EP0675322B1 - Premix burner - Google Patents

Description

Technical field

The invention relates to a premix burner, essentially consisting of a pilot burner and several around the Pilot burners arranged around main burners.

State of the art

Both in oil operation at very high pressure and in gas operation with gases with a high hydrogen content it can be used in premix burners occur that the ignition delay times are such in short that flame retardant burners are no more than so-called Low-Nox burners can be used.

The mixing of fuel into one in a premix channel flowing combustion air flow usually happens by means of radial injection of the fuel into the channel Cross jet mixers. The impulse of the fuel is however so low that an almost complete mixing first after a distance of approx. 100 canal heights. Also Venturi mixers are used. The is also known Injection of the fuel via grid arrangements. Finally is also the injection in front of special swirl bodies applied.

That on the basis of cross beams or stratified flows working devices either have very long mixing distances result or require high injection pulses. At Premix under high pressure and substoichiometric Mixing ratios there is a risk of kickback Flame or even self-ignition of the mixture. Flow separation and dead water zones in the premix pipe, thick boundary layers on the walls or possibly extreme speed profiles above the cross-section through which flow can flow be the cause of auto-ignition in the pipe or form paths, through which the flame from the downstream combustion zone can strike back into the premix tube. The geometry The premixing section must therefore be given the highest attention be given as a gift.

The so-called premix burners can be used as flame-holding burners of the double-cone design. Such Double cone burners are for example from EP-B1-0 321 809 are known and will be described later with reference to FIGS. 1 and 3. The fuel, there natural gas, is in the entry columns in the combustion air flowing in from the compressor via a Injected row of injector nozzles. These are in the Usually evenly distributed over the entire gap.

In order to achieve a reliable ignition of the mixture in the downstream combustion chamber and a sufficient burnout, an intimate mixture of the fuel with the air is required. A good mixing also helps to avoid so-called "hot spots" in the combustion chamber, which among other things lead to the formation of the undesired NO _x .

The above-mentioned injection of the fuel over classic Agents such as cross jet mixers are difficult because the fuel itself has an insufficient pulse, the required large-scale distribution and the fine-scale To achieve mixture.

Presentation of the invention

The invention is therefore based on the object Premix burner of the type mentioned at the beginning of a measure create with which within the shortest distance an intimate Mixing of combustion air and fuel is achieved with at the same time even speed distribution in the mixing zone. Furthermore, with such a burner without Kickback using a mechanical flame holder the flame can be avoided with certainty. The measure should also be suitable for existing premix combustion chambers retrofit.

• dass in die, einen kreisförmigen Kanal aufweisenden Hauptbrenner ein gasförmiger und/oder flüssiger Brennstoff als Sekundärströmung in eine gasförmige Hauptströmung eingedüst wird,
• dass die Hauptströmung zunächst über Wirbel-Generatoren geführt wird, von denen über dem Umfang des durchströmten Kanals mehrere nebeneinander angeordnet sind,
• dass stromabwärts der Wirbel-Generatoren eine Venturidüse angeordnet ist,
• und dass die Sekundärströmung im Bereich der grössten Einschnürung der Venturidüse in den Kanal eingeleitet wird.

According to the invention, this is achieved by

• that a gaseous and / or liquid fuel is injected as a secondary flow into a gaseous main flow into the main burner, which has a circular channel,
• that the main flow is initially conducted via vortex generators, of which several are arranged next to one another over the circumference of the flowed-through channel,
• that a Venturi nozzle is arranged downstream of the vortex generators,
• and that the secondary flow in the area of the largest constriction of the Venturi nozzle is introduced into the channel.

With the new static mixer, the 3-dimensional Representing vortex generators, it is possible in the burner extraordinarily short mixing distances with a short one at the same time To achieve pressure loss. By creating longitudinal vortices without a recirculation area is already after one full vortex revolution a rough mixing of the two Currents performed during a fine mix due to turbulent Flow and molecular diffusion processes already after a route that is a few channel heights corresponds.

This type of mixture is particularly suitable for the fuel with a relatively low form and a large dilution to mix into the combustion air. A small form of the fuel is particularly important when using medium and low calorific fuel gases are an advantage. The the energy required for mixing becomes one essential part from the flow energy of the fluid taken from the higher volume flow, namely the combustion air.

