Method for producing coke

Abstract

Provided is a method for producing coke, in which even if a biomass raw material is blended with briquetted coal for coke production, a decrease in strength of the briquetted coal and coke can be suppressed and high-strength coke can be produced. The method is for producing coke by carbonizing blended coal obtained by mixing briquetted coal containing coal and a biomass-derived carbon material with powdered coal containing powdery coal, wherein the method is characterized in that the volatile matter content in the biomass-derived carbon material contained in the briquetted coal is 4-30 mass%, and the proportion of material having particle diameters of 150 µm or less in the biomass-derived carbon material contained in the briquetted coal is 40 mass% or less.

Description

Method for producing coke

[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 coke and produce high-strength coke when a biomass raw material is blended with formed coke to produce coke.

[0002] Coke for blast furnaces is used in blast furnaces as a reducing agent, a heat source, and a support material for maintaining air permeability and liquid permeability. In order to stably operate a 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, coke strength such as rotary strength is particularly important.

[0003] In recent years, the need to reduce carbon dioxide (CO ２ 2) emissions has been increasing, and in fields that used coal or oil as raw materials, consideration has been given to replacing 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, caking coal with excellent softening and melting properties is used. On the other hand, biomass-derived raw materials do not soften and melt like coal. Therefore, 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, it is necessary to devise a way to suppress a decrease in coke strength.

[0005] Conventionally, as a method for using non-caking coal with poor softening and melting properties in coke production, the formed coke method is known (for example, see Patent Document 1). In the formed coke method, a lump-shaped product (formed coke) is obtained by mechanical compression. Therefore, even when using non-caking coal, the inter-particle distance between coals can be shortened, and even if the caking property is poor, the adhesion between non-caking coals is promoted, improving the coke strength.

[0006] When using non-coking biomass raw materials in coke production, it is 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 the 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.

[0008] Japanese Patent Publication No. 2023-136520 Japanese Patent Publication No. 2011-93980

[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 the decrease in coke strength can be suppressed by blending biomass-derived raw materials into molded coal, similar to the case of non-coking coal. However, the effects of biomass raw materials blended into molded coal on the strength of the molded coal and the strength of the coke have 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 carbonization of 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 using uncarbonized biomass and with strength equivalent to that of ordinary molded charcoal. However, in recent years, CO2 ２ Due to the growing need to reduce emissions, there is a demand to carbonize biomass using carbon-neutral gases and tar generated from the biomass itself. Therefore, it is difficult to use tar generated during the carbonization of biomass 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.

[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 carbonizing a blended coal obtained by mixing molded coal containing coal and biomass-derived carbon material with powdered coal containing powdered coal, characterized in that the volatile content of the biomass-derived carbon 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 carbon material contained in the molded coal that has a particle size of 150 μm or less is 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.

[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 the molded charcoal and coke, and to provide a method for producing high-strength coke.

[0017] 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. This graph shows the relationship between the volatile content of the biomass-derived charcoal 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 charcoal material.

[0018] Embodiments of the present invention will be described below with reference to the drawings. The method for producing coke according to the present invention is a method for producing coke by carbon distillation of a blended coal obtained by mixing molded coal containing coal and biomass-derived carbon material with powdered coal containing powdered coal, characterized in that the volatile content of the biomass-derived carbon 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 carbon material contained in the molded coal that has a particle size of 150 μm or less is 40% by mass or less.

[0019] In the coke production method of the present invention, biomass-derived carbon material is blended with molded charcoal 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 used as raw material for the biomass-derived carbon material of the present invention includes all types of biomass that produce carbonized material when thermally decomposed, such as agricultural, forestry, livestock, fisheries, and waste materials.

