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(11) | EP 2 618 059 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Combustor nozzle/premixer with curved sections |
| (57) An apparatus for premixing fuel and air prior to combustion in a gas turbine engine
includes an annular fuel passage (62) receiving fuel from a fuel source. The annular
fuel passage (62) includes a fuel plenum (68) and has a wave shape with a peak section
surrounded by trough sections. An annular air passage (70) surrounds the annular fuel
passage (62). The annular air passage (70) receives air to be mixed with the fuel
in the fuel passage (62) for downstream combustion. A plurality of swirler vanes (72)
are disposed in the annular air passage (70) adjacent the fuel plenum (68).
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BACKGROUND OF THE INVENTION
[0001] The invention relates to premixing fuel and air prior to combustion in a gas turbine engine and, more particularly, to a combustor nozzle/premixer including curved sections to improve mixing.
[0002] Gas turbine engines generally include a compressor for compressing an incoming airflow. The airflow is mixed with fuel and ignited in a combustor for generating hot combustion gases. The combustion gases in turn flow to a turbine. The turbine extracts energy from the gases for driving a shaft. The shaft powers the compressor and generally another element such as an electrical generator.
[0003] Cold air from the flow sleeve enters into the combustor headend region and is distributed among a plurality of nozzles. Generally, air passes through an inlet flow conditioner (IFC) and becomes uniform in circumferential direction. Subsequently, it is rotated by axially placed vanes, and fuel is injected into the flow through holes in the vanes for premixing of fuel and air.
[0004] The exhaust emissions from the combustion gases generally are a concern and may be subject to mandated limits. Certain types of gas turbine engines are designed for low exhaust emissions operation, and in particular, for low NOx (nitrogen oxides) operation with minimal combustion dynamics, ample auto-ignition, and flameholding margins.
[0005] Low NOx combustors typically include a number of combustion cans circumferentially adjoining each other around the circumference of the engine. Each can may have one or more fuel air mixers or nozzles positioned therein. Nozzles use swirling air to mix fuel and air, and hence are referred to as "swirlers." The swirlers may have a number of circumferentially spaced apart vanes for swirling and mixing the compressed airflow and the fuel as they pass therethrough.
[0006] The combustor nozzle serves to provide fuel air premixing with minimum pressure losses. It would be desirable to perform the premixing function over a shorter distance and more efficiently. With more fuel-air mixing over a shorter distance, combustion emissions can be reduced. Additionally, existing swirler vanes typically include internal passages for fuel, and the swirler vanes are thus larger in size than desired and more expensive to manufacture. It would be desirable to simplify the construction and eliminate the internal passages in the swirler vanes.
BRIEF DESCRIPTION OF THE INVENTION
[0007] An apparatus for premixing fuel and air prior to combustion in a gas turbine engine includes an annular fuel passage receiving fuel from a fuel source, an annular air passage surrounding the annular fuel passage, and a plurality of swirler vanes disposed in the annular air passage adjacent a fuel plenum section. The annular fuel passage has an upstream passage, a neck passage narrower than the upstream passage, and the fuel plenum section that curves from the neck passage to a wider passage. The annular air passage receives air to be mixed with the fuel in the fuel passage for downstream combustion.
[0008] In another aspect, the invention resides in a combustor includes a casing, and a plurality of nozzles disposed in the casing. Each of the nozzles includes the structure of the apparatus for premixing fuel and air prior to combustion in a gas turbine.
[0009] In still another aspect, the invention resides in an apparatus for premixing fuel and air prior to combustion in a gas turbine engine includes an annular fuel passage receiving fuel from a fuel source. The annular fuel passage includes a fuel plenum and has a wave shape with a peak section surrounded by trough sections. An annular air passage surrounds the annular fuel passage. The annular air passage receives air to be mixed with the fuel in the fuel passage for downstream combustion. A plurality of swirler vanes are disposed in the annular air passage adjacent the fuel plenum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 is a side cross-sectional view of a gas turbine engine;
FIG. 2 is a sectional view of the combustor nozzle/premixer;
FIG. 3 is an end view of the combustor nozzle; and
FIG. 4 is a close-up view showing the swirler vanes.
DETAILED DESCRIPTION OF THE INVENTION
[0011] FIG. 1 shows a cross-sectional view of a gas turbine engine 10. The gas turbine engine 10 includes a compressor 20 to compress an incoming airflow. The compressed airflow is then delivered to a combustor 30 where it is mixed with fuel from a number of incoming fuel lines 40. The combustor 30 may include a number of combustor cans or nozzles 50 disposed in a casing 55. As is known, the fuel and the air may be mixed within the nozzles 50 and ignited. The hot combustion gases in turn are delivered to a turbine 60 so as to drive the compressor 20 and an external load such as a generator and the like. The nozzles 50 typically include one or more swirlers.
[0012] FIG. 2 is a sectional view of the combustor nozzle/premixer according to preferred embodiments. The nozzle 50 is one of several disposed in an array within the casing 55. The nozzle 50 includes an annular fuel passage 62 receiving fuel from a fuel source. The annular fuel passage 62 includes an upstream passage 64, a neck passage 66 narrower than the upstream passage 64 as shown, and a fuel plenum section 68 that curves from the neck passage 66 to a wider passage. The fuel passage defines a wave shape as shown with a peak section surrounded by trough sections. An annular air passage 70 surrounds the annular fuel passage 62 and receives air to be mixed with the fuel in the fuel passage 62 for downstream combustion. An entrance 71 of the air passage 70 may be rounded as shown. A plurality of swirler vanes 72 are disposed in the annular air passage 70 adjacent the fuel plenum section 68.
