U.S. patent application number 13/455292 was filed with the patent office on 2012-11-01 for burner for particulate fuel.
This patent application is currently assigned to BABCOCK BORSIG STEINMULLER GMBH. Invention is credited to Stefan Hamel, Christian Storm.
Application Number | 20120272875 13/455292 |
Document ID | / |
Family ID | 46000914 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120272875 |
Kind Code |
A1 |
Hamel; Stefan ; et
al. |
November 1, 2012 |
Burner for Particulate Fuel
Abstract
Disclosed is a burner for particulate fuel, in particular made
of biomass, with a primary tube and a core tube arranged in the
primary tube. The primary tube and the core tube form a primary
tube gap and the primary tube gap is configured to guide a flow of
particulate fuel and gaseous combustion means from an inlet-side
end to an outlet-side opening of the primary tube. In order to
prevent the drawbacks occurring when using coarse-grain particles,
preferably biomass, as a fuel for dust firing, or at least to
reduce them without having to accept an increased outlay for
equipment and/or additional energy losses, at least one device is
provided for centring the flow within the primary tube in the
region of the outlet-side end of the primary tube.
Inventors: |
Hamel; Stefan; (Wenden,
DE) ; Storm; Christian; (Duisburg, DE) |
Assignee: |
BABCOCK BORSIG STEINMULLER
GMBH
Oberhausen
DE
|
Family ID: |
46000914 |
Appl. No.: |
13/455292 |
Filed: |
April 25, 2012 |
Current U.S.
Class: |
110/264 ;
110/265 |
Current CPC
Class: |
F23D 1/02 20130101; F23C
7/008 20130101; F23D 2201/20 20130101 |
Class at
Publication: |
110/264 ;
110/265 |
International
Class: |
F23D 1/00 20060101
F23D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2011 |
DE |
102011018697.2-13 |
Claims
1. A burner for particulate fuel, in particular made of biomass,
comprising a primary tube and a core tube arranged in the primary
tube, wherein the primary tube and the core tube form a primary
tube gap, wherein the primary tube gap is configured to guide a
flow of particulate fuel and gaseous combustion means from an
inlet-side end to an outlet-side opening of the primary tube, and
wherein at least one device is provided for centring the flow
within the primary tube in the region of the outlet-side end of the
primary tube.
2. The burner according to claim 1, wherein the core tube, viewed
in the longitudinal direction of the burner, ends before the
primary tube and wherein the axial spacing between the outlet-side
ends of the core tube and primary tube in the longitudinal
direction of the primary tube is at least 50%, preferably at least
75%, in particular at least 100%, of the mean width of the primary
tube gap.
3. The burner according to claim 1, wherein the core tube is
configured tapering toward its outlet-side end.
4. The burner according to claim 3, wherein the core tube tapers
continuously toward its outlet-side end.
5. The burner according to claim 4, wherein the core tube tapers
conically toward its outlet-side end, preferably at an angle of
inclination .alpha. of less than 20.degree., in particular less
than 10.degree., if necessary approximately 7.degree..
6. The burner according to claim 1, wherein a deflection device is
provided at the outlet-side end of the core tube in the primary
tube gap to deflect the part of the flow guided in the primary tube
gap close to the core tube inwardly.
7. The burner according to claim 6, wherein the deflection device
is configured to deflect about 30% by volume to 70% by volume,
preferably 40% by volume to 60% by volume, of the flow guided in
the primary tube gap.
8. The burner according to claim 6, wherein a flow channel is
provided between the core tube and the deflection device and
wherein the free flow cross section of the flow channel remains
substantially constant in the flow direction.
9. The burner according to claim 1, wherein at least one flow
director is provided in the primary tube gap to influence the swirl
of a part of the flow guided in the primary tube gap close to the
core tube.
10. The burner according to claim 9, wherein the at least one flow
director is oriented in the longitudinal direction of the primary
tube and, preferably, is configured to be much wider in the
longitudinal direction than in the peripheral direction.
11. The burner according to claim 9, wherein the at least one flow
director is inclined transverse to the longitudinal direction of
the primary tube.
12. The burner according to claim 9, wherein the at least one flow
director is provided within the inner 80%, preferably 70%, in
particular 60%, of the width of the primary tube gap.
