US 20080308019A1

(19) United States

(54) RECOVERY BOILER PLANT AND A (30) Foreign Application Priority Data
METHOD IN A RECOVERY BOILER
Jun. 15, 2007 (F1) .................................... .. 20075451
(75) Inventor: Antti Raukola, Kangasala (Fl) Publication Classi?cation
51 I t. Cl.
Correspondence Address: ( ) £1233 30/00 (200601)
VENABLE LLP _
R0‘ BOX 34385 (52) US. Cl. ....................................... .. 110/234, 122/1 R
WASHINGTON, DC 20043-9998 (US) (57) ABSTRACT
_ A recovery boiler plant, Which comprises a recovery boiler,
(73) Asslgnee: Metso Power 0y’ Tampere (FD Wherein in the ?rst part (111) ?ue gases travel in a ?rst direc
tion (F1). The furnace also comprises a second part (1b),
(21) Appl- NO-I 123135180 Where the ?ue gases proceed in a second direction (F2), Which
second direction differs from the ?rst direction (P1). In addi
(22) Filed; Jun, 16, 2008 tion, the invention relates to a method in a recovery boiler.

2 3 4
Patent Application Publication Dec. 18, 2008 Sheet 1 0f 3 US 2008/0308019 A1

Fig. 1
Patent Application Publication Dec. 18, 2008 Sheet 2 0f 3 US 2008/0308019 A1
Patent Application Publication Dec. 18, 2008 Sheet 3 0f 3 US 2008/0308019 A1
US 2008/0308019 A1 Dec. 18,2008

RECOVERY BOILER PLANT AND A [0007] In a large recovery boiler plant the furnace can be
METHOD IN A RECOVERY BOILER several meters high, for example, 50 to 70 meters. Tall houses
are required in order to place such a furnace in a plant.
FIELD OF THE INVENTION BRIEF SUMMARY OF THE INVENTION
[0001] The invention relates to a recovery boiler plant. In [0008] NoW a solution has been created, Which enables a
addition, the invention relates to a method in a recovery loWer structure of a recovery boiler plant structure.
boiler. [0009] To achieve this purpose, the recovery boiler plant
according to the invention is primarily characteriZed in that
the plant comprises a recovery boiler, Wherein in a ?rst part of
BACKGROUND OF THE INVENTION a furnace ?ue gases travel in a ?rst direction, Wherein the
furnace also comprises a second part, Where the ?ue gases
[0002] A recovery boiler is used in a pulping process to travel in a second direction, Which second direction differs
recover the chemicals used in the pulping process and to from the ?rst direction, and in addition the recovery boiler
produce steam. Steam is used in different phases of the pulp plant comprises a superheater area, Which is located horizon
ing process as Well as in producing electricity. tally next to the second part of the furnace. The method
[0003] After the pulping process the used cooking liquor, according to the invention is, in turn, primarily characteriZed
i.e. the so-called black liquor is separated from pulp and in that the ?ue gases in a furnace are brought to a ?rst direction
directed via the evaporator to be combusted in the recovery in a ?rst part of the furnace, Wherein ?ue gases are brought in
boiler. Heat is created in a furnace of the recovery boiler due the furnace also to a second direction in a second part of the
to combustion, Which heat is recovered by utiliZing Walls and furnace, Which second direction differs from the ?rst direc
other heat surfaces. tion, and the ?ue gases are brought from the second part of the
furnace to a superheater area, Which is located horizontally
[0004] FIG. 1 shoWs in principle a structure of a recovery next to the second part of the furnace.
boiler according to prior art in a side vieW in a vertical cross [0010] The basic idea of the invention is to form a furnace
section. The recovery boiler according to FIG. 1 comprises in such a manner that the ?ue gases proceed in the fumace in
the folloWing parts: a furnace i.e. a reactor part, a superheater at least tWo different directions.
area 2, a boiler bank area 3 and an economiZer area 4. The [0011] In an embodiment in a ?rst part of the fumace of the
furnace is surrounded by the Walls of the recovery boiler. The boiler plant ?ue gases travel in a ?rst direction. In addition,
recovery boiler is, for the part of the Wall tubes and ?oor tubes the furnace also comprises a second part, Where ?ue gases
forming the ?oor, typically made of ?nned tubes, Which are travel in a second direction, Which second direction differs
connected together by Welding into planar structures. There is from the ?rst direction. In an embodiment the ?rst direction is
a medium circulation inside the tubes, Which circulation is upWards and the second direction is doWnWards.
substantially Water-steam circulation. The Walls of the recov [0012] In an embodiment the recovery boiler plant com
ery boiler comprise noZZles 5a, by means of Which black prises a superheater area, Which is located horiZontally next to
liquor is supplied to the fumace for combustion. In addition, the second part of the furnace.
the Walls of the recovery boiler comprise air noZZles 5b for [0013] In an embodiment the length of the ?rst part of the
supplying the air required for combustion. Air supply may furnace is 60 to 140% of the length of the second part. Pref
take place in various locations in the fumace. erably, the ?rst part of the furnace and the second part of the
furnace are substantially of the same length.
