Method for manufacturing carbon-based agglomerates

Abstract

Provided is a method for producing high-density, high-strength carbon-based agglomerates from coal with poor caking properties or coal-derived material containing a high concentration of carbon. The method for producing carbon-based agglomerates includes a crushing step of crushing coal having a volatile content of 1% by mass or more and less than 20% by mass on an anhydrous basis to obtain coal powder having a maximum particle size of 300 μm or less, and a hot pressing step of pressurizing and molding the coal powder at a temperature in the range of 600°C to 1250°C in an oxygen-free environment to obtain an agglomerate.

Description

[Technical field]

[0001] The present invention relates to a method for producing agglomerates mainly made of carbon. [Background technology]

[0002] Patent Document 1 discloses a method for producing a high-density carbon material. In this method, a carbonaceous powder having self-sintering properties is heated to 400 to 600°C under atmospheric pressure, and then the heated carbon material is subjected to a pressure of 50 to 400 kg / cm while being maintained in the above temperature range. 2 The self-sintering carbonaceous powders are bulk mesophase, mesocarbon microbeads, and raw coke from petroleum or coal.

[0003] Patent Document 2 discloses a method for estimating the thermal history of coal or coke. The method is characterized in that the maximum temperature reached in the thermal history of coal or coke is estimated in the range of 300°C or more and less than 600°C based on the baseline intensity value of a spectrum obtained by Raman spectroscopy measurement.

[0004] Non-Patent Document 1 discloses the results of a study on coke strength (strength of molded coke for blast furnaces) using an indirect tensile strength test method.

[0005] Non-Patent Document 2 describes a method for producing coke. In this method, various coals including non-caking coals (carbon content is 67.0-84.6 wt%-daf, natural logarithm of fluidity is 0-1.1) are pulverized to a particle size of 106 μm or less or to about 10 μm or less by ball milling, the pulverized material is then molded at a temperature of 240°C and a mechanical pressure of 128 MPa, and the molded material is further carbonized. In this method, coke can be produced with a bulk density of 1.10-1.49 g / cm. 3 It is said that this method can produce coke having a cold tensile strength of 1.6 to 35.1 MPa. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 1-32162 [Patent Document 2] Patent No. 5929075 [Non-patent literature]

[0007] [Non-Patent Document 1] Study on Coke Strength by Indirect Tensile Strength Test Method (I), Journal of the Fuel Association, Vol. 54, No. 584, 1975, P983-993, A. Miyakawa et al., [Retrieved October 14, 2022], Internet<https: / / www.jstage.jst.go.jp / article / jie1922 / 54 / 12 / 54_12_983 / _pdf> [Non-Patent Document 2] K. Uchida, S. Kudo, A. Mori, UPMashik, K. Norinaga, Y. Dohi, K. Uebo and Ji. Hayashi: ISIJ International, 59(2019), P.1449. Summary of the Invention [Problem to be solved by the invention]

[0008] Most solid carbon materials are used by agglomerating coal or a high-concentration carbon-containing material made from coal. In this case, the agglomerates are required to have a certain strength and bulk density depending on the application. Carbon-based agglomerates are produced by agglomerating particles together by bonding or fusing them together using liquid phase components such as caking coal having caking properties or binders such as pitch. However, in agglomeration using a liquid phase, the liquid phase components decompose and generate gas. This causes foaming in the agglomerates, which may cause the agglomerates to become porous and reduce their bulk density, which is problematic. In addition, caking coal is more expensive than non-caking coal, and binders such as pitch are even more expensive than caking coal.

[0009] In the first place, when caking coal, pitch, etc. are not used, the conventional technology has a problem that an agglomerate cannot be obtained, and even if an agglomerate is obtained, it does not have sufficient strength. In addition, there are cases where it is desired to effectively utilize coal or heat-treated coal (heat-treated coal) that has lost its liquid phase component having caking properties for some reason in the coal processing process.

[0010] Under these circumstances, when producing a solid carbon material, it is desired to provide a production method for producing a high-density, high-strength carbon-based agglomerate from coal having poor caking properties or a coal-derived material containing a high concentration of carbon.

[0011] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for producing high-density, high-strength carbon-based agglomerates from coal having poor caking properties or coal-derived materials containing a high concentration of carbon. [Means for solving the problem]

[0012] In order to achieve the above object, the method for producing the agglomerates according to the present invention is as follows.

[0013] [1] A grinding step of grinding coal having a volatile content of 1% by mass or more and less than 20% by mass on an anhydrous basis to obtain coal powder having a maximum particle size of 300 μm or less; and a hot pressing step of pressurizing and molding the coal powder at a temperature in the range of 600°C to 1250°C inclusive in an oxygen-blocked environment to obtain an agglomerate.

[0014] [2] The method for producing a carbon-based agglomerate according to the above [1], wherein the coal has a volatile content of less than 13 mass% on an anhydrous basis.

[0015] [3] The method for producing a carbon-based agglomerate according to the above [1] or [2], wherein the coal is heat-treated coal.

[0016] [4] A heat-treating step of heat-treating coal to obtain heat-treated coal having a volatile content of 1% by mass or more and less than 20% by mass on an anhydrous basis; A pulverization step of pulverizing the heat-treated coal to obtain coal powder having a maximum particle size of 300 μm or less; and a hot pressing step of pressurizing and molding the coal powder at a temperature in the range of 600°C to 1250°C inclusive in an oxygen-blocked environment to obtain an agglomerate.

[0017] [5] The method for producing a carbon-based agglomerate according to the above [4], wherein the heat-treated coal has a volatile content of less than 13 mass% on an anhydrous basis.

