METHOD FOR CONTROLLING A GAS TURBINE OPERATION WITH SELECTED TURBINE OUTLET TEMPERATURE MEASUREMENTS

Abstract

The present disclosure refers to a method for operating a gas turbine having a compressor, a combustor, a turbine downstream of the combustor, and a total number of turbine outlet temperature measurement sensors. The method can include supplying a first fuel flow to one of the burners of one combustor, which is smaller than a second fuel flow to another one of the burners the same combustor, selecting a number of turbine outlet temperature measurements which is smaller than a total number of the turbine outlet temperature measurement sensors, and averaging measured temperatures of the selected turbine outlet temperature measurements to obtain an trimmed turbine outlet temperature which is used for controlling operation of the gas turbine.

Claims

1. Method for operating a gas turbine having a compressor, a combustor with at least two burners, a turbine downstream of the combustor, and a plurality of turbine outlet temperature measurements sensors, the method comprising: supplying a first fuel flow to one of the burners of one combustor, and supplying a second fuel flow to another one of the burners of the same combustor wherein the first fuel flow is smaller than the second fuel flow; measuring a turbine outlet temperature of a respective turbine with the turbine outlet temperature measurements sensor of the respective turbine; selecting a number of turbine outlet temperature measurements sensors which is smaller than a total number of the turbine outlet temperature measurements; averaging measured temperatures of the selected turbine outlet temperature measurements to obtain a trimmed turbine outlet temperature; and controlling operation of the gas turbine with the trimmed turbine outlet temperature.

2. Method as claimed in claim 1, wherein the first fuel flow is zero, and the second fuel flow is greater than zero.

3. Method as claimed in claim 1, wherein the turbine outlet temperature measurements sensors with good data quality are identified, and the trimmed turbine outlet temperature is averaged based on a number of turbine outlet temperature measurement values with good data quality which is smaller than the total number of turbine outlet temperature measurements sensors with good data quality.

4. Method as claimed in claim 1, wherein a proper subset of the turbine outlet temperature measurements sensors is selected for obtaining the trimmed turbine outlet temperature wherein the proper subset of turbine outlet temperature measurements sensors comprises the turbine outlet temperature measurements sensors with the highest measurement values.

5. Method as claimed in claim 1, wherein a proper subset of the turbine outlet temperature measurements is selected for obtaining the trimmed turbine outlet temperature, and the proper subset consists of an i highest to a j highest turbine outlet temperature measurements, wherein i and j are natural numbers, i is 2 or larger than 2, j is equal to or larger than i, and i and j are smaller than the total number of outlet temperature measurements sensors.

6. Method as claimed in claim 1, wherein a proper subset of the turbine outlet temperature measurements sensors is selected for obtaining the trimmed turbine outlet temperature, and the proper subset comprises: at least one turbine outlet temperature measurement sensor which is offset in a circumferential direction around an axis of the gas turbine from a circumferential location of a burner to which a second fuel flow is supplied by an offset angle wherein the offset angle corresponds to a circumferential offset around the axis of the gas turbine to which the hot gas is subjected when traveling from the combustor through the turbine to the turbine outlet temperature measurements sensors.

7. Method as claimed in claim 1, wherein a proper subset of the turbine outlet temperature measurements sensors is selected for obtaining the trimmed turbine outlet temperature, and the proper subset excludes at least one turbine outlet temperature measurement sensor which is offset in a circumferential direction around an axis of the gas turbine from a circumferential location of a burner to which a first fuel flow is supplied by an offset angle wherein the offset angle corresponds to a circumferential offset around the axis of the gas turbine to which hot gas is subjected to when traveling from the combustor through the turbine to the turbine outlet temperature measurements.

8. Method as claimed in claim 1, wherein an average turbine inlet temperature is calculated using an average turbine outlet temperature based on all turbine outlet temperatures measurements and a trimmed turbine inlet temperature is calculated using the trimmed turbine outlet temperature, and a higher value of the average turbine inlet temperature and of the trimmed turbine inlet temperature is used for controlling operation of the gas turbine.

9. Method as claimed in claim 1, wherein an average turbine outlet temperature based on all turbine outlet temperatures measurements is used for controlling operation of the gas turbine when a parameter indicative of the operating condition of the gas turbine is above a threshold value, and the trimmed turbine outlet temperature is used for controlling operation of the gas turbine when the parameter indicative of the operating condition of the gas turbine is below the threshold value.

