Method and apparatus for supplying acid solution to a pickling tank

Abstract

To provide a method and apparatus for supplying acid solution to a pickling tank that can ensure descaling. [Solution] A method for supplying acid solution to a pickling tank 2 for pickling hot-rolled steel strip, comprising: a measurement step of measuring the temperature and concentration of the acid solution in the pickling tank 2; a blending step of preparing a blended acid by blending recovered acid, which is used acid solution recovered from the pickling tank 2 as a raw material, with new acid, which is unused acid solution, based on the temperature of the acid solution in the pickling tank 2; an input amount determination step of determining the amount of blended acid to be added based on the measurement results of the measurement step and the required descaling properties of the hot-rolled steel strip; and an input step of adding the blended acid to the pickling tank in the determined input amount.

Description

[Technical Field]

[0001] The present invention relates to a method for supplying acid solution to a pickling tank and an acid solution supply apparatus. [Background technology]

[0002] A pickling line, one of the facilities used in steel plate manufacturing, is a system for descaling hot-rolled steel strips and consists of multiple pickling tanks containing acidic solution. In the pickling line, descaling of the hot-rolled steel strips is performed by immersing them in the acidic solution in the pickling tanks. Hydrochloric acid, for example, is used as the acidic solution.

[0003] Figure 4 shows an example of a typical pickling line 1a. In the pickling line 1a shown in Figure 4, the hot-rolled steel strip is loaded into the pickling tank 2a, and descaling occurs when the acid solution in the pickling tank 2a reacts with the scale on the surface of the hot-rolled steel strip. After that, the acid solution adhering to the surface of the hot-rolled steel strip is removed in the post-treatment tank 3a. The pickling tank 2a is supplied with new acid, which is the acid solution supplied from the new acid tank 4a, and recovered acid, which is supplied from the recovered acid tank 5a. In addition, waste liquid is collected from the pickling tank 2a and sent to the waste acid tank 6a, and the acid fumes collected by the eliminator 7a and the acid solution collected in the post-treatment tank 3a are sent as waste liquid to the recovery pit 8a. The recovered acid is obtained by adjusting the composition of the waste liquid collected in the waste acid tank 6a and the recovery pit 8a.

[0004] The temperature of the acid solution in the pickling tank 2a constantly fluctuates due to the surface temperature of the hot-rolled steel strip being charged into the pickling tank 2a and seasonal changes. Furthermore, the concentration of the acid solution in the pickling tank 2a constantly fluctuates due to the movement of the acid solution outside the pickling tank 2a, such as the movement of the acid solution to the waste acid tank 6a, the movement of the acid solution to the post-treatment tank 3a due to the removal of the hot-rolled steel strip being passed through the tank, and the absorption of acid fumes by the eliminator 7a. The degree of descaling in the pickling tank 2a is affected by the pickling time during which the hot-rolled steel strip passes through the tank, the temperature of the hydrochloric acid in the tank, and the concentration of the hydrochloric acid in the tank. Furthermore, since the scale thickness differs depending on the type and size of the hot-rolled steel strip being charged and the operating conditions of the hot-rolling process, these conditions also affect the degree of descaling. For this reason, the temperature and concentration of the acid solution, as well as the pickling time, must be appropriately controlled for each type of hot-rolled steel strip.

[0005] Because the temperature and concentration of the acid solution in the pickling tank 2a constantly fluctuate, the descaling performance in the pickling tank 2a may decrease. In such cases, descaling performance can be ensured by adding a new acid solution with a higher concentration to the pickling tank 2a. For example, Patent Document 1 discloses a method of setting an appropriate acid solution concentration value for each steel strip and controlling the acid concentration in the pickling tank according to that setting value. Furthermore, Patent Document 2 discloses a method for supplying a blended acid, which is a mixture of unused acid solution (new acid) and recovered acid recovered from the pickling tank, to the pickling tank. This method involves selectively supplying the new acid to a supply tank and controlling the flow rate so that the blended acid in the tank reaches a target concentration. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-269957 [Patent Document 2] Japanese Patent Application Publication No. 57-104670 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the methods described in Patent Documents 1 and 2 do not take into account the acid solution temperature, which affects the descaling properties of hot-rolled steel strips. As a result, when the hydrochloric acid temperature decreases due to changes in the surface temperature of the hot-rolled steel strips charged into the pickling tank or seasonal changes, it may not be possible to ensure a certain level of descaling. Therefore, the present invention has been made paying attention to the above problems, and an object thereof is to provide an acid solution supply method and an acid solution supply device for an acid pickling tank that can ensure descaling performance.

