Method for melting metal raw material

Abstract

Provided is a method for melting a metal raw material, whereby a large amount of the metal raw material can be melted by setting conditions for melting the metal raw material, which partially contains reduced iron or totally contains reduced iron, using a submerged arc furnace (SAF), and by performing stable energization. A method for melting a metal raw material by an electric furnace in which molten iron, slag, a metal raw material, and an auxiliary raw material are stacked and accommodated in the electric furnace and the molten iron and the slag are discharged, the method being characterized in that: when a current is supplied to the molten metal through an arc or through the slag and the metal raw material to heat the molten metal; the internal resistivity of the electric furnace is set to be in the range of 0.01-0.02 (Omega * m).

Description

Technical Field

[0001] This invention relates to a method for melting metallic raw materials. In particular, this invention relates to a method for melting metallic raw materials capable of producing molten metal by melting metallic raw materials containing reduced iron in an electric furnace or a submerged arc furnace. Background Technology

[0002] In recent years, efforts have been made to reduce CO2 emissions in order to mitigate environmental burdens. In the steel industry, the use of direct reduction (DR) methods to manufacture iron ore as a substitute for the CO2-intensive blast furnace method has attracted significant attention. In the DR method, iron-containing agglomerate is reduced in a shaft furnace, for example, to produce direct reduced iron (DRI). This reduced iron, along with iron scrap and other iron source materials, is then heated and melted in an electric arc furnace (EAF) or submerged arc furnace (SAF), and the molten iron is produced after separating the slag.

[0003] In Japan, research is underway on applying low-grade iron ore from countries such as Australia and India to the direct reduction (DR) process. Existing electric arc furnaces (EAFs) make it difficult to melt reduced iron produced from low-grade iron ore. Therefore, the use of submerged arc furnaces (SAFs) is being investigated.

[0004] Against this technological backdrop, various molten metal manufacturing processes utilizing submerged arc furnaces (SAFs) have been proposed. These processes also include methods for manufacturing molten iron based on so-called flat-pool operation (FBO). For example, molten iron manufacturing based on a SAF is carried out through flat-pool operation (FBO). Flat-pool operation (FBO) employs the following melting process: raw materials and by-products, including metallic materials such as scrap iron, pig iron, direct reduced iron (DRI), or hot-pressed iron (HBI), are continuously fed into the SAF without opening the furnace lid, or raw materials are loaded using a small hopper. During the loading process, electrodes are inserted into the molten slag within the SAF, generating an electric arc between multiple electrodes or between the electrodes and the molten iron. Current flows through the raw material and slag, heating and melting the raw material through resistance heating and heat conduction.

[0005] One problem with submerged arc furnaces (SAFs) is the inefficient heat transfer to the raw material located far from the electrodes. There, incomplete melting due to delayed melting of the metal raw material can lead to concentration gradients, unreliable temperature measurements, unreliable process control, and tapping of excessively hot molten metal. To address this uneven temperature problem, electromagnetic stirring of molten metal disclosed in Patent Document 1 and gas stirring of molten slag disclosed in Patent Document 2 have been developed.

[0006] Furthermore, Patent Document 3 discloses a technique for obtaining molten metal by arc heating a pre-reduced metal. The molten metal manufacturing method described in Patent Document 3 uses a stationary, non-radial symmetrical melting furnace that melts the pre-reduced metal by arc heating, primarily using radiant heat. This furnace includes arc heating electrodes and a pre-reduced metal supply mechanism. Moreover, in the molten metal manufacturing method described in Patent Document 3, the refractory melt index RF, defined by a given formula, is maintained at 400 MWV / m. 2 The molten iron will now be melted.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Publication No. 2020-505579

[0010] Patent Document 2: Japanese Patent Application Publication No. 2002-317918

[0011] Patent Document 3: Japanese Patent Application Publication No. 2003-105415

[0012] Content of the invention

[0013] The problem that the invention aims to solve

[0014] However, the prior art has the following problems. Specifically, the technology described in Patent Document 1 is merely a method for manufacturing molten metal using an electric arc furnace. Furthermore, the technology described in Patent Document 2 is a technology for an electric furnace used in waste melting, and does not aim to achieve mass production of molten metal. From this technical perspective, the issue becomes how to apply a submerged arc furnace (SAF) to the manufacturing method of molten metal and to consider the operational method of an electric furnace that also enables the production of molten metal.

[0015] Furthermore, in the technology described in Patent Document 3, in order to maintain the melt flow index (RF) of the refractory at 400 MWV / m 2 The molten iron is then melted, and the furnace resistance is set to an extremely low level. Therefore, even when the molten metal manufacturing method described in Patent Document 3 is used to melt the reduced iron, a short circuit occurs between the electrodes (PCD). As a result, the technology described in Patent Document 3 cannot provide stable power to the furnace, leading to a problem where the reduced iron cannot be fully melted.

[0016] Furthermore, the melting of reduced iron from low-grade iron ore using a submerged arc furnace (SAF) is difficult for the following reasons. When using a SAF to melt reduced iron, the conditions inside the furnace change drastically depending on the voltage and current settings used to generate the arc for the melting process. For example, if the voltage used to generate the arc is too high, the arc discharge becomes larger. As a result, the radiant heat caused by the arc discharge increases, and the thermal efficiency of the molten iron decreases significantly.

