System and Method

Abstract

The iron oxide concentration inside the melting furnace is stably controlled. [Solution] The system for recycling dust generated during the production process of steel products comprises a collection container 10 for storing the collected dust, a packing device 20 for weighing and packing the dust in the collection container 10, and an arc furnace into which the packed dust is fed.

Description

Technical Field

[0001] The present disclosure relates to a system and method for recycling dust generated in the production process of steel products.

Background Art

[0002] Japanese Patent Laid-Open No. 3-53029 (Patent Document 1) describes a method of reusing steel dust such as shot scale generated in the steelmaking process in an electric furnace.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In steel mills and steel casting plants, powder iron raw materials such as dust generated in the production process of steel products may be handled as melting materials in an electric furnace. Compared with iron scrap, which is the main raw material, the powder iron raw material often has a high iron oxide concentration. It is required to stably control the iron oxide concentration in the melting furnace.

[0005] The present disclosure proposes a technology that enables stable control of the iron oxide concentration in the melting furnace.

Means for Solving the Problems

[0006] According to an aspect of the present disclosure, a system for recycling dust generated in the production process of steel products is proposed. The system includes a recovery container for storing the recovered dust, a packing device for weighing and packing the dust in the recovery container, and an arc furnace into which the packed dust is charged.

[0007] In accordance with certain aspects of this disclosure, a method for recycling dust generated during the production of steel products is proposed. The method comprises the following steps: The first step is to collect and store the dust. The second step is to weigh and pack the dust. The third step is to feed the packed dust into an arc furnace. [Effects of the Invention]

[0008] According to this disclosure, the iron oxide concentration in the melting furnace can be stably controlled. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram illustrating the process of collecting dust into a collection container. [Figure 2] This is a schematic diagram illustrating the process of packing dust. [Figure 3] This is a schematic diagram illustrating the feeding of materials into an arc furnace. [Figure 4] This is a schematic diagram showing the state of a material melting inside an arc furnace. [Modes for carrying out the invention]

[0010] The embodiments will be described below with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated. In the drawings, some configurations may be omitted or simplified for the sake of explanation. It is also intended from the outset that any configuration may be extracted from the embodiments and combined in any way.

[0011] Figure 1 is a schematic diagram illustrating the process of collecting dust 1 in a collection container 10. Dust 1, which is generated during the production process of steel products, is, for example, scale shot dust generated by shot blasting heat-treated cast products. Scale shot dust is a mixture of scale (oxide film, mill scale) scraped off the surface of a product during shot blasting, and crushed abrasive material (shot), and its main component is finely pulverized iron oxide. The iron content of scale shot dust is, for example, 64%. Dust 1 is not limited to scale shot dust, but may also be welding slag, polishing residue, etc.

[0012] The dust collector 100 collects dust 1. The dust 1 collected by the dust collector 100 is collected in the collection container 10. The collection container 10 temporarily stores the collected dust 1. The collection container 10 has an inlet 11 at its top. Dust 1 that falls from the dust collector 100 is collected into the collection container 10 through the inlet 11.

[0013] The collection container 10 comprises a hopper section 12 and a discharge port 13. Dust 1, which is introduced into the collection container 10 from the input port 11, is stored inside the hopper section 12. The discharge port 13 is located at the bottom of the collection container 10. The hopper section 12 has a shape that tapers from top to bottom, that is, from the input port 11 to the discharge port 13. The discharge port 13 is located at the lower end of the hopper section 12. The configuration is such that the dust 1 stored inside the hopper section 12 moves towards the discharge port 13 by its own weight.

[0014] The collection container 10 is equipped with a partition member 14. The partition member 14 is positioned directly above the discharge port 13 in the path of the dust 1 toward the discharge port 13. The partition member 14 is configured to reciprocate between a closed position that closes the path of the dust 1 and an open position that opens the path of the dust 1. The partition member 14 may be configured to be moved manually by an operator. Alternatively, an actuator that generates a driving force to move the partition member 14 may be provided.

[0015] The collection container 10 is supported by a plurality of column sections 15. The column sections 15 are arranged to surround the hopper section 12 and therefore the discharge port 13. A support beam section 16 connects the lower ends of the column sections 15, thereby improving the strength of the collection container 10. A pair of fork insertion openings 17 are provided in the support beam section 16. By inserting the forks of a forklift (not shown) into the fork insertion openings 17, the collection container 10, along with the dust 1 stored inside, can be transported.

