EP0730121A2 - Premix burner - Google Patents

Abstract

The burner (1) has a combustion chamber (16) which is supplied with air by a tubular channel (3), and has radial nozzles (5,12) for supplying a liquid (12a) or gaseous (5a) fuel. Turbulence generators (4,200) are arranged inside the channel, in order to induce a rotational flow in the airstream. The nozzles work in combination with at least one of the generators, in order to create an evaporation region (6) which extends up to the combustion front (9) in the burner. The region may also have a curvature (13) in an axial plane, which projects in a radial direction with respect to the combustion chamber.

Description

Technical field

The present invention relates to a premix burner according to the preamble of claim 1. It also relates to a method for operating such a premix burner.

State of the art

• 1. Indem der Teillastbereich dem tiefsten Premix-Betriebspunkt entspricht, was bei atmosphärisch betriebenen Brennern mit Rauchgasrezirkulation der Fall ist;
• 2. Indem im Teillastbereich Brennstoff über die Kopfstufe (Brennerachse) beigemischt wird, was bei Gasturbinenbetrieb zur Anwendung gelangt.

From EP-0 321 809 a burner has become known which permits premix-like combustion and which also has a number of advantages which are described in detail in this document. This burner essentially consists of at least two hollow, conical, nested partial bodies in the flow direction, the respective longitudinal axes of symmetry of which are offset from one another, in such a way that the adjacent walls of the partial bodies in their longitudinal extension form tangential channels for the inlet of a combustion air stream into the burner. A liquid fuel is preferably injected into the cavity formed by the partial bodies via a central nozzle, while a gaseous fuel is injected through the further nozzles in the area of the tangential channels in the longitudinal direction is introduced. With this burner, flame stabilization in "premix mode" results from the increase in swirl along the cone body. At the burner outlet, where the critical number of swirls is intended, combined with the sudden cross-sectional expansion due to the combustion chamber, this leads to a backflow zone, also called a backflow bubble, on the burner axis. The ignition is initiated at their stagnation point. In the partial load range, with certain constellations, inadequacies regarding flame stabilization can arise. The occurrence of such shortcomings is solved in this burner in two ways:

• 1. By the part load range corresponds to the lowest premix operating point, which is the case with atmospheric burners with flue gas recirculation;
• 2. By adding fuel via the head stage (burner axis) in the partial load range, which is used in gas turbine operation.

However, both solutions are not always satisfactory, since either (1) the pressure drop across the burner can increase with the load, or (2) the NOx emissions can increase due to the transition from premix to diffusion mode. In addition, about 2% of the air is still required to cool the burner front in the burner mentioned. This air is only introduced into the combustion chamber or into the combustion chamber in the area of the flame and thus mixes only incompletely with the previously injected fuel. This increases the flame temperature by approx. 20 ° C: There is therefore a latent danger that NOx emissions could increase as a result. Furthermore, it must be taken into account that the burner should also be operated with a liquid fuel in premix mode without having to accept higher pollutant emissions values.

Presentation of the invention

The invention seeks to remedy this. The invention, as characterized in the claims, is based on the object of proposing a configuration for a premix burner and a method of the type mentioned at the outset, which can produce the same depth of pollutant emissions when operated with both liquid and gaseous fuels. Furthermore, it is an object of the invention to maximize the operational reliability of the premix burner.

The main advantage of the invention can be seen in the fact that the burner can be operated in premix mode with both liquid and gaseous fuels without changing its structure under extremely low emission values. It is therefore possible to change the fuel type as required during operation without having to intervene in the configuration of the burner.

Another advantage of the invention is that the cooling of the thermally highly loaded front wall of the burner, hereinafter referred to as the burner front, and its surroundings is accomplished by a cooling air stream flowing along the loaded walls, such that even in the event of a flashback of the flame inside the flame the burner cannot be destroyed.

The burner has a simple geometric shape, and the length of the evaporation and mixing section can be selected accordingly. After the fuel has been added, there are no internals in the flow field, which means that the flow can be optimally guided. Because the evaporation and mixing section can be freely selected, it can also be provided with a radial deflection which takes the mixing zone away from the direct flame radiation.

Advantageous and expedient developments of the task solution according to the invention are characterized in the further dependent claims.

