JPS6354401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for controlling the concentration of a concentrated liquid to a desired set value using a solution concentrator.

A typical solution concentration control method conventionally used is shown in FIG. Stock solution inlet pipe 1 to concentrate can 11
2. Concentrate outlet pipe 13, steam pipe 14, vapor pipe 1
5 is connected, the flow rate detector 2 provided on the raw solution inlet pipe 12 is connected to an inlet flow rate controller 16, the inlet flow rate controller 16 is connected to the control valve 5, and the flow rate detector 2 provided on the concentrate outlet pipe 13 is connected. The outlet concentration detector 3 is connected to the outlet concentration controller 17.
is connected to the inlet flow rate controller 16, and forms a feedback control loop that controls the inlet stock solution flow rate _F1 in a cascade manner by adjusting the set value of the inlet flow rate controller 16 using the outlet of the outlet concentration controller 17.

The conventional control system is configured as described above and operates as follows. The outlet concentrate concentration D ₀ detected by the outlet concentration detector 3 is input to the outlet concentration controller 17, and the outlet concentration controller 17 calculates the deviation Z between the outlet concentrate concentration D ₀ and the set concentrate concentration (see Figure 2). ), the output MV is output to the inlet flow rate controller 16.

The inlet flow rate controller 16 compares the inlet stock solution flow rate set value adjusted by the output MV from the outlet concentration controller 17 and the inlet stock solution flow rate F1 detected by the stock solution flow rate detector ₂ , and based on the deviation,
The output is sent to the control valve 5, which is adjusted to manipulate the inlet stock solution flow rate _F1 .

FIG. 2 is a block diagram of a conventional concentrate concentration feedback control system. H _S is a transfer function of the converter with respect to the target value, H _d is a transfer function of the outlet concentration detector 3, and G _C is a transfer function of the PID operation of the outlet concentration controller 17. G _A is a transfer function of the entire operation end including the raw solution flow rate detector 2, inlet flow rate controller 16, and control valve 5. Also, G _P is the process transfer function of this concentrated liquid concentration control system. Furthermore, G _A and G _P are used as disturbances.
Between the inlet stock solution concentration D ₁ , stock solution flow rate F ₁ , evaporation amount G ₀ ,
Changes in outlet concentrate concentration _D0 , etc. are added.

The static characteristics of this process are given by the following equation from the mass balance of the concentrator.

D ₀ = F ₁ · D ₁ / F ₁ − G ₀ ...(1) Here, D ₀ is the outlet concentrate concentration, F ₁ is the inlet stock solution flow rate, D ₁ is the inlet stock solution concentration, and G ₀ is the evaporation amount. . That is, the control amount D ₀ changes according to the conditions expressed by equation (1) due to changes in the manipulated variable F ₁ and the disturbance D ₁ G ₀ .

Therefore, the process gain coefficient k _{P of} GP with the controlled variable D ₀ and the manipulated variable F ₁ can be obtained by differentiating equation (1) with respect to F ₁ and is as follows.

k _P = | G _P | _nax = dD ₀ / dF ₁ = −D ₁・G ₀ / (F ₁ − G ₀ ) ² …
…(2) When transformed using equations (1) and (2), k _P becomes as follows.

k _p = D ₁ − D ₀ / F ₁ − G ₀ ...(3) Therefore, the process gain coefficient k _P of G _P is determined by equation (3), and is determined by the elements of D ₁ D ₀ F ₁ G ₀ It changes over time.

Let k _t be the composite closed loop gain coefficient of the control system.
k _t is _{k t = | H d |}
Since G _C is a constant unless the PID is set and changed, the closed loop gain coefficient k _t depends on changes in the process gain coefficient k _P . Therefore, it can be seen that in order to keep the closed loop gain coefficient k _t constant in order to operate the system stably, it is necessary to change the PID constant of _GC according to the change in k _P.

Such conventional methods are widely used because they allow concentration control with a simple control device.
This method assumes that the control constants of the outlet concentration controller 17, that is, the three operating constants of proportional, integral, and differential (hereinafter referred to as PID constants), are adjusted to optimal values for the process characteristics at the design operating point. Good control can be expected.

However, if the design operating point is significantly changed or large disturbances such as changes in the inlet stock solution concentration D ₁ , stock solution flow rate F ₁ , or evaporation amount G ₀ occur, the process characteristics will change significantly, especially the process gain. is remarkable.

