JP2007321174A - Method for controlling acid concentration in pickling process, apparatus therefor, and method for producing steel sheet using them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which reduces a fluctuation of an acid concentration in a pickling tank caused by various factors, stabilizes a surface quality of a pickled metal sheet, and consequently enhances the production efficiency by increasing the pickling speed. <P>SOLUTION: A pickling facility for removing a scale of an oxide on the surface of a metallic sheet (2) by continuously passing the metallic sheet through pickling tanks (4A, 4B, 4C) for making the metallic sheet react with the acid solution therein. The method for controlling the acid concentration in the pickling tanks to a desired value comprises the steps of: determining an estimated value of the acid concentration in the pickling tank (S1), by using a dynamic model (30) which shows a balance among the inflow of the acid flowing into the pickling tank, the outflow of the acid flowing out of the pickling tank and the consumption of the acid due to a chemical reaction of the oxide scale and the acid solution; estimating the disturbance which causes the fluctuation of the acid concentration in the pickling tank from the difference between the estimated value of the acid concentration and the measured value of the acid concentration in the acid solution in the pickling tank (S2); determining an amount of the acid to be charged into the pickling tank, which is necessary for offsetting the influence of the estimated disturbance (S3); and controlling the amount of the acid to be charged according to the estimated amount (S4). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acid concentration control method and apparatus for a pickling process, and a steel plate manufacturing method using the same, and more particularly, to a pickling tank for reacting an acid solution suitable for use in a pickling process of a steel plate. In pickling equipment that removes oxide scale on the surface of a metal plate by continuously passing the plate, the acid concentration in the pickling tank can be controlled to a desired value. The present invention relates to a concentration control method / apparatus and a steel plate manufacturing method using these.

  The pickling process is a process of removing oxide scale on the surface of a metal plate such as a steel plate by reacting with an acid solution such as hydrochloric acid or sulfuric acid. Hereinafter, a steel plate will be described as an example.Generally, dip pickling that allows the steel plate to pass while immersed in a tank filled with an acid solution, jet pickling that allows the acid solution to pass while sprayed in a jet state in the tank, and the like. Are known. In any case, it is general that a plurality of pickling tanks are arranged in series so that they are sequentially passed from the upstream side (the entry side of the process).

  In the dip pickling, the acid solution is supplied to the most downstream tank, and the acid solution is supplied to the upstream tank by overflowing from the downstream tank.

  In the jet pickling, the acid solution is introduced into the most downstream tank and the intermediate tank, and the acid solution is supplied from the downstream tank to the upstream tank via a pump.

  In either case, the acid solution used in the uppermost stream tank is recovered, processed, and reused.

  Since the efficiency of pickling is strongly influenced by the acid concentration in the pickling tank, it is necessary to control the acid concentration in the pickling tank to be constant in order to keep the surface quality of the steel plate after pickling stable. become. Therefore, the concentration of the acid solution in the pickling tank is measured, and the amount of acid input to the pickling tank is manipulated based on the measured concentration.

  The consumption of acid consumed by chemical reaction with the oxide scale of the steel sheet in the pickling tank is the type of steel sheet, the density and properties of the oxide scale, the width of the steel sheet, the speed of the steel sheet passing through the pickling tank, It is greatly affected by the acid concentration and temperature in the pickling tank. When the operating conditions are changed, these change and the acid consumption rate changes. Therefore, the acid concentration changes unless an appropriate amount of acid is put into the acid tank.

  However, the amount of acid in the acid tank is much larger than the amount of acid input per unit time (also referred to as acid flow rate or acid input amount). Since it takes several hours to change, there is a problem that if the operation is performed after the change in the acid concentration is detected, there will be a large delay, and it will not be possible to cope with the change in the acid concentration accompanying the change in operating conditions.

  If the amount of acid input is insufficient, the acid concentration decreases and sufficient pickling cannot be performed, so that the scale remains on the surface of the steel sheet, resulting in defects. On the other hand, if the amount of acid added is excessive, pickling proceeds excessively and discoloration occurs on the surface of the steel sheet, resulting in defects. Further, the acid is wasted and the basic unit is deteriorated.