Means for Solving the Problems

[0008] (1) According to one aspect of the present invention, there is provided an acid solution supply method for supplying an acid solution to an acid pickling tank for pickling a hot-rolled steel strip, the method including: a measurement step of measuring the temperature and concentration of the acid solution in the acid pickling tank; a preparation step of preparing a prepared acid by mixing a recovered acid using the used acid solution recovered from the acid pickling tank and a fresh acid which is an unused acid solution based on the temperature of the acid solution in the acid pickling tank; an input amount determination step of determining the input amount of the prepared acid based on the measurement result of the measurement step and the required descaling performance of the hot-rolled steel strip; and an input step of inputting the prepared acid into the acid pickling tank at the determined input amount.

[0009] (2) In the acid solution supply method for the acid pickling tank of (1) above, the acid pickling tank to which the acid solution is supplied is the final tank of the Nth tank in an acid pickling line in which pickling is continuously performed in N acid pickling tanks of two or more. In the preparation step, the recovered acid and the fresh acid are mixed so as to satisfy the acid concentration [C M in formula (1). In the input amount determination step, the actual descaling performance E calculated using the measurement result of the measurement step, formula (2), and formula (3) is not less than the minimum descaling performance E p for each hot-rolled steel strip determined from past operating conditions, and the input amount V M of the prepared acid calculated by formula (4) is determined.

[0010]

Number

[0011] Here, [C M : Acid concentration of the prepared acid (wt%) T N : Temperature (°C) of the acid solution in the Nth acid pickling tank E: Descaling property N: Number of pickling tanks in the pickling line K i : Reaction rate constant in the i-th pickling tank [C i : Acid concentration (wt%) of the acid solution in the i-th pickling tank v: Pickling speed (mpm) α: Constant T i : Temperature (°C) of the acid solution in the i-th pickling tank V M : Amount of prepared acid added (L) [C Np : Target acid concentration (wt%) of the acid solution in the N-th pickling tank [C N : Acid concentration (wt%) of the acid solution in the N-th pickling tank V N : Amount of acid solution (L) in the N-th pickling tank

[0012] (3) According to one aspect of the present invention, there is provided an acid solution supply device for supplying an acid solution to a pickling tank for pickling a hot-rolled steel strip, the acid solution supply device comprising: measuring equipment for measuring the temperature and concentration of the acid solution in the pickling tank; preparation means for preparing a prepared acid by mixing a recovered acid, which is the used acid solution recovered from the pickling tank, and a fresh acid, which is an unused acid solution, based on the temperature of the acid solution in the pickling tank; an arithmetic unit for determining the input amount of the prepared acid based on the measurement result by the measuring equipment and the required descaling property of the hot-rolled steel strip; and input means for inputting the prepared acid into the pickling tank at the determined input amount.

Effects of the Invention

[0013] According to one aspect of the present invention, there are provided an acid solution supply method and an acid solution supply device capable of ensuring descaling property.

Brief Description of the Drawings

[0014] [Figure 1] It is a configuration diagram showing an acid solution supply device according to an embodiment of the present invention. [Figure 2]This graph shows the vapor pressure curves of water and hydrochloric acid. [Figure 3] This graph shows the relationship between the amount of new acid added and the electrical conductivity of the waste liquid in a comparative example. [Figure 4] This is a diagram showing the configuration of a conventional acid solution supply device. [Modes for carrying out the invention]

