Patent Application
20130199188
Embodiments of the present application relate generally to gas turbine engines and more particularly to combustor assemblies including a trapped vortex cavity.
Gas turbine efficiency generally increases with the temperature of the combustion gas stream. Higher combustion gas stream temperatures, however, may produce higher levels of undesirable emissions such as nitrogen oxides (NOx) and the like. NOx emissions generally are subject to governmental regulations. Improved gas turbine efficiency therefore must be balanced with compliance with emissions regulations.
Lower NOx emission levels may be achieved by providing for good mixing of the fuel stream and the air stream. For example, the fuel stream and the air stream may be premixed in a Dry Low NOx (DLN) combustor before being admitted to a reaction or a combustion zone. Such premixing tends to reduce combustion temperatures and NOx emissions output.
The fuel stream and the air stream are generally premixed in tightly packed bundles of air/fuel premixing tubes to form axial jets in the combustion chamber. The tightly packed bundles of air/fuel premixed axial jets may suffer from blowoff or instability at low-load or part-speed conditions. Accordingly, what is needed is a system that provides reliable, robust ignition and cross-firing, more efficient part-speed and non-loaded operation, and overall improved combustion stability and increased operability when using a DLN combustor having micromixer air/fuel premixing tube bundles.
Some or all of the above needs and/or problems may be addressed by certain embodiments of the present application. According to one embodiment, there is disclosed a combustor assembly. The combustor assembly may include an annular trapped vortex cavity located adjacent to a downstream end of a bundle of air/fuel premixing injection tubes. The annular trapped vortex cavity may include an opening at a radially inner portion of the annular trapped vortex cavity adjacent to the head end of the bundle of premixing tubes. The annular trapped vortex cavity may also include one or more air injection holes and one or more fuel sources disposed about the annular trapped vortex cavity such that the one or more air injection holes and the one or more fuel sources are configured to drive a vortex within the annular trapped vortex cavity.
According to another embodiment, there is disclosed a combustor assembly. The combustor assembly may include a bundle of air/fuel premixing injection tubes having an upstream end, a downstream end, and a flow path therebetween. An annular trapped vortex cavity may be located adjacent to the downstream end of the air/fuel premixing injection tubes. The annular trapped vortex cavity may include an annular aft wall, an annular forward wall, and an annular radially outer wall formed therebetween. The annular trapped vortex cavity may also include an opening at a radially inner portion of the annular trapped vortex cavity spaced apart from the outer wall and extending between the aft wall and the forward wall. One or more air injection holes and one or more fuel sources may be disposed about the annular trapped vortex cavity such that the one or more air injection holes and the one or more fuel sources are configured to drive a vortex within the annular trapped vortex cavity.
Further, according to another embodiment, there is disclosed a combustor assembly. The combustor assembly may include a bundle of air/fuel premixing injection tubes having an upstream end, a downstream end, and a flow path therebetween. An annular trapped vortex cavity may be located adjacent to the downstream end of the air/fuel premixing injection tubes. The annular trapped vortex cavity may include an annular aft wall, an annular forward wall, and an annular radially outer wall formed therebetween. The annular trapped vortex cavity may also include an opening at a radially inner portion of the annular trapped vortex cavity spaced apart from the outer wall and extending between the aft wall and the forward wall. One or more air injection holes and one or more fuel sources may be disposed about the annular trapped vortex cavity such that the one or more air injection holes and the one or more fuel sources are configured to drive a vortex within the annular trapped vortex cavity. Moreover, the combustor assembly may include a combustion chamber surrounded by an annular combustor liner disposed in air flow communication with the bundle of premixing tubes, the annular trapped vortex cavity, the one or more air injection holes, and the one or more fuel sources.
Other embodiments, aspects, and features of the invention will become apparent to those skilled in the art from the following detailed description, the accompanying drawings, and the appended claims.
Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Illustrative embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. The present application may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout.
Illustrative embodiments are directed to, among other things, a combustor assembly including a trapped vortex cavity.
The gas turbine engine 10 may use natural gas, various types of syngas, and/or other types of fuels. The gas turbine engine 10 may be any one of a number of different gas turbine engines offered by General Electric Company of Schenectady, N.Y., including, but not limited to, those such as a 7 or a 9 series heavy duty gas turbine engine and the like. The gas turbine engine 10 may have different configurations and may use other types of components.
Other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together.
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In certain embodiments, the annular trapped vortex cavity 116 may be in communication with a crossfire tube 136. The crossfire 136 tube may provide an ignition source to the annular trapped vortex cavity 116. The crossfire 136 tube may be in communication with one or more annular trapped vortex cavities within the combustor. In other embodiments, the annular trapped vortex cavity 116 may be in communication with an igniter 138. In yet other embodiments, the annular trapped vortex cavity 116 may be in communication with both the crossfire 136 tube and the igniter 138.
In certain embodiments, the fuel sources 128 may include a liquid fuel injector 140. For example, as depicted in
In operation, air enters the combustor assembly via the air flow path 114 formed between the annular combustion liner 112 and the flow sleeve 113. A portion of the air is directed into the bundle of air/fuel premixing injection tubes 102 where it is mixed with a fuel. A portion of the air is also directed into the air injection holes 126 where it drives a vortex 130 in the annular trapped vortex cavity 116. Moreover, a portion of the air is directed into the air/fuel premixing injection tubes 134 and 136 where it is mixed with a fuel within the tube before entering the annular trapped vortex cavity 116 to further drive the vortex 130. As discussed above, the vortex 130 may rotate in a co- or counter-rotation with regard to the air/fuel jet exiting the bundle of air/fuel premixing injection tubes 102 into the combustion chamber 110. In some embodiments, the annular trapped vortex cavity 116 may further include a liquid fuel injector 140, a crossfire tube 136, and/or an igniter 138.
The annular trapped vortex cavity uses a portion of the overall combustion air and a portion of the overall combustion fuel (liquid or gas) to drive a trapped toroidal vortex having co- or counter-rotation with respect to the bundle of air/fuel premixing tubes jet flow path. The annular trapped vortex cavity acts as an annular pilot for the bundle of air/fuel premixing tubes combustion by supplying a stable source of fresh, hot combustion products and radicals to the bundle of air/fuel premixing tubes jet flames. As the annular trapped vortex cavity is a pilot zone, a relatively small amount of the total combustor fuel and air is used, e.g., 10% during operation.
The fuel and air enters the cavity via the micromixer premixing injector jets to drive the vortex. The gas-fuel reactants are premixed and injected as micromixer tubes, or, for the liquid fuel case, injected separately making a diffusion burning zone. The annular trapped vortex cavity reactants can be burned in a lean, rich, or neutral mode (relative to the main bundle of air/fuel premixing tube combustion zone. A lean mode may be used to produce less NOx emission and less stability at loaded conditions. A rich, or neutral mode, may provide greater stability for the main combustion at non- or low-load conditions. The annular trapped vortex cavity also acts as an ignition and/or cross-fire zone for starting the combustor on gas or liquid fuel.
Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the embodiments.
