Method for producing reduced iron briquettes

Abstract

In hot-briquetting of reduced iron, a method which is for producing reduced iron briquettes and which makes it possible to increase the apparent density and strength thereof is proposed. Provided is a method for producing reduced iron briquettes by briquetting, by hot compression molding with molding rollers, a reduced iron group which is constituted by pellet-shaped reduced iron containing an iron component, wherein the rotation speed of the molding rollers and / or the gap between the molding rollers are changed in accordance with the T.Fe content of the pellet-shaped reduced iron, and then the hot compression molding is carried out with respect to the reduced iron group. In a preferred embodiment, with an increasing gangue component ratio, the rotation speed of the molding rollers is changed so as to be slower and / or the gap between the molding rollers is changed so as to be smaller.

Description

Manufacturing method of reduced iron briquettes

[0001] The present invention relates to a method for producing reduced iron briquettes by hot compaction.

[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 higher total Fe (T.Fe) ratio and a larger specific surface area than 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. Conventionally, the technologies described in Patent Document 1 and Patent Document 2 are known as HBI manufacturing technologies.

[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 adjusting the average carbon (C) content of the surface and center portions to a predetermined value. Patent Document 2 discloses a molten iron production apparatus and a molten iron production method for agglomerating reduced iron powder and sintered auxiliary materials at high temperatures.

[0005] Patent No. 5059379 Patent No. 4202326

[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 the DRI. Therefore, while high strength can be achieved, there is no mention of high density. Furthermore, the technology described in Patent Document 2 specifies optimal manufacturing conditions for charging into an electric furnace or blast furnace. Patent Document 2 discloses the desired particle size distribution of the HBI (agglomerate) after DRI molding and immediately before charging into an electric furnace or blast furnace. However, there is no disclosure of any specific means for achieving this desired particle size distribution. Therefore, the technology described in Patent Document 2 does not necessarily achieve high density of the HBI itself, and there remains a risk of long-distance transportation.

[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 when briquetting reduced iron by hot forming.

[0008] The method for producing reduced iron briquettes of the present invention is a method for producing reduced iron briquettes in which a reduced iron mass composed of reduced iron pellets containing an iron component is hot-compressed with molding rolls to form briquettes, characterized in that the hot-compression molding of the reduced iron mass is carried out by changing the rotation speed of the molding rolls and / or the gap between the molding rolls depending on the total iron content of the reduced iron pellets.

[0009] In the method for producing reduced iron briquettes according to the present invention configured as described above, it is considered that the following are more preferable solutions: (1) As the total iron content decreases, the rotation speed of the molding rolls is slowed down and / or the gap between the molding rolls is narrowed down, and (2) The total iron content of the pelletized reduced iron is less than 85 mass%.

[0010] According to the method for producing reduced iron briquettes of the present invention, the rotation speed of the molding rolls or the gap between the molding rolls is changed depending on the total iron content of the pelletized reduced iron in the reduced iron mass, and the reduced iron mass is subjected to hot compression molding, thereby making it possible to obtain reduced iron briquettes with improved apparent density and strength.

[0011] 1 is a graph showing an embodiment of the relationship between HBI apparent density and HBI porosity depending on the raw material grade. FIG. 2 is a graph showing an embodiment of the relationship between the T.Fe content and the gangue component content in normal-grade ore and low-grade ore. FIG. 3 is a schematic diagram for explaining an embodiment of an apparatus configuration for implementing the method for producing reduced iron briquettes of the present invention. FIG. 4 is a schematic diagram for explaining a case where the apparent density of the reduced iron briquette is below the development target. (a) and (b) are schematic diagrams for explaining an example of changing the gap between the molding rolls in the method for producing reduced iron briquettes of the present invention. (a) and (b) are graphs showing the relationship between the porosity and the molding roll rotation speed, and the relationship between the apparent density and porosity, respectively, in the method for producing reduced iron briquettes of the present invention. (a) and (b) are graphs showing the relationship between the porosity and the gap between the molding rolls, and the relationship between the apparent density and porosity, respectively, in the method for producing reduced iron briquettes of the present invention. FIG. 5 is a graph showing the relationship between the T.Fe content and the gangue component content in normal-grade ore and low-grade ore. FIG. 6 is a schematic diagram for explaining an example of changing the gap between the molding rolls in the method for producing reduced iron briquettes of the present invention. 1 is a graph showing the relationship between the amount of Fe and the HBI porosity required when converting DRI into HBI.

