JP2013174001A - Method for producing granular metallic iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a granular metallic iron, with which the yield of the granular metallic iron is enhanced and productivity can be improved, when the granular metallic iron is produced by heating a raw material mixture including iron oxide-containing material and carbonaceous reducing agent with a moving hearth type heating and reducing furnace.SOLUTION: As a raw material mixture, materials which generate slag Z satisfying the following conditions (1) to (6) at 1,150°C, are used. (1) The liquid phase ratio is ≥80%. (2) FeO content is 5 to 60 mass%. (3) SiOcontent is ≥30 mass%. (4) CaO content is 0.5 to 50 mass%. (5) FeO/SiOratio obtained from FeO content and SiOcontent is 0.17 to 2.0. (6) FeO/CaO ratio obtained from FeO content and CaO content is 0.2 to 50.

Description

  The present invention relates to a method for producing granular metallic iron. Specifically, an iron oxide-containing material such as iron ore and a carbonaceous reducing agent such as coal or coke (hereinafter sometimes referred to as carbon material). The present invention relates to a method for producing granular metallic iron by heating a raw material mixture containing a heated hearth type heating and reducing furnace and reducing iron oxide in the raw material mixture with the carbonaceous reducing agent. In the present invention, “granular” does not necessarily mean a true sphere, but also includes an ellipse, an egg shape, or a shape in which they are slightly flattened.

  As a method for producing iron from iron oxide-containing substances such as iron ore and iron oxide, the blast furnace method is the mainstream. On the other hand, as a steelmaking method that is relatively small-scale and suitable for high-mix, low-volume production, a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent (or a simple molded body obtained by compacting the raw material mixture, The carbonaceous material molded body formed into pellets or briquettes) is supplied to a moving hearth-type heating reduction furnace (for example, a rotary hearth furnace), and a heating burner is used while the raw material mixture moves in the furnace. The iron oxide in the raw material mixture is directly reduced with a carbonaceous reducing agent by heating with the combustion heat or radiant heat generated by the process, and the resulting metal iron (reduced iron) is subsequently carburized and melted, and then by-produced slag and A direct reduction iron manufacturing method has been developed in which particles are aggregated while being separated and then cooled and solidified to produce granular metallic iron (reduced iron) (Patent Documents 1 to 3, etc.). Since this direct reduction steelmaking method does not require large-scale equipment such as a blast furnace, research is actively conducted for practical use. However, in order to implement on an industrial scale, there are many problems that must be further improved, including operational stability, safety, economy, and quality of granular metallic iron (product).

One of the problems is improvement of productivity of granular metallic iron. This is because it is impossible to implement on an industrial scale if productivity is poor. Therefore, the present applicant has previously proposed a technique capable of producing granular metallic iron with high productivity (Patent Documents 4 to 6). In these techniques, the basicity [(CaO + MgO) / SiO ₂ ] obtained from the CaO amount, MgO amount, and SiO ₂ amount contained in the slag produced as a by-product when the metallic iron is melted, and the MgO amount in the slag (Patent Document 4), the basicity [(CaO + MgO) / SiO ₂ ] is controlled within a predetermined range, and the raw material mixture is mixed with a Na ₂ O supply substance, a K ₂ O supply substance, Li ₂ O. A supply material or a composite oxide containing at least one alkali metal and having a melting point of 1400 ° C. or lower is blended (Patent Documents 5 and 6).

JP-A-2-228411 JP 2001-279313 A JP 2001-247920 A JP 2004-285399 A JP 2009-7621 A JP 2009-7619 A

  Although the productivity disclosed in Patent Documents 4 to 6 has improved the productivity of granular metallic iron to some extent, there is a need for a technique that further increases the yield of granular metallic iron and further improves the productivity of granular metallic iron. .

  The present invention has been made in view of such a situation, and an object of the present invention is to heat a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent in a moving hearth type heating reduction furnace to form granular metallic iron. It is in providing the manufacturing method of the granular metallic iron which can improve the yield of granular metallic iron and can improve productivity.

The method for producing granular metallic iron according to the present invention that can solve the above-mentioned problem is that a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is heated in a moving hearth type heating reduction furnace, and the raw material mixture This is a method for producing granular metallic iron by reducing the iron oxide therein with the carbonaceous reducing agent, aggregating the produced metallic iron with the slag as a by-product and agglomerating it into particles and then cooling and solidifying it. And the manufacturing method of the granular metal iron of this invention has a summary in the point using the slag Z which satisfy | fills the requirements of following (1)-(6) in 1150 degreeC as said raw material mixture. Yes.
(1) The liquid phase ratio is 80% or more.
(2) The amount of FeO is 5 to 60% by mass.
(3) The amount of SiO ₂ is 30% by mass or more.
(4) CaO amount is 0.5 to 50% by mass.
(5) FeO / SiO ₂ ratio determined from FeO amount and SiO ₂ amount is 0.17 to 2.0.
(6) FeO / CaO ratio obtained from FeO amount and CaO amount is 0.2-50.

