Note: Descriptions are shown in the official language in which they were submitted.
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BURNER, FUEL COMBUSTION METHOD AND
BOILER RETROFIT METHOD
BACKGROUND OF THE INVENTION
TECHNICAL FIELD
The present invention relates to a burner, a fuel combustion method by the
burner,
and a method of retrofitting a boiler provided with an existing burner.
DESCRIPTION OF PRIOR ART
For burners used for boilers or the like, it is required. that they cope with
load
change, various coals, and reduce the concentration of nitrogen oxides (NOx),
and
unburned fuel, etc. In order to satisfy those requirements, various methods of
controlling
combustion conditions have been developed. For example, methods of
apportioning a
flow quantity of air between secondary air and tertiary air by air resistors,
or changing
swirl number, etc.
One method of controlling combustion conditions is by adjusting a secondary
air
flow rate and adjusting an air jetting direction by making a partition wall
between
secondary air and tertiary air movable as proposed in for example, Japanese
Patent
Document JP 60-26922 B published June 26, 1988.
JP 60-26922 B discloses that since it is possible to control the flow of
secondary
air by moving the partition wall in the burner axial direction, the secondary
flame can
burn under the best condition from a viewpoint of low NOx emission and
combustion
efficiency.
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SUMMARY OF THE INVENTION
Certain exemplary embodiments may provide a fuel combustion burner comprising
a
primary nozzle for supplying fuel and primary air, a secondary nozzle for
supplying
secondary air, provided outside said primary nozzle, and a tertiary nozzle for
supplying tertiary air, provided outside said secondary nozzle so as to
contact with the
outside of said secondary nozzle, said secondary nozzle and said tertiary
nozzle being
partitioned by a partition wall, wherein: said primary nozzle has a stabilizer
provided
at an end thereof, said partition wall has thereon a flow path change member
for
changing a flow of tertiary air from a flow along an axis of the burner to an
outward
flow which jets the tertiary air, and said partition wall is movable in the
burner axial
direction allowing to a substantially closed condition of an outlet of said
tertiary
nozzle.
By moving the partition wall provided with the flow path change member in a
direction parallel with the burner axis, a cross-sectional area of a tertiary
air jet of the
tertiary nozzle changes, and a flow rate and a flow speed of the tertiary air
change.
The change in flow rate of the tertiary air changes a flow rate and a flow
speed of the
secondary air. By the change in flow rate of the tertiary air or a flow rate
of the
secondary air, the combustion conditions change. As a result, it is possible
to lower
the temperatures of burner constituent components.
The burner of triple tube construction is constructed so that fuel is ignited
with
primary air to form a reducing flame and lower NOx emissions, and the
secondary air
and tertiary air are mixed with the reducing flame to burn the unburned fuel.
The
burner is known as an in-flame 2-stage combustion burner or an in-flame NOx
reduction burner. In this burner, the delay in mixing of the tertiary air
increases the
region of the reducing flame, whereby low NOx emission is promoted. Many
burners
of this construction have a stabilizer provided at the outlet of the tubular
primary
nozzle, as shown in
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JP 60-26922 B and in the present invention, also, it is possible to provide a
stabilizer at
the outlet of the primary nozzle. There is an inner flame stabilizing ring in
which a
ring-shaped projection is formed at the inside of the outlet of the tubular
primary nozzle
and an outer flame stabilizing ring in which a tubular projection is provided
outside the
outlet of the tubular primary nozzle in the burner axis direcition. Provision
of the
stabilizer forms a flow recirculation region due to turbulent flow eddy in a
wake flow
thereof or in a flow downstream of the stabilizer. The flow recirculation
involves fuel,
for example, pulverized coal particles, to make them into flash points for
high
temperature gas and promote ignition of the pulverized coall. Here, the
secondary air
cools the stabilizer and adjusts a mixing ratio of fuel and air.
The flow path change member, that has a taper-shaped inclined plane so that
the
tertiary air flows, while changing gradually the flow direction from a flow
parallel with
the burner axis to an outward flow is desirable. The rear side, that is, the
side in contact
with the secondary air, of the flow path change member is desirable to be
formed so that
it is inclined along the plane of the tertiary nozzle. By fornr,iing the flow
path change
member in this manner, when the flow path change member is moved such that the
tertiary air jet cross-sectional area becomes small, the secondary air jet
cross-sectional
area increases according to the movement thereof.
In order to make the partition wall move easily without making the burner
construction complicated, it is desirable for the partition wall to be
composed of a fixed
wall and a movable wall, and for the movable wall to be slidable on the
surface of the
fixed wall. In addition, a portion of the tertiary air flows parallel with the
burner axis and
the fixed wall, as a portion of the parallel flow changes in direction outward
as the
movable wall, that is, the latter portion is a portion on which the flow path
change
member is provided. It is desirable for the fixed wall to provide guide
rollers thereon. A
stopper or stoppers may also be provided for stopping movement of the movable
wall on
the fixed wall and /or the movable wall. Since the flow patli change member
and the
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partition wall in the vicinity of the flow path change member are apt to be
heated to a
high temperature, it is preferable to provide fins for cooling. As a means for
moving the
movable wall, a bar-shaped member is mounted on the movable wall for movement
forward and backward in the burner axis direction by manual or automatic
means.
