Method for producing molded coal for coke production, and strength improving material for molded coal

Abstract

Provided is a technique for improving the drop strength of molded coal without increasing the amount of a tacky binder. This method for producing molded coal for coke production is characterized in that cellulose fibers having an average fiber length of 0.5-3.0 mm and an average fibril circumference length of 10% or less are added to and mixed with a raw material for the molded coal and the mixture is press-molded to obtain the molded coal.

Description

Manufacturing method of molded coal for coke production and strength improving material for molded coal

[0001] The present invention relates to a method for producing molded coal for coke production and a strength improver for molded coal.

[0002] Blast furnace coke is used in blast furnaces as a reducing agent, a heat source, and a support material to maintain gas permeability and liquid permeability. Stable blast furnace operation requires coke with excellent properties, such as strength, particle size, and post-reaction strength. Rotational strength and other coke strength characteristics are particularly important.

[0003] In coke production, it is known that increasing the bulk density of coal charged into a coke oven improves the strength of the coke obtained by carbonization. Therefore, various techniques for improving the bulk density of coal charged into a coke oven have been proposed, one of which is a molded coal blending method (see, for example, Patent Documents 1 and 2). The molded coal blending method is a technique for improving the bulk density of raw materials charged into a coke oven by producing high-density molded coal by pressurizing and molding coal powder, and then charging the powdered blended coal and the molded coal together into a coke oven.

[0004] Molded coal used in coke production is usually produced using coal-based, petroleum-based, or organic binders (gluing agents) to prevent disintegration during transportation. Molded coal that has disintegrated and reduced in volume during transportation is sieved and reused as raw material for molded coal. Therefore, by preventing disintegration during transportation, the yield of molded coal can be improved, and improved productivity of molded coal is expected.

[0005] JP-A-52-133301 JP-A-55-7863

[0006] The collapse of molded coal during transportation is mainly caused by transfers on the conveyor and the impact of dropping when being put into a hopper. In conventional molded coal manufacturing methods using coal-based, petroleum-based, or organic binders, the collapse caused by the impact of dropping was the cause of reduced productivity of molded coal.

[0007] Furthermore, conventional coal-based, petroleum-based, and organic binders are sticky, and their stickiness allows them to bond raw material particles together, thereby exerting strength. When increasing the amount of conventional binders to improve the drop strength of molded coal, problems arise, such as raw material adhesion to equipment due to the increased amount of sticky binder. Therefore, a technology that can improve the drop strength of molded coal without increasing the amount of sticky binder has been desired. To improve the drop strength of molded coal without increasing the amount of sticky binder, it is necessary to improve the drop strength of molded coal using a mechanism different from the inter-particle adhesion achieved by conventional sticky binders.

[0008] The present invention has been made in view of the above problems, and its object is to provide a technology for improving the drop strength of molded coal without increasing the amount of adhesive binder.

[0009] The inventors conducted extensive research to solve the above-mentioned problems and found that blending fibrous pulp (cellulose fiber) is an effective way to improve the strength of molded charcoal through a mechanism different from that of adhesive binders. The incorporation of cellulose fiber results in the formation of an entangled network within the molded charcoal, which mechanically binds the coal particles in the molded charcoal, thereby improving the drop strength of the molded charcoal. Furthermore, the inventors further researched and found that the unraveling and dispersion of the cellulose fiber blended during molded charcoal production is an important factor in achieving strength. They also demonstrated that the ease of unraveling of cellulose fiber can be controlled by the fibril circumference, which is an indicator of the degree of fuzz on the cellulose fiber surface, and thus completed the present invention.

[0010] The present invention provides a method for producing molded coal for coke production, comprising blending and mixing cellulose fibers having an average fiber length of 0.5 mm or more and 3.0 mm or less and an average fibril circumference of 10% or less with a raw material for molded coal, and molding the mixture under pressure to obtain molded coal.

