BURNER FOR A REHEATING FURNACE OR HEAT TREATMENT
FURNACE FOR STEEL INDUSTRY
The present invention relates to a combustion system
5 generating a heat flux for heating materials, in
particular for reheating furnaces for steel products.
A combustion system of this type is known from EP 0994
302, corresponding to FR 2 784 449, also filed by the
10 applicant company.
It is known that heat treatment furnaces, in particular
reheating or holding furnaces, are designed to heat
products, in particular slabs, blooms and similar, to
15 the temperatures required for example for rolling or in
order to obtain a given metallurgical structure.
It is also known that the quality of the treatment of a
product, for example for rolling or heat treatment,
20 requires a precise and uniform temperature inside the
product, and that this temperature depends on the type
of treatment required or the chemical composition of
the product being treated.
For example, in reheating furnaces for metal products,
25 the average temperature level is obtained by passing
the products through heating zones that are
characterized by a significant heat flux, which
. achieves a high degree of temperature heterogeneity in
the products being reheated, in particular in furnaces
30 fitted with axisymmetric flame burners according to the
prior art.
In order to achieve the uniform temperatures required
for subsequent treatment, the products leaving the
35 heating zones pass through a soaking zone in which the
heat input is very low, at zone temperatures close to
the furnace discharge temperature, which makes it
possible to equalize the temperatures throughout the
thickness of the products. For economic reasons, the
products cannot stay too long in this soaking zone and
this soaking time is a compromise between the maximum
acceptable heterogeneity value and the costs relating
to construction of this zone of the furnace.
5
A first solution to improve the uniformity of the heat
'flux provided by the axisymmetric burners to the
products in the furnace involves adjusting the wide-
10 flame burner according to EP 0994302. Since
international and local regulations limiting pollutant
emissions, such as NOx, have significantly reduced
acceptable maximum emission levels, burner technology
needs to be improved.
15
The wide-flame burner according to EP 0994302 provides
a significant improvement over axisymmetric flame
burners by distributing the heat flux of the flame over
a large surface parallel to the plane of the products.
20
The wide-flame burner makes it possible to limit the
gradient of the temperature at the surface of the
products that are positioned in the furnace provided
with such burners parallel to the spreading plane of
25 the flame.
This burner makes it possible to:
- reduce the duration of the soaking phase of the
30 products, and therefore the length of the zone of
reheating furnaces in which such soaking is performed,
- limit the risk of localized overheating of the
product due to the absence of any very hot zones or
35 hotspots in the flame. This feature helps to improve
the final metallurgical status of the treated product,
- distribute the combustion throughout a volume that is
Larger than the volume covered by axisymmetric burners,
which helps to better control the mix of reagents and
products of combustion within the furnace enclosure.
5 This reduces emissions of pollutants generated by
comb~stion and reduces the formation of oxides on the
surface of the reheated products.
- reduce the height of the furnace enclosure by
10 reducing the dimension of the flame perpendicular to
the plane of the products,
- replace a significant number of burners installed on
the furnace roof by a smaller number of burners
15 installed on the furnace v~alls. The fuel and oxidant
distribution circuit is smaller, and cheaper to make.
Although these advantages have been recognized by users
of wide-flame burners according to the prior art, the
20 tunnel shape provided for in EP 0994302 limits the
aspiration of ambient flue gases at the root of! the
fuel jets, which results in a local overheating zone of
the products of combustion close to the tunnel, and
this high temperature increases NOx emissions.
25
Emission levels of pollutants , in particular the
level of NOx emitted, would be improved compared to EP
0994302 in order to keep this wide-flame burner
technology as viable as possible by anticipating
30 regulatory developments relating to pollutant emissions
in different countries around the world.
One objective of the invention is to improve the design
of wide-flame burners to help to achieve greater
35 uniformity in the transmission of the heat flux
generated by said flame, in order to reduce the
temperature heterogeneity in the products to be
reheated, and to help to improve heat transfer and to
reduce the . quantity of pollutants emitted, in
particular NOx.
The invention addresses this problem by providing users
5 with a new wide-flame burner technology for reheating
steel products that maintains or improves the form of
the wide flame while better distributing the heat flux
to the product and significantly reducing pollutant
emissions, in particular NOx.
