Method and apparatus for manufacturing reduced iron briquette

Abstract

The present invention provides a method and an apparatus for manufacturing reduced iron briquettes that reuse DRI, fine powder, or the like which failed to be compacted into HBI, and that make it possible to expect improvement of yield of an iron source compared with a related art. A method for producing reduced iron briquettes according to the present invention comprises hot compression molding and briquetting reduced iron clusters composed of pellet-shaped reduced iron containing an iron component, wherein a reduced iron-derived powder is reheated, and the reheated reduced iron-derived powder is returned to the reduced iron clusters. An apparatus for producing reduced iron briquettes according to the present invention is for producing reduced iron briquettes by hot compression molding reduced iron clusters composed of pellet-shaped reduced iron containing an iron component, the apparatus comprising: sieve equipment for sieving the manufactured reduced iron briquettes into reduced iron briquettes as a product and a reduced iron-derived powder that is not the product; and a reheating facility for reheating the reduced iron-derived powder that is not the product and returning the reheated reduced iron-derived powder to the reduced iron clusters.

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 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 eliminated in the hot temperature range where it is easier to process compared to room temperature, and the specific surface area is reduced, thereby lowering reactivity and reducing the risk of heat generation and fire. Patent Document 1 discloses a technology for producing the above-mentioned HBI, which reuses the DRI and fine powder that cannot be molded into HBI and is expected to improve the yield of the iron source.

[0004] Australian Patent No. 2002301887 (AU 2002301887 B2)

[0005] Usually, during the molding and compression process of HBI, DRI that has not been fully converted into HBI and powder derived from DRI generated during the compression of DRI are generated as undersize during molding. In the technology described in Patent Document 1, the powder derived from DRI generated as undersize during molding is returned to DRI and reused. However, there is a problem in that if the powder derived from DRI is returned to DRI and reused indiscriminately, a sufficient bonding effect between the DRI and the powder derived from DRI is not exerted, and the yield is not necessarily improved.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to propose a method and an apparatus for manufacturing reduced iron briquettes that are expected to improve the yield of iron sources compared to conventional methods by reusing DRI, fine powder, and the like that are generated when the briquettes cannot be fully molded into HBI.

[0007] The method for producing reduced iron briquettes of the present invention is a method for producing reduced iron briquettes by hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component into briquettes, characterized in that powder derived from the reduced iron is reheated and the reheated powder derived from the reduced iron is returned to the reduced iron mass.

[0008] In the method for producing reduced iron briquettes according to the present invention configured as described above, the following are considered to be more preferable solutions: (1) the powder derived from reduced iron is powder derived from reduced iron generated by hot compression molding of the reduced iron pellets; (2) the powder derived from reduced iron has a T.Fe content (mass %) that is approximately the same as that of the reduced iron pellets, and the T.Fe content is 70 mass % or more; (3) the powder derived from reduced iron is returned to the reduced iron mass before the start of compression molding of the reduced iron pellets; (4) the powder derived from reduced iron is reheated to a temperature of 800°C or more and then returned to the reduced iron mass; (5) the particle size of the powder derived from reduced iron is 5 mm or less in terms of its long side; and (6) the T.Fe content of the reduced iron pellets is less than 85 mass %.

[0009] 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: a sieving device that sieves the manufactured reduced iron briquettes into finished reduced iron briquettes and powder derived from reduced iron other than the finished product; and a reheating device that reheats the powder derived from reduced iron other than the finished product and returns the reheated powder derived from reduced iron to the reduced iron mass.

[0010] According to the method and apparatus for producing reduced iron briquettes of the present invention, DRI and fine powder that are generated when reduced iron is hot-briquetted into HBI can be reused, and this is expected to improve the yield of iron source compared to conventional methods.

[0011] 1 is a schematic diagram illustrating an embodiment of an apparatus configuration for carrying out a method for producing reduced iron briquettes according to the present invention; 2 is a diagram illustrating the effect of returning powder derived from reheated reduced iron to a reduced iron mass in the present invention; 3 is a graph illustrating a change in yield with respect to the reheating temperature of powder derived from reduced iron in the present invention;

[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] <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.

[0014] 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.

[0015] <Regarding the manufacturing method and manufacturing apparatus for reduced iron briquettes of the present invention> Fig. 1 is a schematic diagram for explaining one embodiment of an apparatus configuration for carrying out the manufacturing method for reduced iron briquettes of the present invention. The embodiment of the apparatus configuration of the present invention shown in Fig. 1 comprises a reduction facility 1, a hopper feeder 2, twin briquette rolls 3 having the same diameter, and a crusher 4.

