JP5103915B2 - Method for producing reduced metal - Google Patents

Description

  The present invention relates to a method for producing a metal-containing material such as reduced iron by charging a metal-containing raw material such as iron ore into a mobile hearth furnace and then heating and reducing it while moving it and melting it at least once. .

  One method for producing crude steel is to use an electric furnace. This method is a technique in which a raw material is heated by electric energy, melted, and further refined in some cases to obtain a desired steel. In addition, this method mainly uses scrap as a raw material. However, in recent years, since the supply and demand of the scrap has deteriorated, the use of reduced iron instead of scrap has been studied.

  The reduced iron is produced, for example, by a method as disclosed in Patent Document 1. In this method, iron ore and a solid reducing agent are mainly loaded on a hearth (moving bed) that moves horizontally in a mobile hearth furnace, and raw materials such as iron ore are radiated from above. Is heated, reduced, and further, the reduced product produced on the moving bed is melted to produce reduced iron, which is also called a moving hearth furnace method.

  The moving hearth furnace used in this method is a furnace that heats and reduces raw materials in the process of moving the hearth (moving bed) arranged in the moving hearth furnace in the horizontal direction. The moving bed is usually in the form of rotation as shown in FIG. 1 and is therefore also called a rotary hearth furnace.

  For example, as shown in FIG. 1, a typical moving hearth furnace includes a heating furnace body 10 of an annular heating furnace divided into a pre-tropical zone 10a, a reduction zone 10b, a melting zone 10c, and a cooling zone 10d. A moving floor 11 that continuously moves while rotating is provided. And this furnace is loaded with the mixed raw material 12 which consists of iron ore (carbon material interior pellets may be used) and a solid reducing agent, and is heated and reduced on the moving bed 11, and then, It is designed to melt at least once. Such a movable floor 11 is usually surrounded by a furnace body 10 lined with a refractory, but as disclosed in Patent Document 1, in order to protect the hearth refractory, separate from the mixed raw material layer. In some cases, a layer of carbon material is provided as a floor covering. In addition, a burner 13 is disposed on the upper portion of the furnace body 10, and iron ore and the like on the moving bed 11 are reduced using the burner 13 as a heat source. In FIG. 1, 14 is a charging device for charging the raw material onto the moving bed 11, and 15 is a discharging device for discharging the reduced product. In addition, the atmospheric temperature in the furnace body 10 is normally adjusted to about 1300 ° C. in the reduction zone, but is controlled to a temperature around 1500 ° C. in the melting zone.

  Iron-containing materials, such as iron ore, usually contain many gangue components, depending on their origin. In addition, ash and the like are also contained in coal, coal char, and coke, which are representative examples of solid reducing agents. Therefore, in the moving hearth furnace method in which only the reduction operation is performed, there is a problem that gangue and ash in the reducing agent are inevitably mixed in the reduced iron as a product. However, in the case of the mobile hearth furnace method, as disclosed in Patent Document 1, since the raw material after reduction is once melted, slag that is a gangue can be easily separated from the metal. . However, this alone does not improve the productivity of reduced iron.

Japanese Patent Laid-Open No. 11-172121

  As described above, the conventional technology lacks the viewpoint of improving productivity due to its development trend, and on the other hand, the demand for reduced iron is increasing greatly, and a solution is required. In addition, even when the reduced iron is melted in an electric furnace, etc., it is possible to improve the efficiency of melting, contribute to the reduction of power consumption, and ensure a highly economical operation. Establishment is required.

  Accordingly, an object of the present invention is to obtain a reduced metal that is excellent in productivity and easy to use in a refining furnace such as an electric furnace when a reduced metal is produced using a mobile hearth furnace.

  In order to solve the above-described problems of the prior art, the inventors have attempted to improve the quality and productivity of the reduced metal while studying the conditions under which the reduction product is separated into metal and slag. In order to facilitate the separation of these, the inventors develop the present invention with the knowledge that the important point is how to increase the carbon concentration in the reduced metal, especially reduced iron. I reached.

That is, the means according to the present invention is that a flooring material is first loaded on a moving floor of a mobile hearth furnace, and a mixed raw material containing a metal-containing material, a solid reducing agent, and a slagging material is powdered thereon. Alternatively, a method of producing reduced metal by charging after agglomeration and heating and reducing while moving in the furnace to produce a reduced product, and then melting and separating slag. in the amount of binding interdendritic distance Lc as a solid reducing agent to be blended into the mixed raw material is 4.24～4.62Mass% or more of carbonaceous material 18Å relative to the content of iron in the mixed raw material A method for producing a reduced metal characterized by mixing is proposed.

  Here, the intercrystal distance Lc is measured by the X-ray diffraction method and is defined by the Scherrer equation described in the reference (Metallurgical and materials transaction B: 31B (2000), P215). In general, the larger the inter-crystal distance Lc, the more graphitized.

In the present invention, the carbonaceous material for the mixed raw material is mixed in an amount corresponding to 2 mass% or more , particularly 4.24 to 4.62 mass% of the iron content in the mixed raw material, and the inter-crystal distance Lc is 18 %. in a Mochiiruko the carbonaceous material is higher, it is desirable that the graphite or petroleum coke.

