JP5494071B2 - Method for producing reduced iron - Google Patents

Description

  The present invention relates to a method for producing reduced iron.

  In recent years, the hearth has been rotated in a horizontal plane as a method for producing reduced iron by heating and reducing powdered iron ore, dust, scale, and sludge generated in ironworks and smelters. A method using a heated floor furnace (hereinafter referred to as a “rotary hearth furnace”) has attracted attention. In this method, the agglomerated material formed by mixing and kneading a powdered iron oxide raw material and a reducing agent such as powdered carbonaceous material is spread on the hearth surface of the rotary hearth furnace, and the agglomerated material is placed in the furnace. Heated and reduced while moving to obtain reduced iron. Also, in response to the trend toward zero emissions at steelworks and smelters, the use of inferior wet dust, high zinc dust, electric furnace dust, etc. with low iron content is being studied as powdered iron oxide raw materials. Yes.

  However, when agglomerated materials using these wet dust, high zinc dust, electric furnace dust, etc. as raw materials are supplied to a rotating bed furnace to produce reduced iron, the agglomerates supplied in the furnace are heated and reduced. It often happens that it explodes / collapses and powders in the process. The powdered agglomerated material hinders the heat supply from the inside of the furnace, so that not only reduction does not proceed, but also the powdered material that has fallen to the hearth surface gradually melts and solidifies on the hearth surface. Produces and grows a strong fusion material, which also hinders continuous operation. In addition, the rotary kiln also has a problem that the powdered material is fused and solidified on the inner wall of the kiln.

As a technique for preventing the explosion and collapse of the agglomerated material, for example, there are techniques disclosed in Patent Documents 1 to 8 shown below.

  For example, Patent Document 1 discloses a rotary hearth in which a mixture of powder containing metal oxide and carbon is left undried in order to omit a prior drying step when reducing a high-moisture and fine powder material in a rotary hearth furnace. In order to prevent explosion at the time of charging into the furnace and entering the furnace interior, a technique for defining the limit value of the atmospheric temperature according to the moisture percentage of the mixture is disclosed.

  In Patent Document 2, in a method of reducing agglomerates formed by mixing an iron oxide raw material and a reducing agent in a rotary bed furnace, the temperature is raised to 900 to 1300 ° C. from the time of supplying the raw material into the furnace. It is disclosed that the rate of temperature increase of the agglomerates during the period is controlled to 500 ° C./min or 400 ° C./min or less.

  Further, Patent Document 3 discloses that when agglomerated material containing blast furnace wet dust is heated and reduced in a heating furnace to produce reduced iron, agglomeration is performed in order to suppress disintegration and powdering during heating and reduction. A technique for defining a mass ratio of pseudo particles having a particle diameter of more than 1 mm in a chemical compound is disclosed.

  Patent Document 4 specifies reduced iron powder produced when taking out the produced reduced iron from the furnace by defining the upper limit of the volatile substance containing Cl, F, Zn, Na, K, and Pb. A technique for preventing the conversion is disclosed.

  Further, in Patent Document 5, as a means for suppressing explosion when the agglomerated material is heated in a vertical furnace such as a blast furnace or cupola, the porosity and inner side of the radially inner half of the carbonaceous material agglomerated material are described. A technique for defining a half porosity ratio and hot forming is disclosed.

  In addition, in Patent Document 6, when zinc-containing pellets are heated in a kiln or the like to be dezinced, in order to suppress the formation of pellet explosions and kiln rings, the amount of pellet internal carbon is reduced and pellet external carbon is added. And the ratio of the amount of exterior carbon to the total amount of carbon is 40% or more.

  Furthermore, in Patent Document 7, when a powdered iron-containing raw material and a soft powdery carbonaceous material are hot-molded to produce a carbonized material agglomerated material and used as a blast furnace raw material, heating in the blast furnace is performed. As a means for suppressing the collapse / pulverization during the reduction, a technique for determining the raw material blending amount so that the specific surface area value of the agglomerated product becomes a preset target value is disclosed.

  Patent Document 8 discloses that the content of crystal water in the carbonized iron oxide agglomerated material for rapid heating and reducing raw materials is controlled to 4% or more, and the total content of crystal water and volatile matter is 10.5. %, And a technique for controlling the adhering moisture to 1.0% or less is disclosed.