[0015] The following detailed description will illustrate embodiments of the present invention with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals, and redundant descriptions are omitted. Each drawing is schematic and may differ from reality. Furthermore, the embodiments shown below are illustrative of apparatus and methods for realizing the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited to the materials, structure, arrangement, etc., of the components described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0016] <Device configuration> Referring to Figure 1, an acid solution supply device 4 according to one embodiment of the present invention will be described. The acid solution supply device 4 is a device that supplies acid solution to the pickling tank 2 in the pickling line 1 for hot-rolled steel strip. The pickling line 1 is provided with two or more N pickling tanks, and the hot-rolled steel strip is continuously pickled in the N pickling tanks. In the pickling process, the hot-rolled steel strip is immersed in the acid solution contained in the pickling tank, and the scale on the surface of the hot-rolled steel strip is removed. In this embodiment, the pickling tank 2 to which the acid solution is supplied by the acid solution supply device 4 is the Nth and final tank used in the final pickling process. In Figure 1, only the related equipment of the final tank, the pickling tank 2, is shown as part of the pickling line 1, and the other pickling tanks are omitted.

[0017] As shown in Figure 1, the pickling line 1 includes the pickling tank 2, the final tank, as equipment related to the pickling tank 2, a post-treatment tank 3, an acid solution supply device 4, a waste acid tank 5, an eliminator 6, and a recovery pit 7. The post-treatment tank 3 is a device that removes the acid solution adhering to the surface of the hot-rolled steel strip that has been pickled in the pickling tank 2. The acid solution supply device 4 is a device that supplies acid solution to the pickling tank 2, and its details will be described later. The waste acid tank 5 is a tank that stores the waste liquid, which is the acid solution used in the pickling process, recovered from the pickling tank 2. The eliminator 6 is a device that sucks up and recovers the acid fumes (hydrochloric acid fumes in the case of hydrochloric acid) in the pickling tank 2. The recovery pit 7 is a device that stores the hydrochloric acid fumes recovered by the eliminator 6 and the acid solution recovered in the post-treatment tank 3.

[0018] The acid solution supply device 4 includes a measuring instrument 41, a mixing means 42, a calculation device 43, and a feeding means 44. The measuring instrument 41 is a device for measuring the acid concentration and temperature of the acid solution in the pickling tank 2. The measured acid concentration and temperature are transmitted to the calculation unit 43. The mixing means 42 is a means for mixing the acid solution to be put into the pickling tank 2, and includes a new acid tank 421, a recovered acid tank 422, two flow control valves 423 and 424, and a mixing tank 425.

[0019] The new acid tank 421 and the recovered acid tank 422 are tanks for storing new acid and recovered acid, respectively. New acid is a new, unused acid solution that has not been used in the pickling process. Recovered acid is an acid solution concentrated and regenerated using the waste liquid, which is the used acid solution recovered from the pickling tank 2, as the raw material. The waste liquid is condensed in a roasting furnace and its concentration is adjusted. The acid concentration of both the new acid and the recovered acid is higher than that of the acid solution in the pickling tank 2, with the new acid having a higher acid concentration than the recovered acid.

[0020] The flow control valve 423 is a valve that adjusts the flow rate of fresh acid supplied from the fresh acid tank 421 to the mixing tank 425. The flow control valve 424 is a valve that adjusts the flow rate of recovered acid supplied from the recovered acid tank 422 to the mixing tank 425. The two flow control valves 423 and 424 adjust the flow rate of the acid solution (fresh acid or recovered acid) by automatically adjusting the valve opening based on the calculation results from the computing device 43. The mixing tank 425 is a tank that stores the mixed acid solution, which is a blended acid, obtained by mixing the fresh acid supplied from the fresh acid tank 421 with the recovered acid supplied from the recovered acid tank 422.

[0021] The calculation device 43 calculates the mixing ratio of fresh acid and recovered acid in the blended acid, and the amount of blended acid to be added to the pickling tank 2. The calculation device 43 is, for example, a computer system such as a personal computer with calculation processing capabilities, and is configured with ROM, RAM, CPU, etc. The calculation device 43 implements the calculation processing functions described later in software by executing various dedicated programs pre-stored in ROM, etc. The method by which the calculation device 43 calculates the mixing ratio of fresh acid and recovered acid and the amount of blended acid to be added to the pickling tank 2 will be described later. The input means 44 is equipment that adds a predetermined amount of the prepared acid, which has been completed in the mixing tank 425, to the pickling tank 2. The amount of prepared acid to be added by the input means 44 is set based on a command from the calculation device 43.

