DE102021123219A1 - Burner for a heating device that can essentially be operated with hydrogen - Google Patents

Abstract

The invention relates to a burner (5) for a heater (1) that can be operated essentially with hydrogen, with a burner jacket (7) which separates an interior (8) from a combustion chamber (2) and channels (12) which are separated from a Stretch the inlet end (10) on a jacket inner surface (14) to an outlet end (11) on a jacket outer surface (15) and which are set up to convey the fuel gas-air mixture (G) from the interior (8) into the combustion chamber (2) to direct, wherein the channels (12) at their outlet end (11) have a flow guide structure (16) which cause an increase in the distance (F) of flames (13) to the outer surface (15) of the jacket.

Description

The invention relates to a burner for a heating device that can be operated with pure hydrogen and/or a fuel gas that essentially contains hydrogen. 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. The present invention is particularly suitable for such heaters that should or can be operated with pure hydrogen or with fuel gas that consists of more than 50%, in particular more than 97%, hydrogen.

Pot-shaped (usually cylindrical) burners, which can also have shapes deviating from the cylindrical shape (e.g. the shape of a rectangle, a rounded rectangle, a curved shape or similar shapes) are widely known in heating devices. 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 combustible 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 is to be aimed for over the entire modulation range (range of differently adjustable output) 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 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 fuel 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.

It is the object of the present invention to at least partially solve the problems described with reference to the prior art and in particular to create a particularly advantageous burner for operation with hydrogen as the fuel.

These objects are solved with the invention according to the features of the independent patent claims. Further advantageous configurations are specified in the dependently formulated patent claims and in the description and in particular also in the description of the figures. It should be pointed out that a person skilled in the art can combine the individual features with one another in a technologically sensible manner and thus arrive at further configurations of the invention.

A burner for a heater that can be operated essentially with hydrogen is to be described here, with a burner shell that separates an interior space from a combustion chamber and channels that extend from an inlet end on a shell inner surface to an outlet end on a shell outer surface and that are set up to to direct the fuel gas-air mixture (G) from the interior into the combustion chamber, the channels having a flow guide structure at their outlet end, which increases the flame amount of distance (F) from flames to the outer surface of the jacket.

The burner jacket can also be referred to as the burner body. The burner casing or the burner body is preferably a cylindrically shaped body which is closed on one side at the end. On the end face opposite the closed side, there is preferably an inlet through which the fuel-air mixture to be burned can be introduced into the interior of the burner. The channels are preferably arranged on the peripheral surface of the burner shell. There are preferably a large number of individual channels, for example 100 or 500 or more channels. The output of the burner is defined by the number of channels. This means that the number of channels determines how much fuel can pass from the interior into the combustion chamber per unit of time and burns and thus generates heat output.

Flame standoff is the distance that the bottom (upstream) end of burner flames is from the outer shell surface of the burner shell during normal operation. It may be that the distance between the flames is not reached for a short time. The distance between the flames may also vary depending on the operating point of the burner. The purpose of the flow guide structure at the outlet end is to fundamentally increase the distance between the flames compared to a corresponding design of the burner jacket and the channels without such interference guide structures.

The flow guide structures make it possible to reduce heat transfer from the flames to the burner jacket. The heat transfer takes place in particular by radiation. Other heat transfer mechanisms such as thermal diffusion and convection may also occur. Increasing the flame spacing reduces the transfer of heat to the burner shell. This can increase the durability of the burner jacket.

It is particularly preferred if the channels have a channel diameter (d) between 0.2 mm [millimeter] and 1 mm [millimeter].

It is also preferred if the channels and/or the flow guide structure are designed and dimensioned in such a way that a flame burning in the combustion chamber is extinguished under all operating conditions within a channel by energy being released to the burner jacket.

The channels are preferably designed with a circular cross-section. A channel cross-sectional area is then defined by the channel diameter. The channel cross-sectional area is preferably <0.8 mm ² . A small channel cross-section or a small channel diameter of less than 1 mm ensures that the mixture flows through the channels at a relatively high speed. At the same time, there is a pressure loss in the mixture as it flows through the channels. In this way, safety against flashback of flames from the combustion chamber into the interior space within the burner shell can be achieved.

In addition, it is preferred if the flow guide structure is implemented by at least one extension of the channels, which extends beyond the outer surface of the casing.

