JPH06214611A - Process control system and operating condition production method for the same - Google Patents

Abstract

PURPOSE:To easily produce a manipulated variable track by acquiring the data on the brand to be switched out of the past operation results stored in a data base and then giving the acquired data to a simulator as the initial data. CONSTITUTION:The operating condition changing result data are fetched and stored in a data base 7 through a decentralized control system 2. A manipulated variable track acquiring means 8 retrieves the data base 7 based on the operating condition changing contents of an input process and extracts the manipulated variable track of the most approximate result to give it to a simulator 4. In other words, the means 8 acquires the data on the brand to be switched out of the past operation results stored in the base 7 and gives the data to the simulator 4 as the initial data. The simulator 4 corrects the manipulated variable track in a trial/error way based on the received initial data and acquires a manipulated variable track accordant with the control conditions. This manipulated variable track is sent to a program controller 2 and used for the actual brand switching operation. Thus the input operation can be simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process control system, and in particular, a process time constant, a dead time, etc. change non-linearly depending on the size of a load and the composition of raw materials such as control when changing the temperature of a reactor. Also, suitable for operating condition change control of plants with large time constants and dead times, and because temperature change trajectories of each stage have a large effect as disturbance of the downstream stage, as in the brand switching operation of the continuous multi-stage polymerization reactor, The present invention relates to a process control system suitable for control in which it is important to comprehensively control a trajectory of a controlled variable, and a method of creating operating conditions thereof.

[0002]

2. Description of the Related Art Conventionally, the following control device has been used for controlling the change of operating conditions of a process (plant) which has a large time constant and dead time and which changes non-linearly depending on the magnitude of load and raw material composition.

(1) "Chemical Engineering Perspective Series, 5th Process Control Technology 1989" (Kansai Chapter, Chemical Engineering Society) 94
The model predicting device described in P to etc., that is, the control amount at the current time is measured, and a reference trajectory that asymptotically approaches the final control amount target value from the control amount measurement value is set, and at the same time, the process model is used The predicted value is predicted by using the measured control amount as a starting point, and the operation amount is determined so that the predicted value is as close as possible to the value of the predetermined time section of the reference trajectory. Control.

(2) The controlled variable and the manipulated variable target trajectory are obtained in advance, and the manipulated variable target value is corrected using the deviation between the controlled variable actual value and the controlled variable target value from the start of the condition change to the current point during the condition change. A program control device for changing the controlled variable in accordance with the controlled variable target value (Japanese Patent Application No. 4-179938, filed on July 7, 1992).

[0005]

However, when the above-mentioned apparatus (1) is applied to control of changing operating conditions in a multistage continuous polymerization process, the following problems occur.

(A) There is no established technique for setting the control amount reference trajectory in the case where the control amount in the preceding stage becomes a disturbance to the control amount in the latter stage as in the multi-stage continuous polymerization process, and it is difficult to set it. For example, when changing the catalyst having a high activity to a catalyst having a low activity, if the timing of raising the internal temperature of the first-stage reactor is set to be late, the polymerization reaction does not proceed in the first-stage reactor and the monomer concentration in the second-stage reactor is increased. Rises, the polymerization rate of the second-stage reactor becomes fast, and if the heat removal limit is exceeded, a runaway reaction will occur. That is, in the case of a multi-stage continuous polymerization process, it is not necessary to simply change the condition from condition 1 to condition 2 in a short time without overshoot, and it is necessary to determine the intermediate orbit in consideration of the latter stage. There are difficulties.

(B) The inlet composition of each stage, which is necessary for accurately predicting the model after the second stage, is not measured or cannot be measured within the time required for accurate control. Normally, it is not possible to obtain the measured value, and the model prediction after the second stage cannot be accurately performed. In particular, in the case of a multi-stage reactor having three or more stages, errors may be accumulated and the accuracy may be deteriorated, and the control limit may be exceeded.

(C) Even if the problems (A) and (B) can be solved by some method, an error always occurs in the model prediction. In model predictive control, as a method of correcting the error,
Using the measured value of the current time of the controlled variable as the starting point, set a reference trajectory that is asymptotic to the final controlled variable target value, and at the same time predict the future value from the controlled variable measured value as the starting point using the process model, A method is used in which the operation of determining the manipulated variable so that the value of the predetermined time interval and the predicted value are as close as possible is repeatedly controlled for each designated time.
However, if the model prediction error is corrected by this method, the controlled variable deviates from the reference trajectory that was initially set and is controlled, which causes large disturbance to the second and subsequent reactors, and the second reactor Subsequent control becomes extremely difficult, and in some cases, it may deviate from the control range and cause a runaway reaction. When the device of (2) above is applied to control of changing operating conditions of a multistage continuous polymerization process, the following problems occur.

(D) Similar to the above (a), it is difficult to set the controlled variable target trajectory.

(E) In the multi-stage continuous polymerization process, a system in which the internal temperature of the reactor which is a controlled variable, the temperature of the heat medium which is a manipulated variable, the composition of the reactor inlet which is a disturbance, etc. is not linear and the control is delayed Therefore, it is difficult to set the manipulated variable target trajectory. In particular, after the second stage reactor, the internal temperature of the previous stage also becomes a disturbance, and setting is extremely difficult.

