GB2437976A

GB2437976A - Burner assembly for gaseous fuel

Info

Publication number: GB2437976A
Application number: GB0609056A
Authority: GB
Inventors: William Anthony Byrne
Original assignee: Valor Ltd
Current assignee: Valor Ltd
Priority date: 2006-05-09
Filing date: 2006-05-09
Publication date: 2007-11-14
Anticipated expiration: 2026-05-09
Also published as: GB0609056D0; GB2437976B

Abstract

A burner assembly has a first, more robust burner means in the form of a series of apertures (18) in an elongate burner housing (10). A second, more fragile, burner means (20) in the form of a porous, heat-resistant ceramic mat overlies the first burner means. Both the first and second burner means are capable of sustaining combustion independently of the other. In normal use, combustion occurs at the outer face of the heat resistant porous ceramic mat (20), which allows the production of aesthetically pleasant flame effects. However, if the porous ceramic mat (20), which is relatively fragile, becomes damaged, the fuel is combusted correctly and safely at the underlying first burner means.

Description

1 2437976

DESCRIPTION

BURNER ASSEMBLY FOR GASEOUS FUEL

The present invention relates to burner assemblies for gaseous fuel and in particular, but not exclusively, to burner assemblies for gas heaters.

Burners for gas heaters generally comprise an elongate hollow metal housing into which combustible gas is fed. The burner has a plurality of apertures through which the combustible gas escapes. Once the gas has been ignited, a self-sustaining flame is produced at the apertures. The oxygen for combustion is normally provided from the air at the apertures. However, in certain arrangements, air is pre-mixed with the combustible gas in the housing prior to discharge from the apertures.

In gas heaters where the flame is not visible in use, the burner can be designed to achieve the most efficient heat output. However, in many designs of gas heater the flame is visible in use and forms part of the aesthetic appeal of the heater.

More recently, burners have been designed such that, instead of producing flames which appear realistic, other aesthetic visual effects are produced. One particularly pleasing visual effect can be obtained by discharging the combustible gas through a porous fibrous layer or mat before combustion. This gives rise to a slow-moving "film" of flame that covers the fibrous layer or mat and causes the fibres of the layer or mat to glow and scintillate.

Suitable porous fibrous layers or mats are commonly formed from chopped-strand mats of sized ceramic fibres, such as Shott Ceramat , which is a porous fibrous mat formed from overlapping ceramic fibres having a silicone carbide coating, the overlapping fibres being welded to each other at points of contact. This produces a highly permeable layer (with porosity up to 95%) which can withstand high temperatures (up to 1000 C).

However, as a result of the construction of the porous fibrous mats, the mats are relatively fragile and, if touched, are damaged relatively easily. If the porous ceramic mat is damaged, it can destroy or impair the intended pleasing visual appearance. More importantly, however, damage to the porous ceramic mat can result in incorrect combustion of the fuel, with the potential consequence that harmful products are thereby formed.

In accordance with a first aspect of the present invention, a burner assembly for gaseous fuel comprises a housing having an inlet for gaseous fuel, first burner means and second burner means overlying the first burner means, each of the first and second burner means being capable of sustaining combustion of the gaseous fuel independently of the other.

By providing two burner means, each of which is capable of sustaining combustion independently of the other, if one of the burner means is damaged, correct combustion of the fuel can still take place via the other burner means.

Normally, the innermost burner means (the first burner means) will be more robust and less prone to damage than the outer burner means (the second burner means). As a consequence, if the second, more fragile, burner means is damaged, combustion can still take place via the inner, more robust burner means.

This allows a burner to be formed with a more fragile outer burner means, which can be used to produce different types of flame, with the reassurance that if it is damaged, correct combustion will still take place at the underlying second burner means.

Preferably, one or both of the first burner means and the second burner means comprises a plurality of apertures, which may conveniently be slots. The slots are preferably provided in the housing.

Preferably, one or both of the first and second burner means comprises a layer of porous heat-resistant material.

For example, the layer of heat-resistant material may comprise ceramic fibres, and may comprise a mat of chopped-strand ceramic fibres. The mat may comprise a plurality of overlapping ceramic strands and a plurality of overlapping strands may be welded to one another where they touch. Preferably, the ceramic fibres are sized, e.g. with silicon carbide.

Preferably, the burner assembly comprises an elongate housing and the first burner means and second burner means are elongate.

Preferably, the second burner means completely covers the first burner means.

The present invention also includes a heating apparatus comprising a burner assembly in accordance with the invention.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:-Fig. 1 is a perspective view of a first embodiment of burner assembly in accordance with the present invention; Fig. 2 is a perspective view of the burner assembly of Fig. 1, shown partly cut-away; Fig. 3 is a transverse cross-section through the burner assembly of Fig. I, looking in the direction of arrows III -III; and Fig. 4 is a perspective view, partly cut-away, of a second embodiment of burner assembly in accordance with the present invention.

Referring to Figs. 1 to 3, a burner assembly comprises an elongate hollow metal tube 10 of circular cross-section. One end of the metal tube 10 is sealed off by means of a circular metal cap 12 which is welded to the interior of the tube around its periphery and the other end is closed off by means of a mounting plate 14 which is welded to the tube. The mounting plate 14 is provided with a circular aperture 16 at each corner for mounting the burner assembly and is also provided with a gas inlet 17 through which gas is supplied to the burner assembly.

