JP6294135B2 - Method for producing reduced iron - Google Patents

Description

  The present invention relates to a method for producing reduced iron by heating 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.

The mainstream of the iron making process using iron ore as a raw material is the blast furnace-converter method. However, the blast furnace-converter method is a so-called indirect iron manufacturing method in which iron ore is reduced in a blast furnace to produce high carbon hot metal, and the obtained hot metal is decarburized in a converter to produce steel. Compared with the direct iron manufacturing method in which iron ore is reduced to directly produce steel, the amount of CO ₂ gas generated is increased. Therefore, in recent years, direct iron manufacturing methods have been reviewed from the viewpoint of suppressing CO ₂ gas emissions.

  As a direct iron manufacturing method, a reduced iron manufacturing process using coal, which is relatively easily available as a carbonaceous reducing agent, has attracted attention. In this reduced iron production process, an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent is charged into a heating furnace, and the iron oxide is reduced by heating in the furnace with gas heating or radiant heat using a heating burner. It is to obtain massive reduced iron. In this reduced iron production process, in addition to using coal as a carbonaceous reducing agent, powdered iron ore can be used directly, and during the reduction, the iron ore and the reducing agent are placed in close proximity. There are advantages that iron can be reduced at high speed and that the carbon content in the product obtained by reduction can be easily adjusted.

As a method of manufacturing granular metallic iron by the reduced iron manufacturing process, the present applicant has previously proposed the technique of Patent Document 1. In the method for producing granular metallic iron disclosed in this document, a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is charged on a hearth of a moving hearth type heating reduction furnace, and heated. In the method for producing granular metallic iron by reducing the iron oxide in the mixture with the carbonaceous reducing agent, aggregating the produced metallic iron into particles while separating it from the by-product slag, and then cooling and solidifying it. ) The basicity of the slag determined from the contents of CaO, MgO and SiO _{2 in} the slag by adjusting the amounts of CaO supply material, MgO supply material and SiO ₂ supply material contained in the raw material mixture [( CaO + MgO) / SiO ₂ ] is set in the range of 1.2 to 1.5, and the MgO content in the slag is 5% by mass or less (not including 0% by mass). (2) CaF ₂ supply to the raw material mixture Mix substances The CaF ₂ content of the slag by those to 2 mass% or more.

JP 2013-36058 A

By the way, the reduced iron obtained by the reduced iron production process includes gangue such as CaO, SiO ₂ and Al ₂ O ₃ contained in iron oxide-containing substances such as iron ore used as a raw material and carbonaceous reducing agents such as coal. Ingredients mix as slag. Therefore, the quality of reduced iron becomes low. Reduced iron with low iron grade needs to be dissolved in, for example, an electric furnace, and slag needs to be separated and removed. However, when the amount of slag contained in reduced iron increases, the yield during refining decreases, so reduced iron obtained by the reduced iron production process is required to have low slag content and high iron quality. .

  In order to increase the iron quality of the reduced iron obtained by the reduced iron production process, it is effective to use an iron oxide-containing substance having a high iron quality as a raw material. However, while steel production is increasing globally, mining of high-grade iron ore is on the decline. As a result, the price of high-grade iron ore is rising. In order to reduce the cost, it is necessary to use an iron oxide-containing material having a low iron quality. However, when an iron oxide-containing substance having a low iron quality was used, the yield of reduced iron was lowered and the productivity of reduced iron was poor.

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to produce an iron grade by heating an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent. An object of the present invention is to provide a technique capable of improving the productivity of reduced iron not only when a high iron oxide-containing substance is used but also when an iron oxide-containing substance having a low iron quality is used.

The method for producing reduced iron according to the present invention that has solved the above-described problems includes a step of agglomerating a mixture containing iron ore and a carbonaceous reducing agent, and heating the obtained agglomerate to produce the agglomerate. A step of reducing iron oxide in the composition. Then, as the agglomerate, as the total amount of CaO in the該塊Narubutsu, total amount of SiO _2, and on the basis of the quartz quantity X value calculated by the following formula (1) of 0.5 to 6.0 The point is to use. In the following formula (1), () indicates the content (% by mass) of each component in the agglomerate. Quartz is a mineral phase in which only Si and O are detected from an analysis object by using both X-ray diffraction and a scanning electron microscope.
X = (total CaO) / [(total SiO ₂ ) − (quartz)] (1)

  The agglomerate may contain 0.5% by mass or more of quartz.

