DE19527453A1 - Pre-mixing burner with integrated pre-mixing path - has nozzle located directly downstream of swirl generators at the periphery of the pre-mixing path - Google Patents

Abstract

At the start of the pre-mixing path (34) is centrally located a fuel lance (30). Axially symmetrical swirls of the fuel-air mixture (4) round the burner axis (5) are formed by several, adjacent swirl generators (31) at the periphery of the pre-mixing path. Directly downstream of the swirl generators is fitted a nozzle (38), in order to extend the pre-mixing path, pref. of Venturi type. The burner may contain an additional, radial fuel system. The section of the axial air flow inlet may be adjustable, e.g. by axial movement of the fuel lance.

Description

Technical field

The invention relates to a premix burner with an integrated Premixing section, central at the beginning of the premixing section a fuel lance is arranged and by means of vortex generators ger in the premixing section axially symmetrical vortex of Fuel-air mixture formed around the burner axis the.

State of the art

Low NOx premix burners are currently being used for gas turbines set, whose pollutant emission values at less than 25 ppm NOx are 15% oxygen. Another permanent and sig significant reduction in NOx emissions, e.g. B. to values below 9 ppm at 15% O₂ due to changes in operating conditions is because of problems with flame stabilization action, pulsation and the ever higher combustion temperatures not possible.

The mixing of fuel into one in a premix channel flowing air flow is usually radial Injection of fuel into the channel using a cross-jet medium shear. However, since the momentum of the fuel is very low,  is an almost complete mixing only after a reached relatively long distance.

The use of venturi mixers and the Injection of the fuel via grid arrangements, as well as that Injection in front of special swirl bodies.

The ar based on cross beams or stratified flows Processing devices either require very long mixing stretch or high injection pulses. With premix under high pressure and substoichiometric mixing ratios there is a risk of the flame kicking back or even of Auto-ignition of the mixture. Flow separations and dead water water zones in the premix pipe, thick boundary layers on the walls or extreme speed profiles above the Cross-flow area can cause auto-ignition dung in the channel or form paths over which the flame spreads the downstream combustion zone into the premix channel can strike back. The geometry of the premixing section must therefore, the highest attention should be paid.

From DE 43 16 474 A1 a premix burner is known which consists of a swirl generator and a connected Ven turi nozzle exists. The swirl generator is used for intermingling combustion air. In the convergent part of the Venturi nozzle increases the flow rate of air until it has its highest value at the bottleneck. At this narrow then the fuel is mixed in. The Art and manner of fuel mixing, e.g. B. opposite or injection in the same direction compared to the direction of the vortex incoming combustion air depends on the properties (Flame speed, calorific value) of the supplied fuel fes off. The pre-mixing section of the burner is then in the diver Gentent part of the Venturi nozzle, the mixture of Brenn material and combustion air before reaching the flame zone closed is.  

The premix burners of the Double cone design can be called. Such a double cone Burners are known for example from EP 0 321 809 B1. They consist of two hollow partial cone bodies, the longitudinal of which axes of symmetry are offset from one another and point tangential air inlet gaps for those from the compressor incoming combustion air. Inside the burner (Cone tip) is a fuel nozzle for liquid burning fabric arranged through which the fuel in a pointed Angle is injected into the hollow cone. The emerging kege current fuel profile is from the tangentially entering Combustion air enclosed, the in the axial direction Concentration of fuel due to mixing with the combustion air decreases continuously. The premix burner can also be with gaseous fuel or in mixed operation be driven. It is already in the entry columns the air through evenly distributed gas injector nozzles shaped fuel injected into the combustion air.

To ensure reliable ignition of the mixture at the exit of the Achieving burners and sufficient burnout is one an intimate mixture of fuel and air is required. In the interior of the double-cone burner arise from the art the injection of axially aligned vortices of the fuel-air Mixture. When the vortex number reaches a critical value the vortex breakdown (bursting of the vertebrae) and it forms a stable downstream of the burner outlet Flame front.

The better the level, the lower the NOx values is the fuel-air premix. A "perfect" Vormi is the key to ensuring that at high flame temperatures very low nitrogen oxide emissions can be achieved.  

