U.S. patent application number 16/312066 was filed with the patent office on 2019-07-04 for burner with open radiant tube.
The applicant listed for this patent is WS-Warmeprozesstechnik GmbH. Invention is credited to Joachim A. Wunning, Joachim G. Wunning.
Application Number | 20190203930 16/312066 |
Document ID | / |
Family ID | 58772548 |
Filed Date | 2019-07-04 |
![](/patent/app/20190203930/US20190203930A1-20190704-D00000.png)
![](/patent/app/20190203930/US20190203930A1-20190704-D00001.png)
United States Patent
Application |
20190203930 |
Kind Code |
A1 |
Wunning; Joachim G. ; et
al. |
July 4, 2019 |
Burner With Open Radiant Tube
Abstract
A recuperative burner (10) fires a furnace chamber (11) in a
substoichiometric manner. The recuperative burner is arranged in a
radiant tube (26) which is open towards and protrudes into the
furnace chamber. Together with the recuperator (18) or a protrusion
(21), the radiant tube (26) forms an exhaust gas channel (19) into
which burn-out air is introduced by an air conducting device (23).
The post-combustion which occurs in the exhaust gas channel (19)
heats the radiant tube (26). The furnace chamber (11) is heated
partly directly by fuel and air and partly indirectly by the
radiant tube (26). An excessive level of CO emission is prevented
by the post-combustion in the exhaust gas channel (19). By using
the resulting heat from the radiant tube (26), excessively high
exhaust gas temperatures are prevented and the thermal use of the
fuel is optimized.
Inventors: |
Wunning; Joachim G.;
(Leonberg, DE) ; Wunning; Joachim A.; (Leonberg,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WS-Warmeprozesstechnik GmbH |
Renningen |
|
DE |
|
|
Family ID: |
58772548 |
Appl. No.: |
16/312066 |
Filed: |
May 11, 2017 |
PCT Filed: |
May 11, 2017 |
PCT NO: |
PCT/EP2017/061373 |
371 Date: |
December 20, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 20/34 20130101;
F23C 9/06 20130101; F23D 14/66 20130101; Y02E 20/348 20130101; F23C
3/00 20130101; F23C 7/06 20130101; F23C 2900/06041 20130101; F23C
2900/99001 20130101; F23D 14/22 20130101; Y02E 20/342 20130101;
F23L 15/04 20130101; F23C 6/04 20130101 |
International
Class: |
F23C 9/06 20060101
F23C009/06; F23L 15/04 20060101 F23L015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2016 |
DE |
10 2016 111 656.4 |
Claims
1. A burner (10) for heating a furnace (12) using preheated air and
fuel exiting from a burner orifice (25), the burner comprising: a
recuperator (18) arranged in or on an exhaust gas channel (19) for
preheating air using exhaust gas heat, a radiant tube (26) that has
an opening (24) located at one end facing away from the burner (10)
and that is arranged on the burner (10) to delimit the exhaust gas
channel (19) in a peripheral direction, an air conducting device
(23) configured to introduce air into the exhaust gas channel
(19).
2. The burner according to claim 1, wherein the burner orifice (25)
is arranged on a portion of the burner (10), said portion of the
burner projecting from the opening (24) of the radiant tube
(26).
3. The burner according to claim 1, further comprising a tube
section (21) provided with air outlet openings (22) which is
connected as the air conducting device (23) to the recuperator
(18).
4. The burner according to claim 3, wherein the recuperator (18)
and the tube section (21) are formed of a single piece of material
and are configured so as to form a seamless transition.
5. The burner according to claim 1, wherein the air conducting
device (23) and the burner orifice (25) are connected to one common
air channel in order to be supplied with air by the common air
channel.
6. The burner according to claim 1, wherein the burner orifice (25)
and the air conducting device (23) are arranged with respect to
each other and to a fuel stream such that an air stream dispensed
by the burner orifice (25) results in a sub stoichiometric
combustion.