10. Method as claimed in claim 1, wherein a turbine inlet temperature error is calculated based on an average turbine outlet temperatures, a trimmed hot gas error is calculated based on the trimmed turbine outlet temperature, the turbine inlet temperature error and the trimmed hot gas error are scaled to match each other, and a lower value of scaled temperature errors is used for control and protection of the gas turbine.

11. Method as claimed in claim 10, wherein: the turbine inlet temperature error is multiplied by a scaling factor to obtain a scaled hot gas temperature error, or in that the trimmed hot gas temperature error is divided by the scaling factor to obtain a trimmed inlet temperature error.

12. Method as claimed in claim 10, wherein the scaling factor is a function of at least one of the gas turbine load, an inlet angle of a variable inlet guide vane, a turbine inlet temperature, and an average turbine outlet temperature.

13. Method as claimed in claim 1, applied to a sequential combustion gas turbine having a first combustor, a first turbine downstream of the first combustor, a total number of first turbine outlet temperature measurements sensors and a second combustor downstream of said first turbine, and a second turbine downstream of said second combustor, wherein selected first turbine outlet temperature measurements of the first turbine are averaged to obtain a trimmed first turbine outlet temperature.

14. Method as claimed in claim 1, applied to a sequential combustion gas turbine having a first combustor, a first turbine downstream of the first combustor, a second combustor downstream of said first turbine, a second turbine downstream of said second combustor, and a total number of second turbine outlet temperature measurements sensors downstream of the second turbine, wherein selected second turbine outlet temperature measurements of the second turbine are averaged to obtain a trimmed second turbine outlet temperature.

15. Gas turbine comprising: a compressor; a combustor, a turbine downstream of the combustor; a total number of turbine outlet temperature measurements, and a controller, wherein the controller is configured to control the gas turbine by: supplying a first fuel flow to one of the burners of one combustor, and supplying a second fuel flow to another one of the burners of the same combustor wherein the first fuel flow is smaller than the second fuel flow; measuring a turbine outlet temperature of a respective turbine with the turbine outlet temperature measurements sensor of the respective turbine; selecting a number of turbine outlet temperature measurements sensors which is smaller than a total number of the turbine outlet temperature measurements; averaging measured temperatures of the selected turbine outlet temperature measurements to obtain a trimmed turbine outlet temperature; and controlling operation of the gas turbine with the trimmed turbine outlet temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The disclosure, its nature as well as its advantages, shall be described in more detail below with the aid of the accompanying schematic drawings.

[0051] Referring to the drawings:

[0052] FIG. 1 shows a gas turbine with sequential combustion and a closed loop controller for its operation,

[0053] FIG. 2a shows the cross section II-II of the combustor with the fuel distribution system,

[0054] FIG. 2b shows the cross section II-II of the combustor with first turbine outlet temperature measurements,

[0055] FIG. 3 shows the cross section III-III of the second turbine outlet with second turbine outlet temperature measurements,

[0056] FIG. 4 shows an exemplary exhaust temperature distribution,

[0057] FIG. 5 shows exemplary control logic to determine a selected turbine inlet temperature error for control of the gas turbine.

EMBODIMENTS OF THE DISCLOSURE

[0058] A control scheme of a gas turbine with sequential combustion (known for example for GT24 or GT26) is shown in FIG. 1. The gas turbine 10 comprises a rotor 11, which is surrounded by a concentric casing. A compressor 12 compresses air that enters a first combustor 13 with a burner of the first combustor 13 through a plenum. Fuel is supplied via a first combustor fuel supply 22. The resulting hot gas leaving the first combustor 13 drives a first turbine 14. Downstream of first turbine 14 fuel is injected via a fuel lance 15 into the exhaust gas of the first turbine 14 which still contains sufficient oxygen for further combustion. The fuel burns in the second combustor 16. The re-heated gas drives a second turbine 17 and finally exits the gas turbine 10. The first turbine outlet temperature measurement 18 can also be integrated or attached to the fuel lance 15.

[0059] The first turbine 14 is also called high-pressure turbine. The second turbine 17 is also called low-pressure turbine.

