Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1998-01-28
2001-08-07
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S725000, C060S747000, C060S748000, C431S114000
Reexamination Certificate
active
06269646
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to industrial turbine engines, and more specifically, to combustors therein.
Industrial power generation gas turbine engines include a compressor for compressing air that is mixed with fuel and ignited in a combustor for generating combustion gases. The combustion gases flow to a turbine that extracts energy for driving a shaft to power the compressor and produces output power for powering an electrical generator, for example. The turbine is typically operated for extended periods of time at a relatively high base load for powering the generator to produce electrical power to a utility grid, for example. Exhaust emissions from the combustion gases are therefore a concern and are subjected to mandated limits.
More specifically, industrial gas turbine engines typically include a combustor design for low exhaust emissions operation, and in particular for low NOx operation. Low NOx combustors are typically in the form of a plurality of burner cans circumferentially adjoining each other around the circumference of the engine, each burner can having a plurality of premixers joined to the upstream end.
Lean-premixed low NOx combustors are more susceptible to combustion instability in the combustion chamber as represented by dynamic pressure oscillations in the combustion chamber. The pressure oscillations, if excited, can cause undesirably large acoustic noise and accelerated high cycle fatigue damage to the combustor. The pressure oscillations can occur at various fundamental or predominant resonant frequencies and other higher order harmonics.
Such combustion instabilities may be reduced by introducing asymmetry in the heat release or for example by axially distributing or spreading out the heat release. One current method commonly used to introduce asymmetry for reducing combustion oscillations is to bias fuel to one or more burners generating more local heat release. Although this fuel-biasing method has been shown to reduce combustion instabilities, NOx emissions are substantially increased by the higher temperatures generated. Distributing the flame axially has been accomplished by physically offsetting one or more fuel injectors within the combustion chamber. A drawback to this offset approach, however, is that the extended surface associated with the downstream injectors must be actively cooled to be protected from the upstream flame. This additional cooling air has a corresponding NOx emissions penalty for the system.
Therefore, it is apparent from the above that there is a need in the art for improvements in combustor dynamics.
SUMMARY OF THE INVENTION
A combustor comprises an outer combustor casing defining a plurality of circumferentially adjoining combustion chambers. Each combustion chamber comprises a dome at an upstream end and an outlet at a downstream end. A plurality of pre-mixers are joined to the combustor dome of each respective combustion chamber. The pre-mixers comprise a duct having an inlet at one end for receiving compressed air, an outlet at an opposite end disposed in flow communication with the combustion chamber and a swirler disposed in the duct adjacent the duct inlet for swirling air channeled therethrough. A fuel injector is provided for injecting fuel into the pre-mixer ducts for mixing with the air in the ducts for flow into the combustion chamber to generate a combustion flame at the duct outlets. A portion of the pre-mixers comprise an altered flameholding capability so as to distribute the resulting combustion flames from the respective portion of the pre-mixers axially downstream with respect to the non-altered pre-mixers so as to reduce the dynamic pressure amplitude of the combustion flames.
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Gulati Anil
Kuwata Masayoshi
Lovett Jeffery Allan
General Electric Company
Ingraham Donald S.
Kim Ted
Patnode Patrick K.
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