JP 2001-303115 A JP 2002-167622 A JP 2003-293019 A Japanese Patent Laying-Open No. 2005-200672 JP 2005-344181 A JP 2006-316333 A JP 2007-077744 JP 2009-035820 A

  However, when the undried raw material is charged into the rotary bed furnace using the technique described in Patent Document 1, the equipment of the rotary bed furnace becomes large and the processing time of the drying process in the previous stage in the furnace becomes long. There is a problem that productivity of reduced iron decreases. Moreover, there is a problem in that productivity is reduced by defining the limit value of the ambient temperature to prevent explosion.

  In addition, controlling the temperature rising rate in the technique described in Patent Document 2 is synonymous with controlling the hearth rotation speed of the rotary bed furnace, and there is a problem that the productivity of reduced iron is reduced. .

  Furthermore, the technique described in Patent Document 3 is a technique in the case where the agglomerated material after reduction is used as a blast furnace raw material, and in the production of reduced iron suitable for a steelmaking process using a melting furnace, the particle diameter is 1 mm. Mixing pseudo particles leads to a decrease in productivity and is not realistic.

  In addition, the technique described in Patent Document 4 prevents powdered reduced iron obtained after the heating / reducing treatment, and prevents the explosion / collapse of the agglomerates generated during the heating / reducing treatment. Can not.

  Furthermore, it is very difficult to produce an agglomerated product having the conditions described in Patent Document 5, and there is a problem that the equipment becomes complicated.

  In addition, the technique described in Patent Document 6 has a problem in that an additional process of covering carbon with pellets is required, which complicates the process. Furthermore, since it is expected that the exterior carbon will not be effectively utilized for reduction, there is a concern that the productivity will be lowered.

  Furthermore, the technique described in Patent Document 7 is a method specialized in the production of blast furnace raw materials, and is difficult to apply to the production of reduced iron suitable for the steelmaking process using a melting furnace.

  In the technique described in Patent Document 8, the upper limit of the allowable content of crystallization water and volatile components is as extremely high as 10.5%. Although the definition of the volatile content is not clarified in Patent Document 8, the value of 10.5% is about 13 for the index R, assuming that the volatile content in the document is a component used for calculating the index R in the present invention. Become. In the case of such a content rate, the possibility of explosion / collapse increases. Further, by analogy with the description in Patent Document 8, coal is mainly assumed as the origin of the volatile matter, and the causative substance of the volatile gas is not clearly specified.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to avoid explosion / collapse of agglomerates during heating / reduction treatment without reducing productivity. An object of the present invention is to provide a method for producing reduced iron that can be realized.

In order to solve the above problems, according to one aspect of the present invention, in the method of heating and reducing agglomerates formed by mixing an iron oxide raw material and a reducing agent, and producing reduced iron, the reduction agents as, a volatile content of 3-7% by weight of the anthracite was added 3-8% by weight, expressed ZnO in the agglomerate, compounds water, the content of low-boiling components consisting of CaSO ₄ and CaCO _3, A method for producing reduced iron is provided in which an index R represented by the following formula 1 is set to 3.0 or more and 4.2 or less.

R = mass% of ZnO in the agglomerate × 22.4 / molecular weight of ZnO + mass% of compound water in the agglomerate × molecular weight of 22.4 / H ₂ O + mass of CaSO _{4 in} the agglomerate % × 22.4 / CaSO ₄ molecular weight + mass% of CaCO _{3 in} the agglomerate × 22.4 / CaCO ₃ molecular weight

... (Formula 1)

  The agglomerated product is preferably heated and reduced in a rotary hearth furnace or rotary kiln.

  The index R may be 4.1 or less, and the index R may be 4.0 or less.

The iron oxide raw material may contain an iron oxide component, sulfur, carbon, SiO ₂ , Al ₂ O ₃ , CaO, and MgO in addition to the readily volatile component .

  As described above, according to the present invention, during the heating / reduction treatment of the agglomerated material, particularly focusing on the explosion / collapse in the initial stage of reduction, the causative component is identified, and the agglomeration that can avoid the explosion / collapse is possible. By prescribing the amount of the causative component in the compound, it is possible to avoid explosion / collapse during heating / reducing treatment of the agglomerate without causing a decrease in productivity.

It is explanatory drawing for demonstrating the manufacturing process of reduced iron. It is explanatory drawing for demonstrating a rotary hearth furnace. It is explanatory drawing for demonstrating reduction | restoration of a briquette. It is the graph which showed the relationship between the parameter | index R which concerns on embodiment of this invention, and the state of a briquette. It is the graph which showed the relationship between reduction time and a metallization rate. It is the graph which showed the relationship between the parameter | index R which concerns on embodiment of this invention, and a metalization rate.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the following description, a method for producing reduced iron according to an embodiment of the present invention will be described taking a rotary hearth furnace as an example. However, the method for producing reduced iron according to the present invention is applied to a reduction furnace such as a rotary kiln. Is also available.