The downstream arrangement of a Venturi nozzle behind the Vortex generators have the advantage of being the largest Constriction of the Venturi nozzle a simple means in has the hand to put the fuel in with the smallest back pressure to initiate the swirled flow. The venturi nozzle has with the correct dimensioning, the advantage that the Flow velocity in it the flame velocity exceeds, so the flame does not enter the injection plane of fuel can kick back.

Draw the vortex generators upstream of the Venturi nozzle is characterized by a roof surface and two side surfaces, the side surfaces being flush with an identical duct wall are and include an arrow angle a and the longitudinal edges of the roof surface being flush with the longitudinal ones protruding into the flow channel Edges of the side surfaces and at an angle of attack e run to the canal wall.

The advantage of such vortex generators is in their particular See simplicity in every way. Manufacturing technology is the element consisting of three walls with flow completely without problems. The roof surface can with the two side surfaces can be put together in different ways. Also the fixation of the element on flat or curved ones Canal walls can be made in the case of weldable materials done by simple welds. From the fluidic From a standpoint, the element has a flow around it very little pressure loss and it creates vortexes without Dead water area. Finally, the element can by its usually hollow interior in various ways and be cooled with various means.

It is appropriate to the relationship height h of the connecting edge to choose the two side faces to the duct height H that the vortex generated immediately downstream of the Vortex generator the full channel height or the full height of the channel part assigned to the vortex generator.

It makes sense if the two include the arrow angle α Side surfaces symmetrical about an axis of symmetry are arranged. This makes vortexes of the same twist generated.

If the two side surfaces enclosing the arrow angle α an at least approximately sharp connecting edge form together with the long edges of the roof surface together forms a peak, the flow cross-section hardly affected by blocking.

The sharp connecting edge is the exit-side edge of the vortex generator and it runs perpendicular to that Channel wall, with which the side surfaces are flush, is so the non-formation of a trailing area is an advantage.

If the axis of symmetry is parallel to the channel axis, and the connecting edge of the two side surfaces downstream edge of the vortex generator forms while consequently, the one running across the channel Edge of the roof surface that was first affected by the channel flow Edge, so there are two on a vortex generator the same but opposite vortices are generated. It is a vortex-neutral flow pattern in which the direction of rotation of the two vertebrae ascending in the area of the connecting edge is.

Further advantages of the invention, in particular in connection with the arrangement of the vortex generators and the introduction of the fuel result from the subclaims.

Brief description of the drawing

In the drawing, several embodiments of the Invention shown schematically.

Fig. 1

einen Teillängsschnitt eines Brenners;

Fig. 2

einen Querschnitt durch den Brenner

Fig. 3A

einen Querschnitt durch einen Vormischbrenner der Doppelkegel-Bauart im Bereich seines Austritts;

Fig. 3B

einen Querschnitt durch denselben Vormischbrenner im Bereich der Kegelspitze;

Fig. 4

eine perspektivische Darstellung eines Wirbel-Generators;

Fig. 5

eine Ausführungsvariante des Wirbel-Generators;

Fig. 6

eine Anordnungsvariante des Wirbel-Generators nach Fig. 4;

Fig. 7

einen Wirbel-Generator in einem Kanal;

Fig. 8

eine weitere Ausführungsvariante des Wirbel-Generators;

Fig. 9

eine Anordnungsvariante des Wirbel-Generators nach Fig 8.

Show it:

Fig. 1

a partial longitudinal section of a burner;

Fig. 2

a cross section through the burner

Figure 3A

a cross section through a premix burner of the double cone type in the region of its outlet;

Figure 3B

a cross section through the same premix burner in the region of the cone tip;

Fig. 4

a perspective view of a vortex generator;

Fig. 5

a variant of the vortex generator;

Fig. 6

a variant of the arrangement of the vortex generator according to FIG. 4;

Fig. 7

a vortex generator in a channel;

Fig. 8

a further embodiment of the vortex generator;

Fig. 9

a variant of the arrangement of the vortex generator according to FIG. 8.

It is only essential for understanding the invention Elements shown. The flow direction of the work equipment is marked with arrows. In the different figures are the same elements with the same reference numerals Mistake. Elements not essential to the invention such as Housing, fastenings, cable bushings, fuel supply, the control devices and the like are omitted.

Way of carrying out the invention

1 and 2 with 53 is a cylindrical burner wall designated. It is on the exit side via suitable means with the front wall 100 of the combustion chamber, not shown connected. This combustion chamber can be both an annular combustion chamber or a silo combustion chamber, several such burners each on the front wall 100 are arranged.

