Note: Descriptions are shown in the official language in which they were submitted.
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A BURNER WITH TILTABLE NOZZLES
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to a low combustibility
fuel firing burner applicable to various types of combustion
apparatuses that burn a low combustibility fuel such as a
pulverized coal boiler.
This application is based on Japanese Patent Application
No. 2006-286692.
2. DESCRIPTION OF RELATED ART
Hitherto, a low combustibility fuel firing burner that
burns a pulverized low combustibility fuel (hereinafter
referred to as "burner") has been used in pulverized coal
boilers fired with a low combustibility fuel such as
anthracite or petroleum coke in a fine powder form.
For example, as shown in Figs. 4 and 5, a burner 10A of
the related art, which burns a fuel that is pulverized coal
obtained by pulverizing anthracite in a furnace 1 of a boiler
is composed of a pulverized coal-air mixture system provided
in the burner center and supplying a mixture of pulverized
coal and a primary air set to about 100 C, and a secondary air
system provided around the pulverized coal-air mixture system
and supplying a secondary air set to about 300 to 350 C.
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The primary air system includes a separator 20A provided
upstream of a burner portion for the purpose of improving an
ignition performance. The separator 20A is based on the
principle of a cyclone. Thus, a portion with many fuel
particles (rich portion) and a portion with few fuel particles
(lean portion) can be obtained.
On the downstream side of the separator, the primary air
system is branched to a rich portion nozzle 24 for introducing
and burning a high-particle-concentration gas containing fuel
particles in a high concentration and a lean portion nozzle 26
for introducing and burning a low-particle-concentration gas
containing fuel particles in a low concentration. In general,
in the case of using a low combustibility fuel, the whole
burner 10A is inclined downwardly to improve the ignition
performance.
Further, the lean portion nozzle 26 is provided on the
side of a furnace wall 2 that forms a furnace 1 and is thus
put under an oxygen atmosphere to prevent slagging.
In Figs. 4 and 5, reference numeral 23 denotes a high-
particle-concentration gas pipe for introducing a high-
particle-concentration gas to the rich portion nozzle 24; and
from the separator 20A, a low-particle-concentration gas
pipe for introducing a low-particle-concentration gas to the
lean portion nozzle 26 from the separator 20A (see Japanese
25 Unexamined Patent Application, Publication No. Hei 8-178210
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(Fig. 5), for instance).
However, according to the above related art, when a gas
flow rate is changed along with change in boiler load or the
like, an ignition performance or combustion stability might be
affected thereby. In particular, in the case of using a low
combustibility fuel, an ignition performance or combustion
stability is affected also by interference of flames of
adjacent nozzles.
To be specific, a distribution rate of fuel particles is
determined in accordance with a separation efficiency of the
separator 20A. Thus, during partial load operations that
cause reduction in gas supply, the separation efficiency of
the separator 20A is accordingly lowered due to a decrease in
centrifugal force. Therefore, it is difficult to attain a
desired distribution rate for the rich portion nozzle 24 and
the lean portion nozzle 26.
Further, if a burner is not used during partial load
operations or a spare burner is used, there is a fear of
backflow of a gas from the lean nozzle pipe 25 to a direction
of the separator 20A due to a negative pressure.
The above change in distribution rate and gas backflow,
or the interference of flames of adjacent nozzles affects the
ignition performance or combustion stability of the low
combustibility fuel firing burner 10A designed to distribute
particles of a low combustibility fuel with the separator 20A,
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so there is an increasing demand to develop a low
combustibility fuel firing burner that overcomes the above
problems.
BRIEF SUMMARY OF THE INVENTION
The present invention has been accomplished in view of
the above circumstances, and it is an object of the present
invention to provide a low combustibility fuel firing burner
that can ensure high ignition performance and combustion
stability even if a gas flow rate is changed along with
changes in boiler load or the like.
The present invention adopts the following solutions with
a view to attaining the above object.
A low combustibility fuel firing burner according to an
aspect of the present invention separates a pulverized low
combustibility fuel supplied together with an air with a
separator, distributes the separated fuel to a rich portion
nozzle and a lean portion nozzle provided in a furnace, and
burns the fuel, wherein a variable control part for changing a
flow path sectional area is provided in at least one of a gas
flow path extending from a downstream side of the separator
and communicating with the rich portion nozzle and a gas flow
path extending from the downstream side of the separator and
communicating with the lean portion nozzle.
