Method for placing raw materials in a coke oven and method for producing coke

Abstract

To propose a technology that can suppress a decrease in coke strength when blending a synthetic resin.SOLUTION: There is provided a method for arranging a raw material in a coke oven, comprising: unevenly distributing a synthetic resin near a machine side and near a coke side of a carbonization chamber when the synthetic resin is charged into the coke oven together with raw coal as a coke raw material; dividing the carbonization chamber equally into four or more regions in a longitudinal direction, and distributing more amounts of the synthetic resin to the region in contact with the machine side and the region in contact with the coke side than in other regions; and preferably controlling a sum of the amounts of the synthetic resin distributed to a region in contact with the machine side and a region in contact with the coke side into 75% or more of the amount of the synthetic resin charged into the entire coke oven. There is also provided a method for manufacturing a coke, comprising carbonizing the synthetic resin and raw coal charged according to the method for arranging a raw material in a coke oven.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for placing raw materials in a coke oven and a method for producing coke when recycling synthetic resins, such as waste plastics, as raw materials for iron making in the coke oven. In the following description, the unit of mass, "t," is 10 3 In this specification, "synthetic resins" includes not only used plastics that are general waste, commonly known as waste plastics, but also plastics that become industrial waste, such as scraps and defective synthetic resins generated in the manufacturing process, and used plastics. [Background technology]

[0002] In recent years, marine pollution caused by waste plastic has become a global problem, with the amount of waste plastic dumped into the ocean estimated to be approximately 8 million tons per year worldwide. Addressing marine pollution was one of the Sustainable Development Goals (SDGs) adopted at the 2015 United Nations Summit. In response, Europe has adopted the EU Plastics Strategy, which aims to strengthen plastic recycling and reduce single-use plastics. Japan enacted the Containers and Packaging Recycling Law in 1995 and has been promoting waste plastic recycling for a long time. In response to growing momentum for further plastic waste reduction, the Act on Promotion of Resource Recycling Related to Plastics came into effect in 2022, calling for further strengthening of waste plastic recycling. In the steel industry, a technology has been put into practical use to recycle waste plastic as raw material for steelmaking by mixing it with coal and charging it into coke ovens. This technology is being implemented as a chemical recycling technology for waste plastic under the Containers and Packaging Recycling Law. However, it is known that mixing waste plastics into coal to produce coke reduces the strength of the coke, and the upper limit of the waste plastic mixing ratio at which coke strength does not decrease is said to be approximately 1 mass% (Non-Patent Document 1). Therefore, various technologies have been developed to suppress the deterioration of coke strength due to the mixing of waste plastics.

[0003] For example, Patent Document 1 describes a glass fiber having no holes or cracks extending from the surface to the inside and an apparent density of 0.85 to 1.1 g / cm 3 and volume is 6000~200000mm 3 (6~200cm 3 A method for carbonizing plastic granules in a coke oven is disclosed. To form such granules, a method is shown in which waste plastic containing thermoplastic resin is heated to a temperature of 180 to 260°C in a molding device that extrudes the waste plastic from a nozzle, and the plastic is extruded from the nozzle while gas is being sucked in, followed by water cooling.

[0004] Patent Document 2 discloses a method for pyrolysis recycling in which waste plastics are charged above the raw materials in the coke oven chamber at least one hour after the raw materials are charged into the chamber. The method claims that by utilizing the space above the coke oven, a large amount of waste plastics can be recycled without affecting the strength of the coke. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-293032 [Patent Document 2] Japanese Patent Application Publication No. 2019-135281 [Non-patent literature]

