Method for producing reduced iron briquettes

Abstract

Proposed is a method for producing reduced iron briquettes, wherein apparent density and strength can be improved even when low grade ore is used in briquetting by hot forming reduced iron. In a method for producing reduced iron briquettes according to the present invention, a reduced iron group composed of reduced iron containing iron components is subjected to hot compression molding to form briquettes, wherein a mixture in which low-grade reduced iron obtained by reducing low-grade ore and high-grade reduced iron obtained by reducing high-grade ore are mixed at a volumetric ratio determined according to the target apparent density of the reduced iron briquettes is used as the reduced iron group.

Description

Manufacturing method of reduced iron briquettes

[0001] The present invention relates to a method for producing reduced iron briquettes (hot-briquetted iron) by hot molding.

[0002] High productivity operation and CO ２ Hot briquette iron (HBI) has attracted attention as a charge material that can address both the challenges of reducing CO2 emissions and reducing CO2 emissions. HBI is a molded product produced by hot compressing direct reduced iron (DRI). DRI has a porous structure in which oxygen has been removed from the oxide (FexOy) inside the material through a reduction reaction. DRI has a high proportion of total iron (T.Fe) and a large specific surface area compared to before reduction, making it highly reactive. When stored in an oxygen atmosphere such as the atmosphere, it reacts with oxygen, resulting in heat generation and ignition due to oxidation heat. Therefore, when storing DRI in this state, it is desirable to store it in an inert gas atmosphere (e.g., nitrogen gas), which poses storage challenges.

[0003] One solution to this problem of DRI storage is to convert DRI into HBI. By converting DRI into HBI, the internal pores of the DRI are crushed and the gaps between the DRI are crushed in the hot temperature range, which is easier to process than at room temperature, and the specific surface area is reduced, thereby lowering reactivity and reducing the risk of heat generation and fire. A conventional HBI manufacturing technology is described in Patent Document 1.

[0004] Patent Document 1 discloses a technology for producing HBI having high strength and weather resistance suitable for use as a raw material to be charged into a blast furnace by setting the average C (Carbon) content of the surface and center portions to a predetermined value.

[0005] Patent No. 5059379

[0006] However, the technology described in Patent Document 1 is a method for producing inexpensive, high-strength, and weather-resistant HBI, and specifies the average C content in the surface and interior of DRI. Meanwhile, there is currently a shortage of high-grade ore, and the use of low-grade ore will be necessary in the future. However, the technology described in Patent Document 1 makes no mention of producing HBI using low-grade ore. When using low-grade ore, there are concerns that the increase in gangue components will result in a decrease in apparent density and strength.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to propose a method for producing reduced iron briquettes that can improve the apparent density and strength even when low-grade ore is used in briquetting reduced iron by hot forming.

[0008] The method for producing reduced iron briquettes of the present invention involves hot compression molding a reduced iron mass composed of reduced iron containing iron components into briquettes, and uses a reduced iron mass in which low-grade reduced iron obtained by reducing low-grade ore is mixed with high-grade reduced iron obtained by reducing high-grade ore at a volumetric ratio determined according to the target apparent density of the reduced iron briquette.

[0009] In the method for producing reduced iron briquettes according to the present invention configured as described above, (1) the lower limit of the mixed volume ratio X of the high-grade reduced iron is determined based on the porosity of the HBI and the true densities of the low-grade reduced iron and high-grade reduced iron in accordance with the target apparent density of the reduced iron briquette (HBI), and satisfies the following formula (3): X = {(100 × target apparent density of HBI) / (1 - porosity of HBI / 100) - 100ρa} / (ρb - ρa) (3), where ρa is the true density of the low-grade reduced iron obtained by reducing low-grade ore, and ρb is the true density of the high-grade reduced iron obtained by reducing high-grade ore, (2) the mixed volume ratio X is a value that satisfies the following formula (4): X ≥ (625 - 100ρa) / (ρb - ρa) (4), (3) The high-grade reduced iron is T. (3) the reduced iron mass is formed by reducing low-grade ore and high-grade ore that have been mixed before being charged into a reduction facility, based on a mixing ratio determined so that a mixing volume ratio X calculated using the expected true densities of the low-grade reduced iron and high-grade reduced iron after reduction satisfies formula (4).