  Several methods have been disclosed for such a problem, but many of them specify factors affecting the efficiency of pickling, predict the impact on acid consumption, and feedforwardly evaluate the acidity. It controls the input amount.

  For example, Patent Document 1 discloses a method of predicting the influence of a change in operating state on a change in acid concentration in an acid tank using a model formula and operating the flow rate of the acid solution so as to cancel it.

  Patent Document 2 discloses a method of operating an acid input amount by obtaining an acid input amount and an acid input distribution ratio to two or more tanks using a scale thickness, a plate width, and a conveying speed of a steel plate.

  Further, Patent Document 3 discloses a method of manipulating the acid discharge amount and the acid solution temperature in jet pickling as a function of the plate thickness, material and hot rolling conditions of a steel plate.

  Further, in Patent Document 4, the descaling rate in the acid bath is determined from the state amount relating to the plate thickness, plate width, and scale amount of the steel plate, the acid concentration supplied to the pickling tank, the supply amount, the liquid temperature, the plate speed, and the like. A method for determining and determining an operation state based on the determination is disclosed.

Japanese Patent Application Laid-Open No. 60-135587 JP 2003-13268 A JP-A-1-254313 Japanese Patent Laid-Open No. 10-306391

  However, all of the methods disclosed in these documents specify factors affecting the pickling efficiency in the pickling tank or the amount of acid consumption, and manipulate the amount of acid input according to the influence of those factors. Therefore, there is a problem that if the influence is not required with high accuracy, the operation of the amount of acid input is insufficient or excessive.

  In addition, there is no effect on acid concentration fluctuations caused by factors not considered in each of the above documents. For example, for a state quantity that is difficult to measure, such as scale properties, it is difficult to estimate the effect in advance and manipulate the amount of acid input.

  Furthermore, since the steel plates are sequentially conveyed from the upstream tank to the downstream tank, the progress of the pickling process in the upstream tank affects the downstream pickling. For example, if sufficient pickling is performed on the upstream side, the amount of oxide scale to be removed on the downstream side is reduced, so that the amount of acid consumed in the downstream tank is reduced.

  Further, since the acid solution is sequentially supplied from the most downstream tank to the upstream tank, the acid concentration in the downstream tank affects the acid concentration in the upstream tank.

  In the conventional method, since the influence between such tanks is not taken into consideration, it was not possible to perform appropriate acid injection into each tank.

  Such a problem of the prior art exists in the idea itself that the factors affecting the fluctuations in pickling efficiency or acid consumption are limited, and the influence is predicted to manipulate the input amount of acid. In other words, there are factors other than those cited in the cited literature, and it is extremely difficult to accurately estimate the influences on the pickling efficiency or acid consumption fluctuation. Further, the conventional technology cannot deal with the acid solution brought out by the steel plate to the downstream tank or the influence between the tanks described above.

  The present invention has been made in order to solve the above-mentioned problems, reduces fluctuations in the acid concentration in the pickling tank due to various factors, keeps the surface quality of the steel sheet after pickling stable, and thus pickling speed. It is an object to provide a technology for improving production efficiency by improving production.

  The present invention provides a pickling facility for removing oxide scale on the surface of the metal plate by continuously passing the metal plate through a pickling bath in which the acid solution is reacted. The amount of acid flowing into the pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by the chemical reaction between the oxide scale and the acid solution From the difference between the acid concentration estimated value and the acid concentration measured value of the acid solution in the pickling tank, the acid concentration estimated value in the pickling tank is obtained by a dynamic model representing the balance between The amount of acid input to the pickling tank required to offset the influence of the estimated disturbance is determined, and the amount of acid input is manipulated according to the amount of input. This solves the above-mentioned problem.

