US3826077A - Method of introducing three streams of air into a combustor with selective heating - Google Patents

Abstract

New combustors, and methods of operating same, which produce lower emissions, particularly lower emissions of nitrogen oxides. Methods and means are provided for supplying separate streams of air to primary and secondary combustion zones of a combustor, for removing heat from said primary combustion zone, and reintroducing said heat into the combustor at a region spaced apart and downstream from said primary and secondary combustion zones.

Description

United States Patent [191 Quigg et al.

[ July 30, 1974 METHOD OF INTRODUCING THREE STREAMS OF AIR INTO A COMBUSTOR WITH SELECTIVE HEATING Inventors: Harold T. Quigg; Robert M.

Schirmer, both of Bartlesville, Okla.

Assignee: Phillips Petroleum Company, Bartlesville, Okla.

Filed: Mar. 27, 1972 Appl. N0.: 238,317

Related US. Application Data Continuation-impart of Scr. No. 208,102, Dec. 15, 1971, abandoned.

US. Cl 60/39.02, 60/3906, 60/3951 R,

Int. Cl. F02c 1/00 Field of Search 60/3902, 39.06, 39.51, 60/3965, 39.69; 431/10 References Cited UNITED STATES PATENTS l/l97l Vickers 60/39.5l

FUEL

OTHER PUBLICATIONS Engineering Know-How in Engine Design, part 19 SAESP 365 Hs-010922 pg. 7.

Primary Examiner-Carlton R. Croyle Assistant Examiner--Warren Olsen New combustors, and methods of operating same, which produce lower emissions, particularly lower emissions of nitrogen oxides. Methods and means are provided for supplying separate streams of air toprimary and secondary combustion zones of a combustor, for removing heat from said primary combustion zone, and reintroducing said heat into the combustor at a region spaced apart and downstream from said primary and secondary combustion zones.

ABSTRACT 19 Claims, 17 Drawing Figures pAlimwJuLsolsm SHEEI 2 OF 7 FIG. 4

PATENTEDJULBOIBH SHEUHIF 7 2 7 K \\\1lli i Jo m METHOD OF INTRODUCING THREE STREAMS OF AIR INTO A COMBUST OR WITH SELE CTIVE HEATING This application is a continuation-in-part of copending application Ser. No. 208,102, filed Dec. I5, 1971 now abandoned.

This invention relates to improved combustors and methods of operating same.

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 automobiles employing conventional piston-type engines burning hydrocarbon fuels are a major contricutor to said .pollution. Vehicle emission standards have been set by the United States Environmental Protection Agency which are sufficiently restrictive to cause .3!E.Q. Qb j ma ia aqw er 9 c r. 9932192915 alternate engines instead of the conventional piston engme.

The gas turbine engine is being given serious consideration as an alternate engine. However, insofar as we presently know, there is no published information disclosing realistic and/or practical 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 standards 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 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 combustor giving reduced emissions approaching siad standards would be a great advance in the art. Such a combustor would have great potential value because it is possible the presently very restrictive standards may be reduced.

The present invention solves the above-described problems by providing improved combustors, and methods of operating same, which produce emissions meeting or reasonably approaching the present strignent standards established by said environmental protection agencies. Said methods comprise preferably supplying separate streams of air to primary and secondary combustion zones of a combustor, removing heat from said primary combustion zone, and reintroducing said heat into the combustor at a region spaced apart from and downstream from said primary and secondary zones.

Thus, according to the invention, there is provided a combustor, comprising, in combination: an outer 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; air inlet means for introducing a first stream of air into the upstream end portion of said flame tube; fuel inlet means for introducing a fuel into the upstream end portion of said flame tube; at least one opening provided in the wall of said flame tube at a first station located intermediate the upstream and downstream ends thereof; an imperforate conduct means extending second stream of air into the interior of said flame tube;

and 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.

Further, according to the invention, there is provided a method for burning a fuel in a combustor, which method comprises: introducing a first stream of air into a primary combustion zone of said combustor; introducing a fuel into said primary combustion zone; burning said fuel; introducing a second stream of air, separate from said first stream of air, into a second zone of said combustor'located downstream from said primary combustion zone; passing a third stream of air, separate from said first and second streams of air, in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus-heated third stream of air into a third zone of said combustor located downstream from said second zone.

FIG. 1 is a view, partially in cross section, of a combustor in accordance with the invention.

FIGS. 2, 3, and 4 are cross section views taken along the line 2-2, 33, and 4-4, respectively, of FIG. 1.

FIG. 5 is a fragmentary perspective view of a combustor flame tube illustrating another type of fin or extended surface which can be employed therein.

FIG. 6 is a cross section view taken along the line 6-6 of FIG. 1.

FIG. 7 is a partial view in cross section of another combustor in accordance with the invention.

FIG. 8 is a view in cross section taken along the line 8-8 of FIG. 7.

FIG. 9 is a partial view in cross section of another combustor in accordance with the invention.

FIGS. 10 and 11 are cross section views taken along the lines 10-10 and 11-11, respectively, of FIG. 9.

FIG. 12 is a view in cross section of another type of dome or closure member which can be employed in the combustors of the invention.

FIGS. 13 and 14 are diagrammatic views, partially in cross section, of other combustors in accordance with the invention.

FIG. 15 is a partial view in cross section of another combustor in accordance with the invention.

FIG. 16 is a front elevation view taken along the line 16-16 of FIG. 15.

FIG. 17 is a cross-sectional elevation view of the swirl plate of the dome or closure member in the combustor of FIG. 15.

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 there is illustrated a combustor in accordance with the invention, denoted generally by the reference numeral 10, which comprises an elongated flame tube 12. Said flame tube 12 is open at its down stream 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 14, is provided for closing the upstream end of said flame tube, except for the openings in said dome member. An outer housing or casing 16 is disposed concentrically around said flanie tube 12 and spaced apart therefrom to form a first annular chamber 18 around said flame tube and said dome or closure member 14. Said annular chamber 18 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 12 and outer housing 16 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 and 17 are provided at the upstream end of said flame tube 12 and said outer housing 16 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 16 which encloses dome member 14 and forms the upstream end portion of said first annular chamber 18. It will be understood that outer housing or casing 16 can be extended, if desired, to enclose dome 14 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 12 and said closure member 14 in the outer housing 16 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 12. As illustrated in FIGS. 1 and 4, said air inlet means comprises a generally cylindrical swirl chamber 22 formed in said dome member 14. The downstream end of swirl chamber 22 is in open communication with the upstream end of flame tube 12. A plurality of air conduits 24 extend from said first annular chamber 18, or other suitable source of air, into swirl chamber 22 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 12. As illustrated in FIG. 1, said fuel inlet means comprises a hollow conduit 26 for introducing a stream of fuel into the upstream end of swirl chamber 22 and axially with respect to said swirling stream of air. Any other suitable fuel inlet means can be employed.

