Patent Application
20250109851
The present invention relates to a burner device, a heat generator with a burner device, a heating system and a service water supply system, each with a heat generator, and a method for vibration adaptation of a burner device.
Burner devices for use in heat generators are known from the prior art, in which a premixed air-fuel mixture is conducted into a flame body in order to be subsequently combusted on an outer surface of the flame body acting as a combustion surface. This concept corresponds to a so-called premix burner.
Depending on the composition of the fuel, the air-fuel mixture can have different flame propagation speeds, which under certain circumstances can lead to an undesired recoil of the burner flame located on the combustion surface into the flame body. This phenomenon can be observed in particular when using hydrogen-containing fuels, since hydrogen has a higher flame propagation speed than conventionally used fossil fuels.
In order to prevent such a recoil, or at least to limit the propagation thereof within the flame body, flame barriers are known from the prior art, inter alia from EP 4 160 092 A1, which allow a permeability for the air-fuel mixture in the direction of the combustion surface, but do not allow passage of a burner flame recoiling from there.
In connection with the premix burners, thermoacoustic problems also arise, which are caused by the acoustic waves emitted during the combustion as a result of thermal expansion being reflected in the combustion chamber and in turn being able to have an effect on the combustion itself and thus constituting a vibrational self-excitation mechanism.
Systems capable of vibration with self-excitation can have, depending on the system architecture and the selected operating parameters, unstable operating states in which vibrations with a comparatively high amplitude occur, in particular in the form of a so-called limit cycle vibration.
If such a state of thermoacoustic instability occurs in a burner device, the vibrations induced by the self-excitation can lead to incomplete combustion of the air-fuel mixture, to flame flashbacks and to an increased sound emission, which are all undesired operating states.
Previous approaches to solving this thermoacoustic problem aim at regulating the individual operating parameters of the burner device, such as, for example, the mass flow of the air-fuel mixture to be combusted, in order thus to exert a targeted influence on the burner flame and thus on the acoustic waves emitted thereby and thus to keep the system in a thermoacoustically stable operating state.
However, this approach reaches its limits in particular with the increasing use of hydrogen-containing fuels, since it becomes difficult with increasing hydrogen content, owing to the low ignition delay times of the hydrogen itself, to exert a targeted influence on the burner flame by regulating.
The present invention is thus based on the object of providing a possibility, which is improved over the prior art, for combustion-based heat generation with a thermoacoustically stabilized burner device, in particular for use with hydrogen-containing fuels.
In order to achieve this object, a burner device according to claim 1 is provided and, based thereon, a heat generator according to claim 13, a heating system according to claim 14 and a service water supply system according to claim 15. Furthermore, the invention provides a method for vibration adaptation of a burner device according to claim 12.
The respective dependent claims relate here to preferred embodiments which can each be provided by themselves or in combination.
According to a first aspect, a burner device for providing thermal energy by combustion of an air-fuel mixture is provided. The burner device comprises a flame body which delimits an interior space which is connected via openings in the flame body to an outer combustion surface of the flame body, on which the combustion of an air-fuel mixture, which is introduced into the interior space and flows through the openings, takes place in one or more burner flames, and a flow guiding device which comprises an axial flow channel, which is located mostly or completely in the interior space, for guiding through the air-fuel mixture, which runs in particular parallel to a longitudinal axis of the flame body, the axial length of which is selected as a function of an oscillation frequency induced by the one or more burner flames.
In this way, a type of resonator for the air-fuel mixture is formed in the interior space, which resonator is adapted to the oscillation frequency and via which the vibration behavior of the entire burner device is significantly changed in comparison with an embodiment without a flow guiding device, in order thus in particular to reduce vibrations of the burner device and/or of the components thereof, as a result of which the risk of incomplete combustion and/or of flame flashbacks is reduced, which in turn increases the efficiency of the burner device. In addition, this results in a lower sound emission during operation, which is perceived by the user as high comfort.
The proposed burner device thus solves the problem of thermoacoustic instability by introducing a structure, which is located upstream of the combustion surface, in the form of the flow guiding device, as a result of which, for example, a regulation of individual operating parameters directed to the thermoacoustic instability would in principle also be superfluous.
In this case, the burner device is preferably configured for the combustion of an air-fuel mixture with hydrogen-containing fuel.