[0011] [2] The method for producing molded charcoal described in [1], wherein the blending ratio of the cellulose fiber is 3.0 mass% or less.

[0012] [3] The method for producing molded coal according to [1] or [2], further comprising blending and mixing the coal with any one of a coal-based, petroleum-based, and organic binder.

[0013] [4] A strength improving material for molded charcoal, characterized by being a cellulose fiber having an average fiber length of 0.5 mm or more and 3.0 mm or less and an average fibril circumference of 10% or less.

[0014] According to the present invention, it is possible to provide a technique for improving the drop strength of molded coal without increasing the amount of adhesive binder. Furthermore, by improving the drop strength of molded coal, collapse of molded coal during transportation can be suppressed, and productivity of molded coal can be improved.

[0015] The present invention provides a method for producing molded coal for coke production, which comprises blending cellulose fibers having an average fiber length of 0.5 mm to 3.0 mm and an average fibril circumference of 10% or less with a raw material for the molded coal, and then molding the resulting cellulose fiber mixture under pressure to obtain molded coal.

[0016] [Raw Material for Molded Coal] As the raw material for molded coal, a material that is solid at room temperature, such as coal used in a general molded coal manufacturing method, can be used. In addition, non- or slightly caking coal, coal carbonization product, biomass, charcoal obtained by heating biomass, and other raw materials mainly composed of carbon may also be used, as long as the quality of the coke obtained by charging the powdered blended coal and molded coal into a coke oven and carbonizing it is not an issue.

[0017] As has been conventionally done, the raw material for the molded coal is preferably crushed using a hammer crusher or the like so that the ratio of particles having a particle size of −3 mm or less is 70 to 100% by mass (crushed so that the proportion of particles having a particle size of 3 mm or less is 70 to 100% by mass) to adjust the particle size before use.

[0018] [Cellulose fiber] "Cellulose fiber" is a fibrous material obtained from a cellulose raw material, which is usually naturally derived. As the cellulose raw material, pulp is preferred, and wood-derived pulp is more preferred. Examples of wood-derived pulp include pulp derived from broad-leaved trees and pulp derived from softwoods.

[0019] Wood-derived pulp can be prepared by known methods, including, for example, a method involving a chemical pulping (cooking) process. The chemical pulping (cooking) process dissolves and removes lignin, a coloring substance, and by combining this with oxygen delignification and bleaching, pulp with high whiteness can be obtained. While oxygen delignification and bleaching are not necessary for this application, they can be performed without causing any problems. In other words, a normal pulp manufacturing process can be applied.

[0020] Chemical pulping (cooking) methods include, for example, sulfite cooking, kraft cooking, soda-quinone cooking, and organosolv cooking, with kraft cooking being preferred from environmental and economical perspectives. The "kraft cooking" method uses alkaline chemicals such as sodium hydroxide, potassium hydroxide, and sodium carbonate in combination with sulfur-containing chemicals such as sodium sulfide and sodium sulfite, and can use quinone-based cooking aids, polysulfides, and other additives.

[0021] In the pulp preparation method, the pulp obtained by cooking can be subjected to oxygen delignification. The known medium-consistency or high-consistency methods can be used as the oxygen delignification method in the present invention. When using the medium-consistency method, the pulp consistency is preferably set to 8 to 15 mass%, and when using the high-consistency method, the pulp consistency is preferably set to 20 to 35 mass%. The alkali used in the oxygen delignification treatment can be sodium hydroxide or potassium hydroxide. The oxygen gas that can be used includes oxygen from a cryogenic separation method, oxygen separated by a pressure swing adsorption (PSA) method, and oxygen separated by a vacuum swing adsorption (VSA) method.

[0022] The reaction conditions for the oxygen delignification treatment are not particularly limited, but for example, the oxygen pressure is 3 to 9 kg / cm ２ The alkali addition rate may be 0.5 to 4 mass%, the temperature may be 80 to 140°C, and the treatment time may be 20 to 180 minutes. Other conditions may be those known in the art. In the present invention, the oxygen delignification treatment may be carried out multiple times.

