Coke manufacturing method

Abstract

To provide a means that presents a new indicator for a biomass-derived raw material replacing part of the coal used in the production of coke using a blast furnace and produces coke that has high strength even when a biomass-derived raw material has been blended with the coal. In the mass distribution of surface tension measured for the carbonized biomass blended with the coal blend for producing coke, the proportion of surface tension values equal to or greater than a lower limit value gammamin is 60 mass% or more of the whole, and the volatile content of the carbonized biomass on an anhydrous basis is 4.0 mass% or more.

Description

[Technical Field]

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

[0002] Coke is a carbon-based lump product obtained by carbonizing 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, the lump coke must have sufficient mechanical strength to ensure stable blast furnace operation.

[0003] To manufacture coke for blast furnaces, a coal blend consisting of several types of coal mixed 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 lumps of coal bonded together. By using a type of coal called caking coal, which has the property of easily softening and melting, as part of the coal blend, high-strength coke can be obtained.

[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"), specified in Japanese Industrial Standard 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, specified in Japanese Industrial Standard 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] Patent Document 1, previously filed by the applicant, describes a new index used in selecting a combination of coal types to compose a coal blend: the measured surface tension of the powder obtained by heating coal to 500°C before blending, cooling it, and pulverizing it. According to this index, when coal powders with a small difference in weighted average values ​​of surface tension are combined, the strength of the resulting coke is higher than when coal powders with a large difference in weighted average values ​​of surface tension are combined.

[0006] 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. For this reason, studies are underway to replace a portion of the coal used to make coke with carbon-neutral materials such as biomass. For example, Patent Document 2 describes a method for producing coke in which a woody biomass material that has been heat-treated at temperatures above 300°C to 400°C is mixed with coal and carbonized in a coke oven. Furthermore, Patent Document 3 describes a method for producing highly reactive coke for blast furnaces in which biomass is heated to at least 1000°C or higher to cause pyrolysis, and the resulting biomass char with a solid content of 1 mm or less in diameter is added to a coal blend. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2013 / 145680 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-272569 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-77086 [Non-patent literature]

[0008] [Non-Patent Document 1] MC Williams and DW Fuerstenau, "A Simple Flotation Method for Rapidly Assessing the Hydrophobicity of Coal Particles", International Journal of Mineral Processing, Vol. 20, No. 1-2, Netherlands, June 1987, p.153-157. Summary of the Invention [Problem to be solved by the invention]

[0009] 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.

[0010] In the prior art, Ro and MF, which are effective as indicators for controlling the strength of coke, 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 biomass-derived raw materials, the properties of coal and biomass are significantly different, so it is impossible to perform the measurements. Even if measurements can be performed, the measured values ​​are not appropriate for use as indicators for controlling the strength of coke containing biomass-derived raw materials.

[0011] Furthermore, the surface tension previously proposed by the applicant as a new index is based on the weighted average of the surface tensions measured individually for coals that soften and melt when heated to 500°C. However, biomass does not soften and melt when heated. Therefore, surface tension alone cannot be used as an index for managing the strength of coke containing biomass-derived raw materials. Therefore, a new index for managing the strength of coke containing biomass-derived raw materials is needed.

[0012] 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. [Means for solving the problem]

[0013] In order to clarify the cause of the decrease in strength of coke that uses biomass as a part of the raw material, the inventors of this patent application conducted detailed observations of defects present inside lumpy coke with decreased strength. As a result of the observations, it became clear that the interior of coke containing biomass-derived raw materials contains the following two main types of defects.

[0014] Type 1 defects are defects in which the softened and melted parts of coal do not fuse to the surface of the biomass-derived raw material, but the two are separated. The reason for Type 1 defects is thought to be that while coal is prone to softening and melting during the temperature rise process of carbonization, biomass-derived raw materials are not carbonized and do not soften and melt.

[0015] Type 2 defects are cracks caused by the destruction of raw materials derived from biomass. The cause of type 2 defects is thought to be the difference in the amount of shrinkage between the coal-derived and biomass-derived parts during the shrinkage process after the softened coal resolidifies. Both type 1 and type 2 defects can be the starting point for the progression of coke destruction. Therefore, to increase the strength of coke, it is necessary to minimize the occurrence of these defects.

