EP0775869A2 - Premix burner - Google Patents

Abstract

The fuel is introduced as a secondary current into a gaseous main current enclosed by an annular premixing duct (20) defined by an inner (21a) and outer (21b) cylinder wall. The main flow is guided by vortex generators (9,9a) which create a vortex leaving behind a residual vortex when the fuel has been completely mixed with the air of the fuel and air mixture. The annular main current duct of constant height (H) has a length (L), downstream from the vortex generators and fuel injector, which is between 5 and 20 times the height. The annular main flow duct widens into a circular main flow duct by closing the inner cylinder wall (21a).

Description

Technical field

The invention relates to a premix burner for the combustion of gaseous and / or liquid fuel, in which the fuel is injected as a secondary flow into a gaseous, channeled main flow, the secondary flow having a substantially smaller mass flow than the main flow.

State of the art

A premix burner is known from EP 0 321 809 B1, which is characterized by low NOx emission values (approx. 25 ppm) and high flame stability. This premix burner, also known as a double-cone burner, consists of hollow, part-cone bodies, which complement one another, with tangential air inlet slots for the combustion air flowing in from the compressor, and feeds for gaseous and liquid fuels, the center axes of the hollow part-cone bodies having a cone inclination widening in the direction of flow and in Longitudinally offset to each other. A fuel nozzle for the liquid fuel is arranged inside the burner (cone tip), through which the fuel is injected into the hollow cone at an acute angle. The resulting tapered liquid fuel profile is enclosed by the tangentially rotating combustion air flow, the concentration of the fuel continuously decreasing in the axial direction due to the mixing with the combustion air. The premix burner can also be operated with gaseous fuel or in mixed operation. The mixture of the gaseous fuel with the combustion air already takes place in the tangential air inlet slots, into which the gaseous fuel is introduced via uniformly distributed nozzles.

In order to achieve a reliable ignition of the mixture at the burner outlet and a sufficient burnout, an intimate mixture of the fuel with the air is required. The type of injection creates axially oriented vortices of the fuel / air mixture in the interior of the double-cone burner. When the number of vortices has reached a critical value, the vortex breakdown occurs (bursting of the vortices) and a stable flame front is formed downstream of the burner outlet.

A further permanent reduction in the pollutant emission values of the double-cone burners, for example to NOx values less than 9 ppm, by changing the operating conditions is not possible because of the problems with flame stability, pulsation and the ever increasing combustion temperatures.

Another disadvantage of the double-cone burner is its complicated geometric shape and the resulting manufacturing difficulties.

EP 0 619 456 A1 discloses a fuel supply system for a combustion chamber with premix combustion, in which a gaseous and / or liquid fuel is injected as a secondary flow into a gaseous, channeled main flow, the secondary flow being a much smaller one Mass flow has as the main flow and the flow through the premixing channel has curved walls. In one embodiment, the channel is ring-shaped and an equal number of vortex generators are strung together in the circumferential direction on the outer and inner ring wall.

These vortex generators have three freely flowing surfaces that extend in the direction of flow, one of which forms the roof and the other two the side surfaces. The side surfaces are flush with the same duct wall and enclose an arrow angle α with one another. The roof surface lies with an edge selling transversely to the flow channel against the same channel wall as the side surfaces and the longitudinal edges of the roof surface, which are flush with the longitudinal edges of the side surfaces projecting into the flow channel, run at an angle of attack Θ to the channel wall. Half vortex generators are also possible, in which only one of the two side surfaces of the vortex generator is provided with an arrow angle α / 2, while the other side surface is aligned straight and in the direction of flow. The connecting edges of two opposing vortex generators can lie on the same radial or be offset by half a division.

With this known fuel supply system according to EP 0 619 456 A1 it is achieved that combustion air and fuel are intimately mixed over a very short distance and at the same time a uniform speed distribution is achieved in the mixing zone. However, statements regarding the achievement of sufficient flame stability are missing here. Since this fuel supply system is used for a self-igniting combustion chamber, flame stabilization is not necessary in this case either.

