EP0789187A2 - Method and device for fuel combustion - Google Patents

Abstract

In a method and a device for burning fuels in a main flow from combustion air, the combustion air is conducted in a channel (8, 20) over at least one delta-shaped body (40). The delta-shaped body consists of at least one essentially triangular vortex generator region (1) and a trapezoidal flame stabilization region (3) located downstream. In the region of the vortex generator area (1), fuel is introduced into the swirled combustion air. The vortex generator area (1) is adjusted by means of a half arrow angle (Φ1) and an angle of attack (α1) in relation to the main flow so that the swirl of the longitudinal vortices induced in the main flow is smaller than the critical swirl for creating a recirculation zone (5). The flame stabilization area (3) is adjusted with respect to the flow by means of a half arrow angle (stell3) and an angle of incidence (α3) such that the swirl of the longitudinal vortices induced in the flow is greater than the critical swirl, which means that each delta-shaped body (40) a pair of dome-shaped recirculation zones (5) are generated and the ignited combustion air / fuel mixture is stabilized. <IMAGE>

Description

Technical field

The invention relates to a method and a device for the combustion of fuels in a main flow from combustion air.

State of the art

Such methods and apparatus are known, for example, from EP-B1-0 321 809. The air is set in rotation by the premix burner designed as a swirl burner, which essentially consists of two conical half-shells. The fuel is blown into the rotating air and mixed there with it. At the burner outlet there is a defined dome-shaped recirculation zone, at the top of which the ignition takes place. The flame itself is stabilized by the recirculation zone in front of the burner without the need for a mechanical flame holder. The thermoacoustic behavior of such burners is stable and they are characterized by a simple and inexpensive construction.

However, some disadvantages can arise, especially when using liquid fuels. The liquid fuel is injected into the combustion chamber with a nozzle usually arranged in the tip of the premix burner. In front The ignition of the atomized fuel makes it difficult to achieve a good mixture of combustion air and fuel, since the fuel does not come into contact with the entire combustion air. When using liquid fuels, this can lead to relatively high exhaust gas emissions, especially to high nitrogen oxide emissions. There may also be pre-ignition near the fuel nozzle or on the half-cones. In the case of rich operation, the burner also exhibits insufficient thermoacoustic behavior.

Presentation of the invention

The invention is based on the object of improving the combustion and reducing the exhaust gas emission in a method and a device for the combustion of fuels in a main flow from combustion air of the type mentioned at the outset.

According to the invention, this is achieved in that the combustion air is conducted in a duct via at least one delta-shaped body, the delta-shaped body consisting of at least one essentially triangular vortex generator area and a trapezoidal flame stabilization area located downstream that in the region of the vortex generator Range fuel is introduced into the swirled combustion air that the vortex generator area is adjusted by means of a half arrow angle and an angle of attack relative to the main flow so that the swirl of the longitudinal vortices induced in the main flow is smaller than the critical swirl to create a recirculation zone that the Flame stabilization area is adjusted by means of a half arrow angle and an angle of incidence in relation to the flow so that the Swirl of the longitudinal vortices induced in the flow is greater than the critical swirl for creating a recirculation zone, which creates a pair of dome-shaped recirculation zones for each delta-shaped body and that the ignited combustion air / fuel mixture is stabilized by the recirculation zones.

A device for carrying out the method is characterized in that a plurality of delta-shaped bodies are arranged in a channel and consist of at least one essentially triangular vortex generator region and a subsequent trapezoidal flame stabilization region located downstream.

The advantages of the invention can be seen, inter alia, in that the various functions, such as premixing and flame stabilization, are spatially divided accordingly by the method and the device. This allows the individual functions to be optimized. The delta-shaped body creates small-scale eddy currents, which means that a very compact design can be achieved. Because of the short mixing and residence times required, this leads to low costs and low emissions, especially nitrogen oxides and carbon monoxide. The structure of a delta-shaped body is also very simple, which further reduces the costs. The mixture of combustion air and fuel is also almost perfect and can be achieved with minimal pressure drops. By forming a pair of counter-rotating recirculation zones per delta-shaped body, the recirculation zones stabilize each other. This minimizes the risk of the flame striking back into the burner and damaging it.