[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 Goals for the Manufacturing Method of Reduced Iron Briquettes of the Present Invention> There are international regulations (IMSBC: International Maritime Solid Bulk Cargoes) for the marine transportation of HBI, and the "apparent density of 5.0 g / cm ３It 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.

[0014] FIG. 1 is a conceptual diagram of the relationship between HBI porosity and HBI apparent density according to the raw material grade. It is known that there is a negative correlation between HBI porosity and HBI apparent density. The graph is based on the assumption that HBI molded from reduced iron (T.Fe content about 90 mass%) of normal grade iron ore is a commercially available HBI example A, B, and C that are distributed on the market as commercial products. These examples have an HBI porosity of 27% or less and meet the target value (5.0 g / cm) of the IMSBC apparent density standard for marine transport. ３ In the case of low-grade ore, the proportion of gangue components (CaO, Al) in the DRI is higher than that of normal-grade ore. ２ O ３ , SiO ２ The ratio of MgO is high, and the total iron content (the ratio of iron components in DRI) is low. Because gangue components have a lower true density than iron, the density of HBI tends to decrease as the grade deteriorates. In the case of low-grade ore and even lower-grade ore, the porosity must be made smaller than that of normal-grade ore in order to achieve the target apparent density. Therefore, in order to establish consolidation technology, it is important to determine the necessary molding conditions (molding temperature, molding pressure) according to the ore grade (total iron).

[0015] In Figure 1, the graphs for low-grade ore and even lower-grade ore are calculated based on the actual graph for normal-grade ore (T.Fe content of approximately 90 mass%), with the T.Fe content reduced by a fixed amount. The T.Fe content of both low-grade ore and even lower-grade ore is less than 85 mass% T.Fe. In Figure 1, the target HBI apparent density can be achieved by setting the HBI porosity to 20% or less for low-grade ore and 15% or less for even lower-grade ore. Figure 2 also shows the relationship between the T.Fe content and the gangue content for normal-grade ore and low-grade ore. As shown in Figure 2, the gangue content varies depending on the DRI grade. Specifically, the lower the DRI grade, the lower the T.Fe content and the higher the gangue content.

[0016] 8 is a diagram showing the relationship between the total iron content of the raw material DRI and the HBI porosity. As shown in FIG. 8, the lower the total iron content of the DRI (the lower the grade), the lower the HBI porosity.

[0017] <Method for Measuring Total Iron Content> Before describing the method and apparatus for manufacturing reduced iron briquettes of the present invention, a method for measuring the total iron content will be described. First, a predetermined amount of sample is measured and decomposed into a solution by either method (a) or (b) below. (a) The sample is decomposed with hydrochloric acid in the presence of tin (II) chloride and filtered. The residue is treated with sulfuric acid and hydrofluoric acid, and then melted with potassium disulfate and combined with the filtrate. (b) The sample is melted with sodium carbonate and sodium peroxide, and the melt is dissolved in warm water. The precipitate is separated by filtration and dissolved in hydrochloric acid.

[0018] Most of the iron(III) in these solutions is reduced to iron(II) with tin(II) chloride, and the remaining iron(III) is reduced with titanium(III) chloride. Excess titanium(III) chloride is quantitatively oxidized with potassium dichromate. The acid concentration of this solution is adjusted with a mixed acid of sulfuric acid and phosphoric acid, and titration is performed with potassium dichromate solution using sodium diphenylamine-4-sulfonate as an indicator. The T.Fe content in the sample is quantitatively calculated from the titrated amount of dichromate. The above measurement method is based on JIS M 8212 "Volumetric Analysis," but other specifications and standards may also be used.

[0019] <Regarding the manufacturing method of reduced iron briquettes of the present invention> In view of the above development objectives, the present invention solves the above-mentioned problems by changing the rotation speed of the molding rolls and / or the gap between the molding rolls depending on the raw material quality, particularly the total iron content, in order to improve the apparent density and strength of HBI. These are all conditions on the briquetting machine side and are independent of the method of keeping the constituent chemical components within the upper and lower limit ranges. Therefore, evaluation can be performed based solely on the effect of the established conditions on molding properties, without relying on control of the raw material properties. Note that the "high density" in this patent is relative to the apparent density of commercial HBI, which is an apparent density of 5.0 g / cm. ３ This is defined as above.