[0006] [Non-Patent Document 1] Nomura, Seiji, Kato, Kenji, Nakagawa, Tomoyuki, Furumaki, Ikuo Journal of the Japan Institute of Energy, Vol. 81, No. 8 (2002) pp. 728-737 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the conventional technology has the following problems. The technology disclosed in Patent Document 1 is characterized by the production of plastic granules that lack holes or cracks extending from the surface to the interior. When molding synthetic resins using a twin-screw extruder, the synthetic resin extruded from the nozzle is cut with a cutter to achieve a uniform length. However, cutting without cracks or holes is practically difficult. Furthermore, while the heating temperature is set to 180-260°C, the specific temperature within the device is not specified. Furthermore, when the heating temperature is set to 180°C or higher, gas is generated by thermal decomposition of the synthetic resins, and the accumulated gas forms voids within the molten synthetic resins, resulting in a decrease in density. While it is possible to suppress the decrease in coke strength by modifying the properties of the synthetic resins, the strength loss due to the generation of voids in the coke remains unresolved. Furthermore, suppressing the decrease in coke strength is difficult when the synthetic resin content is high.

[0008] Furthermore, the technology disclosed in Patent Document 2 can minimize the impact on coke strength by separating coal and waste plastics. However, because the raw material charging lid must be opened after charging coal to charge the waste plastics, strict control is required to ensure that the amount of gas generated does not exceed the amount of gas suction to prevent gas leakage. However, if the amount of gas generated in the coke chamber increases or decreases due to fluctuations in coal quality or other factors, control becomes difficult, and there is a risk of the generated gas leaking outside and causing abnormal combustion. Furthermore, although a large amount of gas is suctioned from the upper part of the coke chamber, if waste plastics are carbonized in the upper part of the coke chamber, a large amount of powdered charred waste plastics is suctioned, which may cause blockages in the gas recovery and cleaning line. In addition, this charred waste plastics may be mixed into the recovered tar, reducing the quality of the tar recovered as a product. Furthermore, because plastics are charged after the raw materials are charged into the coal tower, a dedicated hopper for waste plastics must be provided on top of the coal car. This additional raw material charging procedure reduces the productivity of the coke oven.

[0009] The present invention has been made in consideration of the above circumstances, and aims to propose a method for arranging raw materials in a coke oven and a method for producing coke that can suppress a decrease in coke strength when synthetic resins are blended. [Means for solving the problem]

[0010] The method of arranging raw materials in a coke oven according to the present invention, which advantageously solves the above-mentioned problems, is characterized in that when synthetic resins are charged into a coke oven together with raw coal as coke raw materials, the synthetic resins are unevenly distributed near the machine side and the coke side of the carbonization chamber.

[0011] The method for converting synthetic resins into raw materials for iron making according to the present invention includes the steps of: (a) Dividing the coke chamber into four or more equal regions in the longitudinal direction, and allocating more of the synthetic resins to the region in contact with the machine side and the region in contact with the coke side than to the other regions; (b) The sum of the amounts of the synthetic resins allocated to the area in contact with the machine side and the area in contact with the coke side is 75% or more of the amount of the synthetic resins charged to the entire coke oven; This may be a more preferable solution.

[0012] The method for producing coke according to the present invention, which advantageously solves the above-mentioned problems, is characterized by carbonizing synthetic resins and raw coal charged by any of the above-mentioned methods for placing raw materials in a coke oven. [Effects of the Invention]

[0013] In the present invention, the synthetic resins are concentrated at both ends of the coke chamber in the longitudinal direction, which reduces the mixing ratio of the synthetic resins in other parts and makes it possible to suppress a decrease in coke strength. This makes it possible to process larger amounts of synthetic resins. Although the coke strength decreases at the ends where the synthetic resins are concentrated, the severely deteriorated parts are crushed into fine coke by the impacts they receive in the subsequent coke transport process and cooling process (coke dry quenching device, wet quenching device, etc.). The fine coke can be recovered and used as fuel in processes such as iron ore sintering.

[0014] Furthermore, because synthetic resins volatilize during thermal decomposition, when they are mixed with coal and carbonized, voids form within the coke, and cracks propagate from these voids. When synthetic resins are dispersed in coal and charged, cracks propagate from the dispersed voids during coking, making the coke more susceptible to crumbling, making it difficult to push and discharge from the coke oven. However, by concentrating the synthetic resins on the coke side and machine side, cracks are limited to the ends of the coke cake. This prevents the middle part of the coke cake from collapsing, making it easier to push and discharge the coke.

