JP2015101740A - Method for manufacturing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a reduced iron having a less slag content, comprising: heating an agglomerate including an iron oxide containing material, a carbonaceous reducing agent and a melting point control agent to reduce iron oxide in the agglomerate; heating the iron oxide to melt a part of the reduced iron; aggregating the reduced iron to obtain reduced iron containing a sintered body; pulverizing the obtained reduced iron containing the sintered body; and separating the resultant material into the reduced iron and slag to manufacture the reduced iron.SOLUTION: The method for manufacturing reduced iron includes controlling the blending amount of a carbonaceous reducing agent on the basis of the amount of slag (kg/ton) calculated by the following formula (1) on the basis of the total amount of iron (the T.Fe amount) and amounts of CaO, SiO, AlOand MgO included in an agglomerate. The amount of slag is equal to 1000×[(CaO)+(SiO)+(alO)+(MgO)]/(T.Fe) ... (1)

Description

  The present invention includes an iron oxide source such as iron ore and iron oxide (hereinafter sometimes referred to as “iron oxide-containing substance”), a reducing agent containing carbon (hereinafter also referred to as “carbonaceous reducing agent”), And an agglomerate containing a melting point adjusting agent is heated, and iron oxide in the agglomerate is reduced to produce reduced iron (also referred to as DRI).

  A direct iron making method is known as an iron making process for producing reduced iron using an iron oxide-containing material as a raw material. As the direct iron manufacturing method, the MIDREX method is known, and this MIDREX method uses a large amount of natural gas as a reducing agent for reducing iron oxide. Therefore, there has been a problem that the location conditions of the plant are limited to the natural gas production region.

Therefore, a direct iron manufacturing method using a carbonaceous reducing agent such as coal that is relatively easy to obtain instead of natural gas as a reducing agent has been studied. In this direct iron manufacturing method, an agglomerate obtained by agglomerating a mixture containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point adjusting agent is transferred to a mobile hearth furnace (for example, a rotary hearth furnace). It is a method for producing reduced iron by charging the agglomerate by gas heat transfer or radiant heat by a heating burner provided in the furnace, and reducing the iron oxide contained in the agglomerate with a carbonaceous reducing agent. is there. This direct iron manufacturing method uses a carbonaceous reducing agent such as coal, which is relatively easy to obtain as a reducing agent, and also has the advantage that powdered iron oxide-containing materials can be used as they are, as well as iron oxide-containing materials and carbon. Since the quality reducing agent is arranged close to the agglomerate, there is an advantage that it can be reduced at high speed in a short time and an advantage that the amount of carbon contained in the reduced iron obtained as a product can be adjusted. However, the reduced iron obtained as a product contains gangue (eg, SiO ₂ , Al ₂ O ₃ , MgO, etc.) contained in the iron oxide-containing substance or carbonaceous reducing agent used as a raw material as slag. The iron grade of reduced iron tends to be low. Therefore, when putting the reduced iron obtained as a product into practical use, it is necessary to charge the reduced iron into, for example, an electric furnace and separate and remove the slag. However, when the amount of slag contained in the reduced iron increases, the yield at the time of refining is reduced, so that it is required to produce reduced iron with high iron quality and low slag content.

  As a method of reducing the amount of slag contained in reduced iron, it is conceivable to use an iron oxide-containing substance having a high iron quality as a raw material. However, the range of available iron oxide-containing materials is narrow.

  As a solution to such a problem, Patent Document 1 proposes a method for producing a carbonaceous material-containing iron oxide agglomerate in order to obtain reduced iron with high iron quality. In this method, reduced iron skin (shell part) is generated and grown by heat reduction, and the reduction is continued until iron oxide is substantially absent in the interior (core part), and the generated slag composed of gangue is formed inside. In addition, the reduced iron is agglomerated and the reduced iron and slag are melted and separated (this method is sometimes called the ITmk3 method). However, even if this method is used, when the gangue in the iron ore used as a raw material is extremely large, it becomes difficult to melt and separate reduced iron and slag. For this reason, iron ore containing an extremely large amount of gangue exists all over the world, but what is effective as its utilization technology is not well known at present.

  Examples of a method for producing reduced iron using iron ore containing a large amount of gangue include, for example, a sintered body in which reduced iron and slag are finely mixed without reducing iron and slag being completely melted and separated. It is conceivable to produce reduced iron with high iron purity by mechanically pulverizing and separating this sintered body using the difference in hardness between reduced iron and slag. For example, in Patent Document 2, reduced iron obtained by heat reduction treatment in a high-temperature atmosphere is pulverized, and then subjected to particle size selection with a predetermined particle size as a boundary, and reduced iron particles having a predetermined particle size or less. On the other hand, a technique for separating reduced magnetic force and recovering reduced iron is disclosed.

