Method for producing molten iron

Abstract

Provided is technology for smelting cold (direct-reduced and scrap) iron sources with heightened productivity and reduced electric-power consumption rate. The present invention is a molten-iron production method in which an electric furnace is utilized to smelt a cold iron source by means of electrical energy. Injection holes for injecting fuel and injection holes for injecting combustion-enhancing gas are provided; and in the electric furnace, arranged is a burner that jets flames through the injection holes directed toward the furnace content inside the electric furnace. Upon spraying in auxiliary feedstock that is in powdered form or has been processed into powdered form so as to pass through the flames formed by the burner, the auxiliary-feedstock feed rate or the burner-fuel feed rate is adjusted in accordance with the molten state of the cold iron source in the electric furnace.

Description

Technical Field

[0001] The present invention relates to a technology for melting a cold iron source with high productivity and reduced power consumption per unit of production.

Background Art

[0002] In recent years, from the perspective of preventing global warming, the steel industry has been promoting the development of technologies to reduce the consumption of fossil fuels and the generation of CO2 gas. In a conventional integrated steelworks, pig iron is produced by reducing iron ore with carbon. To produce this pig iron, about 500 kg of carbon source per ton of pig iron is required for the reduction of iron ore and the like. On the other hand, when producing molten steel using a cold iron source such as iron scrap or solid reduced iron as the main raw material, the carbon source required for the reduction of iron ore becomes unnecessary, and only the energy with sufficient heat for melting the cold iron source is required. Therefore, the CO2 emissions can be significantly reduced.

[0003] In cold iron source high-blend operations, electric furnaces such as arc furnaces and induction melting furnaces are often used. At that time, most of the heat of fusion of the cold iron source is supplied by electricity. For improving productivity and reducing the power consumption per unit, for example, in a general operation of an arc furnace, the following technologies are adopted. 1) A combustion burner is arranged on the furnace wall or slag discharge port to promote the melting of the cold iron source such as a cold spot. 2) A so-called oxygen enrichment operation is performed in which oxygen is supplied from an oxygen gas supply lance to impart the oxidation heat of iron.

[0004] However, in the oxygen enrichment operation, the reduction in yield due to the oxidation loss of iron becomes a problem. Also, when using a combustion burner, since the burner flame is formed at the upper part of the furnace body on the molten iron surface, the heat transfer efficiency to the molten iron in the furnace is low, and most of the supplied heat is discharged as the sensible heat of the exhaust gas. Therefore, even if the power consumption per unit can be reduced, the reduction effect of the total energy input including fuel is small. A heat application means capable of efficiently transferring heat to the molten iron and cold iron source in the furnace is desired.

[0005] As a highly efficient means of heat transfer, for example, Patent Documents 1 and 2 disclose a technique in which a lance for introducing granular ore is installed separately from the top-blowing lance that supplies oxidizing gas in an iron bath type melting reduction furnace. In this technique, a burner consisting of an ore flow hole and an injection hole for blowing fuel and oxygen is provided at the tip of the lance, and the ore is supplied so as to pass through the flame generated from the burner. At that time, it has been shown that the utilization of burner combustion heat is dramatically improved by transferring heat from the ore heated in the flame to the molten iron in the furnace. It has also been shown that the temperature of the gas produced by burner combustion, i.e., the exhaust gas temperature, is also reduced by transferring heat from the gas produced by burner combustion to the granular material in the burner flame. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-138207 [Patent Document 2] Japanese Patent Publication No. 2008-179876 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the above-mentioned conventional technology has the following problems. When heating is performed using only the burner without supplying powder to the burner flame, as mentioned above, the efficiency of heat transfer from the burner combustion to the molten iron in the furnace is low. As a result, heat is released outside the furnace due to an increase in the sensible heat of the exhaust gas. As described in Patent Documents 1 and 2, by adding powder, the heat from the burner combustion is transferred to the powder, and the temperature of the gas produced by the burner combustion decreases. However, if the supply rate of powder is low, the amount of heat transferred will also be low, the efficiency of heat transfer to the molten iron in the furnace will be low, and the reduction in combustion gas temperature will be small. As a condition for high-efficiency heat transfer to the molten iron in the furnace and a reduction in exhaust gas temperature, Patent Document 2 indicates that the powder-to-fuel ratio S / Q should be 0.3 or higher when the powder supply rate is S (kg / min) and the calorific value of the burner fuel per unit time is Q (MJ / min). In other words, it indicates that it is necessary to supply a sufficient amount of powder relative to the heat of combustion of the burner.

