Method for producing molten iron

Abstract

Provided is a technique for melting a cold iron source by reducing power consumption per unit with high productivity. A method for producing molten iron in which a cold iron source is melted by electric energy using an electric furnace, the method comprising: disposing a burner in the electric furnace, the burner having an injection hole through which fuel is injected and an injection hole through which combustion-supporting gas is injected, and injecting a flame from the injection hole toward the content in the electric furnace; when a powdery or powdery auxiliary raw material is blown in so as to pass through the flame formed by the burner, the supply speed of the auxiliary raw material or the fuel supply speed of the burner is adjusted in accordance with the melting situation 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 unit power consumption. Background Art

[0002] In recent years, the steel industry has been developing technologies to reduce fossil fuel consumption and CO₂ gas production to prevent global warming. In existing integrated steel mills, iron ore is reduced with carbon to produce molten pig iron. To produce this molten pig iron, an average of approximately 500 kg of carbon source is required per ton of molten pig iron, for example, to reduce the iron ore. On the other hand, when producing molten steel using cold iron sources such as scrap iron and solid reduced iron as the main raw material, the carbon source required for iron ore reduction is not required; only energy sufficient to melt the cold iron source is required. This significantly reduces CO₂ emissions.

[0003] In operations involving high-proportion cold iron source integration, electric furnaces such as electric arc furnaces and induction melting furnaces are often used. In these operations, the majority of the heat of melting of the cold iron source is provided by electricity. To improve productivity and reduce unit electricity consumption, the following techniques are employed in the normal operation of electric arc furnaces. 1) Combustion-supporting burners are placed on the furnace walls and slag outlets to promote the melting of cold iron sources such as cold spots. 2) So-called oxygen enrichment operations are performed, where oxygen is supplied from an oxygen supply lance to provide oxidation heat to the iron.

[0004] However, during oxygen-enriched operation, the reduction in yield associated with iron oxidation loss becomes a problem. Furthermore, when using a combustion-supporting burner, the burner flame forms in the upper portion of the furnace body above the surface of the molten iron. Consequently, heat transfer efficiency to the molten iron in the furnace is low, and a large amount of supplied heat is discharged as exhaust sensible heat. Therefore, even if the specific electricity consumption can be reduced, the effect of reducing the total energy input, including fuel, is minimal. A method for efficiently applying heat to the molten iron and the cold iron source in the furnace is desired.

[0005] As a highly efficient way of imparting heat, for example, Patent Documents 1 and 2 disclose a technique of providing a lance for feeding powdered ores separately from a top-blowing lance for supplying oxidizing gas in an iron bath type molten reduction furnace. In this technique, a flow hole for the ore is provided at the front end of the lance, and a burner formed by injection holes for blowing fuel and oxygen is provided, so that the ore is supplied in a manner passing through the flame generated by the burner. At this time, the ore heated in the flame is transferred to the molten iron in the furnace, thereby showing a significant improvement in the utilization of the burner combustion heat. This indicates that by transferring heat from the gas generated by the burner combustion to the powdered ores in the burner flame, the temperature of the gas generated by the burner combustion, that is, the exhaust temperature, is also reduced.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-138207

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-179876 Summary of the Invention

[0010] Technical problem to be solved by the invention

[0011] However, the above-mentioned prior art has the following problems.

[0012] In the case where the powder is not supplied to the burner flame and the burner alone is used for heating, as described above, the efficiency of heat transfer from the burner combustion heat to the molten iron in the furnace becomes low. Moreover, due to the increase in the sensible heat of the exhaust gas, the heat is discharged outside the furnace. As described in Patent Documents 1 and 2, by adding powder and granular materials, the burner combustion heat is transferred to the powder and the temperature of the gas generated by the burner combustion is reduced. However, when the supply rate of the powder and granular materials is low, the heat transfer amount becomes low, the heat transfer efficiency to the molten iron in the furnace becomes low, and the reduction in the combustion gas temperature is also small. As conditions for efficient heat transfer to the molten iron in the furnace and reduction of the exhaust gas temperature, the molten reduction treatment described in Patent Document 2 shows that when the powder supply rate is set to S (kg / min) and the calorific value of the burner fuel per unit time is set to Q (MJ / min), the powder-fuel ratio S / Q is set to 0.3 or more. That is, it is necessary to supply a sufficient amount of powder and granular materials relative to the burner combustion heat.

