WO2014154401A1

WO2014154401A1 - Gas turbine combustion chamber having secondary air flaps

Info

Publication number: WO2014154401A1
Application number: PCT/EP2014/053382
Authority: WO
Inventors: Marco Link; Marc Tertilt; Martin Wilke
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-03-26
Filing date: 2014-02-21
Publication date: 2014-10-02
Also published as: EP2784393A1

Abstract

The invention relates to a combustion system (1) having a combustion chamber (2), comprising an outer shell (3) having a support structure (4), a compressor-side (5) and a turbine-side end (6), and having burners (7) at the compressor-side end (5), by way of which a fuel and combustion air are conveyed to the combustion chamber (2) during the operation of the internal combustion system (1). In the outer shell (3), flaps (8) are provided which are suitable to convey compressor air past the burners (7) into the combustion chamber (2) during the partial load operation of the combustion chamber (2), wherein an angle between a main flow in the combustion chamber (2) and an air flow forming during the opening of the flaps (8) is smaller than 90⁰.

Description

description

The invention relates to a combustion system that can be operated in partial load operation CO emission compliant.

In the partial load range of the gas turbine, the combustion temperature drops in the combustion chamber. As a result, the primary zone temperature relevant for CO emissions also falls below a minimum value. Due to the resulting increased CO emissions, the usable partial load range of the gas turbine is limited. In this case, if a legal CO emission limit exists, the operator of a gas turbine may be forced to shut down his gas turbine if it is not possible for him to further reduce the output of his gas turbine without simultaneously exceeding the CO emission limit. So far, the usable partial load range could be extended slightly downwards only by special driving style.

The object of the invention is therefore to further develop the combustion system of a gas turbine, so that the gas turbine can be operated in the partial load range CO emission compliant.

According to the invention this object is achieved by the device according to claim 1. Advantageous developments of the invention are defined in the dependent claims. In a combustion system with a combustion chamber comprising an outer shell having a support structure, with a

compressor-side and a turbine-side end, and with burners at the compressor-side end, on the combustion of the combustion system, a fuel and combustion air of the

Combustion chamber are supplied, wherein flaps are provided in the outer shell, which are suitable in the partial load operation of the combustion chamber compressor air past the burners in the To conduct combustion chamber, wherein an angle between a main flow in the combustion chamber and an opening when the flaps forming air flow is less than 90 °, the following is achieved:

To reduce CO emissions in the partial load range of the gas turbine, air can now be led around the combustion zone from the compressor end. The position of the opening flaps should hereby be chosen as far as possible so that the supplied air mass flow does not participate in the combustion in the combustion chamber, whereby the combustion temperature in the combustion zone of the combustion chamber is increased and the CO emissions of combustion are reduced. By opening the flaps, a flow channel is formed, via which the air stream taken from the compressor end flows into the combustion chamber. The channel according to the invention is such that an angle <90 ° is formed between the main flow of the combustion chamber and the secondary air flow. This ensures that no hot gas can flow into the gap between the flap and adjacent heat shield plates and that the support structure of the outer shell is not thermally stressed (for example by scaling). Advantageously, the flaps are connected via rotatable connections with the support structure of the outer shell, wherein the rotatable connections are oriented in the circumferential direction of the combustion chamber. In this way, the redirected amount of air can be well metered and mix in the lowest possible disturbance flowing in the direction of the turbine combustion gases in the combustion chamber.

It is expedient if an amount of bypassed in operation over the valves mass flow of the compressor air is set via a regulator that takes into account CO emissions, so that an optimal operating point between economy and environmental impact is found. With regard to overheating of the flaps during operation of the combustion system, it is advantageous if the combustion chamber comprises heat shield plates whose size substantially corresponds to the size of the flaps and inner sides of the flaps are provided with ceramic heat shield plates.

Furthermore, it is advantageous if the flaps are arranged distributed substantially uniformly over a circumference of the combustion chamber. Thus, the formation of the most uniform temperature profile ermöglichst or it is the temperature profile in front of the turbine influenced as little as possible, especially if the flaps are not located in the compressor near rows of ceramic heat shield plates.

It is expedient if, with the flaps open, exposed end faces of adjacent heat shield plates are provided with an apron in order to protect them from a possible thermal shock and to avoid hot gas intake under heat shield bricks.

