Electric furnace equipment

Abstract

The present invention provides electric furnace equipment that prevents overheating of molten metal by changing heat transfer between the molten metal and slag from heat conduction to forced convective heat transfer, and that improves production yield without making the equipment oversized. This electric furnace equipment stores molten metal, slag, a metal raw material, and an auxiliary raw material in layers, and enables the discharge of the molten metal and the slag. The electric furnace equipment comprises: an arc furnace having a bottom part, a furnace wall, and a furnace lid; and an electromagnetic stirrer disposed at a prescribed position on the bottom part or a side surface of the arc furnace in order to enable stirring of the molten metal that is in the arc furnace.

Description

Electric Furnace Equipment

[0001] The present invention relates to an electric furnace facility for melting metal raw materials including reduced iron to produce molten metal. ３ kg, and the volume unit "L" is 10 －３ m ３ The "N" attached to the unit of gas volume indicates the standard state of 0°C and 101,325 Pa. In this specification, the numerical range "x to y" indicates not less than x and not more than y, and includes the boundary value.

[0002] In recent years, CO ２ In the steel industry, CO emissions are also being reduced. ２ As an alternative to the blast furnace process, which has a large amount of iron emissions, the direct reduction (DR) process for producing iron sources has been attracting attention. In the DR process, for example, iron-containing agglomerates are reduced in a shaft furnace to produce direct reduced iron (DRI). This reduced iron or iron scrap or other iron source raw materials are charged into an electric arc furnace (EAF), submerged arc furnace (SAF), or the like, where they are heated and melted, and the slag is separated to produce molten iron.

[0003] In Japan, studies are underway to apply the DR process to low-grade iron ore produced in Australia, India, etc. However, it is difficult to melt the reduced iron produced from low-grade iron ore using the current EAF. Therefore, the use of a submerged arc furnace (SAF) is being considered.

[0004] The production of molten iron by SAF is a process in which metallic materials and auxiliary materials, such as scrap, pig iron, direct reduced iron (DRI), hot metal, or hot briquetted iron (HBI), are continuously fed or charged in small buckets into a submerged arc furnace (SAF) without opening the furnace lid. This SAF melting process may also be performed in flat-bath operation. During charging, electrodes are inserted into the molten slag in the SAF, and an arc is generated between the electrodes or between the electrodes and the molten iron. An electric current is passed through the material-slag connection, heating and melting the materials by resistance heating or heat transfer.

[0005] One problem with the SAF melting process is the inefficient heat transfer to the source material located away from the electrodes, which slows the melting of the metal source material and causes problems such as concentration gradients, unreliable temperature measurement, unreliable process control, and excessively hot molten metal tapping. To solve this uneven temperature problem, an electromagnetic stirrer was developed, as disclosed in U.S. Pat. No. 6,273,663.

[0006] Special Publication No. 2020-505579

[0007] However, the prior art has the following problems. That is, the technology described in Patent Document 1 is a technology applied to so-called electric arc furnaces. Electric arc furnaces are operated with a low slag ratio and a high Fe content. The technology cannot be directly applied to a technology in which molten metal, slag, raw metal materials, and auxiliary materials are stacked in an electric furnace, and the molten metal and slag are continuously discharged separately, and the furnace is operated in a reducing atmosphere.

[0008] The present invention has been made in consideration of the above circumstances, and has as its object to provide an electric furnace facility that prevents overheating of the molten metal by changing the heat transfer between the molten metal and the slag from thermal conduction to forced convection heat transfer, thereby improving productivity without requiring an excessively large facility.

[0009] The electric furnace equipment of the present invention, which advantageously solves the above-mentioned problems, is an electric furnace equipment that stores molten metal, slag, metal raw materials, and auxiliary materials in layers and is capable of discharging the molten metal and slag, and is characterized by comprising an arc furnace having a bottom, furnace walls, and a furnace cover, and an electromagnetic stirrer arranged at a predetermined position on the bottom or side of the arc furnace to enable stirring of the molten metal in the arc furnace.

[0010] The electric furnace equipment according to the present invention is characterized in that: (a) melting is possible without intentionally supplying oxygen gas; (b) the electromagnetic stirrer has at least one coil configured to generate a linearly progressing magnetic field in one direction, generate a progressing 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 so as to obtain a circumferential rotational flow in the molten metal, or a combination of these; (c) the molten metal discharge port and the slag discharge port are provided on the furnace wall in different directions relative to the center of the furnace bottom; and (d) the arc furnace has an input power of 300 kW / m per surface of the molten metal. ２ or more, and the electromagnetic stirrer has a stirring power density in the range of 4 to 80 W / t; (e) a device is provided that can supply the metal raw materials and the auxiliary materials in a mixed state or separately; (f) a part or all of the metal raw materials are reduced iron; (g) the basicity of the molten iron is in the range of 1.0 to 1.5, where the basicity of the molten iron is the ratio of SiO 2 in the molten iron by mass. ２ (h) the arc furnace has a control device that controls the arc voltage, which is the voltage to ground, and the current per electrode, and the control device is configured to adjust at least one of the electrode height, the arc voltage, and the arc current so that the value E / √I obtained by dividing the arc voltage E (V) by the square root of the current I (A) per arc electrode becomes 2.0 or less; and (i) the arc furnace is a submerged arc furnace. These may be more preferable solutions.

