CA2524136A1 - Flame tube for a burner for hot gas generation - Google Patents

Abstract

A flame tube for a burner for hot gas generation has a hollow body which forms an at least partially enclosed combustion chamber. The hollow body has a first end which is designed for connection to a flame generation unit. The hollow body also has a lateral surface, on which at least one branch tube is arranged. The branch tube, on its outer side, is connected to an intermediate piece and the intermediate piece is secured to the lateral surface.

Description

FLAME TUBE FOR A BURNER FOR HOT GAS GENERATION
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a burner for hot gas generation in mobile field kitchens, and more particu-larly to a flame tube for use in such a burner. Moreover, the invention also relates to a process of manufacturing such a flame tube.

[0002] Mobile field kitchens are required in particular if a large number of people have to be catered remote from civilization for a prolonged period of time. Typical applica-tions include military exercises or any other deployment of large numbers of troops, but also humanitarian work, for exam-ple disaster assistance in an earthquake zone. For these uses, the field kitchens have to be mobile and in particular robust.
This means that it must be possible for the field kitchens to be transported, constructed and operated even under greatly fluctuating demands and difficult conditions. For example, it must be possible for them to be transported on a vehicle even on impassable terrain, which can lead to corresponding impacts and mechanical loads. Furthermore, the mobile field kitchens must work reliably both in hot environments, for example in the desert, and in very cold environments, for example in winter in mountainous areas. On the other hand, it is desirable for the mobile field kitchens, despite the abovementioned demands, to allow professional preparation of varied dishes for a large number of people.

[0003] The present assignee markets field kitchens of this type and cooking modules for such applications. They gen-erally use diesel or multi-fuel burners to heat the cooking zones. It must be possible for the burners to be operated with fuels of varying quality, and moreover the burners have to allow reliable operation under the boundary conditions men-tioned above. Moreover, a high heating power is required in order to heat large-area cooking zones for the preparation of large quantities of dishes. Hitherto, for its mobile field kitchens and cooking zones, the assignee has used flame tube with a hollow body to which 15 branch tubes were welded. The branch tubes are used to discharge the hot gas (flue gasj gen-erated in the hollow body, and they are arranged in such a way that the hot gas which flows out heats a surrounding volume of air and/or a hotplate, a grill, a water bath or the like.

(0004) However, the flame tubes which have been used hitherto have a limited use or service life, in particular when employed under fluctuating, harsh conditions. It has been found that the hot gas which is passed through the branch tubes leads to the formation of scale or even complete dissolution of mate-rial around the branch tubes. After prolonged operation of the flame tubes which have been used hitherto, holes are formed around the branch tubes, and in some cases branch tubes actu-ally fall into the interior of the flame tube. Furthermore, the flame tubes which have been used hitherto are relatively com-plex and correspondingly expensive to produce, since 15 branch tubes have to be individually welded to the lateral surface of the hollow body.

[0005] To reduce the investment and operating costs of the field kitchens and cooking modules, there is a demand for a flame tube which allows a longer service life combined with lower production costs.

[0006] DE 42 444 400 A1 discloses a burner with a flame tube, the lateral surface of which is studded with branch tubes. In this case, the branch tubes are not used to discharge flue gas from the combustion chamber of the hollow body, but rather, on the contrary, to return flue gas which has already escaped from the flame tube. This return of flue gas is known as recirculation and serves to reduce the emission of nitrogen oxides from the burner by the flue gas being returned to the combustion process. Unlike in the above-described burners mar-keted by the assignee, the branch tubes of the burner disclosed in DE 42 44 400 A1 therefore do not have the hot flue gas flow-ing through them from the inside outwards, but rather cooled flue gas flows back into the combustion chamber from the out-side. Problems with the formation of scale and disappearance of material in the region of the branch tubes are not described in DE 42 44 400 A1.

