Corrected parameter control method for a two-shaft gas turbine

1. A control method for a gas turbine comprising:

controlling opening of at least one fuel valve to maintain a temperature (Tfire) of gas at an inlet of the gas turbine and a fuel-air ratio (F/A) within predetermined limits by:

calculating a set point exhaust temperature (TX) as a sum of a reference temperature (TXbase) and a plurality of correction values each of which are associated with a different operating parameter;

wherein corrections values are calculated by computer simulations of the gas turbine, the simulations being conducted by specifying attainment of one of: a maximum of the set point exhaust temperature (TXmaxTfire) and a maximum of the fuel-air ratio (F/A), for each condition differing from a reference condition;

further wherein said plurality of correction values includes four corrections values and wherein said step of calculating further comprises calculating:

TX=TXbase+DeltaTX_Dpin+DeltaTX_Dpout+DeltaTX_Hum+DeltaTX_PCNLP

where:

TX is said set point exhaust temperature:

DeltaTX_Dpin is a correction value for the set point exhaust temperature (TX) associated with a variation of pressure drops in intake pipes with respect to a nominal value of 0 mmH2O,

DeltaTX_Dpout is a correction value for the set point exhaust temperature (TX) associated with a variation of pressure drops in exhaust pipes with respect to a nominal value of 0 mmH2O,

DeltaTX_Hum is a correction value for the set point exhaust temperature (TX) associated with a variation of a relative humidity of air with respect to a nominal value of 60%, and

DeltaTX_PCNLP is a correction value for the set point exhaust temperature (TX) associated with a variation of a speed of a low pressure shaft with respect to a nominal value of 100%.

2. The control method of claim 1 , wherein a maximum exhaust temperature curve is generated for each of a plurality of speeds associated with said gas turbine.

3. The control method of claim 2 , wherein said reference temperature (TXbase) is a reference temperature associated with one of said plurality of speeds associated with said gas turbine (Txbase(PCNLP)).

4. The control method of claim 3 , wherein there are two values of TXbase(PCNLP), a first value related to a curve of maximum temperature (Tfire) and a second value related to a curve of maximum increase of temperature (Trise) of a gas in a combustion chamber of the gas turbine.

5. The control method of claim 4 , further comprising calculating said first value as:

TXmaxTfire=TxbasemaxTfire(PCNLP,PR)+DeltaTX_DPin +DeltaTX_Dpout+DeltaTX_Hum,

and calculating said second value as:

TXmaxTrise=TxbasemaxTrise(PCNLP,PR)+DeltaTX_DPin+DeltaTX_Dpout+DeltaTX_Hum,

where:

TXmaxTfire is said maximum of the set point exhaust temperature;

TxbasemaxTfire is a temperature curve associated with said maximum of the set point exhaust temperature;

TxbasemaxTrise is a temperature curve associated with a maximum permissible rise in temperature;

PR indicates values having a dependence on a compression ratio (PR).

6. The control method of claim 5 , further comprising the step of:

providing said temperature curves TXbasemaxTfire and TXbasemaxTrise as two-dimensional tables, with the compression ratio (PR) and the gas turbine speed (PCNLP) as independent variables.

7. The control method of claim 5 , wherein said maximum temperature (TXmaxTfire), as a function of the compression ratio PR which enables said maximum (TXmaxTfire) to be attained, is a set of curves, each curve associated with a specific value of speed PCNLP, each successive curve generally having an increasingly negative slope as speed increases, and decreasing with a rise in compression ratio PR.

8. The control method of claim 5 , wherein said maximum temperature (TXmaxTrise), as a function of the compression ratio PR which enables the maximum (TXmaxTrise) to be attained, is a set of curves, each curve associated with a specific value of speed PCNLP, each successive curve generally having an increasingly negative slope as speed increases, and decreasing with a rise in the compression ratio PR.

9. The control method of claim 1 , wherein the correction value DeltaTX_Hum depends on a specific humidity (SH) and is expressed as a function of a difference (DeltaSH), which difference (DeltaSH) is defined as a difference between a current specific humidity (SH current) and a specific humidity (SH_60%RH) at a relative humidity RH of 60%.

10. The control method of claim 9 , wherein there is a linear correlation between the correction value DeltaTX_Hum and the difference (DeltaSH).