[0022] <Method for supplying acid solution to the pickling tank> Next, the method for supplying acid solution to the pickling tank 2 according to this embodiment will be described. In this embodiment, first, the measuring instrument 41 measures the acid concentration and temperature of the acid solution contained in the pickling tank 2 (measurement step). The measurement results from the measurement step are transmitted to the computing device 43. After the measurement process, the new acid stored in the new acid tank 421 and the recovered acid stored in the recovered acid tank 422 are mixed to produce a blended acid (blending process). In the blending process, first, the calculation device 43 calculates the acid concentration of the blended acid [C] based on the temperature of the acid solution obtained in the measurement process. M Determine the acid concentration of the compounded acid [C MThe ratio [C] is set based on the vapor pressure relationship between water and acid solution (hydrochloric acid in this embodiment) to prevent the acid solution from evaporating before the water and thus prevent a decrease in the concentration of the acid solution in the pickling tank 2. M ] may be calculated as a value that satisfies the following equation (1). Note that in equation (1), the acid concentration [C] of the compounded acid is calculated as follows. M If ] is determined, the temperature of the acid solution T N It is preferable that the temperature be between 60°C and 90°C.

[0023]

number

[0024] Here, [C M ]: Acid concentration (wt%) of the blended acid T N : Temperature of the acid solution in the Nth pickling tank (°C)

[0025] Next, the computing device 43 determines the mixing ratio of the new acid and the recovered acid using the acid concentrations of the new acid and the recovered acid, so that the determined acid concentration is achieved. Furthermore, the calculation unit 43 determines the flow rate of fresh acid from the fresh acid tank 421 and the flow rate of recovered acid from the recovered acid tank 422 so that the determined mixing ratio is achieved, and transmits the determined flow rates to the flow control valves 423 and 424. Subsequently, the flow control valves 423 and 424 adjust the flow rate of the acid solution and supply the new acid and recovered acid to the mixing tank 425 at the determined flow rate. Next, in mixing tank 425, the supplied new acid and the recovered acid are mixed to produce a compound acid.

[0026] After the mixing process, the calculation device 43 determines the amount of mixed acid to be added based on the acid concentration and temperature of the acid solution in the pickling tank 2, which are the measurement results from the measurement process, and the required descaling properties of the hot-rolled steel strip (amount determination process). In the amount determination process, first, the calculation device 43 determines the minimum descaling property E, which is the required descaling property of the hot-rolled steel strip, according to the hot-rolled steel strip to be pickled. pThe descaling performance E is a value that indicates the scale removal performance in pickling line 1, which is a continuous pickling facility, and is a value that is calculated according to the conditions of the pickling treatment in pickling line 1. The descaling performance E can be obtained from the following equations (2) and (3). In this case, the minimum descaling performance E p This can be used to describe the descaling properties of hot-rolled steel strips that are the same as or similar to those being pickled, based on past operational performance. Hot-rolled steel strips that are the same as or similar to those being pickled are those in which at least one of the following conditions—type (composition), size, and operating conditions in the hot rolling process—is the same as or similar to those being pickled.

[0027]

number

[0028] Here, E: Descaling properties N: Number of pickling tanks in the pickling line K i : Reaction rate constant in the i-th pickling tank [C i ]: Acid concentration (wt%) of the acid solution in the pickling tank of the ith tank v: Pickling speed (mpm) α: constant T i : Temperature of the acid solution in the pickling tank (°C)

[0029] Next, the calculation unit 43 determines that the actual descaling ability E based on the measurement results for the hot-rolled steel strip to be pickled is the minimum descaling ability E p The above conditions must be met (i.e., E≧E p The amount of compounded acid to be added to the pickling tank 2 is determined (so that this is the case). The amount of compounded acid to be added may also be determined using the following equation (4). In this case, the target acid concentration of the acid solution in the pickling tank 2 is such that the descaling ability E is the minimum descaling ability E p The acid concentration is set using equations (2) and (3). The calculation device 43 transmits the determined amount of blended acid to be added to the input means 44.

