WO2023062448A1

WO2023062448A1 - Combustion membrane for a gas burner

Info

Publication number: WO2023062448A1
Application number: PCT/IB2022/056872
Authority: WO
Inventors: Massimo Gilioli; Alberto PEZZIN; Andrea Casoni
Original assignee: Beckett Thermal Solutions S.R.L.
Priority date: 2021-10-15
Filing date: 2022-07-26
Publication date: 2023-04-20
Also published as: CN118103636A; IT202100026447A1; EP4416429A1; KR20240073854A

Abstract

A combustion membrane (14) for a gas burner (2) comprises a fabric (21) having two opposite fabric surfaces (19, 20), which form a combustion surface (19) exposed on the outer side (17) and an inner surface (20) facing towards an inner side (18) respectively, wherein the fabric (21) forms an interlacing of metal wires (22) comprising warp threads and weft threads transverse to the warp threads, wherein: - the fabric (21) has localized first areas (26) with reduced gas permeability, alternated with localized second areas (27) with higher gas permeability than the first areas (26). - both the first areas (26) and the second areas (27) have an extension, in at least one direction in the plane of the fabric (21), greater than the space occupied by at least three consecutive warp threads in the weft direction and greater than the space occupied by at least three consecutive weft threads in the warp direction.

Description

Combustion membrane for a gas burner

DESCRIPTION

[0001] The present invention relates to a combustion membrane for a burner, in particular for a completely or partially premixed burner, for example for boilers, swimming pool heaters, hot air generators, or ovens for industrial processes.

[0002] The burners of the prior art comprise a combustion membrane having:

- an inner surface in flow communication with the feeding system,

- a diffuser layer forming an outer surface (or combustion surface) of the membrane, intended to be facing the combustion chamber,

[0003] in which the combustible gas or the mixture of combustible gas and combustion supporting air (hereafter in the description, the term “gas” denotes both a “combustible gas” and a “mixture of combustible gas and combustion supporting air”) is conveyed through the combustion membrane at the outer side of which the combustion takes place, in the form of a flame pattern on the combustion surface.

[0004] Furthermore, a distributor may be provided upstream of the diffuser layer (with reference to the flow direction of the gas) to distribute the gas in the desired manner towards the combustion membrane. The known distributors are generally made as walls with a plurality of through openings, for example made of perforated metal sheet, and may form an "inner" layer of the combustion membrane or alternatively, a component which is spaced apart from the combustion membrane.

[0005] The heat generated by the combustion is directed by means of the hot combustion gases (convection) and by means of heat radiation to a heat exchanger to heat a fluid, e.g., water, which is then conveyed to a utility, for example a heating system of an industrial process, residential environments or the like and/or domestic water.

[0006] For desirable and satisfactory use of the burner and combustion system, it is desirable, on the one hand, to be able to vary the heating power of the burner and gas flow rate through the combustion membrane in a controlled manner and, on the other hand, to ensure the safest, quietest and longest-lasting operation possible.

[0007] To meet the aforesaid requirements in an increasingly satisfactory manner, it is necessary to reduce or prevent some phenomena which may occur during a suboptimal combustion process, including:

[0008] - a localized or extensive detachment of the flame from the combustion surface, [0009] - a localized or extensive overheating of the combustion membrane,

[0010] - a highly uneven distribution of combustion membrane temperature,

[0011] - a highly uneven distribution of gas flow velocity across the combustion membrane, [0012] - a low or reduced thermal insulation function of the combustion membrane or a single combustion membrane layer during burner operation.

[0013] These undesirable phenomena cause high combustion noise, limited burner resistance to high temperatures, damage to the burner structure itself, especially to metal sheet parts of the combustion membrane, as well as the occurrence of uncontrollable flame phenomena.

[0014] The causal connections between the aforesaid negative phenomena and their detrimental effects on satisfactory combustion have been extensively described in detail in the technical and patent literature concerning gas burners, and are not repeated here for the sake of brevity.

[0015] To reduce or suppress some or all of the listed negative phenomena, it is known to equip gas burners with accessory structures, e.g., inserts or diaphragms, to locally bias the inert masses of the burner and the fluid dynamic conditions of the gas flow and, thus, the fluid dynamic and mechanical behavior of the burner.

[0016] These noise reduction accessories must be optimized on a case-by-case basis for the fluid dynamic, mechanical, dimensional, and combustion conditions of the individual burner model, and their efficacy is often limited to undesirably narrow (gas flow) operating ranges.

[0017] Therefore, the need is felt for additional means and strategies to improve gas burners, particularly premixed or partially premixed gas burners, and to further optimize combustion performed by means of such burners.