[0016] Figure 2 is a schematic diagram illustrating the process of packing dust 1. The packing device 20 includes a support frame 24. The collection container 10 containing dust 1 is moved to the upper part of the support frame 24 by a forklift and mounted on the support frame 24. A column support portion 25 is formed at the upper end of the column portion 15 of the support frame 24. The column support portion 25 supports the lower end of the column portion 15 of the collection container 10, improving the workability of mounting the collection container 10 onto the support frame 24 and facilitating the positioning of the collection container 10 relative to the support frame 24. The packing device 20 may also include a lid to close the input port 11 of the collection container 10 mounted on the support frame 24. The packing device 20 may also include an actuator to move the lid. The actuator may be an air cylinder.

[0017] The dust passage 21 is supported by the beam portion of the support frame 24. The dust passage 21 is a hollow passage with openings at its upper and lower ends. With the collection container 10 mounted on the support frame 24, the discharge port 13 of the collection container 10 is aligned with the opening at the upper end of the dust passage 21. The discharge port 13 of the collection container 10 may be positioned to face the opening at the upper end of the dust passage 21, or the discharge port 13 may be moved into the interior of the dust passage 21.

[0018] The flexible container bag 30 is a bag-shaped container. The flexible container bag 30 may be abbreviated as a flexi-con bag, flexi-con, etc. The flexible container bag 30 may be referred to as a container bag, ton bag, ton sack, jumbo sandbag, cross-container, trans-bag, FIBC (Flexible Intermediate Bulk Container), bulk bag, etc.

[0019] The material of the flexible container bag 30 is a combustible fabric, and a material that does not generate harmful substances during combustion is selected. For example, the flexible container bag 30 may be made of polyethylene or polypropylene.

[0020] Mount the collection container 10 on the support stand 24, and move the partition member 14 of the collection container 10 from the closed position to the open position with the flexible container bag 30 disposed below the dust passage 21. The dust 1 accommodated in the collection container 10 is discharged from the discharge port 13, passes through the dust passage 21, and is accommodated in the flexible container bag 30. In this way, the dust 1 is packed into the flexible container bag 30 in a powder state. It is desirable that the flexible container bag 30 has a specification that allows its mouth to be tied so as to suppress the scattering of the packed dust 1.

[0021] The flexible container bag 30 into which the dust 1 is packed is placed on the weighing device 41. When packing the dust 1 into the flexible container bag 30, the weighing device 41 weighs the dust 1. The weighing of the dust 1 and the packing into the flexible container bag 30 are carried out simultaneously. The weighing device 41 is, for example, a digital scale. By packing while weighing the weight of the dust 1 with the weighing device 41, the dust 1 of a specified weight is packed into the flexible container bag 30.

[0022] The specified value of the weight of the dust 1 may be about 1.3% of the weight of the iron scrap 70 (Fig. 3) melted once in the arc furnace 60 (Fig. 3). For example, when the weight of the iron scrap 70 per melting in the arc furnace 60 is 15 tons, it may be specified to pack the dust 1 with a weight of 200 kg into the flexible container bag 30. The weight of the dust 1 is restricted and managed so that the iron oxide does not become excessive in the arc furnace 60. Thereby, it is possible to stably manage the iron oxide concentration in the arc furnace 60.

[0023] The weighing device 41 is placed on the roller conveyor 42. After packing the dust 1 with a specified weight into the flexible container bag 30 and tying the mouth of the flexible container bag 30, the weighing device 41 and the flexible container bag 30 are moved using the roller conveyor 42. The roller conveyor 42 may be a free conveyor having no drive source such as a motor. In this case, the operator can move the weighing device 41 and the flexible container bag 30 by pushing the weighing device 41. A handle may be attached to the weighing device 41 to facilitate the movement of the weighing device 41 by manual labor of the operator.

