GAS BURNER ARRANGEMENT, GAS HEATER AND USE

Description

[0001] The invention relates to a gas burner arrangement, a gas heater and a use of a gas burner arrangement.

[0002] Gas burners for condensing boilers are often made of perforated metal sheets, which can be flat, curved, or cylindrical. A fuel gas / air mixture supplied to the gas burner flows from the rear through the holes in the sheet and is ignited and burned at the front.

[0003] Depending on the composition of the fuel gas (e.g., propane, methane, hydrogen, or mixtures thereof), different flame speeds occur during combustion. If the flame speed is higher than the outflow velocity of the fuel gas-air mixture from the burner holes, a so-called flashback can occur into the gas-air mixture path upstream of the burner. This type of flashback can also occur if the temperature of the perforated plate on the back is higher than the ignition temperature of the gas-air mixture used.

[0004] In such flashbacks, the gas-air mixture combusts unintentionally upstream of the burner or in the upstream combustion gas-air mixture path. The consequences can be a pressure surge triggered by the combustion and / or high thermal stress on components in the combustion gas-air mixture path and / or other inlets. For example, a (plastic) impeller of a fan in the air supply can become thermally deformed or damaged by a pressure surge.

[0005] To reduce these flashbacks and their consequences for the gas heater, at least one flame arrester can be provided between the air supply and the burner. This flame arrester extends across a cross-section of the fuel gas-air mixture path, the air supply, or the fuel gas supply. By providing a flame arrester in the gas-fired heater, if a flashback occurs in the fuel gas-air mixture path, the flame can be extinguished before thermal overload of components occurs and / or before the pressure pulse resulting from the flashback becomes so high that components are mechanically overloaded.

[0006] The flame arrester can extend across the entire flow cross-section of the fuel gas-air mixture path and, in particular, can prevent any bypass flow. The flame arrester can be made of a high-temperature-resistant material, such as a metal, a ceramic, or mixtures thereof. The flame arrester can be (permanently) fixed in or between housing sections of the fuel gas-air mixture path and / or the gas burner.

[0007] In addition to the mechanical and thermal stability of the flame arrester and its ability to stop or even (at least partially) extinguish an incoming flame front, there are other requirements. These include, for example, that the flame arrester has the lowest possible tendency to become contaminated and / or has a high degree of self-cleaning capability during operation, as dust particles are often introduced via the fuel gas-air mixture (or the ambient air mixed in). Such contamination can lead to a significant increase in pressure loss, which can result in a loss of performance of the gas heater.

[0008] WO 93 / 18342 describes a porous metal fiberboard with a distribution plate as a flame arrester. The porous metal fiberboard and the flame arrester have holes. In the areas not penetrated by the holes, the metal fiberboard exhibits its porous properties. The porosity of the metal fiberboard improves combustion above the metal fiberboard and supports the gas flow through the holes. The flame arrester is only penetrable at the holes.

[0009] EP 3 184 892 A1 describes a double-walled burner device in which two structural elements are arranged one behind the other. The structural elements are grid elements. The structural elements are spaced far enough apart that a combustion flame can still jump between the structural elements.

[0010] It is therefore an object of the invention to at least partially alleviate the problems described with reference to the prior art and, in particular, to provide a flame arrester whose design can be easily, flexibly, and cost-effectively adapted to various operating and ambient conditions in gas burners or gas heaters. Furthermore, a gas heater is to be created in which mechanical and / or thermal stresses due to flashbacks can be reduced or avoided. In particular, a (plastic) impeller of a fan in the air supply is to be protected from high thermal stress and / or a large pressure surge due to flashbacks.

[0011] This object is achieved in particular with a gas burner assembly according to the features of claim 1, a gas heater according to claim 7, and a use according to claim 8. Preferred embodiments are specified in the dependent claims. The features specified in the claims can be combined with one another in any technologically expedient manner and lead to further embodiments. The description, particularly with reference to the figures, explains the invention and provides further embodiments.