Extension of one end of the bar-shaped member out of the wind box of the
burner
simplifies maintenance and reduces failure. The movable wall is moved by
pulling and
pushing the end of the bar-shaped member by hand. Further, it can easily be
moved
forward and backward by gears on the end portion of the ba.r-shaped member and
a
handle having another gear mounted thereon. Alternatively, by providing a
motor or
motors instead of the handle, it is possible to automatically move the
moveable wall.
The burner according to the invention can be used for a burner using oil, gas,
pulverized coal, etc. as fuel, particularly, it is suitable for a lburner
using pulverized coal.
In a pulverized coal burner, sometimes combustion is assisted by providing an
oil burner
inside a primary nozzle.
For the burner according to an exemplary embodiment of the present invention,
it
is possible to add a tertiary air bypass mechanism by which a part of tertiary
air is caused
to bypass the tertiary nozzle into another nozzle. The tertiairy air bypass
mechanism is
formed so that when the partition wall partitioning the secondary nozzle and
the tertiary
nozzle is moved to a predetermined position and a part of the tertiary air
bypasses the
tertiary nozzle into another nozzle. By making holes in the moveable wall and
in the
fixed wall so as to communicate with the above-mentioned hole when the movable
wall
is moved to the predetermined position, the part of the tertiary air can
bypass the tertiary
nozzle into the secondary nozzle. One hole formed in each of the fixed wall
and the
movable wall is sufficient. However, a plurality of holes in a circumferential
direction
can be provided in order to increase a flow rate of the tertiary air.
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By forming a hole in the primary nozzle and connecting the hole with the hole
formed in the fixed wall by a bypass pipe, it is possible to flow the tertiary
air into the
primary nozzle. By forming the bypass pipe so that the tertiary air flows
along the
inner wall of the primary nozzle and jets in the flow direction of fuel, it is
possible to
5 cool the stabilizer by the tertiary air flowing in the primary nozzle.
Certain exemplary embodiments may provide a fuel combustion method by a
burner comprising a primary nozzle for supplying fuel and primary air, a
secondary
nozzle for supplying secondary air, provided outside said primary nozzle, a
tertiary
nozzle for supplying tertiary air, provided outside said secondary nozzle so
as to
contact with the outside of said secondary nozzle, a stabilizer provided at an
end of
said primary nozzle, said secondary nozzle and said tertiary nozzle being
partitioned
by a partition wall, and a flow path change member provided on said partition
wall for
changing a flow of the tertiary air from a flow along the burner axis to an
outward
flow, said partition wall being constituted to be movable in the burner axis
direction,
wherein: said partition wall is moved depending on one or more of a load
change, a
temperature at a burner axis end portion, properties of the fuel, a
concentration of
nitrogen oxides, a concentration of unburned fuel, and a fuel supply stoppage,
said
partition wall allowing adjustment of an outlet of said tertiary nozzle to a
substantially
closed condition. Preferably, a fuel combustion method, wherein at the time of
stoppage of fuel supply to said burner, said partition wall is moved so that a
cross-
sectional area of a tertiary air jetting outlet of said tertiary nozzle
becomes small,
thereby increasing a flow rate of the secondary air from said secondary air
nozzle.
More preferably, a fuel combustion method, wherein said method further
comprises
step of moving said partition wall so that the cross-sectional area for
jetting tertiary air
of said tertiary nozzle decreases when a temperature of said flow path change
member
becomes higher than a set temperature during combustion of fuel by the burner,
and
increasing a flow speed of the tertiary air. Even more preferably, a fuel
combustion
method, wherein a part of the tertiary air supplied to said tertiary nozzle is
caused to
bypass a flow path of said tertiary nozzle into said secondary nozzle during
stoppage
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of fuel supply to said burner. Still more preferably, a fuel combustion
method,
wherein a part of the tertiary air supplied to said tertiary nozzle is caused
to bypass a
flow path of said tertiary nozzle to flow along an inner wall of said primary
nozzle
during stoppage of fuel supply to said burner.
Certain other exemplary embodiments may provide a method of retrofitting a
boiler having a burner which is provided on a furnace wall and comprises a
primary
nozzle for supplying fuel and primary air, a tubular secondary nozzle for
supplying
secondary air, provided outside said primary nozzle so as to enclose said
primary
nozzle, a tubular tertiary nozzle for supplying tertiary air, provided outside
said
secondary nozzle, a stabilizer provided at an end of said primary nozzle, a
tubular
partition wall fixed between said secondary nozzle and said tertiary nozzle,
wherein
said method comprises: removing at least an end portion of said partition
wall; and
providing, around the position of the removed portion of said partition wall,
a tubular
partition wall with a flow path change member for changing a flow of tertiary
air from
a flow along the burner axis to an outward flow so as to be movable in the
burner
axial direction, said tubular partition wall allowing adjustment of an outlet
of said
tubular tertiary nozzle to a substantially closed condition.