Japanese Patent Laid-Open No. 9-256017 JP 2002-363624 A

  According to the technique disclosed in Patent Document 2, iron ore containing a lot of gangue can be used compared to the process proposed in Patent Document 1, and the heating temperature can be set low. Since it is not necessary to carburize and melt the reduced iron, the amount of reducing agent used can be reduced. However, in the technique disclosed in Patent Document 2, in order to grow reduced iron in the inside (core part) of the reduced iron shell (shell part), the gangue is melted as slag early, and the reduced iron is moved. It is necessary to make it easy and to aggregate. However, in general, when iron ore containing a large amount of gangue is used, the distance between the reduced irons is increased, so that the reduced irons are less likely to agglomerate and grow less easily. If the reduced iron is not aggregated, the separability from the slag is deteriorated.

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to heat an agglomerate containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point regulator, and Reduce the iron oxide inside, further heat to melt a part of the reduced iron, aggregate the reduced iron to obtain a reduced iron-containing sintered body, pulverize the obtained reduced iron-containing sintered body, and reduce the reduced iron In producing reduced iron by separating it into slag, it is to provide a method capable of producing reduced iron with a low slag content.

The method for producing reduced iron according to the present invention that has solved the above-mentioned problems is to agglomerate a mixture containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point regulator, and move the obtained agglomerate. The iron oxide in the agglomerate is reduced by charging the hearth of the type hearth furnace and heating, further heating to melt a part of the reduced iron, and agglomerating the reduced iron to reduce the reduced iron In the case of producing reduced iron containing sinter, the obtained reduced iron-containing sintered body is pulverized and separated into reduced iron and slag.
Slag amount (kg / kg) calculated by the following formula (1) based on the total iron amount (T.Fe amount), CaO amount, SiO ₂ amount, Al ₂ O ₃ amount, and MgO amount contained in the agglomerate Ton), the point is that the blending amount of the carbonaceous reducing agent is adjusted. In the following formula (1), () means the amount (% by mass) of each component contained in the agglomerate.
Slag amount = 1000 × [(CaO) + (SiO ₂ ) + (Al ₂ O ₃ ) + (MgO)] / (T.Fe) (1)

When the mass of the agglomerate is 100%, the value obtained by dividing the amount of oxygen in the iron oxide-containing material contained in the agglomerate by the amount of fixed carbon contained in the agglomerate (oxygen amount / fixed) The amount of carbonaceous reducing agent is adjusted so that the amount of carbon) and the amount of slag contained in the agglomerate satisfy the relationship of the following formula (2), and the agglomerate is 1350: It is preferable to heat at a temperature of ° C or higher.
−1.66 × slag amount + 506.6 × oxygen amount / fixed carbon amount + 108.9 ≧ 200 (2)

  When the amount of the slag contained in the agglomerate is 400 kg / ton or more and the mass of the agglomerate is 100%, the amount of oxygen in the iron oxide-containing substance contained in the agglomerate is Adjusting the blending amount of the carbonaceous reducing agent so that the value (oxygen amount / fixed carbon amount) divided by the amount of fixed carbon contained in the agglomerate is in the range of 1.60 to 2.00; and It is also recommended that the agglomerate be heated above 1350 ° C.

  According to the present invention, based on the amount of slag contained in the agglomerate, the amount of carbonaceous reducing agent blended in the agglomerate is adjusted. Specifically, the mass of the agglomerate is 100%. When the amount of oxygen in the iron oxide-containing material contained in the agglomerate is divided by the amount of fixed carbon contained in the agglomerate (oxygen amount / fixed carbon amount), and contained in the agglomerate Since the amount of carbonaceous reducing agent blended in the agglomerate is adjusted so that the amount of slag satisfies a predetermined relationship, melting of slag can be promoted, and aggregation and growth of reduced iron can be accelerated. As a result, since the separability between reduced iron and slag can be improved, reduced iron with a low slag content can be produced.

FIG. 1 is a drawing-substituting photograph in which a cross section of the reduced iron-containing sintered body obtained in the example is photographed. FIG. 2 is a graph showing the relationship between the value on the left side of Equation (2) and the 50% volume particle size of the reduced iron produced in the core part. FIG. 3 is a graph showing the relationship between the 50% volume particle size of the reduced iron produced in the core part and the slag content (residual slag ratio) contained in the reduced iron.

