Method for producing molten iron

Abstract

To provide a method for producing molten iron with which the molten iron is produced at high yield by melting reduced iron.SOLUTION: In a method for producing molten iron, in an electric furnace for discharging slag from a slag discharging port arranged at the side surface of a furnace body, a carbonaceous material is added and solid reduced iron is melted with arc heating to produce molten iron. The VM content in the carbonaceous material to be added is controlled to 30 mass% or less. In the case of a fixed type electric furnace, the molten iron is tapped so as to secure a distance of 100 mm or more between the lower end of the slag discharging port and the molten iron surface. In the case of a tilting type electric furnace, the slag is removed by tilting the furnace body so as to secure a height difference of 100 mm or more between the highest position at the lower end of the slag discharging port and the molten iron surface in the state of tilting the furnace body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing molten iron using an electric furnace. [Background technology]

[0002] In recent years, in order to reduce CO2 emissions, a method of producing molten iron by melting solid reduced iron in an electric furnace and reducing unreduced iron oxide has become widely adopted. When reducing the unreduced iron oxide, carbonaceous materials are added as a reducing agent. Solid reduced iron also contains large amounts of gangue components such as SiO2 and Al2O3, which turn into slag. Therefore, the basicity must be adjusted, and quicklime or other additives are added. Because a large amount of slag is produced during the melting of solid reduced iron, continuous melting of solid reduced iron requires the slag to be removed sequentially.

[0003] Therefore, various techniques have been proposed to efficiently discharge slag and tap molten iron and improve productivity.Patent Document 1 discloses a method for producing molten iron in which melting of solid reduced iron by an arc and discharge of slag from a slag outlet are alternately repeated multiple times, and the molten iron is tapped when a predetermined amount of molten iron is produced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-57431 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, solid reduced iron is continuously charged into an electric furnace, and unmelted solid reduced iron may remain immediately before the slag is discharged. In this case, the apparent density of the solid reduced iron is higher than that of the slag but lower than that of the molten iron, so unmelted solid reduced iron is likely to remain above the molten iron surface at the interface between the molten iron and the slag. In the method described in Patent Document 1, there is a possibility that unmelted solid reduced iron may also be discharged when the slag is discharged from the slag discharge port, resulting in a decrease in iron yield.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a method for producing molten iron by melting reduced iron to produce molten iron with a high yield. [Means for solving the problem]

[0007] The inventors conducted basic experiments to determine how unmelted solid reduced iron remains at the interface between molten iron and slag in order to prevent the unmelted solid reduced iron from being discharged together with the slag. They found that when hot briquetted iron (HBI) is used as the solid reduced iron and HBI is continuously charged, the unmelted HBI forms two layers on average on the molten iron. In other words, when the minor axis of the HBI is about 50 mm, an HBI layer about 100 mm thick exists above the molten iron surface.

[0008] In addition, steam coal or biomass coal is used as a reducing agent and recarburizer. These carbonaceous materials contain volatile matter (VM). When these carbonaceous materials are added, gas is rapidly generated in the furnace, disturbing the molten iron surface. This makes unmelted solid reduced iron more likely to float in the slag. Therefore, the inventors discovered that the iron yield can be improved by preventing the solid reduced iron layer from being discharged together with the slag while taking into consideration the stability of the molten iron surface in the furnace.

[0009] The present invention is as follows. [1] A method for producing molten iron, comprising adding a carbonaceous material and melting solid reduced iron by arc heating in an electric furnace in which slag is discharged from a slag discharge port disposed on a side of the furnace body without tilting the furnace body, the method comprising: The VM content of the carbonaceous material is 30% by mass or less, A method for producing molten iron, characterized in that the molten iron is tapped so that the distance between the lower end of the slag discharge port and the molten iron surface is 100 mm or more. [2] A method for producing molten iron, comprising: adding a carbonaceous material and melting solid reduced iron by arc heating in an electric furnace in which a furnace body is tilted and slag is discharged from a slag discharge port disposed on a side of the furnace body; The VM content of the carbonaceous material is 30% by mass or less, A method for producing molten iron, characterized in that the furnace body is tilted to drain the slag so that the difference in height between the highest point of the lower end of the slag discharge port and the molten iron surface is 100 mm or more, and then the molten iron is tapped. [3] The method for producing molten iron according to the above [1], characterized in that the supply of carbonaceous material is stopped before the distance between the lower end of the slag discharge port and the molten iron surface becomes 150 mm or less. [4] The method for producing molten iron according to the above [2], characterized in that when the furnace body is tilted, the supply of carbonaceous material is stopped before the molten iron surface reaches a height at which the distance between the highest position of the lower end of the slag discharge port and the molten iron surface is 150 mm. [5] The method for producing molten iron according to the above [1] or [2], characterized in that the proportion of fixed carbon derived from carbonaceous materials in the solid carbon source charged into the electric furnace is 95 mass% or less. [6] The method for producing molten iron according to the above [1] or [2], characterized in that the carbonaceous material is added to the slag discharge port side of the furnace center. [Effects of the Invention]