7. The burner according to claim 6, wherein a sum total of the air
stream dispensed by the burner orifice (25) and an air stream
dispensed by the air conducting device (23) is in a stoichiometric
or superstoichiometric relationship with respect to the fuel
stream.
8. The burner according to claim 1, wherein the burner orifice (25)
is oriented axially relative to the burner (10) and the radiant
tube (26).
9. The burner according to claim 1, wherein the burner orifice (25)
comprises at least one opening (24) that is oriented obliquely or
radially relative to a burner axis.
10. The burner according to claim 1, wherein a thermal output of
the radiant tube (26) is fixed at a value between 10% and 30% of a
total thermal output of the burner (10).
11. The burner according to claim 1, wherein the burner is disposed
in a furnace chamber (11) of the furnace (12) to effect and
maintain a flameless oxidation process.
12. A method for heating a furnace chamber with a burner that
comprises a radiant tube (26) that encloses an exhaust gas channel
(19) and is open on its free end, the method comprising: operating
the burner in a substoichiometric manner; and supplementally
introducing burn-out air into the exhaust gas channel.
13. The method according to claim 12, further comprising using the
burn-out air to maintain combustion in the exhaust gas channel,
said combustion being utilized for heating the radiant tube
(26).
14. The method according to claim 12, further comprising directly
heating the furnace chamber to a greater extent with hot gas
produced by the burner (10) and indirectly heating the furnace
chamber to a lesser extent with heat radiated by the radiant tube
(26).
Description
[0001] The invention relates to a burner, in particular a
recuperative burner, for the mixed direct and indirect heating of
material to be heated in a furnace.
[0002] In order to heat semi-finished and finished products, the
industry uses furnaces that are heated by means of burners, wherein
the exhaust gas heat is partially recovered for preheating the air
supplied to the burner.
[0003] Regarding this, publication DE 10 2010 0151 347 A1 describes
a burner that is equipped with a jacket tube acting as the radiant
tube. Inside this radiant tube, the fuel is oxidized in order to
heat the radiant tube so that it emits radiated heat.
[0004] The advantage of such an arrangement is that the heated
material does not come into contact with the combustion gases which
is why a chemical influence on the heated material by the
combustion gases is precluded. Moreover, any indirect heating by
means of the radiant tube offers the possibility of the
inertization of the furnace chamber. However, the thermal output is
limited due to the heat transport through the radiant tube
surface.
[0005] Furthermore, industrial burners for a direct heating of
furnace chambers have been known. Regarding this, publication DE 34
22 229 C2 describes a burner that is equipped with a device for
exhaust gas recovery and comprises a combustion chamber from which
the flames and/or hot exhaust gases for heating the furnace chamber
can escape. In so doing, a limiting of the thermal output as it
occurs in radiant tubes is not necessary. However, the effect of
the combustion gases on the material to be heated needs to be taken
into account. For example, if steel is heated to higher
temperatures, scaling occurs, in which case, typically, is
attempted to limit this by combustion with the lowest possible air
excess. However, this may result in the generation of carbon
monoxide. With too high an air excess, it is possible for a large
amount of nitrogen oxide to form. Carbon monoxide, as well as
nitrogen oxide, must not be allowed to be discharged in the form of
exhaust gas into the environment, and thus require expensive
measures in view of a subsequent conversion of exhaust gas.
[0006] It is the object of the invention to state an improved
burner for heating material to be heated in a furnace. Furthermore,
it is the object of the invention to state an improved method for
heating material to be heated in a furnace.
