JP2014181369A - Method of producing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing reduced iron which can melt rapidly byproduct slag of reduction of iron oxide even when an iron ore containing AlOis used and heated at e.g. 1,500°C or lower and reduce the reaction time of reduction of iron oxide.SOLUTION: A method of producing reduced iron by heating lumps composed of an iron ore containing AlOand a carbonaceous reductant to reduce iron oxide in the lumps uses an iron ore of a Blaine index(BI) of 2,000-3,000 cm/g, and the alkalinity (CaO/SiO) determined from the contents of CaO and SiOin the lumps is adjusted to 0.9-1.2 by adding CaCOto the mixture. With the total amount of CaO, SiOand AlOcontained in the lumps converted as 100 mass%, the amount of AlOis 20 mass% or lower and higher than 0%.

Description

The present invention heats an agglomerate composed of a mixture containing iron ore containing Al ₂ O ₃ and a reducing agent containing carbon such as a carbonaceous material (hereinafter sometimes referred to as a carbonaceous reducing agent), The present invention relates to a method for producing reduced iron by reducing iron oxide in the agglomerate.

  Developed a direct reduction iron manufacturing method in which agglomerates composed of a mixture containing iron ore and a carbonaceous reducing agent are charged into a heating furnace and heated, and iron oxide in the agglomerates is reduced to produce reduced iron. Has been. In this direct reduction iron manufacturing method, coal that was difficult to use in the blast furnace method can be used as a carbonaceous reducing agent, and an agglomerate (for example, pellets) made of a mixture obtained by adding iron ore to this is used as a raw material. . Then, by heating the pellet, iron oxide is reduced by the reducing gas generated from the carbonaceous reducing agent in the pellet, and a reduced iron skin is formed and grows outside the pellet. Inside, the reduction proceeds in a solid state until iron oxide is substantially absent. When heating is further continued, the slag produced as a by-product during the reduction of iron oxide melts and flows out from the inside of the pellet to the outside of the reduced iron skin. The reduced iron and slag obtained in this way are cooled and solidified, and the slag is crushed and the reduced iron solidified is selected by magnetic separation or sieving, or is heated and melted to separate it into hot metal and slag by the difference in specific gravity. Can be obtained (Patent Document 1).

By the way, iron ore is mined from iron ore deposits, and iron ore containing a large amount of Al ₂ O ₃ as a gangue component is mined from sedimentary ore deposits that exist in large quantities among iron ore deposits. It is known that when the amount of Al ₂ O ₃ contained in the iron ore increases, the melting point of the slag formed from the gangue component contained in the iron ore at the time of reduction of iron oxide increases.

Here, the iron ore which has been produced in the world each place of the gangue component contained in iron ore, SiO ₂ and Al ₂ O ratio of the amount of Al ₂ O ₃ to the total amount of _{3 [100 × Al 2 O 3} / FIG. 1 shows the relationship between (SiO ₂ + Al ₂ O ₃ )] and the melting point of slag calculated based on the amounts of SiO ₂ , Al ₂ O ₃ , CaO, and MgO. Figure 1 is intended by the present applicant prepared to organize the data of the world's iron ore, as is clear from FIG. 1, the ratio of the amount of Al ₂ O ₃ to the total amount of SiO ₂ and Al ₂ O ₃ When the content exceeds 30%, the melting point of the slag is found to be 1500 ° C. or higher.

Japanese Patent Laid-Open No. 9-256017

In the direct reduction iron manufacturing method, the temperature at which the agglomerate is heated in a heating furnace is usually about 1500 ° C., and this heating temperature is desired to be lower. Therefore, as described above, when the amount of Al ₂ O ₃ contained in the iron ore as a gangue component increases and the melting point of the slag becomes high (eg, 1500 ° C. or higher), the agglomeration containing the iron ore and the carbonaceous reducing agent. Even if an object is heated to reduce the iron oxide in the agglomerate, melting of the slag is not promoted, so that the reduction of iron oxide does not proceed. Therefore, the reaction time required for the reduction of iron oxide becomes long, and the productivity of reduced iron decreases. In addition, when the melting point of slag becomes high and the slag hardly melts, it becomes difficult to separate the reduced iron from the slag, so the yield of reduced iron is deteriorated.

