U.S. patent number 3,916,619 [Application Number 05/410,105] was granted by the patent office on 1975-11-04 for burning method for gas turbine combustor and a construction thereof.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Tadahisa Masai, Isao Sato.
United States Patent |
3,916,619 |
Masai , et al. |
November 4, 1975 |
Burning method for gas turbine combustor and a construction
thereof
Abstract
A gas turbine combustor comprising a conical liner cone formed
at a liner head of an annular liner wall, a fuel nozzle for
spraying fuel in a conical form provided in the central part of the
liner cone, inwardly directed flow jet ports for discharging air
arranged annularly in the part of the liner cone in the vicinity of
said fuel nozzle, and air jet ports for forming annularly an
outwardly directed flow or a turning flow provided outside said
inwardly directed flow jet ports, and characterized in that fuel is
sprayed by said fuel nozzle to form a central flame, and at the
same time, an annular small flame is formed in the vicinity of the
fuel nozzle.
Inventors: |
Masai; Tadahisa (Hitachi,
JA), Sato; Isao (Hitachi, JA) |
Assignee: |
Hitachi, Ltd.
(JA)
|
Family
ID: |
26447971 |
Appl.
No.: |
05/410,105 |
Filed: |
October 26, 1973 |
Foreign Application Priority Data
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|
|
|
|
Oct 30, 1972 [JA] |
|
|
47-107993 |
Oct 30, 1972 [JA] |
|
|
47-107997 |
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Current U.S.
Class: |
60/756;
60/758 |
Current CPC
Class: |
F23R
3/12 (20130101); Y02T 50/60 (20130101) |
Current International
Class: |
F23R
3/04 (20060101); F23R 3/12 (20060101); F02C
007/22 () |
Field of
Search: |
;60/34.65,39.74R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Husar; C. J.
Assistant Examiner: Garrett; Robert E.
Attorney, Agent or Firm: Craig & Antonelli
Claims
We claim:
1. A gas turbine combustor comprising
a cylindrical liner wall;
a conical liner cap located at one end of said cylindrical liner
wall, whereby said cylindrical liner wall and said liner cap form a
combustion chamber for the gas turbine;
a fuel nozzle provided at said liner cap for spraying fuel in a
conical manner into the combustion chamber;
first air supply ports annularly arranged on said liner cap in the
vicinity of said fuel nozzle in such manner that air flows along
said liner cap toward said fuel nozzle;
second air supply ports annularly arranged on said liner cap
downstream of said first air supply ports with respect to the
stream of fuel sprayed from said fuel nozzle in such manner that a
turning air flow about the axis of the combustion chamber results
and together with the air flow from said first air supply ports
forms a first annular vortex stream along said liner cap in the
vicinity of the fuel nozzle; and
third air supply ports annularly arranged on said liner cap
downstream of said second air supply ports in such manner that air
flows toward the downstream side of the first annular vortex
stream.
2. A gas turbine combustor as set forth in claim 1, wherein said
first air supply ports have a plurality of louvers opening toward
the center of said liner cap for causing the air to flow along said
liner cap toward said fuel nozzle;
said second air supply ports have a plurality of louvers which open
tangentially about a concentric circle of said liner cap; and
said third air supply ports have a plurality of holes for directing
the flow of air toward the downstream side of the first annular
vortex stream in an amount greater than the flow of air from said
first and second air supply ports.
3. A gas turbine combustor as set forth in claim 2, wherein said
plurality of louvers comprising said first air supply ports are
arranged along a plurality of concentric circles on said liner cap;
and said second air supply ports are arranged downstream of said
first air supply ports along a plurality of concentric circles on
said liner cap.
4. A gas turbine combustor as set forth in claim 1, further
comprising fourth air supply ports annularly arranged on the
downstream side of said third air supply ports for spraying air
along said liner cap toward said fuel nozzle; and fifth air supply
ports annularly arranged downstream of said fourth air supply ports
for spraying air in a turning flow about the axis of the combustion
chamber so that the air flow from the fourth and fifth air supply
ports forms a second annular vortex stream along said liner cap on
the downstream side of said third air supply ports.
5. A gas turbine combuster as set forth in claim 1, wherein a
radial line emanating from the fuel nozzle disposed along the axis
of the combustion chamber and said first air supply ports have a
crossing angle in a range of 0.degree. to 45.degree. as viewed in
the axial direction of the combustion chamber.
6. A gas turbine combustor as set forth in claim 1, wherein said
liner cap includes a cup-shaped cone in the vicinity of said fuel
nozzle, and the axis of said third air supply ports are provided
substantially at right angles to the axis of the combustion
chamber.
7. A gas turbine combustor as set forth in claim 1, including an
air chamber for regulating the speed and flow of air arranged on
the surface of said liner cap opposite to the interior burning
surface of said liner cap, said liner cap being cup-shaped in the
vicinity of said fuel nozzle.
8. A gas turbine combustor as set forth in claim 1, including an
air chamber for regulating the speed and flow of air discharged
from said third air supply ports, fourth air supply ports annularly
arranged on the downstream side of said third air supply ports, and
fifth air supply ports annularly arranged downstream of said fourth
air supply ports for spraying air in a turning flow about the axis
of said combustion chamber, wherein said fourth and fifth air
supply ports are arranged on a surface of said liner cap opposite
to the interior burning surface of said liner cap.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a gas turbine
combustor having a means for forming a small flame in the vicinity
of a fuel nozzle jet port.