Therefore, when a change in process characteristics occurs, the closed-loop gain coefficient is adjusted to stabilize the system.
Good control cannot be expected unless the optimum PID constant is set again in order to keep k _t constant and the setting of the optimum PID constant is changed.

In order to set a new optimal PID constant when a change occurs in the process characteristics, it usually takes several tens of minutes to understand the process characteristics in the case of a process with a long dead time or time constant. Moreover, obtaining new optimal PID constants from the collected data of the process characteristics requires the help of an instrumentation engineer. These adjustment operations generally do not fit well with the operator's work, and therefore pose a major hindrance to operation.

Note that among the factors that change the process characteristics, the variation in the inlet stock solution concentration _D1 is an unexpected factor. The stock solution is manufactured in the first stage of the process of the concentrator, but there is generally no concentration control in the stock solution production process, and an example of concentration fluctuation is that the concentration is thin at the beginning of the production of the stock solution, and then it gradually becomes thicker until it reaches its peak and production ends. It becomes thinner as it approaches. Normally, this average value±variation is the inlet condition for the concentration can, and the biggest disturbance for concentration control in the concentration can 11 is concentration fluctuation of the stock solution.

With conventional methods, it is almost impossible to change the optimal PID constant of the outlet concentration controller 17 each time the process characteristics change due to fluctuations such as the inlet stock solution concentration _D1 . It was hot from work.

The present invention was developed in order to eliminate the drawbacks of the conventional solution concentrator control method as described above, and enables safe, high-quality, and stable automatic operation of the solution concentrator using a simple control method. The purpose of this invention is to provide a control method for

The present invention provides a method for controlling a solution concentrator in which the concentration of the concentrated liquid at the outlet is used as a control variable and the flow rate of the stock liquid at the inlet is used as the manipulated variable. Then, an operation is performed using the transfer function Y ₀ to output an output y, and from the output y, an output MV is obtained by PID operation based on a specific PID constant.
is calculated and output, the set value of the inlet stock solution flow rate is adjusted using the output MV, and the inlet stock solution flow rate F ₁ is controlled by the adjusted setting value, and the inlet stock solution flow rate is
F ₁ , the inlet stock solution concentration D ₁ , the evaporation amount equivalent amount G corresponding to the evaporation amount, and the outlet concentrated liquid concentration equivalent amount D corresponding to the outlet concentrated liquid concentration D ₀ are detected, and the process gain coefficient k _P is calculated using these values. This method of controlling a solution concentrator is characterized in that, when α is a fixed coefficient, the transfer function Y ₀ is selected such that Y ₀ =α/k _P and the calculation is performed.

FIG. 3 shows an embodiment of the present invention. Concentrate can 11
A stock solution inlet pipe 12, a concentrate outlet pipe 13, a steam pipe 14, and a vapor pipe 15 are connected to the pipes. The stock solution flow rate detector 2 provided in the stock solution inlet pipe 12 is connected to an inlet flow rate controller 16 and a computing unit 18, respectively, and the inlet flow rate regulator 16 is connected to the control valve 5. Further, the inlet stock solution concentration detector 1 provided in the stock solution inlet pipe 12 is connected to the computing unit 18 . An outlet concentration detector 3 provided on the concentrate outlet pipe 13 is connected to an outlet concentration controller 17 and a computing unit 18 . The evaporation amount detector 4 provided in the vapor pipe 15 is connected to a computing unit 18, the outlet concentration controller 17 is connected to the computing unit 18, the computing unit 18 is connected to the outlet concentration regulator 17, and the outlet concentration controller 17 is connected to the computing unit 18. The controller 17 is connected to the inlet flow controller 16.

One embodiment of the present invention is constructed as described above and operates as follows. The outlet concentrated liquid concentration D ₀ detected by the outlet concentration detector 3 is input to the calculator 18 and the outlet concentration controller 17, the evaporation amount G ₀ detected by the evaporation amount detector 4 is input to the calculator 18, and the inlet stock solution is The concentration _D1 of the inlet stock solution detected by the concentration detector 1 is calculated by the calculator 18.
input the inlet stock solution flow rate _F1 detected by the stock solution flow rate detector 2 into the inlet flow rate controller 16 and the calculator 18.
Enter.

The outlet concentration controller 17 compares the outlet concentrate concentration D ₀ inputted from the outlet concentration detector 3 with the set outlet concentrate concentration, and outputs the deviation Z to the calculator 18 .

