System and method for reducing modal coupling of combustion dynamics

Abstract

A system for reducing modal coupling of combustion dynamics includes a plurality of combustors, and at least one fuel injector in each of the plurality of combustors. The system also includes structure for dithering a combustion instability frequency in at least one combustor in the plurality of combustors. A method for reducing modal coupling of combustion dynamics includes flowing a compressed working fluid at a temperature to a plurality of combustors and flowing a fuel to at least one fuel injector in each of the plurality of combustors. The method further includes dithering at least one of the temperature of the compressed working fluid flowing to the plurality of combustors or the fuel flow to the at least one fuel injector in at least one combustor in the plurality of combustors.

Description

FIELD OF THE INVENTION[0001]The present invention generally involves a system and method for reducing modal coupling of combustion dynamics. In particular embodiments, the system and method may be incorporated into a gas turbine or other turbomachine.BACKGROUND OF THE INVENTION[0002]Combustors are commonly used in industrial and commercial operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, gas turbines and other turbomachines typically include one or more combustors to generate power or thrust. A typical gas turbine used to generate electrical power includes an axial compressor at the front, multiple combustors around the middle, and a turbine at the rear. Ambient air enters the compressor as a working fluid, and the compressor progressively imparts kinetic energy to the working fluid to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or mor...

AI Technical Summary

Benefits of technology

[0009]The present invention may also include a method for reducing modal coupling of combustion dynamics that includes flowing a compressed working fluid at a temperature to a plurality of combustors and flowing a fuel to at least one fuel injector in each of the plurality of combustors. The method further includes dithering at least one of the temperature of the compressed working fluid flowing to the plurality of combustors or the fuel flow to the at least one fuel injector in at least one combustor in the plurality of combustors.

Problems solved by technology

However, higher combustion gas temperatures also promote flame holding conditions in which the combustion flame migrates toward the fuel being supplied by the fuel injectors, possibly causing accelerated wear to the fuel injectors in a relatively short amount of time.

Conversely, a lower combustion gas temperature associated with reduced fuel flow and / or part load operation (turndown) generally reduces the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons.

At particular operating conditions, combustion dynamics at specific frequencies and with sufficient amplitudes, which are in-phase and coherent, may produce undesirable sympathetic vibrations in the turbine and / or other downstream components.

Typically, this problem is managed by combustor tuning Combustor tuning to protect the turbine buckets, however, may impose severe restrictions on the function and operability of the combustor.

Altering the frequency relationship between two or more combustors may reduce the coherence of the combustion system as a whole, diminishing any combustor-to-combustor coupling.

As the combustion dynamics frequency in one combustor is driven away from that of the other combustors, modal coupling of combustion dynamics is reduced, which, in turn, reduces the ability of the combustor tone to cause a vibratory response in downstream components.

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