<About the manufacturing process of reduced iron>
Prior to describing the method for producing reduced iron according to the embodiment of the present invention, first, the production process of reduced iron will be described in detail with reference to FIG. Drawing 1 is an explanatory view for explaining the manufacturing process of reduced iron.

  First, iron oxide raw materials such as iron dust and iron ore, and reducing agents such as coal, coke, and fine carbon are stored in advance in the hopper 11 or the like. The iron oxide raw material and the reducing agent are blended so as to have a preset blending ratio and charged into the pulverizer 13.

  A pulverizer 13 such as a ball mill pulverizes the charged iron oxide raw material and the reducing agent to a predetermined particle size while mixing. The particle sizes of the iron oxide raw material and the reducing agent after pulverization can be set to values suitable for a reduction furnace such as a rotary hearth furnace or a rotary kiln used for the production of reduced iron. The mixture comprising the iron oxide raw material and the reducing agent after pulverization is transported to the kneader 15.

  The kneader 15 kneads the mixture pulverized to a predetermined particle size by the pulverizer 13. In addition, the kneader 15 may perform a humidity conditioning process for adding water to the mixture until the water content is suitable for a reduction furnace used for producing reduced iron. As an example of the kneader 15, for example, a mix muller can be mentioned. The mixture kneaded by the kneader 15 is conveyed to the molding machine 17.

  A molding machine 17 such as a pan pelletizer (dish granulator), a double roll compressor (briquette making machine), or an extrusion molding machine molds a mixture containing an iron oxide raw material and a reducing material, and agglomerates such as pellets. It is a chemical. Here, the agglomerated material refers to pellets, briquettes, extruded products that have been cut by extrusion molding, and granular materials / agglomerated materials such as mass-adjusted agglomerated materials. When the molding machine 17 is dried and heat-reduced, which will be described later, for example, when charged into the melting furnace 23 in the hot state, the above mixture is adjusted so as to have a size larger than the particle size so as not to be scattered by the rising gas flow in the furnace. Agglomerates. The generated agglomerated material is charged into the dryer 19.

  The dryer 19 dries the agglomerated material and has a moisture content suitable for the heat reduction process described later (in other words, a moisture content suitable for each reduction furnace used for producing reduced iron: for example, 1% or less. ). The agglomerated product having a predetermined moisture content is conveyed to a reduction furnace 21 described later.

  For example, a reduction furnace 21 such as a rotary hearth furnace (RHF) or a rotary kiln heats and reduces the charged agglomerate in a heating atmosphere such as an LNG burner or a COG burner, To do. A reduction furnace heats an agglomerate, for example to about 1000-1100 degreeC, performs the reduction process of an agglomerate, and manufactures reduced iron.

<About rotary hearth furnace>
Subsequently, a rotary hearth furnace which is an example of a reduction furnace used in the method for producing reduced iron according to the present embodiment will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is an explanatory diagram for explaining the rotary hearth furnace, and FIG. 3 is an explanatory diagram for explaining the reduction of briquettes.

First, the internal structure of the rotary hearth furnace 21 will be described with reference to FIG.
The rotary hearth furnace 21 has, for example, a substantially cylindrical shape as shown in the upper part of FIG. 2. For example, agglomerated material is charged from an inlet provided on the upper surface of the rotary hearth furnace 21 or the like. The The agglomerated material charged is heated and reduced while moving along the circumferential direction in the furnace to be reduced iron and taken out from the furnace.

A schematic diagram when the rotary hearth furnace 21 is developed along the circumferential direction is shown in the lower part of FIG.
Inside the rotary hearth furnace 21, a rotary hearth 25 that can move in the rotary hearth furnace 21 along the circumferential direction is provided. The briquette B charged from the charging port 27 is developed on the rotary hearth 25. The briquette B is leveled by the hot leveler 29 and moves in the furnace as the rotary hearth 25 moves. The briquette B is heated by the radiant heat of the high-temperature combustion gas generated by the furnace wall or the burner 31 on the furnace in the course of movement, and the iron oxide raw material is reduced by the reducing agent in the briquette B. Reduced iron, which is a reduced iron oxide raw material, is discharged from the rotary hearth furnace 21 by the discharger 33.

