EP0742411B1 - Air supply for a premix combustor - Google Patents

Description

Technical field

The invention relates to a premix burner with an axial or radial air inflow for gas turbine operation, in which the combustion air from a plenum into the burner flows and fuel is added to it on its way through the burner becomes.

State of the art

For environmental reasons, modern burner systems, which are used in gas turbine plants as premix burners executed because it reduces pollutant emissions compared to diffusion burners can be significantly reduced. The premix burners are usually axial or radial flowed with the combustion air.

On the way through the burner, the airflow becomes fuel added. To keep NOx and CO emissions low at Achieving combustion is a homogeneous mixing of Fuel and air necessary, i.e. the fuel addition is to adapt to the air distribution. So that this is guaranteed in all cases remains, the air supply should be controllable his. However, this is not the case with premix burner systems Case.

In the premix burner known from EP 0 321 809 B1 Double-cone design flows the combustion air from one of a plenum surrounded by a hood via tangential air inlet slots into the burner interior. Becomes gaseous fuel burned, the mixture formation occurs directly at the end of the Air inlet slots. When injecting liquid fuel by a centrally located one in the beginning of the burner The nozzle becomes a cone-shaped inside the burner Liquid fuel column formed by a tangential enclosed combustion air stream flowing into the burner becomes. The mixture is ignited at the burner outlet, the flame passing through a backflow zone in the area the burner mouth is stabilized. As a result of the complex Flow situation in the hood, which results from the fact that into the hood both the cooling air that cooled the combustion chamber has, as well as additional air flowing through a bypass what leads to turbulence, there is no uniform Brenneranströmung. The supply of combustion air is not exactly controllable, so that no completely homogeneous Mixing of fuel and air is achieved. The in turn leads to increased pollutant emissions during combustion.

Presentation of the invention

The invention tries to avoid all these disadvantages. you the task is based on a premix burner To create device for flow rectification with which the flow profile of the incoming combustion air evened out, the degree of turbulence increased and the air flow can be adapted to the burner, so that a homogeneous Mixing of air and fuel is achieved.

According to the invention, this is done in a premix burner with an axial or radial air inflow, in which the combustion air from one in the flow direction in front or one around the burner arranged plenum flows into the burner and you fuel is mixed in on the way through the burner, thereby achieved that between the plenum and the burner a perforated component with a certain wall thickness and Openings with a certain diameter and a certain Distance from each other, which is the flowing through Divides combustion air into small defined jets, that reunite after a certain run length, where the ratio of wall thickness to diameter the openings are greater than or equal to one, preferably 1.5 and where the ratio between the flow area of the perforated Component and the possible inflow area in the Burners also larger / equal depending on the type of burner is one.

The advantages of the invention include that a uniform speed profile after the perforated component with increased turbulence level as inflow for the burner is reached. This will mix the Improved and intensified fuel and combustion air, so that the emission values of CO and NOx are reduced. The premix burners have a wider range of applications because they now operate well even under unfavorable inflow conditions can be.

It is advantageous if in a premix burner with radial Air flow into the perforated component around the burner arranged perforated basket and with a burner axial air flow one in front of the burner perpendicular to the Direction of flow of the combustion air is arranged wall.

It is particularly useful if the ratio of barrel length the distance between the openings is greater than or equal to 5.

Furthermore, it is advantageous if an axially flow Premix burner the ratio between the flow area the perforated wall and the inflow surface into the burner is equal to one.

After all, it is an advantage if you have a premix burner the double cone type according to EP 0 321 809 B1, in which the Combustion air via tangential air inlet slots in the burner flows, the ratio between the flow area of the perforated basket and the inflow surface in the Burner is greater than one, preferably four. This ensures that an uneven air distribution along the inflow length of the burner both in the mass distribution can also be rectified in the flow profile. Thereby the fuel rating along the air inlet slot be optimally designed so that the mixture of Fuel and air is improved and the NOx levels at Combustion can be reduced.

Brief description of the drawing

In the drawing are two embodiments of the invention based on a radial flow premix burner of the double cone type for gas turbine combustion chambers and based on a shown axially flowed premix burner.

