Patent Application
20050056022
This application relates generally to gas turbine engines and, more particularly, to gas turbine combustors.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial gas turbines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures which do not allow completion of the fuel-air reaction (HC & CO).
At least some known gas turbine combustors include a plurality of mixers, which mix high velocity air with liquid or gaseous fuels prior to the mixture being ignited. Such mixers usually include a single fuel injector located at a center of a swirler which swirls incoming air to facilitate enhancing flame stabilization and mixing. Both the fuel injector and mixer are coupled to a combustor dome.
At least some known gas turbine engine combustors operate with a fuel to air ratio in the mixer that is fuel-rich, wherein additional air is added through discrete dilution holes prior to the combustion gases exiting the combustor. However, poor mixing and hot spots may occur both at the dome, where the injected fuel must vaporize and mix prior to burning, and in the vicinity of the dilution holes, wherein additional air is added to the rich dome mixture. Other known gas turbine engines use dry-low-emissions (DLE) combustors that create fuel-lean mixtures in the mixer. Because the fuel-air mixture throughout the combustor is lean, DLE combustors typically do not have dilution holes.
In operation, combustion acoustics may limit the operational range of lean premixed gas turbine combustors. To facilitate reducing combustion acoustics, at least some known gas turbine engines utilize mismatched flame temperatures. However, mismatching the flame temperatures may result in increasing NOx emissions. Other known gas turbine engines use a variety of passive means to facilitate reducing the amplitude of the combustion acoustics. For example, at least one known gas turbine engine uses a plurality of quarter-wave acoustic damper tubes to reduce combustor acoustics. Quarter-wave damper tubes operate over a relatively narrow band of frequencies, and are fabricated in a plurality of lengths. To determine the optimum length of a damper tube, a time consuming process may be required. The process includes coupling a damper tube having a predetermined length to the gas turbine, and measuring the resultant combustor acoustics. The process must generally be repeated until the optimal damper tube length has been identified.
In one aspect, a method for operating a gas turbine engine is provided. The method includes coupling an anti-resonant frequency system to a combustor including a premixer assembly and a plurality of damper tubes, and adjusting the anti-resonant frequency system until the anti-resonant frequency of the damper tubes is approximately equal to a resonant frequency of the combustor.
In another aspect, a combustor system for a gas turbine engine is provided. The combustor system includes a premixer assembly, a plurality of damper tubes, and an anti-resonant frequency system coupled to the plurality of damper tubes. The anti-resonant frequency system is configured to adjust the anti-resonant frequency of the damper tubes until the anti-resonant frequency of the damper tubes is approximately equal to a resonant frequency of the combustor.
In a further aspect, a gas turbine engine including a compressor, a turbine coupled in flow communication with the compressor, and a combustor system between the compressor and the turbine is provided. The combustor system includes a premixer assembly, a plurality of damper tubes, and an anti-resonant frequency system coupled to the plurality of damper tubes. The anti-resonant frequency system is configured to adjust the anti-resonant frequency of the damper tubes until the anti-resonant frequency of the damper tubes is approximately equal to a resonant frequency of the combustor.
In operation, air flows through low pressure compressor 12 and compressed air is supplied from low pressure compressor 12 to high pressure compressor 14. The highly compressed air is delivered to combustor 16. Airflow (not shown in
Damper tubes 38 have a central frequency in which damper tubes 38 are effective. The central frequency of damper tubes 38 is based on a length 114 of damper tube 38 and an acoustic velocity of the air contained within damper tubes 38. Accordingly, damper tubes 38 are designed in accordance with:
where:
In operation, gas turbine engine 10 is started and a quantity of air is discharged from combustor 16 through damper tubes 38, extension tubes 104, and into manifold 102. Bleed valve 112 is then adjusted, i.e. opened or closed, to release air from manifold 102 to atmosphere such until the anti-resonant frequency of damper tubes 38 is approximately equivalent to the combustor resonant frequency.
In one embodiment, electrical heating elements 206 are wrapped around an outer surface of damper tubes 38 to facilitate adjusting an air temperature within damper tubes 38. In another embodiment, electrical heating elements 206 are positioned within damper tubes 38 to facilitate adjusting the air temperature within damper tubes 38
As described previously herein, damper tubes 38 have a central frequency in which damper tubes 38 are effective. The central frequency of damper tubes 38 is based on a length 114 of damper tube 38 and an acoustic velocity of air within damper tubes 38. Accordingly, damper tubes 38 are designed in accordance with:
where:
In operation, power supply 204 is energized and an electrical current is passed through electrical cable 202 to each heating element 206. Power supply 204 is then adjusted, i.e. power is increased or decreased, such until the anti-resonant frequency of damper tubes 38 is approximately equivalent to the combustor resonant frequency.
The systems described herein facilitate stable operation of the gas turbine combustor. By actively tuning the anti-resonant frequency of the damper tubes to match the combustor resonant frequency, the performance of the damper tubes can be improved over the current design, and the number of tubes and the number of different lengths of tubes could potentially be reduced.
Exemplary embodiments of an combustor anti-resonant frequency system are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. Each combustor anti-resonant frequency component can also be used in combination with other combustor anti-resonant frequency components.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