In a system in which the characteristics of the system itself are stable, in order to solve the problems (d) and (e), a track record of the same condition is selected from the track record of past condition changes, and the control amount target trajectory is set. Although it is possible to set the manipulated variable target trajectory, in the case of the polymerization process as well, the overall heat transfer coefficient usually changes over time due to factors such as fouling of the heat transfer tube, so this method causes too large an error. . In addition, this method cannot be used even if there is no record of the same conditions in the past.

Therefore, in view of the above-mentioned points, a first object of the present invention is to provide a process control system and an operating condition creating method thereof which can easily create an operation amount trajectory.

A second object of the present invention is to provide a method for creating operating conditions of a process control system suitable for controlling a process in which the process state changes non-linearly.

[0014]

In order to achieve such an object, the invention of claim 1 is to control the operating condition of the plant from the manipulated variable indicating the operating condition of the plant to the control condition of the plant. In a method for creating operating conditions of a process control system that creates a time-series trajectory of the manipulated variable used for actual operation by simulating the controlled variable
The operation amount, the time-series correlation between the control amount and the evaluation criteria for the control amount is predetermined, the trajectory of the operation amount is given in advance, and the trajectory of the given operation amount and the correlation. Is used to calculate the trajectory of the controlled variable, and the trajectory of the controlled variable obtained as a result of the calculation is evaluated whether or not it meets the evaluation criteria. Correct the trajectory of the given operation amount,
Hereinafter, with the corrected trajectory of the manipulated variable as a trajectory of the new given manipulated variable, the calculation of the trajectory of the controlled variable, the evaluation, and the modification are repeated, and an evaluation of conformity with the control criterion was obtained. The trajectory of the operation amount at the time is set as the trajectory of the operating condition.

According to a second aspect of the present invention, in addition to the first aspect of the invention, data indicating the trajectory of the manipulated variable actually used for the operation control for changing the operating conditions of the plant is stored in the form of a database. In addition, it is characterized in that the data retrieved from the database is given as a trajectory of the operation amount of the initial condition.

According to a third aspect of the present invention, in addition to the first aspect of the invention, the plant is divided into a plurality of areas in advance,
It is characterized in that the setting of activation of the operating condition is executed for each region.

According to a fourth aspect of the present invention, for control of changing the operating condition of the plant, the control amount indicating the control state of the plant is simulated from the operation amount indicating the operating state of the plant, and the control amount of the operation amount used for the actual operation is calculated. In a process control system for creating a time-series trajectory, the operation amount and a time-series correlation between the control amount and an evaluation criterion for the control amount are predetermined, and an operation amount giving a trajectory of the operation amount. A trajectory acquisition means, a simulator for calculating the trajectory of the controlled variable using the trajectory of the given operation amount and the correlation, and the trajectory of the controlled variable obtained as a result of the calculation matches the evaluation standard. And the evaluation means for performing an evaluation of whether or not there is a match, if the evaluation of a match is not obtained, the evaluation means corrects the trajectory of the given operation amount. With the trajectory of the work amount as the trajectory of the new operation amount, the calculation of the trajectory of the control amount, the evaluation and the correction are repeatedly performed, and the operation amount when the evaluation of conformity with the control criterion is obtained. A trajectory is set as the operating condition trajectory.

In addition to the invention of claim 4, the invention of claim 5 is, in addition to the invention of claim 4, the first trajectory of the control amount calculated by the simulator, which corresponds to the operating condition trajectory set in the actual operation of the plant. And a second trajectory of the control amount obtained from the measurement result of the plant, and further comprising fuzzy inference means for executing processing for bringing the second trajectory closer to the first trajectory by fuzzy inference processing. .

According to a sixth aspect of the present invention, for control of changing the operating condition of the plant, the control amount indicating the control state of the plant is simulated from the operation amount indicating the operating state of the plant to calculate the amount of operation used for actual operation. In a method for creating operating conditions of a process control system that creates a time-series trajectory, assuming a plurality of tanks into which the plant is divided, and regarding the relationship between the adjacent tanks for the control amount and each of the tanks themselves. A predetermined arithmetic expression including the time series relationship between the operation amount and the control amount is used, and the arithmetic expression is used with the operation amount at the entrance of the plant as an initial value, starting from the brand switching start point. The simulation of the plant is performed by calculating a time-series control amount for all the tanks.

[0020]

According to the first and fourth aspects of the invention, the manipulated variable trajectory is corrected by trial and error so that the simulation result matches the control reference given in advance.

According to the second aspect of the present invention, since the operation amount trajectory data to be initially given is acquired from the database, the user does not need to key in the operation amount trajectory data itself.

According to the third aspect of the present invention, since the area to be simulated is divided into zones, only the upstream side from the zone where the control amount does not match the reference can be the target of correction of the manipulated variable.

According to the fifth aspect of the present invention, the overshoot of the internal temperature of the plant can be reduced by correcting the trajectory of the manipulated variable by using fuzzy inference.

According to the invention of claim 6, the influence of the adjacent position of the plant is added to the simulation calculation of the control amount.
In particular, it is possible to improve the simulation accuracy of the multi-step reaction.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an example of a process control device to which the present invention is applied. In FIG. 1, reference numeral 1 is a plant controlled by a process control device. Reference numeral 2 denotes a program controller, which can be a controller with a program, a distributed control system (hereinafter abbreviated as DCS), or a combination of a controller and a process computer. DCS was used in this example.