[0017] On the other hand, if the voltage used to generate such an electric arc is too low, the distance between the molten iron and the electrodes used to generate the arc becomes too close within the submerged arc furnace (SAF). As a result, the molten iron within the SAF experiences molten level changes, leading to unstable heating of the molten iron. Furthermore, since the raw material can intrude into the circuit formed by the electrodes and molten iron within the SAF, unstable heating of the molten iron also exists. Additionally, there are no reports on an appropriate voltage range applied during the melting of reduced iron when using a submerged arc furnace (SAF).

[0018] The present invention was made in view of the above circumstances, and its object is to provide a method for melting metal raw materials that enables the melting of large quantities of metal raw materials by setting stable energization conditions when melting metal raw materials containing partially or entirely reduced iron using a submerged arc furnace (SAF).

[0019] Problem Solving Methods

[0020] Therefore, in order to solve the above-mentioned problems, the inventors conducted various experiments repeatedly and discovered the following insights: by setting the furnace resistivity of a submerged arc furnace (SAF) as an electric furnace for melting metal raw materials containing some or all of reduced iron, and by stably energizing the electric furnace, it is possible to melt large quantities of metal raw materials containing some or all of reduced iron. This invention is based on the above insights, and its main points are as follows.

[0021] That is, the metal raw material melting method of the present invention, which advantageously solves the above-mentioned problems, is a metal raw material melting method based on an electric furnace in which molten iron, slag, metal raw material and by-product are stacked and contained in an electric furnace, and the molten iron and slag are discharged separately and continuously. In this method, when current is supplied to the molten metal for heating through an electric arc or through slag and metal raw material, the resistivity of the electric furnace is set to the range of 0.01 to 0.02 (Ω·m).

[0022] It should be noted that the melting method of the metal raw materials of the present invention can be set as the following preferred solutions (a) to (j):

[0023] (a) Melting the above-mentioned metal raw materials by means of a flat molten pool operation;

[0024] (b) The metallization rate of the above-mentioned metal raw materials is 60% or more;

[0025] (c) Set the current density flowing through the electrodes of the above-mentioned electric furnace to 50~70 (A / m²). 2 ) range;

[0026] (d) The above electrodes are self-sintering type;

[0027] (e) The above-mentioned electric furnace is either a three-phase AC type with three electrodes or a single-phase type with multiple pairs of electrodes;

[0028] (f) The above-mentioned metal raw materials and by-products are mixed or supplied separately between the electrodes;

[0029] (g) Some or all of the above-mentioned metal raw materials are reduced iron;

[0030] (h) The basicity of the above-mentioned 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.

[0031] (i) The electric furnace is an electric arc furnace, and at least one of the following is adjusted in such a way that the arc voltage E(V), which is the voltage to ground, and the arc current I(A) of each arc electrode of the electric arc furnace satisfy the following relationship (i): the distance from the interface of the molten iron to the arc electrode, the arc voltage, and the arc current.

[0032] [Mathematical Expression 1]

[0033] ;

[0034] (j) The above-mentioned electric furnace is a submerged arc furnace.

[0035] The effects of the invention

[0036] According to the present invention, by using a submerged arc furnace (SAF) as an electric furnace, setting the conditions for melting metal raw materials that contain partially or entirely reduced iron, and stably energizing the electric furnace, a large quantity of metal raw materials can be melted. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the outline of the electric furnace used in implementing the metal raw material melting method of this embodiment.

[0038] Figure 2 This is a schematic diagram showing the state of the electrodes and the vicinity of the electrodes when the electric furnace used in carrying out the metal raw material melting method of this embodiment is energized.

[0039] Figure 3 This is a schematic diagram showing the outline of the single-phase AC submerged arc furnace used in implementing the metal raw material melting method of this embodiment.

[0040] Symbol Explanation

[0041] 1. Electric furnace (submerged arc furnace, SAF)

[0042] 2 Furnace Wall

[0043] 3 electrodes

[0044] 4. Add reduced iron (metallic raw material)

[0045] 5. Electric arc

[0046] P-molten iron (molten pig iron)

[0047] S-molten slag (molten furnace slag)

[0048] M raw materials Detailed Implementation

[0049] [First Implementation]

[0050] The melting method for metal raw materials according to the first embodiment will be described. The melting method for metal raw materials in this embodiment is an electric furnace-based melting method for metal raw materials in which molten iron, slag, metal raw materials, and by-products are layered and contained within an electric furnace, and the molten iron and slag are discharged. When current is supplied to the molten metal for heating via an electric arc or through the slag and metal raw materials, the resistivity of the electric furnace is set to a range of 0.01 to 0.02 (Ω·m). Hereinafter, each step included in the melting method for metal raw materials of this embodiment will be described.

[0051] Figure 1 This is a longitudinal cross-sectional schematic diagram illustrating the structure of the submerged arc furnace used in the metal raw material melting method of this embodiment. (As shown...) Figure 1 As shown, the submerged arc furnace 1 includes a furnace wall 2, multiple electrodes 3, and a transformer (not shown in the figure).

[0052] The submerged arc furnace 1 can be equipped with an electromagnetic stirrer (not shown in the figure) including a linear motor. Additionally, the submerged arc furnace 1 can be configured to blow air bubbles in by blowing gas from a bottom tuyer (not shown in the figure). Thus, the submerged arc furnace 1, which is the preferred electric furnace in the metal raw material melting method of this embodiment, is equipped with a stirring device such as an electric stirrer 6 and a bottom tuyer 7. This allows it to stir the molten iron (molten pig iron) P and conduct the heat generated by the electric arc discharge to the interface of the molten slag (molten furnace slag) S, melting metal raw materials that partially or entirely contain reduced iron.

