WO2011138954A1

WO2011138954A1 - Process for production of metal iron

Info

Publication number: WO2011138954A1
Application number: PCT/JP2011/060558
Authority: WO
Inventors: 杉山　健; 原田　孝夫
Original assignee: 株式会社神戸製鋼所
Priority date: 2010-05-06
Filing date: 2011-05-02
Publication date: 2011-11-10
Also published as: US20130055853A1; JP2011252226A

Abstract

Disclosed is a technique for preventing the fixation of metal iron and/or wustite (which is a material produced by the thermal reduction of iron oxide contained in a powder derived from an aggregated mass that comprises, as a raw material, a mixture containing a iron-oxide-containing substance and a carbonaceous reducing agent) on a heath of a movable furnace heath type heating furnace without largely changing the design of a facility for the production, in the production of metal iron by placing the aggregated mass on the heath and heating the aggregated mass in the heating furnace to reduce iron oxide contained in the aggregated mass. A heath-forming material for preventing the fixation of metal iron and/or wustite (which is a material produced by the thermal reduction of iron oxide contained in the powder derived from the aggregated mass) on the heath is introduced into the furnace together with the aggregated mass.

Description

Manufacturing method of metallic iron

In the present invention, an agglomerate made of a mixture containing an iron oxide source such as iron ore or iron oxide and a carbon-containing reducing agent is charged on the hearth of a moving hearth-type heating furnace and heated. The present invention relates to a method for producing massive metallic iron by reducing iron oxide in a composition.

From a raw material mixture containing an iron oxide source such as iron ore or iron oxide (hereinafter sometimes referred to as an iron oxide-containing substance) and a reducing agent containing carbon (hereinafter sometimes referred to as a carbonaceous reducing agent), metallic iron A direct reduction iron manufacturing method has been developed. In this iron making method, the agglomerate formed from the raw material mixture is placed on the hearth of a moving hearth-type heating furnace, and heated in the furnace by gas heat transfer or radiant heat by a heating burner. Iron oxide is reduced with a carbonaceous reducing agent to obtain massive metallic iron. However, in the iron making method, a part of the agglomerate is pulverized due to rolling, collision, drop impact or the like of the agglomerate. The powder derived from the agglomerate is also charged when the agglomerate is charged on the hearth, and is deposited on the hearth to form a storage layer. This accumulation layer is heated and reduced in the furnace in the same manner as the above agglomerates to produce metallic iron and wustite (FeO). When the produced metallic iron and wustite are left in the furnace, they are deposited on the hearth sequentially, raising the surface of the hearth and making it difficult to operate. Therefore, usually, the accumulation layer is discharged by a discharger (discharger). However, since the accumulation layer deposited on the hearth is thin, it is not discharged when the massive metallic iron formed by heating and reducing the iron oxide in the agglomerate is discharged from the furnace, and it stays on the hearth. Compressed with a discharger, may form solids that are so large that they cannot be finally discharged from the furnace. Moreover, when the produced metallic iron and wustite aggregate to form a lump, when the lump is discharged from the furnace, irregularities are formed on the hearth, which may make operation difficult. Technologies for solving these problems are proposed in Patent Documents 1 to 3.

Among these, in Patent Document 1, as a method for preventing the formation of an iron plate on the hearth, reduced iron obtained by reducing the carbonaceous material-containing iron oxide agglomerate is moved out of the moving hearth type reduction furnace. An operation method has been proposed in which a discharger (discharger) for discharging is provided and the position of the discharger that maintains a gap with the surface of the moving floor is adjusted. According to this technology, it is described that by providing a gap, it is possible to prevent the agglomerate-derived powder mixed into the furnace accompanying the agglomerate from being pushed into the hearth surface and to prevent the formation of a strong iron plate. Has been.

In Patent Document 2, as a method for removing the fixed matter fixed on the hearth from the hearth surface, a crack was generated in the fixed matter fixed on the hearth by quenching the hearth surface of the rotary hearth type reduction furnace. Later, it has been proposed to remove the adherent from the hearth.

Patent Document 3 discloses that metal iron powder staying on the hearth and deposits on the hearth brick are removed, or metal iron powder remaining on the hearth is prevented and the surface of the hearth is always kept clean. A method of maintaining a rotating bed furnace that can be used has been proposed. In this maintenance method, the reduced iron powder remaining on the hearth is removed from the hearth by blowing off with a jet gas flow between the reduced iron discharge part and the raw material charging part.

Japanese Patent No. 3075721 Japanese Patent Laid-Open No. 2002-12906 Japanese Patent Laid-Open No. 11-50120

In the technologies disclosed in Patent Documents 1 to 3, the design of the discharge device for discharging reduced iron to the outside of the moving hearth type reduction furnace, the provision of a new device for rapidly cooling the hearth surface, It is necessary to newly provide a device for blowing off the reduced iron powder, which requires a large capital investment.

The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to use an agglomerate made of a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent as a raw material, and a moving hearth type heating furnace. The iron oxide contained in the powder derived from the agglomerate without drastically changing the design of the equipment when reducing the iron oxide in the agglomerate and producing the metallic iron It is intended to provide a technique for preventing metallic iron and wustite produced by heat reduction of iron from adhering to the hearth.

The method for producing metallic iron according to the present invention, which has solved the above problems, is an agglomerate (particle size is, for example, 5 to 50 mm) made from a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent. In the production of metallic iron by charging iron oxide in the agglomerated material and heating it (eg, 1200-1400 ° C.) on the hearth of the moving hearth type heating furnace, The main point is that a hearth forming material for preventing metallic iron and / or wustite formed by heat reduction of iron oxide contained in the powder from being fixed to the hearth together with the agglomerates is introduced into the furnace. is doing.

(A) When the amount of carbon contained in the agglomerate is 122% (meaning mass%; the same shall apply hereinafter) or more with respect to the amount of carbon necessary for reducing iron oxide in the agglomerate. As for the component composition combining the powder derived from the agglomerate and the hearth forming material, the amounts of CaO, SiO ₂ and Al ₂ O ₃ satisfy the following formulas (1) and (2): It is preferable to adjust the component composition of the hearth forming material. In the following formulas (1) and (2), [] represents the content (% by mass) of each component.
[CaO] / [SiO ₂ ] = 0.25 to 1.20 (1)
[Al ₂ O ₃ ] / [SiO ₂ ] = 0.2 to 0.7 (2)

In the case of (a), the total amount of CaO, SiO ₂ , and Al ₂ O ₃ is 3.0 to 7.0 with respect to the component composition of the powder derived from the agglomerate and the hearth forming material. It is preferable to adjust the component composition of the hearth forming material so as to be%.

