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Title:
PREMIX GAS BURNER
Document Type and Number:
WIPO Patent Application WO/2013/120716
Kind Code:
A1
Abstract:
The invention provides a cylindrical premix gas burner (100) which is comprising a perforated metal plate as cylindrical burner deck (110). The cylindrical premix gas burner (100) is delimited by an end cap (118). An inlet disc (130) is provided for the supply of a premix of combustible gas and air into the burner. The premix gas is to be burned on the outside of the cylindrical burner deck (110) after the premix gas has flown through it. The inlet disc (130) is comprising a plurality of perforations for supplying premix gas supply into the burner. The inlet disc is having a centre point (150), which is where the central axis of the cylindrical premix gas burner (100) crosses the inlet disc (130). The inlet disc (130) is not permeable to premix gas at least within a circle with a diameter of at least 8 mm around the centre point (150).

Inventors:
FOLKERS GEERT (NL)
Application Number:
PCT/EP2013/052122
Publication Date:
August 22, 2013
Filing Date:
February 04, 2013
Export Citation:
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Assignee:
BEKAERT COMB TECHNOLOGY BV (NL)
International Classes:
F23D14/02; F23D14/70
Domestic Patent References:
WO2011069839A12011-06-16
WO2009065733A12009-05-28
WO2009112909A22009-09-17
WO2009065733A12009-05-28
WO2011069839A12011-06-16
Foreign References:
EP2037175A22009-03-18
EP0950853A21999-10-20
EP0283901A11988-09-28
EP2037175A22009-03-18
Attorney, Agent or Firm:
MESSELY, Marc (Zwevegem, BE)
Download PDF:
Claims:
Claims

1 . Cylindrical premix gas burner, comprising a cylindrical burner deck, wherein said cylindrical burner deck is a perforated metal plate, and wherein said cylindrical premix gas burner is delimited by an end cap,

wherein at the opposite side of said end cap, an inlet disc is provided for the supply of a premix of combustible gas and air into said burner, premix gas which is to be burned on the outside of said cylindrical burner deck after the premix gas has flown through it,

wherein said inlet disc is comprising a plurality of perforations for premix gas supply into said burner,

wherein said inlet disc is having a centre point, which is where the central axis of the cylindrical premix gas burner crosses said inlet disc

characterized in that said inlet disc is not permeable to premix gas at least within a circle with a diameter of at least 8 mm around said centre point.

2. Cylindrical gas burner as in claim 1 , wherein said inlet disc is comprising

- a disc which is having a multiple of perforations,

- and at least one plate with an unperforated section,

wherein said at least one plate is fixed onto said disc, wherein said

unperforated section forms a zone on said inlet disc that is not permeable to premix gas at least within a circle with a diameter of at least 8 mm around said centre point.

3. Cylindrical premix gas burner as in claims 1 or 2, wherein the inlet disc is not permeable to premix gas around the centre point of the inlet disc over a zone that is centred at the centre point of the inlet disc.

4. Cylindrical gas burner as in claim 3, wherein said zone has a regular shape.

5. Cylindrical gas burner according to claim 4, wherein said zone has a star shape.

6. Cylindrical gas burner according to claim 4, wherein said zone has a regular polygonal shape.

7. Cylindrical gas burner according to any of the preceding claims, wherein the perforations of the inlet disc all have the same shape and/or same size.

8. Cylindrical gas burner according to any of the claims 1 - 6, wherein the

perforations of the inlet disc have different shapes and/or different sizes.

9. Cylindrical gas burner according to claim 8, wherein the inlet disc comprises perforations of different size, and wherein perforations of larger size are located closer to said centre point than perforations of smaller size.

10. Cylindrical premix gas burner as in any of the preceding claims, wherein each of the perforations of said inlet disc are having a surface area of less than 30 mm2.

1 1 . Cylindrical premix gas burner as in any of the preceding claims, wherein the inlet disc is comprising perforations of at least two different surface areas, with the surface area of a larger perforation at least 50% larger than the surface area of a smaller perforation,

12. Cylindrical premix gas burner as in claim 1 1 , wherein the average distance from the centre point of a smaller perforation is at least 100% higher than the average distance from the centre point of a larger perforation.

13. Cylindrical premix gas burner as in any of the preceding claims, wherein along the length of the cylindrical premix gas burner, said cylindrical burner deck has circumferential sections of different porosity, with at least two sections which have an absolute difference in porosity of more than 3% and with an average porosity of the cylindrical burner deck of less than 1 1 %.