It can be particularly expedient if a further trapezoidal area is arranged between the vortex generator area and the flame stabilization area, which serves as a further mixing and evaporation area. This allows the mixture of combustion air and fuel to be further homogenized.

Brief description of the drawing

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

Fig. 1

eine Draufsicht auf einen deltaförmigen Körper;

Fig. 2

einen Längsschnitt des deltaförmigen Körpers entlang der Linie II-II in Fig.1;

Fig. 3

eine Reihenanordnung der deltaförmigen Körper;

Fig. 4

einen Teillängsschnitt durch einen Kanal mit darin angeordneten deltaförmigen Körpern;

Fig. 5

einen Teilquerschnitt durch den Kanal entlang der Linie V-V in Fig.4;

Fig. 6

eine Draufsicht auf einen Rohrbrenner mit deltaförmigen Körpern;

Fig. 7

eine Draufsicht auf einen Kern-Brenner mit deltaförmigen Körpern und geschichteter Verbrennung.

Show it:

Fig. 1

a plan view of a delta-shaped body;

Fig. 2

a longitudinal section of the delta-shaped body along the line II-II in Fig.1;

Fig. 3

a series arrangement of the delta-shaped bodies;

Fig. 4

a partial longitudinal section through a channel with delta-shaped bodies arranged therein;

Fig. 5

a partial cross section through the channel along the line VV in Figure 4;

Fig. 6

a plan view of a tube burner with delta-shaped bodies;

Fig. 7

a plan view of a core burner with delta-shaped bodies and stratified combustion.

Only the elements essential for understanding the invention are shown.

Way of carrying out the invention

1 and 2 show a premix burner 40, consisting essentially of a delta-shaped body 40 and a fuel injection system 10, 11. The channel arranged around the delta-shaped body 40 and through which a main flow 4 of combustion air, indicated by arrows, flows, is not shown. The delta-shaped body 40 consists of three flat areas 1, 2 and 3, which have the shape of delta wings and is symmetrical with respect to an axis of symmetry 9. The delta-shaped body 40 is made from a heat-resistant material, for example from heat-resistant steel sheet, in accordance with the temperatures occurring.

The first area 1 serves as a vortex generator and as a mixing section and is designed as an equilateral triangle with two side edges 30 and a connecting edge 31. A tip 36 is formed by the two side edges 30. This tip 36 can of course also be designed as a front edge, in which case the first region 1 would be designed as a trapezoid. This vortex generator 1 is defined by means of a half arrow angle Φ1 and by means of an angle of attack α1.

The second area 2 serves as a further mixing and evaporation section. It is designed as an equilateral trapezoid with equally long side edges 32 and connecting edges 31 and 33 and is connected to the area 1 by means of the connecting edge 31. The mixing section 2 is defined by means of a half arrow angle Φ2 and by means of an angle of attack α2.

The third area 3 is used for flame stabilization. It is also designed as an equilateral trapezoid with side edges 34 of equal length, the connecting edge 33 and an edge 35 and is connected to the region 2 by means of the connecting edge 33. The area 3 is defined by a half arrow angle Φ3 and by an angle of attack α3.

Of course, the transitions between the areas 1, 2 and 3, at the connecting edges 31 and 33, can also be made continuously or with jumps. It is essential that the properties of the areas are set by the sweep angle Φi and by an angle of attack αI.

Analogous to EP-B1-0 321 809, a fuel nozzle 10 for injecting liquid or gaseous fuels can now be arranged on the tip 36 formed by the side edges 30 of area 1. To inject gaseous fuel, a fuel line 11 with a plurality of injection openings, not shown, is preferably arranged along the side edges 30. This fuel line can of course also extend over the side edges 32 when using a second region 2.

