JPS60141881A - Method for controlling concentration of pickling solution - Google Patents

Abstract

PURPOSE:To pickle stably a steel strip and to prevent generation of sludge in a pickling soln. by charging continuously fresh acid to a specified amt. of the pickling soln. circulated between a pickling tank and a circulation tank and withdrawing continuously the pickling soln. exceeding the specified amt. therefrom. CONSTITUTION:The fresh acid in a storage tank 14 is supplied by a metering pump 16 into a circulation tank 6 and at the same time water for adjusting concn. is supplied through a water feed pipe 20 into the tank 6. The ratio between the fresh acid and water in this case is determined from the target acid concn. and the total amt. of the fresh acid and water is determined by the prescribed equation. The pickling soln. in the tank 6 adjusted to the prescribed concn. in the above-mentioned way is pumped 7 through a heat exchanger 13 into a pickling tank 1. The pickling soln. used for pickling of a steel strip 2 in the tank 1 has some carry-over by the evaporation and the strip 2 but is mostly returned through an overflow pipe 12 into the tank 6. While the pickling soln. is circulated in such a way, the fresh acid and water are replenished into the soln. in the tank 6 and therefore only the soln. equiv. to the difference between the increase and the decrease in the tank 1 is stored temporarily in a waste acid tank 24 through an overflow pipe 26.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for controlling the concentration of a pickling solution to a predetermined value in a pickling apparatus for continuously pickling a copper strip.

Prior art and its problems In general, copper strips are pickled after hot rolling or cold rolling for the purpose of removing oxidized scale etc. from the surface of the copper strip.
The most important control items in this pickling process are related to the temperature and concentration of the pickling solution. In particular, when pickling stainless steel, several types of acids such as sulfuric acid, hydrofluoric acid, and nitric acid are used, so concentration control is very complicated.

Conventionally, to control the concentration of the pickling solution, the acid concentration and metal concentration (for example, peso, This is done by extracting all the waste acid and adding new acid to return it to a predetermined concentration.

However, in such a patch-like concentration control method, since the concentration control is batch-like, there is a large concentration change before and after the concentration adjustment by removing waste acid and adding new acid, as shown by A in Figure 5. However, there was a problem that stable pickling was not possible.

In addition, if the concentration adjustment is infrequent, the metal concentration will increase, and sludge such as F6SO, for example, will precipitate and accumulate at the bottom of the pickling tank. The pickling solution in the tank must be drained and the sludge that has accumulated and solidified at the bottom of the pickling tank must be removed, which is a problem not only in terms of worker safety but also in terms of production efficiency. Furthermore, since the waste acid is used in batches, the amount of waste acid per batch is large, and therefore there is a problem in that large waste acid equipment is required.

Object and Structure of the Invention An object of the present invention is to solve the above-mentioned problems, and according to the present invention, a pickling solution is circulated between a pickling tank and a circulation tank connected thereto, For example, a predetermined amount of new acid with a predetermined concentration is continuously replenished into this circulating pickling solution in a pickling tank or a circulation tank, and when the pickling solution exceeds a certain amount, all waste acid is continuously extracted from the circulation tank. (8) The concentration of the pickling solution is kept almost constant.

As described above, the present invention involves continuously adding all of new acid to a certain amount of pickling solution circulated between a pickling tank and a circulation tank,
The main idea is to suppress the generation of sludge and maintain a constant acid concentration without impeding the pickling ability of the strip by continuously extracting the pickling liquid that exceeds a certain amount as all waste acid. be.

First, the supply and discharge balance of the pickling liquid in the pickling tank will be explained with reference to Fig. 1. The pickling liquid amount balance equation is expressed by the following equation.

Furthermore, it is basically assumed that there will be no cases of children bringing in acid through IJ Tsubu.

VH = Vy +Vy + Vo (1) In the above formula ■n: new acid input amount (m8/Hr) ■w: acid extraction fi (m8/)Ir)Vv: M total amount (m
8/1(r) Acid removal by VO Nitrip (4) Before (m/T(r)) Moreover, the balance equation for the amount of eluted metal is as follows.

M dD =2-a-b-v・60-dt-D(Vw+
Vo) atM: Amount of pickling solution Cm) D = Metal concentration in pickling solution (kg/I [18) α Required amount of metal elution from the strip surface (#/m8) b = Strip width (m) V: Pickling speed (m/m1n) t: Time (Hr) Rewriting the above equation gives the following equation. When solving by inserting the initial condition (t=0-+D=O) into the above equation, the following equation is obtained.