  The present invention also provides an acid concentration in the pickling tank in the pickling equipment for removing oxide scale on the surface of the metal plate by continuously passing the metal plate through a pickling tank in which the acid solution is reacted. In the acid concentration control device of the pickling process controlled to a desired value, the amount of acid flowing into the pickling tank, the amount of acid flowing out from the pickling tank, the chemistry of oxide scale and acid solution By means of a dynamic model representing the balance of the consumption of acid consumed by the reaction, means for obtaining an acid concentration estimated value in the pickling tank, an acid concentration estimated value obtained by the means and the acid washing tank From the difference from the acid concentration measurement value of the acid solution, a means for estimating a disturbance that causes fluctuations in the acid concentration in the pickling tank, and a method to the pickling tank that is necessary to offset the influence of the estimated disturbance Means for determining the amount of acid input, and input determined by the means According By and means for operating the input amount of acid, and is obtained by solving the above problems.

  Further, the present invention removes the oxide scale on the surface of the metal plate by arranging a plurality of pickling baths for reacting the acid solution in series and continuously passing the metal plates through the plurality of pickling baths. In pickling equipment, in order to control the acid concentration in the pickling tank to a desired value, the amount of acid flowing into each pickling tank, the amount of acid flowing out from the pickling tank, and the oxidation A dynamic model representing the balance between the product scale and the amount of acid consumed by the chemical reaction of the acid solution is used to obtain an estimated acid concentration value in each of the pickling tanks. In order to estimate the disturbance that causes the acid concentration fluctuation in the pickling tank for each pickling tank from the difference from the acid concentration measurement value of the pickling tank, and to offset the influence of the disturbance estimated for each pickling tank The amount of acid input to the pickling tank required for the By operating the input amount of acid to it is obtained by solving the above problems.

  Further, the present invention removes the oxide scale on the surface of the metal plate by arranging a plurality of pickling baths for reacting the acid solution in series and continuously passing the metal plates through the plurality of pickling baths. In the acid concentration control device of the pickling process for controlling the acid concentration in the pickling tank in the pickling equipment to a desired value, the amount of acid flowing into each of the pickling tanks and the acid pickling tank flows out of the pickling tank Means for obtaining an estimated acid concentration value in each of the pickling tanks by means of a dynamic model representing the balance between the acid effluent amount and the acid consumption consumed by the chemical reaction between the oxide scale and the acid solution; Means for estimating, for each pickling tank, a disturbance that causes fluctuations in the acid concentration in the pickling tank from the difference between the acid concentration estimated value obtained in step 1 and the acid concentration measured value of the acid solution in the pickling tank. Necessary to offset the effects of disturbance estimated for each pickling tank Means for determining the amount of acid input to the pickling tank, and means for manipulating the amount of acid input to each pickling tank according to the input amount determined by the means. It has been solved.

  The present invention also provides a method of manufacturing a steel sheet having a pickling process by a pickling facility, wherein the acid concentration control method is used in the pickling facility. .

  The present inventor does not adopt the conventional method of limiting the factor and predicting the influence thereof, but treats the influence on the fluctuation of the acid concentration due to various factors as a disturbance collectively, and estimates and cancels it. A new method of manipulating the amount of acid input was conceived.

  Also, as a method of estimating this disturbance, the acid concentration in the pickling tank is estimated using a dynamic model representing the balance of inflow, outflow and consumption of the acid in the pickling tank, and the estimated value and the measured acid concentration value Invented a new method of estimating from the difference between the two.

  According to the present invention based on these ideas, the factors causing the acid concentration fluctuation in the pickling tank are collectively regarded as disturbances, and the disturbances are pickled by a dynamic model representing the acid concentration balance in the pickling tank. Estimate from the difference between the acid concentration estimated value in the tank and the acid concentration measured value, determine the amount of acid input to the pickling tank so as to offset the effect, and manipulate the acid input amount according to this input amount I am doing so. Therefore, even if the acid concentration varies due to any factor, it is possible to quickly change the amount of acid input before the acid concentration largely fluctuates due to the factor, and the acid concentration variation can be reduced.

  In addition, the only necessary measurement item is the acid concentration in the pickling tank, and it is not necessary to individually measure the factors that cause acid concentration fluctuations, so there is no need for a device that measures the thickness of the scale, the temperature of the acid solution, etc. There is also an effect that the cost of existing devices and the maintenance load thereof can be suppressed.

