Manufacturing method for molded coal

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 briquettes, comprising a step of briquetting briquettes and a step of transporting the briquettes. [Background technology]

[0002] In the steelmaking process, various powdered raw materials are briquetted for use in order to reduce raw material costs, improve the quality of intermediate products, and reduce the environmental impact by preventing scattering.Specific examples include crushing, sorting, and compressing low-quality ores to use them as high-quality raw materials, compressing powders of coal and iron ore to improve bulk density and air permeability, and compressing dust fed into a converter to prevent it from scattering.

[0003] For example, in the coke manufacturing process, coal, which is the raw material of coke, is often pretreated before being charged into a coke oven for reasons such as improving the productivity of coke. As a technology related to such pretreatment, a technology is known in which all or part of the coal (charging coal) charged into a coke oven is made into briquettes by molding coal powder. The technology of making part of the charging coal into briquettes is also called briquettes blending technology. Inside the briquettes, the coal particles are close to each other. Therefore, by charging the briquettes into the coke oven, the charging density of the coal is improved. As a result, the strength of the coke is improved, and it is also possible to save strong 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 form, mixing and kneading it with a binder, and pressurizing and molding it in a molding machine. In addition, a certain level of strength is required to prevent powdering during transportation. Many manufacturing technologies for this molded coal have been disclosed so far.

[0005] That is, in the technology disclosed in Patent Document 1, low-rank coal is dehydrated, heated, and then compressed and molded to produce molded coal, and the molded coal is then subjected to an 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] In addition, the molded coal after production is transported to a coke oven via a conveyor or other conveying path and charged into the coke oven. In general, the molded coal during this transport is transferred between multiple conveyors several times to the coke oven at the end point. Here, when transferring between conveyors, there is a drop between the upstream conveyor and the downstream conveyor, so the molded coal falls onto the downstream conveyor. This drop impact causes the molded coal to become pulverized. If the molded coal becomes pulverized, the effect of improving the coal charging density of the coke oven by the compacted molded coal is reduced, so it is very important to prevent the molded coal from becoming pulverized during transport. However, the above Patent Documents 1 and 2 do not mention the pulverization of molded coal due to the drop impact.

[0007] Regarding the powdering of molded coal, Patent Document 3 proposes measuring the temperature of the molded coal before it reaches the connecting section (transfer section) between multiple conveying paths, and if the temperature of the molded coal is outside the range of 50 to 60°C, adjusting the internal temperature of the molded coal to 50 to 60°C, and adjusting the internal temperature of the molded coal being transported on the final conveying path to below 40°C. [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 Summary of the Invention [Problem to be solved by the invention]

[0009] However, because the form of powdering of molded charcoal differs depending on the type and blending ratio of binder, adjusting the internal temperature to 50-60°C does not necessarily mean that sufficient strength will be obtained. In addition, there is a high possibility that powdering will progress before reaching the final stage, resulting in insufficient strength being obtained. In addition, in Patent Document 3, the drop strength of molded coal during transportation is evaluated based on the results of dropping molded coal multiple times from a height of 2.5 m. However, the transportation route may exceed 2.5 m due to the equipment configuration, and the powdering rate of molded coal varies depending on the drop height, and the molded coal becomes more likely to be powdered as the drop height increases, and detailed knowledge has not been obtained regarding the effect of the drop height on the powdering of molded coal.

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

[0011] As a result of extensive research aimed at solving the above-mentioned problems, the present invention has discovered a method for producing high-strength molded coal, and the gist of the method is as follows. 1. A molded coal production process in which coal powder and a binder are mixed and kneaded, and then molded to produce molded coal; and a transport process in which the molded coal is transported through a transport route in which a plurality of transport routes are connected via a transfer section in which the conveyance route becomes lower from the upstream side to the downstream side; A manufacturing method for molded coal in which the temperature of the molded coal passing through the upstream transfer section is kept below 30°C.

[0012] 2. The method for producing molded coal described in 1 above, wherein the molded coal is cooled in the most upstream conveying path.

[0013] 3. The method for producing molded coal described in 1 or 2 above, wherein the end point of the transport path is a coke oven.

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

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

[0016] 6. A method for producing molded coal according to any one of claims 1 to 5, wherein the mixing and kneading of the coal powder and the binder is carried out at a temperature range of 85°C to 105°C.

