Coke production method

Abstract

Provided is a means for: presenting a novel indicator for a biomass-derived raw material for replacing a portion of coal that is used for producing coke used in a blast furnace; and producing coke having high strength even when a biomass-derived raw material is mixed with coal. Biomass in which the microstrength index (MSI0.21) of test coke obtained by dry-distilling the biomass alone is at least 45 is mixed with mixed coal 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. For this reason, studies are underway to replace a portion of the coal used as a coke raw material with carbon-neutral raw materials such as biomass. For example, Patent Document 1 describes a method for producing coke in which a woody biomass raw material that has been heat-treated at temperatures above 300°C to 400°C is mixed with coal and carbonized in a coke oven. Patent Document 2 also describes a method for producing highly reactive coke for blast furnaces in which biomass is heated to at least 1000°C or higher to pyrolyze it, and the resulting biomass char with a solid content of 1 mm or less in diameter is added to a coal blend.

[0006] JP 2005-272569 A 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] In order to clarify the cause of the decrease in strength of coke that uses biomass as part of its raw materials, the inventors of this patent application conducted detailed observations of defects present inside lumpy coke with decreased strength. As a result of the observations, they found that in coke containing biomass-derived raw materials, the biomass-derived parts have low strength and are prone to fracture when stress is applied from the surroundings. In other words, they presumed that the biomass-derived parts are the origin of fracture, causing the overall strength of the coke to decrease.

[0011] Furthermore, the inventors investigated the micro strength index, which is one of the indicators of microscopic strength, for various types of biomass-derived raw materials and discovered that the micro strength index varies greatly depending on the type of biomass used as the raw material. They then found that by using the biomass micro strength index as a new indicator and selectively using biomass that is suitable for blending with blended coal, it is possible to suppress a decrease in coke strength, thereby completing the present invention.

[0012] The gist and configuration of the present invention completed by the inventors in order to achieve the above object is as follows.

[0013] [1] A method for producing coke, comprising blending biomass with a coal blend for coke production in a predetermined ratio to form a mixture, and carbonizing the mixture to produce coke, wherein the micro strength index of a test coke obtained by carbonizing the biomass alone is 45 or more. [2] A method for producing coke as described in [1] above, wherein the micro strength index is 60 or more. [3] A method for producing coke as described in [1] or [2] above, wherein the temperature for carbonizing the test coke is 1000°C. [4] A method for producing coke as described in any of [1] to [3] above, wherein the volatile content of the biomass on a dry basis is 6.0 mass% or more. [5] A method for producing coke as described in any of [1] to [4] above, wherein the biomass includes at least one of palm kernel shells and woody biomass. [6] A method for producing coke as described in any of [1] to [5] above, wherein the biomass is carbonized biomass obtained by heat-treating unheated biomass. [7] The method for producing coke according to any one of [1] to [6] above, wherein a ratio of the biomass in the mixture is 1.0 mass% or more and 10 mass% or less. [8] The method for producing coke according to any one of [1] to [7] above, wherein a ratio of biomass having a particle size of 3.0 mm or less in the biomass is 70 mass% or more, and a ratio of coal blend having a particle size of 3.0 mm or less in the coal blend is 70 mass% or more.

[0014] 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.

[0015] FIG. 1 is a schematic diagram illustrating an example of a testing device for applying a mechanical shock.

[0016] Hereinafter, embodiments of the present invention will be described in detail.

[0017] In one embodiment, a method for producing coke according to the present invention is characterized in that, when biomass is blended with blended coal for coke production in a predetermined ratio to form a mixture, and the mixture is carbonized to produce coke, the micro strength index of a test coke obtained by carbonizing the biomass alone is 45 or more.

[0018] [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.

[0019] 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.

[0020] The particle size of the biomass is preferably such that the proportion of particles of 3.0 mm or less is 70% by mass or more and 100% by mass or less. If the proportion of particles of 3.0 mm or less is 70% by mass or more and 100% by mass or less, the biomass can be homogeneously mixed with the blended coal. A more preferable particle size range is one in which the proportion of particles of 3.0 mm or less is 100% by mass. There is no lower limit for the particle size. In other words, the particle size may be any size as long as it is greater than 0 (zero).

[0021] When the proportion of biomass particle sizes of 3.0 mm or less is less than 70% by mass, the proportion of biomass particle sizes of 3.0 mm can be adjusted to 70% by mass or more and 100% by mass or less by pulverizing the biomass. The particle size adjustment by pulverization may be performed on the biomass, on the carbonized biomass described below, or on both. A known pulverizer can be used to pulverize the biomass or carbonized biomass.

