Description

Technical Field

[1] The invention relates to the field of heat cells in which cylindrical premix gas burners are used. Such heat cells are used in boilers.

Background Art

[2] Cylindrical premix gas burners can be installed in the combustion chamber of a heat exchanger of a boiler. Cylindrical premix gas burners can be installed in cast aluminum heat exchangers (e.g. in sectional cast heat exchangers as in WO2015/024712 A1 ) or in heat exchangers provided by spirally winding one or more metal tubes (see e.g.

WO2004/097310A1 ).

[3] Such heat exchangers - and thus also the cylindrical burners - exist in different sizes.

Because of legislations imposing reduced emissions of harmful gases, there is a global tendency towards bigger heat exchangers that use premix gas burners.

[4] Cylindrical gas burners exist in different types. A first type comprises a cylindrical burner deck provided by a perforated metal plate, as is e.g. disclosed in WO2009/077505A1. A second type comprises a cylindrical burner deck provided by a fabric composed out of ceramic or metal fibers. US4721456A provides an example of a cylindrical premix gas burner having a cylindrical burner deck provided by a fabric out of ceramic fibers.

WO2012/152571A1 discloses a cylindrical premix gas burner having a cylindrical burner deck comprising a fiber based substrate, e.g. comprising metal fibers.

Disclosure of Invention

[5] The invention relates to a heat cell comprising a cylindrical premix gas burner and a heat exchanger. The cylindrical premix gas burner comprises a mixing chamber, a cylindrical shell provided around the mixing chamber, an impervious end cap provided at a first end of the cylindrical shell, an inlet at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber; and a textile fabric comprising heat resistant fibers. The cylindrical shell comprises a gas permeably burner deck onto which combustion is stabilized after premix gas has flown from the mixing chamber through the burner deck. The textile fabric comprises along the circumference of the cylindrical shell a fabric section extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell. With extending freely is meant that the surface of at least part of the fabric section is not contacting any part of the burner. The heat exchanger comprises a combustion chamber having an end wall. The cylindrical premix gas burner is installed in the combustion chamber. The fabric section of the textile fabric is configured for providing a seal along the circumference of the cylindrical shell between the end of the burner and the end wall of the combustion chamber when the burner is in use. Cylindrical premix gas burners get hot when the burner is in use. An expansion of the burner is the consequence. When the burner is provided in a combustion chamber of a heat exchanger, thermal expansion of the burner must be possible. Therefore, it is common practice to provide a gap between the impervious end cap of the cylindrical gas premix burner and the end wall of the heat exchanger. A bigger gap needs to be provided for longer cylindrical premix gas burners. The presence of the gap provokes a flow of flue gas into the gap generated by the burner. If this flow of flue gas is too big, excessive heating of the end cap occurs. This phenomenon leads to early mechanical failure of the burner, e.g. through mechanical failure of the end cap, of the connection between the end cap and the cylindrical shell of the burner; or of the shell of the burner itself. The fabric section of the textile fabric along the circumference of the cylindrical shell extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell will create a seal. When the burner is installed in the combustion chamber and in operation, the fabric section of the textile fabric will touch the end wall of the heat exchanger along part of or along the full circumference of the burner, creating a flexible seal around the gap between the end of the cylindrical burner and the end wall of the heat exchanger, minimizing or fully preventing the flow of flue gas into the gap. The flexibility of the seal allows thermal expansion of the burner when the burner is in use. Therefore, the invention provides heat cells with cylindrical premix gas burners with a longer lifetime when installed in the heat exchanger of the heat cell.

When the burner is in cold condition, there is a gap between the end of the cylindrical shell and the end wall of the combustion chamber. Preferably, the gap is - in cold condition of the burner - at least 5 mm, more preferably at least 10 mm.

