Manufacturing method of molded charcoal

Abstract

To provide a method for reliably preventing powdering of molded coal at a transfer section between transport paths when transporting molded coal after molding.SOLUTION: There is provided a manufacturing method for molded coal, comprising: a molded coal production step in which coal powder and a binder are mixed and kneaded and then molded to produce molded coal; and a conveying step in which the molded coal is conveyed along a conveying route in which a plurality of conveying paths are connected via transfer sections that slope downward from an upstream side to a downstream side, wherein the temperature of the molded coal passing through the most upstream transfer section is set to 30°C or lower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing molded coal, comprising a step of molding molded coal and a step of conveying the molded coal. [Background Art]

[0002] In ironmaking processes, various powdery raw materials are briquetted for use for the purposes of reducing raw material costs, improving the quality of intermediate products, and reducing environmental load by preventing scattering. Specifically, examples include cases where inexpensive low-grade ore is crushed, sorted, and compression-molded to be used as a high-grade raw material; cases where bulk density and air permeability are improved by compression-molding coal or iron ore powder; and cases where dust scattering is prevented by compression-molding dust charged into a converter.

[0003] For example, in the coke production process, for reasons such as improving coke productivity, coal, which is a raw material for coke, is often pretreated and then charged into a coke oven. As a technology related to such pretreatment, a technology is known in which all or part of the coal charged into a coke oven (charged coal) is formed into molded coal obtained by molding coal powder. The technology of using part of charged coal as molded coal is also called molded coal blending technology. Inside the molded coal, coal particles are in close proximity to each other. Therefore, charging molded coal into a coke oven increases the charging density of coal. As a result, the strength of coke is improved, and it also becomes possible to save strongly caking coal. Furthermore, it becomes possible to actively use inexpensive coal.

[0004] Generally, molded coal is produced by crushing coal as a raw material into powder, mixing and kneading the powder with a binder, and performing pressure molding with a molding machine. In addition, a strength of a certain level or higher is required to suppress pulverization during conveyance. Numerous technologies for producing this molded coal have been disclosed so far.

[0005] In other words, the technology disclosed in Patent Document 1 involves dehydrating and heating low-grade coal, then compressing and molding it to produce molded coal, which is then subjected to oxidation treatment. Patent Document 2 also discloses a technology for producing molded coal. In the technology disclosed in Patent Document 2, molded coal is produced by molding coal using a double-roll molding machine.

[0006] Furthermore, the molten coal produced is transported to the coke oven via conveyors and other transport routes and then fed into the coke oven. During this transport, the molten coal is typically transported to the final coke oven by changing between multiple conveyors several times. Here, when changing between conveyors, there is a difference in height between the upstream and downstream conveyors, causing the molten coal to fall onto the downstream conveyor. This impact causes the molten coal to pulverize. When the molten coal pulverizes, the effect of compacted molten coal in improving the coal charging density of the coke oven is reduced, so it is very important to suppress the pulverization of the molten coal during transport. However, the above-mentioned Patent Documents 1 and 2 do not mention the pulverization of molten coal due to impact from falling.

[0007] Regarding the pulverization of this molded charcoal, Patent Document 3 proposes measuring the temperature of the molded charcoal before it reaches the connecting section (transfer section) between multiple transport paths, and if the temperature of the molded charcoal is outside the range of 50-60°C, adjusting the internal temperature of the molded charcoal to 50-60°C, and adjusting the internal temperature of the molded charcoal being transported in the final transport path to 40°C or lower. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 63-32839 [Patent Document 2] Patent No. 4265422 [Patent Document 3] Patent No. 6819165 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the form of pulverization of molded charcoal varies depending on the type and mixing ratio of the binder. Therefore, even if the internal temperature is adjusted to 50-60°C, sufficient strength may not be obtained. Furthermore, there is a high possibility that pulverization will progress before reaching the final stage, resulting in insufficient strength. Furthermore, Patent Document 3 evaluates the drop strength during the transport of molded charcoal by dropping the charcoal multiple times from a height of 2.5m. However, the transport path may exceed 2.5m due to the equipment configuration, and the pulverization rate of the molded charcoal changes depending on the drop height, with higher drop heights making pulverization easier. Detailed knowledge regarding the effect of drop height on the pulverization of molded charcoal has not been obtained.

