Patent Application
20100300104
The present invention relates to a burner, incorporating a pilot cone and a mounting insert. Further, the invention relates to an operating method for increasing the service life of a burner which incorporates a pilot cone and a mounting insert, in which the pilot cone has a cone side. In addition, the invention relates to an assembly procedure for assembling and disassembling an assembly consisting of a pilot cone with a pilot cone side.
It is known that gas turbines contain the following components: a compressor, for compressing air; a combustion chamber for generating a hot gas by burning fuel in the presence of compressed air, which is produced by the compressor; and a turbine for the depressurization of the hot gas which has been generated in the combustion chamber. It is further known that gas turbines give off unwanted nitrogen oxide (NOx) and carbon monoxide (CO). One factor which is known to influence the emission of NOx is the combustion temperature. The scale of the NOx given off is reduced if the combustion temperature is lowered. However, higher combustion temperatures are desirable in order to achieve a higher efficiency and oxidation of the CO.
Two-stage combustion systems have been developed, which ensure efficient combustion and reduced emissions of NOx. In a two-stage combustion system, diffusion combustion is carried out in the first stage, to produce ignition and stability of the flame. In the second stage, combustion is effected using a premix, to reduce the emissions of NOx.
As shown in
The compressed air 101 flows from the compressor 50 between supporting ribs 7 through the main fuel swirlers 8 into the main combustion zone 9. Each of the main fuel swirlers 8 provides numerous swirler vanes 80. The compressed air 12 is forced through a set of vanes 10, which are located within the ignition swirler 11, into the ignition flame zone. Within the pilot cone 20, the compressed air 12 mixes with the ignition fuel 30 and is transported into the ignition flame zone 23, where it burns.
Another burner system is the combustion system based on jet flames. By comparison with spin-stabilized systems, combustion systems based on jet flames offer advantages, in particular from a thermo-acoustic point of view, due to their distributed heat release zones and the lack of spin-induced swirling.
Jet flames are stabilized by mixing in hot recirculating gases. The recirculation zone temperatures necessary for this cannot be guaranteed in gas turbines, in particular in the lower partial-load range, by the known annular arrangement of the jets with a central recirculation zone. Here again, therefore, additional piloting is required, and again consists of a pilot burner and a pilot cone.
Here, the pilot cone is welded onto a mounting insert. Fuel or combustion air is fed to the combustion chamber through this mounting insert, for example by means of suitable passages. During operation, thermal expansions occur. These are the different thermal expansions of the various components, and also by the radial thermal expansion of the pilot cone. However, the permanent welded joint inhibits these thermal expansions, which leads to very high stresses on the cone itself. Due to the stresses occurring operation, the components are damaged, for example by cracking, and must as a result be replaced sooner. Hence the inhibiting of the thermal expansion leads to a reduction in the cyclic service life of the components, in particular the cone.
It is therefore the object of the present invention to specify a burner which has a longer service life. An object is also to specify a method for increasing the service life of a burner. In addition, another object of the invention is to specify an assembly method for a burner.
In respect of the burner, this object is achieved in accordance with the invention by the specification of a burner incorporating a pilot cone and a mounting insert, where the pilot cone is constructed as a pilot cone assembly which is decoupled from the mounting insert.
The invention is based on the consideration that the service life of the components, i.e. the pilot cone and the mounting insert, is significantly impaired by the inhibition of the thermal expansion of the components in the radial and axial directions, and the associated stresses which occur. Precisely this is now prevented with the aid of the invention, namely the construction of the pilot cone as an assembly and the decoupling of this assembly from the mounting insert. The decoupling of the two components leads to a longer service life for the pilot cone and to a reduction in the stresses.
Preferably, the decoupled pilot cone assembly will have a cone side and will incorporate, apart from the cone side, at least one further side. Here, the cone side is that side which is arranged in the combustion chamber itself and is directly exposed to the hot gas.
The decoupled pilot cone assembly will preferably also incorporate a seating side, which is arranged essentially axially to the direction of flow of the combustion gas.
In a preferred embodiment, the axial seating side has a screw fixing to the mounting insert. Preferably, the axial seating side will be essentially parallel to one of the sides of the mounting insert. This enables the pilot cone assembly to be fixed to the mounting insert. Here, the axial seating side has a side at the rear end, that is essentially at the rear end relative to the direction of flow for the mounting insert. Here, in particular, the temperature is lower. Here the compressor air is only at about 450-500° C. This means that the side of the mounting insert and also the axial mating side heat up and expand equally. Excessive heating of the axial seating side is also avoided. Stresses due to the screw fixing are thereby avoided. The service life of the pilot cone assembly is thereby significantly increased.
In a preferred embodiment, the at least one further side is essentially parallel to one of the sides of the mounting insert. A gap thus results between the mounting insert and the pilot cone assembly. This gap is then so calculated that at operating temperatures a gap is still formed between the front side of the cone, in the direction of flow, and the mounting insert, or the side of the cone which is lower relative to the direction of flow lands exactly on the mounting insert, in a radial direction. Here too, the gap can be purged by compressor air in order to avoid ignition of residual gas, for example, which can accumulate in the gap.
Preferably, the individual sides of the pilot cone assembly will be welded together. However, it is also conceivable that this pilot cone assembly is already formed in this shape during its manufacture. Other types of joint are also conceivable, such as for example soldering or creative forming.