[0008] This means that the amount of heat generated by the burner and the amount of heat that can be supplied to the molten iron in the furnace are limited by the amount of granular material that can be supplied during the refining process. If more granular material is supplied than is actually needed for the refining process, extra sensible heat will be required to heat the excess granular material to the molten iron temperature, resulting in heat loss that exceeds the amount of heat supplied by the burner.

[0009] This invention has been made in view of these circumstances, and aims to provide a highly efficient heat supply means in an electric furnace, and to propose a technology for melting cold iron sources with high productivity and reduced power consumption. [Means for solving the problem]

[0010] The present invention provides a method for producing molten iron that advantageously solves the above problems, and is a method for producing molten iron that uses an electric furnace and melts a cold iron source with electrical energy, wherein a burner is placed in the electric furnace, which is equipped with an injection hole for ejecting fuel and an injection hole for ejecting a combustion-supporting gas, and which injects a flame from the injection hole toward the contents of the furnace, and when blowing in a powder or a powder-processed auxiliary material so that it passes through the flame formed by the burner, the supply rate of the auxiliary material or the fuel supply rate of the burner is adjusted according to the melting state of the cold iron source in the electric furnace.

[0011] Furthermore, the method for producing molten iron according to the present invention is (a) Let Q (MJ / min) be the calorific value of the fuel used in the burner per unit time, and let S (kg / min) be the supply rate of the auxiliary raw materials, then adjust the supply rate of the auxiliary raw materials or the fuel supply rate of the burner so that the powder fuel ratio S / Q (kg / MJ) satisfies the relationship given by equation (1): S / Q ≥ 0.3 × (1 - L / Lh) (where L is the vertical distance (m) between the maximum height position of the unmelted cold iron source in the electric furnace and the position of the molten metal top surface, and is set to 0 if there is no unmelted cold iron source above the position of the molten metal top surface, and Lh is the vertical distance (m) between the burner tip position and the position of the molten metal top surface). (b) The electric furnace is an arc furnace, and the shortest distance between the electrode where the arc is generated and the burner is set to be at least 1.1 times the distance La between the tip of the electrode and the contents of the furnace. These could be more preferable solutions. [Effects of the Invention]

[0012] According to the present invention, by supplying granular material via a burner flame, the granular material is heated within the burner flame and acts as a heat transfer medium. As a result, the burner combustion heat can be used with high efficiency to heat the cold iron source and molten iron in the melting chamber of the electric furnace, thereby reducing electricity consumption. Furthermore, if a large amount of unmelted cold iron source is present in the electric furnace, it is possible to directly heat the unmelted cold iron source with the burner flame. Compared to molten metal, the cold iron source present on the molten metal has a larger surface area, making it possible to transfer the burner combustion heat to the cold iron source in the furnace with high efficiency.

[0013] Conventional methods required supplying a sufficient amount of granular material to achieve high heat transfer efficiency. In the present invention, even when the calorific value of the fuel is excessive relative to the amount of granular material supplied, that is, even when the portion of the burner combustion heat that contributes to heating the granular material is low, it is possible to obtain high heat transfer efficiency by directly heating the undissolved cold iron source in the electric furnace. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic longitudinal cross-sectional view showing the outline of a DC arc furnace, which is an electric furnace according to one embodiment of the present invention. [Figure 2] This is a schematic longitudinal cross-sectional view of the tip of the burner lance used in the above embodiment. [Modes for carrying out the invention]

[0015] The embodiments of the present invention will be described in detail below. Note that the drawings are schematic and may differ from actual examples. Furthermore, the following embodiments are illustrative examples of devices and methods for realizing the technical concept of the present invention, and do not 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 described in the claims.

