxides 3.4 10.7
Carbon Monoxide 10 0 Hydrocarbons 0.6 0.2
In another series of runs wherein the combustor was operated (using
the same fuel) at a pressure of 450 inches of Hg. abs., a gas
velocity of 140 feet per second, and a variable heat input rate, it
was found that when the air inlet temperature was increased over a
range from 400.degree. F. to about 1,150.degree. F., the nitrogen
oxides emissions increased substantially uniformly from about 3 to
about 23.5 lbs. per 1,000 lbs. of fuel burned.
Based on the above data, it was calculated that a combustor or
combustion zone operated in accordance with the method of the
invention, at a primary air inlet temperature of about 300.degree.
F., would have nitrogen oxides emissions of about 0.6 pound per
1,000 pounds of fuel at idle conditions, and about 0.9 pound per
1,000 pounds of fuel at maximum power conditions.
EXAMPLE II
A series of test runs was carried out employing combustors A and B.
Combustor A was like the combustor illustrated in FIG. 3 except
that conduit 15 was omitted and a row of fins 76 replaced baffle
68. Combustor B was like the combustor illustrated in FIG. 9 except
that conduit 15 was omitted and a row of fins 76 replaced baffle
68. Additionally, the fins on the flame tube of combustor B were
modified by placing 1/8 inch bars longitudinally through each row
of fins 76 and each row of fins 78. This provided a more linear
path through enclosed area 48'. Design details of said combustors
are set forth in Table II below. Said combustors and the design
details thereof are here used for illustrative purposes only and
the invention is not to be construed as limited thereto. Any
suitable combustor having any suitable dimensions can be employed
in the practice of the invention. In these runs the heat input
(fuel flow) was varied, with the air flow remaining fixed, at
different combinations of combustor pressure, reference velocity,
and inlet air temperature. Combustor A was run using a prevaporized
fuel. Combustor B was run using a liquid atomized fuel. Properties
of the fuel used in both combustors are set forth in Table I
below.
The method of operation was the same for both combustors. For
example, referring to FIG. 3, a stream of air from a compressor was
passed into the upstream end of annular space 48 and there divided.
A portion of said air was passed as primary air via inlet conduits
56 into the primary combustion region of the combustor. A second
portion of said air was passed as secondary air via annular chamber
64, tubular conduits 72, and openings 70 into a secondary
combustion region of the combustor. A third portion of said air was
passed via enclosed annular chamber 48' and the downstream portion
of annular chamber 48, and openings 74 into the quench region of
the combustor. Like flows were used in the combustor illustrated in
FIG. 9. Using said flows, each of said combustors was operated at
the test points or conditions set forth in Table III below.
Analyses for emissions content in the combustor exhaust gases were
carried out as in Example I. Emissions data for said test runs,
mean values from duplicate runs at each test condition, are set
forth in Tables IV and V below.
TABLE I - PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL
______________________________________ Philjet A-50
______________________________________ ASTM Distillation, F.
Initial Boiling Point 340 5 vol. % evaporated 359 10 vol. %
evaporated 362 20 vol. % evaporated 371 30 vol. % evaporated 376 40
vol. % evaporated 387 50 vol. % evaporated 398 60 vol. % evaporated
409 70 vol. % evaporated 424 80 vol. % evaporated 442 90 vol. %
evaporated 461 95 vol. % evaporated 474 End Point 496 Residue, vol.
% 0.8 Loss, vol. % 0.0 Gravity, degrees API 46.6 Density, lbs/gal.