[0005] Further, the recovery boiler plant comprises super [0014] In an embodiment the recovery boiler plant com
heaters, a ?ue gas channel and economiZers. The superheaters prises a frame, from Where the ?rst part and the second part of
are tube structure elements and there are typically several the furnace are suspended.
parallel ones in the superheater area. The steam ?oWing in the [0015] In an embodiment the ?rst part of the furnace and the
superheaters heats When ?ue gases heat the tubes from the second part of the fumace comprise means for removing
outside. In recovery boilers the superheater area 2 is located smelt. In an embodiment the smelt to be removed from the
above the nose in the upper part of the furnace in the upmost second part of the furnace is directed to the ?rst part of the
part of the recovery boiler, via Which the ?ue gases ?oW from furnace, in Which case the smelt cumulating from the second
the recovery boiler to the ?ue gas channel. The ?ue gas part can be changed to a form that is advantageous from the
channel typically comprises a boiler bank area 3 and an point of vieW of the process.
economiZer area 4. In the boiler bank area 3 the Water inside [0016] The different embodiments of the above-described
the boiler bank boils and the mixture of Water and stem moves arrangement, taken separately and in various combinations,
to a drum that is a part of the Water circulation of the recovery provide several advantages. A loW fumace enables a loW
boiler. There is typically an economiZer area 4 in a part of the structure. An advantage of an application, in turn, is the easier
?ue gas channel, Where in the economiZers the Water that is mountability of different structures of the recovery boiler
supplied to replace the steam removed from the Water system plant.
of the recovery boiler is heated With cooled ?ue gases. [0017] An application enables the modulariZation of the
[0006] The heat surfaces of the recovery boiler plant are recovery boiler plant, in Which case changing the capacity of
connected in different Ways to each other so that the Water can recovery boiler plant during the life cycle of a recovery boiler
be heated and further evaporated by means of different heat is advantageous.
surfaces, such as boiler banks and economiZers, located in [0018] An application provides a possibility to process ?ue
both the recovery boiler and in the ?ue gas channel after it. gases in the second part of the fumace before the superheat
Finally, the saturated steam can be heated in the superheaters ers, for example, in order to control emissions. For example,
so that superheated high-pressure steam is created. there may be additional burners, air noZZles and/or other
US 2008/0308019 A1 Dec. 18,2008

additive supplies in the second part of the furnace for control several planes. A part of the air supply noZZles 5b may also be
ling the corrosiveness of the emissions and/or ?ue gases. located in the second part 1b of the furnace.
[0019] In an embodiment the superheaters are protected [0031] In a recovery boiler according to the example, black
from the radiation of the furnace, as Well as from black liquor liquor is combusted traditionally in the ?rst part 111 of the
drops escaping from the fumace, i.e. the so-called carryover. furnace. Flue gases proceed in the ?rst part 111 of the furnace
An advantage of an application, in turn, is the cheaper super of this application substantially upWards (?rst direction F1).
heater structure made possible by it. From the upper part of the ?rst part 111 of the fumace the ?ue
[0020] An application enables a better optimiZation of the gases move to the second part 1b of the fumace. The ?rst part
heat structure. Optimization of the heat surfaces may be based
111 of the fumace and the second part 1b of the fumace are
on the ?oW velocity of ?ue gases. In the present solution the
connected to each other via some suitable aperture or other
dimensions of the different parts of the fumace and the chan
nels can be selected so that the desired ?oW velocity is structure. The aperture or the like connecting the ?rst part 111
reached in different parts. In addition, the ?ue gas ?oW model of the furnace and the second part 1b of the furnace may
in the superheater area is advantageously better in the present comprise tubes, such as, for example, screen tubes, betWeen
solution than in knoWn solutions, Where ?ue gases travel past Which the ?ue gases may ?oW (the tubes are not shoWn in the
the nose in the superheater area. ?gures). By means of the tubes it is possible to direct Water/
steam betWeen the Walls betWeen the ?rst part 111 and the
DESCRIPTION OF THE DRAWINGS second part 1b of the furnace and the upper part of the boiler.
