EP0347834B1 - Burner head for a forced-draft gas burner - Google Patents

Abstract

Burner head (1) for a forced-draught gas burner with a combustion- gas division (4) and a combustion-air division and having radially arranged combustion-gas nozzles (7) and axially extending combustion-air passage orifices (9, 19), there being formed in the region of nozzles (7) and orifices (9, 19) the flame root, downstream of which webs (12) project radially into the flame region. Arranged equiaxially with the burner tube (10) is a flame tube (13), and between the burner tube (10) and the flame tube (13) there is an annular gap (16) for exhaust-gas recirculation.

Description

The invention relates to a burner head for a forced gas burner according to the preamble of the main claim. In a known fan gas burner of this type (FR-PS 1 507 416), the problem underlying such gas burners can be seen. Since the gas is supplied to the combustion chamber at a relatively low pressure, in order to achieve homogeneous mixing with the combustion air, the gas supply must be fanned out and mixed with the supplied combustion air in a suitable manner as homogeneously as possible. In addition, there is a risk with such blower gas burners that the flame breaks off, which is then automatically re-ignited, which can lead to an unpleasant pulsation. In this known fan gas burner is inside a baffle ring is arranged by the combustion tube, through which the flame is to be stabilized.

The high temperatures, especially in the combustion of natural gas results in a high NO _x content in the exhaust gas, despite the excellent the rest, especially soot-free combustion. The values of this nitrogen oxide content are above the permissible limit value, so that a reduction is necessary. Such a reduction can be achieved by an increased air content and thus a reduction in the flame temperature, which would, however, entail the disadvantage of poorer combustion quality.

In blower oil burners, it is known (WO 86/07434) to achieve an improvement in the poisonous components, in particular nitrogen oxides, in the finally removed exhaust gas by recirculating exhaust gas in the manner of exhaust gas recirculation, recirculation openings being provided between the combustion tube and the flame tube, which is somewhat larger in diameter, so that a cooler jacket of recirculated exhaust gases is created around the flame, which then mix at least in part due to the high turbulence with the oil-air mixture to be burned or penetrate into the burning flame. In contrast to the blower gas burner, however, the oil burner has an oil spray cone generated by the oil burner nozzle of high flow energy, into which the combustion air is blown with likewise high air pressure and under swirl, in order to ensure sufficient combustion for good combustion to achieve the required mixing of oil mist and combustion air. Despite the swirl and baffle plates in the flame tube, this naturally results in a high fuel gas velocity, which causes recirculation through the radial openings between the fuel tube and flame tube. Nevertheless, in this known blower oil burner, the flame tube on the side facing the combustion tube, namely downstream of the recirculation openings, is expanded in order to superimpose a funnel effect on the Venturi effect.

The situation is very different for fan gas burners due to the low gas pressure there. A recirculation of the type described could not take place, since the air velocities in the flame tube are far too low - such radial openings, which in themselves serve the purpose of recirculation, could result in a radial flame escape. In addition there would be uncontrollable pulsations caused by such "false air openings", which could not only result in considerable noise, but would also not meet the safety regulations, which are known to be very strict in the field of fan gas burners.

Underlying task

The invention has for its object to develop a burner head for fan gas burners, with which the NO _x components in the exhaust gas finally discharged to one A value that can be reduced is, if possible, less than 50 ppm NO _x . This object is achieved by the burner head according to the invention with the characterizing features of the main claim.

Advantages of the invention

This burner head according to the invention has the advantage over the known blower gas burners that in a very simple manner and without increasing the pressure of the fuel gas or the supplied combustion air and using the known effect of exhaust gas recirculation, a substantial reduction in the NO _x content is possible, namely up to below 50 ppm. The diameters of the combustion tube and the flame tube can advantageously be kept almost the same, although at these low speeds of the gas / air mass flow with effective exhaust gas recirculation, low NO _x values, reduced CO values and a high burner output with high flame stability can be achieved. In the known burner heads, the diameter of the flame head is significantly larger than that of the burner tube due to the sudden increase in volume of the gas caused by high heat development, with the consequent installation disadvantages.