[0011] The electric furnace system according to the present invention includes an arc furnace and an electromagnetic stirrer at its bottom, and by appropriately stirring the molten metal, it is possible to load sufficient input power and suppress the temperature rise of the molten metal. In addition, it is possible to produce molten metal with high productivity while suppressing wear of the refractory.

[0012] Fig. 1 is a schematic vertical cross-sectional view illustrating an electric furnace facility according to one embodiment of the present invention. (a) to (g) are schematic top views showing examples of the arrangement of electromagnetic stirrers in the electric furnace facility according to the above embodiment. (b) is a graph showing the influence of the stirring power density of molten iron on the relationship between the input power per surface of the molten iron in the electric furnace and the molten iron temperature. (c) is a schematic vertical cross-sectional view showing a submerged arc furnace without a molten metal stirring function.

[0013] The following is a detailed description of embodiments of the present invention. The following embodiments are intended to exemplify equipment and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0014] FIG. 1 is a schematic vertical cross-sectional view illustrating the configuration of a submerged arc furnace (SAF) for explaining electric furnace equipment according to one embodiment of the present invention. FIGS. 2(a)-(g) are schematic top views showing examples of the arrangement of an electromagnetic stirrer 6 composed of a linear motor. The SAF 1 contains stacked raw materials M, consisting of molten pig iron (P), molten slag (S), raw metal materials, and auxiliary materials, within the furnace wall 2. In the SAF 1, electrodes 3 are inserted into the molten slag (S). An arc is generated between the electrodes 3 or between the electrodes 3 and the molten pig iron (P), and the raw materials are heated and melted by radiant heating or resistance heating of the current flowing between the electrodes, raw materials, slag, and molten pig iron, without the intentional supply of oxygen gas. "Without the intentional supply of oxygen gas" does not prevent the intrusion of air during raw material charging, through injection gas, gaps in the refractory, etc. This means that oxidation heat is not used to heat the raw materials.

[0015] In this embodiment, it is preferable to have a device (not shown), such as a hopper, for charging the raw materials 4 from above, and to continuously produce molten metal. The raw material charging positions are preferably arranged symmetrically with respect to the center of the hearth. In this case, it is preferable to have a molten metal discharge port and a slag discharge port, and to arrange them in different directions with respect to the center of the hearth. It is preferable to fill each discharge port with plugging material, and when a predetermined amount of molten metal has been held, to open the plugging material and discharge the molten metal.

[0016] In this embodiment, an iron source material containing reduced iron is charged into a submerged arc furnace. At the same time, an auxiliary material is added to the molten slag S formed on the molten iron P, and the basicity (CaO / SiO ２ The method includes at least one of adding a slag former to adjust the basicity (CaO / SiO ２ ) is the mass fraction of CaO in the molten slag. ２ The device for feeding the raw materials 4 may be prepared separately for the iron source raw material, the slag former, and the carbonaceous material, or they may be mixed and fed together. When mixed, they may be granulated to a predetermined size.

[0017] The reduced iron used in this embodiment may be produced in advance by a direct reduction method, or commercially available reduced iron may be purchased and used. Iron scrap or scale may also be used as the iron source raw material. The mass ratio of the reduced iron to the iron source raw material is preferably 50 to 100%.

[0018] When the metallization rate of the reduced iron is 60% or higher, the power consumption rate is low and energy efficiency is excellent. There is no particular upper limit to the metallization rate. If the metallization rate is too high, the reduced iron, which is the raw material 4 charged from above the molten slag S in the submerged arc furnace 1, may conduct electricity through the slag, resulting in a decrease in resistance heat. Therefore, it is preferable that the upper limit of the metallization rate be approximately 90%.

[0019] The slag-forming material is limestone (CaCO ３ ), quicklime (CaO), and SiO ２ The source is silica (SiO ２ It is preferable to add lumps or powders of slag S together with or mixed with the metal raw material, for example, by granulation. ２) is preferably in the range of 1.0 to 1.5. When the basicity of the molten slag is in this range, it has a composition similar to that of blast furnace slag, making it suitable for reuse as roadbed materials such as cement. In addition, it is preferable that the total iron content in the molten slag is 5.0 mass% or less. This can be achieved by intentionally not supplying oxygen gas, and iron yield is improved.

