U.S. patent application number 13/903502 was filed with the patent office on 2013-12-05 for boiler.
This patent application is currently assigned to Hitachi, Ltd.. The applicant listed for this patent is Hitachi, Ltd.. Invention is credited to Masato HANDA, Yoshiharu HAYASHI, Tsuyoshi SHIBATA.
Application Number | 20130319299 13/903502 |
Document ID | / |
Family ID | 48534253 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130319299 |
Kind Code |
A1 |
HANDA; Masato ; et
al. |
December 5, 2013 |
Boiler
Abstract
In a boiler, a heat exchanger provided in one of two flow paths
formed by partitioning a downstream portion of a flow path for
exhaust gas discharged from a furnace has a smaller total heat
transfer area than a heat exchanger provided in the other of the
two flow paths; the exhaust gases discharged from the flow paths to
outside the boiler are introduced, without being mixed, into an air
heater downstream of the boiler; and, in the air heater, the heat
of the exhaust gases is transferred to the primary air and the
secondary air so as to heat combustion air.
Inventors: |
HANDA; Masato;
(Utsunomiya-shi, JP) ; HAYASHI; Yoshiharu;
(Hitachinaka-shi, JP) ; SHIBATA; Tsuyoshi;
(Hitachiota-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi, Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
48534253 |
Appl. No.: |
13/903502 |
Filed: |
May 28, 2013 |
Current U.S.
Class: |
110/190 ;
110/106; 110/234; 110/265; 110/297; 110/304 |
Current CPC
Class: |
Y02E 20/34 20130101;
F23K 1/00 20130101; Y02E 20/348 20130101; F23L 15/00 20130101; F23L
15/04 20130101; F23L 9/00 20130101; F23N 3/002 20130101; F23D 1/005
20130101 |
Class at
Publication: |
110/190 ;
110/265; 110/304; 110/106; 110/234; 110/297 |
International
Class: |
F23L 15/04 20060101
F23L015/04; F23N 3/00 20060101 F23N003/00; F23L 9/00 20060101
F23L009/00; F23D 1/00 20060101 F23D001/00; F23K 1/00 20060101
F23K001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2012 |
JP |
2012-121630 |
Claims
1. A boiler comprising: a furnace for burning solid fuel; a fuel
mill for pulverizing the solid fuel; a solid fuel feeding pipe for
conveying the solid fuel from the fuel mill to the furnace; a
burner for igniting the solid fuel; an air port for introducing air
into the furnace; an air heater for recovering heat from exhaust
gas and heating primary air and secondary air to be supplied to the
furnace; a primary combustion air supply duct for introducing the
primary air from the air heater to the fuel mill; a secondary
combustion air supply duct for introducing the secondary air from
the air heater into the burner and the air port; an air duct for
introducing air into the air heater; an exhaust gas duct for
introducing exhaust gas into the air heater; a partition wall for
partitioning a downstream portion of a flow path for exhaust gas
discharged from the furnace; and a plurality of heat exchangers
which are provided in the flow paths formed on both sides of the
partition wall, recover heat from the exhaust gases flowing through
the flow paths and heat steam using the recovered heat, wherein the
heat exchanger provided in the flow path on a first side of the
partition wall has a smaller total heat transfer area than the heat
exchanger provided in the flow path on a second side of the
partition wall; wherein the exhaust gases discharged from the flow
paths to outside the boiler are introduced, without being mixed,
into the air heater downstream of the boiler; and wherein, in the
air heater, the heat of the exhaust gases is transferred to the
primary air and the secondary air so as to heat combustion air.
2. The boiler according to claim 1, wherein the air heater
comprises a low-temperature air heater which is provided downstream
of the heat exchanger having a larger heat transfer area and which
heats the primary air and a high-temperature air heater which is
provided downstream of the heat exchanger having a smaller heat
transfer area and which heats the secondary air.
3. The boiler according to claim 1, wherein the heat exchanger
having a larger heat transfer area is used to heat reheat steam and
the heat exchanger having a smaller heat transfer area is used to
heat main steam.
4. The boiler according to claim 2, wherein the heat exchanger
having a larger heat transfer area is used to heat reheat steam and
the heat exchanger having a smaller heat transfer area is used to
heat main steam.
