Method for producing carbon agglomerates

Abstract

Provided is a method for producing a carbonaceous lump, the method being capable of producing a carbonaceous lump having high strength which withstands an application to a blast furnace even when an amount of use of a raw carbon material having poor thermoplasticity is increased. The method for producing a carbonaceous lump according to the present invention comprises: a powder preparation step for preparing carbon material powders which are obtained by applying heat treatment to a raw carbon material having the Gieseler maximum fluidity MF of 5 ddpm, has a volatile content of 6 wt% D.B. or more and less than 20 wt% D.B., and has the maximum particle diameter of 300 μm or less; and a hot pressing step for applying pressure molding to the carbon material powders under a condition having the maximum arrival temperature of 600°C-1250°C in an oxygen-blocked environment to obtain a carbonaceous lump.

Description

[Technical Field]

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

[0002] The conventional method for producing coke involves crushing caking coal (caking coal) to produce powder with a particle size of 3 mm or less at 70 to 100 wt %. This powder is then carbonized to soften and melt the caking coal particles at a temperature range of approximately 400 to 500°C, causing them to bond together, resulting in coke as a carbon agglomerate.

[0003] Patent Document 1 discloses a method for producing a high-density carbon material. In this method, a carbon material raw material made of a self-sintering carbonaceous powder is heated to 400 to 600°C under atmospheric pressure, and then the heated carbon material raw material is subjected to a pressure of 50 to 400 kg / cm while being maintained in the temperature range. 2 The self-sintering carbonaceous powders are bulk mesophase, mesocarbon microbeads, and raw cokes derived from petroleum or coal.

[0004] Thus, conventional carbon agglomerates have been produced by using caking coal (caking coal) as the main raw coal material, adding a binder such as pitch as needed, and agglomerating the particles of the carbonaceous powder together by using liquid phase components such as the caking coal and the binder. In conventional production processes, carbon agglomerates could not be obtained without using caking coal or pitch, and even if carbon agglomerates were obtained, they lacked sufficient strength. In particular, the coke used in the blast furnace process is required to have high strength among carbon agglomerates. Therefore, conventionally, caking coal (caking coal) has been used as a raw material to produce coke for use in blast furnaces.

[0005] Non-Patent Document 1 discloses the results of a study on coke strength (strength of blast furnace coke) using an indirect tensile strength test method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 61-122110 [Non-patent literature]

[0007] [Non-Patent Document 1] Miyakawa A. et al., Study on Coke Strength by Indirect Tensile Strength Test Method (I), Journal of the Fuel Association, Vol. 54, No. 584, 1975, pp. 983-993 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, the availability of caking coal suitable for coke production has been depleted, and there is a demand for expanded use of carbonaceous materials that do not exhibit thermoplasticity, such as coal with poor thermoplasticity and high-carbon-containing materials derived from coal or biomass, which have not been used in coke production until now. However, in order to increase the amount of raw carbonaceous materials with poor thermoplasticity, it is difficult to produce carbon agglomerates solely through the agglomeration technology that uses the liquid phase component to bond or fuse particles together. For this reason, a method for producing carbon agglomerates using a mechanism different from the conventional one has been desired.

[0009] In view of the above problems, the present invention aims to provide a method for producing carbon agglomerates, which is capable of producing high-strength carbon agglomerates that can withstand use in a blast furnace, even when the amount of raw carbonaceous material having poor thermoplasticity used is increased. [Means for solving the problem]

[0010] In order to solve the above problems, the present inventors have conducted extensive research and have discovered the following.

[0011] First, the inventors discovered a carbonaceous powder agglomeration technique based on a novel mechanism that does not rely on a liquid-phase sintering-like phenomenon in which volatile liquid components are used to bond or fuse carbonaceous powder particles together. Specifically, the inventors discovered that by pressurizing a predetermined carbonaceous powder while heating it at a temperature range of 600°C or higher, the carbonaceous powder particles bond together through a solid-phase sintering-like phenomenon, unlike conventional agglomeration based on a liquid-phase sintering-like phenomenon, thereby producing carbon agglomerates. Specifically, the predetermined carbonaceous powder is a fine carbonaceous powder with an appropriately controlled amount of volatile matter and a maximum particle size of 300 μm or less. Conventional agglomeration based on a liquid-phase sintering-like phenomenon occurs when caking coal powder is heated to 400–500°C to soften and melt it. In contrast, in the present invention, the predetermined carbonaceous powder is pressurized at temperatures above 500°C, thereby causing the carbonaceous powder particles to bond together through a solid-phase sintering-like phenomenon. In addition, in conventional agglomeration using a liquid-phase sintering-like phenomenon, excessive particle size reduction of caking coal was considered unsuitable because it would lead to a decrease in melting property. In contrast, small particle size carbonaceous powder was suitable for agglomeration using a solid-phase sintering-like phenomenon.