[0007] The part of the technical problem to be solved that relates
to the provision of a burner is solved by a burner according to
Claim 1:
[0008] The burner according to the invention comprises a radiant
tube that has--on its end facing away from the burner--an orifice
through which fuel and preheated air or also even a flame are
introduced into the furnace chamber and through which exhaust gas
is conducted out of the furnace chamber in a counter-current. The
radiant tube thus delimits an exhaust gas channel which, according
to the invention, is associated with an air conducting device for
introducing burn-out air. In so doing, it becomes possible to allow
a first, preferably substoichiometric, stage of combustion to take
place outside the radiant tube in the furnace chamber and a second
stage of combustion in the radiant tube. As a result of this, it is
possible--e.g., when metals such as steel, copper, etc. are heated,
to fill the furnace chamber with a non-oxidative combustion gas due
to the substoichiometric combustion, and minimal scaling or even
scaling-free heating can be achieved (.lamda.<1). A
CO-containing furnace atmosphere is generated that may have a
protective effect on the material to be heated. The CO-containing
exhaust gas is then post-combusted in the steel pipe by virtue of
air introduced through the air conducting device. Thermal energy
that is released in so doing is radiated by the radiant tube into
the furnace.
[0009] Preferably, the amounts of air of the burner and the
post-combustion are adapted to each other in such a manner that an
overall stoichiometric or superstoichiometric combustion is
achieved, wherein .lamda. preferably ranges between 1 and 1.2. For
example, the furnace chamber is filled with 80% of the required
amount of air (in the furnace chamber, .lamda.=0.8) while the
exhaust gas channel in the radiant tube is filled with 20% to 40%
of the required amount of air (.lamda.=1 . . . 1.2). Preferably,
the amount of air and the air conducting device are adapted in such
a manner that the post-combustion is completed in a part of the
radiant tube located in the furnace chamber and does not extend
into the section in which the recuperator is arranged. In so doing,
the recuperator is preferably confined to the part of the radiant
tube located in the furnace wall and not being disposed for heat
radiation.
[0010] In one advantageous embodiment the burner orifice may be
arranged on a part of the burner that projects from the orifice of
the radiant tube. Consequently, it is particularly easy to achieve
a large-volume exhaust gas recirculation, as a result of which the
burner can be operated employing flameless oxidation. This benefits
a uniform heat introduction in the furnace and a low production of
nitrogen oxide.
[0011] The air conducting device may be a tube provided with air
holes on its periphery, said tube extending through the radiant
tube. This tube or this tube section may consist of metal (e.g.,
steel or ceramic) and it may be seamlessly connected in an integral
manner or attached to the recuperator. In particular, it is
possible to construct the recuperator and the pipe section of the
air conducting device in one piece of the same material. The
recuperator and the air conducting device are preferably coaxially
arranged in the radiant tube. Alternatively, it is also possible to
provide one or more tubes (having the same length or different
lengths) that extend from the burner head through the exhaust gas
channel in the direction of the exhaust gas inlet of the radiant
tube and release air there. Such tubes are then arranged
eccentrically relative to the radiant tube. They may have round or
flat cross-sections.
[0012] The air conducting device and burner orifice may be
connected so as to communicate in view of the flow in a common air
channel in order to be supplied by the latter with preheated air.
In so doing, it is possible to dispense with a regulating device
with which the dimensions of the air currents (burner air for the
burner of burned-out air for the air conducting device) can be
adapted to one another. The adaptation of the air quantities
relative to each other preferably occurs by dimensioning the
cross-sections of the openings of the air conducting device for the
burn-out air to the size of the outlet opening(s) for the burner
head air.
[0013] The burner orifice comprises at least one opening that is
oriented axially relative to the burner or also obliquely or
radially relative to the burner axis. In so doing, burners with the
most diverse heating zones can be provided while utilizing the
principle according to the invention, said principle being based on
the partial combustion in the furnace chamber and on the
post-combustion in the radiant tube.