As shown in FIG. 3, the briquette B moving in the rotary hearth furnace 21 rises in temperature from the outside to the inside of the briquette B due to the radiant heat of the high-temperature combustion gas. It progresses from the outer periphery to the center. At this time, the reaction as shown in FIG. As a result of these reactions, iron oxide components (FeO, Fe ₂ O _{3 and the} like) contained in the briquette are reduced by the reducing agent (carbon C) contained in the briquette to become reduced iron (Fe).

  Here, the inside of the rotary hearth furnace 21 can be divided into three zones as shown in the lower part of FIG. These sections are for convenience, and the actual rotary hearth furnace 21 is not divided as shown in the figure.

  The first zone located in the vicinity of the briquette loading inlet 27 and the second zone, which is a zone adjacent to the first zone, are mainly intended for raising the temperature of the briquette B charged in the rotary hearth furnace 21. It is a zone to do. The third zone that is continuous with the second zone is a zone whose main purpose is the reduction of briquette B. Here, the first zone and the second zone are collectively referred to as the initial stage of heating / reduction, and the third zone is referred to as the reduction period.

  Due to the high-temperature combustion gas generated by the burner 31, the temperature of the agglomerated material in the initial stage of heating and reduction is raised to about 1000 ° C., and after the reduction period, it is kept at about 1000 to 1100 ° C.

  As a result of intensive studies by the inventors of the present application, when producing reduced iron using a reduction furnace, before the reduction reaction of iron oxide by a reducing agent such as carbon material starts, the agglomeration explosion / collapse starts. It has been found that this occurs at the initial stage of heating and reduction in a rotary hearth furnace or the like (the temperature of the agglomerated material is approximately 1000 ° C. or lower). Accordingly, the present inventors have conceived a method for producing reduced iron according to the present invention as described below in order to prevent explosion / collapse in the initial stage of heating / reduction.

<About the manufacturing method of reduced iron>
Based on the above description, the method for producing reduced iron according to the present embodiment will be described in detail below.

  As described above, the method for producing reduced iron according to the present embodiment is a method for producing reduced iron by heating and reducing the agglomerate formed by mixing an iron oxide raw material and a reducing agent. Here, the iron oxide raw material according to the present embodiment is generated in an iron-making dust (for example, an iron-containing cold material melting converter, a refining converter, a dust melting converter, etc., and collected by a wet dust collector or the like. Converter dust, blast furnace dust, mill scale, electric furnace dust, etc.), non-ferrous smelting dust, and iron ore. In addition, as the reducing agent according to the present embodiment, for example, coal such as powdered coal, coke, fine carbon, and the like can be used.

The inventors of the present application have conducted intensive research focusing on the explosion / collapse of agglomerates in the initial stage of heating / reduction, and have been able to identify components that cause explosion / collapse. The causative components of the explosion / collapse were zinc oxide (ZnO), compound water, calcium sulfate (CaSO ₄ ) and calcium carbonate (CaCO ₃ ) contained in the agglomerated material. Below, the origin of the said causal component is demonstrated first.

  ZnO (molecular weight 81.4) is a component mainly contained in ironmaking dust (especially electric furnace dust). When zinc-containing scraps such as galvanized steel sheets are used as ironmaking raw materials, zinc volatilizes in the dust generation process (melting furnace, electric furnace, etc.), and zinc moves into the dust. ZnO is oxidized by oxidation of zinc in the process of moving into dust.

Compound water (H ₂ O: molecular weight 18.0) is a component mainly contained in wet dust. Since the dust generated in each iron and smelting process is high temperature, the generated dust is generally water-cooled and concentrated and collected by a thickener or the like. At this time, water binds to easily hydrated components in the dust (hereinafter referred to as easily hydrated components; for example, CaO, MgO, etc.) to have hydrated water. This hydrated water is called compound water. That is, compound water is water chemically bonded to the easily hydrated component in dust. Unlike adhering water, which is usually referred to as “moisture”, compound water is hydrated by chemical bonds, and therefore does not desorb unless heated to approximately 200 ° C. or higher.

