EP1642065B1 - Burner unit for a gas turbine and gas turbine - Google Patents

Description

The invention relates to a burner unit for a gas turbine with a combustion chamber. It further relates to a gas turbine with a number of such burner units.

Gas turbines are used in many areas to drive generators or work machines. In this case, the energy content of a fuel is used to generate a rotational movement of a turbine shaft. For this purpose, the fuel is burned in a combustion chamber, compressed air being supplied by an air compressor. The working medium produced in the combustion chamber by the combustion of the fuel, under high pressure and at high temperature, is guided via a turbine unit arranged downstream of the combustion chamber, where it relaxes to perform work.

In the design of such gas turbines in addition to the achievable power usually a particularly high efficiency is a design target. An increase in the efficiency can be achieved for thermodynamic reasons basically by increasing the outlet temperature at which the working fluid from the combustion chamber and flows into the turbine unit. Therefore, temperatures of about 1200 ° C to 1300 ° C are sought for such gas turbines and achieved.

In order to keep the nitrogen oxide emissions of the gas turbine particularly small even with a compact design at the relatively high combustion temperatures required for this, modern gas turbines are usually operated in the so-called premix mode. The fuel is supplied via a plurality of injection nozzles and then premixed in a Vormischpassage with compressor air. To provide the required high thermal performance In addition, usually more burners, in which fuel is added and the fuel is premixed with air, connected in parallel, in particular in the so-called annular combustion chamber design several burners can be arranged on a common, annular designed combustion chamber.

Due to the high power densities and the high combustion temperatures such gas turbines may be susceptible to failure, especially in a compact design. However, for reasons of operational safety and the expense associated with the operation of the gas turbine, a high level of safety of gas turbines is desirable. For example, the US 6,164,055 a burner for low nitrogen oxide emissions and a method for its operation, in which the dynamic stability of the flame should be improved.

The invention is therefore based on the object of specifying a burner unit for a gas turbine of the type mentioned above, with which the operational safety and stability of the gas turbine is promoted to a particular extent. Furthermore, a gas turbine is to be specified, which is operable with particularly high operational safety.

With respect to the burner unit for the gas turbine, this object is achieved according to the invention by a plurality of burner stages is arranged on the combustion chamber, which are defined in terms of the sum of the acoustic period of the respective burner stage, as the time period between an acoustic stimulus and the response of the respective Burning stage, and the respective delay time, defined as the period of time that requires a fluid element for the distance between the exit plane of the respective burner stage and the flame front, the burner stages from each other with regard to the acoustic impedance of their fuel supply, the acoustic impedance of their Air passage and / or the flame delay time or the injection delay time differ, wherein the burner stages are arranged with respect to the longitudinal direction of the gas turbine one behind the other.

The invention is based on the consideration that the burner unit can contribute in particular to the operational stability and safety of the gas turbine by possible sources of accident are consistently avoided. As has been found, thermoacoustically induced combustion instabilities, which are not sufficiently limited by external damping mechanisms, can occur, especially in gas turbines designed for high power densities and combustion temperatures in a compact design as a possible source of accident can. In order to consistently suppress such thermoacoustically induced combustion instabilities, the burner unit comprising the combustion chamber should be designed appropriately with regard to its acoustic properties. In particular, the design goal may be to suppress a coupling between the thermoacoustic response times of the burner flames and the acoustic natural frequencies of the combustion system, which could lead to the excitation of thermoacoustically induced combustion instabilities. In order to make this possible and in particular to provide a sufficient number of influenceable parameters, the burner unit should be designed in several stages with regard to the burners used. In this case, a plurality of burner stages are provided, each of which has in the manner of a conventional burner via a fuel gas supply, an air supply, optionally a premixing chamber and a burner outlet.

To ensure the intended design acoustic decoupling or "detuning" of these subsystems from each other, the burner stages should be designed appropriately in terms of their dimensions and the choice of their characteristic parameters. It is provided that the burner stages differ from each other in at least one of the features that characterize the respective acoustic response times of the burner stages to a pressure fluctuation in the combustion chamber, namely the thermoacoustic properties of the fuel supply, characterized by the acoustic impedance of the fuel supply, the thermoacoustic properties of the Air supply, characterized by the acoustic impedance of the air passage, and the delay time of the flame, characterized by the time required for a fluid element from the burner exit to the flame front, also referred to as "flame delay time", or by the time a fuel-enriched fluid element of the injection site needed up to the flame front, also referred to as "injection delay time".

In this case, the impedance generally expresses the relationship between a force excitation and a movement resulting therefrom, ie, for example, in the alternating current technique between the electric field and the resulting current density. In acoustics, the acoustic impedance thus reflects the ratio of a pressure fluctuation to the resulting flow velocity of a medium. Between a pressure fluctuation and a resulting fluctuation in the flow velocity there is an amplitude ratio on the one hand and a phase difference on the other hand. The phase difference expresses the extent to which the fluctuation of the flow velocity precedes or hinders the pressure fluctuation causing it, such that the acoustic impedance is, inter alia, a suitable measure for the time span between an acoustic excitation, for example an acoustic alternating pressure fluctuation, and the response of the respective burner stage this, ie a fluctuation of the exit velocity at the respective Brenneraustrittsebene is.

