Method and equipment for recycling metal powder

Abstract

The method for recycling metal powder includes: an oxide metal powder recovery step (S1) in which oxidized metal powder is generated when a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, is burned in the furnace of a combustion furnace, and oxide metal powder recovery step (S3) in which reduced metal powder is generated when metal powder is reduced in the furnace of a reduction furnace, and post-recovery processing steps (S2, S4) in which at least one of the recovered oxide metal powder and the recovered reduced metal powder is sorted and crushed so that predetermined conditions that affect at least one of the recycling rate and the transport efficiency are met.

Description

Technical Field

[0001] The present disclosure relates to a method for recycling metal powder and equipment for recycling metal powder.

Background Art

[0002] Combustion energy is used in various industrial fields and has the characteristic that energy can be easily obtained using fuel and a combustor. For example, a boiler facility is one of the facilities that utilize combustion energy, and it can boil water by the heat of combustion and extract energy in the form of hot water or steam.

[0003] Fossil fuels such as petroleum or natural gas are often used as fuel. However, fossil fuels generate a large amount of carbon dioxide during combustion and can cause environmental problems. In contrast, metal fuels do not generate carbon dioxide during combustion. For example, Patent Document 1 discloses a system that uses metal powder as fuel in a cement kiln.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, the technique of Patent Document 1, which incorporates the burned metal powder into cement and makes it waste, continuously consumes new metal powder as fuel. Therefore, although carbon dioxide is not emitted in the combustion process, since metal powder as fuel continues to be manufactured and supplied, carbon dioxide is emitted in the process of manufacturing and supplying new metal powder. Therefore, a method for recycling (reusing) metal powder is required. <00​In light of these circumstances, the purpose of this disclosure is to provide a method for recycling metal powder and a metal powder recycling facility that can reduce carbon dioxide emissions. [Means for solving the problem]

[0007] (1) A method for recycling metal powder according to one embodiment of the present disclosure is: A metal oxide powder recovery step involves recovering metal oxide powder, which is oxidized metal powder produced by the combustion of a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, in the furnace of the combustion furnace, from the combustion furnace. A reduced metal powder recovery step involves recovering the reduced metal powder generated by reducing the metal oxide powder in the furnace of the reduction furnace from the reduction furnace, The process includes a post-recovery processing step in which at least one of the recovered metal oxide powder and the recovered metal reduction powder is sorted and crushed such that predetermined conditions affecting at least one of the recycling rate and the transport efficiency are met.

[0008] (2) As one embodiment of the present disclosure, in (1), The aforementioned predetermined conditions include the particle size being greater than or equal to a first threshold, The post-recovery processing step involves sorting at least one of the recovered metal oxide powder and the recovered metal reduction powder.

[0009] (3) In one embodiment of the present disclosure, in (1) or (2), The aforementioned predetermined conditions include the particle size being less than a second threshold, The post-recovery processing step involves grinding at least one of the recovered metal oxide powder and the recovered metal reduction powder.

[0010] (4) A metal powder recycling facility according to one embodiment of the present disclosure is: A metal oxide powder recovery device for recovering metal oxide powder, which is oxidized metal powder produced by the combustion of a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, in the furnace of a combustion furnace, A reduction metal powder recovery device for recovering the reduced metal powder generated by reducing the metal oxide powder in the furnace of the reduction furnace, The system includes a post-recovery processing device that performs sorting and crushing on at least one of the recovered metal oxide powder and the recovered metal reduction powder such that predetermined conditions affecting at least one of the recycling rate and conveying efficiency are met.

[0011] (5) As one embodiment of the present disclosure, in (4), The aforementioned predetermined conditions include the particle size being greater than or equal to a first threshold, The recovery and processing device performs sorting of at least one of the recovered metal oxide powder and the recovered metal reduction powder.