  In particular, it represents the balance between the amount of acid flowing into each pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by the chemical reaction between the oxide scale and the acid solution. Using the dynamic model, the estimated acid concentration in each pickling tank is obtained, and the fluctuation of the acid concentration in the pickling tank is determined from the difference between the obtained acid concentration estimated value and the acid concentration measured value of the acid solution in the pickling tank. For each pickling tank, determine the amount of acid input to the pickling tank necessary to offset the influence of the disturbance estimated for each pickling tank, and according to this determined input amount When the amount of acid input to each pickling tank is controlled, a plurality of pickling tanks for reacting the acid solution are arranged in series, and a metal plate is continuously passed through these pickling tanks. Simple and sufficient in pickling equipment that removes oxide scale on the surface of the metal plate Control accuracy is obtained, adjustment can be easily in the control system of the actual process.

  An embodiment of the present invention will be described based on a flowchart shown in FIG.

  In the present invention, in a pickling facility that removes oxide scale on the surface of a metal plate by continuously passing a metal plate such as a steel plate through a bath in which the acid solution is reacted, the acid concentration in the pickling bath is set to a desired value. In controlling to the value, first, it represents the balance of the amount of acid flowing into the pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by chemical reaction with the oxide scale. An acid concentration estimated value in the pickling tank is obtained by a dynamic model (step S1).

  The role of the dynamic model is to output the value that the acid concentration should take as an estimated value when it is assumed that there is no disturbance that affects the acid concentration in the pickling tank, which is a standard model.

  In the actual pickling process, the density and properties of the oxide scale, the width of the metal plate, the speed of the metal plate passing through the pickling tank, the temperature of the acid solution, the inflow of the acid solution from the downstream bath and the upstream side The acid concentration changes due to various causes, such as outflow to the tank, pickling efficiency in the upstream tank, and removal of the acid solution from the metal plate.

  However, in the present invention, these are collectively regarded as disturbances, and it is considered that the deviation between the actual acid concentration in the pickling tank and the estimated value based on the norm model is caused by the disturbances.

  The disturbance is estimated from the difference between the acid concentration measurement value in the pickling tank and the estimated value based on the reference model one after another (step S2), and the acid to the pickling tank necessary to offset the influence of the estimated disturbance is estimated. (Step S3), the acid input amount is manipulated according to the input amount (step S4), and the acid concentration is controlled.

  By canceling the disturbance with such a method or apparatus, the influence of the disturbance can be canceled before the acid concentration fluctuation due to the influence of the disturbance becomes apparent. With this effect, any disturbance that affects the acid concentration can be strongly suppressed.

  Here, in order to estimate the disturbance from the difference between the acid concentration measured value in the pickling tank and the estimated value based on the reference model, a method by inputting the difference between the acid concentration measured value and the estimated value in the inverse model of the dynamic model Is desirable.

  The dynamic model representing the acid concentration balance in the pickling tank can be expressed as a differential equation or difference equation in the time domain, and as a transfer function of a continuous time system or a discrete time system in the frequency domain.

  In order to obtain the inverse model of the dynamic model, it is preferable to use a transfer function, which can be easily obtained by simply taking the inverse of the transfer function.

  However, since this transfer function is a first-order lag system, a pure differential term appears only by taking the reciprocal number and cannot be realized. To prevent this, it is desirable to connect low-pass filters in series to the inverse model, and to make the product of them a proper transfer function (the numerator order being equal to or less than the denominator order).

  Embodiments according to the present invention will be described below with reference to the drawings.

  As shown in FIG. 2, the pickling process to which this embodiment is applied is a pickling tank 4A, 4B, 4C for pickling the steel plate 2 as a metal plate, and a circulation for supplying an acid solution to these pickling tanks. Tanks 6A, 6B, 6C, an acid supply tank 8 for storing acid solution to be fed into the circulation tank, a waste acid storage tank 10 for storing surplus acid solution, and an acid concentration control device for determining the amount of acid to be charged 12, pumps 14A, 14B, 14C, 15A, 15B, 15C, 16 for sending out the acid solution between the tanks and tanks, and valves 18A, 18B, 18C, 20B, 20C for adjusting the amount to be sent out. . The pickling tank is the first tank 4A, the second tank 4B, and the third tank 4C from the upstream side.

