EP1373799B1 - Burner for a gas and air mixture - Google Patents

Abstract

A burner for a gas/air mixture with an inlet ( 2 ) for the gas/air mixture, wherein a jet tube ( 7 ) is located downstream of the inlet ( 2 ). The jet tube ( 7 ) has a jacket surface with a plurality of breakthroughs ( 8 ) and is surrounded radially a flame stabilizing device.

Description

The invention relates to a burner for a gas / air mixture.

According to the prior art is for example from the DE 43 22 109 A1 a burner for a gas / air mixture known. The combustion takes place axially in a housing with a constant cross-section, which is filled with a total of a porous material. It forms no on the porous material outgoing flame front. The combustion takes place exclusively within the space filled with the porous material. There are no free flames extending from an outer surface of the porous agent into the environment. This is also called a volume burner. With the known burner, a gas / air mixture can be burned with low emissions.

From the JP 59195022 A (Patent Abstracts of Japan), a burner is known in which a perforated tube is surrounded radially with a cylindrical body made of catalytic material. It is a surface burner, ie the flames extend from one surface into the environment.

The US 4,900,245 describes an infrared burner in which a nozzle tube is surrounded by a cylindrical member made of a ceramic foam. The cylindrical element serves to uniformly distribute the gas on its surface. The gas is burned on the surface of the cylindrical member. On the surface of a flame detector is provided. When the flame goes out, it will automatically re-ignite.

The DE 195 08 908 A1 describes a burner tube in which a plurality of radially circumferential slots is provided. The flames fan out from the slots.

From the GB 2 231 949 A is a gas burner known. In this case, a combustible gas mixture is passed through a porous ceramic disc and burned. The disk can be arranged downstream of a layer sequence in the flow direction, which is formed from flat and wavy annular discs. In this case, the gas is burned on an outer surface surrounding the layer sequence.

The EP 0 382 674 describes an infrared burner in which a porous layer formed of ceramic fibers is applied to a cylinder made of a wire mesh. Again, it is a surface burner. Other surface burners are eg from the DE 297 15 119 41 ,of the US 4,679,528 , of the US 5240411 or the US 5 147 201 known.

The object of the invention is to eliminate the disadvantages of the prior art. In particular, a volume burner is to be specified which has improved heat extraction and with which combustion of a gas / air mixture with low emission values can be carried out at the same time. Another aim is to provide a volume burner whose modulability is improved over known volume and surface burners.

This object is solved by the features of claim 1. Advantageous embodiments emerge from the features of claims 2 to 22.

The burner according to the invention has an excellent heat extraction. It is attributed to improved heat transfer by convection and radiation. A gas / air mixture can be burned with particularly low emission values because of improved homogenization in the entire modulation range.

The term "gas / air mixture" herein means a combustible gas, e.g. Natural gas, propane gas and the like, understood with air or other suitable oxidant mixture, the mixing ratio is selected so that combustion is possible.

The diameter of the openings provided in the nozzle tube is expediently chosen so that a flashback into the nozzle tube is not possible. The apertures may have a diameter in the range of 0.5 to 2.0 mm, preferably 1.3 to 1.5 mm.

The combustion of the gas takes place essentially in the means for stabilizing the flame. In particular, no free flames are formed on an outer surface surrounding the means for stabilizing the flame. The means for stabilizing the flame has the function to limit the combustion chamber and at the same time to equalize and lower the flame temperature. Another function is the stabilization of the flame in the transition region between the nozzle tube and the combustion chamber by a stepwise Increase the Peclet number. The means for stabilizing the flame is not directly surrounded by a housing. The heat can be uncoupled unhindered. Because of the radial arrangement of the means for stabilizing the flame, a particularly large area for the heat extraction is achieved. The coupling-out surface can correspond, for example, to the surface of a cylinder jacket. The radial arrangement of the means for stabilizing the flame also has the advantage that the expanded combustion gases can be removed rapidly by a volume of communicating flow channels which is realized radially outwards. There is no accumulation of heat in the means for stabilizing the flame, which further improves the heat extraction. Because of the radial expansion of the cross-sections of the flow channels due to the radial arrangement of the means for stabilizing the flame, the convection velocity of the combustion gases slows down. The flame is thus additionally stabilized fluidically. The modulability of the burner is further increased.

Advantageously, the inlet downstream of a fan for transporting the gas / air mixture into the nozzle tube. This ensures that a sufficient amount of gas / air mixture through the nozzle tube is always supplied to the means for stabilizing the flame.

The nozzle tube may be formed of a refractory ceramic, which is preferably made of ceramic fibers. The refractory ceramic expediently has a porosity of 75 to 95 vol.%. Such a ceramic is characterized in practical use by longevity. In particular, a ceramic produced using ceramic fibers has a long service life because of its particularly good breaking strength. The ceramic is expediently composed of about 50% by weight of aluminum oxide and 50% by weight of silicon oxide. Of course, the nozzle tube may also be made of other suitable materials, eg refractory metals, quartz glass, glass ceramic, foamed ceramic and the like.

