FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“BOILER STRUCTURE”
MITSUBISHI HEAVY INDUSTRIES, LTD., of 16-5, Konan 2-chome,
Minato-ku, Tokyo 108-8215, Japan.
The following specification particularly describes the invention and the
manner in which it is to be performed.
2
DESCRIPTION
BOILER STRUCTURE
Technical Field
[0001]
The present invention relates to a boiler structure
compatible with coal and various fuels containing sulfur.
Background Art
[0002]
To reduce NOx emissions, some recent boilers for use with
fuels such as coal and oil are supplied with air in multiple
stages to form a reducing-combustion zone where combustion
proceeds in a reducing atmosphere between a main burner and an
additional-air supplying portion.
In the reducing-combustion zone, however, furnace wall
surfaces are exposed to a severe corrosive environment where
hydrogen sulfide, which is a corrosive component, is produced
in large amounts. This necessitates maintenance such as spray
coating onto furnace walls or regular replacement of furnace
wall panels. Another concern is slag deposition, since the
reducing-combustion zone is a region with a reducing
atmosphere where the thermal load in the furnace is higher.
[0003]
3
To cope with such problems, some known techniques are
aimed at increasing the oxygen concentration by supplying air
toward the wall surfaces of the furnace. According to one such
technique, for example, burners are disposed at the four
corners in a furnace having a rectangular cross section to
form a swirling flow, with each of the burners forming an air
flow that is offset toward a furnace wall (for example, see
Patent Document 1).
According to a technique disclosed for a pulverized-coalfired
boiler having burners disposed in the centers of furnace
walls to produce a circulating firing flame, nozzles are
provided to supply a curtain of air or a curtain of exhaust
gas for deflecting the flames, thereby preventing slagging
around the burners (for example, see Patent Document 2).
Patent Document 1: the Publication of U.S. Patent No.
6,237,513
Patent Document 2: Japanese Unexamined Patent
Application, Publication No. HEI-7-119923
Disclosure of Invention
[0004]
The conventional technique of Patent Document 1 above,
however, cannot effectively increase the oxygen concentration
because oxygen contained in the air is consumed before it
reaches a target wall surface. In addition, the flow rate at
4
which the air is ejected must be increased to increase the
oxygen concentration. This is undesirable because it leads to
increased auxiliary power, including that of a compressor.
In the conventional technique of Patent Document 2, a
curtain of air or a curtain of exhaust gas must be supplied at
a flow rate high enough to deflect the flames. This is
similarly undesirable because it leads to increased auxiliary
power, including that of a compressor.
[0005]
Against such a backdrop, efficient alleviation or
prevention of corrosion and slagging on furnace walls in a
furnace is demanded of a circulating firing boiler structure
that is compatible with coal and various fuels containing
sulfur and that is configured so that fuel and combustion air
supplied into the furnace from burners disposed at a plurality
of positions on furnace walls forming a rectangular cross
section are combusted so as to form a swirling flow.
An object of the present invention, which has been made
in light of the above circumstances, is to provide a boiler
structure capable of efficiently alleviating or preventing
corrosion and slagging on furnace walls in a furnace.
[0006]
To solve the above problems, the present invention
employs the following solutions.
A boiler structure according to the present invention is
5
a circulating firing boiler structure configured so that fuel
and combustion air supplied into a furnace from burners
disposed at a plurality of positions on furnace walls forming
a rectangular cross section are combusted so as to form a
swirling flow. Air-supplying parts are disposed near flameaffected
portions of furnace wall surfaces, where flames
formed by the respective burners approach or contact, to form
regions having a higher air concentration than the peripheries
thereof.
[0007]
With this boiler structure, in which the air-supplying
parts are disposed near the flame-affected portions of the
furnace wall surfaces, where the flames formed by the
respective burners approach or contact, to form the regions
having a higher air concentration than the peripheries
thereof, the regions having a higher air concentration can be
formed by supplying low-flow-rate air, which requires low
auxiliary power, to regions where there is concern over
corrosion or slagging on the furnace wall surfaces.
[0008]
In the above invention, the regions having a higher air
concentration are preferably formed so as to cover a reducingcombustion
zone inside the furnace in a vertical direction.
This allows the regions having a higher air concentration to
be formed by supplying air at a low flow rate in upper and
6
lower regions where there is concern over corrosion or
slagging in the furnace.
