EP4047269A1 - Burner for a heater and its arrangement in the heater - Google Patents

Abstract

The invention relates to a burner (5) for a heating device (1) with a burner body (7) which has an inner surface (14) facing an interior space (8) and an outer surface (15) facing a combustion chamber (2). a plurality of holes (12) through which a fuel gas-air mixture (G) can flow from the interior (8) of the burner body (7) into the combustion chamber (2), the burner body (7) being attached to the inner surface (14 ) and/or the outer surface (15) has structures (16 to 21) for transporting and/or shielding heat and an arrangement of such a burner (5), the burner (5) having dimensions (L, D) and Positioning in a combustion chamber (2) with heat exchanger (4) the most favorable data for efficient use with regard to a distance (A) to the heat exchanger (4) and a burn-out height (H) of combustion of the combustible gas-air mixture (G). Has flames (13). The present invention makes it possible to build burners for compact heaters that can be adapted to various fuel gases, in particular also to hydrogen, and to largely avoid overheating and flashbacks and to reduce heat losses to the outside.

Description

The invention relates to a burner for a heater that can be operated with different fuel gases, including hydrogen and/or a fuel gas containing hydrogen, and arrangements of such a burner in a combustion chamber of the heater.

Hydrogen as a fuel gas or as an admixture to fuel gases is becoming more and more important, and great efforts are being made to upgrade new or existing heating devices for operation with it. It is not only a question of large systems, but also of wall-mounted units for heating water and, in general, heaters for heating buildings and/or providing hot water. Gas heaters are durable consumer goods and should be able to be adjusted or converted to different gas qualities over the course of their service life and, in the future, also from methane to hydrogen combustion.

Pot-shaped (usually cylindrical) burners are well known in heating appliances. Such a burner is mounted on a burner door built into a combustion chamber with a surrounding heat exchanger. A pre-mixed, combustible mixture of fuel gas and air flows through the burner door into the burner. The fuel gas flows through holes with a definable hole pattern in a (cylindrical) jacket area of the burner into the combustion chamber, where it is ignited and burns. The hole pattern is designed in such a way that the outflow speed of the combustible gas-air mixture into the combustion chamber is matched to the respective flame speed (depending on the fuel gas). In addition, it is important that the flame burns at a certain distance from a surface of a burner body in order to keep its temperature low. This should be aimed at over the entire modulation range (range of different adjustable power) of the heater. The temperature of the burner body must never reach the ignition temperature of the combustible gas-air mixture in order to prevent backfires within the burner (flame flashback into an interior of the burner body).

During its combustion, hydrogen differs from previously used fuel gases in several respects, in particular a hydrogen flame is almost invisible to the human eye (but radiates in the ultraviolet spectral range), radiates less heat than flames produced with carbonaceous fuels, but burns hotter. The present invention is also intended to make heating devices particularly suitable for switching to operation with pure hydrogen or with fuel gas that consists of more than 50%, in particular more than 97%, hydrogen.

In the construction of burner bodies and their arrangement in a combustion chamber, attention has so far mainly been paid to simple and inexpensive manufacture and assembly, with the hole pattern and the dimensions of the burner body and the operating parameters of the heater being the main considerations. However, it is difficult to meet the requirements when using different fuel gases. The cooling of the torch body takes place on the one hand via heat conduction to adjacent components of a device environment, but this leads to a loss of energy. On the other hand, the outflowing mixture of fuel gas and air absorbs heat and dissipates it into the combustion chamber. The concentration of a surface that is actively used for combustion on a cylindrical burner surface tends to lead to higher values temperatures. These are lower with a wide distribution over a large area (a larger burner body), but with the disadvantage that the volume of the combustible gas-air mixture in the interior of the burner body is significantly larger, which leads to a greater detonation potential in the event of a flashback and leads to more sluggish behavior when pressure builds up when the burner starts.

The object of the present invention is to at least partially solve the problems described with reference to the prior art and in particular to create a burner and to arrange it in a combustion chamber in such a way that additional possibilities for cooling the burner body and its surroundings can be used.

A burner according to the independent claim serves to solve this problem. Advantageous refinements and developments of the invention and a corresponding arrangement of such burners are specified in the dependent claims. The description, in particular in connection with the drawing, illustrates the invention and specifies further exemplary embodiments.

