ACCELERATED COOLING OF A GAS TURBINE
In a method for the fast cooling down of a gas turbine ( 1 ) after its operation, and also in a gas turbine ( 1 ) useful for carrying out the method, subsequent to the operation of a gas turbine ( 1 ), the rotor ( 8 ) is operated at low cooling speed (n) in order to cool down the gas turbine ( 1 ) which is heated up as a result of operation. This allows service or maintenance operations to be started early and therefore to reduce the shutdown periods of a gas turbine ( 1 ). After the operation of the gas turbine ( 1 ), cooling is not carried out a constant low cooling speed (n), but the cooling speed (n) is controlled as a function of at least one critical temperature (T k ) and/or of time (t). The cooling speed (n) in this case, in dependence upon the critical temperature (T k ), is kept as high as the resulting thermal and/or cyclic load allows for realizing a fast cool-down.
1 . A method for cooling down a gas turbine after operation of the gas turbine, the method comprising:
operating a rotor of the gas turbine at a cooling speed (n) to cool down the gas turbine; and
controlling the cooling speed (n) as a function of at least one critical temperature (T k ), of time, or of both.
2 . The method as claimed in claim 1 , wherein said at least one critical temperature (T k ) is a cooling-air temperature of the gas turbine.
3 . The method as claimed in claim 1 , further comprising:
calculating the difference between at least one pair of critical temperatures (T k ); and
wherein controlling the cooling speed (n) comprises controlling as a function of said difference, of time, or of both.
4 . The method as claimed in claim 1 , wherein said at least one critical temperature (T k ) is a temperature of the rotor cover.
5 . The method as claimed in claim 1 , wherein said at least one critical temperature (T k ) is a temperature of a casing section or of the rotor.
6 . The method as claimed in claim 1 , wherein controlling the cooling speed (n) comprises controlling proportionally to time.
7 . The method as claimed in claim 1 , wherein controlling the cooling speed (n) comprises increasing the cooling speed (n) proportionally to time until a maximum value is reached, and thereafter maintaining the cooling speed (n) at said maximum value.
8 . The method as claimed in claim 1 , wherein controlling the cooling speed (n) comprises:
first maintaining the cooling speed (n) constant at a first cooling speed (n 1 ) until a critical temperature or a time limit is reached;
thereafter increasing the cooling speed to a second cooling speed (n 2 ); and
thereafter maintaining the cooling speed at said second cooling speed (n 2 ).
9 . The method as claimed in claim 1 , wherein controlling the cooling speed (n) comprises:
first maintaining the cooling speed (n) constant at a first cooling speed (n 1 )until a temperature limit or a time limit is reached;
thereafter increasing the cooling speed in steps to a higher cooling speed (n i ); and
thereafter maintaining the cooling speed at said higher cooling speed (n i ) until reaching another temperature or time limit, until a maximum cooling speed is reached.
10 . The method as claimed in claim 1 , further comprising:
determining at least two permissible cooling speeds (n) as functions of at least two critical temperatures or temperature differences; and
wherein controlling the cooling speed comprises controlling at the lowest of said at least two permissible cooling speeds (n).
11 . A gas turbine comprising:
a rotor configured and arranged to be operated at a cooling speed (n) to cool down the gas turbine; and
means for controlling the cooling speed (n) as a function of at least one critical temperature (T k ), of time, or of both.
12 . The gas turbine as claimed in claim 11 , further comprising:
a component which is thermally highly loaded when the gas turbine is shutting down; and
an air passage;
wherein the means for controlling comprises at least one temperature measuring device configured and arranged to measure a temperature (T k ) which is critical for the cool-down of the gas turbine, the at least one temperature measuring device being installed on said component or in said air passage.
13 . The gas turbine ( 1 ) as claimed in claim 12 , wherein:
the component comprises a rotor cover; and
the at least one temperature measuring device is installed on the rotor cover.
14 . The gas turbine as claimed in claim 12 , wherein:
the component comprises the rotor; and
the at least one temperature measuring device is installed on the rotor.
15 . The gas turbine as claimed in claim 12 , wherein:
the air passage comprises a cooling air passage; and
the at least one temperature measuring device is installed in the cooling air passage.