13. The burner according to claim 9, wherein the at least one flow
director is provided downstream in the flow direction of a swirling
device preferably arranged in the primary tube gap, and wherein the
swirling device is provided to impress a swirl on the flow guided
in the primary tube gap.
14. The burner according to claim 7, wherein the at least one flow
director is provided in the flow direction, preferably directly in
front of the deflection device.
15. The burner according to claim 7, wherein a flame-holder
projecting inwardly into the flow of the primary tube is provided
on the outlet-side end of the primary tube.
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The invention relates to a burner for particulate fuel, in
particular made of biomass, with a primary tube and a core tube
arranged in the primary tube, the primary tube and the core tube
forming a primary tube gap and the primary tube gap being
configured to guide a flow of particulate fuel and gaseous
combustion means from an inlet-side end to an outlet-side opening
of the primary tube.
[0003] 2) Description of Prior Art
[0004] Burners for the combustion of particulate fuels, such as, in
particular, coal, in a combustion chamber have been known for some
time. Dust firing is also referred to in this connection.
[0005] A burner of this type is described, for example, in EP 0 571
704 A2. The burner has a core tube, which has air flowing through
it, and has a burner gun for igniting the particulate fuel.
Arranged concentrically with respect to the core tube is a primary
tube, which, with the core tube, forms an annular gap, which is
connected at its rear end to a dust line. A mixture of coal
particles and primary combustion means (primary air) is supplied
via the dust line to the burner. The mixture of coal particles and
combustion means is made to rotate by means of a swirling body
arranged in the annular gap, so the coal particles are concentrated
in the outer region of the annular gap.
[0006] Additionally provided concentrically with respect to the
primary tube are a secondary tube and a tertiary tube, which, with
the respective inner tube, define a secondary and a tertiary
annular gap, which have secondary and tertiary combustion means
(secondary air and tertiary air) flowing through them. Swirling
bodies are also provided in the secondary and the tertiary annular
gaps in order to impress a swirl on the combustion means. Conical
widenings in the wall of the combustion chamber are provided at the
outlet-side end of the secondary tube and the tertiary tube.
[0007] Provided at the outlet-side end of the primary tube is a
so-called flame-holder, which has a radially inwardly directed edge
leading to stalling and to turbulence of the coal particles. Thus,
a flow is produced, which is directed into the combustion chamber,
with a high degree of turbulence and coal particle concentration.
This flow is "surrounded" by the flows leaving the core tube, the
secondary annular gap and the tertiary annular gap. Owing to the
high degree of turbulence of the particle-rich flow, the volatile
components are very rapidly expelled from the coal particles.
Because of the high particle concentration, the air ratio is
strongly sub-stoichiometric, so less nitrogen oxides (NOx) are
formed.
[0008] The burners of the type mentioned can basically also be used
to burn particulate fuels other than coal, for example biomass. For
this purpose, the biomass has to be very finely ground, however,
which, because of the usually fibrous and tough structure of
conventional biomasses, is linked with an increased outlay for
equipment and energy. In particular, the fine grinding of biomass
often entails a high degree of wear of the equipment used for this.
Biomasses are therefore not generally ground so finely as coal. In
the case of hard coal, the particle size is typically 90% smaller
than 90 .mu.m and, in the case of brown coal, 90% smaller than 200
.mu.m. On the other hand, in biomass, a mean particle size of about
1 mm is desired.
[0009] The volatile components of the biomass particles are already
expelled more slowly because of their size, which can impair stable
combustion of the biomass. In addition, a correspondingly larger
quantity of air, the so-called carrying air, has to be used in
order to transport the larger biomass particles, free of deposits,
from the crusher through the burner into the combustion chamber.
The larger carrying air quantity flowing through the annular gap
between the primary tube and the core tube can, together with a
delayed release of volatile components, lead to a local air excess
during the combustion. As a result of this, more nitrogen oxides
are formed.
[0010] The present invention is therefore based on the object of
preventing the drawbacks occurring during the use of coarse-grain
particles, preferably biomass, as a fuel for dust firing, or at
least to reduce them, without an increased outlay for equipment
and/or additional energy losses having to be accepted.
SUMMARY OF THE INVENTION
[0011] This object is achieved in a burner of the type mentioned at
the outset and described in more detail above in that at least one
device is provided for centring the flow within the primary tube in
the region of the outlet-side end of the primary tube.
