{Technical Field}
The present invention relates to solid-fuel-fired burners and solid-fuel-fired boilers
that combust solid fuel (powdered fiiel) such as pulverized coal.
{Background Art}
Examples of conventional solid-fuel-fired boilers include a pulverized-coal-fired
boiler that combusts pulverized coal (coal) as solid fuel, for example. Examples of this
pulverized-coal-fired boiler include two types of known combustion systems, i.e., a
tangential firing boiler and a wall firing boiler.
Of those boilers, in the tangential firing boiler that combusts pulverized coal,
secondary-air injection ports for injecting secondary air are disposed above and below
primary air injected from a coal-fired burner (solid-fiiel-fired burner) together with
pulverized coal, serving as fuel, so as to perform airflow adjustment of secondary air around
the coal-fired boiler (see Patent Literature 1, for example).
The amount of the above-described primary air needs to be sufficient to convey the
pulverized coal, serving as fuel, and therefore, the amount thereof is specified in a roller mill
for pulverizing coal to generate pulverized coal.
The above-described secondary air is blown at an amount required to form the entire
flame in the tangential firing boiler. Therefore, the amount of secondary air for the
tangential firing boiler is generally obtained by subtracting the amount of primary air fi-om
the total amount of air required for combustion of the pulverized coal.
On the other hand, in a burner of a wall firing boiler, it has been proposed that
secondary air and tertiary air are introduced at an outer side of primary air (for supplying
pulverized coal) to perform fine tuning of the amount of introduced air (see Patent Literature
2, for example).
(Citation List}
{Patent Literature}
{PTLl}
2
the Publication of Japanese Patent No. 3679998
{PTL 2}
Japanese Unexamined Patent Application, Publication No. 2006-189188
{Summary of Invention}
{Technical Problem}
The above-described conventional tangential firing boiler has a configuration in
which one secondary-air injection port for injecting secondary air is provided above and
below the coal-fired boiler, and thus, fine tuning of the amount of secondary air to be injected
fi-om the secondary-air injection ports cannot be performed. Therefore, a high-temperature
oxygen remaining region is formed at the outer circumference of the flame, and in particular,
the high-temperature oxygen remaining region is formed in a region where the secondary air
is concentrated, to cause an increase in the amount of NOx produced, which is undesirable.
In general, the conventional coal-fired burner has a configuration in which a flame
stabilizing mechanism (for tip-angle adjustment, turning, etc.) is disposed at the outer
circvimference of the burner, and further, secondary air (or tertiary air) injection ports are
disposed immediately next to the outer circumference of the flame stabilizing mechanism.
Therefore, ignition is brought about at the outer circumference of the flame, and a large
amoimt of air is mixed at the outer circumference of the flame. As a result, combustion at
the outer circumference of the flame progresses in a high-oxygen high-temperature state in
the high-temperature oxygen remaining region at the outer circumference of the flame, and
therefore, NOx is produced at the outer circumference of the flame.
Since the NOx thus produced in the high-temperature oxygen remaining region at the
outer circumference of the flame passes through the outer circumference of the flame, the
reduction of the NOx is delayed compared with that of NOx produced inside the flame, and
this causes NOx to be produced fi-om the coal-fired boiler.
On the other hand, also in the wall firing boiler, since ignition is performed at the
outer circumference of the flame due to swirling, this similarly causes NOx to be produced at
the outer circumference of the flame.
3
From those circumstances, as in the above-described conventional coal-fired burner
and coal-fired boiler, in solid-fuel-fired burners and solid-fiiel-fired boilers that combust
powdered solid-fuel, it is desired to suppress a high-temperature oxygen remaining region
formed at the outer circumference of the flame to reduce the amount of eventually produced
NOx emitted fi^om an additional-air injection section.
The present invention has been made in view of the above-described circumstances,
and an object thereof is to provide a solid-fiiel-fired burner and a solid-fuel-fired boiler
capable of decreasing the amount of eventually produced NOx emitted from the additionalair
injection section by suppressing (weakening) a high-temperature oxygen remaining region
formed at the outer circumference of the flame.
{Solution to Problem}
In order to solve the above-described problems, the present invention employs the
following solutions.
According to a first aspect, the present invention provides a solid-fiiel-fired burner
that is used in a burner section of a solid-fuel-fired boiler for performing low-NOx
combustion separately in the burner section and in an additional-air injection section and that
injects powdered solid-fuel and air into a furnace, including: a fuel burner having internal
flame stabilization; and a secondary-air injection port that does not perform flame
stabilization, in which an air ratio in the fiiel burner is set to 0.85 or more.
According to this solid-fiiel-fired burner of the first aspect of the present invention,
since the fiiel burner having the internal flame stabilization and the secondary-air injection
port that does not perform flame stabilization are provided, and the air ratio in the fuel burner
is set to 0.85 or more, the amount of air in an additional-air injection section (the amount of
injected additional air) is decreased compared with a case in which the air ratio is set to 0.8,
for example. As a result, in the additional-air injection section where the amount of injected
additional air is decreased, the amoimt of NOx eventually produced is decreased.
The above-described decrease in the amount of injected additional air is enabled when
ignition in the fuel burner is enhanced with the internal flame stabilization by employing the
fuel burner having the internal flame stabilization and the secondary-air injection port that
does not perform flame stabilization, and when the diffusion of air into the inside of the
4
flame is improved to suppress an oxygen remaining region formed in the flame.
Specifically, since a high-temperature oxygen remaining region formed at the outer
circumference of the flame is suppressed, and furthermore, the enhancement of ignition
produces NOx inside the flame to effectively reduce the NOx, the amount of NOx reaching
the additional-air injection section is decreased. Further, since the amount of injected
additional air is decreased in the additional-air injection section, the amount of NOx
produced in the additional-air injection section is also decreased, and, as a result, the amount
of NOx eventually emitted can be decreased.
Further, the adoption of the secondary-air injection port that does not perform flame
stabilization is also effective to decrease the amount of NOx produced at the outer
circumference of the flame.
In the above-described solid-fuel-fired burner, a more preferable air ratio in the fuel
burner is 0.9 or more.
In the solid-fuel-fired burner according to the first aspect of the present invention, it is
preferable that the fuel burner injects powdered fuel and air into the fiimace; the secondaryair
injection port is disposed above and below and/or on the right and left sides of the fuel
burner and has an airflow adjustment means; and one or more splitting members is arranged
at a flow-path fi-ont part of the fiiel burner.
According to this solid-fuel-fired burner, since the solid-fuel-fired burner, which
injects powdered fiiel and air into the furnace, is provided with one or more splitting
members arranged at the flow-path front part of the fiiel burner, the splitting members
fimction as an internal flame stabilizing mechanism near the center of the outlet opening of
the fiiel burner. Since internal flame stabilization is enabled by the splitting members, the
center portion of the flame becomes deficient in air, and thereby NOx reduction proceeds.
In the solid-fiiel-fired burner according to the first aspect of the present invention, it is
preferable that the fiiel burner injects powdered fuel and air into the fiimace; the secondaryair
injection port is disposed above and below and/or on the right and left sides of the fiiel
burner and has an airflow adjustment means; and splitting members are arranged in a
plurality of directions at a flow-path front part of the fiiel burner.
According to this solid-fiiel-fired burner, since the solid-fuel-fired burner, which
injects powdered fiiel and air into the fiimace, is provided with the splitting members
5
arranged in a plurality of directions at the flow-path front part of the fuel burner, crossing
parts of the splitting members, functioning as the internal flame stabilizing mechanism, can
be easily provided near the center of the outlet opening of the fuel burner.
Therefore, in the vicinity of the center of the outlet opening of the fuel burner where
the splitting members cross, the flow of powdered fuel and air is disturbed by the presence of
the splitting members that divide the flow path. As a result, air mixing and diffusion are
facilitated even inside the flame, and further, the ignition area is divided, thereby making the
ignition position come close to the center portion of the flame and decreasing the amount of
unbumed fuel. Specifically, since it becomes easy for oxygen to come into the center
portion of the flame along the splitting members, the high-temperature oxygen remaining
region at the outer circumference of the flame is suppressed, thereby effectively performing
internal ignition. When ignition in the flame is facilitated as described above, reduction
rapidly proceeds in the flame, thus decreasing the amount of NOx produced, compared with a
case where ignition is performed in the high-temperature oxygen remaining region at the
outer circumference of the flame.
Note that, in this solid-fuel-fired burner, it is preferable that a flame stabilizer that is
conventionally disposed at the outer circumference of the burner be eliminated, thereby
further suppressing the amoxmt of NOx produced at the outer circumference of the flame.
In the solid-fuel-fired burner according to the first aspect of the present invention, it is
preferable that an ignition surface length (Lf) constituted by the splitting members be set
larger tlian an outlet-opening circumferential length (L) of the fuel burner (Lf > L).
