U.S. patent application number 12/513959 was filed with the patent office on 2010-02-11 for pulverized coal boiler.
Invention is credited to Akira Baba, Yuki Kamikawa, Hironobu Kobayashi, Koji Kuramashi, Toshihiko Mine, Shinichiro Nomura, Yusuke Ochi, Akihito Orii, Miki Shimogouri, Masayuki Taniguchi.
Application Number | 20100031858 12/513959 |
Document ID | / |
Family ID | 39364465 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100031858 |
Kind Code |
A1 |
Orii; Akihito ; et
al. |
February 11, 2010 |
Pulverized Coal Boiler
Abstract
The present invention provides a highly reliable pulverized coal
boiler that ensures suppression of a rise in flame temperature
caused during the combustion of an unburnt gas in a furnace when
combustion air is supplied from after-air ports so as to reduce the
concentration of thermal NOx generated during the combustion. A
pulverized coal boiler (100) according to the present invention
comprising a furnace (1), burners (2) provided on the wall of the
furnace for supplying pulverized coal to the inside of the furnace
and burning the pulverized coal, and an after-air port (3 or 61)
provided on the wall of the furnace at a position downstream of the
burner for supplying combustion air to the inside of the furnace,
the pulverized coal boiler further comprising: a spray nozzle (6)
disposed near a jet port (3 or 60) of the after-air port for
supplying water, steam, or two fluids including water and steam to
the inside of the furnace; whereby the water, the steam, or the two
fluids including water and steam are sprayed from the spray nozzle
are supplied to the inside of the furnace together with the
combustion air supplied from the after-air port.
Inventors: |
Orii; Akihito; (Hitachi,
JP) ; Taniguchi; Masayuki; (Hitachinaka, JP) ;
Kamikawa; Yuki; (Hitachinaka, JP) ; Kobayashi;
Hironobu; (Hitachinaka, JP) ; Shimogouri; Miki;
(Kure, JP) ; Mine; Toshihiko; (Kure, JP) ;
Nomura; Shinichiro; (Kure, JP) ; Baba; Akira;
(Kure, JP) ; Ochi; Yusuke; (Kure, JP) ;
Kuramashi; Koji; (Kure, JP) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Family ID: |
39364465 |
Appl. No.: |
12/513959 |
Filed: |
November 6, 2007 |
PCT Filed: |
November 6, 2007 |
PCT NO: |
PCT/JP2007/071525 |
371 Date: |
May 7, 2009 |
Current U.S.
Class: |
110/188 ;
110/234; 110/263; 110/297; 110/306 |
Current CPC
Class: |
F23J 2215/101 20130101;
F23L 9/02 20130101; F23L 2900/07008 20130101; F23C 7/02 20130101;
F23L 2900/07009 20130101; F23L 7/002 20130101 |
Class at
Publication: |
110/188 ;
110/234; 110/263; 110/297; 110/306 |
International
Class: |
F23N 3/00 20060101
F23N003/00; F23K 3/00 20060101 F23K003/00; F23L 7/00 20060101
F23L007/00; F23L 9/00 20060101 F23L009/00; F23N 5/24 20060101
F23N005/24 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2006 |
JP |
2006-302881 |
Claims
1. A pulverized coal boiler comprising a furnace, a burner provided
on a wall of the furnace for supplying pulverized coal to the
inside of the furnace and burning the pulverized coal, and an
after-air port provided on the wall of the furnace at a position
downstream of the burner for supplying combustion air to the inside
of the furnace, the pulverized coal boiler further comprising: a
spray nozzle disposed near a jet port of the after-air port for
supplying water, steam, or two fluids including water and steam to
the inside of the furnace; whereby the water, the steam, or the two
fluids including water and steam sprayed from the spray nozzle are
supplied to the inside of the furnace together with the combustion
air supplied from the after-air port.
2. The pulverized coal boiler according to claim 1, wherein a
plurality of after-air ports are disposed in the furnace in a
combustion gas flow direction; and at least one of the plurality of
after-air ports disposed upstream in the combustion gas flow
direction in the furnace supplies the water, the steam, or the two
fluids including water and steam to the inside of the furnace.
3. The pulverized coal boiler according to claim 2, wherein at
least one of the plurality of after-air ports disposed upstream in
the combustion gas flow direction in the furnace supplies
combustion air less than that of combustion air supplied from the
after-air ports disposed downstream in the combustion gas flow
direction.
4. The pulverized coal boiler according to claim 2, wherein each of
the after-air ports for supplying the water, the steam, or the two
fluids including water and steam is provided with a straight flow
path for jetting the combustion air as a straight flow, and a swirl
flow path formed around an outer circumference of the straight flow
path for jetting the combustion air as a swirl flow, internally;
and the water, the steam, or the two fluids including water and
steam are jetted from the swirl flow path.
5. The pulverized coal boiler according to claim 1, further
comprising: a NOx detector for detecting a NOx concentration of an
exhaust gas exhausted from the pulverized coal boiler; and a
controller for controlling a flow rate of the water, the steam, or
the two fluids including water and steam, which are supplied from
the spray nozzle to the inside of the furnace, based on the NOx
concentration detected by the NOx detector.
6. The pulverized coal boiler according to claim 1, further
comprising a controller for controlling a flow rate of the water,
the steam, or the two fluids including water and steam, which are
supplied from the spray nozzle to the inside of the furnace, based
on a load of the pulverized coal boiler.
7. The pulverized coal boiler according to claim 1, wherein a jet
port of the spray nozzle for supplying the water, the steam, or the
two fluids including water and steam into the inside of the furnace
is disposed upstream in a jet flow of combustion air jetted from
the jet port of the after-air port.
8. A pulverized coal boiler comprising a furnace, a burner provided
on a wall of the furnace for supplying pulverized coal to the
inside of the furnace and burning the pulverized coal, an after-air
port provided on the wall of the furnace at a position downstream
of the burner for supplying combustion air to the inside of the
furnace, a wind box for supplying the combustion air into the
after-air port, and a duct pipe for externally supplying the
combustion air into the wind box, the pulverized coal boiler
further comprising: a spray nozzle disposed in the wind box or in
the duct pipe for supplying water, steam, or two fluids including
water and steam; whereby the water, the steam, or the two fluids
including water and steam sprayed from the spray nozzle into the
inside of the wind box or the duct pipe are supplied to the inside
of the furnace together with the combustion air supplied from a jet
port of the after-air port.
9. The pulverized coal boiler according to claim 8, further
comprising: a NOx detector for detecting a NOx concentration of an
exhaust gas exhausted from the pulverized coal boiler; and a
controller for controlling a flow rate of the water, the steam, or
the two fluids including water and steam, which are supplied from
the spray nozzle to the inside of the furnace, based on the NOx
concentration detected by the NOx detector.
10. The pulverized coal boiler according to claim 8, further
comprising a controller for controlling a flow rate of the water,
the steam, or the two fluids including water and steam, which are
supplied from the spray nozzle to the inside of the furnace, based
on a load of the pulverized coal boiler.
Description
TECHNICAL FIELD
[0001] The present invention relates to a pulverized coal boiler
that uses pulverized coal as a fuel, more particularly to a
pulverized coal boiler that suppresses the generation of thermal
nitrogen oxides.
BACKGROUND ART
[0002] Pulverized coal boilers use the two-stage combustion method
because the concentrations of NOx generated during the combustion
of pulverized coal used as a fuel need to be reduced.
[0003] The two-stage combustion method is applied to pulverized
coal boilers in which pulverized coal burners are provided in the
furnace of the pulverized coal boiler and after-air ports are also
provided downstream of the burners, as disclosed in Japanese Patent
Laid-open No. Hei 6(1994)-201105; pulverized coal used as a fuel
and combustion air is supplied from the burners, and combustion air
is supplied from the after-air ports.
[0004] Specifically, for the combustion in the burner section,
combustion air is supplied from the burners by an amount by which
the theoretical stoichiometric ratio necessary for complete
combustion of the pulverized coal used as a fuel is not exceeded,
the combustion air being supplied together with the pulverized coal
as a fuel gas; the pulverized coal included in the fuel gas is
burnt in a state in which air is insufficient in the furnace so
that a reducing atmosphere is created, and NOx generated during the
combustion is reduced to nitrogen to suppress the generation of
NOx.