[0012] A gas burner arrangement contributes to this, comprising at least one gas burner and a flame arrester formed with an inlet along an axis and an outlet oblique to this axis. The at least one flame arrester can be inserted into a burner chamber of a gas burner of the gas heater. The flame arrester and gas burner are designed such that a surface load during operation is in the range of 1.5 to 7.0 W / mm 2< , in particular in the range of 1.5 to 3.0 W / mm 2< [watts per square millimeter]. Furthermore, the at least one flame arrester has a porosity greater than 35% [percent].

[0013] The gas burner arrangement can, in particular, be designed as a coordinated set comprising a flame arrester and a gas burner. The gas burner is designed with an internal, hollow burner chamber in which the flame arrester can be accommodated. The burner chamber is at least partially delimited by a burner wall, which can have a plurality of grouped or evenly distributed openings. The gas burner can be designed (perpendicular to the axis) with a substantially round or rectangular cross-section. The burner wall is preferably formed from a steel sheet.

[0014] The combustion gas-air mixture can be supplied to the gas burner or flame arrester via an inlet. The combustion gas-air mixture can flow in via the inlet essentially along a central axis of the gas burner or burner chamber. A change in the direction of the gas flow can be generated in the gas burner or burner chamber, so that the combustion gas-air mixture then leaves the burner chamber via the burner wall at an angle, in particular at an angle greater than 0° to the axis and preferably essentially perpendicular to the axis. The combustion gas-air mixture flows through the flame arrester and the burner wall, which is provided with a plurality of openings, then ignites and accordingly forms a flame front outside the gas burner. In other words, the flame arrester is spaced from or protected from the (regular) flame front by the burner wall and / or the flame arrester is arranged on a side / surface of the burner wall facing away from the flame front.

[0015] The flame arrester can be adapted to the gas burner in such a way that its outlet spans the outlet of the burner wall, in particular at least largely or even completely covers the outlet. The flame arrester can be designed as a single layer (possibly with several superimposed layers of metal and / or ceramic) that encloses or delimits a partial volume of the burner chamber. The flame arrester can be flowed through by the fuel gas / air mixture in the area of ​​the outlet, wherein it is designed in particular such that it can be flowed through (approximately or exactly) in the same direction as the outlet of the gas burner. It is possible for the flame arrester to be designed such that it can be mounted on the gas burner in the area of ​​the inlet and, when mounted, extends (far) into the burner chamber, e.g. coaxially.The extension of the flame arrester into the gas burner can be at least 50% of the axial length of the burner chamber, preferably at least 80%. The surface area of ​​the flame arrester should be as large as possible to achieve low pressure drops with and without dust contamination. The surface load is preferably adapted to the extension of the flame arrester, e.g., a surface load in the range of 3.0 to 7.0 W / mm 2 is maintained during operation with an extension over 50% to 80% of the axial length of the burner chamber, or a surface load in the range of 1.5 to 3.0 W / mm 2 is maintained during operation with an extension over 80% of the axial length of the burner chamber.

[0016] A flame arrester can also be used in so-called flat burners, which are operated in particular with hydrogen. There, the flame arrester is designed, for example, as a plane parallel to the burner surface. The other parameters and features can be transferred accordingly. In particular, a gas burner arrangement can be provided here, comprising at least one flat flame arrester, wherein the at least one flat flame arrester can be used in a burner chamber of a gas burner of a gas heater, and wherein the flame arrester and gas burner are designed such that a surface load during operation is in the range of 1.5 to 7.0 W / mm2. In this case, the flame arrester can be arranged one behind the other or along the flow direction between the inlet and the burner surface.

[0017] The flame arrester is designed in particular so that the (maximum) surface load during operation of the gas burner is in the range of 1.5 or 1.8 to 3.0 W / mm 2<, preferably in the range of 2.0 to 2.6 W / mm 2<. The surface load can be referred to as the specific surface load. The surface load can be determined from the quotient of the heating output of the gas burner and the active surface of the flame arrester (over which the fuel gas-air mixture flows) (in particular including the outlet). The heating outputs of the gas heater or gas burner are known to the person skilled in the art, so that they can easily design the flame arrester accordingly. For the gas heaters considered here, the maximum or nominal output is in particular in the range of 10 kW [kilowatts] to 200 kW, e.g. in the range of 15 kW to 130 kW or possibly up to 65 kW.For example, if the heating output is 28 kW and the flame arrester is sleeve-shaped with an active surface over an axial extent of 63 millimeters and a diameter of 55 millimeters, the resulting surface load is 2.57 watts / square millimeter. In the range specified here, the flame arrester achieves particularly high effectiveness with a simultaneous low pressure drop. This can result in particularly intensive protection for the fan because, on the one hand, the effectiveness of the flame arrester reliably stops pressure surges and temperature fronts, and, on the other hand, very low fan power is required during regular operation due to the low pressure drop.