[0012] (6) In one embodiment of the present disclosure, in (4) or (5), The aforementioned predetermined conditions include the particle size being less than a second threshold, The recovery and processing device grinds at least one of the recovered metal oxide powder and the recovered metal reduction powder.

[0013] (7) A metal powder recycling facility according to one embodiment of the present disclosure is: A metal oxide powder recovery device for recovering metal oxide powder, which is oxidized metal powder produced by the combustion of a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, in the furnace of a combustion furnace, The recovered metal oxide powder is treated with a post-recovery processing device that performs sorting and crushing on it in such a way that predetermined conditions affecting at least one of the recycling rate and the transport efficiency are met. The reduced metal powder is produced by reducing the metal oxide powder in the furnace of a reduction furnace and is recovered from the reduction furnace.

[0014] (8) The metal powder recycling facility according to an embodiment of the present disclosure includes a reduced metal powder recovery device that recovers reduced metal powder generated by reducing oxidized metal powder in a reduction furnace from the reduction furnace, and a post-recovery treatment device that performs at least one of sorting and pulverization so that a predetermined condition affecting at least one of the recycling rate and the conveyance efficiency is satisfied for the recovered reduced metal powder. The oxidized metal powder is an oxidized metal powder generated by burning solid fuel containing the reduced metal powder in a combustion furnace and recovered from the combustion furnace.

Advantages of the Invention

[0015] According to the present disclosure, it is possible to provide a metal powder recycling method and a metal powder recycling facility that can suppress carbon dioxide emissions.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a diagram showing a configuration example of a metal powder recycling facility according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an example of a flowchart showing the processing of a metal powder recycling method according to an embodiment of the present disclosure.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, a metal powder recycling method and a metal powder recycling facility according to an embodiment of the present disclosure will be described with reference to the drawings.

[0018] Here, each drawing is schematic and may be different from the actual shape or the like. Further, the following embodiments illustrate an apparatus and a method for embodying the technical idea of the present disclosure, and do not specify the configuration to be the following.

[0019] Figure 1 shows an example of the configuration of a metal powder recycling facility according to this embodiment. As described above, in the conventional technology, although carbon dioxide is not generated during combustion by using metal fuel, carbon dioxide is emitted in the process of manufacturing and supplying new metal powder because metal powder as fuel is continuously manufactured and supplied. The metal powder recycling facility according to this embodiment can recycle metal powder with the configuration described below, thereby reducing carbon dioxide emissions.

[0020] In the example shown in Figure 1, the metal powder recycling system comprises an oxide metal powder recovery device, a reduced metal powder recovery device, and a post-recovery processing device. The details of each component are described below.

[0021] (metal powder) Metal powder refers to powdered metal used as a metal fuel, such as iron powder, lithium powder, magnesium powder, aluminum powder, or zinc powder. Iron powder is preferred because it allows for stable transport. However, the metal powder is not limited to any particular type.

[0022] When the metal powder is iron powder, it is preferable that it has the following shape and material. The metal powder is preferably iron powder composed of 0.3% by mass or less of Si, 0.5% by mass or less of Mn, other trace elements, and 96% by mass or more of Fe. The oxygen concentration of the iron powder is preferably 2% by mass or less. Furthermore, the metal powder has a Sauter mean diameter (SMD). 32 It is preferable that the iron powder has an average particle size of 3 μm or more and 200 μm or less, using the Sauter mean particle size. By using the relationship between surface area and volume as a standard, the combustion reaction of the metal powder can be accurately evaluated. General methods such as image analysis or laser diffraction / scattering can be used as methods for measuring particle size (particle diameter).