Inside the burner wall, the inlet end of which in Fig. 1 is shown in dashed lines, are arranged around a centrally Pilot burner 101 grouped around six main burners 52. The pilot burner is in the example case a premix burner of the double cone type, this is not mandatory. The decisive factor is that this pilot burner should have the smallest possible geometry. In it should about 10-30% of the fuel is burned. The Main burners 52 are cylindrical in shape. At their tubular Wall 54 are initially vortex generators in the direction of flow 9 arranged, the outlet into a Venturi nozzle 50 flows. The fuel is the pilot burner and the Main burners supplied via fuel lances 120 and 51 respectively. The combustion air comes from a not shown Plenum into the interior 103 of the housing, from where they in The direction of the arrow flows into the burners 101, 52.

In the schematically shown premix burner 101 according to the 1, 3A and 3B is a so-called Double cone burner, as for example from EP-B1-0 321 809 is known. It essentially consists of two hollow, conical part-bodies 111, 112, which are in the direction of flow are nested. Here are the respective central axes 113, 114 of the two partial bodies offset against each other. The neighboring walls of the the two partial bodies form tangential lines in their longitudinal extent Slots 119 for the combustion air on this Way into the interior of the burner. There is a first one Fuel nozzle 116 arranged for liquid fuel. Of the Fuel is injected into the hollow cone at an acute angle injected. The resulting tapered fuel profile will enclosed by the combustion air flowing in tangentially. The concentration of the fuel is in the axial direction continuously as a result of mixing with the combustion air reduced. In the example, the burner is also operated with gaseous fuel. For this are in Area of tangential slots 119 in the walls of the longitudinally distributed gas inflow openings 117 provided. The mixture formation begins in gas operation with the combustion air already in the zone of Entry slots 20. It is understood that this way Mixed operation with both types of fuel is also possible is.

At the burner outlet 118, the most homogeneous is possible Fuel concentration above the applied annular Cross section. It arises at the burner outlet a defined dome-shaped backflow zone at the Peak the ignition occurs. So far are double cone burners known from the aforementioned EP-B1-0 321 809.

Before installing the new mixing device in the Main burners 52 is received, the one for Effect of the invention essential vortex generator 9 described.

In Figures 4, 5 and 6 is the actual channel that of flows through a main flow symbolized by a large arrow is not shown. According to these figures a vortex generator consists essentially of three free flowed around triangular surfaces. This is a roof area 10 and two side surfaces 11 and 13. In their longitudinal extent these surfaces run at certain angles in Flow direction.

The side walls of the vortex generator, which are made of rectangular ones Triangles exist with their long sides on fixed a channel wall 21, preferably gas-tight. they are oriented so that they have a bump on their narrow sides form including an arrow angle α. The push is designed as a sharp connecting edge 16 and is vertical to that channel wall 21 with which the side surfaces are flush. The two enclosing the arrow angle α Side surfaces 11, 13 are symmetrical in shape in FIG. 4, Size and orientation and are on both sides of an axis of symmetry 17 arranged. This axis of symmetry 17 is rectified like the channel axis.

The roof surface 10 is transverse to the flow Channel extending and very narrow edge 15 the same channel wall 21 as the side walls 11, 13. Its longitudinal edges 12, 14 are flush with the in longitudinal edges protruding into the flow channel of the side surfaces. The roof area runs under one Angle of attack Θ to the duct wall 21. Your longitudinal edges 12, 14 together with the connecting edge 16 form a tip 18.

Of course, the vortex generator can also be used with a Be provided with the floor surface with which he in a suitable manner is attached to the channel wall 21. Such a floor area has no connection with the mode of action of the element.

4 forms the connecting edge 16 of the two side surfaces 11, 13 the downstream edge of the vortex generator. The edge 15 running transversely to the flowed channel the roof surface 10 is thus the first of the channel flow loaded edge.

The vortex generator works as follows: Flow around the edges 12 and 14 becomes the main flow Pair of opposing vertebrae converted. Whirl axes lie in the axis of the main flow. The swirl number and the Location of vortex breakdown, if the latter is desired at all, will be determined by appropriate Choice of the angle of attack Θ and the arrow angle α. With increasing angles, the vortex strength or the swirl number becomes increases and the location of the vortex burst moves upstream down to the area of the vortex generator itself. Depending on the application, these two angles are Θ and α through constructive conditions and through the process given yourself. Then only the need to be adjusted Length L of the element and the height h of the connecting edge 16 (Fig. 7).

