Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-10-06
2001-03-27
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S725000, C431S114000
Reexamination Certificate
active
06205765
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to apparatus and methods for active control of dynamic pressure oscillations in a gas turbine combustion system. More particularly, the invention relates to using active feedback and control drivers to reduce combustion dynamics in an industrial gas turbine combustion system with single or multiple chambers which are linked to each other through their fuel systems and common air supply.
High dynamics can limit hardware life and/or system operability. Thus, there have been various attempts to control combustion dynamics, to prevent degradation of system performance. There are two basic methods for controlling combustion dynamics in an industrial gas turbine combustion system: passive control and active control. As the name suggests, passive control refers to a system that incorporates certain design features and characteristics to reduce dynamic pressure oscillations. Active control, on the other hand, incorporates a sensor to detect, e.g., pressure fluctuations and to provide a feedback signal which, when suitably processed by a controller, provides an input signal to a control device. The control device in turn operates to reduce the dynamic pressure oscillations.
An effective method for passive control of pressure oscillations in industrial gas turbine combustors is disclosed in U.S. Pat. No. 5,211,004, the entire disclosure of which is incorporated herein by this reference. The '004 patent describes a fuel supply system having a fuel passage with an upstream orifice, a downstream discharge orifice and a captured response volume defined between the orifices. The upstream orifice has a high-pressure drop for performing the function of isolating the fuel system from the premix zone and providing uniform fuel distribution. Moreover, the upstream orifice provides a pressure drop such that in the pressure in the captured response volume approximates the pressure of the compressor discharge air. The downstream orifice provides a low pressure drop from the captured response volume to the combustor. The level of the downstream pressure drop is selected so that the fuel system has a specific phase response as compared to that of the air system. This two-stage nozzle has been very effective in reducing combustion dynamics related to the fluctuation of fuel/air ratio concentration by matching fuel system and air system responses to pressure fluctuations.
There have also been developments in the area of active control. See, e.g., Annaswamy et al., “Active Control in Combustion Systems,” IEEE Control Systems, December, 1995, pp 45-63, which is incorporated herein by this reference. As previously mentioned, active control requires that a sensor be provided to supply feedback, a controller to process the feedback signal into a control signal and a control device responsive to the control signal. On laboratory scale combustion test rigs, such systems have been generally effective in controlling dynamic pressure oscillations by applying a control device to either the air system or the fuel system of the combustor. Typically, the pressure control device, such as a loud speaker, has been applied for control of the air system while a flow control device, such as a valve, has been applied for control of the fuel system. Most of the work has focused on controlling a single laboratory scale reaction zone.
However, even with a laboratory scale reaction zone, there have been issues with both the frequency response and power consumption of the control device. Usually, power consumption is a problem for the air system control whereas frequency response is the issue for fuel system control. As will be appreciated, for an industrial scale gas turbine (30-250 mW) the air and fuel flows are orders of magnitude larger. Thus, these issues have severely limited the applicability of active control schemes. To the inventors knowledge there has not been a successful application of such an active control scheme to an industrial gas turbine.
BRIEF SUMMARY OF THE INVENTION
It was the purpose of the invention to provide apparatus and methods of applying active, closed loop control to reduce combustion driven pressure oscillation in a single or multi-chamber combustion system in an industrial gas turbine, to increase operability and life of the parts, and in such a way as to require minimal input power. To accomplish the foregoing, the invention combines passive control and active control thereby to reduce the requirements on the control device. This allows selection of a control device which will have an adequate life in an industrial environment and yet require minimal input power.
Specifically, the invention enhances the performance of the passive control afforded by a two stage fuel nozzle, such as disclosed in U.S. Pat. No. 5,211,004, by the addition of a closed loop active control system. The application of such an active control system to the two stage nozzle enhances the performance of the latter by improving its frequency response capability. In the presently proposed implementation of the invention, the active control is applied to the fuel system rather than directly to the combustion chamber. More specifically, in conjunction with the two stage nozzle concept of U.S. Pat. No. 5,211,004, the control device is positioned to act on the captured response volume located between the high and low pressure drop orifices.
The active control system of the invention can be readily applied to each combustion chamber of a multiple combustor gas turbine as the effects of phase differences from one combustor to the next can be sensed by sensors mounted in each chamber and appropriate closed loop control can be applied to each chamber.
The active control system thus operates by measuring the frequency or frequencies of dynamic pressure oscillations in the respective combustors. That information is fed to a controller which processes the signal using appropriate algorithms and transmits a command signal to a pressure driver, volume driver or similar such control device, to create pressure pulses at specific frequencies and phase angles in the captured response volume. This feedback can be used to control response of fuel flow to the original pressure pulsation so that the variations in fuel/air concentration can be controlled as required. This in turn allows control of the pressure oscillation inside the combustor. The algorithms may be appropriately provided for enhancing or reducing the pressure pulsations in the combustion chamber, as required.
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Hoffman et al; “Application of Active Combustion Control to Siemens Heavy Duty Gas Turbines”; Presented at the Symposium of the AVT Panel on Gas Turbine Engine Combustion, Emissions and Alternative Fuels, Lisbon Oct. 12-16, 1998; pp. 1-12.
Cohen et al; Active Control of Combustion Instability in a Liquid—Fueled Low—NoxCombustor, Presented at the International Gas Turbine & Aeroengine Congress & Exhibition Stockholm, Sweden; Jun. 2-Jun. 5, 1998; pp. 1-9.
Scalzo et al; Solution of Combustor Noise in a Coal Gasification Cogeneration Application of 100-MW-Class Combustion Turbines; Transactions of the ASME Journal of Engineering for Gas Turbines and Power, vol. 112/39; Jan. 1990; pp. 39-43.
Seume et al; Application of Active Combustion Instability Control to a Heavy Duty Gas Turbine; ASME Paper No. 97-AA-119, presented Sep. 30 -Oct. 2, 1997 at the ASME ASIA '97 Congress & Exhibition Singapore; pp. 721-726.
Annaswamy et al; Active Control in Combustion Systems; IEEE Control Systems; IEEE Control Systems; Dec. 1995; pp. 49-63.
Black Stephen Hugh
Davis, Jr. Lewis Berkley
Iasillo Robert J.
Casaregola Louis J.
General Electric Co.
Nixon & Vanderhye
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