Method for manufacturing reduced iron briquettes

Abstract

In the briquetting of reduced iron by hot forming, a method for manufacturing a reduced iron briquette capable of improving the apparent density and strength is proposed. The method for manufacturing a reduced briquette of the present invention is a method for manufacturing a reduced iron briquette in which a reduced iron aggregate composed of pelletized reduced iron containing an iron component is hot-compression molded by a molding roll to form briquettes, and according to the amount of T.Fe in the pelletized reduced iron, the rotational speed of the molding roll and / or the gap between the molding rolls is changed to perform hot-compression molding on the reduced iron aggregate. As a preferred embodiment, as the gangue component ratio increases, the rotational speed of the molding roll is changed to be slower and / or the gap between the molding rolls is changed to be smaller.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing reduced iron briquettes for obtaining reduced iron briquettes by hot forming.

Background Art

[0002] As a charging material capable of addressing the issues on both sides of high milling ratio operation orientation and CO2 emission reduction, hot briquetted iron (hereinafter also referred to as HBI) has attracted attention. HBI is a molded product produced by hot compressing direct reduced iron (hereinafter also referred to as DRI). DRI has a porous structure in which oxygen in the oxide (FexOy) inside the object is removed by a reduction reaction. Since DRI has a higher proportion of total Fe (T.Fe) and a larger specific surface area compared to before reduction, it has high reactivity. When stored in an oxygen atmosphere such as the atmosphere, it reacts with oxygen and leads to heat generation and ignition due to oxidation heat. Therefore, when storing in the state of DRI, it is desirable to store it under an inert gas atmosphere (for example, nitrogen gas), and there were issues with storage.

[0003] As a countermeasure against the storage issues of this DRI, there is the conversion of DRI to HBI. By converting to HBI, in the hot temperature range where it is easier to process compared to normal temperature, while crushing the internal pores of DRI, the voids between DRI are crushed, and the specific surface area is reduced to lower the reactivity and reduce the risk of heat generation and ignition. Conventionally, as technologies for HBI production, the technologies described in Patent Document 1 and Patent Document 2 are known.

[0004] Patent Document 1 discloses a technique for manufacturing HBI with high strength and weather resistance suitable as a charging material for a blast furnace by setting the average C (Carbon) content in the surface portion and the central portion to a predetermined value. Further, Patent Document 2 discloses a molten iron production apparatus and a molten iron production method for high-temperature agglomeration of reduced iron powder and firing auxiliary materials.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent No. 5059379 Gazette Patent Document 2 Japanese Patent No. 4202326 Gazette Summary of the Invention Problems to be Solved by the Invention

[0006] However, the technique described in Patent Document 1 is a method for manufacturing HBI having low cost, high strength, and weather resistance, and defines the average C content in the surface and interior of DRI. Therefore, high strength can be achieved, but there is no mention of high density. Further, the technique described in Patent Document 2 defines the optimum manufacturing conditions at the time of charging an electric furnace or a blast furnace. Patent Document 2 discloses the desired particle size distribution of HBI (lump) immediately before charging an electric furnace or a blast furnace after DRI molding. However, there is no disclosure of any specific means for realizing the desired particle size distribution. Therefore, with the technique described in Patent Document 2, high densification of HBI itself is not necessarily achieved, and risks in long-distance transportation remain.

[0007] The present invention has been made in view of such circumstances, and an object thereof is to propose a method for manufacturing a reduced iron briquette capable of improving the apparent density and strength in the briquetting of reduced iron by hot forming. Means for Solving the Problems

[0008] The method for manufacturing a reduced iron briquette of the present invention is a method for manufacturing a reduced iron briquette in which a reduced iron population composed of pelletized reduced iron containing an iron component is hot compression molded by a molding roll to form a briquette, and according to the T.Fe amount of the pelletized reduced iron, the rotational speed of the molding roll and / or the gap between the molding rolls is changed to perform hot compression molding on the reduced iron population. It is a method for manufacturing a reduced iron briquette, characterized by this.

[0009] In the method for manufacturing a reduced iron briquette according to the present invention configured as described above, (1) changing so as to slow down the rotational speed of the molding roll and / or changing so as to reduce the gap between the molding rolls as the T.Fe amount decreases; (2) the T.Fe amount contained in the pelletized reduced iron is less than 85 mass%; are considered to be more preferable solutions.

Advantages of the Invention

[0010] According to the method for manufacturing a reduced iron briquette of the present invention, by changing the rotational speed of the molding roll or the gap between the molding rolls according to the T.Fe amount of the pelletized reduced iron in the reduced iron population and performing hot compression molding on the reduced iron population, it is possible to obtain a reduced iron briquette capable of improving the apparent density and strength.

Brief Description of the Drawings

[0011]

Figure 1

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be specifically described. Note that the following embodiments illustrate devices and methods for embodying the technical idea of the present invention, and do not specify the configuration to the following. That is, various changes can be made to the technical idea of the present invention within the technical scope described in the claims.

