Method for producing molten pig iron
Patent Information
- Application Number
- JP2024538216
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-06-21
- Publication Date
- 2025-03-06
- Estimated Expiration
- 2044-02-28
AI Technical Summary
The direct reduction method for producing hot metal in the steel industry faces challenges with high energy consumption and cost due to the requirement for high-grade iron ore, making it inefficient when using submerged arc furnaces, especially in regions like Japan where freight rates for high-grade ores are high, and low-grade ores are difficult to process effectively.
A method that involves melting reduced iron with a metallization rate of 60% or more in a submerged arc furnace, using low-grade iron ore pellets and lump ore, adjusting the basicity of the molten slag to 1.0 to 1.3, and adding carbon to achieve a C content of 2 to 5% in the hot metal, optimizing energy efficiency by reducing electricity consumption.
This approach significantly reduces energy consumption and operational costs by maintaining high energy efficiency in the melting process, making it feasible to use low-grade iron ores and improving the overall reduction efficiency in submerged arc furnaces.
Abstract
Description
Molten iron manufacturing method
[0001] The present invention relates to a method for producing molten iron by melting an iron source material containing reduced iron in a submerged arc furnace. ３ In this specification, the term "x to y" representing a numerical range means x or more and y or less, including the boundary value. Furthermore, "t-p" is a unit representing the mass of molten iron.
[0002] In recent years, CO ２ In the steel industry, CO emissions are also being reduced. ２ As an alternative to the blast furnace process, which has a high carbon dioxide emissions, the direct reduction (DR) process for producing pig iron has been attracting attention. In the DR process, for example, iron-containing agglomerates are reduced in a shaft furnace to produce direct reduced iron (DRI). This reduced iron or iron source material, such as iron scrap, is charged into an electric arc furnace (EAF) or submerged arc furnace (SAF) and heated and melted, and the pig slag is separated to produce pig iron.
[0003] Pellets and lump ore are used as agglomerates for direct reduction. Pellets are made by mixing and granulating fine ore or dust with auxiliary materials and a binder, and then firing the mixture. Bentonite is often used as the binder.
[0004] Patent Documents 1 and 2 disclose techniques for obtaining molten metal by arc-heating pre-reduced metal or solid reduced iron. These techniques describe the use of reduced iron with a high metallization rate, which can reduce the thermal energy required for melting the reduced iron, and therefore describe the use of reduced iron with a metallization rate of 60% or more, preferably 80% or more, and more preferably 90% or more.
[0005] Patent Document 3 discloses a method for reducing and melting an iron raw material containing iron oxide, in which the iron raw material containing iron oxide is charged into a DC arc furnace and reduced and melted. Patent Document 3 describes a method using an iron raw material containing iron oxide, in which the iron metallization rate is 45% or more and 95% or less and the iron raw material contains 4 to 20 mass % of oxides other than iron oxide.
[0006] Patent Document 4 discloses an electric furnace equipped with one or more upper electrodes, one or more bottom-blown tuyeres, a mechanical agitator equipped with an impeller, and a charging device for charging an iron oxide-containing raw material. In operation using this electric furnace, the iron oxide-containing raw material is charged onto a seed molten pig iron for melting and reduction. This allows for the melting and reduction of the iron oxide-containing raw material with a high iron yield. This method for melting and reducing an iron oxide-containing raw material using an electric furnace allows the entire amount of CO gas generated in a DC arc furnace to be used as CO gas for reduction in a pre-reduction furnace. Furthermore, this method can suppress an increase in the carbon consumption rate without reducing the overall reduction efficiency, and can suppress an increase in the reduction heat required in the DC arc furnace, thereby preventing an increase in the power consumption rate. This method describes the use of an iron oxide-containing raw material with a metallization rate of 45% or more and 95% or less.
[0007] JP 2003-105415 A JP 2009-074120 A JP 2018-003075 A WO 2019 / 082762
[0008] Conventionally, electric arc furnaces (EAFs) have been used primarily as equipment for melting reduced iron in the DR process. Due to equipment limitations, EAFs require the use of high-quality reduced iron with a low slag ratio (high Fe content). Consequently, high-grade iron ore has inevitably been used as the raw material for the reduced iron, i.e., the raw ore for iron ore pellets. Examples of high-grade iron ore include South American ore, concentrate ore whose grade has been improved by prior ore dressing treatment, and pellet feed ore.
