U.S. patent application number 13/703737 was filed with the patent office on 2013-04-18 for combustion system.
The applicant listed for this patent is Takeshi Aruga, Takuichiro Daimaru, Koutaro Fujimura, Masahiko Matsuda, Hiroshi Suganuma. Invention is credited to Takeshi Aruga, Takuichiro Daimaru, Koutaro Fujimura, Masahiko Matsuda, Hiroshi Suganuma.
Application Number | 20130092062 13/703737 |
Document ID | / |
Family ID | 45347936 |
Filed Date | 2013-04-18 |
United States Patent
Application |
20130092062 |
Kind Code |
A1 |
Matsuda; Masahiko ; et
al. |
April 18, 2013 |
COMBUSTION SYSTEM
Abstract
A combustion system capable of decreasing nitrogen oxide
discharged from exhaust gas is provided. The combustion system
includes: a combustion furnace (2) having a burner unit (2a) for
supplying fuel and combustion oxygen to the inside of the furnace,
a reduction zone formed on a downstream side of the burner unit
(2a) for combusting the fuel, and a combustion oxygen supply port
(2b) for supplying combustion oxygen (21) so that unburned fuel
which has passed the reduction zone completely combusts; and a
smoke removal device (9) for removing smoke in the exhaust gas
discharged from the combustion furnace (2). Part of exhaust gas
(22) diverging from between the combustion furnace (2) and the
smoke removal device (9) is introduced to the burner unit (2a),
while part of exhaust gas (23) diverging from a downstream side of
the smoke removal device (9) is introduced to the combustion oxygen
supply port (2b).
Inventors: |
Matsuda; Masahiko; (Tokyo,
JP) ; Suganuma; Hiroshi; (Tokyo, JP) ; Aruga;
Takeshi; (Tokyo, JP) ; Fujimura; Koutaro;
(Tokyo, JP) ; Daimaru; Takuichiro; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Matsuda; Masahiko
Suganuma; Hiroshi
Aruga; Takeshi
Fujimura; Koutaro
Daimaru; Takuichiro |
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP
JP
JP |
|
|
Family ID: |
45347936 |
Appl. No.: |
13/703737 |
Filed: |
January 17, 2011 |
PCT Filed: |
January 17, 2011 |
PCT NO: |
PCT/JP2011/050622 |
371 Date: |
December 12, 2012 |
Current U.S.
Class: |
110/203 |
Current CPC
Class: |
F23C 99/00 20130101;
Y02E 20/34 20130101; Y02E 20/322 20130101; F23C 2202/10 20130101;
F23J 11/00 20130101; Y02E 20/344 20130101; F23C 9/08 20130101; F23L
2900/07001 20130101; Y02E 20/32 20130101; F23L 7/007 20130101 |
Class at
Publication: |
110/203 |
International
Class: |
F23J 11/00 20060101
F23J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2010 |
JP |
2010-137211 |
Claims
1. A combustion system, comprising: a combustion furnace having: a
burner unit for supplying fuel and combustion oxygen to an inside
of the furnace; a reduction zone formed on a downstream side of the
burner unit for combusting the fuel; and a combustion oxygen supply
port for supplying combustion oxygen so that unburned fuel which
has passed the reduced zone completely combusts; and a smoke
removal device for removing smoke in the exhaust gas discharged
from the combustion furnace, wherein part of exhaust gas diverging
from between the combustion furnace and the smoke removal device is
introduced to the burner unit, while part of exhaust gas diverging
from a downstream side of the smoke removal device is introduced to
the combustion oxygen supply port.
2. The combustion system according to claim 1, wherein the smoke
removal device includes: a denitration unit for removing nitrogen
oxide; a heat exchange unit for conducting heat exchange between
exhaust gas which has passed the denitration unit and exhaust gas
which is introduced to the combustion oxygen supply port; a dust
removal unit for removing dust in exhaust gas which has passed the
heat exchange unit; a desulfurization unit for removing sulfur
oxide in exhaust gas which has passed the dust removal unit; and a
cooling unit for cooling exhaust gas which has passed the
desulfurization unit, wherein part of exhaust gas diverging from
between the desulfurization unit and the cooling unit is introduced
to the combustion oxygen supply port.
3. The combustion system according to claim 2, wherein part of
exhaust gas diverging from between the dust removal unit and the
desulfurization unit is introduced to the combustion oxygen supply
port.