[0016] The gist of the present invention, which was completed by the inventors based on the above observation results regarding defects present inside coke, is as follows.

[0017] [1] When producing coke by carbonizing a mixture obtained by blending blended coal for coke production with carbonized biomass produced by heat treating biomass in a predetermined ratio, In the mass distribution of surface tension measured for the carbonized biomass, the surface tension value is the lower limit value γ min The proportion of the above is 60 mass% or more of the total, The carbonized biomass has a volatile content of 4.0% by mass or more on a dry basis. A method for producing coke, characterized in that [2] The lower limit of surface tension γ min is the mass average value γ in the mass distribution of the surface tension measured for a sample obtained by heating the blended coal to the thermoplastic temperature. ave greater than The method for producing coke described in [1] above. [3] The lower limit value γ of the surface tension min is greater than 35.0±3.0 mN / m, which is the mass average value in the mass distribution of the surface tension measured for a sample obtained by heating the blended coal to 450°C. The method for producing coke described in [1] above. [4] The lower limit value γ of the surface tension min is equal to 38.2 mN / m, The method for producing coke described in [1] above. [5] The proportion of the carbonized biomass in the mixture is 1.0% by mass or more and 8.0% by mass or less, A method for producing coke according to any one of [1] to [4] above. [6] The biomass that is the raw material for the carbonized biomass includes at least one of palm kernel shells and woody biomass, A method for producing coke according to any one of [1] to [5] above. [7] The measurement of the mass distribution of surface tension for the carbonized biomass is carried out by a film flotation method; A method for producing coke according to any one of [1] to [6] above. [8] The proportion of particle sizes of 3.0 mm or less in the carbonized biomass is 70% by mass or more, and the proportion of particle sizes of 3.0 mm or less in the blended coal is 70% by mass or more, A method for producing coke according to any one of [1] to [7] above. [Effects of the Invention]

[0018] 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. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a graph showing the relationship between heat treatment temperature and surface tension of carbonized biomass in an example. [Figure 2] 1 is a graph showing the relationship between heat treatment temperature and volatile content of carbonized biomass in Examples. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail.

[0021] In one embodiment, a method for producing coke according to the present invention includes the steps of: producing coke by carbonizing a mixture obtained by blending a coal blend for coke production with carbonized biomass produced by heat treating biomass in a predetermined ratio; and min The carbonized biomass is characterized in that the proportion of carbonized biomass that is equal to or greater than 60% by mass of the total, and the volatile content of the carbonized biomass on a dry basis is 4.0% by mass or greater.

[0022] [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 as 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.

[0023] 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 broadleaf 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.

[0024] 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.

[0025] The temperature for heat treating biomass may be adjusted appropriately depending on the type of biomass so that the surface tension and volatile content fall within suitable ranges. For example, when palm kernel shells are used as biomass, a temperature of 400°C or higher falls within a suitable range for the surface tension described below, and a temperature of 700°C or lower falls within a suitable range for the volatile content described below, so a temperature of 400°C or higher and 700°C or lower is preferred. Similarly, when cedar is used as biomass, a temperature of 500°C or higher and 800°C or lower is preferred. A higher temperature for heat treating biomass is more preferred from the perspective of surface tension, and a lower temperature is more preferred from the perspective of volatile content. In this specification, the term "heat treatment temperature" refers to the maximum temperature reached by biomass during heat treatment.

[0026] The time for heat treatment 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 preferred heat treatment time is 10 minutes or more. A more preferred 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 until the heat treatment temperature is stopped being maintained.

[0027] The heat-treated biomass is converted into carbonized biomass during the heat treatment process. The particle size of the carbonized biomass is preferably 70% by mass or more and 100% by mass or less of particles of 3.0 mm or less, similar to that of blended coal used in ordinary coke production. If the proportion of particles 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 more preferable particle size range of the carbonized biomass is 100% by mass of particles 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).

[0028] When the proportion of particle sizes of 3.0 mm or less in the carbonized biomass is less than 70% by mass, the proportion of particle sizes of 3.0 mm or less can be adjusted to 70% by mass or more and 100% by mass or less by pulverizing the carbonized biomass. The particle size adjustment by pulverization may be performed on the biomass before heat treatment, on the carbonized biomass after heat treatment, or on both. A known pulverizer can be used to pulverize the biomass or carbonized biomass.

