JP2015196900A - Method for manufacturing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture reduced iron having enhanced separability of reduced iron and a slag, small in the slag content and S content by heating an agglomerate containing an iron oxide-containing material and carbonaceous reductant in a heating furnace and reducing iron oxide in the agglomerate.SOLUTION: There is provided a method for manufacturing reduced iron having FeO amount contained in a slag discharged outside a heating furnace of 2.0 mass% or more and manufacturing reduced iron by heating an agglomerate containing an iron oxide-containing material and carbonaceous reductant in the heating furnace and reducing iron oxide in the agglomerate.

Description

  The present invention heats an agglomerate containing an iron oxide-containing substance such as iron ore or iron-making dust and a carbonaceous reducing agent such as a carbonaceous material in a heating furnace to reduce the iron oxide in the agglomerate. The present invention relates to a method for producing reduced iron.

  High-grade iron ore with low iron and other impurities, such as gangue, has been depleted worldwide. Therefore, there is a demand for a production method for efficiently producing high-quality reduced iron from low-grade iron ore with many impurities and low iron content. Moreover, the iron-making dust discharged | emitted by an iron-making process contains iron oxide, and it is important from the surface of effective utilization of resources to manufacture reduced iron from this.

  As a method of manufacturing reduced iron from iron oxide-containing materials such as iron ore and iron-making dust, pellets obtained by firing the iron oxide-containing material are charged into a shaft furnace, and reduced iron is reduced by reducing gas to produce reduced iron. How to do is known. Moreover, the mixture which mixed the iron oxide containing substance and the carbonaceous reducing agent is agglomerated into pellets and briquettes, and the obtained agglomerates are heated in a heating furnace such as a rotary hearth furnace to produce reduced iron. Methods are also known.

As a method for producing a reduced iron by heating an agglomerate in a heating furnace, for example, techniques of Patent Documents 1 to 3 are known. Among these, Patent Document 1 discloses a method for producing reduced iron comprising a mixture of metallic iron and a slag component by charging an agglomerated material containing an iron oxide raw material and a carbonaceous reducing material into a reduction furnace and reducing the agglomerated material. In forming the agglomerated material, an iron-containing additive containing CaO, SiO ₂ , MgO, Al ₂ O ₃ , MnO is added to the iron oxide raw material, and the slag component in the agglomerated material is added. Slag basicity: (CaO mass% + MgO mass%) / SiO ₂ mass% is controlled to be in the range of more than 0.9, and SiO ₂ and total iron T.I. Relation of content with Fe: SiO ₂ mass% / T. A technique for producing reduced iron by controlling Fe mass% to a range of more than 0.35 and less than 0.6 is disclosed. According to this technique, the generation of iron oxide compounds that reduce the reducibility is suppressed, and the agglomerated product is prevented from melting as a whole, so that reduced iron with high strength and high metalization rate is efficiently used. Can be manufactured well.

  Patent Document 2 was previously proposed by the present applicant, and in this document, in a method of producing metallic iron by heat reduction of a molded product of iron oxide in which a carbonaceous reducing agent is present, A technique for producing and growing metallic iron skin, proceeding reduction until iron oxide is substantially absent inside, and further heating and melting and separating metallic iron and slag to describe the production of metallic iron is described. Yes. According to this technique, high-purity metallic iron having a metallization rate of 95% by weight or more, which cannot be obtained by conventional direct iron making methods, can be efficiently produced by heating and reducing in a very short time.

Patent document 3 is also proposed by the present applicant, and this document includes a process of agglomerating a raw material mixture in which an iron oxide-containing substance and a carbon material are further blended with a melting point regulator. A method for producing a mixture of reduced iron and slag is disclosed which includes a step of heating in such a way that a part of the agglomerate is melted and reducing iron oxide contained in the agglomerate in this order. The melting point adjusting agent contains at least a CaO supply substance, and the amount of the CaO supply substance to be blended in the agglomerate is determined based on the slag basicity [CaO / SiO ₂ obtained from the CaO amount and the SiO ₂ amount in the agglomerate. ₂ ] is adjusted to be 0.2 or more and less than 0.9. According to this production method, a mixture of reduced iron and slag can be obtained at a temperature lower than that of Patent Document 2 and in a short time, and this mixture can be easily converted into reduced iron and slag by, for example, pulverization and magnetic separation. Can be separated.