[0012] However, even when carbonaceous powders having similar volatile contents and particle sizes are subjected to pressure molding, there are cases where high strength sufficient for use in a blast furnace is obtained, and cases where high strength is not obtained. Therefore, the present inventors have further investigated carbonaceous powders that can be used to obtain high-strength carbon agglomerates by agglomeration using a solid-phase sintering phenomenon. As a result, they have found that when carbonaceous powder obtained by heat treating and pulverizing raw carbonaceous material with poor thermoplasticity is subjected to pressure molding, high-strength carbon agglomerates sufficient for use in a blast furnace can be obtained.

[0013] The gist and configuration of the present invention, which has been completed based on the above findings, is as follows. [1] A powder preparation step of preparing a carbonaceous material powder obtained by heat treating a raw carbonaceous material having a maximum fluidity MF of 5 ddpm or less in a Gieseler Plastometer, a volatile content of 6 wt% DB or more and less than 20 wt% DB and a maximum particle size of 300 μm or less; a hot pressing step of pressurizing the carbonaceous powder under a maximum temperature of 600°C to 1250°C in an oxygen-free environment to obtain a carbon agglomerate; The method for producing carbon agglomerates comprising the steps of:

[0014] [2] preparing raw coal material having a maximum fluidity MF of 5 ddpm or less in a Gieseler Plastometer; a step of subjecting the raw carbonaceous material to a heat treatment and an optional pulverization treatment to obtain a carbonaceous material powder having a volatile content of 6 wt% DB or more and less than 20 wt% DB and a maximum particle size of 300 μm or less; a hot pressing step of pressurizing the carbonaceous powder under a maximum temperature of 600°C to 1250°C in an oxygen-free environment to obtain a carbon agglomerate; The method for producing carbon agglomerates comprising the steps of:

[0015] [3] The method for producing carbon agglomerates according to the above [1] or [2], wherein the molding pressure in the pressure molding is 11 MPa or more. [Effects of the Invention]

[0016] According to the method for producing carbon agglomerates of the present invention, it is possible to produce carbon agglomerates with high strength that can withstand use in a blast furnace, even when the amount of raw carbonaceous material with poor thermoplasticity used is increased. [Brief explanation of the drawings]

[0017] [Figure 1] 4 is a graph showing the relationship between the volatile content of carbonaceous powder and the indirect tensile strength of carbon agglomerates in Examples. DETAILED DESCRIPTION OF THE INVENTION

[0018] A method for producing carbon agglomerates according to one embodiment of the present invention includes a powder preparation step of heat-treating a raw carbonaceous material having a maximum fluidity MF of 5 ddpm or less in a Gieseler Plastometer to prepare carbonaceous material powder having a volatile content of 6 wt% DB or more and less than 20 wt% DB and a maximum particle size of 300 μm or less; and a hot-press step of press-molding the carbonaceous material powder at a maximum temperature of 600°C or more and 1250°C or less in an oxygen-free environment to obtain carbon agglomerates.

[0019] A method for producing carbon agglomerates according to another embodiment of the present invention includes the steps of: preparing a raw carbonaceous material having a maximum fluidity MF of 5 ddpm or less in a Gieseler Plastometer; heat treating the raw carbonaceous material and optionally pulverizing the raw carbonaceous material to obtain a carbonaceous material powder having a volatile content of 6 wt% DB or more and less than 20 wt% DB and a maximum particle size of 300 μm or less; and hot pressing the carbonaceous material powder under pressure at a maximum temperature of 600°C or more and 1250°C or less in an oxygen-free environment to obtain carbon agglomerates.