[0013] This means that the amount of powder and granular material that can be supplied during the refining process limits the amount of heat generated by the burners and the amount of heat that can be applied to the molten iron in the furnace. If a larger amount of powder and granular material than the original amount required for the refining process is supplied as auxiliary raw material, the additional sensible heat required to heat the excess powder and granular material to the molten iron temperature will result in heat losses that exceed the heat provided by the burners.

[0014] 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 efficiently applying heat to an electric furnace and to propose a technology for melting a cold iron source with high productivity and reduced power consumption.

[0015] Solutions to the Problem

[0016] The method for manufacturing molten iron of the present invention, which advantageously solves the above-mentioned problems, is a method for manufacturing molten iron by using an electric furnace to melt a cold iron source by electric energy. The method includes: arranging a burner in the electric furnace, the burner having a jet hole for spraying fuel and a jet hole for spraying combustion-supporting gas, and spraying flames from the jet holes toward the furnace contents in the electric furnace, and when blowing in powdered or powdered auxiliary raw materials through the flame formed by the burner, adjusting the supply rate of the auxiliary raw materials or the fuel supply rate of the burner according to the melting condition of the cold iron source in the electric furnace.

[0017] It should be noted that the method for producing molten iron of the present invention may be the following more preferred solutions (a) to (b):

[0018] (a) The calorific value of the fuel used by the burner per unit time is set to Q (MJ / min), the supply rate of the auxiliary raw material is set to S (kg / min), and the supply rate of the auxiliary raw material or the fuel supply rate of the burner is adjusted in such a manner that the powder fuel ratio S / Q (kg / MJ) satisfies the relationship of formula (1): S / Q ≥ 0.3 × (1-L / Lh) (wherein L is the vertical distance (m) between the maximum height position of the unmelted cold iron source in the electric furnace and the upper surface position of the melt, and is set to 0 when there is no unmelted cold iron source above the upper surface position of the melt, and Lh is the vertical distance (m) between the front end position of the burner and the upper surface position of the melt);

[0019] (b) The electric furnace is an electric arc furnace, and the shortest distance between an arc-generating electrode and a burner is at least 1.1 times the distance La between the tip of the electrode and the furnace contents.

[0020] Effects of the Invention

[0021] According to the present invention, by supplying powder and granular material via a burner flame, the powder and granular material is heated within the burner flame and becomes a heat transfer medium. This allows the burner combustion heat to be efficiently used to heat the chill and molten iron within the melting chamber of the electric furnace, thereby reducing electricity consumption. Furthermore, if a large amount of unmelted chill exists within the electric furnace, the burner flame can be used to directly heat the unmelted chill. The chill above the molten metal has a larger surface area than the molten metal, allowing the burner combustion heat to be efficiently transferred to the chill within the furnace.

[0022] Conventional methods require a sufficient supply of powder and granular material to achieve high heat transfer efficiency. The present invention achieves higher heat transfer efficiency by directly heating the unmelted cold iron source in the electric furnace, even when the calorific value of the fuel is excessive relative to the amount of powder and granular material supplied, that is, even when the portion of the burner combustion heat that contributes to heating the powder and granular material is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic longitudinal sectional view schematically showing an outline of a DC arc furnace as an electric furnace according to one embodiment of the present invention.

[0024] Figure 2 It is a schematic longitudinal sectional view of the front end portion of the burner lance used in the above embodiment.

