JP5503420B2 - Method for producing granular metal - Google Patents

Description

  In the present invention, an agglomerate made of a mixture containing a metal oxide and a carbonaceous reducing agent is supplied onto a hearth and heated, and the metal oxide in the raw material mixture is reduced and melted to produce a granular metal. It is about the method.

  In the present specification, the description will be made mainly on the method for producing granular metallic iron in which the present invention is most effectively utilized, but the present invention is not limited to this, for example, chromium-containing ore or nickel-containing It can also be used effectively when ferrochrome or ferronickel is produced by heating or reducing ore. Further, in the present invention, “granular” does not necessarily mean a true sphere, but includes an oval shape, an egg shape, or a flattened shape thereof.

  A direct reduction iron manufacturing method has been developed as a method for obtaining granular metallic iron from an agglomerate obtained from a mixture containing an iron oxide-containing substance such as iron ore or iron oxide and a carbonaceous reducing agent. In this iron making method, the agglomerate is charged onto the hearth of a heating furnace, and the iron oxide in the agglomerate is reduced with a carbonaceous reducing agent by heating in the furnace with gas heat transfer or radiant heat by a heating burner. Then, the obtained reduced iron is subsequently carburized and melted, and then aggregated into granules while being separated from by-product slag, and then cooled and solidified to obtain granular metallic iron.

  Since the iron making method does not require a large-scale facility such as a blast furnace, and coke is not required, it is highly flexible in terms of resources. Therefore, practical research has been actively conducted recently. However, for implementation on an industrial scale, there are many problems that must be further improved, including operational stability, safety, economy, quality of granular metallic iron (product), productivity, and the like. Therefore, the present applicant describes in Patent Document 1 the consumption amount of the carbonaceous reducing agent and the thermal energy required for the heating reduction when producing a metallic iron by heating and reducing a molded body containing the carbonaceous reducing agent and iron oxide. We have previously proposed a method that can minimize iron oxide and reduce iron oxide on a practical scale at a lower cost and more efficiently. In the examples of this document, an example in which metallic iron is produced by heating and reducing pellets having an average diameter of 17 mm produced by blending and granulating iron ore, a carbonaceous material, and a binder is disclosed.

Japanese Patent Laid-Open No. 11-241111

  According to the above-mentioned Patent Document 1, the blending amount of the carbonaceous reducing agent, the stoichiometric amount required for the reduction of iron oxide, the amount of solid solution C in the produced metal iron, and further the melting point of metal iron accompanying the C solid solution By appropriately controlling the heating temperature in consideration of the above, the heat reduction of iron oxide and the separation of slag by melting can be carried out efficiently with the minimum amount of carbonaceous reducing agent used and the heating temperature. We have established a more economical and practical method for producing metallic iron on a scale. However, it is required to further increase the production amount of granular metallic iron per unit time per effective hearth unit area and improve productivity.

  The present invention has been made paying attention to the above-mentioned circumstances, and the object thereof is to heat an agglomerate containing a metal oxide and a carbonaceous reducing agent to thereby include a metal oxide contained in the agglomerate. The purpose of this invention is to propose a technique for further improving the productivity of granular metal in the production of granular metal by reducing melting.

  The method for producing a granular metal according to the present invention capable of solving the above-mentioned problem is to supply an agglomerate containing a metal oxide and a carbonaceous reducing agent onto the hearth of a moving bed type reductive melting furnace and heat it. Then, after reducing and melting the metal oxide, the granular metal obtained is cooled and then discharged to the outside of the furnace to be recovered, and the agglomerated bed density on the hearth is reduced to 0. When heating as 0.5 or more, the present invention is summarized in that an agglomerate having an average diameter of 17.5 mm or more is supplied onto the hearth.

  It is preferable to lay a carbonaceous material in advance on the hearth and supply the agglomerated material in a single layer on the carbonaceous material layer.

  As the metal oxide, for example, iron oxide can be used. As the moving bed type reduction melting furnace, for example, a rotary hearth furnace can be used. As the metal oxide, for example, iron dust can be used.

  According to the present invention, since the average diameter of the agglomerate supplied onto the hearth and the bed density of the agglomerate when heating the agglomerate on the hearth are appropriately controlled, the productivity of the granular metal is increased. Can be improved.