[0018] [6] The heat treatment is performed at a first temperature of 500° C. or more and 1000° C. or less; The method for producing a carbon-based agglomerate according to any one of the above [3] to [5], wherein the pressure molding is carried out at the first temperature or higher.

[0019] [7] The method for producing a carbon-based agglomerate according to any one of [1] to [6] above, wherein the molding pressure in the pressure molding is 20 MPa or more.

[0020] [8] The method for producing a carbon-based agglomerate according to any one of the above [1] to [7], wherein the pressure molding starts heating after pressure is started.

[0021] [9] The method for producing a carbon-based agglomerate according to any one of [1] to [8] above, wherein the coal is a non-caking coal. Effect of the Invention

[0022] According to the present invention, it is possible to provide a method for producing high-density, high-strength agglomerates mainly composed of carbon from coal having poor caking properties or from a coal-derived material containing a high concentration of carbon. [Brief description of the drawings]

[0023] [Figure 1]4 is a graph showing the relationship between the bulk density and the volatile content of the agglomerates in Example 1. [Diagram 2] 4 is a graph showing the relationship between the indirect tensile strength and the volatile content of the agglomerates of Example 1. [Diagram 3] 1 is a graph showing the relationship between the indirect tensile strength of the agglomerates of Example 2 and the heat treatment temperature. [Figure 4] 10 is a graph showing the relationship between the indirect tensile strength and molding pressure of the agglomerates of Example 3. [Diagram 5] 10 is a graph showing the relationship between the indirect tensile strength of the agglomerates of Example 5 and the lower limit temperature of the molding temperature range. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] A method for producing agglomerates mainly made of carbon according to an embodiment of the present invention will be described with reference to the drawings.

[0025] First Embodiment The method for producing a carbon-based agglomerate according to this embodiment includes a grinding step of grinding coal having a volatile content of 1% by mass or more and less than 20% by mass on a dry base (DB) to obtain coal powder with a maximum particle size of 300 μm or less, and a hot pressing step of pressurizing and molding the coal powder at a temperature in the range of 600°C to 1250°C in an oxygen-free environment to obtain an agglomerate. Hereinafter, the volatile content of coal is expressed as mass% on a dry base.

[0026] This production method makes it possible to produce high-density, high-strength carbon-based agglomerates from coal with a volatile content of 1 mass % or more and less than 20 mass %, i.e., coal with poor caking properties or a coal-derived material containing a high concentration of carbon.

[0027] Hereinafter, the carbon-based agglomerates according to the present embodiment may be simply referred to as agglomerates. Note that the term "carbon-based agglomerates" refers to agglomerates having a carbon ratio of 70% by mass or more and 100% by mass or less on an anhydrous basis.

[0028] More specifically, in this manufacturing method, the agglomerates are formed by a solid-phase sintering-like phenomenon, not by a liquid-phase sintering-like phenomenon in which coal powder particles are bonded or fused together using liquid-phase components that can become volatiles. Therefore, it is possible to obtain agglomerates with a high strength that can withstand shocks during transportation and static loads when the agglomerates are packed into a packed bed and stored in a yard or hopper. In addition, the bulk density (apparent density) is 1.1 g / cm 3 Therefore, agglomerates with a high density (high density agglomerates) exceeding the above can be obtained.

[0029] In this embodiment, the bulk density of the agglomerates is the value obtained by dividing the mass of the agglomerates by the external volume of the agglomerates (the total volume of the solid part and the open and closed pores of the target material). The mass of the agglomerates was measured using an electronic balance. The external volume of the agglomerates was calculated by measuring the diameter and height of the cylindrical agglomerates using calipers.

[0030] Further, the strength of the agglomerates in this embodiment refers to the cold indirect tensile strength measured by the method described in Non-Patent Document 1. Hereinafter, the indirect tensile strength measured by this method may be simply referred to as "strength".

[0031] A strength of 1 MPa or more is necessary to withstand shocks during transportation and static loads when the material is packed into a packed bed and stored in a yard or hopper. In the following description, when an agglomerate has a strength of 1 MPa or more, the agglomerate is evaluated as having high strength (high strength). Among these, an agglomerate (i.e., coke) having a strength that can be used in a conventional blast furnace process may be evaluated as usable as high-strength coke. Note that coke having a strength that can generally be used in a blast furnace process has a strength of 3 MPa or more. When comparing with a conventional manufacturing method, an agglomerate produced using coal with a similar volatile content is evaluated as having high strength when the strength is relatively high.

[0032] Examples of coal with a volatile content of 1% by mass or more and less than 20% by mass include some bituminous coal, semi-anthracite, and anthracite. Coal with a volatile content of 1% by mass or more and less than 20% by mass has poor caking properties. Coal with a volatile content of 1% by mass or more and less than 20% by mass may be coal that has lost its volatile content for some reason in the coal processing process, or heat-treated coal that has been heat-treated. That is, the concept of coal with a volatile content of 1% by mass or more and less than 20% by mass in this embodiment includes not only unprocessed coal, but also coal-derived substances that are mainly composed of coal, such as heat-treated coal. In the following description of the first embodiment, when simply referring to coal, it is assumed that coal with a volatile content of 1% by mass or more and less than 20% by mass is meant.

[0033] The volatile matter content of coal is a value measured in accordance with "Coals and cokes -- Industrial analysis methods" (JIS M 8812:2004) specified in the Japanese Industrial Standards (JIS).

[0034] The pulverization step is a process for pulverizing coal to obtain coal powder having a maximum particle size of 300 μm or less. In this embodiment, the particle size means the maximum particle size unless otherwise specified. When measuring with a particle size distribution measuring device, the maximum particle size can be measured as follows.

