U.S. patent application number 13/212592 was filed with the patent office on 2012-03-01 for gas turbine combustor.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Akinori Hayashi, Yoshitaka HIRATA, Tatsuya Sekiguchi, Shohei Yoshida.
Application Number | 20120047897 13/212592 |
Document ID | / |
Family ID | 44677473 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120047897 |
Kind Code |
A1 |
HIRATA; Yoshitaka ; et
al. |
March 1, 2012 |
Gas Turbine Combustor
Abstract
In a gas turbine combustor, mixing of a fuel and air is
accelerated in a mixing chamber of a burner as well as in air
introduction passages provided in a wall of the mixing chamber,
whereby NOx emissions from premixed combustion are reduced while at
the same time, ignition characteristics and flame propagation
characteristics improve. The gas turbine combustor includes a
plurality of combustors 10, a spark plug 13, and a cross-fire tube
15 that propagates a flame between the combustors 10. Each
combustor 10 includes the burner 30 equipped with a fuel nozzle and
the mixing chamber wall 32 forming the mixing chamber 31. A
plurality of air introduction holes 35, 36 for introducing
combustion air, along with the fuel from the fuel nozzle, into the
mixing chamber 31, are provided in the mixing chamber wall 32. The
combustion air and fuel jetted from the air introduction hole 35
into the mixing chamber 31 are mixed in the form of a mixture "m1",
"m2" and directed towards the spark plug 13 and the cross-fire tube
15.
Inventors: |
HIRATA; Yoshitaka; (Tokai,
JP) ; Yoshida; Shohei; (Hitachiohta, JP) ;
Sekiguchi; Tatsuya; (Hitachi, JP) ; Hayashi;
Akinori; (Hitachinaka, JP) |
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
44677473 |
Appl. No.: |
13/212592 |
Filed: |
August 18, 2011 |
Current U.S.
Class: |
60/737 |
Current CPC
Class: |
F23R 3/286 20130101;
F23R 3/48 20130101; F23R 3/343 20130101; F23D 2207/00 20130101 |
Class at
Publication: |
60/737 |
International
Class: |
F23R 3/28 20060101
F23R003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2010 |
JP |
2010-190336 |
Claims
1. A gas turbine combustor, comprising: a plurality of combustors
each for supplying to a gas turbine a combustion gas resulting from
combustion of a mixture of a fuel and combustion air introduced
from a compressor, and each including a burner; a spark plug for
igniting the mixture; and a cross-fire tube for propagating between
the combustors a flame formed by the combustion of the mixture;
wherein: the burner includes a mixing chamber wall for forming a
mixing chamber which opens towards a downstream side in an axial
direction of the combustor, a fuel nozzle for supplying a fuel, and
a plurality of air introduction passages installed in the mixing
chamber wall each for introducing combustion air, along with the
fuel from the fuel nozzle, into the mixing chamber; and flows of
the combustion air and fuel jetted from the air introduction
passages into the mixing chamber are directed towards at least one
of the spark plug and the cross-fire tube.
2. The gas turbine combustor according to claim 1, wherein: in the
mixing chamber wall, the air introduction passages are arranged so
as to form a first row and a second row adjacently to each other,
in the axial direction or in the radial direction; the air
introduction passage for jetting the combustion air which flows
towards the spark plug belongs to the first row; and the air
introduction passage for jetting the combustion air which flows
towards the cross-fire tube belongs to the second row.
3. The gas turbine combustor according to claim 1, further
comprising: a central burner as the burner; and a plurality of
outer peripheral burners each disposed at an outer peripheral side
relative to the central burner; wherein: the central burner
includes a central mixing chamber wall that is the mixing chamber
wall forming a central mixing chamber which is the mixing chamber,
and a central fuel nozzle as the fuel nozzle; the outer peripheral
burners each include an outer peripheral mixing chamber wall
forming an outer peripheral mixing chamber which opens towards a
downstream side in the axial direction, and an outer peripheral
fuel nozzle for supplying a fuel to the outer peripheral mixing
chamber; in the central mixing chamber wall, the combustion air
introduction passages are provided so as to form a first row and a
second row adjacently to each other, in the axial direction; the
air introduction passage for jetting the combustion air which flows
towards at least one of the spark plug and the cross-fire tube
belongs to the first row; and the combustion air jetted from the
air introduction passage belonging to the second row flows towards
an exit of the outer peripheral mixing chamber.
4. The gas turbine combustor according to claim 3, wherein: the
number of the air introduction passages configuring the second row
in the central burner is an integral multiple of the number of the
outer peripheral burners.
5. The gas turbine combustor according to claim 3, wherein: the
number of the air introduction passages configuring an upstream row
of the first row and the second row in the axial direction is six,
the number of the air introduction passages configuring an
downstream row of the first row and the second row is twelve, and
the number of the outer peripheral burners is four or six.
6. The gas turbine combustor according to claim 4, wherein: the
number of the air introduction passages configuring an upstream row
of the first row and the second row in the axial direction is six,
the number of the air introduction passages configuring an
downstream row of the first row and the second row is twelve, and
the number of the outer peripheral burners is four or six.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a gas turbine combustor
including a plurality of combustors for supplying to a turbine,
combustion gases resulting from combustion of a fuel-air mixture, a
spark plug for igniting the mixture, and cross-fire tubes for
propagating flames between the combustors.
[0003] 2. Description of the Related Art
[0004] Among the gas turbine combustors equipped in commonly used
conventional gas turbines is traditionally known a type including a
plurality of can-type combustors. These combustors are constructed
so that each creates high-temperature high-pressure combustion
gases by causing reactions between fuel and air in order to
rotationally drive the turbine. Such a type of combustor is
disclosed in Japanese Patent No. 3940705, for example.
[0005] The combustors in the can-type gas turbine combustor are
arranged circularly in a circumferential direction of the turbine
rotor, and the combustors adjacent to one another in the
circumferential direction are each interconnected by a connecting
pipe, with a cross-fire tube being disposed inside the pipe. The
cross-fire tube is of a tubular shape, and is constructed so that
upon a differential pressure occurring between the pipe-connected
combustors, combustion gases pass through the cross-fire tube.
[0006] During a start of operation, the gas turbine is driven by an
external drive, then reaches a rotational speed at which ignition
is to be started, and introduces fuel and air into all combustors.
The combustor initiates combustion by developing a spark from the
spark plug(s) set in one or two of the combustors. The combustion
in each ignited combustor generates hot combustion gases, raising
an internal pressure of the particular combustor. When adjacent
combustors are not in an ignited condition, the differential
pressure with respect to the ignited combustor causes hot
combustion gases to flow into the unignited combustors through the
cross-fire tubes. In this way, ignition initially starts from one
or two combustors only and then sequentially propagates to other
combustors adjacent thereto, whereby all combustors are ignited in
order.
SUMMARY OF THE INVENTION
[0007] The plurality of combustors constituting a gas turbine
combustor are each equipped with a burner. The burner is inclusive
of a mixing chamber wall forming a mixing chamber, and of a fuel
nozzle, and the mixing chamber wall includes a plurality of air
introduction passages that introduce air for combustion into the
mixing chamber along with a fuel supplied from the fuel nozzle.
Thus, mixing of the fuel and air in the air introduction passages
and in the mixing chamber is accelerated and NOx reduction by
premixed combustion becomes possible.
[0008] The gas turbine exhibits better starting ignition
characteristics and flame propagation characteristics as the
mixture has a higher fuel concentration, that is, a higher fuel-air
ratio. During premixed combustion, however, the starting ignition
characteristics and flame propagation characteristics of the gas
turbine often decrease since the mixture in the mixing chamber
tends to be homogenized in fuel concentration.
[0009] An object of the present invention is to improve starting
ignition characteristics and flame propagation characteristics in a
gas turbine combustor while at the same time reducing NOx during
premixed combustion by accelerating fuel-air mixing in a mixing
chamber of a burner and in air introduction passages provided in a
wall of the mixing chamber.
[0010] According to a first aspect of the present invention, the
gas turbine combustor includes a plurality of combustors each for
supplying to a gas turbine a combustion gas resulting from
combustion of a mixture of a fuel and combustion air introduced
from a compressor; a spark plug for igniting the mixture; and a
cross-fire tube for propagating between the combustors a flame
formed by the combustion of the mixture; wherein: the combustors
each include a burner, the burner including a mixing chamber wall
for forming a mixing chamber which opens towards a downstream side
in an axial direction of the combustor, a fuel nozzle for supplying
a fuel, and a plurality of air introduction passages installed in
the mixing chamber wall each for introducing combustion air, along
with the fuel from the fuel nozzle, into the mixing chamber, flows
of the combustion air and fuel jetted from the air introduction
passages into the mixing chamber are directed towards at least one
of the spark plug and the cross-fire tube.
