EP0844435A1

EP0844435A1 - Gas burner

Info

Publication number: EP0844435A1
Application number: EP96830593A
Authority: EP
Inventors: Feliciano Lasagni
Original assignee: Worgas Bruciatori SRL
Current assignee: Beckett Thermal Solutions SRL
Priority date: 1996-11-26
Filing date: 1996-11-26
Publication date: 1998-05-27

Abstract

The invention relates to a burner (1; 16), either of the atmospheric or premix type, comprising a tubular casing (2, 17) and enclosing a mixing element (6) capable, when used, of creating a mixture of gas and air inside the tubular casing (2; 17); the tubular casing (2; 17) is divided into lower semi-tubular element (12) with concavity facing up and an upper semi-tubular element (13) with concavity facing down; the upper semi-tubular element (13) has a plurality of flame ports (15) to allow the combustion mixture of gas and air out of the tubular casing (2; 17) and the said lower and upper semi-tubular elements (12, 13) are joined to each other through a substantially fluid tight connection in such a way that each element can expand independently of the other in axial direction.

Description

The present invention relates to a gas burner, either of the atmospheric or premix type.

The invention relates in particular to a gas burner with a high resistance to stress resulting from thermal expansion.

Gas burners known in prior art may be divided into two categories, namely, atmospheric burners and premix burners.

Atmospheric burners usually comprise a tubular casing, closed at both ends and coaxially enclosing a venturi tube consisting of a converging portion, a cylindrical throat and a diverging portion. The venturi tube may be a separate part fitted in the burner or it may form an integral part of the burner itself, made, for example, by die forming or other known methods.

The said tubular casing has a plurality of flame ports, usually at the top, designed to allow a combustion mixture of gas and air to flow out of it.

A nozzle injects gas into the opening of the venturi tube and, in accordance with the known principles of fluid mechanics, a certain quantity of air is also sucked into the opening of the venturi tube and mixes well with the gas in the aforesaid cylindrical throat. The gas/air mixture, in the desired and controlled stoichiometric proportions, is then dynamically compressed in the said diverging portion, is discharged into the tubular casing and allowed through the said flame ports into the atmosphere where it is burnt.

Other known types of atmospheric gas burners envisage only a throat and a diverging section or even just a tube-shaped section.

In premix gas burners, on the other hand, the gas and air are supplied by means (consisting typically of fans and mixers) which, in a manner similar to that achieved by the venturi device described above, create a premixture of gas and air outside the tubular casing and supply the combustion mixture to the aforesaid flame ports.

The mixture is ignited through auxiliary systems that do not form part of the subject-matter of the present invention.

The configuration and size of the aforesaid ports are such as to prevent the flame from returning into the tubular casing of the burner but to keep it adjacent to the outer surface of the casing. The flame ports may assume many different sizes and configurations. For example, they may be continuous rows of slits or groups of slits arranged in chequered fashion, offset with respect to each other, or they may be appropriately distributed holes or combinations of slits and holes distributed in any of various different ways, made in a lateral portion (which may even coincide with the entire lateral surface) of the tubular casing which will hereafter be referred to as the "flame port area".

The distance of the flame front from the surface of the tubular casing depends on the type of gas used, on the gas supply pressure and on the shape of the burner. In all cases, because of the nearness of the flame to the said tubular casing, a portion of the tubular casing itself (namely, the flame port area), depending on the type and category of the burner, reaches extremely high temperatures, with peaks of up to 600°C and over. In particular, under certain operating conditions, not frequent in well designed and constructed burners but always possible even in these, the temperature of at least part of the surface of the tubular casing (that around the flame port area) may become so high as to produce considerable deformation, resulting in stress and strain, in particular on the sides of the tubular casing. This deformation, if excessive in that it is normally prevented, is permanent and may lead to burner breakage or malfunctioning even when the overheating ceases. In some cases, such deformation may also make it dangerous to continue using the burner, producing a risk of serious damage to the apparatus where it is fitted or even to the room where it is used.

The aim of the present invention is to overcome the disadvantages mentioned above by providing a burner capable of resisting abnormally high temperatures without being permanently deformed and without reducing its efficiency or giving rise to hazardous situations.

