JP4420943B2 - Self-heating material for steel making in electric furnace and electric furnace operating method using the same - Google Patents

Description

  The present invention relates to a self-heating material for electric furnace steelmaking used in an electric furnace steel mill, and an electric furnace operating method using the same.

  The electric furnace steel mill is a factory that melts iron scrap collected from the market in an electric furnace and adjusts the carbon content and other components to regenerate new steel products. In order to consume a large amount of electric power, it is common to operate using night electric power with a low electricity bill and to stop the operation during the day.

  The electric furnace is equipped with electrodes for melting the scrap and generates an arc by energization to heat and melt the scrap. However, if molten steel exists in the furnace, the arc discharge is efficiently performed and the required time per charge is shortened. Can do. For this reason, after the first charge, an operation method is adopted in which the molten steel is not completely discharged and a part is left as hot water in the furnace. If this method is taken, the melting of the scrap is performed in a short time, and the productivity can be increased.

  However, in the initial charge, there is no such hot water inside the electric furnace, and the furnace temperature is lowered to about 120 ° C to 200 ° C. Therefore, in the first charge, there is a problem that it takes time from the start of energization to the start of full-scale melting, and the basic unit of power consumption increases. In addition, if a long time is required for the initial charge, the number of charges in the low-cost nighttime electricity charge period is reduced, leading to a decrease in productivity.

In addition, according to the inventor's investigation, patent documents relating to speeding up of the initial charge could not be found. Patent Document 1 discloses a carburizing material for steelmaking, which reaches the molten steel through the slag layer that floats on the surface of the molten steel when it is put into the furnace, and is reduced by carbon. This is intended to accelerate the initial charge, and is not intended to speed up the first charge.
In addition, in the known existing technology, there is a disposable body warmer as a heat generating material using iron powder, but the “self-heating” of the product of the present invention starts to generate heat using the residual heat of an electric furnace of 120 ° C. or higher, and 800 It is characterized by raising the temperature to a temperature of ℃ or higher, and is different from these existing heat generating materials.
Japanese Patent Laid-Open No. 1-268814

  The present invention solves the problems for shortening the time required for the initial charge in the electric furnace steel mill and reducing the power consumption, and also contributes to the recycling of waste, and the self-heating material for electric furnace steelmaking and An object of the present invention is to provide a method of operating an electric furnace using this.

  The self-heating material for electric furnace steelmaking of the present invention made to solve the above problems is a powdery carbon source having a carbon content of 35% by mass or more, an average particle size of 10 to 40 μm, and a metal iron content. A powdered iron source of 60% by mass or more is kneaded by adding a binder and water, and is molded into a rod shape or a particle shape having a particle size of 20 to 60 mm.

  The powdery carbon source may be derived from a waste containing 0.2 to 0.5% by mass of chlorine. The powdered iron source preferably contains 70% or more of iron particles having an aspect ratio of 5 or more, and the mass ratio of the powdered carbon source to the powdered iron source is from 1: 3 to 1: 8 is preferable. Furthermore, it is preferable that the water content of the self-heating material for electric furnace steelmaking of the present invention is 3 to 10% by mass.

  Also, the electric furnace operating method of the present invention is such that the above-mentioned self-heating material for steelmaking is introduced into the electric furnace of the first charge 30 minutes to 150 minutes before the introduction of scrap and self-heated by an oxidation reaction. The scrap is heated in advance, and the hot water type is easily formed in the initial stage of energization. In this case, it is preferable to introduce 2 to 10% by mass of the self-heating material for steel making in the electric furnace, which is 2 to 10% by mass of the amount of scrap to be charged at the first charging.

  The self-heating material for steelmaking according to the present invention is a powdered carbon source and a powdered iron source, which are formed into a rod shape or a granular shape by adding a binder and water, and the powdered carbon source is an oxidation contained in scrap. It also functions as a reducing agent for iron, and the powdered iron source self-heats due to the residual heat of the furnace and is itself at a high temperature of 800 ° C. or higher. Has the function of forming. In addition, when a powdery carbon source containing 0.2 to 0.5 mass% of chlorine is used, oxygen is removed from the iron oxide when it is heated by self-heating, and the oxide film is destroyed and the low melting point chlorination is performed. Iron is formed, and the initial hot water type is easily formed. The melting point of iron oxide is 1500 ° C. or higher, whereas the melting point of iron chloride is about 300 ° C., so the advantage of containing salt is great.