[0009]
In the above invention, the air-supplying parts
preferably introduce low-pressure secondary burner air from
the adjacent burners through bypass routes. This avoids a
significant change in structure or an increase in the number
of components, thus simplifying the structure.
[0010]
In the above invention, the air-supplying parts are
preferably disposed around deslagger nozzles. The airsupplying
parts can then form the regions having a higher air
concentration on the furnace wall surfaces in regions where
slagging tends to occur and can also cool the peripheries of
deslagger-nozzle insertion units, which are exposed to severe
thermal conditions.
[0011]
According to the invention described above, in the
circulating firing boiler structure configured so that fuel
and combustion air are combusted so as to form a swirling
flow, the air-supplying parts supply air at a low flow rate to
the vicinities of the flame-affected portions of the furnace
walls, where there is concern over corrosion or slagging, in
the furnace to form the regions having a higher air
concentration than the peripheries thereof. This boiler
7
structure can therefore maintain a high oxygen concentration
on and around the flame-affected portions without the need for
a high auxiliary power for increasing the flow rate of the
supplied air.
[0012]
Accordingly, an air layer having a higher oxygen
concentration is formed on and around the flame-affected
portions in the furnace, so that the reducing atmosphere is
partially replaced by an oxidizing atmosphere. As a result,
corrosion and slagging can efficiently be alleviated or
prevented. The above invention is particularly effective in
alleviating slagging of coal-fired boilers and is particularly
effective in improving corrosion resistance against hydrogen
sulfide of boilers compatible with various fuels containing
sulfur.
In addition, if the air used by the air-supplying parts
is low-pressure secondary burner air introduced from the
adjacent burners through bypass routes, a significant change
in boiler structure or an increase in the number of components
can be minimized, thus simplifying the structure.
Brief Description of Drawings
[0013]
[FIG. 1A] Fig. 1A is a horizontal sectional view of an
embodiment of a boiler structure according to the present
8
invention, showing a reducing-combustion zone in a furnace.
[FIG. 1B] Fig. 1B is a perspective view of the embodiment
of the boiler structure according the present invention,
showing its schematic outline.
[FIG. 2A] Fig. 2A is a sectional view of the furnace,
showing an exemplary structure of an air-supplying part
disposed on a deslagger-nozzle insertion unit.
[FIG. 2B] Fig. 2B is a diagram as viewed from arrow A of
Fig. 2A, showing the exemplary structure of the air-supplying
part disposed on the deslagger-nozzle insertion unit.
[FIG. 3A] Fig. 3A is a horizontal sectional view of a
first modification of the boiler structure according to the
present invention, showing a reducing-combustion zone in a
furnace.
[FIG. 3B] Fig. 3B is a perspective view of the first
modification of the boiler structure according to the present
invention, showing its schematic outline.
[FIG. 4A] Fig. 4A is a horizontal sectional view of a
second modification of the boiler structure according to the
present invention, showing a reducing-combustion zone in a
furnace.
[FIG. 4B] Fig. 4B is a perspective view of the second
modification of the boiler structure according to the present
invention, showing its schematic outline.
[FIG. 5] Fig. 5 is a schematic longitudinal sectional
9
view of a boiler structure that combusts fuel with combustion
air supplied in multiple stages.
Explanation of Reference Signs:
[0014]
10: boiler
11: furnace
11a: furnace wall
12: burner
20: air-supplying part (air-supplying nozzle)
30: deslagger-nozzle insertion unit
Best Mode for Carrying Out the Invention
[0015]
An embodiment of a boiler structure according to the
present invention will now be described with reference to the
drawings.
Referring to Fig. 5, a boiler 10 combusts fuel by
supplying combustion air into a furnace 11 in multiple stages
to reduce NOx emissions. In the multistage supply of this
case, the combustion air is supplied into the furnace 11 in
two stages, that is, from burner portions Ba that are regions
where a plurality of burners 12 are disposed and additionalair
supplying portions Aa that are regions where additionalair
supplying nozzles 13 are disposed above the burner
10
portions Ba. In the boiler 10, specifically, as a measure
against NOx emissions, the two-stage combustion is performed
in a reducing-combustion zone and a complete-combustion zone
by initially supplying about 70% of the required amount of
combustion air from the burner portions Ba before supplying
the rest, namely, about 30%, from the additional-air supplying
portions Aa.
