JP2010265485A - Method for operating arc-furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating an arc-furnace by which electric power consumption can be reduced and operational time can be shortened by efficiently melting cold-iron source in the case of producing molten metal by using the cold-iron source. <P>SOLUTION: In the method for operating the arc-furnace, the arc-furnace 1, which comprises a melting chamber 2 and a shaft-type pre-heating chamber 3 directly connected to the upper part of the melting chamber 2, and pre-heats the cold-iron source 15 in the pre-heating chamber 3 by introducing waste gas generated in the melting chamber 2 into the pre-heating chamber 3, is used. When the cold-iron source 15 is melted by being heated with the arc in the melting chamber 2 while supplying the cold-iron source 15 into the pre-heating chamber 3 so that the cold-iron source 15 holds the existing state in the pre-heating chamber 3 and the melting chamber 2, carbon-concentration of the molten iron tapped off from the arc-furnace 1, is defined as ≥1 mass%. It is desirable that carbonaceous material is added in the melting chamber 2 and, the carbonaceous material to be added into the melting chamber 2 is derived from biomass. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for operating an arc furnace in which a cold iron source such as iron scrap, directly reduced iron, and cold iron is melted by an arc furnace.

  In an arc furnace for steelmaking, an iron source such as iron scrap is heated and melted with arc heat, and then refined in the furnace to produce molten steel. However, since much electric power is consumed, the arc furnace melts during melting. Many methods have been proposed for preheating iron scrap using high-temperature exhaust gas generated from a room and melting the preheated iron scrap to reduce power consumption.

  As disclosed in Patent Document 1, an arc furnace having a melting chamber and a shaft-type preheating chamber that is directly connected to the melting chamber and into which exhaust gas generated in the melting chamber is introduced is disclosed. Used to heat the iron scrap in the melting chamber with an arc while continuously or intermittently charging the iron scrap into the preheating chamber so that the iron scrap is continuously present in the preheating chamber and the melting chamber. When the iron scrap is melted and at least one heat of molten metal has accumulated in the melting chamber, scrap melting in an arc furnace that discharges the molten metal in a state where the iron scrap is continuously present in the preheating chamber and the melting chamber Is the method. Note that the “molten steel for one heat” is the amount of molten steel accommodated in one container of a molten steel holding and conveying container such as a ladle used for casting operations such as continuous casting. The amount is determined from the lifting load of a crane or the like.

  On the other hand, an operation is known in which hot metal is used as an iron source together with iron scrap for the purpose of reducing power consumption.

  For example, as disclosed in Patent Document 2, an operation method in an arc furnace including a melting chamber and a shaft-type preheating chamber that is directly connected to the melting chamber and into which exhaust gas generated in the melting chamber is introduced. In addition, the blast furnace hot metal is directly charged into the melting chamber, and the scrap is continuously or intermittently charged into the preheating chamber so that the iron scrap is continuously present in the preheating chamber and the melting chamber. However, when the iron scrap in the melting chamber and the blast furnace hot metal are heated with an arc to melt the iron scrap, and at least one heat of molten steel has accumulated in the melting chamber, the iron scrap continues into the preheating chamber and the melting chamber. There has been proposed an arc furnace operating method characterized in that molten steel is discharged in the existing state.

JP-A-10-292990 JP 2000-17319 A

  By using the technique described in Patent Document 2 above, scrap can be preheated and efficiently arc-melted, and at the same time, about 50% blast furnace hot metal can be mixed and used to reduce power consumption. Since the amount of scrap dissolved is halved, there is a problem that the processing efficiency of scrap is lowered and the productivity is deteriorated.

  Moreover, the position of the arc furnace in the steel process is a molten steel manufacturing process, and the carbon concentration at the time of tapping is generally operated at less than 1 mass% due to the process restrictions in the subsequent process. For example, in Patent Document 2, the carbon concentration at the time of steelmaking is 0.1 mass%, and when melting is performed using hot metal, there is a problem that the blowing time for lowering the carbon becomes long. Furthermore, since the liquidus temperature (melting point) of iron becomes higher as the carbon concentration becomes lower and the hot water temperature needs to be raised, there is a problem that the amount of power used is increased and the operation time is extended.

