Slag management method and slag material manufacturing method

Abstract

To provide a method for managing a slag capable of controlling an increase in a processing cost of the slag, and to provide a method for producing a slag material.SOLUTION: A method for managing a slag includes: an estimation step of estimating a maximum free lime content in a slag generated by refining, based on a component composition of a secondary raw material to be used in refining molten iron and a Si concentration of molten iron before refining; a first determination step of determining whether or not the maximum free lime content of the slag estimated in the estimation step is a predetermined first threshold value or more; and a decision step of deciding a processing method for the slag based on a result determined in the first determination step.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for managing slag and a method for manufacturing a slag material.

Background Art

[0002] For example, in the steel industry, slag is by-produced during the operation of blast furnaces, pretreatment processes, converters, electric furnaces, etc. Among these slags, the slag by-produced in steelmaking processes such as pretreatment processes, converters, and electric furnaces is particularly referred to as steelmaking slag. In the steelmaking process, a large amount of lime is added as a secondary raw material to remove phosphorus, silicon, etc. contained in hot metal. Therefore, undissolved lime and lime crystallized during cooling remain as free lime (hereinafter, free lime may be described as "f-CaO") in the steelmaking slag.

[0003] This f-CaO has the property of becoming Ca(OH)2 by a hydration reaction and expanding in volume by about twice. Therefore, when steelmaking slag containing a large amount of f-CaO comes into contact with water, the slag expands and collapses due to the hydration reaction of f-CaO. Although roadbed materials are among the uses of steelmaking slag, when using steelmaking slag containing f-CaO as a roadbed material, there is a problem that the roadbed bulges due to the hydration expansion of f-CaO.

[0004] Therefore, when using steelmaking slag as a roadbed material, as disclosed in Patent Document 1, it is necessary to perform pretreatment such as steam aging treatment on the steelmaking slag. Steam aging treatment is a treatment for changing f-CaO contained in steelmaking slag to Ca(OH)2 by a hydration reaction and stabilizing it. The steam aging treatment is carried out by stacking steelmaking slag in a dedicated treatment site and flowing steam from below it.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] For slag containing a large amount of f-CaO, it is difficult to completely eliminate the expansion and collapse properties even with steam aging treatment. Conventionally, f-CaO analysis was performed on all slag, and the necessity and conditions of steam aging treatment were determined based on the f-CaO content of the slag. This method had the problem of increasing the cost of slag treatment because it required performing f-CaO analysis on a huge number of slags, which is a laborious process.

[0007] This invention has been made in view of the problems of the prior art, and its purpose is to provide a method for managing slag and a method for manufacturing slag material that can suppress the increase in slag processing costs. [Means for solving the problem]

[0008] The means to solve the above problems are as follows: [1] A slag management method comprising: an estimation step of estimating the maximum free lime content in the slag generated in the refining process based on the component composition of auxiliary raw materials used in the refining of molten iron and the Si concentration of the molten iron before refining; a first determination step of determining whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a predetermined first threshold; and a determination step of determining a method for processing the slag based on the result determined in the first determination step. [2] The slag management method according to [1], wherein in the estimation step, T.CaO and T.SiO2 are calculated from the Si concentration of the auxiliary raw materials and molten iron before refining, and the maximum free lime content is estimated using the T.CaO and T.SiO2. [3] The slag management method according to [2], wherein the estimation step involves estimating the maximum free lime content of the slag using the following formula (1). Maximum free lime content = T.CaO-1.86×T.SiO2 (1) [4] A slag management method according to any one of [1] to [3], comprising: an analysis step of analyzing the free lime content of slag determined to be above a first threshold in the first determination step; and a second determination step of determining whether the free lime content analyzed in the analysis step is above a predetermined second threshold, wherein the determination step determines a method for processing the slag based on the results determined in the first determination step and the second determination step. [5] The slag management method according to any one of [1] to [3], wherein the first threshold is 15 kg / t-molten iron. [6] The slag management method according to [4], wherein in the determination step, it is determined that the free lime content of the slag determined in the second determination step to be equal to or greater than the second threshold is not subjected to steam aging treatment. A method for producing slag material, comprising processing the slag using a processing method determined in the determination step of the slag management method described in any of [7], [1] to [6], to produce slag material. [Effects of the Invention]