[0035] In this embodiment, the particle size and particle size distribution may be values ​​measured using a commercially available particle size distribution measuring device. In this embodiment, an image type particle size distribution measuring device "Morphologi 4" (hereinafter simply referred to as particle size distribution measuring device) manufactured by Malvern Panalytical is used, images of 55,000 to 74,000 particles are obtained with a microscope built into the device, and particle size and particle size distribution based on the circle equivalent particle diameter (projected area circle equivalent diameter) obtained by image analysis using software attached to the device are used. That is, the particle diameter that is 95% of the particles contained in the mixed powder measured by the particle size distribution measuring device by accumulating the particles from the smallest particle is taken as the maximum particle diameter (maximum value). Hereinafter, when simply referring to particle size or particle size distribution, it means the value measured by the above particle size distribution measuring device.

[0036] If the coal powder contains coarse particles with a particle size exceeding 300 μm, these coarse particles may remain in the agglomerate and reduce its strength. In the subsequent hot pressing step, a solid-phase sintering-like phenomenon that causes the particles in the coal powder to bond together is promoted as the particle size becomes smaller. Therefore, the remaining coarse particles may cause a decrease in strength because they inhibit the bonding between the particles. In addition, defects are likely to form around the coarse particles in the agglomerate, which may cause stress concentration and become the starting point of fracture when an external force is applied, resulting in a decrease in strength.

[0037] The particle size of the coal powder is preferably 100 μm or less. When the particle size of the coal powder is appropriately small, the physical structure in the agglomerate becomes dense and uniform, which contributes to increasing the strength of the agglomerate. The finer the particle size of the coal powder, the higher the strength of the agglomerate, which is preferable. Therefore, the minimum particle size of the coal powder is not limited. However, considering productivity, even if the particle size of the coal powder is reduced, making the maximum particle size of the particles contained in the coal powder less than 20 μm increases the cost of pulverization, but the improvement in the performance of the agglomerate is limited. Therefore, if the maximum particle size is 20 μm or more, an agglomerate with sufficient strength can be manufactured.

[0038] The pulverizing method or pulverizing device is not particularly limited. As a pulverizing device for coal, 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 pulverizing device is not limited to a device that performs only pulverization, and for example, a pulverizer with a built-in classifier may be used.

[0039] The hot pressing step is a process in which the coal powder is pressurized and molded at a temperature in the range of 600° C. to 1250° C. inclusive in an oxygen-blocking environment to obtain an agglomerate.

[0040] In the hot pressing step, the coal powder is mechanically pressed to form, i.e., pressurized and molded. Pressurizing mechanically means compressing the coal powder with a member that serves as a physical wall, such as a pestle and mortar, a metal mold, or a compression roll. Hereinafter, the pressure mechanically applied to the coal powder during pressurization in the hot pressing step is referred to as the molding pressure.

[0041] In the hot pressing step, it is sufficient that the coal powder is pressed (i.e., hot pressed) at a temperature in the temperature range of 600°C to 1250°C. In the hot pressing step, for example, the coal powder may be heated to a temperature in the above temperature range, the heating may be stopped, and the coal powder may be pressurized and molded at a temperature in the above temperature range. In addition, the hot pressing step may be pressurized and molded at a temperature in the above temperature range while heating and increasing the temperature of the coal powder. In this case, pressure may be applied only during a part of the entire process in which the coal powder is heated and increased in temperature, or may be applied throughout the entire process. From the viewpoint of suppressing or preventing a temperature drop during pressure molding, it is preferable that the hot pressing step is performed while heating at least for warmth retention, even if the temperature is not increased.

[0042] There is no particular limitation on the hot press device that performs pressure molding of coal powder at a temperature range including 600° C. or more and 1250° C. or less. The coal powder may be pressed by storing the coal powder in a space surrounded by the above-mentioned walls (e.g., in a mold for hot pressing) and compressing the coal powder through the walls. The heat source for heating the coal powder may be, for example, electric resistance heating, microwave heating, or high-frequency induction heating.

[0043] When coal powder is heated, the coal powder expands due to heat. As a result, the bulk density of the packed bed of coal powder decreases. In contrast, when the coal powder is heated while being pressurized, the packed bed of coal powder is compressed against the thermal expansion, and the decrease in the bulk density of the packed bed of coal powder can be suppressed. This increases the number of contact points between particles and promotes a solid-phase sintering-like phenomenon. As a result, agglomerates with high bulk density and high strength can be obtained more effectively.

[0044] The heating of the coal powder in the hot pressing step may be performed through the wall. The temperature range of the coal powder during pressurization in the hot pressing step is referred to as the molding temperature range. That is, the molding temperature range is the temperature range from the temperature of the coal powder when pressurization starts (the lower limit temperature of the molding temperature range) to the temperature of the coal powder when pressurization ends (the upper limit temperature of the molding temperature range) in the process of heating the coal powder. The upper limit temperature of the molding temperature range is 1250°C, which is the same as the upper limit temperature of the hot pressing step. The lower limit temperature of the molding temperature range is, for example, the temperature of the coal powder when it is placed in a mold for hot pressing.

[0045] In the hot pressing step, the coal powder is heated to 600°C or higher in an atmosphere where the oxygen supply is cut off, and the coal particles of the coal powder are bonded together by a solid-phase sintering phenomenon, resulting in densification. As a result, it is possible to manufacture agglomerates with high bulk density and high strength. Note that solid-phase sintering-like bonding between coal particles generally occurs (appears) at temperatures of 600°C or higher.

[0046] The atmosphere in which the oxygen supply is cut off in the hot pressing step is, for example, an atmosphere in a space in which the inflow of air (oxygen) is prevented and an inert gas such as nitrogen is passed through. In an environment in which oxygen is supplied, the raw materials will burn and disappear.