According to the present invention, when producing a reduced iron by heating the agglomerate, the total CaO amount, the total SiO ₂ amount, and the quartz amount in the agglomerate are adjusted so as to satisfy a predetermined relationship. Therefore, the molten slag is rapidly formed. As a result, aggregation of the reduced iron is promoted, the yield of the reduced iron is improved, and the productivity of the reduced iron can be increased.

FIG. 1 is a graph showing the relationship between the X value calculated by equation (1) and the relative value of the productivity index.

The inventors of the present invention have intensively studied in order to improve the yield of reduced iron by increasing the yield of reduced iron when heating the agglomerate to produce reduced iron. As a result, if the total CaO amount, the total SiO ₂ amount, and the quartz amount in the agglomerate satisfy the predetermined relationship, the gangue is melted early, the molten slag is formed quickly, the molten slag is It was found that productivity of reduced iron can be improved because aggregation of reduced iron is promoted by the rapid formation, and the present invention has been completed.

  First, the background to the completion of the present invention will be described, and then the present invention will be described in detail.

  When reduced iron was produced using an iron oxide-containing substance having a low iron quality, as described above, the yield of reduced iron decreased and the productivity of reduced iron deteriorated. This is due to the gangue contained in the iron oxide-containing material. The iron oxide-containing substance with low iron quality contains a lot of gangue, but when the agglomerate is heated and the gangue remains in a solid state without melting, the reduced iron obtained by reductive melting, This is because it becomes difficult to aggregate and coalesce with each other. For this reason, the reduced iron is refined, the separability from the gangue component is deteriorated, and the yield of the reduced iron is reduced. Therefore, conventionally, in order to quickly melt the gangue, the basicity of the slag was adjusted as proposed in Patent Document 1 above.

The present inventors further examined the relationship between the components of gangue and the yield of reduced iron, and the amount of quartz contained in the silicate mineral, which is the main mineral phase constituting the gangue, is that of the gangue. It was found to have a great influence on That is, conventionally, when measuring the component composition of an iron oxide-containing substance represented by iron ore, Si detected from the iron ore is converted into an oxide of Si (SiO ₂ ) and the component composition is measured. It was. However, some Si contained in the iron oxide-containing material exists as metallic Si, but most of them are quartz (SiO ₂ ), kaolinite [Al ₂ Si ₂ O ₅ (OH) ₄ ], kaolinite. Containing iron oxide, actinolite [(Ca ₂ (Mg, Fe) ₅ Si ₈ O ₂₂ (OH) ₂ ], camingtonite [(Fe, Mg) ₇ Si ₈ O ₂₂ (OH) ₂ ], It exists as a silicate mineral such as glueneite [Fe ₇ Si ₈ O ₂₂ (OH) ₂ ] Among these silicate minerals, quartz is larger than other mineral phases and has a large particle size. Quartz is also poorly reactive because it is covalently bonded and each atom is very tightly bound, so even if the agglomerate is heated, it takes time to hatch the quartz contained in the agglomerate. Therefore, the gangue, iron ore, melting point modifier, etc. react and melt. Even when the lag is formed, quartz hardly reacts and remains in a solid state, and the timing at which the quartz melts was the final stage in which reduced iron was obtained. Even if the mixing ratio of the raw material of the agglomerate is adjusted in order to improve the fluidity of the slag and the basicity of the slag is controlled to satisfy the desired range, the quartz melts and the basicity of the slag is desired When the timing satisfying the above range is the final stage in which reduced iron is obtained, the effect of increasing the yield of reduced iron by increasing the fluidity of slag and improving the separability from reduced iron cannot be enjoyed. In order to enjoy the effect of improving the iron yield, it is necessary to continue heating even after the quartz melts and the basicity of the slag satisfies the desired range, but if the heating time is increased, the reduced iron Productivity Kunar.