[0009] According to the present invention, the maximum free lime content of slag generated during molten iron refining is estimated, and the estimated maximum free lime content is determined using a first threshold. Based on this determination result, it is possible to identify slag that may have a high f-CaO content and slag with a low f-CaO content. Therefore, for slag with a low f-CaO content, the f-CaO analysis that was conventionally performed can be omitted, thereby suppressing the increase in slag processing costs. [Modes for carrying out the invention]

[0010] The present invention will be described in detail below through embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited in any way by these embodiments.

[0011] The slag management method according to this embodiment includes an estimation step of estimating the maximum free lime content (kg / t-molten iron) of the slag generated in the refining process from the auxiliary raw materials used in the refining of molten iron in the converter and the Si concentration in the molten iron before refining; a first determination step of determining whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a predetermined first threshold; and a determination step of determining a slag treatment method based on the result determined in the first determination step. The steps in the slag management method according to this embodiment will be described below. In this embodiment, "molten iron" means molten pig iron and molten steel.

[0012] <Estimated process> First, let's explain the estimation process. In the estimation process, the maximum free lime content of the slag generated in each molten iron refining is estimated. The maximum free lime content of the slag is estimated using the component composition of the auxiliary materials used in the molten iron refining, the amount of auxiliary materials added, the Si concentration in the molten iron, and the amount of molten iron charged. Specifically, the maximum free lime content of the slag is estimated by calculating T.CaO (kg / t-molten iron) and T.SiO2 (kg / t-molten iron) using the component composition of the auxiliary materials, the amount of auxiliary materials added, the Si concentration in the molten iron, and the amount of molten iron charged. Note that T.CaO is the total lime content, and T.SiO2 is the total silica content.

[0013] T.CaO includes not only CaO contained in the auxiliary materials, but also CaCO3, Ca(OH)2, CaMg(CO3)2, etc., which can be converted to CaO by thermal decomposition in high-temperature slag. T.CaO is calculated assuming that all of these substances are converted to CaO by reactions in the slag. Similarly, T.SiO2 is calculated assuming that not only SiO2 contained in the auxiliary materials, but also all Si in the molten iron and Si in the auxiliary materials are oxidized to SiO2. The component composition of the auxiliary materials used in calculating T.CaO and T.SiO2, the amount of auxiliary materials added, the Si concentration in the molten iron, and the amount of molten iron charged can be the same values ​​used in the refinement design of the converter. It is preferable to estimate the maximum free lime content of the slag using these values ​​at the end of the refinement process when the addition of auxiliary materials to the converter is complete.

[0014] When CaO in slag solidifies, it reacts with SiO2 to form a stable crystalline phase represented as 2CaO·SiO2. Therefore, the f-CaO content of the slag can be calculated by subtracting the amount of CaO stabilized by reacting with SiO2, etc., from the total CaO content.

[0015] CaO forms stable crystalline phases with P2O5, Al2O3, and Fe2O3, in addition to SiO2. Furthermore, in the smelting of molten iron using a converter, in addition to the slag components generated by the oxidation of auxiliary materials and molten iron components, there is also incoming slag of unknown composition and quantity, such as slag from the pre-charge in the converter or slag adhering to the molten iron pot. Therefore, the true f-CaO content in the slag is calculated by subtracting the CaO stabilized by reacting with oxide components such as P2O5 and SiO2 in the incoming slag, as well as the SiO2 derived from Si in the molten iron, from T.CaO. However, since P2O5, Al2O3, and Fe2O3 in the slag do not originate from auxiliary materials, it is difficult to determine their amounts from known information. Also, since the amount and composition of the incoming slag are unknown, it is difficult to determine the amount of SiO2 derived from the incoming slag.