(B-1) When the amount of carbon contained in the agglomerate is less than 122% with respect to the amount of carbon required to reduce iron oxide in the agglomerate, The total carbon content of the component composition of the powder and the hearth forming material is 122% or more based on the amount of carbon necessary for reducing iron oxide in the agglomerate, and is derived from the agglomerate The composition of the hearth forming material so that the amounts of CaO, SiO ₂ and Al ₂ O ₃ satisfy the following formulas (3) and (4): It is preferable to adjust the component composition. In the following formulas (3) and (4), [] represents the content (% by mass) of each component.
[CaO] / [SiO ₂ ] = 0.25 to 1.20 (3)
[Al ₂ O ₃ ] / [SiO ₂ ] = 0.2 to 0.7 (4)

(B-2) When the amount of carbon contained in the agglomerate is less than 122% with respect to the amount of carbon required for reducing iron oxide in the agglomerate, the agglomerate The total carbon content of the component composition of the derived powder and the hearth-forming material remains below 122% with respect to the amount of carbon required to reduce the iron oxide in the agglomerate, and Regarding the component composition of the powder derived from the agglomerate and the hearth forming material, the amount of CaO, SiO ₂ , Al ₂ O ₃ , and MgO is at least one of the following formulas (5) to (9): It is preferable to adjust the component composition of the hearth forming material so as to satisfy. In the following formulas (5) to (9), [] represents the content (% by mass) of each component.
[CaO] / [SiO ₂ ] <0.25 (5)
[CaO] / [SiO ₂ ]> 1.20 (6)
[Al ₂ O ₃ ] / [SiO ₂ ] <0.2 (7)
[Al ₂ O ₃ ] / [SiO ₂ ]> 0.7 (8)
[MgO] / [SiO ₂ ]> 0.4 (9)

In the case of (b-2) above, the total amount of CaO, SiO ₂ , and Al ₂ O ₃ is more than 7.0% for the component composition of the powder derived from the agglomerate and the hearth forming material. It is preferable to adjust the component composition of the hearth forming material so that

The ratio of the hearth forming material having a particle diameter of 0.5 to 2 mm to the total amount of the hearth forming material charged in the furnace is preferably 50% by mass or more.

According to the present invention, since the hearth forming material is charged together with the agglomerate on the hearth of the moving hearth heating furnace, the iron oxide contained in the powder derived from the agglomerate is reduced by heating and generated. It is possible to prevent metallic iron and wustite that adhere to the hearth. For this reason, it is possible to prevent solid objects such as iron plates that cannot be discharged from the furnace from being formed on the hearth, and to raise the hearth surface, making it possible to efficiently use metallic iron without making major design changes. Can be manufactured well.

FIG. 1 is a graph showing the relationship between temperature and deformation rate when pellets are reduced by changing [MgO] / [SiO ₂ ]. FIG. 2 is a drawing-substituting photograph in which a cross section of the reduced pellet is photographed. FIG. 3 is a graph showing the results of measuring 40% shrinkage temperature by changing [MgO] / [SiO ₂ ]. FIG. 4 is a graph showing the result of measuring 40% shrinkage temperature by changing [CaO] / [SiO ₂ ]. FIG. 5 shows a SiO ₂ —MgO—FeO ternary equilibrium diagram. FIG. 6 shows a CaO—SiO ₂ —MgO ternary equilibrium diagram. Figure 7 shows a CaO-SiO _₂ -Al ₂ O ₃ based ternary equilibrium diagram.

The technologies proposed in the above Patent Documents 1 to 3 require a significant design change of equipment and require a large capital investment. Therefore, the present inventors minimize the capital investment and prevent the iron oxide contained in the agglomerate-derived powder from being reduced by heating in the furnace to prevent the metallic iron and wustite from sticking to the hearth. In order to provide a method for efficiently producing metallic iron, it is possible to prevent solid objects such as iron plates that cannot be discharged from the furnace from being formed on the hearth and to raise the surface of the hearth. Has been repeated. As a result, it has been found that when the agglomerate is charged into the furnace, the hearth forming material may be charged into the furnace. Specifically, in consideration of the amount of carbon contained in the agglomerate charged into the furnace and the amount of carbon necessary to reduce iron oxide in the agglomerate, the agglomerate-derived The present invention has been completed by finding that the component composition of the hearth forming material may be appropriately adjusted and charged into the furnace so that the combined composition of the powder and the hearth forming material satisfies a predetermined condition. did.

That is, the method for producing metallic iron according to the present invention includes a hearth forming material for preventing iron oxide and / or wustite formed by heat reduction of iron oxide contained in agglomerate-derived powder from being fixed on the hearth. Is characterized in that it is charged into the furnace together with the agglomerates. The powder derived from the agglomerate that accumulates on the hearth is a powder that is charged into the furnace along with the agglomerate, and a powder that breaks down when the agglomerate is rapidly heated in the furnace. When the agglomerate is charged into the furnace, the hearth-forming material and the powder derived from the agglomerate are placed on the hearth by charging the hearth-forming material together in the furnace. Can be mixed. At this time, iron oxide contained in the powder derived from the agglomerate is formed by heat reduction by appropriately adjusting the component composition of the hearth forming material in consideration of the component composition of the powder derived from the agglomerate. It is possible to prevent metallic iron and wustite from sticking to the hearth. Therefore, formation of fixed objects such as an iron plate and the occurrence of the rise of the hearth surface can be suppressed, and the production efficiency of metallic iron can be increased.

The time when the hearth forming material is added is before charging the agglomerate into the furnace, and preferably the time when the hearth forming material is added to the agglomerated material.

To add the hearth former before charging the agglomerate, for example, add the hearth former to the agglomerate on a conveyor that inserts the agglomerate into the hopper, and the agglomerates and hearths What is necessary is just to put these together on a hearth in the state which mixed the forming material. Of the charged mixture, the powder generated from the agglomerate and the fine hearth forming material accumulate in the lower part of the agglomerate, and are mixed and moved when the agglomerate is leveled by the leveler. .

