Description

Technical Field

[0001] The invention relates to the field of cylindrical gas premix burners. 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] Cylindrical premix burners are known. The cylindrical burner deck encloses a mixing chamber. An inlet device can be 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 disk 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.

Disclosure of Invention

[0005] It is the objective of the invention to provide an improved cylindrical premix gas burner. 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 the cylindrical burner deck.

[0006] The first aspect of the invention is a cylindrical gas premix burner comprising:

- a cylindrical burner deck onto which the flames are stabilized when the burner is in use; - a mixing chamber inside the cylindrical burner deck;

- an inlet device mounted perpendicularly to the axial direction of the cylindrical burner deck, for the supply of premix gas into the mixing chamber; and

- an end cap closing off the mixing chamber at the side opposite to the side where the inlet device is provided.

The inlet device comprises a perforated metal plate. The perforations in the perforated metal plate are provided for the supply of premix gas into the mixing chamber. The perforated metal plate is dome shaped, such that perforations in the perforated metal plate are located at different height levels from the base of the cylindrical burner deck. With base of the cylindrical burner deck is meant the end of the cylindrical burner deck where the inlet device is provided. Preferably, the dome shape extends into the mixing chamber.

[0007] Preferably, each of the perforations in the perforated metal plate is smaller than 20 mm ² .

[0008] Preferably, the burner is provided for combusting hydrocarbons, e.g. natural gas,

methane, butane, propane or LPG.

[0009] 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.

[0010] In a preferred embodiment, the dome shape of the perforated metal plate is provided by deep drawing of a perforated metal plate.

[001 1] Preferably, the shape of the inlet device is axisymmetric around the axis of symmetry of the gas premix burner.

[0012] Preferably, the inlet device comprises a flange for mounting the inlet device into the

burner. In an embodiment of the invention, the flange and the perforated plate are integrally formed in one shaped metal plate. In an alternative embodiment, the dome shaped perforated metal plate is attached to the flange, e.g. via welding.

[0013] 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 cylindrical burner deck.

[0014] In a preferred embodiment, the end cap is not permeable to premix gas.

[0015] Preferably, the perforated metal plate is double curved at the central axis of the cylindrical burner deck. With double curved is meant that there is no direction in which the radius of curvature at that point is infinite.

[0016] Preferably, the perforated metal plate comprises a flat central section provided with

perforations. In such embodiment, the perforated metal plate can have a curved segment contacting the flange around the full circumference of the flange, with a flat central section at the inside of the curved segment. The curved segment can e.g. be a spherical segment.

[0017] In a preferred embodiment, the perforated metal plate comprises a spherical segment.

More preferably, the spherical segment is positioned axisymmetrically in the cylindrical gas premix burner.

[0018] In a preferred embodiment, the inlet device comprises a surface for mounting the burner into a heating appliance. The dome shape of the perforated metal plate extends into the inside of the mixing chamber. The largest distance P from the surface of the dome shape of the perforated metal plate to the plane of the surface of the inlet device for mounting the burner into a heating appliance is at least 0.25 times the internal diameter D of the cylindrical burner deck.

[0019] 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 surface for mounting the burner into a heating appliance. The dome shape of the perforated metal plate extends into the inside of the mixing chamber. The largest distance P from the surface of the dome shape of the perforated metal plate to the plane of the surface of the inlet device for mounting the burner into a heating appliance is at least 0.75 times, even more preferably at least 0.9 times the length L1 of the blind zone.

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. [0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] A preferred cylindrical gas premix burner is devoid of a diffuser inside the mixing

chamber.

[0025] A preferred cylindrical 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.

[0026] In a preferred cylindrical 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.

[0027] In a preferred cylindrical 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

[0028] Figure 1 shows an exploded view of a gas premix burner according to the invention.

Figures 2 and 3 show inlet devices that can be used in the invention.

Figure 4 shows a gas premix burner according to the invention

Mode(s) for Carrying Out the Invention

[0029] 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. 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 perforated metal plate 145; the perforations 147 of which are provided for the supply of premix gas into the mixing chamber. The perforated metal plate 145 is dome shaped, such that perforations in the perforated metal plate 145 are located at different height levels from the base of the cylindrical burner deck. In the example, the dome shape extends into the mixing chamber when the inlet device 120 is mounted in the burner 100. The dome shape of the perforated metal plate 145 is provided by deep drawing of a perforated metal plate. When using the burner, premix gas is fed through the perforations 147 of the dome shaped perforated plate 145 of the inlet device 120 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.

[0030] Figures 2 and 3 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.

[0031] Figure 2 shows an inlet device 220 comprising a flange 230 onto which a perforated metal plate 240 is attached, e.g. by means of welding. The perforated metal plate 240 is shaped into a dome. The largest distance P from the surface of the curved shape of the perforated metal plate 240 to the plane of the surface of the flange 230 for mounting the burner into a heating is e.g. 22 mm for a burner with cylindrical burner deck with internal diameter 80 mm.

[0032] Figure 3 shows an inlet device 320 comprising a flange 330 onto which a perforated metal plate 340, is attached, e.g. via welding. The perforated metal plate 340 is shaped into a curved segment 342 and a flat top section 344. The largest distance P from the surface of the flat top section of the perforated metal plate 344 to the plane of the surface of the flange 330 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 342 and the flat top section 344 exist out of different perforated metal plates that are connected to each other, e.g. by means of welding; in such embodiments the perforated metal plates building the curved section and building the flat top section can have the same design or can be different in design (e.g. in density and/or in diameter of perforations).

The perforated metal plate comprises a flat central section provided with perforations. In such embodiment, the curved segment 342 can be a spherical segment.

[0033] Figure 4 shows a premix gas burner 400 according to the invention. The gas premix burner comprises a cylindrical burner deck 410. An exemplary burner has a length L of 600 mm and an internal diameter D of 100 mm. The cylindrical burner deck 410 encloses a mixing chamber. The cylindrical burner deck consists out of a metal sheet that has perforations 414 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 412. The gas premix burner 400 further comprises an inlet device 420, mounted perpendicularly to the axial direction of the cylindrical burner deck 410. The inlet device 420 comprises a flange 430 for mounting the inlet device 420 into the burner 400. The flange 430 can be used to mount the burner to a supporting structure in a heat exchanger via the holes 432 in the flanges and nuts and bolts. The inlet device 420 comprises a dome shaped perforated metal plate 440. When using the burner, premix gas is fed through the perforations 447 of the dome shape perforated metal plate 440 of the inlet device into the mixing chamber. The burner 400 comprises an end cap 480, which closes off the mixing chamber at the side opposite to the side where the inlet device is provided. The exemplary burner 400 of figure 4 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 400 further comprises an ignition pen 490. The ignition pen 490 is provided at the side of the burner where the inlet device 420 is provided; and the ignition pen 490 has a length Lp (e.g. 30 mm, or e.g. 70 mm) along the axial direction of the burner 400. In the same way as the ignition pen, and/or in addition to it, a flame sensing pen can be provided.

Cylindrical burners have been made with internal diameter D 82 mm and length L 588 mm of the burner deck. The burner deck was a perforated metal plate, with a blind zone with length L1 at the base of the burner deck equal to 23 mm. No gas diffusing device was used in the mixing chamber of the burner. Burner A was a prior art burner with a flat perforated plate inlet disk. Burner B was a burner according to the invention with a dome shaped perforated plate inlet disk, with a largest distance P 22 mm from the surface of the dome shaped perforated inlet disk to the plane of the surface of the inlet disk 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 of the combustion gas.

Table I: Number of successful ignitions out of 10 ignition trials