[0053] It should be noted that the submerged arc furnace 1 can be an electric furnace that is roughly circular when viewed from above, or it can be an electric furnace that is rectangular.

[0054] like Figure 1 As shown, the submerged arc furnace 1 includes a furnace wall 2, multiple electrodes 3, and a transformer (not shown in the figure). The refractory material constituting the furnace wall 2 can be any refractory material with excellent refractory properties, heat insulation, and heat preservation properties, without any particular restrictions. It can be selected from one or more of carbon, magnesium oxide, alumina, etc. as the main body.

[0055] Multiple electrodes 3 are provided inside the submerged arc furnace 1. The electrodes 3 can be composed of an electrode group containing three electrodes 3, or an electrode group containing multiple pairs of electrodes 3. When the submerged arc furnace 1 has three electrodes 3, it becomes a three-phase AC submerged arc furnace. On the other hand, when the submerged arc furnace 1 has multiple pairs of electrodes 3, it becomes a single-phase AC submerged arc furnace.

[0056] Electrode 3 can be either a sintered electrode or a self-sintering electrode. The type of electrode 3 is not particularly limited; a graphite electrode, typically used in electric arc furnaces that produce steel by melting iron scrap, can be used. Graphite electrodes are preferred even when the furnace temperature of the submerged arc furnace 1 is around 1600°C. Furthermore, they are preferred even when the temperature at the tip of the graphite electrode is around 3000°C. By using a graphite electrode as electrode 3, a large amount of current can flow within the submerged arc furnace 1, which is also preferred.

[0057] The electrode diameter D and its length of electrode 3 vary depending on the metal raw material melting and processing capacity of submerged arc furnace 1, the power supply, etc. Here, the electrode diameter D of electrode 3 is defined according to the type of electrode as follows. When electrode 3 is a graphite electrode that is a sintering type electrode, the diameter of the sintering type electrode is taken as the electrode diameter D. When electrode 3 is a self-sintering type electrode, the inner diameter of the shell into which the electrode paste containing the raw material of the self-sintering type electrode is loaded is taken as the electrode diameter D.

[0058] For example, when the metal raw material melting capacity of the submerged arc furnace 1 is 20~60t / h, the electrode diameter D of the electrode 3 is 1000~1800mm. The length of the electrode 3 only needs to be sufficient to ensure the vertical movement of the electrode 3 based on the height of the submerged arc furnace 1 and the capacity of molten metal that can be held.

[0059] The submerged arc furnace 1 is equipped with a transformer. The transformer converts the voltage applied between the electrodes formed by the multiple electrodes 3 into an appropriate voltage. The transformer has a tap-switch terminal on its high-voltage side. The output voltage of the transformer can be switched and adjusted via the tap-switch terminal. In addition, the current flowing between the electrodes formed by the multiple electrodes 3 can be adjusted by changing the height of the electrodes 3 loaded into the molten slag (molten furnace slag) S stacked inside the submerged arc furnace 1.

[0060] The metal raw material melting method of this embodiment is implemented in the following manner: Multiple electrodes 3 are inserted into the molten slag (molten furnace slag) S stacked in the submerged arc furnace 1. An electric arc 5 is generated between the multiple electrodes 3 or between the electrodes 3 and the molten iron (molten pig iron) P. The raw material M, including the metal raw material 4 and auxiliary raw materials, is heated and melted by the radiant heating of the electric arc 5. Alternatively, the metal raw material melting method of this embodiment is implemented in the following manner: Multiple electrodes 3 are inserted into the molten slag (molten furnace slag) S stacked in the submerged arc furnace 1. The raw material M, including the metal raw material 4 and auxiliary raw materials, is heated and melted by the resistance heating of the current flowing between the electrodes 3, the raw material M, the molten slag (molten furnace slag) S, and the molten iron P.

[0061] In the metal raw material melting method of this embodiment, it is preferable to feed the metal raw material 4 from the top of the submerged arc furnace 1, melt the raw material M containing the metal raw material 4, and continuously produce molten metal. That is, the metal raw material melting method of this embodiment can continuously discharge the molten iron P and the slag (molten furnace slag) S formed by melting the raw material M containing the metal raw material 4 separately. For example, the raw material M containing the metal raw material 4 can be melted by using a flat melting pool operation. In addition, the metal raw material melting method of this embodiment can sequentially charge the molten iron P, the slag (molten furnace slag) S, and the auxiliary raw materials into the electric furnace. The charging order of these metal raw materials 4 and auxiliary raw materials can also be appropriately changed, and the raw material M containing the metal raw material 4 can be melted without using a flat melting pool operation.

[0062] In this case, the submerged arc furnace 1 preferably has a discharge port for molten metal and a discharge port for molten slag (molten furnace slag) S. The discharge ports for molten metal and molten slag (molten furnace slag) S are preferably arranged in different directions relative to the center of the furnace bottom. Moreover, it is preferable to fill each discharge port with a blocking material, and at a point when a given amount of molten metal has been held, the blocking material is opened to allow the molten metal to be discharged.

