Method for producing coke

Abstract

To provide a technique for producing high-strength coke even when carbonized biomass is blended into a part of a raw material for coke production.SOLUTION: In the method for producing the coke, a carbonized biomass obtained by heat-treating biomass is blended with a part of a blended coal for coke production and carbonized, wherein the volatile content of the carbonized biomass based on anhydrous ash is 7.0 mass% or more and 35 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing coke. [Background technology]

[0002] Blast furnace coke is used in blast furnaces as a reducing agent, a heat source, and a support material to maintain gas permeability and liquid permeability. Stable operation of a blast furnace requires ensuring gas permeability and liquid permeability within the furnace, which requires coke with excellent properties such as strength and particle size. Among these, coke strength, such as rotational strength, is particularly important.

[0003] In recent years, there has been an increasing need to reduce CO2 emissions, and in fields where coal or petroleum has been used as a raw material, studies are underway to replace the raw material with carbon-neutral raw materials such as biomass. For this reason, in the steel industry as well, studies are underway to replace a portion of the coal used as a raw material for coke used in blast furnaces with carbon-neutral raw materials such as biomass. For example, Patent Document 1 describes a method for producing high-reactivity coke for blast furnaces, in which biomass is heated to at least 1000°C or higher to cause thermal decomposition, and the resulting biomass char with a solid content of 1 mm or less in diameter is added to a coal blend.

[0004] Lump coke used in blast furnaces is produced by carbonizing coal in a carbonization furnace, causing the coal to soften and melt, bonding together. Therefore, to produce high-strength coke, caking coal with excellent softening properties is used. However, biomass-derived raw materials do not soften and melt like coal, so using conventional processes to produce coke from coal results in low-strength coke with many defects. Therefore, when using biomass-derived raw materials, it is necessary to devise ways to suppress defects in the coke.

[0005] Previous knowledge has suggested that when biomass is blended as part of the raw materials for coke, blending biomass carbonized at high temperatures is effective in suppressing a decrease in coke strength. For example, Non-Patent Document 1 investigates the rotational strength of coke blended with carbonized biomass using small lump coke with a fixed carbon content of 0.4 g, and shows that biomass carbonized at 500°C or higher (500°C and 1000°C) can suppress the inhibition of bonding between coal particles during carbonization, thereby suppressing a decrease in coke strength. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-77086 [Non-patent literature]

[0007] [Non-Patent Document 1] Y. Ueki, Y. Nunome, R. Yoshiie, I. Naruse, Y. Nishibata and S. Aizawa: ISIJ Int., 54 (2014), 2454. Summary of the Invention [Problem to be solved by the invention]

[0008] When a portion of the coal used as a coke feedstock is replaced with a biomass-derived material, even a small substitution ratio can significantly reduce the strength of the resulting coke. As mentioned above, Non-Patent Document 1, which investigated small coke, suggested that carbonizing the blended biomass at temperatures of 500°C or higher could prevent a decrease in coke strength. However, when the inventors conducted an investigation using large cokes of several tens of millimeters in size, such as those used in blast furnaces, they obtained results that differed from those using small coke. Even when blending biomass carbonized at high temperatures, coke strength could be significantly reduced. Furthermore, practical guidelines are needed to determine whether or not to use carbonized biomass as a feedstock when the production conditions, such as the carbonization temperature, are unknown. Furthermore, a method is needed to modify biomass feedstocks, which significantly reduce coke strength when blended, to a quality suitable for coke production.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a coke production method that can produce high-strength coke even when a portion of the coal used in coke production is replaced with a biomass-derived raw material. [Means for solving the problem]

[0010] In order to clarify the cause of the decrease in strength of coke that uses biomass as part of the raw materials, the inventors conducted detailed observations of defects inside coke produced by blending various biomass-derived raw materials. As a result of the observations, it was revealed that in coke whose strength was decreased by blending biomass-derived raw materials, delamination occurred at the interface between the biomass-derived portion and the coal-derived portion, which was the cause of the decrease in strength.

[0011] Based on the above findings, the present inventors have completed the present invention, which has the following gist and configuration.

[0012] [1] A method for producing coke, comprising blending carbonized biomass obtained by heat treating biomass with a part of blended coal for coke production, and carbonizing the blended coal, The volatile content of the carbonized biomass on an anhydrous ash-free basis is 7.0% by mass or more and 35% by mass or less; Coke manufacturing method.

