Method for producing coke

Abstract

The present invention presents a novel index for a biomass-derived raw material that replaces some of coal to be used for the production of coke for use in blast furnaces, and provides a means by which high-strength coke is produced even when the biomass-derived raw material is added to coal. Carbonized biomass having a shrinkage in the temperature range from 600°C to 1000°C of 4.0-10.0% is mixed with a coal blend to produce coke.

Description

Coke manufacturing method

[0001] The present invention relates to a method for producing coke using biomass as part of the raw material.

[0002] Coke is a carbon-based lump product obtained by carbonization of coal. Blast furnace coke functions as a heat source and reducing agent, as well as a support material that ensures gas permeability and liquid permeability within the blast furnace. Therefore, to ensure stable operation of the blast furnace, the lump coke must have sufficient mechanical strength.

[0003] To produce coke for blast furnaces, a coal blend containing multiple types of coal in a specified ratio is used. The coal blend is carbonized at a temperature of 1000°C or higher, either as is or after molding, to obtain coke in the form of a lump of coal bound together. High-strength coke can be obtained by using, as part of the coal blend, a type of coal known as caking coal, which has the property of easily softening and melting.

[0004] Two types of coal measurements have traditionally been used as indicators for managing coke strength. One is the average maximum reflectance of vitrinite (hereinafter referred to as "Ro"), as specified in Japanese Industrial Standards M 8816:1992, "Method for Measuring Microstructural Components and Reflectance of Coal." The higher the Ro value of coal, the higher the degree of carbonization and the stronger the coke matrix tends to be. The other is the maximum fluidity (hereinafter referred to as "MF") measured by a Gieseler Plastometer, as specified in Japanese Industrial Standards M 8801:2004, "Coals - Testing Methods." The higher the MF value of coal, the more likely it is to soften, melt, and flow when heated.

[0005] In recent years, societal efforts to mitigate the impact of global warming by reducing emissions of carbon dioxide, a greenhouse gas, into the atmosphere have been accelerating. Therefore, studies are underway to replace a portion of coal, which is a raw material for coke, 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 pyrolyze it, and the resulting biomass char, which is a solid component having a diameter of 1 mm or less, is added to a coal blend.

[0006] JP 2014-77086 A

[0007] When attempting to replace a portion of the coal used to make coke with a biomass-derived material, even a small substitution ratio can significantly reduce the strength of the resulting coke.

[0008] In the prior art, Ro and MF, which are effective as indicators for controlling coke strength, are both indicators that are assumed to be measured for coal. Therefore, even if attempts are made to measure Ro and MF for a sample consisting only of raw materials derived from biomass, the properties of coal and biomass are significantly different, so it is impossible to perform the measurement, or even if it were possible to measure them, the measured values ​​cannot be used as indicators for controlling coke strength. Therefore, a new indicator for controlling coke strength is needed.

[0009] The present invention has been made in view of the above-mentioned problems, and its purpose is to present new indicators for biomass-derived raw materials that can replace a portion of the coal used in producing coke for blast furnaces, and to provide a means for producing high-strength coke even when biomass-derived raw materials are blended with coal.

[0010] The gist and configuration of the present invention completed by the inventors in order to achieve the above object is as follows.

[0011] [1] A method for producing coke by carbonizing a mixture obtained by blending a coal blend for coke production in a predetermined ratio with carbonized biomass, the proportion of which is 70% by mass or more and 100% by mass or less and has a particle size of 3.0 mm or less, and the mixture is then carbonized, the shrinkage rate of the carbonized biomass at 600°C to 1000°C being 4.0% or more and 10.0% or less. [2] A method for producing coke by carbonizing a mixture obtained by blending a coal blend for coke production in a predetermined ratio with carbonized biomass, the proportion of which is 70% by mass or more and 100% by mass or less and has a particle size of 1.0 mm or less, and the shrinkage rate of the carbonized biomass at 600°C to 1000°C being 2.0% or more and 10.0% or less. [3] A method for producing coke according to [1] or [2] above, wherein the proportion of the carbonized biomass in the mixture is 1.0% by mass or more and 10.0% or less. [4] The method for producing coke according to any one of [1] to [3] above, wherein the proportion of the coal blend for coke production having a particle size of 3.0 mm or less is 70 mass % or more and 100 mass % or less.