[0063] In the metal raw material melting method of this embodiment, raw material M containing metal raw material 4 is charged into submerged arc furnace 1. The reduced iron contained in metal raw material 4 can be manufactured in advance by direct reduction method, or commercially available reduced iron can be purchased and used. Metal raw material 4 partially or entirely contains reduced iron, and may also contain a small amount of iron scrap and scale in addition to reduced iron. The mass ratio of reduced iron to metal raw material 4 is preferably 5 to 100%.

[0064] The metal raw material melting method of this embodiment has the following technical features: the metallization rate of the metal raw material contained in the electric furnace is set to 60% or more. Here, the metallization rate (DM) of the metal raw material is defined by the following relationship (1) using the mass of the total iron component (T.Fe) and the mass of the metallic iron component (M.Fe) contained in the metal raw material.

[0065] [Mathematical Expression 2]

[0066]

[0067] In the metal raw material melting method of this embodiment, when the metallization rate of the metal raw material 4 is 60% or higher, the unit power consumption of electricity required for melting the metal raw material 4 is lower, resulting in excellent energy efficiency. There is no particular upper limit to the metallization rate of the metal raw material 4. If the metallization rate of the metal raw material 4 is too high, there is a risk that the metal raw material 4, fed from above the molten slag (molten furnace slag) S in the submerged arc furnace 1, will experience reduced resistive heating due to electricity being passed through the molten slag (molten furnace slag) S, which is therefore not preferred.

[0068] Furthermore, in the metal raw material melting method of this embodiment, when the metallization rate of the metal raw material 4 is 60% or more, the amount of molten FeO contained in the slag (molten furnace slag) S generated as a byproduct decreases, thereby increasing the iron yield. In addition, when the metallization rate of the metal raw material 4 is 60% or more, the melting loss of the refractory material constituting the furnace wall 2 of the submerged arc furnace 1 can also be suppressed.

[0069] From this perspective, in the metal raw material melting method of this embodiment, a metallization rate of 80% or more for the metal raw material 4 is more preferable, and 95% is even more preferable. In the metal raw material melting method of this embodiment, if the metallization rate of the metal raw material 4 exceeds 95%, there is a risk that the metal raw material 4 contained in the raw material M, which is fed into the submerged arc furnace 1 from above the molten slag (molten furnace slag) S, will experience a decrease in resistive heat due to electrical conduction within the molten slag (molten furnace slag) S, which is therefore not preferred. Therefore, it is preferable to set the upper limit of the metallization rate of the metal raw material 4 to approximately 90%.

[0070] When the metal raw material 4 charged into the submerged arc furnace 1 contains carbon, the unreduced FeO contained in the metal raw material 4 can be efficiently reduced within the furnace 1. Preferably, the carbon content in the metal raw material 4, which is preferred for achieving such efficient reduction, is 50% or more of the theoretical amount of carbon required for reducing the unreduced FeO.

[0071] In addition, the specific gravity of metal raw material 4 is 1.7 g / cm³. 3 Above and 7.0 g / cm 3 In this case, the metal raw material 4 charged into the submerged arc furnace 1 will not be trapped on the molten slag (molten furnace slag) S and will melt efficiently within the molten slag (molten furnace slag) S, which is therefore preferable. A carburizing material such as a carbon material or other molten metal carburizing material can be charged together with the metal raw material 4. By increasing the carbon concentration in the molten metal, the molten FeO concentration in the molten slag (molten furnace slag) S can be reduced, which is therefore preferable. The carbon concentration in the molten metal is not particularly limited; for example, when the carbon concentration is determined based on the molten FeO concentration, in order to achieve the effect of reducing molten FeO, it is preferable to set the carbon concentration to 1.5 to 4.5% by mass (concentration in the molten metal).

[0072] Therefore, the metal raw material melting method of this embodiment can reduce the heat energy required for melting the metal raw material 4 by setting the metallization rate of the metal raw material 4 charged into the submerged arc furnace 1 to 60% or more, and can perform stable power supply in the submerged arc furnace 1, thereby enabling the melting of a large amount of metal raw material 4.

[0073] In the metal raw material melting method of this embodiment, a by-product containing at least one or both of slag-forming materials and carbon materials may be added together with the metal raw material 4, which may contain partially or entirely reduced iron. The slag-forming material is used to adjust the basicity (CaO / SiO2) of the molten slag (molten furnace slag) S formed on the molten iron P, and the carbon material is used to adjust the C content of the molten iron P. Here, the basicity (CaO / SiO2) of the molten slag (molten furnace slag) S is the ratio of CaO to SiO2 in the slag on a mass basis.

[0074] In the metal raw material melting method of this embodiment, a metal raw material 4 containing partially or entirely reduced iron and by-products can be mixed and supplied to the electrode 3. By mixing the metal raw material 4 containing partially or entirely reduced iron and by-products and supplying it to the electrode 3, the melting of the metal raw material 4 can be carried out efficiently, and is therefore preferred.

[0075] Furthermore, in the metal raw material melting method of this embodiment, the metal raw material 4, which contains partially or entirely reduced iron, and the by-products can be supplied to the electrode 3 separately. By supplying the metal raw material 4, which contains partially or entirely reduced iron, and the by-products to the electrode 3 separately, it is possible to charge only a given amount of the required amount of the metal raw material 4 or by-products containing partially or entirely reduced iron into the submerged arc furnace 1, corresponding to the melting state of the metal raw material 4, thereby promoting the melting of the metal raw material 4, which is therefore preferable.

