Actuating drive for a control valve, in particular steam turbine control valve and method for operating same

Abstract

An actuating drive for a control valve contains a working cylinder which has a piston and a piston rod and forms an actuator for the control valve. The piston bounds a first pressure space and a second pressure space to displace the piston counter to the force of a spring by applying pressure to the first pressure space via a working medium. A working medium circuit is connected to the working cylinder at first and second pressure connections to introduce and evacuate the working medium into/from the first and second pressure spaces. The working medium circuit has a working medium pump connected to convey the working fluid, at a pressure side, to the first pressure connection, and at a suction side, to the second pressure connection. The first pressure space is permanently connected, so as to convey working fluid, to the second pressure space via a bypass line.

Claims

1. An actuating drive for a regulation valve, comprising: a working cylinder; a spring; a piston having a piston rod disposed in said working cylinder, said piston rod forming an actuator for the regulation valve, said piston delimiting a first pressure chamber with a first pressure port and a second pressure chamber with a second pressure port, for displacing said piston with said piston rod counter to a force of said spring assigned to said working cylinder by pressurization of said first pressure chamber by introduction of a pressurized working medium via said first pressure port; an external working medium circuit to which said working cylinder is connected by means of said first and second pressure ports for introducing the pressurized working medium into, or discharging the pressurized working medium from, said first and second pressure chambers, said external working medium circuit having a tank line, a pressure line, a motor and a working medium pump driven by means of said motor, said working medium pump having a suction side and a pressure side and is, by means of said pressure side, connected in working-medium-conducting fashion via said pressure line to said first pressure port and is, by means of said suction side, connected via said tank line to said second pressure port; and a short-circuit line, said first pressure chamber being connected in permanent fluid communication with said second pressure chamber via said short-circuit line.

2. The actuating drive according to claim 1, further comprising a throttle with a constant flow cross section disposed in said short-circuit line.

3. The actuating drive according to claim 1, further comprising one of a throttle with a variably adjustable flow cross section or a regulation valve, disposed in said short-circuit line.

4. The actuating drive according to claim 1, wherein said external working medium circuit has a fast-closure line with a fast-closure valve that branches off from said pressure line and opens into said tank line, wherein said fast-closure valve is an unregulated open/closed valve which has only two switching positions, specifically a first switching position, in which said fast-closure valve shuts off a flow cross section of said fast-closure line, and a second switching position, in which said fast-closure valve opens up the flow cross section of said fast-closure line.

5. The actuating drive according to claim 1, wherein said external working medium circuit has a valve and a reversing line branching off from said tank line and opening into said pressure line, wherein said valve is a check valve which shuts off in a direction of said tank line or is a shut-off valve, disposed in said reversing line.

6. The actuating drive according to claim 1, further comprising a working medium reservoir for a compensation of volume fluctuations is connected to said tank line.

7. The actuating drive according to claim 1, wherein said external working medium circuit has a positive-pressure line with a positive-pressure valve that branches off from said pressure line and opens into said tank line.

8. The actuating drive according to claim 1, wherein said motor is a variable-rotational-speed motor.

9. The actuating drive according to claim 1, wherein said working medium pump can be operated as a hydraulic motor and said motor can be operated as a generator.

10. The actuating drive according to claim 1, wherein said short-circuit line is connected, in parallel with respect to said pressure line and said tank line, to said working cylinder, and/or is integrated into said working cylinder.

11. The actuating drive according to claim 1, wherein said motor is an electric motor.

12. A method for operating an actuating drive for a regulation valve, the actuating drive containing a working cylinder, a spring and a piston having a piston rod disposed in the working cylinder, the piston rod forming an actuator for the regulation valve, the piston delimiting a first pressure chamber with a first pressure port and a second pressure chamber with a second pressure port, for displacing the piston with the piston rod counter to a force of the spring assigned to the working cylinder by pressurization of the first pressure chamber by introduction of a pressurized working medium via the first pressure port, the actuating drive further having an external working medium circuit to which the working cylinder is connected by means of the first and second pressure ports for introducing the pressurized working medium into, or discharging the pressurized working medium from, the first and second pressure chambers, the external working medium circuit having a tank line, a pressure line, a motor and a working medium pump driven by means of the motor, the working medium pump having a suction side and a pressure side and is, by means of the pressure side, connected in a working-medium-conducting fashion via the pressure line to the first pressure port and is, by means of the suction side, connected via the tank line to the second pressure port, the first pressure chamber being permanently connected in permanent fluid communication with the second pressure chamber via said short-circuit line, which comprises the step of: operating the working medium pump permanently and the pressurized working medium is conveyed from the pressure side of the working medium pump to the suction side of the working medium pump via the short-circuit line.

13. The method according to claim 12, which further comprises conveying the pressurized working medium both into and out of the first pressure chamber by means of the working medium pump.

14. The method according to claim 12, wherein the working medium pump, when conveying the pressurized working medium out of the first pressure chamber, is operated as a hydraulic motor and drives the motor as a generator.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be described by way of example below on the basis of an exemplary embodiment and on the basis of the FIGURE.

