Patent Application
20140238025
The subject matter disclosed herein relates to fuel nozzles, and more specifically, to systems to increase fuel/air mixing within the fuel nozzles.
A gas turbine engine combusts a mixture of fuel and air to generate hot combustion gases, which rotate turbine blades to drive a load, such as an electrical generator. The gas turbine engine may include one or more fuel nozzles to direct the mixture of fuel and air into a combustion region of the gas turbine. In addition, the one or more fuel nozzles may be used to premix the fuel and the air. Unfortunately, poor mixing of the fuel and the air may reduce the flame stability within the combustion region. In addition, non-uniform mixtures of fuel and air may increase the amount of undesirable combustion byproducts, such as nitrogen oxides.
Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.
In one embodiment, a system includes a fuel nozzle. The fuel nozzle includes a central hub with a first annular passage extending along a longitudinal axis of the fuel nozzle. A flow conditioner is disposed along the first annular passage. The flow conditioner includes at least one of a straightening vane, a mesh screen, or a multi-passage body having multiple passages generally parallel with the longitudinal axis. An outer shroud is disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle.
In a second embodiment, a system includes a fuel nozzle. The fuel nozzle includes a first annular passage extending along a longitudinal axis of the fuel nozzle, a flow conditioner disposed along the first annular passage, and a plurality of premixing tubes disposed along the first annular passage downstream from the flow conditioner. Each tube of the plurality of premixing tubes includes an air inlet, a fuel inlet, and an air-fuel mixture outlet. The fuel nozzle also includes an outer shroud disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle. In addition, the fuel nozzle includes a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an interior of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and the plurality of premixing tubes.
In a third embodiment, a system includes a fuel nozzle. The fuel nozzle includes a central hub having a first annular passage extending along a longitudinal axis of the fuel nozzle and a flow conditioner disposed along the first annular passage. The flow passage is at least one of a straightening vane, a mesh screen, or a multi-passage body having a plurality of passages generally parallel with the longitudinal axis. The fuel nozzle includes a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an interior of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and an outlet of the fuel nozzle.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
The present disclosure is directed toward systems for improving fuel and air mixing within fuel nozzles of combustors. In particular, air is directed through a swirler and into one or more premixing tubes (e.g., a group of 10 to 100 premixing tubes). A flow conditioner is disposed between the swirler and the premixing tubes, such that the flow conditioner generally straightens (e.g., axially) the flow of air into the premixing tubes. Straightening the flow of air results a more uniform delivery of air into the premixing tubes, thereby improving fuel/air mixing and increasing the efficiency of the combustor.
In certain embodiments, the flow conditioner may be one or more straightening vanes or an annular segment with a plurality of passages or tubes disposed therethrough. As will be discussed further below, the straightening vane is shaped like an airfoil and is partially or entirely arcuate in an axial and circumferential direction of the fuel nozzle. The arcuate shape reduces the circumferential velocity (e.g., swirl) of the air, thereby straightening (e.g., axially) the air upstream of the premixing tubes. In another embodiment, the flow conditioner may be the annular segment having the plurality of passages or tubes. The passages or tubes are generally straight and serve to straighten the air and to direct the air towards the premixing tubes with a decreased swirl. Again, the decreased swirl axially straightens the air, which improves fuel/air mixing within the fuel nozzle and increases the efficiency of the combustor, and subsequently, the gas turbine system.
As used herein, the term “annular” shall mean a ring-shaped. The use of the term “annular” is not intended to limit the scope of the present disclosure with respect to the shape, perimeter, or other geometric feature of the hollow structure. That is, a hollow cylinder, a hollow cone, a hollow polyhedron, a hollow prism, and the like, are all encompassed by the term “annular”.
Turning now to the figures,
As illustrated, the gas turbine system 10 includes a compressor 20, a combustor 22 (e.g., turbine combustor), and a turbine 24. The turbine system 10 may include one or more of the fuel nozzles 12 described below in one or more combustors 22. The compressor 20 receives air 26 from an intake 28 and compresses the air 26 for delivery to the combustor 22. As shown, a portion of the air 26 is routed to the fuel nozzle 12, where the air 26 may premix with fuel 30 before entering the combustor 22. The air 26 and the fuel 30 are fed to the combustor 22 in a specified ratio suitable for combustion, emissions, fuel consumption, power output, and the like. Unfortunately, if the air 26 and the fuel 30 are not well mixed, the flame stability within the combustor 22 may be reduced. Accordingly, the fuel nozzle 12 includes a flow conditioner within an annular passage of the fuel nozzle 12. The flow conditioner straightens the air 26 (e.g., in the axial direction 14) and improves the mixing of the air 26 and the fuel 30 by providing a uniform distribution of air downstream to the premixing tubes, as will be discussed further below.