[0010] According to the present invention, reduced iron can be melted to produce molten iron with a high yield. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram for explaining the operation of a fixed type electric furnace. [Figure 2] FIG. 1 is a diagram for explaining the operation of a tilting type electric furnace. [Figure 3] This is an enlarged view of the area around the slag discharge port in a fixed type electric furnace. [Figure 4] This is an enlarged view of the area around the slag discharge port in a tilting type electric furnace. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present invention, the electric furnace may be of either a DC or AC type, and the method of energization is not particularly limited. Furthermore, the type of solid reduced iron is not particularly limited in the present invention. However, HBI is preferred because it is large in size and tends to accumulate unmelted iron above the molten iron surface at the interface between the molten iron and slag, thereby achieving a more significant effect. Therefore, an example using HBI as solid reduced iron will be described below.

[0013] (First embodiment) In this embodiment, a method for producing molten iron with a high yield in a fixed-type electric furnace in which the furnace body is not tilted when removing slag or pouring molten iron will be described.

[0014] FIG. 1 is a diagram for explaining the operation of a fixed AC electric furnace 10 in this embodiment. The electric furnace 10 includes electrodes 13 that heat the solid reduced iron, molten iron 11, and slag 12 by arcs, a charging section 14 into which the solid reduced iron, carbonaceous material, quicklime, etc. are charged, and an exhaust section 15 for exhausting gas and dust generated by reducing and melting the solid reduced iron. Although two electrodes 13 are shown in Fig. 1, the electric furnace 10 includes another electrode (not shown) behind these, for a total of three electrodes 13.

[0015] A slag discharge port 16 for discharging slag 12 is provided on the side of the furnace body of the electric furnace 10, and a tapping port 17 for tapping molten iron 11 is provided below the slag discharge port 16 and on the side opposite the slag discharge port 16. The slag discharge port 16 and the tapping port 17 are each configured to be able to be opened and closed as needed. The lower end of the slag discharge port 16 is located at a position 500 mm or more higher than the upper end of the tapping port 17. The tapping port 17 may also be provided on the bottom of the furnace instead of on the side.

[0016] Next, a detailed description will be given of a method for producing molten iron in the fixed-type electric furnace 10. First, the slag discharge port 16 and the tapping port 17 are closed, and solid reduced iron (HBI) is charged through the charging section 14 while the seed molten iron remains. The amount of carbonaceous material (and pig iron) required for reduction is also charged through the charging section 14, depending on the carbon concentration and metallization rate of the charged solid reduced iron. Furthermore, a lime source such as quicklime or dolomite is also charged through the charging section 14 to adjust the basicity of the slag 12 to be produced.

[0017] If the carbonaceous material to be charged contains a large amount of volatile matter (VM), the generated gas will significantly disturb the molten iron surface. If the molten iron surface is significantly disturbed, undissolved solid reduced iron will float in the slag, and the undissolved solid reduced iron may be discharged when the slag is discharged. Therefore, in this embodiment, the VM content of the carbonaceous material to be charged is set to 30% by mass or less. Preferably, the VM content is set to 20% by mass or less.

[0018] In this embodiment, steam coal or biomass coal is used as the carbonaceous material to be added, but compared to other carbon sources such as pig iron, the amount of gas generated causes greater disturbance to the molten iron surface. Therefore, among the solid carbon sources, including the carbon in the solid reduced iron, the carbon in the pig iron, and the solid carbon contained in the carbonaceous material, the proportion of fixed carbon derived from the carbonaceous material is preferably 95 mass% or less. Note that the solid carbon source does not include the volatile matter (VM) in the carbonaceous material, and the fixed carbon in the carbonaceous material is the total carbon in the carbonaceous material minus the carbon in the volatile matter (VM).