The webs against which the flame flows can be designed in a wide variety of ways. The decisive factor is that the heat flow experiences a jam with an overpressure zone upstream and a vacuum zone downstream of the web, the former causing flame stabilization and the latter initiating the recirculation of the exhaust gas.

According to an advantageous embodiment of the invention, the device for the fuel gas distribution in the manner of a cross-flow burner has a burner ring arranged transversely to the burner head axis with a burner plate, with radially arranged fuel gas nozzles and with axially provided through openings for the combustion air. This creates so-called torus vortices downstream of the burner ring, as well as flame zones near the fuel gas nozzles with combustion that runs out of air and flame zones near the passage openings with combustion with excess air, although there is an intensive mixing of the gas streams emerging from the fuel gas nozzles with the rotating combustion air. These flame zones form the root of the burner flame, which continues for a second combustion stage downstream of the webs in the flame tube.

According to a further advantageous embodiment of the invention, the edge region of the burner ring towards the combustion tube has notches formed as slits apart from an annular gap as additional through openings for the combustion air. Through these nicks, which according to one embodiment, about a quarter to have a third of the distance between the individual fuel gas nozzles in the outer row of the burner ring facing the nicks, cause a change, in particular enlargement, the air speed and thus intensification of the torus vortex, which results in an improvement in the mixing of fuel gas and combustion air .

According to a further advantageous embodiment of the invention, a swirl disk for combustion air is arranged in the combustion tube upstream of the device for the fuel gas distribution. By means of this swirl disk, which in a known manner has segments which are inclined against one another and which is also known as a swirl disk, causes the combustion air to receive a helical swirl movement. The main result of this is that the combustion air is forced to a longer dwell time on its way to the flame root, apart from the fact that a much better mixing between fuel gas and combustion air is brought about. In combination with the increased air speed caused by the slits, this swirling effect of the combustion air continues through the slits down to the webs, and promotes the standing vortices which form in the flame tube due to the webs and which cause the exhaust gas recirculation. In known swirl disks, these are always arranged downstream of the fuel gas nozzles or air passage openings with a correspondingly different effect.

According to further embodiments of the invention, the webs are arranged on a web ring, which can be designed in a wide variety of ways. The webs on the inside can also be connected to each other by a ring, creating a type of perforated disc.

Further advantages and advantageous embodiments of the invention can be found in the following description, the drawing and the claims.

Fig. 1

den Brennerkopf im Längsschnitt,

Fig. 2

einen Teilschnitt gemäß Linie II-II in Fig. 1,

Fig. 3

die Draufsicht auf die Stegscheibe des Ausführungsbeispiels,

Fig. 4

die Draufsicht auf eine Variante dieser Stegscheibe,

Fig. 5 u. 6

jeweils einen Schnitt gemäß der Linie V-V in Fig. 3 in zwei Varianten,

Fig. 7

eine weitere Variante der Steggestaltung in der Draufsicht,

Fig. 8

einen Schnitt durch die Variante in Fig. 7 gemäß der Linie VIII-VIII in Fig. 7 und

Fig. 9 u. 10

zwei Varianten der Stegscheibe in teilweiser Darstellung in der Draufsicht als Lochscheiben.

An embodiment of the object of the invention is shown in several variants in the drawing and described in more detail below. Show it:

Fig. 1

the burner head in longitudinal section,

Fig. 2

2 shows a partial section along line II-II in FIG. 1,

Fig. 3

the top view of the web washer of the embodiment,

Fig. 4

the top view of a variant of this web washer,

Fig. 5 u. 6

in each case a section along the line VV in Fig. 3 in two variants,

Fig. 7

another variant of the web design in plan view,

Fig. 8

a section through the variant in Fig. 7 along the line VIII-VIII in Fig. 7 and

Fig. 9 u. 10th

two variants of the web washer in partial representation in plan view as perforated washers.