As the hearth forming material, a material that acts so as not to fix metal iron or wustite formed by heat reduction of iron oxide contained in the powder derived from the agglomerate on the hearth may be inserted. Specifically, paying attention to the amount of carbon contained in the agglomerate, this carbon amount is (a) 122% or more with respect to the amount of carbon necessary for reducing iron oxide in the agglomerate. Whether or not it is (b) less than 122%, the case may be divided and the component composition of the hearth forming material may be adjusted and charged into the furnace. Here, the amount of carbon contained in the agglomerate is 100% with respect to the amount of carbon required to reduce the iron oxide in the agglomerate, which means that the iron oxide in the agglomerate is excessive or insufficient. Not all (100%). Further, the fact that the amount of carbon is 122% of the amount of carbon necessary for reducing iron oxide in the agglomerate means that the amount of carbon is 22% excess, and this 22% The amount of carbon corresponds to about 5% of the amount of carbon remaining in the agglomerate after reduction.

The amount of carbon contained in the agglomerate and the amount of carbon necessary for reducing the iron oxide in the agglomerate can be calculated based on the component composition of the raw material mixture constituting the agglomerate. The amount of carbon contained in the agglomerate after heat reduction of iron oxide in the agglomerate is, for example, 1300 ° C. in an inert atmosphere (for example, N ₂ atmosphere) by placing the agglomerate in an electric furnace. The amount of carbon remaining in the agglomerated material heated at (representative temperature) and having undergone the reduction reaction can be analyzed by infrared analysis. If the sum of this analytical value and the amount of carbon necessary for reducing the iron oxide in the agglomerate is calculated, the amount of carbon contained in the agglomerate before heating can be calculated backward.

[(A) 122% or more]
When the amount of carbon contained in the agglomerate is 122% or more with respect to the amount of carbon necessary for reducing iron oxide in the agglomerate (hereinafter sometimes referred to as necessary carbon amount), Regarding the component composition of the powder derived from the composition and the hearth forming material, the hearth forming material so that the amounts of CaO, SiO ₂ , and Al ₂ O ₃ satisfy the following formulas (1) and (2). What is necessary is just to adjust the component composition. In the following formulas (1) and (2), [] represents the content (% by mass) of each component.
[CaO] / [SiO ₂ ] = 0.25 to 1.20 (1)
[Al ₂ O ₃ ] / [SiO ₂ ] = 0.2 to 0.7 (2)

That is, the amount of carbon contained in the agglomerate is more than the required amount of carbon, and when carbon remains after heat reduction, the iron oxide contained in the agglomerate is almost completely reduced, Metallic iron produced by reduction becomes fine particles and exists in a state of being separated from each other. Moreover, since the carburization of metallic iron is accelerated | stimulated by heat reduction when the carbon amount contained in an agglomerate is excessive, metallic iron does not couple | bond together but a hard and brittle slag phase intervenes. Therefore, even if a fixed object such as an iron plate is formed on the hearth, the fixed object can be easily crushed and easily discharged from the furnace.

Therefore, if the amount of carbon contained in the agglomerate is 122% or more of the required amount of carbon, further promoting the granulation of metallic iron is effective in promoting the discharge of metallic iron out of the furnace. It becomes. In order to promote the granulation of metallic iron, the present invention focuses on the slag produced as a by-product during the production of metallic iron and lowers the melting point of this slag to promote the aggregation of metallic iron and granulate. Specifically, for the component composition of the powder derived from the agglomerate and the hearth forming material, the amounts of CaO, SiO ₂ and Al ₂ O ₃ satisfy the above formulas (1) and (2). Thus, the component composition of the hearth forming material is adjusted.

<< About Formula (1) >>
By setting [CaO] / [SiO ₂ ] to preferably 0.25 to 1.20, the melting point of slag can be lowered, and the granulation of metallic iron can be promoted. A more preferred lower limit of [CaO] / [SiO ₂ ] is 0.3, and a more preferred upper limit is 1.1.

<< About Formula (2) >>
By setting [Al ₂ O ₃ ] / [SiO ₂ ] to preferably 0.2 to 0.7, the melting point of the slag can be lowered and the granulation of metallic iron can be promoted. The upper limit of [Al ₂ O ₃ ] / [SiO ₂ ] is more preferably 0.6, and still more preferably 0.4.

When the amount of carbon contained in the agglomerate is 122% or more with respect to the required amount of carbon, CaO, SiO ₂ , and Al ₂ for the component composition of the agglomerate-derived powder and the hearth-forming material It is preferable to adjust the component composition of the hearth forming material so that the total amount of O ₃ is 3.0 to 7.0%. As the amount of molten slag increases, carburization of metallic iron after heat reduction is promoted, so that the granulation of metallic iron can be promoted by setting the total amount of the above components to preferably 3.0% or more. The total amount is more preferably 4.5% or more, still more preferably 5.0% or more. However, when the total amount exceeds 7.0%, the amount of molten slag increases so much that it may flow down and erode the hearth. Therefore, the total amount is preferably 7.0% or less, and more preferably 6.5% or less.

[(B) If less than 122%]
When the amount of carbon contained in the agglomerate is less than 122% of the required amount of carbon,
(B-1) The component composition of the hearth forming material is adjusted so that the total carbon content of the component composition of the agglomerate-derived powder and the hearth forming material is 122% or more of the required carbon amount. Or,

(B-2) Method of adjusting the component composition of the hearth forming material while keeping the total carbon content of the component composition of the agglomerate-derived powder and the hearth forming material less than 122% of the required carbon amount There is.

In the case of the above (b-1), the hearth forming material so that the total carbon content of the component composition of the agglomerate-derived powder and the hearth forming material is 122% or more with respect to the required carbon amount. As for the component composition that combines the agglomerate-derived powder and the hearth-forming material, the amounts of CaO, SiO ₂ , and Al ₂ O ₃ are the following formulas (3) and ( It is important to adjust the component composition of the hearth forming material so as to satisfy 4). In the following formulas (3) and (4), [] represents the content (% by mass) of each component.
[CaO] / [SiO ₂ ] = 0.25 to 1.20 (3)
[Al ₂ O ₃ ] / [SiO ₂ ] = 0.2 to 0.7 (4)

That is, when the amount of carbon contained in the agglomerate is less than 122% of the required amount of carbon, the amount of carbon tends to be insufficient, so a part of the iron oxide contained in the agglomerate-derived powder is reduced. For example, it may remain as wustite. Further, since the amount of carbon that contributes to carburizing of metallic iron is reduced, the granulation of metallic iron is not promoted, and plate-shaped metallic iron is easily generated. Therefore, in order to reduce all the iron oxide contained in the powder derived from the agglomerate and to sufficiently carburize and granulate, a carbonaceous reducing agent is blended as a hearth forming material, and the amount of carbon contained in the agglomerate The component composition of the hearth forming material is adjusted so that the total carbon content of the component composition of the powder derived from the agglomerate and the hearth forming material is 122% or more with respect to the required carbon amount. adjust.