[0019] Then, the electrode 13 is lowered to near the surface of the molten iron, and an arc is generated from the lower end of the electrode 13 to heat the solid reduced iron. As a result, iron oxide (FeO) in the solid reduced iron is reduced by carbon in the solid reduced iron or carbon in the added carbonaceous material. Then, metallic iron in the solid reduced iron melts to become molten iron 11, and gangue components (SiO2 and Al2O3) in the solid reduced iron also melt to become part of slag 12. Furthermore, CO gas is generated by the reduction of the solid reduced iron, causing slag 12 to foam. The CO gas is discharged from the exhaust section 15, and part of the carbon dissolves in the molten iron 11.

[0020] As the reduction and melting of the solid reduced iron progresses as described above, the amounts of molten iron 11 and slag 12 increase. The introduction of the solid reduced iron, carbonaceous material, and lime source through the introduction port 14 and the heating by the arc continue. When the slag level reaches the lower end of the slag discharge port 16, the slag discharge port 16 is opened and the slag 12 is discharged through the slag discharge port 16. At this time, the introduction of the solid reduced iron, carbonaceous material, and lime source and the heating by the arc continue, and the tap port 17 is closed. Therefore, the amount of molten iron 11 increases even while the slag 12 is being discharged. The timing of opening the slag discharge port 16 is not particularly limited; it can be opened whenever the slag level reaches a level higher than the upper end of the slag discharge port 16.

[0021] FIG. 3 is an enlarged view of the vicinity of the slag discharge port 16 in the electric furnace 10 of FIG. 1 . Here, unmelted solid reduced iron remains above the molten iron surface 11X at the interface between the molten iron 11 and the slag 12. When HBI is added as the solid reduced iron, two layers are formed, and the solid reduced iron layer extends approximately 100 mm above the molten iron surface 11X. Therefore, when the slag discharge port 16 is open, the molten iron surface 11X rises due to an increase in the amount of molten iron 11. If the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 becomes less than 100 mm, the unmelted solid reduced iron will be discharged from the slag discharge port 16. Note that the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 is the length of a perpendicular line drawn from the lower end 16X of the slag discharge port to the molten iron surface 11X.

[0022] Therefore, in this embodiment, the tapping port 17 is opened to tap the molten iron 12 before the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 becomes less than 100 mm, ensuring that the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 is 100 mm or more. This prevents unmelted solid reduced iron from being discharged during slag discharge, thereby improving iron yield. While there is no particular upper limit for the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16, the maximum distance varies depending on the size of the furnace and is the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 when the minimum amount of molten iron (only seed molten iron) is present immediately before the end of tapping. When the tapping port 17 is opened to tap the molten iron 12, arc heating by the electrode 13 may be continued or stopped. When the slag level becomes lower than the lower end 16X of the slag outlet 16 due to the tapping, the slag outlet 16 is closed. Note that, when solid reduced iron is continuously charged after the tapping of the molten iron, the slag outlet 16 may be left open.

[0023] Furthermore, in order to prevent unmelted solid reduced iron from being discharged from the tap hole 17, the tap hole 17 is closed before the molten iron surface becomes lower than the upper end of the tap hole 17. The remaining molten iron is used as seed molten iron for the next charge. Note that, although the present embodiment has been described as a method for producing molten iron in a fixed-type electric furnace in which the furnace body does not tilt, the present invention can also be applied to a tilting-type electric furnace in which the furnace body is tilted and slag is discharged without tilting.

[0024] As described above, by adding a carbonaceous material with a VM content of 30% by mass or less, a carbon source can be secured without significantly disturbing the molten iron surface. However, if the carbonaceous material is continued to be added until the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 reaches approximately 100 mm, the molten iron surface is disturbed to some extent, which may cause solid reduced iron to flow out of the slag discharge port 16. Therefore, it is preferable to stop the supply of the carbonaceous material before the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 reaches 150 mm or less. This stabilizes the molten iron surface even if the amount of molten iron increases until just before the distance between the molten iron surface 11X and the lower end 16X of the slag discharge port 16 reaches 100 mm, thereby further reducing the risk of unmelted solid reduced iron flowing out of the slag discharge port 16.