Smoke contained in the exhaust gas of a gas turbine is due to the
carbon in fuel separated from the fuel during an excessive burning
which takes place locally in some part of a burning zone. In order
to prevent the generation of this smoke, the prior art has provided
various methods for introducing air into a combustor liner which
are aimed to eliminate excessive burning spots formed locally in
the burning zone. In particular, a widely used method is to supply
an excessive amount of air to the primary burning zone and produce
turbulence in the air flows using a primary turning blade (called
"turbulater") arranged for such a purpose. However, the supply of
an excessive amount of air to the primary burning zone has often
caused unstable flames, incomplete combustion, difficulty in
firing, and so forth. For the purpose of stabilizing the flame in
gas turbine combustor, there has been generally employed a method
to supply a portion of burning air, which is in the form of a
turning flow, to the combustor liner for forming a turning flame,
which results in a decreased pressure in the vicinity of the center
axis of turning and generation of a circulating flow. In this
method, since the flame surface is formed in a space remote from
the fuel nozzle jet port and is under direct influence of the
flowing movement of primary air, there has remained a disadvantage
that the range of air-fuel ratio for achieving an excellent burning
is narrowed. In gas turbines, it is necessary to perform a good
burning throughout a wide range of operation from firing to rated
load state. The amount of fuel flow changes from 8% at the time of
starting to about 120% at the time of overload. According to said
prior art burning method using a turning flame, it is difficult to
maintain a good burning throughout a wide range of fuel amount
variation of from 8 to 120%. If the burning zone having a small
amount of fuel flow is taken as a standard for optimum burning
state, black smoke will be produced when rated load or overload
operation is carried out. On the other hand, if the burning zone
having a large amount of fuel flow is taken as a standard for
optimum burning state, there will occur, when starting the turbine,
undesirable phenomena such as generation of white smoke and
difficulty in firing. Increasing the amount of primary air to
decrease the amount of smoke contained in exhaust gas means that
the burning zone having a large amount of fuel flow is selected as
a standard for optimum burning state, naturally incurring said
problems. A brief explanation will be given here on the cause of
such phenomena as difficulty in firing at the time of starting,
generation of white smoke, and unstable flames. The difficulty in
firing is principally due to a large air-fuel ratio in the primary
burning zone (decreased fuel density). According to the
experimental results obtained so far, the optimum firing condition
is a state in which fuel is excessive in amount compared with air
in view of a theoretical mixing ratio. Firing performance is
degraded when the air-fuel ratio in the primary burning zone is
made larger. At the same time, owing to the unstable condition of
flame, the once fired flame is often extinguished by a blow of air.
In general, this blowing out phenomenon is included in the category
of difficulty in firing. White smoke at the time of starting is
generated by the cooling of the sprayed fuel particles due to an
excessive amount of the primary air. Generation of white smoke
takes place more often in winter when atmospheric temperature is
low and the cooling effect is great. From the results of component
analysis of the white smoke, it is known that a principal component
of the smoke is hydrocarbon (fuel oil) and the smoke also contains
some amount of CO. This white smoke shows that, owing to the
cooling action of the primary air, fuel particles are discharged to
the atmosphere without undergoing complete evaporation, resulting
in a very low combustion efficiency. After the gas turbine reached
a state of rated operation, the air temperature is, by virtue of
insulation and compression, kept at about 250.degree.-300.degree.C
which is substantially the same as the average boiling point of
fuel oil, and the cooling of fuel particles by primary air is
ceased to terminate the generation of white smoke.
In the flame stabilizing method using a circulating flow described
previously, the turning of a burning air flow is weak and likely to
become unstable because the amount of air flow is small, especially
at the time of firing when the turbine revolves at a low speed.
When operating a gas turbine, stabilization of flame poses nearly
no problem during rated load operation, but has a very important
meaning when the turbine is started. An unstable flame is
particularly likely to take place in the combustors having a smoke
consuming apparatus. According to the prior art, smoke is generated
during rated load operation and complete elimination of the smoke
cannot be attained because, as described previously, it is
impossible to supply an excessive amount of primary air to the
primary burning zone. Nitrogen oxides, which are considered to be
one of the harmful substances contained in the exhaust gas of a gas
turbine, are produced by the reaction of nitrogen and oxygen at a
high temperature. Studies to date shows that the nitrogen oxides
increase in amount in a manner of exponential function at
temperatures exceeding 1,500.degree.C. In the prior art, during
rated load operation, about 150-200 ppm of nitrogen oxides are
contained in the exhaust gas of a gas turbine, due to the fact
that, as described previously, an excessive amount of air cannot be
supplied to the primary burning zone for lowering the flame
temperature. Decrease in amount of the nitrogen oxides can be
achieved by limiting the flame temperature within a range of less
than 1,500.degree.C.
One of the methods according to the prior art for decreasing
nitrogen oxides contained in the exhaust gas of a gas turbine, is
to mix in the burning air a steam having a relatively large value
of specific heat. Temperature of the exhaust gas of a gas turbine
is about 400.degree.-450.degree.C. This is fairly high in
comparison with temperature of the exhaust gas of a boiler. For
this reason, for instance, a waste heat boiler can be connected to
the gas turbine to obtain steam, thereby improving the gas turbine
output and the thermal efficiency. But with the provision of such
an attachment, the gas turbine loses some of its valuable
properties such as rapid starting and needlessness of water. Other
problems entailing this method are generation of black smoke due to
the lowering of burning performance resulting from the mixing of
steam, generation of other harmful substances owing to incomplete
combustion, high temperature corrosion of passage walls and turbine
blades caused by high temperature gases such as hydrogen generated
through decomposition of steam, and the like.
Another method according to the prior art for decreasing nitrogen
oxides employs water discharging. A notable improvement of thermal
efficiency cannot be expected from this method as this method has
disadvantages such as increased loss of exhaust heat due to latent
heat of water, in addition to the problems described above.
Still another method according to the prior art for decreasing
nitrogen oxides is to recirculate exhaust gas. However, this method
also has undesirable features such as compression of exhaust gas,
increased amount of work, and so forth, and results in the decrease
of gas turbine output and the lowering of thermal efficiency.
As described in the foregoing, the prior art relating to gas
turbine combustor involves a large number of problems to be
solved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a combustor in
which a main flame is stabilized by the use of a small flame and an
excellent burning property is obtainable throughout a wide range of
operation.
Another object of the present invention is to provide a combustor
in which a sure firing operation is possible when starting a gas
turbine.
Still another object of the present invention is to prevent the
discharge to atmospheric air of such substances as hydrocarbon and
carbon monoxide produced by incomplete combustion at the time of
starting of a gas turbine.
Further object of the present invention is to decrease the density
of smoke contained in exhaust gas during rated load operation of a
gas turbine.
Further object of the present invention is to decrease the
concentration of nitrogen oxides contained in exhaust gas during
rated load operation of a gas turbine.