10
According to the invention, a burner for a reheating
furnace for steel products, such as billets, blooms or
slabs, or for a heat treatment furnace that is fitted
with a fuel injection device and an oxidant supply body
15 supplying oxidant supply ports, the burner supporting
an axial direction, is characterized in that:
- the injection device is designed to ensure central
injection of the fuel through a port in or
20 substantially parallel to the axial direction of the
burner,
- the oxidant supply body has two sets of four oxidant
supply ports, each set having two ports located above a
25 horizontal plane passing through the axial direction of
the burner and two ports located beneath said plane,
the ports in a second set being further away from said
horizontal plane than the ports in the first set, the
geometric axes of the supply ducts of the two sets of
30 ports having angles of inclination in relation to said
axial direction of the burner.
Preferably, the momentum ratio between the oxidant and
the fuel is between 5 and 50, depending on the
35 characteristics of the reagents, and in particular
between 30 and 50 for natural gas or between 3 and 15
for lean gas.
Advantageously, the angles of inclination of the
geometric axes of the oxidant supply ducts and the
diameters of these supply ports are determined such as
to:
5
a) produce a wide flame by the combination of the
injection of fuel through the fuel port and the
injection of oxidant through the oxidant ports of the
first set,
10
b) extend the volume of the reaction coming from the
jets of the ports of the first set and the fuel port
with the oxidant coming directly from the ports of the
second set, or with the oxidant previously recirculated
15 inside the furnace and diluted during said
recirculation with the products of combustion of the
furnace in a vertical plane,
c) ensure this dilution by recirculating products of
20 combustion such as to mix the reagents in a significant
volume of flue gases before oxidizing the fuel with
the residual oxidant to expand this reaction zone to a
significant volume and limit the creation of hotspots,
25 d) ensure combustion of the diluted fuel and oxidant,
in particular with the products of combustion producing
a limited amount of NOx.
Advantageously, a burner according to the invention is
30 characterized by the combination of the relative
positions of the fuel and oxidant injection ports, the
diameter of the injection ports, the velocity of the
fluids coming from these ports during operation and the
angle of the supply ducts such that the jets of fuel,
35 oxidant and recirculated combustion gases can be
combined to control the convergence and mixing point of
same.
Preferably, the axes of the oxidant supply ports are
Socated within the horizontal planes, substantially
parallel to the plane of the products, and are inclined
i~n relation to the axial direction by an angle (a) for
5 the ports of the second set and by an angle (b) for the
ports of the first set.
The angle (a) of the geometric axes of the pairs of
ports of the second set may be between 5" and 18", and
10 the axes are divergent. The angle (b) of the geometric
axes of the pairs of ports of the first set may be
between 10" and 20°, and the axes are divergent.
The expression "geometric axis of a port" shall be
15 understood to mean the geometric axis of the opening
out of the injection port.
Preferably, the pairs of oxidant supply ports
open out into an output plane that is substantially
20 equal to the plane corresponding to the internal face
of the furnace.
Preferably, each of the two sets of ports comprises two
groups of two ports, the axes of which are located in a
25 plane parallel to the horizontal plane passing through
the axial direction of the burner, the planes of the
axes of the ports 8 or 8' of the second set being
located at a distance Ye from said horizontal plane, and
the planes of the axes of the ports 9 or 9' of the
30 first set being located at a distance Y9, and the ratio
between the distances Yg to Y8 is advantageously between
0.4 and 0.7.
The ports 8 and 8' of the second set are preferably at
35 a distance from the axial vertical plane that is less
than the distance to this plane from the ports 9 and 9'
of the first set, and the ratio of the distances may be
between 0.5 and 0.7.
The burner may be characterized by the presence of two
oxidant boxes that can be supplied by independent
circuits and that are designed to supply respectively
5 the two sets of ports, and a third set of ports that
are located radially inside the ports of the two first
sets, which are designed to provide a long spread
flame, while the third set of ports is designed to
provide a short spread flame.
10
The burner may be characterized by the presence of two
oxidant boxes supplied by independent circuits and that
supply respectively the two sets of ports, and a third
set of ports that are located radially inside the ports
15 of the two first sets, which make it possible to obtain
a long spread flame, while the third set of ports makes
it possible to obtain a short spread flame.
The burner may include a pipe for injecting fuel formed
20 by a plurality of tubes to use several different types
of fuel.
Apart from the arrangements set out above, the
invention comprises a certain number of other
25 arrangements, which are dealt with in greater detail
below in relation to example embodiments described with
reference to the attached drawings, which are in no way
limitative. In these drawings:
30 Figure 1 is a schematic cross sectional view taken
along the vertical plane 1-1 shown in figure 2, passing
through the axial direction of a burner according to
the invention. For the sake of simplicity, the ports
have been shown using an unbroken line, even though
35 they are outside the cross section.