5. The boiler according to claim 2, further comprising a de-NOx
device which the exhaust gas flowing through the flow path provided
with the heat exchanger having a larger heat transfer area enters
before passing through the low-temperature air heater and which
removes nitrogen oxide contained in the exhaust gas, wherein the
secondary air enters, after being heated by the low-temperature air
heater, the high-temperature air heater to be heated therein by the
exhaust gas flowing through the flow path provided with the heat
exchanger having a smaller heat transfer area.
6. The boiler according to claim 4, further comprising a de-NOx
device which the exhaust gas flowing through the flow path provided
with the heat exchanger having a larger heat transfer area enters
before passing through the low-temperature air heater and which
removes nitrogen oxide contained in the exhaust gas, wherein the
secondary air enters, after being heated by the low-temperature air
heater, the high-temperature air heater to be heated therein by the
exhaust gas flowing through the flow path provided with the heat
exchanger having a smaller heat transfer area.
7. The boiler according to claim 5, wherein, after entering the
high-temperature air heater and being heat-exchanged therein, the
exhaust gas flowing through the flow path provided with the heat
exchanger having a smaller heat transfer area enters the de-NOx
device and, along with the exhaust gas flowing through the flow
path provided with the heat exchanger having a larger heat transfer
area, has nitrogen oxide removed therein before entering the
low-temperature air heater.
8. The boiler according to claim 6, wherein, after entering the
high-temperature air heater and being heat-exchanged therein, the
exhaust gas flowing through the flow path provided with the heat
exchanger having a smaller heat transfer area enters the de-NOx
device and, along with the exhaust gas flowing through the flow
path provided with the heat exchanger having a larger heat transfer
area, has nitrogen oxide removed therein before entering the
low-temperature air heater.
9. The boiler according to claim 1, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
10. The boiler according to claim 2, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
11. The boiler according to claim 3, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
12. The boiler according to claim 4, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
13. The boiler according to claim 5, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
14. The boiler according to claim 6, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
15. The boiler according to claim 7, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
16. The boiler according to claim 8, wherein the air duct is
provided with an air flow regulator, the exhaust gas duct is
provided with an exhaust gas flow regulator, and the primary
combustion air supply duct is, at an intermediate portion thereof,
provided with an air thermometer; and wherein the air flow
regulator and the exhaust gas flow regulator operate to adjust an
air flow and an exhaust gas flow based on the output of the air
thermometer so as to keep the temperature measured by the air
thermometer of the primary combustion air flowing through the
primary combustion air supply duct at a desired level.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese Patent
application serial No. 2012-121630, filed on May 29, 2012, the
content of which is hereby incorporated by reference into this
application.
TECHNICAL FIELD
[0002] The present invention relates to a boiler and, more
particularly, to a boiler in which fuel is burned to generate
high-temperature steam for driving a steam-turbine power generation
facility and which is suitably applicable to thermal power
generation.
BACKGROUND ART
[0003] Generally, at a thermal power generation plant where fuel is
burned to generate steam using a boiler, a means for recovering
heat from the exhaust gas discharged from the boiler is used to
improve thermal efficiency.
[0004] Among thermal power generation plants where coal is used as
fuel, in particular, a technique is widely used in which an air
heater is provided on a gas duct coupled to the boiler outlet,
combustion air is heated using the heat of exhaust gas, and the
heated combustion air is supplied to the boiler to promote burning
of fuel so as to improve thermal efficiency of the boiler.
[0005] In Patent Literature 1 (JP-A No. 2008-145007), for example,
a technique is disclosed in which a boiler includes a temperature
detector for detecting the temperature of primary air, a primary
air temperature adjusting means for adjusting the temperature of
primary air, and a control device for controlling the primary air
temperature adjusting means based on the temperature detected by
the temperature detector so as to keep the temperature of the
primary air at a predetermined level and in which the ignitability
and combustibility of coal is stabilized by adjusting the
combustion air temperature according to the quality of coal.