[0029] 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 with a particle size larger than X mm are those that remain on a sieve with a nominal mesh size of X mm when sieved through a sieve. Powders and granular materials with a particle size of Y mm or less are those that fall through a sieve with a nominal mesh size of Y mm when sieved through a sieve.

[0030] When producing large amounts of carbonized biomass on an industrial scale, the yield can be increased and production costs can be reduced by omitting the steps of sieving or adjusting particle size by pulverization, or both. In this case, the proportion of particles with a particle size of 3.0 mm or less in the particle size distribution of the carbonized biomass based on mass is preferably 70 mass% or more. When particle size adjustment is not performed, the proportion of particles with a particle size of 3.0 mm or less is more preferably 80 mass% or more, and even more preferably 90 mass% or more. The upper limit of the proportion of particles with a particle size of 3.0 mm or less in the carbonized biomass 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 powder or particles sieved using multiple sieves with different mesh sizes for a sample taken from the large amount of carbonized biomass produced, or irradiating the sample with a laser.

[0031] [Composition] In the coke production method according to this embodiment, a 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 by measuring the Ro and MF values ​​of the coal blend.

[0032] The proportion of the coal blend for coke production 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 the coal blend having a particle size of 3.0 mm or less is 70% by mass or more. More preferably, the proportion of the coal blend 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 the coal blend 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.

[0033] In a mixture obtained by blending carbonized biomass in a predetermined ratio with a coal blend for coke production, a carbonized biomass ratio of 1.0% by mass or more in the mixture is effective in reducing carbon dioxide emissions, and a carbonized biomass ratio of 8.0% by mass or less prevents a significant decrease in the strength of the resulting coke, so the carbonized biomass ratio is preferably 1.0% by mass or more and 8.0% by mass or less, and more preferably 2.0% by mass or more and 5.0% by mass or less.

[0034] 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.

[0035] 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.

[0036] [Dry distillation] 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.

[0037] A carbonization temperature of 900°C or higher will produce coke of sufficient strength. 950°C or higher is 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 the coke may undergo thermal decomposition, 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.

[0038] [surface tension] In the coke manufacturing method according to this embodiment, in the mass distribution of surface tension measured for carbonized biomass, the surface tension value is set to a lower limit value γ min The proportion of carbonized biomass that is equal to or greater than this is 60 mass % or greater of the total.

[0039] Carbonized biomass is not a substance with a single component and structure, but varies in the degree of carbon concentration, molecular weight of constituent molecules, content of volatile matter, etc. depending on the region. For this reason, the surface tension of carbonized biomass cannot be determined to a single value, but has a distribution. Therefore, in this embodiment, the mass distribution of surface tension is first determined for the carbonized biomass obtained by heat treatment. In this specification, "mass distribution of surface tension" refers to a graph in which the horizontal axis represents the surface tension measured for an aggregate of carbonized biomass powder, and the vertical axis represents the mass or cumulative mass of powder for each division. A specific method for measuring the mass distribution of surface tension will be described later. Next, in the determined mass distribution of surface tension of the carbonized biomass, the surface tension value is calculated by subtracting the predetermined lower limit value γ min Only carbonized biomass in which the proportion of carbonized biomass with a surface tension value of 60% or more by mass is selected, and only the selected carbonized biomass is used. Alternatively, the surface tension value is 60% or more by mass. min The conditions for the heat treatment of the biomass may be adjusted so that the above proportion is 60 mass % or more of the total. By using carbonized biomass that satisfies these conditions, it is possible to produce coke with high strength.

[0040] In this embodiment, the usability of carbonized biomass is not determined based on a single representative value such as a weighted average value derived from the distribution of the surface tension of the carbonized biomass, but rather based on the mass distribution of the surface tension, the surface tension is determined based on the lower limit value γ min Only carbonized biomass in which the proportion of the surface tension or more is 60 mass % or more of the total is used. This makes it possible to accurately determine whether or not carbonized biomass with a wide range of surface tension values ​​can be used. In a preferred embodiment, the surface tension value is less than the lower limit γ min The proportion of the above is preferably 70 mass % or more of the total, and more preferably 80 mass % or more. min The upper limit of the above proportions is 100 mass % of the total.