[0015] Furthermore, it is known that synthetic resins absorb heat when they are thermally decomposed in an oxygen-free environment. If they absorb heat while in contact with the refractory bricks of a coke oven, the temperature drops locally, and thermal stress can reduce the durability of the refractory bricks. However, since heat is removed largely on the coke side and machine side, and the refractory bricks are relatively cool, they are less susceptible to the temperature drop caused by heat absorption. This has the effect of suppressing brick deterioration. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are schematic diagrams illustrating a method for disposing raw materials in a coke oven according to one embodiment of the present invention, in which (a) is a plan view and (b) is a side view. [Figure 2]1A and 1B are schematic diagrams illustrating a method for arranging raw materials in a coke oven according to a comparative example, in which (a) is a plan view and (b) is a side view. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following is a detailed description of embodiments of the present invention. The following embodiments are intended to exemplify equipment and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0018] (Method of arranging raw materials in a coke oven) In this embodiment, when coal and molded synthetic resins are supplied as raw materials into the coke oven carbonization chamber, the synthetic resins are unevenly distributed at the ends of the carbonization chamber in the longitudinal direction. That is, the synthetic resins are arranged so that the mixing ratio (= synthetic resin mass / (coal mass+synthetic resin mass)×100, mass-based percentage) of the synthetic resins on the coke discharge side [hereinafter referred to as the coke side (C / S)] and the coke extrusion side [hereinafter referred to as the machine side (M / S)] is as high as possible.

[0019] In this embodiment, it is preferable to divide the interior of the coke chamber into four or more equal regions in the longitudinal direction of the coke chamber, and charge synthetic resins so that the mixing ratio of the synthetic resins in the region adjacent to the coke side and the region adjacent to the machine side exceeds the mixing ratio of the synthetic resins in the other inner regions. Furthermore, it is more preferable that the mixing ratio ratio is three times or more. In this case, it is preferable that the total mass of the synthetic resins charged in the region adjacent to the coke side and the region adjacent to the machine side is 75% or more of the total. In this case, the mixing ratio of the synthetic resins in the other inner regions is 50% or less of the average mixing ratio of the synthetic resins overall. Therefore, the decrease in strength of the coke after carbonization in that region can be suppressed to 50% or less compared to when the synthetic resins are evenly distributed. While there is no upper limit to the number of regions in the coke chamber, taking into account the installation load of the raw material charging equipment, it is preferable to divide the coke chamber into 10 or less regions, and more preferably 6 or less regions.

[0020] The carbonization chamber of a typical coke oven is a long, narrow, roughly rectangular parallelepiped (for example, W0.6m x D15m x H7m). To distribute the raw materials evenly throughout the chamber, coal is charged through multiple coal inlets aligned along the length of the chamber (direction D). By increasing the mixing ratio of synthetic resins charged through the inlet closest to the coke side or machine side, it is possible to concentrate and unevenly distribute waste plastics near the coke side or machine side.

[0021] In this embodiment, the amount of synthetic resins mixed with coal added to the coke oven is not particularly limited, but is preferably 0.5 mass% or more relative to the total amount of raw materials charged to the coke oven from an environmental perspective. More preferably, it is more than 1.0 mass%, and even more preferably, it is 3.0 mass% or more. There is no particular upper limit, but adding more than 5 mass% may reduce coke strength. In particular, when adding a large amount of synthetic resins, it is preferable to distribute the synthetic resins unevenly in the region near the coke side and machine side so that the amount of synthetic resins is 1.0 mass% or less relative to the raw materials charged in the inner region excluding the region near the coke side and machine side.

[0022] (Synthetic resin moldings) When the same mass of synthetic resins is added, the more they are added, the lower the coke strength becomes. When synthetic resins are carbonized in coal, they have a high volatile content, which causes voids to form after evaporation, resulting in voids inside the coke after carbonization. Since voids are the starting point for cracks inside the coke, it is thought that the more voids there are, the more cracks will occur, and the lower the coke strength becomes.