[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 biomass on an industrial scale, 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 biomass having a particle size of 3.0 mm or less in the particle size distribution of biomass based on mass is preferably 70 mass% or more. When particle size adjustment is not performed, the proportion of biomass having 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 biomass having a particle size of 3.0 mm or less is 100 mass%. The particle size distribution of biomass based on mass can be determined by known methods, such as measuring the weight of powder or granules sieved from a sample collected from a large amount of produced biomass using multiple sieves with different mesh sizes, or irradiating the sample with a laser.

[0024] It is not essential to heat-treat and carbonize the biomass before grinding, but in a preferred embodiment, the grindability of the biomass can be improved by heat-treating unheated biomass to obtain carbonized biomass.

[0025] In heat treatment for carbonizing 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 where air inflow is hindered and an inert gas flows, and the biomass is loaded into the container and heat treated.

[0026] The temperature at which biomass is heat-treated may be adjusted appropriately depending on the type of biomass so that crushability and volatile content fall within suitable ranges. For example, when palm kernel shells are used as biomass, palm kernel shells can be used as is without heat treatment, and heat treatment at 400°C or higher is more preferable because carbonization progresses and crushability improves. On the other hand, a heat treatment temperature of 700°C or lower is preferable because the volatile content described below falls within a suitable range, and 600°C or lower is even more preferable. A higher temperature at which biomass is heat-treated is more preferable from the viewpoint of carbonization progress, and a lower temperature is more preferable from the viewpoint of volatile content. In this specification, "heat treatment temperature" refers to the maximum temperature reached by biomass during heat treatment.

[0027] 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 to when the heat treatment temperature is stopped being maintained.

[0028] [Blending] In the coke production method according to this embodiment, coke is produced by carbonizing a mixture obtained by blending biomass with a coal blend for coke production in a predetermined ratio. The biomass blended in the coal blend may be unheated biomass or carbonized biomass obtained by heat treatment. The coal blend may be any coal blend 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. A coal blend blended with caking coal is an example of a coal blend suitable for coke production.

[0029] The proportion of particles of 3.0 mm or less in the particle size of a coal blend for coke production 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 with a particle size of 3.0 mm or less is 70% by mass or more. More preferably, the proportion of the coal blend with 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 of 3.0 mm or less is preferably 90% by mass or less, and more preferably 85% by mass or less.

[0030] In a mixture obtained by blending biomass in a predetermined ratio with a coal blend for coke production, a biomass ratio of 1.0% by mass or more in the mixture is significant in reducing carbon dioxide emissions, while a biomass ratio of 10% by mass or less prevents a significant decrease in the strength of the resulting coke, so the biomass ratio is preferably 1.0% by mass or more and 10% by mass or less, and more preferably 2.0% by mass or more and 7.0% by mass or less.

[0031] In the coke manufacturing method according to the present invention, the mixture obtained by blending a coal blend and 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 transported by a belt conveyor falls onto the next belt conveyor, a case where the coal blend and biomass are blended and then pulverized using pulverization equipment, and a case where the coal blend and biomass are blended and then the moisture content is adjusted while stirring using coal moisture control equipment. These cases are preferable because they can reduce the equipment and costs required for mixing.

[0032] In the mixture, it is preferable that the blended coal and biomass are uniformly mixed. This can prevent the problem of biomass that 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 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.

[0033] In the coke production method according to the present embodiment, a mixture obtained by blending a coal blend for coke production with biomass at a predetermined ratio is carbonized to produce coke. The mixture is charged into a coke oven and carbonized by heating in an air-tight atmosphere.

[0034] 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. In this specification, the term "carbonization temperature" refers to the maximum temperature reached by the mixture during carbonization.

[0035] [Micro Strength Index] In the coke manufacturing method according to this embodiment, a test coke obtained by carbonizing biomass alone is pulverized, and the resulting powder particles are classified into powder particles that pass through a sieve with a mesh size of 1.18 mm but do not pass through a sieve with a mesh size of 0.60 mm. The classified powder particles are subjected to an impact, and in the mass particle size distribution, the micro strength index, which is the mass percentage of powder particles that do not pass through a sieve with a mesh size of 0.21 mm, is 45 or more. The micro strength index thus obtained is called the MSI. ０．２１ It may be represented by the symbol

[0036] In this embodiment, a small amount of test coke for evaluating the microstrength index is prepared separately from the mixture for producing coke. The test coke can be obtained by independently carbonizing the biomass to be evaluated. The biomass used to prepare the test coke has the same raw material type and heat treatment conditions as the biomass used for coke production. Preferably, the test coke is obtained by independently carbonizing a small sample taken from the biomass used for coke production. The test coke is a sample corresponding to the biomass-derived portion of the coke produced by carbonizing the mixture. When producing the test coke, the maximum temperature, among other carbonization conditions, has a significant impact on the strength of the coke. Therefore, the maximum temperature when carbonizing biomass to produce the test coke is preferably approximately the same as the carbonization temperature during coke production, and is preferably 900°C or higher and 1250°C or lower.

