Note: Descriptions are shown in the official language in which they were submitted.
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IMPINGEMENT COOLED LIN~ER FOR DRY LOW
NOx VlE NTURI COMB~STOR
BACKGROUND OF THE INVENTION
This invention relates to gas turbine
combustors and particularly to gas turbine combustors
of the type having an upstream combustion chamber and
a downstream combustion chamber interconnected by a
venturi throat region.
A dry low NOx combustor is the subject of
U.S. Patent No. 4,292,801 to inventors Wilkes and Hilt
which is issued on October 13, 1981 and assigned to
the assignee of the present invention. In particular,
that patent describes a gas turbine combustor which
has an upstream combustion chamber and a downstream
combustion chamber interconnected by a venturi throat
region. There is an annular array o~ primary nozæles
which input ~uel into the upstream combustion chamber
and a central nozzle which inputs fuel into the
downstream combustion chamber. Low NOx (oxides of
nitrogen) output is achieved, in part, by the method
of operating the subject combustor which includes
operating the combustor in a premix mode during the
normal or base load such that the primary nozzles are
~lamed out but fuel is input through the primary
nozzles to premix with combustion air whereupon the
mixture is ignited in the downstream combustor chamber
by the central nozzle. To achieve success in lowering
NOx output in the combustor design it is important
that fuel-air mixtures be maintained at specific
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desired le~els and that there is a uniform mixture.
It is also important that the combustor parts
be adequately cooled due to the high temperatures found
in a gas turbine combustor~ On such part is the venturi
region of the dual stage, dual mode combustor. Film
cooling has been effected in this region on the upstream
wall of the venturi throat region but it has been found
that introduction of film cooling air in this region has
an adverse effect on the uniform fuel-air mixture in this
region such that there may be created rich/lean pockets;
that is, pockets of unburned fuel or pockets of excess
air.
In the upstream combustion chamber fuel and
air are premixed for ignition to occur during base load
operation in the downstream combustion chamber. It is
also important that the mixture profile be flat; that is,
a uniform mixture. It is also important that the exact
~uel air ratio be employed to improve the low NOx
performance of the combustor and that the liner be
adequately cooled.
: O.BJECTS OF THE INVENTION
It is accordingly one object of the present
invention, to provide improved air~fuel mixing in the
venturi throat region of a gas turbine combustor.
It is another object of the invention to
provide sufficient cooling of the combustor parts in
the venturi throat region of a gas turbine combustor.
It is another object of the invention to
maintain the proper fuel-air ratio in theventuri throat
of a gas turbine combustorO
It is still a further object of the invention
to provide an improved fuel air mixing profile in the
primar~ combustion chamber.
The novel features believed characteristic
of the present invention are set forth in the appended
claims. The invention itself, however, together with
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further objects and advantages thereof may best be
unders-tood with reference to the following description
and drawings.
SUMMARY OF THE: INVENTION
.
An annular shield is positioned in a gas
turbine cornbustor having an upstream combustion chamber
and a downstream combustion chamber interconnected by a
venturi throat region. The annular shield is partially
upstream of the venturi throat region and includes a
radially inwardly slanted shield portion and an axial
shield portion. Both the slanted shield portion and the
axial shield portion are impingement cooled by air from
the venturi air supply holes. A ring is attached to
the venturi throat region to extend in the downstream
direction with a complementary portion of the annular
shield. In the upstream combustion chamber, first and
second inner annular liners extend in the upstream
direction and are cooled by impingement cooling from
the combustor liner and centerbody wall respectively.
The first and second inner annular liners are open at
their upstream ends to dump combustion air into the
upstream combustion chamber. Film cooling holes are
provided upstream of the inner annular liner.
BRIEF DESCRIPTION OF THE DRA~INGS
Figure l is an elevation view of a gas turbine
~ombustor with cutaway portions to show the present
invention.
Figure 2 is a schematic drawing of one
embodiment of the present invention and its application
to a gas turbine combustor.
Figure 3 is a schematic drawing o:E another
embodiment of the present invention and its application
to a gas turbine combustor.
DETPILRD~ DESC~IPTION OF THE PREFERRED EMBODIMENT
Figure l shows a portion of a gas -turbine
combustor 10 taken around a centexline 12. In the
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aforementioned U.S. Patent 4,292,801, it is made clear
that a gas turbine includes three main parts; that is,
a compressor for providing air to a plurality of
combustors, and a turbine which is driven by the hot
products o~ combustion and which, in turn, drives the
compressor. In one model gas turbine there may be as
many as fourteen combustors arranged around the
periphery of the gas turbine.
In that same patent, a unique combustor is
shown which is capable of providing a low NOx (oxides
of nitrogen) output. A similar combustor is shown in
the present invention as having a ~irst stage or
upstream combustion chamber ~6 and a second stage or
downstream combustion chamber 18. These two
combustion stages or chambers are interconnected by a
venturi throat region 20. The venturi throat region,
in general, is a restricted portion between two larger
volumes; in this case, the region between the upstream
and downstream combustion chambers. The venturi
region includes an upstream wall 30 (with respect to
the flow direction of the combustion products) and a
downstream wall 32 interconnected by an axial wall 34.