[0012] The invention recognised that the drawback of an increased
carrying air quantity and larger particle diameters in the
combustion of coarse-grain fuels, such as biomass, can be in any
case partially compensated by a fluidic deflection of a part of the
primary air in the direction of the core zone of the burner mouth.
The deflection makes it possible to guide a part of the primary air
around the flame-holder or to guide it centrally through the
latter, without this part of the primary air arriving in the
turbulent particle flow zone adjoining the flame-holder. This only
takes place at a later point in time, at which the turbulent
particle flow zone has widened and the volatile components of the
fuel particles have escaped to a greater extent. The particle
concentration is consequently high in the particle flow downstream
of the flame-holder. Consequently, the flame of the burner can be
stabilised despite a delayed escape of volatile components. In
addition, the oxygen concentration in the particle flow downstream
of the flame-holder is clearly sub-stoichiometric, which
counteracts the formation of nitrogen oxides.
[0013] The deflection of a part of the primary air in a central
region of the burner is made possible by the swirling of the
primary air in the primary annular gap, which concentrates the fuel
particles in the outer region of the primary annular gap and feeds
them to the flame-holder. The concentration of the fuel particles
in the outer region of the primary annular gap is accompanied by a
depletion of particles in the inner region of the primary air flow.
The invention makes use of the invention to divert a part of the
primary air into the central region of the burner without this
having significant effects on the transport of the fuel particles.
However, it is necessary for the partial diversion of the primary
air flow to adapt the burner geometry in such a way as to provide
space for the primary air flow to be deflected. This space is not
present in conventional burner geometries.
[0014] According to the invention, it is unnecessary for the fuel
particles to be transported by an air flow through the primary tube
gap even if this is appropriate for cost reasons. Instead of air,
another combustion means known per se could also be used. It would
even be conceivable to use an oxygen-free gas if the oxygen
required for the combustion is otherwise provided. For the sake of
simplicity, the term primary air is used, however, below.
[0015] There are also basically no limits with regard to the core
tube. Gas having oxygen or an oxygen-free gas can flow through the
core tube, which may, in particular, be expedient to cool the core
tube. As an alternative or in addition, a burner gun can be
received in the core tube to provide a support or ignition flame.
Quite in general, core tubes may be provided which are constructed
in a manner known per se. As a result of the deflection of a part
of the primary air flow, if necessary, a flow through the core tube
can be dispensed with. This may also favour the deflection of the
primary air into the central region of the burner behind the core
tube.
[0016] The person skilled in the art will recognise that the core
tube and the primary tube preferably have circular cross-sections
and are arranged concentrically with respect to one another as this
is favoured in terms of flow technology. The core tube and the
primary tube then form a primary tube gap in the form of a
symmetric annular gap. Basically, there could be a deviation both
from circular cross-sections of the core tube and primary tube
and/or from a concentric arrangement of these tubes, even if, as a
rule, this is less preferred. However, for the sake of simplicity,
in the present case, only the terms core tube and primary tube are
used instead of core channel and primary channel without this
inevitably having to be interpreted in a restrictive manner.
[0017] In a first configuration of the invention, the core tube
ends before the primary tube, viewed in the longitudinal direction
of the burner. The inner part of the primary air can therefore
arrive on time in front of the flame-holder in a central region of
the burner and, uninfluenced by the flame-holder, in a flow that is
laminar as far as possible, bypass the latter there. So an inner
part of the primary air can reach the central region or core region
of the burner and can form a uniform flow as far as possible, an
adequate spacing has to be provided between the outlet-side end of
the core tube and the outlet-side end of the primary tube or the
flame-holder--if present. In the longitudinal direction of the
primary tube, this spacing should be at least 50% of the mean
radial width of the primary tube gap. From a flow point of view, it
is more favourable, however, if this spacing is at least 75%, in
particular at least 100%. A very short spacing in comparison to
this may be counter-productive, in particular if the core tube ends
abruptly. The flow close to the core tube in the primary gap can be
stalled there and extend the turbulent region after the
flame-holder. Thus, specifically no part flow of the primary air
flow is guided around the flame-holder and the turbulent region of
particle-rich flow adjoining the latter.