[0018] It is the object of the present invention to provide a new and innovative combustion surface and combustion membrane for gas burners and a gas burner, having features such to avoid at least some of the drawbacks of the prior art.

[0019] These and other objects are achieved by means of a combustion membrane of a gas burner according to claim 1. Advantageous embodiments are the object of the dependent claims.

[0020] According to an aspect of the invention, a combustion membrane for a gas burner has an inner side, to which combustible gas is conveyed, and an outer side, on which combustion of the combustible gas occurs after it has crossed through the combustion membrane, said combustion membrane comprising a fabric having two opposite fabric surfaces, which respectively form a combustion surface exposed on the outer side and an inner surface facing towards the inner side, wherein:

[0021] - the fabric forms an interlacing of metal wires comprising warp threads and weft threads transverse to the warp threads, said fabric being made on a loom (unlike knits that are to be considered excluded from the definition of “fabric”),

[0022] - the combustion membrane comprises the features of claim 1 . [0023] In order to better understand the invention and appreciate the advantages thereof, a description is provided below of certain non-limiting exemplary embodiments, with reference to the accompanying drawings, in which:

[0024] figure 1 is a diagrammatic view of a gas combustion system, for example for a boiler, with a burner provided with a combustion membrane,

[0025] figures 2 and 3 are perspective and sectional views of an exemplary burner, provided with a combustion membrane,

[0026] figure 3A is an enlarged and diagrammatic section view of a combustion membrane according to an embodiment of the invention,

[0027] figures 4A and 4B are views of the two sides of a metal fabric of a combustion membrane according to an embodiment of the invention,

[0028] figure 4C shows a drawing, i.e., a graphic representation of the weaving, of the metal fabric according to figures 4A, 4B,

[0029] figure 4D shows a burner with a combustion membrane having a metal fabric according to figure 4C,

[0030] figures 5A and 5B are views of the two sides of a metal fabric of a combustion membrane according to a further embodiment of the invention,

[0031 ] figure 5C shows a drawing, i.e., a graphic representation of the weaving, of the metal fabric according to figures 5A, 5B,

[0032] figure 5D shows a burner with a combustion membrane having a metal fabric according to figure 5C,

[0033] figures 6A and 6B are views of the two sides of a metal fabric of a combustion membrane according to a further embodiment of the invention,

[0034] figure 6C shows a drawing, i.e., a graphic representation of the weaving, of the metal fabric according to figures 6A, 6B,

[0035] figure 6D shows a burner with a combustion membrane having a metal fabric according to figure 6C,

[0036] figures 7A and 7B are views of the two sides of a metal fabric of a combustion membrane according to a further embodiment of the invention,

[0037] figure 7C shows a drawing, i.e., a graphic representation of the weaving, of the metal fabric according to figures 7A, 7B,

[0038] figures 7.1 C and 7.2C show enlargements of figure 7C,

[0039] figure 7D shows a burner with a combustion membrane having a metal fabric according to figure 7C,

[0040] figures 8, 9, and 10 show a metal yarn bound by a water-soluble binding thread, a crimped metal yarn free from binding, and a twisted and hairy spun metal yarn of the metal fabric according to embodiments, figure 11 shows a first side of a metal fabric of a combustion membrane according to a further embodiment of the invention.

[0041] Detailed description of the combustion system 1

[0042] With reference to figure 1 , a gas combustion system 1 , for example for a boiler, comprises:

[0043] a burner 2 for producing heat by means of combustion of combustible gas and combustion air,

[0044] a feeding system 3 for feeding the combustible gas or gas mixture and combustion air to burner 2, said feeding system 3 comprising a gas control device 4 for controlling a flow of the combustible gas (for example, an electrically controllable gas valve or gas conveying means or gas suction means) and, if provided, an air control device 5 (for example, air conveying means or air suction means, an electric fan, a radial fan, an air valve or gate air valve) to control a flow of combustion air,

[0045] an electric ignition device 6 for igniting the combustion, for example an ignition electrode adapted to generate a spark,

[0046] possibly, an ionization sensor 7 arranged at a combustion area 8 of the burner 2 and adapted to provide an electrical ionization signal which varies as a function of a combustion condition of the burner 2,

[0047] an electronic control unit 9 connected to the feeding system 3, the ignition device 6 and the ionization sensor 7, the electronic control unit 9 having a combustion control module 10 adapted to control the ignition device 6 and the feeding system 3 depending on an operating program and user commands and depending on the ionization signal,

[0048] Detailed description of burner 2

[0049] According to an embodiment (figures 2, 3), the gas burner 2 comprises:

[0050] - a support wall 11 forming one or more inlet passages 12 for the introduction (of the mixture) of combustible gas 13 (and combustion air) into the burner 2,

[0051] - a tubular combustion membrane 14, for example cylindrical, and coaxial with respect to a longitudinal axis 15 of the burner 2 and having a first end connected to the support wall 11 in flow communication with the inlet passage 12, a second end closed by a closing wall 16, and a perforation for the passage of the gas 13 and of the gas-air mixture from inside the burner 2 to an outer side 17 of the combustion membrane 14 where the combustion occurs (combustion area 8).