[0025] Explanation of symbols

[0026] 1 DC electric arc furnace (electric furnace)

[0027] 2 burner lances

[0028] 2a Burner flame

[0029] 2b (Powdered) Auxiliary Raw Materials

[0030] 3 Furnace cover

[0031] 4 Furnace wall

[0032] 5. Cold iron source (iron waste)

[0033] 6 Molten Iron

[0034] 7 (Melted) slag

[0035] 8 taphole

[0036] 9 Slag discharge port

[0037] 10 electrodes

[0038] 11 Furnace bottom

[0039] 12 Bottom blowing outlet

[0040] 13 Furnace bottom electrode

[0041] 20 Burner gun front end (nozzle)

[0042] 21 Powder supply pipe

[0043] 22 Fuel supply pipe

[0044] 23 Combustion-supporting gas supply pipe

[0045] 24 Cooling water channel

[0046] 25 housing

[0047] 26 Fuel Gas

[0048] 27 Combustible gas

[0049] 28 Cooling water

[0050] A Arc heating unit DETAILED DESCRIPTION

[0051] The following describes embodiments of the present invention in detail. It should be noted that the drawings are schematic and may differ from actual embodiments. Furthermore, the following embodiments illustrate devices and methods for embodying the technical concepts of the present invention and do not limit the present invention to the following. In other words, the technical concepts of the present invention may be modified in various ways within the technical scope of the claims.

[0052] Figure 1 1 is a schematic longitudinal sectional view showing an outline of a DC arc furnace 1 as an electric furnace according to one embodiment of the present invention, and illustrates the operation mode of the DC arc furnace.

[0053] In this embodiment, the burner lance 2 is inserted into the electric furnace 1 in a manner such that it can be raised and lowered from the burner lance insertion hole provided in the furnace cover 3. Figure 1 In the example, the burner lance 2 is inserted vertically from the furnace cover so as to be liftable, but the present invention is not limited to this. The burner lance 2 can also be inserted obliquely from the upper side of the furnace wall toward the furnace. In addition, the burner is not limited to a liftable lance form, and the nozzle portion can be fixed to the furnace cover 3 or the furnace wall 4. In addition, the burner can be given an oxygen supply function, and oxygen can be supplied from the burner. The burner lance 2 sprays the burner flame 2a toward the surface of the furnace contents such as the cold iron source 5 and the molten iron 6 contained in the electric furnace 1.

[0054] It should be noted that, in the electric furnace 1 , an oxygen injection lance or a carbon material injection lance may be inserted through the furnace roof 3 from above or from the slag discharge port.

[0055] A carbon material injection lance can be used to inject one or more carbon materials such as coke, charcoal, coal, charcoal, and graphite into the molten slag 7 using air, nitrogen, or the like as a transport gas. Alternatively, oxygen can be supplied (injected) from an oxygen injection lance, and the oxygen can be used to push the molten slag 7 and inject oxygen into the molten iron 6.

[0056] Note that, instead of pure oxygen, an oxygen-containing gas, for example, a mixed gas of pure oxygen and air may be blown in from the oxygen injection lance.

[0057] In the electric furnace 1, a taphole 8 is provided at the furnace bottom 11. A slag discharge port 9 is provided on the opposite side of the taphole 8. The taphole 8 is sealed by filling it with sand, mud, etc. The slag discharge port 9 is trough-shaped, allowing the furnace body of the electric furnace 1 to be tilted to discharge slag.

[0058] In the upper part of the electric furnace 1, the electrode 10 is inserted from above through the furnace cover 3 of the openable and closable water-cooled structure. On the other hand, a furnace bottom electrode 13 serving as a counter electrode is provided through the furnace bottom 11. For the furnace bottom electrode 13, a furnace bottom electrode cooling device and a secondary conductor not shown in the figure are also provided. The furnace bottom electrode 13 is electrically connected to the molten iron 6 and the cold iron source 5, and the cold iron source 5 is melted by generating an arc between them and the electrode 10, thereby forming an arc heating part A for heating the molten iron 6. Usually, the electrode 10 is made of graphite or the like and can move up and down. A bottom blowing port 12 can be provided at the furnace bottom 11 to perform stirring based on gas blowing. In Figure 1 In the example shown in FIG, two electrodes 10 are used, but one electrode, three electrodes or more may also be used. Figure 1 In the example of FIG, a burner lance 2 is arranged between two electrodes.