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Still yet another aspect of the present invention is a method of reducing the
tertiary air jet cross-sectional area to increase the momentutm of tertiary
air and increasing
the quantity of tertiary air in the case where the NOx concentration is high
or low
combustibility fuel is used.
Another aspect of the present invention is a method of retrofitting a boiler
provided with an existing burner having a tubular partition wall which
partitions a
secondary nozzle and a tertiary nozzle wherein a part or all of the partition
wall is
removed and a tubular partition wall provided with a flow path change member
arranged
so as the fixed partition wall is movable.
The burner according to an exemplary embodiment of the present invention is
the
in-flame 2-stage combustion type which provides for excellent reduction of
NOx. It is
possible to suppress ash deposit on the burner or damage of'the burner due to
heat while
reducing NOx. By fixing the jet direction of tertiary air to a constant
outward direction
and changing the momentum of the tertiary air, the size or region of flow
recirculation
can be optimized, and it is possible to improve the combustion conditions.
Even if a flow
rate of tertiary air is kept constant, it is possible to make the flow speed
at a downstream
end of a guide sleeve high so that the guide sleeve can be cooled. By
controlling
independently the momentum and the flow rate of the tertiary air, the size of
flame and
the size of flow recirculation determined mainly by the mornentum, and the
size of a
reducing region determined by the flow rate can be controlled independently,
and
favourable combustion conditions can be maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional view of a burner of an embodiment of the present
invention;
Fig. 2 is a sectional view showing the burner of the embodiment of the present
25, invention shown in Fig. 1 in use;
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Fig. 3 is a sectional view taken along III-III of the burner of Fig. 1;
Fig. 4 is a sectional view taken along IV-IV of the burner of Fig. 1;
Fig. 5 is a sectional view of the burner of another er.ribodiment of the
present
invention;
Fig. 6 is a sectional view of the burner shown in Fig. 5 in use;
Fig. 7 is a schematic diagram of a construction of a controller for the burner
according to the present invention;
Fig. 8 is a sectional view of the burner of another enabodiment of the present
invention;
Fig. 9 is a sectional view of the burner of another enabodiment of the present
invention;
Fig. 10 is a sectional view of the burner of another embodiment of the present
invention;
Fig. 11 is a sectional view of the burner of another embodiment of the present
invention;
Fig. 12 is a sectional view of the burner of another embodiment of the present
invention;
Fig. 13 is a sectional view of the burner taken along XIII-XIII of Fig. 12;
Fig. 14 is a sectional view of the burner taken along XIV-XIV of Fig. 12;
Fig. 15 is a sectional view of the burner taken along XV-XV of Fig. 12;
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Fig. 16 is a sectional view of the burner of another embodiment of the present
invention;
Fig. 17 is a sectional view of the burner taken along XVII-XVII of Fig. 16;
Fig. 18 is a sectional view of the burner taken along XVIII-XVIII of Fig. 16;
and
Fig. 19 is a graph showing conditions that the flow rates of fuel and air
supplied
from the burner change according to burner loads.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The burner and the method of using the burner according to the present
invention
will be explained, referring to the Drawings.
EMBODIMENT 1
Figs. 1, 2, 3 and 4 are sectional views showing an einbodiment of the burner
according to the present invention. The burner has a triple tube construction
composed of
a primary nozzle 4, a secondary nozzle 8 and a tertiary nozzle 9. Primary air
and
pulverized coal flow from the primary nozzle 4 as shown by an arrow 11. In the
present
embodiment, the case where pulverized coal is used as fuel is shown, however,
the case
where oil, gas or the like is used is also the same as the abo've-mentioned
case. The
primary nozzle 4 is tubular and its cross-section is shaped in circle or
square. A partition
wall is provided between the secondary nozzle 8 and the tertiary nozzle 9, and
the
partition wall is composed of a fixed wall 1 and a movable wall 2. A guide
sleeve 3 is
provided at an end portion of the movable wal12. The guide sleeve 3 serves to
change
the flow of tertiary air outwardly.
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Secondary air flows from the secondary nozzle 8 shown by arrow 12. Further,
the
tertiary air flows from the tertiary nozzle 9 shown by arrow 13. The movable
wall 2 is
connected to movement control rods 5 at connection portions 14, and handles 33
for
operating are provided out of a wa1128 of a wind box.
A stabilizer 10 having a tubular shape is provided on an end of the primary
nozzle 4. An air resistor (or air resistors) 7 is provided upsl:ream of the
tertiary nozzle 9.