[0076] It should be noted that when the metal raw material 4 and the auxiliary raw material are supplied to the electrode 3 separately, there is no particular limitation on the order of supply to the electrode 3. The order can be appropriately set considering the melting state of the metal raw material 4. The metal raw material 4 can be supplied before the auxiliary raw material or after the auxiliary raw material.

[0077] Furthermore, when supplying the metal raw material 4 and the auxiliary raw material to the electrode 3, the method of supplying the metal raw material 4 and the auxiliary raw material to the electrode 3 in a mixed manner or the method of supplying the metal raw material 4 and the auxiliary raw material to the electrode 3 separately can be adopted, taking into account the melting state of the metal raw material 4, the energizing time of the submerged arc furnace 1, etc.

[0078] For the slag-forming material included in the by-products, limestone (CaCO3) and quicklime (CaO) are preferably added as CaO sources, and silica (SiO2) is added as a SiO2 source. The slag-forming material can be in block, powder, or granular form, and is preferably used in combination with a metallic raw material 4 that contains partially or entirely reduced iron. It is preferable to use the slag-forming material to set the basicity (CaO / SiO2) of the molten slag (molten furnace slag) S to a range of 1.0 to 1.5. When the basicity of the molten slag (molten furnace slag) S is within this range, the composition of the molten slag (molten furnace slag) S becomes a slag composition at the same level as blast furnace slag, which is preferred when it is reused as a roadbed material such as cement. Furthermore, the total iron content in the molten slag (molten furnace slag) S is preferably 5.0% by mass or less. When the total iron content in the molten slag (molten furnace slag) S is 0.1% to 5.0% by mass, the iron yield is improved, which is therefore preferred.

[0079] The carbon material can be coke or coal. Biochar can also be used as the carbon material. The carbon material can be in block form or powder form, and is preferably used together with or mixed with the raw material M containing the metal raw material 4, for example, by granulation. The carbon content in the molten iron P is preferably adjusted to a range of 2.0 to 5.0% by mass. When the carbon content in the molten iron P is within this range, the molten metal obtained by melting the metal raw material 4 can be used directly as pig iron, or it can be used as a raw material for steelmaking in subsequent processes, which is therefore preferred.

[0080] The metal raw material melting method of this embodiment uses electrical energy in the melting of metal raw material 4. Therefore, compared with the blast furnace method and other methods that use the heat of combustion of carbon, the metal raw material melting method of this embodiment can achieve the effect of reducing CO2 emissions. It should be noted that the electrical energy used for melting metal raw material 4 can be electrical energy generated by generating electricity from renewable energy sources.

[0081] The metal raw material melting method of this embodiment is characterized by setting the furnace resistivity ρ of the submerged arc furnace 1, which is used as an electric furnace, to a range of 0.01 to 0.02 (Ω·m). Setting the furnace resistivity ρ of the submerged arc furnace 1 to 0.01 (Ω·m) or higher prevents adverse conditions such as short circuits between electrodes formed by multiple electrodes 3, ensuring stable power supply, and is therefore preferred. Setting the furnace resistivity ρ of the submerged arc furnace 1 to 0.02 (Ω·m) or lower saves some of the electricity required for melting metal raw materials 4 containing reduced iron or entirely composed of reduced iron, and is therefore preferred.

[0082] Figure 2 This is a schematic diagram showing the state of the electrodes and the vicinity of the electrodes in the electric furnace used in implementing the metal raw material melting method of this embodiment when electricity is applied. Figure 2 As shown, the arc current generated by electrode 3 flows in a hemispherical shape from the center point of the cross-section with a current-carrying range radius of r.

[0083] Here, when the radius r of the energized range is much larger than the electrode diameter D of electrode 3, the resistivity ρ (Ω·m) of the submerged arc furnace 1 used as an electric furnace can be calculated by the following relationship (2).

[0084] [Mathematical Expression 3]

[0085]

[0086] In the above relationship (2), ρ is the resistivity of the electric furnace (Ω·m), U ρ Let be the voltage between the electrode and ground (V), D be the electrode diameter (m), and I be the effective value of the current of each electrode (A / electrode).

[0087] Furthermore, in equation (2), the effective value I (A / electrode) of the current of each electrode can be directly measured. Then, using the measured effective value I (A / electrode) of the current of each electrode, the current density J of the current flowing through the electric furnace can be calculated using the following equation (3). e (A / m 2 ).

[0088] [Mathematical Expression 4]

[0089]

[0090] In the above relation (3), J e Current density (A / m) 2 ), where D is the electrode diameter (m).

[0091] When the submerged arc furnace 1 has three electrodes 3, the submerged arc furnace 1 is a three-phase AC submerged arc furnace. Here, in relation (2), in U ρ Let V be the electrode-to-ground voltage (V). In the case of a three-phase AC submerged arc furnace 1, the effective value of the line-to-line voltage formed by the three electrodes 3 is defined as V. L At that time, the voltage U between the electrode and ground ρ (V) and the effective value of the line voltage V between the electrodes formed by electrode 3. L (V) can be represented by the following relation (4).

[0092] [Mathematical Expression 5]

[0093]

[0094] Furthermore, when the submerged arc furnace 1 has multiple pairs of electrodes 3, the submerged arc furnace 1 is a single-phase AC submerged arc furnace. Here, in relation (2), in U ρ Let V be the electrode-to-ground voltage (V). In the case of a single-phase AC submerged arc furnace 1, the effective value of the line-to-line voltage formed by multiple pairs of electrodes 3 is defined as V. L At that time, the voltage U between the electrode and ground ρ (V) and the effective value of the line voltage V between the electrodes formed by electrode 3. L (V) can be represented by the following relation (5).