  The present inventors heat an agglomerate containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point modifier, reduce the iron oxide in the agglomerate, and further heat to a part of the reduced iron. When the reduced iron-containing sintered body is crushed and separated into reduced iron and slag to produce reduced iron, the reduced iron content is aggregated. We have intensively studied to produce a small amount of reduced iron. As a result, based on the amount of slag contained in the agglomerate, the amount of carbonaceous reducing agent to be blended in the agglomerate may be adjusted. Specifically, when the mass of the agglomerate is 100% A value obtained by dividing the amount of oxygen in the iron oxide-containing material contained in the agglomerated material by the amount of fixed carbon contained in the agglomerated material (oxygen amount / fixed carbon amount), and slag contained in the agglomerated material The inventors have found that the amount of carbonaceous reducing agent to be blended in the agglomerate may be adjusted so that the amount satisfies a predetermined relationship, and the present invention has been completed.

  That is, in the present invention, a mixture containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point modifier is agglomerated, and the obtained agglomerate is charged on the hearth of a mobile hearth furnace and heated. Thus, the iron oxide in the agglomerate is reduced, further heated to melt a part of the reduced iron, and the reduced iron is aggregated to form a reduced iron-containing sintered body. This reduced iron-containing sintered body is formed by integrating reduced iron and slag, etc., and is composed of an outer shell (shell portion) and an inner portion (core portion) enclosed in the outer shell. There is a gap between the part and the core part.

  Since the agglomerate is heated by heat transfer from the outside, the iron oxide existing outside the agglomerate is preferentially reduced. As a result, an outer shell (shell portion) made of reduced iron is formed outside the agglomerate. On the other hand, as the heating proceeds, the inside of the agglomerate is heated by transferring heat through the outer shell. Even inside the outer shell, the reduction of iron oxide proceeds to form a core portion in which reduced iron and slag are mixed. Thus, the reduced iron containing sintered compact is comprised by the outer shell (shell part) and the inside (core part), and the outer shell and the inside are comprised by reduced iron and slag. Since reduced iron and slag have a hardness difference, when the reduced iron-containing sintered body is pulverized, it can be relatively easily separated into reduced iron and slag.

  However, when the amount of slag produced inside the agglomerate increases, it may be difficult to separate reduced iron and slag, and only reduced iron with a high slag content may be obtained.

Therefore, in the present invention, the total iron amount (T.Fe amount), CaO amount, SiO ₂ amount, Al ₂ O ₃ amount, and MgO amount contained in the agglomerate are calculated by the following formula (1). Based on the amount of slag (kg / ton), the amount of carbonaceous reducing agent to be blended in the agglomerate is adjusted. Accordingly, among the reduced iron-containing sintered bodies, in particular, it is possible to improve the separability when pulverizing and separating the reduced iron and slag generated in the core portion, and thus it is possible to produce reduced iron with a low slag content. . In the following formula (1), () means the amount (% by mass) of each component contained in the agglomerate.
Slag amount = 1000 × [(CaO) + (SiO ₂ ) + (Al ₂ O ₃ ) + (MgO)] / (T.Fe) (1)

Of the components contained in the agglomerate, the above formula (1) is the total amount (unit: kg) of CaO, SiO ₂ , Al ₂ O ₃ and MgO that can be slag, and T. It shows the relationship with Fe (unit is ton). The smaller the amount of slag represented by the above formula (1), the higher the quality of the agglomerate. The larger the amount of slag, the lower the amount. It means that it is a quality agglomerate.

  And based on the said slag amount, the separability of reduced iron and slag is improved by adjusting the amount of carbonaceous reducing agent mix | blended with the said agglomerate so that the reduced iron produced | generated in a core part may grow. be able to. That is, the greater the amount of slag, the greater the distance between the reduced irons, making it difficult for the reduced irons to grow.

  Therefore, in the present invention, in order to quickly melt the slag, the amount of the carbonaceous reducing agent blended in the agglomerate is adjusted.

As a specific method for producing reduced iron using an agglomerate in which the amount of carbonaceous reducing agent blended in the agglomerate is adjusted based on the slag amount, for example, the mass of the agglomerate is 100. %, The amount of oxygen in the iron oxide-containing material contained in the agglomerate divided by the amount of fixed carbon contained in the agglomerate (oxygen amount / fixed carbon amount), and the agglomeration A method of adjusting the blending amount of the carbonaceous reducing agent and heating the agglomerate at 1350 ° C. or higher so that the amount of slag contained in the product satisfies the relationship of the following formula (2). It is done.
−1.66 × slag amount + 506.6 × oxygen amount / fixed carbon amount + 108.9 ≧ 200 (2)

  The amount of oxygen in the iron oxide-containing material contained in the agglomerate can be calculated by the following procedure.