[0052] The burner 2 in figure 3 further shows a tubular silencing accessory (without reference numeral), which is optional and could be reduced in size or completely eliminated. [0053] According to a further embodiment, the flat combustion membrane 14 can be substantially flat, e.g., planar or curved or convex, or however of non-tubular or non- cylindrical shape, and having a peripheral edge connected to the support housing wall 11 in flow communication with the inlet passage 12, as well as a perforation for the passage of the gas 13 or of the gas-air mixture from inside burner 2 to an outer side 17 of the combustion membrane 14 where the combustion occurs (combustion area 8).

[0054] In analogy with prior solutions with conventional combustion membranes, according to an embodiment, in burner 2, upstream of the combustion membrane 14 (with reference to the flow direction of the combustible gas 13) and spaced apart therefrom, a perforated distributor wall can be positioned in order to distribute the combustible gas 13 in a desired manner towards the combustion membrane 14.

[0055] Detailed description of the combustion membrane 14

[0056] The combustion membrane 14 has an inner side 18 to which a combustible gas 13 is conveyed and an outer side 17 on which the combustion of the combustible gas 13 occurs after it has crossed through the combustion membrane 14, said combustion membrane 14 comprising a fabric 21 having two opposite fabric surfaces 19, 20 which respectively form a combustion surface 19 exposed on the outer side 17 and an inner surface 20 facing towards the inner side 18, wherein the fabric 21 forms an interlacing of metal wires 22 comprising warp threads and weft threads transverse relative to the warp threads, said fabric 21 being made on a loom (unlike knitted cloths that are to be considered excluded from the definition of “fabric”).

[0057] The fabric 21 is advantageously supported by and in contact with a support layer 38, e.g., a perforated metal sheet or wire mesh support, arranged on the inner side 18 of the combustion membrane 14 and forming part of the combustion membrane 14 itself or forming only a support structure for the combustion membrane 14.

[0058] Thus, the combustion membrane 14 can be a single-layer structure (including only the fabric 21 ) or a multilayer structure (containing at least the fabric 21 and the support layer 38 (Figures 3, 3A).

[0059] Description of surface profile characteristics of the fabric 21

[0060] According to an aspect of the invention, both fabric surfaces 19, 20 form ribs 23 in high relief alternating with valleys 24 in low relief, and both the ribs 23 and the valleys 24 have an extension, in at least one direction in the plane of the fabric 21 , greater than the space occupied by at least three consecutive warp threads in the weft direction and greater than the space occupied by at least three consecutive weft threads in the warp direction.

[0061] Due to the ribs 23 in high relief alternating with the valleys 24 in low relief, the metal fabric 21 of the combustion membrane 14 achieves a technical effect of discrete, repetitive but not continuous spacer, and the thickness of the fabric itself is not completely filled with metal material, which improves the thermal insulation capacity and allows a gas distribution through the metal fabric not only in the direction orthogonal to the plane of the fabric but also in the plane of the fabric itself.

[0062] This avoids overheating of the combustion membrane 14, improves the thermal insulation of the combustion membrane 14, it reduces the risk of flame detachment and improves the distribution of gas flow velocity 13 through the combustion membrane 14.

[0063] According to a further aspect of the invention:

[0064] - at the ribs 23, at least one of the fabric surfaces 19, 20 forms one or more floats 25 (i.e., bridging extension of a weft thread over several consecutive warp threads, or bridging extension of a warp thread over several consecutive weft threads),

[0065] - at the valleys 24, at least one of the fabric surfaces 19, 20 forms areas free from floats or with floats shorter than the floats in the ribs 23 of the same fabric surface (wherein “shorter” means “bridging extensions of a weft/warp thread over fewer consecutive warp/weft threads than the floats in the ribs”).

[0066] Description of permeability characteristics of the fabric 21

[0067] The fabric 21 is permeable to gas and has localized first areas 26 with reduced permeability alternated with localized second areas 27 with higher permeability than the first areas 26.