[0010] Therefore, the object of the present invention is to solve the problems of the conventional technology described above and to provide a method for reliably suppressing the pulverization of molded charcoal, even when the height at which the molded charcoal falls at transfer points between transport paths is high when transporting molded charcoal after molding. [Means for solving the problem]

[0011] This invention, the result of diligent research to solve the above-mentioned problems, has found a method for producing high-strength molded charcoal, and its gist is as follows. 1. The process includes a molten coal production step in which coal powder and a binder are mixed, kneaded, and then molded to produce molten coal, and a transport step in which the molten coal is transported along a transport route in which multiple transport paths are connected via transfer sections that decrease in elevation from the upstream side to the downstream side. A method for manufacturing molded coal, wherein the temperature of the molded coal passing through the upstream transfer section is kept below 30°C.

[0012] 2. The method for producing molded charcoal according to paragraph 1, wherein the molded charcoal is cooled in the upstream transport path.

[0013] 3. The method for producing molded coal according to 1 or 2, wherein the end point of the conveyance path is a coke oven.

[0014] 4. The method for producing molded coal according to 1, 2 or 3, further comprising a hopper for temporarily storing the molded coal in the middle of the conveyance path.

[0015] 5. The method for producing molded coal according to any one of 1 to 4, wherein the mixing and kneading of the coal powder and the binder are performed using a horizontal kneader.

[0016] 6. The method for producing molded coal according to any one of 1 to 5, wherein the mixing and kneading of the coal powder and the binder are performed in a temperature range of 85°C to 105°C.

[0017] 7. The method for producing molded coal according to any one of 2 to 6, wherein the cooling of the molded coal is performed by enclosing the most upstream conveyance path with a hood, installing an exhaust fan at an upper part of the hood, and generating an updraft in the hood. Effects of the Invention

[0018] According to the present invention, when conveying molded coal after molding, it is possible to provide a means for reliably suppressing pulverization of the molded coal at a transfer section between conveyance paths. Brief Description of the Drawings

[0019] [Figure 1] It is a diagram showing a production and conveyance flow of molded coal according to an embodiment of the present invention. [Figure 2] It is a diagram showing a relationship between molded coal temperature and molded coal crushing strength according to an embodiment of the present invention. [Figure 3] It is a diagram showing a relationship between molded coal drop strength and molded coal temperature according to an embodiment of the present invention. [Figure 4] It is a schematic diagram showing a structure of a cooling device applied to a cooling method according to an embodiment of the present invention. [Figure 5] It is a diagram showing a relationship between a cooling method and molded coal temperature according to an embodiment of the present invention. [Figure 6]It is a diagram showing the relationship between the kneading and mixing temperature and the crushing strength of molded coal according to an embodiment of the present invention. MODE FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the molded coal production facility used in the present invention shown in FIG. 1. In the present invention, coal powder crushed to a predetermined particle size and a binder are charged at a predetermined blending ratio into, for example, a horizontal paddle-type kneading and mixing machine 1, and kneaded and mixed for a predetermined time. After mixing and kneading the coal powder and the binder, a molding process is performed by a roll molding machine 2 to produce molded coal 3. The molded coal 3 thus obtained is conveyed to a coke oven via a plurality of conveying paths. For example, a conveyor can be used as the conveying path.

[0021] That is, the molded coal 3 molded by the roll molding machine 2 is discharged onto a conveyor 4, transferred through a plurality of conveyors 4, passes through an intermediate hopper 5, and is further transferred through a plurality of conveyors 4 before being charged into a coke oven 6. In addition, in the middle of the conveying path composed of the plurality of conveyors 4 described above, pulverized coal conveyed from another conveying path may be merged, and the molded coal 3 may be conveyed together with the pulverized coal to supply both to the coke oven.

[0022] [Molded Coal Production Step] Here, examples of the powder used as the raw material for molded coal include coal powder, ore powder, and other powders such as dust charged into converters, but in the production of molded coal briquettes for iron manufacturing processes, it is preferable to use coal powder. The particle size of the coal powder is not particularly limited, but finer powder is preferable because it improves the strength of the briquette. For example, it is preferable that coal powder with a particle size of 3 mm or less accounts for 80% by mass or more, and more preferably 90% by mass or more. When the proportion of coal powder with a particle size of 3 mm or less is less than 80% by mass, the particle size may be adjusted to fall within the above range by crushing the entire coal powder or mixing the coal powder with another coal powder of fine particle size.

