METHOD FOR MANUFACTURING CAST IRON WITH AN ELECTRIC ARC FURNACE

Abstract

A method is provided for manufacturing pig iron by melting a cold iron source in an electric arc furnace having a carbonaceous material injection device with which it is possible to efficiently inject a carbonaceous material into the molten iron without compromising safety. In the carbonaceous material injection device, while a carbonaceous material is injected with a carrier gas through a central portion of the carbonaceous material injection device, a fuel (b) and a combustion support gas (c) are injected through the respective outer peripheral portions of the carbonaceous material injection device, wherein the carbonaceous material (a) injected through the central portion passes through a cylindrical combustion flame generated by a combustion reaction between the fuel (b) and the combustion support gas (c) and is injected into molten slag and pig iron.Since the flow rate of the carbonaceous material (a), passing through the cylindrical combustion flame, is unaffected by the surrounding gas flow, the flow rate is not attenuated, resulting in a sustained high flow rate. Therefore, the carbonaceous material (a) separates from the carrier gas, maintaining high inertial force, and reaches the molten slag and molten iron.

Description

METHOD FOR MANUFACTURING CAST IRON WITH AN ELECTRIC ARC FURNACE TECHNICAL FIELD The present invention relates to a method for manufacturing cast iron by melting a cold iron source in an electric arc furnace. PREVIOUS TECHNIQUE In an electric arc furnace, molten iron (pig iron and molten steel) is produced by melting a cold iron source, such as iron slag, with the heat of the arc. Oxygen and carbonaceous material are typically injected to further melt the cold iron source. The injection of carbonaceous material into the molten iron and molten slag reduces the iron oxide (FeO) that has formed through oxygen injection and promotes the melting of the cold iron source with the combustion heat of the carbonaceous material. Additionally, a process known as "slag foaming" occurs, in which molten slag foams due to the CO₂ gas generated as a result of the reduction of iron oxide by the carbonaceous material injection and the combustion of the carbonaceous material.Due to such slag foam formation, and since there is a reduction in the amount of heat by arc radiation, there is an increase in the melting efficiency of the cold iron source. Although examples of a method for injecting a carbonaceous material in the related art include an operation in which, while an operator holds a consumable pipe (steel pipe), a carbonaceous material is injected into a furnace through this pipe, nowadays, for example, a method using a mobile, non-consumable, water-cooled lance is used as described in Patent Literature 1 and Patent Literature 2. With this method, since the work of pipe replacement (connecting a new pipe due to the consumption of a pipe) by an operator is not required, it is possible to decrease the load placed on the operator. In addition, other examples of a method for injecting a carbonaceous material include a method in which, as described in Patent Literature 3, a carbonaceous material is injected into a furnace through a carbon injector fixed to the furnace body. APPOINTMENT LIST Patent Literature PTL 1: Publication of Unexamined Japanese Patent Application No. 7-145422. PTL 2: Publication of Unexamined Japanese Patent Application No. 11-304372. PTL 3: Publication of Unexamined Japanese Patent Application (Translation of PCT Application) No. 2016-509624. BRIEF DESCRIPTION OF THE INVENTION Technical Problem In the case of the methods described in Patent Literature 1 and Patent Literature 2, since a mobile, non-consumable, water-cooled lance is used, it is possible to efficiently inject a carbonaceous material into molten iron and molten slag. However, since the water-cooled lance must be brought close to the molten iron and molten slag, a control system is required to precisely control the lance's height. Furthermore, as the water-cooled lance approaches the molten iron and molten slag, splashes of molten iron and molten slag can adhere to the nozzle tip, potentially clogging it. Additionally, since the nozzle tip and lance body can be damaged by these splashes, there is a risk of a steam explosion due to leakage of the lance's cooling water.Furthermore, since it is necessary to provide an insertion port for the water-cooled lance in the furnace body, there is an increase in the amount of air entering through the opening formed as the insertion port, which also results in a problem of a deterioration in the rate of electrical power consumption due to a reduction in the temperature in the electric arc furnace. On the other hand, if the carbonaceous material injection device is attached to the furnace body and used as described in Patent Literature 3, there is no problem with nozzle clogging due to splashing or an increase in the amount of air entering through the opening. However, problems arise because (i) there is a comparatively large distance between the nozzle tip and the molten iron surface, (ii) the flow rate of the injected carbonaceous material and carrier gas is attenuated by the effect of surrounding gas flows (gas flows due to oxygen gas injected through an oxygen lance, gases generated from the molten slag and molten iron, air entering from outside the furnace, and the like), and so on. As a result, it is not possible to efficiently inject the carbonaceous material into the molten iron and molten slag.Furthermore, since carbonaceous material with a relatively small particle size tends to follow the carrier gas flow, it does not separate from the carrier gas depending on the injection conditions and floats on the liquid surfaces of the molten iron and molten slag along the carrier gas path, eventually dispersing from the furnace. These problems result in a deterioration in the performance of the injected carbonaceous material in the molten iron and molten slag. Furthermore, although it may be possible to inject a carbonaceous material and a carrier gas at a high injection flow rate simply by decreasing the flow channel diameter of a carbonaceous material injection nozzle (e.g., by forming a de Laval nozzle structure or similar), there is a risk of the nozzle becoming clogged with the carbonaceous material if the flow channel diameter is reduced. If the nozzle becomes clogged with the carbonaceous material as described above, the injection of the carbonaceous material must be stopped, resulting in a decrease in productivity. Additionally, there is a risk that the operation of a furnace may be shut down depending on the conditions. Therefore, an object of the present invention is to solve the problems of the techniques of the related art described above and to provide a method for manufacturing cast iron by melting a cold iron source in an electric arc furnace having a carbonaceous material injection device with which it is possible to efficiently inject a carbonaceous material into the melted slag and molten iron without compromising safety. Solution to the Problem The present inventors diligently conducted research to solve the problems described above. As a result, the following were found. While a carbonaceous material is injected with a carrier gas through the central portion of a carbonaceous material injection device, a fuel and a combustion support gas are injected through the respective outer peripheral portions. The carbonaceous material injected through the central portion passes through a cylindrical combustion flame generated by a combustion reaction between the fuel and the combustion support gas. As a result, it was found that, since the flow rate of the injected carbonaceous material and carrier gas is not attenuated, the carbonaceous material separates from the carrier gas while maintaining a high inertial force. This