JP 2012-207241 A Japanese Patent Laid-Open No. 9-256017 JP 2013-127112 A

The reduced iron obtained by the above-described method is put into, for example, an electric furnace and used as an iron source. However, if the reduced iron contains a lot of components that deteriorate the quality of slag such as SiO ₂ , CaO, Al ₂ O ₃ , MgO, and steel materials represented by S, the following problems occur. That is, if the amount of slag contained in the reduced iron is large, the electricity cost for melting the slag in the electric furnace increases. Although it is not generally known how much slag does not cause an increase in electricity bill even if slag is melted in an electric furnace, the reduced iron put into the electric furnace is converted into the reduced iron. Based on the total amount of iron contained (T.Fe) and SiO ₂ and Al ₂ O ₃ , if the slag ratio calculated from the following formula (1) is 5% or less, the increase in the electricity bill is It is not considered a problem. Therefore, it is considered that reducing the slag of the reduced iron to be charged into the electric furnace can be achieved by separating the reduced iron and slag before being charged into the electric furnace and removing the slag. In addition, in following formula (1), [] means content (mass%) of each component in the reduced iron thrown into an electric furnace.
Slag rate (%) = ([SiO ₂ ] + [Al ₂ O ₃ ]) / [T. Fe] × 100 (1)

  Moreover, when there are many component amounts which deteriorate the quality of steel materials, such as S contained in reduced iron, the quantity of reduced iron which can be thrown into an electric furnace will be restrict | limited. This is because when the S concentration of molten steel obtained by melting in an electric furnace is high, the quality of the steel product finally obtained deteriorates. Therefore, it is desirable to reduce the amount of S contained in the reduced iron to be charged into the electric furnace as much as possible. Since S has a property that a certain amount is taken into the slag, if the reduced iron and slag are separated before being put into the electric furnace, the amount of S contained in the reduced iron put into the electric furnace can be reduced. It is done.

  However, the technique of Patent Document 1 does not focus on improving the separation between reduced iron and slag. In the technique of the above-mentioned Patent Document 2, since the slag is melted in the furnace, it is necessary to increase the heating temperature, and the fuel consumption of the heating furnace is poor. In the manufacturing method disclosed in Patent Document 3, a secondary material cost is increased because a melting point regulator is blended. In addition, since the melting point modifier becomes slag after heating, when the amount of slag produced increases, disposal costs such as landfilling increase and the burden on the environment also increases.

  The present invention has been made paying attention to the circumstances as described above, and the purpose thereof is to heat an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent in a heating furnace, and in the agglomerate. In producing reduced iron by reducing the iron oxide, it is intended to improve the separability between reduced iron and slag, to produce reduced iron with low slag content and low S content.

  The method for producing reduced iron according to the present invention that has solved the above-mentioned problems includes heating an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent in a heating furnace, and iron oxide in the agglomerate. This is a method for producing reduced iron by reducing the amount of FeO contained in the slag discharged out of the heating furnace to 2.0% by mass or more.

  The atmosphere in the heating furnace is preferably an oxidizing gas atmosphere. The mixture containing reduced iron and slag obtained by heating is preferably pulverized and then separated into reduced iron and slag.

  According to the present invention, when producing reduced iron by reducing iron oxide, the amount of FeO contained in the slag discharged to the outside of the heating furnace is controlled to 2.0% by mass or more. The reduced iron can be produced with reduced slag content and low S content.

1, the CO ₂ occupying the atmospheric gas in the furnace proportion to the relationship between the slag rate in magnetically attached material, and the CO ₂ occupying the atmospheric gas in the furnace ratio and the FeO content in the non-magnetically attracted material It is a graph which shows a relationship. FIG. 2 is a graph showing the amount of S contained in the magnetically attached material and the non-magnetically attached material when the amount of S contained in each specimen is 100%. FIG. 3 is a graph showing the relationship between the amount of slag contained in the briquette and the slag rate of the magnetic deposit. FIG. 4 is a graph showing the relationship between the basicity of briquettes and the slag rate of magnetic deposits. FIG. 5 is a schematic diagram for explaining an operation process in an actual machine.

  The inventors heated an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent in a heating furnace, and reduced iron oxide in the agglomerate to produce reduced iron. Research has been conducted with the aim of improving the separability from slag, producing reduced iron with low slag content and low S content. As a result, if the amount of FeO contained in the slag discharged to the outside of the heating furnace is controlled to 2.0% by mass or more, the melting point of the slag in the heating furnace can be lowered, so that the reduced iron and slag are separated. As a result, it has been found that reduced iron with a low slag content and a low S content can be produced by improving the separability and improving the separation between reduced iron and slag.

  First, features of the present invention will be described.