[0020] In the manufacturing method of the present embodiment, the particles of the carbonaceous powder are bonded to each other by a solid-phase sintering-like phenomenon, rather than by a liquid-phase sintering-like phenomenon in which liquid-phase components that can become volatile are used to bond or fuse the particles of the carbonaceous powder to each other, thereby forming carbon agglomerates.

[0021] [Powder preparation process] The powder preparation step includes, for example, a step of heat-treating raw carbonaceous material to obtain heat-treated carbonaceous material, and a step of pulverizing the heat-treated carbonaceous material to obtain the carbonaceous material powder.

[0022] In this embodiment, it is important that the maximum fluidity MF of the raw carbonaceous material to be subjected to the heat treatment and optional pulverization treatment is 5 ddpm or less. This can be said in other words that the raw carbonaceous material is unlikely to soften or melt during the heat treatment. In the conventional method for producing carbon agglomerates by a liquid-phase sintering-like phenomenon, it has not been possible to obtain high-strength carbon agglomerates from raw carbonaceous materials that are unlikely to soften or melt. However, in the method for producing carbon agglomerates by a solid-phase sintering-like phenomenon of this embodiment, the fact that the raw carbonaceous material is unlikely to soften or melt is an important factor in developing strength.

[0023] The solid-phase sintering-like phenomenon in the carbon agglomerate manufacturing method of this embodiment is believed to be driven by the aromatization or polycyclization reaction of the carbonaceous powder. Therefore, to form bonds between carbonaceous powder particles, the reaction must occur across the particles. Typically, the aromatization or polycyclization reaction of carbonaceous powder proceeds at the edges of crystallites composed of relatively planar aromatic ring precursors or multiple monocyclic or polycyclic aromatic carbons stacked in layers. Therefore, to form bonds between particles, it is necessary to increase the proximity of the crystallite edges between adjacent particles and to increase the degree of alignment of the stacking direction. Meanwhile, carbonaceous powder particles form a packed bed prior to agglomeration, but because the orientation of each particle cannot be arbitrarily controlled, they are randomly arranged. Furthermore, the solid-phase sintering-like phenomenon is believed to occur only at the limited contact surfaces between particles in the packed bed. In other words, it is difficult to intentionally align the orientation of the crystallites present on the surfaces of opposing particles at the contact surface. Therefore, in order to increase the probability that the edges of the crystallites present at the contact surfaces between adjacent particles are close to each other and that the stacking directions are aligned, it is desirable that the crystallites of the raw carbon material be small and have low orientation.

[0024] When carbonaceous powder is produced by heat-treating and pulverizing a thermoplastic raw carbonaceous material, the crystallites can move within the raw carbonaceous material due to the thermoplastic melting, resulting in large crystallites and highly oriented carbonaceous powder. Furthermore, liquid crystals called mesophases can form, sometimes exhibiting large micrometer-scale orientation as observed under a polarizing microscope. When such carbonaceous powder is subjected to pressure molding, the probability of reaction between the edges of the crystallites of adjacent particles decreases, preventing solid-phase sintering from proceeding sufficiently, making it impossible to obtain high-strength carbon agglomerates.

[0025] In contrast, when carbonaceous powder is produced by heat-treating and pulverizing a raw carbonaceous material that is difficult to thermoplasticize, the movement of crystallites in the raw carbonaceous material is restricted, resulting in carbonaceous powder with low orientation after heat treatment. Therefore, by subjecting the carbonaceous powder obtained by heat-treating and pulverizing a raw carbonaceous material that is difficult to thermoplasticize to pressure molding, a solid-phase sintering-like phenomenon progresses sufficiently, and high-strength carbon agglomerates can be obtained. Therefore, the maximum fluidity MF of the raw carbonaceous material is set to 5 ddpm or less. Since the lower the maximum fluidity MF of the raw carbonaceous material, the better, so there is no particular lower limit. In other words, the maximum fluidity MF of the raw carbonaceous material can be 0 ddpm or more, and more preferably 0 ddpm.

[0026] The maximum fluidity MF of the raw coal material in this embodiment means the maximum fluidity measured by a Gieseler Plastometer in accordance with "Coals - Testing Methods" (JIS M8801:2004) specified in JIS.