  These pickling tanks include sources 22A, 22B, 22C with pumps for sending the acid solution from the circulation tanks 6A, 6B, 6C, and drains 24A, 24B, 24C for returning the acid solution used for the pickling to the circulation tank. The acid concentration meters 26A, 26B, and 26C for measuring the acid concentration in the tank are installed. Although not shown, the pickling tank is provided with a jet tube that sprays the acid solution onto the surface of the steel sheet.

  The pumps include pumps 14A, 14B, and 14C that send acid solution from the circulation tank, pumps 15A, 15B, and 15C that send excess acid solution to the adjacent circulation tank and waste solution storage tank, and supply tanks. There is a new acid solution supply pump (also referred to as an acid solution supply pump) 16 for supplying a new acid solution to the circulation tank.

  The valves include valves 18B and 18C that adjust excess acid solution to the adjacent circulation tanks 6A and 6B, valves 18A that adjust excess acid solution to the waste acid storage tank 10, and acids from the supply tank 8. There are valves for adjusting the liquid (also referred to as acid liquid supply adjusting valves) 20B and 20C.

  The acid concentration control device 12 has a connection for inputting concentration data from the concentration meters 26A, 26B, and 26C and a connection for outputting to the valve.

  Each pickling tank 4A, 4B, 4C is connected to circulation tanks 6A, 6B, 6C for supplying an acid solution via pumps 14A, 14B, 14C.

  In the pickling process to which this embodiment is applied, the steel plate 2 is sequentially passed through three pickling tanks 4A, 4B, and 4C, and jet pickling is performed.

  The acid solution in the circulation tanks 6A, 6B, and 6C is sprayed from the jet pipe in the pickling tank to the steel plate surface by the pumps 14A, 14B, and 14C, and the scale on the steel plate surface is dissolved and removed. The acid solution in each pickling tank is returned to the circulation tanks 6A, 6B, and 6C connected thereto and reused.

  The acid concentration control in the pickling tank is performed by charging the acid solution in the acid supply tank 8 into the circulation tanks 6B and 6C of the second tank and the third tank via the pump 16 and valves 20B and 20C.

  Further, in order to control the liquid level in the circulation tank, the surplus acid solution in the circulation tank 6C of the third tank is transferred to the circulation tank 6B of the second tank via the pump 15C and the valve 18C. The surplus acid solution in the circulation tank 6B passes through the pump 15B and the valve 18B to the first tank circulation tank 6A, and the surplus acid solution in the first tank circulation tank 6A passes through the pump 15A and valve. It is sent to the waste acid storage tank 10 via 18A.

  Thereby, the liquid level in each circulation tank is kept constant. The acid solution in the waste acid storage tank 10 is subjected to chemical treatment and reused.

  The acid concentration in each pickling tub is measured at regular intervals by the acid concentration meters 26A, 26B, and 26C, and the acid is charged according to the control algorithm of the acid concentration controller 12 based on the measured value and the acid concentration setting value. The amount of acid is determined, and the amount of acid charged into the circulation tanks 6B and 6C of the second tank 4B and the third tank 4C is adjusted by opening the valves 20A and 20C. Thereby, the acid concentration control of each pickling tank is automatically performed. In this embodiment, the present invention is applied to an acid concentration control algorithm for each pickling tank.

  Next, a dynamic model representing the acid concentration balance in the pickling tank will be described.

  The acid concentration in the pickling basin is the amount of acid contained in the pickling basin (injection amount) and the amount of acid contained in the pickling basin from the downstream pickling basin (inflow amount). It varies depending on the balance between the amount of acid contained in the acid solution flowing out to the upstream pickling tank (outflow amount) and the amount of acid consumed by the chemical reaction with the oxide scale. This relationship can be expressed by the following three differential equations (1) to (3) for each pickling tank.

  Here, the variables used in the model are as follows.

u ₂ : Actual amount of acid input to the second tank (m ³ / h)
u ₃ : Actual amount of acid input to the third tank (m ³ / h)
C ₁ : Estimated value of acid concentration in the first tank (%)
C ₂ : Prediction value of acid concentration in the second tank (%)
C ₃ : Prediction value of acid concentration in the third tank (%)
d ₁ : disturbance estimated value to the first tank (m ³ / h)
d ₂ : Estimated disturbance value to the second tank (m ³ / h)
d ₃ : estimated disturbance value to the third tank (m ³ / h)

  The parameters used in the model are as follows.