[0016] If we were to calculate the true f-CaO content by taking into account oxide components such as P2O5 contained in the slag and SiO2 contained in the imported slag, that true f-CaO content would be less than the maximum free lime content calculated as described above. In other words, the maximum free lime content calculated from T.CaO and T.SiO2 above is the maximum amount of f-CaO that can remain unstabilized in the slag, i.e., the maximum free lime content.

[0017] The maximum free lime content can also be theoretically estimated from the stoichiometry of 2CaO·SiO2, as shown in equation (1) below. This makes it possible to estimate the maximum free lime content contained in the slag generated during molten iron refining.

[0018] Maximum free lime content (kg / t - molten iron) = T.CaO (kg / t - molten iron) - 1.86 × T.SiO2 (kg / t - molten iron) ··· (1) In the above formula (1), T.CaO is the total lime amount (kg / t - molten iron) obtained by converting CaO, CaCO 3、 Ca(OH)2 and CaMg(CO3)2 into CaO, and T.SiO2 is the total silica amount (kg / t - molten iron) obtained by adding up SiO2 contained in the auxiliary raw materials and SiO2 generated by oxidizing Si contained in the molten iron. Also, the coefficient 1.86 in the above formula (1) is calculated stoichiometrically from the molecular weights of CaO and SiO2 in 2CaO·SiO2.

[0019] As described above, in the present embodiment, by the above calculation using T.CaO and T.SiO2, when it is assumed that the largest amount of f-CaO remains, the f-CaO content, that is, the content contained in the slag, which is difficult to estimate, is estimated as the "maximum free lime content" when P2O5, Al2O3, Fe2O3, and the SiO2 component from the carried-in slag are set to zero. By estimating this maximum free lime content, it becomes possible to predict the risk that the f-CaO content of the slag generated during the refining of molten iron will increase. In other words, by estimating this maximum free lime content, it becomes possible to identify slag with a low f-CaO content that passes the expansion test in a single steam aging treatment.

[0020] <First determination step> Next, the first determination step will be described. In the first determination step, for each refining of molten iron, it is determined whether or not the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a predetermined first threshold value. The first threshold value can be set, for example, by the following procedures (1) to (3) using the operation data of the molten iron refining carried out in the past. (1) Estimate the maximum free lime content from the information on the auxiliary raw materials and molten iron for the refining operation data for which the analysis of past slag has been carried out. (2) Specify the maximum free lime content such that the probability that the free lime content causes the expansion test to fail in one steam aging treatment is, for example, 20%, which is 8% by mass or more in this embodiment. (3) Set the specified content as the first threshold value.

[0021] In order to increase the number of slags to be steam-aged without analyzing the f-CaO content described later, it is preferable to set the first threshold value to as large a value as possible. On the other hand, if the first threshold value is set too large, there is a concern that many slags that will not pass the expansion test in one steam aging treatment will be included. The first threshold value may be set in view of this balance. For example, it is 15 (kg / t - hot metal).

[0022] When the first determination step is carried out using the first threshold value set as described above, the slag determined to have a maximum free lime content of the first threshold value or more is a slag that may not pass the expansion test in one steam aging treatment. On the other hand, the slag determined to have a maximum free lime content less than the first threshold value is a slag that will surely pass the expansion test in one steam aging treatment.

[0023] <Decision step> Next, the decision step will be described. The slag determined to be the first threshold value or more in the first determination step is a slag that may not pass the expansion test in one steam aging treatment. For such slags, it is necessary to analyze the f-CaO content and make a determination again. Therefore, in the decision step, such slags are determined to be slags for analyzing the f-CaO content. On the other hand, the slag determined to be less than the first threshold value in the first determination step is a slag that will surely pass the expansion test in one steam aging treatment. Therefore, in the decision step, such slags are determined to be slags to be steam-aged without analyzing the f-CaO content.

[0024] By determining the slag processing method in this way, it becomes possible to steam-age the slag without analyzing the f-CaO content, and without increasing the risk of the expansion test failing after a single steam aging treatment. As a result, it becomes possible to manufacture slag material that does not expand due to hydration while suppressing the increase in slag processing costs. The expansion test will be measured according to the test method specified in Annex B of JIS A5015:2018.