In an advantageous embodiment of the invention, a stop of the flaps on the compressor side and in each case a circumferential collar between the outside of the flaps and support structure allows opening of the flaps only in the direction of the combustion chamber interior.

In an alternative advantageous embodiment of the invention, a stop of the flaps on the turbine side and, in each case, a circumferential collar between the inside of the flaps and the support structure makes it possible to open the flaps only to the outside.

It is advantageous if the flaps are pressed against the respective collar by resetting springs. The fail-safe position of the flaps is the flap-closed position. To guarantee this and to keep the flaps closed, the flaps are pressed against the surrounding collar in the supporting structure. This is z. B. ensured by a sufficiently strong leaf spring package on the stop side of the flaps or torsion springs with permanent restoring force on the tilting bearing of the flaps. Thus, the mechanism remains in the "closed position" and is not undesirably printed by the pressure difference between the combustion chamber interior and the outer plenum. The contact pressure on the support structure by the springs should be selected so that a minimum contact pressure is not undershot for each pressure difference occurring during operation of the gas turbine. Furthermore, the force required to open the flap is chosen so that it can be applied via the opening mechanism provided for this purpose. In an advantageous embodiment of the invention, a mechanical adjusting device for adjusting an opening width of the flaps is provided. This can be relatively easily realized with a cam which is arranged on a shaft and rests against a flap. Depending on the angle of rotation, the cam has a different radius in the direction of the flap and, with a corresponding rotation, can press on the flap against which it bears continuously. It is expedient if a contact surface for the mechanical adjusting device is provided in a turbine-side region on the cold gas side of the flaps, in particular if in the region of this contact surface a plant block, for example a graphite block or a block of a hard alloy on cobalt Chromium-based, is provided, whereby the sliding properties of the surface of the contact surface, in particular in the present in the combustion system temperatures are improved. It may also be appropriate if the contact surface and the cam are firmly connected to each other, for. B. by a bolt on the flap, in a slot on the Cam is running. Thus, both a compressive and tensile force can be transmitted to the flap.

In order to safely control the flaps from outside the plenum surrounding the combustion chamber, it is advantageous if the cam is connected to a drive shaft with length compensation by a sliding seat, whose one end passed through an outer shell surrounding the outer shell of the combustion chamber and there in a fixed bearing secured against axial displacement.

So that all flaps can be controlled centrally, it is furthermore advantageous if levers or push rods transmit the movement of a flap to adjacent flaps.

In an alternative to the mechanical adjusting device and advantageous embodiment, actuators connected to the outer shell are provided for adjusting an opening width of the flaps. This embodiment is particularly robust and reliable.

It is particularly advantageous if fastening possibilities for the actuators are provided on the outside of the flaps (for example T-slot for receiving a T-shoe or an eyelet for connecting the actuator via a)

Bolt connection).

With the present invention, a gas turbine can now be operated in the partial load range CO emissions compliant. In addition, the combustion system according to the invention could also be used to improve the combustion stability by setting more fat or lean mixtures as needed. The invention will be explained in more detail by way of example with reference to the drawings. Shown schematically and not to scale: 2 shows a detail view of a section through the combustion system parallel to the combustion chamber axis with closed mixing air opening

FIG. 3 shows a detailed view of a section through the combustion system perpendicular to the combustion chamber axis with the mixing air opening closed,

FIG. 4 shows a detailed view of a section through the combustion system parallel to the combustion chamber axis with the opening of the mixed air open,

FIG. 5 shows a detailed view of a section through the combustion system perpendicular to the combustion chamber axis when the mixed air opening is open,

FIG. 6 shows a section through the combustion chamber perpendicular to the combustion chamber axis with the mixing air opening closed,

7 shows a section through the combustion chamber perpendicular to the combustion chamber axis with the mixing air opening open, FIG.