Preferably, the fabric section extends over a length of at least 5 mm - and preferably over at least 10 mm, more preferably over at least 15 mm, more preferably over at least 20 mm, even more preferably over at least 25 mm - beyond the end of the cylindrical shell. Preferably, the length of the cylindrical shell is at least 500 mm, preferably at least 750 mm, more preferably at least 1000 mm. Burners that have a longer length of the cylindrical shell will expand more when in use, as the thermal expansion is directly proportional to the length of the cylindrical shell. As the thermal expansion of such burners is bigger, a larger gap needs to be provided between the end of the cylindrical shell and the end wall of the heat exchanger when installing the burner in the combustion chamber of the heat exchanger. Such larger gap is required to enable thermal expansion. As the gap is bigger, and as manufacturing tolerances are present, there will be a larger gap into which flue gas can flow when the burner is in use. Therefore, these burners with longer length of the cylindrical shell have a much larger risk of early failure due to flue gas flow into the gap between the end of the cylindrical shell and the end wall of the heat exchanger.

Preferably, the diameter of the burner is at least 200 mm, more preferably at least 250 mm; even more preferably at least 300 mm. As the diameter of a burner is most cases related to its length, burners with larger diameter have a higher risk of early failure because of flue gas flowing into the gap between the end of the cylindrical shell and the end wall of the heat exchanger.

Preferably, the end cap closes the mixing chamber. More preferably, the end cap is connected to the cylindrical shell by means of welds or by means of a crimped connection.

Preferably, the end cap is concave when observed from the outside of the burner. Such embodiments facilitate the provision of the seal by the fabric section of the textile fabric sealing the gap between the burner and the end wall of the heat exchanger.

In a preferred embodiment, the freely extending fabric section of the textile fabric is folded over, preferably towards to the inside of the burner. Embodiments wherein the fabric section of the textile fabric is folded over are beneficial as they provide a more effective seal. In a more preferred embodiment, the folded over end is bonded onto the end cap, e.g. by means of spot welds or by means of an adhesive. In a more preferred

embodiment, the textile fabric provides the burner deck onto which combustion is stabilized; and the freely extending fabric section of the textile fabric which is folded over is a separate textile fabric from the textile fabric providing the burner deck onto which combustion is stabilized.

Preferably, the textile fabric is a woven, knitted or braided burner deck. More preferably, the textile fabric comprises metal fibers. Even more preferably, the woven, knitted or braided fabric comprises yarns which comprise a plurality of metal fibers in their cross section. Textile fabrics as disclosed in WO9704152A1 can be advantageously used in the invention.

In a preferred embodiment, the textile fabric provides the burner deck onto which combustion is stabilized. It is meant that - when the burner is in use - the flames are anchored onto the textile fabric. More preferably, the cylindrical shell comprises a perforated plate, woven wire mesh or an expanded metal sheet; and the textile fabric providing the burner deck is provided around and contacting the perforated plate, woven wire mesh or expanded metal sheet.

In a preferred embodiment wherein the textile fabric provides the burner deck onto which combustion is stabilized, the fabric section extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell is another textile fabric than the textile fabric providing the burner deck onto which combustion is stabilized. The fabric section extending freely at the side of the end cap can e.g. be a fabric strip; more preferably, the fabric strip is folded over such that the seal is provided by a double layer of the fabric strip.

In a preferred embodiment, the burner deck is provided by a perforated metal plate. It is meant that the flames are anchored onto the perforated metal plate. More preferably, the perforated plate comprises circular perforations as well as slit shaped perforations. [18] In a preferred embodiment, the end cap is concave when observed from the outside of the burner. The end cap comprises a rim; and the textile fabric - which provides the fabric section extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell - is fixed onto the inside or onto the outside of the rim of the end cap. In a more preferred embodiment, the cylindrical shell comprises a perforated plate, woven wire mesh or an expanded metal sheet; and a textile fabric is provided around and contacting the perforated plate, woven wire mesh or expanded metal sheet, thereby providing the burner deck of the burner. The textile fabric providing the burner deck can be the same textile fabric that provides the fabric section; or it can be a second, separate textile fabric.

[19] In a preferred embodiment, a metal structure is fixed onto the end cap of the burner and the textile fabric is fixed onto the metal structure. The metal structure can be fixed onto the end cap e.g. by means of welds or by means of an adhesive; The metal structure can preferably comprise or consist out of a metal disc having an upstanding rim, and the textile fabric is fixed onto the inside - or more preferably - onto the outside of the rim. The fabric section of the textile fabric extends beyond the rim of the metal disc. In a more preferred embodiment, the cylindrical shell comprises a perforated plate, woven wire mesh or an expanded metal sheet; and a second textile fabric is provided around and contacting the perforated plate, woven wire mesh or expanded metal sheet, thereby providing the burner deck of the burner.