[0011] According to the first aspect, in the gas turbine combustor
including the plurality of combustors, the spark plug, and the
cross-fire tubes, the combustion air is jetted from the air
introduction passages that introduce the combustion air into the
mixing chamber of the burner of each combustor, into the mixing
chamber in the form of a mixture with the fuel supplied from the
fuel nozzle. The jetted mixture flows towards at least one of the
spark plug and the corresponding cross-fire tube. As a result, at a
location of and in vicinity of at least one of the spark plug and
the cross-fire tube, a mixture with a high fuel concentration
exists, which facilitates ignition, improves at least one of
ignition characteristics and flame propagation characteristics, and
thus improves startability of the gas turbine.
[0012] According to a second aspect of the present invention, in
the gas turbine combustor, the mixing chamber wall is such that the
air introduction passages are arranged so as to form a first row
and a second row adjacently to each other, in the axial direction
or in the radial direction; the air introduction passage for
jetting the combustion air which flows towards the spark plug
belongs to the first row; and the air introduction passage for
jetting the combustion air which flows towards the cross-fire tube
belongs to the second row.
[0013] According to the second aspect, since the air introduction
passages for jetting the mixture to be oriented towards the spark
plug and the cross-fire tube are divided into the first and second
rows, the air introduction passages improve in flexibility of
layout and shapes in the mixing chamber wall. This improvement
enables suitable air introduction passages to be designed more
easily for better ignition characteristics and enhanced flame
propagation characteristics.
[0014] According to a third aspect of the present invention, the
gas turbine combustor includes a central burner as the burner; and
a plurality of outer peripheral burners each disposed at an outer
peripheral side relative to the central burner; wherein: the
central burner includes a central mixing chamber wall that is the
mixing chamber wall forming a central mixing chamber which is the
mixing chamber, and a central fuel nozzle as the fuel nozzle; the
outer peripheral burners each include an outer peripheral mixing
chamber wall forming an outer peripheral mixing chamber which opens
towards a downstream side in the axial direction, and an outer
peripheral fuel nozzle for supplying a fuel to the outer peripheral
mixing chamber; in the central mixing chamber wall, the combustion
air introduction passages are provided so as to form a first row
and a second row adjacently to each other, in the axial direction;
the air introduction passage for jetting the combustion air which
flows towards at least one of the spark plug and the cross-fire
tube belongs to the first row; and the combustion air jetted from
the air introduction passage belonging to the second row flows
towards an exit of the outer peripheral mixing chamber.
[0015] According to the third aspect, the combustion air jetted
from air introduction holes along with the fuel will flow towards
an exit of each outer peripheral burner, and hot combustion gases
resulting from combustion of a mixture jetted from the air
introduction passages belonging to the second row will be supplied
to the exit of the outer peripheral burner. Thus, the mixture
supplied from the outer peripheral burner will be easy to burn, and
for example, even if the mixture in the outer peripheral burner is
low in fuel concentration, the combustion can be started easily.
This will improve combustion capabilities of the combustor
including the outer peripheral burner, and enable an operational
load range of the gas turbine to be extended.
[0016] Additionally, since the air introduction passages are
divided into the first and second rows, flexibility of layout and
shapes of the air introduction passages in the mixing chamber wall
improves, which in turn enables suitable air introduction passages
to be designed more easily for an easier start of the combustion of
the mixture supplied from the outer peripheral burner, as well as
for better ignition characteristics and enhanced flame propagation
characteristics.
[0017] According to a fourth aspect of the present invention, the
gas turbine is such that the number of the air introduction
passages constituting the second row in the central burner is an
integral multiple of the number of the outer peripheral
burners.
[0018] According to the fourth aspect, since the number of air
introduction passages is an integral multiple of that of outer
peripheral burners, the air introduction passages for jetting the
mixture to flow towards the outer peripheral burners can be
allocated in equal numbers to each thereof. Additionally, since the
layout and shapes of the air introduction passages to be allocated
can be made equal easily, burner structural simplification and
improvement of combustion stability are realized.
[0019] According to a fifth aspect of the present invention, the
gas turbine combustor is such that in the first row and the second
row, six of the air introduction passages configure an upstream row
in the axial direction, and twelve of the air introduction passages
configure a downstream row; and
[0020] the number of the outer peripheral burners is four or
six.
[0021] According to the fifth aspect, since the row located
downstream has more air introduction passages than the row located
upstream, the mixture that flows towards the downstream side is
oriented in the downstream direction more reliably. In addition,
since the number of air introduction passages in the row located
downstream is an integral multiple of the number of outer
peripheral burners, the fifth aspect works as effectively as the
fourth aspect of the present invention.
[0022] According to the present invention, since the mixing of a
fuel and air in the mixing chamber as well as air introduction
passages of a gas turbine combustor is accelerated, NOx reduction
by premixed combustion is accomplished, with ignition
characteristics and flame propagation characteristics also being
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a sectional view that schematically shows
essential elements of a gas turbine plant which uses a gas turbine
equipped with a gas turbine combustor according to a first
embodiment of the present invention;
[0024] FIG. 2 is a schematic diagram that illustrates combustors
and cross-fire tubes, both equipped in the gas turbine combustor of
FIG. 1;
[0025] FIG. 3 is an enlarged view of the essential elements shown
in FIG. 1, with burner air introduction holes being shown in
simplified form;
[0026] FIG. 4 is a sectional view taken along line IV-IV in FIG.
3;
[0027] FIG. 5 is a sectional view taken along line V-V in FIG.
3;
[0028] FIG. 6 shows a modification of the first embodiment, the
figure corresponding to the essential elements shown in FIG. 3;
[0029] FIG. 7 shows a second embodiment of the present invention,
the figure corresponding to FIG. 3;
[0030] FIG. 8 shows the element of the second embodiment that
corresponds to FIG. 4;
[0031] FIG. 9 is a graph representing a relationship between a gas
turbine load and in-burner fuel flow rates in the second
embodiment;
[0032] FIG. 10 shows a third embodiment of the present invention,
the figure corresponding to FIG. 3;
[0033] FIG. 11 shows elements of the third embodiment that
correspond to FIG. 4;
[0034] FIG. 12 is a graph relating to the third embodiment, the
graph representing a relationship equivalent to that of FIG. 4;
[0035] FIG. 13 shows a fourth embodiment of the present invention,
the figure corresponding to FIG. 3; and
[0036] FIG. 14 shows elements of the fourth embodiment that
correspond to FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] Hereunder, gas turbine combustors according to embodiments
of the present invention will be described with reference to FIGS.
1 to 14.
First Embodiment
[0038] A gas turbine combustor 4 according to a first embodiment of
the invention is described below referring to FIGS. 1 to 5.
[0039] Referring to FIG. 1, a gas turbine plant equipped with a gas
turbine 1 is a power-generating gas turbine plant including an
electric power generator 2 driven by the gas turbine 1.
[0040] The gas turbine 1 includes: a compressor 3 that compresses
air; a gas turbine combustor 4 that creates combustion gases by
burning a fuel by means of combustion air which is part of the
compressed air obtained in the compressor 3; a turbine 5 that
rotates upon being driven by the high-temperature high-pressure
combustion gases created by the gas turbine combustor 4; transition
pieces 6 that guide the combustion gases from the gas turbine
combustor 4 to the turbine 5; a fuel supply system 7 that supplies
the fuel, a gaseous fuel such as liquefied natural gas, to the gas
turbine combustor 4; and a casing 8 serving to support the gas
turbine combustor 4 as well as to form a cylinder 9 through which
the compressed air is to flow after being discharged from the
compressor 3.
[0041] The compressor 3 and the power generator 2 are coupled to
the turbine 5 and rotationally driven by the turbine 5. The
transition pieces 6 are accommodated in the cylinder 9.
[0042] Referring additionally to FIG. 2, the gas turbine combustor
4 includes: a plurality of (in the present embodiment, ten)
can-type combustors 10 equally spaced in a circumferential
direction of the turbine 5 and compressor 3 with a rotational axis
C1 thereof as a center; a spark plug 13 that ignites the mixture
generated when the fuel and the combustion air are mixed;
connecting pipes 14 that each interconnect two adjacent combustors
10; and cross-fire tubes 15 accommodated in the connecting pipes
14, the cross-fire tubes each propagating a flame created between
the two adjacent combustors by the combustion of the mixture.
[0043] One portion of the combustors 10 constituting the gas
turbine combustor 4 includes one or a plurality of (in the present
embodiment, two) first combustors 11, as specific combustors, each
having a spark plug 3, and the remaining combustors 10 are second
combustors 12 without a spark plug 3. The first combustors 11 and
the second combustors 12 have basically the same structure, except
for a structure relevant to the spark plug 13 in the first
combustor 11. In the following description, when no distinction is
drawn between the first combustors 11 and the second combustors 12,
both are referred to simply as the combustors 10.