CaSO ₄ (molecular weight 136.0) is a component widely contained in ironmaking dust, smelting dust of various metals, and the like. As an important refining process in the iron making process, there is a desulfurization process that removes sulfur as an impurity in molten iron. In general, a flux containing Ca is used as a desulfurizing agent, and the sulfur content in the molten iron is removed as calcium sulfide (CaS). This CaS is transferred into the dust generated in the desulfurization process, and the transferred CaS is oxidized to become CaSO ₄ . Also, in the smelting of various non-ferrous metals, the target metal is often obtained by refining the target metal sulfide ore. The dust generated at this time contains a large amount of CaSO ₄ as in the desulfurization process in iron making.

CaCO ₃ (molecular weight 100.0) is a component widely contained in ironmaking dust, smelting dust of various metals, and the like. As described above, the dust contains a large amount of Ca derived from Ca-based flux used during refining. While the dust stays in the exhaust gas, this Ca component reacts with CO ₂ to form CaCO ₃ .

  In the method for producing reduced iron according to the present embodiment, a plurality of types of dust generated in various departments are mixed and used as an iron oxide raw material. Therefore, in the iron oxide raw material, the above-mentioned causal components are present in various ratios depending on the type of dust used, the mixing ratio of dust used, and the like.

  It is a gas component generated by the following chemical reaction at a temperature of 1000 ° C. or lower (low temperature period). As is clear from each chemical reaction formula, the causative component of the collapse / explosion is a gas component generated by the progress of the reaction. Therefore, it can be said that these causal components are components that volatilize at a temperature of 1000 ° C. or less and are liable to generate gas (that is, easily volatile components). As the following reaction proceeds inside the agglomerated material, gas accumulates in the agglomerated material according to the amount of the causative component contained therein. Therefore, when the agglomerate cannot withstand the gas pressure generated by the gas accumulated in the agglomerate, the agglomerate surface peels off, or the agglomerate itself collapses or explodes. . In addition, the temperature described in parentheses in the following chemical reaction formula represents a temperature at which the reaction proceeds.

ZnO + C → Zn + CO ↑ (about 900 ° C.) (Reaction Formula 1)
H ₂ O (hydration water) → H ₂ O (g) ↑ (about 200 to 900 ° C.) (reaction formula 2)
CaSO ₄ → CaO + SO ₃ ↑ (Reaction Formula 3)
CaCO ₃ → CaO + CO ₂ ↑ (about 500 to 900 ° C.) (reaction formula 4)

  Therefore, the inventors of the present application have defined an index R as shown in the following formula 1 as an index serving as a measure of the readily volatile component contained in the agglomerated material.

R = mass% of ZnO in the agglomerate × 22.4 / molecular weight of ZnO + mass% of compound water in the agglomerate × molecular weight of 22.4 / H ₂ O + mass of CaSO _{4 in} the agglomerate % × 22.4 / CaSO ₄ molecular weight + CaCO ₃ mass% in the agglomerate × 22.4 / CaCO ₃ molecular weight (Formula 1)

  Here, the numerical value of 22.4 in the above formula 1 is the volume per 1 mol of the substance (so-called molar volume). That is, the index R defined by the above formula 1 is a parameter representing the content ratio of easily volatile components in the agglomerated material, and as is clear from the above reaction formulas 1 to 4, per unit mass of the agglomerated material. It can be said that this parameter represents the amount of generated gas.

  In the method for producing reduced iron according to the present embodiment, the composition of the iron oxide raw material is determined so that the index R defined by the above formula 1 is 4.2 or less. The particle size of the mixture containing the iron oxide raw material and the reducing agent, the moisture content of the agglomerate formed using the mixture, and the like are applied to a reduction furnace such as a rotary hearth furnace or rotary kiln used for the production of reduced iron. A suitable value can be obtained.

  In the method for producing reduced iron according to the present embodiment, when the index R is set to 4.2 or less, the agglomerate is heated and reduced in the reduction furnace to produce reduced iron, which occurs in the first reduction stage. It becomes possible to suppress the amount of the gas component. Thereby, even if the gas pressure by the generated gas component acts toward the outside from the inside of the agglomerate, the agglomerate can withstand the gas pressure without exploding or collapsing. As a result, it is possible to prevent explosion and collapse of the agglomerates in the initial reduction stage. Here, the explosion / collapse of the agglomerated material represents a state in which the agglomerated material has been ruptured by the gas pressure from the inside to form a plurality of fragments.