[0016]
Referring to Fig. 1A, for example, the boiler 10
described above is a swirling-combustion boiler in which the
furnace 11 has a rectangular cross section. The swirlingcombustion
boiler 10 is configured so that fuel and combustion
air supplied from the plurality of burners 12, which are
disposed on furnace walls 11a, into the furnace 11 are
combusted so as to form a swirling flame in the furnace 11.
In the exemplary structure of the 8-cornered furnace
shown in Fig. 1A, the burners 12, which are disposed at eight
positions in a horizontal cross section, supply fuel and
combustion air so as to form two adjacent swirling flows in
the furnace 11.
[0017]
In this embodiment, the boiler 10 includes air-supplying
parts 20 disposed near flame-affected portions of the furnace
wall surfaces (furnace walls 11a), where flames formed by the
respective burners 12 approach or contact, to form regions
11
having a higher air concentration than the peripheries
thereof. Specifically, in the horizontal cross section of the
8-cornered furnace shown in Fig. 1A, one air-supplying part 20
is provided at an appropriate position on each of the furnace
walls 11a, which form, for example, a rectangle; that is, a
total of four air-supplying parts 20 are provided.
The formation of the regions having a higher air
concentration means formation of regions having a higher
oxygen concentration. In these regions, therefore, the
reducing atmosphere is replaced by an oxidizing atmosphere.
[0018]
That is, the air-supplying parts 20 are provided on the
furnace walls 11a in the furnace 11 to supply air at a low
flow rate from sites where there is concern over corrosion or
slagging, thus forming the regions having a higher air
concentration than the peripheries thereof substantially along
the wall surfaces. In other words, the regions having a higher
air concentration than the peripheries thereof are formed not
by supplying air toward the furnace walls 11a in the regions
where there is concern over corrosion or slagging at a
relatively high flow rate (for example, 40 m/sec or more), but
by supplying air from the air-supplying parts 20 provided on
the furnace walls 11a in the regions where there is concern
over corrosion or slagging at a low flow rate (for example,
about 10 m/sec).
12
[0019]
For example, the air-supplying parts 20 are nozzles for
forming the regions having a higher air concentration by
supplying low-pressure secondary burner air introduced from
the adjacent burners 12 through bypass routes into the furnace
11 at a low flow rate. In a plan view of the furnace 11, the
air supplied from the air-supplying parts 20 forms the regions
having a higher air concentration along the furnace walls 11a
near the flame-affected portions. In addition, the airsupplying
parts 20 are provided in a plurality of stages in
the vertical direction of the furnace 11 to cover the
reducing-combustion zone inside the furnace in the vertical
direction.
[0020]
In the reducing-combustion zone, not only are the wall
surfaces 11a exposed to a severe corrosive environment, but
also there is concern over slag deposition, because this zone
is a region where hydrogen sulfide, which is a corrosive
component, is produced in large amounts and is also a reducing
region where the thermal load in the furnace 11 is higher. In
the reducing-combustion zone, therefore, the air-supplying
parts 20 are provided in the peripheries of the portions on
the furnace walls 11a where the flames approach or contact, at
substantially the same heights as the burners 12. This is
because the flame-affected portions of the furnace walls 11a
13
are formed at substantially the same heights as the burners 12
since the flames are formed so as to extend from the burners
12 substantially in the horizontal direction.
[0021]
In addition, the flame-affected portions of the furnace
walls 11a are formed at a plurality of positions in the
vertical direction because the burners 12 in the reducingcombustion
zone are usually provided in a plurality of stages
in the vertical direction. Accordingly, the air-supplying
parts 20 are provided in the vertical direction in the number
of stages that is equal to the number of stages of the burners
12, in other words, the number of stages of the flames formed
in the vertical direction. This allows the regions having a
higher air concentration to be formed by supplying air at a
low flow rate in upper and lower regions where there is
concern over corrosion or slagging in the furnace 11.
In the reducing-combustion zone, as a result, the air
supplied at a low flow rate from the air-supplying parts 20
provided near the flame-affected portions, which are formed by
the burners 12, of the furnace walls 11a forms the regions
having a higher air concentration than the peripheries
thereof, so that the air functions as an air layer in the
peripheries of the flame-affected portions to insulate the
furnace walls 11a from the flames. This reduces the thermal
effect and so on of the flames and also makes the atmosphere
14
partially oxidizing, thus alleviating or preventing corrosion
and slagging on the furnace walls 11a in the regions where the
flame-affected portions would otherwise be formed.
