Methods for manufacturing molten iron

Abstract

A method for efficiently manufacturing molten iron using an electric arc furnace is provided. The method involves supplying a chill to an electric arc furnace, melting the supplied chill to produce molten iron, wherein the method satisfies a predetermined formula.

Description

Technical Field

[0001] This invention relates to a method for manufacturing molten iron. Prior Technology

[0002] Due to the global push for carbon neutrality, the steel industry is being required to shift from the blast furnace method to the electric arc furnace method for molten iron production. In the blast furnace method, lump ore, sinter, and coke are the main raw materials. Coke is used as fuel for heating and also as a raw material for reducing iron oxide in the iron ore, producing low-melting-point molten pig iron with a carbon concentration of approximately 4% to 5% by mass. Therefore, a large amount of coke is fed into the blast furnace. The carbon in the molten pig iron produced in the blast furnace is removed in the converter process, ultimately becoming carbon dioxide. As a result, approximately 2 tons of carbon dioxide are generated for every 1 ton of iron produced in both blast furnace and converter methods for crude steel production.

[0003] In contrast, the electric arc furnace (EAF) process produces crude steel by heating and melting raw materials such as scrap using electrical energy. Because the EAF uses already reduced iron as raw material, no reduction energy is required, and the energy for heating the raw material is also supplied by electricity. Therefore, the carbon dioxide production is approximately 0.5 tons per ton of iron, which is significantly less compared to methods using blast furnaces and converters.

[0004] Scrap and reduced iron can be cited as raw materials used in the electric arc furnace process. Among the scrap, there is high-quality scrap suitable for manufacturing advanced steel; however, due to its limited quantity, competition for scrap may arise between other companies, including electric arc furnace manufacturers, and between the manufacturer itself and other companies. Therefore, even simply converting molten iron production from the blast furnace process to the electric arc furnace process to promote carbon neutrality may make it difficult to re-secure a large and stable supply of high-quality scrap used in the electric arc furnace process.

[0005] Therefore, the use of reduced iron (RI) as a raw material in the electric arc furnace process can be considered. RI is metallic iron obtained by reducing iron ore. In the case of using the Midlex process to manufacture RI, natural gas is used as the raw material, and a gas containing a large amount of hydrogen is used as the reducing agent. Therefore, compared to the blast furnace process, it is possible to reduce carbon dioxide emissions equivalent to the reduction by hydrogen. Furthermore, a method for manufacturing RI using hydrogen directly as the reducing agent is under development; if realized, it could potentially achieve completely zero-carbon ironmaking.

[0006] However, reduced iron sometimes contains approximately 2% to 10% by mass gangue components from the ore, i.e., impurities other than iron. Therefore, additional energy is required to melt the gangue components and to melt the lime added to neutralize them when melting reduced iron. Consequently, when using an electric arc furnace (EAF), as an example of an electric furnace, compared to a case where all raw materials are scrap, the following problem arises: as the proportion of reduced iron in the raw material increases, the power consumption (electricity required to produce 1 ton of iron) deteriorates. Furthermore, because reduced iron is relatively difficult to melt, it tends to agglomerate and form large lumps (icebergs) within the EAF. This makes reduced iron even more difficult to melt in the EAF, leading to longer steelmaking times and a further deterioration in power consumption.

[0007] To reduce the power consumption of electric arc furnaces and improve productivity, various methods have been developed. For example, methods such as preheating the cold iron source before melting and blowing coke as an auxiliary heat source have been employed. As preheating furnaces for preheating scrap, for example, the CONSTEEL electric furnace has been developed for horizontal preheating furnaces, and the ECOARC (registered trademark) electric furnace, Quantum electric furnace, and SHARC electric furnace have been developed for vertical preheating furnaces.

[0008] Furthermore, research has been conducted on improving the preheating efficiency of cold iron sources. For example, Patent Document 1 discloses a method for manufacturing molten iron, characterized in that, in an electric furnace equipped with a preheating chamber, the apparent bulk density of the iron-based scrap in the preheating chamber is set to be 0.50 t / m3 or more and less than 1.00 t / m3, and the filling height of the scrap in the preheating chamber is set within a predetermined range, etc.