After the raw material mixture is heated to 1150 ° C., when the component composition in the cross section of the surface layer is analyzed at regular intervals of at least 200 points, the component composition satisfies all the requirements (2) to (6). It is preferable to use a raw material mixture in which the ratio of the number of points is 3.5% or more with respect to the total number of analysis points. As the iron oxide-containing substance, it is preferable to use a substance having an Al ₂ O ₃ / SiO ₂ ratio of 0.1 or less determined from the amount of Al ₂ O _{3 and the} amount of SiO _{2 in the} iron oxide-containing substance.

  According to this invention, since the raw material mixture which produces | generates the slag which satisfy | fills predetermined conditions at 1150 degreeC is used, slag fuse | melts at comparatively low temperature and the cohesiveness of slag is accelerated | stimulated. As a result, since the aggregation of the granular metallic iron is promoted, the yield of the granular metallic iron is increased, and the productivity of the granular metallic iron is improved.

FIG. 1 is an explanatory diagram showing the results of an example of the invention in the SiO ₂ —CaO—FeO _n ternary phase diagram showing the relationship between the composition of slag and the liquid phase ratio of slag. FIG. 2 is an explanatory diagram showing the results of a comparative example in a ternary phase diagram of SiO ₂ —CaO—FeO _n showing the relationship between the composition of slag and the liquid phase ratio of slag. FIG. 3 is a schematic explanatory view showing a configuration example of a rotary hearth-type heating reduction furnace. FIG. 4 is a graph showing the relationship between the number of analysis points satisfying all the requirements (a) to (e) shown in the examples and the yield rate (%).

  First, how the present invention was completed will be described. In the production of granular metallic iron by the direct reduction iron manufacturing method, if there is a lot of gangue contained in the raw material mixture, the amount of by-product slag increases, the cohesiveness decreases, and the yield of the obtained granular metallic iron is reduced. It is known to decline. That is, when the cohesiveness of by-product slag decreases, it becomes a state in which the granular metal iron produced by heat reduction and the slag produced as a by-product are mixed, so that it becomes difficult to separate the granular metal iron and the by-product slag. Granularization and agglomeration do not progress sufficiently, and granular metallic iron is embraced with slag, or very fine granular metallic iron is produced in large quantities, making it difficult to separate from by-product slag. The yield of granular metallic iron in the appropriate particle size range is reduced.

  In addition, depending on the type of iron oxide-containing substance and carbonaceous reducing agent to be blended as a raw material mixture, there are few gangue contained therein, but depending on the type and composition, the cohesiveness of by-product slag is poor. It is often observed that

  Then, the present inventors examined aiming at improving the cohesiveness of the slag byproduced when a raw material mixture was heated. As a result, if the melting point of the slag is lowered, the cohesiveness of the slag is improved, and thereby the cohesiveness of the metallic iron obtained by heat reduction is also increased, so that the productivity of the granular metallic iron is improved. It was revealed. And in order to lower melting | fusing point of slag, what is necessary is just to use what produces | generates slag Z which satisfy | fills a predetermined requirement at 1150 degreeC as a raw material mixture, and when operating a moving hearth type heating reduction furnace by this It was revealed that the slag almost melts at a general temperature of about 1450 ° C., so that the cohesiveness of metallic iron is increased and the productivity of granular metallic iron is improved.

  The present invention will be described below.

In the method for producing granular metallic iron according to the present invention, a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is heated in a moving hearth type heating reduction furnace, and the iron oxide in the raw material mixture is reduced to the carbonaceous reduction material. After reducing with an agent and separating the produced metallic iron from the slag as a by-product, it is aggregated into particles and then cooled and solidified to produce granular metallic iron. The present invention is characterized in that a material in which slag Z that satisfies the following requirements (1) to (6) is generated at 1150 ° C. is used as the raw material mixture.
(1) The liquid phase ratio is 80% or more.
(2) The amount of FeO is 5 to 60% by mass.
(3) The amount of SiO ₂ is 30% by mass or more.
(4) CaO amount is 0.5 to 50% by mass.
(5) FeO / SiO ₂ ratio determined from FeO amount and SiO ₂ amount is 0.17 to 2.0.
(6) FeO / CaO ratio obtained from FeO amount and CaO amount is 0.2-50.

  When the raw material mixture that has been subjected to the component adjustment so as to produce slag that satisfies all the above requirements (1) to (6) at 1150 ° C. is heated in a moving hearth type heating and reducing furnace, the slag forming component is rapidly Dissolves and aggregates to form slag quickly. When the slag is formed quickly, the remaining metallic iron is likely to aggregate in a granular form. As a result, the yield of the granular metallic iron is improved and the productivity of the granular metallic iron is improved.

The above ranges (1) to (6) are derived as a result of various experiments conducted by the present inventors. That is, as shown in the examples described later, when iron ores having different component compositions are used and the compound whose components are adjusted so that the dissolution completion time is substantially the same is heated, the results shown in FIGS. 1 and 2 are obtained. It was. FIGS. 1 and 2 are SiO ₂ —CaO—FeO _n ternary phase diagrams showing the relationship between the slag composition and the liquid phase ratio of the slag, and the results of the invention example (FIG. 1) or the comparative example (FIG. 2). It is explanatory drawing which showed. In the figure, ● indicates that the slag liquid phase ratio is 80% or more, ▲ indicates that the slag liquid phase ratio is 30% or more and less than 80%, and ◆ indicates that the slag liquid phase ratio is less than 30%. Show.