[0010] According to the present invention, the reduced iron mass used for briquetting is a mixture of low-grade reduced iron obtained by reducing low-grade ore and high-grade reduced iron obtained by reducing high-grade ore, in a volume ratio determined according to the target apparent density of the reduced iron briquette. This makes it possible to obtain high-strength reduced iron briquettes that have a predetermined apparent density suitable for transport by sea, for example, even when using low-grade ore. Therefore, the method for producing reduced iron briquettes of the present invention is extremely useful when using low-grade ore.

[0011] The present invention relates to a method for producing reduced iron briquettes using a reduced iron briquette containing low-grade reduced iron and a high-grade reduced iron.

[0012] The following describes in detail the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0013] <Development Objective of the Manufacturing Method of Reduced Iron Briquettes of the Present Invention> In the manufacturing method of reduced iron briquettes of the present invention, a reduced iron aggregate is used in which low-grade reduced iron obtained by reducing low-grade ore is mixed with high-grade reduced iron obtained by reducing high-grade ore at a volumetric ratio determined according to the target apparent density of the reduced iron briquette. The volumetric ratio of high-grade reduced iron to low-grade reduced iron is changed according to the target apparent density of the reduced iron briquette, which is the final product, to obtain a reduced iron aggregate that can achieve the present invention. In the following description, the case of marine transportation of reduced iron briquettes (HBI) will be described as one embodiment of the target apparent density of the reduced iron briquette, which is the final product.

[0014] First, we will explain the target apparent density that we want to achieve in HBI. There are international regulations (IMSBC: International Maritime Solid Bulk Cargoes) for the marine transportation of HBI, and they specify an apparent density of 5.0 g / cm ３ It is necessary to satisfy the above requirement of "molding temperature of 650°C or higher." This is one of the important development indicators in establishing HBI technology.

[0015] The relationship between the apparent density, true density, and porosity of HBI is expressed by the following formula (1), and the apparent density increases as the porosity decreases: HBI apparent density = HBI true density × (1 - HBI porosity / 100) (1)

[0016] Low-grade ore contains a large amount of gangue, and the true density of low-grade reduced iron obtained by reducing low-grade ore is low. As will be described later, when only low-grade reduced iron is used, the apparent density is 5.0 g / cm ３Therefore, the inventors have proposed that the apparent density of HBI can be increased to 5.0 g / cm by mixing high-grade reduced iron according to the true density of the low-grade reduced iron. ３ It has been found that this can be achieved.

[0017] <Regarding the Mixed Volume Ratio of High-Grade Reduced Iron> When the mixed volume ratio of high-grade reduced iron is X (%), the apparent density of HBI is expressed by the following formula (2) based on formula (1). Here, ρa is the true density of low-grade reduced iron obtained by reducing low-grade ore, and ρb is the true density of high-grade reduced iron obtained by reducing high-grade ore. Apparent density of HBI = {ρa × (1 - X / 100) + ρb × (X / 100)} × (1 - porosity of HBI / 100) ... (2)

[0018] Based on formula (2), the lower limit of the mixing volume ratio X that can achieve the target apparent density of HBI is expressed by the following formula (3): X = {(100 × target apparent density of HBI) / (1 − porosity of HBI / 100) − 100ρa} / (ρb − ρa) (3)

[0019] Here, as a result of intensive research, the inventors have found that, from an operational viewpoint, it is desirable for the porosity of the HBI to be 15% or more and 20% or less. Attempting to produce HBI with a porosity of less than 15%, for example, about 10%, may accelerate wear of the production equipment itself. On the other hand, if an HBI with a porosity of more than 20% is produced, for example, an HBI with a porosity of about 30%, it will be brittle and prone to breakage. Therefore, in order to achieve the target apparent density in this embodiment, the HBI production conditions are set to an apparent density of 5.0 g / cm, assuming a maximum porosity of 20%. ３ Therefore, the following description will be given assuming that the porosity of HBI is 20%.