[0009] Patent document 2 describes a method for melting waste materials, in which the apparent bulk density of the waste materials in the preheating chamber is set to 0.7 t / m3 or higher in an electric furnace equipped with a preheating chamber. [Existing Technical Documents] [Patent Literature]

[0010] Patent Document 1: International Publication No. 2021 / 049125 Patent Document 2: Japanese Patent Application Publication No. 2012-180560 Summary of the Invention

[0011] [The problem that the invention aims to solve] The technologies described in Patent Documents 1 and 2 primarily aim to improve energy utilization efficiency by enhancing preheating efficiency. However, a technology is needed to further improve the power unit by further increasing melting efficiency. Furthermore, a method is needed to improve melting efficiency regardless of the apparent bulk density of the chill source.

[0012] The present invention was made in view of this situation, and its object is to provide a method for efficiently manufacturing molten iron using an electric arc furnace. [Technical means to solve the problem]

[0013] Through in-depth research, the inventors discovered that the above-mentioned objective can be achieved by adopting the following configuration.

[0014] 1. A method for manufacturing molten iron, comprising supplying a chill to an electric arc furnace and melting the supplied chill to produce molten iron. The method for manufacturing the molten iron satisfies the following equations (1) and (2). [Number 1] [Number 2] in, vI represents the supply rate of the chill source (t / min); P represents the energy input to the electric arc furnace (MW); Tph represents the temperature (°C) of the cold iron source; Tm represents the temperature (°C) of the molten iron inside the electric arc furnace; ρ represents the bulk density (t / m3) of the chill source.

[0015] 2. The method for manufacturing molten iron as described in 1, wherein the chill source comprises scrap and reduced iron.

[0016] 3. The method for manufacturing molten iron as described in 1 or 2, wherein The electric arc furnace includes a measuring device and a control device; The method for manufacturing the molten iron includes: The measuring device measures at least one of the temperature of the chill, the temperature of the molten iron, and the bulk density of the chill; and The control device controls at least one of the input energy and the supply rate based on the measurement results of the measuring device. [The effects of the invention]

[0017] According to the present invention, a method for efficiently manufacturing molten iron using an electric arc furnace can be provided. Simple Explanation of the Diagram

[0018] Figure 1 is a diagram showing an example of an electric arc furnace. Figure 2 shows an example of an electric arc furnace. Figure 3 shows an example of an electric arc furnace. Figure 4 shows an example of an electric arc furnace. Figure 5 is a graph showing the relationship between the temperature of the chill source and the melting time coefficient. Figure 6 is a graph showing the relationship between molten iron temperature and melting time coefficient. Figure 7 is a graph showing the relationship between bulk density and melting time coefficient. Implementation

[0019] The present invention will now be described in detail. The following description is an example of a preferred embodiment of the present invention, and the present invention is not limited to the embodiments described below.

[0020] [Methods for manufacturing molten iron] In a method for manufacturing molten iron according to one embodiment of the present invention, a chill is supplied to an electric arc furnace, and the supplied chill is melted to manufacture molten iron. Furthermore, the manufacturing method is characterized by satisfying the above-described equations (1) and (2). In the electric furnace, if the supply rate of the chill is too high relative to the melting rate, the amount of unmelted chill in the furnace will increase, and the chills may fuse together to form large iron blocks. Since the surface area ratio of the iron blocks to their volume is small, the melting rate is low, and the formation of iron blocks leads to a decrease in productivity and an increase in the required electricity. If the physical properties of the supplied chill and the supply rate of the chill meet the prescribed conditions, the chill can be melted efficiently.