[0023] Synthetic resins are molded, for example, using a twin-screw extruder to produce molded synthetic resin products. The synthetic resins are crushed or pre-granulated before being supplied. In this case, it is preferable to adjust the moisture content of the synthetic resins to 5% by mass or less. By reducing the moisture content of the synthetic resins, the synthetic resins can be molded stably, and the density of the molded product increases. Various types of dryers, including hot air flow dryers, can be used to evaporate the moisture from the synthetic resins.

[0024] Any twin-screw extruder suitable for use in this embodiment and capable of molding synthetic resins may be used, with no difference in basic structure. The feedstock is kneaded by twin screws housed in a casing, and the synthetic resin is extruded through a nozzle attached to a heated plate. The cylindrically extruded synthetic resin is cut by a rotary cutter to a fixed length. The volume per synthetic resin is adjusted by the nozzle inner diameter and the cutter cutting speed. Nozzles with an inner diameter of 2.0 to 3.0 cmφ are typically used. Large-diameter nozzles with an inner diameter of 4.0 to 6.0 cmφ are used for molding, enabling the production of large molded products. The mass of synthetic resin per unit increases, increasing the amount that can be charged for the same number of units.

[0025] The molded synthetic resins are cylindrical with a diameter equal to or slightly larger than the inner diameter of the nozzle, and their length can be adjusted by the rotation speed of the cutter. The length of the molded product is affected by the position and condition of the forming nozzle, so it is difficult to make it a constant length. There is a distribution of molded products ranging from short to long. The volume can be increased by increasing the maximum length of the molded product, but it is preferable that the maximum length within the molded product length distribution be 20 cm or less. This is because the diameter of the charging port at the top of the carbonization chamber of a coke oven is about 40 to 50 cm, and if the maximum length is made longer than this, clogging may occur. The average volume of the molded product is 90 cm. 3 More than 150cm is preferable. 3 More than 200cm is preferable. 3The upper limit depends on the size of the charging port when charging into the coke oven, but is 1000 cm 3 It is preferable that the distance is less than 600 cm 3 It is more preferable that:

[0026] (Coke manufacturing method) The molded synthetic resins are loaded into a hopper, fed at a constant speed by a metering feeder, and then fed onto the coal on a belt conveyor that supplies blended coal to the coke oven. In this embodiment, a larger amount of synthetic resins is distributed through the charging ports closest to the coke side and machine side, and a smaller amount is distributed through the other charging ports. This reduces the mixing ratio of synthetic resins introduced through the other charging ports, thereby suppressing a decrease in coke strength after carbonization in that area. As an index of coke strength, the drum strength index (DI150 / 15) can be measured according to the drum strength measurement method specified in JIS K2151:2004, a coke testing method. After 150 rotations, the coke is charged into a drum testing machine, sieved through a 15 mm mesh sieve, and the mass fraction remaining on the sieve is measured. When using the drum strength index (DI150 / 15), it is preferable to ensure that the decrease in DI150 / 15 is less than one point. It is known that the DI150 / 15 index has a measurement error of about 0.5 points, and a strength drop of 1 point or more clearly indicates a decrease in coke strength. In coke oven operations, a drop in coke strength (DI150 / 15) of 1 point or more is recognized as a decrease in coke strength, and operations such as improving the quality of the coking coal may be carried out.

[0027] The synthetic resin mixture ratio is basically controlled by measuring the coal and synthetic resin feed rates in advance and adjusting the feed rate of the quantitative feeder or gate opening to maintain a constant ratio. Furthermore, the synthetic resin mixture ratio in the longitudinal direction (D direction) of the coke oven chamber is difficult to measure directly. Therefore, it can be estimated from the synthetic resin mixture ratio in each hopper of the coal car above the coke chamber's coal inlet. When raw materials are charged into a single coke oven through multiple inlets, they are simultaneously charged through each inlet, so the synthetic resin mixture ratio directly below each inlet is considered to be the same as the synthetic resin mixture ratio in each hopper of the coal car. The synthetic resin mixture ratio in each hopper of the coal car can be estimated by installing a camera above each hopper, detecting synthetic resins through image analysis, and calculating the synthetic resin charge mass.

