Patent Application
20110225973
The present application generally relates to a combustor for a gas turbine, and more particularly relates to a two-stage low NOx combustor with a pre-mixing primary fuel-nozzle assembly.
Low NOx combustors for gas turbines are known in the industry. For example, U.S. Pat. No. 4,292,801 describes a “Dual Stage-Dual Mode Low NOx Combustor” that creates reduced amounts of nitrogen oxide (NOx) during the combustion process.
On an upstream end, the combustor 100 is enclosed by an end cover 108. The end cover 108 supports a number of fuel nozzles that can communicate fuel into the chambers. More specifically, a number of primary fuel nozzles 110 provide fuel to the first chamber 102 and a secondary fuel nozzle 112 provides fuel to the second chamber 104. The primary fuel nozzles 110 are usually positioned in a circular array about the secondary fuel nozzle 112, which is centrally positioned and extends axially through the first chamber 102 toward the second chamber 104.
So that air can enter the combustion chambers 102, 104, a flow sleeve 114 is positioned about the combustion liner 106. The flow sleeve 114 and combustion liner 106 together define an annular air passageway 116 that is in communication with the compressor. Air from the compressor flows through the annular passageway 116 and enters the combustion chambers 102, 104 through an annular gap 118 between the combustion liner 106 and the end cover 108.
In operation, fuel is selectively introduced through the primary and secondary fuel nozzles 110, 112 to initiate and terminate combustion in one or both of the combustion chambers 102, 104 in a manner that generates reduced NOx emissions. In particular, the combustor 100 can be operated in a diffusion mode or in a pre-mixing mode. In the diffusion mode, fuel is introduced through the primary fuel nozzles 110 and combustion occurs in the first chamber 102. In the pre-mixing mode, fuel is introduced through both the primary and secondary fuel nozzles 110, 112, but combustion occurs only in the second chamber 104. The first chamber 102 serves as a pre-mixing zone where air and fuel are pre-mixed to form an air-fuel mixture, and the second chamber 104 serves as the combustion chamber where the air-fuel mixture is burned to generate hot combustion products. It is well known that combusting an air-fuel mixture that has been pre-mixed generates relatively lower NOx emissions. Therefore, the combustor 100 is typically operated in pre-mixing mode during steady-state operation, while diffusion mode is used in transition to steady state or when reduced output is needed.
One matter with the combustor 100 is that the primary fuel nozzle 110 is not a true pre-mixing nozzle. Instead, the primary nozzle 110 is essentially a fuel peg surrounded at a distal end by a separate air swirler. The air swirler swirls air about the fuel peg just upstream of its distal end, which injects into the air stream. Thus, the primary fuel nozzle 110 is typically considered to be a diffusion nozzle.
Another matter with the combustor 100 is that only a portion of the air that enters the first chamber 102 passes through the annular gap 118 and enters the air swirler. The majority of the air that enters the first chamber 102 passes through mixing holes formed directly in the combustion liner 106. The result is that very little pre-mixing can occur at the nozzle level in diffusion mode, and less pre-mixing may occur in pre-mixing mode than what could occur with better first stage mixing.
One type of known pre-mixing nozzle is a swirling annular fuel nozzle or “swozzle,” which typically includes a number of vanes extending between an inner hub and an outer shroud. The vanes are circumferentially spaced apart and include fuel injection openings. The fuel injection openings receive fuel through fuel passages that extend radially outward from fuel entry openings in the inner hub. In operation, air traveling axially through the swozzle is swirled by the vanes and fuel traveling radially through the swozzle is injected into the swirling air flow. Such a nozzle improves mixing but is typically used in a single stage combustor.
A combustor includes a first combustion chamber, a pre-mixing primary fuel-nozzle assembly associated with the first combustion chamber, a second combustion chamber, and a secondary fuel-nozzle assembly associated with the second combustion chamber. The pre-mixing primary fuel-nozzle assembly includes a number of vanes configured to swirl airflow, each vane comprising a number of fuel injection holes configured to inject fuel into the airflow.
In another aspect of the invention, a pre-mixing primary fuel-nozzle assembly includes an inner annular collar, a number of vanes, and a plurality of fuel injection holes formed in each vane. The vanes extend radially outward from the inner annular collar. The inner annular collar also may include a number of air passage openings.
In yet another aspect of the invention, a combustor includes a first combustion chamber associated with a pre-mixing primary fuel-nozzle assembly and a second combustion chamber associated with a secondary fuel-nozzle assembly. The pre-mixing primary fuel-nozzle assembly is concentrically positioned about the secondary fuel-nozzle assembly.
Other systems, devices, methods, features, and advantages of the disclosed systems and methods will be apparent or will become apparent to one with skill in the art upon examination of the following figures and detailed description. All such additional systems, devices, methods, features, and advantages are intended to be included within the description and are intended to be protected by the accompanying claims.
