U.S. patent application number 11/252344 was filed with the patent office on 2006-02-16 for pore-type burner with silicon-carbide porous body.
This patent application is currently assigned to SGL Carbon AG. Invention is credited to Michael Hoetger, Walter Thiele.
Application Number | 20060035190 11/252344 |
Document ID | / |
Family ID | 33300846 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060035190 |
Kind Code |
A1 |
Hoetger; Michael ; et
al. |
February 16, 2006 |
Pore-type burner with silicon-carbide porous body
Abstract
A porous burner is configured for burning a fuel-air mixture and
to generate a hot flue gas. The burner has a housing and porous
material in the housing. The porous material is formed of silicone
carbide that is resistant to high temperatures and facilitates
combustion. The porous body in the housing is formed of a
siliconized carbon fabric with a regular, uniform structure. The
shape of the silicon carbide fabric deviates from a planar surface,
for example with corrugations, and a plurality of such fabric
sections are laid on top of one another.
Inventors: |
Hoetger; Michael; (Berlin,
DE) ; Thiele; Walter; (Bonn, DE) |
Correspondence
Address: |
LERNER AND GREENBERG, PA
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
SGL Carbon AG
|
Family ID: |
33300846 |
Appl. No.: |
11/252344 |
Filed: |
October 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP04/03968 |
Apr 15, 2004 |
|
|
|
11252344 |
Oct 17, 2005 |
|
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Current U.S.
Class: |
431/329 ;
431/170; 431/326; 431/7 |
Current CPC
Class: |
F23D 14/145 20130101;
F23D 2212/105 20130101; F23D 2203/104 20130101; F23C 99/006
20130101; F23D 2900/14582 20130101 |
Class at
Publication: |
431/329 ;
431/326; 431/170; 431/007 |
International
Class: |
F23D 3/40 20060101
F23D003/40; F23D 14/14 20060101 F23D014/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2003 |
DE |
103 17 857.0 |
Feb 11, 2004 |
DE |
10 2004 006 824.0 |
Claims
1. A pore-type burner for burning a fuel/air mixture for generating
a hot flue gas, comprising: a housing; a porous body with pore
material formed of porous, high-temperature-resistant silicon
carbide disposed in said housing, said pore material being formed
of siliconized woven carbon fabric disposed in an ordered, regular
structure.
2. The pore-type burner according to claim 1, wherein said woven
fabric consists of silicon carbide having a shape diverging from a
plane surface, and a plurality of pieces of woven fabric are
arranged in layers on top of one another.
3. The pore-type burner according to claim 2, wherein the woven
fabric has an undulating shape.
4. The pore-type burner according to claim 1, wherein said woven
fabric consists of completely siliconized fibers.
5. The pore-type burner according to claim 1, wherein said woven
fabric is partially siliconized and contains a core consisting of
pure carbon.
6. The pore-type burner according to claim 1, wherein said ordered
structures are configured to form zones of varying porosity.
7. The pore-type burner according to claim 3, wherein said
undulating shape is defined with axes of curvature and said axes of
curvature of the undulations of a piece of woven fabric lie in a
plane, and the pieces of woven fabric are arranged on top of one
another with respective projections of the wave normals onto such a
plane defined by the axes of curvature extend substantially
perpendicular to one another.
8. The pore-type burner according to claim 7, wherein the wave
normals are disposed to form an angle of approximately 45.degree.
relative to a direction of a flow of the flue gas.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuing application, under 35 U.S.C. .sctn.
120, of copending international application No. PCT/EP 2004/003968,
filed Apr. 15, 2004, which designated the United States; this
application also claims the priority, under 35 U.S.C. .sctn. 119,
of German patent application No. 103 17 857.0, filed Apr. 16, 2003
and German patent application No. 10 2004 006 824.0, filed Feb. 11,
2004; the prior applications are herewith incorporated by reference
in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a pore-type burner for burning a
fuel/air mixture for the purpose of generating a hot flue gas. The
burner includes a housing in which a pore material consisting of
porous, high-temperature-resistant silicon carbide (SiC) is
provided for combustion.
