Lean direct injection for supported premix applications

Abstract

Premix pilot arrangement (100) configured to be connected to a fuel nozzle for a turbine combustion chamber and to premix a pilot fuel with air before the air / pilot fuel mixture is supplied to a combustion zone of the turbine combustion chamber, the premix pilot arrangement (100) comprising: a first cylinder (106), a second cylinder (104) which is configured to optionally contain a first substance of either pilot fuel or air, wherein the second cylinder (104) is arranged in the first cylinder (106) such that an annular region (105) is defined between the first cylinder (106) and the second cylinder (104), wherein the annular region (105) is configured to allow a second substance of pilot fuel or air, which is different from the first substance, to flow through the annular region (105) in the axial direction of the premix pilot arrangement (100); a nozzle (107) connected to the second cylinder (104), wherein the nozzle (107) is configured to form at least one second cylinder opening (110) to direct the first substance flowing through the second cylinder (104) radially outwards, perpendicular to the axial direction of the premix pilot arrangement (100); and an end piece (103) which is connected to the first cylinder (106), wherein the end piece (103) is configured to form at least one first cylinder opening (108) in order to direct the second substance flowing through the annular region (105) radially inwards, perpendicular to the axial direction of the premix pilot arrangement (100), towards the first substance directed by the at least one second cylinder opening (110).

Description

FIELD OF THE INVENTION

[0001] The invention generally relates to combustion chambers for turbines. In particular, the invention relates to a solution for using lean-burn direct injection for premixed assisted combustion. BACKGROUND TO THE INVENTION

[0002] Conventional gas turbine combustors use non-premixed (“diffusion”) flames, where fuel and air freely enter a combustion chamber independently of each other. However, the diffusion flames burn at high temperatures, so excessive levels of nitrogen oxide (NO x ) are emitted.

[0003] A process used to reduce NO xemissions involves the use of lean premixed combustion, where fuel and air are premixed in a premixing section, and the fuel-air mixture is injected into a combustion chamber where it is burned. Lean premixed combustion can achieve low NO in the case of very uniform fuel-air mixtures. x emissions, but such mixtures are usually prone to combustion instability. This instability can be resolved by using a support device. However, a pilot flame usually leads to excessive NO formation. x , which therefore reduces the advantage of using the lean premixed combustion process.

[0004] US 2003 / 0 129 555 A1 describes a diffusion flame burner with a combustion chamber surrounded by a cylindrical combustion chamber wall that surrounds the flame and widens in a funnel shape in the direction of flame radiation. Fuel gas is supplied directly to the combustion chamber through a fuel distribution pipe that opens into the upstream end of the combustion chamber and has fuel injection openings. Combustion air is supplied directly to the combustion chamber through a separate air supply line, an air chamber surrounding the fuel distribution pipe, and air injection openings formed in the cylindrical combustion chamber wall.

[0005] US 6,543,235 B1 describes a combustion chamber with a fuel injector device having an injector tip body with a central axial fuel supply channel opening into angularly oriented fuel injection ports at a tip end of the injector tip body, and having a cylindrical shell surrounding the injector tip body and defining therewith an annular air supply channel. Fuel discharged axially and radially outwardly through the fuel injection ports encounters an air jet discharged axially and radially inwardly through angular air discharge channels at the injector tip end. The fuel and air mix with each other and flow downstream through a swirler into a combustion chamber of the combustion chamber. BRIEF DESCRIPTION OF THE INVENTION

[0006] Embodiments of this invention provide a premix pilot assembly for use in a fuel nozzle for a turbine. The NO emitted by the ignition device x The fuel level is reduced by rapidly mixing the fuel and air at the end of the ignition nozzle, thus avoiding significant zones of rich fuel-air mixtures. The air is mixed with the fuel by means of ports formed in a first cylinder and a second cylinder, one of the cylinders carrying air and the other pilot fuel. The ports can be configured as required to achieve a desired effect on the ignition device.

