Coated hot briquetted iron and method for producing same

Abstract

The present invention improves the weather resistance of a hot briquetted iron (HBI). To this end, provided is a coated hot briquetted iron which comprises a hot briquetted iron and a coating layer that is adhered to the surface of the hot briquetted iron, wherein the coating layer contains at least one selected from the group consisting of a metal oxide, a metal hydroxide, and cement. It is preferable that the metal oxide and the metal hydroxide contain at least one selected from the group consisting of calcium, aluminum, and magnesium. It is preferable that the coverage of the coating layer is 50% or more.

Description

Coated hot briquette iron and method for manufacturing the same

[0001] The present invention relates to coated hot briquette irons and a method for manufacturing the same.

[0002] Conventionally, directly reduced iron (DRI) is known. DRI is used, for example, as an iron source in steelmaking in electric arc furnaces or blast furnaces. DRI is obtained by reducing raw materials such as iron ore using a direct reduction furnace. Through reduction, the iron oxides (Fe) that make up the raw materials are reduced. ｘ O ｙ Because oxygen is removed, the resulting DRI is porous. In other words, DRI has a higher total iron content and a larger specific surface area compared to the unreduced form, making it highly reactive. For this reason, when DRI is stored in an oxygen-rich atmosphere such as air, it reacts readily with oxygen, leading to exothermic reactions and ignition due to oxidation heat.

[0003] Therefore, in recent years, hot briquetted iron (HBI) has been developed (see Patent Document 1). HBI is a molded body composed of multiple DRIs, and is manufactured by hot-compressing the DRIs. That is, by crushing the DRIs in a hot temperature range that is easier to process than room temperature, the pores present inside the DRIs are crushed, and the specific surface area is reduced. In this way, the reactivity of the resulting HBI is reduced, suppressing heat generation and ignition.

[0004] Japanese Patent Publication No. 2008-127580

[0005] Hot briquette iron (HBI) is less reactive than directly reduced iron (DRI), but when exposed to the atmosphere for a long period of time, it oxidizes and its metallization rate decreases.

[0006] Patent Document 1 discloses a technique for improving the weather resistance (oxidation resistance) of HBI by adjusting the carbon (C) content. However, the weather resistance obtained by the technique in Patent Document 1 may be insufficient in some cases.

[0007] This invention has been made in view of the above points, and aims to improve the weather resistance of hot briquette iron (HBI).

[0008] The inventors, after diligent study, have found that the above objective can be achieved by adopting the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [5]. [1] A coated hot briquette iron having a hot briquette iron and a coating layer attached to the surface of the hot briquette iron, wherein the coating layer contains at least one selected from the group consisting of metal oxides, metal hydroxides and cement. [2] The coated hot briquette iron according to [1] above, wherein the metal oxide and the metal hydroxide contain at least one selected from the group consisting of calcium, aluminum and magnesium. [3] The coated hot briquette iron according to [1] or [2] above, wherein the coverage rate of the coating layer is 50% or more. [4] A method for producing a coated hot briquette iron, comprising a hot briquette iron and a coating layer disposed on the surface of the hot briquette iron, comprising: suspending coating layer particles containing at least one selected from the group consisting of metal oxides, metal hydroxides, and cement in water to prepare a slurry-like treatment solution; coating the surface of the hot briquette iron with the treatment solution; and heating the hot briquette iron coated with the treatment solution to remove the water contained in the treatment solution. [5] The method for producing a coated hot briquette iron according to [4], wherein the metal oxide and the metal hydroxide contain at least one selected from the group consisting of calcium, aluminum, and magnesium.

[0009] According to the present invention, the weather resistance of HBI can be improved.

[0010] This is a diagram showing the equipment used to manufacture coated HBI, along with the reduction equipment.

[0011] [Coated HBI] The coated HBI of this embodiment has hot briquette iron (HBI) and a coating layer attached to the surface of the HBI. Details of the HBI and the coating layer will be described later. Oxidation of HBI proceeds when the iron constituting the HBI (especially the iron present on the surface of the HBI) reacts with oxygen in the atmosphere. In this embodiment, however, the surface of the HBI is covered with a coating layer, making it difficult for it to come into contact with oxygen. As a result, even when exposed to the atmosphere for a long time, the HBI is less prone to oxidation and has excellent weather resistance (oxidation resistance). The components of the coated HBI will be described in more detail below.

[0012] <HBI> The HBI in the coated HBI of this embodiment is not particularly limited, and conventionally known HBI can be used. The size of the HBI is preferably one that is easy to handle, for example, a size of about 100 mm x 50 mm x 30 mm is preferred. The HBI is, in general terms, a molded body composed of multiple directly reduced iron (DRI) as described above, and is manufactured by hot compression of the DRI. A more detailed manufacturing method will be described later.