Presentation of the invention

The invention has for its object to develop a premix burner for the combustion of gaseous and / or liquid fuel, with which extremely low NOx emissions are achieved, the burner should be characterized by a simple geometry and a reliable operating behavior. In the burner, an intimate mixture of combustion air and fuel is to be achieved within a very short distance, with a simultaneous uniform distribution of speed in the mixing zone, and furthermore, with such a burner, a blowback of the flame is to be avoided with certainty without the use of a mechanical flame holder.

This is achieved according to the invention in a premix burner according to the preamble of claim 1, which works with a fuel supply system which is known from EP 0 619 456 A1, in that the vortex generators used produce vortices which, after the fuel has been mixed with the air the fuel / air mixture flow leave a residual vortex that the annular main flow channel formed by the channel walls has a constant height downstream of the vortex generators and the fuel injection, which is in the range between 5 to 20 times its height and that the annular main flow channel then widens to a circular main flow channel by closing the inner cylinder wall.

The advantages of the invention are that the fuel supply system and the use of the vortex generators on the one hand result in an intensive, complete mixing of fuel and combustion air in a very short mixing section without separation areas and with a uniform speed profile, which is a prerequisite for minimization is the NOx content and, on the other hand, due to the residual vortex generated by the vortex generators, which is still present after mixing in the fuel / air mixture flow, the recirculation zone is positively influenced, which increases the flame stability and the cross-mixing of the various burners improved in an annular combustion chamber. The ring-shaped premix burner according to the invention is furthermore distinguished by a simple geometry and is therefore structurally easy to manufacture.

To form the recirculation zone, which serves as an ignition source for incoming fresh fuel / air mixture, it is also necessary for the inner cylinder to close after a sufficient length of the annular premixing section. This can expediently take place gradually or abruptly, so that the main flow channel either widens gradually or there is a sudden transition from the ring channel to the circular channel. The recirculation zone then forms in a circular cross section.

It is advantageous if "half" vortex generators of the Deltawing type are used, with one vortex generator having three freely flowed surfaces which extend in the direction of flow and one of which forms the roof surface and the other two the side surfaces that the Side surfaces are flush with the same channel wall and one side surface is provided with a half arrow angle, while the other side surface is straight and oriented in the direction of flow, that the roof surface lies with an edge extending transversely to the annular channel through which flow flows, and that the longitudinal edges of the roof surface, which are flush with the longitudinal edges of the side surfaces protruding into the flow channel, extend at an angle of attack to the channel wall.

When using this type of vortex generators, which are strung together in the circumferential direction, the vortexes, which all have the same direction of rotation, combine to form a large rotating vortex.

Finally, vortex generators are advantageously arranged in the premix burner, which have approximately the shape of a right-angled triangle of small thickness, the two triangular side surfaces flowed parallel to one another and together with the roof surface comprising the connecting surface, the roof surface with an edge and the connecting surface with one edge touch the same duct wall as the two side walls.

If these vortex generators are evenly distributed over the circumference of the two cylinder walls, in such a way that two opposing vortex generators are each offset by half a division, then the direction of swirl on the opposing vortex generators is the same and the main flow gets a very large one Swirl imposed, which is sufficient for a complete mixture with the fuel, but also provides a residual vortex for flame stabilization.

Further advantages of the invention emerge from the subclaims.

Brief description of the drawing

Several exemplary embodiments of the invention are shown schematically in the drawing.

