Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 7
FIELD OF THE INVENTION
The present invention relates to a process for
exploitation of a burner for a rotary tube furnace,
in which fuels and primary air are supplied concentri-
cally.
The present invention also relates to a burnerfor a rotary tube furnace equipped with a burner
nozzle fitted with fuel and primary air conduits
whlch are disposed substantially concentrically with
10 respect to one another, which primary air includes
air set in rotation and air flowing axially.
BACKGROUND OF THE INVENTION
A burner of this type is disclosed in German
Patent DE 2 905 746.
This known burner comprises, in addition to
a central fuel admission for the oil, another fuel
admission disposed concentrically thereto for powdered
coal or any other like fuel.
For the purpose of obtaining a good mixture,
20 this solid fuel admission lies between two streams
of primary air, of which one, which is the central
stream, is set in rotation or eddy, i.e. it comprises
a component in tangential or peripheral direction,
and of which the other, outer, stream comprises an
essentially axial flow velocity for the purpose of
stabilizing the flame which penetrates far in the
rotary furnace.
In other known burners, the stream of primary
air is also provided to extend relatively far in
the interior.
The known burner comprises, at its centre, a
liquid fuel, generally oil, admission. The liquid
fuel is atomized into fine droplets by means of a
spray nozzle and is mixed, after leaving the central
opening of the nozzle, with primary air which issues
--2-
from the opening for outlet of eddying air, which
opening is located radially around the central opening.
The known burners are usually employed with
a proportion of primary air of between 8~ and 25%
of the total quantity of combustion air.
The power of the burner, i.e. the operational
working, is regulated by a respective reduction or
increase of the fuel and the air admission within
a determined range of adjustment, in which the minimum
adjustable working for obtaining a stable flame is
equal to about 20 to 25~ of the maximum working pos-
sible.
When the burner is started, oil must, as a general
rule, be injected through the central orifice of
the nozzle and must be ignited in order to pre-heat
the furnace, since combustion of the solid fuel,
which is supplied concentrically, is possible only
in a sufficiently pre-heated furnace.
With respect to this state of the art, the present
invention has for its object to provide a process
for exploiting a burner of a rotary tube furnace
and also a burner adapted to carry out this process,
which may operate with a smaller proportion of primary
air and present a broader range of adjustment of
the operational working.
SUMMARY OF THE INVENTION
As far as the process is concerned, this object
is attained by providing directly all around a central
fuel supply conduit and/or radially inside an annular
fuel supply conduit, a central dead zone in which,
at the most, a reduced proportion of the primary
combustion air is sent.
Thanks to the presence of a central dead zone,
combustion thus begins at a greater distance in front
of the centre of the nozzle of the burner compared
2~2~
3_
with the heretofore known processes and burners.
In this way, seen in longitudinal section, star-
ting from the centre of the front end of the nozzle,
the resultant f]ame comprises a central zone which
S extends forwardly and radially, in which virtually
no noteworthy combustion of the fuel is produced
with the oxygen of the air.
It is true that such a central flame heart is
also present in principle in the known burners, whilst,
according to the present invention, this central
dead zone is provoked deliberately and enlarged,
more particularly by the fact that the least primary
air possible is supplied in this zone.
However, even if it is not provided in the first
place for combustion, a small proportion of primary
air may be supplied in this central zone, this small
proportion of primary air serving, however, in the
first place to stabilize the flame and to prevent
a rearward return of the combustion gases, the coal
ash and the coke, which, without that, would lead
to the soiling of the central part of the nozzle.
A small stream of primary air in this central
zone, which is below 20% and preferably below 10%
of the total primary air, avoids such a rearward
return of the combustion products, without supplying
much oxygen which would reduce the central zone rich
in fuel.
It has been unexpectedly found that, thanks
to the presence of such enlarged central dead zone,
the range of adjustment of the burner may be conside-
rably increased, up to less than 10% of the maximum
working for which the burner is designed.
Insofar as such a burner must operate especially
with solid and pulverized fuels, this means that,
after a brief pre-heating with oil, it may already
2~3~7
function with the solid fuel.
At the same time, it has been shown that, in
such a process and in a burner designed for this
process, the proportion of primary air which must
be used for stabilizing the flame may be reduced
by 2 to 10% and preferably below 6% with respect
to the overall quantity of combustion air. This facili-
tates manufacture of the primary air supply devices
which may be designed respectively weaker.