[0012] 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. As a result, it is possible to produce high-strength coke even when biomass-derived raw materials are blended with coal. Furthermore, it is possible to reduce carbon dioxide emissions derived from fossil fuels.

[0013] 1 is a graph showing the relationship between the contraction rate of carbonized biomass and the drum strength index of coke using carbonized biomass with a particle size of 3.0 mm or less as part of the raw material, and FIG. 2 is a graph showing the relationship between the contraction rate of carbonized biomass and the drum strength index of coke using carbonized biomass with a particle size of 1.0 mm or less as part of the raw material.

[0014] Hereinafter, embodiments of the present invention will be described in detail.

[0015] In one embodiment, a method for producing coke according to the present invention is characterized in that when carbonized biomass, in which the proportion of particle sizes of 3.0 mm or less is 70 mass % or more and 100 mass % or less, is blended with a coal blend for coke production in a predetermined ratio, and the resulting mixture is carbonized to produce coke, the shrinkage rate of the carbonized biomass at 600°C to 1000°C is 4.0% or more and 10.0% or less.

[0016] [Carbonized Biomass] In this embodiment, "biomass" refers to organic industrial resources derived from plants and animals that exist in the current ecosystem. The organic matter that constitutes 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 when plants and animals grow, and therefore does not affect the increase or decrease in 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 biomass in this embodiment.

[0017] The biomass used in this embodiment 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 production, as long as it satisfies the specified conditions described below. In a preferred embodiment, the biomass includes at least one of palm kernel shells and woody biomass. Palm kernel shells are biomass produced as a by-product after palm oil is extracted from palm kernels. Palm kernel shells are suitable for use in this embodiment because of their low cost and moderate strength. Examples of woody biomass include biomass made from wood from coniferous trees 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 used in construction and papermaking, as well as unused parts such as thinned wood from forestry. Sawdust produced during lumber production is one of the most representative woody biomass materials.

[0018] The method for producing coke according to the present invention uses carbonized biomass produced by heat-treating biomass. In the heat treatment of biomass, the biomass is heat-treated in an air-tight atmosphere. By performing the heat treatment of biomass in an air-tight atmosphere, the progress of combustion of the biomass is hindered, and the biomass can be carbonized. To achieve an air-tight atmosphere, for example, a container is prepared that forms a space that prevents air from entering and through which an inert gas flows, and the biomass is loaded into the container and heat-treated.

[0019] The temperature at which biomass is heat-treated may be adjusted appropriately depending on the type and particle size of the biomass so that the shrinkage rate at 600°C to 1000°C falls within a suitable range. For example, when palm kernel shells are used as biomass, a temperature of 400°C or higher will sufficiently advance carbonization and improve crushability, while a temperature of 800°C or lower will fall within a suitable range for the shrinkage rate described below, so a temperature of 400°C or higher and 800°C or lower is preferred. A higher temperature at which biomass is heat-treated is more preferable from the viewpoint of crushability, and a lower temperature is more preferable from the viewpoint of shrinkage rate. In this specification, "heat treatment temperature" refers to the maximum temperature reached by biomass when heat-treated.

[0020] The heat treatment time varies depending on the type of biomass and the mass of biomass to be heat treated at one time, but is preferably 1 minute or more and 60 minutes or less. A more preferable lower limit of the heat treatment time is 10 minutes or more. A more preferable upper limit of the heat treatment time is 30 minutes or less. In this specification, "heat treatment time" refers to the time from when the temperature of the biomass during heat treatment reaches the heat treatment temperature to when the heat treatment temperature is stopped being maintained.