At this time, the amount of CaO, SiO ₂ , Al ₂ O ₃ satisfies the relationship of the above formulas (3) and (4) for the component composition of the agglomerate-derived powder and the hearth forming material. Need to be. The above formulas (3) and (4) are the same formulas as the above formulas (1) and (2), and are defined based on the same knowledge. That is, the metal iron can be easily discharged out of the furnace by further reducing the granularity of the metal iron by lowering the melting point of the slag.

In the case of (b-2) above, the total carbon content of the component composition of the agglomerate-derived powder and the hearth-forming material is kept below 122% with respect to the required carbon content, Regarding the component composition of the powder derived from the agglomerate and the hearth forming material, the amount of CaO, SiO ₂ , Al ₂ O ₃ , and MgO is at least one of the following formulas (5) to (9): It is important to adjust the component composition of the hearth forming material so as to satisfy. In the following formulas (5) to (9), [] represents the content (% by mass) of each component.
[CaO] / [SiO ₂ ] <0.25 (5)
[CaO] / [SiO ₂ ]> 1.20 (6)
[Al ₂ O ₃ ] / [SiO ₂ ] <0.2 (7)
[Al ₂ O ₃ ] / [SiO ₂ ]> 0.7 (8)
[MgO] / [SiO ₂ ]> 0.4 (9)

No carbonaceous reducing agent is added as the hearth-forming material, and the total carbon content of the component composition of the agglomerate-derived powder and the hearth-forming material is kept below 122% of the required carbon content. In such a case, it is effective to appropriately control the composition of the gangue component. Specifically, by increasing the melting point of the gangue component, solid gangue can be interposed between metallic iron and wustite particles, so the interval between metallic iron and wustite particles can be increased. These aggregations can be suppressed. As a result, it is possible to prevent metallic iron and wustite particles from adhering to the hearth or from adhering to a lump and forming bumps on the hearth surface.

That is, metallic iron produced by reduction of iron oxide contained in the powder derived from the agglomerate is very fine and therefore has a very low mutual bonding force. However, depending on the composition of the gangue components such as CaO, SiO ₂ , and Al ₂ O ₃ , the melting point of the generated slag is lowered, and when molten slag is formed during the heating reduction, metallic iron existing in the vicinity thereof is formed. The Fe atoms on the surface easily move, and the bonding between the metal irons is promoted to form a network-like metal iron bonding layer. When pressure is applied to the metallic iron bonding layer, a dense metallic iron plate (fixed matter) is formed, making it difficult to discharge out of the furnace.

In addition, when iron oxide is not sufficiently reduced, wustite (FeO) is generated. Even in this case, if the molten slag exists, Fe atoms on the surface of wustite easily move and bonds between wustites. Is promoted to become coarse wustite particles. Coarse wustite particles further become large blocks via the molten slag, making it difficult to discharge out of the furnace.

Therefore, if it is possible to prevent metal irons or wustites or metal iron and wustite from being combined, it is considered that metal iron and wustite can be easily discharged from the hearth. Based on these findings, the total carbon content of the combined composition of the powder derived from the agglomerate and the hearth forming material is 122% with respect to the required amount of carbon without adding a carbonaceous reducing agent as the hearth forming material. When the ratio is kept below, it is important to increase the melting point of by-product slag and suppress the formation of molten slag.

<< About Formula (5) and Formula (6) >>
By making [CaO] / [SiO ₂ ] preferably less than 0.25 or preferably more than 1.20, the melting point of by-product slag can be increased, and coarsening of metallic iron and wustite particles can be prevented. . [CaO] / [SiO ₂ ] is more preferably 0.20 or less, and more preferably 1.25 or more.

<< About Formula (7) and Formula (8) >>
By making [Al ₂ O ₃ ] / [SiO ₂ ] preferably less than 0.2 or preferably more than 0.7, the melting point of by-product slag can be increased, and the coarsening of metallic iron and wustite particles Can be prevented. [Al ₂ O ₃ ] / [SiO ₂ ] is more preferably 0.18 or less, further preferably 0.16 or less, and more preferably 0.8 or more.

<< About Formula (9) >>
MgO has the effect | action which suppresses the production | generation of molten slag and can prevent the coarsening of metallic iron and a wustite particle | grain. That is, the gangue component melts from the low melting point composition in the process of increasing the temperature, and the component that raises the melting point is dissolved therein to solidify by dissolution, thereby generating a gangue melt. Even if the average composition of the stone has a high melting point, there is a possibility that a bond is partially formed. However, since MgO is easy to diffuse into solid state FeO, the melting point of slag is increased as its content increases, so that it has an action of suppressing the generation of molten slag.

As will be apparent from FIG. 5 to be described later, since the melting point of the molten slag changes greatly due to the change of [MgO] / [SiO ₂ ], the MgO amount may be adjusted in consideration of the balance with the SiO ₂ amount. . Specifically, [MgO] / [SiO ₂ ] is preferably more than 0.4, thereby suppressing generation of molten slag and increasing solid slag. [MgO] / [SiO ₂ ] is more preferably 0.45 or more, and further preferably 0.5 or more. The upper limit of [MgO] / [SiO ₂ ] is, for example, 0.9.

The above formulas (5) to (9) need only satisfy at least one formula, and if at least one formula is satisfied, the melting point of by-product slag increases.