[0018] Alternatively or in addition, the core tube may taper toward
its outlet-side end. The tapering of the end of the tube, compared
to an abrupt end of the core tube, has the advantage that the flow
can be guided more uniformly. Stalling and turbulences can thus be
avoided in the region of the inner part of the primary air flow. It
is particularly preferred if a tapering of the core tube is
accompanied by a longitudinal-side spacing of the flame-holder or
opening of the primary tube, on the one hand, and the outlet-side
end of the core tube, on the other hand.
[0019] For flow reasons, the core tube may taper constantly toward
its outlet-side end. The tapering may be uniform or non-uniform
here. It is favourable in terms of flow technology if the tapering
decreases to the outlet-side end in order to avoid stalling before
the end of the core tube.
[0020] To even out the flow, it is preferred, in particular in the
case of a round core tube, if the latter tapers conically toward
its outlet-side end. In this case, the angle of inclination of the
cone should not be too great to avoid a stall. Angles of
inclination of less than 20.degree. are preferred here. In order to
avoid a stall even at higher flow speeds, angles of inclination of
less than 10.degree. are appropriate. During testing, particularly
good results were achieved with angles of inclination of about
7.degree., if necessary with a deviation of .+-.1.degree..
[0021] To support the deflection of a part of the primary air, a
deflection device may be provided at the outlet-side end and
outside the core tube in the primary tube to deflect the flow
guided close to the core tube in the primary tube gap inwardly. As
a result, it can, for example, be ensured that the desired
proportion of primary air is also diverted in the direction of the
centre. In addition, the deflected part flow can be guided in a
more laminar manner owing to the additional surfaces of the
deflection device. The deflection device preferably projects into
the primary tube gap, in particular into the primary air flow.
[0022] In order to avoid a deflection of the fuel particles into
the core region of the burner, the deflection device may be
configured to deflect about 30% by volume to 70% by volume of the
air flow in the primary tube gap. In this case, it is appropriate
if the deflection device approximately extends into the primary
tube gap, preferably radially, to over 30% to 70% of the width of
the primary tube gap. Particularly good results are achieved if the
deflection device is configured to deflect about 40% by volume to
60% by volume of the air flow in the primary tube gap and/or
extends therein to over 40% to 60% of the gap width of the primary
tube gap.
[0023] Provided between the core tube and the deflection device is
preferably a flow channel, through which the deflected primary air
flow is guided. In this case, it is particularly preferred from the
technical flow point of view if the free flow cross section in the
flow channel of the deflection device remains constant. An
unfavourable variation with respect to energy of the flow speed can
thus be avoided.
[0024] As an alternative or in addition to further devices, at
least one flow director may be provided in the primary tube gap to
influence the swirl of a part close to the core tube of the flow
guided in the primary tube gap. A widening of the primary air flow
after leaving the primary tube gap can be counteracted, for
example, by influencing the swirl of at least the flow close to the
core tube, which favours the centring of the part flow of the
primary air close to the core tube. A plurality of flow directors,
preferably distributed over the periphery of the primary tube gap,
may also be provided. The number of flow directors should
preferably increase here with the diameter of the primary tube.
[0025] The at least one flow director may be oriented in the
longitudinal direction of the primary tube. The swirl of at least
one part of the primary air flow close to the core tube is at least
weakened thereby, which can have a favourable effect on the flow
conditions. In order to direct the flow but not to lastingly
disrupt it, the at least one flow director should be much wider in
the longitudinal direction than in the peripheral direction of the
primary tube gap.
[0026] The at least one flow director may, as an alternative
thereto, also be oriented transverse to the longitudinal direction,
i.e. partially in the peripheral direction, of the primary tube. In
this case, the orientation of the at least one flow director may
differ from an orientation in the longitudinal direction of the
primary tube in such a way that the swirl of the primary air flow
is intensified by the at least one flow director, at least for a
part of the primary air flow close to the core tube. The at least
one flow director may, however, also reduce the swirl of the
primary air flow in an also possible orientation pointing more in
the longitudinal direction of the primary tube. The at least one
flow director may, however, also be oriented in the opposite
direction to the swirl direction of the primary air flow. This may,
for example, lead to the fact that the swirl direction of the
primary air flow is reversed at least for a part of the primary air
flow close to the core tube. In order to intensify the swirl of the
primary air flow in regions, it may be expedient to incline the at
least one flow director by 35.degree. to 45.degree. relative to the
longitudinal direction of the primary tube. In order to weaken the
swirl of the primary air flow in regions, it may be favourable to
incline the at least one flow director by less than 25.degree., in
particular less than 15.degree., relative to the longitudinal
direction of the primary tube.