FIG. 1 is a plan view schematically showing agglomerates spread on the hearth. FIG. 2 is a drawing-substituting photograph showing a state when an agglomerate having an average diameter of 18.2 mm is spread. FIG. 3 is a graph showing the relationship between the distance r between the agglomerates and the projected area ratio or bed density. FIG. 4 is a graph showing the relationship between the bed density and the amount of agglomerate supplied to the furnace. FIG. 5 is a graph showing the relationship between the average diameter (Dp) of the test material (agglomerate) and the reaction time. FIG. 6 is a graph showing the relationship between the average diameter of agglomerates and the productivity index when granular metallic iron is produced with a fixed density of agglomerates. FIG. 7 is a graph showing the relationship between the average diameter of the agglomerate and the productivity index when the granular metallic iron is produced with a constant distance r between the agglomerates (test materials) on the hearth.

The present inventor supplies and heats an agglomerate containing a metal oxide and a carbonaceous reducing agent onto the hearth of a moving bed type reductive melting furnace to reduce and melt the metal oxide contained in the agglomerate. In order to improve the productivity when producing granular metal, we have made extensive studies. as a result,
(A) Prepare an agglomerate having an average diameter of 17.5 mm or more,
(B) The present inventors have found that the productivity of the granular metal can be improved by heating the agglomerate density on the hearth to 0.5 or more. The background to the completion of the present invention is as follows.

  In Patent Document 1, pellets (agglomerates) having an average diameter of 17 mm are used as a compact when producing a metallic iron by heating and reducing a compact including a carbonaceous reducing agent and iron oxide. The agglomerate having an average diameter of 17 mm is used because the larger the agglomerate, the longer the heat transfer to the agglomerate on the hearth in the furnace, and the longer the reaction time, the higher the productivity. It was because it was thought to be worse.

  However, when the present inventors examined in more detail the relationship between the size of the agglomerate and the productivity, it was possible to improve productivity by using an agglomerate having an average diameter of 17.5 mm or more. The fact became clear. This will be described with reference to FIG.

  FIG. 7 is a graph shown in Examples described later, and shows the relationship between the average diameter of agglomerates and the productivity index. In FIG. 7, the productivity index is a relative value when the productivity when the granular metallic iron is manufactured using an agglomerate having an average diameter of 17.5 mm (1.75 cm) is 1.000. This productivity is the production amount of granular metallic iron per unit time per effective hearth unit area (details will be described later).

  As is clear from FIG. 7, the agglomerate having an average diameter of 17.5 mm or more (specifically, the average diameter is smaller than that of the agglomerate having an average diameter of 16.0 mm (1.6 cm)). It can be seen that using 17.5 to 32 mm) increases the productivity index and improves the productivity.

  FIG. 7 shows the relationship when the distance r between the agglomerates on the hearth is constant based on various experimental results (that is, when the density of the agglomerate on the hearth is changed). The result of re-evaluation (simulation) is shown. FIG. 7 shows the result of re-evaluation based on the result of FIG. 5. As can be seen from the relationship between the average particle size and the reaction time shown in FIG. 5, the actual measurement value varies slightly. A leveling method that approximates the relationship between the two with a curve and re-evaluated using the curve was adopted. This is one of the scientific analysis methods.

  Since the most important factors in evaluating productivity are reaction time and yield (ie, product recovery), these characteristics were particularly leveled and re-evaluated based on experimental data. The apparent density of the agglomerates is also an important factor affecting productivity. For example, the agglomerates having a particle size in the range of 16.0 mm to 32.0 mm have the same agglomeration. As long as the method is adopted, there is little variation in the apparent density, and it is evaluated beforehand that there is no problem even if it is regarded as almost constant in the comprehensive evaluation. Here, the bed density indicates the packing density of the agglomerate laid per effective hearth unit area, and this density can be calculated from the projected area of the agglomerate on the hearth (details will be described later). ). In FIG. 7, as shown in the examples described later, as the average diameter of the agglomerates increases, the bed density of the agglomerates increases (see Table 6). Therefore, it can be read from FIG. 7 that productivity can be improved by appropriately controlling the floor density in addition to the average diameter of the agglomerates. That is, according to this invention, it became clear that productivity of granular metallic iron can be improved by controlling together with the bed density and average diameter of an agglomerate.