Fig. 1

einen Längsschnitt eines erfindungsgemässen Vormischbrenners;

Fig. 2

einen Teillängsschnitt einer zweiten Ausführungsvariante des Vormischbrenners;

Fig. 3

einen Teillängsschnitt einer dritten Ausführungsvariante des Vormischbrenners;

Fig. 4

eine perspektivische Darstellung eines "halben" Wirbel-Generators des Delta-Flügel-Typs;

Fig. 5

eine perspektivische Darstellung einer anderen Ausführungsvariante des Wirbel-Generators;

Fig. 6

eine perspektivische Darstellung einer weiteren Ausführungsvariante des Wirbel-Generators;

Fig. 7

eine Anordnungsvariante der Wirbel-Generatoren nach Fig. 4 im Ringkanal;

Fig. 8

eine weitere Anordnungsvariante der Wirbel-Generatoren nach Fig. 4 im Ringkanal;

Fig. 9

eine Anordnungsvariante der Wirbel-Generatoren nach Fig. 6 im Ringkanal;

Fig. 10

eine Anordnungsvariante der Wirbel-Generatoren nach Fig. 5 im Ringkanal.

Show it:

Fig. 1

a longitudinal section of a premix burner according to the invention;

Fig. 2

a partial longitudinal section of a second embodiment of the premix burner;

Fig. 3

a partial longitudinal section of a third embodiment of the premix burner;

Fig. 4

a perspective view of a "half" vortex generator of the delta wing type;

Fig. 5

a perspective view of another embodiment of the vortex generator;

Fig. 6

a perspective view of another embodiment of the vortex generator;

Fig. 7

an arrangement variant of the vortex generators according to Figure 4 in the ring channel.

Fig. 8

a further arrangement variant of the vortex generators according to Figure 4 in the ring channel.

Fig. 9

an arrangement variant of the vortex generators according to Figure 6 in the ring channel.

Fig. 10

a variant of the arrangement of the vortex generators according to FIG. 5 in the ring channel.

Only the elements essential for understanding the invention are shown. Elements not essential to the invention, for example housings, fastenings and line bushings, are not shown. The direction of flow of the work equipment is indicated by arrows.

Way of carrying out the invention

The invention is explained in more detail below on the basis of exemplary embodiments and FIGS. 1 to 10.

1 shows in a longitudinal section a possible embodiment of the annular premix burner according to the invention. It essentially consists of two cylinders with each other of different diameters, which are arranged concentrically to one another, so that the inner cylinder wall 21a and the outer cylinder wall 21b delimit an annular channel 20. Vortex generators 9 are arranged in the inlet area of the channel 20, the shape and mode of operation of which are described below. The channel 20 has a constant height H and, downstream of the vortex generators, has a length L which lies in the range between 5 to 20 times its height H and forms the premixing section for combustion air 1 and gaseous fuel 2. Directly downstream of the vortex generators 9, gaseous fuel 2 is injected via pipes 3 via openings 4 in the outer cylinder wall 21b as a secondary flow into the main flow of the ring channel 20 and mixed with the combustion air 1. The introduction of the gaseous fuel 2 could of course also take place on the inner cylinder wall 21a or best on both walls 21a and 21b, as shown in the lower part of FIG. 1.

In the variant shown in FIG. 1, the inner cylinder wall 21a closes gradually after the premixing section, so that the inner cylinder is closed off by a cone tip. The outer cylinder wall 21b initially also narrows in the area of the cone tip before it then encloses a circular cross section in which a recirculation zone is formed, which serves as an ignition source for incoming fresh fuel / air mixture.

2 shows a further embodiment variant of the annular premix burner. In contrast to Fig. 1, the inner cylinder suddenly closes here after a sufficiently long premixing section (length L is approximately 5 to 20 times the channel height H), so that the transition from the ring channel 20 to the circular channel in which the Recirculation zone 22 forms, takes place abruptly. The gaseous fuel 2 is in this case through openings on the inner and outer cylinders directly downstream of the vortex generators 9, annular fuel supply lines 5 are introduced as a secondary flow into the main flow swirled by the vortex generators and mixed intensively with the air.