The top of the tube 10 is provided with a first burner means in the form of a row of identical parallel slots 18, each extending transversely with respect to the longitudinal axis of the tube 10. In this particular example, the slots are approximately 1mm wide and extend for approximately 30 of the periphery of the tube 10. Adjacent slots are spaced from each other by approximately 2mm.

The slots extend along virtually the whole length of the tube 10, except for approximately 25mm at each end of the tube, where there are no slots.

The location, dimensions and number of the slots 18 are such that the first burner means is capable of supporting satisfactory combustion of the fuel fed into the burner by itself.

However, a second burner means is located over the first burner means.

The second burner means comprises an elongate flexible gas-permeable rectangular mat 20 which is formed from overlapping chopped-strand sized ceramic fibres which are welded to each other at points of contact. A suitable mat, for example, would be Shott Ceramat fibre mat.

The dimensions of the mat 20 are chosen so that it completely covers all of the slots 18 of the first burner means. In fact, the mat 20 extends virtually along the whole length of the upper portion of the tube 10, in contact with the tube. The mat 20 is held in position by means of two elongate retaining flanges 22, 24 which extend along virtually the whole length of the tube 10, parallel to its longitudinal axis. Each of the flanges 22, 24 is spot-welded to the tube 10 and is adapted to overhang and hold in place a respective one of the two longitudinal edges of the mat.

It should be noted that the mat 20 is capable of supporting combustion entirely by itself, namely without the first burner means. Similarly, and as mentioned previously, the first combustion means is capable of sustaining combustion even without the presence of the mat 20.

In use, the burner is mounted in position in the heating apparatus and gas is fed to the tube 10. The gas passes through the slots 18 in the first burner means and then passes through the porous ceramic mat 20. Upon ignition of the gas emerging from the mat, an unusual and aesthetically pleasing effect is achieved.

The effect is of a slow-moving "film" of flame that covers the mat and causes individual fibres of the mat to glow and/or scintil]ate.

However, the mat 20 is very porous and relatively fragile and is therefore prone to accidental damage. If the mat 20 were to become damaged to the extent that part of it could no longer sustain combustion, the more robust first burner means positioned directly beneath the mat would ensure that combustion of the gas still takes place correctly. Therefore, although the aesthetic effect of the burner assembly might be reduced, particularly in the areas where damage to the mat has occurred, the presence of the underlying first burner means, which is capable of sustaining combustion by itself, ensures that the fuel will still be burned correctly and safely.

A second embodiment of the present invention is illustrated in Fig. 4. The principle of this embodiment is identical to that of the first embodiment.

However, the burner assembly comprises a bowl 40 which is elliptical in shape when viewed from above. As shown in Fig. 4, the open face of the bowl is covered with a metal sheet 42 having an array of slots 44. The number, shape and dimensions of the slots 44 are such that the sheet forms a burner which is capable of sustaining, by itself, combustion of fuel fed into the bowl and passing out through the aperture plate.

However, as seen in Fig. 4, a mat 46 of porous ceramic material, of the same shape as the open face of the bowl 40, and of identical material to the mat 20 of the first embodiment, s placed in abutment with the upper face of the apertured metal plate 42. As for the first embodiment, the mat 46 is capable of sustaining combustion of gas within the bowl even without the apertured metal plate 42.

Indeed, in normal use, gas passes from the bowl, through the apertured metal plate without combustion taking place and through the porous ceramic mat 46, combustion taking place at the outer surface of the ceramic mat, as for the first embodiment.

Thus, in normal use, the aesthetically pleasing effects achieved with combustion on the outer face of the ceramic mat 46are achieved. However, as for the first embodiment, if any portions of the ceramic mat 46 become damaged, to the extent that they cannot sustain proper combustion, the underlying burner means in the form of the slotted plate 42, situated immediately beneath the ceramic mat 46, ensures that correct and safe combustion of the fuel always occurs.

The invention is not restricted to the details of the foregoing embodiments.

Claims

CLAIMS

1. A burner assembly for gaseous fuel, comprising a housing having an inlet for gaseous fuel, first burner means and second burner means overlying the first burner means, each of the first and second burner means being capable of sustaining combustion of the gaseous fuel independently of the other.

2. A burner assembly as claimed in claim 1, wherein the first burner means is more robust than the second burner means.

3. A burner assembly as claimed in claim 1 or claim 2, wherein one or both of the first burner means and the second burner means comprises a plurality of apertures.

4. A burner assembly as claimed in claim 3, wherein the apertures comprise slots.

5. A burner assembly as claimed in claim 3 or claim 4, wherein the apertures are provided in the housing.

6. A burner assembly as claimed in any of the preceding claims, wherein one or both of the first and second burner means comprises a layer of porous heat-resistant mat.

7. A burner assembly as claimed in claim 6, wherein the layer of heat-resistant material comprises ceramic fibres.

8. A burner assembly as claimed in claim 7, wherein the layer of heat-resistant material comprises a mat of chopped-strand ceramic fibres.

9. A burner assembly as claimed in claim 8, wherein the mat comprises a plurality of overlapping ceramic strands and wherein a plurality of overlapping strands are welded to one another where they touch.

10. A burner assembly as claimed in any of claims 7 to 9, wherein the ceramic fibres are sized.

11. A burner assembly as claimed in any of the preceding claims, comprising an elongate housing and wherein the first burner means and second burner means are also elongate.

12. A burner assembly as claimed in any of the preceding claims, wherein the second burner means completely covers the first burner means.

13. A burner assembly substantially as herein described, with reference to and as illustrated in the accompanying drawings.

14. A heating apparatus comprising a burner assembly as claimed in any of the preceding claims.