When the length of the splitting members is set as described above, the ignition
surface determined by the ignition surface length (Lf) is larger than that used in ignition
performed at the outer circumference of the flame. Therefore, compared with the ignition
performed at the outer circumference of the flame, internal ignition is enhanced, thereby
facilitating rapid reduction in the flame.
Further, since the splitting members divide the flame therein, rapid combustion in the
flame is enabled.
In the above-described solid-fuel-fired burner, it is preferable that the splitting
members be disposed densely at the center of an outlet opening of the fuel burner.
6
When the splitting members, serving as the internal flame stabilizing mechanism, are
disposed densely at the center of the outlet opening, as described above, the splitting
members are concentrated at the center portion of the fuel burner, thereby further facilitating
ignition at the center portion of the flame to produce and rapidly reduce NOx in the flame.
Further, when the splitting members are arranged densely at the center, the
unoccupied area in the central part of the fuel burner is decreased, thereby relatively
increasing the pressure loss at the splitting members. Therefore, the flow velocity of
powdered fuel and air flowing in the fuel burner is decreased, and more rapid ignition can be
brought about.
In the above-described solid-fuel-fired burner, it is preferable that the secondary-air
injection ports be each divided into a plurality of independent flow paths each having airflow
adjustment means.
The thus-configured solid-fuel-fired burner can perform flow-rate distribution such
that the amount of secondary air to be injected into the outer circumference of the flame is set
to a desired value by operating the airflow adjustment means for each of the divided flow
paths. Therefore, when the amount of secondary air to be injected into the outer
circumference of the flame is properly set, formation of a high-temperature oxygen
remaining region can be suppressed or prevented.
In the solid-fuel-fired burner according to the first aspect of the present invention, it is
preferable that the fuel burner injects powdered fuel and air into the furnace; the secondaryair
injection port is disposed above and below and/or on the right and left sides of the fuel
burner and divided into a plurality of independent flow paths each having an airflow
adjustment means; and a splitting member is arranged at a flow-path front part of the fuel
burner.
According to this solid-fuel-fired burner, the fuel burner that injects powdered fuel
and air into the furnace; the secondary-air injection ports that are each disposed above and
below and/or on the right and left sides of the fuel burner and that each have airflow
adjustment means, the secondary-air injection ports each being divided into a plurality of
independent flow paths each having the airflow adjustment means; and the splitting member
arranged at the flow-path front part of the fuel burner are further provided. Therefore, flow-
7
rate distribution can be performed such that the amount of secondary air to be injected into
the outer circumference of the flame is set to a desired value by operating the airflow
adjustment means for each of the divided flow paths. Therefore, when the amount of
secondary air to be injected into the outer circumference of the flame is properly set,
formation of a high-temperature oxygen remaining region can be suppressed or prevented.
Further, when the splitting member is provided at the flow-path front part of the fuel
burner, it is possible to disturb the flow of powdered fiiel and air to bring about ignition in the
flame. As a result, NOx is produced in the flame and is rapidly reduced in the flame, which
is deficient in air, because the produced NOx contains many types of hydrocarbons having a
reducing action. In other words, the splitting member can enhance internal flame
stabilization to prevent or suppress the formation of a high-temperature oxygen remaining
region.
Therefore, in this solid-fuel-flred burner, it is preferable that a flame stabilizer that is
conventionally disposed at the outer circumference of the burner be eliminated.
In the above-described solid-fuel-fired burner, it is preferable to further include a flow
adjustment mechanism that applies a pressure loss to a flow of the powdered fuel and air
provided at an upper stream side of the splitting members.
Since this flow adjustment mechanism eliminates flow rate deviation of powdered
fuel caused by passing through a vent provided in a flow path, it is possible to effectively
utilize tlie internal flame stabilizing mechanism constituted by the splitting members.
In the above-described solid-fuel-fired burner, it is preferable that the secondary-air
injection ports be each provided with an angle adjustment mechanism.
When the secondary-air injection ports are each provided with the angle adjustment
mechanism, it is possible to optimally supply secondary air from the secondary-air injection
ports farther outward of the flame. Further, since swirling is not utilized, it is possible to
prevent or suppress formation of a high-temperature oxygen remaining region while
preventing excessive spreading of the flame.
In the above-described solid-fuel-fired burner, it is preferable that distribution of the
amount of air to be injected from the secondary-air injection ports be feedback-controlled
8
based on the amount of unbumed fuel and the amount of nitrogen oxide (NOx) emission.
When this feedback control is performed, the distribution of secondary air can be
automatically optimized. In this control, for example, when the amount of unbumed fuel is
high, the distribution of secondary air to an inner side close to the outer circumferential
surface of the flame is increased; and, when the amoimt of nitrogen oxide emission is high,
the distribution of secondary air to an outer side far from the outer circumferential surface of
the flame is increased.
Note that, to measure the amount of unbumed fuel, collected ash may be analyzed
each time, for example, or an instrument for measuring the carbon concentration from
scattering of laser light may be employed.
In the above-described solid-fuel-fired bumer, it is preferable that the amount of air to
be injected fi*om the secondary-air injection ports be distributed among multi-stage air
injections that make a region from the bumer section to the additional-air injection section a
reducing atmosphere.
When the amount of air is distributed in this way, the amount of nitrogen oxide
produced can be further decreased due to the synergy between a decrease in nitrogen oxide
through suppression of the high-temperature oxygen remaining region formed at the outer
circumference of the flame and a decrease in nitrogen oxide in combustion exhaust gas,
caused by providing the reducing atmosphere.
In the above-described solid-fuel-flred bumer, it is preferable that a system for
supplying air to a coal secondary port of the fuel bumer be separated from a system for
supplying air to the secondary-air injection ports.
When those air supply systems are provided, the amount of air can be reliably
adjusted even when the secondary-air injection ports are each divided into a plurality of ports
to provide multiple stages.
In the above-described solid-fuel-fired bumer, it is preferable that the plurality of
flow paths of the secondary-air injection ports be concentrically provided around the fuel
bumer, which has a circular shape, in an outer circumferential direction in a multi-stage
fashion.
The thus-configured solid-fuel-fired bumer can be applied particularly to a wall firing
9
boiler. Since air is uniformly introduced from its circumference, the high-temperature highoxygen
region can be more precisely decreased.
According to a second aspect, the present invention provides a solid-fuel-fired boiler
in which the above-described solid-fuel-fired burner that injects powdered fuel and air into a
furnace is disposed at a comer or on a wall of the furnace.
According to the solid-fuel-fired boiler of the second aspect of the present invention,
since the above-described solid-fuel-fired burner, which injects powdered fuel and air into
the furnace, is provided, splitting members that are disposed near the center of the outlet
opening of a fuel burner and that function as an internal flame stabilizing mechanism divide
the flow path of powdered fuel and air to disturb the flow thereof As a resuh, air mixing
and diffusion are facilitated even in the flame, and, further, the ignition surface is divided,
thereby making the ignition position close to the center of the flame, decreasing the amount
of unbumed fuel. Specifically, since it becomes easy for oxygen to come into the center
portion of the flame, internal ignition is effectively performed, and therefore, rapid reduction
proceeds in the flame, decreasing the amount of NOx emission.
According to a third aspect, the present invention provides an operation method of a
solid-fuel-fired burner that is used in a burner section of a solid-fuel-fired boiler for
performing low-NOx combustion separately in the burner section and in an additional-air
injection section and that injects powdered solid-fuel and air into a furnace, the solid-fuelfired
burner including: a fuel burner having internal flame stabilization; and a secondary-air
injection port that does not perform flame stabilization, in which operation is performed with
an air ratio in the fuel burner set to 0.85 or more.
According to this operation method of a solid-fuel-fired burner, the solid-fuel-fired
burner includes the fuel burner having the internal flame stabilization and the secondary-air
injection port that does not perform flame stabilization and is operated with the air ratio in the
fuel burner set to 0.85 or more. Therefore, the amount of air (the amount of injected
additional air) in the additional-air injection section is decreased compared with a case in
which the air ratio is 0.8, for example. As a result, in the additional-air injection section
10
where the amount of injected additional air is decreased, the amount of NOx eventually
produced is decreased.
{Advantageous Effects of Invention}
According to the above-described solid-fuel-fired burner and solid-fiiel-fired boiler of
the present invention, since the fuel burner having the internal flame stabilization and the
secondary-air injection port that does not perform flame stabilization are provided, and the air
ratio in the fuel burner is set to 0.85 or more, preferably, to 0.9 or more, a decrease in the
amount of injected additional air decreases the amount of NOx produced in the additional-air
injection section.
Further, since the high-temperature oxygen remaining region formed at the outer
circumference of the flame is suppressed, and NOx produced in the flame, in which
combustion approaching premix combustion is achieved, is effectively reduced, a decrease in
the amount of NOx reaching the additional-air injection section and a decrease in the amount
of NOx produced due to the injection of additional air decrease the amount of NOx
eventually emitted fi-om the additional-air injection section.