[0095] [Mathematical Expression 6]

[0096]

[0097] It should be noted that in equations (4) and (5), the effective value V of the line voltage between the electrodes is... LWhen compared with the line-to-line voltage on the secondary side of the transformer, a voltage drop occurs due to the circuit formed in the submerged arc furnace 1, which correspondingly reduces the amount of voltage reduction based on this voltage drop. However, the amount of voltage reduction based on the voltage drop is relatively small in the circuit formed in the submerged arc furnace 1, so it is acceptable even if it is ignored.

[0098] Therefore, the metal raw material melting method of this embodiment takes into account the power supply method adopted by the submerged arc furnace 1 and the effective value V of the line voltage between the electrodes formed by the multiple electrodes 3 provided by the submerged arc furnace 1. L The relationship between (V) was used to calculate the voltage U between the electrode and ground. ρ (V). Then, based on the calculated electrode-to-ground voltage U, ρ The value of (V) sets the furnace resistivity ρ (Ω·m) of the submerged arc furnace 1.

[0099] On the other hand, the electric furnace used in the metal raw material melting method of this embodiment can be an electric arc furnace. When an electric arc furnace is used in the metal raw material melting method of this embodiment, it is preferable to adjust at least one of the following: the distance from the interface of the molten iron present inside the electric arc furnace to the electric arc electrode provided by the electric arc furnace, the arc voltage E (V) as the voltage to ground, and the arc current I (A) of each electric arc electrode.

[0100] Specifically, these values ​​can be set such that the arc voltage E(V), which is the voltage to ground, and the arc current I(A) of each arc electrode in the electric arc furnace satisfy the following relationship (i).

[0101] [Mathematical Expression 7]

[0102]

[0103] The metal material melting method of this embodiment maintains arc stability and ensures good melting of the metal material by ensuring that the arc voltage E(V), which is the voltage to ground, and the arc current I(A) of each arc electrode in the electric arc furnace satisfy the above-described relationship (i). In relationship (i), if the value obtained by dividing the arc voltage E(V), which is the voltage to ground, by the square root of the arc current I(A) of each arc electrode exceeds 2.0, arc stability cannot be maintained when melting the metal material, and therefore this method is not preferred.

[0104] It should be noted that, in equation (i), the lower limit of the value obtained by dividing the arc voltage E(V), which is the voltage to ground, by the square root of the arc current I(A) of each arc electrode can be appropriately set according to the output power of the electric arc furnace and the stirring conditions of the molten iron. This lower limit is preferably 0.5 or higher.

[0105] As described above, according to the invention of the first embodiment, by setting the conditions for melting metal raw materials containing partially or entirely reduced iron using a submerged arc furnace (SAF) or an electric arc furnace, and by stably energizing the electric furnace, a large quantity of metal raw materials can be melted.

[0106] [Second Implementation]

[0107] The melting method for the metal raw material according to the second embodiment will be described. The characteristic of the melting method for the metal raw material in this embodiment is that, in the melting method for the metal raw material of the above embodiment, the current density flowing through the electrodes of the electric furnace is set to 50~70 (A / m²). 2 The scope of this method is as follows. The characteristic features included in the metal raw material melting method of this embodiment will be described below.

[0108] The characteristic of the metal raw material melting method in this embodiment is that the current density of the current flowing through the electrodes of the electric furnace is set to 50~70 (A / m). 2 The range of current density flowing through the electrodes of the electric furnace is 50 (A / m). 2 When the resistivity of the furnace is set to ensure stable energization, a self-sintering electrode can be manufactured by sintering the carbon paste. Therefore, this is preferred. The current density flowing through the electrodes of the furnace is 70 A / m². 2 When the following conditions are met, it is possible to sinter the carbon paste to produce a self-sintering electrode while maintaining a high level of resistivity inside the electric furnace, which is therefore preferred.

[0109] Regarding the electrodes of the electric furnace used in the metal raw material melting method of this embodiment, the electrodes can be either sintered electrodes or self-sintering electrodes. That is, the electrodes of the electric furnace can be either sintered or self-sintering, or either type. In the case of a self-sintering electrode, it can also be called a Soderberg electrode.

[0110] For example, a self-sintering electrode consists of an electrode shell that extends vertically through an opening in the furnace top or top cover. The upper end of such an electrode shell is open to allow the addition of unsintered carbonaceous electrode paste (carbon paste) used as an electrode material. This unsintered carbonaceous electrode paste softens and melts upon heating, and is then sintered into a solid carbon electrode in the region where the operating current is supplied to the electrode by releasing heat into the carbonaceous electrode paste.

[0111] The self-sintering electrode (Soderberg electrode) manufactured in this way is able to melt metal materials containing reduced iron or entirely reduced iron by performing the arc discharge required to melt the metal material containing reduced iron.

[0112] It should be noted that the front end of the electrode housing can be configured to expose the self-sintering electrode formed by sintering.

[0113] In the metal raw material melting method of this embodiment, the current density of the current flowing through the electrodes of the electric furnace is set to 50~70 (A / m). 2 Within the range of the electric furnace, when the electrode is a self-sintering type electrode, the sintering of unsintered carbonaceous electrode paste (carbon paste) is easy to occur, and a self-sintering type electrode (Soderberg electrode) with excellent performance can be manufactured, so it is preferred.