  Moreover, in the manufacturing method of reduced iron which concerns on this embodiment, it is preferable that the parameter | index R prescribed | regulated by the said Formula 1 shall be 4.1 or less. By setting the index R to 4.1 or less, it is possible to suppress the amount of gas components generated in the initial reduction stage. Thereby, even if the gas pressure by the produced | generated gas component acts toward the outer side from the inside of an agglomerate, generation | occurrence | production of the peeling which arises in an agglomerate can be suppressed. As a result, it is possible to suppress agglomeration separation at the initial stage of reduction and to prevent explosion and collapse.

  Furthermore, in the manufacturing method of reduced iron which concerns on this embodiment, it is still more preferable that the parameter | index R prescribed | regulated by the said Formula 1 shall be 4.0 or less. By setting the index R to 4.0 or less, it becomes possible to suppress the amount of gas components generated in the initial stage of reduction, and the gas pressure due to the generated gas components acts from the inside of the agglomerate to the outside. However, the agglomerates can withstand the gas pressure without delamination and explosion / collapse. As a result, it is possible to prevent agglomeration separation and explosion / disintegration at the initial stage of reduction.

  In addition, the index R prescribed | regulated by the said Formula 1 is a better value, so that it is small. The small index R means that the amount of easily volatile components present in the agglomerated material is small, and the agglomerated material with a small index R becomes dense and difficult to be pulverized.

  In addition, as described above, the value of the index R defined by Equation 1 is preferable because the smaller the value, the better the prevention of explosion / collapse is possible. It has been found that by including a certain amount of readily volatile components in the raw material, fine cracks that do not lead to cracking can be generated on the agglomerate surface in the early stage of reduction, and the reduction reaction can be promoted.

  That is, explosion / collapse due to gas generation can be prevented by setting the index R defined by Equation 1 to 4.2 or less, but in a region where the index R is 4.2 or less, as the value of the index R increases Fine cracks are observed on the surface of the agglomerated product after the reduction. This is due to the gas generated from the agglomerate in the initial stage of reduction by causing the volatilized component to be appropriately contained in the agglomerate, and generating cracks on the agglomerate surface while preventing explosion and collapse, It shows that pores can be generated inside the agglomerated material. The cracks and pores generated in this way promote heat transfer from the high-temperature furnace atmosphere to the agglomerate surface and inside, and as a result, the reduction reaction rate can be improved.

  In order to realize such an improvement in the reduction reaction rate, the index R is preferably set to 3.0 or more. By increasing the reduction reaction rate by setting the index R to 3.0 or more, the metallization rate of the agglomerated product can be reached to a high level in a shorter reduction time. Moreover, even if the agglomerates are stacked in a furnace such as RHF and the ratio of agglomerates under the condition where the radiant heat transfer in the furnace atmosphere is not sufficiently supplied, the reduction rate at low temperatures is increased. Therefore, it is possible to maintain the ultimate metalization rate of the agglomerates of these bottom layers at a high value. That is, the average metallization rate of the entire agglomerate existing in the furnace such as RHF can be reached to a high value.

Here, the method for measuring the content of easily volatile components contained in the iron oxide raw material or the agglomerated material is not particularly limited, and can be selected according to the characteristics of each easily volatile component. . For example, the ZnO content is measured by measuring the Zn content in the iron oxide raw material and the agglomerate using inductively coupled plasma (ICP) emission spectroscopy described in JIS K 0116 (General Rules for Emission Spectroscopy). Can be determined. The content of CaSO ₄ can be determined by measuring the sulfate ion concentration by the method described in Item 41 of JIS K 0102 (Industrial Wastewater Test Method). The content of CaCO ₃ can be determined by measuring the carbonate ion concentration by the inorganic carbon content measuring method described in JIS K 0102 (Industrial Wastewater Test Method), Item 22. In addition, the content of compound water is to measure the amount of steam generated from iron oxide raw materials and agglomerates using the Karl Fischer titration method described in JIS M 8211 (Iron Ore-Compound Water Determination Method). Can be determined.

  When mixing a plurality of inferior raw materials containing many easily volatile components that cause collapse / explosion, such as wet dust, high zinc dust, electric furnace dust, etc., and making it an iron oxide raw material used in the production of reduced iron, The amount of easily volatile components of each of the inferior raw materials is measured in advance by the method as described above. Based on the blending amount of a plurality of inferior raw materials and the amount of easily volatile components known by measurement, the index R is calculated by the above equation 1. Is calculated. By adjusting the blending amount of the inferior raw material so that the value of the index R is equal to or less than the above-described threshold value, explosion and collapse of the agglomerated material in the reduction furnace can be prevented. As a result, the inferior raw material can be stably used while preventing the agglomerates from exploding and collapsing in the reduction furnace. As a result, progress of zero emission and reduction of manufacturing cost of reduced iron can be achieved.