Further, since the splitting members arranged in a plurality of directions that function
as the internal flame stabilizing mechanism are provided at the outlet opening of the fuel
bumer, the flow path of powdered fuel and air is divided to disturb the flow thereof in the
vicinity of the center of the outlet opening of the fuel bumer where the splitting members
cross. As a result, since air mixing and diffusion is facilitated even in the flame, and
further, the splitting members divide the ignition surface, the ignition position comes close to
the center of the flame, and the amount of unbumed fuel is decreased. This is because it
becomes easy for oxygen to come into the center portion of the flame, and internal ignition is
effectively performed with this oxygen, and thereby rapid reduction proceeds in the flame,
decreasing the amount of produced NOx eventually emitted from the solid-fuel-fired boiler.
Furthermore, by adjusting injection of secondary air, concentration of secondary air at
the outer circumference of the flame can be prevented or suppressed. As a result, it is
possible to suppress the high-temperature oxygen remaining region formed at the outer
circumference of the flame, decreasing the amount of nitrogen oxide (NOx) produced.
11
Further, by using an operation method of a solid-fiiel-fired burner in which the burner
is operated with the air ratio in the fuel burner set to 0.85 or more, the amount of air (the
amount of injected additional air) in the additional-air injection section can be decreased,
thereby decreasing the amount of NOx eventually produced in the additional-air injection
section where the amount of injected additional air is decreased.
{Brief Description of Drawings}
{Fig. lA}
FIG. lA is a front view of a solid-fiiel-fired burner (coal-fired burner) according to a
first embodiment of the present invention, when the solid-fiiel-fired burner is seen from the
inside of a furnace.
{Fig. IB}
FIG. IB is a cross-sectional view of the solid-fiiel-fired burner (vertical crosssectional
view thereof) along arrows A-A shown in FIG. 1 A.
{Fig. 2}
FIG. 2 is a diagram showing an air supply system for supplying air to the solid-fuelfired
burner shown in FIGS. 1A and IB.
{Fig. 3}
FIG. 3 is a vertical cross-sectional view showing a configuration example of a solidfuel-
fired boiler (coal-fired boiler) according to the present invention.
{Fig. 4}
FIG. 4 is a (horizontal) cross-sectional view of FIG. 3.
{Fig. 5}
FIG. 5 is an explanatory diagram showing, in outline, the solid-fuel-fired boiler that is
provided with an additional-air injection section and in which air is injected in a multi-stage
fashion.
{Fig. 6A}
FIG. 6A is a view showing one example of the cross-sectional shape of a splitting
member in the solid-fiiel-fired burner shown in FIGS. 1A and IB.
{Fig. 6B}
FIG. 6B is a view showing a first modification of the cross-sectional shape shown in
FIG. 6A.
{Fig. 6C}
12
FIG. 6C is a view showing a second modification of the cross-sectional shape shown
in FIG. 6A.
{Fig. 6D}
FIG. 6D is a view showing a third modification of the cross-sectional shape shown in
FIG. 6A.
{Fig. 7A}
FIG. 7A is a front view showing a first modification of a coal primary port of the
solid-fuel-fired burner shown in FIGS. lA and IB, in which the arrangement of splitting
members is different.
{Fig. 7B}
FIG. 73 is an explanatory diagram for supplementing the definition of an ignition
surface length (Lf) of the coal primary port of the solid-fiiel-fired burner shown in FIGS. lA
and IB.
{Fig. 8}
FIG. 8 is a fi-ont view showing a second modification of the coal primary port of the
solid-fuel-fired burner shown in FIGS. lA and IB, in which the arrangement of the splitting
members is different.
{Fig. 9}
FIG. 9 is a vertical cross-sectional view showing a configuration example in which a
flow adjustment mechanism is provided at a burner base, as a third modification of the solidfiiel-
fired burner of the first embodiment.
{Fig. lOA}
FIG. lOA is a vertical cross-sectional view showing a solid-fiiel-fired burner
according to a second embodiment of the present invention.
{Fig. lOB}
FIG. 1 OB is a front view of the solid-fiiel-fired burner shown in FIG. 10A, as viewed
from the inside of the fiimace.
{Fig. IOC}
FIG. IOC is a diagram showing an air supply system for supplying air to the solidfuel-
fired burner shown in FIGS. lOA and lOB.
{Fig. 11 A}
FIG. IIA is a vertical cross-sectional view showing a configuration example of the
solid-fuel-fired burner provided with a splitting member, as a first modification of the solid-
13
fuel-fired burner shown in FIGS. lOA to IOC.
{Fig. 1 IB}
FIG. 1 IB is a front view of the solid-fuel-fired burner shown in FIG. lOA, as viewed
from the inside of the furnace.
{Fig. 12}
FIG. 12 is a front view of the solid-fuel-fired burner provided with lateral secondaryair
ports, as viewed fi-om the inside of the furnace, as a second modification of the solid-fuelfired
burner shown in FIGS. lOA to IOC.
{Fig. 13}
FIG. 13 is a vertical cross-sectional view showing a configuration example in which a
secondary-air injection port of the solid-fuel-fired burner shown in FIG. lOA is provided with
an angle adjustment mechanism.
{Fig. 14}
FIG. 14 is a diagram showing a modification of the air supply system shown in FIG.
IOC.
{Fig. 15}
FIG. 15 is a vertical cross-sectional view of a solid-fuel-fired burner, showing a
configuration example in which the third modification of the first embodiment, shown in
FIG. 9, and the second embodiment, shown in FIGS. lOA to IOC, are combined.
{Fig. 16}
FIG. 16 is a fi^ont view of a solid-fuel-fired burner suitable for use in a wall firing
boiler, as viewed from the inside of the furnace.
{Fig. 17}
FIG. 17 is a graph of an experimental result showing the relationship between a flame
stabilizer position in internal flame stabilization (flame stabilizer position/actual pulverizedcoal
flow width) and the amount of NOx produced (relative value).
{Fig. 18}
FIG. 18 shows views of comparative examples of a fuel burner, for explaining the
flame stabilizer position indicated in the graph shown in FIG. 17
{Fig. 19}
FIG. 19 is a graph of an experimental result showing the relationship between split
occupancy and the amount of NOx produced (relative value).
{Fig. 20}
14
FIG. 20 is a graph of an experimental result showing relative values of the amounts of
unbumed fuel produced in one-direction split and crossed split.
{Fig. 21}
FIG. 21 is a graph of an experimental result showing relative values of the amounts of
NOx produced in a burner section, in a region between the burner section and an AA section,
and in the AA section, comparing a conventional technology and the present invention.
{Fig. 22}
FIG. 22 is a graph of an experimental result showing the relationship between an air
ratio in the region between the burner section and the AA section and the amount of NOx
produced (relative value), comparing a conventional technology and the present invention.
{Description of Embodiments}
A solid-fuel-fired burner and a solid-fliel-fired boiler according to one embodiment of
the present invention will be described below based on the drawings. Note that, in this
embodiment, as one example of the solid-fuel-fired burner and the solid-fuel-fired boiler, a
tangential firing boiler provided with solid-fuel-fired burners that use pulverized coal
(powdered solid-fuel coal) as fuel will be described, but the present invention is not limited
thereto.
A tangential firing boiler 10 shown in FIGS. 3 to 5 injects air into a furnace 11 in a
multi-stage fashion to make a region from a burner section 12 to an additional-air injection
section (hereinafter, referred to as "AA section") 14 a reducing atmosphere, thereby
achieving a decrease in NOx in combustion exhaust gas.
In the drawings, reference numeral 20 denotes solid-fuel-fired burners that inject
pulverized coal (powdered solid-fuel) and air, and reference numeral 15 denotes additionalair
injection nozzles that inject additional air. For example, as shown in FIG. 3, pulverizedcoal
mixed air conveying pipes 16 that convey pulverized coal by primary air and an air
supply duct 17 that supplies secondary air are connected to the solid-fuel-fired burners 20,
and the air supply duct 17, which supplies secondary air, is connected to the additional-air
injection nozzles 15.
In this way, the above-described tangential firing boiler 10 employs a tangential firing
system in which the solid-fuel-fired burners 20, which inject pulverized coal (coal), serving
as powdered fuel, and air into the furnace 11, are disposed at respective comer portions at
15
each stage to constitute the tangential-firing-type burner section 12, and one or more swirling
flames are formed in each stage.
First Embodiment
The solid-fuel-fired bvimer 20 shown in FIGS. 1A and IB includes a pulverized-coal
burner (fuel burner) 21 that injects pulverized coal and air and secondary-air injection ports
30 that are disposed above and below the pulverized-coal burner 21.