[0021] [Cold Iron Source] The chill source used in this embodiment is not particularly limited, and raw materials containing iron, such as scrap, reduced iron, pig iron, etc., can be used. The chill source can contain scrap and reduced iron, or it can be composed of scrap and reduced iron. As the reduced iron, for example, briquetted iron, i.e., hot briquetted iron (HBI), can be used. As mentioned above, since reduced iron is relatively difficult to melt, the power unit tends to decrease when the proportion of reduced iron in the chill source increases. However, according to the present invention, even when the chill source contains scrap and reduced iron, molten iron can be produced efficiently. Furthermore, the composition of the chill source is not limited. The reduced iron can contain 2% by mass and 10% by mass of components other than iron (Fe) (typically impurities).

[0022] There is no particular limitation on the mixing ratio of the chilled iron source, but the scrap ratio is preferably set in the range of 30% to 70% by mass. Similarly, the reduced iron ratio is preferably set in the range of 30% to 70% by mass. If the scrap ratio is too high, the risk of impurity contamination may increase; if the reduced iron ratio is too high, the melting efficiency may decrease. Therefore, the optimal ratio should be selected based on operating conditions, product quality, and other factors.

[0023] Furthermore, based on the particle size, bulk density, metallization rate, and other physical properties of HBI used as reduced iron, by adjusting the mixing ratio with waste, it is possible to suppress agglomeration and iceberging in the furnace, thereby achieving stable melting behavior.

[0024] The mixing ratio of the cold iron source can be controlled in advance or adjusted during the operation of the electric arc furnace. Specific methods will be described later.

[0025] [Electric Arc Melting Furnace] The electric arc furnace used in this embodiment is illustrated using figures. Figures 1 to 4 show preferred examples of the electric arc furnace.

[0026] The electric arc furnace 1a shown in Figure 1 includes a melting chamber 2a. The upper cover of the melting chamber 2a includes a chill supply device 3 and an opening on the melting chamber side. Chills x, which become raw materials, are supplied to the melting chamber 2a through the opening of the chill supply device 3. The opening of the chill supply device 3 is, for example, the opening for supplying a bucket. The melting chamber 2a includes electrodes 4 for generating an electric arc A and for heating. The chills x supplied to the melting chamber 2a are melted by the electric arc heat to become molten iron m and molten slag s. The obtained molten iron m can be tapped by any method.

[0027] The electric arc furnace 1b shown in Figure 2 includes a melting chamber 2b and a preheating chamber 5b. The chill source x, which becomes the raw material, is loaded into a feeding hopper 6 and transported by a traveling trolley 7 to the top of the required chill source supply port 8. Then, the chill source supply port 8 is opened, and the chill source x is supplied from above to the preheating chamber 5b.

[0028] The chilled iron source x supplied to the preheating chamber 5b is preheated by any method. For example, if the chilled iron source x is preheated by passing the hot exhaust gas previously generated in the melting chamber 2b through the preheating chamber 5b, manufacturing efficiency can be improved. The exhaust gas can be drawn through the preheating chamber 5b by the duct 9, and excess exhaust gas can be discharged through the duct 9.

[0029] The preheated chill source x is supplied to the melting chamber 2b. The chill source x is dropped by opening the opening 10 and supplied by the extruder 11.

[0030] The melting chamber 2b is divided by the furnace wall 12 and the furnace cover 13, and may include an electrode 4 for generating an electric arc A and providing heating, an oxygen lance 14 and a carbon material lance 15 for maintaining the required high temperature, and a burner 16 for localized heating of low-temperature areas. The carbon material lance 15 is a lance that blows powdered carbon material into the furnace. Furthermore, the method of adding carbon material is not limited to this; lumpy coke, lumpy anthracite, etc., can be used from the furnace. Any carbon material functions as an auxiliary heat source for the electric arc, helping to further improve melting efficiency and further reduce the power consumption. In addition, by using a burner, the temperature inside the furnace can be homogenized and melting can be promoted. This stabilizes the melting rate of the chilled iron source and improves operating efficiency. To further achieve this effect, it is preferable to use the burner in conjunction with the oxygen lance and the carbon material lance.