[0023] Furthermore, the softening point and bonding state with coal powder change due to the compatibility effect of mixing multiple types of binders, so the effect of improving the strength after molding differs depending on the type of binder. Therefore, it is preferable to appropriately set the type of binder and mixing ratio necessary to improve the strength of molded coal. Here, for example, tar pitch and tar slag, either one or both, can be used as the binder. Soft oil pitch (SOP) can also be used as another binder.

[0024] When mixing binders, such as tar pitch and tar residue, into coal powder, it is preferable to add them in a mass ratio of 2.0-5.0% for tar pitch and 4.0-9.0% for tar residue relative to the total amount of coal powder and binder. This is because if the amount of binder is too small, its binding effect will be weak, and if it is too large, the cost of the raw materials will increase. For similar reasons, it is preferable to mix in soft oil pitch (SOP) at a concentration of 1.0-6.0%.

[0025] [Conveying Process] As described above, the molded coal 3 is transported to the coke oven 6 via multiple conveyors 4. In this transport process, the molded coal 3 is transported from the upstream conveyor 4 to the downstream conveyor 4 via a transfer section 40 with a drop in height. The molded coal 3 is subjected to considerable impact when it falls at this transfer section 40, so it is necessary to prevent pulverization during this fall.

[0026] In order to avoid pulverization during the fall, the technology disclosed in the aforementioned Patent Document 3 adjusts the internal temperature of the molten coal to 50-60°C before it reaches the transfer section. However, it has recently been found that even when the internal temperature of the molten coal is adjusted to 50-60°C, pulverization of the molten coal at the transfer section cannot be sufficiently suppressed, and in particular, pulverization suppression is insufficient when the drop at the transfer section is large. Therefore, we have diligently investigated ways to reliably suppress pulverization of the molten coal when the drop at the transfer section is large. As a result, we have newly discovered that keeping the temperature of the molten coal 3 passing through the uppermost transfer section 40, i.e., the first transfer section 40, below 30°C is effective in suppressing pulverization of the molten coal. The experimental results that led to this finding will be explained in detail below.

[0027] First, to verify the relationship between the temperature of molded coal and its crushing strength, the following experiment was conducted. Specifically, coal powder (percentage of particles 3.0 mm or less: 91% by mass) and a binder (tar slag and tar pitch) were added in a predetermined ratio (6.0% by mass of tar slag, 4.5% by mass of tar pitch) and mixed for a predetermined time (120 s). The kneading process was carried out at 100°C, and molded coal was produced using a molding machine. Next, a predetermined amount of molded coal was recovered at the discharge position on the exit side of the molding roll, and the temperature of the recovered molded coal was measured. The crushing strength of the molded coal was measured at 5°C intervals during the cooling process from 60°C to 20°C. The crushing strength of the molded coal at each temperature stage is as follows: JIS The measurements were taken in accordance with Z8841. Specifically, molded coal was placed in a compression tester, pressure was applied to the molded coal, and the pressure at which the molded coal collapsed was defined as the collapse strength of the molded coal. The inventors conducted similar tests on a large number of molded coals they had prepared and obtained the results shown in Figure 2. The collapse strength shown in Figure 2 is the average value obtained by measuring 10 molded coals individually. As shown in Figure 2, the collapse strength decreases when the temperature of the molded coal is high. When the collapse strength is low, the molded coal cannot withstand the impact of dropping during transport, so it is easily destroyed and powdering becomes significant.

[0028] When transporting molded coal, the height of the transfer point between conveyors is generally around 2m to 5m, but depending on the installation constraints of the transport equipment, it may be around 8m. Therefore, we investigated the effect of pulverization of molded coal due to dropping at the maximum height during transfer. After preparing molded coal (particle size: 44mm) with different crushing strengths, 8kg of molded coal of the same crushing strength was collected, and a drop test was conducted by dropping the molded coal onto a steel plate. At this time, the drop test was conducted under three conditions: a drop height of 2.5m, 5.5m, and 8.0m, and the drop strength of the molded coal was evaluated. The drop strength was calculated by collecting all the molded coal samples after dropping, sieving them using a sieve with a mesh size of 10mm, measuring the weight of the portion above the sieve (sieved weight), and calculating the ratio of the sieved weight to the sum of the weight below the sieve and the weight above the sieve. Figure 3 shows the relationship between molded coal temperature and drop strength. As shown in Figure 3, when the drop height was 2.5m, the strength tended to be maximum at a molded charcoal temperature of around 60°C. However, when the drop height was 5.5m and 8.0m, the drop strength decreased sharply and pulverization became significant when the molded charcoal temperature exceeded 30°C.