[0009] However, there are challenges in utilizing South American ore, concentrate ore, and pellet feed ore in Japan. Due to Japan's geographical conditions, South American ore inevitably increases freight rates. Concentrate ore and pellet feed ore are also derived from high-grade iron ore, as beneficiation of high-grade iron ore is more efficient than beneficiation of low-grade iron ore, and for the same reason, freight rates increase. Therefore, the direct reduction process using high-grade iron ore poses a cost challenge.
[0010] Therefore, in Japan, studies are underway to apply the DR process to low-grade iron ore produced in Australia, India, etc. However, it is difficult to melt reduced iron produced from low-grade iron ore using the current EAF, so the use of a submerged arc furnace (SAF) is being considered.
[0011] Since the melting process using the SAF requires a large amount of energy (electricity), it is necessary to improve energy efficiency as much as possible. In the EAF, reduced iron with a high metallization rate is generally used to reduce the heat of melting.
[0012] Patent Documents 1 to 4 each describe the use of reduced iron with an appropriate high metallization rate. However, all of these documents are directed to heating by arc heat, and do not mention the effectiveness of heating systems that use Joule heat, such as submerged arc furnaces. Furthermore, they state that the preferred range of metallization rate is 80% or 90% or higher, aiming to improve the reduction efficiency in an electric furnace.
[0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing molten pig iron that can achieve high energy efficiency in the melting step when producing molten pig iron by melting reduced iron in a submerged arc furnace.
[0014] As a result of intensive research aimed at solving the above-mentioned problems, the inventors have found that, as long as the metallization rate of reduced iron charged into a submerged arc furnace is within a predetermined range, energy efficiency can be increased in the processes from pre-reduction to melting. That is, the present invention, which advantageously solves the above-mentioned problems, provides a method for producing molten pig iron, comprising melting an iron source material containing reduced iron having an average metallization rate of 60% or more in a submerged arc furnace to obtain molten pig iron, and adjusting the basicity (CaO / SiO ２ and adding a carbon material to adjust the C content of the molten iron, wherein the metallization rate is a percentage of the ratio of the mass of metallic iron components to the mass of total iron components contained in the reduced iron, and the basicity (CaO / SiO２ ) is SiO of CaO ２ It is characterized in that it refers to the mass fraction relative to
[0015] The method for producing molten pig iron according to the present invention further comprises: (a) a step of preparing raw materials for direct reduction, which further comprises an optional step of preparing iron ore pellets produced from low-grade iron ore having a total Fe content of 63 mass % or less; and a step of producing reduced iron from the raw materials for direct reduction, which comprises an optional step of producing the reduced iron from the raw materials for direct reduction; (b) the raw materials for direct reduction used in the step of producing reduced iron include lump ore; (c) the basicity (CaO / SiO ２ (d) adding the carbon material so that the C content in the molten iron is in the range of 2 to 5 mass %, etc., can be more preferable solutions.
[0016] According to the method for producing molten pig iron of the present invention, high energy efficiency can be achieved when iron source materials containing reduced iron are melted in a submerged arc furnace to produce molten pig iron.
[0017] Fig. 1 is a schematic diagram illustrating a method for producing molten iron according to one embodiment of the present invention; Fig. 2 is a graph showing the relationship between the average metallization rate of reduced iron and the power consumption rate; Fig. 3 is a graph showing the relationship between the average metallization rate of reduced iron and the power efficiency; Fig. 4 is a graph showing the relationship between the treatment time and the metallization rate when iron ore pellets are reduced in an electric furnace; and Fig. 5 is a graph showing the relationship between the metallization rate of reduced iron and the reduction energy per unit metallization rate % required to achieve that metallization rate.
[0018] The following is a detailed description of embodiments of the present invention. The following embodiments are intended to exemplify equipment and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.
[0019] 1 is a schematic diagram illustrating the configuration of a submerged arc furnace suitable for use in a method for producing molten pig iron according to one embodiment of the present invention. The submerged arc furnace 1 holds molten pig iron P and molten slag S within a furnace wall 2. In the submerged arc furnace 1, electrodes 3 are inserted into the molten slag S, and an arc is generated between the multiple electrodes 3 or between the electrodes 3 and the molten pig iron P, and the raw materials are heated and melted by resistance heating.
[0020] In this embodiment, iron source material 4 containing reduced iron is charged into a submerged arc furnace. At the same time, the basicity (CaO / SiO ２ The basicity of the molten slag (CaO / SiO ２ ) is the SiO of CaO in the molten slag ２ This refers to the mass fraction of
[0021] In this embodiment, the iron source raw material to be melted in the submerged arc furnace includes reduced iron. The reduced iron may be produced in advance by a direct reduction method, or commercially available reduced iron may be purchased and used. Iron scrap or scale may also be used as the iron source raw material. The mass ratio of the reduced iron to the iron source raw material is preferably 50 to 100%.
