EP0283901B1 - Plane gas burner for heating boilers - Google Patents

Description

The invention relates to a gas surface burner for heating boilers according to the preamble of the main claim.

Such a gas surface burner is known from DE-A-35 03 553. With such a surface burner, a short-burning surface flame standing in layers above the outflow surface can be generated, but it has been observed that particularly in the peripheral edge region of the poorly burning flame there are protruding, i.e. longer-burning flame regions, which also have negative effects on the measured NOX values to lead. In this regard, it can only be assumed that the conditions given at the peripheral area of the surface flame are responsible for this, because these conditions are different with respect to other flame areas in that these areas no longer have any burning neighboring areas. A further relevant prior art is represented by the following documents: US-A-1,582,634, DE-A-18 06 936 and DE-A-31 13416.

The invention is based on the object, starting from a gas surface burner of the type mentioned, to improve it in such a way that in the form of a surface flame directly behind the opening of the mixing chamber with a relatively low temperature and thus NOX-reducing burning gas-air mixture should also burn in the peripheral edge areas under these conditions.

This object is achieved with a gas surface burner of the type mentioned according to the invention by the features stated in the characterizing part of the main claim. Advantageous and practical embodiments result from the subclaims.

As has been shown, this relatively simple measure of arranging a ring or frame-like edge cover can achieve that the peripheral edge regions burn largely in the manner of a surface flame, i.e. There are no protruding flame areas and the low NOX values to be achieved can be better achieved. With regard to the mode of operation of such an edge cover, it can initially only be assumed that a type of hot air or hot gas recirculation will presumably result in this area, whereby the recirculating hot gases also result in at least similar conditions for the edge areas of the surface flame as do those in the more inner areas the surface flame is present.

In the case of a burner according to GB A 20 76 956, NOx reduction is also sought, but this is not a surface burner, but rather a burner tube which forms the end of an air-gas injector and is provided with an opening row on which a self-contained box is placed tightly and only has a slot arranged above the row of holes in the box lid. A recirculation of hot gases from the combustion chamber is not given and possible, and the problem of stabilizing the edge flames of a surface burner does not exist with such a burner.

An embodiment of the edge covering according to the invention is preferred in that it is provided on the burner side with a peripheral web which extends perpendicular to the surface of the edge cover and which is provided with inflow openings. As far as could be observed, it also seems to be essential with regard to the edge cover that the opening cross section of the ring-shaped or frame-shaped cover corresponds to the flame-retardant cross-section of the surface, i.e. the inner opening edge of the edge cover runs in alignment with the outer peripheral edge of the flame-effective gas outflow surface, which can either be structured like a lattice, but which can also consist of a large number of relatively small individual holes. In addition to this edge covering, it has proven to be advantageous that on the one hand the holes located under the opening edge contour have approximately the same distance from one another and the hole density in the region of the opening edge contour corresponds approximately to the hole density on the entire perforated plate.

The gas supply connection on the box-shaped gas supply housing, which is closed except for a necessary edge area with the burner plate, is arranged centrally for the most uniform gas supply distribution under the burner plate, the end of the mouth being provided with a closure plate provided with holes and openings arranged in the side wall of the end of the mouth are whose diameter is larger than that of the holes in the closure plate. The requirement for equidistant spacing of the holes under the opening edge of the edge cover can be met most simply by arranging the holes in the burner plate in the form of a square grid, which, however, presupposes that the flame-retardant surface of the burner plate is also square and the outermost four rows of holes under the Edge of the corresponding square edge cover. Since the outflowing gas mixture is to burn as a flat flame over the entire burner plate, the holes of the burner plate must have a relatively small diameter, which is of the order of about 1 to 2.5 mm. In order to be able to make such smaller-diameter holes in the plate with as little effort as possible, only punching out is possible. On the other hand, the burner plate must have a sufficient thickness in view of the temperature load in order to avoid warping of the plate. For this reason, the burner plate is formed from at least two spot-welded plate lamellae, the total thickness of which is greater than the diameter of the holes. This design of the burner plate means that its individual lamellae are accessible to a punching process for the attachment of the holes, which are then simply placed one on top of the other in alignment with the punched holes and spot welded the.

In a special and preferred embodiment, in which the burner plate is designed as a hollow body as a whole, this design ensures that every area of the burner plate, including the gas inflow channels, can be cooled. This design also facilitates the manufacture of such a burner insofar as the hollow body can be easily assembled from two suitably perforated and pre-embossed shells, all of the assembly points, of course, having to be gastight and liquid-tight.