[0059] Figure 1 The process is as follows: iron scrap is loaded as the cold iron source 5, power is turned on, and the cold iron source 5 is melted. At this time, powdered auxiliary raw material 2b is sprayed 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 preferred to use a fuel mainly composed of hydrogen or other renewable energy sources such as hydrocarbons or sunlight, wind power, and water power. The fuel mainly composed of hydrogen refers to hydrogen or hydrogen-rich gas fuel. As the hydrogen-rich gas fuel, a mixed gas of hydrogen and methane gas, natural gas, or petroleum gas can be used. From the perspective of reducing the amount of CO2 produced, it is preferred to mix more than 50 vol% of hydrogen.

[0060] In the above embodiment, the DC arc furnace 1 having two electrodes is used as the electric furnace, but an AC arc furnace using three electrodes or the like may also be used.

[0061] exist Figure 2 In the figure, a schematic diagram shows a tip portion 20 of the burner lance 2 as an example of one embodiment of the burner lance 2 used in the above embodiment. A powder supply pipe 21 having an injection hole is arranged in the center, and a fuel supply pipe 22 and a combustion-supporting gas supply pipe 23, each also having injection holes, are arranged in sequence around it. A housing 25 with a cooling water passage 24 is provided on the outside of the burner lance 21. Fuel gas 26 and combustion-supporting gas 27 are supplied from injection holes provided on the outer periphery of the powder supply pipe 21, forming a burner flame 2a. Furthermore, the powdered auxiliary material 2b injected from the powder supply pipe 21 is heated in the burner flame 2a. This makes the powdered auxiliary material 2b a heat transfer medium, thereby improving the efficiency of heat transfer from the flame to the furnace contents, such as the cold iron source 5 and molten iron 6. Consequently, the amount of electricity consumed can be reduced. The combustion-supporting gas 27 can be used, in addition to pure oxygen, as well as a mixture of oxygen and CO2, an inert gas, air, or oxygen-enriched air. Furthermore, the gas used to transport the powdered auxiliary material 2b, which is a powder, can be an inert gas or a combustion-supporting gas.

[0062] In the method for producing molten iron of this embodiment, for example, Figure 1 In an electric furnace such as the DC arc furnace 1 shown, a chill source 5, such as scrap iron or solid reduced iron, is first loaded from a hopper (not shown). After the initial charge of chill source 5 is loaded, power is turned on. A burner lance 2, located in the upper portion of the furnace, is then inserted into the electric furnace 1. The chill source 5 is heated by electricity and the heat of combustion from the burner flame 2a.

[0063] The initial cold iron source 5 is further melted and becomes a flat molten pool state, that is, even if there is unmelted cold iron source 5, it has been immersed in the molten iron 6. Then, slag is discharged through the slag discharge port 9 as needed. Then, the power supply and the use of the burner can be interrupted, the furnace cover 3 is opened, and the second cold iron source 5 is loaded. Preferably, after the second cold iron source 5 is loaded, the power is turned on again, and the burner heating operation is performed in the same way as after the initial loading. It should be noted that the number of times the cold iron source 5 is loaded can be three or more.

[0064] Inventors and others use Figure 1 In the electric furnace 1 shown, the efficiency of heat transfer to the furnace contents was investigated by varying the fuel gas flow rate and the powder supply rate. Here, the ratio of the auxiliary material 2b supply rate (S (kg / min)) to the calorific value per unit time (Q (MJ / min)) of the fuel 26 used in the burner lance 2 was defined as the powder-fuel ratio (S / Q (kg / MJ)).

[0065] As a result, it was found that by supplying a sufficient amount of powder relative to the calorific value of the fuel gas, the heat transfer efficiency to the furnace contents becomes higher and the combustion flame temperature decreases. In the case of a flat melt pool, by setting the powder-fuel ratio S / Q to 0.3 (kg / MJ) or more, the burner combustion heat can be transferred to the furnace contents with high efficiency. In addition, the effect of reducing the unit power consumption and the effect of improving productivity were observed. However, when the calorific value Q of the fuel is too high relative to the powder supply rate S, specifically, when the powder-fuel ratio S / Q is less than 0.3 (kg / MJ), the exhaust gas temperature becomes higher. In addition, the heat transfer efficiency to the furnace contents also becomes lower, and the effect of reducing the unit power consumption and the effect of improving productivity are also small. It can be considered that when the calorific value Q of the fuel is too high relative to the powder supply rate S, the heat transfer of the burner combustion heat to the powder and particles is insufficient, and is discharged to the outside of the furnace as sensible heat of the exhaust gas.