FIG. 1 shows the results of the inventive examples. When the above blend (raw material mixture) was heated to 1150 ° C., (1) the liquid phase ratio was 80% or more, and (2) the amount of FeO was 5 to 5. 60 wt%, (3) SiO ₂ amount is 30 mass% or more, (4) CaO amount is 0.5 to 50 mass%. (5) FeO / SiO ₂ ratio obtained from FeO amount and SiO ₂ amount is in the range of 0.17 to 2.0, (6) FeO / CaO ratio obtained from FeO amount and CaO amount is from 0.2 to 50 Slag that satisfies the entire range is generated.

  On the other hand, FIG. 2 shows the result of the comparative example, and when the above-mentioned composition (raw material mixture) was heated to 1150 ° C., three analysis points with a liquid phase ratio of slag of 80% or more were found. These component compositions do not satisfy any of the requirements (2) to (6).

  In the example shown in FIG. 1, melting of slag is accelerated when heated to 1450 ° C., and as shown in Table 5 below, the yield rate of granular metal iron is 100% or more, and the productivity of granular metal iron is increased. It has improved. On the other hand, in the example shown in FIG. 2, the melting of slag when heated to 1450 ° C. is not accelerated, and the yield rate of granular metallic iron is less than 100% as shown in Table 5 below. Productivity has not improved.

  Hereinafter, each range prescribed | regulated by this invention is demonstrated.

  In the present invention, among the slag generated when the raw material mixture is heated to 1150 ° C., the slag that satisfies the requirements (1) to (6) is referred to as “slag Z”. That is, when the raw material mixture is heated, the gangue contained in the raw material mixture is gradually melted to form molten slag. The melting point of the gangue varies depending on the composition of the gangue. Since the temperature is low at a heating temperature of 1150 ° C, the gangue contained in the raw material mixture partially melts to form a slag in which molten slag and gangue are mixed. There are a lot of things. Therefore, since molten slag contacts with adjacent molten slag and does not aggregate, the solid-liquid mixed state slag is dispersed in the raw material mixture to form a slag group. In the present invention, slag that satisfies all the requirements (1) to (6) in the slag group is referred to as “slag Z”, and a raw material mixture that produces this slag Z is used.

[(1) Liquid phase rate of slag is 80% or more]
In the present invention, attention is paid to slag having a liquid phase ratio of 80% or more at 1150 ° C. based on the volume of the slag. By appropriately controlling the component composition of the raw material mixture so that the liquid phase ratio of slag at 1150 ° C. is 80% or more, the amount of molten slag generated when the raw material mixture is further heated to a high temperature can be increased. As a result, the cohesiveness of the slag is improved. As a result, the cohesiveness of the granular metallic iron is also improved, so that the yield of the granular metallic iron is increased and the productivity of the granular metallic iron is improved.

  The liquid phase ratio of the slag was determined by heating the raw material mixture to 1150 ° C. and then cooling it, and field emission scanning electron microscope (FE-SEM) “JSM-7001F (device name)” manufactured by JEOL Ltd. The component composition of the slag may be measured using an X-ray analyzer (EDX) “JED-2300F (device name)” and obtained based on the melting point of the slag calculated using “FactSage (software name)”.

[(2) FeO amount in slag is 5 to 60% by mass]
If the amount of FeO in the slag is less than 5% by mass or exceeds 60% by mass, the liquid phase ratio of the slag cannot be increased to 80% or more even when heated to 1150 ° C. Moreover, even if it further heats to the temperature exceeding 1150 degreeC, since the liquid phase rate of slag does not become 80% or more, the cohesiveness of slag cannot be improved. Accordingly, the aggregation of the granular metallic iron is inhibited, the yield of the granular metallic iron is lowered, and the productivity of the granular metallic iron cannot be improved. Therefore, in this invention, the amount of FeO in the said slag was made into the range of 5-60 mass%. The amount of FeO in the slag is preferably 8% by mass or more, more preferably 10% by mass or more, preferably 58% by mass or less, more preferably 55% by mass or less.

[(3) SiO ₂ content in slag is 30% by mass or more]
When the amount of SiO ₂ in the slag is less than 30% by mass, the melting point of the slag becomes high and the liquid phase ratio of the slag at 1150 ° C. cannot be increased to 80% or more. Therefore, even when further heated to a temperature exceeding 1150 ° C., slag having a liquid phase ratio of 80% or more is hardly generated, so that the cohesiveness of the slag cannot be increased. Accordingly, the aggregation of the granular metallic iron is inhibited, the yield of the granular metallic iron is lowered, and the productivity of the granular metallic iron cannot be improved. Therefore, in the present invention, the amount of SiO ₂ in the slag is set to 30% by mass or more. The amount of SiO ₂ in the slag is preferably 31% by mass or more, more preferably 32% by mass or more. The upper limit of the amount of SiO ₂ in the slag is not particularly limited, but is preferably 60% by mass or less, more preferably 58% by mass or less, for example.

[(4) CaO amount in slag is 0.5-50 mass%]
By controlling the amount of CaO in the slag in the range of 0.5 to 50% by mass, the melting point of the slag can be lowered, and the liquid phase ratio of the slag at 1150 ° C. can be increased to 80% or more. The amount of CaO in the slag is preferably 0.6% by mass or more, more preferably 0.7% by mass or more, preferably 48% by mass or less, more preferably 45% by mass or less.

