JP4974944B2 - Power plant shutdown system - Google Patents

Description

  The present invention relates to a power plant operation stop system, and more specifically to a vacuum break timing determination system employed in a turbine normal stop / boiler forced cooling stop mode in a thermal power plant stop operation.

  In a thermal power plant, it may be desired to stop operation for some reason. For example, when trouble occurs in a boiler, etc., and a worker enters the inside for inspection and repair, the boiler or turbine is cooled to a safe temperature and the internal pressure is returned to atmospheric pressure (specifically, condensate It is necessary to return to atmospheric pressure by breaking the vacuum of the vessel.)

In addition, as a result of searching using the technical terms “condenser” and “vacuum breakage” for the published patent document at the time of this application, the following patent document 1 was detected.
Japanese Patent Laid-Open No. 5-312004 "Condensed Steam Turbine" (Publication Date: November 22, 1993) However, the above-mentioned Patent Document 1 discloses a vacuum so that the turbine does not increase to an abnormal speed when the turbine trips. This is a technology that opens the release valve and brakes the turbine with air. On the other hand, the present invention relates to a technique for determining the timing of the vacuum break of the condenser, as will be described later.

  No consideration has been made by the plant manufacturer, which is the plant manufacturer, and the electric power company, which is the plant user, as to when the vacuum break is performed.

  Therefore, an object of the present invention is to provide a safe shutdown system for a thermal power plant by providing a reference for determining the timing of vacuum break.

  Another object of the present invention is to provide a method for safely shutting down a thermal power plant by providing a reference for determining the timing of vacuum break.

  In view of the above object, the power plant shutdown system according to the present invention is based on means for predicting the cooling characteristics of the turbine after system disconnection in the turbine normal shutdown mode, and the allowable temperature difference between the upper and lower turbines. Means for determining a turbine metal temperature, and means for determining a vacuum break timing of the turbine based on the determined turbine metal temperature using an expected cooling characteristic of the turbine. The vacuum break of the power plant is executed according to the vacuum break timing.

  Further, in the power plant shutdown system, the vacuum break can be performed by releasing a vacuum break valve of a condenser communicating with the turbine.

  Further, in the power plant shutdown system, the turbine normal stop mode may be a turbine normal stop / boiler forced cooling stop mode for forcibly cooling the boiler.

Further, in the power plant shutdown system, the temperature difference between the upper and lower parts of the turbine is the temperature between the upper part of the casing of the high pressure turbine communicating with the boiler and the lower part of the casing of the high pressure turbine communicating with the condenser. It can also be defined as a difference.

  Further, in the above power plant shutdown system, the allowable temperature difference between the upper and lower turbines may define a plurality of temperature differences corresponding to a plurality of alarm levels.

  Furthermore, a power plant operation stop system according to the present invention includes a central processing unit that controls the entire system, and a control unit that is connected to the central processing unit and controls the operation of the thermal power plant. An operation stop system, wherein the central processing unit has a database in which metal temperature transition characteristic data and metal temperature difference-metal temperature characteristic data are accumulated, and the central processing unit is a turbine at a time when the operation of the power plant is stopped. The expected metal temperature transition is determined from the metal temperature transition characteristic data in the normal stop mode, the metal temperature is determined based on the allowable metal temperature difference corresponding to the alarm level, and the vacuum is determined from the determined metal temperature based on the predicted metal temperature transition. Determine the timing of destruction.

  Further, in the power plant shutdown system, the vacuum break can be performed by releasing a vacuum break valve of a condenser communicating with the turbine.

  Further, in the power plant operation stop system, the turbine normal stop mode may be a turbine normal stop / boiler forced cooling stop mode for forcibly cooling the boiler.

  Further, in the power plant shutdown system, the temperature difference between the upper and lower parts of the turbine is the temperature between the upper part of the casing of the high pressure turbine communicating with the boiler and the lower part of the casing of the high pressure turbine communicating with the condenser. It can also be defined as a difference.

  Further, in the power plant shutdown system, the allowable temperature difference between the upper and lower parts of the turbine may define a plurality of temperature differences corresponding to a plurality of alarm levels.