[0025] The position at which the carbonaceous material is charged is not particularly limited. In the example shown in FIG. 1 , the charging section 14 is provided closer to the slag outlet 16 than the center of the furnace, allowing the carbonaceous material to be charged from the center of the furnace toward the slag outlet 14. This allows unmelted solid reduced iron suspended by gas generated from the carbonaceous material to be pushed toward the side opposite the slag outlet, thereby further preventing the unmelted solid reduced iron from flowing out through the slag outlet 14. In the example shown in FIG. 1 , both the solid reduced iron and the carbonaceous material are charged through the charging section 14. However, a separate charging section for charging the solid reduced iron may be provided on the side opposite the slag outlet 16 than the center of the furnace. This further prevents the unmelted solid reduced iron from flowing out through the slag outlet 16.

[0026] (Second embodiment) In this embodiment, a method for producing molten iron with a high yield in a tilting electric furnace in which the furnace body is tilted when removing slag or pouring molten iron will be described.

[0027] 2 is a diagram illustrating the operation of a tilting-type AC electric furnace 20 in this embodiment. The electric furnace 20 includes electrodes 23 that heat solid reduced iron, molten iron 21, and slag 22 by arcs, a charging section 24 into which the solid reduced iron, carbonaceous material, quicklime, and the like are charged, and an exhaust section 25 for discharging gas and dust generated by reducing and melting the solid reduced iron. Although two electrodes 23 are shown in FIG. 2, the electric furnace 20 includes another electrode (not shown) behind the two electrodes 23, for a total of three electrodes 23.

[0028] A slag discharge port 26 for discharging slag 22 is provided on the side of the electric furnace 20 body, and a tapping port 27 for discharging molten iron 21 is provided on the bottom of the electric furnace 20 body. The slag discharge port 26 and the tapping port 27 are each configured to be openable and closable as needed. The electric furnace 20 can be tilted toward the slag discharge port 26 by a tilting device (not shown). In the example of FIG. 2, the tapping port 27 is provided on the bottom of the furnace, but it may be provided on the side opposite to the slag discharge port 26. In this case, the electric furnace 20 can be tilted toward the slag discharge port 26 and the tapping port 27 by a tilting device (not shown).

[0029] Next, a detailed description will be given of a method for producing molten iron in the tilting electric furnace 20. First, when the electric furnace 20 is not tilted, the slag outlet 26 and the tapping port 27 are closed, and seed molten metal is left. Then, solid reduced iron, carbonaceous material (and pig iron), and lime source material are charged into the charging port 24 in the same manner as in the first embodiment.

[0030] As in the first embodiment, if the molten iron surface is significantly disturbed by gas generation, there is a risk that unmelted solid reduced iron will be discharged from the slag discharge port 26. Therefore, in this embodiment, the VM content of the carbonaceous material to be charged is set to 30% by mass or less. Preferably, the VM content is set to 20% by mass or less. Furthermore, as in the first embodiment, the proportion of fixed carbon derived from the carbonaceous material among the solid carbon sources including carbon in the solid reduced iron, carbon in the pig iron, and solid carbon contained in the carbonaceous material is preferably set to 95% by mass or less.

[0031] The electrode 23 is then lowered to the vicinity of the molten iron surface, and an arc is generated from the lower end of the electrode 23 to heat the solid reduced iron. As a result, the solid reduced iron is reduced and melted to form molten iron, and gangue components in the solid reduced iron become slag. As described above, the amounts of molten iron 21 and slag 22 increase as the reduction and melting of the solid reduced iron progresses. Then, the solid reduced iron, carbonaceous material, and lime source are continuously charged through the charging section 24 and heated by the arc until the amounts of molten iron 21 and slag 22 reach predetermined amounts.