[0021] [Pulverization] In this embodiment, the proportion of carbonized biomass having a particle size of 3.0 mm or less is 70% by mass or more and 100% by mass or less. When the proportion of particle sizes of 3.0 mm or less is 70% by mass or more and 100% by mass or less, the carbonized biomass can be homogeneously mixed with the blended coal. A preferred particle size range for the carbonized biomass is 100% by mass of particle sizes of 3.0 mm or less. There is no lower limit for the particle size. In other words, the particle size may be any size greater than 0 (zero). When pulverization is performed for the purpose of adjusting the particle size of biomass or carbonized biomass, a known pulverizer can be used. Pulverization may be performed on the biomass before carbonization, on the carbonized biomass after carbonization, or on both.

[0022] In this specification, "particle size" corresponds to the nominal mesh size of a test sieve as specified in Japanese Industrial Standards Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves." In other words, powders and granular materials having a particle size larger than X mm are powders and granular materials that remain on a sieve with a nominal mesh size of X mm when sieved through a sieve. Powders and granular materials having a particle size of Y mm or less are powders and granular materials that fall below the sieve when sieved through a sieve with a nominal mesh size of Y mm.

[0023] When producing large amounts of carbonized biomass on an industrial scale, omitting sieving can increase yield and reduce production costs. In this case, the proportion of particle sizes of 3.0 mm or less in the particle size distribution of the carbonized biomass based on mass is 70 mass% or more. When classification is not performed, the proportion of particle sizes of 3.0 mm or less is preferably 80 mass% or more, and more preferably 90 mass% or more. The upper limit of the proportion of particle sizes of 3.0 mm or less is 100 mass%. The particle size distribution of the carbonized biomass based on mass can be determined by known methods, such as measuring the weight of a sample sieved using multiple sieves with different mesh sizes from a sample taken from the large amount of carbonized biomass produced, or irradiating the sample with a laser.

[0024] [Blending] In the coke production method according to this embodiment, coke is produced by carbonizing a mixture obtained by blending a coal blend for coke production with carbonized biomass in a predetermined ratio. The coal blend may be any coal blend as long as it is suitable for coke production. A coal blend suitable for coke production refers to a coal blend from which high-strength coke can be produced by carbonizing only the coal blend as a raw material. Whether a coal blend is suitable for coke production can be predicted from the Ro and MF values ​​of the coal blend.

[0025] In a coal blend for coke production, the proportion of particles having a particle size of 3.0 mm or less is preferably 70% by mass or more and 100% by mass or less. If the particle size of the coal blend is coarse, a property distribution will occur in coke production using a mixture of coal components, such as coals, with different properties. Therefore, it is preferable that the proportion of particles having a particle size of 3.0 mm or less in the coal blend is 70% by mass or more. More preferably, the proportion of particles having a particle size of 3.0 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 having a particle size of 3.0 mm or less is preferably 90% by mass or less, and more preferably 85% by mass or less.

[0026] If the proportion of carbonized biomass in a mixture obtained by blending carbonized biomass in a predetermined proportion with a coal blend for coke production is 1.0 mass% or more, a significant effect in reducing carbon dioxide emissions can be obtained, and if it is 10.0 mass% or less, the strength of the obtained coke does not decrease significantly, so the proportion of carbonized biomass is preferably 1.0 mass% or more and 10.0 mass% or less, and more preferably 2.0 mass% or more and 7.0 mass% or less.

[0027] In the coke manufacturing method according to the present invention, the mixture obtained by blending the blended coal and the carbonized biomass at a predetermined ratio may be sufficiently mixed without performing any special operation specifically for mixing. Specific examples of such cases include a case where the mixture conveyed by a belt conveyor falls onto the next belt conveyor, a case where the blended coal and the carbonized biomass are blended and then pulverized using pulverization equipment, and a case where the moisture content is adjusted while stirring the blended coal and the carbonized biomass using coal moisture control equipment. These cases are preferable because they can reduce the equipment and costs required for mixing.

