JP6250482B2 - Manufacturing method of granular metallic iron - Google Patents

Description

  The present invention relates to a method for producing granular metallic iron by heating, reducing and melting an agglomerate containing an iron oxide-containing substance such as iron ore and 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 the steel is directly produced by reducing the stone, 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 emission.

  As the direct iron production method, a reduced iron production 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. Further, as the reduced iron production process, an agglomerate obtained by mixing an agglomerated iron oxide-containing substance and a carbonaceous reducing agent is supplied to a heating furnace and heated, and the iron oxide contained in the agglomerate is heated. After the reduction, the heated iron is further melted, and the carbonaceous reductant in the agglomerate or the flooring material laid on the hearth is carburized to produce granular metallic iron. There is also a method of separating into slag. The former method is sometimes called the FASTMET method, and the latter method is sometimes called the ITmk3 method.

  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, 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.

Patent Document 1 is known as a document disclosing the ITmk3 method. In this document, the inside of a mobile hearth furnace is moved in a state where a mixed raw material containing an iron-containing oxide, a carbon-based solid reducing material, and a slagging material is loaded on the mobile hearth of the mobile hearth furnace. In the production of reduced iron by reducing the iron-containing oxide by heating while melting and leading to soot separation, the average particle size of the iron-containing oxide is mixed as the mixed raw material. A method for producing reduced iron by a mobile hearth furnace using a composition in which the relationship between the reducible oxygen concentration in the raw material and the carbon material ratio expressed as a ratio of the carbon concentration satisfies the following formula is described. . In the following formula, r means the radius of the iron-containing oxide, and the carbon material ratio means (carbon concentration in the mixed raw material) / (reduced oxygen concentration in the mixed raw material) / 12 × 16.
0.5 <(carbon material ratio) <1.6
log (1 / r) <(− 2.0 × (carbon material ratio) +2.5)

  According to this production method, by making the carbon material ratio represented by the carbon concentration and the reducible oxygen concentration in the mixed raw material and the average particle diameter of the iron-containing oxide in the mixed raw material have a certain relationship Thus, it becomes possible to reliably and easily produce reduced carbon-containing reduced iron having a reduced iron concentration of 4 mass% or more. As a result, it is easy to dissolve reduced iron in an electric furnace or the like, which can contribute to a reduction in product cost.

JP 2011-74438 A

  By the way, when manufacturing granular metal iron by said ITmk3 method industrially, it is also calculated | required that the yield of granular metal iron is favorable. However, in the said patent document 1, the yield of granular metal iron was not considered specially.

  The present invention has been made paying attention to the above circumstances, and its purpose is to agglomerate a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent, and use the obtained agglomerate in a heating furnace. In the production of granular metallic iron by reducing the iron oxide in the agglomerate by charging and heating, further heating to melt the reduced iron and agglomerating the reduced iron, the yield of granular metallic iron It is to establish the technology that can be improved.

The method for producing granular metallic iron according to the present invention, which has solved the above-mentioned problems, agglomerates a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent, and charges the obtained agglomerate into a heating furnace. Heating to reduce the iron oxide in the agglomerate, further heating to melt the reduced iron, and agglomerating the reduced iron to produce granular metallic iron, Average particle size R (mm), oxygen content (mass%) derived from iron oxide-containing material contained in the agglomerate, fixed carbon content (mass%) derived from a carbonaceous reducing agent contained in the agglomerate, and該塊formed product of carbon content in the volatiles from the carbonaceous reducing agent contained in the [C _{VM] (wt%)} has a gist in that satisfies the following formula (1).
6.91 ≦ R ^0.5 × oxygen amount / (fixed carbon amount + 0.3 × [C _VM ]) ≦ 7.19 (1)

  It is preferable that the average particle diameter R of the said agglomerate is 10-30 mm.

According to the present invention, for the agglomerate charged into the heating furnace, the average particle size R (mm) of the agglomerate, the amount of oxygen derived from the iron oxide-containing substance contained in the agglomerate (mass%), The amount of fixed carbon derived from the carbonaceous reducing agent contained in the agglomerate (mass%) and the amount of carbon [C _VM ] (mass%) in the volatile matter derived from the carbonaceous reducing agent contained in the agglomerated material. Since the relationship is appropriately controlled, the iron oxide contained in the agglomerate can be reduced by the reducing agent without excess or deficiency. As a result, the yield of granular metallic iron can be improved.

FIG. 1 is a graph showing the relationship between the value of R ^0.5 × oxygen amount / (fixed carbon amount + 0.3 × [C _VM ]) (Z value) and the yield of granular metallic iron.