Furthermore, in equation (2), equation (2) is shown in a graph as shown in FIG. In other words, if the pickling solution is always withdrawn by Vw and new acid is added by Vn, it can be seen that the metal concentration in the pickling solution becomes saturated to "/B" as time t increases. In terms of operation, the pickling ability is affected by the size of crop A.
Alternatively, since it affects the generation of sludge, A/B may be controlled by the pickling liquid withdrawal amount Vw and the new acid input amount Vn.

By the way, as the metal concentration increases, the pickling ability decreases,
In other words, it is necessary to reduce the pickling speed. Generally, there is a relationship between the metal concentration and the pickling speed V as shown in the following equation.

■=βe−rD (3) In the above equation, β and γ are coefficients of 6 D, (8)
The relationship between the equations is shown in a graph as shown in FIG.

Therefore, if the pickling speed V is determined from the production plan and equipment capacity, the upper limit of the metal concentration in the pickling solution can be determined from equation (3). Note that β in equation (8).

γ must be determined in advance through experiments or the like.

As described above, by calculating the metal concentration in the pickling solution caused by a predetermined pickling speed using equation (8) and substituting this metal concentration into equation (2), the amount of acid solution Vw can be calculated. be done. Therefore, the new acid input amount Vn to be replenished can be determined from equation (1). Note that the required metal elution lid α needs to be determined in advance through experiments or the like.

As is clear from the above, the pickling solution is Vym/
The new acid is extracted continuously at a flow rate of Hr, and at the same time, the new acid is
By charging and replenishing at a flow rate of Hm 8/Hr, the metal concentration in the pickling solution can be kept constant.

However, in reality, it is difficult to accurately measure the amount of evaporation and the amount taken out by the strip, so by controlling only the amount of new acid input and also the amount of waste acid taken out, It is possible to control the washing liquid concentration so as to keep it stable.

Embodiment of the Invention FIG. 4 shows an embodiment of the invention based on the above-mentioned idea. In the figure, 1 is the pickling tank, and 2 is the pickling liquid 8 in the pickling tank 1.
The strip is dipped into the paper and transported perpendicular to the page. The pickling tank 1 is connected to a circulation tank 6 through an inlet pipe 4 and a discharge pipe 5, and the pickling liquid is circulated between the pickling tank 1 and the circulation tank 6 by means of a bong provided in the inlet pipe 4. It is configured. Valves 8, 9. No. 11 is installed and pickling tank 1
A circulation overflow pipe 12 is connected to the lower end of the outlet side of the pickling tank 1, bypassing the valve 10, and connecting the overflow pipe 12 to the discharge pipe 5. It is configured to maintain the liquid level H1. For example, an indirect heat exchanger 18 using steam is connected to the feed pipe 4 to heat the pickling liquid fed into the pickling tank 1 to a desired temperature.

(8) As a device for continuously replenishing a predetermined amount of fresh acid to the pickling liquid that is circulated between the pickling tank and the circulation tank and maintained at a predetermined level in the pickling tank as described above, In the example shown in FIG.
After that, new acid is injected into the circulation tank 6 to replenish it, and on the other hand,
A water supply pipe 20 for concentration adjustment is connected to the circulation tank 6, and water is injected into the circulation tank 6 through a metering valve 21. 22 is an acid receiving pipe connected to the new acid storage tank 14, and can be supplied directly from a tank truck or from another storage facility.

In the illustrated example described above, when replenishing fresh acid, acid and water are supplied separately, but they may be supplied in advance at a predetermined concentration. Furthermore, although the case has been described in which fresh acid is supplied to the circulation tank 6, it may be supplied to the pickling tank 1.

As a device for continuously extracting waste acid from the circulation tank 6, a waste acid discharge pipe 28 is connected to the lower end of the circulation tank 6, and the waste acid is discharged to the waste acid tank 24 through this waste acid discharge pipe 28. It is connected to temporarily store waste acid, and an overflow pipe 26 for extraction is connected to the waste acid discharge pipe 28 by bypassing the valve 25 provided in the waste acid discharge pipe 28 on the outlet side of the circulation tank 6. 26 is appropriately selected to maintain the pickling liquid in the circulation tank 6 at level H2. z7 indicates a valve provided in the overflow pipe 26. A waste acid delivery pipe 28 is connected to the waste acid tank 24, and is configured to send out the waste acid accumulated in the waste acid tank 24 to the waste acid processing equipment by a pump 29 via a valve 30.81.

