DE19527453B4 - premix - Google Patents

Abstract

premix with integrated premixing path (34), wherein at the beginning of the premixing section (34) centrally a fuel lance (30) is arranged and by means of several over the Circumference of the flowed through Pre-mixing section (34) of side-by-side vortex generators (33) in the premix (34) axisymmetric vortex of the fuel-air mixture (4) are formed around the burner axis (5) and the premix burner after the double cone principle works with essentially two hollow, conical, in the flow direction Nested sub-bodies (1, 2), whose respective center axes (1b, 2b) offset from each other are, wherein the adjacent walls of the two body parts (1, 2) in their longitudinal extent tangential channels (19, 20) for forming the combustion air (15), and being in the area of the tangential Air inlet gaps (19, 20) in the walls of the two body parts (1, 2) in the longitudinal direction distributed gas inlet openings (17) are provided and the central fuel lance (30) for further Fuel is arranged in the initial part of the burner, characterized in that immediately downstream of the vortex generator (33) for extension the premix section (34) has a nozzle (38) is arranged ...

Description

Technical area

The The invention relates to a premix burner with integrated premix of the double cone type, being central at the beginning of the premixing a fuel lance is arranged and by means of a vortex generator in the pre-mixing axial symmetric vortex of the fuel-air mixture be formed around the burner axis.

State of the art

At present, low-NOx premix burners are used for gas turbines whose pollutant emission levels are below 25 ppm NOx at 15% oxygen. Another permanent and significant lowering of NOx emissions, e.g. B. to values below 9 ppm at 15% O ₂ , by changes in operating conditions is not possible because of the problems occurring with respect to flame stability, pulsation and the ever higher combustion temperatures.

The Mixing of fuel into a stream of air flowing in a premixing channel takes place in usually by radial injection of fuel in the channel by means of cross-jet mixer. Because the pulse However, the fuel is very low, is an almost complete mixing only reached after a relatively long distance.

Known are also the use of Venturi mixers and the injection of the Fuel over Grid arrangements, as well as the injection of special swirling bodies.

The on the basis of cross-beam or layer flow operating devices need either very long mixing distances or high injection pulses. at Premix under high pressure and under-stoichiometric mixing ratios there is a risk of kickback the flame or even auto-ignition of the mixture. Flow separation and Dead water zones in the premix tube, thick boundary layers on the walls or possibly extreme speed profiles above the cross-section through which the air flows can the cause of self-ignition be in the channel or form paths over which the flame from the strike back downstream combustion zone in the premixing channel can. The geometry of the premix must therefore be given the highest attention be given.

Out DE 43 16 474 A1 a premix burner is known which consists of a swirl generator and an adjoining Venturi nozzle. The swirl generator serves to swirl the combustion air. In the convergent part of the Venturi nozzle, the flow velocity of the air increases until it has its highest value at the bottleneck. At this bottleneck then takes the interference of the fuel. The way of fuel mixing, eg. B. opposing or in the same direction injection compared to the swirl direction of the incoming combustion air, depends on the properties (flame speed, calorific value) of the supplied fuel. The premixing path of the burner is then in the divergent part of the venturi, with the mixture of fuel and combustion air being completed before reaching the flame zone.

US 1874970 A describes a burner in which fuel is supplied twisted while the air supply is not twisted. The fuel and air are guided along a tubular body and gradually mixed. This is to prevent the flame from being hit back.

Flame-retaining burners may be referred to as premix burners of the double-cone type. Such double-cone burners are for example from the EP 0 321 809 B1 known. They consist of two hollow part cone bodies whose longitudinal axes of symmetry offset from each other, and have tangential air inlet gaps for the combustion air flowing in from the compressor. Inside the burner (cone tip) a liquid fuel nozzle is arranged, through which the fuel is injected at an acute angle into the hollow cone. The resulting conical fuel profile is enclosed by the tangentially entering combustion air, wherein in the axial direction, the concentration of the fuel as a result of mixing with the combustion air steadily decreases. The premix burner can also be operated with gaseous fuel or in mixed operation. In the process, the gaseous fuel is injected into the combustion air via evenly distributed injector nozzles in the entry gaps of the air.

Around a reliable one ignition the mixture at the outlet of the burner and a sufficient burnout to achieve is an intimate mixture of fuel with air required. In the interior of the double cone burner arise through the type of injection axially aligned vortex of the fuel-air mixture. If the Vortex number has reached a critical value, the vortex occurs Breakdown (bursting of the vortex) and it forms downstream of the Burner output a stable flame front.

