METHOD OF CALIBRATING THE AIR FLOW OF A SWIRLER OF A GAS TURBINE BURNER

The present invention is related to a calibration means for a swirler of a burner of a gas turbine, the swirler comprising a plurality of vanes and a plurality of mixing channels between the vanes, wherein each mixing channel is enabled to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel. Further, the invention is related to a swirler for a burner of a gas turbine, comprising calibration means, a plurality of vanes and a plurality of mixing channels between the vanes, wherein each mixing channel is enabled to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel, further to a burner of a gas turbine, comprising an air supply, a fuel supply, a swirler and a combustion chamber and further to a gas turbine, comprising at least one burner.

Modern gas turbines are commonly used in industrial

applications. To achieve the goal of an environmental friendly operation of the gas turbine, the gas turbine is operated in a DLE combustion mode (DLE: Dry Low Emission) producing low emissions, especially low NOx emissions. To achieve this goal, a good and uniform mixing of air and fuel in a burner of the gas turbine has to be achieved. In modern gas turbines swirlers are used for this task. Figure 1 shows a sectional view of an example of a gas turbine 40. The gas turbine 40 comprises an air inlet 41, a compressor section 42, a burner section 44 and a turbine section 45 which are generally arranged in flow series and generally in the direction of a longitudinal rotation axis 81. The gas turbine 40 further comprises a shaft 47 which is rotatable about rotational axis 81 and which extends longitudinally through the gas turbine 40. The shaft 47 drivingly connects the turbine section 45 to the compressor section 42. In operation of the gas turbine 40, air 80, which is taken in through the air inlet 41, is compressed by compressor blades 43 in the compressor section 42 and delivered to the burner section 44. The burner section 44 comprises a combustion chamber 63, defined by a double wall can, and at least one burner 60 fixed to the combustion chamber 63. The compressed air 80 passing through the compressor section 42 enters via an air supply 61 into a swirler 20 and is discharged from the swirler 20 into the combustion chamber 63. In mixing channels 22 (not shown) of the swirler 20, the air 80 is mixed with gaseous or liquid fuel, provided by a fuel supply 62 of the burner 60. The air/fuel mixture is burned afterwards in the combustion chamber 63 and the combustion gas or working gas from the combustion is channelled to the turbine section 45. The turbine section 45 comprises a number of turbine blades 46 carrying discs attached to the shaft 47. In the present example, two discs each carry an annular array of the turbine blades 46 are shown. However, the number of blade carrying discs could be different, for instance only one disc or more than two discs. In addition, guiding vanes 48, which are fixed to a stator of the gas turbine 40, are disposed between the turbine blades 46. The combustion gas from the combustion chamber 63 enters the turbine section 45 and drives the turbine blades 46 which in return rotates the shaft 47. The guiding vanes 48 serve to optimise the angle of the

combustion exhaust gas on the turbine blades 46.

As mentioned above, variations in air/fuel distributions in the burner have a negative influence on the temperature distribution and the uniformity of the flame in this specific burner. The variations in air/fuel distributions are mostly caused by the used swirler of the burner. Therefore it is known, to specifically choose the swirler which is suited best for a specific burner form a plurality of ready built swirlers held in stock. By doing so, a uniform flame

distribution in the burner can be achieved. This leads to a low emission operation of the gas turbine and in addition to a longer life time of the hot components of the gas turbine.

It is an object of the present invention to solve the

aforesaid problems and drawbacks at least partly. In

particular, it is an object of the present invention to provide calibration means, a swirler, a burner and a gas turbine, which allow a low emission operation of a gas turbine and improve the life time of the gas turbine

especially in an easy and cost efficient way. The aforesaid problems are solved by calibrations means for a swirler for a burner of a gas turbine according to

independent claim 1 and by a gas turbine having a calibrated swirler according to claim 13. Further features and details of the present invention result from the subclaims, the description and the drawings. Features and details discussed with respect to the calibration means can also be applied to the swirler, the burner and the gas turbine and vice versa, if of technical sense. According to the first aspect of the invention the aforesaid object is achieved by a calibration means for a swirler of a burner of a gas turbine, the swirler comprising a plurality of vanes and a plurality of mixing channels between the vanes, wherein each mixing channels is enable to direct air from a radially outer end of the mixing channel to a radially inner end of the mixing channel. The calibration means according to the invention is characterized in that the calibration means can be arranged at the swirler in such a way that the calibration means is enabled to manipulate the flow of the channelled air in at least one of the mixing channels .