In this context, the shell outer surface is preferably to be understood as a surface that defines an outer basic shape of the burner shell. As already described, this basic shape of the burner casing is, for example, cylindrical. Extensions locally extend beyond this basic form. An extension may individually extend beyond the shell outer surface for a single channel. It is also possible that a plurality of channels positioned close to one another or closely adjacent to one another have a common extension or are formed in a common extension which forms flow guide structures.

By extending the channels, the channels are lengthened away from the outer surface of the shell, as a result of which the mixture is guided away from the outer surface of the shell. This increases the distance of flames from the outer surface of the jacket. In this way, the outer surface of the casing can be protected against flames.

It is also preferred if the at least one extension is designed in the manner of a crater.

Extensions designed as craters can also be understood or described as conical or approximately conical elevations on the outer surface of the casing. Such extensions designed as craters can be produced, for example, by pressing material of the burner shell outwards from the inside (starting from the inner surface of the shell) during the production of channels. This material then preferably extends beyond the outer surface of the jacket and forms the extensions.

It is also preferred if the channels are in reinforced areas where the burner is located jacket has a greater wall thickness (w) than in other areas.

In such embodiments, additional material for the formation of extensions is preferably already present in a starting material for the manufacture of the combustor shell with channels. Particularly preferably, a reinforced area of the burner jacket with a greater wall thickness forms a common extension, in or on which mutually adjacent channels are arranged. The common extension then forms the flow guide structure in the channels formed in or on the area with an increased wall thickness.

In a further preferred embodiment, the ducts are formed by small tubes which are integrated into the burner shell and which extend beyond the outer surface of the shell in order to form flow guide structures designed as an extension of the ducts.

The tubes can be designed, for example, in the form of short cannulas that form a very thin channel on the inside and that are placed in the burner jacket or in a base material of the burner jacket. On the one hand, these tubes or these cannulas are part of the burner jacket. On the other hand, they extend beyond the outer surface of the jacket into the combustion chamber of the burner. Through the use of such small tubes, channels can be formed that extend particularly far into the combustion chamber beyond the outer surface of the jacket. In this way, a particularly large distance between the flames can be achieved. Such small tubes can, for example, be soldered or welded to a base material of the burner jacket.

It is also particularly preferred if the flow guide structure is formed by a channel cross section that decreases in the direction of flow through the channels.

On the one hand, cross sections that decrease in the direction of flow can ensure that the flow of the mixture is accelerated further towards the outlet end and the flames are pushed further away from the outer surface of the jacket by the impulse of the flow of the mixture, thus increasing the distance between the flames. In addition, cross sections that decrease in the direction of flow can also ensure that the static pressure of the mixture continues to decrease with increasing speed along the direction of flow in the channels. This is advantageous in preventing flashback of flames because the flames cannot flash back towards the higher pressure.

It is also preferred if the channels are arranged in protuberances and/or local thickenings of the burner shell towards the combustion chamber.

In addition, crater-shaped extensions can also be produced in which the burner shell is pressed outwards as a whole in the region of the channels, so that a protuberance is formed on the outer surface of the shell and a dent on the inner surface of the shell. The formation of extensions can also be implemented in combination (partly by displacing material from the channels, partly by creating dents on the inner surface of the jacket, which form protuberances on the outer surface of the jacket).

It is also preferred if the channels have a round or slit-shaped channel cross section.

Channels with a round cross-section are often particularly easy to produce. Channels with a slit-shaped cross-section make it possible to design the ratio of diameter to cross-sectional area of the channels in a more targeted manner than with round channel cross-sections. A relatively high flow resistance can be generated in ducts with a large duct cross-sectional area, because the flow resistance essentially occurs at the walls of the duct and the ratio of cross-section through which flow can take place to the wall area is always greater in ducts with a slit-shaped duct cross-section than in ducts with a round duct cross-section.

It is also preferred if the burner casing has a wall thickness (w) of more than 1 mm [millimeter] at least in partial areas and the channels are arranged in these partial areas.

The greater the wall thickness of the burner shell, the longer the channels and the greater the flow resistance of the channels for the mixture. Relatively large wall thicknesses of the burner jacket are proposed here in order to increase the flow resistance of the channels. Slightly larger channel diameters can thus be implemented. Or in other words: In order to achieve a certain flow resistance, it is not necessary to realize such small channel diameters due to the large wall thickness.