[0005] In the reducing atmosphere, unburnt pulverized coal is left
in the fuel gas supplied from the burners into the furnace due to
the oxygen insufficiency, generating CO (carbon monoxide). To
completely burn the unburnt pulverized coal and CO generated in the
reducing atmosphere, combustion air is supplied from the after-air
ports located downstream of the burners to the furnace by an amount
a little more than the amount of air equivalent to an insufficiency
relative to the theoretical stoichiometric ratio, so that the
unburnt pulverized coal and CO are burnt to reduce the generation
of NOx and CO.
[0006] The combustion gas resulting from the combustion of the
pulverized coal included in the fuel is directed down in the
furnace so that the combustion gas exchanges heat with a heat
exchanger (not shown) installed in the furnace to extract heat from
the combustion gas; the combustion gas is then cooled and expelled
from the furnace to the outside of the pulverized coal boiler as an
exhaust gas.
[0007] NOx gases generated in boilers are broadly classified into
fuel NOx and thermal NOx. Fuel NOx is generated when nitrogen
compounds included in coal used as a fuel are oxidized. This type
of fuel NOx is substantially reduced by improved technologies
applied to combustion in burners. Thermal NOx is generated when
nitrogen included in the air is oxidized at high temperature.
[0008] As fuel NOx has been reduced, the amount of thermal NOx
generated can be no longer neglected in recent years. To further
reduce NOx, thermal NOx must be reduced.
[0009] Japanese Patent Laid-open No. 2003-322310 discloses a
technology for reducing thermal NOx, in which retractable and
insertable spray nozzles, each of which has a driving unit, are
inserted from the wall of the furnace at the central part of the
furnace, at which combustion temperature is high and a high thermal
load is applied, the center part being located above the topmost
burner and below a secondary super heater; water or steam is
sprayed from the spray nozzles toward the central part of the
furnace to lower the flame temperature of the combustion gas.
[0010] Patent Document 1: Japanese Patent Laid-open No. Hei
6(1994)-201105
[0011] Patent Document 2: Japanese Patent Laid-open No.
2003-322310
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0012] In the technology disclosed in Japanese Patent Laid-open No.
2003-322310, however, water or steam is sprayed from the
retractable and insertable spray nozzles provided on the wall of
the furnace toward the central part of the furnace, at which the
combustion temperature is high and the thermal load is high, to
lower the flame temperature, as described above. In a method in
which spray nozzles with a structure of this type are provided on
the wall of the furnace, however, the area at high temperature
where thermal NOx is generated is variable due to the load
condition of the boiler, so it is difficult to lower the flame
temperature by reliably spraying water or steam at the area where
the flame temperature is high unless many spray nozzles are
provided on the furnace wall. Accordingly, it is difficult to
sufficiently lower thermal NOx.
[0013] Since it is also necessary to have the spray nozzle include
the driving unit for retracting and inserting the spray nozzle
through which water or steam is supplied, the structure of the
spray nozzle becomes complex, increasing costs for the maintenance
and other services for the unit. It is also conceivable in terms of
reliability that if the spray nozzle is kept inserted into the
inside of the furnace for a long period of time, the spray nozzle
may not withstand prolonged use due to ash adhering to the spray
nozzle and structural member deformation caused by a contact with
the combustion gas at high temperature.
[0014] An object of the present invention is to provide a highly
reliable pulverized coal boiler that ensures suppression of a rise
in flame temperature caused during the combustion of an unburnt gas
in a furnace when combustion air is supplied from after-air ports
so as to reduce the concentration of thermal NOx generated during
the combustion.
Means for Solving the Problems
[0015] A pulverized coal boiler according to the present invention
comprising a furnace, a burner provided on the wall of the furnace
for supplying pulverized coal to the inside of the furnace and
burning the pulverized coal, and an after-air port provided on the
wall of the furnace at a position downstream of the burner for
supplying combustion air to the inside of the furnace, the
pulverized coal boiler further comprising: a spray nozzle disposed
near a jet port of the after-air port for supplying water, steam,
or two fluids including water and steam to the inside of the
furnace; whereby the water, the steam, or the two fluids including
water and steam sprayed from the spray nozzle are supplied to the
inside of the furnace together with the combustion air supplied
from the after-air port.
[0016] A pulverized coal boiler according to the present invention
comprising a furnace, a burner provided on a wall of the furnace
for supplying pulverized coal to the inside of the furnace and
burning the pulverized coal, and an after-air port provided on the
wall of the furnace at a position downstream of the burner for
supplying combustion air to the inside of the furnace, wherein a
plurality of after-air ports are disposed in the furnace in a
combustion gas flow direction; and at least one of the plurality of
after-air ports disposed upstream in the combustion gas flow
direction in the furnace supplies the water, the steam, or the two
fluids including water and steam to the inside of the furnace.
[0017] In the pulverized coal boiler according to the present
invention, wherein at least one of the plurality of after-air ports
disposed upstream in the combustion gas flow direction in the
furnace supplies combustion air less than that of combustion air
supplied from the after-air ports disposed downstream in the
combustion gas flow direction.
[0018] In the pulverized coal boiler according to the present
invention, wherein each of the after-air ports for supplying the
water, the steam, or the two fluids including water and steam is
provided with a straight flow path for jetting the combustion air
as a straight flow, and a swirl flow path formed around an outer
circumference of the straight flow path for jetting the combustion
air as a swirl flow, internally; and the water, the steam, or the
two fluids including water and steam are jetted from the swirl flow
path.
[0019] A pulverized coal boiler according to the present invention
comprising a furnace, burners provided on a wall of the furnace for
supplying pulverized coal to the inside of the furnace and burning
the pulverized coal, an after-air port provided on the wall of the
furnace at a position downstream of the burner for supplying
combustion air to the inside of the furnace, a wind box having the
after-air port, and a duct pipe for externally supplying the
combustion air into the wind box,
[0020] the pulverized coal boiler further comprising:
[0021] a spray nozzle disposed in the wind box or in the duct pipe
for supplying water, steam, or the two fluids including water and
steam; whereby the water, the steam, or the two fluids including
water and steam sprayed from the spray nozzle into the inside of
the wind box or the duct pipe are supplied to the inside of the
furnace together with the combustion air supplied from a jet port
of the after-air port.
Effects of the Invention
[0022] The present invention can achieve a highly reliable
pulverized coal boiler that ensures suppression of a rise in flame
temperature caused during the combustion of an unburnt gas in a
furnace when combustion air is supplied from after-air ports so as
to reduce the concentration of thermal NOx generated during the
combustion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic diagram indicating the structure of a
pulverized coal boiler in an embodiment of the present
invention.
[0024] FIG. 2 is a cross sectional view showing the structure of an
after-air port having a spray nozzle, the after-air port being
applied to the pulverized coal boiler in the embodiment shown in
FIG. 1.
[0025] FIG. 3 shows the cross section of the after-air port having
a spray nozzle, as viewed along line A-A in FIG. 2.
[0026] FIG. 4 shows an exemplary spray pattern of the spray nozzle
disposed in the after-air port shown in FIG. 2.
[0027] FIG. 5 is a cross sectional view showing the structure of
another after-air port having spray nozzles, the after-air port
being applied to the pulverized coal boiler in the embodiment shown
in FIG. 1.
[0028] FIG. 6 shows the cross section of the after-air port having
spray nozzles, as viewed along line B-B in FIG. 5.
[0029] FIG. 7 is also a cross sectional view showing the structure
of other after-air port having spray nozzles, the after-air port
being applied to the pulverized coal boiler in the embodiment shown
in FIG. 1.
[0030] FIG. 8 shows the cross section of the after-air port having
spray nozzles, as viewed along line C-C in FIG. 7.
[0031] FIG. 9 is also a cross sectional view showing the structure
of other after-air port having spray nozzles, the after-air port
being applied to the pulverized coal boiler in the embodiment shown
in FIG. 1.
[0032] FIG. 10 is also a cross sectional view showing the structure
of other after-air port having spray nozzles, the after-air port
being applied to the pulverized coal boiler in the embodiment shown
in FIG. 1.
[0033] FIG. 11 is a schematic diagram indicating the structure of a
pulverized coal boiler in another embodiment of the present
invention.
[0034] FIG. 12 is also a schematic diagram indicating the structure
of a pulverized coal boiler in other embodiment of the present
invention.