8 shows an embodiment of a combustion system according to the invention with actuator and compressor-side stop,

FIG. 9 shows a detailed view of a section through the combustion system with actuator parallel to the combustion chamber axis with the mixing air opening closed,

FIG. 10 shows a detailed view of a section through the combustion system with actuator perpendicular to the combustion chamber axis with the mixing air opening closed,

FIG. 11 shows a detailed view of a section through the combustion system with actuator parallel to the combustion chamber axis with the mixed air opening open,

FIG. 12 shows a detailed view of a section through the combustion system with actuator perpendicular to the combustion chamber axis with the mixed air opening open,

FIG. 13 shows an exemplary embodiment of an actuator,

FIG. 14 shows an exemplary embodiment of a combustion system according to the invention with actuator and turbine-side stop, FIG. 15 shows a detailed view of a section through the combustion system with actuator and turbine-side stop parallel to the combustion chamber axis with the mixing air opening closed,

16 is a detail view of a section through the combustion system with actuator and turbine-side stop perpendicular to the combustion chamber axis with closed mixing air opening,

FIG. 17 shows a detailed view of a section through the combustion system with actuator and turbine-side stop parallel to the combustion chamber axis with the mixing air opening open,

Figure 18 is a detail view of a section through the combustion system with actuator and turbine-side stop perpendicular to the combustion chamber axis with open mixing air opening and

Figure 19 shows an embodiment of an alternative actuator for the combustion system with turbine-side stop the flap.

FIG. 1 shows schematically and by way of example an exemplary embodiment of a combustion system 1 according to the invention arranged between compressor 25 and turbine 26 with a combustion chamber 2, comprising an outer shell 3 with a support structure 4. The combustion chamber 2 has a compressor-side end 5 and a turbine-side end 6 Compressor-side end 5 is supplied in operation via a burner 7, a fuel and air from the compressor 25 of the combustion chamber 2 and burned in the combustion chamber 2. The hot combustion gases are passed through the turbine end 6 of the combustion chamber 2 in the turbine 26.

In part-load operation of the combustion system 1, according to the invention, a part 36 of the air from the compressor 25 is not passed through the burners 7 but past them via flaps 8 in the outer shell 3 into the combustion chamber 2 (FIGS. 4, 5, 8, 11, 12, 14, 17 and 18). The opening width of the flaps 8 is regulated depending on the occurring CO emissions. As a result of this measure, the combustion temperature in the combustion chamber 2 is always kept so high that the primary zone temperature relevant for CO emissions does not fall below a minimum value.

The amount of the redirected air mass flow is determined via a "CO map" stored in a controller and / or the measurement of the current CO emissions. For this purpose, at the turbine end 6 of the combustion chamber 2 and am

Inlet of the turbine 26, a CO emission sensor 27 may be arranged.

In the example of FIG. 1, the flaps 8 are opened to different degrees via a step-less mechanical adjusting device 17. Due to the gap width that forms, there is a variable area through which the amount of bypassed air mass flow can be regulated. The size of the flaps 8 is based on the dimensions of a ceramic heat shield plate 10. To lower the temperature profile before the turbine 26 as evenly as possible, the flaps 8 should be evenly distributed around the circumference of the combustion chamber 2, for example, four to twelve flaps 8 in the upper - and four to twelve in the lower part of the combustion chamber outer shell 3. The flaps 8 in Figure 1 are designed so that an opening takes place in the direction of the combustion chamber space.

The flaps 8 are attached to the support structure 4 of the combustion chamber outer shell 3 and are in the embodiment of Figure 1 in the fourth row of stones 28 (when using the flaps 8 in Silobrennkammern in the lower portion of the flame tube). In the embodiment, another row of stones would be conceivable, for example, the third row of stones 29th

The stop 13 of the flap 8 shown in FIG. 2 is located on the compressor side, the flap 8 being connected to the supporting structure 4 via a rotatable connection 9, eg a bolt. is bound. On the flap side, which is closer to the turbine 26, located on the outside of the flap 8 is a contact surface 19 for the mechanical adjusting device 17. In order to ensure better sliding properties of the surface of the contact surface 19, a sliding block or system block, eg Graphite block, are used.

To open the flap 8 is located on the contact surface 19, a cam 18, which is arranged on a shaft 30. The shaft 30 is rotatably mounted by two bearings 35 (one in front of the valve construction, one behind). The bearings 35 are firmly connected to the combustion chamber outer shell 4 z. B. welded. Between the bearings 35 with the shaft 30 positively connected cam plate 18 is arranged.

The rotational movement of the shaft 30 is converted via the cam 18 in a translational movement. The translation is achieved by the cam 18 by a rotation of z. B. 90 ° a radius Rl evenly extended to a larger radius R2 (see Figures 3 and 5). This translational movement is transmitted via the end face 31 of the cam disc 18 and via the abutment surface 19 to the flap 8, which is thereby pressed into the combustion chamber 2. By an adjustment between 0 and 90 ° thus the flap 8 can be opened differently wide.