It is also preferred if the partial areas are designed as axial and/or circumferential ribs.

Such ribs can, for example, extend axially along the longitudinal axis of the burner shell. However, such ribs can also extend circumferentially around the burner casing.

In addition, it is advantageous if the burner jacket is made in one piece

The fact that the burner jacket is made in one piece means in particular that the burner jacket was made from a single piece. The burner jacket is preferably made from a piece of sheet metal, which is bent over to form a cylinder and is soldered or welded at an axial seam of the cylinder. A one-piece burner jacket is easy to manufacture and particularly stable. In particular, no connections between individual components of the burner casing can become detached from one another.

• 1: einen beschriebenen Brenner;
• 2: ein Heizgerät mit einem beschriebenen Brenner; und
• 3a bis 3f : verschiedene Ausführungsvarianten von Kanälen durch den Brennermantel eines beschriebenen Brenners.

The invention and the technical context of the invention are explained in more detail below with reference to the figures. The figures show preferred exemplary embodiments to which the invention is not restricted. It should be pointed out in particular that the figures and in particular the proportions shown in the figures are only schematic. Show it:

• 1 : a described burner;
• 2 : a heater with a described burner; and
• 3a until 3f : Different design variants of channels through the burner jacket of a described burner.

1 shows a described burner 5, which is, for example, directly connected to a burner door 6, which is preferably covered with insulation 22 outside of the burner 5 in order to be protected from flames 13 in a combustion chamber 2. The burner 5 has a burner casing 7, which can also be referred to as a burner body, and which is designed here as a round cylinder with a longitudinal axis 23, an axial length L and a diameter D. The burner shell 7 separates an interior 8 from the combustion chamber 2 . Shapes other than a round cylinder are possible for the burner jacket 7. Flames 13 only occur outside of the burner jacket 7 in the combustion chamber 2 . Flames 13 should not and cannot flash back into the interior 8. Mixture G of fuel gas and air flows through ducts 12 in the burner jacket 7 from the interior 8 into the combustion chamber 2. Other passages from the interior 8 into the combustion chamber 2 are closed, so that mixture G flows into the combustion chamber 2 only through these ducts 12 can. The burner shell 7 has a shell inner surface 14 oriented toward the interior 8 and a shell outer surface 15 oriented toward the combustion chamber 2. The channels 12 extend from an inlet end 10 on the shell inner surface 14 to an outlet end 11 on the shell outer surface 15. The channels 12 are each with Flow guide structures are designed at the outlet ends 11, which are explained in more detail above in the description and below with reference to the other figures and which influence the flow of the mixture G through the channels 12 and in particular the outflow of the mixture G at the outlet ends 11 of the channels 12 in such a way that that a flame distance F of the flames 13 to the burner shell 7 is increased.

Another feature is in 1 shown that channels 12 can be arranged through the burner shell 7 in the region of ribs 21 of the burner shell 7, in which the burner shell 7 is thickened. This feature in particular is only optional.

2 shows the in 1 The burner 5 shown is inside a (partially) shown heater 1 with a housing 3. It can be seen that a heat exchanger 4 is arranged circumferentially around the burner 5, with which the heat generated by the flames 13 during combustion can be recovered . All housing areas 3 that are not covered by the burner 5 (with the burner casing 7) or the heat exchanger 4 and that adjoin the combustion chamber 2 are preferably provided with insulation 22. These unprotected wall areas 25 can thus be protected from being destroyed or damaged by the flames 13 . In addition, a dissipation of heat via these wall areas is prevented. In 2 also shows that the housing 3 has an inlet 26 through which mixture G can flow into the interior 8, and an exhaust gas outlet 24 through which exhaust gas E can flow out of the combustion chamber 2 as soon as it has given off the heat to the heat exchanger 4 . The flames 13 burn in the combustion chamber 2 in such a way that on the one hand a flame distance F from the burner casing 7 is maintained and on the other hand a burn-out height H (a path that the flames 13 travel, starting from the burner casing 7, before they go out or the mixture G is completely burned is) is smaller than the distance A between the burner jacket 7 and the heat exchanger 4.