Exemplary embodiments of the invention are explained in more detail below with reference to the figure. All elements not necessary for the immediate understanding of the invention have been omitted. The direction of flow of the media is indicated by arrows. Identical elements are provided with the same reference symbols in the various figures.

Brief description of the drawings

Fig. 1

einen Vormischbrenner von ringförmiger Form,

Fig. 2

eine perspektivischer Darstellung eines Wirbel-Generators,

Fig. 3

eine Ausführungsvariante des Wirbel-Generators,

Fig. 4

eine Anordnungsvariante des Wirbel-Generators nach Fig. 3,

Fig. 5

einen Wirbel-Generator im Vormischkanal und

Fig. 6-12

Varianten der Brennstoffzufhrung im Zusammenhang mit Wirbel-Generatoren.

It shows:

Fig. 1

a premix burner of an annular shape,

Fig. 2

a perspective view of a vortex generator,

Fig. 3

a variant of the vortex generator,

Fig. 4

3 shows a variant of the arrangement of the vortex generator according to FIG. 3,

Fig. 5

a vortex generator in the premixing channel and

Fig. 6-12

Variants of fuel supply in connection with vortex generators.

Ways of carrying out the invention, commercial usability

The figure shows a rotationally symmetrical premix burner 1, as can be seen from the central axis 14. The premix burner 1 can, however, also consist of a single tube, or a plurality of tubes can be arranged in a ring around the central axis 14. This premix burner 1 is characterized, inter alia, in the area of the burner front 9 by an inflow channel 8 running radially and in the circumferential direction. Cooling air 7 flows through this inflow duct 8 and continuously cools said burner front 9. The cooling air flow is then continued by a deflection along the outer shell of the premix burner 1. After the cooling process has ended, the cooling air mentioned is preferably introduced into the premix burner 1 at a suitable point. The cooling provided here is in itself a convective cooling system, the tube guide of the premix burner 1 being readily perforated in the circumferential direction and axially, with the result that effusion cooling or. film cooling comes into play. At the beginning of the premix burner 1, swirl bodies 200, hereinafter referred to as vortex generators, are provided, which impose a swirl on the incoming combustion air 2. The design of these vortex generators 200 is discussed in more detail in FIGS. 2-12. This combustion air 2 can be fresh air or a mixture formed with recirculated flue gas, both the fresh air and the mixture optionally being enriched with a fuel. Furthermore, the combustion air 2 can also be pretreated, depending on the type of operation. The actual fuel injection into the premix burner 1 takes place downstream of the vortex generators 200 mentioned. When the premix burner 1 is operated with a liquid fuel 12a, at least one fuel nozzle 12, which is preferably designed as an atomizing nozzle, is arranged in the throughflow channel. Immediately upstream of this fuel nozzle 12 is at least one further swirl generator 4 arranged, which is flowed through axially, radially or at a certain angle compared to the fuel injection immediately downstream. The liquid fuel 12a provided by the fuel nozzle 12 is continuously driven in by the combustion air flow directed due to the design of the swirl generator 4, in such a way that fine atomization of the liquid fuel 12a with droplet sizes <20 μm is produced. The swirl generator 4 mentioned, wherein several can also be arranged on the inner outer wall of the flow cross-section, can have the shape of a vane grille over the circumference or a correspondingly modified shape of the burner recognized in the foregoing according to EP-0 321 809. Of course, these swirl generators 4 can be constructed using the technique of vortex generators 200. The vortex generators 200 arranged upstream at the beginning of the premix burner 1 can be dispensed with under certain circumstances, it being noted that in normal operation they improve the subsequent process by accelerating the combustion air 2 there. These vortex generators 200 are placed differently within the inflow zone 3 around the inner and outer channel wall 17 of the flow cross section. On the outflow side of the atomization of the input liquid fuel 12a taking place due to the interdependence of fuel nozzle 12 and swirl generator 4, a sufficiently long evaporation section 6 should be provided so that the gasification of the liquid fuel 12a is completed before reaching the burner front 9. The cross-sectional area of the premix burner is preferably kept constant from the swirl body 4 to the end of the hub body, that is to say in the area of the burner front 9, after which a vortex burst is achieved by a diffuser-like expansion and additionally by a sudden expansion to the cross-section 10 of the combustion chamber 16. The backflow zone 11 that results from this enables the premix burner 1 to be operated even under very low fuel conditions. For the business The premix burner 1 is supplemented with a gaseous fuel 5a in the circumferential direction and downstream of the swirl generator 4, which is now arranged around the inner wall of the flow cross-section, with a series of injection lances 5, preferably with a corresponding fuel injection for each swirl generator 4, this by the desired fuel ratio to each Achieve longitudinal vertebrae better. For operation in low partial load, additional fuel nozzles 15 for a liquid and / or gaseous fuel 12a, 5a can be provided at the end of the hub body. In general, it can be said that the premix burner 1 can also be operated in dual mode. Downstream of the main fuel injectors 12a, 5a, the cross-sectional guide of the premix burner 1 has a radial deflection in the sense of a bulge 13, which prevents the flame radiation from acting on the fuel spray and igniting it. Since the fuel nozzle 12 is operated in the arrangement described with a very high mass flow ratio, the required degree of gasification of the liquid fuel 12a can be easily achieved.

