Gas burner element

Description

[0001] The invention relates to gas burners.

[0002] For certain applications gas burners with cylindrical elements for surface combustion of a gas/air mixture are required. We have had difficulty in making the elements, at economic cost, with the necessary provision for passage of the gas mixture. We have for example not succeeded with self porous foam ceramic, made by impregnation of an open cell polymer foam with ceramic slip and subsequent firing, because stresses in the resulting elements result in their early breakage in service. Casting from bonded ceramic fibres also proved difficult if pins were used as conventional for the necessary passages for the gas mixture. Such pins, as used for example in the manufacture of flat elements in our U.K. Patent Specification GB-A-1 436 842, are complicated and in practice unworkable for a cylindrical element, in the customary conditions of vacuum forming from a slurry of fibre and bonding clay.

[0003] United States Patent Specification US-A-4 416 619 shows a porous, cylindrical ceramic burner ('reactor') where a gas/air mixture passes through the pores of the body to burn at the surface. The porosity is not discussed but no doubt includes a degree of porosity such that the burner can be self-aerating, the gas/air passages afforded by the porosity offering only a low flow resistance.

[0004] United States Patent Specification US-A-3 881 858 discloses a planar gas burner element, comprising, semi-enclosed ceramic walled combustion chambers or slots (15) fed with a gas/air mixture by a further, longitudinally disposed slot (93).

[0005] The invention provides a self-aerating radiant gas burner disposed to be fed with gas/air mixture by means of a gas jet directed into a venturi and comprising a heat radiant element consisting of a body of unitary and cylindrical shape and of low heat conductivity ceramic material, the mixture entering a distribution chamber in flow communication with a first face of said body, said body having gas/air passages in order to pass the gas/air mixture from said first face of the body to a substantially unobstructed second face of the body, which constitutes a combustion zone of the burner where the entire combustion of the gas/air mixture takes place on the surface of said heat radiant element without striking back of flame into the body, where said gas/air passages are formed by means of two multiple series of slots extending in said body, the slots of the first series being 0.2 to 1.3 mm wide and opening to said second face of the body and the slots of the second series being aligned at an angle to the slots of the first series and extending from said first face of the body towards the second face so that the two series intersect within said body to form said gas/air passages at the positions of intersection.

[0006] The first series of slots are dimensioned to secure combustion without striking back of flame into the body, allowing for different gases and throughputs, without the flame front propagating back in the gas mixture or the heat front creeping back in the ceramic itself.

[0007] Manufacturing requirements are conveniently met by a cast or moulded construction with the slots made in situ or cut afterwards, according to the burner (element) shape. A preferred angle of the two series to each other is 90° though other angles can be used. Large elements can be made without the cost of custom made vacuum forming tools for each design.

[0008] Conveniently in a cylindrical element the slots of one series are generally axially disposed of the element and those of the other series generally circumferentially disposed. Preferably, to minimise hoop stress, the slots at the combustion face are aligned substantially axially of the element. Such cylindrical burners can be used with the gas/ air mixture passing to burn at the outer face or, for example for an annealing furnace for wire or tube, with the mixture passing inwards to burn at the inner face. A plenum chamber surrounding the burner is then required, instead of gas/air mixture passing outwards, but no other change.

[0009] Desirably in all forms of the element the edges of the slots at the combustion face are chamfered to bring the flame front somewhat back into the slot and improve visible production of radiant energy.

[0010] Suitable materials include bonded refractory ceramic fibre, which is well known in the art. Both as such and in relation to the microstructure formed on casting and firing, it is described in detail in our U.K. Patent Specification GB-A-1 436 842 the disclosure of which is incorporated herein by reference. The elements retain the high thermal shock resistance, low thermal conductivity and low thermal capacity referred to in that specification.

[0011] The elements may be mounted in metal or ceramic holders fed with gas and air by a jet and venturi in the conventional way for a self aerating burner. They may be of any generally cylindrical shape, round or not, the term being indicative of radiation of heat over substantially 360° or at least a large arc.

