Patent Application
20100323309
The present invention relates to a method for reducing self-induced flame oscillations and to a burner with which this method can be carried out.
Self-induced flame oscillations frequently occur in combustion chambers and in this context are also known as combustion hum. Combustion chamber oscillations are caused by feedback between pressure changes in the combustion chamber and fluctuations in the mass flow of fuel and air. The combustion chamber oscillations constitute an undesirable side-effect of the combustion process, as they place increased mechanical and thermal stress on the burner components and the combustion chamber components. In addition, combustion hum produces increased levels of noise pollution in the vicinity of the combustion chamber in question.
Reducing combustion hum, i.e. minimizing self-induced flame oscillations, has hitherto been achieved in some cases with the aid of Helmholtz resonators. Another possibility is to supply an increased amount of pilot gas to the burner used. Pilot gas, i.e. pilot fuel, is normally used to stabilize the flame. However, increasing the pilot gas supply results in higher NOX emissions.
The object of the present invention is therefore to provide an advantageous method for reducing self-induced flame oscillations. Another object of the present invention is to provide an advantageous burner.
The first object is achieved by a method as claimed in the claims. The second object is achieved by a burner as claimed in the claims. The dependent claims contain further advantageous embodiments of the invention.
In the method according to the invention for reducing self-induced flame oscillations, into a first mass flow of fluid flowing through a jet nozzle from a fluid inlet opening to a fluid outlet opening, there is injected a second mass flow of fluid at least one axial position on the jet nozzle downstream of the fluid inlet opening, one of the two mass flows of fluid being air. The other mass flow of fluid comprises a fuel. By injecting the fuel and/or air at a plurality of axial positions into a main mass flow of fluid flowing through the jet nozzle, the response e.g. of the mass flow of fuel can be smeared such that resonance can only occur for a small portion of the mass flow. Smearing of the delay between injection and combustion is achieved by the method according to the invention. The method according to the invention can be used in particular for operating a jet burner, while still retaining the positive characteristics of a jet burner.
Alternatively or additionally, the second mass flow of fluid can be injected at at least one radial position on the jet nozzle with respect to the circumference of the jet nozzle.
This likewise achieves the smearing of the delay time between injection and combustion as described above.
Different radial fuel distributions are preferably implemented. Here it is advantageous e.g. during part-load operation to run the inner areas richer, i.e. the areas leading to the center of a housing, thereby enabling flame extinction and CO emissions to be prevented.
The second mass flow of fluid can preferably be injected into the first mass flow of fluid at a plurality of positions around the circumference of the jet nozzle. In particular, the second mass flow of fluid can be injected into the first mass flow of fluid at a plurality of positions disposed mutually offset in the axial direction around the circumference of the jet nozzle. As a result, the flow in the jet nozzle is not always attenuated at the same circumferential position.
The mass flow of fluid comprising a fuel can be, for example, an air/fuel mixture. The fuel used can, in particular, be gaseous fuel, such as natural gas or a synthesis gas. For natural gas, as the mass flows of fuel are much smaller than the air mass flows, there is unlikely to be a significant increase in pressure loss even in the case of injection perpendicular to the flow direction of the air. Moreover, the method can also be applied to liquid fuels.
In addition to the second mass flow of fluid, a third mass flow of fluid can be injected into the first mass flow of fluid. For example, the second mass flow of fluid can comprise a fuel and the first mass flow of fluid can comprise air. The third mass flow of fluid can likewise comprise air, steam or another gas, e.g. an inert gas. The second and/or the third mass flow of fluid can be injected into the first mass flow of fluid at an angle of between 0° and 90°. For example, the second mass flow of fluid can be injected into the first mass flow of fluid at an angle of 90° and the third mass flow of fluid can be injected into the first mass flow of fluid at an angle of 45°. Said first and third mass flow of fluid can be, for example, a mass flow of air, and the second mass flow of fluid can be a mass flow of fuel. The advantage of jet-in-crossflow injection is that it helps to increase the mixing of the air/fuel mixture, while wall film formation is primarily a measure to counteract flashback.
The burner according to the invention comprises at least one jet nozzle with a main fluid inlet opening and a fluid outlet opening, the main fluid inlet opening being connected to a fluid supply line. The burner according to the invention is characterized in that at least one secondary fluid inlet opening connected to a fluid supply line is disposed at least one axial position on the jet nozzle downstream of the main fluid inlet opening.
The fluid supply line connected to the main fluid inlet opening can be implemented, for example, as a fuel supply line, as an air supply line or as a fuel/air mixture supply line. The main fluid inlet opening is preferably connected to an air supply line. Although the fluid supply line connected to at least one secondary fluid inlet opening can preferably be implemented as a fuel supply line, it can also be implemented as an air supply line, as a steam supply line, as a nitrogen supply line or as an air/fuel mixture supply line.