Fig. 1a

das Strömungsprofil bei gleichförmiger Zuströmung der Luft über eine perforierte Wand;

Fig. 1b

das Strömungsprofil bei ungleichförmiger Zuströmung der Luft über eine perforierte Wand;

Fig. 1c

eine schematische Darstellung des Geschwindigkeitsverlaufes der zuströmenden Luft bei schräger Anströmung;

Fig. 2

einen Vormischbrenner der Doppelkegelbauart in perspektivischer Darstellung;

Fig. 3

einen vereinfacht dargestellten Schnitt in der Ebene III-III gemäss Fig. 2;

Fig. 4

einen vereinfacht dargestellten Schnitt in der Ebene IV-IV gemäss Fig. 2;

Fig. 5

einen vereinfacht dargestellten Schnitt in der Ebene V-V gemäss Fig. 2;

Fig. 6

einen Teillängsschnitt des Vormischbrenners gemäss Fig. 2 mit dem erfindungsgemässen Strömungsgleichrichter;

Fig. 7

eine Detailskizze zur Wirkungsweise des Strömungsgleichrichters bei radialer Anströmung gemäss Fig. 6;

Fig. 8

einen Schnitt in der Ebene VIII-VIII gemäss Fig. 6;

Fig. 9

einen Teillängsschnitt eines axial angeströmten Vormischbrenners mit Strömungsgleichrichter.

Show it:

Fig. 1a

the flow profile with a uniform inflow of air over a perforated wall;

Fig. 1b

the flow profile in the event of non-uniform inflow of air through a perforated wall;

Fig. 1c

a schematic representation of the speed curve of the incoming air with an inclined flow;

Fig. 2

a premix burner of the double cone type in a perspective view;

Fig. 3

a simplified section in the plane III-III of FIG. 2;

Fig. 4

a simplified section in the plane IV-IV of FIG. 2;

Fig. 5

a simplified section in the plane VV of FIG. 2;

Fig. 6

a partial longitudinal section of the premix burner according to FIG 2 with the flow straightener according to the invention.

Fig. 7

a detailed sketch of the operation of the flow straightener with radial flow according to FIG. 6;

Fig. 8

a section in the plane VIII-VIII of FIG. 6;

Fig. 9

a partial longitudinal section of an axially flowing premix burner with flow straightener.

It is only essential for understanding the invention Elements shown, e.g. the combustion chamber only hinted at. The direction of flow of the air is indicated by arrows.

Way of carrying out the invention

The invention is explained below using two exemplary embodiments and Figures 1 to 8 explained in more detail.

Fig. 1a initially shows how the how a flow rectifier acting perforated component 24 with an ideal, uniform inflow of air 15, while in Fig. 1b the mode of operation of the perforated component 24 with a non-uniform inflow of air 15 is shown.

The component 24 with a wall thickness s has a number of Openings 25 each with a diameter d. These openings 25 are arranged at a constant distance t from one another. 1a and 1b is through the openings 25 of the component 24 flowing air 15 defined in small Beams split up according to a certain one Combine barrel length 1 behind the hole. It is the barrel length 1 depending on the distance t and the diameter d of the openings 25, and of the beam divergence. As in Fig. 1b can be clearly seen, takes place with a non-uniform Inflow the beam expansion before the perforated Component. After flowing through the wall it becomes uniform Speed profile with an increased small-scale Turbulence level achieved, leading to a favorable inflow leads for the burner, not shown in Fig. 1.

In addition, with curved walls, for example one around perforated basket placed on the burner, a constant exit angle given the flow from the basket and thus can be adapted to the burner.

1c shows a schematic representation of the speed profile of the inflowing air when the perforated component 24 flows at an angle. Before the air 15 hits the component 24, its speed is composed of a vertical component v ₁ and a horizontal component u ₁ , whereby an angle β _{1 is} enclosed by the resultant and by v ₁ . After flowing through the component with a fixed minimum ratio of wall thickness s to hole diameter d, the horizontal component u ₂ and the angle β _{2 are} zero, so that only a vertical velocity component v _{2 is} present, where: v ₁ <v ₂ . If, on the other hand, a perforated component 24 with a very small wall thickness were used, then the horizontal velocity component u ₁ would be retained and the following would apply: u ₂ = u ₁ and β ₂ <β ₁ , while the vertical velocity component v ₂ after component 24 would also be larger than v is ₁ . In this case there is no flow rectification.