The amount of carbon contained in the agglomerate is less than 122% of the required carbon amount, and the total carbon amount of the component composition combining the powder derived from the agglomerate and the hearth forming material is required carbon. When it is less than 122% with respect to the amount, the total amount of CaO, SiO ₂ , and Al ₂ O ₃ is 7.0 with respect to the component composition of the powder derived from the agglomerate and the hearth forming material. It is preferable to adjust the component composition of the hearth forming material so as to exceed%. By making the total amount above 7.0%, the amount of gangue can be increased, so the amount of solid slag is increased, and it is possible to prevent metal iron and wustite from agglomerating and becoming coarse, and sticking to the hearth Can be prevented from being formed. The total amount is more preferably 7.5% or more, and further preferably 8% or more. The upper limit of the total amount is, for example, 10%.

As the hearth forming material, CaO source, SiO ₂ source, Al ₂ O ₃ source, may be blended material as the MgO source. As the CaO source, e.g., burnt lime (CaO) or limestone (main component CaCO ₃₎ or the like can be used. As the SiO ₂ source, for example, a mixture with other components such as silica sand or serpentine can be used. As the Al ₂ O ₃ source, for example, bauxite or a mixture with other components such as alumina-containing iron ore can be used. As the MgO source, for example, an Mg-containing material extracted from MgO-containing slag, seawater, or the like, or magnesium carbonate (MgCO ₃ ), dolomite, or the like can be used.

To adjust the component composition of the hearth forming material so that the composition of the powder derived from the agglomerate and the hearth forming material satisfies the above requirements, the mass of the powder derived from the agglomerate is measured. There is a need.

As a powder derived from agglomerates, after agglomerates are formed using a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent as a raw material, a part of the agglomerates collapses or collapses due to impact or wear. Generated powder (hereinafter sometimes referred to as powder I) and powder produced by collapsing while the agglomerate is charged into the furnace and heated and reduced (hereinafter sometimes referred to as powder II). )) Are considered.

The mass of the powder I is, for example, measuring the total mass of the agglomerate charged into the furnace, classifying the charge, and dividing the agglomerate into agglomerate-derived powder. What is necessary is just to measure the mass of the powder derived from a thing directly. In the present invention, a powder having a particle diameter of 3 mm or less is defined as a powder.

However, in the method of directly measuring the mass of the powder derived from the agglomerate, when the agglomerate is continuously charged in the furnace, it cannot be handled if the properties of the agglomerate change in the middle. Therefore, as shown in the examples described later, a rotational strength test was performed to simulate the movement process until the agglomerate obtained by molding was charged into the furnace, and the particle diameter generated at this time was 3 mm or less. The mass of the powder may be estimated by measuring the mass of the powder.

On the other hand, the mass of the powder II is obtained by measuring the mass of a powder having a particle diameter of 3 mm or less that is generated when the agglomerate is heated in an electric furnace and rapidly heated (for example, a heating rate of 10 ° C./min or more). The mass of the powder derived from the agglomerate may be predicted.

Thus, after predicting the mass of the powder derived from the agglomerate, the component composition of the powder derived from the agglomerate and the hearth forming material can be expressed by the following formulas (21) to (24). it can.
CaO (kg / hr):
H _CaO = (L _CaO × W _L + C _CaO × CW _L + S _CaO × SW _L + A _CaO × AW _L + M _CaO × MW _L ) / 100 (21)
SiO ₂ (kg / hr):
H _SiO2 = (L _SiO2 × W _L + C _SiO2 × CW _L + S _SiO2 × SW _L + A _SiO2 × AW _L + M _SiO2 × MW _L ) / 100 (22)
Al ₂ O ₃ (kg / hr):
H _Al2O3 = (L _Al2O3 * W _L + C _Al2O3 * CW _L + S _Al2O3 * SW _L + A _Al2O3 * AW _L + M _Al2O3 * MW _L ) / 100 (23)
MgO (kg / hr):
H _MgO = (L _MgO × W _L + C _MgO × CW _L + S _MgO × SW _L + A _MgO × AW _L + M _MgO × MW _L ) / 100 (24)

In the above formulas (21) to (24), L _CaO , L _SiO2 , L _Al2O3 and L _MgO are the proportions (mass%) of CaO, SiO ₂ , Al ₂ O ₃ and MgO contained in the agglomerate, respectively. W _L represents the mass (kg) of the powder derived from the agglomerate charged into the furnace per unit time (hr).

C _CaO , C _SiO2 , C _Al2O3 , and C _{MgO respectively} indicate the ratio (mass%) of CaO, SiO ₂ , Al ₂ O ₃ , and MgO contained in the CaO source contained in the hearth forming material. _L represents the mass (kg) of the CaO source contained in the hearth forming material charged into the furnace per unit time (hr).

S _CaO , S _SiO2 , S _Al2O3 , and S _MgO represent the ratio (mass%) of CaO, SiO ₂ , Al ₂ O ₃ , and MgO contained in the SiO ₂ source contained in the hearth forming material, SW _L indicates the mass (kg) of the SiO ₂ source contained in the hearth forming material charged into the furnace per unit time (hr).

A _CaO , A _SiO2 , A _Al2O3 , and A _MgO indicate the ratio (mass%) of SiO ₂ , CaO, Al ₂ O ₃ , and MgO contained in the Al ₂ O ₃ source contained in the hearth forming material, respectively. AW _L represents the mass (kg) of the Al ₂ O ₃ source contained in the hearth forming material charged into the furnace per unit time (hr).

_{_{_{M CaO, M SiO2, M Al2O3}}} , M MgO , respectively, CaO contained in the MgO source contained in the hearth forming material shows the _{_{_{SiO 2, Al 2 O 3,}}} MgO ratio (mass%), MW _L represents the mass (kg) of the MgO source contained in the hearth forming material charged into the furnace per unit time (hr).

With regard to the component composition of the powder derived from the agglomerate and the hearth forming material, if the target component composition is the following formulas (25) to (28), then based on the above formulas (21) to (24) Are represented by the following formulas (29) to (32).
[CaO] / [SiO ₂ ] = 1.3 (25)
[Al ₂ O ₃ ] / [SiO ₂ ] = 0.3 (26)
[MgO] / [SiO ₂ ] = 0.5 (27)
CaO + Al ₂ O ₃ + SiO ₂ = 7 (28)
H _CaO / H _SiO2 = 1.3 (29)
H _Al2O3 / H _SiO2 = 0.3 (30)
H _MgO / H _SiO2 = 0.5 (31)
(H _CaO + H _{Al2 O3} + H _SiO2 ) / (W _L + CW _L + SW _L + AW _L + MW _L ) × 100 = 7 (32)

In general, since no SiO ₂ source is added as the hearth forming material, the calculation may be performed with SW _L = 0. When the SiO ₂ source is added, a provisional numerical value is set for the SiO ₂ source to be added, and the amount of other additives that achieve the target component ratio is determined. If the result does not reach the target value, the solution may be obtained by changing the amount of the SiO ₂ source to be added.