4. The combustion system according to claim 2, wherein part of
exhaust gas diverging from between the denitration unit and the
dust removal unit is introduced to the combustion oxygen supply
port.
5. The combustion system according to claim 2, wherein the
denitration unit includes: an ammonia supply unit for supplying
ammonia into exhaust gas; and a catalyst unit for allowing exhaust
gas supplied by the ammonia supply unit to pass therethrough.
Description
TECHNICAL FIELD
[0001] The present invention relates to a combustion system, and
more particularly relates to removal of nitrogen oxide in exhaust
gas.
BACKGROUND ART
[0002] Coal is generally used as fuel in thermal power plants and
the like since the resource volume of coal is abundant. However,
coal is high in carbon contents in fuel compared with oil and gas.
When coal is combusted by an air combustion boiler system, the
emission amount of carbon dioxide is increased.
[0003] In order to increase concentrations of carbon dioxide for
easy recovery, an oxygen combustion boiler system 101 as shown in
FIG. 5 is used. The oxygen combustion boiler system 101 includes a
coal pulverizer 103 for pulverizing coal, an oxygen combustion
boiler 102 for combusting the coal pulverized by the coal
pulverizer 103 and discharging exhaust gas, a denitration device
104 for removing nitrogen oxide in the exhaust gas discharged from
the oxygen combustion boiler 102, a dust removal device 105 for
removing dust and the like in the exhaust gas, a desulfurization
device 106 for removing sulfur oxide in the exhaust gas, and a gas
cooler 107 for cooling the exhaust gas to remove moisture in the
exhaust gas.
[0004] Carrier gas is introduced into the coal pulverizer 103 for
drying the pulverized coal and conveying the pulverized coal from
the coal pulverizer 103 to the oxygen combustion boiler 102. As the
carrier gas, exhaust gas (hereinafter referred to as "primary
recirculation gas") discharged from the desulfurization device 106
and traveling through the gas cooler 107 is used. The primary
recirculation gas is heated by an air heater 108 provided between
the denitration device 104 and the dust removal device 105 for
drying the coal. The air heater 108 performs heat exchange between
high-temperature exhaust gas discharged from the denitration device
104 and low-temperature exhaust gas which has passed the gas cooler
107, and thereby heats the primary recirculation gas introduced to
the coal pulverizer 103.
[0005] A boiler capable of conducting denitration inside a furnace
(not shown) of the oxygen combustion boiler 102 by two-stage
combustion (e.g., Patent Literature 1) is used as the oxygen
combustion boiler 102. The oxygen combustion boiler 102 includes a
burner unit 102a for supplying oxygen introduced from a combustion
oxygen supply system, later-described secondary recirculation gas,
and coal as fuel into the oxygen combustion boiler 102. The oxygen
combustion boiler 102 also includes an additional air port
(hereinafter referred to as "AA port") 102b provided on the
downstream side of the burner unit 102a for supplying oxygen
introduced from the combustion oxygen supply system and
later-described secondary recirculation gas into the oxygen
combustion boiler 102.
[0006] The oxygen supplied into the oxygen combustion boiler 102
through the burner unit 102a and the AA port 102b contains part of
the exhaust gas (hereinafter referred to as "secondary
recirculation gas") which has been introduced from the downstream
of the gas cooler 107 and mixed therein as dilution gas. The
secondary recirculation gas is heated by the air heater 108 and is
mixed into the oxygen which is introduced to the burner unit 102a
and the AA port 102b.
[0007] The oxygen supplied to the burner unit 102a is adjusted so
that the amount of oxygen introduced from the combustion oxygen
supply system is not larger than 1.0 times the theoretical
combustion oxygen amount of the coal supplied from the coal
pulverizer 103. A remaining amount of the oxygen introduced from
the combustion oxygen supply system is supplied to the AA port
102b. Accordingly, a zone between the burner unit 102a and the AA
port 102b in the oxygen combustion boiler 102 is in an oxygen-poor
state.
[0008] Since oxygen is poor in between the burner unit 102a and the
AA port 102b, the zone between the burner unit 102a and the AA port
102b is made to have a reducing atmosphere. The fuel charged into
the oxygen combustion boiler 102 through the burner unit 102a
combusts and generates exhaust gas. Nitrogen oxide (NOx) contained
in the generated exhaust gas is partially reduced when passing the
reducing atmosphere present between the burner unit 102a and the AA
port 102b. This makes it possible to decrease nitrogen oxide within
the oxygen combustion boiler 102.