The invention as characterized in the claims below, overcomes the abovementioned disadvantages by providing a gas burner of the type comprising a tubular casing closed at its axially opposite ends and enclosing a mixing element capable, when used, of creating a mixture of gas and air inside the tubular casing, characterized in that the said tubular casing is divided into a lower semi-tubular element with concavity facing up and an upper semi-tubular element with concavity facing down; the said lower and upper semi-tubular elements extending longitudinally along parallel axes, the upper semi-tubular element having a plurality of flame ports to allow the combustion mixture of gas and air out of the tubular casing and the said lower and upper semi-tubular elements being joined to each other through a substantially fluid tight connection and in such a way that each element can expand independently of the other in axial direction.

One of the advantages achieved by the present invention is basically that the tubular casing of the burner disclosed can be subjected to extremely high thermal shocks (on the upper and lower semi-tubular elements) without producing permanent deformations that can damage it or make its use dangerous.

The technical characteristics of the invention according to the abovementioned aim are described in the claims below and its advantages are apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate preferred embodiments of the invention and in which:

Figure 1 is a schematic elevation view, partially in cross section, of a burner made in accordance with the present invention;
Figure 2 is a schematic plan view of the burner illustrated in Fig. 1;
Figure 3 is a cross section view of the burner illustrated in Figs.1 and 2 obtained by cutting the burner through a plane III-III, shown in Fig. 1;
Figure 4 is a schematic elevation view, partially in cross section, of another embodiment of the burner disclosed by the present invention;
Figure 5 is a schematic plan view of the burner illustrated in Fig. 4;
Figure 6 is a cross section view of the burner illustrated in Figs. 4 and 5 obtained by cutting the burner through a plane VI-VI, shown in Fig. 4;
Figures 7, 8 and 9 illustrate alternative configurations of the flame ports for the air/gas mixture differing from the flame port area illustrated in Fig. 2.

With reference to Figs. 1 to 3, the numeral 1 indicates a gas burner as a whole, represented in the atmospheric version by way of example only, without thereby restricting the scope of the inventive concepts which may be applied also to burners of the premix type.

The burner 1 comprises a tubular casing 2 extending lengthways along an axis 3 which, when the burner is in use, is horizontal. The tubular casing 2, in cross section, forms a closed shape (in the embodiment illustrated, see Fig. 3, it is substantially ovoid in shape) with one end, illustrated on the right in Fig. 1, closed by a vertical end cap 5 and the other end, on the left-hand side, being closed by a flange 4 with a gas and air inlet port. Inside the tubular casing 2, there is a mixing element consisting of a venturi tube 6 extending along an axis parallel to the axis 3 and comprising, from left to right in Fig. 1, a converging portion 7, a cylindrical throat 8 and a diverging portion 9.

A feeder element, consisting of a nozzle 10, faces the inlet port of the tubular casing 2 through a hole 11 made in the central portion of the flange 4 (the inlet port mentioned above), being fitted at the inlet of the converging portion 7 so that, under operating conditions, it can inject a stream of gas into the converging portion 7 according to known injector technology.

The wall defining the lateral surface of the tubular casing 2 is divided into two portions, namely, a lower, elongated semi-tubular element 12, with concavity facing up and constituting the lower section of the tubular casing 2, and an upper, elongated semi-tubular element 13, with concavity facing down and constituting the upper section of the tubular casing 2. The two lower, horizontal edges of the upper semi-tubular element 13 are connected each to two longitudinal, parallel protrusions 14, whose length is (preferably) equal to the upper semi-tubular element 13 itself. These longitudinal protrusions 14, which hereafter will also be referred to as "guide means", basically constitute extensions of the corresponding edge of the upper semi-tubular element 13 and the spacing between them is slightly wider than the thickness of the lower semi-tubular element 12.

Each of the two upper horizontal edges of the lower semi-tubular element 12 is designed to slide into the space between two corresponding pairs of longitudinal protrusions 14 of the upper semi-tubular element 13 (in such a way as to form a sliding fit); the relative seal is determined by the length of the fit and by the closeness between the overlapping surfaces in such a way as to define a sort of localized leakage labyrinth seal.

The axial ends of the lower semi-tubular element 12 are rigidly connected to the aforesaid flange 4 and end cap 5, whilst one of the axial ends of the upper semi-tubular element 13 is connected to the flange 4 or to the end cap 5 (in a manner illustrated schematically because it is obvious to experts in the trade) in such a manner that, although the connection between the upper semi-tubular element 13 and the flange 4 or the end cap 5 offers a substantially fluid tight seal, at least one of the said axial ends, preferably the one labelled 13m connected to the end cap 5, can move in the axial direction. In the embodiment illustrated, the left-hand end 13f is fixed.

Alternatively, both ends might be left free to move.

