STEAM CYCLE, AND METHOD FOR OPERATING A STEAM CYCLE

Abstract

A steam cycle for a power station, and to a method for operating, in particular for starting, a steam cycle. The steam cycle has a high-pressure turbine, a condenser and a steam generator. The steam generator is connected to the high-pressure turbine via a first line. Live steam quick-closing valves and live steam regulating valves for supplying the high-pressure turbine are arranged in the direction of the steam flow between the steam generator and the high-pressure turbine. A starting line is arranged downstream of the high-pressure turbine in the direction of the steam flow, the starting line connecting a waste steam region downstream of the high-pressure turbine with the condenser. At least one regulator regulates a closing of a starting valve for sealing the starting line, and an opening of the live steam valve, depending on the rotational speed, a temperature and load state of the high-pressure turbine.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] There follows a more detailed explanation of an exemplary embodiment of an inventive steam turbine and of an inventive method for operating, in particular for starting up, such a steam turbine, with reference to the appended drawings. In that context, identical components or components having identical functions are labeled with identical reference signs.

[0024] FIG. 1 shows a schematic representation of a steam circuit according to the invention.

[0025] FIG. 2 shows a flowchart of a method, according to the invention, for operating a steam circuit.

DETAILED DESCRIPTION OF INVENTION

[0026] FIG. 1 shows a steam circuit 10 having a high-pressure turbine 12, an intermediate-pressure turbine 50 and a low-pressure turbine 60. The turbines (12, 50, 60) are arranged on a common shaft which is coupled to a generator (not shown). The steam circuit 10 further comprises a steam generator 30, a condenser 40 and a feed pump 70. The steam generator 30 is connected to the high-pressure turbine 12 via a first line 17, wherein live steam valves 14, 15, which can prevent a flow of steam from the steam generator 30, are arranged on the first line 17. In that context, the live steam valve 14 acts as a live steam quick-closing valve and the live steam valve 15 acts as a live steam controlling valve. A pressure-limiting controller 29 is arranged at the live steam valve 15 and can be used to limit the mass flow of the steam from the steam generator 30 to the high-pressure turbine 12. An exhaust steam region 13 is connected downstream of the high-pressure turbine 12 and is supplied with steam leaving the outlet of the high-pressure turbine 12. The exhaust steam region 13 is connected, via a line section 18 in which there is arranged a check flap 19, to a reheater 20. The reheater 20 is connected, via a line 37 in which there are arranged live steam valves 38, 39 for blocking or controlling the supply of steam, to the intermediate-pressure turbine 50. The reheater 20 is further connected to the condenser 40 via a line 35, wherein in the line 55 there is arranged an intermediate-pressure redirection station 36 with a downstream-connected injection device 33 by means of which it is possible to control the supply of pressure to the intermediate-pressure turbine 50.

[0027] The steam generator 30 is further connected, via a line 21 in which there are arranged a high-pressure redirection station 22 and an injection device 85, to the reheater 20. The exhaust steam region 13 is connected to the condenser 40 via a start-up line 23, 25. In that context, a start-up valve 27 and an injection device 34 are arranged in the start-up line 25. The start-up valve 27 can be controlled by means of a controller 26 and can be partially opened at least in discrete intermediate steps between the fully open and fully closed positions. Alternatively, a fully controllable start-up valve 27 would also be possible. In addition, an emptying line 28 is arranged parallel to the start-up line 25 and also opens into the condenser 40. The emptying line can be opened by means of an emptying valve 24.

[0028] The steam generator 30 is connected to the low-pressure turbine 60 via a line 52, wherein a controlling flap 53 is arranged in the line 52 and controls the supply of steam to the low-pressure turbine 60. The intermediate-pressure turbine 50 is connected to the low-pressure turbine 60 via a line 51, wherein the line 52 opens into the line 51. A line 54 leads from the low-pres sure turbine 60 to the condenser 40, which is in turn connected to the feed pump 70 via a line 41. The feed pump 70 is connected to the steam generator 30 via a line 42.

[0029] During operation of the steam circuit 10, the steam generator 30 is supplied with water via the pressurizing feed pump 70 and the line 42. In the steam generator 30, the water is evaporated and superheated. This steam is fed via the first line 17 to the high-pressure turbine 12, where the steam is partially expanded. In the reheater 20, the steam is again supplied with energy, which it gives off via the intermediate-pressure turbine 50 and the low-pressure turbine 60. The expanded steam then condenses in the condenser 40 and is fed, via the line 41, back to the steam generator 30 as water, thus closing the circuit.

[0030] The respective injection devices 33, 34, 55 can be used to add water to the steam in the lines 21, 25 and 28 in order to lower the temperature of the steam at the inlet into the condenser 40, or into the reheater 20. A controller 26 is provided at the start-up valve 27 and opens the start-up valve 27 in dependence on temperature, pressure and speed of the high-pressure turbine 12. The corresponding sensors for detecting the speed are not shown, but can easily be arranged on the shaft which carries the turbine stages 12, 50, 60 and is connected to the generator.

[0031] The sensors for detecting the temperature and the pressure are sensibly arranged upstream of the inlet into the blading space of the high-pressure turbine 12 or at the outlet of the high-pressure turbine 12, or in the exhaust steam region 13.

[0032] FIG. 2 shows a flowchart for starting up a steam circuit having a steam turbine.

[0033] A first method step [100] involves beginning a start-up procedure for the steam turbine 12, 50, 60. In a further method step [110], the steam turbine 12, 50, 60 is accelerated by fully opening the live steam quick-closing valves 14, 38 and subsequently opening the live steam valves 15, 39. In a subsequent method step [120], the start-up line 25 is opened by opening the start-up valve 27 and the pressure-limiting controller 29 is activated. In the next method step [130], a warm-up speed is reached and the steam turbine 12, 50, 60 is accelerated further to the rated speed.

[0034] The following method step [140] involves operating the steam turbine under no load and synchronization with the grid. In the next method step [150], the output of the steam turbine 12, 50, 60 is further increased until a mass flow of the steam through the high-pressure turbine 12, without a pressure-limiting controller 29, would be so great that with the start-up line 25 closed an exhaust steam temperature downstream of the high-pressure turbine 12 is still just permissible. In the following method step [160], the closing procedure of the start-up valve 27 for closing the start-up line 25 begins. Starting at a defined position of the start-up valve 27, in the subsequent method steps [170], [171], [172], [173] a setpoint pressure value of the pressure-limiting controller 29 is raised in a time-delayed and continuous manner, at a defined rate. This effects defined opening of the fresh steam valves 15, 39. This procedure is continued until the mass flow of the steam through the high-pressure turbine 12 has exceeded a threshold value. In a final method step [180], the start-up line 25, or the start-up valve 27, is fully closed and the steam turbine 12, 50, 60 is switched to output operation.

[0035] Although the invention has been described in detail by way of the preferred exemplary embodiments, the invention is not restricted to the disclosed exemplary embodiment and other variations can be derived herefrom by a person skilled in the art without departing from the scope of protection of the invention.