The present invention has been made paying attention to the above-mentioned circumstances, and the purpose thereof is to reduce iron oxide even when heated at 1500 ° C. or less using an iron ore containing Al ₂ O _3. An object of the present invention is to provide a method for producing reduced iron, in which slag that is sometimes produced as a by-product can be rapidly melted, and the reaction time when reducing iron oxide can be shortened. Another object of the present invention is to produce reduced iron that can satisfactorily separate reduced iron produced by reducing iron oxide and slag produced as a by-product during the reduction, thereby improving the yield of reduced iron. It is to provide a method. Moreover, the other object of this invention is to provide the manufacturing method of reduced iron which can raise the intensity | strength of an agglomerate.

The method for producing reduced iron according to the present invention capable of solving the above-mentioned problem is to heat an agglomerate composed of a mixture containing iron ore containing Al ₂ O ₃ and a carbonaceous reducing agent, A method of producing reduced iron by reducing iron oxide in a composition, and using the iron ore having a Blaine index (hereinafter sometimes referred to as BI) of 2000 to 3000 cm ² / g, By adding CaCO ₃ to the mixture, the basicity (CaO / SiO ₂ ) determined from the contents of CaO and SiO ₂ in the agglomerate is in the range of 0.9 to 1.2, and the agglomerate The amount of Al ₂ O ₃ when converted so that the total amount of CaO, SiO ₂ and Al ₂ O ₃ contained in the composition is 100% by mass is 20% (meaning mass%, the same shall apply hereinafter) or less (0 % Not included) ing. In addition, BI means the specific surface area measured by the Blaine method.

As the agglomerates, those having an apparent density of 2.1 g / cm ³ or more are preferably used. It is also preferable to add a binder to the mixture and to make the amount of the binder contained in the agglomerated material 0.8 to 2.0%.

According to the present invention, iron ore having a BI in a predetermined range is used, and CaCO ₃ is added to a mixture containing iron ore and a carbonaceous reducing agent to adjust the basicity of the agglomerate, and Since the amount of Al ₂ O ₃ contained in the agglomerate is appropriately adjusted, iron ore containing Al ₂ O ₃ is used, for example, even when heated at 1500 ° C. or less, the slag is promptly It can be melted and the reaction time can be shortened.

Figure 1, of the gangue component contained in iron ore, the basis of the ratio of the amount of Al ₂ O ₃ to the total amount of SiO ₂ and _{Al 2 O 3, SiO 2,} Al 2 O 3, CaO, and MgO amount It is a graph which shows the relationship with the melting | fusing point of slag computed by these. FIG. 2 is a graph showing the relationship between the basicity of the pellet and the yield of reduced iron. FIG. 3 is a SiO ₂ —CaO—Al ₂ O ₃ phase diagram when MgO is 5%. FIG. 4 is a graph showing an example of the particle size distribution of iron ore obtained by pulverization. FIG. 5 is a graph showing a relationship between iron ore BI and pellet drop strength.

In order to reduce the reaction time when the iron oxide is reduced by rapidly melting the slag produced as a by-product during the reduction of the iron oxide, even when the iron ore containing Al ₂ O ₃ is used. , Have been intensively studied. As a result, iron ore having a BI of 2000 to 3000 cm ² / g is used, the basicity of the agglomerate is adjusted to an appropriate range, and the amount of Al ₂ O ₃ contained in the agglomerate is below a predetermined amount. The present invention has been completed by finding that the above problem can be solved by reducing it to a minimum. The present invention will be described below.

When using iron ore with a high Al ₂ O ₃ content, there is a method to lower the melting point by lowering the basicity, but if the amount of limestone added is reduced, the concentration of Al ₂ O ₃ increases, so the melting point of the slag Turned out to rise. Therefore, in the present invention, the basicity (that is, the amount of limestone added) is controlled within an appropriate range while taking into account the Al ₂ O ₃ concentration in the slag.