[0114] Therefore, the metal raw material melting method of this embodiment can reduce the heat energy required for melting the metal raw material by setting the current density of the current flowing in the electrodes of the electric furnace, and can successfully manufacture self-sintering electrodes. Moreover, it enables stable operation of the electric furnace equipped with self-sintering electrodes.

[0115] As described above, in the metal raw material melting method of the second embodiment, the current density of the current flowing through the electrodes of the electric furnace is set to 50~70 (A / m). 2 The range of the electric furnace allows for efficient and easy manufacturing of self-sintering electrodes by sintering unsintered carbonaceous electrode paste, which is used as the electrode material in the electric furnace. Furthermore, the metal material melting method of the second embodiment reduces the heat energy required for melting reduced iron, enabling the melting of large quantities of metal materials by stably energizing the electric furnace.

[0116] [Third Implementation]

[0117] The melting method for metal raw materials according to the third embodiment will be described. The characteristic of the melting method for metal raw materials in this embodiment is that, in the melting method for metal raw materials described in the above embodiments, the electric furnace is either a three-phase AC type with three electrodes or a single-phase type with multiple pairs of electrodes. Hereinafter, the characteristic parts included in the melting method for metal raw materials of this embodiment will be described.

[0118] Figure 3 This is a schematic diagram showing the outline of a single-phase AC submerged arc furnace used in implementing the metal raw material melting method of this embodiment. Figure 3 As shown, the single-phase AC submerged arc furnace includes three pairs of electrodes 3, with a total of 6 electrodes. Here, in the metal raw material melting method of this embodiment, the electrode-to-ground voltage U required to set the furnace resistivity ρ (Ω·m) is... ρ (V) and the effective value of the line voltage between the electrodes formed by the three pairs of electrodes 3, V LThis can be expressed by the above relationship (5). That is, the electrode-to-ground voltage U required for a single-phase AC submerged arc furnace to melt metal raw materials containing reduced iron. ρ (V) is the effective value of the line voltage between the three pairs of electrodes 3. L 1 / 2 of.

[0119] That is, in the metal raw material melting method of this embodiment, the effective value V of the line-to-line voltage between electrodes can be determined based on the configuration and output power of the submerged arc furnace used in the metal raw material melting method. L Calculate the voltage U between the electrode and ground. ρ (V) sets the resistivity inside the submerged arc furnace to achieve energization based on stable arc discharge.

[0120] Here, compared to methods such as blast furnace processes that utilize the heat of combustion of carbon, the metal raw material melting method of this embodiment can achieve the effect of reducing CO2 emissions. Therefore, the metal raw material melting method of this embodiment can be expected to be a method for melting large quantities of metal raw materials.

[0121] Therefore, the submerged arc furnace used in the metal raw material melting method of this embodiment is preferably a large-scale electric furnace with a large number of electrodes that is capable of melting a large amount of metal raw materials.

[0122] From this technical point of view, the electric furnace used in the metal raw material melting method of this embodiment can also be set as a single-phase AC submerged arc furnace, and the shape of the single-phase AC submerged arc furnace can be set as a cuboid. By setting the shape of the single-phase AC submerged arc furnace as a cuboid, a large number of pairs of electrodes can be arranged inside the electric arc furnace.

[0123] In addition, large-scale metal raw material melting systems can be constructed. These systems consist of a cuboid single-phase AC submerged arc furnace with multiple pairs of electrodes, forming a single-phase AC submerged arc furnace unit, and multiple such units are combined. Through these large-scale metal raw material melting systems, very large quantities of metal raw materials can be melted.

[0124] On the other hand, when the submerged arc furnace is a three-phase AC submerged arc furnace, the electrode-to-ground voltage U required for melting metal raw materials in this submerged arc furnace is... ρ (V) is the effective value of the line voltage between the three electrodes 3. L 1 / √3.

[0125] As described above, according to the invention of the third embodiment, a cuboid electric furnace with a large number of electrodes can be constructed to correspond to the future large-scale electric furnace, and a large amount of metal raw materials can be melted by stably energizing the electric furnace.

[0126] [Other Implementation Methods]

[0127] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the structure and details of the present invention within the technical scope of the present invention. Furthermore, systems or apparatuses formed by combining the features included in each embodiment in any manner are also included within the technical scope of the present invention.

[0128] Example

[0129] The effects of the present invention will be specifically described below based on the embodiments, but the present invention is not limited to these embodiments.

[0130] (Example 1 of the invention)

[0131] The metal raw material melting method of the present invention is used to melt metal raw materials that partially contain reduced iron or are entirely composed of reduced iron using a submerged arc furnace. In this embodiment, either a three-phase AC submerged arc furnace A or a single-phase AC submerged arc furnace B, as shown in Table 1, is used. In Invention Example 1, a single-phase AC submerged arc furnace B is used. Specifically, a method is used as follows... Figure 1 The 4-6 t submerged arc furnace A or B shown were used to melt metal raw materials containing some or all of reduced iron. Table 1 summarizes the various specifications of the three-phase AC or single-phase AC electric furnaces used in the investigation.