As the hearth forming material, the ratio of the hearth forming material having a particle diameter of 0.5 to 2 mm is preferably 50% by mass or more with respect to the total amount of the hearth forming material charged into the furnace. The hearth forming material is easier to mix with the powder derived from the agglomerates when the particle diameter is smaller, but when the particle diameter is too small, when charging into the furnace or heating in the furnace, It will be blown by the wind pressure, and the desired effect will not be exhibited. Accordingly, the ratio of the particle diameter of the hearth forming material to 0.5 mm or more is preferably 50% by mass or more. However, if the particle diameter becomes too large, it becomes difficult to mix with the powder derived from the agglomerate, and the desired effect is not exhibited. Also, when the gangue begins to melt, it is recommended to increase the surface area of the hearth forming material in order to quickly dissolve CaO and MgO into the melt and promote the reaction to solidify the slag. The Accordingly, the ratio of the particle diameter of the hearth forming material to 2 mm or less is preferably 50% by mass or more.

The agglomerates are formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent. As the iron oxide-containing substance, iron ore, iron sand, non-ferrous smelting residue, etc. may be used. As the carbonaceous reducing agent, a carbon-containing material may be used. For example, coal or coke may be used.

In the raw material mixture, a binder, an MgO source, or a CaO source may be blended as other components. As said binder, polysaccharides (for example, starches, such as wheat flour) etc. can be used, for example. As said MgO source or said CaO source, what was illustrated as a MgO source or CaO source mix | blended with a hearth forming material can be used.

The shape of the agglomerate is not particularly limited, and may be, for example, a pellet shape or a briquette shape. The size of the agglomerate is not particularly limited, but the particle size (maximum diameter) may be 50 mm or less. The lower limit is about 5 mm. In addition, what is necessary is just to let a sphere equivalent diameter be a particle size when an agglomerate is briquette-like.

The above agglomerate may be heated in the furnace so that the temperature of the agglomerate is 1200 to 1400 ° C. to reduce iron oxide in the raw material mixture.

The type of furnace may be a moving hearth furnace, for example, a rotary hearth furnace.

The temperature of the agglomerate is particularly preferably 1250 ° C. or higher. If it is 1250 degreeC or more, the melting time of metallic iron and slag can be shortened. However, if the temperature of the agglomerate becomes too high, the metallic iron melts and bites into the hearth, causing a rise in the hearth. A preferred upper limit for the temperature of the agglomerate is 1350 ° C.

For heating the agglomerate, the temperature of the agglomerate can be adjusted by using a burner and controlling the combustion conditions of the burner.

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.

In Experimental Example 1, an agglomerate made of a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is charged into a heating furnace and heated, and iron oxide in the raw material mixture is reduced to produce metallic iron. The component composition and strength of metallic iron were examined, and the relationship between the adhesion to the hearth and the component composition was evaluated. In Experimental Example 2, the influence of CaO, SiO ₂ , and MgO on the deformation rate of the agglomerate was examined, and the relationship between the component composition and the generation behavior of molten slag was evaluated. In Experimental Example 3, the relationship between the melting temperature of the slag component of Al ₂ O ₃ and the component was examined using a ternary phase diagram.

[Experimental Example 1]
The agglomerates having the component compositions shown in Table 1 below were produced as agglomerates using as a raw material a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent. The shape of the agglomerate is No. in Table 1 below. Nos. 1, 6, and 7 are pillow briquettes (ball equivalent diameter (maximum diameter) is about 22 to 26 mm), 2 to 5 were spherical pellets (particle diameter (maximum diameter) was about 12 to 20 mm). In Table 1 below, TFe is the total iron content, TC is the carbon content (in Table 1, the total carbon content contained in the agglomerate), and FC is the carbon content that is not gasified at 970 ° C. Table 1 below shows [CaO] / [SiO ₂ ], [Al ₂ O ₃ ] / [SiO ₂ ], [MgO] / [SiO ₂ ], [CaO] + based on the agglomerate composition. The values of [Al ₂ O ₃ ] + [SiO ₂ ] are calculated and shown.

The obtained agglomerate was charged into a heating furnace and heated to 1300 ° C. to reduce iron oxide contained in the agglomerate to produce metallic iron. The heating time in the furnace is shown in Table 2 below.

The component composition of the agglomerate after heating was measured, and the results are shown in Table 2 below. In Table 2 below, MFe is the amount of metallic iron, TC is the amount of carbon (in Table 2, the total amount of carbon remaining after heating), TC / TFe × 100 is the ratio of the total amount of carbon to the total amount of iron, MetalFe is the metallization The rate [= metal iron amount (%) / total iron amount (%) × 100].

When the amount of carbon in the residue (agglomerated) after heating is converted to the amount of carbon contained in the agglomerated material before heating, RCs shown in Table 2 below are obtained, and RCs is subtracted from the TC of the agglomerated material before heating. The value obtained is the amount of carbon used for reduction (RedC). The ratio of residual carbon after heating to the carbon necessary for reduction (RCs / RedC × 100) was determined and shown in Table 2 below. As is apparent from Table 2, the amount of carbon at which the residual carbon after heating is about 5% based on the amount of carbon necessary for reduction is about 22%.

Also, the strength of the massive metallic iron (agglomerated material) obtained after heating was measured by a rotational strength test.

《Rotational strength test》
The residue was put in a rotating container and rotated at a total rotational speed of 500 rotations, and sieved in three stages: a particle diameter of 1 mm or less, a particle diameter of 1 mm to 2 mm or less, and a particle diameter of 2 mm or more. The shape of the rotating container is a cylindrical shape having a diameter of 113 mm and a length of 205 mm, and two barrels are provided in the rotating container and are rotated at a rotation speed of 30 rpm.