Contributing to this is a burner for a heater with a burner body, which has an inner surface facing an interior space and an outer surface facing a combustion space, with a large number of holes through which a fuel gas-air mixture can flow from the interior space of the burner body into the combustion space can flow, the burner body having structures for transporting heat and/or for shielding heat on the inner surface and/or the outer surface. A burner body is heated from the outside mainly by radiation (and sometimes convection), while a relatively cold mixture of fuel gas and air flows inside. An important aspect of the present concept is to use the fuel gas-air mixture more for cooling of the torch body than prior art torches. For this purpose, the burner body is provided with structures that can dissipate heat. The concept is also useful in outward protruding structures that may be used to achieve desired heat dissipation and/or component shielding. Instead of very simply shaped burner bodies, somewhat more complex bodies are used here, which, however, can solve some of the problems described above. A large number of such local structures are preferably provided on the surface of the burner body, with these possibly having an overriding pattern and/or a regular distribution.

The structures preferably protrude into the interior of the burner body and are designed to transport heat from the burner body to the fuel gas/air mixture flowing in the interior. The heat transferred to the mixture is not lost, but enters the combustion chamber and can be used there together with the heat generated during combustion. Despite this, the burner temperature remains lower than in the prior art.

In particular, the structures increase an inner surface area of the burner body that is in heat-transferring contact with the fuel gas-air mixture.

According to particular embodiments, the structures are dome-, rib-, lamellar-, fir-tree- and/or antenna-shaped. Any shape that leads to greater heat transfer to the fuel-air mixture is advantageous, so that a production-technically suitable and cost-effective solution can be chosen depending on the requirements. The arrangement of the holes (hole pattern) in the burner body should then be such that the structures do not impede the outflow of the mixture, but the area around the holes is well cooled becomes. This can be achieved by embossed or molded structures or by structures attached in some other way.

In particular if good cooling is ensured by the measures described so far, but also independently of this, it is useful to use structures to enlarge the outer surface of the torch body, specifically in the front-side areas of the torch body. A burner is typically attached to a burner door of a combustion chamber, which is heated by flames and their thermal radiation and convection during operation of the heater, so that heat has to be dissipated there, which is essentially lost. Structures emanating from the torch body can capture and dissipate some of this heat, reducing these losses. The same also applies to the opposite end face of the torch body, where losses to a housing can occur.

It is therefore particularly favorable if the structures are disk-shaped and run approximately perpendicularly to a longitudinal axis of the burner body. Such panes shield areas of the housing that are not protected by heat exchanger surfaces and thus reduce the losses of the heater. This can be achieved particularly favorably in conjunction with other structures, as will be described below.

An arrangement of a burner as previously described also serves to solve the problem, with the dimensions and/or positioning of the burner being arranged in a combustion chamber with a heat exchanger, specifically at a specified distance from the heat exchanger and a specified burn-out height of when the fuel gas is burned -Air mixture resulting flames.

Here, in particular, an arrangement is selected in which the distance and/or the burn-out height is application-oriented and/or as favorable as possible for efficient use.

This means, among other things, that a burner in the present concept no longer has to be dimensioned according to how its permissible maximum temperature can be maintained (it may become too large as a result), but can be built so small that there is an optimal distance in a compact heating device to a surrounding heat exchanger, which means that there is enough space for the flames that develop during combustion (sufficient burn-out height) so that they do not reach the heat exchanger, but only the resulting combustion gases give off their heat there.

In a particular embodiment, the disk-shaped structures run parallel to other disk-shaped structures that are fastened in a heat-conducting manner to a heat exchanger arranged in the combustion chamber, with the disk-shaped structures and the other disk-shaped structures in particular overlapping at least in an overlapping area and with a gap width of 0.1 to 10 mm [millimeters] apart. On the one hand, this creates a practically closed shield for parts of the housing behind the panes, and on the other hand, the overlapping area allows additional heat transfer between the panes (a kind of labyrinth effect). Heat is thus transferred from the warmer disc, which will generally be the one attached to the burner body, to the colder disc (which will usually be the one attached to the heat exchanger). In this way, heat can even be dissipated from the burner body to the heat exchanger.

The disc-shaped structures are preferably designed to shield heat from the flames around the burner body from areas of a housing surrounding the combustion chamber that are not protected by the heat exchanger. This reduces the heat losses to the outside and additional heat can be dissipated from the burner body to the heat exchanger.

Fig. 1:

einen Brennerkörper im Längsschnitt mit domförmigen Strukturen, die in seinen Innenraum ragen,

Fig. 2:

einen Brennerkörper mit außen angeordneten scheibenartigen Strukturen im Längsschnitt, eingebaut in einen Verbrennungsraum mit Wärmetauscher,

Fig. 3:

einen Ausschnitt aus Fig. 2 mit einem Überlappungsbereich von scheibenartigen Strukturen und

Fig. 4:

einen Teil eines Brennerkörpers im Schnitt mit schematisch dargestellten unterschiedlichen Kühlstrukturen in seinem Innenraum.