[0016] In the example shown in Fig. 1 , hot reduced iron 6 (hot DRI) reduced in reduction equipment 1 is sequentially supplied as reduced iron lumps to a hopper feeder 2 directly below. The supplied reduced iron lumps are hot-molded by twin briquetting rolls 3 of the same diameter to produce reduced iron briquettes 7 (HBI). Because the produced HBIs 7 are formed by connecting a plurality of HBIs 7 due to the structure of the twin briquetting rolls 3, they are separated into individual units by a crusher 4.

[0017] The present invention is characterized in that the manufacturing apparatus having the above-described configuration further includes a sieving facility 10 and a reheating facility 5. The sieving facility 10 sieves the manufactured HBI 7 into finished HBI 8 and powder 9 derived from reduced iron other than the finished product. The reheating facility 5 reheats the powder 9 derived from reduced iron other than the finished product and returns the reheated powder 9 derived from reduced iron to the mass of reduced iron in the hopper feeder 2.

[0018] During molding, the amount of HBI 8 that becomes the finished product, DRI that did not become HBI 8 during compression molding, and powder derived from DRI generated during compression are constantly generated as reduced iron-derived powder 9 under the sieve of the sieving equipment 10. Furthermore, the start and end of compression molding are in a non-steady state of molding, which differs from the steady state in which molding is stable. For example, at the start of molding, a reduced iron mass consisting of pelletized hot reduced iron 6 enters the pockets on the surface of the twin briquette roll 3. However, because the twin briquette roll 3 is rotating, a portion of the reduced iron mass is not filled enough to receive sufficient molding pressure from the twin briquette roll 3, and some of the reduced iron mass inevitably passes through the twin briquette roll 3. At the end of molding, there is no guarantee that a sufficient amount of reduced iron mass will be introduced into the pockets, and some of the reduced iron mass will not receive sufficient molding pressure from the twin briquette roll 3. Therefore, reduced iron-derived powder 9 is generated, consisting of DRI that did not become HBI 8 during compression molding and powder derived from DRI generated during compression.

[0019] The reduction equipment 1 corresponds to, for example, a rotary hearth furnace or a direct reduction furnace. The hot reduced iron 6 is a pellet-like material with a diameter of approximately 10 to 15 mm per pellet, and is heated to, for example, approximately 700°C. The hot reduced iron 6 is fed into a hopper feeder 2 as a mass of reduced iron, and is forced into the twin briquette roll 3 by the rotation of a screw feeder provided in the hopper feeder 2.

[0020] The twin briquetting roll 3 is composed of a pair of molding rolls with the same diameter, and pockets in the shape of the briquettes are carved into the outer periphery of the molding rolls. Hot reduced iron 6 is loaded into the pockets one after another, and as the molding rolls rotate, they apply pressure to compress the hot reduced iron 6. Continuous raw material supply and synchronous rotation of the molding rolls generate an amount of HBI corresponding to the production rate (molding roll rotation speed). HBI 7 is continuously produced at the outlet of the molding rolls. Immediately after molding, HBI 7 is molded in a state where individual HBIs are connected to each other, rather than in a state where individual HBIs are separated. Therefore, the HBIs are separated into individual HBIs by a crusher 4. The crusher 4 separates the so-called connected HBIs 7 into small, easily handleable HBIs. The separated HBIs are used according to their intended purpose. For example, they are transported long distances and supplied to blast furnaces, electric furnaces, and melting furnaces.

[0021] In the present invention, in order to effectively utilize the iron source and improve the yield in the apparatus for producing reduced iron briquettes, the powder 9 derived from reduced iron, which is composed of DRI and powder other than the finished product, is reheated by the reheating equipment 5 and returned to the mass of reduced iron composed of hot reduced iron 6 in the subsequent hopper feeder 2. The reheating equipment 5 of the present invention will be described in detail below.

[0022] The reheating equipment 5 is characterized by reheating the reduced iron-derived powder 9, which is composed of particles and powder other than the finished product, to the "sintering temperature." In conventional reduced iron briquette production, the non-finished product is returned to the hopper feeder 2 without being reheated. This is because even if the DRI and powder that constitute the reduced iron-derived powder 9 are returned to the reduced iron mass with the residual heat from molding, a certain degree of yield improvement can be expected due to bonding with the original reduced iron mass through thermoplastic deformation.

[0023] However, if the powder 9 derived from reduced iron is returned to the reduced iron mass without reheating as in the conventional method, the sintering effect acting as a binder does not necessarily occur. Generally, briquettes made from raw materials other than reduced iron are mixed with a chemical binder (bonding promoter) at a temperature of, for example, room temperature to 300°C, rather than being molded at high temperatures of 650°C or higher as in the case of reduced iron. If the temperature of the hot reduced iron 6 at the outlet of the reduction equipment 1 is below 800°C, the temperature of the powder 9 derived from unfinished reduced iron is also below 800°C. Therefore, even if the powder 9 derived from unfinished reduced iron at a temperature below 800°C is added to the reduced iron mass without reheating, the sintering effect does not occur.

