METHOD FOR OPERATING A GAS BURNER

Description

[0001] The invention relates to a method for operating a gas burner. In such a method, a mixture of fuel gas and air is formed in a mixture chamber. The mixture is then conveyed at a controlled flow rate through an outlet opening on a burner surface that defines the boundaries of the mixture chamber. The mixture is subsequently combusted on the burner surface, generating a recirculation vortex. Finally, the exhaust gas produced during combustion is brought into contact with a fluid-cooled heat exchanger located at a distance from the outlet opening. This method has proven highly effective for the combustion of natural gas (i.e., hydrocarbon-containing gas mixtures).

[0002] The invention is based on the objective of improving a method of the type mentioned at the outset. In particular, a method for operating a gas burner is to be provided with which non-carbonous, i.e., carbon-free, gases, especially hydrogen, can also be burned.

[0003] This problem is solved by a method of the type mentioned at the outset by the features listed in claim 1.

[0004] According to the invention, the flow rate for the mixture and the distance between the outlet opening and the heat exchanger are selected such that the recirculation vortex extends from the outlet opening to the heat exchanger and that this (i.e., the recirculation vortex) is cooled at the heat exchanger.

[0005] In other words, the inventive method is characterized by the fact that the recirculation vortex is deliberately brought right up to the heat exchanger – and, in particular, in complete contrast (which will be discussed in more detail below) to natural gas combustion – in order to cool it there. This, in turn, allows the gas recirculated to the burner surface to cool it. As corresponding tests with a carbon-free gas as fuel, specifically hydrogen, have shown, this is very helpful in reliably preventing ignition of the gas-air mixture in the mixture chamber, i.e., a flashback, when using a carbon-free gas as fuel – even with high burner modulation.

[0006] The term "flow rate" used above, as also evident from claim 1, is to be understood as "flow rate per outlet opening," since the crucial factor is to control the exit impulse of the mixture from the outlet opening, as this impulse, being the product of mass flow rate and velocity, determines the length of the recirculation vortex. It is self-evident that the burner surface regularly has a plurality of outlet openings, and accordingly, according to the invention, an overall flow rate must be controlled for all outlet openings.

[0007] Furthermore, if the inventive method were applied to the aforementioned natural gas combustion, the combustion process would be prematurely interrupted, resulting in unacceptably high carbon monoxide emissions.

[0008] Other advantageous developments of the method according to the invention are set out in the dependent patent claims.

[0009] For the sake of completeness, reference is also made to document EP 3 467 383 A1, which does not describe premix combustion. While this solution also involves a recirculation vortex, it is cooled by a cooling element located directly on the burner surface itself.

[0010] The inventive method, including its advantageous further developments according to the dependent claims, is explained in more detail below with reference to the graphic representation of various embodiments.

[0011] It shows Figure 1 schematically shows a gas burner with a recirculation vortex extending to the heat exchanger; Figure 2 is a three-dimensional representation, generated by computer simulation, of a recirculation vortex extending to the heat exchanger; Figure 3 is a three-dimensional representation, generated by computer simulation, of a recirculation vortex not extending to the heat exchanger; Figure 4 is a diagram showing four different recirculation rates plotted against the relative distance between the outlet and the heat exchanger; and Figure 5 is a diagram showing four different mean temperatures of the exhaust gas recirculation plotted against the relative distance between the outlet and the heat exchanger.

[0012] The Figures 1 to 5 serve to explain the inventive method for operating a gas burner, in which (see in particular Figure 1) in a mixture chamber 1 a mixture is formed from a fuel gas and air, in which the mixture is conveyed at a controlled delivery rate through an outlet opening 2 on a burner surface 3 delimiting the mixture chamber 1, in which the mixture is burned on the burner surface 3 forming a recirculation vortex and in which exhaust gas formed during combustion is brought into contact with a fluid-cooled heat exchanger 4 arranged at a distance from the outlet opening 2.

[0013] As mentioned at the beginning, the requirement "one outlet opening" is always to be understood as "at least one outlet opening", whereby in the case of multiple outlet openings, a total funding rate is of course regulated for all existing outlet openings.

[0014] As can be further seen from the figures, it is preferably provided that next to each outlet opening 2 or next to a group of outlet openings 2, an area without outlet openings is always provided on the combustion surface 3, so that the recirculation vortex or vortices have enough space to return to the combustion surface 3. In this regard, particular reference is made to the Figures 2 and 3 References are made to the diagrams, which clearly show that only in one corner of the depicted section of the combustion surface 3 is a small cluster of outlet openings 2 provided, so that sufficient space is created for the resulting recirculation vortex to spread. In other words, the combustion surface 3 always has perforated and non-perforated areas on the one hand.

[0015] Essential for the method according to the invention is that the flow rate for the mixture and the distance between the outlet opening 2 and the heat exchanger 4 are selected such that the recirculation vortex extends from the outlet opening 2 to the heat exchanger 4 and that it is cooled at the heat exchanger 4.

[0016] In other words, it is therefore preferably provided that, based on the size of the outlet opening 2 and the flow rate, a length of the recirculation vortex is set according to a distance between the burner surface 3 and the heat exchanger 4.

[0017] As can be seen from the figures, the recirculation vortex (at least in a somewhat abstracted way) is generated by a vortex chamber enclosed by an outer boundary surface. With regard to the method according to the invention, it is particularly preferred that the longitudinal extent of the recirculation vortex (between the burner surface 3 and the heat exchanger 4) is approximated such that an end of the boundary surface of the recirculation vortex facing away from the outlet opening just touches the heat exchanger 4. This situation is in Figures 1 and 2 depicted. Figure 3 In contrast, this shows a situation in which the boundary surface of the vortex chamber does not reach the heat exchanger 4.