Schematic exemplary embodiments of the invention, to which this is not limited, will now be explained in more detail with reference to the drawing. They represent:

Figure 1:

a burner body in longitudinal section with dome-shaped structures that protrude into its interior,

Figure 2:

a burner body with disc-like structures arranged on the outside in longitudinal section, installed in a combustion chamber with a heat exchanger,

Figure 3:

a snippet 2 with an overlap area of disc-like structures and

Figure 4:

a part of a burner body in section with different cooling structures in its interior shown schematically.

1 shows a schematic longitudinal section of a burner body 7 of a burner 5 for a heater 1, not shown in detail, which can be operated with conventional fuels, but in particular also with hydrogen or a hydrogen-containing fuel gas. The burner body 7 is attached to a so-called burner door (or burner flap) 6 and protrudes into a combustion chamber 2 . The burner body 7 has a length L and (if it is cylindrical as in the present embodiment) a diameter D and a longitudinal axis 9. An inlet-side end face 10 and an outlet-side end face 11 carry a cylindrical shell with holes 12. During operation of the burner 5, a fuel gas-air mixture G exits from these holes 12 from an interior space 8 of the burner body 7 into the combustion chamber 2 and is burned there with the formation of flames 13. It should be noted that with a low outflow speed (low burner 5 output) of the mixture G, the flames 13 are smaller but closer to the burner body 7 than with a higher outflow speed (higher output), so that overheating of the burner body 7 is more likely at low output than is to be feared with high performance. Namely, an outer surface 15 of the burner body is heated mainly by radiation of the flames 13 . To counteract overheating, structures 16, 17, 18, 19, 20 (shown in 1 only dome-shaped structures 16) are present, which protrude from an inner surface 14 of the burner body into the interior 8 and can dissipate heat there to the relatively cold fuel gas-air mixture G flowing there. Any increase in interior surface area 14 that does not increase the radiant heat impinging outside is useful. A wide variety of cooling structures are suitable, in particular all forms of cooling bodies known in the prior art.

2 also shows a schematic and longitudinal section of a burner 5, installed in a combustion chamber 2 with a surrounding heat exchanger 4, both surrounded by a housing 3. Combustion gas-air mixture G flows into the interior 8 of the burner 5 (indicated by a large arrow) and arrives through the holes 12 into the combustion chamber 2 where it burns to form flames 13. The resulting hot combustion gases (indicated by many small arrows) flow through the heat exchanger 4, give off a large part of the heat generated during combustion and then reach an outlet 26 as exhaust gas E. For the efficiency of the heater 1, it is important to have a Distance A between burner body 7 and heat exchanger 4 to be able to choose suitably, in particular greater than a burn-out height H, which the flames 13 need for complete combustion of the combustible gas-air mixture G. In order to still be able to build compact heaters 1, it is helpful to be able to use other measures (not shown here), namely cooling structures 16, 17, 18, 19, 20, to limit the temperature of the burner body 7 than just increasing the length L and/or the diameter D. With a compact design, however, there is another problem, namely the heating of areas 25 of the housing 3 that are not protected by the heat exchanger 4. In particular, this involves the burner door 6 and one of the opposite sides of the Housing 3 (both shown hatched). Disc-like structures 21 on the outside of the torch body 7 can help here, especially if the burner body 7 is cooled by additional measures, but also independently of this, particularly in conjunction with other disc-like structures 22 that are attached to the heat exchanger 4 . Such disk-like structures 21, 22 individually and particularly in combination provide shielding for the unprotected areas 25. For this purpose, the disk-like structures 21 are attached to the outside of the torch body 7 in end-face areas 24 of the torch body 7, essentially perpendicular to the torch axis 9. Parallel to this, further disc-like structures 22 attached to the heat exchanger 4 run, namely with a small gap of, for example, 0.1 to 10 mm gap width S in an overlapping area 23 (even touching the discs does not cause any damage, as long as they can move freely against each other during thermal expansion ). When the gap width S is so small, hardly any gas flows there, so that heat is transferred from the hotter disk to the colder one by radiation and conduction. Which of the two panes should be further out depends on the respective construction. In any case, the disk-like structure 21 and the further disk-like structure 22 not only shield the areas 25 that are not protected by the heat exchanger 4, but also transmit, depending on the circumstances Heat from the burner body 7 to the heat exchanger 4. The losses to the outside are in any case smaller. The exact constellation in the overlap area 23 is in 3 shown in detail.