In accordance with the present invention, a central flame, i.e.,
main flame, is formed by spraying fuel from a fuel nozzle, an
annular small flame is formed in the vicinity of the fuel nozzle,
and with the use of this annular small flame evaporation of the
sprayed fuel is accelerated and primary air is preheated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory longitudinal sectional view of a typical
conventional boiler type combustor;
FIG. 2 is an explanatory longitudinal section view showing a
detailed construction of the combustor of FIG. 1 in the vicinity of
a liner head thereof and the direction of air flow movements within
the liner;
FIG. 3 is a view taken in the direction of P of FIG. 2 illustrating
a liner cone in plan;
FIG. 4 is an explanatory view showing the shape of a flame formed
in the liner of the combustor illustrated in FIG. 1;
FIG. 5 is an explanatory view showing the shape of a flame
including an annular small flame in accordance with the present
invention;
FIG. 6 is an explanatory longitudinal sectional view illustrating
in more detail the formation of the annular small flame in
accordance with the present invention;
FIG. 7 is an explanatory view showing a louver perforation
construction in the vicinity of a fuel nozzle of the liner cone in
accordance with the present invention;
FIG. 8 is a sectional view taken along the line C--C of a louver
perforation illustrated in FIG. 7;
FIG. 9 is a plan view showing inwardly directed flow jet ports
constituted by a plurality of liner cones;
FIG. 10 is a sectional view taken along the line D--D of FIG.
9;
FIG. 11 is a left side view of FIG. 12 illustrating an embodiment
for forming the annular small flame in accordance with the present
invention;
FIG. 12 is a longitudinal sectional view of FIG. 11;
FIG. 13 is a longitudinal sectional view showing another embodiment
for forming the annular small flame in accordance with the present
invention;
FIG. 14 is a left side view of FIG. 15 illustrating still another
embodiment for forming the annular small flame in accordance with
the present invention;
FIG. 15 is a sectional view of FIG. 14 with a symmetrical lower
part omitted;
FIG. 16 is a side view showing a further embodiment for forming the
annular small flame in accordance with the present invention;
FIG. 17 is a longitudinal sectional view illustrating a
construction in the vicinity of a fuel nozzle cap for facilitating
the formation of the annular small flame in accordance with the
present invention;
FIG. 18 is a longitudinal sectional view showing another embodiment
of the combustor in accordance with the present invention; and
FIG. 19 is a longitudinal sectional view illustrating still another
embodiment, different from that of FIG. 18, of the combustor in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Prior to the description of the present invention, an explanation
will be made on the construction of a typical conventional
combustor.
FIG. 1 shows a longitudinal section of a boiler type combustor for
gas turbine and FIG. 2 illustrates a detailed construction in the
vicinity of the liner head shown in FIG. 1. Numeral 1 indicates an
air chamber which will be used as a common air chamber when a
plurality of boiler type combustors are employed. Numerals 2, 3,
and 4 respectively designate completely burning air flows, diluting
air holes, and diluting air flows passing through the diluting air
holes. Numeral 5 is a cooling air to flow along the inner surface
of a liner wall 16 performing a film cooling so that the liner wall
16 is insulated from flame for its own protection. Numerals 6 and 8
are secondary air holes provided in the liner wall 16, and numerals
7 and 9 indicate secondary air flows supplied to the liner through
the secondary air holes 6 and 8. Numeral 10 is a turbulater air
flow to form a part of primary air and numeral 11 is a turbulater
for generating the turbulater air flow 10. Numeral 12 designates a
liner head plate for regulating the amount of primary air flow and
for increasing the strength of the liner. Numeral 13 is a liner
cone portion having openings for supplying the primary air to the
liner. Numeral 14 is a supplying portion of fuel coming from a fuel
pump (not shown). Numeral 15 indicates a fuel nozzle to supply a
fuel spray to the liner, and numeral 17 is a radiation shield plate
for preventing conduction of radiation heat from the flame in the
liner or from the liner wall 16. Numeral 18 is an outer cylinder of
the combustor provided with such means as an attaching seat for
ignition plug. Numeral 19 designates a combustor head plate having
an attaching seat of the fuel nozzle 15 and constituting an end of
the combustor. Numeral 20 is an air chamber wall for forming the
air chamber 1. Numeral 21 is a transition piece to connect the
liner wall 16 with a stationary blade of the turbine (not shown).
Numeral 22 indicates a gas diluting portion for evenly mixing the
diluting air flows 4 and a burning gas. Numeral 23 is a gas flow
generated in the combustor and numeral 24 is a guide for moving an
ignition plug. Numeral 25 is an ignition plug to carry out firing
with the use of a spark obtained by the application of a high
voltage. Numeral 26 designates a fuel nozzle jet port for supplying
fuel coming from the fuel nozzle 15 in the form of a spray. Numeral
27 indicates a primary air chamber for storing and decompressing
the primary air 28 introduced through holes 36 regulating the
amount of primary air. The primary air chamber 27 serves the double
purposes of reinforcing the construction of the liner head and of
adjusting to an optimum value the speed jet port of the primary air
supplied to the liner through the openings of the liner cone
portion 13. Numeral 28 is the primary air introduced into the
primary air chamber 27 through the primary air regulating holes 36
arranged in the liner head plate 12. Numeral 29 is cone louver
perforations provided in the liner cone portion 13, which are
designed to cool the liner cone portion 13 and to regulate air
movements within the primary burning zone in the liner. Numeral 30
designates a turning air flow generated by certain numbers of the
cone louver perforations 29, which further generates turning flows
coming from the turbulater 11 and the liner cone portion 13.
Numeral 31 is flows circulating on the cone generated by certain
numbers of the cone louver perforations 29, and said air flows 31
further generates an inwardly directed flow from the liner cone
portion 13. Numeral 32 is liner wall air flows to perform, in
cooperation with liner louver perforations 35 in the liner wall 16,
the cooling of the liner wall 16 along a wall inside the liner.
Numeral 33 indicates a main circulating flow generated by the
turning air flow 30 and moving toward the fuel nozzle jet port 26.
Numeral 34 is cone portion air holes arranged in the liner cone
portion 13 for discharging the primary air.