[0006] In Patent Literature 2 (International Publication No. WO
94/02784), a device is disclosed which allows gases of different
temperatures to flow through two systems of flow paths without
leaking and which allows flow path switching. The device described
as being applied to a boiler includes two fixed chambers which are
coupled to each other via a partition wall and which are provided
in two systems of flow paths whose flow directions are fixed. In
this configuration, exhaust gas from the boiler is, after being
introduced into a downstream changeover chamber, made to enter a
fixed chamber to be heated by heat storage material therein and is
subsequently guided to the upstream side.
[0007] According to Patent Literature 2, no gas leakage occurs
between the two systems of flow paths and the device with a simple
construction enables flow path switching at high speed. This makes
it possible to improve the performance of an air heater to thereby
improve the thermal efficiency of the whole plant.
CITATION LIST
Patent Literature
[0008] [Patent Literature 1] JP-A No. 2008-145007
[0009] [Patent Literature 2] International Publication No. WO
94/02784
SUMMARY OF INVENTION
Technical Problem
[0010] The problem to be solved by the present invention will be
described below with reference to FIG. 1.
[0011] Generally, for existing types of coal-fired boilers used in
thermal power generation plants, a two-staged combustion method is
used to suppress the generation of nitrogen oxide caused when coal
is burned.
[0012] In the two-staged combustion method, air is fed to a boiler
through two systems, i.e. a primary air system for feeding fuel and
a secondary air system for promoting fuel combustion. The primary
air is fed with an excess air ratio smaller than 1 and undergoes
primary combustion on a rich fuel side. This is to prevent the
nitrogen compound generated by thermal decomposition from being
converted into nitrogen oxide and to promote, using the secondary
air, burning of unburned coal components and decomposition of
nitrogen compound.
[0013] As shown in FIG. 1, the primary and the secondary air are
heated, using the heat of exhaust gas from a boiler 1, at an air
heater 2 provided at the exhaust gas outlet of the boiler 1.
Generally, the exhaust gas temperature is set to about 350.degree.
C. on the air heater 2 inlet side and to about 130.degree. C. on
the air heater 2 outlet side.
[0014] Also, in many cases, to keep the reheat steam temperature at
a desired level, a downstream flow path portion for exhaust gas
(i.e. a portion around an economizer 16, a primary superheater 17
and a primary reheater 20 shown in a right-hand part of FIG. 1) is
partitioned by a partition wall 6; the partitioned flow path formed
on each side of the partition wall 6 is provided, at a downstream
part thereof, with a damper 7 for adjusting the exhaust gas flow
through the partitioned flow path so as to eventually adjust the
heat collection of the primary reheater 20 and the final reheater
21. This configuration is generally designed such that the exhaust
gas temperatures at around the outlets of the respective flow paths
are equal.
[0015] In recent years, in attempts to further improve the thermal
efficiency of power generation systems, various measures are
adopted. In one of such measures, for example, the secondary air is
heated to a higher temperature. Generally, the secondary air
temperature is set to about 330.degree. C. By further raising the
secondary air temperature, unburned components can be further
reduced to improve the thermal efficiency of the boiler 1.
[0016] As described in the foregoing, however, the exhaust gas
temperature at the outlet of an existing type of boiler 1 is about
350.degree. C., whereas the temperature to which air can be heated
by the air heater 2 is about 330.degree. C. at the highest. To
further raise the air temperature, it is necessary to raise the
exhaust gas temperature by appropriately reducing the heat transfer
area of the boiler 1 while maintaining the heat collection of steam
in the whole boiler. Generally, to adjust the heat transfer area of
the boiler, the heat transfer area of heat exchangers such as the
economizer 16, primary superheater 17, and primary reheater 20
provided in an exhaust gas downstream portion are adjusted.
[0017] Reducing the heat transfer area of the primary superheater
17 or the economizer 16 provided in the exhaust gas downstream
portion causes the exhaust gas temperature to rise on the right
side of the partition wall 6, shown in FIG. 1, resulting in
generating a large temperature difference between the two sides of
the partition wall 6. Namely, whereas the exhaust gas temperature
at around the flow path outlet on the left side of the partition
wall 6 is comparable to that in an existing type of boiler, the
exhaust gas temperature at around the flow path outlet on the main
steam side (on the right side of the partition wall 6) becomes
about 500.degree. C.
[0018] Hence, when the exhaust gases from both flow paths are mixed
as they are, the resultant exhaust gas temperature becomes about
420.degree. C. Thus, in existing types of boilers, the secondary
air temperature cannot be largely increased.