[0066] On the other hand, it was found that when there is a large amount of unmelted cold iron source 5 in the furnace and the cold iron source 5 is piled up at a position higher than the surface of the molten iron 6, high heat transfer efficiency can be obtained even when the powder fuel ratio S / Q is less than 0.3 (kg / MJ). It can be considered that this is because the surface area of ​​the cold iron source 5 existing on the bath surface is large, which has the effect of directly heating the cold iron source 5 with the burner flame. Therefore, even when the powder fuel ratio S / Q is small, the burner combustion heat can be efficiently transferred to the furnace contents. The more the amount of unmelted cold iron source 5 in the furnace and the higher the pile height, the greater the effect of direct heat transfer. As a result, high heat transfer efficiency can be obtained even if the powder fuel ratio S / Q is reduced. The result of the arrangement is that, in the case of the vertical distance L (m) between the maximum height position of the unmelted cold iron source 5 in the electric furnace and the position of the upper surface of the melt, and the vertical distance Lh (m) between the front end position of the burner and the position of the upper surface of the melt, the powder fuel ratio S / Q (kg / MJ) needs to be 0.3×(1-L / Lh) or more. If it is less than this value, the heat transfer efficiency decreases. It should be noted that when there is no unmelted cold iron source 5 above the upper surface position of the melt, that is, in the case of a flat melt pool, L=0. It should be noted that as the melting of the cold iron source 5 proceeds, the position of the upper surface of the melt changes all the time, so it is preferable to adjust Lh accordingly.

[0067] When the burner lance 2 is installed in the electric arc furnace 1, the distance between the burner lance 2 and the graphite electrode 10 is too close. If the distance is too close, arcs may splash from the electrode toward the burner lance 2, damaging the burner lance 2. This indicates that the minimum distance Lb between the burner lance 2 and the electrode 10 must be sufficiently large relative to the distance La between the electrode 10 and the furnace contents, which generates an arc at a certain voltage. The minimum distance Lb between the burner lance 2 and the electrode 10 is the distance between the electrode surface and the burner lance surface. The results show that the minimum 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 the distance Lb is less than this, arcing may occur between the electrode 10 and the burner lance 2.

[0068] In this embodiment, the powder type used can be slag-forming materials, dust, or the like, which are powdered or processed into powdered auxiliary raw materials 2b. To efficiently heat the auxiliary raw materials within the burner flame, a large specific surface area is required, and a particle size of approximately 100 μm or less is preferred. If the auxiliary raw materials have large particle sizes, they are preferably processed to a particle size of approximately 100 μm or less by pulverization or the like. The particle size is expressed as a 50% pass rate based on volume.

[0069] Furthermore, any electric furnace that uses electrical energy to melt a cold iron source to produce molten iron can be used. For example, an electric arc furnace can be used not only as the aforementioned DC or AC electric arc furnaces but also as an immersion-type electric arc furnace, in which a Soderberg self-baking electrode or the like is immersed in molten slag for heating. Alternatively, an indirect resistance furnace can be used, in which the material being heated is heated by radiation from a heating element within the furnace, convection within the furnace, and conduction. Furthermore, a plasma arc melting furnace is also possible.

[0070] In this embodiment, the molten iron 6 has a composition equivalent to that of the main raw materials, such as scrap iron and solid reduced iron, and is typically molten steel with a relatively low carbon content. To adjust the composition, alloying can be performed directly in the electric furnace where the steel is melted, or final decarburization and dephosphorization treatments such as oxygen refining can be performed. Furthermore, secondary refining such as desulfurization and vacuum degassing can be performed after tapping. Subsequently, through casting processes such as continuous casting, semi-finished products such as cast slabs can be produced.

[0071] Example

[0072] (Example 1)

[0073] A chill melting experiment was conducted using a DC arc furnace as the electric furnace. Scrap iron was used as the chill source, with a total charge of 100 tons.