[0025] Furthermore, the slag management method according to this embodiment preferably includes an analysis step that analyzes the f-CaO content of slag that may not pass the expansion test after a single steam aging treatment in the first determination step. It is also preferable to have a second determination step that determines whether the f-CaO content analyzed in the analysis step is equal to or greater than a predetermined second threshold. And, in the determination step, it is preferable to determine the slag processing method based on the results determined in the first determination step and the second determination step. Each step will be described below.

[0026] <Analysis process> First, let's explain the analysis process. In the analysis process, the f-CaO content is analyzed for slag that has been determined in the first determination process to have a maximum free lime content equal to or greater than a first threshold. In the analysis process, slag is sampled from the converter or transport container when it is discharged from the converter or when the converter slag is transported, and the f-CaO content of the slag is analyzed by chemical analysis, for example, by ethylene glycol extraction.

[0027] <Second determination process> Next, the second determination step will be explained. In the second determination step, it is determined whether the f-CaO content of the slag analyzed in the analysis step is equal to or greater than a predetermined second threshold. The second threshold can be set using actual slag data, for example, by the following procedure (1) to (3). (1) Prepare slags with different f-CaO content and perform steam aging treatment and expansion tests on a laboratory scale. (2) Determine the upper limit of the f-CaO content that will pass all expansion tests in a single steam aging treatment (96 hours). (3) Set the identified upper limit as the second threshold.

[0028] To reduce the amount of slag used for purposes other than roadbed material without steam aging, as described later, it is preferable to set the second threshold to the largest possible value within that range. On the other hand, if the second threshold is set too high, there is a concern that some slag will be included that does not pass the expansion test after a single steam aging treatment. The second threshold is, for example, 8 mass%.

[0029] When the second determination process is performed using the second threshold set as described above, slag that is determined to have an f-CaO content equal to or greater than the second threshold will fail the expansion test after a single steam aging treatment. On the other hand, slag that is determined to have an f-CaO content less than the second threshold will pass the expansion test after a single steam aging treatment.

[0030] <Decision process> Slag that is determined to be above the first threshold in the first determination step, and also above the second threshold in the second determination step, is slag that will not pass the expansion test after a single steam aging treatment. Suppressing the hydration expansion of such slag requires long-term or multiple steam aging treatments, which increases the cost of processing the slag. For this reason, it is preferable to decide in the decision step not to perform steam aging treatment on such slag and to use the slag material for purposes other than roadbed material where hydration expansion is not a problem.

[0031] On the other hand, slag that is determined to be above the first threshold in the first determination step and below the second threshold in the second determination step is slag that will pass the expansion test with a single steam aging treatment. For this reason, it is preferable to decide in the decision step to steam aging this slag and use the slag material after steam aging for roadbed material applications. This makes it possible to manufacture slag material that does not hydrate and expand while suppressing an increase in slag processing costs.

[0032] Thus, the slag management method according to this embodiment preferably further includes an analysis step and a second determination step, and in the determination step, it is preferable to determine the slag treatment method as described above based on the results determined in the first determination step and the second determination step. This makes it possible to determine whether or not aging treatment is necessary according to the analysis results of the f-CaO content, and makes it possible to avoid situations where the expansion test does not pass after one steam aging treatment and multiple steam aging treatments are performed, thereby further suppressing the increase in slag treatment costs.

[0033] In the above embodiment, an example was shown in which an analysis step to analyze the f-CaO content was performed on the slag determined to be above the first threshold in the first determination step, but the embodiment is not limited to this. Since the slag determined to be above the first threshold in the first determination step is slag that may not pass the expansion test after a single steam aging treatment, it may be decided not to perform steam aging treatment on all of the slag and use the slag material for purposes other than roadbed material where hydration expansion is not a problem.