What does not show Figure 2, is that the contact surface 19 and the cam 18 can also be firmly connected to each other, for. B. by a bolt on the flap 8, which runs in a slot on the cam 18. Thus, both a compressive and tensile force can be transmitted to the flap 8. From Figures 2 to 5 it can be seen that the support structure 4 and the flap 8 abut on the outside of the flap 8 via a peripheral collar 14. An opening of the flap 8 is by this circumferential collar 14 only in the direction of Chamber interior possible. The opening of the flap 8 is achieved by pressing the downstream part of the flap through the mechanism in the direction of the combustion chamber interior. See FIGS. 4 and 5.

By fixing the flap 8 on the compressor side, there is the formation of a circumferential gap between the flap 8 and adjacent support structure 4, can flow through the secondary air into the combustion chamber 2. The gap is wedge-shaped on the sides of the flap 8, rectangular at the downstream edge. By opening the mechanism, the end faces 11 of adjacent heat shield plates 10 are exposed. The surfaces of the end faces 11 are protected by a circumferential protective plate 12 against a possible thermal shock or hot gas intake and scaling both in the closed and in the open state of the flaps 8. The inside of the flap 8 is protected against overheating by a ceramic heat shield 10 that is appropriate for the dimensions of the construction. The attachment of the heat shield 10 on the flap 8 is z. B. by a screw connection.

The fail-safe position of the flap 8, ie the position at which it comes to the least possible damage in the event of a fault, is the flap-closed position. In order to guarantee this and to keep the flap 8 closed, the flap 8 is pressed against the encircling collar 14 in the support structure 4. B. ensured by a sufficiently strong leaf spring package 16 on the abutment side of the flap 8 or torsion springs with permanent restoring force on the tilting bearing of the flap 8 (see Figures 2 and 4). Thus, the mechanism remains in the "closed position" and is not pressed by the pressure difference between annular combustion chamber interior and outer plenum 32 undesirable. The contact pressure on the support structure 4 by the springs 16 is to be chosen so that at each pressure difference occurring during operation of the gas turbine, a minimum contact pressure is not exceeded. Furthermore, the opening of the flap 8 is necessary Force selected so that it can be applied via the mechanical adjusting device 17.

As shown in Figure 1, the torque transmission takes place by a propeller shaft 20 with length compensation by a

Sliding seat 33 for compensating the heat expansion-related relative movement of the combustion chamber 2 relative to the outer housing 21. One end of the propeller shaft 20 is guided by the outer housing 21 of the machine to the outside.

Outside the machine, the shaft 20 is secured in a fixed bearing 22 against axial displacement. In addition to storage, the shaft passage is sealed. A rotational movement of the shaft 20 by e.g. 90 ° is possible. For introducing the torque, a corresponding device is provided on the outer shaft end, for. B. a lever 34 for rotating or a shaft-hub connection for connecting an actuator.

A torque introduced outside the machine is thus transferred via the propeller shaft 20 to the cam 18, which thereby rotates.

There is a mechanical adjusting device 17 over each flap 8 distributed around the circumference. However, only one shaft 30 is extended and led out of the housing 21 with the propeller shaft 20. All other mechanical adjusting devices 17 are adjusted by a transmission of movement via levers and push rods 23, as shown in Figures 6 and 7. There is thus a primary mechanism and a plurality of secondary mechanisms to which the rotational movement of the shaft 30 of the primary mechanism is transmitted. The figure

6 shows the flaps 8, in the closed state and the figure

7 shows the flaps 8 in the opened state. Thus, a flap 8 is actuated by the articulated shaft 20 described from outside the machine and the tilting movement of this one flap 8 is transmitted via the push rod connections 23 to all other flaps 8. Figure 8 shows an alternative embodiment of the invention, in which on the outside of the flap 8 in the turbine 26 nearer area a mounting possibility for an actuator 24 is provided, for. B. a T-groove 37 for receiving a T-shoe 38 (Figure 10) or an eyelet for connecting the actuator 24 via a matching bolt connection.

As with the first embodiment with the mechanical adjusting device 17 are support structure 4 and flap 8 on the outside of the flap 8 via a peripheral collar 14 at. Opening the flap 8 is possible through this circumferential contact surface only in the direction of the combustion chamber interior.

