Coke manufacturing method

Abstract

This invention provides a method for producing coke that suppresses the decrease in strength of molded charcoal and coke, even when biomass raw materials are blended into molded charcoal for coke production, and enables the production of high-strength coke. [Solution] A method for producing coke by carbon distillation of a blended coal obtained by mixing molded coal containing coal and biomass-derived charcoal material with powdered coal containing powdered coal, characterized in that the volatile content of the biomass-derived charcoal material contained in the molded coal is 4% by mass or more and 30% by mass or less, and the proportion of biomass-derived charcoal material with a particle size of 150 μm or less contained in the molded coal is 40% by mass or less.

Description

Technical Field

[0001] The present invention relates to a method for producing coke, and particularly to a method for producing coke that can suppress a decrease in the strength of formed charcoal and produce high-strength coke when a biomass raw material is blended with formed charcoal to produce coke.

Background Art

[0002] Coke for blast furnaces is used as a reducing agent, a heat source, and a support material for maintaining air permeability and liquid permeability in the blast furnace. In order to stably operate the blast furnace, it is necessary to ensure air permeability and liquid permeability in the blast furnace, and coke with excellent properties such as strength and particle size is required. Among these, the strength of coke such as rotary strength is particularly important.

[0003] In recent years, the need to reduce carbon dioxide (CO2) emissions has been increasing, and in fields that used coal or oil as raw materials, studies have been underway to replace those raw materials with carbon-neutral raw materials such as biomass. In the steel industry as well, it is required to utilize biomass-derived raw materials as raw materials for coke used in blast furnaces.

[0004] The lump coke used in blast furnaces is produced by carbonizing coal in a retort furnace, where the coal softens and melts and adheres to each other. Therefore, in order to produce high-strength coke, binding charcoal with excellent softening and melting properties is used. On the other hand, biomass-derived raw materials do not soften and melt like coal, so when used in the process of producing coke from conventional coal, low-strength coke with many defects is obtained. Therefore, when using biomass-derived raw materials, measures are needed to suppress a decrease in coke strength.

[0005] Conventionally, the molded coal method is known as a method for using non-coking coal with poor softening and melting properties in coke production (see, for example, Patent Document 1). In the molded coal method, since agglomerated material (molded coal) is formed by mechanical compression, even when non-coking coal is used, the distance between coal particles can be shortened, promoting adhesion between non-coking coal particles even if the coking properties are poor, and improving the coke strength.

[0006] When using non-coking biomass raw materials in coke production, it is generally considered preferable to use the molded coal method, similar to non-coking coal. However, when biomass-derived raw materials are used, the strength of the molded coal may decrease. Furthermore, the effect of biomass raw materials blended into molded coal on coke strength has not been sufficiently studied.

[0007] Studies have been conducted to date on using biomass raw materials for molded charcoal. For example, Patent Document 2 describes a method for producing molded charcoal by mixing biomass charcoal obtained by carbonization of biomass, tar obtained by carbonization of biomass, coal, and a solid binder, and then pressurizing and molding the mixture. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2023-136520 [Patent Document 2] Japanese Patent Publication No. 2011-93980 [Overview of the project] [Problems that the invention aims to solve]

[0009] As mentioned above, when using biomass raw materials in coke production, measures are needed to suppress the decrease in coke strength. It is thought that it is possible to suppress the decrease in coke strength by blending biomass-derived raw materials into molded coal, as in the case of non-coking coal, but the effect of biomass raw materials blended into molded coal on the molded coal strength and coke strength has not been sufficiently studied.

[0010] Furthermore, the conventional method of incorporating biomass raw materials into molded charcoal, as described above, had its drawbacks. Specifically, the method for producing molded charcoal described in Patent Document 2 involves mixing biomass charcoal obtained by carbonizing biomass, tar obtained during biomass carbonization, coal, and a solid binder, and then press-molding the mixture. This achieves the production of molded charcoal with higher strength than when incorporating uncarbonized biomass, and with strength equivalent to that of ordinary molded charcoal. However, in recent years, with the growing need to reduce CO2 emissions, it has become necessary to carbonize biomass using carbon-neutral gases and tar generated from the biomass itself. Therefore, it is difficult to use tar generated during biomass carbonization in the production of molded charcoal.