[0007] DE 42 32 181 A1 discloses another burner with a flame tube, which is provided with lateral branch tubes in the region of its lateral surface. In this case, the branch tubes only project into the interior of the hollow body, i.e. into the combustion chamber, and according to the description given in DE 42 32 181 A1 they serve as stabilizers for stabilizing the flame. This prior art likewise does not address problems relating to the formation of scale and/or removal of material in the region of the branch tubes.
SUMMARY OF THE INVENTION

[0008] In view of this background, it is an object of the present invention to provide a flame tube for a burner for hot gas generation, which, in mobile use under fluctuating conditions, allows a long service life.

[0009] It is another object to provide a flame tube for a burner for hot gas generation, which can be produced at low cost.

[0010] It is yet another object to provide a flame tube for a burner offering a good heat distribution for large-area cooking zones.

[0011] According to one aspect of the invention, there is provided a flame tube for a burner comprising a flame gen-eration unit, the flame tube having a hollow body forming an at least partially enclosed combustion chamber, and at least one branch tube connected to the hollow body, the hollow body hav-ing a first end designed for being connected to the flame gen-eration unit, and a lateral surface on which the at least one branch tube is arranged, wherein the branch tube, on its outer side, is connected to an intermediate piece, and wherein the intermediate piece is secured to the lateral surface.

[0012] According to another aspect of the invention, there is provided a method for producing a flame tube for a burner having a flame generation unit, the method comprising the steps of: providing a hollow body having a lateral surface for forming an at least partially enclosed combustion chamber, the hollow body having a first end designed for connection to the flame generation unit, and arranging at least one branch tube on the lateral surface, wherein the step of arranging includes a step of connecting the branch tube, on its outer side, to an intermediate piece, a step of securing the interme-diate piece to the lateral surface.

[0013] Preferably, the intermediate piece is welded to the lateral surface.

[0014] The present invention is based on the idea of using an intermediate piece in order to secure the at least one branch tube - at least additionally - to the lateral surface of the hollow body. On account of the fact that the intermediate piece is connected to the branch tube on its outer side, the intermediate piece is not in direct contact with the hot flue gas in the interior of the hollow body. If any flue gas is able to reach the intermediate piece, which depends on the geometry of the branch tubes and the spatial conditions around the flame tube, it has already cooled compared to the temperatures of the hot flue gas in the interior of the hollow body.

[0015] Furthermore, the very hot flue gas from the in-terior of the hollow body also does not flow past the interme-diate piece with its high kinetic energy. Overall, therefore, the intermediate piece is exposed to lower energy loads than the branch tube itself.

[0016] Tests and analyses carried out by the Assignee have shown that the problems encountered hitherto with the formation of scale and the removal of material occurred in particular in those regions where the branch tubes were hith-erto welded to the lateral surface of the hollow body. One possible cause of this could be the "prior damage" to the mate-rial of the lateral surface and the branch tube, in particular caused by welding.

[0017] Since the securing points of the new intermedi-ate piece have been withdrawn from direct contact with the hot flue gas, significantly reduced formation of scale and - at least in the long-term tests carried out to date by the as-signee - no significant disappearance of material are now found. In other words, the new flame tube, in which the branch tubes are secured to the lateral surface by way of said inter-mediate piece, has a significantly longer service life, the end of which is not yet foreseeable in the tests which the assignee is currently carrying out.

[0018] Furthermore, the manufacturing costs are reduced by the use of the new intermediate pieces, since, on account of the new intermediate pieces, the branch tubes can be secured to the lateral surface more easily yet nevertheless with a high degree of stability.

[0019] Finally, on account of the new intermediate pieces, the branch tubes can be very easily secured at various angles of inclination and at virtually any desired positions of the hollow body, so that the heat distribution of the new heat-ing tube can be flexibly optimized.

[0020] In a refinement of the invention, the branch tube and the intermediate piece are of two-part design, with the branch tube and the intermediate piece preferably being welded to one another.