That is, when the amount of Al ₂ O ₃ in the gangue contained in the iron ore increases, the melting point of the slag produced during the reduction of iron oxide increases, so even if the agglomerate is heated in a heating furnace, Melting is not promoted. If the slag does not melt, the reduction of the iron oxide is difficult to proceed, so that the reaction time required for the reduction of the iron oxide becomes long and the productivity of the reduced iron decreases.

Therefore, the present inventors first tried to lower the melting point of slag by adding a secondary material to a mixture containing iron ore and a carbonaceous reducing agent to lower the melting point of gangue contained in the iron ore. . At this time, it was thought that if the contact area between the iron ore and the auxiliary material was increased by pulverizing the iron ore, the reaction rate between the iron ore and the auxiliary material could be increased. Specifically, iron ore having a Blaine index (BI) of 2000 to 3000 cm ² / g was used. BI is an index obtained based on the Blaine method, and is an index representing the specific surface area.

However, even when an auxiliary material was added to the above mixture and an iron ore having a BI of 2000 to 3000 cm ² / g was used, the melting point of the slag was not sufficiently lowered, and the reaction time could not be shortened sufficiently.

Next, the present inventors paid attention to the basicity of slag. This is because it is known that the CaO—SiO ₂ —Al ₂ O ₃ slag generally decreases the melting point of the slag when the basicity (CaO / SiO ₂ ) is lowered.

In order to lower the basicity of slag, among the auxiliary materials blended in the above mixture, the amount of CaCO ₃ that is usually used for adjusting the basicity was reduced. As a result, the basicity determined from the content of CaO and SiO ₂ in the agglomerate was decreased. However, it has been found that the melting point of the slag does not decrease and the melting point of the slag increases. Therefore, the reason why the melting point of the slag cannot be sufficiently lowered even when the basicity is lowered was examined. In the case of the slag having the component composition of the present invention, when the amount of CaCO ₃ is lowered, the agglomerate is reduced. It was found that the amount of Al ₂ O ₃ when converted so that the total amount of CaO, SiO ₂ , and Al ₂ O ₃ contained in the mixture was 100% by mass increased and the melting point of the slag rose.

Therefore, in the present invention, as a result of repeating various experiments, the basicity determined from the contents of CaO and SiO ₂ in the agglomerate is within the range of 0.9 to 1.2, and is included in the agglomerate. CaCO _{3 is} added to the mixture so that the amount of Al ₂ O ₃ when converted so that the total amount of CaO, SiO ₂ and Al ₂ O ₃ is 100% by mass is 20% or less (not including 0%). It was decided to add.

As described above, according to the present invention, the iron ore is finely pulverized to increase the specific surface area (that is, the reaction interfacial area for slag formation), and added to the mixture constituting the agglomerate. By adjusting the ₃ amount, the basicity of the agglomerate and the amount of Al ₂ O ₃ contained in the agglomerate are adjusted. As a result, the melting point of slag is lowered, the reaction time of iron oxide is shortened, and the productivity of reduced iron is improved.

In the present invention, an agglomerate composed of a mixture containing iron ore containing Al ₂ O ₃ and a carbonaceous reducing agent is heated, and iron oxide in the agglomerate is reduced to produce reduced iron. Examples of the iron ore containing Al ₂ O ₃ include Australian and Indian hematite ores.

The amount of Al ₂ O ₃ contained in the iron ore is not particularly limited. In the present invention, even if the iron ore contains 1.0% or more (particularly 1.9% or more) of Al ₂ O ₃ , Can be used. The upper limit of the amount of Al ₂ O ₃ is not particularly limited, but is, for example, 5.0% or less (particularly 4.1% or less). The iron ore may contain MgO or TiO ₂ . MgO and TiO ₂ are also components that act to increase the melting point of slag.