  The present invention has been made in view of such circumstances, and the object of the present invention is to efficiently melt the cold iron source and reduce the amount of power used when manufacturing the molten metal using the cold iron source. The object is to provide an arc furnace operating method capable of shortening the operation time.

The features of the present invention for solving such problems are as follows.
(1) A melting chamber and a shaft-type preheating chamber directly connected to the upper portion of the melting chamber are provided, and exhaust gas generated in the melting chamber is introduced into the preheating chamber to preheat a cold iron source in the preheating chamber. The cold iron source is supplied to the preheating chamber so that the cold iron source is maintained in the preheating chamber and the melting chamber, and the cooling iron is heated by arc heating in the melting chamber. An arc furnace operating method characterized in that, when the iron source is melted, the carbon concentration of the molten metal discharged from the arc furnace is 1 mass% or more.
(2) The method for operating an arc furnace according to (1), wherein a carbonaceous material is added to the melting chamber.
(3) The method for operating an arc furnace according to (2), wherein the carbonaceous material added to the melting chamber is derived from biomass.
(4) The method for operating an arc furnace according to any one of (1) to (3), wherein oxygen is blown into the melting chamber.
(5) A method for producing molten steel, characterized in that molten steel produced by the method for operating an arc furnace according to any one of (1) to (4) is refined in a converter to obtain molten steel.
(6), mixing at least part of the molten metal produced by the method for operating an arc furnace according to any one of (1) to (4) with blast furnace hot metal, and refining in a converter to obtain molten steel A method for producing molten steel.

  According to the present invention, when producing a molten metal using a cold iron source, the cold iron source can be efficiently melted to reduce the amount of power used and the operation time.

  Moreover, the use of biomass-derived charcoal can prevent sulfur contamination and reduce carbon dioxide emissions.

It is one Embodiment of the arc furnace used for implementation of this invention, and is a longitudinal cross-sectional schematic diagram of an arc furnace equipment. It is one Embodiment of the arc furnace used for implementation of this invention, and is a longitudinal cross-sectional schematic diagram of an arc furnace equipment.

  In the present invention, an arc furnace having a melting chamber and a shaft-type preheating chamber directly connected to the upper portion of the melting chamber and introducing the exhaust gas generated in the melting chamber into the preheating chamber to preheat the cold iron source in the preheating chamber When melting the cold iron source by arc heating in the melting chamber while supplying the cold iron source to the preheating chamber so that the cold iron source exists in the preheating chamber and the melting chamber The arc furnace is operated with the carbon concentration of the molten metal discharged from the furnace being 1 mass% or more. By setting the carbon concentration of the molten metal discharged from the arc furnace to 1 mass% or more and lowering the temperature of the molten metal, it becomes possible to quickly melt the cold iron source with a small amount of power consumption.

  By maintaining the carbon concentration of the molten metal discharged from the arc furnace at 1 mass% or more, there is an effect that the problem of dust generation and splash when mixed with the blast furnace molten iron is eliminated. When the carbon concentration is less than 1 mass%, a C—O reaction occurs due to the reaction of C in the blast furnace molten iron and oxygen in the molten metal from the arc furnace when mixed with the blast furnace molten iron. It becomes a problem. Also, when splash occurs, it becomes a safety problem.

On the other hand, from the viewpoint of energy saving and prevention of global warming by CO ₂ reduction, promotion of scrap utilization is desired. The production of hot metal in a blast furnace requires a great deal of energy to reduce and melt iron ore, while scrap requires only heat of melting, reducing the amount of energy consumed for the reduction heat of iron ore. There is an advantage that you can.

  Conventionally, in the process flow scrap utilization by the blast furnace-converter method, the scrap is often directly used for the converter. However, since the converter uses the combustion heat of carbon in the hot metal as the melting heat of the scrap, there is a disadvantage that the blending ratio of a certain amount or more of scrap cannot be increased. Further, in the converter, there has been a problem that the carbonaceous material is added as a melting heat source in order to increase the scrap mixing ratio, and the blowing time becomes longer and the productivity is lowered. Furthermore, when a large amount of scrap is used in the converter, there is a problem that it is difficult to adjust the composition of the molten steel to be produced.

