Note: Descriptions are shown in the official language in which they were submitted.
CA 02394118 2002-07-18
TITLE
GAS TURBINE COMBUSTOR
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a gas turbine
combustor that realizes a low NOx combustion.
Description of the Prior Art
Figs. 4(a) and (.b) schematically show a prior art
gas turbine combustor, wherein Fig. 4(a) is a longitudinal
cross sectional view showing an interior of the combustor
and Fig . 4 ( b ) is a front view of a half portion of the
combustor . In Figs . 4 ( a ) and ( b ) , main fuel 40 flows into
eight pre-mixing nozzles 31, that are arranged within a
combustor body 36 around a central axis thereof, and is
pre-mixed with air, as will be described next, to form a
main pre-mixture to be supplied into a combustion zone of
a combustor 33. The air is supplied from a compressor (not
shown) to be fed into the combustor 33 flowing through an
inner peripheral space portion of the combustor body 36,
as shown by arrows 50 in Fig . 4 ( a ) . On the other hand , pilot
fuel 41 flows into a pilot nozzle 32, that is arranged on
the central axis of the combustor body 36 , to be jetted into
the combustor 33. Thus, the pilot fuel 41 burns with the
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main pre-mixture there to effect a combustion. A flame
holding cone 34 is provided on the pilot nozzle 32 and flame
of the pilot fuel 41 is maintained by a high temperature
gas circulating flow 35, that is formed by the flame holding
cone 34. Such a combustor having the pre-mixing nozzles and
being constructed as described above is generally known as
a low NOx combustor.
In the above described pre-mixed flame type low NOx
combustor in the prior art, the flame of the pilot nozzle
32 is maintained by a diffused flame, that is, the high
temperature gas circulating flow 35, formed by the flame
holding cone 34 and NOx quantity generated by the pre-mixing
nozzles 31 is reduced. However, NOx quantity generated by
the diffused flame of the pilot nozzle 32 cannot be
suppressed and realization of a low NOx generation as a whole
is limited by that extent.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention
to provide a gas turbine combustor that is constructed so
as to improve a flame holding ability by the high temperature
gas circulating f low as well as to improve cooling of the
pre-mixing nozzles to thereby reduce pilot fuel quantity
as well as to reduce NOx quantity generated of the pilot
fuel.
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In order to achieve the mentioned object, the present
invention provides means of the following (1) to (4):
(1) A gas turbine combustor comprising a pilot
nozzle arranged on a central axis of the combustor and a
plurality of pre-mixing nozzles arranged around the pilot
nozzle, characterized in that a diameter of a combustion
zone of the combustor is set such that, where an area is
taken on a radial directional plane of the combustor, the
area inside of the combustion zone and outside of a pitch
circle that is defined as a circle on which all central axes
of the plurality of pre-mixing nozzles are arranged, less
the area taken by the plurality of pre-mixing nozzles outside
of the pitch circle, is a half or more of the area of all
of the plurality of pre-mixing nozzles.
(2) A gas turbine combustor as mentioned in the
means ( 1 ) above, characterized in that each of the plurality
of pre-mixing nozzles has its front end projected beyond
a base plate that supports the pre-mixing nozzle and a
projecting distance of such projected front end is set to
one third or more of an outer diameter of the pre-mixing
nozzle.
(3) A gas turbine combustor as mentioned in the
means ( 1 ) above , characterized in that each of the plurality
of pre-mixing nozzles has its front portion made in a double
structure having inner and outer members with a
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predetermined gap being maintained between the inner and
outer members and air is flowable in the gap.
(4) A gas turbine combustor as mentioned in the
means ( 1 ) above, characterized in that a combustor body as
an outer casing of the combustor comprises therein an inner
cylindrical member and an outer cylindrical member, the
inner cylindrical member is arranged surrounding the
plurality of pre-mixing nozzles and the outer cylindrical
member has its inner diameter made larger than an outer
diameter of the inner cylindrical member and is arranged
surrounding a front end portion of the inner cylindrical
member and extending downstream of the inner cylindrical
member so as to cover the combustion zone to thereby enable
to enlarge the diameter of the combustion zone beyond an
inner diameter of the inner cylindrical member.
In the means (1) of the present invention, the
diameter of the combustion zone in which a high temperature
combustion gas is generated is set such that the cross
sectional area inside of the combustion zone and outside
of the pitch circle, less the cross sectional area of the
pre-mixing nozzles outside of the pitch circle, is a half
or more of the cross sectional area of all the pre-mixing
nozzles. By this structure, the outer peripheral space
portion of the combustion zone is enlarged and a gas
stagnation area is formed in this space portion, that is,
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in the outer peripheral space portion in front of the
pre-mixing nozzles . An outer circulating flow of the high
temperature gas generated by combustion of the pre-mixture
coming from the pre-mixing nozzles is formed in this gas
stagnation area. Also, an inner circulating flow of a high
temperature gas generated of the pilot fuel is formed in
the central space portion of the combustion zone in front
of the pilot nozzle by a flame holding cone. Thus, by the
inner and outer circulating flows of the high temperature
gas, the flame holding ability of the combustor can be
greatly enhanced. Thereby, the pilot fuel quantity, as so
far necessitated for the flame holding, can be reduced, the
NOx quantity generated by combustion of the pilot fuel can
be reduced and a very low NOx generation can be realized
as a whole.