In the present invention, it is important to use the iron ore having a Blaine index (BI) of 2000 to 3000 cm ² / g. When the iron ore BI is less than 2000 cm ² / g, the specific surface area is small, the contact interface with the auxiliary material is small, the melting of the gangue contained in the iron ore cannot be promoted, and the reaction time of the iron oxide is shortened. I can't. Thus the iron ore BI is, 2000 cm ² / g or more, preferably 2100 cm ² / g or more, more preferably 2200 cm ² / g or more. However, if BI of iron ore exceeds 3000 cm ² / g, it is easy to form pseudo particles when mixing with the carbonaceous reducing agent, and uniform mixing becomes difficult. Thus BI of iron ore 3000 cm ² / g or less, preferably 2800 cm ² / g or less, and more preferably not more than 2600 cm ² / g.

  The BI of the iron ore can be measured by the Blaine method, and may be measured based on the method defined in JIS R5201.

In the present invention, iron ore obtained by pulverizing raw iron ore so that BI is 2000 to 3000 cm ² / g can be used.

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

  In the present invention, an agglomerate produced by agglomerating a mixture containing the iron ore and the carbonaceous reducing agent is used. As the carbonaceous reducing agent, for example, coal or coke can be used. it can.

In the present invention, by adding CaCO ₃ to the mixture,
(A) the basicity (CaO / SiO ₂ ) determined from the contents of CaO and SiO ₂ in the agglomerate is in the range of 0.9 to 1.2, and (b) CaO contained in the agglomerate, It is important that the Al ₂ O ₃ content is 20% or less (excluding 0%) when converted so that the total amount of SiO ₂ and Al ₂ O ₃ is 100% by mass.

When (a) basicity basicity is less than 0.9, generally tend to decrease the melting point of the slag, but CaCO ₃ added as basicity below 0.9, dilute the Al ₂ O ₃ effect Therefore, the concentration of Al ₂ O ₃ in the slag increases and the slag becomes difficult to melt. Accordingly, the basicity is 0.9 or more, preferably 0.95 or more, more preferably 1.0 or more. However, if the basicity exceeds 1.2, the melting point of slag increases, so that the reduction of iron oxide is difficult to proceed and the reaction time becomes longer. Accordingly, the basicity is 1.2 or less, preferably 1.15 or less, more preferably 1.1 or less.

(B) the amount of Al ₂ O ₃ amount of Al ₂ O ₃ accounts for the total amount exceeds 20%, the said basicity can not be lowered sufficiently the melting point of the slag is adjusted in the above range, slag Cannot be accelerated and the reaction time of iron oxide cannot be shortened. Therefore, the Al ₂ O ₃ content in the total amount is 20% or less, preferably 18% or less, more preferably 16% or less.

  You may mix | blend a melting | fusing point regulator with the said mixture further. The melting point modifier means a substance that affects the melting point of components (particularly gangue) other than iron contained in the agglomerate, excluding substances that affect the melting point of iron. That is, by adding a melting point adjusting agent as 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, part of the iron oxide is dissolved in the molten slag and reduced in the molten slag to become reduced iron. 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, it is preferable to use one containing a CaO supply substance. As the CaO feed materials, for example, CaO (quicklime), Ca (OH) ₂ (hydrated lime), and CaMg (CO _{3) 2} can be blended at least one selected from the group consisting of (dolomite).

As the melting point adjusting agent, only the CaO supply substance may be added, or in addition to the CaO supply substance, for example, an MgO supply substance, a SiO ₂ supply substance, or the like may be added. Similarly to CaO, MgO and SiO ₂ are substances that affect the melting point of components (particularly gangue) other than iron contained in the agglomerate. As the MgO supply substance, for example, at least one selected from the group consisting of MgO powder, Mg-containing substance extracted from natural ore or seawater, and MgCO ₃ can be used. As the SiO ₂ supply substance, for example, SiO ₂ powder or silica sand can be used.