First, the total iron (T.Fe) and FeO amounts in the agglomerate are determined by chemical analysis. Next, T.W. Among Fe, Fe does not exist as FeO assumes that exist as all Fe ₂ O _3, by the following formula (i), the mass of Fe ₂ O ₃ contained in the agglomerates (W _{Fe2 O3)} Is calculated. In the following formula (i), W _x represents the mass (mass%) of component X, M _x represents the molecular weight of component X, M _Fe is the molecular weight of Fe, 55.85, and M _FeO is the molecular weight of FeO. 71.85, M _Fe2O3 is 159.7 in terms of molecular weight of Fe ₂ O ₃ .

Next, based on the following formula (ii), the amount of oxygen in the iron oxide-containing substance contained in the agglomerate is calculated as the sum of the amount of oxygen contained in Fe ₂ O ₃ and the amount of oxygen contained in FeO. . Wherein, M _{Fe2 O3} is 159.7 in molecular weight of Fe _{2 O 3,} M O is a 16 molecular weight of oxygen.

The value obtained by dividing the amount of oxygen in the iron oxide-containing substance contained in the agglomerated material by the amount of fixed carbon contained in the agglomerated material (oxygen amount / fixed carbon amount) determines the blending amount of the carbonaceous reducing agent. It becomes an index for. That is, iron contained in iron ore, which is a representative iron oxide-containing substance, exists in iron ore as iron oxides such as Fe ₂ O ₃ and Fe ₃ O ₄ (collectively referred to as FeO _x ). ing. On the other hand, as the carbonaceous reducing agent, coal can be suitably used, and the carbon contained in this coal is not lost as volatile matter when heated, but also remains after heating. The remaining carbon is generally called fixed carbon. Volatile carbon contributes little to the reduction of iron oxide, whereas fixed carbon contributes to the reduction of iron oxide. Therefore, the higher the content of fixed carbon, the better the quality of the coal. For this reason, the value obtained by dividing the amount of oxygen in the iron oxide-containing material contained in the agglomerate by the amount of fixed carbon contained in the agglomerate (oxygen amount / fixed carbon amount) is relative to the amount of oxygen to be reduced. It shows how much fixed carbon is present, the smaller this value, the more fixed carbon is present for the reduction of iron oxide, and the higher this value, the more iron oxide. This means that the fixed carbon is in short supply.

  The above formula (2) is derived by the present inventors repeatedly conducting various experiments. When the amount of slag contained in the agglomerate is large, the amount of the carbonaceous reducing agent blended in the agglomerate is calculated. It is derived based on the knowledge that it is thought that it should be reduced. The process of deriving equation (2) will be described.

First, by carrying out multiple regression with the 50% volume particle size of reduced iron produced in the core determined by experiment as a dependent variable, and the value of oxygen amount / fixed carbon amount and slag amount as independent variables, (Iii) was obtained.
−1.66 × slag amount + 506.6 × oxygen amount / fixed carbon amount + 108.9 (iii)

  The 50% volume particle size of reduced iron is used as an index representing the particle size of reduced iron produced in the core part. This is because when the cross section of the reduced iron-containing sintered body is observed, the reduced iron is arranged in order from the smallest particle size in an arbitrary region in the core portion, and the volume of the reduced iron is accumulated. It means the particle size when it becomes 50% with respect to the volume of the total reduced iron observed inside. The procedure for calculating the 50% volume particle size of reduced iron will be described in the Examples section.

  The above formula (iii) is a formula for predicting the 50% volume particle diameter of reduced iron produced in the core part from the value of oxygen amount / fixed carbon amount and the amount of slag, and the value of formula (iii) When a graph is created with the 50% volume particle size of reduced iron produced in the axis and core portions as the vertical axis, a good correlation is recognized as shown in FIG. In FIG. 2, the horizontal axis is expressed as “the value of the left side of equation (2)”, but the left side of equation (2) and the above equation (iii) are the same.

  By the way, when the present inventors conducted a basic experiment in advance, as demonstrated in the section of the examples described later, if the 50% volume particle size of the reduced iron produced in the core part is 200 μm or more, the reduced iron It has been found that the slag content contained in can be reduced to 10% by mass or less. The standard for setting the slag content in the reduced iron to 10% by mass or less is that the slag content in the reduced iron required when used as an iron source in a blast furnace or the like is 10% by mass or less. Because. As shown in FIG. 3 showing the relationship between the 50% volume particle size of reduced iron produced in the core part and the slag content (residual slag ratio) contained in the reduced iron, reduced iron produced in the core part. It can be seen that if the 50% volume particle size is 200 μm or more, the slag content contained in the reduced iron can be reduced to 10 mass% or less.