Hydrogen-containing fuel is to be understood as meaning a fuel which contains a certain proportion of elemental hydrogen (H2). Further combustion gas constituents may be methane, propane, butane or inert gases such as, for example, nitrogen and carbon dioxide. A proportion of the hydrogen is preferably between 10 and 100% by volume, particularly preferably between 30 and 100% by volume. The permissible constituents of the gases (also hydrogen contents) are recorded in relevant standards (for example EN 437), according to which the devices are approved/released.
The longitudinal axis of the flame body is to be understood as meaning a longitudinal axis which runs through the center of the interior and is encased by the surface of the flame body acting as a combustion surface. In other words, said surface is to be understood as meaning a lateral surface which runs along the longitudinal axis. The flame body is preferably configured such that the openings for connecting the combustion surface and the interior space run at an angle, in particular at a right angle, to the longitudinal axis.
To put it simply, the longitudinal axis of the flame body preferably corresponds to a central axis perpendicular to discharge directions of the air-fuel mixture from the openings. A radial direction of the flame body is to be understood below with respect to said longitudinal axis.
In this case, the axial flow channel is obviously impermeable to the air-fuel mixture in said radial direction and also does not fill the entire interior space, but only a partial quantity thereof, so that there are also regions in the interior space through which the air-fuel mixture flows but which are not located in the axial flow channel.
The flame body preferably has a substantially cylindrical shape, in particular a circular cylindrical shape, with a cylinder jacket acting as a combustion surface and preferably an end face which delimits the interior space along in the direction of the longitudinal axis. In the case of the cylindrical shape, the longitudinal axis would in this case be to be understood as meaning a central vertical axis of the cylinder.
The circular cylindrical embodiment in this case allows a flow cross section of the axial flow channel which is substantially constant over the longitudinal axis and is thus easy to implement in terms of design.
Throughout the entire application, the term cylindrical is to be understood as referring to a general cylinder according to the standard definition from mathematics. A circular cylinder in this case is intended to denote a special cylinder with a circular base or top surface.
The delimitation of the interior space in this case is not to be understood as a complete delimitation or encasing of the interior space in all three spatial directions. Rather, the flame body leaves at least one opening open to the interior space, through which opening the air-fuel mixture is introduced into said interior space, preferably via an inlet surface which corresponds entirely or partially to an opening surface of the at least one opening to the interior space or emerges from said opening surface by parallel displacement of a partial surface or of the entire opening surface. In this case, the inlet surface and the opening surface are usually at a right angle to the longitudinal axis of the flame body.
The oscillation frequency, as a function of which the length of the axial flow channel is fixed or selected, is preferably an oscillation frequency of a vibration, which is to be reduced, of the burner device during operation without a flow guiding device or with an “unadapted” length of the flow guiding device.
In this case, it is preferably an oscillation frequency of the burner device itself (as an assembly composed of solid bodies) or an oscillation frequency of the combustion, that is to say an oscillation frequency of the pressure oscillation which arises in this case.
The oscillation frequency can be an oscillation frequency from a measured frequency spectrum of the burner device during operation, preferably an oscillation frequency with a comparatively high amplitude in the frequency spectrum, which oscillation frequency is to be reduced by the flow guiding device.
However, the oscillation frequency can also be determined, that is to say determined in a computer-assisted manner, by simulation, for example by FE and/or CFD simulation, preferably with modal analysis.
The length is preferably selected such that a standing wave of the air-fuel mixture forms in the axial flow channel, the frequency of said standing wave substantially corresponding to the induced oscillation frequency.
In a preferred embodiment, the axial length is selected as a function of an oscillation frequency of the burner device, which oscillation frequency occurs when the burner device is operated without a flow guiding device.
In this way, the frequency range in which a vibration which is to be reduced occurs can be identified particularly well.
In a preferred embodiment, the axial length is additionally selected as a function of the speed of sound of the air-fuel mixture, and preferably as an additional function of a length of the interior space in the direction of the longitudinal axis of the flame body.
In this way, the specific properties of the air-fuel mixture actually used can be taken into account in the design. In particular if hydrogen-containing fuel is used, since said hydrogen-containing fuel has a comparatively great influence on the speed of sound.