[0014] The method according to the invention is based on the
substoichiometric operation of a burner and the conduction of the
thusly produced reducing exhaust gasses through a radiant tube and
the post-combustion of the exhaust gases in this steel tube in that
burn-out air is supplementally introduced in the exhaust gas
channel of the radiant tube. In so doing, a combustion occurs in
the exhaust gas channel, said combustion being utilized for heating
the radiant tube and for at least the extensive elimination of
oxidizable components in the exhaust gas. Consequently, this makes
possible an exhaust gas that is low in NOx and, despite the
substoichiometric operation of the furnace, low in CO, wherein the
utilization of thermal energy is good due to the heat recovery, and
the heat introduction into the furnace is uniform.
[0015] Preferably, the furnace chamber is directly heated to a
greater extent with the hot gas produced by the burner and
indirectly heated to a lesser extent with the heat radiated by the
radiant tube. The division of output is, for example, 80%/20%.
[0016] The invention may also be applied to regenerator
burners.
[0017] Additional details of advantageous embodiments of the
invention are the subject matter of the claims, the description or
the drawings. They show in
[0018] FIG. 1 a schematic sectional view of a furnace chamber with
a burner according to the invention,
[0019] FIG. 2 a schematic sectional view of a modified embodiment
of the burner according to the invention,
[0020] FIG. 3 a longitudinal sectional view of a further modified
embodiment of the burner according to the invention, and
[0021] FIG. 4 an embodiment of the burner according to the
invention with radial or oblique flame ejection.
[0022] FIG. 1 shows a recuperative burner 10 that is disposed for
heating the furnace chamber 11 of a schematically illustrated
industrial furnace 12. In order to heat the latter, it is possible
to provide several burners with heat recovery features, e.g.,
recuperative burners that are preferably constructed and configured
in the same manner as the recuperative burner 10 and that can be
controlled together, individually or in groups.
[0023] The industrial furnace is disposed for the heat treatment of
a material to be heated 13 that, for example, may be semi-finished
or finished products of metal or other materials. For example,
these may be steel components, copper components or the like. The
furnace temperature typically is in the range of several
100.degree. C. and is consistent with the desired application. If
the temperature is above a critical temperature of typically
approximately 850.degree. C., the burner 10 can be operated with
flameless oxidation. If the furnace temperature is below this
limit, the burner 10 preferably is operated in a flame mode. This
mode is also selected during the ramping up stage, in particularly
in the event of a cold start. The cold start may take place with
stoichiometric operation or superstoichiometric operation.
[0024] Preferably, the burner 10 is a so-called recuperative burner
that is disposed to extract thermal energy from an exhaust gas
stream indicated by arrows 14, 15 16, in order to thus supply a
fresh air stream indicated by arrow 17 with heat. To accomplish
this, the recuperative burner 10 comprises a recuperator 18 which
is preferably configured as a profiled tube with closed walls and
the outside of which delimits an exhaust gas channel 19.
[0025] The recuperator 18 may consist of metal, for example, or, as
is preferred, of ceramic and be imparted on its outside with
structures so as to enlarge the surface and provide an improvement
of the heat exchange with the exhaust gas. Such structures may be
elevations and/or recesses, spikes, burls or the like. The
recuperator 18 extends concentrically to the longitudinal center
axis of the recuperative burner 10 and, in so doing, is preferably
held outside the furnace chamber 11 in a burner head 20.
Appropriate holding means have been known from practical
applications and are not specifically shown in FIG. 1.
[0026] Adjoining the actual recuperator 20 is a protrusion 21 that,
likewise, preferably has a tubular shape. The protrusion 21 may be
a direct integral component of the recuperator 18 and extend away
from said recuperator in axial extension. This protrusion 21, too,
may be disposed for recuperation (heat recovery). Preferably, the
recuperator 18 extends through the furnace wall while the
protrusion 21 preferably forms a part extending into the furnace
chamber 11.
[0027] Preferably, the protrusion 21 may have one of the several
openings that extend through its wall and lead from its interior
space out into the exhaust channel 19. These openings 22 act as the
air conducting device 23 for introducing burn-out air into the
exhaust gas channel 19.