[0060] A controller 20, which controls the operation of gas turbine 10, receives measurement values from first turbine outlet temperature measurements 18 being measured at various points via a fuel lance 15 at the outlet of the first turbine 14. Furthermore, it receives measurement values of second turbine outlet temperature measurements 19 of the second turbine 17 being measured at various points (e.g. 20) at the outlet of the second turbine 17. Using the measured data the controller 20 controls the operation of the first combustor 13 by means of a first combustor fuel control line 21 and the operation of the second combustor 16 by means of a second combustor fuel control line 23.

[0061] The gas turbine system can be coupled to a generator (not shown) via the rotor 11. Typically, a gas turbine 10 further comprises a cooling system for the first turbine 14, the second turbine 17, and the sequential combustor arrangement, which is not shown as they are not the subject of this disclosure.

[0062] Exhaust gases leave the second turbine 17. The remaining heat of the exhaust gases is typically used in a subsequent water steam cycle, which is also not shown here.

[0063] FIG. 2a shows a section through the second combustor 16 with burners of the second combustor 25, and also the fuel distribution system with a fuel ring main 30 and burner fuel feeds 27. Eight individual fuel valves 31 are arranged in eight of the burner fuel feeds 27. By closing an individual fuel valve 31, the fuel flow to individual burners 25 can be reduced or stopped and the fuel can be redistributed to the remaining burners 25. The overall fuel flow to the combustor 16 can be controlled via a control valve 28 which is arranged in the fuel feed 29 which supplies fuel to the fuel ring main 30.

[0064] An example of an arrangement of the first turbine outlet temperature measurements 18 is shown in FIG. 2b. FIG. 2b shows the cross section II-II of FIG. 1 through the annular second combustor 16 with a plurality of burners of the second combustor 25 at the upstream end of the second combustor 16. In each burner of the second combustor 25 a first turbine outlet temperature measurement 18 is arranged which is connected to the controller 20.

[0065] An example of an arrangement of the second turbine outlet temperature measurements 19 is shown in FIG. 3. FIG. 3 shows the cross section III-III of FIG. 1 with the outlet of the second turbine 17. A number of second turbine outlet temperature measurement 19 is arranged downstream of the second turbine which is connected to the controller 20. The number of second turbine 17 outlet temperature measurements can for example correspond to the number of burners of the second combustor 25 (in this example 20).

[0066] In FIG. 4 an example of the exhaust temperature distribution is shown. The exhaust temperature is measured at 20 locations which are numbered in clockwise direction from 1 to 20. The temperature itself is normalized with the maximum measured temperature. The example schematically shows the normalized exhaust temperature distribution for the burner and fuel distribution system shown in FIG. 2a with four burners switched off closest to the 3 o'clock and four burners switched off closest to the 9 o'clock position, i.e. the burners closest to the horizontal plane of the gas turbine are switched off. The six burners closest to the 12 o'clock and 6 o'clock (vertical top and bottom of the gas turbine) are operating. The operative burners lead to high exhaust temperatures while the exhaust temperature downstream of the inoperative burners is at a minimum.

[0067] The temperature distribution downstream of the turbine is offset in circumferential direction around the axis 26 of the gas turbine relative to the circumverential location of the burners to which a second fuel flow is supplied by an offset angle . The offset angle corresponds to the circumferential offset around the axis 26 of the gas turbine the hot gas is subjected to when traveling from the combustor through the turbine to the location of turbine outlet temperature measurements. The offset angle in the example of FIG. 4 is 90. Therefore the location of minimum temperatures is offset by 90 relative to the location of the burners which are switched off and therefore produce the minimum inlet temperatures to the turbine. Analougously, the location of maximum temperatures is offset by 90 relative to the location of the burners which are operating with the unrestricted fuel flow and therefore produce the maximum inlet temperatures to the turbine.

[0068] In FIG. 5 an exemplary control logic to determine a selected turbine inlet temperature error for the control of the gas turbine is depicted.

[0069] Based on the operating conditions of the gas turbine and a maximum allowable turbine outlet temperature TAT MAX a maximum calculated turbine inlet temperature for the maximum allowable turbine outlet temperature TIT TAT MAX is calculated in a turbine inlet temperature formula block one TIT Formula I. The smaller one of the maximum allowable turbine outlet temperature for the maximum allowable turbine outlet temperature TIT TAT MAX and the maximum allowable turbine outlet temperature TAT MAX is selected in the minimum selector I to obtain the selected maximum allowable turbine inlet temperature TIT MAX SEL.

[0070] Based on the operating conditions of the gas turbine and the measured average turbine outlet temperature TAT AVG a turbine inlet temperature TIT is calculated in a turbine inlet temperature formula block two TIT Formula II.