In 3a until 3f is shown on a section of the burner casing 7 in each case how the described flow guide structures 16 can be designed. 3a until 3f show examples of different variants of flow guide structures 16. A variant of a specific burner jacket 7 with different Configurations of flow guide structures 16 are possible, but not preferred. Through the representation in 3a until 3f the embodiment variants of the flow guide structures 16 are presented. Usually, all flow guide structures 16 on channels in a burner jacket 7 are designed the same (according to a single embodiment variant). For example, all the flow guide structures 16 of a burner jacket 7 according to the embodiment according to FIG 3a executed. The burner shell 7 has a wall thickness W, an inner shell surface 14 and an outer shell surface 15. The channels 12 extend from the inner shell surface 14 to the outer shell surface 15. The channels 12 begin with an inlet end 10 on the inner shell surface 14 and end on the outer shell surface 15 the outlet end 11. From the inlet end 10 to the outlet end 11, the mixture G flows through the channels 12 with the flow direction 19. The flow guide structure 16 influences the exit of the mixture G from the channels 12 at the exit end 11, so that a flame distance F of the beginning of the flames 13 between the burner casing 7 and the beginning of the flames 13 is ensured.

According to the embodiment variant 3a the channel 12 is arranged in a reinforced area 18 of the burner jacket 7, in which the wall thickness W of the burner jacket 7 is increased. The burner casing 7 is preferably thickened here towards the outer surface 15 of the casing. This increases a length of the channel 12 and the mixture G is carried further away from the shell outer surface 15 before the flame 13 begins. A flow guide structure 16 is thus formed.

According to the embodiment variant 3b a tube 9 forms the channel 12 which extends beyond the outer shell surface 15, forms an extension 17 and carries the mixture G away from the outer shell surface 15 before the flame 13 begins. A flow guide structure 16 is thus formed. The tube 9 can be made in one piece with the other material of the burner jacket 7 . The tube 9 can also be a separate component which is inserted into openings in the outer surface 15 of the jacket. The tube 9 forms the channel 12 with the channel diameter d, which is smaller than the diameter D of an opening in the jacket outer surface 15, in which the tube 9 is inserted. Such a tube 9 can, for example, be soldered or welded into the burner jacket 7 .

According to the embodiment variant 3c an extension 17 is shown, which extends the channel 12 beyond the outer surface 15 of the casing and thus forms a flow guide structure 16 which guides the mixture G away from the outer surface 16 of the casing. The extension 17 or the flow guide structure 16 is designed here as a crater-like structure. Such an extension 17 can be produced, for example, in that the material of the burner jacket 7 is displaced from the channel 12 when the channel 12 is produced, starting from the jacket inner surface 14 and outwards (towards the jacket outer surface 15). The extension 17 shown here is preferably beveled on the outside. In further preferred embodiment variants, the channel 12 is additionally designed in such a way that it tapers along the direction of flow 19 starting from the inlet end 10 towards the outlet end 11 . This means that the channel 12 has a channel cross section 20 that decreases in the direction of flow 19 and/or a channel diameter d that decreases in the direction of flow. As a result, the flowing mixture G is accelerated towards the outlet end 11 . At the outlet end 11, the channel cross section 10 and/or the channel diameter d of a channel 12 are preferably the smallest. For this reason, the greatest velocity of the mixture G preferably occurs at the outlet end 11 . Due to the larger channel cross sections 20 or channel diameters d in other areas of the channel 12, the flow resistance is reduced overall. Lower flow velocities occur there. This causes a higher static pressure of the mixture G upstream. This makes it more difficult for flames 13 to flash back into the channels 12 and possibly even prevents it.

In the variant according to 3d there is no extension 17, but the flow guide structure 16 is (only) realized by reducing the channel cross section 10 and/or the channel diameter d along the flow direction 19 from the inlet end 10 to the outlet end 11. The reduction of the channel cross section 10 and/or the channel diameter d along the direction of flow 19 is not continuous here, but stepped. In a first channel section 27 there is a first channel cross section 20 and/or a first channel diameter d at the inlet end 10, which is preferably constant at least in sections along the direction of flow 19. In a second channel section 28 there is a second channel cross section 20 and/or a second channel diameter d at the outlet end 11, which is preferably constant at least in sections along the direction of flow 19. Between the first channel section 27 and the second channel section 28 there is a third channel section 29 in which the channel cross section 20 or the channel diameter d preferably tapers in the direction of flow 19 in order to form a transition.