  Further, in the method for shutting down the power plant according to the present invention, the turbine normal stop / boiler forced cooling stop mode is selected and the alarm level is set, the expected metal temperature transition of the turbine is determined, and the allowable level corresponding to the level is determined. The metal temperature is determined based on the metal temperature difference, and the vacuum break timing is determined from the determined metal temperature based on the expected metal temperature transition.

  Further, in the above power plant operation stopping method, the vacuum break may be caused by releasing a vacuum break valve of a condenser communicating with the turbine.

  ADVANTAGE OF THE INVENTION According to this invention, the reference | standard which determines the timing of a vacuum break can be provided and the safe operation stop system of a thermal power plant can be provided.

  Furthermore, according to this invention, the reference | standard which determines the timing of a vacuum break can be provided, and the safe operation stop method of a thermal power plant can be provided.

  Hereinafter, embodiments of a power plant operation stop system according to the present invention will be described in detail with reference to the accompanying drawings. This embodiment is an exemplification and does not limit the present invention. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

[Thermal power plant]
(overall structure)
FIG. 1 is a diagram showing an outline of a boiler and a turbine portion of a thermal power plant 1 using coal as fuel. In the thermal power plant 1, thermal energy of fuel such as coal, oil, gas, etc. is changed to mechanical energy, and further changed to electric energy. As shown in FIG. 1, for example, in a thermal power plant using coal as a fuel, coal 12 is sent to a boiler 15 through a bunker 13 and a pulverized coal machine 14 and combusted in the boiler to change the feed water 10 to steam 11, 17, and sent to the intermediate pressure turbine 18 and the low pressure turbine 19. The thermal energy of the steam is converted into mechanical energy by the turbines 17, 18 and 19, the turbine blades are rotated, the generators 20 and 21 connected to the respective turbines are rotated, and electric energy is generated.

  The steam exhausted from the turbine 19 is sent to the condenser 5. The condenser 5 is a device that cools and condenses the exhaust (steam) of the turbine to create a vacuum and collect it as condensate. That is, the steam from the turbine and the seawater from the intake port 2 are taken in as cooling water by the circulation pump 4, non-contact heat exchange is performed, the steam is cooled and recovered as condensate (feed water), and again the feed pump 22 to the boiler 15.

  When operating such a thermal power plant 1, it may be necessary to stop the operation of the plant. The turbine is normally rated and operated. For example, in a thermal power plant owned by the present applicant, the rated pressure of main steam is 24.5 MPa (250 kg / cm 2), and the rated temperature is 600 ° C. . The following embodiments will be described based on data in this thermal power plant.

(Suspension of thermal power plant operation)
If you want to stop the operation of the thermal power plant 1 for any reason, gradually lower the temperature and pressure from the rated operation, turn off the circuit breaker at a certain timing, and disconnect the load (generator) from the system To do.

  Thermal power plant operation stop modes include (1) “turbine cooling stop” and (2) “turbine normal stop”.

  The “turbine cooling stop” mode of (1) is a method of stopping the output of the thermal power plant 1 with a certain load and lowering the metal temperature of the turbine by lowering the steam temperature entering the turbine and then disconnecting. This shortens the rolling (idling) time for preventing the eccentricity of the turbine shaft after disconnection. This is a stop mode that is adopted in the case of scheduled periodic inspections.

  On the other hand, the “turbine normal stop” mode (2) is a mode in which the turbine is stopped as it is without waiting for a decrease in the metal temperature of the turbine. The turbine normal stop is a stop mode that is employed when trouble occurs in the boiler 15 and the thermal power plant 1 needs to be stopped quickly and there is no time to cool the turbine. In this case, the boiler 15 is forcibly cooled in order to quickly cope with troubles such as a boiler, ie, “turbine normal stop / boiler forced cooling stop”.

  Specifically, the boiler 15 is forcedly cooled by circulating water through the boiler to forcibly cool it and blow it down to lower the boiler metal temperature Mt. The forced cooling of the boiler 15 requires about 12 hours after disconnection, and thereafter, water injection to the boiler 15 is stopped and naturally cooled, and then the plant 1 is completely stopped by breaking the vacuum. As shown in FIG. 2, this vacuum break is specifically performed by opening the vacuum break valve 30 connected to the condenser 5 to open the high-pressure turbine 17 (further, the boiler 15, etc.) communicating with the condenser 5. ) Break the vacuum. However, at this time, a phenomenon in which the metal temperature difference Md of the turbine 17 rapidly increases immediately after the vacuum break is observed.