[0071] The difference between the selected maximum allowable turbine inlet temperature TIT MAX SEL and the turbine inlet temperature TIT is determined in the subtraction block I. As a result a turbine inlet temperature error TIT ERR is obtained.

[0072] Based on the operating conditions of the gas turbine and the maximum allowable trimmed turbine outlet temperature TAT TR MAX the maximum trimmed turbine outlet temperature THG TR MAX is calculated in a hot gas temperature calculation block one THG Formula I.

[0073] Based on the operating conditions of the gas turbine and the measured trimmed turbine outlet temperature TAT TR a trimmed hot gas temperature THG TR is calculated in a hot gas temperature formula block two THG Formula II.

[0074] The difference between the maximum trimmed turbine outlet temperature THG MAX TR and the trimmed hot gas temperature THG TR is determined in the subtraction block II. As a result a trimmed hot gas temperature error THG TR ERR is obtained.

[0075] The a trimmed hot gas temperature error THG TR ERR is converted to a trimmed turbine inlet temperature error TIT TR ERR in the function block for Scaling of hot gas temperature to turbine inlet temperature SCALE.

[0076] The smaller one of the turbine inlet temperature error TIT ERR and the trimmed turbine inlet temperature error TIT TR ERR is selected in the minimum selector II to obtain the selected turbine inlet temperature error TIT ERR SEL.

[0077] The selected turbine inlet temperature error TIT ERR SEL is used for control of the gas turbine, in particular for the control of the fuel flow with the control valve 28 (in FIG. 2a).

[0078] All the explained advantages are not limited to the specified combinations but can also be used in other combinations or alone without departing from the scope of the disclosure. Other possibilities are optionally conceivable, for example the second combustor can have can combustors.

LIST OF DESIGNATIONS

[0079] 10 gas turbine [0080] 11 rotor [0081] 12 compressor [0082] 13 first combustor [0083] 14 first turbine [0084] 15 fuel lance [0085] 16 second combustor [0086] 17 second turbine [0087] 18 first turbine outlet temperature measurement [0088] 19 second turbine outlet temperature measurement [0089] 20 controller [0090] 21 first combustor fuel control line [0091] 22 first combustor fuel supply [0092] 23 second combustor fuel control line [0093] 24 burner of the first combustor [0094] 25 burner of the second combustor [0095] 26 axis [0096] 27 burner fuel feed [0097] 28 control valve [0098] 29 fuel feed [0099] 30 fuel ring main [0100] 31 individual fuel valve [0101] Sub I subtraction block I [0102] Sub II subtraction block II [0103] Scale Scaling of hot gas temperature to turbine inlet temperature [0104] TAT AVG average turbine outlet temperature [0105] TAT MAX maximum allowable turbine outlet temperature [0106] TAT TR trimmed turbine outlet temperature [0107] TAT TR MAX maximum allowable trimmed turbine outlet temperature [0108] TAT1 TR trimmed first turbine outlet temperature [0109] TAT2 TR trimmed second turbine outlet temperature [0110] THG hot gas temperature (estimated) [0111] THG TR trimmed hot gas temperature [0112] THG TR ERR trimmed hot gas error [0113] THG-TR MAX maximum trimmed turbine outlet temperature [0114] THG Formula I hot gas temperature calculation block one [0115] THG Formula II hot gas temperature calculation block two [0116] max(TAT1i) maximum turbine outlet temperature measurement [0117] TIT turbine inlet temperature [0118] TIT AVG averaged turbine inlet temperature [0119] TIT TR trimmed turbine inlet temperature [0120] TIT ERR turbine inlet temperature error [0121] TIT ERR SEL selected turbine inlet temperature error [0122] TIT Formula I turbine inlet temperature calculation block one [0123] TIT Formula II turbine inlet temperature calculation block two [0124] TIT-MAX maximum allowable turbine inlet temperature [0125] TIT-MAX SEL selected maximum allowable turbine inlet temperature [0126] TIT TAT MAX maximum calculated turbine inlet temperature for maximum allowable turbine outlet temperature [0127] TIT TR ERR trimmed inlet temperature error [0128] Minimum selector I logic block to select the minimum [0129] p3 turbine inlet pressure [0130] p4 turbine outlet pressure [0131] T2 compressor exit temperature [0132] offset angle