  Further, according to the method for operating the electric furnace of the present invention, the self-heating material for electric furnace steelmaking is put into the electric furnace of the first charge prior to the introduction of scrap and is self-heated by an oxidation reaction. As a result, the self-heating material for electric furnace steelmaking not only reaches a high temperature of 800 ° C. or higher, but also the surrounding scrap is sequentially heated to quickly form hot water at the beginning of energization. Accordingly, the initial charge at the electric furnace steel mill can be quickly melted, and the basic unit of power consumption can be reduced and the productivity can be improved.

Preferred embodiments of the present invention are shown below.
The self-heating material for electric furnace steelmaking according to the present invention is obtained by kneading a powdered carbon source and a powdered iron source with a binder and water added thereto, and molding into a rod shape or granular shape having a particle size of 20 to 60 mm. . As the powdery carbon source, pulverized coal or coke powder can be used. However, if waste-derived carbide is used as the powdery carbon source, cost reduction and effective use of waste can be achieved.

  In this embodiment, the collected municipal waste is put into a carbonization furnace in a low oxygen atmosphere, heated and carbonized, and the extracted carbide is used. Even if this carbide is washed with water, it contains chlorine derived from sodium chloride or the like in the garbage, and the chlorine concentration is adjusted to 0.2 to 0.5% by mass by controlling the washing process. If the chlorine concentration in the powdery carbon source is less than 0.2% by mass, the above-described iron oxide is deprived of oxygen and destroys the oxide film, and the ability to form low melting point iron chloride is insufficient. If it exceeds 0.5 mass%, there is a risk of producing harmful substances such as hydrogen chloride in the electric furnace during combustion or corroding ducts for exhaust gas treatment.

  In this case, the waste is not necessarily limited to municipal waste, but it is desirable that the carbon content of the carbide is 35% by mass or more when carbonized. Wastes with a low carbon content have a high content of impurities even if they are carbonized, which may reduce the quality of the self-heating material for electric furnace steelmaking. Sewage sludge has a high carbon content and is suitable for use, but the chlorine content is low, so it is not as optimal as municipal waste because chlorine needs to be added.

  The particle size of the powdered iron source is 10 to 40 μm. If the particle size is less than 10 μm, self-heating due to reaction with oxygen in the atmosphere becomes excessive, and care must be taken before storage. On the other hand, if the particle size exceeds 40 μm, the self-heating rate at the time of use becomes slow, the temperature cannot be raised rapidly, the dispersibility in the molten steel is deteriorated, and the reduction effect of iron oxide is reduced. In addition, as a powdery iron source, a metal iron content rate of 60 mass% or more is used. When the metal iron content is low, the self-heating rate is slowed, and energy is consumed to reduce the iron oxide, so that the power consumption rate is deteriorated.

  The most suitable powdered iron source is one containing 70% or more of iron particles having an aspect ratio of 5 or more. The ratio of the iron particles described above can be calculated by observing the powdered iron source with a microscope and counting the number.

  The reason why the aspect ratio of the powdered iron source is set to 5 or more is that it is advantageous in securing the strength of the molded product, and it is easy to secure the surface area as compared with the spherical one. Examples of the powdered iron source containing 70% or more of iron particles having such a size and shape include steel scraps and cutting scraps.

  In the present invention, the mass mixing ratio of the powdered carbon source and the powdered iron source is set to 3 to 8 with respect to the powdered carbon source 1. If the amount of powdered iron source is less than this, the self-heating performance will decrease, and conversely if it is greater than this, the heat conduction of the material itself will increase, increasing the heat radiation to the outside, making it difficult to raise the temperature of the material, The ability to reduce iron is reduced. A more preferable range is the powdered iron source 4 to 6 with respect to the powdered carbon source 1.

  The powdery carbon source and the powdered iron source described above are kneaded by adding a binder and water, and formed into a pellet. As the binder, an organic binder such as starch or an inorganic binder such as bentonite can be used. The organic matter disappears in the molten steel, and the inorganic matter floats as slag, so the molten steel is not contaminated. The mixing rate is not particularly limited, but if the molding strength is weak, it will collapse due to the impact at the time of charging or the pressure of the scrap and become powdery, so that the diffusion of air is inhibited and the heat generation is reduced. Addition amount is 7% at maximum.