Further, a tertiary damper 35 and a secondary damper 34 are provided upstream
of the
tertiary nozzle 9 and the secondary nozzle 8, respectively.
By moving the movable wa112 and the guide sleeve 3 provided on the end
thereof, forward and backward in a parallel direction to the burner axis, the
flow rate and
flow speed of the tertiary air, the flow rate and flow speed of the secondary
air and a ratio
of the tertiary air flow rate and the secondary air flow rate are changed
whereby it is
possible to control the combustion conditions. This is the same as changing a
ratio of
tertiary air momentum and secondary air momentum. In the present invention, by
keeping a jet angle of the tertiary air constant and changing an outlet cross-
sectional area
for the tertiary air, it is possible to change the flow rate and flow speed of
the tertiary air.
By always directing the tertiary air outward, the size of the flow
recirculation formed
downstream of the stabilizer 10 and the guide sleeve 3 can always be increased
so that the
combustion conditions can be kept ideal. The momentum of the tertiary air is a
main
factor for determining the size of flame and the size of flow recirculation
and the flow
rate of the tertiary air is a main factor for determining the size of a
reducing region.
Since the momentum and the flow rate of tertiary air can be controlled
independently, it
is possible to make a combustion condition suitable for improving flame
stabilization and
NOx reduction. Further, it is possible to change independently the momentum of
tertiary
air and the flow rate of secondary air, whereby the secondary air can be used
for cooling
of the stabilizer 10, air supply to the fuel flowing in the prinaary nozzle,
etc.
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Fig. 3 shows a III-III sectional view of Fig. 1. Fig. 4 shows a IV-IV
sectional of
Fig. 1. Rollers 23 are mounted so that the movable wal12 rnoves smoothly. In
this
embodiment, four (4) movement control rods 5 are provided, and they are
suitable for
parallel movement of the movable wall 2 to the burner axis. The rollers 23 are
mounted
5 on the fixed wall 1, but they also can be mounted on the mc-vable wall 2.
The temperature of the movable wall 2 may rise when the flow rate of tertiary
air
is low. Damage due to burning or deformation is apt to occur when the
temperature of
the member rises higher than sustainable tolerances. Therefore a material of
high heat
resistance for the movable wall 2 should be utilized.
10 A method of adjusting a burner at the time of trial operation is discussed
below.
Immediately after the burner is installed on the boiler, an intended flow rate
may not be
achieved. This may be caused by manufacturing errors of the burner, asymmetry
of
upstream ducts, setting errors of the resistors, the dampers installed on the
burner, etc.
Further, in some cases, it is necessary to set a flow rate of a:ir according
to deviation of
fuel for each burner. Therefore, by adjusting the air resistor 7 of the
tertiary nozzle 9, the
tertiary damper 35, the secondary damper 34 and the movable wall 2, combustion
conditions suitable for reduction of NOx, CO, unburned fuel, soot, corrosion,
and the
metal temperature of the burner part are achieved. Examples of the adjusting
method are
described below.
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Example 1
In the case where flame stability is poor, the following operations are
conducted
to improve the flame stability:
(1.1) In the case where the momentum of tertiary air is low:
The movable wall 2 is moved to a near side or to the left side in Fig. 1 to
make the flow path area of the tertiary nozzle narrow. Under this condition,
the
pressure loss of the tertiary air increases so that a flow rate of the
tertiary air
decreases and a flow rate of the secondary air increases. In order not to
change
these flow rates, the air resistor 7 or the tertiary darnper 35 of the
tertiary nozzle 9
is opened, or, the secondary damper 34 is closed to stop the secondary air
flow.
By increasing the momentum of the tertiary air, a flow recirculation region
downstream of the stabilizer 10 enlarges and flame stability is increased.
(1.2) In the case where the momentum of secondary air is low:
The flow rate of secondary air is increased, by closing the air resistor 7 of
the tertiary nozzle 9 to increase air swirling or movi:ng the movable wall 2
to the
near side to make the flow speed of the tertiary air high. The increase in
flow rate
and momentum of the secondary air makes the flow recirculation region
downstream of the stabilizer 10 larger and raises the flame stability.
However,
when the secondary air increases too much, in some cases the flow
recirculation is
decreased. An optimum flow rate exists for the secondary air.
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In Fig. 2, by having moved the movable wall 2, the minimum flow path
area between the stabilizer 10 and the guide sleeve 3 has been widened.
Therefore, there
is the possibility that the jetting flow speed of the secondary air decreases.
When the
flow speed is low, a cooling effect of the stabilizer 10 decre:ases, so that
it is beneficial
for the stabilizer 10 to extend in the moving direction of the movable wal12
so that it
does not change the minimum flow path area even if the movable wall 2 is
moved.
Example 2
In the case where the concentration of NOx is high, the following method is
performed:
(2.1) Increasing the stability of the flame decreases the concentration of
NOx.