  Hereinafter, the production method of the present invention will be described in detail.

  In the present invention, an agglomerate having an average diameter of 17.5 mm or more is prepared.

  As the agglomerate, an agglomerate of a mixture containing a metal oxide and a carbonaceous reducing agent is prepared. As the metal oxide, for example, an iron oxide-containing substance, a chromium-containing ore, a nickel-containing ore and the like can be used. In particular, as iron oxide-containing substances, iron ore, iron sand, iron-making dust, non-ferrous smelting residue, iron-making waste, etc. may be used. As the carbonaceous reducing agent, a carbon-containing material may be used, and for example, coal or coke may be used.

You may mix | blend a binder, a MgO containing material, a CaO containing material, etc. with the said mixture as another component. As the binder, for example, a polysaccharide (for example, starch such as wheat flour) can be used. As the MgO-containing substance, for example, MgO-containing substance extracted from MgO powder, natural ore, seawater, etc., or magnesium carbonate (MgCO ₃ ) can be used. As the CaO-containing substance, for example, quick lime (CaO) or limestone (main component is CaCO ₃ ) can be used.

  The average diameter of the agglomerate is 17.5 mm or more. In general, the smaller the average diameter of the agglomerate, the shorter the time required for heat transfer in the furnace, and the reaction time can be shortened. However, if the average diameter of the agglomerates is reduced, it will be difficult to uniformly spread on the carbonaceous material laid on the hearth, and the particle size and unit mass of the granular metal obtained by heating will be inevitable. Becomes smaller. When the obtained granular metal becomes small, special consideration is required for its handling, and it becomes difficult to supply the granular metal to a refining furnace such as an electric furnace or a converter. Moreover, it cannot be said that it is preferable from a viewpoint of a melt | dissolution characteristic that a granular metal becomes small. Therefore, in this invention, the average diameter of an agglomerate shall be 17.5 mm or more. The average diameter of the agglomerate is preferably 18.5 mm or more, more preferably 19.5 mm or more, and still more preferably 20 mm or more. The upper limit of the average diameter of the agglomerate is not particularly limited, but if the average diameter of the agglomerate exceeds 32 mm, it takes too much time for heat transfer in the furnace, so the reaction time becomes longer and the productivity deteriorates. Moreover, when it is going to enlarge the average diameter of an agglomerate, there exists a tendency for granulation efficiency to worsen. Therefore, the average diameter of the agglomerate is preferably 31 mm or less. More preferably, it is 28 mm or less.

  The shape of the agglomerate is not particularly limited, and may be, for example, a pellet shape or a briquette shape.

  The diameter of the agglomerate is obtained by measuring the major axis of the agglomerate and the minor axis measured in the direction perpendicular to the major axis with a caliper and averaging them [diameter = (major axis + minor axis) / 2. ]. The size of the agglomerate is measured with calipers on at least 20 pieces, and the average of these is taken as the average diameter. In addition, when the average diameter of an agglomerate is α mm, the diameter (absolute value) of the agglomerate is preferably distributed in a range of α ± 5 mm.

  In the present invention, it is important to heat-treat an agglomerate having an average diameter of 17.5 mm or more with a floor density of the agglomerate on the hearth being 0.5 or more. In the past, it was thought that productivity would be worsened if the average diameter of the agglomerate was increased. However, according to the present invention, agglomerates having an average diameter of 17.5 mm or more are spread on the hearth. As demonstrated in the examples to be described later, a very important fact is revealed that productivity is improved against conventional common sense, if heating is performed in a state where the density is 0.5 or more. However, if the density of the agglomerate is less than 0.5, the density of the agglomerate spread per effective hearth unit area becomes too small, so even if the particle size is increased to 17.5 mm or more, In particular, the production amount of granular metal is reduced, and productivity cannot be improved. Therefore, the bed density of the agglomerate is 0.5 or more. It is recommended that the floor density be as large as possible, preferably 0.6 or more. The upper limit of the density of the agglomerate is not particularly limited, but if the agglomerate is supplied so that the density of the agglomerate exceeds 0.8, the agglomerate may overlap two or more layers, and the agglomerate is heated uniformly. This makes it difficult to produce high quality granular iron. Therefore, the upper limit of the density of the agglomerated material is preferably 0.8. More preferably, it is 0.7 or less.