[0024] In the present invention, the powder 9 derived from reduced iron outside the product, which has been sieved by the sieving equipment 10, is reheated by the reheating equipment 5 to a temperature substantially equal to the temperature of the DRI during molding, for example, a temperature of 800°C or higher, and then returned to the reduced iron mass. Therefore, sintering can occur between the powder 9 derived from reduced iron outside the product and the hot reduced iron 6, regardless of whether the molding temperature is higher or lower than 800°C or whether the temperature of the powder 9 derived from reduced iron outside the product decreases over time after molding.

[0025] FIG. 2 is a diagram illustrating the effect of returning powder derived from reheated reduced iron to the reduced iron mass in the present invention. As shown in FIG. 2 , when powder 9 derived from non-product reduced iron is returned to hot reduced iron 6 as in the conventional method, the sintering effect does not occur between the powder 9 and the hot reduced iron 6, and the shape of the hot reduced iron 6 remains unchanged before and after the powder 9 is returned. Therefore, in the conventional method, the surface activity of the hot reduced iron 6 depends on the surface area of ​​the hot reduced iron 6. In contrast, in the present invention, the powder 9 derived from the reheated non-product reduced iron aggregates around the hot reduced iron 6 in the subsequent reduced iron mass due to the sintering effect. Therefore, in the present invention, the specific surface area of ​​the hot reduced iron 6 increases, which enhances the reactivity of the hot reduced iron 6 and promotes aggregation and fusion, thereby reducing the generation of non-product powder. From this perspective, the present invention can achieve an improved yield of iron source compared to the conventional method.

[0026] The reheating equipment 5 used in the present invention may be, for example, a rotary kiln (the schematic diagram in FIG. 1 also follows this model). The inner wall of the heating section of the reheating equipment 5 is generally equipped with stirring blades or spiral blades that stir up the raw materials. The rotation allows the raw materials to be heated evenly during heating. After heating, the raw materials can be discharged from the furnace (into the hopper feeder 2) at any desired timing. The powder 9 derived from the non-product reduced iron reheated in the reheating equipment 5 is preferably returned as synchronized as possible with the drop of the hot reduced iron 6 discharged from the reduction equipment 1 into the hopper feeder 2. If the powder 9 is introduced asynchronously, a layer of different particle sizes will be formed between the original reduced iron mass and the powder 9 derived from the non-product reduced iron. In this state, although sintering of the non-product particles is possible, the effect of the particle size difference cannot be fully utilized.

[0027] In the present invention, the reheating equipment 5 is not limited to the above-described example in which the powder 9 derived from reduced iron, which has been intermittently reheated by the rotary kiln, is returned to the hot reduced iron 6 in the hopper feeder 2. For example, equipment in which the powder 9 derived from reduced iron, which has been continuously reheated, is returned to the hot reduced iron 6 in the hopper feeder 2 may also be used.

[0028] 1 described above, the reduced iron-derived powder 9 outside the finished product sieved from the produced HBI 7 by the sieving equipment 10 is reheated and returned, but the present invention is not limited to this. For example, the present invention also includes an example in which the reduced iron-derived powder 9 is prepared in advance and used to improve the yield of the entire apparatus, including the apparatus for manufacturing reduced iron briquettes as a part thereof.

[0029] 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 less than 85 mass% total iron (T.Fe). Alternatively, pelletized reduced iron containing less than 83 mass% or less than 80 mass% total iron (T.Fe) may be defined as the "low-quality raw material." Alternatively, the initial raw material before being pelletized, having a T.Fe content of 63 mass% or less, may be defined as the "low-quality raw material."

[0030] Using the reduced iron briquette manufacturing apparatus shown in FIG. 1 , continuous operation was performed to produce hot reduced iron 6 having a particle size distribution volume zone of approximately 10 mm in diameter at an outlet temperature of 700°C from the reduction equipment 1. The gap between the molding rolls of the twin briquette rolls 3 was 1 mm, the molding roll rotation speed was 15 rpm, and the molding pressure was 120 kN / cm. After molding, the molded HBI 7 was passed through a sieving equipment 10 set to a particle size of 5 mm to screen out powder 9 derived from reduced iron that had a particle size of 5 mm or less. The temperature of the powder 9 derived from reduced iron that had not been produced was lowered to below the outlet temperature of the reduction equipment 1 by heat removal from the wall surface of the hopper feeder 2 or the surface of the twin briquette rolls 3, air cooling, or water cooling. Note that, after passing through the sieving equipment 10, the powder 9 derived from reduced iron that had a long side of 5 mm or less was obtained, but the shape was not particularly considered.