By including the length, it is possible to select the maximum possible length of the flow channel which still fits into the interior space, in order thus to maximize the effect of the resonator.
Alternatively, it is possible to use the average speed of sound of air which, however, delivers less accurate results in the selection of the suitable length.
In a preferred embodiment, a ratio of a cross-sectional area of the axial flow channel in a cross section perpendicular to the longitudinal axis of the flame body to an inlet surface via which the air-fuel mixture is introduced into the interior space is greater than or equal to 15%, in particular greater than or equal to 25%.
In this way, a sufficiently large amount of air can be provided in the resonator in order to effectively reduce the vibrations at the desired frequency.
The ratio of the cross-sectional area of the axial flow channel in the cross section perpendicular to the longitudinal axis of the flame body to the inlet surface is preferably less than or equal to 90%, in particular less than or equal to 80% and in particular less than or equal to 75%.
As a result, sufficient space is available in the interior space in order to ensure a supply of all openings of the flame body with air-fuel mixture despite the flow guiding device located in the interior space.
The interior space and the axial flow channel preferably have a cylindrical cross section, wherein an inner diameter of the flow channel corresponds to at least 25% of a diameter of the inlet surface, in particular 50% of the diameter of the inlet surface.
In a preferred embodiment, the axial flow channel is arranged centrally with respect to the flame body, so that, in the cross section perpendicular to the longitudinal axis of the flame body, it is spaced apart from a circumferential inner wall of the flame body adjoining the interior space.
As a result, a particularly symmetrical design is implemented, in which the resonator is arranged in the center and the air-fuel mixture which does not flow through the axial flow channel flows circumferentially around said resonator.
In a preferred embodiment, the flow guiding device comprises further flow channels for guiding through the air-fuel mixture, which flow channels run in particular parallel to a longitudinal axis of the flame body and which, with respect to the cross section perpendicular to the longitudinal axis of the flame body, are arranged between the axial flow channel and the circumferential inner wall of the flame body.
The plurality of flow channels, which are basically arranged circumferentially with respect to the central, axial flow channel, prevent a formation of vibration modes in a circumferential direction with respect to the longitudinal axis of the flame body in the interior space, which in turn improves the vibration characteristics of the burner device.
In a preferred embodiment, the flow guiding device is designed as a pipe insert which comprises a central pipe element which forms the axial flow channel, and a plurality of fin elements which are arranged directed outwardly on an outer circumference of the central pipe element, wherein in each case two of the plurality of fin elements delimit one of the further flow channels in a circumferential direction of the pipe insert.
This constitutes a variant of the flow guiding device which can be implemented particularly simply and cost-effectively.
The fin elements preferably extend over the entire length of the interior space with respect to the longitudinal axis of the flame body.
In a preferred embodiment, the flow guiding device comprises at least three further flow channels which, with respect to the cross section perpendicular to the longitudinal axis of the flame body, completely surround an outer circumference of the axial flow channel.
The inventors have found that the formation with at least three further flow channels particularly well suppress vibration modes in the circumferential direction.
In a preferred embodiment, the burner device furthermore comprises a flame barrier arranged mostly or completely in the interior space, wherein the flow guiding device is arranged mostly or completely within the flame barrier.
This embodiment is suitable in particular for use with highly hydrogen-containing fuel in which there is an increased risk of a flashback.
The flame barrier has a permeability for the air-fuel mixture in the direction of the combustion surface, but does not allow passage of a burner flame recoiling from there.
The flame barrier preferably has a geometry adapted to the flame body, likewise extends along the longitudinal axis of the flame body and is in particular of cylindrical configuration.
There is a spacing between an outer circumference of the flame barrier and the circumferential inner wall of the flame body, so that the flame barrier does not bear directly there, which improves a flow behavior when flowing out through the openings.
In this case, the air-fuel mixture is introduced merely into the interior of the flame barrier which, like the flame body, has at least one opening, the opening surface of which in this case corresponds to the inlet surface for introducing the air-fuel mixture into the interior space.
In a preferred embodiment with flame barrier, the radial end portions of the fin elements terminate flush with a circumferential inner wall of the flame barrier, such that the further flow channels in the cross section perpendicular to the longitudinal axis of the flame body are formed in each case by a portion of the pipe element, portions of two of the plurality of fin elements and by a portion of the circumferential inner wall of the flame barrier.