Reference numeral 3 denotes a computer which obtains an operation amount trajectory, calculates a control amount trajectory, and gives the operation amount trajectory and the control amount trajectory to the program controller 2 as an operation amount target trajectory and a control amount target trajectory. Is incorporated. The computer 3 may be one computer or a plurality of computers connected by a communication system. If the program control device 2 itself has a computer, the computer can also be used as the computer 3. In the present embodiment, a process computer and a computer capable of faster calculation than the process computer were used as the computer 3, and only the simulator 4 was incorporated in the latter.

In the present embodiment, the calculation results of the simulator 4 are given as the control amount target trajectory and the manipulated variable target trajectory of the program control device 2 to control the plant 1 and its operating conditions.

Further, the program control device 2 measures the control amount by using the deviation between the actual value (measured value) of the control amount and the control amount target value from the start of the operating condition change (brand switching) to the current time during the condition change. The target of the manipulated variable is automatically corrected so that the orbit of (1) approaches the target trajectory of the controlled variable, and the plant control is performed to compensate for the error in the calculation result of the simulator 4. The simulator 4 of the present embodiment inputs the manipulated variable trajectory and calculates the controlled variable trajectory, but the controlled variable trajectory may be input and calculated the manipulated variable trajectory. However, when the manipulated variable orbit is calculated by inputting the controlled variable orbit, the calculated value of the manipulated variable orbit may become an unrealizable orbit in a complicated process such as a continuous multi-stage polymerization reactor, which is not preferable.

Reference numeral 5 is a fuzzy inference means. PID control may be used as a method of correcting the manipulated variable target value by using the deviation between the actual value of the controlled variable and the target value of the controlled variable from the start of changing the operating conditions to the current time during the condition change, but continuous multi-stage polymerization reaction In a complicated process such as a vessel, control performance is improved by executing control using fuzzy inference means.

Reference numeral 6 denotes a plant state quantity calculating means, which is incorporated in the computer 3, obtains operation information, and separately from the measured values of the plant, the state quantity of the plant such as a general heat transfer coefficient (hereinafter referred to as U). Or the plant state quantity at the time of future change of operating conditions is predicted and calculated, and the calculation result is given to the simulator 4. In the present embodiment, for example, the simulation is performed using the general heat transfer coefficient which is different from the general heat transfer coefficient one week ago or one month ago, or the day when the condition is changed.

Reference numeral 7 is a database, which is incorporated in the computer 3, and in this embodiment, the operating condition change record data is fetched and stored through the DCS 2. Reference numeral 8 is a manipulated variable trajectory acquisition means, which searches the database 7 according to the contents of the change in the operating condition of the input process, extracts the closest actual manipulated variable trajectory, and gives the manipulated variable trajectory to the simulator 4. With this function, it is possible to omit the work that requires the skill of inputting the operation amount trajectory to the simulator 4. This function saves the stable operating conditions in the database 7, extracts the operation including the manipulated variable before and after changing the operating conditions according to the contents of the input process, and calculates the manipulated variable trajectory by an appropriate method. After that, the simulator 4 can be replaced by a method of giving an operation amount trajectory. Also in this embodiment, stable operating conditions are also stored in the database 7, and when the past operating condition change record data does not have an appropriate value, the manipulated variable acquisition means 8 determines whether the operating conditions before and after the operating conditions are changed. Database 7 depending on the content
After the operating conditions at the time of stable are retrieved and extracted, and the manipulated variable trajectory is calculated by an appropriate method, the manipulated variable trajectory is given to the simulator 4.

Reference numeral 9 is an evaluation means, which is incorporated in the computer 3 to compare and evaluate a predetermined evaluation standard (control standard of the present invention) and the calculation result of the controlled variable, and operate by an appropriate method until the evaluation standard is satisfied. The quantity trajectory and the like are corrected and given to the simulator 4 for re-simulation. When the above evaluation criteria are satisfied, the switch 12 is closed and the calculation result is displayed on the display input device. With this function, it is possible to omit the work requiring the skill of correcting and inputting the operation amount trajectory into the simulator 4, and at the same time shortening the calculation time until obtaining an appropriate result.

Reference numeral 10 is a display device. Reference numeral 11 denotes an input device, and the display device 10 uses a CRT, a printer, or the like. A keyboard or a mouse is used as the input device 11. In this example, a color CRT attached to a process computer, a keyboard and a mouse were used. Prior to giving the control amount target trajectory and the manipulated variable target trajectory (hereinafter, both may be simply referred to as a target trajectory) from the simulator 4 to the program controller 2, the calculation result is displayed and set by the operator. Switch 1 by inputting a command
3 is closed and the control amount target trajectory and the manipulated variable target trajectory are given from the simulator 4 to the program controller 2. Alternatively,
When the operator inputs an operation amount trajectory change input and a calculation command, the simulator 4 recalculates based on the changed operation amount trajectory, and the recalculation result is displayed again on the display device 10. With this function, it is possible to prevent the vehicle from operating on an incorrect controlled variable target trajectory or controlled variable trajectory due to a system deficiency, and it is also possible to deal with operating conditions for which evaluation criteria are not established.

In this embodiment, the simulator 4, the manipulated variable trajectory acquisition means 8 and the plant state quantity calculation means 6 are also included.
And the evaluation means 9 realizes the function of each of the above means by the computer 3 executing a program defining each processing. The processing contents of these means will be described later, but the flowcharts corresponding to the processing contents are shown in FIGS. 10 to 13 for reference. The database is stored and stored in a disk storage device or the like, and is searched for a keyword by the computer 3.