[0027] The raw coal material having a maximum fluidity of 5 ddpm or less may be, for example, one or more selected from coal and biomass.

[0028] Biomass is a general term for a certain amount of accumulated plant and animal resources and waste materials derived from them (excluding fossil resources). In this embodiment, biomass includes all biomass that produces charcoal when pyrolyzed, such as agricultural, forestry, livestock, fisheries, and waste materials.

[0029] In this embodiment, the biomass used as the raw carbonaceous material preferably includes one with a high effective calorific value, for example, woody biomass.

[0030] Examples of woody biomass include papermaking by-products such as pulp black liquor and chip dust, lumbering by-products such as bark and sawdust, forest residues such as branches, leaves, treetops, and offcuts, thinned wood from cedar, cypress, pine, and other species, and waste logs from specialized forests such as edible fungi, as well as forestry biomass such as firewood forests of castanopsis, oak, and pine, and short-rotation forestry of willow, poplar, eucalyptus, pine, etc. Woody biomass also includes general waste such as pruned branches from municipal street trees and private garden trees, pruned branches from national and prefectural street trees and corporate garden trees, and industrial waste such as construction and building waste.

[0031] Some agricultural biomass such as rice husks, wheat straw, rice straw, sugarcane residue, palm oil, etc., which are classified as agricultural biomass and are generated from waste or by-products, and rice bran, rapeseed, soybeans, etc., which are generated from energy crops, can also be suitably used as woody biomass.

[0032] In this embodiment, it is important that the volatile content of the carbonaceous material powder to be subjected to pressure molding is 6 wt% DB or more and less than 20 wt% DB.

[0033] If the volatile content of the carbonaceous powder is less than 6 wt% DB, it is impossible to obtain carbon agglomerates with sufficient strength to withstand use in a blast furnace. The solid-phase sintering-like phenomenon in the carbon agglomerate manufacturing method according to this embodiment is thought to be driven by the aromatization or polycyclization reaction of the carbonaceous powder. This reaction involves the elimination of hydrogen and other functional groups, resulting in the generation of gas. In other words, the volatile content of the carbonaceous powder corresponds to the amount of hydrogen and other functional groups eliminated during the aromatization or polycyclization reaction, which is the driving force for the solid-phase sintering-like phenomenon, and indicates the potential for the solid-phase sintering-like phenomenon. Therefore, if the volatile content is less than 6 wt% DB, it is impossible to obtain carbon agglomerates with sufficient strength. Therefore, the volatile content of the carbonaceous powder is set to 6 wt% DB or more, preferably 8 wt% DB or more.

[0034] On the other hand, if the volatile content of the carbonaceous powder exceeds 20 wt% DB, gases generated during heating (gases resulting from the volatilization of volatiles or decomposition of volatiles) expand, causing the carbonaceous powder to foam. This inhibits compression of the carbonaceous powder during compaction, making it difficult to apply sufficient pressure to the carbonaceous powder, and inhibits the formation of bonds between the carbonaceous powder particles through a solid-phase sintering-like phenomenon. Furthermore, the gases generated during heating may cause the internal pressure of the space enclosed by walls, such as a mortar or mold, to exceed the pressure applied to the carbonaceous powder during compaction. In such cases, the compaction device or the walls may be damaged. Furthermore, the gases generated during heating may easily stain the walls. Therefore, the volatile content of the carbonaceous powder should be less than 20 wt% DB, preferably 18 wt% DB or less.

[0035] In addition, when the volatile content of the carbonaceous powder is in the range of 6 wt% DB or more and less than 20 wt% DB, the greater the volatile content, the stronger the carbon agglomerates can be obtained.

[0036] In this embodiment, the volatile content of the carbonaceous material powder is a value measured in accordance with "Coals and cokes - proximate analysis methods" (JIS M 8812:2004) specified in the Japanese Industrial Standards (JIS).