  The method for producing reduced iron according to the present invention is characterized in that the amount of FeO contained in the slag discharged out of the heating furnace is 2.0% by mass or more. That is, when an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent is heated in a heating furnace, the iron oxide in the agglomerate is reduced to produce reduced iron, and at this time, slag is by-produced. If FeO remains in the slag, the amount of reduced iron produced decreases, so the yield of reduced iron decreases and the productivity is thought to deteriorate. However, as a result of various studies by the present inventors, if the amount of FeO contained in the slag is 2.0% by mass or more, the melting point of the slag is lowered, so that the separation between reduced iron and slag is improved in the heating furnace. It was revealed that high-quality reduced iron can be produced with low slag content. The amount of FeO contained in the slag is preferably 2.5% by mass or more, and more preferably 3.0% by mass or more. The upper limit of the amount of FeO contained in the slag is not particularly limited. However, when the amount of FeO is excessively large, the yield of reduced iron is reduced. Therefore, the amount of FeO is preferably 15% by mass or less, more preferably 10% by mass. % Or less, more preferably 8% by mass or less.

  It has also been found that the atmosphere in the heating furnace may be an oxidizing gas atmosphere in order to make the amount of FeO contained in the slag 2.0% by mass or more. That is, considering that the agglomerate is heated in a heating furnace and iron oxide in the agglomerate is reduced to produce reduced iron, the atmosphere in the heating furnace may be a reducing gas atmosphere. Recommended. However, in the present invention, part of the reduced iron is intentionally oxidized by making the atmosphere in the heating furnace an oxidizing gas atmosphere. This is because by allowing FeO generated by oxidation to remain in the slag, the melting point of the slag is lowered and the separability of reduced iron and slag is improved. Although the yield of reduced iron is slightly reduced by deliberately oxidizing a portion of the reduced iron, the heating temperature in the heating furnace can be lowered than before by lowering the melting point of the slag. Can be improved. In addition, according to the present invention, since it is not necessary to add a melting point modifier such as CaO in order to lower the melting point of slag, it is possible to reduce the cost of auxiliary materials and increase the amount of slag by adding a melting point modifier. Slag disposal costs can also be reduced.

  According to the present invention, since the separation between reduced iron and slag is good, the mixture containing reduced iron and slag discharged from the heating furnace is easily separated into reduced iron and slag by pulverizing with impact. it can. Therefore, reduced iron with a low slag content can be produced by separating using a sieve or a magnetic separator after pulverization. Since the obtained reduced iron has a low slag content, the amount of S is also reduced.

  In the above, the characteristic part of this invention was demonstrated.

  Next, the manufacturing method of reduced iron is demonstrated. In the method for producing reduced iron according to the present invention, an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent is heated in a heating furnace, and the iron oxide in the agglomerate is reduced to produce reduced iron. Is. As described above, the present invention is characterized in that the amount of FeO contained in the slag discharged out of the heating furnace is 2.0 mass% or more. Since the characteristic part of the present invention has already been described in detail, a process of agglomerating a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent to produce an agglomerate (hereinafter sometimes referred to as an agglomeration process). ) And the agglomerate obtained in the agglomeration step is charged on the hearth of a heating furnace and heated to reduce iron oxide in the agglomerate to produce reduced iron ( Hereinafter, the heating process may be described.

[Agglomeration process]
In the agglomeration step, a mixture containing the iron oxide-containing substance and the carbonaceous reducing agent is agglomerated to produce an agglomerate.

  As the iron oxide-containing substance, specifically, iron oxide sources such as iron ore, iron sand, iron-making dust, non-ferrous refining residue, and iron-making waste can be used. As the iron ore, in addition to high-grade iron ore used in the blast furnace method and converter method, low-grade iron ore containing a large amount of gangue may be used. As the iron-making dust, for example, electric furnace dust can be used. The electric furnace dust is known to have a high slag content and S content among ironmaking dusts.

  As the carbonaceous reducing agent, a reducing agent containing carbon can be used, and examples thereof include coal and coke.

  You may mix | blend a binder with the said mixture further. As the binder, for example, polysaccharides can be used. As said polysaccharide, starches, such as corn starch and wheat flour, etc. can be used, for example.

  You may mix | blend a melting | fusing point regulator with the said mixture further as needed. That is, it is recommended not to use the melting point adjusting agent as much as possible because it increases the amount of slag and increases the cost, but it may be blended to further lower the melting point of the slag. The melting point adjusting agent means a substance having an action of lowering the melting point of gangue in the iron oxide-containing substance and ash in the carbonaceous reducing agent. That is, by adding a melting point modifier to the above mixture, the melting point of components (particularly gangue) other than iron oxide contained in the agglomerate is affected, and for example, the melting point can be lowered. As a result, melting of the gangue is promoted and a molten slag is formed. At this time, a part of the iron oxide is dissolved in the molten slag and reduced in the molten slag. The reduced iron produced in the molten slag is agglomerated as solid reduced iron by coming into contact with the reduced iron reduced in the solid state.

