Refractory lining structure for electric furnace, refractory cooling method for electric furnace, electric furnace, and method for producing molten iron

Abstract

Disclosed is a novel technique capable of reducing refractory wear caused by a hot heel during production of molten iron using an electric furnace. A refractory lining structure for an electric furnace according to the present disclosure comprises a refractory, slag, an iron shell, and a cooling structure. The refractory has a first surface on the electric furnace inner side thereof and a second surface on the opposite side to the first surface. The slag covers at least a part of the first surface. The iron shell is provided on the electric furnace outer side with respect to the second surface. The iron shell has a third surface on the electric furnace inner side thereof and a fourth surface on the opposite side to the third surface. The cooling structure is provided on the electric furnace outer side with respect to the fourth surface, or is provided between the third surface and the fourth surface. The cooling structure cools the slag via the iron shell and the refractory.

Description

Refractory lining structure of electric furnace, refractory cooling method for electric furnace, electric furnace, and method for producing molten iron

[0001] The present application discloses a refractory lining structure for an electric furnace, a refractory cooling method for an electric furnace, an electric furnace, and a method for producing molten iron.

[0002] From the viewpoint of carbon neutrality, methods for producing molten iron using electric furnaces are being considered. In the electric furnace method, for example, it is common to operate the electric furnace only at night when the electricity unit price is low, and repair refractories and the like at other times, which poses a problem in productivity. In order to improve the productivity of molten iron in the electric furnace method, for example, continuous operation with hot heel (residual molten metal) remaining in the electric furnace is necessary. However, in this case, there is a problem that the refractory is easily worn by the hot heel, shortening the furnace life.

[0003] Patent Document 1 discloses a technique for suppressing damage to furnace wall refractories in an iron bath gasification furnace for gasifying solid carbonaceous materials using an iron bath. Patent Document 2 discloses a technique for improving the corrosion resistance of refractories on the inner surface of a steel shell in an electric furnace for producing molten flux for welding. However, neither Patent Document 1 nor Patent Document 2 considers reducing refractory wear due to hot heel when producing molten iron using an electric furnace.

[0004] JP-A-59-147981 JP-A-61-123697

[0005] The present application discloses a new technology that can reduce refractory wear caused by hot heel when producing molten iron using an electric furnace.

[0006] The present application discloses the following multiple aspects as means for solving the above problems: <Aspect 1> A refractory lining structure for an electric furnace, comprising: a refractory, slag, a shell, and a cooling structure, wherein the refractory has a first surface inside the electric furnace and a second surface opposite the first surface, the slag covers at least a portion of the first surface, the shell is provided closer to the exterior of the electric furnace than the second surface, the shell has a third surface inside the electric furnace and a fourth surface opposite the third surface, the cooling structure is provided closer to the exterior of the electric furnace than the fourth surface or is provided between the third surface and the fourth surface, and the cooling structure cools the slag via the shell and the refractory. <Aspect 2> The refractory lining structure for an electric furnace according to Aspect 1, wherein the refractory has a first refractory constituting the first surface and a second refractory constituting the second surface, the first refractory being an MgO-C brick, the effective usable thickness of the first refractory being 200 mm or more and 650 mm or less, and the thermal conductivity of the first refractory being 15 W / (m·K) or more and 40 W / (m·K) or less. <Aspect 3> A method for cooling a refractory for an electric furnace equipped with the refractory lining structure of Aspect 1 or 2, comprising one or both of: cooling the slag to a temperature at which the MgO concentration in the slag reaches its saturated solubility or less, and cooling the slag to a temperature at which the liquid phase fraction of the slag is 80% or less. <Aspect 4> An electric furnace comprising: the refractory lining structure of Aspect 1 or 2; and a metal supply device that supplies metal into an interior of the electric furnace. <Aspect 5> A method for producing molten iron using the electric furnace of Aspect 4, comprising: supplying a solid iron source from the iron source supply device to the interior of the electric furnace; and melting the solid iron source in the electric furnace to obtain molten iron, wherein the slag is present between the molten iron and the refractory.<Aspect 6> The method for producing molten iron according to Aspect 5, comprising: tapping a portion of the molten iron to the outside of the electric furnace while leaving a portion of the molten iron inside the electric furnace; and, after completion of tapping, supplying the solid iron source into the electric furnace where the molten iron remains, wherein the slag is present between the molten iron remaining inside the electric furnace and the refractory.

[0007] According to the technology of the present disclosure, it is possible to reduce wear of refractories due to hot heel when producing molten iron using an electric furnace.