In the means ( 2 ) of the present invention, each of
the pre-mixing nozzles has its front end projected beyond
the base plate so that the base plate may not be directly
exposed to the high temperature gas circulating flows.
Thereby, the base plate is prevented from being overheated
and the effect of the means (1) of the present invention
can be realized more securely.
In the means ( 3 ) of the present invention, each of
the pre-mixing nozzles has its front portion made in the
double structure having the predetermined gap therein and
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air is flowable in the gap for cooling the pre-mixing nozzle.
Thus, the pre-mixing nozzle is prevented from being
overheated and the effect of the means (1) of the present
invention is further ensured.
In the means (4) of the present invention, the
combustor body as the outer casing of the combustor comprises
therein the inner cylindrical member and the outer
cylindrical member. The outer cylindrical member has its
inner diameter made larger than the outer diameter of the
inner cylindrical member. Thus, the diameter of the
combustion zone is enlarged outwardly so that the gas
stagnation area is easily formed in the outer peripheral
space portion of the combustion zone in front of the
pre-mixing nozzles. The outer circulating flow of the high
temperature combustion gas generated by combustion of the
pre-mixture coming from the pre-mixing nozzles is formed
in the gas stagnation area and the flame holding ability
is enhanced. Hence, the effect to realize the low NOx
generation by the means (1) of the present invention can
be further ensured.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs . 1 ( a ) and ( b ) schematically show a gas turbine
combustor of an embodiment according to the present
invention, wherein Fig. 1(a) is a longitudinal cross
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sectional view showing an interior of the combustor and Fig.
1(b) is a front view of a half portion of the combustor.
Fig. 2 is an enlarged longitudinal cross sectional
view of one of pre-mixing nozzles.
Fig . 3 is the same view as Fig . 1 ( a ) in which a hatched
portion is added.
Figs. 4(a) and (b) schematically show a prior art
gas turbine combustor, wherein Fig . 4 ( a ) is a longitudinal
cross sectional view showing an interior of the combustor
IO and Fig. 4(b) is a front view of a half portion of the
combustor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Herebelow, an embodiment according to the present
invention will be described with reference to the appended
drawings.
Figs . 1 ( a ) and ( b ) schematically show a gas turbine
combustor of the embodiment, wherein Fig. 1(a) is a
longitudinal cross sectional view showing an interior of
the combustor and Fig. 1(b) is a front view of a half portion
of the combustor. In Figs. 1(a) and (b), numeral 10
designates a combustor body as an outer casing of the
combustor and eight pre-mixing nozzles 11 are provided
therein being connected to each other around a central axis
of the combustor body 10. The pre-mixing nozzles 11 are
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constructed so as to have their front ends projected beyond
a base plate 17, that will be described later. Numeral 12
designates a pilot nozzle, that is arranged on the central
axis of the combustor body 10. Numeral 13 designates a
combustor, that includes the combustor body 10 and other
components arranged therein. The combustor body 10
comprises therein an inner cylindrical member 13a and an
outer cylindrical member 13b. The outer cylindrical member
13b has its inner diameter made larger than an outer diameter
of the inner cylindrical member 13a as well as larger than
an outer diameter of a cylindrical member of the prior art
combustor. The outer cylindrical member 13b is arranged
surrounding a front end portion of the inner cylindrical
member 13a and extending downstream of the inner cylindrical
member 13a so as to cover a combustion zone of the combustor
13. Numeral 14 designates a flame holding cone, that has
its front end portion eliminated to be made shorter than
the prior art flame holding cone. Numeral 17 designates the
base plate, that is a member supporting the eight pre-mixing
nozzles 11 to an inner circumferential wall surface of the
inner cylindrical member 13a.
Fig. 2 is an enlarged longitudinal cross sectional
view of one of the pre-mixing nozzles 11. The pre-mixing
nozzle 11 has its front portion made in a double structure
having a pre-mixing nozzle portion 21 of the inner side and
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an outer sleeve 23 of the outer side. While illustration
is omitted, the outer sleeve 23 is supported to the
pre-mixing nozzle portion 21 via a plurality of rib members .
While the pre-mixing nozzle in the prior art has its front
end cut at the position of its base plate without pro jecting
further, the pre-mixing nozzle 11 of the present invention
has its front end projected beyond the base plate 17. That
is, a front end of the outer sleeve 23 projects frontward
beyond the position of the base plate 17. Numeral 14
designates a flame holding cone, that has its front end
portion cut by the pro jection of the outer sleeve 23 to be
made shorter. Numeral 22 designates a swirler vane,
construction of which is the same as that of the prior art
one.
