Electric furnace equipment

Abstract

Provided is an electric furnace facility that prevents overheating of molten metal by changing heat transfer between the molten metal and slag from heat conduction to forced retention heat transfer, and that improves productivity without requiring an oversized facility. This electric furnace facility is capable of discharging molten metal and slag in which molten metal, slag, a metal raw material, and an auxiliary raw material are stacked and housed, and is provided with: an electric arc furnace having a bottom section, a furnace wall, and a furnace lid; and an electromagnetic stirrer disposed at a predetermined position on the bottom or side surface of the electric arc furnace so as to be able to stir the molten metal in the electric arc furnace.

Description

Technical Field

[0001] This invention relates to an electric furnace apparatus for producing molten metal by melting metallic raw materials containing reduced iron. In the following description, "t" as a unit of mass represents 10... 3 kg, and "L" as a unit of volume represents 10 -3 m 3 The unit "N" assigned to the volume of a gas indicates a state at 0°C and 101325 Pa as a standard condition. In this specification, "x~y" indicates a numerical range, meaning values ​​above x and below y, including boundary values. Background Technology

[0002] In recent years, efforts have been made to reduce CO2 emissions in order to mitigate environmental impact. In the steel industry, the blast furnace process, which largely replaces CO2 emissions, has seen increased attention regarding the production of iron using direct reduction (DR) methods. In the DR process, for example, iron-containing lumps are reduced in a vertical shaft furnace to produce direct reduced iron (DRI). This reduced iron, along with scrap iron and other iron source materials, is then charged into an electric arc furnace (EAF) or submerged arc furnace (SAF) for heating and melting. The slag is then separated to produce molten iron.

[0003] In Japan, research is underway on applying low-grade iron ore from Australia and India to the DR process. Currently, in the existing EAF (Extended Electrolytic Furnace) system, it is difficult to melt reduced iron produced from low-grade iron ore. Therefore, the use of a submerged arc furnace (SAF) is being studied.

[0004] The production of molten iron using a submerged arc furnace (SAF) involves continuously feeding or loading metallic materials and by-products such as scrap, pig iron, direct reduced iron (DRI), molten iron, or hot-pressed iron (HBI) into the SAF without opening the furnace lid. This SAF melting process is sometimes also carried out using a flat molten pool operation. During the loading of raw materials, electrodes are inserted into the molten slag within the SAF, generating an electric arc between multiple electrodes or between the electrode and the molten iron. Additionally, current flows through the raw material and slag, heating and melting the raw materials through resistance heating and heat transfer.

[0005] One problem with the SAF melting process is the low efficiency of heat transfer to the raw material located far from the electrodes. This leads to problems such as delayed melting of the metal raw material, concentration gradients, unreliable temperature measurement, unreliable process control, and tapping of molten metal at excessively high temperatures. To address this uneven temperature problem, the electromagnetic stirrer disclosed in Patent Document 1 was developed.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2020-505579 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] However, the existing technology has the following problems. Specifically, the technology described in Patent Document 1 is applied to so-called electric arc furnaces. In electric arc furnaces, operations with a low slag ratio and high Fe content are performed. It cannot be directly applied to technologies that involve layering and storing molten metal, slag, metal raw materials, and by-products within an electric furnace, and then separately and continuously discharging the molten metal and slag under a reducing atmosphere.

[0011] The present invention was made in view of the above circumstances, and its object is to provide an electric furnace device that prevents overheating of molten metal by changing the heat transfer between molten metal and slag from heat conduction to forced convection heat transfer, thereby increasing productivity without requiring excessively large equipment.

[0012] Technical solutions for solving technical problems

[0013] The electric furnace equipment of the present invention, which advantageously solves the above-mentioned problems, is an electrical device that stacks and stores molten metal, slag, metal raw materials and by-products, and is capable of discharging molten metal and slag. It is characterized by comprising: an electric arc furnace having a bottom, furnace wall and furnace cover; and an electromagnetic stirrer disposed at a predetermined position on the bottom or side of the electric arc furnace for stirring the molten metal inside the electric arc furnace.