[0068] According to an embodiment, both the first areas 26 and the second areas 27 have an extension, in at least one direction on the plane of the fabric 21 , greater than the space occupied by at least three consecutive warp threads in the weft direction and greater than the space occupied by at least three consecutive weft threads in the warp direction.

[0069] According to an embodiment, at the first areas 26, the fabric 21 forms one or more floats 25, while at the second areas 27 the fabric forms areas free from floats or with floats shorter than the floats 25 in the first areas 26 (i.e., bridging passages of one warp/weft thread over a smaller number of consecutive warp/weft threads than the floats 25 in the first areas 26).

[0070] According to an embodiment, at the floats 25 of the first areas 26 the metal wires 22 forming said floats 25 are locally enlarged with respect to a width of the metal wires 22 at the second areas 27.

[0071] For example, the difference in gas permeability between first areas 26 and second areas 27 is e.g. visible and verifiable against the light as a difference in light transmission through the fabric 21.

[0072] The first localized areas 26 with reduced permeability alternating with the second localized areas 27 with higher permeability than the first localized areas 26 proved advantageous with reference to a reduction in the risk of flame detachment and with reference to a better distribution of gas flow velocity across the combustion membrane 14.

[0073] Description of examples of embodiment of the fabric 21

[0074] According to an embodiment (Figures 4A-D, 5A-D, 6A-D, 7A-D), the fabric 21 forms a plurality of clusters 28 of floats 25 spaced from each other, preferably distributed at a uniform pitch in two directions (but not necessarily equal for the two directions) either transverse or orthogonal in the plane of fabric 21 , each of said clusters 28 comprising:

- on one of the fabric surfaces 19, 20 at least three or more parallel first floats 25’, one directly next to the other,

- on the other of the fabric surfaces 19, 20 at least two or more parallel second floats 25”, one directly next to the other, the second floats 25” being oriented transversely or orthogonally relative to the orientation of the first floats 25’ and superimposed on the first floats 25’ with at least six intersection points 29 between the individual first floats 25’ and the individual second floats 25” of the cluster 28,

- between two consecutive clusters 28, respectively, the fabric forms extra-cluster areas 30 free from floats 25, 25’, 25”.

[0075] Advantageously, the float clusters 28 form the localized first areas 26 with reduced permeability, and the extra-cluster areas 30 form the localized second areas 27 with higher permeability.

[0076] The first floats 25’ of the same cluster 28 can have equal lengths and their ends can be aligned or staggered.

[0077] The second floats 25’ of the same cluster 28 can have equal lengths and their ends can be aligned or staggered.

[0078] The first floats 25’ of the same cluster 28 can have different lengths.

[0079] The second floats 25” of the same cluster 28 can have different lengths.

[0080] Advantageously, in the same cluster 28, the length of the longest float 25 on the inner surface 20 is greater than the length of the longest float 25 on the combustion surface 19.

[0081] In this manner, the longer floats of the cluster are arranged on the side of the fabric facing the inner side of the combustion membrane, while the shorter floats of the cluster are on the side of the fabric facing the outer (combustion) side of the combustion membrane. This effectively protects the longer float which would otherwise be too exposed and too poorly supported and stabilized.

[0082] Description of the embodiments implemented in the example in figures 6A-D [0083] According to an embodiment, the first floats 25’ of the cluster 28 are precisely three and the second floats 25” of the same cluster 28 are precisely three.

[0084] According to an embodiment, the first floats 25’ of the cluster 28 have a first central float 31’ and two first lateral floats 32’ on two opposite sides of the first central float 31’ and a length shorter than the length of the first central float 31’.

[0085] According to an embodiment, the second floats 25” of the cluster 28 have a second central float 31” and two second lateral floats 32” on two opposite sides of the second central float 31” and having a length shorter than the length of the second central float 31” (figure 6C, first floats 25’ dashed, second floats 25” black).

[0086] The first floats 25’ can be positioned and oriented mirror - symmetrically with respect to the second central float 31” (forming the mirror-symmetry line) of the same cluster 28.

[0087] Similarly, the second floats 25” can be positioned and oriented mirror-symmetrical with respect to the first central float 3T (forming the mirror-symmetry line) of the same cluster 28.

[0088] According to an embodiment, the first central float 3T can have a length of 5 passes (five bypassed threads) and the first lateral floats 32’ can have a length of 3 passes (three bypassed threads).

[0089] According to an embodiment, the second central float 31” can have a length of 5 passes (five bypassed threads) and the second lateral floats 32” can have a length of 3 passes (three bypassed threads).

[0090] The features described with reference to figures 6A-D are to be considered not necessarily in the specific and illustrative (though particularly advantageous) combination shown in the example of embodiment in figures 6A-D, but also individually and individually combined with each other, unless otherwise indicated.

