Sintered pellets for reduction and their manufacturing method

Abstract

To provide a fired pellet that is used in a solid reduction furnace and is blended with a specific amount of high-viscosity slag component during its production, so that the risk of mutual contact between low-melting-point slag is reduced to prevent the fusion: thus, the fired pellet is effective in preventing clustering, and a method for producing the same.SOLUTION: The present invention provides a fired pellet for reduction in which the ratio of high-viscosity slag component (Al2O3+MgO+SiO2) to the total Fe (T.Fe) satisfies the formula: (Al2O3+MgO+SiO2) / T.Fe≥0.09 and a method for producing the same, where, Al2O3 denotes the content (mass%) of the component Al2O3 in the fired pellet, MgO denotes the content (mass%) of the component MgO in the fired pellet, SiO2 denotes the content (mass%) of the component SiO2 in the fired pellet, and T.Fe denotes the content (mass%) of the component T.Fe in the fired pellet.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to fired pellets for reduction effective for use in a solid reduction furnace and a method for producing the same.

Background Art

[0002] In recent years, various technological developments have been carried out to reduce the emissions of CO2 in order to avoid global warming caused by its increase.

[0003] Under such circumstances, in the field of the iron and steel industry, an iron-making method using a solid reduction furnace, which is a hydrogen-based reduction process, has been attracting attention, and research on fired pellets used in this method has been underway. By the way, in the solid reduction furnace, when the charged raw material (fired pellet) passes through the high-temperature region in the furnace, when the hematite phase in the fired pellet is reduced and changes to the magnetite phase, it is accompanied by volume expansion and causes a pulverization phenomenon. In addition to the contact and fusion of metallic irons, it is known that the contact and fusion of low-melting-point slags are caused. As a result, it is known that clustering occurs in the furnace and a hanging phenomenon occurs in which the pellets in the furnace cannot move and cannot be taken out from the bottom of the furnace. In particular, in a solid reduction furnace that performs reduction based on hydrogen, this clustering is a very large problem to be solved.

[0004] Under such circumstances, several prior arts have been proposed for the purpose of preventing clustering observed in the above-mentioned solid reduction furnace. For example, Patent Document 1 proposes a method of coating the pellet surface with Ca(OH)2 or Mg(OH)2. Patent Document 2 proposes a method of preventing reduction pulverization and obtaining fired pellets with less swelling by coating the surface of the sintered ore (pellet) with granular solid fuel. And Patent Document 3 aims to prevent the occurrence of clustering in the solid reduction furnace, reduce heat loss, and improve operation efficiency by coating the surface of the fired pellet with cement-blended iron ore. Furthermore, Patent Document 4 proposes a technique of coating a substance containing a calcium iron compound composed of CaxFeyOz (1 < y / x ≤ 2; 1 ≤ z). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 59-10411 [Patent Document 2] Japanese Patent Application Publication No. 62-37325 [Patent Document 3] Japanese Patent Application Publication No. 63-262426 [Patent Document 4] JP 2017-119910 A Summary of the Invention [Problem to be solved by the invention]

[0006] Each of the above-mentioned conventional techniques (Patent Documents 1-4) is a method for reducing contact between metallic iron particles after reduction, which is a cause of clustering observed near the high temperature range (500 to 600°C) in a solid reduction furnace such as a shaft furnace, mainly by interposing a nonmetallic component. However, according to the research of the inventors, the above-mentioned conventional techniques for preventing clustering are insufficient, and there are problems such as the need to adopt a separate coating process for nonmetallic components, which increases costs, and the need to add dedicated equipment.