[0020] If the porosity of HBI is 20%, the apparent density of HBI is 5.0 g / cm ３ The condition for X that can achieve the above is calculated using equation (3) and expressed as the following equation (4): X≧(625−100ρa) / (ρb−ρa) (4)

[0021] Here, the low-grade reduced iron is preferably reduced iron that generally has a total iron content of less than 85 mass% by reduction. As a result of extensive studies, the present inventors have found that the low-grade reduced iron has a true density of approximately 6.20 g / cm ３ Therefore, when only low-grade reduced iron is used, X = 0, ρa = 6.20 g / cm ３ When calculated using equation (2) assuming that the porosity of HBI is 20%, the apparent density is 4.96 g / cm ３ This is less than the 5.0 g / cm required for marine transportation of HBI. ３ I can't achieve more than that.

[0022] Furthermore, the high-quality reduced iron is preferably reduced iron having a total iron content of 85 mass% or more by reduction. As a result of extensive studies by the present inventors, it has been found that the high-quality reduced iron has a true density of approximately 6.30 g / cm ３ It was found that this was the case.

[0023] Here, the true density ρa is 6.20 g / cm ３ and a true density ρb of 7.00 g / cm ３ When the high-quality reduced iron is used, the apparent density becomes 5.0 g / cm when the mixed volume of the high-quality reduced iron is 6.25% or more. ３ By mixing high-grade reduced iron with low-grade reduced iron in this manner, the apparent density of the produced HBI can be improved.

[0024] Furthermore, mixing high-grade reduced iron with low-grade reduced iron can improve the strength of the produced HBI. Solid-phase bonding of Fe not only closes pores within the reduced iron but also contributes to the bonding of the reduced iron particles themselves, making it extremely important for increasing strength. However, the presence of gangue at the iron interface inhibits solid-phase bonding. Therefore, low-grade reduced iron obtained by reducing low-grade ore with a high gangue content is prone to inhibiting solid-phase bonding, resulting in reduced HBI strength. Therefore, mixing high-grade reduced iron obtained by reducing high-grade ore with a low gangue content promotes solid-phase bonding and can improve HBI strength.

[0025] A plurality of types of low-grade reduced iron and high-grade reduced iron may be mixed. In this case, the average true density is calculated in consideration of the true densities of the low-grade reduced irons to be mixed and the volume ratio of the mixed low-grade reduced irons, and this value is used as the true densities ρa and ρb of the low-grade reduced iron and high-grade reduced iron to be used.

[0026] The higher the proportion of high-quality reduced iron, the greater the apparent density and strength of the resulting HBI. Therefore, although there is no particular upper limit, it is preferably 95% or less from the viewpoint of cost.

[0027] <Method for calculating true density> The true density can be determined by analyzing the components of reduced iron and analyzing the constituent substances and their proportions. It can be calculated using the following formula (5) from the constituent proportions of each substance and the density of that substance. True density [g / cm ３ ] = 100 / Σ (composition ratio of component x [mass%] / density of component x [g / cm ３ ]) (5) Here, component x includes iron, gangue, carbon, and other contained components.

[0028] <Method for measuring the amount of T. Fe> The amount of T. Fe is measured according to JIS M 8212 "Volumetric analysis." However, other specifications and standards may also be used.

[0029] <Method for measuring apparent density of HBI> The apparent density of HBI is measured by the method described in "ISO 15968: Direct reduced iron - Determination of apparent density and water absorption of hot briquette iron (HBI)". However, other specifications and standards may also be used.

[0030] <Regarding the manufacturing method and manufacturing apparatus for reduced iron briquettes of the present invention> Fig. 1 is a schematic diagram for explaining one embodiment of an apparatus configuration for carrying out the manufacturing method for reduced iron briquettes of the present invention. The embodiment of the apparatus configuration of the present invention shown in Fig. 1 comprises a reduction facility 1, a hopper feeder 3, twin briquette rolls 4 having the same diameter, and a crusher 6.