It is basically advantageous if the secondary fluid inlet openings are disposed at a plurality of axial positions on the jet nozzle. The secondary fluid inlet openings, which can be disposed at different axial positions, can be, in particular, air inlet openings. In addition, secondary fluid inlet openings can be disposed at a plurality of positions along the circumference of the jet nozzle. In this case it is advantageous if secondary fluid inlet openings are disposed at a plurality of positions disposed mutually offset in the axial direction along the circumference of the jet nozzle. This means that the flow in the jet nozzle is not always attenuated at the same circumferential position.
The main fluid inlet opening can preferably be connected to an air supply line and a portion of the secondary fluid inlet openings can be connected to a fuel supply line. In particular, a first portion of the secondary fluid inlet openings can be connected to a fuel supply line and a second portion of the secondary fluid inlet openings can be connected to an air supply line.
In addition, the secondary fluid inlet openings and the main fluid inlet opening can have a central axis in each case. Said central axes of the secondary fluid inlet openings can be at an angle of between 0° and 90° to the central axis of the main fluid inlet opening and/or to the central axis of the jet nozzle. Advantageously, the central axes of a first portion of the secondary fluid inlet openings can be at 90° to the central axis of the main fluid inlet opening and/or to the central axis of the jet nozzle, and the central axes of a second portion of the secondary fluid inlet openings can be at 45° to the central axis of the main fluid inlet opening and/or to the central axis of the jet nozzle. The advantage of jet-in-crossflow injection is that it helps to increase the mixing of the air/fuel mixture, while wall film formation is primarily a measure to counteract flashback.
The secondary fluid inlet openings and the main fluid inlet opening may have a central axis in each case and the central axes of the secondary fluid inlet openings can be at an angle of between 0° and 90° to a radial direction with respect to the central axis of the main fluid inlet opening. This enables injection to take place tangentially along the circumference of the jet nozzle, thereby producing a wall film on the inner surface of the jet nozzle. Injection along the circumference of the jet nozzle can also be used to produce swirl in the jet nozzle.
A plurality of fluid supply lines connected to secondary fluid inlet openings can be interconnected via an annular distributor disposed along the circumference of the jet nozzle.
In addition, a fuel nozzle can be disposed in the main fluid inlet opening or immediately preceding the main fluid inlet opening. The fuel nozzle can comprise a fuel distributor which is disposed in or immediately preceding the main fluid inlet opening.
At least one secondary fluid inlet opening can be implemented as an annular gap running along the circumference of the jet nozzle. In this case the burner according to the invention can comprise a plurality of jet nozzles, the annular gaps of the different jet nozzles being disposed at different axial positions in each case. Varying the axial positions of the annular gaps provides an additional design parameter for counteracting thermoacoustic flame oscillations.
The burner according to the invention can comprise a plurality of jet nozzles disposed e.g. annularly with respect to the central axis of the burner. It can also incorporate one or more pilot burners.
The burner according to the invention is preferably used in a gas turbine.
Further features, characteristics and advantages of the present invention will now be described in greater detail using exemplary embodiments and with reference to the accompanying drawings in which:
A first exemplary embodiment of the invention will now be explained in greater detail with reference to
The jet nozzle 2 is fluidically connected to a compressor. The compressed air from the compressor is conveyed via an annular gap 22 to the main fluid inlet opening 8 and/or is conveyed radially with respect to the central axis 5 of the jet nozzle 2 via an air inlet opening 23 to the main fluid inlet opening 8. In the event that the compressed air is supplied through the annular gap 22 of the jet nozzle 2, said compressed air flows through the annular gap 22 in the direction of the arrow identified by the reference character 15, i.e. parallel to the central axis 5 of the jet nozzle 2. The air flowing in the direction of the arrow 15 is then deflected through 180° at the back wall 24 of the burner 1 and then flows through the main fluid inlet opening 8 into the jet nozzle 2. The flow direction of the air inside the jet nozzle 2 is indicated by an arrow 10.
Additionally or alternatively to feeding the compressed air through the annular gap 22, the compressed air from the compressor can also be supplied through an opening 23 disposed radially in the housing 6 of the burner 1 with respect to the central axis 5 of the jet nozzle 2. The flow direction of the compressed air flowing through the opening 23 is indicated by an arrow 26. In this case the compressed air is then deflected through 90° and then flows into the jet nozzle 2 through the main fluid inlet opening 8.
The burner according to the invention 1 can basically also be implemented without the outer housing section 27, i.e. without an external casing 27. In this case the compressed air can flow directly into the “plenum”, i.e. the area between the back wall 24 and the main fluid inlet opening 8. The burner according to the invention 1 can also be implemented even without the back wall 24.
