Slag determination method, slag treatment method using the same, and steel-making slag production method

Abstract

To provide a slag determination method, a slag treatment method using the same, and a steel-making slag production method, capable of avoiding generation of a large amount of defective slag that does not satisfy a quality standard determined by a standard such as JIS in a water immersion expansion test without construction of large-scale equipment and a large amount of operation cost.SOLUTION: A slag determination method of the present invention is a method for determining the properties of slag discharged from a converter. The slag is determined to be a non-defective product or a defective product by comparing an index value indicating the amount of free lime in the slag at the time of completion of a refining treatment process with a threshold value indicating a predetermined expansion limit of the slag. Slag discharged in a slag discharging process is treated by using the slag determination method. Further, slag determined to be a non-defective product by using the slag determination method is used as steelmaking slag.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for determining steelmaking slag generated in a converter, a method for treating slag using the same, and a method for producing steelmaking slag. [Background technology]

[0002] In the steelmaking process at steelworks, oxygen sources such as oxygen gas are added to molten pig iron in a converter to produce molten steel through oxidation refining (desiliconization, dephosphorization, and decarburization). In this oxidation refining process, slag is generated by the oxidation reaction of added auxiliary materials and impurities in the molten pig iron. After being recovered, this slag is reused as a raw material for various applications.

[0003] One of the uses of slag generated in converters is as roadbed material. When using slag as roadbed material, the water immersion expansion rate must meet quality standards set by standards such as JIS. For example, JIS standards require it to be 1.5% or less. In order to reduce the water immersion expansion rate of slag, it is necessary to keep the amount of free lime in the slag low. For this reason, a method is used in which a threshold value is set for an index that estimates the amount of free lime from the slag composition, and the amount of auxiliary materials added during the oxidation refining process is preset to control the water immersion expansion rate of slag below that threshold.

[0004] However, even if oxidation refining is performed with a preset amount of auxiliary raw materials, it is necessary to appropriately change the amount of oxygen and the amount of auxiliary raw materials depending on the state of the refining reaction in order to prevent abnormal reactions during the oxidation refining process. Therefore, there are cases where the slag composition does not become as preset. In such cases, slag in which the amount of free lime in the slag cannot be kept low is mixed with other slag in the slag pile, and does not meet the quality standards set by JIS and other standards in the water immersion expansion test, causing a large amount of defective products. Figure 3 is a diagram showing one embodiment of a conventional processing method for determining whether slag generated in the converter refining process is good or bad, as a conventional process.

[0005] As shown in Figure 3, slag generated in the converter is stored in the slag field in the slag conversion yard for each charge, and slag shipping lots are managed in large units of 300 charges per lot. As a result, even a few charges of slag that do not have a low free lime content may be mixed in, causing the slag to fail to meet the quality standards set by JIS and other standards in the water immersion expansion test. In such cases, steam aging must be performed on the entire 3,000 tons of steelmaking slag, which creates problems of heavy workload and high costs.

[0006] A method for avoiding such problems is disclosed in, for example, Patent Document 1. In this method, a modifier that fixes CaO in the converter slag is added to the molten converter slag, and a gas containing oxygen is blown onto the molten converter slag to granulate the converter slag at least once to a particle size of 10 mm or less and oxidize it. In this way, a method is shown in which the CaO in the converter slag is modified to prevent hydration expansion. However, this method is difficult to apply because it requires large-scale equipment and costs to modify the molten slag outside the converter. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2003-155511 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the conventional method, the water immersion expansion rate of slag is controlled by setting a threshold value for an index that estimates the amount of free lime from the slag composition, and then setting the amount of auxiliary materials added during the oxidation refining process to control the amount below the threshold value. However, even if the oxidation refining process is performed with the preset amount of auxiliary materials, it is necessary to appropriately change the amount of oxygen and the amount of auxiliary materials added depending on the state of the refining reaction in order to prevent abnormal reactions during the oxidation refining process. As a result, there are cases where the slag composition does not become as preset. In such cases, slag with a low amount of free lime in the slag is mixed with other slag in the slag pile, and does not meet the quality standards set by JIS and other standards in the water immersion expansion test, resulting in the generation of a large amount of non-defective products, up to 3,000 tons at once.