3 shows a section 2 , namely the area around the overlapping area 23 of the disk-like structure 21 and the further disk-like structure 22. These structures 21, 22 may, since they should also conduct heat, have a thickness of z. B. have 1 to 3 mm. In fact, with a small gap width S, the overlapping area 23 has a similar effect to direct contact (the smaller the gap width S, the more similar). No radiation gets through and hardly any gas, but heat is transferred from the warmer to the colder structure 21,22.

In 4 Various possibilities for cooling structures 16, 17, 18, 19, 20 in the interior 8 of the burner body 7 are shown schematically, specifically in a section through a part of the burner body 7 with holes 12 . B. (between the holes 12) can be embossed and is therefore easy to manufacture. Such domes or dome-like points cause a larger surface and thus heat dissipation. Each type and size of rib-shaped structures 17 also has this effect, which is intensified in the case of structures 19 in the form of a fir tree or structures 20 in the form of antennas. Also lamellar structures 18 can contribute to the cooling.

The present invention makes it possible to build burners for compact heaters that can be adapted to various fuel gases, in particular also to hydrogen, and to largely avoid overheating and flashbacks and to reduce heat losses to the outside.

Reference List

1

heater

2

combustion chamber

3

Housing

4

heat exchanger

5

burner

6

burner door

7

torch body

8th

inner space

9

Longitudinal axis of the torch body

10

Entrance front side

11

Exit face

12

holes

13

Flames

14

inner surface

15

outer surface

16

Dome-shaped structures

17

Ribbed structures

18

Lamellar structures

19

Fir tree shaped structures

20

antenna-shaped structures

21

disk-like structures

22

Other disk-like structures

23

overlap area

24

Frontal area

25

Area not protected by the heat exchanger

26

outlet

A

Distance (torch body to heat exchanger)

E

exhaust

G

Mixture (fuel gas-air)

H

burnout height

L

axial length (of the torch body)

D

diameter (of torch body)

S

gap width

Claims (10)

Burner (5) for a heater (1) with a burner body (7) having an inner surface (14) towards an inner space (8) and an outer surface (15) towards a combustion chamber (2), with a plurality of holes (12) through which a fuel gas-air mixture (G) can flow from the interior (8) of the burner body (7) into the combustion chamber (2), the burner body (7) being at least on the inner surface (14) or the Outer surface (15) has structures (16 to 21) at least for the transport or for the shielding of heat. Burner (5) according to claim 1, wherein the structures (16 to 20) project into the interior (8) of the burner body (7) and are designed to transfer heat from the burner body (7) to the fuel gas flowing in the interior (8). Transport air mixture. Burner (5) according to claim 1 or 2, wherein the structures (16 to 20) increase the inner surface (14) of the burner body (7) which is in heat-transferring contact with the fuel gas-air mixture (G). Burner (5) according to Claim 3, the structures being dome-shaped (16), rib-shaped (17), lamellar-shaped (18), fir-tree-shaped (19) and/or antenna-shaped (20). Burner (5) according to one of the preceding claims, in which the structures (21) enlarge the outer surface (15) of the burner body (7), specifically in end regions (24) of the burner body (7). Burner (5) according to claim 5, wherein the structures (21) are disc-shaped and run approximately perpendicular to a longitudinal axis (9) of the burner body (7). Arrangement of a burner (5) according to one of the preceding claims, wherein the dimensions (L, D) and/or positioning of the burner (5) are arranged in a combustion chamber (2) with a heat exchanger (4), specifically at a predetermined distance (A) to the heat exchanger (4) and a predetermined burn-out height (H) of flames (13) arising during combustion of the combustible gas-air mixture (G). Arrangement of a burner according to claim 6, wherein the disk-shaped structures (21) run parallel to further disk-shaped structures (22) which are thermally conductively attached to a heat exchanger (4) arranged in the combustion chamber (2). Arrangement according to Claim 8, in which the disk-shaped structures (21) and the further disk-shaped structures (22) overlap at least in an overlapping region (23) and there is a gap width (S) of 0.1 to 10 mm between them. Arrangement according to claim 8 or 9, wherein the disk-shaped structures (21) and further disk-shaped structures (22) are designed to receive heat from flames (13) around the burner body (7) from areas (25) not protected by the heat exchanger (4) of a den Shield the combustion chamber (2) surrounding the housing (3).

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