Figure 2 is a front view of the burner from the inside
of the furnace.
Figure 3 is a schematic cross sectional view ofthe
burner in a horizontal plane and seen from above. For
the sake of simplicity, the injection ducts have been
5 shown using an unbroken line, even though they are
outside the cross section.
Figure 4 is a cross sectional top view, similar to the
view in figure 3, showing the fluid plumes coming out
10 of the different ports. For the sake of simplicity, the
ports have been shown using an unbroken line, even
though they are outside the cross section.
Figure 5 is a cross sectional top view, similar to the
15 view in figure 4, showing the volume of the flame
started by the oxidant jets from the first set with the
fuel jet, and the recirculating currents.
Figure 6 is a top view, similar to the view in figure
20 4, showing the volume of the flame with the oxidant
jets from the second set and the recirculating
currents.
Figure 7 is a cross sectional view taken along the
25 vertical plane VII-VII in figure 8, similar to the view
in figure 1, of a variant of the burner according to
the invention, and
Figure 8 is a front view of the burner in figure 7 from
30 inside the furnace.
In the wide-flame burner according to EP 0994302, the
fuel is injected through ports oriented in a horizontal
plane towards the outside of the burner, and the
35 oxidant injection ports are also inclined toward the
outside of the burner to generate the spread flame.
This arrangement has been shown to encourage the rapid
mixing of the oxidant and the fuel close to the front
face of the burner, and therefore the formation of
local hot zones in the flame, which encourages the
formation of thermal NOx in these zones.
5 According to the invention, the injection means for the
fuel and the oxidant have been improved to reduce the
NOx produced, while retaining a spread flame, in order
to ensure a slower fuel oxidization dynamic to reduce
pollutant emissions.
10
Figures 1 to 3 show that the burner comprises an
oxidant baffle 1 installed in the side wall of the
furnace 2, the front face of which is substantially
aligned with the internal face of this furnace wall in
15 the plane P, and an oxidant body 3 fitted with a
connecting flange 4 to a combustion oxidant supply
circuit shown schematically by the arrow 5. The fuel
pipe 6 is connected to a supply circuit 7 shown
symbolically by an arrow.
20
The fuel pipe 6, which is notably rectilinear, opens
out substantially in the plane P of the wall of the
furnace via a port 10 with an axis perpendicular to
this plane. The axial direction of the burner may
25 correspond to the geometric axis of the pipe 6 and of
the port 10. The pipe 6 passes through the entire
thickness of the bafflel.
The pipe may be a single-fuel pipe (as shown in figures
30 1-3) or a multi-fuel pipe incorporating multiple feeds,
for example with a port for natural gas and another
port for another fuel. This arrangement of several
injection means for several fuels may be realized in
any of the ways provided for in the prior art. The fuel
35 is injected in the axial direction of the burner using
a central port or in a direction parallel to the axial
direction of the burner using a port located
substantially on the axis of the burner.
The oxidant body 3 supplies the oxidant injections
using two sets of four ports, specifically two ports 8,
8 and 9, 9 symmetrical about a vertical plane and the
5 ports 8', 8 ' and 9', 9' symmetrical to same about a
horizontal plane. The four ports 9, 9' form a first
set, and the four ports 8, 8' form a second set.
All of the inj'ection ports in figure 3 are located
10 substantially in the plane P of the wall of the
furnace. The geometric axes of the oxidant injection
ducts with ports 8, 8' of the second set are inclined
by an angle (a) in relation to the perpendicular to the
plane P, the geometric axes of the injection ducts of
15 the first set with ports 9, 9' are inclined by an angle
(b) in relation to the perpendicular to the plane P.
The axes of the pairs of ports 8, 8' of the second set
are contained within a single plane parallel to the
20 horizontal plane Ylo, passing through the axis of the
port 10 at a distance Y8, as shown in figure 2. The axes
of the pairs of ports 9, 9' of the first set. are
contained in a single plane parallel to the horizontal
plane at a distance Yg.
25
Operation of the burner is shown schematically in
figure 4, which shows the volumes associated with the
reagent injections, these volumes having different
dimensions depending on the injection points 8, 8', 9,
30 9' and 10. The result sought appears to be achieved by
a specific combination of the positioning of the fuel
and oxidant ports, the respective angles of the ports
in relation to the plane P, and in the axial direction
of the burner, and the momentum of each jet in
35 relation to the neighboring jets. This makes it
possible to control the reaction zones of the reagents
shown schematically by plumes marked by numbers in
square brackets [8], [9] and [lo] in figure 4, in which
the zone [lo] corresponds to the fuel.