A flared expansion passageway 28 is formed in the downstream end portion of dome or closure member 14. Said flared passageway flares outwardly from the o wjadmrfiqn QfJl IUQ 9r osurqmam s the inner wall of flame tube 12.

An imperforate sleeve 30 surrounds an upstream portion of said flame tube 12. The outer wall of said sleeve 30 can be insulated if desired and thus increase its effectiveness as a heat shield. Said sleeve 30 is spaced apart from flame tube 12 so as to longitudinally enclose an upstream portion 18 of said first annular chamber 18 and define a second annular chamber 19 between said sleeve 30 and outer casing 16. An annular wall member 32, secured to the inner periphery of casing 16, is provided for closing the downstream end of said second annular chamber 19. At least one opening 34 is provided in the wall of flame tube 12 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 34, as illustrated. A generally tubular conduit means 36 extends from said second annular chamber 19 into communication with said opening 34 for admitting a second stream of air from said second annular chamber 19 into the interior of flame tube 12. When a plurality of openings 34 are provided, a plurality of said tubular conduits 36 are also provided, with each individual conduit 36 being individually connected to an individual opening 34. The above described structure thus provides an imperforate conduit means comprising second annular chamber 19 and tubular conduit(s) 36 for admitting a second stream of air into the interior of flame tube 12.

At least one other opening 38 is provided in the wall of flame tube 12 at a second station located downstream and spaced apart from said first station for admitting a third stream of air from first annular chamber 18 into the interior of flame tube 12. In most instances, it will be preferred to provide a plurality of openings 38 spaced around the periphery of said flame tube, similarly as illustrated.

Preferably, the outer wall surface of flame tube 12 is provided with an extended surface in the form of fins or tabs mounted thereon in the region surrounded by sleeve 30, and which extend into the portion 18 of said first annular chamber which is enclosed by said sleeve. As illustrated in FIGS. 1, 2, and 3 said fins or tabs 40 and 42 can be arranged in rows which extend around the periphery of the flame tube 12, and which are spaced apart longitudinally on said flame tube..The fins or tabs 40, in each row thereof, can be spaced apart circumferentially to provide passageways 41 therebetween. See FIG. 2. Similarly, passageways 43 can be provided between the circumferentially spaced apart fins or tabs 42. See FIG. 3. FIG. 5 illustrates another type of fin which can be employed. In FIG. 5 the fins 44 extend longitudinally of flame tube 12. Said fins 40, 42, and 44 can extend into enclosed portion 18' any desired distance.

FIG. 6 illustrates one type of structure which can be employed to provide tubular conduits 36. A plurality of boss members 37, spaced apart circumferentially in a row around the periphery of flame tube 12, is provided downstream from the last row of fins 42. Said boss members 37 have the general shape of fins 40 and 42 and passageways 45 are provided therebetween, similarly as for passageways 41 and 43 in the rows of fins 40 and 42. Said imperforate sleeve 30 extends over boss members 37, similarly as for fins 40 and 42, and said conduits 36 can be formed by cutting through said sleeve 30 and said boss members 37 into communication with openings 34 in flame tube 12. Said passageways 41, 43, and 45 thus provide communication from the upstream end of first annular chamber 18, through enclosed portion 18, around tubular conduits 36, and into the downstream portion of first annular chamber 18.

Referring now to FIG. 7, there is illustrated the upstream portion of another combustor in accordance with the invention. The downstream portion not shown is like the combustor of FIG. 1. In FIG. 7, a closure or dome member, designated generally by the reference numeral 46, is provided for closing the upstream end of flame tube 12, except for the openings in said dome member. Said dome member can be fabricated integrally, i.e., as one element. However, in most instances it will be preferred to fabricate said closure member 46 as two or more elements, e.g., an upstream element 48 and a downstream element 50.'A generally cylindrical swirl chamber 52 is formed in said upstream element 48 of closure member 46. The downstream end of said swirl chamber 52 is in open communication with the upstream end of said flame tube 12. An air inlet means is provided for introducing a swirling mass of air into the upstream end portion of said swirl chamber 52 and then into the upstream end of said flame tube. As illustrated in FIGS. 7 and 8, said air inlet means comprises a plurality of air conduits 54 extending into said swirl chamber 52 tangentially with respect to the inner wall thereof. Said conduits 54 extend from first annular passageway or chamber 18 into said swirl chamber 52.

A fuel inlet means is provided for introducing a stream of fuel in a direction which is from tangent to less than perpendicular, but nonparallel, to the periphery of said stream of air. As illustrated in FIGS. 7 and 8, said fuel inlet means comprises a fuel conduit '56 leading from a source of fuel, commujnicating with a passageway 58, which in turn communicates with fuel passageway 60 which is formed by an inner wall of said downstream element 50 of closure member 46 and the downstream end wall of said upstream element 48 of closure member 46. It will be noted that the inner wall of said downstream element is spaced apart from and is complementary in shape to the downstream end wall of said upstream element 48. The direction of the exit portion of said fuel passageway 60 can be varied over a range which is intermediate or between tangent and perpendicular, but nonparallel, to the periphery of the stream of air exiting from swirl chamber 52. Varying the direction of the exit portion of fuel passageway 60 provides one means or method for controlling the degree of mixing between the fuel stream and said air stream at the interface therebetween. As illustrated in FIG. 7, the direction of the exit portion of fuel passageway 60 is at an angle of approximately 45 degrees with respect to the periphery of the air exiting from swirl chamber 52. As mentioned above, the direction of said exit portion can vary from between tangent and perpendicular, but nonparallel, to the periphery of the stream of air from swirl chamber 26. Generally speaking, in most instances, it will be deisred that the exit portion of said fuel passageway 60 have a direction which forms an angle within the range of from about to about 75, preferably about 30 to about 60, with respect to the periphery of the stream of air exiting from swirl chamber 52. In most instances, it will be preferred that the fuel from fuel passageway 60 be introduced in a generally downstream direction. However, it is within the scope of the invention to introduce said fuel in an upstream direction. Shim 62 provides means for varying the width of said fuel passageway 60. Any other suitable means, such as theads provided on the wall of upstream element 48 and downstream element 50, can be provided for varying the width of said fuel passageway 60. As will be understood by those skilled in the art in view of this disclosure, the shape of the upstream inner wall of said downstream element 50 and the shape of the downstream end wall of said upstream element 48 can be changed, but maintained complementary with respect to each other, so as to accommodate the above-described changes in direction and width of said fuel passageway 60.

