BURNER FOR A GAS TURBINE AND METHOD FOR OPERATING THE BURNER

Abstract

A burner with a control unit, a combustion chamber, a pressure sensor and fuel stages which are arranged to supply fuel with a respective mass flow to the combustion chamber, wherein the mass flows are controlled by the control unit, wherein the pressure sensor is adapted to measure a pressure sequence in the combustion chamber or in the burner and to transfer the pressure sequence to the control unit which is adapted to perform a Fourier transformation on at least one determined timespan of the pressure sequence to result in a pressure spectrum having a maximum within a frequency band and wherein the control unit is adapted to perform a comparison of the maximum with a predefined threshold and to control the mass flows by using the comparison to reduce and/or to control pressure fluctuations in the combustion chamber.

Claims

1. A burner, comprising: a control unit, a combustion chamber, a pressure sensor, and fuel stages which are arranged to supply fuel with a respective mass flow to the combustion chamber, wherein the mass flows are controlled by the control unit, wherein the pressure sensor is adapted to measure a pressure sequence in the combustion chamber or in the burner and to transfer the pressure sequence to the control unit which is adapted to perform a Fourier transformation on a multitude of determined timespans of the pressure sequence each to result in a respective pressure spectrum having a respective maximum within a frequency band, and wherein the control unit is adapted to perform a comparison on each of the maxima with a predefined threshold, to count a number of maxima exceeding the threshold within a predetermined number of the timespans and to control the mass flows by using the comparison and by using the number of exceeding threshold to reduce and/or to control pressure fluctuations in the combustion chamber.

2. The burner according to claim 1, wherein the fuel stages comprise a pilot fuel stage and a main fuel stage.

3. The burner according to claim 2, wherein the control unit is adapted to increase the mass flow of the pilot fuel stage when the number exceeds a first threshold number.

4. The burner according to claim 3, wherein the control unit is adapted to decrease the mass flow of the pilot fuel stage when the number is below a second threshold number.

5. The burner according to claim 4, wherein the control unit is adapted to control the mass flows of at least one of the fuel stages different from the pilot fuel stage such that the overall power of the combustion of the fuel within the combustion chamber remains constant.

6. The burner according to claim 1, wherein the control unit comprises a characteristic line describing the mass flow of at least one of the fuel stages in dependence of an engine parameter of the burner and/or an ambient condition of the burner, wherein the control unit is adapted to shift at least a range of the characteristic line when altering the mass flow of the at least one fuel stage.

7. The burner according to claim 6, wherein the control unit has stored an initial characteristic line and is adapted to set the characteristic line back to the initial characteristic line, when the control unit detects a signal failure or a hardware failure.

8. The burner according to claim 1, wherein the fuel supplied to the combustion chamber via one of the fuel stages and the fuel supplied to the combustion chamber via another one of the fuel stages are identical or different.

9. The burner according to claim 1, wherein the pressure sequence comprises a plurality of the determined timespans and the control unit is adapted to calculate a difference between two maxima of two consecutive timespans and to control a velocity of the change of the mass flows and/or a magnitude of the change of the mass flows by using the difference.

10. The burner according to claim 1, wherein the Fourier transformation is a fast Fourier transformation.

11. The burner according to claim 1, wherein the burner comprises an emission sensor adapted to determine a nitrogen oxide concentration in the exhaust gas of the burner and to transfer the nitrogen oxide concentration to the control unit which is adapted to determine a maximum mass flow or a minimum mass flow for one of the fuel stages by using the nitrogen oxide concentration.

12. The burner according to claim 1, wherein the predefined threshold is determined by using an engine parameter of the burner and/or an ambient condition of the burner.

13. A gas turbine, comprising: at least one burner according to claim 1.

14. A method for operating a burner which comprises a control unit, a combustion chamber, a pressure sensor and fuel stages which are arranged to supply fuel with a respective mass flow to the combustion chamber, wherein the mass flows are controlled by the control unit, the method comprising: a) supplying the fuel to the combustion chamber and combusting the fuel in the combustion chamber; b) measuring a pressure sequence in the combustion chamber or in the burner using the pressure sensor and transferring the pressure sequence to the control unit; c) performing a Fourier transformation on a multitude one determined timespans of the pressure sequence to result in a pressure spectrum each having a respective maximum within a frequency band; d) comparing each of the maxima with a predefined threshold; e) counting the number of maxima exceeding the threshold within a predetermined number of the timespans; f) controlling the mass flows by using the comparison of the maximum with the predefined threshold and by using the number of exceeding threshold to reduce and/or to control pressure fluctuations in the combustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above mentioned attributes and other features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein

[0031] FIG. 1 shows a schematic drawing of a burner,

[0032] FIG. 2 shows a schematic diagram of a pressure sequence,

[0033] FIG. 3 shows a schematic diagram of a multitude of pressure spectra,

[0034] FIG. 4 shows a characteristic line diagram, and

[0035] FIG. 5 shows a flow chart.