[(5) FeO / SiO ₂ ratio (mass ratio) determined from FeO amount and SiO ₂ amount in slag is in a range of 0.17 to 2.0]
When the FeO / SiO ₂ ratio is less than 0.17 or exceeds 2.0, the melting point of the slag becomes high, and the liquid phase ratio of the slag at 1150 ° C. cannot be increased to 80% or more. Therefore, even when further heated to a temperature exceeding 1150 ° C., slag having a liquid phase ratio of 80% or more is hardly generated, so that the cohesiveness of the slag cannot be increased. Accordingly, the aggregation of the granular metallic iron is inhibited, the yield of the granular metallic iron is lowered, and the productivity of the granular metallic iron cannot be improved. Therefore, in the present invention, the FeO / SiO ₂ ratio is set in the range of 0.17 to 2.0. The FeO / SiO ₂ ratio is preferably 0.3 or more, more preferably 0.35 or more, still more preferably 0.4 or more, preferably 1.9 or less, more preferably 1.8 or less.

[(6) FeO / CaO ratio (mass ratio) determined from the amount of FeO and CaO in the slag is in the range of 0.2 to 50]
When the FeO / CaO ratio is less than 0.2 or exceeds 50, the melting point of the slag increases, and the liquid phase ratio of the slag at 1150 ° C. cannot be increased to 80% or more. Therefore, even when further heated to a temperature exceeding 1150 ° C., slag having a liquid phase ratio of 80% or more is hardly generated, so that the cohesiveness of the slag cannot be increased. Accordingly, the aggregation of the granular metallic iron is inhibited, the yield of the granular metallic iron is lowered, and the productivity of the granular metallic iron cannot be improved. Therefore, in the present invention, the FeO / CaO ratio is set in the range of 0.2-50. The FeO / CaO ratio is preferably 0.25 or more, more preferably 0.3 or more, preferably 49.8 or less, more preferably 49.5 or less.

  In the present invention, after the raw material mixture is heated to 1150 ° C., when the component composition in the surface layer cross section is analyzed at regular intervals at at least 200 points, the component composition satisfies all the requirements (2) to (6). It is preferable to use a raw material mixture in which the ratio of the number of analysis points satisfying the above is 3.5% or more with respect to the number of all analysis points. When the ratio of the analysis points satisfying the predetermined component composition is 3.5% or more, the yield rate when the raw material mixture is heated and reduced to produce granular metallic iron can be increased to 90% or more. The ratio is more preferably 4.5% or more, and still more preferably 5.5% or more. The number of analysis points for the component composition may be at least 200, and more preferably 500. The analysis of the component composition may be performed, for example, at intervals of 30 to 100 μm in the surface layer cross section (cross section cut in the direction perpendicular to the surface so as to include the surface). Specific procedures for analyzing the component composition will be described in detail in Examples below.

  When the slag Z satisfying the requirements of the above (1) to (6) is generated at 1150 ° C. and heated to 1150 ° C., the component composition in the surface layer cross section is analyzed at regular intervals of at least 200 points. In order for the ratio of the number of analysis points satisfying all the requirements (2) to (6) above to be 3.5% or more with respect to the total number of analysis points, the component composition of the raw material mixture Or the heating pattern of the raw material mixture may be controlled.

That is, the liquid phase ratio at the 1150 ° C. is to produce more than 80% of the slag, as the iron oxide-containing material, Al ₂ determined from the amount of Al ₂ O ₃ and SiO ₂ amount of the iron oxide-containing material in O It is preferable to use one having a ₃ / SiO ₂ ratio (mass ratio) of 0.1 or less. When an iron oxide-containing substance having an Al ₂ O ₃ / SiO ₂ ratio exceeding 0.1 is used, the amount of SiO ₂ is small, so that during the heating reduction (particularly around 1150 ° C.), a FeO—CaO-based high melting point phase is present. It becomes easier to form. On the other hand, when an iron oxide-containing substance having an Al ₂ O ₃ / SiO ₂ ratio of 0.1 or less is used, FeO is brought into contact with iron oxide, gangue, and flux during heating reduction (particularly around 1150 ° C.). A —SiO ₂ —CaO-based low melting point phase is easily formed. Therefore, it becomes easy to produce | generate the slag whose liquid phase rate in 1150 degreeC is 80% or more. The Al ₂ O ₃ / SiO ₂ ratio is more preferably 0.08 or less, and still more preferably 0.06 or less. The iron oxide-containing material inevitably contains Al ₂ O ₃ and SiO ₂ , and is excluded when the Al ₂ O ₃ / SiO ₂ ratio is 0.

In the present invention, the amount of SiO ₂ in the iron oxide-containing substance is preferably 4.0% by mass or more, for example. By using the iron oxide-containing material containing SiO ₂ 4.0% by mass or more, it is possible to lower the melting point of the slag.

The amount of FeO, the amount of SiO _{2 and the} amount of CaO in the slag described above can be controlled by appropriately adjusting the blending amounts of the raw material containing iron oxide and the carbonaceous reducing agent. The iron oxide-containing material usually contains gangue such as SiO ₂ and CaO in addition to FeO, and the carbonaceous reducing agent usually contains gangue such as SiO ₂ and CaO. This is because it becomes a FeO supply material, a SiO ₂ supply material, and a CaO supply material.

