Coke production method

Abstract

Provided is a coke production method by which high-strength coke can be produced even when a biomass-derived raw material is used, without requiring an operation that poses a fire risk. This method for producing coke by charging blended coal into a coke oven and carbonizing the same is characterized in that the blended coal is prepared by blending 1–10 mass %, inclusive, of a carbonaceous material B, which is obtained by heat-treating biomass in which the percentage thereof having a particle diameter of 125 μm or less is 50 mass % or more, with a carbonaceous material A in which the percentage thereof having a particle diameter of 3 mm or more is 10–30 mass %, inclusive, and the percentage thereof having a particle diameter of 0.5 mm or more is 60 mass % or more.

Description

Coke manufacturing method

[0001] The present invention relates to a coke manufacturing method, and more particularly to a coke manufacturing method that can produce high-strength coke when producing coke using biomass raw materials.

[0002] Blast furnace coke is used in the blast furnace as a reducing agent, a heat source, and a support material to maintain gas permeability and liquid permeability. Stable operation of the 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, CO ２ With the growing need to reduce emissions, industries that previously used coal and oil as raw materials are considering replacing them with carbon-neutral materials such as biomass. In the steel industry, too, there is a demand to use biomass-derived raw materials as raw materials for the coke used in blast furnaces.

[0004] Lump coke used in blast furnaces is produced by carbonizing coal in a carbonization furnace, where the coal softens and melts, bonding together. Therefore, to produce high-strength coke, caking coal, which has excellent thermoplasticity, is used. However, biomass-derived raw materials do not soften and melt like coal, so when used in the conventional process for producing coke from coal, they produce low-strength coke with many defects. Therefore, when using biomass-derived raw materials, it is necessary to devise ways to prevent a decrease in coke strength.

[0005] When a coal blend is charged into a coke oven and carbonized to produce coke, it is generally known that the coke strength improves as the bulk density of the charged coal blend increases (see, for example, Non-Patent Document 1). Therefore, various methods for improving the bulk density of the coal blend charged into a coke oven have been investigated.

[0006] As a method for improving the bulk density of gravity-charged coal, for example, Non-Patent Document 2 describes a method for improving the bulk density of coal based on a preheated coal charging method in which coal is preheated and dried at a high temperature of about 200°C and then charged.

[0007] Furthermore, Patent Documents 1 and 2 describe methods for improving the bulk density of coal by adding a bulk density improver to a coal blend.

[0008] JP 2010-77332 A JP 2013-107930 A

[0009] 3rd Edition Steel Handbook Vol. II p. 170 5th Edition Steel Handbook Vol. 1 p. 107

[0010] As mentioned above, when biomass-derived raw materials are used in coke production, it is necessary to devise a way to prevent a decrease in coke strength. If the bulk density of a coal blend containing biomass-derived raw materials can be increased when charged into a coke oven, it is thought that high-strength coke can be produced even when biomass-derived raw materials are used. However, all of the above-mentioned conventional methods for improving the bulk density of a coal blend charged into a coke oven have had problems.

[0011] In the method based on the preheated coal charging method described in Non-Patent Document 2, coal is preheated and dried at a high temperature of about 200°C before being charged, so a nitrogen atmosphere is required to prevent ignition and coal oxidation. Therefore, additional equipment is required to maintain the nitrogen atmosphere, and if the nitrogen atmosphere is not maintained, there is a risk of explosion or ignition due to high-temperature, low-moisture coal.

[0012] Furthermore, in the methods described in Patent Documents 1 and 2, an improvement in bulk density is achieved by using an additive that is generally known to be effective in improving lubricity. However, because raw materials other than those used in normal coke production are added in addition to raw materials derived from biomass, there is a possibility that coke quality such as coke strength may be reduced, and the addition of expensive agents increases costs.

[0013] 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 does not require any operations that pose a risk of fire and that is capable of producing high-strength coke even when using biomass-derived raw materials.

[0014] The present inventors conducted extensive research to solve the above-mentioned problems and discovered the following. Specifically, they found that blending finely powdered carbonized biomass with carbonaceous material of the pulverized particle size used in ordinary coke production allows the finely powdered carbonized biomass to function as a lubricant between carbonaceous material particles, improving the lubricity of the carbonaceous material and increasing the bulk density of the blended coal when charged into a coke oven. They also found that the increase in bulk density when charged into a coal blend allows the production of coke with strength equal to or greater than that of a coal blend without the addition of biomass-derived raw materials.