[0032] FIG. 2(a) shows the state in which slag 22 is being discharged. FIG. 4 is an enlarged view of the vicinity of the slag discharge port 26 of the electric furnace 20 shown in FIG. 3 during slag discharge. When the amounts of molten iron 21 and slag 22 reach a predetermined amount, the introduction of solid reduced iron, carbonaceous material, and lime source material from the charging port 24 and the arc heating are stopped. The furnace body of the electric furnace 20 is tilted toward the slag discharge port 26, and the slag door 28 is opened. The slag discharge port 26 is then opened, and the slag 22 is discharged through the slag discharge port 26. As described above, a layer of unmelted solid reduced iron is formed approximately 100 mm above the molten iron surface. Therefore, the slag 22 is discharged while the furnace body of the electric furnace 20 is tilted so that the height difference between the molten iron surface 21X and the highest point 26X of the lower end of the slag discharge port 26 is at least 100 mm. The distance between the molten iron surface 21X and the highest point 26X of the lower end of the slag discharge port 26 is the length of a perpendicular line drawn from the highest point 26X of the lower end of the slag discharge port 26 to the molten iron surface 21X. The upper limit of the distance between the molten iron surface 21X and the highest point 26X of the lower end of the slag discharge port 26 varies depending on the amount of molten iron and slag and the tilting angle at the start of slag discharge of the slag 22, but the practical upper limit is when solid reduced iron is added to the seed molten metal to start reduction and melting of the solid reduced iron, and the slag 22 is first discharged without tilting the furnace body.

[0033] Furthermore, if the molten iron surface is disturbed by gas generated from the carbonaceous material when the furnace body is tilted to discharge the slag 22 through the slag discharge port 26, unmelted solid reduced iron may flow out of the slag discharge port 26 even when the height difference between the molten iron surface 21X and the highest point 26X of the lower end of the slag discharge port 26 is maintained at 100 mm or more with the furnace body of the electric furnace 20 tilted. Therefore, it is preferable to stop the supply of carbonaceous material before the height difference between the molten iron surface 21X and the highest point 26X of the lower end of the slag discharge port 26 becomes 150 mm or less with the furnace body of the electric furnace 20 tilted. In this case, since the tilting angle is predetermined, it is sufficient to back-calculate the height of the molten iron surface when the furnace body of the electric furnace 20 is not tilted, at which the height difference between the molten iron surface 21X and the highest point 26X of the lower end of the slag discharge port 26 becomes 150 mm with the furnace body tilted, and stop the supply of carbonaceous material before the molten iron surface reaches that height.

[0034] After the slag 22 has been removed, the tilted electric furnace 20 is returned to its untilted position, and the slag door 28 is closed to close the slag outlet 26. Then, as shown in FIG. 2(b), the tap hole 27 is opened and the molten iron 21, excluding the seed molten iron, is poured from the tap hole 27. While FIG. 2 illustrates an example in which the molten iron is poured without tilting the furnace body, if the tap hole is located on the side opposite the slag outlet, the furnace body is tilted toward the tap hole and the tap hole is opened to pour the molten iron. Then, before the molten iron surface becomes lower than the highest point at the top of the tap hole 27, the tap hole is closed to leave an amount of molten iron equivalent to the seed molten iron. Then, for the next charge, the introduction of solid reduced iron, carbonaceous material, and lime source from the input port 24 and arc heating are resumed.

[0035] Alternatively, after the slag discharge, the molten iron may not be discharged, and the furnace body may be returned to its non-tilted state, after which the solid reduced iron, carbonaceous material, and lime source may be introduced through the charging port 24 and arc heating may be resumed. In this case, for example, the amount of molten iron increases by repeatedly melting the solid reduced iron and discharging the slag. However, when the amount of molten iron reaches a point where the distance between the molten iron surface and the highest point of the lower end of the slag discharge port 26 cannot be maintained at 100 mm or more when the furnace body is tilted, the molten iron must be discharged. Because the slag discharge port 26 is closed when the furnace body is not tilted, the distance between the molten iron surface and the lower end of the slag discharge port 26 may be less than 100 mm when the molten iron discharge is initiated. However, if the slag door 28 is made of iron, the molten iron should preferably be discharged before the molten iron surface reaches the lower end of the slag discharge port 26 because of the possibility of the slag door 28 melting.

[0036] In this embodiment, after the slag 22 has been discharged, the tilted electric furnace 20 is returned to its non-tilted state and the slag discharge port 26 is closed, but the slag discharge port 26 may remain open. When the melting of solid reduced iron and the discharge of slag are repeated with the slag discharge port 26 open, the molten iron is tapped before the distance between the surface of the molten iron and the lower end of the slag discharge port 26 becomes less than 100 mm to prevent the solid reduced iron from being discharged from the slag discharge port 26.