As the melting point adjusting agent, for example, CaO supply material, MgO supply material, Al ₂ O ₃ supply material, SiO ₂ supply material, fluorite (CaF ₂ ), and the like can be used. As said CaO supply substance, for example, at least one selected from the group consisting of CaO (quick lime), Ca (OH) ₂ (slaked lime), CaCO ₃ (limestone), and CaMg (CO ₃ ) ₂ (dolomite) is used. be able to. As the MgO feed materials, for example, MgO powder, Mg-containing material to be extracted, such as from natural ore or seawater, may be blended at least one selected from the group consisting of MgCO _3. Examples of the Al ₂ O ₃ supply substance include Al ₂ O ₃ powder, bauxite, boehmite, gibbsite, and diaspore. As the SiO ₂ supply substance, for example, SiO ₂ powder or silica sand can be used.

  The iron oxide-containing substance, the carbonaceous reducing agent, and the melting point adjusting agent are preferably pulverized in advance before mixing. For example, the iron oxide-containing substance may be pulverized so that the average particle diameter is 10 to 60 μm, the carbonaceous reducing agent is average particle diameter is 10 to 60 μm, and the melting point adjuster is average particle diameter is 5 to 90 μm. Recommended.

  The means for pulverizing is not particularly limited, and known means can be employed. For example, a vibration mill, a roll crusher, a ball mill, or the like can be used.

  What is necessary is just to mix the iron oxide containing substance etc. which were mentioned above using the mixer of a rotation container type, or a mixer of a fixed container type. Examples of the rotating container type mixer include, but are not limited to, a rotating cylindrical shape, a double cone shape, and a V shape. Examples of the fixed container type mixer include, but are not limited to, a mixer in which a rotary vane such as a basket is provided in a mixing tank.

Next, the mixture obtained by the mixer is agglomerated to produce an agglomerate. As said agglomerate, 270 kg / (ton-Fe) or more may be sufficient as the amount of slag computed by following formula (2). The amount of slag means the mass (kg) of slag produced when 1 ton of reduced iron is produced. According to the present invention, since the separability of reduced iron and slag becomes good, even if the slag amount is an agglomerate of 270 kg / (ton-Fe) or more, the slag content is small and the S amount is also reduced. High quality reduced iron can be manufactured. The amount of reduced iron slag may be, for example, 300 kg / (ton-Fe) or more, or 400 kg / (ton-Fe) or more. Although the upper limit of the amount of slag of reduced iron is not specifically limited, For example, it is 700 kg / (ton-Fe) or less.
Slag amount [kg / (ton-Fe)] = ([SiO ₂ ] + [Al ₂ O ₃ ] + [CaO] + [MgO]) / [T. Fe] × 1000 (2)

  The shape of the agglomerate is not particularly limited, and may be, for example, a pellet shape or a briquette shape. The size of the agglomerate is not particularly limited, but the particle size is preferably 50 mm or less. If the particle size of the agglomerate is excessively increased, the granulation efficiency is deteriorated. Moreover, when the agglomerate becomes too large, heat transfer to the lower part of the agglomerate becomes worse and productivity is lowered. In addition, the lower limit of the particle size of the agglomerate is about 5 mm.

  Examples of the agglomerating machine for agglomerating the mixture include, for example, a dish granulator (disk granulator), a cylindrical granulator (drum granulator), a twin roll briquette molding machine, and an extruder. Etc. can be used.

[Heating process]
In the heating step, the agglomerate obtained in the agglomeration step is charged on the hearth of the heating furnace and heated, whereby iron oxide in the agglomerate is reduced to produce reduced iron.

  Examples of the heating furnace include an electric furnace and a moving hearth furnace. The moving hearth furnace is a heating furnace in which the hearth moves in the furnace like a belt conveyor, and examples thereof include a rotary hearth furnace and a tunnel furnace. In the rotary hearth furnace, the outer shape of the hearth is designed in a circular shape or a donut shape so that the start point and the end point of the hearth are in the same position. The iron oxide contained in the agglomerate charged on the hearth is heated and reduced during one round of the furnace to produce reduced iron. Therefore, the rotary hearth furnace is provided with charging means for charging the agglomerate into the furnace on the most upstream side in the rotation direction, and with discharging means on the most downstream side in the rotation direction. Since the hearth of the rotary hearth furnace has a rotating structure, the most downstream side in the rotation direction is actually the upstream side of the charging means. The tunnel furnace is a heating furnace in which the hearth moves in the furnace in a linear direction.

The atmosphere in the heating furnace is preferably an oxidizing gas atmosphere. The oxidizing gas atmosphere may be an atmosphere containing an oxidizing gas such as oxygen gas or CO ₂ gas. The ratio of the oxidizing gas in the whole atmosphere gas is, in volume%, for example, preferably 25% or more, more preferably 45% or more, and further preferably 50% or more. The atmospheric gas may be 100% by volume of oxidizing gas.