  Here, the floor density of the agglomerates will be described in detail. The agglomerated bed density is calculated based on the projected area ratio of the agglomerated material spread on the hearth to the hearth. A method of calculating the floor density will be described with reference to FIG.

FIG. 1 is a plan view schematically showing agglomerates spread on the hearth. The projected area ratio of the agglomerate onto the hearth can be calculated by the following formula (1).
Projected area ratio (%) = [projected area of all agglomerates on the hearth / effective hearth area] × 100 (1)

Assuming that the agglomerate is a true sphere, when the average diameter of the agglomerate is Dp and the distance between the agglomerates is r, the projected area ratio of the agglomerate to the hearth is expressed by the following equation (2). It can be calculated.
Projection area ratio (%) = π × (Dp ) 2/4 / {(Dp + r) × (Dp + r) × 3 0.5 / 2} × 100 (%) ··· (2)

  When the distance r between the agglomerates is 0, the projected area ratio takes the maximum value, and the maximum projected area ratio becomes a constant value (90.69%). When this maximum projected area ratio is 1, the relative value of the projected area ratio calculated from the above equation (2) based on the average diameter Dp of the agglomerates and the distance r between the agglomerates is set as the floor density in the present invention. Define.

  Here, in order to explain the actual condition of the bed density in more detail, FIG. 2 shows a state where an agglomerate having an average diameter of 18.2 mm is spread on a flat container of about 61 cm square.

Case. 2 in FIG. (A) is an example in which 9.3 kg of agglomerates per unit area of 1 m ² was filled in the container, and the bed density at this time was 0.4. Since the theoretical filling amount when the floor density is 0.4 is 9.33 kg per 1 m ² of unit area, Case. It can be seen that the filling amount and bed density shown in (a) are almost equal to the theoretical values.

Case. 2 in FIG. (B) is an example in which 13.9 kg of agglomerates per unit area 1 m ² was filled in the container, and the bed density at this time was 0.6. The theoretical filling amount when the floor density is 0.6 is 14.0 kg per 1 m ² of unit area. It can be seen that the filling amount and bed density shown in (b) are substantially equal to the theoretical values.

Case. 2 in FIG. (C) is an example in which 18.5 kg of agglomerates per 1 m ^{2 of} unit area was filled in the container, and the bed density at this time was 0.8. Since the theoretical filling amount when the floor density is 0.8 is 18.66 kg per 1 m ² of unit area, Case. It can be seen that the filling amount and bed density shown in (c) are almost equal to the theoretical values.

Case. 2 in FIG. (D) is an example in which 23.2 kg of agglomerates per 1 m ^{2 of} unit area was filled in the container, and the bed density at this time was 1.0. The theoretical filling amount when the floor density is 1.0 is 23.33 kg per 1 m ² of unit area. It can be seen that the filling amount and bed density shown in (d) are substantially equal to the theoretical values.

  Then, Case. As shown in (d), it is very difficult to spread the agglomerate on the actual hearth so that the bed density is 1.0. When agglomerates are supplied into the furnace, new problems such as overlapping of the agglomerates that have been introduced occur. Therefore, in order to supply the agglomerate into the furnace so as not to overlap, Case. As shown in (c), it has been found that the upper limit of the bed density is preferably about 0.8 through various demonstration experiments.

  Also, Case. As shown in (a), when the bed density is 0.4, it is expected that considerable voids are generated on the hearth and productivity is remarkably lowered. Therefore, the lower limit of the floor density is the Case. (A) and Case. It is thought that it should be about 0.5 which is the middle of (b).

  Next, FIG. 3 shows the relationship between the distance r between the agglomerates and the projected area ratio or bed density. In FIG. 3, ● represents the result of the projected area ratio, and □ represents the result of the floor density. As can be seen from FIG. 3, as the distance r between the agglomerates increases, the projected area ratio of the agglomerates and the bed density of the agglomerates both decrease. A good correlation is recognized between the projected area ratio and the floor density based on the distance r between the agglomerates.