Therefore, the present inventors pay attention to the fact that quartz has a poor hatchability, and by mixing the raw materials in consideration of the characteristics of quartz, the gangue is rapidly melted, the liquid phase ratio is increased, and the molten slag We studied to improve the yield of reduced iron by increasing fluidity. As a result, as an agglomerate, an X value calculated by the following formula (1) based on the total CaO amount, the total SiO ₂ amount, and the quartz amount in the agglomerate is 0.5 to 6.0. It has been found that the use of can improve the yield of reduced iron and increase the productivity of reduced iron. In the following formula (1), () indicates the content (% by mass) of each component in the agglomerate.
X = (total CaO) / [(total SiO ₂ ) − (quartz)] (1)

The above formula (1) is an equation designed in consideration of the poor hatchability of quartz. The numerator is the total CaO amount obtained by converting Ca contained in the agglomerate into CaO, and the denominator is the agglomerate. The value obtained by subtracting the amount of quartz from the total amount of SiO ₂ obtained by converting Si contained in SiO ₂ into SiO ₂ is shown. This X value corresponds to basicity, and in the present invention, the X value is defined as 0.5 to 6.0. In addition, CaO is contained in the gangue contained in the iron oxide-containing substance and the ash contained in the carbonaceous reducing agent, and is also blended into the agglomerate as a melting point adjusting agent described later. Since the property is good, a value obtained by converting Ca contained in the agglomerate into CaO may be used as a molecule.

  If the X value is less than 0.5, the amount of Si-containing material in the agglomerate becomes excessive, the viscosity of the slag is improved, and the fluidity is lowered, so that the yield of reduced iron is lowered. Accordingly, in the present invention, the X value is 0.5 or more, preferably 0.6 or more, more preferably 1.0 or more. However, when the X value exceeds 6.0, CaO becomes excessive and the melting point of slag rises, so that the yield of reduced iron decreases. Therefore, in the present invention, the X value is 6.0 or less, preferably 4.0 or less, more preferably 3.0 or less.

  The amount of quartz contained in the agglomerate can be quantified by using both X-ray diffraction and a scanning electron microscope. In other words, the silicate mineral phase is detected by the mapping function in scanning electron microscope observation, and composition analysis is performed with EDS (Energy dispersive X-ray spectrometry) attached to the scanning electron microscope, and only Si and O are analyzed. When is detected, it is determined as quartz and quantified. On the other hand, when elements other than Si and O, such as Al, Ca, Mg, and Fe, are detected, the mineral phase other than quartz is determined and quantified. In addition, the iron ore used normally contains 0.1 mass% or more of quartz.

  The X value that characterizes 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 and a carbonaceous reducing agent (hereinafter sometimes referred to as an agglomeration process);
Heating the obtained agglomerate and including a step of reducing iron oxide in the agglomerate (hereinafter sometimes referred to as a heat reduction step),
The agglomerate is characterized in that the above-mentioned X value is 0.5 to 6.0.

[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-containing substances such as iron ore, iron sand, iron-making dust, non-ferrous refining residue, and iron-making waste can be used.

  As said carbonaceous reducing agent, coal, coke, etc. can be used, for example.

  The said carbonaceous reducing agent should just contain the quantity of carbon which can reduce | restore the iron oxide contained in the said iron oxide containing substance. Specifically, the iron oxide contained in the iron oxide-containing substance may be contained within a range of 0 to 5% by mass surplus or 0 to 5% by mass with respect to the amount of carbon that can be reduced. That is, the iron oxide contained in the iron oxide-containing substance may be contained in a range of ± 5% by mass with respect to the amount of carbon that can be reduced.

  You may mix | blend a melting | fusing point regulator or a binder with the said mixture containing the said iron oxide containing substance and a carbonaceous reducing agent further.

  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. Thereby, the gangue is promoted to melt and forms molten slag. At this time, a part of the iron oxide is dissolved in the molten slag and reduced in the molten slag to become metallic iron. The metallic iron produced in the molten slag is agglomerated as solid reduced iron by coming into contact with the metallic iron reduced in the solid state.

As the melting point adjusting agent, for example, a CaO supply material, a MgO supply material, an Al ₂ O ₃ supply material, or 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 said binder, polysaccharides, such as starches, such as corn starch and wheat flour, can be used, for example.

In the present invention, the iron oxide-containing substance and the iron oxide-containing substance are selected so that the X value calculated based on the total CaO amount, the total SiO ₂ amount, and the quartz amount in the agglomerate satisfies 0.5 to 6.0. It is important to adjust the blending amounts of the carbonaceous reducing agent, the melting point adjusting agent and the binder to be mixed as necessary.

  The amount of quartz contained in the agglomerate may be 0.5% by mass or more, or 1.0% by mass or more. Furthermore, 1.5 mass% or more may be sufficient. The upper limit of the amount of quartz contained in the agglomerate is not particularly limited as long as the X value calculated based on the above formula (1) satisfies the above range, but the upper limit is, for example, 5.0% by mass. is there. Quartz is a component mainly contained in iron oxide-containing materials (especially iron ore), and the amount of quartz contained in iron oxide-containing materials is combined with X-ray diffraction and scanning electron microscope as described above. Can be quantified.

