COMBUSTION MEMBRANE FOR A GAS BURNER MADE WITH CONTINUOUS FIBER THREADS

Abstract

A combustion membrane for a gas burner is provided. The combustion membrane has a fabric or mesh of interlaced metal wires, having two opposite interlacing surfaces forming a combustion surface and an inner surface of the fabric or mesh, respectively. The metal wires are formed by continuous metal fibers that form a yarn of mass per length ranging from 0.8 g/m to 1.4 g/m.

Claims

1. A combustion membrane for a gas burner, said combustion membrane having an inner side to which a combustible gas is conveyed and an outer side on which combustion of the combustible gas occurs after the combustible gas has crossed the combustion membrane, said combustion membrane comprising a fabric or mesh of interlaced metal wires, having two opposite interlacing surfaces forming a combustion surface exposed on the outer side and an inner surface facing the inner side, respectively, wherein the metal wires are formed by continuous metal fibers which form a yarn with mass per length ranging from 0.8 g/m to 1.4 g/m.

2. The combustion membrane of claim 1, wherein said continuous metal fibers are not mutually twisted and form an untwisted yarn.

3. The combustion membrane of claim 1, wherein the individual continuous metal fibers each have a length substantially corresponding to the length of the yarn formed therewith.

4. The combustion membrane of claim 1, wherein the continuous metal fibers have a waviness that gives an additional extension to the yarn in a direction transverse to a longitudinal direction thereof.

5. The combustion membrane of claim 4, wherein said waviness is a waviness with less wavelength and amplitude than the wavelength and amplitude of a knitting or weaving waviness of the fabric or mesh.

6. The combustion membrane of claim 4, wherein said waviness is formed over the entire length of the yarn.

7. The combustion membrane of claim 1, wherein the continuous metal fibers of a same yarn are detached from one another, at least in stretches, along more than 30%, or more than 50%, of the length of the yarn, thus making the yarn bulged.

8. The combustion membrane of claim 1, wherein the continuous metal fibers have a circular cross-section.

9. The combustion membrane of claim 1, wherein the fabric/mesh or mesh has a weight per area either equal to or greater than 1.2 kg/m.sup.2, or ranging from 1.2 kg/m.sup.2 to 1.5 kg/m.sup.2, or of 1.3 kg/m.sup.2.

10. The combustion membrane of claim 1, wherein: said continuous metal fibers are not mutually twisted and form an untwisted yarn, the continuous metal fibers each have a length substantially corresponding to the length of the yarn formed therewith, the continuous metal fibers have a waviness that gives an additional extension to the yarn in a direction transverse to a longitudinal direction thereof, said waviness being a waviness with less wavelength and less amplitude than the wavelength and amplitude of a knitting or weaving waviness of the fabric or mesh, said waviness is formed over the entire length of the yarn, and the continuous metal fibers have a circular cross-section.

11. The combustion membrane of claim 1, wherein the metal wires consist of continuous metal fibers having a diameter ranging from 30 micrometers to micrometers, or of 40 micrometers.

12. The combustion membrane of claim 1, wherein the metal wires is are made of an FeCrAl alloy doped with Yttrium, Hafnium, Zirconium.

13. The combustion membrane of claim 1, wherein both interlacing surfaces form high-relief ribs alternating with low-relief valleys, and both the high-relief ribs and the low-relief valleys have an extension, in at least one direction in a plane of the fabric or mesh, three times greater than a thickness of the metal wires.

14. The combustion membrane of claim 1, wherein the fabric or mesh has first localized areas with low permeability, alternating with second localized areas with higher permeability than the first localized areas, and wherein both the first and second localized areas have an extension, in at least one direction in a plane of the fabric or mesh, three times greater than a thickness of the metal wires.

15. The combustion membrane of claim 1, wherein the fabric or mesh is supported by and in contact with a support layer arranged on the inner side of the combustion membrane.

16. The combustion membrane of claim 1, wherein the metal wires are at least or only initially bound by a binder selected from a bonding thread, or a bonding adhesive, and a water-soluble binder.