[0024] In the arrangement example shown in Fig. 2, after packing the dust 1 into the flexible container bag 30, the weighing device 41 and the flexible container bag 30 are moved in the left direction in the figure. When packing the dust 1, the flexible container bag 30 is arranged directly below the recovery container 10. After packing, the flexible container bag 30 moves to a position where it does not overlap with the recovery container 10 in plan view. The flexible container bag 30 exits from the space surrounded by the support base 24 of the packing device 20 and moves to the space surrounded by the hoist support base 4​​​A hoist 43 is supported on the beam of the hoist support frame 44. The hoist 43 is, for example, an air hoist. The hoist 43 may also be an electric hoist, a chain block, etc. The flexible container bag 30 is lifted by the hoist 43 and moved onto the pallet 50. Considering that the flexible container bag 30 is lifted by the hoist 43, the load capacity of the flexible container bag 30 may be set to 2.5 times the weight of the dust 1 being packed. When packing 200 kg of dust 1 into the flexible container bag 30, the load capacity of the flexible container bag 30 may be set to 500 kg.

[0026] Multiple flexible container bags 30 are placed on the pallet 50. For example, a pallet 50 capable of holding four flexible container bags 30 may be used. The pallet 50 is provided with a pair of fork insertion openings 57. By inserting the forks of a forklift (not shown) into the fork insertion openings 57, it is possible to move the flexible container bags 30 packed with dust 1 and feed the dust 1 into the arc furnace 60.

[0027] Figure 3 is a schematic diagram illustrating the loading of material into the arc furnace 60. The arc furnace 60 has rod-shaped electrodes 61. The arc furnace 60 melts the iron scrap 70 by utilizing the heat generated by the arc discharge between the loaded iron scrap 70 and the electrodes 61, or between multiple electrodes 61.

[0028] Dust 1, packed in a flexible container bag 30, is fed into the arc furnace 60 and positioned in the middle of the iron scrap 70. Dust 1 is positioned near the center of the iron scrap 70. However, Dust 1 does not need to be positioned at the exact center of the iron scrap 70, nor at the exact center of the arc furnace 60. It is sufficient that Dust 1 is covered from above by the iron scrap 70, and that there is iron scrap 70 below Dust 1. It is sufficient that there is iron scrap 70 between the floor of the arc furnace 60 and Dust 1, and iron scrap 70 between the ceiling of the arc furnace 60 and Dust 1.

[0029] In Figure 3, the reducing agent 1X is also introduced into the arc furnace 60. The reducing agent 1X is introduced directly into the arc furnace 60 without being packed into a flexible container bag 30. The reducing agent 1X shown in Figure 3 is positioned near the center of the iron scrap 70. The reducing agent 1X does not necessarily have to be positioned near the center of the iron scrap 70. As long as both the dust 1 and the reducing agent 1X are introduced into the arc furnace 60, the reducing agent 1X may be placed at any position within the arc furnace 60.

[0030] For example, reducing agent 1X contains aluminum ash. The aluminum ash contains aluminum that acts as a reducing agent. The reducing agent content in the aluminum ash is, for example, 34%. The iron oxide contained in dust 1, and the aluminum as a reducing agent, promote the following chemical reaction.

[0031] [ka]

[0032] For example, reducing agent 1X contains silicon steel sheet scrap. Silicon steel sheet scrap contains silicon, which acts as a reducing agent. The reducing agent content in silicon steel sheet scrap is, for example, 3.6%. The iron oxide contained in dust 1 and the silicon as a reducing agent promote the following chemical reaction.

[0033] [ka]

[0034] This chemical reaction reduces the iron oxide contained in dust 1 to obtain iron, which can then be reused as a melting material, thus reducing the material cost of iron scrap 70. Since dust 1 can be recycled, it does not need to be disposed of as industrial waste, reducing the amount of industrial waste generated and lowering industrial waste disposal costs. The chemical reaction generates heat, which can be used to melt the iron scrap 70, thus reducing electricity consumption, contributing to energy conservation, and reducing carbon dioxide emissions. Reducing agent 1X may also include aluminum ash, silicon steel sheet scrap, carburizing agents, aluminum ingots, etc.

[0035] Since the weight of Dust 1 is measured when packing it into the flexible container bag 30, the appropriate amount of reducing agent 1X can be measured, and Dust 1 and reducing agent 1X can be simultaneously introduced into the arc furnace 60. An excess amount of reducing agent 1X, which provides a margin relative to the weight of iron oxide contained in Dust 1, may also be introduced into the arc furnace 60. For example, even if the weight of Dust 1 exceeds the predetermined value by 20%, the amount of iron oxide reduction by reducing agent 1X may be set to 35% or more of the weight of iron oxide so that the iron oxide contained in Dust 1 can be sufficiently reduced.

