METHOD FOR CONTROLLING THE OPERATION OF A GAS TURBINE WITH SEQUENTIAL COMBUSTION

1 . A method for controlling the operation of a gas turbine with sequential combustion, which gas turbine comprises a compressor with variable inlet guide vanes (VIGV), a first combustor, a high-pressure turbine Downstream of said first combustor, a second combustor downstream of said high-pressure turbine, and a low-pressure turbine downstream of said second combustor, said method comprising the steps of:

verifying that the gas turbine operates under base load conditions;

continuously measuring locally at various points the turbine outlet temperature TAT 1 of the high-pressure turbine;

averaging over the various local TAT 1 measurement values to get an average TAT 1 temperature (TAT 1 AVG);

controlling the operation of the first combustor in dependence of said average TAT 1 temperature (TAT 1 AVG);

checking if at least one local TAT 1 measurement value, which is higher than said average TAT 1 temperature (TAT 1 AVG), is increasing;

adjusting said average TAT 1 temperature (TAT 1 AVG), if said at least one local TAT 1 measurement value is increasing above a predetermined threshold value.

2 . The method as claimed in claim 1 , wherein said base load conditions comprise said variable inlet guide vanes (VIGV) to be open, a turbine inlet temperature (TIT 1 ) of said first combustor being at a base load value, and a turbine inlet temperature (TIT 2 ) of said second combustor being at a base load value.

3 . The method as claimed in claim 1 , wherein the moving average of a plurality of local TAT 1 measurement values, which are higher than said average TAT 1 temperature (TAT 1 AVG), is checked, and said average TAT 1 temperature (TAT 1 AVG) is adjusted, if said moving average is increasing above a predetermined threshold value.

4 . The method as claimed in claim 3 , wherein the largest local TAT 1 measurement value of said moving average is neglected.

5 . The method as claimed in claim 3 , wherein said moving average is evaluated on a time scale of 10 minutes or longer.

6 . The method as claimed in claim 5 , wherein said moving average is evaluated on a time scale of 20 minutes.

7 . The method as claimed in claim 1 , wherein said predetermined threshold value is at least 5 K above a local TAT 1 reference value.

8 . The method as claimed in claim 7 , wherein said predetermined threshold value is 10 K above a local TAT 1 reference value.

9 . The method as claimed in claim 1 , wherein said adjusting of the average TAT 1 temperature (TAT 1 AVG) is done by stepwise decreasing said average TAT 1 temperature (TAT 1 AVG) by a predetermined amount.

10 . The method as claimed in claim 3 , wherein the NOx content of the exhaust gases of the gas turbine is measured by NOx CEMS measuring means, and that said average TAT 1 temperature (TAT 1 AVG) is only adjusted, if in addition the moving average of the NOx CEMS emission measurement values is above a predetermined threshold value.

11 . The method as claimed in claim 10 , wherein said moving average of the NOx CEMS emission measurement values is evaluated on a time scale of 20 minutes, and said threshold value is at 80% of guaranteed NOx emission level.

12 . The method as claimed in claim 10 , wherein pressure pulsations are measured in said first combustor, and that said average TAT 1 temperature (TAT 1 AVG) is only adjusted, if in addition the low frequency part of said measured pressure pulsations, especially in the frequency band between 100 Hz and 150 Hz, are below a predetermined threshold value, of especially 30 mbar.

13 . The method as claimed in claim 12 , wherein said average TAT 1 temperature (TAT 1 AVG) is only adjusted, if all said adjustment criteria are fulfilled for a predetermined number of separate base load cycles and a predetermined time of operation.

14 . The method as claimed in claim 13 , wherein said predetermined number of separate base load cycles is at least 5, and that said predetermined time of operation is at least 120 minutes.