[0014] It should be noted that the electric furnace equipment involved in this invention can be a more preferred solution in the following ways:

[0015] (a) It is capable of melting without the intentional supply of oxygen;

[0016] (b) The electromagnetic stirrer has at least one coil, the coil being configured to generate a linear traveling magnetic field in one direction, generate a traveling magnetic field from the center of the furnace bottom toward the furnace wall or from the furnace wall toward the center of the furnace bottom, and generate a magnetic field to produce a circumferential rotating flow in the molten metal, or a combination of multiple of these functions.

[0017] (c) The outlet for the molten metal and the outlet for the slag are located on different directions of the furnace wall relative to the center of the furnace bottom;

[0018] (d) The electric arc furnace has an input power of 300 kW / m² per unit area of ​​the molten metal surface. 2 The above-mentioned capabilities are achieved by using an electromagnetic mixer with a stirring power density in the range of 4~80W / t.

[0019] (e) It has a device capable of mixing and supplying the metal raw material and the by-product raw material or supplying them separately;

[0020] (f) Some or all of the metal raw material is reduced iron;

[0021] (g) The basicity of the slag is in the range of 1.0 to 1.5. Here, the basicity of the slag refers to the ratio of CaO to SiO2 in the slag on a mass basis.

[0022] (h) The electric arc furnace has a control device that controls the arc voltage as a voltage to ground and the current of each electrode. The control device is configured to adjust at least one of the electrode height, the arc voltage, and the arc current such that the value E / √I obtained by dividing the arc voltage E (V) by the square root of the current I (A) of each arc electrode is 2.0 or less.

[0023] (i) The electric arc furnace is a submerged arc furnace.

[0024] Invention Effects

[0025] The electric furnace apparatus according to the present invention includes an electric arc furnace and an electromagnetic stirrer located at its bottom. By moderately stirring the molten metal, it can withstand sufficient input power and suppress the temperature rise of the molten metal. Furthermore, it can produce molten metal with good productivity while suppressing refractory material loss. Attached Figure Description

[0026] Figure 1 This is a schematic longitudinal cross-sectional view illustrating an embodiment of the electric furnace equipment of the present invention.

[0027] Figure 2 (a) to (g) are schematic top views showing an example of the configuration of the electromagnetic stirrer in the electric furnace equipment according to the above embodiments.

[0028] Figure 3 This is a graph showing the effect of the stirring power density of the molten iron in the electric furnace on the relationship between the input power per unit surface area of ​​the molten iron and the temperature of the molten iron.

[0029] Figure 4 This is a schematic longitudinal cross-sectional view of a submerged arc furnace that does not have a stirring function for the molten metal. Detailed Implementation

[0030] The embodiments of the present invention will now be described in detail. These embodiments illustrate apparatuses and methods for embodying the technical concept of the present invention, and do not specify the structure as described below. That is, the technical concept of the present invention can be modified in various ways within the scope of the claims.

[0031] Figure 1 This is a schematic longitudinal cross-sectional view illustrating the structure of a submerged arc furnace according to an embodiment of the electric furnace equipment of the present invention. Figure 2 (a) to (g) are schematic top views showing an example configuration of an electromagnetic stirrer 6 composed of a linear electric motor. The submerged arc furnace 1 contains molten iron P, molten slag S, and raw material M composed of metallic raw materials and by-products, stacked and housed within the furnace wall 2. In the submerged arc furnace 1, electrodes 3 are inserted into the molten slag S, and an electric arc is generated between multiple electrodes 3 or between electrodes 3 and molten iron P. The raw material is heated and melted by radiation or by resistance heating through the current flowing between the electrodes, raw material, slag, and molten iron, without intentionally supplying oxygen. The phrase "without intentionally supplying oxygen" does not mean preventing the mixing of air from the raw material during loading, the blown-in gas, or gaps in the refractory materials. It means that the heat of oxidation is not utilized in the heating of the raw material.

[0032] In this embodiment, it is preferable to have a device (not shown), such as a hopper, for continuously producing molten metal by feeding raw material 4 from the top. The feeding position of the raw material is preferably arranged symmetrically with respect to the center of the furnace bottom. In this case, it is preferable to have outlets for molten metal and outlets for slag, arranged in different directions relative to the center of the furnace bottom. Preferably, each outlet is filled and sealed with plugging material, and the outlet is opened by passing through the plugging material at a point in time when a predetermined amount of molten metal can be maintained, thereby discharging the molten metal.