[0037] The position at which the carbonaceous material is charged is not particularly limited. Similarly, in the example shown in FIG. 2 , the charging section 24 is provided closer to the slag outlet 26 than the center of the furnace, allowing the carbonaceous material to be charged from the center of the furnace toward the slag outlet 24. This allows unmelted solid reduced iron suspended by gas generated from the carbonaceous material to be pushed toward the side opposite the slag outlet, thereby further preventing the unmelted solid reduced iron from flowing out through the slag outlet 24. In the example shown in FIG. 2 , both the solid reduced iron and the carbonaceous material are charged through the charging section 24. However, a separate charging section for charging the solid reduced iron may be provided on the side opposite the slag outlet 26 than the center of the furnace. This further prevents the unmelted solid reduced iron from flowing out through the slag outlet 24.

[0038] As described above, the first and second embodiments can prevent unmelted solid reduced iron from being discharged together with the slag, thereby further improving iron yield. The height of the molten iron surface can be measured by the following method. First, before adding the solid reduced iron, the electrode is lowered while the seed molten iron remains, and the electrical conductivity is measured. Because the electrical conductivity of slag and molten iron differs, the position at which the electrical conductivity changes significantly is the initial height of the molten iron surface. Furthermore, by measuring the furnace profile with a laser profile meter and understanding the internal structure of the electric furnace in advance, the height of the molten iron surface in the furnace relative to the amount of molten iron can be predicted. The amount of molten iron to be produced is estimated from the amount of solid reduced iron added, and the height relative to the estimated amount of molten iron is added to the initial height of the molten iron surface, thereby determining the height of the molten iron surface (including the tilted state). [Example]

[0039] Next, examples of the present invention will be described, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0040] (First Example) In a 100-ton fixed-type AC electric furnace 10, as shown in Figure 1, with a slag discharge port 16 installed on the side wall of the furnace body and a tap port 17 on the side opposite the slag discharge port 16, an electrode 13 was lowered with 10 t of molten pig iron remaining as seed molten metal, and the electrical conductivity and initial height of the molten iron surface were measured. In addition, a laser profile meter was used to measure the furnace profile, and the relationship between the amount of solid reduced iron charged and the position of the molten iron surface was predicted.

[0041] Subsequently, HBI having the composition shown in Table 1 as solid reduced iron, carbonaceous material having the composition shown in Table 2, and quicklime for adjusting basicity were charged from the charging section 14. Then, the electrode 13 was lowered to the surface of the molten iron to generate an arc, which heated the HBI to produce molten iron. The HBI had an apparent density of 5 g / cm 3 The size of the melting furnace used was 130 to 150 mm in major axis and 50 mm in minor axis. HBI, carbonaceous material, and quicklime were charged at predetermined intervals to continuously melt the HBI. In Examples 2 and 3, pig iron having the composition shown in Table 3 was also charged from the charging part 14 together with the carbonaceous material. Furthermore, the angle of the charging part 14 was adjusted to adjust the charging position of the carbonaceous material depending on the test.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] When the slag surface reached a height of 20 mm from the upper end of the slag discharge port 16 due to the melting of the HBI, the slag door was opened to open the slag discharge port 16, and the slag was discharged without tilting the furnace body. When the height of the molten iron surface reached a position 120 mm below the lower end 16X of the slag discharge port 16, the tapping port 17 was opened to discharge the molten iron, leaving only a seed molten iron (10 t) for the next charge. Five charges of molten iron were produced using the above procedure for each example, and the average iron yield for the five charges was calculated. The iron yield was calculated using the following formula. The results are shown in Table 4. Yield (%) = amount of metal produced (t) / {amount of HBI input (t) × 0.868} × 100

[0046] [Table 4]

[0047] The "proportion of fixed carbon derived from carbonaceous materials (mass%)" in Table 4 represents the proportion of fixed carbon derived from carbonaceous materials out of the total solid carbon sources, which are carbon in the solid reduced iron, carbon in the pig iron, and fixed carbon contained in the carbonaceous materials. Also, the "stop timing" in Table 4 represents the distance between the bottom of the slag discharge port and the molten iron surface when the supply of carbonaceous materials was stopped.

