Method and device for producing reduced iron briquettes

Abstract

Provided is a method for producing reduced iron briquettes enabling improvement of apparent density and strength in briquetting of reduced iron by hot molding. In the method for producing reduced iron briquettes of the present invention, when groups of reduced iron composed of reduced-iron pellets containing an iron component are subjected to hot compression molding, a control step for controlling the particle size distribution of the groups of reduced iron is performed, and then hot compression molding is performed on the groups of reduced iron having the particle size distribution thus controlled. A device for producing reduced iron briquettes of the present invention includes: a reduced iron production facility for producing reduced-iron pellets containing an iron component to form the groups of reduced iron; a pulverizing facility for pulverizing the groups of reduced iron; a classification facility for sieving the groups of pulverized reduced iron by sieves having a plurality of mesh sizes; a mixing facility for mixing the groups of reduced iron having a plurality of levels of grain size after the sieving so as not to be biased for each particle size in a hot compression molding mold; and a reheating facility for heating the mixed groups of reduced iron to a molding temperature required for the hot compression molding.

Description

Method and apparatus for manufacturing reduced iron briquettes

[0001] The present invention relates to a method and an apparatus for producing reduced iron briquettes (hot-formed iron) by hot forming.

[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. 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 densification. 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 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 provide a method and an apparatus for manufacturing 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 characterized in that, when hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component, a control step of controlling the particle size distribution of the reduced iron mass is carried out, and then the hot compression molding of the reduced iron mass with the controlled particle size distribution is carried out.

[0009] In the method for producing reduced iron briquettes according to the present invention configured as described above, (1) the control step includes a reheating step of heating the reduced iron mass to a molding temperature required for hot compression molding; (2) the control step includes a crushing step of crushing the reduced iron mass, a classification step of sieving the reduced iron mass crushed in the crushing step using a sieve having a plurality of sieve openings, and a mixing step of mixing the reduced iron mass having a plurality of particle sizes after sieving in the classification step so as not to be unevenly distributed among particle sizes in the hot compression molding mold, and the reheating step is a step of heating the reduced iron mass mixed in the mixing step to a molding temperature required for hot compression molding; (3) the mixing step is a step of combining the reduced iron having a plurality of particle sizes after sieving in the classification step into one reduced iron mass, and then introducing the reduced iron mass into a rotary container and rotating the container for a certain period of time to mix the reduced iron mass. (4) The control step is a step of adjusting the reference particle size distribution of the reduced iron mass before crushing by a maximum peak height H Ａ and peak width W Ａ The particle size distribution of the reduced iron mass after crushing is defined as a maximum peak height H Ｂ and peak width W Ｂ When this is done, H Ａ >H Ｂ , and W Ａ <W Ｂ where the peak width W Ａ is the maximum peak value H Ａ The width at the height position where the value is half of the peak width W Ｂ is the maximum peak value H Ｂ (5) The reduced iron pellets contain less than 85 mass% of total iron, and the controlling step is performed by Ｂ >(1 / 2)H Ａ , and W Ｂ >2W Ａ It is considered that a more preferable solution is a step of controlling the particle size distribution so that the following relationship is satisfied:

[0010] Furthermore, the apparatus for manufacturing reduced iron briquettes of the present invention is an apparatus for manufacturing reduced iron briquettes by hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component, and is characterized by including: reduced iron manufacturing equipment that produces pellet-shaped reduced iron containing an iron component to form a reduced iron mass; crushing equipment that crushes the reduced iron mass; classification equipment that sieves the crushed reduced iron mass using a sieve having a plurality of meshes; mixing equipment that mixes the reduced iron mass of multiple particle sizes after sieving in a mold for the hot compression molding so as to prevent bias among particle sizes; and reheating equipment that heats the mixed reduced iron mass to a molding temperature required for hot compression molding.

[0011] According to the manufacturing method and manufacturing apparatus for reduced iron briquettes of the present invention, by performing hot compression molding on a mass of reduced iron whose particle size distribution has been controlled, it is possible to obtain reduced iron briquettes with improved apparent density and strength.