The means for stabilizing the flame may be a porous medium having a pore size which allows the formation of a flame.

The means for stabilizing the flame is expediently formed from a multiplicity of annular disks extending radially from the nozzle tube and arranged at an axial distance from one another. The annular discs may be frictionally held on the nozzle tube.

The annular discs may be formed from first and second annular discs, wherein a ring radius of the first annular discs is smaller than the annular radius of the second annular discs. The ring radius of the second annular discs is expediently at least twice as large as the ring radius of the first annular discs. The term "ring radius" is understood here to mean the difference between an inner radius and an outer radius of the annular disc.

According to a further embodiment, the first and the second annular discs are accommodated alternately in the axial direction on the nozzle tube. Due to the alternating sequence of the first and the second annular disks, a radially inner first flame stabilizing zone and a radially outer second flame stabilizing zone without intermediate first annular disks are advantageously formed. The Peclet number of the first flame stabilization zone is expediently smaller than the Peclet number of the second flame stabilization zone. The proposed inward-outward increase of the Peclet number occurs in the prescribed embodiment discontinuous. Nevertheless, it has surprisingly been found that even the provision of two flame stabilization zones enables the realization of a burner with outstanding dynamics.

Of course, it is also possible to realize a sequence of a plurality of flame-stabilizing zones in the means for stabilizing the flame. The Peclet number ideally increases continuously radially from the inside to the outside. In any case, the Peclet number is chosen so that in the means for stabilizing the flame combustion takes place in the manner of a volume burner. The Peclet number of the nozzle tube, however, is chosen so that a flashback into the nozzle tube is impossible. Because of the definition of the Peclet number and the effect and functioning of volume burners is supplemented to the DE 43 22 109 A1 , the disclosure of which is hereby incorporated by reference.

The surface of the annular discs is expediently corrugated, so that between two adjacent annular discs from the nozzle tube to the outer peripheral edge of the annular discs extending flow channels are formed. The wave crest lines of the waves extend, preferably curved, from the center to the peripheral edge of the annular disks, so that preferably two curved, continuous flow channels are formed between two adjacent annular disks from the nozzle pipe to the outer peripheral edge of the annular disks.

According to a further embodiment, flow channels are formed in the means for stabilizing, the cross-section of which increases radially from the inside to the outside. The Peclet number expediently increases radially outwardly in the means for stabilizing. It has been found that such a design brings about a particularly good decoupling of the heat generated by the combustion and an increase in the modulability. Furthermore, it has been found that the radial increase of the cross section from the inside to the outside can significantly reduce a sound emission caused by thermoacoustical excitation. The proposed burner is particularly quiet during operation. In particular, it does not come to low-frequency vibrations, which can lead to destruction of the nozzle tube or the means for stabilizing the flame.

The surface of the annular disks advantageously has a plurality of further openings. The further openings may be rectangular, slit-like or round. The opening area of the further openings is expediently approximately 1 mm ² . The annular discs may be made of a refractory, preferably having a lattice-like structure, ceramic produced. This may be a fabric made of mullite fibers, which is received in a matrix formed from alumina.

According to a further embodiment feature, the annular discs are arranged between two provided in the vicinity of the ends of the nozzle tube further made of a refractory ceramic discs. The other annular disks limit the combustion chamber terminal. They have the function of thermal insulation. They are suitably made of a porous alumina ceramic, which, however, has no openings.

The means for stabilizing the flame may also be made of a three-dimensional metal mesh, a porous ceramic or the like. In any case, it is desirable that the nozzle tube has a Peclet number of <65 and the means for stabilizing the flame has a Peclet number of> 65. This ensures that the flame in the nozzle tube is prevented from hitting back. At the same time is one Combustion possible on the means to stabilize the flame.

The means for stabilizing the flame is surrounded by a particularly advantageous embodiment feature of a heat exchanger. The decoupled from the means for stabilizing the flame heat is transferred with high efficiency to a circulating in the heat exchanger liquid medium. The heat exchanger can in turn be surrounded by a housing.

Fig. 1

eine schematische Seitenansicht eines Brenners,

Fig. 2

eine Draufsicht auf eine Ringscheibe gemäß Fig. 1,

Fig. 3

eine perspektivische Ansicht eines Brenners,

Fig. 4

eine Querschittsansicht nach Fig. 3 und

Fig. 5

eine Detailansicht nach Fig. 4.

Hereinafter, an embodiment of the invention will be explained in more detail with reference to the drawing. Show it:

Fig. 1

a schematic side view of a burner,

Fig. 2

a plan view of an annular disc according to Fig. 1 .