The steam heated by the boiler 15 generally reaches the condenser through the high-pressure turbine 17, the intermediate-pressure turbine 18, and the low-pressure turbine 19 in order, and is condensed and returned to the boiler 15 as feed water. As shown in FIG. 3, the casing of the high-pressure turbine 17 includes, in the axial direction, a GEN-side casing 17 (GEN) connected to the generator side and a GOV connected to a governor valve. Defined as side compartment 17 (GOV). Heated steam from the boiler flows from the nozzles in the circumferential direction of the GEN side compartment 17 (GEN) and out of the GOV side compartment 17 (GOV). A drain valve 25 (see FIG. 2) is connected to the lower part 17 (Down) of the GEN side compartment 17 (GEN) to prevent the steam from being cooled and becoming water droplets, and uses the vacuum of the condenser. Is being pulled in (suction). The drain valve 25 is functioning during the operation of the thermal power plant and before the high pressure turbine vacuum break in the operation stop mode, but the drain valve drawing function is lost after the vacuum break. For this reason, the metal temperature difference Md of the turbine increases rapidly after the vacuum break.

As shown in FIG. 3, a drain valve 25 is connected to a lower part 17 (Down) of the GEN-side casing 17 (GEN) of the high-pressure turbine. When the drain valve 25 is open, the heat of the metal temperature is sucked into the condenser by the vacuum of the condenser. At this time, the metal temperatures of the lower part 17 (Down) of the GEN side compartment and the upper part 17 (Up) of the GEN side compartment are hardly lowered because the upper part is separated from the drain valve 25, but falls within an allowable range. Therefore, the metal temperature difference Md does not appear remarkably.
When the vacuum break is performed, the force sucked from the drain valve 25 to the condenser is lost. The heat of the metal temperature stays in the upper part through air or the like, and the metal temperature in the upper part 17 (Up) of the GEN side compartment is lower than that in the lower part 17 (Down) of the GEN side compartment. It appears prominently as the temperature difference Md.
This tendency also affects the GOV side compartment 17 (GOV), and a temperature difference is also generated above and below the GOV side compartment 17 (GOV) by the same principle as the GEN side compartment 17 (GEN). However, the upper and lower temperature difference data of the GOV side casing 17 (GOV) is approximate to the upper and lower temperature difference data of the GEN side casing 17 (GEN), and is connected to the condenser 5 via the drain valve. The difference in temperature between the upper and lower sides of the GEV side compartment 17 (GEN) will be described unless otherwise specified because the conduit is only in the GEN side compartment 17 (GEN).

  As a result of the temperature difference between the upper and lower casings of the high-pressure turbine 17, the gap between the movable part (not shown) and the fixed part (not shown) of the high-pressure turbine 17 is narrowed, that is, the casing is deformed and the vehicle is deformed. The gap between the rotor part (rotor part) and the casing in the room or the gap between the rotor part (rotor part) and the stator part (stator part) narrows, causing an alarm, or less than the required specification value (control value). There is a risk that the two parts may be touched and damaged in extreme cases.

  In general, in order to reduce the temperature difference Md between the upper and lower sides of the high-pressure turbine GEN side passenger compartment, the metal temperature Mt of the high-pressure turbine 17 is sufficiently cooled and then the vacuum break is executed. However, “turbine normal stop / boiler forced cooling stop” is an operation stop mode that is adopted to promptly deal with troubles such as boilers. It is necessary to perform the vacuum break at an early stage.

  Therefore, in the operation stop mode of “turbine normal stop / boiler forced cooling stop”, the timing at which the vacuum break is important is an important issue.

(Vacuum break timing determination system)
FIG. 4 is a diagram illustrating a configuration of a vacuum break timing determination system. This system includes an operation terminal 30 operated by an operator, a network 32 to which the operation terminal is connected, a central processing unit 34 connected to the network, a database 36 connected to the central processing unit, and a central processing unit 34. A plant control panel 38 that controls the operation of the plant according to a command from the processing device, and a thermal power plant 1 that is controlled by the plant control panel are provided.