[0013] HBI is preferably low in iron oxide (iron oxide) content and high in metallization rate. Specifically, for example, the metallization rate of HBI is preferably 86.0% by mass or more, more preferably 88.0% by mass or more, and even more preferably 90.0% by mass or more. The metallization rate is determined by the method described later.

[0014] <Coating Layer> The coated HBI of this embodiment has a coating layer attached to the surface of the HBI. The coating layer contains particles (coating layer particles) described below.

[0015] 《Types of coating layer particles》 The coating layer particles contain at least one selected from the group consisting of metal oxides, metal hydroxides, and cement.

[0016] (Metal Oxides and Metal Hydroxides) Metal oxides and metal hydroxides preferably contain a metal element other than iron (Fe), and more preferably contain at least one metal element selected from the group consisting of calcium (Ca), aluminum (Al), and magnesium (Mg). Specific examples of metal hydroxides include calcium hydroxide, aluminum hydroxide, and magnesium hydroxide. Specific examples of metal oxides include calcium oxide, aluminum oxide, and magnesium oxide.

[0017] (Cement) Examples of cement include self-hardening cement (Portland cement); latent hydraulic cement (e.g., blast furnace cement); fine powders of blast furnace slag, blast furnace water slag, and steel slag; and among these, Portland cement is preferred. Examples of Portland cement include ordinary Portland cement, rapid-hardening Portland cement, and high-strength Portland cement. These exhibit a strong hydration reaction, such as 3CaO·SiO ２ It contains a large amount of [ingredient] and has excellent hydraulic properties, resulting in good adhesion to HBI. Furthermore, it is inexpensive and readily available.

[0018] HBI, like DRI, is used as an iron source in steelmaking, for example, in electric arc furnaces or blast furnaces. The coating layer particles have the same composition as the slag produced as a by-product during steelmaking and can be removed as slag. For this reason, coated HBI using coating layer particles is suitable as an iron source when used in electric arc furnaces or blast furnaces, without requiring any special processes.

[0019] The proportion of coating layer particles in the coating layer is preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more. On the other hand, the proportion of other components (components other than coating layer particles) in the coating layer is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. Examples of other components include hydrocarbon substances such as pitch, asphalt, coal tar, liquefied coal oil, and petroleum refining residue oil; and metal carbonates such as calcium (Ca), magnesium (Mg), and manganese (Mn). When the coating layer is formed by the method described later, the proportion of coating layer particles and other components in the coating layer will satisfy the above ranges.

[0020] <Coverage Rate> In coated HBI, the coverage rate of the coating layer (the area percentage of the surface of the HBI covered by the coating layer) is, for example, 30% or more, and may be 40% or more. A coverage rate of 50% or more is preferable, 60% or more is more preferable, and 80% or more is even preferable, because the surface of the HBI is less exposed to the atmosphere and has better weather resistance (oxidation resistance).

[0021] On the other hand, if the coverage rate of the coating layer is too high, while weather resistance is excellent, when the coated HBI is used as an iron source in electric furnaces, the yield decreases and power consumption increases. This is because it takes more time to remove the coating layer particles as slag. Therefore, from the viewpoint of operating with reduced power consumption, the coverage rate of the coating layer is preferably 95% or less, more preferably 85% or less, and even more preferably 75% or less.

[0022] The coverage rate of the coating layer is determined by the following method. First, the surface of the coated HBI is observed using a microscope at a magnification of 100x, and 10 fields of view microscope images are obtained. Next, the area percentage of the surface of the HBI covered by the coating layer is calculated from the obtained microscope images by image analysis, and the average value of the 10 fields of view is obtained as the coverage rate of the coating layer (unit: %).

[0023] 《Thickness》 The thickness of the coating layer (average thickness in the cross-sectional direction) is preferably 5.0 μm or more, more preferably 10.0 μm or more, and even more preferably 20.0 μm or more, for the reason that it provides better weather resistance. On the other hand, there is no particular upper limit to the thickness of the coating layer. However, if the coating layer is too thick, the operational efficiency may be reduced when using coated HBI as an iron source in electric furnaces, etc. For this reason, the thickness of the coating layer is preferably 200.0 μm or less, more preferably 100.0 μm or less, and even more preferably 40.0 μm or less.

[0024] The thickness of the coating layer is determined by the following method. First, the coated HBI is mechanically polished to expose its cross-section. The exposed cross-section is observed using a scanning electron microscope (SEM) at a magnification of 300x, and three SEM images are obtained. Next, the thickness of the coating layer on the surface of the HBI is measured at 10 points within one field of view of the obtained SEM images, and the average value of the three fields of view is determined as the thickness of the coating layer (unit: μm).

