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; 5 aburner for ignitingthe solid fuel; an airport 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 10 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 15 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, 2 0 wherein the heat exchanger provided in the flow path on a first side of the partitionwall has a smaller total heat transfer area than theheat exchangerprovidedinthe flowpathonasecond side ofthepartitionwall; wherein the exhaust gases discharged fromthe flowpathsto outsidetheboilerareintroduced, without 25 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. 5 2. The boiler according to claim 1, wherein the exhaust gases discharged from the flow paths on the first side of the partition wall and on the second side ofthe partition wall to outside the boiler are introducedinto the air heater via the exhaust gas ducts separately and 10 respectively.

3. The boiler according to claim 1 or 2, wherein the air heater comprises a low-temperature air heaterwhichisprovideddownstreamoftheheatexchangerhaving 15 a larger heat transfer area and which heats the primary air and a high-temperature air heater which is provided downstream of theheatexchangerhavinga smallerheattransfer area andwhich heats the secondary air. 20 4. The boiler according to one of claims 1 to 3, 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. 25 5. The boiler according to one of claims 3 and 4, further comprisingade-NOxdevicewhichthe exhaust gas flowing through the flow path provided with the heat exchanger having a l a r g e r heat t r a n s f e r area e n t e r s before passing through the low-temperature a i r heater and which removes nitrogen oxide 5 contained i n the exhaust gas, wherein the secondary a i r e n t e r s , a f t e r being heated by the low-temperature a i r heater, thehigh-temperature a i r heater t o be heated t h e r e i n b y the exhaust gas flowing through the flow path provided with the heat exchanger having a smaller h e a t 10 t r a n s f e r area.

6. The b o i l e r according t o claim 5, wherein, a f t e r entering the high-temperature a i r heater andbeingheat-exchangedtherein,theexhaustgasflowingthrough 15 the flow path provided with the heat exchanger having a smaller heat t r a n s f e r area e n t e r s the de-NOx device and, along with the exhaust gas flowing through t h e f l o w p a t h p r o v i d e d w i t h t h e heat exchangerhavinga l a r g e r h e a t t r a n s f e r area, has nitrogenoxide removedthereinbefore e n t e r i n g t h e low-temperature a i r h e a t e r . 2 0

7. The b o i l e r according t o one of claims 1 t o 6, whereintheairductisprovidedwithanair flowregulator, the exhaust gas duct is providedwith an exhaust gas flow regulator, andtheprimarycombustionair supplyduct is, a t anintermediate 25 p o r t i o n t h e r e o f , provided with an a i r 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 5 combustionairflowingthroughtheprimarycombustionairsupply duct at a desired level.

8. Aboiler, substantiallyashereindescribedwithreference to accompanying drawings and examples.

[Title of the Invention]
BOILER
[Technical Field]
5 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 andwhich is suitably applicable to thermal
power generation.
[Background Art]
Generally, at a thermal power generation plant where fuel
isburnedtogeneratesteamusingaboiler, ameans forrecovering
heat from the exhaust gas discharged from the boiler is used
15 to improve thermal efficiency.
Among thermal power generation plants where coal is used
as fuel, in particular, a technique is widely used in which an
air heater is providedona gas duct coupled totheboiler outlet,
combustion air is heated using the heat of exhaust gas, and the
20 heated combustion air is supplied to the boiler to promote burning
of fuel so as to improve thermal efficiency of the boiler.
InPatentLiteraturel (JP-ANo. 2008-145007), forexample,
atechniqueisdisclosedinwhichaboilerincludes atemperature
detector fordetectingthetemperature ofprimaryair, aprimary
25 air temperature adjusting means for adjusting the temperature
.
ofprimaryair, anda control device for controlling the primary
airtemperatureadjustingmeansbasedonthetemperaturedetected
by the temperature detector so as to keep the temperature of
the primary air at a predetermined level and in which the
5 ignitability and combustibility of coal is stabilized by
adjusting the combustion air temperature according to the quality
of coal.
In Patent Literature 2 (International Publication No. WO
94/02784), adeviceis disclosedwhichallows gases of different
10 temperatures to flow through two systems of flow paths without
leaking and which allows flow path switching. The device
describedasbeingappliedtoaboilerincludestwofixedchambers
which are coupled to each other via a partition wall and which
are provided in two systems of flow paths whose flow directions
15 are fixed. In this configuration, exhaust gas from the boiler
is, afterbeing introducedinto adownstreamchangeover chamber,
made to enter a fixed chamber to be heatedby heat storage material
therein and is subsequently guided to the upstream side.