[0019] An object of the present invention is to provide a boiler in
which the secondary air temperature can be efficiently increased
for higher thermal efficiency by appropriately reducing the heat
transfer area of the boiler while maintaining the heat collection
of steam in the whole boiler.
Solution to Problem
[0020] To achieve the above object, a boiler according to the
present invention includes: a furnace for burning solid fuel; a
fuel mill for pulverizing the solid fuel; a solid fuel feeding pipe
for conveying the solid fuel from the fuel mill to the furnace; a
burner for igniting the solid fuel; an air port for introducing air
into the furnace; an air heater for recovering heat from exhaust
gas and heating primary air and secondary air to be supplied to the
furnace; a primary combustion air supply duct for introducing the
primary air from the air heater to the fuel mill; a secondary
combustion air supply duct for introducing the secondary air from
the air heater into the burner and the air port; an air duct for
introducing air into the air heater; an exhaust gas duct for
introducing exhaust gas into the air heater; a partition wall for
partitioning a downstream portion of a flow path for exhaust gas
discharged from the furnace; and a plurality of heat exchangers
which are provided in the flow paths formed on both sides of the
partition wall, recover heat from the exhaust gases flowing through
the flow paths and heat steam using the recovered heat. In the
boiler: the heat exchanger provided in the flow path on a first
side of the partition wall has a smaller total heat transfer area
than the heat exchanger provided in the flow path on a second side
of the partition wall; the exhaust gases discharged from the flow
paths to outside the boiler are introduced, without being mixed,
into the air heater downstream of the boiler; and the heat of the
exhaust gases is transferred to the primary air and the secondary
air in the air heater so as to heat combustion air.
Advantageous Effects of Invention
[0021] In a boiler according to the present invention, the
secondary air temperature can be efficiently increased by
appropriately reducing the heat transfer area of the boiler while
maintaining the heat collection of steam in the whole boiler. This
makes it possible to burn unburned components to improve the
thermal efficiency of the boiler.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a diagram showing the configuration of an existing
type of boiler.
[0023] FIG. 2 is a diagram showing the configuration of a
coal-fired boiler according to a first embodiment of the present
invention.
[0024] FIG. 3 is a diagram schematically showing a rotary heat
storage material type heat exchanger used as an air heater in the
first embodiment of the boiler according to the present
invention.
[0025] FIG. 4 is a diagram showing the configuration of a
coal-fired boiler according to a second embodiment of the present
invention.
[0026] FIG. 5 is a diagram showing the configuration of a
coal-fired boiler according to a third embodiment of the present
invention.
[0027] FIG. 6 is a diagram showing the configuration of a
coal-fired boiler according to a fourth embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0028] A boiler according to the present invention will be
described below based on illustrated embodiments. In the drawings
referred to in the following description, parts identical to those
shown in FIG. 1 representing the configuration of an existing type
of boiler are denoted by reference numerals identical to those used
in FIG. 1.
First Embodiment
[0029] FIG. 2 shows the configuration of a coal-fired boiler
according to a first embodiment of the present invention.
[0030] As shown in FIG. 2, a coal-fired boiler 1 according to the
present embodiment broadly includes: a furnace 23 to burn coal,
i.e. solid fuel; a fuel mill, i.e. a coal mill 10, to pulverize
coal; a solid fuel feeding pipe, i.e. a coal feeding pipe 12, used
to feed coal from the coal mill 10 to the furnace 23; plural
burners 4 used to ignite the coal in the furnace 23; air ports 5
for introducing air into the furnace 23; an air heater 2 which
recovers heat from exhaust gas and heats the primary and secondary
air to be supplied to the furnace 23; a primary combustion air
supply duct 8 to introduce the primary air from the air heater 2
into the coal mill 10; a secondary combustion air supply duct 9 to
introduce the secondary air from the air heater 2 into the burners
4 and air ports 5; air ducts 3b1 and 3b2 to introduce air into the
air heater 2; exhaust gas ducts 3a1 and 3a2 to introduce exhaust
gas into the air heater 2; a partition wall 6 partitioning a
downstream portion of a flow path for the exhaust gas discharged
from the furnace 23; and heat exchangers which, being provided in
the flow paths formed on both sides of the partition wall 6,
recover heat from the exhaust gases flowing through the flow paths
and heat steam, the heat exchangers including an economizer 16, a
primary superheater 17, a secondary superheater 18, a final
superheater 19, a primary reheater 20, and a final reheater 21.