A portion of the upper semi-tubular element 13, the top portion in the embodiment illustrated, has an area with a plurality of flame ports 15, starting at distances L1 and L2 from the ends of the tubular casing 2 and hereafter referred to as "flame port area" 13a. In the embodiment illustrated in Fig. 2, the flame ports consist of a series of apertures (preferably but not necessarily slits) parallel to each other and perpendicular to the aforesaid axis 3. These flame ports 15 may be arranged in any manner, typically along one or more adjacent longitudinal rows (see Fig. 7) or in shorter polygonal groups arranged in line or in chequered fashion (see Fig. 8) or, as mentioned in the introduction, they may be circular, as illustrated in Fig. 9.

During use, the gas is injected into the venturi tube 6 through the nozzle 10 and entrains a flow of air through an appropriate port (not illustrated) made in the aforementioned flange 4. The streams of air and gas enter the converging portion 7 of the venturi tube 6 together and are well mixed before leaving the venturi tube 6 through the diverging portion 9. The gas/air mixture then leaves the tubular casing 2 through the flame ports 15 and is ignited by known means outside the tubular casing 2 adjacent to the flame ports 15.

When the burner 1 is cold, the tubular casing 2 has the nominal dimensions, depending on burner design, and is not subjected to stress.

When the gas/air mixture leaving through the flame ports 15 is ignited, the entire tubular casing 2 starts to expand in the axial direction and there is more thermal expansion around the flame port area 13a of the upper semi-tubular element 13 than there is on the semi-tubular element 12 since the area 13a is in direct contact with, or in the vicinity of, the flame. The difference in the thermal expansion does not subject the upper semi-tubular element 13 to dangerous stress (and even less so the lower semi-tubular element 12) since the upper semi-tubular element 13 is connected in such a way as to allow it to slide axially relative to the semi-tubular element 12 thanks to the aforementioned fit between its longitudinal protrusions 14 and the edges of the lower semi-tubular element 12 itself, the upper semi-tubular element 13 being, therefore, free to expand without obstructions.

Dangerous stresses are those which can give rise to peak strain on the structure (labelled 26 in Fig. 2) adjacent to the flame ports 15, causing the structure and the flame ports 15 themselves to deform. If the shape of the flame ports 15 is modified, there is the risk of the flame flashing back into the burner 1, thus reducing the efficiency of the entire burner 1 or even creating hazardous conditions during its operation.

Thanks to the design of the burner 1 described above, however, the semi-tubular element 13 can expand freely with respect to the element 12 below it, thus making it possible to avoid the peak strain conditions mentioned above.

Figs. 4 to 6 illustrate a burner 16 constituting an alternative embodiment of the burner 1 described above. Where possible, the parts of the burner 16 are labelled with the same reference numbers as the corresponding parts of the burner 1.

In the burner 16, the upper semi-tubular element 13 does not have the longitudinal protrusions 14 but is placed directly onto the upper open end of the lower semi-tubular element 12. The element 12 has an opening 12s which is slightly larger than the aforementioned flame port area 13a. As shown in Fig. 5, in the preferred embodiment, the opening 12s is longer than the flame port area and, for this reason, the distances L3 and L4 from the ends of the tubular casing 17 are shorter than the distances L1 and L2 mentioned previously.

The portions of the edge of the upper semi-tubular element 13 overlap corresponding portions of the edge of the lower semi-tubular element 12 so that the assembly defined by the

semi-tubular elements

12 and 13 forms a substantially closed, fluid tight, tubular casing 17, the seal in this case, too, being provided by the overlapping of the metal sheeting, as described in more detail below.

In this regard, the numeral 20 in Fig. 6 indicates generic upper guide means (not essential) for the upper semi-tubular element 13, two portions 13b of whose edge are placed over and in contact with the corresponding portions 12b of the edge of the lower semi-tubular element 12. The means 20 are designed to prevent the end portions 13b of the edges of the upper semi-tubular element 13 from being "lifted off" the corresponding edges 12b below and breaking the seal when the upper semi-tubular element 13 expands. Alternatively, a similar effect may be obtained by providing guides 20g, whose lower ends are integral with the lower semi-tubular element 12 and whose upper ends overlap the upper semi-tubular element 13. Yet another alternative would be to envisage bands 20f distributed along the length of the

semi-tubular elements

12 and 13 and overlapping both elements (see Figs. 4 and 6).

Alternatively, both ends might be left free to move.