[0018] The at least one flame arrester can have a porosity of at least 35% and preferably a maximum of 50% (in the area of ​​the outlet). The porosity can be determined from the quotient of the sum of all freely flow-through areas (pores) and the entire active surface of the flame arrester (particularly in the area of ​​the outlet). It is possible for the gas burner or the (adjacent) burner wall to be designed (at least in sections) with a significantly smaller porosity, for example by a factor of at least 2, in particular by a factor of at least 5 or even at least 10. In the upstream flame arresters proposed here, the free flow area is increased in order to reduce the pressure loss and at the same time the tendency to fouling for a given extinguishing distance (of the flame), e.g. less than 0.27 mm for hydrogen.

[0019] Porosity particularly concerns the volume porosity of the flame arrester. The dimensions of the freely flowable areas (pores) in the direction of the wall thickness of the flame arrester are also taken into account. The flame arrester may not be designed as a flat structure (made of a single layer of material), but rather, for example, as a (thick-walled) body made of sintered powder or a multi-layer composite of expanded metal and / or nonwoven material. A comparatively high porosity is advantageous for low pressure losses, although the wall thickness of the flame arrester must also be taken into account. Sintered powder beds can be provided as flame arresters as thick-walled components, e.g., with a wall thickness in the range of 2 to 3 mm, which typically achieve relatively low porosities. This tends to result in high pressure losses. Multi-layer sintered expanded metals can be designed comparatively thin (e.g.,with a wall thickness in the range up to a maximum of 1 mm), whereby even a lower volume porosity leads to low pressure losses. Nonwovens and open-pored foams can also be used to construct thicker-walled flame arresters (e.g. with a wall thickness in the range greater than 1 mm) and can also advantageously have high porosities. With regard to the materials and structures of the flame arrester specified here, the following preferred volume porosities are suggested: sintered powder bed in the range of 26 - 48 vol.%; expanded metal (multi-layer) in the range of 35 - 50 vol.%; nonwoven in the range above 65 vol.%; open-pored foam in the range of 70 - 98 vol.%.

[0020] It is preferred that the outlet of the flame arrester can be arranged (or is arranged) perpendicular to the axis at a distance from a burner wall of the gas burner, in particular at a distance of greater than 1 millimeter. This applies in particular when the flame arrester and burner wall are flowed through by the combustion gas-air mixture in the same (in particular radial) flow direction. This means in particular that the outlet of the flame arrester is away from the axis, i.e. the combustion gas-air mixture within the flame arrester is deflected from the central flow parallel to the axis towards the distant outlet. The outlet can be formed by means of a plurality of (micro) openings, (micro) slots or pores. The outlet can be formed in a sleeve-like section of the flame arrester coaxial to the axis.The deflection of the fuel gas-air mixture can be achieved, for example, by means of a non-flowable closure element (the flame arrester) which spans the axis and is located opposite the inlet.