[0041] The lower limit value γ of the surface tension in this embodiment min is set in advance to the lower limit value γ minThe strength of the coke obtained by carbonization of each type of carbonized biomass is examined by preparing multiple types of carbonized biomass with different carbonization ratios, blending each type of carbonized biomass with blended coal, and then carbonizing the blended coal.

[0042] Although the details of why high-strength coke can be produced by using carbonized biomass with adjusted surface tension according to the present embodiment are unclear, it is believed that the following reasons are likely to be involved. As mentioned above, Patent Document 1 describes that when coals with similar weighted average values ​​of surface tension are combined, the strength of the resulting coke is higher than when coals with a large difference in weighted average values ​​of surface tension are combined. This means that, with regard to adhesion between coals, the smaller the difference in surface tension, i.e., the magnitude of interfacial tension, the stronger the bond between the coal blend. In contrast, carbonized biomass is a raw material that does not undergo thermoplasticity like coal. Therefore, when considering the adhesion phenomenon at the interface between coal and carbonized biomass, a different approach is required than the conventional approach to adhesion between coals.

[0043] Generally, when the surface tension of a solid is greater than that of a liquid at the interface between a solid and a liquid, the liquid can wet the surface of the solid. If this is the case, when the surface tension of the carbonized biomass, which is solid, is greater than that of the thermoplastic blended coal, which is liquid, the thermoplastic blended coal can wet and spread on the surface of the carbonized biomass in the carbonization step, which is considered to result in an increase in the strength of the obtained coke. The lower limit value γ of the surface tension in this embodiment is min is determined experimentally or based on the surface tension of the blended coal, and 60 mass % or more of the carbonized biomass is below the lower limit γ min By ensuring that the surface tension is equal to or greater than this, wetting occurs at many locations in the mixture, which is believed to prevent the occurrence of type 1 defects in which the blended coal and the carbonized biomass are separated, thereby enabling the production of coke with high strength.

[0044] To determine the mass distribution of surface tension for carbonized biomass, it is preferable to use the film flotation method described in Non-Patent Document 1. The film flotation method makes it possible to determine the surface tension distribution based on the mass of powder for an aggregate of powders that has a distribution in the magnitude of surface tension, using a relatively simple procedure. The measurement of the mass distribution of surface tension using the film flotation method is outlined below.

[0045] The film flotation method utilizes the property that when powder particles floating on the surface of a liquid with a known surface tension begin to settle, the surface tension of the powder is equal to the surface tension of the liquid. First, several liquids with different surface tensions are prepared. The surface tensions of the liquids are selected to cover the range of surface tension values ​​of the powder to be measured. For example, if an aqueous solution of ethanol is used as the liquid, the surface tension of ethanol at 20°C is 22.6 mN / m, and that of pure water is 72.8 mN / m. Therefore, by adjusting the ethanol concentration, it is possible to prepare liquids with any surface tension between 22.6 mN / m and 72.8 mN / m.

[0046] The number of divisions in the mass distribution of surface tension to be determined is determined by the number of types of liquid prepared. In the present application, the number of types of liquid is not particularly limited, but a number of liquids equal to or greater than 5 increases the measurement accuracy, while a number of liquids equal to or less than 20 allows the measurement to be completed in a short time, so a number of liquids equal to or greater than 5 and equal to or less than 20 is preferable. A more preferable lower limit of the range of the number of divisions is 8 or more. A more preferable upper limit of the number of divisions is 15 or less. It is also preferable to make the difference in surface tension between the liquids as equal as possible.

[0047] Next, the particle size of the carbonized biomass sample to be used for the measurement is adjusted. If the particle size of the sample is 53 μm or more, the sample is less likely to aggregate, and if it is 150 μm or less, the effect of gravity can be ignored. Therefore, it is preferable that the particle size of the sample is 53 μm or more and 150 μm or less.