5 is a so-called half "vortex generator" the base of a vortex generator shown in FIG. 1, at which only one of the two side surfaces of the vortex generator 9a is provided with the arrow angle α / 2. The other side surface is straight and aligned in the direction of flow. In contrast to the symmetrical vortex generator only a vortex is created on the arrowed side here. It there is therefore no vortex-neutral downstream of the vortex generator Field ahead, but the flow becomes a swirl imposed.

In contrast to FIG. 4, the sharp connecting edge is in FIG. 6 16 of the vortex generator 9 that position by the channel flow is applied first. The element is rotated by 180 °. As can be seen from the illustration the two opposite vortices changed their sense of rotation.

7, the vortex generators are in a channel 20 built-in. As a rule, one becomes the height h of the connecting edge 16 with the channel height H - or the height of the channel part, which is assigned to the vortex generator - so vote that the vortex generated immediately downstream of the Vortex generator has already reached such a size that the full channel height H is filled. This leads to a uniform speed distribution in the loaded Cross-section. Another criterion which influence can take on the ratio h / H to be selected the pressure drop that flows around the vortex generator occurs. It goes without saying that with a larger ratio h / H also the pressure loss coefficient increases.

In the example shown, four vortex generators are shown in FIG 9 at a distance over the circumference of the circular cross section distributed. The above mentioned amount of Channel part, which is assigned to the individual vortex generator in this case corresponds to the circle radius. Of course could the four vortex generators 9 on their respective wall segments 21 in the circumferential direction lined up so that no gaps in the Canal wall are left free. Ultimately, this is too generating vortices crucial.

The vortex generators 9 are mainly for mixing two currents used. The main flow in the form of Combustion air attacks the transverse ones in the direction of the arrow Leading edges 15. The secondary flow in the form of a gaseous and / or liquid fuel has an essential smaller mass flow than the main flow. she is in the present case downstream of the vortex generators introduced into the main flow.

1, the fuel is here via a central Fuel lance 51 injected, the mouth of which is downstream of the vortex generators. This lance is for dimensioned about 10% of the total volume flow through the channel 20. A longitudinal injection of the fuel is shown in the direction of flow. In this case the injection pulse corresponds about that of the main flow pulse. I agree a cross-jet injection could be provided as well, the fuel pulse then being about twice that the main flow must be.

The injected fuel is carried along by the eddies and mixed with the main flow. It follows the helical one Course of the vertebrae and becomes downstream the vertebrae evenly distributed in the chamber. This reduces the - in the radial injection of Fuel in an undisturbed flow - risk of impact jets on the opposite wall and the formation of so-called "hot spots".

Because the main mixing process takes place in the vertebrae and largely insensitive to the injection pulse of Secondary flow is, fuel injection can be flexible are kept and adapted to other boundary conditions become. This means that the same injection pulse can be applied across the entire load range to be kept. Since mixing through the Geometry of the vortex generators is determined and not by the machine load, in the example the gas turbine power, the burner configured in this way also works Optimal partial load conditions. The combustion process will by adjusting the ignition delay time of the fuel and Mixing time of the vortex is optimized, which minimizes the Guaranteed emissions.

Furthermore, the intensive mixing has a good effect Temperature profile over the cross section and further reduces the possibility of the occurrence of thermoacoustic Instability. By their presence alone the vortex generators act as a damping measure thermoacoustic vibrations.

To prevent the flame from reigniting in the burner, becomes a Venturi nozzle downstream of the vortex generators 52 provided. This is dimensioned so that at an exit speed of about 80-150 m / sec Flow velocity in the narrowest cross section about 150-180 m / sec. The distance of the narrowest cross section to the Trailing edges 16 of the vortex generators will be chosen so that the generated vortex in the narrowest cross section are already fully trained. The location of the fuel injection is at the level of the largest constriction the Venturi nozzle.

Figures 8 and 9 show a top view of an embodiment variant of the vortex generator and in a front view its arrangement in a circular channel. The two the side surfaces 11 and 13 have a different length. This means, that the roof surface 10 with an oblique flow Channel-extending edge 15a on the same channel wall fits like the side walls. The width of the Vortex generator then of course a different one Angle of attack Θ on. Such a variant has Effect that creates vortices of different strength become. For example, one of the main flows adherent twist. Or through the different vertebrae will be the originally swirl-free Main flow downstream of the vortex generators Swirl forced, as indicated in Fig. 9. A such configuration works well as a standalone, compact burner unit. When using multiple such units, for example in a gas turbine ring combustor, can the swirl imposed on the main flow can be exploited to determine the cross-ignition behavior of the burner configuration, e.g. at partial load.