According to Patent Literature 2, no gas leakage occurs
20 betweenthe two systemsof flowpathsandthedevicewitha 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.
25 [Citation List]
[Patent Literature]
[Patent Literature 11 JP-A No. 2008-145007
[Patent Literature 21 International Publication No. WO
[Summary of Invention]
[Technical Problem]
The problem to be solved by the present invention will
be described below with reference to FIG. 1.
10 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.
Inthetwo-stagedcombustionmethod, air is fedto aboiler
15 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
preventthenitrogencompoundgeneratedbytherma1decomposition
20 from being converted into nitrogen oxide and to promote, using
the secondary air, burning of unburned coal components and
decomposition of nitrogen compound.
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
25 air heater 2 provided at the exhaust gas outlet of the boiler
C
1. Generally, the exhaust gas temperature is set to about 350°C
on the air heater 2 inlet side and to about 130°C on the air
heater 2 outlet side.
Also, in many cases, to keep the reheat steam temperature
5 at a desired level, a downstream flow path portion for exhaust
gas (i. e. aportion around an economizer 16, aprimary 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,
10 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
15 outlets of the respective flow paths are equal.
Inrecentyears, inattemptsto further improve the thermal
efficiency of power generation systems, various measures are
adopted. In one of such measures, for example, the secondary
airisheatedtoahighertemperature. Generally, the secondary
20 air temperature is set to about 330°C. By further raising the
secondary air temperature, unburned components can be further
reduced to improve the thermal efficiency of the boiler 1.
As described in the foregoing, however, the exhaust gas
temperature at the outlet of an existing type of boiler 1 is
25 about 350°C, whereas the temperature to which air can be heated
.
by the air heater 2 is about 330°C .at the highest. To further
raise the air temperature, it is necessary to raise the exhaust
gastemperaturebyappropriatelyreducingtheheattransferarea
of the boiler 1 while maintaining the heat collection of steam
5 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.
10 Reducingtheheattransferareaoftheprimarysuperheater
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 alargetemperature difference between the two sides
15 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 themain steamside (on the right side ofthe partition
20 wall 6) becomes about 500°C.
Hence, when the exhaust gases from both flow paths are
mixedas they are, the resultant exhaust gas temperaturebecomes
about 420°C. Thus, in existing types of boilers, the secondary
air temperature cannot be largely increased.
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
reducingthe heat transfer area of the boiler whilemaintaining
the heat collection of steam in the whole boiler.
5 [Solution to Problem]
To achieve the above object, a boiler according to the
present invention includes: a furnace for burning solid fuel;
a fuel mill forpulverizingthe solid fuel; a solid fuel feeding
pipe for conveying the solid fuel from the fuel mill to the furnace;
10 aburner forignitingthe solid fuel; anairport 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
15 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
20 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
steamusing the recoveredheat. In the boiler: the heat exchanger
25 provided in the flow path on a first side of the partition wall
has a smaller total heat transfer area than the heat exchanger
providedinthe flowpathon a second side ofthe partitionwall;
the exhaust gases discharged from the flow paths to outside the
boiler are introduced, without being mixed, into the air heater
5 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]
In a boiler according to the present invention, the
10 secondary air temperature can be efficiently increased by
appropriatelyreducingtheheattransferareaoftheboilerwhile
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]
FIG. 1 is a diagram showing the configuration of an existing
type of boiler.
FIG. 2 is a diagram showing the configuration of a coal-fired
20 boiler according to a first embodiment ofthe present invention.
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.
FIG. 4 is a diagram showing the configuration of a coal-fired
25 boiler according to a second embodiment of the present invention.
F I G . 5 is a diagram showing the configuration of a coal-fired
boiler according to athirdembodimentofthepresentinvention.
F I G . 6 is a diagram showing the configuration of a coal-fired
boileraccordingtoafourthembodimentofthepresentinvention.
[Description of Embodiments]
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
10 identicaltothoseshowninFIG.1representingtheconfiguration
of an existing type of boiler are denoted by reference numerals
identical to those used in F I G . 1.
[First Embodiment]
FIG. 2 shows the configuration of a coal-fired boiler
15 according to a first embodiment of the present invention.