[20] In a preferred heat cell, the cylindrical premix gas burner is installed in the combustion chamber, such that when the burner is in cold condition, the fabric section of the textile fabric provides a seal along the circumference of the cylindrical shell between the end of the burner and the end wall of the combustion chamber.

[21] In a preferred heat cell, the fabric section of the textile fabric is folded such that the seal is provided at least in part by a multiple number of layers (e.g. two layers) of the textile fabric. Preferably, the fold is made folding the fabric to the inside of the burner.

[22] In an exemplary heat cell according to the invention, the heat exchanger is a sectional heat exchanger comprising a plurality of cast aluminium sections assembled into the heat exchanger. Such heat exchangers are suited to build big heat cells that need to accommodate cylindrical premix gas burners of long length e.g. longer than 500 mm, or even longer than1000 mm or even longer than 2000 mm.

[23] Heat cells according to the invention can be advantageously used in boilers, e.g. boilers used for central heating installations.

Brief Description of Figures in the Drawings

[24] Figures 1 - 6 show sections through the central axis of examples of burners that can be used in the invention.

Figure 7 shows an example of a heat cell according to the invention.

Mode(s) for Carrying Out the Invention Figure 1 shows a section through the central axis of a first example of a cylindrical premix gas burner 100 that can be used in the invention. The cylindrical premix gas burner 100 comprises a mixing chamber 102, a cylindrical shell 104 provided around the mixing chamber, an impervious end cap 106 provided at a first end of the cylindrical shell, an inlet 108 at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber; and a textile fabric 1 10. The inlet is provided by means of a flange 1 12. The flange also allows mounting the burner in a heat exchanger to build a heat cell.

The end cap 106 closes the mixing chamber. The end cap 106 is connected to the cylindrical shell by means of welds 120. Alternatively, the end cap can be connected to the cylindrical shell by means of a crimped connection. In the example, the end cap 106 is concave when observed from the outside of the burner.

The textile fabric 1 10 of the exemplary burner is a knitted fabric comprising yarns which comprise in their cross section a plurality of heat resistant metal fibers. Fabrics as disclosed in WO9704152A1 can be used in the invention.

The cylindrical shell comprises a perforated metal plate 1 14. The perforations 1 16 of the perforated metal plate are covered by the textile fabric 1 10. The textile fabric 1 10 provides the gas permeably burner deck onto which combustion is stabilized after premix gas has flown from the mixing chamber through the burner deck. The textile fabric has along the circumference of the cylindrical shell a fabric section 1 18 extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell.

The length L of the cylindrical shell of the exemplary burner of figure 1 is 1000 mm. The diameter D of the cylindrical burner of figure 1 is 300 mm.

In the example of figure 1 , the fabric section extends over a length I equal to 28 mm beyond the end of the cylindrical shell.

Figure 2 shows a section through the central axis of a second example of a cylindrical premix gas burner 200 that can be used in the invention. The cylindrical premix gas burner 200 comprises a mixing chamber 202, a cylindrical shell 204 provided around the mixing chamber, an impervious end cap 206 provided at a first end of the cylindrical shell, an inlet 208 at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber; and a textile fabric 210. The inlet is provided by means of a flange 212.

The end cap 206 closes the mixing chamber. The end cap 206 is connected to the cylindrical shell by means of welds 220. Alternatively, the end cap can be connected to the cylindrical shell by means of a crimped connection. The end cap 206 is concave when observed from the outside of the burner. The textile fabric 210 of the exemplary burner is a knitted fabric comprising yarns which comprise in their cross section a plurality of heat resistant metal fibers. Fabrics as disclosed in WO9704152A1 can be used in the invention.

The cylindrical shell comprises a perforated metal plate 214. The perforations 216 of the perforated metal plate are covered by the textile fabric 210. The textile fabric 210 provides the gas permeably burner deck onto which combustion is stabilized after premix gas has flown from the mixing chamber through the burner deck. The textile fabric has along the circumference of the cylindrical shell a fabric section 218 extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell. The freely extending fabric section of the textile fabric is folded over towards the inside of the burner, thereby creating an additional fabric layer 230, such that two fabric layers are provided to form the seal sealing the gas between the end of the cylindrical shell of the burner and the end wall of the heat exchanger in which the burner is installed. The length L of the cylindrical shell of the exemplary burner of figure 1 is 1500 mm. The diameter D of the cylindrical burner of figure 1 is 400 mm.