[0007] Therefore, an object of the present invention is to propose a sintered pellet and a manufacturing method thereof that are effective in preventing clustering by reducing the chance of contact between low-melting-point slags and preventing fusion when producing sintered pellets for use in a solid reduction furnace by containing a predetermined amount of a high-viscosity slag component. [Means for solving the problem]

[0008] The present invention is a technology developed to solve the above-mentioned problems of the conventional technology and to achieve the above-mentioned object. First, the ratio of high-viscosity slag components (Al2O3+MgO+SiO2) to total Fe (T.Fe) satisfies the following formula (1), and the porosity is 43 % or more. Note (Al2O3+MgO+SiO2) / T.Fe≧0.09 ···(1) Where Al2O3: Concentration of Al2O3 in the fired pellet (mass%) MgO: MgO concentration in the fired pellets (mass%) SiO2: SiO2 concentration in the fired pellets (mass%) T.Fe: T.Fe concentration in the fired pellets (mass%)

[0009] Secondly, the present invention provides a method for producing the sintered pellets for reduction in which the ratio of the highly viscous slag components (Al2O3+MgO+SiO2) to the total Fe (T.Fe) satisfies the following formula (1) or (2), and the porosity is 43 % or more, the present invention proposes a method for producing sintered pellets for reduction, which is characterized by using an iron-containing raw material blended so that the average LOI (loss on ignition) is 5% or more, and reducing and sintering the raw material. Note (Al2O3+MgO+SiO2) / T.Fe≧0.09 ···(1) (Al2O3+MgO+SiO2) / T.Fe≧0.12 ···(2) Where Al2O3: Concentration of Al2O3 in the fired pellet (mass%) MgO: MgO concentration in the fired pellets (mass%) SiO2: SiO2 concentration in the fired pellets (mass%) T.Fe: T.Fe concentration in the fired pellets (mass%)

[0010] In the present invention, the calcined pellets for reduction are as follows: (a) The ratio of high-viscosity slag components (Al2O3+MgO+SiO2) to total Fe (T.Fe) satisfies the following formula (2); Note (Al2O3+MgO+SiO2) / T.Fe≧0.12 ···(2) Where Al2O3: Concentration of Al2O3 in the fired pellet (mass%) MgO: MgO concentration in the fired pellets (mass%) SiO2: SiO2 concentration in the fired pellets (mass%) T.Fe: T.Fe concentration in the fired pellets (mass%) In producing the sintered pellets for reduction, (b) The iron-containing raw material is pretreated to remove water of crystallization so that the average LOI (loss on ignition) is 2% or less. (c) The pretreatment for removing the water of crystallization is performed by heating and drying the raw material in a rotary kiln, and the average LOI (loss on ignition) of the raw material containing iron is measured by sampling the raw material at the exit of the kiln. 、 but It is believed that this provides a more preferred embodiment. Effect of the Invention

[0011] According to the sintered pellets for reduction of the present invention having the above-mentioned configuration, by containing a relatively large amount of high-viscosity slag components (Al2O3, MgO, SiO2) relative to the total iron, it is possible to reduce the generation of low-melting-point slag due to FeO and its fluidity during reduction in a solid reduction furnace. As a result, it is possible to prevent contact and fusion between pellets due to the presence of such slag, and thus it is possible to effectively prevent the aforementioned clustering in the reduction furnace, which is a problem.

[0012] In addition, according to the production method of the present invention, by blending and using a high LOI raw material as the iron-containing raw material, the sintered pellets obtained are made porous, which reduces the chance of contact between metallic iron particles. This makes it possible to effectively prevent clustering and improve the efficiency of the operation of a solid reduction furnace. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the relationship between (Al2O3+MgO+SiO2) / T.Fe and LOI for Australian iron ore, which is an iron-containing raw material to be blended. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The solid reduction furnace used in the present invention is a furnace that uses hydrogen gas or the like as a reducing gas, charges sintered pellets for reduction into the furnace, and reduces the pellets to a reduction ratio of 90% or more. In the operation of this solid reduction furnace, the properties of the raw material charged into the furnace, i.e., the sintered pellets, are important.