In order to allow airflow adjustment in each port, the secondary-air injection ports 30
are provided with dampers 40 that can adjust the degrees of opening thereof, as airflow
adjustment means, in each secondary-air supply line branched from the air supply duct 17, as
shown in FIG. 2, for example.
The above-described pulverized-coal burner 21 includes a rectangular coal primary
port 22 that injects pulverized coal conveyed by primary air and a coal secondary port 23 that
is provided so as to surround the coal primary port 22 and that injects part of secondary air.
Note that the coal secondary port 23 is also provided with a damper 40 that can adjust the
degree of opening thereof, as airflow adjustment means, as shown in FIG. 2. Note that the
coal primary port 22 may have a circular shape or an elliptical shape.
At a flow-path front part of the pulverized-coal burner 21, specifically, at a flow-path
front part of the coal primary port 22, splitting members 24 are arranged in a plurality of
directions. For example, as shown in FIG. lA, a total of four splitting members 24 are
arranged, two vertically and two horizontally, in a grid-like pattern with a predetermined gap
therebetween at an outlet opening of the coal primary port 22.
In other words, the four splitting members 24 are arranged in two different directions,
that is, the vertical and horizontal directions, in a grid-like pattern, thereby dividing the outlet
opening of the coal primary port 22 of the pulverized-coal burner 21 into nine portions.
When the above-described splitting members 24 employ the cross-sectional shapes
shown in FIGS. 6A to 6D, for example, the flow of pulverized coal and air can be smoothly
split and disturbed.
The splitting member 24 shown in FIG. 6A has a triangular shape in cross section.
The triangular shape shown in the figure is an equilateral triangle or an isosceles triangle, and
16
a side thereof positioned at the outlet facing the inside of the furnace 11 is located so as to be
approximately perpendicular to the flow direction of pulverized coal and air. In other
words, one of the angles constituting the triangular shape in cross section faces the flow
direction of pulverized coal and air.
A splitting member 24A shown in FIG. 6B has an approximately T-shape in cross
section, and a surface thereof that is approximately perpendicular to the flow direction of
pulverized coal and air is located at the outlet facing the inside of the furnace 11. Note that
this approximately T-shape in cross section may be deformed to form a splitting member
24A' having a trapezoidal shape in cross section, as shown in FIG. 6C, for example.
Further, a splitting member 24B shown in FIG. 6D has an approximately L-shape in
cross section. Specifically, it has a shape in cross section obtained by cutting off a part of
the above-described approximately T-shape. In particular, in a case where the splitting
member 24B is disposed in a right-and-left (horizontal) direction, if the splitting member 24B
has an approximately L-shape obtained by removing an upper protruding portion of the
above-described approximately T-shape, it is possible to prevent pulverized coal from being
accumulated on the splitting member 24B. Note that, when a lower protruding portion
thereof is enlarged by an amount equal to the removed upper protruding portion, the required
splitting performance for the splitting member 24B can be ensured.
However, the above-described cross-sectional shapes of the splitting members 24 etc.
are not limited to the examples shown in the figures; they may be an approximately Y-shape,
for example.
In the thus-configured solid-fuel-fired burner 20, the splitting members 24 disposed
near the center of the outlet opening of the pulverized-coal burner 21 split the flow path of
pulverized coal and air to disturb the flow therein, forming a recirculation region in front of
the splitting members 24, thereby serving as an internal flame stabilizing mechanism.
In general, in a conventional solid-fuel-fired burner, pulverized coal, serving as fuel,
is ignited upon receiving radiation at the outer circumference of the flame. When the
pulverized coal is ignited at the outer circumference of the flame, NOx is produced in a hightemperature
oxygen remaining region H (see FIG. IB) at the outer circumference of the
flame where high-temperature oxygen remains, and remains insufficiently reduced, thus
17
increasing the amount of NOx emission.
However, since the splitting members 24 serving as the internal flame stabilizing
mechanism are provided, the pulverized coal is ignited in the flame. Thus, NOx is produced
in the flame and is rapidly reduced in the flame, which is deficient in air, because the NOx
produced in the flame contains many types of hydrocarbons having a reducing action.
Therefore, since the solid-fuel-fired burner 20 is structured such that flame stabilization
realized by disposing a flame stabilizer at the outer circumference of flame is not employed,
in other words, such that a flame stabilizing mechanism is not disposed at the outer
circumference of the burner, it is also possible to suppress the production of NOx at the outer
circumference of the flame.
In particular, since the splitting members 24 are arranged in a plurality of directions,
crossing parts at which the splitting members 24 arranged in the different directions cross are
easily provided near the center of the outlet opening of the pulverized-coal burner 21.
When such crossing parts are provided near the center of the outlet opening of the
pulverized-coal burner 21, the flow path of pulverized coal and air is split into a plurality of
paths near the center of the outlet opening of the pulverized-coal burner 21, thereby
disturbing the flow thereof when the flow is split into a plurality of flows.
Specifically, if the splitting members 24 are arranged in one horizontal direction, air
diffusion and ignition at a center portion are delayed, causing an increase in the amoimt of
unbumed fuel; however, if the splitting members 24 are arranged in a plurality of directions
to form the crossing parts, mixing of air is facilitated, and the ignition surface is divided,
thereby making it easy for air (oxygen) to come into the center portion of flame, resulting in a
decrease in the amount of unbumed fuel.
In other words, when the splitting members 24 are arranged so as to form the crossing
parts, mixing and diffusion of air are facilitated even inside the flame, and further, the
ignition surface is divided, thereby making the ignition position come close to the center
portion (axial center portion) of the flame and decreasing the amount of unbumed pulverized
coal. Specifically, since it becomes easy for oxygen to come into the center portion of
flame, intemal ignition is effectively performed, and thus, rapid reduction proceeds in the
18
flame, decreasing the amount of NOx produced.
As a result, it becomes easier to suppress the production of NOx at the outer
circumference of the flame by using the solid-fuel-fired burner 20 that does not employ flame
stabilization realized by a flame stabilizer disposed at the outer circumference of the flame
and that has no flame stabilizer at the outer circumference of the flame.
Next, a first modification of the coal primary port 22 of the solid-fuel-fired burner 20,
shown in FIG. 1 A, will be described based on FIGS. 7A and 7B, in which the arrangement of
the splitting members 24 is different.
In this modification, at the fiow-path front part of the coal primary port 22, two
splitting members 24 are arranged in the vertical direction of the outlet opening thereof, and
one splitting member 24 is arranged in the horizontal direction of the outlet opening thereof
The splitting members 24 shown in the figures are structured such that an ignition
surface length (Lf) constituted by the splitting members 24 is larger than an outlet-opening
circumferential length (L) of the coal primary port 22 that constitutes the pulverized-coal
burner 2 l(Lf>L).
Here, since the outlet-opening circumferential length (L) of the coal primary port 22
is the sum of the lengths of four sides constituting the rectangle, it is expressed by L = 2H +
2W, where H indicates the vertical dimension, and W indicates the horizontal dimension.
On the other hand, since each splitting member 24, which has a certain width, has
ignition surfaces on both sides thereof, the ignition surface length (Lf) of the splitting
members 24, which is the total length of both sides of each of the three splitting members 24,
is expressed by Lf = 6S, where S indicates the length of the splitting member 24. In this
case, since the length of the short splitting member 24 that is arranged in the vertical
direction is used as the length S, the calculated ignition surface length (Lf) is an estimated
value erring on the safe side even if the presence of the crossing parts is taken into account.
Note that, when calculating the ignition surface length (Lf), if a splitting member 24'
that is structured to have narrow parts 24a at both ends due to a splitting-member
manufacturing method or the like is used, as shown in FIG. 7B, for example, the narrow parts
24a at both ends are also considered as part of the ignition surface.
19
When the length of the splitting member 24 is specified as described above, the
ignition surface determined by the ignition surface length (Lf) is larger than that used in
ignition performed at the outer circimiference of the flame. Therefore, compared with the
ignition performed at the outer circumference of the flame determined by the outlet-opening
circumferential length (L), internal ignition determined by the ignition surface length (Lf) is
enhanced, thereby allowing rapid reduction of NOx produced in the flame.
Further, since the splitting members 24 divide the flame therein, it becomes easy for
air (oxygen) to come into the center portion of the flame, and thus, rapid combustion in the
flame can decrease the amoimt of unbumed fuel.
Next, a second modification of the coal primary port 22 of the solid-fiiel-fired burner
20, shown in FIG. lA, will be described based on FIG. 8, in which the arrangement of the
splitting members 24 is different.
In this modification, five splitting members 24 are disposed in a grid-like pattern
densely at the center of the outlet opening of the coal primary port 22 of the fuel burner 21.