[0037] In a preferred embodiment, the test coke is carbonized at 1000°C. Carbonization at 1000°C allows sufficient carbonization of the test coke, making it suitable as a sample for evaluating the microstrength index. Typical carbonization conditions other than temperature include filling a crucible with biomass, placing the crucible in a heating furnace, and heating the sample in a nitrogen atmosphere at a controlled temperature increase of 3°C per minute until the sample temperature reaches 1000°C. The sample is then maintained at 1000°C for 60 minutes to allow carbonization to proceed. The sample is then allowed to cool naturally in the furnace in the nitrogen atmosphere.

[0038] As used herein, the Micro Strength Index (MSI) ０．２１) is a value measured by the following measurement procedure. After carbonization, the test coke is pulverized and classified into powder particles that pass through a sieve with a mesh size of 1.18 mm but do not pass through a sieve with a mesh size of 0.60 mm. 2.0 g of the test coke sample obtained by classification and 12 steel balls with a diameter of 10.5 mm are placed in a cylindrical container with a diameter of 26 mm and a length of 305 mm and sealed. The cylindrical container is rotated 800 times at 25 rpm to apply an impact to the test coke sample. After the test, the sample is removed from the cylindrical container, and the weight of the powder particles that do not pass through the sieve with a mesh size of 0.21 mm is determined. The mass percentage obtained by dividing this weight by the weight of the test coke sample used in the test is defined as the micro strength index (MSI) in this embodiment. ０．２１ )

[0039] FIG. 1 is a schematic diagram showing an example of a test apparatus for applying an impact to a test coke. This test apparatus 1 includes a cylindrical steel container 2, a motor 3, and a gear 4 for rotating the container 2. The cylindrical container 2 has a rotation axis located at the center of the cylinder's length. The rotation axis is arranged perpendicular to the center line of the container 2, and the direction of the rotation axis is fixed horizontally. By rotating the motor 3, the container 2 rotates around the rotation axis like an airplane propeller. A steel ball falls as the container rotates, applying an impact to the test coke inside the container.

[0040] The test coke can be crushed by a crusher or other known means. The purpose of adjusting the particle size through crushing and classification is to eliminate the influence of macro defects, such as cracks and large pores of a few millimeters, present in the test coke before crushing on the micro strength index measurement. During the crushing process, cracks and large pores act as fracture initiation points, and crushing progresses. Therefore, measuring the micro strength index using the crushed granular material can eliminate the influence of macro defects. Therefore, the micro strength index measured using the crushed test coke is a good indicator of the strength of the matrix portion of the test coke that is not affected by macro defects, i.e., the matrix strength. Therefore, a higher micro strength index indicates a higher matrix strength of the test coke.

[0041] In this embodiment, a sieve is used to classify powder or granular material. The "mesh opening" of a sieve refers to the size of the gaps in the wire mesh. If the particle size (maximum particle size) of the powder or granular material is smaller than the sieve opening, the powder or granular material passes through the sieve and falls, and if the particle size of the powder or granular material is larger than the sieve opening, the powder or granular material does not pass through the sieve and remains on top. By using two or more sieves with different mesh openings, the particle size of the powder or granular material can be adjusted to a predetermined range.

[0042] The opening size of a sieve is sometimes expressed in units called "mesh." A mesh is the number of lines or gaps per inch of wire mesh length. The larger the mesh number, the finer the sieve mesh. Even for sieves with the same mesh number, if the wires making up the wire mesh are thick, the opening size will be smaller than if the wires are thin. For example, a commercially available sieve with an opening size close to 1.20 mm has a mesh size of 14 meshes, but even for the same 14-mesh sieve, the opening size will vary slightly depending on the wire thickness. In this embodiment, a range is set for the opening size, so a commercially available sieve with an opening size within this range can be selected and used.