In Table 2 below, the ratio of the powder having a particle diameter of 1 mm or less to the mass of the sieved powder is calculated and shown. An increase in the proportion of powder having a particle diameter of 1 mm or less means that the residue is easily pulverized, indicating that the residue is not fixed on the hearth and the removability is good. ing. In the present invention, the case where the ratio of the powder having a particle diameter of 1 mm or less is 29% or more is evaluated as being excellent in removability (invention example), and the case where it is less than 29% is evaluated as being inferior in removability (comparative example). .

It can be considered as follows from Table 2 below. First, no. 1, 2, 3, and 5 have a carbon content in the residue of 5% or more (that is, RCs / RedC × 100 value is 22% or more). This is an example of 122% or more with respect to the amount of carbon necessary for reducing iron oxide contained in the agglomerate. Of these, No. 1, 2, and 3 have a [CaO] / [SiO ₂ ] value of 0.25 to 1.20 and a [Al ₂ O ₃ ] / [SiO ₂ ] value of 0 in the agglomerate composition. .2 to 0.7, which satisfies the above formulas (1) and (2). Therefore, the adherence to the hearth is reduced. On the other hand, no. No. 5 has a value of [CaO] / [SiO ₂ ] of 0.23 out of the component composition of the agglomerate, and does not satisfy the above formula (1). No. In No. 5, since the total amount of CaO, Al ₂ O ₃ , and SiO ₂ is less than 3.0%, metallic iron is easily sintered. Therefore, the removability of the residue cannot be improved.

Next, no. 4, 6, and 7, the carbon content in the residue is less than 5% (that is, the value of RCs / RedC × 100 is less than 22%). In this example, the amount is less than 122% with respect to the amount of carbon necessary for reducing the iron oxide contained in the composition. Of these, No. 6 has a value of [CaO] / [SiO ₂ ] of 0.14 out of the component composition of the agglomerate, which satisfies the above formula (5). Accordingly, the melting point of the slag is increased, the bonding force of the residue is lowered and the separation is facilitated, and the removability of the residue is improved. On the other hand, no. Nos. 4 and 7 indicate that in the component composition of the agglomerate, the value of [CaO] / [SiO ₂ ] is in the range of 0.25 to 1.20, and the value of [Al ₂ O ₃ ] / [SiO ₂ ] is 0. The range of 2 to 0.7 is satisfied, and the value of [MgO] / [SiO ₂ ] is 0.4 or less, and none of the above formulas (5) to (9) is satisfied. Therefore, the adhesion to the hearth is increasing.

[Experiment 2]
In the process in which iron oxide is reduced in the presence of CaO, SiO ₂ and MgO, it is difficult to accurately observe the generation behavior of molten slag. That is, since there exists a solid-liquid coexistence state between the solid and the liquid, and each oxide does not exist uniformly, which state of the molten slag promotes the sintering of metallic iron and the coarse bond of wustite. It is not clear whether it contributes.

Pellet (agglomerate) is prepared by blending iron ore containing SiO ₂ as a gangue component with magnesite as the MgO source and limestone as the CaO source, and this is made in an electric furnace at 1300 ° C. for 10 minutes in the air. When heated and fired, and then gas-reduced, the deformation rate of the pellets during reduction was measured, and the results of examining the effects of CaO, SiO ₂ and MgO on the deformation of the pellets were found as “High Temperature Reduction and Softening Properties of Pellets with Magnesite ”(Transactions of the Iron and Steel Institute of Japan, published by the Japan Iron and Steel Institute, vol. 23 (1983), No. 2, p153).

Here, the gas reduction of the calcined pellets is performed at 10 ° C./min while flowing a reducing gas (CO gas: N ₂ gas = 30 vol%: 70 vol%) with a load of 0.5 kg applied to one pellet. The temperature is raised to 1500 ° C. At this time, the amount of SiO ₂ in the pellet was set to 0.3%, and [MgO] / [SiO ₂ ] was changed in the range of 0.01 to 1.32. It is shown in the literature. The result is shown in FIG.

The deformation of the pellet is based on shrinkage deformation due to reduction of iron oxide to metallic iron and deformation due to generation of molten slag, but deformation above 1100 ° C. may be considered as deformation due to the latter. This becomes clear by observing the structure photograph of the pellet cross section shown in the above document. The structure photograph shown in this document is shown in FIG. FIG. 2 is a drawing-substituting photograph in which a cross section of a pellet obtained by heating and reducing a fired pellet of [MgO] / [SiO ₂ ] = 0.59 at 1300 ° C. with a SiO ₂ content of 4.5% is shown in FIG. 2 (1) shows the outer periphery of the pellet, and FIG. 2 (2) shows the internal state of the pellet. In (1), a large amount of metallic iron shown in white is produced, but in (2), it can be seen that wustite shown in gray and molten slag shown in black exist. Further, since the wustite particles are coarsened and the surface thereof is melted to have a rounded shape, it is clear that the deformation at 1100 ° C. or more is caused by the generation of molten slag.

Further, in the above document, the influence of the component composition of the pellet on the deformation of the pellet is evaluated by measuring the temperature at which the pellet shrinks by 40% (hereinafter sometimes referred to as 40% shrinkage temperature). . The results are shown in FIGS.

FIG. 3 shows the results when the amount of SiO ₂ is 4.4% (◯) or 8.3% (×), CaO is not included, and [MgO] / [SiO ₂ ] is changed. Yes. FIG. 4 shows the results when [MgO] / [SiO ₂ ] = 0.72 and [CaO] / [SiO ₂ ] is changed.

As apparent from FIG. 3, when CaO does not coexist, the 40% shrinkage temperature increases monotonically as [MgO] / [SiO ₂ ] increases, but when CaO coexists, [CaO] / [SiO ₂ ] = 0.45, it can be seen that the 40% shrinkage temperature is minimal. The composition of the composition when the 40% shrinkage temperature is 1350 ° C. is shown in FIG. 3 when CaO does not coexist, and [MgO] / [SiO ₂ ] exceeds 0.4 and when CaO coexists from FIG. It is judged that CaO] / [SiO ₂ ] is less than 0.18 or more than 1.05. Although this result is different from the above range when CaO and MgO coexist, the range of [CaO] / [SiO ₂ ] is less than 0.25 or more than 1.20 with an emphasis on the result of Example 1 above. Stipulated.

Qualitatively, it is clarified that such a concept is also valid from the ternary equilibrium diagram.