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. 1. A closure member 64 is mounted in the upstream end of flame tube 12 in any suitable manner so as to close the upstream end of said flame tube except for the openings provided in said closure member. A generally cylindrical swirl chamber 66 is formed in said closure member 64. The downstream end of said swirl chamber is in open communication with the upstream end of said flame tube. An air inlet means is provided for introducing a swirling mass of air into the upstream end portion of said swirl chamber 66 and then into the upstream end of said flame tube 12. As illustrated in FIGS. 9 and 10, said air inlet means comprises a plurality of air conduits 68 extending into said swirl chamber 66 tangentially with respect to the inner wall thereof. Said conduits extend from annular space 74, similarly as in FIG. 1. The fuel inlet means in the combustor of FIG. 9 comprises a fuel supply conduit 70 which is in communication with three fuel passageways 72, which communicate with annular passageway 74, which in turn is in communication with a plurality of fuel conduits 76 extending tangentially through the downstream end portion of said closure member 64 and into a recess 78 formed in the downstream end portion of said closure member, and tangentially with respect to the inner wall of said recess. As illustrated in FIGS. 9 and 10, said air inlet conduits 68 are adapted to introduce air tangentially into swirl chamber 66 in a clock wise direction (when looking downstream), and said fuel inlet conduits 76 in FIG. 11 are adapted to introduce fuel tangentially into said recess 78 in a counterclockwise direction. This is a presently preferred arrangement in one embodiment of the invention. However, it is within the scope of the invention to reverse the directions of said air inlet conduits 68 and said fuel inlet conduits 76, or to have the directions of both said air inlet conduits and said fuel inlet conduits the same, e.g., both clockwise or both counterclockwise.

Referring now to FIG. 12, there is illustrated another type of closure member or dome which can be employed with the flame tubes of the combustors described herein. In FIG. 12 closure member 78 is similar to closure member 64 of FIG. 9. The principal difference is that in closure member 78 a conduit means 80 is provided and extends through said closure member 78 into communication with the upstream end portion of flame tube 12, for example. At least one swirl vane 82 is positioned in said conduit means 80 for imparting a swirling motion to the air passing through said conduit means 80. If desired, conduit means 80 can comprise an annular conduit, instead of the tubular conduit shown, with suitable swirl vanes installed therein.

FIG. 13 is a diagrammatic illustration of a modification of the combustor of FIG. 1. In FIG. 13 a plurality of imperforate individual tubular openings 36' are each connected individually to individual openings 34' in the wall of flame tube 12'. Said tubular conduits 36' extend longitudinally through annular chamber 18' to the upstream end thereof and are provided for admitting a second stream of air into the interior of said flame tube. Outer casing 16' and dome member 14 are essentially like their counterparts in FIG. 1. A third stream of air is admitted to the interior of flame tube 12' via said annular chamber 18' and openings 38.

FIG. 14 is a diagrammatic illustration of another modification of the combustor of FIG. 1, which is similar to the combustor of FIG. 13. The principal difference is that in FIG. 14 the tubular conduits 36 extend transversely through annular chamber 18' and through outer casing 16 and then to the upstream end of the combustor.

Referring now to FIG. 15, there is illustrated the upstream portion of another combustor in accordance with the invention. The downstream portion of the combustor of FIG. is like the combustor of FIG. 1. A closure member or dome, designated generally by the reference numeral 85, is mounted in the upstream end of flame tube 12 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. 17), 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 12. As illustrated in FIGS. 15, 16, and 17, 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 introducting a stream of fuel into the upstream end of flame tube 12. As illustrated in FIG. 15, 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.

It will be understood the combustors of the invention can be provided with any suitable type of ignition means and, if desired, means for introducing a pilot fuel to initiate burning.

In one method of operating the combustor of FIG. 1,

a stream of air from a compressor (not shown) is passed, via a conduit connected to flange 17, into the upstream end of annular space 18. A first stream of air is passed from annular space 18, through tangential conduits 24, and into swirl chamber 22. 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 12. Said first stream of air comprises and can be referred to as primary air.

A stream of fuel, preferably prevaporized, is admitted, via conduit 26, 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 22 via expansion passageway 28 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 zone, i.e., the upstream portion of flame tube 12.

A second stream of air, separate from said first stream of air, is passed from the upstream end of annular chamber 18 via second annular chamber 19, tubular conduits 36, and openings 34 into a secons zone of the combustor which is located downstream from said primary combustion zone. Said second stream of air comprises and can be referred to as secondary air.

A third stream of air, separate from said first and second streams of air, is passed from the upstream end of annular chamber 18, via the enclosed portion 18, around tubular conduit 36, into the downstream portion of annular chamber 18, and then via openings 38 into a third zone of the combustor which is located donwstream from said second zone. Said third stream of air comprises and can be referred to as quench air.

In the above method of operation, combustion of said fuel is initiated at least in said primary combustion zone with said first stream of air (primary air) and essentially completed, if necessary, in said second zone with said second stream of air. The resulting combustion gases are quenched in said third zone and the quenched gases exit the downstream end of the flame tube to a turbine or other utilization such as a furnace, boiler, etc. In the above method of operation, said third stream of air in flowing through enclosed portion 18 removes heat from the wall of the primary combustion zone thus lowering its temperature, thereby increasing the heat loss from the combustion gases, and thereby lowering the flame temperature within the primary combustion zone. Preferably, the outer wall of the primary combustion zone is provided with an extended surface, e.g., fins as shown in FIG. 1, so as to increase said heat removal from the primary combustion zone. A further advantage is realized in that said second stream of air flowing through annular chamber 19 is shielded from the hot wall of the combustor and is relatively cool. This also aids in reducing the flame temperature in the primary combustion zone. The air which is heated by heat loss from the combustor wall is used only in the quench zone of the combustor. This is a further aid in reducing said flame temperature by keeping said heated air out of the primary combustion zone; but the overall efficiency is maintained by the introduction of the heated air into said quench zone. As shown by the examples hereinafter, outstanding results. have been obtained in reducing the emissions content of the combustor gases, particularly with respect to decreasing the nitrogen oxides emissions.