  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 material may be pulverized so that the average particle size is 10 to 60 μm, the carbonaceous reducing agent is 10 to 1000 μm, and the melting point modifier 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 may be used.

  For mixing the raw materials, a rotating container type or a fixed container type mixer can be used. Examples of the type of the mixer include, but are not particularly limited to, a rotating container shape including a rotating cylindrical shape, a double cone shape, and a V shape. As a fixed container type, for example, there is one in which a rotating blade such as a basket is provided in a mixing tank, but it is not particularly limited.

  As the agglomerating machine for agglomerating the mixture, for example, a dish granulator (disk granulator), a cylindrical granulator (drum granulator), a twin roll briquette molding machine or the like is used. be able to.

  The shape of the agglomerate is not particularly limited, and the molding may be performed by any of pellets, briquettes, and extrusion.

[Heat reduction process]
In the heat reduction step, the agglomerate obtained in the agglomeration step is heated to reduce the iron oxide in the agglomerate to produce reduced iron.

  The agglomerate may be heated in an electric furnace or a moving hearth type heating furnace, for example. The moving hearth type heating 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. The rotary hearth furnace is designed to have a round or donut shape 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 with discharging means on the most downstream side in the rotation direction. In addition, since it is a rotating structure, it is actually just upstream of the charging means. The tunnel furnace is a heating furnace in which the hearth moves in the furnace in a linear direction.

  The agglomerate is preferably heated and reduced at 1300 to 1500 ° C. When the heating temperature is lower than 1300 ° C., metallic iron and slag are difficult to melt, and high productivity cannot be obtained. On the other hand, if the heating temperature exceeds 1500 ° C., the exhaust gas temperature becomes high, so the exhaust gas treatment facility becomes large and the equipment cost increases.

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

[Others]
Reduced iron obtained in the heating reduction process is discharged from the furnace together with slag produced as a by-product or flooring material laid if necessary, and sorted using a sieve or a magnetic separator, etc. Collect it.

  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.

  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 A or iron ore B having the composition shown in Table 1 below was used. Among the component compositions of iron ore, T.W. Fe and total FeO are potassium dichromate titrations, total SiO ₂ , total CaO, total Al ₂ O ₃ , total MgO, total MnO, total TiO ₂ , and P are ICP emission spectroscopy, S, and T . C was determined by a combustion infrared absorption method, and total Na ₂ O was determined by an atomic absorption photometry method. Note that the total SiO ₂ includes quartz that is separately quantified later. The amount of quartz contained in the iron ore was quantified by analyzing the component composition of the iron ore with EDS attached to the scanning electron microscope and determining that only Si and O were detected as quartz. On the other hand, in addition to Si and O, for example, when Al, Ca, Mg, Fe, or the like is detected, the mineral phase other than quartz is determined and quantified.

As the carbonaceous reducing agent, a carbon material having a component composition shown in Table 2 below was used. In Table 2, Fix. C is fixed carbon; C represents all carbon. Of the component composition of the carbonaceous material, the volatile content was quantified by the volatile content determination method defined in JIS M8812. Ash content was quantified by the ash content determination method defined in JIS M8812. Fix. C is a fixed carbon mass fraction calculation method defined in JIS M 8812. C = 100-mass of ash-mass of volatile matter (both units are mass%). S and T. C was quantified by the combustion infrared absorption method. Of the ash component composition, total Fe ₂ O ₃ , total SiO ₂ , total CaO, total Al ₂ O ₃ , total MgO, total TiO ₂ , and total P ₂ O ₅ are ICP emission spectroscopy, ₂ O and total K ₂ O were quantified by atomic absorption spectrophotometry.

  Limestone was used as the melting point modifier.

Raw iron pellets having an average diameter of 19 mm using a tire-type granulator, wherein the above iron ore, carbonaceous material, and limestone are further blended with wheat flour as a binder in the ratio shown in Table 3 below and an appropriate amount of water is added. Granulated. The obtained raw pellets were charged into a dryer and heated at 180 ° C. for 1 hour to remove adhering water and dried. Table 3 below shows the total CaO amount, the total SiO ₂ amount, and the quartz amount contained in the obtained dried pellets. Further, based on the total CaO amount, the total SiO ₂ amount, and the quartz amount in the dried pellet, the X value was calculated by the above formula (1), and the results are shown in Table 3 below.