If necessary, by means of the tubes it is also possible to loWer
[0021] In the folloWing, the invention Will be described in the temperature of the ?ue gases When moving from the ?rst
more detail With reference to the appended principle draW part 111 of the fumace to the second part 1b of the furnace.
ings, in Which [0032] The second part 1b of the furnace is next to the ?rst
[0022] FIG. 1 shoWs a knoWn recovery boiler plant part 111 in the example. Flue gases travel in the second part 1b
[0023] FIG. 2 shoWs an embodiment of the fumace of this application substantially doWnWards
[0024] FIG. 3 shoWs another embodiment (second direction P2). In the second part 1b the temperature
[0025] FIG. 4 shoWs a third embodiment of the ?ue gases decreases to the same level as in a furnace of
[0026] For the sake of clarity, the draWings only shoW the a conventional recovery boiler. The temperature of the ?ue
details necessary for understanding the invention. The struc gases is loWered so that the superheaters Will endure better.
tures and details that are not necessary for understanding the For example, the temperature of the ?ue gases When entering
invention but are obvious for anyone skilled in the art have the second part 1b of the furnace is approximately 11500 C.
been omitted from the ?gures in order to emphasiZe the char and When leaving the secondpart approximately 900 to 10000
acteristics of the invention. C.
[0033] From the second part 1b of the fumace it is easy to
DETAILED DESCRIPTION OF THE INVENTION form a Well controlled Zone. The properties can be affected,
for example, by the diameter of the second part 1b of the
[0027] A recovery boiler according to FIG. 1 Was discussed furnace. With the dimensioning and ?ttings of the second part
in connection With the background of the invention and prior 1b of the fumace it is possible to affect, inter alia, the tem
art. The recovery boiler according to FIG. 2 comprises the perature of the ?ue gases, the ?oW velocity and delay, and in
folloWing parts: a furnace i.e. a reactor part, a superheater area addition, emissions. The second part 1b of the fumace may
2, a boiler bank area 3 and an economiZer area 4. also comprise additional burners, air noZZles and/or other
[0028] The furnace 1, i.e. the reactor part is formed of tWo additive supplies. The steady and controlled temperature and
part, Which in this description are called the ?rst part of the ?oW pro?le of the second part 1b of the furnace can, if nec
furnace 1a and the second part of the furnace 1b. It can also be essary be utiliZed, inter alia, in decreasing emissions, for
said that the furnace according to FIG. 2 comprises a ?rst example by using the SNCR method (selective non-catalytic
combustion chamber and a second combustion chamber, reduction). The second part 1b of the furnace can, if neces
Which are connected to each other via a turning chamber. In sary, also be utiliZed for controlling the corrosiveness of ?ue
the ?rst part 111 of the furnace ?ue gases (i.e. gases formed gases.
during combustion) travel in a ?rst direction F1, and in the [0034] In the example of FIG. 2 the removal of ?ue gases
second part 1b of the fumace ?ue gases travel in a second takes place from the second part 1b of the fumace through
direction F2, Which second direction differs from the ?rst such an aperture, Whose upper edge is approximately in the
direction. mid-point of the Wall of the furnace. The presented solution
[0029] The furnace 1 comprises membrane Walls. Advan enables making the furnace 1 of the recovery boiler into such
tageously the Walls of the ?rst part 111 of the fumace and the that its height is 1/2 to 3A of the length of the furnace. The
second part 1b of the furnace are formed of ?nned tubes, length of the fumace 1 here refers to the length of the furnace
Which are connected together by Welding into planar struc in the travel direction F1, E2 of ?ue gases. In the example of
tures. There is a medium circulation inside the tubes, Which FIG. 2 the total length of the furnace 1 is the sum of the height
circulation is substantially Water-steam circulation. of the ?rst part 111 of the fumace and the second part 1b of the
[0030] The material to be combusted (black liquor) is sup furnace, in Which case the height of the fumace is substan
plied to the ?rst part 111 of the fumace, as Well as all or most tially half of the total length of the furnace. The loW structure
of the air needed for combustion With suitable supply devices of the fumace 1 enables a loWer structure of the recovery
5a, 5b, such as, for example, noZZles. In the ?gures the black boiler plant than in knoWn solutions, because the furnace is
liquor noZZles 5a and the air noZZles 5b are shoWn in principle typically the highest part of the recovery boiler plant.