In the above method of operationthe relative volumes of said first, second, and third streams of air can be controlled by varying the sizes of the said openings, relative to each other, through which said streams of air are admitted to flame tube 12. Any other suitable method of controlling said air volumes can be employed. For example, flow meters or calibrated orifices can be employed in the conduits supplying said streams of air.

In one method of operating the combustor of FIG. 7, a stream of air from a compressor (not shown) is passed, via a conduit connected to flange 17, into annular space 18. A first stream of air is passed from annular space 18 through tangential conduits 54 into swirl chamber 52. SAid tangential conduits 54 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 12 upstream toward said swirl chamber 52 during operation of the combustor.

A stream of fuel, preferably prevaporized, is adm te ,X a s me? p ssa a 58, a fuel passageway 60. Fuel exiting from fuel passageway 60 is formed into an annular stratum around the swirling stream of air exiting from swirl chamber 52. This method of introducing fuel and air effects a controlled mixing of said fuel and air at the interface therebetween. Initial contact of said fuel and air occurs upon the exit of said air from said swirl chamber 52. Immediately after said initial contact the fuel and air streams (partially mixed at said interface) are expanded, in a uniform and graduated manner during passage of said fuel and air through the flared portion of member 50, from the volume thereof in the region of said initial contact to the volume of said combustion chamber and at a point in said flame tube downstream from said initial contact. Said expansion of fuel and air thus takes place during at least a portion of the mixing of said fuel and said air. The resulting mixture of fuel and air is burned and combustion gases exit the downstream end of flame tube 12. A second stream of air is admitted to the interior of flame tube 12 from the upstream end of annular chamber 18 via second annular chamber 19, tubular conduits 36, and openings 34 as described above in connection with FIG. 1. A third stream of air is admitted to the interior of flame tube 12 via openings 38 as described above in connection with FIG. 1.

In one presently preferred method of operating the combustor of FIG. 9, the method of operation is similar to that described above for the combustors of FIGS. 1 and 7. A first stream of air is admitted to swirl chamber 66 via tangential inlet conduits 68 which impart a helical or swirling motion to said air. A stream of fuel, preferably prevaporized, is admitted via conduit 70, fuel passageways 72, and tangential fuel conduits 76 into recess 78 formed at the downstream end of said closure member 64. Said fuel isthus formed into an annular stratum around the swirling stream of air exiting from swirl chamber 66. This method of introducing fuel and air effects controlled mixing of said fuel and air at the interface therebetween. Second and third streams of air are admitted to the interior of flame tube 12 in the manner described above in connection with the combustors of FIGS. 1 and 7.

The method of operation of the combustors of FIGS. 13 and 14 can be substantially like that described above for the combustors of FIGS. 1, 7, and 9, taking into consideration the type of dome or closure member employed on the upstream end of flame tubes 12. In the combustors of FIGS. 13 and 14 the second stream of air is admitted to flame tube 12 via tubular conduits 36. The third stream of air is admitted via openings 38'. In FIG. 14 said tubular conduits 36 can be connected to a common source of air (such as a header conduit) which also supplies the first and third streams of air, or said tubular conduits can be connected to a separate source of air. The combustor of FIG. 14 is particularly adapted to be employed in those embodiments of the invention wherein the stream of secondary air admitted through openings 34 can have a temperature greater than the temperature of the primary air admitted through dome or closure member 14. When tubular conduits 36' are connected to the same source of air as in supplying chamber 18 the temperature of the secondary air can be substantially the same as, or can be increased to be greater than, the temperature of the primary air. Similarly, when conduits 36 are connected to a source of air other than that supplying chamber 18, 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 separate heater or heat exchange means for heating the air passing through said conduits 36'.

In one preferred method, the operation of the combustor of FIG. 15 is similar to the above-described operation of the combustor of FIG. 1, and reference is made thereto. The principal difference is in the operation of closure member (FIG. 15) and closure member 14 (FIG. 1). In FIG. 15, primary air is passed through said openings 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 in a generally coneshaped discharge. Said fuel contacts said stream of air, with said air stream assisting the action of nozzle 95 in atomizing'said fuel.

The combustors of the invention wherein heat is removed from the combustion zone and reintroduced into the quench zone are particularly adapted to use fuelshigh in aromatic content. This is completely contra to conventional practice. The ASTM specification for Aviation Turbine Fuels (D 1655) limits the concentration of aromatics in both Jet A and Jet B turbine fuel to 20 percent maximum. Such fules will have a hydrogen content in the range of about 13.5 to 14 weight percent. One reason for this limitation is to reduce flame radiance and loss of heat to the walls of the combustor. However, in the combustors of the invention this problem is solved by the above-described method of introducing three separate streams of air to the combustor. Thus, the use of high aromatic content fuels having high flame radiance is desirable and advantageous in the method of the invention in that nitrogen oxides emissions can be further reduced. Such fuel will have a hydrogen content of less than about l3.5 weight percent, preferably less than about 12 weight percent.

The following examples will serve to further illustrate the invention.

EXAMPLE I A series of test runs was made employing combustors in accordance with the invention and a typical standard" or prior art combustor as a control combustor. The same fuel was used in all of said test runs. Properties of said fuel are set forth in Table I below. Design details of the combustors of the invention are set forth in Table II below. Said design details, e.g., dimensions, are given by way of illustration only and are not to be construed as limiting on the invention. Said dimensions can be varied within wide limits so long as the improved results of the invention are obtained. For example, the formation of nitrogen oxides in a combustion zone is an equilibrium reaction. Thus, in designing a combustion zone, attention should be given to the size thereof so as to avoid unduly increasing the residence time therein. It is desirable that said residence time not be long enough to permit the reactions involved in the formation of nitrogen oxides to attain equilibrium. In said Table II the combustors have been identified by a number whichis the same as the FIGURE number of the drawing in which they are illustrated. Combustor No. l was essentially as illustrated in FIG. 1. Combustor No. 1(a) was like combustor No. 1 except that the fins on the flame tube were modified by placing one-eighth inch bars longitudinally through each row of fins 40 and each row of fins 42. This provided a more linear path through enclosed area 18'. Combustor No. 1(b) was like combustor No. 1(a) except that the dome or closure member 14 was modified to use liquid atomized fuel and swirl vanes were employed to impart the helical swirl to the air admitted through said dome l4. Combustor No. 7(a) was like the combustor illustrated in FIG. 7 except that the fins on the flame tube were modified in the same manner as in combustors 1(a) and 1(b).