The opening of the flap 8 is achieved by the actuator 24 extends and thus pushes the turbine 26 next part of the flap 8 in the direction of the combustion chamber interior. This is shown in FIGS. 9 to 12. By fixing the flap 8 on the side facing the compressor, it is also here to form a circumferential gap between the flap 8 and adjacent support structure 4, through the secondary air, so bypassed compressor air 36 can flow into the combustion chamber 2. The gap is wedge-shaped on the sides of the flap 8, rectangular at the downstream edge.

With respect to the thermal protection of the faces of adjacent Hitzeschilplatten 10 by means of fenders 12, and the attachment of the heat shield plates 10 and also with regard to fail-safe positions of the flaps 8, the same considerations apply as in the case of the mechanical adjusting device 17th

The actuators 24 are connected via corresponding devices 39 fixed to the outer shell 3 of the annular combustion chamber 2. By occurring during operation of the gas turbine thermal expansion and the associated relative movement of the outer shell 3 to the outer housing 21, the actuator 24 remains in the defined position on the flap mechanism. The actuators used as drives 24, eg water-cooled or air-cooled water hydraulic, oil-hydraulically or pneumatically operated cylinder with spring return 45 (fail-safe position: cylinder retracted, flap closed) are so firmly placed over the combustion chamber outer shell that by extending the piston of the Turbine-side region of the flap is pressed inward and the flap 8 thus opens.

FIG. 13 shows an actuator 24 in a greatly simplified representation. The drive is encapsulated air or watertight 40 and is replaced by a continuously flowing medium 41, e.g. Air or water, protected against overheating. The piston 42 of the cylinder is made of a low temperature conductive material and is dimensioned so that the part of the piston, which is exposed to high temperatures during extension, does not come into contact with the interior of the cylinder during reentry, but in front of the actual cylinder housing the cooled enclosure 40 is cooled down.

The connections or lines for inlet 43 and outlet 44 at the cylinders are also actively cooled, z. B. by double-walled lines, which are flowed through in the outer line channel by a continuously flowing medium circuit.

The supply of the actuators 24 with the working medium via one or more pipes 46 through the outer ßengehäuse 21. In the embodiment of Figure 8, the lines 46 are attached to the feedthrough positions on the outer housing 21 via flange connections.

The pipes form inside the gas turbine one or more ring lines 47 which are fixedly connected to the housing. For thermal expansion compensation compensators 51 are provided in the lines 46. The ring lines 47 are at least two parts with pitch in the region of the housing part executed and mounted by releasable connections (eg screw connection with cap screws). Thus, a comparatively simple assembly of the ring line 47 is made possible. In the assembled state can be lifted by loosening the connection in the joint area, the housing upper part, for example, for inspection purposes, without complete disassembly of the ring lines 47 must be done. The lines 48 to the actuators 24 are formed by individual outlets from the loop 47. The lines 48, such as flexible temperature-resistant hoses or rigid pipes with Wärmedeh- compensators, are connected via detachable connections to the actuators 24 and the ring line 47. For Inspection- or maintenance purposes such a disassembly of the lines 48 is possible.

The control of the piston 42 is ideally carried out continuously and individually for each piston 42, but can also be simplified via a pure end position control (flap to / on) and a bundling of the piston by means of ring line.

Figure 14 shows a further embodiment of the invention in which the side of the flap 8 closer to the turbine 26 is connected via a rotatable connection 9, e.g. a bolt to which support structure 4 is connected. On the flap side, which is closer to the compressor 25, located on the outside of the flap 8 is a mounting option for the actuator 24th

Flap 8 and support structure 4 are on the inside of the flap 8 via a peripheral collar 14 at. Opening the flap 8 is only possible to the outside through this circumferential contact surface. The opening of the flap 8 is achieved by the actuator 24 retracts and thus the closer to the compressor 25 part of the flap 8 is lifted from the outer shell 3. By fixing the flap 8 on the turbine side, the rotary movement of the flap 8 about the fixed point and the formation of a circumferential gap between the flap 8 and the supporting structure 4, through which secondary air 36 can flow into the combustion chamber 2, occur. The fail-safe position of the flap 8 is the flap closed position. This is ensured by the difference in pressure between the outer plenum 32 and the annular combustion chamber interior. In order to ensure a defined contact pressure, the flap 8 can be additionally pressed by springs 16, such as torsion springs on the abutment side, to the encircling collar 14 in the support structure 4. In analogy to FIGS. 2 to 5 and 9 to 12, FIGS. 15 to 18 show, in different views, both the closed and the opened flap 8 of the exemplary embodiment of the flap 8 with the actuator 24 and the turbine-side stop 15.