DETAILED DESCRIPTION OF INVENTION

[0036] FIG. 1 shows a burner 1 with a combustion chamber 10, a control unit 11 and fuel stages 2, 3, 5, 6, 8. The fuel stages 2, 3, 5, 6, 8 supply fuel to the combustion chamber 10. The fuel stages 2, 3, 5, 6, 8 are a first liquid fuel stage 2, a first gaseous fuel stage 3, a second gaseous fuel stage 5, a third gaseous fuel stage 6 and a second liquid fuel stage 8. Liquid fuel is supplied to the combustion chamber 10 via the liquid fuel stages 2, 8 and gaseous fuel is supplied to the combustion chamber 10 via the gaseous fuel stages 2, 5, 6. Compressed air 4 is also supplied to the combustion chamber 10. The compressed air 4 is combusted in the combustion chamber 10 together with the fuels. A flame 7 drawn in FIG. 1 represents the combustion and an arrow 9 represents a main flow direction in the combustion chamber 10. The control unit 11 is adapted to control the supply of fuel to the combustion chamber 10 via at least one of the fuel stages 2, 3, 5, 6, 8. The control unit 11 is adapted to control the mass flows of the fuel to the combustion chamber 10 by using a pressure sequence 14 which shows the pressure in the combustion chamber 10. For measuring the pressure sequence, at least one pressure sensor can be placed inside the combustion chamber 10. Alternatively or in addition to this, the pressure sequence shows the pressure in the burner 1. In this case the at least one pressure sensor can be arranged outside from the combustion chamber 10, in particular on a wall confining the combustion chamber 10. A plurality of the pressure sensors can be provided, wherein the pressure sensors are arranged circumferentially around the combustion chamber 10.

[0037] FIG. 2 shows a pressure diagram 15 with a time axis 12 and a pressure axis 13. The pressure diagram 15 shows the pressure in the combustion chamber 10 over the time, represented by the pressure sequence 14. FIG. 2 shows additional timespans t1, t2, t3, t4 which can be used to divide the pressure sequence 14 in timely different parts. FIG. 2 shows that the timespans t1, t2, t3, t4 are located immediately after each other. Alternatively, it is conceivable that the timespans t1, t2, t3, t4 overlap or that there are gaps between consecutive timespans t1, t2, t3, t4. FIG. 2 shows the pressure sequence 14 in its time domain before a Fourier transformation.

[0038] FIG. 3 shows a pressure evolution diagram 20 with a time axis 21, a frequency axis 22 and an pressure amplitude axis 23. Additionally a frequency band 24, a determined threshold 26 and a time range 25 are presented. The pressure evolution diagram 20 shows different pressure spectra 27, 28, 29, 30 after the Fourier transformation of the pressures sequence 14 of the corresponding timespans t1, t2, t3, t4 in the frequency domain. Each of the pressure spectra 27, 28, 29, 30 has a respective maximum 31, 32, 33, 34 within the frequency band 24. A first pressure spectrum 27 has a first maximum 31, a second pressure spectrum 28 has a second maximum 32, a third pressure spectrum 29 has a third maximum 33 and a fourth pressure spectrum 30 has a fourth maximum 34. The pressure spectra 27, 28, 29, 30 are arranged in the pressure evolution diagram 20 along the time axis 21. The pressure evolution diagram 20 shows that some of the maxima 31, 32, 33, 34 exceed the determined threshold 26 and that some of the maxima 31, 32, 33, 34 are below the determined threshold 26. The control unit 11 is adapted to use a comparison of at least one of the maxima 31, 32, 33, 34 with the determined threshold 26 to control the mass flows via at least one of the fuel stages 2, 3, 5, 6, 8 to the combustion chamber 10.

[0039] The amplitude spectrum diagram 20 shows additionally a first vector 35 pointing from the first maximum 31 to the second maximum 32, a second vector 36 pointing from the second maximum 32 to the third maximum 33 and a third vector 37 pointing from the third maximum 33 to the fourth maximum 34. Each vector 35, 36, 37 is determined by the difference of the respective two maxima 31, 32, 33, 34 and the time duration of one of the timespans t1, t2, t3, t4. It is conceivable that the control unit 11 is adapted to calculate the vector 35, 36, 37 between two of the maxima 31, 32, 33, 34 and to control a velocity of the change of the mass flows and/or a magnitude of the change of the mass flows by using the vector 35, 36, 37.