[0011] The present invention has been made in view of the above problems, and its purpose is to provide a method for producing coke that can produce high-strength molded charcoal and high-strength coke even when biomass raw materials are blended into molded charcoal for coke production. [Means for solving the problem]

[0012] The inventors of this invention conducted diligent research to solve the above problems and obtained the following findings. Specifically, they found that when biomass is blended into molded charcoal, it is possible to suppress the decrease in molded charcoal strength by appropriately controlling the particle size of the blended biomass. Furthermore, they found that by controlling the volatile content of the blended biomass, it is possible to significantly suppress the decrease in coke strength caused by the blending of biomass-derived raw materials, and that high-strength coke can be obtained using biomass-derived raw materials.

[0013] Based on the above findings, the gist of the present invention is as follows.

[0014] [1] A method for producing coke by carbon distillation of a blended coal obtained by mixing molded coal containing coal and biomass-derived coal material with powdered coal containing powdered coal, The volatile content of the biomass-derived carbon material contained in the molded charcoal is 4% by mass or more and 30% by mass or less. A method for producing coke, characterized in that the biomass-derived carbon material contained in the molded charcoal has a particle size of 150 μm or less, with a proportion of 40% by mass or less.

[0015] [2] The method for producing coke according to [1], wherein the proportion of the biomass-derived carbon material in the molded charcoal is 4% by mass or more and 30% by mass or less. [Effects of the Invention]

[0016] According to the present invention, even when biomass raw materials are blended into molded charcoal for coke production, it is possible to suppress the decrease in strength of molded charcoal and coke, and to provide a method for producing high-strength coke. [Brief explanation of the drawing]

[0017] [Figure 1] This graph shows the relationship between the proportion of biomass-derived charcoal material with a particle size of 150 μm or less and the strength of the molded charcoal, when 10% by mass of PKS (palm kernel shells) carbonized at 500°C is blended into molded charcoal as a biomass-derived charcoal material. [Figure 2] This graph shows the relationship between the volatile content of biomass-derived carbon material and the drum strength index (DI) of coke when 10% by mass of carbonized PKS with a particle size of -3 mm and different volatile content is blended into molded charcoal as a biomass-derived carbon material. [Modes for carrying out the invention]

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The method for producing coke according to the present invention is a method for producing coke by carbonizing a blended coal obtained by mixing a molded coal containing coal and biomass-derived carbonaceous material with pulverized coal containing powdered coal, wherein the volatile content of the biomass-derived carbonaceous material contained in the molded coal is 4% by mass or more and 30% by mass or less, and the proportion of the biomass-derived carbonaceous material contained in the molded coal having a particle size of 150 μm or less is 40% by mass or less.

[0019] In the method for producing coke of the present invention, a biomass-derived carbonaceous material is blended with the molded coal for coke production. Here, biomass is a general term for a certain amount of accumulated animal and plant resources and waste originating from them (excluding fossil resources). The biomass serving as the raw material for the biomass-derived carbonaceous material of the present invention includes all biomass that produces carbide when thermally decomposed, such as those in the agricultural, forestry, livestock, fishery, and waste categories.

[0020] In the present invention, the biomass used as the raw material for the biomass-derived carbonaceous material preferably includes those with a high calorific value, and for example, preferably includes woody biomass.

[0021] Examples of woody biomass include paper by-products such as pulp black liquor and chip dust, sawmill by-products such as bark and sawdust, forest residues such as branches, leaves, tips, and short logs, thinned wood from cedar, cypress, pine, etc., special forest products such as waste logs of edible fungi, charcoal forests such as oak, konara, pine, etc., and forestry biomass such as short-rotation forestry of willow, poplar, eucalyptus, pine, etc. In addition, as woody biomass, general waste such as pruned branches of street trees in municipalities and garden trees in private houses, pruned branches of street trees of the state and prefectures, garden trees of companies, and industrial waste such as construction and building waste are also included. Furthermore, some of the agricultural biomass classified as agricultural biomass, such as rice husks, wheat straw, rice straw, sugarcane bagasse, palm kernel shell (PKS), etc. generated from waste and by-products, and rice bran, rapeseed, soybeans, etc. generated from energy crops can also be preferably used as woody biomass.

[0022] In the present invention, it is essential that the volatile content of the biomass-derived carbon material blended in the formed carbon is 4% by mass or more and 30% by mass or less. When the volatile content of the biomass-derived carbon material exceeds 30% by mass, the carbonization of the biomass-derived carbon material has not sufficiently proceeded, so the amount of oxygen-containing functional groups in the biomass-derived carbon material increases, and there is a risk of lowering the coke strength by reducing the softening and melting characteristics of the raw material carbon. Therefore, it is not preferable. On the other hand, when the volatile content of the biomass-derived carbon material is less than 4% by mass, the difference in the shrinkage amount from the part derived from the raw material carbon during carbonization becomes large, stress is generated in the coke, and the coke strength is reduced. Therefore, it is not preferable. The volatile content of the biomass-derived carbon material is preferably 6% by mass or more and 30% by mass or less.