In the burner head 1 of a fan gas burner shown in Fig. 1, the actual combustion air blower with motor and fan wheel is not shown, but only part 2 of the gas burner housing which belongs to the burner head, i.e. which is connected directly to the boiler with the combustion chamber. The combustion air is supplied to the burner head 1 in the direction of arrow I via the burner housing, which is otherwise not shown. The fuel gas is fed radially to the burner head 1 here via a gas line 3 and passed on within it via a tubular distributor device 4. The tubular distributor device is closed in the direction of the combustion chamber by a burner ring 5 and a burner plate 6. Radial fuel gas nozzles 7 are provided between the burner plate 6 and the burner ring 5 for an exit of the fuel gas provided transversely to the burner head axis. On the burner ring 5 there are edges 8 on air passage openings 9 on the side against which the combustion air flows, these edges 8 producing so-called toroidal vortices into which the fuel gas strands emerging from the fuel gas nozzles 7 are sucked and are mixed intensively with the rotating combustion air. In this region of the vortices indicated in FIG. 1 downstream of the burner ring, the flame roots of a short burner flame begin without additional baffles being required for this. One of the air passage openings 9 is designed as an annular gap between the burner ring 5 and a burner tube 10 which is inserted over the burner ring 5 and the tubular distributor device 4 and which is plugged radially sealingly into the housing 2 of the gas burner and fastened thereon.

On the end of the combustion tube 10 facing the combustion chamber, a web ring 11 is fastened thereon, which has webs 12 projecting radially inwards into the flame. A flame tube 13, here of the same diameter as an example, is fastened to the combustion tube 10 at a distance, which surrounds the first part of the burner flame 14 and, with the exception of the locations at which fastening tabs 15 are arranged, an annular gap 16 between the combustion tube 10 and the flame tube 13 arises, through which exhaust gases can recirculate from the combustion chamber of the boiler back into the flame tube. The flame tube 13 could also have a larger diameter than the combustion tube 10.

The web ring 11 with the webs 12 causes a slight constriction of the flame mass flow flowing past, which results in a slight acceleration of the flow velocity with a slight deflection at the same time radially inwards, so that "standing" vortices form on the webs 12, which lead to the suction of the exhaust gases from the annular gap 16 and thus to exhaust gas recirculation, and which are also supported by the injector effect of the flame mass flow in the flame tube 13. Through the web ring 11, the cool combustion air flowing in through the air passage openings 9 on the wall of the combustion tube 10 is also partially guided into the flame center, whereby a reduction in the flame temperatures is achieved with the correspondingly slightly cooled, lower-oxygen, recirculating exhaust gases, with a corresponding reduction in the NO _x -Share down to less than 40 ppm.

Upstream of the distributor device 4, a swirl disk 17 is arranged in the burner head 1, which has almost the diameter of the combustion tube 10, and by means of the segments 18 of which are displaced relative to one another, a helical swirl movement of the combustion air is achieved.

As can be seen in FIG. 2, in the edge region of the burner ring 5, the air passage openings 9 are provided with sections 19 which have a corresponding influence on the speed of the combustion air flow and, in conjunction with the swirl of the air flow caused by the swirl disk 17, an improvement in the torus swirls and the fuel gas / combustion air mixture preparation.

In the web ring 11 with webs 12 shown in plan view in FIG. 3, a free inner diameter d remains between the free ends 22 of the webs 12, which has a specific ratio to the outer diameter D and the ring width b of the outer, non-perforated section 21 of the web ring stands. The webs 12 are designed as sheet metal flags of width B, which are evenly distributed with their web foot 20 and in a flat area on the outer ring section 21 of the web ring 11 and merge into section 21 in a rounded manner. The length of the webs between the free ends 22 up to the web foot is marked with L. As a result of this design, the through openings 23 of the web ring 11 between the webs 12 have a drop-shaped cross section which widens radially outward and is open to the inner diameter of the web ring 11.