[0044] Referring to FIGS. 1 and 3, each combustor 10 that supplies
to the gas turbine 1 the combustion gases that have been generated
by the combustion of the fuel-combustion air mixture includes: a
cylindrical inner liner 21 forming a combustion chamber 20; a
cylindrical outer liner 22 disposed around the inner liner 21, the
outer liner 22 forming an ring-shaped air passage 23 in a space
between the inner and outer liners in order to allow the combustion
air from the compressor 3 to flow through the air passage; an end
cover 24 forming an upstream end wall; a burner 30 disposed on the
combustor axis C2, the burner 30 supplying the combustion air and
the fuel to the combustion chamber 30; and a flame holder 25
disposed at an exit of the burner 30, the flame holder serving as a
flame stabilizer to assist in stabilizing the combustion flame.
[0045] The air that has been compressed by the compressor 3 flows
therefrom into the cylinder 9, and part of the compressed air is
supplied to the combustor 10 as the combustion air.
[0046] The combustor axis C2 (also, see FIG. 2) is a central axis
of the inner liner 21 or the combustion chamber 20, the wording
"axial direction" used herein is a direction parallel to the
combustor axis C2, and unless otherwise indicated, radial and
circumferential directions are those with the combustor axis C2
taken as a center.
[0047] In addition, the wording "upstream" and "downstream" relates
to a flow of combustion air in the burner 30 or a flow of
combustion gases in the combustion chamber 20, in the axial
direction.
[0048] The burner 30 disposed so as to have its center positioned
substantially on the combustor axis C2 includes a mixing chamber
wall 32 forming a mixing chamber 31 which opens towards the
combustion chamber 20, in the axial direction, and a fuel nozzle 38
that supplies the fuel. The mixing chamber wall 32 is disposed
upstream relative to the combustion chamber 20, in the axial
direction, the mixing chamber wall 32 being of a hollow conical
shape spread radially towards the combustion chamber 20, in the
axial direction with the combustor axis C2 taken as the axis. The
mixing chamber wall 32, by having a conical mixing-chamber wall
surface 33, forms internally to the wall 32 the mixing chamber 31
spread at an apex angle .alpha. towards the downstream side. The
mixing-chamber wall surface 33, therefore, is of a conical shape
with the apex angle .alpha..
[0049] In the mixing chamber wall 32 are provided a plurality of
air introduction holes, 35, 36, and 37, each forming an independent
air introduction passage to introduce the combustion air into the
mixing chamber 31. Each air introduction hole 35, 36, 37 that is a
rectilinear round hole forms a different angle .beta.1, .beta.2, or
.beta.3, with respect to the mixing-chamber wall surface 33. The
angles .beta.1, .beta.2, and .beta.3 each are an angle formed
between each central axis of the air introduction holes 35, 36, 37
and a generating line (an intersection of the conical
mixing-chamber wall surface 33 and a plane including the combustor
axis C2) of the mixing-chamber wall surface 33.
[0050] The fuel supply system 7 includes a fuel supply device 41, a
fuel distributor 42, and a fuel supply line 43. The fuel supply
line 43 for guiding the fuel received from the fuel supply device
41, via the fuel distributor 42 that distributes the fuel to each
combustor, is connected to the fuel nozzle 38. The fuel supply
system 7 is constructed so that the fuel from the fuel supply line
43 is supplied to the fuel nozzle 38 including a fuel manifold 38a,
and so that the fuel, after being jetted from the fuel nozzle 38,
is fed into all of the air introduction holes 35, 36, 37. Each air
introduction hole 35, 36, 37, therefore, introduces the combustion
air, along with the fuel supplied from the fuel nozzle 38, into the
mixing chamber 31 while generating the mixture of the air and the
fuel.
[0051] In each of two combustors 11, the spark plug 13 is mounted
to the outer liner 22 so that the plug has its igniter 13a
positioned inside the combustion chamber 20.
[0052] Combustors 10 adjacent to each other in a circumferential
direction are interconnected by the connecting pipe 14 that
interconnects the respective outer liners 22. The combustion
chambers 20 or inner liners 21 of the adjacent combustors 10
communicate with each other via a cross-fire tube 15. Opposite open
ends of the cross-fire tube 15 configure an entrance/exit 15a open
to the combustion chamber 20. This means that the entrance/exit 15a
can serve as a flame entrance to an adjacent combustor 10 or as a
flame exit from the adjacent combustor 10.
[0053] When the mixture ignited by the spark plug 13 in the
combustor 11 burns and combustion gases are generated, an internal
pressure of the combustion chamber 20 present internally to the
inner liner 21 increases and a differential pressure occurs between
the combustion chamber 20 of the combustor 11 and that of an
adjacent combustor 12 communicating via the cross-fire tube 15.
This differential pressure moves the combustion gases 27 into the
adjacent combustor 12, thereby igniting the mixture generated by
the adjacent combustor 12. Similar ignition takes place in other
adjacent combustors 12 sequentially, whereby all combustors 10 are
ignited.
[0054] Referring to FIGS. 3 and 4, the air introduction holes 35-37
formed in the mixing chamber wall 32 are arranged side by side in a
plurality of rows, in the first embodiment, three rows (first row
R1 to third row R3), in the axial direction. The rows R1-R3 are
each configured by at least one, in the present embodiment, a
plurality of air introduction holes 35-37 arranged in ring form
with a circumferential spacing, circumferentially at their forming
positions in the axial direction.
[0055] Part of the structure shown in FIG. 3 is omitted from FIG. 4
to avoid complexity of the drawing.
[0056] As shown partially in FIGS. 4 and 5, the air introduction
holes 35-37 belonging to each row R1-R3 are arranged in the mixing
chamber wall 32 concentrically with the combustor axis C2 as their
center. In addition, in order that a swirling flow is generated in
the mixing chamber 31 by the combustion air jetted from the air
introduction holes 35-37, the air introduction hole 37 is formed in
circumferentially offset form and the air introduction holes 35, 36
are formed in axially and circumferentially offset form.
[0057] In terms of axial positions of the first row R1 and the
second row R2, the first row R1 is an upstream row positioned at
the upstream side, and the second row R2 is a downstream row
positioned at the downstream side. In addition, the second row R2
is positioned more outward in the radial direction than the first
row R1, and is disposed on a circumference of a larger diameter
than a circumference having the first row R1 thereupon.
[0058] Referring to FIG. 4, of the air introduction holes 35-37 in
each combustor 10, at least one, in the present embodiment, a
plurality of specific air introduction holes 35a and 35b as
specific air introduction passages, are formed in axially and
circumferentially offset form. Thus, the combustion air jetted from
the specific air introduction holes 35a, 35b into the mixing
chamber 31 will, together with the fuel flowing with the combustion
air through the specific air introduction holes 35a, 35b, be
directed towards the igniter 13a of the spark plug 13 and the
entrance/exit 15a of the cross-fire tube 15. The igniter 13a and
the entrance/exit 15a are both disposed in the inner liner 21.
[0059] More specifically, in the combustor 11, a mixture "m1" of
the fuel and the combustion air jetted from a first specific air
introduction hole 35a will flow towards the igniter 13a, and
mixtures "m2" of the fuel and the combustion air jetted from two
second specific air introduction holes 35b will flow towards the
entrance/exit ports 15a of two cross-fire tubes 15.
[0060] In the combustor 12 (see FIG. 1), a mixture of the fuel and
the combustion air jetted from a second specific air introduction
hole 35b will flow towards the entrance/exit ports 15a of two
cross-fire tubes 15.
[0061] Referring to FIG. 5, since the air introduction hole 37 is
formed at a position offset through an offset distance "s" from the
combustor axis C2 which is also a central axis of the burner 30,
the mixture that has flown in from the air introduction hole 37
generates a swirling flow inside the mixing chamber 31. As with the
air introduction hole 37, the air introduction holes 35, 36 are
also formed at positions offset through the offset distance "s"
from the burner central axis, so each can generate a swirling flow
inside the mixing chamber 31. These swirling flows, in turn,
generate a stable circulating flow at a downstream region of the
burner 30, thus providing combustion stability.
[0062] In the present embodiment, the air introduction holes 35 are
formed such that the mixtures "m1" and "m2" jetted from the
specific air introduction holes 35a and 35b, respectively, of the
air introduction holes 35 belonging to the first row R1 will flow
towards the spark plug 13 and the cross-fire tubes 15,
respectively. The formation of the air introduction holes 35 is
based on the directions in which the mixtures are to flow. The flow
directions of the mixtures are determined by the apex angle .alpha.
of the mixing chamber wall 32 forming the mixing chamber 31, a
forming angle .beta.2 of each air introduction hole, and the offset
distance "s" from the burner central axis or from the combustor
axis C2.