[0009] In addition, the method disclosed in Patent Document 1 requires large-scale equipment and high operating costs to reform the molten slag outside the converter, and therefore has the problem that it cannot be applied to an actual slag production process.

[0010] The object of the present invention is to propose a method for determining slag, a method for treating slag using the same, and a method for producing steelmaking slag, which can avoid the generation of large amounts of non-defective slag that does not meet quality standards set by JIS and other standards in water immersion expansion tests, without the construction of large-scale facilities or large operating costs. [Means for solving the problem]

[0011] The slag determination method of the present invention is a method for determining the properties of slag discharged from a converter, and is characterized in that the index value indicating the amount of free lime in the slag at the end of the refining process is compared with a threshold value (non-expansion threshold value) indicating a predetermined expansion limit of the slag, thereby determining whether the slag is good or bad. Note that in the present invention, the properties of the slag are determined by determining whether the above-mentioned slag is good or bad.

[0012] In the slag determination method according to the present invention configured as described above, (1) In the slag removal process, when the slag generated in the oxidation refining process is discharged into the same slag receiving pan, the index values ​​indicating the amount of free lime in the slag calculated at the end of each of the refining processes are compiled, and a collective judgment is made as to whether the slag is good or bad. (2) calculating an average index value of the index values ​​indicating the amount of free lime in the slag calculated at the end of each of the multiple refining treatment processes to determine whether the slag is good or bad, and comparing the average index value with the threshold value; (3) The judgment of whether the slag is non-defective or not is made by comparing an index value indicating the amount of free lime in the slag calculated at the end of each of the refining processes with the threshold value, and judging that the slag is non-defective if it contains even one non-defective product; This is believed to be a more preferable solution.

[0013] In addition, the slag processing method of the present invention calculates the composition of the slag at the end of the refining process in accordance with the above-mentioned slag judgment method, calculates the index value from the calculated slag composition, compares the index value with the threshold value, and if the comparison results in the slag being judged to be of good quality, places the slag discharged in the slag removal process on a good slag pile, and if the slag is not judged to be of good quality, judges it to be a candidate for non-good quality.

[0014] In the slag treatment method according to the present invention configured as described above, (1) Analyzing a sample of the slag determined to be a candidate for non-good quality, calculating a second index value in the slag from the composition of the sample analysis result, and if the second index value is compared with the threshold value and the slag is determined to be good quality, placing the slag discharged in the slag removal process on the good quality slag pile; if the second index value is compared with the threshold value and the slag is not determined to be good quality, determining the slag to be a non-good quality, and placing the slag discharged in the slag removal process on the non-good quality slag pile; (2) The slag determined to be non-defective is cooled, and then crushed and sized as necessary, and then recycled to the converter, or the slag is aged for a longer period than usual to convert it into non-defective slag. This is believed to be a more preferable solution.

[0015] Furthermore, in the method for producing steelmaking slag of the present invention, an index value indicating the amount of free lime in the slag at the end of the refining process is compared with a threshold value indicating a predetermined expansion limit of the slag, thereby judging the slag as good or bad, and the slag judged to be good is called steelmaking slag. Effect of the Invention

[0016] According to the method for determining slag, the method for treating slag using the same, and the method for producing steel slag of the present invention, a predefined threshold for non-expansion of slag is compared with the free lime index value, and the slag is determined and separated into good and bad products depending on the value of the free lime index value relative to the non-expansion threshold value. This makes it possible to avoid the generation of a large amount of defective slag that does not meet the quality standards set by standards such as JIS in the water immersion expansion test, which would result in a large workload and high costs such as multiple steam aging treatments. In addition, this method has the effect of requiring large-scale capital investment and large operating costs. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram for explaining one embodiment of the generation and treatment method of oxidized slag generated in the refining process of a converter. [Diagram 2] FIG. 1 is a diagram for explaining one embodiment of a processing method for determining whether oxidized slag generated in a converter refining process is good or bad and separating it. [Diagram 3] FIG. 1 is a diagram for explaining one embodiment of a conventional processing method for determining whether slag generated in a converter refining process is good or bad. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following detailed description, numerous specific details are set forth to illustrate embodiments of the present invention in order to provide a thorough understanding of the present invention. However, it will be apparent that one or more embodiments may be practiced without such specific details. Also, for the sake of simplicity, the drawings may show diagrammatic representations of well-known structures and devices.