[0008] 1 shows a schematic diagram of a refractory lining structure of an electric furnace according to one embodiment; 2 shows a flow chart of an electric furnace and a method for producing molten iron using the same according to one embodiment; 3 shows the relationship between the liquid phase fraction and temperature of each of the slags in Cases 1 to 4; and 4 shows the relationship between the saturated solubility of MgO and temperature when the MgO concentration of each of the slags in Cases 1 to 4 is changed.

[0009] Hereinafter, an embodiment of the refractory lining structure of an electric furnace, the refractory cooling method for an electric furnace, the electric furnace, and the method for producing molten iron according to the present disclosure will be described. However, the refractory lining structure of an electric furnace, the refractory cooling method for an electric furnace, the electric furnace, and the method for producing molten iron according to the present disclosure are not limited to the following embodiment.

[0010] 1. Background In order to reduce refractory wear due to hot heel when producing molten iron using an electric furnace, it is effective to protect the working surface of the refractory (the surface facing the molten iron) by coating it with slag. However, simply coating the working surface of the refractory with slag does not sufficiently reduce refractory wear due to hot heel. For example, refractories are susceptible to wear due to chemical erosion, in which refractory components (e.g., MgO) dissolve into the slag until saturated, causing refractory wear, and mechanical abrasion, in which the slag and refractory are worn away by the flow of the hot heel. In this regard, in order to reduce refractory wear due to hot heel in an electric furnace, it is necessary to: (1) reduce the dissolution of the refractory into the slag that coats the working surface of the refractory; and (2) increase the stability of the slag that coats the working surface of the refractory.

[0011] When producing molten iron using an electric furnace, the following are considered effective in suppressing the elution of the refractory into the slag that covers the working surface of the refractory and increasing the stability of the slag: (A) suppressing the elution of MgO from the refractory into the slag by adjusting the MgO concentration in the slag to the saturated solubility; and (B) reducing the liquid phase in the slag and increasing the solid phase, thereby suppressing the elution of MgO from the refractory into the slag and improving the mechanical stability of the slag on the working surface of the refractory.

[0012] In order to achieve the above (A) and (B), for example, the components of the refractory and slag may be adjusted. However, there are limitations on the types of refractories and the like that can be used when producing molten iron in an electric furnace, and it is difficult to say that a sufficient effect can be obtained.

[0013] The present inventors have considered that the above (A) and (B) can be achieved by lowering the temperature of the working surface of the refractory. Specifically, by cooling the back surface of the refractory to lower the temperature of the working surface of the refractory (i.e., indirectly cooling the working surface), the temperature of the slag covering the working surface can be lowered, thereby lowering the saturated solubility of MgO in the slag and reducing the liquid phase of the slag and increasing the solid phase. Based on the above considerations, the present inventors have completed the following technology.

[0014] 1. Refractory Lining Structure of an Electric Furnace As shown in FIG. 1 , a refractory lining structure 100 for an electric furnace according to one embodiment includes a refractory 10, slag 20, a shell 30, and a cooling structure 40. The refractory 10 has a first surface 10a on the interior side of the electric furnace and a second surface 10b opposite the first surface 10a. The slag 20 covers at least a portion of the first surface 10a. The shell 30 is provided closer to the exterior of the electric furnace than the second surface 10b (i.e., outside the refractory 10). The shell 30 has a third surface 30a on the interior side of the electric furnace and a fourth surface 30b opposite the third surface 30a. The cooling structure 40 is provided on the outer side of the electric furnace than the fourth surface 30b (i.e., outside the shell 30), or is provided between the third surface 30a and the fourth surface 30b (i.e., inside the shell 30). The cooling structure 40 cools the slag 20 via the shell 30 and the refractory material 10.

[0015] 1.1 Refractory The refractory 10 may be a combination of multiple types of refractories. As shown in Fig. 1, the refractory 10 may have, for example, a first refractory 11 constituting the first surface 10a and a second refractory 12 constituting the second surface 10b.

[0016] 1.1.1 First Refractory The first refractory 11 functions as a so-called wear refractory. At least a part of the first surface 10a formed by the first refractory 11 is covered with slag 20. This makes it easier to suppress direct contact between the molten iron 1 and the first refractory 11.

