Patent Application
20130125553
The invention relates to gas turbines and, more particularly, to a swirler assembly in a gas turbine combustor including an air circuit in the swirler vanes that directs compressor discharge air to a low pressure side of the swirler vanes.
In a gas turbine combustor, compressed air from the compressor and fuel are mixed upstream of a combustion zone. A swirler assembly includes circumferentially spaced apart vanes for swirling and mixing the compressed air flow and the fuel passing therethrough.
The swirler assemblies, also described as swozzle assemblies, may have flame holding margins limited by flow deficits on a suction side of the vane turning region. This reduced flame holding margin and locally enriched air/fuel regions reduce the performance of the combustor.
In an exemplary embodiment, a swirler assembly in a gas turbine combustor includes a hub, a shroud, and a plurality of vanes connected between the hub and the shroud. The vanes include a high pressure side on which air and fuel impinge the vanes and a low pressure side. An air circuit is provided in each of the plurality of vanes receiving discharge air from a compressor. Each of the air circuits includes an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes.
In another exemplary embodiment, a gas turbine includes a compressor that progressively compresses a working fluid such as air, a combustor injecting fuel into the compressed air and igniting the air and fuel to produce combustion gases, and a turbine using the combustion gases to produce work. The combustor includes a swirler assembly that imparts swirl to the air and the fuel. The swirler assembly comprises a hub, a shroud, a plurality of vanes connected between the hub and the shroud, and an air circuit in each of the plurality of vanes. The air and fuel impinge the vanes on a high pressure side. The air circuit in each of the plurality of vanes receives discharge air from the compressor, where each of the air circuits includes an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes.
In yet another exemplary embodiment, a method of mixing fuel and air in a swirler assembly includes the steps of providing an air circuit in each of the plurality of vanes, each of the air circuits including an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes; and directing airflow from a compressor to the air entry passage into the vanes and through the air exit passage on the low pressure side of the vanes.
A casing surrounds each combustor 14 to contain the compressed working fluid from the compressor 12. Nozzles are arranged in an end cover, for example, with outer nozzles radially arranged around a center nozzle. The compressed working fluid from the compressor 12 flows between the casing and a liner to the outer and center nozzles, which mix fuel with the compressed working fluid, and the mixture flows from the outer and center nozzles into upstream and downstream chambers where combustion occurs.
Air enters the burner from a high pressure plenum 6, which surrounds the entire assembly except the discharge end, which enters the combustor reaction zone 5. Most of the air for combustion enters the premixer via the inlet flow conditioner (IFC) 1. The IFC includes an annular flow passage 15 that is bounded by a solid cylindrical inner wall 13 at the inside diameter, a perforated cylindrical outer wall 12 at the outside diameter, and a perforated end cap 11 at the upstream end. In the center of the flow passage 15 is one or more annular turning vanes 14. Premixer air enters the IFC 1 via the perforations in the end cap and cylindrical outer wall.
The perforated walls 11, 12 perform the function of backpressuring the system and evenly distributing the flow circumferentially around the IFC annulus 15, whereas the turning vane(s) 14, work in conjunction with the perforated walls to produce proper radial distribution of incoming air in the IFC annulus 15.
To eliminate low velocity regions near the shroud wall 202 at the inlet to the swozzle 2, a bell-mouth shaped transition 26 may be used between the IFC and the swozzle.
After combustion air exits the IFC 1, it enters the swozzle assembly 2. The swozzle assembly includes a hub 201 and a shroud 202 connected by a series of air foil shaped turning vanes 23, which impart swirl to the combustion air passing through the premixer (see
In some existing swirler assembly designs, the vanes 23 include a cap feed channel 233 and a corresponding opening 234 in the shroud 202. Compressor discharge air is fed to the cap feed channel 233 through the vane 23 and hub 201 of the swirler assembly then out through the nozzle tip to provide for nozzle tip cooling.
An air circuit is provided in each of the plurality of vanes 23. The air circuit receives discharge air from the compressor. Each of the air circuits includes an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes. In one embodiment, the air entry passage of the air circuit is defined by the cap feed 233. The exit passage comprises holes 235 in the low pressure side 232 of the vane that extend into the cap feed 233. In this embodiment, a portion of the compressor discharge air in the cap feed 233 is diverted through the exit passage 235 to the low pressure side of the vanes 23.
In an alternative embodiment, a dedicated passage 236 through the vane 23 is provided for the air circuit, which passage 236 is separate from the cap feed passage 233. In this embodiment, the air exit passage includes the holes 235 on the low pressure side of the vanes 23. The holes 235 in this embodiment extend into the dedicated passage 236 through which compressor discharge air is directed. In this embodiment, a corresponding hole 237 is provided in the shroud 202.
Preferably, the compressor discharge air is received directly from the compressor. Swirler vane low pressure injection air can be provided from either the compressor discharge or from an alternate pressure feed source. The compressor discharge feed can be taken at any point along the compressor discharge path up to the annular section feeding the combustor head end. Compressor discharge air taken directly from the exit of the compressor will be at a higher pressure (as compared to the combustor head end pressure) which may benefit swirler vane low pressure injection by creating a greater pressure differential on the suction flow deficit region of the vane. An alternate pressure feed may also be utilized to further enhance the flow/pressure differential on the vane suction side injection.
The swirler assembly 2 enables higher pressure clean compressor discharge air to be injected along either the pressure or suction side of the swozzle vane to improve fuel mixing locally. Injecting compressor discharge air along the vane edge can add needed air to low flow regions of the swozzle vane thus increasing flame holding margin, improving fuel mixing, and improving operability and flame stability by reducing local rich fuel pockets. Injection air can be supplied from the compressor discharge either adjacent the compressor exit (highest pressure available) or along the compressor feed circuit up to the annular feed leading to the combustor head end (lowest pressure differential). An alternate air pressure feed could also be utilized from an auxiliary compressor at a further elevated pressure and/or lower temperature. The air injection can occur on the vane suction side and/or vane pressure side and include an upstream air curtain to shroud the vane surface with higher pressure and/or lower temperature air to further facilitate fuel mixing and pressure deficit elimination.
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.