Presentation of the invention

The invention tries to overcome the known disadvantages of the prior art of technology to eliminate. It is based on the task in a premix burner with at least approximately rota tion-symmetrical premixing channel, which vortex generator has the axially aligned vortex of the fuel-air Generate flow, the premix compared to the previously be known state of the art and thereby improve the NOx To further reduce emissions significantly.

According to the invention, this is according to a premix burner Preamble of claim 1 achieved in that a nozzle is arranged downstream of the vortex generator.

The advantages of the invention include that the premixing section of the burner is extended and there through the premixing of fuel and combustion air can go to a higher level, resulting in a sig significant reduction in NOx emissions.

It is advantageous if the nozzle is a Venturi nozzle. By which adjoins the convergent part of the nozzle divergent part becomes an outer corner recirculation of the Flow prevented. This ensures that the Vortex energy used to form the recirculation zone and the flame stability is high.

It is particularly useful if the premix burner is next to it radial fueling for the axial fuel system has material system. By dividing the fuel into an axial and a radial flow, it is possible that To change premix level. On the one hand, at full load operation of the gas turbine an optimal premixing and thus low NOx emission values can be achieved, on the other hand  in partial load operation by lowering the premix quality increased flame stability achieved.

It is also advantageous if the area of the axial flow Entry entry is changeable, for example by a axial movement of a movable central fuel lance. By changing the inlet area, the mass flow can be influenced and an unwanted flow separation prevented. It is also the place where the Vortex Break down takes place, depending on the size of the axial air flow dependent and thus specifically adjustable.

Finally, it is advantageous if the premix burner works according to the double cone principle with essentially two hollow, conical, intermeshed in the direction of flow nested partial bodies, their respective central axes against are offset from one another, the adjacent walls of the two partial bodies in their longitudinal extension tangential Kanä form le for the combustion air, and being in the range of tangential air inlet gaps in the walls of the two Partial body gas inlet openings distributed in the longitudinal direction are provided and a central fuel lance for wide Ren fuel is arranged in the initial part of the burner.

It is useful if the nozzle is connected to the adapter Burner is connectable, the adapter, the two, in their centers not coincident semicircular Surfaces of the double cone burner at the burner outlet into one transferred circular area at the nozzle entrance, its radius is smaller than the inner radius of the partial cone body and where the angle of inclination α of the adapter is the average Flow angle corresponds, so that flow separation prevents is changed. By using the adapter, the flow is prob led into the nozzle.

Brief description of the drawing

Exemplary embodiments of the invention are shown in the drawing shown schematically.

Show it:

FIG. 1 is a partial longitudinal section of a premix burner according to the invention;

Figure 2 is a section in the plane II-II in Fig. 1.

Fig. 3 is a partial longitudinal section of a premix burner according to the invention with venturi;

Fig. 4 shows the dependence of the swirl number of the axial length of a premix burner according to Fig. 3;

Fig. 5 is a perspective view of a premix burner of the double cone type;

Fig. 6 is a section in the plane VI-VI in Fig. 5;

Fig. 7 is a section in the plane VII-VII in Fig. 5;

Fig. 8 is a section in the plane VIII-VIII in Fig. 5;

Fig. 9 is a partial longitudinal section of the double-cone burner with Venturi tube;

Fig. 10 is a perspective view of the double-cone burner with Veturi nozzle;

FIG. 11 is a partial cross section of the adapter;

Fig. 12 is a schematic perspective view of the adapter piece connected to the nozzle.

It is only essential for understanding the invention Chen elements shown. The direction of flow of the work tel is indicated by arrows.

Way of carrying out the invention

In the following, the invention is explained in more detail using exemplary embodiments and FIGS. 1-9.