[0028] The synthetic resin moldings should preferably be cut out from a location where the belt conveyor is low after passing through the coal drying facility (CMC). Because the coal is heated and dried in the CMC, if synthetic resin moldings are added before the CMC, there is a risk that the synthetic resin moldings will melt inside the CMC. The synthetic resin moldings pass through a coal tower and coal transport car together with blended coal and are supplied to the carbonization chamber. The synthetic resins are thermally decomposed in the carbonization chamber, and some remain as charcoal, but most are recycled as gas or tar. [Example]

[0029] (Example 1) A mixture of waste plastics, primarily composed of thermoplastic resins, was crushed, and after confirming that the moisture content was 5% or less, it was extruded from a 40 mm diameter nozzle while being heated using a twin-screw extruder, and then cut and formed into a cylindrical shape. As shown in Figure 1, the resulting molded product 1 was charged into a carbonization vessel 3 together with approximately 40 kg of blended coal 2, which was used as a coke raw material. To arrange the waste plastic molded products 1, the amount of blended coal 2 was divided into eight parts, and first, 1 / 8 of the blended coal was laid out in the carbonization vessel 3. Then, a predetermined amount of waste plastic molded products 1 (1 / 4 of the amount to be charged) was arranged so that it was in contact with one end of the carbonization vessel 3 in the longitudinal direction. Next, another 1 / 8 of the blended coal was charged, until the density of the charged coal reached 830 kg / m 3 The mixture was compressed to a compact size. This process was repeated four times, and the waste plastic molded products 1 were arranged so that they were unevenly distributed at one end of the can in the longitudinal direction. Figure 1(a) is a plan view illustrating the arrangement of the waste plastics in the carbonization can 1. Figure 1(b) is a side view illustrating the arrangement of the waste plastics in the carbonization can 1. The blend ratio of the waste plastics to the blended coal mass was 3 mass%. After carbonization at 700 to 1100 °C for 20 hours in a test carbonization furnace, the mixture was quenched by pouring water over it from above and then dried to obtain coke. The obtained coke was charged into a drum testing machine and rotated 150 times according to the drum strength measurement method specified in JIS K2151:2004, a coke testing method. The mass fraction of the remaining particles was sieved through a 15 mm mesh sieve and measured as the drum strength index DI150 / 15. Many cracks were observed on the side of the carbonized coke where the waste plastic molded products 1 were concentrated, suggesting a decrease in coke strength in this area. On the other hand, the other cokes were in good condition.

[0030] (Comparative Example 1) As shown in Figure 2, waste plastic molded objects 1, produced using the same method as in the example, were distributed as uniformly as possible within approximately 40 kg of coal blend 2. To distribute the waste plastic molded objects 1, the coal blend 2 was divided into eight portions, and 1 / 8 of the coal blend 1 was first laid in the carbonization vessel 3. The waste plastic molded objects 1 were then arranged so that their centers were located at 1 / 4 and 3 / 4 of the length from one end of the carbonization vessel 3 in the longitudinal and transverse directions, respectively. This arrangement was made to correspond to 1 / 4 of the planned amount of waste plastic to be charged. This process was repeated four times, and when the carbonization vessel 3 was divided into four longitudinal portions, the waste plastic mixing ratio was the same in each region. Figure 2(a) is a plan view illustrating the arrangement of waste plastic within the carbonization vessel 1. Figure 2(b) is a side view illustrating the arrangement of waste plastic within the carbonization vessel 1. The waste plastic mixing ratio relative to the coal blend mass was 3% by mass. After carbonization in a test carbonization furnace at 700 to 1100°C for 20 hours, the mixture was quenched by pouring water over it from above and then dried to obtain coke. The obtained coke was charged into a drum testing machine, rotated 150 times, and sieved through a 15 mm sieve, and the mass fraction remaining on the sieve was measured as the drum strength index DI150 / 15, according to the drum strength measurement method specified in JIS K2151:2004, a coke testing method.