The present disclosure may be better understood with reference to the following figures. Matching reference numerals designate corresponding parts throughout the figures, and components in the figures are not necessarily to scale.
Described below are embodiments of two-stage combustor configured for increased primary zone pre-mixing. Also described are embodiments of a pre-mixing primary fuel-nozzle assembly.
Fuel can reach the chambers 202, 204 through fuel nozzles 210, 212. In particular, the combustor 200 includes a secondary fuel-nozzle assembly 212 that is supported by the end cover 208 and extends through the first chamber 202 toward the second chamber 204. The secondary fuel-nozzle assembly 212 may be an embodiment of a secondary fuel nozzle that is now known or is later developed. Because such fuel nozzles are known, further description is omitted here.
The combustor 200 also includes a pre-mixing primary fuel-nozzle assembly 210, which extends into the first chamber 202. The pre-mixing primary fuel-nozzle assembly 210 is supported by the end cover 208 on a rearward side and extends to the combustion liner 206 on a forward side. Thus, the pre-mixing primary fuel-nozzle assembly 210 may be positioned in the annular gap 218, substantially enclosing the annular gap, so that substantially all of the air entering the annular gap 218 from the annular passageway 216 flows through the pre-mixing primary fuel-nozzle assembly 210 before traveling into the combustion chambers 202, 204. Unlike the primary fuel nozzles 110 of
The pre-mixing primary fuel-nozzle assembly 210 is configured for increased primary zone pre-mixing. In particular, the pre-mixing primary fuel-nozzle assembly 210 is generally a “swozzle” or air-swirling fuel nozzle that both swirls incoming air and injects fuel into the air to achieve a relatively uniform air-fuel mixture. Thus, the pre-mixing primary fuel-nozzle assembly 210 achieves improved pre-mixing in the primary zone, which reduces NOx emissions, and imparts swirl or circumferential velocity to the flow, improving flame stability downstream.
The pre-mixing primary fuel-nozzle assembly 210 is further described with reference to
In the illustrated embodiment, the assembly body 220 includes an inner annular hub 228 that supports the vanes 222, which are positioned about the hub 228 in an annular array, extending radially outward. The vanes 222 are spaced apart from each other and are open about an outer annular periphery. Between the vanes 222, the air passage openings 226 are formed through the hub 228. In other words, the vanes 222 and the openings 226 are circumferentially interleaved about the assembly 210.
Each vane 222 includes a fuel passage portion and an air foil portion. The fuel passage portion is positioned adjacent to the end cover 208 while the air foil portion extends away from the fuel passage portion in an axial direction. The fuel injection holes 224 are formed through the air foil portion, such as through one or both of a pressure side and a suction sides of the air foil portion.
With reference back to
When so positioned, fuel travels axially through the end cover 208 into the assembly 210 and air travels radially through the annular gap 218 into the assembly 210. The assembly 210 swirls the air and injects fuel into the swirling air stream. Such a configuration and flow path differs from known “swozzle”-type fuel nozzles, which typically receive fuel in a radial direction and air in an axial direction. Further, such a configuration and flow path differs from known swozzle-type fuel nozzles in that substantially all of the air entering the secondary fuel-nozzles assembly 212 travels through the pre-mixing primary fuel-nozzle assembly 210 and is swirled by the vanes 226.
To direct fuel into the pre-mixing primary fuel-nozzle assembly 210, the end cover 208 includes at least two fuel manifolds 238, and each fuel manifold 238 is in fluid communication with at least one vane 222. Thus, each vane 222 can receive fuel into its fuel passageway from at least one of the fuel manifolds 238. At some point upstream of the end cover 208, each fuel manifold 238 is also associated with a valve assembly 240, which is operable to permit or prevent the flow of fuel into the fuel manifold 238, thereby permitting or preventing the flow of fuel into the associated vanes 222. The valve assemblies 240 may be controlled by a controller 242, which is operable to regulate fuel flow into the fuel manifolds 238 by controlling the valve assemblies 240. Such a configuration facilitates varying the amount of fuel that is injected into the swirling air flow through the pre-mixing primary fuel-nozzle assembly 210. For example, a sub-set of the vanes 222 may be fueled when the combustor 200 is in diffusion mode, and all of the vanes 222 when the combustor 200 is in a pre-mixing mode.
In the illustrated embodiment, the end cover 208 includes two distinct fuel manifolds 238A and 238B. Each fuel manifold 238A, 238B is in fluid communication with a distinct sub-set of the vanes 222, and each vane 222 is in fluid communication with exactly one of the fuel manifolds 238A, 238B. In particular, the illustrated fuel-nozzle assembly 210 includes fifteen vanes 222, five of the vanes 222 are fueled by the first fuel manifold 238A, and the other ten vanes 222 are fueled by the second fuel manifold 238B. The vanes 222 that are fueled by the first fuel manifold 238A are evenly spaced about the assembly 210, meaning that every third vane 222 is fueled by the first fuel manifold 238A while the remaining vanes 222 are fueled by the second fuel manifold 238B. Such spacing evenly distributes fuel throughout the air-fuel mixture.