[0031] In preparation for the next opportunity to mold a mass of reduced iron consisting of the subsequent hot reduced iron 6, the sieved powder 9 derived from the non-finished reduced iron was fed into the reheating equipment 5 and reheated to 850°C by a heater having a rotary heater in the reheating equipment 5. After reheating, the reheated powder 9 derived from the reduced iron was kept warm in the heater until the reduction of the currently operating reduced iron was completed. Thereafter, the powder 9 derived from the non-finished reduced iron heated to 850°C was fed directly from the reheating equipment 5 to the hopper feeder 2 at predetermined intervals so that the powder 9 derived from the non-finished reduced iron heated to 850°C was evenly mixed with the mass of reduced iron consisting of the subsequent hot reduced iron 6 at 700°C. Here, the feeding of the powder 9 derived from the reheated reduced iron by the reheating equipment 5 utilized the falling of the powder 9 derived from the reduced iron by its own weight due to the tilting of the reheating equipment 5. Since it is assumed that the amount of the product is generally greater than the amount of the non-products for a unit throughput of the reduced iron mass, it is not preferable to continuously add the non-products to the product. Therefore, it is preferable to add the non-products at a predetermined cycle so that the reduced iron mass consisting of the hot reduced iron 6 and the powder 9 derived from the reheated reduced iron are mixed evenly.

[0032] Figure 3 is a graph illustrating the change in yield with the reheating temperature of the reduced iron-derived powder in the present invention. As shown in Figure 3, the present invention example in which the hot-reduced iron 6 was reheated achieved a higher yield than the conventional example (reheating temperature 0°C) in which the hot-reduced iron 6 was not reheated. Note that, as mentioned above, when the reheating temperature (re-addition temperature) is 800°C or higher, the reduced iron-derived powder 9, which has been reduced in size outside the finished product, is surface-activated by its increased specific surface area and fuses to the pellet surfaces of the reduced iron 6, facilitating the aggregation of the fused pellet particles. Therefore, when the reheating temperature is 800°C or higher, the yield can be further improved compared to when the reheating temperature is lower than 800°C.

[0033] According to the present invention, the yield can be improved by reheating the powder derived from the reduced iron outside the finished product. Furthermore, in order to maintain a high yield of 95% or more, it is important to reheat the powder DRI to a temperature of 800°C or higher.

[0034] 1 Reduction equipment 2 Hopper feeder 3 Twin briquette roll 4 Crusher 5 Reheating equipment 6 Hot reduced iron (DRI) 7 Reduced iron briquette (HBI) 8 HBI (as a finished product) 9 Powder (derived from reduced iron in an unfinished product) 10 Sieving equipment

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 into briquettes, the method comprising reheating powder derived from the reduced iron and returning the reheated powder derived from the reduced iron to the reduced iron mass.

2. The method for producing reduced iron briquettes according to claim 1, wherein the powder derived from reduced iron is powder derived from reduced iron produced by hot compression molding of the pellet-shaped reduced iron.

3. The method for producing reduced iron briquettes according to claim 1, wherein the powder derived from reduced iron has a T.Fe content (mass%) similar to that of the pellet-shaped reduced iron, and the T.Fe content is 70 mass% or more.

4. The method for producing reduced iron briquettes according to claim 1, wherein the powder derived from the reduced iron is returned to the reduced iron mass before the start of compression molding of the pellet-shaped reduced iron.

5. The method for producing reduced iron briquettes according to claim 1, characterized in that the powder derived from the reduced iron is reheated to a temperature of 800°C or higher before being returned to the reduced iron mass.

6. The method for producing reduced iron briquettes according to claim 1, wherein the powder derived from reduced iron has a particle size of 5 mm or less on the long side.

7. The method for producing reduced iron briquettes according to any one of claims 1 to 6, wherein the pellet-shaped reduced iron contains less than 85 mass% of TFe.

8. A manufacturing apparatus for manufacturing reduced iron briquettes by hot compression molding a reduced iron mass composed of pellet-shaped reduced iron containing an iron component, the manufacturing apparatus comprising: a sieving device for sieving the manufactured reduced iron briquettes into reduced iron briquettes as finished products and powder derived from reduced iron other than the finished product; and a reheating device for reheating the powder derived from reduced iron other than the finished product and returning the reheated powder derived from reduced iron to the reduced iron mass.

Images