[0031] A comparison of the drum strengths of the obtained cokes is shown in Table 1. As a reference example, the strength of coke obtained by carbonizing only blended coal is also shown in Table 1. When waste plastic molded materials 1 are evenly distributed among the coal in the carbonization vessel 3 as in the comparative example, the drum strength of the coke is significantly reduced compared to the reference example. It was found that by concentrating the waste plastic molded materials 1 at one end of the carbonization vessel 3 as in the invention example, the decrease in drum strength compared to the reference example is suppressed.

[0032] [Table 1]

[0033] (Example 2) A mixture of waste plastics, primarily composed of thermoplastic resins, was crushed and confirmed to have a moisture content of 5% or less. It was then heated and extruded through a 40mm diameter nozzle in a twin-screw extruder, cut into pieces 20mm or longer in length, and formed into cylindrical shapes. This material was then mixed with a coke oven coal blend at a mixing ratio of 3% by mass and loaded into the hopper of a coal delivery car above the coke oven as coke raw material. The coal delivery car was equipped with four hoppers. Of the hoppers, the coal mixed with the waste plastics was loaded into the hoppers closest to the machine side and the coke side, respectively, while the inner hopper was loaded with coal alone. Next, coke raw material was simultaneously discharged from the bottom of each hopper on the coal delivery car and loaded into the coke chamber. The waste plastic mixing ratio on the machine side and the coke side of the coke chamber was 3% by mass, and the waste plastic mixing ratio in the middle section was 0% by mass. The average waste plastic mixing ratio in the coke chamber was 1.5% by mass. The strength of the coke obtained after carbonization was measured according to the drum strength measurement method specified in JIS K2151:2004, a test method for cokes. The result was that the drum strength index DI150 / 15, which is the mass fraction of the sieve residue after sieving through a 15 mm mesh sieve after charging into a drum testing machine and rotating it 150 times, was 85.7. Furthermore, the coke cake extrusion property after carbonization was better than that of Comparative Example 2 described below.

[0034] (Comparative Example 2) A mixture of waste plastics, primarily consisting of thermoplastic resins, was crushed and confirmed to have a moisture content of 5% or less. It was then heated and extruded through a 40 mm diameter nozzle using a twin-screw extruder, cut into cylindrical pieces with an axial length of 20 mm or more, and formed into a cylindrical shape. This mixture was mixed with a coke oven coal blend to a blending ratio of 1.5% by mass and then evenly charged into the four hoppers of a coal car above the coke oven as coke raw material. Coal was then simultaneously excavated from the bottom of each hopper of the coal car, ensuring a uniform blending ratio of 1.5% by mass of waste plastics in the coke chamber. The strength of the coke obtained after carbonization was measured according to the drum strength measurement method specified in JIS K2151:2004, a coke testing method. The drum strength index (DI150 / 15), which is the mass fraction of the sieved material remaining on a 15 mm mesh sieve after 150 rotations in a drum testing machine, was 84.0. In addition, the pushability of the coke cake after carbonization was worse than in Example 2, and a larger power was required to discharge the coke cake. [Explanation of symbols]

[0035] 1. (Waste plastic) Molded products 2 Blended coal 3. Carbonization chamber

Claims

1. A method for arranging raw materials in a coke oven, in which synthetic resins are charged into a coke oven together with raw coal as coke raw materials, the carbonization chamber is divided equally into four to six regions in the longitudinal direction, and the mixing ratio of synthetic resins in the region adjacent to the machine side and the region adjacent to the coke side is at least three times the mixing ratio of synthetic resins in other inner regions.

2. A method for arranging raw materials in a coke oven as described in claim 1, in which the synthetic resins are distributed in other inner areas excluding the area in contact with the machine side and the area in contact with the coke side so that the synthetic resins are distributed so as to be 1.0 mass% or less per charged raw material.

3. 3. A method for placing raw materials in a coke oven as described in claim 2, wherein the sum of the amounts of synthetic resins allocated to the area in contact with the machine side and the area in contact with the coke side is 75% or more of the amount of synthetic resins charged to the entire coke oven.

4. A method for producing coke, comprising carbonizing synthetic resins and raw coal charged by the method for disposing raw materials in a coke oven according to any one of claims 1 to 3.

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