V ₁ : Amount of acid solution in the first tank (m ³ )
V ₂ : Acid amount of the second tank (m ³ )
V ₃ : Amount of acid solution in the third tank (m ³ )
k ₁ S ₁ : product of reaction constant and scale amount in the first tank (m ³ / h)
k ₂ S ₂ : product of reaction constant and scale amount in the second tank (m ³ / h)
k ₃ S ₃ : product of reaction constant and scale amount in the third tank (m ³ / h)

  The left side of the model formulas (1), (2), and (3) is the differential amount of the acid concentration in each tank, and the right side represents the variation in the amount of acid due to the inflow and outflow of the acid solution and chemical reaction.

  For example, the first term on the right side of the expression (3) represents the amount brought into the acid tank per unit time by the acid solution put into the third tank 4C, and this is divided by the amount of the acid solution. It becomes an acid concentration fluctuation component by acid input.

  Further, since the amount of the acid solution in the acid tank is kept constant, an amount of acid solution equal to the amount of the charged acid solution flows out to the second tank 4B, so that the acid concentration and acid in the third tank 4C Acid is lost by the product of the input. The second term of the equation (3) represents this.

  Similarly, the third term represents the amount of acid consumed lost by the chemical reaction between the acid and the scale of the steel sheet. The consumption of acid lost per unit time is proportional to the rate of chemical reaction, which can be expressed as the product of acid concentration and scale amount.

Here, d ₁ , d ₂ , and d ₃ depend on the type of steel sheet, the density and properties of the oxide scale, the width of the steel sheet, the speed of the steel sheet passing through the pickling tank, the acid concentration and temperature in the pickling tank, and the like. It is a disturbance term representing acid concentration fluctuations, and it is a feature of the present invention that they are collectively handled without distinguishing what causes these disturbances.

  Next, disturbance estimation will be described.

  The right side of the above formulas (1) to (3) includes the acid concentration and the acid input in the form of a product, which is a nonlinear differential equation. In the present invention, the disturbance is estimated. Since the inverse model of the dynamic model is used, it is easier to use a linearized model.

  Therefore, the equations (1) to (3) are linearized around the steady state, and Laplace transform is performed to express them as a transfer function. In FIG. 3, the dynamic model 30 representing the acid concentration balance includes the first tank dynamic model 32, the second tank dynamic model 34, the third tank dynamic model 36, and the disturbance estimation filter 40 as the second tank dynamic model 30. 42 shows a tank dynamic model inverse model added with a low-pass filter 42 and a tank 3 dynamic model inverse model added with a low-pass filter 44.

The disturbance estimation d _2e or d _{3e multiplies} the difference between the acid concentration estimated value C ₂ or C ₃ by the dynamic model 30 and the acid concentration measured value C _{2_actual} or C _{3_actual by} the product 42 or 44 of the inverse model and the low-pass filter, respectively. Is required. This principle will be described below.

  The manipulated variable (in this case, the amount of acid input) is x, the controlled variable (in this case, the acid concentration) is y, and the transfer function from the manipulated variable to the controlled variable is P. It is assumed that a disturbance d is added to the operation amount. This relationship is as shown in equation (4).

       y = P (x + d) (4)

Assuming that the model is accurate, the output y _e of the model is as follows:

y _e = Px (5)

  By subtracting the equation (4) from this equation (5) and multiplying by the inverse model 1 / P, the following equation is obtained.

d = (y−y _e ) / P (6)

  However, in many cases, since the transfer function is proper (the numerator order is equal to or less than the denominator order), the inverse model becomes unrealizable because the numerator order is larger than the denominator order.

  Therefore, F / P becomes proper by using a low-pass filter F as shown in equation (7).

_{d e = F (y-y} e) / P = Fd ··· (7)

Here, the left side of d _e of equation (7), an estimate of the disturbance d, is equivalent to that observed by the action of low pass filter F to the disturbance d.