The brand switching (hereinafter simply referred to as switching) of the synthetic resin manufacturing plant, which is the control target of this embodiment, will be described in detail. FIG. 2 shows a schematic processing flow of a synthetic resin continuous bulk polymerization plant. The reactor 21 is a plug flow reactor, and the internal temperature control is performed by dividing the whole into 9 zones 31 to 39 and adjusting the temperature of the heat mediums 41 to 49 for each zone. The reactor itself is 1
Although it is the base, it is controlled in 9 zones, and therefore the operation condition change control involves the same difficulties as in the multistage continuous polymerization process. The controlled variable refers to the state variable of the process to be controlled, and in this system, it refers to the internal temperatures 51 to 59 at the rear of the nine zones 31 to 39. The manipulated variable is the state quantity of the process operated to control the controlled variable, and in this system, it is the inlet temperature of each heating medium 41 to 49 corresponding to the internal temperature 51 to 59 of the 9 zones. Say.

Next, the actual operation will be described. First, the upper part of the screen of FIG. 3 is displayed on the display device 10 without starting the system. The operator inputs the scheduled switching date and time, the brand name before and after the switching, and the raw material supply rate before and after the switching (hereinafter abbreviated as the rate) from the input device 11. The input conditions are given to the manipulated variable trajectory acquisition means 8 in FIG. In the present embodiment, in order to give the condition to the manipulated variable trajectory acquisition means 8, manual input was performed using the display device 10 and the input device, but a database storing the production plan is searched and input to the manipulated variable trajectory acquisition means. Information may be given, or input information may be given from the system that controls the production plan. The manipulated variable trajectory acquisition means 8 searches the database 7 by the name of the preceding and following brand and the rate. The database 7 stores the manipulated variable trajectory for each issue switching record, but if there is a switching record that matches the search condition, the date and rank of the switching record are displayed on the display device 10 as shown in FIG. . The rank is an index indicating the degree of goodness or badness with respect to switching, and is information given by an operator's instruction when the switching history is given from the DCS 2 to the process computer 3. The rank is represented by a code such as A, B, and C. In this embodiment, the brand names and rates before and after the switching are used as keywords so that the search can be easily performed. However, data that is searched by operating conditions such as inlet temperature, internal temperature of each zone, inlet composition, etc. A base can also be used. As a result of the search, when a desired actual performance number is input from the input device 11 from the switching performance (information added to the operation data at the time of brand switching) displayed on the display device 10 as shown in FIG. 3, the operation amount trajectory is acquired. The means 8 is data on the operating condition trajectory corresponding to the designated number, that is, the reactor inlet composition target trajectory (for each composition), the reactor inlet temperature target trajectory, the heat medium temperature target trajectory (for each zone) in FIG. 2) is acquired from the database 7, and the time and target value of the vertices of the polygonal lines on these trajectories are given to the simulator 4 as data on the trajectory of the initial manipulated variable.

On the other hand, if the database 7 does not have a desired record, when the operator inputs the number 0, the operation amount trajectory acquisition means 8 in FIG. The operation data in the stable state at is acquired from the database 7. Database 7
In addition to the brand switching record of FIG. 4, the stable operating conditions shown in FIG. 5 are stored for all the brands (for each rate). Be delivered to. The data passed are the reactor inlet composition target value (for each composition), the reactor inlet temperature target value, and the internal temperature target value (for each zone-this target value is safely operated corresponding to the brand and rate before switching). It may be called a condition.), Heat medium temperature standard value (for each zone), brand after switching, stability condition corresponding to rate, and heat medium temperature standard value of each zone. The operation amount trajectory acquisition unit 8 receives the received safe operating conditions before and after the switching, the heat medium temperature reference value, the already input rate,
The operating condition trajectory is calculated according to a predetermined calculation formula using data such as the volume of each predetermined zone of the reactor, and the operating condition trajectory is given to the simulator 4. For example, the heat medium temperature target trajectory of the fourth zone of the reactor is A in FIG.
Given by the coordinates of point and B point. Time coordinates of the point A residence time of up to the first to third zones, in particular given the value obtained by dividing the volume up to the first to third zone (M ³⁾ at a volume flow rate (M ³ / H). Here the volumetric flow rate is calculated from the rate and the density. The density used here is previously held in the manipulated variable trajectory acquisition means 8 as a constant value, and the origin of the time coordinate is the brand switching start time. The time coordinates of point B are 1st to 1st.
Residence times of up to 4 zones are used. As the temperature coordinates at points A and B, the heat medium temperature reference values in the fourth zone before and after switching are used.

From the manipulated variable trajectory acquisition means 8 to the plant state quantity calculation means 6, the scheduled date and time of brand change are given. The plant state quantity computing means 6 measures the temperature and composition of the DCS 2 to the reactor inlet of FIG.
The values of the internal temperatures 51 to 59 of 9 and the temperatures of the heat mediums 41 to 49 are received, U of each zone is calculated, and the calculation result is stored as a trend of U for each zone. The plant state quantity computing means 6 is activated by acquiring the scheduled date and time from the manipulated variable trajectory obtaining means 8, and the predicted value of U in each zone at this scheduled date and time is extrapolated by linearly approximating the latest 20 days of the trend of U. Calculate. The calculation result is given to the simulator 4.