  In order to change the atmosphere in the heating furnace to an oxidizing gas atmosphere, a method of adjusting the composition of the fuel gas so that the burning gas of the burner contains an oxidizing gas, or adjusting the combustion conditions of the burner, heating furnace A method of adjusting the composition of the combustion gas generated by the oxidizing gas supplied to burn the combustible gas existing in the inside, and the oxidizing gas generated in the heating furnace by the air leaking from the outside to the inside of the heating furnace Examples thereof include a method for controlling the composition.

  The agglomerate may be charged on the hearth, heated and reduced, and the heating temperature is preferably 1350 to 1500 ° C. When the heating temperature is lower than 1350 ° C., reduced iron and slag are difficult to melt, and high productivity may not be obtained. Therefore, the heating temperature is preferably 1350 ° C. or higher, more preferably 1400 ° C. or higher. However, when the heating temperature exceeds 1500 ° C., the fuel consumption is deteriorated and the cost is increased. Further, since the exhaust gas temperature becomes high, the exhaust gas treatment facility becomes large and the equipment cost increases. Therefore, the heating temperature is preferably 1500 ° C. or lower, more preferably 1480 ° C. or lower.

  Prior to charging the agglomerate into the heating furnace, it is desirable to lay a floor covering material to protect the hearth. As the floor covering material, in addition to those exemplified as the carbonaceous reducing agent, for example, refractory particles such as refractory ceramics can be used. The upper limit of the particle size of the flooring material is preferably 3 mm or less, for example, so that an agglomerate or a melt thereof does not sink. The lower limit of the particle size of the flooring material is preferably, for example, 0.5 mm or more so that the flooring material is not blown away by the combustion gas of the burner.

[Others]
What is necessary is just to isolate | separate the mixture containing the reduced iron and slag obtained at the said heating process into reduced iron and slag, after grind | pulverizing.

  The means for pulverizing is not particularly limited, and a known pulverizer can be employed. For example, a pulverizer such as a vibration mill, a roll crusher, a disk mill, a ball mill, a hammer mill, a rod mill, or a roller mill can be used. Among these, a vibration mill, a roll crusher, a disk mill, a ball mill, a hammer mill, and a rod mill are devices that perform impact pulverization, and a roller mill is a device that performs extrusion pulverization.

  In the present invention, an apparatus that performs impact pulverization may be used, or an apparatus that performs extrusion pulverization may be used. However, when operating at a high temperature, it is preferable to use an apparatus that performs impact pulverization.

  What is necessary is just to isolate | separate the pulverized material obtained by grind | pulverizing into reduced iron, the slag produced | generated at the time of reduction | restoration of iron oxide, and flooring materials using a magnetic separator, a sieve, etc., for example. When separated using a magnetic separator, the magnetized material is mainly reduced iron, and the non-magnetized material is mainly slag or floor covering produced during the reduction of iron oxide.

  The reduced iron obtained by the recovery can be used as an iron source in an electric furnace, and can also be used as an iron source in, for example, a blast furnace and a converter.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and may be implemented with modifications within a range that can meet the above and the gist described below. Of course, these are all possible and are included in the technical scope of the present invention.

  The agglomerate was heated in a heating furnace, and iron oxide in the agglomerate was reduced to produce reduced iron. At this time, in Experiment 1 below, the influence of the component composition of the atmospheric gas in the heating furnace on the amount of FeO contained in the slag discharged outside the heating furnace and the influence on the separability of reduced iron and slag were examined. . Moreover, the influence which grinding | pulverization and magnetic separation have on the amount of S contained in a magnetized material and a non-magnetized material was examined with respect to the mixture of reduced iron and slag obtained in the heating furnace. In Experiment 2 below, the amount of slag contained in the briquette and the basicity were adjusted, and the influence of these factors on the separability of reduced iron and slag was examined. In Experiment 3 below, an operation process using an actual machine was described.

[Experiment 1]
The agglomerate containing the iron oxide-containing substance and the carbonaceous reducing agent was heated in a heating furnace, and reduced iron was produced by reducing the iron oxide in the agglomerate. As the iron oxide-containing substance, electric furnace dusts A and B having the composition shown in Table 1 below were used. Electric furnace dusts A and B are two lots of electric furnace dust with different operating conditions. As the carbonaceous reducing agent, a carbon material having a component composition shown in Table 2 below was used. An organic binder was further mixed with the electric furnace dust and the carbonaceous material at a blending ratio shown in Table 3 below.

The obtained mixed powder was supplied to a briquetter to produce a briquette. As a result of analyzing the component composition of the obtained briquette, the slag amount calculated by the above formula (2) is 495-531 kg / (ton-Fe), and the basicity calculated by the following formula (3) is 0. .92 to 0.95. In following formula (3), [] means content (mass%) of each component contained in a briquette.
Basicity = [CaO] / [SiO ₂ ] (3)

Next, the obtained briquette was charged into a heating furnace heated to 1400 ° C. and heated for the time shown in Table 4 below to produce reduced iron. The atmosphere in the heating furnace is such that the mixing ratio of CO ₂ gas and N ₂ gas is volume%, CO ₂ gas: N ₂ gas = 0%: 100%, 20%: 80%, 40%: 60%, Adjustments were made to be either 60%: 40%, 75%: 25%, or 100%: 0%. Table 4 below shows the atmospheric gas composition in the heating furnace.