[0015] The gist and configuration of the present invention, which has been completed based on the above findings, is as follows.

[0016] [1] A method for producing coke by charging a coal blend into a coke oven and carbonizing the resulting mixture, the method comprising: preparing the coal blend by blending a carbonaceous material A having a ratio of 10% by mass to 30% by mass and a ratio of 0.5 mm or larger to 60% by mass; and a carbonaceous material B obtained by heat-treating biomass having a ratio of 125 μm or smaller to 50% by mass, in a ratio of 1% by mass to 10% by mass.

[0017] [2] The method for producing coke described in [1], wherein the volatile content of the carbonaceous material B is 2% by mass or more and 50% by mass or less.

[0018] According to the present invention, a coke production method can be provided that does not require any operations that pose a risk of fire and that can produce high-strength coke even when using biomass-derived raw materials.

[0019] 1 is a cross-sectional view showing a schematic diagram of a bulk density measurement device used in a bulk density measurement test. 2 is a graph showing the relationship between the blending ratio of carbonaceous material B and a conventional example (No. 1) obtained by dry distilling only carbonaceous material A containing no carbonized biomass.

[0020] A coke production method according to an embodiment of the present invention is a method for producing coke by charging a coal blend into a coke oven and carbonizing the coal blend, and is characterized in that a coal blend is prepared by blending a carbonaceous material A having a ratio of 10% by mass to 30% by mass and a ratio of 0.5 mm or larger to 60% by mass or larger of a carbonaceous material B obtained by heat treating biomass having a ratio of 125 μm or smaller to 50% by mass or larger, in a ratio of 1% by mass to 10% by mass.

[0021] It is generally known that reducing the particle size of a coal blend used in coke production reduces the bulk density of the coal blend charged into a coke oven, and therefore, in order to improve bulk density, it is desirable to increase the particle size of the coal blend.

[0022] The present inventors believed that if the bulk density could be improved by appropriately controlling the particle size distribution of a coal blend charged into a coke oven, it would be possible to suppress the decrease in coke strength that is a concern when using biomass-derived raw materials. As a result of extensive research based on this belief, they found that by blending fine carbonized biomass with a coal blend used in ordinary coke production, the fine carbonized biomass acts as a bulk density improver, thereby improving the bulk density of the coal blend charged into a coke oven.

[0023] The method for producing coke of the present invention will be described in detail below.

[0024] The coke production method of the present invention is a technology for improving the bulk density of a coal blend at the time of charging by blending a finely divided carbonaceous material (carbonaceous material B) with a coal blend (carbonaceous material A) used in ordinary coke production. Here, the coal blend (carbonaceous material A) used in ordinary coke production is mainly composed of carbonaceous materials such as coal, pitches, oil coke, and coal dry distillate.

[0025] In the coke production method of the present invention, a coal blend is prepared by blending carbonaceous material A having a particle size of 3 mm or more in a proportion of 10 mass % to 30 mass % and a particle size of 0.5 mm or more in a proportion of 60 mass % or more with fine carbonaceous material B having a particle size of 125 μm or less in a proportion of 50 mass % inclusive.

[0026] The carbonaceous material A, which has a proportion of particles with a particle size of 3 mm or more of 10% by mass to 30% by mass and a proportion of particles with a particle size of 0.5 mm or more of 60% by mass or more, has a particle size used in ordinary coke production. It is known from prior art that reducing the particle size of a coal blend reduces the bulk density of the coal blend charged into a coke oven. Therefore, in the present invention, the pulverized particle size of the carbonaceous material A, which accounts for the majority of the coal blend, is controlled so that the proportion of particles with a particle size of 3 mm or more is 10% by mass to 30% by mass.

[0027] If the particle size of the carbonaceous material A is high, a property distribution occurs in coke production using a mixture of various components with different properties, such as coal. Therefore, the particle size of the carbonaceous material A is controlled so that the proportion of particles of 3 mm or more is 30 mass% or less. On the other hand, if the particle size of the carbonaceous material A is low, as previously known, the bulk density of the blended coal during charging decreases, so the proportion of particles of 3 mm or more is controlled so that the proportion of particles of 3 mm or more is 10 mass% or more. Preferably, the proportion of particles of 3 mm or more in the carbonaceous material A is 15 mass% or more and 25 mass% or less. Note that the upper limit of the particle size of the carbonaceous material A is not particularly limited as long as the proportion of particles of 3 mm or more is 30 mass% or less, but it is preferably 25 mm or less from the viewpoint of preventing component imbalance.