The better the level of the fuel-air premix, the lower the NOx values. A perfect pre-mix is the key to making sure that at high flame temperatures low nitrogen oxide emissions can be achieved.

Presentation of the invention

The Invention seeks to overcome the known disadvantages of the prior art to eliminate. It is based on the task, in a premix burner Doppelkegelbauart the premix over the previously known state technology and thereby further reducing NOx emissions considerably to lower.

According to the invention this in a premix burner according to the preamble of claim 1 achieved by downstream of the vortex generator for the purpose of extension the premix a nozzle is arranged and the nozzle over a Adapter can be connected to the burner, the adapter the two, in their centers not coincident semicircular surfaces of the double-cone burner at the burner outlet in a circular area transferred at the nozzle entrance, whose Radius is smaller than the inner radius of the part cone body and wherein the inclination angle α of Adapters corresponds to the average flow angle, so that flow separation prevented becomes.

The Advantages of the invention are, inter alia, that the Premix of the burner is extended and thereby the Premixing of fuel and combustion air at a higher level This can lead to a significant reduction in NOx emission levels leads. By using the adapter, the flow is easily fed into the nozzle.

It is advantageous if the nozzle a Venturi nozzle is. By connecting to the convergent part of the nozzle divergent part becomes an outer one Corner recirculation of the flow prevented. This will ensure that the vortex energy to Forming the recirculation zone is used and the flame stability is high.

It is particularly appropriate if the premix burner in addition to the axial fuel system too still has a radial fuel system. By the division of the Fuel in an axial and a radial flow, it is possible the premix level to change. On the one hand, the gas turbine can be optimally operated at full load Premix and thus low NOx emission levels are achieved On the other hand, at partial load operation by lowering the premix quality increased flame stability is achieved.

Further it is advantageous if the area of axial flow entry variable is, for example, by an axial movement of the movable central Fuel lance. By change of the inlet area, the mass flow can be influenced and an unwanted flow separation is prevented. In addition, the place where the vortex breakdown takes place of the size the axial air flow dependent and thus specifically adjustable.

Short description of the drawing

In the drawing is an embodiment of Invention shown schematically.

It demonstrate:

1 a perspective view of a known Vormischbrenners the double cone type;

2 a section in the plane II-II in 1 ;

3 a section in the plane III-III in 1 ;

4 a section in the plane III-III in 1 ;

5 a partial longitudinal section of the double cone burner with Venturi nozzle;

6 a perspective view of the double-cone burner with Veturidüse;

7 a partial cross section of the adapter;

8th a schematic perspective view of the adapter piece connected to the nozzle and

9 the dependence of the number of vertebrae on the axial length of the premix burner.

It are only for the understanding the invention essential elements shown. The flow direction the work equipment is indicated by arrows.

Way to execute the invention

Hereinafter, the invention with reference to an embodiment and the 1 - 9 explained in more detail. In the 1 to 4 is a double cone burner shown, the basic structure in EP 0 321 908 B1 is described.

For a better understanding of the burner construction, it is advantageous if at the same time 1 and the cuts visible in them after the 2 to 4 be used.

1 shows a perspective view of the double-cone burner with integrated premixing zone. The two partial cone bodies 1 . 2 are with respect to their longitudinal axes of symmetry 1b . 2 B arranged radially offset from one another. This creates on both sides of the partial cone body 1 . 2 In opposite Einströmungsanordnung each tangential air inlet slots 19 . 20 through which the combustion air 15 in the interior 14 of the burner, ie in the of the two partial cone bodies 1 . 2 formed cone cavity flows. The partial cone bodies 1 . 2 expand straight in the flow direction, ie they have a constant angle with the burner axis 5 on. The two partial cone bodies 1 . 2 each have a cylindrical beginning part 1a . 2a , which are also offset. In this cylindrical beginning part 1a . 2a there is a nozzle, which as a fuel lance 30 is formed by the liquid fuel 12 at an acute angle in the interior 14 of the burner is injected. The resulting conical fuel profile is from the tangentially entering combustion air 15 enclosed, wherein in the axial direction, the concentration of the fuel 12 due to mixing with the combustion air 15 constantly decreasing. The burner thus has an integrated premixing path 34 ,

Of course you can the burner even without cylindrical initial part, so purely conical accomplished be.