14. Cylindrical premix gas burner as in any of the preceding claims, wherein the cylindrical burner deck has - at said inlet disc a first section over a length of at least 8 mm as measured in the direction of the axis of the cylindrical premix gas burner, provided with perforations wherein the porosity of said first zone is higher than 12%,; and

- over a length of at least 30 mm as measured in the direction of the axis of the cylindrical premix gas burner, and further away from said inlet disc than said first section, a section with perforations, the porosity of said section is less than 10%.

15. Boiler or instantaneous water heater comprising a cylindrical premix gas

burner as in any of the preceding claims.

Description:
Premix gas burner

Description

Technical Field

[1 ] The invention relates to a cylindrical premix gas burner, and specifically to such burners with a perforated plate as cylindrical burner deck. The cylindrical premix gas burner has a specific inlet disc for the entry of premix of air and combustible gas into the cylindrical premix gas burner. The result is a reduction in thermo-acoustic instabilities of the burner. Such burners find use in boilers and in instantaneous water heaters.

Background Art

[2] Cylindrical premix gas burners that have a perforated plate as cylindrical burner deck are known. Patent publications WO2009/065733,

WO201 1/069839 and EP2037175A2 provide examples of such burners. These examples are provided without the use of a second cylindrical element in the burner that would act as distributor of premix gas inside the burner prior to the premix gas flowing through the cylindrical burner deck. The premix gas is burned at the outside of the cylindrical burner deck.

[3] The cylindrical burners of WO2009/065733 comprise an inlet disc with a multiple of perforations for the supply of premix gas into the chamber enclosed by the cylindrical burner. Such perforations can be made easily, with standard punching equipment, punching pellets out of metal plates thereby creating the perforations.

The cylindrical burners of EP2037175A2 are provided with an inlet having a plurality of through openings or holes. In a specific embodiment, the through openings or holes are obtained by partial cutting and folding of portions of the disc to form embossed tongues developing towards the inner part of the tubular body and are alternated to the same openings.

[4] It is a problem that cylindrical premix gas burners as known in the art can show - when in use - thermo-acoustical instabilities. The originating noise is a nuisance, and hence, solutions are looked for to overcome the thermo-acoustic instabilities in cylindrical premix gas burners. Disclosure of Invention

[5] The primary objective of the invention is to provide cylindrical premix gas burners with a perforated inlet disc and that show reduced thermo-acoustic instabilities than cylindrical premix gas burners that are known in the art.

[6] According to the invention, a cylindrical premix gas burner is provided. The burner can be a fully premixed burner. The cylindrical gas burner is comprising a cylindrical burner deck, in the form of a perforated metal plate. The perforations in the cylindrical burner deck can be of different shapes and sizes, e.g. circular perforations, slits or slot; which can be arranged according to a certain pattern, over the full cylindrical burner deck, or in different patterns in different sections of the cylindrical burner deck. Alternatively, the perforations in the cylindrical burner deck can also by arranged in a random way.

The cylindrical premix gas burner is delimited by an end cap. At the opposite side of the end cap, an inlet disc is provided for the supply of a premix of combustible gas and air into the burner, premix gas which is to be burned on the outside of the cylindrical burner deck after the premix gas has flown through it. The inlet disc is comprising a plurality of perforations for premix gas supply into the burner. With perforation is meant that a through hole is present in the inlet disc whereby material is removed from the inlet disc thereby creating the through hole. Such perforations can be made by means of punching equipment, wherein pellets are punched out of the inlet disc, thereby forming the perforations. The inlet disc is having a centre point, which is where the (virtual) 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 around the centre point with a diameter of at least 8 mm, and more preferably with a diameter of at least 10 mm, even more preferably with a diameter of 14 mm. [7] It is a benefit of burners according to the invention that thermo-acoustic instabilities can be avoided in boilers or instantaneous heaters that are provided with such cylindrical premix gas burners. Surprisingly thermo- acoustic instabilities can be avoided in boilers or instantaneous heaters that are equipped with burners according to the inventions, especially at low CO2 operating conditions of the burner. The burners of the inventions showed to generate less humming at low CO2 operating conditions.

[8] It is the objective that the burner will be used in blue flame mode (and not in red flame mode which is useful when heat is transferred via infrared radiation) whereby hot flue gas is generated that will transfer its energy via conductivity and via convection, e.g. to a fluid (e.g. water) in a heat exchanger (e.g. a cast heat exchanger or a plate heat exchanger or a spiral tube heat exchanger).