[0023] (combustion furnace) A combustion furnace is a furnace that extracts thermal energy by burning solid fuel containing metal powder. Here, the solid fuel includes reduced metal powder, which is metal powder that has been previously reduced. The combustion furnace is not limited to a specific piece of equipment, but in the example in Figure 1, boiler 1 is used. Boiler 1 burns metal powder supplied from supply pipe 5 to heat water, and the steam generated rotates turbine 2. By rotating turbine 2, electricity can be extracted from generator 3. The steam is then cooled by condenser 4 to become water, which is returned to boiler 1. Here, thermal energy is not limited to being extracted as electricity, but may also be extracted via air, steam, or water from boiler 1. A stoker type combustion method may be employed, but the method of injecting solid fuel containing metal powder and burning it with a burner, as in the example in Figure 1, is preferred.

[0024] (Metal oxide powder recovery device) The metal oxide powder recovery device recovers metal oxide powder, which is oxidized metal powder produced by the combustion of solid fuel in the combustion furnace, from the combustion furnace. The recovery method may be air-based dust collection, coagulation and sedimentation, or magnetic recovery, and is not limited to a specific method. However, when iron powder and pulverized coal are co-fired in the combustion furnace, magnetic recovery is preferred to separate coal ash from iron oxide powder. Here, the metal oxide powder recovery device only needs to have the function of recovering metal oxide powder from the combustion furnace and does not need to be configured as an independent device. In the example in Figure 1, a part of the boiler 1 functions as the metal oxide powder recovery device.

[0025] (Metal oxide powder) Metal oxide powders include, for example, iron oxide, magnesium oxide, and aluminum oxide. Iron oxide powder is preferable because it is easily reduced by hydrogen and can be transported stably. However, the metal oxide powder is not limited to any particular type.

[0026] The recovered metal oxide powder undergoes a predetermined treatment process by a post-recovery processing device, is then placed in a container or similar and transported by means of transport to the reduction facility 8 equipped with a reduction furnace. Details of the post-recovery processing device will be described later.

[0027] (Reduction furnace) A reduction furnace is a furnace used to reduce metal oxide powder. The reduction method may be, for example, a method using hydrogen. The reduction furnace may be equipment that directly produces reduced iron (DRI), a shaft furnace, equipment that spreads solid fuel containing metal oxide powder on a belt conveyor and transports it through an annealing furnace in a reducing atmosphere, or a fluidized bed furnace. Here, when reducing a large amount of iron oxide, a shaft furnace is preferably used.

[0028] (Reduced metal powder recovery device) The reduced metal powder recovery device recovers the reduced metal powder generated by reducing metal oxide powder within the reduction furnace. The recovery method may be air-based dust collection, coagulation and sedimentation, or magnetic recovery, and is not limited to any particular method. However, if the concentration of reduced iron is to be increased by separating it from impurities such as Si oxide, magnetic recovery is preferred. Here, the reduced metal powder recovery device only needs to have the function of recovering reduced metal powder from the reduction furnace and does not need to be configured as an independent device. In the example in Figure 1, a part of the reduction furnace provided in the reduction facility 8 functions as the reduced metal powder recovery device.

[0029] (Recovery and post-processing equipment) The post-recovery processing device performs sorting and crushing on at least one of the recovered metal oxide powder and the recovered reduced metal powder so as to satisfy predetermined conditions that affect at least one of the recycling rate and conveying efficiency. In the example in Figure 1, the post-recovery processing device includes a crusher 6 for crushing and a centrifugal separator 7 for sorting, but is not limited to a specific device configuration as long as it has the function of performing at least one of sorting and crushing. Here, the recycling rate is the ratio of the weight of reduced metal powder (metal powder resupplied to the combustion furnace) obtained by processing the metal oxide powder produced by the combustion of the metal powder in the combustion furnace in a reduction furnace, to the weight of the metal powder supplied to the combustion furnace as fuel. For example, if all of the metal powder supplied to the combustion furnace is reduced metal powder without loss and resupplied to the combustion furnace, the recycling rate is 100%.