FIG. 3 is a view taken in the direction of P of FIG. 2 and shows
the construction and shape of the turbulater 11 including a
turbulater jet port 39, the cone portion air holes 34, cone turning
flow louver perforations 37, and cone inwardly directed flow louver
perforations 38.
In the conventional combustor described above, the turning air flow
30 is generated in the liner using such means as the turbulater 11
and the cone turning flow louver perforations 37, and the
stabilization of flame is carried out by the main circulating flow
33 generated by said turning air flow 30 and moving toward the fuel
nozzle jet port 26. A principal purpose of this type of combustor
resides in that, simultaneously with the air flow actions mentioned
above, the flows circulating on the cone 13 are generated by means
of the cone inwardly directed flow louver perforations 38 to
enlarge the flame for reinforcing the flame stabilizing action of
the main circulating flow 33. Thus, the flame stabilizing action of
the main circulating flow 33 is determined by the force of the
turning air flow 30. Hence, the stabilization of flame cannot be
performed satisfactorily when only very slight amount of burning
air flow exists within the turbine, as is the case at the time of
starting.
As described above, when the firing is carried out, the gas turbine
combustor is in a state in which the stabilization of flame is
inadequate, and it often happens that a flame formed using the
ignition plug 25 is blown out by the succeeding air flows.
Particularly, in order to eliminate smoke, it is necessary to
enlarge the turbulater air flow 10 by increasing the size of the
turbulater jet port 39 for increasing air-fuel ratio in the primary
burning zone to avoid the generation of a local excessive fuel
spot. However, in this case, said difficulty in firing is very
likely to take place.
Thus, according to the prior art in which the turning air flow 30
is utilized for stabilizing the flame, it has been impossible to
carry out an efficient burning throughout a wide range of operation
from starting to rated load state. The observations and experiments
show that the combustor liner of the prior art generates a turning
flame such shown in FIG. 4. As long as the gas turbine is kept in
this burning condition, if atmospheric temperature, number of
revolution of the gas turbine, and burning air pressure are all
low, evaporation is delayed owing to the cooling of fuel spray
particles by the low temperature air. As a result, the flame moves
backward (to the left in FIg. 4). In case the burning air
temperature is lower, the flame will be blown out since its
maintenance is made impossible. In gas turbines, as atmospheric
temperature is decreased, the mass of air and the atmospheric
temperature is decreased, the mass of air and the amount of air
flow are increased in inverse proportion to the absolute
temperature of atmospheric air. Therefore, with the decrease of
evaporation speed of fuel due to the decrease of atmospheric
temperature, air-fuel ratio is increased, thus degrading the
burning condition in a multiplying manner. In this condition of
flame, fuel particles sprayed from the fuel nozzle jet port 26 are
preheated from the central part of their mass receiving the
radiation heat of a central flame 45. The fuel spray is, at the
same time, cooled from outer boundary surface thereof by the
turbulater air flow 10 and the primary air supplied through the
turbulater 11 and the openings of the liner cone portion.
Consequently, evaporation of the fuel particles is retarded,
resulting in insufficient increase in flame temperature and
incomplete combustion. Thus, in the exhaust gas are included large
amounts of hydrocarbon, carbon monoxide, and other substances. Fuel
particles sprayed from the fuel nozzle jet port 26 receive the
cooling action of primary air which is much stronger in effect than
the preheating action of radiation heat from the central flame 45,
which they also receive, until they reach an entering point to
circulating flame 44. Under such a burning condition, a large
quantity of white smoke is generated at the starting of gas
turbine. This is undesirable not only from a standpoint of air
pollution but also from a standpoint of increased consumption of
fuel.
In this burning method according to the prior art, owing to the
fact that a great amount of primary air cannot be supplied to the
gas turbine, temperature of a secondary flame 43 is increased
disadvantageously during rated load operation of the turbine, and a
large amount of nitrogen oxides is undesirably produced. The flame
stabilizing method utilizing a turning flame has a number of
drawbacks as described in the foregoing.
The present invention provides a new method for stabilizing flame
with a view to obviating such drawbacks and disadvantages of the
prior art. The present invention will be explained hereinafter in
detail. Throughout the drawings, like numerals or symbols indicate
like parts.
To begin with, the flame in accordance with the present invention
has a section shown in FIG. 5. In comparison with FIG. 4, it is
seen that a small flame 46 is formed in the extreme vicinity of a
fuel nozzle jet port 26. The small flame 46 is located just outside
the outer boundary surface of a fuel spray 40. This annular small
flame 46 provides an effect to accelerate the evaporation of fuel
particles discharged from the fuel nozzle jet port 26 so that
incomplete combustion due to delayed evaporation of fuel can be
prevented in contrast to the prior art combustor of FIG. 4 which is
unable to avoid such an incomplete combustion. Thanks to the
formation of the annular small flame 46, the preheating of primary
air as well as the improved evaporation of fuel spray particles can
be achieved to increase burning speed, thereby completely
eliminating the disadvantages of the prior art described above. If
the annular small flame 46 is extremely stable, an excessive amount
of primary air does not result in the blowing out of flame and a
stabilized burning can be attained so that it is made possible to
prevent the generation of white smoke in exhaust gas during rated
load operation of a gas turbine and to perform efficiently and in a
stable manner a low temperature burning at a temperature of less
than 1,500.degree.C, averting the production of nitrogen
oxides.
As described above, the present invention aims to accomplish the
stabilization of main flame by the use of the annular small flame
46 and differs totally from the conventional flame stabilizing
method utilizing the main circulating flow 33 and can attain a
stable burning throughout an extremely wide range of operation.
Hereinafter explanations will be made on the method for forming the
annular small flame in accordance with the present invention.
Fuel particles sprayed from the fuel nozzle jet port 26 are not
uniform and can be expressed by the following formula:
v(x)=ax.sup.p exp(-bx.sup.q)
In the above formula, a and b are constants inherent in the fuel
nozzle, and p and q are the values determined by spraying method
and spraying condition.
Fuel particles needed to form the annular small flame 46 of the
present invention are extremely fine particles having a diameter of
less than 20 .mu., the distribution of which is expressed in the
above formula. These fuel particles can be readily transferred by
means of air flow. Therefore, if an air flow is provided so that
the annular small flame 46 is formed, the original purpose can be
achieved.