[0091 ] Description of the embodiments implemented in the example in figures 4A-D [0092] According to an embodiment, the first floats 25’ of the cluster 28 are precisely four and the second floats 25” of the same cluster are precisely two.

[0093] According to an embodiment, the first floats 25’ of the cluster 28 all have the same length but are placed in a mutually staggered manner, such as in an alternating staggered manner, as shown in figure 4C (first floats 25’ dashed, second floats 25” black).

[0094] According to an embodiment, the second floats 25” of the cluster 28 all have the same length but are positioned in a mutually staggered manner.

[0095] According to an embodiment, the first floats 25’ can have a length of 3 passes (three bypassed threads) and the second floats 25” can have a length of 5 passes (five bypassed threads).

[0096] The features described with reference to figures 4A-D are to be considered not necessarily in the specific and illustrative (though particularly advantageous) combination shown in the example of embodiment in figures 4A-D, but also individually and individually combined with each other, unless otherwise indicated. [0097] Description of the embodiments implemented in the example in figures 5A-D [0098] According to an embodiment, the first floats 25’ of the cluster 28 are precisely three and the second floats 25” of the same cluster 28 are precisely two.

[0099] According to an embodiment, the first floats 25’ of the cluster 28 all have the same length but are placed in a staggered manner with each other, preferably in an alternating staggered manner, as shown in figure 5C (first floats 25’ black, second floats 25” dashed). [00100] According to an embodiment, the second floats 25” of the cluster 28 have different lengths and are positioned symmetrically relative to a first central float 31’ (symmetry-line) of the three first floats 25’ of the cluster 28.

[00101] According to an embodiment, the first floats 25’ can have a length of 3 passes (three bypassed threads) and the two second floats 25” can have, respectively, a length of 5 passes (five bypassed threads), and the other the length of three passes (three bypassed threads).

[00102] According to an embodiment, in addition to the float clusters 28, the fabric 21 may comprise a plurality of simple intersections 33 of floats, said intersections 33 comprising:

- on one of the fabric surfaces 19, 20 exactly one primary float 33’,

- on the other of the fabric surfaces 19, 20 exactly one secondary float 33” oriented transversely or orthogonally relative to the orientation of the primary float 33’ and superimposed on the primary float 33’ with exactly only one intersection point.

[00103] The features described with reference to figures 5A-D are to be considered not necessarily in the specific and illustrative (though particularly advantageous) combination shown in the example of embodiment in figures 5A-D, but also individually and individually combined with each other, unless otherwise indicated.

[00104] Description of the embodiments implemented in the example in figures 7A- D

[00105] According to an embodiment, the first floats 25’ of the cluster 28 are precisely eight and the second floats 25” of the same cluster 28 are precisely nine.

[00106] According to an embodiment, the first floats 25’ of the cluster 28 are arranged in a staggered step-like manner, defining as a whole a first strip 34 which is oblique relative to the orientation of the individual first floats 25’.

[00107] Similarly, the second floats 25” of the cluster 28 are arranged in a staggered steplike manner defining as a whole a second strip 34” oblique to the orientation of the single second floats 25” and superimposed on the first oblique strip 34.

[00108] According to an embodiment, there may be two or more configurations of clusters 28, 35 of different floats.

[00109] In addition to the float clusters 28 described so far (which can be referred to as “first clusters 28”) there can be second clusters 35 of a different shape and location than the first clusters 28.

[00110] According to an embodiment, the first floats 25’ of the second cluster 35 are precisely nine and the second floats 25” of the same cluster 35 are precisely six.

[00111] According to an embodiment, said first floats 25’ of the second cluster 35 are arranged to form a further first strip 36 oblique relative to the orientation of the individual first floats 25’ but preferably of a different shape from the shape of the first strip 34 of the first cluster 28, e.g., in a zigzag shape.

[00112] Similarly, the second floats 25” of the second cluster 35 are arranged to form a further second strip 36’ oblique relative to the orientation of the individual second floats 25”, but preferably of a different shape from the shape of the second strip 34’ of the first cluster 28, e.g., zigzag-shaped and superimposed on the further first oblique strip 36 (Figures 7.1 C and 7.2C).

[00113] The drawing in figure 7C shows:

- at the top of the figure, only the first floats 25’ (in bold print) of first clusters 28 and second clusters 35 on the fabric surface 21 facing the observer,

- in the central part of the figure, the first floats 25’ (with solid contours) of the first clusters 28 on the surface of fabric 21 facing towards the observer, and the second floats 25” (with dashed contours) of the first clusters 28 on the surface of fabric 21 facing away from the observer,

- in the lower part of the figure, the first floats 25’ (with solid contours) of the first clusters 28 and the second clusters 35 on the surface of the fabric 21 facing towards the observer, and the second floats 25” (in bold print) of the first clusters 28 and the second clusters 35 on the surface of fabric 21 facing away from the observer.