The arithmetic unit 18 inputs the inlet stock solution flow rate F 1 , inlet stock solution concentration D ₁ , evaporation amount G 0 , which are respectively input from the stock solution flow rate detector 2, the inlet stock solution concentration detector 1, the evaporation amount detector ₄ , and the outlet concentration detector ₃ . Using the transfer function Y ₀ calculated as described below from the outlet concentrated liquid concentration D ₀ , the calculation is performed based on the deviation Z input from the outlet concentration controller 17 , and the obtained output y is transferred to the outlet concentration controller 17 .
Output to. The outlet concentration controller 17 inputs the output y from the calculator 18 and outputs the output MV calculated by PID operation to the inlet flow rate controller 16. The inlet flow rate controller 16 is the output from the outlet concentration controller 17.
MV is input, the inlet stock solution flow rate is adjusted and set using the input MV, and compared with the inlet stock solution flow rate _F1 input from the stock solution flow rate detector 2, and an output based on the deviation is output to the control valve 5. Adjust this to manipulate the inlet stock solution flow rate _F1 .

In FIG. 3, the computing unit 18 calculates the inlet stock solution flow rate F ₁ ,
Inlet stock solution concentration D ₁ , evaporation amount G ₀ , outlet concentrated solution concentration D ₀
It has a calculation function for the purpose of correcting the deviation Z using the above-mentioned transfer function Y ₀ calculated by calculating the amount of change in the process gain coefficient k _P due to a change in . This will be explained below.

FIG. 4 is a block diagram of a feedback control system according to the present invention. Y ₀ is a transfer function of the calculator 18 for automatic gain compensation, and the deviation Z from the outlet concentration controller 17 is passed through the transfer function Y ₀ to the input y of the transfer function G _C of the PID operation of the outlet concentration controller 17. The other parts are the same as the conventional method shown in FIG.

The composite closed loop gain coefficient of the control system of the present invention is
If k _t0 , k _t0 becomes k _t0 = |H _d |×|G _C |×|G _A |×Y ₀ ×k _P ……(5). By performing the calculation to make the value of Y ₀ ×k _P constant, the closed loop gain coefficient k _t0 becomes constant, resulting in an extremely stable control system. Here Y ₀
α is a fixed coefficient so that ×k _P is constant, and Y ₀
If we set ×k _P = α, then Y ₀ = α/k _P ...(6).

In this case _, the composite closed-loop gain coefficient k _t0 is k _t0 = |H _d | × | G _C | × | G _A | Both are constants, and the composite closed-loop gain coefficient
k _t0 remains constant.

Therefore, the transfer function Y ₀ in the calculator 18 is defined as the inlet stock solution flow rate F ₁ , the inlet stock solution concentration D ₁ , the outlet concentrate concentration
By calculating the process gain coefficient k _P calculated using equation (3) using the detected value of D ₀ and evaporation amount G ₀ using fixed coefficient α as shown in equation (6), PID can be calculated.
Synthetic closed-loop gain coefficient without changing constants
k _t0 can be kept constant, and system control can be stabilized easily and quickly.

Here, α can be given an arbitrary constant, but for example, if the value of the process gain coefficient based on process data at the design point is α _f , the inlet stock solution flow rate at the design point is f ₁ , the inlet stock solution concentration is d ₁ , and the evaporation amount is Assuming that g ₀ and the outlet concentrated liquid concentration are d ₀ , α _f is calculated from equation (3) as shown below.

α _f = d ₁ - d ₀ / f ₁ - g ₀ ...(8) Also, the instantaneous values of each quantity of the process in any state are expressed as the inlet stock solution flow rate F ₁ , the inlet stock solution concentration D ₁ , and the evaporation amount G ₀ ,
Assuming that the concentration of the concentrated liquid at the outlet is D ₀ , the calculation formula for the transfer function Y ₀ is obtained by substituting equations (3) and (8) into equation (6) as follows.

Y ₀ =F ₁ −G ₀ /D ₁ −D ₀ ×d ₁ −d ₀ /f ₁ −g ₀ ...(9) Now, assuming that each process quantity is in the design state, F ₁ = f ₁ , G ₀ = g ₀ , D ₁ = d ₁ , D ₀
= d ₀ , so Y ₀ =1. That is, in this case, the calculation of Y ₀ is not involved at all in the control system, and at the design point, the function is the same as the conventional method block diagram shown in FIG. Therefore, it is only necessary to set the PID constant of the outlet concentration controller 17 to an optimal value based on the process characteristics at the design point.