According to the low combustibility fuel firing burner of
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the present invention, the variable control part for changing
a flow path sectional area is provided in at least one of the
gas flow path communicating with the rich portion nozzle and
the gas flow path communicating with the lean portion nozzle.
5 Hence, a sectional area of a gas flow path is appropriately
changed and adjusted to the optimum value in accordance with
operation conditions such as partial load operations.
In the low combustibility fuel firing burner, it is
preferred that the variable control part be a movable resistor
provided in a gas flow path for supplying a high-particle-
concentration gas from the separator to the rich portion
nozzle. Thus, a sectional area of a gas flow path for
supplying a high-particle-concentration gas to the rich
portion nozzle can be changed as appropriate. Hence, a gas
flow rate in the gas flow path for supplying a high-particle-
concentration gas is adjusted in accordance with operation
conditions, and a separation efficiency of the separator can
be optimized in accordance with operation conditions such as
partial load operations.
In the low combustibility fuel firing burner, it is
preferred that the variable control part be a flow
adjusting/blocking valve provided in a gas flow path for
supplying a low-particle-concentration gas from the separator
to the lean portion nozzle. Thus, a sectional area of a gas
flow path for supplying a low-particle-concentration gas to
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the lean portion nozzle can be changed from a full-open
position to a totally-closed position as appropriate. Hence,
a gas flow rate in the gas flow path for supplying a low-
particle-concentration gas can be adjusted in accordance with
operation conditions, or the gas flow path can be closed when
the burner is not used.
In the low combustibility fuel firing burner, it is
preferred that a wall against which a low combustibility fuel
supplied into the separator collides be given a hardwearing
finish. Thus, a wear resistance of the wall against which
slag, melted ash, and unburnt carbon collide is improved.
A low combustibility fuel firing burner according to
another aspect of the present invention separates a pulverized
low combustibility fuel supplied together with an air with a
separator, distributes the separated fuel to a rich portion
nozzle and a lean portion nozzle provided in a furnace, and
burns the fuel, wherein a blowoff angle of the rich portion
nozzle and a blowoff angle of the lean portion nozzle are
offset in a vertical direction.
According to the low combustibility fuel firing burner, a
blowoff angle of the rich portion nozzle and a blowoff angle
of the lean portion nozzle are offset in a vertical direction,
so interference of flames of nozzles can be prevented.
A low combustibility fuel firing burner according to
another aspect of the present invention separates a pulverized
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low combustibility fuel supplied together with an air with a
separator, distributes the separated fuel to a rich portion
nozzle and a lean portion nozzle provided in a furnace, and
burns the fuel, wherein a blowoff angle of the lean portion
nozzle is offset to a furnace wall side in a horizontal
direction.
According to the low combustibility fuel firing burner, a
blowoff angle of the lean portion nozzle is offset to a
furnace wall side in a horizontal direction, so it is possible
to prevent slagging on a furnace wall as well as interference
of flames of nozzles.
According to the present invention, in the low
combustibility fuel firing burner structured to distribute
fuel particles of a low combustibility fuel with a separator,
it is possible to prevent changes in distribution rate in
accordance with operation conditions or gas backflow, so high
ignition performance and combustion stability can be ensured.
Further, high ignition performance and combustion
stability can be ensured by preventing interference of flames
of adjacent nozzles as well.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Fig. 1 is a cross-sectional view of a low combustibility
fuel firing burner according to an embodiment of the present
invention;
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Fig. 2 is a longitudinal sectional view of a structural
example of a separator and a primary air pipe of Fig. 1;
Fig. 3 is a longitudinal sectional view showing an
example of a blowoff angle of a rich portion nozzle and a lean
portion nozzle;
Fig. 4 is a cross-sectional view of a low combustibility
fuel firing burner of the related art; and
Fig. 5 is a longitudinal sectional view showing a blowoff
angle of a rich portion nozzle and a lean portion nozzle of
Fig. 4.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a low combustibility fuel
firing burner according to the present invention will be
described with reference to the accompanying drawings.
A low combustibility fuel firing burner (hereinafter
simply referred to as "burner") 10 of Figs. 1 to 3 is provided
in, for example, a furnace 1 of a pulverized coal boiler or
the like. The burner 10 burns a powder (fine powder) of a low
combustibility fuel supplied together with an air in the
furnace 1. Specific examples of the low combustibility fuel
include anthracite and petroleum coke.
