JPS63278101A - Process controller - Google Patents

Abstract

PURPOSE:To stably control the water level after switching in case of control switching in any operating state of plant by providing a control system in normal service and an emergency control system with valve gradually opening and closing signal generators or the like and providing a signal comparator. CONSTITUTION:A gradually closing signal generator 11, a signal switch 21, a gradually opening signal generator 12, and a signal switch 22 are provided between a PID operating part 3 and a regulating valve 5 in normal service in the control system in normal service. A gradually opening signal generator 10, a signal switch 20, a gradually closing signal generator 13, and a signal switch 23 are provided between a PID computing element 7 and an emergency regulating valve 9 in the control system in normal service. A signal comparator 14 is provided which compares the valve opening degree signal to the valve 5 with that to the valve 9 with each other in case of a command of switching to the emergency control system and a command of return to the control system in normal service. Thus, the control system as the switching object is forcibly raised to a control range, and the control system is switched in an intermediate opening degree range where degrees of opening of regulating valves of both control systems are approximately equal to each other, and the operation delay of a control system control part is considerably shortened, and the water level is stably controlled after switching.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a process control device, and more particularly to a process control device having a regular control system and an emergency control system to back up the regular control system as one control target.

[Conventional technology]

In process control, where the state variables of industrial processes such as temperature, pressure, flow rate, liquid level, and concentration are controlled variables, a regular control system and an emergency control system are often installed in parallel for one controlled object. Your number will be given.

The regular control system is generally used to manage control during normal operation, and the emergency control system is used to: ■ When the process state changes when the plant is started or stopped and becomes uncontrollable by the regular control system, the emergency control system is used to to act on your behalf.

■If the process state quantity exceeds the normal range and becomes abnormal, and if the regular control system alone is insufficient to handle the situation, an emergency control system will be installed to back it up.

There are various examples of process control, but here we will discuss drain water level control of a feed water heater that heats feed water to a boiler using turbine bleed air for power generation equipment.

In some conventional process control devices of this type, when switching from a regular control system to an emergency control system, the emergency control system remains automatic and the control valve of the regular control system is forced to fully close and slowly close. A control device that automatically shifts control to the emergency control system due to a rise in the water level, and when switching from the operating state of the emergency control system to the regular control system, the emergency control system remains automatic and the regular control system adjustment section A valve full-open signal is applied to the low-level signal selector installed on the output side to force the control valve to gradually open.As the water level decreases, the control valve of the emergency control system is fully opened and the normal control system control section calculation signal is From the point when the control valve becomes lower than the gradual opening signal (in the direction of suppressing the gradual opening of the valve)
A control device is known in which the output of a control section is selected by a low-level signal selector and the control section of the regular control system is automatically controlled by the control section.

(Japanese Patent Publication No. 53-47841) [Problems to be Solved by the Invention] The above-mentioned prior art is considered to be an effective means when the switching time of the control system is relatively long. However, it is necessary to switch the control system urgently (for example, if the water level of the lower feed water heater that directs the drain by the regular control system rises for some reason,
When the heater is cut, it is necessary to shut off the inflow drain. That is, it is necessary to switch from the regular control system to the emergency control system as soon as possible. Furthermore, if a pump is provided on the drain line of the regular control system, it is necessary to quickly switch from the regular control system to the emergency control system by a drain pump trip. ), so in order to switch from the regular control system to the emergency control system, the control valve of the regular control system is forcibly closed slowly to raise the water level, and the water level is set to the emergency control system's regulator setting value (regular control After the emergency control system's regulator increases the output and controls the emergency control system's control valve, the emergency Due to the delay in the operation of the regulating section of the control system, the water level greatly exceeds the set value of the regulating section, causing water induction to the turbine.

Also, when switching control from the emergency control system to the regular control system (
When returning to heater service after cutting the lower heater, or when resetting the drain pump, the control valve of the normal control system is forcibly opened gradually, and after the water level falls below the opening of the control valve, the control valve of the normal control system is opened. When the output decreases and the output becomes smaller than the gradual opening signal, the low-level signal selector switches control to the regular control section, but there was a problem that water level fluctuations increased due to the delay in the operation of the regular control section. .

An object of the present invention is to provide a process control device that can perform stable water level control after control switching under any plant operating condition.

[Means for solving problems]

The above purpose is to install gradual valve opening and gradual closing signal generators on the control unit output lines of the regular control system and the emergency control system, respectively, and to compare the control valve control signals of the regular control system and the emergency control system. This is achieved by switching the gradual open/close signal generator signal and each adjustment section output signal using the signal from this device and the control system switching signal.