[0031] The chilled iron source x supplied to the melting chamber 2b is melted by electric arc heat to become molten iron m and molten s. Regarding the obtained molten iron m, the tapping gate 17 can be opened to tap the steel from the tapping port 18. Furthermore, regarding the molten s, the slag tapping gate 19 can be opened to discharge the slag from the slag tapping port 20.

[0032] The electric arc furnace 1c shown in Figure 3 includes a melting chamber 2c and a preheating chamber 5c. A chilled iron source x is supplied to the preheating chamber 5c and preheated using any method. The preheated chilled iron source x is then supplied to the melting chamber 2c through the opening of the chilled iron source supply device 3. The structure of the melting chamber 2c is the same as that of the melting chamber 2a.

[0033] The electric arc furnace 1d shown in Figure 4 includes a melting chamber 2d and a preheating chamber 5d. A chill source x is supplied to the preheating chamber 5d and preheated by any method. For example, the chill source x can be preheated by passing high-temperature exhaust gas (arrow in the figure) generated in the melting chamber 2d through the preheating chamber 5d. The chill source x is placed on a conveyor belt 21 included in the preheating chamber 5d and moves towards the melting chamber 2d (to the right in the figure). The chill source x is supplied to the melting chamber 2d through an opening 22 located between the preheating chamber 5d and the melting chamber 2d. The melting chamber 2d includes electrodes 4 for generating an electric arc A and for heating. The chill source x supplied to the melting chamber 2d is melted by the electric arc to become molten iron m and molten s. The obtained molten iron m can be tapped by any method.

[0034] The electric arc furnaces 1a-1d serve as measuring devices, and may include, for example, a thermal camera 23, a probe 24, and a distance meter 25. The thermal camera 23 can be used to measure the temperature Tph of the chill source, and may be located, for example, in the preheating chambers 5b-5d or the chill source supply device 3. The probe 24 can be used to measure the molten iron temperature Tm, and may be located in the melting chambers 2a-2d. The distance meter 25 can be used to measure the bulk density ρ of the chill source, and may be located, for example, in the preheating chambers 5b-5d or the chill source supply device 3. Specifically, the volume of the chill source x in the preheating chamber can be determined using the distance meter 25. Furthermore, by installing a load cell or other weight gauge in the chill source supply device 3 and measuring the weight difference before and after the chill source x is supplied, the weight of the chill source x can be determined. Based on the obtained volume and weight, the bulk density ρ can be determined. Specifically, the bulk density ρ is calculated by dividing the weight of the chill by its volume. Furthermore, when using a conveyor belt or similar device to continuously supply chills, the bulk density can also be calculated by using a weight gauge installed on the conveyor belt to measure the weight of the chill during transport in real time, and combining this with volume measurement by a distance gauge.

[0035] [Supply and melting of chilled iron] In the method for manufacturing molten iron according to this embodiment, a chill source is supplied to an electric arc furnace. Specifically, the chill source can be supplied to the melting chamber located in the electric arc furnace. The method of supplying the chill source is not limited and can be carried out continuously or intermittently.

[0036] The mixing ratio of the chilled iron source can be adjusted during the supply of chilled iron. For example, the mixing ratio can be adjusted by pre-mixing the chilled iron in the supply hopper of the chilled iron supply device 3. Furthermore, the mixing ratio can be continuously controlled simultaneously with the supply of chilled iron in the chilled iron supply device 3. For example, the electric arc furnace may include a control device that controls the mixing ratio of the chilled iron in the chilled iron supply device based on the measurement results of the measuring device. Specifically, the melting behavior can be monitored using measuring devices such as thermal imager 23 and probe 24, and control can be achieved by reducing the ratio of reduced iron when there is a large amount of unmelted residue. Additionally, a feedback mechanism can be provided to control the mixing ratio of the chilled iron based on the measurement results obtained in real time by the measuring device.

[0037] Furthermore, in the molten iron manufacturing method related to this embodiment, molten iron is manufactured by melting a chill supplied to the melting chamber. The chill is typically melted by electric arc heat.