5 and 6, a section through the web ring 11 according to the line VV is shown, wherein it can be seen that the webs 12 have a kink in their longitudinal course, so that they have an end section 24 extending at right angles to the burner head axis and an inclined to Have burner head axis extending foot portion 25. The foot section 25 merges into the conical outer ring section 21, which is adjoined by a cylindrical pipe section 26 with which the web ring 11 is plugged onto the fuel pipe 10. In the variant shown in FIG. 5, this pipe section 26 is larger in diameter than the combustion pipe 10 and is thus plugged onto this, however, in the variant according to FIG. 6, this pipe section 26 is smaller in diameter and thus plugged into the fuel pipe 10 and fastened to it. The assignment of the individual dimensions D, D, L, B, B, the inclination of the foot section 25 and that of the outer ring section 21 play a decisive role in the desired exhaust gas recirculation while maintaining the favorable combustion.

In the variant of the web ring 11 with webs 12 shown in FIG. 4, the lateral boundaries of the web-shaped webs 12 are formed parallel to the web foot 20, and there are also the base edges 27 of the through openings 23 by which the web feet 20 are connected to one another, straight, so that the cross section of the through openings 23 in this variant has the shape of an open top trapezoid.

A further variant of the web ring 11 is shown in FIGS. 7 and 8, in which sheet flaps 28 are fastened in a star-shaped manner, for example spot-welded or riveted, on the web ring 28, which is also in one piece and made up of a tubular section 26 and an outer, non-perforated ring section 21. The remaining passage cross section of the passage openings 23 thus formed corresponds to that of the variant shown in FIG. 4.

Another design of the web ring 11 is shown in FIGS. 9 and 10, in which the web ring is designed in each case as a perforated plate, with oval through openings 23 in FIG. 9 and rectangular through openings 23 in FIG. 10.

The burner head according to the invention works as follows: Combustion air is admixed via the air passage openings 9 and the slots 19 to the fuel gas emerging via the radially inward and outward fuel gas nozzles 7 of the burner ring 5, so that mixtures are present in the flame root, i.e. upstream of the web ring Different gas concentrations are available. While combustion takes place near the air passage openings 9 and 19 with a very large excess of air, the combustion takes place in the vicinity of the fuel gas nozzles 7 with a lack of air. In both cases, the combustion temperature therefore remains low, so that there is a very low NO _x emission in each of these partial flames. It is only in the subsequent flame tube 13 that the final, complete combustion takes place with the desired reduction in the CO content in the exhaust gas. Since the combustion air is additionally swirled via the swirl disk 17, there is an intensification in the mixing of the gas-air mixture, which is on the one hand too lean and on the other hand too rich, so that combustion which is still sufficient for the desired goal is achieved upstream of the web ring 11. Due to the air impulse-like impingement reached via the naps 19, the flame swirling over the swirl disk 17 on the The web ring 11 with the webs 12 creates an overpressure zone upstream of the web ring on the surfaces opposing the flow, which is followed by a vacuum zone on the downstream side. This vacuum zone, which is open towards the annular gap 16 in accordance with the design of the web rings 11, causes the exhaust gases surrounding the combustion tube 10 and the flame tube 13 to be drawn in, so that a desired exhaust gas recirculation occurs. The exhaust gas is thus conducted into the flame through the interstices formed by the webs 12 and has a lowering of the flame temperature and thereby reducing NO _x . In addition, the CO content in the exhaust gas is reduced, quite apart from the fact that the web ring 11 brings about anchoring of the flame, which is desired in gas-blown burners, that is to say prevents the flame from being torn off. This two-stage combustion with exhaust gas recirculation finally has the advantage that a fan gas burner with the burner head according to the invention can be used largely independently of the design of the combustion chamber.