[0022] When the metallization rate of the reduced iron is 60% or higher, the overall power consumption rate is low and energy efficiency is excellent. There is no particular upper limit to the metallization rate. If the metallization rate is too high, the reduced iron, which is the raw material 4 charged from above the slag S in the submerged arc furnace 1, may conduct electricity through the slag, resulting in a decrease in resistance heat. Therefore, the upper limit of the metallization rate is preferably about 90%. More preferably, the upper limit of the metallization rate is 80%.
[0023] The slag-forming material is limestone (CaCO ３ ), quicklime (CaO), and SiO ２ The source is silica (SiO ２ It is preferable to add the basicity (CaO / SiO ２It is preferable that the basicity of the molten slag is in the range of 1.0 to 1.3. If the basicity of the molten slag is in this range, it is suitable for reuse as a roadbed material such as cement.
[0024] The carbonaceous material can be coke or coal. It can be charged in a lump form or in a powder form, which can be sprayed by gas transport. The ash content of the carbonaceous material other than carbon is added to the molten slag S. ＦＬＵＸ The C content in the molten pig iron P is preferably adjusted to a range of 2 to 5 mass %. If the C content is within this range, the pig iron can be used as it is or as a raw material for steelmaking in the next process.
[0025] (Direct Reduction Raw Material Preparation Step) In this embodiment, the direct reduction raw material preparation step preferably includes an optional step of preparing iron ore pellets produced from low-grade iron ore having a total Fe content (hereinafter also referred to as T.Fe) of 63% by mass or less. The raw materials for the iron ore pellets generally consist of iron ore, a binder, and auxiliary materials. In this embodiment, the low-grade iron ore refers to iron ore having a T.Fe content of 63% by mass or less. The low-grade iron ore preferably has a crystal water content of 4% by mass or more.
[0026] Bentonite is preferred as a binder for iron ore pellets. Any known or arbitrary binder, such as an organic or inorganic binder, that provides a similar effect may also be used. Quicklime, limestone, dolomite, or the like may also be mixed as an auxiliary material for the iron ore pellets. Furthermore, lump ore may also be prepared as a raw material for direct reduction in addition to the iron ore pellets. Lump ore is generally iron ore with a size of approximately 10 to 35 mm, and is used in the reduced iron production process without being crushed.
[0027] Iron ore pellets may be prepared by being manufactured through a general crushing, mixing, granulation, and firing process, or pre-manufactured iron ore pellets may be prepared. When manufacturing iron ore pellets, each process can be carried out using conventionally known equipment and conditions as described below. The crushing process can be carried out using a crusher such as a general ball mill. The mixing process can be carried out using a general high-speed stirring mixer or concrete mixer. The granulation process can be carried out using a general pelletizer or drum mixer. The firing process can be carried out using a general rotary kiln or electric furnace.
[0028] (Reduced iron production process) In this embodiment, it is preferable to have a reduced iron production process consisting of any process of producing the reduced iron from raw materials for direct reduction. In the reduced iron production process, reduced iron is produced from iron ore pellets or lump ore as essential raw materials. A solid reduction furnace such as a general shaft furnace may be used to produce reduced iron. There are no particular restrictions on the reducing gas, but it is preferable to use, for example, hydrogen gas produced using renewable energy. For example, H 2 O 3 (vol %) may be used depending on the production method to be used. ２ : 55%, CO: 35%, balance CO ２ , CH ４ a mixed gas consisting of H ２ : 75%, CO: 20%, balance CO ２ , N ２ A mixed gas consisting of the following can be suitably used.
[0029] The specific power consumption and power efficiency per unit mass of molten iron were investigated using a 4- to 6-ton batch-type submerged arc furnace 1, as shown in Figure 1. Table 1 shows the composition of the reduced iron used in the investigation. Both furnaces used the same low-grade ore pellets, with only the metallization rate being changed. In Table 1, M.Fe represents metallic iron.
