Method for controlling gas turbine rotor temperature during periods of extended downtime

1. A method for warming the rotor of a gas turbine during periods of downtime, comprising:

feeding a stream of ambient air to an air blower;

increasing the pressure of said ambient air stream;

extracting a portion of compressed air from the discharge of said air blower;

feeding said portion of compressed air to one side of a heat exchanger;

feeding steam to the other side of said heat exchanger;

passing a resulting heated air stream from said heat exchanger into and through said rotor;

monitoring the air temperature inside said rotor; and

controlling the amount of air and steam fed to said heat exchanger based on said monitored air temperature.

2. A method according to claim 1 , further comprising the step of providing a plurality of air flow passages inside said rotor.

3. A method according to claim 2 , wherein said air flow passages are sufficient in size and number to allow for a continuous flow of said heated air stream to the inner walls and disks of said rotor.

4. A method according to claim 1 , wherein said step of feeding steam to said heat exchanger further includes the step of extracting said steam from an auxiliary boiler.

5. A method according to claim 1 , wherein said step of feeding steam to said heat exchanger further includes the step of extracting saturated steam from a heat recovery steam generator as feed to said heat exchanger.

6. A method according to claim 1 , further including the step of passing said heated air stream through an air filter upstream of said rotor.

7. A method according to claim 1 , further including the step of returning spent steam from said heat exchanger to a bottoming cycle of said gas turbine.

8. A method according to claim 1 , wherein said step of controlling the amount of air and steam fed to said heat exchanger is based on data provided by a feedback control loop.

9. A method according to claim 8 , wherein said data provided by said feedback control loop includes the temperature inside said rotor and the amount of heated air passing into and through said rotor.

10. A method according to claim 1 , wherein said step of feeding steam to said heat exchanger uses a portion of a gland steam from said gas turbine.

11. A structure for warming a gas turbine rotor during periods of downtime, comprising:

an air blower;

a heat exchanger for heating compressed air from said air blower, said heat exchanger transferring heat to said compressed air derived from an outside steam source;

air passages into and out of said rotor sufficient in size to carry a prescribed amount of heated air through said rotor to heat the turbine blades in said rotor;

steam fluid flow passages into and out of said heat exchanger and

a feedback control loop for controlling the amount of air and steam fed to said heat exchanger.

12. A structure according to claim 11 , further including an air filter for said heated air.

13. A structure according to claim 11 , wherein said feedback control loop includes temperature sensors for monitoring the air temperature inside said rotor.

14. A structure according to claim 11 , wherein said feedback control loop includes signal generators for transmitting data relating to the amount of said heated air being fed to said rotor.

15. A structure according to claim 11 , further including an air damper for controlling the amount of air fed to said heat exchanger.