Due to the geometry of the area 1 of the delta-shaped body 40, the main flow 4 is converted into a pair of opposing longitudinal vortices when it flows around the side edges 30 of the vortex generator 1. The vortex axes of these longitudinal vortexes lie in the axis of the main flow. The swirl number of the longitudinal vortices is set by means of the sweep angle Φ1 and the angle of attack α1 so that no vortex breakdown and thus no dome-shaped recirculation zone 5 occurs. The swirl of the longitudinal vertebrae must therefore be smaller than the critical swirl in which a vertebrae burst entry. With increasing angles Φ1 and α1, the vortex strength or the number of swirls can be increased up to the area of the vortex burst. The swirl of the longitudinal vortices sets the distance required to mix the main flow and the fuel flow.

Area 2 is optional and is only used if the mixing section formed by area 1 is not sufficient for homogeneous mixing. Here, too, longitudinal vortices are induced in the flow by means of the side edges 32. Corresponding to area 1, the swirl number of the longitudinal vertebrae is set by means of the sweep angle Φ2 and the angle of attack α2 so that there is no vortex breakdown and thus no recirculation zone 5.

Of course, further areas corresponding to area 2 can also be connected downstream to area 2 in order to achieve a homogeneous mixture.

The area 3 serves to stabilize the flame by means of the longitudinal vortices generated by the side edges 34. The swirl number of the longitudinal vertebrae is set by the sweep angle Φ3 and the angle of attack α3 so that vortex breakdown occurs. A pair of recirculation zones 5 are created for each delta-shaped body 40. The swirl of the longitudinal vertebrae must be greater than the critical swirl, in which a vertebral burst occurs. The gradient in the swirl number from the upstream region 1 or 2 to the region 3 is chosen to be very large in order to achieve a thermoacoustically stable behavior. To support flame stabilization, the cross-section of the channel, not shown, can also be expanded. The delta-shaped body 40 has a thermo-acoustically stable behavior even when it is operated rich.

3, the delta-shaped bodies 40 can be arranged in rows. The delta-shaped bodies 40 are arranged in large numbers in parallel rows or concentric rings, for example in an annular combustion chamber. Typically, a fuel nozzle 10 is then not attached to each tip 36 of the delta-shaped body 40.

4 and 5, four delta-shaped bodies 40 are arranged in a rectangular channel 8 such that the tips 36 come to lie upstream in the center of the channel 8. The four delta-shaped bodies 40 are connected to one another via their tips 36 and to the channel 8 via their edges 35. At the tip 36 of the delta-shaped body 40 there is a fuel nozzle 10. The fuel is blown into the longitudinal vortices generated in the combustion air 4 when the edges 30, 32 flow around and mixed there with the combustion air. Area 2 is omitted here as a result of sufficient mixing by means of area 1. At the burner outlet 7, the region 3 of the delta-shaped body 40 and a cross-sectional expansion at the burner outlet 7 to form a combustion chamber 6 result in eight dome-shaped recirculation zones 5, at the tip of which the ignition takes place. The flame itself is stabilized by the recirculation zones 5 without the need for a mechanical flame holder. The channel 8 can of course also be made round and the number of delta-shaped bodies 40 per channel 8 is arbitrary and must be adapted to the respective conditions.

6, the delta-shaped bodies 40 are arranged in a round channel 20. The arrangement is analogous to Fig.4 and Fig.5. For this purpose, the delta-shaped bodies 40 must be made curved. Around the round channel 20, mixing tubes 21 are without Flame stabilization arranged. Combustion air is blown through the mixing tubes 21 and fuel is injected into the combustion air via the nozzles 10. For better mixing, well-known mixing elements such as deflecting bodies with a wing profile can be arranged in the mixing tubes 21. Such a burner arrangement is suitable for stepped (lean-lean) and stepped (rich-lean) operation. The number of mixing tubes 21 which are arranged around the channel 20 is arbitrary and must be adapted to the respective conditions.

In FIG. 7, a round delta-shaped body is arranged in a burner system according to WO 92/06328. There, a burner with very low nitrogen oxide emissions is described. At the center of the burner system described there is a fuel-rich flame zone surrounded by one or more zones with a low fuel content. For this purpose, the flame is layered radially, which creates a large radial density gradient in the flame. The fuel-rich zone contains less than the stoichiometric content of oxygen. The radial stratification protects the fuel-rich flame core from mixing with the remaining combustion air. The recirculation of combustion gases into the outer, low-fuel layers can further reduce nitrogen oxide emissions. The recirculated combustion gas reduces the oxygen content and the flame temperature.