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. solidfuel; afuelmill, i.e. acoalmill10, topulverize
I,&
coal; a solid fuel feeding pipe, i .e. a coal feeding pipe 12,
20 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 f romexhaust gas andheats the primary and secondary
air to be supplied to the furnace 23; a primary combustion air
25 supply duct 8 to introduce the primary air from the air heater
2 i n t o the coal m i l l 10; a secondary combustion a i r supply duct
9 t o introduce the secondary a i r from the a i r h e a t e r 2 i n t o the
burners 4 and a i r p o r t s 5; a i r ducts 3bl and 3b2 t o introduce
a i r i n t o the a i r h e a t e r 2; exhaust gas d u c t s 3 a l and 3a2 t o introduce
5 exhaust gas i n t o the a i r heater 2; a p a r t i t i o n wall 6 p a r t i t i o n i n g
adownstreamportionofaflowpathfortheexhaustgasdischarged
from the furnace 23; and heat exchangers which, being provided
i n the flow paths formed on both s i d e s of the p a r t i t i o n wall
6, recover heat from the exhaust gases flowing through the flow
10 p a t h s a n d h e a t s t e a m , theheatexchangersincludinganeconomizer
1 6 , a p r i m a r y s u p e r h e a t e r 1 7 , asecondarysuperheater18, a f i n a l
superheater 19, a primary r e h e a t e r 20, and a f i n a l r e h e a t e r 21.
Fuel coal is supplied t o the coal m i l l 10 t o be pulverized
i n t o p a r t i c l e s sized t o be s u i t a b l e f o r burning i n the b o i l e r
15 1. To the coal m i l l 10, the a i r (primary a i r ) heated by the
a i r heater 2 is supplied through theprimarycombustion a i r supply
duct 8. The primary a i r d r i e s the pulverized coal and c a r r i e s
the pulverized coal t o outside the coal m i l l 1 0 .
Thepulverizedcoalisconveyed, t o g e t h e r w i t h theprimary
20 a i r , t o the burners 4 through the coal feeding pipe 12 t o be
I i g n i t e d and t o be then fed i n t o the b o i l e r 1. The b o i l e r 1 a l s o
has the secondary a i r supplied from the a i r h e a t e r 2 through
the secondary combustion a i r supply duct 9 and via the burners
4 and a i r p o r t s 5.
2 5 Burning the pulverized coal using the a i r 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,
5 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
10 (not shown) to have the energy of the steam converted into
electricity therein.
The flowpath forthe exhaust gas is, inadownwardportion
thereof, partitioned into two parts by the partition wall 6.
In FIG. 2, the primary reheater 20 is installed on the left side
15 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
areacomparablewiththat inanexistingtypeofboiler, reducing
the total heat transfer area(s) of one or both of the economizer
20 16 and the primary superheater 17 (for example, making the
economizer16and/ortheprimarysuperheater17 smallershortens
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
25 in the left-side flow path remains about the same as in an existing
typeof 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°C.
In the present embodiment, the low-temperature exhaust
gas flowing through the left-side flow path and the
high-temperatureexhaust gas flowingthroughtheright-side flow
path are introduced into the air heater 2 via separate exhaust
gas ducts 3al and 3a2, respectively.
10 FIG. 3 schematically shows, as an exemplaryconfiguration
ofthepreferredairheater2 ofthepresent embodiment, a rotary
heat storage material type heat exchanger widely used in
coal-fired boilers.
In the present embodiment, to achieve efficient heat
15 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.
Namely, the rotaryheat storage material first passes the
20 exhaust gas flow path (exhaust gas duct 3al) on the
low-temperaturesidetobeheatedbythelow-temperatureexhaust
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
25 3bl) and the primary air flow path (air duct 3b2) in this order
t o release the stored heat while passing the a i r ducts.
The above-described configuration of the present
embodiment makes it possible t o heat the secondary a i r up t o
about 500°C so as t o reduce the unburned components of coal.
5 This improves thermal e f f i c i e n c y of the b o i l e r 1.
As the s e c o n d a r y a i r h e a t e d t o ahightemperatureimproves
the combustionefficiencyof coal, heat c o l l e c t i o n b y the b o i l e r
1 i n i t s upstream gas flow p o r t i o n i n c r e a s e s . Therefore, even
when the heat t r a n s f e r area of one or both of the economizer
10 16 and the primary superheater 17 is reduced t o be smaller than
inexistingtypesofboilers asmentionedabove, heat c o l l e c t i o n
b y t h e b o i l e r as awholecanbe secured. Whennecessaryto secure
a d e q u a t e h e a t c o l l e c t i o n b y t h e b o i l e r 1 , t h e h e a t t r a n s f e r area
of the secondary superheater 18 or f i n a l superheater 19 may be
15 increased.