The oxidant ports 9 and 9' shown in figures 2 and 3 are
5 located in the immediate proximity of the fuel output
port 10 and the axes of the ducts of same are inclined
at an angle (b) of between 10" and 23" in relation to
the perpendicular to the plane P. Said axes are within
a horizontal plane and offset from the center of the
10 burner such as to spread the flame out, i.e. there are
not two independent and symmetrical flames, but a
single flame spread out in the main directions
determined by the ports 9 and 9', as shown by [11] in
figure 5 and specific to this type of wide-flame
15 burner.
This result is obtained by combining the relative
positions of the fuel and oxidant injection ports, the
. diameter of the injection ports, the velocity of the
20 fluids coming from these ports during operation and the
angle of the supply ducts such that the fuel jets and
the combustion gas/oxidant mixture jets can be combined
to control the convergence and mixing point of same.
The fuel jets and the recirculated combustion
25 gas/oxidant mixture jets are cone-shaped and more open
than the plumes shown for the sake of simplicity in
figure 4, and the convergence point refers to the point
of intersection of the fuel jet and the recirculated
combustion gas/oxidant mixture jets. This makes it
30 possible to control the progressive oxidation of the
fuel and the dilution of the reagents with the products
of combustion of the furnace.
A momentum ratio (mass flow multiplied by velocity) of
35 the oxidant jets to the fuel jets is determined for the
burner according to the invention. The momentum ratio
between the oxidant and the fuel is between 5 and 50,
depending on the characteristics of the reagents, and
in particular between 30 and 50 for natural gas or
between 3 and 15 for lean gas.
The oxidation of the fuel injected into the furnace via
5 the port 10, in the plume [lo] shown schematically,
occurs gradually with the oxidant injected via the
ports 9, 9' to spread the combustion throughout a
significant flame volume, which lowers the average
temperature of this flame. This phenomenon is
10 accelerated by the recirculation of flue gases from the
furnace, as shown by arrows 12 and 13 in figure 6,
which gives the reagents time to mix before combining,
which increases the volume of the flame and helps to
slow down the phenomenon of 'oxidation of the fuel and
15 to lower the average temperature of the flame. The
dilution of the reagents, i.e. fuel and oxidant, in the
furnace is effected with the products of combustion or
flue gases present in this furnace at a temperature
typically between 850°C and 1450°C. The temperature of
20 the oxidant injected in [ 8 ] and 191 is typically
between 400°C and 650°C.
Unlike the flames in burners in the prior art, in which
combustion is essentially propagated on the surface
25 with reaction zones at very high temperatures,
according to the invention the oxidation reactions
occur in the volume since the mixtures are at
temperatures higher than the spontaneous combustion
temperature, i.e. the temperature of the reaction
30 enclosure and/or the temperature of the reagents when
same are introduced into the furnace are high enough
for these reactions to occur.
Since the oxidation reactions of the reagents according
35 to the invention occur in a larger volume, the
temperature of this volume is more uniform, with fewer
high-temperature zones in the flame, which
significantly reduces NOx production. This phenomenon
is characterized by the formation of a flame with
reduced luminosity compared to flames obtained in the
prior art, this being obtained by recirculating
combustion gases inside the furnace with the reagents
5 injected via the ports 8, 8 ' , 9 and 9'.
Figure 6 shows the device for controlling the
combustion carried out using the injection ports 8 and
8' of the second set arranged in planes parallel to the
10 horizontal plane. The axes of the ports 8 and 8' are
located at distances Yg greater than the distances Yg
from the holes 9 and 9' to the horizontal plane of
symmetry Ylo of the burner.
15 The injection angles (a) of the geometric axes of the
ports 8 in relation to the perpendicular to the plane P
are advantageously set between 5" and 18" such as to
produce the folloriing effects on the flame created by
injections from the ports 9, 9' and 10:
2 0
1) spreading of the flame in the horizontal plane to
ensure compatibility with the height available in the
furnace and to encourage the horizontal spreading of
the combustion zone,
25
2) oxidation of the residual fuel that has not reacted
with the oxidant jets 9, 9',
3) induction of recirculating currents comparable to
30 those illustrated by the arrorSrs 12 and 13 in figure 6
in order to further dilute the reagents with the flue
gases from the furnace, which slows down the oxidation
reaction of the fuel and causes this reaction to occur
in a larger fuel volume, which thereby helps to reduce
35 the hotspots in the flame, and therefore to limit the
quantity of pollutants produced, primarily NOx.