[0035] FIG. 13 is a cross sectional view of a wind box, which has
spray nozzles, applied to the pulverized coal boiler in another
embodiment shown in FIG. 12.
[0036] FIG. 14 is the cross section of the wind box having spray
nozzles, as viewed along line D-D in FIG. 13.
[0037] FIG. 15 is a block diagram showing the structure of a
controller disposed in the pulverized coal boiler in the embodiment
shown in FIG. 1 of the present invention to control the amount of
cooling fluid sprayed.
[0038] FIGS. 16A and 16B are graphs indicating characteristics for
controlling a valve that adjusts the flow rate of the cooling fluid
in the controller shown in FIG. 15. FIG. 16A shows a relation ship
between the NOx concentration of an exhaust gas and the opening of
the valve. FIG. 16B shows a relationship between a boiler load and
the opening of the valve.
[0039] FIG. 17 is a schematic diagram indicating the structure of a
pulverized coal boiler in other embodiment of the present
invention.
[0040] FIG. 18 is also a schematic diagram indicating the structure
of a pulverized coal boiler in other embodiment of the present
invention.
LEGENDS
[0041] 1: Furnace, 2: Burner, 3: After-air port, 3a: Opening of the
after-air port, 4: Wind box of the burner, 5, 5a: Wind box of the
after-air port, 6: Spray nozzle, 7: Mill, 8, 9: Damper, 10:
Combustion gas, 10a: Unburnt gas, 11: Exhaust gas, 12: Blower, 13:
Heat exchanger, 14: Duct pipe, 15: Chimney, 16: Pump, 17, 22:
Valve, 18: Water, 18a: Spray range, 20: Steam, 21: Steam tank, 30:
Straight flow path, 31: Swirl flow path, 33, 34: Damper, 40: Jet
flow, 41: Mixed area, 42, 43: Pipe, 50: Controller, 51: Boiler load
setting unit, 52: NOx concentration setting unit, 53: Spray amount
calculator, 55: NOx detector, 60: sub after-air port, 61: main
after-air port, 100: Pulverized coal boiler.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Next, a pulverized coal boiler in an embodiment of the
present invention will be described with reference to the
drawings.
First Embodiment
[0043] FIG. 1 is a schematic diagram indicating the structure of a
pulverized coal boiler, in a first embodiment of the present
invention, that burns pulverized coal used as a fuel. The
pulverized coal boiler 100 comprises, on the wall of a furnace 1,
burners 2, and after-air ports 3, each of which has a spray nozzle
6 for spraying water, to supply combustion air.
[0044] In the pulverized coal boiler 100 in the embodiment in FIG.
1, the spray nozzle 6, which is a single-fluid nozzle, is disposed
on the after-air port 3.
[0045] The pulverized coal boiler 100 in FIG. 1 has a furnace 1, on
the wall of which a plurality of burners 2 are disposed; a fuel
gas, in which pulverized coal used as a fuel and combustion air are
mixed, is supplied from the plurality of burners 2.
[0046] The burners 2 supply the combustion air by an amount by
which the theoretical stoichiometric ratio necessary for complete
combustion of the pulverized coal used as a fuel is not exceeded,
the combustion air being supplied together with the pulverized coal
as a fuel gas to the inside of the furnace 1; the fuel gas is burnt
in a state in which there is an insufficient amount of air in the
furnace so that a reducing atmosphere is created, and NOx generated
during the combustion is reduced to nitrogen to suppress the
generation of NOx.
[0047] A plurality of after-air ports 3 are provided at positions
downstream of the burners 2 on the wall of the furnace 1.
[0048] Part of the fuel gas supplied from the burners 2 to the
inside of the furnace 1 is left as an unburnt gas 10a, which has
not been burnt due to the insufficient oxygen in the reducing
atmosphere. To completely burn the unburnt gas 10a and CO generated
in the reducing atmosphere, combustion air is supplied from the
after-air ports 3 to the inside of the furnace 1 by an amount a
little more than the amount of air equivalent to an insufficiency
relative to the theoretical stoichiometric ratio, so that the
pulverized coal included in the unburnt gas 10a and CO are burnt to
reduce the generation of NOx and CO.
[0049] Coal used as a fuel in the pulverized coal boiler 100 is
crushed into powder by a plurality of mills 7, resulting in
pulverized coal. The pulverized coal is then supplied through pipes
7b to the burners 2, and further supplied from the burners 2 to the
inside of the furnace 1 together with combustion air supplied by a
blower 12 through a duct. pipe 14, as a fuel gas, and the fuel gas
is burnt therein.
[0050] The combustion air for burning the unburnt gas 10a, which is
part of the fuel gas supplied from the burners 2 to the inside of
the furnace 1 and left unburnt, is externally supplied by the
blower 12 to a heat exchanger 13, where a heat exchange occurs
between the combustion air and hot exhaust gas 11 exhausted from
the furnace 1, heating the combustion air to about 300.degree. C.
The heated combustion air is then supplied to the after-air ports 3
through the duct pipe 14.
[0051] Part of the hot air resulting from the heat exchange is
adjusted for the amount to be apportioned by dampers 8 disposed at
intermediate points on the duct pipe 14. The apportioned air is
supplied to each wind box 4, which is provided on the wall of the
furnace 1 and internally includes burners 2, and further supplied
from the wind box 4 to the inside of the furnace 1 as outer
circumferential air of the burners 2.
[0052] Another part of the hot air is also adjusted for the amount
to be apportioned by dampers 9. The apportioned air is supplied to
a wind box 5, which is provided on the wall of the furnace 1 and
internally includes the after-air port 3, and further supplied from
the wind box 5 through the after-air port 3 to the inside of the
furnace 1 as the combustion air, as described above.
[0053] A combustion gas 10 resulting from the combustion of the
pulverized coal included in the furnace 1 flows in the furnace 1
toward the downstream side and is exhausted through a pipe 14b to
the outside of the furnace 1, as an exhaust gas 11. Since the heat
exchanger 13 is disposed in the pipe 14b, a heat exchange occurs in
the heat exchanger 13 between the exhaust gas 11 and the combustion
air. Denitrification and desulfurization (not shown) are then
performed for the combustion air, after which the exhaust gas 11 is
released from a chimney 15 with which the pipe 14b connects.
[0054] The spray nozzle 6 is disposed in the after-air port 3
provided on the wall of the furnace 1. Water 18, which is a cooling
fluid for suppressing the generation of thermal NOx during the
combustion of the combustion gas, is supplied from a pump 16
through a pipe 42 to the spray nozzle 6.
[0055] The flow rate of the water 18 (cooling fluid) to be sprayed
from the spray nozzle 6 toward the inside of the furnace 1 is
adjusted based on the NOx concentration of the exhaust gas 11, the
NOx concentration being detected by a NOx detector 55 provided in
the pipe 14b though which the exhaust gas 11 from the furnace 1 is
exhausted to the outside.
[0056] Specifically, a NOx concentration signal about the exhaust
gas 11 detected by the NOx detector 55 is input to a controller 50.
The controller 50 then compares the NOx concentration with a
desired NOx setting, calculates a flow rate command signal about
the cooling fluid to be sprayed from the spray nozzles 6 toward the
inside of the furnace 1 so that the NOx concentration of the
exhaust gas 11 is maintained at the desired setting, and outputs
the command signal to a valve 17 used for flow rate adjustment,
which is provided in a pipe 42, through which the water 18 (cooling
fluid) is supplied to the spray nozzles 6.
[0057] If the NOx detector 55 detects, from the exhaust gas 11, a
higher NOx value than the desired setting, the opening of the valve
17 is adjusted in response to the flow rate command signal
calculated by the controller 50 to raise the flow rate of the water
18 (cooling fluid) to be supplied from the spray nozzles 6, so that
a rise in the flame temperature is suppressed and NOx is
reduced.
[0058] If the NOx detector 55 detects, from the exhaust gas 11, a
lower NOx value than the desired setting, the opening of the valve
17 is adjusted in response to the flow rate command signal
calculated by the controller 50 to lower the flow rate of the water
18 (cooling fluid) or the supply of the water 18 is stopped, so
that an appropriate amount of water is sprayed from the spray
nozzle 6 and an efficient operation is performed.
[0059] In addition to responding to the NOx concentration of the
exhaust gas 11, the flow rate of the water 18 (cooling fluid) to be
sprayed from the spray nozzles 6 toward the inside of the furnace 1
may be controlled based on the load of the pulverized coal boiler
100.