[0019] <Regarding the steelmaking slag manufacturing method for implementing the slag evaluation method of the present invention> In the steel manufacturing method according to the present embodiment, molten pig iron tapped from a blast furnace is placed in a converter and oxidized to produce molten steel. In the following, molten pig iron and molten steel are collectively referred to as molten iron. The molten pig iron to be oxidized may be subjected to a molten pig iron pretreatment such as desiliconization, dephosphorization, and desulfurization in another refining facility.

[0020] In this embodiment, as shown in FIG. 1, first, molten iron, which is molten pig iron, is charged into a converter, and then an inert gas is blown into the molten iron from a plurality of bottom-blowing tuyeres, and oxygen gas is injected into the molten iron from a top-blowing lance, thereby performing an oxidation refining process. The oxidation refining process is a process in which an oxygen source is added to the molten iron, and impurity components such as carbon and phosphorus in the molten iron are oxidized and removed. In this embodiment, the oxidation refining process at least causes a decarburization reaction in which carbon is removed from the molten iron, and a dephosphorization reaction in which phosphorus is removed from the molten iron. In the following, the addition of oxygen gas (oxygen source) to the molten iron by injection of oxygen gas from the top-blowing lance is also referred to as blowing.

[0021] In the refining process, the carbon in the molten iron is oxidized and removed by the decarburization reaction, and molten steel with a low carbon concentration is produced. In the refining process, auxiliary materials such as slag-forming agents are added into the converter to promote the dephosphorization reaction. At this time, multiple types of slag-forming agents with different composition are added in amounts according to the target slag composition. The auxiliary materials such as slag-forming agents are determined in advance according to various blowing conditions such as the composition and temperature of the molten iron before the oxidation refining process, the target composition and target temperature of the molten iron after the oxidation refining process, the efficiency of the refining reaction, and the free lime content in the slag after the oxidation refining process. The determined input amount is then input at the beginning of the oxidation refining process. In the composition of the slag, the ratio of the CaO concentration (mass%) to the SiO2 concentration (mass%) ((%CaO) / (%SiO2)) is called the basicity. The amount of auxiliary materials to be added is calculated before the oxidation refining process based on the mass balance of the molten iron components, the planned amount of oxygen source to be added, etc., but additional auxiliary materials may be added to suppress the blowing up of slag and granular iron during the refining process. In the refining process, auxiliary materials are added and the blowing process is performed, and the oxidation refining process is completed when the molten iron components and temperature reach the target values.

[0022] First, the amount of oxide contained in the main raw material (scrap and ingots recovered from slag) charged into the converter before the oxidation refining process is calculated. In addition, the amount of auxiliary raw materials charged during the oxidation refining process, the amount of oxide generated by the oxidation of the components in the molten iron by the oxygen source, the amount of slag carried over from the previous oxidation refining process, the amount of refractory bricks lining the converter, etc. are calculated, including some estimates as necessary. Then, based on these calculated values, the amount of slag in the converter and the calculated slag composition are derived. The estimated basicity of the slag calculated from this calculated slag composition is also called the calculated basicity. From this calculated slag composition, a free lime index value indicating the amount of free lime in the slag according to the embodiment is calculated.

[0023] After the oxidation refining process, the converter is tilted to discharge the molten iron from the converter in the tapping process. The discharged molten iron is collected in a ladle (not shown) located below the converter and sent to the next process. After the tapping process, slag remains in the converter. The slag remaining in the converter is then discharged downward from the throat by tilting the converter in the opposite direction to the tapping process.

[0024] The discharged slag is collected in a slag receiving ladle located below the converter, and then discharged to a slag pile where it is cooled. If necessary, it is also separated into good and bad slag for management.