[0031] The reduction equipment 1 corresponds to, for example, a rotary hearth furnace or a direct reduction furnace. Hot reduced iron (DRI) 2 is heated to, for example, about 700° C. The hot reduced iron 2 is introduced into a hopper feeder 3 as a mass of reduced iron, and is forced into a twin briquette roll 4 by the rotation of a screw feeder provided in the hopper feeder 3.

[0032] The twin briquetting roll 4 is composed of a pair of molding rolls with the same diameter, and pockets in the shape of the briquettes are carved into the outer circumferential surface of the molding rolls. Hot reduced iron 2 is sequentially loaded into the pockets, and as the molding rolls rotate, they apply pressure to compress the hot reduced iron 2. Continuous raw material supply and synchronous rotation of the molding rolls generate an amount of HBI corresponding to the production rate (molding roll rotation speed). Reduced iron briquettes (HBI) 5 are continuously produced at the outlet of the molding rolls. Immediately after molding, the HBI 5 is molded in a state where individual HBIs are connected to each other, rather than in a state where individual HBIs are separated. Therefore, the HBIs are separated into individual HBIs by a crusher 6. The crusher 6 separates the connected HBIs 5 into small, easily handleable HBIs, for example, approximately 100 x 50 x 30 mm in size. The separated HBIs are used according to their intended purpose. For example, they are transported long distances and supplied to blast furnaces, electric furnaces, and melting furnaces.

[0033] In the present invention, the method for mixing the low-grade ore and high-grade ore as raw materials is not particularly limited. For example, the low-grade ore and high-grade ore may be mixed before being introduced into the reduction equipment. In this case, the true densities of the low-grade reduced iron and high-grade reduced iron after reduction can be predicted by conducting a reduction test simulating actual reduction conditions in advance. The true densities are then used to calculate the mixing volume ratio X from equation (3). The mixing ratio of the low-grade ore to the high-grade ore may be determined so that the calculated mixing volume ratio X satisfies equation (4).

[0034] In this case, the hot reduced iron 2 (reduced iron mass) is produced by reducing the low-grade ore and the high-grade ore mixed before being charged into the reduction equipment according to the mixing ratio determined as described above. Alternatively, high-grade reduction equipment and low-grade reduction equipment may be prepared, and the reduced iron discharged from each equipment may be mixed between the reduction equipment and the HBI manufacturing machine; the mixing method is not limited. However, in the latter example, high-grade reduction equipment and low-grade reduction equipment are required, which increases the cost of the equipment configuration. In this respect, the former example is preferable to the latter example.

[0035] Using the apparatus for producing reduced iron briquettes shown in Fig. 1, low-grade reduced iron and high-grade reduced iron having an outlet temperature of 700°C from reduction equipment 1 were mixed to obtain a mass of reduced iron, which was then continuously produced as hot reduced iron 2. The gap between the forming rolls of the twin briquetting rolls 4 was 1 mm, the forming roll rotation speed was 7 rpm, and the forming pressure was 180 kN / cm.

[0036] As the hot reduced iron 2, low-grade reduced iron was used [true density 6.19, 6.11, 6.02, 5.93, 5.84, 5.76, 5.67 g / cm ３ , 7 types in total], and high-quality reduced iron has a true density of 7.00 g / cm ３ The low-grade reduced iron and the high-grade reduced iron were mixed at various volume ratios to produce HBI.

[0037] The apparent density of HBI was measured by the method described in "ISO 15968". ３ Those with a value of 5.0 g / cm or more were considered to be within the applicable range. ３ Those with an apparent density and a crushing strength of less than 5.0 tonf were determined to be outside the applicable range. The crushing strength was measured using an Amsler testing machine. A load was applied perpendicular to the compression direction of the HBI, and those with a load of 5.0 tonf or more were determined to be within the applicable range, while those with a load of less than 5.0 tonf were determined to be outside the applicable range. Those with both an apparent density and a crushing strength within the applicable range were determined to be examples of the present invention, and those with both an apparent density and a crushing strength outside the applicable range were determined to be comparative examples. The measurement results are shown in Table 1 below.