A particular advantage of the reduced consumption
of primary air resides in the resulting saving of
energy for an equal performance and also in the reduc-
tion of the proportion of nitrogen oxides in the
combustion gases.
According to the invention, it is provided that,
separately from the introduction of a small proportion
of primary air in the central zone, at least two
other separate streams of primary air are supplied,
one of which is essentially axial and the other has
20 a major part of the flow components in peripheral
direction.
As far as the device mentioned above is concerned,
the object of the invention is attained by locating
the orifices for admission of the eddying air and
25 of the axial air, outside the orifices for admission
of the fuel, and the minimum radial distance with
respect to the centre of the nozzle of the burner
- from the outlet orifices for the eddying air and
the axial air, is at least equal to twice the radius
30 of a central orifice of the flame stabilizer.
The flame stabilizer comprises a flange which
surrounds a central opening, and which is located
at the centre of the nozzle of the burner and, prefe-
rably at the end of a nozzle holder for the oil.
35 It contributes to forming and stabilizing the flame.
~2~3~7
The flame stabilizer which projects radially with
respect to the central nozzle-holder for the oil,
thus procures a sufficient radial distance from the
other annular openings for the primary air and/or
other fuels which are located radially outside the
flame stabilizer.
The radii of the central opening of the flame
stabilizer and of the annular orifice for the principal
stream of primary air located more to the inside
are chosen, with the result that the inner stream
of primary air lies at a distance from the centre
of the nozzle which corresponds to at least double
the central opening of the flame stabilizer. In this
way, the central opening of the flame stabilizer
corresponds substantially to the orifice of the nozzle
of the central fuel conduit.
In this way, the fuel issuing centrally does
not come into contact too soon with the oxygen of
the principal streams of primary air.
In addition, in the preferred embodiment of
the invention, there is provided in addition an annular
conduit for a solid and/or gaseous fuel, disposed
radially inside the primary air conduit and radially
outside the flame stabilizer.
The expression "primary air conduit" generally
refers to the major part of the primary air which
is supplied axially or in eddying form and must not
cover the small proportion of primary air (central
air) which is supplied in the central zone of the
flame to avoid the rearward return of the combustion
products.
For the supply of this latter small proportion
of primary air, according to the invention, openings
are provided in the flame stabilizer, outside the
central opening-
2~2~7
The circulation of this small part oE primary
air takes place in an annular conduit included between
the central support of the oil nozzle and the following
inner wall in radial direction for another admission
of fuel or for one of the principal streams of primary
air.
In addition, it is advantageous if the outlet
opening for the axial air stream lies as far to the
outside as possible in the radial direction and if
it presents, furthermore, an axially projecting outer
edge.
This outer ring contributes to a better constancy
of the axial direction of the air, with the result
that combustion is improved and the flame is stabilized.
lS According to the invention, the annular conduits
for supplying primary air and~or solid or gaseous
fuel, have conical walls and these walls as well
as the concentric tubes connected -thereto are axially
displaceable with respect to one another, so that
the free transverse section of the annular passage
can thus be adjusted.
However, the ends of each conduit are preferably
cylindrical in order to avoid a divergent flow parallel
to the direction of the conical walls.
According to the invention, in the conical part
of the annular conduit for the axial air, radial
partitions are disposed, intended for the axial orienta-
~ tion and for the circulation of the primary air in
separate channels, which are disposed on a ring and
which extend essentially in axial direction.
These partitions contribute to an additional
axial orientation of the corresponding primary air
and also increase the axial outlet velocity, in that
they reduce the free section of the annular conduit
and they divide it into a plurality of individual
-7- 2~
channels disposed all around a ring. Moreover, in
a preferred embodiment of the invention, some of
these channels are closed at least partly or are
adjustable. To that end, the partitions may for example
be made sufficiently wide in peripheral direction
to obturate a channel at least partly or they corres-
pond to a closed channel.
It is thus possible to obtain that the sum of
the free sections of the channels be less than the
transverse section of the annular conduit for the
primary air flowing in axial direction.
As has already been explained, the axial flow
velocity of the air is thus increased, which further
contributes to stabilizing the flame.
In addition, according to the invention, the
flame stabilizer is provided to be offset rearwardly
in axial direction with respect to the openings for
outlet of the principal part of the primary air and
the solid or gaseous fuels. This may be effected
for example by ~ixing the flame stabilizer to the
tube enveloping the pipe of -the burner, which is
axially displaceable, which tube is consequently
offset axially.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more readily understood
on reading the following description with reference
to the accompanying drawings, in which:
Figure 1 is an overall view of a burner with
part of the supply installations.