[0030]

number

[0031] Here, [C Np ]: Target acid concentration (wt%) of the acid solution in the Nth pickling tank [C N ]: Concentration of the acid solution in the Nth pickling tank (wt%) V N : Amount of acid solution (L) in the Nth pickling tank

[0032] After the input amount determination step, the input means 44 inputs the amount of pickling solution determined in the input amount determination step into the pickling tank 2 (input step). The series of processes from the measurement step to the input step may be repeated while the pickling treatment is being carried out.

[0033] In this embodiment, a blended acid, prepared by mixing new acid and recovered acid, is added to the pickling tank 2. In other words, the acid solution added to the pickling tank 2 is a blended acid with a lower acid concentration than the new acid. By doing so, the volatilization of the added acid solution can be reduced compared to directly adding the new acid with a high acid concentration to the pickling tank 2, thereby reducing the loss of acid solution due to volatilization. Furthermore, in the blending process, the blended acid is prepared according to the temperature measured in the measurement process. Moreover, the blended acid is prepared so that its concentration does not evaporate before the water. By doing so, the volatilization of the acid solution added to the pickling tank can be prevented, and the loss of acid solution due to volatilization can be significantly reduced.

[0034] Furthermore, the eliminator 6 recovers the acid fumes generated by the volatilization of the acid solution and sends them to the recovery pit 7. However, in the conventional method, when new acid is directly added, the electrical conductivity of the waste liquid recovered in the recovery pit 7 increases as the amount of new acid added increases. When the electrical conductivity of the waste liquid exceeds the upper limit of management, it is necessary to reduce the amount of water in the recovery pit 7 from an environmental perspective. In this case, it is necessary to reduce the transport speed of the hot-rolled steel strip in order to reduce the amount of liquid sent to the recovery pit 7, which reduces production efficiency. However, according to this embodiment, the volatilization of the acid solution can be suppressed or prevented, so the decrease in production efficiency can also be suppressed.

[0035] Furthermore, in this embodiment, the amount of compounded acid to be added is determined in the input amount determination step by considering the descaling properties obtained from the acid concentration and temperature of the acid solution in the pickling tank 2. As a result, even if the temperature of the acid solution in the pickling tank 2 changes due to changes in the surface temperature of the hot-rolled steel strip charged into the pickling tank 2 or seasonal changes, the descaling properties can be kept constant, and defects such as residual scale can be prevented.

[0036] <Variation> Although the present invention has been described above with reference to specific embodiments, this description is not intended to limit the invention. By referring to the description of the present invention, those skilled in the art will also see other embodiments of the invention, including various modifications, in addition to the disclosed embodiments. Accordingly, the embodiments of the invention described in the claims should be understood to include embodiments that include these modifications described herein, either individually or in combination. For example, in the above embodiment, the pickling tank 2 to which the acid solution is supplied is the final tank, but the present invention is not limited to such examples. The pickling tank 2 to which the acid solution is supplied may be a pickling tank 2 provided before the final tank in the pickling line. [Examples]

[0037] The present inventors will now describe an example they performed. In the example, the acid supply method according to the above embodiment was used to perform an acid pickling treatment on the hot-rolled steel strip pickling line 1. In the example, the minimum descaling performance E was determined from the type and size of the hot-rolled steel strip and the operating conditions of the hot-rolling process. p The descaling ability E in pickling line 1 is determined to be the minimum descaling ability E. p The amount of compounded acid to be added was determined accordingly. As a comparative example, the pickling treatment was also performed using a conventional method in which recovered acid was continuously added to pickling tank 2, and new acid was added when the concentration fell below the specified concentration. The results of the example showed that even when the acid concentration and temperature of the hydrochloric acid solution in the pickling tank 2 changed, the descaling properties could be maintained, and yield loss due to scaling defects could be reduced by about 20% compared to the comparative example.

[0038] Furthermore, in the examples and comparative examples, hydrochloric acid with an acid concentration of approximately 35 wt% was used as the new acid. Figure 2 shows the vapor pressure curves of water and hydrochloric acid. As shown in Figure 2, for example, in an environment where the pickling tank 2 is approximately 90°C, hydrochloric acid can only exist up to approximately 27 wt%, so it was inferred that when the new acid was added, it would volatilize immediately upon addition. In addition, in the example in which the acid concentration of the blended acid was adjusted according to equation (1) compared to the comparative example, it was confirmed that the amount of new acid added could be reduced by approximately 8%.