[0030] The post-recovery processing unit, when dealing with recovered metal oxide powder, performs sorting of the metal oxide powder in accordance with the reduction method in the reduction furnace and transportation to the reduction furnace. Furthermore, when dealing with recovered reduced metal powder, the post-recovery processing unit performs sorting of the reduced metal powder in accordance with the combustion method in the combustion furnace and transportation to the combustion furnace. For example, the particle size of metal oxide powder recovered by a metal oxide powder recovery device varies. To increase the recycling rate, it is preferable that the particle size of the metal oxide powder be suitable for insertion into the reduction furnace and handling. For example, if the particle size of the metal oxide powder is too small, the risk of overheating or ignition increases, and recovery becomes more difficult; therefore, a certain degree of particle size is preferable. Also, for example, a certain degree of particle size of metal oxide powder can increase the amount of combustion energy per unit volume. On the other hand, for example, if the particle size of the metal oxide powder is too large, the gaps between particles become larger when contained in containers, requiring more containers, reducing transportation efficiency, and increasing carbon dioxide emissions. Therefore, the particle size should not be too large. The same applies to the particle size of reduced metal powder. The post-recovery processing device performs sorting and crushing on at least one of the recovered metal oxide powder and the recovered metal reduction powder so that the required recycling rate or transport efficiency is achieved.

[0031] (Selection) The recovery and processing equipment (centrifuge 7 in the example in Figure 1) sorts at least one of the recovered metal oxide powder and the recovered reduced metal powder so as to satisfy predetermined conditions. The predetermined conditions may include the particle size being equal to or greater than a first threshold (for example, 3 μm). Here, not only sorting using the first threshold, but also classification by particle size (dividing into 3 or more groups) may be performed. The sorting method may be a method using a sieve, a method using filtration, or a method using the centrifuge 7. Furthermore, sorting (classification) according to the degree of oxidation of the metal oxide powder may be performed in order to increase the reactivity in the reduction treatment.

[0032] (Crush) The post-recovery processing device (pulverizer 6 in the example in Figure 1) pulverizes at least one of the recovered metal oxide powder and the recovered metal reduction powder so that predetermined conditions are met. The predetermined conditions may include the particle size being less than a second threshold (for example, 200 μm). The pulverization method may be a method using pulverizer 6 or a milling method, etc.

[0033] Grinding is preferably performed on metal oxide powder. Metal oxide powder has low toughness and can be easily ground. On the other hand, reduced metal powder is ductile, and grinding it requires a lot of energy and cost.

[0034] In grinding, it is even more preferable that the average particle size of the metal powder be between 30 μm and 100 μm. If the powder is ground to less than 30 μm, the amount of fine-particle metal powder that is difficult to recover increases, significantly reducing the yield during grinding. Also, if the powder is ground to a size greater than 100 μm, coarse particles remain, significantly reducing the yield when sieving and classifying the easily combustible, small-particle metal powder.

[0035] (Configuration of the metal powder recycling facility) The recycling facility shown in Figure 1 comprises a metal oxide powder recovery device configured as part of a combustion furnace, a post-recovery treatment device downstream of the metal oxide powder recovery device, a reduced metal powder recovery device configured as part of a reduction furnace, and a post-recovery treatment device downstream of the reduced metal powder recovery device. However, the metal powder recycling facility is not limited to the configuration shown in Figure 1. For example, assuming the existence of other fuel furnaces (or other reduction furnaces), it would suffice if the metal powder could be recycled between these other fuel furnaces (or other reduction furnaces).

[0036] For example, a metal powder recycling system may be configured to include an oxide metal powder recovery device and a post-recovery treatment device downstream of the oxide metal powder recovery device. In this case, the metal powder is recycled between the system and an external facility, which is a reduction furnace and a reduced metal powder recovery device. Alternatively, a metal powder recycling system may be configured to include a reduced metal powder recovery device and a post-recovery treatment device downstream of the reduced metal powder recovery device. In this case, the metal powder is recycled between the system and an external facility, which is a combustion furnace and a oxide metal powder recovery device. Furthermore, the post-recovery treatment device may be installed downstream of either the oxide metal powder recovery device or the reduced metal powder recovery device.

