BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] 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.
2. Description of the Related Art
[0002] 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.
[0003] 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.
[0004] 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.
[0005] In
EP 2065643 A2 a combusting system includes a plurality of combustors each including a fuel pipe
that supplies fuel to a fuel nozzle, and a fuel purge system connected to the fuel
pipe, wherein adjacent ones of the plurality of combustors are interconnected through
a cross fire tube, and some of the plurality of combustors each include a ignitor,
and a device for delaying fuel injection from the combustion nozzle of the combustor
including the ignitor from fuel injection from the combustion nozzle of the combustor
not including the ignitor.
EP 1655456 A2 discloses a gas turbine combustor according to the preamble of claim 1.
SUMMARY OF THE INVENTION
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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, characterized in that at least one
specific air introduction passage among the air introduction passages is formed in
axially and circumferentially offset form such that flows of the combustion air and
fuel jetted from the specific air introduction passages into the mixing chamber are
directed towards at least one of the spark plug and the cross-fire tube.
[0010] 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.
[0011] According to a second aspect of the present invention, in the gas turbine combustor,
the at least one specific air introduction passage comprises a plurality of specific
air introduction passages, and the mixing chamber wall is such that the plurality
of specific 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 specific air introduction passage for jetting the combustion air which flows towards
the spark plug belongs to the first row; and the specific air introduction passage
for jetting the combustion air which flows towards the cross-fire tube belongs to
the second row.
[0012] 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.
[0013] 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 plurality of 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 specific
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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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
the number of the outer peripheral burners is four or six.
[0019] 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.
[0020] 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
[0021]
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;
Fig. 2 is a schematic diagram that illustrates combustors and cross-fire tubes, both
equipped in the gas turbine combustor of Fig. 1;
Fig. 3 is an enlarged view of the essential elements shown in Fig. 1, with burner
air introduction holes being shown in simplified form;
Fig. 4 is a sectional view taken along line IV-IV in Fig. 3;
Fig. 5 is a sectional view taken along line V-V in Fig. 3;
Fig. 6 shows a modification of the first embodiment, the figure corresponding to the
essential elements shown in Fig. 3;
Fig. 7 shows a second embodiment of the present invention, the figure corresponding
to Fig. 3;
Fig. 8 shows the element of the second embodiment that corresponds to Fig. 4;
Fig. 9 is a graph representing a relationship between a gas turbine load and in-burner
fuel flow rates in the second embodiment;
Fig. 10 shows a third embodiment of the present invention, the figure corresponding
to Fig. 3;
Fig. 11 shows elements of the third embodiment that correspond to Fig. 4;
Fig. 12 is a graph relating to the third embodiment, the graph representing a relationship
equivalent to that of Fig. 4;
Fig. 13 shows a fourth embodiment of the present invention, the figure corresponding
to Fig. 3; and
Fig. 14 shows elements of the fourth embodiment that correspond to Fig. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Hereunder, gas turbine combustors according to embodiments of the present invention
will be described with reference to Figs. 1 to 14.
(First Embodiment)
[0023] A gas turbine combustor 4 according to a first embodiment of the invention is described
below referring to Figs. 1 to 5.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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 α towards the downstream side. The mixing-chamber
wall surface 33, therefore, is of a conical shape with the apex angle α.
[0034] 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 β1, β2, or β3, with respect
to the mixing-chamber wall surface 33. The angles β1, β2, and β3 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] Part of the structure shown in Fig. 3 is omitted from Fig. 4 to avoid complexity
of the drawing.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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
α of the mixing chamber wall 32 forming the mixing chamber 31, a forming angle β2
of each air introduction hole, and the offset distance "s" from the burner central
axis or from the combustor axis C2.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] In the first embodiment, the mixing chamber wall 32 is formed at the apex angle α
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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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 α of the mixing chamber 31. If the spraying angle of the liquid-fuel nozzle
39 is greater than the apex angle α, 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 α helps prevent coking from occurring.
(Second Embodiment)
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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)
[0092] A third embodiment of the present invention is described below referring to Figs.
10 to 12.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] 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.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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.
[0108] 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.
[0109] 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) .
[0110] 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.
[0111] 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.
[0112] 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.
[0113] 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.
[0114] 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.
[0115] 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.
[0116] 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.
[0117] 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.
[0118] 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.
[0119] 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.
[0120] 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)
[0121] A fourth embodiment of the present invention is hereinafter described with reference
to Figs. 13 and 14.
[0122] 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.
[0123] 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.
[0124] 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.
[0125] 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.
[0126] 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.
[0127] 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
[0128] 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.
[0129] 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.
[0130] 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.
[0131] 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.
[0132] 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.
[0133] 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.
[0134] 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.
[0135] 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.
[0136] 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.
[0137] 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.
[0138] A description is given of configurations of modified examples of the embodiments
described above.
[0139] 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.
[0140] The air introduction passage may be formed of a tubular member.
[0141] 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.
[0142] 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.
[0143] The first row R1 may be located at a downstream side and the second row R2 may be
located at an upstream side.
[0144] 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.
[0145] 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.