[0020] Coke or coal can be used as the carbonaceous material. Biomass charcoal can also be used. It is preferable to use a lump or powdered material together with or mixed with the metal raw material, for example, by granulation. The C content in the molten pig iron P is preferably adjusted to the range of 2.0 to 5 mass%. Within this range, it is suitable for use as pig iron directly or as a raw material for steelmaking in the next process.

[0021] In this embodiment, electric energy is used to melt the metal raw material, for example, reduced iron. Therefore, compared to the case where heat from combustion of carbon is used, such as in the blast furnace method, CO ２ This has the effect of reducing emissions. It is preferable to use electrical energy generated by renewable energy.

[0022] When a submerged arc furnace without a molten metal stirring function, as shown in FIG. 4, is used to operate an electric furnace for producing molten metal in the same manner as in this embodiment, the submerged arc furnace receives no oxygen from the outside and no solid or liquid flows within the furnace. Therefore, heat is transferred from the molten iron P to the raw materials M via the molten slag S almost exclusively by thermal conduction. Furthermore, the electrodes 3 are typically positioned centrally when viewed from above. Therefore, the heat supply to the raw materials M located far from the electrodes is limited. Even if the input power is increased, most of the input power is consumed in heating the molten metal. This reduces the input power used to melt the raw materials M, particularly the heat supply to the raw materials M located far from the electrodes 3. A power density of 250 kW / m per surface of the molten iron is 250 kW / m. ２ Therefore, in a normal submerged arc furnace, the power density per molten iron surface is 250 kW / m ２ In most cases, furnaces are operated at about this level. To produce a large amount of molten metal using such a furnace requires large-area equipment and numerous pieces of equipment, resulting in excessive investment.

[0023] As a result of extensive research, the inventors have found that the relationship between the power density per surface of the molten iron and the temperature of the molten iron P depends on the stirring power ε. Figure 3 shows the results of this research. For example, in a normal submerged arc furnace, the stirring power density ε is 0, and in a conventional submerged arc furnace, the stirring power density is 250 kW / m ２ Furthermore, we have newly discovered that by adding even a small amount of stirring power, a large amount of electricity can be input into the furnace without raising the temperature of the molten iron P.

[0024] 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 means for stirring the molten metal. The submerged arc furnace 1 of this embodiment has an input power of 300 kW / m per surface of the molten metal. ２ It is preferable that the electromagnetic stirrer 6 has a stirring power density in the range of 4 to 80 W / t. This makes it possible to achieve high productivity and stable operation without making excessive capital investments. The input power per surface of the molten metal is 300 to 2500 kW / m. ２ It is more preferable that the stirring power density is in the range of 8 to 24 W / t.

[0025] If the stirring power density is below the lower limit, the stirring power density is too low, and the molten metal may overheat within the required power density range, which may accelerate wear of refractories such as furnace walls.If the stirring power density is above the upper limit, the molten metal flow rate may be too high, which may accelerate wear of refractories.

[0026] As an example of a means for stirring the molten metal, an electromagnetic stirrer 6 as shown in FIG. 1 is preferably installed on the bottom or side. The bottom or side on which the electromagnetic stirrer 6 is installed is preferably made of a non-magnetic material. The stirring power density of the electromagnetic stirring can be determined, for example, by numerical analysis or experimentation relative to the output of the electromagnetic stirring. For example, it can be set to about 0.5% of the output power of the electromagnetic stirring.

[0027] In this embodiment, it is preferable that the molten metal flow F improves heat transfer to the slag-metal interface. In addition, it is preferable that the molten metal around the hot spot electrode flow toward the furnace wall. For example, as shown in FIG. 2(a), an electromagnetic stirrer 6 that generates a magnetic field can be installed on the furnace bottom or furnace wall to direct the molten metal at the bottom side toward the furnace wall (flow F). Also, as shown in FIG. 2(b), an electromagnetic stirrer 6 that generates a magnetic field can be installed on the furnace bottom or furnace wall to direct the molten metal at the bottom side toward the furnace wall (flow F). As shown in FIG. 2(c), electromagnetic stirrers 6 can be arranged opposite each other across the center of the furnace bottom, generating magnetic fields traveling in different directions. Alternatively, as shown in FIG. 2(d), electromagnetic stirrers 6 can be arranged circumferentially to generate a swirling flow in the molten metal. A linear traveling magnetic field can also be generated in one direction, as shown in FIGS. 2(e) and 2(f). The shape of the electric furnace is not limited to a circular shape when viewed from above; it can also be an ellipse or a rectangle, as shown in FIGS. 2(f) and 2(g). As shown in FIG. 2(g), the magnetic fields of adjacent electromagnetic stirrers 6 may be directed in opposite directions.