[0029] The above findings differ from the experimental results described in Figure 2 of Patent Document 3, which is presumed to be due to the drop height. When the drop height was low at 2.5m, the impact on the molten charcoal upon impact with the landing surface was relatively small, resulting only in minute cracks on the surface of the molten charcoal, and the molten charcoal after the drop test had a particle size of 10mm or more, regardless of temperature. On the other hand, when the drop height was 5.5m and 8.0m, the impact during the drop increased significantly, causing the molten charcoal to shatter into pieces after the drop, and the proportion of particles larger than 10mm decreased drastically under conditions of high molten charcoal temperature.

[0030] From the experimental results described above, we have newly discovered that keeping the temperature of the molded coal 3 passing through the first transfer section 40 below 30°C is effective in suppressing pulverization of the molded coal, even when the drop height at the transfer section 40 is high. Specifically, it is preferable to apply a cooling treatment to the molded coal 3 on the conveyor 4 at the uppermost conveyor 4 leading to the transfer section 40. This is because the temperature of the molded coal obtained after the process of mixing and kneading coal powder and binder and then molding exceeds 30°C and reaches about 60°C. For this reason, it is preferable to install a cooling device 7 on the conveyor 4 on the exit side of the roll molding machine 2.

[0031] Next, we investigated cooling methods to reduce the temperature of the molded coal to 30°C or lower after molding. Here, we compared various methods by changing the presence or absence of a hood covering the entire length of the upstream conveyor 4, and the method of cooling the molded coal on the conveyor (upward blowing, downward blowing, or exhaust). Each cooling method (cooling device) is shown in Figure 4. In Figure 4, reference numeral 8 denotes a fan for blowing or exhausting air, and the direction of blowing or exhausting air relative to the molded coal 3 is indicated by an arrow. Reference numeral 9 denotes a hood that covers the entire length of the conveyor 4.

[0032] Furthermore, Figure 5 shows the results of measuring the temperature of the molded coal after cooling using each method. The molded coal temperature was measured by collecting the sample at the outlet of the upstream conveyor. When the molded coal was not cooled, the temperature was a high 65°C. On the other hand, as a result of cooling using each method, it became possible to keep the molded coal temperature below 30°C by using a method in which exhaust is performed from the top of the hood with a fan.

[0033] Furthermore, the operating conditions for the fan used in the above-mentioned upper exhaust method are determined by calculating the airflow from the conveyor area so that the average air velocity inside the hood of the cooling device 7 is 5 m / s or more, and then determining the required number of fans. In this invention, in order to cool the molded charcoal to 30°C or below, 35 Nm 3 / min*m 2 That much airflow was needed.

[0034] [Mixing machine] Furthermore, it is preferable to use a horizontal kneader in the mixing and kneading machine 1 that performs the mixing and kneading of the coal powder and binder described above. In other words, a horizontal kneader can perform kneading and mixing simultaneously by optimizing the arrangement of the paddles inside the kneader, and it is possible to reduce equipment costs and save space compared to a vertical kneader.

[0035] [Mixing and kneading conditions] The mixing and kneading of coal powder and binder, which are the raw materials for molded coal, is preferably carried out in a temperature range of 85°C to 105°C. The experimental results that led to these mixing and kneading conditions are described in detail below.

[0036] Specifically, the effects of kneading and mixing temperature before molten coal production were investigated. The amount of steam introduced into the horizontal kneader was changed to prepare samples at different kneading temperatures. After molding each sample into molten coal, the crushing strength of the molded coal was measured. The crushing strength of the molten coal was measured in accordance with JIS Z8841. That is, the molten coal was set in a compression tester, pressure was applied to the molten coal, and the pressure at which the molten coal collapsed was defined as the crushing strength of the molten coal.

[0037] As shown in Figure 6, these measurement results revealed that high-strength molded charcoal can be produced by maintaining a mixing temperature in the range of 85°C to 105°C. In other words, under conditions where the mixing temperature exceeds 105°C, if the cooling system's capacity is insufficient, the molded coal temperature may rise above 30°C, potentially reducing the strength of the molded coal. While increasing the length of the cooling system (i.e., the conveyor length) could prevent this reduction in molded coal strength, it is not practical due to the increased equipment length.