The following description is directed to the burner 10
supplied with a fuel that is pulverized coal obtained by
pulverizing anthracite as a low combustibility fuel.
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The burner 10 is composed of a pulverized coal supply
system supplied with pulverized coal together with a primary
air at a relatively low temperature, about 100 C, and a
secondary air system supplied with a secondary air at a
relatively high temperature, about 300 to 350 C.
The pulverized coal supply system is positioned at almost
the center of the burner 10 and provided with a separator 20
for distributing a mixture of a primary air and pulverized
coal to a rich portion and a lean portion as described later
for the purpose of improving an ignition performance. The
separator 20 has a cyclone structure that is based on
centrifugal separation. A primary air pipe 22 for supplying a
mixed gas from a tangent line direction is connected to a side
wall of an external cylinder 21. A high-particle-
concentration gas pipe 23 is connected to a small diameter
portion 21a obtained by tapering the external cylinder 21 into
a cone shape, and a rich portion nozzle 24 that is open to the
furnace 1 is provided at its tip end.
Further, a low-particle-concentration gas pipe 25 is
concentrically inserted into the external cylinder 21. The
low-particle-concentration gas pipe 25 extends from the
external cylinder 21 to the opposite side to the high-
particle-concentration gas pipe 23 and makes a U-turn. A lean
nozzle 26 is provided adjacent to the rich portion nozzle 24
at substantially the same level, at a tip end of the low-
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particle-concentration gas pipe 25. Incidentally, an opening
25a of the low-particle-concentration gas pipe 25 is
positioned on the downstream side (rich portion nozzle 24
side) of a joint of the primary air pipe 22 in a flow
5 direction of the mixed gas.
As for a positional relationship between the rich portion
nozzle 24 and the lean portion nozzle 26, the lean portion
nozzle 26 for burning a low-particle-concentration gas is
provided on the side of a furnace wall 2 that forms the
10 furnace 1.
A variable control part for changing a flow path
sectional area is provided in at least one of a gas flow path
communicating with the rich portion nozzle 24 and a gas flow
path communication with the lean portion nozzle 26 on the
downstream side of the separator 20.
In the illustrated structure, a core 27 that is, for
example, triangular in section is provided as a movable
resistor that can reciprocate in a gas flow direction, in the
small diameter portion 21a connected to the high-particle-
concentration gas pipe 23 for supplying a high-particle-
concentration gas from the separator 20 to the rich portion
nozzle 24. Along with movement of the core 27 in the small
diameter portion 21a in an axial direction as indicated by an
arrow 28, a sectional area of a flow path extending from the
separator 20 to the high-particle-concentration gas pipe 23 is
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changed. In other words, a sectional area of a flow path of
the high-particle-concentration gas pipe 23 is substantially
changed.
Incidentally, the movable resistor is not limited to the
illustrated core 27. For example, a butterfly valve or other
such members capable of changing a sectional area of a flow
path of the high-particle-concentration gas pipe 23 can be
used.
In a gas flow path for supplying a low-particle-
concentration gas from the separator 20 to the lean portion
nozzle 26, that is, in an appropriate position in the low-
particle-concentration gas pipe 25, a flow adjusting/blocking
valve 29 such as a butterfly valve is provided as the variable
control part. The flow adjusting/blocking valve 29 changes a
valve member position from a totally-closed position to a
full-open position to thereby adjust a sectional area of a
flow path extending from the separator 20 to the low-particle-
concentration gas pipe 25. Further, the flow
adjusting/blocking valve 29 can totally close the low-
particle-concentration gas pipe 25 (flow path sectional
area=0) if necessary.
A secondary air supply path (secondary air pipe) 30 that
communicates with the furnace 1 is provided around the rich
portion nozzle 24 and the lean portion nozzle 26 so as to
0
surround the two nozzles. Here, the secondary air supply path
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30 serves as a secondary air system provided for supplying an
air at relatively high temperatures to the both of the nozzles
24 and 26.