  As the metal-containing material, one kind or a mixture of two or more kinds of ores such as iron ore, metal-containing dust such as iron-making dust, or metal-containing sludge such as iron-making sludge is used.

As the solid reducing agent, in addition to graphite, a carbon material such as coal, coal char, or petroleum coke such as pitch coke and oil coke is used. This carbon material is also an intercrystal distance determined by an X-ray diffraction method. Lc is a carbonaceous material greater graphite structure than 18 Å, using mixed low carbonaceous material degree of graphitization, such as coal.

As the ironmaking material, any one or two or more mineral substances selected from CaO, MgO and Na ₂ O, for example, limestone, desulfurized slag, converter slag, dolomite, serpentine or fluorite Among these, one kind or a mixture of two or more kinds is used.

  According to the present invention, a high-quality (high carbon concentration) reduced metal can be efficiently produced by a mobile hearth furnace, and the carbon concentration in the reduced metal can be increased. As a result, the melting point of the reduced metal decreases, and melting in a refining furnace such as an electric furnace becomes easy (improvement of melting efficiency). In the case of reduced metal produced by applying the present invention, the carbon of the reduced metal can be used as a fuel at the time of melting in the operation of an oxygen blown converter or electric furnace in recent years. This will lead to a reduction in the basic unit, making it possible to operate the furnace more economically.

  The following description describes an example of producing reduced iron as a reduced metal. However, the present invention is effective not only for the production of reduced iron exemplified below but also for the production technology of other metal materials.

  First, an experiment that triggered the development of the present invention will be described. In this experiment, the inventors first charged a mixed raw material composed of iron ore, coke, limestone, etc. into a graphite crucible installed in a vertical furnace instead of a mobile hearth furnace, The state of the mixed raw material in the crucible was observed while supplying heat simulating the in-furnace temperature pattern of the hearth furnace. And it stopped in the middle of temperature rising, and the composition analysis of the product in that time was performed.

  As a result, the iron ore in the mixed raw material first reacts with the carbonaceous material mixed in the mixed raw material, and at least a part is reduced to FeO and Fe, and then melts to produce FeO-based slag. To do. At this time, in addition to the direct reduction by the carbonaceous material in the furnace, the CO gas generated at this time also undergoes a reduction reaction. By these reactions, a reduced product is obtained from the mixed raw material, and molten metal and molten slag are separated and produced from the reduced product.

  The FeO concentration in the molten slag thus produced is in a high state of about 30 mass% when the molten slag and the molten metal are separated. Therefore, the molten slag and the molten metal are easily wetted with each other, and the molten slag at this time is considered to be in a “completely wet” state that completely covers the entire surface of the molten metal (droplet). . Therefore, it has been found that when these solidify as they are, the metal and the slag remain in a strongly adhered state and are difficult to separate easily.

  When the reduction of FeO in the molten slag further progresses and the FeO concentration in the molten slag decreases to about 10 mass% or less, the wettability between the molten metal and the molten slag gradually deteriorates and the contact angle also increases. The molten slag begins to slide off the surface of the molten metal. And the adhesive force of both falls and both come to isolate | separate easily after cooling.

  From the above, in order to efficiently separate the molten metal from the molten slag, by promoting the reduction of FeO, the FeO concentration in the molten slag is reduced to about 10 mass% or less as fast as possible, and the metal grains and slag grains are separated. It turned out that it was important to make it easy to peel off each other.

  To confirm this, the inventors continued further experiments on the reduction behavior of FeO in molten slag. In general, FeO in molten slag is reduced at the interface between the slag and the metal by reducing the FeO in the molten slag by carbon dissolved in the molten metal or by CO gas generated by the reduction reaction. It is known to go by. Therefore, in order to promote the reduction of FeO in the molten slag, measures such as increasing the supply rate of carbon in the metal that becomes the reducing agent (solid carbon or CO gas) in contact with the FeO in the molten slag are effective. It is thought that it becomes.

  Therefore, in the present invention, as a means for increasing the supply rate of the reducing agent, a solid reducing agent contained in the mixed raw material, that is, a carbonaceous material was examined. As a result, it has been determined that a preferable carbon material condition is that a carbon material having a graphite structure with an intercrystal distance Lc measured by X-ray diffraction method larger than 18 mm is mixed and used at least partially. It was. By using such a carbon material, in the present invention, a sufficient carbon component can be supplied into the solid metal generated in the initial stage of the reaction, and the melting of the solid iron occurs at a low temperature. It is considered that diffusion of carbon in the metal is promoted even in a short initial stage, the supply rate of molten carbon as a reducing agent is increased, and separation of the molten metal and molten slag is promoted.

  That is, when the carbon material is used as a solid reducing agent, the solid metal that is a molten reduction product comes into contact with surrounding graphite, carburization occurs due to diffusion in the solid metal, and the internal carbon concentration is 2 When the amount exceeds 0.1 mass%, a liquid phase is generated to form liquid metallic iron, and flow occurs to dramatically increase the diffusion rate of carbon, thereby promoting the supply of the reducing agent. Incidentally, such an effect produces the same effect even when the mixed raw material is agglomerated.