The actual inflow zone 3 is not shown in FIGS. 2, 3 and 4. In contrast, the flow of the combustion air 2 is shown by an arrow, which also specifies the direction of flow. According to these figures, a vortex generator 200, 201, 202 essentially consists of three freely flowing triangular surfaces. These are a roof surface 210 and two side surfaces 211 and 213. In their longitudinal extent, these surfaces run at certain angles in the direction of flow. The side walls of the vortex generators 200, 201, 202, which preferably consist of right-angled triangles, are fixed with their long sides on the channel wall 17 already mentioned, preferably gas-tight. They are oriented so that they form a joint on their narrow sides, including an arrow angle α. The joint is designed as a sharp connecting edge 216 and is perpendicular to each channel wall 17 with which the side surfaces are flush. The two side surfaces 211, 213 including the arrow angle α are symmetrical in shape, size and orientation in FIG. 4, they are arranged on both sides of an axis of symmetry 217 which is oriented in the same direction as the channel axis.
The roof surface 210 lies with a very narrow edge 215 running transversely to the channel through which it flows and on the same channel wall 17 as the side surfaces 211,. 213. Their longitudinal edges 212, 214 are flush with the longitudinal edges of the side surfaces 211, 213 projecting into the flow channel. The roof surface 210 extends at an angle of inclination Θ to the channel wall 17, the longitudinal edges 212, 214 of which, together with the connecting edge 216, form a point 218. Of course, the vortex generator 200, 201, 202 can also be provided with a bottom surface with which it is fastened in a suitable manner to the channel wall 17. Such a floor area is, however, unrelated to the mode of operation of the element.

The mode of operation of the vortex generator 200, 201, 202 is as follows: When flowing around the edges 212 and 214, the main flow 2 is converted into a pair of opposing vortices, as is schematically outlined in the figures. The vortex axes lie in the axis of this main flow. The number of swirls and the location of the vortex breakdown (return flow zone = vortex breakdown), if the latter is aimed for, are determined by a corresponding choice of the angle of attack Θ and the arrow angle α. With increasing angles, the vortex strength or the number of swirls is increased, and the location of the vortex bursting shifts upstream into the region of the vortex generator 200, 201, 202 itself. Depending on the application, these two angles Θ and α are due to structural conditions and determined by the process itself. These vortex generators only have to be adjusted with regard to Length and height, as will be detailed below in FIG. 5.

In FIG. 2, the connecting edge 216 of the two side surfaces 211, 213 forms the downstream edge of the vortex generator 200. The edge 215 of the roof surface 210 running transversely to the flow through the channel is thus the edge which is first acted upon by the channel flow.

FIG. 3 shows a so-called half "vortex generator" based on a vortex generator according to FIG. 2. In the vortex generator 201 shown here, only one of the two side surfaces is provided with the arrow angle α / 2. The other side surface is straight and oriented in the direction of flow. In contrast to the symmetrical vortex generator, only one vortex is generated on the arrowed side, as is shown in the figure. Accordingly, there is no vortex-neutral field downstream of this vortex generator, but a swirl is forced on the flow.

FIG. 4 differs from FIG. 2 in that the sharp connecting edge 216 of the vortex generator 202 is the point which is first acted upon by the channel flow. The element is therefore rotated by 180 °. As can be seen from the illustration, the two opposite vortices have changed their sense of rotation.