[0016] Figure 1 is a schematic vertical cross-sectional view showing an overview of a DC arc furnace 1 as an electric furnace according to one embodiment of the present invention, illustrating the form and style of operation of a DC arc type electric furnace.

[0017] In this embodiment, a burner lance 2 is inserted into an electric furnace 1 through a burner lance insertion hole provided in a furnace lid 3 so as to be movable up and down. In the example of FIG. 1, the burner lance 2 is inserted into the furnace lid so as to be vertically movable up and down, but it is not limited thereto. The burner lance 2 may be inserted obliquely into the furnace from above the furnace wall. Further, the burner is not limited to the form of a movable lance, and a form in which a nozzle portion is fixed to the furnace lid 3 or the furnace wall 4 may be used. Further, an oxygen supply function may be imparted to the burner to supply oxygen from the burner. The burner lance 2 injects a burner flame 2a toward the surface of the furnace contents such as a cold iron source 5 and molten iron 6 accommodated in the electric furnace 1.

[0018] Note that an oxygen injection lance or a carbon material injection lance may be inserted into the electric furnace 1 from above through the furnace lid 3 or from the slag discharge port.

[0019] From the carbon material injection lance, one or more carbon materials such as coke, char, coal, charcoal, and graphite may be blown into the molten slag 7 using air or nitrogen as a carrier gas. Further, oxygen may be supplied (injected) from the oxygen injection lance, and the molten slag 7 may be pushed aside by this oxygen so that oxygen is blown into the molten iron 6.

[0020] Note that from the oxygen injection lance, an oxygen-containing gas, for example, a mixed gas of pure oxygen and air, may be blown instead of pure oxygen.

[0021] An outlet 8 is provided in the bottom 11 of the electric furnace 1. Further, a slag discharge port 9 is provided on the opposite side of the outlet 8. The outlet 8 is closed by packing sand, a mud agent, or the like filled therein. The slag discharge port 9 is in the form of a trough, and the furnace body of the electric furnace 1 can be tilted to discharge slag.

[0022] The upper part of the electric furnace 1 has electrodes 10 inserted from above, passing through a furnace lid 3 with an openable and closable water-cooled structure. On the other hand, a furnace bottom electrode 13 is provided as a counter electrode, passing through the furnace bottom 11. A furnace bottom electrode cooling device and secondary conductors (not shown) are also installed for the furnace bottom electrode 13. The furnace bottom electrode 13 is connected to the molten iron 6 and the cold iron source 5, and an arc is generated between these and the electrode 10 to melt the cold iron source 5 and heat the molten iron 6, forming an arc heating section A. Typically, the electrode 10 is made of graphite or the like and is movable up and down. A bottom-blowing tuyeres 12 may be installed in the furnace bottom 11 to stir by blowing gas. In the example in Figure 1, an example with two electrodes 10 is shown, but one electrode or three or more electrodes may also be used. In the example in Figure 1, a burner lance 2 is placed between the two electrodes.

[0023] Figure 1 shows the state in which iron scrap is charged as the cold iron source 5, and power is turned on to melt the cold iron source 5. During this time, powdered auxiliary material 2b is blown from the burner lance 2 through the burner flame 2a to promote the melting of the cold iron source 5. In this operation, it is preferable to use fuel mainly consisting of hydrocarbons or hydrogen gas produced by renewable energy such as solar, wind, or hydroelectric power. A fuel mainly consisting of hydrogen gas refers to hydrogen gas or hydrogen-enriched gaseous fuel, and as hydrogen-enriched gaseous fuel, a mixture of hydrogen gas with methane gas, natural gas, or petroleum gas can be used. From the viewpoint of reducing CO2 emissions, it is preferable to mix in 50 vol% or more of hydrogen gas.

[0024] In the above embodiment, a DC arc furnace 1 having two electrodes was used as the electric furnace, but an AC arc furnace with three electrodes or the like may also be used.