  Next, FIG. 4 shows the relationship between the bed density and the supply amount of the agglomerate into the furnace when the average particle size of the agglomerate is changed within the range of 14.0 to 32.0 mm. The supply amount of the agglomerate indicates the supply mass per effective hearth area.

  In FIG. 4, the straight line connecting the points (A) and (B) uses an agglomerate having an average diameter of 17.5 mm or more, and enters the furnace when the agglomerated bed density is 0.5. The straight line connecting points (C) and (D) uses agglomerates having an average diameter of 17.5 mm or more, and the agglomerated bed density is 0. .8 shows the range of the agglomerate supply amount in the furnace. As apparent from FIG. 4, in order to control the agglomerated bed density on the hearth to 0.5 or more, the average diameter of the agglomerate and the supply amount of the agglomerate into the furnace (effective hearth It can be seen that the supply mass per area) should be adjusted.

  The agglomerated material is heated in a moving bed type reducing melting furnace to reduce and melt the metal oxide in the agglomerated material to produce a granular metal. The moving bed type reduction melting furnace used in the present invention and the heating conditions in the furnace are not particularly limited, and known conditions can be adopted.

  As the moving bed type reduction melting furnace, for example, a rotary hearth furnace can be used. Although the hearth width of the moving bed type reductive melting furnace is not particularly limited, according to the present invention, the productivity of granular metal can be improved under economically advantageous conditions if the hearth width is 4 m or more. it can.

  Prior to supplying the agglomerate onto the hearth, a carbonaceous material (hereinafter sometimes referred to as a floor covering material) is laid on the hearth in advance, and the lump is placed on the carbonaceous material layer. It is preferable to supply the composition so as to form one layer. The flooring material serves as a carbon supply source when the carbon contained in the agglomerate is insufficient, and also acts as a hearth protection material.

  The thickness of the flooring material is not particularly limited, but is preferably 3 mm or more. That is, when an actual machine is used as the moving bed type reduction melting furnace, the hearth width becomes several meters, so it is difficult to spread the floor covering material uniformly in the width direction, and the thickness is about 2 to 8 mm. Variation may occur. Therefore, in order not to generate a hearth portion that is not covered with the flooring material, it is preferable to lay the flooring material at 3 mm or more. More preferably, it is 5 mm or more, More preferably, it is 10 mm or more. In the present invention, since the agglomerate is particularly large, the agglomerate is hardly buried in the flooring material even if the flooring material is thickened, and the reduction efficiency is hardly lowered. Specifically, when using an agglomerate having an average diameter of 20 mm or more, a thicker flooring material is particularly effective. The upper limit of the thickness of the flooring material is not particularly limited. However, if the thickness of the flooring material exceeds 30 mm, the agglomerate sinks into the flooring material in the present invention, so that the heat to the agglomerate is reduced. Supply may be hindered and reduction efficiency may be reduced. As a result, the granular metal is likely to be deformed or the internal quality is easily deteriorated. Therefore, the flooring material is preferably 30 mm or less, more preferably 20 mm or less, and still more preferably 15 mm or less.

  As the carbonaceous material used as the floor covering material, those exemplified as the carbonaceous reducing agent can be used. For example, it is recommended to use a carbonaceous substance having a particle diameter of 3.0 mm or less. When the particle diameter exceeds 3.0 mm, the molten slag flows down through the gap between the carbonaceous materials and reaches the hearth surface, which may erode the hearth. The particle size of the carbonaceous material is more preferably 2.0 mm or less. However, if the ratio of the carbonaceous material having a particle size of less than 0.5 mm becomes too large, the agglomerate will sink into the flooring, which will reduce the heating efficiency and reduce the productivity. I can't say that.

  It is preferable to supply the agglomerate so that the agglomerate supplied on the hearth on which the flooring material is laid is a single layer. In order to increase the production amount of granular metallic iron, it is usually considered to increase the amount of agglomerates supplied into the furnace. When the supply amount of these agglomerates is increased, the agglomerates are placed on the hearth. Laminated in two or three or more layers. In this case, the upper agglomerate receives sufficient heat from the furnace body and is reduced and melted. However, since heat is not sufficiently supplied to the lower agglomerate, an unreduced portion tends to remain. If only the upper agglomerates are reduced and melted, and the molten iron is integrated with the lower undissolved reduced iron or the like, it becomes impossible to recover high-quality granular metallic iron. Therefore, when solid reduction and carburization and melting are reliably performed in the furnace as in the present invention, it is recommended to supply the agglomerate so that the agglomerate on the hearth is generally one layer.