17. A gas burner comprising a combustion membrane according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] In order to better understand the invention and appreciate the advantages thereof, a description is provided below of some non-limiting exemplary embodiments, with reference to the accompanying drawings, in which:

[0032] FIG. 1 is a diagrammatic view of a gas combustion system, for example for a boiler, with a burner provided with a combustion membrane,

[0033] FIGS. 2 and 3 are perspective and sectional views of an exemplary burner, provided with a combustion membrane,

[0034] FIG. 3A is an enlarged and diagrammatic section view of a combustion membrane according to an embodiment of the present invention,

[0035] FIG. 4 shows a burner with a combustion membrane according to an embodiment,

[0036] FIG. 5 shows a detail of a metal yarn bound with a bonding thread according to an embodiment, and

[0037] FIGS. 5.1 and 5.2 show further details of a metal yarn of a combustion membrane, according to embodiments.

DETAILED DESCRIPTION

Detailed Description of the Combustion System 1

[0038] With reference to FIG. 1, a gas combustion system 1, e.g., for a boiler, comprises:

[0039] a burner 2 for producing heat by combustion of combustible gas and combustion air,

[0040] a feeding system 3 for feeding the combustible gas or mixture of gas and combustion air to the burner 2, said feeding system 3 comprising a gas control device 4 for controlling a flow of the combustible gas (e.g., an electrically controllable gas valve or gas conveying means or gas suction means) and, if provided, an air control device 5 (e.g., air conveying means or air suction means, an electric fan, a radial fan, an air valve or an air gate valve) to control a flow of combustion air,

[0041] an electric ignition device 6 for igniting the combustion, e.g., an ignition electrode adapted to generate a spark,

[0042] possibly, an ionization sensor 7 arranged at a combustion area 8 of the burner 2 and adapted to provide an electrical ionization signal varying as a function of a combustion condition of the burner 2, and

[0043] 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.

Detailed Description of the Burner 2

[0044] According to an embodiment (FIGS. 2, 3), the gas burner 2 comprises:

[0045] 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, and

[0046] a tubular combustion membrane 14, e.g., cylindrical in shape, and coaxial 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 gas 13 or the gas-air mixture to pass from inside the burner 2 to an outer side 17 of the combustion membrane 14 where the combustion occurs (combustion area 8).

[0047] A tubular silencing accessory (without reference numeral) is also shown in the burner 2 in FIG. 3, which is optional and could be reduced in size or completely eliminated.

[0048] According to a further embodiment, the 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 wall 11 in flow communication with the inlet passage 12, as well as a perforation for the gas 13 or the gas-air mixture to pass from inside the burner 2 to an outer side 17 of the combustion membrane 14 where the combustion occurs (combustion area 8).

[0049] Similarly to prior solutions with conventional combustion membranes, according to an embodiment, in the 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.

Detailed Description of the Combustion Membrane 14

[0050] 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 the combustion membrane 14, said combustion membrane 14 comprising a fabric or a mesh, indicated as a whole by reference numeral 21, of interlaced metal wires 22 having two opposite interlacing surfaces 19, 20 forming a combustion surface 19 exposed on the outer side 17 and an inner surface 20 facing the inner side 18, respectively, where the metal wires 22 are formed by continuous metal fibers 22 which form a yarn 22 with mass per length ranging from 0.8 g/m to 1.4 g/m.

[0051] Advantageously, the continuous metal fibers 22 are not mutually twisted and form an untwisted yarn 22.

[0052] With a further advantage, the individual continuous metal fibers 22 each have a length substantially corresponding to the length of the yarn 22 formed therewith.

[0053] Preferably, the metal fibers 22 have a waviness which gives an additional extension to the yarn 22 in a direction transverse to a longitudinal direction thereof.

[0054] The continuity of the fibers 22 and the waviness of the yarn 22 by mechanically crimping the entire yarn 22 or the individual fibers 22 makes the yarn 22 advantageously bulky, and forms an improved alternative to a twisted yarn obtained by conventional spinning techniques (short fibers twisted together, the so-called twisted spun yarn), which, when applied to the metal yarns and fibers considered here, exhibits considerable complications of the spinning and weaving process.