In this way, it is ensured that the introduced air-fuel mixture flows through one of the flow channels defined by the flow guiding device without flowing over into another flow channel in the process. As a result, the flow behavior is particularly uniform, which in turn reduces sources of other vibrations, for example caused by turbulence.
In an equivalent embodiment without flame barrier, radial end portions of the fin elements terminate flush with a circumferential inner wall of the flame body, such that the further flow channels in the cross section perpendicular to the longitudinal axis of the flame body are formed in each case by a portion of the pipe element, portions of two of the plurality of fin elements and by a portion of the circumferential inner wall of the flame body.
According to a second aspect of the invention, a heat generator for transferring thermal energy onto a fluid is provided, in particular for use in a heating system or in a service water supply system, wherein the heat generator comprises at least one burner device according to the first aspect or a preferred embodiment thereof and a heat exchanger which is coupled to the burner device and via which thermal energy provided by the burner device can be transferred onto the fluid.
As a result, the burner device operating particularly efficiently and reliably can be used for heating any desired fluid, which in turn can in turn be used in numerous other systems or systems.
The advantages already described with respect to the burner device likewise also apply to the heat generator comprising said burner device, which heat generator, in particular in the case of hydrogen-containing fuel, permits efficient combustion which is stable in terms of vibration, which in the case of the heat generator is equivalent to efficient and reliable heating of said fluid.
For example, the heat exchanger may be a planar, lamellar or spiral-wound heat exchanger.
According to a third aspect of the invention, a heating system for heating a building is provided, which heating system comprises at least one pipe system for transporting a fluid energy transport medium and a heat generator according to the second aspect of the invention, which heat generator is configured for heating the energy transport medium to be transported through the pipe system.
According to a fourth aspect of the invention, a service water supply system for supplying service water is provided, which service water supply system comprises at least one pipe system for transporting the service water and a heat generator according to the second aspect of the invention, which heat generator is configured for heating the service water to be transported through the pipe system.
By using the heat generator according to the invention as part of a heating system and/or a service water supply system of a building, the advantages already described of reliable and efficient combustion, in particular of hydrogen-containing fuel, can be implemented in the region of heating and also in the region of hot water supply.
According to a fifth aspect of the invention, a method for vibration adaptation of a burner device, in particular a premix burner device, which is configured for providing thermal energy by combustion of an air-fuel mixture, is provided. The burner device comprises a flame body which delimits an interior space which is connected via openings in the flame body to an outer combustion surface of the flame body, on which the combustion of an air-fuel mixture, which is introduced into the interior space and flows through the openings, takes place in one or more burner flames, comprising operating the burner device with combusting the air-fuel mixture on the outer combustion surface of the flame body, detecting an oscillation frequency of the burner device during operation, in particular with a detection point in a combustion chamber of the burner device or in an environment of the burner device, for example with an oscillation measurement sensor, providing a flow guiding device which comprises an axial flow channel for guiding through the air-fuel mixture, providing a flow guiding device which comprises an axial flow channel for guiding through the air-fuel mixture, in turn comprising determining an axial length of the axial flow channel as a function of the detected oscillation frequency; and creating the flow guiding device, the axial flow channel of which has a length which corresponds to the determined axial length, and inserting the provided flow guiding device into the interior space of the burner device.
The detection of an oscillation frequency in this case preferably comprises detecting a frequency spectrum of the vibrations of the burner device, for example in the form of an FFT spectrum for amplitude and phase, or the like, and selecting an oscillation frequency from the detected oscillation spectrum.
The oscillation frequency is preferably selected such that the oscillation frequency at which the detected frequency spectrum has a peak, that is to say a comparatively high amplitude, is selected.
In this way, a critical oscillation frequency (also referred to as problem frequency) can be identified particularly easily, since this is represented by the peak in the noise which is otherwise detected and is likewise contained in the frequency spectrum.
The oscillation frequency to be selected is preferably in a range from 500 to 7000 Hz.
A possible variant for determining the axial length of the axial flow channel is described below with reference to exemplary equations.
In the following, f* denotes the problem frequency and c denotes the speed of sound of the air-fuel mixture.