[0017] 7. A method for producing molded coal described in any one of items 2 to 6, in which the cooling of the molded coal is carried out by surrounding the most upstream transport path with a hood and installing an exhaust fan above the hood to generate an ascending air current within the hood. Effect of the Invention

[0018] According to the present invention, it is possible to provide a method for reliably preventing pulverization of molded coal at transfer sections between transport paths when transporting the molded coal after molding. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a diagram showing a production and transportation flow of molded coal according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the relationship between the molded coal temperature and the molded coal crushing strength according to the embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing the relationship between the briquette drop strength and the briquette temperature according to the embodiment of the present invention. [Figure 4] 1 is a schematic diagram showing a cooling device structure applied to a cooling method according to an embodiment of the present invention; [Diagram 5] FIG. 4 is a diagram showing a relationship between a cooling method and a briquette temperature according to an embodiment of the present invention. [Figure 6]FIG. 4 is a diagram showing the relationship between the mixing temperature and the crushing strength of molded coal according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0021] That is, the molded coal 3 molded by the roll molding machine 2 is discharged onto a conveyor 4, transfers between multiple conveyors 4, passes through a hopper 5 on the way, and then transfers between multiple conveyors 4 again before being thrown into a coke oven 6. Note that, midway along the transport path consisting of the multiple conveyors 4, powdered coal transported from another transport path may be merged, and the molded coal 3 may be transported together with the powdered coal, and both may be supplied to the coke oven.

[0022] [Molded charcoal production process] Here, examples of powders that can be used as raw materials for molded coal include coal powder, ore powder, and other powders such as converter input dust. In the manufacture of molded coal briquettes in the steelmaking process, it is preferable to use coal powder. The particle size of the coal powder is not particularly limited, but a finer particle size is preferable because the strength of the briquette is improved. For example, it is preferable that 80 mass % or more of coal powder having a particle size of 3 mm or less is contained, and more preferably 90 mass % or more is contained. Note that, when the proportion of coal powder having a particle size of 3 mm or less is less than 80 mass %, the coal powder may be pulverized as a whole or mixed with coal powder of another fine particle size to adjust the particle size to the above-mentioned range.

[0023] In addition, when multiple types of binders are mixed, the softening point changes and the bonding state with the coal powder changes due to the compatibility effect, so the strength improvement effect after molding varies depending on the type of binder. Therefore, it is preferable to appropriately set the type of binder and the mixing ratio required to improve the strength of the molded coal. Here, for example, either tar pitch or tar slag or both can be used as the binder. As another binder, soft oil pitch (SOP) can also be used.

[0024] The ratio of binders such as tar pitch and tar slag to be mixed with the coal powder is preferably 2.0 to 5.0% by mass for tar pitch and 4.0 to 9.0% by mass for tar slag relative to the total of the coal powder and binder. If the amount of binder is too small, the binding effect is weakened, and if the amount is too large, the cost of the raw material increases. For the same reason, it is preferable to mix soft oil pitch (SOP) at 1.0 to 6.0%.

[0025] [Transportation process] The molded coal 3 molded as described above is transported to the coke oven 6 via multiple conveyors 4. In this transport process, the molded coal 3 is transported through a transfer section 40 with a drop from the upstream conveyor 4 to the downstream conveyor 4. Since the molded coal 3 receives no small amount of impact when it falls at this transfer section 40, it is necessary to prevent it from being pulverized when it falls.

[0026] In order to avoid this pulverization during the drop, the technology disclosed in the above-mentioned Patent Document 3 adjusts the internal temperature of the briquettes to 50 to 60°C before the briquettes reach the transfer section. However, it has been newly discovered that even when the internal temperature of the briquettes is adjusted to 50 to 60°C, there are cases where the pulverization of the briquettes at the transfer section cannot be sufficiently suppressed, and in particular, when the drop in the transfer section is large, the suppression of pulverization is insufficient. Therefore, in the case where the drop in the transfer section is large, a method for reliably suppressing the pulverization of the briquettes was earnestly studied. As a result, it was newly discovered that setting the temperature of the briquettes 3 passing through the transfer section 40 at the most upstream, i.e., the first transfer section 40, to 30°C or less is effective in suppressing the pulverization of the briquettes. The experimental results that led to this finding will be described in detail below.