[0043] In this embodiment, the micro strength index is 45 or more. The reason for setting the lower limit of the micro strength index at 45 is that the value of the micro strength index measured under the same conditions for coke obtained by carbonizing a coal blend that does not contain biomass is approximately 45. If coke is produced using a mixture that is mixed with biomass having a micro strength index equal to or greater than the micro strength index of the coal blend, the progression of fracture originating from the biomass-derived portion can be prevented. This improves the strength of the entire coke. The micro strength index is preferably 60 or more.

[0044] Although the reason why high-strength coke can be produced by using biomass that satisfies the micro strength index specified in this embodiment is not clear in detail, it is thought that the reason is probably as follows. As described above, in coke containing raw materials derived from biomass, the matrix strength of the biomass-derived portion is low, and therefore, when stress is applied from the surroundings, this portion may be easily broken. However, the matrix strength of the biomass-derived portion is not always lower than that of the portion derived from the coal blend, and the strength of the resulting coke may or may not decrease depending on the type of biomass mixed with the coal blend.

[0045] As described above, the micro strength index defined in this embodiment varies depending on the type and portion of biomass used. In this embodiment, only biomass having a micro strength index of 45 or more, which is the mass percentage of powder or granular material that does not pass through a sieve with a mesh size of 0.21 mm, is selected in the mass particle size distribution of the biomass after impact application, and only the selected biomass is used in the mixing step and the carbonization step. Alternatively, the type and portion of biomass used, as well as the production conditions, may be adjusted so that the micro strength index is 45 or more. By using biomass that satisfies these conditions, high-strength coke can be produced.

[0046] [Volatile content] In a preferred embodiment, the volatile content of the biomass on an anhydrous basis is 6.0% by mass or more. Analysis of the volatile content of the 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 an anhydrous basis, the volatile content can be appropriately controlled even if moisture subsequently adheres to the biomass.

[0047] In this preferred embodiment, the volatile content of biomass is analyzed, and only biomass with a volatile content of 6.0% by mass or more is selected, and only the selected biomass is used in the mixing step and the carbonization step. Alternatively, the conditions of the heat treatment in the carbonization step may be adjusted so that the volatile content is 6.0% by mass or more. By using biomass with a volatile content of 6.0% by mass or more, high-strength coke can be produced. In a more preferred embodiment, the volatile content of the biomass on an anhydrous basis is 7.0% by mass or more, and in an even more preferred embodiment, 10% by mass or more.

[0048] Although the details of why high-strength coke can be produced by using biomass with a volatile content of 6.0% by mass or more are unknown, 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 biomass, the greater the amount of contraction of the biomass due to the release of volatiles.

[0049] When the volatile content of the biomass is less than 6.0% by mass, the biomass-derived portion hardly shrinks, while the surrounding coal-blend-derived portion shrinks, which is thought to result in stress being applied to the biomass-derived portion and causing it to break. In a preferred embodiment, the volatile content of the biomass is 6.0% by mass or more, so that the biomass-derived portion and the surrounding coal-blend-derived portion shrink to the same extent. This is thought to suppress breakage of the biomass-derived portion and increase the strength of the coke.

[0050] The higher the heat treatment temperature of biomass, the less volatile matter contained in the biomass. This is thought to be because the higher the heat treatment temperature of biomass, the more volatile matter is released from the biomass. Therefore, if the volatile matter measured for biomass is less than 6.0% by mass, the heat treatment temperature of the biomass can be changed to a lower temperature, or the biomass can be heat-treated at all, so that the volatile matter content of the biomass is 6.0% 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, changing the type of biomass used, etc. Of these means, changing the heat treatment temperature is preferred because it is easy to control.

[0051] In a preferred embodiment, the lower limit of the volatile content of biomass on a dry basis is 6.0% by mass or more, but there is no particular upper limit. However, since the volatile content of biomass that has not undergone any heat treatment is approximately 75% by mass, taking this into consideration, it is preferable that the volatile content does not exceed 80% by mass.

[0052] As described above, in a preferred embodiment, by using biomass having a volatile content within a predetermined range, it is possible to produce coke with higher strength. The conditions for heat treatment to achieve a volatile content of 6.0 mass% or more vary depending on the type of biomass used, but in most cases, the volatile content can be adjusted to 6.0 mass% or more by performing heat treatment at a temperature of approximately 700°C or less.

[0053] [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).

[0054] 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.

[0055] 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.