  In the case of the present invention, the dynamic model P of each tank is a model obtained by linearizing the first-order differential equations (1) to (3). Therefore, if expressed by a transfer function, the first-order lag as shown in FIG. Become a system. That is, in the case of the third tank model, the following equation is obtained.

Here, f ₃ , g ₃ , and h ₃ are parameters obtained from the equation (3).

Therefore, a first-order low-pass filter is used as F and multiplied by the inverse model 1 / P so that F / P becomes proper. If the constant and Q ₃ when, the following equation.

  From the equations (9) and (8), the disturbance estimation filter F / P becomes the following equation.

Therefore, if x = u ₃ and y _e = C ₃ , the following expression (11) is obtained from the expressions (5) and (8).

  Similarly, the following equation (12) is obtained from the equations (7) and (9).

Therefore, the estimated disturbance value d _3e is obtained from the equations (11) and (12).

Here, C _{3_actual} is the actual acid concentration value of the third tank 4C.

Next, a recommended acid input amount u _{3 is obtained} by the following equation (13) based on the estimated disturbance value d _3e .

u ₃ = −d _3e (13)

At this time, from the equation (7), u ₃ = −Fd ₃ (14)
_Therefore, from the equation (4), C _{3_actual} = P (u ₃ + d ₃ ) = P (1−F) d ₃ (15)
Thus, the influence of the disturbance d ₃ on the control amount C ₃ is multiplied by 1-F. 1-F is almost 0 in the low frequency range, and the influence of the disturbance d does not appear in the control amount y.

  Next, a simulation was performed on this example, and a comparison with a method by manual control was performed.

  FIG. 4 shows the actual amount of acid input by manual control and the actual acid concentration value at that time. The amount of acid input to the third tank 4C and the second tank 4B is manipulated corresponding to the acid concentration fluctuation, but a fluctuation of about ± 2% is seen in the acid concentration results. The target value of the acid concentration is indicated by a thick broken line in FIG.

  FIG. 5 shows the estimated disturbance value according to the present invention, and FIG. 6 shows the recommended value of the acid input amount according to the present invention and the value predicted by the model of the acid concentration when it is applied in the case of the manual control in FIG. Shown again.

The actual value in the case of manual control is indicated by a thick broken line in FIG. In addition, the time constant Q _{3 in the} equation (9) is set to 1 [hour], and the acid input recommended value u obtained by the equation (13) is set to 1 [m ³ / hour] for comparison with the acid input amount by manual control. Discretized in units of.

  In the case where the present invention is applied, the acid input amount operation is finely made based on the estimated disturbance value, and as a result, the fluctuation of the acid concentration is reduced to about ± 1%. I understand more.

  In this embodiment, the acid input amount of the second tank 4B is determined based on the estimated disturbance value to the second tank 4B, but if the acid input amount to the third tank 4C is operated, The influence on the acid concentration of the second tank 4B due to can be considered. However, since the influence is due to the acid concentration fluctuation to the third tank 4C, it can be almost ignored as compared with the change caused by the acid input to the second tank 4B.

  Therefore, in this example, a method was adopted in which the disturbance was estimated for each tank and the amount of acid input was determined for each tank. This method is very practical because a simple and sufficient control accuracy is obtained and adjustment in the control system of the actual process is easy.

  Moreover, the metal plate to which the present embodiment is applied is not limited to a steel plate, and may be a metal such as copper or aluminum.

  In addition, by using the acid concentration control method and apparatus as described above for the steel sheet manufacturing method and apparatus, the acid concentration fluctuation in the pickling tank due to various factors is reduced, and the surface quality of the steel sheet after pickling is stabilized. Therefore, it is possible to provide a method for producing a steel sheet that improves production efficiency by increasing the pickling speed.