[0015] For the fired pellets, it is most important to prevent clustering due to contact and adhesion between pellets in the high temperature region (500 to 800 °C) in the solid reduction furnace. In response to such a demand, the present invention has examined the relationship between iron-containing raw materials such as metallic iron, i.e., iron oxides such as iron ore, iron sulfide, and iron-making dust, and highly viscous slag components. As a result, it has been found that it is preferable to properly manage the relationship between the raw materials, particularly the highly viscous slag components, from the viewpoint of the fluidity of the raw materials in the furnace. In other words, by always producing highly viscous slag in the furnace, undesirable flow in the high temperature region can be suppressed, and therefore, the fusion of the slag can be prevented, and clustering can be prevented.

[0016] As described above, in the present invention, it has been found to be effective to make the iron-containing raw material, or the iron ore and auxiliary raw materials to be mixed contain a certain proportion of a highly viscous slag component.

[0017] Focusing on Al2O3, MgO, and SiO2 as components that can become highly viscous slag, when the total amount of these components is maintained at a specific ratio to the total iron (T·Fe), it becomes possible to effectively prevent the slag generated in the furnace from melting together.

[0018] This means that the composition of the sintered pellets for reduction must contain a certain ratio of the highly viscous slag components (Al2O3+MgO+SiO2) relative to the total iron (T·Fe) in the iron-containing raw materials; in other words, the sintered pellets must satisfy the relationship in formula (1) below. Note (Al2O3+MgO+SiO2) / T.Fe≧0.09 ···(1)

[0019] In the above formula (1), Al2O3 is the component concentration (mass%) of Al2O3 in the sintered pellets for reduction, MgO is the component concentration (mass%) of MgO in the sintered pellets for reduction, SiO2 is the component concentration (mass%) of MgO in the sintered pellets for reduction, and T.Fe is the total Fe concentration (mass%) in the sintered pellets for reduction.

[0020] In the present invention, from the viewpoint of preventing contact and fusion between slags in the high temperature region in the furnace, a more preferable relationship between the above-mentioned high viscous slag components (Al2O3+MgO+SiO2) and total iron (T.Fe) is as shown in the following formula (2), in which the amount of high viscous slag components is greater. Note (Al2O3+MgO+SiO2) / T.Fe≧0.12 ···(2)

[0021] In the above formula (2), Al2O3 is the component concentration (mass%) of Al2O3 in the sintered pellets for reduction, MgO is the component concentration (mass%) of MgO in the sintered pellets for reduction, SiO2 is the component concentration (mass%) of MgO in the sintered pellets for reduction, and T.Fe is the total Fe concentration (mass%) in the sintered pellets for reduction.

[0022] In the present invention, the total Fe in the iron-containing raw materials refers to the total concentration of iron consisting of metallic iron and iron compounds (iron oxide, iron sulfide, calcium ferrite, etc.), while the highly viscous slag components refers to the total concentration of Al2O3, MgO, and SiO2 contained in iron-containing raw materials such as iron ore and steelmaking dust, auxiliary raw materials (limestone, quicklime, dolomite, etc.), and binders (bentonite, etc.).

[0023] The Al2O3 concentration, MgO concentration, and SiO2 concentration can be determined by measuring the Al concentration, Mg concentration, and Si concentration by elemental analysis such as fluorescent X-rays, and multiplying the concentration by the molecular weight / atomic weight, respectively. Specifically, for example, the Al2O3 concentration can be determined by multiplying the Al concentration measured by elemental analysis such as fluorescent X-rays by Al2O3 molecular weight / Al atomic weight = 101.96 / 26.98 = 3.779.

[0024] Next, for the pellets for sintering for reduction according to the present invention, it is also important to control the porosity of the pellets. 43 By making the porosity (porosity: 0.05% or more), the number of contact points between the pellets can be reduced, which reduces contact between the metallic iron pellets and prevents them from fusing together, which in turn contributes to preventing the above-mentioned clustering. 43 %, it is not effective in preventing fusion. The upper limit is about 60% from the viewpoint of strength.

