Description

Technical Field

[0001] The invention relates to the field of gas premix burners with a cylindrical burner deck.

Such burners include a mixing chamber within the contours of the burner deck; and an inlet to supply premix gas into the mixing chamber.

Background Art

[0002] Gas premix burner types with cylindrical burner deck are known. The burner deck

encloses a mixing chamber. An inlet device is provided for supplying premix gas (combustible gas and air) into the mixing chamber. The gas is combusted after it has flown through the burner deck. The burner deck stabilizes the combustion.

[0003] EP2037175A2 discloses a premix burner comprising a perforated tubular body. The body is closed on a head by a plate welded or crimped along its side surface. The burner comprises a disk, fixed to the opposite head of the tubular body. The disc is provided with a plurality of through openings or holes and constitutes the supply and distribution head of the air-gas mixture into the tubular body.

[0004] WO13120715A1 and WO13120716A1 disclose cylindrical premix gas burners comprising a cylindrical burner deck. The cylindrical premix gas burner is delimited by an end cap. At the opposite side of the end cap, an inlet disc with perforations is provided for the supply of a premix of combustible gas and air into the burner; and which is to be burnt on the outside of the cylindrical burner deck after the premix gas has flown through it.

The inlet disc of the burner of WO13120715A1 comprises a multiple of perforations for premix gas supply in a central zone of the plate, and a multiple of perforations for premix gas supply in the peripheral zone of the inlet disc. The porosity of the inlet disc is higher in the central zone than in a peripheral zone. The average surface area of the perforations in the central zone of the inlet disc is less than 20 mm ² .

The inlet disc of the burner of WO13120716A1 comprises a plurality of perforations for supplying premix gas supply into the burner. The inlet disc has a centre point, which is where the central axis of the cylindrical premix gas burner crosses the inlet disc. The inlet disc is not permeable to premix gas at least within a circle with a diameter of at least 8 mm around the centre point.

[0005] EP3006826A1 discloses a gas premix burner comprising a cylindrical burner deck and an inlet device mounted perpendicularly to the axial direction of the cylindrical burner deck. The cylindrical burner deck encloses a mixing chamber.

[0006] WO2015/054323A1 discloses a combustion system such as a furnace or boiler including a perforated reaction holder configured to hold a combustion reaction that produces very low oxides of nitrogen (NOx). The system can comprise a flat burner deck and can be provided with a flat flame arrestor, e.g. a wire mesh or perforated sheet metal.

Disclosure of Invention [0007] It is the objective of the invention to provide an improved gas premix burner with a cylindrical burner deck. It is a specific objective of the invention to provide such a burner that can be ignited more easily, and at which flame sensing can be done more easily. It is a specific objective to provide such a burner with a large L/D ratio, wherein L is the axial length of the burner deck and D is the internal diameter of cylindrical burner deck. It is a further objective to provide an efficient and effective burner comprising a minimal number of parts.

[0008] The first aspect of the invention is a gas premix burner. The burner comprises a

cylindrical burner deck. An inlet device is mounted perpendicularly to the axial direction of the cylindrical burner deck. The cylindrical burner deck encloses a mixing chamber. The inlet device comprises a metal mesh through which when the burner is in use, premix gas flows into the mixing chamber. Preferably, the burner is for combusting hydrocarbons, e.g. natural gas, methane, butane, propane or LPG. Combustion occurs on the surface of the cylindrical burner deck after the premix gas has flown from the mixing chamber through the cylindrical burner deck. In preferred embodiments, the burner deck comprises or consists out of a perforated metal sheet.

[0009] In a metal mesh, the openings have - unlike the through holes drilled or punched in a perforated metal plate - a shape that is not constant along the length of the opening through the object.