[0037] Figure 2 is a flowchart showing the process of the metal powder recycling method performed in the metal powder recycling facility according to this embodiment.

[0038] The metal oxide powder generated by the combustion of a solid fuel containing reducing metal powder in the combustion furnace is recovered from the combustion furnace by a metal oxide powder recovery device (Step S1, metal oxide powder recovery step).

[0039] The recovered metal oxide powder is subjected to sorting and crushing by a post-recovery processing device so that predetermined conditions affecting at least one of the recycling rate and conveying efficiency are met (step S2, post-recovery processing step).

[0040] The reduced metal powder, which is produced by reducing metal oxide powder in the furnace of the reduction furnace, is recovered from the reduction furnace by a reduced metal powder recovery device (step S3, reduced metal powder recovery step).

[0041] The recovered reduced metal powder is subjected to sorting and crushing by a post-recovery processing device so that predetermined conditions that affect at least one of the recycling rate and conveying efficiency are met (step S4, post-recovery processing step).

[0042] Here, step S2 or step S4 may be omitted depending on the configuration of the metal powder recycling facility. For example, if the post-recovery treatment device is provided only downstream of the metal oxide powder recovery device, the post-recovery treatment step (step S4) for the recovered reduced metal powder is omitted. Also, if the post-recovery treatment device is provided only downstream of the reduced metal powder recovery device, the post-recovery treatment step (step S2) for the recovered metal oxide powder is omitted. Furthermore, the reduced metal powder that has undergone sorting and crushing in step S4 is again used as solid fuel in a combustion furnace and the processing in step S1 is performed again.

[0043] (Examples) The effects of this disclosure will be described in detail below based on the examples, but this disclosure is not limited to these examples.

[0044] As shown in Table 1, the above-described metal powder recycling method was simulated as an example. In the simulation, the following process was performed: Solid fuel containing the raw material metal powder was fed into boiler 1, and thermal energy was recovered by combustion. Subsequently, the metal oxides after combustion were recovered, sorted, and transported to a reduction furnace. In the reduction furnace, the metal oxides were reduced. The reduced metal powder was recovered, sorted, and then fed back into the combustion furnace for combustion. In addition, a comparative example was provided in which the recovered metal oxide powder and recovered reduced metal powder were not sorted (post-recovery processing step).

[0045] [Table 1]

[0046] The recycling rate was evaluated by the weight ratio of the metal powder initially fed into the combustion furnace to the metal powder that was fed back into the combustion furnace as reduced metal powder. In addition, the filling rate of the containers used to transport the metal powder was calculated as an evaluation of transport efficiency. In this specification, the filling rate is defined as the ratio of the actual density of the metal powder in the container to the apparent density of the metal powder. If there is some coarse metal powder or lumps, the actual density in the container decreases relative to the apparent density, increasing transport costs. On the other hand, the higher the filling rate, the closer the ratio of the density of the metal powder to the actual density of the metal powder in the container approaches 100%, reducing the number of containers required for transport, thus increasing transport efficiency and reducing carbon dioxide emissions from transport. Here, experiments were conducted in advance to determine the first and second thresholds so that both the recycling rate and the filling rate were 90% or higher. In this embodiment, the first threshold is 3 μm. The second threshold is 200 μm. In other words, in Examples 1 to 6, metal oxide powder with a particle size of 3 μm or more and less than 200 μm is transported to a reduction furnace and subjected to reduction treatment. Also in Examples 1 to 6, reduced metal powder with a particle size of 3 μm or more and less than 200 μm is transported to a combustion furnace and burned.

[0047] As shown in Table 1, both the recycling rate and the filling rate exceeded 90% in all of the examples. On the other hand, in Comparative Examples 1 and 2, where no post-collection processing step was performed, the reduction did not proceed completely, resulting in a lower recycling rate.