results in the carbonaceous material reaching and entering the molten slag and molten iron. Furthermore, it was also found that by controlling the fuel and combustion support gas injection flow rates to be higher than the carbonaceous material carrier gas injection flow rate, there is an increase in the flow rate of the carbonaceous material and carrier gas passing through the cylindrical combustion flame, further increasing the effects described above. The present invention has been completed based on the knowledge described above, and the object of the present invention is as follows. [1] A method for making pig iron with an electric arc furnace, wherein a source of cold iron is melted to make pig iron, the electric arc furnace has a carbonaceous material injection device, wherein in the carbonaceous material injection device, while a carbonaceous material (a) is injected with a carrier gas through a central portion of the carbonaceous material injection device, a fuel (b) and a combustion support gas (c) are injected through respective outer peripheral portions of the carbonaceous material injection device, and the carbonaceous material (a) injected through the central portion passes through a cylindrical combustion flame generated by a combustion reaction between the fuel (b) and the combustion support gas (c) and is injected into molten slag and molten iron. [2] The method for manufacturing cast iron with an electric arc furnace in accordance with point [1] above, wherein the injection flow rates of the fuel (b) and combustion support gas (c) in the carbonaceous material injection device are higher than an injection flow rate of the carbonaceous material carrier gas (a) in the carbonaceous material injection device. [3] The method for manufacturing cast iron with an electric arc furnace in accordance with point [1] or [2] above, wherein the combustion support gas (c) is supplied in such a way that the ratio of oxygen to the amount of fuel (b) supplied to the carbonaceous material injection device is from 1.0 to 1.1. [4] The method for manufacturing cast iron with an electric arc furnace in accordance with any of the above points [1] to [3], wherein the carbonaceous material injection device has a structure in which a carbonaceous material injection pipe (1), a fuel injection pipe (2), and a combustion support gas injection combustion pipe (3) are arranged, in a mentioned order, coaxially to the central portion of the carbonaceous material injection device. [5] The method for manufacturing cast iron with an electric arc furnace in accordance with any of the above points [1] to [4], wherein the fuel injection flow rates (b) and combustion support gas (c) in the carbonaceous material injection device are 100 m / s and 500 m / s. [6] The method for manufacturing cast iron with an electric arc furnace in accordance with any of the above points [1] to [5], wherein the combustion rate of the fuel (b) in the carbonaceous material injection device is 400 Mcal / ho plus per carbonaceous material injection device. [7] The method for manufacturing cast iron with an electric arc furnace in accordance with any of the above points [1] to [6], wherein the ratio between a fuel combustion rate (b) and a carbonaceous material injection rate (a) in the carbonaceous material injection device is 0.1 Mcal / kg or more. Advantageous Effects of the Invention According to the present invention, when a cold iron source is melted to produce pig iron in an electric arc furnace having a carbonaceous material injection device, it is possible to efficiently inject a carbonaceous material into the molten slag and the molten iron. Consequently, there are advantages in that (1) it is possible to decrease the rate of electrical energy consumption due to an increase in the melting efficiency of the cold iron source, because there is an improvement in the performance of the carbonaceous material injected into the molten slag and the molten iron, and (2) there is an improvement in casting performance, because the carbonaceous material effectively reduces iron oxide. Furthermore, there are advantages in that (3) it is also possible to decrease the rate of electrical energy consumption due to an increase in the melting efficiency of the cold iron source, because the heat generated by the combustion flame produced by the combustion reaction between the fuel and combustion support gas is absorbed by the molten iron and molten slag, (4) there is no risk of nozzle clogging, because it is not necessary to decrease the diameter of the flow channel of a carbonaceous material injection nozzle, (5) there is an improvement in operability, because as a result of fixing the carbonaceous material injection device to the body of the electric arc furnace, air does not enter through a part where the carbonaceous material injection device is attached, (6) there is an improvement in safety due to a decrease in the effect of molten iron and molten slag splashing,because it is not necessary to bring a nozzle tip close to the molten slag and molten iron, (7) there is also an improvement in the working environment due to a decrease in the amount of dust floating around the electric arc furnace, because there is a decrease in the amount of carbonaceous material scattered outside the furnace, and so on. Furthermore, by controlling the fuel and combustion support gas injection flow rates to be higher than the carbonaceous material carrier gas injection flow rate, there is an increase in the flow rate of the carbonaceous material and carrier gas in the process where the carbonaceous material and carrier gas pass through the cylindrical combustion flame, and thus it is possible to inject the carbonaceous material more efficiently into the molten slag and molten iron. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A-1B are a diagram illustrating the principle of carbonaceous material injection using the carbonaceous material injection device according to the present invention compared to a method according to the related art, wherein Figure 1A and Figure 1B illustrate the method according to the present invention and the method according to the related art, respectively. Figure 2 is a longitudinal section diagram that schematically illustrates an example of the carbonaceous material injection device modality used in the present invention. Figure 3 is a cross-sectional view along line lll-lll of Figure 2. Figure 4 is a diagram that schematically illustrates an example of operation of the modality of the present invention (longitudinal section view in the radial direction of the electric arc furnace). Figure 5 is a schematic diagram illustrating the installation positions of carbonaceous material injection devices in the electric arc furnace used in the Examples. Figure 6 is a graph illustrating an example of the relationship between the rate of consumption of injected carbonaceous material and the rate of consumption of electrical energy in the Examples. DESCRIPTION OF THE MODALITIES A method for manufacturing cast iron with an electric arc furnace according to the present invention is a method in which a source of cold iron is melted in an electric arc furnace having a carbonaceous material injection device for manufacturing cast iron and in which, in the carbonaceous material injection device, while a carbonaceous material (a) (particulate and powdered carbonaceous material) is injected with a carrier gas through a central portion of the carbonaceous material injection device, a fuel (b) and a combustion support gas (c) are injected through the respective outer peripheral portions of the carbonaceous material injection device.Consequently, the carbonaceous material (a) injected through the central portion passes through a cylindrical combustion flame generated by a combustion reaction between the fuel (b) and the combustion support gas (c) and is injected into molten slag and molten iron. Here, the