[0012] 1 is a graph showing one embodiment of the relationship between HBI apparent density and HBI porosity depending on the quality of raw material. FIG. 2 is a schematic diagram for explaining one embodiment of an apparatus configuration for carrying out the method for producing reduced iron briquettes of the present invention. FIG. 3 is a graph for explaining one embodiment of particle size control by crushing in the method for producing reduced iron briquettes of the present invention. FIG. 4 is a graph for explaining the relationship between particle size control and HBI apparent density in the method for producing reduced iron briquettes of the present invention.

[0013] 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.

[0014] <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.

[0015] 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 amount of T.Fe is low. Because gangue components have a lower true density than iron, the density of HBI tends to decrease as the grade deteriorates. For low-grade ore and even lower-grade ore, the target apparent density cannot be achieved unless the porosity is reduced compared to normal-grade ore. The graphs for low-grade ore and even lower-grade ore are calculated using examples in which the amount of T.Fe is reduced by a fixed amount from the actual graph for normal-grade ore (approximately 90% T.Fe by mass). The T.Fe amounts for both low-grade ore and even lower-grade ore are less than 85% T.Fe by mass. In Figure 1, the target apparent density of HBI 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.

[0016] <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.

[0017] 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.

[0018] <Regarding the Manufacturing Method and Apparatus for Reduced Iron Briquettes of the Present Invention> In view of the above development objectives, the present invention solves the above-mentioned problems by controlling the particle size distribution of a pellet-like material mass to be compacted prior to compaction in order to improve the apparent density and strength of HBI. Controlling particle size distribution is a physical property and is independent of methods for confining constituent chemical components within upper and lower limits. This is advantageous in that it allows evaluation based solely on the effects of compaction conditions on compaction characteristics, without relying on control of raw material properties. Furthermore, particle size distribution control methods, such as sieving, crushing, and pulverization, are relatively simple in terms of equipment configuration, and their introduction is not difficult. Note that, in the present invention, "high density" is a relative expression based on the apparent density of commercial HBI. Furthermore, commercial HBI refers to an apparent density of 5.0 g / cm. ３ This is defined as above.

[0019] FIG. 2 is a schematic diagram illustrating one embodiment of a manufacturing apparatus for implementing the method for manufacturing reduced iron briquettes of the present invention. The embodiment of the manufacturing apparatus of the present invention shown in FIG. 2 includes reduced iron production equipment 1, crushing equipment 2, classification equipment 3, mixing equipment 4, reheating equipment 5, hopper 7, compression molding rolls 8, and a crusher 10. Reduced iron aggregates composed of a plurality of pellet-shaped reduced irons produced in the reduced iron production equipment 1 are input as raw material into the crushing equipment 2. The crushing equipment 2, classification equipment 3, and mixing equipment 4 control the particle size distribution of the reduced iron aggregates. The reduced iron aggregates after particle size distribution control are heated in the reheating equipment 5 to become heated DRI 6 at the molding temperature. The heated DRI 6 is input into the hopper 7. The heated DRI 6 input into the hopper 7 is compression-molded by the compression molding rolls 8 to become HBI 9. The resulting HBI 9 is input into the crusher 10.

[0020] The reduced iron production equipment 1 is any type of reduced iron production equipment, such as a rotary hearth furnace or a direct reduction furnace. The reduced iron produced in the reduced iron production equipment 1 is a pellet-shaped material with a diameter of approximately 10-15 mm per pellet, and is operated at a temperature of approximately 700°C. The crushing equipment 2 crushes a portion of the pellet-shaped reduced iron aggregates, accompanied by deformation processing, to change the particle size distribution of the reduced iron aggregates before compression molding. Changing the particle size distribution in the crushing equipment 2 contributes to reducing the void ratio of the pellet-shaped reduced iron aggregates in the mold during compression molding. The process of controlling the particle size distribution includes a classification process using a classification equipment 3 with multiple sieve openings after crushing the pellet-shaped reduced iron aggregates with deformation processing. The classification equipment 3 determines the proportion of each particle size in the reduced iron aggregate crushed in the crushing equipment 2. An automatic classifier with multiple sieve openings can quantitatively determine the amount of crushed reduced iron present in each sieve opening. The process of controlling the particle size distribution includes a mixing process to prevent the reduced iron with multiple particle sizes after sieving by the classification equipment 3 from becoming unevenly distributed within the hot compression molding mold. The mixing equipment 4 is equipment for mixing the reduced iron after classification. In order to more thoroughly fill the voids within the molding mold in the subsequent molding, it is necessary to stir the reduced iron to a certain extent so that uneven particle size distribution does not occur when the reduced iron with each particle size determined by the classification equipment 3 is added back into a single group. The stirring method is, for example, to place the group into a rotary container such as a kiln and rotate it for a certain period of time.