Fig. 3

a perspective view of a burner,

Fig. 4

a cross-sectional view after Fig. 3 and

Fig. 5

a detailed view after Fig. 4 ,

In Fig. 1 an inlet 2 for a gas / air mixture is provided in a housing half shell 1 of a fan not shown in detail here. A blower outlet 3 is located opposite a baffle plate 5 received in an antechamber 4. The baffle plate 5 has the function to ensure a homogeneous flow rate as possible at the inlet cross-section 6 of a nozzle tube 7. The nozzle tube 7 has a plurality of radially extending apertures 8 with a diameter of about 1.0 to 2.0 mm. The openings 8 are uniformly distributed over the lateral surface of the nozzle tube 7.

On the outer circumferential surface of the nozzle tube 7 are received annular discs 9, which are advantageously formed corrugated in cross section. The annular discs 9 are axially spaced from each other. Between two adjacent annular disks 9 flow channels 10 are formed. In the vicinity of the ends of the nozzle tube 7 further annular disks 11 are received on the outer circumferential surface of the nozzle tube 7. The further annular disks 11 are made of a thermally insulating ceramic, e.g. a highly porous alumina ceramic. They have no breakthroughs. The further annular disks 11 define in the axial direction a combustion chamber containing the annular disks 10. The reference numeral 12 tubes of a heat exchanger are designated. The tubes 12 and the nozzle tube 7 with the annular disks 9 and 11 received thereon are accommodated in a common housing G.

Fig. 2 shows a plan view of an annular disc 9, which is received on the nozzle tube 7. The annular disk 9 is made of a ceramic having a lattice-like structure. Such a ceramic can be made by impregnating a fabric made of mullite fibers with an aluminum oxide slurry by sintering the impregnated mullite fiber composite after drying the slurry. In this case formed further breakthroughs are designated 15. It has proven to be particularly useful to form the surface of the annular disc 9 corrugated. The wave crest lines are the Fig. 2 indicated by the reference numeral 13. They run from the nozzle tube 7 curved to the peripheral edge 14 of the annular disc 9, so that a Schaufelradartige structure is formed. Advantageously, the annular discs 9 each have an odd number of wave crest lines 13. If such annular discs 9 are arranged in succession so that their wave crest lines 13 are aligned in axial succession, flow channels 10 are formed whose cross-section increases from the nozzle tube 7 to the peripheral edge 14 out. Such flow channels 10 facilitate the discharge of the expanding hot combustion gases. A particularly efficient combustion and an effective heat extraction are achieved.

The annular discs 9 may also be made of a nonwoven fabric made of mullite fibers. The fleece is dimensionally stable. It can be made by pressing mullite fibers. The shape is expediently designed so that the annular discs have a corrugation. The required apertures, which may be in the form of holes or slots, may be made by statute. Subsequently, the dimensionally stable mullite nonwoven is impregnated with an alumina slurry, dried and then sintered. The result is a dimensionally stable heat-resistant annular disc with the desired shape.

The annular discs may also be provided with a catalytically active coating according to a further embodiment feature. Such a coating may contain lead, platinum or other suitable metals. A burner with such catalytically coated annular disks has particularly low emission values.

In the Fig. 3 to 5 a further embodiment of a burner is shown. In this case, first annular discs 16 and second annular discs 17 are received on the nozzle tube 7. The first 16 and second annular discs 17 have radially outwardly extending corrugations 18. Through the corrugations 18 flow channels 10 are formed, the cross section widens radially from the inside out. A ring radius R1 of the first annular discs 16 is about half as large as a ring radius R2 of the second annular discs 17. The term "ring radius" is present in the difference between an inner radius and an outer radius of the annular disc Understood. For explanation will be on Fig. 4 referenced, in which the ring radii R1, R2 are shown.

How out Fig. 4 It can be seen that the alternating sequence of the first annular discs 16 with the second annular discs 17 forms a first flame stabilization zone B1. The annular sections of the second annular discs 17 extending over the first flame stabilization zone B1 form a radially outer second flame stabilization zone B2. A Peclet number of a zone A formed by the nozzle tube 7 is <than 65. This reliably avoids flashback of flames into the nozzle tube 7. A Peclet number of the flame stabilizing zones B1, B2 is> 65, the Peclet number of the second flame stabilizing zone B2 being greater than the Peclet number of the first flame stabilizing zone B1.

In the burners according to the invention, combustion takes place in the means for stabilizing the flame formed by the annular disks 9, 16, 17. Virtually no flames extend from a surface surrounding the means for stabilizing the flame. The proposed burner has excellent dynamics, that is, it can be modulated in a wider range than previously known volume or surface burners.

