EP2348196A2

EP2348196A2 - Turbine protection device and method for controlling a steam turbine

Info

Publication number: EP2348196A2
Application number: EP10173147A
Authority: EP
Inventors: Yosuke Hirakawa; Mitsuru Sudo; Ichiro Hiraga; Tsugutomo Teranischi
Original assignee: Hitachi Ltd
Current assignee: Mitsubishi Power Ltd
Priority date: 2009-08-18
Filing date: 2010-08-18
Publication date: 2011-07-27
Anticipated expiration: 2030-08-18
Also published as: JP5118672B2; JP2011038500A; EP2348196B1; EP2348196A3; US20110041503A1; EP2348196A8

Abstract

An object of the present invention is to provide a turbine protection device which can interrupt steam flowing backward from a deaerator (5) to a turbine (2) completely even if a check valve (3a) provided between the deaerator (5) and the turbine (2) can not interrupt the steam flowing between the deaerator (5) and the turbine (2) completely. In order to achieve the above object, a control unit (11) sends commands to a shutdown valve device (12) so as to close the shutdown valve device (12) when a differential pressure resulted from subtracting a pressure of a extraction steam from a pressure within the deaerator (5) becomes equal to or greater than a first predetermined value. As a result, the steam flowing backward from the deaerator (5) to the turbine (2) is interrupted by a stop valve of the shutdown valve device (12).

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims benefit of the filing date of Japanese Patent Application No. 2009-189423 filed on August 18, 2009 which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a turbine protection device to protect a turbine of a steam turbine system.

Description of Related Art

For example, a steam turbine system of an electric-power generating steam turbine plant is provided with a deaerator to store a condensate which is prepared by heating a condensate exhausted from a condenser using a extraction steam from a turbine so as to deaerate gases such as oxygen, etc.
Also, at the time of normal operation of the steam turbine system, a pressure within the deaerator (a deaerator internal pressure) is decreased from a pressure of the extraction steam (an extraction pressure) due to a pressure loss of a path through which the extraction steam passes from the turbine to the deaerator, thereby the deaerator internal pressure is balanced at a lower pressure than the extraction pressure.
However, when the extraction pressure is decreased quickly associated with a quick drop in a load of the turbine at the time of an occurrence of a turbine trip, or an interruption of a load, etc, a decompression speed of the extraction pressure exceeds that of the deaerator internal pressure, and a balance between the deaerator internal pressure and the extraction pressure may break down. That is, the deaerator internal pressure may become equal to or greater than the extraction pressure.
Also, during normal operation of the steam turbine system, when the load of the turbine drops, the extraction pressure is decreased depending on the drop in the load. At this moment, the higher a drop rate of the load of the turbine, the higher the decompression speed of the extraction pressure.
On the other hand, regarding the deaerator having large capacity, the more condensate stored within the deaerator, the larger a heat capacity of the deaerator. Also, it becomes difficult to decrease a temperature within the deaerator. As a result, it becomes difficult to decrease the deaerator internal pressure.
Therefore, in the case where the capacity of the deaerator is large, when the drop rate of the load of the steam turbine system is high and the decompression speed of the extraction pressure is high, the decompression speed of the extraction pressure deaerator internal pressure may become lower than the decompression speed, the balance between the deaerator internal pressure and the extraction pressure may break down, and the deaerator internal pressure may become equal to or higher than the extraction pressure.
When the balance between the deaerator internal pressure and the extraction pressure breaks down and the deaerator internal pressure becomes higher than the extraction pressure, a low-temperature steam flows from the deaerator to the turbine and a water induction is generated.
Hereinafter, a flow of steam from the deaerator to the turbine is defined as a backflow.
If the water induction is generated in the turbine, a casing and a rotor of the turbine at high temperature are cooled by the low-temperature steam suddenly, and then the casing and the rotor are deformed. Also, a contact between a rotational body such as the rotor and a stationary body such as the casing, or an abnormal vibration occurs, resulting in damage of the turbine. That is, it is necessary to suppress generation of the water induction. For this reason, it is necessary to prevent steam from flowing backward from the deaerator to the turbine.
Therefore, a check valve is conventionally provided between the turbine and the deaerator so as to prevent the steam from flowing backward from the deaerator to the turbine.
Further, a shutdown valve device is provided so as to interrupt the steam flowing between the turbine and the deaerator.
For example, JP 11-148310 A discloses a technique for a water induction protection device which is provided with a shutdown valve (a shutdown valve device) to interrupt steam flowing between a feedwater heater and a turbine in a steam turbine system, and prevents the water induction from being generated when a water level of a feedwater heater is increased abnormally.
According to JP 11-148310 A , for example, if a water level of a feedwater heater is increased by water leakage from a tube within the feedwater heater, the shutdown valve interrupts the steam flowing between the turbine and the feedwater heater so as to prevent the water induction from being generated.
For example, if the technique disclosed in JP 11-148310 A is applied to the deaerator, it is possible to prevent the water induction caused by increase in the water level within the deaerator from being generated.
In this way, by providing the check valve and the shutdown valve device between the deaerator and the turbine, it is possible to prevent the steam from flowing backward from the deaerator to the turbine. Also, it is possible to prevent the water induction caused by increase in the water level within the deaerator from being generated.