[0025] Next, a method for producing the fired pellets according to the present invention will be described. In producing the fired pellets for reduction according to the present invention, in order to realize the above-mentioned relationship between the highly viscous slag components (Al2O3+MgO+SiO2) and the total iron (T.Fe) in the resulting fired pellets, for example, it is possible to use a blend of one or more types of iron ore having the above-mentioned component composition, and to select and use two or more types of iron ore that show the above-mentioned relationship. For example, one or more types of iron ore (brands) shown in Figure 1 are blended from Australian iron ores, and binders and auxiliary materials such as bentonite and quicklime are added as necessary, and then granulated.

[0026] When the above-mentioned fired pellets are charged into a solid reduction furnace and reduced, it is important to make them have properties that do not cause the clustering in the high-temperature reducing atmosphere in the furnace. For this purpose, the present invention has focused on LOI (Loss on Ignition) and investigated its suitable value. That is, in the manufacturing method according to the present invention, if some of the iron ores (A to Z) shown in FIG. 1 are selected and used (blended) so that the LOI (Loss on Ignition) value is 5% or more, and LOI≧5% is satisfied, clustering can be reduced more effectively. The reason is that when the LOI is dissociated and vaporized during the pellet firing process and dissipates outside the pellet, the volume of the mineral phase remaining in the pellet shrinks, and voids are generated between the mineral phases.

[0027] Next, in the manufacturing method according to the present invention, in order to realize the LOI ≧ 5% for the iron-containing raw material, it is preferable to make the iron ore used have an LOI ≦ 2% by performing a pre-treatment such as a crystal water removal treatment in advance. The reason for this is that since many iron-containing raw materials such as raw iron ore contain a lot of crystal water, the pellets often burst due to the water vapor generated due to the crystal water during granulation, and therefore it is necessary to raise the temperature slowly.

[0028] In addition, in the pretreatment for removing the water of crystallization, it is desirable to manage the evaluation of the LOI using a measured value at the exit side (discharge position) of a granulator such as a rotary kiln.

[0029] (Example) Example 1: This example (including comparative examples) clarifies how the relationship between the T.Fe of the firing pellets for reduction and the highly viscous slag components (Al2O3+MgO+SiO2) affects clustering in a solid reduction furnace.

[0030] The iron-containing raw materials used in the experiment, i.e., iron ore, were mainly one or more of the Australian iron ores (A to Z) shown in Figure 1, and auxiliary raw materials and reagents (commercially available Al2O3 reagents, etc.) were used as needed. An example of the blend is shown in Table 1.

[0031] All raw materials, including one or more of the Australian raw materials mentioned above (examples shown in Figure 1) (A to Z), were pulverized in a ball mill, then granulated into pellets of 9 to 16 mm in size using a pelletizer while adding moisture. The resulting pellets were placed in a dryer and dried at 110°C for 24 hours, then placed in an electric furnace, heated at 7°C / min, held at 1250°C for 10 hours, and then cooled at a rate of 7°C / min. The resulting fired pellets shown in Table 1 were evaluated using porosity and clustering index.

[0032] (Clustering evaluation test) 500 g of sample was placed in a 100φ vertical cylindrical furnace and heated to 1000°C in a N2 atmosphere. When the temperature reached 1000°C, the reducing gas was added at 24 L / min, H2:N2 = 20:80 (vol%), and a load of 1 kg / cm was applied. 2 The pellets were then held at 400° C. for 3 hours and cooled in a N2 atmosphere to produce reduced iron. The pellets were then sieved through a 16 mm sieve, the maximum size of which is 16 mm, and their weight was measured (Wa(g)). The sieved pellets were placed in a type I testing machine (cylindrical container (132 mmφ×700 mL)) and rotated at 30 rpm for 5 minutes, after which the amount of the pellets sieved through the 16 mm sieve, Wb(g), was evaluated.