  In order to make the agglomerate on the hearth into a single layer, the agglomerate supplied into the furnace is uniformly spread over the entire width of the effective hearth before entering the heating reaction zone. For example, if a pellet leveler is used, it is possible to adjust the agglomeration on the hearth.

  Conventional heating conditions can be used for heating the agglomerate in a moving bed type reductive melting furnace to reduce and melt the metal oxide contained in the agglomerate. That is, the above agglomerates are supplied onto the hearth, subjected to solid reduction at a predetermined temperature, and further heated and held until dissolved, thereby producing slag (oxide) made of impurities and granular metallic iron. The agglomerates on the hearth are heated by the heat from the combustion flames of a plurality of burners installed in the upper part (for example, the ceiling) and side walls of the furnace, or by radiant heat from the refractories in the furnace heated to a high temperature. The solid reduction reaction proceeds by transferring heat from the outer periphery to the inside of the product.

  In the first half of the furnace, the agglomerate undergoes a reduction reaction while maintaining a solid state, and in the second half of the furnace, the finely reduced iron in the agglomerate after solid reduction has dissolved through a carburization reaction. In the process, the particles agglomerate with each other to form granular metallic iron while separating from impurities (slag component) in the agglomerate.

  In the first half region of the furnace, it is preferable to control the furnace temperature to about 1300 to 1450 ° C. in order to reduce the iron oxide in the agglomerates in a solid state. In the latter half of the furnace, the temperature in the furnace is preferably controlled to about 1400 to 1550 ° C. in order to carburize, melt, and aggregate the reduced iron in the agglomerate. In addition, when the inside of the furnace is heated to over 1550 ° C., excessive heat is supplied to the agglomerate, and as a result of exceeding the heat transfer rate into the agglomerate, a partially molten state is obtained before the solid reduction is completed. As a result of the rapid reaction, a smelting reduction reaction in which abnormal slag forming occurs is caused.

  The in-furnace temperature in the second half of the furnace may be set higher than the in-furnace temperature in the first half of the furnace.

In the present invention, the productivity when the agglomerate is heated and the metal oxide is reduced and melted to produce a granular metal is expressed in an effective furnace in unit time (hours) as shown by the following formula (3). Evaluation is based on the production amount (ton) of granular metal per floor unit area (m ² ).
Productivity (ton / m ² / hour) = granular metal production (ton / hour) / effective hearth area (m ² ) (3)

In the above formula (3), the production amount (ton / hour) of the granular metal is represented by the following formula (4).
Production amount of granular metal (granular metal ton / hour) = amount of agglomerate charged (agglomerated ton / hour) × mass of granular metal produced per ton of agglomerate (granular metal ton / agglomeration) Product ton) x product recovery rate (4)

  In the above formula (4), the product recovery rate is the ratio of the granular metallic iron having a diameter of 3.35 mm or more to the total amount of the obtained granular metal [the mass of the granular metallic iron having a diameter of 3.35 mm or more / the granular metallic iron Total amount × 100].

  In Experimental Examples 2 and 3 of the following examples, in order to quantitatively evaluate the effect of the present invention, a test material (agglomerated material) having an average diameter of 17.5 mm was used as a standard agglomerated material. The productivity of each agglomerate when the productivity of the agglomerate is 1.000 is shown as a relative value (productivity index).

  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.

[Experimental Example 1]
An agglomerate using a mixture containing a metal oxide and a carbonaceous reducing agent as a raw material is prepared, and this agglomerate is supplied onto the hearth of a moving bed type reduction melting furnace and heated, and the metal in the raw material mixture is heated. Particulate metallic iron was produced by reducing and melting the oxide.