[0013] [2] The method for producing coke according to the above [1], wherein the carbonized biomass is obtained by oxidizing carbonized biomass obtained by heat-treating biomass.

[0014] [3] The method for producing coke according to [1] or [2] above, wherein the proportion of the carbonized biomass having a particle size of 3 mm or less is 70 mass % or more and 100 mass % or less.

[0015] [4] The method for producing coke according to any one of [1] to [3] above, wherein the blended coal has a blending ratio of the carbonized biomass of 1 mass% or more and 10 mass% or less. [Effects of the Invention]

[0016] The present invention clarifies the properties of biomass-derived raw materials suitable for replacing a portion of the coal used in the production of coke for blast furnaces. This provides a coke production method that can produce high-strength coke even when biomass-derived raw materials are blended with coal. Furthermore, by replacing coal with biomass-derived raw materials, carbon dioxide emissions from fossil fuels can be reduced. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a graph showing the relationship between the volatile content of carbonized biomass on an anhydrous ash-free basis and the DI of coke produced by blending 5 mass% of carbonized biomass in a coal blend. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the embodiment described below is an example of a specific embodiment of the present invention, and the configuration of the present invention is not limited to this specific example.

[0019] The coke production method of the present invention is characterized in that when coke is produced by blending carbonized biomass obtained by heat-treating biomass with a portion of a coal blend for coke production and carbonizing the blend, the volatile content of the carbonized biomass on an anhydrous ash-free basis is 7.0 mass% or more and 35 mass% or less.

[0020] Biomass refers to organic industrial resources derived from plants and animals that exist in the current ecosystem. The organic matter that makes up biomass circulates within the ecosystem while changing its form. The carbon dioxide generated when biomass is burned originates from the carbon originally absorbed by living organisms as they grow, and therefore does not affect the total amount of carbon dioxide in the atmosphere and is considered to be in a so-called carbon-neutral state. In contrast, the carbon dioxide generated when fossil fuels are burned originates from underground resources isolated from the current ecosystem and is therefore not considered to be in a carbon-neutral state. Therefore, fossil fuels such as coal and oil are not included in the biomass of this invention.

[0021] The biomass used in the present invention may be any type of biomass that can be used as an industrial resource, including products produced in fields such as agriculture, forestry, livestock farming, and fisheries, as well as waste generated during the production process, as long as it satisfies the specified conditions described below.

[0022] In the present invention, the biomass used as the raw material for carbonized biomass preferably includes biomass with a high effective calorific value, for example, woody biomass.

[0023] Examples of woody biomass include biomass made from wood from conifers such as cedar, pine, and cypress, and broad-leaved trees such as zelkova, birch, and eucalyptus. The part of the wood is not limited. Woody biomass also includes waste wood from construction, unused parts of thinned wood generated in forestry, and papermaking by-products such as pulp black liquor and chip dust. Furthermore, some agricultural biomass, such as rice husks, wheat straw, rice straw, sugarcane bagasse, and palm oil, which originate from waste or by-products, and rice bran, rapeseed, and soybeans, which are generated from energy crops, can also be suitably used as woody biomass.

[0024] The method for producing coke according to the present invention utilizes carbonized biomass produced by heat-treating biomass. The heat treatment of biomass is preferably carried out in an atmosphere where oxygen supply is blocked. For example, the heat treatment is preferably carried out in a state where the raw biomass is housed in a container that forms a space where air inflow is blocked and in which an inert gas flows (i.e., in a non-oxidizing atmosphere). The heat treatment of the raw biomass can be carried out by heating the container that houses the raw biomass and using heat transfer from the container.

[0025] The heat treatment temperature of biomass can be adjusted appropriately depending on the type of biomass, etc., so that the volatile content of the carbonized biomass on an anhydrous ash-free basis falls within a suitable range. Generally, the higher the heat treatment temperature of biomass, the lower the volatile content. For example, when palm kernel shells (hereinafter referred to as "PKS") are used as biomass, the volatile content on an anhydrous ash-free basis can be adjusted to a range of 7.0% by mass to 35% by mass by performing the carbonization treatment at a temperature of approximately 350°C to 600°C.

[0026] Typically, the reaction rate of the pyrolysis reaction of biomass during heat treatment is fast, so the time required for pyrolysis to be completed is short. Therefore, the lower limit of 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 biomass and the container, allowing the entire raw biomass to be uniformly heat-treated. Furthermore, it becomes possible to reliably raise the temperature of the entire raw biomass to the heat treatment temperature (i.e., heat evenly) and perform the heat treatment, thereby suppressing quality variation in the carbonized biomass.