[0033] In this embodiment, an iron source material containing reduced iron is charged into a submerged arc furnace. Simultaneously, as by-products, at least one or both of the following are included: slag-forming materials added to adjust the basicity (CaO / SiO2) of the molten slag S formed on the molten iron P, and carbon materials added to adjust the C content of the molten iron P. The basicity (CaO / SiO2) of the molten slag refers to the ratio of CaO to SiO2 by mass fraction in the molten slag. The feeding device for the raw material 4 can be prepared separately for the iron source material, slag-forming materials, and carbon materials, or they can be supplied mixed together. In the case of mixing, the raw material can be granulated to a specified size.

[0034] The reduced iron used in this embodiment can be manufactured in advance by direct reduction, or commercially available reduced iron can be purchased. Scrap iron or iron oxide scale can also be used as the iron source material. The preferred mass ratio of reduced iron in the iron source material is 50-100%.

[0035] If the metallization rate of reduced iron is above 60%, the power consumption per unit area is low and the energy efficiency is excellent. There is no specific upper limit to the metallization rate. If the metallization rate is too high, the resistance heat generated when the raw material 4, i.e., reduced iron, is fed into the molten slag S from above in the submerged arc furnace 1 and electrified in the slag may decrease. Therefore, the upper limit of the metallization rate is preferably around 90%.

[0036] In the slag-forming material, limestone (CaCO3) and quicklime (CaO) are preferably added as CaO sources, and silica (SiO2) is preferably added as a SiO2 source. It is preferable to use lumpy or powdered slag-forming materials together with or mixed with the metal raw materials, for example, after granulation. It is preferable to have the basicity (CaO / SiO2) of the molten slag S in the range of 1.0 to 1.5. If the basicity of the molten slag is within this range, it has a composition similar to that of blast furnace slag, making it suitable for reuse as a roadbed material such as cement. Furthermore, the total iron content in the molten slag is preferably 5.0% by mass or less. This can be achieved by intentionally withholding oxygen, thus increasing iron recovery.

[0037] Carbon materials can be coke, coal, or biochar. Pulp carbon materials are preferred, either in block or powder form, and are used together with or mixed with the metal raw materials, for example, after granulation. The carbon content in the molten iron (P) is preferably adjusted to a range of 2.0–5% by mass. If within this range, it is suitable for direct use as pig iron or as a raw material for the next steelmaking process.

[0038] In this embodiment, electrical energy is used in the melting of metallic raw materials, such as reduced iron. Therefore, compared to methods such as the blast furnace method that use the heat of combustion of carbon, a reduction in CO2 emissions can be achieved. It is preferable to use electrical energy generated from renewable energy sources.

[0039] If using Figure 4 The submerged arc furnace shown does not have a stirring function for the molten metal. When operating the electric furnace in the same way as in this embodiment to produce molten metal, no oxygen is supplied from the outside, and there is no flow of solids or liquids within the furnace body. Therefore, the heat transfer from molten iron P to the raw material M via molten slag S is almost entirely thermal conduction. Furthermore, the electrode 3 is typically positioned centrally when viewed from above. Therefore, the heat supply to the raw material M, located far from the electrode, is limited. Even with increased input power, most of the input power is consumed in heating the molten metal, thus reducing the input power required for melting the raw material M, especially the heat supply to the raw material M located far from the electrode 3. The power density per unit area of ​​the molten iron surface is 250 kW / m². 2 Around 1500℃, the temperature of the molten iron will reach or exceed 1500℃. Therefore, most submerged arc furnaces use a power density of 250kW / m² per unit area of ​​the molten iron surface. 2 It can be operated from left to right. If such a furnace is to be used to produce large quantities of molten metal, it would require a large area of ​​equipment and a large amount of machinery, resulting in an excessive investment.

[0040] The inventors conducted in-depth research and discovered that the relationship between the power density per unit area of ​​molten iron surface and the temperature of molten iron P depends on the stirring power ε. Figure 3This indicates their research results. For example, the stirring power density ε=0 in a typical submerged arc furnace also explains why, in previous submerged arc furnaces, a stirring power density of 250kW / m³ was achieved. 2 The operation can be performed from left to right. Furthermore, a new discovery has been made that by applying slight stirring power, a large amount of electricity can be supplied to the furnace without increasing the temperature of the molten iron (P).