  The operation terminal 30 is a device that is operated by an operator to instruct operation stop of the thermal power plant 1 with respect to the central processing unit 34, for example, “turbine normal stop / boiler forced cooling stop” mode.

  The network 32 includes, for example, a public line such as a dedicated line, ISDN, or Internet line.

  The central processing unit 34 controls the entire system, and although not shown, a normal CPU, a ROM storing operation control programs, a working RAM, a monitor for sequentially displaying control contents, various types Input / output devices.

  The database 36 is an external storage means connected to the central processing unit 34. For example, “metal temperature transition characteristic data” described with reference to FIG. 5 and “metal temperature difference−” described with reference to FIG. “Characteristic data of the metal temperature Mt” and the like are accumulated.

  The plant control panel 38 is a dedicated control device for the operation of the thermal power plant 1, and in accordance with a command from the central processing unit 34, the operation stop mode is set and an alarm level (case 1 or 2) for the operation stop operation described later is set. This is a control panel that performs settings, forced cooling time settings, timer settings, system disconnection operations, and the like.

  FIG. 5 illustrates the contents of the “metal temperature transition characteristic data” stored in the database 36. This metal temperature Mt transition characteristic data is actual data at the time of turbine cooling in the past, the horizontal axis indicates the elapsed time t when the system is disconnected (start), and the vertical axis is the metal temperature (high pressure). Mt) is measured on the GOV side of the first stage outlet of the turbine. In the database 36, the metal temperature data Mt for the elapsed time t is stored as a table along this graph, and when the elapsed time t is input, the corresponding metal temperature Mt is output.

  FIG. 6 shows the content of “metal temperature difference-metal temperature characteristic data” similarly stored in the database 16. The vertical axis represents the metal temperature difference Md, and the horizontal axis represents the metal temperature Mt corresponding to the metal temperature difference Md. As described above, when the vacuum break valve 30 connected to the condenser 5 is opened and the boiler 15 is vacuum broken, a phenomenon occurs in which the metal temperature difference Md of the turbine 17 rapidly increases immediately after that. The characteristic data of the metal temperature difference Md−metal temperature Mt is a linear approximation of the peak value of the metal temperature difference Md that has increased in the past when the metal temperature Mt = 334 degrees C, 419.1 degrees C, and 434.9 degrees C. This is the data interpolated (interpolated). The metal temperature Mt is indicated by a solid line on the GOV side and a broken line on the GEV side of the first stage outlet of the high pressure turbine, respectively. In the database 16, along with this graph, metal temperature Mt data with respect to the metal temperature difference Md is accumulated as a table, and the metal temperature difference Md is input based on the setting of the alarm level (case 1 or 2) of the operation stop operation. And the corresponding metal temperature Mt is output.

  FIG. 7 is a flowchart showing a method for determining the timing of vacuum break in the turbine normal stop / boiler forced cooling stop stop mode, which is executed by the vacuum break timing determining system shown in FIG.

  In step S <b> 10, the operator instructs the central processing unit 34 from the terminal device 30 to stop the operation of the thermal power plant 1. At this time, regarding the operation stop, the turbine normal stop / boiler forced cooling stop mode is selected, the case 1 or 2 is selected, the alarm level at the time of operation stop is set, and the forced cooling time (t1) is further set. .

  Case 1 (normal alarm level) and case 2 (emergency alarm level) are defined as alarm levels when the operation is stopped.

  Case 1 (normal alarm level) is a safe level that never generates a metal temperature difference Md alarm. For example, there is a margin of about 2 days from system disconnection to repair work, and it is necessary to break the vacuum early. Adopted when there are few. On the other hand, Case 2 (emergency warning level) is a level that allows the alarm of the metal temperature difference Md to be generated but avoids the rise of the metal temperature difference Md to the final control value. It is adopted when it is necessary to break the vacuum early in order to start.

  In the present embodiment, for example, the metal temperature difference Md is defined as 50 degrees C in case 1 (normal alarm level), and the metal temperature difference Md is defined as 56 degrees C in case 2 (emergency alarm level). The operator selects Case 1 or Case 2 from the situation of the thermal power plant 20.