  The agglomerate may further contain a binder as a component other than iron ore, a carbonaceous reducing agent, and a melting point adjusting agent. Examples of the binder include polysaccharides (for example, starch such as corn starch and wheat flour).

  The amount of the binder contained in the agglomerate is preferably 0.8 to 2.0%. By setting the binder amount to 0.8% or more, the strength of the agglomerate can be increased. The amount of the binder is more preferably 0.9% or more, and further preferably 1.0% or more. However, if the amount of the binder exceeds 2.0%, the cost becomes high, and the amount of the binder becomes excessive, so that the strength of the agglomerate decreases. Accordingly, the binder amount is preferably 2.0% or less, more preferably 1.5% or less, and still more preferably 1.2% or less.

  As a mixer which mixes the said mixture, a rotating container type mixer and a fixed container type mixer can be used, for example. As the rotary container type mixer, for example, a rotary cylinder type, double cone type, V type mixer or the like can be used. As the fixed container mixer, for example, a mixer provided with rotating blades (for example, a bowl) in a mixing tank can be used.

  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 may be, for example, a lump shape, a granular shape, a briquette shape, a pellet shape, a rod shape, or the like, and preferably 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. In addition, heat transfer to the lower part of the agglomerate is deteriorated, and productivity is lowered. In addition, the lower limit of the particle size of the agglomerate is about 5 mm.

In the present invention, as the agglomerates, those having an apparent density of 2.1 g / cm ³ or more are preferably used, and the yield of reduced iron can be improved. The apparent density of the agglomerate is more preferably 2.2 g / cm ³ or more, and still more preferably 2.3 g / cm ³ or more. Note that the upper limit of the apparent density may be, for example, 2.5 g / cm ³ or less.

  The apparent density of the agglomerate is a value obtained by immersing the agglomerate in mercury (liquid) and measuring its buoyancy. The apparent density of the agglomerate may be calculated by simply coating the surface of the agglomerate thinly with molten paraffin and measuring the volume and mass.

  The method for increasing the apparent density is not particularly limited. For example, the time (granulation time) for granulating the mixture may be increased and granulated over time.

  The granulation time is, for example, preferably 5 minutes or more, more preferably 8 minutes or more, and further preferably 10 minutes or more. The upper limit of the granulation time is not particularly limited, but is preferably 15 minutes or less from the viewpoint of productivity.

  The agglomerate may be charged in a heating furnace and heated, and reduced iron may be produced by reducing iron oxide in the agglomerate.

  As the heating furnace, for example, a moving hearth furnace can be used. The moving hearth furnace 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 so that the outer shape of the hearth is circular (doughnut shape) so that the start point and end point of the hearth are in the same position, and the agglomerate supplied on the hearth is During one round of the inside, it is reduced by heating (granular) to produce reduced iron. Therefore, the rotary hearth furnace is provided with charging means for supplying the agglomerate into the furnace on the most upstream side in the rotation direction, and the most downstream side in the rotation direction (since it is a rotating structure, Discharging means is provided immediately upstream of the means). The tunnel furnace is a heating furnace in which the hearth moves in the furnace in a linear direction.

  The agglomerate may be heated and reduced, for example, at 1300 to 1500 ° C. in the heating furnace, preferably 1300 to 1450 ° C.

  It is also a preferable aspect that a floor covering material is laid on the hearth of the moving hearth heating furnace prior to charging the agglomerate into the furnace. You can protect the hearth by laying the floor covering. As the floor covering material, refractory particles can be used in addition to those exemplified as the carbonaceous reducing agent.

  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.

(Experiment 1)
In Experiment 1, the influence of the basicity (CaO / SiO ₂ ) determined from the contents of CaO and SiO ₂ in the agglomerate on the yield of reduced iron was examined.

An agglomerate composed of a mixture containing iron ore containing Al ₂ O ₃ and a carbonaceous reducing agent was heated, and iron oxide in the agglomerate was reduced to produce reduced iron.

  The composition of the iron ore is shown in Table 1 below. In Table 1 below, T.W. Fe means the total iron content, and LOI means the ignition loss.