[0028] In the mixture, it is preferable that the blended coal and the carbonized biomass are uniformly mixed. This can prevent the problem of the carbonized biomass, which does not soften or melt when heated, being unevenly distributed in one place and remaining unsolidified after the carbonization process. If mixing is insufficient, a coal mixer can be used to mix the blended coal and the carbonized biomass. As the coal mixer, for example, a mixer that mainly performs convective mixing, a mixer that mainly performs shear mixing, or a mixer that performs a combination of convective and shear mixing can be used. Here, convective mixing refers to mixing that mainly involves convection and diffusion of the sample, and shear mixing refers to mixing that involves shearing, collision, grinding, etc. of the sample.

[0029] In the coke production method according to the present embodiment, coke is produced by carbonizing a mixture obtained by blending a coal blend for coke production with carbonized biomass at a predetermined ratio. The mixture is charged into a coke oven and carbonized by heating in an air-tight atmosphere.

[0030] If the carbonization temperature is 900°C or higher, coke of sufficient strength can be obtained. 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. The carbonization temperature refers to the maximum temperature reached by the mixture during carbonization.

[0031] [Shrinkage Rate] The coke production method according to this embodiment is characterized in that the shrinkage rate of the carbonized biomass at 600°C to 1000°C is 4.0% or more and 10.0% or less.

[0032] A sample for shrinkage measurement can be prepared by pulverizing carbonized biomass and molding it to a size that meets the specifications of the measurement device. Setting the pulverized particle size of the carbonized biomass to one-tenth or less of the height of the sample for shrinkage measurement, i.e., the length measured in the direction of shrinkage measurement, is preferred because it eliminates the influence of anisotropy in the shrinkage of the carbonized biomass sample and enables stable measurement results to be obtained. From this perspective, the pulverized particle size of the carbonized biomass is preferably, for example, 0.3 mm or less, and more preferably 0.1 mm or less.

[0033] Furthermore, since the purpose is to measure the shrinkage rate of the carbonized biomass itself, the sample for shrinkage rate measurement after molding is required to have few voids. Therefore, although it depends on the density of the carbonized biomass itself used in the test, the density of the sample for shrinkage rate measurement is 0.2 g / cm ３ It is preferable that the density is 0.4 g / cm or more. ３ It is more preferable that:

[0034] If it is difficult to obtain a molded body as a sample for shrinkage measurement, the sample may be filled into a container having dimensions that conform to the specifications of the measuring device, and used as the sample for shrinkage measurement. In this case, in order to eliminate the influence of thermal expansion of the container, it is preferable that the container be made of a material such as alumina, which has a small thermal expansion coefficient.

[0035] The shrinkage of a sample can be measured using a known measuring device such as a thermomechanical analyzer (TMA) or a thermal dilatometer. The measuring device used to measure the shrinkage must be capable of heating the sample up to 1000°C while controlling the temperature, and of measuring the change in length of the sample in the direction in which the shrinkage is to be measured. It is also preferable that the measuring device be equipped with a mechanism such as a contactor that can detect the change in size when the sample shrinks.

[0036] In this embodiment, the shrinkage rate of the sample is measured in a temperature range from 600°C to 1000°C. Generally, biomass releases moisture and volatile matter as the temperature increases, which causes shrinkage. In contrast, caking coal, which is widely used in coke production, undergoes complex changes with increasing temperature that are not observed in biomass. That is, caking coal softens and melts at temperatures above 300°C, causing the caking coal particles to bond together. It then resolidifies at temperatures above 500°C, becoming a solid as a whole. After resolidification, it further contracts while releasing volatile matter in a temperature range of 1000°C. Therefore, in this embodiment, the shrinkage rate of carbonized biomass is measured in a temperature range above 600°C after the softening and resolidification of the caking coal is completed. This allows for a direct comparison of the shrinkage rate of caking coal that softens and that of carbonized biomass that does not soften.