In the above separator 20, a mixed gas supplied from the
primary air pipe 22 flows while whirling around the low-
particle-concentration gas pipe 25 in the external cylinder 21
to thereby centrifuge the mixture to a peripheral rich portion
and a central lean portion. As a result, a high-particle-
concentration gas containing pulverized coal in a high
particle concentration flows in a gas flow direction while
whirling around the low-particle-concentration gas pipe 25,
and is guided to the rich portion nozzle 24 through the small
diameter portion 21a and the high-particle-concentration gas
pipe 23. On the other hand, a low-particle-concentration gas
containing pulverized coal in a low particle concentration
flows in a gas flow direction while whirling around the low-
particle-concentration gas pipe 25 and then makes a U-turn to
the opening 25a of the low-particle-concentration gas pipe 25,
and is guided to the lean portion nozzle 26 through the low-
particle-concentration gas pipe 25.
With regard to a distribution rate of fuel particles
suitable in the case of using pulverized coal obtained by
pulverizing anthracite as a fuel, that is, a distribution rate
of fuel particles suitable to keep high ignition performance
and combustion stability, about 93% of pulverized coal and
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about 50% of air in the total amount of mixed gas are
distributed to the rich portion nozzle 24, and about 7% of
pulverized coal and 50% of air in the total amount of mixed
gas are distributed to the lean portion nozzle 26.
In the thus-structured nozzle 10, if a mixed gas supply
is changed along with changes in boiler load or the like, the
distribution rate of fuel particles is changed, so a
predetermined distribution rate of fuel particles is kept by
adjusting the core 27 position.
To be specific, the opening 25a of the low-particle-
concentration gas pipe 25 is designed to obtain a desired
distribution rate of fuel particles with an amount of mixed
gas supplied under predetermined operation conditions such as
rated operations. Thus, if a supply of the mixed gas is
decreased, an amount of pulverized coal distributed to the
high-particle-concentration gas side tends to decrease due to
reduction in centrifugal force. To that end, the core 27 is
moved in the arrow 28 direction in accordance with the
decrease in mixed gas supply to thereby increase a sectional
area of a flow path communicating with the high-particle-
concentration gas pipe 23 from the separator 20. As a result,
a resistance of the flow path extending to the rich portion
nozzle 24 is lowered, and an amount of pulverized coal
distributed to the rich portion nozzle 24 side is increased.
Hence, a distribution rate of pulverized coal is adjusted to a
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predetermined value.
On the other hand, if a supply of mixed gas is increased,
an amount of pulverized coal distributed to the high-particle-
concentration gas side tends to increase due to an increase in
centrifugal force. To that end, the core 27 is moved in the
arrow 28 direction in accordance with an increase in mixed gas
supply to thereby decrease a sectional area of a flow path
communicating with the high-particle-concentration gas pipe 23
from the separator 20. As a result, a resistance of a flow
path extending to the rich portion nozzle 24 is increased and
an amount of pulverized coal distributed to the rich portion
nozzle 24 side is decreased. In this case as well, a
distribution rate of pulverized coal is adjusted to a
predetermined value.
Further, the distribution rate can be adjusted by
controlling the flow adjusting/blocking valve 29 provided in
the low-particle-concentration gas pipe 25.
To be specific, if the mixed gas supply is decreased, the
flow adjusting/blocking valve 29 is closed in accordance with
the decrease in mixed gas supply to thereby reduce a sectional
area of a flow path of the low-particle-concentration gas pipe
25. As a result, a resistance of a flow path extending to the
lean portion nozzle 26 is increased, while a resistance of a
flow path extending to the rich portion nozzle 24 is
relatively decreased, so an amount of pulverized coal
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distributed to the rich portion nozzle 24 side is increased,
and a distribution rate of pulverized coal is adjusted to a
predetermined value.
On the other hand, if the mixed gas supply is increased,
5 the flow adjusting/blocking valve 29 is opened in accordance
with the increase in mixed gas supply to thereby increase a
sectional area of a flow path of the low-particle-
concentration gas pipe 25. As a result, a resistance of a
flow path extending to the lean portion nozzle 26 is
10 decreased, while a resistance of a flow path extending to the
rich portion nozzle 24 is relatively increased, so an amount
of pulverized coal distributed to the rich portion nozzle 24
side is decreased, and a distribution rate of pulverized coal
is adjusted to a predetermined value.
15 In this way, the distribution rate of pulverized coal can
be adjusted by moving the core 27 or opening/closing the flow
adjusting/blocking valve 29, so at least one of the core 27
and the flow adjusting/blocking valve 29 has only to be
provided. However, both of the core 27 and the flow
adjusting/blocking valve 29 may be moved at the same time to
adjust the rate.