  The amount of FeO in the slag described above can be adjusted by controlling the heating pattern. For example, in the case of producing metallic iron by heating and reducing the raw material mixture containing the iron oxide-containing substance and the carbonaceous reducing agent to 1450 ° C., the final mixed temperature (here 1450) is supplied after supplying the raw material mixture to the furnace. It is preferable to change the rate of temperature rise between about 450 to 550 ° C. (especially 500 ° C.) and about 1150 to 1190 ° C. (particularly 1170 ° C.). Specifically, the heating pattern may be controlled as follows. That is, the temperature rising rate from room temperature to about 450 to 550 ° C. is 590 to 610 ° C./min, the temperature rising rate from about 450 to 550 ° C. to about 1150 to 1190 ° C. is 140 to 160 ° C./min, and about 1150 to 1190. What is necessary is just to make the temperature increase rate from 45 degreeC to 1450 degreeC into 45-55 degreeC / min. Most preferably, the temperature increase rate from room temperature to about 500 ° C. is 600 ° C./min, the temperature increase rate from about 500 ° C. to about 1170 ° C. is 150 ° C./min, and the temperature increase rate from about 1170 ° C. to 1450 ° C. What is necessary is just to set it as 50 degree-C / min. The maximum temperature reached is not limited to 1450 ° C., and may be, for example, 1400 to 1500 ° C.

Note that iron ore, which is a typical example of an iron oxide-containing substance, and coal and coke, which are typical examples of a carbonaceous reducing agent, are natural products, and the contents of FeO, SiO ₂ and CaO vary depending on the type. . For this reason, it is difficult to uniformly define the blending amounts thereof, but it is preferable to appropriately adjust in consideration of the component composition of the iron oxide-containing substance and the component composition of the carbonaceous reducing agent. In addition, as described later, when carbonaceous powder is used as a floor covering material to be laid on the hearth, the amount of the iron oxide-containing substance and the carbonaceous reducing agent is determined in consideration of the components and the amount of the carbonaceous powder. By adjusting, the amount of SiO _{2 and the} amount of CaO in the slag may be controlled.

The raw material mixture used in the present invention may contain, in addition to the iron oxide-containing substance and the carbonaceous reducing agent described above, a slag composition adjusting auxiliary raw material, a binder, a CaF ₂ supply substance, and the like.

  The slag composition adjusting auxiliary raw material may contain “other CaO supply material” other than the iron oxide-containing material and the carbonaceous reducing agent described above, an MgO supply material, and the like. That is, the raw material mixture used in the present invention, in addition to the iron oxide-containing substance and the carbonaceous reducing agent described above, other “other CaO supply substances” (from the viewpoint of the iron oxide-containing substance and the carbonaceous reducing agent, (External additive substance) may be included. In this case, the amount of CaO in the slag is finally adjusted by adjusting the amounts of the iron oxide-containing material and the carbonaceous reducing agent in consideration of the component composition of the “other CaO supply material” and the blending amount thereof. Can be controlled.

The other types of CaO feed material is not particularly limited, for example, quick lime (CaO) or limestone (main component CaCO _3), such as dolomite ore and the like. These may be blended singly or in combination.

The kind of the MgO supply substance is not particularly limited, and examples thereof include an Mg-containing substance extracted from MgO powder, natural ore, seawater, and the like, or magnesium carbonate (MgCO ₃ ). MgO powder and magnesium carbonate are preferred, and these may be blended alone or in combination.

  Although the kind in particular of the said binder is not restrict | limited, For example, polysaccharide (for example, starches, such as wheat flour) is mentioned.

The type of the CaF ₂ supply substance is not particularly limited, and examples thereof include fluorite. From the viewpoint of emphasizing environmental measures, it is desirable not to mix CaF ₂ supply materials such as fluorite containing harmful fluorine into the raw material mixture. According to the present invention, it is sufficient even if no CaF ₂ supply material is added. In addition, the cohesiveness of granular metallic iron can be improved. However, if a CaF ₂ supply substance is added to the raw material mixture, the cohesiveness of the granular metallic iron can be further improved. Moreover, if a CaF ₂ supply substance is blended in the raw material mixture, the desulfurization ability of slag is improved, and the amount of S (sulfur amount) contained in the granular metallic iron can be reduced. Therefore, as long as the effects of the present invention are not impaired, a CaF ₂ supply substance may be added to the raw material mixture.

  Next, the manufacturing method of the granular metallic iron using the moving hearth type heating reduction furnace which concerns on this invention is demonstrated in detail, referring FIG. FIG. 3 shows an example of a moving hearth type heat reduction furnace preferably used in the production method of the present invention, but the present invention is not limited to this.

  FIG. 3 is a schematic explanatory view showing a configuration example of a rotary hearth type heating reduction furnace A among the moving hearth type heating reduction furnaces. In addition, in order to show the internal structure of a furnace, a part of furnace is notched and the inside is shown.

  In the rotary hearth-type heating reduction furnace A, a raw material mixture 1 containing an iron oxide-containing substance and a carbonaceous reducing agent is supplied onto a rotary hearth 4 through a raw material charging hopper 3.