With regard to the design of the perforated component 24 a fixed area ratio between the flow area of the component and the inflow surface into the premix burner observed. The pressure loss across the perforated component 24 is determined by these two surfaces. As well may have a fixed ratio between the diameter d of the Openings 25 and the wall thickness s must not be undercut, because this ratio also determines the amount of pressure loss. It has been shown that the ratio s / d≥1 to 1.5 should be. The distance t is determined by these requirements of the openings 25 to each other, which in turn Flow profile behind the component 24 determines the ratio 1 / t ≥ 5, because of the beam divergence then the individual rays have grown together again and the speed profile is very even.

Fig. 2 shows as an embodiment of the invention in Perspective view of a burner 18 of the double cone type with integrated premixing zone, its principal Structure is described in EP 0 321 809 B1. For better understanding of the burner structure, it is advantageous if at the same time FIG. 2 and the sections shown in FIG. 3 to 5 can be used.

The burner 18 consists of two partial cone bodies 1, 2, which relate their longitudinal symmetry axes 1b, 2b radially offset from one another are arranged. This creates on both sides the partial cone body 1, 2 in the opposite inflow arrangement each tangential air inlet slots 19, 20, through which the combustion air 15 in the interior 14 of the Burner 18, i.e. in the two conical bodies 1, 2 formed cone cavity flows. Expand the partial cone bodies 1, 2 straight in the direction of flow, i.e. they point a constant angle with the burner axis. The two Partial cone bodies 1, 2 each have a cylindrical initial part 1a, 2a, which also run offset. In this cylindrical Starting part 1a, 2a there is an atomizing nozzle 3, the openings of which are approximately in the narrowest cross section of the conical Interior 14 of the burner 18 is arranged. Of course, the burner 18 can also be without a cylindrical one Initial part, so be made purely conical. By the nozzle 3 is injected liquid fuel 12, so that a drop spray 4 forms in the interior 14 of the burner 18.

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 long side with openings 17 through which another fuel 13 flows. This gaseous Fuel 13 becomes the through the tangential air inlet slots 19, 20 combustion air flowing into the burner interior 14 15 admixed, which is represented by the arrows 16 becomes. Mixed operation of the burner 18 via the nozzle 3 and the fuel feeds 8, 9 is possible. About that In addition, this air supply ensures that flame stabilization takes place at the exit of the burner. There poses there is a stable flame front 7 with a backflow zone 6 on.

A front plate 10 with openings is arranged on the combustion chamber side 11, through which, if necessary, dilution air or cooling air are fed to the combustion chamber 22.

3 to 5, the arrangement of baffles 21 a, 21 b. These can be around a pivot point, for example 23 can be opened or closed, so that the original gap size of the tangential air inlet slots 19, 20 is changed. Of course, the Burners can also be operated without these baffles 21a, 21b.

6, the burner 18 described above is one Hood 26 surround a plenum 27 for the burner incoming combustion air 15 forms. Thereby the Combustion air 15 on the one hand together from the cooling air 15a, which has previously convectively cooled the walls of the combustion chamber 5, and on the other hand from the air 15b, which does not have a the bypass line shown also flows into the plenum 27, so that additional swirls arise. In the hood 26 there is therefore a very complex flow situation. In order to is not uniform according to the current state of the art Inflow of air 15 through the tangential air inlet slots 19, 20 guaranteed in the burner, so that the gaseous fuel 13 and the combustion air 15 can not be optimally mixed, what the use of Burner under unfavorable inflow conditions or the NOx values under more favorable outflow conditions lowers enough.

Therefore, as shown in Figs. 6, 7 and 8, a perforated one Basket 24 placed around the radially flowed burner 18, which causes a flow rectification. With a contour adjustment the basket 24 is an optimal flow of Brenners allows. The flow of the burner is controlled by the Invention of the complex flow situation in the hood decoupled.

The area ratio between the flow area of the perforated Basket 24 and the inflow surface into the burner 18th (Air inlet slots 19, 20) is in the illustrated embodiment 4. This ensures that the pressure loss corresponds approximately to a dynamic pressure above the perforated basket. If the flow area, i.e. the area of the openings 25 in the basket 24 essential under otherwise constant conditions lower, there would be too high a pressure loss.