[0027] There is no particular upper limit to the heat treatment time, but if the heat treatment time is too long, the energy required for the heat treatment increases, which is undesirable as it increases costs. A heat treatment time of 60 minutes or less is usually sufficient. The heat treatment time refers to the time during which the temperature of the raw material biomass is maintained at the specified heat treatment temperature from the time it reaches this temperature.

[0028] The heat treatment can be carried out using a heating device such as a rotary kiln, a fluidized bed heating furnace, an electric furnace, a screw type heating furnace, a shaft furnace, or a carbonization furnace.

[0029] In the method for producing coke according to the present invention, the volatile content of the carbonized biomass on a dry and ash-free basis is 7.0 mass % or more and 35 mass % or less.

[0030] Since it is believed that the carbonaceous portion excluding ash in the carbonized biomass forms bonds with the coal-derived portion, when evaluating the bond-forming ability of the carbonized biomass, it is necessary to exclude the influence of ash. Therefore, in the present invention, the volatile content on an anhydrous ash-free basis is used as an evaluation index for the volatile content of the carbonized biomass.

[0031] In the present invention, the analysis of the volatile content of carbonized biomass is performed in accordance with the JIS standard "Coals and cokes - Methods of proximate analysis" (JIS M 8812:2004). Furthermore, the analytical values ​​of the volatile content and ash content of the carbonized biomass obtained by the analysis can be converted to the volatile content on an anhydrous ashless basis in accordance with the JIS standard "Coals and cokes - General rules for sampling, analysis and testing" (JIS M 8810:1994). By using the volatile content on an anhydrous ashless basis, the bond-forming ability of the carbonized biomass with the coal portion can be evaluated without being affected by the ash content of the biomass.

[0032] If the volatile content of the carbonized biomass on an anhydrous ash-free basis is less than 7.0% by mass, bonding between the coal-derived portion and the carbonized biomass-derived portion is hindered during the carbonization process, resulting in defects around the carbonized biomass and a decrease in strength. Therefore, the volatile content of the carbonized biomass on an anhydrous ash-free basis is 7.0% by mass or more. The volatile content of the carbonized biomass on an anhydrous ash-free basis is preferably 10% by mass or more.

[0033] When coke is produced using a typical coal blend consisting solely of coking coal as a raw material, melted coking coals fuse together to form agglomerates. However, when carbonized biomass is used as part of the raw material, the carbonized biomass does not melt, so bonds must be formed between the molten coking coal and the unmelted carbonized biomass. The bond between the coking coal and the carbonized biomass is thought to be formed by a bond reaction between the respective molecules. Since this reaction is thought to involve the elimination of functional groups from the coal and the carbonized biomass, a carbonized biomass with a high volatile content means that it has many functional groups that can be eliminated during bond formation, which contribute to the bond between the coal portion and the carbonized biomass. Therefore, a carbonized biomass with a higher volatile content is thought to promote bond formation with the coking coal, making it possible to suppress the occurrence of defects around the carbonized biomass.

[0034] On the other hand, if the volatile content of the carbonized biomass exceeds 35% by mass on an anhydrous ash-free basis, the carbonization of the biomass is insufficient, which inhibits the thermoplasticity of the raw coal and causes a decrease in coke strength. Therefore, the volatile content of the carbonized biomass on an anhydrous ash-free basis is 35% by mass or less. The volatile content of the carbonized biomass on an anhydrous ash-free basis is preferably 25% by mass or less.

[0035] Carbonized biomass with a volatile content of less than 7.0% by mass on an anhydrous ash-free basis can be used as a coke raw material by increasing the volatile content of the carbonized biomass, for example, by oxidation treatment, so that the volatile content is adjusted to be in the range of 7.0% to 35% by mass on an anhydrous ash-free basis, thereby preventing a decrease in coke strength during blending. The oxidation treatment causes the carbonized biomass to react with oxygen in the air to form oxygen-containing functional groups, which are released during heating, and the oxidation increases the volatile content of the carbonized biomass on an anhydrous ash-free basis.