[0017] 1.1.1.1 Material and Composition of First Refractory The material and composition of the first refractory 11 are not particularly limited. Any known ware refractory provided on the furnace wall or furnace bottom of an electric furnace for melting a solid iron source can be used as the first refractory 11. The first refractory 11 may be a shaped refractory (e.g., brick) or a monolithic refractory. In one embodiment, the first refractory 11 may be an MgO—C brick. The MgO—C brick contains MgO and C. The MgO content in the MgO—C brick may be, for example, 45% by mass or more and 90% by mass or less, or 45% by mass or more and 75% by mass or less. The C content in the MgO—C brick may be, for example, 5% by mass or more and 50% by mass or less, or 20% by mass or more and 50% by mass or less. The content of components other than MgO and C in the MgO—C brick may be 1% by mass or more and 10% by mass or less, or 3% by mass or more and 7% by mass or less. When the first refractory 11 is made of such components, the first refractory 11 tends to have high corrosion resistance and thermal conductivity.

[0018] 1.1.1.2 Effective Usable Thickness of First Refractory The effective usable thickness of the first refractory 11 is not particularly limited. The "effective usable thickness of the first refractory" refers to the length from the first surface 10a of the first refractory 11 to the surface (back surface) facing the second refractory 12. According to the findings of the present inventors, when the effective usable thickness of the first refractory 11 is 200 mm or more and 650 mm or less, the first refractory 11 has a sufficient lifespan and the slag 20 is more easily cooled appropriately by the cooling structure 40 described below. The effective usable thickness of the first refractory 11 may be 250 mm or more, 300 mm or more, 350 mm or more, 400 mm or more, or 450 mm or more, or may be 600 mm or less or 550 mm or less.

[0019] The effective usable thickness of the first refractory 11 may be thicker, thinner, or the same as the effective usable thickness of the second refractory 12 described later. １ and the effective usable thickness T of the second refractory 12 ２ Relative to T １ / T ２may be 1.0 or more and 15.0 or less, or 2.5 or more and 10.0 or less.

[0020] 1.1.1.3 Thermal Conductivity of First Refractory The thermal conductivity of the first refractory 11 is not particularly limited. The "thermal conductivity of the first refractory" refers to the thermal conductivity of the first refractory 11 at 500°C. From the viewpoint of efficiently cooling the slag 20 using the cooling structure 40 described below, it is preferable that the thermal conductivity of the first refractory 11 be as high as possible. However, since there are certain limitations on the materials that can be used for the first refractory 11, the thermal conductivity of the first refractory 11 may also be limited to a certain range. According to the findings of the present inventors, when the thermal conductivity of the first refractory 11 is 15 W / (m·K) or more and 40 W / (m·K) or less, the first refractory 11 has a sufficient lifespan, and the first surface 10a of the first refractory 11 is more appropriately cooled by the cooling structure 40 described below, which facilitates more appropriate cooling of the slag 20.

[0021] 1.1.2 Second Refractory The second refractory 12 functions as a so-called permanent refractory (backup refractory), and is provided on the back side of the first refractory 11 (the side opposite to the first surface 10a).

[0022] 1.1.2.1 Material and Composition of Second Refractory The material and composition of the second refractory 12 are not particularly limited. Any known permanent refractory provided on the furnace wall or furnace bottom of an electric furnace for melting a solid iron source can be used as the second refractory 12. The second refractory 12 may be a shaped refractory (e.g., brick) or a monolithic refractory. In one embodiment, the second refractory 12 may be an MgO brick. The MgO brick contains MgO. The MgO content of the MgO brick may be, for example, 90% by mass or more and 99% by mass or less, or 92% by mass or more and 96% by mass or less. Furthermore, the content of components other than MgO in the MgO brick may be 1% by mass or more and 10% by mass or less, or 4% by mass or more and 8% by mass or less. Alternatively, in one embodiment, the second refractory 12 may be an alumina brick. The alumina brick contains Al ２ O ３ Contains Al in alumina bricks ２ O３ The content of Al in the alumina brick may be, for example, 40% by mass or more and 99% by mass or less, or 50% by mass or more and 90% by mass or less. ２ O ３ The content of the other components may be 1% by mass or more and 60% by mass or less, or 10% by mass or more and 50% by mass or less.

[0023] 1.1.2.2 Effective Usable Thickness of Second Refractory The effective usable thickness of the second refractory 12 is not particularly limited. The "effective usable thickness of the second refractory" refers to the length from the surface of the second refractory 12 facing the first refractory 11 to the surface (back surface) facing the shell 30. In one embodiment, the effective usable thickness of the second refractory 12 may be 20 mm or more and 200 mm or less. The effective usable thickness of the second refractory 12 may be 30 mm or more or 40 mm or more, or may be 195 mm or less, 130 mm or less, or 65 mm or less.