[0010] Burners with a cylindrical burner deck are provided with an igniter (ignition electrode) and frequently also with a flame sensing probe (flame sensing electrode). It is common practice to install the igniter and - if present - the flame sensing probe at the base of the cylindrical burner deck, meaning at the side of the inlet device. Prior art burners have shown problems with ignition (difficult and/or unreliable ignition) and difficult and/or unreliable flame sensing. Surprisingly the burner of the invention provides stable ignition and reliable flame sensing, even when using short length igniters and short length flame sensing probes installed close to or at the inlet side of the burner. Even more surprisingly, the benefits were also present, and even to a larger extent, for cylindrical burners with a large L/D ratio, e.g. with an L/D ratio of more than 3, or even more than 6. For the L/D ratio, L is the axial length of the burner deck and D is the internal diameter of the cylindrical burner deck. It is a further benefit that the inventive burner has a lower pressure drop compared to prior art burners, e.g. compared to prior art burners that have a perforated plate as inlet device. It was surprising to notice the benefits of the burner of the invention compared to a similar prior art burner having a perforated plate inlet disc with the same open area as the metal mesh of the inventive burner.

It is believed that the different three-dimensional geometry of the openings in metal meshes compared to the drilled or punched holes in perforated plate inlet discs creates a difference in the way the gas mix flows through the openings of the inlet device and contributes to or provides the beneficial effects that have been noticed, beneficial effects that have been described in this paragraph.

[001 1] Preferably, the inlet device comprises a flange. Preferably, the metal mesh is attached to the flange, e.g. by means of welding. The flange is provided for mounting the inlet device into the burner.

[0012] Preferably, the metal mesh comprises or consists out of metal wires. The metal mesh can comprise or consist out of a woven metal wire mesh or a knitted metal wire mesh.

Preferred are metal meshes comprising metal wires with wire diameters less than 2 mm, e.g. less than 1.2 mm. As an example a woven wire mesh can be used comprising metal wires of 0.6 mm diameter in weft and in warp direction; and a distance in between wires of 1 mm in weft and in warp direction. Another example of a square woven wire mesh that can be used has wires of 1.2 mm diameter in weft and in warp direction; and a distance in between successive wires in the woven fabric of 2 mm in weft and in warp direction.

[0013] Preferred are woven wire meshes of which the wires have the same diameter in weft and in warp direction; and wherein the weft and the warp density are the same. Such woven wire meshes have shown surprisingly beneficial results.

[0014] Preferably, the metal mesh comprises or consists out of an expanded metal sheet.

[0015] Preferred metal meshes have mesh sizes less than 30 mm ² , preferably less than 20 mm ² .

With mesh size is meant the surface area of an individual open area of the metal mesh.

[0016] Preferably, the open area of the metal mesh is more than 30%, and preferably less than 60%. With open area is meant the total open surface area of the metal mesh as a percentage of the total surface area of the metal mesh.

[0017] Preferably, the metal mesh comprises or has a curved shape, preferably a double curved shape. Preferably, the curved or double curved shape extends into the inside of the mixing chamber.-ln a more preferred embodiments wherein the mesh comprises or consists out of a curved shape, the metal mesh comprises a flat central section. With central section is meant the section around the central axis of the cylindrical burner deck. The flat section can e.g. be achieved by welding a separate metal mesh onto a curved ring shaped metal mesh.

[0018] In a preferred embodiment, the metal mesh comprises or has a dome shape, preferably wherein the dome extends inside the mixing chamber.

[0019] In a preferred embodiment, the metal mesh comprises or has a conical shape, preferably wherein the conical shape extends inside the mixing chamber.

[0020] In a preferred embodiment, the metal mesh comprises or has a frusto-conical shape, preferably wherein the frusto-conical shape extends inside the mixing chamber. [0021] In a preferred gas premix burner the inlet device comprises a flange. The metal mesh is attached to the flange. The shape of the metal mesh extends into the inside of the mixing chamber. The flange is provided for mounting the burner into a heating appliance via a surface of the flange. The largest distance P from the surface of the metal mesh to the plane of the surface of the flange for mounting the burner into a heating appliance is at least 20 mm, more preferably at least 30 mm, even more preferably more than 50 mm, even more preferably at least 60 mm; and preferably less than 80 mm.

[0022] In a preferred gas premix burner, the inlet device comprises a flange. The metal mesh is attached to the flange. The shape of the metal mesh extends into the inside of the mixing chamber. The flange is provided for mounting the burner into a heating appliance via a surface of the flange. The largest distance P from the surface of the metal mesh to the plane of the surface of the flange for mounting the burner into a heating appliance is at least 0.25 times the internal diameter D of the cylindrical burner deck.