  Water is not only necessary for improving moldability, but also becomes water vapor and affects the oxidation action of iron. If there is little moisture, exothermicity will deteriorate, and conversely if too much, energy for evaporating will be wasted. For this reason, the range of 3-10 mass% is preferable.

  The molding is performed by an extrusion molding machine, a briquette machine, or the like, and is molded into a rod shape or a pellet shape. The size is 20 to 60 mm. If the particle size is smaller than this range, the intrusion of air between the particles is hindered and the self-heating property is deteriorated. If the particle size is larger than this range, it takes time for the oxidation to proceed to the inside, which is not preferable.

  The above-described self-heating material for electric furnace steelmaking according to the present invention is handled in a packaged state as shown in FIG. 1, but is mainly composed of a powdered iron source having a metal iron content of 60% by mass or more. The bag can be adsorbed by an electromagnet.

  The above-described self-heating material for steelmaking of the electric furnace according to the present invention is put into the center of the bottom of the electric furnace 1 of the first charge as shown in FIG. The electric furnace 1 at the start of the first charge is empty, but the interior thereof is maintained at a temperature of about 120 ° C. to 200 ° C. due to residual heat. One charge is usually divided into about three times, and scrap is charged, but the amount of self-heating material for electric furnace steelmaking is preferably 2 to 10% by weight, particularly preferably 3 to 7% by weight of the initial scrap input. .

  When this amount of self-heating material for steelmaking is introduced into the electric furnace 1 of the first charge 30 to 150 minutes prior to the introduction of scrap, and as shown in FIG. Oxidation reaction due to contact between the residual heat of the furnace and air causes self-heat generation sequentially from the surface, and the temperature rises to 800 ° C. or more, and the heating zone expands to the surrounding scrap 2 as shown in FIG. Thereafter, as shown in FIG. 5, when energization heating by the electrode 4 is started, the material at a high temperature immediately melts to become a hot water seed, and the scrap 2 gradually melts. In order to perform such a reaction quickly, the amount of the self-heating material for electric furnace steelmaking is set to 2 to 10% by mass of the initial amount of scrap input.

  Thereafter, the second and third scraps are sequentially added, and when all the scraps become molten metal, the hot water is discharged and the initial charge is completed. At this time, a part of the molten metal is left in the furnace and used as the hot water for the next charge. The time required for one charge after the second charge is about one hour. By reducing the first charge operation time according to the present invention, the number of charges that can be operated within the cheap nighttime electricity charge time zone or the final charge is increased. There are effects such as shortening the time when the charge exceeds the nighttime electricity charge time zone or reducing the amount of scrap melted in the final charge to operate within the nighttime electricity charge time zone and eliminating the need to shorten the operation time. is there.

  As described above, according to the operation method of the electric furnace of the present invention, the initial charge can be rapidly melted, and the basic unit of power consumption can be reduced and the productivity can be improved. Furthermore, it can also contribute to the recycling of waste.

  Examples of the present invention are shown below. Example 1 is a basic test, in which a material was filled in a wire mesh container that is a cube with a side of 100 mm installed in a thermostat, and the internal temperature change was measured while maintaining the external temperature of the material at a constant temperature. . The results are shown in Tables 1 to 3.