The swirler described in the preamble is used in a burner of a gas turbine to produce an air/fuel mixture. This air/fuel mixture is afterwards burned in a combustion chamber of the burner. To achieve a very uniform temperature distribution in the flame and therefore to operate the burner of the gas turbine in a low NOx emission regime and additionally

extending the life time of the hot components of the burner, an initially uniform distribution of the air/fuel mixture is necessary. A calibration means according to the invention allows to use a ready built swirler in a burner of a gas turbine and to achieve an especially uniform distribution of the air/fuel mixture provided by the swirler without

exchanging the swirler in total. The calibration means according to the invention is able to manipulate the flow of the channelled air in at least one of the mixing channels. Therefore the flow of the channelled air in this at least one mixing channel of the swirler can be changed such that the swirler in total provides a uniform air/fuel mixture

distribution. Especially and in addition the calibration means can enhance turbulences in the channelled air in the at least one mixing channel of the swirler and therefore enhance the mixing of the air with fuel fluid. Thus an even better mixing of air and fuel can be achieved. By using of

calibration means according to the invention therefore a broad variety of swirlers can be adapted to be used in a specific burner of a gas turbine. Only the calibration means has to be chosen such that with a specific swirler a uniform distribution of the air/fuel mixture provided by the swirler can be achieved. This allows reducing the amount of swirlers held in stock and therefore lowers the cost in the production and assembling of burners for gas turbines. In addition the evenness of the distribution of the air/fuel mixture provided by the swirler can be improved and therefore a more uniform flame temperature in the burner of the gas turbine can be achieved. This causes lower NOx emissions and a longer life time of the hot components in the burner and/or the gas turbine .

Further, calibration means according to the invention can be characterized in that the calibration means can be arranged at and/or near the radially outer end of the mixing channels. To achieve a good mixing of air and fuel, fuel outlets can be arranged in the mixing channels of the swirler. As mentioned above, with a calibration means according to the invention a flow of the channelled air in the mixing channels of the swirler with an improved evenness and a better turbulence characteristic respectively can be created. Such an improved stream of channelled air in the mixing channels mixes better with the fuel provided from the fuel outlets. Therefore a positioning of calibration means according to the invention at and/or near the radially outer end of the mixing channel allows ensuring all effects mentioned above in a very easy way, and especially ensures that the calibration means according to the invention is placed before fuel outlets arranged in the mixing channels.

In a further advanced arrangement of a calibration means according to the invention, the calibration means is attached to a closing plate, wherein the closing plate is enabled to be arranged at the swirler. It is known to use closing plates with swirlers. Such closing plates often form the upper capping of the swirler. With calibration means attached to a closing plate it is therefore especially easy to place the calibration means in such a position relative to the swirler, in which the calibration means are able to manipulate the flow of the channelled air in at least one of the mixing channels of the swirler. For a calibration of the swirler, especially to achieve a uniform distribution of the air/fuel mixture provided by the swirler, it is therefore sufficient, to choose a closing plate with appropriate calibration means to achieve this goal without changing the swirler in total. This reduces the costs of the calibration process of a swirler for a burner of a gas turbine.

In addition, calibration means according to the invention can be characterized in that the calibration means comprises a plurality of calibration elements; in particular the calibration means comprises a calibration element for each mixing channel, wherein each calibration element is enabled to manipulate flow of the channelled air in one of the mixing channels. This feature allows the calibration of several mixing channels at once and only one calibration means. In particular, all of the mixing channels of a swirler can be calibrated with only one calibration means. This is a very easy and simple way of achieve a very uniform distribution of the air/fuel mixture provided by the swirler, the swirler calibrated by calibration means according to the invention.