A practical embodiment of such a gas burning device can consist in that the gas inflow channels are designed in the form of inserted tubes which extend from one wall to the other wall of the hollow body. It is readily possible to arrange the tubes inserted into the hollow body in a gas- and liquid-tight manner, at least on the flame side, projecting beyond the wall of the hollow body in question. For the integration of the tubes, ring-shaped, outward bends are expediently provided in the two hollow body walls, which can be easily formed when the respective shell is cut and pressed.

Apart from this embodiment, it is also possible to design the gas inflow channels in the form of wall impressions on the gas supply-side hollow body wall and to connect the two walls of the hollow body around the gas outflow openings in a gas-tight and liquid-tight manner, which will be explained in more detail and where there is certainly the possibility of to establish the connection with a correspondingly dimensioned annular spot welding electrode around the respective outflow opening. Viewed from the gas supply side, the embossed wall of the hollow body then represents itself similar to a waffle iron, whereby it must of course be ensured that the remaining cavity can be flowed through from the supply to the return connection. In this embodiment, it can advantageously also be ensured during the pressing process of the flame-side shell that ring-shaped offsets directed towards the flame side arise around the gas outflow openings.

The design principle of a coolable burner plate and its double-shell design also has the advantage of being able to dimension the sheet metal blanks larger and to keep the peripheral areas around free of gas outflow openings, the hole-free edges of the hollow body then being formed perpendicular to the burner plate surface to form a coolable peripheral wall limitation of the perforated burner plate . In this embodiment, a water-cooled shaft wall is thus created around and formed by the burner plate itself, which is also advantageous in terms of NOx reduction. The aforementioned cover ring can be used here, but does not have to be provided.

This embodiment can also experience an advantageous further development in that one or the other wall of the hollow body, which extends perpendicular to the burner plate surface, is dimensioned longer than the other and in the protruding wall part, which is therefore no longer water-cooled, can flow through at least one gas, the free cross section heat exchanger approximately covering the burner plate at a distance above the burner plate and the short burner shaft together form a water-cooled element, so it is advantageously also easily possible to integrate a suitable heat exchanger without problems, for which the burner plate, which has been shaped into a pot, also forms the holder.

The gas surface burner according to the invention is explained in more detail below with reference to the drawing of exemplary embodiments.

It shows schematically

• 1 shows a section through an embodiment of the burner.
• Figure 2 shows in section a surface burner in connection with an integrated heat exchanger.
• FIG. 3 shows a top view of the gas supply connection according to FIG. 2;
• Figure 4 is a plan view of a perforated burner plate.
• 5 shows a section through a special embodiment of the burner;
• FIG. 6 shows a top view of the burner according to FIG. 5;
• Fig. 7 shows a partial section through the hollow body forming the burner plate in another embodiment and
• Fig. 8 in section a special embodiment of the burner plate.

As can be seen from FIG. 1, the gas surface burner consists of a mixing tube 14 provided with a blower connection with a central gas supply tube 13 which has perforations 16 in the area of the mixing tube 14 so that the gas can flow out there and with the air supplied by the blower rotor 15 can mix for which the mixing tube in the area of the blower housing 11 is provided with corresponding air inlet slots (not shown). This mixing tube 14 is expediently arranged axially adjustable in the blower housing 11, which - as can be seen - is advantageously designed as a flat chamber 12. As can be seen, the gas mixing tube 14 opens into a mixing chamber 5 which is relatively large in cross section and which is closed on the outflow side with a suitable perforated plate or a grating which forms the flame-effective surface 1. At a distance from this surface 1, the annular or frame-shaped edge cover 2 is arranged in its peripheral edge region, adapted to the cross-sectional shape of the surface, the opening cross section 3 of which corresponds to the flame-effective cross section of the surface 1. If it is a simple washer, this is of course fi at the desired distance by means of appropriate holding elements (not shown) xiert. Advantageously and as shown, the edge cover on the fan side is provided with a circumferential web 4 which extends perpendicular to the plane of the edge cover 2. A circumferential gap 6 can be provided between the mixing chamber 5 and the circumferential web 4, but care must be taken to ensure that recirculating hot gas 6 can flow into this circumferential gap, as indicated below with a dashed arrow. As shown, however, the circumferential web 4 is advantageously provided with openings 7, so that hot gas can recirculate through these openings 7 from the combustion chamber 17 and then flow out again through the edge regions of the opening cross section 3 of the cover 2. This recirculating hot gas appears to create conditions for the edge areas of the flame which are automatically given for the flame areas located further inward, which are to a certain extent mutually supportive. As can also be seen, the circumferential web 4 is provided with a heat-insulating enclosure 8, for example made of ceramic fiber material or the like, which prevents heat radiation from the circumferential web 4. In the same way, the blower-side bottom 9 of the mixing chamber 5 is formed from heat-insulating material of the same type, this material being arranged directly on the blower housing 11, which forms a flat chamber 12 in which the blower rotor 15 with its motor 10 is eccentrically inserted Mixing chamber 5 leading mixing tube 14 is arranged. The openings 7 can be more or less large and arranged in a more or less dense distribution on the circumferential web 4, which need not necessarily be circular holes as shown, but can also be slots or the like. Openings. Small, the swirl-imparting guide webs mediating the gas-air mixture can be arranged within the axially adjustable mixing tube, which then ensure a gas distribution in the mixing chamber 5 as a result of the swirl imparted in order to weaken a massive direct inflow of the central region of the surface 1. Possibly. can also be arranged at the closed end of the gas supply pipe in the mixing chamber 5, as indicated by dashed lines, there a perforated shielding screen.