The simulator 4 is a manipulated variable trajectory acquisition means 8
Also, an unsteady state controlled variable is simulated by the operating condition trajectory and U of each zone given from the plant state quantity calculating means, and the internal temperature, composition, molecular weight, etc. are calculated for each predetermined region and time step. The calculation result is given to the evaluation means 9 together with the operating condition trajectory.

When the plug flow model is adopted as the simulation model, the basic equation becomes a partial differential equation in the unsteady state. Therefore, a perfect mixing tank array model in which the basic equation becomes an ordinary differential equation is adopted. The number of zones was set to 9 (see FIG. 3) and the number of complete mixing tanks was set to 30 in each zone, 270 tanks in total, so that the temperature and the internal temperature of each zone could be in a one-to-one correspondence.

When the simulator 4 performs a simulation in an unsteady state, it is necessary to first calculate initial conditions such as temperature and composition of each complete mixing tank. This initial condition is calculated by steady-state simulation using a model equivalent to the model used for unsteady-state simulation. The mass balance and heat balance of the complete mixing tank are described in detail in “Chemical Engineering III” (Oden Takeo, Iwanami Zensho) and the like, but the calculation method of the monomer concentration is shown as a specific example. The balance formula for the monomer concentration in each tank is as shown in the following (Equation 1), and the amount of operation at the inlet of the plant is used as an initial value to solve from the first tank to the last tank in order. In order to calculate the concentration, in addition to the value of the N-1st tank, the radical concentration and density of the Nth tank, the activity coefficient, the reaction rate constant, etc. are necessary, that is, they are simultaneous equations. There are various solutions to simultaneous equations,
In this embodiment, each value of the Nth tank is calculated, each assumed value is compared with each calculated value, and if the difference is smaller than the reference value, each calculated value is positive, and if the difference is large, each assumed value is corrected. We adopted a method to calculate again until the difference becomes smaller than the reference value.

[0043]

[Number 1] _{F (M N-1 -M N} ) -K N V N ρ N R N γ N M N = 0 symbols used in this formula is as follows.

F: flow rate (KG / H) M: monomer concentration (KG / KG) K: reaction rate constant (/ H) V: tank volume (M ³ ) ρ: density (KG / M ³ ) R: radical Concentration (KG / KG) γ: Activity coefficient (−) The subscript N indicates the Nth tank. N-1 = 0 indicates the entrance of the reactor.

When performing the above calculation, the heating medium temperature trajectory of each zone is simultaneously corrected by the predicted value of U of each zone at the switching date and time. Specifically, the temperature of each tank is sequentially obtained from the upstream by a heat balance formula. At that time, the required heat medium temperature is calculated by using the value before switching given from the manipulated variable trajectory acquisition means 8 as an initial value, When the calculation has proceeded to the tank corresponding to the internal temperature measurement position, the calculated value of the internal temperature of the tank is compared with the target value given from the manipulated variable trajectory acquisition means 8, and the difference between the calculated value and the target value is compared. Correct the heat transfer medium temperature until is less than the reference value and recalculate from the first tank in the zone. The heat medium temperature at that time when the difference becomes smaller than the reference value is defined as the heat medium temperature of the zone. Also, the same calculation is performed under the operating conditions after switching to correct the heat medium temperature.
Further, the value during switching of the heating medium temperature target trajectory is proportionally distributed and corrected. With this correction, past heat medium temperature trajectories that could not be used as they were in the past can now be used.

When the initial conditions are obtained, the simulator 4 further executes an unsteady state calculation to calculate the monomer concentration, molecular weight, radical concentration, density, viscosity, etc. in addition to the internal temperature of each tank. As a specific example, a method for calculating the monomer concentration will be shown. The mass balance equation relating to the monomer concentration in each tank is expressed by the following equation 2. The non-steady-state operation formula is a differential equation, which is combined with other mass balance equations and heat balance equations to form a simultaneous ordinary differential equation. In this embodiment, the Runge-Kutta method is used as the solution, but the calculation from the first tank to the last tank is repeated in order at predetermined time intervals, and the calculation is performed until a predetermined time.

[0047]

[Number 2] _{F N-1 M N-1} -F N M N -K N V N ρ N R N γ N M N = V N (d (ρ N M N) / dt) is used in this formula The symbols are as follows.

F: flow rate (KG / H) M: monomer concentration (KG / KG) K: reaction rate constant (/ H) V: tank volume (M ³ ) ρ: density (KG / M ³ ) R: radical Concentration (KG / KG) γ: Activity coefficient (−) t: Time (H) d: Differential symbol Subscript N indicates the Nth tank. N-1 = 0 indicates the entrance of the reactor.

In the equation 2, the change in the monomer concentration per unit time in the N-th tank (d (ρ _{N MN} ) / dt) is adjacent to the N-th
It is shown that it is determined by the monomer concentration in one tank. In other words, the monomer concentration at a certain time point is the Nth time point at the previous time point.
Tank, monomer concentration of N-1th tank and others, above Nth tank
It is shown that it depends on the condition value of the tank. When the calculation is completed, the simulator 4 gives the calculation result to the evaluation means 9. The evaluation means 9 evaluates the calculation result in accordance with a predetermined evaluation standard. When the evaluation standard is satisfied, the switch 12 is closed and the calculation result is displayed on the display device 10. When the evaluation standard is not satisfied, Correct the driving condition trajectory according to a predetermined rule and give it to the simulator 4,
Run the simulation again. The switch 12 is a function for switching to a program for displaying the calculation result,
Closing the switch 12 means activating the result display program. The evaluation criteria used here are provided for the internal temperature of the tank and the molecular weight of the reactor outlet 22 corresponding to the rear temperature 51 to 59 of each zone in FIG. 2, and are provided for the absolute value and the time until stabilization. If this evaluation criterion is not satisfied, the heat medium inlet temperature trajectory of the upstream zone including the zone that does not satisfy the evaluation criterion is corrected. The operating condition trajectories other than the heat medium inlet temperature trajectory are not automatically changed by the evaluation means 9, but are displayed on the display device 10 and then input from the input device 11. The evaluation of the evaluation means 9 is performed up to a predetermined number of times. When the number of evaluations exceeds the upper limit, the calculation result is displayed on the display device 10 even if the evaluation criteria are not satisfied.