[9] In a first way of providing an inlet disc for a burner according to the

invention, the inlet disc is not perforated at least within a circle around the centre point with a diameter of at least 8 mm, and more preferably with a diameter of at least 10 mm, even more preferably with a diameter of 14 mm.

[10] In an alternative way, a disc is provided that can have perforations in the central zone as well, but a plate is fixed on one side, or plates are fixed on both sides of the disc in order to close off locally the perforations of the disc. This way, an inlet disc (comprising the disc and the one or more plates) can be provided that is not perforated (and hence not permeable to premix gas) at least within a circle around the centre point with a diameter of at least 8 mm, and more preferably with a diameter of at least 10 mm, even more preferably with a diameter of 14 mm. The fixation between the disc and the one or more plates can e.g. be by means of welding. It is a benefit of this way of providing an inlet disc for burners according to the invention, that small series of inlet discs (and small series of burners) can be produced more easily, using discs perforated in a uniform and regular way, combined with one or more unperforated plates fixed (e.g. welded) to the disc to make a central section of the inlet disc impermeable to premix gas.

[1 1 ] Preferably, the cylindrical premix gas burner is devoid of a diffuser inside the cylindrical perforated burner deck; meaning that the cylindrical gas burner is devoid of a diffuser inside the chamber enclosed by the inlet disc, the cylindrical burner deck and the end cap. It means that gas premix is flowing through the inlet disc, and without no further physical obstacles it is flowing through the perforations of the cylindrical burner deck to be burned on the outside of the cylindrical burner deck.

[12] In a preferred embodiment, the perforated part of the inlet disc (which is the part of the inlet disc that is provided with perforation) is flat, which has as benefit that the perforations can be made more easily.

[13] Preferably, the inlet disc is not permeable to premix gas around the centre point of the inlet disc over a zone that is centred at the centre point of the inlet disc.

Even more preferred is when that zone has a regular shape. With "regular shape" is meant that two lines can be defined on the inlet disc that cross in the centre point which - between the two lines - contain a part of that zone, that when repeating that part around the centre point a number of times (e.g. three times, e.g. four times, e.g. six times), the whole zone of the inlet disc that is not permeable to premix gas is covered and this is centred around the centre point.

That zone can have a star shape. Such an embodiment has been shown to be particularly advantageous in the reduction of humming at low CO2 levels of the burner.

Alternatively, that zone has a regular polygonal shape. More preferred is when that zone is having a regular hexagonal shape, as the perforations in the inlet disc - around the zone that is not perforated - can, from a manufacturing point of view - be made more easily. [14] Preferably at least part of the perforations for premix gas supply in the inlet disc are of cylindrical shape, more preferably all perforations are of cylindrical shape.

Preferably, the inlet disc comprises at least fifteen perforations, and more preferably at least twenty perforations, and even more preferably at least thirty perforations, for premix gas supply into the burner, the higher number is preferred to reduce acoustic instabilities.

Preferably, the perforations of the inlet disc all have the same shape and/or same size and/or same surface area. This facilitates the production of the perforations of the inlet disc and the tooling required for it.

[15] In an alternative embodiment, the perforations of the inlet disc for supply of premix gas have different shapes and/or different sizes and/or different surface areas.

Preferred is when the inlet disc comprises perforations of different size or different surface area, and when perforations of larger size (or of larger surface area) are located closer to the centre point than perforations of smaller size (or of smaller surface area). This embodiment has the benefit that lower NOX (nitrogen oxide) emissions are obtained when using the burner.

Preferred is when the average distance from the centre point of a smaller perforation is at least 100% higher than the average distance from the centre point of a larger perforation.

In a preferred embodiment, the inlet disc is comprising perforations of at least two different surface areas, with the surface area of a larger perforation at least 50% (and preferably more than 100%, but preferably less than 200%) larger than the surface area of a smaller perforation.

Surprisingly, burners according to this embodiment have shown to have reduced NOX levels, which is beneficial in view of more stringent legislation on emissions of burners.

[16] In a preferred embodiment, each of the perforations of the inlet disc are having a surface area of less than 30 mm 2 , and preferably less than 20 mm 2 , and more preferably less than 13 mm 2 and even more preferably less than 12 mm 2 . [17] In a preferred embodiment, the cylindrical premix gas burner has along the length of the cylindrical burner deck, circumferential sections of different porosity (of preferably at least 25% of the length of the perforated zone of the cylindrical metallic burner membrane), with at least two sections which have an absolute difference in porosity of more than 3% (e.g. 15% in one zone, 7.5% in another section) and with an average porosity of the cylindrical burner deck of less than 1 1 %. The term "porosity of the burner deck" is to be understood, in the light of this invention, as the ratio of the surface of the holes, slots or other perforations divided by the surface of the burner (or the section) over which the perforated part(s) is (are) located.