[0013] <Regarding the Development Goals in the Method for Manufacturing the Reduced Iron Briquette of the Present Invention> For the marine transportation of HBI, there are international regulations (IMSBC: International Maritime Solid Bulk Cargoes), and it is necessary to satisfy "apparent density of 5.0 g / cm 3 or more and a forming temperature of 650°C or more". This point is one of the important development indicators in establishing the technology of HBI.

[0014] Figure 1 is a conceptual diagram showing the relationship between the HBI porosity and the HBI apparent density according to the raw material grade. It has been found that there is a negative correlation between the HBI porosity and the HBI apparent density. HBI formed from reduced iron of ordinary-grade iron ore (T.Fe amount of about 90 mass%) is a graph assumed from commercially available HBI examples A, B, and C that are on the market as commercial products. They have an HBI porosity of 27% or less and a target value of the apparent density standard of IMSBC (5.0 g / cm 3) has been achieved. In the case of low-grade ore, compared with normal-grade ore, the ratio of gangue components (CaO, Al2O3, SiO2, MgO) in DRI is higher, and the amount of T.Fe (the ratio of Fe component in DRI) is lower. Since the true density of gangue components is lower than that of iron, the density of HBI tends to decrease as the grade deteriorates. In the case of low-grade ore and even lower-grade ore, if the porosity cannot be made smaller than that of normal-grade ore, the apparent density of the development target cannot be achieved. Therefore, in establishing the compaction technology, it is important to determine the necessary molding conditions (molding temperature, molding pressure) according to the ore grade (T.Fe).

[0015] In addition, in FIG. 1, the graphs of low-grade ore and even lower-grade ore are graphs obtained by calculation for examples in which the amount of T.Fe is reduced by a certain amount with respect to the actual graph of normal-grade ore (T.Fe amount of about 90 mass%). The amount of T.Fe in both low-grade ore and even lower-grade ore is less than 85 mass% of T.Fe. In FIG. 1, the target apparent density of HBI can be achieved by setting the HBI porosity to 20% or less in the case of low-grade ore and 15% or less in the case of even lower-grade ore. Also, the relationship between the amount of T.Fe and the amount of gangue components in normal-grade ore and low-grade ore is shown in FIG. 2. As shown in FIG. 2, it can be seen that the ratio of gangue components varies according to the grade of DRI. Specifically, it can be seen that as the grade of DRI decreases, the amount of T.Fe decreases and the ratio of gangue components increases.

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

[0017] <Regarding the measurement method of T.Fe amount> Here, prior to the description of the method and apparatus for manufacturing the reduced iron briquette of the present invention, the measurement method of the amount of T.Fe will be described. First, a predetermined amount of the sample is measured and decomposed and solubilized by either of the following methods (a) and (b). (a) Decompose with hydrochloric acid in the presence of tin(II) chloride and filter. Treat the residue with sulfuric acid and hydrofluoric acid, melt with potassium disulfate, and combine with the filtrate. (b) Melt with sodium carbonate and sodium peroxide, dissolve the melt in warm water, filter the precipitate, and dissolve in hydrochloric acid.

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

[0019] <Regarding the method for manufacturing the reduced iron briquette of the present invention> In view of the above development goals, the present invention is characterized by changing the rotational speed of the molding roll and / or the gap between the molding rolls according to the raw material quality, particularly the amount of T.Fe, in order to improve the apparent density and strength of HBI, and solves the above problems. All of these are conditions on the briquette machine side, and are methods independent of the method of keeping the constituent chemical components within the upper and lower limit value ranges, and the establishment conditions can be evaluated only by the influence on the molding characteristics without relying on the control of the raw material properties. Note that the "high density" in this patent is relative based on the apparent density of commercial HBI, and commercial HBI means that the apparent density is 5.0 g / cm 3 is defined as above.

[0020] Figure 3 is a schematic diagram for explaining an embodiment of the apparatus configuration for implementing the method for manufacturing the reduced iron briquette of the present invention. In an embodiment of the apparatus configuration of the present invention shown in Figure 2, the heated DRI1 at the molding temperature is charged into the hopper 2. The heated DRI1 charged into the hopper 2 is compression-molded by the molding roll 3 to become HBI4. The obtained HBI4 is charged into the crusher 5.

[0021] The heated DRI1 is put into the hopper 2 and supplied in a manner that it is pushed into the molding roll 3 by the rotation of the screw feeder. The molding roll 3 is composed of a pair of molding rolls with the same diameter, and on the outer peripheral surface of the molding roll 3, pocket portions in the shape of the molded product are engraved. The heated DRI1 pushed in from the hopper 2 is sequentially loaded into the pocket portions, and by the rotation of the molding roll, the molding roll 3 applies pressure to the heated DRI1 and compresses it. Due to continuous raw material supply and synchronous rotation of the molding rolls, HBI4 corresponding to the production speed (roll rotation speed) is generated. The HBI4 immediately after molding is molded in a state where the individuals are connected to each other. Thereafter, the connected HBI4 is separated into individual pieces by the crusher 5.

[0022] For the stable production of the molded product, it is necessary to establish appropriate production conditions in the briquetting machine. In the briquetting machine, the molding (raw material) temperature, molding pressure, roll rotation speed, pocket shape, and roll gap are generally known as parameters. In the present invention, in order to efficiently manufacture high-density HBI, the rotation speed of the molding roll and / or the gap between the molding rolls is changed according to the ratio of the gangue component in the pelletized reduced iron group to be compression-molded.