[0024] 1.1.2.3 Thermal Conductivity of Second Refractory The thermal conductivity of the second refractory 12 is not particularly limited. Note that the "thermal conductivity of the second refractory" refers to the thermal conductivity of the second refractory 12 at 500°C. The thermal conductivity of the second refractory 12 may be lower than, higher than, or the same as the thermal conductivity of the first refractory 11. In one embodiment, the thermal conductivity of the second refractory 12 may be 3 W / (m K) or more and 40 W / (m K) or less.

[0025] 1.2 Slag The slag 20 functions to protect the refractory 10 by covering at least a portion of the first surface 10a of the refractory 10. That is, the refractory lining structure 100 according to one embodiment may have at least a portion of the first surface 10a of the refractory 10 coated with a so-called slag coating. In this embodiment, the slag 20 is cooled by the cooling structure 40 (described later). This prevents the slag 20 from becoming molten even when the slag 20 comes into contact with molten iron. This maintains the mechanical stability of the slag 20, making it easier to maintain the first surface 10a covered with the slag 20. As a result, contact between the refractory 10 and the molten iron 1 is suppressed, and wear of the refractory 10 is reduced. This embodiment can also reduce wear of the refractory 10 due to, for example, hot heeling.

[0026] 1.2.1 Slag Composition The slag 20 can have various compositions as long as it functions as a protective layer. For example, the slag 20 may be composed of iron and SiO ２ The composition of the slag 20 may include, for example, T. Fe: 10 mass% or more and 40 mass% or less, SiO ２ : 10 mass% or more and 30 mass% or less, CaO: 20 mass% or more and 50 mass% or less, MgO: 1 mass% or more and 20 mass% or less, MnO: 0 mass% or more and 10 mass% or less, P ２ O ５ : 0 mass% or more and 10 mass% or less, and Al ２ O ３ : 0 mass % or more and 10 mass % or less,

[0027] 1.2.2 Thickness of the Slag The thickness of the slug 20 covering the first surface 10a is not particularly limited. The thickness of the slug 20 may be, for example, 1 mm or more and 30 mm or less, or 5 mm or more and 20 mm or less.

[0028] 1.3 Shell The shell 30 is the shell of the electric furnace and supports the furnace body. The shell 30 has a third surface 30a on the inside of the electric furnace and a fourth surface 30b on the opposite side (back side) of the third surface 30a. The shell 30 is provided on the outside of the electric furnace relative to the second surface 10b of the refractory 10. For example, the refractory 10 (first refractory 11 and second refractory 12) lines the third surface 30a of the shell 30. The shell 30 may be a typical shell for an electric furnace, and its thickness and other properties are not particularly limited.

[0029] 1.4 Cooling Structure The cooling structure 40 is provided on the outer side of the electric furnace relative to the fourth surface 30b of the shell 30 (i.e., outside the shell 30), or is provided between the third surface 30a and the fourth surface 30b of the shell 30 (i.e., inside the shell 30). In this embodiment, it is important that the cooling structure 40 is configured to cool the slag 20 via the shell 30 and the refractory 10. That is, cooling by the cooling structure 40 reaches the slag 20 through the shell 30 and the refractory 10. As described above, when melting a solid iron source or refining molten iron using an electric furnace, cooling the first surface 10a of the refractory 10 with the cooling structure 40 reduces the temperature of the slag 20 covering the first surface 10a. This reduces the saturated solubility of MgO in the slag 20 and also reduces the liquid phase and increases the solid phase of the slag 20. As a result, the elution of the refractory 10 into the slag 20 is suppressed, the mechanical stability of the slag 20 is improved, and wear of the refractory due to hot heel is more easily suppressed.

[0030] As described above, the cooling structure 40 may have various structures as long as it can cool the slag 20 via the shell 30 and the refractory material 10. For example, by providing a flow path on the outer surface of the shell 30 or inside the shell 30 and circulating a cooling medium through the flow path, the cooling energy of the cooling medium can be transmitted to the slag 20 via the shell 30 and the refractory material 10. The cooling medium may be, for example, water. In other words, the cooling structure 40 may be a water-cooled structure. The temperature and flow rate of the cooling medium in the cooling structure 40 may be appropriately determined depending on the temperature of the slag 20 to be achieved, etc.