It is a benefit of this embodiment that thermo-acoustical instabilities could be further reduced, thanks to the synergy between the features of the inlet disc and the feature of the perforations on the cylindrical burner deck. More preferably, the section with higher porosity is located closer to the inlet disc than a section with lower porosity.

[18] Even more preferably, the cylindrical burner deck has

- at the inlet disc a first section over a length of at least 8 mm (and preferably at least 10 mm and preferably below 25 mm, more preferably below 15 mm) as measured in the direction of the axis of the cylindrical premix gas burner, provided with perforations wherein the porosity of the first section is higher than 12%, preferably between 14 and 16%; and

- over a length of at least 30 mm (and preferably at least 50 mm at preferably below 100 mm) as measured in the direction of the axis of the cylindrical premix gas burner, and further away from the inlet disc than the first section, a section with perforations, wherein the porosity of that section is less than 10%, preferably between 7 and 8.5%.

Surprisingly, the burner according to this embodiment of the invention has shown to have even better results in terms of thermo-acoustic instabilities thanks to the synergy of the features of the inlet disc and the perforations on the burner deck.

In a further preferred embodiment, the burner deck has a third section, further away from the inlet disc than the perforated section with porosity less than 10%, wherein the third section is having a porosity higher than 12%, preferably between 14 and 16%.

[19] A preferred use of the cylindrical premix gas burners according to the

invention is in boilers or instantaneous water heaters. Such boilers and instantaneous water heaters have less acoustical instabilities compared to when using prior art cylindrical gas premix burners.

Brief Description of Figures in the Drawings

[20] Figure 1 shows an example of a cylindrical premix gas burner according to the invention.

Figures 2, 3 and 4 show examples of inlet discs that can advantageously be used in the invention.

Figure 5 shows an example of a cylindrical premix gas burner according to the invention.

Figure 6 shows an alternative way to provide an inlet disc that can be used in a cylindrical premix gas burner according to the invention.

Mode(s) for Carrying Out the Invention

[21 ] Figure 1 shows an example of a cylindrical premix gas burner 100

according to the invention. The cylindrical gas burner 100 is comprising a cylindrical burner deck 1 10, in the form of a perforated metal plate. In the example, the cylindrical gas burner has an internal diameter of 69 mm, but other internal diameters are possible, preferably between 50 and 95 mm. The cylindrical premix gas burner 1 10 does not comprise a diffuser within the room enclosed by the cylindrical burner deck 1 10. The cylindrical premix gas burner 1 10 is delimited by an end cap 1 18. At the opposite side of the end cap 1 18, an inlet disc 130 is provided for the supply of a premix of combustible gas and air into the burner 100, premix gas which is to be burned on the outside of the cylindrical burner deck 1 10 after the premix gas has flown through it. The inlet disc 130 is comprising a plurality of perforations 140 for premix gas supply into the burner 100. In the example, all perforations 140 in the inlet disc for supply of premix gas are of the same size, e.g. circular with a diameter of 2.5 mm, or of 3.6 mm. However, it is also possible to have perforations of other shape (e.g. slits), of different size and/or different dimensions or of different surface area over the surface of the inlet disc 130. Such perforations can be made by punching the inlet disc with appropriate tooling thereby punching out pellets from the inlet disc and making the perforations. The inlet disc 130 can be provided with a flange 143 with holes 145 for the connection of the burner, e.g. in a boiler housing.

The inlet disc 130 is having a centre point, which is where the (virtual) central axis 147 of the cylindrical premix gas burner crosses the inlet disc 130. The inlet disc is not permeable to premix gas within a circle 150 around the centre point with a diameter of e.g. 14 mm.

[22] Figure 2 shows an example of an inlet disc 130 that can be used in the invention. The inlet disc is provided with perforations 141 , 142 of two different dimensions. Larger perforations 141 of e.g. 3.6 mm diameter are located more centrally on the inlet disc 130 compared to smaller perforations 142 of e.g. 2.5 mm diameter. In the centre of the inlet disc 130, the inlet disc 130 is impermeable to gas premix in a star shaped zone 152. In its centre, the star shaped zone includes a circle of at least 8 mm diameter, e.g. of diameter 12 mm. The inlet disc 130 can be provided with a flange 143 with holes 145 for the connection of the burner, e.g. in a boiler housing.