List of reference numbers

1

Burner head

2nd

Housing part

3rd

Gas pipe

4th

tubular distributor device

5

Burner ring

6

Burner plate

7

Fuel gas nozzles

8th

edge

9

Air vents

10th

Fuel tube

11

Web ring

12

Walkways

13

Flame tube

14

Burner flame

15

Mounting tabs

16

Annular gap

17th

Vertebral disc

18th

Segments

19th

Nicks

20th

Bridge foot

21

outer, non-perforated (ring) section,

22

free ends of 12

23

Through opening

24th

End section

25th

Foot section

26

Pipe section

27

Base edge

28

Sheet metal rag

Claims (16)

1. Burner head for a ventilated gas burner with combustion pipe designed to hold a device for distributing the combustion gas and the combustion air, with combustion gas nozzles and air inlet/outlet openings, and with a flame-pipe connected to the combustion pipe characterised by at least one radial opening (16), serving for the recirculation of the exhaust gas, being present between the combustion pipe (10) and the flame-pipe (13), and by cross-members (12) which project inwards being present in the flame root area between the combustion tube (10) and the flame-pipe (13) upstream of the radial opening (16) but downstream of the combustion gas nozzles (7) and the air inlet/outlet openings (9, 19) and cross-wise to the longitudinal axis of the burner head.
2. Burner head along the lines of Claim 1, characterised by the device for distributing the combustion gas having, in the manner of a cross-flow burner, a burner ring (5) mounted crosswise to the axis of the burner head and fitted with a burner plate (6), with combustion gas nozzles (7) arranged radially and air inlet/outlet openings arranged axially (9).
3. Burner head along the lines of Claim 2 characterised by the periphery of the burner ring (5) having apertures (19) towards the combustion tube (10) as well as a ring slot in the form of notches as additional air inlet/outlet openings for the combustion air.
4. Burner head along the lines of Claim 3 characterised by the notches (19) having an internal width of a quarter to one-third of the distance between the combustion gas nozzles (7) in the external row of the burner ring (5) on the side facing the notches (19).
5. Burner head along the lines of one of the foregoing Claims characterised by a vortex plate (17) for the combustion air in the combustion tube (10) being fitted upstream of the device of the distribution of the combustion gas (4).
6. Burner head along the lines of one of the foregoing Claims characterised by the cross-members (12) being arranged as baffles in the direction of the combustion air flowing in the inlet/outlet openings (9, 19).
7. Burner head along the lines of one of the foregoing Claims characterised by the cross-members (12) being part of a ring of cross-members (11) with an external, non-perforated ring section (21) and with a cross-section which is determined by the existing inlet/outlet openings (23) between the cross-members (12) and the ring section (21).
8. Burner head along the lines of Claim 7 characterised by the cross-member ring (11) having a central opening.
9. Burner head along the lines of one Claims 7 or 8 characterised by the cross-member ring (11) being limited outwards by a cylindrical section of tube (26) corresponding with the diameter of the combustion tube (10) and being fastened to it.
10. Burner head along the lines of one of the Claims 7 to 9 characterised by the radial limit edges of the cross-members (12) running parallel to one another with the length of the cross-member (L) being at least twice as great as its breadth (B).
11. Burner head along the lines of Claim 10 characterised by the cross-members (12) being rounded and widened at the foot end (20) and the cross-members having free ends (22) radially inwards, so that the cross-section of the inlet/outlet openings (23) takes on the shape of a tear-drop (Fig. 3).
12. Burner head along the lines of Claim 10 characterised by the inlet/outlet openings (23) in the cross-member ring (11) having a trapezium-shaped, rectangular, or long-slot cross-section (Figs. 4 to 10).
13. Burner head along the lines of one of the Claims 8 to 12 characterised by the inlet/outlet openings (23) in the cross-member ring (11) being open towards the inner opening of the cross-member ring.
14. Burner head along the lines of one of the Claims 7 to 13 characterised by the cross-members being formed as metal flaps (28) which are fastened to the outer, non-perforated section (21).
15. Burner head along the lines of one of the Claims 7 to 14 characterised by the outer, non-perforated ring section (21) of the cross-member ring (11) having a conical shape which tapers away in the control direction.
16. Burner head along the lines of Claim 15 characterised by at least one foot section (25) of the cross-members (12) have the same angle of inclination as the external ring section.

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