[0036] A bucket (not shown) is prepared for loading materials into the arc furnace 60, and materials are placed into the bucket in order and stacked using a magnetic crane. When the lower end of the bucket is opened and the materials are loaded into the arc furnace 60, the materials fall into the arc furnace 60 generally maintaining the stacked order. Alternatively, about half the amount of iron scrap 70 and reducing agent 1X may be loaded into the arc furnace 60, then the dust 1 in the flexible container bag 30 may be loaded into the arc furnace 60, and the remaining amount of iron scrap 70 and reducing agent 1X may be loaded into the arc furnace 60 from above. In this way, the position of the materials in the arc furnace 60 can be controlled, and the dust 1 can be positioned near the center of the iron scrap 70.

[0037] Since the dust 1 is packed inside the flexible container bag 30 and placed inside the iron scrap 70, the dust 1 is prevented from being sucked into the dust collector attached to the arc furnace 60, which would reduce the yield. Also, since the dust 1 is packed inside the flexible container bag 30, the dust 1 is prevented from dispersing inside the arc furnace 60 and accumulating at the bottom of the arc furnace 60. The dust 1 is prevented from being placed at the bottom of the arc furnace 60 containing air or moisture, and the expansion of that air or moisture inside the furnace during operation of the arc furnace 60 is prevented.

[0038] Figure 4 is a schematic diagram showing the state of material melting in an arc furnace 60. High power is supplied to the electrode 61, generating an arc discharge and melting the iron scrap 70. As the material melts in the arc furnace 60, the electrode 61 extends towards the bottom of the furnace. This makes it possible to melt all of the material introduced into the arc furnace 60 without waste.

[0039] The flexible container bag 30 disappears as the temperature rises inside the arc furnace 60. Since the dust 1 is located near the center of the iron scrap 70 and is covered with molten iron scrap 70, the dust 1 is not collected by the dust collector even when the flexible container bag 30 burns. By introducing both the dust 1 and the reducing agent 1X into the arc furnace 60, the above chemical reaction can be efficiently carried out.

[0040] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Industrial applicability]

[0041] In steelmaking or foundry plants, the main raw materials for products are iron scrap and metal shavings from ferrous materials. These raw materials are widely used in various types of furnaces, including arc furnaces and induction furnaces. While these materials are easy to store and transport, they are more expensive than the powder materials described later due to their high metallic iron content.

[0042] In the manufacturing process of steel products, powdered iron raw materials such as dust collected during shot peening and shot blasting also contain a large amount of metallic iron and iron oxide, and are therefore sometimes treated as melting materials. Since iron oxide cannot be used as a raw material as is, it is necessary to remove the oxygen through a reduction reaction to convert it into metallic iron. Commonly used reducing agents include metallic aluminum, aluminum ash generated during aluminum ingot manufacturing, silicon-rich silicon steel scrap, pig iron, and ferrosilicon. Because the reaction in which these reducing agents reduce iron oxide is a strongly exothermic reaction, it is also expected to have the effect of assisting the electrical energy required for melting and heating.

[0043] Powdered iron raw materials are relatively inexpensive, although they are difficult to handle as raw materials due to their drawbacks such as being prone to scattering and difficult to store and transport, and requiring a reduction reaction to convert iron oxide components into metallic iron. These powdered iron raw materials often have a higher iron oxide concentration compared to iron scrap, which is the main raw material. If the iron oxide concentration becomes too high in the melting furnace, the risk of rapid combustion of carbon monoxide generated by the reaction of iron oxide with carbon in the molten steel increases. On the other hand, if the iron oxide concentration becomes too low, the amount of phosphorus components, which are impurities in molten steel, that are removed decreases, and the quality of the molten steel deteriorates. Therefore, the iron oxide concentration in the melting furnace must be stably controlled, and an appropriate amount of reducing agent must be weighed and added simultaneously to the raw material containing iron oxide to reduce it. However, powdered materials are prone to scattering and difficult to transport and weigh, making it difficult to stably control the iron oxide concentration in the furnace.

[0044] Furthermore, in arc-type and induction-type melting furnaces, dust collectors are used during operation to suppress the scattering of dust generated during operation and improve the working environment. If powder material is placed in the upper part of the furnace, it will be sucked up by the dust collector, reducing the yield of the material. Also, if powder material is placed at the bottom of the furnace to prevent this and melting is started, the powder material will remain unmelted at the bottom of the furnace with air contained within it, and there is a risk that the air at the bottom of the furnace will expand due to heat in the later stages of the melting process.