  By setting the carbon concentration of the molten metal to 1 mass% or more, the hot metal produced using the arc furnace can be incorporated into a part of the process flow by the blast furnace-converter method. For example, since the temperature of the hot metal preliminary treatment (desiliconization, desulfurization, dephosphorization) performed from the blast furnace to the converter is performed at 1250 ° C. to 1450 ° C., if the concentration of tapping carbon from the arc furnace is set to 4 mass% or more. Various hot metal pretreatments can be performed.

In order to set the carbon concentration of the molten metal discharged from the arc furnace to 1 mass% or more, it is preferable to add carbonaceous material as a carburizing and auxiliary heat source in the melting chamber. As described below, when oxygen is blown into the melting chamber, the amount of carbon and oxygen added to the arc furnace is preferably 1 kg or more with respect to 1 Nm ³ of oxygen (carbon content). Thereby, even if oxygen is blown in, reduction of carbon in the molten metal can be prevented.

  It is preferable to blow oxygen into the dissolution chamber. By blowing oxygen, the carbon in the hot metal can be burned with oxygen. In addition, when the carbon material added to the melting chamber is carburized into molten iron and oxygen is blown to burn the carbon in the hot metal with oxygen, the combustion heat of carbon becomes an alternative to electric power energy, and at the same time, the generated high-temperature CO Since the gas preheats the iron scrap in the shaft, the reduction of the power consumption and the speed of melting are further promoted. Moreover, by burning the carbonaceous material with oxygen, the carbonaceous material exhibits the same effect as the carbon in the hot metal and contributes to the reduction of the power consumption.

  The carbonaceous material added to the melting chamber is preferably derived from biomass. Coke generally used as a carbon material contains sulfur (S), but it can prevent S contamination from the carbon material by being derived from biomass. Furthermore, since biomass is carbon neutral, it is possible to reduce carbon dioxide emissions, which is one of the causes of global warming.

  As the cold iron source, a high carbon content cold iron source is preferably used. As described above, the cold iron source only needs to have iron as a main component such as iron scrap, iron scrap, directly reduced iron, cold iron, etc., but particularly when a high carbon content cold iron source is used. It can be dissolved quickly with the amount of power used. The addition of charcoal may be unnecessary. In addition, the high carbon content cold iron source of the present invention is a cold iron source having a carbon concentration of 1.0 mass% or more, for example, directly reduced iron (carbon concentration; 1 to 2 mass%) or cold iron (carbon concentration; 3 to 5 mass%), which is a cold iron source with a much higher carbon content than steel scrap mainly composed of steel with a low carbon concentration. The cold iron is obtained by solidifying hot metal produced in a blast furnace, a smelting reduction furnace, or a cupola. Furthermore, since these high carbon-containing cold iron sources have few impure elements, it is possible to dilute impurity elements such as Cu, Sn, and Cr resulting from iron scrap, and to high-grade steel produced by the blast furnace-converter method. Comparable steel can be manufactured.

  In the above invention, it is preferable that the molten metal is discharged from the arc furnace in a state where the cold iron source is continuously present in the preheating chamber and the melting chamber.

  Next, the present invention will be described with reference to the drawings. 1 and 2 show an embodiment of an arc furnace used for carrying out the present invention. 1 and 2 are schematic longitudinal sectional views of an arc furnace facility, FIG. 1 is a diagram showing a case where carbon material is blown into a melting chamber from a lance, and FIG. 2 is a diagram showing carbon material into the melting chamber. It is a figure which shows the case where it uses from the combined use of a lance and a carbonaceous material supply apparatus, or only a carbonaceous material supply apparatus.

  1 and 2, an arc furnace 1 includes a melting chamber 2 and a preheating chamber 3, the inside of which is constructed of a refractory, and a shaft type is provided at the top of the melting chamber 2 having a furnace bottom electrode 6 at the bottom. The preheating chamber 3 and the water-cooled furnace wall 4 are disposed, and the upper opening of the furnace wall 4 not covered with the pre-heating chamber 3 is covered with a water-cooling furnace lid 5 that can be freely opened and closed. An upper electrode 7 made of graphite that can move up and down into the melting chamber 2 through the furnace lid 5 is provided, and the base of the DC arc furnace 1 is configured. The furnace bottom electrode 6 and the upper electrode 7 are connected to a DC power source (not shown), and an arc 19 is generated between the furnace bottom electrode 6 and the upper electrode 7.