[0023] The pulp that has been subjected to the oxygen delignification treatment may then be sent to a washing step, for example, and after washing, may be subjected to a bleaching treatment as described below.

[0024] In the preparation of pulp, in addition to chemical pulping (cooking) and oxygen delignification, a bleaching treatment can also be carried out, which results in a pulp with a higher brightness. Examples of bleaching treatment methods include subjecting pulp delignified by a conventional method to chlorine treatment (C), chlorine dioxide bleaching (D), alkaline extraction (E), hypochlorite bleaching (H), hydrogen peroxide bleaching (P), alkaline hydrogen peroxide treatment stage (Ep), alkaline hydrogen peroxide-oxygen treatment stage (Eop), ozone treatment (Z), chelate treatment (Q), and combinations of two or more of these treatments. Examples of combinations (sequences) of two or more treatments include D-E / P-D, C / D-E-H-D, Z-E-D-P, Z / D-Ep-D, Z / D-Ep-D-P, D-Ep-D, D-Ep-D-P, D-Ep-P-D, Z-Eop-D-D, Z / D-Eop-D, and Z / D-Eop-D-E-D (the " / " in the sequence means that the treatments before and after " / " are performed consecutively without washing). The bleaching treatment is not limited to the above examples, and a commonly used method may be used. Pulp that has undergone bleaching treatment is usually in a fluidized state (fluidized pulp).

[0025] The moisture content of the pulp described above is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, for example, when a pulp sheet is subjected to a crushing treatment. Furthermore, in order to prevent the raw material fibers from being shortened before and after the crushing of the cellulose fibers of the present invention, the moisture content is more preferably 30% by mass or more, and particularly preferably 40% by mass or more. The moisture content of the pulp is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less. By adjusting the moisture content of the pulp within this range, the cellulose fibers can be easily adjusted during the crushing treatment.

[0026] When the cellulose fibers are prepared by beating the pulp sheet in water without crushing it, the moisture content of the pulp is not particularly limited and can be selected appropriately.

[0027] The average fiber length of the cellulose fibers used in the method for producing molded charcoal according to the present invention is 0.5 mm or more and 3.0 mm or less. The strength of the molded charcoal is achieved by forming an entangled network of cellulose fibers in the molded charcoal and mechanically binding the coal particles in the molded charcoal. Therefore, the cellulose fibers used must be fibrous cellulose fibers, not pulp finely crushed into powder, and must have an average fiber length of 0.5 mm or more. If the average fiber length is less than 0.5 mm, the cellulose fibers cannot form an entangled network in the molded charcoal, and the drop strength improvement effect cannot be obtained. Furthermore, the upper limit of the average fiber length of the cellulose fibers used is not particularly limited from the viewpoint of improving the strength of the molded charcoal. However, since the average fiber length of cellulose fibers produced from raw materials derived from conifers, which are generally known to have long fiber lengths, is approximately 3.0 mm or less, the method for producing molded charcoal according to the present invention uses cellulose fibers having an average fiber length of 3.0 mm or less.

[0028] The average fiber length of cellulose fibers can be determined using an image analysis-type fiber analyzer, such as a fractionator manufactured by Valmet or an L&W Fiber Tester Plus manufactured by ABB Corporation. Specifically, for example, 300 ml of an aqueous dispersion diluted to contain 0.1 g of cellulose fibers in solid form is subjected to an image analysis-type fiber analyzer (product name: L&W Fiber Tester Plus, manufactured by ABB Corporation), and measurement is performed for 300 seconds to determine the length-weighted fiber length (n=2). At this time, the measurement is performed after setting the Max value of Fines Limit to 0.2 and the Min value of Length class 1 to 0.2 on the Sample type screen, which defines the measurement conditions.