As the iron oxide-containing substance, iron ore (eg, magnetite ore) or iron oxide is usually used. As the carbonaceous reducing agent, coal or coke is usually used. If necessary, the raw material mixture 1 may further contain the above-described auxiliary material for adjusting the slag composition, a binder, a CaF ₂ supply substance, and the like.

  The form at the time of supplying the said raw material mixture 1 is not specifically limited, What is necessary is just to supply what mixed the said iron oxide containing substance, the said carbonaceous reducing agent, etc. moderately. In addition, a simple molded body obtained by pressing and solidifying the iron oxide-containing substance and the carbonaceous reducing agent is supplied, or the iron oxide-containing substance and the carbonaceous reducing agent are molded into pellets or briquettes. You may supply a carbon material interior molded object.

  Here, the procedure when supplying the raw material mixture 1 etc. to the heating reduction furnace A is demonstrated concretely. Prior to the supply of the raw material mixture 1, the carbonaceous powder 2 is preferably supplied as a floor covering from the raw material charging hopper 3 onto the rotary hearth 4 and then the raw material mixture 1 is supplied thereon.

  There are no particular restrictions on the addition method of the CaO supply substance or MgO supply substance that can be blended in addition to the iron oxide-containing substance and the carbonaceous reducing agent. At the same time, or separately from the above, it is possible to adopt a method of charging the rotary hearth in advance or supplying it separately from above simultaneously with the supply of the raw material mixture or after the supply of the raw material mixture.

  The example shown in FIG. 3 shows an example in which one raw material charging hopper 3 is commonly used for supplying the carbonaceous powder 2 and supplying the raw material mixture 1. Of course, it is also possible to supply the powder 2 and the raw material mixture 1 separately.

  In addition, use of the carbonaceous powder 2 supplied on the hearth as a flooring material is not necessarily required, and supply may be omitted, but if the carbonaceous powder 2 is supplied on the hearth as a flooring material, the furnace This is preferable because the reduction potential can be increased more efficiently, and both the effects of improving the metallization rate and reducing the sulfur content can be exhibited more effectively.

  In order to exhibit such a function as a floor covering more reliably, it is desirable to spread the carbonaceous powder 2 on the hearth with a thickness of about 2 mm or more. If the carbonaceous powder 2 is spread as a flooring material in a certain layer, this flooring layer becomes a buffer material for the raw material mixture and the hearth refractory, or the hearth refractory against by-product slag, etc. It becomes a protective material and helps to extend the life of hearth refractories. However, the thickness of the floor covering layer is desirably suppressed to about 7.5 mm or less. If the flooring layer becomes too thick, the raw material mixture may sink into the flooring layer on the hearth and cause problems such as inhibition of the progress of reduction.

  The kind of carbonaceous powder used as the flooring material is not particularly limited, and normal carbon or coke or the like may be pulverized and preferably adjusted appropriately in particle size. When using coal, it is preferable to use anthracite which has low fluidity and does not swell or stick on the hearth. As the carbonaceous powder charged as the floor covering material, it is preferable to use a carbonaceous powder having a lower sulfur content than the carbonaceous reducing agent blended in the raw material mixture 1.

  Returning to FIG. The rotary hearth 4 of the heating reduction furnace A shown in FIG. 3 is rotated counterclockwise. The rotational speed of the rotary hearth 4 varies depending on the size and operating conditions of the heating reduction furnace A, but is usually a speed that makes one turn in about 8 to 16 minutes. A plurality of heating burners 5 are provided on the wall surface of the furnace body 8 in the heating and reducing furnace A, and heat is supplied to the hearth by the combustion heat of the heating burner 5 or its radiant heat. The heating burner 5 may be provided on the ceiling of the furnace.

  The raw material mixture 1 supplied onto the rotary hearth 4 made of a refractory material moves in the heating reduction furnace A in the circumferential direction on the rotary hearth 4, while the combustion heat and radiant heat from the heating burner 5. Heated by. And while passing through the heating zone in the heating and reducing furnace A, the iron oxide in the raw material mixture 1 is reduced and then separated from the by-product molten slag and carburized by the remaining carbonaceous reducing agent. The molten metal aggregates into granular metallic iron 10 while being melted and is cooled and solidified in the downstream zone of the rotary hearth 4, and then sequentially discharged from the hearth by a discharge device 6 such as a screw. At this time, slag produced as a by-product is also discharged, but after passing through the hopper 9, the metal iron and the slag are separated by an arbitrary separating means (for example, a sieve or a magnetic separator). In FIG. 3, reference numeral 7 denotes an exhaust gas duct.

  As described above, in the present invention, the melting point of slag can be lowered by using a raw material mixture that produces slag Z that satisfies a predetermined requirement at 1150 ° C. As a result, since the aggregation of the molten reduced iron can be promoted, the iron aggregability is improved, the iron yield is improved, and the productivity of the granular metallic iron can be improved.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention. The following examples show the results of tests using a small experimental heating and reducing furnace.

Iron ore was used as the iron oxide-containing substance, coal was used as the carbonaceous reducing agent, and these were mixed to obtain a raw material mixture. The component composition of iron ore is shown in Table 1 below, and the component composition of coal is shown in Table 2 below. Table 1 below shows the Al ₂ O ₃ / SiO ₂ ratio (mass ratio) calculated from the Al ₂ O ₃ content and the SiO ₂ content contained in the iron ore. In Table 2 below, “others” in the analysis value means solid carbonaceous matter.