The means for stabilizing the flame can also be formed from spirally arranged radially extending from the nozzle tube surfaces. It can also be designed in the form of turbine blade-like or Schaufelradartiger annular discs.

LIST OF REFERENCE NUMBERS

1

Blower half shell

2

inlet

3

blower

4

antechamber

5

flapper

6

Inlet cross-section

7

nozzle tube

8th

breakthrough

9

washer

10

flow channel

11

another ring disk

12

pipe

13

Crest line

14

circumferential edge

15

further breakthroughs

16

first annular disc

17

second annular disc

18

curl

A

Zone

B1

first flame stabilization zone

B2

second flame stabilization zone

R1

first ring radius

R2

second ring radius

G

casing

Claims (22)

1. Burner for a gas/air mixture with an inlet (2, 6) for the gas/air mixture, wherein a jet tube (7) is provided down-current after the inlet (2, 6), the jet tube (7) having a jacket surface with a plurality of breakthroughs (8), wherein a zone A created by the yet tube (7) has a Péclet number preventing flames from backfiring in the yet tube (7), and wherein the jet tube (7) is surrounded radially by a flane-stabilisation means (9, 16, 17).
2. Burner as defined, in one of the preceding claims, wherein the combustion of the gas takes place primarily in the flame-stabilisation means (9, 16, 17).
3. Burner as defined in claim 1 or 2, wherein a blower to transport the gas/air mixture into the jet tube (7) is located after the inlet (2).
4. Burner as defined in one of the preceding claims, wherein the jet tube (7) is made from a fireproof ceramic material, preferably from ceramic fibers.
5. Burner as defined in claim 4, wherein the fireproof ceramic material has a porosity of 75 to 95 vol. %.
6. Burner as defined in one of the preceding claims, wherein the flame-stabilisation means is created from foam ceramic material.
7. Burner as defined in one of the preceding claims, wherein the flame-stabilisation means consists of a plurality of ring disks (9, 16, 17) arranged radially from the jet tube (7) and spaced at an axial distance from each other.
8. Burner as defined in one of the preceding claims, wherein the ring disks (9, 16, 17) are created from first (16) and second ring disks (17), and wherein a ring radius (R1) of the first ring disks (16) is smaller than a ring radius (R2) of the second ring disks (17).
9. Burner as defined in one of the preceding claims, wherein a ring radius (R1) of the second ring disks (17) is at least twice as large as the ring radius (R1) of the first ring disks (16).
10. Burner as defined in one of the preceding claims, wherein the first (16) and the second ring disks (17) are placed alternately on the jet tube (7) in axial direction.
11. Burner as defined in one of the preceding claims, wherein the alternating succession of the first (16) and the second ring disks (17) creates a first flame-stabilisation zone (B1) located radially inside as well as a second flame-stabilisation zone (B2) located radially outside without first ring disks (16) in between.
12. Burner as defined in one of the preceding claims, wherein the Péclet number of the first flame-stabilisation zone (B1) is less than the Péclet number of the second flame-stabilisation zone (B2).
13. Burner as defined in one of the preceding claims, wherein the surface of the ring disks (9, 16, 17) is rippled so that current flow canals (19) are created between twc adjacent ring disks (9, 16, 17) from the jet tube (7) to the outside circumference edge (14) of the ring disks (9, 16, 17).
14. Burner as defined in one of the preceding claims, wherein wave crest lines (13) of the ripples (18) run, preferably bent, from the centre to the circumference edge (L4) of the ring disks (9, 16, 17) so that continuous, preferably bent, current flow canals (10) are created between two adjacent ring disks (9, 16, 17) from the jet tube (7) to the circumference edge (14).
15. Burner as defined in one of the preceding claims, wherein a cross section of the current flow canals (10) increases radially from the inside to the outside.
16. Burner as defined in one of the preceding claims, wherein the Péclet number in the flame-stabilisation means increases radially towards the outside.
17. Burner as defined in one of the preceding claims, wherein the surface of the ring disks (9, 16, 17) has a plurality of additional breakthroughs (15).
18. Burner as defined in one of the preceding claims, wherein the ring disks (9, 16, 17) are made from a fireproof ceramic material, preferably of a mesh-type structure.
19. Burner as defined in claim 17, wherein the ceramic material is created from mullite fibers on an aluminium oxide matrix.
20. Burner as defined in one of the preceding claims, wherein the ring disks (9, 16, 17) are arranged between two additional, fireproof ceramic ring disks (11) located in the vicinity of the ends of the jet tube (7).
21. Burner as defined in one of the preceding claims, wherein the jet tube (7) has a Péclet number of < 65 and the means (9, 16, 17) of stabilisation of the flame has a Pellet number of > 65.
22. Burner as defined in one of the preceding claims, wherein the means (9, 16, 17) of stabilisation of the flame is surrounded by a heat exchanger (12).

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