[0029] The average fiber length of cellulose fibers can be controlled during the pulp production process. Generally, short fiber length cellulose fibers are obtained when wood chips derived from broad-leaved trees are used as raw materials, while long fiber length cellulose fibers are obtained when wood chips derived from coniferous trees are used as raw materials. Furthermore, the fiber length of cellulose fibers decreases during the pulp production process through processes such as crushing, beating, and pulverization. In order to obtain the cellulose fibers of the present invention, crushing treatment is particularly preferred.

[0030] The cellulose fibers used in the method for producing molded charcoal of the present invention have an average fibril perimeter of 10% or less. The "average fibril perimeter" is an index of the degree of fluffiness of the cellulose fiber surface, with a larger average fibril perimeter indicating a fluffier cellulose fiber. The larger the average fibril perimeter of the cellulose fibers (in other words, the fluffier the fibers), the stronger the bonds between the cellulose fibers. This increases the risk that the cellulose fibers will disintegrate and clump together in the raw coal during the mixing process of molded charcoal production, resulting in defects in the molded charcoal. In order for the cellulose fibers to form an entangled network in the molded charcoal and develop strength, they must be widely dispersed in the molded charcoal. In this regard, cellulose fibers with a large average fibril perimeter cannot achieve the objective of improving the drop strength of molded charcoal of the present invention. Therefore, the average fibril perimeter of the cellulose fibers used in the present invention is 10% or less, more preferably 8% or less, and even more preferably 5% or less. On the other hand, the lower limit of the average fibril perimeter of cellulose fibers is not limited in terms of improving the strength of molded charcoal, but making it extremely small is difficult in the production of ordinary cellulose fibers and requires special treatment, which leads to reduced productivity. Therefore, the average fibril perimeter of cellulose fibers is preferably 0.5% or more, more preferably 1.0% or more. In this specification, the average fibril perimeter is calculated as follows: Average fibril perimeter (%) = (perimeter of fibrillated part) / (perimeter of fibrillated part + perimeter of original fiber) × 100

[0031] The average fibril perimeter of cellulose fibers can be measured, for example, using an L&W Fiber Tester Plus manufactured by ABB Corporation. Specifically, 300 ml of an aqueous dispersion diluted to contain 0.1 g of cellulose fibers in solid form is first prepared. The prepared aqueous dispersion is then subjected to an image analysis fiber analyzer (product name: L&W Fiber Tester Plus, manufactured by ABB Corporation) and measurement is performed for 300 seconds to determine the mean fibril perimeter (n=2). The measurement is performed after setting the Max value of Fines Limit to 0.2 and the Min value of Length class 1 to 0.2 on the Sample type screen, which defines the measurement conditions.

[0032] The average fibril circumference of cellulose fibers increases with the progress of beating during pulp production. Therefore, in order to control the average fibril circumference to 10% or less, it is effective to weaken the degree of beating during pulp production or to directly crush the pulp sheet without performing a beating step.

[0033] In the method for producing molded charcoal according to the present invention, it is preferable to blend cellulose fibers at a blending ratio of 3.0% by mass or less. Here, the "blend ratio" is a value calculated based on the dry mass of all raw materials. In other words, blending cellulose fibers at a blending ratio of 3.0% by mass or less means blending cellulose fibers so that the dry weight of the cellulose fibers is 3.0% by mass or less, when the total dry mass of raw materials (coal, coal dry distillate, pitch, other carbonaceous materials, etc., excluding cellulose fibers) that are solid at room temperature used to produce molded charcoal is taken as 100% by mass.

[0034] When a biomass-derived raw material such as cellulose fiber is mixed with coal to produce coke, the biomass-derived raw material not only does not thermoplasticize, but also reduces the thermoplasticity of the raw coal, which can easily cause defects in the coke after carbonization and reduce the coke strength. Therefore, the cellulose fiber content is preferably 3.0% by mass or less. The cellulose fiber content is more preferably 0.1% by mass or more and 3.0% by mass or less, and even more preferably 0.1% by mass or more and 2.0% by mass or less.