[0023] In a preferred embodiment, the cylindrical burner deck comprises at its end where the inlet device is provided a blind zone onto which no combustion occurs when the burner is in use. The blind zone is preferably provided as a ring on the cylindrical burner deck. The blind zone has a length L1 measured from the end of the cylindrical burner deck where the inlet device is provided. The inlet device comprises a flange. The metal mesh is attached to the flange. The shape of the metal mesh extends into the inside of the mixing chamber. The flange is provided for mounting the burner into a heating appliance via a surface of the flange. The largest distance P from the surface of the metal mesh to the plane of the surface of the flange for mounting the burner into a heating appliance is at least 0.5 times the length L1 of the blind zone; and preferably at least 0.75 times, even more preferably at least 0.9 times the length L1 of the blind zone. Surprisingly, inventive burners according to such embodiments have shown further improved performance in terms of ignition and/or flame sensing with flame sensing electrodes.

The blind zone can be realized in a perforated metal sheet burner deck by absence of perforations in the blind zone.

The blind zone can be realized in a burner having a textile fabric as burner deck provided in contact at its inner side with a perforated metal sheet, by absence of perforations in the perforated metal sheet in the blind zone.

[0024] In a preferred embodiment, the cylindrical burner deck has an L/D ratio of more than 3, more preferably more than 4, more preferably more than 5, more preferably more than 6. And preferably less than 7. L is the axial length of the burner deck and D is the internal diameter of the largest enclosed circle in a cross section of the cylindrical burner deck perpendicular to its central axis. [0025] Preferably, the cylindrical burner deck comprises or consists out of a perforated metal sheet or of a steel wire mesh. As steel wire mesh, a woven or knitted steel wire mesh can be used.

[0026] In a preferred embodiment, the burner deck comprises a perforated metal sheet or a steel wire mesh onto which the flames are stabilized when the burner is in use. When a steel wire mesh is used, the steel wire mesh can be a woven or knitted steel wire mesh. In a more preferred embodiment, the burner is provided so that when the burner is in use, the premix gas flows through the perforated metal sheet of the cylindrical burner deck or through the steel wire mesh of the cylindrical burner deck without further passing through another object once the premix gas has flown through the mesh of the inlet device.

[0027] In a preferred embodiment, the cylindrical burner deck comprises a fiber based burner deck. The fiber based burner deck is preferably a metal fiber based burner deck.

Preferably, the fiber based burner deck comprises fiber yarns, wherein preferably the fiber yarns comprise a multiple number of fibers in the yarn cross section, preferably metal fibers. The fiber based burner deck can e.g. be a knitted or woven or braided fabric comprising metal fibers or comprising metal fiber yarns, preferably wherein the metal fiber yarns comprise a multiple number of metal fibers in the yarn cross section. Preferably, the burner is provided so that when the burner is in use the flames are stabilized on the surface of the fiber based burner deck.

[0028] Preferably, when the cylindrical burner deck comprises a fiber based burner deck, the fiber based burner deck is supported by a perforated metal sheet or by a steel wire mesh. When a steel wire mesh is used, a woven or a knitted steel wire mesh can be used.

[0029] A preferred gas premix burner is devoid of a diffuser inside the mixing chamber.

[0030] A preferred gas premix burner is provided so that in use of the burner, the premix gas flows from the inlet device through the cylindrical burner deck without further passing a gas diffusing device. In such preferred embodiment, the burner deck consists out of a perforated metal sheet.

[0031] In a preferred gas premix burner, the mixing chamber comprises a diffuser. Preferably, the diffuser comprises or consists out of an open pore cylindrical object, preferably positioned between 1 and 8 mm, more preferably between 1 and 3 mm, from the inside of the cylindrical burner deck, and preferably parallel with it.

[0032] A preferred gas premix burner comprises an end cap, closing off the mixing chamber at the side opposite to the side where the inlet device is provided. In a more preferred embodiment, the end cap is not permeable to premix gas.

[0033] In a preferred gas premix burner, an ignition pen and/or a flame sensing pen is provided.

The ignition pen and/or the flame sensing pen are provided at the side of the burner where the inlet device is provided. Preferably, the ignition pen and/or the flame sensing pen are provided parallel with the axis of the cylindrical burner deck. Preferably, along the burner deck, the length of the ignition pen is less than 20 % of the length of the cylindrical burner deck, and more preferably less than 10 % of the length of the cylindrical burner deck.