[0025] After that, after crushing and magnetic separation, the slag undergoes aging treatment to convert the free lime in the slag into lime hydroxide. The oxidized slag that has undergone the aging treatment undergoes a water immersion expansion test according to the JIS A 5015 test method to determine whether it can be shipped as roadbed material, and non-defective products are shipped as roadbed material.

[0026] <About the method for determining slag, the method for treating slag using the same, and the method for producing steelmaking slag of the present invention> In this embodiment, as shown in Fig. 2, the composition of the slag is calculated at the end of the refining process, the free lime index value in the slag is calculated from the calculated slag composition, and the free lime index value is compared with a predefined non-expansion threshold value of the slag. If the slag is judged to be good as a result of the comparison, it is placed in a good slag pile-up area. If it is not judged to be good, it is judged to be a candidate for a non-good slag.

[0027] As a method of judgment, a design may be made so that a product is judged to be good if the free lime content index value is equal to or less than the non-expansion threshold (or is less than the non-expansion threshold). Also, a product may be judged to be a non-good candidate if the free lime content index value is equal to or more than the non-expansion threshold (or exceeds the non-expansion threshold). This design is based on the characteristics of the free lime content index value, and the relationship is not limited.

[0028] In this embodiment, if the free lime content index value is below the non-expansion threshold, it is judged to be a good product, and the slag discharged in the slag removal process is placed in a good slag pile, and if the free lime content index value exceeds the non-expansion threshold, it is judged to be a candidate for a non-good product.

[0029] One example of the free lime index value is the following formula (1). In formula (1), the amount of CaO contained as a compound in the minerals in the slag is first estimated from the abundance ratio of oxides in each mineral to CaO, based on the amount of oxides such as SiO2, Al2O3, Fe2O3, and P2O5 in the slag. Then, the amount of CaO contained as a compound in the minerals is subtracted from the amount of CaO in the slag composition, and the remainder is calculated as the amount of free lime, and this value is often used.

[0030] Free lime index value (estimated formula) ≒ T.CaO-CaO(in 2CaO SiO2)-CaO(in 2CaO Al2O3)-CaO(in 2CaO Fe2O3)-CaO(in 3CaO P2O5)···Equation (1)

[0031] The following method is one example of a method for pre-determining the non-expansion threshold value of slag. First, the slag generated from multiple blows is collected and cooled at a slag pile, and a sample is taken. The free lime index value is calculated from the composition analysis value of the sample slag using formula (1) or the like. Then, the calculated free lime index value is compared with the results of a water immersion expansion test of the slag according to the test method of JIS A 5015 to determine the threshold value that satisfies the quality standards for roadbed material.

[0032] For slag determined to be a non-good candidate, a slag sample is analyzed, and a second free lime index value in the slag is calculated from the composition of the sample analysis results. If the calculated second free lime index value is equal to or less than the non-expansion threshold, the slag is determined to be good, and the slag discharged in the slag discharge process is placed in a good slag pile. On the other hand, if the second free lime index value exceeds the non-expansion threshold, the slag is determined to be bad, and the slag discharged in the slag discharge process is placed in a non-good slag pile. Note that the comparison between the second free lime index value and the non-expansion threshold (settings such as "greater than," "less than," "less than," "greater than," etc.) may be designed in any way, similar to the above.

[0033] The above-mentioned slag samples can be collected by inserting a ladle into the slag discharged into the slag receiving ladle, or by inserting a ladle into the slag discharged into the slag pile after the slag has been discharged into the slag receiving ladle. For the subsequent task of separating the good and bad slag, it is more preferable to collect samples from the slag discharged into the slag receiving ladle. The samples collected by the above-mentioned method are cooled and then analyzed using an analyzer that uses a technique such as X-ray fluorescence, and the composition analysis results are often obtained as the mass percentage values ​​of oxides such as CaO, SiO2, MnO, Fe2O3, Al2O3, and P2O5.

[0034] In the slag removal process, when the slag generated from multiple oxidation refining processes is discharged into the same slag receiving pan, the free lime index values ​​in the slag from multiple processes, calculated at the end of each refining process, can be compiled and used to make a collective judgment on whether the slag is good or bad.

[0035] In this case, the overall pass / fail judgment may be made by comparing an average index value calculated from the free lime index values ​​in the slag calculated at the end of each of the multiple refining treatment processes with a non-expansion threshold value.