  The forced cooling time (t1) is a time during which water is poured into the boiler 15 for forced cooling in order to shorten the cooling time of the plant 1. The forced cooling time t1 is defined as a time appropriate for shifting to the subsequent natural cooling (for example, t1 = 12 hours in the present embodiment) by several experiments in the past. The operator sets the forced cooling time (t1). Thus, the flow for determining the timing of the vacuum break in the turbine normal stop / boiler forced cooling stop stop mode is started.

  In step S11, the central processing unit 34 instructs the plant control panel 38 to disconnect the thermal power plant 1, and the plant control panel 38 executes this. Simultaneously with the command for releasing, the measurement of the elapsed time t is started.

  In step S12, the central processing unit 34 instructs the plant control panel 38 to measure the current metal temperature Mt of the thermal power plant 1, and the plant control panel 38 executes this to centralize the metal temperature Mt data. Send to processing device 34.

  In step S <b> 13, the central processing unit 34 instructs the plant control panel 38 to perform forced cooling, and the plant control panel 38 starts pouring water into the boiler 15.

  In step S14, the central processing unit 34 uses the forced cooling time (t1) set in step S10 and the current metal temperature Mt measured in step S12 to store the metal temperature transition characteristic data ( The expected metal temperature Mt transition data of the turbine 17 at this time is created using FIG. Based on the created metal temperature Mt transition data, the metal temperature Mt can be predicted from the elapsed time t.

  In step S15, based on the alarm level (case 1 or case 2) set in step S10, an alarm is generated using “metal temperature difference-metal temperature characteristic data” (see FIG. 6) stored in the database 36. The metal temperature Mt at the time of vacuum break corresponding to the level is determined. In this embodiment, for example, in case 1 (normal alarm level: metal temperature difference Md = 50 degrees C), the metal temperature Mt at the time of vacuum break is determined to be 340 degrees C, and case 2 (emergency alarm level: metal temperature difference). In Md = 56 degrees C), the metal temperature Mt at the time of vacuum break is determined to be 380 degrees C.

  Based on the metal temperature at the time of vacuum break determined in step S16 (340 degrees C for case 1 and 380 degrees C for case 1), the metal temperature Mt transition data created in step 14 (see step S14) Is used to determine the vacuum break timing (t2).

  In step S17, it is determined whether or not the elapsed time t (see step S10) from the disconnection has reached the set forced cooling time (t1).

  If the forced cooling time (t1) has been reached in step S18, the forced cooling ends.

  In step S19, the process thereafter proceeds to natural cooling.

  In step S20, it is determined whether or not the elapsed time t (see step S10) from the disconnection has reached the vacuum break timing (t2) determined in step S16. The vacuum break timing (t2) differs between Case 1 and Case 2. In order to ensure that the peak value of the metal temperature difference Md is less than or equal to each alarm level, it is preferable to make a determination by t ≧ t2 + x (where x is a margin time) in order to have a margin.

  If the vacuum break timing (t2) has been reached in step S21, the vacuum break is executed. The vacuum break is performed by releasing the vacuum break valve 30 of the condenser 5. As a result, the metal temperature difference Md increases. However, as described above, the increase is guaranteed to be within the prescribed metal temperature difference Md = 50 degrees C or less in case 1 and within the prescribed metal temperature difference Md = 56 degrees C in case 2. .

  In step S22, it is determined whether or not there is an abnormality in the system. Unless there is an abnormality, the determination and execution of the vacuum break timing in the turbine normal stop / boiler forced cooling stop mode are completed.

[Others]
As mentioned above, although embodiment of the shutdown system of the power plant concerning this invention was described, these are illustrations and this invention is not limited to this. The present invention includes additions, deletions, changes, improvements and the like that can be easily made by those skilled in the art. The technical scope of the present invention is defined by the description of the appended claims.

It is a figure which shows the outline | summary of the boiler and turbine part of the thermal power plant which uses coal as a fuel. FIG. 2 is a system diagram of a high-pressure, intermediate-pressure, and low-pressure turbine and a condenser of the thermal power plant shown in FIG. 1. It is a figure explaining the detail of the high pressure turbine shown in FIG. It is a figure which shows the structure of the timing determination system of a vacuum break. The content of the metal temperature transition characteristic data stored in the database 36 is illustrated. Similarly, the contents of the metal temperature difference-metal temperature characteristic data stored in the database 36 are illustrated. 6 is a flowchart showing a method for determining the timing of vacuum break in the turbine normal stop / boiler forced cooling stop stop mode, which is executed by the vacuum break timing determining system shown in FIG. 4.