As said iron ore, what was grind | pulverized so that a Blaine index | index (BI) might be set to 2280 cm < ² > / g using the ball mill was used.

Based on the component composition shown in Table 1, among the gangue components contained in the iron ore, SiO ₂ and Al ₂ Al to the total amount of O _{3 2} O ₃ amount ratio [100 × Al ₂ O ₃ / (SiO ₂ + Al ₂ O ₃ )] was calculated to be 35% as shown in the following formula.
100 × Al ₂ O ₃ / (SiO ₂ + Al ₂ O ₃ ) = 100 × 1.69 / (3.10 + 1.69) = 35%

Based on the calculated proportion of the Al ₂ O ₃ amount and FIG. 1 shown above, the melting point of the gangue component was read to be 1580 ° C.

  As the carbonaceous reducing agent, bituminous coal having the composition shown in Table 2 below was used. In Table 2 below, T.M. S means the total amount of sulfur. In addition, as the bituminous coal, that whose mass of the powder which passes a 200-mesh sieve exceeds 80% with respect to the mass of the whole bituminous coal was used.

The iron ore and bituminous coal were blended with CaCO ₃ (limestone), dolomite, and fluorite as melting point modifiers, and starch-based starch was blended as a binder to produce pellets (agglomerates). The blending ratios of iron ore, bituminous coal, limestone, dolomite, fluorite, and binder are shown in Table 3 below. The pellets were granulated so that the particle diameter was 19 mm.

Based on the blending ratio shown in Table 3 below, pellets were produced with the basicity (CaO / SiO ₂ ) adjusted to the range of 0.7 to 1.3 by changing the amount of CaCO ₃ added.

  The obtained pellets were charged into an electric furnace and heated (about 10 minutes) at 1450 ° C. until the reduced iron and slag melted and separated to produce reduced iron.

Reduced iron, slag, and the like obtained by heating were discharged from the furnace, and the yield of reduced iron was calculated. The yield of reduced iron was calculated based on the ratio of the mass of reduced iron having a particle size of 3.35 mm or more with respect to the total amount of iron contained in the raw material (pellet) charged into the heating furnace.
Yield (%) = 100 × (mass of reduced iron having a particle size of 3.35 mm or more) / (total amount of iron contained in raw material)

  The relationship between the basicity of the pellet and the yield of reduced iron is shown in FIG. As shown in FIG. 2, the yield of reduced iron was 92% or more when the basicity was in the range of 0.9 to 1.2. On the other hand, from FIG. 2, when the basicity of the pellet was less than 0.9 or exceeded 1.2, a tendency for the yield to decrease could be read. That is, when the basicity was less than 0.9 and became 0.7, the yield of reduced iron decreased at a stretch to about 87%. When the basicity was 0.7, the yield calculated based on the mass of reduced iron having a particle size of 3.35 mm or more was 87%, but the yield of all recovered iron was 96%. Therefore, it can be seen that when the basicity was 0.7, a large amount of reduced iron having a particle size of less than 3.35 mm was produced. Further, even when the basicity exceeded 1.2 and reached 1.25, the yield of reduced iron showed a decreasing tendency, and the yield was about 89.5%.

  From the above results, it was found that the yield of reduced iron can be improved by controlling the basicity within the range of 0.9 to 1.2.

(Experiment 2)
In Experiment 1, it was found that the yield of reduced iron was improved by adjusting the basicity of the agglomerates to an appropriate range. Therefore, in Experiment 2, the relationship between basicity and the melting point of slag was examined. That is, in Experiment 2, while maintaining the mass ratio of the amount of iron contained in the iron ore shown in Table 3 of Experiment 1 and the amount of fixed carbon contained in the bituminous coal to be constant, the composition of CaCO ₃ Pellet having different basicity (CaO / SiO ₂ ) was produced by changing the ratio.

  First, pellets having the blending ratio shown in Table 3 above were used. The pellets having the blending ratios shown in Table 3 below had a basicity of 1.05, and the amount of MgO contained in the pellets was 0.50%.