Specifically, the splitting members 24, three of which are arranged in the vertical direction
and two of which are arranged in the horizontal direction, are disposed with the gaps
therebetween being narrowed at the center of the coal primary port 22. Therefore, center
portions of the outlet opening of the coal primary port 22, divided by the splitting members
24, have areas smaller than other portions at the outer circumferential side thereof
In this way, when the splitting members 24, serving as the internal flame stabilizing
mechanism, are arranged densely at the center of the coal primary port 22, the splitting
members 24 are concentrated at the center portion of the pulverized-coal burner 21, thereby
further facilitating ignition at the center portion of the flame to rapidly produce and reduce
NOx in the flame.
Further, when the splitting members 24 are arranged densely at the center, the
unoccupied area in the central part of the pulverized-coal burner 21 is decreased.
Specifically, since the ratio of pulverized coal and air passing through the cross-sectional area
of a flow path that is almost straight without any obstacle with respect to those flowing in the
20
coal primary port 22 of the pulverized-coal burner 21 is decreased, the pressure loss at the
splitting members 24 is relatively increased. Therefore, in the fuel burner 21, since the flow
velocity of pulverized coal and air flowing in the coal primary port 22 is decreased under the
influence of an increase in the pressure loss, more rapid ignition can be brought about.
Next, a configuration example according to a third modification of the coal primary
port 22 of the solid-fuel-fired burner 20, shown in FIG. lA, will be described based on FIG.
9, in which a flow adjustment mechanism is provided at a burner base. Note that the
configuration example shown in the figure employs the splitting members 24A having an
approximately T-shape in cross section, but the shape thereof is not limited thereto.
In this configuration example, in order to apply the pressure loss to a flow of
pulverized coal and air, a flow adjustment mechanism 25 is provided at an upstream side of
the splitting members 24A. The flow adjustment mechanism 25 prevents flow rate
deviation in a port cross-section direction, and it is effective to dispose an orifice or a venturi
that can restrict the flow-path cross-sectional area to approximately 2/3, preferably, to
approximately 1/2, for example.
The flow adjustment mechanism 25 may have any structure so long as it can apply a
certain pressure loss to a powder transfer flow that conveys pulverized coal, serving as fuel,
by primary air, and therefore, the flow adjustment mechanism 25 is not limited to an orifice.
Further, the above-described fiow adjustment mechanism 25 is not necessarily formed
as a part of the solid-fuel-fired burner 20 and just needs to be disposed, at the upstream side
of the splitting member 24A, in a final straight pipe portion (straight flow-path portion
without a vent, a damper, etc.) in the flow path in which pulverized coal and primary air
flow.
When the flow adjustment mechanism 25 is an orifice, it is preferable to provide a
straight pipe portion (Lo) that extends from the outlet end of the orifice to the outlet of the
coal primary port 22, specifically, to the inlet ends of the splitting members 24A, in order to
eliminate the influence of the orifice. It is necessary to ensure that the length of the straight
pipe portion (Lo) is at least 2h or more, where h indicates the height of the coal primary port
22, and, more preferably, the length of the straight pipe portion (Lo) is lOh or more.
21
When this flow adjustment mechanism 25 is provided, it is possible to eliminate flow
rate deviation in which an imbalance is caused in the distribution in a cross section of the
flow path when pulverized coal, serving as powdered fuel, is influenced by a centrifugal
force afler passing through a vent provided in the flow path for supplying the pulverized coal
and primary air to the coal primary port 22.
Specifically, although the pulverized coal conveyed by the primary air has, after
passing through the vent, a distribution deviating outward (in the direction of increasing vent
diameter), when the pulverized coal passes through the flow adjustment mechanism 25, the
distribution in a cross section of the flow path is eliminated, and the pulverized coal flows
into the splitting members 24A almost uniformly. As a result, the pulverized-coal burner 21
having the flow adjustment mechanism 25 can effectively utilize the internal flame
stabilizing mechanism constituted by the splitting members 24A.
Further, in the above-described embodiment and modifications thereof, the splitting
members 24 are arranged in a plurality of (vertical and horizontal) directions at the flow-path
front part of the coal primary port 22; however, one or more splitting members 24 may be
provided in the horizontal direction or in the vertical direction. When such splitting
members 24 are provided, since they function as the internal flame stabilizing mechanism
near the center of the outlet opening of the pulverized-coal burner 21, internal flame
stabilization can be realized by the splitting members 24, and the center portion becomes
more deficient in air, thus facilitating NOx reduction.
Second Embodiment
Next, a solid-fuel-fired burner according to a second embodiment of the present
invention will be described based on FIGS. lOA to IOC. Note that identical reference
symbols are assigned to the same items as those in the above-described embodiment, and a
detailed description thereof will be omitted.
In a solid-fuel-fired burner 20A shown in the figures, the pulverized-coal burner 21
includes the rectangular coal primary port 22 that injects pulverized coal conveyed by
primary air and the coal secondary port 23 that is provided so as to surround the coal primary
port 22 and that injects part of secondary air.
Secondary-air injection ports 30A for injecting secondary air are provided above and
22
, below the solid-fuel-fired burner 21. The secondary-air injection ports 30A are each
divided into a plurality of independent flow paths and ports, and the flow paths are provided
with the respective dampers 40 that can adjust the degrees of opening thereof, as secondaryair
airflow adjustment means.
In a configuration example shown in the figures, both of the secondary-air injection
ports 30A disposed above and below the pulverized-coal burner 21 are vertically divided into
three ports, which are inner secondary-air ports 31a and 31b, middle secondary-air ports 32a
and 32b, and outer secondary-air ports 33a and 33b, disposed in that order from the inner side
close to the pulverized-coal burner 21 to the outer side. Note that the number of ports into
which the secondary-air injection ports 30 are each divided is not limited to three and can be
appropriately changed according to the conditions.
The above-described coal secondary port 23, inner secondary-air ports 31a and 31b,
middle secondary-air ports 32a and 32b, and outer secondary-air ports 33a and 33b are each
coimected to an air supply line 50 having an air supply source (not shown), as shown in FIG.
IOC, for example. The dampers 40 are provided in flow paths that are branched from the air
supply line 50 to communicate with the respective ports. Therefore, by adjusting the degree
of opening of each of the dampers 40, the amount of secondary air to be supplied can be
independently adjusted for each of the ports.
With the solid-fuel-fired burner 20A and the tangential firing boiler 10 that includes
the solid-fuel-fired burner 20A, since each solid-fuel-fired burner 20A includes the
pulverized-coal burner 21, which injects pulverized coal and air, and the secondary-air
injection ports 30A each divided into three ports and disposed above and below the
pulverized-coal burner 21, it is possible to perform flow-rate distribution such that the
amount of secondary air to be injected into the outer circumference of the flame F is set to a
desired value by adjusting the degree of opening of the damper 40 for each of the ports into
which the secondary-air injection ports 30A are divided.
Therefore, when the distribution proportion of the amovmt of secondary air to be
injected into the iimer secondary-air ports 31a and 31b, which are closest to the outer
circumference of the flame F, is decreased, and those of the amounts of secondary air to be
injected into the middle secondary-air ports 32a and 32b and the outer secondary-air ports
33a and 33b are sequentially increased in proportion to the decrease, it is possible to suppress
23
. a local high-temperature oxygen remaining region (hatched portion in the figure) H formed at
the outer circumference of the flame F.
In other words, when the proportion of the amount of secondary air to be injected into
an outer side away from the flame F is increased, and the proportion of the amount of
secondary air to be injected into the vicinity of the outer circimiference of the flame F is
decreased, diffusion of secondary air can be delayed. As a result, concentration of
secondary air at the circimiference of the flame F can be prevented or suppressed, and
therefore, the local high-temperature oxygen remaining region H is weakened and decreased
in size, thereby decreasing the amount of NOx produced in the tangential firing boiler 10.
In other words, when the amoimt of secondary air to be injected into the outer circumference
of the flame F is properly specified, formation of the high-temperature oxygen remaining
region H can be suppressed or prevented to achieve a decrease in the amount of NOx in the
tangential firing boiler 10.
On the other hand, when diffusion of secondary air is required due to the properties of
the pulverized coal or the like, it is necessary merely to reverse the distribution proportions
for the secondary-air injection ports 30A, specifically, to increase the distribution proportions
for the inner secondary-air ports 31a and 31b.
Specifically, even when pulverized coal obtained by pulverizing coal having a
different fuel ratio, such as that including a large amount of volatile components, is used, the
flow-rate distribution of secondary air to be injected from each of the ports into which the
secondary-air injection ports 30A are divided is appropriately adjusted, thereby making it
possible to select either appropriate combustion with a decrease in the amount of NOx or
imbumed fuel.
Dividing the secondary-air injection ports 30A into a plurality of ports to provide
multiple stages in this way can also be applied to the solid-fuel-fired burner 20 described
above in the first embodiment.
Incidentally, as in a first modification of this embodiment, shown in FIGS. IIA and
IIB, for example, the above-described solid-fuel-fired burner 20A is preferably provided
with a splitting member 24 disposed at a nozzle end of the pulverized-coal burner 21 so as to
24
r vertically split the opening area.