[0060] In this case, the load of the pulverized coal boiler 100 is
structured so that the flow rate of the water 18 (cooling fluid) to
be sprayed from the spray nozzles 6 toward the inside of the
furnace 1 is adjusted based on a boiler load signal commanded from
a control room.
[0061] Specifically, the boiler load signal commanded from the
control room is entered to the controller 50, and then the
controller 50 calculates a flow rate command signal about the
cooling fluid to be sprayed from the spray nozzles 6 toward the
inside of the furnace 1. The command signal is output from the
controller 50 to the valve 17, used for flow rate adjustment, which
is disposed on the pipe 42 for supplying the cooling fluid to the
spray nozzles 6 so that the flow rate of the cooling fluid is
adjusted.
[0062] The flow rate of the water 18 (cooling fluid) to be sprayed
from the spray nozzles 6 is adjusted so that if the load of the
pulverized coal boiler 100 is low, the opening of the valve 17 is
adjusted to lower the flow rate of the water 18, or if the load is
high, the opening is adjusted to raise the flow rate of the water
18. Then, it becomes possible to spray an appropriate amount of
cooling fluid and perform an efficient operation.
[0063] The structure of the controller 50, which calculates the
flow rate command signal about the cooling fluid to be sprayed from
the spray nozzles 6 and outputs a command signal about a valve
opening to the valve 17 to control the flow rate of the cooling
fluid, will be described below. FIG. 15 is a block diagram showing
the structure of the controller 50. As shown in the drawing, the
controller 50 includes a spray amount calculator 53 to which the
boiler load signal and the NOx detection value of the exhaust gas
11, which is detected by the NOx detector 55, are input.
[0064] The controller 50 also includes a boiler load setting unit
51 for setting an operation load for the boiler and a NOx
concentration setting unit 52 for setting a NOx concentration.
[0065] The spray amount calculator 53 in the controller 50 compares
the boiler load signal with the load setting (threshold) in the
boiler load setting unit 51. If the detected value exceeds the
setting, the spray amount calculator 53 calculates the flow rate of
the water 18 (cooling fluid) that corresponds to the difference
between the setting and detected value, and outputs an opening of
the valve 17, which corresponds to the calculated spray amount, to
the valve 17 as a command signal so that the flow rate of the water
18 to be sprayed from the spray nozzles 6 toward the inside of the
furnace 1 is adjusted.
[0066] Similarly, the spray amount calculator 53 in the controller
50 compares the NOx detection signal, detected by the NOx detector
55, about the exhaust gas 11 with a NOx setting (threshold) in the
NOx concentration setting unit 52. If the detected value exceeds
the setting, the spray amount calculator 53 calculates the flow
rate of the water 18 (cooling fluid) that corresponds to the
difference between the setting and detected value, and outputs an
opening of the valve 17, which corresponds to the calculated spray
amount, to the valve 17 as a command signal so that the flow rate
of the water 18 to be sprayed from the spray nozzles 6 toward the
inside of the furnace 1 is adjusted.
[0067] The opening of the valve 17 operated by the controller 50 to
adjust the flow rate of the water 18 to be sprayed will be
described below. FIGS. 16A and 16B are graphs indicating
characteristics for controlling the valve that adjusts the flow
rate of the cooling fluid. In FIG. 16A, the vertical axis indicates
the detected NOx concentration of the exhaust gas 11, and the
horizontal axis indicates the opening of the valve 17, while the
dashed line indicates a setting and the solid line indicates
opening characteristics of the valve 17 with respect to the
detected NOx concentration.
[0068] In FIG. 16B, the vertical axis indicates the boiler load and
the horizontal axis indicates the opening of the valve 17, while
the dashed line indicates a setting and the solid line indicates
the opening characteristics of the valve 17 with respect to the
boiler load.
[0069] As seen from the characteristic chart in FIG. 16A, if the
value of the detected NOx concentration of the exhaust gas 11 is
lowered to or below the setting (an NOx emission standard, for
example) as a result of control by the controller 50, the opening
of the valve 17 is set to 0 (closed) to stop the water from being
sprayed from the spray nozzles 6. If the value of the detected NOx
concentration exceeds the setting, the valve 17 is opened based on
the opening of the valve 17, which corresponds to a calculated
spray amount based on a difference from the setting, so that the
spray of the water from the spray nozzles 6 is controlled.
Although, in the drawing, there is a proportional relationship
between the NOx concentration and the opening of the valve 17, this
is not a limitation.
[0070] Similarly, as seen from the characteristic chart in FIG.
16B, when the boiler load is lowered due to control by the
controller 50, the opening of the valve 17 is set to 0 (closed) to
stop the water from being sprayed from the spray nozzles 6 because
the amount of NOx emissions is originally small. As the boiler load
is increased and brought close to a rated load, the amount of NOx
emissions also increases. Accordingly, as the boiler load
increases, the water spray from the spray nozzles 6 is controlled
by opening the valve 17 based on the opening of the valve 17, which
corresponds to a calculated spray amount based on a difference from
the setting. Although, in the drawing, there is a proportional
relationship between the NOx concentration and the opening of the
valve 17, this is not a limitation.
[0071] Even when the boiler load is high, if the NOx concentration
of the exhaust gas is lower than or equal to the setting (emission
standard) shown in FIG. 16A, there is no need to reduce the NOx
concentration to a lower value than necessary by further spraying
water from the spray nozzles 6.
[0072] Accordingly, when the boiler load is raised (near the
rating) due to control by the controller 50 and the NOx
concentration of the exhaust gas is high, if water is sprayed from
the spray nozzles 6, the boiler can be operated in an efficient
manner.
[0073] Next, the after-air port 3 used in the pulverized coal
boiler in this embodiment of the present invention will be
described in detail.
[0074] FIG. 2 is an enlarged view showing part of the structure of
the after-air port 3, which has a spray nozzle, the after-air port
3 being used in the pulverized coal boiler, shown in FIG. 1, in
this embodiment of the present invention. In FIG. 2, the after-air
port 3 in this embodiment is provided on the wind box 5 at one end;
at the other end, the after-air port 3 has a straight flow path 30,
which is cylindrical and communicates with an opening 3a of the
after-air port 3, which is formed in the wall of the furnace 1.
[0075] The after-air port 3 also has a swirl flow path 31, which
has a truncated cone shape, on the outer circumference of the
straight flow path 30; an end of the swirl flow path 31 is
connected to the wall of the furnace 1, forming an external edge of
the opening 3a of the after-air port 3.
[0076] A straight flow 35, which is part of the combustion air, is
led from a hole formed in the barrel of the straight flow path 30
to the inside of the straight flow path 30, and supplied from an
opening at the end of the straight flow path 30 to the inside of
the furnace 1.
[0077] A swirl flow 36, which is also part of the combustion air,
is adjusted for its swirl intensity by means of a register 32
provided in the swirl flow path 31, which has a truncated cone
shape and is formed around the outer circumference of the straight
flow path 30, and supplied from the opening at the end of the swirl
flow path 31 to the inside of the furnace 1.
[0078] A movable damper 33 is provided outside the hole formed in
the barrel of the straight flow path 30, and another movable damper
34 is also provided upstream of the swirl flow path 31. The
apportionment of the flow rate of the combustion air flowing down
in the straight flow path 30 is adjusted by operating the damper
33. Similarly, the apportionment of the flow rate of the combustion
air flowing down in the swirl flow path 31 is adjusted by operating
the damper 34.
[0079] The spray nozzle 6 is disposed in the jet port at the end of
the cylindrical straight flow path 30 formed in the after-air port
3. The spray nozzle 6 is placed along the center of the axis of the
straight flow path 30 so that the end of the spray nozzle 6 is
positioned near the opening 3a of the after-air port 3. The water
18 (cooling fluid) is sprayed from the end of the spray nozzle 6
toward the inside of the furnace 1 to suppress NOx generation.
[0080] When the water 18 (cooling fluid) is sprayed from the spray
nozzle 6 toward the inside of the furnace 1, the effect of
suppressing NOx generation is obtained as described below.