SUMMARY OF THE INVENTION

However, because the check valve is instantaneously closed so as to prevent the steam from flowing backward from the deaerator to the turbine when the deaerator internal pressure is equal to or greater than the extraction pressure, for example, the check valve is instantaneously closed when the extraction pressure drops quickly (e.g., when the turbine trip occurs). Therefore, if the check valve is opened and closed frequently, a component such as a valve disc may be deformed by an impact at the time of closing the check valve, and the steam flowing backward from the deaerator to the turbine may not be interrupted completely.
Therefore, an object of the present invention is to provide a turbine protection device which can interrupt the steam flowing backward from the deaerator to the turbine completely even if the check valve provided between the deaerator and the turbine can not interrupt the steam flowing between the deaerator and the turbine completely.
In order to achieve the above object, the present invention provides a turbine protection device comprising: a shutdown valve device, in which the shutdown valve device is operated so as to interrupt steam flowing backward from a deaerator to a turbine when a deaerator internal pressure is equal to or greater than an extraction pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a steam turbine system;
FIG. 2 is a graph showing a status in which an extraction pressure and a deaerator internal pressure are decreased;
FIG. 3 is a flowchart showing a procedure by which a control unit controls a shutdown valve device; and
FIG. 4 is a flowchart showing a procedure by which a control unit having an internal timer controls the shutdown valve device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be explained in detail with reference to FIGS. 1-4.
As shown in FIG. 1, in a steam turbine system 1 according to this embodiment, the steam generated in the boiler 13 rotates a high-pressure turbine 14, and is taken into a reheater 13a of the boiler 13. The steam reheated by the reheater 13a rotates a middle-pressure turbine 15 and a low-pressure turbine 16, and is taken into a condenser 18 to be condensed into a condensate.
In addition, for example, a generator 17 is connected to the low-pressure turbine 16 as a load.
The condensate generated by condensing the steam in the condenser 18 is pressurized by a condensate pump 19, is heated by a low-pressure heater 4 (e.g., using the extraction steam from the low-pressure turbine 16), is fed to the deaerator 5, is heated using the extraction steam from the middle-pressure turbine 15 (or the low-pressure turbine 16) so as to deaerate gases, and is stored in the deaerator 5.
Also, the condensate stored in the deaerator 5 is pressurized by a feed pump 6, is heated in a high-pressure heater 7 (e.g., using the extraction steam from the high-pressure turbine 14 or the middle-pressure turbine 15), and is taken into the boiler 13.
Hereinafter, the high-pressure turbine 14, the middle-pressure turbine 15, and the low-pressure turbine 16 are referred to as a turbine 2 in a mass.
The turbine 2 is connected to the deaerator 5 via an extraction steam inlet tube 3 (inlet tube), and the extraction steam from the turbine 2 passes through the extraction steam inlet tube 3 so as to be taken into the deaerator 5 as the extraction steam for heating and deaerating.
Two check valves 3a, for example, are connected to the extraction steam inlet tube 3 in series, and a flow direction of the steam in the extraction steam inlet tube 3 is limited to a direction from the turbine 2 to the deaerator 5.
In addition, the extraction steam inlet tube 3 is connected to any one or more of the high-pressure turbine 14, the middle-pressure turbine 15, and the low-pressure turbine 16.
Because the extraction steam from the turbine 2 is taken into the deaerator 5 through the extraction steam inlet tube 3, an extraction pressure of the extraction steam from the turbine 2 (hereinafter, denoted by "P1") is decreased due to a pressure loss caused by passing through the extraction steam inlet tube 3.
Therefore, at the time of normal operation of the steam turbine system 1, the deaerator internal pressure (hereinafter, denoted by "P2") becomes lower than the extraction pressure P1.
That is, at the time of normal operation of the steam turbine system 1, the deaerator internal pressure P2 is balanced at a pressure which is lower than the extraction pressure P1 so as to prevent the steam from flowing backward from the deaerator 5 to the turbine 2.
Although the two check valves 3a are opened so as to allow the steam to flow from the turbine 2 to the deaerator 5 when the deaerator internal pressure P2 is less than the extraction pressure P1, the two check valves 3a are instantaneously closed so as to interrupt the steam flowing backward from the deaerator 5 to the turbine 2 when the deaerator internal pressure P2 is equal to or greater than the extraction pressure P1 at the time of an occurrence of the turbine trip, etc.
Also, the extraction steam inlet tube 3 is provided with a shutdown valve device 12 between the two check valves 3a and the deaerator 5. The shutdown valve device 12 includes a stop valve 12a to interrupt the steam flowing through the extraction steam inlet tube 3, and a valve driving unit 12b to open and close the stop valve 12a rapidly.