[0045] To prevent such phenomena and utilize powdered materials, a typical piece of equipment and technology is an injection machine, which uses air pressure to directly inject powder into molten steel. However, because injection machines need to be installed adjacent to the melting furnace, they can reduce the workspace around the furnace and impair work efficiency. The initial cost of injection machines is also high. Skills and experience are also required to adjust the injection angle and flow rate of the powder into the steel bath.

[0046] Another technique involves mixing a binder such as resin or water glass with the powder and compressing it in a briquette machine to form briquettes. However, this also requires the introduction of specialized equipment such as mixing facilities and briquette machines, as well as ongoing costs for binders. Since the materials contained in the binder become impurities, careful selection of binders and refinement of solidification techniques are necessary to minimize their adverse effects on the molten steel.

[0047] In the technical concept of this disclosure, an arc-type melting furnace is used when melting powdered iron raw materials. An arc-type melting furnace is a melting facility based on the slag metal reaction and is suitable for the chemical reaction that reduces iron oxide to metallic iron. Because impurities can be removed using oxides in an arc-type melting furnace, even low-quality iron scrap containing impurities can be melted.

[0048] The powdered iron raw material is weighed in advance and packed into flexible container bags. The material of the flexible container bag is selected to be a flammable fabric that disappears as the temperature rises in the arc furnace and does not generate harmful substances such as dioxins when burned. By using a flammable flexible container bag instead of a drum or other container for the powdered iron raw material, the phenomenon of gas expanding and compressing inside the container as the furnace heats up is prevented. Packing the powdered iron raw material into flexible container bags in advance prevents the working environment from deteriorating due to scattering during storage and transportation.

[0049] When packing into flexible container bags, the weight is standardized and managed in advance. This measure facilitates the adjustment and management of the amount of reducing agent used to reduce the iron oxide contained in the powdered raw materials. For example, by deciding to "pack 200 kg of powdered iron raw materials with an iron oxide content of 50% per flexible container bag," it is known that each flexible container bag contains 100 kg of iron oxide. This prevents human error when calculating the appropriate amount of reducing agent.

[0050] The initial placement of the flexible container bag is adjusted to a position near the center of the molten material. As mentioned above, if the powder material is placed on top of the molten material, the powder will be collected, reducing the yield of the material. If it is placed at the bottom of the furnace, there is a risk of air expansion inside the furnace. This measure is taken to reduce these risks. Since the powdered iron raw material is bundled in a flexible container bag, it becomes easier to control its placement.

[0051] According to the technical concept of this disclosure, the storage and transportation of powdered iron raw materials such as dust can be made easier and scattering can be prevented. Dedicated equipment such as injection machines are not required, so the workspace around the arc furnace is not encroached upon and initial costs can be reduced. The amount of reducing agent added can be easily adjusted and managed, preventing human error. Because the amount of iron oxide in the furnace can be easily controlled, the risk of rapid foaming of slag and molten steel in the furnace is reduced, and the phosphorus removal function can be easily adjusted. [Explanation of symbols]

[0052] 1 Dust, 1X reducing agent, 10 Recovery container, 11 Inlet, 12 Hopper section, 13 Outlet, 14 Partition member, 15 Column section, 16 Support beam section, 17, 57 Fork insertion port, 20 Packing device, 21 Dust passage, 24 Support frame, 25 Column support section, 30 Flexible container bag, 41 Weighing device, 42 Roller conveyor, 43 Hoist, 44 Hoist support frame, 50 Pallet, 60 Arc furnace, 61 Electrode, 70 Iron scrap, 100 Dust collector.

Claims

1. A system for recycling dust generated during the production process of steel products, A collection container for storing the collected dust, A packing device for weighing and packing the dust in the collection container, A system comprising an arc furnace into which the packed dust is fed.

2. The packing device packs the dust into a flexible container bag, according to claim 1.

3. A method for recycling dust generated during the production process of steel products, The aforementioned dust is collected and stored, The aforementioned dust is weighed and packed, A method comprising feeding the packed dust into an arc furnace.

4. The method according to claim 3, further comprising adding a reducing agent to the arc furnace.

5. The method according to claim 4, wherein aluminum ash or silicon steel sheet scrap is used as the reducing agent.

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