[0034] Furthermore, in the above embodiment, it was decided that slag determined to be above the second threshold in the second determination step would not undergo steam aging treatment, and an example was shown in which the slag material would be used for purposes other than roadbed material where hydration expansion is not a problem. However, the embodiment is not limited to this. For slag determined to be above the second threshold in the second determination step, it may be decided to extend the steam aging time by 1.5 to 2.0 times. This reduces transportation costs compared to when the slag fails the expansion test and undergoes steam aging treatment again, thereby suppressing an increase in the processing cost of the slag. [Examples]

[0035] Next, the present invention will be specifically described based on an example. In this example, the slag management method according to this embodiment was applied to the slag generated in the decarburization refining of molten iron using a converter. First, the analytical values ​​of the CaO content and SiO2 content in the auxiliary raw materials used in the decarburization refining, the analytical value of the Si concentration of the molten iron, and the amount charged were determined. Then, at the point when the input of auxiliary raw materials in the decarburization refining of the converter was completed, an estimation process was carried out, and T.CaO and T.SiO2 were calculated using the amount of auxiliary raw materials input, the CaO concentration and SiO2 concentration in the auxiliary raw materials, the Si concentration of the molten iron, and the amount of molten iron charged. Using these values ​​and equation (1) above, the maximum free lime content of the slag generated by the decarburization refining was estimated. Note that T.SiO2 was calculated assuming that all Si contained in the molten iron would be converted to SiO2 by oxidation.

[0036] In Invention Examples 1 and 2, the first determination step was performed using "maximum free lime content: 10 kg / t-molten iron (Invention Example 1)" and "maximum free lime content: 15 kg / t-molten iron (Invention Example 2)" as first thresholds for the estimated maximum free lime content. In both Invention Examples 1 and 2, for slags determined in the first determination step to have a maximum free lime content equal to or greater than the first threshold, an analysis step was performed to analyze the f-CaO content of the slag. For slags determined in the first determination step to have a maximum free lime content less than the first threshold, aging treatment was performed without performing an analysis step. On the other hand, in Comparative Examples 1 and 2, the first determination step was not performed, and an analysis step was performed on all slags.

[0037] In the analysis process, the free lime content of the slag was analyzed. To analyze the free lime content, 50g of slag was sampled from the slag pot using a metal rod and rapidly cooled. After cooling to room temperature, the sample was crushed, and the free lime content of the slag was analyzed by chemical analysis using ethylene glycol extraction.

[0038] In Invention Examples 1 and 2, a second determination step was performed on the slag that had undergone the analysis step. In Invention Examples 1 and 2, the second determination step was performed using "free lime content: 8% by mass" as the second threshold. In the second determination step, in both Invention Examples 1 and 2, slag that was determined to have a free lime content equal to or greater than the second threshold was not subjected to steam aging in the decision step and was decided to be used for purposes other than roadbed material. Slag that was determined to have a free lime content less than the second threshold was subjected to steam aging in the decision step and was decided to be used for roadbed material. An expansion test was performed on the slag material after steam aging, and slag that failed the expansion test was subjected to repeated steam aging until it passed the expansion test. The conditions for one steam aging treatment in the examples are as follows. Slag loading volume: 1000 tons Aging time per cycle: 96 hours Steam temperature: 100℃ Steam inflow conditions: Steam is uniformly introduced into the slag so that the slag temperature reaches 90°C or higher before 48 hours have elapsed.

[0039] On the other hand, in Comparative Examples 1 and 2, without performing the second determination step, all slag was subjected to steam aging treatment and it was decided to use it for roadbed material. An expansion test was conducted on the aged slag material, and the slag that failed the expansion test was subjected to repeated steam aging treatment until it passed the expansion test. The results for Invention Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0040] [Table 1]

[0041] As shown in Table 1, in Invention Examples 1 and 2, slag samples were selected for free lime analysis based on their maximum free lime content. As a result, the proportion of slag samples subjected to free lime analysis was 43% (Invention Example 1) and 24% (Invention Example 2) of the total slag sample. This allowed for a reduction in the number of slag samples analyzed for free lime while avoiding an increase in the number of slag samples that fail the expansion test after a single steam aging treatment, thus suppressing an increase in slag processing costs.