In the example of figure 2, the fabric section extends over a length I equal to 20 mm beyond the end of the cylindrical shell.

Figure 3 shows a section through the central axis of a third example of a cylindrical premix gas burner 300 as can be used in the invention. The cylindrical premix gas burner 300 comprises a mixing chamber 302, a cylindrical shell 304 provided around the mixing chamber, an impervious end cap 306 provided at a first end of the cylindrical shell, an inlet 308 at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber; and a textile fabric 310. The inlet is provided by means of a flange 312. The flange also allows mounting the burner in a heat cell.

The end cap 306 closes the mixing chamber. The end cap 306 is connected to the cylindrical shell by means of welds 320. Alternatively, the end cap can be connected to the cylindrical shell by means of a crimped connection. The end cap 306 is concave when observed from the outside of the burner.

The cylindrical shell 304 is provided by a perforated metal plate comprising a plurality of perforations 334. Circular perforations as well as slit (= rectangular) shaped perforations are provided. The perforated metal plate acts as burner deck, as the flames are anchored onto the perforated metal plate after premix gas has flown from the mixing chamber through the perforations of the perforated metal plate; and ignition taking place after the premix gas has flown through the perforations of the perforated metal plate.

The textile fabric 310 of the exemplary burner is a knitted fabric comprising yarns which comprise in their cross section a plurality of heat resistant metal fibers. Fabrics as disclosed in WO9704152A1 can be used in the invention. The fabric can be bonded onto the cylindrical shell 304 by means of welds. The textile fabric has along the circumference of the cylindrical shell a fabric section 318 extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell.

The length L of the cylindrical shell of the exemplary burner of figure 1 is 1000 mm. The diameter D of the cylindrical burner of figure 1 is 300 mm.

In the example of figure 3, the fabric section extends over a length I equal to 20 mm beyond the end of the cylindrical shell.

Figure 4 shows a section through the central axis of an example of a cylindrical premix gas burner 400 as can be used in the invention. The cylindrical premix gas burner 400 comprises a mixing chamber 402, a cylindrical shell 404 provided around the mixing chamber, an impervious end cap 406 provided at a first end of the cylindrical shell, an inlet 408 at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber; and a textile fabric 410. The inlet is provided by means of a flange 412. The flange also allows mounting the burner in a heat exchanger to build a heat cell.

The end cap 406 closes the mixing chamber. The end cap 406 is connected to the cylindrical shell by means of welds 420. Alternatively, the end cap can be connected to the cylindrical shell by means of a crimped connection. In the example, the end cap 406 is concave when observed from the outside of the burner.

The textile fabric 410 of the exemplary burner is a knitted fabric comprising yarns which comprise in their cross section a plurality of heat resistant metal fibers. Fabrics as disclosed in WO9704152A1 can be used in the invention. The textile fabric 410 is fixed onto the inside of the rim 468 of the concave end cap, e.g. by spot welding or by means of adhesive. The textile fabric 410 has along the circumference of the cylindrical shell a fabric section 418 extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell.

The cylindrical shell comprises a perforated metal plate 414. The perforations 416 of the perforated metal plate are covered by a second textile fabric 470. The second textile fabric 470 - e.g. as disclosed in WO9704152A1 - provides the gas permeably burner deck onto which combustion is stabilized after premix gas has flown from the mixing chamber through the burner deck.

Figure 5 shows a section through the central axis of an example of a cylindrical premix gas burner 500 as can be used in the invention. The cylindrical premix gas burner 500 comprises a mixing chamber 502, a cylindrical shell 504 provided around the mixing chamber, an impervious end cap 506 provided at a first end of the cylindrical shell, an inlet 508 at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber. The inlet is provided by means of a flange 512. The flange also allows mounting the burner in a heat exchanger to build a heat cell. The end cap 506 closes the mixing chamber. The end cap 506 is connected to the cylindrical shell by means of welds 520. Alternatively, the end cap can be connected to the cylindrical shell by means of a crimped connection. In the example, the end cap 506 is concave when observed from the outside of the burner.