[0028] Furthermore, if the particle size of carbonaceous material A is too small, the bulk density of the coal blend will decrease and the difference in particle size with carbonaceous material B will become small, and the bulk density improvement effect of the present invention will not be obtained. Therefore, in the present invention, the proportion of particles of carbonaceous material A with a particle size of 0.5 mm or more is set to 60 mass% or more. That is, the proportion of particles of 0.5 mm or more and less than 3 mm is set to 30 mass% or more and 90 mass% or less. Furthermore, the proportion of particles of 0.5 mm or more in carbonaceous material A is preferably set to 80 mass% or less. Furthermore, the proportion of fine particles of carbonaceous material A with a particle size of less than 0.5 mm is set to less than 40 mass%, and preferably less than 20 mass%. If a large amount of fine particles less than 0.5 mm are obtained during pulverization, they may be removed by sieving or the like.

[0029] On the other hand, carbonaceous material B, in which the proportion of particles having a particle size of 125 μm or less is 50% by mass or more, is a carbonaceous material obtained by heat treating biomass, and is blended in a proportion of 1% by mass to 10% by mass or less with respect to the entire coal blend. In the present invention, blending carbonaceous material B, which has an extremely small particle size relative to carbonaceous material A, provides an effect of improving bulk density. Specifically, when the coal blend is charged into a coke oven, the fine carbonaceous material B enters between the coarse carbonaceous material A particles, functioning as a lubricant and improving the slipperiness of the coal blend and the bulk density. In addition, the fine carbonaceous material B enters between the coarse carbonaceous material A particles and disrupts the water bridges between the carbonaceous material particles in the coal blend, thereby also providing an effect of improving the slipperiness of the carbonaceous material. The blending ratio of carbonaceous material B is preferably 1% by mass to 9% by mass, more preferably 2% by mass to 5% by mass.

[0030] Here, biomass is a general term for a certain amount of accumulated animal and plant resources and waste materials derived from these resources (excluding fossil resources). The biomass used for the carbonaceous material B of the present invention includes all biomass derived from agriculture, forestry, livestock, fisheries, waste, etc. that produces charcoal when pyrolyzed.

[0031] In the present invention, the biomass used as the raw material for carbonized biomass preferably includes one with a high effective calorific value, for example, woody biomass.

[0032] Examples of woody biomass include papermaking by-products such as pulp black liquor and chip dust, lumbering by-products such as bark and waste, forest residues such as branches, leaves, treetops, and short pieces of wood, thinned wood from cedar, cypress, pine, and other species, and waste logs from edible fungi grown in specialized forests, as well as forestry biomass such as firewood forests of castanopsis, oak, and pine, and short-rotation forestry of willow, poplar, eucalyptus, pine, etc. Woody biomass also includes general waste such as pruned branches from municipal street trees and private garden trees, pruned branches from national and prefectural street trees and corporate garden trees, and industrial waste such as construction and building waste. Furthermore, some agricultural biomass such as rice husks, wheat straw, rice straw, sugarcane residue, palm oil, etc., which are classified as agricultural biomass and are generated from waste or by-products, and rice bran, rapeseed, soybeans, etc., which are generated from energy crops, can also be suitably used as woody biomass.

[0033] The carbonaceous material B preferably has a volatile content of 2% by mass or more and 50% by mass or less. If the volatile content exceeds 50% by mass, the carbonization of the biomass is not advanced, resulting in poor pulverizability and a decrease in the productivity of the fine powder of the carbonaceous material B, which is undesirable. On the other hand, if the volatile content is less than 2% by mass, the decrease in coke strength due to the blending of the carbonaceous material B is greater than when the volatile content is 2% by mass or more, and there is a possibility that the blending ratio of the carbonaceous material B cannot be increased. The volatile content of the carbonaceous material B is more preferably 4% by mass or more and 45% by mass or less, and even more preferably 6% by mass or more and 30% by mass or less.