The evaluation correction process for the simulation described above will be described in detail with a specific example. It is assumed that the calculation result of the internal temperature of the fifth zone 55 in FIG. 2 changes as shown by the curve in FIG. Regarding the absolute value of the temperature, the normal range is defined between the higher temperature + T1 of the target temperature before switching and the target temperature after switching and the temperature -T2 of the lower target temperature before switching and the lower target temperature after switching (see FIG. 7). ).
Here, T1 and T2 are predetermined values. In FIG. 7, the evaluation range is deviated from the normal range in the section from point D to point E, and it is determined that the evaluation criteria are not satisfied. The time until the state stabilizes is the time t2 at the point (F point) where the target temperature after switching does not deviate from the target temperature ± T3 and the target temperature before switching ± T3.
It is the difference t3 of the time t1 of the point (point C) which is out of the range of (1) for the first time. Here, T3 is a predetermined value. If t3 is longer than a predetermined stability limit time t4, it is determined that the criterion is not satisfied. When a plurality of zones that do not satisfy the standard occur, correction is performed in order from the upstream. In this example, the fifth zone was the most upstream zone that did not meet the criteria.

If there is a zone that does not satisfy the evaluation criteria, the monomer concentration of the tank corresponding to the outlet of each upstream zone is compared with a predetermined evaluation criteria, and the heat medium of the most upstream zone among the zones that do not meet the criteria is compared. Correct the target temperature trajectory. If the standard for the monomer concentration is satisfied in all the zones on the upstream side, the heat medium target temperature trajectory of the zone where the internal temperature does not satisfy the standard is corrected.

The standard for the monomer concentration (corresponding to the control standard of the present invention) will be described with reference to FIG. The curve shown in FIG. 8 is the calculation result of the monomer concentration in the third zone with respect to time, and the third zone was the most upstream zone that did not satisfy the standard. In the process of transitioning from the state before switching to the state after switching, the monomer after switching from the point G (time t5) where the calculated value first deviates from the range of M0 (calculated value before switching) ± M1 (upper and lower limit range). Concentration range (M3 ±
The H point (time t) that does not deviate from the range of M2 (see FIG. 8)
In the section between 6), (M0, t5), (M2, t
A straight line connecting the points 6) is drawn, and the range above and below the straight line ± M4 is defined as the normal range. If the curve deviates from this range, it is judged that the evaluation criteria are not satisfied. In the example of FIG. 8, since the section from point I to point J deviates from the normal range, it is determined that the evaluation criterion is not satisfied. Here, M1, M3, and M4 are predetermined values, and have a relationship of M4> M1 and M4> M3.

An example of a method of correcting the heat medium target temperature trajectory will be described with reference to FIG. The curve in FIG. 9 is the calculation result of the monomer concentration in the third zone, the broken line is the heat medium target temperature trajectory of the third zone, the broken line is the corrected heat medium temperature target trajectory of the third zone, and the monomer concentration is I The range from the point (time t7) to the point J (time t8) is outside the normal range. The heat medium temperature target trajectory correction section is from t7-t9 to t8-
In the section of t9 (see FIG. 9), the correction direction is the same as the direction out of the normal range of the monomer concentration calculation value,
The correction amount is T4 × M5. Since the heat medium temperature target trajectory is stored in the memory as the coordinates of the vertex of the polygonal line,
Actually, the correction is performed as shown in FIG. 9 including before and after the correction section.

Every time one zone is corrected, the evaluation means of FIG. 1 gives the corrected target temperature of the heat medium temperature and the operation command to the simulator 4, the simulator 4 re-executes the unsteady operation, and the operation result is sent to the evaluation means. return. Evaluation means 9
Evaluates and corrects until the evaluation criteria are met or a predetermined number of evaluation iterations is reached.

When the evaluation is completed, the evaluation means 9 activates the display program corresponding to the switch 12, and the display device 10
Display the calculation result on. In the display device 10, the horizontal axis represents time, and the vertical axis represents the position of the reactor (corresponding to each tank). The three-dimensional graph showing the height of the calculation result in color, and the horizontal axis the time or the position of the reactor, the vertical axis. Display a two-dimensional graph as the calculation result for which you want to display the axis. The two-dimensional graph is 3 above
The cross-section is displayed at any position on the dimensional graph.