According to a further development of calibration means according to the invention, the calibration' s elements of the calibration means are constructed identically. A calibration means with identical calibration elements can be especially produced more easily, because the construction process is the same for all of the calibration elements. A very cost

efficient production of the calibration elements of the calibration means can therefore be achieved.

Alternative, according to another development of the

invention, the calibration elements of the calibration means are adapted for the respective mixing channel. Especially the calibration elements of the calibration means can be

different from each other. The adaption of a calibration element to a respective mixing channel of the swirler allows especial good calibration of the flow of the channelled air in this mixing channel. A very uniform distribution of the channelled air in all of the mixing channels manipulated by calibration elements of the calibration means can therefore be achieved. A burner of a gas turbine with a swirler with such calibration means can therefore achieve a very good burning performance, especially is able to run in a very low emission mode.

According to another preferred development of the invention a calibration means comprises a blocking device to block at least partly the flow of the channelled air in at least one of the mixing channels, wherein in particular the blocking device comprises at least one aperture, in particular a hole. Naturally, such a blocking device can be a calibration element according to the invention. With a blocking device, the amount of air in the respective mixing channel can be reduced in a controlled way. Even further, such a blocking device produces on its edges turbulences in the flow of the channelled air. This causes a better mixing of the channelled air with fuel provided in the swirler. Identical or different blocking devices for several or all of the mixing channels can be provided achieving the advantages already described above in respect to the calibration elements. An aperture, especially a hole, enhances the amount of turbulences caused in the channelled air by the blocking device. A gain in turbulences in the channelled air improves the ability to mix with fuel provided in the swirler. An even better mixing of fuel and air can therefore be achieved.

In another alternative development of the invention, the calibration means comprises a wire mesh to manipulate the flow of the channelled air in at least one of the mixing channels. Naturally, also such a wire mesh can be a

calibration element according to the invention. Such a wire mesh produces turbulences in the channelled air in a very easy way by the interaction of the wires of the wire mesh with the channelled air. A wire mesh is very low in weight and easy to produce. In addition, a wire mesh is a mass product and therefore low in costs.

According to a further development of the invention, the wire mesh completely covers the radially outer end of at least one of the mixing channels. This ensures a very efficient

turbulence production in the channelled air caused by the wire mesh. Preferentially all mixing channels are covered completely with the wire mesh. In particular, the complete outer boundary of the swirler is circumferential covered with a wire mesh. This is a very easy way to automatically cover all radially outer ends of all mixing channels.

According to another development of the invention a

calibration means can be provided, characterized in that the wire mesh has a uniform gauge. Such a wire mesh is a bulk product and therefore extremely low in cost. This allows providing a calibration of a swirler in a very low cost regime . Further, according to an alternative development of the invention, the wire mesh has a non-uniform gauge, in

particular along a height of the calibration means. With a non-uniform gauge an even better calibration, especially an individual calibration for each of the mixing channels, can be achieved. It is also possible, that near the fuel outlet a thinner gauge of wire is used for the wire mesh, causing more turbulence in this area. Therefore a better mixing of such manipulated air with the fuel provided from a fuel outlet can be achieved. In another possibility to achieve a non-uniform gauge, also the mesh spacing and/or density can be altered; especially a mesh with 45° up to 90° can be used.

According to a further preferred development of the invention the wires of the wire mesh comprise turbulence generating elements, in particular the wires of the mesh are constructed as swirling elements. Such swirler elements enhance further the turbulence production caused by the wire mesh and

therefore improve the mixing of the manipulated channelled air with fuel provided in the swirler. Such swirling elements can for instance be fins or ribs attached to the wires.

Alternative or additional the wires themselves can be

constructed as swirling elements. To achieve this, the wires can for instance be spiral-shank or serrated. Naturally other embodiments of swirler elements or wires constructed as swirler elements are possible.