Figure 2a is a longitudinal section through
a first embodiment of a burner nozzle.
Figure 2b is a partial left-hand view of Figure
2a.
Figure 3 is a longitudinal section through another
embodiment of a burner nozzle with possibility of
,
. .
-8- 202~7
supplying pulverized solid fuels.
Figure 4 is a longitudinal section through a
burner nozzle with additional possibility of supplying
a gaseous fuel.
Figure 5 is a longitudinal section through a
burner nozzle with additional possibility of supplying
a solid fuel and a gaseous fuel.
DETAILED DESCRIP~ION OF THE DRAWINGS
Keferring now to the drawings, Figure 1 shows
a burner nozzle 1 placed at the end of an outer burner
tube 5", which is at the same time the outer wall
of a conduit 5' for primary air which flows in axial
direction.
At the other end of the outer tube 5", different
supply devices are fixed or connected by flanges.
The axial air arrives via a tube 25, the eddying
air arrives via a tube 24, and these two primary
air parts are adjustable separately by respective
valves 45 and 44 and are connected to the same princi-
pal primary air conduit. At the rear end of the burner
shown in Figure 1, a conduit 22 branches from this
principal prima~y air conduit and this branch termi-
nates in a tube which concentrically surrounds the
tube enveloping the burner pipe 10'.
In this way, a small part of the primary air
coming from *he branch 22 flows through an annular
conduit 11' and issues through openings 13 (cf. Figure
2b) in the central zone of the flame. A liquid fuel
such as oil is supplied centrally to the nozzle of
the burner via conduit 21.
A tube 23, which is intended for supplying pulve-
rized solid fuels, generally powdered coal, is connec-
ted to the annular conduit 15' visible in Figures
3 and 5.
~ o ~
-8-
supplying pulverlzed solid fuels.
Figure 4 is a longitudinal section through a
burner nozzle with additional possibility of supplying
a gaseous fuel.
Figure 5 is a longitudinal section through a
burner nozzle with additional possibility of supplying
a solid fuel and a gaseous fuel.
DETAILED DESCRIPTION OF TH~ DRAWINGS
Referring now to the drawings, Figure 1 shows
a burner nozzle 1 placed at the end of an outer burner
tube 5", which is at the same time the outer wall
of a conduit 5' for primary air which flows in axial
direction.
At the other end of the outer tube 5", different
supply devices are fixed or connected by flanges.
The axial air arrives via a tube 25, the eddying
air arrives via a tube 24, and these two primary
air parts are adjustable separately by respective
valves 45 and 44 and are connected to the same princi-
pal primary air conduit. At the rear end of the burner
shown in Figure 1, a conduit 22 branches from this
principal primary air conduit and this branch termi-
nates in a tube which concentrically surrounds the
tube enveloping the burner pipe 10'.
In this way, a small part of the primary air
coming from the branch 22 flows through an annular
conduit 11' and issues through openings 13 (cf. Figure
2b) in the central zone of the flame. A liquid fuel
such as oil is supplied centrally to the nozzle of
the burner via conduit 21.
A tube 23, which is intended for supplying pulve-
rized solid fuels, generally powdered coal, is connec-
ted to the annular conduit 15' visible in Figures
3 and 5.
g
The concentric tubes 10", 11", 4", 5", 15" and
19", which are engaged in one another, have different
lengths. The innermost tubes project axially towards
the rear beyond the outermost tubes, with the result
that, as shown in Figure 1, adjusting devices 33,
34, 35 may be positioned which allow a relative axial
displacement of the tubes with respect to one another.
To that end, the individual tubes are connected to
one another by means of deformable gussets.
A monitoring unit 30 serves to monitor and control
the streams of primary air.
Figure 2a shows a longitudinal section and Figure
2b a partial front view of a burner nozzle which
is designed to operate exclusively with a fuel, for
example oil, arriving at the centre.
The flame stabilizer 3, which is located at
the end of tube 10', which envelops the nozzle-holder
pipe of the oil burner and which projects radially
with respect to the opening of the nozzle, guarantees
that the opening 4 of the annular supply conduit
along 4' opens out at a considerable radial distance
from the central opening 2 of the fIame stabilizer.