[0063] In addition, in the present embodiment, a ratio of the
offset distance "s" from the burner axis with respect to an inside
diameter "d" (see FIG. 5) of the mixing chamber 31 forming the air
introduction holes 35-37, that is, "s/d" can be set optionally.
Thus, the fuel-combustion air mixtures "m1" and "m2" (see FIG. 4)
jetted from the air introduction holes 35 will deflect towards the
locations of the spark plug 13 and the cross-fire tubes 15.
Furthermore, the circulating flow necessary to obtain combustion
stability can be generated at a downstream region of the burner 30
by controlling the ratio "s/d" of the air introduction holes 35-37.
Therefore, the gas turbine combustor 4 is supplied that is
satisfactory in ignition characteristics and in flame propagation
characteristics and achieves stable combustion.
[0064] Referring to FIGS. 3, 4, during a start of the gas turbine 1
in the thus-constructed gas turbine combustor 4, when the gas
turbine combustor 4 is ignited, the fuel from the fuel supply
device 41 (also, see FIG. 1) is supplied to the fuel nozzle 38. The
fuel is jetted from the fuel nozzle 38, towards the air
introduction holes 35-37, and mixed with the combustion air in the
air introduction holes 35-37 and in the mixing chamber 31, thereby
generating mixtures. The mixtures that have thus been jetted from
the air introduction holes 35-37 are ignited by the spark plug 13,
to initiate premixed combustion.
[0065] The specific air introduction holes 35a, 35b of the air
introduction holes 35 constituting the first row R1 of the first to
third rows (R1 to R3), that is, the second row from the upstream
side (in FIG. 3, the second row from left) are formed so that the
mixtures "m1", "m2" are jetted from the specific air introduction
holes 35a, 35b, towards the igniter 13a of the spark plug 13 and
the entrance/exit ports 15a of the cross-fire tubes 15.
[0066] In the combustor 11, therefore, a mixture higher in fuel
concentration, that is, higher in fuel-air ratio, is present at and
near the igniter 13a of the spark plug 13, so ignition becomes
easier and ignition characteristics improve.
[0067] In addition, since the ignition of the combustor 11 raises
the internal pressure of the combustion chamber 20, the combustion
gases 27 become jetted towards unignited adjacent combustors 11 via
corresponding cross-fire tubes 15. In the present embodiment, since
the mixture "m2" is jetted from the specific air introduction holes
35a, 35b, towards the entrance/exit ports 15a of the cross-fire
tubes 15, a mixture of a higher fuel concentration is present at
and near the entrance/exit 15a in the combustor 11 (in this case,
the entrance/exit 15a functions as the exit), so a combustion gas
higher in temperature can be generated. Accordingly, the hot
combustion gas (a flame) is jetted towards the combustion chamber
20 of an adjacent combustor 12 through a cross-fire tube 15.
[0068] Meanwhile, in the adjacent combustor 12 to which the flame
from the combustor 11 propagates, the mixture of a higher fuel
concentration from a specific air introduction hole 35b is being
jetted towards the entrance/exit 15a of the cross-fire tube 15 (in
this case, the entrance/exit 15a functions as the entrance).
Accordingly the combustion gas flowing in from the combustor 11
through the cross-fire tube 15 facilitates flame propagation, makes
combustion easier to start, and hence improves flame propagation
characteristics.
[0069] In the first embodiment, the mixing chamber wall 32 is
formed at the apex angle .alpha. and forms the conical mixing
chamber 31, and in the mixing chamber 31, the fuel jetted from the
fuel nozzle 38 is mixed with the combustion air and fuel jetted
from the air introduction holes 35-37. An effect of NOx emissions
being further reduced by premixed combustion with an even more
homogeneous mixture is anticipated as a result. The improvement of
combustion stability by an increase in swirling strength is also
anticipated since the swirling flows of mixtures in the mixing
chamber 31 are restrained by the mixing chamber wall 32.
[0070] Additionally, the hollow conical shape of the mixing chamber
wall 32 dimensionally increases a forming region of the air
introduction holes 35-37 in the mixing chamber wall 32, compared
with a case in which the mixing chamber wall 32 is a ring-shaped
flat plate, for example. Such an increase creates an advantage of
increased flexibility in determination of air introduction hole
specifications such as the number of air introduction holes 35-37
and diameters thereof. The air introduction holes 35-37 also become
easier to form.
[0071] If an inside diameter of the inner liner 21 is expressed as
D, and an axial distance from an upstream end of the inner liner 21
to the igniter 13a or the entrance/exit 15a is expressed as L, an
axial design position of the spark plug 13 or cross-fire tube 15 in
the inner liner 21 is usually determined for a ratio of L/D to lie
in a range of 0.3<L/D<0.7. For this reason, the specific air
introduction holes 35a, 35b are desirably formed so that the
mixtures jetted therefrom will be directed towards a position at
the inner liner 21 where 0.3<L/D<0.7 is satisfied.
[0072] In addition, since ignition characteristics of the spark
plug 13 can be improved by adjusting its radial insertion position
in the inner liner 21, if the axial positions of the spark plug 13
and the cross-fire tube 15 significantly differ, the specific air
introduction hole 35b is desirably formed so that the mixture "m2"
is jetted towards the position at which the entrance/exit 15a of
the cross-fire tube 15 is formed.
[0073] In a modification of the first embodiment, if the air
introduction holes 35-37 are formed in a plurality of rows next to
one another in an axial direction, an air introduction hole 35
belonging to a first row R1 which is one of the axial rows may be
formed in offset form so that a mixture "m1" from that air
introduction hole 35 is directed towards the igniter 13a of the
spark plug 13, and an air introduction hole 36 belonging to a
second row R2 different from the first row R1 may be formed in
offset form so that a mixture "m2" from that air introduction hole
36 is directed towards the entrance/exit 15a of the cross-fire tube
15. Additionally if a third row R3 as the remaining row is present
(the number of third rows can be more than one), an air
introduction hole 37 may be formed in the third row R3 so that a
mixture from this air introduction hole 37 contributes to stable
combustion by generating a swirling flow inside the mixing chamber
31.
[0074] This, as in the first embodiment, will improve ignition
characteristics and flame propagation characteristics, and hence,
the startability of the gas turbine 1, thus enabling a burner 30
satisfactory in combustion stability to be supplied.
[0075] In addition, since the specific air introduction holes 35a
and 35b that jet the mixtures "m1" and "m2" to be directed towards
the igniter 13a and the entrance/exit 15a are divided into the
first row R1 and the second row R2, respectively, the air
introduction passages 35, 36 improve in flexibility of layout and
shapes in the mixing chamber wall 32. This improvement enables
suitable air introduction holes 35, 36 to be designed more easily
for better ignition characteristics and enhanced flame propagation
characteristics.
[0076] Furthermore, the gas turbine combustor 4 according to the
first embodiment may use, in addition to a gaseous fuel as a first
fuel, a liquid fuel (e.g., a class-A fuel oil or a light oil) as a
second fuel for the gas turbine 1. In connection with this, another
modification of the first embodiment is described below referring
primarily to FIG. 6 with reference also being made to FIGS. 3 and
4.
[0077] A combustor 10 includes a liquid-fuel nozzle 39 disposed as
a second fuel nozzle at an upstream side of a mixing chamber 31 in
a burner 30 having a fuel nozzle 38 used as a first fuel nozzle to
supply a gaseous fuel as the first fuel, the liquid-fuel nozzle 39
being provided to blast a liquid fuel as the second fuel. The
liquid fuel from a fuel supply device 44 which a fuel supply system
7 includes is supplied to the liquid-fuel nozzle 39.
[0078] The liquid-fuel nozzle 39 is intended to atomize and spray
the liquid fuel so that it mixes with hot combustion air 5 in the
mixing chamber 3 and evaporates to burn easily. The liquid-fuel
nozzle 39 plays a crucial role particularly in atomizing the fuel
into smaller droplets. In general, liquid fuel is atomizable using
either an air-atomize fuel nozzle that forms fine particles by
utilizing its force of shearing air, or a pressure-atomize fuel
nozzle that forms fine particles by utilizing its fueling pressure.
The present invention works effectively with either scheme/method
or with a liquid-fuel nozzle of an atomizing type other than those
described above.
[0079] In the present embodiment, the liquid-fuel nozzle 39 is
positioned on the combustor axis C2 of the burner 30 and at the
upstream side of the mixing chamber 31, so that the droplets
conically sprayed from the liquid-fuel nozzle 39 will mix in the
mixing chamber 31 with the combustion air jetted from the air
introduction holes 35-37 in the burner 30.