The splitting member 24 shown in the figures has a triangular shape in cross section
and is disposed so as to vertically split and diffuse pulverized coal and primary air that flow
in the nozzle, thereby enhancing flame stabilization and suppressing or preventing formation
of the high-temperature oxygen remaining region H.
Specifically, when pulverized coal and primary air pass through the splitting member
24, a flow of a high concentration of pulverized coal is formed at the outer circumference of
the splitting member 24, which is effective to enhance flame stabilization. The flow of a
high concentration of pulverized coal formed by passing through the splitting member 24
flows into a negative-pressure area formed on a downstream side of the splitting member 24,
as indicated by dashed arrows fa in the figure. As a result, the flame F is also drawn into the
negative-pressure area due to this air flow, thereby further enhancing the flame stabilization
and thus, facilitating combustion to rapidly consume oxygen.
Note that the number of splitting members 24 is not limited to one, and, for example,
a plurality of splitting members 24 may be provided in the same direction or a plurality of
splitting members 24 may be provided in different directions, as described in the first
embodiment. Further, the cross-sectional shape of the splitting member 24 may be
appropriately modified.
Furthermore, as in a second modification of this embodiment, shown in FIG. 12, for
example, the above-described solid-fuel-fired burner 20A is preferably provided with one or
more lateral secondary-air ports 34R and one or more lateral secondary-air ports 34L at right
and left sides of the pulverized-coal burner 21. In a configuration example shown in the
figure, one lateral secondary-air port 34R and one lateral secondary-air port 34L, which are
each provided with a damper (not shown), are provided on the right and left sides of the
pulverized-coal burner 21; but they may be each divided into a plurality of ports whose the
flow rate can be controlled.
With this configuration, secondary air can also be distributed to the right and left
sides of the flame F, thereby preventing excessive secondary air at the upper and lower sides
of the flame F. In other words, the distribution of the amount of secondary air to be injected
into the upper and lower sides and the right and left sides of the outer circumference of the
25
^ flame F can be appropriately adjusted, thereby allowing more precise flow rate distribution.
Those lateral secondary-air ports 34L and 34R can also be applied to the abovedescribed
first embodiment.
Further, in the above-described tangential firing boiler 10, the secondary-air injection
port 30A is preferably provided with an angle adjustment mechanism that vertically changes
the injection direction of secondary air toward the inside of the furnace 11, as shown in FIG.
13, for example. The angle adjustment mechanism vertically changes a tilt angle 9 of the
secondary-air injection port 30A relative to a level position and facilitates the diffusion of
secondary air, preventing or suppressing the formation of the high-temperature oxygen
remaining region H. Note that, in this case, a suitable tih angle 9 is approximately ±30
degrees, and a more desirable tilt angle 9 is ±15 degrees.
With this angle adjustment mechanism, since the angle at which secondary air is
injected from the secondary-air injection port 30A toward the flame F in the furnace 11 can
be adjusted, air diffusion in the furnace 11 can be more precisely controlled. In particular,
in a case where the type of pulverized coal fuel is significantly changed, if the angle of
injection of secondary air is appropriately changed, the NOx decrease effect can be further
improved.
This angle adjustment mechanism can also be applied to the above-described first
embodiment.
Further, in the above-described tangential firing boiler 10, it is preferable that the
distribution of the amounts of air to be injected fi-om the secondary-air injection ports 30A be
adjusted through feedback control of the degrees of opening of the dampers 40, based on the
amounts of unbumed fuel and NOx emission.
Specifically, in the tangential firing boiler 10, when the amount of unbumed fuel is
high, the distribution of secondary air to the inner secondary-air ports 31a and 31b, which are
close to the outer circumferential surface of the flame F, is increased; and, when the amount
of NOx emission is high, the distribution of secondary air to the outer secondary-air ports 33a
and 33b, which are far from the outer circumferential surface of the flame F, is increased.
In this case, an instrument for measuring the carbon concentration from scattering of
laser light can be used to measure the amount of unbumed fuel, and a known measurement
26
> instrument can be used to measure the amount of NOx emission.
When this feedback control is performed, the tangential firing boiler 10 can
automatically optimize the distribution of secondary air according to the combustion state.
Further, in the above-described tangential firing boiler 10, the amounts of secondary
air to be injected from the secondary-air injection ports 30A are preferably distributed among
multi-stage air injections, which make a region from the burner section 12 to the AA section
14 the reducing atmosphere.
Specifically, the amount of secondary air to be injected from the secondary-air
injection ports 30A, which are each divided into a plurality of ports, can be decreased by
using two-stage combustion in which air is also injected from the AA section 14 in a multistage
fashion. Therefore, the amoimt of NOx produced can be fiirther decreased due to the
synergy between a decrease in NOx through suppression of the high-temperature oxygen
remaining region H formed at the outer circumference of the flame F and a decrease in NOx
in combustion exhaust gas, caused by providing the reducing atmosphere.
In this way, according to the above-described tangential firing boiler 10 of the present
invention, since the amount of secondary air to be injected from the secondary-air injection
ports 30A that are each divided into a plurality of ports is adjusted for each of the ports, it is
possible to prevent or suppress concentration of secondary air at the outer circumference of
the flame F, and thus, to suppress the high-temperature oxygen remaining region H formed at
the outer circumference of the flame F, thus decreasing the amount of NOx produced.
In the above-described embodiments, although a description has been given of the
tangential firing boiler 10, in which air is injected in a multi-stage fashion to make the region
from the bimier section 12 to the AA section 14 the reducing atmosphere, the present
invention is not limited thereto.
Further, as shown in FIG. 14, for example, in the above-described solid-fuel-fired
burner 20A, it is preferable to separate a system for supplying air to the coal secondary port
23 of the pulverized-coal burner 21 from a system for supplying air to the secondary-air
injection ports 30A. In a configuration example shown in the figure, the air supply line 50
is divided into a coal secondary port supply line 51 and a secondary-air injection port supply
27
^line 52, and the supply lines 51 and 52 are provided with dampers 41.
With such air supply systems, it is possible to distribute the amount of air by adjusting
the degree of openings of the respective dampers 41 for the coal secondary port supply line
51 and the secondary-air injection port supply line 52 and to further adjust the amount of air
for each port by adjusting the degree of opening of each of the dampers 40. As a result, the
amount of air for each port can be reliably adjusted even when the secondary-air injection
ports 30A are each divided into a plurality of ports to provide muhiple stages.
The above-described first and second embodiments are not limited to separate use but
may also be used in combination.
In a solid-fuel-fired burner 20B shown in FIG. 15, both of the secondary-air injection
ports 30A disposed above and below the pulverized-coal burner 21 shown in FIG. 9 are each
divided into three ports in the vertical direction. Specifically, the solid-fuel-fired burner
20B shown in the figure has an example configuration in which internal flame stabilization
realized by the splitting members 24 and the flow adjustment mechanism 25 is combined
with the multi-stage secondary-air injection ports 30A.
Since the thus-configured solid-fuel-fired burner 20B can decrease the amount of
NOx through the internal flame stabilization and also can adjust the diffusion speed of
secondary air to optimize air diffusion in the flame, the required amount of air for
combustion of volatile components and char can be supplied at an appropriate timing. In
other words, by performing the internal flame stabilization and the secondary-air diffusion
speed adjustment, a further decrease in the amoimt of NOx can be achieved due to the
synergy of the two.
Note that the cross-sectional shape and the arrangement of the splitting members 24,
the presence or absence of the flow adjustment mechanism 25, the division count of the
secondary-air injection port 30A, and the presence or absence of the lateral secondary-air
ports 34L and 34R are not limited to those in the configurations shown in the figures, and a
configuration in which the above-described items are appropriately selected and combined
can be used.
Further, in the embodiment and the modifications in which the multi-stage secondary-
28
k air injection ports 30A are used, some of the secondary-air injection ports 30A can be used as
oil ports.
Specifically, in a solid-fiiel-fired boiler such as the tangential firing boiler 10, an
operation performed using gas or oil as fuel is necessary to start up the boiler, thus requiring
an oil burner for injecting oil to the furnace 11. Then, in a start-up period requiring the oil
burner, the outer secondary-air ports 33a and 33b of the multi-stage secondary-air injection
ports 30A are temporarily used as oil ports, for example, and thus, it is possible to decrease
the number of ports used in the solid-fiiel-fired burner, reducing the height of the boiler.
Next, a solid-fiiel-fired burner suitable for use in a wall firing boiler will be described
with reference to FIG. 16.
In a solid-fiiel-fired burner 20C shown in the figure, a secondary-air injection port
3 OB that includes a plurality of concentric ports is provided at the outer circumference of a
coal primary port 22A having a circular shape in cross section. The secondary-air injection
port 30B shown in the figure is constituted of two stages, i.e., an inner secondary-air injection
port 31 and an outer secondary-air injection port 33, but the configuration of the secondaryair
injection port 303 is not limited thereto.