[0038] [Equation (1) and Equation (2)] The method for manufacturing molten iron related to this embodiment satisfies the above equations (1) and (2). Hereinafter, the experiments conducted to derive the above equations (1) and (2) will be described.

[0039] First, experiments were conducted to investigate the effects of chill temperature Tph (unit: °C) on melting time, molten iron temperature Tm (unit: °C) on melting time, and chill bulk density ρ (unit: t / m3) on melting time. The experimental results are shown in Figures 5-7. The following approximate formula was established for the melting rate (melting rate coefficient) y under the baseline conditions (chill temperature Tph: 20 °C (no preheating), molten iron temperature Tm: 1580 °C, chill bulk density ρ: 2.6 t / m3) set to 1. [Number 3]

[0040] Next, under the aforementioned baseline conditions, the effect of the chill supply rate on operation was investigated. While maintaining a constant energy input to the electric arc furnace and a consistent chill supply rate, the chill was intermittently supplied to the melting chamber, and melting was carried out. As a result, when the chill supply rate (unit: t / min) exceeded 6.8 × 10⁻² P (P: energy input to the electric arc furnace (unit: MW)), the reduced iron agglomerated and formed large lumps within the electric arc furnace. Consequently, the reduced iron became difficult to melt within the electric arc furnace. Furthermore, the inability to supply the chill at a consistent rate and the extended time required for additional chill supply resulted in a prolonged steelmaking time. On the other hand, when the chill supply rate was less than 1.9 × 10⁻² P, the molten iron temperature increased, and the heat loss due to radiant heat from the molten iron increased, leading to a prolonged steelmaking time. Based on the above, under the aforementioned baseline conditions, it is determined that molten iron can be efficiently manufactured by setting the conditions to 1.9×10⁻²P≦vI≦6.8×10⁻²P.

[0041] When the melting rate of the chilled iron source changes, the upper and lower limits of the supply rate at which molten iron can be efficiently produced also change accordingly. Therefore, for the condition 1.9×10⁻²P≦vI≦6.8×10⁻²P, by introducing the correction term based on the above approximation, the above equations (1) and (2) are obtained. By satisfying the above equations (1) and (2), molten iron can be produced efficiently.

[0042] Furthermore, in equations (1) and (2) above, the supply rate vI of the chill source is the ratio of the supply amount of the chill source to the time required for supplying the chill source. The temperature Tph of the chill source is the temperature at which the chill source is supplied to the melting chamber; in the case of an electric arc furnace with a preheating chamber, it is the preheating temperature; in the case of an electric arc furnace without a preheating chamber, it is usually room temperature. The bulk density ρ of the chill source is the ratio of the supply amount of the chill source to the volume of the chill source in air, which includes the voids between the particles constituting the chill source and the voids within it.

[0043] The temperature Tph of the cold iron source is not particularly limited, but it can be set to, for example, 20°C or higher. Preheating can further increase the supply rate of the cold iron source, so Tph can be 300°C or higher, or 700°C or higher. On the other hand, Tph can be, for example, below 1200°C.

[0044] The temperature Tm of the molten iron is not particularly limited, but it can be set to, for example, 1550°C or higher. By increasing the temperature of the molten iron, the supply rate of the chill can be further increased, so Tm can be 1650°C or higher, or 1655°C or higher. On the other hand, Tm can be, for example, 1700°C or lower.

[0045] The bulk density ρ of the chilled iron source is not particularly limited, but it can be set to 0.5 t / m3 or higher, for example. On the other hand, ρ can be 4.0 t / m3 or lower, 2.8 t / m3 or lower, or 2.4 t / m3 or lower, for example.

[0046] The input energy P of an electric arc furnace refers to the electrical power supplied to the electric arc furnace. In addition to the electric arc power, heating energy from carbon materials and burners can also be supplied to an electric arc furnace. However, in this embodiment, the heating energy from carbon materials and burners is not included in the input energy P of the electric arc furnace.