[0041] The submerged arc furnace 1 of this embodiment includes a bottom, a furnace wall 2, a furnace cover (not shown), and an electromagnetic stirrer 6 as a stirring mechanism for the molten metal. Preferably, the submerged arc furnace 1 of this embodiment has an input power of 300 kW / m² per unit area of ​​the surface of the molten metal. 2 The above-mentioned capabilities are achieved. Furthermore, the stirring power density of the electromagnetic stirrer 6 is preferably in the range of 4~80 W / t. This allows for high productivity and stable operation without excessive equipment investment. More preferably, the input power per unit area of ​​the molten metal surface is set to 300~2500 kW / m². 2 The stirring dynamic density is preferably in the range of 8~24 W / t.

[0042] When the stirring power density is below the lower limit, the stirring power density is too low. Within the required power density range, the overheating of the molten metal may exacerbate the wear and tear on refractory materials such as the furnace wall. When the stirring power density exceeds the upper limit, the molten metal flow rate is too fast, which may also exacerbate the wear and tear on refractory materials.

[0043] As an example of a stirring mechanism for molten metal, preferably Figure 1 An electromagnetic stirrer 6 is installed at the bottom or side as shown. The bottom or side of the electromagnetic stirrer 6 is preferably made of a non-magnetic material. The stirring power density of the electromagnetic stirrer relative to its output can be determined, for example, through numerical analysis or experimentation. For example, it can be approximately 0.5% of the output power of the electromagnetic stirrer.

[0044] In this embodiment, it is preferable to increase the flow rate F of the molten metal to improve heat transfer to the slag-metal interface. Furthermore, it is preferable that the molten metal around the electrodes, which become hot spots, flows towards the furnace wall. For example, as... Figure 2 As shown in (a), an electromagnetic stirrer 6 that generates a magnetic field can be installed at the furnace bottom and furnace wall to make the molten metal at the furnace bottom flow F from the center of the furnace bottom toward the furnace wall. Additionally, as... Figure 2 As shown in (b), an electromagnetic stirrer 6 that generates a magnetic field can be installed at the furnace bottom and furnace wall to make the molten metal at the furnace bottom flow F from the furnace wall toward the center of the furnace bottom. Additionally, as... Figure 2 As shown in (c), electromagnetic stirrers 6 can also be arranged opposite each other at the center of the furnace bottom to generate traveling magnetic fields in different directions. Alternatively, as shown in... Figure 2 (d) An electromagnetic stirrer 6 is configured in the circumferential direction to create a swirling flow of molten metal. For example... Figure 2 (e) Figure 2 As shown in (f), a linear traveling magnetic field can be generated in one direction. The shape of the electric furnace, when viewed from above, is not limited to a circle; it can also be elliptical or... Figure 2 Rectangles like (f) and (g). For example... Figure 2 As shown in (g), the traveling magnetic fields of adjacent electromagnetic stirrers 6 can also be made to be in opposite directions.

[0045] The submerged arc furnace 1 of this embodiment preferably has a control device for controlling the arc voltage (voltage to ground) and the current of each electrode. In a submerged arc furnace, since the current flows between the electrode, raw material, slag, and molten iron, the voltage to ground at the same current value is lower compared to an electric furnace that typically generates an arc in air. This is because the conductivity of slag is much greater than that of air. Therefore, the control device of the submerged arc furnace 1 of this embodiment controls the value obtained by dividing the arc voltage E (V) by the square root of the current I (A) of each arc electrode as an index. That is, the control device is preferably configured to adjust at least one of the electrode height, arc voltage, and arc current so that the index E / √I is 2.0 or less. More preferably, the index E / √I is 1.5 or less.

[0046] Example

[0047] use Figure 1 A continuous submerged arc furnace with a capacity of 4 to 6 tons, as shown, was investigated. Table 1 summarizes the specifications of the three-phase AC electric furnaces used in the investigation.