The embodiment according to FIGS. 2 to 4 will now be described, all reference numerals beginning with a 2.

As can be seen from Fig. 2, the surface burner consists of a box-shaped gas supply housing 212 with gas supply connection 27 and perforated burner plate 21 in association, as shown, wherein according to the embodiment, the gas supply housing 212 forms the lower part of a small heat exchanger arranged above it, which does not require any further explanation here. The whole structure can practically be viewed as a small boiler.

The cross section of the gas supply housing 212 and thus also of the attached heating boiler is square according to the exemplary embodiment in FIG. 2, which is not binding, i.e. the whole could also have a circular cross section. At a distance from the perforated burner plate 21, the annular or frame-shaped edge cover 22 is arranged over its edge regions, adapted to the cross-sectional shape of the burner plate 21, the opening cross section 23 of which corresponds to the flame-retardant surface of the perforated burner plate 21, ie the outermost holes 25 of the burner plate 21 are located under the opening edge 24 of the edge cover 22, which is provided with side openings 213 in the formation or profiling, for example, for the recirculation of hot gases from the area outside the edge cover professional. The outer holes 25 of the burner plate 21 located under the opening edge 24 of the edge cover 22 are, as shown in FIG. 4, arranged at the same or approximately the same distance from one another, the hole density of the burner plate 21 in the region below the opening edge 24 being the same or approximately the same the hole density of the entire burner plate 21. This arrangement and allocation of the holes 25 would be easiest to implement if the holes 25 of the burner plate 21 were arranged in the form of a square grid. If, in this case, the burner plate were punched out in a circle, the condition of equidistant spacing of the holes under the opening edge 24 and the requirement for approximately the same hole density in the edge region would no longer be met. When arranging the holes 24 in the sense of FIG. 4 on concentric circles, care must be taken to ensure that evenly spaced holes 25, seen in projection, are present under the opening edge of the cover 22 and in the edge region, i.e. approximately the same hole density as is present in the entire burner plate 21 within the opening edge 24. In the exemplary embodiment shown in FIG. 4, the holes 25 are therefore thinned out to a certain extent on the concentric circles 214 and to a certain extent this also applies to the respective end regions of the concentric circles or circular sections up to the circle 214 '. In the case of a square grid on a circularly cut burner plate 21, this would be achieved by correspondingly omitting and adding holes 25.

In order to supply gas to the burner plate 21 as uniformly as possible, the mouth end of the gas supply connection 27 is arranged centrally under the burner plate, the mouth end 26 being provided with a closure plate 29 provided with holes 28 (FIG. 3), with openings 211 around the side wall 210 of the mouth end 26 are arranged, the diameter of which is larger than that of the holes 28 in the closure plate. If these lateral openings 211 were not present, there would be a preferred flow against the center area of the burner plate 21, which would, however, prevent the formation of a surface-burning flame.

For the reasons mentioned in the introduction, namely the punchability of the relatively small-diameter holes 25, the burner plate 21 is formed from at least two spot-welded plate lamellae 21 ', the total thickness of which is greater than the through Knife of the holes 25. In the exemplary embodiment shown, the thickness of the two plate lamellae 21 'is 2.5 mm and can therefore still be punched with respect to the holes 25 if they also have a diameter of 2.5 mm, for example. Due to the aligned joining and spot welding of the two plate fins 21 ', the burner plate 21 is then sufficiently stable against thermal distortions. 0.5 to 4 gas mixture passage openings are preferably provided per cm ^{2 of} burner area.