[0023] In addition, in this specification, the volatile content of the biomass-derived carbon material is a value measured according to the "Coals and Cokes - Proximate Analysis Method" (JIS M 8812:2004) specified in the Japanese Industrial Standards (JIS).

[0024] The volatile content of the biomass-derived carbon material can be adjusted according to the conditions when heat-treating the biomass raw material. Generally, the higher the heat-treatment temperature of the biomass raw material, the lower the volatile content of the biomass-derived carbon material.

[0025] The heat treatment of the biomass serving as the raw material of the biomass-derived carbon material is preferably carried out in an atmosphere where oxygen supply is blocked. For example, it may be carried out in a state where the biomass as the raw material is accommodated in a container that forms a space where the inflow of air is inhibited and an inert gas (for example, nitrogen gas, noble gas) flows (that is, in a non-oxidizing atmosphere). The heat treatment of the biomass as the raw material can be carried out by heating the container in which the biomass as the raw material is accommodated and by heat transfer from the container.

[0026] Normally, the reaction rate of the thermal decomposition reaction of biomass during heat treatment is high, so the time required to complete the thermal decomposition reaction is short. Therefore, the heat treatment time is preferably 1 minute or more, and more preferably 10 minutes or more. This eliminates the temperature difference between the raw material biomass and the container, allowing the entire raw material biomass to be heat-treated uniformly. Furthermore, it becomes possible to reliably raise the temperature of the entire raw material carbon to the heat treatment temperature (i.e., heat it evenly) and perform the heat treatment, thereby suppressing variations in the quality of the heat-treated carbon material and carbon powder. There is no particular upper limit set for the heat treatment time, but if the heat treatment time is too long, the energy required for heat treatment increases, which increases costs and is therefore undesirable. A heat treatment time of 60 minutes or less is usually sufficient. Note that the heat treatment time is the time from the point when the temperature of the raw material biomass reaches the predetermined heat treatment temperature until it is maintained at this heat treatment temperature.

[0027] Furthermore, when heat-treating biomass, the biomass raw material is sometimes finely crushed before heat treatment in order to suppress unevenness in the heat treatment temperature. As described later, the particle size of the biomass-derived char material blended into molded charcoal needs to be controlled to a large extent in order to suppress the decrease in molded charcoal strength, so it is not desirable to make the particle size excessively small before heat treatment.

[0028] Heat treatment can be carried out using heating equipment such as a rotary kiln, fluidized bed furnace, electric furnace, screw furnace, shaft furnace, or carbonization furnace.

[0029] In the coke production method of the present invention, the reduction in strength of the molded charcoal is suppressed by blending biomass-derived charcoal material with a large particle size into the molded charcoal for coke production. In the coke production method of the present invention, it is important to use biomass-derived charcoal material blended into the molded charcoal in a proportion of 40% by mass or less of material with a particle size of 150 μm or less.

[0030] When incorporating biomass-derived charcoal into molded charcoal, a challenge arises in suppressing the reduction in the strength of the molded charcoal. In molded charcoal, a lack of binders that bond the particles together causes a decrease in the strength of the molded charcoal. If the particle size of the biomass-derived charcoal incorporated into the molded charcoal is small, the surface area that needs to be bonded by the binder increases significantly, leading to poor inter-particle bonding and a decrease in the strength of the molded charcoal. On the other hand, as mentioned above, when heat-treating biomass, the biomass raw material is sometimes finely crushed before heat treatment in order to suppress temperature unevenness during the heat treatment. Therefore, when manufacturing biomass-derived charcoal for use in molded charcoal, it is important to adjust the particle size, including the manufacturing process.

[0031] The inventors conducted extensive research on the particle size of biomass-derived charcoal materials blended into molded charcoal and found that increasing the proportion of biomass-derived charcoal materials with particularly small particle sizes significantly reduces the strength of the molded charcoal. It is possible to suppress the reduction in strength of the molded charcoal by limiting the proportion of biomass-derived charcoal materials with a particle size of 150 μm or less to 40% by mass or less. Preferably, the proportion of biomass-derived charcoal materials with a particle size of 150 μm or less is 30% by mass or less. The proportion of materials with a particle size of 150 μm or less may be zero. While there is no particular upper limit on the particle size of biomass-derived charcoal materials from the viewpoint of molded charcoal strength, it is preferable that the proportion of particles 3 mm or larger is 30% by mass or less from the viewpoint of suppressing component imbalance in the molded charcoal.