The burner comprises a textile fabric 570 providing the gas permeably burner deck onto which combustion is stabilized after premix gas has flown from the mixing chamber through the burner deck. The textile fabric 570 is provided around a perforated cylindrical metal plate 514. The perforations 516 of the perforated metal plate are covered by the textile fabric 570.

The burner further comprises a second textile fabric 510 which has along the

circumference of the cylindrical shell of the burner a fabric section 518 extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell. The second textile fabric is folded over towards the inside of the burner and its end is fixed onto the inside of the rim 568 of the end cap, the other end is fixed by means of welds onto the outside of the textile fabric 570.

In the burner of figure 5, the folded over fabric section is provided by another textile fabric than the textile fabric providing the burner deck. In an alternative example of the invention, only one textile fabric is used and the textile fabric providing the burner deck is folded over and fixed - in the same way as the second textile fabric of figure 5 - to the inside of the rim of the concave end cap.

Figure 6 shows a section through the central axis of an example of a cylindrical premix gas burner 600 as can be used in the invention. The cylindrical premix gas burner 600 comprises a mixing chamber 602, a cylindrical shell 604 provided around the mixing chamber, an impervious end cap 606 provided at a first end of the cylindrical shell, and an inlet 608 at the second end of the cylindrical shell provided for the supply of premix gas into the mixing chamber. The inlet is provided by means of a flange 612. The flange also allows mounting the burner in a heat exchanger to build a heat cell.

The end cap 606 closes the mixing chamber. The end cap 606 is connected to the cylindrical shell by means of welds 620. The end cap 606 is concave when observed from the outside of the burner.

The cylindrical shell comprises a perforated metal plate 614. The perforations 616 of the perforated metal plate are covered by a first textile fabric 670. The first textile fabric 670 - e.g. as disclosed in WO9704152A1 - provides the gas permeably burner deck onto which combustion is stabilized after premix gas has flown from the mixing chamber through the burner deck.

The burner comprises a metal plate structure having a shape of a disc 666 with a rim 668. The diameter of the disc is slightly smaller than the diameter of the end cap. The disc 666 is fixed onto the end cap by means of one or more rivets 672. However, other techniques can be used to fix the disc onto the end cap (e.g. by means of an adhesive). Fixed (e.g. by means of welds) to the outside of the rim 668 is a textile fabric 610. The textile fabric 610 provides along the circumference of the cylindrical shell a fabric section 618 extending freely at the side of the end cap in the length direction of the burner beyond the end of the cylindrical shell. The fabric section will provide a seal when the burner is installed in a heat exchanger.

Figure 7 shows an example of a heat cell 700 according to the invention. The heat cell 700 comprises a cylindrical premix gas burner 701 as in the first aspect of the invention (e.g. the burner of figure 1 ) and a heat exchanger 740. The heat exchanger comprises a combustion chamber 742 having an end wall 744. The cylindrical premix gas burner is installed in the combustion chamber, such that when the burner is in use, the fabric section 718 of the textile fabric 710 provides a seal along the circumference of the cylindrical shell between the end of the burner and the end wall of the combustion chamber.

In the example of figure 7, the heat exchanger is a sectional heat exchanger comprising a plurality of cast aluminium sections assembled into the heat exchanger. The sectional heat exchanger comprises two end segments 753, 754 and one or more intermediate segments 756 provided between the two end segments. The intermediate segments and the two end segments are assembled in the heat exchanger. The combustion chamber 742 is provided in the sectional heat exchanger, perpendicular to the one or more intermediate segments.

Each of the one or more intermediate segments comprises at least one flow channel 758 for a fluid to be heated. In between each two consecutive segments a flow channel 760 for flue gas is present, wherein the flow channel extends from at the combustion chamber, allowing flue gas generated in the combustion chamber by the burner 701 to flow from the combustion chamber through the flow channels for flue gas.

The walls 762 of the intermediate segments and of the end segments between the flow channel for fluid to be heated and the flow channel for flue gas are provided with means, e.g. pins 764 extending from the walls into the flue gas channel to increase the heat transfer through the walls.