In fact, a portion of the oxidant only reacts with the
fuel after recirculation and dilution by the flue gases
, which results in:
5 1) an increase in the reaction volume,
2) a lower average temperature of the reaction zone
because same occurs in a larger reaction volume,
10 3) a reduction in thermal NOx emissions as a result of
the reduction in the number and volume of hotspots in
the flame.
It appears that the optimization of the flame produced
15 by this fuel injector set 10 and the two sets of
oxidant injectors 8, 8' and 9, 9' is preferably
achieved through a combination of the following
arrangements:
20 1) the position, diameter and angle of the oxidant
injectors and ports of the first set 9, 9' located
close to the plane of the fuel injector 10,
2) optimization of the number and relative positions of
25 the oxidant injectors 9, 9' of the first set, the angle
of inclination (b) of same and the diameters of same,
and of the fuel injector 10, in combination with the
ejection velocity of the reagents coming out of these
injectors,
3 0
3) the position of the oxidant injectors 8, 8' of the
second set, the angle of inclination (a) of same and
the diameters of same in order to spread the reaction
zone through the horizontal plane and generate a
35 secondary recirculation of oxidant injected by the jets
from these ports 8, 8' and the flue gases around the
reaction zone,
4) the volume of the reaction zone achieved by the
injectors 9, 9 ' , the injectors 8, 8' and 10 makes it
possible to achieve a significant reaction volume with
a degree of uniformity that is well suited to heating
5 steel products.
In a preferred embodiment of the invention, the ratio
between the distances Yg and Ya is between 0.4 and 0.7.
10 The ports 8, 8' of the second set are preferably at a
distance from the axial vertical plane, via the axis of
the pipe 6, that is less than the distance to this
plane from the ports 9, 9' of the first set, and the
ratio of the distances may be between 0.5 and 0.7.
15
Figures 7 and 8 show a variant embodiment of the burner
according to the invention in a flame-modulation
application, i.e. enabling the burner to produce a long
spread flame' or a short spread flame depending on the
20 operating mode of same.
Figure 7 shows that the burner in the preceding figures
is retained, with the oxidant body 3 of same supplying
the pairs of ports 8, 8' and 9, 9' from the connecting
25 flange 4 to the circuit 5. A partition 14, in
particular a cylindrical partition, separates the
oxidant body 3 from another chamber 15 forming an
oxidant body supplied by the flange 16 from a circuit
17 summarily represented by an arrow. The oxidant body
30 3 supplies the two sets of pairs of ports 8, 8' and 9,
9 ' , the position, angle of inclination, diameter and
fluid velocity of which are set such as to produce a
long spread flame similar to the one described above,
and a third set of ports 18, distributed concentrically
35 about the port 10, to produce a short spread flame. The
ports 18, for example the six ports shown in figure 8,
are advantageously distributed about a circumference
centered on the geometric axis of the fuel port 10.
The two sets of oxidant ports 8, 8' and 9, 9' used to
produce the long spread flame are substantially
identical to those described above. They are positioned
5 radially outside the third set of ports 18, as shown in
figure 8.
This third set of ports 18, positioned radially inside
the two first sets, makes it possible to obtain a short
10 spread flame close to the wall of the furnace 2, which
transmits energy to the extremity of the product
located close to this wall, thereby enabling control of
the distribution of thermal power to the product by
selecting the long spread flame produced by the ports
15 8, 8' and 9, 9' supplied by the elements 5 and 4 and 3,
or with a short spread flame obtained using the ports
18 supplied by the elements 17 and 15 and 16.
The burners working according to the invention
20 therefore produce a diluted spread flame that enables
the reagents to be diluted before oxidation of same
with low levels of NOx production, either with a long
spread flame or with a single burner with a long or
short spread flame.
25
This burner is particularly suited to controlling the
heat profile of the product in the furnace, for example
according to the method described in EP 0994302.
30 Tests carried out on a test bench have demonstrated
that the level of NOx produced by this type of burner,
in particular with a long spread flame, is much lower
than the limits set in current and future regulations.
This very low NOx emissions level makes it possible to
35 anticipate regulatory limits of pollutant emissions and
therefore the related local taxes.