[0032] The proportion of biomass-derived charcoal in the molded charcoal is preferably 4% by mass or more and 30% by mass or less. If the proportion of biomass-derived charcoal in the molded charcoal is less than 4% by mass, the proportion of biomass-derived raw materials in the overall blended charcoal is low, and the CO2 emission reduction effect from using biomass-derived charcoal may not be sufficiently obtained. On the other hand, if the proportion of biomass-derived charcoal in the molded charcoal exceeds 30% by mass, the proportion of non-meltable biomass-derived charcoal in the molded charcoal increases, which reduces the overall softening and melting properties of the molded charcoal. This necessitates measures such as adding a large amount of highly meltable raw coal, which may lead to a significant increase in costs. The proportion of biomass-derived charcoal in the molded charcoal is preferably 5% by mass or more and 25% by mass or less.

[0033] In this invention, the molded coal prepared as described above is mixed with powdered coal containing pulverized coal to make blended coal. Here, the powdered coal is produced by crushing raw materials containing coking coal using a normal operation. Specifically, the raw materials containing coking coal are crushed so that the proportion of particles with a particle size of 3 mm or less is 70% by mass or more and 100% by mass or less. If the particle size of the powdered coal is large, a property distribution will occur in coke production, which uses a mixture of coal and other components with different properties. For this reason, it is preferable that the proportion of particles with a particle size of 3 mm or less is 70% by mass or more, and more preferably 75% by mass or more. From the viewpoint of preventing the occurrence of a property distribution, there is no particular upper limit to the proportion of particles with a particle size of 3 mm or less in the powdered coal. On the other hand, if the particle size of the powdered coal becomes too small, the density of the blended coal charged into the coke oven will decrease, which may be a factor in reducing the coke strength. For this reason, it is more preferable that the proportion of particles with a particle size of 3 mm or less in the powdered coal is 90% by mass or less, and even more preferable that the proportion of particles with a particle size of 3 mm or less is 85% by mass or less. Furthermore, the crushing of raw materials, including coking coal, may be carried out using conventionally known operations and methods.

[0034] The proportion of molded coal to the total blended coal is not particularly limited, but it is preferably 5% by mass or more and 50% by mass or less. If the proportion of molded coal is less than 5% by mass, it may not be possible to effectively enjoy the benefits of improving coke strength and increasing the proportion of non-coking coal used by the molded coal method. For this reason, it is preferable to blend 5% by mass or more of molded coal into the blended coal. On the other hand, if the proportion of molded coal exceeds 50% by mass, the overall bulk becomes larger and the bulk density decreases. For this reason, it may not be possible to effectively obtain the effect of improving coke strength. For this reason, it is preferable to blend 50% by mass or less of molded coal into the blended coal. It is more preferable that the proportion of molded coal be 10% by mass or more and 35% by mass or less.

[0035] Coke is produced by carbonizing the blended coal obtained as described above. The carbonization method for the blended coal is not particularly limited; it is sufficient to carbonize the blended coal in a general chamber-type coke oven at a temperature of 900°C to 1300°C. [Examples]

[0036] The following describes embodiments of the present invention. However, the present invention is not limited to the following embodiments and can be modified as appropriate without departing from the spirit of the invention.

[0037] Table 1 shows the types of biomass-derived carbon materials blended into the molded charcoal, their volatile content, the proportion of materials with a particle size of 150 μm or less, and their blending ratio in the molded charcoal. No. 1 is a reference example that does not contain biomass-derived carbon materials, while Nos. 2-12 and 15-16 are examples of inventions in which the proportion of biomass-derived carbon materials with a particle size of 150 μm or less among those blended into the molded charcoal falls within the scope of the present invention. Furthermore, Nos. 13-14 are comparative examples in which the proportion of biomass-derived carbon materials with a particle size of 150 μm or less among those contained in the molded charcoal falls outside the scope of the present invention, and No. 17 is a comparative example in which the volatile content of the biomass-derived carbon material falls outside the scope of the present invention.