term “molten iron” denotes molten pig iron or molten steel, and it may be the case that the molten pig iron and molten steel contain alloying elements such as chromium and nickel. Figures 1A-1B are a diagram illustrating the principle of carbonaceous material injection using the carbonaceous material injection device according to the present invention compared to a method according to the related art, wherein Figure 1A and Figure 1B illustrate the method according to the present invention and the method according to the related art, respectively. In the method according to the related technique illustrated in Figure 1B, a carbonaceous material injection device consists of a single-pipe nozzle, and a carbonaceous material is conveyed with a carrier gas and injected into the molten slag and molten iron in the furnace. At this point, since the flow velocity of the carbonaceous material and the carrier gas, which are injected through the single-pipe nozzle, is rapidly attenuated due to the surrounding gas flow, the carbonaceous material and the carrier gas diffuse freely, resulting in a decrease in the length of a potential core (area over which the initial velocity is maintained).Furthermore, since a carbonaceous material that has a comparatively small particle diameter tends to follow the flow of the carrier gas, the carbonaceous material does not separate from the carrier gas depending on the conditions and floats on the liquid surfaces of the molten iron and molten slag along the carrier gas path, causing the carbonaceous material to eventually disperse out of the furnace. Furthermore, in the method according to the present invention illustrated in Figure 1A, a cylindrical combustion flame is generated by the combustion reaction between a fuel (b) (gaseous and / or liquid fuel) and a combustion support gas (c), and a carbonaceous material (a) and a carrier gas pass through the cylindrical combustion flame and are injected into molten slag and molten iron. Since the flow rate of the carbonaceous material (a) and the carrier gas, passing through the cylindrical combustion flame, is unaffected by the surrounding gas flow, the flow rate is not attenuated, resulting in a sustained high flow rate. This means there is an increase in the length of a potential core. Therefore, the carbonaceous material (a) separates from the carrier gas while maintaining a high inertial force, reaches the molten slag and molten iron, and enters the molten slag and molten iron.Consequently, the carbonaceous material (a) is efficiently injected into the molten slag and molten iron. Furthermore, by controlling the fuel injection flow rates (b) and the combustion support gas (c) to be higher than that of the carbonaceous material carrier gas (a), there is an increase in the flow rate of the carbonaceous material (a) and the carrier gas as they pass through the cylindrical combustion flame. Consequently, given the increased effect described above, it is possible to inject the carbonaceous material more efficiently into the molten slag and molten iron. Carbonaceous material (a) is powdery and particulate. Examples of carbonaceous material include coke dust, which is a byproduct when coke is manufactured, coal (finely pulverized coal), plastic (in particulate or powder form, including waste plastic), and the like, and one or more of these materials may be used. As fuel (b), a gaseous fuel and / or a liquid fuel may be used. Examples of gaseous fuels include LPG (liquefied petroleum gas), LNG (liquefied natural gas), hydrogen, a gas derived from a steel plant (gas-C, gas-B, or similar), and a mixture of two or more of these gaseous fuels, and one or more of these gaseous fuels may be used. Examples of liquid fuels include heavy oil (Bunker A, Bunker B, or Bunker C), light oil, kerosene, waste oil, and similar fuels, and one or more of these liquid fuels may be used. In addition, the gaseous and liquid fuels mentioned above may be used in combination.However, it is preferable to use a gaseous fuel such as fuel (b) from the point of view of, for example, ease of combustion (the ignition temperature of the fuel generally decreases in the order of a solid fuel, a liquid fuel, and a gaseous fuel). Therefore, in the description above, a case will be described in which gaseous fuel is used as fuel (b). As a combustion support gas (c), one of pure oxygen (pure industrial oxygen), oxygen-enriched air and air can be used. Examples of a gas that can be used as a carrier gas for carbonaceous material (a) include one or more inert gases such as nitrogen or argon, air, and similar gases. If air is used as the carrier gas, it is preferable that the risk of ignition or explosion of the carbonaceous material or similar gas be reduced by installing a flashback arrestor or similar device. Furthermore, by using an inert gas such as nitrogen or argon, the risk of auto-ignition of the carbonaceous material can be reduced. The carbonaceous material injection device used in the present invention has injection pipes such that each of the carbonaceous material (a), the fuel (b), and the combustion support gas (c) is injected through the respective pipes. In this carbonaceous material injection device, the injection pipe for the carbonaceous material powder is arranged in the central portion of the device, and the injection pipes for the fuel and the combustion support gas are arranged in the outer peripheral portions of the device. Figure 2 and Figure 3 illustrate an example of the carbonaceous material injection device used in the present invention, wherein Figure 2 is a longitudinal sectional view and Figure 3 is a sectional view along line III-III of Figure 2. In this carbonaceous material injection device, a main body for supplying the fuel (b) (gaseous fuel in the present embodiment), the combustion support gas (c), and the carbonaceous material (a) has a triple-pipe structure in which three pipes are arranged coaxially. That is, this triple-pipe structure is formed by a carbonaceous material injection pipe (1) arranged in the central portion, a fuel injection pipe (2) arranged outside pipe (1), and a combustion support gas injection pipe (3) arranged outside pipe (2).Here, spacers are typically arranged between the injection pipes that form the triple pipe structure to maintain the spaces between the injection pipes. The interior space of the carbonaceous material injection pipe (1) forms a carbonaceous material flow channel (10), a space between the fuel injection pipe (2) and the carbonaceous material injection pipe (1) forms a fuel flow channel (20), and a space between the combustion support gas injection pipe (3) and the fuel injection pipe (2) forms a combustion support gas flow channel (30). The front ends of the carbonaceous material injection pipe (1), the fuel injection pipe (2), and the combustion support gas injection pipe (3) open to form a carbonaceous material delivery port (11) (injection port), a ring-shaped fuel delivery port (21) (injection port), and a ring-shaped combustion support gas supply port (31) (injection port), respectively. Furthermore, at the rear end of the carbonaceous material injection device, a combustion support gas supply port (32) for supplying combustion support gas to the combustion support gas flow channel (30) is installed on the combustion support gas injection pipe (3). Similarly, a fuel supply port (22) for supplying fuel to the fuel flow channel (20) is installed on the fuel injection pipe (2). Likewise, a carbonaceous material supply port (12) for supplying carbonaceous material via the carrier gas flow channel (10) is installed on the carbonaceous material injection pipe (1). Furthermore, although not illustrated, an inner pipe and an outer pipe are arranged coaxially outside the combustion support gas injection pipe (3), and the cooling fluid flow channels (outer channel and inner channel for cooling fluid), which are interconnected, are