In the variant according to 3e there is no extension 17, but the flow guide structure 16 is (only) by reducing the Channel cross-section 10 and / or the channel diameter d realized along the flow direction 19 from the inlet end 10 towards the outlet end 11, which, however, from the inlet end 10 towards the outlet end 11 is continuous.

In the variant according to 3f there is a protuberance 30 of the burner casing 7 beyond the outer surface 15 of the casing, which is produced, for example, by pressing out a section of the burner casing 7 starting from the inner surface 14 of the casing. A dent 31 that recedes into the burner shell 7 compared to the inner shell surface 14 preferably also occurs on the inner shell surface 14. The protuberance 30 forms an extension 17 and thus also the flow guide structure 16. The dent 31 itself also forms part of the channel 12 or an inlet area into the channel 12 at the entry end 10.

Variants are also recorded, according to which the exemplary embodiments 3c and 3f are designed to be combined with one another, so that on the one hand the combustion jacket 7 is (slightly) protruded and protuberances 30 and dents 31 arise and on the other hand material is displaced outwards by the production of the channel 12 . The extension 17 or the flow guide structure 16 is then preferably formed from the material of the burner jacket 7 , which was partially displaced to the outside by the formation of the indentation 31 and partially by the formation of the channel 12 .

Reference List

1

heater

2

combustion chamber

3

Housing

4

heat exchanger

5

burner

6

burner door

7

burner jacket

8th

inner space

9

tube

10

entry end

11

exit end

12

channel

13

Flames

14

jacket inner surface

15

shell outer surface

16

flow guide structure

17

extension

18

reinforced area

19

flow direction

20

channel cross-section

21

rib

22

insulation

23

longitudinal axis

24

exhaust outlet

25

unprotected wall areas

26

inlet

27

first canal section

28

second canal section

29

third canal section

30

protuberance

31

dent

A

Distance

E

exhaust

G

mixture

H

burnout height

L

axial length

D

diameter

f

flame distance

i.e

channel diameter

W

wall thickness

Claims (13)

Burner (5) for a heating device (1) that can be operated essentially with hydrogen, with a burner jacket (7) which separates an interior space (8) from a combustion chamber (2) and channels (12) which extend from an inlet end (10) stretch on an inner surface (14) to an outlet end (11) on an outer surface (15) and which are set up to conduct the fuel gas-air mixture (G) from the interior (8) into the combustion chamber (2), the Channels (12) have a flow guide structure (16) at their outlet end (11), which causes an increase in a flame distance (F) from flames (13) to the outer surface (15) of the casing. Burner (5) after claim 1 , wherein the channels (12) have a channel diameter (d) between 0.2 mm [millimeter] and 1 mm [millimeter]. Burner (5) after claim 1 or 2 , Wherein the channels (12) and / or the flow guide structure (16) are designed and dimensioned so that a The flame (13) burning in the combustion chamber (2) is extinguished under all operating conditions within a duct (12) due to the transfer of energy to the burner jacket (7). Burner (5) according to one of the preceding claims, in which the flow guide structure (16) is formed by at least one extension (17) of the channels (12) which extends beyond the outer surface (15) of the jacket. Burner (5) after claim 4 , wherein the at least one extension (17) is designed in the manner of a crater. Burner (5) according to one of the preceding claims, in which the channels (12) are located in reinforced areas (18) where the burner shell (7) has a greater wall thickness (W) than in other areas. Burner (5) according to any one of the preceding Claims 1 , the channels being formed by small tubes (9) which are integrated into the burner jacket (7) and which extend beyond the outer surface (15) of the jacket in order to form flow guide structures (16) designed as an extension (17) of the channels (12). . Burner (5) according to one of the preceding claims, wherein the flow guide structure (16) is formed by a channel cross section (20) decreasing in the direction of flow (19) through the channels (12). Burner (5) according to one of the preceding claims, in which the channels (12) are arranged in protuberances (30) and/or reinforced areas (18) of the burner jacket (7) towards the combustion chamber (2). Burner (5) according to one of the preceding claims, in which the channels (12) have a round or slot-shaped channel cross section (20). Burner (5) according to one of the preceding claims, wherein the burner casing (7) has a wall thickness (W) of more than 1 mm [millimeter] at least in partial areas and the channels (12) are arranged in these partial areas. burner (5) claim 11 , wherein the partial areas are designed as axial and/or circumferential ribs (21). Burner (5) according to one of the preceding claims, in which the burner casing (7) is made in one piece.

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