[0030]
[0031] Reduced iron equivalent to 500 kg of molten pig iron and a predetermined amount of blast furnace slag were charged into the submerged arc furnace 1, and heating was initiated by applying current to the electrodes 3. After the start of current application, 400 kg of reduced iron was charged eight times, each time with a power consumption of 350 kWh. The power consumption per unit mass of molten pig iron (kWh / t-p) was calculated from the power consumption when the molten pig iron temperature reached approximately 1600°C after all the charged reduced iron was melted. The power efficiency was calculated by dividing the theoretical sum of the heating energy of the molten pig iron, the heating energy of the slag, and the reduction energy of iron oxide by the power consumption. Table 2 shows the investigated conditions and results. The amount of reduced iron charged was kept constant, and the average metallization ratio of the charged reduced iron was adjusted by changing the blending ratio of reduced iron DRI1 and reduced iron DRI2. The slag basicity was 1.26, and the carbon content of the molten pig iron was adjusted to 2.5 to 4.5 mass%. The slag ratio in the furnace, which is the mass fraction of molten slag per unit mass, was adjusted to 1.5 t / t-p using a slag former. The input power was kept constant at 2.7 MW.
[0032]
[0033] Figure 2 shows the relationship between the average metallization rate and the power consumption rate in Table 2. Figure 3 shows the relationship between the average metallization rate and the power efficiency in Table 2. The results in Figure 2 indicate that the power consumption rate decreases almost linearly with the average metallization rate. This indicates that the energy required for reduction in a submerged arc furnace per unit percentage decrease in the metallization rate remains almost constant. This is consistent with the fact that the power efficiency shown in Figure 3 remains almost constant. The reason for the slight decrease in power efficiency in No. T8 is thought to be that the metallization rate of the reduced iron was so high that electricity was passed through the raw material layer deposited on the slag layer rather than the slag layer.
[0034] The relationship between the time and the metallization rate when iron ore pellets, which were the raw material for reduced iron DRI1 and DRI2 shown in Table 1, were gas-reduced in an electric furnace is shown in Figure 4. The reduction was performed using 50% CO2-50% H2O. ２The reduction test was conducted in an atmosphere at 1000°C and 900°C. As is clear from Figure 4, the reduction rate was fast in the early stages of reduction and then slowed as the metallization rate increased. The reason for this is thought to be as follows: In gas reduction, reduction begins at the periphery of the pellet. Therefore, as the metallization rate of the pellet increases, the gas diffusion resistance from the surface to the unreduced central portion and the reaction interface itself become smaller. Therefore, in gas reduction to produce reduced iron, the energy required for reduction per unit percent of metallization rate increases as the metallization rate increases. The energy required for the reduction test was converted into the amount of reduced iron charged into the submerged arc furnace. Figure 5 shows the relationship between the energy required for reduction per unit mass of metallic iron and the metallization rate of the reduced iron, converted into the amount of reduced iron charged into the submerged arc furnace. Meanwhile, as mentioned above, the energy required per unit mass of molten iron per unit percent of metallization rate of the reduced iron in the submerged arc furnace was almost constant, at approximately 6 (kWh / t-p) / %. This shows that reduction using a submerged arc furnace requires less energy when the metallization rate is 60% or higher, and this difference tends to widen. Considering fluctuations in operation, it is preferable that the metallization rate of the reduced iron charged into the submerged arc furnace be between 60% and 80%.
[0035] 1 Submerged arc furnace (SAF) 2 Furnace wall 3 Electrode 4 (Charged) raw materials P Molten iron S Molten slag
Claims
1. A raw iron source material containing reduced iron having an average metallization rate of 60% or more is melted in a submerged arc furnace to obtain molten iron, and the basicity (CaO / SiO ２ and / or adding a carbon material to adjust the C content of the molten iron; Here, the metallization rate is a percentage of the ratio of the mass of metallic iron components to the mass of the total iron components contained in the reduced iron, and the basicity of the molten slag (CaO / SiO ２ ) is SiO of CaO ２ A method for producing molten iron, where the mass fraction of
2. Further, a step of preparing raw materials for direct reduction including an optional step of preparing iron ore pellets produced using low-grade iron ore having a total Fe content of 63% by mass or less as a raw material; and a reduced iron producing step of producing the reduced iron from the raw materials for direct reduction according to claim 1 .
3. The method for producing molten iron according to claim 2 , wherein the raw materials for direct reduction used in the reduced iron production step include lump ore.
4. The basicity of the molten slag (CaO / SiO ２ 4. The method for producing molten iron according to claim 1 , wherein the slag former is added so that the ratio of the melting temperature to the melting temperature is in the range of 1.0 to 1.
3.
5. The method for producing molten iron according to any one of claims 1 to 3, wherein the carbonaceous material is added so that the C content in the molten iron is in the range of 2 to 5 mass%.