[0022]
In addition, low-flow-rate air, which requires low
auxiliary power, can be used because the air-supplying parts
20 supply the air from the vicinities of the flame-affected
portions to the peripheries thereof. That is, high-pressure,
high-flow-rate air does not have to be supplied using, for
example, a compressor that operates with high power, unlike
the case where the air is supplied toward a remote position.
In particular, the use of low-pressure secondary air
introduced from the burners 12 reduces the auxiliary power and
also avoids a significant change in structure or an increase
in the number of components, thus simplifying the structure.
[0023]
Referring to Fig. 1B, for example, the air-supplying
parts 20 are provided around deslagger nozzles 31 in
deslagger-nozzle insertion units 30 between the burner
portions Ba and the additional-air supplying portions Aa. The
deslagger-nozzle insertion units 30 are devices for removing
slag deposited on the furnace walls 11a. Referring to Fig. 2A,
for example, the deslagger-nozzle insertion units 30 clean the
furnace walls 11a with steam ejected from the deslagger
nozzles 31, which are inserted in the furnace 11.
15
That is, it is effective to form the regions having a
higher air concentration by supplying air because the
deslagger-nozzle insertion units 30 are provided at sites
where there is concern over slag deposition because of the
high thermal load due to the reducing atmosphere in the
furnace 11.
[0024]
An exemplary structure of the air-supplying parts 20
provided around the deslagger-nozzle insertion units 30 will
now be described with reference to Figs. 2A and 2B.
In Fig. 2A, the deslagger nozzle 31 is attached to the
deslagger-nozzle insertion unit 30 by inserting the deslagger
nozzle 31 in a nozzle hole 32 extending through the furnace
wall 11a. The deslagger nozzle 31 is supplied with steam to be
ejected for removing slag through a steam duct 33. Reference
numeral 34 in the drawing denotes a seal member provided
between a nozzle body 21 of the air-supplying nozzle (airsupplying
part) 20, to be described below, and the deslagger
nozzle 31.
[0025]
The air-supplying nozzle 20, on the other hand, has an
air flow channel 22 formed of an annular space between the
deslagger nozzle 31 and the nozzle hole 32, and the nozzle
body 21 has a circular flange 21a at one end of its
cylindrical shape and is attached to the furnace 11. The
16
nozzle body 21 is fixed to, for example, the circumferential
surface of the deslagger nozzle 31 with the seal member 34
disposed therebetween, and the flange 21a in the furnace 11
faces the furnace wall 11a so as to be substantially parallel
thereto with a predetermined distance therebetween. Hence, air
supplied from the nozzle body 21 into the furnace 11 collides
with the flange 21a, thus flowing outward along the furnace
wall 11a around the entire circumference in the
circumferential direction.
[0026]
The air-supplying nozzle 20 has a wind box 23 provided
outside the furnace 11. The wind box 23 communicates with the
nozzle body 21 in the furnace 11 through the air flow channel
22 to supply air from an air supply 24. In this case, the air
supply 24 used is preferably, for example, the low-pressure
secondary air introduced from the burners 12, although the
primary air or compressed air may be used if necessary.
[0027]
The air-supplying nozzle 20 can form a region having a
higher air concentration along the furnace wall 11a of the
furnace 11 in a region where slagging tends to occur and can
also cool the periphery of the deslagger-nozzle insertion unit
30, which is exposed to severe thermal conditions.
Accordingly, an air layer having a higher air concentration
than the periphery thereof is formed around the furnace wall
17
11a in a region where slagging tends to occur, so that a
partial oxidizing atmosphere can prevent or alleviate
corrosion of the wall surface, thus extending the life of the
furnace wall.
[0028]
In addition, the air supplied into the nozzle body 21 of
the air-supplying part 20 flows beside the circumferential
surface of the deslagger nozzle 31. The air flow can therefore
cool, for example, the seal member 34, which is exposed to
severe thermal conditions.
Furthermore, as the air concentration is increased in the
vicinity of the furnace wall 11a, on which the air-supplying
nozzle 20 is provided, the oxygen concentration is increased,
thus creating an oxidizing atmosphere. The oxidizing
atmosphere can alleviate slagging because the melting
temperature of slag is increased thereby.