[0023] <Regarding the rotation speed of the molding roll> The rotational speed of the forming roll affects the ease of solidification of the formed product. For example, when the forming roll is rotated faster than the reference speed, the contact time between the roll surface and the raw material becomes shorter compared to the reference rotational speed, making it difficult to apply the load (pressure) required for a smaller porosity. Figure 4 is a schematic diagram for explaining the case where the apparent density of the reduced iron briquette fails to reach the development target. As in this embodiment, as HBI4, HBI4-1 in which the apparent density of the reduced iron briquette reaches the development target and HBI4-2 in which the apparent density of the reduced iron briquette fails to reach the development target are generated after compression molding by the forming roll. Therefore, in the present invention, by setting the rotational speed of the forming roll slower than the normal reference rotational speed and increasing the contact time compared to the conventional reference rotational speed, the apparent density of the formed HBI4 is increased.

[0024] <Regarding the gap between the forming rolls> When the gap between the forming rolls changes, the number of DRI entering between the pocket rolls changes. The forming pressure applied to each DRI also changes. By reducing the gap between the forming rolls, the forming pressure per DRI particle can be increased, and the apparent density of the HBI can be increased. Figures 5(a) and (b) are schematic diagrams for explaining examples of changing the gap between the forming rolls in the method for manufacturing the reduced iron briquette of the present invention. Figure 5(a) shows an example where the gap between the forming rolls is at the reference roll position in normal operation, and as shown in Figure 4, there is HBI4-2 in which the apparent density of the reduced iron briquette fails to reach the development target. Figure 5(b) shows an example where the gap between the forming rolls is changed to be narrower than the reference roll position in Figure 5(a), and there is no HBI4-2 in which the apparent density of the reduced iron briquette fails to reach the development target, and only HBI4-1 in which the apparent density of the reduced iron briquette reaches the development target exists. At this time, there is a limit to shortening the roll gap. If it is shortened too much, internal cracks will occur in the formed product due to excessive pressure, and conversely, there is a drawback that the strength decreases. Therefore, an appropriate forming pressure magnitude is desirable.

[0025] In the above description, the influence of the change in the rotational speed of the molding roll and the influence of the change in the gap between the molding rolls were separately described. In addition to separately changing the rotational speed of the molding roll and the gap between the molding rolls as described above, it goes without saying that the present invention can also be achieved when both the rotational speed of the molding roll and the gap between the molding rolls are changed simultaneously.

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

[0027] Incidentally, the present invention is particularly effective when the raw material has a lower grade. Here, the "low-grade raw material" is, for example, pelletized reduced iron containing an iron component with a T.Fe content of less than 85 mass%. Alternatively, pelletized reduced iron with a T.Fe content of 83 mass% or less than 80 mass%, which has a lower iron component content than that, may be used as the "low-grade raw material". Alternatively, the first raw material before it becomes pelletized, with a T.Fe content of 63 mass% or less, may be defined as the "low-grade raw material".

Example

[0028] Hereinafter, the preconditions for DRI·HBI are assumed. ·DRI particle weight: 5.0 g / particle ·DRI particle diameter: Φ10 - 15 mm / particle ·HBI dimensions: (long side 100 mm × short side 50 mm × thickest part 30 mm) / piece ·HBI shape: pillow type ·HBI weight: 500 g / piece Since the total amount of DRI loaded per pocket becomes one HBI, one HBI is composed of (500 g / piece) / (5.0 g / particle) = 100 particles / piece of DRI.

[0029] However, the porosity inside the molded DRI that constitutes the HBI and the void ratio between the DRI pieces 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 (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 Fig. 6(a) and (b), when the reference rotation speed of the molding roll is 10 rpm, as shown in Fig. 6(a), the porosity of the molded HBI is 20%. And, as shown in Fig. 6(b), at a porosity of 20%, the apparent density is the target value of 5.0 g / cm. 3 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 (b) are graphs showing the relationship between porosity and gap between 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 (b), when the reference value of the gap between 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 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 to convert that DRI into HBI. Table 1 below summarizes the total iron content and the HBI porosity required to convert that DRI into HBI for five sample DRIs.

[0033]

Table 1

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

[0035] Also, according to the graph in Figure 8, the relationship between the T.Fe content of DRI and the HBI porosity required when converting the DRI into HBI can be formulated by the following formula (1). Y = 1.0062X - 68.338 ··· Formula (1) Y: HBI porosity required when converting into HBI (%) X: T.Fe content of DRI (mass%)

Explanation of Reference Signs

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

Claims

1. 1. A method for producing reduced iron briquettes, comprising hot compression molding a reduced iron mass composed of pelletized reduced iron containing an iron component using a molding roll to produce briquettes, the method comprising the steps of: changing a rotation speed of the molding roll and / or a gap between the molding rolls in accordance with a T.Fe content of the pelletized reduced iron, and performing hot compression molding on the reduced iron mass.

2. 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.

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