[0035] The molding method for molded coal is not particularly limited, but an example of a general molding method for molded coal is a method in which a binder is added to a molded coal raw material that is a mixture of multiple coals and / or carbon materials, and the mixture is kneaded in a kneader, and then compacted and molded in a double-roll molding machine.

[0036] [Binders other than cellulose fibers] In addition to the cellulose fibers described above, conventionally used binders can be blended and mixed with coal. Examples of such binders include coal-based binders (coal tar pitch, solvent-refined coal, tar, tar slag, etc.), petroleum-based binders (asphalt, asphalt pitch, propane-deasphalted asphalt, etc.), and organic binders (starch, molasses, synthetic polymer compounds, resins, etc.).

[0037] The method for producing molded charcoal according to the present invention can improve drop strength by blending cellulose fibers with controlled average fiber length and average fibril circumference with raw materials used in general molded charcoal production. In order to improve the dispersion of cellulose fibers in the molded charcoal raw materials, the molded charcoal can be produced by blending the cellulose fibers with the molded charcoal raw materials and molding them under pressure.

[0038] Examples of methods for mixing the molded charcoal raw materials with the cellulose fibers include mechanical mixing using a mixer and kneading while heating by introducing steam, and these methods can be combined as necessary. The mixing method is not particularly limited, but when a coal-based, petroleum-based, or organic binder is used in addition to the cellulose fibers, it is preferable to include a heating and kneading step for the purpose of reducing the viscosity of the binder.

[0039] By producing briquettes using the method of the present invention, the drop strength of the briquettes is improved and the collapse of the briquettes due to the impact of dropping during transportation is suppressed. Here, the drop strength of the briquettes is roughly divided into warm drop strength and cold drop strength.

[0040] The warm drop strength is the drop strength of molded coal in a warm state immediately after molded coal is produced by pressure molding raw materials for molded coal heated by heating and kneading, etc. An example of such a situation is when molded coal immediately after molding falls from a molding machine onto a conveyor directly below. Coal-based, petroleum-based, and organic binders conventionally used in the production of molded coal often develop strength by cooling and solidifying, and in many cases, viscosity decreases in a warm state, making it difficult to develop strength. Therefore, the mechanical restraint provided by pulp is expected to improve warm strength, which was difficult to achieve with conventional binders. In this specification, the warm drop strength is defined as the drop strength evaluated when the temperature of molded coal is 60°C or higher.

[0041] On the other hand, the cold drop strength is the drop strength after cooling after molding. Examples of such situations include when molded coal is transferred on a conveyor during transport or when it falls inside a hopper when being fed into the hopper. Coal-based, petroleum-based, and organic binders conventionally used in the production of molded coal often solidify and develop strength after cooling. However, when the deformation rate is very high, as in the case of a drop impact, the solidified binder cannot keep up with the deformation, which can result in cracks in the molded coal. Therefore, it is expected that the pulp will bind the coal particles together in the molded coal, thereby improving the cold drop strength. In this specification, the cold drop strength is defined as the drop strength evaluated when the molded coal temperature is room temperature (e.g., 25°C).

[0042] (Strength improving agent for molded charcoal) Next, the strength improving agent for molded charcoal according to the present invention will be described. The strength improving agent for molded charcoal according to the present invention is characterized in that it is cellulose fiber having an average fiber length of 0.5 mm or more and 3.0 mm or less, and an average fibril circumference of 10% or less.

[0043] The cellulose fibers may be the same as those used in the method for producing molded charcoal according to the present invention. The requirements for the cellulose fibers may be the same as those for the cellulose fibers used in the method for producing molded charcoal described above.

[0044] As described above, by blending cellulose fibers having an average fiber length of 0.5 mm to 3.0 mm and an average fibril circumference of 10% or less as a binder with the raw material for molded coal, mixing the resulting mixture, and molding it under pressure, molded coal with excellent drop strength can be produced. Furthermore, by improving the drop strength of the molded coal, collapse of the molded coal during transportation can be suppressed, and productivity of molded coal can be improved.