[0037] In a typical coke production process, when the temperature of coal during carbonization reaches 1000°C, the release of volatile matter is almost complete and the resulting coke is sufficiently carbonized, and therefore, in this embodiment, the upper limit of the temperature range for measuring the shrinkage rate of the sample is set to 1000°C. By measuring the shrinkage rate of the sample in a temperature range from 600°C to 1000°C, the shrinkage rate of the carbonized biomass in the carbonization process of a mixture of blended coal and carbonized biomass can be determined.

[0038] The shrinkage rate of the carbonized biomass obtained in the carbonization step varies depending on the type of carbonized biomass, the part used, etc. In this embodiment, carbonized biomass is selected and used such that the shrinkage rate at 600°C to 1000°C measured on a sample taken from the carbonized biomass is 4.0% or more and 10.0% or less.

[0039] Although the details of why high-strength coke can be produced by using carbonized biomass that satisfies the range of shrinkage rate specified in this embodiment are unknown, it is believed that the reason is probably as follows: As described above, coal shrinks while releasing volatile matter in a temperature range of 600°C or higher. If the amount of shrinkage of the coal blend when the mixture is carbonized differs significantly from the amount of shrinkage of the carbonized biomass, stress is generated due to the difference in shrinkage. The portion derived from the coal blend has already resolidified, so the stress cannot be relieved. For this reason, strain is thought to accumulate throughout the coke, resulting in a decrease in strength.

[0040] Carbonized biomass that satisfies the range of shrinkage rate specified in this embodiment has a shrinkage rate close to that of the blended coal. Therefore, it is thought that stress generation and strain accumulation due to differences in the amount of shrinkage are unlikely to occur, and that a decrease in strength is unlikely to occur.

[0041] The shrinkage rate measured using a sample for shrinkage rate measurement at temperatures between 600°C and 1000°C can be controlled by the type of biomass and the conditions of heat treatment during carbonization. The higher the heat treatment temperature, the lower the shrinkage rate. The conditions for heat treatment that result in a shrinkage rate of 4.0% or more and 10.0% or less vary depending on the type of biomass used and can be adjusted appropriately, but in many cases, the shrinkage rate can be adjusted to 4.0% or more by performing heat treatment at a temperature generally below 700°C.

[0042] In this embodiment, the temperature rise rate in measuring the contraction rate of the sample is preferably 1°C or more per minute, since this does not take too long for the measurement. Furthermore, since the temperature rise rate of coal in normal coke production is slow, a temperature rise rate of 10°C or less per minute is preferred. Therefore, the temperature rise rate in measuring the contraction rate of the sample is preferably 1°C or more and 10°C or less per minute. A more preferred lower limit of the temperature rise rate is 2°C or more per minute. A more preferred upper limit of the temperature rise rate is 5°C or less per minute.

[0043] In this embodiment, the atmosphere in which the shrinkage rate of the sample is measured is preferably an atmosphere in which air is blocked, for example, an atmosphere in which an inert gas is circulated. By measuring in an atmosphere in which air is blocked, it is possible to prevent the sample from burning, and to obtain information on the shrinkage rate close to the shrinkage rate during carbonization.

[0044] In another embodiment, the method for producing coke according to the present invention is characterized in that when carbonized biomass, the proportion of which is 70% by mass or more and 100% by mass or less and the proportion of which is 1.0 mm or less, is blended with blended coal for coke production in a predetermined ratio, and the resulting mixture is carbonized to produce coke, the shrinkage rate of the carbonized biomass at 600°C to 1000°C is 2.0% or more and 10.0% or less.

[0045] By changing the particle size of the carbonized biomass mixed with the blended coal from 3.0 mm or less to 1.0 mm or less, the range of the shrinkage rate of the carbonized biomass to which the present invention can be applied can be expanded to a range lower than 4.0%. Specifically, when the particle size of the carbonized biomass is 1.0 mm or less, carbonized biomass with a shrinkage rate of 2.0% or more and 10.0% or less at 600°C to 1000°C can be used.