The valve driving unit 12b drives the stop valve 12a so as to close the extraction steam inlet tube 3, to interrupt the steam flowing backward from the deaerator 5 to the turbine 2, and to prevent an occurrence of a water induction, when a water level within the deaerator 5 measured by a water level gauge (not shown) becomes greater than a predetermined value.
Also, the steam turbine system 1 according to this embodiment includes a turbine extraction pressure gauge 9 to measure the extraction pressure P1 of the extraction steam from the turbine 2, a deaerator internal pressure gauge 10 to measure the deaerator internal pressure P2 of the deaerator 5, and a control unit 11 to control the shutdown valve device 12 by sending commands to the valve driving unit 12b.
For example, the turbine extraction pressure gauge 9 is provided in proximity to a juncture between the turbine 2 and the extraction steam inlet tube 3, and measures the extraction pressure P1 on condition that the pressure loss caused by the extraction steam inlet tube 3 does not occur.
The control unit 11 calculates the extraction pressure P1 based on a measured signal input from the turbine extraction pressure gauge 9, and calculates the deaerator internal pressure P2 based on a measured signal input from the deaerator internal pressure gauge 10.
Also, the control unit 11 send commands to the valve driving unit 12b so as to drive the stop valve 12a to close the extraction steam inlet tube 3, when the deaerator internal pressure P2 becomes equal to or greater than the extraction pressure P1. That is, the shutdown valve device 12 is closed.
Therefore, the stop valve 12a interrupts the steam flowing backward from the deaerator 5 to the turbine 2.
After that, the deaerator internal pressure P2 is decreased. When the deaerator internal pressure P2 becomes less than the extraction pressure P1, the control unit 11 sends commands to the valve driving unit 12b so as to drive the stop valve 12a to open the extraction steam inlet tube 3. That is, the shutdown valve device 12 is opened.
The extraction steam from the turbine 2 passes through the extraction steam inlet tube 3 so as to be taken into the deaerator 5.
Also, in this embodiment, a turbine protection device 20 includes the turbine extraction pressure gauge 9, the deaerator internal pressure gauge 10, the control unit 11, and the shutdown valve device 12.
As shown in FIG. 2, on condition that the extraction pressure P1 is P1H and the deaerator internal pressure P2 is P2H which is lower than P1H slightly, in the case where the steam turbine system 1 (see FIG. 1) is in normal operation, for example, when an amount of electric-power generation required for the generator 17 (see FIG. 1) is decreased and the load of the turbine 2 drops, the extraction pressure P1 is decompressed to P1L at the time t1 associated with a drop in the load.
Also, the deaerator internal pressure P2 is decreased to P2L at the time t2 associated with depression in the extraction pressure P1.
However, for example, in the case where the capacity of the deaerator 5 (see FIG. 1) is large and the drop rate of the load of the turbine 2 (see FIG. 1) is high, when the decompression speed of the extraction pressure P1 is higher than that of the deaerator internal pressure P2, for example, the extraction pressure P1 is decreased to the deaerator internal pressure P2 at the time t3. After that, the deaerator internal pressure P2 is kept higher than the extraction pressure P1 until the time t4 at which the deaerator internal pressure P2 is decreased to P1L.
As described above, when the deaerator internal pressure P2 becomes equal to or greater than the extraction pressure P1 (deaerator internal pressure P2 ≥ extraction pressure PI), two check valves 3a (see FIG. 1) are closed so as to prevent the steam flowing backward from the deaerator 5 (see FIG. 1) to the turbine 2 (see FIG. 1).
However, for example, in the case where the valve discs of two check valves 3a, etc., are deformed and the steam flowing through the extraction steam inlet tube 3 (see FIG. 1) can not be interrupted completely, the turbine 2 may be damaged by the steam flowing backward from the deaerator 5 to the turbine 2.
For this reason, the control unit 11 according to this embodiment (see FIG. 1) controls the shutdown valve device 12 so that the shutdown valve device 12 (see FIG. 1) is closed from the time t5 at which a differential pressure ΔP, which is resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 when the steam turbine system 1 (see FIG. 1) is in normal operation, becomes equal to or greater than a first predetermined value (ΔPf1) which is set in advance till the time t6 at which the differential pressure ΔP becomes less than a second predetermined value (ΔPf2) which is set in advance.
Also, after the time t6 at which the differential pressure ΔP becomes equal to or less than the second predetermined value ΔPf2, the control unit 11 controls the shutdown valve device 12 to be closed.
When the differential pressure ΔP becomes equal to or greater than the first predetermined value ΔPf1 which is resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2, the control unit 11 sends commands to the valve driving unit 12b (see FIG. 1) so that the stop valve 12a (see FIG. 1) closes the extraction steam inlet tube 3 so as to close the shutdown valve device 12 (see FIG. 1).
Also, when the differential pressure ΔP becomes equal to or less than the second predetermined value ΔPf2, the control unit 11 sends commands to the valve driving unit 12b so that the stop valve 12a opens the extraction steam inlet tube 3 so as to open the shutdown valve device 12.
