Note: Descriptions are shown in the official language in which they were submitted.
CA 02632412 2008-05-23
1 Pulverized coal burner for firing fuel which is fed by dense phase
conveyance
2
3 The invention is directed towards a burner, especially a pulverized coal
burner, with a fuel
4 conveying tube and a primary air tube which is concentrically arranged
within it, wherein the
primary air tube on the mouth discharge side terminates at a distance to the
mouth opening of
6 the fuel conveying tube, and the burner is connected, or can be connected,
to a feed line which
7 conveys pulverous fuel in dense phase. Furthermore, the invention is
directed towards a
8 method for combustion of particulate fuel, especially pulverized coal,
preferably dry brown coal,
9 in a burner with primary air tube and fuel conveying tube, wherein the fuel
is fed to the burner by
dense phase conveyance and is conveyed by dense phase conveyance inside the
burner along
11 the longitudinal axis of the burner and mixed with combustion air.
12
13 For the combustion of particulate fuel, especially pulverized coal and
pulverized dry brown coal,
14 it is known to combust this in burners which in addition to a core air feed
have a primary air
feed, a secondary air feed and a tertiary air feed. Such burners are
especially used in
16 conjunction with the firing of furnaces of large steam generators. The
primary air feed,
17 secondary air feed and tertiary air feed in this case are formed and
arranged in the form of
18 annular conveying cross sections, which are arranged concentrically to each
other, or in the
19 form of concentric arrangements coaxially around a central core air tube,
in which an oil burner
lance or suchlike can be arranged. The pulverous fuel in this case as a rule
is guided together
21 with the primary combustion air (primary air) in a primary air tube inside
the burner to the burner
22 mouth. Swirlers, which are arranged on the outer side of the core jacket
tube, are then provided
23 in this primary air tube and impart a desired swirl to the pulverized
coal/primary air mixture, so
24 that as a result the combustion is optimized, but at least improved,
especially with regard to a
low-NOx combustion of the fuel. These burners as a rule are used in plants in
which the
26 pulverous fuel is conveyed by means of a pneumatic conveyor from the mill
directly to the
27 burner. Attached to this is the disadvantage of being operated with low
transporting gas loads
28 and high conveying speeds in the process. This leads to an extensive wear
of the transporting
29 tubes. Furthermore, the conveying tubes have relatively large dimensions
(conveying cross
sections).
31
32 For avoiding these disadvantages, a generic-type burner and a generic-type
method, in which
33 the pulverous fuel is pneumatically conveyed to the burner, and in the
bumer, by means of
34 dense phase in a dense phase conveying system, have already been proposed
in DE 197 15
373 Al. With this, pulverized dry brown coal is conveyed in a single stage by
means of a dense
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1 phase conveying system, and with a transporting gas load of at least 60 kg
of pulverized coal/kg
2 of transporting gas, or with a conveyed stream density of between 100 and
350 kg of pulverized
3 coal/m3, is fed to a steam generator burner. For controlling the mass stream
of pulverized coal
4 and the loading of the conveying lines, water vapour or a hot inert gas,
such as flue gas or
nitrogen, is used as pneumatic conveying medium. In this case, burners are
described in DE
6 197 15 973 Al, in which the fuel is fed to the burner in a central feed
line, and then, during
7 discharge from this central line, is mixed with primary and secondary air
streams which issue
8 from annular passage-form openings arranged concentrically around it, is
dispersed, and
9 distributed into the furnace in a suspended state. Another burner has a
central primary air tube
which is concentrically encompassed by secondary and tertiary air lines. With
this burner, the
11 fuel is introduced into the burner in a pulverized coal pipe which is
guided in a coiled manner
12 around the primary air tube, and inside the burner is discharged into the
secondary air passage
13 at a distance from the mouth opening of the burner.
14
This known burner indeed already has the advantage that the combustion air
streams, which
16 are fed to the burner, and the fuel stream are spatially separated from
each other so that a
17 dense phase conveyance of the fuel is possible, wherein transporting gas
loads of over 20 kg of
18 pulverized coal/kg of transporting gas and conveying gas speeds of 3 to
about 20 m/s at
19 pressures of < 10 bar, are understood by dense phase conveyance in the
present application,
but the combustion is not yet optimized with regard to a low-NOX combustion.