[0048]

[0049] Shredder-crushed materials, carbonaceous materials, and blast furnace slag are loaded into the submerged arc furnace 1 and electricity is applied for initial melting. The pre-charge amount is adjusted to 750 kg of molten iron and 1500 kg of slag. After the pre-charge is fully melted, reduced iron, which will be the main raw material, and pre-mixed auxiliary raw materials such as carbonaceous materials, lime, alumina, and MgO source, used to adjust the carbon concentration in the molten iron and the composition of the slag, are continuously added. The maximum amount of molten iron is targeted at 4 tons, and is adjusted according to the amount of raw materials added. The final thickness of the molten iron is 140 mm.

[0050] The input power of a submerged arc furnace is adjusted by tap voltage and electrode position to achieve the specified power conditions.

[0051] The transformer used in the electromagnetic stirring device is set to 200kVA, and the output power has been adjusted. The power factor at maximum output is approximately 50%, and the maximum output is around 100kW. Since the contribution rate of electromagnetic stirring is difficult to measure in practice, it is pre-calculated using numerical analysis and set to 0.5%. This value is typical for electromagnetic stirring devices and will not vary significantly. Furthermore, the configuration of the electromagnetic stirring device is set as follows: Figure 2 Configuration (e). The operating conditions and results are shown in Table 2.

[0052] In the judgment column, the refractory loss (mm) under the conditions of Test No. 1 is standardized as 1. Cases where the loss is less than twice the normal value and 4 tons of molten iron can be produced within 100 minutes are evaluated as ○. Even with the same input power of the electric furnace, if the melting time is shortened or the refractory loss is reduced by electromagnetic stirring, it is evaluated as △. In addition, the values ​​of the operating indicators are also recorded in Table 2.

[0053]

[0054] Explanation of reference numerals in the attached figures

[0055] 1: Electric furnace (submerged arc furnace, SAF)

[0056] 2: Furnace wall

[0057] 3: Electrode

[0058] 4: (Input) Raw materials

[0059] 5: Electric arc

[0060] 6: Electromagnetic mixer (linear motor)

[0061] P: Molten iron

[0062] S: Molten slag

[0063] M: Raw material.

Claims

1. An electric furnace apparatus that stacks and stores molten metal, slag, metal raw materials, and by-products, and is capable of discharging the molten metal and slag, wherein... have: An electric arc furnace, comprising a bottom, furnace walls, and a furnace lid; and An electromagnetic stirrer is positioned at a predetermined location on the bottom or side of the electric arc furnace in order to stir the molten metal inside the furnace.

2. The electric furnace equipment according to claim 1, wherein, It can melt without the intentional supply of oxygen.

3. The electric furnace equipment according to claim 1, wherein, The electromagnetic stirrer has at least one coil, which is configured to perform any one or a combination of the following: generating a linear traveling magnetic field in one direction, generating a traveling magnetic field from the center of the furnace bottom toward the furnace wall or from the furnace wall toward the center of the furnace bottom, and generating a magnetic field to produce a circumferential rotating flow in the molten metal.

4. The electric furnace equipment according to claim 1, wherein, The outlet for the molten metal and the outlet for the slag are located on the furnace wall in different directions relative to the center of the furnace bottom.

5. The electric furnace equipment according to claim 1, wherein, The electric arc furnace has an input power of 300 kW / m² per unit area of ​​the molten metal surface. 2 The above abilities, The stirring power density of the electromagnetic mixer is in the range of 4~80W / t.

6. The electric furnace equipment according to claim 1, wherein, It has a device capable of mixing and supplying the metal raw material and the by-product raw material or supplying them separately.

7. The electric furnace equipment according to claim 6, wherein, Some or all of the metal raw material is reduced iron.

8. The electric furnace equipment according to claim 1, wherein, The basicity of the slag is in the range of 1.0 to 1.

5. Here, the basicity of the slag refers to the ratio of CaO to SiO2 in the slag on a mass basis.

9. The electric furnace equipment according to claim 1, wherein, The electric arc furnace has a control device that controls the arc voltage (which is the voltage to ground) and the current of each electrode. The control device is configured to adjust at least one of the electrode height, arc voltage, and arc current such that the value E / √I obtained by dividing the arc voltage E (V) by the square root of the current I (A) of each arc electrode is 2.0 or less.

10. The electric furnace equipment according to claim 1, wherein, The electric arc furnace is a submerged arc furnace.

Images