[0029]
In this boiler structure, the air-supplying parts 20 are
disposed near the flame-affected portions of the furnace walls
11a, where the flames formed by the respective burners 12
approach or contact, to form the regions having a higher air
concentration than the peripheries thereof. Because the oxygen
concentration is increased around the flame-affected portions,
the reducing atmosphere is partially replaced by an oxidizing
atmosphere. As a result, corrosion and slagging can be
18
alleviated or prevented, thus extending the life of the wall
surfaces. This boiler structure is particularly effective in
alleviating slagging of coal-fired boilers and is particularly
effective in improving corrosion resistance of boilers
compatible with various fuels containing sulfur.
[0030]
The optimum positions of the air-supplying parts 20 in
the horizontal cross section vary depending on the conditions,
including the shape of the furnace 11, the positions and
number of the burners 12, and the type of swirling flame
formed. That is, the regions of the flame-affected portions of
the furnace walls 11a, where the flames formed by the
respective burners 12 approach or contact, vary with, for
example, the arrangement of the burners 12 and the type of
swirling flame formed. Accordingly, the positional
relationship between the burners 12 and the air-supplying
parts 20 differs between different boiler structures, for
example, the 8-cornered furnace shown in Figs. 1A and 1B and
4-cornered furnaces shown in Figs. 3A and 3B and Figs. 4A and
4B.
[0031]
In the exemplary structure shown in Figs. 1A and 1B, the
furnace 11 is rectangular, and four burners 12 are disposed on
each of the two opposing long sides to form two swirling flows
on the left and right. In this case, the burners 12 are tilted
19
toward substantially the centers of the respective swirling
flows, that is, toward substantially the centers of squares
formed by dividing the rectangle in half, so that the two
swirling flows each have a substantially oval shape.
In this case, therefore, the flame-affected portions,
where the flames approach or contact, are formed near two
corners and the centers of the long sides, and the airsupplying
parts 20 are provided at four positions so as to
cover these regions.
[0032]
In an exemplary structure (first modification) shown in
Figs. 3A and 3B, the furnace 11 is square, and the burners 12
are disposed at four positions offset from the centers of the
respective sides to form a single swirling flow. In this case,
the swirling flow is formed by the offset of the burners 12
because the burners 12 are directed toward the opposite wall
surfaces. In this arrangement of the burners 12, the flames
flow toward the vicinities of the centers of the wall surfaces
on the downstream side of the swirling flow under the effect
of the flames formed on the upstream side.
In this case, therefore, the flame-affected portions are
near the centers of the respective sides, and accordingly the
air-supplying parts 20 are provided at four positions in the
centers of the respective sides so as to cover these regions.
[0033]
20
In an exemplary structure (second modification) shown in
Figs. 4A and 4B, the furnace 11 is square, and the burners 12
are disposed at the four corners to form a single swirling
flow. In this case, the flame-affected portions are near the
centers of the respective sides, and accordingly the airsupplying
parts 20 are provided at four positions in the
centers of the respective sides so as to cover these regions.
Thus, the optimum positions of the air-supplying parts 20
may be selected on the basis of, for example, the arrangement
of the burners 12.
The present invention is not limited to the embodiments
described above; modifications are permitted so long as they
do not depart from the spirit of the invention.
21
CLAIMS
1. A circulating firing boiler structure configured so that
fuel and combustion air supplied into a furnace from burners
disposed at a plurality of positions on furnace walls forming
a rectangular cross section are combusted so as to form a
swirling flow,
wherein air-supplying parts are disposed near flameaffected
portions of furnace wall surfaces, where flames
formed by the respective burners approach or contact, to form
regions having a higher air concentration than the peripheries
thereof.
2. The boiler structure according to Claim 1, wherein the
regions having a higher air concentration are formed so as to
cover a reducing-combustion zone inside the furnace in a
vertical direction.
3. The boiler structure according to Claim 1 or 2, wherein
the air-supplying parts introduce low-pressure secondary
burner air from the adjacent burners through bypass routes.
4. The boiler structure according to one of Claims 1 to 3,
wherein the air-supplying parts are disposed around deslagger
nozzles.

Dated this 06u" day of July 2010

ANUPAM TRIVEDI
OF K & S PARTNERS
AGENT FOR THE APPLICANT