[0048] Next, the mass of the carbonized biomass sample with adjusted particle size is measured and then sprayed onto the surface of the prepared liquid. After a period of time, the sample that does not settle but remains floating on the surface is collected, its mass measured after drying, and its ratio to the mass of the sample before spraying is calculated. This calculated value indicates the proportion of samples with a surface tension lower than that of the liquid. By repeating this series of procedures for all liquids, the mass distribution of surface tension can be determined. Note that the surface tension of a liquid is usually measured at 20°C, so it is preferable to control the temperature of the liquid at 20°C when spraying the carbonized biomass sample.

[0049] As described above, the mass distribution of surface tension can be expressed by a graph with the surface tension on the horizontal axis and the mass or cumulative mass of powder for each category on the vertical axis. min The percentage of samples that are above the lower limit can be calculated as the total area above the lower limit in a frequency distribution graph, or as the difference between the reading at the lower limit and 100% in a cumulative frequency graph. min When is midway between the surface tension segments, the graph reading at the midpoint can be estimated by interpolating the values ​​on either side.

[0050] The mass distribution of surface tension measured by the above method shifts in the direction of increasing the surface tension value as the heat treatment temperature of the biomass in the carbonization process increases. This is thought to be because the higher the treatment temperature of the biomass, the more the carbonization of the biomass progresses, and the surface properties of the carbonized biomass change in the direction of increasing the surface tension. Therefore, in the mass distribution of surface tension measured for the carbonized biomass, when the surface tension value is below the lower limit value γ min If the proportion of samples with a surface tension of 1000 or more is less than 60% by mass, the heat treatment temperature of the biomass in the carbonization process should be increased to a higher temperature, and the surface tension value should be increased to the lower limit γ min The proportion of samples having this or higher content may be adjusted to 60 mass % or more of the total.

[0051] In a preferred embodiment, the lower limit value γ of the surface tension minThe mass average value γ in the mass distribution of surface tension measured for a sample obtained by heating a blended coal to its thermoplastic temperature ave As mentioned above, the wettability between a coal blend and carbonized biomass becomes an issue when the mixture is heated to the thermoplastic temperature of the coal blend during the carbonization process. Coal blends are generally thought to thermoplastically melt in the temperature range of 350°C or higher and 550°C or lower. Therefore, theoretically, if the surface tension of the carbonized biomass is greater than that of the coal blend in this temperature range, the wettability between the two is considered to be good. However, as mentioned above, the film flotation method uses a liquid at 20°C, and there is no known means for measuring the mass distribution of surface tension in situ in the temperature range of 350°C or higher.

[0052] Therefore, in a preferred embodiment, instead of measuring the surface tension of a coal blend in situ at the thermoplastic temperature, the mass distribution of the surface tension of a sample obtained by heating the coal blend to the thermoplastic temperature is measured using a liquid at 20°C, and the mass average value (weighted average) γ ave Then, the lower limit value of the surface tension for carbonized biomass, γ min is the mass average value γ ave This sets the lower limit of the surface tension γ min Rather than being experimentally determined by trial and error, it can be determined in fewer steps based on reasonably obtained measurements.

[0053] The reason why the surface tension measured at 20°C serves as an indicator of wettability in the temperature range of 350°C or higher and 550°C or lower, where the surface of a coal blend softens and melts, is as follows. In a sample obtained by heating a coal blend to its softening temperature, the chemical composition of the material changes to such an extent that the measured surface tension changes due to the softening of the coal. These changes remain in the coal blend as a thermal history, and the changed state is maintained even after it is cooled to 20°C. Therefore, the measured surface tension at 20°C is thought to reflect the changes in state when heated to the softening temperature. Similarly, for heat-treated carbonized biomass, the thermal history experienced at the heat treatment temperature is thought to be reflected in the measured surface tension at 20°C.

[0054] In a preferred embodiment, the lower limit value γ of the surface tension min However, this is greater than the mass average value of 35.0±3.0 mN / m in the mass distribution of surface tension measured for a sample obtained by heating a coal blend to 450°C. When the fluidity of coal used in coke production is measured using a Gieseler plastometer, many coals exhibit a maximum value (MF) around 450°C. In other words, from the viewpoint of fluidity, coal thermoplasticity is considered to be most advanced at 450°C. Therefore, in this preferred embodiment, the temperature at which the coal blend thermoplasticity occurs is represented by 450°C.