The mixture of the air 26 and the fuel 30 is subsequently combusted in the combustor 22, forming hot combustion products. The hot combustion products enter the turbine 24 and force blades 32 of the turbine 24 to rotate, thereby driving a shaft 34 of the gas turbine system 10 into rotation. The rotating shaft 34 provides the energy for the compressor 20 to compress the air 26. For example, in certain embodiments, compressor blades are included as components of the compressor 20. Blades within the compressor 20 may be coupled to the shaft 34, and will rotate as the shaft 34 is driven to rotate by the turbine. In addition, the rotating shaft 34 may rotate a load 36, such as an electrical generator or any device capable of utilizing the mechanical energy of the shaft 34. After the turbine 24 extracts useful work from the combustion products, the combustion products are discharged to an exhaust 38.
As noted previously, the gas turbine system 10 includes one or more fuel nozzles 12 with features to improve uniformity in the air distribution and the mixing of the air 26 and the fuel 30.
The various flow conditioners 46, used independently or in combination with each other, may provide varying degrees of air straightening in the axial direction 14 (i.e., may reduce the swirl of the air 26 by varying amounts or percentages). In certain embodiments, it may be desirable to provide the fuel nozzles 12 with varying amounts of swirl, depending on their placement about the head end 40 of the combustor 22. For example, it may be desirable to straighten air flow within the central fuel nozzle 44 (e.g., upstream of the premixing tubes 70) in order to improve flame stability. Accordingly, the outer fuel nozzles 42 and the central fuel nozzle 44 may be equipped with different flow conditioners 46. That is, in certain embodiments, the central fuel nozzle 44 may include the straightening vanes 48, whereas the outer fuel nozzles 42 include both the mesh screen 50 and the annular segment 52. In yet other embodiments, the central fuel nozzle 44 may include one of the flow conditioners 46, while the outer fuel nozzles lack the flow conditioners 46. Again, the fuel nozzles 12 may employ any combination of the straightening vanes 48, the mesh screen 50, and the annular segment 52 to reduce the swirl of the air 26. It should be noted that when more than one flow conditioner 46 is employed, their ordering may be implementation-specific. For example, although the mesh screen 50 is illustrated as upstream of the annular segment 52, in other embodiments, the mesh screen 50 may be downstream of the annular segment 52. As shown, the mesh screen 50 (e.g., perforated sheet) is a permeable grid of material (e.g., plastic, metal, ceramic, etc.) with small openings 51 that allow fluid to pass through. The openings 51 may vary in size, and may be, for example, between approximately 5 to 50 mm, or 0.1 to 20 mm, and all subranges therebetween. The mesh screen 50 extends crosswise (e.g., circumferentially 18) to the longitudinal axis 17 of a first annular passage 60 defined below. The mesh screen 50 may further axially straighten the air 26 and/or help distribute the air 26 more uniformly across the flow passage.
The geometry of the fuel nozzle 12 is discussed below. As illustrated, the fuel nozzle 12 includes a central hub 53 with an inner wall 54 and a hub wall 56 (e.g., outer wall of the central hub 53). The inner wall 54 defines a central passage 58 (e.g., inner cylindrical passage), and the hub wall 56 defines the first annular passage 60 that surrounds the central passage 58. During operation of the fuel nozzle 12, liquid fuel may be routed through the central passage 58 in the axial direction 14, as shown by arrows 62. The central hub 53 increases the flexibility of the fuel nozzle 12 by enabling liquid fuels to be used in combination with gas fuels for combustion within the combustor 22.
An outer wall 64 surrounds the hub wall 56, defining a second annular passage 66. The second annular passage 66 surrounds both the first annular passage 60 and the central passage 58. During operation of the fuel nozzle 12, the fuel 30 is routed through the second annular passage 66 in the axial direction 14, as shown by arrows 68. The fuel 30 enters premixing tubes 70 in the radial direction 16 through fuel holes or inlets 71 located in a side wall 73 of the premixing tube 70, as indicated by arrows 72. The premixing tubes 70 are circumferentially 18 distributed about the annular passage 60. Air 26, via the first annular passage 60, enters air inlets 75 of the premixing tubes 70 and flows in the axial direction 14 towards outlets 76 (e.g., air-fuel mixture outlets) of the premixing tubes 70. Within the premixing tubes 70, the fuel 30 mixes with the air 26 to form a combustible mixture and is directed into the combustor 22 via the outlets 76.
A shroud 78 (e.g., annular shroud wall) is disposed about the outer wall 64, defining a third annular passage 80. The third annular passage 80 surrounds the second annular passage 66, the first annular passage 60, and the central passage 58. As depicted, the third annular passage 80, the second annular passage 66, the first annular passage 60, and the central passage 58 are concentrically arranged with respect to the longitudinal axis 17 of the fuel nozzle 12. A first portion of the air 26 enters the third annular passage 80 upstream of a swirler 84 and travels in the axial direction 14 toward the outlet 74 of the fuel nozzle 12, as indicated by arrows 82. However, a second portion of the air 26 (e.g., vane curtain air) enters the first annular passage 60 radially 16 through the swirler 84, which includes one or more swirl vanes 86 circumferentially 18 spaced about an axis 17 of the fuel nozzle 12. More specifically, the second portion of the air 26 may enter the first annular passage 60 through the vane curtain air passages 83 disposed within the swirl vanes 86. The fuel 30 may enter the second annular passage 66 and flow through fuel passages 81 disposed within the swirl vanes 86 (upstream of the vane curtain air passages 83) and subsequently injected through fuel holes 79 into the third annular passage 80, where the fuel 30 may mix with the air 26 and enter the combustor.