In particular, with
21 the so-called DS (swirl flow) burners, which are characterized by an
especially low-NO,,
22 combustion, it is not possible to feed the pulverous fuel to the burner
either in the central core
23 air tube or in a central air tube, or via an additional fuel conveying line
which is guided in a
24 coiled manner in the secondary air feed passage. In order to achieve a low-
NOx combustion, it
is a technical aim to enrich the fuel concentration in the radially viewed
outermost zone of the
26 primary air stream which is guided in the burner, before its discharge into
the furnace, wherein
27 this enrichment is to be carried out uniformly over the circumference of
the primary air jet. In the
28 case of the burners which are known from DE 197 15 973 Al, this aim is not
achievable. In the
29 case of the burner with feed of fuel by dense phase conveyance through a
central conveying
tube, the feed of the fuel is directly centred in the region of the extension
of the longitudinal axis
31 of the burner, so that the primary air stream which is arranged around it
just has no enrichment
32 by fuel particles in its radial outer region. In the case of the other
burner which is known from
33 this publication, the fuel is indeed conveyed in a secondary air stream
which in the radial
34 direction is circumferentially arranged around the primary air stream.
However, this is carried
out with a coiled conveying tube of small cross section so that the fuel
discharges into the
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1 secondary air only in a small area of the annular passage which conveys the
secondary air, and
2 consequently there is no uniform distribution of the pulverous fuel over the
cross section of the
3 entire annular conveying passage of the secondary air. Also, in this case,
the fuel is conveyed
4 into the secondary air stream so that an enrichment of the outer region of
the primary air stream
with fuel is not carried out.
6
7 A pulverized coal burner for the steam-oxygen gasification of pulverized
coal which is
8 introduced in dense phase, is indeed already known from DD 251 476 A3, in
which the fuel,
9 which is uniformly distributed around a central feed of a combustion gas and
of an oxidizing
agent, via an annular passage cross section, is fed by dense phase conveyance.
In this case,
11 however, the admixing of a steam-oxidizing agent mixture is only then
carried out in the further,
12 subsequent stream path outside a combustion chamber. This burner serves for
the gasification
13 of the fuel and for producing a gasifying gas, which is why in addition to
the oxidizing agent
14 steam is also blown into the pulverized coal stream. This technology,
however, cannot be used
with a burner for the firing of a furnace of a steam generator.
16
17 The invention is based on the object of creating a solution which makes it
possible to equip a
18 low-NOX burner, which is suitable for firing the furnace of a steam
generator, with a dense
19 phase conveyance of fuel, without disadvantageously affecting the low-NOX
combustion
characteristic of the burner.
21
22 In the case of a burner of the type which is referred to in the
introduction, this object is achieved
23 according to the invention by the inside space of the primary air tube
being able to be
24 connected, or being connected, to a primary air feed line, and the fuel
conveying space which is
formed between the primary air tube and the fuel conveying tube being able to
be connected, or
26 being connected, to the feed line which feeds pulverous fuel in dense phase
to the burner.
27
28 In the case of a method of the type which is referred to in the
introduction, this object is
29 achieved according to the invention by the fuel being conveyed inside the
burner in an annular
passage-form fuel conveying space which is formed radially outside a primary
air line, and also
31 by the primary air stream which issues from the primary air line being
admixed in a swirled state
32 with the fuel stream after discharge from the fuel conveying space inside
the fuel conveying
33 tube.
34
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1 By means of the invention, a solution is now created by which it is
possible, without
2 disadvantageously affecting the low-NOx combustion characteristic of the
burner, to feed
3 pulverous fuel to the burner by dense phase conveyance and to first mix the
fuel with
4 combustion air in the bumer. This is achieved by an annular passage being
formed and
provided, in which just before the mouth region on the discharge side of the
burner to the
6 fumace, the pulverous fuel, especially puiverized dry brown coal, is
conveyed in the bumer
7 along the longitudinal axis of the burner. This annular passage in this case
is concentrically
8 circumferentially arranged around the primary air stream. The primary air
stream is now
9 furthermore swirled, for which swirlers are arranged and formed in the
primary air stream at a
suitable point, so that at the end of the annular passage-form conveying
channel it mixes with
11 the fuel which is conveyed by dense phase conveyance, so that consequently
at the mouth end
12 on the discharge side of the burner to the furnace the radially outer
region of the primary air
13 stream is circumferentially uniformly enriched with the fuel, or there is
fuel exclusively in this
14 region. By means of this measure, fuel is therefore conveyed by dense phase
conveyance
almost only in the outer circumferential region of the primary air stream.