[0004] Such a pore-type burner is employed, for example, in order
to apply a hot stream of flue gas to a steam superheater. The steam
arising in the steam superheater has high temperatures and is under
intense pressure. The energy stored in the steam can then be made
usable in the form of mechanical or electrical energy, for example
as a result of decompression in an expansion engine for the purpose
of driving a generator. The hotter the steam and the higher the
pressure, the better the efficiency of such machines.
Correspondingly, it is necessary for the stream of flue gas to
exhibit temperatures that are as high as possible. Typical
temperatures lie within the range between 850.degree. C. and
1400.degree. C.
[0005] The pore-type burners for generating a hot stream of flue
gas differ, in particular, from a pure radiation burner in which
only the radiant heat of the burner is utilized and the flue gas
arising is drawn off as a secondary product via a chimney or an
exhaust-air pipe. Such radiation burners are, for example,
artificial open fires or radiation burners for the purpose of
drying lacquer coatings. Although the radiant heat of a pore-type
burner can also be utilized, the significant portion of the energy
transferred to the steam-generator comes from the flue gas.
[0006] A pore-type burner for the combustion of a
fuel/oxidizing-agent mixture is known from German patent DE 199 39
951 C2. The pore-type burner is filled with globular filling
materials. The size of the pores that arise is determined by the
size of the filling materials. The prior art pore-type burner is
designed in such a way that an excessive temperature in the
reaction chamber is avoided by means of an additional cooling
gas.
[0007] German patent DE 195 27 583 C2 describes a pore-type burner,
which contains porous material that exhibits spatially contiguous
cavities which are formed from a packing consisting of heat-proof
wire material, foil material or sheet-metal material. A defined
flame zone forms in these cavities. The material is not suitable
for high temperatures.
[0008] Moreover, pore-type burners are known--for example, from
U.S. Pat. No. 5,890,886--which are filled with a ceramic that is
formed with a plurality of cavities. Other foam ceramics, metallic
foams or metallic sponges are also known, from German published
patent application DE 196 21 638 A1 for example. These foams or
sponges have the disadvantage that they are expensive to
manufacture. In addition, they are very sensitive to mechanical and
thermal loads. They tear or crack in the event of excessive
loading, resulting in diminished performance and increased emission
of noxious substances.
[0009] German published patent application DE 198 47 042 A1
describes a highly porous burner mat, which consists of metallic or
ceramic fibers that are welded to one another in irregular
structures. The mat is provided with holes, through which the gas
flows. Regions of varying flow velocities arise, by virtue of which
an irregular carpet of flame arises which lifts off from the
surface of the mat.
SUMMARY OF THE INVENTION
[0010] It is accordingly an object of the invention to provide a
porous burner with silicon-carbide porous body which overcomes the
above-mentioned disadvantages of the heretofore-known devices and
methods of this general type and which provides a pore-type burner
that exhibits uniform combustion and that has a pore structure
which is capable of being directly influenced in the production
process.
[0011] With the foregoing and other objects in view there is
provided, in accordance with the invention, a pore-type burner for
burning a fuel/air mixture for generating a hot flue gas,
comprising:
[0012] a housing;
[0013] a porous body with pore material formed of porous,
high-temperature-resistant silicon carbide disposed in said
housing, said pore material being formed of siliconized woven
carbon fabric disposed in an ordered, regular structure.
[0014] In other words, the objects of the invention are achieved by
the porous body comprising siliconized woven carbon fabric that
is/are disposed in an ordered, regular structure. The invention is
based on the perception that the properties of a pore-type burner
can be influenced if the pore structure is capable of being
produced for a specific purpose. An interweaving of the hard and
brittle material silicon carbide is not possible. However, by
siliconizing a suitably shaped woven carbon fabric it is possible
to create an appropriately configured woven-fabric structure
consisting of SiC. The siliconized woven fabric is capable of being
produced inexpensively. It withstands mechanical and thermal loads
very well. The mesh width and planar shape of the woven fabric are
just as individually adaptable as are its size and contours, so an
optimization of the properties of the burners is possible when use
is made of materials of such a type by way of a porous body for
pore-type burners.
