WO2012069534A1

WO2012069534A1 - Burner with secondary axial flow elements

Info

Publication number: WO2012069534A1
Application number: PCT/EP2011/070805
Authority: WO
Inventors: Dinand Lamberts; Arnoldus Martinus Van Wijk
Original assignee: Bekaert Combustion Technology B.V.
Priority date: 2010-11-26
Filing date: 2011-11-23
Publication date: 2012-05-31
Also published as: CN103228989A; EP2643635A1

Abstract

A premix gas burner (10) with a mixing chamber and a burner deck (12) of cylindrical or frusto-conical shape around the mixing chamber has an entry. A primary axial flow element (26), the so-called anti-noise tube, is inserted in the entry and guides part of the premixed gas and air' mixture into a mixing chamber. This primary axial flow element (26) has a first length L₁, in the direction of the flow of the premixed gas and air' mixture and a first diameter D₁, in a plane perpendicular to the direction of the flow of the premixed gas and air mixture.

Description

Burner with secondary axial flow elements

Description

Technical Field

[0001 ] The invention relates to a premix gas burner with a cylindrical or frusto- conical shape burner deck.

Background Art

[0002] Premix gas burners of cylindrical or frusto-conical shape have a burner plate (or burner surface or burner deck) of cylindrical or frusto-conical shape around a mixing chamber. The premixed gas and air mixture is supplied together via an inlet and gets further mixed in a mixing chamber lying inside the burner deck. From the mixing chamber the gas and air is supplied to the burner deck through holes in the burner deck. The flames are produced on the external surface of the burner deck (or burner plate or burner surface). The process of gas being mixed with air immediately followed by the heavy burner reaction and flames gives rise to waves travelling in the direction of the gas-air mixture and to waves travelling back from the burner plate in the opposite direction. Depending upon the mode of the combustion and the geometry of the combustion system a resonance phenomenon may be created. Inside the volume of the mixing chamber and the volume of the burner plate standing waves are present. These standing waves generate noise and are the cause of an incomplete burner reaction.

[0003] EP-A-1087180 solves this problem of noise and incomplete burner

reaction by inserting an axial flow element in the entry of a cylinder or cone shaped burner surface. So called short circuit openings are arranged parallel to this axial flow element. The axial flow element together with the parallel openings avoid or at least decrease the generation of standing waves and thus reduce the level of noise and improve the quality of the combustion. The solution provided by EP-A-1087180 has been called the anti-noise tube. This anti-noise tube also has some drawbacks. First of all, since there is an additional and separate part, it is an expensive solution. Secondly, the creation of the short-circuit openings is mainly carried out by welding the anti-noise tube on a flange and leave a small gap between. This mounting is difficult and time consuming.

[0004] WO2009/1 12909A2 shows a burner comprising an inlet for the premix gas to be burnt. The inlet, a channelling element, can be surrounded by one or more holes in the plate around the tubular element through which further premix gas is flowing into the mixing chamber. However, this inlet system is not in all circumstances giving satisfactorily noise reduction.

Disclosure of Invention

[0005] It is an object of the present invention to avoid the drawbacks of the prior art.

[0006] It is another object of the present invention to reduce the noise level and improve the quality of the combustion in an inexpensive way.

[0007] It is still another object of the present invention to have an anti-noise tube that is easy to mount.

[0008] According to the present invention there is provided a premix gas burner.

The burner deck is positioned around a mixing chamber. The burner deck can have a cylindrical shape or a frusto-conical shape. The burner has an entry for introducing premixed gas and air mixture into the mixing chamber. A primary axial flow element, the so-called anti-noise tube is inserted in the entry and guides part of the premixed gas and air mixture into a mixing chamber. This primary axial flow element has a first length L-i , in the direction of the flow of the premixed gas and air mixture and a first diameter D-i , in a plane perpendicular to the direction of the flow of the premixed gas and air mixture.