The multi-stage embodiment of the burner unit can be implemented in a particularly favorable manner by the burner stages are arranged one behind the other with respect to the longitudinal direction of the gas turbine.

A particularly favorable and compact design with regard to the achievable power density is achievable in that the combustion chamber of the burner unit is advantageously designed as an annular combustion chamber. Due to the design as an annular combustion chamber is also due to their rotational symmetry seen in the circumferential direction comparatively homogeneous temperature and flow distribution achievable.

The targeted adjustment of the acoustic properties of the burner stages can by suitable dimensioning and parameter selection, in particular with regard to the length of the fuel and / or air passage, so the distance between the fuel injection and the burner exit, and / or with respect to the length of the flow passages and volume sizes upstream of the fuel injection. In order to provide, however, still further degrees of freedom for the design-based acoustic decoupling of the burner stages from one another, the burner stages are advantageously provided in each case with a number of throttle devices and / or with a number of resonator units. The throttle devices may be designed in particular for the targeted generation of pressure losses in the interior of the burner stages, for example in their premixing chambers, wherein, for example, perforated plates with suitably dimensioned bore diameters may be provided as throttling device. Additionally or alternatively, resonators may be used, preferably in flow passages upstream or downstream of the fuel gas injection, advantageously in such a way that they open into the air passage and / or into the fuel passage of the respective burner stage.

For a reliable acoustic decoupling or detuning of the burner stages from each other they are advantageously designed such that the sum of the so-called acoustic period of each burner stage, so given by the acoustic impedances of the respective burner stage period between the acoustic stimulus and the response of the respective burner stage , And the so-called delay time, ie the period of time, which requires a fluid element for the distance between the exit plane of the respective burner stage and the flame front, different from each other. The flame delay time is advantageously set via the specification of a suitably selected outlet speed at the respective burner outlet and / or via integrated swirl-generating means, wherein in particular the ratio of the size of the circumferential velocity component to the meridional velocity component of the flow medium flowing out of the respective burner stage is used.

With regard to the gas turbine, the stated object is achieved by designing its burner unit as a burner unit of the aforementioned type.

The advantages achieved by the invention are in particular that a consistent acoustic decoupling of the individual burner stages from each other can be achieved by the multi-stage design of the burner unit with burner stages, which differ in terms of their thermoacoustic properties suitable from each other. As a result, the possible excitation of thermoacoustically induced combustion instabilities in the combustion system of the gas turbine can be kept particularly low. A burner unit designed in this way is therefore particularly stable to pressure fluctuations in the combustion chamber, so that a gas turbine with such a burner unit has a particularly high operational stability.

FIG 1

einen Halbschnitt durch eine Gasturbine, und

FIG 2

im Längsschnitt eine Brennereinheit der Gasturbine nach FIG 1.

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

FIG. 1

a half section through a gas turbine, and

FIG. 2

in longitudinal section, a burner unit of the gas turbine after FIG. 1 ,

Identical parts are provided in both figures with the same reference numerals.

The gas turbine 1 according to FIG. 1 has a compressor 2 for combustion air, a burner unit 3 with a combustion chamber 4 and a turbine 6 for driving the compressor 2 and a Not shown generator or a working machine. For this purpose, the turbine 6 and the compressor 2 are arranged on a common, also called turbine rotor turbine shaft 8, with which the generator or the working machine is connected, and which is rotatably mounted about its central axis 9.

The combustion chamber 4 is equipped with a number of burners 10 for the combustion of a liquid or gaseous fuel. It is also provided on its inner wall with heat shield elements not shown.

The turbine 6 has a number of rotatable blades 12 connected to the turbine shaft 8. The blades 12 are arranged in a ring on the turbine shaft 8 and thus form a number of blade rows. Furthermore, the turbine 6 comprises a number of fixed vanes 14, which are also fixed in a ring shape with the formation of rows of vanes on an inner casing 16 of the turbine 6. The blades 12 serve to drive the turbine shaft 8 by momentum transfer from the turbine 6 flowing through the working medium M. The vanes 14, however, serve to guide the flow of the working medium M between two seen in the flow direction of the working medium M consecutive blade rows or blade rings. A successive pair of a ring of vanes 14 or a row of vanes and a ring of blades 12 or a blade row is also referred to as a turbine stage.