[00114] Similarly, the drawing in figure 7.1C shows the first floats 25’ (in bold print) of the first clusters 28 and of the second clusters 35 on the surface of the fabric 21 facing towards the observer, and the drawing in figure 7.2C shows the first floats 25’ (with solid contours) of the first clusters 28 and of the second clusters 35 on the surface of the fabric 21 facing toward the observer, and the second floats 25” (in bold print) of the first clusters 28 and second clusters 35 on the surface of the fabric 21 facing away from the observer.

[00115] The first clusters 28 and/or second clusters 35 may be arranged to define a plurality of sequences of clusters 28, 35 extended in the weft or warp direction of the fabric 21 and formed by strips 34, 36; 34’, 36’ oblique relative to the warp and weft directions.

[00116] The embodiments described are only by way of example and represent possibilities for practical embodiments of the described technical features.

[00117] Such practical embodiments have been tested and achieve the desired technical effects.

[00118] However, the aesthetic impression or features visible from only one side of the fabric 21 or the combustion membrane 14 or visible from only the outer side (the only visible side) of the burner 2, and resulting from the light reflection effect, the orientation of the metal fabric 21 relative to the burner 2, color, etc.), may be subject to significant variability and do not contribute to achieving the technical effect of the invention. Thus, the invention has the additional advantage of leaving wide freedom of aesthetic choice to burner 2 manufacturers and the technical characteristics described can be obtained even with different exterior aesthetic choices than the illustrated embodiments.

[00119] Description of the metal wire 22

[00120] According to an embodiment, the metal wires 22 comprise bundles of metal fibers, e.g., non spun, or bundles of parallel or twisted or spun metal fibers, e.g., of the long fiber filament or short fiber filament type.

[00121] The metal wires 22 can be at least or only initially bonded by means of a binder, e.g., water-soluble or non-soluble bonding thread 37, e.g., PVA or polyester, or by means of a water-soluble or non-soluble bonding adhesive, e.g., polymeric.

[00122] Advantageously, the fabric 21 is a “heavy” or “coarse” fabric, i.e., a fabric with a weight per fabric area equal to or greater than 1 .3 kg/m² or in the range from 1 .3 kg/m² to 1 .6 kg/m².

[00123] Advantageously, the metal wire 22 is a yarn of weight per length in the range from 0.8 g/m to 1.4 g/m, advantageously from 0.9 g/m to 1.1 g/m, e.g., 1g/m.

[00124] Advantageously, the metal wire 22 consists of fibers with diameters in the range from 30 micrometers to 50 micrometers, e.g., approximately 40 micrometers.

[00125] “Big” fibers and “big” yarns allow economical and industrially advantageous manufacture of “coarse” fabrics that are not excessively gas proof.

[00126] According to an embodiment, the material of the metal wires 22 or metal fibers can be, for example, a ferritic steel, or a FeCrAI alloy, e.g., doped by means of Yttrium, Hafnium, Zirconium.

[00127] The metal wire 22 may be, for example, a Y, Hf, Zr doped FeCrAI alloy yarn, weighing 1g/m and consists of fibers having a diameter of 40 micrometers, untwisted, possibly crimped (wavy), retained by means of a binding thread 37, possibly PVA or polyester binding thread, and having, for example, the following “doped” composition:

[00128] According to a further embodiment, the material of metal wires or metal fibers can be, for example, a ferritic steel, or a FeCrAI alloy, e.g., additionally containing Yttrium, Hafnium, Zirconium.

[00129] The metal wire may be, for example, a Y, Hf, Zr doped FeCrAI alloy yarn, weighing 1 g/m and composed of fibers 40 micrometers in diameter, spun, e.g., with 30 to 150 twists per meter, possibly with fiber ends divergently protruding from the yarn (“hairy”), with fibers shorter than the yarn, e.g., with fiber lengths in the range of 7cm to 30cm, not necessarily but possibly restrained by means of a binding thread 37, possibly made of PVA or polyester, and having, for example, the same “doped” composition as shown in the table above.