[0009] Patent Literature 2 and Patent Literature 3 disclose oxygen
combustion boilers for receiving part of exhaust gas introduced as
secondary recirculation gas which has passed a denitration device,
an air heater, a dust removal device, and a desulfurization
device.
CITATION LIST
Patent Literature
{PTL 1}
[0010] The Publication of Japanese Patent No. 3068888
(PTL 2)
[0011] Japanese Unexamined Patent Application, Publication No.
Hei6-94212
(PTL 3)
[0012] Japanese Unexamined Patent Application, Publication No.
Sho59-195013
SUMMARY OF INVENTION
Technical Problem
[0013] However, in the oxygen combustion boiler of the invention
disclosed in Patent Literature 3 as well as in the oxygen
combustion boiler system 101 shown in FIG. 5, the exhaust having a
high nitrogen oxide concentration discharged from the oxygen
combustion boiler 102 was recirculated as secondary recirculation
gas and was recharged into the oxygen combustion boiler 102. As a
consequence, the denitration device 104 provided on the downstream
side of the oxygen combustion boiler 102 had a heavy treatment
burden.
[0014] Moreover, since the concentration of nitrogen oxide treated
by the denitration device 104 was high, the consumption of ammonia
sprayed to the exhaust gas passing the denitration device 104
increased.
[0015] In view of the above-stated problems, an object of the
present invention is to provide a combustion system capable of
decreasing nitrogen oxide discharged from exhaust gas.
Solution to Problem
[0016] A combustion system of the present invention employs the
following solutions to solve the foregoing problems.
[0017] A combustion system according to the present invention
includes: a combustion furnace having a burner unit for supplying
fuel and combustion oxygen to an inside of the furnace, a reduction
zone formed on a downstream side of the burner unit for combusting
the fuel, and a combustion oxygen supply port for supplying
combustion oxygen so that unburned fuel which has passed the
reduction zone completely combusts; and a smoke removal device for
removing smoke in the exhaust gas discharged from the combustion
furnace, wherein part of exhaust gas diverging from between the
combustion furnace and the smoke removal device is introduced to
the burner unit, while part of exhaust gas diverging from a
downstream side of the smoke removal device is introduced to the
combustion oxygen supply port.
[0018] In the combustion system according to the present invention,
part of exhaust gas diverging from between the combustion furnace
and the smoke removal device is resupplied to the inside of the
combustion furnace through the burner unit. A zone under reducing
atmosphere (reduction zone) is formed between the burner unit of
the combustion furnace and the combustion oxygen supply port.
Consequently, the exhaust gas diverging from between the combustion
furnace and the smoke removal device can be reduced in the zone
under reducing atmosphere formed in the combustion furnace and then
be discharged. This makes it possible to decrease the flow rate of
the exhaust gas introduced from the combustion furnace to the smoke
removal device and to decrease the amount of smoke. Therefore, the
capacity of the smoke removal device can be reduced.
[0019] Moreover, part of exhaust gas diverging from the downstream
side of the smoke removal device is the exhaust gas having the
concentration of nitrogen oxide, which is smoke, decreased by the
smoke removal device. The exhaust gas having a decreased nitrogen
oxide concentration is introduced to the combustion oxygen supply
port and is used for promoting complete combustion of the unburned
fuel contained in the exhaust gas which has partially been reduced
by passing the reducing atmosphere inside the combustion furnace.
Therefore, the exhaust gas can be discharged out of the combustion
furnace while the concentration of nitrogen oxide contained therein
is maintained low. The exhaust gas having a decreased nitrogen
oxide concentration is recirculated to the combustion furnace and
the smoke removal device, so that increase in the concentration of
nitrogen oxide in an outlet of the combustion furnace can be
suppressed.
[0020] Further, in the combustion system according to the present
invention, the smoke removal device includes: a denitration unit
for removing nitrogen oxide in the exhaust gas discharged from the
combustion furnace; a heat exchange unit for conducting heat
exchange between exhaust gas which has passed the denitration unit
and exhaust gas which is introduced to the combustion oxygen supply
port; a dust removal unit for removing dust in exhaust gas which
has passed the heat exchange unit; a desulfurization unit for
removing sulfur oxide in exhaust gas which has passed the dust
removal unit; and a cooling unit for cooling exhaust gas which has
passed the desulfurization unit, wherein part of exhaust gas
diverging from between the desulfurization unit and the cooling
unit is introduced to the combustion oxygen supply port.