In Figs. 1 and 2, a first embodiment of the premix burner according to the invention. Before the mixing burner is used for example for the operation of a combustion chamber 18 in a gas turbine system. It is rota formed tion symmetrical and is in accordance with the partial longitudinal section shown in FIG. 1 essentially consists of a movably arranged fuel lance 30, the axial outlets, to 31 comprising the gaseous fuel 32 and out of the fuel lance downstream 30 arranged radial vortex generators 33, which axially symmetrical vortex the combus- tion air 15 and the gaseous fuel 13 around the Bren nerachse 5 form in the premixing channel 34 , and an adjoining nozzle 38th

The combustion air 15 is compressed in a compressor not shown here. Part of the combustion air flows through a plenum 35 as an axial air flow into the pre-mixing duct 34 . The inlet area 36 of the axial air flow and thus the mass flow of the inflowing air 15 can be changed by an axial movement of the fuel lance 30 . The inlet region 36 and the fuel lance 30 must be matched to one another so that flow separation is prevented.

By changing the axial air flow 15 , the level of the vortex that arises at the downstream end of the vortex generator 33 is changed. This allows the vertebrae to be adapted to different operating conditions. In this way, the position of the vortex breakdown area and thus the flame position can be influenced or the flame stability can be increased if there is a pulsation.

Fig. 2 shows a cross section through the vortex generator 33 in the plane II-II, from which the radial air supply and ra diale inlet openings 37 for gaseous fuel, and the concentrically formed around the burner axis 5 we bel the fuel-air mixture 4 well are recognizable. The supply lines of the radial fuel or air system are not shown. Splitting the fuel into an axial and a radial flow allows a change in the premix level. On the one hand, optimal premixing can be achieved when low emission values are required, ie at full turbine load, and on the other hand, by reducing the quality of the mixture, increased flame stability can be achieved with low gas turbine load.

The centerpiece of the invention is the nozzle 38 which directly adjoins the vortex generator 33 . In this convergent part of the nozzle 38 , the axial component of the vortex is increased so that the number of vertebrae is reduced. This leads to an additional premix length Δl, which in turn is expressed in an improved mixture quality and ultimately lower NOx emissions from the burner.

Fig. 3 shows a further embodiment of the invention. It differs from the embodiment shown in FIGS . 1 and 2 only in that the adjoining the wire generator 33 We nozzle 38 is a Venturi nozzle. The second part of the Venturi nozzle, which acts as a diffuser, reduces the axial component of the fuel-air flow, which leads to an increase in the number of vortices until the critical number of vortices is reached and the vortex breakdown, i.e. the vortices burst. The controlled expansion that is made possible by the second part of the Venturi nozzle prevents any external corner recirculation and thus ensures that the vortex energy is used to form the central recirculation zone.

Fig. 4 shows in a diagram the dependence of the number of Wirbelan W on the axial length 1 of the burner. The number of vortices W increases from the axial inlet 36 (point A) to the downstream end of the radial vortex generator 33 (point B), decreases until the venturi nozzle reaches its narrow point (point C) and rises downstream, ie with increasing axial length 1 of the burner again until the critical vortex number W _crit above which the vortex bursts is reached in point D (position of the vortex breakdown 6 ).

At the same time, the dependence of the number of vortices W and thus the dependence of the location of the vortex breakdown 6 on the size of the axial air flow can be seen from the diagram shown in FIG. 4. If the fuel lance 30 moved axially in the direction of flow, so 30 is reduced in comparison to the normal is equal to the position of the lance entering into the burner axial air flow, since the axial Eintrittsge Bidding is reduced 36th The result is that the critical vortex number W _{crit is} already reached after flowing through a smaller axial length l at D '. On the other hand, an axial displacement of the fuel lance 30 in a direction opposite to the direction of flow leads to the fact that, due to the stronger axial air flow (enlarged inlet area 36 ), the critical vortex number W _{crit is} only reached after flowing through a greater axial length l at D '' .

In Figs. 5 to 9, another embodiment of handle is shown a double-cone burner, the Prinzi pieller construction is described in EP 0321908 B1.

For a better understanding of the burner structure, it is advantageous if, at the same time, FIG. 5 and the sections shown in FIGS . 6 to 8 are used.