[0040] FIG. 4 shows a characteristic line diagram 40. The characteristic line diagram 40 shows a mass flow 42 of fuel supplied via one of the fuel stages 2, 3, 5, 6, 8 over an engine parameter 41 of the burner 1, for example the mass flow of the pilot fuel stage over a gas turbine load. It is conceivable that the characteristic line diagram 40 shows a ratio of mass flows, for example the mass flow of the pilot fuel stage to the mass flow of the main fuel stage. The engine parameter 41 of the burner 1 can be for example a gas turbine load, a fuel temperature, an emission value or a fuel pressure. An upper boundary 44 and a lower boundary 45 limit an operational envelope 47 in which the characteristic line 43 can be located. It is possible that the upper boundary 44 or that the lower boundary 45 is determined by using an emission value. If, for example, the characteristic line diagram 40 shows the ratio of the mass flow of the pilot fuel stage to the mass flow of another of the fuel stages 2, 3, 5, 6, 8, the upper boundary 44 can be determined by a maximal nitrogen oxide concentration in the exhaust gas. The control unit 11 is adapted to alter at least a range of the characteristic line 43 by using the comparison of at least one of the maxima 31, 32, 33, 34 with the predetermined threshold 26. Arrows 46 show possible altering directions of the characteristic line 43.

[0041] FIG. 5 shows a flow chart 50 of a possible operating program of the burner 1. The operating program can be implemented in the control unit 11. The flow chart 50 uses a first element 51 to indicate a steady state of the burner 1, a second element 52 to indicate maxima comparing, a third element 53 to indicate counting a number of timespans, a fourth element 54 to indicate a combination of results, a fifth element 55 to indicate an emission set point, a sixth element 56 to indicate a change of the pilot mass flow, a seventh element 57 to indicate a final pilot mass flow, an eight element 58 to indicate a pilot mass flow maximum and a pilot mass flow minimum, a ninth element 59 to indicate a pilot characteristic line and a tenth element 65 to indicate an emission value of the burner 1.

[0042] The elements are linked together which is represented via arrows. A first arrow 66 points from the first element 51 to the second element 52, a second arrow 67 points from the second element 52 to the fourth element 54, a third arrow 68 points from the second element 52 to the third element 53, a fourth arrow 69 points from the third element 53 to the sixth element 56, a fifth arrow 70 points from the fifth element 55 to the fourth element 54, a sixth arrow 71 points from the fourth element 54 to the sixth element 56, a seventh arrow 72 points from the sixth element 56 to the seventh element 57, an eight arrow 73 points from the eight element 58 to the seventh element 57, a ninth arrow 74 points from the ninth element 59 to the seventh element 57 and a tenth arrow 75 points from the seventh element 57 to the combustion chamber 10 of a gas turbine 60.

[0043] The gas turbine 60 comprises a compressor 61, the combustion chamber 10, a turbine 63 and a shaft 64. The compressor 61 compresses air and the compressed air is supplied to the combustion chamber 10, indicated via an eleventh arrow 76. The combustion chamber 10 combusts the compressed air together with the fuel. Exhaust gas of the combustion is supplied to the turbine 63, indicated via a twelfth arrow 78. The turbine 63 drives the compressor 61 via the shaft 64. Emissions are measured in the exhaust gas of the combustion chamber 10 which is indicated via a thirteenth arrow 79 and a tenth element 65. A fourteenth arrow 80 points from the emission element 65 to the fourth element 54.

[0044] The target of the program is to determine the final pilot mass flow (element 59) and to control the burner 1 accordingly (arrow 75). The final pilot mass flow depends on the pilot characteristic line of the pilot mass flow (element 59 and arrow 74) and on the pilot mass flow maximum and the pilot mass flow minimum (element 58 and arrow 73). The final pilot mass flow is determined by using the change of the pilot mass flow (element 56 and arrow 72). The change of the pilot mass flow depends on a number of maxima 31, 32, 33, 34 exceeding the determined threshold 26 (element 52 and 54 and arrows 67, 68 and 71) within the predetermined number of the timespans t1, t2, t3, t4 (element 53 and arrow 69) and on the nitrogen oxide concentration in the exhaust gas (element 65 and arrows 79, 80) of the burner 1 in combination with the emission set point (element 55 and arrow 70). The change of the pilot mass flow can be an increase of the pilot mass flow or a decrease of the pilot mass flow. The program starts with the steady state (element 51 and arrow 66).

[0045] Although the invention is described in detail by the embodiments herein, the invention is not constrained by the disclosed examples and other variations can be derived by the person skilled in the art, without leaving the extent of the protection of the invention.