[Second Embodiment]
FIG. 4 shows the configuration of a c o a l - f i r e d b o i l e r
according t o a second embodiment of the p r e s e n t i n v e n t i o n .
The b o i l e r of the second embodiment includes many p a r t s
20 i d e n t i c a l i n operation t o those used i n the f i r s t embodiment.
In the following, the b o i l e r of the second embodiment w i l l be
described only with regard t o what it d i f f e r s from the b o i l e r
of the f i r s t embodiment. The p a r t s of the b o i l e r not described
i n the followingareidenticalinoperationandeffectstothose
25 used i n the f i r s t embodiment.
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
5 path downstreamofthe boiler is recoveredby alow-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 usedtoheatthe secondary
10 air.
The above-described configuration of the present
embodiment also makes it possible to obtain the advantageous
effects ofthe foregoing first embodiment. Furthermore, in the
present embodiment, with the two separate air heaters, i .e. the
15 low-temperature air heater 2a and the high-temperature air heater
2b, provided, it is easy tomaintainhighheat-exchange efficiency,
so that the secondary air can be stably maintained at high
temperature.
It is fearedthataheatexchangerof a rotaryheatstorage
20 material type involves leakage between flowing gases. In the
present embodiment, however, leakage occurs neitherbetweenthe
low-temperatureandthehigh-temperatureexhaustgasnorbetween
the primary and the secondary air, so that stable heat exchange
is realized.
25 [Third Embodiment]
FIG. 5 shows the configuration of a coal-fired boiler
according to a third embodiment of the present invention.
The boiler of the third embodiment includes many parts
identical in operation to those used in the second embodiment.
5 In the following, the boiler of the third embodiment will be
described only with regard to what it differs from the boiler
ofthe second embodiment. The parts oftheboiler not described
in the following are identical inoperation andeffects tothose
used in the second embodiment.
10 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 3al) where a heat exchanger having a large
15 heat transfer area is installed is introduced into the
low-temperatureairheaterzaviaade-NOxdevice15 forremoving
nitrogenoxidecontainedintheexhaustgas. Aseconddifference
is that, after passing through the low-temperature air heater
2 a u s e d t o h e a t t h e p r i m a r y a i r , the secondaryairis, for further
20 heating, made to flow through the high-temperature air heater
2b along with the high-temperature exhaust gas.
Namely, the exhaust gas flowing through the exhaust gas
duct 3al on the low-temperature side where a heat exchanger having
a large heat transfer area is installed passes, before entering
25 the low-temperature air heater Za, 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
5 exhaust gas duct 3a2 in which a heat exchanger having a small
heat transfer area is installed.
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
10 being heat-exchangedtherein, 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 3al 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
15 low-temperature air heater 2a.
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
efficientlyremovingnitrogenoxideoperates optimallyatabout
20 350°C and is normally installed on the upstream side of an air
heater.
In cases where, as assumed in the present embodiment, the
outlet temperature of the boiler 1 becomes 400'~ or higher, the
location where the de-NOx device is installed in the present
25 embodiment is appropriate. Namely, using the configuration of
the present embodiment makes it possible not only to obtain
advantageous effects similar to those obtainedinthe foregoing
second embodiment but also to maintain high performance for
nitrogen oxide removal.
5 [Fourth Embodiment]
FIG. 6 shows the configuration of a coal-fired boiler
according to a fourth embodiment of the present invention.
The boiler of the fourth embodiment includes many parts
identical in operation to those used in the second embodiment.
10 In the following, the boiler of the fourth embodiment will be
described only with regard to what it differs from the boiler
ofthe secondembodiment. The parts of theboiler not described
in the followingareidenticalinoperationandeffectstothose
used in the second and third embodiments.
In the present embodiment shown in FIG. 6, the
2b are provided as in the second embodiment. The present
embodiment, however, differs from the second embodiment as
follows: an air flow regulator lla is coupled to the air duct
20 3bl; an air flow regulator llb is coupled to the air duct 3b2;
an air flow regulator llc is coupled to an air communication
duct 3b3 intercoupling the air duct 3bl 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
25 exhaustgasduct3a2; anexhaust gas flowregulator13cis coupled
to an exhaust gas communication duct 3a3 intercoupling the
exhaust gas duct 3al and the exhaust gas duct 3a2; and an air
thermometer 22 is coupled to the primary combustion air supply
duct 8.