Fig. 5 shows a perspective view of the double-cone burner with integrated premixing zone. The two partial cone bodies 1 , 2 are arranged radially offset from one another with respect to their longitudinal axes 1 b, 2 b. This creates on both sides of the partial cone body 1 , 2 in the opposite inflow arrangement each tangential air inlet slots 19 , 20 through which the combustion air 15 flows into the interior 14 of the burner, ie in the cone cavity formed by the two Teilke gel bodies 1 , 2 . The Teilke gel body 1 , 2 expand rectilinearly in the flow direction, ie they have a constant angle with the Bren ner axis 5 . The two partial cone bodies 1 , 2 each have a cylindrical initial part 1 a, 2 a, which also runs ver sets. In this cylindrical initial part 1 a, 2 a there is a nozzle 3 through which liquid fuel 12 is injected at an acute angle into the interior 14 of the burner. The resulting tapered fuel profile is enclosed by the tangentially entering combustion air 15 , the concentration of the fuel 12 in the axial direction constantly decreasing as a result of mixing with the combustion air 15 .

Of course, the burner can also be without a cylindrical one Initial part, so be made purely conical.

The two partial cone bodies 1 , 2 have along the air inlet slots 19 , 20 each have a fuel feed line 8 , 9 , which are provided on the longitudinal side with openings 17 through which another gaseous fuel 13 flows. This fuel 13 is the slots through the tangential air inlet slots 19 , 20 in the burner interior combustion air 15 mixed, which is shown by the arrows 16 . Mixed operation of the burner via the nozzle 3 and the fuel feeds 8 , 9 is possible.

On the combustion chamber side, a front plate 10 is arranged with openings 11 through which, if necessary, dilution air or cooling air can be supplied to the combustion chamber 22 . In addition, this air supply ensures that flame stabilization takes place at the outlet of the burner. There is a sta ble flame front 7 with a backflow zone 6 .

The arrangement of guide plates 21 a, 21 b can be seen from FIGS . 6 to 8. These can be opened or closed, for example, about a pivot point 23 , so that the original gap size of the tangential air inlet slots 19 , 20 is changed. Of course, the burner can also be operated without these baffles 21 a, 21 b. So far the double cone burner is known.

As shown in FIG. 9, according to the invention, at the outflow end of the known double-cone burner, which acts here as vortex generator 33 , which forms axially symmetrical vortexes around the burner axis 5 and provides a fuel-air mixture for generating a well-anchored premixing flame, a Venturi nozzle 38 arranged. The convergent part of the nozzle 38 is designed so that the axial component of the flow is increased, which leads to a reduction in the number of vortices and thus to a delay in the occurrence of the vortex breakdown. The length of the fuel-air mixture is lengthened by the amount Δl.

The nozzle 38 must be designed in such a way that flow separation on the burner walls is prevented and the length of the enlarged premixing section is kept to a minimum. The latter is based on emission requirements to reduce the deterioration of the vortices due to friction losses. The second, divergent part of the Venturi nozzle serves to enable a controlled vortex breakdown. The expansion of the nozzle leads to the prevention of external recirculation, which would reduce the strength of the central recirculation zone and the flame stability. Furthermore, the expansion of the nozzle 38 causes a large speed gradient between the venturi walls and the vortex breakdown, where kickback problems and any existing wall cooling requirements are reduced. The exact profile of the venturi 38 is determined by the type of vortex generator, the emissions and premix requirements, the pressure drop requirements, the flame stability requirements and the flow separation problems on the wall.

From the perspective view of the double cone burner in Fig. 10, the adapter piece 39 is clearly visible, which is necessary to "close" the nozzle 38 to the double cone burner, that is, the two axes 1 b, 2 b must be brought together so that on downstream end (from occurs) of the adapter 39 or at the entry into the nozzle 38 a circular surface is formed.