Continuing with the illustrated embodiment, the first fuel manifold 238A is associated with a first valve assembly 240A, and the second fuel manifold 238B is associated with a second valve assembly 240B. The valve assemblies 240A, 240B can be controlled, such as via the controller 242, to control the flow of fuel into the vanes 222. For example, fuel can be directed into the first fuel manifold 238A to fuel the five interspaced vanes 222 but not the remaining ten vanes 222. Fuel also can be directed into both fuel manifolds 238A, 238B to fuel all fifteen vanes 222.
A range of other configurations are also envisioned within the scope of the present disclosure. For example, any number of vanes 222 may be positioned about the fuel-nozzle assembly 210, the end cover 208 may have any number of fuel manifolds 238, and the fuel manifolds 238 may communicate fuel into any number or combination of the vanes 222. For example, in one embodiment the first fuel manifold 238A is in fluid communication with a sub-set of the vanes 222 and the second fuel manifold 238B is in fluid communication with all of the vanes 222. Thus, the sub-set of vanes 222 can be fueled by directing fuel into the first fuel manifold 238A and all of the vanes 222 can be fueled by directing fuel into the second fuel manifold 238B. With such a configuration, however, those vanes 222 that are in communication with both fuel manifolds 238 may experience cross-talk between the fuel manifolds 238, wherein fuel from one fuel manifold travels rearward into the other fuel manifold instead of exiting the fuel injection holes 224 into the swirling air flow. Such cross-talk between the fuel manifolds 238 can be eliminated by fueling each vane 222 with only one fuel manifold 238 as described above.
In operation, air from the compressor is driven by a pressure differential along the annular passageway 216 and into the annular gap 218. Substantially all of the air traveling through the annular gap 218 is directed into the pre-mixing primary fuel-nozzle assembly 210. In embodiments in which the combustion liner 206 is substantially continuous about the first chamber 202, substantially all of the head end air passes through the pre-mixing primary fuel-nozzle assembly 210.
The air travels radially inward between the vanes 222, which swirl the air flow, and fuel is injected through the fuel injection holes 224 into the swirling air flow, creating an air-fuel mixture. A portion of the air-fuel mixture turns and travels axially through the assembly 210 into the first chamber 202, while another portion of the air travels radially through the openings 226, turns, and travels axially through the secondary fuel-nozzle assembly 212 into the second chamber 204. Such a configuration differs from the combustor 100, wherein any one of the primary fuel nozzles 110 interacts with only a portion of the air in the first chamber 202 and none of the air in the second chamber 204. Such a configuration also differs from the combustor 100 because all of the primary zone air, and potentially all of the head-end air, is pre-mixed in the pre-mixing primary fuel-nozzle assembly 210.
Some or all of the vanes 222 may be fueled depending on the operating mode. For example, fuel may be provided to only one of the fuel manifolds 238 to fuel a distinct sub-set of the vanes 222, or fuel may be provided to both of the fuel manifolds 238A, 238B to fuel all of the vanes 222. In the illustrated embodiment, five of the vanes 222 may be fueled in one mode while all fifteen vanes 222 may be fueled in another mode. The flow of fuel into the vanes 222 is controlled by the controller 242, which operates the valves assemblies 240A, 240B to permit or prevent the flow of fuel into the fuel manifolds 238 and therefore the vanes 222.
The combustor 200 may be operated in a diffusion mode, wherein combustion occurs in the first chamber 202, and in a pre-mixing mode wherein the first chamber 202 serving as a pre-mixing zone and the second chamber 204 serves as the combustion zone. Like prior combustors, the diffusion mode is used in transition to the pre-mixing mode or in times when a reduced output is desired, while the pre-mixing mode is used during steady-state operation or when increased output is desired. Unlike prior combustors, however, the pre-mixing primary fuel-nozzle assembly 210 performs vane-level pre-mixing in the primary zone during both modes. Substantially all of the primary-zone air, and in some cases substantially all of the air entering the combustor, is pre-mixed at the vane level in the primary zone. The improved vane-level pre-mixing in the primary zone leads to lowers NOx emissions, especially in the pre-mixing mode. (Lower NOx emissions in diffusion mode also may be realized, although the mixing length may be too short due to the proximity of the flame to the pre-mixing primary fuel-nozzle assembly 210). The pre-mixing primary fuel-nozzle assembly 210 imparts swirl or circumferential velocity to the flow, improving flame stability. Thus, the flow is more uniform and yet is stable. Substantially all of all of the primary-zone air, and in some cases substantially all of the air entering the combustor, passes through the pre-mixing primary fuel-nozzle assembly 210 and therefore substantially all of the air is swirled. The increased swirl enables the swirl to propagate farther downstream than with conventional systems that swirl only a portion of the air, improving flame stability. Thereby, less fuel may be burned and emissions may be improved.
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.