In the production of granular metallic iron by heating, reducing and melting an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent in a heating furnace, in order to improve the yield of granular metallic iron, We have been studying earnestly. As a result, in addition to the amount of oxygen derived from the iron oxide-containing substance contained in the agglomerate that affects the reduction of iron oxide and the amount of fixed carbon derived from the carbonaceous reducing agent contained in the agglomerate, attention has been paid in the past. By appropriately controlling the average particle size R of the agglomerate that was not present and the amount of carbon [C _VM ] in the volatile matter derived from the carbonaceous reducing agent contained in the agglomerate, the yield of granular metallic iron is improved. The present invention has been completed by finding out what can be done. The characteristic portions of the present invention will be described below along with the background that led to the completion of the present invention.

  If the amount of carbonaceous reducing agent is excessive relative to the amount of oxygen derived from the iron oxide-containing material contained in the agglomerated material, the remaining carbon that is not consumed by the reduction of iron oxide will inhibit the aggregation of reduced iron. The yield of granular metallic iron is reduced. On the other hand, if the amount of the carbonaceous reducing agent is insufficient with respect to the amount of oxygen derived from the iron oxide-containing material contained in the agglomerate, the iron oxide cannot be reduced, so that reduced iron cannot be produced, and granular metallic iron Yield decreases.

Coal is mainly used as the carbonaceous reducing agent industrially. This coal has fixed carbon (Fixed Carbon, hereinafter abbreviated as “Fix.C”) that remains even when heated, and volatile matter (Volatile Matter; hereinafter, abbreviated as “VM”). .) Of these, almost 100% of fixed carbon contributes to the reduction of iron oxide. On the other hand, although not all volatiles contribute to the reduction of iron oxide, it has been found that a part of this carbon contributes to the reduction of iron oxide because the volatile matter contains carbon. And when the present inventors repeated examination, it became clear that 30% of the carbon in the volatile matter derived from the carbonaceous reducing agent contained in the agglomerate contributes to the reduction of iron oxide. That is, the amount of carbon consumed by the reduction calculated from the ratio of CO gas to CO ₂ gas generated during the test and the amount of oxygen contained in the oxide is greater than the solid carbon content in the agglomerate. There was found. This excess amount was found to correspond to 30% of the carbon contained in the volatile matter derived from the carbonaceous reducing agent. In the present specification, the amount of carbon in the volatile matter derived from the carbonaceous reducing agent contained in the agglomerate is expressed as [C _VM ] (mass%).

Therefore, in order to reduce the iron oxide in the iron oxide-containing material contained in the agglomerate, the amount of fixed carbon (mass%) derived from the carbonaceous reducing agent contained in the agglomerate and the volatilization derived from the carbonaceous reducing agent. Ratio of oxygen content (mass%) derived from iron oxide-containing substances contained in the agglomerate to the total quantity of carbon content [C _VM ] (mass%) of 30% in the fraction [oxygen content / (fixed carbon The amount + 0.3 × [C _VM ])] needs to be controlled. This ratio is an index indicating how much carbon is present relative to the amount of oxygen to be reduced. When this ratio is small, it indicates that there is sufficient carbon for reduction, and when this ratio is large, it indicates that carbon becomes deficient.

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

  First, the total iron (T.Fe) amount and FeO amount in the agglomerate are determined by chemical analysis.

Next, T.W. Of Fe, Fe that does not exist as FeO exists as iron oxide such as Fe ₂ O ₃ and Fe ₃ O _4, but it is assumed that all exist as Fe ₂ O ₃ , and the following formula (i) To calculate the mass of Fe ₂ O ₃ (W _Fe2O3 ) contained in the agglomerate.

In the following formula (i), W _x represents the mass (mass%) of the component X, and M _x represents the molecular weight of the component X. Specifically, W _T.Fe is T.Fe. The mass (mass%) of Fe, W _FeO means the mass (mass%) of FeO, and W _Fe2O3 means the mass (mass%) of Fe ₂ O ₃ . M _Fe is 55.85 in terms of the molecular weight of Fe, M _FeO is 71.85 in terms of the molecular weight of FeO, and M _Fe2O3 is 159.7 in terms of the molecular weight of Fe ₂ O ₃ .

Next, based on the following formula (ii), the total amount of oxygen contained in Fe ₂ O ₃ and the amount of oxygen contained in FeO is the amount of oxygen (% by mass) derived from the iron oxide-containing substance contained in the agglomerate. ) Is calculated. In the following formula (ii), M 2 _O is 16 as the molecular weight of oxygen.