[0055] In order to measure the surface tension of a coal blend, several types of coal with different origins and grades were carbonized up to 450°C in an inert gas atmosphere to obtain semi-coke. The mass distribution of the surface tension of the obtained semi-coke was measured by a film flotation method, and the mass average value was found to be in the range of 35.0±3.0 mN / m. Therefore, in this preferred embodiment, the lower limit value γ of the surface tension is min is set to a value greater than 35.0±3.0 mN / m. The surface tension of semi-coke varies within the range of ±3.0 mN / m, so the lower limit of the surface tension γ minIt is more preferable to set the lower limit of the surface tension γ to a value greater than 38.0 mN / m. min is preferably set to a value of 40.0 mN / m or less.

[0056] In a preferred embodiment, the lower limit value γ of the surface tension min is equal to 38.2 mN / m. The surface tension of a water (80%)-ethanol (20%) mixed solution at 20°C is 38.2 mN / m. This value happens to be larger than 38 mN / m. In addition, a water (80%)-ethanol (20%) mixed solution can be easily prepared. Therefore, the lower limit value γ of the surface tension in this preferred embodiment is min The value is set to 38.2 mN / m.

[0057] In this preferred embodiment, instead of determining the mass distribution of surface tension in the film flotation method, the measurement of surface tension can be simplified by using only one liquid: a water (80%)-ethanol (20%) mixed solution. Specifically, a carbonized biomass sample whose particle size has been adjusted using the above method is sprayed onto the surface of a water (80%)-ethanol (20%) mixed solution at 20°C. After a period of time, the sample that has not settled but is floating on the surface is collected and its mass after drying is measured. The mass of the settled sample is calculated by subtracting the mass of the floating sample from the mass of the sample before spraying. Since the surface tension of the settled sample is 38.2 mN / m or more, if its proportion is 60 mass% or more, the surface tension condition of the present invention is met.

[0058] [Volatile content] In the coke production method according to this embodiment, the volatile content of the carbonized biomass is 4.0% by mass or more on a dry basis. The analysis of the volatile content of the carbonized biomass in this embodiment is performed in accordance with the method specified in Japanese Industrial Standards M 8812:2004, "Coals and cokes - proximate analysis method." By using the volatile content on a dry basis, the volatile content can be appropriately controlled even if moisture subsequently adheres to the carbonized biomass.

[0059] In this embodiment, the volatile content of carbonized biomass is analyzed, and only carbonized biomass with a volatile content of 4.0% by mass or more is selected, and only the selected carbonized biomass is used. Alternatively, the conditions for the heat treatment of biomass may be adjusted so that the volatile content is 4.0% by mass or more. By using carbonized biomass with a volatile content of 4.0% by mass or more, high-strength coke can be produced. In a preferred embodiment, the volatile content of the carbonized biomass on a dry basis is 5.0% by mass or more.

[0060] Although the details of why high-strength coke can be produced by using carbonized biomass with a volatile content of 4.0% by mass or more according to this embodiment are unclear, it is believed that the reason is likely as follows: In the process of producing coke by carbonizing coal, the coal softens and melts at temperatures above 300°C, adhering to each other, and then solidifies again at temperatures above 500°C, becoming a solid as a whole. When the coal is then heated to 1000°C, contraction occurs as the volatiles contained in the coal are released. In this process, it is believed that the more volatiles contained in the coal, the greater the amount of contraction of the coal due to the release of volatiles. Similarly, it is believed that the more volatiles contained in the carbonized biomass, the greater the amount of contraction of the carbonized biomass due to the release of volatiles.

[0061] As described above, defects (type 2 defects) consisting of cracks caused by destruction of the biomass-derived raw material portions exist inside coke containing biomass-derived raw materials. The cause of these defects is thought to be the difference in the amount of shrinkage between the coal-derived portion and the biomass-derived portion during the shrinkage process after the thermoplastic coal resolidifies. It is presumed that when the volatile content of the carbonized biomass is less than 4.0% by mass, the carbonized biomass-derived portion barely shrinks, while the surrounding blended coal-derived portion shrinks, resulting in stress being applied to the carbonized biomass-derived portion and cracking. In this embodiment, since the volatile content of the carbonized biomass is 4.0% by mass or more, the carbonized biomass-derived portion and the surrounding blended coal-derived portion shrink to the same extent, which is thought to prevent the occurrence of type 2 defects.