3 shows a third variant of the premix burner. As in the examples above, vortex generators 9 are also arranged in the annular channel 20, via which the air 1 is guided and swirled as the main flow before gaseous fuel is injected immediately downstream of the vortex generators 9. To increase the vortex effect, 9 deflection vanes 8 are arranged in the annular channel 20 upstream of the vortex generators. The same effect can be achieved if the main flow enters the annular space into the annular space 20 via tangential slots (not shown here) and thereby receives a tangential velocity component. The inner cylinder also closes gradually here, but not to a cone tip, but to a hemisphere. In the inner cylinder, lines 6 are arranged for the supply of liquid fuel 7, which is injected into the circular cross section of the burner at the end of the premixing section for the combustion air 1 and the gaseous fuel 2 from nozzles arranged in the hemispherical end of the inner cylinder.

Of course, in another embodiment variant, not shown in the drawing, instead of injecting gaseous fuel 2 into the ring channel 20, liquid fuel 7 can also be introduced, for example via a fuel lance, and mixed with the air swirled by the vortex generators in the annular space 20.

The vortex generators 9 installed in the ring channel 20 can have different shapes. It is essential for the invention that they produce longitudinal vortices without a recirculation area and thereby enable a complete mixing of the fuel with the combustion air within a very short distance, on the other hand after the mixing a residual vortex remains in the flow, which is present along the wake of the inner cylinder. This residual vortex influences the recirculation zone and ensures high flame stability on the one hand and good cross-mixing of the various burners in the ring combustion chamber on the other.

The vortex generators 9 shown schematically in the above exemplary embodiments are half delta wings, i.e. (see FIG. 4) that a vortex generator 9 has three freely flowing surfaces 10, 11, 12, which extend in the direction of flow and one of which forms the roof surface 10 and the other two the side surfaces 11, 13, that the side surfaces 11 , 13 are flush with the same channel wall 21 and one side surface 11 is provided with an arrow angle α / 2, while the other side surface 13 is straight and oriented in the flow direction, that the roof surface 10 with an edge 15 running transversely to the channel 20 through which flow flows same channel wall 21 as the side surfaces 11, 13, and that the longitudinal edges 12, 14 of the roof surface 10, which are flush with the longitudinal edges of the side surfaces 11, 13 projecting into the flow channel 21, extend at an angle of attack Θ to the channel wall 21. The two side surfaces 11, 13 comprise a connecting edge 16 with one another which, together with the longitudinal edges 12, 14 of the roof surface 10, forms a tip 18, the connecting edge running in the radial direction of the curved channel wall 21. The connecting edge 16 and / or the longitudinal edges 12, 14 of the roof surface 10 are at least approximately sharp.

The actual channel, through which a main flow symbolized by a large arrow flows, is not shown in FIGS. 4 to 6.

It is advantageous if the connecting edge 16 of the vortex generators 9 described in FIG. 4 forms the downstream edge of the vortex generator 9 and the edge 15 of the roof surface 10 which runs transversely to the channel 20 through which flow flows is the edge first acted upon by the main flow because the vortex can build up particularly well.

The vortex generator works as follows: When flowing around the edge 14 of the side surface 11 provided with the half arrow angle α / 2, the main flow is converted into a vortex, the axis of which lies in the axis of the main flow. No swirl is generated on the straight side surface 13, which is oriented in the direction of flow of the main flow, so that a swirl is forced on the flow and no swirl-neutral field is present. If the fuel is introduced into the main flow as a secondary flow immediately downstream of the vortex generators 9, the combustion air 1 and the fuel 2 are mixed intensively.

5 shows a further embodiment of a vortex generator 9a, which can be used for the premix burner according to the invention. The vortex generator 9a has approximately the shape of a right-angled triangle of small thickness, the two triangular side surfaces 11, 13 around which flow flows parallel to one another and together with the roof surface 10 comprise the connection surface 19, the roof surface 10 with an edge 15 and the connection surface 19 rest with an edge 17 on the same duct wall as the two side walls 11, 13 and the side surfaces 11, 13 form an angle β with the main flow direction of the incoming air. The roof surface 10 can also be concave or convex curved. In comparison to vortex generators 9a with a straight roof surface, this has the advantage that the same vortex strength is generated with a lower pressure drop can. Another advantage of the vortex generators 9a is that they can be manufactured extremely simply, for example by punching out thin sheets. Since the width of the roof surface 10 in the vortex generators 9a is extremely small, the vortex formation practically only occurs on one side and a very large vortex is formed which has a positive influence on the fuel / air mixture formation.