Further, a total of four splitting members 24 in two different (vertical and horizontal)
' directions are arranged in a grid-like pattern at the center of the outlet of the coal primary
port 22A. Note that the number of the splitting members 24, the arrangement thereof, and
the cross-sectional shape thereof described in the first embodiment can be applied to the
splitting members 24 used in this case.
Since the thus-configured solid-fiiel-fired burner 20C gradually supplies secondary
air, it does not provide excessive reducing atmosphere but generally provides a short flame
and a strong reducing atmosphere, thereby decreasing sulfide corrosion etc. caused by
produced hydrogen sulfide.
In this way, in the solid-fiiel-fired burners of the above-described embodiments and
modifications, since the splitting members arranged in a plurality of directions that fimction
as the internal flame stabilizing mechanism are provided at the outlet opening of the
pulverized-coal burner, the flow path of powdered fiiel and air is divided to disturb the flow
thereof, in the vicinity of the center of the outlet opening of the fuel bumer where the
29
t^ splitting members cross. Since this disturbance facilitates mixing and diffusion of air even
in the flame, and further, the splitting members divide the ignition surface to make it easy for
oxygen to come into the center portion of the flame, the ignition position comes close to the
center of the flame, decreasing the amount of unbumed fuel. Specifically, since internal
ignition is effectively performed by using oxygen in the flame center portion, reduction
rapidly proceeds in the flame, and, as a result, the amount of NOx produced eventually
emitted from the solid-fuel-fired boiler having the solid-fuel-fired burner is decreased.
Further, when the secondary-air injection ports are made to provide multiple stages to
adjust the injection of secondary air, concentration of the secondary air at the outer
circumference of the flame can be prevented or suppressed, thereby suppressing the hightemperature
oxygen remaining region formed at the outer circvmiference of the flame,
decreasing the amount of nitrogen oxide (NOx) produced.
Further, since the solid-fuel-fired burner and the solid-fiiel-fired boiler having the
solid-fuel-fired burner according to the present invention can perform powerful ignition in
the flame and can increase the air ratio in the burner section, it is possible to decrease the
excess air rate in the entire boiler to approximately 1.0 to 1.1, thus leading to a boilerefficiency
improving effect. Note that a conventional solid-fiiel-fired burner and a
conventional solid-fiiel-fired boiler are usually operated at an excess air rate of approximately
1.15, and thus, the air ratio can be decreased by approximately 0.05 to 0.15.
FIGS. 17 to 22 are graphs of experimental results showing advantages of the present
invention.
FIG. 17 is a graph of an experimental resuh showing the relationship between a flame
stabilizer position in internal flame stabilization and the amount of NOx produced (relative
value). In this case, the width (height) of the splitting members 24A functioning as a flame
stabilizer is indicated by flame stabilizer position a, and the width of a flow path in which
pulverized coal actually flows is indicated by actual pulverized-coal flow width b, in
comparative examples shown in FIG. 18. In the graph, "a/b" is indicated on the horizontal
axis, and the relative value of the amount of NOx produced is indicated on the vertical axis.
Note that, although the splitting member 24A shown in FIG. 6B is employed in FIG. 18, the
type of a splitting member is not limited thereto.
In this experiment, the amounts of NOx produced in Comparative Example 1 (a/b =
30
y 0.77) and Comparative Example 2 (a/b = 0.4) were measured with the same flow velocity of
primary air and pulverized coal, the same flow velocity of secondary air, and the same air
distribution between primary air and secondary air.
Here, in the coal primary port 22 used in Comparative Example 1, an inverted core 26
serving as an obstacle is disposed in the flow path, and therefore, pulverized coal flows out
with a width b that approximately matches the width of the inner wall of the inverted core 26.
On the other hand, in the coal primary port 22 used in Comparative Example 2, pulverized
coal flows along the iimer wall of a flow path having no obstacle and flows out with a width
b that approximately matches the width of the flow path. Therefore, even with the same
flame stabilizer position a and the same inner diameter of the coal primary ports 22, the
presence or absence of an obstacle causes a difference in the actual pulverized-coal flow
width b, which is the denominator, and, as a result, the amount of NOx produced is different.
In other words, the experimental result shown in FIG. 17 indicates that, when the ratio
(a/b) of the width a of the splitting members to the actual pulverized-coal flow width b is set
to approximately 75% or less, the amount of NOx produced is decreased.
Specifically, according to this experimental result, it is understood that, when the ratio
(a^) of the width a of the splitting members to the actual pulverized-coal flow width b is
decreased fi-om 0.77 to 0.4, the relative value of the amount of NOx produced is decreased to
0.75, leading to an approximately 25% decrease. In other words, it is understood that,
optimizing the width a of the splitting members functioning as the internal flame stabilizing
mechanism is effective to decrease NOx in the solid-fuel-fired burner and the solid-fuel-fired
boiler.
At this time, if drifts occur when the flow adjustment mechanism 25 is not provided,
the positions of the splitting members may be at an outer side with respect to a flow of
pulverized coal, resulting in an increase in NOx. Thus, the flow adjustment mechanism is
important.
FIG. 19 is a graph of an experimental result showing the relationship between the
split occupancy and the amount of NOx produced (relative value). Specifically, it is an
experimental graph showing how the amount of NOx produced changes according to the
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V ratio of the above-described width a of the splitting members to the height (width) of the coal
primary port 22.
According to this experimental result, the larger the split occupancy is, the smaller the
amount of NOx produced is; and therefore, it is understood that installation of splitting
members is effective to decrease NOx.
On the other hand, according to the above-described experimental result shown in
FIG. 17, when the ratio (a^) of the width a of the splitting members to the actual pulverizedcoal
flow width b is decreased, the relative value of the amount of NOx produced is also
decreased, and thus, installation of splitting members having an appropriate width a is
necessary to decrease the amount of NOx produced. In other words, in internal flame
stabilization, to decrease the amount of NOx produced, h is important to provide splitting
members having an appropriate width a to enhance ignition, thereby more quickly emitting
and reducing NOx.
FIG. 20 shows a comparison of the amount of imbumed fuel produced for the case of
a one-direction split in which splitting members are disposed in one direction and the case of
a crossed split in which splitting members are arranged in a plurality of directions. In this
experiment, the same conditions as those in the experiment shown in FIG. 17 are specified,
and the amount of imbumed fuel produced is compared between the one-direction split and
the crossed split.
According to the experimental result, the relative value of the amount of unbumed
fuel produced when the crossed split is used is 0.75 relative to the amount of unbumed fuel
produced when the one-direction split is used, and it is imderstood that the amount of
unbumed fuel produced is decreased by approximately 25%. Specifically, the crossed split,
in which the splitting members are arranged in a plurality of directions, is effective to
decrease the amount of unbumed fuel in the solid-fuel-fired bumer and the solid-fuel-fired
boiler.
From the experimental result shown in FIG. 20, it is conceivable that, by disposing
the splitting members in different directions, ignition in the flame is further enhanced, and
diffusion of air into the inside of the flame is improved, thereby decreasing the amoxmt of
unbumed fuel.
32
On the other hand, it is conceivable that the amount of unbumed fuel is higher when
tlie one-direction split is used because air is supplied to the outer side of the flame, thus
delaying air diffusion into the flame formed at the inner side.
An experimental result shown in FIG. 21 is obtained by comparing the amounts of
NOx produced in a burner section, in a region from the burner section to an AA section, and
in the AA section, for a conventional solid-fuel-fired burner and the solid-fuel-fired burner of
the present invention; and values relative to the amount of NOx produced in the AA section
of the conventional solid-fuel-fired burner, which is set to a reference value of 1, are shown.
Note that splitting members arranged in a plurality of directions, as shown in FIG. lA, for
example, are employed to obtain this experimental result.
Further, this experimental result is obtained through comparison at the same amount
of unbumed fuel, and the air ratio (the ratio of the amount of injected air that is obtained by
subtracting the amoimt of injected additional air from the total amount of injected air, relative
to the total amount of injected air) in the region from the burner section to the AA section is
set to 0.8 in the conventional technology and is set to 0.9 in the present invention. The total
amoimt of injected air used herein is an actual amount of injected air determined in
consideration of the excess air rate. Note that when the additional-air injection rate is set to
30%, and the excess air rate is set to 1.15, the air ratio in the region from the burner section to
the AA section is approximately 0.8 (the air ratio in the region from the burner section to the
AA section = 1.15 x (1 - 0.3) = 0.8).
According to this experimental result, the amount of NOx eventually produced from
the AA section is decreased to 0.6, a 40% decrease compared with the conventional
technology. It is conceivable that this is because the present invention employs internal
flame stabilization by arranging splitting members in a plurality of directions to further
enhance ignition by the splitting members, thereby producing NOx in the flame and
effectively reducing the NOx.