[0013] The fuel plenum section 68 includes fuel holes 74 in the annular fuel passage 62. In an exemplary embodiment, the nozzle includes at least 40 fuel holes 74. Preferably, the fuel holes 74 are disposed in the wider passage (widest section) of the fuel plenum section 68. As shown in FIG. 2, the fuel plenum section 68 narrows downstream of the wider passage such that the wider passage defines a peak section. The fuel holes 74 are preferably disposed in the peak section. Additionally, the swirler vanes 72 are disposed surrounding the annular fuel passage 62 adjacent the peak section. The fuel holes 74 are positioned between the swirler vanes. With continued reference to FIG. 2, the fuel holes 74 may be positioned upstream of a trailing edge of the swirler vane 72 such that the fuel has sufficient axial velocity, which reduces the risk of flameholding.
[0014] By virtue of the curved fuel passage 62 and correspondingly curved air passage 70, an exterior surface of the annular air passage is similarly curved substantially corresponding to the fuel plenum section 68. The curved exterior surface 76 provides for slight compression/diffusion with the casing 55 and thereby reduces incoming circumferential non-uniformities. That is, along with the surface of the casing 55, the nozzle 50 forms a convergent/divergent passage that acts a flow conditioner. Non-uniformities from the compressor due to the 180° turn of the air may be smoothed out efficiently. Overall, air will be distributed without significant non-uniformities via the outside curvature and rounded entrance.
[0015] In contrast with the prior designs, instead of an axial swirler, the structure of the described embodiment is curved or wavy. Air from the headend passes through the rounded entrance 71 to maintain circumferential uniformity. The air in the annular air passage 70 flows up the curved section, which further serves to remove non-uniformities. Subsequently, the air passes through the vanes 72 and is mixed with fuel entering the air path via the fuel holes 74. Since the vanes do not include passages for fuel, the vanes can be made highly aerodynamic. Additionally, the vanes can be made about 50% shorter than existing vanes, which provides extra fuel/air premixing length or alternatively, the nozzle can be shortened. Additionally, the vanes can be made thinner in the absence of the fuel passages, which serves to decrease the overall weight of the swirler. The curved or wavy shape enables air to travel radially upward and to come down at fuel injection. The resulting radial current facilitates fuel and air mixing (radial current is not present in an axial swirler).
[0016] Fuel is injected from the downstream curvature of the nozzle but still at a high radius such that premixing is efficient. The fuel plenum beneath can be made diffusive to decrease pressure variations. Multiple fuel hole locations between two vanes or downstream of the vanes can be provided. Hole locations should be such that fuel from multiple holes does not mix, and the fuel stream is not directed towards the trailing edge of the vanes. As noted, by placing the fuel holes in the region of slightly high axial velocity, a risk of flameholding is reduced. The structure effects a slight radial current, resulting in early mixing. Moreover, there is no flow conditioning device needed, and the overall pressure drop reduces to a greater extent.
[0017] The shorter and aerodynamic vanes along with the rounded entrance make the nozzle highly efficient in terms of pressure drop. The only pressure drop will be due to the rotation of the flow in the burner tube. Moreover, since the swirler is independent of the vane core and cavity, it can be made shorter, providing opportunities to reduce the length of the swirler or provide for better mixing with the same length. On the exterior of the nozzle, with the convergent-divergent passage, the design filters out non-uniformities in CDC air after flow sleeve exit. Since the compression-diffusion is smooth, associated pressure losses are minimized.
[0018] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
1. An apparatus for premixing fuel and air prior to combustion in a gas turbine engine
(10), the apparatus comprising:
an annular fuel passage (62) receiving fuel from a fuel source, the annular fuel passage (62) having an upstream passage (64), a neck passage (66) narrower than the upstream passage (64), and a fuel plenum section (68) that curves from the neck passage (64) to a wider passage;
an annular air passage (70) surrounding the annular fuel passage (62), the annular air passage (70) receiving air to be mixed with the fuel in the fuel passage (62) for downstream combustion; and
a plurality of swirler vanes (72) disposed in the annular air passage (70) adjacent the fuel plenum section (68).
2. An apparatus according to claim 1, wherein the fuel plenum section (68) comprises
fuel holes (74) in the annular fuel passage (62), the fuel holes (74) being disposed
in the wider passage of the fuel plenum section (68).
3. An apparatus according to claim 2, wherein the fuel holes (74) are disposed upstream
of a trailing edge of the swirler vanes (72) such that the fuel has sufficient axial
velocity.
4. An apparatus according to claim 2 or 3, wherein the fuel plenum section (68) narrows
downstream of the wider passage such that the wider passage defines a peak section,
and wherein the fuel holes (74) are disposed in the peak section.
5. The apparatus of claim 4, wherein the annular fuel passage (62) has a wave shape with
the peak section being surrounded by trough sections.
6. An apparatus according to claim 4 or 5, wherein the swirler vanes (72) are disposed
surrounding annular fuel passage (62) adjacent the peak section.
7. An apparatus according to any of claims 2 to 6, wherein the fuel holes (74) are disposed
between the swirler vanes (72).
8. An apparatus according to any of claims 2 to 7, comprising at least 40 fuel holes
(74).
9. An apparatus according to any preceding claim, wherein an exterior surface (76) of
the annular air passage (70) is curved substantially corresponding to the fuel plenum
section (68), the curved exterior surface (76) reducing incoming circumferential non-uniformities
of input air.
10. An apparatus according to any preceding claim, wherein an entrance (71) to the annular
air passage (70) is rounded.
11. A combustor (30) comprising:
a casing (55); and
a plurality of nozzles (50) disposed in the casing, wherein each of the nozzles includes the apparatus of any of claims 1 to 10.
12. A combustor according to claim 11, when dependent on claim 9, wherein an interior
surface of the casing (55) defining a headend air passage, wherein the headend air
passage is shaped to reduce incoming circumferential non-uniformities of input air.