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

[0021] Woody biomass includes papermaking by-products such as pulp black liquor and chip dust, sawmilling by-products such as bark and wood scraps, forest residues such as branches, leaves, canopies, and short pieces of wood, thinned timber from cedar, cypress, and pine, and special forest products such as spent logs for edible fungi, as well as forestry biomass such as fuelwood forests of oak, chestnut, and pine, and short-rotation forests of willow, poplar, eucalyptus, and pine. Woody biomass also includes general waste such as pruned branches from street trees in municipalities and garden trees in private homes, as well as industrial waste such as pruned branches from street trees in national and prefectural governments and garden trees in companies, and construction waste. Furthermore, some agricultural biomass, such as rice husks, wheat straw, rice straw, sugarcane bagasse, and palm kernel shells (PKS), which are classified as agricultural biomass and originate from waste and by-products, as well as rice bran, rapeseed, and soybeans, which originate from energy crops, can also be suitably used as woody biomass.

[0022] In this invention, it is essential that the volatile content of the biomass-derived carbon material blended into the molded charcoal is between 4% by mass and 30% by mass. If the volatile content of the biomass-derived carbon material exceeds 30% by mass, the carbonization of the biomass-derived carbon material has not progressed sufficiently, resulting in a large amount of oxygen-containing functional groups in the biomass-derived carbon material. As a result, the softening and melting characteristics of the raw coal may decrease, potentially reducing the coke strength, which is undesirable. On the other hand, if the volatile content of the biomass-derived carbon material is less than 4% by mass, the difference in shrinkage between the raw coal-derived portion and the biomass-derived carbon material becomes large during carbonization, generating stress in the coke and reducing the coke strength, which is also undesirable. Preferably, the volatile content of the biomass-derived carbon material is between 6% by mass and 30% by mass.

[0023] In this specification, the volatile content of biomass-derived carbon materials is the value measured in accordance with the Japanese Industrial Standard (JIS) "Coal and coke - Industrial analytical methods" (JIS M 8812:2004).

[0024] The volatile content of biomass-derived charcoal can be adjusted by controlling the heat treatment conditions of 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 charcoal.

[0025] The heat treatment of biomass used as raw material for biomass-derived charcoal should be carried out in an atmosphere where oxygen supply is blocked. For example, the heat treatment should be carried out in a container that creates a space where air inflow is inhibited and an inert gas (e.g., nitrogen gas, noble gas) flows (i.e., in a non-oxidizing atmosphere). The heat treatment of the raw material biomass can be carried out by heating the container containing the raw material biomass and transferring heat 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. Usually, a heat treatment time of 60 minutes or less is 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 the strength of the molded charcoal, 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 decrease in the 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 decrease in the strength of the molded charcoal. In molded charcoal, a lack of binders that bond the particles together causes a decrease in strength. 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, adjusting the particle size, including the manufacturing process, is important.

[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 molded charcoal strength 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 carbon material in the molded charcoal is preferably 4% by mass or more and 30% by mass or less. If the proportion of biomass-derived carbon material 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 CO2 emissions from using biomass-derived carbon material are reduced. ２In some cases, the reduction in emissions may not be sufficient. 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, reducing the overall softening and melting properties of the molded charcoal. As a result, it becomes necessary to add a large amount of highly meltable raw coal, which can lead to a significant increase in costs. It is preferable that the proportion of biomass-derived charcoal in the molded charcoal be between 5% by mass and 25% by mass.

[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 amount of 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.

[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 charcoal 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 include biomass-derived charcoal materials, while Nos. 2-12 and 15-16 are inventive examples in which the proportion of biomass-derived charcoal 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 charcoal 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 charcoal material falls outside the scope of the present invention.

[0038]

[0039] Briquettes were produced by blending various biomass-derived carbon materials described in Table 1. The production procedure of the briquettes is as follows. First, coal blended so that the average maximum reflectance Ro of vitrinite is 1.0 [%] and the common logarithm value of the maximum fluidity (MF) of the Gieseler plastometer, log MF, is 2.3 [log ddpm] was pulverized so that the total amount becomes 3 mm or less, and blended with various biomass-derived carbon materials described in Table 1. Next, tar pitch was added to the blend of coal and biomass-derived carbon material at a ratio of 4% by mass, and tar sludge was added at a ratio of 6.5% by mass. After mixing and steam kneading, briquettes with a volume of 34 cm ３ were produced using a double-roll molding machine.