[0025] Figure 2 shows a schematic diagram of the tip portion 20 of the burner lance 2 used in the above embodiment as an example. A powder supply pipe 21 having an injection hole is placed in the center, and a fuel supply pipe 22 and a combustion-supporting gas supply pipe 23, both having injection holes, are arranged in order around it. The outside is provided with an outer shell 25 having a cooling water passage 24. Fuel gas 26 and combustion-supporting gas 27 are supplied from injection holes provided on the outer circumference of the powder supply pipe 21 to form a burner flame 2a. Then, the powdery auxiliary material 2b injected from the powder supply pipe 21 is heated in the burner flame 2a. In this way, the powdery auxiliary material 2b acts as a heat transfer medium, making it possible to improve the heat transfer efficiency of the flame to the furnace contents such as the cold iron source 5 and molten iron 6. As a result, it is possible to reduce the amount of electricity used. As the combustion-supporting gas 27, pure oxygen, a mixed gas of oxygen and CO2 or an inert gas, air, or oxygen-enriched air can be used. Furthermore, the gas used to transport the powdered auxiliary material 2b can be an inert gas or a combustion-supporting gas.

[0026] In the molten iron manufacturing method according to this embodiment, for example, a cold iron source 5, such as iron scrap or solid reduced iron, is first loaded into an electric furnace, such as the DC arc furnace 1 shown in Figure 1, from a bucket (not shown). After the initial loading of the cold iron source 5, the power is turned on. Then, a burner lance 2 installed in the upper part of the furnace is inserted into the electric furnace 1, and the cold iron source 5 is heated by the electricity and the combustion heat of the burner flame 2a.

[0027] When the initial cold iron source 5 has melted further and reached a flat bath state, meaning that any unmelted cold iron source 5 is immersed in the molten iron 6, slag may be discharged from the slag outlet 9 as needed. After that, the power supply and burner use may be interrupted, the furnace lid 3 may be opened, and the second batch of cold iron source 5 may be charged. After the second batch of cold iron source 5 is charged, it is preferable to resume power supply and perform burner heating operations in the same manner as after the initial charge. Note that the number of times the cold iron source 5 is charged may be three or more.

[0028] The inventors used an electric furnace 1 as shown in Figure 1 and investigated the heat transfer efficiency to the furnace contents by changing various fuel gas flow rates and powder supply rates. Here, the ratio of the supply rate S (kg / min) of auxiliary material 2b to the calorific value Q (MJ / min) of fuel 26 used in the burner 2 is defined as the powder-fuel ratio S / Q (kg / MJ).

[0029] As a result, it was found that supplying a sufficient amount of powder relative to the calorific value of the fuel gas resulted in high heat transfer efficiency to the furnace contents and a decrease in combustion flame temperature. In the case of a flat bath, setting the powder-to-fuel ratio S / Q to 0.3 (kg / MJ) or higher resulted in highly efficient heat transfer from the burner to the furnace contents. This led to reduced power consumption and improved productivity. However, when the calorific value Q of the fuel was excessive relative to the powder supply rate S, specifically when the powder-to-fuel ratio S / Q was less than 0.3 (kg / MJ), the exhaust gas temperature was high. The heat transfer efficiency to the furnace contents was also low, and the reduction in power consumption and productivity improvements were small. It is thought that when the calorific value Q of the fuel is excessive relative to the powder supply rate S, the heat transfer from the burner to the powder is insufficient and is instead discharged outside the furnace as sensible heat in the exhaust gas.