[0048] Examples 1 and 2 are examples using different biomass charcoals, and both were carbonaceous materials with low VM contents, so the yield was higher than in the comparative example. Example 3 is an example in which part of the carbonaceous material was replaced with pig iron, and the same biomass charcoal as in Example 2 was used as the carbonaceous material. Since the amount of carbonaceous material added was smaller than in Example 2, disturbance of the molten iron surface could be further suppressed, so the yield was higher than in Example 2.

[0049] Example 4 is an example in which pig iron was used as the carbon source in the same ratio as in Example 3, and the positions at which the carbonaceous material and pig iron were introduced were changed. The unmelted solid reduced iron was kept away from the slag discharge port, resulting in a higher yield than in Example 3. Example 5 is an example in which the timing for stopping the supply of the carbonaceous material and pig iron was earlier than in Example 4, and the molten iron surface was stabilized more quickly during slag discharge, resulting in a higher yield than in Example 4. On the other hand, Comparative Examples 1 and 2 used biomass coal or steam coal with a VM content exceeding 30% by mass, which significantly disturbed the molten iron surface, resulting in a lower yield than Examples 1 and 2.

[0050] (Second Example) In a 100-ton tiltable AC electric furnace with a slag discharge port 26 on the side wall and a tap port 27 at the bottom, as shown in FIG. 2, the initial height of the molten iron surface was measured using the same procedure as in Example 1, with 10 t of molten pig iron remaining as seed molten iron. The relationship between the amount of solid reduced iron charged and the position of the molten iron surface was predicted. Subsequently, HBI with the composition shown in Table 1, carbonaceous material with the composition shown in Table 2, and quicklime for adjusting basicity were charged into the furnace through the charging port 24. The electrode 23 was then lowered to the molten iron surface, generating an arc to heat the HBI and produce molten iron. The HBI was the same as in Example 1. The HBI, carbonaceous material, and quicklime were charged at predetermined intervals to continuously melt the HBI. In Examples 12 and 13, pig iron with the composition shown in Table 3 was also charged into the furnace through the charging port 24 along with the carbonaceous material. Furthermore, the angle of the charging part 24 was adjusted to adjust the charging position of the carbonaceous material depending on the sample.

[0051] When the slag level reached a height of 20 mm above the top of the slag discharge port 26, the furnace body was tilted, the slag door 28 was opened, and the slag was discharged through the slag discharge port 26. The tilting angle was adjusted to 15 degrees. After the slag was discharged, the furnace body was returned to its non-tilted state, the slag door 28 was closed, the slag discharge port 26 was closed, and the introduction of HBI and melting were resumed. The melting of HBI and the discharge of slag were then repeated. When the molten iron level reached a position 120 mm below the bottom of the slag discharge port 26, the tap hole 27 was opened and the molten iron was discharged, leaving only a seed molten iron (10 t) for the next charge. Five charges of molten iron were produced in each example using the above procedure, and the average iron yield for the five charges was calculated. The results are shown in Table 5.

[0052] [Table 5]

[0053] The "proportion of fixed carbon derived from carbonaceous materials (mass%)" in Table 5 represents the proportion of fixed carbon derived from carbonaceous materials out of the total solid carbon sources, which are carbon in the solid reduced iron, carbon in the pig iron, and fixed carbon contained in the carbonaceous materials. Also, the "stop timing" in Table 5 represents the distance between the highest position of the bottom end of the slag discharge port and the molten iron surface when the furnace body is tilted at the timing when the supply of carbonaceous materials is stopped.

[0054] Examples 11 and 12 were examples using different biomass charcoals, and both were carbonaceous materials with low VM contents, so the yield was higher than that of the comparative examples. Example 13 was an example in which part of the carbonaceous material was replaced with pig iron, and the same biomass charcoal as in Example 12 was used as the carbonaceous material. Since the amount of carbonaceous material added was smaller than in Example 12, disturbance of the molten iron surface could be further suppressed, so the yield was higher than that of Example 12.

[0055] Example 14 is an example in which pig iron was used as the carbon source in the same ratio as in Example 13, and the positions at which the carbonaceous material and pig iron were introduced were changed. The unmelted solid reduced iron was kept away from the slag discharge port, resulting in a higher yield than in Example 13. Example 15 is an example in which the timing for stopping the supply of the carbonaceous material and pig iron was earlier than in Example 14, and the molten iron surface could be stabilized more quickly during slag discharge, resulting in a higher yield than in Example 14. On the other hand, Comparative Examples 11 and 12 used biomass coal or steam coal with a VM content exceeding 30% by mass, which significantly disturbed the molten iron surface, resulting in a lower yield than in Examples 11 and 12.