5 to 7, all reference numerals begin with a third

As can be seen from FIG. 5, the burner also consists of a gas supply housing 318 with a gas connection 319 and with a multiplicity of gas outflow openings which are arranged uniformly distributed in a coolable burner plate 31 which closes the housing 318. For all the special embodiments shown, the burner plate 31 is designed as a hollow body 32 and is provided with supply and return connections 33, 34, the gas inflow channels 36 leading to the gas outflow openings 35 of the plate 31 being arranged in the hollow body 32, the walls of which 37 separate the interior of the hollow body 32 from the channels 36, which means nothing else that all areas of the burner plate 31 are directly accessible from the cooling medium. 5, 6, the gas inflow channels 36 are designed in the form of gas and liquid-tight tubes 38, which extend from one wall 32 'to the other wall 32 "of the hollow body 32 and, in a preferred embodiment, at least on the flame side via the wall 32' of the hollow body 32. The tubes 38 are, as can be seen from the sectional area in FIG. 1, enclosed in annular, outwardly directed crimps 310 of the two hollow body walls 32 ', 32 ".

Another possible and even easier to implement embodiment is illustrated in Fig. 7, which represents only a portion of the burner plate. Here, the gas inflow channels 36 are designed in the form of wall impressions 39 of the gas supply-side hollow body wall 32 ″, the two walls 32 ′, 32 ″ of the hollow body 32 being connected to one another in a gas-tight and liquid-tight manner around the gas outflow openings 35. In this embodiment, the manufacture of such a burning device is reduced to simple sheet metal cutting and stamping or embossing processes. If a burner plate designed in this way is to be designed in a development according to FIG. 5, the wall impressions 39 in the region of the circumferential edges to be set vertically must of course also be eliminated there, like the tubes 38. Apart from the fact that burner plates designed as such in the sense of FIGS. 5 and 7 can be installed as such in suitable housings, the embodiment shown in FIG. 5 is preferred, in which the hollow body is formed from two shells and that of the gas outflow openings 35 kept free edges 312 of the hollow body 32 to form a coolable peripheral wall 313 of the perforated burner plate 31 perpendicular to the burner plate surface 314. As a result, the entire burner plate is shaped into a pot-like structure, the side walls of which can also be cooled directly in the area of the flame front. Corresponding embossments 320 in the region of the coolable peripheral boundary wall 313 serve to stiffen the entire pot.

As can also be seen from FIG. 5, the wall 32 ′ of the hollow body 32 extending perpendicular to the Benner plate surface 314 is also longer than the other. The resulting and protruding wall part 315 can be used as a holder for a gas-flowable, the free cross section approximately covering the burner plate 31 covering heat exchanger 316, which is arranged at a suitable distance above the burner plate 31. The hollow body 32 is expediently connected on the return side to the flow connection 317 of the heat exchanger 316, so that there is a continuous flow for the cooling medium for the whole, namely from the burner plate connection to the heat exchanger flow.

As has been shown, in view of the thermal load on the burner plate, as can be seen from FIG. 8, it is advantageous to make it concave in relation to the flame side. This can easily be provided for the embodiments according to FIGS. 5 to 7 without any problems. Such a curvature stabilizes the burner plate against warping of the shape and thus also contributes to the flame front stabilization.

Advantageously - and as can also be seen from Fig. 8 - the burner plate or the gas mixture outflow openings on the gas mixture inflow side are covered with a fine-meshed grille 41, which once equalizes the mixture inflow to the openings and in particular counteracts the risk of flashback in the mixture inflow chamber under the burner plate. The arrangement of such a grid 41 or single-mesh screen can also be used in the embodiments according to FIGS. 5 to 7.

Claims (19)

1. A gas surface burner including a blower of a low compression for heating system boilers, comprising a gas mixing portion having a gas supply pipe (13) and an outlet portion exhibiting a mixing chamber (5), confined by a surface (1) of grid-type structure or provided with orifices (25) and masking the entire opening cross-section of the mixing chamber (5), characterized in that, in forming a circumferential gap (6) for the in-flow of hot gas to the orifices (25) disposed along the circumferential rim of the surface (1) at a distance ahead of the surface (1), in the circumferential rim area thereof is disposed a ring-or frame-type marginal masking (2) conforming to the cross-sectional shape of the surface, with the opening cross-section (3) of the said marginal masking corresponding to the flame-effective cross- section of the surface (1).

