Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2002-09-13
2004-03-16
Gartenberg, Ehud (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06705087
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
(Not Applicable)
FIELD OF THE INVENTION
The present invention relates in general to gas turbines and, more particularly, to swirler assemblies.
BACKGROUND OF THE INVENTION
Gas turbines generally comprise the following elements: a compressor for compressing air; a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor; and a turbine for expanding the hot gas produced by the combustor.
As shown in
FIG. 1
, an example of a prior art gas turbine combustor
10
comprises a nozzle housing
12
having a nozzle housing base
14
. A diffusion fuel pilot nozzle
16
, having a pilot fuel injection port
18
, extends through nozzle housing
12
and is attached to nozzle housing base
14
. In the shown configuration, main fuel nozzles
20
, each having at least one main fuel injection port
22
, extend substantially parallel to pilot nozzle
16
through nozzle housing
12
and are attached to nozzle housing base
14
. Fuel inlets
24
provide fuel
26
to main fuel nozzles
20
. A main combustion zone
28
is formed within a liner
30
. A pilot cone
32
, having a diverged end
34
, projects from the vicinity of pilot fuel injection port
18
of pilot nozzle
16
. Diverged end
34
is downstream of main fuel swirlers
36
. A pilot flame zone
38
is formed within pilot cone
32
adjacent to main combustion zone
28
.
Compressed air
40
from compressor
42
flows between support ribs
44
through main fuel swirlers
36
. Each main fuel swirler
36
is substantially parallel to pilot nozzle
16
and adjacent to main combustion zone
28
. Within each main fuel swirler
36
, a plurality of swirler vanes
46
generate air turbulence upstream of main fuel injection ports
22
to mix compressed air
40
with fuel
26
to form a fuel/air mixture
48
. Fuel/air mixture
48
is carried into main combustion zone
28
where it combusts. Compressed air
50
enters pilot flame zone
38
through a set of stationary turning vanes
52
located inside pilot swirler
54
. Compressed air
50
mixes with pilot fuel
56
within pilot cone
32
and is carried into pilot flame zone
38
where it combusts.
FIG. 2
shows a detailed view of an exemplary prior art fuel swirler
36
. As shown in
FIG. 2
, fuel swirler
36
is substantially cylindrical in shape, having a flared inlet end
58
and a tapered outlet end
60
. A plurality of swirler vanes
46
are disposed circumferentially around the inner perimeter
62
of fuel swirler
36
proximate flared end
58
. In the shown configuration, fuel swirler
36
surrounds main fuel nozzle
20
proximate main fuel injection ports
22
. Fuel swirler
36
is positioned with swirler vanes
46
upstream of main fuel injection ports
22
and tapered end
60
adjacent to main combustion zone
28
. Flared inlet end
58
is adapted to receive compressed air
40
and channel it into fuel swirler
36
. Tapered outlet end
60
is adapted to fit into sleeve
64
. Swirler vanes
46
are attached to a hub
66
. Hub
66
surrounds main fuel nozzle
20
.
FIG. 3
shows an upstream view of combustor
10
. Pilot nozzle
16
is surrounded by pilot swirler
54
. Pilot swirler
54
has a plurality of stationary turning vanes
52
. Pilot nozzle
16
is surrounded by a plurality of main fuel nozzles
20
. A main fuel swirler
36
surrounds each main fuel nozzle
20
. Each main fuel swirler
36
has a plurality of swirler vanes
46
. The diverged end
34
of pilot cone
32
forms an annulus
68
with liner
30
. Main fuel swirlers
36
are upstream of diverged end
34
. Fuel/air mixture
48
flows through annulus
68
(out of the page) into main combustion zone
28
(not shown in FIG.
3
).
Fuel swirler
36
is attached to liner
30
via attachments
70
and swirler base
72
. With respect to the latter manner of attachment, the distal end of sleeve
74
is adjacent to the swirler base plate
72
as shown in FIG.
2
. The distal end of sleeve
74
and the base plate
72
typically do not come into contact and are actually spaced approximately 10 mils apart.
FIG. 3
shows a circular array of six swirlers, but other quantities, such as a series of eight swirlers, can be employed.
The other manner of attaching the swirler
36
to liner
30
is by way of attachments
70
. In initial designs, attachments
70
comprised dual straight pins, each pin being welded at one end to liner
30
and at the other end to the swirler
36
. This design, however, often fails due to fatigue induced cracking of the pins at the support casing. One prior design revision includes replacing the straight pin attachments with hourglass-shaped pins (as shown) to provide improved weld areas on both the swirler
36
and the liner
30
. However, this design also suffers from fatigue-related failures, primarily occurring at the weld joint between the hourglass-shaped pin attachments
70
and the swirler
36
.
The fatigue failures stem from a swirler's exposure to vibrational forces generated during combustor operation. Combustion dynamics typically range from approximately 110-150 Hz, although variations outside this range are possible depending on the system design. Prior swirlers, when only adjacent to or abutting the base plate, generally had a natural frequency of approximately 145 Hz, falling within the typical vibrational range experienced during combustion dynamics. Consequently, when a swirler is subjected to such forces, the swirler will resonate, and repeated resonance of the swirler ultimately fatigues the weld joints of the support pins.
Thus, high cycle fatigue failures are a recurring problem with respect to swirlers and other turbo machinery components. The problem has been exacerbated by combustion design changes to reduce emissions and increase efficiency. These design changes have increased the severity of the combustion dynamics, requiring more robust swirler assemblies. Therefore, there is a continuing need for a swirler assembly that can avoid vibration-induced resonance and that can further enhance the inherent damping characteristics of the swirler to constrain any vibratory motion.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a swirler assembly that is adapted to tolerate the severity of the dynamics of combustors designed for reduced emissions and greater efficiencies.
It is another object of the invention to provide a more robust swirler assembly that can accommodate changes due to thermal expansion.
These and other objects of the invention are achieved by a swirler assembly adapted to interface with a supporting base plate so as to raise the resonant frequency of the swirler assembly above the vibrational range of the combustion environment and to increase the damping of the swirler response to the combustion dynamics. The present invention applies particularly to a swirler assembly that includes a swirler, a generally cylindrical swirler sleeve and a plate. The swirler has an inlet and an outlet end. The sleeve has a proximal end and a distal end. The outlet end of the swirler extends into the sleeve through the proximal end. The plate has an opening that, due to manufacturing processes, is elongated into an elliptical shape.
According one aspect of the invention, the distal end of the sleeve extends into the plate opening and contacts the inner ring-like surface of the plate opening at least partially around its periphery so that portions of the sleeve contact the surface along the minor axis of the elliptical opening and transition to a clearance along the major axis. The contact areas between the sleeve and the plate stiffen the interface and increase the natural frequency of the swirler. For example, the natural frequency can be increased to 700 Hz, well above the operational combustion dynamics, in the neighborhood of 110-150 Hz. The contact areas also increase frictional forces to damp the vibrational response of the swirler.
The sleeve preferably tapers from a larger diameter outside the plate openin
Ohri Rajeev
Parker David M.
Gartenberg Ehud
Siemens Westinghouse Power Corporation
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