U.S. patent application number 09/512307 was filed with the patent office on 2002-05-09 for flat flame burners.
Invention is credited to Giraud, Patrick, Montgermont, Jean-Claude.
Application Number | 20020055078 09/512307 |
Document ID | / |
Family ID | 9542546 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020055078 |
Kind Code |
A1 |
Giraud, Patrick ; et
al. |
May 9, 2002 |
Flat flame burners
Abstract
Flat-flame burner for reheat, holding and heat-treatment
furnaces for iron and steel products, comprising at least one
fuel-injection pipe lying along the axis of the body of the burner,
a combustion tunnel and a combustion-air feed, the air being
distributed in and by the said body, wherein the fuel is introduced
via the injection pipe or pipes through at least one axial orifice
lying in a plane close to the external plane of the combustion
tunnel, into the combustion products so as to produce a first
dilution of the fuel in these combustion products, the
fuel/combustion products mixture thus obtained being diluted
further in the combustion air.
Inventors: |
Giraud, Patrick; (Paris,
FR) ; Montgermont, Jean-Claude; (Le Mee Sur Seine,
FR) |
Correspondence
Address: |
Morris Liss
Pollock Vande Sande & Amernick R L L P
P O Box 19088
Washington
DC
20036-3425
US
|
Family ID: |
9542546 |
Appl. No.: |
09/512307 |
Filed: |
February 24, 2000 |
Current U.S.
Class: |
431/349 |
Current CPC
Class: |
F23C 2202/40 20130101;
F23D 14/22 20130101 |
Class at
Publication: |
431/349 |
International
Class: |
F23D 014/58 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 1999 |
FR |
99 02378 |
Claims
1. Flat-flame burner for reheat, holding and heat-treatment
furnaces for iron and steel products, comprising at least one
fuel-injection pipe lying along the axis of the body of the burner,
a combustion tunnel and a combustion-air feed, the air being
distributed in and by the said body, wherein the fuel is introduced
via the injection pipe or pipes through at least one axial orifice
lying in a plane close to the external plane of the combustion
tunnel, into the combustion products so as to produce a first
dilution of the fuel in these combustion products, the
fuel/combustion products mixture thus obtained being diluted
further in the combustion air.
2. Burner according to claim 1, further including at least one
fuel-injection pipe provided with at least one axial orifice for
introducing the fuel, said orifice lying in the immediate vicinity
of the plane of flame development so as to premix the fuel with the
recirculated combustion products at the burner head.
3. Burner according to claim 1, further comprising at least one
injection pipe for introducing the fuel axially with a low
momentum.
4. Burner according to claim 2, wherein the axial fuel-injection
orifices have a large diameter so as to limit the momentum of the
fuel.
5. Burner according to claim 1, wherein the injection pipe or pipes
is or are made of materials resistant to high temperatures, such as
chrome steel, nickel steel and ceramics.
6. Burner according to claim 1, further comprising two fuel
injection means, these being fitted at different levels in the
combustion tunnel, for controling the mixing between the fuel or
fuels, the combustion air and the recirculated combustion products
at the head of the said burner.
7. Burner according to claim 6, wherein the said fuel injection
means are used separately with the flow of fuel being divised
between the two injection means, for controling the shape of the
flame, the quality of the premixture and the emission of
pollutants.
8. Burner according to claim 6, wherein the said fuel injection
means are used simultaneously with the flow of fuel being divised
between the two injection means, for controling the shape of the
flame, the quality of the premixture and the emission of
pollutants.
9. Burner according to claim 6, wherein one of the said injection
means are used for igniting the burner and the other is used to
reduce the amount of pollutants produced.
Description
[0001] The present invention relates to improvements to a
flat-flame burner intended for equipping reheat, holding or
heat-treatment furnaces, in particular for iron and steel products,
so as to lower its NOx production appreciably.
[0002] In order to properly understand the technical field to which
the improvements forming the subject of the present invention
apply, as well as the corresponding prior art, reference will
firstly be made to FIGS. 1 to 4 of the appended drawings which
illustrate, respectively:
[0003] FIG. 1: a schematic view in longitudinal axial section, of a
furnace of known type for reheating iron and steel products;
[0004] FIG. 2: a schematic view, in vertical axial section, of an
embodiment of a roof burner according to the prior art, which can
be mounted in a furnace as in FIG. 1;
[0005] FIG. 3: a schematic sectional view, in vertical axial
section, of an alternative embodiment of a roof burner according to
the prior art, which can be used in the furnace forming the subject
of FIG. 1; and
[0006] FIG. 4: also a schematic view, in vertical axial section, of
a flat-flame burner according to the prior art, designed so as to
reduce the amount of NOx produced by this burner.