An annular channel 20 with delta-shaped bodies 40 arranged therein is surrounded by two concentric, annular channels 22 and 23. A fuel nozzle 10 is arranged at the tip 36 of the delta-shaped bodies. The delta premix burner 40 is now operated stoichiometrically, ie fuel-rich. A possibly swirled exhaust gas / air mixture is fed axially via the concentric channels 22, 23. The number of concentric channels 22, 23 the Channel 20 is arbitrary and must be adapted to the respective conditions.

Of course, the invention is not limited to the exemplary embodiments shown and described. The delta-shaped bodies can also be fastened in the channel in other ways, for example so that the downstream edge of the third region forms a slot with the channel and that the tips do not touch. The delta premix burner can also be installed in any other burner configuration.

Reference list

1

Vortex generator and mixing section

2nd

Mixing and evaporation section

3rd

Flame stabilization

4th

Main flow / combustion air

5

dome-shaped backflow zone

6

Combustion chamber

7

Cross-sectional expansion, burner outlet

8th

channel

9

Axis of symmetry

10th

Fuel nozzle

11

Fuel injection line

20th

round channel

21

Mixing tubes

22, 23

concentric channel

30th

Leading edge

31, 33

Connecting edge

32, 34

Side edge

35

Edge

36

top

40

delta-shaped body

α1, α2, α3

Angle of attack

Φ1, Φ2, Φ3

half arrow angle

Claims (9)

Process for the combustion of fuels in a main flow from combustion air,
characterized,
that the combustion air is conducted in a duct (8, 20) over at least one delta-shaped body (40), the delta-shaped body consisting of at least one essentially triangular vortex generator region (1) and a trapezoidal flame stabilization region (3) located downstream that in the region of the vortex generator area (1), fuel is introduced into the swirled combustion air, that the vortex generator area (1) is adjusted by means of a half arrow angle (hal1) and an angle of incidence (α1) so that the Swirl of the longitudinal vortex induced in the main flow is smaller than the critical swirl for creating a recirculation zone (5) that the flame stabilization area (3) is adjusted with respect to the flow by means of a half sweep angle (Φ3) and an angle of attack (α3) the swirl of the longitudinal vortices induced in the flow is greater than the critical one Swirl to create a recirculation zone (5), which creates a pair of dome-shaped recirculation zones (5) for each delta-shaped body (40) and that the ignited combustion air / fuel mixture is stabilized by the recirculation zones (5). Method according to claim 1,
characterized,
that between the vortex generator area (1) and the flame stabilization area (3) at least one more Trapezoidal area (2) is arranged which serves as a further mixing and evaporation area and is adjusted by means of a half arrow angle (Φ2) and an angle of attack (α2) in relation to the main flow so that the swirl of the longitudinal vortices induced in the flow is smaller than the critical one Swirl. Device for carrying out the method according to claim 1,
characterized,
that a plurality of delta-shaped bodies (40) are arranged in a channel (8, 20) and consist of at least one essentially triangular vortex generator area (1) and a subsequent trapezoidal flame stabilization area (3) located downstream. Device according to claim 3,
characterized,
that at least one further trapezoidal region (2) is arranged between the vortex generator region (1) and the flame stabilization region (3). Device according to claim 3,
characterized,
that a fuel nozzle (10) is arranged on at least one tip (36) formed by the side edges (30) of the vortex generator region (1). Device according to claim 3,
characterized,
that fuel injection lines (11) are arranged on the side edges (30) of the vortex generator area (1). Device according to claim 3,
characterized,
that the delta-shaped bodies (40) are connected to one another via a tip (36) formed by the side edges (30) of the vortex generator region (1) and via a downstream edge (35) of the flame stabilization region (3) to the channel (8, 20 ) are connected. Device according to claim 3,
characterized,
that several mixing tubes (21) are arranged around the channel (8, 20). Device according to claim 3,
characterized,
that at least one concentric channel (22, 23) is arranged around the channel (8, 20).

Images