  That is, an agglomerate was produced using iron ore having the component composition shown in Table 1 below as the metal oxide and coal having the component composition shown in Table 2 below as the carbonaceous reducing agent. Specifically, the mixture of the iron ore and the coal was mixed with flour as a binder and limestone or dolomite as an auxiliary material to prepare pellet-like agglomerates (test materials) having different average diameters. Table 3 below shows the composition of the test material (percentage of the weighed value). Moreover, the major axis and minor axis of the test material were measured with calipers, the average diameter was calculated, and the results are shown in Table 4 below. The average diameter of the test material is an average value when 20 pieces are measured.

  Table 4 below also shows the unit mass and apparent density of each specimen. The unit mass of the test material is an average value of the results of measuring 20 masses. The apparent density of the test material is a value obtained by immersing the agglomerate in a liquid (mercury) and measuring its buoyancy.

  The time required to reduce and melt the iron ore contained in the specimen by heating the specimens with different average diameters in a small laboratory furnace (temperature in the furnace is 1450 ° C.). (Reaction time) was examined. The measurement results of the reaction time are shown in Table 4 below.

  FIG. 5 shows the relationship between the average diameter (Dp) of the test material and the reaction time. In FIG. 5, the curve indicated by the dotted line represents an approximate curve of the plot points, and is represented by a quadratic expression based on the average diameter of the specimen. As is clear from FIG. 5, it can be seen that the reaction time increases as the average diameter of the specimen increases.

  Based on the results of the experimental example 1, the reaction time and the product recovery rate are normalized, and the distance between the test materials (experimental example 2 below) or the floor density of the test material (experimental example 3 below) is changed. Productivity was evaluated comprehensively.

[Experiment 2]
In Experimental Example 2, a test material having an average diameter of 16.0 to 28.0 mm (1.60 to 2.80 cm) was used, and a moving bed type reduction melting furnace of an actual machine was used. The effect of the average diameter of the test material on the productivity of the granular metallic iron when the granular metallic iron was produced was heated comprehensively.

  Using a rotary hearth furnace as a moving bed type reductive melting furnace, supplying the above test material on the hearth and heating it so that the bed density of the test material on the hearth becomes 0.66, and reducing or melting the iron ore The granular metallic iron was manufactured. The temperature in the furnace was set to 1400 ° C. in the first half region and 1470 ° C. in the second half region. The first half area is the area where solid reduction of iron ore in the test material is performed, and the second half area is carburized, dissolved, and finally agglomerated by the micro-reduced iron melted in the test material. Thus, the molten iron and slag are separated from each other.

  The density of the test material on the hearth was controlled by adjusting the amount of the test material supplied into the furnace and the moving speed (rotational speed) of the hearth. That is, the moving speed of the hearth is determined so that the iron ore is reduced and melted in the heating region under the atmospheric condition set based on the result of the preliminary experiment, and the moving speed of the test material is taken into consideration. The supply amount was adjusted, and the floor density of the test material on the hearth was controlled to 0.66. Table 5 below shows the distance r between the test materials as a reference value.

  The productivity when each sample material was reduced and melted to produce granular metallic iron was calculated based on the above formula (3). The productivity of each of the test materials was shown as a relative value (productivity index) with the productivity of the 12 test materials (standard agglomerates) as a standard (productivity index 1.000). The productivity index of each test material is shown in Table 5 below. FIG. 6 shows the relationship between the average diameter of the test material and the productivity index.

  As is clear from FIG. 6, when the bed density on the hearth is constant, the average diameter of the test material is increased to 17.5 mm or more than when the average diameter of the test material is 16.0 mm. It can also be seen that productivity can be improved. That is, as the average diameter of the test material is increased, the productivity is gradually improved. When the average diameter of the test material is 22.0 mm, the productivity index becomes the maximum value.

  However, when the average diameter of the test material is increased to more than 26.0 mm, the productivity tends to deteriorate gradually. The reason why the productivity is deteriorated is considered to be that the reaction time becomes longer because the test material becomes larger. Therefore, when the floor density is constant, by adjusting the average diameter of the test material between 17.5 and 26.0 mm, the productivity can be improved as compared to using the test material with an average diameter of 16.0 mm. I understand.