[0047] [Preheating of the cold iron source] In the method for manufacturing molten iron related to this embodiment, the chill source can be preheated before the chill source is supplied.

[0048] [Control of operating conditions] In the molten iron manufacturing method related to this embodiment, at least one of the chill supply rate vI and the energy P input to the electric arc furnace can be controlled. That is, at least one of vI and P can be determined, and the chill supply and melting are carried out under the determined operating conditions.

[0049] The method for determining the operating conditions is not limited, but Tph, Tm, and ρ can be obtained, and the operating conditions are determined based on the obtained results. The method for obtaining Tph, Tm, and ρ is not limited, but it is preferable to obtain them by means of a measuring device. For example, the current Tph can be obtained by a thermal imager. For example, the current Tm can be obtained by a probe. For example, ρ can be obtained by a distance meter. In other words, in the molten iron manufacturing method related to this embodiment, at least one of the temperature of the chill source, the temperature of the molten iron, and the bulk density of the chill source can be measured by a measuring device.

[0050] The method of determining the operating conditions based on the obtained results is not particularly limited as long as the determined operating conditions satisfy the above equations (1) and (2), and it is not necessary to use the above equations (1) and (2) for calculation. However, it is preferable to use the above equations (1) and (2) for calculation.

[0051] Here is an example of using equations (1) and (2) above for calculation. Given vI, Tph, Tm, ρ, and P are obtained. By substituting these parameters into equations (1) and (2) above, the range of values ​​for vI is determined. vI is then determined from the values ​​contained within this range using any method. Specifically, the center value of this range can be set as vI, or vI can be adjusted based on the center value of this range according to pre-defined operating procedures. Similarly, given P, Tph, Tm, ρ, and vI are further obtained. By substituting these parameters into equations (1) and (2) above, the range of values ​​for P is determined. P is then determined from the values ​​contained within this range using any method. Specifically, the center value of this range can be set as P, or P can be adjusted based on the center value of this range according to pre-defined operating procedures. The range of values ​​for P can also be determined by transforming equations (1) and (2) above into the following equations (3) and (4). [Number 4] [Number 5] Furthermore, given the values ​​of vI and P, the range of vI / P is obtained by substituting the obtained Tph, Tm, and ρ into equations (1) and (2) above. vI and P can be determined in any way to satisfy this range. Specifically, the center value of this range can be determined as vI / P, or vI / P can be adjusted according to predetermined operating guidelines, etc., based on the center value of this range. After determining vI / P, vI and P can be determined in any way, for example, according to predetermined operating guidelines, etc.

[0052] There is no particular limitation on the number and frequency of decisions regarding operating conditions. However, when the chill source is supplied intermittently, the chill source supply rate can be defined as the amount of chill source supplied each time relative to the period from the first supply to the next. Furthermore, it is preferable to determine at least one of the chill source supply rate and the energy input to the electric arc furnace each time chill source is supplied (e.g., in all the supply cycles). On the other hand, when the chill source is supplied continuously, it is preferable to make at least one decision per minute, namely, determining at least one of the chill source supply rate and the energy input to the electric arc furnace.

[0053] The electric arc furnace of this embodiment may include a device for determining at least one of vI and P. Furthermore, it may include a device for determining at least one of vI and P through an output (e.g., a display output). By confirming the result of the display output, the operator can operate the electric arc furnace to satisfy the above equations (1) and (2).

[0054] Furthermore, at least one of VI and P, preferably both, can be automatically controlled. In other words, the electric arc furnace may include a control device, and the molten iron manufacturing method related to this embodiment may include the control device controlling VI and P based on the measurement results of the measuring device. Alternatively, it may be configured as a feedback mechanism that controls VI and P based on the measurement results obtained in real time by the measuring device. This allows for further optimization of operating conditions and further improvement of melting efficiency.