[0021] Alternatively, it would generally also be con-ceivable for the intermediate piece and the branch tube to be formed integrally (as a single piece), for example with the aid of a suitable casting mould. However, the preferred refinement allows greater flexibility of production and also allows the use of standardized components.

[0022] It is preferable for the branch tube and inter-mediate piece - like the intermediate piece and lateral surface - to be welded together, since this joining process allows very robust flame tubes which are suitable for the intended applica-tion described in the introduction to be produced in a very inexpensive way.

[0023] In a further refinement of the invention, the branch tube is secured to the lateral surface only by way of the intermediate piece.

[0024] As an alternative, it would generally also be possible for the intermediate piece to be used in addition to direct securing of the branch tube to the lateral surface.

[0025] The preferred refinement has the advantage that there is no join in the immediate vicinity of the hot gas stream, i.e. the material which is directly exposed to the hot gas stream does not suffer any "prior damage". The risk of the disappearance of material in the region of the join between branch tube and lateral surface is thereby reduced still fur-ther. The service life of the new flame tube is then even longer.

[0026] Irrespective of this, however, when producing the new flame tube it may be advantageous for the branch tube initially to be provisionally fixed to the lateral surface by means of a "small" weld, solder or adhesive spot, in order to facilitate the subsequent securing of the branch tube with the aid of the intermediate piece and the correct alignment of the branch tube. If it is ensured that no "material damage" which is directly exposed to the hot gas stream is formed during this provisional securing of the branch tube, the advantages of this configuration are still achieved to the same extent.

[0027] In a further refinement, the branch tube is fit-ted flush onto the outer side of the lateral surface.

[0028] In other words, in this refinement of the inven-tion, the branch tube does not project into the interior (com-bustion chamber) of the hollow body. This refinement has the advantage that there are no materially weak edges and projec-tions in the area immediately affected by the flame and the hot gases flowing within the combustion chamber. The risk of the removal of material, with the associated restrictions in the service life, is further reduced. Furthermore, this refinement also contributes to simpler and less expensive production while achieving the same production quality.

[0029] In a further refinement, the lateral surface has an opening with a first internal diameter below the branch tube, and the branch tube has a second internal diameter, the second internal diameter being greater than the first internal diameter.

[0030] This refinement contributes to further simplify-ing production of the new flame tube, since in this refinement the branch tube can easily be fitted onto the outer side of the lateral surface. Furthermore, this configuration further re-duces the risk of material being removed at or around the branch tube.

[0031] In a further refinement, the intermediate piece is an angle piece with at least two and preferably three limbs which surround the branch tube.

[0032] This refinement achieves very stable securing of the branch tube to the lateral surface, in particular if the branch tube does not have or has at most a slight provisional securing to the lateral surface. The stability is particularly advantageous for mobile use of the new flame tube under harsh conditions. Furthermore, in this configuration it is very easy to secure the branch tubes) with a constant high quality stan-dard.

[0033] In a further refinement, the lateral surface has a first half and a second half, as seen in the circumferential direction, and a plurality of branch tubes are secured only to the first half.

[0034] This refinement is particularly advantageous for the new flame tube to be used as a heating source for mobile field kitchens and the like, since the new flame tube in this case allows hot flue gas to flow out in a defined, preferential direction. This in particular allows very efficient heating of a hotplate, grill or the like located directly above the branch tubes.

[0035] In a further refinement, the second half is com-pletely closed.

[0036] By contrast, many flame tubes have holes or other inlets or outlets all the way around their outer circum-ference, whether for manufacturing reasons or as inlet openings for recirculation of flue gas. The complete closure of the half which is not provided with branch tubes seals off the flame tube on one side. This inter alia makes it possible to ensure that it is impossible for any fuel to escape in the region of the second half even in the event of the burner misfiring. As a result, the new flame tube can be optimally used to heat hot-plates, grill plates or the like in mobile field kitchens.