FIG. 6 shows a modified embodiment of the vortex generator 9a shown in FIG. 5, in which the two side surfaces 11 and 13 do not have the shape of a right-angled triangle, but are trapezoidal. These vortex generators 9a are also outstandingly suitable for generating vortexes.

FIGS. 7 to 10 show different arrangement variants of the vortex generators 9 and 9a in the ring channel 20 of the premix burner.

In FIG. 7, vortex generators 9 according to FIG. 4 are arranged both on the inner cylinder wall 21a and on the outer cylinder wall 21b. They have a height h that fills almost the entire duct height H.

In FIG. 8, the vortex generators 9, which are arranged on the inner cylinder wall 21a, are smaller than those arranged on the outer wall 21b, their height h is only approximately H / 2, while the height h of the outer vortex generators 9 is equal to the channel height H. The use of vortex generators 9 of different geometry creates vortices of different strengths, which has a favorable effect on the residual vortices required for flame stabilization.

FIG. 9 shows an arrangement of vortex generators 9a with a geometry according to FIG. 6. Their height h corresponds to the channel height H, ie they fill the entire channel height H. Of the flattened part of the roof surface 13 adjoins the inner cylinder wall 21a. The resulting vortices are marked with arrows.

Finally, FIG. 10 shows an arrangement variant of the vortex generators 9a according to FIG. 5 in the ring channel 20. The vortex generators 9a are arranged on the inner cylinder wall 21a as well as on the outer cylinder wall 21b, for example welded on. Two opposite vortex generators 9a are each offset by half a pitch to one another in the circumferential direction, so that the swirl direction outside and inside is the same and the vortexes add up as desired to form a large vortex that is both sufficient for the complete mixing of air and fuel also subsequently contributes to flame stabilization as a residual vortex.

The premix burner is also ideally suited for operation at partial load because the geometry of the burner makes it easy to inject pilot gas or secondary gas directly into the recirculation zone. This increases the stability limit of the burner.

There is no possible risk of kickback in the burner according to the invention, since high flow velocities prevail in the mixing zone and no recirculation areas are generated in the mixing zone by the choice of the vortex generator type described above. It is also possible without any problems to operate an annular combustion chamber with several premix burners according to the invention.

Reference list

1

Combustion air

2nd

fuel

3rd

Pipeline

4th

Opening in pos. 21

5

Loop

6

Liquid fuel line

7

liquid fuel

8th

Deflector blade

9.9a

Vortex generator

10th

Roof area

11

Side surface

12th

Long edge

13

Side surface

14

Long edge

15

transverse edge of item 10

16

Connecting edge

17th

Edge of 19th

18th

top

19th

Interface

20th

Ring channel

21a, b

Cylinder wall

22

Recirculation zone

α

Arrow angle

β

Angle between the main flow direction and item 13

Θ

Angle of attack

H

Height of pos. 9, 9a

H

Height of item 20

L

Length of item 20

Claims (17)