Further, if the flow adjusting/blocking valve 29 is
totally closed, the low-particle-concentration gas pipe 25 can
be blocked. Hence, it is possible to prevent backflow from
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the lean portion nozzle 26 to the separator 20 side, for
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example, if the burner 10 is not used.
Incidentally, the external cylinder 21 of the separator
20 has an area against which pulverized particles flowing
therein from the primary air pipe 22 at high speeds collide.
To that end, on an inner wall of the area, a wear-resistant
wall 21b that is optionally given a hardwearing finish is
formed as shown in Fig. 2.
To elaborate, conceivable examples of the hardwearing
finish include bonding with a ceramic material or wear-
resistant hardfacing (25Cr cast iron, CHR-3, etc.). A wear
resistance is improved by forming the wear-resistant wall 21b,
so even if pulverized coal particles collide against the
cylinder, the cylinder does not thin out at an early stage,
and a durability of the separator 20 can be improved.
Further, as for the positional relationship between the
rich portion nozzle 24 and the lean portion nozzle 26, the
lean portion nozzle 26 is provided close to the furnace wall 2
side. In addition, the lean portion nozzle 26 is preferably
attached with an offset relative to the furnace wall 2 side in
a horizontal direction. That is, as shown in the plane view
of Fig. 1, a blowoff angle of the lean portion nozzle 26 is
offset from that of the rich portion nozzle 24 that ejects a
gas in a direction parallel to the furnace wall 2 as viewed in
the horizontal direction of Fig. 1, and an ejection direction
of the lean portion nozzle 26 is directed toward the furnace
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wall 2 side. In this case, a preferred blowoff angle Oh is
about 10 degrees; the blowoff angle 9h is an angle offset from
the rich portion nozzle 24 toward the furnace wall 2 side with
respect to the horizontal direction.
As described above, if the blowoff angle of the lean
portion nozzle 26 is offset to the furnace wall 2 side in the
horizontal direction, it is possible to prevent interference
of flames of the adjacent rich portion nozzle 24 and lean
portion nozzle 26, and a fuel can be continuously burned under
satisfactory conditions with a small loss. In addition, an
ignition performance can be improved. Moreover, the ejection
direction of the lean portion nozzle 26 is directed to the
furnace wall 2 side due to the offset, so slagging as
adherence of foreign materials such as coal ash to the furnace
1 wall can be suppressed.
Further, as for the positional relationship between the
rich portion nozzle 24 and the lean portion nozzle 26, the
lean portion nozzle 26 is provided close to the furnace wall 2
side. In addition, as shown in Fig. 3, the lean portion
nozzle 26 is preferably attached with an offset between the
blowoff angle of the rich portion nozzle 24 and the blowoff
angle of the lean portion nozzle 26 in the vertical direction.
More specifically, it is preferred to set the ejection
direction of the lean portion nozzle 26 to a horizontal
O
direction, and to tilt the rich portion nozzle 24 downwardly
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by a predetermined blowoff angle Av. In this case, a
preferred inclination angle 9v of the rich portion nozzle 24
is approximately -10 degrees to 30 degrees, most preferably,
30 degrees on the provision that an angle increases (+) as a
distance from the horizontal position as a reference position
increases. This is because if the inclination angle Av is
larger than 30 degrees, interference of flames of adjacent
upper and lower nozzles 24 occurs this time.
An offset is set between the blowoff angles of the rich
portion nozzle 24 and the lean portion nozzle 26 in the
vertical direction as described above, making it possible to
prevent interference of flames of the adjacent rich portion
nozzle 24 and lean portion nozzle 26. Hence, a fuel can be
continuously burned under satisfactory conditions with a small
loss, and an ignition performance can be improved.
Incidentally, if the blowoff angles of the rich portion
nozzle 24 and the lean portion nozzle 26 have offsets in
vertical and horizontal directions, interference of flames can
be prevented more easily.
According to the present invention, in the burner 10
structured to distribute fuel particles of a low
combustibility fuel with the separator 20, the core 27 or the
flow adjusting/blocking valve 29 is moved to prevent changes
in distribution rate in accordance with operation conditions
and gas backflow, so high ignition performance and combustion
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stability can be ensured. Further, an offset is set between
ejection directions of the rich portion nozzle 24 and the lean
portion nozzle 26 to prevent interference of flames of
adjacent nozzles to thereby ensure high ignition performance
and combustion stability.
The present invention is not limited to the above-
described embodiment and might be modified as appropriate
without departing from the scope of the present invention.
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