[0021] It is preferred that, in the direction of gas flow, the distance between the outlet of the flame arrester and a burner wall of the gas burner is in the range from 3 to 20 mm [millimeters], in particular in the range from 5 to 10 mm. It is very particularly preferred that a selected distance is essentially constant over the entire outlet. The distance can increase and / or decrease; in particular, there can be a (slightly) conical envelope volume between the outlet of the flame arrester and the burner wall of the gas burner. The distance between the outlet of the flame arrester and the outlet of the gas burner or the section of the burner wall through which flow can take place is to be determined in the direction of gas flow. It is therefore proposed in particular that the flame arrester does not lie directly against the rear side of the burner wall, but that a preferably uniform gap with a predetermined distance is initially provided there.The distance is designed in such a way that in the event of a flashback, the flame front can spread into the gap and thus cover a larger area of ​​the flame surface. The specified upper limit of the distance is useful in order to limit the ignitable volume of the combustion gas-air mixture in the combustion gas-air mixture path. This reduces the noise development and / or the pressure wave of the flashback. The upper limit of the distance can be selected depending on the specific shape of the burner body and, if necessary, the structure or load limit of the layers of the flame arrester. A further advantage of this distance is that the heat input into the flame arrester can be adjusted or limited during normal operation of the gas heater, which benefits the long-term, consistent functionality of the flame arrester.If the distance between the (hot) burner body and the flame arrester is too small, there is also a risk that the flame arrester will heat up to such an extent that the ignition temperature of the gas-air mixture is reached, resulting in an unwanted ignition. Even if the ignition temperature is not reached, if the flame arrester is too hot, heat dissipation will decrease, negatively impacting the extinguishing effect.

[0022] It is considered very advantageous to allow cross-flow between the flame arrester and the burner surface so that the entire (active) surface of the flame arrester can be flowed through and used. With a distance of 0 mm, the flow would pass through the flame arrester surface directly below or adjacent to the burner holes. During normal operation, this results in high pressure losses through the flame arrester. If, on the other hand, a distance is provided, a burner hole with a cross-sectional area of ​​0.5 mm 2 < [square millimeters], for example, is supplied from a cross-sectional area of ​​the flame arrester with a cross-sectional area of ​​5.0 mm 2 <, for example. This significantly reduces the pressure losses of the flame arrester. The distance or the selected distance is also important in the event of a flashback, for example due to delayed ignition, because it reduces the surface load on the flame arrester. The hot gas flowing back through the burner surface is distributed over a larger area in the gap, which also reduces the heat or the amount of gas that has to be absorbed.Energy is distributed over a larger area. Furthermore, the flow velocity is reduced and the residence time is increased, which promotes flame extinguishing.

[0023] A combustion volume can be provided in the burner chamber which lies between the at least one flame arrester and the burner wall of the gas burner and which (greater than 0) amounts to a maximum of 70%, preferably at least 40% or even only at least 22% of the burner chamber. The combustion volume can be described as the envelope volume between the flame arrester and the burner wall. The combustion volume describes in particular the area in the gas burner in which the flame flashback spreads. The flame arrester and the gas burner are in particular matched to one another in such a way that the volume between the two components is as small as possible because the combustion gas-air mixture burns in this area in the event of a flame flashback. The energy converted in this process can therefore be kept low. It is possible to specifically adapt the burner volume orto be reduced, for example by (local) deviations of the basic shape of the gas burner, installations in the gas burner or the like, without reducing the active burner area.

[0024] It is possible that a combined flow through the flame arrester and the gas burner is adjusted in such a way that a Péclet number of less than 65 is present. It is particularly preferred that a Péclet number of less than 15 is present, whereby this limit should apply in particular when the arrangement is operated with hydrogen or a fuel gas-air mixture comprising hydrogen.

[0025] The Péclet number is a criterion familiar to those skilled in the art, which can be used to determine whether a flame front propagates in a material or an accumulation of material. The (modified) Péclet number is calculated using the laminar burning rate instead of the flow rate. The characteristic length used is an effective pore diameter, which, in contrast to the conventional formulation, which is calculated using a length equivalent to flow processes, represents a measure equivalent to heat transport. This length can be understood as the extinguishing distance of a pipe for the same mixture composition. The (modified) Péclet number can thus be understood as the ratio of heat production (burning rate) to the reaction to heat dissipation through heat conduction. Further explanations, to which reference can be made in full, can be found in DE 43 22 109 A1.

[0026] It is also proposed, if appropriate, to select a design of the gas burner arrangement without restriction of the surface load but with characterization of the Péclet number, in particular with at least the following features: Gas burner arrangement comprising at least one flame arrester formed with an inlet (along an axis) and an outlet (oblique to this axis). The at least one flame arrester can be inserted into a burner chamber of a gas burner of a gas heater. A combined flow through the flame arrester and gas burner is coordinated such that a Péclet number of less than 65 is achieved. If appropriate, this arrangement can be the basis for all further designs of the gas burner and / or the flame arrester proposed here.