[0037] Moreover, this refinement allows the second half of the flame tube to be used in a burner for a mobile field kitchen without any special insulation or sealing. Conse-quently, heat can be radiated out via the second half, which avoids excessively high thermal stresses on the material in the region of the second half and therefore likewise contributes to lengthening the service life of the new flame tube.

[0038] In a further refinement of the invention, the at least one branch tube is a hot gas outlet.

[0039] This refinement ties in with the above-described use of the flame tube for heating hotplates, grills and the like. The advantages of the invention are particularly benefi-cial for this use. The use of the branch tube as hot gas outlet allows very efficient heating of even large-area hotplates, as are required to cater for a large number of people. The prob-lems described above occur to a particular extent for these applications, on account of the high energy load on the branch tubes. In principle, however, the present invention can also be used to advantageous effect for branch tubes where the branch tubes are used for recirculation, i.e. to return partially cooled flue gas to the combustion chamber.

[0040] In a further refinement, the hollow body has a second end which is at least substantially closed.

[0041] This refinement too is particularly advantageous if the new flame tube is to be used to heat hotplates, grills and the like in a mobile field kitchen. On account of the hol-low body being closed at the second end, the emergence of hot gas is concentrated on the branch tube(s), which allows par-ticularly efficient heating of large-area hotplates.

[0042] In a further refinement, the new flame tube has at least four branch tubes which are arranged on one half of the lateral surface in such a way that when the half is seen in plan view they approximately define a rectangle. In a particu-larly preferred configuration, there are precisely four branch tubes.

[0043] Practical tests carried out by the Assignee have shown that a flame tube of this type allows particularly effi-cient and uniform heating of a large-area hotplate, such as for example a grill. This was not initially expected, since the flame tubes that have been used hitherto always employed a very much larger number of branch tubes. Furthermore, it has hith-erto been deemed necessary to use significantly more branch tubes in the direction of the second end of the flame tube (i.e. remote from the flame generation unit) than further back, in order on the one hand to allow a short and compact overall form and on the other hand to compensate for the radiant heat in the region of the flame generation unit. Surprisingly, it has now been found that an excellent distribution of heat over a rectangular cooking area can be achieved even using four uniformly distributed branch tubes, which are preferably ar-ranged in the region of the second end of the flame tube.

[0044] In a further refinement, the four branch tubes, include two first branch tubes, which are arranged closer to the first end, and two second branch tubes, which are arranged further away from the first end, the two first branch tubes being inclined towards the first end, while the two second branch tubes are inclined away from the first end.

[0045] This refinement likewise contributes to an opti-mum distribution of heat if the new flame tube is used to heat a large-area, rectangular hotplate. Inclining the first two branch tubes towards the rear means that the hot gas flowing through them is diverted by more than 90°. By contrast, the hot gas flows out of the combustion chamber through the two second tubes with considerably less diversion. It has been found that in this configuration approximately 60~ of the hot flue gas flows through the second branch tubes, whereas only approxi-mately 40~ of the hot flue gas flows through the first branch tubes. However, this uneven distribution is compensated for by the fact that more radiant heat is produced in the rear region of the flame tube, on account of the flame generation unit being arranged there. Overall, this preferred refinement leads to an excellent heat distribution over a large-area cooking hob, while on the other hand the production costs are signifi-cantly reduced compared to the flame tube that has been used hitherto. Furthermore, it has been found that the inclination allows good dissipation of expansion forces yet nevertheless produces a stable seat for the branch tubes.

[0046] In a further refinement, the new flame tube has a metal radiation protection sheet which is suspended from the hollow body with a clearance between them. It is preferable for the metal radiation protection sheet to be angled around the hollow body.