(2.2) In the case where the flame is sufficiently stabilized, and it is
desired to
further reduce the concentration of NOx, it is effective to delay mixing of
the air. In
order to delay the mixing of air, it is effective to decrease the flow rate of
the secondary
air and increase the flow rate of the tertiary air. To perforrr.i this, the
secondary
damper 34 is closed, or the movable wall 2 is moved so that the tertiary air
outlet is
opened. Further, it can be achieved by increasing the momentum of tertiary
air. The
delay of mixing of air can also be attained by closing the aiir resistor 7 of
the tertiary
nozzle 9 and increasing swirling of tertiary air. In this case, it is
necessary to close the
secondary damper 34 so that the flow rate of the tertiary air does not
decrease.
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Example 3
In the case where unburned fuel is significant, the following method is
performed:
(3.1) There is a possibility that unburned fuel could significantly increase
without conducting flame stability. Therefore, it is effective to take a
setting similar to
the setting for improvement on flame stability.
(3.2) In the case where the flame is sufficiently stabilized, it is desired to
further
reduce the unburned fuel, it is effective to increase secondary air. In this
case, there is a
possibility that the momentum of tertiary air decreases and the flame
stability decreases
when the secondary damper 34 is opened. Therefore, it is effective to increase
the flow
speed of tertiary air by moving the movable wall 2 to the near side or to make
the
swirling stronger by closing the air resistor 7 of the tertiary nozzle 9.
(3.3) For reduction of unburned fuel, it is effective to raise the burner air
ratio.
The flow rate of air increases by raising the burner air ratioõ mixing of air
and fuel
improves, and the concentration of NOx increases. In ordeir to reduce the
concentration
of NOx, the method described in the example 2 can be applied.
Example 4
To reduce corrosion, adjustment is conducted by the following method:
(4.1) Low air flow around the wall makes the concentration of gas and
corrosion speed higher. To supply air around the wall, it is effective to
increase the flow
rate of tertiary air. Therefore, it is effective to open the movable wall 2 to
make the flow
path area of the tertiary nozzle 9 wider as to increase the tertiary air flow
rate. Further,
increasing air circulation around the wall by increasing the momentum of
tertiary air is
possible by closing the secondary damper 34.
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(4.2) Since it is also possible to decrease the flame stability and to
decrease
reducing gas, it is possible to perform an operation reverse to that in the
example 1.
(4.3) The reducing gas and corrosion can be reduced, also by increasing air
quantity to the burner close to the wall that is apt to corrode;. Therefore,
it is effective to
adjust air distribution by adjusting the movable wall 2, the iresistor, and
the damper for
each burner to increase the air quantity.
Example 5
In the case where it is desired to greatly change the type of fuel used,
adjustment
is conducted by the following method:
(5.1) When the type of fuel is greatly changed, or pulverization and an amount
of volatile matters in the fuel changes, it is better to change the damper
opening, the
position of the movable wall 2 and the setting of the air resistor 7 in order
to keep the
flame stabilized and reduce NOx. In the case where fuel is changed from a fuel
of high
combustibility to a fuel of low combustibility, there is a possibility that
the flame stability
decreases. In this case, it is better to make adjustments to improve the flame
stability.
(5.2) Low fuel combustibility can result in an increased concentration of NOx
therefore requiring adjustments to reduce NOx.
Example 6
In the case where ash is deposited in the fuel, the following method can be
performed:
(6.1) In the case where the flame stability is high and ashes in the fuel melt
and
deposit around the burner, the movable wall 2 is moved forward (to the
opposite side to
the near side) to increase the outlet cross-sectional area for itertiary air,
decrease the flow
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speed of the tertiary air and reduce the flame stability. By operating in this
way, the
combustion temperature decreases, so that deposition of aslies is reduced. At
the same
time, secondary air also increases, the temperature around the stabilizer 10
decreases and
the ashes can be prevented from melting.
5 (6.2) In the case where molten ash deposits on the wall of boiler, it is
beneficial
to supply air around the wall. Therefore, it is better to operate so that air
is supplied
around the wall by moving the movable wall 2 to the near side to change the
jetting
direction of tertiary air outwardly.
Example 7
10 In the case where the temperature of the stabilizer 10 is high, the
following
operation is conducted:
When the temperature of the stabilizer 10 is high, it is effective to increase
the
flow speed of secondary air. In order to increase the flow rate of secondary
air, the
tertiary damper 35 or the air resistor 7 is closed. In this case, there is
such a possibility
15 that the momentum of tertiary air decreases and the stabilization of flame
decreases.
Therefore, the movable wall 2 is moved to the near side instead of closing the
tertiary
damper 35 and the air resistor 7 keeping both the flame stabilized and
reducing the
temperature.
Example 8
Decreasing the minimum load of the boiler is conducted as follows:
Boiler load is not always 100% but it is changed according to power demands.