When Al ₂ O _{3 is set} to 20% (constant), the basicity (CaO / SiO ₂ ) is decreased in order of 1.14 → 0.87 → 0.67, as shown in FIG. 3 by b1 → b2 → b3. In addition, the melting point decreases from 1460 ° C. → 1340 ° C. → 1320 ° C. Thus, when Al ₂ O ₃ moves on a straight line where 20% is constant, the melting point of slag is lowered and the melting becomes easier when the basicity is reduced.

However, reducing the basicity reduces the amount of limestone (CaCO ₃ amount) to be blended, so the effect of diluting Al ₂ O ₃ with CaO is diminished. Therefore, the Al ₂ O ₃ concentration in the slag becomes high. Therefore, when the basicity is decreased, the Al ₂ O ₃ concentration actually increases as the basicity decreases, as indicated by a1 → a2 in FIG. At this time, if the basicity is lowered, the melting point once decreases, but the melting point rises again and the slag becomes difficult to dissolve. Therefore, when the relationship between the basicity and the Al ₂ O ₃ concentration in the slag was examined, it was confirmed that the Al ₂ O ₃ concentration in the slag increases when the basicity is decreased.

From the above results, the basicity (CaO / SiO ₂ ) determined from the content of CaO and SiO _{2 in} the pellet is in the range of 0.9 to 1.2, and CaO, SiO ₂ , and Al contained in the pellet _It can be seen that the melting point of the slag can be lowered if the amount of Al ₂ O ₃ when converted so that the total amount of ₂ O ₃ is 100% by mass is 20% by mass or less. If the melting point of slag can be lowered, it is considered that the reaction time when reducing iron oxide can be shortened.

(Experiment 3)
In Experiment 3, in order to increase the contact efficiency between the auxiliary raw material and the slag, the relationship between the iron ore particle size and the drop strength of the dried pellets was examined focusing on the iron ore particle size.

An example of the particle size distribution of iron ore obtained by grinding is shown in FIG. In FIG. 4, the horizontal axis indicates the particle diameter (diameter Dp) of the iron ore powder, and the vertical axis indicates the accumulation (%). In FIG. 4, ● indicates the result of BI of 1540 cm ² / g, and ○ indicates the result of BI of 2310 cm ² / g.

The basic compounding proportions shown in Table 3 in the above experiment 1, BI to 1200 cm ² / g of iron ore, 1500cm ² / g, or a 2300 cm ² / g, the amount of binder 0.6 to 1.2% Pellets were produced in the range of. As the binder, starch-based starch was used.

  About the obtained pellet, drop strength was investigated in the following procedure. The pellet drop strength is such that the obtained pellet is naturally dropped from a position 45 cm above the steel plate, and the proportion of small fragments separated from the pellet body is 10% by mass with respect to the mass of the agglomerate before the number of drops is measured. The number of times immediately before exceeding was the number of drops. The measurement was performed on 10 agglomerates, and the average value of the measurement results was taken as the drop strength.

  The relationship between the iron ore BI and the drop strength of the pellets is shown in FIG. From FIG. 5, it can be considered as follows. When the blending amount of the binder is constant (0.6%, 0.8%, 1.0%, or 1.2%), as the BI becomes larger and the iron ore becomes finer, the drop strength of the pellet becomes smaller. The tendency to decline can be read. When iron ore is pulverized, the specific surface area of the iron ore increases (that is, BI increases). Therefore, in order to ensure the strength of the pellets, it is necessary to increase the blending amount of the binder.

Also, BI is constant in the case of ^{(1200cm 2 / g, 1500cm 2} / g or 2300 cm ² / g,), as increasing the amount of binder, read tends to drop strength of the pellets is increased. However, increasing the blending amount of the binder increases the cost, which is a negative factor economically.

From the above results, it is considered that when the iron ore having a BI of 2000 to 3000 cm ² / g is used, the amount of binder contained in the agglomerate may be controlled in the range of 0.8 to 2.0%.