[0031] Fuel coal is supplied to the coal mill 10 to be pulverized
into particles sized to be suitable for burning in the boiler 1. To
the coal mill 10, the air (primary air) heated by the air heater 2
is supplied through the primary combustion air supply duct 8. The
primary air dries the pulverized coal and carries the pulverized
coal to outside the coal mill 10.
[0032] The pulverized coal is conveyed, together with the primary
air, to the burners 4 through the coal feeding pipe 12 to be
ignited and to be then fed into the boiler 1. The boiler 1 also has
the secondary air supplied from the air heater 2 through the
secondary combustion air supply duct 9 and via the burners 4 and
air ports 5.
[0033] Burning the pulverized coal using the air heated by the air
heater 2 using exhaust gas as described above causes
high-temperature combustion gas to be generated in the boiler 1.
The heat of the combustion gas is transferred to water or steam at
a group of heat exchangers (secondary superheater 18, final
superheater 19, final reheater 21, primary superheater 17,
economizer 16, primary reheater 20) installed in the boiler 1 to
generate high-temperature, high-pressure steam. The
high-temperature, high-pressure steam is fed, through a steam pipe
(not shown), to a steam turbine power generation facility (not
shown) to have the energy of the steam converted into electricity
therein.
[0034] The flow path for the exhaust gas is, in a downward portion
thereof, partitioned into two parts by the partition wall 6. In
FIG. 2, the primary reheater 20 is installed on the left side of
the partition wall 6, whereas the economizer 16 and the primary
superheater 17 are installed on the right side of the partition
wall 6. With the primary reheater 20 having a heat transfer area
comparable with that in an existing type of boiler, reducing the
total heat transfer area(s) of one or both of the economizer 16 and
the primary superheater 17 (for example, making the economizer 16
and/or the primary superheater 17 smaller shortens the heat
transfer pipe correspondingly reducing the total heat transfer
area) results in a higher exhaust gas temperature in the right-side
flow path whereas the exhaust gas temperature in the left-side flow
path remains about the same as in an existing type of boiler. If,
for example, the heat transfer area is reduced by an area
equivalent to the whole area of the economizer 16 in the present
state, the temperature of the exhaust gas near the damper 7 in the
right-side flow path becomes about 550.degree. C.
[0035] In the present embodiment, the low-temperature exhaust gas
flowing through the left-side flow path and the high-temperature
exhaust gas flowing through the right-side flow path are introduced
into the air heater 2 via separate exhaust gas ducts 3a1 and 3a2,
respectively.
[0036] FIG. 3 schematically shows, as an exemplary configuration of
the preferred air heater 2 of the present embodiment, a rotary heat
storage material type heat exchanger widely used in coal-fired
boilers.
[0037] In the present embodiment, to achieve efficient heat
exchange, four separate gas flow paths (ducts), i.e. two each on
the exhaust gas side and on the air side, are arranged, as shown in
FIG. 3, along the rotary direction of the heat storage
material.
[0038] Namely, the rotary heat storage material first passes the
exhaust gas flow path (exhaust gas duct 3a1) on the low-temperature
side to be heated by the low-temperature exhaust gas; next passes
the exhaust gas flow path (exhaust gas duct 3a2) to be further
heated by the high-temperature exhaust gas; and subsequently passes
the secondary air flow path (air duct 3b1) and the primary air flow
path (air duct 3b2) in this order to release the stored heat while
passing the air ducts.
[0039] The above-described configuration of the present embodiment
makes it possible to heat the secondary air up to about 500.degree.
C. so as to reduce the unburned components of coal. This improves
thermal efficiency of the boiler 1.
[0040] As the secondary air heated to a high temperature improves
the combustion efficiency of coal, heat collection by the boiler 1
in its upstream gas flow portion increases. Therefore, even when
the heat transfer area of one or both of the economizer 16 and the
primary superheater 17 is reduced to be smaller than in existing
types of boilers as mentioned above, heat collection by the boiler
as a whole can be secured. When necessary to secure adequate heat
collection by the boiler 1, the heat transfer area of the secondary
superheater 18 or final superheater 19 may be increased.