[0047] By contrast, hitherto either a non-metallic in-sulation or a metal radiation protection sheet which was welded to the hollow body has been used. Securing the new metal radia-tion protection sheet to the hollow body with a clearance be-tween them, i.e. with freedom for relative movement, by con-trast, avoids thermally induced material stresses. The forma-tion of cracks and the like is reduced. The absence of a non-metallic insulation around the hollow body likewise reduces the risk of the formation of cracks, since the hollow body can dissipate heat all the way around.

[0048] It will be understood that the features men-tioned above and those yet to be explained below can be used not only in the combinations described but also in other combi-nations or as stand-alone measures without departing from the scope of the present invention.
BRIEF DESCRIPTION OF THE FIGURES

[0049] Exemplary embodiments of the invention are il-lustrated in the drawings and explained in more detail in the description which follows. In the drawing:

[0050] Figure 1 shows a partially sectional side view of a burner having a flame tube according to the invention, [0051] Figure 2 shows the burner from Figure 1 in a view along line II-II from Figure 1, [0052] Figure 3 shows a simplified diagrammatic il-lustration of a further exemplary embodiment of the new flame tube in the form of a cross-sectional view, and [0053] Figure 4 shows a likewise simplified illustra-tion of an exemplary embodiment of the new flame tube in the form of a plan view onto the branch tubes.
DESCRTPTION OF PREFERRED EMBODIMENTS

[0054] In Figure 1, a burner comprising an exemplary embodiment of the new flame tube is denoted overall by refer-ence numeral 10. The burner 10 is in this case what is known as a push-in burner, which in the position shown in Figure 1 can be pushed into a cooking module (not shown here), as marketed by the Assignee for the present invention under the name BFK, from left to right. The new flame tube is denoted overall by reference numeral 12.

[0055] The flame tube 12 has a hollow body 14, which is in this case cylindrical in form. This is advantageous for manufacturing reasons and with a view to heat distribution.
However, the invention is not restricted to this form and can equally be used for other shapes of hollow bodies for flame tubes.

[0056] That end 16 of the hollow body 14 which is on the left-hand side in Figure 1 is designed in such a way that it can be connected to a flame generation unit 18. The flame generation unit 18 includes in particular a nozzle 20, which is fed with fuel via a feed line 22. Reference numeral 24 denotes a fuel pump, by means of which fuel is sucked in from a tank (not shown), for example a portable fuel canister, and can be fed to the nozzle 20. Furthermore, in the left-hand part of the burner illustrated in Figure 1 there is a control panel 26, which can be used to adjust the fuel supply and operating mode of the burner 10 (permanent operation, cyclical operation and the like).

[0057] In the region of its second end 27, the flame tube 12 has four branch tubes, of which only the branch tubes 28 and 30 can be seen in Figure 1. Two further branch tubes are arranged in mirror-image fashion on the side of the flame tube 12 which is not visible in Figure l, as can be seen from Figure 2. In Figure 2, the branch tubes lying in mirror-image fashion with respect to one another at the end of the flame tube 12 are denoted by reference numerals 28a and 28b.

[0058] The branch tubes 28, 30 are secured to the lat-eral surface 34 of the hollow body 14 by means of intermediate pieces 32. Furthermore, they are arranged in such a manner that they are inclined with respect to the longitudinal centre axis 36 of the hollow body 14, with the two end-side flame tubes 28a, 28b inclined away from the flame generation unit 18, whereas the branch tubes 30 (cf. Fig. 4) are inclined towards the flame generation unit 18. In all cases, the angle of incli-nation is 45° with respect to the longitudinal centre axis 36 of the hollow body 14.

[0059] At their free ends (the upper ends in the illus-tration presented in Figure 1), the branch tubes 28, 30 have been cut to length at an angle, specifically likewise at an angle of 45°, so that the opening plane of the branch tubes 28, 30 lies approximately parallel to the region of the lateral surface 34 in which the branch tubes 28, 30 are respectively arranged.