(Experiment 4)
In Experiment 4, pellets having different apparent densities were produced by changing the granulation time based on the blending ratio shown in Table 3 in Experiment 1 above.

As the iron ore, BI of 1540 cm ² / g or 2310 cm ² / g was used. The blending amount of the binder was 0.8%, 0.9%, or 1.0%. The basicity (CaO / SiO ₂ ) determined from the contents of CaO and SiO ₂ in the pellet was 1.04 to 1.25. The Al ₂ O ₃ content when converted so that the total amount of CaO, SiO ₂ and Al ₂ O ₃ contained in the pellets was 100% was 17.96 to 18.93%.

  These mixtures were granulated with a granulator to produce pellets. The granulation time is no. When the granulation time in 1 was the standard granulation time (= 1.0), it was expressed as a relative value (relative granulation time).

  The apparent density of the pellet was determined by immersing the agglomerate in mercury (liquid) and measuring its buoyancy. Further, the drop strength of the pellets was measured by the procedure shown in Experiment 3 above.

The iron ore BI, the binder content, the basicity of the pellet, the amount of Al ₂ O ₃ contained in the pellet, the relative granulation time, the apparent density of the pellet, and the drop strength are shown in Table 4 below.

  Next, the obtained pellets were charged into an electric furnace and heated (about 10 minutes) at 1450 ° C. until the reduced iron and slag were melted and separated to produce reduced iron. At this time, the reaction time until the pellet was dissolved was monitored by monitoring with a video camera. Further, the yield of reduced iron was calculated by the same procedure as in Experiment 1. The reaction time and yield are also shown in Table 4 below.

  From Table 4 below, it can be considered as follows. No. In Nos. 1 and 4, since the BI of the iron ore used was outside the range defined in the present invention, the reaction time was long. No. In No. 5, since the basicity of the pellet was outside the range defined in the present invention, the reaction time was long.

  On the other hand, no. Examples 2 and 3 are examples that satisfy the requirements defined in the present invention. Shorter than 1. In addition, the yield of reduced iron was improved. No. 3 is No.3. Since the granulation was performed with the relative granulation time 1.8 times that of 2, the apparent density of the pellets increased. As a result, the yield of reduced iron was No. Improved than 2. No. In No. 3, since the apparent density was increased, the binder amount was No. Even if it is less than 1, the drop strength of the pellet is No. 1. Higher than 1.

Here, no. No. 3, no. The productivity index of reduced iron with respect to 1 was calculated based on the following formula. As a result, no. The productivity of No. 3 is no. 18.9% higher than 1.
Productivity index = A x B x C
However, A to C are as follows.
A = (apparent density of No. 3) / (apparent density of No. 1)
B = (No. 1 reaction time) / (No. 3 reaction time)
C = (No. 3 yield) / (No. 1 yield)
Productivity index = (2.319 / 2.093) × (9.00 / 8.80) × (98.8 / 94.1) = 1.189

Claims (3)

In the method for producing reduced iron by heating an agglomerate comprising a mixture containing iron ore containing Al ₂ O ₃ and a carbonaceous reducing agent, and reducing iron oxide in the agglomerate,
As the iron ore, one having a Blaine index (BI) of 2000 to 3000 cm ² / g,
By adding CaCO ₃ to the mixture,
The basicity (CaO / SiO ₂ ) determined from the contents of CaO and SiO ₂ in the agglomerate is in the range of 0.9 to 1.2, and CaO, SiO ₂ contained in the agglomerate, and The amount of Al ₂ O ₃ when converted so that the total amount of Al ₂ O ₃ is 100% by mass is 20% (meaning mass%; the same shall apply hereinafter) or less (not including 0%). A method for producing reduced iron. The manufacturing method according to claim 1, wherein an agglomerated material having an apparent density of 2.1 g / cm ³ or more is used. While further blending a binder to the mixture,
The manufacturing method of Claim 1 or 2 which makes the amount of binders contained in the said agglomerate 0.8 to 2.0%.