Next, the obtained reduced iron was pulverized with a disk mill for 10 seconds and then magnetically separated to separate into a magnetic material and a non-magnetic material. The magnetic separation was repeated by adjusting the magnetic force at the sample position between 200 gauss and 500 gauss. The component composition of the magnetically and non-magnetically obtained materials obtained by magnetic separation was measured. As for the magnetic deposit, the T.I. Fe content, SiO ₂ content was measured amount of Al ₂ O _3. As a result, the magnetic deposit was mainly reduced iron. Table 4 below shows T.V. The amount of Fe is shown. In addition, T.I. Fe content, SiO ₂ amount, and based on the amount of Al ₂ O _3, was calculated slag ratio by the above formula (1). The results are shown in Table 4 below. The slag rate was acceptable when it was 6.5% or less, and rejected when it exceeded 6.5%. The threshold value of 6.5% was set on the assumption that reduced iron was put into an electric furnace and used as an iron source.

  On the other hand, the non-magnetized material is mainly slag, and the amount of FeO contained in the non-magnetized material was measured. The measurement results are shown in Table 4 below.

From Table 4 below, it can be considered as follows. No. 1, 3, and 4 are examples that do not satisfy the requirements defined in the present invention. When the amount of CO ₂ contained in the atmospheric gas in the heating furnace is 0 to 20% by volume, the amount of FeO contained in the non-magnetized product cannot be made 2.0% by mass or more. As a result, even if the briquette is heated for 11 to 15 minutes in the heating furnace, the slag rate contained in the magnetic deposit cannot be suppressed to 6.5% or less.

On the other hand, no. 2, 5 to 8 are examples that satisfy the requirements defined in the present invention. When the amount of CO ₂ contained in the atmospheric gas in the heating furnace is adjusted to exceed 20% by volume, the amount of FeO contained in the non-magnetized product can be set to 2.0% by mass or more. As a result, the slag rate contained in the magnetic deposit can be suppressed to 6.5% or less.

Next, in FIG. 1, including the relationship between the slag rate in proportion and magnetically attached of CO ₂ occupying the atmospheric gas in the furnace ◆, and on the proportion and the non-magnetically attached of CO ₂ occupying the atmospheric gas in the furnace The relationship with the amount of FeO is indicated by □.

The following can be considered from FIG. It can be seen that when the ratio of CO ₂ to the atmospheric gas in the heating furnace is in the range of 0% by volume to 30% by volume, the slag rate in the magnetic deposit decreases in proportion to the increase in the amount of CO ₂ . It can also be seen that there is a positive correlation between the proportion of CO ₂ in the atmospheric gas in the heating furnace and the amount of FeO contained in the non-magnetized material. As the ratio of CO ₂ increases, the slag rate decreases because the increase in the ratio of CO ₂ decreases the melting point of slag produced as a by-product during the reduction of iron oxide, and the reduced iron and slag. This is thought to be due to the improved separability.

Next, the influence of pulverization and magnetic separation on the amount of S contained in magnetic and non-magnetic deposits was examined. The briquettes obtained with the formulation b shown in Table 3 above were charged into a heating furnace heated to 1400 ° C. and heated for 13 minutes to produce reduced iron. The atmosphere in the heating furnace was adjusted so that the mixing ratio of CO ₂ gas and N ₂ gas was volume%, and CO ₂ gas: N ₂ gas = 0%: 100%.

  The obtained reduced iron was used as test material 1, this was not crushed, component analysis was performed, and the S content was measured.

  A specimen 2 (corresponding to No. 4 in Table 4 above) was obtained by grinding the specimen 1 for 10 seconds with a disk mill. The sample material 2 was magnetically selected manually using a magnet, the components of the collected magnetic and non-magnetized materials were analyzed, and the S content was measured.

Further, reduced iron is manufactured by adjusting the atmosphere in the heating furnace so that the mixing ratio of CO ₂ gas and N ₂ gas is volume% and CO ₂ gas: N ₂ gas = 40%: 60%. did. The obtained reduced iron was pulverized with a disk mill for 10 seconds to give a specimen 3 (corresponding to No. 5 in Table 4 above). The sample material 3 was magnetically selected manually using a magnet, the components of the collected magnetic and non-magnetized materials were analyzed, and the S content was measured.