[0038] [Table 1]

[0039] Molded coal was produced by blending various biomass-derived carbon materials listed in Table 1. The manufacturing procedure for the molded coal was as follows: First, coal blended to have an average maximum reflectance Ro of 1.0 [%] and a logMF (log ddpm), which is the common logarithm of the maximum fluidity (MF) of a Gieseler plastometer, of 2.3 [log ddpm] was crushed to a total size of 3 mm or less and blended with the various biomass-derived carbon materials listed in Table 1. Next, tar pitch was added to the mixture of coal and biomass-derived carbon materials in a ratio of 4 mass% and tar slag in a ratio of 6.5 mass%. After mixing and steam kneading, the mixture was molded into a volume of 34 cm³ using a double-roll molding machine. 3 They manufactured molded charcoal.

[0040] To evaluate the quality of the molded charcoal, 12 pieces were randomly selected from the manufactured charcoal and their crushing strength was measured. The average value is shown in Table 1 as the crushing strength of that level. Here, a crushing strength of 45 kgf or higher indicates that the molded charcoal is of a level that is acceptable for practical use. Furthermore, a crushing strength of 50 kgf or higher indicates that the molded charcoal has particularly excellent strength.

[0041] Figure 1 is a graph showing the relationship between the proportion of biomass-derived carbon material with a particle size of 150 μm or less and the strength of the molded charcoal when PKS carbonized at 500°C is blended at 10% by mass into the molded charcoal. According to Figure 1, no significant decrease in crushing strength was observed when the proportion of biomass-derived carbon material with a particle size of 150 μm or less was 40% by mass or less, but when it exceeded 40% by mass, the crushing strength decreased significantly, falling below 45 kgf.

[0042] Next, to confirm the impact on coke quality, a carbonization test was conducted using the manufactured molded coal. The carbonization test procedure was as follows: First, coal blended to have an Ro of 1.0 [%] and a logMF of 2.5 [log ddpm] was crushed to a size of 3 mm or less, and the coal's moisture content was adjusted to 8% by mass. Then, at each level, 12.8 kg of the crushed and moisture-adjusted coal was taken on an anhydrous basis, and 3.2 kg of the manufactured molded coal was added to it (the proportion of molded coal was 20% by mass) to create the blended coal. Subsequently, the blended coal was poured into a stainless steel container at an anhydrous basis at a rate of 800 kg / m³. 3 The mixture was filled in such a manner and then charged into an electric furnace with nitrogen gas flowing through it for carbonization. Specifically, a container filled with the blended coal was charged into an electric furnace set to a furnace wall temperature of 1050°C, and carbonization was carried out for 6 hours from the time of charging while maintaining the furnace wall temperature. After that, the container was moved to a cooling facility with nitrogen gas flowing through it at room temperature for cooling to obtain coke.

[0043] The drum strength index (DI) of the obtained coke was measured in accordance with the rotational strength test method of JIS K2151. The DI was measured under conditions of a drum rotation speed of 150 rpm and a sieve opening of 15 mm, and the measurement results are shown in Table 1. Here, when the DI is 76% or higher, the coke strength is within the range where it can be adjusted by adjusting the quality of the blended coal and the manufacturing conditions, and therefore, coke that is practically acceptable is obtained. Furthermore, when the DI is 77% or higher, coke with particularly excellent strength is obtained.

[0044] Figure 2 is a graph showing the relationship between the volatile content of biomass-derived carbon material and the DI of coke when 10% by mass of carbonized PKS with a particle size of -3 mm and different volatile content is blended into molded charcoal. According to Figure 2, no significant decrease in DI was observed when the volatile content of the biomass-derived carbon material was in the range of 4% by mass to 30% by mass, but when the volatile content fell below 4% by mass, the DI decreased significantly, falling below 76%.

[0045] The results above demonstrate that by controlling the proportion of volatile components and particles with a particle size of 150 μm or less of the biomass-derived carbon material blended into the molded charcoal, it is possible to blend biomass-derived carbon material into molded charcoal without reducing the strength of the molded charcoal or coke. [Industrial applicability]

[0046] According to the present invention, even when biomass raw materials are blended into molded charcoal for coke production, the decrease in strength of the molded charcoal and coke can be suppressed, and high-strength coke can be produced.

Claims

1. A method for producing coke by carbonizing a blended coal obtained by mixing molded coal containing coal and biomass-derived coal material with powdered coal containing powdered coal, The volatile content of the biomass-derived carbon material contained in the molded charcoal is 4% by mass or more and 30% by mass or less. A method for producing coke, characterized in that the biomass-derived carbon material contained in the molded charcoal has a particle size of 150 μm or less, with a proportion of 40% by mass or less.

2. The method for producing coke according to claim 1, wherein the proportion of the biomass-derived carbon material in the molded charcoal is 4% by mass or more and 30% by mass or less.

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