[0021] In the combustion system according to the present invention,
part of the exhaust gas diverging from between the desulfurization
unit and the cooling unit is introduced to the combustion oxygen
supply port of the combustion furnace. This makes it possible to
decrease the flow rate of nitrogen oxide in the exhaust gas
introduced to the denitration unit as well as to decrease the flow
rate of the exhaust gas introduced to the cooling unit. Therefore,
it becomes possible to downsize the denitration unit and to reduce
the capacity of the cooling unit.
[0022] Further, in the combustion system according to the present
invention, part of exhaust gas diverging from between the dust
removal unit and the desulfurization unit is introduced to the
combustion oxygen supply port.
[0023] In the combustion system according to the present invention,
part of the exhaust gas diverging from between the dust removal
unit and the desulfurization unit is introduced to the combustion
oxygen supply port. This makes it possible to decrease the flow
rate of nitrogen oxide in the exhaust gas introduced to the
denitration unit as well as to decrease the flow rate of the
exhaust gas introduced to the desulfurization unit and the cooling
unit. Therefore, it becomes possible to downsize the denitration
unit and to reduce the capacity of the desulfurization unit and the
cooling unit.
[0024] Further, in the combustion system according to the present
invention, part of exhaust gas diverging from between the
denitration unit and the dust removal unit is introduced to the
combustion oxygen supply port.
[0025] In the combustion system according to the present invention,
part of the exhaust gas diverging from between the denitration unit
and the dust removal unit is introduced to the combustion oxygen
supply port. This makes it possible to decrease the flow rate of
nitrogen oxide in the exhaust gas introduced to the denitration
unit as well as to decrease the flow rate of the exhaust gas
introduced to the heat exchange unit, the dust removal unit, the
desulfurization unit and the cooling unit. Therefore, it becomes
possible to downsize the denitration unit and to reduce the
capacity of the heat exchange unit, the dust removal unit, the
desulfurization unit and the cooling unit.
[0026] Further, in the combustion system according to the present
invention, the denitration unit includes: an ammonia supply unit
for supplying ammonia into exhaust gas; and a catalyst unit for
allowing exhaust gas supplied by the ammonia supply unit to pass
therethrough.
[0027] In the combustion system according to the present invention,
the exhaust gas having a decreased flow rate of nitrogen oxide is
introduced to the denitration unit. Therefore, the amount of
ammonia to be supplied can be reduced as compared with the case
where the exhaust gas whose flow rate of nitrogen oxide is not
decreased.
Advantageous Effects of Invention
[0028] In the present invention, part of exhaust gas diverging from
between the combustion furnace and the smoke removal device is
resupplied to the inside of the combustion furnace through the
burner unit. A zone under reducing atmosphere is formed between the
burner unit of the combustion furnace and the combustion oxygen
supply port. Consequently, the exhaust gas diverging from between
the combustion furnace and the smoke removal device can be reduced
in the zone under reducing atmosphere formed in the combustion
furnace before being discharged. This makes it possible to decrease
the flow rate of the exhaust gas introduced from the combustion
furnace to the smoke removal device and to decrease the flow rate
of smoke. Therefore, the capacity of the smoke removal device can
be reduced.
[0029] Moreover, part of exhaust gas diverging from the downstream
side of the smoke removal device is the exhaust gas having the
concentration of nitrogen oxide, which is smoke, decreased by the
smoke removal device. The exhaust gas having a decreased nitrogen
oxide concentration is introduced to the combustion oxygen supply
port and is used for promoting complete combustion of the unburned
fuel contained in the exhaust gas which has partially been reduced
by passing the reducing atmosphere inside the combustion furnace.
Therefore, the exhaust gas can be discharged out of the combustion
furnace while the concentration of nitrogen oxide contained therein
is maintained low. The exhaust gas having a decreased nitrogen
oxide concentration is recirculated to the combustion furnace and
the smoke removal device, so that increase in the concentration of
nitrogen oxide in the outlet of the combustion furnace can be
suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is a schematic structure view of a combustion system
according to a first embodiment of the present invention.
[0031] FIG. 2 is a schematic structure view of a combustion system
according to a second embodiment of the present invention.
[0032] FIG. 3 is a schematic structure view of a combustion system
according to a third embodiment of the present invention.
[0033] FIG. 4 is a schematic structure view of a combustion system
according to a fourth embodiment of the present invention.