According to a second aspect of the invention, the object is solved by a swirler for a burner of a gas turbine, comprising calibration means, a plurality of vanes and a plurality of mixing channels between the vanes, wherein each mixing channel is enabled to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel. A swirler according to the invention is

characterized in that the calibration means is constructed according to the first aspect of the invention. The use of such a calibration means provides the same advantages, which have been discussed in detail according to the calibration means according to the first aspect of the invention.

Further, according to a third aspect of the invention, the object is solved by a burner of a gas turbine, comprising an air supply, a fuel supply, a swirler and a combustion

chamber. A burner according to the invention is characterized in that the swirler is constructed according to the second aspect of the invention. The use of such a swirler provides the same advantages, which have been discussed in detail according to a swirler according to the second aspect of the invention.

In addition, according to a fourth aspect of the invention, the object is solved by a gas turbine, comprising at least one burner. A gas turbine according to the invention is characterized in that the burner is constructing according to the third aspect of the invention. The use of such a burner provides the same advantages, which have been discussed in detail according to a burner according to the third aspect of the invention.

The present invention is described with respect to the accompanying figures. The figures show schematically:

Fig. 1 a sectional view of a gas turbine,

Fig. 2 a first embodiment of a swirler with calibration means according to the invention, Fig. 3 a second embodiment of a swirler with calibration means according to the invention and

Figs. 4A-4D show alternatives of the second embodiment.

In Fig. 2, a schematic view of a swirler 20 according to the invention is shown. The swirler 20 has an axis 27 and

comprises a plurality of vanes 21 extending axially from a base plate 26. Between the vanes 21 a plurality of mixing channels 22 are formed, the mixing channels 22 facilitate air from a radially outer end or inlet 24 to a radially inner end or outlet 23. Further a fuel supply 62 is shown, which is used to provide the fuel to be mixed in the swirler 20 with the channelled air. The mixing channels 22 are capped with a closing plate 25. On this closing plate 25 calibration means 1 are attached. In this embodiment of the calibration means 1, according to the invention, are constructed as blocking devices 4 with apertures 5, the apertures shaped as holes 5. Although shown as holes 5, in other embodiments, the free edge of any one of the blocking devices 4 can have a scallop 5' either alone or in combination with a hole 5. Both the holes 5 and scallops 5' can be referred to as cut-outs 5, 5' .

In this embodiment for each of the mixing channels 22 a calibration element 3, especially shaped as a blocking device 4 is provided. Air channelled in the mixing channels 22 is manipulated by the blocking devices 4. In the flow of the air additional turbulences are produced and therefore the mixing of the channelled air with fuel provided by the fuel supply 62 is improved. To find a swirler 20 which is ideal for a specific burner 60 (not shown) only the calibration means 1 has to be adapted to achieve a uniform flow of the channelled air through the several mixing channels 22. A replacement or exchange of the complete swirler 20 to achieve this goal is not necessary. That's why this is a very cost efficient way to calibrate a swirler 20 of a burner 60.

The calibration element 3 is formed as a series of blocking devices 4, which, in this example, are an annular array of plates extending from the closing plate 25. Each plate extends to cover part of the mixing channel 22.

Alternatively, rather than individual plates 4, a ring 9, shown in part by dashed lines, may extend from the closing plate 25. The ring 9 comprises an annular array of cut-out 5, 5', each cut-out being aligned with a mixing channel.

The plates 4 or ring 9 and the closing plate 25 are

integrally formed as one piece or may be formed by bonding or welding the plates 4 or ring 9 and the closing plate 25 to form the calibration means 1. The size of the cut-out 5, 5' or even the number of cut-outs can be designed to achieve a desired influence on the flow characteristic through the mixing channels 22.