[0132] In addition, in this embodiment, the metal raw material containing partially or entirely reduced iron was configured with 88-94% by mass of T.Fe (main iron content), 83-88% by mass of M.Fe (metallic iron content), a metallization rate (M.Fe / T.Fe) of 94%, a carbon concentration of 1.0-1.5% by mass, and an apparent bulk density of 2.5-3.5 t / m³. 3 Raw materials with a thickness of 5~20mm.

[0133]

[0134] A single-phase submerged arc furnace B was prepared, and the operating conditions of the flat melting pool were set. Melting of metallic raw materials containing some or all of reduced iron was carried out. Specifically, in Invention Example 1, crushed waste, carbon materials, and blast furnace slag were charged into the single-phase submerged arc furnace B, and electricity was applied for initial melting. The charging amount was pre-adjusted so that the molten pig iron was 750 kg and the slag was 1500 kg. After all the pre-charged materials were melted, metallic raw materials containing some or all of reduced iron as the main raw material, and a pre-mixed raw material consisting of carbon materials, lime, alumina, MgO source, etc., used to adjust the C concentration in the molten pig iron and the composition of the slag, were continuously added. The maximum amount of molten pig iron was targeted at 4 t, and the amount of raw material added was adjusted accordingly. The final thickness of the molten pig iron reached 140 mm.

[0135] When melting a metal raw material that contains partially or entirely reduced iron, the line voltage is adjusted using a tap to ensure the power supply is within a given condition. The current value is adjusted by adjusting the electrode height. Furthermore, the current density and voltage to ground are adjusted to bring the furnace resistivity to a given range. In Invention Example 1, the condition is set such that the furnace resistivity is 0.0115 (Ω·m). The flat pool operating conditions and evaluation of the electrical stability during the melting of molten iron implemented in Invention Example 1 are shown in Table 2. The molten steel temperature is set to a range of 1400~1700°C. In addition, the value E / √I, obtained by dividing the arc voltage E (V), which is the voltage to ground, by the square root of the current I (A) of each arc electrode, is calculated. Then, at least one of the electrode height, arc voltage, and arc current is adjusted so that E / √I is 2.0 or less.

[0136] It should be noted that the evaluation of power-on stability in Table 2 is based on the following criteria.

[0137] ○: Stable power supply enables flat molten pool operation.

[0138] ×: Due to unstable power supply caused by factors such as arc interruption, flat molten pool operation cannot be achieved.

[0139]

[0140] (Invention Examples 2-7, Comparative Examples 1-5)

[0141] The electric furnace used for melting molten iron was a single-phase AC submerged arc furnace B, and the flat molten pool operating conditions were modified. Otherwise, the melting of metallic raw materials containing partially or entirely reduced iron was performed, similar to Example 1. It should be noted that in Examples 2-7, the furnace resistivity was set to 0.012-0.017 (Ω·m). On the other hand, in Comparative Examples 1-5, it was set to less than 0.010 (Ω·m). Table 2 shows the evaluation of the flat molten pool operating conditions and electrical stability during the melting of molten iron in Examples 2-7 and Comparative Examples 1-5.

[0142] Based on the above, it can be confirmed that the metal raw material melting method of the present invention is a method that can melt a large amount of metal raw materials by stably energizing a submerged arc furnace (SAF).

[0143] Industrial applicability

[0144] The metal raw material melting method according to the present invention uses a submerged arc furnace (SAF) as an electric furnace and provides stable power to the furnace, which enables the melting of large quantities of metal raw materials. Therefore, it is helpful for the development of related fields such as the steel industry and is very useful in industry.

Claims

1. A method for melting metal raw materials, comprising a method for melting metal raw materials based on an electric furnace, wherein molten iron, slag, metal raw materials and by-products are layered and contained within an electric furnace, and the molten iron and slag are discharged, wherein... When an electric current is supplied to molten metal through an electric arc or via slag and metal raw materials for heating... The resistivity of the electric furnace is set to the range of 0.01~0.02 (Ω·m).

2. The method for melting metal raw materials according to claim 1, wherein, The metal raw material is melted by a flat molten pool operation.

3. The method for melting metal raw materials according to claim 1, wherein, The metallization rate of the metal raw material is over 60%.

4. The method for melting metal raw materials according to claim 1, wherein, The current density flowing through the electrodes of the electric furnace is set to 50~70 (A / m). 2 ) range.

5. The method for melting metal raw materials according to claim 4, wherein, The electrode is self-sintering type.

6. The method for melting metal raw materials according to claim 1, wherein, The electric furnace is either a three-phase AC type with three electrodes or a single-phase type with multiple pairs of electrodes.

7. The method for melting metal raw materials according to claim 1, wherein, The metal raw materials and by-products are mixed or supplied separately between the electrodes.

8. The method for melting metal raw materials according to claim 7, wherein, Some or all of the metal raw material is reduced iron.

9. The method for melting metal raw materials according to claim 1, wherein, The basicity of the slag is in the range of 1.0 to 1.

5. The basicity of the slag refers to the ratio of CaO to SiO2 in the slag, based on mass.

10. The method for melting metal raw materials according to claim 1, wherein, The electric furnace is an electric arc furnace, and at least one of the following selected factors—the distance from the interface of the molten iron to the electric arc electrode, the electric arc voltage, and the electric arc current—is adjusted such that the electric arc voltage E(V), which is the voltage to ground, and the electric arc current I(A) of each electric arc electrode in the electric arc furnace satisfy the following relationship (i). 。 11. The method for melting metal raw materials according to claim 1, wherein, The electric furnace is a submerged arc furnace.

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