[0038] In this invention, it is preferable to select a horizontal kneader as the equipment for mixing and kneading coal powder and binder. Here, examples of equipment types for mixing and kneading coal powder and binder include the Henschel type mixer and the vertical paddle type. However, in the case of the Henschel type mixer, it is a batch mixing method, and multiple units are required when processing large quantities, which increases equipment costs. Also, in the case of the vertical paddle type (vertical kneader), the equipment configuration only has the function of mixing, so a separate mixing device is required, which increases the area required for installation and thus increases equipment costs.

[0039] As an example of a raw material heating method, the steam injection method is described, but other heating methods may also be used, such as microwave irradiation or the installation of a heat transfer medium around or inside the mixer (e.g., electric heaters or gas combustion devices). In the case of the steam injection method, the heat source can be secured within the steelworks, and costs can be kept relatively low. Also, when using microwave irradiation, the heating time can be shortened compared to other methods, making it an effective means when it is necessary to shorten the processing time. When using electric heaters or gas combustion methods, it is possible to handle higher temperature conditions compared to steam heating.

[0040] [hopper] As shown in Figure 1, it is preferable to have a hopper 5 for temporarily storing molded coal in the middle of the transport path consisting of multiple conveyors 4. In other words, the hopper 5 can be used to store molded coal when the transport line is temporarily stopped due to production adjustments or other reasons. [Examples]

[0041] Molded coal was produced using the molded coal manufacturing equipment shown in Figure 1, according to the conditions shown in Table 1. The drop strength, pulverization rate, and crushing strength of the obtained molded coal were measured and evaluated in the same manner as in the experiment described above. For comparison, the drop strength, pulverization rate, and crushing strength of the molded coal obtained without cooling were also measured and evaluated in the same manner. The drop height at the transfer point was 8 m.

[0042] Furthermore, the pulverization rate was evaluated by sampling the molded charcoal at the outlet of hopper 5, as shown in Figure 1. Specifically, 8 kg of molded charcoal was recovered from the outlet of hopper 5, and this recovered portion was sieved using a sieve with a mesh size of 15 mm. The weight of the portion below the sieve was measured, and the ratio of the weight below the sieve to the sum of the weight above and below the sieve was defined as the pulverization rate. In addition, the crushing strength was measured in accordance with JIS Z8841 using molded charcoal recovered at the outlet of cooling device 7.

[0043] As shown in Table 1, the molded charcoal produced according to the present invention showed suppressed pulverization even when dropped from a high height. Furthermore, pulverization during transport was suppressed without a decrease in the crushing strength of the molded charcoal.

[0044] [Table 1] [Explanation of Symbols]

[0045] 1. Mixing machine 2 Roll molding machine 3 Molded coal 4 Conveyor 5 Hopper 6. Coke oven 7 Cooling device 8 Fans 9 Food 40 Transfer section

Claims

1. The process includes a molten coal production step in which coal powder is mixed and kneaded with at least one binder, which is one of tar pitch, tar slag, and soft oil pitch, in proportions of 2.0 to 5.0% by mass for tar pitch, 4.0 to 9.0% by mass for tar slag, and 1.0 to 6.0% by mass for soft oil pitch, and then molded to produce molten coal; and a transport step in which the molten coal is transported along a transport route in which multiple transport paths are continuous, with transfer sections having a drop height of 5.5 m or more, and the transport paths decrease in height from upstream to downstream. A method for manufacturing molded charcoal, wherein the temperature of the molded charcoal passing through the uppermost transfer section is kept below 30°C.

2. The method for producing molded charcoal according to claim 1, wherein the molded charcoal is cooled in the upstream transport path.

3. The method for producing molded charcoal according to claim 1 or 2, wherein the end point of the transport route is a coke oven.

4. A method for producing molded charcoal according to claim 1 or 2, wherein the transport path includes a hopper for temporarily storing the molded charcoal in the middle.

5. The method for producing molded coal according to claim 1 or 2, wherein the mixing and kneading of the coal powder and binder is performed using a horizontal kneader.

6. The method for producing molded coal according to claim 1 or 2, wherein the mixing and kneading of the coal powder and binder is carried out in a temperature range of 85°C to 105°C.

7. The method for manufacturing molded charcoal according to claim 2, wherein the cooling of the molded charcoal is performed by enclosing the upstream transport path with a hood and installing an exhaust fan on top of the hood to generate an upward airflow inside the hood.

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