The jet nozzle 2 is encircled radially by an annular distributor 7 which is supplied with fuel 12 via a fuel supply line 13. The annular distributor 7 has a number of secondary fluid inlet openings 14 through which fuel can be injected into the mass flow of air flowing through the jet nozzle 2. The secondary fluid inlet openings 14 can be implemented as a slit or an oval nozzle. This is particularly advantageous for synthesis gas injection, as it means that a smaller inflow surface is offered to the flow of air. This also results in a lesser tendency to recirculation downstream of fuel injection. The flow direction of the fuel 12 injected into the jet nozzle 2 through the secondary fluid inlet openings 14 is indicated by arrows 17. Said flow direction 17 of the injected fuel 12 runs perpendicular to the central axis 5 of the jet nozzle 2 and therefore also perpendicular to the main flow direction 10 of the compressed air 11 flowing through the jet nozzle 2.
In
Inside the jet nozzle 2, the injection of fuel 12 into the compressed air 11 flowing through the jet nozzle 2 creates a fuel/air mixture which leaves the jet nozzle 2 through the fluid outlet opening 9 in the direction of the combustion chamber 18.
In addition to the features already described in connection with
In
The fuel can basically be supplied via one or more fuel supply lines 13 and transported to the individual jet nozzles 2 via an annular distributor 7. If a plurality of fuel supply lines 13 are present, these can be advantageously disposed along the circumference of the burner. It is further advantageous if the injection of the fuel into the air jet is carried out at more than one axial position of the jet pipe 2. In addition, to ensure better mixing, injection can take place at a plurality of circumferential positions on the jet pipe 2.
A second exemplary embodiment will now be described in greater detail with reference to
In
Disposed at different axial positions on the jet nozzle 2 are further secondary fluid inlet openings 25 through which compressed air can be injected into the jet nozzle 2. Said compressed air is fed to the secondary fluid inlet openings 25 via an annular gap 22. In
In
The air used for the axially stepped air injection in this exemplary embodiment can either be extracted from the annular gap 22 or directly from a plenum surrounding the burner 301 and injected into the fuel/air mixture in the jet nozzle. Said air can be introduced as a jet into the crossflow or as a wall film. The advantage of jet-in-crossflow injection is that it helps to increase the mixing of the fuel/air mixture, while wall film formation is primarily a measure to counteract possible flashback. In addition, the air can be injected into the jet nozzle 2 tangentially to the circumference thereof. Said wall film can be produced over the entire inner surface of the jet nozzle 2. Tangential injection can also be used to generate swirl in the jet nozzle 2.
It is also conceivable for jet-in-crossflow injection to be combined with wall film injection by disposing the nozzles in very close succession. Jet-in-crossflow injection ensures improved mixing, particularly also in the core region of the jet, and the film of the second nozzle strengthens the flow boundary layer, thereby preventing flashback. This design is particularly advantageous for central co-flow injection into the main fuel injection, e.g. for synthesis gas. If there is a high proportion of air in the axial stepping, it is possible to adjust the nozzle diameter of the jet nozzle such that the flow rate in the nozzle remains essentially the same.
A third exemplary embodiment will now be explained in greater detail with reference to
Each jet nozzle 2 comprises a main fluid inlet opening 8 and a fluid outlet opening 9. The fluid outlet opening 9 leads into the combustion chamber 18. A fuel nozzle 19 is disposed in the main fluid inlet opening 8. The fuel nozzle 19 comprises a fuel distributor 20 which enables fuel 12 to be injected into the jet nozzle 2 at different radial positions and different circumferential positions of the main fluid inlet opening 8. The flow direction of the injected fuel 12 is indicated by arrows 17.
An annular gap 21 is disposed at another axial position on the jet nozzle 2 downstream in respect of the flow directions 10 and 17. Air is injected into the jet nozzle 2 through the annular gap 21. The flow direction of the injected air is indicated by arrows 16. Said air is injected into the jet nozzle 2 virtually parallel to the central axis 5 thereof. In contrast to the variant shown in
The variants shown in
In all the exemplary embodiments and variants, the inventive burner 1, 101, 201, 301, 401 can also be implemented without the outer housing section 27 or rather without an outer casing 27. In this case, the compressed air can flow directly into the “plenum”, i.e. the area between the back wall 24 and the main fluid inlet opening 8. The inventive burner 1, 101, 201, 301, 401 can also be implemented without the back wall 24.
Varying the axial positions of the annular gaps 21 provides an additional design parameter to guard against thermoacoustic flame oscillations. It is also possible to provide different jet nozzles 2 of a burner 401 with annular gaps 21 at different axial positions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08000497.1 | Jan 2008 | EP | regional |
This application is the US National Stage of International Application No. PCT/EP2008/054969, filed Apr. 24, 2008, and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08000497.1 EP filed Jan. 11, 2008. All of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/054969 | 4/24/2008 | WO | 00 | 8/20/2010 |