In this way, the control unit 11 controls the shutdown valve device 12 by sending commands based on the differential pressure ΔP between the deaerator internal pressure P2 and the extraction pressure P1.
For example, considering measurement errors of the turbine extraction pressure gauge 9 and the deaerator internal pressure gauge 10, and changes (microseisms) in the deaerator internal pressure P2 and the extraction pressure P1, etc., the first predetermined value ΔPf1 and the second predetermined value ΔPf2 are set to values as small as possible. The first predetermined value ΔPf1 may differ from or may be the same as the second predetermined value ΔPf2.
Also, the first predetermined value ΔPf1 and the second predetermined value ΔPf2 may be "0".
In the case where the first predetermined value ΔPf1 is "0", the control unit 11 closes the shutdown valve device 12 (see FIG. 1) when the deaerator internal pressure P2 becomes equal to or greater than the extraction pressure P1. In the case where the second predetermined value ΔPf2 is "0", the control unit 11 opens the shutdown valve device 12 (see FIG. 1) when the extraction pressure P1 becomes equal to or greater than the deaerator internal pressure P2.
In addition, the first predetermined value ΔPf1 and the second predetermined value ΔPf2 are set as differential pressures resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2. Therefore, in the case the extraction pressure P1 is higher than the deaerator internal pressure P2, the first predetermined value ΔPf1 and the second predetermined value ΔPf2 becomes negative values.
With reference to FIG. 3, a procedure by which the control unit 11 controls the shutdown valve device 12 will be explained (see FIGS. 1 and 2).
For example, this procedure is incorporated in a program which the control unit 11 runs as a subroutine, and may be run by the control unit 11 at intervals of 100 ms, etc.
When the procedure to control the shutdown valve device 12 starts, the control unit 11 calculates the extraction pressure P1 (step S1), and further calculates the deaerator internal pressure P2 (step S2).
As described above, the control unit 11 can calculate the extraction pressure P1 based on the measured signal input from the turbine extraction pressure gauge 9, and can calculate the deaerator internal pressure P2 based on the measured signal input from the deaerator internal pressure gauge 10.
In this way, the control unit 11 calculates the extraction pressure P1 and the deaerator internal pressure P2 at every time the procedure to control the shutdown valve device 12 is executed. Therefore, the control unit 11 monitors the extraction pressure P1 and the deaerator internal pressure P2 at all times.
The control unit 11 calculates the differential pressure ΔP by subtracting the extraction pressure P1 from the deaerator internal pressure P2 (step S3).
Also, when the calculated differential pressure ΔP is equal to or greater than the first predetermined value ΔPf1 (step S4 --> Yes), if the shutdown valve device 12 is opened (step S5 --> Yes), the control unit 11 sends commands to the valve driving unit 12b so as to drive the stop valve 12a to close the shutdown valve device 12 (step S6), and the procedure to control the shutdown valve device 12 is completed (RETURN). If the shutdown valve device 12 is not opened (step S5 --> No), i.e., if the shutdown valve device 12 is closed, the procedure to control the shutdown valve device 12 is completed (RETURN).
On the other hand, when the calculated differential pressure ΔP is less than the first predetermined value ΔPf1 (step S4 --> No), if the differential pressure ΔP is greater than the second predetermined value ΔPf2 (step S7 --> No), the control unit 11 completes the procedure to control the shutdown valve device 12 (RETURN).
Also, when the differential pressure ΔP is equal to or less than the second predetermined value ΔPf2 (step S7 --> Yes), if the shutdown valve device 12 is closed (step S8 --> Yes), the control unit 11 sends commands to the valve driving unit 12b so as to drive the stop valve 12a to open the shutdown valve device 12 (step S9), and completes the procedure to control the shutdown valve device 12 (RETURN). If the shutdown valve device 12 is not closed (step S8 --> No), i.e., if the shutdown valve device 12 is opened, the procedure to control the shutdown valve device 12 is completed (RETURN).
The method by which the control unit 11 judges whether the shutdown valve device 12 is opened or closed is not limited.
For example, the control unit 11 may includes a flag OP to indicate whether the shutdown valve device 12 is opened or closed, and the control unit 11 sets the flag OP to "0" in step S6 when the shutdown valve device 12 is closed and sets the flag OP to "1" in step S9 when the shutdown valve device 12 is opened.
The control unit 11 judges that the shutdown valve device 12 is opened if the flag OP is "1", and judges that the shutdown valve device 12 is closed if the flag OP is "0".
Also, the shutdown valve device 12 may be provided with a sensor (not shown) to detect whether the stop valve 12a closes or opens the extraction steam inlet tube 3. For example, if the sensor (not shown) sends a detection signal to indicate whether the stop valve 12a closes or opens the extraction steam inlet tube 3 to the control unit 11, the control unit 11 can detect whether the stop valve 12a closes or opens the extraction steam inlet tube 3 based on the detection signal from the sensor (not shown). Also, the control unit 11 can judge whether the shutdown valve device 12 is opened or closed.