In the illustrated example apparatus described above, the fresh acid storage tank 1
New acid supply pipe 111t
't'' to the circulation tank 6, and water for concentration adjustment is supplied to the circulation tank 6 via the water supply pipe 20.The ratio of fresh acid and water in this case is determined based on the target acid concentration, and , the total amount of new acid and water is determined by vn in equation (1).

All of the pickling liquid in the circulation tank 6, which has been adjusted to a predetermined acid concentration in this way, is fed into the pickling tank 1 through the feed pipe 4 via the heat exchanger 18'j7 by the pump 7. The pickling liquid used for pickling the strip 2 in the pickling tank 1 evaporates and is carried out by the strip 2, but most of it returns to the circulation tank 6 via the overflow pipe 12. In this way, the pickling solution is circulated in the circulation tank 6 with a new acid supply pipe 15.
Since fresh acid and water are replenished through the water supply pipe 20, an amount equal to the difference between this increased amount and the reduced amount in the pickling tank 1 is temporarily stored in the waste acid tank 24 through the overflow pipe 26. This waste acid is sent to a waste acid treatment facility by a pump 29. Therefore, by controlling only the amount of fresh acid supplied to the circulation tank 6, it is possible to stably maintain the pickling liquid at a predetermined concentration.

Example Thickness of SUS 480 stainless steel after hot rolling 8.0
Friend, 25 m of l1lti41260+U strip.
H, So, 20±8 in pickling tank 1 at a pickling speed of /min
There was (11) g in the pickling solution.

The above-mentioned equation (3) can be expressed as the following equation by determining the coefficients β and γ in advance through experiments.

v = 43.04f3-6.186 X 10 D Substitute ■-25 into the above formula and calculate D = 88.5''/
m8 is seen.

Therefore, from equations (2) and (1), Vw = 1
．． 28-v.

Vn = 1.28 + Vv be criticized.

From the above calculation results, taking into account the margin, the new acid input amount Vn
As a result of operating as q 1.5''/1 (r), the U, SO, and SO concentrations were stably maintained at the target concentration of 20±8%, as shown in Figure 6.The conventional batch method shown in Figure 5 The concentration of H2SO was reliably stabilized compared to the case where the pickling solution was used, and no sludge was generated at all. (12) Effects of the Invention According to the present invention, the concentration of the pickling solution can be stably maintained at the target value. This not only prevents the generation of sludge in the pickling solution, thereby improving the surface quality of the treated material and increasing productivity, but also automates the replenishment of new acid and the removal of waste acid. , the effect of improving work safety and efficiency can be obtained.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the supply and discharge balance of the pickling liquid in the pickling tank. Figure 2 is a graph showing the change in metal concentration in the pickling liquid over time. Figure 8 is the metal concentration in the pickling liquid and pickling. Graph showing the relationship with speed, Figure 4 is a route map of the device according to the present invention, Figure 5 is a graph showing changes in the concentration of pickling solution in the case of new acid replenishment using the conventional batch method, Figure 6 is It is a graph showing the fluctuation of the pickling solution concentration in the case of continuous fresh acid replenishment according to the present invention. 1... Pickling tank 2... Strip 8... Pickling liquid 4... Inlet pipe 5... Discharge pipe 6... Circulation tank 7... Pump 8, 9, 10, 11 ...Valve 1
2... Circulation overflow pipe 18... Heat exchanger] 4... New acid storage tank 15.
... New acid supply pipe 16 ... Metering pump 17, 18
, 19... Valve 2o... Water supply pipe for concentration adjustment 21...
- Metering valve 22... Piping for receiving new acid 28... Waste acid discharge pipe 24... Waste acid tank 25... Valve 26... Overflow pipe for extraction 27... Valve 28... - Waste acid delivery pipe 29...pump 80, 81...valve. Sophistry type / 呵mi)

Claims (1)

[Claims] L A pickling solution is circulated between a pickling tank and a circulation tank connected thereto, and a predetermined amount of new acid of a predetermined concentration is continuously replenished to the pickling solution, and a predetermined amount of new acid is added to the pickling solution. A pickling solution replenishment method characterized by continuously extracting all waste acid from a circulation tank. & Connect an overflow pipe to the pickling tank and the circulation tank at a predetermined level to keep the ti of the pickling solution constant, continuously replenish a predetermined amount of new acid with a predetermined concentration, and overflow the waste liquid from the circulation tank. A method of replenishing a pickling solution according to claim 1, wherein the pickling solution is continuously extracted.