[0047] The molding temperature range in the hot press step must include a temperature in the range of 600°C to 1250°C. The molding temperature range preferably includes a temperature in the range of 600°C to 1000°C. In other words, a part or all of the molding temperature range must overlap with the temperature range of 600°C to 1250°C. This allows the coal powder to be agglomerated by generating a solid-phase sintering-like phenomenon. As described above, the solid-phase sintering-like phenomenon occurs at 600°C or higher. The solid-phase sintering-like phenomenon occurs particularly remarkably at 600°C to 1250°C. At the temperature of 600°C to 1250°C in the hot press step, carbonization proceeds and the hot press step also serves as a carbonization treatment, so it is not necessarily necessary to perform a separate carbonization treatment, but a further carbonization treatment may be performed after the hot press step also serves as a carbonization treatment.

[0048] When carbonization is performed after the hot pressing step, it is performed in an atmosphere where oxygen supply is blocked, as in the hot pressing step. The carbonization temperature, which is the temperature of the carbonization process, is preferably 600°C or higher. This is because the solid-phase sintering phenomenon that causes the bonding of particles in the coal powder occurs at 600°C or higher, as described above. On the other hand, if the carbonization temperature exceeds 1250°C, the agglomerates are desorbed of hetero elements, and the strength decreases. If the carbonization temperature is 1250°C or lower, the higher the carbonization temperature, the higher the bulk density and strength of the agglomerates. In the case of blast furnace coke applications, the agglomerates are required to have high strength (3MPa or higher, preferably 5MPa or higher), so the carbonization temperature is preferably 900°C or higher and 1250°C or lower, more preferably 900°C or higher and 1100°C or lower. In addition, the carbonization temperature is preferably performed at a temperature higher than the temperature of the hot pressing step. For example, when the hot pressing step is performed at 700°C, the agglomerates can be shrunk and their density increased, and their strength can be further increased by performing the carbonization treatment at a temperature higher than 700°C. Note that when the hot pressing step also serves as the carbonization treatment, the maximum temperature reached in the hot pressing step becomes the carbonization temperature.

[0049] When the temperature of the coal powder is increased while the coal powder is molded under pressure, it is desirable to have a lower lower limit temperature of the molding temperature range. When the temperature of the coal powder is increased while the coal powder is molded under pressure, it is desirable to have a higher upper limit temperature of the molding temperature range. This is because, when the temperature of the coal powder is increased while the coal powder is molded under pressure, the reaction time can be extended by widening the molding temperature range. The lower limit temperature of the molding temperature range is the temperature (e.g., room temperature) at the start of pressurization in the hot press step. A part of the temperature range during the temperature increase process may be used as the molding temperature range, but in order to widen the molding temperature range, it is advisable to start pressing after the start of heating the coal powder, for example, when heating starts or immediately after heating starts.

[0050] The temperature rise rate is preferably 30° C. / min or less. By setting the temperature rise rate to 30° C. / min or less, it is possible to reduce temperature variations and avoid localized reduction in strength.

[0051] The higher the molding pressure, the more the number of contact points between the coal particles in the coal powder increases, promoting a solid-phase sintering phenomenon. Therefore, the higher the molding pressure, the higher the bulk density of the agglomerates, and therefore the higher the strength.

[0052] When the molding pressure is 20 MPa or more, the bulk density and strength of the agglomerates (i.e., the quality of the agglomerates) are stable. When the molding pressure is less than 20 MPa, a high-strength molded product may not be obtained. Therefore, the molding pressure is preferably 20 MPa or more. However, if the molding pressure is too high, the manufacturing cost may increase. A molding pressure of 300 MPa or less is sufficient.

[0053] When the volatile content of the coal used as the raw material for the coal powder is less than 1% by mass, it may not be possible to obtain an agglomerate with an appropriate bulk density or strength from the coal powder. The solid-phase sintering-like phenomenon that occurs in the hot pressing step is thought to be driven by the reaction of the raw material coal or heat-treated coal being aromaticized or polycyclized. In this reaction, hydrogen is released. In addition, CO, methane, and other hydrocarbons are released due to the decomposition of oxygen-containing functional groups and alkyl groups. In other words, the volatile content of the raw material corresponds to the amount of hydrogen, CO, methane, and other hydrocarbons released when the aromatization or polycyclization reaction that drives the solid-phase sintering-like phenomenon occurs, and indicates the potential for the solid-phase sintering-like phenomenon. In other words, when the volatile content is less than 1% by mass, the solid-phase sintering-like phenomenon is less likely to occur.

[0054] If the volatile content is too high, such as exceeding 20% ​​by mass, the gas generated during heating (gas generated by the volatilization of the volatile content or gas generated by the decomposition of the volatile content) expands, and the coal powder melts and foams. This inhibits the compression of the coal powder by the hot press device during pressure molding, making it impossible to sufficiently pressurize the coal powder, which may result in a decrease in the bulk density of the agglomerates. In addition, the gas generated during heating may cause the internal pressure of the space surrounded by the walls of the hot press device, such as a mortar or a metal mold, to exceed the pressure to be applied to the coal powder. In such a case, there is a risk that the hot press device or the walls may be damaged. In addition, the gas generated during heating may easily cause the walls to become dirty. For this reason, the volatile content of coal is set to be less than 20% by mass.

[0055] In order to obtain an agglomerate having a strength of 3 MPa or more, which is particularly suitable as blast furnace coke, the coal volatile content should be 8 mass% or more. In the range of coal volatile content of 1 mass% or more and less than 20 mass%, the higher the coal volatile content, the stronger the agglomerate can be obtained. By setting the coal volatile content to 8 mass% or more and less than 20 mass%, it is possible to provide a low-cost method for producing coke that has a strength sufficient for use in conventional blast furnace processes.

