Method for operating a power plant

1. A method for operating a power plant, including a gas turbine having a compressor and a steam power generation system that drive at least one electric generator, the method comprising:

supplying flue gases produced by the gas turbine into a boiler of the steam power generation system;

generating, by the gas turbine in a steady operation, net output power less than zero; and

generating, by the steam power generation system, a net output power greater than zero, wherein a total generated power of the power plant is a sum of the net output power of the gas turbine and the net output power of the steam power generation system and is substantially equal to a house load of the power plant.

2. The method according to claim 1 , comprising:

generating the second output power larger than the house load with the steam power generation system; and

using the power generated by the steam power generation system in excess of the house load to drive the gas turbine.

3. The method according to claim 1 , wherein the electric generator is connected to a grid.

4. The method according to claim 1 , wherein the gas turbine operates at grid frequency.

5. The method according to claim 1 , wherein the gas turbine, steam powered generation system and at least one electric generator are all arranged on a single shaft.

6. The method according to claim 1 , wherein the power plant includes a gas turbine electric generator and a steam power generation system electric generator and the gas turbine electric generator and the steam power generation system electric generator are connected to each other via a line, the method comprising transferring power directly between the gas turbine electric generator and a steam power generating system electric generator directly via the line.

7. A method for starting up a power plant including a gas turbine having a compressor and a steam power generation system that drive at least one electric generator, wherein the gas turbine produces flue gases that are supplied into a boiler of the steam power generation system, the method comprising:

starting up and loading up the gas turbine to generate a net output power greater than zero and substantially equal to a house load;

starting up and loading up the steam power generation system to generate a net output power greater than zero;

while the steam power generation system is loaded up, decreasing the first output power below zero, a total generated power of the power plant being a sum of the net output power of the gas turbine and the net output power of the steam power generation system, and being substantially equal to a house load of the power plant; and then

maintaining the power plant in a steady state operation with the total generated power being substantially equal to a house load of the power plant.

8. The method according to claim 7 , comprising:

connecting the electric generator to a grid.

9. The method according to claim 7 , wherein the gas turbine has a stator and a rotor, the method comprising:

generating steam within the boiler and expanding the steam in one or more turbines of the steam power generation system; and

regulating the gas turbine while decreasing the first output power, to get a steam minimum temperature compatible with the rotor.

10. The method according to claim 7 , wherein the gas turbine operates at grid frequency.

11. The method according to claim 7 , wherein the gas turbine, steam powered generation system and at least one electric generator are all arranged on a single shaft.

12. The method according to claim 7 , wherein the power plant includes a gas turbine electric generator and a steam power generation system electric generator and the gas turbine electric generator and the steam power generation system electric generator are connected to each other via a line, the method comprising transferring power directly between the gas turbine electric generator and a steam power generating system electric generator directly via the line.

13. A method for reducing the power of power plant including a gas turbine having a compressor and a steam power generation system that drive at least one electric generator, wherein the gas turbine produces flue gases that are supplied into a boiler of the steam power generation system, wherein steam is generated that is then expanded in a turbine of the steam power generation system, the turbine having a stator and a rotor, the method comprising:

decreasing a net output power of the gas turbine; then

decreasing a net output power of the steam power generation system;

further decreasing the net output power of the gas turbine below zero such that a total generated power of the power plant as a sum of the net output power of the gas turbine and the net output power of the steam power generation system is substantially equal to a house load of the power plant; and then

maintaining the power plant in a steady state operation with the total generated power substantially equal to a house load of the power plant.

14. The method according to claim 13 , wherein an initial decreasing of the net output power of the gas turbine comprises:

decreasing the net output power to achieve a minimum steam temperature compatible with the rotor.

15. The method according to claim 13 , comprising:

disconnecting the power plant from the grid.

16. The method according to claim 13 , wherein the gas turbine operates at grid frequency.

17. The method according to claim 13 , wherein the gas turbine, steam powered generation system and at least one electric generator are all arranged on a single shaft.

18. The method according to claim 13 , wherein the power plant includes a gas turbine electric generator and a steam power generation system electric generator and the gas turbine electric generator and the steam power generation system electric generator are connected to each other via a line, the method comprising transferring power directly between the gas turbine electric generator and a steam power generating system electric generator directly via the line.