6.615 Heat of Combustion, net, Btu/lb. 18,670 Hydrogen Content, wt.
% 14.2 Smoke Point, mm 27.2 Sulfur, wt. % 0.001 Gum, mg/100 ml 0.0
Composition, vol. % Paraffins 52.8 Cycloparaffins 34.5 Olefins 0.1
Aromatics 12.6 Formula (calculated) (C.sub.11 H.sub.22)
Stoichiometric Fuel/Air Ratio, lb./lb. 0.0676
______________________________________
TABLE II - COMBUSTOR DESIGN ______________________________________
Combustor Number Variable A B
______________________________________ Closure Member Air Inlet
Diameter, inches 0.875 0.625 Inlet type Tangent Swirl Hole
Diameter, inches 0.188 0.250 Number of Holes 6 6 Total Hole Area,
square inches 0.166 0.295 % Total Combustor Hole Area 3.213 5.571
Fuel Nozzle Type -- Simplex Spray Angle, degrees -- 45 Fuel Tube
Diameter, inches 0.250 -- Flame Tube First Station Hole Diameter,
inches 5/16.times. 1* 5/15.times. 1* Total Number of Holes 8 8
Total Hole Area, square inches 2.500 2.500 % Total Combustor Hole
Area 48.393 47.214 Second Station Hole Diameter, inches 5/16.times.
1* 5/16.times. 1* Total Number of Holes 8 8 Total Hole Area, square
inches 2.500 2.500 % Total Combustor Hole Area 48.393 47.214
Combustor Cross-Section Area, square inches 3.355 3.355 Total
Combustor Hole Area, square inches 5.166 5.295 % Cross-Sectional
Area 153.933 157.777 Combustor Inside Diameter, inches 2.067 2.067
Primary Zone Length, inches 7.375 7.375 Volume, cubic inches 24.748
24.748 Combustor Length, inches 18.437 18.437 Volume, cubic inches
61.867 61.867 ______________________________________ *Holes are
5/16 inch diameter at ends; slots are 1 inch long.
TABLE III - TEST CONDITIONS -- COMBUSTORS A & B
__________________________________________________________________________
Test Condition Number Primary Inlet Air Temperature, .degree.F.
Combustor Pressure, in Hg. abs Cold Flow Reference Velocity, Heat
Input, Btu/lb. Air Flow, lb./sec. Fuel Flow,
__________________________________________________________________________
lb./hr. 1 1100 110 250 75 0.545 7.9 2 do. do. do. 110 do. 11.6 3
do. do. do. 150 do. 15.8 4 do. do. do. 185 do. 19.4 5 do. do. do.
225 do. 23.6 6 do. do. do. 260 do. 27.3 7 do. do. do. 300 do. 31.5
8 900 110 250 75 0.625 9.0 9 do. do. do. 110 do. 13.3 10 do. do.
do. 150 do. 18.1 11 do. do. do. 185 do. 22.3 12 do. do. do. 225 do.
27.1 13 do. do. do. 260 do. 31.3 14 do. do. do. 300 do. 36.2 15 700
110 250 75 0.733 10.6 16 do. do. do. 110 do. 15.5 17 do. do. do.
150 do. 21.2 18 do. do. do. 185 do. 26.1 19 do. do. do. 225 do.
31.8 20 do. do. do. 260 do. 36.7 21 do. do. do. 300 do. 42.4 22 500
110 250 75 0.885 12.8 23 do. do. do. 110 do. 18.8 24 do. do. do.
150 do. 25.6 25 do. do. do. 185 do. 31.6 26 do. do. do. 225 do.
38.4 27 do. do. do. 260 do. 44.4 28 do. do. do. 300 do. 51.2
__________________________________________________________________________
TABLE IV - SUMMARY OF EMISSION DATA FROM COMBUSTOR A
______________________________________ Primary Zone
______________________________________ Emissions, lb./1000 lb. fuel
Test Condition Number Residence Time, msec Equivalence Ratio, dia.
NO.sub.x (as NO) CO HC (as C)
______________________________________ 1 76.6 1.85 19.8 2 0.6 2 do.
2.72 9.4 28 0.3 3 do. 3.71 3.2 26 0.2 4 do. 4.55 3.0 14 0.2 5 do.
5.54 2.4 10 0.2 6 do. 6.40 2.2 9 0.1 7 do. 7.40 2.6 3 0.2 8 76.6
1.84 9.5 51 0.5 9 do. 2.72 4.1 35 1.2 10 do. 3.71 1.6 54 0.8 11 do.