Therefore, in the present invention, in order to obtain conditions for setting the 50% volume particle size of the reduced iron produced in the core part to 200 μm or more, it is considered effective to optimize the blending amount of the carbonaceous reducing agent. The inequality of (2) was derived.
−1.66 × slag amount + 506.6 × oxygen amount / fixed carbon amount + 108.9 ≧ 200 (2)

  The amount of slag contained in the agglomerate may be 400 kg / ton or more.

  As a specific method for producing reduced iron using an agglomerate in which the amount of carbonaceous reducing agent to be blended in the agglomerate is adjusted based on the slag amount, for example, the above-mentioned agglomerate contained in the agglomerate When the amount of slag is 400 kg / ton or more and the mass of the agglomerate is 100%, the amount of oxygen in the iron oxide-containing material contained in the agglomerate is determined as the fixed carbon contained in the agglomerate. The blending amount of the carbonaceous reducing agent is adjusted so that the value (oxygen amount / fixed carbon amount) divided by the amount is in the range of 1.60 to 2.00, and the agglomerate is 1350 ° C. or higher. The method of heating with is also mentioned.

  In this method, the amount of the slag contained in the agglomerate is 400 kg / ton or more. Thus, when a reduced iron-containing sintered body containing reduced iron and slag is manufactured under conditions where the amount of slag is large, the separability of reduced iron and slag usually deteriorates, and reduced iron with a low slag content is manufactured. It is difficult. However, according to the present invention, even if the amount of slag is 400 kg / ton or more, the blending amount of the carbonaceous reducing agent is adjusted so that the value of the oxygen amount / fixed carbon amount falls within the above range. If the composition is heated at 1350 ° C. or higher, reduced iron with a low slag content can be produced.

  That is, if the blending amount of the carbonaceous reducing agent is adjusted so that the value of oxygen amount / fixed carbon amount is 1.60 or more, the 50% volume particle size of reduced iron produced in the core part is 200 μm or more. Therefore, the separability of reduced iron and slag is improved when pulverized and separated. As a result, reduced iron with a low slag content can be produced. The value of oxygen amount / fixed carbon amount is more preferably 1.70 or more. However, if the value of oxygen amount / fixed carbon amount exceeds 2.00, the amount of fixed carbon becomes insufficient and the oxygen amount becomes excessive, so that the reduction of iron oxide does not proceed and the yield of reduced iron decreases. Therefore, the value of oxygen amount / fixed carbon amount is preferably 2.00 or less, more preferably 1.90 or less.

  The adjustment of the blending amount of the carbonaceous reducing agent that is a feature of the present invention has been described above.

  Next, the manufacturing method of the reduced iron which concerns on this invention is demonstrated.

The method for producing reduced iron according to the present invention includes:
A process of agglomerating a mixture containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point modifier (hereinafter, sometimes referred to as an agglomeration process);
A step of reducing the iron oxide in the agglomerate by charging the obtained agglomerate on the hearth of the mobile hearth furnace and heating, and further heating to melt a part of the reduced iron (Hereinafter sometimes referred to as a heating step)
It includes a step of aggregating reduced iron to form a reduced iron-containing sintered body, pulverizing the obtained reduced iron-containing sintered body, and separating it into reduced iron and slag (hereinafter sometimes referred to as a pulverizing and separating step). Yes, as described above, the amount of the carbonaceous reducing agent is adjusted based on the amount of slag contained in the agglomerate. Since the method of adjusting the blending amount of the carbonaceous reducing agent has been described in detail above, other parts will be described below.

[Agglomeration process]
In the agglomeration step, an agglomerate is produced by agglomerating a mixture containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point modifier.

  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 carbonaceous reducing agent, a reducing agent containing carbon, for example, coal or coke can be used.

  The mixture containing the iron oxide-containing substance and the carbonaceous reducing agent needs to further contain a melting point adjusting agent.

  The melting point modifier means a substance having an action of lowering the melting point of gangue in the iron oxide source or 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.

  You may further mix | blend a binder etc. with said mixture as components other than an iron oxide containing substance, a carbonaceous reducing agent, and a melting | fusing point regulator. Examples of the binder include polysaccharides (for example, starch such as corn starch and wheat flour).

  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 the iron oxide-containing material or the like 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, a V shape and the like. Examples of the fixed container type mixer include, but are not limited to, a mixer in which rotating blades (for example, a basket) are provided in a mixing tank.

  Next, the mixture obtained by the mixer is agglomerated to produce an agglomerate. 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 (maximum 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 mobile hearth furnace and heated to reduce iron oxide in the agglomerate and further heat. Then, reduced iron is produced by melting a part of the reduced iron.

  The mobile hearth furnace for heating the agglomerate 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.