Since the ratio of wall thickness s to hole diameter d is greater / equal 1, preferably 1.5 must be with this Claim in addition to the above Area ratio the distance t the Openings 25 are fixed to each other, which in turn is the flow profile determined behind the perforated basket 24. The Air 15, as already described above, flows through of the basket 24 divided into small defined rays that unite again after opening 1 behind opening 25. The common flow profile can thus be precisely defined and tailored to the respective burner needs become. The advantage is that it is uneven Air distribution along the inflow length of the burner 18 both in the mass distribution as well as in the flow profile can be rectified. This allows the fuel rating optimally designed along the air inlet in the burner 18 be, which in addition to increasing the turbulence of the air improves the mixture of fuel and combustion air and thus pollutant emissions are reduced. The The burner can therefore operate under unfavorable inflow conditions be used. By adjusting the contour of the basket 24 is also an optimal local flow to the burner possible.

Of course, the invention is not limited to that just described Embodiment limited. 9 is therefore another embodiment shown, the one axially flowed premix burner 18 relates. The combustion air 15 flows here from the plenum 27 through the openings 25 one in front of the burner perpendicular to the direction of flow arranged perforated wall 24 which e.g. a perforated sheet can be in the burner 18. There the fuel 13 becomes radial mixed in in front of the swirl body 28. For stabilization The system becomes pilot fuel via a central feed 29 passed into the burner. Because the air flow is evened out by the wall 24 and also that small-scale turbulence level after the wall 24 is increased, can be a homogeneous mixture of fuel and combustion air take place, what to the above Advantages leads.

LIST OF REFERENCE NUMBERS

1, 2

Partial conical bodies

1a, 2a

cylindrical initial part

1b, 2b

Center axis of the partial cone body

3

atomizing nozzle

5

combustion chamber

4

Fuel droplet spray

6

Backflow zone (vortex breakdown)

7

flame front

8, 9

fuel supply line

10

front panel

11

Openings in the front panel

12

liquid fuel

13

additional fuel (mostly gaseous)

14

Interior of the burner

15

Combustion air flow

16

Injection fuel

17

openings

18

burner

19, 20

tangential air inlet slot

21a, 21b

baffle

22

Combustion chamber downstream of the burner

23

pivot point

24

perforated component

25

Openings in pos. 24

26

Hood

27

plenum

28

swirler

29

pilot fuel

d

Diameter from item 25

s

Thickness of item 24

t

Distance from two openings

1

yardage

v ₁

vertical speed component before item 24

u ₁

horizontal speed component before item 24

β ₁

Angle between v ₁ and the speed resultant

v ₂

vertical velocity component after flow from item 24

u ₂

horizontal velocity component after flow from item 24

β ₂

Angle between v ₂ and the speed resultant

Claims (6)

1. Premix burner (18) having axial or radial air inflow, in which premix burner (18) the combustion air (15) flows out of a plenum (27), arranged in the direction of flow before or around the burner (18), into the burner (18) and fuel (12, 13) is mixed with it on the way through the burner (18), characterized in that a perforated component (24) having a wall thickness (s) and openings (25) of in each case a diameter (d) and at a distance (t) apart is arranged between the plenum (27) and the burner (18), which component (24) splits the combustion air (15) flowing through into small defined jets which reunite after a certain running length (1), the ratio of wall thickness (s) to the diameter (d) of the openings (25) being greater than/equal to one, and the ratio between the throughflow area of the perforated component (24) and the possible inflow area to the burner (18) being greater than/equal to one as a function of the type of burner.
2. Premix burner (18) having radial air inflow according to Claim 1, characterized in that the perforated component (24) is a perforated basket arranged around the burner (18).
3. Premix burner (18) having axial air inflow according to Claim 1, characterized in that the perforated component (24) is a perforated wall, preferably a perforated plate, arranged in front of the burner (18) perpendicularly to the direction of flow of the combustion air (15).
4. Premix burner (18) according to one of Claims 1 to 3, characterized in that the ratio of running length (1) to the distance (t) between the openings (25) is greater than/equal to 5.
5. Premix burner (18) according to one of Claims 1 to 3, characterized in that the ratio of wall thickness (s) to the diameter (d) of the openings (25) is 1.5.
6. Premix burner (18) according to Claim 3,
   characterized in that the ratio between the throughflow area of the perforated wall (24) and the inflow area to the burner (18) is equal to one.

Images