[0056] The present invention includes the following methods. [Method 1] A method for producing molten iron, comprising adding a carbonaceous material and melting solid reduced iron by arc heating in an electric furnace in which slag is discharged from a slag discharge port disposed on a side of the furnace body without tilting the furnace body, the method comprising: The VM content of the carbonaceous material is 30% by mass or less, A method for producing molten iron, characterized in that the molten iron is tapped so that the distance between the lower end of the slag discharge port and the molten iron surface is 100 mm or more. [Method 2] A method for producing molten iron, comprising: adding a carbonaceous material and melting solid reduced iron by arc heating in an electric furnace in which a furnace body is tilted and slag is discharged from a slag discharge port disposed on a side of the furnace body; The VM content of the carbonaceous material is 30% by mass or less, A method for producing molten iron, characterized in that the furnace body is tilted to drain the slag so that the difference in height between the highest point of the lower end of the slag discharge port and the molten iron surface is 100 mm or more, and then the molten iron is tapped. [Method 3] 2. The method for producing molten iron according to method 1, wherein the supply of the carbonaceous material is stopped before the distance between the lower end of the slag discharge port and the molten iron surface becomes 150 mm or less. [Method 4] The method for producing molten iron according to method 2, characterized in that the supply of carbonaceous material is stopped before the molten iron surface reaches a height at which the distance between the highest position of the lower end of the slag discharge port and the molten iron surface is 150 mm when the furnace body is tilted. [Method 5] 5. The method for producing molten iron according to any one of methods 1 to 4, wherein the proportion of fixed carbon derived from carbonaceous materials in the solid carbon source charged into the electric furnace is 95 mass % or less. [Method 6] 6. The method for producing molten iron according to any one of methods 1 to 5, wherein the carbonaceous material is added to the slag discharge port side of the furnace center. [Explanation of symbols]

[0057] 10, 20 Electric furnace 11, 21 Molten iron 11X, 21X Molten iron surface 12, 22 Slug 13, 23 electrode 14, 24 Input section 15, 25 Exhaust section 16, 26 Slag discharge port 16X Bottom end of slag discharge port 26X Highest position of the bottom of the slag discharge port 17, 27 Tap Outlets 28 Slag Door

Claims

1. A method for producing molten iron, comprising adding a carbonaceous material and melting solid reduced iron by arc heating in an electric furnace in which slag is discharged from a slag discharge port disposed on a side of the furnace body without tilting the furnace body, the method comprising: The VM content of the carbonaceous material is 30% by mass or less, A method for producing molten iron, characterized in that the molten iron is tapped so as to ensure a distance of 100 mm or more between the lower end of the slag discharge port and the molten iron surface.

2. A method for producing molten iron, comprising: adding a carbonaceous material and melting solid reduced iron by arc heating in an electric furnace in which a furnace body is tilted and slag is discharged from a slag discharge port disposed on a side of the furnace body; The VM content of the carbonaceous material is 30% by mass or less, A method for producing molten iron, characterized in that the furnace body is tilted to discharge the slag so that the difference in height between the highest position of the lower end of the slag discharge port and the molten iron surface is 100 mm or more, and then the molten iron is tapped.

3. 2. The method for producing molten iron according to claim 1, wherein the supply of carbonaceous material is stopped before the distance between the lower end of the slag discharge port and the molten iron surface becomes 150 mm or less.

4. 3. The method for producing molten iron according to claim 2, wherein the supply of carbonaceous material is stopped before the molten iron surface reaches a height at which the distance between the highest position of the lower end of the slag discharge port and the molten iron surface is 150 mm when the furnace body is tilted.

5. 3. The method for producing molten iron according to claim 1, wherein the proportion of fixed carbon derived from carbonaceous materials in the solid carbon source charged into the electric furnace is 95 mass % or less.

6. 3. The method for producing molten iron according to claim 1, wherein the carbonaceous material is added to a position closer to the slag discharge port than the center of the furnace.

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