«Modified Example»

As described above, the control unit 11 of the steam turbine system 1 according to this embodiment shown in FIG. 1 monitors the extraction pressure P1 and the deaerator internal pressure P2 at all times, closes the shutdown valve device 12 when the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 becomes equal to or greater than the first predetermined value ΔPf1, and opens the shutdown valve device 12 when the differential pressure ΔP becomes equal to or less than the second predetermined value ΔPf2.
However, when the turbine extraction pressure gauge 9 measures the extraction pressure P1, the measured value can slightly change. Likewise, the measured value of the deaerator internal pressure gauge 10 can slightly change.
Therefore, the extraction pressure P1 and the deaerator internal pressure P2 calculated by the control unit 11 can also slightly change, and further the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 can also slightly change.
If the differential pressure ΔP changes across the first predetermined value ΔPf1 and the second predetermined value ΔPf2, the control unit 11 sends commands to the valve driving unit 12b so as to close the shutdown valve device 12 at every time the differential pressure ΔP becomes equal to or greater than the first predetermined value ΔPf1, and sends commands to the valve driving unit 12b so as to open the shutdown valve device 12 at every time the differential pressure ΔP becomes equal to or less than the second predetermined value ΔPf2. Therefore, the control unit 11 frequently sends commands to the valve driving unit 12b so as to control the shutdown valve device 12, and the shutdown valve device 12 is opened and closed frequently. As a result, there arises a problem that the stop valve 12a and the shutdown valve device 12 are degraded.
For this reason, in a modified example of the present invention, for example, the control unit 11 may be provided with an internal timer, and may close the shutdown valve device 12 when a condition that the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 is equal to or greater than the first predetermined value ΔPf1 continues for a predetermined time period.
Likewise, when a condition that the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 is equal to or less than the second predetermined value ΔPf2 continues for a predetermined time period, the control unit 11 may open the shutdown valve device 12.
With reference to FIG. 4, a procedure by which the control unit 11 having the internal timer controls the shutdown valve device 12 (see FIGS. 1 and 2).
Like the procedure shown in FIG. 3, this procedure is incorporated in a program which the control unit 11 runs as a subroutine, and may be run by the control unit 11 at intervals of 100 ms, etc.
In addition, the same reference numbers are used to denote the same steps as those in FIG. 3, and their repeated explanations will be omitted.
When the procedure to control the shutdown valve device 12 starts, the control unit 11 calculates the extraction pressure P1 (step S1), calculates the deaerator internal pressure P2 (step S2), and further calculates the differential pressure ΔP by subtracting the extraction pressure P1 from the deaerator internal pressure P2 (step S3).
Also, when the calculated differential pressure ΔP is equal to or greater than the first predetermined value ΔPf1 (step S4 --> Yes), the control unit 11 stops a measuring of an opening valve waiting time (step S10), and if the shutdown valve device 12 is opened (step S5 --> Yes), the control unit 11 judges whether a closing valve waiting time is being measured or not (step S11).
The opening valve waiting time means a waiting time during which the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 becomes equal to or less than the second predetermined value ΔPf2 and the control unit 11 opens the shutdown valve device 12.
Also, the closing valve waiting time means a waiting time during which the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 becomes equal to or greater than the first predetermined value ΔPf1 and the control unit 11 closes the shutdown valve device 12.
Also, if the closing valve waiting time is not being measured (step S11 --> No), the control unit 11 starts measuring of the closing valve waiting time by the internal timer (step S12), and the procedure to control the shutdown valve device 12 is completed (RETURN).