This does not
16 disadvantageously affect the low-NOx combustion characteristics of the
respective burner, on
17 the contrary these are assisted, boosted and optimized as a result. By
means of the invention,
18 it is possible to maintain the swirling of the primary air stream and to
distribute the pulverized
19 coal stream or coal mass stream uniformly over the circumference of the
primary air stream on
its radial outer edge region. Since, furthermore, the swiriers which are
provided for swirling the
21 primary air stream are not arranged in the pulverized coal stream or coal
mass stream, these
22 are also not exposed to the abrasive wear of the fuel particles, so that
the burner according to
23 the invention is characterized as well by a reduced wear compared with the
conveyance of fuel
24 in the primary air mixture.
26 In order to swirl the primary air stream and to be able to also use the
dense phase conveyance
27 which is provided according to the invention with a swirl flow burner, it
is expedient if at least
28 one swirler is arranged in the inside space of the primary air tube, which
the invention provides
29 in a development.
31 In order to also be able to operate the bumer with an oil bumer lance or
suchlike, it is
32 advantageous according to a development of the invention if a core air tube
is arranged
33 concentrically to the primary air tube within it. An oil burner lance or
suchlike, as this is known
34 from customary burners, can then be arranged in the core air tube.
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1 Since the conveyance of the particulate fuel, especially pulverous fuel, is
carried out in dense
2 phase, large conveying cross sections, such as annular passage cross
sections or pipeline
3 cross sections, are not necessary for this conveyance, so that the invention
is furthermore
4 characterized in that the radial distance between core air tube and primary
air tube is greater
than the radial distance between primary air tube and fuel conveying tube.
6
7 In this case, it is furthermore especially advantageous and especially
expedient if the core air
8 tube extends in the longitudinal axial direction beyond the mouth end on the
discharge side of
9 the primary air tube into the region of the mouth opening on the discharge
side of the fuel
conveying tube. As a result of this, a mixing chamber, in which the swirled
primary air stream
11 and the dense stream conveyed stream of fuel are mixed with each other, is
formed inside the
12 burner at the mouth end on the discharge side of the burner to the furnace.
As a result of this, it
13 is especially possible to re-use the geometry of previously existing
burners and to retrofit these
14 simply by introducing a new primary air tube for the combustion of fuel
which is conveyed in
dense phase. The originally available primary air tube then becomes the fuel
conveying tube.
16 Greater or more costly constructional steps are not to be otherwise taken
on the furnace which
17 is provided with burners.
18
19 Since for conveying the primary air stream a furthermore relatively larger
opening cross section
is made available, it is possible to arrange there a plurality of swirlers, to
arrange these on the
21 outer generated surface of the core air tube, especially when a central
coaxial core air tube is
22 available. The invention, therefore, furthermore provides that a plurality
of swirlers, preferably in
23 the form of a vane ring, circumferentially distributed on the outer surface
of the core air tube, are
24 arranged radially on the outer side in the annular passage to the primary
air tube.
26 Furthermore, it is advantageous if the burner according to the invention is
also equipped with an
27 oil burner ignition lance, for which reason, according to a development of
the invention, an
28 ignition lance, especially an oil burner ignition lance, is arranged
coaxially in the core air tube.
29
Since with the configuration according to the invention especially low-NOX
burners are to be
31 provided, it is expedient if these additionally also have a secondary air
feed and a tertiary air
32 feed. The invention, therefore, is further characterized by a secondary air
feed which
33 encompasses the fuel conveying tube, and also a tertiary air feed which
encompasses the
34 secondary air feed.
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1 In a further expedient development, it is then also expedient, especially
for low-NOx burners, if a
2 radially inwards extending stabilizing ring is arranged at the end on the
combustion chamber
3 mouth side of the fuel conveying tube.