Further, reduced iron is manufactured by adjusting the atmosphere in the heating furnace so that the mixing ratio of CO ₂ gas and N ₂ gas is volume% and CO ₂ gas: N ₂ gas = 60%: 40%. did. The obtained reduced iron was pulverized with a disk mill for 10 seconds to be a test material 4 (corresponding to No. 6 in Table 4 above). The sample material 4 was magnetically selected manually using a magnet, the components of the collected magnetic deposits and non-magnetic deposits were analyzed, and the S content was measured.

  FIG. 2 shows the amount of S contained in the magnetically attached material and the non-magnetically attached material when the amount of S contained in each test material is 100%. In addition, since the specimen 1 was not pulverized and separated by magnetic separation, the S content was 100%.

It can be considered as follows from FIG. Since the test material 1 does not grind and magnetically separate the obtained reduced iron, all S remains in the test material 1. On the other hand, as shown in the test materials 2 to 4, it was found that the amount of S contained in the magnetic deposit can be reduced to about half that of the test material 1 by pulverizing and separating the obtained reduced iron. Thereby, the quantity of the reduced iron which can be thrown into an electric furnace can be increased. Specimen 2 is an example in which briquettes are heated in an N ₂ gas atmosphere to produce reduced iron, and specimens 3 and 4 are briquettes in a mixed atmosphere of CO ₂ gas and N ₂ gas. It is the example which heated and grind | pulverized what manufactured reduced iron. Specimen 2 is No. in Table 4 above. As shown in FIG. 4, despite the high slag rate of the magnetic deposit, the amount of S in the magnetic deposit was almost equal to that of the test materials 3 and 4.

In general, increasing the amount of CO ₂ gas in the atmosphere during heating is known to change the S partition ratio in the gangue component and iron, reducing the proportion of the S amount taken into the gangue component. ing. Therefore, the amount of S contained in the magnetic article obtained by magnetic separation of the specimen 2 is approximately the same as the amount of S contained in the magnetic article obtained by magnetic separation of the specimens 3 and 4. This is probably because there was much S remaining in the gangue component. Thus, by heating the briquette in a CO ₂ gas atmosphere, the S concentration in iron slightly increases, but the separability of the slag is increased accordingly, so that the S amount of the magnetized material becomes equal.

[Experiment 2]
As shown in Experiment 1, when electric furnace dust, carbonaceous material, and organic binder were mixed, the amount of slag contained in the briquette was 495-531 kg / (ton-Fe), and the basicity was 0.92-0. .95. In actual operation, the amount of slag contained in the briquette may increase or decrease depending on the composition of the raw material, or the basicity may vary due to changes in the amount of CaO and SiO ₂ contained in the briquette. Moreover, when the amount of slag increases, aggregation of reduced iron will be inhibited and it is thought that the separability of reduced iron and slag worsens. Moreover, since the melting point of slag changes when the basicity varies, it is considered that the separability between reduced iron and slag is affected.

  Therefore, in Experiment 2, limestone was added to the mixed powder, the amount of slag and basicity contained in the briquette were adjusted, and the influence of these factors on the separability of reduced iron and slag was examined.

Similarly to Experiment 1, after adding an organic binder to the electric furnace dust and charcoal, limestone (main component is CaCO ₃ ) was further mixed to produce a briquette. The component composition of limestone is shown in Table 5 below. In addition, LOI shown in the following Table 5 has shown the ignition loss (ignition loss).

  Table 6 below shows the mixing ratio of each component.

  Further, the amount of slag contained in the briquette and the basicity of the briquette were calculated in the same procedure as in the experiment 1. The calculation results are shown in Table 6 below.

Next, the obtained briquette was charged in a heating furnace heated to 1400 ° C. and heated for 13 minutes to produce reduced iron. The atmosphere in the heating furnace was adjusted so that the mixing ratio of CO ₂ gas and N ₂ gas was volume% and CO ₂ gas: N ₂ gas = 75%: 25%. As a comparative example, reduced iron was manufactured by heating the atmosphere in the heating furnace to 100% by volume of N ₂ gas.

  Next, the obtained reduced iron was pulverized under the same conditions as in Experiment 1 above, magnetically separated, and separated into magnetized and non-magnetized articles. The component composition of the magnetic deposit obtained by magnetic separation was measured, and the slag ratio of the magnetic deposit was calculated in the same manner as in Experiment 1 above. The calculation results are shown in Table 7 below. On the other hand, the non-magnetized material is mainly slag, and the amount of FeO contained in the non-magnetized material was measured. The measurement results are shown in Table 7 below.

FIG. 3 shows the relationship between the amount of slag contained in the briquette and the slag rate of the magnetic deposit. In FIG. 3, ◆ shows the result when the briquette is heated in a mixed atmosphere of CO ₂ gas and N ₂ gas, and ■ shows the result when the briquette is heated in an N ₂ gas atmosphere.