DESCRIPTION OF THE INVENTION

(2) The single FIGURE of the drawing illustrates an exemplary embodiment of an actuating drive according to the invention, comprising a working cylinder 1 in which a piston 2 divides a first pressure chamber 5 from a second pressure chamber 7 and which is connected to a piston rod 3 for the purposes of alternately retracting the piston rod 3 into the working cylinder 1 or deploying the piston rod 3 out of the working cylinder 1 in a manner dependent on the introduction of working medium into the first pressure chamber 5 and/or second pressure chamber 7. The piston 2 is preloaded by a spring 4, in this case in the direction of a deployment of the piston rod 3.

(3) In the exemplary embodiment illustrated, the piston rod 3 serves as an actuator for a steam turbine regulation valve 102, which is arranged in the steam feed line 103 of a steam turbine 104. By means of the piston rod 3, a valve body 100 can be displaced relative to a valve seat 101 in order to open or close the steam turbine regulation valve 102 to a greater or lesser extent. In the exemplary embodiment shown, the spring 4 or the deployment of the piston rod 3 out of the working cylinder 1 effects a closure of the steam turbine regulation valve 102. It would however also be possible for some other logic to be selected, or for some valve other than a steam turbine regulation valve 102 to be actuated by means of the actuating drive.

(4) The working cylinder 1 is connected to an external working medium circuit 10, which has a pressure line 16, which is connected to a first pressure port 6 of the first pressure chamber 5, and a tank line 9, which is connected to a second pressure port 8 of the second pressure chamber 7.

(5) In the external working medium circuit 10 there is provided a working medium pump 13 which is driven by a motor 12, in particular electric motor. The working medium pump 13 has a suction side 14 and a pressure side 15. On the side of the suction side 14, there is connected to the tank line 9 a working medium reservoir 11 for the purposes of compensating volume fluctuations in the external working medium circuit 10.

(6) By means of the working medium pump 13, working medium can be conveyed from the suction side 14 to the pressure side 15 and via the pressure line 16 into the first pressure chamber 5 for the purposes of retracting the piston rod 3 into the working cylinder 1 counter to the force of the spring 4. To deploy the piston rod 3 out of the working cylinder 1, it is firstly possible to utilize the force of the spring 4, and it is advantageously possible for the working medium pump 13 to be operated as a hydraulic motor, such that working medium flows through the working medium pump 13 from the pressure side 15 to the suction side 14, and thus the working medium pump 13 is hydraulically driven and drives the motor 12 as a generator. The drive energy can then be converted in the motor 12, or in a connected converter, and stored, in particular in the form of electrical energy.

(7) Provision may additionally or alternatively also be made for the working medium pump 13 to be driven by the motor 12 in a direction of rotation opposite to the direction of rotation described above with regard to the retraction of the piston rod 3 into the working cylinder 1, and thus for the pressure side 15 to become the suction side 14 and for the suction side 14 to become the pressure side 15. Then, working medium is actively pumped by means of the working medium pump 13 from the first pressure chamber 5 into the second pressure chamber 7, and a force is additionally exerted on the piston 2, which force is in the same direction as the force of the spring 4.

(8) If the piston 2, and thus the piston rod 3, are now held static in the working cylinder 1, it would be necessary for the working medium pump 13 to impart the pressure for compensating the force of the spring 4 in the case of a very small volume flow through the working medium pump 13. This would lead to heating-up of the working medium pump 13, because the small volume flow is not capable of discharging heat from the working medium pump 13. According to the invention, a short-circuit line 18 is therefore provided which permanently connects the first pressure chamber 5 in working-medium-conducting fashion to the second pressure chamber 7. Owing to said permanent conducting of working medium, the working medium flow conveyed through the working medium pump 13 is increased, such that the desired discharging of heat is realized even when the piston 2 is in the static state.

(9) In the exemplary embodiment shown, there is provided in the short-circuit line 18 a short-circuit valve 19, for example in the form of a throttle with a constant or variable flow cross section, or in the form of a regulation valve. In this way, the working medium flow passing through the short-circuit line 18 can either be set in pressure-dependent fashion or actively changed, for example held constant independently of pressure.

(10) In the exemplary embodiment shown, a reversing line 21 in which a check valve 17 is provided branches off from the tank line 9. The check valve 17 opens in the direction of the pressure line 16 and closes in the direction of the tank line 9. It is thus possible, whenever a higher working medium pressure prevails in the tank line 9 than in the pressure line 16, wherein the required relative positive pressure is defined by the spring force of the check valve 17, for working medium to flow from the tank line 9 into the pressure line 16 and thus from the second pressure chamber 7 into the first pressure chamber 5, specifically bypassing the working medium pump 13. In this way, in the event of possible erroneous operation, a situation is avoided in which the working medium pump 13 falls into a negative-pressure range during reversing operation. This would be the case if the piston 2 can move no further but the working medium pump 13 would simultaneously continue to operate in reversing operation.

(11) A fast-closure line 23 with a fast-closure valve 24 branches off from the pressure line 16 in order that, as a result of opening of the fast-closure valve 24, as fast as possible a movement of the piston 2 is effected by the force of the spring 4 in order to attain a fail-safe position. Here, the stroke speed is defined by the throttle 25 which is likewise provided, in series with respect to the fast-closure valve 24, in the fast-closure line 23.

(12) Furthermore, the positive-pressure line 26 branches off from the pressure line 16, which positive-pressure line likewise opens into the tank line 9. In the positive-pressure line 26 there is provided a positive-pressure valve 27 which opens above a predefined pressure in order to avoid inadmissible pressure states in the positive-pressure line 16.