By the way, as described above, carbon contained in the agglomerate is consumed when iron oxide is reduced, and it has been found that the amount of carbon consumed is affected by the size of the agglomerate. That is, when iron oxide is reduced, CO ₂ gas is generated inside the agglomerate. The produced CO ₂ gas is released to the outside through the inside of the agglomerate. At this time, if the agglomerate is large and the gas flow path becomes long, the CO ₂ gas reacts with carbon existing in the middle of the flow path discharged to the outside of the agglomerate and is reduced to produce CO gas. Therefore, the larger the agglomerate, the more carbon is consumed by the CO ₂ gas produced inside the agglomerate.

Therefore, in the present invention, based on the amount of oxygen derived from the iron oxide-containing substance contained in the agglomerate, the amount of fixed carbon derived from the carbonaceous reducing agent contained in the agglomerate, and the amount of carbon in the volatile matter [C _VM ]. It is necessary to multiply the ratio [oxygen amount / (fixed carbon amount + 0.3 × [C _VM ])] calculated by the above-mentioned effect of the size of the agglomerate, and the effect of the size of the agglomerate. The degree was found to be R ^0.5 when the average particle size of the agglomerate was R, and the following formula (1) was derived. R ^0.5 is a value derived by the present inventors through repeated studies.
R ^0.5 × oxygen amount / (fixed carbon amount + 0.3 × [C _VM ]) ≧ 6.2 (1)

When the value [R ^0.5 × oxygen amount / (fixed carbon amount + 0.3 × [C _VM ])) on the left side of the above formula (1) is taken as the Z value, this Z value is set to 6.2 or more. If the Z value is less than 6.2, the amount of carbon tends to be insufficient, so that reduced iron cannot be produced sufficiently and the yield of granular metallic iron is reduced. Therefore, in the present invention, the Z value is 6.2 or more, preferably 6.5 or more, more preferably 6.8 or more. The upper limit of the Z value is not particularly limited, but if the Z value is too large, the production of granular metallic iron takes too much time, so the productivity is lowered. Therefore, the Z value is preferably 8.0 or less. The Z value is more preferably 7.8 or less, still more preferably 7.6 or less.

  The method for measuring the particle size of the agglomerate is not particularly limited. For example, when the agglomerate is spherical like a pellet, calipers are used, and the three directions of x axis, y axis, and z axis perpendicular to each other are used. What is necessary is just to measure the average particle diameter R of an agglomerate by measuring the diameter of these and averaging these. If the agglomerate is not spherical but shaped like a briquette, the volume of the agglomerate is obtained, the equivalent sphere diameter is calculated, and this may be used as the average particle size R of the agglomerate.

  The average particle size R (mm) of the agglomerate is not particularly limited, but is preferably 10 mm or more, more preferably 15 mm or more, preferably 30 mm or less, more preferably 25 mm or less.

  Next, the manufacturing method of granular metallic iron is demonstrated.

The method for producing granular metallic iron according to the present invention comprises agglomerating a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent, charging the obtained agglomerate into a heating furnace, and heating the agglomerate. The iron oxide in the composition is reduced, further heated to melt the reduced iron, and the reduced iron is aggregated to produce granular metallic iron. And as above-mentioned, the average particle diameter R (mm) of the said agglomerate, the oxygen amount (mass%) derived from the iron oxide containing material contained in this agglomerate, the carbonaceous reduction contained in this agglomerate The amount of fixed carbon derived from the agent (% by mass) and the amount of carbon [C _VM ] (% by mass) in the volatile component derived from the carbonaceous reducing agent contained in the agglomerate satisfy the above formula (1). There is a feature. Hereinafter, a step of agglomerating a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent (hereinafter sometimes referred to as an agglomeration step), and the obtained agglomerate is charged into a heating furnace and heated. The process of reducing the iron oxide in the agglomerate, further heating to melt the reduced iron, and agglomerating the reduced iron to produce granular metal iron (hereinafter sometimes referred to as a heating process) is described. To do.

[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, a SiO ₂ 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 the SiO ₂ supply substance, for example, SiO ₂ powder or silica sand can be used.

  As said binder, polysaccharides, such as starches, such as corn starch and wheat flour, can be used, for example.

  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.

  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 a tire mold. A granulator or the like can be used.