Second Embodiment
[0041] FIG. 4 shows the configuration of a coal-fired boiler
according to a second embodiment of the present invention.
[0042] The boiler of the second embodiment includes many parts
identical in operation to those used in the first embodiment. In
the following, the boiler of the second embodiment will be
described only with regard to what it differs from the boiler of
the first embodiment. The parts of the boiler not described in the
following are identical in operation and effects to those used in
the first embodiment.
[0043] In the second embodiment, unlike in the first embodiment,
two air heaters are used as shown in FIG. 4. Namely, the heat of
the exhaust gas, whose temperature is about the same as in existing
types of boilers, flowing through the left-side flow path
downstream of the boiler is recovered by a low-temperature air
heater 2a and is used to heat the primary air. The heat of the
high-temperature exhaust gas flowing through the right-side flow
path, on the other hand, is recovered by a high-temperature air
heater 2b and is used to heat the secondary air.
[0044] The above-described configuration of the present embodiment
also makes it possible to obtain the advantageous effects of the
foregoing first embodiment. Furthermore, in the present embodiment,
with the two separate air heaters, i.e. the low-temperature air
heater 2a and the high-temperature air heater 2b, provided, it is
easy to maintain high heat-exchange efficiency, so that the
secondary air can be stably maintained at high temperature.
[0045] It is feared that a heat exchanger of a rotary heat storage
material type involves leakage between flowing gases. In the
present embodiment, however, leakage occurs neither between the
low-temperature and the high-temperature exhaust gas nor between
the primary and the secondary air, so that stable heat exchange is
realized.
Third Embodiment
[0046] FIG. 5 shows the configuration of a coal-fired boiler
according to a third embodiment of the present invention.
[0047] The boiler of the third embodiment includes many parts
identical in operation to those used in the second embodiment. In
the following, the boiler of the third embodiment will be described
only with regard to what it differs from the boiler of the second
embodiment. The parts of the boiler not described in the following
are identical in operation and effects to those used in the second
embodiment.
[0048] There are two differences between the present embodiment
shown in FIG. 5 and the second embodiment. A first difference is
that, in the present embodiment, the exhaust gas flowing through
the exhaust gas flow path on the low-temperature side (exhaust gas
duct 3a1) where a heat exchanger having a large heat transfer area
is installed is introduced into the low-temperature air heater 2a
via a de-NOx device 15 for removing nitrogen oxide contained in the
exhaust gas. A second difference is that, after passing through the
low-temperature air heater 2a used to heat the primary air, the
secondary air is, for further heating, made to flow through the
high-temperature air heater 2b along with the high-temperature
exhaust gas.
[0049] Namely, the exhaust gas flowing through the exhaust gas duct
3a1 on the low-temperature side where a heat exchanger having a
large heat transfer area is installed passes, before entering the
low-temperature air heater 2a, the de-NOx device 15 for removing
nitrogen oxide contained in the exhaust gas. At the same time, the
secondary air enters, after being heated in the low-temperature air
heater 2a, the high-temperature air heater 2b to be heated therein
by the exhaust gas flowing through the exhaust gas duct 3a2 in
which a heat exchanger having a small heat transfer area is
installed.
[0050] The exhaust gas flowing through the exhaust gas duct 3a2 in
which a heat exchanger having a small heat transfer area is
installed enters the high-temperature air heater 2b and, after
being heat-exchanged therein, enters the de-NOx device 15. In the
de-NOx device 15, the exhaust gas, along with the exhaust gas
flowing through the exhaust gas duct 3a1 in which a heat exchanger
having a large heat transfer area is installed, has nitrogen oxide
removed from it to be then introduced into the low-temperature air
heater 2a.
[0051] The de-NOx device 15 used in the present embodiment is for
removing nitrogen oxide contained in exhaust gas. The catalyst
de-NOx device of an ammonia spray type capable of efficiently
removing nitrogen oxide operates optimally at about 350.degree. C.
and is normally installed on the upstream side of an air
heater.