  The rotary hearth furnace is designed to have a circular (donut-shaped) hearth appearance so that the start point and end point of the hearth are in the same position, and is included in the agglomerate charged on the hearth The iron oxide produced is reduced by heating while making a round in 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 the most downstream side in the rotation direction (because of the rotating structure, The discharge means is provided on the upstream side of the input means. The tunnel furnace is a heating furnace in which the hearth moves in the furnace in a linear direction.

  In the present invention, only a part of the reduced iron is melted, and not all is melted. If all of the reduced iron is melted, the separation between the reduced iron and the slag becomes worse.

  The agglomerate is preferably heated at 1350 ° C. or higher and reduced by heating. 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 exhaust gas temperature becomes high, so that 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 agglomerated material into the mobile hearth 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, refractory particles (for example, refractory ceramics) can be used.

  The particle size of the flooring material is preferably 3 mm or less so that an agglomerate or a melt thereof does not sink. The lower limit of the particle size of the floor covering is preferably 0.5 mm or more so as not to be blown off by the burner combustion gas.

[Crushing separation process]
In the pulverization and separation step, the reduced iron obtained in the heating step is agglomerated to obtain a reduced iron-containing sintered body, and the obtained reduced iron-containing sintered body is pulverized and separated into reduced iron and slag. to recover.

  The means for pulverizing the reduced iron-containing sintered body is not particularly limited, and known means can be employed, for example, pulverization using a vibration mill, roll crusher, disk mill, ball mill, hammer mill, rod mill, roller mill or the like. That's fine. 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.

  The pulverized product obtained by pulverization may be separated into a magnetized product and a non-magnetized product using a magnetic separator or the like, and the magnetized product may be recovered as reduced iron. The non-magnetized material is slag produced as a by-product during the production of reduced iron or a floor covering material.

  According to the present invention, reduced iron having a 50% volume particle size of 200 μm or more can be recovered, and the residual slag ratio contained in the reduced iron is 10% or less (particularly 5% or less).

Residual slag ratio is meant the ratio of the amount of SiO ₂ and the amount of Al ₂ O ₃ contained in the reduced iron can be calculated by the following formula (iv).
Residual slag ratio (%) = 100 × [(SiO ₂ ) + (Al ₂ O ₃ )] / (T.Fe) (iv)

  In the above formula (iv), () means the content (% by mass) of each component contained in the reduced iron. T. T. et al. Fe means total iron.

The gangue includes CaO and MgO in addition to SiO ₂ and Al ₂ O ₃ , which form slag. In the present invention, the amount of SiO ₂ and Al ₂ O ₃ remaining in the reduced iron Based on this, the residual slag rate was calculated. This is because CaO can be used as a source of CaO to be added as a refining agent in, for example, a blast furnace or a converter, and thus is considered a useful component, and MgO has a low content.

  The reduced iron recovered in the pulverization and separation step can be used as an iron source in, for example, a blast furnace, a converter, an electric furnace, and the like.

  When used as an iron source, the residual slag rate is preferably 10% or less when used in a blast furnace, and the residual slag rate is 5% or less when used in a converter or electric furnace. Recommended.

  The reduced iron that can be recovered in the present invention can be used as an iron source in a blast furnace because its residual slag rate is stably 10% or less.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  A mixture containing the iron oxide-containing material, the carbonaceous reducing agent, and the melting point modifier was agglomerated to produce an agglomerate.

  As the iron oxide-containing substance, iron ore having the composition shown in Table 1 below was used. In Table 1, T.W. Fe means total iron.

  As the carbonaceous reducing agent, a carbon material having a component composition shown in Table 2 below was used. In Table 2, VM means volatile matter.

As the melting point adjusting agent, limestone and Al ₂ O ₃ reagent (“White Fused Alumina 50R” (trade name) manufactured by Taihei Random Co., Ltd., particle size: 200 Mesh (75 μm) under, purity: 99.6%) Using.

A binder is further mixed with the iron oxide-containing substance (iron ore), the carbonaceous reducing agent (carbon material), and the melting point modifier (limestone, Al ₂ O ₃ reagent) in the ratio shown in Table 3 below, and an appropriate amount The mixture containing water was granulated into raw pellets having an average diameter of 19 mm using a tire type granulator. As the binder, flour was used.

  The obtained raw pellets were charged into a dryer and heated at 180 ° C. for 1 hour to remove adhering water to produce spherical dry pellets. The component composition of the obtained dried pellet (agglomerated product) is shown in Table 4 below. In Table 4, T.W. Fe means total iron.

Table 4 below shows the amount of slag (1) based on the total iron amount (T.Fe amount), CaO amount, SiO ₂ amount, Al ₂ O ₃ amount, and MgO amount contained in the dried pellets. (kg / ton) is calculated.