[0080] As in the first embodiment, the air introduction holes 35
are formed in axially and circumferentially offset form so that the
combustion air therefrom are jetted towards the igniter 13a of the
spark plug 13 and the entrance/exit 15a of the cross-fire tube 15,
the igniter 13a and the entrance/exit 15a both being disposed in
the inner liner 21. Therefore, a mixture from the air introduction
holes 35 and a mixture from the liquid-fuel nozzle 39, the latter
mixture containing the atomized liquid fuel, are supplied to the
locations of the igniter 13a and the entrance/exit 15a. Of the two
mixtures, the higher in fuel concentration improves ignition
characteristics and flame propagation characteristics.
[0081] The liquid-fuel nozzle 39 in the burner 30 is set so that a
spraying angle of the nozzle (i.e., a spread angle of the liquid
fuel sprayed) will be smaller than the apex angle .alpha. of the
mixing chamber 31. If the spraying angle of the liquid-fuel nozzle
39 is greater than the apex angle .alpha., the droplets sprayed
from the nozzle 39 are liable to collide against the mixing chamber
wall 32 and become carbonized thereupon (this event is called
coking). Coking could deteriorate various performance
characteristics of the burner 30. Setting the liquid-fuel nozzle 39
to have a spraying angle smaller than the apex angle .alpha. helps
prevent coking from occurring.
Second Embodiment
[0082] A second embodiment of the present invention is described
below referring to FIGS. 7 to 9. The second embodiment includes a
plurality of main burners 50, 60 disposed at an outer peripheral
side of the burner 30, with all other constituent elements of the
embodiment being basically the same as in the first embodiment.
[0083] In the second embodiment and in third and fourth embodiments
described later herein, description substantially of the same
elements as those of the first embodiment is omitted or simplified,
with attention being focused primarily upon differences. In
addition, the same members as used in the first embodiment, or
corresponding members in each of the second to fourth embodiments
are each assigned the same reference number or symbol as
appropriate. The second to fourth embodiments yield substantially
the same operation and effect as those of the first embodiment.
[0084] Furthermore, the mixing chamber walls, mixing chambers 31,
and fuel nozzles in the second to fourth embodiments are central
mixing chamber walls, central mixing chambers, and central fuel
nozzles, respectively, and each mixing chamber wall, mixing
chamber, and fuel nozzle are an outer peripheral mixing chamber
wall, an outer peripheral mixing chamber, and an outer peripheral
fuel nozzle, respectively. The burner and a pilot burner are
central burners, and the main burners are outer peripheral
burners.
[0085] Moreover, in figures relating to the second to fourth
embodiments, only mixtures "m3" and "m4" (described later herein)
that will be directed towards, for example, part of the main
burners, are shown to avoid complexity of the drawing.
[0086] Referring to FIGS. 7 and 8, the burners 30, 50, 60 in
combustors 10 equipped in a gas turbine combustor 4 according to
the second embodiment include the burner 30 as the pilot burner,
and the main burners 50, 60.
[0087] At least one, in the present embodiment, six, main burners
50, 60 arranged at the outer peripheral side (i.e., radially
outwardly) of the burner 30 are configured by the same number of
(six) main burners, that is, three first main burners 50 and three
second main burners 60.
[0088] Each main burner 50, 60 includes a mixing chamber wall 52,
62 that serves as an outer peripheral mixing chamber wall forming a
mixing chamber 51, 61 formed as an outer peripheral mixing chamber
which opens towards a downstream side in an axial direction. The
main burner 50, 60 also includes a fuel nozzle 59, 69 serving as an
outer peripheral fuel nozzle to supply a fuel. The mixing chamber
wall 52, 62 disposed at a downstream side of a combustion chamber
20 in the axial direction of the burner includes an upstream wall
52a, 62a having a conically shaped mixing-chamber wall surface 53,
63 spread towards the combustion chamber 20, in the axial direction
with a combustor axis C2 as a center. The mixing chamber wall 52,
62 also includes a cylindrical downstream wall 52b, 62b connecting
to the upstream wall 52a, 62a, the downstream wall 52b, 62b also
extending in a downstream direction. The mixing chamber wall 52, 62
forms a mixing chamber 51, 61 inside the wall. The mixing chamber
wall 52, 62 further includes a cylindrical outer surface.
[0089] While the main burner 50, 60 is basically of the same
construction as that of the burner 30, the mixing chamber 51, 61
has an axial length greater than that of the mixing chamber 31 in
the burner 30, to accelerate mixing of combustion air and fuel in
the mixing chamber 51, 61.
[0090] A plurality of air introduction holes 55 to 57 and 65 to 67,
for introducing the combustion air independently or along with the
fuel into the mixing chamber 51, 61, are formed in the upstream
wall 52a, 62a. The air introduction holes 55-57 and 65-67 are
arranged in three axial rows, with a second row R2 being closer to
an exit of the burner 30 and an exit of the main burner 50, 60,
than a first row R1, in the axial direction.
[0091] The fuel nozzle 59, 69 includes a fuel manifold 59a, 69a
formed at an upstream section of the main burner 50, 60, and fuel
nozzle ports 59b, 69b that make the fuel manifold 59a, 69a and the
air introduction holes 55-57 and 65-67 communicate with each
other.
[0092] A fuel supplied to the fuel manifold 59a, 69a from a fuel
supply device 45, 46 provided in a fuel supply system 7 is supplied
by being jetted from the fuel nozzle ports 59b, 69b into the air
introduction holes 55-57 and 65-67.
[0093] The fuel, after being supplied to the air introduction holes
55-57 and 65-67, mixes with combustion air in the air introduction
holes 55-57 and 65-67 and in the mixing chamber 51, 61, and forms a
premixed flame in the combustion chamber 20 located downstream with
respect to the main burner 50, 60, followed by premixed
combustion.
[0094] Whereas the main burner 50 thus has substantially the same
construction as that of the main burner 60, fuel is supplied from a
fuel supply device 45 different from the fuel supply device 46 of
the main burner 60. More specifically, therefore, fuel is supplied
from independent supply devices to the seven burners; from a fuel
supply device 41 to the burner 30, from the fuel supply device 45
to the three main burners 50, and from the fuel supply device 46 to
the other three main burners 60.
[0095] Next, a method of operating the gas turbine 1 (see FIG. 1)
equipped with the gas turbine combustor 4 according to the second
embodiment is described below with reference being made to FIG.
9.
[0096] While a load as an operational state indicator for the gas
turbine 1 lies in a load state range from load "a" (non-loaded) to
a level less than load "b", fuel is supplied to the burner 30 and
the gas turbine 1 is operated using the burner 30 alone. Under a
load state from load "b" to a level less than load "c", a flow rate
of fuel in the burner 30 is reduced under load "b", whereas fuel is
supplied to each main burner 50 and the gas turbine 1 is operated
using both of the burner 30 and the main burner 50. Under a load
state from load "c" to rated load "d", the flow rates of fuel in
the burner 30 and in the main burner 50 are reduced under load "c",
whereas fuel is supplied to each main burner 60 and the gas turbine
1 is operated using all of the burner 30 and the main burners 50,
60.
[0097] Under rated load "d" that is a rated operating load, low-NOx
combustion can be conducted by ensuring combustion stability and
then adjusting a ratio between the fuel flow rate in the burner 30
and those of the main burners 50, 60.
[0098] In this way, low-NOx operation and combustion stability can
be simultaneously achieved in the second embodiment by disposing
the burner 30 centrally on the combustor axis C2 of the combustor
10, arranging the six main burners 50, 60 at the outer peripheral
side of the burner 30, and during rated operation, adjusting the
ratio between the fuel flow rate in the burner 30 for diffuse
combustion and the fuel flow rates in the main burners 50, 60 for
premixed combustion.
[0099] As shown in FIGS. 7 and 8, in the combustor with the main
burners 50, 60 arranged at the outer peripheral side of the burner
30 and with the spark plug 13 and the cross-fire tubes 15 further
arranged at an outer peripheral side of each main burner, the
ignition characteristics and flame propagation characteristics of
the burner 30 are likely to be reduced by the combustion air jetted
from the main burners 50, 60 during the ignition of the
combustor.
[0100] Additionally, in the combustor 10 of the present second
embodiment, as shown in FIG. 9, from the independent operational
state of the burner 30 which is a pilot burner, fuel is supplied to
the main burners 50 under load state "b" and premixed combustion is
started using the main burners 50, and further under load "c", fuel
is supplied to the main burners 60 and operation with all burners
is started. Accordingly, when premixed combustion with the main
burners 50, 60 is started and/or stopped, combustion may become
unstable depending on the particular load state. A range in which
the gas turbine 1 is put into stable operation, therefore, is
desirably such that the turbine be operated at a load higher than
load "c" under which fuel is supplied to all burners 30, 50, 60. On
the other hand, if load "c", the operational load state under which
fueling to all burners 30, 50, 60 is started, is set to be slightly
lower, operational flexibility increases since the load range in
which the gas turbine 1 can be stably operated is extended.