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

[Heating process]
In the heating step, the agglomerate obtained in the agglomeration step is charged into a heating furnace and heated to reduce iron oxide in the agglomerate and further heated to melt the reduced iron. Then, reduced iron is agglomerated to produce granular metallic 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 agglomerates are preferably reduced and melted by heating at 1300-1500 ° 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 above heating process is discharged from the furnace together with slag produced as a by-product or flooring material laid as necessary, and collected using a sieve or a magnetic separator to recover the reduced iron do 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.

The mixture containing the iron oxide-containing substance and the carbonaceous reducing agent is agglomerated, and the obtained agglomerate is charged in a heating furnace and heated, thereby reducing the iron oxide in the agglomerate and further heating. Then, the reduced iron was melted and the reduced iron was agglomerated to produce granular metallic iron. At this time, the average particle size of the agglomerate, the amount of oxygen derived from the iron oxide-containing substance contained in the agglomerate, the amount of fixed carbon derived from the carbonaceous reducing agent contained in the agglomerate, and the carbon contained in the agglomerate The effect of the amount of carbon [C _VM ] in the volatile matter derived from the quality reducing agent on the yield of granular metallic iron was investigated.

As the iron oxide-containing substance, iron ores A and B having the composition shown in Table 1 below were used. In Table 1 below, T.W. Fe means total iron. The results of calculating the amount of oxygen in FeO contained in iron ore and the amount of oxygen in Fe ₂ O ₃ contained in iron ore are also shown in Table 1 below. Further, when FeO and Fe ₂ O ₃ contained in iron ore are collectively referred to as FeOx, the amount of oxygen in FeOx contained in iron ore is also shown in Table 1 below.

  As the carbonaceous reducing agent, carbon materials a to f having the component compositions shown in Table 2 below were used. In Table 2 below, T.M. C means all carbon.

  A mixture obtained by mixing the iron ore and the carbonaceous material with a melting point adjusting agent and a binder and further blending an appropriate amount of water was granulated into raw pellets using a tire type granulator. The obtained raw pellets were charged into a dryer to remove adhered water, and spherical dry pellets were produced. The component composition of the obtained dry pellet is shown in Table 3 below. “Others” shown in Table 3 below are melting point adjusting agents and binders. Limestone, dolomite, and fluorite were used as the melting point modifier. As the binder, flour was used.

  Moreover, the particle diameter of ten obtained dry pellets was measured with calipers, and the average particle diameter R (mm) was calculated. The calculation results are shown in Table 3 below. Table 3 below calculates the value of R to the 0.5th power (that is, the value of √R) and also shows the result.

Next, the amount of oxygen derived from the iron oxide-containing substance contained in the obtained dried pellet, the amount of fixed carbon derived from the carbonaceous reducing agent contained in the dried pellet, and the T.O. derived from the carbonaceous reducing agent contained in the dried pellet. C and the amount of carbon [C _VM ] in the volatile matter derived from the carbonaceous reducing agent contained in the dry pellets were calculated, and the results are shown in Table 3 below.

  Here, No. 1 shown in Table 3 below. The calculation procedure will be specifically described with reference to 1 dry pellet.

(Oxygen content)
As shown in Table 3 below, dry pellet No. 1 is 71.34%, and the amount of oxygen in FeOx contained in the iron ore is 27.67% from Table 1 below. 1 when the mass of 1 is 100%. The amount of oxygen derived from iron ore contained in 1 is 19.74%.
71.34 × (27.67 / 100) = 19.74

(Fixed carbon content)
As shown in Table 3 below, dry pellet No. 1 is 16.27%, and the amount of fixed carbon contained in the carbon material is 78.00% from Table 2 below. 1 when the mass of 1 is 100%. The amount of fixed carbon derived from the carbonaceous material contained in 1 is 12.69%.
16.27 × (78.00 / 100) = 12.69

(TC)
As shown in Table 3 below, dry pellet No. The amount of carbon material contained in 1 is 16.27%. Since C is 86.87% from the following Table 2, dry pellet No. 1 when the mass of 1 is 100%. 1 derived from carbonaceous materials contained in 1. C is 14.13%.
16.27 × (86.87 / 100) = 14.13

(Carbon content [C _VM ])
As shown in Table 3 below, dry pellet No. 1 when the mass of 1 is 100%. 1 derived from carbonaceous materials contained in 1. C is 14.13%, and dry pellet No. 1 when the mass of 1 is 100%. 1 is 12.69% from the carbonaceous material contained in the carbonaceous material, The carbon content [C _VM ] in the volatile matter derived from the carbonaceous material contained in 1 is 1.44%.
14.13-12.69 = 1.44