[0034] FIG. 5 is a schematic structure view of a conventional
oxygen combustion boiler system.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0035] FIG. 1 is a schematic structure view of a combustion system
according to the first embodiment of the present invention.
[0036] The combustion system 1 includes a coal fired boiler
(combustion furnace) 2, a coal pulverizer 3 for pulverizing coal
supplied to the coal fired boiler 2, and a smoke removal device
9.
[0037] The coal fired boiler 2 is an oxygen combustion boiler which
can conduct denitration inside the furnace (not shown) by two-stage
combustion. The coal fired boiler 2 includes a furnace inside for
combusting fuel, a burner unit 2a, and an additional air port
(hereinafter referred to as "AA unit") 2b. Coal as fuel supplied
from the coal pulverizer 3, oxygen (combustion oxygen) introduced
from a combustion oxygen supply system 21, and later-described
secondary recirculation gas for burner unit 22 are introduced to
the burner unit 2a. Remaining part of the oxygen introduced from
the combustion oxygen supply system 21 to the burner unit 2a and
later-described secondary recirculation gas for AA unit 23 are
introduced to the AA unit (combustion oxygen supply port) 2b.
[0038] The coal pulverizer 3 is for pulverizing the coal, which is
supplied to the coal fired boiler 2, into fine powder of a size of
several .mu.m to hundreds of .mu.m. Part of exhaust gas
(hereinafter referred to as "primary recirculation gas") 24
discharged from the smoke removal device 9 is introduced to the
coal pulverizer 3 as high-temperature carrier gas for drying the
pulverized coal and conveying the pulverized coal from the coal
pulverizer 3 to the coal fired boiler 2.
[0039] The smoke removal device 9 includes a denitration device
(denitration unit) 4, a gas heater (heat exchange unit) 8, a dust
removal device (dust removal unit) 5, a desulfurization device
(desulfurization unit) 6, and a gas cooler (cooling unit) 7.
[0040] The denitration device 4 includes an ammonia supply unit
(not shown) for spraying ammonia to the exhaust gas, and a catalyst
unit (not shown) for allowing the exhaust gas having ammonia
sprayed thereto to pass therethrough. The denitration device 4 is
for removing nitrogen oxide in the exhaust gas by spraying ammonia
to the introduced exhaust gas and for having the exhaust gas pass
the catalyst unit.
[0041] The gas heater 8 is for conducting heat exchange of the
high-temperature exhaust gas, which has come from the coal fired
boiler 2 and passed the denitration device 4, with the primary
recirculation gas 24 and the secondary recirculation gas for AA
unit 23. As a consequence of the heat exchange, the primary
recirculation gas 24 reaches a temperature suitable for drying the
coal pulverized by the coal pulverizer 3, while the secondary
recirculation gas for AA unit 23 reaches a temperature suitable for
being introduced to the inside of the furnace through the AA unit
2b of the coal fired boiler 2.
[0042] The dust removal device 5 is for removing dust in the
exhaust gas, and the desulfurization device 6 is for removing
sulfur oxide in the introduced exhaust gas.
[0043] The gas cooler 7 is for cooling the introduced exhaust
gas.
[0044] Description is now given of the flow of exhaust gas in the
present embodiment.
[0045] Oxygen introduced from the combustion oxygen supply system
21, part of exhaust gas (hereinafter referred to as "secondary
recirculation gas for burner") 22 introduced from between the coal
fired boiler 2 and the denitration device 4, and coal introduced
from the coal pulverizer 3 are supplied to the burner unit 2a of
the coal fired boiler 2. The secondary recirculation gas for burner
22 is used as diluents for diluting the oxygen introduced from the
combustion oxygen supply system 21.
[0046] Oxygen introduced from the combustion oxygen supply system
21 and part of exhaust gas (hereinafter referred to as "secondary
recirculation gas for AA unit") 23 purified by passing the smoke
removal device 9 are supplied to the AA unit 2b of the coal fired
boiler 2. The secondary recirculation gas for AA unit 23 is used as
dilution gas for diluting the oxygen introduced from the combustion
oxygen supply system 21.
[0047] The amount of oxygen supplied from the combustion oxygen
supply system 21 to the coal fired boiler 2 through the burner unit
2a and the AA unit 2b is set to be 1.15 times the theoretical
combustion oxygen amount of the coal supplied to the inside of the
furnace through the burner unit 2a. The amount of oxygen supplied
to the inside of the furnace of the coal fired boiler 2 is not
larger than 1.0 times the theoretical combustion oxygen amount of
the coal supplied to the inside of the furnace through the burner
unit 2a.