[0031] The cooling structure 40 is preferably provided as close as possible to the first surface 10a of the refractory 10. When the interior of an electric furnace is divided into an upper section and a lower section, refractory wear due to hot heel is likely to occur in the lower section of the electric furnace. In this regard, when the interior of an electric furnace is divided into an upper section and a lower section, the cooling structure 40 may cool the slag 20 via the shell 30 and the refractory 10 in at least a portion of the lower section. For example, the cooling structure 40 may cool the slag 20 via the shell 30 and the refractory 10 at least at a position below the height of the molten iron 1 in the electric furnace. Furthermore, the cooling structure 40 may cool the slag 20 via the shell 30 and the refractory 10 in at least a portion of the bottom of the electric furnace, or may cool the slag 20 via the shell 30 and the refractory 10 in at least a portion of the side wall of the electric furnace. Alternatively, the cooling structure 40 may cool the slag 20 through the iron shell 30 and the refractory material 10 over the entire side wall of the electric furnace.

[0032] In addition, the refractory material 10 is easily worn in the furnace wall of the electric furnace, particularly in hot spots close to the electrodes. In this regard, the cooling structure 40 may cool the slag 20 through the shell 30 and the refractory material 10 at least in the portion of the refractory material 10 closest to the electrodes.

[0033] 1.5 Other Configurations In an electric furnace, configurations other than the above-described refractory lining structure are not particularly limited and may be known configurations. The electric furnace, for example, has a melting furnace for melting an iron source. The melting furnace may be defined by a furnace lid, an inner furnace wall, and a furnace bottom. The planar shape of the melting furnace may be circular. The melting furnace may have a constant bath depth or a constant furnace diameter. The bath depth and furnace diameter of the melting furnace are not particularly limited. Means for generating an arc in an electric furnace are also known. For example, a direct current type using an upper electrode and a lower electrode may be used, or an alternating current type may be used. In the case of a direct current type, the upper electrode may be a cathode and the lower electrode may be an anode. The upper electrode may be installed so as to be inserted into the furnace through the furnace lid. The lower electrode is installed at the furnace bottom. In the case of a direct current type, the number of upper and lower electrodes is at least one. The positions of the upper and lower electrodes are not particularly limited.

[0034] 2. Refractory Cooling Method for Electric Furnace The technology disclosed herein also has an aspect as a refractory cooling method for an electric furnace. That is, a refractory cooling method for an electric furnace according to one embodiment is a refractory cooling method for an electric furnace equipped with the refractory lining structure 100, and may include one or both of: (I) cooling the slag 20 to a temperature at which the MgO concentration in the slag 20 reaches the saturated solubility or lower; and (II) cooling the slag 20 to a temperature at which the liquid phase fraction of the slag 20 reaches 80% or lower. The refractory cooling method for an electric furnace according to the present disclosure may be performed only when molten iron 1 is present inside the electric furnace.

[0035] As described above, when producing molten iron using an electric furnace, the following are effective in suppressing the elution of the refractory into the slag (slag coating layer) that coats the working surface of the refractory and increasing the stability of the slag: (A) suppressing the elution of MgO from the refractory into the slag by adjusting the MgO concentration in the slag to the saturated solubility; and (B) reducing the liquid phase in the slag and increasing the solid phase, thereby suppressing the elution of MgO from the refractory into the slag and improving the mechanical stability of the slag on the working surface of the refractory.

[0036] In contrast, a refractory cooling method for an electric furnace according to one embodiment includes: (I) cooling the slag 20 to a temperature below the temperature at which the MgO concentration in the slag 20 reaches its saturated solubility. This achieves the above (A). As described above, the lower the temperature of the slag 20, the lower the saturated solubility of the MgO concentration in the slag 20. That is, in the above (I), the temperature and flow rate of the cooling medium in the cooling structure 40 may be controlled so that the temperature of the slag 20 covering the first surface 10a is controlled to be below a threshold value, thereby allowing the MgO concentration in the slag 20 to reach its saturated solubility. The relationship between the saturated solubility of the MgO concentration in the slag 20 and the temperature is determined by the composition of the slag 20, etc. When producing molten iron using an electric furnace, whether the temperature of the slag 20 is below the threshold value may be determined by directly measuring the temperature of the slag 20 or by estimating the temperature of the slag 20 using heat transfer calculations, etc.

[0037] Furthermore, in one embodiment of the refractory cooling method for an electric furnace, the above-described (B) is achieved by including: (II) cooling the slag 20 to a temperature or lower at which the liquid fraction of the slag 20 is 80% or less. As described above, as the temperature of the slag 20 decreases, the liquid fraction of the slag 20 decreases and the solid fraction increases. That is, in the above-described (II), the temperature and flow rate of the cooling medium in the cooling structure 40 are controlled so that the temperature of the slag 20 covering the first surface 10a is controlled to be equal to or lower than a threshold value, thereby making the liquid fraction of the slag 20 equal to or lower than 80%. The relationship between the liquid fraction and the temperature of the slag 20 is determined by the composition of the slag 20, etc. As described above, whether the temperature of the slag 20 is equal to or lower than the threshold value may be determined by directly measuring the temperature of the slag 20 or by estimating the temperature of the slag 20 using heat transfer calculations, etc.