Each vane 14 has a platform 18, also referred to as a blade root 19, which is arranged to fix the respective vane 14 on the inner housing 16 of the turbine 6 as a wall element. The platform 18 is a thermally comparatively heavily loaded component which forms the outer boundary of a heating gas channel for the working medium M flowing through the turbine 6. Each blade 12 is in analog Said manner attached to the turbine shaft 8 via a blade root 19, also referred to as a platform 18, wherein the blade root 19 each carries a profiled airfoil 20 extending along a blade axis.

Between the spaced-apart platforms 18 of the guide vanes 14 of two adjacent rows of guide vanes is in each case a guide ring 21 on the inner housing 16 of the turbine 6 is arranged. The outer surface of each guide ring 21 is also exposed to the hot, the turbine 6 flowing through the working medium M and spaced in the radial direction from the outer end 22 of the blade 12 opposite him through a gap. The guide rings 21 arranged between adjacent rows of guide blades serve in particular as cover elements which protect the inner wall 16 or other housing installation parts from thermal overload by the hot working medium M flowing through the turbine 6.

To ensure a high operational safety and in particular to avoid thermoacoustically induced combustion instabilities, the burner unit 3, which is in FIG. 2 is shown in a longitudinal section, executed in several stages, wherein seen at the combustion chamber designed as an annular combustion chamber 4 in the flow direction of the working medium M a plurality of burner stages 30 is arranged one behind the other. Each burner stage 30 is in each case connected to a schematically indicated air supply or air passage 32 and to a not shown in detail, each opening in a number of inlet openings 34 fuel supply line. Starting from the Brenneraustrittsebene 36 each burner stage 30 is formed during operation of the gas turbine 1 in the interior of the combustion chamber 4, one of the respective burner stage 30 associated flame front 38. In the embodiment according to FIG. 2 three burner stages 30 are shown; but it can also be provided only two or four or more burner stages 30.

To ensure the thermoacoustic decoupling or detuning of the burner stages 30 from each other, which is to ensure the avoidance of the excitation thermoacoustically induced combustion instabilities, the burner stages 30 with respect to the acoustic impedance of their fuel supply, the acoustic impedance of their air passage 32 and / or their flame delay time designed differently from each other. In each case time constants can be derived from the acoustic impedances of the fuel supply line and the air passage 32, which are the time span between a pressure fluctuation occurring in the interior of the combustion chamber 4 and the subsequent reaction of the respective burner stage 30, ie a fluctuation of the exit velocity on exit of the flow medium respective exit plane 36, play. After the addition of the so-called flame delay time, ie the time span required by a fluid element in the operating state of the gas turbine 1 in accordance with the design in order to arrive from the exit plane 36 of the respective burner stage 30 to the flame front 38 associated therewith, this time constant results in the total for the acoustic one Design of the respective burner stage 30 to be considered period. The burner stages 30 are designed such that they differ from one another with regard to this characteristic period of time.

To generate these differences in the design of the burner stages 30 to each other, in the dimensioning and parameterization of the burner stages 30 in particular the parameters, length of the fuel and / or air passage, length of the flow passages and volume sizes upstream of the fuel injection, pressure losses in the supply lines Exit velocity in the burner exit plane 36, stabilization (swirl stabilized or bluff body stabilized) and / or ratio of the size of the peripheral velocity component to the size of the meridional velocity component in the emerging from the respective burner stage 30 flow suitable selected. Furthermore, in the exemplary embodiment seen in the flow direction of the working medium M first burner stage 30 equipped with an integrated throttle device 40, in the embodiment, a perforated plate, and arranged in the flow passages upstream and downstream of the fuel gas injection, resonators, not shown.

Claims (6)

1. Burner unit (3) for a gas turbine (1) having a combustion chamber (4) on which is arranged a plurality of burner stages (30) which differ from one another with respect to the sum of the acoustic timespan of the respective burner stage (30), defined as the time span between an acoustic excitation and the response of the respective burner stage (30), and the respective delay time, defined as that timespan which a fluid element requires to travel between the outlet plane (36) of the respective burner stage (30) and the flame front (38), wherein the burner stages (30) differ from one another with respect to the acoustic impedance of their fuel supply line, the acoustic impedance of their air passage and/or the flame delay time or the injection delay time, characterized in that the burner stages (30) are arranged one behind the other with respect to the longitudinal direction of the gas turbine (1).
2. Burner unit (3) according to Claim 1, whose combustion chamber (4) is designed as an annular combustion chamber.
3. Burner unit (3) according to either of Claims 1 and 2, whose burner stages (30) are each provided with a number of throttle devices (40).
4. Burner unit (3) according to one of Claims 1 to 3, whose burner stages (30) are each provided with a number of resonator units which preferably discharge into the air passage and/or into the fuel passage of the respective burner stage (30).
5. Burner unit (3) according to one of Claims 1 to 4, in whose burner stages (30) the respective flame delay time is set by defining an outlet velocity at the respective burner outlet and/or by means of integrated swirl-generating means.
6. Gas turbine (1) having a number of burner units (3) according to one of Claims 1 to 5.

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