The flowchart which shows the procedure which concerns on this invention Explanatory drawing which shows typically the structure of the pickling process which applied the Example Block diagram showing dynamic model and disturbance estimation filter representing acid concentration balance according to the present invention Diagram showing actual values of acid input and acid concentration by manual control Diagram showing estimated disturbance value based on this embodiment The diagram which shows the comparison of the acid input amount based on a present Example, the predicted value of the acid concentration when operating based on it, and the actual value of the acid input amount and acid concentration by manual control

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Steel plate 4A, 4B, 4C ... Pickling tank 6A, 6B, 6C ... Circulation tank 8 ... Acid feed tank 10 ... Waste acid storage tank 12 ... Acid concentration control device 16 ... Acid solution supply pump 20B, 20C ... Acid solution supply Adjustment valve 26A, 26B, 26C ... acid concentration meter

Claims (5)

In a pickling facility that removes oxide scale on the surface of the metal plate by continuously passing the metal plate through a pickling bath that reacts with the acid solution, the acid concentration in the pickling bath is controlled to a desired value. In doing
A dynamic model representing the balance between the amount of acid flowing into the pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by the chemical reaction between the oxide scale and the acid solution By obtaining the acid concentration estimated value in the pickling tank,
From the difference between the acid concentration estimation value and the acid concentration measurement value of the acid solution in the pickling tank, estimate the disturbance that causes the acid concentration fluctuation in the pickling tank,
Obtain the amount of acid input to the pickling tank necessary to offset the influence of the estimated disturbance,
An acid concentration control method for a pickling process, characterized in that the amount of acid input is manipulated according to the amount of input. The acid concentration in the pickling tank is controlled to a desired value in the pickling equipment for removing the oxide scale on the surface of the metal plate by continuously passing the metal plate through the pickling tank in which the acid solution is reacted. In the acid concentration control device of the pickling process,
A dynamic model representing the balance between the amount of acid flowing into the pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by the chemical reaction between the oxide scale and the acid solution Means for obtaining an estimated acid concentration value in the pickling tank;
Means for estimating the disturbance that causes the acid concentration fluctuation in the pickling tank from the difference between the acid concentration estimated value obtained by the means and the acid concentration measurement value of the acid solution in the pickling tank;
Means for determining the amount of acid input to the pickling tank necessary to offset the influence of the estimated disturbance;
Means for manipulating the acid charge according to the charge determined by the means;
An acid concentration control apparatus for a pickling process, comprising: A plurality of pickling tanks for reacting the acid solution in series, in the pickling equipment to remove the oxide scale on the surface of the metal plate by continuously passing the metal plate through the plurality of pickling tanks, In controlling the acid concentration in the pickling tank to a desired value,
Dynamic representing the balance between the amount of acid flowing into each pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by the chemical reaction between the oxide scale and the acid solution By the model, the acid concentration estimated value in each pickling tank is obtained,
From the difference between the acid concentration estimated value and the acid concentration measurement value of the acid solution in the pickling tank, a disturbance causing the acid concentration fluctuation in the pickling tank is estimated for each pickling tank,
Find the amount of acid input to the pickling tank necessary to offset the influence of disturbance estimated for each pickling tank,
An acid concentration control method for a pickling process, characterized in that the amount of acid fed into each pickling tank is manipulated according to the amount fed. A plurality of pickling tanks for reacting the acid solution in series, and the acid in the pickling equipment for removing oxide scale on the surface of the metal plate by continuously passing the metal plate through the plurality of pickling tanks In the acid concentration control device of the pickling process for controlling the acid concentration in the washing tank to a desired value,
Dynamic representing the balance between the amount of acid flowing into each pickling tank, the amount of acid flowing out from the pickling tank, and the amount of acid consumed by the chemical reaction between the oxide scale and the acid solution Means for obtaining an estimated acid concentration value in each pickling tank according to the model;
From the difference between the acid concentration estimated value obtained by the means and the acid concentration measurement value of the acid solution in the pickling tank, the disturbance that causes the acid concentration fluctuation in the pickling tank is estimated for each pickling tank. Means,
Means for determining the amount of acid input to the pickling tank necessary to offset the influence of disturbance estimated for each pickling tank;
Means for operating the amount of acid input to each pickling tank according to the amount of input determined by the means;
An acid concentration control apparatus for a pickling process, comprising: A method for producing a steel sheet having a pickling process by a pickling facility,
A method for producing a steel sheet, wherein the acid concentration control method according to claim 1 or 3 is used in the pickling equipment.

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