[0020] Fig. 3 is a schematic diagram illustrating one embodiment of an apparatus configuration for carrying out the method for producing reduced iron briquettes of the present invention. In the embodiment of the apparatus configuration of the present invention shown in Fig. 2, heated DRI 1 at a molding temperature is charged into a hopper 2. The heated DRI 1 charged into the hopper 2 is compression-molded by molding rolls 3 to become HBI 4. The obtained HBI 4 is charged into a crusher 5.

[0021] The heated DRI 1 is fed into a hopper 2 and is forced into a molding roll 3 by the rotation of a screw feeder. The molding roll 3 is composed of a pair of molding rolls of the same diameter, and the outer surface of the molding roll 3 has pockets carved in the shape of the molding product. The heated DRI 1 pushed from the hopper 2 is sequentially loaded into the pockets, and as the molding roll 3 rotates, the molding roll 3 applies pressure to the heated DRI 1, compressing it. The continuous supply of raw material and the synchronous rotation of the molding rolls generate HBI 4 according to the production speed (roll rotation speed). Immediately after molding, the HBI 4 is molded in a state where the individual pieces are connected to each other. The connected HBI 4 is then separated into individual pieces by a crusher 5.

[0022] For stable production of briquettes, it is necessary to establish appropriate production conditions in the briquetting machine. Commonly known parameters for briquetting machines include the molding (raw material) temperature, molding pressure, roll rotation speed, pocket shape, and roll gap. In the present invention, the molding roll rotation speed and / or the gap between the molding rolls are changed depending on the ratio of gangue components in the pellet-shaped reduced iron mass to be compressed and molded, so that high-density HBI can be efficiently produced.

[0023] <Regarding the Rotational Speed ​​of the Molding Roll> The rotational speed of the molding roll affects the ease of solidification of the molded product. For example, when the molding roll is rotated faster than the reference speed, the contact time between the roll surface and the raw material is shorter than at the reference rotational speed, making it more difficult to apply the load (pressure) necessary to reduce the porosity. FIG. 4 is a schematic diagram illustrating a case in which the apparent density of the reduced iron briquette is below the development target. As shown in this embodiment, HBI4 is produced after compression molding using the molding roll, with HBI4-1 having an apparent density of the reduced iron briquette that meets the development target, and HBI4-2 having an apparent density of the reduced iron briquette that does not meet the development target. Therefore, in the present invention, the rotational speed of the molding roll is slower than the normal reference rotational speed, thereby increasing the contact time compared to the conventional reference rotational speed, thereby increasing the apparent density of the molded HBI4.

[0024] <Regarding the Gap Between the Molding Rolls> When the gap between the molding rolls is changed, the number of DRI particles entering between the pocket rolls also changes. The molding pressure applied to each DRI particle also changes. By narrowing the gap between the molding rolls, the molding pressure per DRI particle can be increased, thereby increasing the apparent density of the HBI. Figures 5(a) and 5(b) are schematic diagrams illustrating an example of changing the gap between the molding rolls in the method for producing reduced iron briquettes of the present invention. Figure 5(a) shows an example in which the gap between the molding rolls is at the standard roll position for normal operation, and HBI4-2, whose apparent density of the reduced iron briquette is below the development target, is present, as shown in Figure 4. Figure 5(b) shows an example in which the gap between the molding rolls is narrower than the standard roll position in Figure 5(a), and there is no HBI4-2, whose apparent density of the reduced iron briquette is below the development target, and only HBI4-1, whose apparent density of the reduced iron briquette is present and meets the development target. In this case, there is a limit to how short the gap between the rolls can be; if it is made too short, excessive pressure can cause internal cracks in the molded product, which in turn reduces its strength, so it is desirable to apply an appropriate molding pressure.

[0025] In the above explanation, the influence of changing the rotation speed of the forming rolls and the influence of changing the gap between the forming rolls have been explained separately. As such, in addition to the case where the rotation speed of the forming rolls and the gap between the forming rolls are changed independently, it goes without saying that the present invention can be achieved even when both the rotation speed of the forming rolls and the gap between the forming rolls are changed simultaneously.

[0026] As described above, according to the present invention, it is possible to mold high-density HBI by changing the rotation speed of the molding rolls and / or the gap between the molding rolls in accordance with the ratio of gangue components in the mass of pellet-like material to be compression-molded.