formed between the outer pipe and the inner pipe and between the inner pipe and the combustion support gas injection pipe (3). Although the fuel supply port (21) and the combustion support gas supply port (31) are ring-shaped in the present embodiment, each of the supply ports may be formed, for example, by several gas ports arranged at predetermined intervals in the circumferential direction at the end of the injection pipe. In such a carbonaceous material injection device, at the time of carbonaceous material injection, a carbonaceous material such as coke dust and a carrier gas are injected through the carbonaceous material injection pipe (1), a fuel (b) (fuel gas) such as LNG is injected through the fuel injection pipe (2), and a combustion support gas (c), such as oxygen, is injected through the combustion support gas injection pipe (3). The fuel (b) (fuel gas) and the combustion support gas (c) generate a cylindrical combustion flame, and the carbonaceous material (a) and the carrier gas pass through the cylindrical combustion flame and are injected into the molten slag and molten iron. Examples of a device having a structure similar to that of the carbonaceous material injection device according to the present embodiment include an auxiliary burner for an electric arc furnace. However, a carbonaceous material is used as a solid fuel in such an auxiliary burner. That is, the carbonaceous material (solid fuel) is burned (burns completely) together with a gaseous fuel such as LNG to allow a source of cold iron to absorb the heat from the combustion flame and eliminate a cold spot (which is distant from an electrode and where uneven melting occurs). Therefore, such a device differs from the carbonaceous material injection device used in the present invention in terms of its intended use, function, and method of using the carbonaceous material. In the present invention, the carbonaceous material (a) injected through the central portion of the carbonaceous material injection device passes through a cylindrical combustion flame generated by a combustion reaction between the fuel (b) and the combustion support gas (c) and is injected into molten slag and molten iron. That is, most of the carbonaceous material (a) passes through the cylindrical combustion flame unburned, reaches the molten slag and molten iron, and enters the molten slag and molten iron. The factors necessary for combustion include three elements: a combustible material, oxygen, and temperature (a source of ignition). Furthermore, the combustibility of combustible materials decreases from gas to liquid to solid. This is because, in the gaseous state, the combustible material and oxygen mix readily, leading to a chain reaction and further combustion. Additionally, in the case of solids, which have the lowest combustibility, combustion begins only after the temperature has reached their ignition point. From these points of view, the factors that prevent the carbonaceous material (a) from being burned are the following elements: (1) supplying the combustion support gas (c) in a sufficient quantity to burn only the fuel (b), (2) increasing the flow rate of the carbonaceous material (a) (carrier gas) to prevent the temperature of the carbonaceous material (a) from reaching its ignition temperature, (3) preventing the particle diameter of the carbonaceous material (a) from decreasing excessively, because the time required for the carbonaceous material (a) to reach its ignition temperature and begin to burn is reduced with a decrease in the particle diameter, and so on. With respect to point (1) above, in the present invention, since the fuel (b) is brought into contact with the combustion support gas (c) and burned immediately after being injected through the nozzle, it is preferable that the flow rate of the combustion support gas be equivalent or approximately equivalent to the oxygen ratio sufficient to burn only the fuel (b). Specifically, it is preferable that the quantity of combustion support gas (c) supplied be controlled so that the oxygen ratio to the quantity of fuel (b) supplied is from 1.0 to 1.1. Here, the term “oxygen ratio” denotes “(quantity of oxygen substantially supplied by the combustion support gas) / (theoretical oxygen demand to completely burn the fuel).” With regard to point (2) above, for example, if coal is used as the carbonaceous material (a), given that the ignition temperature of the carbonaceous material is several hundred degrees Celsius (1000°C or higher in the case of coke), it is preferable to increase the flow rate of the carbonaceous material (a) (carrier gas) to prevent the temperature of the carbonaceous material (a) from reaching its ignition temperature. The heating rate of the carbonaceous material particles in a combustion field is generally considered to be approximately 10°C / ms.In the case where the distance between the injection port of the carbonaceous material injection device and the molten slag and molten steel is approximately 1 to 2 m, when the flow velocity of the carbonaceous material (a) (carrier gas) is, for example, approximately 20 m / s to 100 m / s, the time required for the carbonaceous material (a) injected through the injection port to reach the molten slag and molten iron is as short as 10 ms to 100 ms. It is considered that, in such a short time, the temperature of the carbonaceous material (a) does not rise to its ignition temperature; in other words, the carbonaceous material (a) reaches the molten slag and molten iron without burning. Therefore, it is preferable for the flow velocity of the carbonaceous material (a) (carrier gas) to be approximately 20 m / s to 100 m / s. If the particle diameter of the carbonaceous material (a) is excessively small, in addition to point (3) above, there is a risk that the carbonaceous material (a) will be less likely to separate from the carrier gas as a result of following the carrier gas flow. Therefore, it is preferable that the mean diameter (D50) of the carbonaceous material (a) be 20 pm or greater. The mean diameter (D50) can be determined based, for example, on the particle diameter distribution of the carbonaceous material (a) obtained using a laser diffraction scattering particle size distribution measurement device. It is preferable that the carbonaceous material (a), the fuel (b) and the combustion support gas (c) be injected through the carbonaceous material injection device taking into account, for example, points (1)a (3) above. It is preferable that the injection flow rates of the fuel (b) and the combustion support gas (c) be as high as possible to efficiently inject the carbonaceous material (a). However, if the injection flow rates are excessively high, the flame is lost, and there is a risk that a stable cylindrical combustion flame cannot be generated. On the other hand, if the injection flow rates of the fuel (b) and the combustion support gas (c) are excessively low, the potential core length is reduced due to a comparatively shorter combustion flame length, thus diminishing the effectiveness of the present invention.Furthermore, if the combustion flame length is short, since the flame is lost due to extinguishing caused by disturbances in the furnace, there is a risk that a stable combustion flame cannot be generated even in this case. Therefore, it is preferable that the fuel injection flow rates (b) and the combustion support gas (c) be approximately 100 m / s to 500 m / s. Furthermore, if the combustion rate of fuel (b) is excessively low, the combustion flame tends to be unstable due to disturbances in the furnace. Therefore, it is preferable for the combustion rate of fuel (b) to be 400 Mcal / h plus the amount of carbonaceous material injected. There are also preferable conditions to apply to the flow rate of the carrier gas for the carbonaceous material (a), and it is preferable that the ratio between the amount of carbonaceous material (a) and the carrier gas flow rate be approximately 0.5 kg / Nm³ to 15 kg / Nm³. If the ratio between the amount of carbonaceous material (a) and the carrier gas flow rate is greater than 15 kg / Nm³, the transportability of the carbonaceous material (a) deteriorates, and operational problems, such as a flow channel becoming clogged with carbonaceous material (a), tend to occur. On the other hand, if the ratio between the amount of carbonaceous material (a) and the carrier gas flow rate is 7CQbnn / 77n7 / B / YIAI lower than 0.5 kg / Nm3, since there is a decrease in temperature in the furnace due to the carrier gas, there is a risk of deterioration in the operating capacity. It is possible to calculate the combustion support gas flow rate (c) using formula (1) below from the fuel flow rate (b) (fuel gas), the theoretical oxygen demand of the fuel (theoretical amount of oxygen required to completely burn the fuel) and the oxygen ratio. Combustion support gas flow rate = (oxygen ratio concentration in combustion support gas) x (oxygen ratio) (coefficient) x (fuel flow rate) x (theoretical oxygen demand of the fuel)] ··· (1) Therefore, for example, if the combustion support gas (c) is pure oxygen (with an oxygen concentration of 100%), the fuel (b) is LNG, and the LNG flow rate is 100 Nm³ / h, the flow rate of the combustion support gas (c) is calculated as follows. The theoretical oxygen demand of the fuel is calculated from the carbon and hydrogen or similar content in the fuel, and the theoretical oxygen demand of LNG is considered to be approximately 2.2 Nm³ oxygen / Nm³ LNG. In the case where the oxygen ratio is 1.1, the flow rate of the combustion support gas is calculated as 242 Nm³ / h (=1 x 1.1 x [100 x 2.2]) using formula (1) above. Furthermore, there are also preferred conditions to apply to the ratio of the fuel combustion rate (b) to the carbonaceous material injection rate (a) (Mcal / kg) in the carbonaceous material injection device, and it is preferable that the ratio of the fuel combustion rate (b) to the carbonaceous material injection rate be 0.1 Mcal / kg or more. This is because, if the fuel combustion rate (b) is small compared to the carbonaceous material injection rate, the flame at the burner tip is extinguished by the injected carbonaceous material, resulting in an unstable combustion flame and insufficient achievement of the effect of the present invention. Figure 4 is a diagram schematically illustrating an example of operation of the embodiment of the present invention (longitudinal sectional view in the radial direction of the electric arc furnace), wherein reference (4) indicates a furnace body, reference (5) indicates an electrode, reference (6) indicates the carbonaceous material injection device, reference (7) indicates molten iron, and reference (8) indicates molten slag. The carbonaceous material injection device (6) is installed in the furnace body (4) at a suitable angle to the furnace body (4). Typically, one, two, or more carbonaceous material injection devices (6) are installed in the furnace body (4). As the preceding description indicates, according to the method for manufacturing cast iron with an electric arc furnace according to the present invention, when a source of cold iron is forged in an electric arc furnace having a carbonaceous material injection device (6) to manufacture the cast iron (7), it is possible to efficiently inject the carbonaceous material (a) into the molten slag and the molten iron. Consequently, the results described in points (1) and (2) below are achieved. (1) Since there is an improvement in the performance of the carbonaceous material (a) injected into the molten slag and molten iron, it is possible to decrease the rate of electrical energy consumption due to an increase in the melting efficiency of the cold iron source. 7CQbnn / 77n7 / B / YIAI (2) Since iron oxide is efficiently reduced by carbonaceous material (a), there is an improvement in casting performance. Furthermore, according to the method of manufacturing cast iron with an electric arc furnace according to the present invention, the following effects are obtained. (3) Since the heat generated by the combustion flame produced by the combustion reaction between the fuel (b) and the combustion support gas (c) is absorbed by the molten iron and molten slag, it is possible to decrease the rate of electrical energy consumption due to an increase in the melting efficiency of the cold iron source from another point of view. (4) Since it is not necessary to reduce the diameter of the flow channel of a carbonaceous material injection nozzle, there is no risk of nozzle obstruction. (5) Since, as a result of attaching the carbonaceous material injection device to the body of the electric arc furnace, no air enters through a portion where the carbonaceous material injection device is attached, there is an improvement in the operating capability. (6) Since it is not necessary to bring a nozzle tip close to the molten slag and molten iron, there is an improvement in safety due to a decrease in the effect of splashing from the molten iron and molten slag. (7) Since there is a decrease in the amount of carbonaceous material scattered outside the furnace, there is also an improvement in the working environment due to a decrease in the amount of dust floating around the electric arc furnace. Furthermore, when the fuel injection flow rates (b) and the combustion support gas (c) are controlled to be higher than that of the carbonaceous material carrier gas (a), there is an increase in the flow rate of the carbonaceous material (a) and the carrier gas as they pass through the cylindrical combustion flame, thus amplifying the effect described above. As a result, it is possible to inject the carbonaceous material more effectively into the molten slag and molten iron. EXAMPLES The tests (examples (1) to 9) were performed using an electric arc furnace having a carbonaceous material injection device with the structure illustrated in Figure 2 and Figure 3. In addition, for comparison, a test (comparative example) was performed using an electric arc furnace having a single-pipe nozzle-type carbonaceous material injection device according to the related art (see Figure 1B). Figure 5 is a schematic horizontal cross-sectional view of the electric arc furnace used for the tests. This electric arc furnace was a direct current type electric arc furnace with a furnace diameter of approximately 6.3 m, a furnace height of approximately 4.1 m, a drawdown capacity of approximately 120,000 kilograms (120 tonnes), a water-cooled oxygen lance, and an electrode in the central portion thereof.In Examples 1 to 9, as illustrated in Figure 5, three carbonaceous material injection devices were arranged in the circumferential direction of the furnace body. Furthermore, in the comparative example, three single-pipe nozzle-type carbonaceous material injection devices, according to the related technique, were arranged in the circumferential direction of the furnace body. The operating conditions of the electric arc furnace in the present EXAMPLES are given in Table 1. zcofrnn / zznz / E / YiAi Table 1 Quantity of Iron Slag Loaded: Approximately 130,000 kilograms (130 tons) Type of Iron Slag: Heavy H2 Quantity of Casting: Approximately 120,000 kilograms (120 tons) Oxygen Lance Flow Rate: 3000 Nm3 / h Quantity of Lump Coke Loaded: 1000 kg Quantity of Quicklime Loaded: 500 kg The type of iron slag used was Heavy H2 (in accordance with the "Uniform Standards for Ferrous Slag" prepared by the Japan Ferrous Raw Materials Association). After loading the iron slag into a bucket, it was charged into the electric arc furnace in two stages: before the start of operations and halfway through, for a total quantity of approximately 130,000 kilograms (130 tons). Additionally, before the start of operations, coke pieces (1,000 kg), used as an auxiliary fuel, and quicklime (500 kg), used as a slag-forming agent, were charged into the electric arc furnace via an auxiliary raw material hopper (unpolished). The injection of the carbonaceous material was carried out during the period between the middle stage of the operation and the late stage of the operation, where molten iron and molten slag were formed to some degree. The conditions of use of the carbonaceous material injection device in examples 1 to 9 are given in Table 2. Table 2 Carbonaceous Material Injection Rate 60 kg / min to 80 kg / min Carrier Gas Type of Gas Air Flow Rate 360 ​​Nm3 / h Fuel Gas Type of Gas LNG Flow Rate 20 Nm3 / ha 220 Nm3 / h Combustion Support Gas Type of Gas Pure Oxygen Flow Rate 48 Nm3 / 'ha 532 Nm3 / h Air was used as the carrier gas for the carbonaceous material, LNG as the gaseous fuel, and pure oxygen (pure industrial oxygen) as the combustion support gas. In examples 1 to 8, the injection rate of the carbonaceous material was 60 kg / min, and the air flow rate, which was the carrier gas for the carbonaceous material, was 360 Nm³ / h. Furthermore, in example 9, the injection rate of the carbonaceous material was 80 kg / min, and the air flow rate, which was the carrier gas for the carbonaceous material, was 360 Nm³ / h. In the case of examples 1 to 9, the LNG flow rate was varied in a range of 20 Nm3 / ha to 220 Nm3 / h, and the pure oxygen rate, which was a combustion support gas, was varied in a range of 48 Nm3 / ha to 532 Nm3 / h according to the LNG flow rate so that the oxygen ratio was constantly 1.1.Furthermore, in the comparative example, the injection rate of the carbonaceous material was 60 kg / min, and air (air flow rate 360 ​​Nm³ / h) was used as the carrier gas for the carbonaceous material. The carbonaceous material used was one of the coke powder A, coke powder B, and coke powder C specified in Table 3. Table 3 Coke Powder Type Coke Powder A Coke Powder B Coke Powder C Fixed Carbon (% by mass) 88.9 87.3 88.1 Volatile Matter (% by mass) 0.35 0.57 0.46 Ash Content (% by mass) 10.8 12.2 11.5 Average Diameter D50 (pmm) 126 15 22 In the present EXAMPLES, ten injection charges of carbonaceous material were carried out in each of Examples 1 to 9, such that the charges from the first to the tenth were performed with a carbonaceous material consumption rate of 1 kg / t, 2 kg / t, 3 kg / t, 4 kg / t, 5 kg / t, 6 kg / t, 7 kg / t, 8 kg / t, 9 kg / t, and 10 kg / t, respectively, adjusting the carbonaceous material injection time to adjust the injected carbonaceous material consumption rate. For each of the examples, the average value of the injected carbonaceous material consumption rate in the ten charges and the average value of the electrical energy consumption rate in the ten charges were calculated from the injected carbonaceous material consumption rate and the electrical energy consumption rate, respectively, in each of the ten charges. Furthermore, in each of the examples, when creating a simple regression equation from the values ​​of the injected carbonaceous material consumption rate and the values ​​of the electrical energy consumption rate at the ten loads, the slope a (simple regression equation: y = - ax + b) was defined as the efficiency of the carbonaceous material (kWh / t / (kg / t)) and was used for the evaluation. For example, Figure 6 illustrates the relationship between the injected carbonaceous material consumption rate and the electrical energy consumption rate in Example 2. In this case, the efficiency of the carbonaceous material was 4.3 kWh / t / (kg / t). The higher the carbonaceous material efficiency value, the greater the efficiency. The evaluation criteria are as follows: a case of carbonaceous material efficiency less than 1.0 was considered as “x”, a case of carbonaceous material efficiency of 1.0 or more and less than 2.0 was considered as “Δ”, a case of carbonaceous material efficiency of 2.0 or more and less than 4.0 was considered as “O”, and a case of carbonaceous material efficiency of 4.0 or more was considered as “O”. Furthermore, to evaluate the performance of the carbonaceous material introduced into the molten iron, an analytical sample of the molten iron was taken from the furnace after melting the iron slag, and the carbon concentration in the molten iron was analyzed. The higher the carbon concentration in the molten iron, the greater the efficiency. The evaluation criteria are as follows: a case of carbon concentration in the molten iron of less than 0.050% was considered “x”, a case of carbon concentration in the molten iron of 0.050% or more and less than 0.055% was considered “Δ”, a case of carbon concentration in the molten iron of 0.055% or more and less than 0.060% was considered “Ό”, and a case of carbon concentration in the molten iron of 0.060% or more was considered “O”. Furthermore, when the electric arc furnace cover was opened between charges, the state of the combustion flame generated in the carbonaceous material injection device was checked by visual observation. At that time, a case in which the combustion flame was generated stably was considered “Ό”, a case in which the combustion flame was unstable such that, for example, the flame flickered or pulsed was considered “Δ”, and a case in which the flame was completely lost was considered “x”. In addition, the state of the flame and the dust (including carbonaceous material) ejected through the openings of the electric arc furnace body was visually observed. At that time, a case in which there was a decrease in the degree of flame and dust ejected through the furnace body openings compared to the comparative example was considered “0”, a case in which there was no difference in the degree of flame and dust ejected through the furnace body openings compared to the comparative example was considered “Δ”, and a case in which there was an increase in the degree of flame and dust ejected through the furnace body openings compared to the comparative example was considered “x”. Furthermore, in terms of the comprehensive evaluation, a case that was considered as “x” with respect to at least one of the carbonaceous material efficiency, the carbon concentration in the molten iron, the state of the generated combustion flame and the state of the flame and dust blowing through the openings of the electric arc furnace body described above was considered as “x”, a case that was considered as “Δ” with respect to at least one of such indices was considered as “Δ”, and other cases were considered as “O”. The results of the evaluations described above are given in Table 4 along with the injection conditions of the carbonaceous material injection device. zcofrnn / zznz / E / YiAi Table 4 zcQbnn / zznz / B / Y Comprehensive Evaluation oo -1 -1 o State of Dust and Combustion Flames Blowing Through the Inside oooo -1 o State of Combustion Flame Generated ooooo Carbon Concentration in Iron (% by mass) [The Evaluation Is In Parentheses) i*· kritsoo oossto; oo=ii®; i)C900 (0)990 0 0 057(0; íwoo (0)=900 1)8900 Efficiency of Carbon Material íkWW(kg4;i) [The Evaluation Is In Parentheses) 2-2(01 4-3(01 4-8(®i S- 2.4(01 (o)se ivin 3.1(01 Electricity Consumption Rate'2 (kW) 395 8 3900 £ 37U 391 0 385 5 381 0 9 381 0 391 8 Water Consumption Rate of injected Carbonaceous Material iL'tl £ £ fe fe fe fe fe fe fe Carbonaceous Material Injection Device (per Device) | Combustion Rate of GNU Carbonaceous Material Injection Rate (McalíRgi) fe 2 si fe £ i £ Carbonaceous Material Injection Rate [kg / min); SS sssss S s fe Coke Powder Rate C 0 Oxygen Reaction - - - - - - - - - Oxygen Injection Flow Rate [misi] fe fe fe fe fe fe fe fe fe fe Oxygen Injection Flow Rate (m / s- S fe fe - Oxygen Flow Rate (Nm Wi - S δ fe fe - Combustion Rate of (Mcalm; δ Sí 1940 99« 5 § δ GN Injection Flow Rate (m / s} sg 5 £ £ S fe s LNG Flow Rate l'NmVhj fe s § fe s § fe fe fe 3new Condition Number Comparative Example | Example' | Example 2 | Examples