[0048] A remaining amount of the oxygen, which is introduced from
the combustion oxygen supply system 21 to the burner unit 2a, is
used as the oxygen supplied to the inside of the furnace through
the AA unit 2b. The amount of oxygen supplied through the AA unit
2b is up to about 40% of the amount of oxygen introduced from the
combustion oxygen supply system 21 to the coal fired boiler 2.
[0049] The amount of oxygen charged to the inside of the furnace
through the burner unit 2a is made not larger than 1.0 times the
theoretical combustion oxygen amount of coal, and oxygen is also
charged to the inside of the furnace through the AA unit 2b. As a
consequence, a zone between the burner unit 2a and the AA unit 2b
becomes short of oxygen. Due to the shortage of oxygen in the zone
between the burner unit 2a and the AA unit 2b, the zone between the
burner unit 2a and the AA unit 2b inside the furnace is put in the
state of reducing atmosphere.
[0050] Nitrogen oxide in the exhaust gas generated by combustion of
coal and oxygen charged to the inside of the furnace through the
burner unit 2a is reduced when passing the zone under reducing
atmosphere through the burner unit 2a. Consequently, nitrogen oxide
in the exhaust gas generated within the coal fired boiler 2 is
removed inside the furnace of the coal fired boiler 2.
[0051] The concentration of nitrogen oxide contained in the exhaust
gas discharged from the coal fired boiler 2 is decreased by
in-furnace NOx removal in the coal fired boiler 2. The exhaust gas
with a decreased nitrogen oxide concentration is introduced to the
smoke removal device 9. As the concentration of nitrogen oxide
decreases, the amount of exhaust gas introduced from the coal fired
boiler 2 to the smoke removal device 9 is decreased.
[0052] The exhaust gas introduced to the smoke removal device 9 is
introduced to the denitration device 4 which constitutes the smoke
removal device 9, where residual nitrogen oxide is removed. The
exhaust gas with nitrogen oxide removed is introduced to the air
heater 8. The temperature of the exhaust gas introduced to the air
heater 8 is high. In the air heater 8, the high-temperature exhaust
gas is subjected to heat exchange with the secondary recirculation
gas for AA unit 23 and the primary recirculation gas 24. After heat
exchange in the air heater 8, the high-temperature exhaust gas
introduced from the denitration device 4 is cooled and then
introduced to the dust removal device 5.
[0053] The exhaust gas introduced to the dust removal device 5 is
subjected to removal of dust and the like before being discharged.
The exhaust gas discharged from the dust removal device 5 is
introduced to the desulfurization device 6, where sulfuric
compounds are removed. The exhaust gas purified through the
denitration device 4, the dust removal device 5, and the
desulfurization device 6 is mostly composed of carbon dioxide and
steam. This purified exhaust gas is introduced to the gas cooler 7,
where the temperature thereof is lowered. The exhaust gas whose
temperature is lowered by the gas cooler 7 is discharged from the
smoke removal device 9.
[0054] Part of the exhaust gas discharged from the smoke removal
device 9 is introduced to the air heater 8 as secondary
recirculation gas for AA unit 23, where heat exchange is conducted
between the secondary recirculation gas for AA unit 23 and the
high-temperature exhaust gas discharged from the denitration device
4, so that the temperature of the secondary recirculation gas for
AA unit 23 increases. The thus-obtained high-temperature secondary
recirculation gas for AA unit 23 is then introduced to the AA unit
2b of the coal fired boiler 2. Part of the exhaust gas discharged
from the smoke removal device 9 is further introduced to the air
heater 8 as primary recirculation gas 24. The primary recirculation
gas 24 introduced to the air heater 8 is heated by exchanging heat
with the high-temperature exhaust gas discharged from the
denitration device 4. The thus-obtained high-temperature primary
recirculation gas 24 is then introduced to the coal pulverizer 3.
The high-temperature primary recirculation gas 24 introduced to the
coal pulverizer 3 is used as carrier gas for drying coal and for
conveying pulverized coal to the coal fired boiler 3.
[0055] The exhaust gas purified by the smoke removal device 9 is
mostly introduced to a system such as a carbon dioxide recovery
system (not shown) where carbon dioxide in the exhaust gas is
recovered. Thus, the exhaust gas with carbon dioxide, nitrogen
oxide, and sulfur oxide removed therefrom is emitted to the outside
of the combustion system 1.