[0060] The second end 27 of the hollow body 14 is closed here. Furthermore, the lateral surface 34 is closed here all the way around, so that the branch tubes 28, 30 represent the only outlet for flue gas or hot gas from the interior of the hollow body 14. The branch tubes 28, 30 therefore act as outlet nozzles, from which a hot gas stream emerges at the top.
This hot gas stream is used in the Assignee's cooking modules (not shown in more detail here) to heat a hotplate (likewise not shown here), such as for example a hob or grill.

[0061] As can be seen in Figures 1 and 2 and described in more detail below with reference to Figures 3 and 4, the intermediate pieces 32 are designed as angle pieces with a profile which is U-shaped when seen from above (cf. Figure 4).
When seen from the side, each intermediate piece 32 has a tri-angular profile which is matched to the desired angle of incli-nation of the branch tubes 28, 30.

[0062] At the burner 10, the flame tube 12 is arranged in a trapezium-shaped trough 38 (Figure 2). At the second end 27 of the flame tube 12, the trough 38 is closed off by an inserted metal sheet 40. At the burner 10, an insulation layer 42 consisting of thermally insulating ceramic material is lo-cated beneath the trough 38. On account of the new design of the flame tube 12, however, it will also be possible in future to do without the insulation layer 42 and instead simply to use a metal radiation protection sheet, as illustrated in Figure 3.

[0063] The following text will explain a preferred process for securing the branch tubes 28, 30 to the lateral surface 34 of the hollow body 14 with reference to Figure 3. In this figure, identical reference symbols denote the same ele-ments as previously.

[0064] Figure 3 illustrates the new flame tube 12 below a hotplate 50, as is the case for the intended use in the burner 10. As an alternative, however, the new flame tube can also be used in other surroundings, for example in combustion chambers from which hot gas is fed to a "consumer" via a system of pipes. One example of this is ovens, in which the hot gas which emerges from the flame tube 12 is passed via a heat ex-changer. Furthermore, the new flame tube is not restricted to applications in mobile field kitchens, but rather can be used wherever a hot gas stream is to be generated with the aid of a burner.

[0065] In the situation illustrated in Figure 3, how-ever, the flame tube 12 is used to heat the hot plate 50. This is done by the hot or flue gases which are generated in the interior (combustion chamber) 52 of the hollow body being passed via the branch tubes 28, 30 to the hotplate 50, as is symbolically illustrated by the arrow 54 at the branch tube 28b. The hot flue gases are then discharged from the region below the hotplate 50 via an extractor (not shown here).

[0066] According to the present invention, the branch tubes 28, 30 are in this case fitted flush onto the outer side of the lateral surface 34 of the hollow body 14. Each branch tube 28, 30 has an internal diameter D which is slightly larger than the internal diameter d of an opening 58 in the lateral surface 34 which lies beneath the branch tubes 28, 30. Conse-quently, it is easy for the branch tubes 28, 30 to be placed onto the lateral surface 34.

[0067] In an exemplary embodiment of the invention, the branch tubes 28, 30 are then provisionally fixed to the lateral surface 34 using a small weld spot or a soldered join or adhe-sive bond and aligned at the desired angle of inclination with respect to the longitudinal centre axis 36. Definitive securing of the branch tubes 28, 30 is effected by way of the angular intermediate pieces 32, which are placed onto the lateral sur-face 34 around the branch tubes 28, 30 and are then welded to the lateral surface 34 outside the branch tubes 28, 30. More-over, the branch tubes 28, 30 are also welded to the angular intermediate pieces 32 in order to achieve stable securing of the branch tubes 28, 30 to the lateral surface 34. In a par-ticularly preferred exemplary embodiment, the weld spots are in each case positioned in such a way that there is no weld spot in the direct gas stream 54.

[0068] In an alternative embodiment of the process, the branch tubes 28, 30 are first of all welded to the angled in-termediate pieces 32, and then the combination of branch tube and intermediate piece is positioned on the lateral surface 34 of the hollow body 14, appropriately orientated and likewise welded in place. This second alternative has the advantage that the branch tubes 28, 30 can be secured without being "directly"
attached to the hollow body 14. Furthermore, it is in principle also possible for the intermediate piece and branch tube to be formed integrally with one another.