[0007] A first aspect of the invention provides a premix pilot assembly configured to be connected to a fuel nozzle for a turbine combustor and to premix a pilot fuel with air before the air / pilot fuel mixture is supplied to a combustion zone of the turbine combustor, the premix pilot assembly comprising: a first cylinder; a second cylinder configured to selectively contain a first species of pilot fuel or air, the second cylinder being arranged within the first cylinder such that an annular region is defined between the first cylinder and the second cylinder, the annular region being configured to allow a second species of pilot fuel or air, different from the first species, to flow through the annular region in the axial direction of the premix pilot assembly;a nozzle connected to the second cylinder, the nozzle configured to form at least one second cylinder opening for directing the first substance flowing through the second cylinder radially outward, perpendicular to the axial direction of the premix pilot assembly; and an end piece connected to the first cylinder, the end piece configured to form at least one first cylinder opening for directing the second substance flowing through the annular region radially inward, perpendicular to the axial direction of the premix pilot assembly, against the first substance directed by the at least one second cylinder opening.

[0008] A second aspect of the invention provides a fuel nozzle comprising: a housing defining a main fuel nozzle; a center body tube disposed within the housing; and a premix pilot assembly as described above connected to one end of the center body tube. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a prior art main fuel nozzle for a gas turbine. Fig. 2-4 show sectional views of various designs for a premix pilot device according to embodiments of this invention. Fig. 5 shows a sectional view of a construction for a premix pilot device according to an embodiment which as such does not fall under the subject matter of the claimed invention.

[0009] Please note that the drawings of the invention are not to scale. The drawings are intended to illustrate only typical aspects of the invention and should therefore not be considered limiting the scope of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Gas turbines usually contain several combustion chambers, and each combustion chamber has several main fuel nozzles. Such a main fuel nozzle 10, as known from the prior art, is shown in Fig. 1. The main fuel nozzle 10 includes a burner tube 18 having deflection vanes 16 and an inlet flow conditioner (IFC) 20 through which main air enters the nozzle 10. The main fuel nozzle 10 further includes a central body 14 based on a tube or cylinder disposed within the main fuel nozzle 10. A liquid fuel cartridge 12 is disposed within the central body 14. The Fig. 1 at one end of the central body 14 and the liquid fuel cartridge 12 by the dashed line is an area referred to as the diffusion nozzle 22, which is usually connected, for example, by a weld, to the end of the fuel nozzle 10. Embodiments of the invention discussed herein include modifying or replacing the diffusion nozzle 22 to incorporate a premix pilot device 100 (see Fig. 2-4).

[0011] Fig. Figure 2A shows a sectional view of a premix pilot device 100 incorporated into a main fuel nozzle 101 according to embodiments of this invention. The premix pilot device 100 of the main fuel nozzle 101 can be added by any known method. For example, the premix pilot device 100 can be mounted against the diffusion nozzle 22 ( Fig. 1), or the diffusion nozzle 22 known from the prior art can be modified to include the elements of the premix pilot device 100 discussed here. For example, the premix pilot device 100 can be connected to one end of the Fig. 1, and a person skilled in the art can modify the main fuel nozzle 10 as needed to branch air and fuel through the premix pilot device 100 and, if desired, to utilize the liquid fuel cartridge 12. Such an arrangement for branching air and fuel through the premix pilot device 100 is shown in Fig. 2A shown.

[0012] With reference to Fig. 2B shows an enlarged sectional view of the premix pilot device 100. The premix pilot device 100 includes a first cylinder 106 and a second cylinder 104 disposed within the first cylinder 106. Essentially, an annular region 105 is formed between the first cylinder 106 and the second cylinder 104. The cylinder 104 carries fuel, while the annular region 105 carries air. It should be noted that while the cylinders 104 and 106 are Fig. 2-4 are shown as cylindrical, one skilled in the art will understand that any suitably sized or shaped passageway may be used. It should also be noted that while the cylinder 104 in Fig. 2-4 as a hollow cylinder carrying fuel, one skilled in the art will understand that additional elements, such as additional passageways or mechanical elements, may be included in the cylinder 104 to assist the premix pilot device 100 in interacting with the fuel nozzle 10.