[0056] 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 particle sizes of 3.0 mm or less was adjusted to 100% by mass. Two types of biomass, palm kernel shells and cedar, were prepared. A portion of this biomass was heat-treated in an air-tight atmosphere by maintaining the temperature for 30 minutes after the biomass temperature reached the target temperature of 400°C, 500°C, 600°C, or 700°C, to obtain carbonized biomass. The unheated biomass and carbonized biomass were pulverized to produce biomass in which the proportion of particle sizes of 3.0 mm or less was adjusted to 100% by mass.

[0057] The obtained biomass was loaded into a crucible and heated in a nitrogen atmosphere at a controlled temperature increase rate of 3°C per minute until it reached 1000°C, after which it was maintained at 1000°C for 60 minutes for carbonization. The mixture was then allowed to cool naturally in the furnace while still in the nitrogen atmosphere, yielding a test coke. The obtained test coke was crushed and classified to obtain a sample that passed through a sieve with a 1.18 mm opening and that did not pass through a 0.60 mm opening. The microstrength index (MSI) of the classified test coke having the pre-test particle size was measured. ０．２１ The volatile content of the same biomass was also measured on a dry basis. The results are shown in Table 1.

[0058]

[0059] According to the above measurement results, when the biomass was palm kernel shell, the micro strength index was 60.2 or more and 63.4 or less, regardless of whether heat treatment was performed or the heat treatment temperature. These values ​​were higher than the micro strength index of 45 for blended coal. Furthermore, the volatile content value was 74.6% for palm kernel shell that was not heat treated, and decreased as the heat treatment temperature increased. The volatile content was 6.0% when the heat treatment temperature was 700°C. On the other hand, when the biomass was cedar, the micro strength index was low, being 13.8 or more and 14.6 or less, regardless of the heat treatment temperature. The volatile content was 6.7% when the heat treatment temperature was 700°C.

[0060] Next, the blended coal and biomass were blended so that the blending ratio of biomass in the mixture was 2.0%, 5.0%, or 7.0%, and the moisture content was adjusted to 8.0 mass%. 16 kg of each mixture was prepared for each type of 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. ３The 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 nitrogen gas at room temperature was circulated and cooled, thereby obtaining a coke containing biomass as a raw material. In addition, in order to compare the drum strength index, only the coal blend of the reference example was carbonized under the same conditions to obtain a coke containing 100% coal blend that did not contain biomass as a raw material. Next, the drum strength index (DI) of the obtained coke was measured under conditions of a drum rotation speed of 150 rpm and a sieve opening of 15 mm. The obtained measured values ​​are shown in Table 2.

[0061]

[0062] According to Tables 1 and 2, the cokes of Examples 1 to 9, which were blended with biomass having a microstrength index of 45 or more, all exhibited a DI value of 77 or more. This DI value indicates that the coke has strength sufficient for use in a blast furnace. Furthermore, the cokes of Examples 1 to 8, which had a volatile content of 7.0 mass% or more, all exhibited a DI value of 78 or more. These cokes have DI values ​​closer to that of the blended coal of the Reference Example, and are therefore cokes with particularly excellent strength. On the other hand, the cokes of Comparative Examples 1 to 3, which exhibited low microstrength index values, exhibited a significant decrease in drum strength index. These facts demonstrate that the coke manufacturing method of the present invention can produce coke with higher strength based on more reliable predictions than the prior art.

[0063] 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.

[0064] 1 Test device 2 Container 3 Motor 4 Gear

Claims

1. A method for producing coke, comprising blending biomass in a predetermined ratio with blended coal for coke production to form a mixture, and carbonizing the mixture to produce coke, wherein the micro strength index of a test coke obtained by carbonizing the biomass alone is 45 or more.

2. The method for producing coke according to claim 1, wherein the micro strength index is 60 or more.

3. The method for producing coke according to claim 1 or 2, wherein the temperature for carbonizing the test coke is 1000°C.

4. The method for producing coke according to any one of claims 1 to 3, wherein the volatile content of the biomass on an anhydrous basis is 6.0 mass% or more.

5. The method for producing coke according to any one of claims 1 to 4, wherein the biomass includes at least one of palm kernel shells and woody biomass.

6. The method for producing coke according to any one of claims 1 to 5, wherein the biomass is carbonized biomass obtained by heat-treating unheated biomass.

7. A method for producing coke according to any one of claims 1 to 6, wherein the ratio of the biomass in the mixture is 1.0 mass% or more and 10 mass% or less.

8. A method for producing coke as described in any one of claims 1 to 7, wherein the proportion of biomass having a particle size of 3.0 mm or less in the biomass is 70 mass% or more, and the proportion of coal blend having a particle size of 3.0 mm or less in the coal blend is 70 mass% or more.

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