  Table 4 below also shows the result of calculating a value (oxygen amount / fixed carbon amount) obtained by dividing the oxygen amount in the iron oxide-containing substance contained in the dry pellet by the fixed carbon amount contained in the dry pellet. Show.

  Here, No. shown in Table 4 below. The procedure for taking 1 and calculating the value of oxygen amount / fixed carbon amount will be described.

(Oxygen content)
As apparent from Table 4 below, the dry pellet No. 1 included in T.1. Fe (W _T.Fe ) is 48.21% by mass, of which 21.29% by mass exists as FeO (W _FeO ). T.A. Assuming that all of Fe not present as FeO is Fe ₂ O ₃ , dry pellet No. The mass of Fe ₂ O ₃ contained in 1 (W _Fe2O3 ) can be calculated from the following formula (i). In the following formula (i), W _X means the mass (mass%) of the component X, and M _X means the molecular weight of the component X. M _Fe has a molecular weight of Fe of 55.85, M _FeO has a molecular weight of FeO of 71.85, and M _Fe2O3 has a molecular weight of Fe ₂ O ₃ of 159.7. Table 4 below shows the calculated mass of Fe ₂ O ₃ (W _Fe2O3 ).

Dry pellet No. The amount of oxygen in the iron oxide contained in 1 is the sum of the amount of oxygen contained in Fe ₂ O ₃ and the amount of oxygen contained in FeO, as shown by the following formula (ii). Wherein, M _{Fe2 O3} is 159.7 in molecular weight of Fe _{2 O 3,} M O is a 16 molecular weight of oxygen. Therefore, dry pellet No. The amount of oxygen in the iron oxide contained in 1 is 18.3% by mass. The amount of oxygen calculated in this way is shown in Table 4 below.

(Fixed carbon content)
As shown in Table 4 below, dry pellet No. The amount of fixed carbon contained in 1 is 14.35% by mass. Therefore, the value (oxygen amount / fixed carbon amount) obtained by dividing the oxygen amount in the iron oxide contained in the dry pellets by the fixed carbon amount contained in the dry pellets is 1.28.

  Next, the value of the left side of the above formula (2) was calculated based on the slag amount shown in Table 4 below, the value of oxygen amount / fixed carbon amount, and the above formula (2). The results are also shown in Table 4 below.

  Next, the obtained dry pellets are charged into a heating furnace and heated at 1330 ° C. to 1450 ° C. to reduce iron oxide in the pellets, and part of the reduced iron is melted to obtain a reduced iron-containing sintered body. Manufactured. As the heating furnace, an electric furnace was used instead of the mobile hearth furnace. The heating temperature is shown in Table 4 below.

  Prior to charging the dry pellets, charcoal (anthracite) having a maximum particle size of 2 mm or less was laid on the hearth of the heating furnace to protect the hearth.

  After heating, the sample containing the reduced iron-containing sintered body was discharged from the furnace.

  The 50% volume particle size of reduced iron produced in the core portion of the obtained reduced iron-containing sintered body was measured by the following procedure.

  That is, the obtained reduced iron-containing sintered body was placed in the center, cut in the vertical direction, filled with resin, and observed with an optical microscope to photograph a two-dimensional cross-sectional image. The observation magnification with an optical microscope was 100 times. An example of a photograph taken is shown in FIG. 1 shows No. 1 shown in Table 4. 5 is taken.

As is clear from FIG. 1, when the photographed image is observed, the shell part and the core part of the reduced iron-containing sintered body can be easily discriminated visually, so that the area A ( μm ² ) was measured. The area A of reduced iron was measured using image analysis software (Image J).

The reduced iron is not necessarily a true sphere, but in order to obtain the particle size d, the reduced iron particle size d (μm) was calculated based on the following equation (v) assuming a true sphere.
d = 2 × (A / π) ^1/2 (v)

  The reduced irons produced in the core part were arranged in ascending order of the particle diameter d, the volume was calculated assuming that the reduced iron was a true sphere, and the cumulative volume was obtained. The particle diameter d when the cumulative volume became 50% with respect to the volume of all reduced iron produced in the core portion was determined as the 50% volume particle diameter. The results are shown in Table 4 below.

  Moreover, the relationship between the value of the left side of Formula (2) shown in following Table 4 and the 50% volume particle size of the reduced iron produced | generated in the core part is shown in FIG.

  In the present invention, the case where the 50% volume particle size was 200 μm or more was evaluated as acceptable, and the case where the 50% volume particle size was less than 200 μm was rejected.

  In addition, in the basic experiment conducted by the present inventors in advance, the 50% volume particle size was determined to be 200 μm or more. The following Table 5 shows the 50% volume particle size and the residual slag ratio contained in the magnetic deposit. This is because the data shown in FIG.