[00130] Description of an example embodiment of the basic fabric 21

[00131] According to an embodiment (Figure 11), the ribs 23 and the valleys 24 define a repetitive pattern of first rows 133, preferably straight, inclined with respect to the weft 36_T and warp 36_O directions in a first direction, and second rows 134, preferably straight, inclined with respect to the weft 36_T and warp 36_O directions in a second direction transverse to the first direction, wherein said first rows 133 and second rows 134 intersect delimiting rhombus-shaped areas 135, wherein the two diagonals of the rhombus-shaped area 135 (the segments joining the opposite vertices of the rhombus) are parallel to the warp and weft directions of fabric 21 .

[00132] The shape of the fabric 21 thus configured has proven to be surprisingly advantageous with reference to the characteristics of porosity, thermal insulation, deformability in various three-dimensional shapes, and fabrication by industrial weaving.

[00133] Advantages of the invention

[00134] By virtue of the ribs in high relief alternating with the valleys in low relief, the metal fabric of the combustion membrane achieves a technical effect of discrete, repetitive but not continuous spacing, and of a thickness of the fabric which itself is not completely filled with metal material, which improves the thermal insulation capacity and allows gas distribution through the metal fabric not only in the direction orthogonal to the plane of the fabric but also in the plane of the fabric itself.

[00135] This avoids overheating of the combustion membrane, it improves the thermal insulation of the combustion membrane, it reduces the risk of flame detachment, and it improves the distribution of gas flow velocity through the combustion membrane. [00136] The first localized areas with reduced permeability alternating with the second localized areas with higher permeability than the first localized areas proved advantageous with reference to a reduction in the risk of flame detachment and with reference to a better distribution of gas flow velocity across the combustion membrane.

[00137] The configuration of the metal fabric with the clusters of floats spaced apart from each other and with the extra-cluster areas free of floats allows for a practical, industrially advantageous embodiment of the high relief ribs alternating with the low relief valleys and/or the first localized areas with reduced permeability alternating with the second localized areas with higher permeability.

[00138] Therefore, the individual aspects of the invention are not only individually significant in solving the problems of the prior art, but a combination thereof provides further synergy.

Claims

1. A combustion membrane (14) for a gas burner (2), said combustion membrane (14) having an inner side (18) to which a combustible gas (13) is conveyed and an outer side

(17) on which combustion of the combustible gas (13) occurs after it has crossed through the combustion membrane (14), said combustion membrane (14) comprising a fabric (21) having two opposite fabric surfaces (19, 20), which respectively form a combustion surface (19) exposed on the outer side (17) and an inner surface (20) facing towards the inner side

(18), wherein the fabric (21) forms an interlacing of metal wires (22) comprising warp threads and weft threads transverse relative to the warp threads, characterized in that:

- the fabric (21) has localized first areas (26) with reduced gas permeability, alternated with localized second areas (27) with higher gas permeability than the first areas (26).

- both the first areas (26) and the second areas (27) have an extension, in at least one direction on the plane of the fabric (21), greater than the space occupied by at least three consecutive warp threads in the weft direction and greater than the space occupied by at least three consecutive weft threads in the warp direction.

2. A combustion membrane (14) according to claim 1 , wherein:

- in the first areas (26) the fabric (21 ) forms one or more floats (25),

- in the second areas (27) the fabric forms areas free from floats or with floats shorter than the floats (25) in the first areas (26).

3. A combustion membrane (14) according to claim 2, wherein at the floats (25) of the first areas (26) the metal wires (22) forming said floats (25) are locally enlarged with respect to a width of the metal wires (22) at the second areas (27).

4. A combustion membrane (14) according to any one of the preceding claims, wherein both fabric surfaces (19, 20) form ribs (23) in high relief alternating with valleys (24) in low relief.

5. A combustion membrane (14) according to claim 4, wherein both the ribs (23) and the valleys (24) have an extension, in at least one direction in the plane of the fabric (21 ), greater than the space occupied by at least three consecutive warp threads in the weft direction and greater than the space occupied by at least three consecutive weft threads in the warp direction.

6. A combustion membrane (14) according to claim 4 or 5, wherein

- at the ribs (23) at least one of the fabric surfaces (19, 20) forms one or more floats (25),

- at the valleys (24) at least one of the fabric surfaces (19, 20) forms areas free from floats or with floats shorter than the floats in the ribs (23) of the same fabric surface (19, 20).

7. A combustion membrane (14) according to any one of the preceding claims, wherein the fabric (21) forms a plurality of clusters (28) of floats (25), said clusters (28) being spaced apart from each other and distributed in two transverse directions in the plane of the fabric (21 ), each of said clusters (28) comprising:

- on one of the fabric surfaces (19, 20) at least three or more parallel first floats (25'), one directly next to the other,

- on the other of the fabric surfaces (19, 20) at least two or more parallel second floats (25"), one directly next to the other, the second floats (25") being oriented transversely relative to the orientation of the first floats (25') and superimposed on the first floats (25') with at least six intersection points (29) between the individual first floats (25') and the individual second floats (25") of the cluster (28),

- between two consecutive clusters (28), respectively, the fabric forms extra-cluster areas (30) free from floats (25, 25', 25").