[0101] In the second embodiment, therefore, the air introduction
holes 36 belonging to the second row R2 are formed so that the
mixtures "m3" and "m4" from the air introduction holes 36 are
jetted towards the exits of the main burners 50, 60, and thus,
high-temperature combustion gases are supplied to the exits of the
main burners 50, 60. This allows premixed combustion in the main
burners 50, 60 to be started, even under the conditions that the
mixtures supplied from the main burners 50, 60 are low in fuel
concentration, that is, under a low-load operational state of the
gas turbine 1. The above in turn allows a lower load to be set as
load "c" that is the starting load of the combustion in all burners
30, 50, 60. Thus, the operating load range of the gas turbine 1 can
be extended.
[0102] As shown in FIG. 8, as in the first embodiment, the mixture
"m1" from a specific air introduction hole 35a in the combustor 11
is jetted towards the igniter 13a of the spark plug 13, and the
mixture "m2" from a specific air introduction hole 35b is jetted
towards the entrance/exit 15a of the cross-fire tube 15. Therefore,
the mixture "m1" or "m2", whichever is the higher in fuel
concentration, can be supplied to the locations of the spark plug
13 and the cross-fire tube 15, and this improves the starting
ignition characteristics and flame propagation characteristics of
the gas turbine 1.
[0103] Additionally, since the spark plug 13 and the cross-fire
tube 15 are arranged substantially midway in the main burner 50,
60, in the circumferential direction, the mixtures "m1", "m2" are
made less susceptible to any impacts of the combustion air or air
jetted from the main burner 50, 60. This advantage also helps
improve ignition characteristics and flame propagation
characteristics.
[0104] Furthermore, as indicated by the fact that six air
introduction holes 35 and twelve air introduction holes 36 are
formed in the burner 30 and six main burners 50, 60 are arranged at
the outer peripheral side of the burner 30, if the number of air
introduction holes 36 in the burner 30 is increased to an integral
multiple of the number of main burners 50, 60 and appropriate
circumferential positions of the air introduction holes 35 in the
first row R1 are set, the mixture that the burner 30 generates can
be used efficiently to improve the starting ignition
characteristics and flame propagation characteristics of the gas
turbine 1. In addition, if appropriate circumferential positions of
the air introduction holes 36 in the second row R2 are set, heat
energy of the combustion gases from the burner 30 can be
efficiently transferred to the main burners 50, 60 that conduct
premixed combustion. Operation of the gas turbine 1 with all
burners can therefore be started, even under low load, and this
advantage also aids in stable turbine operation and in extending
the load range.
[0105] Furthermore, since the specific air introduction holes 35a
and 35b that jet the mixtures "m1" and "m2" to be directed towards
the igniter 13a and the entrance/exit 15a, and the specific air
introduction holes 36 that jet the mixtures "m3" and "m4" to be
directed towards the exits of the main burners 50, 60 are divided
into the first row R1 and the second row R2, respectively, the air
introduction holes 35, 36 improve in flexibility of layout and
shapes in the mixing chamber wall 32. This improvement enables
suitable air introduction holes 35, 36 to be designed more easily
for better ignition characteristics and enhanced flame propagation
characteristics.
[0106] Furthermore, since the number of air introduction holes 36
is an integral multiple of that of main burners 50, 60, the air
introduction holes 36 for jetting the mixtures to be directed
towards the main burners 50, 60 can be allocated in equal numbers
to each thereof. Additionally, since the layout and shapes of the
air introduction holes 36 to be allocated can be made equal easily,
burner structural simplification and improvement of combustion
stability are realized. Moreover, since the second row R2
positioned more downstream relative to the first row R1 has more
air introduction holes than the first row R1, the mixtures that
flow in the downstream direction can be directed more reliably
towards the main burners 50, 60.
Third Embodiment
[0107] A third embodiment of the present invention is described
below referring to FIGS. 10 to 12.
[0108] Referring to FIGS. 10, 11, burners 70, 80 in combustors 10
equipped in a gas turbine combustor 4 according to the third
embodiment include a pilot burner 70 equivalent to the burner 30 in
the second embodiment, and a main burner 80.
[0109] The pilot burner 70 includes a mixing chamber wall 72 that
forms a conical mixing chamber 71 opening towards a downstream side
in an axial direction. The pilot burner 70 also includes a fuel
nozzle 79 serving as a central nozzle to supply a fuel. The mixing
chamber wall 72 has a mixing chamber wall surface 73 formed into a
conical shape, thereby forming the conical mixing chamber 71.
[0110] In the mixing chamber wall surface 72, a plurality of air
introduction holes 75, 76 that form a plurality of air introduction
passages for introducing combustion air independently or along with
fuel into the mixing chamber 71, are arranged in two axial rows,
namely, a first row R1 and a second row R2. The fuel nozzle 79 that
supplies fuel by jetting it into each air introduction hole 75, 76,
is disposed at an upstream side of the mixing chamber wall 72.
[0111] The first row R1 is configured by at least one, in the
present embodiment, six air introduction holes 75 formed spacedly
in a circumferential direction, and the second row R2 is configured
by at least one, in the present embodiment, twelve air introduction
holes 76 formed spacedly in the circumferential direction.
[0112] In addition, each air introduction hole 75, 76 includes a
linear portion 75c, 76c and offset portions 75d, 76d connecting to,
and at a downstream side of, the linear portion 75c, 76c. The
offset portions 75d, 76d, exits to the air introduction hole 75,
76, is formed in axially and circumferentially offset form so that
the combustion air or mixture jetted from the air introduction hole
75, 76 will create a swirling flow inside the mixing chamber 71.
The linear portion 75c, 76c that includes an entrance to the air
introduction hole 75, 76, extends substantially in parallel from
the offset portions 75d, 76d, in an axial direction towards an
upstream side, and is formed to have at least twice an axial length
of the offset portions 75d, 76d. In addition, fuel from a fuel
supply device 41 is supplied to the fuel nozzle 79 having a fuel
manifold 79a, and the fuel from the fuel nozzle 79 is jetted to be
fed into each air introduction hole 75.
[0113] The main burner 80, disposed at an outer peripheral side
relative to the pilot burner 70, includes a cylindrical mixing
chamber wall 82 that forms a mixing chamber 81 opening towards a
downstream side in an axial direction. The main burner 80 also
includes a fuel nozzle 89 that supplies fuel. The mixing chamber
wall 82 as an outer peripheral mixing chamber wall, includes an
outer peripheral chamber wall 82a and an inner peripheral chamber
wall 82b.
[0114] The mixing chamber 81 with an axial length greater than that
of the mixing chamber 71 extends axially and is formed circularly,
with the fuel nozzle 89 being disposed at an upstream side of the
mixing chamber 81 and an annularly shaped bluff body 84 being
disposed at an exit of the mixing chamber 81.
[0115] Fuel from a fuel supply device 47 equipped in a fuel supply
system 7 is supplied to a fuel manifold 88. The fuel jetted from
the fuel nozzle 89 mixes with combustion air in the mixing chamber
81, whereby a mixture of the fuel and the combustion air is
generated. The mixture flows downstream towards the combustion
chamber 20, where premixed combustion takes place stably by an
action of a circulating flow formed at a downstream side of the
bluff body 84. A pilot burner cone 78 is disposed between the pilot
burner 70 and the main burner 80, in a radial direction.
[0116] Referring to FIG. 11, the mixing chamber 81 of the main
burner 80 is divided into four mixing chambers, 81a to 81d, by four
separating walls 87 as separators disposed inside the mixing
chamber 71. In order to suit this mixing chamber arrangement, the
fuel supply device 47 is also divided into four independent fuel
supply devices, 47a-47d, as many as there actually the mixing
chambers 81a-81d. In addition, the fuel nozzle 89 is likewise
divided into four independent fuel nozzles, 89a to 89d, in order
that fuel is supplied from each of the fuel supply devices, 47a-47d
independently.
[0117] For these reasons, the main burner 80 is configured by four
independent main burners, 80a to 80d. The main burners 80a-80d each
include the corresponding fuel nozzle 89a-89d plus a mixing chamber
wall configured by a segment and separating wall 87 of one of the
mixing chamber walls 82 forming the mixing chambers 81a-81d. The
fuels supplied to the four fuel nozzles, 89a-89d, can be separately
controlled in flow rate.
[0118] In this way, since the mixing chamber 81 is axially longer
than the mixing chamber 71 of the pilot burner 70, the combustor 10
in the third embodiment includes the main burner 80 that is the
very-low-NOx type of burner that accelerates fuel-combustion air
mixing. In addition, since axial length of the air introduction
hole 75, 76 includes the linear portion 75c, 76c, the combustor 10
in the third embodiment further includes the pilot burner 70 longer
than the air introduction holes 35, 36 of the first or second
embodiment that only include nearly a portion equivalent to the
offset portions 75d, 76d.