[0012] Gas burner elements according to the invention are illustrated by way of example in the accompanying drawings in which:

Fig. 1 is a schematic part sectional view of an element mounted for feeding from a gas jet through a venturi;

Figs. 2 and 3 are detail sectional views of the body of the burner element, Fig. 2 being in a plane through the longitudinal axis of the element and

Fig. 3 in a plane transverse of the axis;

Fig. 4 is a partial view of a tool for vacuum casting of the element;

Fig. 5 is a view of the end cap of such a tool;

Fig. 6 is a part view of an alternative burner element; and

Fig. 7 is a fragmentary view of part of the element of Fig. 6 from the interior.

[0013] In Fig. 1 there is shown a burner body 1 of vacuum cast bonded refractory ceramic fibre such as is referred to above. This particular example is 10.2 cm outside diameter and 7.8 cm internal diameter. The body has a distribution bore 2, and is mounted on a schematically indicated mounting plate of steel 3 carrying a venturi tube 4 which is 26 cm long and 5 cm diameter and is also made of steel. The venturi tube is fed with natural gas (methane) at 8" (ca. 20 cm) water gauge from a conventional jet 5 of which the manufacturers reference is "Amal 470" (1.9 mm diameter). Externally of the body a series of multiple slots 6 is provided in the form of 59 turns of a continuous spiral groove machined by a high speed slitting wheel traversed past the body 1 while the body is rotated. A closed cap 7 of the same material as the body closes the open end of the body.

[0014] Details of the slots are seen in Figs. 2 and 3 where the width is seen as 0.9 mm in the axial direction of the body, the radial depth as 6.5 mm, the axial spacing 4 mm. The wall thickness of the body is 1.2 cm. Internally the body has formed in it 36 equidistantly spaced vertical slots 0.9 mm wide in the circumferential direction and 7 mm deep in the radial direction. These slots are referenced 8. The sum of the depths of the slots is 1.35 cm so that they overlap or intersect within the body to the extent of 0.15 mm and form in effect a rectangular array of small gas passages at positions indicted at 9 in Figs. 2 and 3.

[0015] The element of Fig. 1 is manufactured on a tool which is shown in Fig. 4. A per se conventional filter casting mesh 10 in cylindrical form is surrounded by a schematically indicated array of metal strips 11 to form the slots 8. The mesh and strips are fitted into end caps 12 one of which is shown in Fig. 5. Filter casting proceeds in the ordinary way and it is found surprisingly that on removal of one of the end caps the tool can be removed without undue friction or damage from the green body formed, which is fired in the ordinary way.

[0016] In Fig. 6 an alternative element is shown in which the slots 8 are replaced by much wider slots 13 which in this particular example are machined into the filter cast body rather than cast in situ, though they can also be cast. This construction gives a gas passage in the form of a slot fully open to the exterior as shown at 14 in Fig. 7 rather than the small gas passages 9 referred to in relation to Fig. 1. It is found that both constructions give an effective control of the passage of the gas/air mixture entering the distribution bore.

Claims

1. A self-aerating radiant gas burner disposed to be fed with gas/air mixture by means of a gas jet directed into a venturi and comprising a heat radiant element consisting of a body of unitary and cylindrical shape and of low heat conductivity ceramic material, the mixture entering a distribution chamber in flow communication with a first face of said body, said body having gas/air passages in order to pass the gas/air mixture from said first face of the body to a substantially unobstructed second face of the body, which constitutes a combustion zone of the burner where the entire combustion of the gas/air mixture takes place on the surface of said heat radiant element without striking back of flame into the body, wherein said gas/air passages are formed by means of two multiple series of slots extending in said body, the slots of the first series being 0.2 to 1.3 mm wide and opening to said second face of the body and the slots of the second series being aligned at an angle to the slots of the first series and extending from said first face of the body towards the second face so that the two series intersect within said body to form said gas/ air passages at the positions of intersection.

2. A gas burner according to claim 1 characterised in that, to minimise hoop stress, the slots at the combustion face are aligned substantially axially of the element.

3. A gas burner according to either preceding claim, characterised in that the edges of the slots at the combustion face are chamfered to bring the flame front somewhat back into the slot and improve visible production of radiant energy.