[0055] The fabric or mesh 21 is advantageously supported by and in contact with a support layer 38, e.g., a perforated sheet metal or a support metal net, 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.

[0056] The combustion membrane 14 can thus be a single-layer structure (including only the fabric or mesh 21) or a multilayer structure (containing at least the fabric or mesh 21 and the support layer 38 (FIGS. 3, 3A).

[0057] The fabric or mesh 21 can only consist of a fabric made with warp and weft threads by means of a weaving loom, thus excluding meshes made by interlacing a thread from a continuous coil.

[0058] Similarly, the fabric or mesh 21 can only consist of a mesh made by interlacing a thread 22 from a continuous coil, thus excluding fabrics made with warp and weft threads using a weaving loom.

Detailed Description of the Metal Wire 22

[0059] The metal wires 22 are formed by metal fibers 22 forming a yarn 22 of mass per length ranging from 0.8 g/m to 1.4 g/m.

[0060] According to an embodiment, the continuous metal fibers 22 are not mutually twisted and form an untwisted yarn 22.

[0061] According to an embodiment, the individual continuous metal fibers 22 each have a length substantially corresponding to the length of the yarn 22 formed therewith.

[0062] According to an embodiment, the metal fibers 22 have a waviness which gives an additional extension to the yarn 22 in a direction transverse to a longitudinal direction thereof.

[0063] The waviness is a waviness with less wavelength and less amplitude than the wavelength and amplitude of a knitting or weaving waviness of the fabric or mesh 21.

[0064] According to an embodiment, said waviness is formed over the entire length of the yarn 22.

[0065] According to an embodiment, the continuous metal fibers 22 of the same yarn 22 are detached from one another, at least in stretches, along more than 50%, or more than 22%, of the overall length of the yarn (22) 22, thus making the yarn (22) 22 bulged.

[0066] According to an embodiment, the metal fibers 22 have a circular cross-section.

[0067] According to an embodiment, the fabric or mesh 21 has a mass per area either equal to or greater than 1.3 kg/m.sup.2, or ranging from 1.2 kg/m.sup.2 to 1.5 kg/m.sup.2.

[0068] According to an embodiment, the metal wires 22 comprise bundles of metal fibers 22 of the non-twisted long fiber filament type, but advantageously locally wavy, preferably over substantially the entire length of the wire 22.

[0069] The metal wires 22 can be at least or only initially bound by means of a binder, e.g., a water-soluble or non-soluble bonding thread 37, e.g., made of PVA or polyester, or by means of a water-soluble or non-soluble bonding adhesive, e.g., polymeric.

[0070] According to an embodiment, the metal wires 22 can be selected from the group of so-called long or continuous filament crimped yarns as defined, for example, in Fundamentals of Yarn Technology 2003, CRC Press LLC, Chapter 1.2.1, Table 1.1.

[0071] In order to ensure the substantially continuous extension of both the yarn 22 and the individual fibers 22, as well as the manufacture and weaving or knitting thereof, the yarn and/or fibers can have knotted connecting stitches, preferably narrow.

[0072] According to an embodiment, the metal wires 22 are of the long filament type.

[0073] Advantageously, the fabric or mesh 21 is a heavy or coarse fabric or mesh, i.e., having a weight per area of fabric either equal to or greater than 1.2 kg/m.sup.2 or ranging from 1.2 kg/m.sup.2 to 1.5 kg/m.sup.2, preferably of 1.3 kg/m.sup.2.

[0074] Advantageously, the metal wire 22 is a yarn of weight per length ranging from g/m to 1.4 g/m, advantageously from 0.9 g/m to 1.1 g/m, e.g., of 1 g/m.

[0075] Advantageously, the metal wire 22 consists of fibers with diameter ranging from micrometers to 50 micrometers, e.g., of about 40 micrometers.

[0076] The big fibers 22 and the big wires 22 allow for an economical and industrially advantageous manufacture of coarse fabrics/meshes 21 which are not excessively impermeable.

[0077] According to an embodiment, the material of the metal wires 22 or metal fibers 22 can be, for example, a ferritic steel, or an FeCrAl alloy, e.g., doped with Yttrium, Hafnium, Zirconium.