[0069] Moreover, as a modification to the illustration shown in Figure 3, it is also possible for the branch tubes 28, 30 to project into the combustion chamber 52 of the hollow body 14, as is known, for example, from the two documents DE 42 32 181 A1 and DE 42 44 400 A1 cited in the introduction. It will be understood that in this case the (internal) diameter D of the branch tubes 28, 30 needs to be smaller than the internal diameter d of the openings 58.

[0070] In the preferred exemplary embodiment illus-trated here, the intermediate pieces 32 are sheet-metal pieces which are angled off twice and have two respective triangular side parts 60 connected via a rectangular base part 62. In plan view, this produces a U-shaped profile which surrounds the branch tubes 28, 30 (cf. Figure 4). The angle ratios of the triangular side parts 60 correspond to the desired angle of inclination of the branch tubes 28, 30 with respect to the longitudinal centre axis 36 of the hollow body 14, as can be seen in Fig. 1.

[0071] As an alternative to this, in other embodiments of the invention, the intermediate pieces 32 may also be de-signed differently, for example as V-shaped brackets, of which one limb is secured to a branch tube 28, 30 and a second limb is secured to the lateral surface 34 of the hollow body 14 (not shown here).

[0072] A further alternative is annular intermediate pieces which concentrically surround each branch tube 28, 30 (not illustrated here either).

[0073] In any case, the intermediate pieces are con-nected to the branch tubes on the outer side of the latter and that the intermediate pieces in turn fix the branch tubes to the lateral surface, so that the hot gas which emerges from the combustion chamber 52 through the branch tubes does not flow directly onto or around the securing points, in particular the welds.

[0074] As is also illustrated in Figure 3, the hollow body 14 here comprises two half-shells 68, 70, with only the upper half-shell 68 being provided with branch tubes 28, 30. By contrast, a metal radiation protection sheet 72 which is angled approximately in a trapezium shape is releaseably secured to the lower half-shell 70. In the preferred exemplary embodiment, the metal radiation protection sheet 72 is provided with elon-gate slots 74, into which nooks 76 on the lateral surface 34 engage with a clearance. The clearance allows the hollow body 14 to move relative to the metal radiation protection sheet 72, with the result that stress cracks caused, inter alia, by dif-ferent thermal expansion of hollow body 14 and metal radiation protection sheet 72 are avoided.

[0075] As illustrated in Figure 4, in the preferred ex-emplary embodiment the four radiation tubes 28, 30 are arranged in such a way on the upper half-shell 68 that they define a rectangle 80 when seen from above. In this case, the branch tubes 28, 30 are located in the end-side portion 82 of the hollow body 14, i.e. the branch tubes 28, 30 are closer to the second end 27 of the hollow body 14 than to the first end 16, to which the flame generation unit 18 is connected.

[0076] Although this means that there is uneven distri-bution of branch tubes 28, 30 over the length of the hollow body 14, and although only approximately 40~ of the flue gas passes through the branch tubes 30 inclined towards the flame generation unit 18, this arrangement achieves very uniform heating of a planar, rectangular hotplate 50.

[0077] In the preferred exemplary embodiment, both the hollow body 14 and the branch tubes 28, 30 and the intermediate pieces 32 are produced from metal sheets with a thickness of 2 mm. The relatively great thickness of the sheet-metal parts likewise makes a contribution to lengthening the service life of the new flame tube.