[0056] Second Embodiment In the first embodiment, a case was described in which a pulverization step and a hot press step were included as a method for producing carbon-based agglomerates, and the pulverization step was described as a step of pulverizing coal having a volatile content of 1% by mass or more and less than 20% by mass to obtain coal powder having a maximum particle size of 300 μm or less. As examples of coal having a volatile content of 1% by mass or more and less than 20% by mass, some bituminous coal, semi-anthracite, anthracite, and coal that has lost its volatile content for some reason in the coal processing process or heat-treated coal obtained by heat-treating coal were exemplified. This embodiment differs from the first embodiment in that the method for producing carbon-based agglomerates further includes a heat treatment step of heat-treating coal to obtain heat-treated coal having a volatile content of 1% by mass or more and less than 20% by mass, but is otherwise similar. That is, in the second embodiment, a heat treatment step is performed prior to the pulverization step as a method for producing carbon-based agglomerates, and the heat-treated coal obtained in the heat treatment step is pulverized in the pulverization step. In the following description, the description of the same parts as in the first embodiment will be omitted as appropriate.

[0057] The heat treatment step is a step for obtaining heat-treated coal for use in the pulverization step. In the heat treatment step, as described below, the coal is heated to 500°C or higher and 1000°C or lower in an oxygen-free environment.

[0058] The volatile content of the coal to be heat-treated in the heat treatment step (hereinafter referred to as raw coal) is, for example, 1% by mass or more and 45% by mass or less. Examples of coal with such a volatile content include lignite, subbituminous coal, bituminous coal, semi-anthracite, and anthracite.

[0059] Raw coal with a high volatile content tends to have high fluidity. Raw coal with a low volatile content tends to have low fluidity. Thus, the fluidity varies depending on the amount of volatile content, but in the method for producing agglomerates according to this embodiment, the fluidity of the raw coal can be selected as desired. For example, when caking coal with high fluidity is used as the raw coal and is heat-treated at 500°C or higher in an oxygen-blocked environment, the liquid phase components are thermally decomposed and polycondensed. Then, of the decomposed or polycondensed components, the light components evaporate, and the heavy components solidify and remain. After the heat treatment, the caking coal loses its liquid phase components and completely loses its fluidity. Therefore, any coal showing any fluidity can be used.

[0060] In this embodiment, the raw coal preferably has a common logarithm of maximum fluidity (MF: Maximum Fluidity according to JIS M8801, logMF) of 0.8 or more. When such raw coal is used, the bulk density of the agglomerates can be increased in some cases to be higher than that of agglomerates produced by conventional technology (for example, agglomerates produced by the method of Non-Patent Document 2. When the logMF of the raw coal is 0.8 or more, foaming due to volatile matter generated in the liquid phase becomes significant, and the bulk density of the agglomerates tends to decrease as the logMF increases).

[0061] As described above, the heat treatment of the raw coal is carried out by heating to 500° C. or more and 1000° C. or less in an oxygen-blocking environment.

[0062] The lower the heat treatment temperature, the more volatile matter remains in the heat-treated coal, and the more the solid-phase sintering phenomenon occurs in the hot pressing step, resulting in agglomerates with high bulk density and high strength.

[0063] If the heat treatment temperature is below 500° C., excessive volatile matter and tar will remain in the heat-treated coal and coal powder. For example, if the volatile matter of the heat-treated coal exceeds 20 mass%, as explained in the first embodiment, this is not preferable because it may cause a decrease in bulk density due to melting, foaming, or expansion of the coal powder in the hot press step, or damage or contamination of the hot press device, etc.

[0064] If the heat treatment temperature exceeds 1000° C., the amount of volatile matter remaining in the heat-treated coal and coal powder may be less than 1 mass %, which makes it difficult for a solid-phase sintering-like phenomenon to occur, as described in the first embodiment.

[0065] The heat treatment of the raw coal may be carried out in an atmosphere in which the supply of oxygen is blocked. The heat treatment of the raw coal may be carried out, for example, in a state in which the raw coal is housed in a container that forms a space in which the inflow of air is prevented and through which an inert gas flows. The heat treatment of the raw coal may be carried out by heating the container that houses the raw coal and by heat transfer from the container. That is, the heat treatment of the raw coal may be carried out by heating the container in a state in which the raw coal is housed in the container, thereby heating the raw coal to 500°C or more and 1000°C or less.

[0066] Typically, the reaction rate of the thermal decomposition reaction of raw coal in heat treatment is fast, so the time required for the thermal decomposition reaction to be completed in the heat treatment is short. Therefore, the treatment time required for the heat treatment is 1 minute or more. The time for which the heat treatment is performed (the treatment time of the heat treatment, hereinafter referred to as the heat treatment time) is preferably 10 minutes or more. This eliminates the temperature difference between the temperature of the raw coal and the temperature of the container, and the entire raw coal can be heat-treated uniformly. In addition, it is possible to perform the heat treatment by reliably raising the temperature of the entire raw coal to the heat treatment temperature evenly (i.e., by heating evenly), and the quality variation of the heat-treated coal can be suppressed.

[0067] 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. The heat treatment time refers to the time during which the temperature of the raw coal is maintained at a specified heat treatment temperature (hereinafter referred to as the first temperature) of 500°C or higher and 1000°C or lower.

[0068] 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.

[0069] The hot pressing step is the same as in the first embodiment, but the following improvements may be further implemented.