[0074] A burner lance with a fuel supply pipe and an oxygen supply pipe is provided on the furnace cover of the electric furnace. Figure 2 The same multi-tube structure as shown. Propane gas was used as the burner fuel. Comparisons were made between a case where no burner was used (Treatment No. 1), a case where burner fuel was supplied but no powder was supplied, and the furnace contents were heated by the burner flame alone (Treatment No. 2), and a case where powdered lime was blown into the burner flame (Treatments Nos. 3 to 10). The tapping temperature was set at 1650°C.

[0075] After power is turned on, the initial cold iron source is melted, the level of the charge in the furnace is lowered, and when the molten pool becomes flat, the burner lance is lowered, and heating by burner flame is used in combination. Argon is used as a carrier gas for the supply of powder, and powdered lime is supplied to the electric furnace at a total amount of 50 kg / t-molten iron at a supply rate of 100 kg / min. The supply rate of propane gas as fuel gas is set at 2.2~11.1 Nm 3The range of 1000 smelting times per minute varied for each melting batch in the electric furnace. The pulverized fuel ratio, S / Q, was set within a range of 0.1 to 0.51 kg / MJ. Furthermore, oxygen was supplied as a combustion-supporting gas to burn the propane fuel gas during each melting batch. After slag removal from the slag outlet, the power supply and burner were disconnected, and the furnace lid was opened to load the second and subsequent chill sources. After the second chill source was loaded, the power supply was resumed, and the same procedures as after the initial loading were followed. This ultimately produced molten steel at 1650°C, which was then tapped into a ladle.

[0076] For each treatment condition, a comparison was made of the unit power consumption, the electric furnace treatment time, and the heat transfer efficiency of the burner combustion heat. The unit power consumption was calculated by dividing the power consumption of each treatment condition by the power consumption of treatment No. 1, and the value obtained was used as an index. The electric furnace treatment time was the time (min) from the start of power supply to the start of iron tapping. The heat transfer efficiency of the burner combustion heat represents the ratio of the heat generated by the burner fuel to the heat transferred to the furnace contents. The results are shown in Table 1.

[0077]

[0078] Compared to Treatment No. 1, which did not use a burner, in Treatment No. 2, where the furnace contents were heated by a single burner flame, the burner combustion heat was not efficiently transferred, resulting in roughly the same specific electricity consumption and furnace processing time. Treatments Nos. 3 to 10, where the pulverized lime was heated within the burner flame, showed reduced specific electricity consumption and furnace processing time. This is because the pulverized lime was heated within the burner flame, and a portion of the burner combustion heat was transferred to the furnace contents. However, when the calorific value of the fuel is excessive relative to the pulverized lime supply rate, the heat transfer efficiency of the burner combustion heat decreases, reducing the effect of reducing specific electricity consumption and furnace processing time. This is because the heat transfer to the pulverized lime reaches its limit, increasing the proportion of the burner combustion heat that is discharged as sensible heat in the exhaust gas.

[0079] (Example 2)

[0080] Using the same equipment structure and fuel as in Example 1, the cold iron source was melted to obtain molten steel. The tapping temperature was set to 1650°C. After the power was turned on, the melting of the initial cold iron source proceeded, the height of the charge in the furnace decreased, and when a space was formed in the upper part of the furnace, the burner lance was lowered, and heating based on the burner flame was used in combination. Argon was used as a carrier gas for the supply of powder, and the powdered lime was set to a total amount of 50kg / t-molten iron and supplied to the electric furnace at a supply rate of 100kg / min. When the unmelted cold iron source was accumulated in the furnace, when the distance between the maximum height position of the cold iron source and the upper surface of the melt was set to L (m), and the vertical distance between the front end position of the burner lance and the upper surface of the melt was set to Lh (m), the powder fuel ratio S / Q was changed in a manner such that it was 0.3×(1-L / Lh) or more, and the propane gas flow rate was circulated as much as possible. Lh is 2.0m, and the monitoring result inside the furnace shows that L changes from 1.4m to 0m (flat molten pool state). During this period, the propane gas flow rate is increased from 12.3Nm 3 / min changes to 3.7Nm 3 / min. Calculated based on the pulverized fuel ratio S / Q, this is equivalent to a decrease from 0.089kg / MJ to 0.30kg / MJ.