[Effect]

The process control switching device uses a control switching command to cause the control system that was in the automatic control state at the time of switching to continue the control state, and to open the control valves of other control systems to an intermediate opening (if the control system was in the automatic control state at the time of switching). 60 of the control valve opening degree of the control system
The control valve is forcibly opened gradually until the opening equivalent to % minute opening) and the automatic control state continues until the control valve opening of the other control system that is being forced to gradually open becomes less than the The control valves in the control system that were in the automatic control state are forced to gradually close, and the control valves that have been forced to gradually open are switched to the automatic control state based on the control section signal. As a result, switching of the control system can be performed by raising the control section of the control system to be switched to the control range and in the intermediate opening range where the control valve openings of the surface control system are approximately equal. Since the operation delay of the control system adjustment section can be greatly reduced and the disturbance caused by switching can be minimized, the safety and operability of the plant can be improved.

〔Example〕

An embodiment of the present invention will be explained with reference to FIGS. 1, 3, and 4. FIG. 3 is a system diagram showing the feed water heater water level control device. The feed water heater 50 heats the feed water 51 using turbine bleed air 52, and the turbine bleed air 52 becomes drain (hot water) through heat exchange and is stored in the feed water heater 5o. A water level detector 1 for detecting the water level of this drain is attached to the feed water heater 50. The drain is drain pipe 53
Water is sent to the lower stage feed water heater or condenser via the water level control valves 5 and 9 provided above. FIG. 4 is a system diagram showing the feed water heater drain tank water level control device. The feed water heater drain tank 60 is a drain 61 from the upper feed water heater.
During normal operation, the drain is pumped through the drain pump 62 provided on the drain pipe 53 and the regular control valve 5.
It is collected in a condensate pipe that maintains a constant drain water level. When the drain pump stops (in a low load area or if the drain pump stops for some reason), the drain is sent to the condenser via the emergency control valve 9 provided on the drain pipe 53 while keeping the water level constant. be discharged. The water level control valves 5 and 9 are controlled as shown in FIG. 1 as follows. That is, the output signal of the water level detector 1 is sent to the deviation calculation section 2 of the regular control system.
The deviation signal is sent to the PID calculator 3 and compared with the set value (signal equivalent to NWL). The deviation signal is PI
The D calculator 3 performs proportional, integral, and differential calculations, and the signals are transmitted to the regular control valve 5 via the electric/pneumatic converter 4 as valve open/close signals. In addition, the output signal of the water level detector 1 is sent to the deviation calculator 6 of the emergency control system, and the set value (N W L + 50 nn
++), and its deviation signal is PI
The signal is sent to the D calculator 7. The deviation signal is subjected to proportional, integral and differential calculations in the PID calculator 7 and is transmitted to the emergency control valve 9 via the electric/pneumatic converter 8 as a valve open/close signal. However, P
The output signal of the ID calculator 7 issues a signal to open the emergency control valve 9 only when the water level rises and exceeds the set value of the deviation calculator 6 (equivalent to NWL+50mn). Therefore, when the normal control system is controlling the water level to NWL, the output signal of the PID calculator 7 of the emergency control system is a valve fully open signal, and the emergency control valve 9 is in a fully closed state. . In addition, P is connected to the regular and emergency control systems from the control lines to control valves 5 and 9.
Tie back lines 17a and 17b are provided to the ID calculators 3 and 7. This tie bank line introduces a forced signal to the output side of the PID calculator 3 or 7 of the regular or emergency control system (when a gradual close or gradual open signal is introduced via the signal switchers 20 to 23) If the
The output is transmitted to the PID calculator 3 or 7, and the calculation output of the PID calculator 3 or 7 is continuously made to follow the forced signal, and then the forced signal is cut off and the PID calculator 3 or 7 When switching to control based on 7, smooth transition to control is possible. (This diagram shows tieback line 1
Although illustration of switching between 7a and 17b is omitted,
Generally, a signal switch is installed on the tieback line,
At the same time as the forced signal is introduced and cut off to the control valve control line, the tieback line is turned ON-OFF. ) The difference from the conventional configuration is the PID calculator 3 and the regular control valve 5 of the regular control system.
Between the gradual closing signal generator 11 and the signal switch 21. A gradual opening signal generator 12 and a signal switching device 22 are provided, and a gradual opening signal generator 10 and a signal switching device 20. The gradual closing signal generator 13 and the signal switch 23 are provided, and a command to switch to the emergency control system and a command to return to the normal control system (in the figure, the command to switch to the emergency control system is not included) )
A signal comparator 14 is provided to compare the valve opening signal to the regular control valve 5 and the valve opening signal to the emergency control valve 9 in order to provide interlock conditions to the above-mentioned devices.