A detailed explanation will be given here, with reference to FIGS.
6 through 10, on the formation of the annular small flame 46 in
accordance with the principles of the present invention.
First of all, first inwardly directed flow jet ports 47 and second
inwardly directed flow jet ports 48 are arranged about the jet port
26 of a fuel nozzle 15 mounted at a liner center axis. Although
said jet ports 47 and 48 preferably have the shape of a continuous
annular slit, the same effect can be obtained even if they are
formed as discontinuous louver perforations as shown in FIG. 3.
In FIG. 6 are shown two rows of the first jet ports 47 and the
second jet ports 48. However, when the spray capacity of fuel
nozzle is small, only one row of the jet ports can perform the job
satisfactorily. If the spray capacity is very large and a liner 16
has a large diameter, it is necessary to provide more than three
rows of the inwardly directed flow jet ports. The reason for this
is that, with the increased spray capacity of fuel nozzle, the
annular small flame 46 must be increased in size proportionally to
effectively carry out the evaporation of fuel spray and the
preheating of primary air. A first annular jet flow and a second
annular jet flow flowing in through the first inwardly directed
flow jet ports 47 and the second inwardly directed flow jet ports
48 shown in FIG. 6, are preferably inwardly directed flows which do
not make a turning movement and move toward the fuel nozzle jet
port 26. However, said first and second annular jet flows may make
a slight turning movement. The experimental results shows that the
object of the present invention can be attained if the first and
second annular jet flows flow in maintaining a crossing angle
.theta. within a range of 0.degree. to 45.degree. with the radial
line starting from the fuel nozzle jet port 26 (assuming that the
jet port 26 is arranged on the liner center axis) as shown in FIG.
7. The first annular jet flow 51 and the second annular jet flow 52
passing through the first inwardly directed flow jet ports 47 and
the second inwardly directed flow jet ports 48 are formed into
annular turning flows shown in FIG. 6 due to the influence of
inwardly directed flows. If said crossing angle .theta. exceeds
45.degree., velocity vector of the turning flows becomes larger
than that of the inwardly directed flows so that the first annular
jet flow 51 and the second annular jet flow 52 taking directions
shown in FIG. 6 vanish. Thus, the object of the present invention
cannot be achieved.
In order to reinforce the annular jet flows 51 and 52 shown in FIG.
6, there are provided in a liner cone portion 13 first turning flow
jet ports 49 and second turning flow jet ports 50. By means of the
first turning flow jet ports 49 and the second turning flow jet
ports 50, turning air flows 30 are generated, and due to the
turning effect of said turning air flows 30, main circulating flows
33 are put in movements shown by the broken lines. Turning
direction of the main circulating flows 33 is opposite to that of
the first and second annular jet flows 51 and 52. At the points of
contact, the main circulating flows 33 and the first and second
annular jet flows 51 and 52 form flows moving toward the liner cone
portion 13. As the first annular jet flow 51 and the second annular
jet flow 52 are reinforced by the main circulating flows, fine fuel
particles sprayed by the fuel nozzle jet port 26 are carried by the
strong annular jet flows 51 to 52 to form an annular small flame.
Though the annular jet flows 51 and 52 have as their principal
purpose the formation of said annular small flame, they can also
prevent carbon accumulation on the liner cone portion 13 and the
jet port surface of the fuel nozzle 15. The annular jet flows 51
and 52 further have a cooling effect as they form film-like air
flows.
On the other hand, secondary air flows 9 flowing in through
secondary air holes 8 reach the central part of the liner with the
aid of the main circulating flows 33 so that the mixing of fuel and
burning air can be improved. In contrast to the flame stabilizing
method for gas turbine combustor according to the prior art which
utilizes the main circulating flows, the present invention has a
distinct feature that the same effect is achieved by the annular
small flame 46 formed in the vicinity of the fuel nozzle jet port
26.
FIG. 7 shows the construction in the vicinity of the fuel nozzle as
far as the second inwardly directed flow jet ports 48. The
construction outside the jet ports 48 is not shown. The first
inwardly directed flow jet ports 47 and the second inwardly
directed flow jet ports 48 shown in FIG. 7 are louver perforations
having a section shown in FIG. 8. As the object of the present
invention to form inwardly directed flows such as the first annular
jet flow 51 and the second annular jet flow 52 shown in FIG. 6, any
suitable construction other than the louver perforations, for
example, the construction of FIG. 9, may be employed.
FIG. 9 shows a construction comprising a first small cone portion
54 and a second small cone portion 55 combined with a liner cone
portion 13, which constitute inwardly directed flow jet ports 56
and inwardly directed flow jet ports 57. On the outer peripheral
surfaces of the first cone portion 54 and the second cone portion
55 are respectively provided first small cone projections 58 and
second small cone projections 59 to form the inwardly directed flow
jet ports 56 and 57. The inwardly directed flow jet ports 56 and 57
may also be formed by arranging projections on the inner peripheral
surfaces of the second small cone portion 55 and the liner cone
portion 13.
FIG. 10 is a sectional view taken along the line D--D of FIG. 9.
The second small cone projections 59 are provided on the outer
periphery of the second small cone portion 55 to be in contact with
the liner cone portion 13 for forming the inwardly directed flow
jet ports 57. By investigating FIG. 10, the construction of FIG. 9
can be understood more readily. Although two rows of the inwardly
directed flow jet ports 56 and 57 are shown in FIG. 9, only one row
of the jet ports is enough when the spray capacity of fuel nozzle
is small. But if the fuel nozzle has a large spray capacity, it is
naturally needed to provide three or more rows of the jet
ports.
As the fundamental operational principles of the present invention
have been described in the foregoing, the present invention will be
explained hereinafter with reference to the embodiments
thereof.
FIGS. 11 and 12 show an embodiment of the present invention. A
liner cone portion 13 has louver perforations constituting inwardly
directed flow jet ports and turning flow jet ports, and primary air
supply holes 63 are arranged as shown in the figure, thereby to
form double annular flames throughout the cone portion.