[0038] In particular, the refractory cooling method for an electric furnace according to one embodiment is expected to be more effective when it includes both of the above (I) and (II).

[0039] 3. Electric Furnace The technology of the present disclosure also has an aspect of an electric furnace itself. That is, as shown in Fig. 2 , an electric furnace 1000 according to one embodiment includes the above-described refractory lining structure 100 and an iron source supply device 200 that supplies a solid iron source 2 into the electric furnace 1000.

[0040] The iron source supply device 200 may supply the solid iron source 2 from, for example, a side wall of the electric furnace 1000 to the interior of the electric furnace 1000. More specifically, in the electric furnace 1000, the solid iron source 2 may be supplied to the interior of the electric furnace 1000 through an iron source supply port 300 provided in the side wall of the electric furnace 1000. Alternatively, in the electric furnace 1000, the solid iron source 2 may be supplied to the interior of the electric furnace 1000 through an iron source supply port provided in a furnace cover (not shown) of the electric furnace 1000. The iron source supply device 200 may have a mechanism for transporting the solid iron source to the iron source supply port 300 of the electric furnace 1000. The iron source supply device 200 may include one or more of a conveyor, a chute, and a hopper. The iron source supply device 200 may supply the solid iron source 2 continuously or intermittently.

[0041] As described above, the electric furnace 1000 may be used to melt a solid iron source. In other words, the electric furnace 1000 may be an electric furnace for melting metals, i.e., an electric metal melting furnace.

[0042] 4. Manufacturing Method of Molten Iron Using an Electric Furnace The technology disclosed herein also has an aspect of a method for manufacturing molten iron using an electric furnace. As shown in Fig. 2 , a method for manufacturing molten iron according to one embodiment may include: supplying a solid iron source 2 from an iron source supply device 200 into an electric furnace 1000; and melting the solid iron source 2 in the electric furnace 1000 to obtain molten iron 1. At this time, slag 20 is present between the molten iron 1 and the refractory 10. This suppresses contact between the refractory 10 and the molten iron 1, and makes it easier to reduce wear of the refractory 10.

[0043] 2 , a method for producing molten iron according to one embodiment may include: tapping a portion of the molten iron 1 to the outside of the electric furnace 1000 while leaving a portion of the molten iron 1 inside the electric furnace 1000; and, after completion of tapping, supplying a solid iron source into the electric furnace 1000 where the molten iron 1 remains. That is, in the electric furnace 1000, the supply of the solid iron source 2, melting of the solid iron source 2, and tapping of the molten iron 1 may be repeated while leaving a hot heel (residual molten iron) inside the electric furnace 1000. This improves the efficiency of producing molten iron. At this time, slag 20 is present, for example, between the molten iron 1 (hot heel) remaining inside the electric furnace 1000 and the refractory 10. This suppresses contact between the refractory 10 and the hot heel, and facilitates reducing wear of the refractory 10.

[0044] Furthermore, in this embodiment, when the molten iron 1 is present inside the electric furnace 1000, the method may include at least one or both of: cooling the slag 20 so that the MgO concentration in the slag 20 reaches the saturated solubility; and cooling the slag 20 so that the liquid phase ratio of the slag 20 is 80% or less. Note that known methods may be used for supplying the solid iron source 2 into the electric furnace 1000 and melting the solid iron source 2. The cooling method for the slag 20 is as described above.

[0045] In the method for producing molten iron according to an embodiment, the type of the solid iron source 2 is not particularly limited. The solid iron source 2 may include, for example, scrap, reduced iron, or another iron source. Furthermore, in the method for producing molten iron according to an embodiment, after melting the solid iron source 2 and before pouring the molten iron 1, refining of the molten iron 1 may be performed. Furthermore, in the method for producing molten iron according to an embodiment, after melting the solid iron source 2 and before pouring the molten iron 1, at least a portion of the slag present on the surface of the molten iron 1 may be removed.