[0040] To evaluate the quality of the briquettes, 12 briquettes were randomly sampled from the produced briquettes, and the crushing strength was measured. The average value is shown in Table 1 as the crushing strength of that level. Here, when the crushing strength is 45 kgf or more, briquettes at a practically problem-free level are obtained. Also, when the crushing strength is 50 kgf or more, briquettes with particularly excellent strength are obtained.

[0041] Figure 1 is a graph showing the relationship between the proportion of biomass-derived carbon materials with a particle size of 150 μm or less in the briquettes and the briquette strength when 10% by mass of PKS carbonized at 500 °C is blended in the briquettes. According to Figure 1, no significant decrease in the crushing strength was observed in the range where the proportion of biomass-derived carbon materials with a particle size of 150 μm or less is 40% by mass or less. However, when it exceeds 40% by mass, the crushing strength significantly decreases and is less than 45 kgf.

[0042] Next, to confirm the influence on coke quality, a carbonization test was conducted using the produced briquettes. The test procedure for the carbonization test is as follows. First, coal blended so that Ro is 1.0 [%] and log MF is 2.5 [log ddpm] was pulverized so that the total amount becomes 3 mm or less, and the moisture content of the coal was adjusted to 8% by mass. Next, for each level, 12.8 kg of the pulverized and moisture-adjusted coal was sampled on an anhydrous basis, and 3.2 kg of the produced briquettes was blended (the blending ratio of the briquettes is 20% by mass) and mixed to obtain a blended coal. Subsequently, the blended coal was placed in a stainless steel container at 800 kg / m on an anhydrous basis ３It was filled so as to obtain the following, charged into an electric furnace through which nitrogen gas was circulated, and carbonization was carried out. Specifically, a container filled with blended coal was charged into an electric furnace set at a furnace wall temperature of 1050°C, and carbonization was carried out for 6 hours from the charging under the condition of maintaining the furnace wall temperature. Then, the container was transferred to a cooling facility through which nitrogen gas at room temperature was flowing for cooling to obtain coke.

[0043] For the obtained coke, the drum strength index (DI) was measured in accordance with the rotary strength test method of JIS K2151. DI was measured under the conditions that the number of rotations of the drum was 150 rotations and the sieve opening was 15 mm, and the measurement results are shown in Table 1. Here, when DI is 76% or more, it is in the range where the coke strength can be adjusted by adjusting the quality of the blended coal and the production conditions, so coke with no practical problems is obtained. Also, when DI is 77% or more, coke with particularly excellent strength is obtained.

[0044] Figure 2 is a graph showing the relationship between the volatile content of the biomass-derived carbon material and the DI of coke when 10% by mass of carbonized PKS with a particle size of -3 mm having different volatile contents is blended into the formed carbon. 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 or more and 30% by mass or less, but it can be seen that when the volatile content is less than 4% by mass, DI significantly decreases and becomes less than 76%.

[0045] From the above results, it was shown that by controlling the volatile content of the biomass-derived carbon material blended into the formed carbon and the proportion of those with a particle size of 150 μm or less, it is possible to blend the biomass-derived carbon material into the formed carbon without reducing the strength of the formed carbon and coke.

[0046] According to the present invention, even when a biomass raw material is blended into the formed carbon for coke production, it is possible to suppress a decrease in the strength of the formed carbon and coke and produce high-strength coke.

Claims

1. A method for producing coke by carbon distillation of a blended coal obtained by mixing molded coal containing coal and biomass-derived carbon material with powdered coal containing powdered coal, characterized in that the volatile content of the biomass-derived carbon 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 carbon material contained in the molded coal that has a particle size of 150 μm or less is 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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