[0037] The carbonaceous material powder in this embodiment can be obtained through a step of heat-treating a raw carbonaceous material to obtain a heat-treated carbonaceous material having a volatile content of 6 wt% DB or more and less than 20 wt% DB, and a step of pulverizing the heat-treated carbonaceous material. However, the order of pulverization and heat treatment is not limited to this, and the raw carbonaceous material may be pulverized and then heat-treated to obtain the carbonaceous material powder. Also, if the raw carbonaceous material is originally a powder, the raw carbonaceous material may be heat-treated without pulverization to obtain a carbonaceous material powder having a volatile content of 6 wt% DB or more and less than 20 wt% DB. Alternatively, the raw carbonaceous material may be roughly pulverized and then heat-treated to obtain a volatile content of 6 wt% DB or more and less than 20 wt% DB, and then further pulverized to obtain the carbonaceous material powder.

[0038] The heat treatment of the raw carbonaceous material is preferably carried out by heating the raw carbonaceous material to a heat treatment temperature of 500°C or higher but lower than 900°C in an oxygen-blocked environment. If the heat treatment temperature is lower than 500°C, the volatile content remaining in the carbonaceous material powder will be 20 wt% DB or higher. Therefore, the heat treatment temperature is preferably 500°C or higher, and more preferably 600°C or higher. On the other hand, if the heat treatment temperature is 900°C or higher, the volatile content remaining in the carbonaceous material powder will be less than 6 wt% DB, making it difficult for a solid-phase sintering-like phenomenon to occur. Therefore, the heat treatment temperature is preferably lower than 900°C, and more preferably lower than 800°C. Note that within the heat treatment temperature range of 500°C or higher but lower than 900°C, the volatile content in the carbonaceous material powder will increase as the heat treatment temperature decreases, thereby strongly exhibiting a solid-phase sintering-like phenomenon in the hot-pressing process and enabling the production of high-strength carbon agglomerates.

[0039] The heat treatment of the raw carbonaceous material is preferably carried out in an atmosphere in which the supply of oxygen is blocked. The heat treatment of the raw carbonaceous material is preferably carried out, for example, in a state in which the raw carbonaceous material is accommodated in a container that forms a space in which the inflow of air is blocked and through which an inert gas flows. The heat treatment of the raw carbonaceous material can be carried out by heating the container that accommodates the raw carbonaceous material and by heat transfer from the container.

[0040] Usually, the reaction rate of the thermal decomposition reaction of the raw carbonaceous material during heat treatment is fast, so the time required for the completion of the thermal decomposition reaction is short. Therefore, the heat treatment time is preferably 1 minute or more, more preferably 10 minutes or more. This eliminates the temperature difference between the raw carbonaceous material and the container, allowing the raw carbonaceous material as a whole to be uniformly heat-treated. Furthermore, it becomes possible to perform the heat treatment by reliably raising the temperature of the entire raw carbonaceous material to the heat treatment temperature (i.e., by heating evenly), thereby suppressing quality variations in the heat-treated carbonaceous material and carbonaceous material powder. There is no particular upper limit for the heat treatment time, but if the heat treatment time is too long, the energy required for the heat treatment increases, which is undesirable as it increases costs. A heat treatment time of 60 minutes or less is usually sufficient.

[0041] The heat treatment time refers to the time during which the temperature of the raw carbonaceous material is maintained at a predetermined heat treatment temperature of 500°C or higher but lower than 900°C, from the time the temperature reaches this heat treatment temperature.

[0042] The heat treatment can be carried out using a heating device such as an electric furnace, a rotary kiln, a fluidized bed heating furnace, a screw type heating furnace, a shaft furnace, or a carbonization furnace.

[0043] In this embodiment, it is important that the maximum particle size of the carbonaceous powder used in the pressure molding is 300 μm or less. If the carbonaceous powder contains many coarse particles with a particle size exceeding 300 μm, these coarse particles may remain in the carbon agglomerates, reducing their strength. In the subsequent hot pressing process, a solid-phase sintering-like phenomenon that causes bonding between carbonaceous powder particles is promoted as the particle size of the carbonaceous powder becomes smaller. Therefore, the remaining coarse particles hinder the bonding between particles, reducing their strength. Furthermore, defects are likely to form around the coarse particles in the carbon agglomerates, which can cause stress concentration and become the starting point for fracture when an external force is applied, thereby reducing their strength.

[0044] The maximum particle size of the carbonaceous powder is preferably 100 μm or less. When the particle size of the carbonaceous powder is appropriately small, the physical structure in the carbon agglomerates becomes dense and uniform, which contributes to increasing the strength of the carbon agglomerates.