  Moreover, pores can be generated in the agglomerated material so as not to cause explosion or collapse by intentionally containing a readily volatile component in the agglomerated material so that the index R is 3.0 or more. . As a result, the efficiency of heat transfer to the agglomerated material is improved, and the reduction reaction can be promoted even in an environment where the initial stage of reduction or the ambient temperature is low. Thereby, reduced iron with a high metallization rate can be produced with higher productivity.

  Hereinafter, the method for producing reduced iron according to the present invention will be further described with reference to Examples and Comparative Examples. The following embodiment is merely a specific example of the present invention, and the present invention is not limited to the embodiment described below.

<Relationship between index R and explosion / collapse>
In the following examples and comparative examples, the composition of iron-making dust used as an iron oxide raw material is changed, the amount of readily volatile components in the agglomerated material is changed to various values, and agglomerated materials having different indices R (Iron-made dust tablet) was manufactured. The size of the iron-made dust tablet is φ30 mm × H about 15 mm. The manufactured iron-making dust tablet was reduced in an electric furnace maintained at an atmospheric temperature of 1250 ° C. The content of easily volatile components and the index R of the manufactured tablet are as follows.

  In addition, content of the easily volatile component in Table 1 was determined with the following measuring methods.

ZnO: Inductively coupled plasma (ICP) emission spectroscopic method described in JIS K 0116 (general rules for emission spectroscopic analysis) Compound water: Karl Fischer titration method described in JIS M 8211 (iron ore-compound water quantification method) CaSO ₄ : JIS K 0102 (Industrial wastewater test method) The method for measuring the sulfate ion concentration described in Item 41 CaCO ₃ : JIS K 0102 (Industrial wastewater test method) The method for measuring the amount of inorganic carbon described in Item 22

Further, in the calculation of the index R according to Equation 1, the molecular weight of ZnO is 81.4, the molecular weight of H ₂ O is 18.0, the molecular weight of CaSO ₄ is 136.0, and the molecular weight of CaCO ₃ is 100.0. did.

In addition, in each agglomerated material shown in Table 1, as components other than those shown in Table 1, various components included in iron-making dust, components of coal and slag, and the like were included. These components are, for example, iron oxide components such as FeO and Fe ₂ O ₃ , sulfur, carbon, SiO ₂ , Al ₂ O ₃ , CaO, and MgO.

  Here, in the above-mentioned agglomerated material, coal was added as a reducing agent for iron-making dust. However, as a reducing agent in a process for industrially producing reduced iron from iron-making dust, including a method using RHF. The usual method is to add coal. Although the volatile matter is contained in the coal, in general, only an anthracite having a volatile content of 3 to 7% by mass is added to the agglomerated material in an amount of about 3 to 8% by mass. The ratio of volatile matter in coal to the total amount of readily volatile components is small. In addition, the volatile matter in coal is a complex mixture of carbon monoxide, hydrogen, combustible gas, etc., and each component gas is gradually generated during the temperature rising process of the agglomerate. The gas generation rate is considered to be lower than Therefore, the influence of the volatile matter of coal on the readily volatile component of the agglomerated material is extremely small. Also in the embodiment of the present invention, when determining the index R of the content ratio of the readily volatile components in the agglomerated material, the volatile content in the coal added as a reducing agent is not included.

  Table 1 shows the state after reduction of the reduced iron-making dust tablet (that is, reduced iron). In the notation of Table 1, × represents a tablet in which explosion / disintegration has occurred, Δ represents a tablet in which peeling has occurred, and ○ represents a normal tablet. The criteria for normality, separation, explosion / collapse are as follows.

Normal: Does not correspond to explosion / collapse or delamination Delamination: Does not correspond to explosion / collapse, but during reduction, the tablet surface (φ30mm) is pushed up from the center of the tablet, and the surface is 3mm or more Concavities and convexities Explosion / collapse: During reduction, the tablet is divided into two or more pieces, and the weight of each piece is less than 90% of the total weight of the pieces.

  FIG. 4 shows the correspondence between the index R and the state of the tablet after reduction. As is clear from Table 1 and FIG. 4, it can be seen that the tablet having the index R exceeding 4.2 has many explosions / collapses. Moreover, although the tablet with the index R of 4.2 or less has one tablet where peeling occurred, many tablets did not explode or collapse. In addition, tablets with an index R of 4.1 or less were normal with neither peeling nor explosion / disintegration.