  The carbon supplied into the molten metal by such a reaction (carburization) reduces the FeO concentration in the slag, causes a decrease in wettability, and induces separation of the molten metal and the molten slag. That is, rapid carburization into the molten metal and promoting the reduction reaction of FeO facilitates the separation of the molten metal and the molten slag, thereby enabling a process suitable for the purpose of the present invention to improve productivity. It is. This also leads to an increase in the carbon concentration in the reduced iron. That is, the carbon in the metallic iron is consumed by the reduction reaction, but the amount of carbon supplied by the carburization reaction overcomes this, resulting in an increase in the carbon concentration of the reduced iron.

  The carburization rate (K) of the reducing agent (carbon) into the metal is described in the reference (Metallurgical and materials transaction volume 31B February (2000), P215-216) as shown in FIG. It is reported as a relationship between Lc and carburization rate. According to the report, it can be seen that the higher the degree of graphitization and the greater the inter-crystal distance Lc, the greater the rate of carburization reaction, especially for carbonaceous materials of 18 mm or more. Therefore, in order to promote the carburization reaction to the molten metal, it is advantageous to use a carbon material that is at least partially graphitized and has a large inter-crystal distance Lc as the carbon material. Through this promotion, productivity can be improved.

Incidentally, the amount of the corresponding carbonaceous material 2mass% or more relative to the content of iron content in the mixed raw material (metal), is preferably a 4.24～4.62Mass% as described in Table 3 of Example . The reason for the 2 mass% / metal is that, according to the iron-carbon phase diagram, if this amount is equal to the liquid-phase generated carbon concentration and a liquid phase can be generated in the metal, carbon atoms in the metal liquid phase This is because it is considered that the diffusion of slag increases dramatically.

  Moreover, only the thing with a large distance between crystals (Lc) may be used for the carbonaceous material to mix | blend. The amount of carbon material is blended so that the amount of carbon in the carbon material is about 1.2 times the amount of oxygen to be reduced (oxygen bonded to the metal oxide) in the powder raw material. This is the upper limit of the amount of carbonaceous material.

  The inventors conducted a test operation in an actual plant to confirm the above facts. This test operation was carried out by using a rotary hearth furnace 1 as shown in FIG. 1 as a mobile hearth furnace, iron ore having the composition shown in Table 1, carbonaceous materials having chemical composition as shown in Table 2, and limestone as a slagging agent. Were blended in the proportions shown in Table 3. Then, the mixed raw material 2 shown in Table 3 is charged and deposited on the floor covering 3 loaded on the moving bed 11 in the furnace, and the moving bed 11 is set so that the maximum furnace temperature becomes 1500 ° C. Moved to produce reduced iron and slag. The rotary hearth furnace is a heating furnace having a furnace center diameter of 7 m and a hearth width of 1 m. Table 4 shows the specifications of this furnace.

  FIG. 3 shows the productivity of each example in comparison. Productivity is indicated by the amount of granular iron produced per day in the unit hearth area of a mobile hearth furnace. Table 5 shows the C concentration in the granular iron produced under each example. As shown in this figure, productivity was improved by blending graphite under conditions suitable for the present invention. It has also been found that the carbon concentration in the granular iron is higher in the method adapted to the example of the present invention.

  As can be understood from the above description, according to the present invention, carbon contained in metal particles (granular iron) can be used as fuel by blowing oxygen at the time of melting. In this case, there is an effect of reducing the basic unit of electric power. As a result, the market value of granular iron can be increased, and the effect of improving the economic efficiency of the method according to the present invention can be expected.

  The present invention proposes a technique for efficiently producing reduced metal, particularly reduced iron (high productivity) by a mobile hearth furnace, but also as a method for producing reduced metal other than iron. Applicable.

It is a conceptual diagram of a mobile hearth furnace. It is a graph which shows the relationship between the distance between crystals and the carburization reaction rate. It is a productivity comparative graph in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotary hearth furnace 2 Mixed raw material 3 Floor covering material 10 Furnace 10a Pre-tropical zone 10b Reduction zone 10c Melting zone 10d Cooling zone 11 Moving bed 12 Mixed raw material 13 Burner 14 Charger 15 Discharger

Claims (3)

First, the flooring material is loaded on the moving floor of the mobile hearth furnace, and then the mixed raw material containing the metal-containing material, the solid reducing agent and the faux material is powdered or agglomerated and then charged. In the method of producing a reduced metal by heating and reducing while moving the inside of the moving bed to produce a reduced product, and then separating the slag by melting, the solid blended in the mixed raw material the reduced metal to formation interdendritic distance Lc as a reducing agent is characterized by mixing an amount of a 4.24～4.62Mass% or more of carbonaceous material 18Å relative to the content of iron in the mixed raw material Production method.   The method for producing a reduced metal according to claim 1, wherein the carbon material is graphite, coal, coal char, or petroleum coke. The method for producing a reduced metal according to claim 1 or 2, wherein the iron making material is any one or two or more mineral substances selected from CaO, MgO, and Na ₂ O. .

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