[0028] The submerged arc furnace 1 of this embodiment preferably has a control device that controls the arc voltage (voltage to ground) and the current per electrode. In a submerged arc furnace, current flows between the electrode, raw materials, slag, and molten iron. Therefore, compared to an electric furnace that generally generates an arc in air, the voltage to ground is lower for the same current value. This is because the electrical conductivity of slag is significantly higher than that of air. Therefore, the control device for the submerged arc furnace 1 of this embodiment controls the arc voltage using an index, E / √I, which is the arc voltage E (V) divided by the square root of the current I (A) per arc electrode. 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.

[0029] The investigation was carried out using a 4 to 6 ton continuous submerged arc furnace 1 as shown in Figure 1. Table 1 shows the specifications of the three-phase AC electric arc furnace used in the investigation.

[0030]

[0031] Shredder chips, carbonaceous material, and blast furnace slag were charged into the submerged arc furnace 1, and electricity was applied to perform initial melting. The pre-charged amounts were adjusted to 750 kg of hot metal and 1,500 kg of slag. After the pre-charged materials were completely melted, a pre-mixed raw material consisting of reduced iron as the main raw material and auxiliary raw materials such as carbonaceous material, lime, alumina, and MgO source for adjusting the C concentration in the hot metal and the slag composition was continuously charged. The maximum amount of hot metal was targeted to be 4 t, and was adjusted by the amount of raw material charged. The final thickness of the hot metal was 140 mm.

[0032] The input power of the submerged arc electric furnace was adjusted by adjusting the tap voltage and electrode position so that the power was adjusted to a predetermined condition.

[0033] The transformer of the electromagnetic stirrer used for electromagnetic stirring was set to 200 kVA, and the output was adjusted. The power factor at maximum output was approximately 50%, and a maximum output of approximately 100 kW was possible. Since it is difficult to actually measure the contribution rate of electromagnetic stirring, it was calculated in advance using a numerical analysis method and set to 0.5%. This value is a typical value for electromagnetic stirrers and does not change significantly. The electromagnetic stirrer was arranged as shown in Figure 2(e). The operating conditions and results are shown in Table 2.

[0034] In the evaluation column, the refractory wear (mm) was normalized to the wear under the conditions of Test No. 1, which was set to 1, and the cases in which 4 tons of molten pig iron was produced within 100 minutes were evaluated as "good." Even if the input power of the electric furnace was the same, cases in which the melting time was shortened or the refractory wear was reduced by electromagnetic stirring were evaluated as "fair." The values ​​of the index E / √I during operation are also shown in Table 2.

[0035]

[0036] 1 Electric furnace (submerged arc furnace, SAF) 2 Furnace wall 3 Electrode 4 (Charged) raw material 5 Arc 6 Electromagnetic stirrer (linear motor) P Molten iron S Molten slag M Raw material

Claims

1. An electric furnace facility capable of storing molten metal, slag, raw metal materials, and auxiliary materials in layers and discharging the molten metal and slag, comprising: an arc furnace having a bottom, furnace walls, and a furnace cover; and an electromagnetic stirrer disposed at a predetermined position on the bottom or side of the arc furnace to enable stirring of the molten metal in the arc furnace.

2. The electric furnace equipment according to claim 1, which is capable of melting without intentionally supplying oxygen gas.

3. The electric furnace equipment according to claim 1, wherein the electromagnetic stirrer has at least one coil configured to generate a linearly progressing magnetic field in one direction, generate a progressing 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 so as to obtain a circumferential rotating flow of the molten metal, or to perform a combination of two or more of these.

4. An electric furnace facility as claimed in claim 1, wherein the molten metal discharge port and the slag discharge port are provided on the furnace wall in different directions relative to the center of the hearth.

5. The electric arc furnace has an input power of 300 kW / m2 per surface of the molten metal. ２ 2. The electric furnace facility according to claim 1, wherein the electromagnetic stirrer has a stirring power density in the range of 4 to 80 W / t.

6. The electric furnace facility according to claim 1, further comprising a device capable of supplying the metal raw material and the auxiliary raw material either mixed together or separately.

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

8. The basicity of the slag is in the range of 1.0 to 1.5, where the basicity of the slag is the ratio of SiO ２ The electric furnace installation according to claim 1, wherein the ratio of CaO to CaO is 0.01 to 0.

01.

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

10. The electric furnace installation of claim 1, wherein said arc furnace is a submerged arc furnace.

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