As is clear from the examples and comparative examples shown in Table 1 and FIG. 4, the index R representing the content ratio of easily volatile components composed of ZnO, compound water, CaSO ₄ and CaCO ₃ in the agglomerated product is 4.2. By setting it as the following, the explosion and collapse which can arise in an agglomerate by the reduction process of an agglomerate can be prevented.

<Relationship between index R and reduction time>
In the same manner as in the above example, as a representative example of the agglomerated material in which the index R of the content ratio of easily volatile components in the agglomerated material was changed, an iron-made dust tablet having a diameter of about 30 mm × H of about 15 mm was produced, and the ambient temperature was 1250 ° C. Reduction was performed in an electric furnace maintained at 1150 ° C. At this time, the value of the index R of the tablet to be prepared was adjusted by adding Ca (OH) ₂ containing compound water. FIG. 5 shows the result of plotting the metallization rate ((M.Fe / T.Fe) × 100%) of the tablet together with the reduction time. Note that none of the iron dust tablets shown in FIG. 5 exploded or collapsed.

As is clear from FIG. 5, compared to a tablet with a low content of easily volatile components (index R = 2.8), a tablet with an increased index R value by adding Ca (OH) ₂ containing compound water ( It can be seen that the index R = 3.0, 3.4, 4.0) has a higher reduction rate in the initial reduction.

Even when the ambient temperature is lowered by 100 ° C. to 1150 ° C., the tablet with the index R = 4.0 to which Ca (OH) ₂ is added has a reduction rate more than the tablet with the index R = 2.8. It can be seen that it has improved. This result shows that even if the agglomerate temperature is low, such as the agglomerate laminated in the furnace such as RHF, the metallization rate is reduced. It shows that iron can be obtained.

  Here, each tablet shown in FIG. 5 has an index R <4.2, and although no explosion due to gas generation is observed, as the index R becomes larger, the surface of the tablet after the reduction becomes finer. Cracks were observed. That is, in these tablets, cracks on the surface of the agglomerate and pores inside the agglomerate are generated by the gas generated from the inside of the agglomerate in the early stage of reduction.

  The index R was plotted on the horizontal axis as an index of the reduction rate at the initial stage of reduction, and the metallization rate when reduced at an atmospheric temperature of 1250 ° C. for 7 minutes and 10 minutes was plotted on the vertical axis. The obtained result is shown in FIG. As is clear from FIG. 6, the slope between R = 2.8 and R = 3.0 is large, and it can be seen that the metallization rate difference in this range is large. This result also shows that if the value of the index R is 3.0 or more, the effect of improving the reduction rate in the initial reduction can be fully enjoyed.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 11 Hopper 13 Crusher 15 Kneading machine 17 Molding machine 19 Dryer 21 Rotary hearth furnace 23 Melting furnace 25 Rotary hearth 27 Loading 29 Hot leveler 31 Burner 33 Discharger B Briquette

Claims (5)

In the method of manufacturing reduced iron by heating and reducing the agglomerate formed by mixing iron oxide raw material and reducing agent,
As the reducing agent, add 3-8% by mass of anthracite having a volatile content of 3-7% by mass,
It represents the content ratio of readily volatile components composed of ZnO, compound water, CaSO ₄ and CaCO ₃ in the agglomerated material, and the index R represented by the following formula 1 is 3.0 or more and 4.2 or less. A method for producing reduced iron.

R = mass% of ZnO in the agglomerate × 22.4 / molecular weight of ZnO + mass% of compound water in the agglomerate × molecular weight of 22.4 / H ₂ O + mass of CaSO _{4 in} the agglomerate % × 22.4 / CaSO ₄ molecular weight + mass% of CaCO _{3 in} the agglomerate × 22.4 / CaCO ₃ molecular weight

... (Formula 1)
The method for producing reduced iron according to claim 1 , wherein the agglomerated material is heated and reduced in a rotary hearth furnace or a rotary kiln. The method for producing reduced iron according to claim 1 or 2 , wherein the index R is 4.1 or less. The said index R shall be 4.0 or less, The manufacturing method of reduced iron of any one of Claims 1-3 characterized by the above-mentioned. In addition to the readily volatile components, the iron oxide raw material includes iron oxide components, sulfur, carbon, SiO ₂ , Al ₂ O ₃ The manufacturing method of reduced iron of any one of Claims 1-4 containing CaO and MgO.

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