[0045] It is preferable that the particle size of the carbonaceous powder is smaller because the strength of the carbon agglomerates is improved. Therefore, there is no particular lower limit on the maximum particle size of the carbonaceous powder. However, taking productivity into consideration, setting the maximum particle size of the carbonaceous powder to less than 20 μm increases the cost of fine pulverization, but the improvement in the performance of the carbon agglomerates is limited. Therefore, if the maximum particle size of the carbonaceous powder is set to 20 μm or more, carbon agglomerates with sufficient strength can be produced.

[0046] In this embodiment, the particle size and particle size distribution (volume basis) of the carbonaceous powder can be measured using a commercially available particle size distribution measuring device. For example, a laser diffraction / scattering particle size distribution measuring device "Laser Micronsizer LMS-3000" manufactured by Malvern Panalytical can be used. In the particle size distribution of the carbonaceous powder, the particle size (circle-equivalent particle size) that accounts for 95% of the particles in the carbonaceous powder when calculated from the smallest particle size is defined as the maximum particle size.

[0047] The pulverization method and pulverization device for pulverizing the raw carbonaceous material or the heat-treated carbonaceous material are not particularly limited. As the pulverization device, a media mill such as a cutter mill, a hammer mill, a pin mill, a jet mill, or a ball mill may be used. The pulverization device is not limited to a device that performs only pulverization, and for example, a pulverizer with a built-in classifier may be used.

[0048] [Hot press process] In the hot pressing process, the carbonaceous powder obtained in the powder preparation process is pressurized and molded in an oxygen-free environment at a maximum temperature of 600°C to 1250°C to obtain a carbon agglomerate.

[0049] In the hot pressing process, the carbonaceous powder is mechanically pressed to form a compact, i.e., pressurized. Mechanical pressing refers to compressing the carbonaceous powder with a physical wall member such as a pestle and mortar, a mold, or a compression roll.

[0050] In the hot pressing process, the carbonaceous powder is pressurized (i.e., hot pressed) while being heated. Pressurizing the carbonaceous powder while being heated includes a case where pressurization is performed only in a part of the entire process of heating the carbonaceous powder, and a case where pressurization is performed throughout the entire process. Heating the carbonaceous powder, in other words, refers to a state where the temperature of the carbonaceous powder is increased.

[0051] The hot press device for pressurizing and molding the carbonaceous material powder while heating it is not particularly limited. The pressurization of the carbonaceous material powder may be performed by placing the carbonaceous material powder in a space surrounded by the above-mentioned walls (for example, in a mold for hot pressing) and compressing it through the walls. The heat source for heating the carbonaceous material powder may be, for example, electric resistance heating, microwave heating, or high-frequency induction heating.

[0052] When carbonaceous powder is heated, the carbonaceous powder expands thermally. As a result, the bulk density of the packed bed of carbonaceous powder decreases. In contrast, by heating the carbonaceous powder while applying pressure, the packed bed of carbonaceous powder is compressed against the thermal expansion, increasing the contact points between the particles of the carbonaceous powder and promoting a solid-phase sintering phenomenon.

[0053] In the hot pressing process, the carbonaceous powder is heated in an oxygen-blocked atmosphere, and the particles of the carbonaceous powder are bonded together by a solid-phase sintering phenomenon. An oxygen-blocked atmosphere is, for example, an atmosphere in a space where the inflow of air (oxygen) is blocked and an inert gas is circulated. In an oxygen-blocked environment, the carbonaceous powder will burn and disappear.

[0054] The carbonaceous powder may be heated through the wall in the hot pressing process. In the hot pressing process, the temperature of the carbonaceous powder at the start of pressing the carbonaceous powder is referred to as the "molding start temperature," and the maximum temperature of the carbonaceous powder during the pressing period is referred to as the "maximum reached temperature."

[0055] The maximum temperature reached in the hot pressing process must be between 600°C and 1250°C, because in this temperature range, bonding between particles occurs significantly due to a phenomenon similar to solid-phase sintering.