[0030] On the other hand, we found that when a large amount of undissolved cold iron source 5 is present in the furnace and stacked above the molten iron surface 6, high heat transfer efficiency can be obtained even when the powder fuel ratio S / Q is less than 0.3 (kg / MJ). This is thought to be because the cold iron source 5 present on the surface of the bath has a large surface area, and the burner flame directly heats the cold iron source 5. Therefore, even when the powder fuel ratio S / Q is small, the heat from the burner combustion can be efficiently transferred to the furnace contents. The larger the amount of undissolved cold iron source 5 in the furnace and the greater the height of the stacking, the greater the effect of direct heat transfer, resulting in high heat transfer efficiency even when the powder fuel ratio S / Q is reduced. In summary, given the vertical distance L(m) between the maximum height of the unmelted cold iron source 5 in the electric furnace and the molten metal surface, and the vertical distance Lh(m) between the burner tip and the molten metal surface, a powder fuel ratio S / Q (kg / MJ) of 0.3 × (1-L / Lh) or higher was required. Below this level, the heat transfer efficiency decreased. Note that if there is no unmelted cold iron source 5 above the molten metal surface, i.e., in a flat bath, L=0. Note that as the melting of the cold iron source 5 progresses, the molten metal surface changes moment by moment, so it is preferable to adjust Lh accordingly.

[0031] When installing the burner lance 2 in the arc furnace 1, if the distance between the burner lance 2 and the graphite electrode 10 was too short and they were too close, an arc was observed to jump from the electrode towards the burner lance 2, damaging the burner lance 2. It was found that the shortest distance Lb between the burner lance 2 and the electrode 10 must be sufficiently maintained relative to the distance La between the electrode 10 and the furnace contents where the arc occurs at a certain voltage. The shortest distance Lb between the burner lance 2 and the electrode 10 is the distance between the electrode surface and the burner lance surface. In summary, the shortest distance Lb between the burner lance 2 and the electrode 10 must be at least 1.1 times the distance La between the electrode 10 and the furnace contents. If it is less than that, there is a possibility that an arc will occur between the electrode 10 and the burner lance 2.

[0032] In this embodiment, the powder type can be a slag-forming material, dust, or the like, which is a secondary material 2b processed into a powder. In order to heat efficiently in the burner flame, it is necessary to increase the specific surface area, and the particle size is preferably about 100 μm or less. If the particle size of the secondary material is large, it is preferable to process it to a particle size of about 100 μm or less by grinding or the like. Here, the particle size is expressed as the 50% passability based on volume.

[0033] Furthermore, any electric furnace that uses electrical energy to melt a cold iron source and obtain molten iron is applicable. For example, in the case of an arc furnace, it may be not only the DC or AC arc furnaces mentioned above, but also an immersion type arc furnace in which a Zetaberg self-firing electrode or the like is immersed in slag for heating. It may also be an indirect resistance furnace that heats the material to be heated by radiation from a heating element installed in the furnace, or by convection and conductive heat transfer within the furnace. Moreover, it may also be a plasma arc melting furnace.

[0034] The molten iron 6 produced in this embodiment has a composition equivalent to that of the iron scrap or solid reduced iron used as the main raw material, and is usually molten steel with a relatively low carbon content. To adjust the composition, alloys may be added directly in the electric furnace after molten iron, or a final decarburization treatment by oxygen blowing or a dephosphorization treatment may be performed. Furthermore, after tapping, secondary refining such as molten steel desulfurization and vacuum degassing may be performed. After that, semi-finished products such as cast slabs are produced through casting processes such as continuous casting. [Examples]

[0035] (Example 1) A cold iron source melting test was conducted using a DC arc furnace as the electric furnace. Scrap was used as the cold iron source, with a total charge of 100 tons.

[0036] A burner lance equipped with fuel and oxygen supply lines was installed on the furnace lid of the electric furnace, and the tip of the burner lance had a multi-tube structure similar to that shown in Figure 2. Propane gas was used as the burner fuel. The following cases were compared: without using a burner (Process No. 1), with burner fuel supplied but no powder supplied, and the furnace contents heated by the burner flame alone (Process No. 2), and with powdered lime blown into the burner flame (Processes No. 3-10). The hot water temperature was set to 1650°C.