2. A burner according to claim 1, characterized in that the marginal masking (3), toward the blower side, is provided with a circumferential bridge (4) extending in a direction vertical to the surface (1).

3. A burner according to claim 2, characterized in that holes (7) are provided in the circumferential bridge (4).

4. A burner according to any one of claims 1 to 3, characterized in that the casing (11) of the blower is in the form of a flat chamber (12), and that the blower rotor (15) is eccentrically disposed therein toward the axially adjustable mixing pipe (14) leading into the mixing chamber (5).

5. A burner according to any one of claims 1 to 4, characterized in that the outer holes (25) of the plate (21) provided underneath the opening rim (24) of the marginal masking (22) are at an equal or approximately equal space from one another, with the hole frequency in the area of the opening rim (24) corresponding or approximately corresponding to the hole frequency throughout the burner plate (21).

6. A burner according to claim 1, characterized in that disposed centrally underneath the burner plate (21) is the opening end (26) of the gas supply connection (27), and that the opening end (26) is provided with a closure plate (29) provided with holes (28), and that, in the side wall (210) of the opening end (26), holes (11) are circumferentially located, the diameters of which exceed those of the holes (28) in the closure plate (29).

7. A burner according to any one of claims 1 to 6, characterized in that the burner plate (21) is formed of at least two joined-together plate lamellas (21') the total strength of which exceeds the diameter of the holes (25).

8. A burner according to claim 7, characterized in that the two plate lamellas (21') are spot-welded together.

9. A burner according to any one of claims , to 6, characterized in that the burner plate (31) is generally formed as a hollow body (32) and is provided with forward and backward flow connections (33, 34), with gas in-flow channels (26) leading to the gas out-flow openings (35) of the plate (31) being provided in the hollow body (32), with the walls (37) of such gas in-flow channels (26) separating the interior chamber of the hollow body (32) from the channels (36).

10. A burner according to claim 9, characterized in that the gas in-flow channels (36) are in the form of gas- and liquidtight plugged-in tubules (38) extending from one wall (32') to the other wall (32') of the hollow body (32).

11. A burner according to claim 9, characterized in that the gas in-flow channels (36) are in the form of wall impressions (39) of the gas supply-sided wall (32") of the hollow body, and that the two walls (32', 32") of the hollow body (32) about the gas out-flow openings (35) are interconnected in gas- and liquidtight manner.

12. A burner according to claim 10, characterized in that the tubules (38) inserted into the hollow body (32), at least on the flame side, are disposed in a manner to protrude beyond the wall (32') of the hollow body, and that the tubules (38) are framed in annular, outwardly directed goosenecks (310) of the two walls (32', 32") of the hollow body.

13. A burner according to claim 11, characterized in that the flame-sided wall (32') of the hollow body (32), about the gas outflow openings (35), is provided with annular goosenecks (311) directed toward the flame side.

14. A burner according to any one of claims 9 to 13, characterized in that the hollow body (32) is of a dual-shell configuration and the rims (312) of the hollow body (32) kept free from the gas out-flow openings (35), for forming a coolable circumferential confining wall (313) of the perforated burner plate (31) extend in a direction vertical to the burner plate face (314).

15. A burner according to claim 14, characterized in that the one or the other wall (32', 32") of the hollow body (32) extending in a direction vertical to the burner plate face (314) is of a greater length than the respectively other wall, and that located in the protruding wall section (315) is at least one heat exchanger (316) permitting gas flow therethrough and approximately masking the free crosssection above the burner plate (31), at a distance above the burner plate (31).

16. A burner according to claim 15, characterized in that the hollow body (32), at the return flow side, is connected to the forward flow connection (317) of the heat exchanger (316).

17. A burner according to any one of claims 1 to 16, characterized in that, per cm² burner plate, 0.5 to 4 gas mixture passage openings having hole diameters of between 0.1 and 3 mm, preferably 2.5 mm, are provided.

18. A burner according to any one of claims 1 to 17, characterized in that the burner and the burner plate, respectively, are of a curved configuration, viz. relative to the flame side, preferably of a concave-curved configuration.

19. A burner according to any of claims 1 to 18, characterized in that the burner plate and the gas mixture out-flow holes, respectively, at the mixture flow-off side, are masked by a fine-mesh grid (41).

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