To complete the general description of the
gas turbine combustor, the upstream and downstream
combustion chambers are surrsunded by a combustion
liner 40 which may include along its axial length a
plurality of circumferential slots 42 which provide
film cooling within the combustion liner. In
addition, there are combustion air hcles 44 which
provid~ combustion air into the combustor liner and
dilution air holes 46 which quench the combustion
process. In each comhustor, there are also a
plurality of primary fuel nozzles 50 arranged in
annular array upstream from the primary combustion
chamber; and, in one typical example ~here may be as
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many as six primary fuel nozzles per combustor. There
may also be one secondary fuel nozzle 60 that ignites
the fuel flow into the second or downstream combustion
chamber during periods when the upstream combustion
chambers are used primarily as premix chambers. While
the secondary noæzle 60 is shown as the so-called
combined diffusion and premix nozzle, it should be
understood that this is not a requirement of the
present invention and that a simple diffusion nozzle
could also be utilized in combustion with the present
invention.
The combustion liner and its contents,
having been described in general terms, is surrounded
by a flow sleeve 70 which guides compressor (not
shown) discharga air in reverse flow to the combustor
liner. Also shown, is an end cover 72 which closes
the upstream end of the combustor and locates the
secondary fuel nozzle. An annular wrapper 74
(partially shown) surrounds the flow sleeve to
complete the con~truction of the combustor.
Referring now to Figure 2 in combination
with Figure 1, the combustor liner 40 and its contents
as they pertain to the present invention are shown in
schematic. The primary nozzles 50 are omitted from
the upstream combustion chamber 16 and the secondary
nozzle 60 is shown just upstream from the downstream
combustion chamber lg. Part of the secondary nozzle
is an annular can or cylinder called a centerbody 76.
The centerbody is removable from the combustion liner
with the secondary nozzle and as indicated by the
louvers may be film cooled.
The venturi throat reyion is described with
respPct to the direction of combustion products flow as
including the upstream wall 0 and the downstream wall
32 interconnectad by the axial wall 34. An annular
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shield 80 comprises a radially inward slanted portion
82 and an axial portion 84. The radially inward sl.anted
poxtion is positioned upstream from the upstream wall 30
of the venturi and is cooled by impingement cooling holes
92. Cooling air is fed to the upstream wall impingement
cooling holes through air supply holes 89 located in the
combustion liner. Furthermore, the axial portion of
the annular shield is also impingement cooled by means
of impingement cooling holes 94 in the venturi axial
wall 34~ Formerly, the upstream and axial walls of the
venturi were film cooled which tended to dilute the
fuel/air ratio in the region of the venturi. The
present invention will protect the venturi region from
the hot combustion products without adding air to the
critical burnïng region.
The axial portion of the annular flow shi.eld
is further extended downstream of the venturi axial wall
34 to form an axial extended portion 86. The venturi
axial wall is also extended in the axial direction by
2Q means of a r.ing 88 whi.ch defines an acute angle "a"
with the downstream wall of the venturi. The shield
axial extended portion 86 and the ring 88 are substantially
coaxial with one another and the centerline axis 12 of
the combustor. The addition of the shield axial extended
portion 86 and the ring 88 act together to form a flow
guide which takes the impingement cooling air downstream
in the combustor and away from the flame region thereby
disposing of the air in a more favorable region with
respect to the maintenance of a desired fuel/air ratio.
Finally, with respect to the annular shield,
the shield extended portion has a free end 90 which
ter~ninates further downstream in the combustor liner
than the free end of the ring 88.. This causes the
cooling air to inhibit hot combustion gases from
contacting the downstream wall of the venturi.
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Referring to Fiyure 3, which is a half
elevation view schematic, taken around centerline 12,
wherein like numbers are assigned to like parts; there
is shown a further improvement to the present invention.
In the primary combustion chamber 16, a first inner
annular liner 96 extends upstream from the venturi
throat region and is impingement cooled by impingement
cooling holes 98 in the combustion liner. Likewise,
a second inner annular liner 100 extends upstream from
lQ the venturi throat region but closely adjacent to the
centerbody wall 76 and is impingement cooled by means
of impingement cooling holes 102 in the centerbody wall.
By controlling the spacing of the first and second
inner annular liners from the combustion liner and
centerbody wall respectively the proper amount of com-
bustion air (see flow arrows 103~ for the upstream
combustion chamber can be metered to the elimination
of the combustion air holes 44 in Figure 1. The exact
dimensions of each inner liner with respect to its
adjacent wall could be determined by knowing the
desired flow o:E combustion air and in a manner similar
to determining the dimensions of the combustion air
holes. As pointed out with respect to the annular shield
in the venturi region, the achieved advantage is that the
air used for impingement cooling can be added to the
combustion zone without diluting the desired fuel/air
ratio. The regions upstream from the first and second
inner annular liners may be cooled by process o~ film
cooling without adversely afecting the downstream
fuel/air mixture.
In accordance with the aforestated objects
of the invention, the fuel/air mixture delivered to the
venturi region of a dry low NOx combustor has been improved
by the cooperation of an annular shield in the venturi
region and upstream first and second inner annular
linexs in the first or upstream combustion zone. The
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annular shield in the venturi region is impingement
cooled with the impingement cooling air being dumped
downstream and away from the flame in the secondary
fuel nozzle. Correspondingly, the upstream first and
second inner annular liners are impingement cooled and
dump the impingement air upstream in the first or
upstream combustion zone in a metered amount so that a
uniform fuel/air mixture (meaning no fuel or air pockets)
can be achieved prior to combustion occurring in the
venturi region.
While there is described and shown what is
considered to be, at present, the preferred embodiment
of the invention, it is, of course understood that various
other modifications may be made therein. It is intended
to claim all such modifications as would fall within the
true spirit and scope of the present invention.
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