In the combustor described above with reference to
Figs . 1 and 2 , main fuel 40 flows into the eight pre-mixing
nozzles 11 and is pre-mixed with air to form a pre-mixture
for combustion in the combustion zone of the combustor 13.
The air is supplied from a compressor ( not shown ) to be fed
into the combustor 13 flowing through an inner peripheral
space portion of the combustor body 10, as shown by arrows
50 in Fig. 1(a) , and further flowing through the pre-mixing
nozzle portion 21 as well as through an outer peripheral
space portion of the pre-mixing nozzle portion 21 , as shown
by arrows 51 in Fig. 2. On the other hand, pilot fuel 41
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is supplied into the combustor 13 through the pilot nozzle
12 of the combustor central position and burns there together
with the pre-mixture.
In a front central space portion of the flame holding
cone 14 of the pilot nozzle 12, a high temperature gas inner
circulating flow 15 is generated by the pilot fuel. Also,
in an inner peripheral space portion of the outer cylindrical
member 13b in front of the pre-mixing nozzle 11, a high
temperature gas outer circulating flow 16 is generated by
the pre-mixture coming from the pre-mixing nozzle 11. Thus,
by these two circulating flows 15, 16, the flame holding
is securely effected. A gas stagnation area is formed in
the inner peripheral space portion of the outer cylindrical
member 13b in front of the pre-mixing nozzle 11 by the
construction of the combustor 13 comprising the inner
cylindrical member 13a and the outer cylindrical member 13b
and having the inner diameter of the outer cylindrical member
13b made larger. Thus, the high temperature gas outer
circulating flow 16 is formed in this gas stagnation area
as a circulating flow of a high temperature combustion gas
generated by combustion of the main pre-mixture.
As the flame holding effected by the high temperature
gas inner circulating flow 15 generated by the flame holding
cone 14 is added, the flame holding ability is greatly
enhanced by the construction of the high temperature gas
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inner and outer circulating flows 15 , 16 . Thus , the pilot
fuel quantity, as so far necessitated for the flame holding,
can be reduced and thereby the NOx quantity generated of
the pilot fuel can be reduced and a very low NOx combustion
can be realized.
As described with reference to Fig. 2, the pre-mixing
nozzle 11 comprises the swirler vane 22, the pre-mixing
nozzle portion 21 and the outer sleeve 23. The outer sleeve
23 is arranged with a predetermined gap being maintained
from the pre-mixing nozzle portion 21 of the inner side
thereof and the air , as shown by the arrows 51 , f lows into
the gap, so that the pre-mixing nozzle portion 21 and the
outer sleeve 23 that are heated by the high temperature gas
can be sufficiently cooled.
Moreover, the front end of the pre-mixing nozzle 11,
that is formed by the front end of the outer sleeve 23,
projects beyond the base plate 17. By this projecting
portion, the base plate 17, that is directly exposed to the
high temperature gas outer circulating flow 16, is prevented
from being overheated. In Fig. 2, where L is a projecting
distance of the projecting portion, that is, a distance
between a front side surface of the base plate 17 and the
front end of the pre-mixing nozzle 11, and D is an outer
diameter of the pre-mixing nozzle 11, that is, an outer
diameter of the outer sleeve 23, if L is set to D/3 or more
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(L?D/3), then the effect to prevent the overheat of the base
plate 17 can be enhanced.
Fig. 3 is the same view as Fig. 1 (b) in which a hatched
portion is added. In Fig. 3, letter P is defined as a pitch
circle that is a circle on which central axes of all of the
pre-mixing nozzles 11 are arranged. An inner diameter of
the outer cylindrical member 13b, that corresponds to a
diameter of the combustion zone in the combustor, is set
such that, where an area is taken on a radial directional
plane of the combustor, the area inside of the outer
cylindrical member 13b and outside of the pitch circle P,
less the area taken by the pre-mixing nozzles 11 outside
of the pitch circle P, that is, the area shown by the hatched
portion in Fig. 3, is a half or more of the area of all the
pre-mixing nozzles 11. By so selecting the diameter of the
combustion zone in the combustor, the abovementioned gas
stagnation area is effectively formed in the front outer
side space portion of the pre-mixing nozzles 11 and the flame
holding ability can be greatly enhanced.
According to the gas turbine combustor constructed
as described above, a remarkable NOx reduction effect can
be obtained. For example, NOx quantity of 25 PPM in the prior
art can be reduced to 10 PPM or less.
While the preferred form of the present invention
has been described, it is to be understood that the invention
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is not limited to the particular construction and
arrangement herein illustrated and described but embraces
such modified forms thereof as come within the scope of the
appended claims.
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