The burner 16 works in exactly the same way as the burner 1. In particular, when the tubular casing 17 is heated by the flame, the expansion of the upper semi-tubular element 13 occurs in the same way as that described with reference to the burner 1, that is, without any obstructions and without creating undue strain capable of damaging the upper semi-tubular element 13.

From the above description, it is clear that the

burners

1 and 16 fully achieve the abovementioned aims in that they are capable of withstanding overheating (or high temperature differences between the upper and lower elements) of the surfaces directly concerned without creating permanent deformations in the

burners

1 and 16 such as to reduce their efficiency or give rise to hazardous situations.

As stated above, the inventive concepts described can be applied also to premix burners in a manner obvious to an expert in the trade in the light of the above description. The dashed line in Fig. 5 indicates the generic element 6p for premixing the gas and air mixture outside the tubular casing 2, the said mixture being then forced into the tubular casing under pressure to reach the combustion area.

The invention described can be subject to modifications and variations without thereby departing from the scope of the inventive concept.

For example, the longitudinal protrusions 14 might be integral with the upper horizontal edges of the lower semi-tubular element 12 and the lower edges of the upper semi-tubular element 13 might be housed between corresponding pairs of longitudinal protrusions 14.

Moreover, all the details of the invention may be substituted by technically equivalent elements.

Claims

A gas burner, either of the atmospheric or premix type, comprising a tubular casing (2, 17) associated with an element (6) for mixing gas and air and capable, when used, of creating a mixture of gas and air inside the tubular casing (2, 17), characterized in that the said tubular casing (2, 17) is divided into a lower semi-tubular element (12) with concavity facing up and an upper semi-tubular element (13) with concavity facing down; the said lower and upper semi-tubular elements (12, 13) extending longitudinally along parallel axes, the upper semi-tubular element (13) having a plurality of flame ports (15) to allow the combustion mixture of gas and air out of the tubular casing (2, 17) and the said lower and upper semi-tubular elements (12, 13) being joined to each other through a substantially fluid tight connection and in such a way that each element can expand independently of the other in axial direction.
The burner according to claim 1 characterized in that the two free edges of the upper semi-tubular element (13), parallel to the said axes, are equipped with guide means (14) designed to mate with the corresponding free edges, also parallel to the said axes, of the lower semi-tubular element (12).
The burner according to claim 1, characterized in that the two free edges of the lower semi-tubular element (12), parallel to the said axes, are equipped each with guide means (14) designed to mate with the corresponding free edges, also parallel to the said axes, of the upper semi-tubular element (13).
The burner according to claim 2 or 3 characterized in that the said guide means comprise, for each of the said free edges, a pair of longitudinal parallel protrusions (14) equal in length to the corresponding semi-tubular element (12, 13), the spacing between the longitudinal protrusions (14) being slightly wider than the thickness of the semi-tubular element (12, 13) connected to it.
The burner according to claim 1 characterized in that upper semi-tubular element (13) is placed over and in contact with the lower semi-tubular element (12).
The burner according to claim 5 characterized in that two portions (13b) of the edge of the said upper semi-tubular element (13) are placed over and in contact with the corresponding portions (12b) of the edge of the lower semi-tubular element (12), overlapping in such way as to provide a fluid tight seal.
The burner according to claim 1 characterized in that the semi-tubular element (13) is placed over the upper portion of the lower semi-tubular element (12); the said upper semi-tubular element (13) having made in it the said plurality of flame ports (15) defining a flame port area (13a); the said lower semi-tubular element (12) having an opening (12s) which is almost the same size as the flame port area (13a).
The burner according to claim 7 characterized in that the said opening (12s) is slightly larger than the flame port area (13a).
The burner according to claims 5 to 8 characterized in that it envisages guide means (20) for the upper semi-tubular element (13) designed to prevent the end portions (13b) of the edges of the upper semi-tubular element (13) from being lifted and breaking the seal when the upper semi-tubular element (13) slides relative to the lower semi-tubular element (12).
The burner according to claim 9 characterized in that the said guide means (20) consist of guides (20g), whose lower ends are integral with the lower semi-tubular element (12) and whose upper ends overlap the upper semi-tubular element (13).
The burner according to claim 9 characterized in that the said guide means (20) consist of bands (20f) distributed along the length of the semi-tubular elements (12) and (13) and overlapping both of these elements.
The burner according to any one of the foregoing claims from 1 to 8 characterized in that the said tubular casing (2, 17) is associated with the means (6) for mixing gas and air; there being envisaged means (10) for supplying a stream of gas/air mixture to the mixing means (6) when the burner is used.