[0048] As described above, the metal powder recycling method and metal powder recycling equipment according to this embodiment enable the recycling of metal powder and reduce carbon dioxide emissions through the above configuration.

[0049] While embodiments of this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art will find it easy to make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are included within the scope of this disclosure. [Explanation of Symbols]

[0050] 1. Boiler 2 Turbines 3 Generators 4. Condenser 5 Supply pipe 6. Crusher 7. Centrifugal separator 8. Rebate facilities

Claims

1. A metal oxide powder recovery step involves recovering metal oxide powder, which is oxidized metal powder produced by the combustion of a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, in the furnace of the combustion furnace, from the combustion furnace. A reduced metal powder recovery step involves recovering the reduced metal powder generated by reducing the metal oxide powder in the furnace of the reduction furnace from the reduction furnace, The process includes a post-recovery processing step in which at least one of the recovered metal oxide powder and the recovered metal reduction powder is sorted and crushed such that predetermined conditions affecting at least one of the recycling rate and the transport efficiency are met, The aforementioned predetermined conditions include the particle size being greater than or equal to a first threshold, The post-recovery processing step involves sorting at least one of the recovered metal oxide powder and the recovered reduced metal powder, in a method for recycling and utilizing metal powder.

2. The aforementioned predetermined conditions include the particle size being less than a second threshold, The method for recycling and utilizing metal powder according to claim 1, wherein the post-recovery processing step involves grinding at least one of the recovered metal oxide powder and the recovered metal reduction powder.

3. A metal oxide powder recovery device for recovering metal oxide powder, which is oxidized metal powder produced by the combustion of a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, in the furnace of a combustion furnace, A reduction metal powder recovery device for recovering the reduced metal powder generated by reducing the metal oxide powder in the furnace of the reduction furnace, The system includes a post-recovery processing device that performs sorting and crushing on at least one of the recovered metal oxide powder and the recovered metal reduction powder such that predetermined conditions affecting at least one of the recycling rate and conveying efficiency are met, The aforementioned predetermined conditions include the particle size being greater than or equal to a first threshold, The recovery and post-treatment device is a metal powder recycling and utilization facility that sorts at least one of the recovered metal oxide powder and the recovered metal reduction powder.

4. The aforementioned predetermined conditions include the particle size being less than a second threshold, The metal powder recycling equipment according to claim 3, wherein the post-recovery processing device grinds at least one of the recovered metal oxide powder and the recovered metal reduction powder.

5. A metal oxide powder recovery device for recovering metal oxide powder, which is oxidized metal powder produced by the combustion of a solid fuel containing reduced metal powder, which is metal powder that has been previously reduced, in the furnace of a combustion furnace, The recovered metal oxide powder is treated with a post-recovery processing device that performs sorting and crushing on it in such a way that predetermined conditions affecting at least one of the recycling rate and the transport efficiency are met. The aforementioned reduced metal powder is produced by reducing the aforementioned metal oxide powder in the furnace of a reduction furnace, and is recovered from the reduction furnace. The aforementioned predetermined conditions include the particle size being greater than or equal to a first threshold, The recovery and post-treatment device is a metal powder recycling and utilization facility that sorts the recovered metal oxide powder.

6. A reduction metal powder recovery device for recovering reduced metal powder generated by reducing metal oxide powder inside a reduction furnace, The system includes a post-recovery processing device that performs sorting and crushing on the recovered reduced metal powder in such a way that predetermined conditions affecting at least one of the recycling rate and conveying efficiency are met. The aforementioned metal oxide powder is an oxidized metal powder, which is produced by the combustion of a solid fuel containing the aforementioned reduced metal powder in the furnace of a combustion furnace, and is recovered from the combustion furnace. The aforementioned predetermined conditions include the particle size being greater than or equal to a first threshold, The recovery and post-treatment device is a metal powder recycling and utilization facility that sorts the recovered reduced metal powder.

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