[0037] After power was turned on, as the initial cold iron source melted and the height of the charge in the furnace decreased, creating a flat bath, the burner lance was lowered and heating with the burner flame was used in combination. For the supply of powder, argon gas was used as the conveying gas, and powdered lime was supplied into the electric furnace at a supply rate of 100 kg / min, totaling 50 kg / t of molten iron. The supply amount of propane gas as fuel gas was 2.2 to 11.1 Nm³. 3 The flow rate was varied within the range of / min for each heat cycle of the electric furnace. The powder fuel ratio S / Q ranged from 0.1 to 0.51 kg / MJ. In addition, oxygen gas was supplied as a combustion-supporting gas to burn the propane fuel gas during each heat cycle. After slag was discharged from the exhaust port, the power supply and burner use were interrupted, the furnace lid was opened, and the cold iron source was charged for the second and subsequent loads. After the second load of cold iron source was charged, the power supply was restarted, and operation was carried out in the same manner as after the initial load. In this way, molten steel at 1650°C was finally obtained and poured into a ladle.

[0038] For each processing condition, we compared the power consumption per unit, electric furnace processing time, and the heat transfer efficiency of burner combustion heat. The power consumption per unit is calculated by dividing the amount of electricity used for each processing condition by the amount of electricity used for processing No. 1. The electric furnace processing time is the time (min) from the start of power supply to the start of hot water discharge. The heat transfer efficiency of burner combustion heat represents the ratio of the amount of heat transferred to the furnace contents to the amount of heat generated by the burner fuel. The results are shown in Table 1.

[0039] [Table 1]

[0040] In contrast to process No. 1, which did not use a burner, in process No. 2, where the furnace contents were heated solely by the burner flame, the burner combustion heat was not effectively transferred, resulting in nearly the same power consumption and electric furnace processing time. In processes No. 3 to 10, where powdered lime was heated within the burner flame, the power consumption and electric furnace processing time were reduced. This is because the powdered lime was heated within the burner flame, and some of the burner combustion heat was transferred to the furnace contents. However, under conditions where the calorific value of the fuel was excessive relative to the powdered lime supply rate, the heat transfer efficiency of the burner combustion heat decreased, and the reduction in power consumption and electric furnace processing time became smaller. This is because the amount of heat transferred to the powdered lime plateaued, and the proportion of the burner combustion heat discharged as sensible heat in the exhaust gas increased.

[0041] (Example 2) Using the same equipment configuration and fuel as in Example 1, molten steel was obtained by melting a cold iron source. The tapping temperature was set to 1650°C. After the start of power supply, as the initial cold iron source melted and the height of the charges in the furnace decreased, creating space at the top of the furnace, the burner lance was lowered and heating by the burner flame was used in combination. For the supply of powder, argon gas was used as the conveying gas, and powdered lime was supplied into the electric furnace at a supply rate of 100 kg / min in an amount of 50 kg / t-molten iron. When unmelted cold iron source was piled up in the furnace, the powder-fuel ratio S / Q was adjusted to be 0.3 × (1-L / Lh) or more, and the propane gas flow rate was increased as much as possible, with L (m) being the distance between the maximum height of the cold iron source and the top of the molten metal, and Lh (m) being the vertical distance between the tip of the burner lance and the top of the molten metal. Lh was 2.0m, and as a result of in-furnace monitoring, L fluctuated from 1.4m to 0m (flat bath state). During that time, the propane gas flow rate was 12.3Nm 3 / min to 3.7Nm 3 The ratio was varied down to / min. This corresponds to a powder fuel ratio S / Q from 0.089 kg / MJ to 0.30 kg / MJ.

[0042] In addition, oxygen gas was supplied as a combustion-supporting gas to burn the propane fuel gas during processing. After removing the slag from the slag outlet, the power supply and burner use were interrupted, the furnace lid was opened, and the cold iron source was charged for the second and subsequent loads. After the second load of cold iron source was charged, the power supply was restarted, and operation was carried out in the same manner as after the initial load. In this way, molten steel at 1650°C was finally obtained and poured into a ladle.

[0043] Regarding the processing conditions, we investigated the power consumption per unit of time, the electric furnace processing time, and the heat transfer efficiency of the burner combustion heat. The power consumption per unit of time is calculated by dividing the amount of electricity used for each processing condition by the amount of electricity used for processing No. 1 in Example 1. The electric furnace processing time is the time (in minutes) from the start of power supply to the start of hot water discharge. The heat transfer efficiency of the burner combustion heat represents the ratio of the amount of heat transferred to the furnace contents to the amount of heat generated by the burner fuel. The results are shown in Table 2.