[0081] A jet flow 40 of combustion air is formed in the inside of
the furnace 1, the inside communicating with the opening 3a of the
after-air port 3; the jet flow 40 spreads from the opening 3a
toward the center of the furnace 1, as shown in FIG. 2, by the
combustion air supplied from the straight flow path 30 and swirl
flow path 31 formed in the after-air port 3.
[0082] When the jet flow 40 of combustion air is supplied from the
straight flow path 30 and swirl flow path 31 through the opening 3a
of the after-air port 3 to the inside of the furnace 1, the jet
flow 40 is mixed with the unburnt gas 10a, including unburnt
pulverized coal, which flows down from the burners 2 to the
after-air port 3 on the downstream side in the inside of the
furnace 1, together with the combustion gas 10, forming a mixed
area 41 along the outer edge of the jet flow 40 of combustion
air.
[0083] In the mixed area 41, the unburnt gas 10a is burnt as a
result of mixing the combustion air supplied as the jet flow 40 and
the unburnt gas 10a; when the temperature of a generated flame
rises, thermal NOx is generated.
[0084] The amount of thermal NOx generated is univocally determined
by the flame temperature. When the flame temperature reaches about
1700K, the generation of thermal NOx starts. The amount of thermal
NOx generated is approximately proportional to the square of the
flame temperature rise; the higher the temperature is, the more the
amount of generation increases significantly.
[0085] Accordingly, in this embodiment, the water 18 (a cooling
fluid), which has been led through the pipe 42 from the spray
nozzle 6 disposed near the opening 3a of the after-air port 3, is
sprayed in a spray range 18a that overlaps the mixed area 41. The
latent heat and sensible heat of the water 18 sprayed in the spray
area 18a overlapping the mixed area 41 deprive the heat of the
flame resulting from the combustion of the unburnt gas 10a in the
mixed area 41, suppressing the flame temperature from rising. The
generation of thermal NOx can then be reduced in the mixed area 41
in which thermal NOx is most easily generated.
[0086] According to this embodiment, the water 18 can be sprayed
with precision in the spray area 18a overlapping the mixed area 41
from the spray nozzle 6, so it is possible to suppress the flame
temperature of the unburnt gas 10a burnt in the mixed area 41 to
about 1600K or below, preferably about 1600K to about 1400K. The
concentration of NOx generated in the boiler can thereby be reduced
by about 10% to 30%.
[0087] Since the spray nozzle 6 in this embodiment is disposed near
the opening 3a of the after-air port 3, it becomes possible to
prevent ash from adhering to the spray nozzle and the structural
members from being deformed due to contact with the combustion gas
at high temperature and thereby obtain a highly reliable spray
nozzle that can withstand prolonged use.
[0088] The water 18 (cooling fluid) is sprayed in the spray area
18a, from the spray nozzle 6 toward the mixed area 41 formed in the
furnace 1, as described above. To have the water 18 precisely
sprayed in the spray area 18a overlapping the mixed area 41, where
the water 18 is mixed with the unburnt gas 10a, according to the
spread and shape of the jet flow 40 of combustion air supplied from
the after-air port 3, the spray nozzle 6 may be structured so that
it can be turned and move fore and aft in the axial direction.
[0089] FIG. 3 shows the opening 3a of the after-air port 3 having
the spray nozzle 6, as viewed along line A-A in FIG. 2. In FIG. 3,
the water 18 (cooling fluid) is sprayed so that it spreads
concentrically from the spray nozzle 6, as one form of the spray
range 18a overlapping the mixed area 41, where the jet flow 40 of
combustion air supplied from the opening 3a of the after-air port 3
shown in FIG. 2 is mixed with the unburnt gas 10a.
[0090] Even if, as another form of the spray range 18a, as shown in
FIG. 4, a spray pattern different from in FIG. 3 is used by
changing the shape of the end of the spray nozzle 6 so that the
water 18 is sprayed in a cone-like shape, the same effect is
obtained because the moisture of the water 18 (cooling fluid) is
supplied to the spray range 18a overlapping the mixed area 41,
where the jet flow 40 of combustion air and the unburnt gas 10a are
mixed, which is the area where NOx is generated.
[0091] The above embodiment in the present invention can achieve a
highly reliable pulverized coal boiler that ensures suppression of
a flame temperature rise that is caused during the combustion of an
unburnt gas in a furnace when combustion air is supplied from
after-air ports, so as to reduce the concentration of thermal NOx
generated during the combustion.
Second Embodiment
[0092] Next, FIGS. 5 and 6 show part of the structure of an
after-air port in another embodiment that is used in the pulverized
coal boiler shown in FIG. 1, which embodies the present
invention.
[0093] FIG. 5 shows the structure of the after-air port, having
spray nozzles, in the other embodiment. FIG. 6 shows a section as
viewed along line B-B in FIG. 5. A pulverized coal boiler in which
the after-air port 3 in this embodiment is used has the same
structure as the pulverized coal boiler 100 in the embodiment shown
in FIG. 1, so the explanation of the pulverized coal boiler
including the after-air port 3 in this embodiment will be
omitted.
[0094] The basic structure of the after-air port 3 in this
embodiment shown in FIGS. 5 and 6 is the same as the basic
structure of the after-air port 3 in the embodiment shown in FIGS.
2 to 4, so the explanation of the same basic structure will be
omitted and only different parts will be described.
[0095] In the after-air port 3 in this embodiment shown in FIGS. 5
and 6, in which spray nozzles used in the pulverized coal boiler
are included, a plurality of spray nozzles 6 are provided in the
opening in the swirl flow path 31, which is formed around the outer
circumference of the straight flow path 30. The end of each spray
nozzle 6 for spraying water (cooling fluid) is positioned near the
opening 3a of the after-air port 3, as in the structure of the
after-air port 3 shown in the embodiment shown in FIG. 2.
[0096] In the after-air port 3 in this embodiment as well, the
water 18 (cooling fluid) can be precisely sprayed from the spray
nozzles 6 in the spray range 18a overlapping the mixed area 41,
where the jet flow 40 of combustion air and the unburnt gas 10a are
mixed, the jet flow 40 being jetted from the after-air port 3 to
the inside of the furnace 1, the inside communicating with the
opening 3a of the after-air port 3.
[0097] Accordingly, in this embodiment, the latent heat and
sensible heat of the sprayed water 18 deprive the heat of the flame
resulting from the combustion of the unburnt gas 10a in the mixed
area 41, so it is possible to suppress the flame temperature to
about 1600K or below, preferably about 1600K to about 1400K. The
concentration of NOx generated in the boiler can thereby be reduced
by about 10% to 30%.
[0098] Since the spray nozzles 6 in this embodiment are also
disposed near the opening 3a of the after-air port 3, it becomes
possible to prevent ash from adhering to the spray nozzles and the
structural members from being deformed due to contact with the
combustion gas at high temperature and thereby obtain a highly
reliable spray nozzle that can withstand prolonged use.
Furthermore, since a plurality of spray nozzles are provided, even
if some of the plurality of spray nozzles are clogged, a necessary
amount of cooling fluid can still be sprayed by the remaining spray
nozzles, so it becomes possible to obtain highly reliable spray
nozzles that can withstand prolonged use.
Third Embodiment
[0099] Next, FIGS. 7 and 8 show part of the structure of an
after-air port in other embodiment that is used in the pulverized
coal boiler shown in FIG. 1, which embodies the present
invention.
[0100] FIG. 7 shows the structure of the after-air port, having
spray nozzles, in the other embodiment. FIG. 8 shows a section as
viewed along line C-C in FIG. 7. A pulverized coal boiler in which
the after-air port 3 in this embodiment is used has the same
structure as the pulverized coal boiler 100 in the embodiment shown
in FIG. 1, so the explanation of the pulverized coal boiler
including the after-air port 3 in this embodiment will be
omitted.
[0101] The basic structure of the after-air port 3 in this
embodiment shown in FIGS. 7 and 8 is the same as the basic
structure of the after-air port 3 in the embodiment shown in FIGS.
2 to 4, so the explanation of the same basic structure will be
omitted and only different parts will be described.
[0102] In the after-air port 3 in this embodiment shown in FIGS. 7
and 8, in which spray nozzles used in the pulverized coal boiler
are included, a plurality of spray nozzles 6 for spraying water
(cooling fluid) are provided in the opening inside the straight
flow path 30 and the opening in the swirl flow path 31, which is
formed around the outer circumference of the straight flow path 30.