If
it can be run at a very low load, the operation efficiency of ithe boiler
increases. Usually,
burners are designed so that the performance is optimal at 100% load. When the
load is
low, respective flow rates of fuel and air entering the furnace from the
burner decrease,
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so that there is a possibility that the air momentum becomes unbalanced and
the flame
stability decreases. For example, when the momentum of tertiary air is low, it
is effective
to increase the momentum by moving the movable wall 2 to the near side. This
operation
is the same as the method of increasing the stability of the flame as
described in the
example 1. However, when the stability of the flame is incireased under the
low load
operation, in some cases, the combustibility becomes low at a high load. It is
better to set
in such a range of operation such that the combustibility does not become low
even at a
high load.
EMBODIMENT 2
Fig. 5 is a sectional view of another embodiment of the burner according to
the
present invention. The present embodiment 2 differs from ithe embodiment 1 in
that
motor boxes 6 are provided and the movement of the movalble wall 2 is
electrically
driven. Further, in Fig. 5, although the motor boxes 6 are installed inside
the wind box, it
is possible to install them outside the wind box. Further, an air resistor 15
is provided in
the secondary nozzle 8. It is possible to control the flow rate and swirling
force by
combining the air resistor 15 and the secondary damper 34.
A benefit of driving the movable wall 2 by the motor 6 is that the movable
wall 2
is controlled according to the algorithm of combustion adjustment described in
the
embodiment 1, and an optimum combustion condition can be maintained. As
explained
below it is possible to provide a suitable operation condition by changing
flow rate
conditions.
In some cases, the burner is out of service without fiael being supplied.
Under
such a condition, there is a possibility that the out of service; burner being
heated by
radiant heat from other burners and the temperatures of the guide sleeve 3,
the
stabilizer 10, etc. rise. To prevent this phenomenon, it is necessary to
supply air to the
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burner even when it is out of service. When a flow rate of air to be supplied
to the out of
service burner is large, an air adjustment quantity is small. Therefore, it is
necessary to
reduce the flow rate of air to be supplied to the out of service burner. When
the flow rate
is decreased under the condition that the movable wall 2 is fixed, the flow
speeds of
tertiary air and secondary air decrease, and it is impossible to sufficiently
cool the guide
sleeve 3 and the stabilizer 10.
In the present invention, the burner is adjusted to the condition as shown in
Fig. 6
when the burner is out of service. That is, the movable wall 2 is moved to the
rear side,
the jet portion area of tertiary air is almost zero. Since the flow speed at
the end of the
guide sleeve 3 is high, the guide sleeve 3 can be cooled even with a small
quantity of
tertiary air. Further, by increasing the flow rate of secondary air, it is
possible to increase
the flow speed of secondary air and effectively cool the stabilizer 10. Since
secondary air
is lower in flow rate than tertiary air, it is possible to decrease the whole
air flow rate
even if the secondary air is increased.
In the above-described embodiments, the tertiary nozzle is provided with the
air
resistor 7. However, it is possible to form it without provision of such an
air resistor 7.
The air resistor 7 is for controlling a combustion field by swirling the
tertiary air, because
in the present invention the same effect can be attained by moving the movable
wall 2
forward and backward in the burner axis direction. Further, the air resistor
15 of the
secondary nozzle is not essential. In this case, the secondary damper 34 is
necessary
because any method of adjusting a flow rate of secondary air is not available.
A construction of a controller used for the embodiment 2 is shown in Fig. 7.
The
controller 101 receives signals from measuring instrument and sends signals
for moving
movable parts of the burner 102. For example, signals for driving a movable
wall
moving motor 111, an air resistor 7, driving motor 112, a tertiary damper
driving
motor 113, a secondary damper driving motor 114, an air resistor 15, driving
motor 115,
CA 02496644 2005-05-13
18
etc. are provided. The controller 101 has software incorporated for realizing
the method
described in embodiment 1. The measuring instrument installed in the burner
includes a
flame detector 107, a temperature detector or thermometer 108 for burner
metal, a
pressure gauge 109 for combustion air, a flow meter 110 for burner air, etc.
The
measuring instrument mounted on a boiler 116 includes a temperature detector
or
thermometer 103 for steam, an ash deposition sensor 104, an NOx sensor 105, an
unburned fuel sensor 106 for measuring CO concentration and unburned
components of
solids, etc. For example, in order to examine the stability of the flame, the
flame
detector 107 is used. A flame detector that can detect luminous intensity can
be utilized.
It is possible to evaluate the stability of the flame by the lurninous
intensity and change in
operation conditions. The NOx sensor 105 can be installed at a downstream side
of the
boiler 116, at which the reaction has terminated. It is beneficial to install
a plurality of
the NOx sensors and adjust the movable wall 2, the resistor and the damper for
each
burner while examining concentration distribution of NOx. The unburned fuel
sensor 105 can be installed at a downstream side of the boiler 116 as
installation of the
NOx sensor.