[0046] Although the details of why the range of the shrinkage rate of carbonized biomass to which the present invention can be applied can be expanded to a range lower than 4.0% by reducing the particle size of carbonized biomass are unclear, it is thought that the reason is probably as follows: The finer the particle size of carbonized biomass, the smaller the absolute value of the shrinkage amount per granular material. As a result, the difference in the absolute value of the shrinkage amount between the granular material and the granular material in the surrounding coal blend becomes smaller, so that the distortion caused by the difference in shrinkage amount becomes smaller, and as a result, it is thought that the strength of the obtained coke does not decrease.

[0047] [Strength Evaluation] The effects of the present invention can be confirmed by evaluating the strength of the coke obtained by the coke manufacturing method according to this embodiment. There are various methods for evaluating coke strength, but the method of evaluating rotational strength by the drum method specified in Japanese Industrial Standards K 2151:2004, "Cokes - Test Methods," is a test that simulates the generation of dust from coke, which is a problem when used in a blast furnace. This method is currently the most widely used in Japan, and is therefore preferred. The drum method involves inserting a sample into a specified drum testing machine, rotating it at a specified speed for a specified number of rotations, sieving it through a specified sieve, determining the mass of each classification, and expressing the added percentage (%) of the sample as the drum strength index (symbol: DI).

[0048] As will be described later, in the examples of this specification, the drum rotation speed was set to 150 rpm, and the ratio of the mass of coke that did not pass through a sieve with a 15 mm mesh size after rotation to the mass of coke inserted into the drum testing machine was defined as the drum strength index (%). The drum strength index indicates the mass ratio of coke that was not crushed to a size of 15 mm or less even after rotation in the drum testing machine. A larger DI value indicates higher coke strength.

[0049] 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 the embodiments of the present invention can be modified as desired without departing from the gist of the present invention.

[0050] A coal blend with an Ro of 1.0% and a common logarithm of MF (log(MF / ddpm)) of 2.5 was prepared. This coal blend was pulverized to produce a coal blend in which the proportion of particles with a particle size of 3.0 mm or less was adjusted to 100% by mass. Two types of biomass, palm kernel shells and cedar, were prepared. These biomasses were heat-treated for 60 minutes in an air-tight atmosphere under five conditions, with the biomass temperatures ranging from 400°C to 900°C, to obtain carbonized biomass. These carbonized biomasses were pulverized to produce carbonized biomass in which the proportion of particles with a particle size of 3.0 mm or less or 1.0 mm or less was adjusted to 100% by mass. However, for some carbonized biomass (Examples 6 and 7), carbonized biomass in which the proportion of particles with a particle size of 3.0 mm or less was adjusted to 72% by mass was produced.

[0051] The shrinkage rate of carbonized biomass was measured using the following method. The carbonized biomass was crushed to 0.1 mm or less, and the crushed sample was filled into a cylindrical alumina cell with a diameter of 6.7 mm and a height of 9.2 mm to a height of 7.0 mm to prepare a sample for shrinkage rate measurement. The sample was placed in a thermomechanical analyzer TMA-60 manufactured by Shimadzu Corporation, and the temperature was raised in a nitrogen atmosphere at a rate of 3°C per minute to measure the shrinkage rate in the height direction of the sample in the temperature range from 600°C to 1000°C. The obtained measured values ​​are shown in Table 1.

[0052]

[0053] The above measurement results show that the higher the heat treatment temperature of biomass, the smaller the shrinkage rate. The shrinkage rate of palm kernel shells was 3.3% or less when the heat treatment temperature was 800°C or higher. The shrinkage rate of cedar was 0.8% when the heat treatment temperature was 900°C or higher.