[0013] The first cylinder 106 further includes an end piece 103 configured to form at least one first cylinder opening 108 (also referred to as air openings) for radially inwardly directing the air flowing through the annular region 105. The premix pilot device 100 also includes a nozzle 107 at one end of the second cylinder 104. The nozzle 107 is configured to form at least one second cylinder opening 110 (also referred to as fuel openings) for radially outwardly directing the pilot fuel flowing through the second cylinder 104. In this way, a sufficient amount of pilot fuel flows out of the second cylinder 104 through the openings 110 to maintain a pilot flame 109.As discussed herein, one or more air ports 108 allow air in the annular region 105 to be blown directly against the pilot fuel exiting the fuel ports 110 located in the second cylinder 104. This air flow from the air ports 108 is illustrated by the arrows labeled "a," while the pilot fuel flow from the fuel ports 110 is represented by the arrows labeled "f." The air is blown radially inward directly against the fuel as it exits the second cylinder 104. Accordingly, the air and fuel are separated until the fuel exits the second cylinder 104, so that zones of rich fuel-air mixtures are substantially avoided. Once the air and fuel have mixed, the fuel-air mixture (labeled by the arrows "f+a") flows downstream, i.e.away from the second cylinder 104 and the nozzle 107, and will begin to burn approximately where in . Fig. 2 pilot flames 109 are shown. Essentially, intensive mixing of air and fuel occurs in a mixing region within a short axial distance from the fuel nozzle 107. Furthermore, according to embodiments of this invention, blowing the air against the fuel creates a zone that promotes stable combustion for the pilot flame 109.

[0014] The openings 108, 110 may have any shape or size to achieve mixing of air and fuel with the desired intensity and at the desired inclination. For example, in one embodiment shown in the perspective view in Fig. 3A-3C, one or more discrete, separate openings formed along the nozzle 107 and the second cylinder 104, respectively, with each opening serving as an independent nozzle to inject the air and fuel, respectively. In yet another embodiment (not shown), the fuel openings 110 and the air openings 108 may include one or more circumferential, annular openings arranged around the entire nozzle 107 and the entire second cylinder 104, respectively. It should be understood that any arrangement of annular openings or discrete, separate openings may be used. For example, both the fuel opening 110 and the air opening 108 may be circumferential, annular openings, or both openings 108, 110 may be discrete, separate openings.In one variation, the fuel opening 110 may be a circumferential annulus, while the air openings 108 may be discrete, separate openings, and vice versa. Regardless of whether the openings 108, 110 are circumferential (annular) or discrete and separate, the openings 108, 110 may also have any desired shape or geometric cross-section.

[0015] The openings 108, 110 may be formed in the second cylinder 104 and the nozzle 107 to achieve a desired degree of mixing of air and fuel. For example, if the openings 108, 110 are discrete, separate openings, the openings 108 may be configured as shown in Fig. 4A, with a corresponding opening 110, so that a fuel stream directly impinges on an air stream. In a modification, as shown in Fig. 4B, the openings 108 may be offset relative to the openings 110 so that a fuel stream does not directly impinge on an air stream.

[0016] While the openings 108, 110 in the embodiments of the invention according to Fig. 2-4 are shown as directing the air flow substantially perpendicularly against the fuel, the openings 108, 110 may alternatively, in non-inventive embodiments or in inventive embodiments, additionally be formed obliquely to achieve the mixing of air and fuel at a desired angle. For example, in one embodiment of the invention, only one of the openings 108, 110 may be formed obliquely, while the other opening is substantially perpendicular to the cylinders 104, 106. As shown in the simplified schematic representation in Fig. 5, which as such does not show an inventive embodiment of the premixing pilot device, an angle α is, for example, the angle between two surfaces of the nozzle 107 having the fuel openings 110, and can range from about 0° to about 60°. An angle θ is the angle between a horizontal plane of the cylinder 106 and a surface of the air openings 108. The angle θ can range from about 120° to about 180°. Although these angle ranges are suggested as an example of how the openings 108, 110 can be inclined to achieve a desired mixing of air and fuel, it is understood that the suggested angles are not intended to limit the invention described herein, since any angle can be used for either of the openings 108 or 110 to achieve a desired result. Although in Fig.2-5 shows air being blown against the fuel in a substantially perpendicular or slightly downstream direction (ie, away from the premix pilot device 100 in the direction of the flame 109), air may also be sprayed against the fuel in an upstream direction.

[0017] While in the embodiments discussed herein, the second cylinder 104 contains the fuel, and the annular region 105 formed by the first cylinder 106 contains air, it should be understood that the reverse is also disclosed. The second cylinder 104 may contain air, and therefore air may be directed radially outward through the openings 110, while the annular region 105 may contain fuel, and therefore fuel may be directed radially inward through the openings 108 formed in the first cylinder 106.