[0062] The amount of volatile matter contained in carbonized biomass decreases as the heat treatment temperature of biomass in the carbonization process increases. This is thought to be because the higher the treatment temperature of biomass, the more volatile matter is released from the biomass. Therefore, if the volatile matter measured for carbonized biomass is less than 4.0% by mass, the heat treatment temperature of the biomass can be changed to a lower temperature to adjust the volatile matter to 4.0% by mass or more. In addition to changing the heat treatment temperature, the volatile matter can also be adjusted by changing the heat treatment time or the type of biomass used. Of these methods, changing the heat treatment temperature is preferred because it is easy to control.

[0063] In the coke manufacturing method according to this embodiment, the lower limit of the volatile content of the carbonized biomass on a dry basis is set to 4.0 mass% or more, but there is no particular upper limit. However, when the volatile content is adjusted by changing the heat treatment temperature of the biomass in the carbonization step, as described above, the lower the heat treatment temperature of the biomass in the carbonization step, the lower the surface tension value. Therefore, when the surface tension value is lower than the lower limit γ minThe heat treatment temperature cannot be lowered until the cumulative mass of the carbonized biomass, which is equal to or greater than 60% by mass, becomes less than 60% by mass. Taking this into consideration, it is preferable that the volatile content does not exceed 35% by mass.

[0064] As described above, in this embodiment, high-strength coke can be produced by using carbonized biomass whose surface tension and volatile content fall within a predetermined range. The heat treatment conditions that bring the surface tension and volatile content within the predetermined ranges vary significantly depending on the type of biomass used. Therefore, it is preferable to determine the heat treatment conditions individually for each type of biomass used. Among the heat treatment conditions, the temperature varies depending on the type of biomass and other heat treatment conditions, but in many cases, the surface tension and volatile content can be adjusted to fall within the ranges of this embodiment by performing heat treatment at a temperature of approximately 400°C or higher and 800°C or lower.

[0065] [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 drum method, which evaluates rotational strength as 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. It is currently the most widely used method 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 percentage (%) of the sample as the drum strength index (symbol: DI).

[0066] As will be described later, in the examples of this specification, the drum rotation speed was set to 150 rpm, and the drum strength index (%) was defined as the ratio of the mass of coke that did not pass through a 15 mm sieve after rotation to the mass of coke inserted into the drum testing machine. The drum strength index indicates the mass ratio of coke that was not crushed to sizes of 15 mm or less even after rotation in the drum testing machine. A larger DI value indicates higher coke strength. [Example]

[0067] 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.

[0068] 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 with a particle size of 3.0 mm or less at 100% by mass. Two types of biomass, palm kernel shells and cedar, were prepared. These biomasses were individually heat-treated in an air-tight atmosphere at biomass temperatures of 400°C, 500°C, 700°C, 800°C, or 900°C to obtain carbonized biomass. These carbonized biomasses were pulverized to produce carbonized biomass samples with a particle size of 3.0 mm or less at 100% by mass. The mass proportion of the carbonized biomass samples with a surface tension of 38.2 mN / m or more was measured using a water (80%)-ethanol (20%) mixture at 20°C, and the volatile content on an anhydrous basis was also measured. The measured values ​​are shown in Table 1. Figure 1 shows the change in the mass ratio of samples with a surface tension of 38.2 mN / m or more versus the heat treatment temperature, and Figure 2 shows the change in the volatile content on an anhydrous basis.

[0069] [Table 1]

[0070] According to the above measurement results, the higher the heat treatment temperature of the carbonized biomass, the greater the mass proportion of samples with a surface tension of 38.2 mN / m or higher and the lower the volatile content. The heat treatment temperatures at which the proportion of samples with a surface tension of 38.2 mN / m or higher was 60 mass% or more and the volatile content was 4.0 mass% or higher were in the range of 400°C or higher and 700°C or lower for palm kernel shells, and 500°C or higher and 800°C or lower for cedar.