Said control combustor basically embodies the prin cipal features of combustors employed in modern aircraft-turbine engines. It is a straight-through can-type combustor employing fuel atomization by a single simplex-type nozzle. The combustor liner 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. Said control combustor had dimensions generally comparable to the above-described combustors of the invention.

Each of said combustors of the invention and said control combustor was run at 12 test points or conditions, i.e., 12 different combinations of inlet-air temperature, combustor pressure, flow velocity, and heat input rate. Test points or conditions 1 to 6 simulate idling conditions, and test points 7 to 12 simulate maximum power conditions. The combustors of the invention were run using a prevaporized fuel. The control combustor was run using an atomized fuel. In all runs the air stream to the combustors was preheated by conventional means. Analyses for content of nitrogen oxides (reported as NO), carbon moboxide, and hydrocarbons (reported as carbon) in the combustor exhaust gases were made at each test condition for each combustor. Nitrogen oxides were determined by the Saltzman technique, Anal. Chem. 26, No. 12, 1954, pages 1949-1955. Carbon monoxide was measured by a chromatographic technique. Hydrocarbon was measured by the technique of Lee and Wimmer, SAE Paper 680679. Each pollutant measured is reported in terms of pounds per 1,000 pounds of fuel fed to the combustor. The results from test conditions 1 to 6 are set forth in Table III BELOW. The results from test conditions 7 to 12 are set forth in Table IV below. The data set forth in Tables 111 and IV are mean values from duplicate fruns at each test condition.

TABLE I PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL Philjet A-50 ASTM Distillation, F.

Initial Boiling Point 340 5 vol. evaporated 359 vol. evaporated 362 10 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 5 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, lb./ga1. 6.615 t 2 Heat of Combustion, net, Btu/lb. 18,670 Hydrogen Content, wt. 14.2 Smoke Point, mm 27.2 Sulfur, wt. 0.001 Gum, mg/l00 ml. 0.0 Composition, vol.

Paraffins 52.8 Cycloparaffins 34.5 Olefins 0.1 Aromatics 12.6 Formula (calculated) (C H Stoichiometric Fuel/Air Ratio, lb./lb. 0.0676

TABLE II COMBUSTOR DESIGN Combustor Number:

Variable 1 1(a) 7(a) 1(b) Closure member Air inlet diameter, in. 0.875 0.875 0.875 0.625

Inlet type tangent tangent tangent swirl Hole diameter, in. 0.188 0.188 0. 0 0.250 Number of holes 6 6 6 6 Total hole area, sq. in. 0.166 0.166 r 0.295 0.295 total combustor hole area 3.213 3.213 5.571 5.571 Fuel slot, inc. 0.005 Fuel nozzle type Simplex Spray angle, deg. 45 Fuel tube diameter,

in. 0.250 0.250 Flame tube 1st station (34) Hole diameter, in. 5/16 l" 5/16X1 5I16 1 5/16X1 Total number of holes 8 8 8 8 Total hole area, sq. in. 2.500 2.500 2.500 2.500 Total combustor hole area 48.393 48.393 47.214 47.214 2nd station (38) Hole diameter, in. 5/16X1 5/16Xl S/16X1 5/16Xl Total number of holes 8 8 8 8 Total hole area, sq. in. 2.500 2.500 2.500 2.500 Total combustor hole area 48.393 48.393 47.214 47.214

Combustor cross-sect. area, sq. in. 3.355 3.355 3.355 3.355

Total combustor hole area, sq. in. 5.166 5.166 5.295 5.295 cross-sectional area 153.933 153.933 157.777 157.777

Combustor inside diameter, in. 2.067 2.067 2.067 2.067 Primary zone length,

in. 7.375 7.375 7.375 7.375 Volume, cu. in. 24.748 24.748 24.748 24.748 Combustor length. in. 18.437 18.437 18.437 18.437 olume, cu. in. 61.867 61.867 61.867 61.867

Holes are 5/16" diameter at ends; slots are 1" long.

TABLE Vl.Summary of Emission Data From Combustor No. 1

Primary zone Resi- Test dence Equiv- Emissions, lbs.l1000 lbs. fuel condition time, alence N01 l-lC number msec ratio, (15 (as NO) CO (as C) TABLE VII.Summary of Emission Data For Combustor No. 1(b) Bi 11299 Resi- Emissions, lbs/1000 lbs. fuel dence Equivtime, alence NO, I-IC msec ratio, 4; (as NO) CO (as C) TABLE Vll.Summary of Emission Data for Combustor No. 1(b)Continued Primary zone RB i- Emissions,lbs./l000 lbs. fuel Test dence Equivcondition time, alence NO, HC number msec ratio, (as NO) CO (as C) The data in the above Tables V1 and VII show that decreasing the temperature of the inlet air to the primary combustion zone decreases the NO, emissions. The temperature of the inlet air to the second zone of the combustor (inlet at openings 34) was not measured but approximated the temperature of the primary air introduced through airinlet conduits 24. CO emissions decreased with an increase in temperature of the inlet air to the second zone of the combustors. Thus, as discussed further hereinafter, 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 air admitted to the primary combustion zone.

Said data also show that, generally speaking, increasing combustor pressure increases NQ emissions; but increasing reference velocity decreases NO, emissions. In general NO, emissions decrease with increasing equivalence ratio in the primary combustion zone (increasing fuel-rich mixture), and tend to plateau at low levels with increase in heat input. Said equivalence ratios were calculated from the percent Total Combustor Hole Area for the air inlet conduits 24 to the primary combustion zone. See combustors l and 1(b) in Table II. In general, CO emissions tended to peak at intermediate levels of heat input, decreased with an increase in combustor pressure, and increased with an increase in reference velocity.