[0018] The terms "first," "second," and the like herein do not specify an order, quantity, or ranking, but rather serve to distinguish one item from another. The indefinite article and its grammatical forms herein do not imply a limitation of quantity, but rather that at least one such item is present. The modifying term "about," used in connection with a quantity, includes the stated value and implies the meaning given by the context (e.g., includes the error variance that may be present in a measurement of the specific quantity).

[0019] While various embodiments are described herein, it will be apparent from the description that various combinations of elements, variations, or improvements therein may be made by those skilled in the art which fall within the scope of the invention. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential spirit and scope of the invention. It is therefore not intended to limit the invention to the particular embodiment considered to be the best mode contemplated for carrying out the invention, but rather to include all embodiments falling within the scope of the appended claims.

[0020] Embodiments of this invention provide a premixed ignition arrangement for use in a fuel nozzle 10, 101 for a turbine. The proportion of nitrogen oxide (NO x The fume emitted by the igniter is reduced by rapidly mixing the fuel and air at the end of the ignition nozzle, thus avoiding significant zones of fuel-rich fuel-air mixtures. The air is mixed with the fuel using ports formed in a first cylinder 106 and a second cylinder 104, one of which carries air and the other pilot fuel. The ports can be configured as needed to have a desired effect on the igniter. List of reference symbols: 10, 101 Main fuel nozzle 12 liquid fuel cartridges 14 central body 16 deflection vanes 18 burner tube 20 Inlet Flow Conditioners (IFC) 22 Diffusion nozzle 100 Premix pilot device 103 End piece 104 Second cylinder 105 Annular area 106 First cylinder 107 Nozzle 108 Air opening 109 pilot lights 110 fuel ports

Claims

[1] A premix pilot assembly (100) adapted to be connected to a fuel nozzle for a turbine combustion chamber and to premix a pilot fuel with air before the air / pilot fuel mixture is supplied to a combustion zone of the turbine combustion chamber, the premix pilot assembly (100) comprising: a first cylinder (106), a second cylinder (104) configured to selectively contain a first species of either pilot fuel or air, the second cylinder (104) being disposed within the first cylinder (106) such that an annular region (105) is defined between the first cylinder (106) and the second cylinder (104), the annular region (105) being configured to allow a second species of pilot fuel or air, different from the first species, to flow through the annular region (105) in the axial direction of the premix pilot assembly (100); a nozzle (107) connected to the second cylinder (104), the nozzle (107) being adapted to form at least one second cylinder opening (110) for directing the first substance flowing through the second cylinder (104) radially outward, perpendicular to the axial direction of the premix pilot assembly (100); and an end piece (103) connected to the first cylinder (106), the end piece (103) being adapted to form at least one first cylinder opening (108) for directing the second substance flowing through the annular region (105) radially inwardly, perpendicular to the axial direction of the premix pilot arrangement (100), against the first substance directed by the at least one second cylinder opening (110). [2] The premix pilot assembly of claim 1, wherein the at least one first cylinder opening (108) comprises one or more circumferential annular openings and wherein the at least one second cylinder opening (110) comprises one or more circumferential annular openings. [3] The premix pilot assembly of claim 1, wherein the at least one first cylinder port (108) comprises one or more circumferential annular ports and wherein the at least one second cylinder port (110) comprises one or more discrete, separate ports. [4] The premix pilot assembly of claim 1, wherein the at least one first cylinder port (108) comprises one or more discrete, separate ports and wherein the at least one second cylinder port (110) comprises one or more circumferential annular ports. [5] The premix pilot assembly of claim 1, wherein the at least one first cylinder port (108) comprises one or more discrete, separate ports and wherein the at least one second cylinder port (110) comprises one or more discrete, separate ports. [6] The premix pilot assembly of claim 5, wherein each of said at least one first cylinder opening (108) is aligned with a corresponding one of said at least one second cylinder opening (110). [7] The premix pilot assembly of claim 5, wherein the at least one or more discrete, separate ports (108) of the first cylinder (106) are offset with respect to the one or more discrete, separate ports (110) of the second cylinder (104). [8] Premix pilot arrangement according to claim 1, further comprising a mixing region in which mixing of air and pilot fuel takes place. [9] Fuel nozzle, which includes: a housing (18) defining a main fuel nozzle (101, 10); a central body tube (14) arranged in the housing (18); and a premix pilot assembly (100) according to any one of the preceding claims connected to one end of the central body tube (14).

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