In addition to the iron oxide-containing substance (iron ore) and the carbonaceous reducing agent (coal), the raw material mixture was blended with a binder, a secondary raw material for adjusting the slag composition, and a CaF ₂ supply substance to obtain a blend. As the binder, wheat flour was blended. As an auxiliary material for adjusting the slag composition, slag produced as a by-product by blending dolomite ore (the main component is CaCO ₃ .MgCO ₃ and the detailed component composition is shown in Table 3 below) and limestone as a CaO supply substance. The components were adjusted so that the basicity of each sample was almost the same in each sample (target basicity was 1.2). As the CaF ₂ supplying substance, fluorite was blended. The component composition of the blend is shown in Table 4 below.

  An appropriate amount of water was added to the resulting blend and granulated into raw pellets having a diameter of about 19 mm using a tire type granulator. The obtained raw pellets were supplied to a dryer and heated at 180 ° C. for 1 hour to completely remove the attached water, thereby obtaining a raw material molded body.

  Next, the obtained raw material compact was supplied into a small experimental heating and reducing furnace and reduced by heating. On the hearth, coal (carbonaceous powder) having the composition shown in Table 2 below was laid as a floor covering material with a thickness of about 5 mm. The furnace temperature was adjusted to 1450 ° C.

  The heat history from when the raw material compact is supplied into the experimental heating and reducing furnace until the temperature of the raw material compact reaches 1450 ° C. is as follows. That is, the temperature rising rate from room temperature to about 500 ° C. is 600 ° C./min, the temperature rising rate from about 500 ° C. to about 1170 ° C. is 150 ° C./min, and the temperature rising rate from about 1170 ° C. to 1450 ° C. is 50 ° C. / Min.

  The iron oxide in the raw material compact supplied on the hearth of the heating and reducing furnace is reduced while maintaining the solid state while being heated in the furnace for about 10 minutes, and the produced reduced iron remains after the reduction. While undergoing carburization with the carbonaceous powder, the melting point dropped and agglomerated each other. The slag produced as a by-product at this time partially or almost completely melted and aggregated with each other, and was separated into molten metallic iron and molten slag. Thereafter, the molten granular metallic iron and molten slag are cooled, cooled to below the melting point (specifically, cooled to about 1100 ° C.) and solidified, and then discharged out of the furnace as solid granular metallic iron or slag. Discharged. At this time, after the raw material compact was charged into the experimental heat reduction furnace, the inside of the heat reduction furnace was visually observed, and the time taken to dissolve all the compacts found in the field of view (dissolution Completion time) was measured. The dissolution completion time is shown in Table 5.

  In addition, Table 5 below shows the component composition of the obtained granular metallic iron and by-product slag. Moreover, the ratio (yield rate;%) of the amount of Fe obtained as agglomerated granular metallic iron with respect to the amount of Fe obtained based on the component composition of the blend was calculated, and the results are shown in Table 5 below.

Next, in heating the raw material molded body with the above-described thermal history, the heating was stopped when the temperature of the raw material molded body reached 1150 ° C. and cooled to room temperature. About the raw material compact after cooling, JEOL field emission scanning electron microscope (FE-SEM) “JSM-7001F (device name)” and JEOL energy dispersive X-ray analysis attached to this Using a device (EDX) “JED-2300F (device name)”, the component composition of slag in the surface layer cross section was randomly analyzed. Specifically, for a field of view of about 0.24 mm ² (width 0.6 mm × length 0.4 mm) observed with the FE-SEM, the composition of the component corresponding to the slag phase is 10 per field of view. ˜30 points were measured. The number of observation visual fields was 5-10 visual fields. In addition, the score which analyzed component composition is No. of following Table 5. 1 is 71 points. 2 was 111 points. Based on the component composition at these analysis points, “FactSage (software name)” was used to calculate the melting point of each slag, and the liquid phase ratio of the slag at 1150 ° C. was obtained.

No. in Table 5 below. For Table 1, the following Table 6 and Table 7 show the MgO content, Al ₂ O ₃ content, SiO ₂ content, FeO content, CaO content, CaF ₂ content, and 1150 ° C. in all individual slags whose component compositions were analyzed. The liquid phase rate of slag was shown. Further, the FeO / SiO ₂ ratio (mass ratio) and the FeO / CaO ratio (mass ratio) were calculated and shown together.

On the other hand, no. For 2, the MgO content, the Al ₂ O ₃ content, the SiO ₂ content, the FeO content, and the CaO content in the slag whose liquid phase ratio at 1150 ° C. is 80% or more among the slags analyzed for the component composition in Table 8 below. The liquid phase ratio of slag at 1150 ° C. was shown for the amount of CaF ₂ . Further, the FeO / SiO ₂ ratio (mass ratio) and the FeO / CaO ratio (mass ratio) were calculated and shown together.

  The following Table 5 to Table 8 can be considered as follows. No. 1 and No. In No. 2, the components were adjusted so that the basicity of the slag produced as a by-product was almost equal, so the dissolution completion time was the same. However, No. 1 satisfying the requirements defined in the present invention. 1 and No. 1 that do not satisfy the requirements specified in the present invention. In No. 2, a difference of 22.5% occurred in the yield rate of granular metallic iron.