4.56 1.0 46 0.2 12 do. 5.54 0.6 24 0.2 13 do. 6.40 0.9 17 0.1 14
do. 7.40 1.2 2 0.2 15 76.6 1.85 5.7 0 0.5 16 do. 2.70 3.8 94 0.3 17
do. 3.70 1.4 108 0.2 18 do. 4.55 0.9 80 0.2 19 do. 5.54 0.7 30 0.2
20 do. 6.40 0.8 20 0.1 21 do. 7.40 1.4 40 0.7 22 76.6 1.85 4.1 6
1.0 23 do. 2.72 3.5 116 0.9 24 do. 3.70 1.1 134 0.2 25 do. 4.56 0.9
109 0.4 26 do. 5.54 0.8 72 0.4 27 do. 6.40 0.5 86 4.2 28 do. 7.40
0.8 101 8.2 ______________________________________
TABLE V - SUMMARY OF EMISSION DATA FROM COMBUSTOR B
______________________________________ Primary Zone
______________________________________ Emissions, lb./1000 lb. fuel
Test Condition Number Residence Time, msec Equivalence Ratio, dia
NO.sub.x (as NO) CO HC (as C)
______________________________________ 1 44.2 1.07 18.8 0 0.5 2 do.
1.57 7.0 32 0.3 3 do. 2.14 5.7 14 0.4 4 do. 2.63 2.1 6 0.1 5 do.
3.19 1.9 2 0.1 6 do. 3.70 2.2 2 0.2 7 do. 4.26 2.0 1 0.0 8 44.2
1.06 9.4 4 0.5 9 do. 1.57 3.9 77 0.3 10 do. 2.14 1.4 53 0.1 11 do.
2.63 1.4 22 0.3 12 do. 3.20 1.5 7 0.2 13 do. 3.70 1.6 2 0.2 14 do.
4.27 1.8 0 0.1 15 44.2 1.07 6.7 7 0.5 16 do. 1.56 2.8 112 0.3 17
do. 2.13 1.6 122 0.2 18 do. 2.63 1.1 76 0.2 19 do. 3.20 1.0 28 0.2
20 do. 3.69 1.3 10 0.1 21 do. 4.26 1.2 4 0.0 22 44.2 1.07 3.1 10
1.4 23 do. 1.57 1.4 191 0.5 24 do. 2.13 1.1 232 0.3 25 do. 2.63 1.2
153 0.2 26 do. 3.20 0.9 107 0.4 27 do. 3.70 1.0 50 0.6 28 do. 4.26
1.0 26 0.4 ______________________________________
The data in the above Tables IV and V show that decreasing the
temperature of the inlet air to the primary combustion zone
decreases the NO.sub.x emissions. The temperature of the inlet air
to the second zone of the combustor (inlet at openings 70) was not
measured but approximated the temperature of the primary air. Thus,
the data also show that CO emissions increase with decreasing inlet
air temperatures to the secondary combustion zone, and decrease
with increasing inlet air temperatures to said secondary combustion
zone.
The data from the above runs thus illustrate the advantages of
operating a combustor and heat energy utilization system in
accordance with the invention. By heat exchanging an exhaust gas
stream from the heat energy utilization zone (such as turbine
exhaust gases) with one or more other air streams to the combustor
such as the quench air (and also heating the secondary air if
desired), instead of the primary air, a combustor can be operated
with a low primary air inlet temperature, a controlled secondary
air inlet temperature which can be the same as or greater than the
temperature of the inlet primary air, and a heated quench air
stream which can have a greater temperature than either said
primary air or said secondary air. The method of the invention thus
provides for a low primary inlet air temperature to give low
NO.sub.x emissions values, a controlled secondary air inlet
temperature to give desired CO emissions values, and a heated
quench inlet air to conserve heat energy and increase the overall
efficiency of the system.