FIG. 19 shows an embodiment of an actuator 24 for a flap 8 with a turbine-side stop 15. This actuator 24 is similar to that shown in FIG. However, the fail-safe position is reached here when the cylinder is extended, which is ensured by a spring preload 49. Furthermore, a stop 50 may be provided for a defined end position. The flap 8 opens by retraction of the piston 42.

Claims

Combustion system (1) having a combustion chamber (2) comprising an outer shell (3) with a support structure (4), with a compressor-side (5) and a turbine-side end (6), and with burners (7) at the compressor-side end (5), via which, during operation of the combustion system (1), a fuel and combustion air are supplied to the combustion chamber (2), characterized in that flaps (8) are provided in the outer shell (3) which are suitable for compressor air in part-load operation of the combustion chamber (2) leading past the burners (7) into the combustion chamber (2), wherein an angle between a main flow in the combustion chamber (2) and an air flow forming when the flaps are opened is less than 90 °.

A combustion system (1) according to claim 1, wherein the flaps (8) are connected to the support structure (4) of the outer shell (3) via rotatable connections (9) and the rotatable ones

Compounds (9) in the circumferential direction of the combustion chamber (2) are oriented.

A combustion system (1) according to any one of claims 1 or 2, wherein an amount of compressor air mass flow redirected via the flaps (8) during operation is determined via a regulator taking into account CO emissions.

A combustion system (1) according to any one of the preceding claims, wherein the combustion chamber (2) comprises heat shield plates (10) substantially equal in size to the flaps (8) and inner sides of the flaps (8) with ceramic heat shield plates (10) for protection Überhitzug are provided.

Combustion system (1) according to one of the preceding claims, wherein the flaps (8) are distributed substantially uniformly over a circumference of the combustion chamber (2). Combustion system (1) according to one of the preceding claims, wherein, when the flaps (8) are open, exposed end faces (11) of adjacent heat shield plates (10) are provided with an apron (12). A combustion system (1) according to any one of the preceding claims, wherein a stop (13) of the flaps (8)

Compressor side is and in each case a circumferential collar (14) between the outside of the flaps (8) and support structure (4) allows opening of the flaps (8) only in the direction of the combustion chamber interior. Combustion system (1) according to one of claims 1 to 6, wherein a stop (15) of the flaps (8) on the turbine side and in each case a circumferential collar (14) between the inside of the flaps (8) and supporting structure (4) opening the flaps ( 8) only to the outside. A combustion system (1) according to any one of claims 7 or 8, wherein the flaps (8) are urged against the respective collar (14) by return springs (16). Combustion system (1) according to one of claims 1 to 7, wherein a mechanical adjusting device (17) for adjusting an opening width of the flaps (8) is provided. A combustion system (1) according to claim 10, wherein the mechanical adjusting device (17) comprises a cam (18). Combustion system (1) according to one of claims 10 and 11, wherein a contact surface (19) for the mechanical adjusting device (17) is provided in a turbine-side region on the cold gas side of the flaps (8). Combustion system (1) according to claim 12, wherein in the region of the contact surface (19) an abutment block for improving the sliding properties is provided. A combustion system (1) according to claims 11 and 12, wherein the abutment surface (19) and the cam (18) are fixedly connected to each other. Combustion system (1) according to claim 11, wherein the cam disc (18) with a drive shaft (20) with length compensation by a sliding seat is connected, one end of which through an outer shell (3) of the combustion chamber (2) surrounding the outer housing (21) and There is secured in a fixed bearing (22) against axial displacement. A combustion system (1) according to any one of claims 10 to 15, wherein levers or push rods (23) transmit movement of a flap (8) to adjacent flaps (8). Combustion system (1) according to one of claims 1 to 9, wherein actuators (24) fixedly connected to the outer shell (3) are provided for setting an opening width of the flaps (8). Combustion system (1) according to claim 17, wherein attachment possibilities for the actuators (24) are provided on the outside of the flaps (8).