[0036] When carbonized biomass with a volatile content of less than 7.0 mass% on an anhydrous ash-free basis is oxidized for use, the oxidation conditions are not particularly limited as long as the volatile content of the carbonized biomass falls within a predetermined range, but oxidation can be carried out, for example, by storing the biomass in an oxidizing atmosphere (e.g., in air). Furthermore, oxidation can be promoted by heat treatment at about 200°C in an oxygen-containing atmosphere (e.g., in air), which can promote oxidation more than storage.

[0037] Carbonized biomass with a volatile content of more than 35% by mass on an anhydrous ash-free basis can be used as a coke raw material by reducing the volatile content on an anhydrous ash-free basis by subjecting it to additional carbonization treatment and adjusting it to a range of 7.0% by mass or more and 35% by mass or less, thereby suppressing a decrease in coke strength during blending.

[0038] In the coke production method of the present invention, as described above, carbonized biomass obtained by heat-treating biomass and then oxidizing the carbonized biomass can be used as the carbonized biomass. Here, in the present invention, "oxidized carbonized biomass" refers to a case in which the volatile content of the carbonized biomass on an anhydrous ash-free basis increases compared to the carbonized biomass immediately after the heat treatment.

[0039] The particle size of the carbonized biomass is preferably 70% by mass or more and 100% by mass or less of particles having a size of 3 mm or less. If the proportion of particles having a size of 3 mm or less is 70% by mass or more and 100% by mass or less, the blended coal can be homogeneously mixed. More preferably, the particle size of the carbonized biomass is 80% by mass or more and 100% by mass or less of particles having a size of 3 mm or less.

[0040] The particle size of the coal blend for coke production is preferably 70% by mass or more and 100% by mass or less of particles of 3 mm or less. If the particle size of the coal blend is coarse, property distribution will occur in coke production using a mixture of coal components with different properties. Therefore, it is preferable that the particle size of the coal blend be 70% by mass or more of 3 mm or less. More preferably, the proportion of the coal blend having a particle size of 3 mm or less is 75% by mass or more. On the other hand, if the particle size is too fine, the bulk density of the coal blend charged into the coke oven will decrease, which may cause a decrease in coke strength. Therefore, the proportion of particles of 3 mm or less is preferably 90% by mass or less, and more preferably 85% by mass or less. Here, the particle size of the coal blend refers to the particle size of the entire coal blend, including the coal and carbonized biomass used in coke production.

[0041] When the proportion of carbonized biomass in a mixture obtained by blending carbonized biomass with a coal blend for coke production in a predetermined ratio is 1.0% by mass or more, a significant effect in reducing carbon dioxide emissions is obtained, and when it is 10.0% by mass or less, the strength of the obtained coke does not decrease significantly, so the proportion of carbonized biomass is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 2.0% by mass or more and 8.0% by mass or less.

[0042] In the coke production method according to the present invention, coke is produced by blending carbonized biomass obtained by heat-treating biomass with a part of a coal blend for coke production, and carbonizing the blended coal. The coal blend obtained by blending the carbonized biomass is charged into a coke oven and carbonized by heating in an air-blocked atmosphere.

[0043] If the carbonization temperature is 900°C or higher, coke of sufficient strength can be obtained. A carbonization temperature of 950°C or higher is more preferable. On the other hand, if the carbonization temperature exceeds 1250°C, not only will a huge amount of energy be required for heating, but thermal decomposition of the coke may occur, resulting in a decrease in strength. Therefore, the carbonization temperature is preferably 1250°C or lower, and more preferably 1100°C or lower. In this specification, the carbonization temperature refers to the maximum temperature reached by the blended coal during carbonization. [Example]

[0044] Examples of the present invention will be described below. Note that the embodiments of the present invention are not limited to the following examples and can be modified as desired without departing from the gist of the present invention.

[0045] Two types of biomass were prepared as biomass feedstocks: PKS and cedar. These biomass materials were heat-treated in an air-tight atmosphere to the heat treatment temperatures listed in Table 1, yielding carbonized biomass. These carbonized biomass materials were then pulverized to produce carbonized biomass with a particle size of 3 mm or less (100%). Furthermore, the PKS heat-treated at 700°C was further heat-treated in an air atmosphere at 200°C for 3 to 7 hours after the heat treatment to obtain oxidized carbonized biomass. The volatile content of the resulting carbonized biomass was measured on an anhydrous and ash-free basis. The measured values ​​are shown in Table 1.