[0025] [Method for Manufacturing Coated HBI] Next, a method for manufacturing coated HBI according to this embodiment will be described based on Figure 1. Figure 1 is a configuration diagram showing the equipment for manufacturing coated HBI 11 together with the reduction equipment 1. The equipment for manufacturing coated hot briquette iron 11 (coated HBI 11) generally comprises a hopper feeder 3, a double briquette roll 4, a crusher 6, a cooling tank 7, a coating treatment tank 8, a heating furnace 9, and a dewatering furnace 10, as shown in Figure 1.

[0026] Reduction equipment 1 is a reduction furnace (direct reduction furnace) such as a shaft furnace or rotary hearth furnace. In reduction equipment 1, for example, raw materials such as iron ore (not shown) are treated with CO and H ２ Reduced iron 2 (DRI2) is directly produced by reduction using a reducing gas containing [a specific substance]. The DRI2 produced by reduction equipment 1 is heated to approximately 700°C.

[0027] Next, hot briquette iron 5 (HBI 5) is produced using DRI 2 manufactured in reduction equipment 1, and then coated HBI 11 is produced.

[0028] More specifically, first, the DRI2 mass produced in the reduction facility 1 is fed into a hopper feeder 3 equipped with a screw feeder (not shown). The DRI2 mass fed into the hopper feeder 3 is supplied by being pushed into the twin briquette rolls 4 by the rotation of the screw feeder.

[0029] The twin briquette rolls 4 are a pair of molding rolls of the same diameter, and their outer surfaces are provided with pockets shaped like the molded body (i.e., HBI5). The DRI2 is sequentially loaded into the pockets and pressurized by the rotation of the twin briquette rolls 4. In this way, the DRI2 is compressed and the molded body, HBI5, is produced. Due to the continuous supply of DRI2 and the synchronous rotation of the twin briquette rolls 4, HBI5 is continuously produced according to the production speed (rotational speed).

[0030] Immediately after being formed by the twin briquette roll 4, as shown in Figure 1, multiple HBIs 5 are connected, so a crusher 6 is used to separate them into individual HBIs 5.

[0031] The separated HBI5 is cooled in a cooling tank 7. The method of cooling the HBI5 is not particularly limited and may be air-cooled or water-cooled. The HBI5 cooled in the cooling tank 7 is transported to the coating treatment tank 8 using a conveyor 12a.

[0032] The coating treatment tank 8 stores a treatment liquid containing coating layer particles. Prior to this, a slurry-like treatment liquid is prepared by suspending the coating layer particles in water, and this is stored in the coating treatment tank 8. The coating layer particles used are at least one selected from the group consisting of metal oxides, metal hydroxides, and cement. The metal oxides and metal hydroxides each contain at least one metal element selected from the group consisting of, for example, Ca, Al, and Mg. The metal oxides react with water to form metal hydroxides. The concentration of coating layer particles in the treatment liquid (unit: g / L) is adjusted as appropriate, for example, according to the desired coating rate.

[0033] The HBI5 conveyed to the coating treatment tank 8 using the conveyor 12a is immersed in the coating treatment tank 8. The HBI5 immersed in the treatment liquid is appropriately stirred. By such a method, HBI5 with its surface coated with the treatment liquid is obtained.

[0034] The method of coating the treatment liquid on the surface of HBI5 is not limited to the dipping method described above. For example, a method of spraying the treatment liquid onto HBI5 using a spray may be employed. The coating rate of the coating layer in the finally obtained coated HBI11, etc., can be controlled by adjusting, for example, the stirring time after immersing HBI5 in the treatment liquid, the number of times of spraying the treatment liquid onto HBI5, and the like.

[0035] The HBI5 with its surface coated with the treatment liquid is carried out of the coating treatment tank 8 by the conveyor 12b and heated (dried) in the heating furnace 9. Thus, the moisture of the treatment liquid for coating HBI5 is evaporated and removed. The heating method is not particularly limited, and examples include methods using steam heating, electric heating, microwaves, dielectric current, etc. The heating temperature in the heating furnace 9 is preferably 100°C or higher. As the atmospheric gas inside the heating furnace 9, a gas with a low CO ２ concentration is preferable, and a gas with a CO ２ concentration of 1000 volume ppm or less (for example, an inert gas, air, combustion gas subjected to CO ２ removal treatment, heating steam, etc.) is more preferable.

[0036] The HBI5 heated in the heating furnace 9 is carried to the dehydration furnace 10 by the conveyor 12c and further heated in the dehydration furnace 10. By the heating in the dehydration furnace 10, dehydration reactions represented by the following formulas (1) to (3) occur, and a coating layer is formed. Since the reactions of the following formulas (1) to (3) proceed in a temperature range of 300 to 500°C or higher under atmospheric pressure, the heating temperature in the dehydration furnace 10 may be appropriately determined to be this temperature or higher. Ca(OH) ２ →CaO + H ２ O...(1) 2Al(OH) ３ →Al ２ O ３ + 3H ２ O...(2) Mg(OH) ２ →MgO + H ２ O...(3)

[0037] Thus, the coated HBI 11 with a coating layer adhering to the surface of the HBI 5 is obtained. As described above, the coated HBI 11 is suitably used as an iron source for steelmaking, for example, in an electric furnace (not shown).