[0078] In the embodiment described, the new flame tube 12 is particularly suitable for small, low combustion chambers.
The arrangement and distribution of the branch tubes described in this case allows a good distribution of heat over flat sur-faces, and moreover the new flame tube is very inexpensive and easy to produce. On the other hand, the use of steel sheets and the securing of the branch tubes by way of weld spots at the intermediate pieces leads to a very robust design which allows reliable and prolonged operation even in mobile use and under fluctuating operating conditions (fuel quality, ambient tem-peratures, alternating operation and the like).
WHAT IS CLAIMED IS:

Claims (20)

1. A flame tube for a burner comprising a flame genera-tion unit, the flame tube having a hollow body forming an at least partially enclosed combustion chamber, and at least one branch tube connected to the hollow body, the hollow body having a first end designed for being con-nected to the flame generation unit, and a lateral surface on which the at least one branch tube is arranged, wherein the branch tube, on its outer side, is connected to an intermediate piece, and wherein the intermediate piece is secured to the lateral surface.

2. The flame tube of Claim 1, wherein the intermediate piece is welded to the lateral surface.

3. The flame tube of Claim 1, wherein the branch tube and the intermediate piece are of two-part design, with the branch tube and the intermediate piece 3 being welded to one another.

4. The flame tube of Claim 1, wherein the branch tube is secured to the lateral surface only by way of the intermediate piece.

5. The flame tube of Claim 1, wherein the lateral sur-face has an outer side, and the branch tube is fitted flush onto the outer side.

6. The flame tube of Claim 1, wherein the lateral sur-face has an opening with a first internal diameter, the opening being located below the branch tube, and wherein the branch tube has a second internal diameter, the second internal diame-ter being greater than the first internal diameter.

7. The flame tube of Claim 1, wherein the intermediate piece is an angle piece with at least two limbs surrounding the branch tube.

8. The flame tube of Claim 7, wherein the intermediate piece is an angle piece with three limbs which surround the branch tube.

9. The flame tube of Claim 1, wherein the intermediate piece is a bracket having two limbs, with one limb being se-cured to the branch tube and a second limb being secured to the lateral surface.

10. The flame tube of Claim 1, wherein the intermediate piece is a ring surrounding the branch tube.

11. The flame tube of Claim 1, wherein the lateral sur-face has a first half and a second half as seen in a circumfer-ential direction, and wherein a plurality of branch tubes are secured only to the first half.

12. The flame tube of Claim 11, wherein the second half is completely closed.

13. The flame tube of Claim 11, comprising four branch tubes arranged on the first half in such a way that when the first half is seen in plan view the branch tubes approximately define a rectangle.

14. The flame tube of Claim 13, wherein the four branch tubes include two first branch tubes, which are arranged closer to the first end, and two second branch tubes, which are ar-ranged further away from the first end, the two first branch tubes being inclined towards the first end, while the two sec-ond branch tubes are inclined away from the first end.

15. The flame tube of Claim 1, wherein the at least one branch tube forms a hot gas outlet.

16. The flame tube of Claim 1, wherein the hollow body has a second end which is substantially closed.

17. The flame tube of Claim 1, further comprising a metal radiation protection sheet suspended from the hollow body with a clearance between them.

18. The flame tube of Claim 17, wherein the metal radia-tion protection sheet is angled around the hollow body.

19. A burner for generating hot gases, the burner com-prising a flame tube and a flame generation unit connected to the flame tube, and the flame tube having a hollow body forming an at least partially enclosed combustion chamber, and at least one branch tube connected to the hollow body, the hollow body having a first end connected to the flame generation unit, and a lateral surface on which the at least one branch tube is arranged, wherein the branch tube, on its outer side, is connected to an intermediate piece, and wherein the intermediate piece is secured to the lateral surface.

20. A method for producing a flame tube for a burner hav-ing a flame generation unit, the method comprising the steps of:
providing a hollow body having a lateral surface for form-ing an at least partially enclosed combustion chamber, the hollow body having a first end designed for connection to the flame generation unit, and arranging at least one branch tube on the lateral surface, wherein the step of arranging includes a step of connect-ing the branch tube, on its outer side, to an intermediate piece, a step of securing the intermediate piece to the lateral surface.