[0028] On its free end, the protrusion 21 is provided with at least
one opening 24 that forms a burner orifice 25 and is arranged
concentrically with respect to the burner axis. The openings 22, as
well as the opening 24, are filled with fresh air that--as
indicated by arrow 17--is introduced at the burner head 20 into the
chamber of the recuperator 18 and leaves as burner air (primary
air) at the opening 24 and as burn-out air (secondary air) at the
openings 22.
[0029] The recuperator 18 and the protrusion 21 are enclosed by a
tube 26 that extends through the furnace wall and projects into the
chamber 11. Preferably, the tube 26 is arranged concentrically with
respect to the recuperator 18 and the protrusion 21 and delimits
the exhaust gas channel 19 in radially outward direction.
Preferably, the protrusion 21 extends through the tube 26 so that
the burner orifice 25 projects from the tube 26. The part of the
tube 25 projecting into the furnace chamber 11 acts as the radiant
tube. It is heated by the exhaust gas flowing in the exhaust gas
channel 19 and by the post-combustion taking place therein, said
post-combustion being maintained by the burn-out air supplied by
the air conducting device 23. Preferably, the post-combustion is
completed in the exhaust gas stream before the exhaust gas stream
reaches the recuperator 18. The protrusion 21 may contribute as an
ancillary function to the recuperation. This improves the energy
yield of the burner 10.
[0030] A fuel supply line 27 extends centrally through the
recuperator 18 and the protrusion 21, said fuel supply line having
an open end directed at the burner orifice 25 and dispensing fuel
through said orifice into the furnace chamber 11.
[0031] The recuperative burner 10 described so far operates as
follows:
[0032] During operation, liquid or gaseous fuel is introduced into
the burner--as indicated by arrow 28--via the fuel line 27.
Furthermore, air (arrow 17) is introduced into the recuperator and
exhaust gasses are evacuated through the exhaust gas channel 19
(arrows 14, 15, 16). During stationary operation, the exhaust gas
flowing downstream through the exhaust gas channel 19 heat the
protrusion 21 and the recuperator 18 which, in turn, heats
inflowing air. A stream consisting of preheated air and fuel leaves
the burner orifice 25, said stream--depending on the operating
mode--either combusts with flame or oxidizes without flame due to a
large-volume exhaust gas recirculation and a sufficient impulse of
fresh air and fuel in the heated furnace chamber. Consequently, the
burner 10 can be set up as specifically needed, either for
flameless oxidation or for flame operation.
[0033] The supplied amount of fuel and the primary air amount
flowing out through the opening 24 are adapted to each other in
such a manner that a substoichiometric combustion results in the
furnace chamber 11. For example, only 70% to 90%, preferably only
80%, of the air required for a complete combustion are dispensed at
the opening 24, as a result of which a reducing furnace atmosphere
is formed (.lamda.=0.8). This furnace atmosphere may contain fuel
residues, partially combusted fuel and, in particular, also carbon
monoxide. This exhaust gas--as indicated by arrows 14, 15--enters
into the exhaust gas channel 19. Now, via the openings 22, the
remaining 20% of the air required for the complete combustion are
dispensed as burn-out air into the exhaust gas channel. The
post-combustion taking place here heats the affected part of the
tube 26 and then flows toward the recuperator 18.
[0034] The allocation of the air to the burner orifice 25 and the
air conducting device 23 is preferably determined by the ratio of
the cross-sections of the openings 24, 22 to one another.
Consequently, the air allocation can be firmly specified at the
time of manufacture of the recuperative burner 10. The recuperative
burner 10 is preferably fired in pulsed mode or in continuous mode.
Modulating mode is possible, however not necessary in most
applications. Due to the pulsed operation, the recuperative burner
10 ultimately knows only three operating states, i.e., (a) ramping
up mode, (b) heated mode, and (c) stoppage mode. During heated
mode, the recuperative burner 10 is operated with the specified
fuel and air supply and exhaust gas discharge. In so doing, it is
ensured that the ratio between burner air and burn-out air is
maintained as specified.