[0036] Alternatively, the overall judgment of whether the slag is good or bad may be made by comparing the free lime index value in the slag calculated at the end of each of the multiple refining processes with the non-expansion threshold value, and judging the slag to be good if it contains even one non-good product.

[0037] The slag that is judged to be non-defective can be cooled, crushed and sized as necessary, and then recycled to the converter, or the slag can be aged for a longer period of time than usual to convert it into non-defective slag.

[0038] In an embodiment of the steelmaking slag manufacturing method of the present invention, slag that is determined to be good using the above-mentioned slag determination method is used as steelmaking slag. For example, in an embodiment of the steelmaking slag manufacturing method of the present invention, the slag may be determined to be good or bad by comparing an index value indicating the amount of free lime in the slag at the end of the refining process with a threshold value indicating a predetermined expansion limit of the slag, and the slag that is determined to be good may be used as steelmaking slag. This makes it possible to manufacture steelmaking slag suitable for applications such as roadbed material. EXAMPLES

[0039] Using the same steel manufacturing method as in the above embodiment, molten iron was refining processed in a converter. The free lime content index value in the slag generated during the refining process was calculated, and the free lime content index value was compared with the non-expansion threshold value. If the free lime content index value was equal to or less than the non-expansion threshold value, the slag was determined to be a good product, and the slag discharged in the slag discharging process was placed on a good slag pile. If the free lime content index value exceeded the non-expansion threshold value, the slag was determined to be a non-good product, and a sample of the slag was analyzed again, and a second free lime content index value in the slag was calculated from the composition of the sample analysis result. If the second free lime content index value was equal to or less than the non-expansion threshold value, the slag was determined to be a good product, and the slag discharged in the slag discharging process was placed on a good slag pile. If the second free lime content index value exceeded the non-expansion threshold value, the slag was determined to be a non-good product, and the slag discharged in the slag discharging process was placed on a non-good slag pile.

[0040] Slag samples that were determined to be non-defective were analyzed by inserting a sampling ladle into the slag discharged into the slag receiving pan, and the collected samples were then cooled, crushed, and sized before being analyzed using a fluorescent X-ray analyzer. The results obtained as a percentage of mass were used.

[0041] In addition, when calculating the free lime index value, when the slag generated from multiple oxidation refining processes is discharged into the same slag receiving ladle, the free lime index values ​​in the slag from multiple processes, calculated at the end of each of the multiple refining processes, are combined to make a collective judgment on whether the slag is good or bad.

[0042] The judgment of whether the slag was good or bad was carried out in the following two ways. In the first method, the free lime index value in the slag was calculated at the end of each of the multiple refining processes, and the average index value was calculated and compared with the non-expansion threshold value. In the second method, the judgment of whether the slag was good or bad was carried out in the same way, and the index value of the free lime index in the slag was calculated at the end of each of the multiple refining processes, and compared with the non-expansion threshold value, and if even one non-good item was included, it was judged to be a non-good item.

[0043] By applying this embodiment, it was possible to prevent the generation of a large amount of defective slag that does not meet the quality standards set by standards such as JIS in the water immersion expansion test due to the mixing of good slag with non-good slag. This made it possible to avoid the occurrence of a large workload and high costs such as multiple steam aging treatments. The following Table 1 shows the results when this embodiment was applied and when it was not applied.

[0044] [Table 1]

[0045] In determining whether a product was good or bad, the free lime index value was calculated using the following formula (2). As for the non-expansion threshold, first, the slag generated in multiple blows was collected and cooled at a slag pile, and a sample was taken. The free lime index value was calculated from the composition analysis value of the sample slag using formula (2). Next, the calculated free lime index value was compared with the results of a water immersion expansion test of the slag in accordance with the test method of JIS A 5015, and the threshold value that satisfies the quality standard for roadbed material was set at 0.45. Products below this non-expansion threshold of 0.45 were determined to be good products, and products above 0.45 were determined to be bad products.