The amount of fixed carbon derived from the carbonaceous reducing agent contained in the dry pellet thus calculated (mass%), and the amount of carbon [C _VM ] (mass in the volatile matter derived from the carbonaceous reducing agent contained in the dry pellet. %), A value of “fixed carbon amount + 0.3 × [C _VM ]” is calculated. As a result, it becomes 13.12%.
12.69 + 0.3 × 1.44 = 13.12

Moreover, when the oxygen amount (mass%) derived from the iron oxide-containing substance contained in the dried pellet is divided by the above-mentioned “fixed carbon amount + 0.3 × [C _VM ]”, it becomes 1.50%.
19.74 / 13.12 = 1.50

Therefore, when the value of “R ^0.5 ” is multiplied by the value of “oxygen amount / fixed carbon amount + 0.3 × [C _VM ]” shown in Table 3 below, the value on the left side of the above equation (1) (Z value) ) And its value is 6.56.
Z value = R ^0.5 × oxygen amount / (fixed carbon amount + 0.3 × [C _VM ]) = 6.56

  Next, the obtained dry pellets are charged on the hearth of a heating furnace and heated at 1450 ° C. to reduce the iron oxide in the dry pellets, and further heated to melt the reduced iron and aggregate the reduced iron. To produce granular metallic iron. An electric furnace was used as the heating furnace. Prior to charging the dry pellets, anthracite having a maximum particle size of 3.35 mm or less was laid on the hearth of the electric furnace to protect the hearth. When heating the dried pellets on the hearth of the electric furnace, the composition of the atmospheric gas in the electric furnace was adjusted so that the volume ratio of nitrogen gas / carbon dioxide gas was 60/40.

After the reduction, the sample containing granular metallic iron was discharged from the electric furnace. The obtained sample was magnetically selected, and the magnetic deposits were classified using a sieve having an opening of 3.35 mm, and the residue remaining on the sieve was collected as a product. The residue collected as a product was mainly granular metallic iron, and its mass was measured. The mass (g) of granular metallic iron and T.O. Based on the mass (g) of Fe, the yield (%) of granular metallic iron was calculated, and the results are shown in Table 3 below. In addition, since granular metal iron contains C etc. in addition to Fe, the yield of granular metal iron may exceed 100%.
Yield (%) = (mass of granular metallic iron / mass of T.Fe contained in dry pellet) × 100

  When the agglomerate is heated, reduced, and melted, a mixture of granular metallic iron and slag is obtained. After cooling, this mixture is separated into granular metallic iron and slag by sieving and magnetic separation. However, since granular metal iron with a small particle size cannot be separated well from slag even by magnetic separation, it is difficult to obtain granular metal iron with high purity. Therefore, in the present invention, when calculating the yield of granular metallic iron, a reference is provided for mass, and only granular metallic iron having a certain size or more is counted. Specifically, when the above mixture was classified using a sieve having an opening of 3.35 mm, the residue remaining on the sieve was used as a product, and the mass of this product was used for calculating the yield of granular metallic iron.

  FIG. 1 shows the relationship between the Z value and the yield of granular metallic iron.

The following table 3 and FIG. 1 can be considered as follows. No. Nos. 5 , 6 , 8-10 , and 13 are invention examples satisfying the requirements defined in the present invention , No. 1, 2, 7, 12, 14, 16 , and 17 are reference examples , and since the Z value can be controlled to 6.2 or more, the yield of granular metallic iron can achieve 95% or more. On the other hand, no. 3, 4, 11, and 15 are comparative examples that do not satisfy any of the requirements defined in the present invention. Since the Z value is less than 6.2, the yield of granular metallic iron is less than 95%.

Claims (2)

The mixture containing the iron oxide-containing substance and the carbonaceous reducing agent is agglomerated, and the obtained agglomerate is charged in a heating furnace and heated, thereby reducing the iron oxide in the agglomerate and further heating. A method for producing granular metallic iron by melting reduced iron and agglomerating the reduced iron,
Average particle diameter R (mm) of the agglomerates,
The amount of oxygen (% by mass) derived from the iron oxide-containing substance contained in the agglomerate,
The amount of fixed carbon derived from the carbonaceous reducing agent contained in the agglomerate (mass%) and the amount of carbon [C _VM ] (mass%) in the volatile matter derived from the carbonaceous reducing agent contained in the agglomerated material The manufacturing method of granular metallic iron characterized by satisfying the following formula (1).
6.91 ≦ R ^0.5 × oxygen amount / (fixed carbon amount + 0.3 × [C _VM ]) ≦ 7.19 (1)   The manufacturing method according to claim 1, wherein an average particle diameter R of the agglomerate is 10 to 30 mm.

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