[0018] Furthermore, it is preferably provided that the exhaust gas, cooled at the heat exchanger 4 and returned to the burner surface 3 by means of the recirculation vortex, heats the burner surface 3, in particular the outlet opening 2, to a lesser extent compared to recirculated exhaust gas that has not been cooled at the heat exchanger 4. In other words, the burner surface 3 is ultimately heated less by the exhaust gas cooled at the heat exchanger 4 than by exhaust gas that has been recirculated but not cooled at the heat exchanger. This requirement ultimately and advantageously results in lower nitrogen oxide levels in the exhaust gas.

[0019] Regarding the gas burner, it is particularly preferred that it be used with outlet openings 2 with a so-called hydraulic diameter (see also https: / / de.wikipedia.org / w / index.php?title=Hydraulischer_Durchmesser& oldid=207793375) of 0.6 to 1.2 mm.

[0020] Furthermore, it is preferably provided that a gas burner is used in which the outlet openings 2 are located a maximum of 30 to 100 mm away from the heat exchanger 4, based on their shortest possible distance to it.

[0021] Furthermore, as can ultimately be seen from a three-dimensional abstraction of the Figure 1 This results, preferably, in the optional use of a cylindrically shaped burner surface 3 and / or a cylindrically shaped heat exchanger 4. Also in the Figures 2 and 3, which show the corresponding cylinder segments, it is assumed that the burner surface 3 or the heat exchanger 4 has a corresponding design.

[0022] With regard to the aforementioned fuel gas, it is preferably provided, and the inventive method is particularly well suited to this application, that a carbon-free gas is used as the fuel gas. More precisely, it is preferably provided that a gas containing at least some hydrogen is used as the fuel gas. Most preferably, (practically pure) hydrogen is used as the fuel gas.

[0023] Finally, we will also mention the Figures 4 and 5 Note: As mentioned above, in Figure 4Four curves of the recirculation rate R are plotted against the relative distance A between the burner surface 3 and the heat exchanger 4. The recirculation rate R is the ratio of the actually recirculated mass flow rate to the mass flow rate at the outlet 2. The recirculation rate R is therefore a dimensionless quantity. The relative distance A is also dimensionless, where the burner surface 3 corresponds to the value 0 and the heat exchanger 4 to the value 100. Curves 1 to 3 show curves in which the recirculation vortex does not reach the heat exchanger 4. In contrast, this is the case in the fourth curve (solid line).

[0024] In Figure 5The mean temperature T (in °C) of the recirculated exhaust gas is plotted against the dimensionless distance A for the same four situations. As can be seen, the temperature of the exhaust gas (curves 1 to 3) that does not reach the heat exchanger 4 is approximately 1600°C. However, if the recirculation vortex reaches the heat exchanger 4 by adjusting the flow rate accordingly (given a specific size of the outlet opening 2 and a specific distance between the burner surface 3 and the heat exchanger 4), the exhaust gas can cool down by around 600°C at the heat exchanger 4. This, in turn, means that the gas burner can be operated effectively, especially with hydrogen, even with high burner modulation. Reference symbol list

[0025] 1 Mixing chamber 2 Outlet opening 3 Burner surface 4 Heat exchanger

Claims

1. A method for operating a gas burner, in which a mixture of fuel gas and air is formed in a mixing chamber (1), in which the mixture is conveyed at a controlled flow rate through an outlet opening (2) on a burner surface (3) delimiting the mixing chamber (1), in which the mixture is burned on the burner surface (3) with the formation of a recirculation vortex, and in which the exhaust gas produced during the combustion is brought in contact with a fluid-cooled heat exchanger (4) arranged at a distance from the outlet opening (2), wherein the flow rate for the mixture and the distance between the outlet opening (2) and the heat exchanger (4) are chosen such that the recirculation vortex extends from the outlet opening (2) to the heat exchanger (4) and is cooled at the heat exchanger (4).

2. The method according to claim 1, wherein a length of the recirculation vortex is adjusted in accordance with a distance between the burner surface (3) and the heat exchanger (4) on the basis of a size of the outlet opening (2) and the flow rate.

3. The method according to claim 1 or 2, wherein the recirculation vortex is generated with a vortex chamber enclosed by an outer boundary surface, and wherein a longitudinal extent of the recirculation vortex is approximated in such a way that an end of the boundary surface of the recirculation vortex facing away from the outlet opening just touches the heat exchanger (4).

4. The method according to one of claims 1 to 3, wherein the exhaust gas that is cooled at the heat exchanger (4) and returned to the burner surface (3) by means of the recirculation vortex heats the burner surface (3) to a lower temperature than recirculated exhaust gas that has not been cooled at the heat exchanger (4).

5. The method according to one of claims 1 to 4, wherein a gas burner with outlet openings (2) having a diameter of 0.6 to 1.2 mm is used.

6. The method according to one of claims 1 to 5, wherein a gas burner is used, in which the outlet openings (2) are located at a maximum distance of 30 to 100 mm from the heat exchanger (4) in relation to their shortest possible distance from the heat exchanger (4).

7. The method according to one of claims 1 to 6, wherein a cylindrical burner surface (3) is used.

8. The method according to one of claims 1 to 7, wherein a cylindrical heat exchanger (4) is used.

9. The method according to one of claims 1 to 8, wherein a carbon-free gas is used as fuel gas.

10. The method according to one of claims 1 to 9, wherein a gas containing at least a proportion of hydrogen is used as fuel gas.