[0027] Depending on the boundary conditions in terms of flow
technology, each of these orientations of the at least one flow
director may entail positive effects. Basically, by means of a
swirl, which has a different strength or is differently directed,
of parts of the primary air flow, a separation in terms of flow
technology of these parts can be achieved, as the latter have
different properties in terms of flow technology. To enable a
control of the burner, the at least one flow director may be
variable with regard to its orientation, i.e. incline compared to
the core tube.
[0028] It is also conceivable for the at least one flow director to
have a varying incline in the longitudinal direction of the primary
tube in order to achieve a gradual change in the swirl direction of
the part of the primary air flow close to the core tube.
Alternatively or in addition, however, a plurality of flow
directors or groups of flow directors distributed over the
periphery of the core tube may also be provided one after the
other. In this case, it is particularly preferred if the incline
changes relative to the longitudinal direction of the primary tube
from flow director to flow director or from one group of flow
directors to the next group of flow directors in the longitudinal
direction of the primary tube.
[0029] Moreover, it can easily be achieved that the swirl of the
outer flow in the primary tube gap remains uninfluenced by the at
least one flow director in order to not impair the flame stability.
For this purpose, the flow director is not provided in the last
outer 20% of the primary tube gap. If the outer 30% or even 40% of
the primary tube gap can be kept free of flow directors, this is
favoured in terms of flow technology. The outer flow director-free
region may, for example, be increased in that the number of flow
directors arranged on the peripheral side is increased.
[0030] To adjust defined flow conditions in the primary tube gap,
it may be preferred if the at least one flow director is connected
downstream in the flow direction of the primary air flow from a
swirling device to impress a swirl on the primary air flow. The
swirling device is, in this case, in particular provided in the
primary tube gap even if the flow can basically already be made to
rotate by being supplied to the primary air gap. The impressing of
the swirl on the primary air flow may take place by means of
swirling bodies, for example in the form of guide vanes or guide
plates. These may preferably be inclined by 20.degree. to
30.degree., in particular about 25.degree., compared to the
longitudinal direction of the primary tube.
[0031] The at least one flow director is preferably provided in
front of a deflection device in the flow direction, so the primary
air flow of the deflection device can be supplied in a suitable
manner. In this case, the flow director may, if necessary, be
provided directly in front of the deflection device. It may even be
provided that the flow director and the deflection device are
connected to one another in order to rule out a possible impairment
of the flow in the intermediate space. In order to avoid increased
abrasion by fuel particles, wear-resistant materials, such as hard
welding applications or ceramics, may be used for the flow
directors.
[0032] A flame-holder projecting inwardly into the flow of the
primary tube may be provided at the outlet-side end of the primary
tube to stabilise the flame. The edge of the flame-holder
preferably pointing radially inwardly may be continuous or
interrupted. A toothed edge, which can produce a high degree of
turbulence, is also conceivable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The invention will be described in more detail below with
the aid of drawings showing only embodiments. In the drawings
[0034] FIG. 1 shows a first embodiment of the burner according to
the invention in a longitudinal section;
[0035] FIG. 2 shows a detail of the burner according to FIG. 1 in a
longitudinal section;
[0036] FIG. 3 shows a detail of a second embodiment of the burner
according to the invention in a longitudinal section;
[0037] FIG. 4 shows a detail of a third embodiment of the burner
according to the invention in a longitudinal section; and
[0038] FIG. 5 shows a detail of a fourth embodiment of the burner
according to the invention in a longitudinal section.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] FIG. 1 shows a longitudinal section through a burner 1,
which is arranged in a wall W of a combustion chamber F. The inner
part of the burner 1 from FIG. 1 is shown to an enlarged scale in
FIG. 2 for improved clarity.