The two partial cone bodies 1 . 2 point along the air inlet slots 19 . 20 one fuel supply each 8th . 9 on which longitudinally with openings 17 are provided, through which another, gaseous fuel 13 flows. This fuel 13 gets through the tangential air inlet slots 19 . 20 combustion air flowing into the burner interior 15 mixed, what with the arrows 16 is pictured. A mixed operation of the burner via the nozzle (fuel lance 30 ) and the fuel supplies 8th . 9 is possible.

The combustion chamber side is a front plate 10 arranged with openings 11 through which if necessary dilution air or cooling air to the combustion chamber 22 (= Combustion chamber 18 in 5 ). In addition, this air supply ensures that a flame stabilization takes place at the output of the burner. There is a stable flame front 7 with a backflow zone 6 one.

From the 2 to 4 is the arrangement of baffles 21a . 21b refer to. These can be, for example, a pivot point 23 be opened or closed, so that thereby the original gap size of the tangential air inlet slots 19 . 20 is changed. Of course, the burner even without these baffles 21a . 21b operate.

So far is the double cone burner known.

As in 5 is shown according to the invention at the downstream end of the known double-cone burner, here as a vortex generator 33 acts, which axisymmetric vortex around the burner axis 5 forms and a fuel-air mixture 4 to produce a well-anchored premix flame, a venturi nozzle 38 arranged. The convergent part of the nozzle 38 is designed to increase the axial component of the flow, resulting in a reduction in the number of swirls and thus a delay in the occurrence of the vortex breakdown. This will be the premix length of the fuel-air mixture 4 extended by the amount Δl, which in turn expressed in improved mixing quality and ultimately lower NOx emissions of the burner. The acting as a diffuser second part of the venturi reduces the axial component of the fuel-air flow, which leads to an increase in the number of vertebrae until the critical vortex number is reached and the Vortex Breakdown, ie a bursting of the vortex occurs. The controlled expansion provided by the second part of the venturi prevents any external corner recirculation and ensures that the vortex energy is used to form the central recirculation zone.

The nozzle 38 must be designed in such a way as to prevent flow separation on the burner walls and to keep the length of the enlarged premix section at a minimum value. 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 allow a controlled vortex breakdown. The extension of the nozzle results in the prevention of external recirculation, which would reduce the strength of the central recirculation zone and the flame stability. Furthermore, by the extension of the nozzle 38 a large velocity gradient is created between the venturi walls and the vortex breakdown, which will reduce backlash problems and any wall cooling requirements that may be present. The exact profile of the Venturi nozzle 38 is determined by the nature of the vortex generator, emissions and premix requirements, pressure loss requirements, flame stability requirements, and wall stall problems.

From the perspective view of the double cone burner in 6 is the adapter piece 39 clearly recognizable, which is necessary to the nozzle 38 to "connect" to the double-cone burner, ie the two axes 1b . 2 B must be brought together so that at the downstream End (exit) of the adapter 39 or at the inlet to the nozzle 38 a circular surface is created.

7 and 8th show the adapter 39 more accurate. The inner radius R _{i of} the two cone bodies 1 . 2 is greater than the outlet radius R _{aa of} the adapter 39 , The height h and the size of the angle α of the adapter 39 are from the entry form into the adapter 39 dependent. The angle α corresponds to the average flow angle, so that no separation can occur. In the example shown, α is 25 °. The free-flowing surface of the adapter 39 decreases in the direction from entry to exit of the adapter 39 , therefore, here and not only in the actual nozzle 38 the flow accelerates.

9 shows in a diagram the dependence of the number of vertebrae W on the axial length l of the burner. The number of vertices W increases from the axial inlet 36 (Point A) to the downstream end of the radial vortex generators 33 (Point B), decreases until it reaches the constriction of the venturi (point C) and rises downstream, ie with increasing axial length l of the burner again, until at point D (position of the Vortex Breakdowns 6 ) the critical vortex number W _crit above which the vortexes burst is reached.

At the same time is from the in 9 illustrated diagram dependency of the number of vertices W and thus the dependence of the location of the vortex breakdown 6 to be taken from the size of the axial air flow. Will the fuel lance 30 axially displaced in the direction of flow, so reduced in comparison to the normal position of the lance 30 the axial airflow entering the burner, since the axial entry region 36 is reduced. This leads to the fact 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 which is opposite to the flow direction, due to the fact that due to the stronger axial air flow (increased entrance area 36 ) the critical vortex number W _{crit is reached} only after flowing through a greater axial length l at D ''.