[0055] After supplying and melting the chilled iron source under the conditions of satisfying equations (1) and (2) above, P can be set to 0 to end the melting process. After the melting process ends, a process for tapping molten iron from the melting chamber of the electric arc furnace can be set up. In addition, a process for discharging slag from the melting chamber of the electric arc furnace can be set up. [Example]

[0056] The following description pertains to embodiments performed to confirm the function and effects of the present invention. In this embodiment, an electric arc furnace with the configuration shown in FIG1 was used for testing. Furthermore, regarding the embodiment for preheating, an electric arc furnace with the configuration shown in FIG3 was used.

[0057] As a chill source, a chill source consisting of scrap steel as waste and HBI as reducing iron is used.

[0058] As scrap steel, it uses general iron-based scrap as specified in the "Unified Specifications for the Acceptance of Iron Scrap" of the Japan Iron Source Association. That is, it mainly uses steel plate processed products as the base material, which are crushed by a shredder and separated by a magnetic separator as scrap steel.

[0059] As reduced iron, agglomerated reduced iron, i.e., HBI, is used. The HBI used has a total iron content (T.Fe) of 88–94% by mass, a metallic iron content (M.Fe) of 83–88% by mass, a metallization rate (M.Fe / T.Fe) of 94%, a carbon content of 1.0–1.5% by mass, and a bulk density of 2.0–3.0 t / m³. Furthermore, the HBI has a thickness (t) of 30 mm, a width (w) of 50 mm, and a length (l) of 110 mm or less.

[0060] In this embodiment, the amount of chill supplied to the electric arc furnace is 100 tons, the amount of molten iron obtained by melting the chill is approximately 80 tons, the amount of residual melt (molten iron remaining in the furnace) is approximately 10 tons, and the amount of slag is approximately 10 tons. Here, the chill is a mixture of scrap and reduced iron, supplied in two batches of 50 tons each time.

[0061] The table shows the manufacturing conditions of the molten iron in each embodiment. Tph, Tm, and ρ were measured using a thermal imager, probe, and distance meter included in the electric arc furnace, respectively. In some embodiments, Tm was set to exceed 20°C by preheating. The input energy P was constant during operation. Furthermore, the time interval from the first supply to the second supply was the same as the time interval from the second supply to the end.

[0062] The electrical power supplied to the electric arc furnace for producing 1 t of iron is shown in Table 1 as the unit of electricity. Under the same conditions of P, Tph, Tm and ρ, the unit of electricity is lower when the manufacturing conditions of satisfying Equations (1) and (2) are met, compared with the case where the manufacturing conditions of satisfying Equations (1) and (2) are not met.