8. A combustion membrane (14) according to claim 7, wherein the clusters (28) form the first localized areas (26) with reduced permeability and the extra-cluster areas (30) form the second localized areas (27) with higher permeability.

9. A combustion membrane (14) according to claim 7, wherein:

- the first floats (25') of the cluster (28) have a first central float (31') and two first lateral floats (32') on two opposite sides of the first central float (31 ') and having a length shorter than the length of the first central float (31 '),

- the second floats (25”) of the cluster (28) have a second central float (31”) and two second lateral floats (32”) on two opposite sides of the second central float (31”) and having a length shorter than the length of the second central float (31”),

- the first floats (25') are positioned and oriented mirror-symmetrical to a symmetry line formed by the second central float (31 ") of the same cluster (28),

- the second floats (25") are positioned and oriented mirror-symmetrical to a symmetry line formed by the first central float (31') of the same cluster (28).

10. A combustion membrane (14) according to claim 7, wherein: 16

- the first floats (25') of the cluster (28) all have the same length, but are positioned in a mutually staggered manner or in an alternating staggered manner,

- the second floats (25”) of the cluster (28) all have the same length but are positioned in a mutually staggered manner.

11. A combustion membrane (14) according to claim 7, wherein:

- the first floats (25') of the cluster (28) all have the same length but are positioned in a mutually staggered manner or in an alternated staggered manner,

- the second floats (25”) of the cluster (28) have different lengths and are positioned symmetrically relative to a symmetry line formed by a first central float (31 ') of the first floats (25') of the cluster (28),

- the fabric (21) comprises a plurality of simple intersections (33) of floats, said intersections (33) comprising:

- on one of the fabric surfaces (19, 20) exactly one primary float (33'),

- on the other of the fabric surfaces (19, 20) exactly one secondary float (33") oriented transversely relative to the orientation of the primary float (33') and superimposed on the primary float (33') with exactly only one intersection point.

12. A combustion membrane (14) according to claim 7, wherein:

- the first floats (25') of the cluster (28) are arranged in a staggered step-like manner, defining as a whole a first strip (34) which is oblique relative to the orientation of the individual first floats (25');

- the second floats (25”) of the cluster (28) are arranged in a staggered step-like manner defining as a whole a second strip (34”) oblique to the orientation of the single second floats (25”) and superimposed on the first oblique strip (34).

13. A combustion membrane (14) according to claim 12, wherein:

- in addition to the clusters (28) which form first clusters, the fabric (21 ) forms second clusters (35) of a different shape and position than the first clusters (28),

- the first floats (25') of the second cluster (35) are arranged to form a further first strip (36) oblique relative to the orientation of the individual first floats (25') but of a different shape from the shape of the first strip (34) of the first cluster (28),

- the second floats (25”) of the second cluster (35) are arranged to form a further second strip (36') oblique relative to the orientation of the individual second floats (25"), but of a different shape from the shape of the second strip (34') of the first cluster (28) and superimposed on the further first oblique strip (36). 17

14. A combustion membrane (14) according to claim 11 or 12, wherein:

- the first clusters (28) and/or second clusters (35) are arranged to define a plurality of sequences of clusters (28, 35) extended in the weft or warp direction of the fabric (21) in the form of strips (34, 36; 34', 36') oblique relative to the warp and weft directions.

15. A combustion membrane (14) according to any one of the claims from 7 to 14, wherein, in the same cluster (28), the length of the longest float (25) on the inner surface 20 is greater than the length of the longest float (25) on the combustion surface (19).

16. A combustion membrane (14) according to any one of the preceding claims, wherein:

- the fabric (21 ) has a mass per area equal to or greater than 1 .3 kg/m² or in the range from 1 .3 kg/m² to 1 .6 kg/m²,

- the metal wire (22) is a yarn of mass per length in the range from 0.8 g/m to 1 .4 g/m, or in the range from 0.9 g/m to 1 .1 g/m.

- the metal wire (22) is composed of fibers with diameters in the range from 30 micrometers to 50 micrometers or 40 micrometers.

17. A combustion membrane (14) according to any one of the preceding claims, wherein the fabric (21 ) is supported by and in contact with a support layer (38) arranged on the inner side (18) of the combustion membrane (14).

18. A gas burner (2) comprising a combustion membrane (14) according to any one of the preceding claims.