EXAMPLE III Another series of test runs was carried out employing combustor 1 of Example I and five modifications thereof, i.e., combustors 1(c), 1(d), 1(e), IQ), and 1(g). Referring to FIGS. 1 and 4, said five modified combustors were essentially like combustor 1 except for the diameter of air inlet conduits 24. Design details of said combustors are set forth in Table VIII below. Design details of combustor 1 are set forth in Table [1 above. Said design details, e.g., dimensions, are given by way of illustration only and are not to be construed as limiting on the invention. Said dimension can be varied within wide limits so long as the improved results of the invention are obtained.

Each of said combustors was run at 12 test points or conditions, i.e., 12 different combinations of inlet-air temperature, combustor pressure, flow velocity, and heat input rate, similarly as in Example I. Said combustors were run using the same fuel, prevaporized, as in Examples I and 11. Operating conditions are set forth in 5 TABLE Vlll.-Combustor Design Combustor number Variable 1(d) l(e) 1(0 Closure member:

Air inlet diameter, (in.) 0.875 0.875 0.875 0.875 lnlet type Tangent Tangent Tangent Tangent Hole diameter, (in.). 0.125 0.164 0.211 0.230 Number of holes..... -6 6 6 6 Total hole ares, (sq. |n.)....... 0.074 0.127 0.210 0.249 Percent total comb. hole area. 1.458 2.477 4.030 4.743

Fuel nozzle'type Spray angle, deg..

Fule tube diameter 0.250 0.250 0.250 0.250

Flame tube:

1st station (34):

Hole diameter, (in.). 5/16 X 1 5/1 X1 5/16 X 1 5/16 X 1 Number of holes....... 8 8 8 8 Total hole area, (sq. in. 2.500 2.500 2.500 2.500 Percent total comb. hole area 49.271 48.761 47.985 47.628 2nd station (38):

Hole diameter, (in.) 5/16 X 1 5/16 X 1 5/16 X 1 5/16 X 1 Number of holes 8 8 8 8 Total hole area, (sq. in.) 2.500 2.500 2.500 2.500 Percent total comb. hole area 49.271 48.761 47.985 47.628 Comb. cross-sect. area, (sq. in.) 3.355 3.355 3.355 3.355 Total comb. hole area, (sq. in.) 5.074 5.127 5.210 5.249 Percent cross-sect. area... 151.119 152.771 155.244 156.406 Combustor inside diameter, (in. 2.067 2.067 2.067 2.067 Primary zone length, (in.) 7.375 7.375 7.375 7.375 Volume, (cu. in.) 24.748 24.748 24.748 24.748 Combustor length, (in.). 18.437 18.437 18.437 18.437 Volume. (cu. in.) 61.867 61.867 61.867 61.867

TABLE V1l1)- Combustor design- Continued Combustor number Variable 1(g) 1(h) 1(i) 1(j) Closure member:

Air inlet diameter, (in.) 0.875 0.875 0.875 0.625 Inlet type Tangent Tangent Tangent Swirl Hole diameter, (in.)... 0.250 0.188 0.250 0.250 Number of holes 6 6 6 6 Total hole area, (sq. in.) 0.295 0.166 0.295 0.295 Percent total comb. hole area 5.571 3.213 5.571 5.571

Fuel nozzle type Simplex Spray angle, deg. 45

Fuel tybe diameter.... 0.250 0.250 0.250

Flame tube:

1st station (34):

Hole diameter, (in.) 5/16 X 1 5/16 X 1 5/16 X 1 5/16 X 1 Number of holes 8 8 8 8 Total hole area, (sq. in.)...... 2.500 2.500 2.500 2.500 Percent total comb. hole are 47.214 49.393 47.214 47.214

2nd station (38):

' Hole diameter, (in.) 5/16 X 1 5/16 X 1 5/16 X 1 5/16 x 1 Number of holes 8 8 8 8 Total hole area, (sq. in.)... 2.500 2.500 2.500 2.500 Percent total comb. hole area. 47.214 48.393 47.214 47.214

Comb. cross-sect. area, (sq. in.).. 3.355 3.355 3.355 3.355

Total comb. hole area. (sq. in). 5.295 5.166 5.295 5.295 Percent cross-sect. area.... 157.777 153.933 157.777 157.777

Combustor inside diameter, (in.) 2.067 2.067 2.067 2.067

Primary zone length, (in.). 7.375 7.375 7.375 7.375 Volume. (cu. in.)... 24.748 24.748 24.748 24.748

Combustor length, (in.). 18.437 18.437 18.437 18.437

Volume. (cu. in.)...... 61.867 61.867

sure; and CO emissions increased with an increase in reference velocity.

ple 1(j) was a modification of combustor 1 EXAMPLE IV Another series of test runs was carried out employing three additional combustors 1(h), 1(i), and Combustors 1(h) was essentially like combustor l of Example I. Combustor 1(i) was a modification of combustor l and was essentially like combustor 1(g) of Exam and was essentially like combustor 1(b) of Example I. Design details of said combustors are set forth in Table TABLE IX.-Test Conditions Combustors l. l(c). l(d), [(e), l(0.and 1(a) Com- Cold Primary bustor flow inlet air presrefer Heat tempersure, ence input, Air Fuel ature, in. Hg. velocity, Btu/lb. flow, flow, F abs. ftJsec. air lb./sec. lb./hr.

---------- 10 III. Combustor Test condition number y, and

1 22 2 2 1 000000 7287 25 J .2 233460 334572 I l I 322222 111112 000000 728725 J I 233460 222348 I Each of said combustors was run at 12 test points or conditions, i.e., 12 different combinations of inlet air 25.2 20 temperature, combustor pressure, flow velocit u I I u a a I u I u u 2482 N222223l 00O000 4 698 .5J2 S M s 456796 334572 a f a 1 l VIII above. Said design details, e.g., dimensions, are

given by way of illustration only and are not to be con- 15 strued as limiting on the invention. Said dimensions can be varied within wide limits so long as the improved results of the invention are obtained.