Of course it is the invention is not limited to the embodiment shown here. The Geometry of the nozzle In its simplest form, it can be a simple pipe right through to a strongly narrowing / dilating Venturi nozzle with maximum Angles that limit pressure, vortex loss, and flow separation become. The concrete length the nozzle is flexible and hangs from the burner requirements.

1, 2

Partial conical bodies

1a, 2a

cylindrical initial part

1b, 2 B

Longitudinal axes of symmetry

4

Fuel-air mixture

5

Brenner

6

Backflow zone (Vortex Breakdown)

7

flame front

8th, 9

fuel supply lines

10

front panel

11

openings in the front panel

12

liquid fuel

13

gaseous fuel

14

inner space of the burner

15

Combustion air flow

16

Injection fuel

17

openings

18

combustion chamber

19 20

tangential Air inlet slots

21a, 21b

baffle

22

combustion chamber downstream of the burner

23

pivot point

30

fuel lance

33

vortex generators (radial vortex, axisymmetric)

34

premix, premix

36

axial Air intake area

38

jet

39

adapter axial length

l

axial length

.DELTA.l

additional Vormischlänge

R _i

Inner radius of Pos. 1 . 2 at the burner outlet

R _ad

Outlet radius from pos. 38

R _aa

Outlet radius from pos. 39 or entry radius from pos. 38

H

Height of pos. 39 Inclination angle of pos. 39 which corresponds to the average flow angle

α

Inclination angle of pos. 39 which corresponds to the average flow angle

A

position the axial inlet into the burner

B

downstream end of pos. 33

C

bottleneck the Venturi nozzle

D D ', D' '

position the Vortex Breakdown

W

swirl number

W _crit

critical swirl number

Summary

In a premix burner of the double cone type with integrated premixing path ( 34 ), where at the beginning of the premix ( 34 ) centrally a fuel lance ( 30 ) is arranged and by means of several over the circumference of the flow-through premix ( 34 ) juxtaposed vortex generators ( 33 ) in the premix line ( 34 ) axial symme trical vortices of the fuel-air mixture ( 4 ) around the burner axis ( 5 ) is immediately downstream of the vortex generator ( 33 ) for the purpose of extending the premix route ( 34 ) a nozzle ( 38 ), in particular venturi, arranged, which via an adapter 839 ) is connected to the burner.

Claims (4)

Premix burner with integrated premixing line ( 34 ), where at the beginning of the premix ( 34 ) centrally a fuel lance ( 30 ) is arranged and by means of several over the circumference of the flow-through premix ( 34 ) juxtaposed vortex generators ( 33 ) in the premix line ( 34 ) axisymmetric vortex of the fuel-air mixture ( 4 ) around the burner axis ( 5 ), and the premix burner according to the double-cone principle works with essentially two hollow, conical, nested in the flow direction partial bodies ( 1 . 2 ), whose respective central axes ( 1b . 2 B ) are offset from each other, wherein the adjacent walls of the two body parts ( 1 . 2 ) in their longitudinal extent tangential channels ( 19 . 20 ) for the combustion air ( 15 ), and wherein in the region of the tangential air inlet gaps ( 19 . 20 ) in the walls of the two partial bodies ( 1 . 2 ) longitudinally distributed gas inlet openings ( 17 ) and the central fuel lance ( 30 ) is arranged for further fuel in the initial part of the burner, characterized in that immediately downstream of the vortex generator ( 33 ) for the purpose of extending the premix route ( 34 ) a nozzle ( 38 ) is arranged and the nozzle ( 38 ) via an adapter ( 39 ) is connectable to the burner, wherein the adapter ( 39 ) the two, in their centers ( 1b . 2 B ) non-coincident semicircular surfaces of the double-cone burner at the burner outlet in a circular area at the nozzle entrance transferred whose radius R _{aa is} smaller than the inner radius R _{i of} the partial cone body ( 1 . 2 ) and wherein the inclination angle α of the adapter corresponds to the average flow angle, so that flow separation is prevented. Premix burner according to claim 1, characterized in that the nozzle ( 38 ) is a Venturi nozzle. Premix burner according to claim 1 or 2, characterized that the premix burner in addition having a radial fuel system. 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 ).