11. The control method of claim 10 , further comprising the step of: determining the specific humidity (SH 60%RH) at a relative humidity of RH 60% as a function of atmospheric temperature by interpolating the following values, where the temperature is expressed in degrees Rankine:

SH_60% RH

(T = 419.67)

= 0.000070

SH_60% RH

(T = 428.67)

= 0.000116

SH_60% RH

(T = 437.67)

= 0.000188

SH_60% RH

(T = 446.67)

= 0.000299

SH_60% RH

(T = 455.67)

= 0.000464

SH_60% RH

(T = 464.67)

= 0.000707

SH_60% RH

(T = 473.67)

= 0.001059

SH_60% RH

(T = 482.67)

= 0.001560

SH_60% RH

(T = 491.67)

= 0.002263

SH_60% RH

(T = 500.67)

= 0.003324

SH_60% RH

(T = 509.67)

= 0.004657

SH_60% RH

(T = 518.67)

= 0.006367

SH_60% RH

(T = 527.67)

= 0.008670

SH_60% RH

(T = 536.67)

= 0.011790

SH_60% RH

(T = 545.67)

= 0.015966

SH_60% RH

(T = 554.67)

= 0.021456

SH_60% RH

(T = 563.67)

= 0.028552

SH_60% RH

(T = 572.67)

= 0.037585

SH_60% RH

(T = 581.67)

= 0.048949.

12. The control method of claim 1 , wherein the correction value DeltaTX_Dpout is expressed directly as a function of a measured pressure drop (DPout).

13. The control method of claim 12 , wherein there is a linear correlation between the correction value DeltaTX_Dpout and the measured pressure drop (Dpout).

14. A control method for a gas turbine comprising:

controlling opening of a vent valve to maintain a temperature rise (Trise) of gas in a combustion chamber of the gas turbine within predetermined limits using values of an exhaust temperature (TX) as a function of a compression ratio (PR), which values have been obtained for a plurality of operating conditions of the gas turbine; and

calculating the exhaust temperature (TX) as a linear approximation of a sum of a reference temperature (Txbase) plus correction values associated with an environmental or operating parameter.

wherein there are four of the correction values such that the exhaust temperature (TX) is expressed as:

TX=TXbase+DeltaTX_DPin+DeltaTX_Dpout+DeltaTX_Hum+DeltaTX_PCNLP

where:

TXbase is determined as: TXbase=TTX/((518.67/TCD)x), where:

518.67 is a reference temperature;

TCD is an exhaust temperature of a compressor, expressed in a unit of measurement compatible with that of the reference temperature;

x is a nondimensional exponent calculated to minimize a mean quadratic deviation between values of TTX and the single control function; and

TTX is a transformed exhaust temperature;

DeltaTX_Dpin is a correction value for the exhaust temperature (TX) associated with a variation of pressure drops in intake pipes with respect to a nominal value of 0 mm H2O; DeltaTX_Dpout is a correction value for the exhaust temperature (TX) associated with a variation of pressure drops in exhaust pipes with respect to a nominal value of 0 mm H2O;

DeltaTX_Hum is a correction value for the exhaust temperature (TX) associated with a variation of relative humidity of air with respect to a nominal value of 60%; and

DeltaTX_PCNLP is a correction value for the exhaust temperature (TX) due to a variation of a low pressure shaft speed with respect to a nominal value of 100%.

15. The control method of claim 14 , wherein said values are associated with a control function that is defined for each of a plurality of values of atmospheric temperature.

16. The control method of claim 15 , wherein said control functions represent a relationship between the exhaust temperature (TX) for partial loads at a given speed of a low pressure shaft of the gas turbine and the compression ratio (PR), wherein each control function is associated with a value of atmospheric temperature, each control function generally having higher values as temperature rises and decreasing as the compression ratio (PR) decreases.

17. The control method of claim 14 , wherein said values are associated with a single control function without a dependence on atmospheric temperature.

18. The control method of claim 17 , further comprising:

determining a set point associated with said controlling step based on inverse of the transformation for a known compression ratio (PR).

19. The control method of claim 14 , wherein a set of functions, one for each value of speed (PCNLP), is expressed in terms of the maximum temperature (TX) as a function of the compression ratio (PR).

20. The control method of claim 19 , further comprising:

evaluating said exhaust temperature (TX) by calculating:

TX=TXbase(PCNLP)+DeltaTX_DPin+DeltaTX_Dpout+DeltaTX_RH

where:

TXbase(PCNLP) is a reference temperature associated with a speed of the gas turbine; and

DeltaTX_RH is a change in exhaust temperature associated with relative humidity.

21. The control method of one of claims 18 or 20 , wherein the exponent X is a function of a speed of a low pressure wheel of the gas turbine.

22. The control method of claim 21 , wherein the exponent X, for intermediate speeds (PCNLP), is calculated by interpolation of values of X which have been calculated at other speeds (PCNLP) as follows:

if PCNLP=105%, X=0.323;

if PCNLP=100%, X=0.33225;

if PCNLP=90%, X=0.34;

if PCNLP=80%, X=0.34425;

if PCNLP=70%, X=0.351;

if PCNLP=60%, X=0.348; or

if PCNLP=50%, X=0.3505.

23. The control method of claim 20 , wherein the correction value DeltaTX_RH is calculated based on three ambient temperatures, three levels of relative humidity, and load characteristics according to a cubic law.