[0070] As described above, in this embodiment, the raw coal is heat-treated at a first temperature in the heat treatment step to obtain heat-treated coal. That is, the heat-treated coal has completed the pyrolysis reaction that can occur at or below the first temperature, and no further pyrolysis reaction occurs unless it is heated to or above the first temperature. Therefore, in order to cause the pyrolysis reaction that drives the solid-phase sintering phenomenon, it is necessary to heat the coal powder to or above the first temperature. Therefore, in the hot press step, the molding temperature range is preferably set to the first temperature or higher.

[0071] (Variation 1) In the above embodiment, the coal to be pulverized in the pulverization step is coal with a volatile content of 1% by mass or more and less than 20% by mass, and as examples of coal with a volatile content of 1% by mass or more and less than 20% by mass, some bituminous coal, semi-anthracite, anthracite, coal that has lost its volatile content for some reason in the coal processing step, or heat-treated coal obtained by heat-treating coal have been exemplified. In the second embodiment, it has been explained that when the heat treatment step is performed at a first temperature or less, the carbonization temperature during heat molding in the hot press step may be set to the first temperature or more. However, when an agglomerate is produced using coal that has lost its volatile content for some reason in the coal processing step, for example, coal that has been unintentionally subjected to the same heat treatment as in the heat treatment step, the first temperature at which the coal was heat-treated may be unknown.

[0072] In the case where the first temperature at which the coal is heat-treated in this manner is unknown, the first temperature at which the coal is heat-treated may be estimated using, for example, a method for estimating the thermal history of coal or coke as disclosed in Patent Document 2, and the molding temperature range in the hot-press step may be determined based on this estimated first temperature.

[0073] (Variation 2) In the above embodiment, the case where the agglomerates are obtained by performing the hot pressing step has been described. The agglomerates obtained by the hot pressing step can be further processed into a graphite material by a graphitization treatment. When producing a graphite material from the agglomerates, the agglomerates are heated after the hot pressing step in an oxygen-free atmosphere as a graphitization treatment, preferably at 2000°C or higher, more preferably at 2200°C or higher. EXAMPLES

[0074] An example will be described below.

[0075] Example 1 In Example 1, raw coal or heat-treated coal having various volatile contents was used, and agglomerates were produced by the production method according to this embodiment and evaluated.

[0076] Various raw coals were pre-pulverized to a particle size of 74 μm or less (200 mesh pass), and heat-treated at different heat treatment temperatures in the range of 600°C to 900°C to obtain heat-treated coal (heat treatment step). In the case of raw coals with a high volatile content (for example, when the raw coal is caking coal), the heat treatment may cause agglomeration. Therefore, in this embodiment, the heat-treated coals produced from any raw coal were pulverized to a particle size of 74 μm or less after the heat treatment to obtain coal powder (pulverization step). Some raw coals (those with a volatile content of less than 20% by mass) were not heat-treated, and were pulverized as they were to obtain coal powder. Note that an ultracentrifugal pulverizer (manufacturer: Verder Scientific, model: ZM200) was used for all of the above pulverization processes.

[0077] The coal powder was further subjected to hot pressing (hot pressing step). First, 1.32 g of coal powder was filled into a mold (metal mold, diameter: 12 mm). Then, while applying a molding pressure (mechanical pressure) of 50 MPa under a nitrogen flow, the mixture was heated from room temperature to 1000°C at a temperature increase rate of 20°C / min. After the mold reached 1000°C, the mixture was held at 1000°C for 5 minutes. The temperature was then lowered, and the agglomerates (1-1 to 1-15) according to Example 1 were collected.

[0078] The bulk density and indirect tensile strength of the agglomerates were measured. The indirect tensile strength was measured as a cold indirect tensile strength measured using the method described in Non-Patent Document 1. The bulk density was calculated from the dimensions of the external volume measured with a vernier caliper and the mass measured with an electronic balance, as described above. Table 1 shows the heat treatment temperature of the coal used in producing each agglomerate in Example 1, the volatile content after the heat treatment, the bulk density and indirect tensile strength of the agglomerates. FIG. 1 shows a graph showing the relationship between the bulk density and the volatile content of the agglomerates in Example 1. FIG. 2 shows a graph showing the relationship between the indirect tensile strength and the volatile content of the agglomerates in Example 1.

[0079] [Table 1]

[0080] Comparative Example 1 As Comparative Example 1, raw coal or heat-treated coal having various volatile contents was used, and agglomerates were produced by the coke production method (conventional method) described in Non-Patent Document 2 and evaluated.

[0081] 1.50 g of coal powder obtained in the same manner as in Example 1 was filled into a mold (metal mold, diameter: 12 mm). A mechanical pressure of 100 MPa was applied to obtain a molded product. Next, this molded product was heated at a temperature increase rate of 3°C / min until the temperature inside the electric furnace reached 1000°C. After the temperature inside the electric furnace reached 1000°C, it was held at 1000°C for 5 minutes. The temperature was then lowered, and the agglomerates (R1-1 to R1-26) according to Comparative Example 1 were collected.

[0082] The bulk density and indirect tensile strength of the above agglomerates were measured in the same manner as in Example 1. Table 2 shows the heat treatment temperature of the coal used in producing each agglomerate, the volatile content after heat treatment, and the bulk density and indirect tensile strength of the agglomerates in Comparative Example 1. In addition to the results of Example 1, FIG. 1 shows a graph showing the relationship between the bulk density and the volatile content of the agglomerates in Comparative Example 1. Similarly, in addition to the results of Example 1, FIG. 2 shows a graph showing the relationship between the indirect tensile strength and the volatile content of the agglomerates in Comparative Example 1.