5 shows the basic geometry of a vortex generator 200 installed in a channel 3. As a rule, the height h of the connecting edge 216 will be coordinated with the channel height H, or the height of the channel part which is assigned to the vortex generator that the vortex generated immediately downstream of the vortex generator 200 already reaches such a size that the full channel height H is filled. This leads to a uniform speed distribution in the cross-section applied. A Another criterion that can influence the ratio of the two heights h / H to be selected is the pressure drop that occurs when the vortex generator 200 flows around. It goes without saying that the pressure loss coefficient also increases with a larger ratio h / H.

The vortex generators 200, 201, 202 are mainly used when it comes to mixing two flows. The main flow 2 attacks the transverse edge 215 or the connecting edge 216 in the direction of the arrow. The secondary flow in the form of a gaseous and / or liquid fuel, which is possibly enriched with a portion of supporting air, has a substantially smaller mass flow than the main flow. In the present case, this secondary flow is introduced into the main flow downstream of the vortex generator, as can be seen particularly well from FIG. 1.

The vortex generators 200 are distributed at a distance from one another over the outer and inner wall of the channel 3. Of course, the vortex generators can also be lined up in the circumferential direction so that no gaps are left on the channel wall 17. The vortices to be generated are ultimately decisive for the choice of the number and the arrangement of the vortex generators.

FIGS. 6-12 show further possible forms of introducing the fuel into the main combustion air flow 2. These variants can be combined in a variety of ways with one another and with a central fuel injection.

In FIG. 6, in addition to channel wall bores 220, which are located downstream of the vortex generators, the fuel is also injected via wall bores 221, which are located directly next to the side surfaces 211, 213 and in their longitudinal extent are in the same channel wall 17 on which the vortex generators are arranged. The introduction of the fuel through the wall bores 221 gives the generated vortices an additional impulse, which extends the lifespan of the vortex generator.

7 and 8, the fuel is injected via a slot 222 or via wall bores 223, both precautions being located directly in front of the edge 215 of the roof surface 210 running transversely to the flow channel and in the longitudinal extension thereof in the same channel wall 17 on which the Vortex generators are arranged. The geometry of the wall bores 223 or of the slot 222 is selected such that the fuel is introduced into the main flow 2 at a certain injection angle and largely shields the subsequently placed vortex generator as a protective film against a now hot main flow 2 by flow around it.

In the examples described below, the secondary flow (cf. above) is first introduced into the hollow interior of the vortex generators via guides (not shown) through the channel wall 17. This creates an internal cooling facility for the vortex generators without providing any additional equipment.

In FIG. 9, the fuel is injected via wall bores 224, which are located inside the roof surface 210 directly behind and along the edge 215 running transversely to the flow channel. The vortex generator is cooled more externally than internally. The emerging secondary flow forms when flowing around the roof surface 210 a protective layer shielding against a possibly hot main flow 2.

In FIG. 10, the fuel is injected via wall bores 225, which are staggered within the roof surface 210 along the line of symmetry 217. With this variant the channel walls 17 are particularly well protected from a possibly hot main flow 2, since the fuel is first introduced on the outer circumference of the vortex.

11, the fuel is injected via wall bores 226, which are located in the longitudinal edges 212, 214 of the roof surface 210. This solution ensures good cooling of the vortex generators, since the fuel escapes from its extremities and thus completely flushes the inner walls of the element. The secondary flow is fed directly into the resulting vortex, which leads to defined flow conditions.

In FIG. 12, the injection takes place via wall bores 227, which are located in the side surfaces 211 and 213, on the one hand in the area of the longitudinal edges 212 and 214, and on the other hand in the area of the connecting edge 216. This variant is similar in effect to that from FIG. 6 (bores 221 ) and from Fig. 11 (bores 226).

Reference list

1

Premix burner

2nd

Combustion air, main flow

3rd

Inflow zone

4th

Swirl generator

5

Injection lances

5a

Gaseous fuel

6

Evaporation path

7

Cooling air

8th

Cooling air inflow channel

9

Burner front

10th

Cross section of the combustion chamber

11

Backflow zone

12th

Fuel nozzles

12a

Liquid fuel

13

Bulge

14

Central axis

15

Fuel nozzles

16

Combustion chamber

17th

Canal wall

200, 201, 202

Vortex generators

210

Roof area

211, 213

Side faces

212, 214

Longitudinal edges

215

Transverse edge

216

Connecting edge

217

Axis of symmetry

218

top

220-227

Drilling holes for fuel injection

L, h,

Dimensions of the vortex generator

H

Height of the channel

α

Arrow angle

Θ

Angle of attack

Claims (13)