Brief Description of Figures in the Drawings

[0034] Figure 1 shows an exploded view of a gas premix burner according to the invention.

Figures 2 - 6 show inlet devices that can be used in the invention.

Figure 7 shows a gas premix burner according to the invention.

Mode(s) for Carrying Out the Invention

[0035] Figure 1 shows an exploded view of a premix gas burner 100 according to the invention.

The gas premix burner comprises a cylindrical burner deck 1 10. The cylindrical burner deck comprises at its end where the inlet device is provided a blind zone onto which no combustion occurs when the burner is in use; the blind zone has a length L1 measured from the end of the cylindrical burner deck where the inlet device is provided. An exemplary burner has a length L 600 mm and an internal diameter D 100 mm. Another example of such burner has a length L 300 mm and an internal diameter D 70 mm. Yet another example of such burner has a length L 450 mm and an internal diameter D 80 mm. The cylindrical burner deck 1 10 encloses a mixing chamber. The cylindrical burner deck consists out of a metal sheet that has perforations 1 14 in the form of circular holes and/or slits. The perforated metal sheet has been bent into a cylindrical shape and welded at its edges 1 12.

[0036] The gas premix burner 100 further comprises an inlet device 120, mounted

perpendicularly to the axial direction of the cylindrical burner deck 1 10. The inlet device 120 comprises a flange 130 for mounting the inlet device 120 into the burner 100. The flange 130 can also be used to mount the burner into a heating appliance. The inlet device 120 comprises a metal mesh 140. In the example, the metal mesh is a flat woven wire mesh attached to the flange 130. An example of a metal mesh that can be used is a woven wire mesh with wire diameter 0.6 mm (in weft and warp direction) and a distance in between successive wires 1 mm (in weft and in warp direction), thus with a distance between the axis of successive wires 1 .6 mm. As an alternative, an expanded metal sheet can be used as metal mesh.

[0037] When using the burner, premix gas is fed through the metal mesh of the inlet device into the mixing chamber. The burner 100 comprises an end cap 180, which closes off the mixing chamber at the side opposite to the side where the inlet device is provided. The exemplary burner 100 of figure 1 is provided such that in use of the burner, the premix gas flows from the inlet device through the cylindrical burner deck without further passing a gas diffusing device. [0038] Figures 2 - 6 show cross sections of inlet devices that can be used in the invention. The cross sections are taken along a plane through the axis of symmetry of the gas premix burner. Preferably, the shape of the inlet devices is axisymmetric around the axis of symmetry of the gas premix burner.

[0039] Figure 2 shows an inlet device 220 comprising a flange 230 onto which a flat metal mesh 240, e.g. a woven wire mesh, is attached, e.g. via welding.

[0040] Figure 3 shows an inlet device 320 comprising a flange 330 onto which a metal mesh 340 is attached, e.g. a woven wire mesh. The metal mesh 340 is shaped into a dome. The largest distance P mm from the surface of the curved shape of the metal mesh 340 to the plane of the surface of the flange 330 for mounting the burner into a heating appliance is e.g. 22 mm for a burner with cylindrical burner deck with internal diameter 80 mm; such burner e.g. has a burner deck with a blind zone with length L1 23 mm.

[0041] Figure 4 shows an inlet device 420 comprising a flange 430 onto which a flat metal mesh 440, e.g. a woven wire mesh, is attached, e.g. via welding. The metal mesh 440 is shaped into a curved section 442 and a flat top section 444. The largest distance P from the surface of the flat top section of the metal mesh 444 to the plane of the surface of the flange 430 for mounting the burner into a heating appliance is e.g. 18 mm for a burner with cylindrical burner deck with internal diameter 80 mm. It is also possible that the curved section 442 and flat top section 444 exist out of different metal meshes that are connected or bonded to each other, e.g. by means of welding. The metal meshes building the curved section and building the top section can have the same design or can be different in design (e.g. porosity).

[0042] Figure 5 shows an inlet device 520 comprising a flange 530 onto which a metal mesh 540 is attached, e.g. a woven wire mesh. The metal mesh 540 is formed into a cone, e.g. by forming a metal sheet mesh and welding the edges to each other. The largest distance P from the top of the cone to the plane of the surface of the flange 530 for mounting the burner into a heating appliance is e.g. 42 mm for a burner with cylindrical burner deck with internal diameter 80 mm.