Fig. 11 and Fig. 12 show the adapter 39 in more detail. The inner radius R _{i of} the two partial cone bodies 1 , 2 is larger than the exit radius R _{aa of} the adapter 39 . The height h and the size of the angle α of the adapter 39 are dependent on the entry form in the adapter 39 . The angle α speaks to the average flow angle, so that no separation can occur. In the example shown, α is 25 °. The flow-through free surface of the adapter 39 verrin Gert in the direction from inlet to outlet of the Adap ters 39, therefore, is here and will not accelerate the flow only in the eigentli chen nozzle 38th

Of course, the invention is not based on the ge here showed embodiments limited. The geometry of the In its simplest form, the nozzle can be a simple tube up to a strongly narrowing / expanding venturi nozzle with maximum angles from the pressure, the vortex loss and the flow separation are limited. The concrete The length of the nozzle is flexible and depends on the burner shape from.

Reference list

1 , 2 partial cone bodies
1 a, 2 a cylindrical initial part
1 b, 2 b longitudinal symmetry axes
3 nozzle
4 Fuel-air mixture
5 burner axis
6 backflow zone (vortex breakdown)
7 flame front
8 , 9 fuel supply lines
10 front panel
11 openings in the front panel
12 liquid fuel
13 gaseous fuel
14 Burner interior
15 Combustion air flow
16 Fuel injection
17 openings
18 combustion chamber
19 , 20 tangential air inlet slots
21 a, 21 b baffle
22 combustion chamber downstream of the burner
23 pivot point
30 fuel lance
31 axial openings
32 gaseous fuel
33 vortices (radial vortices, axially symmetrical)
34 premixing channel, premixing section
35 plenary
36 axial air inlet area
37 radial fuel inlets
38 nozzle
39 adapters
1 axial length
Δl additional premix length
R _i inner radius of items 1 , 2 at the burner outlet
R _ad exit radius of item 38
R _aa exit radius from item 39 or entry radius from item 38
h Height of item 39
α angle of inclination of item 39 , which corresponds to the average flow angle
A Position of the axial inlet in the burner
B downstream end of item 33
C Constriction of the venturi nozzle
D, D ′, D ′ ′ position of the vortex breakdown
W number of eddies
W _crit critical number of vertebrae

Claims (6)

1. premix burner with integrated premixing section ( 34 ), a fuel lance ( 30 ) being arranged centrally at the beginning of the premixing section ( 34 ) and by means of a plurality of vortex generators ( 33 ) arranged alongside one another over the circumference of the premixing section ( 34 ) in the premixing section ( 34 ) Axially symmetrical vortices of the fuel-air mixture ( 4 ) are formed about the burner axis ( 5 ), characterized in that a nozzle ( 38 ) is arranged immediately downstream of the vortex generator ( 33 ) for the purpose of extending the premixing section ( 34 ). 2. Premix burner according to claim 1, characterized in that the nozzle ( 38 ) is a Venturi nozzle. 3. premix burner according to claim 1 or 2, characterized records that the premix burner also has a radia les fuel system. 4. premix burner according to claim 1, characterized in that the area of the axial air flow inlet ( 36 ) is variable, in particular by axial movement of the fuel lance ( 30 ). 5. premix burner according to one of claims 1 to 4, characterized in that the premix burner works according to the double-cone principle with essentially two hollow, conical, in the flow direction nested partial bodies ( 1 , 2 ), the respective with tel axes ( 1 b, 2 b) are offset from one another, the adjacent walls of the two partial bodies ( 1 , 2 ) forming tangential channels ( 19 , 20 ) for the combustion air ( 15 ) in their longitudinal extent, and wherein in the area of the tangential air inlet gaps ( 19 , 20 ) in the walls of the two partial bodies ( 1 , 2 ) in the longitudinal direction direction gas inlet openings ( 17 ) are provided and a central fuel lance ( 30 ) for further fuel is arranged in the initial part of the burner. 6. premix burner according to claim 5, characterized in that the nozzle ( 38 ) via an adapter ( 39 ) to the Bren ner can be connected, the adapter ( 39 ) at the, in their centers ( 1 b, 2 b) not collapsed semicircular surfaces of the double-cone burner at the burner outlet are converted into a circular surface at the nozzle inlet, the radius R _{aa of which is} smaller than the inner radius R _{i of} the partial cone body ( 1 , 2 ) and the angle of inclination α of the adapter corresponds to the average flow angle, so that flow separation is prevented.