[0056] If the maximum temperature reached in the hot pressing step is less than 600°C, the bonding between particles due to a solid-phase sintering-like phenomenon will not proceed sufficiently. From the viewpoint of ensuring sufficient bonding between particles due to a solid-phase sintering-like phenomenon, the maximum temperature reached is set to 600°C or higher, preferably 700°C or higher, and more preferably 900°C or higher.

[0057] If the maximum temperature in the hot pressing process exceeds 1250°C, the hetero elements may be removed, preventing sufficient bonding between particles and inhibiting the formation of bonds between particles due to a solid-phase sintering phenomenon. Therefore, the maximum temperature is set to 1250°C or less, and preferably 1100°C or less.

[0058] A carbonization treatment may be further carried out after the hot pressing step. That is, after pressure molding, the carbon agglomerates may be unloaded and subsequently heated without pressure. In this case, from the viewpoint of increasing the strength of the carbon agglomerates, it is preferable that the carbonization temperature (the maximum temperature of the carbon agglomerates during the carbonization treatment) is higher than the maximum temperature reached in the hot pressing step. However, for the same reason as the maximum temperature reached in the hot pressing step, the carbonization temperature is set to 1250°C or lower, preferably 1100°C or lower. In this embodiment, since the heating in the hot pressing step can also serve as the carbonization treatment, the carbonization treatment after the hot pressing is optional.

[0059] When the temperature of the carbonaceous powder is increased while the carbonaceous powder is being molded under pressure, it is desirable that the molding start temperature in the hot pressing step is as low as possible, typically room temperature (for example, 10°C or higher and 35°C or lower). This allows the temperature range of the carbonaceous powder in the hot pressing step to be widened, and the reaction time to be extended. In other words, it is advisable to start pressing when or immediately after heating of the carbonaceous powder is started.

[0060] The rate of temperature rise from the molding start temperature to the maximum temperature is preferably 1°C / min or more and 30°C / min or less. By setting the rate of temperature rise to 1°C / min or more and 30°C / min or less, a decrease in strength can be avoided.

[0061] The holding time at the maximum temperature is preferably 1 minute or more from the viewpoint of suppressing variations in strength due to temperature unevenness in the carbon agglomerates, and is preferably 60 minutes or less because holding at the maximum temperature for a long period of time does not result in any further improvement in performance, while there is a problem of reduced productivity.

[0062] In the hot pressing process, the pressure mechanically applied to the carbonaceous powder is called the molding pressure. The higher the molding pressure, the more contact points between the carbonaceous powder particles there are, facilitating a solid-phase sintering phenomenon. Therefore, the higher the molding pressure, the stronger the carbon agglomerates become. When the molding pressure is 11 MPa or higher, the strength of the carbon agglomerates becomes stable. When the molding pressure is less than 11 MPa, it may not be possible to obtain high-strength carbon agglomerates. Therefore, the molding pressure is preferably 11 MPa or higher, and more preferably 20 MPa or higher. However, if the molding pressure is too high, the production cost may increase. A molding pressure of 300 MPa or lower is sufficient.

[0063] [Carbon agglomerates] According to the method for producing carbon agglomerates of this embodiment, it is possible to produce high-strength carbon agglomerates that can withstand use in a blast furnace without using any liquid phase components. In this embodiment, a carbon agglomerate having a strength of 4 MPa or more is evaluated as having a strength that is strong enough to be used in a conventional blast furnace process (i.e., high-strength coke). In this embodiment, the strength of the carbon agglomerates means the cold indirect tensile strength measured by the method described in Non-Patent Document 1.

[0064] In this embodiment, the term "carbon agglomerate" refers to an agglomerate mainly composed of carbon produced by the production method according to this embodiment, and has a carbon content of 70 wt% DB or more and 100 wt% DB or less. [Example]

[0065] Heat-treated carbonaceous materials were obtained by heat-treating raw carbonaceous materials of the type and maximum fluidity MF shown in Table 1. The heat treatment was carried out in an electric furnace through which nitrogen gas was circulated, under conditions in which the raw carbonaceous materials were heated to the heat treatment temperature shown in Table 1 and then held for 30 minutes.

[0066] The heat-treated carbonaceous material was then pulverized to obtain carbonaceous powders with the maximum particle sizes listed in Table 1. An ultracentrifugal pulverizer (Verder Scientific, Model: ZM200) was used for the pulverization process. Table 1 also shows the volatile content of the carbonaceous powders.