FIG. 12 is a sectional view of FIG. 11. Air passing through primary
air regulating holes 36 is supplied to each jet port by way of a
primary air chamber 27. Air coming in through inner periphery air
supply holes 68 passes through an air reservoir 69 constituted by a
fuel nozzle collar 53 and an inside ring 60 and through an inner
periphery jet port 70 to be discharged in the form of a film toward
a liner center axis. Air is also discharged into the liner toward
the liner center axis through first inwardly directed flow jet
ports 61 comprising louver perforations in the liner cone portion
13. On the outer periphery of the series of the first inwardly
directed flow jet ports 61 are arranged, as shown in the figure,
first turning flow jet ports 62 comprising louver perforations to
give a turning movement to the air flows within the liner.
Thanks to the operational principles of the present invention
described previously, a primary annular small flame can be formed
about a fuel nozzle jet port 26 in the central part of the liner
cone portion 13 by means of the inner periphery jet port 70, first
inwardly directed flow jet ports 61, and first turning flow jet
ports 62. The primary air supply holes 63 are provided on the outer
periphery of the series of the first turning flow jet ports 62 for
accelerating the mixing of air and fuel in the primary burning zone
to prevent the generation of smoke caused by burning. On the outer
periphery of the series of the primary air supply holes 63 are
arranged second inwardly directed flow jet ports 64 and third
inwardly directed flow jet ports 65 all in the form of louver
perforations to again form air flows directed toward the liner
center axis. These air flows can form a secondary annular flame by
joining in the air flows coming in through second turning flow jet
ports 66 comprising louver perforations located on the outermost
periphery of the liner cone portion 13. It is known from the
experimental results that only the annular small flame is formed
with the secondary annular flame lacking if a small amount of fuel
is sprayed as is when the gas turbine is started. However, if the
amount of fuel spray is large, as is in rated load operation, the
secondary annular flame is formed in addition to the primary
annular small flame to a stable burning condition. Since the
annular flames are formed in response to the variation in the
amount of fuel spray as described above, a very efficient burning
can be obtained throughout a wide range of variation in fuel spray
amount. Air flows discharged from the first turning flow jet ports
62 not only form the primary annular small flame but also preheat
the primary air passing through the primary air supply holes 63.
For this reason, a stable, high-efficiency burning operation can be
performed even when the burning air temperature is very low, such
as the time of starting of a gas turbine during cold winter.
FIG. 13 shows another embodiment in accordance with the present
invention. Unique features of this embodiment will be evident if
compared with FIG. 12. The part of a liner cone portion 13 inwardly
of primary air flow supply holes 74 is constructed in a cup-like
shape to increase the stability of annular small flame. By
providing the primary air flow supply holes 74 in a direction
toward the central part of a liner, primary air jet flows 81 can be
supplied to a part in the vicinity of the central part the liner so
that the local excessive fuel spots are avoided to prevent the
generation of smoke. In FIG. 13, a cup-shaped structure in the
central part of the liner cone portion 13 has a relatively small
depth. It is known from the experiments that the most stable
annular small flame is obtained when said cup-shaped structure has
a depth substantially equal to the largest radius thereof. However,
if fuel spray cone discharged from a fuel nozzle 15 has a very
large vertical angle, there is a possibility that the fuel spray
collides with the liner cone portion 13 to burn it. In designing
this cup-shaped structure, the depth thereof should be determined
taking this fact into consideration. In comparison with the
construction of FIG. 12, a second inwardly directed flow jet port
group 72 is added to the construction shown in FIG. 13. As
described previously, the number of rows of such jet ports should
be determined at an optimum value depending upon the capacity and
spraying property of respective fuel nozzle. It should not be
understood as an invariable factor usable for all liner designs.
When fuel nozzle has an extremely good spraying property, fine fuel
particles carried by annular jet flows 78 through 80 are increased
in amount, resulting in an annular small flame which is too large
in proportion to a main flame. In this case, it is necessary to
increase opening area, number of row, and other factors of the
inwardly directed flow jet ports. Increase in the spray capacity of
fuel nozzle also brings about increased fuel particles. In this
case, too, opening area and number of row of the inwardly directed
flow jet ports must be increased.
The method for forming an annular small flame so far described
utilizes the combinations of inwardly directed flows and turning
flows. However, the object of the present invention can also be
achieved by using the combinations of inwardly directed flows and
outwardly directed flows.
FIG. 14 is a plan view of an embodiment of the present invention
employing the above described method. FIG. 15 is a sectional view
of said embodiment showing the movement of air flow passing through
each jet port. An inside ring 60 is arranged on the outer periphery
of a fuel nozzle 15 for forming an annular jet flow 92. On the
outer periphery of said inside ring 60 is provided a first inwardly
directed flow jet port group 86 to generate an annular jet flow 93.
On the outer periphery of said first inwardly directed flow jet
port group 86 is arranged a first outwardly directed flow jet port
group 87 to generate an outwardly directed jet flow 96. On the
outer periphery of said first outwardly directed flow jet port
group 87 are provided primary air supply holes to generate a
primary air jet flow 97. On the outer periphery of the series of
said primary air supply holes is arranged a second inwardly
directed flow jet port group 89 to generate second annular jet flow
98. On the outer periphery of said second inwardly directed flow
jet port group 89 is provided a third inwardly directed flow jet
port group 90 to generate a second annular jet flow 99. And on the
outer periphery of said third inwardly directed flow jet port group
90 is arranged a first turning flow jet port group 91 to generate a
main turning and circulating flow 100. In this embodiment, an
annular small flame formed in front of the fuel nozzle 15 is not
made into a turning flow about a liner center axis 101. However, in
actual practice, said annular small flame begins to make a slow
turning movement about the liner center axis 101 under the
influence of the first turning flow jet port group 91. Needless to
say, it is within the scope of the present invention to give a
turning function to both of, or any one of, the first inwardly
directed flow jet port group 86 and the first outwardly directed
flow jet port group 87.
As is apparent from FIG. 15, by combining the inwardly directed
flows and the outwardly directed flow, annular circulating flows 94
and 95 are obtained. The annular circulating flows 94 and 95 are
further combined with the annular jet flow 92 and the annular jet
flow 93 to form an extremely stable annular small flame.