[0044] [Table 2]

[0045] (Example 3) Under the operating conditions of process No. 6 in Example 1, the position in which the burner lance was inserted was changed, and the shortest distance Lb between the electrode where the arc was generated and the burner lance was investigated in relation to the distance La between the electrode and the top surface of the molten metal.

[0046] For each processing condition, the power consumption per unit, electric furnace processing time, and the heat transfer efficiency of burner combustion heat were investigated. The power consumption per unit is calculated by dividing the amount of electricity used for each processing condition by the amount of electricity used for processing No. 1 in Example 1. The electric furnace processing time is the time (in minutes) from the start of power supply to the start of hot water discharge. The heat transfer efficiency of burner combustion heat represents the ratio of the amount of heat transferred to the furnace contents out of the amount of heat generated by the burner fuel. The distance between the electrode and the burner is expressed as the Lb / La ratio. The results are shown in Table 2.

[0047] [Table 3]

[0048] In processes No. 12 and 13, where the burner lance and electrode were in close proximity, the arc jumped onto the burner lance, making operation impossible. Under conditions where the shortest distance Lb between the burner lance and the electrode was 1.1 times or more the distance La between the electrode and the molten metal surface, stable operation was possible without problems.

[0049] The unit of mass "t" used in this specification is 10 3 It represents kg. The "N" prefix used for gas volume units indicates the volume under standard conditions of 0°C and 101325 Pa. [Industrial applicability]

[0050] The present invention provides a method for producing molten iron that improves heat transfer efficiency, allows the melting of a cold iron source using a heat source with reduced CO2 emissions, reduces power consumption per unit of production, and minimizes environmental impact, making it industrially useful. It is particularly suitable for applications in processes such as smelting furnaces that require a heat source with reduced CO2 emissions and the addition of powdered auxiliary materials. [Explanation of symbols]

[0051] 1. DC arc furnace (electric furnace) 2 Burner Lances 2a Burner flame 2b (powder) auxiliary raw material 3 Hearth lid 4 Furnace wall 5. Cold iron source (iron scrap) 6 Molten iron 7 (molten) slag 8. Hot water outlet 9. Sludge outlet 10 electrodes 11 hearth bottom 12 Bottom-blown tuyere 13 Hearth electrode 20. Burner lance tip (nozzle) 21 Powder supply pipe 22 Fuel supply pipe 23 Combustion-supporting gas supply pipe 24 Cooling water passage 25 Outer shell 26 Fuel gas 27 Combustion-supporting gases 28 Cooling water A Arc heating section

Claims

1. A method for producing molten iron using an electric furnace and dissolving a cold iron source with electrical energy, A burner is provided in the electric furnace, which has an injection port for ejecting fuel and an injection port for ejecting combustion-supporting gas, and which injects a flame from the injection port toward the contents of the electric furnace. When blowing in a powder or a powdered auxiliary material so that it passes through the flame formed by the burner, Depending on the melting state of the cold iron source in the electric furnace, A method for producing molten iron, wherein the amount of heat generated per unit time of the fuel used in the burner is Q (MJ / min), and the supply rate of the auxiliary raw material as a heat transfer medium is S (kg / min), and the supply rate of the auxiliary raw material or the fuel supply rate of the burner is adjusted so that the powder fuel ratio S / Q (kg / MJ) satisfies the following equation (1). S / Q≧0.3×(1-L / Lh) (1) Here, L is the vertical distance (m) between the maximum height position of the unmelted cold iron source in the electric furnace and the position of the top surface of the molten metal, and is set to 0 if there is no unmelted cold iron source above the top surface of the molten metal, and Lh is the vertical distance (m) between the position of the burner tip and the position of the top surface of the molten metal.

2. The electric furnace is an arc furnace, A method for producing molten iron according to claim 1, wherein the shortest distance between the electrode that generates the arc and the burner is set to be 1.1 times or more the distance La between the tip of the electrode and the contents of the furnace.

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