[0007] FIG. 1 therefore illustrates an embodiment of a furnace for
reheating iron and steel products, with top and bottom heating. The
products to be reheated, denoted by the reference 1, are supported
and transported within the furnace by a system of fixed and walking
beams 2 and 3. The walking beams are moved in a motion comprising a
rectangular cycle by virtue of the conjugate actions of a
translation frame 4 and a lifting frame 5, in an arrangement well
known to those skilled in the art. The furnace is produced in the
form of a thermally insulated chamber 6 in which long-flame burners
7 and flat-flame burners 8 are placed, the latter burners being
fitted into the roof of the furnace. The present invention relates
to improvements to the flat-flame burners 8.
[0008] FIGS. 2 and 3 illustrate two embodiments of roof burners
according to the prior art.
[0009] Shown schematically in the FIG. 2 at 9 is the combustion
tunnel of a burner which has a flared opening, the shape of which
is substantially in the form of a quadrant of a circle so as to
propagate the stream of air and the flame of the burner along the
profile of the combustion tunnel, by the Coanda effect, and along
the plane P of the roof. The burner is fed with combustion air,
which may or may not be preheated, via a feed pipe 10 and this air
is distributed in the body of the burner through orifices 11 made
in the air distributor, these orifices causing the combustion air
to swirl so that this air flows helically around the fuel-injection
pipe 12. The latter lies along the axis of the burner so as to
bring the fuel or fuels into a zone conducive to obtaining good
mixing with the combustion air. Introduction of the fuel or fuels
takes place through one or more orifices 14 so as to obtain the
flow portrayed by the arrow 15 in this FIG. 2.
[0010] A disc 13 is provided on the injection end of the pipe 12,
the function of this disc 13 being to force the combustion air to
be pressed against the internal wall of the combustion tunnel 9 so
as to promote the formation of a flat flame and create a suction
vortex for the combustion gases in the burner head. In FIG. 2, this
vortex is portrayed by the arrow 16. The combustion gases within
the chamber of the furnace are therefore recirculated at the burner
head by induction of the vortex 16 created by the high-speed
circulation of the air/gas mixture coming from the burner. The
flame produced by this air-gas mixture spreads, as at 17, following
the profile of the combustion tunnel 9 and the plane P of the roof
of the furnace.
[0011] According to the prior art (FIG. 3), the roof burners may
also be provided with twin fuel-injection pipes 18 and 19 having
respective injection orifices 20 and 14. Moreover, this known type
of burner is similar to the burner forming the subject of FIG. 2,
the twin injection pipe allowing the use of two different types of
fuel. A single injection of fuel via the orifices 20 may be
employed, for example during the burner ignition phase, allowing
better attachment of the flame at low fuel rates, particularly when
the temperature of the furnace chamber is less than 750.degree. C.
(no spontaneous ignition of the mixture).
[0012] Until recently, the prior art of the flat-flame burner
illustrated in FIGS. 2 and 3 was technically satisfactory from the
standpoint of controlling the flame geometry and the heat flux
distribution. The technique according to the prior art was
optimized entirely according to combustion criteria for the purpose
of obtaining an intensive flame of suitable shape. In this
approach, the emission of pollutants, particularly of NOx, was
regarded as secondary.
[0013] The trend in local, European and world-wide regulations has
forced operators to reduce NOx emissions from their plants.
Research on burner design has incorporated this constraint,
particularly in the case of flat-flame burners which generate much
greater amounts of NOx than long-flame burners and which have
formed the subject of extensive research and numerous improvements
for the purpose of limiting their discharge.
[0014] It is known that the production of NOx gases in a flame
depends on its temperature and on the oxygen partial pressure in
the reaction zone of this flame. In particular, it is known that
the amount of NOx produced increases significantly for flame
temperatures greater than 1200.degree. C. All research on reduction
of NOx products has therefore been carried out so as to reduce the
temperature of the burner flame and to increase the volume of its
reaction zone, particularly by diluting it with the combustion
products contained within the furnace chamber and recirculated at
the burner head.
[0015] FIG. 4 of the appended drawings shows a burner according to
the prior art, designed so as to reduce the amount of NOx produced.
In this type of burner, the fuel is injected right at the very end
of the combustion tunnel of the burner, into the vortex 16 of the
combustion products. The burner has a fuel-injection pipe lying
along its axis and emerging in the combustion tunnel via a number
of radial injectors 14. By this means, the fuel is injected
radially at high speed, through the said injectors 14, into the
combustion air level with the tunnel in a zone in which the
combustion air is diluted with the gases from the furnace
environment. This high-speed fuel injection via a small number of
radial injectors furthermore divides the flame into several "small
flames" which are less intensive and whose total volume is
increased with respect to a single flame.
[0016] Based on this prior art, the object of the present invention
is to reduce the amount of NOx produced by flat-flame burners using
the principle of flame dilution for the purpose of reducing its
temperature and lowering the oxygen partial pressure in its
reaction zone.