[0046] 5. Effects As described above, the refractory lining structure for an electric furnace, the refractory cooling method for an electric furnace, the electric furnace, and the method for producing molten iron disclosed herein can reduce wear of the refractory 10 (particularly the first refractory 11) caused by the molten iron 1 (e.g., hot heel) when producing molten iron 1 using the electric furnace 1000. Therefore, for example, the continuous operating time of the electric furnace 1000 can be extended, and the productivity of molten iron can be improved, compared to conventional methods.

[0047] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention.

[0048] 1. Cooling verification of the working surface of the refractory One type of refractory corrosion is chemical static erosion, in which refractory components dissolve in the slag until they are saturated. This chemical static erosion can be suppressed by lowering the temperature of the working surface of the refractory to reduce the liquid phase ratio of the slag and / or the saturated solubility of MgO in the slag.

[0049] 1.1 Estimation of Liquid Phase Fraction of Slag Table 1 below shows the composition of the slag examined in this example. The liquid phase fraction of the slag examined in this example drops to 80% at approximately 1380-1470°C. Figure 3 shows specific estimation results. It was found that the liquid phase fraction reaches 80% or less by cooling the slag in Case 1 to 1450°C, the slag in Case 2 to 1450°C, the slag in Case 3 to 1470°C, and the slag in Case 4 to 1380°C.

[0050] 1.2 Estimation of MgO Saturation Solubility Figure 4 shows the relationship between MgO saturation solubility and temperature when the MgO concentration of each slag is changed in Cases 1 to 4. In addition, the temperature at which the actual MgO concentration reaches the saturated solubility was determined for each slag in Cases 1 to 4. It was found that the MgO concentration reaches the saturated solubility at 1420°C for the MgO concentration of slag in Case 1, 1400°C for the slag in Case 2, 1420°C for the slag in Case 3, and 1360°C for the slag in Case 4.

[0051] 1.3 Verification by Simulation The effect of cooling the back surface of the refractory by water cooling was verified by temperature simulation. As calculation conditions, Table 3 shows the refractory quality, and Tables 4 to 6 show the verified refractory linings. As shown in Table 3, four types of refractories were used: two types of wear bricks A and B, and two types of perm bricks C and D. As shown in Tables 4 to 6, nine examples were verified by combining wear bricks and perm bricks. In the example shown in Table 4, the thickness of the wear brick (effective usable thickness) was 550 mm, in the example shown in Table 5 it was 650 mm, and in the example shown in Table 6 it was 200 mm. In addition, in Tables 4 and 5, the cooling water flow rate in the case of water cooling was 90 m ３ / h.

[0052] Table 7 below shows the boundary conditions for steady-state calculations. In Table 7 below, the heat transfer coefficient values ​​for the outside of the furnace are taken from Non-Patent Document 1 below, and the heat transfer coefficient values ​​for the inside of the furnace are taken from Non-Patent Document 2 below. Non-Patent Document 1: Energy Conservation Center, Foundation, Revised Edition of Energy Management Technology, Thermal Management, 2003 Non-Patent Document 2: Vito Logar et al., A Computational Model for Heat Transfer Coefficient Estimation in Electric Arc Furnace, Steel Research International. 87 (2016) No. 3, pp. 330-338

[0053] Table 8 below shows the calculation results for the linings in Table 4. As shown in Table 8, in Example 1-1 (without water cooling), the temperature of the interface between the wear brick and the slag (wear working surface) was 1546°C, whereas in Examples 2-1 and 3-1 (with water cooling), the temperatures of the working surface could be reduced to 1358°C and 1290°C, respectively.

[0054] Table 9 below shows the calculation results for the linings in Table 5. As shown in Table 9, in Example 1-2 (without water cooling), the temperature of the interface between the wear brick and the slag (wear working surface) was 1549°C, whereas in Examples 2-2 and 3-2 (with water cooling), the temperatures of the working surface could be reduced to 1377°C and 1309°C, respectively.

[0055] Table 10 below shows the calculation results for the linings in Table 6. As shown in Table 10, in Example 1-3 (without water cooling), the temperature of the interface between the wear brick and the slag (wear working surface) was 1534°C, whereas in Examples 2-3 and 3-3 (with water cooling), the temperatures of the working surface could be reduced to 1249°C and 1205°C, respectively.

[0056] 2. Erosion Suppression Test Based on the above verification results, a rotary erosion furnace test was conducted to verify the effectiveness. Specifically, a rotary erosion test was conducted under the test conditions (slag composition: Case 4) shown in Table 11 below. Table 12 shows the test results. The wear rate for Comparative Example 1 was 0.25 (mm / ch), while the wear rates for Example 1 and Example 2 were 0.20 (mm / ch) and 0.18 (mm / ch), respectively, confirming a tendency for a reduction. When the wear rate index for Comparative Example 1 is taken as 100, the wear rate index for Example 1 was 80 and the wear rate index for Example 2 was 72, indicating a reduction in the wear rate by more than 20%. In particular, the use of bricks with high thermal conductivity in Example 2 likely resulted in a lower operating surface temperature, which significantly reduced the wear rate.