The correction deviation y, which is the input of the regulator G _C , is as follows.

y=Y ₀ ×Z ...(10) Z is the outlet concentrate concentration from the outlet concentrate concentration setting value
D is the deviation minus ₀ .

In the above explanation, the fixed coefficient α included in the equation (6) for Y ₀ is the process gain coefficient α _f at the design point, but α can take any value as described above.

For example, α may be set to 1. The point is that the PID constant of the concentration controller should be set to the optimal value for the set value of α, so it is not limited to the process gain α _f at the design point as in equation (8).

Next, another embodiment of the present invention will be described. Arithmetic unit 1
8 calculation elements F ₁ G ₀ D ₁ D ₀ are for each detector 1 in Fig. 3.
~4, but the evaporation amount G ₀ can be substituted by detecting the amount of supply of the heating source of the concentrator, for example, if steam is used as the heating source, the amount of steam supplied can be substituted as shown in the formula below. be able to. That is,
The evaporation amount G ₀ itself may be used as the evaporation amount equivalent amount, or the vapor amount F _S may be used.

G ₀ = k ₁・F _S + k ₂ ...(11) Here, F _S is the steam flow rate to be supplied, and k ₁ and k ₂ are G ₀ =
This is a constant for the relational expression f( _FS ) to hold true.

FIG. 5 shows a circuit diagram of a control method when the above points are adopted. In order to convert the steam flow rate F _S detected by the steam flow rate detector 6 installed in the steam pipe 14 into the evaporation amount _G0 , it is connected to a calculator 19 that calculates equation (11), and the output of the calculator 19 is It is input to the computing unit 21. Further, the outputs of the other detectors, such as the stock solution flow rate detector 2, the inlet stock solution concentration detector 1, and the outlet concentration detector 3, are input to the calculator 21 as in the example shown in FIG. In this case, the transfer function Y ₀ ' of the arithmetic unit 21 is determined by using equation (11) instead of G ₀ from equation (9), Y ₁ '=F ₁ − (k ₁・F _S + k ₂ )/D ₁ − D ₀ ×d ₁ −d ₀ /f ₁ −g ₀ …
...(12), and the calculation of equation (12) can also be an effective means of performing automatic gain compensation, similar to equation (9).

Further, another embodiment of the present invention will be explained with reference to FIG. A stock solution inlet pipe 12, a concentrate outlet pipe 13, a steam pipe 14, and a vapor pipe 15 are connected to the concentrator 11, respectively. The stock solution flow rate detector 2 provided on the stock solution inlet pipe 12 is connected to an inlet flow rate controller 16 and a computing unit 18, respectively, and the inlet flow rate regulator 16 is connected to the control valve 5. Further, the inlet stock solution concentration detector 1 provided in the stock solution inlet pipe 12 is connected to the computing unit 18 and the computing unit 22.

An outlet concentration detector 3 provided on the concentrate outlet pipe 13 is connected to an outlet concentration controller 17 and a computing unit 18 . The evaporation amount detector 4 provided in the vapor pipe 15 is connected to the computing device 18 and the computing device 22, the outlet concentration setting device 20 is connected to the outlet concentration controller 17 and the computing device 22, and the outlet concentration controller 17 is connected to the computing device 22. The computing unit 18 is connected to the outlet concentration controller 17, the outlet concentration controller 17 is connected to the computing unit 23, the computing unit 22 is connected to the computing unit 23, and the computing unit 23 is connected to the inlet concentration controller 17. It is connected to a flow rate controller 16.

In this embodiment, the outlet concentration controller 17 receives an outlet concentration setting value inputted from an outlet concentration setting device 20.
D _S and the outlet concentrated liquid concentration D ₀ inputted from the outlet concentration detector 3 are compared, and the deviation Z is calculated by the calculator 1.
Output to 8.