The following can be considered from FIG. When the briquette is heated in a mixed atmosphere of CO ₂ gas and N ₂ gas, the slag rate of the magnetic deposit is substantially constant and is not more than 6.5% even if the amount of slag contained in the briquette increases. I understand that. On the other hand, when the briquette is heated in an N ₂ gas atmosphere, the slag rate of the magnetic deposit becomes higher than 6.5%, and it can be seen that the separability between reduced iron and slag is poor.

Next, FIG. 4 shows the relationship between the basicity of briquettes and the slag rate of magnetic deposits. In FIG. 4, ♦ shows the result when the briquette is heated in a mixed atmosphere of CO ₂ gas and N ₂ gas, and ■ shows the result when the briquette is heated in an N ₂ gas atmosphere.

It can be considered as follows from FIG. When the briquette is heated in a mixed atmosphere of CO ₂ gas and N ₂ gas, the slag rate of the magnetic deposit may be substantially constant and may be 6.5% or less even if the basicity of the briquette varies. I understand. On the other hand, when the briquette is heated in an N ₂ gas atmosphere, the slag rate of the magnetic deposit becomes higher than 6.5%, and it can be seen that the separability between reduced iron and slag is poor.

  From the above results, if the briquette is heated and the amount of FeO contained in the slag discharged out of the heating furnace is 2.0% by mass or more, the amount of slag contained in the briquette increases or the basicity of the briquette Even if it fluctuates, it can be seen that the slag rate of the magnetic deposit can be reduced to 6.5% or less and the quality of the product can be improved.

[Experiment 3]
In Experiment 1 and Experiment 2, tests were performed using laboratory-level equipment. In Experiment 3, an operation process using an actual machine will be described.

  FIG. 5 is a schematic diagram for explaining an operation process in an actual machine. In FIG. 5, 1 is a rotary hearth furnace, 2 is a floor covering placed on the hearth, 3 is an agglomerate, 4 is a discharger (discharger), 5 is a cooler, 6 is a sieve, 7 and 8 are Each shows a magnetic separator. In addition, the rotary hearth furnace 1 has shown the expanded view developed along the rotation direction of the hearth.

  The agglomerate 3 charged on the hearth of the rotary hearth furnace 1 is heated by heat from a combustion burner (not shown) provided in the rotary hearth furnace 1 to cause a reduction reaction. At this time, the heat reduction is performed in an atmosphere in which the amount of FeO contained in the slag is 2.0% by mass or more so that the melting point of the slag by-produced during the reduction of the iron oxide is lowered. The gas composition of the atmosphere in the rotary hearth furnace 1 is the combustion gas generated by the combustion gas of the burner, the oxidizing gas supplied to burn the combustible gas existing in the rotary hearth furnace 1, the rotary hearth What is necessary is just to adjust by controlling the oxidizing gas etc. which are produced | generated by the air which leaks into the furnace 1. FIG.

  An object to be treated containing reduced iron obtained by heating while moving in the rotary hearth furnace 1 is discharged out of the furnace by the discharger 4. The object to be processed discharged outside the furnace is cooled by the cooler 5 and then classified into coarse particles # 1 and fine particles # 4 using the sieve 6. Coarse grain material # 1 may be magnetically separated by magnetic separator 7 and separated into magnetic material # 3 and non-magnetic material # 2. The magnetic deposit # 3 is mainly reduced iron, and the non-magnetic deposit # 2 is mainly slag. On the other hand, the fine particle # 4 may be magnetically separated by the magnetic separator 8 and separated into the magnetic material # 6 and the non-magnetic material # 5. The magnetized article # 6 is mainly reduced iron, and the non-magnetized article # 5 is mainly a floor covering. Coarse grain material # 1 may be pulverized by a pulverizer (not shown) before magnetic separation by the magnetic separator 7. Fine particle # 4 may be pulverized by a pulverizer (not shown) before magnetic separation by the magnetic separator 8. Further, instead of the magnetic separator 7 and the magnetic separator 8, a sieve may be used.

DESCRIPTION OF SYMBOLS 1 Rotary hearth furnace 2 Floor covering material 3 Agglomerate 4 Discharge machine 5 Cooler 6 Sieve 7 and 8 Magnetic separator

Claims (3)

In a method for producing reduced iron by heating an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent in a heating furnace and reducing the iron oxide in the agglomerate,
The method for producing reduced iron, wherein the amount of FeO contained in the slag discharged to the outside of the heating furnace is 2.0 mass% or more.   The manufacturing method according to claim 1, wherein the atmosphere in the heating furnace is an oxidizing gas atmosphere.   The manufacturing method of Claim 1 or 2 which isolate | separates into the reduced iron and slag, after grind | pulverizing the mixture containing the reduced iron and slag obtained by heating.