  That is, no. No. 1, when the raw material molded body was heated to 1150 ° C., the liquid phase ratio was 80% or more, and slag satisfying the component composition defined in the present invention was generated. Melting of slag progressed quickly, and slag aggregation was promoted. As a result, the aggregation of the granular metallic iron was promoted, the yield rate of the granular metallic iron became 100% or more, and the productivity was improved. On the other hand, no. In No. 2, when the raw material molded body was heated to 1150 ° C., slag having a liquid phase ratio of 80% or more was generated, but the component composition of the slag did not satisfy the requirements defined in the present invention. Therefore, even when heated to 1450 ° C., the melting of the slag hardly progressed, and the aggregation of the slag was not promoted. As a result, the aggregation of the granular metallic iron was inhibited, the yield rate of the granular metallic iron was as low as less than 100%, and the productivity could not be improved.

Next, the component composition in the surface layer cross section of the raw material molded body after the cooling was analyzed using the FE-SEM and the EDX attached thereto. Specifically, with respect to a field of view of about 3.2 mm ² (horizontal 2 mm × longitudinal 1.6 mm) observed by FE-SEM, the horizontal direction (horizontal direction) is 50 points at intervals of 40 μm and the vertical direction (vertical direction). The component composition at 20 analysis points at 80 μm intervals and a total of 1000 analysis points was analyzed by EDX attached to the FE-SEM. The acceleration voltage when observing with FE-SEM is 15 kV, the imaging method is a backscattered electron image method, the acceleration voltage when analyzing with EDX is 15 kV, the analysis method is a point analysis method, and the measurement time per analysis is 60 seconds. It was.

About 1000 analysis points where the component composition was analyzed, (a) the number of analysis points where the amount of FeO is 5 to 60% by mass, (b) the number of analysis points where the amount of SiO ₂ is 30% by mass or more, (c ) Number of analysis points where the CaO amount is 0.5-50% by mass, (d) Number of analysis points where the FeO / SiO ₂ ratio determined from the FeO amount and the SiO ₂ amount is 0.17-2.0, (E) The number of analysis points where the FeO / CaO ratio determined from the FeO amount and the CaO amount is 0.2 to 50 is shown in Table 9 below. In addition, the number of analysis points satisfying all of the above (a) to (e) is also shown.

  As apparent from Table 9 below, the above No. 1 is that among the 1000 analysis points, the number of analysis points satisfying all the requirements (a) to (e) is 66, which is 6.6% of the total number of analysis points. In contrast, no. 2 was 17 points, and was 1.7% based on the total number of analysis points.

  FIG. 4 shows the relationship between the number of analysis points satisfying all the requirements (a) to (e) shown in Table 9 below and the yield rate (%) shown in Table 5 below.

  As is clear from FIG. 4, in order to increase the yield rate to 90% or more, the ratio of the number of analysis points satisfying all the requirements (a) to (e) described above is based on the number of all analysis points. It can be seen that it should be 3.5% or more (35 or more out of 1000 points).

  As is apparent from the above results, paying attention to the liquid phase rate of slag by-produced at 1150 ° C. and the component composition of slag, the liquid phase rate at 1150 ° C. is 80% or more, and the component composition satisfies a predetermined condition. Thus, it can be seen that adjusting the component composition of the raw material mixture can increase the yield of the granular metallic iron and improve the productivity.

A Rotary hearth type heating reduction furnace 1 Raw material mixture 2 Carbonaceous powder 3 Raw material charging hopper 4 Rotary hearth 5 Heating burner 6 Discharge device 7 Exhaust gas duct 8 Furnace body 9 Hopper 10 Granular metal iron

Claims (3)

A raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is heated in a moving hearth type heating and reducing furnace, iron oxide in the raw material mixture is reduced by the carbonaceous reducing agent, and the produced metallic iron is by-produced. In a method for producing granular metallic iron by agglomerating into particles while being separated from slag to be cooled and solidified,
A method for producing granular metallic iron, characterized in that a slag Z that satisfies the following requirements (1) to (6) is generated at 1150 ° C. as the raw material mixture.
(1) The liquid phase ratio is 80% or more.
(2) The amount of FeO is 5 to 60% by mass.
(3) The amount of SiO ₂ is 30% by mass or more.
(4) CaO amount is 0.5 to 50% by mass.
(5) FeO / SiO ₂ ratio determined from FeO amount and SiO ₂ amount is 0.17 to 2.0.
(6) FeO / CaO ratio obtained from FeO amount and CaO amount is 0.2-50.   After the raw material mixture is heated to 1150 ° C., when the component composition in the cross section of the surface layer is analyzed at regular intervals of at least 200 points, the component composition satisfies all the requirements (2) to (6). The method according to claim 1, wherein a raw material mixture is used in which the ratio of the number of points is 3.5% or more with respect to the number of all analysis points. Examples of iron oxide-containing substance, according to claim 1 or 2 Al ₂ O ₃ of the iron oxide containing material and Al ₂ O ₃ / SiO ₂ ratio is determined from the amount of SiO ₂ is used as less than 0.1 Manufacturing method.