On the other hand, the second inwardly directed flow jet port group
89 and the third inwardly directed flow jet port group 90 are not
only capable of generating the second annular jet flows 98 and 99
shown in FIG. 15 but also has a function to send the primary air
jet flow 97 coming in through the primary air supply holes 88 to
the area in close vicinity to the liner center axis 101 for
preventing the generation of smoke. Therefore, there is a necessity
to make the second annular jet flows 98 and 99 stronger than the
main turning and circulating flow 100 passing through the first
turning flow jet port group 91. Considering the prevention of smoke
generation, two rows of jet port, i.e., the second inwardly
directed flow jet port group 89 and the third inwardly directed
flow jet port group 90, are arranged in the construction shown in
FIG. 14. If the first outwardly directed flow jet port group 87 is
omitted in the construction of FIG. 15, force of the annular
circulating flows 94 and 95 will be decreased, although the annular
small flame is formed. In this case, stable range of the annular
small flame will be decreased to a large degree. This construction
without the first outwardly directed flow jet port group 87 is not
suitable for use in gas turbines where a burning state stable
throughout a wide range of operation is required, but may be used
in other combustion equipment where only a narrow range of
operational variation is needed.
Explanations have been given in the foregoing on the basic
embodiments in accordance with the present invention. Further,
applied examples of the present invention will be described
hereinafter.
FIG. 16 shows an applied example in accordance with the present
invention. This applied example has an object to prevent the
generation of smoke caused by the annular small flame by providing
annular flow air holes 102 so that air is supplied to the annular
small flame of the present invention. The annular small flame will
become unstable if total area of the annular flow air holes 102 is
unproportionally larger than that of a first inwardly directed flow
jet port group 86. From the experiments it is known that the
annular small flame is extinguished if total area of the annular
flow air holes 102 exceeds about 1.8 times that of the first
inwardly directed flow jet port group 86. Particularly it has been
clearly observed that the annular small flame tends to vanish if
the pitch between the annular flow air holes 102 is made
smaller.
In determining size, number, and other factors of the annular flow
air holes 102, it is necessary to take into consideration the
experimental results described above. A second feature of this
applied example lies in the fact that an outwardly directed turning
flow jet port group 103 is provided on the outer periphery of the
first inwardly directed flow jet port group 86. The method for
forming the annular small flame using the combination of the first
inwardly directed flow jet port group 86 and the outwardly directed
turning flow jet port group 103 is a method utilizing both the
embodiments shown in FIGS. 11 and 14. The first inwardly directed
flow jet port group 86 must have a crossing angle .theta. shown in
FIG. 7 of less than 45.degree. to generate a strong inwardly
directed flow and a weak turning flow. However, as is apparent from
FIGS. 11, 14, and 16, there is no restriction in determining the
crossing angle of the outwardly directed turning flow jet port
group 103.
FIG. 17 shows an applied example in accordance with the present
invention in which an annular inner periphery flow jet port 112 is
arranged on a fuel nozzle cap. Most gas turbines have a
construction wherein both liquid fuel and gas fuel can be used. In
such a construction, the fuel nozzle cap 108 is attached to a fuel
nozzle 15. Thus, in the fuel nozzle cap 108 are provided inner
periphery air supply holes 109 to supply air to an air chamber 110.
Air is discharged in an inward direction from annular inner
periphery flow jet ports 112 through air supply holes 111. Air
discharged from the annular inner periphery flow jet ports 112 must
have, as is the case with the first inwardly directed flow jet port
group 86, the weakest possible turning flow. Said air from the jet
ports 112 preferably has no turning flow. In gas turbines designed
to be compact and light weight such as jet engines, it is common to
employ an annular combustor having an annular space construction
different from the construction of the boiler type combustor
described in the foregoing. There are also used a so-called
cannular combustor having a common combustor outer cylinder 18. In
these combustors, it is also possible to form the annular small
flame of the present invention about the fuel nozzle jet port in
the same manner as in the boiler type combustor described above. In
the figure, numerals 105, 106 107, 113, and 114 indicate
respectively a nozzle body, a nozzle holder, a packing, direction
of fuel supply, and an attaching flange portion.
FIG. 18 shows one of the applied examples of the combustor liner in
accordance with the present invention. Difference between this
combustor liner and the typical conventional combustor liner shown
in FIG. 2 is that the primary air chamber 27 is reduced in volume
to form a primary air chamber 115 covering only the area in the
vicinity of the fuel nozzle 15. In the conventional combustor liner
construction, the primary air regulating holes 36 limits the amount
of air supplied to the primary air chamber 27 so that the primary
air supplied to the liner through the cone louver perforations 29
and the cone portion air holes 34 has a decreased flowing speed.
Thus, said primary air moves over a decreased flowing distance
without reaching the central part of liner due to its low flowing
speed. It is known from the smoke density distribution experiments
that the largest smoke density is shown in the central part of
liner. This fact evidences the shortage of air supply to the
central part of liner. According to the conventional construction,
said flowing distance can be increased by employing larger primary
air regulating holes 36. But increase in size of said primary air
regulating holes 36 has a certain limit because flame becomes
unstable if extremely large holes 36 are used. In actual practice,
total area of the primary air regulating holes 36 has been
determined to be equal to or less than total area of all the
openings of the liner cone portion 13. In order to supply the
primary air to the area in the vicinity of the central part of
liner, the prior art employs the turbulater 11 as shown in FIG. 2
for generating the turbulater air flow 10. If the air not turning
is directed toward the liner center, air supply to the area in the
vicinity of the central part of liner can be achieved effectively.
However, in this case, the blowing out takes place very often owing
to unstable condition of flame. In solving this problem, the prior
art gives to the turbulater 11 a turning function within a range of
20.degree. to 30.degree. to attain the stabilization of flame.