[0017] This technical problem is solved by a flat-flame burner
having at least one fuel-injection pipe lying along the axis of the
body of the burner and a combustion-air feed, this burner being
characterized in that the fuel is introduced via the said injection
pipe or pipes, through one or more axial orifices lying in a plane
close to the external plane of the combustion tunnel, into the
combustion products so as to produce a first dilution of the fuel
in these combustion products and in that the fuel/combustion
products mixture thus obtained is diluted further in the combustion
air.
[0018] Further features and advantages of the present invention
will emerge from the description given below with reference to FIG.
5 of the appended drawings which illustrate one embodiment thereof,
this being devoid of any limiting character. This FIG. 5 is a
schematic view, in vertical axial section, of an improved burner
according to the invention.
[0019] As will have been understood and as mentioned above, the
burner forming the subject of the invention uses the principle of
flame dilution in order to reduce its temperature and lower the
oxygen partial pressure in its reaction zone. This flame dilution
is achieved with the combustion products located within the furnace
chamber. The novelty of the present invention lies in the fact that
the fuel is introduced in two steps so as to obtain double
dilution: a first dilution of the fuel with the combustion products
of the furnace and then a second dilution of the fuel/combustion
products mixture thus obtained with the combustion air.
[0020] The embodiment of the invention illustrated by FIG. 5
includes a double fuel-feed system. This is a non-limiting example,
the improvements according to the invention being able to be
employed on a burner with a single fuel feed. Again in this burner
there is the combustion tunnel 9, the air feed 10, the air being
possibly preheated and being distributed in the body of the burner
via the orifices 11, and the system of two fuel-injection pipes 18
and 19, the injection taking place along the axis of the
burner.
[0021] According to the invention, the fuel is introduced via one
or more axial orifices with which the injection pipes such as 18
and 19 are provided, thereby making it possible for the fuel to be
fed with a low momentum. The fuel-injection pipe or pipes 18 and 19
is/are made of materials resistant to high temperatures, especially
refractory materials, such as chrome steel or nickel steel or
ceramics.
[0022] Axial introduction of the fuel (arrow 21) through one or
more axial injection orifices 25 in the pipe 19, these lying,
according to the invention, in the immediate vicinity of the plane
of flame development, takes place in the combustion products (arrow
22) from the furnace environment, thereby allowing the first
dilution to be achieved. This dilution is promoted by the
positioning of the orifices 25 which allow the fuel to be premixed
with the recirculated combustion gases at the burner head. The
axial fuel-injection orifice or orifices 25 is/are of large
diameter so as to limit the momentum of the fuel in order to
achieve mixing with the combustion gases. This low momentum does
not disturb the vortex of recirculating the combustion products
induced at the burner head by the combustion air, unlike
high-momentum radial injection which "cuts" the vortex and disturbs
this recirculation.
[0023] The fuel/combustion gas mixture thus obtained, portrayed by
the arrow 23 in FIG. 5, is entrained by the vortex existing at the
burner head and then diluted with the combustion air (arrow 24)
which is itself diluted with some of the recirculated combustion
products (arrow 22) at the burner head.
[0024] Thus, the burner forming the subject of the present
invention makes it possible to achieve a double dilution--of the
fuel and the combustion products and of the combustion air and the
combustion products--and finally to mix the two diluted
premixtures. This optimization of the "combustion air +fuel
+combustion products" mixture makes it possible to obtain a
non-intensive flat flame which reduces the emissions of pollutants,
particularly of NOx, it being possible for this reduction to be in
a ratio of above two with respect to a burner of the same type,
according to the prior art.
[0025] As illustrated in FIG. 5, the burner according to the
present invention may retain the double fuel feed, with fuel being
injected at different levels in the combustion tunnel 9, so as to
control the mixing between the fuel or fuels, the combustion air
and the recirculated combustion gases at the burner head. The two
fuel-injection pipes may be used separately or simultaneously, with
the flow of fuel being divided between the two injections, so as to
control the shape of the flame, the quality of the premixture and
the emission of pollutants.
[0026] One of the injection pipes may be used for starting the
burner, for example when the temperature of the furnace is less
than 700.degree. C. in order to obtain better flame attachment, the
other possibly being used in the steady state for reducing the
amount of pollutants produced.
[0027] The invention therefore makes it possible to solve the
problem of reducing the amount of NOx produced by a flat-flame
burner, ensuring combustion of the fuel within a large volume
(mixing of the combustion air, fuel and combustion products of the
furnace) which makes it possible to produce a flame of lower
temperature, the oxygen partial pressure of which reaction zone is
reduced.
[0028] Of course, it remains the case that the present invention is
not limited to the embodiments described and/or mentioned above,
rather it encompasses all variants thereof.
* * * * *