  Above the preheating chamber 3, a bottom-opening type supply bucket 13 suspended from the traveling carriage 24 is provided, and an openable / closable supply port 20 provided at the upper portion of the preheating chamber 3 is provided from the supply bucket 13. A cold iron source (for example, iron scrap) 15 is charged into the preheating chamber 3. The duct 21 provided at the upper end of the preheating chamber 3 is connected to a dust collector (not shown), and the high-temperature exhaust gas generated in the melting chamber 2 is sucked through the preheating chamber 3 and the duct 21 in this order, and the preheating chamber. The cold iron source 15 in 3 is preheated. The preheated cold iron source 15 falls freely into the melting chamber 2 in accordance with the amount of the cold iron source 15 melted in the melting chamber 2 and is inserted into the melting chamber 2.

  An oxygen blowing lance 8 and a carbonaceous material blowing lance 9 that pass through the furnace lid 5 and can move up and down in the melting chamber 2 are provided, and oxygen is blown into the melting chamber 2 from the oxygen blowing lance 8, and the carbonaceous material. From the blowing lance 9, coke, char, coal, charcoal, graphite, biomass charcoal, or a mixture of these materials is blown into the melting chamber 2 using air, nitrogen, or the like as a carrier gas. Also, on the opposite side of the melting chamber 2 from the part where the preheating chamber 3 is installed, there is a steel outlet 11 in which the outlet side is pressed against the furnace bottom by a door 22 and filled with packed sand or mud agent. The side wall is provided with an outlet 12 that is pressed on the outlet side by a door 23 and filled with stuffed sand or mud agent. A burner 10 is attached to the furnace cover 5 at a position corresponding to the upper part of the steel outlet 11. The burner 10 burns fossil fuel and biomass fuel such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas in the dissolution chamber 2 with air, oxygen, or oxygen-enriched air. The burner 10 can be attached as needed.

  In the case of FIG. 2, above the melting chamber 2, there is a hopper 26, a cutting device 28 provided at the lower part of the hopper 26, and an upper end thereof connected to the cutting device 28, and a lower end passing through the furnace lid 5. A charcoal material supply device 25 configured with the chute 29 is installed. The hopper 26 contains a carbonaceous material 27 of coke, char, coal, charcoal, graphite, biomass charcoal, etc., or a mixture thereof, and the charging amount of the carbonaceous material 27 is controlled by a cutting device 28. The melting chamber 2 can be directly charged via the supply chute 29.

  A crane (not shown) is installed above the melting chamber 2 and the upper electrode 7, the oxygen blowing lance 8, the charcoal blowing lance 9, the burner 10, and the charcoal supply device 25 are removed in advance. 5 is opened, and the cold iron source 15 can be charged into the melting chamber 2.

  In operation in the DC arc furnace 1, first, the cold iron source 15 is charged into the preheating chamber 3 from the supply bucket 13. The cold iron source 15 charged into the preheating chamber 3 is also charged into the melting chamber 2 and eventually fills the preheating chamber 3. In order to uniformly charge the cold iron source 15 into the melting chamber 2, the cold iron source 15 and the carbonaceous material are charged into the melting chamber 2 opposite to the preheating chamber 3 with the furnace lid 5 opened. You can also Further, hot metal may be charged into the melting chamber 2 when the cold iron source 15 is charged. By using hot metal, the amount of power used can be significantly reduced by the heat of the hot metal. The hot metal can be charged into the melting chamber 2 with a ladle for supply (not shown) or a hot metal (not shown) connected to the melting chamber 2.

  Next, while feeding a direct current between the furnace bottom electrode 6 and the upper electrode 7, the upper electrode 7 is moved up and down, and between the furnace bottom electrode 6 and the upper electrode 7, or the inserted cold iron source 15 and An arc 19 is generated between the upper electrode 7 and the cold iron source 15 is melted by the arc heat. At the same time, the flux is melted to produce molten slag 18. The molten slag 18 keeps the generated molten metal 17 warm. If the amount of the molten slag 18 is too large, it can be discharged from the spout 12 during operation.

  When the oxygen blowing lance 8 and the carbonaceous material blowing lance 9 can be inserted into the melting chamber 2 after energization, as shown in FIGS. It is preferable to blow the carbon material into the molten metal 17 or the molten slag 18 in the melting chamber 2. The carbon material can be added from the lance 8 and the carbon material supply device 25.

The carbon in the molten metal 17 reacts with oxygen and is decarburized, and the reaction product CO gas forms the molten slag 18 and the arc 19 is wrapped in the molten slag 18, so that the heat receiving efficiency of the arc 19 is increased. Further, the high-temperature CO gas generated in a large amount and the CO ₂ gas generated by burning this CO gas efficiently preheats the iron scrap 15 in the preheating chamber 3. Oxygen blowing amount per tonne 15 Nm ³ of the molten metal 17 to be retained in the melting chamber 2 between the dissolution start to tapping (hereinafter referred to as "Nm ³ / t".) Is preferably not less than.

  Carbon material dissolved in the molten metal 17 or suspended in the molten slag 18 added to the melting chamber 2 reacts with oxygen to generate combustion heat, and acts as an auxiliary heat source to use power. And at the same time, the heating efficiency of the arc 19 is increased and the preheating efficiency of the cold iron source 15 is improved. The amount of the carbon material added is determined according to the oxygen blowing amount. That is, it is preferable to blow in a carbon material whose carbon content is equal to or greater than the chemical equivalent of oxygen to be blown. If the amount of carbon is smaller than the oxygen gas blown in, excessive oxidation of the molten metal 17 and the carbon concentration are lowered, which is not preferable.

  Further, as the cold iron source 15 in the melting chamber 2 is melted, the cold iron source 15 in the preheating chamber 3 falls into the melting chamber 2 according to the amount melted in the melting chamber 2 and decreases. In order to compensate for this decrease, the cold iron source 15 is charged from the supply bucket 13 to the preheating chamber 3. The cold iron source 15 is charged into the preheating chamber 3 continuously or intermittently so that the cold iron source 15 is continuously present in the preheating chamber 3 and the melting chamber 2. At that time, it is preferable that the amount of the cold iron source 15 continuously present in the preheating chamber 3 and the melting chamber 2 is 50 mass% or more of the cold iron source 15 of a single hot water output.

  In this way, the cold iron source 15 and the molten metal 17 are heated to melt the cold iron source 15, the molten metal 17 is stored in the melting chamber 2, the carbon concentration of the molten metal 17 is measured, and if necessary, the carbon material blowing lance 9. And the carbon concentration of the molten metal 17 is adjusted to 1 mass% or more by adjusting the amount of carbon material added from the carbon material supply device 25. Next, the melting chamber 2 is tilted by a tilting device (not shown), and the molten metal 17 is discharged from the hot water outlet 11. In this case, since the cold iron source 15 is buried in the molten metal 17 and coexists, a large degree of molten metal superheat cannot be obtained. Therefore, it is preferable to heat the molten metal 17 with the burner 10 at the time of hot water discharge in order to prevent troubles such as blockage of the hot water outlet 11 due to a decrease in the molten metal temperature.

  After the hot water is passed through a desulfurization step of desulfurization, decarburization treatment is performed in a converter to obtain molten steel. Also, molten steel can be obtained by mixing at least part of the molten metal from the arc furnace with blast furnace hot metal and performing a desulfurization process in which desulfurization is performed, and performing a decarburization process in the converter.

  After the molten metal 17 is discharged and the molten slag 18 is further discharged, the melting chamber 2 is returned to the horizontal position by the tilting device, and the hot water 11 and the hot water outlet 12 are filled with sand or mud material, and then the next heat is applied. Start dissolving.

  Thus, by heating and melting the cold iron source 15, all the cold iron sources 15 that are melted by the subsequent heat are preheated and can be operated with extremely high preheating efficiency. It is possible to improve and reduce power consumption.

  Moreover, if the molten metal after the arc furnace tapping is mixed with the blast furnace hot metal, it can be used for the production of high-grade steel due to the dilution effect. At this time, by maintaining the carbon concentration of the molten metal discharged from the arc furnace at 1 mass% or more, the problem of dust generation when the molten metal discharged from the arc furnace and the blast furnace molten iron are mixed as described above can be avoided. it can.

  In the above description, the case where the arc furnace 1 is a direct current type has been described, but the present invention can be applied without any problem even if an alternating current type arc furnace is used.

  An embodiment of the present invention using the DC arc furnace shown in FIG. 1 will be described below. In the arc furnace, the melting chamber has a furnace diameter of 7.2 m, a height of 4 m, the preheating chamber has a width of 3 m, a length of 5 m, a height of 7 m, and a furnace capacity of 180 tons.

First, about 70 tons of cold iron source at room temperature is charged into the preheating chamber, then 50 tons of cold iron source at room temperature and 1 ton of coke are charged into the melting chamber, and a graphite upper electrode with a diameter of 30 inches. Was used to start dissolution with a power supply capacity of 750 V and 130 KA at maximum. Immediately after energization, quick lime and fluorite were blown, and oxygen was blown into the melting chamber from two oxygen blowing lances at 1800 Nm ³ / hr and carbon material was blown into coke at 200 kg / min. Quicklime and fluorite were heated to form molten slag, and by blowing oxygen and coke, the molten slag formed and the tip of the upper electrode was buried in the molten slag. The voltage at this time was set to 550V. For scrap dissolution, the oxygen blowing rate was 15 Nm ³ / t, the coke blowing rate was 56 kg / t, and the power consumption was 270 kWh / t.

  After that, when the iron scrap in the preheating chamber descends as it melts, the iron scrap is charged into the preheating chamber with the supply bucket, and continues to melt while maintaining the iron scrap height in the preheating chamber at a constant height, and When 140 tons or more of molten metal was generated in the melting chamber, 140 tons of molten metal was discharged into a ladle. The molten metal was heated with a heavy oil burner when the hot water was discharged. The carbon concentration of the molten metal at the time of tapping was 3.9 mass%, the sulfur concentration was 0.04 mass%, and the molten metal temperature was 1390 ° C. After 140 tons of hot water, slag forming operation was carried out while feeding acid and coke, and melting was continued. When the amount of molten metal reached 140 tons or more, 140 tons of hot water was repeatedly carried out.

  About 35 tons of molten metal after tapping is mixed with 265 tons of blast furnace hot metal, desulfurized to a total of 300 tons, then decarburized in a converter, heated to 1620 ° C, and then the molten steel is discharged and continuously Casted by a casting machine. The remaining molten metal discharged from the arc furnace to the ladle was similarly processed and cast.

Next, as a comparative example, in the DC arc furnace shown in FIG. 1, about 70 tons of cold iron source at room temperature is charged in the preheating chamber, and then 50 tons of cold iron source at room temperature and 1 ton of cold iron in the melting chamber. Coke was charged and a graphite upper electrode having a diameter of 30 inches was used, and melting was started at a maximum power supply capacity of 750 V and 130 KA. Immediately after energization, quick lime and fluorite were blown into the melting chamber, oxygen was supplied from an oxygen blowing lance at 1800 Nm ³ / hr, and coke was blown from a charcoal blowing lance at 48 kg / min. Quicklime and fluorite were heated to form molten slag, and by blowing oxygen and coke, the molten slag formed and the tip of the upper electrode was buried in the molten slag. The voltage at this time was set to 550V. For scrap dissolution, the oxygen blowing rate was 15 Nm ³ / t, the coke blowing rate was 15 kg / t, and the power consumption was 360 kWh / t.

  After that, when the iron scrap in the preheating chamber descends as it melts, the iron scrap is charged into the preheating chamber with the supply bucket, and continues to melt while maintaining the iron scrap height in the preheating chamber at a constant height, and When 140 tons or more of molten metal was generated in the melting chamber, 140 tons of molten metal was discharged into a ladle. The molten metal was heated with a heavy oil burner when the hot water was discharged. The molten steel had a carbon concentration of 0.2 mass%, a sulfur concentration of 0.04 mass%, and a molten metal temperature of 1600 ° C. After 140 tons of hot water, slag forming operation was carried out while feeding acid and coke, and melting was continued. When the amount of molten metal reached 140 tons or more, 140 tons of hot water was repeatedly carried out.

  In Table 1, the case where the carbon concentration of the molten metal at the time of tapping is 3.9 mass% is referred to as Example 1, and the case where the carbon concentration of the molten metal at the time of tapping is 0.2 mass% is a comparative example. Indicates.

  Compared with the case where the carbon concentration of the molten metal was 0.2 mass%, when the carbon concentration was 3.9 mass%, it was possible to perform the operation with the temperature of the molten metal lowered. In addition, the power consumption rate decreased, and the tap-tap time could be shortened. The tap-tap time is the time from the start of hot water to the next start of hot water.

  An embodiment of the present invention using the DC arc furnace shown in FIG. 2 will be described below. The DC arc furnace shown in FIG. 2 is obtained by installing a carbonaceous material supply device on the DC arc furnace shown in FIG.

First, about 70 tons of cold iron source at room temperature is charged into the preheating chamber, then 50 tons of cold iron source at room temperature and 1 ton of coke are charged into the melting chamber, and a graphite upper electrode with a diameter of 30 inches. Was used to start dissolution with a power supply capacity of 750 V and 130 KA at maximum. Immediately after energization, quick lime and fluorite were blown into the melting chamber, oxygen from the oxygen blowing lance was 1800 Nm ³ / hr, and coke was blown from the carbon material blowing lance to 96 kg / min. Quicklime and fluorite were heated to form molten slag, and by blowing oxygen and coke, the molten slag formed and the tip of the upper electrode was buried in the molten slag. The voltage at this time was set to 550V. Thereafter, coke was continuously fed into the melting chamber at 500 kg / min from a carbonaceous material supply device located above the melting chamber to continue melting. For scrap melting, the amount of power used is 15 Nm ³ / t, the amount of coke blown from the lance is 20 kg / t, and the amount of coke added from the carbon material feeder is 36 kg / t. Was 280 kWh / t.

  After that, when the iron scrap in the preheating chamber descends as it melts, the iron scrap is charged into the preheating chamber with the supply bucket, and continues to melt while maintaining the iron scrap height in the preheating chamber at a constant height, and When 140 tons or more of molten metal was generated in the melting chamber, 140 tons of molten metal was discharged into a ladle. The molten metal was heated with a heavy oil burner when the hot water was discharged. The carbon concentration of the molten metal at the time of tapping was 4.1 mass%, the sulfur concentration was 0.04 mass%, and the molten metal temperature was 1390 ° C. After 140 tons of hot water, slag forming operation was carried out while feeding acid and coke, and melting was continued. When the amount of molten metal reached 140 tons or more, 140 tons of hot water was repeatedly carried out.

  Table 1 shows the operation conditions and the operation results.

  When the DC arc furnace shown in FIG. 2 was used, the carbon concentration of the molten metal at the time of tapping could be increased even if the amount of carbonaceous material added was the same. Further, the amount of carbon material blown from the lance was reduced, so that the blowing time was shortened and the tap-tap time was shortened.

  Under the conditions of Example 1, coconut shell (PKS) charcoal was used as bio-coke instead of coke.

  Table 1 shows the operation conditions and the operation results.

  Operation was possible without problems even when using coconut husk charcoal, and the sulfur concentration of the molten metal was 0.01 mass% or less, and the sulfur concentration in the molten metal could be reduced by using bio-coke, which is a biomass-derived charcoal. .

  Under the conditions of Example 2, coconut shell (PKS) charcoal was used as bio-coke instead of coke.

  Table 1 shows the operation conditions and the operation results.

  Operation was possible without problems even when using coconut husk charcoal, and the sulfur concentration of the molten metal was 0.01 mass% or less, and the sulfur concentration in the molten metal could be reduced by using bio-coke, which is a biomass-derived charcoal. .

  Under the conditions of Example 2, the amount of coke added was changed to 15 kg / t from the lance and 20 kg / t from the carbonaceous material supply device for the dissolution of scrap. The carbon concentration of the molten metal at the time of tapping was 1.9 mass%, the sulfur concentration was 0.04 mass%, and the molten metal temperature was 1500 ° C.

  Table 1 shows the operation conditions and the operation results.

  Compared with the case where the carbon concentration of the molten metal is 0.2 mass%, when the carbon concentration is 1.9 mass%, it was possible to perform the operation with the temperature of the molten metal lowered. In addition, the power consumption rate decreased, and the tap-tap time could be shortened.

  Under the conditions of Example 2, the amount of coke added was changed to 18 kg / t from the lance and 20 kg / t from the carbonaceous material supply device for the dissolution of scrap. The carbon concentration of the molten metal at the time of tapping was 2.2 mass%, the sulfur concentration was 0.04 mass%, and the molten metal temperature was 1500 ° C.

  Table 1 shows the operation conditions and the operation results.

  Compared with the case where the carbon concentration of the molten metal was 0.2 mass%, when the carbon concentration was 2.2 mass%, it was possible to perform the operation with the temperature of the molten metal lowered. In addition, the power consumption rate decreased, and the tap-tap time could be shortened.

  In order to clarify the influence of dust generation and splash when mixing the molten metal discharged from the arc furnace and the blast furnace molten iron, a survey test was conducted. In the experiment method, first, 212 kg of hot metal having a carbon concentration of 4.6 mass% was melted in a melting furnace (molten metal A) and transferred to a pan-like container. 28 kg of molten metal (molten metal B) whose carbon concentration was changed from 0.2 to 4.2 mass% at intervals of 0.4 mass% was poured into this hot metal-containing container, and the amount of dust and splash was visually examined. The results are shown in Table 2.

  Test No. 1 in which the carbon concentration of the molten metal B is 1.0 mass% or less. 1 and no. In No. 2, there was a large amount of dust and splash accompanying the C—O reaction, and there was an environmental problem. Moreover, foaming (forming) occurred in the molten metal in the pan, and the molten metal overflowed. Therefore, it was difficult to continue the operation because of the danger.

  Dust generation and splash tend to decrease as the carbon concentration of the molten metal B increases. In Nos. 3 to 6, dust generation and splash associated with the CO reaction were small, and the operation could be safely performed without forming the molten metal from the pan with a small amount of forming.

  Test No. 7 and no. In No. 8, dust generation, splash and forming were not recognized, and the operation could be performed in an environmentally favorable state.

DESCRIPTION OF SYMBOLS 1 Arc furnace 2 Melting chamber 3 Preheating chamber 4 Furnace wall 5 Furnace lid 6 Furnace bottom electrode 7 Upper electrode 8 Oxygen blowing lance 9 Carbon material blowing lance 10 Burner 11 Steel outlet 12 Steel outlet 13 Supply bucket 15 Cold iron source 17 Molten metal 18 Molten slag 19 Arc 20 Supply port 21 Duct 22 Door 23 Door 24 Traveling cart 25 Charcoal material supply device 26 Hopper 27 Carbon material 28 Cutting device 29 Supply chute

Claims (6)

  An arc furnace comprising a melting chamber and a shaft-type preheating chamber directly connected to an upper portion of the melting chamber, and introducing an exhaust gas generated in the melting chamber into the preheating chamber to preheat a cold iron source in the preheating chamber. Used to melt the cold iron source by arc heating in the melting chamber while supplying the cold iron source to the preheating chamber so that the cold iron source remains in the preheating chamber and the melting chamber. When performing, the carbon concentration of the molten metal discharged from the said arc furnace shall be 1 mass% or more, The operating method of the arc furnace characterized by the above-mentioned.   The method for operating an arc furnace according to claim 1, wherein a carbonaceous material is added to the melting chamber.   The method for operating an arc furnace according to claim 2, wherein the carbonaceous material added to the melting chamber is derived from biomass.   The method of operating an arc furnace according to any one of claims 1 to 3, wherein oxygen is blown into the melting chamber.   A molten steel produced by the arc furnace operating method according to any one of claims 1 to 4, wherein a molten steel is obtained by refining in a converter.   A molten steel obtained by mixing at least a part of the molten metal produced by the method for operating an arc furnace according to any one of claims 1 to 4 with a blast furnace hot metal and refining in a converter to obtain molten steel. Manufacturing method.

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