[0015] In one configuration of the invention the woven fabric
consisting of silicon carbide has a shape diverging from a plane
surface. A plurality of pieces of woven fabric can then be arranged
in layers on top of one another. In this way, a three-dimensional
configuration is created with which the pore-type burner is capable
of being filled, without additional spacers or the like.
[0016] The woven fabric may be shaped in an undulating manner,
i.e., with a rounded corrugation. But other shapes are also
possible, such as a profile that is sawtooth-shaped or box-shaped
in cross-section. Then, in order to obtain a small pore size, on
the one hand the parameters of the woven fabric may be kept small,
and on the other hand the wavy shape may then be composed of a
plurality of small undulations.
[0017] The woven fabric may consist of completely siliconized
fibers. But for some applications it may also be sensible for the
woven fabric to be partially siliconized and to contain a core
consisting of pure carbon.
[0018] In a particularly preferred configuration of the invention,
the ordered structures are designed in such a way that zones of
varying porosity are formed. In this case the porous body of the
burner may be designed in two or more zones of varying pore size.
The inlet-side part of the porous body then exhibits a smaller pore
size than the outlet-side porous body. With this configuration the
flame forms in the coarse-pored zone, whereas a mixing and
preheating of the fuel/air mixture take place in the fine-pored
zone. This results in a particularly low noxious-substance content
of the flue gas in the course of combustion of the customary fuels
such as natural gas, gasoline or such like. The pore size can be
realized particularly well by virtue of the selected woven fabric
and its arrangement--such as, for example, its stacking.
[0019] In an alternative configuration of the invention the
fine-pored part is produced from materials forming conventional
pores, whereas the coarse-pored part consists of siliconized woven
carbon fabric. The material of the fine-pored part is preferably
poorly conducting, so that a transfer of heat out of the combustion
zone into the premixing zone is avoided. In this way, a backfiring
of the flames is prevented.
[0020] The axes of curvature of the undulations of a piece of woven
fabric may lie in a plane, and the pieces of woven fabric may be
arranged above one another in such a manner that the projections of
the wave normals onto such a plane defined by the axes of curvature
extend perpendicular to one another. The wave normals then
preferably each form an angle of approximately 45.degree. relative
to the direction of flow of the flue gas. A wave normal here is the
perpendicular to a wavefront; it lies in the plane defined by the
axes of curvature. With this configuration of the invention the
pore structure is formed from stacked undulating SiC mats. In this
case the individual planes are arranged rotated by an angle of
approximately 90.degree. in relation to one another. This
arrangement is particularly favorable for the combustion behavior
of the burner. The structure that is flowed through in such a way
is designated as a static mixer. In the process, the fuel and the
combustion air are mixed with one another in such a way that the
fuel is burnt in a particularly low-emission manner and
completely.
[0021] The housing of the burner is preferably provided with an
insulating layer. In this way, an undesirable convective transfer
of heat through the housing into the periphery of the burner is
avoided.
[0022] Alternatively, the wall of the housing may be flowed through
by a cooling medium which is either conducted away separately into
the environment or mixed with the hot flue gas in the outlet region
of the burner.
[0023] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0024] Although the invention is illustrated and described herein
as embodied in a pore-type burner with silicon-carbide porous body,
it is nevertheless not intended to be limited to the details shown,
since various modifications and structural changes may be made
therein without departing from the spirit of the invention and
within the scope and range of equivalents of the claims.