[0057] 3. Supplementary Information: Although the above-mentioned Examples 1 and 2 correspond to examples in which the working surface (and slag) was cooled to (1) a temperature below the temperature at which the MgO concentration in the slag reaches saturation solubility, and (2) a temperature below the temperature at which the liquid phase fraction of the slag is 80% or less, the cooling temperature of the slag is not limited to those satisfying (1) and (2). Lowering the slag temperature is believed to reduce the elution and diffusion of MgO from the wear bricks and improve the mechanical stability of the slag covering the working surface, resulting in a reduction in the wear rate. In other words, when the slag temperature is lowered, the wear rate can be reduced compared to when the slag temperature is not lowered, regardless of the cooling temperature. For example, even when the slag is cooled to satisfy only one of the above conditions (1) and (2), the wear rate can be significantly reduced. However, when the working surface is cooled to satisfy both conditions (1) and (2), as in Examples 1 and 2, the wear rate can be more significantly reduced.

[0058] 4. Summary From the above results, it can be said that by adopting a refractory lining structure that satisfies the following requirements (I) to (VII) in an electric furnace, it is possible to reduce refractory wear due to hot heel when producing molten iron using an electric furnace. (I) The refractory lining structure has a refractory, slag, a steel shell, and a cooling structure. (II) The refractory has a first surface on the interior side of the electric furnace and a second surface opposite the first surface. (III) The slag covers at least a portion of the first surface. (IV) The steel shell is provided on the exterior side of the electric furnace relative to the second surface. (V) The steel shell has a third surface on the interior side of the electric furnace and a fourth surface opposite the third surface. (VI) The cooling structure is provided on the exterior side of the electric furnace relative to the fourth surface, or is provided between the third surface and the fourth surface. (VII) The cooling structure cools the slag through the shell and the refractory material.

[0059] REFRACTORY LIST 1 molten iron 10 refractory 10a first surface 10b second surface 11 first refractory 12 second refractory 20 slag 30 iron shell 30a third surface 30b fourth surface 40 cooling structure 100 refractory lining structure 200 iron source supply device 300 iron source supply port 1000 electric furnace

Claims

1. A refractory lining structure for an electric furnace, comprising: a refractory, slag, a shell, and a cooling structure, wherein the refractory has a first surface on the interior side of the electric furnace and a second surface opposite the first surface, the slag covers at least a portion of the first surface, the shell is provided on the exterior side of the electric furnace relative to the second surface, the shell has a third surface on the interior side of the electric furnace and a fourth surface opposite the third surface, the cooling structure is provided on the exterior side of the electric furnace relative to the fourth surface or is provided between the third surface and the fourth surface, and the cooling structure cools the slag via the shell and the refractory.

2. A refractory lining structure for an electric furnace according to claim 1, wherein the refractory comprises a first refractory constituting the first surface and a second refractory constituting the second surface, the first refractory being an MgO-C brick, the effective usable thickness of the first refractory being 200 mm or more and 650 mm or less, and the thermal conductivity of the first refractory being 15 W / (m·K) or more and 40 W / (m·K) or less.

3. A method for cooling refractories in an electric furnace equipped with the refractory lining structure of claim 1 or 2, comprising one or both of: cooling the slag to a temperature below which the MgO concentration in the slag reaches saturated solubility; and cooling the slag to a temperature below which the liquid phase ratio of the slag reaches 80% or less.

4. An electric furnace comprising: a refractory lining structure according to claim 1 or 2; and an iron source supply device that supplies a solid iron source into the electric furnace.

5. A method for producing molten iron using an electric furnace as defined in claim 4, comprising: supplying a solid iron source from the iron source supply device into the interior of the electric furnace; and melting the solid iron source inside the electric furnace to obtain molten iron, wherein the slag is present between the molten iron and the refractory.

6. A method for producing molten iron as set forth in claim 5, comprising: pouring a portion of the molten iron to the outside of the electric furnace while leaving a portion of the molten iron inside the electric furnace; and, after completion of the pouring, supplying the solid iron source into the electric furnace where the molten iron remains, wherein the slag is present between the molten iron remaining inside the electric furnace and the refractory.