Also, if the closing valve waiting time is being measured (step S11 --> Yes), in the case where a predetermined time Tm1 (a first predetermined time) has elapsed since measuring of the closing valve waiting time started (step S13 --> Yes), the control unit 11 closes the shutdown valve device 12 (step S6) and completes the procedure to control the shutdown valve device 12 (RETURN), and in the case where the predetermined time Tm1 has not elapsed (step S13 --> No), the control unit 11 completes the procedure to control the shutdown valve device 12 (RETURN) without closing the shutdown valve device 12.
Returning to step S5, if the shutdown valve device 12 is not opened (step S5 --> No), i.e., if the shutdown valve device 12 is closed, the control unit 11 completes the procedure to control the shutdown valve device 12 (RETURN).
In step S13, for example, the predetermined time Tm1 to determine whether the shutdown valve device 12 should be closed or not may be determined as a time during which the control unit 11 can close the shutdown valve device 12 with the proper timing based on an experiment, etc.
Returning to step S4, when the calculated differential pressure ΔP is less than the first predetermined value ΔPf1 (step S4 --> No), the control unit 11 compares the differential pressure ΔP and the second predetermined value ΔPf2 (step S7). Also, when the differential pressure ΔP is greater than the second predetermined value ΔPf2 (step S7 --> No), the control unit 11 completes the procedure to control the shutdown valve device 12 (RETURN).
Also, when the differential pressure ΔP is equal to or less than the second predetermined value ΔPf2 (step S7 --> Yes), the control unit 11 stops the measuring of the closing valve waiting time (step S14). If the shutdown valve device 12 is closed (step S8 --> Yes), the control unit 11 judges whether the opening valve waiting time is being measured or not (step S15).
In addition, when the shutdown valve device 12 is not closed (step S8 --> No), i.e., when the shutdown valve device 12 is opened, the control unit 11 completes the procedure to control the shutdown valve device 12 (RETURN).
Also, if the opening valve waiting time is not being measured (step S15 --> No), the control unit 11 starts measuring of the opening valve waiting time by the internal timer (step S16), and completes the procedure to control the shutdown valve device 12 (RETURN). Also, if the opening valve waiting time is being measured (step S15 --> Yes), in the case where the predetermined time Tm2 (a second predetermined time) has elapsed since measuring of the opening valve waiting time started (step S17 --> Yes), the control unit 11 closes the shutdown valve device 12 (step S9) and completes the procedure to control the shutdown valve device 12 (RETURN), and in the case where the predetermined time Tm2 has not elapsed (step S17 --> No), the control unit 11 completes the procedure to control the shutdown valve device 12 (RETURN) without opening the shutdown valve device 12.
In step S17, for example, the predetermined time Tm2 to determine whether the shutdown valve device 12 should be opened or not may be determined as a time during which the control unit 11 can open the shutdown valve device 12 with the proper timing based on an experiment, etc., and may be the same as or differ from the predetermined time Tm1 in step S13.
As shown in FIG. 4, in the modified example, when the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 is equal to or greater than the first predetermined value ΔPf1, the control unit 11 (see FIG. 1) starts measuring of the closing valve waiting time by the internal timer (step S12), and when the predetermined time Tm1 has elapsed on condition that the differential pressure ΔP is equal to or greater than the first predetermined value ΔPf1, the control unit 11 closes the shutdown valve device 12 (see FIG. 1)(step S13). In this way, after the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 becomes equal to or greater than the first predetermined value ΔPf1, when the predetermined time Tm1 (the first predetermined time) has elapsed on condition that the differential pressure ΔP is equal to or greater than the first predetermined value ΔPf1, the control unit 11 closes the shutdown valve device 12.
Also, when the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 is equal to or less than the second predetermined value ΔPf2, the control unit 11 (see FIG. 1) starts measuring of the opening valve waiting time by the internal timer (step S16), and when the predetermined time Tm2 has elapsed on condition that the differential pressure ΔP is equal to or less than the second predetermined value ΔPf2, the control unit 11 opens the shutdown valve device 12 (see FIG. 1)(step S17). In this way, after the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 becomes equal to or less than the second predetermined value ΔPf2, when the predetermined time Tm2 (the second predetermined time) has elapsed on condition that the differential pressure ΔP is equal to or less than the second predetermined value ΔPf2, the control unit 11 closes the shutdown valve device 12.
