Method for operating a power plant

1. A method for operating a steam power plant, comprising a steam generator, a steam turbine and a steam/water cycle, at least consisting of a water-cooled condenser, a deaerator and a feedwater pump, whereby a cooling water pump is provided for pumping cooling water through said water-cooled condenser, and evacuating means are connected to said water-cooled condenser for evacuating at least said water-cooled condenser, said operating method being related to a shut down and start-up of said power plant after said shut down and comprising the steps of:

a) shut down of the steam turbine;

b) restoration of a good vacuum within the condenser by using said evacuating means;

c) stopping said cooling water pump of said water-cooled condenser and said evacuating means, and filling up the vacuum portion of the steam/water cycle, at least said condenser, with steam up to slightly above atmospheric pressure;

d) controlling the pressure with a flow of said cooling water;

e) after a certain shut-down period starting the cooling water pump just before start-up of the plant; and

f) starting the plant.

2. A method for operating a combined cycle power plant, comprising a gas turbine and a steam/water cycle with a heat recovery steam generator, through which the exhaust gases of the gas turbine flow, a water-cooled condenser, a feedwater pump and a steam turbine, whereby a cooling water pump is provided for pumping cooling water through said water-cooled condenser, and evacuating means are connected to said water-cooled condenser for evacuating at least said water-cooled condenser, said operating method being related to a shut down and start-up of said power plant after said shut down and comprising the steps of:

a) shut down of the steam turbine and gas turbine and/or a combustor of said gas turbine ;

b) restoration of a good vacuum within the condenser by using said evacuating means;

c) stopping said cooling water pump of said water-cooled condenser and said evacuating means, and filling up the vacuum portion of the steam/water cycle, at least said condenser, with steam up to slightly above atmospheric pressure;

d) controlling the pressure with a flow of said cooling water;

e) after a certain shut-down period starting the cooling water pump just before start-up of the plant; and

f) starting the plant.

3. The method according to claim 1 , wherein the steam turbine comprises a low-pressure steam turbine, and the condenser and said low-pressure steam turbine are filled up with steam in step (c).

4. The method according to claim 1 , wherein the steam for filling up said condenser is taken from the steam/water cycle.

5. The method according to claim 4 , wherein the steam turbine has a steam-sealed gland, and gland steam is used for filling up said condenser.

6. The method according to claim 4 , wherein the steam turbine has a low-pressure steam turbine with a steam bypass, and the steam for filling up the vacuum portion of the steam/water cycle, at least said condenser, is taken from the LP steam bypass.

7. The method according to claim 4 , wherein the steam turbine has a low-pressure steam turbine with an auxiliary LP drum, and the steam for filling up the vacuum portion of the steam/water cycle, at least said condenser, is taken from the LP steam bypass.

8. The method according to claim 1 , wherein at least the condenser has an insulation.

9. The method according to claim 1 , further comprising a condenser bypass is used to control the pressure in the condenser.

10. The method according to claim 1 , wherein the built up inversion layer on the hot well is used to avoid heat loss.

11. The method according to claim 1 , wherein the ejector is started as soon as possible at startup procedure to extract the gases diffused into the steam.