[0038] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples described below.

[0039] 〈HBI〉 Using the equipment described based on FIG. 1, direct reduced iron (DRI) and hot briquette iron (HBI) were continuously produced. At this time, the outlet temperature of the reduction equipment (shaft furnace) was set to 700°C. For the double-briquette roll, the roll gap was set to 1 mm, the roll rotation speed was set to 7 rpm, and the molding pressure was set to 180 kN / cm. The metallization rate of the obtained HBI was 92.2% by mass immediately after being molded by the double-briquette roll.

[0040] The metallization rate (unit: mass%) was calculated from the following formula using the total iron content (T.Fe) and metallic iron content (M.Fe) of the sample. Metallization rate = (M.Fe / T.Fe) × 百 T.Fe was calculated using the total iron quantification method described in JIS M 8212. M.Fe was measured by the bromine methanol method. That is, using a bromine methanol solution, the metallic iron in the sample was dissolved and quantified from the mass change at that time.

[0041] 〈Treatment liquid〉 Commercially available calcium oxide, calcium hydroxide, aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, and cement (Portland cement) were pulverized to a particle size of 1 mm or less, and the obtained particles (coating layer particles) were suspended in water at the concentrations (unit: g / L) shown in Table 1 below to prepare a slurry-like treatment liquid.

[0042] <Coated HBI> The HBI was immersed in a treatment solution, then heated in a heating furnace set to 80°C for 30 minutes to dry it, and then heated in a dehydration furnace set to 500°C for 1 hour. In this way, coated HBI was obtained in which a coating layer was formed on the surface of the HBI. The coverage rate of the coating layer was determined for the obtained coated HBI using the method described above. The results are shown in Table 1 below.

[0043] In the obtained coated HBI, the thickness of the coating layer was in the range of 5.0 μm to 40.0 μm.

[0044] However, in Comparative Example 1, no coating layer was formed on the surface of the HBI, and the HBI was used as is. Therefore, "-" is indicated in the "Coverage Rate" column of Table 1 below.

[0045] The obtained coated HBI (Examples 1-7) and HBI (Comparative Example 1) were placed outdoors, and the metallization rate was measured after 6 months. The results are shown in Table 1 below. A higher metallization rate after 6 months indicates superior weather resistance (oxidation resistance).

[0046]

[0047] <Summary of Evaluation Results> As shown in Table 1 above, the coated HBIs of Examples 1 to 7 showed a higher metallization rate after 6 months and superior weather resistance compared to the HBI of Comparative Example 1.

[0048] Comparing Examples 1 to 7, Examples 1 and 4 to 7, with a coverage rate of 50% or more, showed better weather resistance than Examples 2 to 3, with a coverage rate of less than 50%. Comparing Examples 1 and 4 to 7, Examples 4 and 6 to 7, with a coverage rate of 60% or more, showed even better weather resistance than Examples 1 and 5, with a coverage rate of less than 60%. Comparing Examples 4 and 6 to 7, Example 4, with a coverage rate of 80% or more, showed even better weather resistance than Examples 6 to 7, with a coverage rate of less than 80%.

[0049] 1: Reduction equipment 2: Direct reduced iron (DRI) 3: Hopper feeder 4: Double briquette roll 5: Hot briquette iron (HBI) 6: Crusher 7: Cooling tank 8: Coating tank 9: Heating furnace 10: Dehydration furnace 11: Coated hot briquette iron (coated HBI) 12a, 12b, 12c: Conveyor

Claims

1. A coated hot briquette iron comprising a hot briquette iron and a coating layer attached to the surface of the hot briquette iron, wherein the coating layer contains at least one selected from the group consisting of metal oxides, metal hydroxides, and cement.

2. The coated hot briquette iron according to claim 1, wherein the metal oxide and the metal hydroxide contain at least one selected from the group consisting of calcium, aluminum, and magnesium.

3. The coated hot briquette iron according to claim 1 or 2, wherein the coverage rate of the coating layer is 50% or more.

4. A method for producing coated hot briquette iron, comprising hot briquette iron and a coating layer disposed on the surface of the hot briquette iron, comprising: suspending coating layer particles containing at least one selected from the group consisting of metal oxides, metal hydroxides, and cement in water to prepare a slurry-like treatment solution; coating the surface of the hot briquette iron with the treatment solution; and heating the hot briquette iron coated with the treatment solution to remove the water contained in the treatment solution.

5. The method for producing coated hot briquettes iron according to claim 4, wherein the metal oxide and the metal hydroxide contain at least one selected from the group consisting of calcium, aluminum, and magnesium.

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