Also, associated with changes in measured values of the turbine extraction pressure gauge 9 and the deaerator internal pressure gauge 10, in the case where the differential pressure ΔP calculated by the control unit 11 changes across the first predetermined value ΔPf1 at intervals shorter than the predetermined time Tm1, even if the differential pressure ΔP is equal to or greater than the first predetermined value ΔPf1, the control unit 11 does not close the shutdown valve device 12._o
Likewise, in the case where the differential pressure ΔP calculated by the control unit 11 changes across the second predetermined value ΔPf2 at intervals shorter than the predetermined time Tm2, even if differential pressure ΔP is equal to or less than the second predetermined value ΔPf2, the control unit 11 does not open the shutdown valve device 12.
Therefore, the shutdown valve device 12 is prevented form being operated frequently so as to suppress the problem that the shutdown valve device 12 is degraded.
As described above, in the turbine protection device 20 of the steam turbine system 1 according to this embodiment shown in FIG. 1, the control unit 11 monitors the extraction pressure P1 and the deaerator internal pressure P2 at all times. When the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 is equal to or greater than the first predetermined value ΔPf1, the control unit 11 closes the shutdown valve device 12 so as to interrupt the steam flowing backward from the deaerator 5 to the turbine 2 by the stop valve 12a.
When the deaerator internal pressure P2 becomes equal to or greater than the extraction pressure P1, two check valves 3a are closed so as to interrupt the steam flowing backward from the deaerator 5 to the turbine 2.
However, if the valve disc of two check valves 3a, etc. are deformed and two check valves 3a can not interrupt the steam flowing through the extraction steam inlet tube 3 completely, the turbine 2 may be damaged by the steam flowing backward from the deaerator 5 to the turbine 2.
Even if two check valves 3a can not interrupt the steam flowing through the extraction steam inlet tube 3 completely, the steam turbine system 1 according to this embodiment can interrupt the steam flowing through the extraction steam inlet tube 3 by the stop valve 12a of the shutdown valve device 12, and can interrupt the steam flowing backward from the deaerator 5 to the turbine 2 effectively.
Also, after the differential pressure ΔP resulted from subtracting the extraction pressure P1 from the deaerator internal pressure P2 becomes equal to or greater than the first predetermined value ΔPf1, when the predetermined time Tm1 has elapsed, the control unit 11 closes the shutdown valve device 12. After the differential pressure ΔP becomes equal to or less than the second predetermined value ΔPf2, when the predetermined time Tm2 has elapsed, the control unit 11 opens the shutdown valve device 12.
In this way, the shutdown valve device 12 is prevented from being operated frequently so as to suppress the problem that the shutdown valve device 12 is degraded.
In addition, not only at the time of normal operation of the steam turbine system 1 but also at the time of an occurrence of a turbine trip, or an interruption of a load, etc, even if the deaerator internal pressure P2 becomes equal to or greater than the extraction pressure P1 associated with a quick drop in a load of the steam turbine system 1, the control unit 11 can close the shutdown valve device 12. Therefore, even if two check valves 3 a can not interrupt the steam flowing through the extraction steam inlet tube 3 completely, the steam flowing backward from the deaerator 5 to the turbine 2 can be interrupted completely, and the turbine 2 can be prevented from being damaged.
Although the turbine protection device 20 is provided between the deaerator 5 and the turbine 2 in this embodiment as shown in FIG. 1, for example, the turbine protection device 20 according to this embodiment may be provided between the feedwater heater (not shown) and the turbine 2.
In this case, even if the pressure within the feedwater heater becomes higher than the extraction pressure P1, the steam flowing backward from the feedwater heater to the turbine 2 can be interrupted by the stop valve 12a, and the turbine 2 can be prevented from being damaged.