In the present invention, as shown in FIG. 18, the primary air
chamber 115 is provided about the fuel nozzle to form an extremely
stable annular flame on the first cone portion 116. The optimum
amount of air flow is obtained by primary air adjusting holes 117
so that air is discharged at an optimum speed from first primary
air jet ports 118, second primary air jet ports 119, third primary
air jet ports 120, and first turning flow jet ports 121. Very
stable flames can be obtained since this stable annular flame
performs simultaneously the evaporation of sprayed fuel particles
and the preheating of primary air. Thanks to this arrangement, the
stabilization of flame is not threatened when a primary air hole
jet flow 123 coming in through primary air holes 122 is directed
toward the liner center. Thus, air-fuel ratio in the zone after a
second cone portion 124 can be increased to achieve a low
temperature burning with an excess amount of air so that the
production of smoke and nitrogen oxides can be prevented during
normal operation of gas turbine. With the provision of the second
cone portion 124 and the primary air holes 122 enabled by the
elimination of a part of the primary air chamber 27 according to
the prior art (FIG. 2), flowing speed of the air flowing into the
liner is increased and the fuel particles and the primary air are
mixed uniformly. Thus, the air shortage in the central part of
liner experienced in the conventional liners can be solved and the
burning is carried out efficiently throughout a wide range of load
variation. Fourth primary air jet ports 125 and fifth primary air
jet ports 126 are provided directed inwardly so that the primary
air hole jet flow 123 can reach the area in the vicinity of the
liner center and a secondary annular flame can be formed on the
second cone portion 124 with the use of a fourth primary air jet
flow 127, a fifth primary air jet flow 128, and a second turning
jet flow.
FIG. 19 shows another embodiment different from that of FIG. 18. As
is readily seen when compared with the embodiment shown in FIG. 18,
the embodiment of FIG. 19 has a double chamber construction
comprising a primary air chamber 50 and an air chamber 129 arranged
outside said primary air chamber 50. The amount of the air flowing
in each of said chambers 50 and 129 is regulated by outer air
regulating holes 131 and inner air regulating holes 132 provided in
an air regulating head plate 130 so as to achieve more proper
introduction and distribution of air in the primary burning zone.
The first reason of employing the double chamber construction is to
maintain the burning in the primary burning zone in the best
condition. The second reason of employing the double chamber
construction is that a liner cone portion 13 can be readily
replaced with new one thanks to this separate and independent
construction when it is burned or damaged for one reason or
another. In this burning method, since the primary air larger in
amount than the primary air according to the prior art is
introduced through the liner cone portion 13 for performing a low
temperature burning to prevent the production of nitrogen oxides, a
flame formed inside a liner wall 16 has a smaller quantity of
radiation heat conducted to the liner wall 16 so that the
durability of the liner wall 16 is improved greatly. On the other
hand, the liner cone portion 13 has a durability inferior to that
of the liner wall 16 due to the fact that a relatively high
temperature zone is established on the liner cone portion 13 for
forming a stable annular small flame. Thus, the liner cone portion
13 can be easily repaired or replaced with a new one at a low cost
thanks to this advantageous separate and independent construction.
The third reason of employing the double chamber construction is to
attain a sure support of the combustor liner. Especially in the
reverse flow type combustor shown in FIG. 1, spacers are arranged
between the combustor outer cylinder 18 and the liner head outer
cylinder 133 for supporting the liner. For this reason, a certain
amount of mechanical strength is required for the liner head. In
this case, the double chamber construction shown in FIG. 19 can be
used to full advantage. In case of the double chamber construction,
total area of the inner air regulating holes 132 for supplying air
to a primary air chamber 116 should be equal to or a little smaller
than total area of all the openings of the part of liner cone
portion 13 facing the primary air chamber 116 to obtain a large
fluidity resistance at the inner air regulating holes 132. Total
area of the outer air regulating holes 131 for supplying air to the
air chamber 129 should be equal to or larger than total area of all
the openings of the part of liner cone portion 13 facing the air
chamber 129. The experiments have shown that an excellent burning
performance is available by following the above procedures. The
reason is that a stable annular small flame is formed by making
small the amount and speed of the air coming in through the
openings of the part of liner cone portion 13 facing the primary
air chamber 116. In particular, the optimum amount of air should be
determined by the spray propery of fuel nozzle. For instance, a
larger amount of air is required for a fuel nozzle spraying a great
quantity of fine fuel particles of less than 20 .mu. size. On the
other hand, by making large the amount and speed of the air coming
in through the openings of the part of liner cone portion 13 facing
the air chamber 116, the mixing of primary air and sprayed fuel
particles is improved, a low temperature burning can be carried out
thanks to the increased air fuel ratio in the primary burning zone,
and the flowing distance of primary air hole jet flow flowing in
through primary air holes 134 can be increased. Thus, the object of
the present invention can be achieved satisfactorily by making
large the fluidity resistance of the inner air regulating holes 132
and by making small the fluidity resistance of the outer air
regulating holes 131.
Although the present invention has been described in detail with
reference to the boiler type combustor, it is also applicable to
other types of gas turbine combustor, i.e., cannular type combustor
and annular type combustor.
The burning method in accordance with the present invention can be
applied to, in addition to gas turbines, other burning equipment
such as boiler and small heating apparatus since it has a distinct
feature that the production of unburned hydrocarbon, carbon
monoxide, soot, and nitrogen oxides, which cause air pollution, is
limited to the lowest level.
With the formation of the annular small flame in accordance with
the present invention, it is possible to decrease the amount of
harmful substances such as unburned hydrocarbon (observed mostly as
a white smoke) and carbon monoxide heretofore produced by
incomplete combustion at the time of starting in cold winter.
Further, by inserting an ignition plug in the annular small flame,
a very sure firing can be performed. In this instance, a quite
reliable firing is possible because extremely fine fuel particles
gather in the annular small flame and the firing is carried out in
a manner as if a gas fuel were ignited.
On the other hand, in normal load operation, the evaporation of
fuel particles is accelerated so that complete combustion is
accomplished to prevent the generation of smoke.
The burning method in accordance with the present invention, in
contrast to the conventional hydrodynamic flame stabilizing method,
utilizes the extremely stable annular small flame and is capable of
increasing to a large degree the excessive amount of air in the
primary and secondary burning zones located adjacent to the annular
small flame to obtain a reduced main flame temperature for
effectively decreasing nitrogen oxides produced by the burning
operation. Thus, the present invention can provide a gas turbine
power plant with a very low level of environmental pollution since
the harmful substances described above, which are the source of air
pollution, are produced only in the slightest possible amount if
the burning method in accordance with the present invention is
applied to a gas turbine.
* * * * *