[0034] The lower the volatile content of carbonaceous material B, the greater the effect of improving the bulk density of the blended coal by blending carbonaceous material B. A low volatile content of carbonaceous material B means that the carbonization of biomass by heat treatment has progressed more, and carbonaceous material B has become hydrophobic. It is thought that the more hydrophobic carbonaceous material B is, the greater the effect of breaking the cross-links between particles by the water in the blended coal, and therefore the greater the effect of improving the lubricity of the carbonaceous material.

[0035] In this specification, the volatile content is a value measured in accordance with "Coals and cokes - proximate analysis methods" (JIS M 8812:2004) specified in the Japanese Industrial Standards (JIS).

[0036] The heat treatment of the biomass as the raw material for the carbonaceous material B is preferably carried out in an atmosphere where the supply of oxygen is blocked. For example, the heat treatment may be carried out in a state where the raw biomass is housed in a container that forms a space where the inflow of air is blocked and an inert gas is circulated (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 by heat transfer from the container.

[0037] Typically, the reaction rate of the thermal decomposition reaction of biomass during heat treatment is fast, so the time required for the thermal decomposition reaction to be completed is short. Therefore, the heat treatment time is preferably 1 minute or more, 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 is possible to perform heat treatment by reliably raising the temperature of the entire raw carbonaceous material to the heat treatment temperature (i.e., by uniform heating), thereby suppressing quality variations in the heat-treated carbonaceous material and carbonaceous material powder. There is no particular upper limit for the heat treatment time, but a long heat treatment time is undesirable because it increases the energy required for the heat treatment and 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 biomass is maintained at this heat treatment temperature from the time it reaches the predetermined heat treatment temperature.

[0038] 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.

[0039] The method for adjusting the particle size of the carbonaceous material B is not particularly specified as long as a predetermined particle size is obtained, but in order to finely pulverize a large amount of carbonaceous material used in coke production, equipment such as a roller mill or a tower mill can be used.

[0040] The moisture content of the coal blend in the present invention is preferably 6% by mass or more and 9% by mass or less. If the moisture content of the coal blend is less than 6% by mass, the drying of the coal blend may increase the risk of ignition and may also increase dust generation. On the other hand, if the moisture content of the coal blend is higher than 9% by mass, the increase in water may reduce the effect of improving bulk density by blending the fine carbonaceous material B, and a large amount of heat is required to evaporate the water during carbonization in coke production, which is undesirable.

[0041] Examples of the present invention will be described below. Note that the present invention is not limited to the following examples and can be modified as desired without departing from the gist of the present invention.

[0042] Table 1 shows the particle size of carbonaceous material A, the particle size and blending ratio of carbonaceous material B in the coal blend used in the bulk density measurement test, and the moisture content of the coal blend.

[0043]

[0044] FIG. 1 is a cross-sectional view schematically illustrating a bulk density measurement device used in the bulk density measurement test. As shown in FIG. 1, the bulk density measurement device 1 includes a sample hopper 2, a guide 3 installed below the sample hopper, and a box-shaped container 4. The guide 3 has an inlet diameter of 300 mm and an outlet diameter of 150 mm. The container 4 is a rectangular box-shaped container measuring 250 mm wide, 250 mm long (depth direction in FIG. 1), and 200 mm high, with only the top surface being open. A slide gate 5 is installed below the sample hopper 2. When the slide gate 5 is opened, the blended coal in the hopper 2 falls into the container 4 via the guide 3. The height from the slide gate 5 installed below the hopper 2 to the bottom of the container 4 is 2 m.

[0045] In this example, the bulk density measuring device described above was used to measure the bulk density of various coal blends listed in Table 1. The procedure for measuring the bulk density is described below.

[0046] First, carbonaceous material A and carbonaceous material B, each adjusted to the particle size shown in Table 1, were blended, and water was added and mixed to obtain a coal blend. Next, 32 kg of the coal blend was loaded into hopper 2, and then slide gate 5 was opened to drop the coal blend into container 4. Subsequently, the coal blend protruding from the top of container 4 after the drop was removed, and the mass of the coal blend loaded in the container was measured. Thereafter, the weighed coal blend was divided into smaller pieces to measure its moisture content, and the bulk density (dry basis, d.b.) of the coal blend was calculated using the following formula (1). The measurement of the coal loading bulk density was performed twice for each level, and the average of the two measurements was used as the bulk density for each level.