24. The control method of claim 23 , wherein nine simulations are conducted, each associated with different fuel-air ratio F/A values, to determine a reference level, current values of TX are then plotted as functions of PR, while a difference between the functions and base curves yields the correction value DeltaTX_RH, as expressed in the formula:

DeltaTX_RH =TX−TXbase.

25. The control method of claim 24 , wherein said values of the correction value DeltaTX_RH are plotted as a function of a difference (DeltaSH) between a current value of specific humidity (SH_current) and a specific humidity at a relative humidity of 60% (SH_60%RH) such that:

DeltaSH=SH_current−SH_60% RH.

26. The control method of claim 25 , wherein the function comprises two straight lines rising with an increase in the difference (DeltaSH), of which a first one of said straight lines is valid when DeltaSH is less than 0 and has a greater slope than a second one of said straight lines which is valid when DeltaSH is greater than 0, the two straight lines passing through a point near an origin of the function's axes.

27. The control method of claim 14 , wherein the correction value DeltaTX_Dpin is a function of a measured pressure drop (DPin).

28. The control method of claim 27 , further comprising the step of:

determining said correction value DeltaTX_Dpin taking into account three ambient temperatures, three pressure drops in an intake and load characteristics according to a cubic law.

29. The control method of claim 28 , wherein nine simulations are conducted, each associated with different fuel-air ratio F/A values, to reach a reference level, current values of TX are then plotted as functions of PR, while a difference between the functions and base curves yields the correction value DeltaTX_Dpin, as expressed in the formula:

DeltaTX_Dpin=TX−TXbase.

30. The control method of claim 29 , wherein said correction values (DeltaTX_Dpin) are linearly correlated with the measured pressure drop Dpin such that the correction values of DeltaTX_Dpin increase with a rise in the measured pressure drop Dpin.

31. The control method of claim 14 , wherein the correction value (DeltaTX_Dpout) is a function of the measured pressure drop DPout.

32. The control method of claim 31 , further comprising: determining said correction value DeltaTX_Dpout taking into account three ambient temperatures, three pressure drops in the exhaust and load characteristics according to a cubic law.

33. The control method of claim 32 , wherein nine simulations are conducted, each associated with different fuel-air ratio F/A values, to reach a reference level, the current values of TX are then plotted as functions of PR, while a difference between the functions and base curves yields the correction value DeltaTX_Dpout, as expressed in the formula:

DeltaTX_Dpout=TX−TXbase.

34. The control method of claim 33 , wherein the correction values DeltaTX_Dpout are linearly correlated with the exhaust pressure Dpout, such that the correction values DeltaTX_Dpout increase with a rise in the exhaust pressure Dpout.

35. The control method of claims 26 , 30 or 34 , wherein a correlation for calculating the maximum exhaust temperature TX is:

TX=TTX(PCNLP, PR)/((518.67/TCD)x(PCNLP)+DeltaTX_RH (DeltaSH)+DeltaTX_Dpin (Dpin)+DeltaTX_Dpout (Dpout).

36. The control method of claim 1 or 14 , wherein said control method is used to control a two-shaft gas turbine and further comprising the step of:

providing said two-shaft gas turbine with a dry nitrogen oxide (NOx) reduction system.

37. A control method for a gas turbine comprising:

controlling opening of at least one fuel valve to maintain a temperature (Tfire) of gas at an inlet of the gas turbine and a fuel-air ratio (F/A) within predetermined limits by:

calculating a set point exhaust temperature (TX) as a sum of a reference temperature (TXbase) and a plurality of correction values each of which are associated with a different operating parameter;

wherein said plurality of correction values includes four corrections values and wherein said step of calculating further comprises calculating:

TX=TXbase+DeltaTX_Dpin+DeltaTX_Dpout+DeltaTX_Hum+DeltaTX_PCNLP

where:

TX is said set point exhaust temperature:

DeltaTX_Dpin is a correction value for the set point exhaust temperature (TX) associated with a variation of pressure drops in intake pipes with respect to a nominal value of 0 mmH2O,

DeltaTX_Dpout is a correction value for the set point exhaust temperature (TX) associated with a variation of pressure drops in exhaust pipes with respect to a nominal value of 0mmH2O,

DeltaTX_Hum is a correction value for the set point exhaust temperature (TX) associated with a variation of a relative humidity of air with respect to a nominal value of 60%, and

DeltaTX_PCNLP is a correction value for the set point exhaust temperature (TX) associated with a variation of a speed of a low pressure shaft with respect to a nominal value of 100%; and

controlling opening of a vent valve to maintain a temperature rise (Trise) of gas in a combustion chamber of the gas turbine within predetermined limits using values of an exhaust temperature (TX) as a function of a compression ratio (PR), which values have been obtained for a plurality of operating conditions of the gas turbine.