METHOD FOR DETERMINING AT LEAST ONE FIRING TEMPERATURE FOR CONTROLLING A GAS TURBINE AND GAS TURBINE FOR PERFORMING THE METHOD
The invention relates to a method for determining at least one firing temperature for controlling a gas turbine that comprises at least one compressor, at least one combustion chamber and at least one turbine, compressed air being drawn off at the compressor in order to cool the turbine and being fed to the turbine via at least one external cooling duct and via a control valve arranged in the cooling duct, in which method a plurality of temperatures and pressures of the working medium being measured in various positions of the gas turbine and the at least one firing temperature being derived from the measured temperatures and pressures. A more flexible and more accurate control is achieved additionally by determining the cooling air mass flow via the external cooling duct and by taking said flow into account when deriving the at least one firing temperature.
1 . A method for determining at least one firing temperature for controlling a gas turbine having at least one compressor, at least one combustion chamber and at least one turbine; the method comprising:
for cooling the turbine, compressed air is extracted at the compressor and is fed to the turbine via at least one external cooling line and a controlling valve arranged in the cooling line, in which method a plurality of temperatures and pressures of the working medium are measured at various points in the gas turbine and the at least one firing temperature is derived from the measured temperatures and pressures, characterized in that, in addition, the cooling air mass flow rate through the external cooling line is determined and is taken into account when deriving the firing temperature.
2 . The method as claimed in claim 1 , wherein the firing temperature has a correction factor which is determined by the change in the turbine inlet pressure as a function of the moisture content relative to a reference value of the turbine inlet pressure.
3 . The method as claimed in claim 2 , wherein the moisture content is used for calibrating the aging-induced change in the reference value.
4 . The method as claimed in claim 1 , wherein the position of the controlling valve and the pressures upstream and downstream of the controlling valve are measured in order to determine the cooling air mass flow rate.
5 . The method as claimed in claim 4 , wherein the controlling valve has a valve characteristic, and in that the valve characteristic is used for determining the cooling air mass flow rate.
6 . The method as claimed in claim 1 , wherein the firing temperature is determined according to the equation
T
x
=
f
1
(
T
7
,
p
6
p
7
,
x
d
,
p
10
p
11
,
θ
1
)
where f 1 is a function of first- and higher-order terms of the expressed variables, T 7 denotes the temperature of the working medium at the turbine outlet, p 6 /p 7 is the quotient of turbine inlet pressure and turbine outlet pressure, x d denotes the water/steam content in the working medium, p 10 /p 11 is the quotient of the pressures upstream and downstream of the controlling valve in the cooling line, and θ 1 characterizes the position of the controlling valve.
7 . A gas turbine for performing the method as claimed in claim 1 comprising at least one compressor, at least one combustion chamber and at least one turbine, wherein, for cooling the turbine, compressed air is extracted at the compressor and is fed to the turbine via at least one external cooling line and a controlling valve arranged in the cooling line, wherein, at various points in the gas turbine, a plurality of measurement points are provided for measuring temperatures and pressures of the working medium and are connected, via assigned signal lines, to a controller which emits control signals for controlling the fuel supply to a fuel supply line to the combustion chamber, characterized in that means are provided for determining the cooling air mass flow rate through the external cooling line.
8 . The gas turbine as claimed in claim 7 , wherein measurement points for measuring the pressures upstream and downstream of the controlling valve, and for measuring the position of the controlling valve, are provided on the controlling valve and are connected to the controller via signal lines.
9 . The gas turbine as claimed in claim 7 , wherein the controller is part of a closed control circuit for controlling a firing temperature of the gas turbine.