[0046] Free lime index value = (%CaO)-1.87 x (%SiO2)-1.1 x (%Al2O3)-0.7 x (%T.Fe) x α-1.18 x (%P2O5) Equation (2) Here, α is a coefficient calculated from the actual ratio of the T.Fe value and the Fe2O3 value in the slag. Since the fluorescent X-ray analysis used in this example cannot directly calculate Fe2O3 as an analysis result, the actual ratio of the T.Fe value and the Fe2O3 value in the converter slag calculated by a different analysis method is used instead. In this example, α=0.64.

[0047] In this embodiment, the calculation of the free lime index value in the slag generated during the refining process and the judgment of whether the free lime index value is equal to or less than the non-expansion threshold value were automatically performed using a process computer. When the slag generated in multiple oxidation refining processes is discharged to the same slag receiving ladle, the free lime index values ​​in the slag calculated at the end of each refining process are combined and the overall judgment of pass / fail is automatically calculated using a process computer, and the result is automatically notified to the person in charge of the converter operation room and also to the person in charge of the slag field. When the slag receiving ladle containing the non-pass slag is transported, the person in charge of the slag field is reliably notified by turning on a red patrol light (registered trademark) installed near the work area and sounding an alarm. This also introduced a mechanism to prevent the person in charge of the slag field from placing pass and non-pass slag in the wrong slag pile.

[0048] The following two methods are introduced as setting items in the process computer so that they can be used selectively: (1) The method of collectively determining whether the slag is good or bad by calculating an average value of the free lime content index values ​​in the slag calculated at the end of each of the refining processes for a plurality of times, and comparing the average value with a non-expansion threshold value; and (2) The method of judging whether the slag is non-defective or not, by comparing the index value of the free lime content in the slag calculated at the end of each of the multiple refining processes with a non-expansion threshold value, and judging the slag as non-defective if it contains even one non-defective product.

Claims

1. A method for determining the properties of slag discharged from a converter, comprising the steps of: A method for determining whether the slag is good or bad by comparing an index value indicating the amount of free lime in the slag at the end of a refining process with a threshold value indicating a predetermined expansion limit of the slag.

2. 2. The slag judgment method according to claim 1, wherein in the slag removal process, when the slag generated in multiple oxidation refining processes is discharged into the same slag receiving pan, index values ​​indicating the amount of free lime in the slag calculated at the end of each of the multiple refining processes are compiled, and a collective judgment is made as to whether the slag is good or bad.

3. The slag judgment method according to claim 2, wherein the collective judgment of pass / fail is performed by calculating an average index value of index values ​​indicating the amount of free lime in the slag calculated at the end of each of the refining process steps, and comparing the average index value with the threshold value.

4. The slag judgment method according to claim 2, wherein the collective judgment of whether the slag is good or bad is performed by comparing an index value indicating the amount of free lime in the slag calculated at the end of each of the refining process steps with the threshold value, and judging the slag to be good if it contains even one non-good product.

5. A slag processing method comprising the steps of: calculating the composition of the slag at the end of the refining process according to the slag determination method of any one of claims 1 to 4; calculating the index value from the calculated slag composition; comparing the index value with the threshold value; and, if the slag is determined to be good quality as a result of the comparison, placing the slag discharged in the slag removal process on a good slag pile; and, if the slag is not determined to be good quality, determining it to be a candidate for a non-good quality.

6. A slag processing method as described in claim 5, further comprising the steps of: analyzing a sample of slag determined to be a candidate for non-good quality; calculating a second index value in the slag from the composition of the sample analysis result; and if the second index value is compared with the threshold value and the slag is determined to be good quality, placing the slag discharged in the slag removal process on the good slag pile; and if the second index value is compared with the threshold value and the slag is not determined to be good quality, determining the slag to be non-good quality, and placing the slag discharged in the slag removal process on the non-good slag pile.

7. The slag determined to be non-defective is cooled, and then crushed and sized as necessary, and recycled to the converter, or the slag is aged for a longer period of time than usual to convert it into non-defective slag.

8. A method for producing steelmaking slag, in which an index value indicating the amount of free lime in the slag at the end of a refining process is compared with a threshold value indicating a predefined expansion limit of the slag, thereby judging the slag as good or bad, and the slag judged to be good is used as steelmaking slag.

Images