Explanation of symbols

1: Thermal power plant, 2: Water intake, 4: Circulation pump, 5: Condenser, 11: Steam, 12: Coal, 13: Bunker, 14: Pulverized coal machine, 15: Boiler, 17: High-pressure turbine, 17 (GEN): GEN side compartment, 17 (GOV): GOV side compartment, 17 (Up): upper part, 17 (Down): lower part, 18: medium pressure turbine, 19: low pressure turbine, 20, 21: generator 22: Water supply pump, 25: Drain valve, 30: Operation terminal, 32: Network, 34: Central processing unit, 36: Database, 38: Plant control panel,
Mt: Metal temperature, Md: Metal temperature difference

Claims (12)

In a power plant shutdown system,
Means for predicting the cooling characteristics of the turbine after system disconnection in turbine normal shutdown mode;
Means for determining the turbine metal temperature from the allowable temperature difference between the upper and lower turbines;
Means for determining a vacuum break timing of the turbine based on the determined turbine metal temperature using the predicted cooling characteristics of the turbine, and the vacuum of the power plant is determined by the determined vacuum break timing. Shutdown system that performs destruction. In the power plant shutdown system according to claim 1,
The shutdown system, wherein the vacuum break is performed by releasing a vacuum break valve of a condenser communicating with the turbine. In the power plant shutdown system according to claim 1,
The turbine normal stop mode is an operation stop system in which a turbine normal stop / boiler forced cooling stop mode for forcibly cooling a boiler is used. In the power plant shutdown system according to claim 1,
The operation stop system, wherein the temperature difference between the upper part and the lower part of the turbine is defined as a temperature difference between an upper part of a casing of a high-pressure turbine communicating with a boiler and a lower part of a casing of a high-pressure turbine communicating with a condenser. In the power plant shutdown system according to claim 1,
The allowable temperature difference between the upper and lower turbines is a shutdown system in which a plurality of temperature differences are defined corresponding to a plurality of alarm levels. A central processing unit that controls the entire system;
In a power plant operation stop system that is connected to the central processing unit and includes a control unit that controls the operation of the thermal power plant.
The central processing unit has a database in which metal temperature transition characteristic data and metal temperature difference ( metal temperature difference between the upper and lower parts of the turbine) -metal temperature characteristic data are accumulated,
The central processing unit determines an expected metal temperature transition from the metal temperature transition characteristic data in the turbine normal stop mode when the power plant is shut down, and an allowable metal temperature difference according to an alarm level (an upper portion of an allowable turbine and A power plant shutdown system that determines a metal temperature of a turbine based on a lower metal temperature difference and determines a vacuum break timing based on the predicted metal temperature transition from the determined metal temperature. In the operation stop system of the power plant according to claim 6,
The shutdown system, wherein the vacuum break is performed by releasing a vacuum break valve of a condenser communicating with the turbine. In the operation stop system of the power plant according to claim 6,
The turbine normal stop mode is an operation stop system in which a turbine normal stop / boiler forced cooling stop mode for forcibly cooling a boiler is used. In the operation stop system of the power plant according to claim 6,
The operation stop system, wherein the metal temperature difference between the upper part and the lower part of the turbine is defined as a temperature difference between an upper part of a casing of a high-pressure turbine communicating with a boiler and a lower part of a casing of a high-pressure turbine communicating with a condenser. In the operation stop system of the power plant according to claim 6,
The acceptable upper and metal temperature difference at the bottom of the turbines, a plurality of temperature difference corresponding to a plurality of alarm levels are defined, shutdown system. In a power plant shutdown method,
The turbine normal stop / boiler forced cooling stop mode is selected and the alarm level is set.
The expected metal temperature transition of the turbine is determined,
The metal temperature of the turbine is determined based on the allowable metal temperature difference corresponding to the level ( allowable metal temperature difference between the upper and lower parts of the turbine ) ,
A method for shutting down a power plant, wherein the timing of vacuum break is determined from the determined metal temperature based on the expected metal temperature transition. In the power plant operation stop method according to claim 11,
The vacuum break is an operation stop method in which a vacuum break valve of a condenser communicating with a turbine is released.

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