Fig. 3 shows another embodiment of calibrations means 1 for a swirler 20. The calibration means 1 comprises a calibration element 3, in this case shaped as a wire mesh 6. The wire mesh 6 covers the radially outer ends 24 of the mixing channels 22 along the complete height 2 of the calibration means 1. The calibration means 1 extends around the complete radially outer surface of the swirler, thus covering all the mixing channels 22. This ensures a very efficient

manipulation of the air channelled through the mixing

channels 22 from the radially outer end 24 to the radially inner end 23. The wires 7 of the wire mesh 6 can be equipped with swirling elements 8 such as fins or rips. Another possibility is that the wires 7 themselves are constructed as swirling elements 8, for instance the wires can be spiral- shanked or serrated. Such swirling elements 8 enhance the production of turbulence in the air channelled through the mixing channels 22 and therefore the mixing of air with fuel provided in the swirler 20.

One advantage of the present invention is that the calibration means 1 can be selected for its known influence on a flow characteristic of the air passing through the swirler. Thus depending on the flow characteristic of each individual swirler a calibration means 1 can be selected and applied to that swirler to ensure that all the swirlers on one engine or all engines are within a tolerance of each other and thus each swirler or engine set of swirlers have a known and desired air flow and performance. This ensures optimal performance of the combustion system and ensures a more even temperature distribution for downstream components. Furthermore, better fuel/air mixing and more consistent or optimal fuel/air ratios within each combustor is now

achievable. Thus can help reduce and maintain emissions such as carbon, nitrous and sulphur oxides.

Fig.3 also shows an alternative wire mesh 6' which has a height 10 which is less than the height 2 of the inlet of the mixing channel 22. Thus the calibration means 1 can be designed and/or selected based on its height 10 and therefore its influence on the flow characteristic of the air passing through the mixing channels 22 or swirler 20 as a whole to ensure all calibrated swirlers 20 have a predetermined flow characteristic within an acceptable tolerance.

Figs.4A-4D show further alternative embodiments of the wire mesh. Fig.4A shows a higher density mesh 6A compared to the mesh 6 shown in Fig.3. The mesh 6A has similarly spaced crossing sets of wires 11, 12. Fig.4B shows a mesh 6B which has a greater number of wires 11 in a first direction and a lesser number of wires 12 in a second direction. Each set of wires 11, 12 can have a spacing chosen to produce a

calibration means having a desired influence on the flow characteristic through the mixing channels 22.

Fig.4C shows a mesh 6C having a different wire gauge or thickness of one or both sets of wires 11, 12. In this case the wires 11, 12 are thicker than as shown in Fig.3 and therefore the mesh 6C has a greater influence on the flow characteristic through the mixing channels 22 than the mesh 6. Fig.4D shows a mesh 6D having non-straight wires 11, 12. One or both sets of wires 11, 12 can be S-shaped, sinusoidal or even castellated. The amplitude and/or frequency of the non-straight shape can determine the mesh' s influence on the flow characteristic through the mixing channels 22.

The sets of wires 11, 12 do not need to be perpendicular to one another, but instead can form apertures in square or other parallelogram shapes and indeed any other shapes as shown in Fig.4D.

It should be appreciated that the wire mesh type calibration means 1 can be formed by a combination of any of the various parameters described above in relation to Figs.3, 4A-4D.

Similarly, the plate type calibration means 1 can have various combinations of hole or scallop sizes and/or numbers. Although each swirler is manufactured to the same nominal dimensions it has been found that the manufacturing

tolerances cause an undesirable variation in flow

characteristics between swirlers with the aforementioned associated problems. The flow characteristic of the swirler can be the swirler' s mass flow rate or the effective flow area of the mixing channels. Therefore, each swirler can be tested or evaluated to check its flow characteristic and then a calibration means 1 can be fitted. The calibration means 1 is selected from a collection of calibration means 1 with different and known influences on the flow characteristic to achieve an engine set of calibrated swirlers having flow characteristics within an acceptable tolerance.