The further side will preferably have a sealing ring, which is arranged between the further side and the mounting insert. The gap between the mounting insert and the pilot cone assembly is then closed off by means of the sealing ring. This makes it possible to avoid the purging of the gap by compressor air. Also, residual gas can no longer accumulate in the gap itself. If the gap is closed off by means of a sealing ring, it is then possible to reduce the length of both the further side and also the axial seating side. The welding of all the sides is no longer necessary. The pilot cone is thereby made lighter in weight, and material costs can be saved.
The sealing ring will preferably be a C-ring or a piston ring. This fulfills very well the sealing function and, if necessary, a defined leakage can be arranged, for example to effect purging.
A gas turbine will preferably be equipped with such a burner.
In respect of the method, this objective is, in accordance with the invention, by the specification of an operating method for increasing the service life of a burner, which incorporates a pilot cone assembly and a mounting insert, where the pilot cone assembly has a cone side, where the pilot cone assembly incorporates in addition to the cone side at least one further side, where this further side is arranged to be essentially parallel to and spaced away from one of the sides of the mounting insert, so that between the further side and the side of the mounting insert there is a defined gap, which in operation is significantly reduced, at least at one point of contact between the further side and the side of the mounting insert, by the thermal expansion.
In respect of the assembly method, this objective is achieved in accordance with the invention by the specification of an assembly method, for assembling and disassembling a pilot cone assembly with a pilot cone side, and of a mounting insert where the pilot cone assembly incorporates a cone side and in addition at least one axial seating side, where the axial seating side is parallel to a screw attachment side on the mounting insert, onto which it is bolted during assembly/disassembly. This simple screw fixing permits the pilot cone assembly to be simply and rapidly detached from the mounting insert. The fact that the pilot cone assembly is decoupled from the mounting insert prevents damage during assembly/disassembly.
In what follows, an example of the invention is explained in more detail by reference to a drawing.
In this are shown, in a simplified form and not to scale:
In all the figures, parts which are the same have the same reference marks.
This is now avoided with the aid of the invention.
The decoupled assembly thus permits thermally induced expansion of the individual components, that is of the pilot cone assembly and also the mounting insert 110. Stresses on the components are thereby avoided, by which means the service life is lengthened.
The gap 220, which results between the essentially parallel and spaced-apart long side 260 and the further side 180 of the assembly is calculated to be defined such that, during operation, it is significantly narrowed or is closed up by thermal expansion at least at one point of contact 300, 310 between the further side 180 and the long side 260. Here, the gap 220 can be adjusted in such a way that—as with the weld point for a state of the art burner—the point of contact 300 between the further side 180 and the long side 260 lies essentially downstream. That is to say, after the operating temperature has been reached the gap 220 is closed up on the cone side 105 (here the front edge of the cone 290) and the long side 260. Here too, the gap 220 can have a through-flow of cooling or compressor air, so-called barrier air, to avoid a flashback. The point of contact 310 between the further side 180 and the long side 260 can also lie essentially upstream. The cone side 105, i.e. the front edge 290 of the cone, can then continue to form a gap 220 with the long side 260, even at operating temperature. After the operating temperature has been reached, the further side 180 lies radially against the long side 260, so to speak at the lower upstream end of the mounting insert 110.
In addition to the further side 180, the assembly also incorporates an axial seating side 190. This is essentially parallel to one side of the mounting insert 110, which is referred to in what follows as the screw attachment side 280. For the purpose of attaching the entire pilot cone assembly to the mounting insert 110, the axial seating side 190 is bolted to the screw attachment side 280 by a screw fixing 240. In this region, the compressor air has a temperature of only 450-500° C.; this represents a comparatively lower temperature than is the case, for example, in the combustion chamber. As the temperatures here are lower, the cone assembly and the mounting insert 110 expand equally in this region. This has the advantage that the stresses which can now arise even with the inventive screw fixing 240, for example due to inhibition of the thermal expansion of the components, are now significantly reduced both in the case of the mounting insert 110 and also for the pilot cone assembly, which also lengthens the service life of both components. In addition, a significantly simpler assembly/disassembly of the pilot cone assembly and also of the mounting insert 110 is possible, because these are no longer joined to each other by welding, but represent in each case a decoupled component. It is also possible to provide an axial seal 360 between the axial seating side 190 and the screw attachment side 280, that is to say on the so-called cold side of the burner. Since the two sides there are only dependent on the prewarming of the air, and not on the heat transfer on the hot gas side, the thermal expansion is then equal for both sides. As a result, the proposed axial seal 360 is therefore tight to engineering standards. In addition, or alternatively, a leakage bore hole 380 can also be provided. This can consist, for example, of one or more bore holes. If the gap 220 is cooled with barrier air, the leakage bore hole 380 permits precise adjustment of this barrier air. This has the advantage that the air is uniformly distributed around the perimeter. In addition, it has the advantage that unwanted effects on the flame stability or the combustion regime, due to excessive or undistributed barrier air, are avoided. The barrier air can thus be precisely adjusted using the leakage bore hole 380. Higher emissions can thereby be avoided.
The method in accordance with the invention and also the inventive burner with a decoupled pilot cone assembly and mounting insert 110 thus make it possible significantly to reduce the stresses on the two components. The inventive pilot cone assembly and mounting insert 110 exhibit a higher service life. The improved assembly method increases the assembly/disassembly of the pilot cone assembly and also of the mounting insert 110. The actual decoupling between the pilot cone assembly and the mounting insert 110 also contributes to improved assembly/disassembly of the two components.