4
The method according to the invention in an expedient development first of all
provides that the
6 primary air is admixed with the fuel stream in the mouth region of the
burner in a mixing
7 chamber before discharging into the furnace. As a result of this, the
possibility arises of using
8 the geometry of existing burners and of creating an intensive mixture of
primary air and
9 pulverous fuel for low-NOx combustion. Finally, in this case then it is
still especially
advantageous if air, especially heated air, recirculated flue gas or a mixture
of air and
11 recirculated flue gas, is fed to the burner as primary air.
12
13 The invention is subsequently exemplarily explained in more detail with
reference to a drawing.
14 This shows in the single figure, in schematic view in detail, a cross
section along the longitudinal
axis of the end on the combustion chamber side of a low-NOx burner which is
arranged in the
16 wall of a combustion chamber or of a furnace of a steam generator,
especially of a large power
17 plant.
18
19 The burner 1, on the discharge side, leads into the combustion chamber or
into the furnace 2 of
a steam generator and is arranged in its circumferential wall. The burner 1
has an oil burner
21 ignition lance 4 which is arranged centrally along its longitudinal axis 3.
This is arranged in the
22 centre of a core air tube 5 which coaxially encompasses the oil burner
ignition lance 4. The air
23 guiding device 6, which is arranged around the oil burner ignition lance 4
at its end which faces
24 the furnace 2, ends flush with the mouth end on the burner discharge side
of a fuel conveying
tube 7, in which primary air, which is fed to the burner through a primary air
line 18 and mixed
26 with particulate fuel which is fed through the fuel conveying tube 7,
discharges into the furnace
27 2. The fuel conveying tube 7 is concentrically arranged around the oil
burner ignition lance 4
28 and also around the core air tube 5, and with the outer generated surface
of a primary air tube
29 9, and, downstream of the end of the primary air tube towards the furnace
2, with the outer
generated surface of the core air tube 5, forms in each case an annular
passage-form
31 conveying cross section. At the end on the combustion chamber discharge
side of the fuel
32 conveying tube 7, an air deflecting throat 8, which extends over the whole
circumference of the
33 fuel conveying tube 7, is formed on the outer side. On the inner side of
the fuel conveying tube
34 7, a stabilizing ring 14, which is provided with teeth, extends in this
region radially inwards into
the conveying cross section of the fuel conveying tube 7 and forms the
termination of the fuel
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1 conveying tube 7 at this point. The core air tube 5 terminates on the burner
inner side at a
2 distance to the mouth end on the combustion chamber discharge side of the
fuel conveying tube
3 7 in the region of the air guiding device 6.
4
In the annular passage-form conveying cross section, which is formed between
core air tube 5
6 and fuel conveying tube 7, the primary air tube 9 is arranged coaxially to
the core air tube 5 and
7 to the fuel conveying tube 7 so that a fuel conveying space 13 is formed
with an annular
8 passage-form conveying cross section. The mouth end of the primary air tube
9 which faces
9 the furnace 2 terminates at a distance from the mouth ends on the burner
discharge side both of
the core air tube 5 and of the fuel conveying tube 7, so that on the burner
inner side a mixing
11 cross section or mixing chamber 10 is formed. The end on the mouth side of
the primary air
12 tube 9 is located approximately in the region of the arrangement of
swirlers 15 which in the case
13 of low-NOX burners are customarily provided in the primary air stream. In
the exemplary
14 embodiment, the primary air tube 9 extends into the burner 1 to such an
extent that its end on
the mouth side is arranged in the positioning region of adjustable swirlers
11, 12 which are
16 located in a secondary air feed 19 and in a tertiary air feed 20. The
primary air tube 9,
17 furthermore, is arranged relative to the core air tube 5 and to the fuel
conveying tube 7 in such a
18 way that its radial distance to the core air tube 5 is greater than to the
fuel conveying tube 7.
19 Therefore, the annular passage-form fuel conveying space 13 is formed
between the outer side
of the primary air tube 9 and the inner side of the fuel conveying tube 7.