In general, said data also show that NO.sub.x emissions decrease
with increasing equivalence ratio in the primary combustion zone
(increasing fuelrich mixture), and tend to plateau at low levels
with an increase in heat input. Said equivalence ratios were
calculated from the percent Total Combustor Hole Area for the air
inlet conduits to the primary combustion zone.
The data set forth in the above Tables IV and V show that
combustors can be operated in accordance with the invention to give
low NO.sub.x, low CO, and low HC emissions when using either a
prevaporized fuel or an atomized liquid fuel. Said data also show
that the various operating variables or parameters are
interrelated. Thus, a change in one variable or parameter may make
it desirable to adjust one or more of the other operating variables
or parameters in order to obtain desirable results with respect to
all three pollutants NO.sub.x, CO, and HC (hydrocarbons).
In one presently preferred method of the invention, the primary
combustion zone is preferably operated fuel-rich with respect to
the primary air admitted thereto. Thus, the equivalence ratio in
the primary combustion zone is preferably greater than
stoichiometric. In this method of operation, the second zone
(secondary combustion zone) of the combustor is preferably operated
fuel-lean with respect to any unburned fuel and air entering said
second zone from said primary zone, and any additional air admitted
to said second zone. Thus, the equivalence ratio in said second
zone preferably is less than stoichiometric. This method of
operation is preferred when it is desired to obtain both low
NO.sub.x and low CO emissions from a combustor. In general, it is
preferred that the transition from the fuel-rich condition in the
primary combustion zone to the fuel-lean condition in the secondary
zone be sharp or rapid, e.g., be effected as quickly as possible.
While it is presently preferred that the primary combustion zone be
operated fuel-rich as described, it is within the scope of the
invention to operate the primary combustion zone fuel-lean. Thus,
it is within the scope of the invention to operate the primary
combustion zone with any equivalence ratio which will give the
improved results of the invention.
For example, in the practice of the invention as carried out in low
compression ratio combustors, e.g., compression ratios up to about
5, the equivalence ratio in the primary combustion zone can have
any value such that the NO.sub.x emissions value in the exhaust
gases from the combustor is not greater than about 5 pounds,
preferably not greater than about 3.5 pounds, per 1,000 pounds of
fuel burned in said combustor. Preferably, said equivalence ratio
will be at least 1.5, more preferably at least 3.5, depending upon
the other operating variables or parameters, e.g., temperature of
the inlet air to the primary combustion zone.
It will be understood that said NO.sub.x emission values referred
to in the preceding paragraph can be greater than the values there
given when operating high performance combustors. For example,
combustors such as the intermediate compression ratio combustors
having a compression ratio of about 5 to 15 atmospheres and the
high compression ratio combustors having a compression ratio of
about 15 to about 40 atmospheres used in jet aircraft and other
high performance engines. The NO.sub.x emissions from such high
performance or high compression ratio combustors will naturally be
higher than the NO.sub.x emissions from low compression ratio
combustors. Thus, greatly improved results in reducing NO.sub.x
emissions from a high performance combustor can be obtained without
necessarily reducing said NO.sub.x emissions to the same levels as
would be obtained from a low performance combustor.
As used herein and in the claims, unless otherwise specified, the
term "equivalence ratio" for a particular zone is defined as the
ratio of the fuel flow (fuel available) to the fuel required for
stoichiometric combustion with the air available. Stated another
way, said equivalence ratio is the ratio of the actual fuel-air
mixture to the stoichiometric fuel-air mixture. For example, an
equivalence ratio of 2 means the fuel-air mixture in the zone is
fuel-rich and contains twice as much fuel as a stoichiometric
mixture.
The data in the above examples show that the temperature of the
inlet air to the primary combustion zone can be an important
operating variable or parameter in the practice of the invention.
As stated above, the invention is not limited to any particular
range or value for said inlet air temperature. It is within the
scope of the invention to use any primary air inlet temperature
which will give the improved results of the invention, for example,
from ambient or atmospheric temperatures or lower to about
1,500.degree. F. or higher. However, considering presently
available practical materials of construction, about 1,200.degree.