[0040] A core tube 2, in which a burner gun, not shown, can be
provided, is provided in the centre of the burner 1. Other devices
are also possible, which are shown here purely schematically. The
core tube 2 is arranged concentrically with respect to a primary
tube 3, so a peripheral concentric primary tube gap 4 is provided
between the core tube 2 and the primary tube 3. A mixture of
particulate biomass and combustion means, the primary air, is
supplied to said primary tube gap by devices, not shown. Provided
in the primary tube gap 4 is a swirling device 5 in the form of
guide vanes which are set at about 25.degree. relative to the
longitudinal extent of the primary tube and which make the primary
air flow rotate. The biomass particles then migrate in the flow
direction, because of centrifugal forces, to the outside, where the
biomass particle concentration increases, while it accordingly
decreases in a region close to the core tube. A flame-holder 7,
which defines the outlet opening 8 of the primary tube 3, is
provided at the outlet-side end 6 of the primary tube 3. A toothed
edge 9, which points radially inwardly, is provided on the inside
of the flame-holder 7 and comes into contact with the primary air
flow and the biomass particles and, following this, ensures a
swirling of the flow, which is indicated in FIG. 1 by the sharply
curved arrows A.
[0041] A secondary tube 10 which, with the primary tube 3, forms a
secondary tube gap 11, is provided concentrically with respect to
the primary tube 3. The secondary tube gap 11 has secondary air
flowing through it, said secondary air having a swirl impressed on
it by means of swirling devices 12 in the form of guide vanes set
relative to the longitudinal extent of the primary tube in the
secondary tube gap 11. The secondary air does not have to be air in
the actual sense. Provided at the outlet-side end 13 of the
secondary tube 10 is a secondary groove 14, which is a conical
widening of the secondary tube 10 and deflects the secondary air
flow radially outwardly.
[0042] Provided on the outlet-side end 6 of the primary tube 3 is
an outwardly pointing primary groove 15 in the form of a conical
widening, which contributes to the outward deflection of the
secondary air flow and leads to a stalling at the flame-holder 7.
This stalling assists the configuration of the turbulent swirling
of the biomass particles after the flame-holder 7, as is shown by
the arrows B in FIG. 1.
[0043] Arranged concentrically with respect to the secondary tube
10 is a tertiary tube 16, which, with the secondary tube 10, forms
a tertiary tube gap 17. The tertiary air is guided to the
combustion chamber F in the tertiary tube gap 17, this not having
to be air in the traditional sense, which is made to rotate by
means of swirling devices 18 in the tertiary tube gap 17. The
tertiary tube 16, at its outlet-side end 19, has a conical
widening, which is also called a muffle 20 and preferably has a
larger angle of inclination than the secondary groove 14. The
muffle 20 is used to deflect the tertiary tube flow outwardly. For
the purpose of cooling, cooling lines L associated with the muffle
20 are provided in the wall W of the combustion chamber F. In the
shown and to this extent preferred burner 1, the secondary groove
14 is set back inwardly relative to the muffle 20. The secondary
groove 14 could, however, also be configured aligned with the
muffle 20, in particular flush with the wall W of the combustion
chamber F.
[0044] The outlet-side end 21 of the core tube 2 does not only end
significantly in front of the flame-holder 7. The core tube 2, at
the outlet-side end 21, also has a conical taper 22. The axial
spacing D between the core tube 2 and the flame-holder 7, in the
shown and to this extent preferred burner 1, is at least equal to,
if not greater than, the radial spacing R between the core tube 2
and the primary tube 3, in other words the width of the primary
tube gap 4.
[0045] Accordingly, the outer diameter of the core tube 2 in the
region of the outlet-side end 21 decreases with an increasing
closeness to the outlet-side end 21 in the longitudinal direction.
In the shown and to this extent preferred embodiment, the conical
taper 22 at the outlet-side end 21 has a constant angle of
inclination a of substantially 7.degree.. As a result of this
configuration of the core tube 2 and the axial spacing D between
the core tube 2 and the flame-holder 7, a part flow of the primary
air close to the core tube is deflected at the outlet-side end 21
of the core tube 2 and thereafter in the direction of the axial
core region of the burner 1. A centring of the primary air flow at
the outlet-side end of the core tube 2, in particular, however, at
the outlet-side end of the primary tube 3, thus takes place. This
centring, as illustrated by the arrows C in FIG. 1, leads to a part
of the primary air being deflected centrally around the
flame-holder 7, in particular around the edge 9, which is directed
inwardly, of the flame-holder 7, without this part flow arriving
directly in the highly turbulent particle-rich flow region produced
by the flame-holder 7. At a later time, at which the centrally
deflected part flow of the primary air is located further in the
interior of the combustion chamber F, the deflected part flow may,
however, very well come into close contact with the fuel particles,
if necessary, in order to oxidise them.