EMBODIMENT 3
Figs. 8, 9, 10 and 11 are sectional views showing another embodiment of the
burner according to the present invention. In an example oiP Fig. 8, holes 16,
32 for
tertiary air bypass are formed in the fixed wall 1 and the mcivable wall 2 of
the partition
wall partitioning the secondary nozzle 8 and the tertiary nozzle 9,
respectively, and
tertiary air flows through those holes into the secondary nozzle 8 as shown by
an
arrow 17, bypassing the tertiary nozzle 9. In this case, the tertiary air
flows into the
secondary nozzle under the condition that the movable wall 2 is moved to the
near side
and fuel supply is out of service as shown in Fig. 8. With this construction,
even in the
case where the movable wall 2 has been moved to the near side and the
secondary air has
been stopped, air is automatically supplied into the seconda:ry nozzle 8 and
it is possible
CA 02496644 2005-05-13
A 1
19
to prevent the temperature of the stabilizer 10 from rising. It is possible to
make the flow
rate larger by providing not only one hole 16, 32 for tertiary air bypass but
a plurality of
the holes 16, 32.
Fig. 9 shows an example in which the tertiary air bypasses the tertiary nozzle
9
and is supplied to the primary nozzle. In this example, holes are formed in
the tubular
wall of the primary nozzle 4, and bypass pipes 18 connect between the holes
provided in
the fixed wall 1 and the holes formed in the primary nozzleõ In the case where
the burner
is out of service, little air is supplied to the primary nozzle, and the inner
side of the
stabilizer cannot be cooled.
In the case where the concentration of oxygen in the air carrying fuel is low,
it is
beneficial to decrease the tertiary air jet sectional area of the tertiary
nozzle 9 by moving
the movable wall 2 to the near side, to increase the flow rate of bypass air.
When lignite
is used, the fuel easily ignites and is carried with flue gas. 'When the
burner load is high,
even if the oxygen concentration of primary air is low, stable combustion is
possible
because the gas temperature is high inside the combustion apparatus, for
example, the
boiler. However, when the load decreases, the gas temperature inside the
combustion
apparatus decreases and unburned fuel increases and is carried with flue gas
unless the
oxygen concentration of the primary air increases. In such a low load case,
tertiary air
flows into the primary nozzle 4 to enable stable combustion.. Although a
construction
such that tertiary air always bypasses and flows into the priinary nozzle 4 is
also
considered, combustion is promoted when the load is high and the possibility
of an
explosion and ash deposit becomes high, therefore as the load decreases, the
air flow
should be increased.
Fig. 10 shows an example in which bypassed secondary air is supplied to the
primary nozzle. In this example, holes are formed in the tube wall of the
primary
nozzle 4, and air is supplied from the secondary nozzle to the primary nozzle
through
CA 02496644 2005-05-13
bypass pipes 18. In the case where the burner is out of service, the movable
wall 2 is
moved to the near side and the air resistor 15 is closed whei-eby secondary
air is supplied
along the wall of the primary nozzle.
Further, in a similar manner to the example of Fig. 9, when the oxygen
5 concentration of the primary air is low, it is possible to effect stable
combustion by
increasing the flow rate of bypass air. When it is desired to decrease the
combustion
speed, the pressure at the intake port of bypass air is lowered. For example,
the movable
wall 2 is moved to widen the jet area of tertiary air, or open the air
resistor 15.
Fig. 11 shows an example where bypassed tertiary air is used for cooling a
10 pulverized coal concentrator 20 provided inside the primary nozzle 4. The
pulverized
coal concentrator 20 is formed so as to gradually narrow the flow path of the
primary
nozzle toward a downstream side and gradually widen the flow path toward a
further
downstream side as shown in Fig. 11, and serves to increase the pulverized
coal
concentration on the wall side of the primary nozzle. In the out of service
condition, the
15 flow rate of primary air is small, so that it is difficult to cool the
pulverized coal
concentrator 20. Therefore, a construction is required such that tertiary air
flows to the
pulverized coal concentrator 20 under the out of service condition. In Fig.
11, bypass
tubes 19 are provided, and each of the bypass tubes 19 conriects the hole of
the fixed
wall 1 and the hole of the primary nozzle 4 and is extended to the pulverized
coal
20 concentrator 20. The air used for cooling the pulverized coal concentrator
20 is jetted
into the furnace from the end of the pulverized coal concentrator 20.
In some instances, the pulverized coal burner is provided with an oil burner
formed so as to spray oil 21 for assisting combustion from an atomizer 31 as
shown in
Fig. 11. By moving the movable wall 2, it is possible to change a ratio of the
flow rate of
air flowing in a central portion of the burner and the flow rate of air
flowing outside
thereof. Thereby it is possible to control NOx and soot.