The end of each spray nozzle 6 is positioned near the opening 3a of
the after-air port 3, as in the structure of the after-air port 3
shown in the embodiment shown in FIG. 2.
[0103] In the after-air port 3 in this embodiment as well, the
water 18 (cooling fluid) can be precisely and evenly sprayed from
the plurality of spray nozzles 6 in the spray range 18a overlapping
the mixed area 41, where the jet flow 40 of combustion air and the
unburnt gas 10a are mixed, the jet flow 40 being jetted from the
after-air port 3 to the inside of the furnace 1, the inside
communicating with the opening 3a of the after-air port 3.
[0104] Accordingly, in this embodiment, the latent heat and
sensible heat of the sprayed water 18 deprive the heat of the flame
resulting from the combustion of the unburnt gas 10a in the mixed
area 41, so it is possible to precisely suppress the flame
temperature to about 1600K or below, preferably about 1600K to
about 1400K. The concentration of NOx generated in the boiler can
thereby be reduced by about 10% to 30%.
[0105] Since the spray nozzles 6 in this embodiment are also
disposed near the opening 3a of the after-air port 3, it becomes
possible to prevent ash from adhering to the spray nozzles and the
structural members from being deformed due to contact with the
combustion gas at high temperature. Furthermore, since a plurality
of spray nozzle are provided, even if some of the plurality of
spray nozzles are clogged, a necessary amount of cooling fluid can
still be sprayed by the remaining spray nozzles, so it becomes
possible to obtain highly reliable spray nozzles that can withstand
prolonged use.
Fourth Embodiment
[0106] Next, FIGS. 9 and 10 show part of the structures of
after-air ports in other embodiments that are used in the
pulverized coal boiler shown in FIG. 1, which embodies the present
invention.
[0107] FIGS. 9 and 10 show the structures of the after-air ports,
having spray nozzles, in the other embodiments. Pulverized coal
boilers in which the after-air ports 3 in this embodiment are used
have the same structure as the pulverized coal boiler 100 in the
embodiment shown in FIG. 1, so the explanation of the pulverized
coal boilers including the after-air ports 3 in this embodiment
will be omitted.
[0108] The basic structure of the after-air ports 3 in this
embodiment shown in FIGS. 9 and 10 are the same as the basic
structure of the after-air ports 3 in the embodiments shown in
FIGS. 5 and 7, so the explanation of the same basic structure will
be omitted and only different parts will be described.
[0109] In FIGS. 9 and 10, each spray nozzle 6, included in the
after-air port 3 in each embodiment, from which the water 18
(cooling fluid) is sprayed, is disposed so that the end of the
spray nozzle 6 is positioned near the wall of the wind box 5 rather
than the opening 3a of the after-air port 3 to leave a distance
from the furnace 1; the end of the spray nozzle 6 is located, in
the after-air port 3, at an upstream position of the jet flow 40 of
combustion air, relative to the opening 3a of the after-air port
3.
[0110] According to this embodiment, the water 18 (cooling fluid)
is sprayed from each spray nozzle 6 at an upstream position of the
jet flow 40 of combustion air supplied from the opening 3a of the
after-air port 3 into the inside of the furnace 1, and vaporized so
that moisture is further evenly mixed with the jet flow 40 of
combustion air supplied from the after-air port 3, adding the
moisture to the jet flow 40 itself of the combustion air supplied
from the after-air port 3. Accordingly, the moisture can be more
precisely supplied to the spray range 18a overlapping the mixed
area 41, where the jet flow 40 and the unburnt gas 10a are mixed,
and thereby a rise in flame temperature can be more surely
suppressed.
[0111] Although the spray nozzles 6 disposed in the after-air ports
3 in this embodiment have been indicated as one-fluid spray nozzles
that spray the water 18 as the cooling fluid, the embodiment can
also be applied to a two-fluid spray nozzle that sprays a cooling
liquid including water 18 and steam 20.
[0112] Although not described, control of the cooling fluid by the
spray nozzles 6 in the after-air ports 3 in this embodiment, shown
in FIGS. 9 and 10, can be carried out by having the controller 50
adjust the flow rate of the cooling fluid as in the embodiments
described above.
[0113] The above embodiments in the present invention can also
achieve a highly reliable pulverized coal boiler that ensures
suppression of a flame temperature rise that is caused during the
combustion of an unburnt gas in a furnace when combustion air is
supplied from after-air ports so as to reduce the concentration of
thermal NOx generated during the combustion.
Fifth Embodiment
[0114] Next, a pulverized coal boiler in another embodiment of the
present invention will be described with reference to the
drawings.
[0115] FIG. 11 is a schematic diagram indicating the structure of a
pulverized coal boiler 100 in another embodiment of the present
invention. The pulverized coal boiler 100 comprises, on the wall of
a furnace 1, burners 2 for burning pulverized coal used as a fuel
and after-air ports 3, each of which has a spray nozzle 6 for
spraying both water and steam.
[0116] The basic structure of the pulverized coal boiler in this
embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown in FIG. 1, so the
explanation of the same basic structure will be omitted and only
different parts will be described.
[0117] In the pulverized coal boiler 100 in this embodiment shown
in FIG. 11, a two-fluid nozzle, which can spray two fluids
including water 18 and steam 20 is used as the spray nozzle 6
disposed in the after-air port 3.
[0118] A system for supplying the water 18 to the spray nozzles 6,
each of which sprays the two fluids including water 18 and steam 20
as the cooling fluid uses the same the pipe 42 and the valve 17 as
shown in FIG. 1.
[0119] A system for supplying the steam 20 to the spray nozzles 6,
each of which sprays the two fluids, has a steam tank 21 to which
part of steam used in a power generation plant is supplied for
storage purposes, the pressure in the steam tank 21 being set to a
prescribed value. The system also has a pipe 43 through which the
steam 20 stored in the steam tank 21 is supplied to the spray
nozzles 6, a valve 22 for adjusting the flow rate of the steam 20
supplied is provided on the pipe 43.
[0120] The opening of the valve 22, which adjusts the flow rate of
the steam 20 sprayed from the two-fluid spray nozzles 6 into the
inside of the furnace 1, is controlled by the controller 50.
Specifically, as with control of the opening of the valve 17 for
adjusting the amount of spray of the water 18, the spray amount
calculator 53 in the controller 50 compares a boiler load and the
NOx emission concentration of the exhaust gas 11, which is detected
by the NOx detector 55, with the setting in the boiler load setting
unit 51 and the setting in the NOx concentration setting unit 52,
respectively. Then, the spray amount calculator 53 calculates the
amount of the steam 20 that needs to be supplied. The opening of
the valve 22 that corresponds to the amount of steam is commanded
as an opening signal by the spray amount calculator 53 in the
controller 50 for the valve 22 so that the necessary amount of
steam 20 is sprayed from the spray nozzles 6.
[0121] The steam 20 is sprayed from the two-fluid spray nozzle 6
toward the inside of the furnace 1 in a form similar to the spray
range 18a, which overlaps mixed area 41, extending from the spray
nozzle 6 shown in FIGS. 2 to 4.
[0122] The opening of the valve 22 is controlled by the controller
50 in the same way as the opening of the valve 17 is controlled by
the controller 50 as shown in FIGS. 16A and 16B.
[0123] Due to the above arrangement in this embodiment, the flow
rate of the steam 20 sprayed from the spray nozzles 6, which spray
two fluids including water 18 and steam 20 can follow a change in
the flow rate of the water 18 sprayed.
[0124] Accordingly, when the two-fluid spray nozzle 6 in this
embodiment is used, droplets of the cooling fluid sprayed toward
the inside of the furnace 1 become finer and evaporation of the
water is facilitated, quickly suppressing the rise in the flame
temperature.
[0125] The above embodiment in the present invention can also
achieve a highly reliable pulverized coal boiler that ensures
suppression of a flame temperature rise that is caused during the
combustion of an unburnt gas in a furnace when combustion air is
supplied from after-air ports so as to reduce the concentration of
thermal NOx generated during the combustion.
Sixth Embodiment
[0126] Next, a pulverized coal boiler in another embodiment of the
present invention will be described with reference to the
drawings.
[0127] FIG. 12 is a schematic diagram indicating the structure of a
pulverized coal boiler 100 in other embodiment of the present
invention. The pulverized coal boiler 100 comprises burners 2 for
burning pulverized coal used as a fuel, after-air ports 3 for
supplying combustion air, and spray nozzles 6 for spraying water
(cooling fluid) into the after-air ports 3.