[0038] FIG. 2 is a diagram showing the results of an experiment investigating the apparent density and / or strength of reduced iron briquettes as a function of the true density of low-grade reduced iron and the mixing volume ratio of high-grade reduced iron.

[0039] Based on the data in Table 1, the relationship between the volume ratio of high-grade reduced iron and the true density of low-grade reduced iron for apparent density is shown in the figure. Furthermore, based on the data in Table 1, the relationship between the volume ratio of high-grade reduced iron and the true density of low-grade reduced iron for crushing strength is shown in the figure. When the apparent density of HBI is 5.0 g / cm ３ Those with a value of 5.0 g / cm or more were evaluated as "Good" and those with a value of 5.0 g / cm or more were evaluated as "Good". ３ In the case where the HBI crushing strength was less than 5.0 tonf and was marked "X", and in the case where the HBI crushing strength was 5.0 tonf or more and was marked "Good" and the HBI crushing strength was less than 5.0 tonf and was marked "X", the results were as shown in FIG. 2.

[0040]

[0041] From the measurement results in Table 1 and the results in FIGS. 2 and 3 based on the data in Table 1, it can be seen that the present invention example using the reduced iron mass in which high-grade reduced iron was mixed with low-grade reduced iron at a mixing volume ratio X so as to satisfy formula (3) had an apparent density of 5.0 g / cm ３ It was found that it was possible to produce HBI having the above mentioned properties and high strength.

[0042] In this example, the outlet temperature of the reduction equipment 1 was 700°C, the gap between the forming rolls of the twin briquette rolls 4 was 1 mm, the forming roll rotation speed was 7 rpm, and the forming pressure was 180 kN / cm, but the conditions for implementing the present invention are not limited to these. The present invention can be implemented by appropriately changing the outlet temperature of the reduction equipment 1 within the range of 650 to 850°C, the gap between the forming rolls of the twin briquette rolls 4 to 0.5 to 5 mm, the forming roll rotation speed to 1 to 12 rpm, and the forming pressure to 150 to 250 kN / cm, for example.

[0043] 1 Reduction equipment 2 Hot reduced iron (DRI) 3 Hopper feeder 4 Twin briquette roll 5 Reduced iron briquette (HBI) 6 Crusher

Claims

1. A method for producing reduced iron briquettes, which involves hot compression molding a reduced iron mass composed of reduced iron containing iron components into briquettes, wherein the reduced iron mass is a mixture of low-grade reduced iron obtained by reducing low-grade ore and high-grade reduced iron obtained by reducing high-grade ore, in a volumetric ratio determined according to the target apparent density of the reduced iron briquette.

2. The method for producing reduced iron briquettes according to claim 1, wherein the lower limit of the mixing volume ratio X of high-grade reduced iron is determined based on the porosity of HBI and the true densities of low-grade reduced iron and high-grade reduced iron in accordance with a target apparent density of the reduced iron briquette (HBI), and is a value that satisfies the following formula (3): X={(100×target apparent density of HBI) / (1−porosity of HBI / 100)−100ρa} / (ρb−ρa) (3), where ρa is the true density of the low-grade reduced iron obtained by reducing low-grade ore, and ρb is the true density of the high-grade reduced iron obtained by reducing high-grade ore.

3. The method for producing reduced iron briquettes according to claim 2, wherein the mixing volume ratio X satisfies the following formula (4): X≧(625−100ρa) / (ρb−ρa) (4) 4. The method for producing reduced iron briquettes according to claim 3, wherein the high-grade reduced iron has a total iron content of 85 mass% or more, and the low-grade reduced iron has a total iron content of less than 85 mass%.

5. The method for producing reduced iron briquettes according to claim 3 or 4, wherein the reduced iron mass is obtained by reducing low-grade ore and high-grade ore mixed before being charged into a reduction facility, based on a mixing ratio determined so that a mixing volume ratio X calculated using the expected true densities of the low-grade reduced iron and high-grade reduced iron after reduction satisfies formula (4).

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