[0083] [Table 2]

[0084] From the results of Example 1 and Comparative Example 2 shown in Tables 1 and 2 and FIGS. 1 and 2, the agglomerates of Example 1 produced using coal or heat-treated coal with a volatile content of less than 13 mass% have higher bulk density and strength than the agglomerates of Comparative Example 1 produced by the conventional method.

[0085] The agglomerates according to Example 1 all had a bulk density of 1.1 g / cm 3 That's it, it's high density.

[0086] In particular, when the volatile content is less than 9 mass%, agglomeration is not possible in Comparative Example 1, but is possible in Example 1. That is, the agglomerates of Example 1 have higher bulk density and strength than the agglomerates of Comparative Example 1.

[0087] When the volatile content is 8 mass % or more, the agglomerates of Example 1 achieve a strength sufficient for use as high-strength coke.

[0088] When the volatile content was 13 mass % or more, the agglomerates of Example 1 were comparable to those of Comparative Example 1 in bulk density and strength.

[0089] As described above, from the results of Example 1 shown in FIGS. 1 and 2 , it can be sufficiently estimated that the method for producing agglomerates according to this embodiment makes it possible to produce agglomerates using coal or heat-treated coal having a volatile content of at least less than 20 mass%.

[0090] From the above results, it is evident that the method for producing agglomerates according to this embodiment can produce high-density, high-strength agglomerates mainly composed of carbon from coal having poor caking properties, i.e., coal with a volatile content of 1 mass % or more and less than 20 mass %, or from coal-derived material containing high concentrations of carbon (e.g., heat-treated coal).

[0091] Example 2 In order to confirm the effect of the heat treatment temperature, the agglomerates according to Example 2 were produced and evaluated as follows.

[0092] In Example 2, coals subjected to different heat treatment temperatures were used to produce agglomerates, and the bulk density and indirect tensile strength were measured. As the raw coal, non-caking coal (1) (volatile content: 10.0% by mass) and non-caking coal (2) (volatile content: 20.0% by mass) were used.

[0093] The production of the agglomerates in Example 2 was carried out in the same manner as in Example 1, except that the heat treatment temperature was varied within the range of 600°C or more and 1100°C or less to obtain heat-treated coal, and the agglomerates (2-1 to 2-12) according to Example 2 were obtained.

[0094] The bulk density and indirect tensile strength of the agglomerates of Example 2 were measured in the same manner as in Example 1. Table 3 shows the type of coal used in producing each agglomerate, the heat treatment temperature, the volatile content after heat treatment, the bulk density and indirect tensile strength of the agglomerates in Example 2. Figure 3 is a graph showing the relationship between the indirect tensile strength of the agglomerates of Example 2 and the heat treatment temperature.

[0095] [Table 3]

[0096] From Table 3 and FIG. 3, it can be seen that as the heat treatment temperature increases, the volatile content decreases monotonically, and the strength of the agglomerates also decreases monotonically accordingly. In particular, when the heat treatment temperature is 900°C or higher, agglomerates are obtained, but the strength is significantly reduced. For example, the strength of agglomerates 2-5, 2-10, and 2-11 is below 1.0 MPa. Furthermore, when the heat treatment temperature is 1100°C, the volatile content is less than 1 mass%, and no agglomerates are obtained. When the heat treatment temperature is 800°C or lower, the agglomerates have high density and high strength. Even when the heat treatment temperature is higher than 800°C and is 900°C or higher, the heat-treated coal with volatile content that could not even be agglomerated by the conventional technology (see the case where the volatile content is less than 9 mass% in Comparative Example 1) can be agglomerated to a strength that allows the strength to be measured, and it can be said that agglomerates with higher strength than the agglomerates of the conventional technology were obtained. In addition, because the bulk density and strength of the agglomerates also depend on the amount of volatile matter in the heat-treated coal after heat treatment, it is not the case that a heat treatment temperature exceeding 1000°C immediately makes it impossible to produce high-density, high-strength agglomerates, but regardless of the type of coal used for heat treatment, the amount of volatile matter decreases monotonically as the heat treatment temperature increases, and becomes close to or less than 1 mass% above 1000°C. Therefore, it is considered preferable for the heat treatment temperature to be 1000°C or lower.

[0097] Example 3 In order to confirm the effect of molding pressure, the agglomerates according to Example 3 were produced and evaluated as follows.

[0098] The production of the agglomerates in Example 3 was carried out in the same manner as in Example 1, except that coal (1) was used as the raw coal, heat treatment was performed only at a heat treatment temperature of 600°C to obtain heat-treated coal, and molding pressures were set to 10 MPa, 20 MPa, 35 MPa, and 50 MPa, to obtain agglomerates (3-1 to 3-4) according to Example 3.

[0099] The bulk density and indirect tensile strength of the agglomerates of Example 3 were measured in the same manner as in Example 1. Table 4 shows the molding pressure during production of each agglomerate, and the bulk density and indirect tensile strength of the agglomerates in Example 3. Fig. 4 is a graph showing the relationship between the indirect tensile strength and molding pressure of the agglomerates of Example 3. The heat-treated coal in Example 3 (coal (1) after heat treatment) had a volatile content of 8.2 mass%.

[0100] [Table 4]

[0101] From Table 4 and the graph shown in Figure 4, it can be seen that a molding pressure of 20 MPa or more is desirable. If the molding pressure is 20 MPa or more, the agglomerates have high density and high strength. If the molding pressure is less than 20 MPa (10 MPa), agglomerates can be obtained, but the strength is less than 1.0 MPa.

[0102] Example 4 In order to confirm the effect of the molding temperature range, the agglomerates according to Example 4 were produced and evaluated as follows.