[0027] This criterion can now be used to determine an effective pore diameter for the flame arrester for a given composition of the fuel gas-air mixture, which can prevent flame propagation. Although the Péclet number criterion was formulated for a static gas mixture in a cold porous medium, it is applied here to porous media through which a gas flows. For this purpose, the modified Péclet number (Pe) is defined as the product of the effective pore diameter of the flame arrester (DP) and the laminar burning velocity (vB) divided by the thermal diffusivity (a) of the fuel gas mixture (Pe = (DP x vB / a)). The effective pore diameter of the flame arrester is the diameter for a circular pore; for other pore shapes, it is a corresponding "hydraulic" diameter.The laminar burning speed (sometimes also called "laminar flame speed") depends on the fuel gas-air mixture and is therefore also a function of the air ratio. The laminar burning speed for fuel gas-air mixtures reaches its maximum at a stoichiometric ratio. The laminar burning speed for a hydrogen-air mixture at a stoichiometric ratio (T=27°C, P=1 bar) is 200 cm / s. The laminar burning speed for a methane-air mixture at a stoichiometric ratio (T=27°C, P=1 bar) is 38.39 cm / s.

[0028] According to a further aspect, a gas heater is provided with a predetermined power range which is in the range of 10 to 200 kW and has a gas burner arrangement of the type disclosed here.

[0029] The features disclosed for the gas burner assembly can also be used individually and / or in combination with one another to characterize the gas heater. The gas heater is particularly configured for the combustion of hydrogen or a hydrogen-containing fuel gas-air mixture. The gas heater may comprise an ignition device, a control and regulation unit, a gas delivery unit, and a flame monitor.

[0030] According to a further aspect, the use of a gas burner arrangement of the type disclosed here is proposed for preventing or extinguishing flashbacks during the combustion of hydrogen-containing gases.

[0031] The invention and the technical environment are further explained below with reference to figures. It should be noted that the features illustrated in the figures—unless explicitly stated otherwise—are extractable and / or can be combined in any technological manner with other features of the other figures, the general description, or claims. The figures are schematic and generally not suitable for depicting actual proportions. They show: Fig. 1: a gas heater with a gas burner arrangement in partial section, Fig. 2: a first embodiment of the gas burner arrangement, and Fig. 3: a second embodiment of the gas burner arrangement

[0032] Fig. 1 shows the basic structure of a gas heater 8. This forms a fuel gas-air mixture path 18, through which, for example, a mixture of a fuel gas (such as hydrogen or natural gas) and ambient air can flow in a flow direction 10 (during regular operation), whereby this fuel gas-air mixture path 18 opens or ends in a gas burner 7. The fuel gas-air mixture path 18 can be created or formed from two line connections, a line connection for fuel gas with an actuating element 17 (valve) for the metered, controlled addition of fuel gas into a stream of ambient air, which can be added by a conveyor device 16 (blower) via a combustion air path 15. The fuel gas-air mixture or gas mixture passes through the gas burner 7 and can be ignited externally by means of an ignition device 19. The resulting flames 14 are normally arranged outside the gas burner 7 in a combustion chamber, whereby e.g.an external heat exchanger 13 through which heating water flows can be heated. This describes regular operation.

[0033] In the event of an (undesired) flashback, i.e. when a flame formation occurs in the inner area or in the burner chamber 6 of the gas burner 7, a gas burner arrangement 1 with a (single) flame arrester 2 ensures that the flame front is stopped or extinguished there.