[0056] The combustion system according to the present embodiment
has following operation effects.
[0057] In the combustion system according to the present
embodiment, the secondary recirculation gas for burner (part of
exhaust gas) 22 diverging from between the coal fired boiler
(combustion furnace) 2 and the smoke removal device 9 is resupplied
to the inside of the furnace (not shown) of the coal fired boiler 2
through the burner unit 2a. Consequently, the exhaust gas
containing high-concentration nitrogen oxide introduced to the
smoke removal device 9 is decreased. Therefore, it becomes possible
to reduce the load of the denitration device 4.
[0058] Moreover, the reducing atmosphere is formed between the
burner unit 2a and the AA unit (combustion oxygen supply port) 2b
of the coal fired boiler 2. Consequently, the secondary
recirculation gas for burner unit 22 diverging from between the
coal fired boiler 2 and the smoke removal device 9 can be reduced
in the zone under reducing atmosphere formed in the coal fired
boiler 2 and then be discharged. This makes it possible to decrease
the flow rate of the exhaust gas introduced from the coal fired
boiler 2 to the smoke removal device 9 and to decrease the flow
rate of nitrogen oxide in smoke. Therefore, the capacity of the
smoke removal device 9 can be reduced.
[0059] The secondary recirculation gas for AA unit 23 which is part
of the exhaust gas discharged from the downstream side of the smoke
removal device 9 is the exhaust gas having the concentration of
nitrogen oxide decreased by the denitration device 4. This exhaust
gas is introduced to the coal fired boiler 2 through the AA unit 2b
and is used for promoting complete combustion of unburned
pulverized coal contained in the exhaust gas which is partially
reduced by passing the reducing atmosphere inside the furnace of
the coal fired boiler 2. Therefore, the exhaust gas is discharged
out of the furnace of the coal fired boiler 2 while the
concentration of nitrogen oxide contained therein is maintained
low. As a result, the exhaust gas having a decreased nitrogen oxide
concentration is recirculated between the coal fired boiler 2 and
the smoke removal device 9, so that increase in the concentration
of nitrogen oxide in the outlet of the furnace of the coal fired
boiler 2 can be suppressed.
[0060] The exhaust gas with a decreased flow rate of nitrogen oxide
is introduced to the denitration device (denitration unit) 4, so
that the amount of ammonia sprayed from the ammonia supply unit
(not shown) to the exhaust gas can be decreased as compared with
the case where the exhaust gas whose flow rate of nitrogen oxide is
not decreased is introduced to the denitration device 4. Therefore,
it becomes possible to downsize the denitration device 4.
Second Embodiment
[0061] Hereinafter, the second embodiment of the present invention
will be described. A combustion system of the present embodiment is
different from the first embodiment in the point that the secondary
recirculation gas for AA unit is introduced from between the
desulfurization device and the gas cooler. Other structural members
are similar to those of the first embodiment. Therefore, like
structural members and flows are designated by like reference signs
to omit description.
[0062] FIG. 2 is a schematic structure view of a combustion system
according to the second embodiment of the present invention.
[0063] Oxygen (combustion oxygen) introduced from a combustion
oxygen supply system 21 and part of exhaust gas diverging from
between a desulfurization device (desulfurization unit) 6 and a gas
cooler (cooling unit) 7 which constitute a smoke removal device 9
are supplied to an AA unit (combustion oxygen supply port) 2b of a
coal fired boiler (combustion furnace) 2 as secondary recirculation
gas for AA unit 23.
[0064] The combustion system according to the present embodiment
has following operation effects.
[0065] In the combustion system according to the present
embodiment, the secondary recirculation gas for AA unit (part of
exhaust gas) 23 diverging from between the desulfurization device
(desulfurization unit) 6 and the gas cooler (cooling unit) 7 is
introduced to the AA unit (combustion oxygen supply port) 2b of the
coal fired boiler (combustion furnace) 2. Accordingly, the flow
rate of the exhaust gas introduced to the gas cooler 7 can be
decreased. This makes it possible to reduce the capacity of the gas
cooler 7 and to decrease the flow rate of nitrogen oxide in the
exhaust gas introduced to the denitration device (denitration unit)
4 for the same reason as that in the first embodiment. As a result,
the denitration device 4 can be downsized.