[0063] [Table 1] Table 1 Manufacturing conditions Evaluation results P (MW) Tph (°C) Tm (°C) ρ (t / m3) The right side of equation (1) The right side of equation (2) vI (t / min) Satisfying equations (1) and (2)? Original power unit (kWh / t) Comparative Example 1-1 60 20 1555 2.6 1.1 0.3 0.1 no 452 Comparative Examples 1-2 60 20 1555 2.6 1.1 0.3 2.1 no 455 Example 1-1 60 20 1555 2.6 1.1 0.3 0.7 yes 442 Comparative Example 2-1 90 20 1555 2.6 1.6 0.5 0.3 no 430 Comparative Example 2-2 90 20 1555 2.6 1.6 0.5 2.6 no 433 Example 2-1 90 20 1555 2.6 1.6 0.5 1.0 yes 418 Comparative Example 3-1 150 20 1555 2.6 2.7 0.8 0.5 no 402 Comparative Example 3-2 150 20 1555 2.6 2.7 0.8 3.7 no 405 Example 3-1 150 20 1555 2.6 2.7 0.8 1.7 yes 387 Comparative Example 4-1 200 20 1555 2.6 3.6 1.0 0.6 no 387 Comparative Example 4-2 200 20 1555 2.6 3.6 1.0 4.6 no 390 Example 4-1 200 20 1555 2.6 3.6 1.0 2.3 yes 375 Comparative Example 5-1 90 800 1555 2.6 3.8 1.1 0.6 no 334 Comparative Example 5-2 90 800 1555 2.6 3.8 1.1 4.8 no 337 Example 5-1 90 800 1555 2.6 3.8 1.1 2.5 yes 329 Comparative Example 6-1 90 20 1600 2.6 10.4 2.9 1.9 no 437 Comparative Example 6-2 90 20 1600 2.6 10.4 2.9 11.4 no 440 Example 6-1 90 20 1600 2.6 10.4 2.9 6.7 yes 432 Comparative Example 7-1 90 20 1555 3.0 1.1 0.3 0.1 no 436 Comparative Example 7-2 90 20 1555 3.0 1.1 0.3 2.1 no 439 Example 7-1 90 20 1555 3.0 1.1 0.3 0.7 yes 430 Comparative Example 8-1 90 20 1555 0.7 10.1 2.8 1.8 no 427 Comparative Example 8-2 90 20 1555 0.7 10.1 2.8 11.1 no 430 Example 8-1 90 20 1555 0.7 10.1 2.8 6.4 yes 421 Comparative Example 9-1 60 700 1555 1.0 10.6 3.0 2.0 no 375 Comparative Example 9-2 60 700 1555 1.0 10.6 3.0 11.6 no 382 Example 9-1 60 700 1555 1.0 10.6 3.0 4.0 yes 365 Comparative Example 10-1 90 700 1555 1.0 16.0 4.5 3.5 no 374 Comparative Example 10-2 90 700 1555 1.0 16.0 4.5 17.0 no 381 Example 10-1 90 700 1555 1.0 16.0 4.5 6.0 yes 364 Comparative Example 11-1 200 350 1555 1.0 24.1 6.7 5.7 no 352 Comparative Example 11-2 200 350 1555 1.0 24.1 6.7 25.1 no 359 Example 11-1 200 350 1555 1.0 24.1 6.7 10.8 yes 342 Comparative Example 12-1 200 350 1555 1.8 11.2 3.1 2.1 no 369 Comparative Example 12-2 200 350 1555 1.8 11.2 3.1 12.2 no 376 Example 12-1 200 350 1555 1.8 11.2 3.1 8.0 yes 359

[0064] 1a, 1b, 1c, 1d: Electric arc furnace 2a, 2b, 2c, 2d: Melting chamber 3: Cold iron source supply device 4: Electrode 5b, 5c, 5d: Preheating chamber 6: Supply baskets 7: Traveling trolley 8: Cold iron source supply port 9: Air duct 10: Open and closed mouth 11: Extruder 12: Furnace wall 13: Stove lid 14: Oxygen is blown into the spray gun 15: Carbon material is blown into the spray gun 16: Burner 17: Gate for iron removal 18: Taphole 19: Slag Removal Door 20: Slag outlet 21: Conveyor Belt 22: Opening 23: Thermal Imager 24: Probe 25: Distance Meter A: Electric arc m: Molten iron s: molten slag x: Cold Iron Source

Claims

1. A method for manufacturing molten iron, comprising supplying a chill to an electric arc furnace, melting the supplied chill to manufacture molten iron, wherein the method for manufacturing molten iron satisfies the following equations (1) and (2), [Equation 1] [Equation 2] where, vI represents the supply rate of the chill (t / min); P represents the energy input to the electric arc furnace (MW); Tph represents the temperature of the chill (°C); Tm represents the temperature of the molten iron in the electric arc furnace (°C); ρ represents the bulk density of the chill (t / m3).

2. The method for manufacturing molten iron as claimed in claim 1, wherein the chill source comprises scrap and reduced iron.

3. The method for manufacturing molten iron as described in claim 1 or 2, wherein the electric arc furnace includes a measuring device and a control device; The method for manufacturing the molten iron includes: The measuring device measures at least one of the temperature of the chill, the temperature of the molten iron, and the bulk density of the chill; The control device controls at least one of the input energy and the supply rate based on the measurement results of the measuring device.

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