F. to about 1,500.degree. F. is a practical upper limit for said
primary air inlet temperature in most instances. Considering other
practical aspects such as not having to cool the compressor
discharge stream, about 200.degree. to 400.degree. F. is a
practical lower limit for said primary air inlet temperature in
many instances. However, it is emphasized that primary air inlet
temperatures lower than 200.degree. F. can be used, e.g., in low
compression ratio combustors.
The data in the above examples also show that the temperature of
the air admitted to the second zone of the combustor (secondary
combustion air) can be an important operating variable or
parameter, particularly when the lower primary air inlet
temperatures are used, and it is desired to obtain low CO emission
values as well as low NO.sub.x emission values. Said data show that
both low NO.sub.x emission values and low CO emission values can be
obtained when the temperature of the inlet air to both the primary
combustion zone and the second zone of the combustor are at least
about 900.degree. F. As the temperature of the inlet air to said
zones decreases, increasingly improved (lower) values for NO.sub.x
emissions are obtained, but it becomes more difficult to obtain
desirably low CO emission values. It is preferred that the
temperature of the inlet air to the primary combustion zone not be
greater than about 700.degree. F. Thus, in some embodiments of the
invention, it is preferred that the temperature of the secondary
air admitted to the second zone of the combustor be greater than
the temperature of the primary air admitted to the primary
combustion zone. For example, depending upon the temperature of the
inlet air to the primary combustion zone, it is preferred that the
temperature of the inlet secondary air be in the range of from
about 100.degree. to about 500.degree. F. greater than the
temperature of said inlet primary air.
As a guide to those skilled in the art, but not to be construed as
necessarily limiting on the invention, the presently preferred
operating ranges for other variables or parameters are: heat input,
from 30 to 500 Btu per lb. of total air to the combustor; combustor
pressure, from 3 to 10 atmospheres; and reference air velocity,
from 50 to 250 feet per second.
Reference has been made herein to vehicle emission standards which
have been set by the United States Environmental Protective Agency
for 1975-1976. These standards or goals have been related to gas
turbine engine combustors, by assuming 10.0 miles per gallon fuel
economy and 6.352 pounds per gallon JP-4 fuel, as follows:
Emission Level Criteria ______________________________________
Pollutant EPA Vehicle Standard, grams/mile Gas Turbine Engine Goal
lb./1000 lb. fuel ______________________________________ burned
Nitrogen Oxides 0.40 (as NO.sub.2) 0.9 Carbon Monoxide 3.4 11.8
Hydrocarbons 0.41 (as hexane) 1.2 (as carbon) Particulates 0.03 0.1
______________________________________
The data set forth in the above examples show that the invention
can be practiced to give pollutant emission levels meeting tha
above standards or goals. However, the invention is not limited to
meeting said standards or goals. Many persons skilled in the art
consider said standards or goals to be unduly restrictive. It is
possible that said standards or goals may be relaxed. Thus, a
combustor, and/or a method of operating a combustor, to obtain
reduced levels of pollutant emissions approaching said standards or
goals has great potential value. While it is not to be considered
as limiting on the invention, it is believed that practical
maximums for low compression ratio gas turbine engine goals would
be in the order of, in lbs. per 1,000 lbs. of fuel burned:
NO.sub.x, 5; CO, 25; and hydrocarbons, 2.
Thus, in the practice of the invention, while it is desirable to
reduce the nitrogen oxides emissions from the combustors or
combustion zones employed therein to values of not more than about
2.5, preferably not more than about 1.8, pounds per 1,000 pounds of
fuel burned at idle conditions; and not more than about 5,
preferably not more than about 3.5, pounds per 1,000 pounds of fuel
burned at maximum power conditions, the invention is not limited to
said values.
Thus, while certain embodiments of the invention have been
described for illustrative purposes, the invention is not limited
thereto. Various other modifications or embodiments of the
invention will be apparent to those skilled in the art in view of
this disclosure. Such modifications or embodiments are within the
spirit and scope of the disclosure.
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