[0043] Figure 6 shows an inlet device 620 comprising a flange 630 onto which a flat metal mesh 640, e.g. a woven wire mesh, is attached, e.g. via welding. The metal mesh 640 is shaped into a frusto-conical shape, with a conical section 645 and a flat top section 646. The largest distance P from the surface of the flat top section of the metal mesh 646 to the plane of the surface of the flange 530 for mounting the burner into a heating appliance is e.g. 18 mm for a burner with cylindrical burner deck with internal diameter 80 mm. It is also possible that the conical section 445 and the flat top section 446 exist out of different metal meshes that are connected to each other, e.g. by means of welding. The metal meshes building the curved section and building the top section can have the same design or can be different in design (e.g. porosity, metal wires, weft and warp density of the woven wire meshes). [0044] As alternatives for woven wire meshes, expanded metal sheets or knitted wire meshes can be used in the examples of inlet devices shown in figures 2 - 6.

[0045] Figure 7 shows a premix gas burner 700 according to the invention. The gas premix burner comprises a cylindrical burner deck 710. An exemplary burner has a length L of 600 mm and an internal diameter D of 100 mm. The cylindrical burner deck 710 encloses a mixing chamber. The cylindrical burner deck consists out of a metal sheet that has perforations 714 in the form of circular holes and/or slits. The perforated metal sheet has been bent into a cylindrical shape and welded at its edges 712. The gas premix burner 700 further comprises an inlet device 720, mounted perpendicularly to the axial direction of the cylindrical burner deck 710. The inlet device 720 comprises a flange 730 for mounting the inlet device 720 into the burner 700. The flange 730 can be used to mount the burner to a supporting structure via the holes 732 in the flanges and e.g. using nuts and bolts. The inlet device 720 comprises a metal mesh 740. In the example, the metal mesh is a flat woven wire mesh attached to the flange 730. The example shows an inlet device with a flat metal mesh in the inlet device; however, other shapes of metal mesh can be used, e.g. the ones shown in figures 2 - 6. When using the burner, premix gas is fed through the metal mesh 740 of the inlet device into the mixing chamber. The burner 700 comprises an end cap 780, which closes off the mixing chamber at the side opposite to the side where the inlet device is provided. The exemplary burner 700 of figure 7 is provided so that in use of the burner, the premix gas flows from the inlet device through the cylindrical burner deck without further passing a gas diffusing device. Alternative burners however, can be provided with a diffuser into the mixing chamber.

The burner 700 further comprises an ignition pen 790. The ignition pen 790 is provided at the side of the burner where the inlet device 720 is provided; and the ignition pen 790 has a length Lp (e.g. 30 mm, or e.g. 70 mm) along the axial direction of the burner 700. In the same way as the ignition pen, and/or in addition to it, a flame sensing pen can be provided.

[0046] Tests have shown the beneficial ignition characteristics of the burners with inlet devices as shown in figures 2, 3, 4, 5, and 6. However, inlet devices as shown in figures 3, 4, 5 and 6 have been shown to provide even better ignition characteristics than the inlet device of figure 2.

[0047] Cylindrical burners have been made with internal diameter D 82 mm and length L of the burner deck 588 mm. The burner deck was a perforated metal sheet, with a blind zone with length L1 equal to 23 mm at the base of the burner deck. No gas diffusing device was used in the mixing chamber of the burner. Burner A was a prior art burner with a perforated plate inlet disk. Burner B was a burner according to the invention, with a flat woven wire mesh inlet disk. Burner C was a burner according to the invention with a dome shaped woven wire mesh inlet disk, with a largest distance P 22 mm from the surface of the metal mesh to the plane of the surface of the flange for mounting the burner into a heating appliance. Ignition of each of the burners was tested 10 times at four different air over gas premix gas ratios. The four different air over gas premix gas ratios are indicated by the C0 ₂ percentage in the combustion gas; respectively 8 %, 8.5 %, 9 % and 9.5 %. Table I indicates the number of successful ignitions (each time out of 10 trials). The test results show the improved ignition results of the burners according to the invention, especially when the burners are operating at low C0 ₂ percentages in the combustion gas.

Table I: Number of successful ignitions out of 10 trials