[0067] 1.32 g of carbonaceous powder was filled into a mold (a metal mold with a diameter of 12 mm) and pressure-molded under the pressure molding conditions shown in Table 1. In cases where the molding start temperature was room temperature, the carbonaceous powder was compressed at room temperature under the molding pressure shown in Table 1, and then heated at a heating rate of 20°C / min under a nitrogen gas flow with the molding pressure shown in Table 1 until the maximum temperature shown in Table 1 was reached. In cases where the molding start temperature was other than room temperature, the carbonaceous powder was heated at a heating rate of 20°C / min under a nitrogen gas flow without applying molding pressure until the molding start temperature shown in Table 1 was reached, and then heated at a heating rate of 20°C / min under a nitrogen gas flow with the molding pressure shown in Table 1 until the maximum temperature shown in Table 1 was reached. The carbonaceous powder was then held at the maximum temperature shown in Table 1 for 5 minutes. The resulting carbon agglomerates were then cooled and collected.

[0068] In addition, in the examples where the maximum temperature reached under the pressure molding conditions shown in Table 1 was less than 900°C, a separate carbonization treatment was carried out after pressure molding. That is, after the molding pressure was released at the maximum temperature reached, the carbonaceous powder was heated at a heating rate of 20°C / min up to the carbonization temperature shown in Table 1 and maintained at that carbonization temperature for 5 minutes. Thereafter, the obtained carbon agglomerates were cooled and collected.

[0069] The indirect tensile strength of the obtained carbon agglomerates was measured. The indirect tensile strength was measured according to the method described in Non-Patent Document 1. Table 1 shows the indirect tensile strength of the carbon agglomerates for each example. FIG. 1 is a graph showing the relationship between the volatile content of the carbonaceous powder and the indirect tensile strength of the carbon agglomerates in Examples (Invention Examples 1 to 9 and Comparative Examples 10 to 18). In Inventive Examples 1 to 9, 19, and 21 to 25, carbon agglomerates with a strength of 4 MPa or more, which can withstand use in a blast furnace, were obtained. In contrast, in Comparative Examples 10 and 11, in which the volatile content of the carbonaceous powder was less than 6%, and in Comparative Examples 12 to 18, in which the maximum fluidity MF of the raw carbonaceous material exceeded 5 ddpm, the strength of the carbon agglomerates was below 4 MPa. Furthermore, in Comparative Example 20, in which the maximum temperature reached during pressure molding of Inventive Example 1 was changed to 500°C, no agglomeration was performed.

[0070] [Table 1] [Industrial Applicability]

[0071] According to the method for producing carbon agglomerates of the present invention, it is possible to produce carbon agglomerates with high strength that can withstand use in a blast furnace, even when the amount of raw carbonaceous material with poor thermoplasticity used is increased.

Claims

1. a powder preparation step of preparing a carbonaceous material powder obtained by heat treating a raw carbonaceous material having a maximum fluidity MF of 5 ddpm or less in a Gieseler Plastometer, the carbonaceous material powder having a volatile content of 6 wt% D.B. or more and less than 20 wt% D.B. and a maximum particle size of 20 μm or more and 300 μm or less; a hot pressing step of pressurizing the carbonaceous powder under a maximum temperature of 600°C to 1250°C in an oxygen-free environment to obtain a carbon agglomerate; The method for producing carbon agglomerates comprising the steps of:

2. preparing a raw coal material having a maximum fluidity (MF) of 5 ddpm or less as measured by a Gieseler Plastometer; a step of subjecting the raw carbonaceous material to a heat treatment and an optional pulverization treatment to obtain a carbonaceous material powder having a volatile content of 6 wt% D.B. or more and less than 20 wt% D.B. and a maximum particle size of 20 μm or more and 300 μm or less; a hot pressing step of pressurizing the carbonaceous powder under a maximum temperature of 600°C to 1250°C in an oxygen-free environment to obtain a carbon agglomerate; The method for producing carbon agglomerates comprising the steps of:

3. 3. The method for producing carbon agglomerates according to claim 1, wherein the pressure molding is performed at a molding pressure of 11 MPa or more.

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