Next, No. 1 prepared at the blending ratio shown in Table 3 below. Each of the 1 to 4 dry pellets was supplied to a heating furnace 30 at a time and heated at 1450 ° C. to reduce the iron oxide in the dry pellets to produce reduced iron. In order to protect the hearth of the heating furnace, a floor covering material was laid on the hearth prior to the introduction of the dry pellets. As the floor covering material, a carbon material (anthracite) having a maximum particle size of 2 mm or less was used. During the heating, a mixed gas in which 40% by volume of nitrogen gas and 60% by volume of carbon dioxide gas were mixed was supplied into the heating furnace so that the gas flow rate was 440 NL / min. After completion of the reduction, the object to be heated containing reduced iron was discharged from the heating furnace and sieved. A sieve having an opening of 3.35 mm was used for sieving the material to be heated, and the residue on the sieve was collected as a product. Based on the mass (kg) of the residue on the sieve and the total mass (kg) of iron charged in the heating furnace, the yield (%) of reduced iron was calculated by the following formula (2). In addition, since the residue on a sieve contains C, Si, Mn, etc. other than Fe, the yield of reduced iron may exceed 100%.
Yield (%) = (Mass of residue on sieve / Total mass of iron charged in heating furnace) × 100 (2)

  Moreover, the time from supplying the dried pellets to the heating furnace until discharging the sample containing reduced iron was measured as the reaction time (hours).

The productivity index when producing the residue remaining on the sieve was calculated by the following formula (3). That is, first, the total mass (kg) of iron supplied to the heating furnace is divided by the area (m ² ) of the hearth on which the dried pellets are laid to obtain the iron amount (kg / m ² ) per unit area. It was. Next, multiply the amount of iron per unit area (kg / m ² ) by the yield (%) of reduced iron to obtain the mass (kg / m ² ) of the residue remaining on the sieve collected per unit area. It was. Next, the mass (kg / m ² ) of the residue remaining on the sieve collected per unit area is divided by the reaction time (hours) to obtain the productivity index (kg / kg) of the residue remaining on the sieve. m ² / h).
Productivity index (kg / m ² / h) = [(total mass of iron supplied to heating furnace / area of hearth covered with dry pellets) × yield] / reaction time (3)

  No. shown in Table 3 below. 1-4, no. The productivity index in No. 4 is 1.00. The relative values of the productivity indexes of 1 to 3 were calculated, and the results are shown in Table 3 below. In the present invention, a case where the relative value of the productivity index is 1.10 or more was regarded as acceptable, and it was evaluated that the productivity of reduced iron was improved.

  Further, FIG. 1 shows the relationship between the X value of the formula (1) and the relative value of the productivity index. In FIG. The results of Nos. 1 to 3 are shown. The result of 4 is shown.

The following table 3 and FIG. 1 can be considered as follows. No. 4 is an example that does not satisfy the requirements defined in the present invention. That is, the X value calculated by the above formula (1) based on the total CaO amount, the total SiO ₂ amount, and the quartz amount contained in the dry pellets does not satisfy the requirements defined in the present invention. On the other hand, no. 1-3 are examples which satisfy the requirements defined in the present invention. That is, since the X value calculated by the above formula (1) based on the total CaO amount, total SiO ₂ amount, and quartz amount contained in the dry pellets satisfies the predetermined range, the productivity is No. . Compared to 4, it was improved by 10% or more.

Claims (2)

Agglomerating a mixture comprising iron ore and a carbonaceous reducing agent;
Heating the resulting agglomerate to reduce iron oxide in the agglomerate,
As the agglomerates, those having an X value of 0.5 to 6.0 calculated by the following formula (1) based on the total CaO amount, the total SiO ₂ amount, and the quartz amount in the agglomerates are used. The manufacturing method of reduced iron characterized by the above-mentioned.
X = (total CaO) / [(total SiO ₂ ) − (quartz)] (1)
In formula (1), () indicates the content (% by mass) of each component in the agglomerate. Quartz is a mineral phase in which only Si and O are detected from an analysis object by using both X-ray diffraction and a scanning electron microscope.   The said agglomerate is a manufacturing method of Claim 1 containing 0.5 mass% or more of quartz.

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