[0081] During the process, oxygen was supplied as a combustion-supporting gas to fuel the propane fuel gas. After slag removal from the slag outlet, the power supply and burner were disconnected, and the furnace lid was opened to load the second and subsequent chill sources. After the second chill source was loaded, power was resumed, and the same procedures as after the initial loading were followed. This ultimately produced molten steel at 1650°C, which was then tapped into a ladle.

[0082] For the treatment conditions, a study was conducted on the unit power consumption, the electric furnace treatment time, and the heat transfer efficiency of the burner combustion heat. For the unit power consumption, the value obtained by dividing the power consumption of each treatment condition by the power consumption of treatment No.1 in Example 1 was used as an index. The electric furnace treatment time is the time (minutes) from the start of power supply to the start of iron tapping. The heat transfer efficiency of the burner combustion heat represents the ratio of the heat generated by the burner fuel to the heat transferred to the furnace contents. The results are shown in Table 2.

[0083]

[0084] (Example 3)

[0085] Under the operating conditions of Process No. 6 of Example 1, the position where the burner lance was inserted was changed, and the shortest distance Lb between the electrode generating the arc and the burner lance was studied based on the relationship between the distance La from the electrode to the upper surface of the melt.

[0086] For each treatment condition, a study was conducted on the unit power consumption, the electric furnace treatment time, and the heat transfer efficiency of the burner combustion heat. The unit power consumption was the value obtained by dividing the power consumption of each treatment condition by the power consumption of treatment No. 1 in Example 1 as an index. The electric furnace treatment time is the time (minutes) from the start of power-on to the start of iron tapping. The heat transfer efficiency of the burner combustion heat represents the ratio of the heat generated by the burner fuel to the heat transferred to the furnace contents. The distance between the electrode and the burner is expressed as the ratio Lb / La. The results are shown in Table 3.

[0087]

[0088] In treatments No. 12 and 13, where the burner lance and electrode were close together, arc splashed onto the burner lance, making operation impossible. However, stable operation was possible without problems when the shortest distance Lb between the burner lance and electrode was at least 1.1 times the distance La between the electrode and the melt surface.

[0089] The unit of mass "t" used in this specification means 10 3 The unit "N" added to the volume of a gas indicates the volume under standard conditions of 0°C and 101325 Pa.

[0090] Industrial Applicability

[0091] The method for producing molten iron according to the present invention improves heat transfer efficiency, utilizes a heat source with reduced CO₂ emissions to melt the cold iron source, reduces unit electricity consumption, and alleviates the environmental burden, making it industrially useful. It is suitable for use in processes such as refining furnaces that require a heat source with reduced CO₂ emissions and require the addition of powdered secondary raw materials.

Claims

1. A method for producing molten iron, which is a method for producing molten iron by using an electric furnace to melt a cold iron source using electric energy, the method comprising: A burner is arranged in the electric furnace. The burner has an injection hole for injecting fuel and an injection hole for injecting combustion-supporting gas, and injects flames from the injection holes toward the furnace contents in the electric furnace. When the auxiliary raw material in powder form or processed into powder form is blown into the flame formed by the burner, The supply rate of the auxiliary raw material or the fuel supply rate of the burner is adjusted according to the melting condition of the cold iron source in the electric furnace.

2. The method for producing molten iron according to claim 1, wherein: The calorific value of the fuel used by the burner per unit time is Q (MJ / min), the supply rate of the auxiliary material is S (kg / min), and the supply rate of the auxiliary material or the fuel supply rate of the burner is adjusted so that the pulverized fuel ratio S / Q (kg / MJ) satisfies the following formula (1): S / Q ≥ 0.3 × (1-L / Lh) (1) Wherein, L is the vertical distance (m) between the maximum height position of the unmelted cold iron source in the electric furnace and the upper surface position of the melt, and is set to 0 when there is no unmelted cold iron source above the upper surface position of the melt. Lh is the vertical distance (m) between the front end position of the burner and the upper surface position of the melt.

3. The method for producing molten iron according to claim 1, wherein: The electric furnace is an electric arc furnace, The shortest distance between the electrode generating the arc and the burner is set to be at least 1.1 times the distance La between the tip of the electrode and the furnace contents.

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