[0021] The reheating equipment 5 reheats the reduced iron mixed in the mixing equipment 4. The mixed iron is controlled to a mass of reduced iron with the desired particle size distribution up to the mixing equipment 4. However, during this control process, the temperature of the mass of reduced iron drops from the reduction temperature in the reduced iron production facility 1, raising concerns that it may fall below the molding temperature (650°C). The particle size of each particle of reduced iron after crushing is smaller than that before crushing, allowing for a larger specific surface area, improving the efficiency of reheating. In other words, the significance of crushing and particle size distribution adjustment is particularly significant in hot molding. Additionally, the reheating equipment 5 is significant because it is located between crushing / sieving and molding, in that it can raise the temperature to the molding temperature even when the reduction temperature at the reduced iron production facility 1 is lower than the molding temperature.

[0022] The heated DRI 6 composed of the above is fed into a hopper 7 and is forced into a compression molding roll 8 by the rotation of a screw feeder. The compression molding roll 8 is composed of a pair of compression molding rolls 8 of the same diameter, and the outer surface of the compression molding roll 8 is engraved with pockets in the shape of the molded product. The heated DRI 6 pushed from the hopper 7 is sequentially loaded into the pockets, and as the compression molding roll 8 rotates, the compression molding roll 8 applies pressure to the heated DRI 6, compressing it. Continuous raw material supply and synchronous rotation of the compression molding roll 8 generate HBI 9 according to the production speed (roll rotation speed). HBI 9 is continuously produced at the outlet of the compression molding roll 8. Immediately after molding, the HBI 9 is molded in a state where the individual HBIs are connected to each other, rather than in a separated state. The HBI 9 is separated into individual pieces in a crusher 10. The disintegrator 10 separates the connected HBI 9 into HBI 9 pieces each having a size of, for example, approximately 100 x 50 x 30 mm. The separated HBI 9 pieces are used according to their intended purpose. For example, they are transported long distances and then supplied to an electric furnace or a melting furnace at their destination. In this way, the HBI 9 pieces are transported in a manner consistent with the "apparent density of 5.0 g / cm3" regulation for the marine transport of reduced iron. ３ It is possible to manufacture high density HBIs with the goal of "more than 100%."

[0023] In other words, according to the present invention, it is possible to accurately achieve a desired particle size distribution and efficiently achieve densification of HBI. In particular, more efficient densification of HBI may be achieved by sequentially performing the steps of crushing, sieving, mixing, reheating, and hot compacting.

[0024] 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.

[0025] 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.

[0026] However, the porosity inside the molded DRI and the void ratio between the DRIs that make up the HBI vary 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. It is important to reduce the pocket void ratio by controlling the particle size distribution and increase the number of DRIs loaded per pocket. As the number of DRIs increases, more large and small DRIs fill the pockets, and the size and shape of the pockets remain unchanged, making it possible to produce a higher-density HBI.

[0027] 3 is a graph for explaining one embodiment of particle size control by crushing in the method for producing reduced iron briquettes of the present invention. The particle size distribution before crushing is used as a reference, and the maximum peak height in the reference particle size distribution is expressed as H Ａ , the peak width is W Ａ The particle size distribution after crushing is also similar to H Ｂ , W Ｂ Define the peak width W Ａ is defined as the maximum peak height H ＡThe width was set at a height position where the value was half of the reference particle size distribution. As a representative example, the peak position was set to 12 mm, the particle size of the reduced iron, based on the particle size of the constituent pellets. By crushing before molding, the particle size of some of the reduced iron mass before crushing becomes smaller, and after crushing, the proportion of the peak in the reference particle size distribution (peak height) becomes lower compared to the reference, and the peak shifts to a position smaller than the reference 12 mm, and the width of the peak also becomes wider. In the case of Figure 3, it is shown that by crushing most of the pellet-like particle size Φ12 mm before crushing, the volume zone was reduced in diameter to about Φ8 mm. From the above, it can be seen that the control of particle size distribution is achieved by H Ａ >H Ｂ , W Ａ <W Ｂ It is clear that it is preferable to perform the process so as to satisfy the relationship:

[0028] When the pelletized reduced iron as a raw material is low-grade, the particle size distribution may be controlled so as to have a wider distribution. For example, when the T.Fe content of the pelletized reduced iron is less than 85 mass%, H Ｂ >(1 / 2)H Ａ , and W Ｂ >2W Ａ By controlling the particle size distribution in this way, it is possible to more efficiently achieve a high density of HBI.

[0029] Figure 4 is a graph illustrating the relationship between particle size control and HBI apparent density in the manufacturing method of reduced iron briquettes of the present invention. The results in Figure 4 show that the apparent density of HBI molded with the crushed particle size distribution can be expected to be approximately 10% higher than that of a standard commercial product. The apparent density was evaluated in accordance with ISO 15968: Direct reduced iron - Determination of apparent density and water absorption of hot briquette (HBI).

[0030] REFERENCE SIGNS LIST 1 Reduced iron manufacturing equipment 2 Crushing equipment 3 Classification equipment 4 Mixing equipment 5 Reheating equipment 6 Heating DRI 7 Hopper 8 Compression molding roll 9 HBI 10 Crusher

Claims

1. A method for producing reduced iron briquettes, characterized in that when hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component, a control process is carried out to control the particle size distribution of the reduced iron mass, and then hot compression molding is carried out on the reduced iron mass with the particle size distribution controlled.

2. The method for producing reduced iron briquettes according to claim 1, wherein the control step includes a reheating step of heating the reduced iron mass to a molding temperature required for hot compression molding.

3. The method for producing reduced iron briquettes described in claim 2, characterized in that the control process includes a crushing process for crushing the reduced iron mass, a classification process for sieving the reduced iron mass crushed in the crushing process using a sieve having multiple sieve holes, and a mixing process for mixing the reduced iron mass of multiple particle sizes after sieving in the classification process so that there is no bias in terms of particle size within the hot compression molding mold, and the reheating process is a process for heating the reduced iron mass mixed in the mixing process to a molding temperature required for hot compression molding.

4. The method for producing reduced iron briquettes described in claim 3, characterized in that the mixing process is a process in which reduced iron of multiple particle sizes after sieving in the classification process is combined into a single reduced iron mass, the reduced iron mass is then placed in a rotating container, and mixed by rotating for a certain period of time.

5. The control step is to adjust the reference particle size distribution of the reduced iron mass before crushing to a maximum peak height H Ａ and peak width W Ａ The particle size distribution of the reduced iron mass after crushing is expressed by a maximum peak height H Ｂ and peak width W Ｂ Then, H Ａ >H Ｂ , and W Ａ <W Ｂ The method for producing reduced iron briquettes according to claim 3, further comprising the step of controlling the particle size distribution so as to satisfy the relationship: Ａ is the maximum peak value H Ａ The peak width W Ｂ is the maximum peak value H Ｂ The width at the height position where the value is half of this.

6. The pellet-shaped reduced iron contains less than 85 mass% of T.Fe, and the control step includes: Ｂ >(1 / 2)H Ａ , and W Ｂ >2W Ａ The method for producing reduced iron briquettes according to any one of claims 1 to 5, further comprising controlling a particle size distribution so as to satisfy the relationship:

7. A manufacturing apparatus for producing reduced iron briquettes by hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component, comprising: a reduced iron production facility for producing pellet-shaped reduced iron containing an iron component to form a reduced iron mass; a crushing facility for crushing the reduced iron mass; a classification facility for sieving the crushed reduced iron mass through a sieve having a plurality of sieve openings; a mixing facility for mixing the reduced iron mass having a plurality of particle sizes after the sieving so as not to be biased according to particle size in a mold for the hot compression molding; and a reheating facility for heating the mixed reduced iron mass to a molding temperature required for hot compression molding.