Of course, the invention is not limited to that described and examples shown. Regarding the Arrangement of the vortex generators in the network are many combinations possible without leaving the scope of the invention. Also the introduction of the secondary flow into the main flow can be done in a variety of ways for example only or additionally via wall holes in the Venturi tube

Reference list

9, 9a

Vortex generator

10th

Roof area

11

Side surface

12th

Long edge

13

Side surface

14

Long edge

15

transverse edge of 10

16

Connecting edge

17th

Line of symmetry

18th

top

20, a

channel

21, a, b

Canal wall

Θ

Angle of attack

α, α / 2

Arrow angle

H

Height of 16

H

Channel height

L

Length of the vortex generator

50

Venturi nozzle

51

Fuel lance

52

Main burner

53

Brenner wall

54

Main burner wall

100

Front wall of the combustion chamber

101

Double cone burner

102

Air intake

103

Interior of the housing

111

Partial body

112

Partial body

113

Central axis

114

Central axis

116

Fuel nozzle

117

Gas inflow opening

118

Burner outlet = combustion chamber

119

tangential gap

120

Fuel lance

Claims (9)

1. Premixing burner, essentially comprising a pilot burner (101) and a plurality of main burners (52) arranged around the pilot burner (101),
   characterized in that

   a gaseous and/or liquid fuel is injected into the main burner (52), which has a circular duct (20), as a secondary flow into a gaseous main flow,

   in that the main flow is first of all guided over vortex generators (9), a plurality of which are arranged next to one another around the circumference of the duct (20) through which flow takes place,

   in that a venturi nozzle (50) is arranged downstream of the vortex generators (9),

   and in that the secondary flow is introduced into the duct (20) in the region of maximum constriction of the venturi nozzle (50).
2. Premixing burner according to Claim 1, characterized in that the pilot burner (101) operates on the double-cone principle, with essentially two hollow conical partial bodies (111,112) which are interleaved in the direction of flow and the respective centre lines (113, 114) of which are offset relative to one another, the adjacent walls of the two partial bodies (111, 112) forming along their length tangential slots (119) for the combustion air and longitudinally distributed gas inlet openings (117) being provided in the walls of the two partial bodies in the region of the tangential slots.
3. Premixing burner according to Claim 1,
   characterized in that

   a vortex generator (9) has three surfaces around which flow can take place freely, which surfaces extend in the direction of flow, one of them forming the top surface (10) and the two others forming the side surfaces (11, 13),

   in that the side surfaces (11,13) abut the same wall segment (21) of the duct and enclose a V-angle (α) between them,

   in that the top surface (10) lies with an edge (15) extending transversely to the duct (20) through which flow takes place on the same wall segment (21) as the side walls,

   and in that the longitudinally directed edges (12, 14) of the top surface, which abut the longitudinally directed side surface edges protruding into the flow duct, extend at an angle of incidence () to the wall segment (21).
4. Premixing burner according to Claim 3, characterized in that the two vortex generator (9) side surfaces (11, 13) enclosing the V-angle (α) are arranged symmetrically about an axis of symmetry (17).
5. Premixing burner according to Claim 3, characterized in that the two side surfaces (11, 13) enclosing the V-angle (α) include between them a connecting edge (16) which, together with the longitudinally directed edges (12, 14) of the top surface (10), forms a point (18), and in that the connecting edge lies radially with respect to the circular duct (20).
6. Premixing burner according to Claim 5, characterized in that the connecting edge (16) and/or the longitudinally directed edges (12, 14) of the top surface (10) are designed so as to be at least approximately sharp.
7. Premixing burner according to Claim 4, characterized in that the axis of symmetry (17) of the vortex generator (9) extends parallel to the duct axis, the connecting edge (16) of the two side surfaces (11, 13) forming the downstream edge of the vortex generator (9), and that edge (15) of the top surface (10) which extends transversely to the duct (20) through which flow takes place being the edge which the main flow meets first.
8. Premixing burner according to Claim 1, characterized in that the ratio between the height (h) of the vortex generator and the duct height (H) is selected in such a way that the vortex generated fills the complete duct height, or the complete height of the duct part assigned to the vortex generator, directly downstream of the vortex generator (9).
9. Premixing burner according to Claim 1, characterized in that the secondary flow is introduced via a fuel lance (51) arranged centrally in the duct (20), by means of longitudinal injection or cross-jet injection.

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