[0046] [Table 1]

[0047] According to the above measurement results, when the biomass feedstock was PKS, the carbonized biomass heat-treated at 350°C to 600°C had a volatile content of 7.5% to 34.9% by mass on an anhydrous ash-free basis, making it suitable for use in the coke production method of the present invention. Furthermore, when cedar was used as the biomass feedstock, the carbonized biomass heat-treated at 500°C had a volatile content of 23.1% by mass on an anhydrous ash-free basis, making it suitable for use in the coke production method of the present invention. Furthermore, the volatile content of the carbonized biomass obtained by heat-treating PKS at 700°C on an anhydrous ash-free basis was 6.4% by mass, but the volatile content increased with oxidation treatment, and after 3 to 7 hours of oxidation treatment, the volatile content was 9.1 to 10.0% by mass on an anhydrous ash-free basis.

[0048] Carbonization tests were conducted using the obtained carbonized biomass. Several types of raw coal were blended so that the average maximum reflectance (Ro) of vitrinite was 1.0 (%) and the common logarithm of the maximum fluidity (MF) measured by a Gieseler plastometer (log(MF / ddpm)) was 2.50. The carbonized biomass was then blended to produce a coal blend. Coke was produced using the following method, and the coke strength was evaluated.

[0049] Water was added to a coal blend containing carbonized biomass at the blending ratio shown in Table 1 to adjust the moisture content to 7%, and the resulting coal blend for carbonization was prepared. 16.5 kg of this coal blend was mixed to prepare a coal blend with a bulk density of 775 kg / m on a dry coal basis. 3The coal was loaded into a carbonization vessel at a bulk density of 1000 kJ / kg and carbonized in an electric furnace. After carbonization for 6 hours at a furnace wall temperature of 1,050°C, it was cooled under a nitrogen atmosphere to obtain coke. To compare the drum strength index (DI), a coke without carbonized biomass as a raw material was obtained by carbonizing only the blended coal under the same conditions (Reference Example). The DI of the obtained coke was measured using a drum rotation speed of 150 rpm and a sieve opening of 15 mm in accordance with the JIS K2151 rotational strength test method. The difference (ΔDI) between the DI of the Reference Example, which did not contain carbonized biomass as a raw material (78.4), and that of the Reference Example, which did not contain carbonized biomass as a raw material, was calculated. The calculated values ​​are shown in Table 1. Figure 1 shows the relationship between the volatile content on an anhydrous ash-free basis of the blended carbonized biomass and ΔDI when the carbonized biomass blending ratio was 5% by mass.

[0050] According to Figure 1, when the volatile content of the carbonized biomass on an anhydrous ash-free basis was between 7.0% and 35% by mass, the ΔDI did not decrease beyond -2.0. In this case, coke strength can be adjusted by adjusting the quality of the coal blend or the production conditions, so this level is considered to be practically acceptable. In particular, when the volatile content of the carbonized biomass on an anhydrous ash-free basis was between 10% and 25% by mass, the ΔDI did not decrease beyond -1.0. In this case, coke strength can be adjusted by minor adjustment of the coal quality or the production conditions, so this carbonized biomass is particularly suitable for coke production.

[0051] On the other hand, when the volatile content of the carbonized biomass blended on an anhydrous ashless basis was less than 7.0 mass% or more than 35 mass%, a large decrease in DI was observed. Furthermore, even when the volatile content of the anhydrous ashless basis was increased by oxidation treatment (Examples 12 and 13), it was confirmed that the decrease in strength when blending carbonized biomass could be suppressed by keeping the volatile content of the anhydrous ashless basis between 7.0 mass% and 35 mass%. [Industrial Applicability]

[0052] According to the coke production method of the present invention, it is possible to provide a technology for producing high-strength coke even when carbonized biomass is blended as part of the raw materials for coke production.

Claims

1. A method for producing coke, comprising blending carbonized biomass obtained by heat treating biomass with a part of blended coal for coke production, and carbonizing the blended coal, The volatile content of the carbonized biomass on an anhydrous ash-free basis is 7.0% by mass or more and 35% by mass or less; Coke manufacturing method.

2. The coke production method according to claim 1 , wherein the carbonized biomass is obtained by oxidizing carbonized biomass obtained by heat-treating biomass.

3. The method for producing coke according to claim 1 or 2, wherein a proportion of the carbonized biomass having a particle size of 3 mm or less is 70 mass% or more and 100 mass% or less.

4. The method for producing coke according to claim 3 , wherein the blended coal has a blending ratio of the carbonized biomass of 1 mass % or more and 10 mass % or less.

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