This annular fuel
21 conveying space 13 is connected, or can be connected, to a feed line, which
is not shown, by
22 which fuel is pneumatically fed by dense phase conveyance to the burner 1,
and then is also
23 pneumatically conveyed in the fuel conveying space 13 in dense phase. The
fuel is particulate
24 fuel, especially pulverized coal, preferably pulverous dry brown coal. The
dense phase
conveyance is carried out with a load of 20 - 90 kg of pulverized coal/kg of
conveying gas, and a
26 conveying speed of 3 to 20 m/s at pressures of < 10 bar. The radial
distance between the outer
27 side of the primary air tube 9 and the inner side of the fuel conveying
tube 7, and consequently
28 the passage height of the fuel conveying cross section or fuel conveying
space 13, can be
29 approximately as great as the length by which the teeth of the stabilizing
ring 14 extend radially
inwards in the direction of the burner axis 3.
31
32 Primary air is fed to the burner 1 through the annular passage-form
conveying cross section
33 which is formed between the inner side of the primary air tube 9 and the
outer side of the core
34 air tube 5. The primary air can be air, especially preheated air, but can
also be recirculated flue
gas or a mixture of recirculated flue gas and air. The primary air, which is
conveyed through the
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1 primary air line 18 with circular passage-form conveying cross section, when
discharging is
2 transferred into a swirled stream by means of adjustable swirlers 15 which
are arranged on the
3 inner side on the primary air tube 9 between core air tube 5 and primary air
tube 9 at the end on
4 the discharge side. The swirlers 15 are formed in the form of a vane ring
consisting of guide
vanes which are arranged in a uniformly distributed manner on the outer
circumference of the
6 core air tube 5.
7
8 Furthermore, the burner 1, as known from customary burners, has a secondary
air tube 16
9 which is arranged on the outer side coaxially around the fuel conveying tube
7, and a tertiary air
tube 17 which in turn is arranged on the outer side coaxially at a distance
around the secondary
11 air tube. Secondary air is fed through the secondary air tube 16 to the
furnace 2, and tertiary air
12 is fed through the tertiary air tube 17 to the furnace 2, as this is known
from known burners for
13 creating a multistage low-NOx combustion.
14
For controlling a possibly desired swirling both of the primary air and of the
secondary air in the
16 secondary air feed and of the tertiary air in the tertiary air feed, it is
provided that the respective
17 swirlers 15, 11 and 12 which are arranged therein are formed with
adjustment capability.
18 However, it is also possible to form the swirlers 15, 11 and/or 12 in each
case without
19 adjustment capability.
21 During operation of the burner 1 according to the invention, pulverized
coal is pneumatically
22 conveyed through the fuel conveying space 13 by dense phase conveyance
inside the burner 1
23 along the burner axis 3. This fuel conveying space 13 is located radially
outside the primary air
24 line 18 through which primary air is conveyed and which is formed by the
inside space of the
primary air tube 9 and the outer generated surface of the core air tube 5. The
supplied primary
26 air is swirled in the discharge region of the primary air line 18, or of
the primary air conveying
27 cross section, by means of swirlers 15, and mixes with the dense stream of
fuel which leaves
28 the fuel conveying space 13. In the mixing cross section or mixing space
10, which is formed in
29 this region of the burner 1, a mixing-through of the two components, which
are primary air and
fuel, is carried out, forming an enrichment of the radial outer region of the
developing air stream
31 with fuel, so that the coal material is conveyed into the region of the
teeth of the stabilizing ring
32 14 and then discharges into the furnace 2. The primary air stream which is
loaded with coal
33 particles in this way leaves the burner 1 with a conveying speed of about
15 - 25 m/s, preferably
34 18 - 20 m/s.
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1 With the burner construction according to the invention, it is therefore
possible to convey fuel by
2 pneumatic dense phase conveyance into the direct discharge region of a
burner 1 and to first
3 mix the fuel with primary air there. Only the smaller cross sections which
are required for the
4 dense phase conveyance are necessarily made available. Moreover, the
swiriers 15 which
cause swirling of the primary air are not exposed to the pulverized coal
stream, so that these
6 are not subjected to wear loading by pulverized coal particles.
7
8 Even if the embodiment above represents a construction with a centrally
arranged ignition
9 burner, then, however, it is also possible to provide burners which are
constructed without core
air feed and ignition burners. The necessary geometric conditions are then
created depending
11 upon burner construction. According to the invention, it is only important
in this case that
12 primary air is conveyed centrally on the inner side in a primary air tube
with regard to the
13 longitudinal axis of the burner, and then, in a swirled state, is admixed
with a fuel stream which
14 is conveyed radially outside the primary air stream in dense phase.
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