[0128] The basic structure of the pulverized coal boiler in this
embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown in FIG. 1, so the
explanation of the same basic structure will be omitted and only
different parts will be described.
[0129] FIG. 13 shows the structure of the wind box 5, which
includes the after-air ports 3 used in the pulverized coal boiler
100 in the embodiment of the present invention shown in FIG. 12.
FIG. 14 shows a section as viewed along line D-D in FIG. 13.
[0130] In this embodiment, the spray nozzles 6 are provided on the
wall of the wind box 5 as shown in FIGS. 13 and 14. The water 18
(cooling fluid) is sprayed from the spray nozzles 6 toward the
spray range 18a in the wind box 5.
[0131] When combustion air is supplied from the opening 3a of each
after-air port 3 disposed in the wind box 5 into the inside of the
furnace 1 as the jet flow 40, the temperature of the combustion air
is about 300.degree. C. in the wind box 5, which is sufficiently
high for combustion air to vaporize the water 18 sprayed from the
spray nozzle 6 into the spray area 18a in the wind box 5.
[0132] After being vaporized in the wind box 5, the water 18 is
adequately and evenly mixed with the flow of combustion air in the
wind box 5, and the mixture of the water 18 and the flow of
combustion air is supplied, as part of the jet flow 40 of
combustion air, from the opening 3a of the after-air port 3 toward
the inside of the furnace 1. Then, the mixture is supplied to the
mixed area 41, where the jet flow 40 of combustion air and the
unburnt gas 10a are mixed, reducing the temperature of the flame in
the combustion of the unburnt gas 10a.
[0133] In this embodiment as well, the jet flow 40 of combustion
air, with which the water 18 (cooling fluid) sprayed from the spray
nozzle 6 into the wind box 5 and vaporized is mixed, can be
precisely and evenly sprayed in the mixed area 41, where the jet
flow 40 of combustion air and the unburnt gas 10a are mixed, the
jet flow 40 being jetted toward the inside of the furnace 1, the
inside communicating with the opening 3a of the after-air port
3.
[0134] Accordingly, in this embodiment, the latent heat and
sensible heat of the water 18 sprayed from the spray nozzle 6
deprive the heat of the flame resulting from the combustion of the
unburnt gas 10a in the mixed area 41, so it is possible to suppress
the flame temperature to about 1600K or below, preferably about
1600K to about 1400K. The concentration of NOx generated in the
boiler can thereby be reduced by about 10% to 30%.
[0135] In this embodiment, any spray pattern is allowed if the
water 18 (cooling fluid) sprayed from the spray nozzle 6 in the
wind box 5 is vaporized. It is not necessary that the sprayed water
18 is completely vaporized. The water 18 remaining in the wind box
5 without being vaporized may be collected as drain water and
reused.
[0136] According to this embodiment, since the water 18 sprayed
from the spray nozzle 6 is vaporized in the wind box 5 and moisture
is evenly mixed with the jet flow 40 itself supplied from the
after-air port 3 into the inside of the furnace 1, the moisture can
be precisely supplied to the mixed area 41, suppressing a flame
temperature rise that is caused during combustion in the mixed area
41.
[0137] Due to the evaporation of the sprayed moisture, the
temperature of the combustion air in the wind box 5 is lowered and
thereby the jet flow 40 itself supplied from the after-air port 3
into the inside of the furnace 1 becomes cold, more precisely
suppressing the flame temperature rise that is caused during
combustion in the mixed area 41.
[0138] Although a case in which the water 18 is used as the cooling
fluid sprayed from the spray nozzle 6 has been described in this
embodiment, the steam 20 or two fluids including the water and
steam may be sprayed instead of the water.
[0139] Although not described, control of the cooling fluid by the
spray nozzles 6 disposed in the wind boxes 5 in this embodiment can
be carried out by having the controller 50 adjust the flow rate of
the cooling fluid as in the embodiments described above.
[0140] The above embodiment in the present invention can also
achieve a highly reliable pulverized coal boiler that ensures
suppression of a flame temperature rise that is caused during the
combustion of an unburnt gas in a furnace when combustion air is
supplied from after-air ports so as to reduce the concentration of
thermal NOx generated during the combustion.
Seventh Embodiment
[0141] Next, a pulverized coal boiler in other embodiment of the
present invention will be described with reference to the
drawings.
[0142] FIG. 17 is a schematic diagram indicating the structure of a
pulverized coal boiler 100 in other embodiment of the present
invention. The pulverized coal boiler 100 comprises burners 2 for
burning pulverized coal used as a fuel, after-air ports 3 for
supplying combustion air, and spray nozzles 6 for spraying water
(cooling fluid) into a duct pipe 14 through which the combustion
air is supplied to the after-air ports 3.
[0143] The basic structure of the pulverized coal boiler in this
embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown in FIG. 1, so the
explanation of the same basic structure will be omitted and only
different parts will be described.
[0144] In this embodiment, the spray nozzles 6 are disposed in the
pipe 14 positioned further upstream than the wind boxes 5 through
which combustion air is supplied to the after-air ports 3, and the
water 18 (cooling fluid) is sprayed from these spray nozzles 6 to
the combustion air flowing in the pipe 14, so the sprayed water 18
is mixed with the combustion air. Accordingly, the water 18 stays
in the combustion air at high temperature, which is supplied to the
after-air ports 3, for an increased period of time.
[0145] As a result, the ratio of the vaporization of the water 18
sprayed from the spray nozzle 6 is increased and lessens drainage
water, and thereby the water 18 (cooling fluid) sprayed from the
spray nozzle 6 is more efficiently vaporized.
[0146] According to this embodiment, since the water 18 sprayed
from the spray nozzle 6 is vaporized in the pipe 14 disposed
upstream of the wind box 5 and moisture is evenly mixed with the
jet flow 40 itself supplied from the after-air port 3 into the
inside of the furnace 1, the moisture can be precisely supplied to
the mixed area 41, suppressing a flame temperature rise that is
caused during combustion in the mixed area 41.
[0147] Due to the evaporation of the sprayed moisture, the
temperature of the combustion air supplied to the inside of the
wind box 5 is lowered and thereby the jet flow 40 itself supplied
from the after-air port 3 into the inside of the furnace 1 becomes
cold, more precisely suppressing the flame temperature rise that is
caused during combustion in the mixed area 41.
[0148] Although a case in which the water 18 is used as the cooling
fluid sprayed from the spray nozzle 6 has been described in this
embodiment, the steam 20 or two fluids including the water and
steam may be sprayed instead of the water.
[0149] Although not described, control of the cooling fluid by the
spray nozzles 6 disposed in the wind boxes 5 in this embodiment can
be carried out by having the controller 50 adjust the flow rate of
the cooling fluid as in the embodiments described above.
[0150] Accordingly, in this embodiment, the latent heat and
sensible heat of the water 18 sprayed from the spray nozzle 6
deprive the heat of the flame resulting from the combustion of the
unburnt gas 10a in the mixed area 41, so it is possible to suppress
the flame temperature to about 1600K or below, preferably about
1600K to about 1400K. The concentration of NOx generated in the
boiler can thereby be reduced by about 10% to 30%.
[0151] The above embodiment in the present invention can also
achieve a highly reliable pulverized coal boiler that ensures
suppression of a flame temperature rise that is caused during the
combustion of an unburnt gas in a furnace when combustion air is
supplied from after-air ports so as to reduce the concentration of
thermal NOx generated during the combustion.
Eighth Embodiment
[0152] Next, a pulverized coal boiler in other embodiment of the
present invention will be described with reference to the
drawings.
[0153] FIG. 18 is a schematic diagram indicating the structure of a
pulverized coal boiler 100 in other embodiment of the present
invention. The pulverized coal boiler 100 comprises, on the wall of
the furnace 1, burners 2 for spraying and burning pulverized coal
used as a fuel, main after-air ports 61 for supplying combustion
air, and sub after-air ports 60, each of which has the spray nozzle
6 for spraying both water and steam to supply combustion air.
[0154] The basic structure of the pulverized coal boiler in this
embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown in FIG. 17, so the
explanation of the same basic structure will be omitted and only
different parts will be described.