In the embodiment shown, the radial distance
D of the annular opening 4 with respect to the axis
of the burner is more than triple the radius d of
the opening 2. The corresponding distances are indica-
ted in Figure 4, in which the ratio D/d is even greater.
~ The zone located essentially in front of the
flame stabilizer constitutes a central dead zone
20, which is located outside the central fuel stream
and clearly within the principal admission of primary
air issuing from the annular openings 4 and 5.
This dead zone may extend axially up to a multiple
of the diameter of the flame stabilizer. A mixture
of the primary combustion air and of the fuel suffi-
'~2~
- 10-
cient for the formation of a flame is produced only
outside this central dead zone. The flame stabilizer
3 comprises a hub in the form of a flange surrounding
a central orifice 2. This hub comprises small openings
13. The outer face of the hub, i.e. the front face,
bears fins 12 which guide the small proportion of
primary air issuing from openings 13.
The outer supply conduit 5' comprises at its
end conical walls 6 which diverge outwardly. In the
10 zone of these walls 6 are located juxtaposed partitions
6' which have a longitudinal section of triangular
shape. These triangular walls are juxtaposed along
a common side which is parallel to the axis of the
burner and which is placed at the same radial distance
15 from this axis as the outer wall of the conduit 5'.
In this way, it is possible to displace the
tube 4" axially with respect to tube 5" without the
function of partitions 6' being influenced thereby.
Figure 2b shows a front view of the front edges
20 Of the partitiOnS 6'.
However, partitions 6' may also have, in periphe-
ral direction, a sufficient width for them to corres-
pond to the parts located between the channels 5
shown in Figure 2. These parts may also be considered
as closed channels 5.
The supply conduit 4' comprises in front of
the conical end, a device 14 for eddying the air,
i.e. for setting it in rotation about the axis of
the burner. This device is essentially con5tituted
by fins for guiding the air which are oriented oblique-
ly with respect to the axis of the burner.
Thanks to the axial displacement of tube 11'
with respect to tube 4', the distance between the
conical walls 7 of conduit 4' may be varied, with
the result that the transverse section of conduit
--ll--
4' may thus be modified. The terminal part of conduit
4' in the zone of opening 4 is, however, again cylin-
drical in order to avoid a divergent flow of the
eddying air lssuing from this opening.
Similarly, edge 8, which projects forwardly
in axial direction, procures an axial outlet direction
of the axial air stream.
In connection with the outlet direction and
the acceleration of the axial air in conduit 5, this
guarantees an axial air flow which is stable, uniform
and of broad scope.
Figure 3 shows an embodiment of the burner nozzle
which differs from the embodiment shown in Figure
2, essentially by the presence of an additional conduit
1~ 15', for powdered solid fuels, which is located between
the flame stabilizer 3 and the conduit 4' of eddying
primary air.
It is generally question of powdered coal which
is transported in the burner by a vector gas, for
20 example air. Due to the abrasive properties of such
a solid fuel, the terminal zone of conduit 15' is
only slightly conical in order to allow passage of
the fuel which is as easy as possible.
Figure 4 shows an embodiment comprising, in
25 place of conduit 15' ~or a solid fuel, another conduit
19' for a gaseous fuel, whose terminal section may
be conical, like conduit 4', and which may also com-
prise a device for eddying the gas issuing from this
conduit. In that case too, the terminal section of
30 conduit 19' is cylindrical in the zone of opening
19, in order to avoid a divergence of the gaseous
fuel which issues therefrom.
Figure 5 shows an embodiment which comprises
both a supply conduit 15' for solid fuels and a conduit
35 19' for gaseous fuels.
2 ~ 7
-12-
Conduits 4' and 5' for the principal proportion
of primary air in the form of eddying air and air
having an axial direction are disposed outside these
two fuel conduits in radial direction. The inner
edge of the opening 15, by which a considerable part
of the primary combustion air may penetrate in the
burner in the form of vector gas for the solid fuel,
is located at a distance D' from the axis of the
burner, which is more than double the radius d of
the opening 2 of the flame stabilizer, with the result
that, in all cases, the existence is guaranteed at
the centre of the flame of a sufficiently large dead
zone which procures the advantageous properties of
the present invention.
Thanks to the invention, a burner and a process
for exploiting a buxner equipping a rotary tube furnace
have been created, which allow a reduced proportion
of primary air and a broader range of adjustment
of the burner, this leading to reduced energy consump-
tion and a reduction of the formation of nitrogenoxides detrimental to the environment.