The average particle diameter in the table indicates a cumulative 50% particle diameter measured by a laser diffraction scattering method.
The aspect ratio of 5 or more refers to the ratio of particles having a long side / short side length ratio of 5 or more to the total number of particles observed with a microscope.
The content of metallic iron indicates the proportion of metallic iron measured by IPC spectroscopy in a dry state of the iron source.
The molding strength is determined by measuring the amount of fine particles of 1 mm or less generated when the molded product is dropped from a height of 5 m and pulverized. The fine particles are less than 20% by mass, ◯, 20% or more and less than 40%. 40% or more was evaluated as x.
The self-heating start temperature indicates the initial external temperature required for the temperature of the material to rise to 300 ° C or higher due to self-heating in the test facility. From the intermittent operation of the electric furnace to the start of the next operation In order to prevent self-heating due to self-heating due to the residual heat of the electric furnace being held, and to prevent fires due to self-heating during storage and transportation, materials are generated by self-heating at an initial external temperature of 120 ° C or higher and lower than 160 ° C. When the temperature rose to 300 ° C. or higher, ◯, 160 ° C. or higher and lower than 200 ° C., Δ, 200 ° C. or higher or lower than 120 ° C. as x.
The self-heating rate indicates the time from the start of the test until it reaches 300 ° C. when the temperature of the material rises to 300 ° C. or more due to self-heating in the test facility. The case where it was reached in less than 150 minutes was marked with ◯, the case where it reached within 150 minutes to less than 210 minutes was indicated as Δ, and the case where it took 210 minutes or more was indicated as x.
In the comprehensive evaluation, the case where there was at least one x was indicated as x, the case where there was no x and there was at least one △, and the case where all were ◯.

Next, the results of an operation test using an arc type AC electric furnace having a transformer capacity of 20,000 kVA with 44 tons of scrap per charge (21 tons for the first time, 15 tons for the second time, and 8 tons for the second time) are shown. 4 and shown in Table 5.
The self-heating material used was granular (cylindrical) with a diameter of 20 mm and a length of 40-60 mm, an average particle size of iron source of 20 μm, an aspect ratio of 5 or more is 80%, a metallic iron content of 80%, an average of carbon source The particle size is 30 μm, the carbon content is 45%, the chlorine content is 0.4%, the moisture content of the molded product is 3%, and the binder amount is 5%.

  Self-heating materials were charged before the start of the first charge, and scrap was charged 15 minutes later. The operation was performed three times under the same conditions, and the average value was recorded in the table. The material input time in the table is the time from when the material is input until the start of energization. Regarding the operation time of the first charge, the case where there was a time shortening effect of 5 minutes or more was evaluated as “◯”, the case of 2-5 minutes as “Δ”, and the case of less than 2 minutes as “X”. In addition, the power consumption rate was evaluated as “◯” for a reduction of 5 kWh / t or more, “Δ” for a reduction less than 5 kWh / t, and “x” for no effect or deterioration. In the comprehensive evaluation, the case where there was at least one x was indicated as x, the case where there was no x and there was at least one △, and the case where all were ◯. Note that number 1 in Table 4 is a conventional operation example in which no self-heating material is used.

It is explanatory drawing which shows the state in which the self-heating material is packed and handled. It is sectional drawing of the state which supplied the self-heating material. It is sectional drawing of the state which started self-heating. It is sectional drawing of the state in which the surrounding scrap was heated. It is sectional drawing of the state in which the hot water seed was formed in the initial stage of the energization heating by an electrode.

Explanation of symbols

1 Electric furnace 2 Scrap 3 Hot water type 4 Electrode

Claims (7)

  A powdered carbon source having a carbon content of 35% by mass or more and a powdered iron source having an average particle size of 10 to 40 μm and a metal iron content of 60% by mass or more are kneaded by adding a binder and water, A self-heating material for steel making in an electric furnace, characterized by being formed into a rod shape or a particle shape having a particle size of 20 to 60 mm.   The self-heating material for electric furnace steelmaking according to claim 1, wherein the powdery carbon source is derived from a waste containing 0.2 to 0.5 mass% of chlorine.   2. The self-heating material for electric furnace steelmaking according to claim 1, wherein the powdered iron source contains 70% or more of iron particles having an aspect ratio of 5 or more.   The self-heating material for electric furnace steelmaking according to claim 1, wherein the mass ratio of the powdered carbon source and the powdered iron source is 1: 3 to 1: 8.   The self-heating material for steel making in an electric furnace according to claim 1, wherein the moisture content is 3 to 10% by mass.   The self-heating material for electric furnace steelmaking according to any one of claims 1 to 5 is charged into the electric furnace of the first charge prior to the charging of the scrap and is self-heated by an oxidation reaction, and the scrap is heated in advance and energized. An electric furnace operating method characterized by forming hot water seeds in the initial stage.   The method for operating an electric furnace according to claim 6, wherein 2 to 10% by mass of the self-heating material for steel making of the electric furnace is charged with respect to the amount of scrap charged at the first charge of the first charge.

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