[0034] Fig. 2 shows a (cylindrical) gas burner arrangement 1 schematically and in longitudinal section, which has a (cylindrical) flame arrester 2. On the left in Fig. 2 and illustrated by the arrow, the combustion gas-air mixture flows via the inlet 3 into the burner chamber 6 or the flame arrester 2. The gas burner 7 can be designed with a flange 20, wherein the flame arrester 2 can be mounted there in an aligned manner, if necessary also via a collar. It can thus be provided that the burner wall 9 of the gas burner 7 and the flame arrester 2 are formed at least partially coaxially around a central axis 4. The flow direction 10 of the combustion gas-air mixture corresponds approximately to the course of the axis 4 in the region of the inlet 3. Furthermore, the flame arrester 2 forms (radially and circumferentially) a (large-area) outlet 5, which ensures that the combustion gas-air mixture flows out at an angle or, in this case, perpendicular to this axis 4.

[0035] It is also illustrated that the flame arrester 2 is inserted into the burner chamber 6 of the gas burner 7 or is completely accommodated by it. It should be noted that the gas burner 7 has a significantly greater length in the direction of the axis 4 than the extension of the flame arrester 2 in this direction. Therefore, a closure element 21 was provided in the gas burner 7, which extends into the burner chamber 6 to reduce the volume between the burner wall 9 and the flame arrester 2.

[0036] The flame arrester 2 and the gas burner 7 are designed such that a surface load during operation is in the range of 1.8 to 3.0 W / mm2. For this purpose, the spatial dimensions and / or the position of the two components relative to each other can be adjusted or coordinated accordingly.

[0037] Fig. 3 illustrates another embodiment of a (cylindrical) gas burner in longitudinal section. Since the same components are provided with the same reference numerals, reference can be made to the above explanations in full.

[0038] Deviating from Fig. 2 Here, a flat, plate-shaped end element 21 (cover) is provided, to which the outer surface of the flame arrester 2 is fastened. In the gas burner 2, the flame arrester 2 is integrated, i.e. the flame arrester 2 is inseparably connected to the gas burner 2. In this example, the cover and flange of the gas burner 2 also provide the fastening surfaces for the flame arrester 2. The flame arrester 2 is thus formed over the entire axial length of the gas burner 2. It is further provided that these two components form a constant (small) distance 11 from one another, so that a combustion volume 12 (small) is preset.

[0039] The solutions proposed here can at least partially alleviate the problems described with reference to the state of the art. In particular, a flame arrester was specified whose design is simple, flexible, and cost-effective to adapt to various operating and environmental conditions in gas burners and gas heaters. Furthermore, a gas heater was demonstrated in which mechanical and / or thermal stresses due to flashbacks can be reduced or avoided.

Claims

1. Gas burner arrangement (1), comprising at least one gas burner (7) and a flame arrester (2), formed with an inlet (3) along an axis (4) and an outlet (5) at an angle to this axis (4), the at least one flame arrester (2) being insertable in a burner chamber (6) of the gas burner (7) of a gas heating appliance (8), the flame arrester (2) and gas burner (7) being designed such that a surface load in operation is in the range from 1.5 to 7.0 W / mm2, characterised in that the at least one flame arrester (2) has a porosity greater than 35%.

2. Gas burner arrangement (1) according to claim 1, characterised in that the surface load in operation is in the range from 1.8 to 3.0 W / mm23. Gas burner arrangement (1) according to claim 1, characterised in that the porosity is a volume porosity of the flame arrester (2).

4. Gas burner arrangement (1) according to one of the preceding claims, characterised in that the outlet (5) of the flame arrester (2) can be arranged perpendicular to the axis (4) at a distance from a burner wall (9) of the gas burner (7).

5. Gas burner arrangement (1) according to one of the preceding claims, characterised in that in the direction of flow (10) of the gas, a distance (11) from the outlet (5) of the flame arrester (2) and a burner wall (9) of the gas burner (7) is in the range from 3 to 20 mm.

6. Gas burner arrangement (1) according to one of the preceding claims, characterised in that a combustion volume (12) in the burner chamber (6) between the at least one flame arrester (2) and a burner wall (9) of the gas burner (7) is at most 70% of the burner chamber (6).

7. Gas heater (8) with a predetermined power range, which is in the range from 10 to 200 kW, characterised in that it has a gas burner arrangement (1) according to one of the preceding claims.

8. Use of a gas burner arrangement (1) according to one of the preceding claims for preventing or extinguishing flashbacks during the combustion of hydrogen-containing gases.