Furthermore, in the present invention, since mixing in the flame is excellent, the
combustion approaches premix combustion, providing more uniform combustion, and thus, it
is confirmed that a sufficient reducing capability is afforded even at an air ratio of 0.9.
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I Specifically, in the conventional technology, since a high-temperature high-oxygen
region is formed at the outer circumference of the flame, and thus, approximately 30% of
additional air injection (AA) is required to sufficiently reduce NOx, it is necessary to
decrease the air ratio in the region from the burner section to the AA section to approximately
0.8. Therefore, since approximately 30% of the total amount of injected air, determined in
consideration of the excess air rate, is injected into the AA section, NOx is produced also in
the AA section.
However, in the present invention, since combustion can be performed even at the air
ratio of approximately 0.9 in the region from the burner section to the AA section, the
amount of injected additional air can be decreased to approximately 0 to 20% of the total
amount of injected air, determined in consideration of the excess air rate. Therefore, the
amount of NOx produced in the AA section can also be suppressed, thereby eventually
allowing an approximately 40% decrease in the amount of NOx produced.
In FIG. 22, the horizontal axis indicates the air ratio in the region from the burner
section to the AA section, and the vertical axis indicates the relative value of the amount of
NOx produced. According to this experimental resuh, in the present invention, an air ratio
of 0.9 is the optimal value in the vicinity of the burner, at which an approximately 40%
decrease in NOx has been confirmed. Therefore, from FIG. 22, the air ratio in the region
from the burner section to the AA section, which is the ratio of the amount of injected air
obtained by subtracting the amount of injected additional air from the total amount of
injected air to the total amount of injected air determined in consideration of the excess air
rate, is preferably set to 0.85 or more, at which the amount of NOx can be decreased by
approximately 30%, and is more preferably set to the optimal value of 0.9 or more.
In the experimental result of the present invention, the amoimt of NOx produced is
increased to 1 or more around the air ratio of 0.8 because NOx is produced due to the
injection of additional air.
Further, the upper limit of the air ratio differs depending on the fiiel ratio: it is 0.95
when the fiiel ratio is 1.5 or more, and it is 1.0 when the ftiel ratio is less than 1.5. The fiiel
ratio in this case is the ratio of fixed carbon to volatile components (fixed carbon/volatile
components) in fiiel.
34
In this way, according to this embodiment, described above, the pulverized-coal
burner 21, which has internal flame stabilization, and the secondary-air injection ports 30,
which do not perform flame stabilization, are provided, and the air ratio in the pulverizedcoal
burner 21 is set to 0.85 or more, preferably, to 0.9 or more, thereby decreasing the
amount of injected additional air in the AA section 14 and also decreasing the amount of
NOx produced in the AA section 14. Further, since the high-temperature oxygen remaining
region H formed at the outer circumference of the flame is suppressed, and NOx produced in
the flame, in which combustion approaching premix combustion is achieved, is effectively
reduced, the amount of NOx eventually emitted from the AA section 14 is decreased by a
decrease in the amount of NOx reaching the AA section 14 and by a decrease in the amount
of NOx produced in the AA section 14 due to the injection of additional air.
As a result, in the solid-fuel-fired burner 20 and the tangential firing boiler 10, the
amount of eventually produced NOx to be emitted from the AA section 14 is decreased.
Further, by using a solid-fuel-fired burner operating method in which the operation is
performed with the air ratio in the pulverized-coal burner 21 set to 0.85 or more, the amount
of air (the amount of injected additional air) in the AA section 14 is decreased compared with
a case in which the air ratio is 0.8, for example, and thus, the amount of NOx eventually
produced is decreased in the AA section 14 where the amount of injected additional air is
decreased.
Note that the present invention is not limited to the above-described embodiments,
and appropriate modifications can be made without departing from the scope tliereof For
example, the powdered solid fuel is not limited to pulverized coal.
{Reference Signs List}
10 Tangential firing boiler
11 Furnace
12 Burner section
14 Additional-air injection section (AA section)
20,20A-20C Solid-fiiel-fired burner
21 Pulverized-coal burner (Fuel burner)
22 Coal primary port
23 Coal secondary port
35
24,24A, 24B Splitting member
25 Flow adjustment mechanism
30,30A Secondary-air injection port
31, 31 a, 31 b Inner secondary-air port
32a, 32b Middle secondary-air port
33, 33a, 33b Outer secondary-air port
34L, 34R Lateral secondary-air port
40,41 Damper
F Flame
H High-temperature oxygen remaining region
36

We Claim:
{Claim 1}
A solid-fliel-fired burner that is used in a burner section of a solid-fuel-fired boiler for
performing low-NOx combustion separately in the burner section and in an additional-air
injection section and that injects powdered solid-fuel and air into a furnace, comprising:
a fuel burner having internal flame stabilization; and
a secondary-air injection port that does not perform flame stabilization,
wherein an air ratio in the fuel burner is set to 0.85 or more.
{Claim 2}
A solid-fuel-fired burner according to claim 1, wherein the air ratio in the fuel burner
is set to 0.9 or more.
{Claims}
A solid-fuel-fired burner according to claim 1 or 2, wherein:
the fuel burner injects powdered fuel and air into the furnace;
the secondary-air injection port is disposed above and below and/or on tlie right and
left sides of the fuel bvimer and has an airflow adjustment means; and
one or more splitting members is arranged at a flow-path front part of the fuel burner.
{Claim 4}
A solid-fuel-fired burner according to claim 1 or 2, wherein:
the fuel burner injects powdered fuel and air into the furnace;
the secondary-air injection port is disposed above and below and/or on the right and
left sides of the fuel burner and has an airflow adjustment means; and
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.-• splitting members are arranged in a plurality of directions at a flow-path front part of the fuel
burner.
{Claim 5}
A solid-fuel-fired burner according to claim 4, wherein an ignition surface length (Lf)
constituted by the splitting members is set larger than an outlet-opening circumferential
length (L) of the fuel burner (Lf > L).
{Claim 6}
A solid-fuel-fired burner according to claim 4 or 5, wherein the splitting members are
disposed densely at the center of an outlet opening of the fuel burner.
{Claim 7}
A solid-fuel-fired burner according to one of claims 4 to 6, wherein the secondary-air
injection ports are each divided into a plurality of independent flow paths each having airflow
adjustment means.
{Claim 8}
A solid-fuel-fired burner according to claim 1 or 2, wherein:
the fuel burner injects powdered fuel and air into the furnace;
the secondary-air injection port is disposed above and below and/or on the right and
left sides of the fuel burner and divided into a plurality of independent flow paths each
having an airflow adjustment means; and
a splitting member is arranged at a flow-path front part of the fuel burner.
{Claim 9}
A solid-fuel-fired burner according to one of claims 4 to 8, further comprising a flow
adjustment mechanism that applies a pressure loss to a flow of the powdered fiiel and air
provided at an upper stream side of the splitting members.
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{Claim 10}
A solid-fliel-fired burner according to one of claims 4 to 9, wherein the secondary-air
injection ports are each provided with an angle adjustment mechanism.
{Claim 11}
A solid-fuel-fired burner according to one of claims 4 to 10, wherein distribution of
the amount of air to be injected from the secondary-air injection ports is feedback-controlled
based on the amount of unbumed fuel and the amount of nitrogen oxide (NOx) emission.
{Claim 12}
A solid-fiiel-fired burner according to one of claims 4 to 11, wherein the amount of
air to be injected from the secondary-air injection ports is distributed among multi-stage air
injections that make a region from the burner section to the additional-air injection section a
reducing atmosphere.
{Claim 13}
A solid-fuel-fired burner according to one of claims 4 to 12, wherein a system for
supplying air to a coal secondary port of the fuel burner is separated from a system for
supplying air to the secondary-air injection ports.
{Claim 14}
A solid-fuel-fired burner according to claim 7, wherein the plurality of independent
flow paths of the secondary-air injection ports are concentrically provided around the fuel
burner, which has a circular shape, in an outer circumferential direction in a multi-stage
fashion.
{Claim 15}
A solid-fuel-fired boiler comprising a solid-fuel-fired burner according to one of
claims 1 to 14, the solid-fuel-fired burner being disposed at a comer or on a wall of the
furnace,
39
{Claim 16}
An operation method of a solid-fiiel-fired burner that is used in a burner section of a
solid-fuel-fired boiler for performing low-NOx combustion separately in the burner section
and in an additional-air injection section and that injects powdered solid-fuel and air into a
furnace, the solid-fuel-fired burner comprising:
a fuel burner having internal flame stabilization; and
a secondary-air injection port that does not perform flame stabilization,
wherein operation is performed with an air ratio in the fuel burner set to 0.85 or more.
Dated this 22"'' Day of December, 2011
Aparna Kareer
Of Obhan & Associates
Agent for the Applicant
Indian Patent Agent No: 1359
40