[0042] Furthermore, in Invention Examples 1 and 2, the average number of steam aging treatments was 1.02 times (Invention Example 1) and 1.00 times (Invention Example 2). In Invention Examples 1 and 2, for slags in which the free lime content analyzed in the analysis step was 8% by mass or more, it was decided in the decision step not to steam aging the slag and to use it for purposes other than roadbed material. As a result, the number of slags that failed the expansion test after one steam aging treatment was reduced, and it was confirmed that almost all of the steam-aged slags passed the expansion test after one steam aging treatment.

[0043] On the other hand, in Comparative Examples 1 and 2, the first judgment step was not performed, so the analysis step had to be performed on all slag. As a result, the increase in slag processing costs could not be suppressed. Also, since all slag was subjected to steam aging treatment, a large number of slags failed the expansion test after just one steam aging treatment. In fact, the average number of steam aging treatments performed was 1.23 (Comparative Example 1) and 1.08 (Comparative Example 2), indicating that an increasing number of slags failed the expansion test after just one steam aging treatment and required multiple steam aging treatments.

[0044] These results confirm that by determining whether or not to steam-age the slag based on the free lime content analyzed in the analysis step and the results of the second judgment step, the percentage of slag that pass the expansion test in a single steam-aging treatment can be increased. If the expansion test is passed in a single steam-aging treatment, additional treatment is unnecessary, further suppressing the increase in steam-aging costs.

Claims

1. An estimation step is performed to calculate T. CaO and T. SiO₂ from the component composition of auxiliary raw materials used in the smelting of molten iron and the Si concentration of the molten iron before smelting, and to estimate the maximum free lime content contained in the slag generated in the smelting using the stoichiometry of T. CaO, T. SiO₂ and 2CaO・SiO₂, and A first determination step is to determine whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a predetermined first threshold, A determination step in which a method for processing the slag is determined based on the result determined in the first determination step, A method for managing slag, which includes the following.

2. The slag management method according to claim 1, wherein the estimation step involves estimating the maximum free lime content of the slag using the following formula (1). Maximum free lime content = T. CaO - 1.86 × T. SiO ２ ・・・(1)

3. An analysis step which involves analyzing the free lime content of the slag that was determined to be above the first threshold in the first determination step, A second determination step is to determine whether the free calcium content analyzed in the above analysis step is above a predetermined second threshold, It has, The slag management method according to claim 1 or claim 2, wherein the determination step determines the slag processing method based on the results determined in the first determination step and the second determination step.

4. The slag management method according to claim 1 or claim 2, wherein the first threshold is 15 kg / t - molten iron.

5. The slag management method according to claim 3, wherein in the determination step, it is determined that the slag whose free lime content is determined to be equal to or greater than the second threshold in the second determination step will not be subjected to steam aging treatment.

6. A method for producing slag material, comprising processing the slag using a processing method determined in the determination step of the slag management method described in claim 1 or claim 2 to produce slag material.

7. A method for producing slag material, comprising processing the slag using a processing method determined in the determination step of the slag management method described in Claim 3 to produce slag material.

8. A method for producing slag material, comprising processing the slag using a processing method determined in the determination step of the slag management method described in Claim 4 to produce slag material.

9. A method for producing slag material, comprising processing the slag using a processing method determined in the determination step of the slag management method described in Claim 5 to produce slag material.

10. An estimation step of estimating the maximum free lime content contained in the slag generated in the refining process based on the component composition of auxiliary raw materials used in the refining of molten iron and the Si concentration of the molten iron before refining, A first determination step is to determine whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a predetermined first threshold, A determination step in which a method for processing the slag is determined based on the result determined in the first determination step, An analysis step which involves analyzing the free lime content of the slag that was determined to be above the first threshold in the first determination step, Whether the free calcium content analyzed in the aforementioned analysis step is above a predetermined second threshold. A second determination step to determine whether, It has, In the aforementioned determination step, based on the results determined in the first determination step and the second determination step A method for managing slag, which determines the slag processing method.

11. The slag management method according to claim 10, wherein in the determination step, it is determined that the slag whose free lime content is determined to be equal to or greater than the second threshold in the second determination step will not be subjected to steam aging treatment.

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