Ansprüche

1. Selbstbelüftender Strahlungsgasbrenner, vorgesehen zur Speisung mit einem Gas/Luftgemisch mittels einem in einen Lufttrichter geleiteten Gasstrahl, mit einem aus einem einteiligen zylinderförmigen Körper bestehenden Wärmestrahlungselement aus einem Keramikmaterial mit niedriger Wärmeleitfähigkeit, wobei das Gemisch in eine Verteilungskammer eintritt, die mit einer ersten Fläche des besagten Körpers in Fussverbindung steht, wobei der besagte Körper Gas/Luftdurchtrittskanäle aufweist, durch die das Gas/Luftgemisch von der besagten ersten Fläche des Körpers zu einer im wesentlichen freien zweiten Fläche des Körpers fliessen kann, die einer Verbrennungszone des Brenners bildet, wo die gesamte Verbrennung des Gas/Luftgemisches auf der Oberfläche des besagten Wärmestrahlungselementes stattfindet, ohne dass dabei die Flamme in den Körper zurückschlägt, wobei die besagten Gas/Luftdurchtrittskanäle aus zwei Gruppen von sich in den Körper erstreckenden Schlitzen gebildet werden, wobei die Schlitze der ersten Gruppe 0,2 bis 1,3 mm breit sind und sich zu der besagten zweiten Fläche des Körpers hin öffnen und die Schlitze der zweiten Gruppe in einem Winkel zu den Schlitzen der ersten Gruppe ausgerichtet sind und sich von der besagten ersten Fläche des Körpers gegen die zweite Fläche erstrecken, so dass sich die zwei Gruppen im besagten Körper schneiden, um an den Schnittpunkten die besagten Gas/Luftdurchtrittskanäle zu bilden.

2. Gasbrenner nach Anspruch 1, dadurch gekennzeichnet, dass die Schlitze im wesentlichen axial gegen das Element ausgerichtet sind, um die Umfangsspannung auf ein Minimum zu reduzieren.

3. Gasbrenner nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Kanten der Schlitze auf der Verbrennungsfläche abgerundet sind, um die Flammenfront etwas in den Schlitz zurückzubringen und die sichtbare Erzeugung von Strahlungsenergie zu verbessern.

Revendications

1. Brûleur à gas rayonnant et à auto-aération adapté pour être alimenté avec un mélange gaz/ air au moyen d'un jet de gaz qui est dirigé dans un venturi, ce brûleur comprenant un élément rayonnant thermiquement qui comprend un corps monobloc de forme cylindrique fait en un matériau céramique à faible conductibilité thermique, ledit mélange pénétrant dan une chambre de distribution qui est en communication avec une première face dudit corps, ce dernier présentant des passages gaz/air qui permettent audit mélange gaz/air de passer de ladite première face du corps à une seconde face de celui-ci pratiquement non-obstruée, ladite seconde face formant une zone de combustion du brûleur dans laquelle a lieu la combustion totale du mélange gaz/air sur la surface dudit élément rayonnant thermiquement, sans qu'il puisse se produire un retour de flamme dans ledit corps, lesdits passages gaz/air étant formées par deux séries multiples de fentes s'étendant dans ledit corps, les fentes de la première série ayant une largeur entre 0,2 et 1,3 mm et s'ouvrant vers ladite seconde face du corps, tandis que les fentes de la seconde série sont alignées sous un certain angle par rapport aux fentes de la première série et s'étendent à partir de la première face du corps jusqu'à la seconde face de telle manière que les deux séries se croisent à l'intérieur dudit corps pour que lesdits passages gaz/air soient formés aux points de croisement.

2. Brûleur à gaz selon la revendication 1, caractérisé en ce que, pour réduire au minimum les contraintes circonférentielles, les fentes situées à la face de combustion sont alignées à peu près axialement par rapport à l'élément.

3. Brûleur à gaz selon l'une ou l'autre des revendications précédentes, caractérisé en ce que les bords des fentes situés à la face de combustion, sont chanfreinés pour ramener le front de flammes quelque peu en arrière dans la fente afin d'améliorer ainsi une production visible de l'énergie rayonnante.

Drawing