FIG. 5 shows a SiO ₂ —MgO—FeO ternary equilibrium diagram. In FIG. 5, when a constant value of [MgO] / [SiO ₂ ] = 0.4 is entered, it becomes a straight line, and the melting point at this time shows 1450 ° C. even if the amount of FeO changes, and [MgO] It can be seen that the melting point decreases monotonously with a decrease in / [SiO ₂ ].

Even if the melting point is 1450 ° C., for example, all gangue components are not always solid at 1350 ° C. Since a part of the gangue component melts at about 1200 ° C. or higher, a high melting point only means a state where the amount of melting is small.

FIG. 6 shows a CaO—SiO ₂ —MgO ternary equilibrium diagram. In FIG. 6, [MgO] / [SiO ₂ ] = 0.4, [MgO] / [SiO ₂ ] = 0.72, [CaO] / [SiO ₂ ] = 0.25, [CaO] / [SiO ₂ ] = 0.45 and a constant value of [CaO] / [SiO ₂ ] = 1.20 is a straight line, and even if [MgO] / [SiO ₂ ] is constant, [CaO] / [SiO ₂ ] ] Changes to a compound CaO.MgO.2SiO ₂ having a [CaO] / [SiO ₂ ] of 0.45 and a melting point of about 1400 ° C. That is, the closer the composition of the low melting point compound is, the more melt is generated. As shown by the dotted line in FIG. 6, it can be seen that [CaO] / [SiO ₂ ] should be less than 0.25 or more than 1.20 in order to make the melting point of slag about 1450 ° C. or higher.

[Experiment 3]
In Experimental Example 2, the influence of Al ₂ O ₃ on the deformation of the pellet was examined.

Figure 7 shows a CaO-SiO _₂ -Al ₂ O ₃ based ternary equilibrium diagram. In FIG. 7, [Al ₂ O ₃ ] / [SiO ₂ ] = 0.2, [Al ₂ O ₃ ] / [SiO ₂ ] = 0.7, [CaO] / [SiO ₂ ] = 0.25, When a constant value of [CaO] / [SiO ₂ ] = 1.20 is entered, a straight line is obtained. The region surrounded by the straight line is a region where a part of the low melting point slag having a melting point of about 1250 ° C. is generated. Therefore, it is considered that the amount of molten slag produced can be reduced if it is outside this region.

According to the present invention, it is possible to prevent a solid material such as an iron plate that cannot be discharged from the inside of the furnace from being formed on the hearth or to raise the hearth surface, so that the design of the equipment is not significantly changed. Metallic iron can be produced efficiently.

Claims

An agglomerate made of a mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is charged on the hearth of a moving hearth heating furnace and heated to reduce the iron oxide in the agglomerate. In producing metallic iron,
A hearth forming material for preventing metallic iron and / or wustite formed by heat reduction of iron oxide contained in the powder derived from the agglomerate on the hearth is charged into the furnace together with the agglomerate. The manufacturing method of metallic iron characterized by the above-mentioned.
When the amount of carbon contained in the agglomerate is 122% (meaning mass%; the same shall apply hereinafter) or more with respect to the amount of carbon necessary to reduce iron oxide in the agglomerate,
For component composition combined with the hearth forming material powder from the agglomerates, CaO, the amount of SiO 2, Al 2 O 3 is the so as to satisfy the following formula (1) and (2) The manufacturing method of Claim 1 which adjusts the component composition of a hearth forming material.
[CaO] / [SiO 2 ] = 0.25 to 1.20 (1)
[Al 2 O 3 ] / [SiO 2 ] = 0.2 to 0.7 (2)
[In Formula (1) and Formula (2), [] represents the content (% by mass) of each component. ]
When the amount of carbon contained in the agglomerate is less than 122% with respect to the amount of carbon required to reduce iron oxide in the agglomerate,
The total carbon content of the component composition combining the powder derived from the agglomerate and the hearth forming material is 122% or more with respect to the carbon amount required to reduce iron oxide in the agglomerate, for and the hearth-forming material as the composition of the combined powder from the agglomerates, CaO, so that the amount of SiO 2, Al 2 O 3 is, it satisfies the following formula (3) and (4) The manufacturing method of Claim 1 or 2 which adjusts the component composition of the said hearth forming material.
[CaO] / [SiO 2 ] = 0.25 to 1.20 (3)
[Al 2 O 3 ] / [SiO 2 ] = 0.2 to 0.7 (4)
[In Formula (3) and Formula (4), [] represents the content (% by mass) of each component. ]
When the amount of carbon contained in the agglomerate is less than 122% with respect to the amount of carbon required to reduce iron oxide in the agglomerate,
The total carbon amount of the component composition of the powder derived from the agglomerate and the hearth forming material remains below 122% with respect to the amount of carbon required to reduce iron oxide in the agglomerate. And the amounts of CaO, SiO 2 , Al 2 O 3 , and MgO are the following formulas (5) to (9) for the component composition of the agglomerate-derived powder and the hearth forming material: The manufacturing method of Claim 1 or 2 which adjusts the component composition of the said hearth forming material so that at least one of these may be satisfied.
[CaO] / [SiO 2 ] <0.25 (5)
[CaO] / [SiO 2 ]> 1.20 (6)
[Al 2 O 3 ] / [SiO 2 ] <0.2 (7)
[Al 2 O 3 ] / [SiO 2 ]> 0.7 (8)
[MgO] / [SiO 2 ]> 0.4 (9)
[In the formulas (5) to (9), [] represents the content (% by mass) of each component. ]
Regarding the component composition of the powder derived from the agglomerate and the hearth-forming material, the hearth so that the total amount of CaO, SiO 2 and Al 2 O 3 is 3.0 to 7.0%. The manufacturing method of Claim 2 which adjusts the component composition of a forming material.
For component composition combined with the hearth forming material powder from the agglomerates, CaO, SiO 2, and Al 2 O 3 the total amount the furnace floor forming member such that 7.0 percent The manufacturing method of Claim 4 which adjusts a component composition.
The production method according to claim 1, wherein the ratio of the hearth forming material having a particle diameter of 0.5 to 2 mm to 50 mass% or more with respect to the total amount of the hearth forming material charged in the furnace.
The production method according to claim 1, wherein the agglomerate has a particle size of 5 to 50 mm.
The production method according to claim 1, wherein the agglomerate is heated at 1200 to 1400 ° C in the moving hearth furnace.