Once the vane curtain air enters the first annular passage 60, the air 26 passes through one or more flow conditioners 46, as shown by arrows 85. The flow conditioners 46 straighten the flow of the air 26 (e.g., in the axial direction 14) upstream of the premixing tubes 70, which provides a uniform distribution of the air 26 to the premixing tubes 70 and improves fuel/air mixing within the premixing tubes 70 and the overall efficiency of the gas turbine system 10.
As shown, the flow path of the vane curtain air is defined by a flow length or axial distance 87 from the vane curtain air passages 83 of the swirler 84 to an upstream end 89 of the premixing tubes 70. The flow conditioners 46 are disposed along the flow length 87 (between the swirler 84 and the premixing tubes 70) to straighten and uniformly distribute the vane curtain air before it enters the premixing tubes 70. In certain embodiments, the flow conditioners 46 may be disposed within the first air passage 60 directly at the outlet of the swirler 84 or at the inlet of the premixing tubes 70 (see
Returning to
As illustrated, vane curtain air (e.g., air 26) flows radially 16 through the vane curtain air passages 83 of the swirl vanes 86 of the swirler 84, as shown by arrows 88. The air 26 exits the swirler 84 into the first annular passage 60 of the central hub 53. The radial entrance of the air 26 into the first annular passage 60 results in a circumferential velocity about the axis 17 of the fuel nozzle 12, which may decrease the uniform profile of the air across the first annular passage 60 and the premixing tubes 70. The air 26 continues to flow axially 14 and circumferentially 18 about the annular passage 60 until it encounters the straightening vanes 48. When the air 26 encounters the straightening vanes 48, they guide the air 26 along the axial direction 14, thereby reducing the circumferential velocity of the air 26. Accordingly, the shape of the straightening vanes 48 is designed to reduce the circumferential velocity of the air 26, as illustrated by
As depicted in
The presence of the straightening vane 48 straightens the flow of the air 26 within the first annular passage 60 (as indicated by dashed line 102), while reducing the amount of pressure drop (e.g., relative to the pressure drop in the absence of the straightening vane 48) within the first annular passage 60. As the air 26 exits the outlet 90 of the vane curtain air passage 83, it encounters the arcuate portion 96 of the upstream end portion 92 of the straightening vane 48. The arcuate portion 96 gradually or smoothly transitions from the upstream end portion 92 to the downstream portion 94 of the straightening vane 48. This gradual transition may reduce the amount of pressure drop experienced by the air 26 as it enters and flows along the first annular passage 60. Upon encountering the upstream end portion 92 of the straightening vane 48, the air 26 (i.e., dashed line 102) flows downstream along the arcuate portion 96 to the straight portion 98 of the downstream end 94 of the straightening vane 48. The flow of the air 26 (i.e., dashed line 102) results in the gradual straightening of the air flow 26 to flow generally in the axial direction 14.
The straightening vane 48 has an axial length 108 from the upstream end portion 92 to the downstream end portion 94. As noted earlier, the axial length 108 may affect the straightening of the air 26. In general, a longer axial length 108 increases the straightening of the air 26. Thus, in certain embodiments, the axial length 108 may be between approximately 5 to 95, 20 to 80, or 40 to 60 percent, and all subranges therebetween, of the total axial distance 87 along the first annular passage 60 from the vane curtain air passages 83 of the swirler 84 to the upstream end 89 of the premixing tubes 70 (see
As shown, the annular segment 52 extends an axial length 122. In general, a longer axial length 122 provides longer passages or tubes 112, which increases the straightening of the air 26, but also increases pressure drop through the annular segment 52. Accordingly, in certain embodiments, the axial length 122 may be optimized by having a length between approximately 5 to 95, 20 to 80, or 40 to 60 percent, and all subranges therebetween, of the total axial distance 87 along the first annular passage 60 from the vane curtain air passages 83 of the swirler 84 to the upstream end 89 of the premixing tubes 70 (see
Technical effects of the disclosed embodiments include providing the flow conditioners 46 to axially straighten the flow of the air 26 within the first annular passage 60 of the fuel nozzle 12. Straightening the air 26 uniformly distributes the air 26 into the premixing tubes 70, thus improving the mixing of fuel and air within the premixing tubes 70 of the fuel nozzle 12, thereby increasing the efficiency of the gas turbine system 10. The flow conditioner 46 may be the straightening vanes 48, the mesh screen 50, the annular segment 52, or any combination thereof.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