[0052] In cases where, as assumed in the present embodiment, the
outlet temperature of the boiler 1 becomes 400.degree. C. or
higher, the location where the de-NOx device is installed in the
present embodiment is appropriate. Namely, using the configuration
of the present embodiment makes it possible not only to obtain
advantageous effects similar to those obtained in the foregoing
second embodiment but also to maintain high performance for
nitrogen oxide removal.
Fourth Embodiment
[0053] FIG. 6 shows the configuration of a coal-fired boiler
according to a fourth embodiment of the present invention.
[0054] The boiler of the fourth embodiment includes many parts
identical in operation to those used in the second embodiment.
[0055] In the following, the boiler of the fourth embodiment will
be described only with regard to what it differs from the boiler of
the second embodiment. The parts of the boiler not described in the
following are identical in operation and effects to those used in
the second and third embodiments.
[0056] In the present embodiment shown in FIG. 6, the
low-temperature air heater 2a and the high-temperature air heater
2b are provided as in the second embodiment. The present
embodiment, however, differs from the second embodiment as follows:
an air flow regulator 11a is coupled to the air duct 3b1; an air
flow regulator 11b is coupled to the air duct 3b2; an air flow
regulator 11c is coupled to an air communication duct 3b3
intercoupling the air duct 3b1 and the air duct 3b2; an exhaust gas
flow regulator 13a is coupled to the exhaust gas duct 3a1, an
exhaust gas flow regulator 13b is coupled to the exhaust gas duct
3a2; an exhaust gas flow regulator 13c is coupled to an exhaust gas
communication duct 3a3 intercoupling the exhaust gas duct 3a1 and
the exhaust gas duct 3a2; and an air thermometer 22 is coupled to
the primary combustion air supply duct 8.
[0057] In the present embodiment, the air flow regulators 11a, 11b
and 11c and the exhaust gas flow regulators 13a, 13b and 13c
function to adjust the respective air flows and exhaust gas flows
based on the output of the air thermometer 22 so as to keep the
temperature measured by the air thermometer 22 of the primary
combustion air passing through the primary combustion air supply
duct 8 at a desired level.
[0058] The above-described configuration of the present embodiment
also makes it possible to obtain the advantageous effects of the
foregoing second embodiment. Furthermore, the present embodiment in
which the air flow regulators 11a, 11b and 11c, the exhaust gas
flow regulators 13a, 13b and 13c, and the air thermometer 22 are
provided so as to keep the temperature of the primary air at a
desired level can be flexibly applied to boilers using diversified
kinds of coal.
[0059] While the present invention has been described with
reference to its preferred embodiments, it is to be understood that
the invention is not limited thereto but may be otherwise variously
embodied within the scope of the invention. Typically, the
embodiments have been described in detail so as to illustrate the
present invention clearly, and the present invention is not limited
to ones including all the described configurations. Substitution of
part of a configuration of one embodiment with a configuration of
another embodiment is possible; and addition of a configuration of
one embodiment to a configuration of another embodiment is also
possible. Additions, deletions, and substitutions of part of a
configuration of an embodiment with or by another configuration can
also be made.
REFERENCE SIGNS LIST
[0060] 1 . . . Boiler [0061] 2 . . . Air heater [0062] 2a
Low-temperature air heater [0063] 2b High-temperature air heater
[0064] 3a1, 3a2 Exhaust gas duct [0065] 3a3 Exhaust gas
communication duct [0066] 3b1, 3b2 Air duct [0067] 3b3 Air
communication duct [0068] 4 Burner [0069] 5 Air port [0070] 6
Partition wall [0071] 7 Damper [0072] 8 Primary combustion air
supply duct [0073] 9 Secondary combustion air supply duct [0074] 10
Coal mill [0075] 11a, 11b, 11c Air flow regulator [0076] 12 Coal
feeding pipe [0077] 13a, 13b, 13c Exhaust gas flow regulator [0078]
15 De-NOx device [0079] 16 Economizer [0080] 17 Primary superheater
[0081] 18 Secondary superheater [0082] 19 Final superheater [0083]
20 Primary reheater [0084] 21 Final reheater [0085] 22 Air
thermometer [0086] 23 Furnace
* * * * *