The axial flow channel acts as a type of resonator, the length of which is selected as a function of an oscillation frequency, for example such that a standing wave which acts as a type of vibration absorber for the entire burner device forms in said axial flow channel in the air-fuel mixture in the axial direction.
By way of example, the axial flow channel can be assumed to be a resonator with two open ends, in which frequencies of standing waves approximately satisfy the following equation 1, in which L corresponds to a length of the flow channel and n is a natural number greater than or equal to 1 which specifies the order of oscillation of the standing wave (n=1 in this case forms the fundamental oscillation).
If fn=f* is applied and equation 1 is solved for L, the following expression according to equation 2 can be derived for suitable lengths of the flow channel, in which standing waves with the selected frequency can form.
By way of example, the expression Ln=n·0.1715 m for suitable lengths of the axial flow channel is obtained here for a speed of sound c=343 m/s for air and a frequency to be absorbed of 1000 Hz. In the first harmonic with n=1, this would correspond to a length of 17.15 cm.
The flow channel is preferably selected in accordance with the length for the first harmonic, but higher harmonics are also possible.
The design of the axial flow channel is in no way restricted to the above explanations. Thus, it is also possible to select other boundary conditions, for example open and closed ends, or to use other orders of oscillation or even modes or modeling approaches which also take into account, for example, temperature or other state variables or a flow speed of the air-fuel mixture.
According to a further aspect, a burner device is provided which has been adapted according to a method according to the fifth aspect or one of the preferred embodiments thereof.
Further aspects and the advantages thereof and also more specific exemplary embodiments of the abovementioned aspects and embodiments are described below with the aid of the drawings shown in the accompanying figures.
It is emphasized that the present invention is in no way limited to the exemplary embodiments described below and the exemplary features thereof. The invention furthermore comprises modifications of the exemplary embodiments mentioned, in particular those which emerge from modifications and/or combinations of individual or a plurality of features of the exemplary embodiments described within the scope of protection of the independent claims.
In the following figures, flow directions of the air-fuel mixture G are indicated by the arrows which are partially denoted by G.
The burner device 100 is configured for providing thermal energy by combustion of an air-fuel mixture G and comprises a flame body 1 and a flow guiding device 2.
The flame body 1 delimits an interior space 11 which is connected via openings in the flame body 1 to an outer combustion surface 12 of the flame body 1, on which the combustion of an air-fuel mixture G, which is introduced into the interior space 11 and flows through the openings, takes place in one or more burner flames.
The flow guiding device 2 is arranged in the interior space 11 and comprises an axial flow channel 21, which is located in the interior space 11, for guiding through the air-fuel mixture G, which runs parallel to the longitudinal axis LA of the flame body 1 in the first exemplary embodiment. Furthermore, the flow guiding device 2 comprises three further flow channels 22 which, with respect to a cross section perpendicular to the longitudinal axis LA of the flame body 1, completely surround an outer circumference of the axial flow channel 21 (see
The axial length L of the axial flow channel 21 is selected as a function of an oscillation frequency induced by the one or more burner flames. With respect to the flame body 1, the axial flow channel 21 is arranged centrally, so that, in the cross section perpendicular to the longitudinal axis LA of the flame body 1, it is spaced apart from a circumferential inner wall of the flame body 1 adjoining the interior space 11.
The flow guiding device 2 is designed as a pipe insert which comprises a central pipe element 23 which forms the axial flow channel 21, and three fin elements 24 which are arranged directed outwardly on an outer circumference of the central pipe element 23, wherein in each case two of the plurality of fin elements 24 delimit one of the three further flow channels 22 in a circumferential direction of the pipe insert.
Radial end portions of the fin elements 24 terminate flush with a circumferential inner wall of the flame body 1, such that the three further flow channels 22 in the cross section perpendicular to the longitudinal axis LA of the flame body 1 are formed in each case by a portion of the pipe element 23, portions of in each case two of the three fin elements 24 and by a portion of the circumferential inner wall of the flame body 1 (see
In this case, the air-fuel mixture G is introduced via the right-hand opening of the circular cylindrical flame body 1 to the interior space 11, the opening surface of which in this case also corresponds to an inlet surface 13 for the air-fuel mixture G.