[0035] In modulated mode, it is possible that--due to different
non-linear flow resistances of the openings 22 and 24--the ratio
between the burner air (primary air) and the burn-out air
(secondary air) shifts relative to full load in the event of
partial load. This effect can also be consciously used in
combination with pulsed mode in order to control the composition of
the furnace atmosphere.
[0036] The recuperative burner 10 shown in FIG. 1 heats the
material to be heated 13, partially directly by flame or flameless
oxidation and partially indirectly by heat radiation from the tube
26. It combines high utilization of fuel due to heat recovery with
careful heating of the material to be heated 13 by avoiding local
heat peaks and by avoiding oxidative loading of the material to be
heated, with good exhaust gas values.
[0037] FIG. 2 shows a modified embodiment of a recuperative burner
10, to which the description hereinabove applies analogously, while
the same reference signs are being used. However, in contrast with
the recuperative burner 10 described hereinabove, the air
conducting device 23 is restricted to a few openings 22 that are
provided in the vicinity of the front end of the protrusion 21.
Consequently, the introduction of air into the exhaust gas channel
19 is restricted to the part of the (radiant) tube 26 that is close
to the exhaust gas inlet. In so doing, the openings 22 can be
oriented radially as indicated in FIGS. 1 and 2. The size of the
openings 22 may be the same for all openings 22. Alternatively, the
size of the openings 22 may also vary in axial direction of the
protrusion 21 in one embodiment according to FIG. 1. For example,
it may increase or decrease away from the burner orifice 25.
[0038] As is shown by FIG. 3 the openings 22 for the burn-out air
may also be provided approximately at the level of the end of the
radiant tube 26 and impart the leaving burn-out air flow with an
axial component in addition to the radial component. In all
embodiments, flame as well as flameless oxidation is possible in
the exhaust gas channel 19.
[0039] As depicted by FIG. 4, the burner orifice 25 may also have
several outlet openings 24; this may be of particular importance
when their direction of exit is directed radially or obliquely
relative to the axial line of the recuperative burner 10. Such a
recuperative burner 10 can always be arranged suspended in a
furnace chamber 12 according to FIG. 1, for example on the upper
side of the furnace chamber, and still prevent the fuel stream from
impinging on the material to be heated 13.
[0040] According to the invention a recuperative burner 10 is
provided which fires a furnace chamber 11 in a substoichiometric
manner. The recuperative burner is arranged in a radiant tube 26
which is open towards the furnace chamber and which protrudes into
the furnace chamber. Together with the recuperator 18 or a
protrusion 21, the radian tube 26 forms an exhaust gas channel 19
into which burn-out air is introduced by means of an air conducting
device 23. The post-combustion which thus occurs in the exhaust gas
channel 19 heats the radiant tube 26. The furnace chamber 11 is
thus heated partly directly by fuel and air and partly indirectly
by the radiant tube 26. An excessive level of CO emission is
prevented by the post-combustion in the exhaust gas channel 19. By
virtue of the use of the resulting heat by the radiant tube,
excessively high exhaust gas temperatures are prevented and the
thermal use of the fuel is optimized.
LIST OF REFERENCE SIGNS
TABLE-US-00001 [0041] 10 Burner/recuperative burner 11 Furnace
chamber 12 Industrial furnace 13 Material to be heated (e.g., steel
parts, copper parts, other metal parts or parts of nonmetallic
material) 14-16 Arrows for exhaust gas 17 Arrows for fresh gas 18
Recuperator 19 Exhaust gas channel 20 Burner head 21 Protrusion 22
Opening(s) 23 Air conducting device 24 Opening 25 Burner orifice 26
Pipe (radiant tube) 27 Fuel line 28 Arrow
* * * * *