[0027] First, the following experiment was carried out to verify the relationship between the temperature and the crushing strength of molded coal. Specifically, coal powder (proportion of particles with a particle size of 3.0 mm or less: 91% by mass) and binder (tar slag and tar pitch) were added to a mixing chamber in a prescribed ratio (tar slag 6.0% by mass, tar pitch 4.5% by mass) and mixed for a prescribed time (120 s). The kneading treatment was carried out at 100°C, and molded coal was produced in a molding machine. Next, a prescribed amount of molded coal was collected at the discharge position on the exit side of the molding roll, the temperature of the molded coal after collection was measured, and the crushing strength of the molded coal was measured at temperatures at 5°C intervals during the temperature drop from 60°C to 20°C. The crushing strength of the molded coal at each temperature step was measured according to the JIS The measurement was performed according to Z8841. That is, the molded coal was set in a compression tester, pressure was applied to the molded coal, and the pressure at which the molded coal was crushed was taken as the crushing strength of the molded coal. The inventors performed the same test on many molded coals they had prepared, and obtained the results shown in FIG. 2. The crushing strength shown in FIG. 2 is the average value of measurements taken on 10 molded coals. As shown in FIG. 2, the crushing strength decreases when the temperature of the molded coal is high. When the crushing strength decreases, the molded coal cannot withstand the impact of being dropped during transportation, and the molded coal is easily broken and powdered significantly.

[0028] During the transfer of briquettes, the height of the transfer section between conveyors is generally about 2m to 5m, but may be about 8m depending on the installation constraints of the transfer equipment. Therefore, the influence of briquettes powdering due to dropping at the maximum height during transfer was investigated. After producing briquettes (grain size: 44mm) with different crushing strengths, 8kg of briquettes with the same crushing strength were collected and a drop test was conducted in which the briquettes were dropped onto an iron plate. The drop height was 2.5m, 5.5m, and 8.0m, and the drop strength of the briquettes was evaluated. The drop strength was calculated by collecting all the briquettes after dropping, measuring the weight of the sieved portion after sieving using a sieve with 10mm mesh, and calculating the ratio of the sieved weight to the combined value of the undersieve weight and the oversieved weight. Figure 3 shows the relationship between the briquettes temperature and the drop strength. As shown in Figure 3, when the drop height was 2.5 m, the strength tended to be maximum when the molded coal temperature was around 60°C. However, when the drop height was 5.5 m or 8.0 m, the drop strength rapidly decreased and powdering became noticeable when the molded coal temperature exceeded 30°C.

[0029] The above findings are different from the experimental results shown in Fig. 2 of Patent Document 3, but this is presumably due to the drop height. When the drop height was low at 2.5 m, the impact of the molded coal colliding with the drop surface was relatively small, so that only small cracks were generated on the molded coal surface, and the molded coal after the drop test had a particle size of 10 mm or more regardless of the temperature. On the other hand, when the drop height was 5.5 m or 8.0 m, the impact of the drop was significantly increased, so the molded coal after the drop was broken into pieces, and the ratio of molded coal with a particle size of 10 mm or more was drastically reduced under conditions of high molded coal temperature.

[0030] From the above experimental results, it has been newly discovered that keeping the temperature of the molded coal 3 passing through the first transfer section 40 at 30°C or less is effective in suppressing powdering of the molded coal even when the height of the molded coal falls at the transfer section 40 is high. Specifically, it is preferable to perform a cooling treatment on the molded coal 3 on the conveyor 4 at the most upstream conveyor 4 leading to the transfer section 40. This is because the temperature of the molded coal obtained through the process of mixing and kneading the 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 keep the molded coal temperature below 30°C after molding. Here, we compared various methods, including the presence or absence of a hood that covers the entire length of the most upstream conveyor 4, and changing the method of cooling the molded coal on the conveyor (upward blowing, downward blowing, or exhaust). Each cooling mode (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 the 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] Figure 5 shows the results of measuring the molded coal temperature after cooling using each method. The molded coal temperature was measured by collecting samples at the exit of the most upstream conveyor. When the molded coal was not cooled, the temperature was high at 65°C. On the other hand, after cooling using each method, it was found that by using a method in which the air is exhausted by a fan from above the hood, it was possible to keep the molded coal temperature below 30°C.

[0033] As for the operating conditions of the fan used in the above-mentioned top exhaust system, the air volume is calculated from the conveyor area so that the average wind speed inside the hood of the cooling device 7 is 5 m / s or more, and the number of fans required is determined. In the present invention, in order to keep the cooling temperature of the molded coal at 30°C or less, a fan speed of 35 Nm is required. 3 / min*m 2 A volume of airflow of 100m was required.

[0034] [Kneading mixer] In addition, it is preferable to use a horizontal kneader for the kneading mixer 1 that mixes and kneads the above-mentioned coal powder and binder. That is, a horizontal kneader can simultaneously knead and mix by optimizing the arrangement of paddles inside the kneader, and can reduce equipment costs and save space for the device compared to a vertical type.