[0047] (1)

[0048] Table 1 shows the results of measuring the bulk density of each coal blend. In Levels 1 to 5, which are conventional examples that do not contain fine carbonaceous material B, the bulk density decreased as the mass ratio of particles less than 3 mm increased. As is conventional knowledge, the lower the crushed particle size, the lower the bulk density. On the other hand, in Levels 6 to 26, which are inventive examples in which fine carbonaceous material B was blended with carbonaceous material A, the bulk density was improved compared to the conventional example in which no carbonaceous material B was blended. Furthermore, in Level 27, a comparative example in which the blending ratio of carbonaceous material B exceeded 10 mass%, the bulk density was lower compared to the conventional example (Level 3) in which no carbonaceous material B was blended. These results confirm that blending fine carbonized biomass in a proportion of 1 mass% to 10 mass% with a coal blend used in normal coke production allows the fine carbonized biomass to act as a bulk density improver, thereby improving the bulk density of the coal blend when charged.

[0049] Next, a carbonization test was conducted to examine the influence of the bulk density improvement effect of blending fine carbonized biomass on coke strength. Carbonized material A, a blended coal with a vitrinite average maximum reflectance (Ro(-)) of 1.0 [%] and a Gieseler Plastometer maximum fluidity (MF [ddpm]) of 2.50, was blended with carbonized material B, a fine carbonized biomass, to produce coke in the following manner, and the coke strength was evaluated.

[0050] Coal blend A and carbonaceous material B, each prepared to have a particle size as shown in Table 2, were blended at the blending ratios shown in Table 2, and then water was added and mixed to make the moisture content 7%, to prepare a coal blend for carbonization. 16.5 kg of this coal blend was loaded into a carbonization can at the bulk density shown in Table 2 and carbonized in an electric furnace. After carbonization for 6 hours at a furnace wall temperature of 1,050°C, the coke was cooled under a nitrogen atmosphere, and the resulting coke was used to measure drum strength. The drum strength DI_150 / 15 index was measured in accordance with the rotational strength test method of JIS K2151. The strength difference from a conventional example (No. 1) obtained by carbonizing only carbonaceous material A containing no carbonized biomass was expressed as ΔDI (ΔDI = [DI_150 / 15 index of the target level] - [DI_150 / 15 index of No. 1]), and is shown in Table 2.

[0051]

[0052] In Table 2, level 1 is a conventional example in which carbonaceous material B is not blended, levels 2 to 18 are invention examples in which carbonaceous material B is blended, and level 19 is a comparative example in which the blending ratio of carbonaceous material B is outside the range of the present invention. The bulk density at the time of carbonization for each level reflects the bulk density measurement results in Table 1. In levels 2 to 18, which are invention examples in which fine carbonaceous material B is blended with carbonaceous material A and an improvement in bulk density is achieved, ΔDI exceeds 0, indicating that the blending of carbonaceous material B has the effect of improving coke strength. On the other hand, in level 19, in which the blending ratio of carbonaceous material B is outside the range of the present invention, ΔDI is less than 0, and strength is reduced.

[0053] Figure 2 shows the relationship between the blending ratio of carbonaceous material B and ΔDI for Level 1, in which no carbonaceous material B was added, and Levels 3 to 5, 9, 10, and 19, in which cedar heat-treated at 500°C (the proportion of particles of 106 μm or less is 100% by mass) was blended as the carbonaceous material B, among the Examples listed in Table 2. As shown in Figure 2, it can be seen that when the blending ratio of carbonaceous material B is in the range of 1% by mass or more and 10% by mass or less, an improvement in bulk density is obtained, and ΔDI exceeds 0.

[0054] According to the present invention, it is possible to provide a technique for producing high-strength coke even when using a biomass-derived raw material, without requiring any operation that poses a risk of fire.

[0055] 1 Bulk density measuring device 2 Hopper 3 Guide 4 Container 5 Slide gate

Claims

1. A method for producing coke by charging a coal blend into a coke oven and carbonizing it, characterized in that the coal blend is prepared by blending carbon material A, which has a ratio of particles of 3 mm or more of 10% by mass to 30% by mass to particles of 0.5 mm or more of 60% by mass to carbon material B, which is obtained by heat-treating biomass, which has a ratio of particles of 125 μm or less of 50% by mass or more, in a ratio of 1% by mass to 10% by mass.

2. The method for producing coke as described in claim 1, wherein the volatile content of the carbonaceous material B is 2 mass% or more and 50 mass% or less.

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