[0119] In the pilot burner 70, whose mixing chamber wall surface 73
is of a conical shape and whose upstream end wall surface 74 is of
a planar shape, the air introduction hole 75, 76 can have its
linear portion 75c, 76c into a shape extending in parallel in an
axial direction, fuel-combustion air mixing in the air introduction
hole 75, 76 is fully accelerated, and NOx emissions from a flame
formed by the pilot burner 70 are therefore reduced.
[0120] In the third embodiment, the air introduction hole 75 at an
inner peripheral side (or an upstream side) of the pilot burner 70
is formed by six circumferential holes, and the air introduction
hole 76 at an outer peripheral side (or a downstream side) is
formed by twelve circumferential holes. Accordingly, the air
introduction hole 76 located radially outward relative to the air
introduction hole 75 is longer than the air introduction hole 75,
so a fuel-combustion air mixing distance in the air introduction
hole 76 is longer and mixing is correspondingly accelerated for
further reduced NOx.
[0121] Additionally, the offset portions 75d, 76d of the air
introduction hole 75, 76 are axially and circumferentially offset,
and advantageous effects obtained in connection with this
offsetting are substantially the same as in the first and second
embodiments.
[0122] More specifically, according to the third embodiment, fuel
sprayed from a fuel nozzle 79 is mixed with combustion air in the
air introduction hole 75, 76 and jetted into the mixing chamber 71.
The axially and circumferentially offset shape of the air
introduction hole 75, 76 then creates a swirling flow in the mixing
chamber 71. An angle at which the mixture is jetted from the air
introduction hole 75, 76 can be controlled by adjusting the offset
angle thereof.
[0123] After the creation of the swirling flow, as shown in FIG.
11, a mixture "m1" jetted from a specific air introduction hole 75a
of the air introduction hole 75 is directed towards an igniter 13a
of a spark plug 13. A mixture "m2" jetted from a specific air
introduction hole 75b of the air introduction hole 75 is directed
towards an entrance/exit 15a of a cross-fire tube 15. A mixture of
a higher fuel concentration is therefore formed at and near the
igniter 13a of the spark plug 13 and the entrance/exit 15a of the
cross-fire tube 15, and the formation of the mixtures improves
starting ignition characteristics and flame propagation
characteristics of the gas turbine 1 (see FIG. 1).
[0124] In addition, a mixture "m3" jetted from the air introduction
hole 76 flows towards a downstream region of bluff bodies 84 (see
FIG. 10) of each main burner 80a-80d constituting the main burner
80. During a start of premixed combustion with the main burner 80,
therefore, hot combustion gases are supplied to the downstream
region of each bluff body 84. This enables premixed combustion to
be started under the conditions of a low fuel concentration, and
hence improves the combustion characteristics (hereinafter,
referred to as switching characteristics) developed during the
start of premixed combustion with the main burner 80.
[0125] Next, a method of operating the gas turbine combustor 4
according to the third embodiment is described below referring
primarily to FIG. 12, with reference also being made to FIGS. 10
and 11.
[0126] After an operational start of the gas turbine 1 (see FIG.
1), the gas turbine 1 reaches load level "e" shown in FIG. 12, a
graph that represents changes in no-load rated turbine speed. The
load of the gas turbine 1 increases upon fuel being supplied to the
pilot burner 70 only.
[0127] Upon the gas turbine 1 arriving at load level "f", the flow
rate of the fuel in the pilot burner 70 is reduced, then fuel is
supplied to the main burner 80a, and in the bluff body 84, a
premixed flame is formed at a downstream side of a region
corresponding to the mixing chamber 81a. At this time, the fuel
flow rates in the pilot burner 70 and the main burner 80a are
substantially equal and the mixture jetted from the mixing chamber
71 can obtain high-calorie heat energy of the hot combustion gases
from the pilot burner 70, at the downstream side of the bluff body
84. The result is that the premixed flame formed at the downstream
side of the mixing chamber 81a exhibits appropriate switching
characteristics.
[0128] After the load of the gas turbine 1 has increased to load
level "g", fuel is also supplied to the main burner 80b. At load
level "h", fuel is supplied to the main burner 80c as well and the
main burners 80b and 80c then start premixed combustion. However, a
consequential decrease in the rate of the fuel flow in the pilot
burner 70 to that required for remixed combustion causes a
switching tolerance to tend to decrease (or narrow).
The switching tolerance here is an indicator of breadth of a
fuel-air ratio tolerance needed to ensure combustion stability
during switching. As the switching tolerance increases, switching
with the required combustion stability ensured in a wider fuel-air
ratio range is achievable and switching characteristics
improve.
[0129] Load level "i" indicates a load state under which the pilot
burner 70 and the entire main burner 80 (therefore, the main
burners 80a-80d) start the combustion. In this operational state,
since the fuel flow rate in the pilot burner 70 decreases relative
to that of the main burner 80, the energy level of the heat
supplied from the pilot burner 70 decreases and the switching
tolerance in switching characteristics decreases.
[0130] In the present third embodiment, however, since a mixture
"m5" from the air introduction hole 75 in the first row R1 is
jetted towards the downstream side of each mixing chamber 81a-81d
and since the mixture "m3" from the air introduction hole 76 in the
second row R2 is jetted towards the downstream side of each mixing
chamber 81a-81d, hot combustion gases can be concentrated at the
downstream side of the bluff body 84, at positions corresponding to
each mixing chamber 81a-81d. The switching characteristics at load
level "i" can be improved as a result.
[0131] In addition, in the present third embodiment with the main
burner 80 having its mixing chamber 81 divided into the four mixing
chambers (81a-81d), the air introduction hole 76 in the pilot
burner 70 is configured by 12 holes, this number being an integral
multiple of the number of mixing chambers 81a-81d. Consequently,
the heat energy of the combustion gases from the pilot burner 70
can be equally supplied to the downstream side of the mixing
chambers 81a-81d.
[0132] Furthermore, since six air introduction holes 75 are formed
in the first row R1 at the inner peripheral side of the pilot
burner 70, a mixture of a higher fuel concentration is formed at
and near the igniter 13a of the spark plug 13 and the entrance/exit
15a of the cross-fire tube 15. At the same time, at the load level
"i" where the switching tolerance is minimized, the mixtures "m5",
"m3" from the air introduction holes 75, 76 are jetted towards the
exit and vicinity of the mixing chamber 81d. Thus, the supply rate
of the mixture from each air introduction hole 75 at the inner
peripheral side becomes twice that obtained at the mixing chamber
81b, 81c. This allows effective use of the heat energy of the
combustion gases, and hence the improvement of the switching
characteristics.
[0133] As shown in FIG. 12, at load level "i", increasing the fuel
flow rate in the pilot burner 70 controls the switching
characteristics to improve, but if the heat energy from the pilot
burner 70 is too great, this elevates temperature of the premixed
flame and increases thermal NOx emissions. In order to avoid these
events, after switching at load level "i" to all-burner combustion,
the fuel flow rate in the pilot burner 70 is reduced and that of
the main burner 80 is increased, whereby NOx emissions are
reduced.
[0134] In this fashion, the third embodiment allows the axial
length of the air introduction hole 75 to be extended. In addition,
if the pilot burner 70 designed so that the jetting directions of
the combustion air and mixture jetted from the air introduction
hole 75 are adjustable at the exits of the air introduction holes
75, 76 is combined with the main burner 80 having the axially
extended mixing chamber 81, then the gas turbine combustor 4 can be
supplied that is satisfactory in ignition characteristics and in
flame propagation characteristics and is able to burn at a very low
NOx level under the rated load as well as to reduce the switching
load of the gas turbine 1.
Fourth Embodiment
[0135] A fourth embodiment of the present invention is hereinafter
described with reference to FIGS. 13 and 14.
[0136] Burners 90, 100 in combustors 10 equipped in a gas turbine
combustor 4 according to the fourth embodiment include a pilot
burner 90 equivalent to the burner 30 in the second embodiment, and
a main burner 100.
[0137] The pilot burner 90 includes a mixing chamber wall 92
forming a mixing chamber 91 which opens towards a combustion
chamber 20 in the axial direction, and fuel nozzles 98, 99 that
supply fuel. A mixing chamber wall surface 93 of the mixing chamber
wall 92 is formed in a conical surface shape to provide the mixing
chamber 91 formed in a conical shape. The mixing chamber wall 92 is
formed with a plurality of air introduction holes 95, 96 arranged
in two rows, i.e., in first and second rows R1, R2. The air
introduction holes 95, 96 are adapted to eject a mixture of
combustion air and fuel. The fuel nozzle 98 is disposed at the
upstream side of the air introduction holes 95, 96 in the axial
direction at a position facing the air introduction holes 95, 96.