In this case, the axial flow channel 21, which is likewise of circular cylindrical configuration, in the cross section perpendicular to the longitudinal axis LA of the flame body 1 has approximately a diameter which corresponds to 50% or more of the diameter of the inlet surface 13.
By means of the flow guiding device 2, a type of resonator for the air-fuel mixture G is formed in the interior space 11, which resonator is adapted to the oscillation frequency and via which the vibration behavior of the entire burner device 100 is significantly changed in comparison with an embodiment without a flow guiding device 2, in order thus in particular to reduce vibrations of the burner device 100 and/or of the components thereof, as a result of which the risk of incomplete combustion and/or of flame flashbacks into the interior space 11 is reduced, which in turn increases the efficiency of the burner device 100. In addition, this results in a lower sound emission during operation, which is perceived by the user as high comfort.
The basic construction corresponds approximately to that of the first exemplary embodiment, for which reason a further description is dispensed with at this point.
The essential difference between the first and the second exemplary embodiment is that the latter also has a flame barrier 3 arranged mostly in the interior space 11, which is suitable in particular for use with hydrogen-containing fuels.
In this case, the inlet surface 13 corresponds to the opening surface of the right-hand opening of the flame barrier 3 from
Thus, the introduction into the flame barrier 3 takes place, which is permeable for the air-fuel mixture G, so that during operation the air-fuel mixture G flows from the partial region of the interior space 11 located in the interior of the flame barrier 3 through the flame barrier 3 into one of the remaining partial regions of the interior space 11 and exits from there through the openings in the flame body onto the combustion surface 12.
In contrast to the first exemplary embodiment from
In this way, the flow guiding device 2 is arranged upstream (with respect to the flow direction of the air-fuel mixture G during the operation of the burner device 100) of the flame barrier 3 and can contribute there to the vibration reduction, wherein said flame barrier is not only protected against recoiling flames, but rather also does not impede a flow of the air-fuel mixture G in the region of the openings of the flame body 1.
The flow guiding device 2 is designed as a pipe insert which is fitted either into the flame body 1 from
The pipe insert comprises a central pipe element 23 which forms the axial flow channel 21 with the axial length L selected as a function of the oscillation frequency, and three fin elements 24 which are arranged directed outwardly on an outer circumference of the central pipe element 23.
The pipe insert in this case can be manufactured from one piece. Alternatively, the finished fin elements 24 can also be cohesively connected to the pipe element in order to provide the pipe insert.
At least one of the fin elements 24 has, on the rear side, a cutout which serves as an anti-rotation safeguard within the interior space 11 or within the flame barrier 3.
In step S1, a burner device is operated with combusting an air-fuel mixture on an outer combustion surface of the flame body.
In this case, the burner device is configured for providing thermal energy by combustion of the air-fuel mixture and for this purpose comprises the flame body which delimits an interior space which is connected via openings in the flame body to the outer combustion surface of the flame body, on which the combustion of the air-fuel mixture, which is introduced into the interior space and flows through the openings, takes place in one or more burner flames.
In step S2, an oscillation frequency of the burner device is detected during operation, in turn comprising the substeps S2.1 and S2.2.
In step S2.1, a frequency spectrum of the vibrations of the burner device is detected and, in step S2.2, an oscillation frequency is selected from the detected oscillation spectrum, in particular such that the frequency spectrum at the selected oscillation frequency has a peak with respect to the oscillation amplitude.
In step S3, a flow guiding device is provided which comprises an axial flow channel for guiding through the air-fuel mixture, for which an axial length takes place in substep S3.1 as a function of the oscillation frequency selected in step S2 and on the basis of which the flow guiding device is created in substep S3.2, the axial flow channel of which has a length which corresponds to the determined axial length from substep S3.1.
In step S4, the provided flow guiding device is inserted into the interior space of the burner device.
Exemplary embodiments of the present invention and the advantages thereof have been described in detail above with reference to the accompanying figures.
It is again emphasized that the present invention is in no way limited to the exemplary embodiments described above and the exemplary features thereof. The invention furthermore comprises modifications of the exemplary embodiments mentioned, in particular those which emerge from modifications and/or combinations of the features of the exemplary embodiments described within the scope of protection of the independent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102023126739.6 | Sep 2023 | DE | national |