Claims

A turbine protection device provided in a steam turbine system, the steam turbine system comprising:
a turbine (2) driven by steam generated in a boiler (13);

a condenser (18) to condense the steam exhausted from the turbine (2) into a condensate;

a deaerator (5) to store the condensate which is prepared by being heated and deaerated;

an inlet tube (3) to take the extraction steam for heating and deaerating into the deaerator (5); and

a check valve (3a) provided in the inlet tube (3), comprising:
a pressure gauge (10) to measure a pressure of the extraction steam and a pressure within the deaerator (5);

a shutdown valve device (12) provided in the inlet tube (3); and

control unit (11) to control the shutdown valve device (12) using commands based on the pressure of the extraction steam and the pressure within the deaerator (5),

wherein the shutdown valve device (12) is opened and closed by the commands from the control unit (11), and when the shutdown valve device (12) is closed, the shutdown valve device (12) interrupts the steam flowing from the deaerator (5) to the turbine (2).
The turbine protection device according to claim 1, wherein the control unit (11)
sends commands to the shutdown valve device (12) so as to close the shutdown valve device (12) when a differential pressure resulted from subtracting the pressure of the extraction steam from the pressure within the deaerator (5) becomes equal to or greater than a first predetermined value which is set in advance, and
sends commands to the shutdown valve device (12) so as to open the shutdown valve device (12) when the differential pressure becomes equal to or greater than a second predetermined value which is set in advance.
The turbine protection device according to claim 1 or 2, wherein the control unit (11)
sends commands to the shutdown valve device (12) so as to close the shutdown valve device (12) when a first predetermined time has elapsed on condition that a differential pressure resulted from subtracting the pressure of the extraction steam from the pressure within the deaerator (5) is equal to or greater than a first predetermined value which is set in advance after the differential pressure becomes equal to or greater than the first predetermined value, and
sends commands to the shutdown valve device (12) so as to open the shutdown valve device (12) when a second predetermined time has elapsed on condition that the differential pressure is equal to or less than a second predetermined value which is set in advance after the differential pressure becomes equal to or less than the second predetermined value.
A method for controlling a steam turbine system, the steam turbine system comprising:
a turbine (2) driven by steam generated in a boiler (13);

a condenser (18) to condense the steam exhausted from the turbine (2) into a condensate;

a deaerator (5) to store the condensate which is prepared by being heated and deaerated;

an inlet tube (3) to take the extraction steam for heating and deaerating into the deaerator (5); and

a check valve (3 a) provided in the inlet tube (3), comprising the steps of:
measuring a pressure of the extraction steam and a pressure within the deaerator (5);

opening and closing a shutdown valve device (12) provided in the inlet tube (3) based on a differential pressure between a pressure of the extraction steam and a pressure within the deaerator (5); and

interrupting the steam flowing from the deaerator (5) to the turbine (2) by closing the shutdown valve device (12).
The method according to claim 4, wherein further comprising the steps of:
sending commands to the shutdown valve device (12) so as to close the shutdown valve device (12) when a differential pressure resulted from subtracting the pressure of the extraction steam from the pressure within the deaerator (5) becomes equal to or greater than a first predetermined value which is set in advance, and

sending commands to the shutdown valve device (12) so as to open the shutdown valve device (12) when the differential pressure becomes equal to or greater than a second predetermined value which is set in advance.
The method according to claim 4 or 5, wherein further comprising the steps of:
sending commands to the shutdown valve device (12) so as to close the shutdown valve device (12) when a first predetermined time has elapsed on condition that a differential pressure resulted from subtracting the pressure of the extraction steam from the pressure within the deaerator (5) is equal to or greater than a first predetermined value which is set in advance after the differential pressure becomes equal to or greater than the first predetermined value, and

sending commands to the shutdown valve device (12) so as to open the shutdown valve device (12) when a second predetermined time has elapsed on condition that the differential pressure is equal to or less than a second predetermined value which is set in advance after the differential pressure becomes equal to or less than the second predetermined value.