Third Embodiment
[0066] Hereinafter, the third embodiment of the present invention
will be described. A combustion system of the present embodiment is
different from the first embodiment in the point that the secondary
recirculation gas for AA unit is introduced from between the dust
removal device and the desulfurization device. Other structural
members are similar to those of the first embodiment. Therefore,
like structural members and flows are designated by like reference
signs to omit description.
[0067] FIG. 3 is a schematic structure view of a combustion system
according to the third embodiment of the present invention.
[0068] Oxygen (combustion oxygen) introduced from a combustion
oxygen supply system 21 and part of exhaust gas diverging from
between a dust removal device (dust removal unit) 5 and a
desulfurization device (desulfurization unit) 6 which constitute a
smoke removal device 9 are supplied to an AA unit (combustion
oxygen supply port) 2b of a coal fired boiler (combustion furnace)
2 as secondary recirculation gas for AA unit 23.
[0069] The combustion system according to the present embodiment
has following operation effects.
[0070] In the combustion system according to the present
embodiment, the secondary recirculation gas for AA unit (part of
exhaust gas) 23 diverging from between the dust removal device
(dust removal unit) 5 and the desulfurization device
(desulfurization unit) 6 is introduced to the AA unit (combustion
oxygen supply port) 2b. Accordingly, the flow rate of the exhaust
gas introduced to the desulfurization device 6 and a gas cooler 7
can be decreased. This makes it possible to reduce the capacity of
the desulfurization device 6 and the gas cooler 7 and to decrease
the flow rate of nitrogen oxide in the exhaust gas introduced to
the denitration device (denitration unit) 4 for the same reason as
that in the first embodiment. As a result, the denitration device 4
can be downsized.
Fourth Embodiment
[0071] Hereinafter, the fourth embodiment of the present invention
will be described. A combustion system of the present embodiment is
different from the first embodiment in the point that the secondary
recirculation gas for AA unit is introduced from between the
denitration device and the air heater. Other structural members are
similar to those of the first embodiment. Therefore, like
structural members and flows are designated by like reference signs
to omit description.
[0072] FIG. 4 is a schematic structure view of a combustion system
according to the fourth embodiment of the present invention.
[0073] Oxygen (combustion oxygen) introduced from a combustion
oxygen supply system 21 and part of exhaust gas diverging from
between a denitration device (denitration unit) 4 and an air heater
(heat exchange unit) 8 which constitute a smoke removal device 9
are supplied to an AA unit (combustion oxygen supply port) 2b of a
coal fired boiler (combustion furnace) 2 as secondary recirculation
gas for AA unit 23.
[0074] The combustion system according to the present embodiment
has following operation effects.
[0075] In the combustion system according to the present
embodiment, the secondary recirculation gas for AA unit (part of
exhaust gas) 23 diverging from between the denitration device
(denitration unit) 4 and the air heater (heat exchange unit) 8 is
introduced to the AA unit (combustion oxygen supply port) 2b.
Accordingly, the flow rate of the exhaust gas introduced to the air
heater 8, the dust removal device (dust removal unit) 5, the
desulfurization device (desulfurization unit) 6, and the gas cooler
(cooling unit) 7 can be decreased. This makes it possible to reduce
the capacity of the air heater 8, the dust removal device 5, the
desulfurization device 6 and the gas cooler 7 and to decrease the
flow rate of nitrogen oxide in the exhaust gas introduced to the
denitration device (denitration unit) 4 for the same reason as that
in the first embodiment. As a result, the denitration device 4 can
be downsized.
REFERENCE SIGNS LIST
[0076] 1 Combustion system [0077] 2 Coal fired boiler (combustion
furnace) [0078] 2a Burner unit [0079] 2b AA unit (combustion oxygen
supply port) [0080] 3 Coal pulverizer [0081] 4 Denitration device
(denitration unit) [0082] 5 Dust removal device (dust removal unit)
[0083] 6 Desulfurization device (desulfurization unit) [0084] 7 Gas
cooler (cooling unit) [0085] 8 Air heater (heat exchange unit)
[0086] 9 Smoke removal device [0087] 21 Combustion oxygen supply
system (combustion oxygen) [0088] 22 Secondary recirculation gas
for burner unit (part of exhaust gas) [0089] 23 Secondary
recirculation gas for AA unit (part of exhaust gas) [0090] 24
Primary recirculation gas (part of exhaust gas)
* * * * *