[0045] Examples of the present invention will be described below.

[0046] First, cellulose fibers to be used in the method for producing molded charcoal were produced as follows.

[0047] <Production Example 1> A pulp sheet (brightness 47.2%, solids content 53% by mass / moisture content 47% by mass) obtained by subjecting unbleached pulp derived from hardwood to oxygen delignification was dispersed in water to form a 4% by mass aqueous dispersion. The resulting aqueous dispersion was then treated with a single-disc refiner (product name: 14-inch LabRefiner (manufactured by Aikawa Iron Works Co., Ltd.), clearance 0.15 mm) and beaten to a Canadian Standard Freeness (csf) of 400 ml. The beaten aqueous dispersion was then adjusted to a solids content of 30% by mass using a centrifugal dehydrator to obtain a wet sheet-like product. The resulting wet sheet-like product was then crushed by treatment with a single-disc refiner (product name: BR-300CB LabRefiner (manufactured by Kumagaya Riki Kogyo Co., Ltd.), clearance 3.95 mm) to obtain cellulose fiber A having an average fiber length of 0.92 mm and an average fibril circumference of 3.7%.

[0048] <Production Example 2> Cellulose fiber B having an average fiber length of 1.89 mm and an average fibril circumference of 10.0% was obtained in the same manner as in Production Example 1, except that an unbleached pulp sheet derived from coniferous wood (whiteness 22.8%, solid content 45% by mass / moisture content 55% by mass) was dispersed in water to form a 3% by mass aqueous dispersion.

[0049] <Production Example 3> An unbleached pulp sheet derived from a conifer (brightness 22.8%, solid content 45% by mass / moisture content 55% by mass) was disintegrated by treating it directly in a single-disc refiner (product name: BR-300CB Labo Refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.), clearance 2.5 mm) without making it into an aqueous dispersion, to obtain cellulose fibers C having an average fiber length of 2.15 mm and an average fibril circumference of 2.7%.

[0050] <Production Example 4> As in Production Example 3, without preparing an aqueous dispersion, the pulp sheet was pre-treated with a soft material grinder (product name: SR-360, manufactured by Horai Co., Ltd., outlet screen diameter: φ50 mm) and then crushed by processing with a single disc refiner (clearance 0.5 mm), to obtain cellulose fiber D having an average fiber length of 1.96 mm and an average fibril circumference of 2.1%.

[0051] <Production Example 5> A bleached pulp sheet derived from coniferous trees (brightness 79.0%, solid content 44% by mass / moisture content 56% by mass) was manually coarsely crushed into pieces of approximately 5 cm square, and then disintegrated by processing in a single-disc refiner (clearance 3 mm) to obtain cellulose fiber E having an average fiber length of 2.03 mm and an average fibril circumference of 1.9%.

[0052] <Production Example 6> Cellulose fiber F having an average fiber length of 0.70 mm and an average fibril circumference of 2.3% was obtained in the same manner as in Production Example 4, except that a bleached pulp sheet derived from hardwood (brightness 86.2%, solid content 52 mass% / moisture content 48 mass%) was used and the clearance of the single-disc refiner was changed to 1.0 mm.

[0053] <Production Example 7> A pulp sheet (brightness 38.0%, solid content 46% by mass / moisture content 54% by mass) made from unbleached pulp derived from coniferous trees that had been subjected to oxygen delignification treatment was used, and the aqueous dispersion was beaten until the Canadian Standard Freeness (csf) reached 200 ml, adjusting the solid content to 28% by mass. Cellulose fiber G having an average fiber length of 1.78 mm and an average fibril circumference of 11.0% was obtained in the same manner as in Production Example 2.

[0054] <Production Example 8> Cellulose fiber H having an average fiber length of 0.74 mm and an average fibril circumference of 28.7% was obtained in the same manner as in Production Example 1, except that the aqueous dispersion was beaten until the Canadian standard freeness (csf) was 0 ml and the solid content was adjusted to 23 mass%.