The arithmetic unit 18 inputs the inlet stock solution flow rate F 1 , inlet stock solution concentration D ₁ , evaporation amount G 0 , which are respectively input from the stock solution flow rate detector 2, the inlet stock solution concentration detector 1, the evaporation amount detector ₄ , and the outlet concentration detector ₃ . Transfer function Y ₀ calculated in the same manner as the example in FIG. 3 using the outlet concentrated liquid concentration D ₀
is used to calculate the deviation Z input from the outlet concentration controller 17, and output the obtained output y to the outlet concentration controller 17. The outlet concentration controller 17 inputs the output y from the calculator 18 and outputs the output MV _b calculated by PID operation to the calculator 23.

The calculator 22 calculates the value based on the inlet stock solution concentration D ₁ inputted from the inlet stock solution concentration detector 1 , the evaporation amount G ₀ inputted from the evaporation amount detector 4 , and the outlet concentration setting value D _S inputted from the outlet concentration setting device 20 . The output MV _f is calculated and output to the calculation unit 23. The calculator 23 calculates the output MV from the output MV _f from the calculator 22 and the output MV _b from the outlet concentration controller 17,
Output to the inlet flow rate controller 16.

Other operations are the same as the embodiment shown in FIG.

The calculation formula for MV _f in the calculator 22 is MV _f =G ₀ ·D _S /D _S −D ₁ . Here, G ₀ is the evaporation amount, D _S is the outlet concentration setting value, and D ₁ is the inlet stock solution concentration.

The calculation formula for MV in the calculator 23 is MV=MV _f -a+k·MV _b . Here, a is a constant and k is a coefficient.

Other calculations are the same as in the embodiment shown in FIG.

The present invention has the above-described configuration and operation, and is capable of clarifying factors that change process characteristics in a concentrate concentration feedback control system and a feedforward control system, and also to eliminate process gain coefficients that change without warning. By automatically compensating with temporal continuity, it is possible to control the concentration of the concentrated liquid in an extremely stable manner. In other words, the concentration remains constant regardless of changes in the process gain coefficient caused by changes in the inlet stock solution concentration D ₁ which is the main disturbance, changes in the inlet stock solution flow rate F ₁ which is the manipulated variable, changes in the amount of evaporation, changes in the desired exit concentrate concentration, etc. The PID setting value of the controller is completely automatically and continuously compensated without changing the initial setting value, and the PI and D setting values can be compensated automatically without requiring the labor of an instrumentation engineer. This control method enables operation under a wide range of operating conditions. As described above, the present invention enables safe and extremely stable continuous control of the solution concentrator, and has extremely great practical effects.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional control method, Fig. 2 is a block diagram of a conventional control method, Fig. 3 is a circuit diagram of an embodiment of the present invention, and Fig. 4 is a block diagram of a control method of the present invention. 5 and 6 are circuit diagrams of other embodiments of the present invention. 1... Inlet stock solution concentration detector, 2... Stock solution flow rate detector, 3... Outlet concentration detector, 4... Evaporation amount detector, 5... Control valve, 6... Steam flow rate detector, 11
... Concentrator can, 12 ... Raw solution inlet pipe, 13 ... Concentrate liquid outlet pipe, 14 ... Steam pipe, 15 ... Vapor pipe,
16... Inlet flow rate controller, 17... Outlet concentration controller, 18... Arithmetic unit, 19... Arithmetic unit, 20...
Outlet concentration set value, 21... computing unit, 22... computing unit, 23... computing unit.

Claims (1)

[Claims] 1. A method for controlling a solution concentrator in which the concentration of the concentrated solution at the outlet is the controlled variable and the flow rate of the raw solution at the inlet is the manipulated variable,
Deviation Z is calculated by comparing the outlet concentrated liquid concentration and the set value.
is output, an operation is performed using the transfer function _Y0 from the deviation Z, an output y is output, and a specific P.
The output MV is calculated and output by PID operation based on the ID constant, the set value of the inlet stock solution flow rate is adjusted by the output MV, the inlet stock solution flow rate F ₁ is controlled by the adjusted setting value, and the inlet stock solution flow rate F ₁ , inlet stock solution concentration D ₁ , evaporation amount G ₀ or evaporation amount equivalent value G,
Outlet concentrate concentration D ₀ or outlet concentrate concentration equivalent value D
and these values determine the process gain coefficient.
A method for controlling a solution concentrator, characterized in that when k _p is calculated and α is a fixed coefficient, the calculation is performed by selecting the transfer function Y ₀ such that Y ₀ =α/k _p . 2 Steam flow rate of the heating source as the evaporation amount equivalent value G
A method according to claim 1 using F _s .