Patent Application
20120288807
The subject matter disclosed herein generally relates to combustors. More particularly, the subject matter is directed to mitigation of combustion dynamics in combustors.
As emissions requirements for gas turbines have become more stringent, there has been a movement from conventional diffusion flame combustors to Dry Low NOx, (DLN) or Dry Low Emissions (DLE) or Lean Pre Mix (LPM) combustion systems. These DLN/DLE/LPM combustors use lean fuel air mixtures (equivalence ratio of 0.58 to 0.65) during fully premixed operation mode to reduce NOx and CO emissions. Because these combustors operate at such lean fuel/air (f/a) ratios, small changes in velocity fluctuations can result in large changes in mass flow and fuel air fluctuations.
The fluctuations can result in large variations in the rate of heat release and can result in high-pressure fluctuations in the combustion chamber. Interaction of the chamber acoustics, fuel/air fluctuation, vortex-flame interactions and unsteady heat release leads to a feed back loop mechanism resulting in dynamic pressure pulsations in the combustion system. This phenomenon of pressure fluctuations is called thermo acoustic or combustion dynamic instabilities. Combustion dynamics is a major concern in DLN/DLE/LPM combustors.
In the prior art, it has been suggested to mitigate combustion dynamics by providing a combustion liner cap assembly, and forming a second set of circumferentially spaced cooling holes through the cylindrical outer sleeve. Other prior art attempts to mitigate combustion dynamics include providing an external resonator, and active control by changing fuel flow.
In order to mitigate combustion dynamics a steam injection combustor casing is utilized which includes a ring plate configured to reduce the volume of the casing. The ring plate within the casing acts as a dampener to reduce low frequency combustion dynamics. More particularly, the combustor casing head end volume is reduced by provision of the ring plate which carries inwardly protruding walls thereby forming an integrated dampener within the combustor casing.
In one exemplary implementation the ring plate carries a continuous inwardly protruding wall around the diameter of the ring plate. Other exemplary implementations include ring plates with discontinuous or segmented inwardly protruding wall portions or lobes of various shapes. For example the discontinuous or segmented inwardly protruding wall portions or lobes can be contoured, or triangular, etc.
In yet other exemplary implementations the casing is integrally formed with a ring having a continuous inwardly protruding wall or a ring having inwardly protruding wall segments. If inwardly protruding wall segments are integrally formed within the casing, the shape of the wall segment lobes can be contoured, or triangular, etc.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The ring plates 20, 30, and 40 have been shown as a separate part which allows for the retrofitting of existing combustors. However, an inwardly angled continuous wall 62 can also be integrally formed within the combustor casing 60, as shown in
This written description uses example implementations of apparatuses to disclose the inventions, including the best mode, and also to enable any person skilled in the art to practice the inventions, including making and using the devices or systems. The patentable scope of the inventions is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements or process steps that do not differ from the literal language of the claims, or if they include equivalent structural elements or process steps with insubstantial differences from the literal language of the claims.