[0025] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic perspective representation of a
pore-type burner;
[0027] FIG. 2 shows a detail from a piece of woven fabric shaped in
a corrugation and consisting of silicon carbide;
[0028] FIG. 3 is a longitudinal section through a schematically
represented pore-type burner; and
[0029] FIG. 4 is a section along the line IV-IV in FIG. 3 and shows
the outlet of a pore-type burner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Referring now to the figures of the drawing in detail and
first, particularly, to FIG. 1 thereof, there is shown a schematic
representation of a pore-type burner 10. The pore-type burner
consists of a housing 12, into which a fuel-gas/air mixture is
introduced. The direction of flow of the inflowing gas is
represented by the arrows 14. In the housing 12 a plurality of
pieces of woven fabric 16 are arranged in layers on top of one
another. In a first zone 18 the pores are smaller, and in a second
zone 20 the pores are larger. The porous material of the first zone
18 is not represented. In the second zone an oxidation takes place
in the pores without genuine formation of flame. In the process,
hot flue gas arises which is represented in FIG. 1 by arrows 22.
The flue gas is utilized in order to heat a steam-generator. In
this case there is the possibility of arranging the steam-generator
within the radiation field of the pore-type burner 10, so that not
only the heat transferred by the flue gas but, in addition, the
radiant heat is also utilized.
[0031] The pieces of woven fabric 16 are represented again in FIG.
2 in detail. They consist of a substantially rectangular, net-like
woven fabric. A plurality of these pieces of woven fabric 16 are
arranged in layers one on top of the other. Each piece of woven
fabric 16 is curved in an undulating manner, or corrugated, about
an axis of curvature 37. The pieces of woven fabric are arranged in
layers on top of one another in such a way that the crests 24 and
troughs 26 of the curvatures are always situated on top of one
another, offset alternately by substantially 90 degrees. This is
evident in FIG. 3. For instance, the piece of woven fabric 30 rests
on the piece of woven fabric 28, offset by 90 degrees. The
pore-type burner is filled up completely with the pieces of woven
fabric 16. As a result, a pore structure forms that allows a
particularly good, uniform evolution of flame. The porous body is
flowed through by the fuel/air mixture parallel to the planes of
the individual layers of woven fabric and in the direction of the
bisectors 34 of the angle of rotation between the wave normals 35
and the wave normals 39 of the layers.
[0032] In the present case the pore-type burner 10 has a
rectangular cross-section and is therefore also filled with
rectangular pieces of woven fabric 16. Of course, if the pore-type
burner 10 has a differently shaped cross-section, the shape of the
pieces of woven fabric is also adapted correspondingly.
[0033] Moreover, a coolant flows through the housing 12 of the
pore-type burner. The cooling air in this case is fed separately
into a cooling duct 38 (FIG. 4) of the housing 12 and is mixed with
the flue gas at the outlet 40.
[0034] The pore size can be influenced through the size of the
woven-fabric meshes 32, the radii of curvature of the wave troughs
and wave peaks, and the number of curvatures per piece of woven
fabric. In the present exemplary embodiment the pore size is
smaller in zone 18 (FIG. 1) and larger in zone 20.
[0035] The pieces of woven fabric consist of silicon carbide.
Silicon carbide is a carbidic ceramic material and as such is not
weavable. For the purpose of producing woven fabric of such a type,
use is therefore made of a woven carbon fabric which is brought
into the appropriate shape and then siliconized. Various processes
are suitable for the purpose of siliconizing. In the case of the
liquid siliconizing process, molten silicon is infiltrated into a
porous substrate consisting of carbon-fiber-reinforced carbon (C/C)
and is caused to react directly with the carbon of the matrix so as
to form SiC. The process is known and, for example, described on
the Internet under
http://www.fz-juelich.de/iwv/iwv1/index.php?index=8 and therefore
does not need to be elucidated in any detail.
[0036] After this process the siliconized pieces of woven fabric 16
are stiff and can be inserted into the burner without further
change of shape. The material is resistant to high temperature. The
production process for planar SiC structures is inexpensive,
compared with sponge-like ceramic bodies, and the mechanical and
thermal load-bearing capacity is significantly higher in comparison
with ceramic sponges.
* * * * *
References