Premix burner, essentially consisting of at least one axially or quasi-axially extending tubular channel for the supply of combustion air, of means arranged within the tubular channel for generating a swirl flow and of nozzles for introducing a fuel, characterized in that the means for generating a swirl flow in the duct (3) through which the combustion air flows (2) vortex generators (4, 200, 201, 202) are such that the premix burner (1) has radially arranged nozzles (5, 12) for introducing a liquid (12a) or Gaseous (5a) fuel that the nozzles (5, 12) are operatively connected to at least one vortex generator (4, 200, 201, 202), that on the outflow side of the nozzles (5, 12) one to the burner front (9) of the premix burner (1) extending evaporation path (6) is present. Premix burner according to claim 1, characterized in that the evaporation section (6) in the axial plane with respect to the combustion chamber (16) has a bulge (13) projecting in the radial direction. Premix burner according to claim 1, characterized in that the evaporation section (6) merges into the combustion chamber (16) with a cross-sectional jump (10). Premix burner according to claim 1, characterized in that the burner front (9) is cooled with cooling air (7). Premix burner according to claim 1, characterized in that the premix burner (1) has an annular flow cross-section. Combustion chamber according to claim 1, characterized in that a vortex generator (200) has three freely flowing surfaces which extend in the direction of flow, one of which forms the roof surface (210) and the other two the side surfaces (211, 213), that the side surfaces (211, 213) are flush with an identical wall segment (17) of the channel (3) and enclose the arrow angle (α) with one another, so that the roof surface (210) has an edge (215) running transversely to the channel (3) through which the flow flows. abuts the same wall segment of the channel (3) as the side surfaces (211, 213), and that longitudinal edges (212, 214) of the roof surface (210) are flush with the longitudinal edges of the side surfaces (211, 213) projecting into the channel (3) ) and are at an angle of attack (Θ) to the wall segment of the channel (3). Combustion chamber according to claim 6, characterized in that the two side surfaces (211, 213) of the vortex generator (200) including the arrow angle (α) are arranged symmetrically about an axis of symmetry (217). Combustion chamber according to Claim 6, characterized in that the two side surfaces (211, 213) including the arrow angle (α, α / 2) comprise a connecting edge (116) which together with the longitudinal edges (212, 214) of the roof surface (210 ) form a tip (218), and that the connecting edge (216) lies in the radial of the circular channel (5). Combustion chamber according to claim 8, characterized in that the connecting edge (216) and / or the longitudinal edges (212, 214) of the roof surface (210) is at least approximately sharp. Combustion chamber according to claims 1, 6 to 8, characterized in that the axis of symmetry (217) of the vortex generator (200) runs parallel to the channel axis, that the connecting edge (216) of the two side surfaces (211, 213) the downstream edge of the vortex Generator (200), and that the edge (215) of the roof surface (210) which runs transversely to the channel (3) through which the flow flows is the edge which is first acted upon by the combustion air (2). Combustion chamber according to claim 1, characterized in that the ratio height (h) of the vortex generator to the height (H) of the channel (3) is selected such that the vortex generated immediately downstream of the vortex generator (200) is the full height ( H) of the channel (3) and the full height (h) of the channel part assigned to the vortex generator (200). A method of operating a premix burner according to claim 1, consisting essentially of at least one axially or quasi-axially extending tubular channel for supplying combustion air, means arranged within the tubular channel for generating a swirl flow and nozzles for introducing a fuel, thereby characterized in that the premix burner is operated with a liquid (12a) or gaseous (5a) fuel, that the nozzle (12) for the liquid fuel (12a) directly with at least one swirl generator (4) to form a minimized atomization of the injected liquid Fuel (12a) operates, that the nozzle (5) for the gaseous fuel (5a) operates with the same and / or further swirl generators (200, 201, 202), that the combustible mixture is optimized via a subsequent evaporation path (6), and that at the end of the premix burner (1) at the transition to the combustion chamber (16) a Rüchström zone (11) forming there stabilizes the flame front. Method according to claim 12, characterized in that the operation of the premix burner (1) in low partial load is maintained by further fuel nozzles (15) arranged within the evaporation path (6).

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