In the present embodiment, the air flow regulators lla,
llb and llc 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
10 primary combustion air passing through the primary combustion
air supply duct 8 at a desired level.
The above-described configuration of the present
embodiment also makes it possible to obtain the advantageous
effects of the foregoing second embodiment. Furthermore, the
15 present embodiment in which the air flow regulators lla, llb
and llc, the exhaust gas flow regulators 13a, 13b and 13c, and
the air thermometer 22 areprovidedso as to keep the temperature
of the primary air at a desired level can be flexibly applied
to boilers using diversified kinds of coal.
2 o 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
variouslyembodiedwithin the scope of the invention. Typically,
theembodimentshavebeendescribedindetailsoastoillustrate
25 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
5 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]
10 1 Boiler
2 ... Air heater
2a Low-temperature air heater
2b High-temperature air heater
3a1, 3a2 Exhaust gas duct
15 3a3 Exhaust gas communication duct
3b1, 3b2 Air duct
3b3 Air communication duct
4 Burner
5 Air port
20 6 Partition wall
7 Damper
8 Primary combustion air supply duct
9 Secondary combustion air supply duct
10 Coal mill
25 lla, llb, Ilc Air flow regulator
12 Coal feeding pipe
13a, 13b, 13c Exhaust gas flow regulator
15 De-NOx device
16 Economizer
5 17 Primary superheater
18 Secondary superheater
19 Final superheater
20 Primary reheater
21 Final reheater
lo 22 Air thermometer
23 Furnace

We Claim:
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;
5 aburner for ignitingthe solid fuel; an airport 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
10 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
15 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,
2 0 wherein the heat exchanger provided in the flow path on
a first side of the partitionwall has a smaller total heat transfer
area than theheat exchangerprovidedinthe flowpathonasecond
side ofthepartitionwall; wherein the exhaust gases discharged
fromthe flowpathsto outsidetheboilerareintroduced, without
25 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.
5 2. The boiler according to claim 1,
wherein the exhaust gases discharged from the flow paths
on the first side of the partition wall and on the second side
ofthe partition wall to outside the boiler are introducedinto
the air heater via the exhaust gas ducts separately and
10 respectively.
3. The boiler according to claim 1 or 2,
wherein the air heater comprises a low-temperature air
heaterwhichisprovideddownstreamoftheheatexchangerhaving
15 a larger heat transfer area and which heats the primary air and
a high-temperature air heater which is provided downstream of
theheatexchangerhavinga smallerheattransfer area andwhich
heats the secondary air.
20 4. The boiler according to one of claims 1 to 3,
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.
25 5. The boiler according to one of claims 3 and 4, further
comprisingade-NOxdevicewhichthe exhaust gas flowing through
the flow path provided with the heat exchanger having a l a r g e r
heat t r a n s f e r area e n t e r s before passing through the
low-temperature a i r heater and which removes nitrogen oxide
5 contained i n the exhaust gas,
wherein the secondary a i r e n t e r s , a f t e r being heated by
the low-temperature a i r heater, thehigh-temperature a i r heater
t o be heated t h e r e i n b y the exhaust gas flowing through the flow
path provided with the heat exchanger having a smaller h e a t
10 t r a n s f e r area.
6. The b o i l e r according t o claim 5,
wherein, a f t e r entering the high-temperature a i r heater
andbeingheat-exchangedtherein,theexhaustgasflowingthrough
15 the flow path provided with the heat exchanger having a smaller
heat t r a n s f e r area e n t e r s the de-NOx device and, along with the
exhaust gas flowing through t h e f l o w p a t h p r o v i d e d w i t h t h e heat
exchangerhavinga l a r g e r h e a t t r a n s f e r area, has nitrogenoxide
removedthereinbefore e n t e r i n g t h e low-temperature a i r h e a t e r .
2 0
7. The b o i l e r according t o one of claims 1 t o 6,
whereintheairductisprovidedwithanair flowregulator,
the exhaust gas duct is providedwith an exhaust gas flow regulator,
andtheprimarycombustionair supplyduct is, a t anintermediate
25 p o r t i o n t h e r e o f , provided with an a i r 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
5 combustionairflowingthroughtheprimarycombustionairsupply
duct at a desired level.
8. Aboiler, substantiallyashereindescribedwithreference
to accompanying drawings and examples.