[0054] Next, the blended coal and biomass were blended so that the blending ratio of biomass in the mixture was 2.0%, 5.0%, or 8.0%, and the moisture content was adjusted to 8.0 mass%. 16 kg of each mixture was prepared. This mixture was filled into a stainless steel container, inserted into an electric furnace through which nitrogen gas was circulated, heated, and carbonized. The bulk density of the mixture in the container was 775 kg / m on an anhydrous basis. ３The results were as follows: The container filled with the mixture was charged into an electric furnace set at a furnace wall temperature of 1,050°C, and carbonization was performed while maintaining the furnace wall temperature for 6 hours from the time of charging. After that, the container was transferred to a cooling facility through which room-temperature nitrogen gas was circulating and cooled, thereby obtaining a coke containing biomass as a raw material. To compare the drum strength index (DI), only the Reference Example coal blend was carbonized under the same conditions to obtain a coke containing 100% biomass-free coal blend. The drum strength index of the obtained coke was then measured under conditions of a drum rotation speed of 150 rpm and a sieve opening of 15 mm, and the difference ΔDI from the drum strength index of a coke containing 100% biomass was calculated. The calculated values ​​are shown in Table 1. The relationship between the shrinkage rate and ΔDI when the maximum particle size of the carbonized biomass was 3.0 mm is shown in Figure 1, and the relationship between the shrinkage rate and ΔDI when the maximum particle size of the carbonized biomass was 1.0 mm is shown in Figure 2.

[0055] According to Figure 1, when the proportion of carbonized biomass with particle sizes of 3.0 mm or less was 72% by mass and 100% by mass, the ΔDI did not decrease by more than -2.0% when the shrinkage rate was in the range of 4.7% to 8.9%. In this case, the coke strength can be adjusted by adjusting the quality of the coal blend and the production conditions, so it can be said that this is at a level that is not problematic for practical use. On the other hand, the cokes of Comparative Examples 1 to 4, which had shrinkage rates of less than 4.0%, showed a significant decrease in the drum strength index. These facts demonstrate that the coke production method of the present invention can produce coke with higher strength based on more reliable predictions than conventional techniques.

[0056] According to Figure 2, when the proportion of carbonized biomass particle sizes of 1.0 mm or less was 100% by mass, the ΔDI did not decrease by more than -2.0% when the shrinkage rate was in the range of 3.3% to 6.9%. The cokes of Comparative Examples 5 and 6, which had shrinkage rates of less than 2.0%, showed a large decrease in the drum strength index, but the degree of decrease was smaller than that shown in Figure 1. A comparison of Figures 1 and 2 shows that by reducing the particle size of carbonized biomass, the range of shrinkage rates of carbonized biomass to which the present invention can be applied can be expanded to a lower range.

[0057] According to the coke manufacturing method of the present invention, it is possible to produce coke with high strength that can withstand use in a blast furnace, even when part of the coal that is the raw material for the coke is replaced with a raw material derived from biomass.

Claims

1. A method for producing coke, comprising blending carbonized biomass, the proportion of particle sizes of 3.0 mm or less being 70% by mass or more and 100% by mass or less, with a coal blend for coke production in a predetermined ratio, and carbonizing the resulting mixture to produce coke, wherein the shrinkage rate of the carbonized biomass at 600°C to 1000°C is 4.0% or more and 10.0% or less.

2. A method for producing coke, comprising blending carbonized biomass, the proportion of particle sizes of 1.0 mm or less being 70% by mass or more and 100% by mass or less, with a coal blend for coke production in a predetermined ratio, and carbonizing the resulting mixture to produce coke, wherein the shrinkage rate of the carbonized biomass at 600°C to 1000°C is 2.0% or more and 10.0% or less.

3. The method for producing coke according to claim 1 or 2, wherein the ratio of the carbonized biomass in the mixture is 1.0 mass% or more and 10.0 mass% or less.

4. A method for producing coke as described in any one of claims 1 to 3, wherein the proportion of the coal blend for coke production having a particle size of 3.0 mm or less is 70 mass % or more and 100 mass % or less.

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