This primary axial flow element offers little resistance in the direction of the flow of the premixed gas and air mixture and offers more resistance in the opposite direction, so that the likelihood for creation of standing waves is decreased. At least one secondary axial flow element is also positioned in the entry parallel to the primary axial flow element. The secondary axial flow element has a second length L₂, in the direction of the flow of the premixed gas and air mixture and a second diameter D₂, in a plane perpendicular to the direction of the gas and air.

The second length L₂ is different from the first length l_i and the second diameter D₂ is smaller than the first diameter D-i . Both the primary axial flow element and the secondary axial flow elements are introducing premixed gas and air mixture into the mixing chamber where further mixing occurs and distribution to the burner plate on which outer surface combustions occurs.

The secondary axial flow element or elements offer little resistance in the direction of the flow of the premixed gas and air mixture and offer more resistance in the opposite direction. These secondary axial flow elements, taken in isolation, thus also decrease the likelihood of generation of standing waves. In addition, due to the fact that the geometry of the secondary axial flow elements is different from the geometry of the first axial element, the combined action of both the first axial flow element and the secondary axial flow element or elements decreases the likelihood of the creation of standing waves over a wider frequency spectrum. So the invention particularly avoids thermo acoustic instabilities.

[0009] In addition to the advantage of having an improved thermo acoustic

stability, the secondary axial flow elements improve the cooling of the burner plate or burner deck through the introduction of the moving premixed gas and air mixture. In particular, the secondary axial flow elements preferably have a tubular or frusto-conical shape, which improves the heat transfer e.g. compared to through holes in a plate.

[0010] The flow of the premixed gas-air mixture through the primary axial flow element and the secondary axial flow element or elements is an

optimization for the distribution of the gas-air mixture. This improved distribution is vital for low emissions, good ignition and flame stability and thus leads to an improved quality of combustion.

[001 1 ] Preferably, the premixed gas air mixture is entered in the primary axial flow element and in the secondary axial flow element via one supply, which means that the premixed gas air mixture is entering at the same pressure the primary axial flow element and the secondary axial flow elements.

[0012] Various and different configurations are possible.

[0013] The second length L₂ is preferably smaller than the first length L-i .

[0014] Preferably more than one secondary axial flow element is provided.

There may be four, six, eight, twelve, sixteen, twenty-four, thirty-six, fourth- eight secondary axial flow elements.

[0015] In case of a plurality of secondary axial flow elements, they all may have the same diameter D₂ or some may have a diameter D₂ differing from the diameter of others.

[0016] In case of a plurality of secondary axial flow elements, they all may have the same second length L₂ or some may have a second length L₂ differing from the diameter of others.

[0017] In case of a plurality of secondary axial flow elements, these secondary axial flow elements(e.g. more than four, or e.g. more than five, or e.g. more than six) may be arranged in a circle around the primary axial flow element.

[0018] In order to simplify construction and mounting and also to reduce costs, the primary axial flow element and the secondary axial flow element or elements (e.g. of tubular shape or of frusto conical shape) are arranged on a single-piece flange, e.g. of plate thickness between 0.5 and 1 .5 mm, e.g. of plate thickness 1 mm. This avoids the welding operation and reduces the number of parts.

Brief Description of Figures in the Drawings

[0019] Figure 1 shows a perspective view of a flange with primary and secondary axial flow elements to be used in a premix gas burner according to the invention; [0020] Figure 2 shows a bottom view of a flange with primary and secondary axial flow elements to be used in a premix gas burner according to the invention;

[0021 ] Figure 3 shows a cross-section of a premix gas burner according to the invention.