CA 02496644 2005-05-13
21
EMBODIMENT 4
Fig. 12 is a sectional view of a burner of another ernbodiment of the present
invention. In this embodiment, the motor boxes 6 are mounted out of the wall
28 of the
wind box. The secondary air and tertiary air are at a tempeirature of 300 C or
more, and
in some cases it includes ash. When the motor boxes 6 are mounted in such a
location,
they may become inoperable and difficult to repair. Further, in the present
embodiment,
the fixed wall 1 is shorter than that in Fig. 5. With this construction, even
if a portion
close to the end of the movable wa112 is deformed by heat, a portion
contacting with the
fixed wall 1 is disposed in a deeper bowel of the burner, reciucing the
possibility that
movement is obstructed.
Further, a stopper 2 on movable wal12 is provided to prevent excessive forward
movement due to sensor failure, etc. Although not shown i:n Fig. 12, in a
similar manner,
a stopper can be provided to limit movement of movable wa112 to the near side.
Further, in Fig. 12, the cooling efficiency is raised by providing cooling
fins 22 on
the movable wall 2 and the guide sleeve 3. The cooling fins 22 also serve to
increase the
strength.
In Fig. 12, temperature detectors of thermostats 29 are mounted on the guide
sleeve 3 and the stabilizer 10, respectively. The position of'the movable wall
2 can be
controlled, based on values of the thermostats. In this case, when the
temperature of the
end of the guide sleeve is higher than a limit value, the flow speed of the
tertiary air is
slow, such that the operation that the flow rate of the secondary air is
reduced and the
flow speed of the tertiary air is raised. When the temperatu:re of the
stabilizer is higher
than a limit value, the operation condition of the example 7 of the embodiment
1 can be
taken. In the case where the temperatures of the guide sleeve and the
stabilizer are higher
than the limit values, respectively, the quantity of the whole air can be
increased.
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22
Figs. 13, 14 and 15 are a sectional view taken along XIII-XIII, XIV-XIV and
XV-XV of Fig. 12, respectively and show various configuration examples. The
configurations shown in Figs. 13 to 15 can be used for not only the burner of
Fig. 12, but
the burner of Fig. 1. Fig. 13 shows an example where four movement control
rods 5 are
moved by gears 26 and power transmission shafts 27 driven by one motor 25.
This
enables reducing the number of motors and allows the displ[acements of the
movement
control rods 5 to be equal. Fig. 14 is an example where the motor 25 shown in
Fig. 13 is not utilized and the movement control rods 5 are moved by rotation
of a manual
handle 27. Fig. 15 shows an example where four motors 25 are used and even if
one of
the motors 25 is out of order and the rods 5 can be driven by the other
motors.
EMBODIMENT 5
Figs. 16, 17 and 18 are sectional views of another embodiment of the burner
according to the present invention. Fig. 17 is a sectional view taken along
XVII-XVII of
Fig. 16, and Fig. 18 is a sectional view taken along XVIII-XVIII of Fig. 16. A
difference
from Fig. 1 is that the burner is not made of triple tubes, a primary nozzle 4
and a
secondary nozzle 8 each are made of a square tube, and a tertiary nozzle 9 is
separated
into an upper portion and a lower portion. In this case, it is possible to
make an optimum
operational condition by moving a movable wall 2 having a. guide sleeve 3
forward and
backward in a similar manner to the embodiment 1. In the present embodiment,
since the
movable wall 2 is separated into an upper portion and a lower portion, it is
possible that
they are not moved forward and backward in an interlocked manner. Therefore,
as
shown in Fig. 17, it is possible to connect the movable walls 2 by connecting
plates 36.
In the present embodiment, as shown in Fig. 18, handles 33 are mounted at four
positions, and the movable wall 2 is moved manually, however, it can be moved
by a
motor or motors as in the embodiment 2.
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23
EMBODIMENT 6
An example of alternate uses of the burner according to the present invention
will
be explained. In Fig. 19, the x-axis defines the burner load. Air for cooling
flows evenly
at a burner load of 0%, and in this case, in order to cool the stabilizer 10,
the movable
wall 2 is moved so that the outlet of tertiary air becomes a condition near to
full closing.
For the coal firing burner, since combustion is assisted by oil at the time of
a low load, oil
and coal are supplied. When it reaches a state at which conibustion can be
performed
with only coal, the flow rate of oil is reduced to zero. When the oil is
burned, it is better
to increase a flow rate of air at a position near to a central portion to
which oil is supplied,
so that the movable wal12 is moved to the near side so that the outlet of
tertiary air is
nearly closed. A flow rate of supplied air is increased as a flow rate of coal
increases.
Since stable combustion can be performed even if the momentum of tertiary air
is low,
the movable wa112 is moved to the near side to increase the size of the
tertiary air outlet
to nearly fully open.
The present invention makes it possible to cool the burner while reducing NOx
by
controlling the combustion condition optimum. The possibility of utility of
the burner
according to the present invention is large to make thermal failure of the
burner less.