[0071] Next, the blended coal and carbonized biomass were blended so that the blending ratio of carbonized biomass in the mixture was 2.0%, 4.0%, or 5.0%, and the moisture content was adjusted to 8.0 mass%. 16 kg of each mixture was prepared for each type of carbonized biomass. 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. 3 The container filled with the mixture was charged into an electric furnace set at a furnace wall temperature of 1,050°C. After carbonization, the furnace wall temperature was maintained for 6 hours from the time of charging, and the container was then transferred to a cooling system where room-temperature nitrogen gas was circulating and cooled, yielding a coke containing biomass as a raw material. To compare drum rotation strength, the same blended coal alone was carbonized under the same conditions to obtain a coke without biomass as a raw material. The drum strength index (DI) of the resulting coke was then measured at a drum rotation speed of 150 rpm and a sieve opening of 15 mm. The measured DI of the base coke without carbonized biomass was 79.1. The difference (ΔDI) between the measured value and that of the coke without biomass as a raw material was calculated. The calculated ΔDI values ​​are shown in Table 2.

[0072] [Table 2]

[0073] According to Tables 1 and 2, the ΔDI values ​​of the cokes of Examples 1 to 9, which were made from mixtures containing carbonized biomass that satisfied the surface tension and volatile content ranges of the present invention, did not decrease by more than -2.0%. If the ΔDI does not decrease by more than -2.0%, the strength of the coke can be adjusted by adjusting the quality of the coal blend and the production conditions, and therefore the level is considered to be acceptable for practical use. On the other hand, the cokes of Comparative Examples 1 to 6, which had surface tensions or volatile content outside the ranges of the present invention, showed a significant decrease in drum rotation strength. 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. [Industrial Applicability]

[0074] 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. In producing coke by carbonizing a mixture obtained by blending a predetermined ratio of carbonized biomass produced by heat-treating biomass with blended coal for coke production, In the mass distribution of surface tension measured for the carbonized biomass, the surface tension value is the lower limit value γ ｍｉｎ the proportion of the above is 60 mass % or more of the total, the lower limit value γ min of the surface tension is greater than the mass average value γ ave in the mass distribution of the surface tension measured for a sample obtained by heating the coal blend up to its thermoplastic temperature, The carbonized biomass has a volatile content of 4.0% by mass or more on a dry basis. A method for producing coke, characterized in that

2. When producing coke by carbonizing a mixture obtained by blending a predetermined ratio of carbonized biomass produced by heat-treating biomass with blended coal for coke production, In the mass distribution of the surface tension measured for the carbonized biomass, the proportion of the surface tension value equal to or greater than the lower limit value γ min is 60 mass % or more of the total, and the lower limit value γ ｍｉｎ is greater than 35.0±3.0 mN / m, which is the mass average value in the mass distribution of the surface tension measured for a sample obtained by heating the coal blend to 450°C, The carbonized biomass has a volatile content of 4.0% by mass or more on a dry basis. A method for producing coke, characterized in that

3. When producing coke by carbonizing a mixture obtained by blending a predetermined ratio of carbonized biomass produced by heat-treating biomass with blended coal for coke production, In the mass distribution of the surface tension measured for the carbonized biomass, the proportion of the surface tension value equal to or greater than the lower limit value γ min is 60 mass % or more of the total, and the lower limit value γ ｍｉｎ is equal to 38.2 mN / m, The carbonized biomass has a volatile content of 4.0% by mass or more on a dry basis. A method for producing coke, characterized in that

4. The ratio of the carbonized biomass in the mixture is 1.0% by mass or more and 8.0% by mass or less, A method for producing coke according to any one of claims 1 to 3.

5. The biomass that is the raw material for the carbonized biomass includes at least one of palm kernel shells and woody biomass, A method for producing coke according to any one of claims 1 to 3.

6. The measurement of the mass distribution of surface tension for the carbonized biomass is carried out by a film flotation method. A method for producing coke according to any one of claims 1 to 3.

7. The proportion of particle sizes of 3.0 mm or less in the carbonized biomass is 70% by mass or more, and the proportion of particle sizes of 3.0 mm or less in the blended coal is 70% by mass or more. A method for producing coke according to any one of claims 1 to 3.

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