Patent Application
20130091858
This invention relates to turbine combustor nozzles and specifically, in one exemplary embodiment, to an effusion-cooled burner tube.
In certain known combustor designs, a burner tube is connected to the outlet or downstream end of a nozzle head and forms a fuel preparation chamber for a fuel/air mixture introduced into the burner tube from the nozzle head. Typically, the burner tube is surrounded by an impingement cup formed with a plurality of cooling holes or apertures by which compressor discharge air may be introduced into an annular space between the impingement cup and the burner tube, to thereby impingement cool the tube. The impingement cooling air may be routed to mix with fuel at the fuel nozzle head, or to mix with the fuel/air mixture downstream of the burner tube as the mixture enters the combustion chamber.
There remains a need, however, for better utilization of the cooling air used to cool the burner tube.
In accordance with a first exemplary but nonlimiting aspect, the invention provides a fuel nozzle for a combustor comprising a nozzle head configured to supply a fuel/air mixture to a burner tube attached to the nozzle head and extending downstream of the nozzle head; the burner tube provided with cooling holes for introducing a fluid into the burner tube to thereby treat (e.g. cool) an interior wall of the burner tube by effusion.
In accordance with another exemplary but nonlimiting aspect, there is provided a nozzle for a gas turbine comprising a nozzle head formed with plural fuel orifices at an aft end; a burner tube attached to the aft end of the nozzle head and extending downstream of the plural fuel orifices; a swirler arranged about the aft end of the nozzle head, adapted to introduce air for mixing with fuel exiting the plural fuel orifices; the burner tube provided with plural cooling holes downstream of the swirler for introducing cooling air into the burner tube, wherein the plural cooling holes are arranged in axially-spaced, circumferentially extending rows about the burner tube, and slanted in a downstream direction.
In accordance with still another exemplary embodiment, there is provided a method of effusion treating a burner tube in a turbine combustor comprising a locating a burner tube at an outlet end of a fuel nozzle, adapted to receive a fuel/air mixture; providing plural holes about the burner tube and introducing a fluid into the burner tube through the plural holes; and slanting the plural holes in a downstream direction at an angle sufficient to direct the fluid along an interior surface of the burner tube.
The invention will now be described in detail in connection with the drawings identified below.
Instead, plural holes, e.g., effusion cooling holes are formed directly in the burner tube 44 such that cooling air flows directly into the burner tube to mix with the fuel/air mixture from the nozzle head 34 and swirler 38. At the downstream end of the burner tube 44, both the impingement plate 46 and splash plate 48 are now fixed to the aft end of the burner tube 44.
The effusion cooling holes 42 are preferably slanted in an axial direction, e.g., at an angle of between 30-60°, so that the effusion cooling air tends to flow along the inside of the burner tube 44 to thereby cool the hot side of the burner tube and, at the same time, keep the fuel away from the burner tube wall. The effusion cooling air thus enters directly into the burner tube but in part-axial direction so that air remains close to the burner tube surface as it travels at higher velocity axially along the length of the tube.
The cooling holes 42 may also be slanted in one or the other of counterclockwise and clockwise, circumferential directions to cause the cooling air to swirl as it enters the burner tube 44, either swirling with or counter to, the swirling air/fuel mixture.
Two circumferential, axially-spaced rows of apertures or holes 42 are shown, but it will be appreciated that the number, diameter and pattern of the holes may vary. In one example, the cooling holes may have diameters in the range of from about 0.020 to about 0.060 in. In addition, the burner tube itself is formed with a slight conical shape, via tapered interior surface 50 with the narrower end located at the aft end of the burner tube, thereby increasing velocity and improving mixing as the mixture moves from left to right and into the combustion chamber 52.
Now that an aft row of cooling holes 52 adjacent the splash plate 48 are slanted at a more acute angle (15°-30°) relative to cooling holes 42, thereby directing some portion of the effusion cooling air in a more axial direction at the aft end of the burner tube, thus also providing some cooling to the splash plate 48.
Other benefits not already mentioned include increased durability of the burner tube and nozzle head or tip; reduced soot formation on startup; better flame holding margin and reduced emissions.
The cooling arrangement as described herein may be beneficially employed with various nozzle types including standard combustor nozzles, diffusion nozzles, DLN, combustor nozzles, primary nozzles, syngas nozzles and the like.
It will be appreciated that in the event the cooling air maintains the burner tube temperature constant, i.e., prevents overheating, it may be more appropriate to state that the burner tube is “treated” with air or other fluid rather than “cooled”.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