[23] Figure 3 shows an example of an alternative inlet disc 130 that can be used in the invention. The inlet disc is provided with perforations 141 , 142 of two different dimensions. Larger perforations 141 of e.g. 3.6 mm diameter are located more centrally on the inlet disc 130 compared to smaller perforations 142 of e.g. 2.5 mm diameter. In the centre of the inlet disc 130, the inlet disc 130 is impermeable to gas premix in an alternative star shaped zone 154. In its centre, the star shaped zone includes a circle of at least 8 mm diameter, e.g. of diameter 12 mm. The inlet disc 130 can be provided with a flange 143 with holes 145 for the connection of the burner, e.g. in a boiler housing. [24] Figure 4 shows an example of an alternative inlet disc 130 that can be used in the invention. The inlet disc is provided with perforations 141 , 142 of two different dimensions. Larger perforations 141 of e.g. 3.6 mm diameter are located more centrally on the inlet disc 130 compared to smaller perforations 142 of e.g. 2.5 mm diameter. In the centre of the inlet disc 130, the inlet disc 130 is impermeable to gas premix in a regular hexagonal shaped zone 156. In its centre, the star shaped zone includes a circle of at least 8 mm diameter, e.g. of diameter 10 mm. The inlet disc 130 can be provided with a flange 143 with holes 145 for the connection of the burner, e.g. in a boiler housing.

[25] Figure 5 shows an example of a cylindrical premix gas burner 500 of the invention. The burner has a length of 92.6 mm and diameter of 70.4 mm. The burner deck 510 has a length of 92.6 mm and is perforated over a length of 73.2 mm. The perforations in the perforated plate that forms the burner deck 510 are a combination of slits and round holes. The thickness of the perforated plate is 0.6 mm, the slits are 4.0 * 0.5 mm, the holes have a diameter of 0.8 mm. The perforations are grouped in patterns: the first 1 1 .8 mm of the perforated burner deck length (meaning closest to the inlet disc 520) has a porosity of 15%, thereafter is a zone of 55.6 mm of the burner deck length with a porosity of 7.3% and the last zone with a length of 5.8 mm of the burner deck length having a porosity of 16.5%. This pattern is repeated over the burner deck on the circumference of the burner. This provides a burner deck which has an overall porosity of 9.8%. The burner does not contain a diffuser inside the cylindrical burner deck. The burner comprises an inlet disc 520 according to the invention, e.g. an inlet disc as shown in figures 1 , 2, 3 or 4.

[26] Figures 6A and 6B show an alternative way to provide an inlet disc that can be used in a cylindrical premix gas burner according to the invention. The inlet disc 630 is comprising a disc 635, which is comprising

perforations 641 . The disc 635 can have a flange 643 with through holes 645 for the fixation of the inlet disc 630 e.g. to a burner housing. An unperforated plate 660 is welded centrally on top of the first plate 635. The dimensions of the imperforated plate 660 are selected to create

impermeability of the inlet disc 630 to premix gas in a central section of the inlet disc 630. The imperforated plate can e.g. have a circular shape (e.g. of diameter 14 mm), or another shape, e.g. a star shape, or a regular polygonal shape (e.g. a regular hexagonal shape). Figure 6B shows the cross section of inlet disc 630 along line Ι-Γ.

[27] As an example, the observation is given of comparative trials in a boiler set-up with a burner according to the invention compared to another burner. Both burners were cylindrical burners with a length of 84 mm and a diameter of 70 mm. The burners had along the length of the cylindrical burner deck three zones with different porosity levels, with (starting from at the inlet plate) a first zone of 1 1 .8 mm length having a porosity of 15%, a next zone of 46.8 mm length having a porosity of 7.3% and a third zone with a length of 5.8 mm having a porosity of 16.5%. The average porosity of the burner deck is 9.5%.

A first burner (burner not according to the invention) that was tested had an inlet disc with a multiple of perforations in the inlet disc, including perforations at the centre of the inlet disc. The burner had a humming sound, especially at low CO2 operating conditions.

This burner was compared with a burner according to the invention with an inlet disc as shown in figure 4. The inlet disc was having small perforations (of 2.5 mm diameter) and bigger perforations (of 3.6 mm). As is shown in figure 4, perforations are absent around the central point of the inlet disc (seven of the "expected" perforations are missing). Contrary to the first burner, the burner according to the invention was not producing a humming sound, even not at low CO2 operating conditions.

[28] Features of the examples and of the embodiments of the invention can be combined while staying within the concept of the invention.




 
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