[0035] [Mixing and kneading conditions] The mixing and kneading of the coal powder and binder, which are the raw materials for the 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] That is, the influence of mixing temperature and kneading before making molded coal was investigated. After changing the amount of steam put into the horizontal kneader and making samples with different mixing temperatures, each sample was molded into molded coal and the crushing strength of the molded coal was measured. The crushing strength of the molded coal was measured in accordance with JIS Z8841. That is, the molded coal was placed in a compression tester, pressure was applied to the molded coal, and the pressure at which the molded coal was crushed was taken as the crushing strength of the molded coal.

[0037] As shown in FIG. 6, the measurement results show that high-strength molded coal can be produced by keeping the mixing temperature in the range of 85°C to 105°C. That is, when the temperature during mixing exceeds 105°C, if the capacity of the cooling device is insufficient, the molded coal temperature may rise above 30°C, and the strength of the molded coal may decrease. Note that the decrease in the strength of the molded coal can be avoided by increasing the length of the cooling device (i.e., the conveyor length), but this is not realistic because the equipment length would increase.

[0038] In the present invention, it is preferable to select a horizontal kneader as the equipment for mixing and kneading the coal powder and the binder. Here, examples of equipment methods for mixing and kneading the coal powder and the binder include a Henschel mixer and a vertical paddle type. However, in the case of a Henschel mixer, the kneading and mixing method is a batch type, and multiple units need to be installed when performing large-scale processing, which increases the equipment costs. In addition, in the case of a vertical paddle type (vertical kneader), since the equipment configuration only has the function of kneading, a separate mixing device is required, which increases the area required for installation and increases the equipment costs, etc.

[0039] Although the steam injection method has been described as an example of a method for heating the raw materials, other heating methods such as microwave irradiation or the installation of a heat medium around or inside the mixer (e.g., electric heater or gas combustion device) may be used in addition to steam injection. In the case of the steam injection method, the heat source can be secured within the steelworks, and costs can be kept relatively low. In addition, when microwave irradiation is used, it is possible to shorten the heating time compared to other methods, so it is an effective means for shortening the processing time. When an electric heater method or gas combustion method is used, it is possible to handle higher temperature conditions than steam heating.

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

[0041] Briquette coal was produced under the conditions shown in Table 1 using the briquette coal production equipment shown in Figure 1. The drop strength, powdering rate and crushing strength of the obtained briquette coal were measured and evaluated in the same manner as in the above-mentioned experiment. For comparison, the drop strength, powdering rate and crushing strength of the obtained briquette coal without cooling were also measured and evaluated in the same manner. The drop height at the transfer section was 8 m.

[0042] The powdering rate was evaluated by sampling the molded coal at the outlet of the hopper 5 shown in Fig. 1. That is, 8 kg of the molded coal at the outlet of the hopper 5 was collected, and the weight of the under-sieve portion after sieving the collected portion using a sieve with a mesh size of 15 mm was measured, and the ratio of the under-sieve weight to the combined weight of the under-sieve weight and the over-sieve weight was defined as the powdering rate. The crushing strength was measured according to JIS Z8841 for the molded coal collected at the outlet of the cooling device 7.

[0043] As shown in Table 1, the briquettes produced according to the present invention were prevented from pulverizing even when dropped from a high height. Furthermore, the crushing strength of the briquettes was not reduced, and pulverization during transportation was also prevented.

[0044] [Table 1] [Explanation of symbols]

[0045] 1. Kneading mixer 2. Roll forming machine 3 Molded coal 4. Conveyor 5. Hopper 6. Coke Oven 7 Cooling device 8 Fans 9. Food 40 Transfer Section

Claims

1. The method includes a molded coal preparation process in which coal powder and a binder are mixed and kneaded, and then molded to prepare molded coal; and a transport process in which the molded coal is transported through a transport route in which a plurality of transport paths are connected via a transfer section in which the conveyance path becomes lower from the upstream side to the downstream side, A method for producing molded coal, in which the temperature of the molded coal passing through the most upstream transfer section is 30°C or lower.

2. The method for producing molded coal according to claim 1 , wherein the molded coal is cooled in the most upstream conveying path.

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

4. The method for producing molded coal according to claim 1 or 2, further comprising a hopper for temporarily storing the molded coal, the hopper being disposed in the middle of the conveying path.

5. The method for producing molded coal according to claim 1 or 2, wherein the coal powder and the binder are mixed and kneaded 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 the binder is carried out at a temperature in the range of 85°C to 105°C.

7. 3. The method for producing molded coal according to claim 2, wherein the molded coal is cooled by surrounding the most upstream transport path with a hood and by installing an exhaust fan on an upper portion of the hood to generate an ascending air current within the hood.

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