In this embodiment, in order to restore the emergency control system to the original backup system of the regular control system when the return to the regular control system is completed, the valve opening signal to the emergency control valve 9 becomes 0% or less. A monitor relay 15 is provided to detect this, and when the valve opening degree to the emergency control valve 9 becomes 0% or less, the emergency control valve 9
The function is to release the forced gradual closing interlock.

FIG. 2 shows the valve operation by switching the control valve.

Next, the functions and control operations of the component devices will be explained.

When the water level is controlled by the regular control system, that is, the command to return to the regular control system (in the figure, the command N to switch to the emergency control system)
Displayed in OT. ), AND circuit 3
0 and 31 are OFF. The signal switchers 20 and 21, which are the transmission destinations, switch from A to C, that is, the PID
It is switched to the side where the outputs of the computing units 3 and 7 are guided to each control valve.

(Here, each AND circuit 30, 31, 33.34 is OF
In case of F, side A- leads the PID calculator output to the control valve.
>C, the signal switchers 20, 21, 22゜23 are switched, and when ON, the outputs of the respective gradual open/slow close signal generators 10.12 and 11.13 are transferred to the side B-+C which leads to the control valve. The signal switchers 20, 21, 22 and 23 are switched. In addition, these signal switching devices can be opened gradually or only once by the switching command from the control system.
Alternatively, it shall have a function of capturing gradual closing signals. Furthermore, the output of the signal comparator 14 is in the OFF state (the valve opening signal M V 1 to the regular control valve is larger than the valve opening signal M V 2 to the emergency control valve, so it is OFF). ), the AND circuit 33 is also in the O, FF state, and the output of the PID calculator 3 is given to the regular control valve 5. On the other hand, since the AND circuit 34 guides the signal of the signal comparator 14 via the NOT circuit 35, the ON
state, and the output of the gradual closing signal 13 is being given to the emergency control valve 9. At this time, if the emergency valve is fully opened, this is detected by the monitor relay 15 and an ON signal is transmitted to the hold circuit 16. Along with this, the AND circuit 3 introduces the signal of the hold circuit 16 via the NOT circuit 38.
4 is in the OFF state, and the output of the PID calculator 7 is given to the emergency control valve 9. (The ON signal of the hold circuit turns OFF when a 5-valve → 9-valve switching command is given to the wipeout 37.) If a switching command to the emergency control system is given in this state (this command is, for example, In the case of a system like the control system diagram in Figure 3, the lower feed water heater is provided to cut off the inflow drain when the water level rises for some reason and the heater is cut off.
In the case of a system like the control system diagram shown in the figure, this is caused by the stoppage of the drain pump. ) includes a signal comparator, an AN which leads the 14 signals through a NOT circuit.
The D circuit 30 is turned on, the output of the gradual opening signal generator 10 is given to the emergency control valve 9, and the valve starts gradually opening.

From this point on, the PID calculator 7 connects to the tieback line 17b.
This always works to follow the output of the gradual opening signal generator 10. When the emergency control valve 9 opens, the PID calculator 3
The output of is reduced, and the normal control valve is controlled in the closing direction. (When the emergency control valve 9 opens, the water level is about to drop, so the valve operates in the valve closing direction in an attempt to maintain the water level at NWL.) Due to these operations, the valve opening signal M Vi to the normal control valve changes to the emergency control valve. Valve opening signal M V to control valve 9
2, and the signal ratio device 14 is turned on. As a result, the AND circuit 31 is turned on and the gradual closing signal generator 11
The output is given to the regular control valve 5, and the regular control valve 5 is gradually closed until it is fully open. Also, the AND circuit 30 is turned OFF, and the output of the PID calculator 7 is given to the emergency control valve 9 (
The output of the PID calculator 7 before switching is the tieback line 17.
b), the water level is controlled by the emergency control system.

In this way, the PID calculation section of the control system to be switched is brought up to the control range, and since the switching is performed in the intermediate opening range where the control valve openings of both control systems are approximately equal, the PID calculation of the control system is It is possible to greatly reduce the delay in the operation of the parts, and to perform stable switching with less disturbance.

Next, when a command to return to the normal control system from the control state (switching command to the emergency control system N0T) is issued, each AND circuit state and the signal given to each control valve are set to the initial control state. It will be as explained in. Here, the control operation will be briefly explained.