[0103] The production of the agglomerates in Example 4 was carried out in the same manner as in Example 1, except that coal (1) was used as the raw coal, heat treatment was performed only at a heat treatment temperature of 600°C to obtain heat-treated coal, and molding pressure was applied in the hot press step within a specific temperature range of 200°C from room temperature to 1000°C during the temperature rise process, to obtain agglomerates (4-1 to 4-5) according to Example 4.

[0104] The bulk density and indirect tensile strength of the agglomerates of Example 4 were measured in the same manner as in Example 1. Table 5 shows the molding temperature range, and the bulk density and indirect tensile strength of the agglomerates in Example 4. Note that the heat-treated coal in Example 4 (heat-treated coal (1)) had a volatile content of 8.2 mass%, as shown in Example 3.

[0105] [Table 5]

[0106] As shown in Table 5, it is understood that when the molding temperature range does not include the temperature range of 600°C or higher, agglomerates cannot be obtained. Also, when the molding temperature range includes temperatures in the range of 600°C or higher and 1000°C or lower (when pressure molding is performed at a temperature in the range of 600°C or higher and 1000°C or lower), agglomerates with high bulk density and strength can be obtained.

[0107] Example 5 In order to confirm the effect of the molding temperature range, the agglomerates according to Example 5 were produced and evaluated as follows.

[0108] The production of the agglomerates in Example 5 was carried out in the same manner as in Example 4, except that in the hot press step, the lower limit temperature of the molding temperature range was set to 25°C, 200°C, 400°C, 600°C, and 800°C, and the upper limit temperature of the molding temperature range was set to 1000°C (i.e., only the lower limit temperature of the molding temperature range was changed) and molding pressure was applied, thereby obtaining agglomerates (5-1 to 5-5) of Example 5.

[0109] The bulk density and indirect tensile strength of the agglomerates of Example 5 were measured in the same manner as in Example 1. Table 6 shows the lower limit temperature of the molding temperature range and the bulk density and indirect tensile strength of the agglomerates in Example 5. Fig. 5 is a graph showing the relationship between the indirect tensile strength of the agglomerates of Example 5 and the lower limit temperature of the molding temperature range.

[0110] [Table 6]

[0111] As shown in Table 6 and Fig. 5, it can be seen that the strength of the agglomerates increases as the lower limit temperature becomes lower. Therefore, it can be concluded that in order to increase the strength of the agglomerates, it is preferable to have a lower lower limit of the molding temperature range. Also, it can be seen from Table 6 that the bulk density of the agglomerates increases as the lower limit temperature becomes lower. Therefore, it can be concluded that in order to increase the bulk density of the agglomerates, it is preferable to have a lower lower limit of the molding temperature range.

[0112] Looking at the results shown in Tables 5 and 6 overall, the following can be seen. When the molding temperature range includes a temperature in the range of 600°C or more and 1000°C or less (when pressure molding is performed at a temperature in the range of 600°C or more and 1000°C or less), agglomerates with high bulk density and high strength can be obtained. Furthermore, it is preferable that the molding temperature range includes a temperature range below 600°C, since the bulk density or strength of the agglomerates may be further improved. In other words, it is preferable that a part of the molding temperature range overlaps with a temperature range of room temperature (25°C) or more and less than 600°C. A particularly preferable specific example is to continue applying molding pressure from the start to the end of heating in the hot press, as in agglomerate 5-1.

[0113] In this manner, a method for producing high-density, high-strength carbon-based agglomerates from poorly caking coal or coal-derived carbon-containing materials with a high concentration can be provided. The agglomerates produced by this method can have a strength sufficient to withstand, for example, impacts during transportation and static loads when the agglomerates are packed into a packed bed and stored in a yard or hopper, or can have a strength sufficient to be used in a conventional blast furnace process.

[0114] In addition, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, provided no contradiction arises. Furthermore, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0115] The present invention can be applied to a method for producing agglomerates mainly made of carbon.

Claims

1. A grinding step of grinding coal having a volatile content of 1% by mass or more and less than 20% by mass on an anhydrous basis to obtain coal powder having a maximum particle size of 300 μm or less; and a hot pressing step of pressurizing and molding the coal powder at a temperature in the range of 600°C to 1250°C inclusive in an oxygen-blocked environment to obtain an agglomerate.

2. 2. The method for producing carbon-based agglomerates according to claim 1, wherein the coal has a volatile content of less than 13% by mass on a dry basis.

3. 2. The method for producing carbon-based agglomerates according to claim 1, wherein the coal is heat-treated coal.

4. A heat-treating step of heat-treating coal to obtain heat-treated coal having a volatile content of 1% by mass or more and less than 20% by mass on a dry basis; A pulverization step of pulverizing the heat-treated coal to obtain coal powder having a maximum particle size of 300 μm or less; and a hot pressing step of pressurizing and molding the coal powder at a temperature in the range of 600°C to 1250°C inclusive in an oxygen-blocked environment to obtain an agglomerate.

5. 5. The method for producing carbon-based agglomerates according to claim 4, wherein the heat-treated coal has a volatile content of less than 13% by mass on a dry basis.

6. The heat treatment is performed at a first temperature of 500° C. or more and 1000° C. or less, The method for producing a carbon-based agglomerate according to any one of claims 3 to 5, wherein the pressure molding is performed at a temperature equal to or higher than the first temperature.

7. The method for producing a carbon-based agglomerate according to any one of claims 1 to 5, wherein the pressure molding is performed at a molding pressure of 20 MPa or more.

8. The method for producing a carbon-based agglomerate according to claim 1 , wherein the pressure molding starts heating after pressure is started.

9. The method for producing a carbon-based agglomerate according to any one of claims 1 to 5, wherein the coal is a non-caking coal.

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