Premix burner for the combustion of gaseous and / or liquid fuel, the premix burner working with a fuel supply system in which the fuel is injected as a secondary flow into a gaseous, channeled main flow, the secondary flow having a substantially smaller mass flow than the main flow, the premix channel through which the fuel flows (20) is annular and is delimited by an inner (21a) and an outer cylinder wall (21b) and the main flow is conducted via vortex generators (9, 9a), which produce longitudinal vortices without a recirculation area, of which the circumference of the Ring channel (20) on at least one channel wall (21) are arranged next to one another, and means for fuel injection are arranged immediately downstream of the vortex generators (9, 9a) on the inner and / or outer channel wall (21a, 21b) featured, - that the vortex generators (9, 9a) produce vortices which, after the fuel has been completely mixed with the air, leave a residual vortex in the fuel / air mixture flow, - That the annular main flow channel (20) formed by the channel walls (21a 21b) with a constant height (H) has a length (L) downstream of the vortex generators (9) and the fuel injection, which is in the range between the 5th to 20th -fold its height (H) and - That the annular main flow channel (20) then by closing the inner cylinder wall (21a) expanded into a circular main flow channel. Premix burner according to claim 1, characterized in that the main flow channel gradually widens. Premix burner according to claim 1, characterized in that the main flow channel increases by leaps and bounds. Premix burner according to claim 1, characterized in that - that a vortex generator (9) has three freely flowing surfaces (10, 11, 12) which extend in the direction of flow and one of which forms the roof surface (10) and the other two the side surfaces (11, 13), - That the side surfaces (11, 13) are flush with the same channel wall (21) and one side surface (11) is provided with a half arrow angle (α / 2), while the other side surface (13) is aligned straight and in the direction of flow, - That the roof surface (10) lies with an edge (15) running transversely to the channel (20) through which it flows, on the same channel wall (21) as the side surfaces (11, 13), - And that the longitudinal edges (12, 14) of the roof surface (10) which are flush with the longitudinal edges of the side surfaces (11, 13) protruding into the flow channel (21) at an angle of attack (Θ) to the channel wall (21) . Premix burner according to claim 4, characterized in that the two side surfaces (11, 13) comprise a connecting edge (16) which together with the longitudinal edges (12, 14) of the roof surface (10) forms a tip (18), and that the connecting edge runs in the radial of the curved channel wall (21). Premix burner according to claim 4, characterized in that the connecting edge (16) and / or the longitudinal edges (12, 14) of the roof surface are at least approximately sharp. Premix burner according to Claim 6, characterized in that the connecting edge (16) forms the downstream edge of the vortex generator (9) and the edge (15) of the roof surface (10) which runs transversely to the channel (20) through which the flow flows first Edge is. Premix burner according to claim 1, characterized in that the vortex generators (9a) have approximately the shape of a right-angled triangle of small thickness, the two triangular side surfaces (11, 13) around which flow and run parallel to one another and together with the roof surface (10) the connecting surface ( 19), the roof surface (10) with an edge (15) and the connecting surface (19) with an edge (17) abutting the same channel wall as the two side walls (11, 13) and the side surfaces (11, 13) form an angle (β) with the main flow direction of the incoming air. Premix burner according to claim 8, characterized in that the side surfaces (11, 13) of the vortex generators (9a) are trapezoidal. Premix burner according to claim 8, characterized in that the roof surface (10) is convex or concave. Premix burner according to claim 8 or 9, characterized in that the connecting surface (19) forms the downstream surface of the vortex generator (9a) and the The edge (15) of the roof surface (10) which runs transversely to the channel (20) through which the flow flows is the edge which is first acted upon by the main flow. Premix burner according to one of claims 4, 8 or 9, characterized in that the height (h) of the vortex generator (9, 9a) corresponds to the height (H) of the channel (20). Premix burner according to claim 4 or 9, characterized in that an equal number of vortex generators (9, 9a) are arranged on the inner channel wall (21a) and on the outer channel wall (21b), two opposite vortex generators (9 , 9a) are arranged offset by half a division. Premix burner according to claim 4 or 9, characterized in that an equal number of vortex generators (9, 9a) are arranged on the inner duct wall (21a) and on the outer duct wall (21b), the inner and outer vortex generators (9, 9a) have a different geometry. Premix burner according to claim 1, characterized in that gaseous fuel is supplied via openings in the inner and / or outer channel wall (21a, 21b) downstream of the vortex generators (9, 9a). Premix burner according to claim 1, characterized in that liquid fuel is injected via a lance arranged downstream of the vortex generators (9, 9a). Premix burner according to claim 15 or 16, characterized in that liquid fuel is additionally injected at the end of the inner cylinder.

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