only as single planes. HoWever, it is advantageous to place [0035] The ?rst part 111 of the furnace and the second part
especially air noZZles 5b to the Walls of the fumace 1 on 1b of the furnace are advantageously equally long. The length
US 2008/0308019 A1 Dec. 18, 2008

ofthe ?rst part 111 ofthe furnace may also be 60 to 140% ofthe superheater area 2 is located next to the second part 1b of the
length of the second part 1b of the furnace, depending on the furnace. The superheater 2 is not located directly above the
application. furnace 1, especially the ?rst part 111 of the fumace. Thus, the
[0036] After the furnace 1 ?ue gases ?oW to the superheater superheater area 2 is not in direct contact With the ?ames. The
area 2. The superheater area 2 is in the example located superheaters of the superheater area 2 are protected from the
substantially loWer than in conventional recovery boilers. radiation of the furnace, as Well as from black liquor drops
Thanks to the tWo-part furnace, the superheaters 2 are not in escaping from the furnace, i.e. the so-called carryover. The
direct visual contact With the ?ames of the furnace 1. This has advantageous location of the superheater area enables
an advantageous effect on the durability of the superheaters 2. cheaper superheater structures than in knoWn solutions.
Flue gases are directed from the second part 1b of the furnace
to the superheater area 2, Where the superheaters are located [0043] In the furnace 1 the ?ue gases comprise substances
sequentially in a cross-?oW. In the example the superheaters used in the pulping process, Which in the temperatures pre
2 are of a so-called suspended type, in Which case the stay vailing in the furnace are in a molten form. These substances
clean easier. Heat exchange of the superheater area 2 can be are recovered for further use, Which is shy the ?rst part 111 of
e?iciently optimiZed by the ?oW velocity of ?ue gases. In the the furnace and the second part 1b of the furnace comprise
present solution the dimensions of the different parts 1a, 1b of suitable means for recovering the smelt. For example, the
the furnace and the channels can be selected so that the second part 1b of the fumace can be equipped With such smelt
desired ?oW velocity is achieved for ?ue gases. removal structures 6b, Which bring the smelt from the second
[0037] The boiler bank area 3 is located immediately after part to the ?rst part 111 of the furnace, substantially to the char
the superheater area 2. The boiler bank area 3 comprises heat bed on the bottom of the ?rst part of the furnace, as shoWn in
surfaces formed by elements formed of parallel tubes, i.e. FIGS. 2 and 3. The char bed is a smelt layer forming of the
boiler banks. In the example the boiler bank is also in an residue from the combustion process on the bottom of the
e?icient cross-?oW. furnace of the recovery boiler, Which layer has a hill-like
[0038] The economiZer area 3 comprises heat surfaces, i.e. form.) Advantageously the smelt accumulating from the sec
economiZers, Which are also formed by elements formed of ond part 1b of the fumace can be changed in the ?rst part 111
parallel tubes. The economiZers in the economiZer area 4 may of the fumace to a better form from the point of vieW of the
be of a cross-?oW type. It is also possible to use longitudinal pulping process. The ?rst part 111 of the fumace is preferably
?oW economiZers, in Which case, hoWever, their length may equipped With smelt removal structures 6a, through Which the
have to be limited. smelt is directed to the tank. For example, the smelt can be
[0039] In addition, FIG. 2 shoWs a drum 9 belonging to the removed through spouts and apertures placed in the loWer
Water and steam system. During use the drum 9 contains both part of the furnace. It is also possible to place the smelt spouts
Water and steam, Which are directed via pipeWorks to differ 6a, 6b in the loWer part of the ?rst part 111 of the furnace and
ent targets for heating the Water and/for superheating the the second part 1b of the fumace in such a manner that via the
steam. For example, the drum 9 is connected to the Walls of smelt spouts the smelt is directed to a common tank for further
the furnace 1 and to different heat surfaces. Naturally the use. One such a solution is shoWn in FIG. 4.
recovery boiler plant also comprises other structures, Which [0044] In the example the recovery boiler plant comprises a
are not shoWn in the ?gures. These kinds of structures are frame 7, Which is used for supporting the structures of the
obvious to a person skilled in the art, but they are not essential recovery boiler plant. In the example the recovery boiler is
for explaining and understanding the invention. suspended from the frame 7 in such a manner that both the
[0040] In the example according to FIG. 2 both the ?rst part ?rst part 111 of the furnace and the second part 1b of the
111 of the fumace and the second part 1b of the furnace are furnace are attached to the frame of the recovery boiler plant
vertical, i.e. ?ue gases F1, F2 travel substantially vertically in With suspension structures 8. Suspension takes place advan
them. In another application according to FIG. 3 the ?rst part tageously from the upper part of the fumace 1. The length of
111 of the furnace is vertical and the second part 1b of the the boiler of the recovery boiler plant may vary due to the
furnace is horizontal, in Which case ?ue gases F2 travel sub changes in the temperature, in Which case the location of the
stantially vertically in the second part. In a third application loWer part of the suspended boiler varies.
according to FIG. 4 the ?rst part 111 of the fumace is vertical [0045] The discloses fumace structure 1 enables the modu
and the second part 1b of the fumace is diagonal, in Which lariZation of the recovery boiler plant, in Which case adding
case ?ue gases F2 travel substantially diagonally in the sec and/or reducing the capacity of the recovery boiler plant is
ond part. possible Within certain limits by adding/removing modules.