[0055] <Production Example 9> Cellulose fiber I having an average fiber length of 0.99 mm and an average fibril circumference of 34.1% was obtained in the same manner as in Production Example 7, except that the aqueous dispersion was further beaten until the Canadian standard freeness (csf) was 400 ml and the solid content was adjusted to 23 mass%.

[0056] Table 1 shows the average fiber length, average fibril circumference, and blending ratio of the cellulose fibers used in this example. Reference Example No. 1 is a standard level in which no cellulose fibers were blended. Inventive Examples Nos. 2 to 12 are examples in which cellulose fibers suitable for the method of manufacturing molded charcoal of the present invention were blended. Comparative Examples Nos. 13 to 15 are examples in which the average fiber length or average fibril circumference of the blended cellulose fibers was outside the range of the present invention. The average fiber length and average fibril circumference of the cellulose fibers used were determined by the methods described above.

[0057]

[0058] Molded charcoal was produced and evaluated using the various cellulose fibers listed in Table 1 using the following production method. The coal used as the raw material for the molded charcoal was pulverized to a particle size of 3 mm or less. Cellulose fiber was blended with the pulverized coal at the blending ratio (external ratio) listed in Table 1, and 5% by mass of tar slag (external ratio) and 3% by mass of coal tar pitch (internal ratio, since it is solid at room temperature) were further blended as binders to prepare the raw material for the molded charcoal. The raw material for the molded charcoal was mixed in a mixer at room temperature for 90 seconds, and then heated and kneaded for 3 minutes while blowing steam into a kneader. The kneaded raw material was molded in a double-roll molding machine to produce a Massec-type molded charcoal with a volume of approximately 30 cc.

[0059] The warm and cold drop strengths of the produced molded charcoal were measured, and the strength ratios to a reference example (No. 1) containing no cellulose fiber were designated as the cold drop strength index and warm drop strength index, respectively, and are shown in Table 1. Ten molded charcoal pieces were sampled and dropped three times from a height of 2 m onto a concrete floor. The percentage of chunks measuring 15 mm or larger was taken as the drop strength, and the average value of two similar tests was used as the drop strength for that level. The warm drop test was conducted when the molded charcoal was at 60°C or higher immediately after molding, and the cold drop test was conducted after the molded charcoal had been cooled to room temperature.

[0060] From Table 1, it can be seen that in Nos. 2 to 12, which are invention examples produced according to the method for producing molded coal of the present invention, both the warm drop strength index and the cold drop strength index exceeded 1, and the blending of cellulose fibers had the effect of improving the strength of the molded coal. On the other hand, in Nos. 13 to 15, which are comparative examples in which the fibril circumference of the blended cellulose fibers was outside the range of the present invention, the warm drop strength index or the cold drop strength index was below 1, and the effect of improving the strength of the molded coal was not obtained.

[0061] It should be noted that the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these embodiments, and can be modified as appropriate within the scope of the purpose of the present invention.

[0062] According to the present invention, a technique can be provided for improving the drop strength of molded coal without increasing the amount of adhesive binder.

Claims

1. A method for producing molded coal for coke production, comprising mixing cellulose fibers having an average fiber length of 0.5 mm or more and 3.0 mm or less and an average fibril circumference of 10% or less with the raw material for molded coal, and then molding the mixture under pressure to obtain molded coal.

2. A method for producing molded charcoal as described in claim 1, wherein the blending ratio of the cellulose fibers is 3.0 mass% or less.

3. The method for producing molded coal according to claim 1 or 2, further comprising mixing the coal with any one of a coal-based, petroleum-based, and organic binder.

4. A strength improving material for molded charcoal, characterized in that it is a cellulose fiber having an average fiber length of 0.5 mm or more and 3.0 mm or less and an average fibril circumference of 10% or less.

Images