heat input rate, similarly as in Example I. Said combustors were run using the same fuel as in the other examg 1 & O l l o 1 n kw l 1, a S ..D r m lu m u 922222 1 f000000 4 698 JA .6 S n 0 456796 222348 B b 0 S 6 m m I w w m I ll wmm Ham Hnu HM o n 6 m .s .s 2o2 .jsiflszm I11 I I v C m 2 2C WOOOOOOe7287 5m983629 m 0 H 1 m233460 4568 8 E c I s l n 1e 11 r t O b C C M F a 1 H e 5 444 555 555 222 w m T 888 555 444 7772 a S 222 44 4 555 8 80 M D m 000 000 000 000 W n S W m 4 m 050 O O50 050 n .m m 075 075 520 520 m m 223 223 23 23 2 E M f o 3 v. t 000 000 000 000 M 555 000 555 000 m 222 444 222 444 r m v u w s 2 H mmm mmm www wmm m X 111 111 E L I .2 B A 000 000 000 000 000 000 000 000 E T 999 999 III 111 III III m w T m m I S H M UH n 2 b n mm H n u u 23 456 WHU Cn The data in the above Table X show that practially ples. Combustors 1(h) and- 1(i) were run using prevaporized fuel. Combustor 10') was run using atomized liquid fuel. Operating conditions were the same as for the runs in Example III and are set forth in Table IX above. Analyses of the combustor exhaust were carried combustor pressure. and the reference velocity at fixed out as in the other examples. Emission data, mean values from duplicate runs at each test condition, are set forth in Table XI below.

all NO emission values obtained were good low values for the runs there set forth. Said data also show, in general, that: CO emissions decrease with an increase in heat input when holding the inlet air temperature, the

values; CO emissions decreased with an increase in inlet air temperature and increase in combustor pres- TA BLF. Xl.- Summary of Emission Data Combustors 1(h), l(i),und 1(j) Emissions. lbs/1000 lbs. fuel for combustor confg. Nos.

NO, (as NO) CO HC (as C) Test :on- Combustor No. Combustor No. Combustor No.

ition Number 1(h) 1(i) 1 3 1(h) 1(i) 1 3 1(h) 1(i) Hi) 7 3.2 Lo 24,1 35 50 2 9 2 0,6 0.4 8 2.9 1.8 2.0 6 10 7 0.2 0.2 0.2 t 9... 2.4 1.8 2.0 2 4 0.1 0.2 0.1

in general, the data in Table X1 confirm the data set forth in Table X above.

In the above examples, the fuel to the combustors of the invention, except for combustor Nos. 1(b) and IQ), was prevaporized. The invention is clearly not limited to using prevaporized fuels and it is within the scope of the invention to employ atomized liquid fuels. For comparison purposes, all the runs set forth in the above examples were carried out'under the conditions of inlet air temperature, combustor pressure, flow velocity, and heat input rate set forth in Tables 111, V and 1X. The invention is not limited to the values there given for said variables. It is within the scope of the invention to operate the combustors of the invention under any conditions which give the improved results of the invention. For example, it is within the scope of the invention to operate said combustors at inlet air temperatures within the range of from ambient temperatures or lower to about l,500 F. or higher; at combustor 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 ft. 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. Generally speaking, operating conditions in the combustors 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. In one preferred method of operating the combustors of the invention, the above-referred-to first and second stream of air will be relatively cool (compared to the third stream of air), and can be at substantially the same temperature. Said third stream of air preferably will be heated to a temperature within the range of 100 to 500 F. greater than the temperature of said first and second streams of air, in many instances.

in another preferred method of operating the combustors of the invention, the temperature of the abovereferred-to second stream of air can be from about 100 to about 500 F. greater than said first stream of air. In this embodiment of the invention, said third stream of air can, if desired for best results, have a temperature from about 100 to about 500 F. greater than the temperature of said first stream of air or second streamof air.

The relative volumes of the above-described first, second, and third streams of air will depend upon the other operating conditions. Generally speaking, the combined volume of saidfirst stream of air comprising primary air and said second stream of air comprising secondary air will be a minor proportion of the total air to the combustor, e.g., less than about 50 volume percent, with said first stream of air being in the range of up to about 25 volume percent and said second stream of air being in the range of up to about 24 volume percent. The volume of said third stream of air comprising quench air will be a major portion of the total air to the combustor, e.g., more than about 50 volume percent.

The data set forth in the above Tables 111, IV, VI, VII, X, and XI show that combustors can be operated in accordance with the invention to give low N0 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 ob tain desirable results with respect to all three pollutants N0 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, 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 operatethe 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 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 emission values referred to in the preceding paragraph can be greater than the valves there given when operating high performance combustors. For example, combustors such as the intermediate compression ratio combustors having a compression ratio of about to 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, emissions from such high performance or high compression ratio combustors will naturally be higher than the NO,, emissions from low compression ratio combustors. Thus, greatly improved results in reducing NO, emissions from a high performance combustor can beobtained without necessarily reducing said NO, 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 F. or higher. However, considering presently available practical materials of construction, about l,200 F. to about l,500 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 to 400 F. is a practical lower limit for said primary air inlet temperature in many instances. However, it is emphasied that primary air inlet temperatures lower than 200 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 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, emission values. Said data show that both low NO, 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 F. As the temperature of the inlet air to said zones decreases, increasingly improved (lower) values for NO, emissions are obtained, but it becomes more difficult to obtain desirably low CO emission values. In some instances, it is preferred that the temperature of the inlet air to the primary combustion zone not be greater than about 700 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, in

. such instances, depending upon the temperature of the inlet air to the primary combustion zone, it is preferred that the temperature of the inlet air to the secondary zone be in the range of from about to about 500 F. greater than the temperature of said inlet primary air. Any suitable means can be employed for heating said secondary air. The combustors illustrated in FIGS. 13 and 14 are well suited for introducing heated streams of secondary air via tubular conduits 36.

As a further guide to those skilled in the art, but not to be considered as limiting on the invention, 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 Nitrogen oxides 0.9 Carbon monoxide Hydrocarbons Particulates 0.40 (as N0 3.4 ll.8 0.41 (as hexane) L2 (as carbon) 3 0.l

The data set forth in the above examples show that' the invention can be practiced to give pollutant emission levels meeting the above standards or goals. How ever, 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: N0 5; CO, 25; and hydrocarbons, 2.

The term air is employed generically herein and in the claims, for convenience, to include air and other combustion-supporting gases.

While the invention has been described, in some instances, with particular reference to combustors employed in combination with gas turbine engines, the invention is not limited thereto. The combustors of the invention have utility in other applications, e.g., boilers, other stationary power plants, etc.