[Experiment 3]
In Experimental Example 3, a test material having an average diameter of 16.0 to 32.0 mm (1.60 to 2.80 cm) is assumed, and the test materials on the hearth are used by using a real moving bed type reduction melting furnace. Investigate the influence of sample density on the productivity of granular metallic iron when the granular metal iron is manufactured by changing the density of the sample r to constant (0.42 cm) and heating did.

  Using a rotary hearth furnace as a moving bed type reductive melting furnace, supplying the specimens with the average diameter shown in Table 6 below onto the hearth and heating them, and reducing or melting iron ore to produce granular metallic iron This is an example of evaluation. The heating conditions in the furnace are the same as in Experimental Example 2 above. Table 6 shows the floor density of the test material on the hearth.

  The productivity when each sample material was reduced and melted to produce granular metallic iron was calculated based on the above formula (3). The productivity of each of the test materials was shown as a relative value (productivity index) with the productivity of the 22 test materials (standard agglomerates) as the standard (1.000). The productivity index of each sample material is shown in Table 6 below. FIG. 7 shows the relationship between the average diameter of the test material and the productivity index.

  As is clear from Table 6 and FIG. 7, when the distance r between the specimens is constant, the specimen diameter on the hearth is increased by increasing the average diameter of the specimens to 17.5 mm or more. It can be seen that the floor density can be increased. In addition, it can be seen that increasing the average diameter of the test material can improve productivity more than when the average diameter of the test material is 16.0 mm. That is, as the average diameter of the test material is increased, the productivity is gradually improved. When the average diameter of the test material is 24.0 mm, the productivity index becomes the maximum value.

  However, when the average diameter of the test material is increased to more than 24.0 mm, the productivity tends to gradually deteriorate. The reason for the decrease in productivity is considered to be a longer reaction time due to an increase in the test material. Therefore, it can be seen that by adjusting the average diameter of the test material between 17.5 and 32.0 mm, the productivity can be improved as compared with the use of the test material having an average diameter of 16.0 mm.

  When the results of Experimental Examples 2 and 3 are combined, as shown in Experimental Example 2, when an agglomerate having a large average diameter (for example, an agglomerate having an average diameter exceeding 28.0 mm) is used, the bed density is reduced. In certain cases, the productivity may decrease. However, as shown in Experimental Example 3, if the floor density is increased, for example, the productivity can be increased even if an agglomerate having an average diameter exceeding 28.0 mm is used. It can be seen that can be improved. That is, when heating the agglomerated material (test material) on the hearth with a bed density of 0.5 or more, by supplying an agglomerate having an average diameter of 17.5 mm or more to the hearth, productivity is improved. It can be seen that it can be improved. In other words, if an agglomerate having an average diameter of 17.5 mm or more is prepared and the agglomerate density on the hearth is 0.5 or more and heated in the furnace, the granular metal can be produced with high productivity. I understand.

Claims (5)

An agglomerate containing a metal oxide and a carbonaceous reducing agent is supplied and heated on the hearth of a moving bed type reductive melting furnace, and after reducing and melting the metal oxide, the resulting granular metal is cooled. A method for producing a granular metal that is discharged from the furnace and recovered.
In the heating, the furnace temperature in the first half of the furnace for solid reduction of iron oxide in the agglomerate is 1300 to 1450 ° C., and the furnace in the latter half of the furnace for carburizing, melting, and agglomerating the reduced iron in the agglomerate. The internal temperature is set to 1400 to 1550 ° C.,
Relative of the projected area ratio of the agglomerates spread on the hearth to the hearth floor relative to the maximum projected area ratio of the agglomerates spread on the hearth when the distance between the agglomerates spread on the hearth is 0 When the value is the bed density, the agglomerate having an average diameter of 19.5 mm or more and 32 mm or less is heated when the bed density of the agglomerate on the hearth is 0.5 or more and 0.8 or less. A method for producing a granular metal, characterized by being supplied onto a hearth.   The manufacturing method according to claim 1, wherein a carbonaceous material is laid in advance on the hearth, and the agglomerate is supplied on the carbonaceous material layer so as to form one layer.   The manufacturing method according to claim 1, wherein iron oxide is used as the metal oxide.   The manufacturing method according to claim 1, wherein a rotary hearth furnace is used as the moving bed type reductive melting furnace.   The manufacturing method according to claim 1, wherein iron-made dust is used as the metal oxide.