First, the output of the gradual opening signal generator 12 is applied to the regular control valve to gradually open the regular control valve, and accordingly, the emergency control valve 9 is operated in a controlled state in the closing direction. The valve opening signal M V 1 to the regular control valve 5 is the valve opening signal M V to the emergency control valve 9.
2, the output of the gradual closing signal generator 13 is given to the emergency control valve 9, and the emergency control valve 9 is gradually closed until it is fully closed.
The regular control valve 5 is given the output of the calculator 3 from P and enters a controlled state (before switching, the output of the PID calculator 3 follows the output of the gradual opening signal generator 12 by the tieback line 17a). . Incidentally, when the emergency control valve 9 becomes fully open, the gradual closing signal is canceled and the state is shifted to a controlled state based on the output of the PID calculator 7. As described above, the operation delay of the PID calculating section of the control system can be greatly reduced, and switching with less disturbance can be performed.

Furthermore, the functions of the conventional emergency control system can also be maintained.

In the present invention, the PID calculators 3, 7 . Signal switch 20.2
1, 22, 23 gradual opening and closing signal generator 10.12 and 11, 13. Signal comparator 14.AND circuit 30-34.
Although each element such as a NOT circuit is displayed individually, it is clear that when these control calculations are performed by a digital control device, a software program having the above-mentioned functions is used instead.

〔Effect of the invention〕

According to the present invention, the control system to be switched can be forcibly started up to the control range, and the control system can be switched in the intermediate opening range where the control valve openings of both control systems are approximately equal. The delay in operation of the adjustment section can be greatly reduced, and the disturbance caused by switching can be minimized, which has the effect of improving the safety and operability of the plant.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram of a feed water heater water level control device according to an embodiment of the present invention, Fig. 2 is a diagram showing control valve operation at the time of switching,
FIG. 3 is a system diagram showing a feed water heater water level control device as an example of process control, and FIG. 4 is a system diagram showing a feed water heater drain tank water level control device as an example of process control. 2.6... Deviation calculator, 3,7... PID calculator,
5゜9...Control valve, 10.12... Gradual opening signal generator, 11゜13... Gradual closing signal generator, 20,21. '2
2.23...Signal switcher, 14...Signal comparator, 15
...Monitor relay, 16...Hold circuit, 17a
, 17b...Kaya 2nd figure - Zaiyoba vinegar 4f opening degree 1 - 耶訃子Gobenmeiyuoki → L: / Senjuku Akira 5 Sukoshun Kugisasen wisteria grass 5th figure

Claims (1)

[Scope of Claims] 1. A detection unit that detects a control amount of a process control target; an adjustment unit that receives a signal from the detection unit, compares it with a target value, and performs an appropriate control calculation on the result; In a control device in which a regular control system consisting of a control valve that receives a signal from a control section and acts on a controlled object, and another emergency control system installed in parallel for the controlled object, only the regular control system is used. When switching from the control state to the control state using the emergency control system, or from the control state of the emergency control system to the control state of the regular control system, the control system that was in the automatic control state before switching remains automatic. The control state is continued, the control valve of another control system is forcibly opened gradually to an intermediate opening, and the opening of the control valve in automatic control continuation is forced to gradually open. When the following occurs, the control valve of the control system, which has been in an automatic control state until now, is forced to gradually open, and the control valve of the control system is switched to an automatic control state by a control section signal. process control equipment. 2. The steam generated by the steam generator flows into the turbine, the steam that has done some work in the turbine heats the water supplied to the steam generator, and the drain generated by heat exchange is stored in the steam generator. A heater provided on a water supply/condensate line, a detection unit that detects a drain water level for discharging the drain from the heater to the heater on the low pressure side while adjusting the amount of drain, and receives a signal from the detection unit. Condensate is guided by a regular control system and a regular control system, which are composed of a control unit that compares the measured value with a target value and performs appropriate control calculations on the result, and a control valve that adjusts the drain discharge amount in response to a signal from the control unit. a control device installed in parallel with an emergency control system for discharging condensate to the heater or to a condenser on a lower pressure side than the low pressure side heating, a drain tank for storing condensate from the heater, and a drain tank for storing condensate from the heater; A control device in which a regular control system having the same device configuration as described above, which collects condensate to a condensate line while controlling the condensate water level through a pump and a control valve, and an emergency control system, which discharges condensate to a condenser, are installed in parallel, When switching from a control state using only the normal control system to a control state using the emergency control system or from a control state of the emergency control system to a control state using the normal control system, the control that was in the automatic control state before switching The system continues the automatic control state as it is, and the control valves of other control systems are forcibly and gradually opened to an intermediate opening, and the control valves in the automatic control continuation are forced to gradually open. When the opening becomes below, the control valve of the control system, which had been in the automatic control state until now, is forcibly opened gradually, and the forced opening valve of the control system is switched to the automatic control state by the control unit signal. A process control device characterized by: