Title of invention: Electric furnace and method for dissolving and reducing iron oxide-containing iron raw material
Technical field
[0001]
　The present invention relates to an electric furnace for producing hot metal using an iron oxide-containing iron raw material, and a method for dissolving and reducing the iron oxide-containing iron raw material using the electric furnace.
　The present application claims priority based on Japanese Patent Application No. 2017-204540 filed in Japan on October 23, 2017, the contents of which are incorporated herein by reference.
Background technology
[0002]
　In the direct reduction ironmaking method for producing reduced iron from iron ore and dust generated from iron mills, shaft furnaces, rotary kilns, rotary hearth furnaces, fluidized beds, etc. are used for reduction furnace types and natural gas for reducing agents. , Coal, etc. are used. Various iron-making processes based on these combinations have been proposed and industrialized.
[0003]
　Further, among these direct reduction ironmaking methods, the reduction furnace type was manufactured by a method of using a natural gas as a reducing agent in a shaft furnace, or the reducing furnace type was manufactured by a method of using coal as a reducing agent in a rotary hearth furnace. As a method for producing hot metal using an iron oxide-containing iron raw material, a method of producing hot metal by melting an iron oxide-containing iron raw material having a high reduction rate in an arc furnace is currently the most mainstream.
[0004]
　However, in order to produce iron oxide-containing iron raw materials with a high reduction rate, a large amount of reducing agent is used, and a residence time is required until the reduction reaction of iron oxide is almost completed. Is difficult to adopt because of cost and productivity. Therefore, instead of producing iron oxide-containing iron raw materials with a high reduction rate in these direct reduction furnaces, the direct reduction furnace is used as a preliminary reduction furnace, and the reduction rate produced by performing preliminary reduction in this preliminary reduction furnace is relatively low. A method of producing hot metal by melting and reducing an iron oxide-containing iron raw material using an arc furnace or a melting converter has been adopted. On page 66 of Patent Document 1, a mixture raw material (pellet or granular mixture raw material) containing semi-reduced iron pre-reduced in a rotary hearth furnace (RHF) is charged in a submerged arc furnace (SRF), It is stated that a final refining is carried out for the purpose of final reduction and dissolution. In the SRF, oxygen gas and coal are supplied, and hot metal and recovered gas are obtained. It should be noted that in the SRF, it is necessary to charge seed hot water such as hot metal at the time of starting the furnace, but this is not necessary in the steady operation state due to the presence of the iron bath in the furnace. In Patent Document 2, the carbonaceous material is internally agglomerated in the dust generated in the converter, agglomerated, and heated at a high temperature in a preliminary reduction furnace to preliminarily reduce the internal carbonaceous material as a reducing material. As a part, a method of supplying the molten steel to a melting-only converter in which seed hot water is present and reusing it is disclosed.
[0005]
　In the method for producing the hot metal, the iron oxide-containing iron raw material produced by pre-reduction is put into an arc furnace in which a seed water is present to melt and reduce, and the iron oxide-containing iron raw material that has been introduced is somehow devised. Unless the hot metal is stirred, for example, when the hot metal is not stirred, it is dissolved and reduced in a state of floating on the hot metal surface because of its small specific gravity. Further, since the iron oxide-containing iron raw material contains slag components such as CaO and SiO 2 , the slag floats on the hot metal surface as the melting progresses, and the raw material charged from the furnace is trapped by the slag and comes into contact with the hot metal. Since it inhibits, it does not dissolve and causes a decrease in iron yield. In order to accelerate the dissolution and reduction of the introduced iron oxide-containing iron raw material, the introduced iron oxide-containing iron raw material is melted and reduced by using the high temperature part as much as possible and being entangled in the hot metal by flow control. There is a method.
[0006]
　Various proposals have heretofore been made on a method of introducing an oxide raw material into a high temperature region by an arc of a DC electric furnace or an AC electric furnace, and applying bottom blowing stirring to dissolve and reduce the material.
[0007]
　For example, Patent Document 3 describes an invention of a smelting reduction method for metal oxides using a three-phase AC electric furnace. In the three-phase alternating current electric furnace, the invention supplies powdery metal raw material ore, for example, chromium ore to an arc formation region, melts the metal raw material ore by arc heat, and further, gas at the bottom of the electric furnace. The present invention relates to an electric furnace refining method characterized in that a blowing nozzle is arranged to blow a gas into a molten metal in an electric furnace. The distinction between the effect of improving the reduction reaction due to and the effect of improving the reduction reaction due to contact between the molten metal and the raw ore is unclear.
[0008]
　Patent Document 4 discloses a method in which a carbon-containing fuel and an oxygen-containing gas are blown into a steelmaking arc furnace and oxygen is supplied by a nozzle arranged at the bottom of the arc furnace. It is described that an ore, pre-reduced ore, etc. are blown through a hollow electrode using an arc furnace having three electrodes to give bottom-blown stirring when producing a metal melt, but the high temperature created by the arc No mention is made of the concentration of the number of ores and pre-reduced ores in the field, the positional relationship of the bottom blowing nozzles in the furnace bottom, and the yield of the input raw materials.
Prior art documents
Patent literature
[0009]
Patent Document 1: International Publication WO01/018256
Patent Document 2: Japanese Unexamined
Patent Publication No. 2000-45012 Patent Document 3: Japanese Unexamined Patent Publication No. 1-294815
Patent Document 4: Japanese Unexamined Patent Publication No. 63-125611
Summary of the invention
Problems to be Solved by the Invention
[0010]
　Regarding an electric furnace that manufactures hot metal by introducing iron oxide-containing iron raw material that has been pre-reduced into a hot bath to melt and reduce it, gas is blown into the molten iron from the bottom of the furnace in a conventionally known electric furnace. Even if the method of introducing the iron oxide-containing iron raw material with stirring is adopted, it is not possible to wind the iron oxide-containing iron raw material and sufficiently mix it with the hot metal. Further, the iron oxide-containing iron raw material having a small specific gravity could not be retained in the high-temperature molten metal surface portion under the upper electrode, and the effect of improving the iron yield was not sufficient.
[0011]
　The present invention is an electric furnace in which an iron oxide-containing iron raw material is put into a hot metal seed to dissolve and reduce, and an iron yield is high, and an electric furnace that enables dissolution and reduction of the iron oxide-containing iron raw material, An object is to provide a method for dissolving and reducing an iron oxide-containing iron raw material using the electric furnace.
Means for solving the problem
[0012]
　The gist of the present invention is as follows.
(1) An electric furnace according to an aspect of the present invention includes a mechanical stirrer having one or more upper electrodes, one or more bottom blown tuyere, an impeller, and a charging for charging an iron oxide-containing iron raw material. And a device.
(2) The following configuration may be adopted in the electric furnace according to (1) above: Three or more bottom blowing tuyeres; a plurality of upper electrodes; each of the above in plan view. Among two line segments that connect the center of the upper electrode and the center of the impeller, the shortest line segment is divided into three equal parts, and a straight line orthogonal to the line segment is drawn at a point closer to the impeller. At this time, at least three or more of the bottom blown tuyere of the bottom blown tuyere are located closer to the upper electrodes than the orthogonal straight lines.
(3) In the electric furnace according to (2), in the plan view, all the centers of the respective upper electrodes and the raw material charging port of the charging device are closer to the upper electrodes than the straight lines intersecting at right angles. It may be inside the polygon connecting the centers of the three or more bottom-blown tuyere on the near side.
(4) The method for dissolving and reducing an iron oxide-containing iron raw material according to one aspect of the present invention uses the electric furnace according to any one of (1) to (3) above. In this method for melting and reducing iron oxide-containing iron raw material, the iron oxide-containing iron raw material having a metallization ratio of iron of 45% or more and 95% or less is charged from the charging device into the electric furnace in which the molten metal exists. Upon melting and reducing, the impeller of the mechanical stirrer is immersed in the molten metal and rotated to stir the slag and the molten metal on the surface of the molten metal.
Effect of the invention
[0013]
　According to the above aspect of the present invention, the iron oxide-containing iron raw material is supplied onto the hot metal, and in an electric furnace used when producing hot metal by melting and reducing, slag and oxidation are caused by gas blowing from the bottom blowing tuyere. High by combining bottom-blown stirring that promotes the mixing of iron-containing iron raw material and hot metal, and mechanical stirring that causes the slag floating on the hot metal by rotating the impeller and the iron oxide-containing iron raw material to be rolled into the hot metal. The iron yield enables dissolution and reduction of iron oxide-containing iron raw materials.
[0014]
　Furthermore, with three or more bottom-blown tuyeres, the top electrode and the iron oxide-containing iron raw material charging port are arranged inside the polygon that connects the centers of the bottom-blown tuyeres in plan view. By supplying the raw material to the inside of the polygon, it is possible to prevent the iron oxide-containing iron raw material from being introduced into the high temperature portion immediately below the upper electrode and immediately moving from the high temperature portion to the side wall side. You can This promotes the dissolution and reduction of the iron oxide-containing iron raw material. In addition, by rotating the impeller installed in a place apart from the high temperature portion in the vicinity immediately below the upper electrode, the slag that has moved from the high temperature portion and the iron oxide-containing iron raw material that has not been melted or reduced into the hot metal. Since it can be involved, the reduction of FeO in the slag and the dissolution and reduction of the iron oxide-containing iron raw material are further promoted, and a high iron yield can be stably achieved.
Brief description of the drawings
[0015]
FIG. 1 is a vertical sectional view showing an example of an electric furnace in the present invention.
FIG. 2A is a plan sectional view of the electric furnace.
FIG. 2B is a plan sectional view showing another example of the electric furnace in the present invention.
FIG. 3 is a view showing the electric furnace of FIG. 2A and a view taken along the line AA of FIG. 2A.
FIG. 4 is a graph showing the influence of the presence or absence of bottom blowing on the slag FeO concentration during the dissolution and reduction treatments during operation without mechanical stirring.
FIG. 5 is a graph showing the effect of mechanical stirring on the slag FeO concentration during the dissolution and reduction treatments during operation without bottom blowing.
FIG. 6 is a graph showing the influence of both bottom blowing and mechanical stirring on the slag FeO concentration during the dissolution and reduction treatments in the operation according to the present invention.
MODE FOR CARRYING OUT THE INVENTION
[0016]
　The present invention is directed to an electric furnace capable of producing a hot metal by introducing an iron oxide-containing iron raw material from the furnace into the hot metal of the hot metal, melting and reducing the heat by contact between the arc heat and the hot metal of the hot metal. .. Further, the iron oxide-containing iron raw material charged from the furnace stays in the high temperature part due to the arc generated by the upper electrode, and the mechanical stirrer installed outside the high temperature part is rotated to dissolve the iron oxide containing iron raw material and its melting. Provided is an electric furnace that enables slag having a high FeO concentration generated in association with iron to be entrained in the hot metal and can produce hot metal with a high iron yield.
[0017]
　The present invention preferably applies a DC arc furnace as the arc furnace. The present invention can also be applied to an AC arc furnace. A mode for carrying out the present invention will be described in detail below with reference to FIGS. 1 to 3, taking a DC arc furnace as an example.
[0018]
　The electric furnace 1 of the present embodiment includes one or more upper electrodes 2, one or more bottom blowing tuyeres 3, a mechanical stirrer 5 equipped with an impeller 4, and an iron oxide-containing iron raw material charging device 6. With. The iron oxide-containing iron raw material charging device 6 holds the iron oxide-containing iron raw material in the device itself, or the iron oxide-containing iron raw material in the device itself, although not the device itself. It is connected to a container holding an iron oxide-containing iron raw material so that the raw material can be supplied through a transport mechanism. The example shown in FIGS. 1 to 3 has two upper electrodes 2 and three bottom blowing tuyeres 3. Further, it has one mechanical stirrer 5 and one charging device 6. FIGS. 1 to 3 are views showing an example of an electric furnace 1 which is used when iron oxide-containing iron raw material 13 is supplied, melted and reduced to produce hot metal. In FIG. 1, an iron oxide-containing iron raw material 13 is charged from a charging device 6. In this electric furnace 1, the upper electrode 2 forms an arc 14 with the surface of the molten metal 11, gas is blown into the molten metal 11 from the bottom blowing tuyere 3 to stir the molten metal 11 and the iron oxide-containing iron raw material. 13 and the slag 12 and the molten metal 11 are also mixed. The impeller 4 of the mechanical stirrer 5 rotates with its lower half immersed in the molten metal 11, thereby stirring the molten metal 11, the slag 12, and the iron oxide-containing iron raw material 13.
　Since the electric furnace 1 shown in FIG. 1 is a DC electric furnace, it has a furnace bottom electrode 10. A solid electrode may be used as the upper electrode 2. The iron oxide-containing iron raw material 13 is charged from the raw material charging port 7 of the charging device 6 toward the surface of the molten metal 11.
[0019]
　As shown in FIG. 1, the mechanical stirrer 5 has a shaft 5a extending along the vertical direction, an impeller 4 fixed to the lower end of the shaft 5a, and an upper portion of the shaft 5a held around the vertical axis. And a drive unit 5b for rotating the drive unit. The impeller 4 is a rotating body having a center 17 along the vertical direction, and has, for example, four wings around it. The impeller 4 has an outer shape that tapers downward, and by rotating itself, the iron oxide-containing iron raw material 13 and the slag 12 which are floating around are impregnated and sent downward.
[0020]
　The electric furnace 1 having the above basic configuration promotes the mixing of the iron oxide-containing iron raw material 13 and the slag 12 with the hot metal by the gas blowing from the bottom blowing tuyere 3. In addition, by rotating the impeller 4, the slag 12 and the iron oxide-containing iron raw material 13 floating on the hot metal can be wound into the hot metal (the molten metal 11). Therefore, the iron oxide-containing iron raw material 13 can be dissolved and reduced with a high iron yield.
[0021]
　However, since the arc 14 is formed between the upper electrode 2 and the molten metal 11 and the high temperature region H is formed in the vicinity of the arc 14, the iron oxide-containing iron raw material 13 charged into the electric furnace 1 is rapidly melted. In order to reduce the iron oxide-containing iron raw material 13, the raw material charging port 7 of the iron oxide-containing iron raw material 13 is arranged as close to the high temperature region H as possible near the arc 14, and the charged iron oxide-containing iron raw material 13 is kept in the high temperature region H. It is preferable to set. In order to achieve the object, in the preferred embodiment of the present invention, the electrode center 16 of each upper electrode 2 and the center 17 of the impeller 4 of the mechanical stirrer 5 are connected in a plan view as shown in FIG. 2A. The shortest line segment 20 of each line segment is divided into three equal parts. Then, of two points (21) that divide the line segment 20 into three equal parts, a straight line 22 orthogonal to the line segment 20 is drawn at a point 21a on the side closer to the impeller 4. Of the bottom blowing tuyeres 3, the centers 18 of at least three tuyeres 3 are closer to the upper electrode 2 than the straight lines 22 orthogonal to each other, and all the electrodes of the upper electrode 2 The center 16 and the raw material input port 7 into the electric furnace 1 of the iron oxide-containing iron raw material input device 6 are located at a position closer to each upper electrode 2 than the orthogonal straight lines 22 are. It is inside the polygon 23 (triangle in this example) that connects the centers 18.
[0022]
　The arrangement of the bottom blowing tuyeres 3 is such that, in a plan view, a line segment 20 that connects the electrode center 16 of the upper electrode 2 and the center 17 of the impeller 4 is divided into three equal parts, that is, a point 21a on the impeller 4 side of the two points (21). Then, when a straight line 22 orthogonal to the line segment 20 is drawn, at least three tuyere centers 18 are installed so that they are closer to the upper electrode 2 than the orthogonal straight lines 22 are. As shown in FIG. 2A, when there are two or more upper electrodes 2, the shortest line segment 20 of the two horizontal line segments connecting each electrode center 16 and the impeller center 17 is divided into three equal parts. At a point 21a on the side closer to the impeller 4 among the two points (21) to be performed, a straight line 22 that is orthogonal to the line segment 20 and horizontal is used as a reference. In FIG. 2A, the three bottom blowing tuyeres 3 are arranged at the illustrated positions in a state where the impeller 4 and the respective upper electrodes 2 are aligned in a horizontal row. It should be noted that it is not a rule that excludes that there is another bottom blown tuyere on the side closer to the impeller 4 than the straight line 22.
[0023]
　Further, the impeller 4 and the upper electrode 2 do not have to be in a horizontal row. As an example thereof, FIG. 2B shows that the two upper electrodes 2 are equidistant from the impeller 4. Also in this case, the positions of the three bottom blowing tuyeres 3 are higher than the above-mentioned straight line 22 position obtained by drawing a line segment 20 connecting the center 17 of the impeller 4 and the electrode center 16 at three equal points 21. It is located on the electrode 2 side. In this example, the positions 18 of the tuyere centers 18 of the three bottom blowing tuyere 3 are equidistant from each other, but they are not necessarily equidistant.
[0024]
　The position of the orthogonal straight line 22 should be drawn so as to be orthogonal to the midpoint of the line segment 20 connecting the electrode center 16 and the impeller center 17 by utilizing the high temperature region H immediately below the upper electrode 2. It can be said that the iron-containing iron raw material 13 is more preferable for the characteristics of the present invention in which it is dissolved and reduced.
[0025]
　Further, in plan view, all the electrode centers 16 of one or more upper electrodes 2 and the raw material charging port 7 into the electric furnace 1 of the charging device 6 of the iron oxide-containing iron raw material 13 are defined by the orthogonal straight lines 22. Also needs to be inside the polygon 23 connecting the centers 18 of the three or more bottom blowing tuyeres 3 on the upper electrode 2 side. By defining the relationship between the position of the bottom-blowing tuyere 3 and the electrode center 16 and the raw material inlet 7 in this way, the bottom-blowing gas flowing from each bottom-blowing tuyere 3 connects the centers 18 of those tuyere. The flow toward the center of the polygon 23 (see reference numeral F1 in FIGS. 2A and 3) is formed, and the iron oxide-containing iron raw material 13 charged into the polygon 23 stays in the vicinity of the high-temperature region H, so that the oxidation is performed. This is because an effect of promoting dissolution of the iron-containing iron raw material 13 is expected.
[0026]
　In this way, each bottom blowing tuyere 3 is arranged so as to have the upper electrode 2 and the raw material charging inlet 7 of the iron raw material 13 containing iron oxide inside the polygon 23 connecting the centers 18 of each bottom blowing tuyere 3. Therefore, the horizontal shortest distance between the bottom blowing tuyeres 3 is naturally determined in consideration of the facility-like condition. Further, the horizontal maximum distance between the bottom blowing tuyeres 3 may be appropriately determined from the relationship with the side wall of the electric furnace 1. The mutual distance between the bottom blowing tuyeres 3 forming the polygon 23 is within the above-described range, and the iron oxide-containing iron raw material 13 charged on the hot metal is surrounded by the bottom blowing gas, and is preferably composed of a surrounded space. It may be appropriately determined from the viewpoint of not letting it escape. From this point of view, it can be said that the larger the number of bottom blowing tuyeres 3, the more effective, but if the number of bottom blowing tuyeres 3 becomes too large, the tuyere cost will increase, and if the furnace bottom electrode 10 is provided, interference with the arrangement will occur. , About 6 is the usual upper limit.
[0027]
　With such a structure, the iron oxide-containing iron raw material 13 is added to the vicinity of the high temperature region H immediately below the upper electrode 2, and at the same time, it is surrounded by the bottom-blown gas and is strongly stirred with the hot metal. Will be done.
[0028]
　When the hollow upper electrode 2 is used as shown in FIG. 1, the iron oxide-containing iron raw material 13 is fed into the electric furnace through the mutual passages of the upper electrodes 2 and the internal passages of the hollow upper electrode 2. It can be thrown into 1. Since the high-temperature arc 14 is formed between the upper electrode 2 and the molten metal 11 in the electric furnace 1, the raw material (iron oxide-containing iron raw material 13) charged into the molten metal 11 through the internal passage of the hollow upper electrode 2 is formed. Is preferable because it is heated to a high temperature when passing through the arc 14 and easily melts.
[0029]
　By the way, the iron oxide-containing iron raw material 13 charged into the electric furnace 1 is melted and reduced while floating on the surface of the molten metal 11 because its specific gravity is lighter than that of the molten pig iron (molten metal 11). When the iron oxide-containing iron raw material 13 is dissolved and reduced , the unreduced iron oxide portion also becomes slag along with CaO and SiO 2 in the raw material , which also has a lower specific gravity than the hot metal (molten metal 11). Then, a layer of the slag 12 having a high FeO concentration is formed by floating on the surface of the molten metal 11. Even with the preferred form described above, this FeO-rich slag 12 will sooner or later flow out of the enclosure (polygon 23) together with the iron oxide-containing iron raw material 13 which has not been dissolved and reduced. .. As it is, neither the iron oxide-containing iron raw material 13 which has not been dissolved or reduced nor the FeO contained in the slag 12 are in sufficient contact with C (reducing material) in the molten metal 11, and the reduction is not sufficiently promoted.
[0030]
　Therefore, the present invention has a mechanical stirrer 5 equipped with an impeller 4, the molten metal 11 in the furnace, the iron oxide-containing iron raw material 13 which has not been melted and reduced and the slag 12 having a high FeO concentration, Stir with impeller 4. By arranging the impeller 4 and rotating it in the molten metal 11, as shown by reference numeral F2 in FIG. 3, the slag formed by melting and reducing the iron oxide-containing iron raw material 13 charged into the electric furnace 1 is formed. In addition to the slag in which the iron oxide part which has not been reduced in the raw material is integrated, the iron oxide-containing iron raw material 13 that remains as it is can also be rolled into the hot metal. When the bath depth is shallow as in the electric furnace 1, it is inefficient to wind the slag 12 and the iron oxide-containing iron raw material 13 present on the bath surface into the bath by stirring with the bottom-blown gas, but the impeller 4 stirs the mixture. If so, the efficiency is good because the bath flow F2 can be formed vertically downward by the rotation of the impeller 4.
[0031]
　However, since the impeller 4 is a swirl vane made of a refractory material, if it is installed in a high temperature portion near the upper electrode 2, there is a possibility that melting loss will be severe. Therefore, it is preferable to install it at a position away from the upper electrode 2. Specifically, as described above, in the preferred embodiment of the present invention, as shown in FIGS. 2A and 2B, the shortest line segment connecting the electrode center 16 and the impeller center 17 in plan view. When a straight line 22 orthogonal to the line segment 20 is drawn at a point 21a on the impeller side out of two points (21) that divide the line segment into three equal parts, each center 18 of at least three bottom blowing tuyeres 3 is It is specified that the straight line 22 is drawn so that the straight line 22 can be installed so as to be closer to each upper electrode 2 than the orthogonal straight line 22. Therefore, the position of the impeller 4 is separated from the high temperature region H near the upper electrode 2. By arranging in this way, as shown in FIG. 3, the impeller 4 is separated from the high temperature region H immediately below the upper electrode 2, and the bottom blown gas exists between the high temperature region H and the impeller 4. Therefore, it becomes easy to maintain the life of the impeller 4. Further, it effectively fulfills the role expected of the impeller 4, that is, the slag 12 having a high FeO concentration and the undissolved iron oxide-containing iron raw material 13 flowing out from the area of ​​the polygon 23 are caught in the bath. be able to.
[0032]
　Interfacial area where carbon in the hot metal reacts with iron oxide in the slag 12 by mixing and stirring the hot metal with slag having a high FeO concentration generated by the dissolution of the iron oxide-containing iron raw material 13 at a high temperature portion. And the heat supply from the hot metal is promoted, the reduction of the slag 12 and the like can be promoted.
[0033]
　As described above, in the present embodiment, in the electric furnace 1 for producing the hot metal by supplying the iron oxide-containing iron raw material 13 from above, the slag 12 and the iron oxide are blown by the gas blown from each bottom blowing tuyere 3. It has both bottom-blown stirring that promotes mixing of the iron-containing raw material 13 and the hot metal, and mechanical stirring that causes the slag 12 and the iron oxide-containing iron raw material 13 floating on the hot metal by rotating the impeller 4 to be caught in the hot metal. Therefore, it is possible to dissolve and reduce the iron oxide-containing iron raw material 13 with a high yield.
[0034]
　In the present embodiment, nitrogen gas, argon gas, oxygen-containing gas, or the like can be used as the gas species blown from the bottom blowing tuyere 3. In the case of nitrogen gas or argon gas, the bottom blowing tuyere 3 can be a single tube tuyere. When blowing an oxygen-containing gas, for example, pure oxygen, it is advisable to use a double tube tuyere, to flow the oxygen-containing gas from the inside of the inner tube and to flow the cooling gas from the space between the inner tube and the outer tube. The flow rate of the gas blown from one bottom blowing tuyere 3 may be about 3 to 15 Nm 3 /h per ton of hot metal . If this flow rate is too low, the effect of accelerating dissolution and reduction of the iron oxide-containing iron raw material 13 by bottom blowing will not clearly appear, but if it is too high, the effect will be saturated and the wear rate of the bottom blowing tuyere 3 This is because the deterioration of operations and the frequent occurrence of sloping will not lead to a comprehensive improvement in operations.
[0035]
　The iron oxide-containing iron raw material 13 to be dissolved and reduced in the present embodiment preferably has an iron metallization rate of 45% or more and 95% or less. The metallization ratio (%) of iron means the mass% of metallic iron in the iron oxide-containing iron raw material 13 (mass of metallic iron/total iron content, total mass of iron×100).
[0036]
　In the present embodiment, as described above, after the iron oxide-containing raw material such as iron ore and dust is heated and pre-reduced by the preliminary reduction furnace such as the shaft furnace and the rotary hearth furnace to form the iron oxide-containing iron raw material 13, The present invention relates to an electric furnace 1 which is used when the iron oxide-containing iron raw material 13 is supplied into a furnace and is melted and reduced in the hot metal to produce hot metal. Using the CO gas generated when reducing the raw material using carbon as a reducing agent in a DC arc furnace as a preliminary reducing agent in the preliminary reducing furnace can significantly reduce or eliminate the use of natural gas. This is preferable because a new process that is not directly related to the molten steel manufacturing process such as a gas generation furnace can be made unnecessary.
[0037]
　If the iron metallization ratio of the iron oxide-containing iron raw material 13 produced by preliminary reduction is 45% or more, the entire amount of CO gas generated in the DC arc furnace is used as CO gas for reduction in the preliminary reduction furnace. In addition, it is possible to prevent the reduction of the overall reduction efficiency and suppress the increase of the carbonaceous material consumption rate, and suppress the increase of the required reduction heat in the DC arc furnace to prevent the increase of the electricity consumption rate. .. On the other hand, when reducing mainly CO gas without using natural gas in a preliminary reduction furnace such as a shaft furnace, it is difficult to produce reduced iron with an upper limit of reduction rate of more than 95%. It is preferable that the upper limit of the metallization rate of iron in the iron content 13 is 95%.
[0038]
　The iron oxide in the iron oxide-containing iron raw material 13 is reduced by using carbon contained in the hot metal of the seed bath as a reducing agent. As a result, the carbon concentration in the hot metal of the seed bath is reduced, and it is necessary to supply the carbon source. The iron oxide-containing iron raw material 13 may contain a carbon-containing substance as a reducing agent that contributes to reduction in an arc furnace. Further, the additional carbon source may be supplied separately from the iron oxide-containing iron raw material 13 by introducing a carbon-containing substance into a DC arc furnace.
[0039]
　The iron oxide-containing iron raw material 13 preferably contains a total of 4 to 24 mass% of oxides other than iron oxide. Specific examples of the oxide include CaO, SiO 2 , Al 2 O 3 , and MgO. These oxides are slag components. The slag component in the raw material is not melted because the slag floats on the surface of the hot metal as the melting progresses, and the raw material charged from the furnace is captured by the slag and hinders contact with the hot metal, leading to a decrease in iron yield. Therefore, the upper limit of the slag component in the raw material is set to 24% by mass. On the other hand, the iron oxide-containing iron raw material 13 is used as sinter or pellets in order to heat and pre-reduce the iron oxide-containing iron raw material such as iron ore and dust in a preliminary reduction furnace. For that purpose, it is usual to contain at least 4% by mass of the above-mentioned oxides, so the lower limit of the slag component in the raw material is 4% by mass.
Example
[0040]
　Examples of the present invention will be described below, including comparative examples.
　As the electric furnace 1, the direct current electric furnace shown in FIGS. 1, 2A and 3 was used. The electric furnace 1 has a furnace inner radius of 4 m in a plan view, can accommodate 100 tons of hot metal as the molten metal 11, and has a hollow structure with an outer diameter of 800 mm and an inner diameter of 200 mm. Two upper electrodes 2 are arranged at positions shown in FIGS. 1 and 2A with a space of 2 m.
[0041]
　Each of the three bottom blowing tuyere 3 was a single tube and had an inner diameter of 15 mm, and N 2 gas was blown from each at a rate of 110 Nm 3 /h. The raw material charging port 7 of the charging device 6 is located near the center 9 of the polygon 23 connecting the centers 18 of the tuyere. Further, the impeller 4 of the mechanical stirrer 5 was arranged at the position shown in FIGS. 1 and 2A. The mechanical stirrer 5 has an impeller 4 made of alumina castable as a refractory material. Impeller-4 has four stirring blades, the diameter of the stirring blade is 1.0 m, and the height of the stirring blade is 0.3 m. With the impeller 4 immersed in the hot metal so that the height from the furnace bottom to the bottom surface of the impeller 4 is 50 mm, the center 17 of the impeller 4 is 2 mm from the center of the electric furnace 1 (inner radius 4 m). It was installed at a position of 0.2 m.
[0042]
　The impeller 4 is a point 21a on the impeller 4 side among the two points (21) that divide the shortest line segment 20 into three equal parts in each line connecting the electrode center 16 and the impeller center 17 in plan view. When a straight line 22 orthogonal to the line segment 20 is drawn, at least three tuyere centers 18 are installed so as to be closer to the upper electrode 2 than the orthogonal straight line 22. Therefore, it is possible to stir the slag 12 floating on the hot metal and the undissolved iron oxide-containing iron raw material 13 so as to be caught in the hot metal at a place apart from the high temperature portion near the upper electrode 2.
[0043]
　Using the electric furnace 1 described above, the iron oxide-containing iron raw material 13 was charged into the furnace in which the seed water was present, and the melting and reducing operations were performed.
[0044]
　As the iron oxide-containing iron raw material 13, the iron oxide-containing iron raw material preliminarily reduced in the rotary hearth furnace was used. The composition of the iron oxide-containing iron raw material 13 was as shown in Table 1. The metallization ratio of iron is 65.6%, and the oxide content other than iron oxide is 17.8 mass %.
[0045]
[table 1]

[0046]
　The electric furnace 1 was charged with 50 tons of hot metal hot metal having an average temperature of 1450° C. to 1500° C. and a C concentration of 3.5% to 4.0% by mass, and was placed between two upper electrodes 2. The iron oxide-containing iron raw material 13 having a particle diameter of 1 mm to 50 mm is continuously fed from the raw material charging port 7 at a rate of 2.5 t/min in terms of the amount of hot metal for 20 minutes (50 ton of hot metal) in the high temperature part of the furnace. Then, the solution was supplied by gravity drop and then dissolved and reduced for 40 minutes. The carbon in the hot metal of the seed bath is consumed as the reduction progresses, and the carbon concentration decreases. Therefore, in order to supplement the consumed carbon content, soil graphite as a carbon-containing substance is sequentially charged into the furnace from the hollow portion of the upper electrode 2. did. After 60 minutes from the start of supplying the iron oxide-containing iron raw material 13, 50 ton of hot metal was poured into a pan, and the iron oxide-containing iron raw material 13 was dissolved and reduced by repeating the above work. During the dissolution and reduction operation, slag sampling was performed every 5 minutes to evaluate the FeO concentration in the slag.
[0047]
　For comparison, as an example in which only the stirring conditions are changed, (i) mechanical stirring is not performed, and (ii) bottom blowing is not performed. A description will be given together with the operation results of the present invention in which bottom blowing is performed. In order to explain the effect according to the present invention, the situation of the change in FeO concentration in the slag over time during dissolution and reduction was adopted as an index of iron yield. The results are shown collectively in FIGS. 4, 5, and 6.
[0048]
　In the case of (i) (comparative example: without mechanical stirring), as shown in FIG. 4, when bottom blowing is applied, the rate of increase in FeO concentration in the slag due to dissolution of the iron oxide-containing iron raw material 13 is It was higher than when no blow was applied. However, the reduction rate of the slag after dissolution of the iron oxide-containing iron raw material 13 did not differ significantly between the two conditions. From this, in this example, the iron oxide-containing iron raw material 13 is charged into a high temperature portion immediately below the upper electrode 2 and bottom blowing is applied at that location, whereby the iron oxide-containing iron raw material 13 is rapidly dissolved. I was able to proceed to. Further, it can be said that the reduction of the molten FeO generated by the dissolution also had a reduction promoting effect because the maximum concentration did not change despite the rapid dissolution. The overall effect of this is that since the dissolution could be completed earlier, the subsequent reduction time became longer, and when 60 minutes had passed since the start of the dissolution and reduction operation, the FeO concentration in the slag was relatively adjusted. It had the effect of lowering it.
[0049]
　In the case of (ii) (comparative example: no bottom blowing), as shown in FIG. 5, even when mechanical stirring is applied, the increase rate of the FeO concentration in the slag due to the dissolution of the iron oxide-containing iron raw material 13 is There was no significant difference in the number of rotations as compared with the case where the mechanical stirrer 5 was not provided. However, the reduction rate of the slag after the dissolution of the iron oxide-containing iron raw material 13 increased as the rotation speed increased, and both were higher than when no stirring was applied. From this, in this example, the rotation by the mechanical stirrer 5 is applied so that the slag 12 and the iron oxide-containing iron raw material 13 are entrained in the hot metal by the rotation up to a high temperature portion in the vicinity of just below the upper electrode 2. In some cases, there was no difference in the dissolution rate of the iron oxide-containing iron raw material 13 as compared with the case without it. However, the reduction of the slag containing FeO generated by the dissolution can be rapidly advanced even in a place away from the high temperature part, and at the end of 60 minutes, the FeO concentration in the slag is reduced by the rotation. There was an effect of lowering it depending on the inclusion strength.
[0050]
　In the case of (iii) (example of the present invention: both mechanical stirring and bottom blowing), as shown in FIG. 6, the rising speed of the FeO concentration in the slag 12 due to the dissolution of the iron oxide-containing iron raw material 13 is bottom blowing. As a result, the reduction speed of the slag 12 increased as the rotation speed of the impeller 4 increased. It can be seen that, as compared with the case where neither bottom blowing nor mechanical stirring was applied (□ in the figure), both were high.
[0051]
　Considering the results of the cases (i) and (ii) together, in the bottom blowing in the present invention example, the iron oxide-containing iron raw material 13 floating on the hot metal surface was stirred to form a high-temperature molten metal surface portion directly below the upper electrode 2. The effect of rapidly dissolving the iron oxide-containing iron raw material 13 was exhibited by holding the iron oxide-containing iron raw material 13 as long as possible and stirring it with the hot metal there. At this time, the reduction of FeO generated along with the dissolution was also proceeding, and the maximum concentration of FeO was the same as in the cases of (i) and (ii) above, despite rapid dissolution. Since the time until the FeO concentration reached the maximum was almost the same as in the case of (i) above, it can be said that there was almost no influence of mechanical stirring during this period.
　However, in the mechanical stirring in the example of the present invention, the slag 12 containing FeO derived from the iron oxide-containing iron raw material rapidly dissolved by bottom blowing and the undissolved iron oxide-containing iron raw material 13 were rolled into the hot metal, The effect of promoting contact with carbon and the heat supply of the hot metal was exhibited in the same manner as in the case of (ii) above. Since the decreasing rate of the FeO concentration from the time when the FeO concentration reached the maximum was almost the same as in the case of (ii) above, it can be said that there was almost no influence of the bottom blow during this period.
[0052]
　However, as an effect of using both bottom blowing and mechanical stirring, the iron oxide-containing iron raw material 13 was rapidly dissolved, while the maximum concentration of FeO was equivalent to the case where it took time to dissolve without bottom blowing. Since the reduction rate of FeO from the maximum value of such FeO concentration was high, it can be said that there was an effect of reducing the reached FeO concentration when evaluated in 60 minutes. Further, in the example in which the bottom blowing is performed and the rotation speed of the impeller 4 is set to 50 rpm, the FeO concentration is reduced to 5% or less in 35 minutes, and thus it can be evaluated as an efficiency improving effect.
[0053]
　In a hot metal manufacturing operation using an iron oxide-containing iron raw material in an ordinary DC arc furnace, the FeO concentration in the slag of 10% or less within 40 minutes from the start of the raw material supply is an operation with a very high iron yield. Can be said.
Industrial availability
[0054]
　According to the present invention, it is possible to provide an electric furnace capable of dissolving and reducing an iron oxide-containing iron raw material having a high iron yield, and a method for dissolving and reducing the iron oxide-containing iron raw material using the electric furnace. .. Therefore, the industrial applicability is great.
Explanation of symbols
[0055]
　1 Electric Furnace
　2 Upper Electrode
　3 Bottom Blowing Tubular Mouth
　4 Impeller
　5 Mechanical Stirrer
　6 Feeding Device
　7 Raw Material Feeding Port
　10 Furnace Bottom Electrode
　11 Molten 　Metal
　12 Slag
13 Iron Oxide-Containing Iron Raw Material
　14 Arc
　15 Inner Circumference
　16 Electrode Center (upper Electrode Center)
　17 Center of impeller
　18 Center of tuyere
　20 　Line segment
　21 Point
22 Straight line
　23 Polygon
The scope of the claims
[Claim 1]
An electric furnace 　comprising 　one or more upper electrodes,
　one or more bottom blown tuyere,
a mechanical stirrer having an impeller, and
　a charging device for charging an iron oxide-containing iron raw material
.
[Claim 2]
　It has three or more bottom blowing tuyeres; it has a
　plurality of upper electrodes; in a
　plan view,
　　the shortest line segment among the line segments connecting the center of each upper electrode and the center of the impeller is 3 Of the two equally divided points, when a straight line orthogonal to the line segment is drawn at a point closer to the impeller, the center of
　　at least three or more of the bottom blowing tuyeres of each of the bottom blowing tuyeres Is on the side closer to each of the upper electrodes than the orthogonal straight lines;
The electric furnace according to claim 1, wherein
[Claim 3]
　In the plan view, all the centers of the respective upper electrodes and the raw material feeding port of the charging device have three or more bottom blowing tuyeres located on the side closer to the respective upper electrodes than the orthogonal straight lines.
The electric furnace according to claim 2, wherein the electric furnace is inside a polygon connecting the respective centers .
[Claim 4]
　A method for melting and reducing an iron oxide-containing iron raw material using the electric furnace according to any one of claims 1 to 3,
　wherein a metallization ratio of iron is 45 in the electric furnace in which the molten metal exists. % Or more and 95% or less of the iron oxide-containing iron raw material is charged from the charging device to be melted and reduced, the impeller of the mechanical stirrer is immersed in the molten metal and rotated to thereby obtain a surface of the molten metal. A
method for dissolving and reducing an iron oxide-containing iron raw material, which comprises stirring the slag and the molten metal described in 1.