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.

We claim:

1. A method for burning a fuel in a combustor, which method comprises:

establishing separate streams of air as a first stream of air, a second stream of air, and a third stream of air;

Claims (19)

1. A method for burning a fuel in a combustor, which method comprises: establishing separate streams of air as a first stream of air, a second stream of air, and a third stream of air; introducing said first stream of air into a primary combustion zone of said combustor; introducing a fuel into said primary combustion zone; burning said fuel; introducing said second stream of air, maintained separate from said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; flowing said third stream of air, maintained separate from said first and second streams of air, in a downstream direction over and in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus-heated third stream of air into a third zone of said combustor located downstream from said second zone.

2. A method according to claim 1 wherein said first stream of air comprising primary air is not more than about 25 percent of the total air introduced into said combustor.

3. A method according to claim 1 wherein said first streAm of air comprising primary air is not more than about 5.6 percent of the total air introduced into said combustor.

4. A method according to claim 1 wherein both said first and said second streams of air are relatively hot and have a temperature of at least about 900* F.

5. A method according to claim 1 wherein said fuel has a hydrogen content of less than about 13.5 weight percent.

6. A method according to claim 1 wherein: the temperature of the inlet air to said primary combustion zone is not greater than about 1,200* F. to about 1,500* F.; and the equivalence ratio in said primary combustion zone is greater than stoichiometric and has a value such that the NOx value in the exhaust gases from said combustor is not greater than about 5 pounds per 1,000 pounds of fuel burned in said combustor.

7. A method according to claim 6 wherein the CO value in said exhaust gases is not greater than about 25 pounds per 1,000 pounds of fuel burned in said combustor.

8. A method according to claim 6 wherein said equivalence ratio is at least 1.5.

9. A method according to claim 6 wherein said equivalence ratio is at least 3.5.

10. A method for burning a fuel in a combustion zone having a primary combustion zone, a secondary combustion zone located downstream from said primary combustion zone, and a quench zone located downstream from said secondary combustion zone, which method comprises: establishing separate streams of air as a first stream of air comprising primary air, a second stream of air comprising secondary air, and a third stream of air comprising quench air; introducing a stream of fuel into said primary combustion zone; introducing said first stream of air comprising primary air into said primary combustion zone in an amount relative to said fuel sufficient to provide a fuel-rich mixture having an equivalence ratio in said primary combustion zone greater than stoichiometric; burning said fuel; introducing said second stream of air comprising secondary air, maintained separate from said first stream of air, into said secondary zone, in an amount sufficient to provide a fuel-lean mixture in said secondary zone with respect to any unburned fuel entering said secondary zone from said primary zone, and at a temperature at least 100*F. greater than the temperature of said introduced primary air; flowing said third stream of air, maintained separate from said first and second streams of air, in a downstream direction over and in heat exchange relationship with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said third stream of air; and introducing said thus-heated third stream of air into said quench zone at a temperature greater than the temperature of said secondary air.

11. A method for burning a fuel in a combustor, which method comprises: introducing a first stream of air into a primary combustion zone of said combustor; introducing a fuel into said primary combustion zone; burning said fuel; introducing a second stream of air, separate from said first stream of air, and at a temperature at least 100*F. greater than the temperature of said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; passing a third stream of air, separate from said first and second streams of air, in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus-heated third stream of air into a third zone of said combustor located downstream from said second zone.

12. A method for burning a fuel in a combustor, which method comprises: introducing a first stream of air into a primary combustion zone of said combusTor; introducing a fuel into said primary combustion zone; burning said fuel; introducing a second stream of air, separate from said first stream of air, and at a temperature within the range of from about 100* to about 500*F. greater than the temperature of said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; passing a third stream of air, separate from said first and second streams of air, in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus-heated third stream of air into a third zone of said combustor located downstream from said second zone.

13. A method according to claim 12 wherein the temperature of said first stream of air is not greater than about 700* F.

14. A method according to claim 13 wherein the equivalence ratio in said primary combustion zone is greater than stoichiometric and has a value such that the NOx emissions value in the exhaust gases from said combustor is not greater than about 5 pounds per 1,000 pounds of fuel burned in said combustor.

15. A method according to claim 14 wherein the CO emissions value in the exhaust gases from said combustor is not greater than about 25 pounds per 1,000 pounds of fuel burned in said combustor.

16. A method according to claim 15 wherein the equivalence ratio in said primary combustion zone is at least about 3.5.

17. A method for burning a fuel in a combustion zone having a primary combustion zone, a secondary combustion zone located downstream from said primary combustion zone, and a quench zone located downstream from said secondary combustion zone, which method comprises: introducing a stream of fuel into said primary combustion zone; introducing a first stream of air comprising primary air into said primary combustion zone at a temperature not greater than about 700*F. and in an amount relative to said fuel sufficient to provide a fuel-rich mixture having an equivalence ratio in said primary combustion zone greater than stoichiometric; burning said fuel; introducing a second stream of air comprising secondary air, separate from said first stream of air, into said secondary zone, in an amount sufficient to provide a fuel-lean mixture in said secondary zone with respect to any unburned fuel entering said secondary zone from said primary zone, and at a temperature within the range of from about 100* to about 500*F. greater than the temperature of said introduced primary air; passing a third stream of air, separate from said first and second streams of air, in heat exchange relationship with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said third stream of air; and introducing said thus-heated third stream of air into said quench zone at a temperature greater than the temperature of said secondary air.

18. A method according to claim 17 wherein the exhaust gases from said quench zone have a NOx emissions value not greater than about 5 pounds per 1,000 pounds of said fuel burned, and a CO emissions value not greater than about 25 pounds per 1,000 pounds of said fuel burned.

19. A method for burning a fuel in a combustor, which method comprises: introducing a first stream of air into a primary combustion zone of said combustor; introducing a fuel into said primary combustion zone; burning said fuel; introducing a second stream of air, separate from said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; passing a third stream of air, separate from said first and second streams of air, in heat exchange with an outer wall of sAid primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus-heated third stream of air into a third zone of said combustor located downstream from said second zone; and wherein said third stream of air is passed in a first annular stream surrounding said wall of said primary combustion zone and at least a portion of said second zone, and then introduced into said third zone; and said second stream of air is passed in a second annular stream surrounding but separated from said first annular stream, and then introduced into said second zone.

Images