[0033] (Porosity) The porosity of the fired pellets was evaluated by measuring the apparent density and then the true density. The porosity was evaluated by measuring the apparent density and then the true density. Reference Examples 1 to 4 and Working Example 5 The clustering index is 7 for each Or zero It was confirmed that the fired pellets had good properties.

[0034] [Table 1]

[0035] In addition, Table 2 below is the same as Table 1 reference 1 shows the component compositions of the fired pellets obtained in Examples 1 and 2.

[0036] [Table 2]

[0037] Example 2: Next, the above-mentioned Table 1 Porosity 49vol% A test was carried out to evaluate whether the sample of Example 5 could be granulated and fired without being damaged during granulation by subjecting the sample to a pretreatment for removing water of crystallization. The temperature rise rate was set to 200° C. / min.

[0038] As a result, it was found that whether or not the water of crystallization is removed by the dewatering treatment determines whether or not the water of crystallization is removed. For example, if a large number of pores remain in the dewatered-crystallization ore, it may burst. On the other hand, if the water of crystallization is sufficiently removed, the ore will not burst. Furthermore, it was found that if the LOI of the ore before the treatment is sufficiently high, it is possible to produce a product of good quality even if the LOI of the ore after the dewatering-crystallization treatment is low.

[0039] [Table 3] [Industrial Applicability]

[0042] The solid reduction sintered pellets according to the present invention are a technology developed primarily for application in hydrogen-based direct reduction processes, but can also be used as a raw material in blast furnaces and the like.

Claims

1. Highly viscous slag components (Al ２ O ３ + MgO + SiO ２ ) satisfies the following formula (1), and the porosity of the sintered pellet for reduction is 43% or more. Note (Al ２ O ３ +MgO+SiO ２ ) / T.Fe≧0.09 ・・・(1) However, Al ２ O ３ : Al in fired pellets ２ O ３ Concentration of components (mass%) MgO: MgO component concentration (mass%) in the fired pellet SiO ２ : SiO in the fired pellets ２ Concentration of components (mass%) T.Fe: Component concentration (mass%) of T.Fe in fired pellets

2. Highly viscous slag components (Al ２ O ３ + MgO + SiO ２ 2. The sintered pellet for reduction according to claim 1, characterized in that the ratio of the above-mentioned components satisfies the following formula (2): Note (Al ２ O ３ +MgO+SiO ２ ) / T.Fe≧0.12 ・・・(2) However, Al ２ O ３ : Al in fired pellets ２ O ３ Concentration of components (mass%) MgO: MgO component concentration (mass%) in the fired pellet SiO ２ : SiO in the fired pellets ２ Concentration of components (mass%) T.Fe: Component concentration (mass%) of T.Fe in fired pellets

3. Highly viscous slag components (Al ２ O ３ + MgO + SiO ２ ) satisfies the following formula (1) or (2) and the porosity is 43% or more. The method for producing sintered pellets for reduction comprises reducing and sintering an iron-containing raw material blended so that the average LOI (loss on ignition) is 5% or more. Note (Al ２ O ３ +MgO+SiO ２ ) / T.Fe≧0.09 ・・・(1) (Al ２ O ３ +MgO+SiO ２ ) / T.Fe≧0.12 ・・・(2) However, Al ２ O ３ : Al in fired pellets ２ O ３ Concentration of components (mass%) MgO: MgO component concentration (mass%) in the fired pellet SiO ２ : SiO in the fired pellets ２ Concentration of components (mass%) T.Fe: Component concentration (mass%) of T.Fe in fired pellets

4. 4. The method for producing sintered pellets for reduction according to claim 3, characterized in that the iron-containing raw material is pre-treated to remove water of crystallization so that the average LOI (loss on ignition) is 2% or less.

5. The method for producing sintered pellets for reduction according to claim 4, characterized in that the pre-treatment for removing the water of crystallization is performed by heating and drying using a rotary kiln, and the average LOI (loss on ignition) of the iron-containing raw material is measured by sampling at the exit of the kiln.

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