[0046] FIG. 3 shows a detail of a burner 30 in a longitudinal
section in accordance with FIGS. 1 and 2. The same components have
been given the same reference numerals here. The important
difference between the burners 1, 30 shown in FIG. 1 and FIG. 3 is
that the core tube 2, peripherally on its outer lateral surface 31,
has a plurality of flow directors 32, which are thin in the
peripheral direction. The flow directors 32 extend parallel to the
longitudinal extent of the burner 30 or the core tube 2 and
therefore deflect a part of the primary air in the axial
direction.
[0047] The flow directors could, however, alternatively also be
inclined to the left or right, i.e. extend both in the longitudinal
direction and transverse to the longitudinal direction of the
primary tube 2, similarly to that which is the case with the
swirling devices. Depending on in which direction and with which
incline the flow directors are inclined in the peripheral direction
of the core tube, the swirl of the part of the primary air flow
close to the core tube is intensified or weakened. An incline of
greater than 45.degree. to 90.degree. is basically less preferred
here as the primary air flow is thus clearly decelerated.
[0048] The flow directors 32 of the shown and to this extent
preferred burner 30 allow the rotation of the primary air to be
eliminated at least for a part of the primary air flow close to the
core tube. In the burner 30 shown, the outer primary air part flow
adjoining the primary tube 3 is not influenced by the flow
directors 32. This primary air flow thus continues to rotate. For
this purpose, the radial extent of the flow directors 32 in the
shown and to this extent preferred burner 30 merely corresponds to
about 40% of the radial spacing R between the core tube 2 and the
primary tube 3.
[0049] The substantially axial core flow in the primary tube gap 4
is particularly well deflected into a central region of the burner
1 by the conical region 22 of the core tube 2 and the axial spacing
D from the flame-holder 7, as indicated by the arrow C in FIG.
3.
[0050] FIG. 4 shows a detail of a burner 40 in the longitudinal
section, which in addition to the burner 30 according to FIG. 3,
has a deflection device 41. The deflection device 41 is associated
with the outlet-side end 21 of the core tube 2 and forms a
concentric annular gap adjoining the core tube 2. In the shown and
to this extent preferred burner 40, the deflection device 41 covers
the conically tapering portion 22 of the core tube 2, which is
formed in the embodiment by a reduction in the material thickness
of the core tube 2. Before the conically tapering portion 22, the
deflection device 41 forms an inlet region 42, in which the flow is
oriented substantially axially, but not radially. The inlet region
42 may be formed by a concentric tube sleeve. In the region of the
conically tapering portion 22 of the core tube 2, the deflection
device 41 in the shown and to this extent preferred burner has a
portion tapering at the same angle of inclination a as the core
tube 2. So that the flow cross section in the deflection device 41
does not decrease too sharply, the conical portion of the
deflection device 41 may also be slightly less inclined, if
necessary, than the conical portion 22 of the core tube 2, so a
constant flow cross section is provided, for example, in the
deflection device 41. The deflection device 41 is preferably
configured as an axially peripheral component, which ends in the
same plane as the core tube 2. The deflection device 41 is spaced
apart from the flow directors 43 and, in the shown and to this
extent preferred burner 40, has a substantially similar radial
overall height as the flow directors 43.
[0051] FIG. 5 shows the detail of a burner 50, in which the flow
directors 51 arranged distributed over the periphery of the core
tube 2 are directly connected to the deflection device 52. Put more
simply, the flow directors 51 guide the part flow close to the core
tube in the primary tube gap 4 into the deflection device 52, which
is configured as an axially peripheral component. In the burner 50
shown in FIG. 4, the deflection device 52 extends further in the
direction of the outlet-side end 6 of the primary tube 3 or the
flame-holder 7, than the core tube 2. The deflection device 52 thus
ultimately projects relative to the core tube 2 in the flow
direction for sealing off relative to the turbulences produced by
the flame-holder 7.
* * * * *