The correction of the operating condition trajectory is performed by rewriting the time and the set value of the apex of the operating condition trajectory displayed on the display device 10 using the mouse and keyboard as the input device 11 to rewrite the values used last time. After correcting the time and the set value, the simulator 4 is made to re-execute the simulation operation according to the instruction from the input device 11. Also,
By inputting a setting command from the input device 11, the switch 1
3 is closed and the program control device 2 is provided with the operating trajectory including the target trajectory of each zone and the scheduled switching date and time. Here, the switch 13 is a program for writing to the target trajectory file of the DCS 2, and it means that when the switch 13 is closed, this writing program is started. DCS
In order to perform control by the standard function, when the simulator 4 gives the data about the internal temperature target trajectory to the program controller 2, the internal temperature target trajectory is approximated to a polygonal line and given at the coordinates of its apex.

Unless there is a particular change, the program controller 2 starts program control for the plant at the scheduled switching date and time, and sets each operating condition trajectory given from the simulator 4 except the internal temperature of each zone. A control called PID that takes a value is executed. The internal temperature of each zone is controlled by correcting the corresponding heat medium inlet temperature set value using the given internal temperature trajectory as a set value.
In this case, if control results other than the internal temperature deviate from the set value to the extent that the internal temperature is affected, it is necessary to incorporate the deviation into the simulation model.

The internal temperature of each zone is controlled as follows. When switching control is performed, the program control device (DC
The CPU of S) 2 outputs the value of the internal temperature target trajectory of each zone corresponding to the elapsed time from the start of switching as a set value to the internal temperature controller of each zone. The internal temperature controller of each zone is set value and PID calculation,
The heat medium temperature correction value is output to the CPU. The CPU adds the heating medium temperature correction value to the value of the heating medium temperature target trajectory of each zone corresponding to the elapsed time from the start of switching, and outputs it to the heating medium temperature controller of each zone. The heat medium temperature controller of each zone performs PID control based on the given set value.

Further, in order to calculate the heat medium temperature correction value of each zone, in the present embodiment, fuzzy inference means 5 is provided and fuzzy control can be used instead of the above PID control, but fuzzy control is more suitable for internal temperature. It was possible to reduce the overshoot and so on. The fuzzy inference means 5 samples the actual value of each internal temperature and the set value of each internal temperature for each predetermined time, and deviates between the measured value and the set value and the deviation between the measured value and the set value. The fuzzy control is performed by calculating a correction value of the corresponding heat medium temperature and correcting the heat medium temperature trajectory in accordance with a predetermined rule using as a membership function.

The trend of the actual measurement value of the internal temperature of each zone being switched and the target value of the heat medium are DC together with the operating condition trajectories.
It is stored in the disk S and is provided to the database 7 together with the rank input by the operator after the switching is completed. As a guide for ranking, for example, if the internal temperature control works well and the amount of switching intermediate product that occurs in the product is small, A is used, and if the internal temperature control is successful but the amount of intermediate product is large, B is used. Can be used if the internal temperature control is not successful.

As described above, if the brand switching in the continuous bulk polymerization process of synthetic resin as in this embodiment is performed, the brand switching operation conventionally performed by the experienced operator with full know-how is as follows. It's just a simple operation like. That is, the operator inputs the scheduled switching date and time, the brand names before and after the switching, and the rate, selects appropriate data from the past results displayed, and sets the operating conditions by looking at the displayed simulation results. It is only necessary to perform an operation for giving a command, and the operating conditions are automatically created by the device, so that the process control becomes safe and reliable. In addition, the technical staff took a long time to examine the operating conditions for brand switching without a past operating record, and the actual operating conditions were determined only after conducting a switching test. Then, in the present embodiment, since the operating conditions can be automatically created, the technical staff is freed from the operating condition creating process. In this embodiment, since the molecular weight of the reactor outlet, which greatly affects the physical properties of the product, can be calculated by the simulator, the user can search for the operating condition that minimizes the intermediate product and enables stable switching. Specifically, the user can search the preferable operating condition while correcting the operating condition trajectory such as the heating medium temperature condition trajectory while viewing the simulation result displayed on the display device. It is also possible to change the time until the molecular weight of the reactor outlet stabilizes by changing the evaluation criteria of the evaluation means, and it is possible to find suitable operating conditions by using these treatments together.

Further, in this embodiment, the internal temperature of each zone is obtained from the temperature at the adjacent position, and the control is determined so that there is a margin. Therefore, the accuracy of the relationship between the internal temperature and the heat medium temperature in the operating condition trajectory is poor. However, there is an advantage that automatic correction can be performed by the program control device during control. In addition, in this embodiment, the user can check the automatically created operating condition trajectory on the display device, and if necessary, the operating condition trajectory can be corrected by the input device, so that optimum operating conditions can be set.

In addition to this embodiment, the following example can be carried out.

1) In the present embodiment, the simulation result is displayed as a graph, but it is also possible to specify the past operation record to be searched for in the database and display it in a graph.

2) The computer used for the simulator may be determined according to the calculation amount of the simulation, and it has a communication function from a small computer such as a personal computer, and is large in size capable of processing a large amount of information such as time sharing. A computer can be used.

3) In the present embodiment, the brand switching control is shown as an example of the operating condition changing control, but the present invention can also be applied to changing the operating condition for the rate control of the production amount.

4) The correlation between the manipulated variable and the controlled variable may be expressed by a mathematical expression, or may be expressed by a table in which the value of the controlled variable is associated with the value of the manipulated variable.

5) The evaluation standard used in this embodiment may be defined in advance in software or may be given by the user from the keyboard input device. Which form to take depends on the system contents. For example, if the operation condition change content is one type and the evaluation criteria can be fixed, it is possible to omit the user's input operation by defining it on the software.