Mode(s) for Carrying Out the Invention

[0022] Referring to Figure 1 , Figure 2 and Figure 3 at the same time, a premix gas burner 10 comprises a burner plate or burner deck 12. In the examples shown, the burner plate (burner deck) 12 is of a cylindrical type. This burner plate 12 is preferably made out of metal, e.g. steel, which is welded together and is surrounding the mixing chamber. The burner plate 12 is provided with perforations which show a potentially varying pattern over the height of the burner 10. A closed cover plate 14 is provided at the top of the premix gas burner 10. The burner plate 12 and the closed cover plate 14 surround a mixing chamber. A bottom flange 16 is provided at the bottom or entry side of the premix gas burner 10. The circular bottom flange 16 is provided with a first vertical partition 18, which fits inside the lower part of the burner plate 12. Going to the centre or middle of the bottom flange 16, a horizontal annular part 20 houses a plurality of secondary air flow elements 22, which are in this example of tubular shape. Further to the centre or middle of the bottom flange 16, a second vertical partition forms a primary axial flow element 26. Premixed gas air mixture is introduced into the mixing chamber of the burner via the secondary flow elements 22 and via the primary air flow element 26 via one single supply and hence at the same pressure.

[0023] The following geometry and dimensions are given as example:

- first diameter of the primary axial flow element Di = 24 mm

- first length or height of the primary axial flow element l_i = 20 mm

- second diameter of the secondary axial flow element D₂ = 3.0 mm

- second length or height of the secondary axial flow element L₂ = 2.0 mm.

[0024] Typically Di may range between 20 mm and 38 mm, l_i may range

between 8 mm and 50 mm. D₂ may range between 0.5 mm and 4.0 mm, e.g. between 1 .0 mm and 3.0 mm, L₂ may range between 0.5 mm and 6.0 mm, e.g. between 1 .5 mm and 5.0 mm, and preferably between 2.5 and 5 mm.

List of reference numbers

10 premix gas burner

12 burner plate or burner deck

14 cover plate

16 bottom flange

18 first vertical partition

20 horizontal part of flange

22 secondary air flow elements

24 second vertical partition

26 primary air flow element

Claims

1 . A premix gas burner with a mixing chamber and a burner deck of cylindrical or frusto-conical shape around the mixing chamber, said burner having an entry and comprising a primary axial flow element in said entry guiding premixed gas and air mixture into the mixing chamber, said primary axial flow element having a first length l_i and a first diameter D-i ,

and at least one secondary axial flow element is also positioned in said entry parallel to said primary axial flow element,

said at least one secondary axial flow element having a second length L₂ and a second diameter D₂,

said second length L₂ being different from said first length l_i and

said second diameter D₂ being smaller than said first diameter D-i .

2. A premix gas burner according to any of the preceding claims, wherein one single supply is supplying gas and air mixture into said primary axial flow elements and into said secondary axial flow elements.

3. A premix gas burner according to any of the preceding claims, wherein said secondary axial flow elements are having a tubular or frusto-conical shape.

4. A premix gas burner according to any of the preceding claims, wherein said second length L₂ is within the range of 0.5 to 6 mm.

5. A premix gas burner according to any of the preceding claims, wherein said second length L₂ is smaller than said first length l_i

6. A premix gas burner according to any of the preceding claims, wherein more than one secondary axial flow element is provided.

7. A premix gas burner according to claim 6, wherein said more than one

secondary axial flow elements all have the same second diameter D₂.

8. A premix gas burner according to claim 6, wherein said more than one

secondary axial flow elements form two or more groups, a secondary axial flow element belonging to one group having a second diameter differing from the second diameter of another secondary axial flow element belonging to another group.

9. A premix gas burner according to one of claims 6 to 8, wherein all second lengths L₂ are equal.

10. A premix gas burner according to one of claims 6 to 8, wherein some of said second lengths are different from other second lengths.

1 1 . A premix gas burner according to one of claims 6 to 10 wherein said

secondary axial flow elements are arranged in a circle around said primary axial flow element.

12. A premix gas burner according to any one of the preceding claims wherein said primary axial flow elements and said at least one secondary axial flow element are arranged in a single flange.