[0041] It can be said that the furnaces according to FIGS. 2 For example, the ?rst part 111 of the fumace is its oWn module,
to 4 comprise a ?rst combustion chamber (corresponds sub as Well as the second part 1b of the furnace. Also the super
stantially to the ?rst part 111 of the fumace) and a second heaters 2, boiler banks 3 and economiZers 4 are advanta
combustion chamber (corresponds substantially to the second geously their oWn modules. For example, in the beginning of
part 1b of the fumace), Which are connected to each other via the life cycle of a recovery boiler plant, less poWer is needed,
an inversion chamber. In addition, the solutions according to but increased need of poWer should be prepared for. Thus, it is
FIGS. 2 and 4 comprise a second turning chamber, Which possible to obtain a relatively large ?rst part 111 of the fumace,
connects the second combustion chamber to the superheater to Which it is possible to supply larger amounts of fuel. A
area 2. In the combustion chamber the ?ue gases F1, F2 travel small module is selected as the second part 1b of the fumace,
substantially linearly and in the turning chamber the direction to Which the superheaters 2, boiler banks 3 and economiZers
of ?ue gases is changed. 4 are connected. At a later stage When the poWer is increased,
[0042] In the recovery boiler plants shoWn in FIGS. 2 to 4 a module of another second part 1b of the furnace is con
the superheater area 2 and the furnace 1 are located in such a nected to the ?rst part 111 of the fumace and to it, correspond
manner that they are horizontally parallel. Especially the ingly, the superheaters 2, boiler banks 3 and economiZers 4.
US 2008/0308019 A1 Dec. 18,2008

Thus, the recovery boilerplant comprises double second parts 4. The recovery boiler plant according to claim 3, Wherein
1b of the furnace and superheaters 2, boiler banks 3 and the ?rst part of the furnace and the second part of the furnace
economiZers 4. are equally long.
[0046] By combining, in various Ways, the modes and 5. The recovery boiler plant according to claim 1, Wherein
structures disclosed in connection With the different embodi the recovery boiler plant comprises a frame, from Which the
ments of the invention presented above, it is possible to pro ?rst part and the second part of the furnace are suspended.
duce various embodiments of the invention in accordance 6. The recovery boiler plant according to claim 4, Wherein
With the spirit of the invention. Therefore, the above-pre the ?rst part of the furnace and the second part of the furnace
sented examples must not be interpreted as restrictive to the comprise means for removing smelt.
invention, but the embodiments of the invention may be freely 7. The recovery boiler plant according to claim 1, Wherein
varied Within the scope of the inventive features presented in the second part of the fumace comprises means for control
the claims hereinbeloW. ling the corrosiveness of the emissions and ?ue gases.
8. A method in a recovery boiler, Wherein ?ue gases in a
1. A recovery boiler plant, Which comprises a recovery furnace are brought to a ?rst direction in a ?rst part of the
boiler, Wherein in a ?rst part of a furnace ?ue gases travel in furnace, Wherein ?ue gases are brought in the furnace also to
a ?rst direction, Wherein the furnace also comprises a second a second direction in a second part of the furnace, Which
part, Where the ?ue gases travel in a second direction, Which second direction differs from the ?rst direction, and the ?ue
second direction differs from the ?rst direction, and in addi gases are brought from the second part of the fumace to a
tion the recovery boiler plant comprises a superheater area, superheater area, Which is located horizontally next to the
Which is located horizontally next to the second part of the second part of the furnace.
furnace. 9. The method according to claim 8, Wherein in the second
2. The recovery boiler plant according to claim 1, Wherein part of the furnace additives are supplied to the ?ue gases in
the ?rst direction is upWards and the second direction is order to control emissions and corrosiveness.
doWnWards. 10. The method according to claim 8, Wherein the ?rst
3. The recovery boiler plant according to claim 1, Wherein direction is upWards and the second direction is doWnWards.
the length of the ?rst part of the fumace is 60 to 140% of the
* * * * *
length of the second part of the furnace.