The present invention particularly lends itself to a method of calibrating a swirler for a burner of a turbine engine comprises the steps of determining a flow

characteristic of the swirler, calculating the difference between the determined flow characteristic of the swirler and a predetermined flow characteristic of the swirler, and dependent on the difference and applying a calibration means 1 to the swirler to alter its flow characteristic. As mentioned above the calibration means 1 has a known influence on the flow characteristic such that the altered flow

characteristic is within an acceptable tolerance of the predetermined flow characteristic. In one example, the acceptable tolerance band is +/-3sigma, where lsigma

corresponds to 1%. Sigma is the standard deviation of components as result of the manufacturing process. Previously, the swirler was manufactured to a nominal configuration and where the flow characteristic was below a certain level the swirler was scrapped. For the present inventive calibration method, the swirler 20 is manufactured to a nominal configuration to give a nominal flow

characteristic which is greater than the desired flow

characteristic. Therefore, for some swirlers with a flow characteristic at a low end of the tolerance range there may be no need to apply a calibration device or a calibration means with a relatively small influence on the flow

characteristic. For other swirlers with a flow

characteristic at a high end of the tolerance range there may be no need to apply a calibration means 1 with a relatively large influence on the flow characteristic. In one example, the swirler has a nominal flow characteristic which is up to 3sigma greater than the desired flow characteristic.

As mentioned above, the method comprises selecting the calibration means 1 from a group of calibration means 1, each calibration means 1 having a different and known influence on the flow characteristic of the swirler. Such a group of calibration means 1 comprises calibration means 1 having known influences on the flow characteristics of swirlers of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%. In other words, the calibration means reduces the effective flow area of the mixing channel or at least the area of the inlet to the mixing channel. It should be understood that the area of the calibration means or it's the open area as a percentage of the area of the mixing channel can be different to its reduction in the effective flow area of the mixing channel or its mass flow rate. Thus selection and application of any one of these calibration devices or means will ensure that the swirler is within the desired tolerance.

Similar to the first embodiment described with reference to Fig.2, the embodiments of the calibration means 1 in

Figs.3, 4A-4D may be in the form of a ring 9' which is applied around the outer perimeter of the swirler vanes 21. Furthermore, the wire meshes 6, 6' , 6A-6D may be formed as a separate ring element or may be formed as part of the closing plate 25. Alternatively, the calibration means 1 can be welded or brazed on the base plate 26. By applying the above inventive method a turbine engine results in having an array of combustors with at least one of the combustors having a calibrated swirler and more

preferably all swirlers calibrated. Thus, at least one combustor and preferably all combustors have a swirler comprising a calibration means 1. Here the turbine engine has all combustors having their swirlers comprising a flow characteristic within the acceptable tolerance of the

predetermined flow characteristic. This acceptable tolerance is preferably within lsigma and can be within 0.5sigma.

It should be noted that the predetermined flow

characteristic value can be set at a level where all swirlers require a calibration means 1. This is advantageous because each swirler will benefit from increased turbulence and improved mixing of the fuel and air by virtue of the

calibration means interacting with the air passing around and/or through it.

In summary calibration means according to the invention allow a calibration of the channelled air in a swirler in a very easy and cost efficient way. Once a swirler is chosen to be used in a burner of a gas turbine calibration means can be used to calibrate the chosen swirler and to allow a use of the swirler in the optimum location in a gas turbine with an optimum performance. For this calibration for instance calibration means with different calibration elements such as blocking devices, wire mesh and/or swirling elements can be used to achieve an optimum calibration of the swirler. A swirler with such a calibration means has several advantages. A more uniform temperature distribution in the combustion chamber of the burner using such a swirler with a calibration means can be achieved, thus resulting in a longer life time of hot components of the burner. In addition, enhanced mixing of fuel and air and a reduction of the temperature hot spots result in a lower emission operation of the gas turbine, especially in respect to NOx production. Also a reduced down time and an improved serviceability is caused by the more uniform air distribution in the mixing channels produced by the calibration means. In addition during the construction of the gas turbine an enhanced flexibility in choosing a swirler for the gas turbine and therefore an adequate stock

management in respect to swirlers is possible.