[0027] The present invention is particularly effective as the raw material has a lower quality. Here, the "low-quality raw material" refers to, for example, pelletized reduced iron containing an iron component with a total iron content of less than 85 mass%. Alternatively, the "low-quality raw material" may refer to pelletized reduced iron containing an iron component with a total iron content of less than 83 mass% or 80 mass%. Alternatively, the "low-quality raw material" may refer to an initial raw material before being formed into pellets, which has a total iron content of 63 mass% or less.

[0028] The following are the tentative assumptions for DRI and HBI: DRI particle weight: 5.0 g / particle DRI particle diameter: Φ10-15 mm / particle HBI dimensions: (long side 100 mm x short side 50 mm x thickest part 30 mm) / unit HBI shape: pillow type HBI weight: 500 g / unit Since the total number of DRIs loaded per pocket is one HBI, one HBI is composed of (500 g / particle) / (5.0 g / particle) = 100 DRI particles / unit.

[0029] However, the porosity inside the molded DRI and the void ratio between the DRIs that make up the HBI differ depending on the DRI molding conditions. Just before the DRI is compressed, when the DRI is loaded into the pocket, the void ratio of the pocket can be quantitatively evaluated based on the particle size distribution index, harmonic mean diameter, etc.

[0030] 6(a) and 6(b) are graphs showing the relationship between porosity and the rotation speed of the molding roll, and the relationship between apparent density and porosity, respectively, in the manufacturing method of reduced iron briquettes of the present invention. According to one embodiment of the present invention shown in 6(a) and 6(b), when the reference rotation speed of the molding roll is 10 rpm, as shown in 6(a), the porosity of the molded HBI is 20%. And, as shown in 6(b), at a porosity of 20%, the apparent density is the target value of 5.0 g / cm. ３ At this time, when the molding roll rotation speed was changed to 5 rpm, the porosity of the molded HBI became 10%, and the apparent density was reduced to the target value of 5.0 g / cm. ３ It can be seen that the above can be achieved.

[0031] 7(a) and 7(b) are graphs showing the relationship between porosity and the gap between the forming rolls, and the relationship between apparent density and porosity, respectively, in the manufacturing method of reduced iron briquettes of the present invention. According to one embodiment of the present invention shown in Fig. 7(a) and 7(b), when the reference value of the gap between the forming rolls is set to 3 mm, as shown in Fig. 7(a), the porosity of the formed HBI is 20%. And, as shown in Fig. 7(b), at a porosity of 20%, the apparent density is the target value of 5.0 g / cm. ３ In this case, when the gap between the forming rolls was changed to 1 mm, the porosity of the formed HBI became 10% and the apparent density became 5.0 g / cm ３ It can be seen that the above can be achieved.

[0032] There is a certain correlation between the total iron content of DRI and the HBI porosity required when converting that DRI into HBI. Table 1 below summarizes the total iron content and the HBI porosity required when converting that DRI into HBI for five sample DRIs.

[0033]

[0034] Fig. 8 is a graph based on Table 1, showing the relationship between the total iron content of DRI and the HBI porosity required when converting the DRI into HBI in the method for producing reduced iron briquettes of the present invention. As shown in Fig. 8, for example, compared with normal-grade DRI having a total iron content of about 92 mass%, in the case of low-grade DRI having a total iron content of about 84 mass%, the porosity required when converting the DRI into HBI (porosity that satisfies the apparent density required by IMSBC) is lower, at about 17%.

[0035] 8, the relationship between the total iron content of DRI and the HBI porosity required for converting the DRI into HBI can be formulated by the following formula (1): Y = 1.0062X - 68.338... formula (1), where Y is the HBI porosity (%) required for converting the DRI into HBI, and X is the total iron content of DRI (mass%).

[0036] 1 Heating DRI 2 Hopper 3 Forming roll 4, 4-1, 4-2 HBI 5 Crusher

Claims

1. A method for producing reduced iron briquettes, comprising hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component using a molding roll to produce briquettes, characterized in that the hot compression molding of the reduced iron mass is carried out by changing the rotation speed of the molding roll and / or the gap between the molding rolls depending on the T.Fe content of the pellet-shaped reduced iron.

2. The method for producing reduced iron briquettes according to claim 1, wherein the rotation speed of the molding rolls is changed to be slower and / or the gap between the molding rolls is changed to be smaller as the T.Fe content decreases.

3. The method for producing reduced iron briquettes according to claim 1 or 2, wherein the pellet-shaped reduced iron contains less than 85 mass% of T.Fe.

Images