Steam cycle, and method for operating a steam cycle

1. A steam circuit for a power plant, comprising:

a high-pressure turbine, a condenser and a steam generator,

wherein the steam generator is connected to the high-pressure turbine via a first line,

wherein, in the flow direction of the steam, at least one live steam valve is arranged between the steam generator and the high-pressure turbine, and

wherein, in the flow direction of the steam, a start-up line is arranged downstream of the high-pressure turbine and connects an exhaust steam region downstream of the high-pressure turbine to the condenser,

at least one controller which, in dependence on operating parameters of the high-pressure turbine, controls closing of a start-up valve for closing the start-up line and opening of the at least one live steam valve,

wherein opening of the start-up valve is controllable, at least stepwise, between the positions “fully open” and “fully closed”, and a setpoint pressure value of the controller is raised in dependence on the opening of the start-up valve.

2. The steam circuit as claimed in claim 1 ,

wherein the operating parameters of the high-pressure turbine are a rotational speed, a temperature, a pressure and/or a load state of the high-pressure turbine.

3. The steam circuit as claimed in claim 1 ,

wherein the controllers are integrated into a common module.

4. The steam circuit as claimed in claim 1 , further comprising:

a reheater provided between the high-pressure turbine and a further turbine stage.

5. The steam circuit as claimed in claim 4 ,

wherein the start-up line branches off between the high-pressure turbine and the reheater, and opens into the condenser.

6. The steam circuit as claimed in claim 4 , further comprising:

a check device in a line section between the high-pressure turbine and the reheater, which prevents the steam flowing back toward the high-pressure turbine.

7. The steam circuit as claimed in claim 1 , further comprising:

another line arranged parallel, at least in sections, to the start-up line and also connects the high-pressure turbine to the condenser.

8. A method for operating, a steam circuit having a high-pressure turbine, a condenser and a steam generator, the method comprising:

beginning a start-up procedure of the steam turbine,

accelerating the steam turbine by opening live steam valves,

opening a start-up line and activating a pressure-limiting controller,

accelerating the steam turbine to its rated speed,

operating the steam turbine in no-load operation and synchronization with the grid,

increasing the output of the steam turbine, until a steam mass flow through the high-pressure turbine reaches a threshold value,

beginning the procedure of closing the start-up line by closing a start-up valve,

from a defined position of the start-up valve, controlled raising of the pressure upstream of the inlet into the high-pressure turbine by means of the pressure-limiting controller, and

ending the procedure of closing the start-up line by fully closing the start-up valve and transition of the steam turbine into output operation.

9. The method as claimed in claim 8 ,

wherein the pressure upstream of the inlet into the high-pressure turbine is raised in a time-delayed and continuous manner, at a predefined rate.

10. The method as claimed in claim 9 ,

wherein raising the pressure upstream of the inlet into the high-pressure turbine takes place at a defined position of the start-up valve.

11. The method as claimed in claim 10 ,

wherein opening of the live steam valves is controlled via the raising of a setpoint pressure value at the pressure-limiting controller upstream of the inlet into the high-pressure turbine.

12. The steam circuit as claimed in claim 2 ,

wherein the temperature comprises the temperature in the exhaust steam region.

13. The steam circuit as claimed in claim 6 ,

wherein the check device comprises a check flap.

14. The steam circuit as claimed in claim 7 ,

wherein the another line comprises a line for emptying the high pressure turbine.