coidiLel} | | Examples | Example? I Examples soleáala |. In Table 4, in the comparative example where the carbonaceous material was simply injected with the carrier gas through the single-pipe nozzle-type carbonaceous material injector, a decrease in the flow rate of both the injected carbonaceous material and the carrier gas meant that much of the carbonaceous material may have been dispersed outside the furnace without reaching the molten slag or molten iron. When the carbonaceous material was injected, a flame burst through openings such as an electrode port, which is considered to correspond to the lost amount of injected carbonaceous material. The electrical energy consumption rate was 395.8 kWh / t, and the efficiency of the carbonaceous material was 0.9 kWh / t / (kg / t). Both indices were very low, and therefore this case was considered "x" with respect to the efficiency of the carbonaceous material. Furthermore, since the carbon concentration in the molten iron was 0.0.49% by mass, this case was also considered “x” with respect to carbon concentration. Therefore, the comparative example was considered “x” as with respect to the Comprehensive evaluation. Conversely, in the case of the examples of the present Invention, since the carbonaceous material passed through a cylindrical combustion flame generated by the combustion reaction between LNG and oxygen and was efficiently injected into the molten slag and molten iron, there is an increase in the rate of electrical energy consumption and the efficiency of the carbonaceous material, and there is also an increase in the concentration of carbon in the molten iron. In the case of example f, given that there was an improvement in the electrical energy consumption rate to 390.0 kWh / t and in the efficiency of the carbonaceous material to 2.2 kWh / t / (kg / t), example 1 was considered “0” with respect to the efficiency of the carbonaceous material. Furthermore, given that the carbon concentration in the cast iron was 0.053% by mass, example 1 was considered “A” with respect to this index. Furthermore, in the case of Example 2, given the improvement in the electrical energy consumption rate to 377.7 kWh / ty and the carbonaceous material efficiency to 4.3 kWh / t / (kg / t), Example 2 was considered "0" with respect to the carbonaceous material efficiency. Additionally, given that the carbon concentration in the cast iron was 0.059% by mass, Example 2 was considered "0" with respect to this index. Furthermore, in the case of Example 3, given the improvement in the electrical energy consumption rate to 371.4 kWh / ty and the carbonaceous material efficiency to 4.3 kWh / t / (kg / t), Example 2 was considered "0" with respect to this index.8 kWh / t / (kg / t), Example 3 was considered “Q” with respect to the efficiency of the carbonaceous material. Furthermore, since the carbon concentration in the cast iron was 0.06f% by mass, Example 3 was considered “O” with respect to this index. Furthermore, in the case of examples 1 through 3, since the generation of a stable combustion flame was confirmed by visual observation, these cases were considered "0" with respect to the state of the generated combustion flame. Similarly, since there was a significant decrease in the degree of powder explosion and flame through openings such as an electrode port when the carbonaceous material was injected, compared to the comparative example, these cases were also considered "0" with respect to this index. Based on the results described above, Example 1 was considered “Δ” with respect to the overall assessment. Examples 2 and 3 were considered “O” with respect to the overall assessment. In the case of Example 4, since the LNG flow rate was as low as 30 Nm³ / h, the LNG injection flow rate was 72 m / s, i.e., lower than in Examples 1 to 3, resulting in a deterioration of the combustion flame stability. Furthermore, it is considered that there was also a decrease in the acceleration of the carbonaceous material and the carrier gas compared to Examples 1 to 3. Additionally, it is considered that, since the ratio of the LNG combustion rate to the carbonaceous material injection rate was 0.08 Mcal / kg, the combustion rate was excessively low, resulting in the effect of the present invention not being sufficiently achieved. Consequently, the electricity consumption rate was 391.0 kWh / t, and the efficiency of the carbonaceous material was 1.3 kWh / t / (kg / t).Therefore, Example 4 was rated “Δ” with respect to the efficiency of the carbonaceous material. Furthermore, given that the carbon concentration in the molten iron was 0.053% by mass, Example 4 was rated “Δ” with respect to this index. Additionally, given that the combustion flame was sometimes flickering, i.e., unstable, depending on the state in the furnace, Example 4 was rated “Δ” with respect to the state of the generated combustion flame. Moreover, given that there was a difference in the degree of flame explosion and dust emission through openings in the furnace body, such as the electrode port, when the carbonaceous material was injected compared to the comparative example, Example 4 was rated “A” with respect to this index. Based on the results described above, Example 4 was rated “A” with respect to the overall evaluation. Example 5 was performed under the same conditions as Example 2, except that coke powder B was used as the carbonaceous material. In Example 5, the electrical energy consumption rate was 385.5 kWh / t, and the efficiency of the carbonaceous material was 2.4 kWh / t / (kg / t). Therefore, Example 5 was rated as “0” with respect to the efficiency of the carbonaceous material. Furthermore, since the carbon concentration in the molten iron was 0.055% by mass, Example 5 was rated as “0” with respect to this index. Additionally, since a stable combustion flame was confirmed by visual observation, Example 5 was rated as “0” with respect to the state of the generated combustion flame.Furthermore, given the difference in the degree of flame and dust explosion through openings in the furnace body, such as the electrode port, when the carbonaceous material was injected compared to the comparative example, Example 5 was considered “Δ” with respect to this index. Based on the results described above, Example 5 was considered “Δ” with respect to the overall evaluation. In the case of Example 5, there was a reduction in the efficiency of the carbonaceous material compared to Example 2. This is thought to be due to a difference in the particle diameter of the coke powder between Examples 2 and 5. Specifically, because the particle diameter of coke powder B, used in Example 5, was smaller than that of coke powder A, used in Example 2, coke powder B was less likely to separate from the carrier gas, resulting in a reduction in the efficiency of the carbonaceous material. In Example 6, given that the LNG flow rate was 220 Nm³ / h, there was a deterioration in combustion flame stability due to an increase in the LNG injection flow rate to 527 m / s, which was higher than in Examples 1–3. This resulted in a reduction in the effect of increasing the carbonaceous material's performance. Consequently, the electrical energy consumption rate was 381.0 kWh / t, and the carbonaceous material efficiency was 3.2 kWh / t / (kg / t). Therefore, Example 6 was considered "0" with respect to carbonaceous material efficiency. Furthermore, since the carbon concentration in the molten iron was 0.057% by mass, Example 6 was considered "Ό" with respect to this index. Additionally, since a combustion flame was sometimes pulsating, Example 6 was considered "Δ" with respect to the state of the generated combustion flame.Furthermore, given the significant decrease in the degree of dust and flame explosion through openings such as electrode ports when the carbonaceous material was injected, compared to the comparative example, Example 6 was rated as “0” with respect to this