CLAIMS
1. A burner for a reheating furnace for steel products,
such as billets, blooms or slabs, or for a heat
5 treatment furnace that is fitted with a fuel injection
device and an oxidant supply body supplying oxidant
supply ports (8) and (9), the burner having an axial
direction, characterized in that:
10 - the injection device is designed to ensure central
injection of the fuel through a port (10) in or
substantially parallel to the axial direction of the
burner,
15 - the oxidant supply body has two sets of four oxidant
supply ports (8, 8') and (9, 9 each set having two
ports(8, 9) located above a horizontal plane passing
through the axial direction of the burner and two ports
( 8 9') located beneath said plane, the ports (8, 8')
20 in a second set being further away from said horizontal
plane than the ports (9, 9') in the first set, the
geometric axes of the supply ducts of the ports of the
two sets having angles of inclination (a, b) in
relation to said axial direction of the burner.
25
2. A burner according to claim 1, characterized in
that the momentum ratio between the oxidant and the
fuel is between 5 and 50, depending on the
characteristics of the reagents, and in particular
30 between 30 and 50 for natural gas or between 3 and 15
for lean gas.
3. A burner according to claim 1, characterized in that
the angles of inclination (a, b) of the geometric axes
35 of the oxidant supply ports (8, 9) and the diameters of
these supply ports are determined such as to:
a) produce a spread flame by the combination of the
injection of fuel through the fuel port (10) and the
injection of oxidant through the oxidant ports (9, 9')
of the first set,
5
b) extend the volume of the reaction coming from the
jets of the ports (9, 9') of the first set and the fuel
port (10) with the oxidant coming directly from the
ports (8, 8') of the second set, or with the oxidant
10 previously recirculated inside the furnace and diluted
during said recirculation with the products of
combustion of the furnace in a vertical plane,
C) ensure this dilution by recirculating products of
15 combustion such as to mix the reagents in a significant
volume of flue gases before oxidizing the fuel with
the residual oxidant to expand this reaction zone to a
significant volume and limit the creation of hotspots,
20 d) ensure combustion of the diluted fuel and oxidant,
in particular with the products of combustion producing
a limited amount of NOx.
4. A burner according to claim 3, characterized by the
25 combination of the relative positions of the fuel and
oxidant injection ports, the diameter of the injection
ports, the velocity of the fluids coming from these
ports during operation and the angle of the supply
ducts such that the jets of fuel and of mixtures of
30 oxidant and combustion gas can be combined to control
the convergence and mixing point of same.
5. A burner according to any one of the preceding
claims, characterized in that the axes of the oxidant
35 supply ports fall within the horizontal planes,
substantially parallel to the plane of the products,
and are inclined in relation to the perpendicular to
the output plane by an angle (a) for the ports (8, 8')
of the second set and by an angle (b) for the ports (9,
9') of the first set.
6. A burner according to claim 5, characterized in that
5 the angle (a) of the geometric axes of the pairs of
ports (8, 8') of the second set is between 5" and 18",
and the axes are divergent.
7. A burner according to claim 5 or 6, characterized in
10 that the angle (b) of the geometric axes of the pairs
of ports (9, 9') of the first set is between 10" and
2 0 ° , and the axes are divergent.
8. A burner according to any one of the preceding
15 claims, characterized in that the pairs of oxidant
supply ports (8, 8') and (9, 9') open out into an
output plane that is substantially equal to the plane
(P) corresponding to the internal face of the furnace.
20 9. A burner according to any one of the preceding
claims, characterized in that each set of ports
comprises two groups of trio ports (8, 8; 8 ' , 8') (9, 9;
9', 9') located in a plane parallel to the horizontal
plane Ylo passing through the axial direction of the
25 burner, the planes of the ports of the first set being
located at a distance Yg from said horizontal plane Ylo
and the planes of the ports of the second set being
located at a distance Y e , and in that the ratio between
the distances Yg to Ye is between 0.4 and 0.7.
30
10. A burner according to any one of the preceding
claims, characterized by the presence of two oxidant
boxes (3, 15) supplied by independent circuits (5, 17)
and supplying respectively the two sets of ports (8,
35 8', 9, 9 and a third set of ports (18) that are
located radially inside the ports of the first two sets
and that make it possible to obtain a long spread
flame, while the third set of ports makes it possible
to obtain a short spread flame.
11. A burner according to any one of the preceding
5 claims, characterized by the use of a fuel pipe (10)
formed by a plurality of tubes for using several
different types of fuel.