[0039] Furthermore, in the example, it was confirmed that the hydrochloric acid fume could be reduced by adjusting the acid concentration of the hydrochloric acid added, thereby suppressing the electrical conductivity of the recovery pit 7. In contrast, in the comparative example, as shown in Figure 3, it was confirmed that the electrical conductivity of the waste liquid in the recovery pit 7 tended to increase as the amount of new acid added increased. It was also confirmed that there were cases where the electrical conductivity exceeded the control limit. In the example, the electrical conductivity did not exceed the control limit, and considering the frequency of exceeding the control limit in the comparative example, it was confirmed that the production efficiency of the example was improved compared to the comparative example, and an increase in production of about 0.2% could be expected. [Explanation of Symbols]

[0040] 1. Pickling Line 2 Pickling tank 3. Post-treatment tank 4 Acid liquid supply device 41 Measuring equipment 42. Preparation methods 421 New Acid Tank 422 Acid Recovery Tank 423,424 Flow control valve 425 Mixing Tank 43 Arithmetic unit 44 Input means 5. Waste acid tank 6 Eliminator 7 Recovery Pit

Claims

1. A method for supplying an acid solution to a pickling tank for pickling hot-rolled steel strips, A measurement step for measuring the temperature and concentration of the acid solution in the pickling tank, Based on the temperature of the acid solution in the pickling tank, a blending step is performed to prepare a blended acid by mixing the recovered acid, which is the used acid solution recovered from the pickling tank, with a new acid, which is an unused acid solution. An input amount determination step is performed to determine the amount of the blended acid to be added based on the measurement results of the measurement step and the required descaling properties of the hot-rolled steel strip. An input step of adding the prepared acid in the determined input amount to the pickling tank, A method for supplying acid solution to a pickling tank, comprising the following features.

2. The pickling tank to which the acid solution is supplied is the Nth and final tank in a pickling line in which pickling is performed continuously in two or more N pickling tanks. In the aforementioned blending step, the acid concentration [C] satisfying equation (1) is Ｍ The recovered acid and the new acid are prepared in such a way that the following occurs: In the input amount determination step, the actual descaling ability E calculated using the measurement results from the measurement step and equations (2) and (3) is determined from the minimum descaling ability E for each hot-rolled steel strip determined from past operating conditions. ｐ As described above, the amount of the blended acid to be added V is calculated using equation (4). Ｍ A method for supplying acid solution to a pickling tank according to claim 1, wherein the following is determined. [Math 1] Here, [C Ｍ ]: Acid concentration (wt%) of the blended acid T Ｎ : Temperature of the acid solution in the Nth pickling tank (°C) E: Descalability N: Number of pickling tanks in the pickling line K ｉ : Reaction rate constant in the i-th pickling tank [C ｉ ]: Acid concentration (wt%) of the acid solution in the i-th pickling tank. v: Pickling speed (mpm) α: constant T ｉ : Temperature of the acid solution in the i-th pickling tank (°C) V Ｍ : Input amount of blended acid (L) [C Ｎｐ ]: Target acid concentration (wt%) of the acid solution in the Nth pickling tank [C Ｎ ]: Concentration of the acid solution in the Nth pickling tank (wt%) V Ｎ : Amount of acid solution (L) in the Nth pickling tank

3. A device for supplying acid solution to a pickling tank for pickling hot-rolled steel strips, A measuring instrument for measuring the temperature and concentration of the acid solution in the pickling tank, A compounding means for producing a compounded acid by compounding a recovered acid, which is made from the used acid solution recovered from the pickling tank, with a new acid, which is an unused acid solution, based on the temperature of the acid solution in the pickling tank. A calculation device that determines the amount of the blended acid to be added based on the measurement results from the measuring instrument and the required descaling properties of the hot-rolled steel strip, An input means for adding the prepared acid in the determined amount to the pickling tank, A device for supplying acid solution to a pickling tank, equipped with the necessary components.

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