index. Based on the results described above, Example 6 was rated as “Δ” with respect to the overall evaluation. In the case of Example 7, it is considered that, given the LNG flow rate of 20 Nm³ / h, the LNG injection flow rate was as low as 48 m / s, which was lower than that of the carrier gas. This resulted in a deterioration in the stability of the combustion flame, and it was not possible to achieve the effect of increasing the flow rate of the carbonaceous material and the carrier gas due to the combustion flame. Furthermore, it is considered that, given the ratio between the LNG combustion rate and the carbonaceous material injection rate of 0.05 Mcal / kg, i.e., the combustion rate was excessively low, it was not possible to sufficiently realize the effect of the present invention. Consequently, the electrical energy consumption rate was 392.5 kWh / t, and the efficiency of the carbonaceous material was 1.1 kWh / t / (kg / t). Therefore, Example 7 was considered to have a “Δ” with respect to the efficiency of the carbonaceous material.Furthermore, since the carbon concentration in the molten iron was 0.052% by mass, Example 7 was considered “Δ” with respect to this index. Additionally, since the combustion flame was sometimes flickering, i.e., unstable, depending on the state in the furnace, Example 7 was considered “Δ” with respect to the state of the generated combustion flame. Furthermore, since there was a difference in the degree of flame explosion and dust ejected through openings in the furnace body, such as the electrode port, when the carbonaceous material was injected compared to the comparative example, Example 7 was considered “Δ” with respect to this index. Based on the results described above, Example 7 was considered “Δ” with respect to the overall evaluation. Example 8 was performed under the same conditions as those applied in Examples 2 and 5, with the exception that coke powder C was used as the carbonaceous material. In Example 8, the electrical energy consumption rate was 381.0 kWh / t, and the efficiency of the carbonaceous material was 3.1 kWh / t / (kg / t). Therefore, Example 8 was rated as “0” with respect to the efficiency of the carbonaceous material. Furthermore, since the carbon concentration in the molten iron was 0.056% by mass, Example 8 was rated as “0” with respect to this index. Additionally, since a stable combustion flame was confirmed by visual observation, Example 8 was rated as “0” with respect to the state of the generated combustion flame.Furthermore, given the significant decrease in the degree of flame and dust explosion through openings such as the electrode port when the carbonaceous material was injected, compared to the comparative example, Example 8 was rated as “0” with respect to this index. Based on the results described above, Example 8 was also rated as “0” with respect to the overall evaluation. zcofrnn / zznz / E / YiAi The reason the results in example 8 were better than those in example 5 is considered to be because, since the particle diameter of the coke dust was larger in example 8 than in example 5, there was an increase in the carrier gas separation capacity. Example 9 was performed under the same test conditions as those applied in Example 1, with the exception that the injection rate of the carbonaceous material was 80 kg / min. It was determined that, since the ratio between the LNG combustion rate and the carbonaceous material injection rate was 0.09 Mcal / kg, meaning the combustion rate was excessively low, it was not possible to sufficiently realize the effect of the present invention. Consequently, the electrical energy consumption rate was 391.8 kWh / t, and the efficiency of the carbonaceous material was 1.7 kWh / t / (kg / t). Therefore, Example 9 was considered to have a “Δ” with respect to the efficiency of the carbonaceous material. Furthermore, since the carbon concentration in the molten iron was 0.053% by mass, Example 9 was also considered to have a “Δ” with respect to this index.Furthermore, since the combustion flame was sometimes flickering, i.e., unstable, when the carbonaceous material was injected, Example 9 was considered “Δ” with respect to the state of the generated combustion flame. Additionally, since there was a difference in the degree of flame explosion and dust emission through openings in the furnace body, such as the electrode port, when the carbonaceous material was injected compared to the comparative example, Example 9 was considered “Δ” with respect to this index. Based on the results described above, Example 9 was considered “A” with respect to the overall evaluation. List of Reference Signs (1) carbonaceous material injection pipe (2) fuel injection pipe (3) combustion support gas injection pipe (4) furnace body (5) electrodes (6) carbonaceous material injection device (7) molten iron (8) molten slag (10) carbonaceous material flow channel (11) carbonaceous material administration port (12) carbonaceous material supply port (20) fuel flow channel (21) fuel administration port (22) fuel supply port (30) combustion support gas flow channel (31) combustion support gas administration port (32) combustion support gas supply port (a) carbonaceous material (b) fuel (c) combustion support gas

Claims

1. A method for manufacturing pig iron with an electric arc furnace, wherein a source of cold iron is melted to manufacture pig iron, the electric arc furnace having a carbonaceous material injection device, wherein in the carbonaceous material injection device, while a carbonaceous material (a) is injected with a carrier gas through a central portion of the carbonaceous material injection device, a fuel (b) and a combustion support gas (c) are injected through respective outer peripheral portions of the carbonaceous material injection device, and the carbonaceous material (a) injected through the central portion passes through a cylindrical combustion flame generated by a combustion reaction between the fuel (b) and the combustion support gas (c) and is injected into molten slag and molten iron.

2. The method for manufacturing cast iron with an electric arc furnace according to claim 1, wherein the injection flow rates of the fuel (b) and the combustion support gas (c) in the carbonaceous material injection device are higher than the injection flow rate of the carbonaceous material carrier gas (a) in the carbonaceous material injection device.

3. The method for manufacturing cast iron with an electric arc furnace according to claim 1 or 2, wherein the combustion support gas (c) is supplied in such a way that the ratio of oxygen to the amount of fuel (b) supplied to the carbonaceous material injection device is from 1.0 to 1.

1.

4. The method for manufacturing cast iron with an electric arc furnace according to any of claims 1 to 3, wherein the carbonaceous material injection device has a structure in which a carbonaceous material injection pipe (1), a fuel injection pipe (2) and a combustion support gas injection combustion pipe (3) are arranged, in a mentioned order, coaxially to the central portion of the carbonaceous material injection device.

5. The method for manufacturing cast iron with an electric arc furnace according to any of claims 1 to 4, wherein the fuel injection flow rates (b) and the combustion support gas (c) in the carbonaceous material injection device are 100 m / s and 500 m / s.

6. The method for manufacturing cast iron with an electric arc furnace according to any of claims 1 to 5, wherein the combustion rate of the fuel (b) in the carbonaceous material injection device is 400 Mcal / ho plus per carbonaceous material injection device.

7. The method for manufacturing cast iron with an electric arc furnace according to any of claims 1 to 6, wherein the ratio between a fuel combustion rate (b) and a carbonaceous material injection rate (a) in the carbonaceous material injection device is 0.1 Mcal / kg or more.