Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-04-06
2002-07-02
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S760000
Reexamination Certificate
active
06412268
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to cooling of turbo machinery combustor components and specifically, to the cooling of transition ducts that connect a plurality of combustors to the first stage of a gas turbine.
In a typical arrangement, an annular array of combustors are connected to the first stage of the turbine by the transition ducts that are each shaped at one end to conform to a respective cylindrical combustor liners, and at the opposite end to conform to the turbine stage inlet. At the latter end, the transition duct has an external end frame by which the transition duct is secured to the turbine. In dry, low NOx combustion systems in the assignee's gas turbine product line, a perforated impingement cooling sleeve surrounds the transition duct, and is used to direct compressor discharge cooling air into contact with the transition duct. This cooling air eventually mixes with the fuel in the combustor.
Some of the cooling air is removed from the annulus between the transition duct and the surrounding impingement sleeve through holes in the transition duct end frame. This air, which is used to cool the end frame, dumps into the hot gas from the combustor exit just before entering the gas turbine first stage nozzle. The problem with this current method is that this cooling air by-passes the combustor, thereby effectively increasing the flame temperature and NOx emissions. On new, advanced design combustion systems, the flame temperature increase due to this combustion air loss may be as large as 8 to 10 degrees F, or equivalent to 1 to 2 ppm NOx emissions. As a result, this “by-pass air” becomes an important factor in trying to achieve gas turbine operation with single digit NOx performance.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, transition duct end frame cooling air is reused, i.e., recirculated to the combustor, thereby lowering combustion flame temperature by about 8-10° F. More specifically, a first array of holes is drilled into the outer perimeter of the end frame and a lip or recess is milled into the face of the end frame and then sealed. The recess also communicates with a second array of holes drilled substantially axially within the end frame, and previously utilized to remove air from the annulus between the impingement sleeve and the transition duct. Now, compressor discharge air can be directed through the first array of holes to impinge on the lip milled into the face of the end frame, cooling both the lip of the end frame as well as a U-shaped strip seal component attached to the forward edge of the end frame, and then redirected through the second array of substantially axially oriented holes into the annulus between the transition duct and the impingement cooling sleeve. This air then mixes with air passing through cooling holes in the impingement sleeve, and is eventually directed to the combustion flame zone in the combustor. The substantially axially extending holes through the end frame may be turbulated to improve cooling effectiveness. The effect of reusing (instead of losing) the end frame cooling air is that the flame temperature can be reduced, thus also reducing NOx emissions.
In its broader aspects, the present invention includes a transition duct assembly for a gas turbine comprising a transition duct having opposite ends, one of the ends adapted to communicate with an inlet to a first turbine stage; an impingement cooling sleeve surrounding the transition duct with an annulus therebetween, the impingement cooling sleeve having a plurality of cooling apertures formed therein; a transition duct end frame connected to the one end of the transition duct, a forward edge of the impingement cooling sleeve received in the end frame; the end frame having a first plurality of cooling holes axially beyond the forward edge of the impingement cooling sleeve, each cooling hole communicating at the one end with space external of the impingement cooling sleeve; and a second plurality of cooling holes in the end frame, each communicating at one end with the annulus, and at an opposite end with the first plurality of cooling holes.
In another aspect, the invention relates to an end frame combustor for a gas turbine transition duct comprising a closed peripheral member adapted for attachment to a forward end of a transition duct, the peripheral member having a forward edge, a rearward edge, a top surface and a bottom surface; closed chamber about the forward edge; a first plurality of cooling bores extending from the top surface to the chamber; and a second plurality of cooling bores extending from the rearward edge to the chamber.
In still another aspect, the invention relates to a method of cooling a transition duct end frame in a gas turbine wherein an impingement cooling sleeve having a plurality of cooling apertures therein surrounds the transition duct creating an annulus therebetween, and wherein a transition duct end frame is secured to a forward edge of the transition duct, with a forward flange of the impingement sleeve also received in the end frame, the method comprising a) directing cooling air into the end frame from a region external of the transition duct and the impingement cooling sleeve; and b) redirecting the cooling air from the end frame into the annulus between the transition duct and the impingement cooling sleeve.
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Bechtel William Theodore
Cromer Robert Harold
Sutcu Maz
Freay Charles G.
Gartenberg Ehud
General Electric Company
Nixon & Vanderhye P.C.
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