[0078] The metal wire 22 can be, for example, a yarn made of FeCrAl alloy doped with Y, Hf, Zr, weighing 1 g/m and consisting of fibers with a diameter of 40 micrometer, either wavy or crimped, such that it is less one-dimensional and more transversely bulged. The wire 22 is possibly held by a bonding thread 37, e.g., made of PVA or polyester, and having, for example, the following doped composition:

TABLE-US-00001 C Mn Si Al Cu Cr Y Hf Zr P S Ti N Ni Fe Min. 5.5 19 0.03 0.03 0.03 rest Max. 0.04 0.4 0.5 6.5 0.03 22 0.03 0.03 0.5 0.02 0.3

Description of Surface Profile Characteristics of the Fabric/Mesh 21

[0079] According to an embodiment of the invention, both interlacing surfaces 19, 20 form high-relief ribs 23 alternating with low-relief valleys 24, and both the ribs 23 and the valleys 24 have an extension, in at least one direction in the plane of the fabric or mesh 21, three times greater, preferably four times greater than the thickness of the metal wires 22.

[0080] By virtue of the high-relief ribs 23 alternating with the low-relief valleys 24, the metal fabric or mesh 21 of the combustion membrane 14 achieves a technical effect of a discrete, repetitive but not continuous spacer, and a thickness of the fabric or mesh itself not completely filled with metal material, which improves the thermal insulation capacity and allows a gas distribution through the metal fabric or mesh not only in the direction orthogonal to the plane of the fabric or mesh but also in the plane of the fabric or mesh itself.

[0081] This obviates an overheating of the combustion membrane 14, improves the thermal insulation of the combustion membrane 14, reduces the risk of flame detachments, and improves the flow velocity distribution of the gas 13 across the combustion membrane 14.

Description of Permeability Characteristics of the Fabric/Mesh 21

[0082] The fabric or mesh 21 is permeable to gases and has localized first areas 26 with low permeability alternating with localized second areas 27 with higher permeability than the first areas 26.

[0083] According to an embodiment, said first areas 26 and second areas 27 have an extension, in at least one direction in the plane of the fabric or mesh 21, three times greater, preferably four times greater than the thickness of the metal wire 22.

[0084] For example, the difference in gas permeability between the first areas 26 and the second areas 27 is visible and verifiable against the light as a difference in light transmission through the fabric or mesh 21.

[0085] The first localized areas 26 with low permeability alternating with the second localized areas 27 with higher permeability than the first localized areas 26 proved to be advantageous with reference to a reduction in the risk of flame detachments and with reference to a better flow velocity distribution of the gas across the combustion membrane 14.

Advantages of the Invention

[0086] By using continuous fibers and large threads, which are diametrically coarse per se or bulged, it is possible to make similarly coarse or heavy fabrics and meshes which inherently have a lower thread count density per unit area and thus a higher and desired gas permeability, also in the presence of greater thicknesses (and thus thermal insulation properties) and/or greater mass (and thus thermal inertia), than the light or thin fabrics of the prior art.

[0087] By virtue of the high-relief ribs alternating with the low-relief valleys, the metal fabric or mesh of the combustion membrane achieves a technical effect of a discrete, repetitive but not continuous spacing, and a thickness of the fabric or mesh itself not completely filled with metal material, which improves the thermal insulation capacity and allows a gas distribution through the metal fabric or mesh not only in the direction orthogonal to the plane of the fabric or mesh but also in the plane of the fabric or mesh itself.

[0088] This obviates the overheating of the combustion membrane, improves the thermal insulation of the combustion membrane, reduces the risk of flame detachments, and improves the flow velocity distribution of the gas across the combustion membrane.

[0089] The first localized areas with low permeability alternating with the second localized areas with higher permeability than the first localized areas proved to be advantageous with reference to a reduction in the risk of flame detachments and with reference to a better flow velocity distribution of the gas across the combustion membrane.

[0090] Therefore, the individual aspects of the present invention are not only individually significant to solve the problems of the prior art, but a combination thereof is further synergistic.