That is, the agglomerate was heated at a heating temperature of 1330 to 1450 ° C., and the 50% volume particle size of reduced iron produced in the core portion of the obtained reduced iron-containing sintered body was measured by the above procedure. On the other hand, the residual slag rate contained in the magnetic deposit was calculated by the following procedure. That is, the obtained reduced iron-containing sintered body was pulverized by a disc mill for a maximum of 3 minutes. The obtained pulverized product was magnetically separated with a magnetic separator, and separated into a magnetized product and a non-magnetized product. The obtained magnetic deposit was subjected to chemical analysis, and the residual slag ratio contained in the magnetic deposit was calculated. The residual slag rate was the ratio of the total amount of SiO ₂ and Al ₂ O _{3 to} the total iron amount (T.Fe) contained in the magnetic deposit.
Residual slag ratio (%) = 100 × [(SiO ₂ ) + (Al ₂ O ₃ )] / (T.Fe) (iv)

  FIG. 3 is a graph in which the 50% volume particle size shown in Table 5 below is the horizontal axis, and the residual slag rate contained in the magnetic deposit is the vertical axis.

  From the following Table 5 and FIG. 3, it was found that when the 50% volume particle size is 200 μm or more, the residual slag rate is 10% or less.

  Based on the results of the above basic experiment, the following can be considered from Table 4 and FIG.

No. 1, 2, and 5 are examples satisfying the requirements defined in the present invention, and the total iron content (T.Fe content), CaO content, SiO ₂ content, Al ₂ O ₃ contained in the dry pellets. Since the blending amount of the carbonaceous reducing agent is adjusted based on the amount of slag (kg / ton) calculated by the above formula (1) based on the amount and the amount of MgO, the 50% volume particle size of the magnetic deposit Is 200 μm or more. Therefore, it is considered that the pulverization and separation properties are good.

In contrast, no. Examples 3 and 4 are examples that do not satisfy the requirements defined in the present invention. Slag amount (kg / ton) calculated by the above formula (1) based on the total iron amount (T.Fe amount), CaO amount, SiO ₂ amount, Al ₂ O ₃ amount, and MgO amount contained in the dried pellets Therefore, the amount of carbonaceous reducing agent is not adjusted, and the relationship between the value of oxygen amount / fixed carbon amount and the amount of slag does not satisfy the relationship defined by the above formula (2). Therefore, the 50% volume particle size of the magnetic deposit is less than 200 μm. Therefore, it is considered that the pulverization and separation properties are poor.

Claims (3)

By agglomerating a mixture containing an iron oxide-containing substance, a carbonaceous reducing agent, and a melting point modifier, and charging the obtained agglomerate on the hearth of a mobile hearth furnace, the agglomeration is performed. Reduce the iron oxide in the product, further heat to melt a part of the reduced iron, aggregate the reduced iron to obtain a reduced iron-containing sintered body, pulverize the obtained reduced iron-containing sintered body, and reduce In producing reduced iron by separating it into iron and slag,
Slag amount (kg / kg) calculated by the following formula (1) based on the total iron amount (T.Fe amount), CaO amount, SiO ₂ amount, Al ₂ O ₃ amount, and MgO amount contained in the agglomerate ton), and adjusting the blending amount of the carbonaceous reducing agent.
Slag amount = 1000 × [(CaO) + (SiO ₂ ) + (Al ₂ O ₃ ) + (MgO)] / (T.Fe) (1)
[In said formula (1), () means the quantity (mass%) of each component contained in an agglomerate. ] When the mass of the agglomerate is 100%, the value obtained by dividing the amount of oxygen in the iron oxide-containing material contained in the agglomerate by the amount of fixed carbon contained in the agglomerate (oxygen amount / fixed) The amount of carbonaceous reducing agent is adjusted so that the amount of carbon) and the amount of slag contained in the agglomerate satisfy the relationship of the following formula (2), and the agglomerate is 1350 The production method according to claim 1, wherein the heating is performed at a temperature not lower than ° C.
−1.66 × slag amount + 506.6 × oxygen amount / fixed carbon amount + 108.9 ≧ 200 (2) The amount of slag contained in the agglomerate is 400 kg / ton or more,
When the mass of the agglomerate is 100%, the value obtained by dividing the amount of oxygen in the iron oxide-containing material contained in the agglomerate by the amount of fixed carbon contained in the agglomerate (oxygen amount / fixed) The amount of the carbonaceous reducing agent is adjusted so that the carbon amount is in the range of 1.60 to 2.00, and the agglomerate is heated at 1350 ° C or higher. Manufacturing method.