[0155] On the wall of the furnace 1 in the pulverized coal boiler
100 in this embodiment shown in FIG. 18, the sub after-air ports 60
are disposed in the direction in which the combustion gas 10 flows
in the furnace 1 on the upstream side and main after-air ports 61
are disposed on the downstream side.
[0156] The sub-after port 60 has the spray nozzle 6, from which
water or both water and steam is sprayed.
[0157] In the pulverized coal boiler 100 in this embodiment, the
amount of air supplied from the sub after-air port 60 is smaller
than the amount of air supplied from the main after-air port
61.
[0158] In the pulverized coal boiler 100 structured as described
above, air sprayed from the sub-after ports 60 into the inside of
the furnace 1 flows as air flows 62 and air sprayed from the main
after-air ports 61 into the inside of the furnace 1 flows as air
flows 63, as schematically shown in FIG. 18.
[0159] The air flows 62 supplied from the sub-after ports 60 into
the inside of the furnace 1 by being sprayed are directed toward
the downstream side along the inner wall of the furnace 1 because
the amount of air sprayed is small.
[0160] The air flows 63 supplied from the main after ports 61 into
the inside of the furnace 1 by being sprayed reaches the central
part of the furnace 1 because the amount of air sprayed is
large.
[0161] While flowing from downstream to upstream in the furnace 1,
the combustion gas 10a is mixed with the air flows 62 and 63. Near
the wall of the furnace 1, the temperature of the combustion gas
10a mixed with the air flow 62 on the upstream side is higher than
the temperature of the combustion gas 10a mixed with the air flow
63 on the downstream side.
[0162] The temperature of the combustion gas 10a is highest at the
central part of the furnace 1 because it is distant from the
wall.
[0163] When the hot combustion gas 10a including the unburnt gas is
mixed with the supplied air, a combustion reaction proceeds and the
temperature of the mixture of the combustion gas 10a and the
supplied air is raised. At that time, nitrogen gas in the air or
the combustion gas 10a is oxidized in a hot oxidization atmosphere,
generating nitrogen oxides (NOx), which is so-called thermal NOx.
The higher the temperature is, the more thermal NOx is
generated.
[0164] Since the pulverized coal boiler 100 in this embodiment is
structured so that water is sprayed from the spray nozzles 6
disposed in the sub after-air ports 60 on the upstream side, the
air flow 62 includes much moisture supplied from the sub after-air
port 60 toward the inside of the furnace 1.
[0165] The water sprayed from the spray nozzle 6 deprives
evaporation heat from the surrounding air during the evaporation,
lowering the temperature of the air.
[0166] Since the air flow 62 includes much moisture, its specific
heat is raised. Accordingly, when the combustion gas 10a is mixed
with the air flow 62 jetted from the sub after-air ports 60, it is
possible to suppress the combustion reaction by the amount of
moisture included in the air flow 62 and thereby the combustion
temperature can be reduced
[0167] Therefore, the amount of thermal NOx generated during the
combustion reaction can be reduced.
[0168] In the pulverized coal boiler 100 in this embodiment, after
the air flow 62 including moisture has been mixed with the
combustion gas 10a, part of the air flow 62 is further mixed with
the air flow 63 jetted from the main after-air port 61 located
downstream of the air flow 62.
[0169] When the part of the air flow 62 including moisture is mixed
with the air flow 63, part of a gas already burnt in an inner wall
vicinity 64 in the furnace 1 is involved in the air flow 63 jetted
from the main after-air port 61, so a burnt gas including moisture
flows along the outermost circumference of the air flow 63.
[0170] Accordingly, when the unburnt gas including moisture, the
air flow 63, and the combustion gas 10a are mixed, the combustion
temperature can be reduced due to the specific heats of the
moisture included in the burnt gas. As a result, the amount of
thermal NOx generated at the central part of the furnace 1 can be
reduced.
[0171] When the air flow jetted from the after-air port and the
combustion gas 10a are mixed, as described above, the air flow
including much moisture and the burnt gas including moisture are
supplied to the inner wall vicinity 64 in the furnace 1 in a
relatively upstream region, the central part 65 of the furnace 1,
and other parts where high temperature is easily reached, enabling
the amount of thermal NOx generated to be suppressed to a small
value.
[0172] Since the burnt gas including much moisture is involved in
the outermost circumferential part of the air flow 63, both
reduction in the amount of water supply and suppression of thermal
NOx can be achieved.
[0173] Although the thermal efficiency is lowered by the supplied
water, since thermal NOx is suppressed, it is possible to suppress,
at a downstream site of the furnace 1, power for operating units to
reduce NOx and the amount of chemicals supplied.
[0174] In this embodiment, a situation in which the amount of air
in the air flow 62 supplied from the sub after-air port 60 disposed
upstream of the furnace 1 is smaller than the amount of air in the
air flow 63 supplied from the main after-air port 61 disposed
downstream has been described. However, even if the amount of air
in the air flow 62 supplied from the sub after-air port 60 disposed
upstream of the furnace 1 is larger than the amount of air in the
air flow 63 supplied from the main after-air port 61, almost the
same effect can be obtained.
[0175] To reduce thermal NOx generated in this case, it is clear as
described above that much more water must be sprayed from the spray
nozzle 6 disposed in the sub after-air port 60 than described
above.
[0176] However, since much air of the air flow 62 supplied from the
sub after-air port 60 is mixed with the combustion gas 10a upstream
of the furnace 1, the amount of unburnt gas can be reduced at the
exit of the furnace 1.
[0177] Although a case in which the water 18 is used as the cooling
fluid sprayed from the spray nozzle 6 has been described in this
embodiment, the steam 20 or two fluids including water 18 and steam
20 may be sprayed instead of water 18.
[0178] In this embodiment, a case in which the end of the spray
nozzle 6 is positioned in the opening of the sub after-air port 60
has been described. Even if, however, the spray nozzle 6 is
disposed in a wind box 5a, which accommodates the sub after-air
port 60, or the pipe 14, through which air is supplied to the wind
box 5a, as in the sixth embodiment shown in FIG. 12 and the seventh
embodiment shown in FIG. 17, the same effect as describe above can
be obtained.
[0179] The effect obtained when the spray nozzle 6 is disposed at
one of the above positions is the same as in the sixth embodiment
shown in FIG. 7 and the seventh embodiment shown in FIG. 17.
[0180] It is also possible to dispose the spray nozzle 6 in the
opening in the swirl flow path 31, which is formed around the outer
circumference of the straight flow path 30, as in the second
embodiment of the present invention shown in FIGS. 5 and 6.
[0181] In this case, the swirl flow causes much of the water 18
jetted from the spray nozzle 6 to flow around the outer
circumference of the air flow 62, so much moisture is included in
the mixture of the combustion gas 10a and the air flow 62.
Accordingly, the concentration of the thermal NOx can be reduced
with a small amount of water.
[0182] In the pulverized coal boiler 100 in this embodiment, the
cooling fluid sprayed from the spray nozzle 6 disposed in the sub
after-air port 60 is controlled by the controller 50, as in the
embodiments described above.
[0183] Specifically, a NOx concentration signal about the exhaust
gas 11 detected by the NOx detector 55 is entered to the controller
50. The controller 50 then compares the NOx concentration with a
desired NOx setting, calculates a flow rate command signal about
the cooling fluid to be sprayed from the spray nozzles 6 toward the
inside of the furnace 1 so that the NOx concentration of the
exhaust gas 11 is maintained at the desired setting, and outputs
the command signal to the valve 17 used for flow rate adjustment,
which is disposed in the pipe 42, through which the water 18
(cooling fluid) is supplied to the spray nozzles 6. This
arrangement enables the flow rate of the cooling fluid to be
appropriately controlled and thereby the thermal NOx concentration
to be reduced.
[0184] The pulverized coal boiler 100 described above can be a
highly reliable pulverized coal boiler that ensures suppression of
a flame temperature rise that is caused during the combustion of an
unburnt gas in a furnace when combustion air is supplied from
after-air ports so as to reduce the concentration of thermal NOx
generated during the combustion.
INDUSTRIAL APPLICABILITY
[0185] The present invention can be applied to a pulverized coal
boiler that uses pulverized coal as a fuel, more particularly to a
pulverized coal boiler that suppresses the generation of thermal
nitrogen oxides. The present invention can also be applied to
conventional pulverized boilers with ease.
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