The fuel nozzle 98 jets and supplies fuel into the air introduction
holes 95, 96. The air introduction holes 95, 96 are each formed in
axially and circumferentially offset form so that the combustion
air or the mixture jetted from the air introduction holes 95, 96
may produce a swirl flow in the mixing chamber 91.
[0138] The fuel nozzles 98, 99 are composed of a gas fuel nozzle 98
as a first fuel nozzle adapted to supply gas fuel as a first fuel
and a liquid fuel nozzle 99 as a second fuel nozzle adapted to
supply liquid fuel as a second fuel.
[0139] Fuel which is gas fuel from a fuel supply device 41 included
in a fuel supply system 7 is jetted and supplied from the fuel
nozzle 98 having a fuel manifold portion 98a into the air
introduction holes 95, 96.
[0140] Fuel which is liquid fuel from a fuel supply device 46
included in the fuel supply system 7 is jetted into the mixing
chamber 91 from the liquid fuel nozzle 99 installed on the upstream
side of the combustion chamber 20 on a combustor axis C2. As
described above, fuels are individually supplied to the fuel
nozzles 98, 99. Therefore, the pilot burner 90 allows for single
combustion of gas fuel, single combustion of liquid fuel, and mixed
combustion of gas fuel and liquid fuel.
[0141] The six main burners 100 are arranged at circumferential
intervals on the outer circumferential side of the pilot burner 90.
The main burners 100 are each such that a plurality of air
introduction holes 105-107 arranged in a concentric pattern are
axially arranged in three rows with the burner central axis of the
main burner 100 as a center. Fuel nozzles 109 are disposed for the
air introduction holes 105-107. The fuel nozzles 109 substantially
axially jet and supply fuel to the air introduction holes 105-107
in parallel
[0142] Fuel as gas fuel from the fuel supply devices 48 included in
the fuel supply system 7 (see FIG. 1) is supplied to fuel nozzles
109 having respective fuel manifold portions 109a. In addition, the
fuel from the fuel nozzles 109 are jetted and supplied into the air
introduction holes 105-107.
[0143] Combustion air, along with the fuel jetted from the fuel
nozzles 109, is jetted into the combustion chamber 20 through the
air introduction holes 105-107. When the mixture of combustion gas
and fuel is jetted from the respective narrow spaces of the air
introduction holes 105-107 to the wide space of the combustion
chamber 20, the mixture flow produces large turbulent. Thus, mixing
of combustion gas with fuel is accelerated in the combustion
chamber 20.
[0144] In the fourth embodiment, a large number of the air
introduction holes 105, 106, 107 are formed in the respective main
burners 100. In addition, the fuel nozzles 109 are arranged in
association with the corresponding air introduction holes 105-107.
Fuel is previously dispersed in accordance with the number of the
air introduction holes 105-107. Thus, a boundary area between
combustion air and fuel is increased. This accelerates the mixing
of combustion air with fuel even if the axial distance in mixing of
air and fuel is short, which allows for ultralow NOx
combustion.
[0145] In general, if the axial length of the mixing chamber 91 is
large, there is a risk that flame goes back in the mixing chamber
91. However, the main burner 100 in the fourth embodiment mixes
fuel with combustion air in the combustion chamber 20; therefore,
it is possible to avoid the risk that flame goes back in the main
burner 100.
[0146] In the fourth embodiment, since the mixing of fuel with
combustion air is accelerated as described above, the fuel
concentration of the mixture jetted to the downstream of the main
burner 100 is uniform, which is effective for low NOx
combustion.
[0147] However, the mixture jetted from the main burner 100 is
uniform in fuel concentration, i.e., does not have a portion with
increased concentration. Therefore, it is conceivable that the
mixture becomes hard to be ignited and ignition characteristics
decrease when premixed combustion is started upon receipt of
thermal energy from the flame produced by the pilot burner 90.
Because of this, as long as the gas turbine 1 (see FIG. 1) does not
have a high load, combustion in all burners 90, 100 becomes
impossible. Consequently, there is a possibility that load range in
which to operate the gas turbine 1 becomes narrow.
[0148] To eliminate such a possibility, as shown in FIG. 14, the
first row R1 is configured by at least one, in the fourth
embodiment, six air introduction holes 95 formed spacedly in a
circumferential direction, and the second row R2 is configured by
at least one, in the fourth embodiment, twelve air introduction
holes 96 formed spacedly in the circumferential direction, similar
to the second embodiment. Thus, the number of the air introduction
holes 96 is the integral multiple of the number of the main burners
100.
[0149] A mixture "m1" from a specific air introduction hole 95a of
the air introduction holes 95 is jetted towards an igniter 13a of a
spark plug 13. A mixture "m2" from specific air introduction holes
95b of the air introduction holes 95 is emitted towards the
entrance/exit 15a of cross-fire tubes 15. A mixture "m3" from the
air introduction holes 96 is emitted towards corresponding
respective exits of the main burners 100. In this way, the thermal
energy of the flame (i.e., also combustion gas) produced by the
pilot burner 90 can efficiently be used for ignition, flame
propagation and further the ignition of premised flame. Therefore,
the ignition characteristics, flame propagation characteristics and
switching characteristics are improved. As a result, the gas
turbine combustor 4 can be provided that is satisfactory in
ignition characteristics and in flame propagation characteristic.
Also the gas turbine combustor 4 can lower the switching load of
the gas turbine 1, and allows for ultralow NOx combustion under the
rated load condition.
[0150] Since the main burner 100 used in the fourth embodiment does
not permit flame to go back thereinto, it can be applied as a low
NOx combustor for hydrogen-containing fuel having fast fuel speed.
Hydrogen-containing fuel may be used as fuel for a gas turbine. In
such a case, since hydrogen has a wide combustible range, in some
cases liquid fuel (e.g. light oil) is used for ignition and flame
propagation and then hydrogen-containing fuel is used for
combustion, thereby avoiding explosion due to ignition failure
during ignition.
[0151] On the other hand, in the fourth embodiment, the pilot
burner 90 is provided with both the fuel nozzle 98 for gas fuel and
the fuel nozzle 99 for liquid fuel. Therefore, the pilot burner 90
allows for single combustion of gas fuel, single combustion of
liquid fuel, and mixed combustion of gas fuel and liquid fuel. In
addition, it also is satisfactory in ignition characteristics and
flame propagation characteristics during the use of liquid fuel.
Thus, the gas turbine combustor 4 according to the fourth
embodiment is effective for a gas turbine combustor using
hydrogen-containing fuel.
[0152] A description is given of configurations of modified
examples of the embodiments described above.
[0153] The mixing chamber in the burner 11 according to the first
embodiment and the mixing chambers in the pilot burners according
to the second-fourth embodiments are formed in a conical shape
spread towards the downstream of the combustor. However, the
downstream side shape of the pilot burner may be formed in a flat
plate shape or in a convex shape whose central portion projects
towards the downstream side. In other words, the downstream side
shape of the pilot burner is formed so that the combustion air from
the air introduction hole and the mixture of the fuel and
combustion air are each jetted towards a corresponding one of the
igniter of the spark plug, the entrance/exit of the cross-fire
tube, and the outlet port of the main burner for premixed
combustion. In short, it is needed only to adjust the ejecting
direction of the air introduction hole of the pilot burner so that
the thermal energy of the flame of the pilot burner may be used
effectively.
[0154] The air introduction passage may be formed of a tubular
member.
[0155] Fuel may not be supplied to an air introduction hole other
than the specific air introduction holes. In such a case, such an
air introduction hole is adapted to eject only combustion air into
the mixing chamber.
[0156] The combustion air- and fuel-containing mixture jetted from
the specific air introduction hole may be deflected, by deflection
means (e.g. a deflection plate or deflection air flow), towards the
igniter 13a or the entrance/exit 15a and its vicinity before it
will reach the igniter 13a or the entrance/exit 15a and its
vicinity.
[0157] The first row R1 may be located at a downstream side and the
second row R2 may be located at an upstream side.
[0158] The plurality of air introduction passages may be formed in
a plurality of rows in the radial direction. In such a case, the
same operation and effect as in the case where the rows are formed
in the axial direction can be provided. If the plurality of air
introduction passages are formed in a plurality of, i.e., three or
more, rows in the axial direction or in the radial direction, first
and second rows are applied to any two rows of the plurality of
rows.
[0159] The present invention can be applied, in addition to a gas
turbine combustor for a power generation gas turbine, to a gas
turbine constituting part of a cogeneration system capable of
supply of both heat and electric power, a gas turbine for driving a
machine such as a pump, a compressor or the like, or other various
gas turbines.
* * * * *