[0069]

As described above, according to the present invention,
Since the operation amount trajectory used for the simulation can be automatically created, the user does not need to perform the operation amount creating process and its key input operation, and the plant operation preparation time can be shortened. Further, since the simulation result obtained in the present invention takes into consideration the influence of the adjacent position in the reactor (plant), it can sufficiently deal with the multi-stage process.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of this embodiment.

FIG. 2 is a schematic cross-sectional view showing a schematic flow of a synthetic resin continuous bulk polymerization plant that is a control target of this example.

FIG. 3 is an explanatory diagram showing a display example of input information according to the present embodiment.

FIG. 4 is an explanatory diagram showing contents of a database relating to a switching record.

FIG. 5 is an explanatory diagram showing the contents of a database relating to stable operating conditions.

FIG. 6 is an explanatory diagram showing an example of a heating medium temperature target trajectory.

FIG. 7 is an explanatory diagram showing an example of a calculation result of an internal temperature.

FIG. 8 is an explanatory diagram showing an example of a calculation result of a monomer concentration.

FIG. 9 is an explanatory diagram showing the contents of correction of the heat medium target temperature.

FIG. 10 is a flowchart showing the processing contents of an operation amount trajectory acquisition unit.

FIG. 11 is a flowchart showing the processing contents of the plant state quantity computing means.

FIG. 12 is a flowchart showing the processing contents of the simulator.

FIG. 13 is a flowchart showing the processing contents of the evaluation means.

[Explanation of symbols]

 1 Controlled Plant 2 Program Control Device 3 Computer 4 Simulator 5 Fuzzy Inference Means 6 Plant State Calculator 7 Database 8 Manipulation Trajectory Acquisition Means 9 Evaluation Means 10 Display Device 11 Input Device 12 Switch 13 Switch 20 Reactor Inlet 21 Reaction Vessel 22 reactor outlet 31-39 zone 41-49 heat medium 51-59 internal temperature

Claims (6)

[Claims] 1. A time-series trajectory of an operation amount used for actual operation by simulating a control amount indicating the control state of the plant from an operation amount indicating the operation state of the plant for controlling the operation condition change of the plant. In the operating condition creating method of the process control system for creating the operation amount, the operation amount, the time series correlation between the control amount and the evaluation criterion for the control amount are predetermined, and the trajectory of the operation amount is given in advance, The trajectory of the controlled variable is calculated using the given trajectory of the manipulated variable and the correlation, and it is evaluated whether or not the trajectory of the controlled variable obtained as a result of the calculation matches the evaluation standard. If the match is not evaluated, the trajectory of the given manipulated variable is corrected, and the trajectory of the corrected manipulated variable is set as a new trajectory of the given manipulated variable. Of the process control system characterized in that the trajectory of the manipulated variable when the evaluation of conformity to the control criterion is obtained is repeatedly set as the trajectory of the operating condition by repeating the calculation of the trajectory, the evaluation and the correction. How to create operating conditions. 2. The data indicating the trajectory of the manipulated variable actually used for the operation control for changing the operating condition of the plant is stored in the form of a database, and the data retrieved from the database is stored as the initial data. The operating condition creating method for a process control system according to claim 1, wherein the operating condition is given as a trajectory of an operation amount. 3. The operating condition creation of the process control system according to claim 1, wherein the plant is divided into a plurality of regions in advance, and the setting of activation of the operating condition is executed for each region. Method. 4. A time-series trajectory of an operation amount used for actual operation by simulating a control amount indicating the control state of the plant from an operation amount indicating the operation state of the plant for controlling the operating condition change of the plant. In the process control system for creating the operation amount, the operation amount trajectory acquisition means for predetermining an evaluation criterion for the time series correlation between the operation amount and the control amount and the control amount, and giving an operation amount trajectory, A simulator that calculates the trajectory of the controlled variable using the given trajectory of the manipulated variable and the correlation, and whether or not the trajectory of the controlled variable obtained as a result of the calculation matches the evaluation criteria. If the evaluation means for executing the evaluation and the evaluation of the agreement cannot be obtained, the evaluation means corrects the trajectory of the given operation amount, and As the trajectory of the given operation amount, the trajectory of the operation amount is calculated when the trajectory of the control amount is calculated, the evaluation and the correction are repeatedly performed, and the trajectory of the operation amount when the evaluation of conformity with the control criterion is obtained is the operating condition. A process control system characterized by setting a trajectory. 5. In the actual operation of the plant, a first trajectory of a controlled variable calculated by the simulator and a second controlled variable obtained from the measurement result of the plant corresponding to the operating condition trajectory set. The process control system according to claim 4, further comprising fuzzy inference means for performing a process of comparing the orbit with the orbit and bringing the second orbit closer to the first orbit by a fuzzy inference process. 6. A time-series trajectory of an operation amount used for actual operation by simulating a control amount indicating the control state of the plant from an operation amount indicating the operation state of the plant for controlling the operation condition change of the plant. In a method for creating operating conditions of a process control system, a plurality of tanks obtained by dividing the plant are assumed, the relationship between the adjacent tanks for the control amount, and the operation amount for each of the tanks themselves. A calculation formula including a time-series relationship with the control amount is determined in advance, and the operation amount at the entrance of the plant is used as an initial value for all tanks using the calculation formula as a starting point from the start of brand switching. A method for creating operating conditions of a process control system, characterized in that the plant simulation is performed by calculating a time-series controlled variable.